Influence of mandibular length on mouth opening

Theoretically, mouth opening not only reflects the mobility of the temporom andibular joints (TMJs) but also the mandibular length. Clinically, the exa ct relationship between mouth opening, mandibular length, and mobility of T MJs is unclear. To study this relationship 91 healthy subjects, 59 women an d 32 men (mean age 27.2 years, s.d. 7.5 years, range 13-56 years) were recr uited from the patients of the Department of Oral and Maxillofacial Surgery of University Hospital, Groningen. Mouth opening, mobility of TMJs and man dibular length were measured. The mobility of TMJs was measured as the angu lar displacement of the mandible relative to the cranium, the angle of mout h opening (AMO). Mouth opening (MO) correlated significantly with mandibula r length (ML) (r=0.36) and AMO (r=0.66). The regression equation MO=C-1 x M L x AMO + C-2, in which C-1=0.53 and C-2=25.2 mm, correlated well (r=0.79) with mouth opening. It is concluded that mouth opening reflects both mobili ty of the TMJs and mandibular length.