Microarchitecture of medication-related osteonecrosis of the jaw (MRONJ); a retrospective micro-CT and morphometric analysis.

Medication-related osteonecrosis of the jaw (MRONJ) is a severe side effect of antiresorptive (AR) drugs such as bisphosphonates (BP) and denosumab (Dmab). Although several risk factors are described, the etiology of MRONJ is still not fully elucidated. Bone-strengthening is the primary aim of antiresorptive therapy; however, overly increased bone mass and microcrack accumulation are also discussed in MRONJ etiologies. The aim of this study is to evaluate the microarchitecture of jaw bones with micro-computed tomography (micro-CT) in AR-treated patients with or without MRONJ. Human jaw bone samples of AR-treated patients were separated into 11 groups by AR treatment bisphosphonate (BP), denosumab (Dmab), both (M) and control groups. Subgroups were divided according to the clinical localization as AR-exposed vital jaw bone (BP(exp), Dmab(exp), M(exp)), osteonecrosis-margin of a sequestrum (BPO(mar), DmabO(mar), MO(mar)) and osteonecrosis-sequestrum (BPO(seq), DmabO(seq), MO(seq)). Healthy jaw bone (C(HB)) and osteoporotic jaw bone (C(OP)) represent control groups. Samples underwent retrospective micro-CT and morphometric analysis in representative units by bone volume fraction (BV/TV), bone surface density (BS/BV), trabecular thickness (Tr.Th.), trabecular number (Tr.N.), trabecular space (Tr.Sp.), Euler characteristic for bone connectivity, bone mineral density (BMD) and tissue mineral density (TMD). A total of 141 samples from 78 patients were analyzed. BV/TV of M(exp) group (mean: 0.46 +/- 0.27) was significantly higher than in the C(OP) group (mean: 0.14 +/- 0.05; p = 0.0053). Tr.Th. differed significantly between the BP(exp) group (mean: 0.32 +/- 0.15) and the M(exp) group (mean: 0.57 +/- 0.20; p = 0.0452) as well as between the BPO(seq) group (mean: 0.25 +/- 0.10) and the MO(seq) group (mean: 0.39 +/- 0.18; p = 0.0417). Signs of trabecular thickening and unorganized trabecular microarchitecture from AR-exposed- to sequestrum groups, were analyzed in 3D reconstructions. However, BS/BV, Tr.N., and Tr.Sp. showed no significant differences. Euler characteristic of the BPO(seq) group (median: 7.46) doubled compared to that of the BP(exp) group (median: 14.97; p = 0.0064). Mineralization parameters BMD and TMD were similar in all groups. Findings show evidence of enhanced bone mass and suspect microarchitecture in some AR-treated jaw bone compared to osteoporotic jaw bone. Despite increased bone mass, some MRONJ samples showed decreased trabecular connectivity by Euler characteristic compared to AR-treated jaw bone. These samples may indicate extensive ossification and ineffective bone mass with superficially higher bone mass without existing or even reduced mechanical stability, indicated by connectivity loss. This result might also suggest a high risk to microcrack accumulation. At some point, possibly some kind of over-ossification could lead to under-nourishment and microarchitectural weakness, creating instability, subsequently increasing vulnerability to MRONJ.