Actinomyces lesions and acute inflammation predominate in osteonecrosis of the jaw associated with osteoclast-suppressing therapy in contrast to non-medication-related osteonecrosis

Actinomyces colonies were more prevalent in medication-related osteonecrosis (85%) compared to non-medication-related cases (51%; p < 0.001) and were mainly associated with necrotic bone. Inflammation was present in most samples; however, in medication-related osteonecrosis, it was predominantly acute (58%) and rarely chronic (5%), whereas in non-medication-related biopsies, inflammation was acute in 38% and chronic in 27% of biopsies (p < 0.001). Enhanced MMP-8 immunoreactivity was observed in 61% of medication-related osteonecrosis vs. 38% in non-medication-related biopsies (p = 0.002), and MMP-8 was especially expressed alongside actinomycotic lesions (57% vs. 34%; p < 0.001). In multivariable logistic regression, the medication-related group was independently associated with a higher prevalence of Actinomyces colonies.

Medication-related osteonecrosis was independently linked to a higher prevalence of Actinomyces compared to non-medication-related osteonecrosis. Furthermore, acute inflammation and collagenase activity seemed to be effects of Actinomyces-associated infection. The presence of Actinomyces may suggest immunological differences between these osteonecrosis types.