Effect of Water Sorption on the Mechanical Properties of Surgical Splint Materials: 3D-printed vs Conventional Resin

Recently, digital technologies have become common in clinical dental practice, which may provide benefits to clinicians and patients. This study investigated how water absorption affected the mechanical properties of three-dimensionally (3D)-printed surgical splint materials used to position bones during orthognathic surgery.

Two 3D-printing materials, Dental LT Clear (Formlabs) and Splint (SprintRay), as well as a conventional acrylic resin (Unifast III, GC), were purchased for this study. We prepared wire (2 × 2 × 25 mm) and disc-shaped (14 mm diameter and 2 mm in thickness) specimens via 3D-printing or pouring into silicon molds. All materials were subjected to the ISO 4049 three-point bending test, and the water absorptions of samples immersed in artificial saliva for 28 days were calculated as per ISO 10477. Changes in mechanical properties (hardness, and the modulus of elasticity) were evaluated via nanoindentation testing. Chemical parameters were determined using Fourier-Transform Infrared Spectroscopy (FTIR). The data were compared using ANOVA and the Tukey multiple comparisons test.

The bending strengths and elongations of both 3D-printed materials were significantly greater than those of conventional acrylic resin. The FTIR data indicated that the water absorptions of both 3D-printed materials were significantly greater than those of conventional PMMA (polymethyl methacrylate)-based resin. The hardness and elastic modulus values of both 3D-printed materials (obtained using the nanoindentation test) decreased significantly as the immersion period rose; those of the conventional acrylic resin did not.

The improved mechanical properties of 3D printed materials would demonstrate greater resistance to the stresses imparted by the muscles associated with functional mandibular movement, while also reducing the risk of splint chipping during intermaxillary fixation. On the other hand, there is concern that the stability of the mechanical properties of 3D printed materials may be compromised by water absorption in moisture-rich environments.

Although 3D-printed materials exhibit superior mechanical properties, their water absorption and extent of degradation on immersion in artificial saliva were higher than those of a conventional PMMA-based resin.