Effect of number of pontics and impression technique on the accuracy of four-unit monolithic zirconia fixed dental prostheses

Abstract

STATEMENT OF PROBLEM: Because of their relatively small scanning area, intraoral scanners may result in less accurate fixed dental prostheses (FDPs) than do laboratory scanners. PURPOSE: The purpose of this in vitro study was to evaluate the accuracy of monolithic zirconia FDPs with different numbers of pontics fabricated with different impression techniques. MATERIAL AND METHODS: The mandibular right premolars and molars of an acrylic resin model were prepared to receive 4-unit FDPs. Three master models were fabricated with epoxy resin: model NP, no pontic; model 1P, 1 pontic; and model 2P, 2 pontics. Each master model was scanned by using direct (DD) and indirect digitalization (ID). Four-unit monolithic zirconia FDPs were fabricated and divided into 3 groups (groups NP, 1P, and 2P) and then subdivided according to the digitalization technique (group DD and ID; n=10). The FDPs were also evaluated based on the presence (Po) or absence (NPo) of an adjacent pontic. The marginal, axial, and occlusal gap widths of each FDP were measured, and statistical analyses were performed to evaluate and compare the amount of gap present (alpha=.05). RESULTS: For direct digitalization, group 2P had significantly greater marginal (69.4 mum versus 60.9 mum or 62.3 mum; P<.001) and axial gap widths (127.1 mum versus 108.9 mum or 110.4 mum; P<.001) than group NP or 1P. Group DD resulted in significantly smaller gaps compared with group ID at marginal (64.8 mum versus 73.6 mum), axial (114.8 mum versus 124.3 mum), and occlusal (172.6 mum versus 184.1 mum) measurement locations (P<.001). Greater marginal and axial gaps were noted in group Po than NPo (P<.001). CONCLUSIONS: The length of the edentulous area significantly influenced the extent of the marginal and internal gap with the use of direct digitalization. Direct digitalization resulted in significantly smaller gap widths in all measurement areas than indirect digitalization; however, the mean differences were less than 12 mum, which is considered clinically insignificant. The presence of an adjacent pontic had a significant effect on the adjacent marginal and axial gap widths.