Effect of a Modified Stepped Osteotomy on Implant Primary Stability

Objectives: The primary predictor of implant osseointegration is achievement of primary stability.  The assessment of implant prognosis can be provided by measurement of primary stability via insertion torque (IT) and computerized tomography (CT).  In order to improve primary stability in poor quality bone, modified surgical techniques have been developed for implant placement.  The purpose of this study is to evaluate the effects of the step back osteotomy technique on implant primary stability in areas of poor osseous quality. 

Methods: Spiral CT imaging of human cadaver maxillas was used to examine bone volume and density in Hounsfield Units (HU).  Appropriate recipient sites were determined by 10mm vertical osseous height and 5mm osseous widths within a range of 150-350HU.  Five implants were placed in a conventional surgical protocol and five in a modified stepped osteotomy.  Immediately after implants were placed primary stability was measured using insertion torque via the Zimmer Implant Motor System and confirmed with the Thommen torque driver.

Results: The range of HU obtained was 226.12 – 303.7HU with a mean 265.226HU.  The mean IT for the conventional osteotomy preparation was 19Ncm and 28Ncm for the modified  stepped osteotomy.  Minimum IT value of 5Ncm was found in the conventional osteotomy and a maximum value of 45Ncm in the stepped osteotomy.  The mean modified stepped osteotomy IT was significantly greater than the conventional osteotomy.

Conclusions: This study indicates that a modified stepped osteotomy could result in significant increases in primary stability in terms of IT.  CT evaluation can allow the practitioner to preoperatively determine bone quality and quantity.  This preoperative evaluation may allow the surgeon to plan surgical technique and plan for required materials prior to implant placement.