Correlation between implant angulation and crestal bone changes: A 5-year retrospective study

Statement of problem: The effects of nonaxial forces on peri-implant bone loss have been investigated, mostly in reference to buccal mesiodistal implant angulations as potential risk indicators. However, when implant angulations are multidirectional, including the buccolingual aspect, evaluations of peri-implant bone loss based solely on mesiodistal measurements may skew the correlation. Purpose: The purpose of this retrospective study was to evaluate the correlation between the magnitudes of multidirectional implant angulations and peri-implant crestal bone loss. Material and methods: Data were retrospectively collected and analyzed from clinical records, periapical radiographic images, and computer-aided design (CAD) files of custom abutments. The study included 288 patients with 506 dental implants, and the mean follow-up duration after the placement of definitive prostheses was 5.1 years. Patients with uncontrolled systemic disease were excluded. Variables such as age, sex, type of unit (single-unit or multi-unit), location (maxillary or mandibular and anterior, premolar, or molar), and antagonist (natural tooth, implant-supported prosthesis, or removable prosthesis) were evaluated. The angulation of the implant (mesiodistal and buccolingual) and status of attrition (normal, localized, or generalized) were assessed using the CAD file. The angulation of the implant was then derived from the mesiodistal and buccolingual angle measurements by using a mathematical formula. Peri-implant bone loss was measured from periapical radiographs. A comparison of peri-implant bone loss between axial and nonaxial implants was performed using the Student t test (α=.05). Additional comparative evaluations were performed according to the type of unit, location, antagonist, and status of attrition in reference to the angulation categories. Results: The mean ±standard deviation peri-implant bone loss over 5 years was 0.10 ±0.39 mm in the axial implants and 0.22 ±0.48 mm in the nonaxial implants. Statistical analysis showed that nonaxial implants had a significantly greater bone loss (P<.05), which was more pronounced when the antagonists were implant-supported prostheses (P<.05) and when the implants were located in the mandible (P<.05). Conclusions: A significant correlation was observed between implant angulation and peri-implant bone loss. Nonaxially positioned implants exhibited greater bone loss compared with axially positioned implants. Additionally, the location of the implant and the type of antagonist were found to influence the extent of bone loss. These findings suggest that careful consideration of implant angulation, as well as the position and type of antagonist, is crucial in minimizing peri-implant bone loss.