Forces produced by lip bumpers on mandibular molars.

The purpose of this study was to measure the forces produced by a lip bumper on the mandibular permanent first molars. The forces in a sample of 38 patients were measured bilaterally with specially designed gauges at rest but with their lips lightly touching, speaking the words church, phone, and pop, and swallowing water. Forces were compared between two types of lip bumpers, i.e., wire or shield, and between various anteroposterior and vertical positions of the lip bumper. The resting forces produced by the wire lip bumper 2 mm anterior to the incisors and vertically positioned at the middle of the incisor crown were 5.93 +/- 4.84 gm for the left side and 4.66 +/- 4.8 gm for the right. The forces were found to be significantly higher when the wire lip bumper was placed 4 mm anterior to the incisors and at a more gingival position, measuring 16.68 +/- 8.7 gm for the left side and 13.88 +/- 8.28 gm for the right. The shield lip bumper had higher forces both at the center of the incisor as well as when it was positioned gingivally. A large individual variation was observed. There were no statistically significant differences in force levels between male and female subjects. Speaking the words church, pop, and phone, produced forces between 11 and 23 gm, using a wire lip bumper. Swallowing produced the highest forces, between 32 and 36 gm. Lip thickness and height did not appear to affect the force levels.