Thermo-hygrometric aging increases marginal gap of lithium disilicate and leucite-reinforced CAD/CAM veneers but not resin nano-ceramic: an in-vitro comparative study

Thermo-hygrometric aging increases marginal gap of lithium disilicate and leucite-reinforced CAD/CAM veneers but not resin nano-ceramic: an in-vitro comparative 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 Article Thermo-hygrometric aging increases marginal gap of lithium disilicate and leucite-reinforced CAD/CAM veneers but not resin nano-ceramic: an in-vitro comparative study Mohammed AbdulAziz AlBaili, Salah M. Bin Hafedh This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8243485/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 Backgound: Marginal adaptation is a critical determinant of veneer longevity; thermo‑hygrometric artificial accelerated aging (AAA) may alter luting interfaces and material‑specific deformations. Methods: Using the same 30‑specimen dataset as Article 1, vertical marginal gap (µm) was measured by USB microscope and image analysis before and after 300 h AAA (UV‑B 280–320 nm; 4 h UV at 50 °C + 4 h condensation cycles). Results: Non‑aged vs aged mean gaps (µm) were Lava Ultimate 62.0±22.6→85.3±24.1 (ns), IPS e.max CAD 52.9±17.7→84.4±5.4 (p=0.009), and IPS Empress CAD 61.6±7.2→89.4±12.3 (p=0.009). Between‑materials differences were not significant at either timepoint. Conclusions: AAA significantly widened marginal gaps for glass‑ceramics but not for the resin nano‑ceramic, consistent with polymer‑matrix resilience. All gaps remained within common clinical acceptability ranges (≈40–120 µm) in this setup. Physical sciences/Materials science Health sciences/Medical research marginal adaptation marginal gap AAA CAD/CAM veneers lithium disilicate leucite‑reinforced glass‑ceramic resin nano‑ceramic Figures Figure 1 Figure 2 Background Indirect veneer longevity depends on three coupled pillars: accurate marginal adaptation, durable adhesive bonding, and adequate fracture resistance. Marginal and internal gaps permit fluid ingress and biofilm accumulation and, if excessive, are associated with marginal discoloration, debonding, and secondary caries [ 1 – 3 ]. While an absolute universal threshold does not exist, contemporary syntheses repeatedly report acceptable ranges on the order of 50–120 µm depending on restoration type and measurement protocol [ 4 – 7 ]. A broad range of metrologies have been described for gap assessment. Direct viewing under optical microscopy or SEM offers accessibility and speed but provides 2‑dimensional sampling at exposed margins. Replica techniques enable cross‑sectional assessment away from the margin but introduce additional processing variability. Micro‑computed tomography (micro‑CT) and cone‑beam CT (CBCT) permit 3D mapping of the cement space and absolute marginal discrepancy. Methodological reviews emphasize that, regardless of technique, investigators should report sampling density (number of measurement points) and calibration procedures to ensure clinically interpretable values [ 1 , 8 – 11 ]. In CAD/CAM veneers, material microstructure and stiffness affect machinability and milling‑induced edge quality, which in turn influence baseline adaptation. Resin nano‑ceramic (RNC) blocks feature a polymer matrix reinforced with nano‑ceramic fillers and typically demonstrate high machinability and reduced edge chipping, which may benefit marginal adaptation compared with brittle glass‑ceramics [ 12 , 13 ]. Conversely, lithium disilicate (LDS) and leucite‑reinforced glass‑ceramics (LEU) provide stable esthetics and strength but can be more susceptible to marginal micro‑chipping during milling and finishing if parameters are sub‑optimal [ 14 – 16 ]. Recent studies on advanced LDS (e.g., Tessera) show chairside efficiency with clinically acceptable marginal gaps and internal fits, though long‑term stability following aging remains under exploration [ 2 , 3 , 11 ]. Thermo‑hygrometric artificial accelerated aging (AAA) is frequently used as a standardized stressor to simulate ultraviolet exposure, heat, and humidity. Although equivalence to clinical time is imperfect, 300 h of UV‑condensation cycling is often referenced