Journal of Dental Medicine

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The purpose of this study was to assess the fluoride release of three fluoride- containing materials exposed to fluoride solutions. This study compared the initial fluoride release and release following re-fluoridation (neutral or acidic 2% NaF) of three different filling materials, conventional glass ionomer cement (CG1C), resin- modified glass ionomer cement (RMGIC), polyacid- modified composite resin (PAMCR). Twenty discs of each material, measuring 2mm height and 6mm diameter, were suspended in separate vials of 2" laboratory artificial saliva. The amount of fluoride release was measured over two periods of 28 days each. Fluoride release was determined at 1,3,7,14 and 28 days of each period. Fluoride was measured with a fluoride ion- specific electrode and an ion analyzer previously calibrated with standard solution .T- test and ANOVA were used to evaluate the data. Fluoride release for all products at days 1 and 3 was significantly greater than the rest of the time intervals. Then, the fluoride release decreased significantly. CGIC released significantly more fluoride than the other products. This was followed by RMGIC, which exhibited significantly more fluoride release than PAMCR. In second period of experiment, the specimens were assigned to two subgroups often each. The samples exposed to two different solution of NaF (neutral or acidic). All groups showed the capacity of re-fluoridation and fluoride uptake. The specimens exposed to acidic NaF solution showed statistically more significant rechargeability than the neutral NaF solution. It may be concluded that glass ionomer cements act as a rechargeable slow fluoride release systems and as an effective caries preventive material in caries preventing programs for caries susceptible children.

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Composite resin restorative materials, that nowadays are used as tooth-colour materials, have both benefits and weaknesses. One of these weaknesses is the contraction resulted from resin polymerization which influences on the composite dentin bond strength and it has been tried to be eliminated by different bonding systems. The aim of this in-vitro study was to compare the dentin bond strength of two dentine adhesive systems: multi-step Scoth Bond Multipurpose (SBMP) and single- step Excite, by two composites of Ideal Makoo and Tetric. One hundred sixty (160) sound human molars were selected. At first they were debrided and mounted with acrylic resin in molds. The enamel of the buccal surface was eliminated by diamond burs. To provide a flat dentin surface, it was removed about lmm. Then, based on the type of dentin adhesive, they were divided into two groups of 30 teeth and were applied on the exposed dentine surface according to the manufacturer's instructions. Then, each group was divided into two subgroups of 15, based on the type of composite resin. Cylinders of the desired composite resin, attached to the dentin surface, were used for 80 seconds. The samples were stored in 100% humidity (37°c) for 24 hours. The bond strengths was measured by a cross head blade with the speed of 2mm/min. Variance analysis and Duncan test, with 95% confidence level, showed that statistically, two factors of adhesive and composite, interact on each other, in bond strength. There was no significant difference in bond strength, between two composites with similar adhesives, however, comparing two different adhesives with the same composite, showed that the bond strength of Tetric with Excite (28.39) was more than that of SBMP (17.98 Mpa). Finally, it was recognized that among four experimental groups, there was only a significant difference in bond strengths, between Tetric-Excite with Tetric- SBMP. This study shows that dentin bond strength is influenced by dentin bonding agents, composite type and dentin structure, and using a type of composite with a dentin bonding agent, manufactured by the same company, results in a higher bond strength.

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Statement of Problem: The construction of dental materials has been developing inside the country.Cold- cured acrylic resins are of such materials which are used in removable prostheses.
Purpose: The aim of this study was to compare the dimensional changes of two types of cold-cured acrylic resins, Acropars and Meliodent.
Material and Methods: Forty acrylic discs, with diameter of 13.7 mm, were made of Acropars and Meliodent acrylic resins (20 samples in each group). Then, each group was randomly divided into two parts. The first group was kept in usual environment, whereas the samples of the second group were placed in the boiling water for five minutes. The dimensional changes of the samples, at different intervals and seven days post curing, were measured by light microscope and recorded. Variance analysis was used to analyze the results.
Results: Acropars resins, comparing to Meliodent ones, showed a considerable dimensional changes,which was statistically significant. Boiling of Acropars resins, for five minutes, lead to a significant shrinkage. The maximum shrinkage occured at 24 hours post curing.
Conclusion: If the tray is made of Acropars acrylic resin, it is recommended to take impression, 24 hours
after its setting.

