Abstract||Objective: To determine the long-term prosthodontic maintenance requirements of mandibular unsplinted, two-implant overdentures, using different attachment systems and loading protocols.
Materials and Methods: An original total of 106 participants were randomly allocated to one of four different implant systems (Brånemark, Steri-Oss, Straumann and Southern Implant systems). Three different loading strategies were used (2-weeks, 6-weeks and 12-weeks). A total of six different unsplinted attachment systems for mandibular two-implant overdentures were used with the four implant systems. These attachment systems included; the Brånemark gold matrix, Straumann gold matrix, Straumann titanium matrix, Southern Implants plastic matrix, Southern Implants palladium matrix and the Steri-Oss rubber matrix. Each matrix group was allocated to one or more loading strategies and data related to prosthodontic maintenance events was collected prospectively from overdenture insertion (baseline) to year eight, according to predefined categories. Data were analysed using SPSS, and levels of statistical significance were set at P < 0.05. To test for significance between multiple groups, ANOVA was used. Where a statistically significant difference existed, a one way ANOVA with Post Hoc tests was performed.
Results: A total of 90 participants from all matrix groups were followed for six-years and loading comparisons could only be made up to this time. The Southern palladium matrix was followed for only six-years therefore it could not be included in the eight year analysis. A total of 69 participants remained in the randomised controlled trial after eight years. Mandibular two-implant overdentures fitted with the Steri-Oss rubber matrix displayed the highest mean number of maintenance events at 32.2 (SD 14.5) followed by the Brånemark matrix group at 28.8 (SD 12.6), the Straumann titanium matrix group at 24.9 (SD 10.7) and the Straumann gold matrix group at 12.8 (SD 8.2), over an eight year period. The Southern plastic matrix group had the lowest average number of maintenance events (8.7 SD 4.2) over the eight-year period and this was significant compared with all other groups (P < 0.05). Over six years, there were no significant differences found between the number of prosthodontic maintenance events and the loading strategy used. On average, the Straumann gold matrix lasted for 3.9 (SD 2.1) years which was significantly longer than all other matrices (P < 0.05) over six years. The Southern palladium (3.1 SD 1.7), Brånemark gold (2.7 SD 1.5) and Southern plastic (2.5 SD 1.4) matrices all lasted significantly longer than the Straumann titanium (1.7 SD 0.8) and the Steri-Oss rubber (1.4 SD 0.7) matrices over six years.
Conclusions: Mandibular two-implant overdentures using the Southern Implants plastic cap required significantly less prosthodontic maintenance events compared with all other matrix groups. The Straumann gold matrix required significantly less prosthodontic maintenance compared with the Steri-Oss rubber matrix (P<0.05). The Straumann gold matrix also demonstrated the greatest longevity compared with all other matrices (P<0.05). There was no significant difference in the number of prosthodontic maintenance events of two-implant overdentures when loaded at 2, 6 or 12-weeks after implant placement. The prosthodontic maintenance requirements of unsplinted mandibular two-implant overdentures are dependant upon the attachment system chosen.