as a convenient proxy for roughly a year of intraoral exposure [ 20 ]. Understanding how AAA influences marginal adaptation across material classes can inform selection and maintenance strategies for minimally invasive veneers. Methods Study design. We conducted an in‑vitro comparative analysis using thirty CAD/CAM laminate veneers allocated to three material groups (n = 10 per group): resin nano‑ceramic (Lava Ultimate), lithium disilicate (IPS e.max CAD), and leucite‑reinforced glass‑ceramic (IPS Empress CAD). A single ivory maxillary central incisor was prepared with a butt‑joint incisal design and duplicated into highly filled epoxy resin dies (E ≈ 14.7 GPa) to standardize substrate modulus. Uniform labial reduction (~ 0.5 mm) ensured predominant enamel bonding. CAD/CAM fabrication and finishing. Veneers were designed using the same CAD software parameters and milled per the manufacturers’ instructions; IPS e.max CAD restorations were crystallized prior to finishing. Finishing used multi‑step rubberized abrasives to minimize edge chipping and produce a high gloss. Surface treatment and cementation. Glass‑ceramics were hydrofluoric‑etched and silanated; the RNC was airborne‑abraded with Al2O3 and ultrasonically cleaned before bonding. A light‑cure veneer cement (RelyX Veneer) was applied to the intaglio surface and seating was standardized with a custom loading device applying 250 g for one minute. Excess cement was removed and polymerization was completed from facial, palatal, and incisal aspects per manufacturer recommendations. Marginal gap measurement. Vertical marginal gap (µm) was measured with a USB digital microscope at fixed 90× magnification. Images were calibrated in ImageJ against a ruler standard. For each specimen, five equidistant landmarks were recorded on each surface (mesial, labial, distal, incisal) and each point measured five times; averages were used for analysis. This sampling strategy aligns with recommendations to acquire ≥ 20–50 measurements per restoration to obtain clinically meaningful estimates [ 1 , 10 ]. Artificial accelerated aging (AAA). All specimens were exposed to UV‑condensation cycles in an environmental incubator (Jeio Tech TEMI 300) using UV‑B (280–320 nm): 4 h UV at 50°C followed by 4 h condensation, repeated to 300 h total. This regimen produces thermo‑hygrometric stress that can affect both materials and luting interfaces. Statistics. Normality was assessed using the Shapiro–Wilk test. Between‑materials comparisons at each timepoint were performed with the Kruskal–Wallis test. Within‑material comparisons (pre‑ vs post‑aging) used paired t‑tests or Wilcoxon signed‑rank tests as appropriate (two‑tailed, α = 0.05). Results Descriptive outcomes. Mean marginal gaps (µm) before/after AAA were: Lava Ultimate 62.0 ± 22.6 → 85.3 ± 24.1; IPS e.max CAD 52.9 ± 17.7 → 84.4 ± 5.4; IPS Empress CAD 61.6 ± 7.2 → 89.4 ± 12.3. Between‑materials differences were not significant at either timepoint. Within‑material comparisons demonstrated significant gap increases for IPS e.max CAD and IPS Empress CAD (p = 0.009 each), whereas Lava Ultimate showed a nonsignificant change. All means remained within common clinical acceptability ranges (≈ 40–120 µm). Figures 1 – 2 illustrate group means, standard deviations, and the change after aging; numerical summaries appear in Tables 1–3 (separate file). Discussion Interpretation. The finding that glass‑ceramics exhibited significant increases in marginal gaps after AAA, while the resin matrix material did not, supports a mechanistic hypothesis grounded in elastic‑modulus mismatch and differential thermal and hygroscopic responses. As brittle materials, LDS and LEU may develop micro‑defects at the adhesive interface under cyclic moisture and temperature changes; these defects can manifest as increased vertical gaps at accessible margins. In contrast, RNC’s polymeric phase can dissipate interfacial strain and accommodate minor dimensional changes without opening the interface to the same extent. Alignment with literature. Baseline marginal gaps reported here are consistent with values commonly observed for CAD/CAM veneers fabricated from LDS and LEU as well as from resin‑matrix