JOURNAL OF DENTISTRY (SHIRAZ UNIVERSITY OF MEDICAL SCIENCES)
Year:2009 | Volume:9 | Issue:4 (21)|Papers Count:14

Statement of problem: The application of elastomeric ligatures is one of the methods of archwires ligation to orthodontic brackets. Knowledge about modulus of elasticity of these ligatures is useful for selecting a specific brand of elastomeric ligature for a special condition.Purpose: The purpose of this study was to compare elastic modulus of seven commercially available elastomeric ligatures in the initial condition and after 28 days immersion in a simulated oral environment. Changes in the modulus of elasticity were also surveyed for each brand of ligatures after 28 days.Materials and Method: 'In this experimental laboratory-based study, elastomeric ligatures were obtained from different companies and their modulus of elasticity were measured in the initial condition and after 28 days immersion in a simulated oral environment using Zwick testing machine at 5mm/mm cross head speed. The data were analyzed using SPSS software and ANOVA, Duncan and student's t-test.Results: Different brands of elastomeric ligatures showed significant differences in elastic modulus both in the as-received condition and after 28 days immersion in the simulated oral environment (p<0.05). Ligatures from American Orthodontics and Ortho Technology showed the lowest and ligatures from Dentaurum revealed the highest elastic modulus in the as-received condition. Modulus of elasticity in the ligatures from American Orthodontics, Ortho Technology and ITO increased significantly while in ligatures from Dentaurum it was decreased significantly after 28 days immersion in the simulated oral environment (p<0.05).Conclusion: Ligatures from American Orthodontics and Ortho Technology are suitable for immediate use after bonding and in sliding mechanics while ligatures from Dentaurum are not suitable to use immediately after bonding.

Statement of problem: Self etch acidic primers may be unable to etch the enamel and penetrate the thick dentinal smear layer and as a result produce inadequate bond strength.Purpose: The present study aimed to evaluate the effect of the second layer application of two self-etch primers on etching pattern and micro-shear bond strength to the enamel and dentin.Materials and Method: In an experimental study, 104 human premolar teeth were divided into two groups. The buccal surfaces of the teeth were prepared for enamel and dentinal evaluation. Self-etch primer of clearfil SE Bond and clearfil S3 Bond were applied in one or two layers on the prepared enamel and dentin surfaces. One specimen of each prepared group was selected for SEM group evaluation. The composite resin cylinders were bonded to the rest of the specimens for micro-shear bond strength measurement. The data were analyzed using two- way ANOVA and HSD -Turkey's tests.Results: Application of the second layer had no significant effect on micro-shear bond strength to the enamel and dentin (p>0.05). The dentinal micro- shear bond strength values of the specimens treated by Clearfil SE Bond, were significantly higher compared to Clearfil S3 Bond (p<0.05) but no significant effect was found on enamel bond strength (p>0.05).Conclusion: Application of one layer of self- etch primer produced sufficient bond strength and there is no need to apply the second layer.

Statement of Problem: There is limited information available regarding the adhesive ability of resin- modified glass ionomers and polyacid resin modified composites to primary dentin.Purpose: The aim of this study was to compare the shear bond strength of compoglass with and without phosphoric acid %37 with a resin- modified glass ionomer (Fuji II LC) to primary molars' dentin.Materials and Method: In this experimental study, 30 human extracted primary molars were used in this experimental study. The teeth were mounted in stone. After preparation, the specimens were randomly divided into three equal groups (n=10). In group I, the specimens were bonded with compoglass following the manufacturer’s instructions. In group II, after the specimens were etched with phosphoric acid %37, they were bonded with compoglass. In group III, the specimens were bonded with glass ionomer (Fuji II LC). Shear bond strength was measured for the bonded specimens using an Instron at a crosshead speed of 1mm/minute. The results were analyzed using ANOVA and Tamhane test.Results: The mean value of shear bond strength of compoglass with and without acid was 14.19±2.47, and 10.20±2.58 Mpa, respectively. The mean value of shear bond strength of Fuji II LC was 6.11±1.12 Mpa. There were significant differences between compoglass with and without phosphoric acid and glass ionomer Fuji II LC (p=0.001).Conclusion: The findings showed that compoglass tested in this study had higher shear bond strength than glass ionomer (Fuji II LC). Also, the use of acid phosphoric before bonding in compoglass improved the shear bond strength.

