Stress Distribution Pattern in Roots of Incisors with Various Root Resorptions: A Finite Element Study

Objectives Root resorption is a dangerous side effect in orthodontics, and maxillary incisors are at the highest risk for root resorption. It is important to understand optimal force considerations for patients with altered root lengths.The purpose of this study was to investigate the effects of root length on stress distribution on roots by means of three-dimensional finite element method (FEM).Methods Three dimensional FEM models of maxillary central and lateral incisors were made. Then, root length of the incisors was changed in the increments of 1 mm from 0-4 mm. Applying 50 g (0.5 N) of force perpendicular to the tooth crown simulated uncontrolled tipping. Stresses and strains for each model were calculated and Pearson correlation coefficient was used to analysis the data.Results There were significant correlations between root length of incisors and maximum stress in PDL. In the centrals with various root lengths, maximum stress was between 0.010884 and 0.056520 MPa, and in the laterals, it was between 0.027297 and 0.221040 MPa. By reducing root length of incisors, the maximum stress in buccal apical (r= 0.933,p<0.001 and 0.995, p<0.001 prospectively) and lingual crestal areas (r= 0.974 p=0.005 and 0.992, p=0.001  respectively) were reduced.Conclusion Although in lateral incisors, stress at the lingual crestal area was more than buccal apical area, in central incisors with more than 2 mm resorption, the stress distribution of buccal apical was higher. Therefore, in maxillary central incisors with more root resorption, force control might be even more critical

Efficacy of Different Reminders to Reduce Missed Orthodontic Appointments

Objectives: Since forgetfulness is the major cause of missed appointments, reminder systems can be used prior to appointments. The present study aimed to evaluate the efficacy of different reminders [e-mails, social networks, telephone, and short message service (SMS)] in order to reduce missed appointments by orthodontic patients.Methods: Of a total of 751 active orthodontic patients, 379 were assigned to the reminder group and 372 to the control group. The former group was randomly divided into four subgroups who received a reminder 2 days before their appointments either by telephone, e-mail, SMS, or a message on Facebook. Patients allocated to the control group received no reminder. The percentage of missed appointments and the demographic characteristics of patients in each group were analyzed with the chi-squared test.Results: The percentage of missed appointments was significantly higher in the control group (41.39%) than the reminder group (11.08%) (P<0.001). There was no difference in the attendance rate of patients among telephone, SMS, and e-mail groups. Missed appointments were insignificantly higher in patients whose parents had the highest educational level (P=0.8). In patients with low family income, the percentage of missed appointments was the lowest, but this difference was not statistically significant (P=0.5).Conclusion: The study results indicated that sending reminders is an effective strategy to reduce missed appointments. E-mails and social networks can be employed to send reminders easily and cost-effectively and prevent missed appointments

Evaluation of canonical correlations between masticatory muscle orientation and craniodentofacial morphology in 10-17 year-olds

Objectives Different theories have been suggested to define factors involved in skeletal and craniofacial morphology. Many of these theories explain that the bone morphology is the result of the bone tissue capability to adapt in response to biomechanical forces exerted during growth. Also, it seems logical to hypothesize that there is a relationship between biomechanical connections of muscles to bones with the morphology of musculodentoskeletofacial complex. A few studies have evaluated muscle orientation in different skeletal occlusions (class I, II and III). The aim of this study was to evaluate correlations between masticatory muscle orientation and craniodentofacial morphology in different skeletal malocclusions.Materials and Methods A total of 160 lateral cephalograms of patients between 10–17 years in a dental clinic were evaluated for the orientation of masticatory muscles and craniofacial morphology. All cephalograms were traced and confirmed by an orthodontist. Thirty- seven parameters (skeletal, dental, muscular) were measured. For statistical analysis, canonical correlation, variation and linear regression analysis were performed.Results Increase of the masseter muscle angulation was accompanied by a more superior position of the muscle in female subjects with Class II malocclusion. Increase of temporalis muscle angulation was seen in long face males. Increase of the masseter muscle angulation and its higher position were seen in short face males.Conclusion Increase of the masseter muscle angulation was accompanied by a more superior position of the muscle in female patients with class II properties. Increase of temporalis muscle angulation was seen in male patients with long face characteristics. Increase of the masseter muscle angulation and its higher position were seen in male patients with short face properties

Evaluation of Histological Impacts of Three Types of Orthodontic Fixed Retainers on Periodontium of Rabbits

