INTRODUCTION Chemical adhesion in dentistry has been groomed up by Acid Etchiing Technique. 1 Through this the issue of bonding of dental materials to enamel has been solved but to dentine is still more difficult. 1 In the 1970s, Dennis Smith developed the first chemically adhesive dental cement, called polycarboxylate cement. 2 Later, Wilson, Crisp, and McLean derived glass ionomer cement from silicate cements. 3 GIC has been classified into two broad categories of chemical cure – GIC and resin modified dual cure. 4 The advantages of Resin Modified Glass Ionomer Cement (RMGIC) include improved tensile and compressive strength compared to Zinc Phosphate (ZP) and GIC and resistance to water contamination during initial setting reaction compared to GIC. 5 Disadvantages include that RMGIC is hydrophilic 6 that leads to water adsorption and hygroscopic expansion lead to crack formation, cement deterioration and leakage. 6,7 Sandwich restoration or “composite-laminated GIC” technique has been used in class 1,2,5 cavities, 8-10 with composite materials for large restorations on both vital and endodontically treated teeth. 8,9 The main purpose for using this technique is not only to provide base against thermal, and chemical insults to the pulp but also to reduce the polymerization shrinkage of composite by reducing the bulk of restorative material. 2,3,8 There are two types – closed and open sandwich techniques. When a glass ionomer is placed in an area where there is no contact with the cavosurface of the preparation and the material is completely covered with the restorative material, it is called closed technique while open is vice versa. 8 According to manufacturers' instructions, both conventional and resin-modified GIC may be used for this purpose. 4,11 GIC provides a floor for etching thereby protect the pulp. Strength is improved as polymerization shrinkage of composite has been reduced by reducing bulk of material. Fluoride release prevents recurrent caries. Chemical bonding is available for the tooth substance. 12 Journal of the College of Physicians and Surgeons Pakistan 2015, Vol. 25 (11): 781-784 781 ORIGINAL ARTICLE Micromechanical Intervention in Sandwich Restoration Tabinda Nawaz Khan 1 , Syed Yawar Ali Abidi 2 , Khush Bakht Nawaz Khan 3 , Shahbaz Ahmed, 2 Fazal Ur Rehman Qazi 2 and Noureen Saeed 4 ABSTRACT Objective: To evaluate the sealing ability of two different types of Glass Ionomer Cements (GICs) used for sandwich restorations and assess the effect of acid etching of GIC on microleakage at GIC-resin composite interface. Study Design: Experimental study. Place and Duration of Study: Department of Operative, DIEKIOHS (DUHS) and NED University, Karachi, from February to June 2011. Methodology: Eighty cavities were prepared on the proximal surfaces of 40 permanent human premolars (2 cavities per tooth), assigned to 4 groups (n=20) and restored as follows: Group CIE - Conventional GIC (CI) was applied onto the axial and cervical cavity walls, allowed setting for 5 minutes and acid etched (E) along the cavity margins with 37% phosphoric acid for 15 seconds, washed for 30 seconds and dried; the adhesive system was applied and light cured for 10 seconds, completing the restoration with composite resin light cured for 40 seconds; Group CIN - same as Group CIE, except for acid etching of the CI surface; Group RME - same as CIE, but using a resin modified GIC (RMGIC); Group RMN - same as Group RME, except for acid etching of the RMGIC surface. Specimens were soaked in 1% methylene blue dye solution at 37ºC for 24 hours, rinsed under running water for 15 minutes, bisected mesiodistally and dye penetration was measured following the ISO/TS 11405-2003 standard. Kruskal Wallis and post Hoc tests significant differences in the microleakage among all the four groups. Results: There was a significant difference between the two groups of GICs (RMGIC and CI, p=0.001). There was no significant difference in between the two sub-groups that is between CIN and CIE (p=0.656), and between Groups RME and RMN (p=0.995). Conclusion: Phosphoric acid etching of GIC, prior to the placement of composite resin, does not improve the sealing ability of sandwich restorations. RMGIC was more effective in preventing dye penetration at the GIC-resin composite dentine interfaces than CI. Key Words: Glass ionomer. Microleakage. Sandwich technique. 1 Department of Dental Materials / Operative Dentistry 2 / Oral Pathology 4 , Dr. Ishrat-ul-Ebad Khan Institute of Oral Health Science, (DUHS), Karachi. 3 Department of Pathology, Dow International Medical College, Karachi. Correspondence: Dr. Tabinda Nawaz Khan, 2-D, 16/7, Nazimabad, Karachi. E-mail: tabinda.nawaz@duhs.edu.pk Received: July 28, 2012; Accepted: September 03, 2015.