An Orthodontic Study of Non-syndromic Oligodontia: An Examination of Occlusion and Occlusal Support

The aim of this study was to analyze orthodontic data to investigate occlusal conditions, the relationship between malocclusion and the number of congenitally missing teeth, and occlusal support of maxillomandibular teeth in patients with oligodontia. The study included 66 patients with permanent dentition from two orthodontic clinics belonging to Tokyo Dental College who had received a diagnosis of oligodontia between 2003 and 2014. The materials used for the analysis comprised intraoral photographs, panoramic radiographs, and lateral cephalometric radiographs. The antero-posterior occlusal relationships, assessed by overjet, showed a high prevalence of anterior crossbite, while the vertical occlusal relationships, evaluated by overbite, indicated a predominance of deep bite. There were no significant differences in the total number of missing teeth in the three groups divided according to degree of overjet. The same tendency was observed in the case of overbite. The number of missing teeth in the maxilla was significantly higher than that in the mandible. The high occurrence of anterior crossbite in oligodontia is believed to be related to skeletal factors, such as deficiency of the maxillary apical base and a greater number of missing teeth in the maxilla compared to in the mandible. Based on their Eichner Index scores, 98.5% of cases were classified as Class B. Among these, B2 was the most prevalent (60.6%), suggesting that patients with oligodontia have low occlusal support. The average number of Occlusal Units (OUs) was 6.4 out of 12. Nearly half of the second deciduous molars were retained in both the maxilla and the mandible. When deciduous molars were treated as premolars, there was a significant increase in number of OUs. No significant differences were observed in the actual occlusal support score, however. Therefore, oligodontia with many defects in the premolar region resulted in a low level of occlusal support, and although the survival rate of the deciduous molars was high, they were not useful in providing occlusal support.