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Statement of Problem:Iranian product, Acropars autopolymerizing acrylic resin is nowadays widely used in dental prostheses. Dimensional change is a common problem among Iranian made acrylic resins in making custom trays and record bases, seems to be more than the similar foreign products. In order to achieve a technique for making a record base with minimum dimensional changes, more research is necessary.
Purpose: The aim of the present study was to determine a curing technique for Iranian autopolymerizing acrylic resins leading to the least polymerization shrinkage and the most adaptation between record bases and stone casts.
Materials and Methods: In this experimental study, 40 stone casts were divided into four 10- member group. For each group, polymerization shrinkage was determined at three points with one of the following techniques: Bench curing, Curing under a coat of petroleum jelly , Curing in a monomer saturated atmosphere, Curing in boiled water. Adaptation between bases and stone casts were measured at three points (the right and left crests of the ridge and the midpalatal region) with a light-measuring microscope. To analyze
the data, Variance analysis was used.
Results: The monomer atmosphere technique showed the minimum dimensional changes and the samples in boiled water group had the maximum dimensional changes. No statistical differences were observed between other groups.
Conclusion: More adaptation between record bases and stone casts was observed in monomer atmosphere polymerization technique. The differences between bench curing and curing under a coat of petroleum jelly techniques with this method were not statistically significant. Therefore, it is suggested for making base records with maximum adaptation.

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Statement of Problem: Composite reins have recently become popular for posterior teeth restorations. Gap formation and subsequent microleakage are of the complications resulting from such restorations. One of the techniques to overcome polymerization shrinkage of composite resins is sandwich technique (application of glass ionomer as a base beneath the composite resin). Since polymerization patterns in two types of composite resins (light cure and self cure) differ from each other, various effects on the bond strength between glass ionomer and dentin are expected.
Purpose: The aim of this in vitro study was to evaluate the effects of self- cure and light- cure composite resins in sandwich technique on the bond strength of light cure glass ionomer and dentin.
Materials and Methods: 40 extracted human premolars were selected and divided into four groups:Group 1: Light cure glass ionomer of 1mm thickness was placed on dentin.Group 2: 1mm thickness of light cure glass ionomer plus a mass of self cure composite resin of 2mm thickness were placed.Group 3: 1mm thickness of light cure glass ionomer plus light cure composite resin as two separate 1mm layer were placed.Group 4: 1mm thickness of light cure glass ionomer with 37% phosphoric acid etching followed by two separate layers of light cure composite resin of 1 mm thickness were placed.SEM was used to determine gap size ai Gl- dentin and Gi- composite interlaces. The findings were analyzed by ANOVA and t-student tests.

Results: Groups 1 and 2 showed no gap at Gl-dentm interface and also cracks were not observed in all these specimens. In group 3, there was gap between light cure GI and light cure composite resin and cracks were seen in GI, too. Group 4 showed gap at both interfaces and more cracks were seen in GI. Groups I and 2 showed the least gap formation and group 4 showed the most. Statistically significant difference was found between groups 3, 4 and group 1 (control), 2.
Conclusion: Base on this study, the application of self-cure composite resin on light cure GI showed no gap and crack formation on Gl-dentin and Gl-composite interfaces and GI itself. However, light cure composite resins and glass ionomer etching aggregated crack and gap formation.

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Statement of Problem: In a previous study it was reported that a durable resin-ceramic tensile bond could be obtained by an appropriate silane application without the need for HF acid etching the ceramic surface. Evaluation of the appropriate application of silane by other test methods seems to be necessary.

Purpose: The purpose of this study was to compare the interfacial fracture toughness of smooth and roughened ceramic surfaces bonded with a luting resin.

Materials and Methods: Ceramic discs of 10 mm in diameter and 2 mm in thickness were prepared. Four different surface preparations (n=10) were carried out consisting of (1) ceramic surface polished to a 1µm finish, (2) gritblasted with 50µm alumina, (3) etched with 10% HF for 2 min, and (4) gritblasted and etched. The ceramic discs were then embedded in PMMA resin. For the adhesive area, the discs were masked with Teflon tapes. A circular hole with diameter of 3 mm and chevron-shaped with a 90° angle was punched into a piece of Teflon tape. The exposed ceramic surfaces were treated by an optimised silane treatment followed by an unfilled resin and then a luting resin cylinder of 4mm in diameter and 11 mm in length was built. Specimens were stored in two different storage

conditions: (A): Distilled water at 37°C for 24 hours and (B): Distilled water at 37°C for 30 days. The interfacial fracture toughness (GIC) was measured at a cross-head speed of 1 mm/min. The mode of failure was examined under a stereo-zoom microscope and fracture surfaces were examined under Scanning Electron Microscope.