Statement of the Problem: Fixed retainers were developed to maintain incisor alignments after orthodontic treatments. Although the effects of fixed retainers on periodontal health are clinically studied, no studies have still evaluated the histological changes in the periodontium after the placement of thefixed retainers. Purpose: The aim of this study was to evaluate the effects of customised retainers on periodontium histologically. Materials and Method: Forty pairs of maxillary and mandibular central incisors of twenty rabbits were randomly divided into four equal groups: The first group was considered as the control and in the second group, Fiber Reinforced Composite (FRC), in the third group, 0.014 inch stainless steel (SS) wire and in the fourth group, 0.175 inch multistrand stainless steel (MSS) wire were bonded on the labial surfaces of the incisors. After sixty days; animals' periodontium were evaluated histologically. Results: The number of bone resorption lacuna in the control group was significantly less than FRC and 0.014 SS groups. The periodontal vessel count and their diameter in the control group was significantly lower than the other groups. The pulp vessel count and their diameter in controls were significantly more than the 0.014 SS and the 0.175 MSS groups. Conclusion: Findings of this study suggest that FRC fixed retainer might cause detrimental effects on the periodontal ligaments and supporting bone and the 0.014- inch and 0.175- inch fixed retainers can cause hyalinization and possibly the necrosis of the pulp

Evaluation of Histological Impacts of Three Types of Orthodontic Fixed Retainers on Periodontium of Rabbits

ABSTRACT Statement of the Problem: Fixed retainers were developed to maintain incisor alignments after orthodontic treatments. Although the effects of fixed retainers on periodontal health are clinically studied, no studies have still evaluated the histological changes in the periodontium after the placement of thefixed retainers. Purpose: The aim of this study was to evaluate the effects of customised retainers on periodontium histologically. Materials and Method: Forty pairs of maxillary and mandibular central incisors of twenty rabbits were randomly divided into four equal groups: The first group was considered as the control and in the second group, Fiber Reinforced Composite (FRC), in the third group, 0.014 inch stainless steel (SS) wire and in the fourth group, 0.175 inch multistrand stainless steel (MSS) wire were bonded on the labial surfaces of the incisors. After sixty days; animals' periodontium were evaluated histologically. Results: The number of bone resorption lacuna in the control group was significantly less than FRC and 0.014 SS groups. The periodontal vessel count and their diameter in the control group was significantly lower than the other groups. The pulp vessel count and their diameter in controls were significantly more than the 0.014 SS and the 0.175 MSS groups. Conclusion: Findings of this study suggest that FRC fixed retainer might cause detrimental effects on the periodontal ligaments and supporting bone and the 0.014-inch and 0.175-inch fixed retainers can cause hyalinization and possibly the necrosis of the pulp

Relationship of third molar movement during orthodontic treatment and root angulation

Background: Curved roots of teeth might cause difficulty in root canal treatment and removal. Beside genetic factors, root morphology of the third molars is affected by environmental factors such as mesial migration. However no studies examine the relation between the amount of third molars′ movement and their root angles. The purpose of this study was to evaluate the relation between the amount of third molar movement during orthodontic treatment and the angulation of third molar roots. Materials and Methods: The records of 39 patients who had apical closure after orthodontic treatment were evaluated. Root curvature was measured on panoramics using the angle between an occlusal reference line and central line of the most apical ninth of the root. The amount of tooth movement of third molars was measured on the pre- and post- treatment lateral cephalometric radiographs by measuring tooth distance from a perpendicular line. Pearson correlation analysis was preformed to obtain relation of the amount of third molar′s movement and its root angulation. Results: In maxillary arch the correlation between tooth movement and root angulation was positive and not significant relation but in mandibular arch this relation was negative and not significant. ( P > 0.05) Conclusion: The relation between the amount of third molar movement and its root angulation was not statistically significant. Therefore movement of third molars during orthodontic treatment should not be assumed as an etiologic factor of root angulations

Esthetic effect of the buccal corridor size and amount of tooth-gingival display on smile attractiveness in two student population

3- Dentist   Background and Aims: An attractive, well-balanced smile is a paramount treatment objective of the modern orthodontic therapy. The purpose of this study was to determine the effects of the buccal corridor size and tooth-gingival display on the smile esthetics as perceived by two groups of the students.   Materials and Methods: A colored image of a woman frontal posed smile was selected. The image was altered digitally to produce different buccal corridor sizes (6%, 12.5% and 20%) and different tooth-gingival displays (maxillary central incisors and 2 mm of gingival, maxillary central incisors and dental papilla and 80% of the maxillary central incisors). The different buccal corridor sizes and tooth-gingival displays were combined to produce 9 images. These altered images were rated by 120 medical and dental students using Visual Analogue Scale (VAS). Data were analyzed using Mann-Whitney test, Pairwise comparison LSD test, Repeated measure MANOVA and ICC (Intraclass Correlation Coefficient).   Results: The smile which had the buccal corridor size of 12.5% and complete incisor display without gingival display received the highest rates among the nine smile images in the dental students group. But in the medical students group the smile with the buccal corridor size of 12.5% and 2 mm gingival display, received the highest rates among the nine smile images. There was no significant difference in judging between the male and female raters for the both groups (P>0.05). The dental students were more critical about the increasing of the gingival display.   Conclusion: In the treatment procedure that may lead to the combination of wide buccal corridor and more tooth-gingival show, more caution should be considered

