Bone strains around apically free versus grafted implants in the posterior maxilla of human cadavers

The objective of this study was to compare the bone strains of apically free versus grafted implants in the posterior maxilla. The experiments were undertaken in four edentulous maxillary posterior regions of fresh human cadavers, having a minimum bone height of 8 mm. In each bone fragment, two Ø 4.1 mm x 12 mm Straumann implants were placed, and insertion torque values (ITV) and implant stability quotients (ISQ) of the implants were quantified to determine implant anchorage. Two splinted crowns were fabricated for each experimental model. Strain gauges were bonded on the buccal and sinus floor cortical bones around apically free and grafted implants. Microstrains were recorded by a data acquisition system and corresponding software at a sample rate of 10 KHz under central and buccally oriented lateral-axial static loads of 100 and 150 N in separate cases. The data were compared by independent T test at a significance level set at P<0.05. Bone tissue strains on the buccal cortical areas adjacent to apically free implants were higher than those of apically grafted implants (P<0.05). The differences ranged between 10 and 48 mu epsilon under central and lateral axial loads of 100 and 150 N. The shift in load application from central to buccally oriented lateral axial mode increased strains between 60 and 201 mu epsilon on buccal cortical bone around apically free and grafted implants (P<0.05). Bone strains around anterior implants were higher than those of posterior implants. Microstrains in the sinus floor cortical bone in apically grafted models were slightly higher than apically free models. Bone tissue strains on the buccal cortical areas adjacent to apicallyfree implants are higher than those of apically grafted implants. Sinus lifting, resulting in an enhanced apical support, slightly increases strains at the sinus floor region, but leads to a decrease in bone strains around the collar of supporting implants.