الفهرس 
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Abstract
This in vitro study was conducted to asses the effect of diode laser assisted bleaching of a dental composite resin and a dental resin modified glass ionomer on the surface roughness, surface microhardness, color change, shear bond strength to dentin.
A total of 120 disc shaped specimens were prepared with dental composite resin and dental resin modified glass ionomer for three tests (surface roughness, surface microhardness, color change tetsing). (60 disc specimsns for dental composite resin and 60 disc specimens for dental resin modified glass ionomer). A total of 40 sound human anterior natural teeth were prepared with dental composite resin and dental resin modified glass ionomer for one test (shear bond strength testing). (20 teeth with dental composite resin and 20 teeth with dental resin modified glass ionomer).
Split teflon molds were used to prepare a total of 120 disc specimens with different dimensions as follows:
3- (10 mm in diameter and 2 mm in thickness) for the surface roughness test and the color change test subgroups (10 mm in diameter and 2 mm thickness).
4- (6.5 mm in diameter and 2 mm thickness) for the surface microhardness test subgroups.
These dimentions based on previous studies and ISO standard.
These disc specimens assigned to each testing procedure (surface roughness, surface microhardness, color change tests). First a celluloid matrix was placed over a glass microscopic slide then the mold was placed over it. The dental composite resin and dental resin modified glass ionomer were condensed in a single increment and covered with a celluloid matrix and another glass slide.
To obtain a flat surface free of voids, a weight of 500 g was placed over the glass slide for 1 minute. After the removal of the weight, the specimen was light cured through the glass slide by LED light cure with a light intensity of 1200 mW/cm2 output (3M ESPE, Elipar, Deep cure-L Germany), for 20 seconds according to the manufacturer’s instructions.
A total of 40 sound human anterior natural teeth prepared for shear bond strength to dentin testing. First the teeth were cleaned by ultrasonic scaler to remove hard and soft deposits. Then the teeth were examined to be free of any cracks or caries to be used for bond strength test. Then the teeth were immersed in 0.5% chloramine T solution for the purpose of disinfection and stored in distilled water at 4°C until use.
The teeth were sectioned at cementoenamel junction with a diamond saw with a low speed handpiece. The crowns were sectioned in mesiodistal direction before preparation for the shear bond strength to dentin testing.
Each sectioned half was totally embedded in polyester resin up to the cementoenamel junction such that a flat dentin surface on the remaining tooth structure was exposed for bonding. The surface of each specimen was finished and polished using a sequence of (400-800-1200) grit aluminum oxide discs (Zhitian Industrial Area, Gongyi City, Henan Province, China) to standardize the surface smoothness.
Regardin to the surface roughness, stylus profilometer (TR 220 Surface roughness tester, TIME Group, Pittsburgh, PA, USA) used to record the surface roughness befor and after laser bleaching procedure using a cut-off value of 0.25 mm.
The results of the surface roughness for the dental composite resin showed higher mean value of (Ra) was recorded in the laser bleached dental composite resin disc specimens subgroup (A2), with significant difference (P<0.001**) when compared to the non bleached dental composite resin disc specimens subgroup (A1)
The results of the surface roughness for the dental resin modified glass ionomer showed higher mean value of (Ra) was recorded in the laser bleached subgroup (E2) with highly significant difference (p<0.001**) when compared to the non bleached subgroup (E1).
Regarding to the surface microhardness, Vickers hardness tester (Wilson Buehler microhardness-Germany) was used to record the surface microhardness befor and after laser bleaching procedure. The results of the surface microhardness for the dental composite resin showed higher mean value of (VHN) was recorded in the non bleached dental composite resin disc specimens subgroup (B1) with significant difference (p<0.014*) when compared to the laser bleached dental composite resin disc specimens subgroup (B2)
The results of the surface microhardness for the dental resin modified glass ionomer showed higher mean value of (VHN) was recorded in the non bleached dental resin modified glass ionomer disc specimens subgroup (F1), with highly significant difference (p<0.001**) when compared to the laser bleached dental resin modified glass ionomer disc specimens subgroup (F2)
Regarding to the color change, spectrophotometer used to record the color change. The improvement of the color after laser bleaching is not as the original color of the dental composite resin and dental resin modified glass ionomer restorations and thus it need to replace.
Regarding to the shear bond strength to dentin, a universal testing machine used to record the shear bond strength to dentin with a cross head speed of 0.5 mm per minute until failure using a chisel was applied over the bonded interface between tooth and specimen.
The results of the shear bond strength to dentin for the dental composite resin, higher mean value was recorded in the laser bleached dental composite resin bonded to anterior natural teeth subgroup (D2) with significant difference (p=0.037*) when compared to the non bleached dental composite resin bonded to anterior natural teeth subgroup (D1).
The results of the shear bond strength to dentin for the dental resin modified glass ionomer, higher mean value was recorded in the laser bleached dental resin modified glass ionomer bonded to anterior natural teeth subgroup (H2), with significant difference (p<0.005*) when compared to the non bleached dental resin modified glass ionomer bonded to anterior natural teeth subgroup (H1).