Ability of dental students in detection of proximal caries

Objective: Tooth decay is one of the most common chronic diseases in the world. After pit and fissures, enamel of proximal surface is the second region prone to rot. Bitewing images are one of the most important diagnostic tools for the detection of caries. Given the importance of accurate and timely detection of decay, the current study was aimed to evaluate the ability and skill of the final year dental students to identify the presence and depth of proximal caries in dental bitewing radiography

Methods: In this descriptive cross-sectional study 208 inter proximal surfaces among the 13 dental bitewing radiographs were selected randomly. The radiographs were evaluated by two experienced dental specialists [a radiologist and a restorative specialist] to detect inter proximal decay between teeth. These diagnoses were considered as the gold standard. The radiographs were further assessed by fourteen final-year dental students. Finally, the collected data were analyzed by SPSS-17 software using Kappa coefficient of agreement and ICC. The sensitivity and specificity values were also determined

Results: The value of Kappa correlation coefficient to assess the similarity between students' responses and gold standards was obtained as 0.28 [p<0.001]. The Kappa correlation coefficient for evaluation of the precision of the data was 0.71. The sensitivity in the whole population was 0.43, while the specificity was 0.84

Conclusion: According to the results obtained in this study, the performance of final year dental students to identify the presence and depth of proximal caries from bitewing radiographs was not satisfactory. Moreover, the ability to detect normal surfaces was unacceptable

Influence of different power outputs of Er:YAG laser on shear bond strength of a resin composite to feldspathic porcelain

Statement of the Problem: Porcelain may fracture or chip if exposed to any traumas and can be repaired by using a resin composite

Purpose: This study was aimed to evaluate the influences of Er:YAG laser on shear bond strength [SBS] of resin composite to feldspathic porcelain

Materials and Method: Seventy-two porcelain blocks were divided into six groups [n=12]: G1: no treatment [control group]; G2: 9% hydrofluoric acid [HF]; G3-6 were separately irradiated with Er:YAG laser using four energy parameters: 2W, 100mj [G3]; 3W, 150mj [G4]; 4W, 200mj [G5] and 5W, 250mj [G6], respectively; and 20 Hz frequency in long-pulse mode. After silane treatment, a resin composite rod was bonded to each of the porcelain block. The SBS was measured following storage and thermocycling. Data were analyzed by one-way ANOVA, Tamhane and Chi-Square tests

Results: The highest SBS [12.29 +/- 3.04 MPa] was obtained with HF [G2]. The lowest SBS [2.23 +/- 0.60 MPa] was observed in G4, followed by G3 [1.96 +/- 0.76 MPa]. G6 had a significantly higher SBS [8.00 +/- 2.22 MPa] than other laser irradiation groups

Conclusion: Although, Er:YAG laser irradiation at 5W, 250mJ/20 Hz was effective in promoting adhesion of resin composite to feldspathic porcelain compared with the control group, it cannot be used as a safe alternative method to HF acid. Laser irradiation with the evaluated parameters in this study does not promote an effective adhesion on porcelain surface to create adequate bond for clinical use

Effect of three light curing protocols and load cycling on microleakage of class V composite restorations

Objective: Different methods have been suggested to overcome the polymerization shrinkage of composite restorations. Changing the light curing protocol to improve polymerization by using new light curing units is among these methods. The new devices are more efficient, portable and durable and produce less heat. This study aimed to assess the marginal microleakage of class V composite restorations subjected to three different light curing protocols and mechanical cycles

Methods: This was an in-vitro experimental study. Class V cavities measuring 2x3x1.5 mm were prepared on the buccal and lingual surfaces of 90 extracted human premolar teeth 1.5 mm above and below the cement enamel junction [CEJ]. The samples were selected using convenience sampling and divided into 9 experimental groups of 10 each by using the Table of Random Numbers to control for the bias. The cavities were restored with packable composite resin along with Tetric-NBond and cured using three light curing protocols of conventional [680 mW/cm[2] for 30s], soft-start [380 mW/cm[2] for 10s followed by 680 mW/cm[2] for 20s] and pulse [680 mW/cm[2] for 30s,1s interval and 1s of lighting]. The teeth were then subjected to mechanical cycles of 0, 500,000 and 1,000,000 and immersed in 2% Fuchsin for 24h. The teeth were then sectioned in half from the middle of the restoration buccolingually and the degree of microleakage was evaluated under a stereomicroscope [Zeiss, Germany] with 40X magnification. Data were analyzed using the Kruskal Wallis and the Mann-Whitney tests

Results: Despite the structural differences between the enamel and dentin margins, no significant difference was found in the degree of microleakage between the enamel [occlusal wall, p>0.05] and dentin [gingival wall, p>0.05] margins among the understudy groups

Conclusion: The degree of marginal microleakage in soft-start [SS] polymerization was not significantly different from that in conventional and pulse polymerizations of class V composite restorations

[Comparison of solvent evaporation in the self etch and total etch adhesives in different air draying times]

