Journal of Dental Medicine

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  Current study is aimed to compare fluride release in conventional glass ionomer, light-cured glass ionomer and compomers. Standard samples from the aforementioned materials were prepared and measured by selective fluride ion electrode in intervals of 24hours, 1,2,3 and 4 weeks in neutral PH of 7 and acidic PH of 4.5. The obtained data represented that fluride ion release decreased in time but the pattern of this issue was different. Besides, it was found that in lower Ph fluride release is significantly affected. Compomer relatively releases less fluride than the others but as long as this amount can sufficiently prevent caries development, it can be stated that based on clinical status any of above choices can be selected. Besides, the more easily handled and available materials are used, the more successful the clinical results will be achieved.

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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.

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Discoloration of composite resins is considered to be a major factor in esthetic restoration failures. The aim of this study was to evaluate color stability of IDM composite (both light and self cure samples namely IL and IS), and to compare it with a self-cure composite (Degufill named DS) and a light cure ormocer composite (Definite, called DL in the Report). 60 disk shaped samples of each composite were prepared, according to ISO-7491. The samples were divided into 3 groups and aged as follows: A- (Control) 7 days in dark 37°c chamber B- Foil covered and kept in 100% humidity, and 37°c in xenotest chamber for 24 hours, then transferred to a dark 37°c chamber for 6 more days.C- Kept in 37°c, 100% humidity under the emission of xiiion lamp of xenotest chamber for 24 hours,and then transferred to 37°c dark chamber for 6 more days The lightness and chromaticity values of samples were measured both before and after aging using a spectrophotometer (Data Flash). The total color changes as well as changes in lightness and chromaticity values were measured in the CIE L * a * b * scale, and analyzed. Color change was recorded to be significant in all samples after aging. The maximum change belonged to IL, which was significantly
different from DL and DS. It seems, in order to have a durable esthetic restoration using IDM, more scientific and professional consideration is needed in the production process.

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Oral cancers account for a relatively high percent of neoplasms in the elderly population. Treatment protocols often include anti-neoplastic pharmaco-therapeutics, irradiation of the head and neck region, and surgery. These treatments, specially radiation, have detrimental effects on oral hard and soft tissues. Salivary glands undergo a distinct and longterm dysfunction, which leads to decrease in salivary How. Xerostomia is a common clinical problem in these patients which contributes to dry mouth, mucosites, change in oral ecosystem and dental caries, followed by difficulties in speech, swallowing and use of dentures which cause malnutrition. This phenomenon has an irreversible weakening effect on the patient's health. To prevent this negative impact on oral health in this group of patients, definitive dental treatments prior to the initiation of medical therapies is imperative, and will decrease the morbidity rates. Today's dentistry benefits from improved methods and materials, which enable us to give these patients a better preventive dental treatment. Consultation between dentist and medical team would be the best way to help our sufferer patients.

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 Polymerization shrinkage of light cure composite resins causes many complications in conservative and esthetic restorations. The objective of this in-vitro study was to evaluate the polymerization shrinkage, degree of conversion and the amount of filler in IDM and tetric ceram composites. Ten disk shaped, uncured specimens (8mm×1.547mm) of each composite were placed on glass slide in the center of the metal attached to it. Then specimens were light cured for 60s from underneath. After 30 minutes, the thickness of specimens, using a micrometer and the percent of the polymerization shrinkage of each sample were measured. Statistical analysis was carried out by t-test (P<0.05). Also the degree of conversion of specimens was evaluated with FTIR and the mineral filler content was measured by burning in electric oven. Polymerization shrinkage in IDM and tetric ceram was not significantly different. Degree of conversion and mineral filler content in tetric ceram was greater than that of IDM.

It is assumed that the low degree of conversion in IDM is due to its chemical composition and filler content. Also, the similarity in linear polymerization shrinkage between IDM and tetric ceram may be caused by the low degree of conversion in IDM.

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Statement Problem: A few studies have been conducted about bioglass posts.
Aim: The aim of this study was to compare bioglass posts with prefabricated metallic posts in clinical performance of extensive composite restorations for anterior endodontically treated teeth.

