Effect of Distance to the Heat Source During Firing on the Final Color of Metal-Ceramic Restorations: An In Vitro Study

Effect of Distance to the Heat Source During Firing on the Final Color of Metal-Ceramic Restorations: An In Vitro Study | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Effect of Distance to the Heat Source During Firing on the Final Color of Metal-Ceramic Restorations: An In Vitro Study Berkman Albayrak, İzim Türker Kader, Emir Yüzbaşıoğlu, Murat Kurt This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6797246/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Background This study aimed to evaluate the influence of furnace positioning and sequential firing procedures on the final color of metal-ceramic restorations. Methods Forty-two disc-shaped metal-ceramic specimens were fabricated and veneered with dentin, enamel, transparent, and glaze porcelain layers. Specimens were positioned at three different zones within the porcelain furnace (inner, middle, and outer) and subjected to standardized firing cycles. Color measurements were performed using a spectrophotometer after each firing phase. Color differences (ΔE*) were calculated between the control (center) and each group, and the clinical relevance was interpreted according to perceptibility (ΔE*=1.74) and acceptability (ΔE*=3.48) thresholds. Statistical analysis was conducted using two-way ANOVA and post hoc Tukey's HSD tests (α = 0.05). Results Both furnace position (p < 0.05) and firing procedure (p 0 < 0.05) significantly affected color differences. The greatest color changes were observed in specimens placed in the outer zone (ΔE = 6.90), whereas specimens in the inner zone exhibited minimal color differences (ΔE = 1.80). Outer and middle specimens exceeded the clinical acceptability threshold, while inner specimens remained within clinically acceptable limits. Conclusions The position of metal-ceramic restorations within the furnace during firing procedures significantly affects the final color outcome. Careful placement of restorations during porcelain firing is essential to ensure optimal color stability. color stability dental porcelain metal-ceramic restorations porcelain firing porcelain furnace Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 INTRODUCTION In esthetic dentistry, achieving natural appearance and shade matching is of the utmost importance, and success varies depending on the material. Various materials such as metal, polymer and ceramic that can be used in prosthetic treatments have different properties that give them superiority over each other, so they can be preferred in different indications. 1 Feldspathic ceramics are frequently used in prosthetic restorations due to their superior optical properties; 2 however, they are mostly preferred as veneering ceramics on a metal and ceramic substructure in full crown and bridge restorations due to their mechanical properties. 3 Although ceramics with high flexural strength and fracture toughness, such as zirconia, are frequently preferred as substructures under the veneering ceramics, 4 metal-ceramic restorations are still accepted as the gold standard, particularly for implant-supported restorations and long-span fixed partial dentures (FPDs). 5 A critical component for the aesthetic reproduction of natural dentition is accurate shade selection and the transfer of the information to the dental laboratory. The aesthetic failure may be frequently caused by improper use of the shade guides or inability to transfer the required information to the dental technicians, 6 but also manipulative variables of porcelain generate color variability. 7 The ceramic restorations are fired in the furnace many times until the desired color and form are achieved, 8 and they need to be exposed to consistent heat to both reach sufficient hardness and reduce the porosity they contain. 9 The final color of ceramic restorations can be influenced by various factors, including the firing process 10 and temperature, 11 the thickness of the ceramic layers, 12 the powder-to-liquid mixing ratio, 13 and condensation techniques. 14 In addition, limitations in the available shade range, individual differences in color perception, 15 the type of metal alloy used, 16 substructure thickness and variations in ceramic material composition 17 may also affect the final color outcome. It is very crucial that porcelain powders with different colors and optical properties that are mixed in a slurry are fired in accordance with the manufacturer's instructions. In this respect, ceramic restorations that will be placed in a sintering chamber must be subjected to homogeneous heat exposure. Color acceptance is commonly assessed in terms of two thresholds: perceptibility and acceptability. 18 The perceptibility threshold refers to the level at which 50% of observers can detect a color difference (ΔE) between two specimens, while the remaining 50% cannot. The acceptability threshold sets an upper limit for a color difference between specimens that is recognized by most people as an acceptable match. 19 Douglas and Brewer 20 , reported that the 50% acceptability threshold for metal-ceramic crowns ranges between 1.7 and 2.7 for the b* parameter and between 0.5 and 1.5 for the a* parameter. Ghinea et al. 21 reported that the perceptibility threshold for dental ceramics is 1.74, and the acceptability threshold is 3.48, based on evaluations using the CIE Lab ΔE formula and a novel TSK fuzzy approximation method. The optical properties and color stability of ceramics in relation to the number of firings and the temperatures they are subjected to have been widely evaluated, and these factors have been shown to significantly influence the final color of restoration. 2 Machado et al. 22 evaluated the translucency of feldspathic ceramics based on their positioning within the porcelain furnace and the varying heat intensities they may encounter. Notably, during the firing and glazing stages, certain segments of long-span metal-ceramic FPDs are positioned closer to the center of the furnace, while others are located nearer to the periphery, closer to the heat source, which may lead to uneven thermal exposure. To the best of the author's knowledge, although several studies have investigated the effects of substructure type (e.g., different metal alloys, all-ceramic systems and zirconia), 22 , 23 veneering ceramic and substructure thickness, 24 positioning within the furnace and number of restorations fired simultaneously, 22 , 23 and repeated firing cycles, 20 , 22 , 25 , 26 no study has specifically evaluated the color change of widely used metal-ceramic restorations based on their placement in inner, middle, or outer zones of the porcelain furnace, each subjected to four distinct firing procedures (dentin, enamel, transparent, and glaze). Therefore, the aim of this study is to investigate the color differences of metal-ceramic restorations according to their position in the porcelain furnace during the firing stages of dentin, enamel, transparent, and glaze ceramics. The null hypothesis of this study was that the position of the restoration in the furnace during ceramic firing would not affect any veneering phase and the final color outcome. MATERIAL AND METHODS A total of 42 disc-shaped metal-ceramic specimens of A2 shade were fabricated using a base-metal nickel-chromium alloy (Wiron 99; BEGO, Bremen, Germany) with a substructure thickness of 0.5 mm. Disc-shaped specimens were produced in a laser sinter device (HBD 350; HBD, Shangai, China) and prepared after necessary cleaning and oxidation processes were carried out. Specimens were randomly divided into 3 groups (n = 14) based on their distance from the heat source in the porcelain furnace during firing processes. Three of them were positioned in three concentric zones within the firing chamber (inner, middle, and outer) in each firing. One additional specimen placed at the center of the firing tray served as the control ( Fig. 1 ) . First, all specimens were covered with an opaque porcelain layer (VITA VMK Master Opaque; VITA Zahnfabrik, Bad Säckingen, Germany) of 0.2 mm thickness after bonding (VITA NP BOND Paste; VITA Zahnfabrik, Bad Säckingen, Germany) applied to the surface to be veneered. Initial firing was performed in a porcelain furnace (Programat P3010; Ivoclar Vivadent AG, Schaan, Liechtenstein) at 950°C for 20 minutes. Veneering layers of 0.3 mm dentin and 0.5 mm enamel porcelain (VITA VMK Master; VITA Zahnfabrik, Bad Säckingen, Germany) were subsequently applied and fired at 920°C for 25 minutes ( Fig. 2 ) . Surface irregularities were smoothed using a diamond rotary instrument under water cooling. A final layer of translucent (VITA VMK Master; VITA Zahnfabrik, Bad Säckingen, Germany) and glaze porcelain (Akzent Plus; VITA Zahnfabrik, Bad Säckingen, Germany) was applied and fired once at 895°C for 12 minutes ( Fig. 3 ) . Thickness was regularly verified using a micrometer (C-Master; Mitutoyo Corp., Kanagawa, Japan) to achieve a final uniform thickness of 1.5 mm ± 0.05 mm for each specimen. They were ultrasonically cleaned in distilled water (Eurosonic Energy; Euronda SpA, Vicenza, Italy) for 10 minutes and dried with oil-free air for 30 seconds before color measurements. Color measurements were performed using a spectrophotometer (VITA Easyshade Advance; VITA Zahnfabrik, Bad Säckingen, Germany) by a single calibrated and experienced operator to minimize inter-examiner variability. Each specimen’s color was measured three times under standardized lighting conditions, and the mean CIE Lab* value was recorded as the “specimen color.” The CIE Lab* value of the centrally placed control specimen was designated as the “target color.” Also, the measurements were repeated after each of the dentin, enamel, translucent and glaze porcelain firings and the effect of the possible temperature difference on ceramics with different characteristics was also evaluated. The ΔE* between study and the control groups were calculated using the following formula:​ Δ E* ab = [(Δ L *)2 + (Δ a* )2 + (Δ b* )2] 1/2 , where L* S , a* S , b* S represent the values for the study specimens, and L* T , a* T , b* T for the target specimen. The clinical relevance of the color differences was evaluated in reference to visual perception thresholds, including the 50:50% perceptibility threshold (ΔE*=1.74) and the 50:50% acceptability threshold (ΔE*=3.48), as defined by ISO/TR 28642. 