BACKGROUND: Kissing molars (KMs) is defined as a state in which the apex of two impacted molars face opposite directions and the occlusal surfaces touch each other and the crown is in one follicle. Class III KMs have been reported previously; however, reports on class III KMs in young people (< 18 years of age) are limited.
METHODS: Here, we present the case of KMs class III confirmed at an early age, supported by a review of the literature. The patient was a 16-year-old female and experienced discomfort in the left molar of the lower jaw and visited in our department. We diagnosed KMs based on an impacted teeth on the buccal side, near the lower jaw wisdom teeth, and a cyst-like low-density area observed around the crown of both teeth, as revealed by computed tomography. We decide to extract the tooth and enucleate the cyst under local anesthesia as the patient experienced discomfort due to occlusion. Furthermore, the cyst-like structure removal and tooth extraction including tooth root were necessary as the patient had KM class III, possibly inducing complicated malocclusion. Although no previous reports recommended timing for KMs tooth extraction, we propose that extraction at an early stage is important regardless of age especially in class III cases.
CONCLUSIONS: We report a case of KM class III detected at an early age.

BACKGROUND: Kissing molars (KMs) are a scarcely reported form of molar impaction in which the occlusal surfaces contact each other within a single dental follicle and the roots point in opposite directions. The direction of KMs impaction is generally tilted. KMs with vertical direction impaction have not been reported in the literature.
METHODS: A 25-year-old female visited a dentist for right maxillary wisdom teeth extraction and was diagnosed with two vertically impacted KMs in the left mandible on panoramic radiography. After cone-beam computed tomography examination confirmed no secondary complication, the patient chose to undergo observation and regular follow-up. A literature review of KMs revealed that vertical impacted KMs are rare; high-quality evidence regarding their prevalence is still lacking. At present, the causality of KMs is controversial. In this study, we have tried to provide a detailed definition of KMs to allow an accurate evaluation of their prevalence and classification based on their impaction direction which may be related to their pathogenesis. The treatment plan of KMs depends on the condition and location of the affected teeth and associated complications; they may be either directly extracted or treated using a multidisciplinary approach including maxillofacial surgeons and orthodontists.
CONCLUSIONS: KMs are a rare clinical condition of impacted teeth with unclear pathogenesis. Vertically impacted KMs were seldom reported. Reasonable definition and classification of KMs can help in the understanding of their causes and prevalence.

Supernumerary teeth (ST) is defined as an additional number of teeth compared to the normal dental formula. The prevalence rate of ST varies from 0.5 to 3.8% in the permanent dentition. When ST located distal to the third molar is acclaimed as distomolar. Moreover, kissing molar is an extremely scarce condition of distomolars, pointed in the opposite direction in a single follicular space. Meanwhile, macrodontia is also a rare shape anomaly characterized by a large crown and tapering root.
A 22-year-old Chinese man presented a combination of kissing molars, maxillary bilateral supernumerary teeth and macrodontia. Radiographically, two maxillary bilateral distomolars located at the buccal side of adjacent third molars. One mandibular distomolar with the adjacent third molar was contacted by occlusal surfaces while roots were pointed oppositely, which could be diagnosed as KM. Furthermore, the left mandibular third molar can be inferred to be a macrodontia, characterized by a large crown and tapering root. After a thorough investigation, we excluded the possibilities of systemic diseases and genetic inheritance. However, the etiology of this rare combination deserves to be further explored.
The combination of kissing molars, maxillary bilateral supernumerary teeth and macrodontia is very rare, especially presented in the patient with no syndromes. As there were no complications with these conditions, long-term observation has been recommended for the patient. In addition, the true etiology need a further exploration.

Kissing molars (KMs) is an extremely rare condition of impacted third molars, pointed in the opposite direction in a single follicular space; it consists exactly in a full impacted of permanent molars which occurs only in the lower jaw. Actually, about less than thirty cases have been reported in scientific literatures. The aetiology and pathogenesis of this pathological double dental inclusion remain unknown; above all events that lead two molars to appear, as KMs remain mysterious. The association to metabolic connective diseases such as mucopolysaccharidosis was emphasized. KMs considered as an isolated event, may be associated to an abnormal position of the tooth-bud from lower permanent molars, or fourth supernumerary tooth (distomolar). Recently, hyperplastic dental follicle (HDF), with a down regulation of matrix metal-proteinases and up regulation of several genes of collagens, has been mentioned in association with KMs. In this paper, after having analyzed three new cases of KMs that have been treated, we report a new hypothesis. This last is based on the failure in the dental follicle\'s ability to initiate or continue properly resorption of the overlying alveolar bone, by many exogenous factors which may act on eruptive phase that would lead to its rotation with its contents coming out a pathological situation of KMs. The therapy of choice is related to the surgical removal of KMs through a double odontectomy with transalveolar method. Other treatments can be, eventually, orthodontic therapy of the impacted teeth and a radiological follow-up without surgery.

The occurrence impacted teeth, single or multiple is very common. But, phenomenon of kissing molars is an extremely rare phenomenon. Mandibular third molars are the most common impacted teeth. Mandibular first or second molars does not share the same frequency of occurrence. But, there are rare cases in which the occlusal surfaces of impacted molars are united by the same follicular space and the roots point in the opposite direction, and are termed as kissing molars. Sometimes, these teeth will be associated with pathologies. This article reports a rare case of mandibular bilateral kissing molars.

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