Platform switching: A panacea for bone loss??

The goal of modern implant therapy entails more than just the successful osseointegration of the implant. A successful result must also include an esthetic and functional restoration surrounded by stable peri-implant tissue levels that are in harmony with the existing dentition. In an attempt to improve long-term bone maintenance around implants, a new implant-to abutment connection referred to as "platform switching" has been proposed. It refers to the use of an abutment of smaller diameter connected to an implant neck of larger diameter. Platform switching is a simple and effective way to control circumferential bone loss around dental implants. This short communication aims to present an overview of concept of platform switching in dental implantology.

INTRODUCTION

The peri-implant bone level has been used as one of the criteria to assess the success of dental implants. It is an important prerequisite for preserving the integrity of gingival margins and interdental papillae. Marginal bone loss seems to be unavoidable after implant placement. The peri-implant bone remodeling occurs once the implant is exposed to the oral environment in a second surgical procedure or when the abutment is placed immediately after implant placement. Over the years, attempts have been made to prevent or reduce marginal bone loss through modification of the implant-abutment connection.

THE IMPLANT ABUTMENT INTERFACE – THE MICROGAP

The connection between implant fixture and its restorative abutment is termed the implant abutment interface (IAI) or “microgap”. In most cases, it is susceptible to micromovements during clinical function and also permits micro-leakage of fluids. This infiltration results in the permanent presence of an area of abutment inflammatory cell infiltrate (aICT). The sustained state of inflammation promotes osteoclast formation and activation, which contributes to bone loss [Figure 1].

Figure 1

The microgap

FACTORS CONTRIBUTING TO MARGINAL BONE LOSS AROUND IMPLANTS

Marginal bone loss around implants may pose a threat to its long-term survival. The remodeling process involves marginal bone resorption that is affected by one or more of the following factors: (1) infectious process; (2) excessive loading conditions; (3) the location, shape, and size of the implant-abutment microgap and its microbial contamination; (4) biologic width geometry and implant surface roughness; (5) peri-implant inflammatory infiltrate; (6) micro-movements of the implant and prosthetic components; (7) repeated screwing and unscrewing; (8) implant-neck; and (9) traumatic surgical technique.[1]

CONCEPT OF PLATFORM SWITCHING

In 1991, Implant Innovations, Inc. (3i, Palm Beach Gardens, FL) introduced 5 mm and 6 mm diameter implants. They were intended to increase the bone to implant contact, when placing shorter implants in areas of limited bone height. At that time, prosthetic components of similar dimension were not easily available; hence clinicians restored them with standard 4.1 mm diameter components, which created a 0.45-0.95 mm circumferential horizontal difference in dimension between the implant seating surface and the attached component.[2]

After a 5-year period, the typical pattern of crestal bone resorption was not observed in platform switched implants. Thus, the discovery of the concept was a coincidence. Platform switching concept was introduced in the literature by Lazzara,[2] Porter,[2] and Gardner.[3]

Various biologic and mechanical theories have been proposed to justify this phenomenon. It was suggested that the inward positioning of the implant-abutment interface allowed the biologic width to be established horizontally, as an additional horizontal surface area is created for soft tissue attachment [Figure 2]. Hence, less vertical bone resorption is required to compensate for the biologic width. Furthermore, this design increases the distance between the inflammatory cell infiltrate at the microgap and the crestal bone, thereby minimizing the effect of inflammation on marginal bone remodeling.[4] Another theory supported by finite element analysis, reports reduction in stresses, especially in the crestal region by shifting the stresses away from the bone implant interface.[5]

Figure 2

Inward shifting of connective tissue maintaining the biologic width

LITERATURE SHOWING POSITIVE EFFECT

Canullo et al.[6] observed that implants restored according to the platform-switching concept experienced significantly less marginal bone loss than implants with matching implant-abutment diameters. Cappiello et al.[7] confirmed the important role of the microgap between the implant and abutment in the remodeling of the peri-implant crestal bone. Platform-switching seemed to reduce peri-implant crestal bone resorption and increase the long-term predictability of implant therapy. Prosper et al.[8] in a randomized prospective study compared platform-switched implants and implants with an enlarged platform to cylindrical implants inserted with conventional surgical protocols having abutments of matching diameter. A significantly reduced post-restorative crestal bone loss was seen, when implants were placed in both two-stage and one-stage techniques. Atieh et al.[9] reported similar results and in addition, also observed that the degree of marginal bone resorption is inversely related to the extent of the implant-abutment mismatch. Calvo Guirado et al.[10] noted that platform switched implants had minimal marginal resorption (less than 0.8 mm) and a highly satisfactory aesthetic results in the anterior zone.

LITERATURE SHOWING NO POSITIVE EFFECT

Crespi et al.[11] found no differences in the bone level changes between “platform-switched” and conventional external-hexagon implants after 24 months. Enkling et al.[12] in a split mouth study suggested that the extent of microbial colonization had a greater impact on the amount of peri-implant bone loss than the platform design. Vigolo et al.[13] reported the longest follow up (5 years), with a positive effect of platform switching on bone preservation after 1 year. However, at 5 years the marginal bone change was insignificant as compared to that seen at 1 year around both switched and non-switched platforms. These results suggest that under normal circumstances, the pattern of marginal bone loss associated with platform switched implants was identical to that of conventional implants, where the greatest amount of bone changes occurred between surgery and crown/abutment placement, after which the changes were minimal. In a 3D FEA analysis, Hsu et al.[14] reported that platform switching leads to a small but insignificant reduction of <10% in crestal bone strain. However, it does not significantly influence crestal bone strain or micro movement.

BENEFITS OF PLATFORM SWITCHING

Increased implant longevity

Improved esthetics

The effect of inter-implant distance is minimized. A minimum of 3 mm inter-implant distance is needed to preserve marginal bone.

LIMITATIONS OF PLATFORM SWITCHING

If normal sized abutments are to be used, implants of larger size need to be placed. This might not be possible clinically always

If normal implants are to be used, smaller diameter abutments may compromise the emergence profile in aesthetic areas

Around 3 mm of soft tissue should be present to place platform switched implants or else bone resorption is likely to occur[15]

For platform switching to be effective, the under sizing of the components must be carried out during all phases of the implant treatment.

CONCLUSION

Many factors contribute to marginal bone loss around implants and its solution cannot be attributed to any single parameter. However, an appropriate understanding and use of platform switching concept in routine treatment improves crestal bone preservation and controlled biologic space repositioning. It appears be a promising tool in preserving peri-implant bone and further research is needed to substantiate its application in contemporary implantology.