27 Data were statistically analyzed using SPSS software (V 23.0; IBM Corp., Armonk, NY, USA). Compliance with normal distribution was examined with Shapiro-Wilk test. A two-way ANOVA and post-hoc Tukey’s HSD test were performed to analyze variables that conformed to normal distribution and evaluate the effects of distance to the heat source and firing procedures on color difference. The significance level was set at p < 0.05. RESULTS The results of colorimetric analysis revealed that the distance to the heat source effects the final color of metal-ceramic crowns. Depending on the results of the two-way ANOVA test, distance to the heat source (F = 124,547; p < 0.05) and firing procedure (F = 60,254; p < 0.05) color were significantly affected by the ΔE values. Interaction terms were also significant (F = 23,746; p < 0.05) as shown in Table 1 – 4 . Table 1 Effect of distance to the heat source and firing procedures on the color difference (ΔL) values based on two-way ANOVA and Tukey’s test.) Source Type III Sum of Squares df Mean Square F Sig. Firing step of veneering ceramic 1447,376 3 482,459 395,455 < 0,001 Distance to heat source 544,761 2 272,381 223,261 < 0,001 Firing step of veneering ceramic * distance to heat source 1109,206 6 184,868 151,530 < 0,001 Table 2 Effect of distance to the heat source and firing procedures on the color difference (Δa) values based on two-way ANOVA and Tukey’s test.) Source Type III Sum of Squares df Mean Square F Sig. Firing procedure 38,158 3 12,719 102,219 < 0,001 Distance to heat source 14,470 2 7,235 58,144 < 0,001 Firing step of veneering ceramic * distance to heat source 12,480 6 2,080 16,717 < 0,001 Table 3 Effect of distance to the heat source and firing procedures on the color difference (Δb) values based on two-way ANOVA and Tukey’s test.) Source Type III Sum of Squares df Mean Square F Sig. Firing procedure 163,659 3 54,553 26,138 < 0,001 Distance to heat source 81,763 2 40,882 19,587 < 0,001 Firing step of veneering ceramic * distance to heat source 103,300 6 17,217 8,249 < 0,001 Table 4 Effect of distance to the heat source and firing procedures on the color difference (ΔE) values based on two-way ANOVA and Tukey’s test.) Source Type III Sum of Squares df Mean Square F Sig. Firing procedure 418,358 3 139,453 130,551 < 0,001 Distance to heat source 576,502 2 288,251 269,852 < 0,001 Firing step of veneering ceramic * distance to heat source 329,740 6 54,957 51,449 < 0,001 The mean values of ΔE differed significantly among all tested groups (p 0.05). In enamel firing, there were no significant differences among all tested groups in terms of Δa* and Δb* (p > 0.05), except the mean values of ΔL* of outer group differed significantly from inner and middle groups (p < 0.001). In translucent firing, there were significant differences between all groups in terms of ΔL* (p < 0.05). In glaze firing, there were significant differences between all groups in terms of ΔL* (p 0.05) and between middle and inner groups (p > 0.05) in terms of Δa* and Δb*. Figure 4 – 6 illustrate the distribution of ΔL, Δa*, and Δb* values, respectively, across all firing stages (dentin, enamel, translucent, glaze) and furnace positions (inner, middle, outer). The interactions between distance to the heat source and firing procedure on color parameters (ΔL*, Δa*, Δb* and ΔE*) values were displayed in Table 5 . Table 5 Mean ± standard deviation (SD) of CIE ΔL, Δa, Δb and ΔE values for each group according to distance to the heat source and firing step of veneering ceramic. Dentin Enamel Translucent Glaze ΔL outer -3,83 ± 0,59 a 2,57 ± 0,80 d 10,89 ± 0,68 g 6,79 ± 1,00 f middle -3,54 ± 0,76 a 0,56 ± 1,00 c 6,76 ± 1,04 f 4,71 ± 1,30 e inner 0,54 ± 1,47 c -0,03 ± 1,93 bc -0,91 ± 0,85 b -0,80 ± 1,11 bc Δa outer 1,83 ± 0,18 d 0,21 ± 0,26 ab -0,16 ± 0,29 a 0,33 ± 0,15 bc middle 1,54 ± 0,23 d 0,70 ± 0,54 c 0,17 ± 0,51 ab 0,21 ± 0,36 ab inner 0,26 ± 0,15 ab -0,16 ± 0,59 d -0,04 ± 0,36 ab -0,10 ± 0,23 ab Δb outer 1,41 ± 0,32 e -1,80 ± 1,18 ab -3,29 ± 1,11 a -1,29 ± 0,33 bc middle 1,60 ± 0,66 e 0,77 ± 1,78 de -1,93 ± 2,31 ab -0,73 ± 1,35 bcd inner 0,33 ± 0,85 cde 0,44 ± 2,39 cde 0,21 ± 1,80 cde 0,71 ± 1,34 de ΔE outer 4,49 ± 0,53 cd 3,37 ± 0,7 bc 11,43 ± 0,54 f 6,92 ± 0,99 e middle 4,21 ± 0,88 cd 2,03 ± 1,25 a 7,32 ± 1,48 e 4,92 ± 1,47 d inner 1,62 ± 0,76 a 2,81 ± 1,23 ab 1,95 ± 0,97 a 1,75 ± 1,02 a Same superscript lowercase letters represent no significant difference according to each color parameter (ΔL, Δa, Δb and ΔE) (p < 0.05). According to the ΔE values, minimum and maximum color changes were obtained in inner (ΔE = 1.75 ± 1.06) and outer (ΔE = 6.92 ± 1.03) groups. When the mean ΔE values were evaluated, the outer (ΔE = 6.90) and middle (ΔE = 4.9) resulted in a clinically unacceptable value (ΔE > 1.74) for metal-ceramic samples. The ΔE values of inner group (ΔE = 1.80) were in the range of visual perceptibility but clinical acceptability (1.74 < ΔE < 3.48). Figure 7 presents the ΔE values by furnace position and firing stage, with dashed lines indicating the 50:50% perceptibility (ΔE = 1.74) and acceptability (ΔE = 3.48) thresholds. DISCUSSION The null hypothesis of this study, which stated that the position of metal-ceramic restorations within the porcelain furnace would not affect color changes, was rejected. Specimens placed closer to the heat source exhibited greater color differences, while those located at the center of the furnace showed significantly less color change. An exception was observed during the enamel firing stage, where no significant difference in color change was found between the specimens positioned in the inner and middle zones. The methodology utilized to assess color stability in the present study was determined according to previous studies conducted with spectrophotometer using CIELab (ΔE*ab) coordinate system. 28 , 29 Although the CIEDE2000 (ΔE 00 ) color difference formula is a more up-to-date option compared to the CIELab formula in the evaluation of color difference thresholds of dental restorations, the color difference can be determined quantitatively and reliably using the CIELab color space and the associated ΔE*ab. A recent study has demonstrated significant correlations between ΔEab and ΔE00 values. 15 When the specimens were positioned closer to the heat source in the porcelain furnace, the greatest color changes were obtained in the outer group (ΔE = 6.92 ± 1.03), whereas the least color changes were recorded in the inner group (ΔE = 1.75 ± 1.06). According to the ΔE values, specimens in the outer (ΔE = 6.90) and middle (ΔE = 4.9) zones exhibited clinically unacceptable color differences (ΔE > 3.48). In contrast, the ΔE values of the inner group (ΔE = 1.75) fell within the range of visual perceptibility but clinical acceptability (1.74 < ΔE < 3.48). Similarly, Machado et al. 22 reported that feldspathic porcelains placed at the center of the porcelain furnace exhibited lower translucency levels compared to those positioned near the periphery. The most traditional heating methods used for ceramic synthesis and sintering —based on thermal conduction, radiation, and convection—include electric resistance and fuel-based systems, and are classified as contact heating methods, where thermal energy is transferred by direct contact with the material. In contrast, non-contact heating methods, such as induction, radiofrequency, and microwave heating, transfer energy through electromagnetic radiation, coupling with the material, thereby eliminating the need for direct contact. 30 A porcelain furnace is specifically designed to process dental porcelains to optimal levels of maturity while maintaining essential properties of the restoration, such as surface texture, translucency, value, hue, and chroma. 31 Although conventional furnaces are routinely used for veneering processes in dental practice, they do not produce a uniform heating environment. Heat is initially applied to the surface of the ceramic and subsequently transferred to the core by thermal conduction, resulting in the formation of high temperature gradients and internal stresses within the material. 32 To ensure consistent thermal exposure, it is recommended that ceramic restorations be placed in specific, standardized locations within firing chamber. Some advanced furnace systems incorporate specially designed muffles to achieve a more homogenous temperature distribution, thereby eliminating the hot or cold spots commonly observed in traditional configurations. Whether the restoration is positioned on a firing pin or a firing pillow, these optimized muffle configurations aim to deliver uniform sintering conditions. 31 Consistent with these principles, the findings of the present study demonstrated that the position of porcelain restorations within the furnace significantly affects color outcomes. Previous studies have demonstrated that repeated firings also have an effect on color stability of porcelain restorations. Yilmaz et al. 25 reported that successive porcelain firings (including opaque, repetitive dentin, and glaze firings) significantly influenced the color of a 0.1 mm thick layer of opaque porcelain across different alloy groups. In their study, the magnitude of color change after the first denting firing was greater than that observed after subsequent firings, regardless of the alloy type. These findings are consistent with those of Mulla et al. 26 , who similarly reported significant color alterations following the initial firing, with less pronounced changes after additional firings. In the present study the greatest color differences were observed in the translucent ceramic application between the outer (ΔE = 11.4), middle (ΔE = 7.3) and the inner group (ΔE = 1.9). Repeated firings in porcelain restorations may induce color changes due to the effects of metal oxides. Some metal oxides have been reported to degrade under high firing temperatures, leading to pigment breakdown and subsequent alterations in color. 25 Furthermore, repeated firings can cause burning of the porcelain’s color pigments and promote devitrification processes. 33 In the present study, the observed color changes, particularly in specimens positioned closer to the heat source, may be attributed to the thermal instability of metal oxides. Consistently, ΔE values in the outer zone specimens were higher than those in the inner zone across all firing procedures. Barghi 34 reported that the slight change in color after repeated firings may be attributed to the increased material density resulting from the reduction of air bubbles trapped within the porcelain structure. Due to the high viscosity of porcelain at its low melting temperature, the diffusion of ionic species within the molten glassy matrix is significantly limited. In the present study, the observed color changes in specimens located closer to the heat source may similarly be attributed to enhanced ionic diffusion into the softened glassy phase of the viscous porcelain, as suggested by Barghi 34 . Studies evaluating the color alteration of ceramic surfaces after firing have demonstrated that pigments can degrade at elevated firing temperatures. Ceramic specimens fired at 1.6°C and 21°C above the manufacturer-recommended firing temperatures exhibited substantial differences in both shade and value. 