Materials and Methods: Sixty endodontocally maxillary anterior teeth, with horizontally or vertically destruction, were selected. Teeth were divided into two groups based on the kind of post: Metallic prefabricated parapost and bioglass post. Each group was divided into three subgroups based on anterior bite: normal, deep bite and edge to edge. Gutta-percha was removed from 2/3 of canal length for parapost and 1/3 for bioglass post. After etching with phosphoric-acid (37%) and applying dentine bonding syntac, Duo cement was used for the adhesion of bioglass post and a self cured composite (Degufil) for parapost. Restoration was done with a hybrid composite (Heliomolar). Follow up studies, radio-graphically and clinically, were done every three months for a 1.5-year period. Exact Fisher and Pearson tests were used for data analysis.
Results: Apical lesion was not observed in any of the radiographs. Post seal was increased by resin cement and dentin bonding agent. Post type did not significantly affect on the clinical success rate of the restorations. The retention of restoration, for both posts, was the same. Crown destruction had no significant effect on success rate. The type of anterior bite had a significant effect on success rate, as the total 6.6% failure rate was related to the patients with anterior deep bite.
Conclusion: It is suggested to use metallic paraposts and bioglass posts, in extensive composite restorations for patients with deep-bite, more conservatively.

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Statement of Problem: A lot of efforts have been made to create a complete adaptation between tooth and amalgam restorations.
Purpose: The aim of this study was to evaluate microleakage and interfacial micromorphology of amalgam restorations lined with dentin adhesives, namely One Coat Bond, Syntac, Excite and Copalite,as liners.
Materials and Methods: 144 intact human canine teeth were selected. Then class V cavities, with enamel and dentinal margins, were prepared on each of them. Cavities were lined with different dentin bonding systems (Syntac, One Coat Bond and Excite) according to the manufacturer's instructions and restored with Oralloy and Cinalloy, non gamma 2 spherical amalgams and Aristaloy a non gamma 2 Admixed alloy. Copalite was used in the group, served as controls. After thirty days storage in synthetic saliva at 37°c, the specimens were thermocycled in saliva (4000 cycles). The degree of microleakage was assessed by means of basic fushin dye penetration and recorded. The gap width was evaluated with Scanning Electron Microscope. Pearson and %2 tests were used to analyze the results.
Results: None of the systems, tested in this study, eliminated microleakage completely, Pearson's correlation coefficient showed a positive correlation between gap and microleakage (P<0/05).Statistical significant differences were revealed among the liners regarding gap and microleakage (P<0.05).One Coat Bond and Syntac appeared to leak less than other groups. The gap width by One Coat Bond and Syntac were respectively 0.35 and 0.3 urn in dentine, 0.2 and 0.1 in enamel. Excite and copalite gap width in dentine and enamel were 1,3-1.36 urn and 0.3-0.6, respectively. The type of amalgam did not have any effect in the degree of microleakage and gap width (P>0/05).
Conclusion: One Coat Bond and Syntac, comparing to Excite and Copalite, showed less microleakage and gap width.

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Statement of Problem: Considering that the role of collagen fibers in dentin adhesion has not been thoroughly established yet, the removal of exposed collagen fibers with a deproteinization agent such as sodium hypochlorite following etching may facilitate access of adhesive resins to a substrate that is more penetrable and less sensitive to water content which in turn would lead to a more durable bonding system. Furthermore, due to sodium hypochlorite clinical application as a cleanser or canal irrigator, its effects on the surface before etching may influence adhesive bonding strength.

Purpose: The goal of this study was to evaluate the effects of a two-minute 5.25% NaOCL application on composite restorations microleakage, using two different adhesive systems.

Materials and Methods: In this interventional experimental study, on seventy-two extracted boving incisors class V cavities were prepared on dentinal surfaces. The specimens were then randomly divided into six equal groups: A1) Acid etch (AE) dentin bonding Scontchbond Multipurpose Plus (SBMBP), A2) AE/ dentin bonding One Step (OS), B1) NaOCL/ AE/SBMPp, B2) NaOCL/AE/OS, C1) AE/NaOCL/SBMPp, C2) AE/NaOCL/OS. After bonding procedures according to the manufacturer’s instructions, cavities were restored using Z100 composite. Then, the specimens were thermocycled for 500 times in water baths of 5 and 55C. After thermocycling, the specimens were immersed in a 0.2% solution of basic fuchsin for 24 hours. A buccolingual section at the center of each restoration was obtained and examined with a stereomicroscope to evaluate color penetration into cavities. The data were subjected to two-way variance analysis.

Results: The microleakage of group B was significantly less than those of A and C (P<0.001). No significant difference was found between groups A and C (P=0.73). There were also no significant differences within groups A, B and C (P=0.852). No interaction was observered between dentin bondings and surface treatment (P=0.946).

