[Occlusion variation of posterior implant-supported single crown: a prospective 4-year follow-up study]

Objective: To analyze the longitudinal variation of occlusal force distribution and occlusal contact time in posterior implant-supported single crown with the computerized occlusal analysis system. Methods: Partially edentulous patients who visited the Department of Prosthodontics, Peking University School and Hospital of Stomatology between December 2012 and December 2013, and had received implant-supported single crown in the posterior region were enrolled. The participants underwent occlusal examinations with the computerized occlusal analysis system at 2 weeks, 3 and 6 months, 1, 2, 3, and 4 years after implant prosthesis delivery. The relative occlusal force (ROF) of implant prostheses, mesial adjacent teeth, and control teeth (corresponding teeth on the contralateral side) were recorded, and implant prosthesis occlusion time ratios (implant prosthesis occlusion time/occlusion time) were calculated. The interproximal contact between implant prostheses and adjacent teeth was evaluated using metal contact gauge and dental floss. Mechanical complications of implant prostheses were recorded. The paired t test or Wilcoxon signed-rank test was used to compare the implant prosthesis occlusion time ratios and ROF of implant prostheses at 2 different times as a self-control. The differences in ROF between implant prostheses and control teeth in the same participant at the same time were also analyzed using paired t test. Using a complementary log-log model, the correlation between the occurrence of veneering material fracture and ROF of implant prosthesis was analyzed with gender, age and follow-up time as the control variables. Results: Thirty-seven posterior fixed implant-supported single crowns in 33 participants, including 16 men and 17 women aged (42.8±12.9) years (23.9 to 70.0 years) were followed up for 2 weeks to 4 years [(38.3±15.2) months]. The ROF of implant prostheses increased significantly (P<0.01) from 2 weeks [(7.0±4.2)%] to 3 months [(9.9±6.8)%], whereas those of control natural teeth decreased significantly (P<0.05) from (13.1±6.1)% to (11.4±5.5)%. The ROF of implant prostheses continued to increase from 6 months to 1 year, from 1 year to 2 years and from 2 years to 3 years, with significant differences (P<0.05). Implant prosthesis occlusion time ratios also increased significantly between 2 weeks and 3 months and between 3 months and 6 months (P<0.05). No significant differences were found between other time points (P>0.05). For comparison between implant prosthesis and control teeth at the same time point, the ROF of the implant prostheses [(7.5±4.2)%] were significantly lower than those of the control teeth [(13.8±6.0)%] at 2 weeks (P<0.01). While at 4 years, ROF of implant prostheses [16.7% (8.6%, 32.4%)] became significantly higher than those of control teeth [9.5% (4.9%, 18.0%)] (P<0.05). ROF of the implant prostheses did not differ significantly with those of the control teeth in other follow-up time points (P>0.05). The 4-year cumulative incidence of proximal contact loss rate was 32% (22/68). The incidences of veneering material fracture and prostheses loosening were 16% (6/37) and 8% (3/37), respectively. Logistic regression showed a significant correlation between veneering material fracture and ROF of implant prostheses (r=0.26, P<0.05). Conclusions: The occlusal force and occlusal contact time of posterior implant-supported single crown change over time in 4-year follow-up period, which is mainly reflected in the increasing occlusal force and occlusal contact time. The occlusion of posterior implant prostheses should be carefully monitored during follow-up examinations, and occlusal adjustment should be considered when necessary.