On bone quality and implant stability measurements

Abstract: In conjuction with placement of oral implants, the jaw bone quality assessment is mainly based on quantitative radiographic measures and the subjective opinion of the performing surgeon. While the primary implant stability is discussed in terms of the pre-set motor torque and the subjective hand-felt perception during final tightening of implants, the secondary stability is defined as the absence of implant mobility. The objectives of the present thesis were to evaluate the technique of true cutting resistance, designed to define and objectively measure the bone quality or bone hardness, with regard to its reliability and applicability to the clinical situation. Correlation analyses were performed between values of cutting resistance and bone density, as well as between cutting resistance and total bone area of maxillae and mandibles. Further, the resonance frequency technique was utilized, aiming at objectively measure the obtained primary and secondary implant stabilities in maxillae and mandibles. Correlation analyses were performed between values of cutting torque and resonance frequency. The one-stage surgical protocol was executed in mandibles for repeated stability measurements during healing. Implants placed according to the two-stage surgical protocol, using the standard and an adapted preparation technique with extended healing periods, were compared with regard to various failure patterns. The true cutting resistance technique was found reliable and applicable to the clincal situation, and significant correlations were demonstrated between the measured bone density and total bone area, respectively, and values of cutting resistance. Significantly more total bone, i.e. mainly compact bone, was seen in mandibles as compared to maxillae and values of cutting resistance were significantly higher in mandibles. No lower limit value at which implants were at risk was possible to identify, since cutting torque values were similar for successful and failed implants. Implant stability, as measrued with resonance frequency, increased more in bone of low density than in bone of medium or high density during healing and initial loading periods. A significant correlation between the values of cutting torque of the crestal bone and resonance frequency was observed. While the implant outcome was favourable using the one-stage protocol and no increase in stability was demonstrated for implants placed in the anterior mandible, a concept of one-stage surgery and direct loading may be recommended for implants inserted in similar bone texture. The early failure rate was found equal (1.5%) for the two separately conducted two-stage surgical approaches, and implants in maxillae failed to a higher extent than mandibular ones. When using a standard treatment protocol, limited bone volume and poor bone texture were major determinants for early failures. When using an adapted preparation technique and extended healing, no such early failure patterns were seen. With regards to late failures, implants placed in maxillary bone of limited volume still represented more failures, while no such finding was demonstrated in bone of poor texture. Thus, early and late implant failure rates were equally low in bone of poor texture, when using the adapted surgical technique.

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