Conclusion: The findings of this study revealed that NaOCL application after etching, for hybrid layer removal, did not make any difference on microleakage as compared with conventional bonding systems. However, its application before etching improved the seal of restoration. Additionally, there was not any significant difference between two different dentin bondings.

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Statement of Problem: Parafunctional habits are the most important factor in the creation of non-carious cervical lesions and correcting of these habits may affect cervical lesions.

Purpose: The goal of this study was to survey the effects of one-year occlusal adjustment on clinical success of non- carious cervical restorations.

Materials and Methods: In this clinical study, sixty tooth-colored cervical restorations on canines and premolars in patients with parafunctional habits (bruxism and clenching) were studied. The teeth, according to the type of restorative material, were randomly divided into two groups: One group with a composite resin (Tetric Flow Group A: n=30) and the other group with a compomer (Compoglass Flow Group B: n=30). After restoration, each group was divided into two subgroups: (A1, B1) with occlusal adjustment (case group), (A2, B2) without occlusal adjustment (control group). The evaluation was perfumed single blind at 6 and 12 months after restorative operations according to Us Public Health Service (USPHS) classification. Assessment criteria included: marginal integrity, marginal discoloration, recurrent caries, postoperative sensitivity and loss of filling. Statistical analysis was completed using Fisher’s exact test.

Results: In 12 month period between two groups of compoglass Flow restorations, group B1 showed superior results than group B2, however, no significant difference was found between both groups of tetric flow restorations (A1 and A2). There was also no difference in clinical conditions between A2 and B2 groups.

Conclusion: Considering the results of this study, it can be concluded that occlusal adjustment puts a considerable effect on clinical success of compoglass non- carious cervical restorations. However, it should be mentioned that such and effect was not found among Tetric flow restoration.

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Statement of Problem: Bleaching materials are able to change the surface morphology as well as mineral and organic content of tooth structure. Considering that bleaching is done for aesthetic purpose, awareness of the possible effect of these materials on hard tissue is important, because it may affect the restorative treatments.

Purpose: The aim of this study was comparing the effect of two bleaching materials, Kimia and Ultradent both containing 35% H2O2, on tooth enamel by SEM.

Materials and Methods: Five intact central incisors were cut into three sections vertically and each part was randomly divided into three groups. Group 1 (control), without any bleaching. Group 2, bleached with Kimia 35% H2O2. Group 3, bleached with Ultradent 35% H2O2. Each tooth served as its own control. Then the samples were observed by SEM with 250 and 500 magnifications.

Results: In the control group some scratches and small white grains were observed which seems to be the result of mastication trauma and pumice powder. In the other groups, morphologic changes like increased surface roughness, deepening of cracks, rod exposure and presence of new cracks were observed. The two experimental materials did not differ in these regards.

Conclusion: It seems that both studied materials have limited destructive effects on tooth enamel which seems to be of no clinical importance.

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Background and Aim: With recent introduction of packable composites, it is claimed that they apply less stress on tooth structure because of reduced polymerization shrinkage, and similarity of coefficient of thermal expansion to tooth structure. However, the high viscosity may in turn cause less adaptation, so it is not clearly known whether these materials strengthen tooth structure or not. The aim of this study was to evaluate fracture resistance of maxillary premolars, receiving hybrid or packable composite restorations with different methods of application and curing.

Materials and Methods: In this experimental study, seventy five intact premolars were randomly assigned to five groups of 15 teeth each. One group was maintained intact as the control group. Similar MOD cavities were prepared in the other teeth. The teeth in group two were restored with Spectrum in incremental layers and light cured with 500 mw/cm2 intensity. The third group were filled with Surefil and cured with light intensity of 500 mw/cm2. The groups four and five were restored with Surefil in bulk technique with two different modes: 500 mw/cm2 intensity and a ramp mode (100-900 mw/cm2) respectively. After thermocycling, force to fracture was assessed and degree of conversion (DC) at the bottom of cavities was evaluated for different modes and methods. The curing and placement methods in groups tested for DC (A to D) were the same as fracture resistance groups (2 to 5). Data were analyzed using one way ANOVA and Tukey HSD tests with p<0.05 as the limit of significance.

Results: All the restored groups showed significantly less fracture resistance than the control group, but had no significant difference among themselves. DC of Spectrum was higher than Surefil. Bulk method with 500 mw/cm2 light intensity, significantly decreased DC. DC in bulk method with high light intensity was not significantly different from incremental method with 500 mw/cm2 light intensity.