Results: The mean interfacial fracture toughness values were Group A: 1) 317.1±114.8, 2) 304.5±109.2, 3) 364.5±169.8, and 4) 379.4±127.8 J/m2±SD. Group B: 1) 255.6±134.4, 2) 648.0±185.1, 3) 629.3±182.6 and 4) 639.9 ±489.0 J/m2±SD. One way Analysis of Variance showed that there was no statistically significant difference in the mean interfacial fracture toughness for groups A1-A4 (P>0.05). However, the mean interfacial fracture toughness for group B1 was significantly different from that for groups B2, B3 and B4 (P<0.05). Independent-ٍٍٍSamples T-Test results showed that there was a significant increase in the GIC mean value for groups B2 and B3 after 30 days water storage (P<0.05). The modes of failure were predominantly interfacial or cohesive within the resin. Conclusions: The fracture toughness test method used in this study would be appropriate for analysis of the adhesive zone of resin-ceramic systems. From the results, it can be concluded that micro-mechanical retention by gritblasting the ceramic surfaces could be sufficient with no need for HF acid etching the ceramic surfaces when an appropriate silane application procedure is used.

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Statement of Problem: Because dental amalgam does not adhere to tooth structure, using adhesive cements in amalgam-bonded restorations have been increased.

Purpose: The goal of this in-vitro study was to compare the effects of three types of glass ionomer as adhesive liners as well as varnish liner in increasing fracture resistance of teeth restored with amalgam.

Materials and Methods: Seventy extracted human maxillary premolars were selected and MOD cavities were prepared on them excluding ten intact teeth as positive control group and ten cavity prepared teeth without restoration as negative control group. All the prepared teeth were then restored with spherical amalgam (gs.80) with one of the following liners silver alloy glass ionomer liner, conventional glass ionomer liner, varnish liner, resin-modified glass ionomer and resin-modified glass ionomer with delayed light curing. The teeth were stored in 37C distilled water for 7 days and were then loaded under compressive strength using an Instron testing machine. The force required to fracture teeth were recorded and the data were analyzed statistically using ANOVA and Tukey HSD tests.

Results: Statistically significant differences were observed in fracture resistance between restored and non-restored samples. Comparisons between groups attributed significant effects to resin-modified glass ionomer in increasing fracture resistance of amalgam restored teeth (P<0.05). In most specimens, one cusp was separated from tooth structure whereas amalgam remained bonded to the intact cusp. Conclusion: According to these findings, resin-modified glass ionomer put a statistically significant effect in fracture resistance of amalgam-restored teeth.

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Statement of Problem: The use of dentine bondings on enamel and dentin in total etch protocols has recently become popular. Unfilled resin is hydrophobic and dentin bonding is hydrophilic in nature. This chemical difference could be effective in enamel bonding process. Purpose: The aim of this study was to compare the shear bond strength of unfilled resin to dry enamel and dentin bonding to dry and moist enamel.

Materials and Methods: In this experimental study, a total of 30 incisor teeth were used. The specimens were randomly assigned to three groups of 10. 37% phosphoric acid etchant was applied to the enamel surfaces in each group for 15 seconds, rinsed with water for 20 seconds and dried for 20 seconds with compressed air in groups one and two. After conditioning, group 1 received unfilled resin (Margin Bond, Colten) and group 2 received dentin bonding (Single Bond, 3M) and in group 3 after conditioning and rinsing with water, a layer of dentin bonding (Single Bond) was applied on wet enamel. The enamel and dentin bonding were light cured for 20 seconds. A ring mold 3.5 mm in diameter and 2 mm height was placed over the specimens to receive the composite filling material (Z100, 3M). The composite was cured for 40 seconds. The specimens were thermocycled and shear bond strengths were determined using an Instron Universal Testing Machine. The findings were analyzed by ANOVA One-Way and Tukey HSD tests.

Results: Shear bond strength of dentin bonding to dry enamel was significantly less than unfilled resin to dry enamel (P<0.05). There was no significant difference between the bond strength of dentin bonding to moist and dry enamel. In addition bond strength of dentin bonding to wet enamel was not significantly different from unfilled resin to dry enamel.

Conclusion: Based on the findings of this study, it is suggested that enamel surface should remain slightly moist after etching before bonding with single bond but when using unfilled resin, the enamel surface should be kept dry.

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Statement of Problem: Blood contamination is a common problem in dentistry that can decrease bond strength dramatically which may be affected by methods of decontamination as well.

