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# ABSTRACTS

## FORCE SYSTEM DEVELOPED FROM CLOSED COIL SPRINGS

Biret Melsen, Lars Falkenberg
Topp, Hans Michael Melsen and
Svend Terp

The present paper provides data on load-deflection rate and maximal force generated for 19 coil springs. The force level at activation and deactivation was registered at intervals of 5mm between 0 and 100 per cent extension. Ten springs of each type were analysed. The following questions were answered. How many of the springs exhibited the behaviour of a superelastic spring and how many types of springs differed significantly from each other with respect to force deflection rate and maximal force level at 100 per cent extension?

Of the products tested only the springs from GAC exhibited the behaviour characteristic of the superelastic wire.

The 19 products could, from a clinical point of view, be classified into four different groups with regard to force deflection rate and five groups with regard to maximal force.

The variation within each product also differed between the products with the lowest intra-product variation seen in the TP springs.

In light of the present findings it is obvious that manufacturers' information was not satisfactory. The need for more thorough user information is stressed.

European Journal of
Orthodontics
1994; 16: 531-539.

## CT-SCANNING AND RADIOGRAPHIC ANALYSIS OF TEMPOROMANDIBULAR JOINTS AND CEPHALOMETRIC ANALYSIS IN A CASE OF HERBST TREATMENT IN LATE PUBERTY

Hans Ulrik Paulsen, Agnete Karle,
Merete Bakke and Anders Herskind

From a consecutive sample of 100 patients treated with the Herbst appliance after the peak of puberal growth, a boy was chosen to show the total effect of the Herbst treatment. Changes in the dentofacial morphology and the structure of the temporomandibular joints (TMJ) were followed by radiologic examinations and the function of the craniomandibular system was studied by clinical examinations, and electromyographic and bite-force recordings. Treatment resulted in marked dentoalveolar changes, an increase of mandibular length, ramus height, and gonion angle. Three months after insertion of the appliance CT-scanning and orthopantomograms of the TMJ revealed new bone formation as a double contour in the fossa articularis and on the posterior part of the condylar process as a result of adaptive bone remodelling. Function was affected by treatment, but was markedly restored at control.

European Journal of
Orthodontics
1995; 17: 165-175.

## TRANSITION AND DETERMINANTS OF ORTHODONTIC ROOT RESORPTION-REPAIR SEQUENCE

Pongsri Brudvik and Per Rygh

When severe root resorption is observed during orthodontic treatment the clinician needs to know how the active process can be stopped. It is generally assumed that if active force is discontinued, the root resorption will end. The determinants of the resorption/repair sequence are, however, not well understood.

The aim of the present study was to register and analyse determinants that may influence the extent of resorbed root surface, as well as the transition of a process of active root resorption into a process of tissue deposition/repair in the resorption lacunae.

Using an experimental model that would stimulate the first force-activation cycle, the upper first molars of rats were moved mesially by a fixed orthodontic appliance for periods between 2 and 21 days. The results revealed that (1) the extent of root resorption after 21 days corresponded with the maximal extent of the hyalinized zone; (2) a process of repair started for the periphery in the resorbed lacunae where the periodontal ligament (PDL) had been re-established, while ongoing active resorption was observed beneath the existing hyalinized tissues; and (3) root resorption continued in the area where hyalinized tissue persisted even after active force had terminated. It is hypothesized that determinants of continued resorption/repair generally seem to be associated with the persistence and removal of the necrotic tissue.

European Journal of
Orthodontics
1995; 17: 177-188.

## NATURAL HEAD POSITION AND NATURAL HEAD ORIENTATION: BASIC CONSIDERATIONS IN CEPHALOMETRIC ANALYSIS AND RESEARCH

Lundström A., Lundström F.,
Libretto L.M.L. and Moorrees C.F.A

Natural head position (NHP) provides the key for meaningful cephalometric analysis because an extracranial reference line is used instead of intercranial reference lines, known to be subject to considerable biological variation in their inclination.

Although the principle of natural head position is being recognized in the orthodontic literature, its registration may contain an element of unavoidable error that requires correction. A new concept of natural head orientation (NHO) has been introduced to maximize the contribution of NHP to
cephalometrics. It is defined as the head orientation of the subject perceived by the clinician, based on general experience, as the natural head position in a standing, relaxed body and head posture, when they the subject is looking at a distant point at eye level.

