Accuracy of Reduction Depths of Tooth Preparation for Porcelain Laminate Veneers Assisted by Different Tooth Preparation Guides: An In Vitro Study

Abstract

Purpose: To evaluate the accuracy (trueness and precision) of reduction depths of guided veneer preparation assisted by four tooth preparation guides. Materials and Methods: Fifty resin artificial teeth were randomly divided into five groups (n = 10): a freehand group (F), silicone guide group (S), thermoplastic guide group (T), 3D printed uniform guide group (D), and 3D printed auto-stop guide group (A). A preparation for a window veneer on the maxillary right central incisor was performed by two surgeons who used tooth preparation guides for assistance. The maxillary right central incisors were scanned before and after the preparation. The reduction depths were measured in the cervical, middle, and incisal thirds of the prepared surface, and depth maps were created using Geomagic Control X software. The accuracy of the reduction depths at each third was evaluated using both trueness and precision values. The trueness of the reduction depths was determined by calculating the mean absolute differences (MADs) compared to the planning depth, and precision was determined by the standard deviation (SD). The collected data were statistically analyzed using one-way ANOVA and the least significant difference test (α = 0.05). Results:The MAD ± SD values of the reduction depths in the cervical-third region in groups F, S, T, D, and A were 0.19 ± 0.04, 0.12 ± 0.03, 0.09 ± 0.02, 0.07 ± 0.02, and 0.05 ± 0.01 mm, respectively. In the middle-third region, the MAD ± SD values of groups F-A were 0.19 ± 0.05, 0.13 ± 0.02, 0.09 ± 0.01, 0.06 ± 0.01, and 0.05 ± 0.01 mm. In the incisal-third region, the MAD ± SD values were 0.27 ± 0.05, 0.16 ± 0.04, 0.11 ± 0.03, 0.07 ± 0.01, and 0.05 ± 0.01 mm, respectively. Significant differences in trueness and precision values were found across different groups (F = 45.378, p = 0.000), where group F showed higher MADs than the other 4 groups (p = 0.000), and the highest MADs were detected in group S among the 4 groups in all regions (p = 0.000). Group T showed significantly higher MADs than groups D (P = 0.008) and A (p = 0.001), except in the cervical-third region, where no significant difference was observed between groups T and D (p = 0.077). There was no significant difference between groups D and A (p = 0.148). The deviation map showed significant differences among groups (F = 15.963, p = 0.000), group T presented less deviation than group F (p = 0.000) and group S (p = 0.027) and showed more deviation than group A (p = 0.007). Conclusion:Tooth preparation guides provided more accuracy for veneer preparation than freehand preparation. Among the 4 guides, the 3D printed auto-stop guide presented the lowest absolute difference (0.05 mm) and the silicone guide showed the highest absolute difference of preparation (0.12-0.16 mm).

Accuracy of the preparation depth in mixed targeted restorative space type veneers assisted by different guides: An <i>in vitro</i> study

“…Therefore, thermoplastic guides could provide more stable measurement points, and deviations caused by manual trial restoration are avoided [34]. The deviation of the preparation depth in this study was higher than the previously reported depths of 0.09 ~ 0.11 mm [19], which may be because the insufficient trimming of the prereduction region affected the fit of the thermoplastic guide.…”

“…The freehand preparation provided inconsistent accuracy with MADs of 0.237 mm, which was higher than that reported in a previous study [19]. This was possible because space evaluation was more complicated when the TRS contour differed from the original tooth.…”

“…The preparation depth can be measured by evaluating the space between the tooth surface and the guide [17,18]. To date, the accuracy of guided preparation has been proven to be better than that of freehand preparation [19,20]. However, most published investigations have been conducted on standard tooth preparation models with homogeneous preparation depths [20,21].…”

An Innovative 3D Printed Tooth Reduction Guide for Precise Dental Ceramic Veneers

“…Another study evaluated tooth reduction for veneer preparation on the cervical third, middle third, and incisal thirds of maxillary central incisors using freehand preparation, a silicone guide, a thermoplastic guide, 3D printing with a uniform guide, and 3D printing with auto-stop features. The results showed that freehand resulted in significantly more tooth reduction in all thirds prepared, while both types of 3D printed guides offered the least amount of tooth reduction and the most accurate preparation [27]. The two types of 3D guides can be classified as a 3D printed uniform and 3D printing with auto-stop.…”

“…Lastly, freehand techniques may be employed by experienced clinicians capable of visualizing the amount of tooth removal and space needed for the ceramic veneer without any reference. A recent study evaluated the free-hand, silicone guide, thermoplastic guide, and two different types of 3D printed tooth reduction guides and concluded that any type of tooth reduction guide provided more accuracy for veneer preparation than freehand preparation [27]. Therefore, it can be suggested that tooth reduction should be performed with a reduction aid in order to guarantee a controlled tooth reduction.…”