Purpose: The aim of this study was to evaluate and compare the influence of blood contamination on shear bond strength of composite and compomer to dentin using Prompt L-Pop as an adhesive system. Also, to assess the effectiveness of different surface treatments on the bond strength.

Materials and Methods: In this experimental study, 120 molar teeth were sectioned to provide flat occlusal dentinal surfaces. Specimens were embedded in acrylic resin with the flat surface exposed. The dentinal expose surfaces were polished to 600 grit. The teeth were randomly divided into five groups of twelve specimens (F1–F5) for compomer material and five other groups (Z1- Z5) for composite resin. After application of Promt L-Pop to dentinal surfaces of specimens, the surfaces in all groups, except for F1 and Z1, (as controls) were contaminated with human blood and then one of the following surface treatments was applied. Groups F2 and Z2 without any treatment, groups F3 and Z3 rinsing with water, groups F4 and Z4 rinsing with water and reapplication of adhesive, groups F5 and Z5 rinsing with NaOCl and using Prompt L-Pop again. Restorative materials were applied to treated surfaces using plastic molds. After thermocycling, shear bond strengths, mode of failures and morphology of dentin-material interfaces were evaluated. The data were statistically analyzed using Factorial analysis of Variance, One-Way ANOVA, Duncan, T-student and Chi-Square tests with P<0.05 as the limit of significance.

Results: Compomer showed statistically significant higher bond strength in comparison to composite (P<0.001). Duncan test showed significant differences between all compomer groups, except between groups F4 and F5, and between all composite groups except for groups Z1 and Z4 and for groups Z2 and Z3.

Conclusion: Based on the findings of this study, shear bond strength of compomer material was significantly higher than composite. Blood contamination reduced bond strength, but rinsing contaminated dentin with water or NaOCl and reusing Prompt L-Pop increased bond strength in both materials.

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Statement of Problem: Evaluation of fracture properties is a basic principle for true assessment of brittle materials’ properties. Resin–based composite materials are being used extensively in today’s dentistry. Fracture toughness is considered an important parameter for providing useful information about material’s nature, properties and its resistance to fracture.

Purpose: The purpose of this study was to evaluate the fracture toughness of a resin composite produced in the country and to compare it with that of other standard materials.

Materials and Methods: Four types of resin composite materials were used as follow to prepare 60 specimens (n=15 for each group), A) Tetric Ceram (Ivoclar–Vivadent) B) Brilliant (Coltene-Whaledent) C) SpectrumTPH (Dentsply) and D) Ideal Macoo (Ideal Macoo, Iran). Specimens of 5 mm diameter ( 0.1 mm) and 2 mm depth (±0.1 mm) were prepared in a central notch (90 notch angle) PTFE mold. Then specimens were light cured with two applications of overlapping exposures for a total of 120 s and were stored in distilled water at 37ºC for 48 hours, A cylindrical roller of 3 mm diameter was seated inside the V sections and fracture was accomplished in a universal testing machine at a crosshead speed of 0.5 mm/min. Data were analyzed by one–way ANOVA and post-hoc paired Tukey HSD test with P<0.05 as the limit of significance.

Results: The mean KIC and torque to fracture (T) values for each material tested were A) 3.080.42, 16.992.34, B) 2.880.63, 16.041.98 C) 3.400.53, 18.752.93 and D) 2.870.46, 15.782.57 MN/m3/2SD and N/mmSD, respectively. Group C showed significantly the highest mean KIC and T values among groups tested which was significantly higher than that of group B and D (P<0.05). The mean KIC and T values for groups A, B, and D were not significantly different (P>0.05).

Conclusion: From evaluating the fracture properties of materials tested in this study it was concluded that the mean fracture toughness value for SpectrumTPH (Dentsply) was significantly higher than that of Ideal Macoo resin composite material (Ideal Macoo, Iran). The F.T value for Ideal Macoo was considered acceptable as it was not significantly different from that of other resin composite materials tested.

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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.

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Background and Aim: Water sorption and solubility are important properties of acrylic resins. Denture base acrylic resins have low solubility. This solubility results from the leaching out of unreacted monomer and water soluble additives into the oral fluids. The solubility of denture bases can cause oral soft tissue reactions. In addition, water absorbed into this material acts as a plasticizer and decreases the mechanical properties such as hardness, transverse strength, fatigue limit and also can change the color and dimensional stability. The aim of this study was to compare the water sorption and solubility of Acropars and Meliodent heat cure acrylic resins.

