Bonwill’s triangle - the uncharted anatomic geometry

Background: Mandibular fractures include a significant bulk of cases encountered in craniofacial trauma. When the fracture occurs, it affects the patient's occlusion significantly, causing infection and leads to considerable amount of pain. Interventions to prevent these sequelae require either closed or open forms of reduction and fixation. The proper alignment of the fractured fragment is essential to maintain the normal anatomy, function and aesthetics.(1) Through this study I wish to shed light on a long-forgotten theory that could simplify the reconstruction of mandibular defects. Dr. William Gibson Arlington Bonwill believed that there was a geometrical basis for occlusion and a 4-inch equilateral triangle exists between the two condyles and anterior teeth of the mandible.(2) He played a pivotal role in developing the first anatomical articulator utilized in construction of complete dentures in dentistry.(3) Objective: • To determine the existence of the equilateral triangle subtended between the mandibular condyles and the incisal point. • To reappraise the Bonwill’s triangle that has been ignored from Medical Anatomy literature. Materials and methods: A cross-sectional observational study was conducted at Department of Anatomy, Vydehi Institute of Medical Sciences & Research Centre, Whitefield, Bangalore, utilizing 100 adult human mandibles irrespective of age and gender. Digital Vernier Caliper with a resolute accuracy of 0.01mm +/- 0.02mm (<100mm), was utilized to measure the parameters. Three parameters measured were - Right Condyle center to the point between medial mandibular Incisors (X), Left Condyle center to the point between medial mandibular Incisors (Y), and between the centers of both Condyles (Z). A paired student t test was employed to determine whether any significant relation existed between the variables X, Y and Z. Data analysis was carried out using SPSS Version 16 and validation of Bonwill’s historical geometric theory was deemed possible only if p value exceeded 0.05. Result: All mandibles studied fulfill Bonwill's geometric theory, thereby establishing the existence of the equilateral triangle between the bony landmarks. Conclusion: Patients who succumb to mandibular injuries can be benefited through modest surgical interventions, utilizing the geometric theory of Dr Bonwill, with the aid of head and neck radiology.(4) Apart from its clinical relevance, shedding light on its existence will add value to the current literature pertaining to mandibular anatomy.