# ABSTRACTS

## LONG-TERM EFFECTS OF THE HERBST APPLIANCE ON THE DENTAL ARCHES AND ARCH RELATIONSHIPS: A BIOMETRIC STUDY

K. Hansen, P. Iemammueisuk, H. Pancherz

The purpose of this study was to evaluate biometrically the treatment and post-treatment effects of the Herbst appliance on the dental arches and arch relationships. The sample consisted of 53 Class II, Division I malocclusion patients (33 boys and 20 girls) treated with the Herbst appliance. The mean age of the patients before treatment was 12.5 years (SD=1.2 years). Dental casts were analysed before treatment, after treatment, 6 months post-treatment and at the end of the growth period (5-10 years post-treatment). The following variables were assessed: sagittal molar and canine relationships, overjet, overbite, maxillary and mandibular arch perimeters, and inter-molar and inter-canine dental arch widths. During treatment, the overjet, overbite, and sagittal molar relationship were over-corrected in most of the cases, while the sagittal canine relationship was normalized. The maxillary and mandibular arch perimeters increased during treatment, as did dental arch widths (molar and canine).

In the long-term (mean=6.7 years), Herbst appliance treatment resulted in a normal or overcorrected sagittal molar relationship in 79 per cent and a normal canine relationship in 68 per cent of the cases. Eighty-three per cent of the subjects had an overjet of 4.5 mm or less. In the long-term, the arch perimeters seemed to follow a normal dental development pattern. The increase of the upper molar and canine dental arch widths during treatment remained virtually stable whilst the lower intermolar arch widths seemed unaffected by treatment.

British Journal of Orthodontics
1995; 22: 123-134

## LONG-TERM EVALUATION OF TREATED CLASS II DIVISION 1 MALOCCLUSIONS UTILIZING THE PAR INDEX

O.D. Otuyemi, S.P. Jones

The PAR Index was used to evaluate treatment and long-term post-retention results obtained from 50 Class II Division I malocclusions. Dental casts were used to record the occlusions pre- and post-treatment, as well as one and ten years post-retention. The results suggested a high treatment standard, as indicated by mean percentage PAR score reduction. However, maintenance of post-treatment results one and ten years post-retention was only achieved in 60 and 30 per cent of cases, receptively. The major factor involved in this deterioration appeared to be late lower anterior crowding.

British Journal of Orthodontics
1995; 22:171-178.

## THE INTERRELATIONSIHP OF INTERNAL DERANGEMENTS OF THE TEMPOROMANDIBULAR JOINT, HEADACHE, VERTIGO, AND TINNITUS: A SURVEY OF 25 PATIENTS

Eugene H. Williamson, DDS, MS

It has been over 50 years since the first reference to ear symptoms and their relationship to temporomandibular joint

dysfunction appeared in the literature. The usual otalgic complaints associated with TMJ dysfunction include ear pain, fullness in the ear, vertigo, and dizziness. These otalgic symptoms have been related to bite discrepancies when observed in the absence of defined pathosis. In recent years, interest and research in internal derangements of the joint have produced new information about the physiology of condyle-disk relationships. These derangements may be defined as anterior and medial displacements of the disk relative to the mandibular condyle and may include perforations of diskal or peridiskal tissues. Most often, a non-surgical attempt at reduction is tried first and is successful 90 per cent of the time. This technique is implemented by utilising jaw repositioning appliances made to the position where the reduction occurs. If this procedure fails, arthrography is performed and usually is followed by arthroplasty. The purpose of this study is to present 25 clinical cases in which vertigo and associated ear symptoms underwent remission upon jaw repositioning. Hypotheses regarding the anatomic and physiologic etiology of otalgic symptoms and their relationship to internal derangements of the temporomandibular joint also are formulated.

Facial Orthopedics and Temporomandibular Arthrology
1986; 3(1): 13.

## MYOMONITOR REST POSITION IN THE PRESENCE AND ABSENCE OF STRESS

Eugene H. Williamson, Deverne E. Marshall Jr.

In 1934, Niswonger was the first to refer to a repetitive mandibular rest position. Since then, proponents of an inviolate resting posture of the mandible have generated numerous research efforts and clinical observations. However, other authors have reported that interocclusal vertical dimension is highly variable. When the mandible closes from rest position to maximum intercuspation, it must do so in a manner that is not noxious to the mechano-receptor response in the periodontal ligament. Hence, the
existence of a sensori-motor feedback mechanism has been confirmed. This mechanism forms an engram within the central nervous system which allows the mandible to close without interference from the cusps of the teeth. Swerdlow has reported that the phonetic method for determining clinical rest position is reliable. Most often, this method involves having the patient repeat the word 'Mississippi' and then allowing the jaw to rest with the lips lightly touching. Because teeth must be present to incorporate this reflex mechanism from the periodontal ligament, another feedback system must be available when an edentulous state exists. Moyers studied neonates and demonstrated postural reflexes electromyographically within the masticatory musculature. It is well known that a postural position also exists in the edentulous adult. In a review of neuromuscular mechanisms involved with mandibular function, Mohl described the reflex pathways that govern this response. The elevator muscles of mastication contain muscle spindles which are stretch receptors. These spindles are excitatory to the neurons in the trigeminal nucleus that supply the muscles of mastication and dictate their resting length of the reticular formation in the hypothalamus (emotional stress) through descending central connections to the trigeminal nucleus which synapse there with the motor efferent supply to the muscle tissue of the spindle itself. In this manner, tension may be placed on the spindle which allows it to be more susceptible to stretching of the muscle of mastication. In a situation of emotional stress, it would take less stretch of the muscle of mastication to elicit a myotactic reflex, which causes the skeletal muscle to contract or shorten. Hypothetically, the resting posture of the mandible then would be closer to maxilla under stressful conditions. The purpose of this study was to compare the resting posture of the mandible determined clinically and with transcutaneous nerve stimulation (TENS) in the presence and absence of stress.

