In vitro evaluation of shape-memory hydrogels for removable dental prostheses and optimization of phase-transition temperature for intraoral use.

STATEMENT OF PROBLEM: Removable dental prostheses require periodic relining with the loss of intaglio surface fit because of mucosal shape changes over time. Therefore, a new material with high adaptability to tissue changes over time would be beneficial. PURPOSE: This study focused on a shape-memory gel (SMG) that softens when heated, retains its shape when cooled, and returns to its original shape when reheated. The purpose was to optimize SMG for intraoral use by controlling the ratio of 2 acrylate monomers and to evaluate the changes in the shape memory and physical properties of SMG with temperature and to evaluate biocompatibility. MATERIAL AND METHODS: SMG specimens were synthesized using the following mixing ratios of 2 monomers, docosyl acrylate (DA) and stearyl acrylate (SA): 0:100, 25:75, 50:50, 75:25, and 100:0. SMG specimens were photopolymerized using a fluorescent light-polymerizing unit. To evaluate shape memory as a function of temperature, permanent deformation was measured based on the standardized compression set test for thermoplastic rubber. For evaluation of the physical properties and cytotoxicity, a 3-dimensionally printed denture base material was used as the control material. All assessments were compared between the groups by using 1-way analysis of variance followed by the Tukey-Kramer multiple comparison test (α=.05). RESULTS: SMGs with a higher amount of DA maintained their compressed shape at room and intraoral temperatures. However, the SMG matrices softened and recovered their original shapes above 60 °C. SMGs showed Shore A hardness equivalent to that of the denture-base polymer material at intraoral temperatures because of the high phase-transition temperature. The low water solubility of SMGs supported the biocompatibility test results. CONCLUSIONS: SMG, in which the phase-transition temperature was controlled by mixing acrylate monomers with different melting points, exhibited shape memory in the intraoral environment. The results indicate the feasibility of applying SMG for the fabrication of removable dental prostheses because of its high adaptability to tissue changes over time and biocompatibility.

A workflow for fabricating a hollow obturator by using 3D digital technologies.

Conventional methods used for fabricating hollow obturator prostheses have numerous problems. The workflow presented in this article integrates 3D digital technologies into a functional protocol, enabling the fabrication of single-piece hollow prostheses with no joints by using an optical 3D scanner and a laminating molding device.

Evaluation of water absorption properties and fabrication of hollow obturator model using 3D digital dentistry.

Fluid accumulation in the hollow spaces of obturator is a continuing problem when fabricating hollow obturator prostheses using the conventional method. To address this problem, the three-dimensional (3D) digital technology was used to evaluate water absorption in the inner hollow obturator spaces. Solid and hollow obturator specimens were fabricated using a 3D printer with photocurable resin. Then, the hermeticity was examined by leak testing. These specimens were immersed in distilled water at 37°C. Each specimen was weighed every 24 h for 120 days, and weight changes between each group were compared. Water accumulation in the hollow obturator was not visually observed. Although water absorption was significantly higher in solid specimens, the weight increase rate was also significantly higher in hollow specimens. Applying a laminating 3D photo fabrication made the fabrication of a completely unified hollow obturator model possible.