Effect of a static magnetic field on orthodontic tooth movement in the rat.

Orthodontic tooth movement may be enhanced by the application of a magnetic field. Bone remodelling necessary for orthodontic tooth movement involves clastic cells, which are tartrate-resistant acid phosphatase (TRAP) positive and which may also be regulated by growth hormone (GH) via its receptor (GHR). The aim of this study was to determine the effect of a static magnetic field (SMF) on orthodontic tooth movement in the rat. Thirty-two male Wistar rats, 9 weeks old, were fitted with an orthodontic appliance directing a mesial force of 30 g on the left maxillary first molar. The appliance incorporated a weight (NM) or a magnet (M). The animals were killed at 1, 3, 7, or 14 days post-appliance insertion, and the maxillae processed to paraffin. Sagittal sections of the first molar were stained with haematoxylin and eosin (H&E), for TRAP activity or immunohistochemically for GHR. The percentage body weight loss/gain, magnetic flux density, tooth movement, width of the periodontal ligament (PDL), length of root resorption lacunae, and hyalinized zone were measured. TRAP and GHR-positive cells along the alveolar bone, root surface, and in the PDL space were counted. The incorporation of a SMF (100-170 Gauss) into an orthodontic appliance did not enhance tooth movement, nor greatly alter the histological appearance of the PDL during tooth movement. However significantly greater root resorption (P = 0.016), increased width of the PDL (P = 0.017) and greater TRAP activity (P = 0.001) were observed for group M at day 7 on the compression side. At day 14 no differences were observed between the appliance groups.

Orthodontic tooth movement in the prednisolone-treated rat.

Adverse effects of corticosteroids on bone metabolism raise concerns as to whether steroid treatment may influence orthodontic movement. This study examined the effect of prednisolone on orthodontic movement using an established rat model. The corticosteroid treated group (N = 6) was administered prednisolone (1 mg/kg) daily, for a 12-day induction period; the control group (N = 6) received equivalent volumes of saline. On day 12, an orthodontic appliance was placed which exerted 30 g of mesial force to the maxillary first molar. Animals were sacrificed on day 24 and tooth movement was measured. Sagittal sections of the molars were stained with haematoxylin and eosin, and for tartrate-resistant acid phosphatase (TRAP) activity. While there were no significant differences in the magnitude of tooth movement between the 2 groups, steroid-treated rats displayed significantly less root resorption on the compression side and fewer TRAP-positive cells within the PDL space on the same side. This suggests steroid treatment suppressed clastic activity.

Removal of orthodontic bonding resin residues by CO2 laser radiation: surface effects.

OBJECTIVE: The purpose of this in vitro study was to evaluate the potential use of pulsed CO2 laser radiation to remove selectivity residues of orthodontic bonding resin that remain after debonding of fixed orthodontic appliances. SUMMARY BACKGROUND DATA: Current techniques used for removal of orthodontic bonding resin after removal of fixed appliances include rotary instruments, debonding pliers, and ultrasonic scalers. These techniques, however, are time-consuming and inefficient, and may damage tooth enamel. METHODS: A standardized cylinder of orthodontic bonding resin was bonded to the buccal surfaces of 100 extracted premolar teeth, which were then divided into 10 groups of 10 specimens each. In 9 groups, the resin was ablated using 1 of 9 different laser parameters, while in the remaining control group, the resin was removed with a slow speed tungsten carbide bur. Specimens were evaluated by light microscopy and scanning electron microscopy (SEM) to assess the amount of resin remaining and the extent of the damage to the underlying enamel. RESULTS: The 2 W/100 ms combination was optimal, with a high efficiency of resin removal and the least enamel damage. Higher laser powers increased the extent of enamel damage without enhancing resin removal. CONCLUSIONS: This laser technique appears promising, however, further studies of the extent of thermal changes at the level of the dental pulp are necessary to establish more fully the risk-benefit ratio.

Lingual orthodontics: a review of its history.

When lingual orthodontics was first introduced about twenty years ago some called it the 'ultimate aesthetic appliance'. Patients and practitioners embraced this new treatment alternative with high expectations. Reports of disappointing results and high costs dampened much of the initial excitement and enthusiasm gradually waned. By the late 1980s, the number of practitioners using the technique had fallen sharply, leaving only a handful who still believed in its potential. Relatively little has been written on lingual orthodontics, almost nothing in recent years. This article takes an objective view of its present status.

Prevalence of malocclusion traits in an Australian adult population.

The prevalence of certain malocclusion traits in an Australia adult population was examined in a sample of 113 female and 103 male adult subjects aged between 18 and 64 years (average age = 38.1 years). If cross-sectional studies of younger population groups are to be used for research into the long-term physiological effects of malocclusion, it is essential to know if certain and specific malocclusion traits are stable over time. In this cross-sectional study, the prevalence of many malocclusion traits did not change; however, with advancing age, the incidence of posterior crowding, posterior rotations, posterior crossbite and anterior irregularity increased significantly.

Perceptions of orthodontic appliances among grade seven students and their parents.