Conclusion: Placement techniques, light intensity and type of composite had no influence on the fracture resistance. The use of packable composite with bulk technique and 500 mw/cm2 intensity or less is not recommended in 4 mm depth cavities due to insufficient DC.

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Background and Aim: Nanoleakage can cause discoloration around restoration margins, secondary caries, postoperative sensitivity and finally loss of restoration, thus adequate hybrid layer is of primary importance in prevention of nanoleakage in adhesive restorations. Because of structural differences between primary and permanent dentin, evaluation of nanoleakge in primary teeth is very important. The aim of this study was to evaluate the nanoleakage in composite restorations following application of self -etch and total-etch adhesives in primary and permanent teeth.

Materials and Methods: In this experimental study, Cl V cavities were prepared in buccal surfaces of 20 extracted primary molars and 20 extracted premolars. Each group was divided into 2 subgroups: In group (A), Gluma One Bond and in group (B), iBond adhesive materials were applied. After silver nitrate staining, specimens were mesiodistally sectioned and polished and then SEM examination was carried out to measure the nanoleakage .Data were analyzed statistically using, ANOVA and Duncan tests with p<0.05 as the limit of significance.

Results: Factors tested had no significant effect on each other. Primary teeth showed more nanoleakage than permanent teeth (P<0.05). Mean nanoleakage was significantly higher in cervical than occlusal margins (P<0.05) and also in iBond than in Gluma One Bond in primary teeth (P<0.05). In permanent teeth, the lowest nanoleakage was observed in Gluma One Bond.

Conclusion: The result of this study indicates that the use of total etch dentin adhesives (Gluma One Bond) in bonded restorations results in less nanoleakage in primary and permanent teeth.

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Background and Aim: Stainless steel crown (SSC) is the most durable and reliable restoration for primary teeth with extensive caries but its metalic appearance has always been a matter of concern. With advances in restorative materials and metal bonding processes, composite veneer has enhanced esthetics of these crowns in clinic. The aim of this study was to evaluate the shear bond strength of SSC to composite resin using different surface treatments and adhesives.

Materials and Methods: In this experimental study, 90 stainless steel crowns were selected. They were mounted in molds and divided into 3 groups of 30 each (S, E and F). In group S (sandblast), buccal surfaces were sandblasted for 5 seconds. In group E (etch) acidic gel was applied for 5 minutes and in group F (fissure bur) surface roughness was created by fissure diamond bur. Each group was divided into 3 subgroups (SB, AB, P) based on different adhesives: Single Bond, All Bond2 and Panavia F. Composite was then bonded to specimens. Cases were incubated in 100% humidity at 37°C for 24 hours. Shear bond strength was measured by Zwick machine with crosshead speed of 0.5 mm/min. Data were analyzed by ANOVA test with p<0.05 as the limit of significance.

Results: There was no statistical interaction between surface treatment and adhesive type (P>0.05) so the two variables were studied separately. No significant difference was observed in mean shear bond strength of composite among the three kinds of adhesives (P>0.05). Similar results were obtained regarding surface treatments (P>0.05).

Conclusion: Based on the results of this study, treating the SSC surface with bur and using single bond adhesive and composite can be used successfully to obtain esthetic results in pediatric restorative treatments.

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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: The efficiency of disinfecting materials and procedures in removal of contamination from dental surfaces and equipments is essential. In authors' previous study, daily use of 2:100 dilution of 5% sodium hypochlorite in water and disposable covers were recommended since HBV contamination was found on semi-critical parts of the operative dentistry department. The aim of this study was to evaluate the HBV contamination following application of the recommended procedures.

Materials and Methods: The study was conducted in two parts. In the first cross-sectional part, samples were collected from 17 sites of dental surfaces. In the second interventional part samples were collected from 10 sites of 9 dental and 3 sites of 2 light cure units, before and after disinfection with 5% sodium hypochlorite solution diluted to 2:100. Sterile cotton swabs moistened with sterile BSAS (Bovine Serum Albumin in Sodium Chloride) solution were used for sampling. Samples were tested by PCR technique in Pasteur Institute, Iran.

Results: None of the samples collected in the first part of the study showed contamination. In the second part of the study, from 96 samples taken from various parts of dental and light cure units, before and after disinfection, there was only one HBV contaminated site before disinfection which showed no contamination after disinfection.

Conclusion: Based on the results of this study, disinfecting procedure with 5% sodium hypochlorite solution diluted to 2:100 along with using disposable covers is effective in preventing HBV contamination.

