Orthodontic Reduction of an Increased Overbite in Adolescents - the Mechanism and Rate of Occlusal Adaptation

The correction of a deep overbite is assumed to involve incisor intrusion and the extrusion or eruption of premolars and molars. The latter is also assumed to be the major contributor for growing patients where the vertical facial growth increase accommodates for the additional eruption of posterior teeth with anterior bite plane appliances.

In this study the nature and rate of adaptation of the occlusal changes following insertion of a fixed anterior bite plane for the reduction of a deep overbite in growing patients will be investigated.

All subjects who meet the inclusion criteria will be informed of the study and written consent sought for their participation. Subjects will be recruited from the new patient clinics and routine treatment waiting list. A standard initial lateral cephalogram will be taken of all subjects, unless this is already available within the specified age range. Active growth will be determined using the Bacetti CVM method. For the Intervention group - an intra-oral scanner will be used to accurately record the occlusal relationships prior to insertion of the fixed anterior bite plane (T0) and repeated immediately after placement (T1). Each subject will then be re-scanned on a six weekly basis for a period of six months (T2-T5). Conventional clinical photographs and three-dimensional stereophotogrammetry will be used to assess the vertical facial relationships at T0-T5. A further lateral cephalogram will be taken at T5 to assess for skeletal change and assess for evidence of intrusion and eruption as well as determine if there has been an alteration in incisor inclination.

A control group of subjects from the treatment waiting list who meet the inclusion criteria will be used. An intra-oral scanner will record the baseline occlusal relationship (T0) and will be repeated after six months (T5). The control group will also have a standard pre-treatment lateral cephalogram taken, as well as conventional and three-dimensional stereophotogrammetry at baseline (T0) and after six months (T5). This will allow changes resulting from growth to be assessed whilst no active orthodontic treatment has taken place.

The primary outcomes to be assessed will be the nature of the change in occlusal-vertical dimension and the rate of occlusal adaptation in relation to facial growth changes. The intra-oral scans and photographs will be analysed using three-dimensional technology to determine the immediate change and any resultant occlusal adaptation and change in lower face height on a six weekly basis for six months.

All subjects and guardians in the intervention group will be asked to complete a short questionnaire immediately after visits T1 and T5. This will assess their experience of the 3-D scanning and bite planes (if applicable). We will also assess their knowledge of overbite definition, process of overbite reduction and effects of an increased overbite on oral health. The control group will be asked to complete the same questionnaire at T0.

The economic impact of managing the increased overbite as an initial phase of treatment versus single phase comprehensive treatment will be investigated. A cost analysis will be performed to investigate any economic difference in using bite turbos versus a removable appliance to reduce the overbite.

Eligibility Criteria:
Inclusion Criteria:

* Class II division 2 malocclusion
* No history of active orthodontic treatment
* Increased overbite (greater than one third lower incisal coverage)
* Age 9-16

Exclusion Criteria:

* Restorations on the palatal surface of the maxillary incisors
* Increased overjet where the lower incisor edge occludes distal to the cingulum of the upper incisor
* Profound hypodontia (\>1 missing tooth per quadrant)
* Subjects beyond pubertal growth stage
* Suspected or identifiable syndromes
* Subjects with cleft lip and palate
* Growth anomalies or taking growth accelerating/ inhibiting medication