Three-dimensional observations of the effects of third molars on orthodontic treatment.

Abstract

Many scholars have described the relationship between third molar eruption and posterior discrepancy, but there is no consensus by orthodontists. Therefore we read the article by Aliaga–Del Castillo et al in the October 2018 issue with great interest (Aliaga–Del Castillo A, Janson G, Arriola-Guillén LE, Laranjeira V, Garib D. Effect of posterior space discrepancy and third molar angulation on anterior overbite. Am J Orthod Dentofacial Orthop 2018;154:477-86). Although the authors provided an excellent counterexample to Sato's1Sato S. Alteration of occlusal plane due to posterior discrepancy related to development of malocclusion—introduction to denture frame analysis.Bull Kanagawa Dent Coll. 1987; 15: 115-123Google Scholar classic theory, we have several questions. First, although the authors emphasized that the target of their discussion was the anterior overbite rather than the third molar, and they included samples that shared a mean age of 14.53 ± 2.53 years (which is not the age of third molar eruption but just after second molar eruption), these points should not interfere with their results. At this stage, the third molars are still soft dental bulbs and alveolar bone development is ongoing, which means that the extent of posterior discrepancy will change in an unpredictable manner during aging. Previous studies have reported that during the development of the third molars in the preeruptive period, changes observed in the sagittal projection continue to occur.2Phillips C. White Jr., R.P. How predictable is the position of third molars over time?.J Oral Maxillofac Surg. 2012; 70: S11-S14Scopus (13) Google Scholar, 3Sandhu S. Kaur T. Radiographic study of the positional changes and eruption of impacted third molars in young adults of an Asian Indian population.J Oral Maxillofac Surg. 2008; 66: 1617-1624Abstract Full Text Full Text PDF PubMed Scopus (14) Google Scholar It is therefore difficult to assess the extent of significant effects of third molar angulation on overbite using such unstable parameters. Second, only a single researcher (A.A.D.C.) performed cephalometric tracings rather than 2 or more researchers. Although the number of samples was sufficient (131/40), the lack of observer bias control is a critical oversight. Third, although 2-dimensional tracing is a classic method to assess the direction of third molar eruption, measuring 3-dimensional objects with the use of 2-dimensional images leads to unavoidable errors.4Nguyen T. Cevidanes L. Franchi L. Ruellas A. Jackson T. Three-dimensional mandibular regional superimposition in growing patients.Am J Orthod Dentofacial Orthop. 2018; 153: 747-754Abstract Full Text Full Text PDF PubMed Scopus (22) Google Scholar To improve the reliability of such measurements, direction of eruption should be analyzed 3-dimensionally. Because cone-beam computed tomography (CBCT) is already widely used in the clinic, 3-dimensional images can be obtained. For the reasons mentioned above, we encourage researchers studying third molar eruption to use CBCT 3-dimensional images and several observers. Authors' responseAmerican Journal of Orthodontics and Dentofacial OrthopedicsVol. 155Issue 5PreviewWe are pleased that our article has generated comments from AJO-DO readers. Thank you for your interest and for the opportunity to address your concerns. Full-Text PDF Effect of posterior space discrepancy and third molar angulation on anterior overbiteAmerican Journal of Orthodontics and Dentofacial OrthopedicsVol. 154Issue 4PreviewIn this study, we aimed to determine the effect of maxillary and mandibular posterior space discrepancies and third molar angulations on the overbite. Full-Text PDF