Amir Ghasemi

Effects of pulsed Nd:YAG laser on microleakage of composite restorations in class V cavities.

OBJECTIVE The purpose of this study was to evaluate the effects of pulsed Nd:YAG laser on decrease of dentinal microleakage beneath the restoration. METHODS Thirty-two sound extracted premolar teeth were subjected to two standardized, V-shaped, class V cavity preparations on both buccal and lingual surfaces. Cavities were located at 1-2 mm below the cemento-enamel junction (CEJ) line. The teeth were divided into two groups of experimental and control in an random manner. Both 20 and 15 mJ/pulse laser energies were tested. Etching, bonding, and filling were performed using Tetric ceram composite material. All samples were thermocycled for 1000 cycles, followed by an immersing period of 1 week in 2% basic fuchsin solution. Specimens were then sliced longitudinally and evaluated under a digital scanner for the extent of dye penetration. RESULTS Our results indicated that the level of microleakage of laser-treated cavities was significantly less than that of untreated cavities (p < 0.05) for 20 mJ/pulse laser energy. No significant decrease in microleakage level was observed for the 15 mJ/pulse laser energy. CONCLUSION The short pulsed Nd:YAG laser with the energy of 20 mJ/pulse and aforementioned features appeared to be able to reduce microleakage toward pulp.

Effect of different laser surface treatment on microshear bond strength between zirconia ceramic and resin cement

AIM The purpose of this study was to evaluate the effect of sandblasting, carbon dioxide (CO₂), and erbium,chromium:yttrium-scandium-gallium-garnet (Er,Cr:YSGG) lasers on the microshear bond strength of zirconia to resin cement. METHODS Sixty-one sintered yttria stabilized tetragonal zirconia blocks (10 × 5 × 2 mm) were prepared and divided into four experimental groups (n = 15); one sample was retained as a control. The samples were treated by aluminium oxide air abrasion, CO₂4W, Er,Cr:YSGG 3W, and Er,Cr:YSGG 2W, respectively. One sample from each group and the control sample were analyzed by scanning electron microscope. Panavia F2.0 resin microcylinders were prepared and placed on treated surfaces, light cured, and incubated for 48 h. Microshear bond strength testing was done by a microtensile tester machine, and the type of bond failures were determined by stereomicroscope. Data were analyzed by one-way anova and Tukeys test at a significance level of P < 0.05. RESULTS Air abrasion showed the highest microshear bond strength (P < 0.05) among all groups. CO₂and Er,Cr:YSGG 3W laser showed significantly higher bond strength than Er,Cr:YSGG 2W (P < 0.05). Apparent micromechanical roughening and irregularities were seen in the air abrasion-treated samples, and the bond failure was mostly mixed type. In the laser-treated surfaces, the roughness was much less than the air abrasion-treated surfaces, and the mode of failure was almost pure adhesive. CONCLUSION Air abrasion has a greater effect than CO₂and Er,Cr:YSGG lasers in the treatment of zirconia ceramic surfaces to enhance the bonding strength of resin cement to zirconia. CO₂laser at 4W and Er,Cr:YSGG laser at only 3-W output power can be regarded as surface treatment options for roughening the zirconia surface to establish better bond strength with resin cements.

The effect of two types chewing gum containing casein phosphopeptide-amorphous calcium phosphate and xylitol on salivary Streptococcus mutans.

Aim: The aim was to evaluate the effect of sugar-free chewing gum containing casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) and xylitol on salivary Streptococcus mutans. Materials and Methods: A total of 60 dental students of 20-25 years old, who volunteered after checking their health condition and signing an informed consent, were randomly allocated to receive one of the following interventions: (A) Chewing gum containing CPP-ACP; (B) containing xylitol. Subjects within the experimental groups were taken the gums 3 times daily, after each meal for a period of 3 weeks. Pre- and post-intervention unstimulated saliva samples were quantified for S. mutans counts. Results: A statistically significant reduction of salivary S. mutans was displayed in both groups A and B after the intervention when compared with baseline (P < 0.001), and group A shows more statistically significant reduction of salivary S. mutans than group B (P = 0.011). Conclusion: Daily consumption of chewing gum containing CPP-ACP and xylitol significantly reduces the level of salivary S. mutans, but chewing gum containing CPP-ACP can reduce the level of salivary S. mutans in more than xylitol chewing gum.

