Cervical dentin thickness and root-to-crown ratio in endodontically treated versus healthy teeth: a retrospective cone-beam computed tomography study

<title>Abstract</title> <p>Background Cervical dentin thickness (CDT) and root-to-crown ratio (RCR) are anatomical parameters associated with structural stability and fracture susceptibility in endodontically treated teeth. Population-specific cone-beam computed tomography (CBCT) data comparing treated teeth with structurally intact healthy teeth remain limited. This study compared CDT and RCR between endodontically treated teeth and healthy controls in a Turkish population and identified predictors of CDT. Methods This retrospective CBCT study analyzed 794 endodontically treated teeth and 200 healthy controls from scans obtained at Ankara University Faculty of Dentistry (January 2020–December 2025). Images were acquired using Planmeca ProMax 3D and analyzed with Synapse 7.1. CDT was measured as the shortest distance between the root canal wall and the external root surface at the cementoenamel junction; RCR was calculated as root length divided by crown length. Results Mean CDT was significantly lower in endodontically treated teeth than in healthy controls (1.427 ± 0.522 mm vs. 1.781 ± 0.529 mm; p &lt; 0.001; mean difference 0.354 mm; Cohen’s d = 0.68). Overall, 20.0% of treated teeth had CDT ≤ 1.0 mm versus 4.0% of controls. Mandibular incisors showed the lowest CDT among treated teeth (77.8–85.7% ≤ 1.0 mm). Tooth type explained a modest proportion of CDT variance in the study group (η² = 0.072) but a large proportion in controls (η² = 0.722). Sex predicted CDT in controls (B = − 0.201, p &lt; 0.001; females approximately 0.2 mm thinner) but not in the study group (p = 0.284). Mean RCR did not differ between groups (1.409 ± 0.466 vs. 1.502 ± 0.382; p = 0.082). Conclusions Endodontically treated teeth showed significantly lower CDT than healthy controls, with the largest reductions in molars; after Bonferroni correction, only molar tooth types retained significant between-group differences. Mandibular incisors showed CDT below the 1.0 mm threshold regardless of endodontic status. Given the retrospective design and absence of pretreatment scans, these differences represent associations rather than causal effects. The findings support conservative access preparation, cautious instrumentation, and individualized restorative planning in structurally vulnerable teeth.</p>