Influence of Tapered and External Hexagon Connections on Bone Stresses Around Tilted Dental Implants: Three-Dimensional Finite Element Method With Statistical Analysis

• Localización: Journal of periodontology, ISSN 0022-3492, Nº. 2, 2014, págs. 261-269
• Idioma: inglés
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• Resumen

  • Background: The purpose of this study is to analyze the tension distribution on bone tissue around implants with different angulations (0°, 17°, and 30°) and connections (external hexagon and tapered) through the use of three-dimensional finite element and statistical analyses.

    Methods: Twelve different configurations of three-dimensional finite element models, including three inclinations of the implants (0°, 17°, and 30°), two connections (an external hexagon and a tapered), and two load applications (axial and oblique), were simulated. The maximum principal stress values for cortical bone were measured at the mesial, distal, buccal, and lingual regions around the implant for each analyzed situation, totaling 48 groups. Loads of 200 and 100 N were applied at the occlusal surface in the axial and oblique directions, respectively. Maximum principal stress values were measured at the bone crest and statistically analyzed using analysis of variance. Stress patterns in the bone tissue around the implant were analyzed qualitatively.

    Results: The results demonstrated that under the oblique loading process, the external hexagon connection showed significantly higher stress concentrations in the bone tissue (P <0.05) compared with the tapered connection. Moreover, the buccal and mesial regions of the cortical bone concentrated significantly higher stress (P <0.005) to the external hexagon implant type. Under the oblique loading direction, the increased external hexagon implant angulation induced a significantly higher stress concentration (P = 0.045).

    Conclusions: The study results show that: 1) the oblique load was more damaging to bone tissue, mainly when associated with external hexagon implants; and 2) there was a higher stress concentration on the buccal region in comparison to all other regions under oblique load.

    Anatomic limitations for the placement of implants are still a great challenge.1 In these situations, the need for bone graft procedures or other advanced surgical techniques has led to a search for alternative procedures, such as the use of short2 or tilted3 implants. Moreover, tilted implants could reduce the need for complex surgeries, and longitudinal studies have proven the predictability of their use on splinted multiple implant�supported prostheses.4-7 A major challenge within implantology is the preservation of bone level around implants for long-term functionality. Thus, some studies in the biomechanics field have gained importance because they evaluate occlusal load characteristics, implant and prosthesis material properties, effectiveness of the quantity and quality of bone tissues for implant-supported prostheses, and some implant-intrinsic characteristics (e.g., geometry and angulation).8-11 All of these factors contribute to the tension that is dissipated in the bone tissue.

    The oblique force over tilted implants may overload bone tissue and lead to osseointegration failure.11,12 Furthermore, some studies report that high tilting of implants increases the tension concentration around them and, consequently, could lead to bone resorption.13-15 Despite the noticeable use of external hexagon implants that possess some advantages, such as antirotational mechanism, reversibility, and compatibility among different systems,16 the literature states that they have disadvantages related to screw loosening and screw fracture,17 as well as implant saucerization.18,19 A tapered connection allows a prosthetic abutment adaptation to fit more precisely to the implant interface, and its conical geometry of imbrication could lead to better stress dissipation by the implants.20,21 Moreover, this implant connection presents biologic advantages such as a bacterial seal and biologic space maintenance.18 Longitudinal studies point to the predictable use of external hexagon22,23 and tapered24 implants. However, there is a need for studies evaluating the biomechanical effects of these different implant geometries.

    The correct understanding of all factors interacting on rehabilitation planning optimizes treatment success. Learning about biomechanical factors involved in this context helps final decision-making in critical clinical situations such as severe mandibular resorption.1-3 Thus, testing tilted implants with different connections could contribute to a better understanding of the biomechanics involved. Unfortunately, the literature lacks information about biomechanics studies on tilted implants and their direct effects on cortical bone.

    This study seeks to analyze the tension distribution on bone tissue around implants (regions: mesial, distal, buccal, and lingual) with different angulations (0°, 17°, and 30°) and connections (external hexagon and tapered) through the use of three-dimensional finite element analysis while searching for the interactions among implant angulations and connections that are related to their cortical bone effects. The study�s hypothesis is that, by finite element and statistical analyses, the placement of a tilted implant with a tapered connection is more favorable to the tension distribution in peri-implant bones than that with an external hexagon connection in a single implant�supported prosthesis.