35 However, the present study has some limitations. First, it did not investigate the specific ionic mechanisms underlying the direction of color change. Second, only a single shade (A2) and metal-ceramic restorations were evaluated. Further studies incorporating different ceramic types, various shades, and varying distances from the heat source are required to comprehensively understand these effects. CONCLUSIONS Within the limitation of this study, the following conclusions were drawn: The final color of metal-ceramic restorations is significantly affected by their position within the firing chamber of the porcelain furnace. Restorations positioned away from the center of the furnace during the application stages of dentin, enamel, translucent, and glaze ceramics are more susceptible to color changes due to increased exposure to the heat source. Declarations Ethics approval and consent to participate: - Consent for publication: - Availability of data and materials: - Competing interests: - Funding: None Authors' contributions: Emir Yüzbaşıoğlu and Murat Kurt contributed to conceptualization and constructed the material method. Murat Kurt prepared the samples and fired them, while Emir Yüzbaşıoğlu performed the color measurements. İzim Türker Kader collected data, took the pictures and performed statistical analysis. Berkman Albayrak wrote the manuscript beside contributing the firing processes of samples. Acknowledgements: - Clinical trial number: not applicable Author Contribution Emir Yüzbaşıoğlu and Murat Kurt contributed to conceptualization and constructed the material method. Murat Kurt prepared the samples and fired them, while Emir Yüzbaşıoğlu performed the color measurements. İzim Turker Kader collected data and performed statistical analysis. Berkman Albayrak wrote the manuscript beside contributing the firing processes of samples. References Patil VV, Sowmya S, Vathare AS, et al. Evaluating the Impact of Prosthetic Material Choices on the Clinical Outcomes of Implant-Supported Restorations. J. Pharm. Bioallied Sci. 2024;16 Suppl 3:2752-4. doi:10.4103/jpbs.jpbs_372_24 Fredericci C, Yoshimura HN, Molisani AL, Pinto MM, Cesar PF. Effect of temperature and heating rate on the sintering of leucite-based dental porcelains. Ceram. Int. 2011;37 (3):1073-8. doi:10.1016/j.ceramint.2010.11.040 Cesar PF, Soki FN, Yoshimura HN, Gonzaga CC, Styopkin V. Influence of leucite content on slow crack growth of dental porcelains. Dent. Mater. 2008;24 (8):1114–22. doi: 10.1016/j.dental.2008.01.003 Salido MP, Martinez-Rus F, del Rio F, Pradies G, Ozcan M, Suarez MJ. Prospective clinical study of zirconia-based posterior four-unit fixed dental prostheses: four-year follow-up. Int J Prosthodont. 2012;25:403–9. doi:10.5167/uzh-75527 Tan K, Pjetursson BE, Lang NP, Chan ES. A systematic review of the survival and complication rates of fixed partial dentures (FPDs) after an observation period of at least 5 years. Clin Oral Implants Res. 2004;15:654–66. doi:10.1111/j.1600-0501.2004.01119.x Douglas RD, Brewer JD. Acceptability of shade differences in metal ceramic crowns. J Prosthet Dent. 1998;79(3):254-60. doi:10.1016/s0022-3913(98)70233-1 Uludag B, Usumez A, Sahin V, et al. The effect of ceramic thickness and number of firings on the color of ceramic systems: an in vitro study. J Prosthet Dent. 2007;97:25-31. doi: 10.1016/j.prosdent.2006.11.002 Wee AG, Monaghan P, Johnston WM. Variation in color between intended matched shade and fabricated shade of dental porcelain. J Prosthet Dent. 2002;87(6):657-66. doi: 10.1067/mpr.2002.125727 Tang X, Nakamura T, Usami H, Wakabayashi K, Yatani H. Effects of multiple firings on the mechanical properties and microstructure of veneering ceramics for zirconia frameworks. J Dent. 2012;40(5):372-80. doi:10.1016/j.jdent.2012.01.014 Ozturk O, Uludag B, Usumez A, Sahin V, Celik G. The effect of ceramic thickness and number of firings on the color of two all-ceramic systems. J Prosthet Dent. 2008;100:99–106. doi:10.1016/S0022-3913(08)60156-0 Hammad IA, Stein RS. A qualitative study for the bond and color of ceramometals. Part II. J Prosthet Dent. 1991;65(2):169-79. doi:10.1016/0022-3913(91)90158-s Corciolani G, Vichi A, Louca C, Ferrari M. Influence of layering thickness on the color parameters of a ceramic system. Dent Mater. 2010;26(8):737-42. doi:10.1016/j.dental.2010.03.018 Zhang Y, Griggs JA, Benham AW. Influence of powder/liquid mixing ratio on porosity and translucency of dental porcelains. J Prosthet Dent. 200491(2):128-35. doi:10.1016/j.prosdent.2003.10.014 O'Brien WJ, Kay KS, Boenke KM, Groh CL. Sources of color variation on firing porcelain. Dent Mater. 1991;7(3):170-3. doi: 10.1016/0109-5641(91)90038-z Hammad IA. Intrarater repeatability of shade selections with two shade guides. J Prosthet Dent. 2003;89(1):50-3. doi:10.1067/mpr.2003.60 Anitha KV, Dhanraj M, Haribabu R. Comparison of the effect of different ceramic alloys and porcelain systems upon the color of metal-ceramic restorations: An in vitro study. J Indian Prosthodont Soc. 2013;13(3):296-302. doi: 10.1007/s13191-013-0267-5 Ghulman MA, Awad MA. Color variation between matched and fabricated shades of different ceramics. J Prosthodont 2013;22 :472-7. doi:10.1111/jopr.12027 Khashayar G, Bain PA, Salari S, Dozic A, Kleverlaan CJ, Feilzer AJ. Perceptibility and acceptability thresholds for colour differences in dentistry. J Dent. 2014;42(6):637-44. doi:10.1016/j.jdent.2013.11.017 Alghazali N, Burnside G, Moallem M, Smith P, Preston A, Jarad FD. Assessment of perceptibility and acceptability of color difference of denture teeth. J Dent. 2012;40,e10-e17. doi:10.1016/j.jdent.2012.04.023 Douglas RD, Brewer JD. Acceptability of shade differences in metal ceramic crowns. J Prosthet Dent. 1998;79:254–60. doi:10.1016/s0022-3913(98)70233-1 Ghinea R, Perez MM, Herrera LJ, et al. Color difference thresholds in dental ceramics. J Dent. 2010;38 (Suppl 2):e57–64. doi:10.1016/j.jdent.2010.07.008 Machado PS, Camponogara JG, Rodrigues CDS, Jacques LB, Valandro LF, Rippe MP. Influence of number and position of porcelain specimens in the furnace on flexural strength and translucency. Braz J Oral Sci. 2023;22:e231377. doi:10.20396/bjos.v22i00.8671377 Machado PS, Pereira GKR, Rodrigues CDS, Guilardi LF, Valandro LF, Rippe MP. Fatigue behavior and colorimetric differences of a porcelain-veneered zirconia: effect of quantity and position of specimens during firing. J Prosthodont Res. 2021;65(2):202-7. doi:10.2186/jpr.JPOR_2019_336 Fathi A, Farzin M, Giti R, Kalantari MH. Effects of number of firings and veneer thickness on the color and translucency of 2 different zirconia-based ceramic systems. J Prosthet Dent. 2019;122(6):565.e1-565.e7. doi:10.1016/j.prosdent.2019.08.020 Yılmaz B, Ozcelik TB, Wee AG. Effect of repeated firings on the color of opaque porcelain applied on different dental alloys. J Prosthet Dent. 2009;101(6):395-404. doi:10.1016/S0022-3913(09)60085-8 Mulla FA, Weiner S. Effects of temperature on color stability of porcelain stains. J Prosthet Dent. 1991;65:507-12. doi:10.1016/0022-3913(91)90290-d International Organization for Standardization. ISO/TR 28642 Dentistry—guidance on color measurement. Geneva: International Organization for Standardization; 2011. Sabatini C, Campillo M, Aref J. Color stability of ten resin-based restorative materials. J Esthet Restor Dent. 2012;24(3):185–199. doi:10.1111/j.1708-8240.2011.00442.x Kim BJ, Lee YK. Influence of the shade designation on the color difference between the same shade-designated resin composites by the brand. Dent Mater. 2009;25(9):1148–1154. Agrawal DK. Microwave processing of ceramics. Curr Opin Solid St M. 1998;3(5):480-485. doi:10.1016/j.dental.2009.04.001 Patrick B. Inside Dental Technology. 2011;Vol 2:Issue 3. Katz JD. Microwave Sintering of Ceramics. Annu Rev Mater. 1992;22:153-70. doi:10.1146/annurev.ms.22.080192.001101 Gonuldas F, Yılmaz K, Ozturk C. The effect of repeated firings on the color change of dental ceramics using different glazing methods. J Adv Prosthodont. 2014;6(6):427–33. doi:10.4047/jap.2014.6.6.427 Barghi N. Color and glaze: effects of repeated firings. J Prosthet Dent. 1982;47:393-5. doi:10.1016/s0022-3913(82)80088-7 Jorgenson MW, Goodkind RJ. Spectrophotometric study of five porcelain shades relative to the dimensions of color, porcelain thickness, and repeated firings. J Prosthet Dent. 1979;42:96-105. doi:10.1016/0022-3913(79)90335-4 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6797246","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":473744587,"identity":"59ed992c-8c96-40bb-98c0-e180c4b5fcc3","order_by":0,"name":"Berkman Albayrak","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABEUlEQVRIiWNgGAWjYBACAwYGZjCDTwJMJciByAMPiNHCBtViDNaSQIqWxAYwhUeLOXvvY6MbNXfk2aSbn0lX1KSlzw87/BBoi52cbgN2LZY9x42Tc449M2yTOWYmeeZYTu7G22kGQC3JxmYHcDjsRhrz4Ry2w4xtEglmkg1sFbkbZyeAtBxI3IZLy/1nQC3/Dtu3SaR/k2z4V5FuODv9A34tN9iYk3PbDie2SeSYSTa25STIS+fgt8WyJ43ZOLfvcHKbzJliy8a+NMMN0jkFBxIMcPvFnP0Ys3TOt8O2/dLtG282fEuWl5+dvvnDhwo7OVxakAELOGoMwCoNCCsHAeYPIFK+gTjVo2AUjIJRMHIAAOqkYtPPfQ9QAAAAAElFTkSuQmCC","orcid":"","institution":"Bahçeşehir University","correspondingAuthor":true,"prefix":"","firstName":"Berkman","middleName":"","lastName":"Albayrak","suffix":""},{"id":473744588,"identity":"ce6c41da-2528-43e6-9b0e-5ac08598c961","order_by":1,"name":"İzim Türker Kader","email":"","orcid":"","institution":"Bahçeşehir University","correspondingAuthor":false,"prefix":"","firstName":"İzim","middleName":"Türker","lastName":"Kader","suffix":""},{"id":473744589,"identity":"2271999e-c12d-478f-94c0-f1e1b353fbfa","order_by":2,"name":"Emir Yüzbaşıoğlu","email":"","orcid":"","institution":"Private Practice","correspondingAuthor":false,"prefix":"","firstName":"Emir","middleName":"","lastName":"Yüzbaşıoğlu","suffix":""},{"id":473744590,"identity":"6ff7bf79-9709-4bbb-a908-509d0cf3e1a7","order_by":3,"name":"Murat Kurt","email":"","orcid":"","institution":"Bahçeşehir University","correspondingAuthor":false,"prefix":"","firstName":"Murat","middleName":"","lastName":"Kurt","suffix":""}],"badges":[],"createdAt":"2025-06-01 18:38:16","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6797246/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6797246/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":85076336,"identity":"a4bd59a9-4c43-4e28-acdf-af81a26e40c9","added_by":"auto","created_at":"2025-06-20 16:40:25","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":699148,"visible":true,"origin":"","legend":"\u003cp\u003ePlacement of metal-ceramic specimens in inner, middle, and outer zones within the porcelain furnace.