Let's get this straight: A students guide to the orthodontic assessment

By Kouthar Salih, University of Plymouth

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Introduction

The management of malocclusion amounts to the practice of orthodontics, a speciality which primarily aims to improve dentofacial appearance and correct occlusal function,¹ via the provision of various appliances and force vectors to achieve a desired movement. The General Dental Council (GDC) Scope of Practice document enables any dentist to carry out orthodontic treatment,² however, more complex cases will require timely referral to an orthodontic specialist. Thus, the importance of grasping the fundamental principles of an orthodontic assessment enables the clinician to decipher whether a deviation from the norm exists - which may warrant further investigation and referral.

Step 1: The extraoral examination

In order to deduce any skeletal discrepancies, an extraoral examination must be carried out in three planes: anterior posterior (AP), vertical and transverse. Firstly, the patient should be orientated in the 'Natural Head Position'.³ The Gonzalez-Ulloa method of assessing the AP involves dropping a zero-degree meridian line down vertically from soft tissue nasion,⁴ and evaluating the position of the mandible relative to the maxilla, whereby a class I skeletal relationship would present with the mandible positioned 2-4mm posterior to the maxilla, a class II with the mandible greater than 4mm posterior to the maxilla and class III less than 2mm posterior.⁵

The vertical position provides the clinician with an idea of the overbite and should be assessed by observing the intersection of the Frankfort plane to the Mandibular plane, in order to obtain the Frankfort-Mandibular Plane Angle (FMPA). An average FMPA would intersect at the occiput. If the intersection is made anterior to this, the patient is said to have an increased FMPA, which may manifest as an anterior open bite. If the intersection is made posterior to the occiput, the patient has a reduced FMPA, which may indicate as a deep overbite exists.

Students and general practitioners may also play a crucial role in identifying certain patient habits

Facial symmetry carries a heavy weighting on overall facial attractiveness,⁶ it may also act as a marker of phenotypic and genetic quality and is preferred during mate selection in a variety of species.⁷ Orthodontists assess symmetry by looking at the transverse plane, essentially this is achieved by drawing a line down the mid face, whereby any deviations noted may impact patient centrelines and give rise to occlusal interferences.

A comment on lip position should also be made, with 'competent' lips forming an anterior oral seal whilst the muscles of mastication and facial expression are in the physiological rest position.⁸ A lower lip trap will inhibit this seal, adversely affecting the inclination of the upper incisors and consequently contribute to a class II division I malocclusion.

Stage 2: Intraoral assessment

Be systematic - clearly identify what dentition you are assessing (primary, mixed, permanent). The importance of counting the teeth should not be overlooked such that hypodontia, hyperdontia and the presence of supernumery teeth are not missed. Assess alignment of labial and buccal segments by observing the degree of crowding or spacing, and quantify this into mild, moderate or severe. Finally, clinicians should familiarise themselves with the classification of incisor and molar malocclusion and this should be documented for each patient, as shown in Tables 1 and 2.

Table 1 Incisor classification

Table 2 Angle's molar classification

Stage 3: Consider referral

Routine dental examinations of patients in the developing dentition enable the practitioner to identify orthodontic disturbances and refer appropriately for timely interceptive treatment. The importance of buccal palpation of the maxillary canine annually from the age of eight cannot be emphasised enough,⁹ with studies demonstrating that 93% of ectopically positioned canines were in contact with the roots of the adjacent lateral incisor and 38% showed resorption of those roots.¹⁰ Therefore, to avoid damage to the incisors and potential litigation claims, early identification of an ectopic canine must be prioritised. This may be aided with the use of the parallax technique, which utilises the principles of tube shift to assist in diagnosis. Likewise, cases involving an unerupted permanent incisor greater than six months of the contralateral incisor will require further investigation, as this may have negative impacts on facial and dental aesthetics, which may affect self-esteem and social interactions.¹¹ Students and general practitioners may also play a crucial role in identifying certain patient habits, for example, continued thumb-sucking which predisposes the development of an anterior open bite should be addressed early with cessation advice. No improvement may require referral for the fabrication of a Hayrake appliance to help break the habit.¹² Overall, multidisciplinary care provides the cornerstone of holistic orthodontic treatment and the fundament principles of assessment should be mastered so that early recognition of any abnormalities can be treated appropriately.