Journal of Dentistry, Shiraz University of Medical Sciences
Volume:7 Issue: 1, 2007

Statement of Problem: Overcoming the side effects of polymerization phenomenon has provoked many researches to find out the solution. Since a desirable polymerization of composite resin is effective in success rate of restorations with these materials, and as there is a direct relationship between light intensity and desirable polymerization or curing depth, therefore it is expected that a suitable exposure pattern to produce a desirable curing depth to could overcome the side effects of polymerization phenomenon. The aim of this study was to present a new light exposure pattern for composite curing and evaluation of its effect on microhardness and degree of polymerization of composite in respect to some other light exposure patterns. In an in vitro study, 4 groups of 5 brass cylinders were used and one bulky was filled with Tetric ®Ceram composite. Then samples in the first three groups were exposed 80 seconds to 3 types of Astralis 7® light exposed patterns, including: HIP (High Intensity Program), LOP (Low Intensity Program) and PUL (Pulse Program). The forth group was also exposed same time with SUP (Suggestive Progressive Polymerization) respectively. After sample preparation, they were analyzed with micro hardness tester in 6 different depths and dye penetration test was done for all samples and were evaluated by stereomicroscope. The data were analyzed statistically using One-way ANOVA and Duncan test through SPSS software. In absence of depth factor consideration, the mean micro hardness in all four groups of exposure patterns had no significant difference (p=0.362). The HIP, LOP, PUL, SUP light exposure patterns produced significantly different micro hardness in 0-5 mm depth significantly (p=0.001). In other words there was a significant difference in micro hardness in different depths in each testing group. In the same depths, there was no significant difference in composite microhardness between the 4 groups up to 4 mm depth, but at the depth of 5 mm in HIP group, micro hardness was significantly higher than the depth of 5 mm in the other group. The analyzes clarified that the suggestive light exposure pattern (sup) can control and guide the rate of polymerization along with having the same quality to the other light exposure patters in producing hardness up to the depth of 4 mm of composite restorations.

Statement of Problem: Dimensional changes of denture base acrylic resins are one of the most frequent phenomena that occur during the production of the dentures in different steps of curing and different times of deflasking.

Measurement of the effect of different deflasking times on dimensional stability of acrylic resin can reduce the dimensional changes of these materials. The objective of this study was to compare these dimensional changes in different times of deflasking in two different acrylic resins (Acropars and Meliodent).

In this experimental study, the dimensional changes of two heat-cured poly methyl metacrylate resins (Meliodent and Acropars) were studied in different deflasking times. The initial model included one steel sheet approximately 3 mm thick, cut in the form of a dumbbell and fifty specimens of the same piece were regularly flasked and processed. Acrylic specimens, in different bench cooling times (4 hours, 12, 24, 48, 5 days) were taken out and measured in 4 areas with an accuracy of 0.01 mm using a digital caliper, subsequently, the results were studied using the One Way Anova method.

Dimensional changes in two types of acrylic resins (Meliodent and Acropars) showed significant differences after 5 days deflasking (P=0.000), and had the least dimensional changes. No significant differences were observed between the average dimensional changes in reference points. Keeping Meliodent acrylic resin for at least 4 hours and Acropars acrylic resin for at least 12 hours after processing can reduce dimensional changes significantly.

Iranian specimens of Acropars acrylic resin even show smaller dimensional changes than German specimens of Meliodent acrylic resin. After 5 days, deflasking time has the least dimensional changes in both acrylic resins.

Statement of Problem: Dentin hypersensitivity is characterized by a short and sharp pain that arises when thermal, evaporative, mechanical or osmotic stimuli are applied to exposed dentin. Most of vital teeth after preparation for fixed crowns encounter dentin hypersensitivity. There are some available categories of materials such as Gluma desensitizer and potassium nitrate designed for treating this problem which needs more clinical evaluation to confirm their efficiency. This study was performed to compare the effect of Gluma desensitizer and potassium nitrate on reduction of hypersensitivity of prepared teeth for full crowns. This research was performed on 75 vital teeth in 25 patients who needed a fixed prosthesis treatment. After completing routine examinations, the hypersensitivity of teeth was determined with the air sensitivity test. The measurement was done by a VAS scale before preparation, after preparation, before using desensitizers, after using desensitizers and before cementation. Each tooth was randomly assigned in one of the three groups (potassium nitrate, gluma and control). It was shown that both desensitizers decreased dentinal hypersensitivity in vital teeth prepared for fix prosthesis; but potassium nitrate was more effective after application and before cementation. Meanwhile in 88% of the cases which gluma was used on, a vascular pain (with pulse) was seen. Considering the results, both desensitizers were effective in decreasing dentinal hypersensitivity in vital teeth prepared for fix prosthesis; but potassium nitrate showed better results. Therefore, this substance can be used in a therapeutic protocol.

