Interlabial gap and freeway space at rest position: a cephalometric study

Abstract

Abstract Objectives The aim of this prospective study was to assess the amount of interlabial gap (ILG) and freeway space (FWS) at rest position (RP) according to gender, age, and skeletal pattern, and to evaluate the cephalometric measurements at maximum intercuspal position (MIP) and at RP to define the cephalometric changes from MIP to RP related to the amount of ILG and FWS. Methods Lateral cephalograms and photographs of selected subjects (47 females, 57 males) were obtained at MIP and RP. Cephalometric measurements at MIP and RP and their differences were measured and compared. Results ILG (P > 0.05) and FWS (P < 0.01) were greater in males than in females. ILG (P < 0.05) and FWS (P > 0.05) were greater in adolescents than in adults. ILG and FWS were not significantly related with the vertical skeletal pattern (FHR, facial height ratio). ILG was the greatest in Class II cases but without significance. FWS was significantly greater in Class III than in Class I and Class II cases (P < 0.05). At MIP, the ILG at RP increased as overjet (P < 0.05) and upper lip to the aesthetic line (P < 0.01) increased. At RP, the ILG increased as upper incisor exposure and the lips to the aesthetic line increased (P < 0.001), and FWS decreased as overbite decreased (P < 0.001). From MIP to RP, lip length showed the greatest decrease (P < 0.001) in the large ILG group. Additionally, Bjork sum (the sum of the saddle, articular, and gonial angles), mandibular plane angle, anterior facial height, and ANB (P < 0.001) showed the greatest increase, while OB (P < 0.001) showed the greatest decrease in the large FWS group. The lip competent group showed the largest frequency distribution in the small ILG and FWS groups, while smile line frequency distribution showed no relationship with the level of ILG and FWS. Conclusions Taking cephalometric measurements at RP would be helpful to evaluate the ILG and FWS more accurately, and to provide a more accurate diagnosis and treatment plan.