In this case, the patient exhibited not only a scarce example of multiple ST but also a rare combination of bilateral distomolars, KM-type ST and macrodontia. This kind of case hasn’t been founded till date. ST might occur singly or multiply, unilaterally or bilaterally in any position of the dentition or even in the jaw. The most common type is single, located in the anterior maxilla. A few multiple ST are reported to be accompanied by systematic disorders. Therefore, the presence of three distomolars that we presented, with no syndromes and family history is rare. Especially we represented two peculiar dentition conditions in individuals.
The prevalence rate of distomolars was between 1 and 2.2%. Previous studies suggested that the probability of distomolar occurrence in the maxilla is between 69 and 91% . Interestingly, our case not only showed maxillary and mandibular distomolars, but also appeared bilateral distomolars. Elif Kaya et al.  at 2015 reported only three cases of bilateral maxillary distomolars in 10,111 patients aged 18–60 years old. Concerning our case, it is infrequent to find bilateral maxillary distomolars. In addition, our case also represented a more unusual condition-KM. KM is a rare form of inclusions that we only found 32 cases published from 1973 till date. This condition can be found between the second and third molars, and also exited between the third molar and distomolar. Other than cases reported before represent only the occurrences of KM. Our case showed a typical feature of KM, an unwonted combination of bilateral distomolars and macrodontia. Macrodontia is a scarce anomaly of tooth’s shape. Also, macrodontia is mostly reported in mandibular premolars or molars. It is not usual that macrodontia occurred in the third molar like our case .
Nowadays the etiology of ST still is not clear. There are many theories trying to explain the occurrence of ST. The tooth germ dichotomy theory proposed that the dichotomy of dental buds leads to the occurrence. While the hyperactivity theory revealed that ST was caused by local, conditional and independent hyperactivity of the dental lamina. In addition, it’s also stated that ST may be hereditary, however, there is no simple Mendelian pattern . And KM is kind of special ST so the theories of occurrence are alike. Some reports proposed high cystic formation or fourth molar may lead to bone loss and finally the existence of KM . Furthermore, macrodontia is usually accompanied by syndromes while the mechanism of macrodontia still is not clear . In this case, parents didn’t have ST or KM. Thus, the probability of heredity was relatively low. Meanwhile, the maxillofacial examination of the patient did not show any maxillofacial abnormalities and cranial clavicular syndrome. Combined with past history, we excluded the possibility of systemic diseases. Therefore, the reason of combination of bilateral distomolars, KM-type ST and macrodontia needs to be further explored.
An accurate diagnosis for ST could be through clinical or radiographic examination. A radiographic examination is needed if abnormal clinical symptoms are found . Nowadays appropriate diagnosis with CBCT is more recommended. As CBCT could provide 3D information of teeth’ morphologies and positions, it is routinely considered to evaluate teeth with volumetric analysis of pulp/tooth ratio . In this case, we performed CBCT detection along with Dolphin software analysis. We confirmed that two ST in the maxillary were located at the buccal side of third molars; ST in the mandible was contacted the adjacent tooth by their occlusal planes, and their roots were pointed in the opposite direction. Compared to the conventional radiographs as radiographic examination, evaluation with the CBCT revealed detailed imaging of significant anatomical structures and objects of interest, with highly accurate anatomical and morphologic imaging in contrast to the intraoperative findings .
ST causes many complications, such as root absorption, decayed teeth, ectopic eruption, overcrowding, periapical absorption of permanent teeth, and migration into the nasal cavity or maxillary sinus. The large crown size of macrodontia causes problems with the eruption and disrupts the dentition. But in our case, the patient didn’t show any symptoms or pathologic change associated with ST and macrodontia. Though the dominated treatment of ST is extraction, ST along with the condition of the circumambient teeth should be taken into consideration. While KMs would be treated if they cause harmful symptoms, such as high risk of odontoma, decayed teeth, periodontal complications, cystic pathology or progressive bone loss . Surgical extraction of KMs is the most frequent protocol. Some also presented orthodontic treatment. As for macrodontia, following surgical removal, orthodontic therapy is initiated to correct the malocclusion. In our case, the patient removed tooth 18 to prevent more serious caries. Since there’s no risk of compression and absorption of adjacent roots in the patient’s ST and macrodontia, observation should be reserved for the time being. While it is necessary to take examinations regularly for review, aiming to evaluate development of any related pathologies in the future.
In conclusion, we presented a rare case of the combination of kissing molars, maxillary bilateral supernumerary teeth and macrodontia, which has not been reported till date. However, further investigations about etiology and treatment are still needed to be explored.