Mandible matrix necrosis in beagle dogs after 3 years of daily oral bisphosphonate treatment

Abstract

Purpose: An increasing number of reports have implicated bisphosphonates as contributing to osteonecrosis of the jaw. The goal of this study was to evaluate mandible necrosis in beagle dogs treated for 3 years with oral alendronate (ALN).

Materials and methods: Skeletally mature female beagles were treated daily for 3 years with oral doses of vehicle (VEH) or ALN (0.20 or 1.0 mg/kg/day). These doses approximate, on a mg/kg basis, those used for postmenopausal osteoporosis and Paget's disease, respectively. At necropsy, the second molar region of the mandible was excised, stained en bloc with basic fuchsin, and assessed for matrix necrosis and intracortical bone turnover rate using histology. Matrix necrosis was defined as a region greater than 500 microm(2) that was void of basic fuchsin stain, assessed using both bright-field and confocal microscopy.

Results: No animals developed exposed bone lesions in the oral cavity during the 3-year study. Matrix necrosis was observed in 25% of ALN0.2 animals, 33% of ALN1.0 animals, and was noticeably absent from all vehicle animals (P < .05 pooled ALN doses vs VEH). These necrotic regions occurred predominately in the alveolar bone and were clearly void of patent canaliculi. Intracortical bone turnover rate of the alveolar mandible bone region was significantly lower (-75%, P < .05) in ALN-treated animals compared with VEH.

Conclusions: Three years of daily oral bisphosphonate treatment reduces bone turnover significantly and increases the incidence of matrix necrosis within the mandible of dogs.

Figure 1

Basic fuchsin stained histological section through the 2^nd molar region. Dotted line at the base of the tooth root separates the alveolar (above line) and non-alveolar (below line) regions for classifying locations of necrosis and bone turnover rate.

Figure 2

Matrix necrosis in the mandible of dogs treated for 3 years with alendronate. The second molar region was stained en bloc with basic fuchsin with regions of matrix necrosis defined as those regions void of stain uptake. Necrotic bone matrix can be observed using brightfield microscopy (A, D, E). Due to its fluorescent properties, stained regions can be visualized using confocal microscopy, revealing patent canalicular networks (B,G). Conversely, necrotic regions which are void of stain can are without patent canalicular networks (C, F, H).

Figure 2

Matrix necrosis in the mandible of dogs treated for 3 years with alendronate. The second molar region was stained en bloc with basic fuchsin with regions of matrix necrosis defined as those regions void of stain uptake. Necrotic bone matrix can be observed using brightfield microscopy (A, D, E). Due to its fluorescent properties, stained regions can be visualized using confocal microscopy, revealing patent canalicular networks (B,G). Conversely, necrotic regions which are void of stain can are without patent canalicular networks (C, F, H).

Figure 3

Bisphosphonates significantly reduce intracortical bone formation rate in the mandible. There was a significant reduction in the overall bone formation rate of the mandible with both doses of alendronate (ALN) or when the two doses of ALN were pooled. There was no significant difference between the two doses of ALN. The greatest suppression of turnover was noted in the alveolar portion of the mandible with no significant effect of ALN treatment on turnover suppression in the non-alveolar portion. Across all groups turnover was 84% lower in the non-alveolar region compared to the alveolar region. * p < 0.05 versus VEH.