Statement of problem: Recurrent aphthous ulcers (RAU) are one of the most common ulcers in the oral cavity.Several studies have shown conflicting variations for inflammatory cytokines and other biologic markers in recurrent aphthous ulcers.Purpose: The aim of the present study was to determine the level of IL-S and IL-6 in the serum of patients with recurrent aphthous ulcers.Materials and Method: In this case- control study, the serum levels of IL-S and lL-6 were measured in patients with recurrent aphthous ulcers (n=40) and in healthy control subjects (n=40). The cytokines levels were measured in the serum by ELISA. The data were analyzed with SPSS software using T- test.Results: The mean value of the IL-S and IL-6 in the patient group was 52.24 pg/ml and 9.39 pg/ml which were 10 and 4 times higher than that of the control group, respectively. The differences were statistically significant (p<0.01).Conclusion: The results of the present study showed that the serum levels of IL-S and lL-6 were elevated in the patient group, IL-S level being more considerable.

Statement of problem: The accuracy and dimensional stability of dental impression materials and technique is an important factor in the accuracy and fitness of the final restoration. Condensation- reaction polysilicone impression material has adequate accuracy and is the most commonly used material in fixed prosthodontic restorations with putty- wash technique. There are different considerations and controversies in the literature about the effect of impression technique on the accuracy of restoration.Purpose: The aim of this study was to compare the accuracy and dimensional stability of two polysiloxane putty- wash impression techniques with and without spacer.Materials and Method: A laboratory model with two metallic dies was used. In one of the dies a horizontal notch was applied as an undercut. Ten impressions were made without spacer and another ten with spacer.Twenty stone models were made from both techniques. Dimensions of the stone models were measured and comparison was made with the laboratory model dimensions. The results were analyzed using T- test.Results: The results showed that the height of the dies without undercut was decreased in both groups, being significant in non- spacer technique (p<0.001). The distance between the two dies increased in both techniques. The difference was significant in technique without spacer (p<0.002). The height of the dies above the undercut increased and in both techniques they proved to be statistically significant (without spacer p<0.003 and with spacer p<0.001).Conclusion: The polysiloxane putty- wash impression technique with spacer is more accurate for fabricating the stone die.

Statement of the problem: New techniques have recently been employed to reduce the time used for clinical procedures and multi-step polishing systems have been replaced by one-step systems.Purpose: Determination of the effect of multi-step and one-step polishing systems on microhybrid and nanofilled composites and ceramic restorations.Materials and Method: Point-4 and Premise composites and Colorlogic porcelain were selected for this study. 33 specimens of each material were prepared. Composite specimens were cured with LED-Starlight. Porcelain specimens were prepared according to the manufacture's instruction. All the specimens were roughened with 25 mm diamonds and then polished with Enhance (3 steps), Super-Snap (4 steps) and One-Gloss (1 step) polishing systems. Roughness was measured with Taylor-Hobson-Surtronic profilometer. The data was analyzed with one-way ANOVA and Duncan's tests.Results: Mean surface roughness of cured or glazed surfaces, roughened surfaces, surfaces polished with Enhance, Super-Snap and One-Gloss were 0.39, 2.49, 0.54, 0.44 and 0.45mm for Point-4 and 0.31, 2, 0.42, 0.38, 0.39mm for Premise and 1.19, 1.38, 0.65, 0.64, 0.57mm for Colorlogic, respectively. The difference of surface roughness between roughened subgroups and other subgroups in the composite group was significant. Also, glazed and roughened porcelain specimens were significantly different. Differences between glazed porcelain, cured composites and roughened surfaces of the three materials were significant. The specimens polished with Enhance had a significant difference (P<0.05).Conclusion: Multi-step polishing systems can be replaced by one-step systems for polishing of composite and porcelain restorations.