materials [ 2 , 3 , 11 – 16 ]. Micro‑CT studies of partial coverage restorations corroborate that preparation design and cement space substantially influence adaptation and that post‑aging changes may occur, particularly in brittle ceramics [ 8 , 9 , 11 ]. Recent J Prosthet Dent reports on advanced LDS laminate veneers demonstrate clinically acceptable vertical gaps and internal fits; however, our data suggest that thermo‑hygrometric stress can still widen margins despite acceptable baseline fit [ 2 , 3 ]. Preparation design considerations. For veneers and occlusal veneers, design choice (e.g., butt‑joint, hollow chamfer, overlap) alters stress distribution, ceramic thickness, and potential location of tensile stresses after bonding, with downstream effects on both fracture resistance and marginal adaptation [ 4 , 5 , 22 – 24 ]. Notably, BMC Oral Health studies from 2024–2025 found that while all evaluated designs remained within clinically acceptable gap ranges after aging, fracture behavior varied, reinforcing that adaptation metrics should be interpreted alongside strength data [ 4 , 5 , 22 – 24 ]. Clinical acceptability thresholds and measurement protocols. Contemporary reviews remark that a single numeric threshold is unrealistic because measured gap values depend on technique (direct viewing vs replica vs micro‑CT), sampling density, and whether vertical marginal gap or absolute marginal discrepancy is being quantified [ 1 , 7 , 10 , 11 ]. Nevertheless, ranges of ≤ 100–120 µm are broadly cited as acceptable for indirect restorations, and our results—spanning ~ 53–89 µm—fall within these ranges. Future veneer studies should report the exact number and distribution of measurement points and consider adding micro‑CT/CBCT‑based assessments of internal fit and absolute marginal discrepancy for completeness [ 1 , 8 – 11 ]. Strengths and limitations. Strengths include strict standardization of veneer geometry, substrate modulus, seating load, and a single, well‑defined AAA regimen, as well as high measurement density with repeated measures per point to reduce random error. Limitations include the 2D nature of the measurement, absence of occlusal loading, evaluation of a single luting agent/finishing protocol, and moderate sample size. These constraints motivate confirmatory research using 3D imaging and factorial designs testing cement spaces, finishing approaches, and alternative resin‑matrix and glass‑ceramic systems. Practical implications. When marginal adaptation stability is prioritized in cases with high thermal or hygroscopic challenges, a polymer‑containing CAD/CAM material may be advantageous. Conversely, when superior long‑term optical stability is paramount, glass‑ceramics remain compelling but may warrant meticulous control of cement space, edge finishing, and periodic recall to monitor adaptation. Conclusions Thermo‑hygrometric ultraviolet‑condensation aging significantly increased marginal gaps in lithium disilicate and leucite‑reinforced veneer restorations but not in resin nano‑ceramic veneers. All means remained within commonly cited clinical acceptability ranges. Material selection and protocol optimization (cement space calibration, seating load, finishing, and maintenance) should be considered together when planning minimally invasive CAD/CAM veneers. Clinical significance Post‑cementation marginal gap stability can be enhanced by: (1) precise CAM‑defined cement space and standardized seating load; (2) multi‑step finishing minimizing edge chipping; (3) strict adhesive protocols (etch/silane vs alumina‑air abrasion as indicated); and (4) scheduled maintenance with repolishing if surface roughness increases. For patients with high thermo‑hygrometric stress exposure (e.g., hot beverage consumption, dry/humid environmental cycling), resin matrix ceramics may exhibit superior marginal adaptation stability. Declarations Ethics approval and consent to participate: Not applicable (in‑vitro study; no human or animal participants). Consent for publication: Not applicable. Availability of data and materials: The raw marginal gap measurements and analysis scripts will be deposited in OSF/Zenodo upon acceptance; persistent links will be