Accuracy of Complete-Arch Implant Digital Scans: Effect of Scanning Protocol, Number of Implants, and Scan Body Splinting.

PURPOSE: To determine the effect of scanning protocol, number of implants, and implant splinting on the accuracy of digital scanning in the edentulous arch. MATERIALS AND METHODS: A resin-based model of an edentulous mandible with six implants was scanned with a coordinate measurement machine as a reference and then with two intraoral scanner (IOS) systems (Trios 3 and Primescan). Ten scans were taken per IOS for three experiments, and each scan was compared to the reference data to evaluate trueness and precision. Analysis involved measurement of linear and angular discrepanices using engineering software. In experiment 1, three scanning protocols were compared (curvilinear, zigzag, and half-arch). In experiment 2, three clinical situations were simulated (6 implants, 4 implants-short arch, and 4 implants-long arch). In experiment 3, the effect of implant splinting with a suture thread was measured. Normal distribution of data was examined with Shapiro-Wilk test. Levene test was used for equality of variance (α = .05). Statistical differences in distance and angular deviations were analyzed using Student t test or ANOVA with post hoc Tukey test (α = .05). RESULTS: The best results in terms of trueness and precision were obtained with a linear scanning protocol and six implants. The results were as follows: Trios 3: trueness = 52 µm/0.42 degrees, precision = 40 µm/0.26 degrees; Primescan: trueness = 24 µm/0.28 degrees, precision = 18 µm/0.27 degrees. The scanning protocol did not significantly affect distance or angular deviation accuracy. Trueness and precision significantly decreased with four implants using Primescan and TRIOS 3. Splinting implants negatively affected accuracy with both IOS devices. CONCLUSION: Both IOS devices achieved clinically satisfying accuracy for distance (< 100 µm) and angular (< 0.5 degrees) deviations with six implants and a linear scanning protocol. With four implants, angular deviations sometimes differed between implants within the same group depending on the IOS and the clinical situation. Int J Prosthodont 2023;36:219-227. doi: 10.11607/ijp.7332.

Sodium carbonate improves adherence of two-layer alginate for preliminary impressions of complete dentures.

PURPOSE: This in vitro study evaluated the effect of sodium carbonate (Na2CO3) concentration on adhesion between two layers of irreversible hydrocolloid wash impression material. METHODS: The first layer of irreversible hydrocolloid was brushed with three concentrations (0.1, 0.7, or 7.0 wt.%) of Na2CO3. Irreversible hydrocolloid not brushed with Na2CO3 was used as a negative control. Adhesion between the two layers (bond strength and adhesion energy) was then evaluated using a traction test, and the fracture modes were identified. The results of traction test were analyzed with a one-way ANOVA followed by a Tukey post hoc test. Chi-square test was used for analyzed failure mode after testing (α= 0.05). RESULTS: The bond strength (0.034 ±0.005 MPa) and adhesion energy (60.240 ±12.817 J.m⁻ ²) of the 0.7% Na2CO3 group were significantly higher than those of the other groups (P< 0.05). The 0.7% Na2CO3 group displayed only cohesive failure (ײ= 16; P< 0.0001). CLINICAL SIGNIFICANCE: Conditioning the surface of the first layer of irreversible hydrocolloid with 0.7% sodium carbonate improved adhesion between the two layers and may help clinicians improve the quality of the preliminary impressions of removable complete dentures.