Statement of the problem: Endosseous implants are being increasingly used for the retention of mandibular restorations in recent years. It has been suggested that there is a risk of maxillary bone resorption under complete dentures in patients wearing mandibular implant-retained overdentures as well as mandibular all-on-four hybrid prosthesis. However, there was little evidence-based information about the effect of these 2 treatment modalities on the maxillary bone changes.
Patients and methods: This is a prospective parallel randomized controlled clinical study, in which forty eight implants were placed in mandibles of 12 completely edentulous male patients. Patients were randomly allocated into one of the two groups: group A, where 6 patients received 4 parallel implants with implant retained overdenture and group B, where 6 patients received 4 implants in the anterior part of the mandible, 2 axial implants in the center and 2 tilted implants at the distal ends with all-on four hybrid prosthesis. All patients received maxillary removable complete dentures. Radiographic evaluation was made using the CBCT to asses bone height changes that occur in the anterior and posterior maxillary areas 6 months and 12 months following denture insertion and functional loading in comparison to time of loading. Collected data were tabulated and statistically analyzed.
Results: Comparison of radiographic bone changes under complete maxillary denture at the anterior and posterior maxilla, between group A and group B, showed no significant differences between the two groups at any time interval. However, pair-wise comparison of bone height changes over time for each group showed significant difference between immediate time point and 12- month post-loading time point in group A, both in anterior and posterior maxilla, where the P value was <0.05. On the other hand there was no significant difference between the same time points in group B, both in anterior and posterior maxilla.Conclusion: There is inevitable gradual bone loss in the maxillary arches under complete denture when opposed by four implant-retained mandibular over dentures or all-on-four hybrid mandibular prosthesis. Although the prosthesis type has no effect on the amount of bone loss, slower rate of bone resorption was found in all-on-four group throughout the study period both in anterior and posterior maxilla.