A Drug Holiday Reduces the Frequency and Severity of Medication-Related Osteonecrosis of the Jaw in a Minipig Model

Abstract

Treatment of medication-related osteonecrosis of the jaw (MRONJ) is challenging and no clear consensus has been achieved. This study investigated preventive measures recommended for tooth extractions under antiresorptive (AR) treatment and the role of discontinuation of AR therapy to avoid the onset of MRONJ in a minipig model. Thirty-six Göttingen minipigs were divided into four groups. Group 1 (negative control): tooth extractions but no zoledronate (ZOL). Group 2 (positive control): weekly ZOL infusions for 12 weeks followed by tooth extractions without wound management followed by 8 weeks of ZOL treatment. Group 3: weekly ZOL infusions for 12 weeks followed by tooth extractions; surgical wound management (resection of sharp bone edges, mucoperiosteal coverage); and continuation of ZOL infusions for 8 weeks plus antibiotic treatment. Group 4: 12 weeks of ZOL infusions followed by a drug holiday for 6 weeks. Tooth extractions with preventive wound management followed by antibiotic treatment for 8 weeks but no ZOL infusions. Jawbones were subjected to macroscopic, radiological (CT and micro-CT) and histopathological investigations. No clinical cases of MRONJ were observed in the negative group, in the positive control all animals developed MRONJ. Group 3 developed MRONJ in 83% of cases. With a drug holiday, 40% developed MRONJ in areas of tooth extraction. This is the first large animal model that reduces the occurrence of MRONJ following tooth extraction by the implementation of a drug holiday combined with antibiotic prophylaxis and smoothening of sharp bony edges. © 2020 The Authors. Journal of Bone and Mineral Research published by American Society for Bone and Mineral Research..

Keywords: ANIMAL MODEL; BISPHOSPHONATES; BRONJ; MINIPIG; MRONJ; OSTEONECROSIS; PREVENTION; PROPHYLAXIS; ZOLEDRONATE.

Fig 1

Schematic of groups, detailing the timing of intervention.

Fig 2

Violin plot of the clinical analysis (incidence of MRONJ stages/group at euthanasia [8 weeks post‐Sx]). Stage definition according to Ruggiero and colleagues^{( 18 )} AAOMS). AAOMS = American Association of Oral and Maxillofacial Surgeons; Sx = surgery.

Fig 3

Results of CT analysis. Filling of the tooth socket with newly formed bone (in % of ROI), at euthanasia (8 weeks post‐Sx). Bone threshold defined by a density of >450 mg HA/mL. Kruskal‐Wallis one‐way ANOVA was used to investigate differences between groups.

Fig 4

HR‐pQCT data analysis at euthanasia (8 weeks post‐Sx). Filling of the tooth socket with newly formed bone was corrected for growth of teeth. Bone threshold defined by a density of >300 mg HA/mL.

Fig 5

HR‐pQCT data analysis at euthanasia (8 weeks post‐Sx). BV/TV was calculated as a % of ROI.

Fig 6

Results of the histological analysis. Severity of the selected histological changes characteristic for MRONJ (mean severity grade/group). Note: in group 4 (after exclusion of the two animals that developed MRONJ before Sx) the severity of the five parameters (ulceration with denuded bone, inflammation, infection, bone death, and bone degradation) were comparable to control.

Fig 7

Results of the histological analysis. Severity of the selected histological changes characteristic for MRONJ (mean severity grade/group). Kruskal‐Wallis one‐way ANOVA was used to investigate differences between groups.

Fig 8

Histological overview of the region of the left‐sided extraction alveoli M1 of the tooth‐only control group (left image section) compared to the corresponding region of the opposite side (right). There is an intact epithelial integrity, no exposed bone, no signs of inflammation, and no endosteal or periosteal bone proliferation.

Fig 9

Histological overview of the extraction alveoli M1 (left image section) and the corresponding opposite side of the MRONJ group (tooth extraction under BP medication without prophylaxis measures). It shows a pronounced gingival ulceration with exposed necrotic bone (blue) with signs of osteolysis and bacterial osteomyelitis (red) as well as empyema formation in the sinus mandibularis (black) and pronounced endosteal and periosteal proliferations (yellow).

Fig 10

Histopathological changes in group 2/positive control (mandibular M1 extraction site). (A) (magnification ×0.5, scale bar = 1 cm): Marked (grade 4) gingival ulceration with orally denuded bone (black open asterisk) which characterizes this sample as being positive for MRONJ) at the persisting alveolar cone after tooth extraction. (B) (magnification ×10): Large area with empty osteocytic lacunae (osteonecrosis, grade 4), and marked bacterial colonization (infection, grade 4) on its surface. (C) (magnification ×100 oil): Presence of Giemsa‐positive coccid bacteria in direct contact to brownish‐beige discolored, cloud‐like bone remnants (focal demineralization of extracellular bone matrix, grade 1). (D) (magnification ×10): Marked inflammatory cell infiltration of the bone marrow (osteomyelitis, grade 4) and irregular, ruffled surface of the bone characterized by Howship lacunae with/without presence of osteoclasts (osteolysis, grade 3) leading to rarefaction and reduced density of the remaining bone stock at the extraction socket region. (E) (magnification ×100 oil): The sinus mandibularis is filled with large amounts of bluish colored content (pus) consisting of inflammatory cells and acellular debris (empyema, grade 4). Presence of bluish condensed (Splendore‐Hoeppli material, yellow solid asterisk) representing extracellular bacterial deposits (characteristic but not specific for certain bacteria of the oromucosal biome (eg, Actinomyces ssp.). (F) (magnification ×2.5): Marked bone proliferation (grade 4) in form of trabecular bone at the corpus mandibulae (often recorded in cases of MRONJ).

Fig 11

Histological overview of the extraction alveoli M1 and the corresponding region of the opposite side in an animal from the ZOL + PM group (tooth extraction under bisphosphonate medication with perioperative antibiotic prophylaxis, bone smoothing and locally plastic cover, but without drug holiday) with incomplete epithelial integrity and a small proportion of exposed bone, wherein the underlying bone already has inflammatory changes, but without empyema formation in the sinus mandibularis and bone proliferation at the base mandibulae.

Fig 12

(A) Histological overview of the extraction alveoli M1 as well as the corresponding region of the opposite side in another animal from drug holiday + PM with only limited successful prophylaxis in changes already existing at the time of extraction in region M1. It shows a gingival ulceration with exposed bone and changes of the underlying bone, but without the formation of an empyema in the area of the sinus mandibularis and without bone proliferation at the base mandibulae. (B) Histological overview of the region of the extraction alveoli and the corresponding region of the opposite side of drug holiday + PM (extraction M1 in zoledronate application with preoperative drug holiday, perioperative antibiotic prophylaxis, bone smoothing and local plastic cover). It shows an intact epithelial integrity without reference to ulcerations and exposed bones. There is also no evidence of inflammatory infiltration or endosteal or periosteal proliferation.