Journal of Dental Medicine

Indirect esthetic restorations have recently gained popularity, and choosing suitable cement is an important concern in this regard. A wide variety of resin cements with different curing models:(chemical, light, dual), have been introduced to the profession, and among them the dual systems are claimed to be able to continue polymerization after stopping the light. In order to study and compare the polymerization process of different curing systems, this research was performed.The present study measured the degree of conversion (DC) of three types of resin cements: a self cured,a light cured and a dual cured cement. The samples were prepared as follows:1-The self cured samples were made according to the manufacturer.2-The light cured samples were exposed to the curing light for 60 seconds, through a 2 mm thick wafer
of porcelain.3- The dual cured samples were divided into 2 groups. The first was lighted similar to the light cured samples, and the second did not receive any light.The degree of polymerization was measured by FTIR at time levels of 5, 10,20,30,45,60 minutes and 24 hours post mixing. The infrared spectrum of the samples were recorded and degree of conversion were determined. The results demonstrated an increase in mean DC of all groups at post mixing time, but this was significant only in the lighted dual cured cement (PO.05). The light cure resin showed high DC at the base line time (5min). At the end of 60 minutes, the self cure resin had the most DC. The unlighted dual cement had a very low DC and didn't improve in polymerization during the post mixing controls.The lighted dual cement had a significant improve in curing at post mixing times, and it was significantly different from unlighted dual cement. So the dual cure cement needs to receive sufficient light energy to initiate the curing process and the chemical component of this cement could not improve the DC completely.After 24 hours migration of unpolymerized monomers, seams to decrease the DC at the surfaces and removing the most superficial layer, showed that the underlying parts, had improved DC. It seems that in order to be sure of what happens at the restoration-tooth interface, it is appropriate to use self cure cements with improved flow and film thickness.

Statement of Problem: Recently, investigators have presented new methods to reduce polymerization shrinkage of composite resin restorations. It is claimed that more powerful light cure systems associated with a change in radiation patterns, lead to improved mechanical properties and reduced microleakage.

Purpose: The aim of the present study was to evaluate the effects of two curing systems, known as Soft-Start, Pulse-Delay, on microleakage and degree of conversion of composite resin restorations.

Materials and Methods: To evaluate microleakage, dye penetration method in class V cavities was applied. 30 extracted human molars filled with three different curing techniques, namely conventional, Soft-Start and Pulse-Delay, were compared. Degree of conversion was measured by FTIR Spectroscopy method immediately after sample curing. Kruskal- Wallis and Mann-Whitney test were used to compare groups.
Results: The degree of microleakage in enamel and dentin among three groups was not significantly different, however, microleakage in gingival and occlusal walls showed a significant difference among Pulse-Delay curing (P=0.001) and Soft-Start curing (P=0.28) groups, meaning that leakage gingival in wall was significantly higher than occlusal wall. This difference was not significant in conventional group. Moreover, the degree of conversion was not statistically significant among three groups (P-0.909).
Conclusion: Soft-Start and Pulse-Delay curing systems, with a two intensity start curing light, do not provide better marginal adaptation in class V composite resin restorations. It should be mentioned that polymerization degree is not also reduced in these methods.

Statement of Problem: Gingival overgrowth is a side effect commonly induced by Cyclosporin treatment. The effects of Azithromycin, a macrolidic antibiotic, has been focused on gingival enlargement treatment induced by cyclosporine in numerous articles.

Purpose: The goal of the present study was to survey the effects of systemic Azithromycin in the treatment of gingival overgrowth induced by cyclosporine among renal transplant patients.

Materials and Methods: In this clinical trial study, 18 renal transplant patients (6 females and 12 males) with gingival overgrowth were studied. Samples were randomly divided into two groups: case group were treated by systemic Azithromycin and controls were treated by systemic placebo. Periodontal parameters including bleeding on probing (BOP), clinical crown length (CL), periodontal pocket depth (PPD), gingival overgrowth (GOI) and stent-IDP (vertical distant between a stent or plate with teeth occlusal planes at least from three of the most anterior contact points to mesial papillae) before treatment, two and six weeks after treatment were measured. To analyze the data, Wilcoxon and Mann-Whitney tests were used.