Different adhesives with different solvents may have different solvent evaporation rates. The purpose of this study was to evaluate the solvent evaporation in the self etch and total etch adhesive in different air drying times. Five adhesives were used in this study: Excite, Prime and Bond NT, UNO, Single Bond, SE Bond Primer. Twelve drops of each adhesive were used for each period of air drying [5, 15, 30 sec]. The percentage of mass loss was measured during each test. Data were analized using two-way ANOVA and Tukey. Acetone base adhesives showed more loss of mass than other adhesives [P<0.01]. P and B NT showed more loss of mass than other adhesives in all air drying times [P<0.01]. Adhesives showed different evaporation rates in different air times [P<0.01]. Adhesives with acetone/ water or alcohol/water solvent shows more stable behavior in comparison with adhesives containing pure aqueous solvents

[Effect of bleaching on the microhardness of tooth-colored restorative materials]

Bleaching agents not only affect the tooth structure, but also may later 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. 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. 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/mm[2], respectively. for office bleaching [P=0.011] and 95.38 and 92.39 kg/mm[2] for home bleaching [P<0.001]. In Z350 resin composite, the microhardness values before and after bleaching were 98.29 and 92.41 kg/mm[2], for office bleaching [P<0.001] and 97.35 and 93.44 kg/mm[2] 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/mm[2], respectively. for office bleaching [P=0.045] and 102.61 and 98.16 kg/mm[2] 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/mm[2], respectively. for office bleaching [P=0.004] and 54.17 and 46.50 kg/mm[2] for home bleaching [P<0.001]. There was no significant difference between two bleaching agents [P=0.365]. Dental bleaching agents decrease the microhardness of tooth-colored restorative materials

[Effect of re-application of microbrush on micro tensile bond strength of an adhesive to dentin]

Re-application of microbrush may affect the micro tensile bond strength of adhesives to dentin. The aim of this study was to evaluate the effect of re-application of microbrushes on the micro tensile bond strength of an adhesive to dentin. Thirty freshly extracted molars teeth were collected and enamel of occlusal surface were removed to expose superficial dentin. Then superficial dentin was etched, washed and partially air dried. According to the times of application of microbrush, teeth were divided into two test groups. In group 1, new microbrushs were used, but in group 2, the ones that were already used for twice were included. Ambar dentin bonding agent [FGM/Brazil] was applied to the etched dentin with microbrushes according to the manufacturer's instructions. Then the crown of teeth was built up with LLiss [FGM/Brazil] composite resin. The teeth were sectioned in buccolingual direction to obtain 1mm slabs. Then 50 hourglass- shape samples were made from 30 teeth [25 Specimens per group]. The microtensile bond strength of the specimens was tested using MTD500 [SD Mechatronik, Germany]. The data were statistically analyzed by T-test. The mean values for the microtensile bond strength were 30.49 +/- 7.18 and 23.61 +/- 9.06 MPa +/- SD for the first and second groups, respectively. There was significant difference between the groups [P=0.005]. Microbrushes should not be used for more than one cavity preparation.

[Effect of different air-drying periods on microtensile bond strength of an adhesive to dentin]

Today, use of adhesive systems is the most common materials in restorative dental procedures. The aim of this study was to evaluate the effect of different air-drying periods on the microtensile bond strength of composite to dentin using adhesive. 15 sound molar teeth were selected. The occlusal surfaces of teeth were removed with silicon carbide disks [3M/USA] to reach the flat surface of dentin. Then according to the air drying of solvent, the teeth were divided to five groups. After 5 sec etching and rinsing for 15 sec, the teeth were air dried for 3 sec. Then Singlebond [3M] was used with different air-drying times [0s, 2s, 5s, 10s, 30s] and cured. Then after insertion and curing of Saremco [microhybrid low shrinkage/Switzerland] composite, the teeth were thermocycled for 500 cycles. Then hour glass slabs with 1 mm[2] interface was created. Specimens were then subjected to microTBS force until fracture. Data were analyzed using ANOVA and Bonferroni tests. Statistical tests showed that there were significant differences between bond strength of groups [P=0.002]. The mean of microTBS for the 2 Sec and 30 Sec evaporating time was the most and the least vawes, respectively. An optimum air-drying time for solvent evaporation was the lowest time recommended by the manufacturer. Over and under evaporation time decreased microTBS significantly.

