# ABSTRACTS

## THE EFFECTS OF A FOUR-FOLD INCREASED ORTHODONTIC FORCE MAGNITUDE ON TOOTH MOVEMENT AND ROOT RESORPTIONS. AN INTRA-INDIVIDUAL STUDY IN ADOLESCENTS

Py Owman-Moll, Jüri Kurol and Dan Lundgren

This clinical and histological study was designed as an intra-individual study to investigate the effect on tooth movements and adverse tissue reactions (root resorption) when a fixed orthodontic appliance was activated with a controlled, continuous force of 50 cN (≈ 50g) or with a four-fold larger force (200 cN ≈ 200g). The first premolar on both sides of the maxilla in eight individuals, six boys and two girls (mean age 13.0 years), was moved buccally during 7 weeks with 50 cN and 200 cN alternately on the right or left side. During the first week a force reduction of 18 and 28 per cent (on average) was registered in the in the 50 cN and 200 cN group respectively. Tooth movements were studied by means of dental casts using a co-ordinate measuring machine. The magnitude of the mean horizontal crown movement increased 50 per cent when a force of 200 cN was applied compared with a 50 cN force (3.4-5.1 mm on average) and the difference was significant. Root resorptions were registered in histological sections of the extracted test teeth with no significant difference in frequency or severity between the two forces used. Individual variations were large regarding both tooth movement and root resorption. Possible reasons to explain the results as well as the clinical implication of the findings are discussed.

European Journal of Orthodontics
18; 1996: 287-294

## SHEAR BOND STRENGTH OF A NEW POLYCARBONATE BRACKET — AN IN VITRO STUDY WITH 14 ADHESIVES

Nilgün Akin-Nergiz, Ibrahim Nergiz, Kerstin Behlfelt and Ursula Platzer

Shear bond strength and failure location were used to evaluate the effectiveness of plastic bracket primers for bonding diacrylate adhesives on a new fibre-reinforced polycarbonate bracket.

Maxillary incisor polycarbonate and mesh-based brackets as control were bonded to human incisors with 14 different adhesives (four filled diacrylate two-paste, six diacrylate one-step and four powder-liquid acrylic adhesives), and after thermo-cycling for 2000 cycles between 5° and 55°C, tested in shear. A non-parametric test (Mann-Whitney U test) was used to compare the shear bond strength of the polycarbonate brackets with the mesh based brackets and a One-way test (according to Scheffe) to compare the shear bond strength of different adhesives. The following conclusions can be made:

1. Seven of the 14 adhesives used in this study with both types of brackets demonstrated adequate shear bond strength values for the clinical application. The exceptions were: Achieve Mix, No-Mix: 30 Silkon, Lee Insta-Bond, Ortho-Loc and Bond-Eze, all with too low a shear bond strength for one or both types of brackets, and finally Quasar, which used with the plastic brackets sometimes caused enamel fractures, due to a very high bond strength.

2. The adhesives with their own plastic primer demonstrated higher bond strength values than those without plastic primer, and two-paste adhesives used with plastic primer displayed a higher bond strength than the other adhesives.

3. Generally, the shear bond strength values of the one-step adhesives were lower compared with the two-paste adhesives.

4. The liquid-powder adhesives demonstrated very different values for bond strength.

European Journal of Orthodontics
18; 1996: 295-301

## PREVALENCE OF TEMPOROMANDIBULAR JOINT DYSFUNCTION (TMJD) IN CHINESE CHILDREN AND ADOLESCENTS. A CROSS-SECTIONAL EPIDEMIOLOGICAL STUDY

Yu-meng Deng, Min-Kui Fu and Urban Hägg

The aim of this study was to investigate the prevalence of temporomandibular joint dysfunction (TMJD) in Chinese children and adolescents, and the relationship between TMJD and type of occlusion. The sample consisted of 3105 Chinese children, 3-19 years of age, divided into four groups by the stage of dental maturation.

The prevalence of TMJD for the entire group was 17.9 per cent and there was no significant sex difference. TMJD increased in the mixed and early permanent dentitions, but decreased in the permanent and deciduous dentitions. In the subjects with TMJD, the most common pain was registered in 0.6 per cent only. A single sign was registered in 88.5 per cent, a combination of sound and abnormal jaw movement in 11.0 per cent, and combinations of other signs in less than 1.0 per cent. Sound as a single sign increased with the specific stages of dental development (P<0.001).

European Journal of Orthodontics
17; 1995: 305-309

## CONDYLAR CONDITION AND MANDIBULAR GROWTH DURING EARLY FUNCTIONAL TREATMENT OF CHILDREN WITH JUVENILE CHRONIC ARTHRITIS

Thomas Klit Pedersen, Janne Grønhøj, Birte Melsen and Troels Herlin

TMJ involvement in children with Juvenile Chronic Arthritis (JCA) will frequently cause disturbance of the growth of the mandible. Orthodontic treatment of these patients often includes orthognathic surgery, and are complicated to handle with respect to the damaged joint and impaired function. The aim of this presentation is to suggest an early treatment with a functional splint appliance, a distraction splint, with the purpose of increasing function of the joint and ensuring continuous growth of the mandible.

