In vitro effect of zirconia type on marginal and internal fit of a three-unit bridge.

The purpose of this study is to evaluate the effect of the type of zirconia (multilayer or monochrome) on the marginal and internal fit of a three-unit bridge.

In a maxillary model, the first premolar and first molar were prepared to receive 3-unit zirconia fixed dental prostheses and then scanned. Each scan was used to make two bridges (one with multi-layer and the other with monochrome zirconia). With Exocad software, the bridge was designed and then milled. The bridges milled in the previous stage were evaluated and compared with the replica method in terms of internal and marginal fit. For statistical analysis, an independent t-test was used to evaluate marginal, cervical, and axial fit, and the Mann-Whitney test was used to evaluate occlusal fit. (P = 0.05)

The average marginal and cervical gaps in monochrome zirconia were 65.30±20.00 and 72.42 ±10.11 micrometers, respectively, and in multi-layer zirconia were 70.76±14.71 and 78.74±11.91 micrometers, and this difference was not statistically significant (P>0.05). The average axial and occlusal gaps in monochrome zirconia were 102.5±10.70 and 118.9±18.52 micrometers respectively and in multilayer zirconia 114.8±18.88 and 141.6±29.88 micrometers, this difference was statistically significant and the average gap in monochrome zirconia was less than multilayer zirconia (P<0.05).

Monochrome zirconia restorations show similar marginal and internal fit compared to multilayer zirconia restorations. Although the occlusal and axial gap in multi-layer zirconia is more than in monochrome zirconia, it is within the clinically acceptable range. Multilayer zirconia is generally clinically usable.