Journal of Dental Medicine
Year:2007 | Volume:20 | Issue:2 (51)|Papers Count:12

Background and Aim: All ceramic, inlay-retained resin bonded fixed partial denture is a conservative method for replacement of missing teeth, because of minimal tooth reduction. The connector between the retainer and the pontic is the weak point of these bridges. Reinforcement of ceramic core will increase the clinical longevity. The aim of this study was to determine the effect of zirconia on flexural strength of IPS Empress 2 core ceramic.Materials and Methods: In this experimental in vitro study, twenty eight bar shape specimens (17x3.1x3.1 mm) were made of four different materials: (1) Slip casting in-ceram alumina core (control group) (2) Hotpressed lithium disilicate core ceramic (IPS Empress 2) (3) IPS Empress 2 with cosmopost (zirconia post) inserted longitudinally in the center of the bar (4) IPS Empress 2 with cosmopost (zirconia post) inserted longitudinally in bottom of the bar. Specimens were subjected to three-point flexure loading with the span of 15mm, at a cross-head speed of 0.5 mm/min. Failure loads were recorded and analyzed using one-way ANOV A and Tomhane Post-hoc tests and p<0.05 was set as the level of significance. Fractured surfaces were then observed by scanning electron microscope (SEM). Four additional samples were made as the third group, and zirconia-IPS interface was observed by SEM before fracture.Results: Mean values and standard deviations of three point flexural strengths of groups 1 to 4, were: 378.4±44.6, 258.6±27.5, 144.3±51.7, 230±22.3 MPa respectively. All the groups were statistically different from each other (P<0.05), except groups 2 and 4. The flexural strengths of groups 2, 3, 4 were significantly lower than group 1. Group 3 had the lowest flexural strength. SEM analysis showed that the initiated cracks propagated in the interface of zirconia post and IPS Empress 2 ceramic.Conclusion: Based on the results of this study, insetting zirconia post (cosmopost) in IPS Empress 2 ceramic does net reinforce all-ceramic inlay retained resin bonded fixed partial dentures.

Background and Aim: The final objective of root canal therapy is to create a hermetic seal along the length of the root canal system from the coronal opening to the apical termination and to accomplish the best adaptation of obturation material with canal walls. The purpose of this study was to compare the microleakage during lateral condensation of 0.04 and 0.02 tapered gutta-percha master cones.Materials and Methods: In this experimental in vitro study, seventy two single canal teeth were selected and the crowns were removed. Canals were prepared using a step-back technique. Patency of the apical foramen was maintained and the teeth were divided into two experimental groups of 31 each ten teeth were used as control group, out of which five served as negative and five as positive controls. The first and second groups were obturated with 0.02 and 0.04 tapered master cones respectively. All the teeth were obturated using lateral condensation technique. The teeth were placed in 100% humidity and 37oc for three days. The roots were coated with two layers of nail varnish and one layer of stick wax except for the apical 2 mm. Teeth were placed in Pelikan ink for one week and sectioned vertically. The maximum depth of dye penetration for each tooth was recorded by two evaluators with stereomicroscope. The results were statistically analyzed using t-test with p<0.05 as the level of significance.Results: The mean linear dye penetration for the first and second groups was 2.53±0.88mm and 4.89±1.20 mm respectively. The difference was statistically significant (P<0.001).Conclusion: The results of this study showed that 0.02 tapered gutta-percha master cone, provided a significantly better apical seal than 0.04 tapered gutta-percha master cone.

