The purpose of this study was to investigate the effect of 2 different abutment types on the stress distribution in peri-implant bone and within the implant-abutment complex using 3-dimensional finite element analysis. A simple cylindrical implant (4 × 11 mm) was used in this study for efficacy calculation. One model simulated a 4.00-mm-diameter abutment connection, and the other was narrower, using a 3.2-mm-diameter abutment connection assuming a platform-switching configuration. The stress level in the cervical bone area at the implant was greatly reduced when the narrow-diameter abutment was connected compared with the regular-sized one, despite the fact that the stress level in the implant-abutment complex was increased. The results obtained in the platform-switching model can contribute to reduce the stress level at the implant-bone interface area. Results from this study showed the platform-switching procedure has the biomechanical advantage of shifting the stress concentration area away from the cervical bone-implant interface. The disadvantage of the configuration is the increasing stress in the abutment and implant-abutment junction.
Since the preliminary studies on osseointegration, dental implants have been extensively used for the rehabilitation of completely and partially edentulous patients over past the 4 decades.1–3 The implant treatment has been well documented and shown to have predictable outcomes.4 Despite the high success rates reported by a vast number of various clinical studies, early or late implant failures are still inescapable.5 Early or late peri-implant bone loss has been observed in many implant systems and after different surgical approaches.4,6 Crestal bone loss in particular is one of the leading symptoms of implant failure after osseointegration and the achievement of primary stability.7 Bone resorbtion close to the first thread of osseointegrated implants is frequently observed during initial loading.8
Several long-term clinical studies have shown a mean marginal bone loss around dental implants of 1.5 to 2 mm in the first year after implant function.4,9,10 Bone reabsorption at the implant neck area is not unavoidable. Some clinical observations have indicated that less bone reabsorption with bone preservation is possible when the narrower diameter of abutment is connected to the implant, so-called platform switching.11
According to the study by Lazzara and Porter,12 radiography follow-up shows that platform switching reduces the loss of crestal bone height. They attribute this to the shifting inflammatory cell, which instead of infiltrating is minimalized and eventually dissipates from the crestal bone, despite such infiltration that might appear within the gap of the implant-abutment junction.
Recent studies have also shown the biomechanical performance and value of platform switching. Because platform switching changes the traditional design of the abutment-implant connection, the stress distributions from the abutment to the implant and from the implant to the bone might be affected when occlusal loading occurs.13,14
For problems involving complicated geometries, it is very difficult to achieve an analytical solution. Therefore, the use of numerical methods such as finite element analysis (FEA) is required. Finite element analysis is a technique for obtaining a solution to a complex mechanical problem by dividing the problem domain into a collection of much smaller and simpler domains (elements) in which the field variables can be interpolated with the use of shape functions. An overall approximated solution to the original problem is determined based on variational principles.15
The components in a dental implant bone system are geometrically extremely complex. As a result, the FEA has been viewed as the most suitable tool for analyzing them.15
The aim of this study was to observe the biomechanical advantages of the platform-switching configuration in terms of stress distribution in the implant-abutment system and the bone.
aterı als and M ethods
The aim of this study is to observe the stress distribution in and around implants in 2 different specially designed implant-abutment connection systems. In the system, referred to as the platform-switching system, the diameter of abutment is more narrow in comparison to the implant. In the other system, designated as the standard system, the implant and the abutment have the same platform size. The implants in both systems have the same properties in terms of form and structure.
A simple cylindrical implant of 4 × 11 mm without a surface screw structure was used in this study for efficacy calculation. One model simulated a 4.00-mm-diameter abutment connection (standard model), and the other was narrower, using a 3.2-mm-diameter abutment connection assuming a platform-switching configuration (PLS model; Figure 1). In both models, implant and abutment are interlocked with a connective screw. The length of the screw is 10 mm and the diameter of the screw is 1.4 mm. The bone model used in this study comprised compact and spongious bone assumed to be homogeneous, isotropic, and linearly elastic.
Three-dimensional (3D) geometric models of the implant systems were created by the advanced drawing system (CATIA) in which 3D finite element models were constructed simulating an osseointegrated implant with bone by using the prepost processor (MSC.Patran) and analyzed by the linear FEA software (MSC.Nastran).
Material properties for bone and implant components were designated according to previous studies (Table 1).16,17 The connection between bone and implant components was assumed to be firm osseointegration. V100-Newton and oblique 50-Newton loads were applied to the flat surface of the implant supported by an Ni-Ti crown (Figure 2). Results were analyzed by the distribution of stresses in the abutment, implant, connective screw, and implant-bone interface area around the implant.
There were differences in stress distribution patterns among the abutment, implant, bone, and connective screw. A high-stress distribution was found around the periphery of the implant's top surface and along its lateral surface as well as in the bone facing that area in the standard model, while this high-stress area shifted toward the center of the implant in the PLS model (Figure 3). In the PLS model, the stresses in bone are lower than in the standard model, and in both models, the stress distribution is greater in the cortical bone than in comparision with the cancellous bone (Figure 4). The stresses in the abutment were infinitely higher in the PLS model compared with the standard model (Figure 5). The stress level in the implant-abutment connection was increased when the narrow diameter of the abutment was connected compared with the regular-sized one (Figure 6). The stress distribution in the connective screw was higher in the PLS model than in the standard model (Figure 7). Von Mises stresses in both models' components can be seen in Table 2.
The results obtained in the PLS model can contribute to reduce the stress level at the implant-bone interface area. The reduction of the stress concentration at the implant-bone interface area is a favorable development to ensure the continuity of osseointegration. Another possible explanation of the efficacy of the platform-switching configuration is the relocation and redefiniton of the implant-abutment connection at the bone level.
Taking into account the limitations present within this study, it was nevertheless suggested that platform switching has the biomechanical advantage of shifting the stress concentration away from the implant-bone interface. This may have the disadvantage of increasing stress in the abutment and the abutment screw. Despite the obvious potential these facts convey, the platform-switching procedure is a subject that needs extensive investigation. Further studies using modified 3D finite element models and animal experiments are necessary as well as are longitudinal clinical observations.