added at proof stage. Competing interests: The authors declare no competing interests. Funding: No external funding. Authors’ contributions: Experimental concept and dataset as per thesis; manuscript drafting and revision by AlBaili and Bin Hafedh; both authors approved the final version. Use of generative AI in writing: Large‑language‑model assistance was used for language and structural editing under author supervision; no AI tools were used for data collection or analysis. Tables 1–3 are supplied in a separate Word file per BMC Oral Health submission guidance. References Parenti A, et al. Advantages and drawbacks of different methods to measure marginal gaps in dental restorations: a review. J Dent. 2024;139:104800. doi:10.1016/j.jdent.2024.104800. Al‑Haj Ali S, et al. Effects of preparation design on marginal and internal fit of lithium disilicate partial restorations before and after thermomechanical aging: a 3D micro‑CT study. J Prosthet Dent. 2025. https://www.sciencedirect.com/science/article/pii/S0022391325000071 Elbattawy M, et al. 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Accessed 2025. https://paperpile.com/s/bmc-oral-health-citation-style/ Tables Table 1 to 3 are available in the Supplementary Files section. Additional Declarations No competing interests reported. Supplementary Files EditorialManagerChecklist.docx Supplementaryanalysesandrobustness.docx 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-8243485","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":559859796,"identity":"26849c7f-ed18-43b1-9f2a-9894d8e9a9f9","order_by":0,"name":"Mohammed AbdulAziz AlBaili","email":"","orcid":"","institution":"Sana'a University","correspondingAuthor":false,"prefix":"","firstName":"Mohammed","middleName":"AbdulAziz","lastName":"AlBaili","suffix":""},{"id":559859797,"identity":"fab05bbd-66c2-4421-b2ab-7d2db6deee84","order_by":1,"name":"Salah M. 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1","display":"","copyAsset":false,"role":"figure","size":114981,"visible":true,"origin":"","legend":"\u003cp\u003eMarginal gap (mean ± SD) before and after artificial accelerated aging by material (Lava Ultimate; IPS e.max CAD; IPS Empress CAD).\u003c/p\u003e","description":"","filename":"FigA2MarginalGapBeforeAfter.png","url":"https://assets-eu.researchsquare.com/files/rs-8243485/v1/d9f60c09de5f19fcc1bc1d4e.png"},{"id":98766423,"identity":"6520b446-e475-4ed8-b514-1b7fcb2821ca","added_by":"auto","created_at":"2025-12-22 10:16:00","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":117227,"visible":true,"origin":"","legend":"\u003cp\u003eChange in marginal gap (aged − non‑aged, µm) by material after artificial accelerated aging.\u003c/p\u003e","description":"","filename":"FigA2DeltaGap.png","url":"https://assets-eu.researchsquare.com/files/rs-8243485/v1/8bb423b099b49a27f0a92410.png"},{"id":108490814,"identity":"37cedfbb-77cb-4bdd-bdac-e5f6f7576c9e","added_by":"auto","created_at":"2026-05-05 09:48:57","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":400338,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8243485/v1/044acfe2-32eb-4213-8037-911323ac0438.pdf"},{"id":98780026,"identity":"b3bd2bb6-5140-4357-8d59-ecdff912b81b","added_by":"auto","created_at":"2025-12-22 12:30:59","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":26925,"visible":true,"origin":"","legend":"","description":"","filename":"EditorialManagerChecklist.docx","url":"https://assets-eu.researchsquare.com/files/rs-8243485/v1/60b1d8d58613ca5d53f494c5.docx"},{"id":98779087,"identity":"38f1e54c-f347-4bea-ad6b-3463f8f55353","added_by":"auto","created_at":"2025-12-22 12:29:57","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":18385,"visible":true,"origin":"","legend":"","description":"","filename":"Supplementaryanalysesandrobustness.docx","url":"https://assets-eu.researchsquare.com/files/rs-8243485/v1/2e6f30fb5b018449b9860d47.