Factors influencing proximal contact loss between fixed implant prostheses and adjacent natural teeth: a retrospective study

Objectives: To investigate the causal factors of proximal contact loss (PCL) between an implant prosthesis and the adjacent natural teeth using cast model analysis. Materials and Methods: Patients who underwent restoration using dental implants in the posterior region were analyzed. To identify factors associated with PCL incidence, cast model analyses were conducted based on sex, implant site, jaw position, Angle’s classification, anterior overbite, preexisting interproximal gap between consecutive (mesial side) natural teeth adjacent to the implant, generalized gap of the full arch, and mandibular anterior crowding. Chi-square, multivariate logistic regression, and multivariate generalized estimating equation (GEE) analyses were used to evaluate the impact of each factor. The incidence of PCL over time was analyzed using Kaplan–Meier analysis. Results: Of 653 implants, 293 implants were selected from 240 patients. Ninety implant sites (30.7%) showed PCL between the implant prostheses and the adjacent teeth. The analysis of PCL incidence revealed a gradual increase over time, with half of PCL cases occurring by 19.2 months. The chisquare test revealed significant associations between a pre-existing interproximal gap between adjacent natural teeth and a generalized overall gap in the corresponding arch and PCL (P=0.002 and P=0.027). The logistic regression (P=0.007, odds ratio [OR]: 2.684) and GEE (P=0.003, OR: 3.255) showed significant correlations between PCL and a pre-existing interproximal gap between adjacent natural teeth. Conclusion: The occurrence of PCL between implant prostheses and adjacent teeth is influenced by the pre-existing interproximal gap between consecutive natural teeth adjacent to the implant. This factor should be carefully monitored.