EVALUATION OF THE VERTICAL FORCES GENERATED BY THE CERVICAL BITEPLATEFACEBOW

The biteplate facebow has been recommended for use in the correction o f Class II malocclusions with deep overbites. This facebow is similar in design to the conventional cervical face bow with the addition of a n inner bow metal plate. The plate presses against the maxillary incis ors and prevents the patient from fully closing, thus acting as a bite plate. A test apparatus was constructed to simulate the force system p resent during application of the facebow. In this study, high resoluti on force transducers were used to measure the intrusive forces on the maxillary and mandibular incisors. Static force analysis techniques we re then used to calculate the vertical force component of the first mo lars. Analyses were performed using a wide range of relative bow angle s, neck strap tensions of 200 grams and 400 grams, and various mandibu lar incisor occluding forces. The molar eruptive forces of the bitepla te facebow are found to exceed those of the standard cervical facebow by a low of 158% to a high of 537%, depending on the neck strap tensio n and the inner bow/outer bow angle. While the intrusive forces on the maxillary incisors were excessive, no intrusion is anticipated becaus e the biteplate disarticulates the posterior teeth and the eruption of the unopposed maxillary molars would likely cause the occlusal plane to tip in a counter-clockwise direction. Consequently, the overbite co rrection would be obtained through maxillary molar eruption accompanie d by occlusal plane tipping. Before considering use of the biteplate f acebow, a patient's anticipated growth pattern, the magnitude of the i ntrusive forces and the treatment objectives should be evaluated.