Influence of dental chair backrest inclination on the three dimensional positioning of the mandible: A Clinical Trial

BACKGROUND: The maxillo-mandibular component of the craniofacial system consists of a group of organs and tissues that act harmoniously with interdependent mechanism. In conjunction with the neuromuscular system, the temporomandibular joint allows the mandible to perform various movements in the three dimensions. The mandibular position is influenced by various factors and functions like mouth opening, speech and chewing. Patient position and head orientation in the dental chair plays a major role in occlusal rehabilitation. So the head position of the patient plays a major role while recording centric relation and in prosthetic rehabilitation. Thus it is important to identify the influence of backrest inclination, on the registration of the mandibular position during dental treatment procedures. AIM AND OBJECTIVE: To study the influence of dental chair backrest inclinations on the 3-Dimentional positioning of the mandible. MATERIALS AND METHODS: Total of 10 subjects with permanent dentition up to second molar with healthy periodontium and normal motor and temporomandibular functions to be selected. The chair was stabilized to check mandibular positions at 2 inclinations: 90°and 180°. To register the mandibular position, inter-occlusal records were made in centric relation for each subject at the said inclinations. Two CBCT were made for each subject with the inter-occlusal records registered at two different inclinations of the dental chair backrest respectively. The CBCT images were analyzed to study the 3-dimentional positioning of the mandible to the temporomandibular joint. RESULT: There was a significant retrusion of the mandible coupled with an upwards and forwards rotation of the mandible. The mandible is also superiorly positioned as seen by the reduction of the intra capsular space. CONCLUSION: It is essential to make registrations of the mandible with the patient seated erect and the chair at 90*, or else a change in mandibular position will complicate rehabilitation