الفهرس 
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Abstract
A major advancement in the current practice of dentistry is the restoration of teeth with tooth colored, adhesive materials. The success and longevity of a dental restorations depend on sealing of the cavity walls as well as, the retention to the tooth surface. When glass ionomer cements were developed by Wilson and Kent in 1972, it caught the attention of researchers and practicing dentists, because it was reported to form chemically adhesive bonds to the tooth structure.
Glass carbomer, a new glass ionomer-based restorative material, has been developed in recent years and it is distinguished from glass ionomer by its nano-sized powder particles and fluorapatite crystals. It has been presented with claims of enhanced physical characteristics in contrast to GIC.
There was a considerable variation in the reported time required to achieve full maturation among cement products therefore, the aim in the present study was to evaluate the shear bond strength of a new generation of glass ionomer (Glass Carbomer) to dentin versus a glass ionomer (Fuji IX GP) after different aging periods(24h,1 month and 3 months).
The study included crowns of 60 primary molars exfoliated or extracted for orthodontic reason; teeth were mounted in acrylic blocks exposing buccal surface. Surfaces were gently ground with water cooled silicon carbide abrasive papers to obtain flat dentin surfaces.
The prepared specimens (n= 60) were divided into two main groups (30/ each): group I (test) (Glass carbomer), group II (control) (Fuji IX GP) then, the specimens in each group were further subdivided into three subgroups (10 /each) according to the artificial aging period (24h,1 month and 3 months). After that, the specimens were subjected to 500 thermal cycles. Subsequently, aging the specimens in artificial saliva was done in 37º C in incubator. Finally, Shear bond strength (SBS) between dentin surface and the bonded material was measured using a universal testing machine. All the debonded surfaces of the specimens were examined under a stereomicroscope to record the mode of failure and 3 randomly selected debonded interfaces from each sub group were re-examined under SEM for further verification.
The results revealed that, Fuji IXGP give higher mean SBS than glass carbomer. In addition, in both groups it was found that; shear bond strength increased after 1 month compared to the base line data (24 h) which was the lowest values. After 3 months glass carbomer SBS continued to increase while, Fuji IXGP SBS values decreased
Concerning the modes of failure, although there was no statistical significance difference between the 3 sub-groups of both study materials but there was a difference in the percentage of each mode of failure in each aging period in both groups.
Based on the results of the present study it can be concluded that, aging has affected the shear bond strength of both cements with higher numerical values for Fuji IXGP. The behavior of glass carbomer cement was better than Fuji IXGP as the shear bond strength continued to increase for 3 months while in Fuji IX, shear bond strength decreased after 3 months. Regarding the mode of failure detected, the aging time did not have any significant effect in both materials.