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Journal of Oral Science & Rehabilitation Volume 2 | Issue 1/2016 51 Fig. 2 Study design scheme for the 320 implant beds prepared in synthetic bone blocks with different bone densities. with the 2.0 mm diameter drill, followed by asteppeddrillwith2.4/2.8mmdiametersteps andfinishedwithasteppeddrillwith3.2/3.6mm diameter steps. I m p l a n t c h a r a c t e r i s t i c s – Replace Select Tapered: This implant possess- esaconicalprofilewiththesamethreadprofile. Thebodyistapered,theneckhasmicro-threads and the connection is conical (Fig. 3b). – NobelActive: This implant possesses a vari- able-threadprofile,wider(vertically)andshort- er (horizontally) as it progresses from the neck area, in which there are micro-threads. In the apical region, the implant has a pronounced tapered body with sharp threads to facilitate insertion and cutting of unprepared bone. The connection is conical and the coronal region is back-tapered coronally, which results in a reduction of the platform diameter (Fig. 3a). I m p l a n t p l a c e m e n t A total of 160 implants were placed in a random scheme in 320 implant bed preparations, until theyreachedthecrestallevel,leavingtheimplant platforms flush with the block surface (Fig. 4). The implantswere placedfirst intothe soft bone and primary stability was evaluated afterwards. The implantswerethen retrieved and placed into the hard bone for the evaluation of primary sta- bility.Atotalof320 evaluationswere performed. P r i m a r y s t a b i l i t y e v a l u a t i o n Theevaluationofprimarystabilitywasperformed according to the insertion torque (IT) and the im- plant stability quotient (ISQ) as follows: - IT was measured during implant insertion by the implant motor (DENTSPLY, Waltham, Mass., U.S.) and was recorded in N cm. The peak values were reached when the implant platformwas located atthe surface ofthe bone block (11.5 mm). Each placed implant resulted in a single value, and mean values were collat- ed by group and compared. - ISQ was recorded using resonance frequency analysis with the Osstell Mentor device (Oss- tell, Göteborg, Sweden). Specific transducers were used, and replaced after ten uses until all of the measurements had been performed. Measurements were taken as follows: The transducerwas screwedtothe placed implant. The probe was laterally oriented in relation to thetransducerand measurementsweretaken. Each measurement was repeated in triplicate and mean values were recorded. All measure- ments were performed by an independent, F a c t o r s a f f e c t i n g p r i m a r y s t a b i l i t y o f t a p e r e d i m p l a n t s w i t h d i f f e r e n t t h r e a d d e s i g n Fig. 2 Volume 2 | Issue 1/201651