The effect of implant distribution on functional and patient-reported outcomes of mandibular overdentures retained by four mini-implants

Purpose
This study investigated the effects of implant distribution on functional and patient-reported outcomes of patients treated with a mandibular overdenture retained by four mini implants.

Materials and Methods
Seventy-four participants received four titanium–zirconium mini implants in the anterior mandible, and the relative position of the implants was assessed in post-treatment computed tomography scans with three reference points in the incisal region and first molars of the overdenture. DICOM files were analysed using Blooming Artefact Reduction filters to allow the visualisation of the mini implants in their three-dimensional position without overlapping bone structures. The implant distribution parameters were the polygon area formed by the four mini implants (implant area), anterior and posterior cantilever extensions, and antero-posterior spread. Outcomes included anterior and posterior maximum voluntary bite force (MBF), masticatory performance (MP), oral health-related quality of life impacts (OHIP-Edent) and satisfaction with the overdenture. Paired t-test, Pearson's correlation test and multiple regression were used for data analysis.

Results
The implant distribution area was the most relevant variable for all functional parameters. The larger the distribution, the better the MP (p = 0.003), and the anterior (p = 0.011) and posterior MBF (p < 0.001). Concerning patient-reported outcomes, no effect of implant distribution was observed (p > 0.05), suggesting that the potential benefit of better distribution may not affect patients' perception of the treatment.

Conclusion
Findings corroborate the influence of implant distribution of the four mini implants on functional parameters and, although the best implant distribution may depend highly on anatomical factors, these parameters should be considered an important prognostic factor for treatment success.