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Statement of the problem. Implant placement in an ideal position where stresses are transmitted vertically along the long axis of the implant rarely if ever coincides with the most esthetically pleasing position dictated by prosthetic planning. This situation could be dealt with by placing the implant at an angle in the most favourable position surgically and using angled abutments to compensate for the deviation from the previously planned prosthetic site of the final restoration. This may lead to excessive stresses on the inclined side of the implant which could cause bone resorption. Purpose. The aim of this study was to evaluate the effect of implant platform switching on strain developed around implants with straight and angled abutments. Materials and Methods. Twenty root-form titanium implants were inserted in epoxy resin blocks. According to the direction of implant insertion in the epoxy resin block, the twenty implants were divided into two main groups: Group I: (n=10) Straight implants with straight abutments. Group II :( n=10) Inclined implants with angled abutments (15 degrees). Each group was sub-divided into two sub-groups according to the abutment diameter in relation to the implant diameter: Sub-group A :( n=5) 4.5 mm diameter Implants received 4.5 mm diameter abutments. Sub-group B:(n=5) 4.5 mm diameter Implants received smaller 3.75 mm diameter abutments (platform switching). The 20 implant abutments received Ni-Cr full metal crowns. The blocks were trimmed to 1mm thickness around the implant then each sample received four strain gauges to represent the mesial, distal, buccal and lingual surfaces around the implant. A computerized universal testing machine was used for loading the implants by 300N, at a rate of 1 N/Sec. The load was applied progressively starting from zero to 300 N during which readings from the strain meter were recorded on the computer. Results. It was found that Group II (Angled abutments) with matching diameter Sub-group A showed statistically significantly (P ≤ 0.05) highest mean micro-strains (435.1± 215.7) followed by Group I (Straight abutment) with matching diameter Sub-group A (346.2 ± 175.3) followed by Group II (Angled abutments) with platform switching Sub-group B (307.1 ± 135.0). Group I (Straight abutment) with platform switching Sub-group B showed statistically significantly lowest mean micro-strains (239.0± 165.4) . Conclusions. Straight implants with straight platform-switched abutments were associated with the least micro-strain values.

EFFECT OF IMPLANT PLATFORM SWITCHING ON STRAIN DEVELOPED AROUND IMPLANTS WITH STRAIGHT AND ANGLED ABUTMENTS