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Thermo-hygrometric aging increases marginal gap of lithium disilicate and leucite-reinforced CAD/CAM veneers but not resin nano-ceramic: an in-vitro comparative study","fulltext":[{"header":"Background","content":"\u003cp\u003eIndirect veneer longevity depends on three coupled pillars: accurate marginal adaptation, durable adhesive bonding, and adequate fracture resistance. Marginal and internal gaps permit fluid ingress and biofilm accumulation and, if excessive, are associated with marginal discoloration, debonding, and secondary caries [\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. While an absolute universal threshold does not exist, contemporary syntheses repeatedly report acceptable ranges on the order of 50\u0026ndash;120 \u0026micro;m depending on restoration type and measurement protocol [\u003cspan additionalcitationids=\"CR5 CR6\" citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eA broad range of metrologies have been described for gap assessment. Direct viewing under optical microscopy or SEM offers accessibility and speed but provides 2‑dimensional sampling at exposed margins. Replica techniques enable cross‑sectional assessment away from the margin but introduce additional processing variability. Micro‑computed tomography (micro‑CT) and cone‑beam CT (CBCT) permit 3D mapping of the cement space and absolute marginal discrepancy. Methodological reviews emphasize that, regardless of technique, investigators should report sampling density (number of measurement points) and calibration procedures to ensure clinically interpretable values [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan additionalcitationids=\"CR9 CR10\" citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn CAD/CAM veneers, material microstructure and stiffness affect machinability and milling‑induced edge quality, which in turn influence baseline adaptation. Resin nano‑ceramic (RNC) blocks feature a polymer matrix reinforced with nano‑ceramic fillers and typically demonstrate high machinability and reduced edge chipping, which may benefit marginal adaptation compared with brittle glass‑ceramics [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Conversely, lithium disilicate (LDS) and leucite‑reinforced glass‑ceramics (LEU) provide stable esthetics and strength but can be more susceptible to marginal micro‑chipping during milling and finishing if parameters are sub‑optimal [\u003cspan additionalcitationids=\"CR15\" citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Recent studies on advanced LDS (e.g., Tessera) show chairside efficiency with clinically acceptable marginal gaps and internal fits, though long‑term stability following aging remains under exploration [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThermo‑hygrometric artificial accelerated aging (AAA) is frequently used as a standardized stressor to simulate ultraviolet exposure, heat, and humidity. Although equivalence to clinical time is imperfect, 300 h of UV‑condensation cycling is often referenced as a convenient proxy for roughly a year of intraoral exposure [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Understanding how AAA influences marginal adaptation across material classes can inform selection and maintenance strategies for minimally invasive veneers.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003eStudy design. We conducted an in‑vitro comparative analysis using thirty CAD/CAM laminate veneers allocated to three material groups (n\u0026thinsp;=\u0026thinsp;10 per group): resin nano‑ceramic (Lava Ultimate), lithium disilicate (IPS e.max CAD), and leucite‑reinforced glass‑ceramic (IPS Empress CAD). A single ivory maxillary central incisor was prepared with a butt‑joint incisal design and duplicated into highly filled epoxy resin dies (E\u0026thinsp;\u0026asymp;\u0026thinsp;14.7 GPa) to standardize substrate modulus. Uniform labial reduction (~\u0026thinsp;0.5 mm) ensured predominant enamel bonding.\u003c/p\u003e \u003cp\u003eCAD/CAM fabrication and finishing. Veneers were designed using the same CAD software parameters and milled per the manufacturers\u0026rsquo; instructions; IPS e.max CAD restorations were crystallized prior to finishing. Finishing used multi‑step rubberized abrasives to minimize edge chipping and produce a high gloss.