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Background and Aim: Because of polymerization shrinkage and high viscosity of posterior composites, there are some difficulties in using them in posterior restorations. Several methods have been represented to reduce the effect of shrinkage. The aim of this study was to investigate the effect of curing flowable composites under condensable ones in adaptation and microleakage reduction of posterior composite restorations.

Materials and Methods: In this experimental in vitro study, forty class II MO cavities were prepared on extracted intact molar and premolar human teeth. Gingival margins were placed 1 mm apical to CEJ. The teeth were divided into two groups. In group 1, flowable composite (Filek Flow, 3M, ESPE, USA) with 0.5-1 mm thickness was applied and cured following application of bonding agent (Single Bond, 3M, ESPE, USA). The rest of the cavity was filled by condensable composite (p60, 3M, ESPE, USA). In group 2 the flowable composite was not cured, and the condensable composite was applied in two increments. After light curing of composites, all the specimens were thermocycled and then immersed in 0.3% basic fuschin. Specimens were sectioned and evaluated for degree of dye penetration under a stereomicroscope. Data were analyzed by Mann-Whitney test with p<0.05 as the level of significance.

Results:. There was no significant difference between the two studied groups regarding microleakage.

Conclusion: Based on the results of this study, neither cured nor uncured flowable composite under condensable composite can omit microleakage in posterior composite restorations.

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Background and Aim: Amalgam is one of the mostly used restorative materials, but has some disadvantages. Microleakage is one of the short comings of amalgam which may lead to sensitivity and recurrent caries. The aim of this study was to evaluate the effect of three dentin bonding systems on reduction of microleakage in amalgam restorations.

Materials and Methods: Class II amalgam restorations were made in 40 noncarious molar and premolar teeth. Then the specimens were divided into four equal groups. Scotch Bond Multi Purpose, Single bond,
iBond, were used as liner in groups one to three respectively and in group four no liner was used. The teeth were restored with high copper spherical amalgam. After thermocycling for 500 cycles at 5⁰C and 55⁰C, the specimens were immersed in basic fuchsin for 24 hours, bisectioned mesiodistally and evaluated under stereomicroscope at X25 for dye penetration. The data were analyzed by Kruskal-wallis and Scheffe. P<0.05 was considered as the level of significance.

Results: The groups showed significant difference (p=0.003). The group four had significantly less microleakage than the first and second groups (p<0.05). The second and third groups showed significantly different microleakage (p=0.038).

Conclusion: Based on the results of this investigation applying dentin bonding agents has no effect on reducing microleakage in amalgam restorations, however more studies are recommended.

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Background and Aim: Various studies have shown that reliable bond at the root - post - core interfaces are critical for the clinical success of post - retained restorations. Severe stress concentration at post - cement interface increases post debonding from the root. To form a bonded unit that reduces the risk of fracture, it is important to optimize the adhesion. Therefore, some post surface treatments have been proposed. The purpose of this study was to investigate the influence of various surface treatments of tooth - colored posts on the bonding of resin cement.

Materials and Methods: In this interventional study, 144 tooth colored posts were used in 18 groups (8 samples in each group). The posts included quartz fiber (Matchpost), glass fiber (Glassix), and zirconia ceramic (Cosmopost) and the resin cement was Panavia F 2.0. The posts received the following surface treatments: 1- No surface treatment (control group), 2- Etching with HF and silane, 3- Sandblasting with Cojet sand, 4- Sandblasting with Cojet sand and application of silane, 5- Sandblasting with alumina particles, 6- Sandblasting with alumina particles and application of silane. Then, posts were cemented into acrylic molds with Panavia F 2.0 resin cement. The specimens were placed in water for 2 days and debonded in pull - out test. Statistical analysis was performed using ANOVA followed by Tamhane and Tukey HSD. Failure modes were observed under a stereomicroscope (10 ). P<0.05 was considered as the significant level.

Results: Surface treatments (sandblasting with Cojet and alumina particles ,with or without silane) resulted in improved bond strength of resin cement to glass fiber post (Glassix) and zirconia ceramic (Cosmopost) [p<0/05], but not to the quartz fiber post (Matchpost). In general, higher bond strengths resulted in a to higher percentage of cohesive failures within the cement.

Conclusion: Based on the results of this study, sandblasting with cojet and alumina particles increases bond strength of resin cement to glass fiber post (Glassix) and zirconia ceramic (Cosmopost).Generally, the bond strength of resin cement to the posts is affected by the post's composition and surface treatment.

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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.