Facial Orthopedics and Temporomandibular Arthrology
1986; 3(2):14.

## TEMPOROMANDIBULAR JOINT PAIN DYSFUNCTION AND MANDIBULAR ASYMMETRY

Jack D. Swemer,
Eugene H. Williamson,
Sherri R. Brown, P. Kenneth Morse

Temporomandibular joint pain dysfunction involves displacement of the articular disk(s) and/or myofascial pain dysfunction of the craniomandibular muscles. Macro-trauma to the condyle, intracapsular joint structures, or muscles of mastication as the result of overt external injury is a principal cause of this condition. Microtrauma to the intracapsular joint structures or muscles of mastication as the result of mandibular spatial adaptation to the maxilla and cranium in order for teeth to occlude is also a factor in the etiology.

Facial Orthopedics and Temporomandibular Arthrology
1986; 3(5):12.

## TEMPOROMANDIBULAR JOINT MENISCUS REPAIR SURGERY: A FOLLOW-UP STUDY

Robert A. Bays

Surgery for the treatment of temporomandibular joint complaints remains somewhat controversial and poorly defined. The purpose of this paper, therefore, is to present an approach to the surgical management of temporomandibular joint complaints that are referable to disc displacement.

Facial Orthopedics and Temporomandibular Arthrology 2(2).

## CLINICAL ASSESSMENT OF THE EFFECT OF LIGATED ANTERIOR REPOSITIONING SPLINT THERAPY ON FACIAL GROWTH

Eugene H. Williamson

Interest in the use of functional appliances has increased greatly during the last decade. The work of McNamara and Petrovic on animals has helped clarify the physiologic responses occurring with some of these

appliances. With the exception of the Herbst appliance, all popular functional appliances are removable. The Herbst appliance holds the mandible in the prescribed position by means of telescoping arms rather than by muscle function as most other functional appliances do. Patient co-operation in using removable appliances can be a problem, and whenever the patient is eating, the appliance must be removed from the mouth. As most parents will attest, children between the ages of 6 and 14 seem to eat continuously. Therefore, it seemed prudent to develop an appliance which would allow continuous wear and also require the patient to hyperpropulse the mandible with his own muscle force. Such an appliance has been developed and is referred to as a ligated anterior repositioning splint or LARS.

Facial Orthopedics and Temporomandibular Arthrology
1985; 2(12):12.

## TOOTH DISPLACEMENT ANALYSED ON HUMAN AUTOPSY MATERIAL BY MEANS OF A STRAIN GAUGE TECHNIQUE

E. Pedersen, K. Andersen and B. Melsen

Tooth displacement was analysed on human autopsy material for various types of orthodontic force systems using an electronic strain gauge technique. Tooth movements were registered in two dimensions with low force clip gauges on three sections of the mandible, containing the first premolar and the first molar. The sensitivity was 0.1 µm when horizontal forces of 50, 100, and 150 cN were applied at different horizontal levels producing different M/F ratios.

The relationship between a force system and the resulting tooth movement was described by the position of the centre of rotation, CR, and the angle of rotation. The centre of resistance was determined for the three autopsy specimens, and depended on tooth geometry, root length, and level of bony margin. Important differences in location were found. The dynamics of initial
tooth movement were analysed within the first minute of load application. Force/displacement curves were generated to evaluate the behaviour of the periodontal ligament. There was a linear correlation between the two variables. Freezing the autopsy material some days before testing had no detectable effect. The results from measurements on human autopsy material were compared with previously derived *in vivo* measurements.

European Journal of Orthodontics
1991; 13: 65-74.

A SPLINT FOR IMMEDIATE SURGICAL ORTHOGNATHIC FIXATION AND RELEASE DURING ORTHODONTIC TREATMENT

Robert T. Lee

A splint has been designed for surgical use during the course of orthodontic treatment. The two-piece splint is ligated directly to the orthodontic arch wires. Surgically, the splint has the advantage of saving operative time, of ensuring precise location rapidly in all three planes, and allowing immediate release and replacement. Orthodontically, the splints allow a shorter pre-operative phase of orthodontics, with the orthodontic treatment being completed post-operatively to ensure precise tooth positions and functional occlusion.

European Journal of Orthodontics
1991; 13: 209-211.

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