A survey of 468 Grade Seven students and 437 parents in the North Brisbane region was undertaken to determine perceptions of orthodontic appliances. Based on responses to statements on the survey, a Perception Score was created for both students and parents in relation to both fixed and removable appliances. Both students and parents had more negative perceptions of fixed appliances than of removable appliances. Fixed appliances were perceived to attract more teasing, to cause more problems in the maintenance of oral hygiene and to be more painful than a removable plate. Respondents also felt that children would have to be more careful about what they eat when wearing fixed appliances. Approximately forty per cent of students and parents did not know whether teeth could be damaged by orthodontic appliances nor whether the appliances would cause discomfort. Parents had significantly more negative perceptions of both types of orthodontic appliances than did the students. The Perceptions scores were not significantly influenced by whether the students attended a private or public sector dentist, the frequency of dental visits, any history of orthodontic treatment, nor by the parents' level of education and their occupations. A forewarning about experiences of orthodontic appliances would better prepare patients and assist operators in providing the community with a more comprehensive orthodontic service.

A family case report: disturbances in tooth form and eruption of the second premolar.

This report describes a family who demonstrated anomalies of tooth form and eruption of the lower second premolar. Observation of the second premolars remaining in the mother's and father's dentitions included ectopic eruption with impaction and substantial spacing between the first and second premolars. Four siblings were also examined--three boys aged 15, 14 and 12 years, and one girl aged 11 years. Anomalies of the second premolar recorded in the males and female include: congenital absence, ectopic eruption with impaction, delayed eruption and spacing. Associated anomalies included: congenital absence of other permanent teeth and spacing. It appears that the defect in tooth form and eruption is of a genetic origin, affecting both males and females. The condition(s) did not appear to be associated with a syndrome and the human papilloma virus lesions noted in all family members were not considered to be related to the dental defects. This family demonstrated two anomalies of the lower second premolar: congenital absence and disturbance in tooth eruption. The question raised by this case report is whether these two anomalies are inherited as separate traits or whether failure of tooth eruption is a variation in expression of the same genetic factor that results in oligodontia.

Collagen responsible for tooth eruption? A study of the eruption of rat incisors.

The rate of turnover of collagen in periodontal ligament (PDL) is closely associated with the process of tooth eruption and tissue adaptation allowing good anchorage of the tooth within the socket. Collagen may even be associated with orthodontic relapse. As the collagen protein seems to play a key role in tooth eruption, the investigation concentrated on the presence and maturation of collagen and its possible function in the process of tooth eruption.

Lathyrism and the half-life of collagen.

Maturation of collagen in the periodontal ligament has often been designated as the cause of tooth eruption. The fact that collagen has a high turnover rate provided some sort of proof of this hypothesis. It is well known that lathyrogens decrease eruption rate. Experiments were performed, using Wistar rats, which looked into the relationship between collagen turnover and lathyrism. The collagen turnover was established in teeth not erupting after the administration of lathyrogens. These results were compared to those obtained after having stopped eruption by the placement of a goldcrown on the lower incisors. It was found that lathyrism, and therefore collagen maturation, did not influence turnover rate. Thus the supposition, that collagen is responsible for tooth eruption, becomes doubtful.

Reliability of eruption rate measurements of the rat incisor.

The reliability of the easy method to measure rat tooth eruption proposed by Schour and Van Dyke has frequently been challenged. To assess its true trustworthiness an experiment was set up using three different groups of rats and two different methods for eruption assessment. One group was used for 'control'. The second group received a potent lathyrogen, while the third group was used as pair-fed+ for the second group. Measurements were made clinically and radiographically. Comparison between the three groups led to the conclusion that the much easier and less expensive method, using the clinical manual measuring method is reliable and may be used in future calculations of eruption rate of rat incisors. It furthermore provides an excellent method to assess the lathyrogenic condition of these animals.

Lathyrogens and the role of collagen in the eruption of rat incisors.

Collagen fibres in the periodontal ligament may have two functions: to resist displacing forces and to cause the tooth to erupt. Their function was examined in the continuously-erupting incisor of the rat using various concentrations and types of lathyrogens. Lathyrogens retarded tooth eruption and increased the quantity of salt-soluble collagen in the ligament, indicating inhibition of the maturation of salt-soluble (young) collagen into salt-insoluble (old) collagen, which would lead to reduction in the tensile strength of the fibres and decrease resistance to occlusal forces. The easy extractability of the teeth is explained by the greater susceptibility to lathyrogens of the fibres in the alveolar-related part of the periodontal ligament, compared with those in the other parts.

Development of cartilage in transplanted future coronal sutures.

From fetal rat skulls, tissue containing the 19-day-old presumptive coronal suture was excised and transplanted onto the exposed dura mater of adult rats. Host animals were sacrificed after 1, 2, 3, 4, 5 and 6 days. From the results of these experiments, the following conclusions can be drawn: (1) in all transplants chondrogenic activity occurred, resulting in the production of ectopic cartilage, and (2) cartilage development only starts on the cerebral side of the transplanted embryonic dura mater just beneath the area of the presumptive suture. Transplanted presumptive sutures of 21-day-old rats do not produce cartilage. The findings suggest that the suture undergoes a process of maturation. The existence of an osteogenesis-inhibiting mechanism, located in embryonic sutural tissue and being transmitted to the developing dura, is discussed.