Comparisons of analog and digital methods to produce an accurate trial restoration

Statement of problem

A trial restoration is an important diagnostic tool that can be fabricated through analog or digital pathways. Digital workflows may have improved accuracy, but this is yet to be demonstrated conclusively.

Purpose

The purpose of this in vitro study was to compare the dimensional accuracy of trial restorations produced by different analog (molded) and digital (milled and 3D printed) methods. Parameters studied included fabrication methods, Shore-A hardness of silicone putty indices, length of span, and labial tooth levels.

Material and methods

Digital additive trial restorations were designed on a single virtual cast from maxillary right to left lateral incisor teeth (4 teeth) and from maxillary right to left first premolar teeth (8 teeth). Both designs were identical on the 4 anterior teeth. Each digital trial restoration was 3-dimensionally (3D) printed to produce reference casts. The original cast was 3D printed to produce 44 replica casts. There were 8 experimental groups (4 analog and 4 digital) with 10 specimens each. For the analog groups, 20 silicone indices per reference cast were made: 10 from standard silicone putty (63 to 70 Shore-A hardness) and 10 from hard silicone putty (90 Shore-A hardness). The analog trial restorations were molded on replica casts with silicone indices and bis-acryl resin. The digital trial restorations were either milled or 3D printed and adapted onto replica casts. Each trial restoration was scanned and digitally superimposed onto respective scanned reference casts. Measurements were recorded at 3 levels: cervical, middle, and incisal. The independent samples Kruskal-Wallis, 2-sample Mann-Whitney, and Bonferroni tests were used to compare the distribution of accuracy among all groups (α=.05).

Results

The dimensional accuracy of the different trial restoration fabrication methods was comparable in terms of median values of trueness (how close the readings were to the reference), and no statistically significant difference was found among them (P>.05). When the dimensional accuracy in terms of precision (how close the readings were to each other) were analyzed, the hard putty groups demonstrated a statistically significant better outcome, whereas standard putty consistently showed the poorest result. The incisal level displayed the most significant deviation (P=.005) when all groups were compared. The incisal discrepancy values of the short-span standard putty trial restoration varied by as much as 0.84 mm in some specimens.

Conclusions

Milled and 3D printed trial restoration fabrication techniques showed dimensional accuracy comparable with that of the analog groups. However, the choice of silicone putty was shown to affect the dimensional accuracy of an analog molded trial restoration. A high Shore-A hardness silicone putty produced the best precision and should be used when fabricating an analog molded trial restoration.