The Introduction of a new lateral cephalometric method and its potential application in open bite deformities

Abstract

Open bite deformity is a dentofacial anomaly characterised by a space between the upper and lower teeth when the jaws are brought together. When the posterior teeth are in contact and there is separation between the upper and lower incisal edges, the condition is referred to as an anterior open bite (AOB). Anterior open bite occurs more commonly among the Black African race groups, and unless recognised and intercepted early in life, treatment of the condition can become complicated, extended and expensive. Some of the aetiological factors cited in the development of the condition include, an unfavourable growth pattern, finger sucking habits, enlarged tonsillar lymphoid tissue, abnormal tongue and orofacial muscular activity and hereditary factors. Morphologically AOB can involve only the dentoalveolar regions of the craniofacial anatomy, in which case the AOB is said to be a dental AOB; it may be the result of a disproportion between the jaws and is then referred to as a skeletal AOB, or it may be a mixture of the two. The aetiology and structural components of AOB would largely determine the mode of treatment, which can be orthodontic treatment, orthognathic surgery or a combination of the two. Previous studies into the prevalence of AOB in South Africa have reported it to be as high as 27%. Since a major percentage of the patients seen at the School of Dentistry of the University of Limpopo are of the South African Black race group it became relevant to investigate the prevalence of AOB at this institution and to develop a fresh assessment method with standardised values for this population sample. A retrospective study was therefore undertaken among patients visiting the School of Dentistry of the University of Limpopo to determine the prevalence of AOB over a 15-year time period from 1992 to 2006. All xvii patients with an AOB were documented with regard to age, gender, severity and aetiology. The criteria for determining open bite was a measure of at least 1 mm vertical separation between the incisal edges of the upper and lower incisors when the posterior teeth are in occlusion, as determined from the lateral cephalograms and confirmed by the study models. A review of the literature pertaining to craniofacial growth, the aetiology, pathogenesis, clinical presentation and treatment of AOB is also presented as well as investigative techniques for the assessment of AOB. A revised lateral cephalometric assessment method proposed as the Dawjee Analysis was designed and developed and is introduced. It consists of 12 measurements of which nine have never been previously mentioned in the literature and are being defined and described for the first time in this proposed analysis. These parameters are measured against existing and tested anatomical landmarks and planes, combined with the introduction of one new landmark and seven new measuring planes that have not been cited or described in other established analyses. These landmarks, planes and measurement parameters of the analysis are presented and its utility is described. A case study of a patient with AOB is included with an assessment of pre-treatment and post-treatment changes using this analysis. In order to establish standardised values for this population sample, the proposed Dawjee analysis was applied to a control group consisting of 50 adult male and 50 adult female subjects whose cephalometric analysis conformed to the standardised values for this race group. The analysis was also applied to an AOB sample from the retrospective study consisting of 46 male and 59 female cephalograms. Based on the amount of incisor separation this group was divided into mild, moderate and severe AOB. All subjects in both the AOB and control samples were in their permanent dentition stage, having their first permanent molars in a Class I relation. xviii In testing the validity of the proposed Dawjee Analysis, 20 cephalograms from the control group and 20 from the AOB group were also evaluated using other established cephalometric methods and the results thereof were compared to the findings of the proposed Dawjee Analysis From the 15-year retrospective investigation this study found the prevalence of AOB to be 9.67% with the male to female ratio of 46:54. The condition appears to be more common before the age of 13 years than after 13 years with a ratio of 68:32. The aetiology of the AOB in order of rank was found to be thumb or finger sucking, hereditary, nasal obstruction and unknown causes. Over the 15-year period the number of AOB patients attending the Orthodontic Department, School of Dentistry of the University of Limpopo, decreased from 16% to 8%. While this could be due to the realization that the principal cause (thumb or finger sucking) carries a social stigma, a concerted effort must be made to educate communities so that this detrimental habit can be minimised and eradicated. Standardised values for the proposed Dawjee Analysis are presented and potential flaws are outlined. When comparisons are drawn between the control and AOB group it was found that the latter differs from the control sample in 8 of the 12 of the parameters, namely: 1. Incisor separation 2. Anterior cranial base inclination 3. Posterior maxillary position 4. Posterior mandibular position 5. Interalveolar angle 6. Point B position 7. Apex of the maxillary triangle 8. Apex of the mandibular triangle The null hypothesis, which states there are no difference in the cephalometric values of the proposed Dawjee Analysis between AOB xix subjects and a control group for this population sample, was therefore rejected. These morphological differences were supported by the findings of other established analysis that were tested on the AOB and control groups. The difference of the proposed Dawjee Analysis from other cephalometric methods lies in its capability to identify and separate the skeletal from the dental components of an AOB for this study sample. Diagnosis involves a comparison to population standards and the aim of cephalometrics is to describe the standardised morphology of a population. To this end standardised values for the proposed Dawjee Analysis in a South African Black population sample have been determined which focuses on identifying the morphological basis of an AOB.