Bond Strength Between A Hard Chairside Reline and A Printed Denture Base Compared to A Conventional Heat Polymerized Denture Base: An In Vitro Study

Introduction: The aim of this study was to test the shear and tensile bond strengths (MPa) of a hard chairside reline to a 3D printed denture base and compare it to a conventional heat polymerized denture base.

Material and methods: Sixty (n=15/test) blocks (70mm x 9mm x 9mm) of a printed polymethyl methacrylate (P-PMMA) (DENTCA 3D Printed Dentures) were provided by the manufacturer, while sixty (n=15 per test) blocks (70mm x 9mm x 9mm) of thermopolymerizable polymethyl methacrylate (T-PMMA) (Diamond D. Keystone) were prepared. Three millimeters of hard liner (Tokuso-Tokuyama America Inc.) was applied between two blocks. All the tests were conducted with an INSTRON Universal Testing machine.

Results: Statistically significant differences were found in the bond strength for the shear (p<0.003) and the tensile (p<0.0001) tests between the materials. In both instances, the bond strength of the hard liner with the P-PMMA was weaker compared to the T-PMMA with 6.22MPa±0.78SE and 9.82MPa±0.78SE respectively in the shear test, and 3.61MPa±0.42SE and 6.68±0.42SE respectively in the tensile test. The force of rupture was also significantly lower in the P-PMMA 101.99MPa±12.04SE versus the T-PMMA with 143.64MPa±12.04SE during the shear test (p<0.021) and the tensile test (p<0.0002) with 360.96MPa±41.97SE versus 611.18MPa±41.97SE respectively

Conclusion: In the context of this study, the bond between the hard liner and the printed polymethyl methacrylate was shown to be weaker when compared to the thermopolymerizable polymethyl methacrylate. Further investigation of the surface properties of CAD/CAM denture bases such as surface chemistry and the clinical impact of these results are suggested. As the use of CAD/CAM technology gains in popularity, more materials developed for traditional dentures should be studied for compatibility.

Keywords: CAD/CAM; Printed denture; Polymethyl methacrylate; Hard reline; Tensile bond strength; Shear bond strength

Abbreviations: CAD/CAM: Computer-aided design and computer-aided manufacturing; P-PMMA: Printed polymethyl methacrylate; T-PMMA: Thermopolymerizable polymethyl methacrylate; MPa: Megapascal; SE: Standard error