Background and Aim: Halogen lamp is the commonly used light source for composite photo polymerization.Recently, high power halogen lamps, LED and plasma arc are introduced for improving the polymerization.The aim of this study was to investigate the effect of conventional and high power halogen lamps and LED light curing unit on degree of conversion of two different composite resins.Materials and Methods: In this in vitro experimental study two halogen units (Coltolux 50 with the intensity of 330 mW/cm2 and Optilux 501 with two different operating modes of standard with the intensity of 820 mW/cm2 and Ramp with the intentsiy of 100-1030mW/cm2) and one LED light curing unit (620 mW/cm2) were used. The composites were hybrid (Tetric ceram) and nanofilled (Filteke supreme). Each materials/curing method contained three samples and degree of conversion (DC) was measured with FTIR.Data were analyzed statistically with one way and two ways ANOV A, Tukey HSD. P<0.05 was considered as the limit of significance.Results: Tetric ceram revealed higher DC than Supreme. Tetric ceram showed a significant decrease in DC when Coltolux 50 was used in comparison to LED and Optilux 501. The latters did not show significant effect on DC of this material. DC of Supreme polymerized with various curing modes was not significantly different.Conclusion: Based on the results of this study, degree of conversion in hybrid composites was higher than nanofilled. In comparison with conventional halogen lamp (Coltolux 50), high intensity halogen lamps and LED unit significantly lead to higher degree of conversion in hybrid composites.

Background and Aim: During root canal therapy, it is necessary to remove as many bacteria as possible from the root canal. The use of medicaments is recommended t6 reduce the microbial population prior to root filling. Calcium hydroxide pastes have been used because of their antibacterial effects and the ability of tissue dissolving. The aim of this study was to evaluate the effect of calcium hydroxide/glycerine mixture, calcium hydroxide/normal saline mixture and calcium hydroxide/distilled water mixture on root dentin microhardness in storage times of 7 and 14 days.Materials and Methods: In this in vitro study, fifteen extracted maxillary canines and central incisors were selected. The crowns of the teeth were removed and the canals were prepared. Teeth were sectioned transversally to produce a total of 30 dentin discs from the middle third of the roots. Specimens were divided into three groups of 10 discs each. Dentin samples were subjected to calcium hydroxide/glycerine, calcium hydroxide/normal saline and calcium hydroxide/distilled water' mixtures for 7 and 14 days. Dentin microhardness was measured by a Vickers indenter with a load of 200 g for IS seconds. Data were analyzed using ANOVA, Paired t-test and LSD with p<0.05 as the level of significance.Results: Statistical analysis showed that all three mixtures decreased dentin microhardness. After 7 days, reduction in dentin microhardness by calcium hydroxide/glycerine combination was significantly higher than calcium hydroxide/normal saline and calcium hydroxide/distilled water combinations. After 14 days, reduction in dentin microhardness by calcium hydroxide/distilled water combination was significantly higher than the other two groups.Conclusion: Based on the results of this study, the use of calcium hydroxide combinations for intracanal dressing reduces dentin microhardness. After 7 days calcium hydroxide/glycerine combination and after 14 days calcium hydroxide/distilled water combination are the most effective combinations.

Background and Aim: An important purpose of adhesive dentistry is restriction of cavity preparation to carious dentin removal and conservation of sound dentin. Application of caries disclosing agents and cavity disinfectants can help achieving this goal. The aim of this study was to evaluate the effect of caries disclosing agents and cavity disinfectants on microleakage of composite resin restorations.Materials and Methods: This experimental in-vitro study was performed on class V cavities in 48 extracted human sound premolars. The teeth were randomly divided into four equal groups. In group I caries detector dyes (Seek, Ultradent, USA) and in group 2 cavity disinfectant (Consepsis, Ultradent, USA) was applied on dentinal surfaces. In group 3 both mentioned materials were applied. Group 4 was considered as control group. PQ1 bonding agent and Amelogen composite were used to restore the cavities. Gingival microleakage was assessed by dye penetration. Data were analyzed by Kruskall Wallis and Dunn tests. P<0.05 was the level of significance.Results: Group 2 showed the least and group 4 showed the highest microleakage; however no statistical significant difference was found among the groups.Conclusion: The use of caries disclosing agent (Seek) and cavity disinfectant (Consepsis Liquid) did not adversely affect the sealing ability of dentin bonding resins.