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-6797246/v1/5086abeb8cb365fea66e9c70.png"},{"id":85076338,"identity":"c0be0689-b24b-4ccd-b343-8aa82500eae7","added_by":"auto","created_at":"2025-06-20 16:40:25","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":960074,"visible":true,"origin":"","legend":"\u003cp\u003eSpecimens placed in inner, middle, and outer zones of the furnace tray after dentin (left) and enamel (right) porcelain firings.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-6797246/v1/48ce2365e6562da9b6b87f8c.png"},{"id":85076341,"identity":"f63f9dd1-00bb-4852-9908-e333e19e347d","added_by":"auto","created_at":"2025-06-20 16:40:25","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1050041,"visible":true,"origin":"","legend":"\u003cp\u003eSpecimens placed in inner, middle, and outer zones of the furnace tray after dentin (left) and enamel (right) porcelain firings.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-6797246/v1/1d42652ad1c03431f19cb556.png"},{"id":85076337,"identity":"910eb8d5-14b8-4107-b774-8d2baa7f564c","added_by":"auto","created_at":"2025-06-20 16:40:25","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":80775,"visible":true,"origin":"","legend":"\u003cp\u003eLine graph of ΔL (lightness) values of metal-ceramic specimens after each firing stage (dentin, enamel, translucent, glaze) according to their position within the porcelain furnace (inner, middle, outer).\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-6797246/v1/5e4dd3efa1b376650d42ab5a.png"},{"id":85077434,"identity":"e54d5445-6cbb-4efc-ac50-3a79d34baa42","added_by":"auto","created_at":"2025-06-20 16:56:25","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":87868,"visible":true,"origin":"","legend":"\u003cp\u003eLine graph of Δa (green-red axis) values of metal-ceramic specimens after each firing stage (dentin, enamel, translucent, glaze), according to their position within the porcelain furnace (inner, middle, outer).\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-6797246/v1/cedd03fb3663be22efc822b2.png"},{"id":85076650,"identity":"bbbff6b8-5af9-4161-bade-129b3ff0a4df","added_by":"auto","created_at":"2025-06-20 16:48:25","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":78470,"visible":true,"origin":"","legend":"\u003cp\u003eLine graph of Δb (blue-yellow axis) values of metal-ceramic specimens after each firing stage (dentin, enamel, translucent, glaze), according to their position within the porcelain furnace (inner, middle, outer).\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-6797246/v1/b032441d73121e0f83d8d4c0.png"},{"id":85076658,"identity":"19c4da13-2181-49ad-84bf-611ea0a06b14","added_by":"auto","created_at":"2025-06-20 16:48:25","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":93760,"visible":true,"origin":"","legend":"\u003cp\u003eLine graph of ΔE values of metal-ceramic specimens across different firing procedures (dentin, enamel, translucent, glaze) and furnace positions (inner, middle, outer).\u003c/p\u003e\n\u003cp\u003e*Dashed lines represent the 50:50% perceptibility threshold (ΔE=1.74) and clinical acceptability threshold (ΔE=3.48).\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-6797246/v1/e40d1ed2561c2fabc4aa1265.png"},{"id":86706050,"identity":"8467b668-61c8-432c-8b03-ceb2271e4a43","added_by":"auto","created_at":"2025-07-14 17:16:38","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3652654,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6797246/v1/4f78ac2b-8908-47b5-b312-ae353b58c1a0.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Effect of Distance to the Heat Source During Firing on the Final Color of Metal-Ceramic Restorations: An In Vitro Study","fulltext":[{"header":"INTRODUCTION","content":"\u003cp\u003eIn esthetic dentistry, achieving natural appearance and shade matching is of the utmost importance, and success varies depending on the material. Various materials such as metal, polymer and ceramic that can be used in prosthetic treatments have different properties that give them superiority over each other, so they can be preferred in different indications.\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e Feldspathic ceramics are frequently used in prosthetic restorations due to their superior optical properties;\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e however, they are mostly preferred as veneering ceramics on a metal and ceramic substructure in full crown and bridge restorations due to their mechanical properties.\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e Although ceramics with high flexural strength and fracture toughness, such as zirconia, are frequently preferred as substructures under the veneering ceramics,\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e metal-ceramic restorations are still accepted as the gold standard, particularly for implant-supported restorations and long-span fixed partial dentures (FPDs).\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eA critical component for the aesthetic reproduction of natural dentition is accurate shade selection and the transfer of the information to the dental laboratory. The aesthetic failure may be frequently caused by improper use of the shade guides or inability to transfer the required information to the dental technicians,\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e but also manipulative variables of porcelain generate color variability.\u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e The ceramic restorations are fired in the furnace many times until the desired color and form are achieved,\u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e and they need to be exposed to consistent heat to both reach sufficient hardness and reduce the porosity they contain.\u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e The final color of ceramic restorations can be influenced by various factors, including the firing process\u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e and temperature,\u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e the thickness of the ceramic layers,\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e the powder-to-liquid mixing ratio,\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e and condensation techniques.\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e In addition, limitations in the available shade range, individual differences in color perception,\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e the type of metal alloy used,\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e substructure thickness and variations in ceramic material composition\u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e may also affect the final color outcome. It is very crucial that porcelain powders with different colors and optical properties that are mixed in a slurry are fired in accordance with the manufacturer's instructions. In this respect, ceramic restorations that will be placed in a sintering chamber must be subjected to homogeneous heat exposure.\u003c/p\u003e \u003cp\u003eColor acceptance is commonly assessed in terms of two thresholds: perceptibility and acceptability.\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e The perceptibility threshold refers to the level at which 50% of observers can detect a color difference (ΔE) between two specimens, while the remaining 50% cannot. The acceptability threshold sets an upper limit for a color difference between specimens that is recognized by most people as an acceptable match.\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e Douglas and Brewer\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e, reported that the 50% acceptability threshold for metal-ceramic crowns ranges between 1.7 and 2.7 for the b* parameter and between 0.5 and 1.5 for the a* parameter. Ghinea et al.\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e reported that the perceptibility threshold for dental ceramics is 1.74, and the acceptability threshold is 3.48, based on evaluations using the CIE Lab ΔE formula and a novel TSK fuzzy approximation method.\u003c/p\u003e \u003cp\u003eThe optical properties and color stability of ceramics in relation to the number of firings and the temperatures they are subjected to have been widely evaluated, and these factors have been shown to significantly influence the final color of restoration.\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e Machado et al.\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e evaluated the translucency of feldspathic ceramics based on their positioning within the porcelain furnace and the varying heat intensities they may encounter. Notably, during the firing and glazing stages, certain segments of long-span metal-ceramic FPDs are positioned closer to the center of the furnace, while others are located nearer to the periphery, closer to the heat source, which may lead to uneven thermal exposure.\u003c/p\u003e \u003cp\u003eTo the best of the author's knowledge, although several studies have investigated the effects of substructure type (e.g., different metal alloys, all-ceramic systems and zirconia),\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e,\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e veneering ceramic and substructure thickness,\u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e positioning within the furnace and number of restorations fired simultaneously,\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e,\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e and repeated firing cycles,\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e,\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e,\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e,\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e no study has specifically evaluated the color change of widely used metal-ceramic restorations based on their placement in inner, middle, or outer zones of the porcelain furnace, each subjected to four distinct firing procedures (dentin, enamel, transparent, and glaze). Therefore, the aim of this study is to investigate the color differences of metal-ceramic restorations according to their position in the porcelain furnace during the firing stages of dentin, enamel, transparent, and glaze ceramics. The null hypothesis of this study was that the position of the restoration in the furnace during ceramic firing would not affect any veneering phase and the final color outcome.