The purpose of this study was to examine the changes in lip pressure before and after orthognathic surgery for skeletal Class III patients. The subject groups were 32 female and 31 male patients diagnosed with mandibular prognathism and/or maxillary retrognathism who underwent orthognathic surgery. Control groups consisted of 20 women and 20 men with normal occlusion without dento-alveolar deformity. Maximum and minimum lip closing force was measured with Lip De Cum ® for the control groups and subject groups preoperatively and 6 months postoperatively. The difference between the pre- and postoperative values of the groups was examined statistically. The maximum lip closing force in men was significantly larger than that in women in both the preoperative Class III group ( p = 0.0330) and the control group ( p = 0.0097). The preoperative Class III group was significantly smaller than the control group in maximum lip closing force in both men ( p < 0.0001) and women ( p < 0.0001). The postoperative maximum lip closing force was significantly larger than the preoperative value in both men ( p = 0.0037) and women ( p = 0.0273) in the Class III group. This study suggested that the maximum lip closing force increases after orthognathic surgery in Class III patients.
Many muscles converge or intermingle in the lip and cheek area. Their functional harmony and balance is important in the growth and development of the dento-alveolar morphology and craniofacial region. The influence of the forces exerted by the perioral musculature on the position of the teeth has been the object of several scientific studies .
In some patients with maxillary protrusion or severe Class II Division 1 malocclusion, lip incompetency and muscle imbalance are observed . Using a device for measuring the strength of the lips, Posen found that subjects with bimaxillary protrusion had low lip strength, compared with Class I and Class II Division 2 patients. Ruan et al. reported that patients aged 4–6 years with Class III malocclusion had lower perioral forces and this muscle hypofunction might be secondary to the spatial relation of the jaws.
Orthognathic surgery induces morphological and functional improvements. Surgical orthodontic correction of skeletal Class III physiology reportedly has favourable effects on the function of the mandible, such as an increased range of maximum motion in the anterior, posterior, and lateral excursions . Several studies have examined the opening and closing movements and the chewing rhythm and path , but there is no report regarding the lip closing force in adult patients with jaw deformity who should undergo orthognathic surgery.
The purpose of this study was to examine the changes in lip pressure before and after orthognathic surgery for patients with Class III malocclusion.
Patients and methods
The subjects consisted of 31 men (average age 25.5 ± 7.7 years) and 32 women (average age 32.9 ± 12.5 years) with Class III malocclusion. All cases were diagnosed as skeletal Class III including mandibular prognathism and/or maxillary retrognathism on the basis of a lateral cephalogram analysis and the patients underwent orthognathic surgery. Control groups consisted of 20 women (average age 29.5 ± 4.9 years) and 20 men (average age 29.5 ± 3.9 years) with normal occlusion without dento-alveolar deformity.
The cephalograms were entered into a computer and analysed using appropriate computer software (Cephalometric A to Z, Yasunaga Labo Com, Fukui, Japan). Measurement landmarks were SNA, SNB, ANB, U1 to FH plane, gonial angle, ramus inclination (FH), occlusal plane (FH), interincisal angle, Po-N perpent.(distance between Pog and nasion parallel to FH plane), mandibular length (Co-Gn), incisor overjet, incisor over bite, and convexity. These measurements were used to examine which variants significantly correlated to maximum lip closing force by stepwise regression analysis.
One skilled observer performed all the digitization so that errors in the cephalometric method were small and acceptable for the purposes of this study. Error analysis by digitization and remeasurement of 10 randomly selected cases generated an average error of less than 0.4 mm for the linear measurements and 0.5° for the angular measurements.
Maximum and minimum lip closing forces were measured with Lip De Cum LDC-110R ® (Cosmos instruments Co. Ltd., Tokyo, Japan) for both groups preoperatively and 6 months postoperatively. This device consists of a sensor with a lip adaptor and digital display . The lip closure strength (force) indicator (Lip De Cum ® ) was set up with a lip holder (Ducklings ® ) mounted to the sensor, and the subject was instructed to bite the holder between the upper and lower lips ( Fig. 1 ). The lip closure strength (force) of the subject was measured while the subject was sitting upright (with the FH plane parallel to the floor plane). The subject was instructed to close the upper and lower lips with their utmost strength but never to allow the upper and lower teeth to touch. The device contains four strain gauges at the sensor and converts the measurement value into load value (N). During measurement for 30 s, the shape of the wave is shown on the display of a personal computer connected to the Lip De Cum ® ( Fig. 2 ). The largest and smallest values of the wave were defined as the maximum and minimum values, respectively.
Data were statistically analysed with Stat View 4.5 (ABACUS Concepts, Inc., Berkeley, CA, USA) and Dr. SPSSII (SPSS Japan Inc., Tokyo, Japan). Differences between the groups were analysed by non-paired comparison using Scheffe’s F test. Differences between the pre- and postoperative values were analysed by paired t -test. Stepwise regression analysis was carried out to examine the morphological factors affecting the maximum lip closing force. Differences were considered significant at p < 0.05.
Twelve of 31 men with mandibular prognathism underwent Le Fort I osteotomy with bilateral sagittal split ramus osteotomy (SSRO), 16 underwent SSRO alone, 2 underwent Le Fort I osteotomy alone and 1 underwent Le Fort I osteotomy with bilateral intra-oral vertical ramus osteotomy (IVRO). 10 of 32 women with mandibular prognathism underwent Le Fort I osteotomy with bilateral SSRO, 19 underwent SSRO, 2 underwent maxillary anterior segmental osteotomy with bilateral SSRO, and 1 underwent unilateral SSRO and IVRO. The mean setback amount by SSRO with and without Le Fort I osteotomy was 6.4 ± 3.5 mm on the right side and 5.6 ± 3.8 mm on the left side in men, and 5.8 ± 3.5 mm on the right side and 6.1 ± 3.6 mm on the left side in women. There were no significant differences in setback amount between men and women. When the postoperative recording at 6 months was performed, the occlusion was normal and stable in all patients.
Results for lip closing force are given in Table 1 . The maximum lip closing force in men was significantly larger than that in women in both the preoperative Class III group ( p = 0.0330) and the control group ( p = 0.0097). The preoperative Class III group was significantly smaller than the control group regarding maximum lip closing force in both men ( p < 0.0001) and women ( p < 0.0001). The postoperative maximum lip closing force was significantly larger than the preoperative value in both men ( p = 0.0037) and women ( p = 0.0273) in the Class III group.
|Maximum (N)||Minimum (N)||Maximum (N)||Minimum (N)|