ABSTRACT
Statement of problem: Mandibular overdentures assisted by mini-implants induce sever bone changes in posterior mandible.
Purpose: This study aimed to evaluate the posterior mandibular ridges height changes using the digital panoramic radiographic technique under mandibular overdentures assisted by four mini-implants, in case of interforaminal distribution and in case of wide distribution after wearing overdentures for 6 years.
Methods and material: The subjects enrolled for this study (n = 20). They were treated with maxillary complete dentures, randomly assigned into two equal groups: group І received mandibular overdentures assisted by four mini-implants distributed equally in the interforaminal region, exposed to immediate loading protocol. Group II received mandibular overdentures assisted by four mini-implants (two mini-implants inserted in canine regions and two mini-implants inserted in first molar regions) exposed to immediate loading protocol. Digital panoramic radiographic evaluation of posterior mandibular region was done for every patient of both groups, recorded at the time of mini-implants insertion and after 6 years.

Results: There was statistically significant difference in bone heights changes between interforaminal and wide distribution groups after six years. There is bone apposition in the wide distribution at 15mm and 20mm distal to mental foramen.

Conclusion: Posterior mini implants placement resulted in improved denture support and minimal overdenture displacement. The functional load on posterior mini implants has a positive effect on preservation of the residual alveolar ridge. Wide mini implants distribution is an acceptable alternative prosthodontic design to four-interforaminal mini implants distribution when anatomical and economical factors permit.