مهدی عرق بیدی کاشانی

Elastomeric chains are known as a current device with the purpose of dental movement in orthodontic treatments. The aim of this study was to compare the elastomeric behavior and force degradation rate between different elastomeric chains existing in Iran in different time durations.

11 different elastomeric chains used in this study were: Class One, ASTAR, G&H, TSNPT, MIB (French and Chinese type), Ultra Chain and both American, Ortho Technology (simple and memory type). All chains were stretched upon to exert 150 g force and then force degradation rate in 6 time duration (1, 3, 24 hours and 3, 7, 21 days) and modulus of elasticity (MOE) in 2 time duration (start and 21 days) were investigated. All Data were analyzed statistically by ANOVA, Tukey, Games-Howel tests.

All chains up to the 21th day showed a significant decrease in MOE except for the G&H, ClassOne, simple orthotechnology and a significant force degradation except for the American (memory type). The most significant force degradation rate was in ASTAR gray (P<0.05) and the least in MIB (French), Ultra Chain, and American (P<0.05).

All chains showed significant time-dependent force degradation (mostly in the first day). Only, this rate was not significant in any time duration for the American (memory). In all groups, the most force degradation rate belonged to ASTAR gray and the least to Ultra Chain, MIB (French) and American after 21th day.

Extraction of the upper first premolars and mesial movement of molars result in mandibular counterclockwise rotation and reduced facial vertical dimension. On the other hand, molar extrusion during the orthodontic treatment changes facial vertical dimension. Therefore, it is possible to avoid vertical changes of the face by maintaining the vertical position of posterior teeth. This study was designed to evaluate changes in the vertical dimension of the face in class II div I patients treated by extraction of the upper first premolars. This cross-sectional study was conducted on 20 patients, with a mean age of 17.8 years, who were selected from a private office. The subjects had class II malocclusion and normal vertical growth. To decreasing the effect of growth on the results, we selected subjects >15 years of age. As a part of their orthodontic treatment their upper first premolars had been extracted. The lateral cephalometric radiographs of the patients were digitized. Image analyses were conducted using View box 3.1.1 software program and data was analyzed with SPSS 20. Paired t-test was used to compare each variable before and after treatment (α = 0.05). In this study, there was no statically significant differences in skeletal variables. However, dental variables of U1-NA (mm), U1-NA, U1-FH, and overjet exhibited significant decreases (p value < 0.05). There was no significant differences in lower incisor variables. U6-palatal P, interincisal angle, U 1-palatal P exhibited significant increases. The results of this trial showed that treatment of class II div I through extraction of upper first premolars results in molar extrusion and in a decrease in upper incisor protrusion with no changes in the facial vertical dimension.

Stability of mini screws depends on mechanical factors in the primary phase and biological factors after osseointegration. The mini screws can transfer thermal shocks in the oral cavity to the bone marrow. It has been shown that level of osseointegration and inflammation are related to the failure of mini screws. The aim of this study was to compare the tissue response to mini screws with and without composite coating in the head.
In this in vitro, experimental study, mini screws with 1.4mm diameter and 6mm length were implanted in the maxilla of 12 male rabbits. One mini screw was implanted in each of the right and left quadrants of the maxilla. The right side mini screws had composite coatings on their head. The left side mini screws did not have such coatings. In the next three months, cold (1C) and warm water (40C) were injected into their mouth, 10 times daily. After three months, the rabbits were sacrificed and paraffinized tissue blocks were prepared. The tissue reaction was examined under light microscopy. The paired t-test and Wilcoxon Signed Rank test were used for statistical analysis.
The mean rate of osseointegration of mini screws with and without composite coatings was 32.1±5.3 and 20.4±3.43, respectively. The rate of osseointegration was significantly higher for mini screws with composite coatings than mini screws without them (P>0.0001). In both groups, the newly formed bone was woven and no inflammatory reaction was noted.
The rate of osseointegration of mini screws with composite coatings in the head was higher than that of miniscrews without them.

The aim of this descriptive longitudinal study was to determine the type of teeth that were more prone in accidental bracket debonding and also to investigate the relationship between broken bracket bond and intervening factors such as age, type of malocclusion and sex. We used a pilot study to determine the correct sample size for this study. According to the pilot study which consisted of 20 records of patients, it was concluded that 576 patient’ records was needed. The mean time for a bracket before it fails was also measured using Kaplan-Meier method. Cox regression analysis was done to examine the effect of age, gender, and class of malocclusion on each tooth with broken bracket. Data were analyzed using the software SPSS 20. Results showed that the percentage of unexpected broken bracket bond for each tooth varied and they were significantly related only in second premolars in both jaws with malocclusion that was different for each tooth (P=0.037, P=0.004). Maxillary second premolars and mandibular second premolars had the highest rate of unexpected broken bracket bond in CL II CL I malocclusion respectively. Age, gender and malocclusion had no effect on the unexpected broken bracket bond for other teeth.

Fluoride releasing adhesives are favorable for bracket bonding since they decrease the risk of demineralization around orthodontic brackets given that they provide acceptably high shear bond strength (SBS). The aim of this study was to evaluate the SBS of resin-modified glass ionomer cements (RMGIC) reinforced by nano-zinc oxide (NZnO) and nano-hydroxyapatite (NHA) particles in comparison with composite resins. In this experimental study, 80 extracted human premolars were used. The teeth were randomly divided into 4 groups as follows: Group 1: Transbond XT as the control group, Group 2: RMGIC (Fuji II LC), Group 3: RMGIC with 5% NHA and Group 4: RMGIC with 2% NZnO. After enamel etching, brackets were bonded. The SBS was calculated for each group. The percentage of adhesive remained on the enamel was quantified by calculating the adhesive remnant index (ARI). The data were analyzed using one-way ANOVA and the Kruskal Wallis test. According to the results of ANOVA, there were no significant differences in SBS of groups (P=0.075). The mean SBS in groups 1 to 4 was 15.43 ± 4.61, 14.95 ± 4.34, 17.97 ± 3.65 and 17.08 ± 3.59 MPa, respectively. According to the Kruskal-Wallis test, there were no significant differences in degree of ARI among groups (P=0.413). The SBS was similar among all groups and adding NZnO and NHA particles had no negative effect on SBS of RMGIC. In all groups, less than half the adhesive remained on the enamel after bond failure.