Referring crown-to-root ratio and root surface area to assess periodontitis severity and prognosis

Background: Whether the linear crown-to-root ratio (CRR) decided by 3D and 2D clinical attachment loss (CAL) can be applied to evaluate the periodontitis severity and tooth prognosis was rarely examined. Materials: Sixty-six mandibular and maxillary single-rooted human premolars were surveyed by micro-computed tomography. CRRs at the levels of defined mild, moderate and severe periodontitis severity were analyzed. Statistical significance was confirmed by t -testes. Results: Along with the definitions, both the findings of coronal 25% root surface area (RSA) with CRR=1:1 corresponded to ≤3.0 mm linear radiographic bone loss (L-RBL) and 20% RSA with CRR=4:5 at L-RBL=1.6‒1.9 mm signified ≤15% L-RBL were categorized as mild periodontitis. Similarly, the results of coronal RSA≤52% with CRR≤3:2 at L-RBL≤5.0 mm and RSA=40% with CRR=5:4 at 4.0 mm L-RBL denoted 30% L-RBL were characterized moderate periodontitis. Additionally, relying on whether a 1.0mm connective tissue attachment (CTA) was included, CRR=1:1 at 25% L-RBL or CRR=4:3 at 35% L-RBL corresponded to a 25% clinical attachment loss (CAL), which could be used to distinguish a fair prognosis from a good prognosis. Either the level with 50% L-RBL at CRR=2:1, or the level with 50% CAL and 60% L-RBL at CRR=5:2 could be applied to differentiate a poor prognosis from a questionable prognosis. Conclusions: The periodontitis severity and tooth prognosis defined by 2015 academic classification could be evaluated according to a range of corresponding RSAs and CRRs. The length and morphology of the tapered roots and decreasing CTA enclosure partially explained the findings.