Dental Implant Design and Its Relationship to Long-Term Implant Success

Dental Implant Design and Its Relationship to Long-Term Implant Success
December 2003
By: Steigenga, Jennifer T. DDS; Al-Shammari, Khalaf F. DDS, MS; Nociti, Francisco H. DDS, PhD; Misch, Carl E. DDS, MDS; Wang, Hom-Lay DDS, MSD
LWWOnline / The International Journal of Oral Implantation
Abstract:
The purpose of this review is to evaluate the effects of the biomechanical aspects of dental implant design on the quality and strength of osseointegration, the bone-implant interface, and their relationships to the long-term success of dental implants. The engineering design of implants is based on many interrelated factors, including the geometry of the implant, mechanical properties, and the initial and long-term stability of the implant-tissue interface. There is no one optimal design criterion. However, implants can be engineered to maximize strength, interfacial stability, and load transfer by using different materials, surfaces, and thread designs. Limited information is currently available in addressing how implant thread design influences the overall implant success. Therefore, this article reviews and discusses design elements of various dental implant systems currently in use as they affect the quality of osseointegration and their relationship to overall long-term success patterns.
A major advance in dentistry has been the successful replacement of lost natural teeth by osseointegrated implants. Years of clinical experience have fostered a consensus regarding many of the placement criteria and techniques to maximize the chance for long-term implant stability and function. 1 The use of dental implants for the oral rehabilitation of fully and partially edentulous patients has greatly broadened the scope of clinical dentistry, creating additional treatment options in complex cases in which functional rehabilitation was previously limited or inadequate. The predictability and long-term success of dental implants have been well documented, both in removable and fixed prostheses. 2-5 Most of the studies reported have shown multiyear success rates of more than 90% for implants placed in fully edentulous 6-8 or partially edentulous patients. 4,9-14
Nevertheless, success rates have been reported to vary in different areas of the mouth and in different patients. For example, lower success rates have been reported for maxillary implants than for mandibular implants. 2,15,16 Attempts have been made to understand the factors that could compromise implant success. Factors such as material biocompatibility, implant design and surface, surgical technique, host bed, and the loading conditions have all been shown to influence the implant osseointegration. 17 Available bone volume has long been considered an important factor in achieving implant predictability. 18 Studies showed higher failure rates for implants shorter than 10 mm. 3 Another important influencing factor for implant success is bone density, because higher failure rates have been reported for regions with poor quality bone, eg, the posterior maxilla. 15,19-21
Consequently, modifications in implant body design and implant surfaces have been suggested to increase the success in poor quality bone by, hypothetically, gaining better anchorage and providing more surface area of load to decrease stress to the softer bone types. 15 In a rabbit study, Carlsson 22 found a more complete bone-to-implant contact around screw-shaped implants than around double cylinders and T-shaped implants. Also demonstrated was the fact that a stronger biomechanical bond was obtained with a rough implant surface than with a similarly shaped, but polished, implant surface. Furthermore, other in vivo studies have agreed that a rough surface is more suitable for implant integration than a comparatively smoother implant surface by demonstrating a higher degree of bone integration. 23-26 Surface roughness can influence the degree of osseointegration. For example, the pattern size and distribution of peaks and valleys that compose the surface roughness can significantly influence the overall intimacy and mechanical interlocking of the bone-implant interface. However, the surface condition is not the only factor that could influence osseointegration. Implant design can affect surgical insertion (eg, stability) and the bone-implant interface after occlusal loading. Implant design and surface conditions are 2 independent conditions that can alter implant success rates. This article reviews and discusses design elements of dental implants as they affect the quality of osseointegration and their relationship to long-term success.
The Impact of Occlusal Overload
Implant overload can be caused by a multitude of factors, including suboptimal implant design and size, an insufficient number of implants to support the restoration, improperly splinted abutments, violation of conventional prosthetic limitations for natural dentition, excessively cantilevered pontics; splinting to natural dentition (even with a stress-breaking attachment), improperly positioned implants, the wrong type of restoration for the clinical condition, loss of supporting bone, excessive parafunctional forces, and nonmaintenance of the components. 47 Crestal bone loss as well as loosened screws are frequently the first detectable signs of implant overload and warrant immediate action. To eliminate or reduce the excessive stress at the crestal bone-implant interface is a goal accomplished by balancing the whole arch, reducing occlusal contacts to the area of the implant-supported regions, and shortening or eliminating cantilevers whenever possible. This uniquely specific occlusal philosophy of endosteal implant prostheses has been referred to as implant-protected occlusion.30 Implant orientation and the influence of load direction, the surface area of implants, occlusal table width, and protecting the weakest area are blended together from a biomechanical rationale to provide support for a specific occlusal philosophy.
Appropriate implant design selection through careful treatment planning is imperative to lower the magnitude of loads imposed on the vulnerable implant-to-bone interface. The following section will review design elements that could affect the force transfer and the quality of osseointegration.
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