24 November 2021

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Monolithic multilayer zirconia fixed partial dentures (FPDs): conventional vs digital impression fabrication

Co-authors: A. Comba, F. Del Bianco

Lorenzo Breschi

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Monolithic translucent and multilayer zirconia fixed partial dentures are relatively new treatment that gained popularity thanks to the evolution of dental digital workflows. 
Morsy et al. noticed that the modified microstructure of these material improved aesthetic outcomes, however the effect of such modifications on the fit of the restoration and the clinical success still need to be investigated. In addition, the authors pointed out that also the impression could influence the results of a precise fixed partial denture.
For these reasons they conducted a study to compare the accuracy of conventional and digital impressions based on the fit of produced threeunit fixed partial dentures (FPDs) in vivo and the trueness and precision of both impression techniques. 

Material & Methods
Morsy et. al, from the University of Alexandria, Egypt,  selected twelve patients that received both a conventional polyether impression (group C, control, n=12) and a digital impression with CS3500 (group D, test, n=12). Monolithic multilayer zirconia FPDs were fabricated, and the internal and marginal fit were assessed by the authors using the replica technique, trueness and precision of both impression methods were assessed in vitro. In order to create a reference the authors created a master model. Furthermore, the master model received conventional impressions (group C, control, n=5) and digital impressions (group D, test, n=5) by the researchers. The virtual models of both groups were superimposed over the reference scan (5 superimpositions) using a three-dimensional (3D) processing software, and the 3D deviations were measured and averaged to obtain trueness value. For precision, the virtual models of each group were superimposed over each other (10 superimpositions) and the average deviation value was calculated. The data were analyzed by the authors using one-tailed Mann–Whitney U test at P ≤ 0.05.

Results
The researchers  from Egypt noticed that Group D resulted in a significantly better marginal and internal fit (30.91±15.15 and 30.86±13.57 μm for group D and 40.02±19.50 and 41.86±18.94 μm for group C). Furthermore the mean values of trueness and precision for conventional and digital techniques noticed by the authors were comparable (trueness: 62.8±5.45 and 62.72±12.01 μm and precision: 56.47±27 and 60.9±14.5 μm, respectively).

Conclusions
Morsy et al. concluded that no significant difference was found between conventional and digital impressions in 3D datasets accuracy. In addition, both techniques resulted in FPDs with an acceptable clinical fit. However, the authors noticed that FPDs fabricated using the digital technique displayed better internal and marginal fit.

For more information: Fit of monolithic multilayer zirconia fixed partial dentures fabricated by conventional versus digital impression: a clinical and laboratory investigations.