Results: Most of the measured indices, among case and control groups, were significantly improved, after two weeks (P<0.05). No statistically significant differences were found between two groups except for BOP index (P<0.05). In other words, more BOP improvement was observed in the case group after six weeks comparing to the control group.

Conclusion: Considering the findings of this study, one can assume that the reported effects of Azithromycine on gingival overgrowth, induced by cyclosporine is somehow exaggerated and the effects attributed this medicine is probably inflammation reduction.

Statement of Problem: Despite the improvements achieved in the field of dental composites, their strength, longevity, and service life specially in high stress areas is not confirmed. Finding better fillers can be a promising step in this task.

Purpose: The purpose of this study was to investigate the effect of the filler type on the mechanical properties of a new experimental dental composite and compare these with the properties of composite containing conventional glass filler.

Materials and Methods: Experimental composites were prepared by mixing silane-treated fillers with monomers, composed of 70% Bis-GMA and 30% TEGDMA by weight. Fillers were different among the groups. Glass, leucite ceramic and lithium disilicate were prepared as different filler types. All three groups contained 73% wt filler. Comphorquinone and amines were chosen as photo initiator system. Post curing was done for all groups. Diametral tensile strength (DTS), flexural strength and flexural modulus were measured and compared among groups. Data were analyzed with SPSS package using one-way ANOVA test with P<0.05 as the limit of significance.

Results: The results showed that the stronger ceramic fillers have positive effect on the flexural strength. Ceramic fillers increased the flexural strength significantly. No significant differences could be determined in DTS among the groups. Flexural modulus can be affected and increased by using ceramic fillers.

Conclusion: Flexural strength is one of the most significant properties of restorative dental materials. The higher flexural strength and flexural modulus can be achieved by stronger ceramic fillers. Any further investigation in this field would be beneficial in the development of restorative dental materials.

Statement of Problem: The relatively poor wear resistance of dental composite in stress bearing posterior situations has restricted wider clinical application of this restorative material.

Purpose: The aim of this study was to evaluate the three body abrasive wear of a dental composite based on a new filler (leucite: KAl Si2O6) and to compare it with the wear resistance of a composite based on commonly used Aluminium – Barium Silicate filler.

Materials and Methods: This research was an interventional study done in Iran polymer institute. Five specimens were considered in each group. All ceramic IPS Empress® (Ivoclar- Vivadent) ingots based on leucite crystals were ball milled, passed through an 800 sieve and used as filler. Experimental composites were prepared by mixing the silane- treated fillers with monomers (BisGMA and TEGDMA). Camphorquinone and amine were used as photoinitiator system. Degree of conversion of the light-cured and post-cured composites was measured using FTIR spectroscopy. The prepared pastes were inserted into plexy-glass mold and light cured (700 mw/cm2, 40 s). Then for maximum degree of conversion specimens were post- cured (120ºC, 5 hours). Three body abrasion wear testing was performed using a wear machine with 50 rpm rotational movement. In this machine, pumice (150 meshes) was used as the third body. Weight loss of specimens in each group was measured by balance after each 50 hours. After wear testing SEM examination was made specimens in each group. The data were analyzed and compared using ANOVA and Tukey HSD tests (P<0.05). Tetric Ceram was tested as commercial composite.

Results: There were significantly differences between three body abrasive wear of composites. The ranking from lowest to highest was as follows: leucite composite (19%) < Tetric Ceram (22%) < glass composite (28%). leucite composite showed the highest wear resistance value, propably due to the crystalliniy and hardness of filler.

Conclusion: Introduction of this new filler as an alternative to glass filler, significantly increases the wear resistance of the resin composites. Further investigations on mechanical properties of new composites would be beneficial in the development of new dental materials.

Background and Aim: The majority of commercial curing units in dentistry are of halogen lamp type. The new polymerizing units such as blue LED are introduced in recent years. One of the important side effects of light curing is the temperature rise in composite resin polymerization which can affect the vitality of tooth pulp. The purpose of this study was to evaluate the temperature rise in two different composite resins during polymerization with halogen lamps and blue LED.