\u003c/p\u003e"},{"header":"MATERIAL AND METHODS","content":"\u003cp\u003eA total of 42 disc-shaped metal-ceramic specimens of A2 shade were fabricated using a base-metal nickel-chromium alloy (Wiron 99; BEGO, Bremen, Germany) with a substructure thickness of 0.5 mm. Disc-shaped specimens were produced in a laser sinter device (HBD 350; HBD, Shangai, China) and prepared after necessary cleaning and oxidation processes were carried out. Specimens were randomly divided into 3 groups (n\u0026thinsp;=\u0026thinsp;14) based on their distance from the heat source in the porcelain furnace during firing processes. Three of them were positioned in three concentric zones within the firing chamber (inner, middle, and outer) in each firing. One additional specimen placed at the center of the firing tray served as the control \u003cb\u003e(\u003c/b\u003eFig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e\u003cb\u003e)\u003c/b\u003e.\u003c/p\u003e \u003cp\u003eFirst, all specimens were covered with an opaque porcelain layer (VITA VMK Master Opaque; VITA Zahnfabrik, Bad S\u0026auml;ckingen, Germany) of 0.2 mm thickness after bonding (VITA NP BOND Paste; VITA Zahnfabrik, Bad S\u0026auml;ckingen, Germany) applied to the surface to be veneered. Initial firing was performed in a porcelain furnace (Programat P3010; Ivoclar Vivadent AG, Schaan, Liechtenstein) at 950\u0026deg;C for 20 minutes. Veneering layers of 0.3 mm dentin and 0.5 mm enamel porcelain (VITA VMK Master; VITA Zahnfabrik, Bad S\u0026auml;ckingen, Germany) were subsequently applied and fired at 920\u0026deg;C for 25 minutes \u003cb\u003e(\u003c/b\u003eFig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e\u003cb\u003e)\u003c/b\u003e. Surface irregularities were smoothed using a diamond rotary instrument under water cooling. A final layer of translucent (VITA VMK Master; VITA Zahnfabrik, Bad S\u0026auml;ckingen, Germany) and glaze porcelain (Akzent Plus; VITA Zahnfabrik, Bad S\u0026auml;ckingen, Germany) was applied and fired once at 895\u0026deg;C for 12 minutes \u003cb\u003e(\u003c/b\u003eFig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e\u003cb\u003e)\u003c/b\u003e. Thickness was regularly verified using a micrometer (C-Master; Mitutoyo Corp., Kanagawa, Japan) to achieve a final uniform thickness of 1.5 mm\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05 mm for each specimen. They were ultrasonically cleaned in distilled water (Eurosonic Energy; Euronda SpA, Vicenza, Italy) for 10 minutes and dried with oil-free air for 30 seconds before color measurements.\u003c/p\u003e \u003cp\u003eColor measurements were performed using a spectrophotometer (VITA Easyshade Advance; VITA Zahnfabrik, Bad S\u0026auml;ckingen, Germany) by a single calibrated and experienced operator to minimize inter-examiner variability. Each specimen\u0026rsquo;s color was measured three times under standardized lighting conditions, and the mean CIE Lab* value was recorded as the \u0026ldquo;specimen color.\u0026rdquo; The CIE Lab* value of the centrally placed control specimen was designated as the \u0026ldquo;target color.\u0026rdquo; Also, the measurements were repeated after each of the dentin, enamel, translucent and glaze porcelain firings and the effect of the possible temperature difference on ceramics with different characteristics was also evaluated.\u003c/p\u003e \u003cp\u003eThe ΔE* between study and the control groups were calculated using the following formula:​ Δ\u003cem\u003eE*\u003c/em\u003e\u003csub\u003e\u003cem\u003eab\u003c/em\u003e\u003c/sub\u003e= [(Δ\u003cem\u003eL\u003c/em\u003e*)2 + (Δ\u003cem\u003ea*\u003c/em\u003e)2 + (Δ\u003cem\u003eb*\u003c/em\u003e)2]\u003csup\u003e1/2\u003c/sup\u003e, where L*\u003csub\u003eS\u003c/sub\u003e, a*\u003csub\u003eS\u003c/sub\u003e, b*\u003csub\u003eS\u003c/sub\u003e represent the values for the study specimens, and L*\u003csub\u003eT\u003c/sub\u003e, a*\u003csub\u003eT\u003c/sub\u003e, b*\u003csub\u003eT\u003c/sub\u003e for the target specimen. The clinical relevance of the color differences was evaluated in reference to visual perception thresholds, including the 50:50% perceptibility threshold (ΔE*=1.74) and the 50:50% acceptability threshold (ΔE*=3.48), as defined by ISO/TR 28642.\u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eData were statistically analyzed using SPSS software (V 23.0; IBM Corp., Armonk, NY, USA). Compliance with normal distribution was examined with Shapiro-Wilk test. A two-way ANOVA and post-hoc Tukey\u0026rsquo;s HSD test were performed to analyze variables that conformed to normal distribution and evaluate the effects of distance to the heat source and firing procedures on color difference. The significance level was set at p\u0026thinsp;\u0026lt;\u0026thinsp;0.05.\u003c/p\u003e"},{"header":"RESULTS","content":"\u003cp\u003eThe results of colorimetric analysis revealed that the distance to the heat source effects the final color of metal-ceramic crowns. Depending on the results of the two-way ANOVA test, distance to the heat source (F\u0026thinsp;=\u0026thinsp;124,547; p\u0026thinsp;\u0026lt;\u0026thinsp;0.05) and firing procedure (F\u0026thinsp;=\u0026thinsp;60,254; p\u0026thinsp;\u0026lt;\u0026thinsp;0.05) color were significantly affected by the ΔE values. Interaction terms were also significant (F\u0026thinsp;=\u0026thinsp;23,746; p\u0026thinsp;\u0026lt;\u0026thinsp;0.05) as shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eEffect of distance to the heat source and firing procedures on the color difference (ΔL) values based on two-way ANOVA and Tukey\u0026rsquo;s test.)\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSource\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eType III Sum of Squares\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003edf\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMean Square\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eF\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eSig.\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFiring step of veneering ceramic\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1447,376\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e482,459\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e395,455\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0,001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDistance to heat source\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e544,761\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e272,381\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e223,261\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0,001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFiring step of veneering ceramic * distance to heat source\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1109,206\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e184,868\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e151,530\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0,001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eEffect of distance to the heat source and firing procedures on the color difference (Δa) values based on two-way ANOVA and Tukey\u0026rsquo;s test.)\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSource\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eType III Sum of Squares\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003edf\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMean Square\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eF\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eSig.\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFiring procedure\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e38,158\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e12,719\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e102,219\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0,001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDistance to heat source\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e14,470\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e7,235\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e58,144\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0,001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFiring step of veneering ceramic * distance to heat source\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e12,480\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2,080\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e16,717\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0,001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eEffect of distance to the heat source and firing procedures on the color difference (Δb) values based on two-way ANOVA and Tukey\u0026rsquo;s test.)\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSource\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eType III Sum of Squares\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003edf\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMean Square\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eF\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eSig.\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFiring procedure\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e163,659\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e54,553\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e26,138\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0,001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDistance to heat source\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e81,763\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e40,882\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e19,587\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0,001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFiring step of veneering ceramic * distance to heat source\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e103,300\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e17,217\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e8,249\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0,001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eEffect of distance to the heat source and firing procedures on the color difference (ΔE) values based on two-way ANOVA and Tukey\u0026rsquo;s test.)