Comparing the mechanical properties of pressed, milled, and 3D-printed resins for occlusal devices.

STATEMENT OF PROBLEM: Comparisons of the material qualities of pressed, milled, and 3D-printed occlusal devices are sparse, complicating informed decisions on material choice. PURPOSE: The purpose of this in vitro study was to compare the material properties of pressed, milled, and 3D-printed resins, as well as how these are affected by thermal aging. These data were then used to estimate the likely clinical performance of the tested materials. MATERIAL AND METHODS: Three pressed (ProBase Cold; Ivoclar Vivadent AG, Palapress clear; Kulzer GmbH, Aesthetic Blue clear; Candulor), 3 milled (Temp Premium Flexible Transpa; Zirkonzahn, idodentine PMMA transparent; Unión Dental S.A., Yamahachi PMMA clear; Yamahachi Dental MFG), and three 3D-printed (Freeprint splint; DETAX GmbH, LuxaPrint Ortho Plus; DMG GmbH, Nextdent Ortho Clear; Vertex-Dental B.V.) resin materials were evaluated. Flexural strength, Martens hardness (HM), Vickers hardness (HV), water sorption, water solubility, and surface topography were analyzed. The tests were carried out after 50 hours of water storage at 37 °C (baseline) and after simulated aging (50 hours of water storage at 37 °C, followed by 20 000 thermocycles [TC] at 5 °C and 55 °C). RESULTS: At baseline, the mean flexural strength values were 92.8 to 99.5 MPa for pressed, 95.1 to 122.0 MPa for milled, and 19.5 to 91.3 MPa for 3D-printed materials. After aging, these values were 87.6 to 93.5 MPa for pressed, 93.1 to 116.0 MPa for milled, and 13.0 to 63.3 MPa for 3D-printed resins. The mean HM values were 130.1 to 134.1 N/mm for pressed and 130.3 to 158.5 N/mm for milled resins. After aging, the mean HM ranged from 121.6 to 124.2 N/mm for pressed and 116.2 to 149.7 N/mm for milled resins. The mean HV values were 18.2 to 19.9 for pressed and 18.4 to 23.0 for milled resins before aging and 16.9 to 18.7 for pressed and 17.3 to 22.3 N/mm for milled resins after aging. Printed resins could not be measured. At baseline, the mean modulus of elasticity ranged from 4.6 to 4.8 GPa for pressed and from 4.7 to 5.3 GPa for milled resins. For 3D-printed resins, only 1 material could be measured (3.7 GPa). The mean sorption values were 8.6 to 9.2 µg/mm3 for pressed, 7.9 to 10.5 µg/mm3 for milled, and 9.2 to 21.2 µg/mm3 for additive resins. After aging, these values were 21.1 to 22.6 µg/mm3 for pressed, 20.5 to 23.7 µg/mm3 for milled, and 19.4 to 45.5 µg/mm3 for 3D-printed resins. The mean solubility values ranged from 0.3 to 1.4 µg/mm3 for pressed, 0.4 to 1.7 µg/mm3 for milled, and -3.5 to 11 µg/mm3 for 3D-printed materials. CONCLUSIONS: Pressed and milled resins can be considered equivalent in terms of their material properties. Relative to the pressed and milled resins, the 3D-printed resins had lower flexural strength and hardness values and higher water sorption and solubility.

Dental Students' Perceptions of Digital and Conventional Impression Techniques: A Randomized Controlled Trial.

