Discussion
The patho-etiology of unerupted third molars remains unresolved and controversial. In a recent study [14] it was found that over half (52%) of adults above 18 years had at least one impacted third molar regardless of the skeletal/dental antero-posterior relationship. Some have suggested that as modern humans evolved the jaws became diminutive, leading to end-molar impaction. However, evolutionary history suggests that the teeth became larger in size through an increased number of cusps [15] with thicker enamel [16]. Recently, Olsson et al. [17] reported that although the MSX1 gene is expressed differently for impacted maxillary third molars, in general, other changes in gene expression are not found, suggesting an epigenetic mechanism for third molar impaction. Similarly, Isomura et al. [18] concluded that while third molar eruption was more similar in monozygotic twins compared to dizygotic twins, the identification of genetic trends, such as those encoding for reduced stature, influence third molar treatment options. In fact, Adeyemo et al. [19] found that subjects with lower third molar impactions were often shorter in height. In a similar study [20], insufficient bony dimensions for the eruption of the third molars were found in teenagers with Class II malocclusions. Because of these concepts, some believe that extraction of other teeth can result in favorable treatment outcomes for third molars [21]. In our present study, Case #6640 appears to support this approach. After the extraction of four, healthy, first premolars, biomimetic oral appliance therapy appears to have aided in the eruption of the third molars in an adult aged 22yrs at the beginning of treatment. Indeed, although the early extraction of healthy teeth is debatable given the uncertainty of the developing third molars erupting, it is essential to assess the third molars’ eruptive potential and provide sufficient functional space. Park et al. [22] reported spontaneous eruption of a third molar after extraction of an ankylosed mandibular first molar. In that case, orthodontic intrusion of the maxillary first molar and mesialization of the root of the second molar was completed before third molar root formation.
While a deficiency of retromolar space is a known risk factor for end-molar impaction, Marchiori et al. [23] investigated delayed third molar development as a factor leading to impacted wisdom teeth. They found that a lack of jaw space distal to the second molars was related to less well-developed third molars, and a severe deficiency of space was associated with an absence of third molar tooth germ development in early childhood. In our study, for case #3044 (a 9-year-old male), panoral radiography revealed the absence of developing #1 and #16 tooth germs (Fig. 9). By the end of treatment, however, while tooth #16 was found to be congenitally absent, the other three third molars erupted into occlusion (Fig. 12). This somewhat surprising outcome might be associated with the use of biomimetic oral appliance therapy, which putatively increases midfacial bone volume [13]. Tamer et al. [24] consider eruptive issues associated with third molars ought to be diagnosed and treated early, using orthodontic repositioning, surgical uprighting or extractions (with or without transplantation). In this way, induced third molar eruption was reported by Jung et al. [25]. However, in that case they utilized a mini-screw placed in the maxilla with cross-arch elastics to induce eruption prior to exodontia, which contrasts with the biomimetic approach described in this case, since the third molars erupted naturally and did not require extraction. Therefore, treatment timing is an essential factor in the management of third molars.
There is a dearth of literature on the use of devices to recapture retromolar space to aid in the eruption of third molars. One study [25] compared mandibular third molar eruption in teenagers with Class II malocclusions using a Forsus device. They found that the device led to mesialization of the lower arch, which increased the retromolar space but there was only little uprighting of the third molars. In contrast, using biomimetic oral appliance therapy, both Case #5535 and Case #8476 showed eruption of the third molars in all four quadrants (Fig. 4 and Fig. 7, respectively). Indeed, both of these cases initially presented to the dental office with craniofacial pain. Mksoud et al [26] investigated the correlation of orofacial pain, jaw muscle pain, headache/migraine to third molar eruption status. They reported that although impacted third molars are not associated with masticatory muscle pain or migraines headaches, they can be a cause of chronic orofacial pain. In our study, Case #5535 was concerned with TMJ issues and Case #8476 had gross caries masking and/or masquerading as third molar odontalgia. Both of these cases showed resolution of craniofacial pain and spontaneous eruption of the third molars (Fig. 4 and Fig. 7, respectively). Indeed, De Bruyn et al. [28] include adequate eruptive space as one reason for retaining third molar teeth since approx. one third (32%) can erupt into proper occlusion. Therefore, this case series describes the use of a novel, biomimetic midfacial development protocol to illustrate how successful patterns of third molar eruption might be achieved. Further studies are now indicated to test the robustness of these initial findings.