INTRODUCTION: Primary stability and bone quality are key factors in implant success in early stages of placement while osseointegration comes further on. OBJECTIVES: The aim of this study was to compare the effect of osseodensification on peri-implant strain during functional loading of a 4-unit monolithic zirconia bridge as well as its effect on primary stability and insertion torque. MATERIALS AND METHODS: Sixteen IS-II active implants were used in this study; the implants were divided into 2

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... groups. Group (A) were placed in conventionally drilled osteotomy sites with progressive subtractive enlargement and Group (B) were placed in osseo-densified osteotomy sites. All implants were inserted in unicortical polyurethane test blocks mimicking medium quality bone while recording insertion torque and implant stability quotient (ISQ) using Osstell for all implants. Each block contained two parallel implants carrying a 4-unit fixed partial denture (FPD). FPD were cemented then thermocycled for 5000/cycle and mechanically loaded at 100N, 2.5×10*5 cycles. A load of 400N and 600N and 800N was applied at connector areas in FPD. Strain gauges were connected to strain meter to record the peri-implant strain for both implants in all groups. RESULTS: Regarding insertion torque and peri-implant insertion torque strain Group (A) had significantly lower values than group B (p<0.05) while insignificant Osstell values. Concerning peri-implant strain after loading group A had significantly higher strain values than Group (B) (p<0.05). CONCLUSION: Osseodensification drilling protocol increased insertion torque values and peri-implant insertion torque strain in comparison to conventional drilling protocol while decreasing peri-implant strain after loading.