Does partial adhesive preparation design and finish line depth influence trueness and precision of intraoral scanners?

STATEMENT OF PROBLEM: Intraoral scanners (IOSs) are widely used for partial-coverage adhesive restorations, but data on their performance in such preparations with complex geometries are sparse. PURPOSE: The purpose of this in vitro study was to investigate whether the partial-coverage adhesive preparation design and finish line depth affect the trueness and precision of different IOSs. MATERIAL AND METHODS: Seven partial-coverage adhesive preparation designs (4 different onlays, 2 endocrowns, and 1 occlusal veneer) were tested on copies of the same tooth placed in a typodont mounted on a mannequin. Each preparation was scanned 10 times with 6 different IOSs (total 420 scans) under the same light conditions. Trueness and precision, defined according to the International Organization for Standardization (ISO) 5725-1 standard, were analyzed with a best-fit algorithm by superimposition. The obtained data were analyzed by a 2-way analysis of variance to examine the effects of partial-coverage adhesive preparation design, IOS, and their interactions (α=.05). RESULTS: Significant differences were found among different preparation designs and IOSs (P<.05) in terms of both trueness and precision. Significant differences were also found among mean positive and negative values (P<.05). Moreover, crosslinks observed between the preparation area and the adjacent teeth correlated with the finish line depth. CONCLUSIONS: Complex partial adhesive preparation designs affect the trueness and precision of IOSs, resulting in significant differences among them. Interproximal preparations should take into account the IOS's resolution and placing the finish line close to adjacent structures should be avoided.

Post-Fatigue Fracture Resistance of Lithium Disilicate and Polymer-Infiltrated Ceramic Network Indirect Restorations over Endodontically-Treated Molars with Different Preparation Designs: An In-Vitro Study.

The aim of the present study was to evaluate the fatigue to cyclic and static resistance of indirect restorations with different preparation designs made either of lithium disilicate (LS) or polymer-infiltrated ceramic network (PICN). Eighty-four (n = 84) molars were chosen, endodontically treated, and prepared with standardized MOD cavities. The molars were randomly divided into 6 study groups (n = 14) taking into account the "preparation design'' (occlusal veneer with 1.2 mm occlusal thickness; overlay with 1.6 mm occlusal thickness; adhesive crown with 2 mm occlusal thickness) and the "CAD/CAM material'' (E-max CAD, Ivoclar vivadent; Vita Enamic, Vita). A fatigue test was conducted with a chewing simulator set at 50 N for 1,500,000 cycles. Fracture resistance was assessed using a universal testing machine with a 6 mm diameter steel sphere applied to the specimens at a constant speed of 1 mm/min. A SEM analysis before the fracture test was performed to visually analyze the tooth-restoration margins. A statistical analysis was performed with a two-way ANOVA and a post-hoc pairwise comparison was performed using the Tukey test. The two-way ANOVA test showed that both the preparation design factor (p = 0.0429) and the CAD/CAM material factor (p = 0.0002) had a significant influence on the fracture resistance of the adhesive indirect restorations. The interaction between the two variables did not show any significance (p = 0.8218). The occlusal veneer had a lower fracture resistance than the adhesive crown (p = 0.042) but not lower than the overlay preparation (p = 0.095). LS was more resistant than PICN (p = 0.002). In conclusion, in the case of endodontically treated teeth, overlay preparation seems to be a valid alternative to the traditional full crown preparation, while occlusal veneers should be avoided in restoring non-vital molars with a high loss of residual tooth structure. LS material is more resistant compared to PICN.