Statement of Problem: Postcuring techniques improve mechanical properties of indirect composites significantly. Eventhought this technique has been suggested for direct composites, but its effect for direct composites is still questionable. This study was undertaken to evaluate the effect of various postcuring techniques on surface hardness of two different types of composites. Eighty circular specimens of Nulite F (40 specimens) and Gradia (40 specimens) composites were made and light cured. Ten of each type was kept as control group and 10 of each type was postcured with oven for 5 minutes at 120°C. The other ten ones was postcured with microwave for 5 minutes and the last 10 ones were postcured with labolite for 5 minutes. The specimens were polished and were kept in 37°C water for one week. Then surface hardness testing was performed and data were analyzed using one-way ANOVA and Kruskal wallis tests. The results revealed that the surface hardness (VHN) of Nulite F composite in control group was greater than Gradia composite in control group (p<0.05). All postcuring techniques increased the VHN of all groups significantly. The effects of postcuring on increasing surface hardness of Nulite F were more significant in all techniques, especially by the usage of labolite set in Nulite F composite in comparison with Gradia composite. There was no statistically significant difference between surface hardness of microwave and oven groups in Nulite F composite. No statistically significant difference was noticed between surface hardness of microwave and labolite groups in Gradia composite. The effect of postcuring with oven on surface hardness of Gradia composite was statistically significant compared to the two other techniques. By evaluation of various samples in this study it was concluded that all postcuring techniques (labolite, microwave and oven) increased the surface hardness (VHN) of both direct composites (Gradia and Neulife F) significantly.

Statement of Problem: Despite the fact that polymethyl methacrylate is the most popular material in denture base construction, one of its main defects is the polymerization shrinkage that frequently leads in time consuming clinical problems. Several ways have been suggested to solve this problem; among them is "injection molding method". The purpose of this study was the assessment of dimensional accuracy of the two acrylic resins cured by injection molding method. In this experimental study, the dimensional accuracy of two acrylic resins after curing by injection molding method (Unipress system) was assessed by profile projector measurement. Twenty master casts were made of a master dye simulating both maxillary and mandibular edentulous arch. They were divided in two groups, each group containing 10 casts used for making denture bases. Three reference points were determined, one in the central incisor region and the other two symmetrical points in the posterior region in molar area. Three measurements were made: 1. on the master cast, 2. on the denture base just after removing the denture base from the master cast, and 3. after immersion in water for one week. The measurements were analyzed using Friedman and Mann-Whitney tests. All the denture bases in both groups, revealed significant shrinkage after removing from casts (p<0.05). After immersion in water, there was no significant dimensional change (p>0.05) in any of the groups. Statistical analysis revealed no significant difference between the two acrylic resins too. Since there was no significant difference between dimensional accuracy of the two acrylic resins, it could be conclude that using Bayer acrylic resin with Unipress injection molding system would lead in acceptable results concerning dimensional accuracy.

Statement of Problem: Apical root resortpion of maxillary incisors is relatively a common phenomenon at the end of orthodontic treatment. Therefore, recognizing risk factors in root resorption before starting the treatment is very important. The aim of this study was to compare the amounts of apical root resorption in different malocclusion groups. The amount of apical root resorption in 219 fixed orthodontic (70 Cl 1, 76 Cl II and 73 Cl III patients) with first or second maxillary premolars extraction and with mean age of 15±0.5 years were evaluated through the examination of parallel radiographies (long cone) before and after treatment. The amount of apical root resorption was measured in groups by using Photoshop program (Version 7.0). Then, the groups were compared and analyzed by t-test and one way ANOVA. One hundred percent of patients (84.96% of teeth) showed first degree resorption, 18%, zero degree resorption; 1.37%, third degree and 12.8% showed second degree resorption. The greater resorption of second degree was observed in Cl II patients. Left and right incisors and central and lateral incisors had no significant differences among all the three groups. The comparison between apical root resorption in CI, Cl II and Cl III groups indicated that the resorption in Cl II group was more than Cl I and Cl III groups (p<0.001).

