Amelogenin Knockout Mice Mimic Physical Tooth Characteristics of Human Amelogenesis Imperfecta

We have earlier reported that amelogenin knockout (AKO) mice display tooth defects such as tooth discoloration, hypoplastic enamel, and cuspal attrition, similar to those seen in amelogenesis imperfecta (AI) affected patients. However, the AKO mouse teeth were not evaluated for their physical characteristics using clinically relevant tests such as adhesion of composite resins that are used in the treatment of AI affected teeth. Objectives: To investigate whether the physical defects in teeth from AKO mice adversely affect bonding of composite resins in a manner similar to that reported in AI patients. Methods: We determined shear and tensile bond strengths of a composite resin (Z-100, 3M, MN) bonded to wild-type (WT) control and AKO incisor and molar teeth (n=13/group/test) using a universal Instron machine. Statistical comparisons of mean strengths were made using two-sample t-tests. After shear and tensile tests, tooth specimens were subjected to scanning electron microscopy (SEM). Results: Mean tensile (AKO, 0.32 ±0.32; WT, 1.71±1.29, p<0.004) and shear bond strengths (AKO, 0.46±0.30; WT, 1.37 ±1.10, p<0.04) from AKO mouse teeth were significantly lower than those from control WT mice. SEM analysis revealed a narrower hybrid layer in the AKO mice teeth as compared to WT. Conclusions: These data indicate that the structural alterations in the enamel of amelogenin KO mice affect adhesion of composite resins. These alterations resemble those reported in the teeth affected by certain forms of AI. These results therefore provide direct evidence that the AKO mouse is a suitable animal model to study AI tooth defects and develop therapeutic approaches. NIDCR support to A.B.K (Z01-DE00698-05). Correspondence: g.kulkarni@utoronto.ca