Effects of solvent drying time on mass change of three adhesives

Aim: Adhesives may change their mass due to water sorption or dilution of components after curing. The aim of this study was to evaluate the influence of air-drying time and water storage on mass changes (MC) of three adhesives; Adper Single Bond2 (ASB), One-step plus (OSP), Clearfil S3 Bond (CSB). Materials and Methods: Rectangular-shape samples from each adhesive were prepared and cured for 120 s with a halogen light curing unit. Prior to curing, their solvent was evaporated by means of three different procedures depending on the passive air-drying time (i.e., no air drying, equal to active air drying, complete evaporation after 3 h). Each group was further divided into two subgroups based on the time of water storage (1-day, 7-days), prior to measurement of MC (n = 10). The data were analyzed using a three-way ANOVA. Results: Adhesives showed different patterns of MC in relation to air drying and water storage; (P < 0.05). In OSP and CSB with increasing water storage and air drying, the MC increased significantly (P < 0.01). Conclusion: The highest MC in the etch-and-rinse adhesives was observed when the adhesive was not dried, while in the self-etch adhesive the highest changes were observed when the adhesive was completely dried.

Effect of bonding application time on the microleakage of Class V sandwich restorations

BACKGROUND The aim of this study was to assess the effect of bonding application time on the microleakage of Class V sandwich restorations. METHODS Eighty non-carious third molars were randomly divided into 16 groups. Two Class V cavities were prepared on the buccal and lingual surfaces of teeth. Three groups were restored with Fuji II GIC and treated with a total-etch bonding system (Stea/SDI) immediately after insertion, at 7 minutes and 15 minutes after mixing the glass ionomer cements (GICs). Another three groups were restored with Riva Self Cure GIC and treated with the total-etch system identically. The other six groups were subjected to self-etching bonding (Frog/SDI) after GIC placement in an identical procedure. The remaining groups were made using light cure GICs (Fuji II or Riva Light Cure) in conjunction with the total-etch or self-etching systems. Cavities were then restored with composite (Valux plus, 3M/ESPE). Samples were subsequently immersed in 2% methylene blue solution for 48 hours and observed under a stereomicroscope after sectioning. Four-scale grading was used to assess microleakage in occlusal and gingival walls. Data were analysed using Kruskal-Wallis and Mann-Whitney tests. RESULTS The self-etching bonding system exhibited more microleakage in occlusal margins regardless of time. Over time, microleakage significantly decreased in gingival margins in all self-cure groups except for Riva Self Cure treated with the total-etch system (p < 0.05). CONCLUSIONS Bonding application time had no effect on the microleakage of occlusal margins. However, maturation of GICs induced a decreased microleakage in gingival margins.

The Effect of Composite Thickness on the Stress Distribution Pattern of Restored Premolar Teeth with Cusp Reduction

PURPOSE Different thicknesses of restorative material can alter the stress distribution pattern in remaining tooth structure. The assumption is that a thicker composite restoration will induce a higher fracture resistance. Therefore, the present study evaluated the effect of composite thickness on stress distribution in a restored premolar with cusp reduction. MATERIALS AND METHODS A 3D solid model of a maxillary second premolar was prepared and meshed. MOD cavities were designed with different cusp reduction thicknesses (0, 0.5, 1, 1.5, 2.5 mm). Cavities were restored with Valux Plus composite. They were loaded with 200 N force on the occlusal surface in the direction of the long axis. Von Mises stresses were evaluated with Abaqus software. RESULTS Stress increased from occlusal to gingival and was maximum in the cervical region. The stressed area in the palatal cusp was more than that of the buccal cusp. Increasing the thickness of composite altered the shear stress to compressive stress in the occlusal area of the teeth. CONCLUSION The model with 2.5 mm cusp reduction exhibited the most even stress distribution.

Effects of pulsed Nd:YAG laser on microleakage of composite restorations in class V cavities

Abstract The purpose of this study was to evaluate the effects of the pulsed Nd:YAG laser on the decrease of dentinal microleakage beneath the restoration. Materials and method: 32 sound extracted premolar teeth were subjected to two standardized, V shaped, class V cavity preparations on both buccal and lingual surfaces. Cavities were located at 1–2 mm below the Cemento–Enamel Junction (CEJ) line. The teeth were divided into two groups of experimental and control in a random manner. Both 20 and 15 mJ/ pulse laser energies were tested. Etching, bonding and filling were performed using Tetric ceram composite material. All samples were thermocycled for 1000 cycles followed by an immersing period of 1 week in 2% basic fuchsin solution. Specimens were then sliced longitudinally and evaluated under a digital scanner for the extent of dye penetration. Result: results indicated that the level of microleakage of laser-treated cavities was significantly less than that of untreated cavities (P