Statement of Problem: The treatment of immature teeth with open apex by Gutta percha in one visit apexification requires an optimum material as apical barrier. One of the desirable properties of the apical barrier material is its sealing ability. This study was performed to compare the sealing ability of calcium hydroxide and a new experimental material (cold ceramic) when used as an apical barrier. Fifty extracted single canal human teeth were collected and stored in saline solution. The crowns were resected and by conventional step back method, canals were instrumented and then extended by Piso Reamer, so that, root ends were formed divergently. Samples were divided into two group including 23 teeth as study and 4 teeth as positive and negative control groups and then all teeth were mounted in a plaster cast. The two experimental materials (Cold ceramic and calcium hydroxide) were placed in the root ends for producing apical barrier, and canals were obturated with Gutta percha. The teeth in the positive and negative groups were obturated with Gutta percha, and in the negative group, cavit was placed at the end of root. In the 3 groups (calcium hydroxide, cold ceramic and positive group), all surfaces of the teeth were covered by two layers of the nail polish except 2 to 3 mm of the roots end and in the negative control group, samples were covered completely by two layers of the nail polish. Then, photographs of teeth were scanned and amount of leakage was calculated with the Photoshop software. The data were analyzed by t-test. Amount of cold ceramic leakage was less than calcium hydroxide and this difference was statistically significant (p=0.0001). Results showed that apical plug with cold ceramic was more resistant than the apical plug with calcium hydroxide. The results of this study confirmed optimum sealing ability of the new experimental material for creating of apical barrier in one appointment apexification.

Statement of Problem: One of the most important problems in dentistry is to produce a suitable bond between tooth and all ceramic restoration, but there is little information on the use of resin cements and the importance of different surface treatments on their adhesion to high alumina containing ceramics. The aim of this study was to find the optimal choice of surface treatments and luting cement for bonding to In-Ceram, an aluminum oxide reinforced glass ceramic material. The bond strength of two different luting cement to the ceramic material was evaluated. The effect of surface treatment, etching, sandblasting, and silanizing was also investigated. Thirty In-ceram discs were fabricated and assigned to 3 groups. Group 1 specimens were treated with HF and Silane, Group 2 were sandblasted and then silane was applied, Group 3 were treated only with silane. Rely X cement was placed on all specimens and shear bond strength test was done.After the test, the discs were polished again and treated as previously mentioned in 3 groups. Then they received Panavia F cement and shear bond strength was evaluated using Instron testing machine. Using Tukey HSD test, it was shown the Panavia F provided higher bond strength values than Rely X cement. One way ANOVA determined that the use of sandblast provided higher bond strength values than other groups. Surface etching with 9.5% HF also increased bond strength in comparison with silanization alone. Based on the results of this study, the use of Panaiva F was better for In-Ceram restorations. Sandbalsting is preferred to etching for the increase of bond strength of resin cements to alumina ceramic.

Statement of Problem: In Orthodontic diagnosis and treatment planning one of the most important issue is an accurate anteroposterior measurement of jaw relationship. The most commonly used angular and linear measurements that have been proposed, such as ANB angle and Wit’s appraisal can be inaccurate and misleading due to their dependence on various factors. This study was aimed at establishing a new cephalometric measurement, named the µ angle, to assess the sagittal jaw relationship with accuracy and reproducibility. The µ angle uses 3 skeletal landmarks, point A, point B and a perpendicular line from point A to the mandibular plan. One hundred and fifteen pretreatment cephalometric radiographs of orthodontic patients (mean age 16±2 years) were selected on the basic of inclusion criteria according to their skeletal and profile patterns. The patients compromised of 30 class I, 45 class II and 40 class III skeletal relationships and profile pattern, the mean and standard deviation for the new angel (µ) and the previous reported angle (β) were evaluated. One way analysis of variance (ANOVA) and the Newman- Keuls test were used for data analysis as well as, dermination of the new angle’s specifity and sensitivity comparing with β angle. The results obtained showed that a patient with a µ angle between 16.1o and 23.9 o can be considered to have a class I skeletal pattern. A more acute µ angle is an indication of a class II skeletal pattern and a more obtuse µ angle indicates a class III skeletal pattern. The new angle (µ angle) has an acceptable specificity and sensitivity in determining the anteroposterior relation of jaws and thus can be used for assessing the type and severity of jaw discrepancies, besides the other diagnostic parameters.