\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSource\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eType III Sum of Squares\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003edf\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMean Square\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eF\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eSig.\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFiring procedure\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e418,358\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e139,453\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e130,551\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0,001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDistance to heat source\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e576,502\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e288,251\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e269,852\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0,001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFiring step of veneering ceramic * distance to heat source\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e329,740\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e54,957\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e51,449\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0,001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe mean values of ΔE differed significantly among all tested groups (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). In dentin firing, there were no significant differences between outer and middle groups in terms of ΔL*, Δa*, and Δb* (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05). In enamel firing, there were no significant differences among all tested groups in terms of Δa* and Δb* (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05), except the mean values of ΔL* of outer group differed significantly from inner and middle groups (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). In translucent firing, there were significant differences between all groups in terms of ΔL* (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). In glaze firing, there were significant differences between all groups in terms of ΔL* (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05), and there were no significant differences between outer and middle groups (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05) and between middle and inner groups (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05) in terms of Δa* and Δb*. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e illustrate the distribution of ΔL, Δa*, and Δb* values, respectively, across all firing stages (dentin, enamel, translucent, glaze) and furnace positions (inner, middle, outer). The interactions between distance to the heat source and firing procedure on color parameters (ΔL*, Δa*, Δb* and ΔE*) values were displayed in Table\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab5\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation (SD) of CIE ΔL, Δa, Δb and ΔE values for each group according to distance to the heat source and firing step of veneering ceramic.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eDentin\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eEnamel\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eTranslucent\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eGlaze\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eΔL\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eouter\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-3,83\u0026thinsp;\u0026plusmn;\u0026thinsp;0,59 \u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2,57\u0026thinsp;\u0026plusmn;\u0026thinsp;0,80 \u003csup\u003ed\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e10,89\u0026thinsp;\u0026plusmn;\u0026thinsp;0,68 \u003csup\u003eg\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e6,79\u0026thinsp;\u0026plusmn;\u0026thinsp;1,00 \u003csup\u003ef\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003emiddle\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-3,54\u0026thinsp;\u0026plusmn;\u0026thinsp;0,76 \u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0,56\u0026thinsp;\u0026plusmn;\u0026thinsp;1,00 \u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e6,76\u0026thinsp;\u0026plusmn;\u0026thinsp;1,04 \u003csup\u003ef\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e4,71\u0026thinsp;\u0026plusmn;\u0026thinsp;1,30 \u003csup\u003ee\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003einner\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0,54\u0026thinsp;\u0026plusmn;\u0026thinsp;1,47 \u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-0,03\u0026thinsp;\u0026plusmn;\u0026thinsp;1,93 \u003csup\u003ebc\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-0,91\u0026thinsp;\u0026plusmn;\u0026thinsp;0,85 \u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-0,80\u0026thinsp;\u0026plusmn;\u0026thinsp;1,11 \u003csup\u003ebc\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eΔa\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eouter\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1,83\u0026thinsp;\u0026plusmn;\u0026thinsp;0,18 \u003csup\u003ed\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0,21\u0026thinsp;\u0026plusmn;\u0026thinsp;0,26 \u003csup\u003eab\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-0,16\u0026thinsp;\u0026plusmn;\u0026thinsp;0,29 \u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0,33\u0026thinsp;\u0026plusmn;\u0026thinsp;0,15 \u003csup\u003ebc\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003emiddle\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1,54\u0026thinsp;\u0026plusmn;\u0026thinsp;0,23 \u003csup\u003ed\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0,70\u0026thinsp;\u0026plusmn;\u0026thinsp;0,54 \u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0,17\u0026thinsp;\u0026plusmn;\u0026thinsp;0,51 \u003csup\u003eab\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0,21\u0026thinsp;\u0026plusmn;\u0026thinsp;0,36 \u003csup\u003eab\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003einner\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0,26\u0026thinsp;\u0026plusmn;\u0026thinsp;0,15 \u003csup\u003eab\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-0,16\u0026thinsp;\u0026plusmn;\u0026thinsp;0,59 \u003csup\u003ed\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-0,04\u0026thinsp;\u0026plusmn;\u0026thinsp;0,36 \u003csup\u003eab\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-0,10\u0026thinsp;\u0026plusmn;\u0026thinsp;0,23 \u003csup\u003eab\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eΔb\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eouter\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1,41\u0026thinsp;\u0026plusmn;\u0026thinsp;0,32 \u003csup\u003ee\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-1,80\u0026thinsp;\u0026plusmn;\u0026thinsp;1,18 \u003csup\u003eab\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-3,29\u0026thinsp;\u0026plusmn;\u0026thinsp;1,11 \u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-1,29\u0026thinsp;\u0026plusmn;\u0026thinsp;0,33 \u003csup\u003ebc\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003emiddle\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1,60\u0026thinsp;\u0026plusmn;\u0026thinsp;0,66 \u003csup\u003ee\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0,77\u0026thinsp;\u0026plusmn;\u0026thinsp;1,78 \u003csup\u003ede\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-1,93\u0026thinsp;\u0026plusmn;\u0026thinsp;2,31 \u003csup\u003eab\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-0,73\u0026thinsp;\u0026plusmn;\u0026thinsp;1,35 \u003csup\u003ebcd\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003einner\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0,33\u0026thinsp;\u0026plusmn;\u0026thinsp;0,85\u003csup\u003ecde\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0,44\u0026thinsp;\u0026plusmn;\u0026thinsp;2,39 \u003csup\u003ecde\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0,21\u0026thinsp;\u0026plusmn;\u0026thinsp;1,80 \u003csup\u003ecde\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0,71\u0026thinsp;\u0026plusmn;\u0026thinsp;1,34 \u003csup\u003ede\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eΔE\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eouter\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4,49\u0026thinsp;\u0026plusmn;\u0026thinsp;0,53 \u003csup\u003ecd\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3,37\u0026thinsp;\u0026plusmn;\u0026thinsp;0,7 \u003csup\u003ebc\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e11,43\u0026thinsp;\u0026plusmn;\u0026thinsp;0,54 \u003csup\u003ef\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e6,92\u0026thinsp;\u0026plusmn;\u0026thinsp;0,99 \u003csup\u003ee\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003emiddle\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4,21\u0026thinsp;\u0026plusmn;\u0026thinsp;0,88 \u003csup\u003ecd\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2,03\u0026thinsp;\u0026plusmn;\u0026thinsp;1,25 \u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e7,32\u0026thinsp;\u0026plusmn;\u0026thinsp;1,48 \u003csup\u003ee\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e4,92\u0026thinsp;\u0026plusmn;\u0026thinsp;1,47 \u003csup\u003ed\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003einner\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1,62\u0026thinsp;\u0026plusmn;\u0026thinsp;0,76 \u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2,81\u0026thinsp;\u0026plusmn;\u0026thinsp;1,23 \u003csup\u003eab\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1,95\u0026thinsp;\u0026plusmn;\u0026thinsp;0,97 \u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1,75\u0026thinsp;\u0026plusmn;\u0026thinsp;1,02 \u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"6\"\u003eSame superscript lowercase letters represent no significant difference according to each color parameter (ΔL, Δa, Δb and ΔE) (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05).