Materials and Methods: This experimental study investigated the temperature rise in two different composites (Hybrid, Tetric Ceram/Nanofilled, Filteke Supreme) of A2 shade polymerized with two halogen lamps (Coltolux 50, 350 mW/cm2 and Optilux 501 in standard, 820 mW/cm2 and Ramp, 100-1030 mW/cm2 operating modes) and one blue LED with the intensity of 620 mW/cm2. Five samples for each group were prepared and temperature rise was monitored using a k-type thermocouple. Data were analyzed by one-way ANOVA, two-way ANOVA and Tukey HSD tests with P<0.05 as the limit of significance.

Results: Light curing units and composite resins had statistically significant influence on the temperature rise (p<0.05). Significantly, lower temperature rise occurred in case of illumination with Coltolux 50.There was no significant difference between Optilux 501 in standard curing mode and LED. Tetric Ceram showed higher temperature rise.

Conclusion: According to the results of this study the high power halogen lamp and LED could produce significant heat which may be harmful to the dental pulp.

Background and Aim: Chlorhexidine is a mouthwash with known antibacterial effect but its antifungal effect is not clear. The aim of this study was to compare the antimicrobial effects of nystatin and chlorhexidine mouthwashes (one Iranian product and the other, commercial) on Candida albicans under in vitro condition. Materials and Methods: In this experimental study, the strains of Candida albicans used consisted of one standard strain (PTCC 5027) and ten local isolates. The latter were obtained from patients referred to different dental clinics in Kerman city. The specimens were taken from the gum and palate area by sterile swabs and dipped into Stewards transport medium, transferred to the laboratory within one hour, and cultured on Sabauraud dextrose Agar. Colonies showing the characteristic appearance of Candida were further cultured and routine differential tests including germ tube formation were performed to confirm the diagnosis of

C.albicans. These were used to prepare a microbial cell suspension of 0.5 Mc Farland concentration. Each cell suspension was inoculated over duplicate plates of SDA and 4 wells of 5 mm diameter were made using sterile cork borers. Each previously coded mouthwash was placed in corresponding well and incubated for 24-48 hours and the diameter of inhibition zone was measured with ruler. The minimum inhibitory concentration (MIC) of each mouthwash for each isolate of Candida albicans was determined using dilution tube technique. Data were analyzed by SPSS package using proper statistical tests with P<0.05 as the limit of significance.

Results: There was a significant difference between the antimicrobial effects of the four tested mouthwashes. The results indicated that Iranian nystatin mouthwash had the greatest effect and the average inhibition zone from the highest to the lowest was associated with Iranian nystatin, foreign nystatin, Iranian chlorhexidine and foreign chlorhexidine respectively. The MIC determination revealed that generally nystatin was more effective than chlorhexidine. No statistical difference was seen between the Iranian and foreign samples.

Conclusions: Despite the antifungal effects of chlorhexidine, more investigations on different strains of C.albicans is required before recommending its cilinical application.

Background and Aim: Insufficient polymerization of resin cements is of considerable clinical importance, because of mechanical deficiencies and biological side effects of uncured resin. Dual cure resin cements are getting popular in luting tooth colored posts and although their curing is claimed to proceed chemically, polymerization efficiency in deep areas of canal is uncertain. The aim of this study was to evaluate degree of polymerization of dual-cure resin cements used for luting translucent and opaque fiber posts in different distances from the light tip.

Materials and Methods: In this experimental in vitro study, degree of conversion of two dual cured resin cements, Rely X ARC (3M, ESPE) and Nexus 2 (Kerr, USA) were measured when used with DT-Light and DT-White posts (RTD, France). The light curing unit used was Optilux 501, with output of 650-700 mw/cm2 with emitting time of 60 seconds. Degree of conversion was measured in three different depths (4, 6, 8 mm) by FTIR. The data were analyzed using ANOVA and Post hoc tests. P<0.05 was considered as the level of significance.