Background and Aim: Mineral Trioxide Aggregate (MTA) is a material used in many endodontic problems.Recently a number of studies have reported that Portland Cement (PC) and MTA have similar physical, chemical and biologic properties. In addition, a material known as Root MTA which is produced in Iran has been claimed to have similar properties to Pro Root MTA. If these claims are true, possible use of PC and Root MTA in clinic instead of Pro Root MTA will be quite cost effective. The aim of this study was to investigate the toxicity of Pro Root MTA, Root MTA and Portland Cement on L929 mouse fibroblasts.Materials and Methods: In this experimental study 0, 4, 24 hours and 7 days' extracts of materials were transferred to cell culture plates containing L929 fibroblasts. After 24 hours incubation, cells were stained by Neutral Red (NR), and optical density (OD) of each cell was read with ELISA reader. Data were analyzed using Tukey HSD and one way analysis of variance. P<0.05 was considered as the level of significance.Results: In all surveyed groups and negative control group, at all time points separated cells from the base of the well were round. Refraction which is a characteristic of cellular death was not observed, whereas the separated cells from the base of well in positive control group showed refractional characteristic.Conclusion: Based on the findings of this study Pro Root MTA, PC and Root MTA have the same biocompatibility. PC seems to have the potential to be used in the same clinical situation as MTA. However in order to replace MTA with these less expensive materials more in vitro and in vivo studies are suggested.

Background and Aim: Light cured composites and other restorative materials are quite common in dentistry today. Successful restorations are dependent on efficiency of curing light unit, ego the intensity of emitted light and its wave length. The aim of this study was to evaluate the efficiency units of curing, in private dental offices in Tehran.Materials and Methods: In this descriptive cross sectional study, light curing devices in 240 private dental offices were evaluated randomly. Light intensity was measured by radiometer, debris 'On the fan and cracks and scratches on the filter were directly observed and the age of the device, frequency of changing the bulb and satisfaction of the dentist with regard to the light curing unit were recorded in a questionnaire. Data were analyzed using Spearman and t test, with p<0.05 as the level of significance.Results: The results showed that 53.8% of the units had intensities more than 300 mW/cm2. The intensity of 30.4% of curing light units were between 20 and 300 mW/cm2 and 15.8% had .intensities lower than 200 mW/cm2. There was a negative relation between light intensity and the age of the unit, frequency of bulb changing or scratches on the filter and debris on the fan.Conclusion: The results of this study showed that the light intensities of about 46% of light curing units used in private dental practices and clinics were inadequate. Since factors like aging of the curing light unit, frequent bulb changing, increasing the amount of debris on the fan and scratches on the filter reduce the light intensity, regular quality control of these devices is essential.

Background and Aim: One of the complications following major oral surgeries is mucosal defects and delayed healing process. Up to now, various mucocutaneous grafts have been used in this field and recently, amniotic membrane has been proposed as a biological dressing in dermatologic, ophthalmologic and otolaryngologic practices. The purpose of this pilot study was to evaluate the healing process following human amniotic membrane graft on oral keratinized mucosa of rabbit.Materials and Methods: In this experimental animal study, two surgical mucosal defects with the same size were made in palatal mucosa of 10 rabbits with the same weight, gender and race and a graft of human amniotic membrane was used on one of the defects. On the 7th, 14th and 28th postoperative days, surgical biopsies were randomly obtained from grafted and ungrafted regions of 3, 4 and 3 rabbits, respectively and submitted for microscopic study.Results: According to the results, grafted regions showed more surface epithelialization and thicker newly formed epithelium. Also inflammatory cells infiltration was less in these areas. In all cases, there was a remarkable cartilage formation in the connective tissue of the recipient sites.Conclusion: The results of this study suggest that the use of amniotic membrane graft in oral surgery could be effective in healing process. Additional studies should be done using animal and human models with more samples. Furthermore, the formation of cartilage in the grafted sites and its possible potential in reconstruction of bone defects needs to be studied.

