Lip Morphology: a Factor Leading to Bimaxillary Dentoalveolar Protrusion

The objective of this study was to see the effect of lip morphology in the study sample presenting with bimaxillary dentoalveolar protrusion on normal skeletal pattern. This cross sectional study comprised 50 subjects having bimaxillary dentoalveolar protrusion on class I skeletal pattern. Age of the subjects ranged from 18-25 years. The sampling comprised random selection of the subjects. The method involved Cephalometric analysis of skeletal, dental and soft tissues made on lateral cephalograms taken in natural head position of the subjects. A total of twenty variables were used in this study, comprising six skeletal, three dental and eleven soft tissue variables. Data were analyzed using SPSS version 10.00. Descriptive analysis and Independent ttest were carried out for significance (P < 0.05). Variables of the skeletal analysis were found within norms, whereas dental variables showed an increased value of Upper Incisor to Sella-Nasion plane (UI-SN) 115.120 (SD 5.500), Incisor Mandibular Plane Angle (IMPA) 102.700 (SD 3.400) and consequent decrease in Frankfort Mandibular Incisor Angle (FMIA) 55.500 (SD 5.490). Soft tissue analysis determined full profile with greater vermilion of upper and lower lips, deficient lip strain and decreased length of upper and lower lips. Among six variables of skeletal analysis four were found very highly significant, among three variables of dental analysis only one was analyzed as significant and among eleven variables of soft tissue analysis four were found as very highly significant. This study concluded that the yielding effect of lips, because of relaxed orbicularis oris muscle and greater lip vermilion is the contributing factor in bimaxillary protrusion. ORTHODONTICS