The present investigation was aimed to study the effect of variation in adhesivesystems chemistry and technology on microshear bond strength of resin compositerestorations to dentin in order to evaluate the microshear bond strength of single bonduniversal adhesive system to dentin. The study compared the microshear bondstrength of self-etch and Etch & rinse approaches of single bond universal to itscorrespondence in self-etch and etch & rinse adhesive systems at three differentstorage periods.A total of 60 freshly extracted human molars were used in this study. The teeth weremolded and ground until dentin surface was exposed. Each tooth was used for thepreparation of two resin composite cylinders so that a total of 120 specimens wereobtained. The specimens were divided into four main groups, 30 specimens each,according to the selected bonding approach either Etch & rinse approach using abonding system specified for this approach, self-etch approach using a bondingsystem which is only used for such approach. The third main group was used for theuniversal bonding system with etch & rinse approach, while in the fourth main groupthe universal bonding was used with self-etch approach. Each group was divided intothree subgroups according to the time of storage of the specimens after bonding, 10specimens each.Each type of adhesive systems was used according to the manufacturer’s instructions.A resin composite micro-cylinder was obtained by condensing the resin compositeinto a piece of polyethylene tube using thin metallic endodontic plugger. Thecomposite cylinder was cured according to the manufacturer′s instructions. Two resincomposite cylinders were bonded on each occlusal dentin surface such that we have atotal of 120 specimens. After curing, the polyethylene tube was cut carefully using alancet and removed from around the composite. The specimens were stored for 1month and 3 months in distilled water at 37oC using a special incubator until testingprocedures. Distilled water was changed every three days. The prepared specimenswere conducted for microshear bond strength test after 24 hours of preparation ofeach specimen for immediate subgroup and after one and three months for the secondand third subgroups.The results of the present study revealed that after 24 hours immediate testing, onemonth and three months storage periods the single bond universal adhesive with etch& rinse approach showed the highest microshear bond strength value to dentin. Whilethe self-etch adhesive showed the lowest microshear bond strength in all storageperiods. The microshear bond strength of etch & rinse adhesive systems graduallydecreased through storage time, while the microshear bond strength of self-etchadhesive showed higher results at one month than immediate testing. However thebond strength of self-etch adhesive decreased again at three months storage period.Conclusions:1. Etch & rinse approach is the technique of choice of universal adhesivesystems.2. Microshear bond strength of resin composite to dentin is time dependant.3. The relative increase in microshear bond strength of resin composite to dentinafter one month may be due to continuous etching process causing moreexposure of collagen fibrils.