[Comparison of degree of conversion of packable and hybrid composites by fourier transform infrared spectroscopy]

Clinical performance of light cured resin composites is related to their degree of polymerization. The purpose of this study was to compare the degree of conversion of packable and hybrid composites by FTIR [Fourier Transform Infrared Spectroscopy]. In this experimental study, 40 composite disks were prepared in two groups from Z250 and P60 composites. Each group was divided into four subgroups [2mm thickness cured with QTH unit, 2mm thickness cured with LED unit, 5mm thickness cured with QTH unit, and 5mm thickness cured with LED unit]. Then samples were evaluated by FTIR to determine the degree of conversion [DC]. Data were analyzed by Kolmogorov-Smirnov and three way ANOVA. There was not a significant difference among the DC of the materials tested. LED significantly increased the degree of conversion of materials tested [P<0.001]. DC values were significantly greater in 2mm diameter samples vs 5mm ones [P<0.001]. The use of incremental technique in deep cavities restored with these composites is suggested. Also using LED is advised for curing composites because of a better result

[Effect of two surface sealants on microleakage of class V resin composite restorations]

When composite resin polymerizes, shrinkage stresses tend to produce gaps at the tooth/ restoration interfaces. Surface sealants may reduce or avoid problems related to the marginal interface. The aim of this study was to evaluate the effect of two different surface sealants [Fortify and Optiguard] on the microleakag of class V resin composite restorations. Twenty three sound noncarious molars were collected. Totally, 45 Class V cavities wit the occlusal margins in enamel and cervical margins in cementum were prepared in both buccal and lingua surfaces. The specimens were randomly assigned in three groups [15 cavities in each group] and then restorec with a resin composite. After the finishing and polishing procedures, the restorations in each group were coverec with a specific surface sealant, except for the control samples, which were not sealed. After placing restorations the specimens were thermocycled and then immersed in a 50% silver nitrate solution [tracer agent] for four hours sectioned longitudinally and analyzed for leakage using a stereomicroscope in a blind manner. The margina microleakage was evaluated at the occlusal and cervical interfaces and compared among the three groups using the Kruskall-Wallis and the Mann-Whitney U tests. Microleakage was found in all groups at both occlusal and cervical margins. Significantly greater leakage was observed at the cervical margins compared to the enamel margins of the material groups [P=0.005]. There was no statistically significant difference among the groups at occlusal margins [P=0.66]. In the cervical region, Fortify showed improved results and statistically presented the lowest degree of microleakage [P=0.003]. The used sealant materials presented different rates of effectiveness and Fortify decreased marginal microleakage significantly

Effect of curing direction on microtensile bond strength of fifth and sixth generation dental adhesives

Composite restorative materials and dental adhesives are usually cured with light sources. The light direction may influence the bond strength of dental adhesives. The aim of this study was to evaluate the effect of light direction on the microtensile bond strength of fifth and sixth generation dental adhesives. Prime and Bond NT and Clearfil SE bond were used with different light directions. Sixty human incisor teeth were divided into 4 groups [n=15]. In groups A and C, Clearfil SE bond with light curing direction from buccal was used for bonding a composite resin to dentin. In groups B and D, Prime and Bond NT with light curing direction from composite was used. After thermocycling the specimens were subjected to tensile force until debonding occurred and values for microtensile bond strength were recorded. The data were analyzed using two-way ANOVA and Tukey post hoc test. The findings showed that the bond strength of Clearfil SE bond was significantly higher than that of Prime and Bond NT [P<0.001]. There was no significant difference between light curing directions [P=0.132]. Light curing direction did not have significant effect on the bond strength. Sixth generation adhesives was more successful than fifth generation in terms of bond strength to dentin

Comparison of bond strength of different restorative materials in mandibular anterior teeth class V restorations

The aim of the present study was to determine the effect of different restorative materials on fracture resistance of mandibular teeth with class V restorations. One hundred intact mandibular incisors were selected and divided into ten groups with 10 samples in each. Three types of restorative materials; Tetric flow composite [Vivadent Ets, Schaan/Liechtenstein], Compoglass [Vivadent Ets,Schaan/Liechtenstein] and light curing glass ionomer [GC Corporation Tokyo JAPAN] were used in our study. Each of these materials were applied in cavities with 2, 3 and 4 mm widths. Group 10 was considered as the control group in which no restorations was done. All teeth were mounted in cold cure acrylic resin [Tray Resin II, Shofu Inc, Kyoto, Japan] and the samples were tested by applying shear force with cross head speed of 5mm/min in a universal testing machine [Instron corp., Canton, MA,USA]. Data were analyzed with two way ANOVA and Dunnet multiple comparisons test using SPSS 10 software package. Regardless of the types of materials, cavities with 4mm width had less bond strength than those with 2 and 3 mm widths [P-value=0.555]. In the Compoglass and glass ionomer L.C. groups, cavities with 2 and 3mm widths had significant greater strength than cavities with 4mm width [P-value=0.0002]. In groups with Tetric flow restorative material no significant difference in shear force among different widths of cavities were detected [P-value=0.4948]. The mean shear force in this group was comparable with the control group [P-value=0.0001]. In cavities 2 and 3 mm widths, there was not any significant difference in shear force between Tetric flow and compoglass restorative materials. Glass ionomer and Tetric flow had the least and the highest shear bond strength ,respectively. The results showed that although all the restorations need an average load more than masticatory forces in the mouth to fail, but Tetric flow composite with combination of chemical adhesion properties and optimum elastic characteristics was proven to be the restorative material of choice for cervical Defects with different widths