<i>In vitro </i> evaluation of force-expansion characteristics in a newly designed orthodontic expansion screw compared to conventional screws

<b>Objective</b> : Expansion screws like Hyrax, Haas and other types, produce heavy interrupted forces which are unfavorable for dental movement and could be harmful to the tooth and periodontium. The other disadvantage of these screws is the need for patient cooperation for their regular activation. The purpose of this study was to design a screw and compare its force- expansion curve with other types. Materials and <b> Methods</b> : A new screw was designed and fabricated in the same dimension, with conventional types, with the ability of 8 mm expansion (Free wire length: 12 mm, initial compression: 4.5 mm, spring wire diameter: 0.4 mm, spring diameter: 3 mm, number of the coils: n0 ine, material: s0 tainless steel). In this in vitro study, the new screw was placed in an acrylic orthodontic appliance, and after mounting on a stone cast, the force-expansion curve was evaluated by a compression test machine and compared to other screws. <b> Results</b> : Force-expansion curve of designed screw had a flatter inclination compared to other screws. Generally it produced a light continuous force (two to 3.5 pounds) for every 4 mm of expansion. <b>Conclusion</b> : In comparison with heavy and interrupted forces of other screws, the newly designed screw created light and continuous forces

Problem Based Learning: An Experience of a New Educational Method in Dentistry

Introduction: Considering the necessity of dentistry students' involvement in learning treatment topics and, in order to achieve deeper learning, this study was performed to evaluate problem based learning method and compare it to traditional method of teaching orthodontics to dentistry students. Methods: This interventional study was performed on 64, fifth year dentistry students in 2007-2008 academic years. After selection and orientation of tutors, a trainer helped them to adjust to the new method. After orientation of students about PBL method, the groups were identified and the PBL method was performed in four steps. A pretest was taken from students to assess their attitude and satisfaction about traditional method of lecture. Then, A post-test evaluated their attitude toward and satisfaction with the new method. The domains of this method were assessed by 5 point Likert scale. Results were analyzed by SPSS software using descriptive and inferential statistics. Results: The average of achieved scores out of the total score of five was as so in areas of material organization (main subjects) (3.41±0.75), internal motivation (3.41±0.7), assignments appropriateness (3.38±0.53), and suitability of evaluation method (3.67±1.17). The mean of satisfaction score was 14 out of the total score of 20 which demonstrates agreement higher than average. Conclusion: By promoting learner's internal motivation, enhancing the quality of education, and, increasing continuous learning, PBL method could prove useful in teaching dentistry students

Which method of teaching would be better cooperative or lecture?

Introduction: Most of the knowledge acquired through lecturing is forgotten rapidly. As dentistry is becoming a more complicated field of study and as new techniques are introduced, the use of modern educational approaches to promote lifelong learning becomes necessary. This study is to compare cooperative teaching method and lecture method in terms of their impact on students' learning and their satisfaction in school of dentistry in Shiraz University of Medical Sciences. Methods: In this quasi experimental study sampling was census and all 9th semester students (60 students) taking theoretical orthodontics(I) were included. One topic, etiology of mandibular abnormalities, was taught to both randomly selected experiment & control groups. First, to assess knowledge & satisfaction of the students with lecture methods for etiology, a pre-test was applied. Then both groups were taught the control group received instruction through lecture method and the experiment group formed 5-member subgroups and received instruction through cooperation. Then, both groups took a post-test. Data were analyzed through Wilcoxon and Mann-Whitney U using SPSS 12. Results: A significant difference was found between the mean scores of the students' satisfaction before and after applying the cooperative method. Also, there was a significant difference between the pre–test scores in the lecture group and the cooperative group (p<0.001), but no significant difference was observed between post-test scores of the two groups (P=0.1). Conclusion: The study showed that cooperative teaching method could be useful in teaching dentistry students and could enhance their intrinsic motivation, which in turn could improve learning quality