Accuracy of impression methods through the comparison of 3D deviation between implant fixtures.

AIM: To compare the accuracy of three impression methods by comparing the distance between the reference points of the implant fixture, especially in curved maxillary anterior teeth. MATERIALS AND METHODS: Implant fixtures were placed in the maxillary central incisor and canine regions. A maxillary master cast was made using a model scanner and 3D printer. Ten impressions were taken from the three experimental groups constructed (group P: pick-up impression coping; group I: scan body with an intraoral scanner; group B: bite impression coping). The distance between the reference points, the angle between the scan bodies, and displacement of the 3D surface area were measured. RESULTS: The distances between the reference points were significantly different between groups I and B in the maxillary incisors, and between group P and the other two groups in the maxillary canines. Group P had the least amount of displacement in both fixtures. Both fixtures showed the highest displacement in group B. Displacement of the 3D surface area in the maxillary incisors showed no significant difference between the groups. There was a significant difference in the maxillary canines between groups P and I. CONCLUSIONS: In the present study, all three implant impression methods showed changes in the position and angle of the fixture compared with the master cast. The highest accuracy was shown by the impression method using the pick-up impression coping, but the impression method using the intraoral scanner also showed clinically acceptable accuracy. It should be noted that errors may occur when taking impressions using a bite impression coping.

Risk factors associated with screw loosening in CAD-CAM custom abutments: A 6-year retrospective study.

STATEMENT OF PROBLEM: Custom abutments made by using computer-aided design and computer-aided manufacturing (CAD-CAM) are often used for implant-supported prostheses. However, studies on screw loosening of implant prostheses using custom abutments are lacking. PURPOSE: The purpose of this retrospective study was to investigate the risk factors of screw loosening in implant-supported prostheses using custom abutments made with CAD-CAM. MATERIAL AND METHODS: Clinical charts, radiographic images, and CAD custom abutment design file data were collected and analyzed retrospectively. The study included 255 patients with 401 dental implants, and the follow-up duration was 6 years. Age, sex (male/female), type of unit (single-unit or multiunit), location of the implant (maxilla or mandible and anterior, premolar, or molar tooth), type of antagonist, and experience of the prosthodontist were reviewed, and implant angulation (mesiodistal and buccolingual), location of the screw access hole (mesiodistal and buccolingual distances from center), and attrition status (none, localized, or generalized) were measured by using a CAD file. The frequencies and percentages of risk factors were evaluated with the Fisher exact test, and the Bonferroni correction was used as a post hoc test. Multiple logistic regression with the Firth method was performed to calculate the odds ratios and their confidence intervals (α=.05). RESULTS: Screw loosening showed a correlation with the severity of attrition (P<.001). Single-unit prostheses had a higher risk of screw loosening than multiunit prostheses (P<.001). Experience of the prosthodontist (P<.001). Buccolingual angulation of the implant and abutment significantly influenced the incidence of screw loosening (P<.05). Age, sex, location of the implant, type of antagonist, mesiodistal implant angulation, and buccolingual and mesiodistal location of the screw access hole did not significantly influence the incidence of screw loosening (P>.05). CONCLUSIONS: The degree of attrition, buccolingual angulation of the implant and abutment, type of unit, and experience of the prosthodontist (>3 years or <3 years) were risk factors in the incidence of screw loosening.

Assessment of the fit of lithium disilicate crowns at various locations fabricated by three different methods using the triple-scan protocol.

AIM: The present study aimed to evaluate the marginal and internal fit of lithium disilicate crowns at various locations. MATERIALS AND METHODS: A typodont maxillary left first molar was prepared for a lithium disilicate crown, scanned, and a master die fabricated. Three groups were created according to fabrication method (n = 10): conventional impression and press method (group C); scanning of definitive cast and milling method (group D); and intraoral scanning and milling method (group I). Assessment was performed using the triple-scan protocol. At the buccopalatal and mesiodistal sections, the absolute marginal discrepancy (AMD), marginal gap (MG), axial internal gap (AI), and line angle internal gap (LI) were measured. One-way analysis of variance (ANOVA) and post hoc Tukey HSD tests were used for statistical analysis (α = 0.05). RESULTS: AMD values were significantly lower in group C than in groups D and I (P < 0.05). MG values in group C were significantly lower than those in the buccal and distal areas in group D and all areas in group I (P < 0.05). AI values in the buccal and palatal areas in group D were significantly lower than those in the mesial and distal areas in group D and all areas in groups C and I (P < 0.05). LI values were significantly lower in group C than in groups D and I (P < 0.05). CONCLUSION: All three methods were clinically acceptable except for the marginal fit of the intraoral scanning and milling method, which was on the borderline of a clinically acceptable fit. (Int J Comput Dent 2023;26(1): 37-0; doi: 10.3290/j.ijcd.b3818305).