Abstract

No Abstract Available.

Abstract

No Abstract Available.

Abstract

No Abstract Available.

Abstract

No Abstract Available.

Abstract

No Abstract Available.

Abstract

No Abstract Available.

Abstract

No Abstract Available.

Abstract

No Abstract Available.

Abstract

When the long span of wire in a 2×4 orthodontic appliance enters a bracket in a nonparallel manner, it develops a couple and tendency for rotation called a moment. The moment of a couple creates inherent equal and opposite Newtonian equilibrium forces not readily sensed clinically. Moments at successive brackets, producing rotations in opposite directions, create equilibrium forces also in opposite directions which are subtractive from each other. When these equilibrium forces are equal and opposite, they cancel each other out. If the moments produce rotations in the same direction, the equilibrium forces are also in the same direction and are additive. The apparent simplicity of the 2×4 appliance conceals the fact that it is a powerful orthodontic tool that uses engineering mechanics in a way not possible with fully bracketed appliances. Clearly the application of engineering mechanics is a distinguishing characteristic of modern orthodontics.

Abstract

The purpose of this study was to compare the effectiveness of a 1100 ppm fluoride toothpaste used alone, or together with a 0.05% NaF rinse used once daily or a 0.4% SnF₂ gel applied twice daily, in controlling the decalcification that often accompanies orthodontic treatment. Ninety-five consecutively treated adolescent patients were matched for age and sex and assigned to one of these three regimens. Single blind assessments of decalcification were performed on all labial surfaces of all erupted teeth before appliances were placed and 3 months after appliances were removed. Because the first molars had the highest decalcification scores, data for the whole mouth and for first molars were analyzed separately.

When pre-treatment levels of decalcification were subtracted from post-treatment values, significantly lower decalcification scores (p < 0.05) were found for both whole mouth and first molars in the rinse and gel groups as compared with the control group (toothpaste alone). Although the gel group consistently had less decalcification than the rinse group, this difference only approached statistical significance. These results indicate that twice daily use of a 1100 ppm fluoride toothpaste and either a once-daily 0.05% NaF rinse or a twice-daily 0.4% SnF₂ gel provides additional protection against decalcification beyond that achieved with toothpaste alone.

Abstract

Oligodontia is defined as the congenital absence of many teeth. The aim of the present study was to evaluate tooth formation in patients with oligodontia who were missing six or more teeth. The oligodontia sample was compared to a control group matched for race, sex and age. Calcification stages of the teeth of the left side of the mandible were rated.

Patients with oligodontia showed a tendency for delayed tooth formation. Significant differences in tooth formation were found between males with oligodontia and the control group for several stages of tooth formation. In females only stage 5 of the second mandibular molar showed a significant difference. Because of the great individual variation in tooth formation in patients with oligodontia, tooth formation in patients with oligodontia should be individually examined before starting treatment.

Abstract

To overcome the problem of variation of reference points in cephalometric analysis two methods have been used: 1) fixed relations between consistently recognizable anatomical points and 2) centers of gravity.

The linear distance between each point and every other point was calculated from their coordinates measured on radiographs of 60 fetuses (49–212 mm crown-rump length).

For each distance between every permutation of points the variance was calculated for the series of 60 fetuses. The sum of the variances for each individual point against all other points was added together and the mean variance for each point derived by dividing by the total number of points.

On the basis of mean variance the centroid of the total skull outline showed least variation and was therefore the most stable point measured. This was closely followed by the origin of the coordinate reference grid based on fixed relations theory. All the centroid points showed less variation than the anatomical points upon which the origin of the grid was based.

Abstract

No Abstract Available.

Abstract

The purpose of this investigation is to re-evaluate an existing sample of Caucasian individuals, of mostly Northern European ancestry and undefined ethnic origins, who have been characterized as having excellent occlusions and balanced facial proportions (from a subjective assesment). The focus is the emergence of sexual dimorphism in the skeletal and dental relationships. Serial lateral cephalograms of 51 subjects were obtained from the Bolton-Brush Study at ages 6, 9, 12, 14, 16 and 18 yrs. At each age, the records of 16 males and 16 females were selected. Cephalometric evaluation indicated that the length of the anterior cranial base was larger in males but the cranial base angle was similar for both sexes at all age intervals studied. The effective lengths of the maxilla and mandible were similar in both sexes up to 14 years; thereafter in females this length remained relatively constant while in males it increased. The direction of facial growth was similar for both sexes, with a tendency towards a more horizontal growth pattern in females.

Abstract

Assessment of malocclusion is important for documentation of the prevalence and severity of malocclusion in population groups. Such information is needed in Hong Kong where less than 25 qualified orthodontists serve a population of about 6 million citizens.

The objective of the present study was to compare the Occlusal Index (OI) and the Index of Orthodontic Treatment Need (IOTN) when used to assess orthodontic treatment needs in a local population. Only a weak association (Spearman's correlation coefficient = 0.31) was found between the two indices. The shortcomings of both indices are discussed. Neither OI nor the IOTN is perfect, but using the IOTN is less time consuming, making the study of a large population group more practical.

Abstract

No Abstract Available.

Abstract

A study of nickel-titanium springs was undertaken to determine whether their mechanical properties are affected by prolonged exposure to a static, simulated oral environment. Stainless steel springs and polyurethane elastic chains were also studied for comparison. The springs were elongated to twice their rest length and held at that length while immersed in artificial saliva at body temperature for 0, 2, 4 or 6 weeks. Plots of force vs. deformation were made as the springs were stretched from rest length to three times that length and then relaxed back to rest. Nickel-titanium springs suffered no degradation of their spring properties in the simulated oral environment. In contrast, stainless steel springs became slightly more compliant to stretching, and polyurethane elastics lost a large portion of their force-generating capacity. These findings confirm and extend earlier reports which indicate that nickel-titanium is a preferred material for many orthodontic applications.

Abstract

The application of laser irradiation to etch dental enamel in preparation for direct bonding of orthodontic appliances has been studied. Forty extracted human teeth were divided into four groups of 10 teeth. Within each group, five teeth were subjected to a 30 sec acid etch of the buccal enamel surface; the other five in each group were etched with a laser. Four power settings on the laser etching unit were used: 80mJ, 1W, 2W and 3W. After etching, brackets were adhered to the prepared buccal enamel surfaces with composite resin. Shear bond strength was tested 7 days later.

The findings showed that an acceptable shear bond strength, viz. ≥0.6kg/mm, could be achieved at laser power settings of 1 to 3W but not at the lowest setting (80 mJ). However, the mean shear bond strengths obtained with laser treatment of the enamel at 80mJ, 1W and 2W were lower (p<0.01 or 0.001) than that achieved with acid etching.

Abstract

No Abstract Available.

Abstract

No Abstract Available.