Case Description and Diagnosis
A 14-year-old patient was referred to assess the potential for comprehensive orthodontic treatment. It was noted that the patient was in the late mixed dentition with an atypical Class II indefinite malocclusion. The overjet was determined to be 2mm and the maxillary incisors covered approximately 25% of the mandibular incisors in the vertical plane. Although the maxillary and mandibular midlines were coincident with each other, both dental midlines were located 2mm to the right side of the facial midline. The right-side molar relationship was Class III, however, the right-side canine relationship was half-unit Class II. The crown of the mandibular right first permanent molar (46) was also deemed to have a significant mesial tip. The mandibular right second primary molar (85) was not clinically visible, and there was no record of this tooth being extracted. Due to the presence of the mandibular left second primary molar (75), the left-side molar relationship had a mild Class II tendency and the left-side canine relationship was Class I. A posterior lingual crossbite was present on the left-side and no associated functional shift from the retruded contact position to the position of maximum intercuspation was evident (Figure 1).
A panoramic radiograph (Figure 2a) revealed ankylosis and severe submergence of the 85 along with displacement and impaction of the developing 45. It appeared that the ankylosis and submergence of the 85 had disrupted the alveolar development in this region, which in turn resulted in the localised distortion of the posterior teeth in the fourth quadrant. Despite the highly unusual radiographic appearance in this area, no current or previous pain or discomfort was reported by the patient. It was also noted that the mandibular left second premolar (35) was congenitally missing and the mandibular left second primary molar (75) was over-retained with significant remaining root structure. The 75 showed no evidence of infraocclusion and was clinically sound and non-mobile. All third molars were present in the crown stage of development.
A lateral cephalograph and subsequent cephalometric analysis revealed that the patient had a horizontal skeletal Class I relationship, a brachyfacial vertical facial morphology and normal angulation of the maxillary and mandibular incisors. Soft tissue analysis determined that the facial features were symmetrical, along with a pleasing facial profile and competent lip function (Figure 2b).
The relevant diagnostic findings are summarized in Table 1 and as a prioritized problem list in Table 2. Due to the severe submergence of the 85 and impaction of the 45, the patient was referred to an oral and maxillofacial surgeon for assessment of this area and to plan the required surgical management. Several potential treatment options were considered (Table 3). Each of these treatment options have been summarised and compared along with their specific advantages and disadvantages (Table 4).
Following extensive communication between the orthodontist, general dentist and the oral and maxillofacial surgeon, it was determined that the most predictable treatment option involved removal of the submerged 85 and the impacted 45. The oral and maxillofacial surgeon indicated that removal of the ankylosed 85 would necessitate significant bone removal and the impacted 45 would be likely to be damaged during in this process. In addition, surgical exposure and subsequent orthodontic traction with a gold chain to disimpact the 45 was expected to be both prolonged and challenging. As the 35 was also congenitally missing, a decision was also required regarding the over-retained 75. Given that the mandibular third molars were developing and that over-retained primary teeth generally have reduced longevity compared to healthy permanent teeth, removal of the 75, uprighting of the 46 and complete orthodontic space closure through bilateral mandibular molar mesialisation was recommended. This treatment option would require the use of temporary anchorage devices (TADs) to ensure maximum predictability of these challenging orthodontic tooth movements. Complete orthodontic space closure in the mandibular arch through bilateral mandibular molar mesialisation would be associated with the numerous potential benefits for the patient. Firstly, this option would eliminate the need for future prosthodontic replacement for the congenitally missing 35 and the irretrievable 45. The process of orthodontic tooth movement has been shown to be osteo-inductive and has the ability to regenerate atrophic alveolar bone resulting from congenital absence of teeth and/or iatrogenic issues. Effective mandibular molar mesialisation would also protect the harmonious pre-treatment incisor angulation and lip positions whilst also creating significant space for spontaneous future eruption of the developing third molar teeth into functional positions.