It is reported that the temporomandibular joint is full-grown morphologically and histologically in persons in their twenties. Moreover, after the growth ends, aging changes are strongly seen compared with the capita of the joints of limbs. Mandibular condylar shapes have been classified by observation from the posterior side (Yale et al., 1963, 1966; Öberg et al., 1971; Carlson and Öberg, 1974; Wedel et al., 1978; Richards et al., 1981; Solberg et al., 1985; Whittaker et al., 1990). There are few differences in the frequency of the convex type, observed mainly by age and race. Similarly, in this study, we found that the convex (or slightly round) type of mandibular condyle was the standard morphology even in elderly individuals. An important question is whether the angled-type condyle occurs with higher frequency than the flattened-type condyle in elderly individuals >70 years old. This is because the flattened type was found to be increased in elderly persons in past studies, although it was expected in this study that many flattened-type condyles would also be observed, many angled-type condyles were observed rather than the flattened type. This represents a new finding in the field. This fact suggested that, in the modern elderly, condyles not only can be flat, but also exhibit an eminence. This is considered to be due to the influence of the modern lifestyle, including eating habits. For temporomandibular disorders, the relevance of shape, and lifestyle should be investigated clinically, and it is expected that this will contribute to the prevention and treatment of such disorders. Mandibular condyles show hypocalcification due to decreasing cartilage with aging and constant exposure to mechanical stress. A number of studies have reported tendencies toward a decrease in the round type and an increase in the flattened type with aging (Yale et al., 1962, 1966; Richards et al., 1981; Whittaker et al., 1985, 1990; Laheim et al., 1999; Nishijima et al., 2009). This study was performed using cadavers from elderly individuals (>70 years old). Therefore, we hypothesized that the frequency of the flattened type would be higher. A morphological study of young people (mean age, 26 years) by Sorberg et al. (1985) classified condyles in 50% of subjects into the round type, with 30% flattened and 20% angled. Solberg used donated cadavers less than 3 days after death, and performed condylar classification for ages 13–37 years (mean, 26.4 years). The posterior side view yielded three types: slightly round, flat, and gabled. In our study, these are equivalent to convex, flattened, and angled, respectively. Therefore, we can compare the condoyles of modern younger and older persons. In this study, the frequencies were about 42% for the convex type, 17% for flattened, and 29% for angled in the posterior view. The flattened type was thus less frequent than the angled type, an unanticipated result. As cartilage cells decrease in older condyles, it was expected that the flattened tendency would more frequent than in younger condyles. When the results of this study were compared with Sorbergs', inversion of the rates of angled and flattened condyles was found. The flattened type is produced by flattening of the convex type. The next important question is why the angled type occurs because, in past studies, it was not clear whether the angled type developed as a result of increasing cartilage and bone on the convex type, or decreasing cartilage and bone on the convex type. Although the possibility of the former is high considering the findings of this study, various factors such as occlusion, eating habits, and oral habits can be considered as the cause.
Histological examination in the present study demonstrated fewer cartilage cells in the flattened type than in the convex type (Fig. 6), whereas the angled type showed an increased number of cartilage cells in the prominent portion (Fig. 5). The results obtained here suggested that increased cartilage and bone led to the angled condylar shape. In addition, these findings suggested the possibility of progressive remodeling in which cartilage cells increase on the mandibular condyle in the elderly, as proposed by Moffet et al. (1964). Mandibular condyles may tend to not only become flatter with age, but also undergo progressive changes such as protrusion.
In this study, we observed the shape in more detail than previously by adding observation from the lateral side to that from the posterior side. Understanding the relationship between the posterior and lateral morphologies of the mandibular condyle is important. Clinical observation of the condylar shape is dependent on inspection of pictures. In this case, the back and front shapes could be observed by P-A and the side shape could be observed by orthopantomography or the Schuller method. Thus, the observation directions in this study corresponded to the back and front directions, as well as the side, and can considered as basic data when performing future clinical examinations. With regard to classification from the lateral view, we chose simple criteria to allow comparison with the posterior view. The angled type in the lateral view was subclassified into anteriorly, centrally and posteriorly angled types. In the current study, the centrally angled type in the lateral view was the most common morphological type, as described by Sugawara et al. (1995). Posterior and lateral morphological types tend to be similar in the elderly.
Given these results, we determined the morphology of mandibular condyles in the elderly. This will facilitate an understanding of the relationship between macroscopic morphological and histological features. Since this study targeted condyles from donated cadavers of individuals aged 70 and over, it is a longitudinal study investigating the condylar shape at the time of death. Therefore, since we did not observe any individual's condylar shape covering the entire life, it was not possible to determine how condylar shape changed over the course of aging. Moreover, since it was also impossible to investigate the existence of temporomandibular disorders, eating habits, oral habits, etc., in life, it was not possible to examine how such factors influenced the shape. Although the number of remaining teeth could be investigated, we had no information about the existence and the time for beginning to use dentures, which can influence changes in shape. Nor did we perform comparison and examination of the right and left condyles in the same donated cadavers. This study investigated what kinds of shapes existed in human condyles by comparison and examination with past studies, and what kinds of differences there were histologically between the shapes, rather than investigating the causes by which shape changes take place or diachronic changes with aging.
However, considering the macroscopic and the histological observations of this study, it was suggested that changes in shape take place due to changes in cartilage cells. Therefore, the findings of this study should be useful as basic data for investigating condylar shape changes and the positioning of the condyle in the articular fossa cross-sectionally in X-ray photographs clinically, and the histological background can also be postulated.