Effect of Scanning Direct-preparation, Impression and Cast on CAD/CAM Design

Objectives: The aim of this study was to assess the effect of scanning the direct preparation, impression and cast on the design of CAD/CAM onlay restorations.
Methods: Fifty standardized MOB onlay preparations were made on first mandibular molars of a Columbia typodont. Fifty impressions of mandibular and maxillary arches were done with silicone elastomeric dental impression materials (Aquasil Easy Mix Putty and Aquasil UltraXLV, Dentsply) and alginate (Jeltrate Chroma, Dentsply), respectively. Impressions were then poured with gypsum according to manufacturer’s instructions. The preparation, buccal bite, and opposing teeth were scanned using an E4D Planmeca scanner. The virtual models were obtained by scanning 3 different options (n=50): 1) typodont (simulated mouth); 2) impressions; and 3) gypsum casts. One hundred-fifty onlay restorations were designed by the Planmeca PlanCAD Design Center software. Five factors were considered in the virtual onlay designs evaluation by a calibrated observer (k=0.81-1.00): 1) large adjustments; 2) small adjustments; 3) material thickness; 4) occlusal contacts; and 5) interproximal contact. The ideal parameters for an onlay restoration provided by the software were used as reference. The data were assessed statistically by descriptive statistics, chi-square test (χ²) followed by the z-residual test with Bonferroni’s adjustment (α=.05).
Results: Factors 1, 2 and 3 did not present significant statistical difference (χ²=1.10-5.03; p=0.08-0.58). For occlusal contacts, the highest frequency of ideal occlusal contacts (92%) was observed by scanning the typodont (χ²=44.92; p<0.01). For interproximal contact, there was no statistical difference of the casts compared to the typodont and impressions. However, scanning the impressions presented greater frequency of ideal interproximal contact (28%) than the typodont (8%) (χ²=8.332; p=0.01).
Conclusions: It was concluded that scanning the typodont provided the most ideal occlusal contacts for the virtual designed CAD/CAM onlay restorations. Scanning the impressions provided a more ideal interproximal contact than scanning the typodont.