European Journal of Orthodontics
17; 1995: 385-394
## PROPERTIES OF SUPERELASTIC WIRES AND THEIR RELEVANCE TO ORTHODONTIC TREATMENT

Dietmar Segner and Dagmar Ibe

In this study tools were developed to test and compare levelling archwires that the manufacturers claim to have superelastic properties. As the classic spring model and Hook's law cannot be applied, new parameters had to be found. It could be shown that three parameters are necessary to describe a superelastic archwire adequately: the distinctiveness of the pseudo-elastic plateau, the deflection at the beginning of the plateau, and the force level of the plateau. The results showed that many materials either did not show any pseudoelastic properties at all or that the wire parameters were such that they did not give any advantage over conventional work-hardened NiTi materials. In many archwires the beginning of the plateau and thereby the desired characteristics began only when the archwire was displaced 1 mm or more. For many archwires the force level of this plateau also proved to be rather high with values often above 500 g.

European Journal of Orthodontics

17; 1995: 395-402

## DIFFERENTIAL SCANNING CALORIMETRY (DSC) ANALYSES OF SUPERELASTIC AND NON-SUPERELASTIC NICKEL-TITANIUM ORTHODONTIC WIRES

Thomas Gerard Bradley, William A. Brantley and Bill M. Culbertson

The purpose of this study was to determine the transformation temperatures for the austenitic, martensitic, and rhombohedral (R) structure phases in representative as-received commercial nitinol (NiTi) orthodontic wire alloys, to reconcile discrepancies among recent publications. Specimens were examined by differential scanning calorimetry (DSC) over a temperature range from approximately -170°C to 100°C, with a scanning rate of 10°C per minute. Two different pathways, with the intermediate R structure either absent or present, were observed for the transformation from martensitic to austenitic NiTi, whereas the reverse transformation from

austenitic to martensitic NiTi always included the R structure. The enthalpy (ΔH) for the transformation from martensite to austenite ranged from 0.3 to 3.5 calories per gram. The lowest ΔH value for the nonsuperelastic Nitinol wire is consistent with a largely work-hardened, stable, martensitic microstructure in this product. The DSC results indicate that the transformation processes are broadly similar in superelastic, body-temperature shape-memory, and non-superelastic NiTi wires. Differences in bending properties for the NiTi orthodontic wires at room temperature and 37°C are due to the relative proportions of the metallurgical phases in the microstructures.

American Journal of Orthodontics and Dentofacial Orthopedics

1996; 109: 589-597.

## MAXILLARY AND CRANIAL BASE CHANGES DURING TREATMENT WITH FUNCTIONAL APPLIANCES

Michael Courtney, Michael Harkness and Peter Herbison

The purpose of this prospective study was to investigate the maxillary and the cranial base changes after treatment with the Harvold activator and the Fränkel function regulator appliances. Forty-two children, who are 10 to 13 years old, with Class II, Division 1 malocclusions were matched in triads according to age and sex and randomly assigned to either the control, Harvold activator, or Fränkel function regulator group. Lateral cephalometric radiographs were taken at the start of the study and 18 months later. Both appliances reduced the overjet by tipping the maxillary incisors palatally and, as a consequence, the length of the maxillary arch was reduced. The appliances had no effect on either the horizontal or vertical position of the maxillary molars. Small, but statistically significant, changes in the cranial base angle in the Fränkel function regulator group were attributed to relatively large changes at basion in several children, influencing the results because of the small size of the sample. The appliances had no effect on the position of the maxilla.

American Journal of Orthodontics and Dentofacial Orthopedics

1996; 109: 616-624.

## ORTHODONTICS AND TEMPOROMANDIBULAR JOINT INTERNAL DERANGEMENT

Richard W. Katzberg, Per-Lennart Westesson, Ross H. Tallents and Christiana M. Drake

The purpose of this investigation is to compare the prevalence of internal derangement of the temporomandibular joints (TMJ) in asymptomatic volunteers versus symptomatic subjects using magnetic resonance imaging (MRI), with a detailed comparison to clinical signs and symptoms and with attention to a prior history of orthodontic treatment. Bilateral MRI scans were obtained of the TMJs in 76 asymptomatic volunteers and 102 symptomatic patients. A comparison was made to the clinical signs and symptoms, a history of orthodontic treatment, and to the MR findings. The MRI scans were reviewed using established criteria for disk displacement and the reviewers were blinded as to the clinical information. Our results show a prevalence of disk displacement in 25 of 76 (33%) volunteers and 79 of 102 (77%) patients with a statistically significant difference (p<0.001). No statistical link was noted between a history of prior orthodontic treatment and internal derangement of the TMJ.

American Journal of Orthodontics and Dentofacial Orthopedics

1996; 109: 515-520.