Optimizing additively manufactured mouthguards: An evaluation of multi-layer materials for improved shock absorption and durability compared to conventionally fabricated samples

Abstract

Although sports mouthguards (MGs) are mandatory in some contact sports, the use of conventional fabricated materials for making MGs is time-consuming and lacks precision, limiting their widespread application. In this study, we compared mouthguards designed using digital software with conventional ones. The conventional mouthguards were categorized into two types: those constructed from a poly-(ethylene vinyl acetate)-base material, and those constructed from MG21, a polyolefin-base material. The shock absorption and durability were assessed through a free-falling steel ball test and a fatigue test. The durability of the MGs was evaluated by measuring the retention force in the inner layer and deviations at consistent points on the outer layer during various fatigue test stages. Additively manufactured samples showed superior shock absorption performance, except for the double-layer samples with an inner layer of Shore A hardness 95. All single-layer additively manufactured MGs were damaged during the mid-fatigue test stage, while both double-layer additively manufactured and conventional MGs remained undamaged. Throughout all fatigue test stages, the retention force of double-layer additively manufactured MGs was significantly lower than that of conventional MGs. However, the retention force of double-layer additively manufactured samples with an inner layer of Shore A hardness 70 (D-A70) was superior to the average of all MGs in the wet condition, which was 6.4 ± 2.5 N in the previous study. The results of this study demonstrated the benefits of a hybrid design of hard and soft materials, particularly the promising combination of D-A70, which exhibited comparable shock absorption and durability to conventional MGs.