Dental chair inclination

Fixed Prosthodontics Dental chair inclination Background.—The various organs and tissues of the stomatognathic system work together harmoniously with several physiopathologic interdependencies. The TMJs and neuromuscular system act together to permit the mandible to perform three-dimensional movements and achieve various positions. Various factors influence the mandible’s position and can interfere with mouth opening, speech, and chewing. These include the body’s position, the quality of sleep, psychological factors that compromise muscle tone, proprioception, occlusal changes, muscle spasms, and temporomandibular joint dysfunction (TMD). Articulator-mounted casts are used to register maxillomandibular relationships. Based on clinical observations that the dental chair’s backrest position may change the distribution of occlusal contact points, it was theorized that changing the chair’s inclination may lead to a different head inclination and different mandible position. The influence of chair inclinations of 90 degrees, 120 degrees, and 180 degrees on mandibular position registration was investigated. Methods.—Ten subjects age 18 and 30 years volunteered for the study. All had complete permanent dentition and lacked motor function compromise, tooth mobility, and TMD. Interocclusal contacts were measured using an autopolymerizing methylmethacrylate device adapted to the maxillary anterior teeth and a composite resin increment added to the mandibular central incisors. Contacts were registered at the three chair backrest inclinations. Standardized digital photographs were taken at each position and the images superimposed to measure distances in registration between the three chair inclinations. Data were then analyzed. Results.—Inclining the backrest of the chair to 120 degrees and holding the patient’s head at 45 degrees with the chin facing up is the recommended position for bimanual manipulation. Ninety degrees is the most

vertical position for the backrest and 180 degrees is the most horizontal position. Changing from a 90- to a 120-degree position repositioned the mandible posteriorly a mean of 0.67 mm, which was not statistically significant. Changing from a 90- to a 180-degree position repositioned the mandible a mean of 1.41 mm, which was statistically significant. Discussion.—Varying the dental chair backrest inclination altered mandibular position, especially the 180-degree inclination. Mandibular position was not altered at the 120degree inclination and not significantly altered at 90 degrees.

Clinical Significance.—During occlusal rehabilitation, it is important to maintain balance in the stomatognathic system. The long-term prognosis is improved by obtaining a correct centric relation register. Typically centric relation is determined with bimanual manipulation, pushing the condyles up into the fossa with four fingers under the mandibular angle of a supine patient, or using a jig or leaf gauge. Dentists need to be aware of the influence of the dental chair’s backrest inclination and should avoid the 180-degree position because it can significantly alter mandibular position.

Coelho MF, Calvalcanti BN, Neves ACC, et al: Influence of dental chair backrest inclination on the registration of the mandibular position. J Prosthet Dent 114:693-695, 2015 Reprints available from SM Rode, Eng Francisco Jos
e Longo, 777, Jardim S~ao Dimas-S~ao Jos
e dos Campos/SP 12245-000, Brazil; e-mail: [email protected]

Impression materials Background.—Elastomeric impression materials have successfully captured dental impressions for many years, but recent technological advances have introduced computer-aided design and computer-aided manufacturing (CAD/CAM) methods and intraoral digital scanners as an

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Dental Abstracts

alternative. To be considered successful, these alternatives should yield crowns with similar or better clinical success than those of conventional approaches. Tooth-colored, highly esthetic restorations are greatly desired by patients. Ceramic systems have more shade matches and similar