Statement of Problem: The risk of the enamel damage increases if the debonding fracture site shifts toward the junction between the enamel and adhesive.Purpose: The aim of this study was to determine the in-vitro bond strength and the fracture site after debonding the mechanically-bonded ceramic and metallic brackets.Materials and Method: Sixty extracted premolars were randomly selected from orthodontic patients in a private clinic. All the samples were divided into two groups and 30 metallic and 30 ceramic brackets were mechanically bonded to the teeth, using light curing adhesive. After one week, all the brackets were debonded by bracket-removing pliers assembled on a testing machine. This design simulated clinically-applied debonding compressive forces precisely. By the use of stereomicroscope and trans-illumination technique, the amount of adhesive remnant on the brackets' surfaces or on the teeth was evaluated and calculated using Photoshop and Auto Cat software program in the bonded areas in order to determine different fracture sites. Descriptive analysis was used to describe the findings and independent t-test was used to compare the differences between the two bracket groups.Results: Debonding fracture was mostly observed in the interface between brackets and adhesive and within adhesive but there were no statistically significant differences in the location of the debonding fracture between the two groups.Conclusion: The risk of enamel damage after debonding both metallic and ceramic brackets is low due to the minimal chance of debonding failure between the enamel and adhesive.

Statement of Problems: The aim of impression is accurate registration of the ridge, teeth and surrounding tissues.Condensation silicones are impression materials used frequently in fixed prosthesis. These materials have different brand names that make their selection not easy by the dentists.Purpose: This study was designed to investigate the accuracy of two condensation silicone Impression materials, speedex and Irasil, in putty- wash technique.Materials and methods: In this quazi- experimental study, we designed a laboratory model with 2 metallic dies.One of them had an undercut and was similar to the molar teeth and the other had no undercut and was similar to the premolar teeth. These dies had 3 degrees convergence in walls and were round in cross section. Then impressions were taken with Irasil and Speedex impression materials and the stone models were prepared. Five dimensions of 30 models were measured and compared with laboratory model by the use of T-test.Results: These two impression materials had a statistically significant effect on the die height without underecut but on other dimensions they had not any statistical significant effect. Die height without undercut was increased with speedex impressions but decreased with Irasil impressions. Die diameter without undercut and the distance between dies were increased with speedex and Irasil impressions. The die diameter beneath the undercut was increased with speedex but decreased with Irasil impressions. The die height above the undercut was decreased in Irasil and speedex impressions.Conclusion: The usage of Irasil compared n to speedex impression material has a higher effect in only one dimension (die height above undercut) but in other dimensions speedex is better than Irasil.

Statement of problem: Missed canal is one of the main reasons of the failure of root canal therapy. Poor knowledge of root canal anatomy may result in this problem. Each tooth has specific anatomical characteristics which could relatively be assessed by radiography.Purpose: This study aimed to survey the variety of second maxillary molar root canal anatomy in Mashhad population.Materials and Methods: In this descriptive study, 103 human adult second maxillary molar extracted in different districts in Mashhad were chosen. After preparation of the access cavity, the teeth were embedded in Naocl 5.25% for resolution of the pulp tissue. For decalcification, the teeth were soaked in HCL 10% for 24 hours and washed in running water for 12 hours. They were dehydrated in alcohol 70-100% and finally cleared by Methylsalicylate and pure alcohol after 3 hours of soaking. Methylen blue 2% was injected to the canals and immediately evaluated with 8x magnification. The root canals were classified by Vertucci category.Results: Different types of canals in mesiobuccal root were as follows: 45.7% type I, 16.5%type II, 5.8% type III, 12.6% type IV, 6.9% type V, 4.9% type VI and 3.9% type VII. In two teeth, the distobuccal and palatal root were fused, having a C-Shaped canal, and 2 teeth had only two roots (buccal and palatal). Therefore, type I was seen 96% and 98% in the distobuccal and palatal roots, respectively.Conclusion: Due to the high prevalence of extra canal in the mesiobuccal root of the second maxillary molar (52.5%), the clinicians have to carefully explore the four canals in radiography and perform clinical evaluation; otherwise, treatment failure is inevitable.

