[Evaluation of induced stress in PDL of anterior maxillary teeth by applying intrusive forces distal to the maxillary canine]

One of the precise methods for evaluating periodontal responses to orthodontic forces is finite element method. The aim of this study was to evaluate induced stresses in PDL of anterior teeth by application of intrusive forces distal to the canine. Solid works software was used to translate bidimentional images of the maxillary teeth [central, lateral, canine] into tridimentional images. PDL and alveolar bone around teeth were simulated and anterior teeth were positioned in an ideal arch with appropriate tip and torque, and rectangular wire was stablished rigidly on labial surfaces of the teeth. Models were modified to "Finite element model" by means of MSC-NASTRAN. Intrusive forces [35 gr] were applied on anterior wire distal to the canine and induced stresses were analyzed by means of MSC-PATRAN. By delivery of intrusive forces between the lateral and canine teeth, the maximum stress was concentrated in PDL of canine [8.38 x 10[-3] N/mm2] and the minimum stress was in PDL of central [7.6 x 10[-6] N/mm2]. Application of intrusive forces on the distal of canine teeth lead to un homogenous stress distribution in anterior area due to intrusive and unintended labiodistal movement. Therefore distal of canine is not an appropriate point for intrusive forces application

[ comparative study between treatment outcomes of class I cases treated by Begg and Edgewise orthodontic systems]

Today there are two common and different systems available for orthodontic treatments: Begg and Edgewise techniques. Occlusal indices have the greatest reliability for comparing treatment outcomes, so in this study we used Peer Assessment Rating index for comparison of treatment outcomes of these two systems. Peer Assessment Rating index evaluates buccal occlusion [Antero-posterior, vertical and transverse], overjet, overbite and midline by scoring them. The purpose of this study which has been conducted for the first time, was to compare occlusal PAR index in class I patients treated by means of Begg and Edgewise methods. In this cross sectional study, 120 pre-treatment models of 60 class I patients were evaluated by Peer Assessment Rating index. [30 class I patients with Begg method and 30 class I patients treated with edgewise method were selected randomly from two separate private clinics]. Pre-treatment PAR indices in both groups were comparable. Changes in PAR index after treatment was compared between the two groups. Result were analyzed by general linear model and mANOVA. Sex and age distribution between the two groups were matching. Using PAR index, only improvement in buccal occlusion in Begg group was more significant than edgewise group. Considering total PAR index, no significant difference was obtained between the two groups, although duration of treatment in Begg method was significantly shorter than Edgewise. Occlusal outcomes [total PAR index] were similar in Begg and Edgewise methods. Treatment results by Begg method accomplished in shorter duration than Edgewise treatment

[ comparative study between pattern of eruption of second molars in class II and class III malocclusion with class I]

In many of orthodontic treatments of patients with jaw discrepancies it is important to understand more about the pattern of growth and eruption of teeth. The aim of this study was to compare the pattern of eruption of upper and lower second molars in class I, II and III malocclusions to select the best time and treatment mechanics. 192 panoramic radiographs from 45 class I, 97 class II and 50 class III orthodontic patients in the range of 11-12 years were selected. They were classified dentally by Angle's classification and skeletally by cephalometric analysis. Eruption stage of second molars was determined by Nolla's method and compared statistically X2 Pearson and Fisher exact test. There was no significant difference between different malocclusions and sexes in pattern of eruption and percentage root formation of upper and lower second molars. The only significant difference was seen in girls with class II malocclusion, in which maxillary second molars were in the lower stages of eruption comparing with mandibulars [P=0.024]. No significant difference was seen between right and left molars. In both sexes upper and lower second molars were in equal distances to the occlusal plane. There was no significant difference between different malocclusion and sexes in eruption stage of upper and lower second molars. o There was significant difference between different malocclusions and sexes in percentage of root formation of upper and lower second molars. o Exceptionally girls in with class II malocclusion, percentage of root formation in lower second molars was higher then upper second molars. o In both sexes and all types of malocclusions the distance of upper second molars to occlusal plane was more than lowers

effect of chemical recycling on shear bond strength of orthodontic metal brackets