Materials and Methods: This experimental study was performed on the basis of ADA specification No.12 and ISO No.1567 and standards NO: 2571 of Institute of Standards & Industrial Research of Iran. Six disc form samples of each acrylic resin were prepared, with the dimension of 50×0.5 mm. After desiccating, the samples were kept in an oven for 24 hours and weighed. Then they were immersed in water, kept in oven for 7 days and weighed again. After this phase, the samples were carried to a dessicator, for 24 hours and kept in an oven for drying and were weighed for the third time. Data were analyzed with Mann Whitney and one sample t-test. P<0.05 was considered as the limit of significance.

Results: Water sorption mean values were 30.5±0.1 µg/mm3 or 0.76±0.01 mg/cm2 for Meliodent samples and 30.7±0.87 µg/mm3 or 0.77±0.009 mg/cm2 for Acropars samples. No significant difference was observed in water sorption of these two materials (P=0.9). Meliodent acrylic resin showed lower solubility (1.7±0.097 µg/mm3 or 0.042±0.001 mg/cm2) than Acropars acrylic resin (2.5±0.13 µg/mm3 or 0.062±0.001 mg/cm2) (P=0.002).

Conclusion: Acropars heat cure acrylic resin matched well with the requirements of the international standards for water sorption, but its solubility was not favorable. This problem is probably the result of high concentration of residual monomer, the amount and type of cross linking agents and plasticizers as well as the amount of water soluble additives in this material.

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Background and Aim: Cementation is one of the most critical steps of the porcelain restoration technique. However, limited information is available concerning the bond strength of current ceramic bonding systems. The aim of this study was to evaluate the shear bond strength of three dual-cure resin cements to IPS-Empress2 ceramics.

Materials and Methods: In this experimental study, 30 pairs of IPS-Empress 2 ceramic discs were fabricated with 10 and 8 mm diameters and 2.5 mm thickness. After sandblasting and ultrasonic cleaning, the surfaces of all specimens were etched with 9% hydrofluoric acid for 60 seconds. Then, the three groups of 10 bonded specimens were prepared ceramic bonding resin systems including Panavia F2, Variolink II and Rely X ARC. After storage in 37±1c water for 24 hours and thermocycling in 5c and 55c water for 500 cycles with 1-minute dwell time, the shear bond strengths were determined using Instron machine at speed of 0.5mm/min. Data were analyzed by One Way ANOVA test. For multiple paired comparisons, the Tukey HSD method was used. The mode of failure was evaluated by scanning electro microscope (SEM). P<0.05 was considered as the limit of significance.

Result: Significant differences were found between different cement types (P<0.05). Variolink II provided the highest bonding values with IPS-Empress2. A combination of different modes of failure was observed.

Conclusion: Based on the results of this study, according to the highest mode of cohesive failure, Variolink II seems to have the strongest bond with IPS-Empress2 ceramics.

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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.

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Background and Aim: Patients always complain about metallic color of amalgam restorations. Covering amalgam by composite can solve this problem. Since polymerization shrinkage is a serious shortcoming in composites, application of the combined amalgam and composite restoration is one of the methods to reduce leakage in the cervical margins of posterior restorations. The aim of this invitro study was to evaluate the microleakage of amalgam/composite interface when Rely-X ARC adhesive resin cement was used in the joint.

Materials and Methods: Twenty-four sound extracted premolars were chosen. Mesial and distal class II conventional cavities were prepared and the samples were divided into 4 groups of 12. In all groups, the bases of the cavities were restored with amalgam and then the remaining part was filled by composite resin. Specimens in groups 1 and 2 were restored with composite-resin, immediately after condensing amalgam without or with application of Rely-X ARC (3M, ESPE) respectively. In groups 3 and 4, composite resin were applied 24 hours after condensation of amalgam, without or with application of Rely-X ARC respectively. After polishing and thermocycling, all specimens were prepared for dye penetration and the degree of leakage was scored and analyzed using Kruskall Wallis test with p<0.05 as the level of significance.

Results: The frequency of dye penetration in different groups was obtained. The most and the least scores were observed in groups 3 and 4 respectively. No statistically significant difference was observed in different methods.

Conclusion: None of the methods in this study could seal the amalgam/composite-resin interface.

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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, eg. 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.

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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.