The present study was designed to determine the accuracy and validity of NHO, using lateral profile photographs cut in a circular shape, obtained from 27 orthodontic patients, 10-14 years old. Findings among four investigators showed a high correlation (r = 0.82-0.96), in orientating these profile photographs in estimated natural head position (NHP). Moreover, investigators showed good correlation (r = 0.57-0.84) in head orientation after a 3-week interval. Mean differences for the same period varied between 0.1 and 2.9 degrees. The validity of NHO was supported also by a panel investigation.

Clinicians as well as auxiliary personnel can be trained to make a critical judgement of the recorded natural head position and correct head orientation, whenever indicated, to enhance the reliability of cephalometric analysis in clinical practice and research.

European Journal of
Orthodontics
1995; 17: 111-120.

# THE EFFECT OF A LIP BUMPER ON LOWER DENTAL ARCH DIMENSIONS AND TOOTH POSITIONS

Johannes Grossen and Bengt Ingervall

The effect of a lip bumper on the dimensions of the lower dental arch and on the inclination of the incisors and first molars was studied in 40 children, aged 9-12 years. The children wore their lip bumper full time for 7-10 months.

The effects of the lip bumper therapy were recorded on dental casts and profile cephalograms made before and after the treatment. The positions and stages of development of the lower second molars were determined on pretreatment intra-oral radiographs.

The lip bumper treatment resulted in an increase of the dental arch widths between the molars, premolars and canines. the arch length increased through proclination of the incisors and uprighting of the first molars. The stages of development and the positions of the second molars had no influence on the effect of the treatment. Simultaneous treatment in the maxilla with a headgear, a transpalatal arch or removable plate had no influence on the outcome of the lip bumper therapy.

European Journal of
Orthodontics
1995; 17: 129-134.

# MORPHOLOGICAL CHARACTERISTICS OF DENTITIONS DEVELOPING EXCESSIVE ROOT RESORPTION DURING ORTHODONTIC TREATMENT

Inger Kjaer

The present study focuses on orthodontically provoked, excessive root resorption. The purpose was to identify in these cases common morphological features in radiographic diagnostic material taken before treatment. The material was submitted by 35 Danish orthodontists. The goal was to improve the future orthodontic diagnostics of the dentition in order to prevent severe root resorption during treatment.

The study indicates that (1) there is a strong connection between various dental morphological characteristics, such as invagination, length of root, and root shapes, especially taurodentism, and the tendency to root resorption during orthodontic treatment; (2) there is a connection between anomalies in the dentition, particular ectopia and agenesis, and the tendency to root resorption during orthodontic treatment; (3) there seems to be a connection between the pattern of resorption in the primary dentition and the tendency to root resorption in the permanent dentition following orthodontic treatment; (4) girls are more susceptible to root resorption than boys; (5) one ought to be on the lookout for connections between condylar changes, root resorptions, and anterior open bites in connection with orthodontic treatment.

The observation regarding root resorption in dentitions in which invaginations and taurodental root shapes occur has not previously been reported. Also, the findings of deviant resorption patterns in both the primary and permanent dentitions. In a considerable number of patients are new observations, which ought to be incorporated into orthodontic treatment planning.

European Journal of
Orthodontics
1995; 17: 25-34.

# A THREE-DIMENSIONAL COMPARISON OF CONDYLAR POSITION CHANGES BETWEEN CENTRIC RELATION AND CENTRIC OCCLUSION USING THE MANDIBULAR POSITION INDICATOR

