The positions of implant heads in relation to the fixed dental prosthesis: a comparison of multiple zygomatic implants with standard implants for the reconstruction of the atrophic maxilla.

Purpose: The aim of this study was to investigate the positions of dental implants at the crestal level and the occlusal level of a fixed dental prosthesis (FDP) in severely and moderately resorbed maxillae. Restorations supported by multiple zygomatic implants were compared with restorations supported by standard implants.

Material And Methods: Between 2004 and 2007, measurements were performed on FDPs and working casts. Two groups were investigated: (1) patients with severe atrophy and extensive resorption into basal bone treated with multiple zygomatic implants (Zyg) and (2) patients with moderate atrophy with standard implants only (Stand). The areas bounded by the FDP at the implant level (A(impl)) and at the occlusal level (A(prost)) were calculated, and A(prost) -A(impl) represented the total horizontal overjet of the FDP. A(prost)/A(impl) was established as the degree of overlapping of these two areas. The transverse and sagittal dimensions at the implant level (T(impl) and S(impl)) and at the occlusal level (T(prost) and S(prost)) were also measured. T(impl)/S(impl) and T(prost)/S(prost) represented the shape of the superstructure at these respective levels.

Results: Seven consecutive patients in the Zyg group were matched by age and gender with seven individuals in the Stand group. In the Zyg group, 28 zygomatic and 5 standard implants were placed; in the Stand group, 41 standard implants were placed, of which 3 were lost. All patients received an FDP. T(impl) was shorter and S(impl) was longer in the Zyg group, yielding a smaller T(impl)/S(impl) in this group. The Zyg group also displayed less overjet and a smaller A(prost)/A(impl) compared to the Stand group.

Conclusion: Multiple zygomatic implants emerged through the residual crest with a more even distribution in the sagittal plane compared to standard implants and with a better congruence with the occlusal location of the FDP.