[Experimental comparison of hygroscopic expansion in three different composite resins]

These days dental composites are very popular because they look good and are similar to human teeth regarding color. Hygroscopic expansion is one of the physical properties of dental composites. A dental composite may lose its efficiency as a restoration material because of water absorption. The objective of this study was to compare the hygroscopic expansion of three dental composites. In this experimental study, to assess the effective factors of hygroscopic expansion, we used three different dental composites [Kalore, P90 and Z250]. The length of these composites in water and saliva were measured eighteen times in a three-month period. We used the marginal modeling technique, in which the correlation between response data can be included for analysis. The results of marginal modeling showed that the type of composite is significantly related to hygroscopic expansion [P<0.05]; demonstrating the highest hygroscopic expansion for P90 and the lowest for Z250. In addition, time as an independent variable had a statistically significant effect on hygroscopic expansion [P<0.05]. However, we found no significant difference between the hygroscopic expansion of saliva and water [P>0.05]. Overall, our findings showed that hygroscopic expansion is significantly related to the type of composite and time. Therefore, we should utilize the composites with lower hygroscopic expansion [such as Z250] for filling the patients' teeth

[ clinical efficacy of microabrasion and microabrasion with office bleaching in the esthetic improvement of fluorotic teeth]

Development of fluorosis is increasing due to the higher consumption of fluoride. Microabrasion is the most conservative technique for the management of this disorder. The present study assessed the esthetic improvement of fluorotic teeth after microabrasion with office bleaching. This clinical trial was carried out on 20 fluorotic teeth. Microabrasion was performed for 10 minutes followed by office bleaching. Digital images were obtained of all stages of the treatment. The esthetic improvement was determined by visual analogue scale along with the color parameters of Lab and [deltaE] after microabrasion [M], microabrasion plus office bleaching [MO] and one week later the data were subjected to One-way analysis of variance [ANOVA] for repeated measures, LSD and Friedman tests. No significant differences were found between fluorotic areas and non- fluorotic areas of the teeth after different stages of [M] regarding Lab and deltaE parameters. The mean deltaE was estimated to be 10.05, 14.51 and 20.28 for M, MO and one week later, respectively. Significant differences were observed between these stages [p<0.001]. In addition, the mean visual analogue scores for these stages were 4.15, 5.22 and 6.36, respectively, which were significantly different [p<0.0001]. This study showed that the microabrasion technique significantly improved the esthetic appearance of fluorotic teeth at all stages of treatment. The most improvement was observed with [MO] after one week and the least was related to [M], while immediate results of [MO] were moderate

[Effect of combined use of ozone and fluoride on primary root caries]

It has been suggested that delivering ozone into a carious lesion might reduce the number of cariogenic bacteria. This possibly could arrest the progress of the lesion and in the presence of fluoride perhaps allow remineralization. This study investigated the effect of ozone on leathery primary root caries. The study was a clinical trial using a split mouth design. A total of 23 pairs of bilateral leathery primary root caries were selected from Shahid Beheshti Dental School. After brushing, DIAGNODENT values of the samples were recorded in three points. Half of the samples which had been randomly selected were treated for 12 seconds using OZOTOP [MECTRON SWISS Inc.] The opposite arch was selected as the control group. Fluoride therapy was performed on both groups and DIAGNODENT values were measured again. This process was repeated a month later and DIAGNODENT values were recorded. Three months after the initial treatment DIAGNODENT values were measured again. Results were evaluated by using paired t test. The statistical significance level was set at P<0.05. The highest reduction was observed within the group of combined use of fluoride and ozone after 3 months [2.0439]. Comparisons between 3 months from baseline in the intervention group and the control group using paired t-test determined statistically significant differences [P value<0.001]. In a 3-month period, the combined effect of fluoride and ozone in reducing the DIAGNODENT value was higher than using fluoride alone

[Efficacy of two coating agents on the surface hardness of Fuji II and Fuji IX]