\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eAccording to the ΔE values, minimum and maximum color changes were obtained in inner (ΔE\u0026thinsp;=\u0026thinsp;1.75\u0026thinsp;\u0026plusmn;\u0026thinsp;1.06) and outer (ΔE\u0026thinsp;=\u0026thinsp;6.92\u0026thinsp;\u0026plusmn;\u0026thinsp;1.03) groups. When the mean ΔE values were evaluated, the outer (ΔE\u0026thinsp;=\u0026thinsp;6.90) and middle (ΔE\u0026thinsp;=\u0026thinsp;4.9) resulted in a clinically unacceptable value (ΔE\u0026thinsp;\u0026gt;\u0026thinsp;1.74) for metal-ceramic samples. The ΔE values of inner group (ΔE\u0026thinsp;=\u0026thinsp;1.80) were in the range of visual perceptibility but clinical acceptability (1.74\u0026thinsp;\u0026lt;\u0026thinsp;ΔE\u0026thinsp;\u0026lt;\u0026thinsp;3.48). Figure\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e presents the ΔE values by furnace position and firing stage, with dashed lines indicating the 50:50% perceptibility (ΔE\u0026thinsp;=\u0026thinsp;1.74) and acceptability (ΔE\u0026thinsp;=\u0026thinsp;3.48) thresholds.\u003c/p\u003e"},{"header":"DISCUSSION","content":"\u003cp\u003eThe null hypothesis of this study, which stated that the position of metal-ceramic restorations within the porcelain furnace would not affect color changes, was rejected. Specimens placed closer to the heat source exhibited greater color differences, while those located at the center of the furnace showed significantly less color change. An exception was observed during the enamel firing stage, where no significant difference in color change was found between the specimens positioned in the inner and middle zones.\u003c/p\u003e \u003cp\u003eThe methodology utilized to assess color stability in the present study was determined according to previous studies conducted with spectrophotometer using CIELab (ΔE*ab) coordinate system.\u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e,\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e Although the CIEDE2000 (ΔE\u003csub\u003e00\u003c/sub\u003e) color difference formula is a more up-to-date option compared to the CIELab formula in the evaluation of color difference thresholds of dental restorations, the color difference can be determined quantitatively and reliably using the CIELab color space and the associated ΔE*ab. A recent study has demonstrated significant correlations between ΔEab and ΔE00 values.\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eWhen the specimens were positioned closer to the heat source in the porcelain furnace, the greatest color changes were obtained in the outer group (ΔE\u0026thinsp;=\u0026thinsp;6.92\u0026thinsp;\u0026plusmn;\u0026thinsp;1.03), whereas the least color changes were recorded in the inner group (ΔE\u0026thinsp;=\u0026thinsp;1.75\u0026thinsp;\u0026plusmn;\u0026thinsp;1.06). According to the ΔE values, specimens in the outer (ΔE\u0026thinsp;=\u0026thinsp;6.90) and middle (ΔE\u0026thinsp;=\u0026thinsp;4.9) zones exhibited clinically unacceptable color differences (ΔE\u0026thinsp;\u0026gt;\u0026thinsp;3.48). In contrast, the ΔE values of the inner group (ΔE\u0026thinsp;=\u0026thinsp;1.75) fell within the range of visual perceptibility but clinical acceptability (1.74\u0026thinsp;\u0026lt;\u0026thinsp;ΔE\u0026thinsp;\u0026lt;\u0026thinsp;3.48). Similarly, Machado et al.\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e reported that feldspathic porcelains placed at the center of the porcelain furnace exhibited lower translucency levels compared to those positioned near the periphery.\u003c/p\u003e \u003cp\u003eThe most traditional heating methods used for ceramic synthesis and sintering \u0026mdash;based on thermal conduction, radiation, and convection\u0026mdash;include electric resistance and fuel-based systems, and are classified as contact heating methods, where thermal energy is transferred by direct contact with the material. In contrast, non-contact heating methods, such as induction, radiofrequency, and microwave heating, transfer energy through electromagnetic radiation, coupling with the material, thereby eliminating the need for direct contact.\u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e A porcelain furnace is specifically designed to process dental porcelains to optimal levels of maturity while maintaining essential properties of the restoration, such as surface texture, translucency, value, hue, and chroma.\u003csup\u003e\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eAlthough conventional furnaces are routinely used for veneering processes in dental practice, they do not produce a uniform heating environment. Heat is initially applied to the surface of the ceramic and subsequently transferred to the core by thermal conduction, resulting in the formation of high temperature gradients and internal stresses within the material.\u003csup\u003e\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/sup\u003e To ensure consistent thermal exposure, it is recommended that ceramic restorations be placed in specific, standardized locations within firing chamber. Some advanced furnace systems incorporate specially designed muffles to achieve a more homogenous temperature distribution, thereby eliminating the hot or cold spots commonly observed in traditional configurations. Whether the restoration is positioned on a firing pin or a firing pillow, these optimized muffle configurations aim to deliver uniform sintering conditions.\u003csup\u003e\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e Consistent with these principles, the findings of the present study demonstrated that the position of porcelain restorations within the furnace significantly affects color outcomes.\u003c/p\u003e \u003cp\u003ePrevious studies have demonstrated that repeated firings also have an effect on color stability of porcelain restorations. Yilmaz et al.\u003csup\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e reported that successive porcelain firings (including opaque, repetitive dentin, and glaze firings) significantly influenced the color of a 0.1 mm thick layer of opaque porcelain across different alloy groups. In their study, the magnitude of color change after the first denting firing was greater than that observed after subsequent firings, regardless of the alloy type. These findings are consistent with those of Mulla et al.\u003csup\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e, who similarly reported significant color alterations following the initial firing, with less pronounced changes after additional firings. In the present study the greatest color differences were observed in the translucent ceramic application between the outer (ΔE\u0026thinsp;=\u0026thinsp;11.4), middle (ΔE\u0026thinsp;=\u0026thinsp;7.3) and the inner group (ΔE\u0026thinsp;=\u0026thinsp;1.9).\u003c/p\u003e \u003cp\u003eRepeated firings in porcelain restorations may induce color changes due to the effects of metal oxides. Some metal oxides have been reported to degrade under high firing temperatures, leading to pigment breakdown and subsequent alterations in color.\u003csup\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e Furthermore, repeated firings can cause burning of the porcelain\u0026rsquo;s color pigments and promote devitrification processes.\u003csup\u003e\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e In the present study, the observed color changes, particularly in specimens positioned closer to the heat source, may be attributed to the thermal instability of metal oxides. Consistently, ΔE values in the outer zone specimens were higher than those in the inner zone across all firing procedures.\u003c/p\u003e \u003cp\u003eBarghi\u003csup\u003e\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/sup\u003e reported that the slight change in color after repeated firings may be attributed to the increased material density resulting from the reduction of air bubbles trapped within the porcelain structure. Due to the high viscosity of porcelain at its low melting temperature, the diffusion of ionic species within the molten glassy matrix is significantly limited. In the present study, the observed color changes in specimens located closer to the heat source may similarly be attributed to enhanced ionic diffusion into the softened glassy phase of the viscous porcelain, as suggested by Barghi\u003csup\u003e\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eStudies evaluating the color alteration of ceramic surfaces after firing have demonstrated that pigments can degrade at elevated firing temperatures. Ceramic specimens fired at 1.6\u0026deg;C and 21\u0026deg;C above the manufacturer-recommended firing temperatures exhibited substantial differences in both shade and value.\u003csup\u003e\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u003c/sup\u003e However, the present study has some limitations. First, it did not investigate the specific ionic mechanisms underlying the direction of color change. Second, only a single shade (A2) and metal-ceramic restorations were evaluated. Further studies incorporating different ceramic types, various shades, and varying distances from the heat source are required to comprehensively understand these effects.\u003c/p\u003e"},{"header":"CONCLUSIONS","content":"\u003cp\u003eWithin the limitation of this study, the following conclusions were drawn:\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003eThe final color of metal-ceramic restorations is significantly affected by their position within the firing chamber of the porcelain furnace.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eRestorations positioned away from the center of the furnace during the application stages of dentin, enamel, translucent, and glaze ceramics are more susceptible to color changes due to increased exposure to the heat source.\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003eEthics approval and consent to participate: -\u003c/p\u003e\n\u003cp\u003eConsent for publication: -\u003c/p\u003e\n\u003cp\u003eAvailability of data and materials: -\u003c/p\u003e\n\u003cp\u003eCompeting interests: -\u003c/p\u003e\n\u003cp\u003eFunding: None\u003c/p\u003e\n\u003cp\u003eAuthors\u0026apos; contributions: Emir Y\u0026uuml;zbaşıoğlu and Murat Kurt contributed to conceptualization and constructed the material method. Murat Kurt prepared the samples and fired them, while Emir Y\u0026uuml;zbaşıoğlu performed the color measurements. İzim T\u0026uuml;rker Kader collected data, took the pictures and performed statistical analysis. Berkman Albayrak wrote the manuscript beside contributing the firing processes of samples.\u003c/p\u003e\n\u003cp\u003eAcknowledgements: -\u003c/p\u003e\n\u003cp\u003eClinical trial number: not applicable\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eEmir Y\u0026uuml;zbaşıoğlu and Murat Kurt contributed to conceptualization and constructed the material method. Murat Kurt prepared the samples and fired them, while Emir Y\u0026uuml;zbaşıoğlu performed the color measurements. İzim Turker Kader collected data and performed statistical analysis. Berkman Albayrak wrote the manuscript beside contributing the firing processes of samples.