The aim of this randomized controlled trial was to analyze inexperienced dental students' perceptions of the difficulty and applicability of digital and conventional implant impressions and their preferences including performance. Fifty undergraduate dental students at a dental school in Switzerland were randomly divided into two groups (2×25). Group A first took digital impressions in a standardized phantom model and then conventional impressions, while the procedures were reversed for Group B. Participants were asked to complete a VAS questionnaire (0-100) on the level of difficulty and applicability (user/patient-friendliness) of both techniques. They were asked which technique they preferred and perceived to be more efficient. A quotient of "effective scan time per software-recorded time" (TRIOS) was calculated as an objective quality indicator for intraoral optical scanning (IOS). The majority of students perceived IOS as easier than the conventional technique. Most (72%) preferred the digital approach using IOS to take the implant impression to the conventional method (12%) or had no preference (12%). Although total work was similar for males and females, the TRIOS quotient indicated that male students tended to use their time more efficiently. In this study, dental students with no clinical experience were very capable of acquiring digital tools, indicating that digital impression techniques can be included early in the dental curriculum to help them catch up with ongoing development in computer-assisted technologies used in oral rehabilitation.

Time efficiency, difficulty, and operator's preference comparing digital and conventional implant impressions: a randomized controlled trial.

OBJECTIVES: The aim of this randomized controlled trial was to analyze implant impression techniques applying intraoral scanning (IOS) and the conventional method according to time efficiency, difficulty, and operator's preference. MATERIAL AND METHODS: One hundred participants (n = 100) with diverse levels of dental experience were included and randomly assigned to Group A performing digital scanning (TRIOS Pod) first or Group B conducting conventional impression (open tray with elastomer) first, while the second method was performed consecutively. A customized maxillary model with a bone-level-type implant in the right canine position (FDI-position 13) was mounted on a phantom training unit realizing a standardized situation for all participants. Outcome parameter was time efficiency, and potential influence of clinical experience, operator's perception of level of difficulty, applicability of each method, and subjective preferences were analyzed with Wilcoxon -Mann-Whitney and Kruskal-Wallis tests. RESULTS: Mean total work time varied between 5.01 ± 1.56 min (students) and 4.53 ± 1.34 min (dentists) for IOS, and between 12.03 ± 2.00 min (students) and 10.09 ± 1.15 min (dentists) for conventional impressions with significant differences between the two methods. Neither assignment to Group A or B, nor gender nor number of impression-taking procedures did influence working time. Difficulty and applicability of IOS was perceived more favorable compared to conventional impressions, and effectiveness of IOS was rated better by the majority of students (88%) and dentists (64%). While 76% of the students preferred IOS, 48% of the dentists were favoring conventional impressions, and 26% each IOS and either technique. CONCLUSIONS: For single-implant sites, the quadrant-like intraoral scanning (IOS) was more time efficient than the conventional full-arch impression technique in a phantom head simulating standardized optimal conditions. A high level of acceptance for IOS was observed among students and dentists.

Digital Michigan splint - from intraoral scanning to plasterless manufacturing.

AIM: To investigate whether the fully digital, plasterless fabrication of clinically usable Michigan splints can be accomplished in a time- and cost-efficient manner. MATERIALS AND METHODS: Digital scans of the maxillary and mandibular arches of 10 subjects were acquired with an intraoral scanner (3Shape, Copenhagen) and used to generate virtual models of the dental arches. Jaw relation records were made using jigs placed on the subjects' anterior teeth, and silicone registration material was referenced to the jaw models. The data sets were then sent via the company's online portal to the dental laboratory, where computer-aided design (CAD) of the Michigan-type maxillary splints was performed. After receiving the designs, the splints were milled in-office using computer-aided manufacturing (CAM) software, and finished manually. During try-in, the splints where checked for fit, retention quality, and occlusal contacts of the mandibular teeth on the splint surfaces in static and dynamic occlusion. RESULTS: Fit and retention were clinically acceptable in 10 splints and 9 splints, respectively. The number of initial occlusal contacts on the splint surfaces ranged from 4 to 16. CONCLUSIONS: The question addressed in this study can be answered in the affirmative. Some of the main advantages of digital manufacturing of Michigan splints over traditional, conventional, impression-based manufacturing are the time-efficient manufacturing process, the high material quality, and the possibility of manufacturing duplicate splints.