Establishment of an Animal Model of Bisphosphonate-Related Osteonecrosis of the Jaws in Spontaneously Diabetic Torii Rats.

BACKGROUND:We evaluated the side effects of bisphosphonate (BP) on tooth extraction socket healing in spontaneously diabetic Torii (SDT) rats, an established model of non-obese type 2 diabetes mellitus, to develop an animal model of BP-related osteonecrosis of the jaws (BRONJ). MATERIALS AND METHODS:Male Sprague-Dawley (SD) rats and SDT rats were randomly assigned to the zoledronic acid (ZOL)-treated groups (SD/ZOL or SDT/ZOL) or to the control groups (SD/control or SDT/control). Rats in the SD/ZOL or SDT/ZOL groups received an intravenous bolus injection of ZOL (35 μg/kg) every 2 weeks. Each group consisted of 6 rats each. Twenty-one weeks after ZOL treatment began, the left maxillary molars were extracted. The rats were euthanized at 2, 4, or 8 weeks after tooth extraction, and the total maxillae were harvested for histological and histochemical studies. RESULTS:In the oral cavity, bone exposure persisted at the tooth extraction site in all rats of the SDT/ZOL group until 8 weeks after tooth extraction. In contrast, there was no bone exposure in SD/control or SDT/control groups, and only 1 of 6 rats in the SD/ZOL group showed bone exposure. Histologically, necrotic bone areas with empty lacunae, microbial colonies, and less invasion by inflammatory cells were observed. The number of tartrate-resistant acid phosphatase-positive osteoclasts was lower in the SDT/ZOL group than in the SD/control group. The mineral apposition rate was significantly lower in the SDT/ZOL group compared with the SD/control group. CONCLUSIONS:This study demonstrated the development of BRONJ-like lesions in rats and suggested that low bone turnover with less inflammatory cell infiltration plays an important role in the development of BRONJ

Validation of the diabetic phenotype of SDT rats.

<p>Changes in body weight (<b>A</b>) and blood glucose levels (<b>B</b>) in SD and SDT rats. □: SD/control, ■: SD/ZOL, ○: SDT/control, ●: SDT/ZOL. Data are expressed as means ± SD (n = 6). *<i>p</i><0.005 versus SD/control. Macroscopic opacity of the lens observed at approximately 32 weeks of age in SDT rats (<b>C</b>).</p

Macroscopic view of extraction sockets in SD/control (A-C), SD/ZOL (D-F), SDT/control (G-I), and SDT/ZOL (J-L) rats.

<p>Two representative specimens are shown. Normal healing after molar extraction was observed in SD/control (<b>A</b>) and SD/ZOL (<b>D</b>) rats by 2 weeks after extraction. Extraction sockets in both groups were covered with intact epithelium at 4 weeks (<b>B, E</b>) after extraction and at 8 weeks (<b>C, F</b>) after extraction. Apparent mucosal disruption with exposed bone (arrows) was seen at the extraction site at 2 (<b>G</b>) and 4 (<b>H</b>) weeks, but not at 8 weeks (<b>I</b>) after extraction in the SDT/control group and at 2 (<b>J</b>), 4 <b>(K</b>), and at 8 weeks (<b>L</b>) after extraction in the SDT/ZOL group.</p

Photomicrographs of extraction sockets in SD/control (A-C), SD/ZOL (D-F), SDT/control (G-I), and SDT/ZOL (J-L) rats.

<p>Healed gingival mucosa with complete epithelial coverage in the SD/control group. (<b>D, E</b>) Partial deficiency of epithelial coverage at 2 and 4 weeks in the SD/ZOL group (arrow). (<b>F</b>) Nonkeratinized oral epithelium grew towards the sequestrum at 8 weeks after tooth extraction in 1 of 6 SD/ZOL rats (arrow). (<b>G</b>) Unhealed open socket with an area of exposed bone and no mucosal coverage at 2 weeks after extraction in the SDT/control group. (<b>H</b>) Interstitial tissue (★) under bone sequestra at 4 weeks after extraction. (<b>I</b>) Healed gingival mucosa with complete epithelial coverage at 8 weeks after extraction in the SDT/control group. (<b>J, K</b>) Unhealed open sockets with an area of exposed bone and no mucosal coverage at 2 and 4 weeks after extraction in the SDT/ZOL group. (<b>L</b>) Open sockets without epithelial lining (left right arrow) at 8 weeks after extraction in the SDT/ZOL group. H&E stain, original magnification, ×40. <b>Photomicrographs of magnifying dotted square area in (H) and (L)</b>. (<b>M</b>) Necrotic bone sequestra (SQ) with empty osteocyte lacunae covered with bacterial colonies (BC) and marked inflammation in (H) of SDT/control rat. (<b>N</b>) Necrotic bone sequestra (SQ) with empty osteocyte lacunae covered with bacterial colonies (BC) and less inflammation in (L) of SDT/ZOL rat. H&E stain, original magnification, ×200. <b>(O)</b> High magnification of empty osteocyte lacunae and <b>(P)</b> bacterial colonies in SDT/ZOL rats. H&E stain, original magnification, ×400.</p

TRAP-stained sections 4 weeks after tooth extraction.

<p><b>(A)</b> TRAP-positive osteoclasts on the bone surface in the upper alveolar bone. Original magnification, 200×. <b>(B)</b> The number of multinuclear TRAP-positive cells was counted in four non-overlapping fields of alveolar bone at a magnification of 200×.</p

Time to onset of bisphosphonate-related osteonecrosis of the jaws: a multicentre retrospective cohort study

Objectives: Osteonecrosis of the jaw (ONJ) is a potentially severe adverse effect of bisphosphonates (BP). Although the risk of ONJ increases with increasing duration of BP treatment, there are currently no reliable estimates of the ONJ time to onset (TTO). The objective of this study was to estimate the TTO and associated risk factors in BP-treated patients. Subjects and Methods: Retrospective analysis of data from 22 secondary care centres in seven countries relevant to 349 patients who developed BP-related ONJ between 2004 and 2012. Results: The median (95%CI) TTO was 6.0 years in patients treated with alendronate (n = 88) and 2.2 years in those treated with zoledronate (n = 218). Multivariable Cox regression showed that dentoalveolar surgery was inversely associated, and the use of antiangiogenics directly associated, with the TTO in patients with cancer treated with zoledronate. Conclusions: The incidence of ONJ increases with the duration of BP therapy, with notable differences observed with respect to BP type and potency, route of administration and underlying disease. When data are stratified by BP type, a time of 6.0 and 2.2 years of oral alendronate and intravenous zoledronate therapy, respectively, is required for 50% of patients to develop ONJ. After stratification by disease, a time of 5.3 and 2.2 years of BP therapy is required for 50% of patients with osteoporosis and cancer, respectively, to develop ONJ. These findings have significant implications for the design of future clinical studies and the development of risk-reduction strategies aimed at either assessing or modulating the risk of ONJ associated with BP