Occlusal analysis of pre and post crown insertion of posterior single-implant restoration

Background: The concept of “light contact” was promoted as the optimal dental implant occlusion to maximize oral function and prevent adverse consequences for single posterior implant restorations. However, this concept would seem questionable, since these ideas would stick to a static system which unfortunately does not exist. The limitations of current literature were concerned because of insufficientclinical evidences of how light this “light contact” was, and how about the changes and durations, as well as the risk of bias from treating the single implant retained restoration in isolation. Objectives: The purposes of this study were to analyze the effects of single posterior implant restorations delivery on the redistribution of bite force and to evaluate the changes in occlusal force distribution of prostheses and potential influencing factors on occlusion variation at different stages. Materials and methods: Thirty-two single posterior restorations in 30participants (18 women and 12 men aged 27 to 75 years) were placed into either a unilateral single-tooth defect (n = 17) or on either side of a bilateral teeth defects (n =15). The bite force (%) of the prostheses, teeth and segments at the maximum intercuspation position (MIP) was evaluated using a T-scan at 5 stages (pre-placement, immediately following placement, and 2 weeks, 3 months, and 6 months postplacement).Meanwhile, the initial tooth contacts and center of occlusal force (COF) were also recorded. Results: The occlusal force of implant-supported prostheses was significantly (P = .000) lower than those of the control natural teeth at the baseline, then no significant difference was found with that of the mesial teeth at 3 months, and finally it was significantly (P = .000) lower than that of the distal teeth at 6 months; meanwhile, it significantly (P = .008) increased by a mean of 2.04 times from 2 weeks (3.39 ±2.61%) to 3 months (6.90 ± 4.77%), whereas no significant difference (P = .900) was found from 3 months (6.90 ± 4.77%) to 6 months (7.31 ± 4.60%). In addition, the results of COF position showed that there were significant differences (P = .034) in different types of functional teeth units in the initial occlusions. After the placement of restorations, the bite force of the posterior segment on the restored side of both unilateral and bilateral gaps was significantly (P = .013, .001) improved by 3.31% and 6.83%, respectively, although the discrepancy in bite force significantly (P = .039) increased from an initial 3.52% to 5.02% for subjects with bilateral defects, accompanying increases in the proportion (15.38%) of the level Ⅲ bilateral bite force deviation (P > .05).Furthermore, no significant changes in the position of initial contact were found during the observational periods, and the most common initial contact position was 17 and 47(20.27%), followed by 14 and 44(9.46%), 16 and 46(8.11%), 23 and 33(6.76%), respectively. The analysis of stepwise regression revealed that the implant length (P = .012), sex (P = .027) and initial category of defect (P = .008), implant diameter (P = .044), implant is distal free end (P = .001) and opposing teeth (P = .002) had significant effects on the distribution of force at different stages. Conclusions: Bite force and masticatory ability can be improved with the immediate delivery of a single posterior implant restoration. The bite force distributed on the implant prosthesis inevitably increases after placement of implant prostheses, a routine follow-up and occlusal evaluation are strongly needed.