Medical Hypotheses xxx (2015) xxx–xxx
Contents lists available at ScienceDirect
Medical Hypotheses journal homepage: www.elsevier.com/locate/mehy
Potential use of a polycarbonate-urethane matrix reinforced with polyethylene fibers for shock-absorbing dental implants Ramtin Sheikhhassani a,⇑,1, Pasha Anvari b,2, Simin Taei d,3, Yasmin Sheikhhassani c,3 a
Department of Aerospace and Mechanical Engineering, University of Southern California, Los Angeles, CA 90089, USA Department of Ophthalmology and Ophthalmic Research Center, Farabi Eye Hospital, Tehran University of Medical Sciences, Tehran, Iran c School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran d Private Practice, Tehran, Iran b
a r t i c l e
i n f o
Article history: Received 4 February 2015 Accepted 2 May 2015 Available online xxxx
a b s t r a c t The absence of a shock-absorbing mechanism in commercial dental implants is a likely factor in the resulting bone loss and possible implant failure. The aim of the current study is to generate a shock-absorbing dental implant that resembles the periodontal ligament, which naturally absorbs occlusal overloading forces. To achieve this, a polycarbonate-urethane composite reinforced with polyethylene fibers will be constructed. Tests based on finite element analysis and mechanical testing are proposed to further examine this novel implant type. Ó 2015 Elsevier Ltd. All rights reserved.
Introduction The ideal dental implant should closely mimic the biomechanical properties of a natural tooth. In the presence of overloading, a shock-absorption mechanism should be implemented within or around the implant to help dissipate the impacting forces. However, most commercially available dental implants do not have such overload absorption advancements. It has been reported that occlusal overloading can be destructive for implants and can cause bone loss [1], screw loosening, fracture, or implant failure [2]. In the event of excessive loading, the periodontal ligament (PDL) serves as a shock absorber for the natural tooth [3]. The primary function of the PDL is to connect the teeth to the alveolar bone. The PDL displays both viscous and elastic behavior and is thus considered a viscoelastic material [4]. In completely elastic materials, all stored energy is recovered once the applied force is removed. However, in viscous materials, the stored energy is not recovered. In a viscoelastic system, some of the energy is recovered and the remainder is dissipated. From an anatomical viewpoint, intra- and extravascular fluids in the PDL resist light and moderate forces, while the principal fibers resist heavier forces. The PDL consists mainly of collagenous fibers, including alveolar crest, horizontal, oblique, apical, and interradicular fibers [5].
⇑ Corresponding author. 1 2 3
E-mail address: [email protected] (R. Sheikhhassani). PhD. MD, MPH. DDS.
Oblique fibers withstand the occlusal forces along the long axis of the tooth. Apical and interradicular fibers (which are only present in multi-rooted teeth) withstand forces in the occlusal direction [6]. When masticatory force is exerted, the tooth rapidly moves apically, and the adjoining teeth support this loading. As the masticatory force grows larger, tooth movement slowly decreases. The tooth will gradually return to its primary position as the force dissipates. These biomechanical actions distribute the force and absorb the shock received by the tooth [7]. Significance/Prevalence Conventional implants lack the potential to be supported by a cushion-like structure. Therefore, these implants are more vulnerable to traumatic overloading, which has been shown to be a major reason for implant failure [8]. Because the failure rate of implants is 4.93% for the mandible and 8.16% for the maxilla [9], a robust damping system designed to minimize traumatic overloading may help to prevent such failures. Background literature The issue of shock absorption by implants has been theoretically discussed in previous literature [10]. To reduce tension on the bone, some studies [11,12] have suggested using a silicone-based abutment (connecting element). Moreover, some of the newly designed prototypes [7] use silicone for part of the model (e.g., the resilient ring). Nonetheless, silicone is not an appropriate bio-inert material for direct contact with the
http://dx.doi.org/10.1016/j.mehy.2015.05.003 0306-9877/Ó 2015 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Sheikhhassani R et al. Potential use of a polycarbonate-urethane matrix reinforced with polyethylene fibers for shockabsorbing dental implants. Med Hypotheses (2015), http://dx.doi.org/10.1016/j.mehy.2015.05.003
2
R. Sheikhhassani et al. / Medical Hypotheses xxx (2015) xxx–xxx
Table 1 Various shock-absorbing materials used in the past. Application
Inventor
Material/Mechanism
Dental
Kanth [15], [11] Koch [16], Kirsch [12]
Dental
Mobile-implant (SIS-Inc., Klagenfurt, Austria) Gaggl and Schultes [17] Carvalho [18]
Silicon abutments, direct contact with gingiva, inflammation Conic implant with three silicon rings enclosed in center Silicone rubber between abutment and crown Selectively controlled progressive loading, silicone O- rings Partial cannular cylinder, resilient silicone ring
Dental Dental
Compliant Keeper (CK) system Mensor et al. [19]
Dental
Chen, et al. [7]
pre-implant tissue region, and it may induce a host immune reaction [13]. In addition, the finite element methods used to analyze and verify the aforementioned model have been restricted to isotropic and homogenous materials, whereby the assumption is that the materials have a consistent structure in all directions. This assumption does not reflect the actual mechanical properties of biological tissues. Recently, the shock-absorption capacity of a zirconia implant abutment was assessed using the PeriometerÒ, a percussion device that measures damping [14]. The inclusion of composite resin components (e.g., an abutment or restoration) has demonstrated shock-absorbing characteristics that mimic natural teeth. It was suggested that further studies should be conducted to evaluate the long-term and fatigue behavior of the implant. Advantages and disadvantages All of the shock-absorption solutions in the dental implants listed in Table 1 use silicone. When in direct contact with the gingiva, silicone causes inflammation. For implants that use silicone in an enclosed chamber, there is concern that an accident leading to implant breakage would result in the silicone contacting oral tissue. Although plain silicone is viscoelastic, it demonstrates linear behavior [20]. The PDL has a non-linear characteristic. The PDL consists of collagenous fibers. A mechanism for mimicking the fibers is absent in all previously described techniques.
