Orthodontic Treatment of Anterior Dental Open Bite with Drawbridge Effect : A Case Report

Orthodontic Journal of Nepal, Vol. 3, No. 1, June 2013 A young lady presented to Department of Orthodontics with a chief complain of gap between upper and lower front teeth. On analysis she had Class I dental and skeletal malocclusion with proclined and forwardly placed incisors, and open bite. The treatment was carried out with extraction of all four first premolars and retraction was done with the help of mini-implant screws. Successful correction of open bite was achieved with “drawbridge effect”. ABSTRACT


INTRODUCTION
Open bite is a malocclusion characterized by lack of vertical overlap between the maxillary and mandibular dentition. Openbite may be anterior or posterior. Profit 1 defined anterior open bite as 'no vertical overlap of incisors'. An anterior open bite (AOB) is a negative overbite between the incisal edges of the maxillary and mandibular anterior teeth, with the posterior teeth in occlusion. The prevalence of anterior open bite ranges from 1.5% to 11% and varies among ethnic groups, and by age and dentition. [2][3][4][5] The various etiological factors thought to be responsible for causing open bite includes unfavorable growth pattern, heredity, digital habits, and tongue function. 6 Some studies have found a correlation between oro-facial musculature and facial structures, suggesting a relationship between weak musculature and a long face anterior bite pattern. 7,8 For the successful treatment of open bite, it is necessary to identify the contribution of skeletal component. As such Sassouni 9 classified open bite into dental and skeletal. Dental open bite is associated with some or all of the following clinical features: 1,10-13 normal craniofacial pattern, proclined incisors, under-erupted anterior teeth, normal or slightly excessive molar height, mesial inclination of posterior dentition, failure of eruption of teeth without known etiology, divergent upper and lower occlusal planes, no gummy smile, no vertical maxillary excess, thumb and finger sucking habits, tongue thrusting habit, without remarkable cephalometric findings. Skeletal open bite is associated with one or more of the following features: 1,10-14 steep mandibular plane angle, increased gonial angle, short mandibular ramus, downward rotation of the posterior part of the maxilla or palatal plane tipped up anteriorly, increased lower anterior facial height, decreased upper anterior facial height, increased anterior and decreased posterior facial heights, increased flexure of the cranial base (Na-S-Ba), steep anterior cranial base, shorter nasion-basion distance, small mandibular body and ramus and retrognathic mandible.
The treatment of anterior open bite is dependent on the etiology of malocclusion, age and the expectation of the patient. Mizrahi 15 described four modalities of treatment: growth modulation; orthodontic mechanotherapy; orthognathic surgery and the combination of two or more of the above.
It is important to determine which form of treatment is the most suitable for each individual case. In case of dental anterior open bite in adult patients, extraction and retraction have been recommended to reduce overjet and open bite and elongate anterior teeth by a "drawbridge effect". 11

CASE REPORT
A young lady (DOB February 16,1990) was presented to our department with the chief complain of gap between upper the lower front teeth (Figure 1).
On examination she had mesoprosopic face with convex profile. On intra-oral examination, she had Angle's Class I molar relationship with anterior open bite of 5 mm with obvious lip strain. On cephalometric analysis, she had ANB of 5 0 , normal growth pattern (SN-GoGn 33 0 ) and proclined and forwardly placed upper (30 0 /7mm) as well as lower incisors (37 0 /7mm).

TREATMENT PROCEDURE
Extraction of all four first premolars and absolute anchorage with mini-implant screws were planned. Following steps were followed during the clinical procedure:  5. On August 10, 2013, the normal overjet and overbite was obtained ( Figure 6).

DISCUSSION:
Anterior open bite is considered to be one of the most   Long-term stability of AOB extraction treatment for permanent dentition has been documented18. After