Oral bacteria sustain medication-related osteonecrosis of the jaw

Osteonecrosis means the death of bone tissue due to poor blood supply. Medication-related osteonecrosis of the jaw (MRONJ) is a long-term condition which causes pain in the affected bone, purulent discharge, and tooth loss.

Medication-related osteonecrosis is rare: in standard treatment of osteoporosis, it was diagnosed in 0.3% of patients. However, up to 9% of patients receiving high-dose medication usually used in bone metastasis developed MRONJ in a Finnish study cohort.

MRONJ is treated with surgical debridement, systemic antibiotics, and antimicrobial mouth rinsing to prevent microbial growth. The treatment usually improves the condition. Recovery typically takes from several months to a year, but in some cases, it may take several years.

Bacteria sustain osteonecrosis of the jaw

Medications used in osteoporosis and cancer bone metastasis are the most common cause of osteonecrosis, but it can also be caused by radiation of the jaw or an infection. Biopsies from 191 patients with jaw osteonecrosis were compared at HUS. In approximately half of the samples, necrosis was caused by medication used for osteoporosis and cancer bone metastasis, and in the other half by other reasons. No comparable extensive study has been done previously. 

Inflammation was present around necrotic bone in nearly all cases. Inflammation was usually acute in medication-related samples, while chronic inflammation was more common in the other cases.

Actinomyces colonies were present in 82% of cases with medication-related osteonecrosis. In cases associated with radiation therapy or other causes, they were present in only 47%.

Actinomyces lesions formed a biofilm, which is a dense layer of bacteria, on the necrotic bone surface. The necrotic bone also contained other oral bacteria, such as streptococci and Prevotella.

“Tissue damage caused by Actinomyces-associated infection and the related inflammation seems to sustain osteonecrosis in the bone that is linked to the medication used in cancer bone metastasis and osteoporosis. Medication-related lesions were also slower to heal than osteonecrosis of the jaw caused by other reasons,” says Marjo Kivelä-Rajamäki, an infectious diseases specialist at HUS Inflammation Centre.

Active inflammation also in the soft tissue

Inflammation causing tissue destruction was observed in the soft tissue surrounding the necrotic bone. Inflammation was especially discovered around Actinomyces colonies.

The acute inflammation seemed to be linked to an Actinomyces infection rather than directly to the necrotic bone. Active inflammation was evident, with inflammatory cells and proteolytic enzyme activity surrounding the Actinomyces colonies.

Kivelä-Rajamäki states that nearly all patients had received antibiotics that are effective against Actinomyces, but mostly as short and repeated courses.

“Actinomyces must be included in bacterial examinations of osteonecrosis of the jaw. Also, a pathologist should be able to recognize if the bacteria are linked to a biofilm on the bone. In the future, this finding may lead to improved treatment of osteonecrosis, but it needs to be verified with clinical trials,” Kivelä-Rajamäki adds.

Source: Kivelä-Rajamäki M, Välimaa H, Furuholm J, Haglund C, Sorsa T, Hagström J, Järvinen A. Actinomyces lesions and acute inflammation predominate in osteonecrosis of the jaw associated with osteoclast-suppressing therapy in contrast to non-medication-related osteonecrosis. Eur J Clin Microbiol Infect Dis. 2026 Apr 6. doi: 10.1007/s10096-026-05501-9.

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