Recycling of brackets can significantly reduce the price of fixed orthodontic appliances but if the bond is more prone to failure during treatment, this potential benefit will disappear. The aim of this study was to investigate the effect of chemical recycling on bond strength of metal orthodontic brackets and failure pattern of recycled brackets. In this experimental study Instron machine was used to measure shear bond strength [SBS] of brackets in two stages on 60 human maxillary first premolars using No-Mix composite. Shear bond strength and pattern of failure were compared between recycled and new brackets in two stages. Data were analyzed by ANOVA and Duncan tests. Adhesive Remnant Index was evaluated in different groups by Pearson Chi-square test. P<0.05 was considered as the limit of significance. Statistical analysis showed that the mean values of SBS for new bracket group was 12.00 MPa and for recycled group and double recycled group, 9.94 Mpa and 10.00 MPa respectively. A significant reduction [about 18%] in bond strengths of brackets was observed at the first time of recycling. Recycling at the second time had no significant influence on the bond strength. Pattern of bond failure of these brackets showed that a great amount of residual adhesive material was remained on the teeth surfaces after debonding of recycled brackets which indicates that cleaning the teeth surfaces after debonding of recycled brackets is more time consuming. Based on the results of this study, before using recycled brackets, several advantages and disadvantages must be considered

[Stress analysis of anterior maxillary teeth by applying intrusive forces between lateral and canine]

One of the precise methods for evaluating periodontal responses to orthodontic forces is finite element method [FEM]. In the following study PDL of anterior maxillary teeth [central, lateral, canine] has been analysed by FEM after applying intrusive forces. The Aim of this study was to evaluate induced stresses in PDL of anterior teeth by application of intrusive forces between lateral incisore and canine. Solid works software was used to translate bidimentional images of the maxillary anterior teeth [central, lateral, canine] into three dimentional images. PDL and alveolar bone around these teeth were simulated and anterior teeth were positioned in an ideal arch with appropriate tip and torque, and rectangular wire was established rigidly on labial surfaces of the teeth. Models were modified to [Finite element model] by means of MSC-NASTRAN software. Intrusive forces [35 gr] were applied on the wire between lateral and canine and induced stresses was analyzed by means of MSC-PATRAN. By delivery of intrusive forces between lateral and canine, maximum stresses were found in PDL of lateral incisor [4.23×10[-3] N/mm[2]] and minimum stresses were observed in PDL of central incisor [2.02×10[-6] N/mm[2]]. By application of intrusive forces between latral incisor and canine, maximum stresses were focused at the apex of lateral incisor and minimum stresses were in appical third of central's root

investigation on stress distribution of the anterior maxillary teeth PDL during the application of intrusive forces in midline

Finite element method is one of the highly precise methods to evaluate periodontal responses to orthodontic forces. The goal of the present study was to investigate the PDL response of anterior maxillary teeth [central, lateral, canine] during the application of intrusive forces using FEM. Solid works software was used to translate bidimensional images of the mentioned maxillary teeth into tridimensional ones. Then, PDL and alveolar bone were simulated around teeth and anterior teeth were positioned in an ideal arch with appropriate tip and torque and rectangular wire was placed rigidly on labial surfaces of teeth. These models were then modified to "Finite element model" by MSC-NASTRAN software. Intrusive forces were applied mesially on the anterior wire and induced stresses were analyzed by MSC-PATRAN. The maximum stress was observed in the PDL of lateral incisors [2.53x10[-3] N/mm[2]] and the minimum stress was in the PDL of canines [9.07.x10[-5] N/mm[2]]. Applying the intrusive forces in midline maximum stresses were focused on the apical part of lateral incisor and the minimum stresses were in the apically third of canine

comparative study between bond strength of rebonded and recycled orthodontic brackets

A large number of orthodontists prefer to rebond the failed bonded brackets or use recycled brackets in some instances. The aim of this study was to compare the shear bond strength of rebonding with using recycled brackets on enamel surface. Bonding of brackets on the surface of extracted first bicuspids was tested in five different groups to compare their shear bond strength [SBS]: Group N, new bracket on enamel surface of newly extracted teeth as a control group; Group R, recycled bracket on newly extracted teeth; Group NR, new bracket on the cleaned enamel surface of previously bonded teeth with Tungsten Carbide bur; Group RE, reused bracket on cleaned surface of previous teeth; and RR group, with brackets undergone two times of recycling on the newly extracted bicuspids. Adhesive Remnant Index was specified for each group. Twenty teeth were studied in each group. The highest SBS was related to control group [group N] which rated as 12.00 Mpa, and the next scores were related to groups NR, RE, RR, and R with 11.85, 10.80, 10.00 and 9.94 Mpa, respectively. The differences between groups N and NR with groups R and RR were significant [P<0.05]. Rebonding had no significant effect on reduction of SBS. Tungsten Carbide burs are suitable for removing of remaining composite from brackets and enamel surface and finally, chemically recycled brackets had a clinically acceptable SBS