Transmission of bone strain in the craniofacial bones of edentulous human skulls upon dental implant loading

Abstract

Statement of Problem. Little is known about how craniofacial bones that are distant from dental implants are loaded. Whether bone experiences different strain when implants of different diameters are loaded is unknown. Purpose. This study was designed to (1) characterize bone strain both adjacent to and distant from dental implants and (2) compare bone strain in response to the same loads on small-diameter and large-diameter implants. Material and Methods. On 4 edentulous, dry adult human skulls, the buccopalatal midpoint of the edentulous occlusal surface was marked unilaterally in the maxillary first molar area with a round bur. A hole for implant placement was prepared, and 2 self-tapping titanium implants (3.75 × 7 mm and 4 × 7 mm) were placed in the same location and at the same orientation, one after the other. A 4-mm-long titanium abutment was connected to the implant. Each implant was loaded 10 degrees lateral to its longitudinal axis, simulating a lateral occlusal force in 3 of the skulls. In skull 2, loading was along the longitudinal axis of the implant and simulated a vertical occlusal force. The magnitude of the ramp forces was 0 to 100 N. Uniaxial strain gages and/or 3-element strain rosettes were implanted in the supramolar cortical bone, the supraincisor cortical bone, the zygomaticomaxillary suture, and the zygomaticotemporal suture. All strain gages/rosettes were excited with 500 mV DC, and the output signals were recorded with a strain conditioner. Tensile strain was expressed as positive values and compressive strain as negative values. Student t tests were used to test for normal distribution of bone strain within each skull; Wilcoxon tests were applied for skewed distribution between small- and large-diameter implants and between 50-N and 100-N loads (P≤.05). Results. Bone strain both adjacent to and distant from the implants was complex: compressive strain in the buccal cortical bone superior to the implants; tensile strain in the ipsilateral supraincisor cortical bone but compressive strain in the contralateral supraincisor cortical bone; and tensile strain anterior to the zygomaticotemporal suture but compressive strain posterior to the suture. With the same applied loads, bone strain was higher for large-diameter implants than for small-diameter implants for all the above cortical locations (P<.01 to.001) except posterior to the zygomaticotemporal suture. Conclusion. Within the limitations of this study, bone strain resulting from dental implant loading was distributed to cortices not only adjacent to but also distant from dental implants. The large-diameter implant was more facilitative of stress transfer to cortical bone than the small-diameter implant tested. (J Prosthet Dent 2002;88:192-9.)