Effect of the degree of polymerization on the intrinsic discoloration of light activated resin composite restorations

This study was carried out to investigate the effect oft he degree of polymerization on the intrinsic discoloration of light activated resin composite restorations. Three different commercially available resin composites were used in this study. Each group was subdivided into three sub groups, according to time of curing. Half of the specimens in each sub group, where stored in dry condition while the other half was stored in coffee. Color was assessed by the spectrophotometer and degree of polymerization was measured by FTIR. The collected data were statistically analyzed using two way analysis of variance [ANOVA]. Reverse relationship was found between the intrinsic discoloration and the degree of polymerization. The curing time should not be less than 40 sec. to ensure better color stability of different resin composites

effect of combining different bonding agents on the shear bond strength to dentine

Dentine bonding adhesives [DBAs] possess different modes of adhesion that may affect their bond strength to dentine. Forty extracted sound premolars were selected and divided into four equal groups of ten teeth each. A circular area of dentine, of 3 mm. in diameter, was denuded on the labial surface using a diamond wheel stone running parallel to the long axis of the teeth. The dentine surface of the samples were treated with EDTA, cleaned, dried and then treated with the DBA. Group I was treated wild Gluma while group II was treated with J and J DBA. Group III received a combinational of both adhesives using a layering technique while group IV was treated by admixed combination of both adhesives. The shear bond strength scores [SBS] of the samples were tested using an Instron machine. The highest mean shear bond strength values were obtained by the combined adhesives applied by the layering technique [12.08 MPa] followed by the samples treated by the Gluma adhesive [9.67 MPa] then those treated by the J and J DBA [6.69 MPa] and finally the samples treated by the admixed combined adhesives. One way analysis of variance and Duncan's Multiple Range test revealed high significant difference between the tested groups and a percentage increase of 140.46 percent of the SBS of the Gluma/J and J DBAs combination if applied by the layering technique denoting its superiority when compared to the admixed technique. These findings were attributed to the reaction of the combined DBAs with more adhesive moities of both organic and inorganic nature. The low SBS of the admixed combined DBA was attributed to the incompatibility of the material in the well mixed technique due to the glutaraldehyde organic solvent action due to the affection of the functional adhesive groups in the J and J DBA

Flextural bond strength and electron microscopic observation of repaired high copper amalgam

The aim of this study is to compare the flextural bond strength values of nonrepaired, mercury repaired and Amalgambond [a 4-META based resin] repaired high copper amalgam alloys. Four amalgam alloys were investigated [Dispersalloy, Contour, Sybralloy and Tytin]. The flextural bond strength was determined by using a three point bending test on an Instron testing machine at a crosshead speed of 0.5mm/mn. Scanning electron microscopic examinations between x l00 and x2500 revealed a cohesive pattern of failure for the nonrepaired specimens, a dominating adhesive failure for the mercury repaired specimens and a combined adhesive-cohesive type of failure for the Amalgambond-repaired specimens. An ANOVA test and a Duncan's multiple range test at P<.05 indicated a statistically significant difference between the bond strength of the non-repaired Contour specimens and the other three alloys. It also revealed no statistically significant difference between all the mercury-repaired specimens, and no statistically significant difference between all the Amalgambond repaired specimens. However, a significant difference existed between the mercury-repaired and the Amalgambond-repaired amalgams. The bond strength of the mercury-repaired amalgams was almost half that of the non-repaired ones, whereas the bond strength of the Amalgambond-repaired amalgams was again nearly half of the mercury repaired ones for the four types of alloys tested