Statement of Problem: Alginate is the common impression material in dentistry and its preparation with water in various temperatures is required in some instances. Does the temperature of water affect on dimensional accuracy of alginate is the question of studies? The aim of this study was to compare the effect of different temperatures of water on dimensional accuracy of stone models in impression with Iralgin and Bayer alginate. In this experimental study, one laboratory model was used with two metallic dies and alginate impression materials (Iralgin and Bayer). Sixty impressions were taken at temperatures of 8 C, 23 C and 28 C for Iralgin and Bayer alginate and stone models were poured. Five dimensions of 60 models including height and diameter for each die and distance between the dies were measured by digital caliper and compared with laboratory model by the use of ANOVA and t tests and LSD analysis. Temperature change of water had statistically significant effect on dimensional accuracy of stone model. At 8 C, all dimensions of Iralgin and Bayer increased. There was statistically significant changes (p<0.05) in diameter and external distance between the two dies for Iralgin and in diameter of small die for Bayer. At 28 C, all of the dimensions of the dies decreased, that in Bayer except for the diameter of the large die and in Iragin only for small die, the difference was statistically significant. The results of this research showed that at 23 C temperature of water, Bayer alginate was more accurate than Iralgin alginate. At 28 C, Iralgin and at 8 C, Bayer alginate was the most accurate.

Statement of Problem: According to some studies, diagnosis of carotid artery calcification in panoramic radiography could be a good marker and an aid for the prediction and prevention of cerebrovascular and cardiovascular accidents. Doppler sonography is an important diagnostic method for the recognition of calcified atheroma and carotid artery stenosis, With respect to the importance of the recognition of calcified atheroma and vast usage of panoramic radiography in dental treatments, the purpose of this study was to evaluate the degree of agreement between panoramic radiography and Doppler sonography in the diagnosis of calcified carotid artery. In this descriptive-analytic study, panoramic radiographs were taken from 35 nephrolo‌‌gic and neurologic patients with carotid Doppler sonography, in order to evaluate calcified carotid atheroma. Panoramic radiographs were designed in a form that, the most of cervical vertebrae height to the level of the 4th and 5th intervertebral spaces, could be seen. The data related to the presence or absence of calcified atheroma in Doppler sonography and panoramic radiography were collected by SPSS software. The degree of agreement between the two methods was evaluated by Kappa analysis. Panoramic radiograph and Doppler sonography in both male and female patients in right side showed an average to good agreement rate. Overall, this agreement in patients with cerebrovascular complications without paying any attention to the affected side was from good to average degree. The presence of linear and nodular opacities in the level of 3rd-4th or 4th-5th intervertebral spaces in panoramic radiography especially at the right side could be considered serious. If positive risk factors are also present, the patients could be referred, with great confidence and economical justification, for precise medical examinations, (Doppler Sonography).

Statement of Problem: There is a principle rule about marginal seal in durability and clinical success of restorative treatments. Polymerization shrinkage and microleakage are critical limitations of dental composites. The aim of this study was to evaluate the effect of two different curing units on microleakage of class V composite restorations in different conditions. In this in vitro study, class V cavities were prepared on the buccal surfaces of 80 extracted premolar teeth. Conventional halogen curing unit (optilux 501) and high intensity light-emitting-diodes (LEDmetron) were used to polymerize resin composite (Z100) from two distance 2 and 8 mm. Four groups after 24 hours and the other four groups were restored for 3 months in water at 37oC, immersed in dye solution and then teeth were sectioned longitudinally and evaluated for dye penetration. Data were statistically analyzed using Kruskal-Wallis and Mann-Withney tests to compare the different groups. Using Kruskal Wallis test, no significant difference in microleakage was demonstrated between the different light cure units in the 8 groups. Mann-Whitney test at the dentin side showed that, QTH could significantly reduce the microleakage compared to LED (p=0.007). Increase in distance and storage time did not influence the microleakage. At 2 mm distance, the difference between LED and QTH was significant (p=0.038), but no significant difference was seen at 8 mm distance. Increased distance for LED and QTH did not cause any microleakage. According to the results of this study, it can be concluded that the use of turbo light guide in LED would decreases the output of the light. Therefore, QTH system is recommended to be used in shallow cavities.