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003ePatil VV, Sowmya S, Vathare AS, et al. Evaluating the Impact of Prosthetic Material Choices on the Clinical Outcomes of Implant-Supported Restorations. J. Pharm. Bioallied Sci. 2024;16 Suppl 3:2752-4. doi:10.4103/jpbs.jpbs_372_24\u003c/li\u003e\n\u003cli\u003eFredericci C, Yoshimura HN, Molisani AL, Pinto MM, Cesar PF. Effect of temperature and heating rate on the sintering of leucite-based dental porcelains. Ceram. Int. 2011;37 (3):1073-8. doi:10.1016/j.ceramint.2010.11.040\u003c/li\u003e\n\u003cli\u003eCesar PF, Soki FN, Yoshimura HN, Gonzaga CC, Styopkin V. Influence of leucite content on slow crack growth of dental porcelains. Dent. Mater. 2008;24 (8):1114\u0026ndash;22. doi: 10.1016/j.dental.2008.01.003\u003c/li\u003e\n\u003cli\u003eSalido MP, Martinez-Rus F, del Rio F, Pradies G, Ozcan M, Suarez MJ. Prospective clinical study of zirconia-based posterior four-unit fixed dental prostheses: four-year follow-up. Int J Prosthodont. 2012;25:403\u0026ndash;9. doi:10.5167/uzh-75527\u003c/li\u003e\n\u003cli\u003eTan K, Pjetursson BE, Lang NP, Chan ES. A systematic review of the survival and complication rates of fixed partial dentures (FPDs) after an observation period of at least 5 years. Clin Oral Implants Res. 2004;15:654\u0026ndash;66. doi:10.1111/j.1600-0501.2004.01119.x\u003c/li\u003e\n\u003cli\u003eDouglas RD, Brewer JD. Acceptability of shade differences in metal ceramic crowns. J Prosthet Dent. 1998;79(3):254-60. doi:10.1016/s0022-3913(98)70233-1\u003c/li\u003e\n\u003cli\u003eUludag B, Usumez A, Sahin V, et al. The effect of ceramic thickness and number of firings on the color of ceramic systems: an in vitro study. J Prosthet Dent. 2007;97:25-31. doi: 10.1016/j.prosdent.2006.11.002\u003c/li\u003e\n\u003cli\u003eWee AG, Monaghan P, Johnston WM. Variation in color between intended matched shade and fabricated shade of dental porcelain. J Prosthet Dent. 2002;87(6):657-66. doi: 10.1067/mpr.2002.125727\u003c/li\u003e\n\u003cli\u003eTang X, Nakamura T, Usami H, Wakabayashi K, Yatani H. Effects of multiple firings on the mechanical properties and microstructure of veneering ceramics for zirconia frameworks. J Dent. 2012;40(5):372-80. doi:10.1016/j.jdent.2012.01.014\u003c/li\u003e\n\u003cli\u003eOzturk O, Uludag B, Usumez A, Sahin V, Celik G. The effect of ceramic thickness and number of firings on the color of two all-ceramic systems. J Prosthet Dent. 2008;100:99\u0026ndash;106. doi:10.1016/S0022-3913(08)60156-0\u003c/li\u003e\n\u003cli\u003eHammad IA, Stein RS. A qualitative study for the bond and color of ceramometals. Part II. J Prosthet Dent. 1991;65(2):169-79. doi:10.1016/0022-3913(91)90158-s\u003c/li\u003e\n\u003cli\u003eCorciolani G, Vichi A, Louca C, Ferrari M. Influence of layering thickness on the color parameters of a ceramic system. Dent Mater. 2010;26(8):737-42. doi:10.1016/j.dental.2010.03.018\u003c/li\u003e\n\u003cli\u003eZhang Y, Griggs JA, Benham AW. Influence of powder/liquid mixing ratio on porosity and translucency of dental porcelains. J Prosthet Dent. 200491(2):128-35. doi:10.1016/j.prosdent.2003.10.014\u003c/li\u003e\n\u003cli\u003eO\u0026apos;Brien WJ, Kay KS, Boenke KM, Groh CL. Sources of color variation on firing porcelain. Dent Mater. 1991;7(3):170-3. doi: 10.1016/0109-5641(91)90038-z\u003c/li\u003e\n\u003cli\u003eHammad IA. Intrarater repeatability of shade selections with two shade guides. J Prosthet Dent. 2003;89(1):50-3. doi:10.1067/mpr.2003.60\u003c/li\u003e\n\u003cli\u003eAnitha KV, Dhanraj M, Haribabu R. Comparison of the effect of different ceramic alloys and porcelain systems upon the color of metal-ceramic restorations: An in vitro study. J Indian Prosthodont Soc. 2013;13(3):296-302. doi: 10.1007/s13191-013-0267-5\u003c/li\u003e\n\u003cli\u003eGhulman MA, Awad MA. Color variation between matched and fabricated shades of different ceramics. J Prosthodont 2013;22 :472-7. doi:10.1111/jopr.12027\u003c/li\u003e\n\u003cli\u003eKhashayar G, Bain PA, Salari S, Dozic A, Kleverlaan CJ, Feilzer AJ. Perceptibility and acceptability thresholds for colour differences in dentistry. J Dent. 2014;42(6):637-44. doi:10.1016/j.jdent.2013.11.017\u003c/li\u003e\n\u003cli\u003eAlghazali N, Burnside G, Moallem M, Smith P, Preston A, Jarad FD. Assessment of perceptibility and acceptability of color difference of denture teeth. J Dent. 2012;40,e10-e17. doi:10.1016/j.jdent.2012.04.023\u003c/li\u003e\n\u003cli\u003eDouglas RD, Brewer JD. Acceptability of shade differences in metal ceramic crowns. J Prosthet Dent. 1998;79:254\u0026ndash;60. doi:10.1016/s0022-3913(98)70233-1\u003c/li\u003e\n\u003cli\u003eGhinea R, Perez MM, Herrera LJ, et al. Color difference thresholds in dental ceramics. J Dent. 2010;38 (Suppl 2):e57\u0026ndash;64. doi:10.1016/j.jdent.2010.07.008\u003c/li\u003e\n\u003cli\u003eMachado PS, Camponogara JG, Rodrigues CDS, Jacques LB, Valandro LF, Rippe MP. Influence of number and position of porcelain specimens in the furnace on flexural strength and translucency. Braz J Oral Sci. 2023;22:e231377. doi:10.20396/bjos.v22i00.8671377\u003c/li\u003e\n\u003cli\u003eMachado PS, Pereira GKR, Rodrigues CDS, Guilardi LF, Valandro LF, Rippe MP. Fatigue behavior and colorimetric differences of a porcelain-veneered zirconia: effect of quantity and position of specimens during firing. J Prosthodont Res. 2021;65(2):202-7. doi:10.2186/jpr.JPOR_2019_336\u003c/li\u003e\n\u003cli\u003eFathi A, Farzin M, Giti R, Kalantari MH. Effects of number of firings and veneer thickness on the color and translucency of 2 different zirconia-based ceramic systems. J Prosthet Dent. 2019;122(6):565.e1-565.e7. doi:10.1016/j.prosdent.2019.08.020\u003c/li\u003e\n\u003cli\u003eYılmaz B, Ozcelik TB, Wee AG. Effect of repeated firings on the color of opaque porcelain applied on different dental alloys. J Prosthet Dent. 2009;101(6):395-404. doi:10.1016/S0022-3913(09)60085-8\u003c/li\u003e\n\u003cli\u003eMulla FA, Weiner S. Effects of temperature on color stability of porcelain stains. J Prosthet Dent. 1991;65:507-12. doi:10.1016/0022-3913(91)90290-d\u003c/li\u003e\n\u003cli\u003eInternational Organization for Standardization. ISO/TR 28642 Dentistry\u0026mdash;guidance on color measurement. Geneva: International Organization for Standardization; 2011.\u003c/li\u003e\n\u003cli\u003eSabatini C, Campillo M, Aref J. Color stability of ten resin-based restorative materials. J Esthet Restor Dent. 2012;24(3):185\u0026ndash;199. doi:10.1111/j.1708-8240.2011.00442.x\u003c/li\u003e\n\u003cli\u003eKim BJ, Lee YK. Influence of the shade designation on the color difference between the same shade-designated resin composites by the brand. Dent Mater. 2009;25(9):1148\u0026ndash;1154.\u003c/li\u003e\n\u003cli\u003eAgrawal DK. Microwave processing of ceramics. Curr Opin Solid St M. 1998;3(5):480-485. doi:10.1016/j.dental.2009.04.001\u003c/li\u003e\n\u003cli\u003ePatrick B. Inside Dental Technology. 2011;Vol 2:Issue 3.\u003c/li\u003e\n\u003cli\u003eKatz JD. Microwave Sintering of Ceramics. Annu Rev Mater. 1992;22:153-70. doi:10.1146/annurev.ms.22.080192.001101\u003c/li\u003e\n\u003cli\u003eGonuldas F, Yılmaz K, Ozturk C. The effect of repeated firings on the color change of dental ceramics using different glazing methods. J Adv Prosthodont. 2014;6(6):427\u0026ndash;33. doi:10.4047/jap.2014.6.6.427\u003c/li\u003e\n\u003cli\u003eBarghi N. Color and glaze: effects of repeated firings. J Prosthet Dent. 1982;47:393-5. doi:10.1016/s0022-3913(82)80088-7\u003c/li\u003e\n\u003cli\u003eJorgenson MW, Goodkind RJ. Spectrophotometric study of five porcelain shades relative to the dimensions of color, porcelain thickness, and repeated firings. J Prosthet Dent. 1979;42:96-105. doi:10.1016/0022-3913(79)90335-4\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"color stability, dental porcelain, metal-ceramic restorations, porcelain firing, porcelain furnace","lastPublishedDoi":"10.21203/rs.3.rs-6797246/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6797246/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground\u003c/h2\u003e \u003cp\u003eThis study aimed to evaluate the influence of furnace positioning and sequential firing procedures on the final color of metal-ceramic restorations.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e \u003cp\u003eForty-two disc-shaped metal-ceramic specimens were fabricated and veneered with dentin, enamel, transparent, and glaze porcelain layers. Specimens were positioned at three different zones within the porcelain furnace (inner, middle, and outer) and subjected to standardized firing cycles. Color measurements were performed using a spectrophotometer after each firing phase. Color differences (ΔE*) were calculated between the control (center) and each group, and the clinical relevance was interpreted according to perceptibility (ΔE*=1.74) and acceptability (ΔE*=3.48) thresholds. Statistical analysis was conducted using two-way ANOVA and post hoc Tukey's HSD tests (α\u0026thinsp;=\u0026thinsp;0.05).\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eBoth furnace position (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05) and firing procedure (p 0\u0026thinsp;\u0026lt;\u0026thinsp;0.05) significantly affected color differences. The greatest color changes were observed in specimens placed in the outer zone (ΔE\u0026thinsp;=\u0026thinsp;6.90), whereas specimens in the inner zone exhibited minimal color differences (ΔE\u0026thinsp;=\u0026thinsp;1.80). Outer and middle specimens exceeded the clinical acceptability threshold, while inner specimens remained within clinically acceptable limits.\u003c/p\u003e\u003ch2\u003eConclusions\u003c/h2\u003e \u003cp\u003eThe position of metal-ceramic restorations within the furnace during firing procedures significantly affects the final color outcome. Careful placement of restorations during porcelain firing is essential to ensure optimal color stability.\u003c/p\u003e","manuscriptTitle":"Effect of Distance to the Heat Source During Firing on the Final Color of Metal-Ceramic Restorations: An In Vitro Study","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-06-20 16:40:20","doi":"10.21203/rs.3.rs-6797246/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"ab4766ef-424c-498d-9ed5-3a01244a057c","owner":[],"postedDate":"June 20th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-07-14T17:08:30+00:00","versionOfRecord":[],"versionCreatedAt":"2025-06-20 16:40:20","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6797246","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6797246","identity":"rs-6797246","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}