Thomas W. Utt, Charles E. Meyers, Thomas F. Wierzba and Steven O. Hondrum

The mandibular position indicator (MPI) was used to compare condylar position between centric relation (CR) and centric occlusion (CO) for 107 patients before orthodontic treatment. The MPI data were examined to determine frequency, direction, and magnitude of CO-CR difference; and data analyzed for possible correlation to the patient's Angle classification, ANB angular measurement, age, or gender. Only one patient (0.9%) had no measurable CO-CR difference in all three spatial planes. Six subjects (5.6%) showed a shift in condylar position in the transverse plane without a measure difference in the sagittal plane. Twenty patients (18.7%) experienced a superoinferior (SI) or anteroposterior (AO) condylar displacement of at least 2.0 mm on one or both sides; 17 (15.9%) displayed a transverse shift at the level of the condyles of 0.5mm or greater. No statistical difference was found between the 31 patients with Class I malocclusions and 72 patients with ClassII malocclusions when comparing the amount or direction of CO-CR change. The amount of CO-CR difference was nearly identical for right and left sides with the amount of SI
displacement (x=0.84 mm) consistently greater than AP displacement (x=0.61 mm). Only weak correlations were found between movements of right and left condyles. The average transverse CO-CR difference was 0.27mm. Patient age, ANB angle, gender, or Angle classification cannot be used to predict frequency, magnitude, or direction of CO-CR changes at the level of the condyles.

**American Journal of Orthodontics and Dentofacial Orthopaedics**
1995; 107: 298-308.

## THE EFFECTIVENESS OF AN EXTREME CANINE-PROTECTED SPLINT WITH LIMITED LATERAL MOVEMENT IN TREATMENT OF TEMPOROMANDIBULAR DYSFUNCTION

W.Alex Willis

This study suggests that a splint design incorporating extreme canine guidance with limited lateral movement may be effective in the treatment of temporomandibular dysfunction (TMD) symptoms. Fifty consecutively treated TMD patients were evaluated with the TMJ Scale before and after treatment. A group of 11 similar patients identified as having TMD, but who declined treatment, were used as a control group.

**American Journal of Orthodontics and Dentofacial Orthopaedics**
1995; 107: 229-34.

## THE EFFECTS OF FRANKEL'S FUNCTION REGULATOR (FR-4) THERAPY ON THE TREATMENT OF ANGLE CLASS I SKELETAL ANTERIOR OPEN BIT MALOCCLUSION

Elif Erbay, Türköz Ugur and Mustafa Ülgen

The present study attempts to evaluate cephalometrically the effects of Frankel's function regulator (FR-4) appliance on the treatment of Angle Class I skeletal anterior open bite malocclusion. Forty Turkish children (26

girls and 14 boys), with Angle Class I skeletal anterior open bite, were randomly divided into two groups of 20 (13 girls and boys). Patients who had not undergone treatment served as the control group, whereas a second group was treated with lip-seal training and the FR-4 appliance. Chronilogic mean decimal age at initial period of the investigation was 8.7 years in the treated group, and 8.9 years in the control group. Treatment and observation periods were 2 years. Investigation was carried out on lateral cephalograms taken before and after the study period. The results indicate that a spontaneous downward and backward growth direction of the mandible observed in the control group could be changed to an upward and forward direction by FR-4 therapy. The skeletal anterior open bite was successfully corrected through upward and forward rotation.

**American Journal of Orthodontics and Dentofacial Orthopaedics**
1995; 108: 9-21.

## RISK FACTORS FOR APICAL ROOT RESORPTION OF MAXILLARY ANTERIOR TEETH IN ADULT ORTHODONTIC PATIENTS

A. Davide Mirabella and Jon Artun

The purpose of this study was to identify risk factors for apical root resorption in adult orthodontic patients. Standardized periapical radiographs of maxillary anterior teeth and cephalograms made before and after treatment and treatment charts of 343 adults, representing groups of consecutively treated patients from four orthodontics practices, were examined. Apical root resorption was calculated by subtracting post-treatment tooth length measurements from the corresponding pre-treatment measurements. Root width was measured from the mesial to the distal outline of the roots 4 mm from the apex. Root form was scored subjectively as normal, pointed, eroded, blunt, bent and bottle shaped. Root movement was calculated by measuring the superimposed tracings of pre-treatment and post-treatment cephalograms. Proximity of the central incisor roots to the palatal

cortical bone was scored subjectively as present or absent. Severity of initial malocclusion and treatment variables were collected from the charts. Multiple linear regression analyses revealed that amount of root movement, long roots, narrow roots, abnormal root shape, and use of Class II elastics were significant risk factors. However, the statistical model had a low explained variance, strongly suggesting a weak prediction power. No associated was found between type of initial malocclusion, treatment time, use of rectangular arch wires, proximity of the root to the palate or treatment with maxillary osteotomy, and root resorption. Endodontic treatment was a preventative factor.

**American Journal of Orthodontics and Dentofacial Orthopaedics**
1995; 108: 48-55.