Accuracy and its impact on fit of injection molded, milled and additively manufactured occlusal splints

Abstract

Occlusal devices to reduce symptoms of bruxism and temperomandibular disorders can nowadays be manufactured in a digital workflow but studies comparing the accuracy of those occlusal devices are still limited. Therefore, the aim of this investigation was to investigate the accuracy of injection molding compared with four computer-aided design (CAD) and computer-aided manufacturing (CAM) techniques for the manufacturing of occlusal devices. In addition, the number of contact points and retention were evaluated to assess clinical relevance. A conventional workflow consisting of alginate impression, wax-up, and injection molding (IM) and digital workflows including intraoral scanning, digital design, and subtractive manufacturing (SM) or additive manufacturing by using stereolithography (SLA), digital light processing (DLP), and material jetting (Polyjet) were investigated. Sixteen splints were fabricated with each method. The intaglio surfaces of the splints were laser scanned and superimposed with the reference data sets to analyze the surface deviations. In addition, the number of contact points after repositioning the splints on the reference model was evaluated with occlusal foil. Finally, the retention was measured in a tensile test. One-way ANOVA with post hoc Tukey tests were used for statistical analyses (α = .05). IM and SM splints demonstrated the highest manufacturing accuracy without significant differences to each other (P > .985). Additive manufactured splints revealed greater deviations with equal results for SLA and Polyjet (P > .949) and significantly higher deviations for DLP compared to all other groups (P < .002). Comparable retention force was measured for IM, SM, and SLA (P > .923), whereas Polyjet splints showed the greatest variability. IM and SM splints presented the most contact points (P = .505). Additive manufactured splints demonstrated fewer contacts without significant difference to each other (P > .116). It can be concluded, that there is no difference in manufacturing accuracy, retention, and number of contacts between IM and SM splints. AM splints demonstrated higher, however, clinically acceptable deviations.