Owing to a rapid increase in aging population in recent years, the deterioration of motor function in older adults has become an important social problem, and several studies have aimed to investigate the mechanisms underlying muscle function decline. Furthermore, structural maintenance of the muscle–tendon–bone complexes in the muscle attachment sites is important for motor function, particularly for joints; however, the development and regeneration of these complexes have not been studied thoroughly and require further elucidation. Recent studies have provided insights into the roles of mesenchymal progenitors in the development and regeneration of muscles and myotendinous junctions. In particular, studies on muscles and myotendinous junctions have—through the use of the recently developed scRNA-seq—reported the presence of syncytia, thereby suggesting that fibroblasts may be transformed into myoblasts in a BMP-dependent manner. In addition, the high mobility group box 1—a DNA-binding protein found in nuclei—is reportedly involved in muscle regeneration. Furthermore, studies have identified several factors required for the formation of locomotor apparatuses, e.g., tenomodulin (Tnmd) and mohawk (Mkx), which are essential for tendon maturation.

Apical periodontitis is usually diagnosed based on clinical findings and dental X-rays. Recently, however, dental cone beam computed tomography (CBCT), which provides 3-D images of the maxillofacial region, has enabled dentists to examine patients undergoing endodontic therapy more effectively, improving diagnostic accuracy. Here, we describe a positive treatment outcome achieved using CBCT to diagnose apical periodontitis of the maxillary premolars, which had proven difficult to diagnose based on clinical findings and dental radiography alone. The patient was a 42-year-old Japanese man who presented with the chief complaint of gingival swelling in the maxillary right premolar region. Our initial diagnosis, based on clinical findings and dental X-ray, was apical periodontitis of the maxillary right second premolar, and treatment was started. However, after the patient failed to respond to the treatment, CBCT was performed. Based on these new findings, the diagnosis was changed to one of apical periodontitis of the upper right first premolar, and the patient was treated accordingly. Previous studies have described the complex anatomical morphology of the upper premolars, noting multiple roots and variation in the morphology of the root canals. The 3-D images provided by dental CBCT allow better assessment of oral conditions than the traditional 2-D images provided by dental X-rays, which in turn enables the dentist to better select the most appropriate treatment. Here, the patient showed no symptoms and was progressing well at a 6-month follow-up visit. The present results indicate that when clinical findings and dental X-rays alone are insufficient to allow a secure diagnosis, CBCT offers an effective alternative which will enable the appropriate treatment to be selected more reliably.

The present study aimed to classify variations in tooth root cross-sectional morphology after conventional endodontic microsurgery in the maxillary first molars and to accurately predict the risk of concealed isthmus deeper in the root based on the observed morphology. Using micro-CT data, tooth root cross-sections obtained at 3-6 mm from the apex were classified as Types I-V according to the isthmus classifications of Hsu and Kim. The rates of mismatch between isthmus classifications in the cross-sections at 3 mm from the apex and those obtained deeper in the root at 4-6 mm from the apex were calculated. High rates of match were observed between classifications in tooth root cross-sections at 3 mm from the apex and those deeper in the tooth root (4-6 mm) in the distobuccal (83%) and paratal (90%) roots, while the rate of match in the mesiobuccal root was low (36%). In mesiobuccal roots with incomplete isthmus at 3 mm from the apex, the probability of complete isthmus deeper in the root was 90% or higher. Accessory root canals and lateral branches were often found not only close to the apex, but also concealed deeper in the root more than 3 mm from the apex in the mesiobuccal roots of the maxillary first molars. Thus, as with cases of complete isthmus, treatment requires enlargement of the root canal to create a cavity that encompasses the main root canal and any smaller structures, followed by retrograde filling.