\u003c/p\u003e \u003cp\u003eSurface treatment and cementation. Glass‑ceramics were hydrofluoric‑etched and silanated; the RNC was airborne‑abraded with Al2O3 and ultrasonically cleaned before bonding. A light‑cure veneer cement (RelyX Veneer) was applied to the intaglio surface and seating was standardized with a custom loading device applying 250 g for one minute. Excess cement was removed and polymerization was completed from facial, palatal, and incisal aspects per manufacturer recommendations.\u003c/p\u003e \u003cp\u003eMarginal gap measurement. Vertical marginal gap (\u0026micro;m) was measured with a USB digital microscope at fixed 90\u0026times; magnification. Images were calibrated in ImageJ against a ruler standard. For each specimen, five equidistant landmarks were recorded on each surface (mesial, labial, distal, incisal) and each point measured five times; averages were used for analysis. This sampling strategy aligns with recommendations to acquire\u0026thinsp;\u0026ge;\u0026thinsp;20\u0026ndash;50 measurements per restoration to obtain clinically meaningful estimates [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eArtificial accelerated aging (AAA). All specimens were exposed to UV‑condensation cycles in an environmental incubator (Jeio Tech TEMI 300) using UV‑B (280\u0026ndash;320 nm): 4 h UV at 50\u0026deg;C followed by 4 h condensation, repeated to 300 h total. This regimen produces thermo‑hygrometric stress that can affect both materials and luting interfaces.\u003c/p\u003e \u003cp\u003eStatistics. Normality was assessed using the Shapiro\u0026ndash;Wilk test. Between‑materials comparisons at each timepoint were performed with the Kruskal\u0026ndash;Wallis test. Within‑material comparisons (pre‑ vs post‑aging) used paired t‑tests or Wilcoxon signed‑rank tests as appropriate (two‑tailed, α\u0026thinsp;=\u0026thinsp;0.05).\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eDescriptive outcomes. Mean marginal gaps (\u0026micro;m) before/after AAA were: Lava Ultimate 62.0\u0026thinsp;\u0026plusmn;\u0026thinsp;22.6 \u0026rarr; 85.3\u0026thinsp;\u0026plusmn;\u0026thinsp;24.1; IPS e.max CAD 52.9\u0026thinsp;\u0026plusmn;\u0026thinsp;17.7 \u0026rarr; 84.4\u0026thinsp;\u0026plusmn;\u0026thinsp;5.4; IPS Empress CAD 61.6\u0026thinsp;\u0026plusmn;\u0026thinsp;7.2 \u0026rarr; 89.4\u0026thinsp;\u0026plusmn;\u0026thinsp;12.3. Between‑materials differences were not significant at either timepoint. Within‑material comparisons demonstrated significant gap increases for IPS e.max CAD and IPS Empress CAD (p\u0026thinsp;=\u0026thinsp;0.009 each), whereas Lava Ultimate showed a nonsignificant change. All means remained within common clinical acceptability ranges (\u0026asymp;\u0026thinsp;40\u0026ndash;120 \u0026micro;m).\u003c/p\u003e \u003cp\u003eFigures \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e illustrate group means, standard deviations, and the change after aging; numerical summaries appear in Tables\u0026nbsp;1\u0026ndash;3 (separate file).\u003c/p\u003e "},{"header":"Discussion","content":"\u003cp\u003eInterpretation. The finding that glass‑ceramics exhibited significant increases in marginal gaps after AAA, while the resin matrix material did not, supports a mechanistic hypothesis grounded in elastic‑modulus mismatch and differential thermal and hygroscopic responses. As brittle materials, LDS and LEU may develop micro‑defects at the adhesive interface under cyclic moisture and temperature changes; these defects can manifest as increased vertical gaps at accessible margins. In contrast, RNC\u0026rsquo;s polymeric phase can dissipate interfacial strain and accommodate minor dimensional changes without opening the interface to the same extent.\u003c/p\u003e \u003cp\u003eAlignment with literature. Baseline marginal gaps reported here are consistent with values commonly observed for CAD/CAM veneers fabricated from LDS and LEU as well as from resin‑matrix materials [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan additionalcitationids=\"CR12 CR13 CR14 CR15\" citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Micro‑CT studies of partial coverage restorations corroborate that preparation design and cement space substantially influence adaptation and that post‑aging changes may occur, particularly in brittle ceramics [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Recent J Prosthet Dent reports on advanced LDS laminate veneers demonstrate clinically acceptable vertical gaps and internal fits; however, our data suggest that thermo‑hygrometric stress can still widen margins despite acceptable baseline fit [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e].