BMC Oral Health最新文献

Objectives: This study was to investigate the enamel thickness in different anatomical landmarks of occlusal surfaces of first molars and to evaluate probability of dentin exposure (DE) and percentage of remaining occlusal enamel areas following occlusal veneer preparation at different depths.

Materials and methods: Cone beam computed tomography (CBCT) images of maxillary and mandibular first permanent molars (N = 90, each 45) were used to measure occlusal enamel thickness at specific landmarks. The probability of DE after different preparation depths was calculated. Two freshly-extracted first molars were scanned using a Micro-CT to obtain STLm files. 72 resin models were 3D-printed and randomly assigned to 12 groups (n = 6) before they were prepared for occlusal veneer at 0.6-2.0 mm of depths. The prepared models were scanned to obtain STLp files that were aligned and superimposed to STLm. Prepared occlusal enamel surface areas and dentin exposure areas were analyzed.

Results: Enamel thickness ranged from 0.93 to 1.93 mm in maxillary first molars and 0.98-1.91 mm in mandibular first molars. The central fossa (CF) showed the thinnest enamel in both maxillary and mandibular first molars. After tooth preparation of occlusal veneer of first molar, probability of DE was zero at 0.6 mm, < 20% at 0.8 mm, < 60% at 1.0 mm, around 80% at 1.2 mm, in which the highest probability of DE was CF. Even at 1.2 mm, percentage of occlusal enamel area of first molar was 82.10 ± 1.45% (maxillary) and 94.83 ± 1.66% (mandibular).

Conclusions: For bonding to high percentage (≥ 80%) of occlusal enamel areas of unworn tooth, tooth preparation of occlusal veneers should be not deeper than 1.2 mm, and for bonding to total occlusal enamel area, tooth reduction should be around 0.6 mm.

Clinical relevance: Dentists should carefully consider occlusal enamel thickness distribution for tooth preparation of occlusal veneer because middle-aged and senior people often have tooth wear to some degree.

Background: This in vitro study aimed to investigate the accuracy of a modified scanning technique that incorporated a simple scan aid (SSA) and a novel scanning pattern (segmented scanning pattern, SSP) for complete-arch implant scan.

Methods: An edentulous maxillary stone cast with 4 parallel analogs was used as the master model. 10 scans were performed with an intraoral scanner (Trios3) using different scanning methods: a conventional scanning pattern (CSP) without SSA (Group I), CSP with SSA (Group II), SSP with SSA (Group III) and conventional splinted open-tray impression (Group IV). The reference scan was obtained by digitizing the master model using a dental laboratory scanner. The related files were imported into inspection software for trueness and precision assessment. One-way ANOVA, Kruskal-Wallis, SNK-q and Bonferroni test were used to evaluate the values. The level of significance was set at α=0.05.

Results: For the overall accuracy assessment (trueness and precision), group I exhibited the largest linear and angular deviation (p<0.001) followed by group II (p<0.001). For local accuracy assessment, all intraoral scan bodies (ISB A, B, C, and D) exhibited smaller linear and angular deviations in group III (p<0.05) and group IV (p<0.05) than that in group I. No differences were found between group III and IV (p>0.05), either in the overall accuracy or local accuracy assessment.

Conclusions: SSA combined with SSP could significantly improve the accuracy of complete-arch digital implant impressions.