Comparison of three occlusal splint material systems manufactured by conventional, subtractive, and additive techniques

Objectives To compare the thermal–viscoelastic behavior, hygroscopic properties, color stability, and surface morphology of three commercial occlusal splint material systems produced by conventional heat polymerization, CAD/CAM milling, and 3D printing. The null hypothesis was that the three material systems would not differ in thermal-viscoelastic behavior, hygroscopic properties, or color stability. Surface morphology was assessed qualitatively as a complementary outcome. Materials and methods Heat-polymerized polymethyl methacrylate (HEC), CAD/CAM-milled polymethyl methacrylate (CAD-M), and a 3D-printed photopolymer resin (3DP) were evaluated. Dynamic mechanical analysis was performed to determine glass transition temperature (Tg), tan δ, and thermal heterogeneity ( n = 5). Water sorption (WS), solubility (SL), and color change after coffee immersion (ΔE00) were assessed ( n = 8). Surface morphology was qualitatively analyzed by atomic force microscopy and scanning electron microscopy. Results Significant differences were observed among the material systems for thermal and hygroscopic outcomes. CAD-M presented the highest mean Tg (149.58 ± 0.95 °C), the lowest water sorption (18.76 ± 0.56 µg/mm³), the lowest solubility (2.59 ± 0.48 µg/mm³), and a ΔE00 of 2.29 ± 1.20 after 7 days of coffee immersion. Conversely, 3DP showed the lowest Tg (83.18 ± 7.87 °C), highest WS (35.12 ± 0.82 µg/mm³), highest SL (6.16 ± 0.40 µg/mm³), greatest color change, and a more irregular surface morphology. Conclusions The three evaluated commercial material systems differed in thermal-viscoelastic behavior, hygroscopic properties, color stability, and surface morphology. Among the specific systems tested, CAD-M showed the most favorable overall laboratory profile. Because each manufacturing approach was represented by a single commercial material with a distinct composition, these differences cannot be attributed exclusively to the manufacturing route. Clinical relevance Under the in vitro conditions tested, the milled material system showed a higher glass transition temperature and lower water sorption, solubility and coffee-induced discoloration than the 3D-printed system. Whether these laboratory differences translate into differences in the clinical performance of occlusal splints was not assessed in this study.