Do denture processing techniques affect the mechanical properties of denture teeth?

Denture tooth fracture may limit the longevity of dental prostheses. Whether the strength of the denture tooth material is affected by the denture processing technique is unclear. The purpose of this in vitro study was to investigate whether the denture processing technique affects the mechanical properties of denture tooth materials. Two denture processing techniques, injection and compression molding, were tested for 3 types of denture teeth: nanohybrid composite (NHC), interpenetrating network (IPN), and microfiller-reinforced polyacrylic (MRP). Denture teeth were processed by using an injection-molded resin or a compression-molded resin. Unprocessed denture teeth served as the control. After teeth were processed, they were sectioned into rectangular beams for 3-point bend testing (n=20 to 24). Elastic moduli were determined from load deflection and maximum stress from maximum bending load. The results were statistically analyzed by using 2-way ANOVA and multiple comparisons (α=.05). The processing technique and the type of denture tooth affected both the elastic modulus and the maximum stress. The injection-molded technique resulted in significantly higher (24% to 26%) elastic modulus for NHC and IPN (12% higher in MRP, but not statistically significant) and higher (12% to 17%) maximum stresses for IPN and MRP (3% lower in NHC, but not statistically significant). Compression-molded technique increased the elastic modulus of IPN and NHC by 10% to 17% (3% lower in MRP but not statistically significant), but maximum stresses were not statistically significantly different in any of the tested teeth. Regardless of processing, MRP teeth had the highest elastic modulus (8.0 to 9.2 GPa) but the lowest maximum stresses (97 to 124 MPa), whereas IPN teeth had the lowest elastic modulus (5.5 GPa) but high or highest maximum stress (171 to 192 MPa). The injection-molded technique significantly increased the elastic modulus of NHC and IPN teeth and significantly increased the maximum stress of IPN teeth. The compression-molded technique did not significantly affect mechanical properties of denture teeth.