Bengt Ingervall

A clinical study of maxillary canine retraction with a retraction spring and with sliding mechanics

The efficiency of maxillary canine retraction by means of sliding mechanics along an 0.018-inch labial arch and an AlastiK chain was compared with that using the canine retraction spring designed by Gjessing. The rate of canine retraction and degree of tipping, and rotation of the canines were studied in 21 subjects by one of these two methods on either side of the dental arch. Measurements were made in the mouth and on photographs of dental casts. The canine was retracted faster and with less distal tipping with the spring than with the sliding mechanics. The canine retraction spring was not superior to the sliding mechanics in controlling canine rotation during the retraction.

Pressure from the lips on the teeth and malocclusion

The relationship between lip strength and lip pressure (pressure from the lips on the teeth) was studied in 84 children (aged 7 to 16 years) with varying types of malocclusion. The lip strength was recorded with a dynamometer. The lip pressure was measured on the upper and lower central incisors in the rest position, and during chewing and swallowing of crispbread. The lip pressure measurements were made with an extraoral pressure transducer incorporated in a water-filled system with an intraoral mouthpiece. The muscle activity of the lips was recorded electromyographically. Bite and facial morphologies were studied on dental casts and profile cephalograms. There was no correlation between lip strength and lip pressure. Lip strength was lower in children with Angle Class II, Division 1 malocclusion than in children with Class I malocclusion. The lip pressure on the upper incisors, on the other hand, was higher in Class II, Division 1 than in Class I malocclusion, and was lowest in children with Class II, Division 2 malocclusion. The findings suggest that the pressure from the lips on the teeth is a result of the incisor position.

Pattern of tooth contacts in eccentric mandibular positions in young adults

Tooth contact patterns in laterotrusion, protrusion of the mandible, and in the retruded position were recorded in young men with varying types of occlusion. The tooth contacts were recorded clinically with alginate (irreversible hydrocolloid) indices. In addition, the functional state of the masticatory system was evaluated by the recording of signs and symptoms of mandibular dysfunction and of the abrasion of the teeth. On protrusion, most subjects had contacts only on anterior teeth. Protrusive contacts only on posterior teeth were rare. On laterotrusion, most subjects had group function on the functional side. Contact on the nonfunctional side was found in half of the subjects in a 1.5 mm laterotrusive position and in one third of them in a 3 mm laterotrusive position. No correlation between the types of tooth contacts and mandibular dysfunction was found.

Effect of surgical reduction of the tongue on oral stereognosis, oral motor ability, and the rest position of the tongue and mandible

The oral ability to recognize forms and oral motor ability were studied by means of two specific tests in 27 subjects, 10 to 23 years of age, before and after tongue reduction because of macroglossia. Recordings were made before and 6 and 12 months after the operation. At the same time the natural position of the head and of the cervical column, the craniocervical relation, the position of the tongue and the hyoid bone, and the rest position of the mandible were studied with profile roentgen-cephalometry. The surgical reduction of the tongue had a minor influence on the subjects performance in the test of oral ability to recognize forms, where the number of false identifications increased somewhat. The oral motor ability and the positions of the head, the cervical column, and the hyoid bone were unaffected. After the operation, the tongue did not fill out the oral cavity as much as before and the freeway space decreased.

Does the mandible alter its functional position during activator treatment

The study aimed at revealing possible changes, in activator-free periods, in the positions and movements of the mandible induced by the wearing of an activator. Twenty-one children being treated with three different types of activator for the correction of Angle Class II, Division 1 malocclusion were studied. The movement capacity of the mandible, the rest position, and the position of tooth contact during chewing were recorded with a Sirognathograph before treatment and repeatedly during the first year of treatment. With the exception of a slight increase in the maximal protrusion, no changes in mandibular movement capacity were found. The anteroposterior position of the mandible in the rest position was constant during the period of treatment, but the freeway space increased. No changes in the position of the point of tooth contact during chewing were found. The study produced no evidence of a treatment-induced forward positioning of the mandible in activator-free periods.