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Periodontal disease is an inflammatory disease caused by periodontopathogenic bacteria, which eventually leads to bone tissue (alveolar bone) destruction as inflammation persists. Periodontal tissues have an immune system against the invasion of these bacteria, however, due to the persistent infection by periodontopathogenic bacteria, the host innate and acquired immunity is impaired, and tissue destruction, including bone tissue destruction, occurs. Osteoclasts are essential for bone destruction. Osteoclast progenitor cells derived from hematopoietic stem cells differentiate into osteoclasts. In addition, bone loss occurs when bone resorption by osteoclasts exceeds bone formation by osteoblasts. In inflammatory bone disease, inflammatory cytokines act on osteoblasts and receptor activator of nuclear factor-κB ligand (RANKL)-producing cells, resulting in osteoclast differentiation and activation. In addition to this mechanism, pathogenic factors of periodontal bacteria and mechanical stress activate osteoclasts and destruct alveolar bone in periodontitis. In this review, we focused on the mechanism of osteoclast activation in periodontitis and provide an overview based on the latest findings.

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Objective: This multicenter clinical study was to assess the clinical usability of an oral moisturechecking device in detecting the dry mouth patients and evaluating the optimal measurement site. Materials and Methods: The study group comprised 250 patients with dry mouth and 241 healthy volunteer subjects at 13 medical centers. This device was used to measure the moisture degrees of the lingual mucosa and the buccal mucosa. Subjective oral dryness, objective oral dryness, and saliva flow rates were also compared between the two groups. For statistical analysis, receiver-operating characteristic analysis was performed to calculate the area under the curve (AUC). Results: The moisture degree of the lingual mucosa was significantly lower in the dry mouth group (27.2 ± 4.9) than that in the healthy group (29.5 ± 3.1, AUC = 0.653). When a lingual mucosa moisture degree of 31.0 or higher was defined as normal, less than 27.0 as dry mouth, and 27.0 to less than 31.0 as borderline zone of dry mouth, both the sensitivity and the specificity for the diagnosis of dry mouth were close to 80%. Conclusion: These results suggest that the oral moisture-checking device is a usable screening device for dry mouth.

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