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Background and Aim: Nonmetallic tooth- colored posts adhere to canal walls by dentin bonding agents and resin cements. Better retention and proper distribution of stress result from enough and proper bonding. The purpose of this study was to evaluate bond strength of D.T. Light - post with two different resin cements (self-cure & dual-cure) and to investigate the effect of irrigating solutions applied in root canal on bond strength of the resin cements and D.T.Light- post to root canal wall.

Materials and Methods: In this experimental study 40 single root teeth (maxillary canine & central) were selected and stored in 0.1% thymol solution for one week and transferred to distilled water. The teeth were decoronated 2mm above CEJ. The canal space was mechanically enlarged using k-files (up to # 70). The teeth were randomly divided into two groups. The first group was irrigated with 2.6% NaOCl, and the second was irrigated with normal saline. After drying, the teeth were filled with gutta percha cones using lateral condensing method. After two weeks the post space was prepared and D.T.Light- post was inserted in each subgroup using self or dual-cure cements according to manufacturer's instructions. After thermocycling, the apical part was cut 1cm below CEJ. The remained length was divided into 9 equal sequential sections. Each section was submitted to shear push-out test in universal testing machine. Statistical analysis of the bond strength data was performed using ANOVA and post hoc tests with p<0.05 as the level of significance. All failed specimens were examined under stereomicroscope. Degrees of conversion of the cements were determined by FTIR.

Results: Significant difference in bond strength values were found among sites (P=0.001) and cements (P=0.03). With increasing in depth, bond strength decreased. The mean bond strength value in dual-cure resin cement was higher than self-cure cement. The irrigating solutions caused no significant difference in bond strength (P=0.46). DC% had significant difference in various depths.

Conclusion: According to the results of this investigation, bond strength of dual-cure cement is higher than self-cure one in D.T Light- post because of post's translucency. 2.6% sodium hypochlorite does not affect the bond strength.

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Background and Aim: Polymerization shrinkage of resin cements during setting leads to stress on teeth receiving indirect esthetic restorations. Some methods like blocking out undercuts during cavity preparation with glass Ionomer can reduce the mass of resin cement and therefore the amount of stress. The aim of this study was to evaluate the fracture resistance of molar teeth, receiving class I ceramic inlays with two different methods of blocking out undercut.

Materials and Methods: In this experimental study, thirty intact molar teeth were randomly divided into three groups of 10 each. One group was maintained intact as the control group. Similar class I cavities with identical undercuts were prepared on the other groups. In group 2 the undercut was filled with light cured glass Ionomer (vitremer 3M) before making impression, and in group 3 they were blocked out in the lab before preparation of the inlay. All the teeth in test groups were restored with indirect ceramic inlays.(vitadur - Alpha/ single bond / Rely X ARC). After thermocycling load causing fracture was assessed by universal testing machine. All the specimens were examined under a steriomicroscope (X40) to determine type of fracture. The results were analyzed by one way ANOVA and Tukey HSD tests. P< 0.05 was considered as the level of significance.

Results: The restored groups showed significantly less fracture resistance than the control group. The difference between two test groups was not significant. The fracture in group2 had less destruction.

Conclusion: According to the findings of this study, blocking out the undercut with two different methods (using glass ionomer/ or blocking it out on the die) made no diferrence in fracture resistance.

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Background and Aim: Debonding is the most common failure type of fiber posts. This in vitro study aimed to evaluate the bond strength of 3 different fiber posts cemented with a resin luting agent in three regions of prepared post spaces after being subjected to termocycling.

Materials and Methods Thirty six mandibular first premolars were sectioned at the cemento-enamel junction and were treated endodontically. After one week the post spaces were prepared and roots were divided into 3 groups of 12 specimens according to the post types (D.T.Composipost, D.T.White, D.T.Light). Sealbond Cement Dual II was used in all groups. One day after cementation, specimens were subjected to 3500 thermal cycles (5^oC/55^oC). Each root was then embedded in acrylic resin and sectioned perpendicular to long axis. Three 1-mm tick segments from apical, middle and cervical thirds were prepared. Push out test was performed. Data were analyzed with 2-way ANOVA (P<0.05). All root segments and dislodged posts were observed with stereomicroscope to figure out their failure modes.

Results: The post type had no significant effect on bond strength (p=0.08). However bond strength at the coronl segment was higher than the other segments (p=0.005). Mixed mode was the mostly occurred failure mode with D.T.Composipost and D.T.Light but with D.T.White, the mostly occurred failure mode was adhesive between the post and cement.

Conclusion: Different fiber posts have relatively similar bond strength to root dentin, bond strength at the coronl segment was higher than the other segments.