Background and Aim: Dental anxiety is a common problem in pediatric dentistry and results in behaviors like fear and anger that can negatively affect dental treatments. Exposure to various dental treatments and distressful experiences are reasons for anxiety during dental treatments. The aim of this study was to evaluate effect of cognitive behavioral interventions in reduction of stress during dental procedures in children.Materials and Methods: In this clinical trial, 42 boys and girls, undergoing dental treatments were selected from dental clinics in Tehran. Patients were assigned to cognitive-behavioral interventions, placebo and control conditions. The fear scale, anger facial scale, pain facial scale and physiologic measure of pulse beat were evaluated. One way ANOV A and Tukey test were used to analyze the results and p<0.05 was the level of significance.Results: Results showed significant differences between cognitive-behavioral interventions, placebo and control groups regarding fear, anger, pain and pulse beat. Comparison tests revealed that cognitive-behavioral interventions were more effective in reducing fear, anger, pain and pulse beat compared to the placebo or control.Conclusion: According to the results of this study cognitive-behavioral interventions can be used to reduce distress of children undergoing dental procedures.

Background and Aim: In recent years, different substances have been considered in gingival cervical fluid (GCF) as diagnostic markers due to the evaluation of biologic events and biochemical process related to bone turnover during orthodontic movements. IL-6 concentration increases in GCF during the first week after force loading. The aim of this study was to investigate the levels of IL-6 in GCF during orthodontic movements.Materials and Methods: Fourteen orthodontic patients (9 females and 5 males, mean age 15.1±2.5 years) with Cl I malocc1usionneeding first bicuspid extraction participated in this clinical trial. In each patient one maxillary canine was distalized (DC) with a NiTi push coil spring. The contra-lateral canine (CC) was included in the orthodontic appliance but was not subjected to the orthodontic force and one of the mandibular canines was used as control with no orthodontic appliance (Antagonist canine: AC). The concentration of IL-6 was evaluated at the baseline and 14th and 28th days after intervention. GCF was taken with periopapers from both mesial and distal sides of tooth before appliance activation, on the 14th and 28th days. Concentration of IL-6 in DC, CC, and AC detected by ELISA reader was compared by repeated measure ANOVA and LSD multiple comparison, P<0.05 was considered statistically significant.Results: Although the inflammatory gingival indices increased in both DC and CC teeth but it was not significant.The amount of IL-6 in GCF increased on day 14th in DC teeth in comparison with AC and CC teeth. In addition, the concentration of IL-6 in DC teeth was significantly greater than the 1st and 28th days. The maximum concentration of IL-6 was detected in both pressure and tension sides of DCs at T14. At T28, although the IL-6 levels were significantly higher than baseline levels but, it was significantly less than T14.Conclusion: The results of this study support the hypothesis that mechanical stimuli cause an inflammatory reaction within the periodontal tissues.

Background and Aim: Designing removable partial dentures is one of the most important phases of prosthetic treatments. Computer can be used to facilitate and increase accuracy of removable partial denture design. The aim of this study was to develop a software for removable partial denture design.Materials and Methods: A questionnaire (discussed in part I) and major textbooks, were used to determine the design rules. The software (RPD Graph) was developed using Visual C++ and Maryam program. The RPD Graph can determine the classification of partial edentulous arch. With defining the missing teeth and providing data about prognosis and conditions of abutment teeth, the removable partial design will be developed by RPD Graph. This software is a knowledge-based system which has specific characteristics. It can be used as an educational tool for teaching RPD design and as a clinical tool for supporting clinician's decision. In addition it can be developed to more complete softwares.

Odontomas are benign tumors of odontogenic origin characterized by their slow growth. They are considered to be a common type of odontogenic tumor, but rarely occur in the primary dentition. The etiology of odontomas is unknown, although local trauma, infection and genetic factors have been suggested.Odontomas often cause disturbances in the eruption of teeth such as, impaction or delayed eruption, and retention of primary teeth and abnormalities in the position of teeth such as tipping or displacement of adjacent teeth. In this paper, a case of unerupted right mandibular primary cuspid in a 5 years old girl due to the presence of a compound odontoma is presented.