Statement of Problem: Developmental anomalies of the tongue frequently occur in patients with other congenital or developmental defects. The aim of this study was to assess the prevalence of developmental anomalies of the tongue among handicapped students of Yazd city. In this cross-sectional study, 400 handicapped children were randomly selected among the special educational centers. Their age range was 6 to 13 years old (220 females, 180 males), among them, 280 cases were mental retarded and 120 cases were physically handicapped. All children were examined and any developmental anomalies of the tongue were recorded. Analysis of data was done by t and Chi-Square tests and analysis of variance. In this study, the prevalence of tongue anomalies was found to be 6.8%. Results showed that 3.7% of cases had fissured tongue, 2% cleft tongue, 0.5% macroglossia, 0.3% microglossia, 0.3% ankyloglossia and no cases of aglossia and bifid tongue were observed. There was no significant difference in prevalence rates of the developmental anomalies in relation to sex, age, IQ and type of retardation. As fissured tongue showed to be the most common anomaly in these students, a follow-up examination is recommended for prevention of unwanted changes.

Statement of Problem: Situation of the condyle in glenoid fossa has a direct effect on the anteroposterior or vertical position of the mandible. Therefore, condylar situation and its shape has a special significance on producing facial morphology. The aim of this study was to evaluate the condylar height and width in patients with class III and class I malocclusion by using panoramic radiographs and lateral cephalograms. This study was performed on 80 pretreatment lateral cephalograms and panoramic films. Mean age in girls was 11 years and 4 months and in boys, it was 12 years and 2 months. Condylar characteristics were surveyed from the point of condylar width and condylar height. Condylar height was surveyed on the panoramic film. Condylar width was analyzed on the lateral cephalograms. Data were analyzed using t.test and ANOVA. Patients with class I malocclusion had a significantly longer condylar width relative to the patients with class III malocclusion. The condylar height in class III malocclusions was longer than class I malocclusion. This study revealed that in patients with class III malocclusion, condylar height was longer but condylar width was smaller than class I malocclusion.

Statement of Problem: Particular attention should be paid to select the optimal combination of an emulsion solution, as different combinations of film and processing materials will produce different qualities of film and processing solution influencing the quality of radiographs with regard to visual characteristics such as density, contrast and fog. This study was performed to determine the best combination of the two different panoramic films, Agfa and Primax with three different processing solutions (Champion, Teifsaz, and Darootasvir). In this experimental study, a total of 30 films were developed in three different processing solution: (1) Champion, (2) Teifsaz and (3) Darootasvir. A skull mankan of human was used in this investigation. Unexposed films of the same batch were developed together with exposed films in order to determine the fog and base densities. After processing densities, several spots were measured with a densitometer. Densitometry of films showed that there was a significant difference between mean density and contrast and fog of the two films in the three different solution (p<0.001). Agfa and Primax panoramic films had the best combination regarding the contrast, density and fog with Champion solution followed by Teifsaz. To use Teifsaz solution we need more resarches to reach the best quality.

Statement of Problem: β Thalassemia is a hereditary hematologic disease with the manifestation of sever dental problems in affected patients. The aim of this study was to examine dental arch dimentions and occlusion in patients with β-thalassemia in Children Hospital of Tabriz in 2005. The sample consisted of patients suffering from β-thalassemia with mean age of 14.9±3.2 and an unaffected control group with mean age of 13.5±3.9. Impressions were made and measurements obtained with a Caliper. Over jet, Overbite and molar relation were recorded clinically. Statistical analysis was then performed using the two-tailed t-test and significance was set at p<0.05. In mandibular arch, when compared with thalassemic patients, healthy subjects showed a significantly larger incisor width, larger arch depth, and larger left and right anterior arch lengths. In the maxillary arch, statistically significant differences were found in mean incisor width, arch depth, intermolar width and left anterior arch length. The canine widths, premolar width, left and right posterior arch length and curve of Spee of both arches showed no statistically significant differences between the two groups. When compared to unaffected subjects, patients with β-thalassemia exhibited a narrower maxilla, a shorter maxilla and mandible, smaller incisor width for the maxillary and mandibular arches.