Statement of problem: Oral lichen planus (OLP) is an immunologic mucocutanous disorder. Many factors such as stress, diabetics, HCV, Trauma and hypersensitivity have been introduced as its predisposing factors. Recently, much attention has been paid to the relationship between HCV and OLP.Purpose: According to different specifications of the virus in different races and geographic conditions, the purpose of this study was the assessment of the presence of HCV in oral lichen planus lesions.Materials and Methods: We prepared 43 paraffin blocks (29 from OLP and 14 from normal oral mucosa). The OLP blocks were selected from the archive of Pathology department, dental faculty, Esfahan University of Medical Science. After preparing H & E slides from the paraffin blocks, diagnosis of the lesions was confirmed by a pathologist. Then, all the samples were examined by PCR for HCV genome. The data were analyzed using SPSS software and Fisher's Exact rest with Pvalue of 0.05.Results: Among 43 samples examined, 3 were positive and 26 negative in the OLP group and all the 14 samples belonging to the normal mucosa were negative.Conclusion: According to this study, there was no significant correlation between the presence of Hepatitis C virus genome and OLP lesions (p>0.05). So, researches on other viruses that are effective in oral diseases with more cases and also doing PCR on the blood and serum of OLP patients are recommended.

Statement of Problem: Considering the high prevalence of Class II malocclusions and its side effects on facial esthetic, treatment of patients with functional therapy may improve their facial esthetic.Purpose: The purpose of this study was to determine the treatment effects of Farmand appliance on the facial soft tissue profile in patients with Class II div I malocclusion with mandibular deficiency.Materials and Methods: In this pre-post clinical trial study, 35 patients with class II div I malocclusion were selected, and treated by Farmand functional appliance for II months. The age range of the females was 10-13 years and for the males it was 11-14 years. Pre- and post- treatment cephalometric radiographs of the patients were traced.Treatment changes were analyzed by certain linear and angular measurements of the soft tissue profile and lips.Paird t-test was used to compare the differences of the mean values Pre- and post- treatment.Results: In this study, the mentolabial angle was increased (p=0.001) and the lower labial sulcus depth (p=0.003) was decreased. These changes were statistically significant. The thickness of the upper lip showed a statistically significant increase (p=0.001), which resulted in detectable decrease in the strain of the upper lip (p=0.001). The thickness and height of the lips were closed to the normal range. The position of the lips also improved to the 8, E and H plans.Conclusion: Treatment with Farmand functional appliance in patients with Class II div I lead to significant alteration in the soft tissue profile and improvement of the nose, lips and chin relationships.

Statement of Problem: Recently, usage and demand for posterior composite restorations (PCRs) have been rising in dentistry.Purpose: The purpose of this study was to determine the Iranian dental students' opinion regarding the teaching quality of PCRs.Materials and Method: In this descriptive study, 450 undergraduate dental students in the 5th and 6th years of education were randomly selected. A questionnaire was prepared with 41 questions based on the similar studies and restorative dentistry textbooks. The questionnaire contained question about the participants' satisfaction about the theoretical and practical methods of PCRs and their knowledge and ability in performing the PCRs. Validity and reliability of the questionnaire were confirmed by specialists of restorative dentistry and using test-retest. The data were analyzed by descriptive statistical methods.Results: The students had lower satisfaction concerning the quality of theoretical and practical teaching of PCRs than amalgam restorations and believed that there was no balance between the theoretical and practical teaching of PCRs. 1.6% of them believed that the time allocated to the teaching of PCRs was sufficient; 54.4% answered that self-evaluation of their learning was acceptable and 42.9% believed that preclinical teaching was not satisfactory.The content of the PCRs teaching covered only 50% of their needs in clinical practice. Also they believed that in their schools the amalgam was more preferred than composite and 97% stated that the amalgam restorations were taught before PCRs. The students' knowledge about contraindications of PCRs, principles of cavity design, indications for lining and basing, matrix and wedging techniques was assessed at a relatively good level of quality.Conclusion: The satisfaction level of the dental students about the time and amount of teaching in theoretical, preclinical and clinical courses of PCRs was less than that about amalgam restorations. Accordingly, it is noteworthy to modify the method of PCRs teaching especially in clinical courses.