Absence of exposed bone following dental extraction in beagle dogs treated with 9 months of high-dose zoledronic acid combined with dexamethasone

Abstract

Purpose: Factors contributing to osteonecrosis of the jaw with anti-remodeling drug treatment are unclear. Epidemiologic and experimental studies have suggested the combination of bisphosphonates and dexamethasone results in osteonecrosis of the jaw more often than either agent alone. The goal of this study was to assess the combination of these 2 drugs in a large animal model previously shown to be susceptible to exposed bone in the oral cavity when treated with bisphosphonates.

Materials and methods: Skeletally mature beagle dogs were untreated controls or treated with zoledronic acid (ZOL), dexamethasone (DEX), or ZOL plus DEX. ZOL and DEX were given at doses based on those used in humans. All animals underwent single molar extraction at 7 and 8 months after the start of the study. Extraction sites were obtained at month 9 for assessment of osseous healing using micro-computed tomography and histology.

Results: No animals were observed to have exposed bone after dental extraction, yet 1 animal treated with ZOL and 1 treated with ZOL plus DEX had severely disrupted extraction sites as viewed by computed tomography and histology. These 2 animals had an intense periosteal reaction that was less obvious but still present in all ZOL-treated animals and absent from untreated animals. There was no significant difference in bone volume within the socket among groups at 4 or 8 weeks after healing, yet the ratio of surface to volume was significantly higher in animals treated with ZOL plus DEX at 8 weeks compared with control animals.

Conclusions: These findings suggest a more complex pathophysiology to osteonecrosis of the jaw than is implied by previous epidemiologic studies and those in rodents and raise questions about the potential role of DEX in its etiology.

Figure 1

Micro-computed tomography assessment of the extraction site in a zoledronate-treated animal (A) and each of the two zoledronate-treated animals that had abnormal healing (B and C). Images represent the mid-socket cross-section at 8 weeks post-extraction. Clear morphological differences can be observed between those that have abnormal healing compared to the zoledronate-treated animals including lack of alveolar socket woven bone, highly irregular/scalloped surfaces, and intense periosteal bone formation on the buccal surface.

Figure 1

Micro-computed tomography assessment of the extraction site in a zoledronate-treated animal (A) and each of the two zoledronate-treated animals that had abnormal healing (B and C). Images represent the mid-socket cross-section at 8 weeks post-extraction. Clear morphological differences can be observed between those that have abnormal healing compared to the zoledronate-treated animals including lack of alveolar socket woven bone, highly irregular/scalloped surfaces, and intense periosteal bone formation on the buccal surface.

Figure 1

Micro-computed tomography assessment of the extraction site in a zoledronate-treated animal (A) and each of the two zoledronate-treated animals that had abnormal healing (B and C). Images represent the mid-socket cross-section at 8 weeks post-extraction. Clear morphological differences can be observed between those that have abnormal healing compared to the zoledronate-treated animals including lack of alveolar socket woven bone, highly irregular/scalloped surfaces, and intense periosteal bone formation on the buccal surface.

Figure 2

Histological appearance of non-healing socket in zoledronate-treated animal. Consistent with the CT images, the histological section revealed dramatic destruction of the alveolar bone (A) and dramatic periosteal bone formation (A,B,C). The periosteal bone was continuing to form even 8 weeks post-extraction as evident by the osteoblasts and osteoid (C).

Figure 2

Histological appearance of non-healing socket in zoledronate-treated animal. Consistent with the CT images, the histological section revealed dramatic destruction of the alveolar bone (A) and dramatic periosteal bone formation (A,B,C). The periosteal bone was continuing to form even 8 weeks post-extraction as evident by the osteoblasts and osteoid (C).

Figure 2

Histological appearance of non-healing socket in zoledronate-treated animal. Consistent with the CT images, the histological section revealed dramatic destruction of the alveolar bone (A) and dramatic periosteal bone formation (A,B,C). The periosteal bone was continuing to form even 8 weeks post-extraction as evident by the osteoblasts and osteoid (C).

Figure 3

Micro-computed tomography assessment of the extraction site osseous healing. Three-dimensional analysis of the entire socket region support document that after 4 weeks of healing there was no difference in bone volume/tissue volume (BV/TV, %) or bone surface/total volume among the groups. After 8 weeks of healing, BV/TV was significantly higher in all treatment groups compared to the 4 week time-point. Bone surface / total volume (BS/TV) was significantly lower at 8 weeks compared to 4 weeks in CON, DEX, and ZOL groups but not ZOL+DEX. At the 8-week time point BS/TV was significantly higher in ZOL and ZOL+DEX compared to CON. p < 0.05 versus 4 week time-point within group (#), versus CON-treatment within time point (*), or versus DEX- treatment within time point (^).

Figure 3

Micro-computed tomography assessment of the extraction site osseous healing. Three-dimensional analysis of the entire socket region support document that after 4 weeks of healing there was no difference in bone volume/tissue volume (BV/TV, %) or bone surface/total volume among the groups. After 8 weeks of healing, BV/TV was significantly higher in all treatment groups compared to the 4 week time-point. Bone surface / total volume (BS/TV) was significantly lower at 8 weeks compared to 4 weeks in CON, DEX, and ZOL groups but not ZOL+DEX. At the 8-week time point BS/TV was significantly higher in ZOL and ZOL+DEX compared to CON. p < 0.05 versus 4 week time-point within group (#), versus CON-treatment within time point (*), or versus DEX- treatment within time point (^).

Figure 4

Histological assessment of intra-cortical bone formation rate in the alveolar region of the mandible. Labeled osteon number (A) and bone formation rate (B) were assessed in the alveolar bone adjacent to the extraction site by measuring fluorochrome labels injected at the end of the experiment. Both parameters were significantly lower at both 4 and 8 weeks post-healing in ZOL and ZOL+DEX groups compared to both CON and DEX groups. p < 0.05 versus CON-treatment within time point (*) or versus DEX- treatment within time point (^).

Figure 4

Histological assessment of intra-cortical bone formation rate in the alveolar region of the mandible. Labeled osteon number (A) and bone formation rate (B) were assessed in the alveolar bone adjacent to the extraction site by measuring fluorochrome labels injected at the end of the experiment. Both parameters were significantly lower at both 4 and 8 weeks post-healing in ZOL and ZOL+DEX groups compared to both CON and DEX groups. p < 0.05 versus CON-treatment within time point (*) or versus DEX- treatment within time point (^).

Figure 5

MicroCT images from human ONJ specimens that suggest a similar type of periosteal reaction as noted in the present study. Specimens were scanned and analyzed for a separate study [18].

Figure 5

MicroCT images from human ONJ specimens that suggest a similar type of periosteal reaction as noted in the present study. Specimens were scanned and analyzed for a separate study [18].