\u003c/p\u003e \u003cp\u003ePreparation design considerations. For veneers and occlusal veneers, design choice (e.g., butt‑joint, hollow chamfer, overlap) alters stress distribution, ceramic thickness, and potential location of tensile stresses after bonding, with downstream effects on both fracture resistance and marginal adaptation [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan additionalcitationids=\"CR23\" citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. Notably, BMC Oral Health studies from 2024\u0026ndash;2025 found that while all evaluated designs remained within clinically acceptable gap ranges after aging, fracture behavior varied, reinforcing that adaptation metrics should be interpreted alongside strength data [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan additionalcitationids=\"CR23\" citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eClinical acceptability thresholds and measurement protocols. Contemporary reviews remark that a single numeric threshold is unrealistic because measured gap values depend on technique (direct viewing vs replica vs micro‑CT), sampling density, and whether vertical marginal gap or absolute marginal discrepancy is being quantified [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Nevertheless, ranges of \u0026le;\u0026thinsp;100\u0026ndash;120 \u0026micro;m are broadly cited as acceptable for indirect restorations, and our results\u0026mdash;spanning\u0026thinsp;~\u0026thinsp;53\u0026ndash;89 \u0026micro;m\u0026mdash;fall within these ranges. Future veneer studies should report the exact number and distribution of measurement points and consider adding micro‑CT/CBCT‑based assessments of internal fit and absolute marginal discrepancy for completeness [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan additionalcitationids=\"CR9 CR10\" citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eStrengths and limitations. Strengths include strict standardization of veneer geometry, substrate modulus, seating load, and a single, well‑defined AAA regimen, as well as high measurement density with repeated measures per point to reduce random error. Limitations include the 2D nature of the measurement, absence of occlusal loading, evaluation of a single luting agent/finishing protocol, and moderate sample size. These constraints motivate confirmatory research using 3D imaging and factorial designs testing cement spaces, finishing approaches, and alternative resin‑matrix and glass‑ceramic systems.\u003c/p\u003e \u003cp\u003ePractical implications. When marginal adaptation stability is prioritized in cases with high thermal or hygroscopic challenges, a polymer‑containing CAD/CAM material may be advantageous. Conversely, when superior long‑term optical stability is paramount, glass‑ceramics remain compelling but may warrant meticulous control of cement space, edge finishing, and periodic recall to monitor adaptation.\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eThermo‑hygrometric ultraviolet‑condensation aging significantly increased marginal gaps in lithium disilicate and leucite‑reinforced veneer restorations but not in resin nano‑ceramic veneers. All means remained within commonly cited clinical acceptability ranges. Material selection and protocol optimization (cement space calibration, seating load, finishing, and maintenance) should be considered together when planning minimally invasive CAD/CAM veneers.\u003c/p\u003e\n\u003ch3\u003eClinical significance\u003c/h3\u003e\n\u003cp\u003ePost‑cementation marginal gap stability can be enhanced by: (1) precise CAM‑defined cement space and standardized seating load; (2) multi‑step finishing minimizing edge chipping; (3) strict adhesive protocols (etch/silane vs alumina‑air abrasion as indicated); and (4) scheduled maintenance with repolishing if surface roughness increases. For patients with high thermo‑hygrometric stress exposure (e.g., hot beverage consumption, dry/humid environmental cycling), resin matrix ceramics may exhibit superior marginal adaptation stability.