Effect of index thickness on the accuracy of direct restorations using composite resin injection technique with VPS indices

Objectives

To evaluate the accuracy of direct restorations using transparent vinyl polysiloxane (VPS) indices with different thicknesses for composite resin injection technique.

Methods

Thirty-six standard resin teeth of tooth #11 were divided into 3 groups based on the index thickness including 2, 4, and 6 mm (n = 12). VPS indices were fabricated using customized trays corresponding to each thickness. Tooth defect was created by sectioning 4 mm of the crown, which was then restored using the composite resin injection technique under the VPS index. Pre- and post-treatment scans were fitted, generating a deviation distribution map of tooth #11. Overall root mean square (RMS) and distance deviations along the central longitudinal section were recorded for accuracy evaluation. One-way ANOVA with Tukey post hoc comparisons and the Levene test were used for statistical analysis (α = 0.05).

Results

Both mean and standard deviation values of RMS for injected restorations decreased as index thickness increased, with no significant differences observe between 4-mm and 6-mm index groups. Distance deviations of the injected restorations were generally less than 0 in all groups, and deviations of the middle third of the lingual surface significantly exceeded 50 μm in 2-mm index group.

Conclusions

The accuracy including trueness and precision of direct restorations using the composite resin injection technique improved with increasing index thickness, but no significant differences were found between the 4-mm and 6-mm indices. Besides, all the results were within the clinically acceptable error values for the 4-mm and 6-mm indices.

Clinical significance

For achieving clinically acceptable accuracy in restorations using the composite resin injection technique, a VPS index thickness of 4 mm is both the minimum requirement and sufficient, ensuring satisfactory esthetic and functional outcomes.