Results: DC% of Rely X with either of the posts was not significantly different in the studied depths (P>0.05). Nexus used with DT-Light had lower DC% in 8 mm depth (P<0.05). Nexus used with DT-White showed lower DC% in 8 mm depth compared to 4 mm depth. The control groups of both cements showed significant increased DC% in 4 mm depth compared to 6 and 8 mm depths (P<0.05). DT-White caused decreased DC% in both cements in 4 mm. DT-Light caused increased DC% of Rely X in 6 mm depth compared to DT-White and control. DT-Light increased DC% of Nexus in 6 and 8 mm depths, compared to DT-White and control groups.

Conclusion: Based on the results of this study, application of translucent fiber posts has a significant effect on degree of polymerization in dual-cure resin cements, compared to opaque types. Their better light transmission to deep areas due to the effect of optical fibers, can lead to better results.

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 way ANOVA, Tukey HSD. P<0.05 was considered as the limit of significance.

Results: Tetric ceram revealed higher DCthan 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 Aims: In spite of the advances achieved in the field of dentin adhesives, the longevity of bond to dentin is still a challenge. According to recent studies, Matrix Metaloproteinase (MMP) inhibitors can increase clinical longevity of bonding and decrease leakage. The aim of this study was to evaluate the amount and pattern of doxycycline release from an experimental dentin adhesive containing this MMP inhibitor.

Materials and Methods: In this experimental study, specimens containing 0.25 and 0.5 loading percent of doxycycline in an experimental monomer were prepared in cylindrical moulds of 12 mm diameter and 2 mm thickness. The adhesive monomer was composed of 12 wt% Bis-GMA, 10 wt% TMPTMA, 28 wt% HEMA and 50 wt% ethanol. Camphorquinone and amine were used as initiators.

Results: Addition of 0.25 and 0.5 w% doxycycline showed linear release in both groups. Increasing the loading percent of doxycycline caused more release. The release continued during the test period.

Conclusion: Doxycycline release was observed from the experimental adhesive. Further studies in this field will help in preparing adhesive systems with more clinical longevity.

  Background and Aims: Bleaching agents not only affect the tooth structure, but also may alter the properties of restorative materials. The aim of this in vitro study was to evaluate the effect of different bleaching regimens on the microhardness of four tooth-colored restorative materials.

  Materials and Methods: Eighty specimens of four restorative materials (Microhybrid resin composite (Z250 (3M, ESPE), nanohybrid composite Z350 (3M, ESPE), packable composite P60 (3M, ESPE), and resin modified glass ionomer Vitremer (3M, ESPE)) were fabricated and were polished after 24 h with Soflex discs (3M,ESPE). Then the specimens were divided into two groups: In office bleach group, 40 specimens (10 of each restorative material) were bleached with hydrogen peroxide 37.5% for 30 min in two sessions with 7 days interval. In home bleaching group, 40 specimens were bleached with carbamid peroxide 22%, 6 h a day for 14 days. Vickers microhardness test were done before and after bleaching (baseline). Finally data were evaluated using analysis of Variance.

  Results: Two bleaching regimens were significantly decreased the microhardness values. In Z250 resin composite, the microhardness values before and after bleaching were 95.30 and 92.67 kg/mm², respectively. for office bleaching (P=0.011) and 95.38 and 92.39 kg/mm² for home bleaching (P<0.001). In Z350 resin composite, the microhardness values before and after bleaching were 98.29 and 92.41 kg/mm², for office bleaching (P<0.001) and 97.35 and 93.44 kg/mm² for home bleaching (P<0.001) respectively. In P60 resin composite, the microhardness values before and after bleaching were 103.10 and 96.16 kg/mm², respectively. for office bleaching (P=0.045) and 102.61 and 98.16 kg/mm² for home bleaching (P=0.001). In resin modified glass ionomer (Vitremer), the microhardness values before and after bleaching were 56.79 and 49.41 kg/mm², respectively. for office bleaching (P=0.004) and 54.17 and 46.50 kg/mm² for home bleaching (P<0.001). There was no significant difference between two bleaching agents (P=0.365).

  Conclusion: Dental bleaching agents decrease the microhardness of tooth-colored restorative materials.