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003eEthics approval and consent to participate: Not applicable (in‑vitro study; no human or animal participants).\u003c/p\u003e\n\u003cp\u003eConsent for publication: Not applicable.\u003c/p\u003e\n\u003cp\u003eAvailability of data and materials: The raw marginal gap measurements and analysis scripts will be deposited in OSF/Zenodo upon acceptance; persistent links will be added at proof stage.\u003c/p\u003e\n\u003cp\u003eCompeting interests: The authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003eFunding: No external funding.\u003c/p\u003e\n\u003cp\u003eAuthors\u0026rsquo; contributions: Experimental concept and dataset as per thesis; manuscript drafting and revision by AlBaili and Bin Hafedh; both authors approved the final version.\u003c/p\u003e\n\u003cp\u003eUse of generative AI in writing: Large‑language‑model assistance was used for language and structural editing under author supervision; no AI tools were used for data collection or analysis.\u003c/p\u003e\n\u003cp\u003eTables 1\u0026ndash;3 are supplied in a separate Word file per BMC Oral Health submission guidance.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eParenti A, et al. 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Accessed 2025. https://bmcoralhealth.biomedcentral.com/submission-guidelines/preparing-your-manuscript/database-article\u003c/li\u003e\n \u003cli\u003ePaperpile. BMC Oral Health reference style (Vancouver). Accessed 2025. https://paperpile.com/s/bmc-oral-health-citation-style/\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003eTable 1 to 3 are available in the Supplementary Files section.\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"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":"marginal adaptation, marginal gap, AAA, CAD/CAM veneers, lithium disilicate, leucite‑reinforced glass‑ceramic, resin nano‑ceramic","lastPublishedDoi":"10.21203/rs.3.rs-8243485/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8243485/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eBackgound: Marginal adaptation is a critical determinant of veneer longevity; thermo‑hygrometric artificial accelerated aging (AAA) may alter luting interfaces and material‑specific deformations.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eMethods: Using the same 30‑specimen dataset as Article 1, vertical marginal gap (µm) was measured by USB microscope and image analysis before and after 300 h AAA (UV‑B 280–320 nm; 4 h UV at 50 °C + 4 h condensation cycles).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eResults: Non‑aged vs aged mean gaps (µm) were Lava Ultimate 62.0±22.6→85.3±24.1 (ns), IPS e.max CAD 52.9±17.7→84.4±5.4 (p=0.009), and IPS Empress CAD 61.6±7.2→89.4±12.3 (p=0.009). Between‑materials differences were not significant at either timepoint.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eConclusions: AAA significantly widened marginal gaps for glass‑ceramics but not for the resin nano‑ceramic, consistent with polymer‑matrix resilience. All gaps remained within common clinical acceptability ranges (≈40–120 µm) in this setup.\u003c/p\u003e","manuscriptTitle":"Thermo-hygrometric aging increases marginal gap of lithium disilicate and leucite-reinforced CAD/CAM veneers but not resin nano-ceramic: an in-vitro comparative study","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-12-22 10:15:51","doi":"10.21203/rs.3.rs-8243485/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":"7dcea1dc-ce91-422f-beb1-15dac1fd91da","owner":[],"postedDate":"December 22nd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":59605758,"name":"Physical sciences/Materials science"},{"id":59605759,"name":"Health sciences/Medical research"}],"tags":[],"updatedAt":"2026-04-29T05:55:52+00:00","versionOfRecord":[],"versionCreatedAt":"2025-12-22 10:15:51","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8243485","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8243485","identity":"rs-8243485","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}