Many protective materials such as varnishes as well as specially designed agents are used to protect glass ionomer cements against hydration and dehydration. The use of enamel bonding agents is also purposed. This study was conducted to evaluate the efficacy of an enamel bonding agent. Vickers microhardness was used as the criteria for judgment. Forty five discs [26 mm] were made from each of the two glass ionomer cements using Fuji II and Fuji IX. They were divided equally into three subgroups, which were protected with either finishing gloss/3M, Margin bond/Coltene or without protection [control]. Microhardness of the specimens was evaluated at 24 hours, one week and one month after preparation. Data were analyzed by 3-way ANOVA and Tukey post-hoc test. The highest Vickers hardness number [VHN] for Fuji IX and Fuji II was recorded when protected with Margin bond at 1 month [110.54 +/- 6.52 and 106.43 +/- 8.30, respectively], whereas the lowest VHN was observed for the control group at 1 day [80.29 +/- 6.78 and 62.18 +/- 7.46, respectively]. There was no significant difference between Fuji II and Fuji IX coated specimens at all time intervals. Protecting the glass ionomer cements with either of the two agents exhibited similar results. Microhardness of the tested glass ionomers increased during the test period; however, the only differences detected were between one day and one month specimens. The performance of enamel bonding agent in protecting the glass ionomers was similar to that of especially designed coating material

[Fatigue resistance and failure mode of endodontically restored premolars with indirect composite resin restoration-in vitro]

The present study aimed at determination of the fatigue resistance and failure mode of cusp-replacing onlays in endodontically treated premolars using indirect composite resin restorations. In this experimental study, 84 human premolars were randomly divided into 7 groups of 12. These groups were prepared as follows: Intact teeth used in group1 as control, the second group covers the endodontically treated teeth, restored with indirect onlays using Z-250 composite resin, the next two groups [i.e. 3, 4] were similar to the second group, but subjected to 1 and 2 million fatigue load cycles, respectively. Groups 5, 6, 7 were similar to groups 2, 3, 4, respectively, however, in these groups Tetric Ceram used as the restorative material. All specimens were loaded using a Universal Testing Machine until fracture occurred and the mode of failure observed with naked eye. Kruskal-Wallis and Chi-Square tests were used to analyze the data [alpha=.05]. All specimens withstood the masticating simulation. The mean fracture strength for groups 1 to 7 were: 1276.92, 1269.05, 1217.80, 1188.13, 1228.97, 1127.86, 1105.58, respectively. No statistically significant differences were found between the groups in fracture strength and failure mode. There was no statistically significant difference between two types of resin composite [P=0.203] and load cycles [P=0.298] after zero, 4 and 8 years aging. Within the limitation of this study, restored premolars with indirect composite onlays show fatigue resistance equal to natural tooth up to 8 years after restoration. Furthermore, no statistically significant differences were found between 4 and 8 years of load cycles. Tetric Ceram Z-250 restoration agent showed no effect on the tooth fracture resistance with the most observed fractures to be occur under CEJ with no capability to be restored

[Evaluation of compressive strength in conventional and pack able composite materials]

The mechanical properties of composite resin have significant effect on performance and success of a restorative procedure. The aim of present investigation was to evaluate the compressive strength of conventional and pack able composite materials. A stainless steel mold of 4 mm in diameter by 6 mm in height was used to fabricate 50 study specimens. The cylindrical specimens were divided in five groups [n=10]. The materials used in this study were Alert, Charmfil Plus, P60, Z100 and Spectrum. Following photo polymerization by using Radi Plus light curing unit [SDI Limited], the specimens were stored in distilled water at 37°C for 48 hours. The specimens were subjected to compressive stress using mechanical testing machine [Zwick/Roell] at cross head speed of 0.5 mm/min. One-Way ANOVA and Tukey's Post-hoc tests were employed to determine group differences and the significance level if any of the restorative materials could show significant difference among others. There were significant statistical differences between groups [P < 0.05]. Z 100 showed the highest and Charmfil Plus demonstrated the lowest amount of compressive strength. There was no significant statistical difference between Z 100 and P 60, but, differences were significant between Z 100 and other materials. Based on the findings of this investigation, the compressive strength of packable composites was not proving better than conventional composites

