Characteristics of the convergent angles of tapered implants based on a premolar root model

Statement of problem: Developing tapered implants with the most appropriate angular characteristics requires an improved analysis of the anatomy of premolar roots. Purpose: The purpose of this observational study was to analyze the 3D anatomy of premolar roots by determining the tapered slope and convergent angle (TS/CA), to transform the TS/CA patterns into those in which the tapered implants mimic natural tooth roots, and to provide TS/CA references for future investigations. Material and methods: A total of 73 human single-rooted premolars were surveyed and analyzed by microcomputed tomography and an associated software program. The 3D root surface area (RSA), the radius/diameter (R/D) at the planned first to tenth millimeter levels apical to the cementoenamel junction (CEJ), and the TS/CA at corresponding levels were calculated. The results were statistically analyzed by using an independent samples t test to assess the general differences of tested parameters between maxillary and mandibular premolars. A paired t test was used to examine the significant intragroup TS/CA differences between sequential coronoapical levels. One-way ANOVA was applied to study the general significance of developmental patterns in maxillary and/or mandibular groups. Two-way ANOVA was used to inspect the TS/CA significance at various measurements coronoapically between the maxillary and mandibular premolars (α=.05). Results: Generally, the RSA, root length, R/D, and TS/CA parameters examined for the maxillary premolar roots differed significantly from those for the mandibular roots at the evaluated levels (P<.05). According to the measurements, the maxillary premolar roots generally exhibited nonsignificant RSA and R/D reduction patterns, with a decreasing angle of TS=13.44 degrees and CA=24.53 degrees coronoapically. However, mandibular premolar roots exhibited a significant reduction pattern, with TS=11.25 degrees and CA=21.06 degrees coronoapically according to both individual and general evaluations. Conclusions: Based on the developmental patterns of the evaluated TSs/CAs, tapered implants imitating premolar root anatomy should have a conical rather than a cylindrical shape, and the R/D of these models should be reduced to half at the apical third. However, further studies are warranted to identify more TS/CA characteristics related to the tapered implants, including the TSs/CAs of other tooth types.