[Effect of Er,Cr:YSGG laser on fissure sealant retention: Comparative in-vitro study]

Use of pit and fissure sealants are safe and effective preventive procedures for occlusal caries. Long term retention of pit and fissure sealants is essential for their success and depends partly on the method of fissure preparation. Recently, new technologies such as laser and air abrasion have been used to increase bond of sealants. This in vitro study compared the effect of laser with other methods [air abrasion and conventional] on retention of sealants by measuring micro shear bond strength. This experimental in-vitro study used sound premolar teeth. They were sectioned mesiodistally in order to use the buccal and lingual surfaces. Samples were randomly divided into 3 groups. Group I samples were prepared with 37% acid phosphoric. Group II samples were exposed to air abrasion and then acid etching. Group III specimens were exposed to Er,Cr:YSGG [2W power] and then acid etching. Bonding was applied on all samples and sealants in microbore tygon tube [0.7 mm in diameter and 1mm height] were cured. Data on micro shear bond strength was measured and analyzed statistically by One-Way ANOVA and Tukey tests. Mean micro shear bond strength for group I, II, III, were 23.51[ +/- 6.9], 39.09[ +/- 15.11], 21.44[ +/- 6.18] MPa respectively. A significant statistical difference [P<0.01] was detected in group II [air abrasion with etching] compared with other groups. Considering the smooth surface enamel used in this study, it can be concluded that irradiation of the laser before etching can not increase fissure sealant retention. However, air abrasion technique before etching showed greater sealant retentions

comparative study of fluoride release from available glass-ionomers: 2-months data

Fluoride released from restorative materials was known as an effective factor to prevent secondary caries. The purpose of this study was to compare the fluoride ion release from two conventional glass-ionomers; lonocid-F and Fuji II and two Resin- modified glass-ionomers; lono Gem LC and Fuji II LC. In this experimental study, five disc - shaped specimens [7x2mm] from each material were prepared. The specimens were placed in plastic containers with l0cc of deionized water. The solutions were changed daily up to one week and thereafter every 12 days for three consecutive days. This regimen was repeated four times over a period of 2 months. Solutions were buffered with TISAB II and fluoride measurements were carried out using a fluoride ion-selective electrode connected to a pH ion-selective electrode meter. The results were converted to ppm. Statistical analysis were conducted using ANOVA and Scheffe. All of the materials showed high initial release values which decreased significantly in second day. lonocid-F [267.643 +/- 17.916 ppm] released significantly more fluoride ions during two months which followed by lono Gem LC [101.284+10.068 ppm], Fuji II LC [23.276 +/- 2.609 ppm] and Fuji II [20.027 +/- 4.232 ppm]. However, there was no significant difference between Fuji II LC and Fuji II. There was a wide variation of fluoride ion release from the materials but patterns of release were similar

Comparison of the solubility of conventional glass ionomer and modified cements: an in vitro study

Solubility of restorative materials leads to loss of marginal intergrity, surface properties and aesthetics. Thus, the solubility of these materials is of considerable importance. The aim of this in vitro study was to measure the solubility of two types of conventional and resin-modified restorative glass-ionomer cements [GIC]. Two conventional GICs [Ionocid F and Fuji II] and two resin-modified GICs [Iono Gem LC, Fuji II LC] were employed in the present study. A Perspex mould, 7mm in diameter and 2mm thick was used to fabricate five specimens from each material. Samples were suspended in 50 cc distilled water during the study period. To measure solubility, all specimens were dried and weighed at different time intervals, up to one month. Solubility was expressed as the mean weight loss percentage. The results were analyzed using ANOVA with repeated measurements on one factor and Scheffe and t-paired tests [P<005]. Ionocid F and Fuji II LC demonstrated the highest [24.09% +/- 0.87%] and lowest [1.05% +/- 0.74%] solubility values, respectively. The solubility of Iono Gem LC [7.34% +/- 2.20%] and Fuji II [9.01% +/- 1.33%] were intermediate between the other two cements, An increase in solubility was observed during the test period for all studied materials. The solubility of Iranian GICs was significantly higher than Fuji II and Fuji II LC cements