Procedure: Preliminary design, material selection, finite element analysis (FEA), prototype generation, and mechanical testing. Materials: Possible materials that can be used to absorb stress include fiber-enhanced viscoelastic damping polymers [26] and PCU with PE fibers. Devices: Fiber-reinforced polymers are prepared by molding processes that generate the correct shape. Measurements: The size, dimension, and thickness of the damping structure required for shock resistance must be computed. Design parameters To develop an optimal design, the following suggestions, based on FEA available from the literature, will be considered. Size In larger diameter implants, the stress distribution becomes more uniform [27,28], and the magnitude of cortical bone stresses decreases [28]. To protect the bone and dissipate occlusal forces over a larger area, it has been recommended to avoid short implants. Lum et al. [29] showed that occlusal forces are primarily distributed to the crestal bone rather than being evenly distributed throughout the surface area of the implant-bone interface. The typical diameter (D) and length (L) for the implant are as follows: D = [3.5 mm, 4 mm, 4.5 mm, 5 mm, 6 mm]; and, L = [9 mm, 10 mm, 11 mm, 12 mm, 13 mm]. Here, mid-range values of D = 4.5 mm and L = 11 mm are selected. Shape Mailath et al. [28] reported that implants with cylindrical shapes are more suitable than cone-shaped implants. Holmgren et al. [30] showed how, in terms of distribution, stepped cylindrical implants are preferable. Mechanical properties The data available in the literature offer contradictory measures for the elastic modulus of the PDL [31]. The ultimate tensile strength of Bionate PCU 55D is 60.5, which is close to the PDL strength reported by Cook et al. [32]. Although masticatory and bruxing forces may reach 500 N in females and 700 N in males [33], some FEA reports have only considered forces up to 100 N [34].
Hypothesis In the search for a biocompatible dental implant material, an approach similar to that for an orthopedic problem was adopted. The meniscus is a C-shaped, bi-phasic piece of cartilage [21] that cushions the knee and acts as a shock-absorber; it consists of water (63–75%) and collagenous fibers [22]. The meniscus may undergo tears during traumatic events. In 85% of cases, surgical intervention (i.e., meniscectomy) is required to remove all or part of the torn meniscus [23]. A synthetic meniscus replacement made from a polycarbonate-urethane (PCU) matrix reinforced with polyethylene fibers (PE) was recently developed to treat patients who suffer from post-meniscectomy syndrome [23]. Importantly, PCU shows a low wear rate [24] and good compatibility with natural tissues [25]. Proposed materials and methods Objective: Conceptual design of a mechanism for shock absorption in dental implants that is biologically safe for patients.
Fig. 1. Suggested design. A cylindrical implant with squared threads is depicted.
Please cite this article in press as: Sheikhhassani R et al. Potential use of a polycarbonate-urethane matrix reinforced with polyethylene fibers for shockabsorbing dental implants. Med Hypotheses (2015), http://dx.doi.org/10.1016/j.mehy.2015.05.003
R. Sheikhhassani et al. / Medical Hypotheses xxx (2015) xxx–xxx
3
Summary In summary, commercially available implants do not have a mechanism for shock absorption. Although silicone has been previously suggested for use in a shock-resistant implant, its bio-incompatibility in the oral cavity is a major concern. Implementation of PCU-PE reinforced composites for shock-resistant components provides a better design for improving the shock-absorbing properties of dental implants. In addition, an ideal geometric shape to minimize the effects of stress on the implant is provided. Conflict of interest None declared. References
Fig. 2. Cross-section view. Cross section of the proposed shock-absorber implant is shown. The blue parts represent three O-rings made of PCU-PE placed inferiorly, laterally, and superiorly, in the areas that are most likely to have stress concentrations. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Chun et al. [34] reported that an elevated stress concentration occurs in the region of the jaw bone and in the uppermost thread of the implant. They also demonstrated that stress is more evenly distributed for implants that have a square thread. Thus, our suggested design is as follows (Fig. 1). To increase the area for osseointegration, a slit will be placed through the implant to create a hollow region. The threads will be square-shaped, as suggested in previous studies. The composite shock absorber (Fig. 2) will be placed in three regions throughout the implant: inferiorly, laterally, and superiorly, where the stress is most concentrated. Evaluation of the hypothesis Computations will be performed for a preliminary design. Von Misses stress criteria will be used to show resistance against overloading in implants with and without damping. The strength of the implant will be compared with that of natural teeth. FEA software (ANSYS, ABAQUS) will be used to simulate the forces applied to the damping system. After successfully passing these criteria, a prototype will be created. Force–displacement curves for the prototype will be obtained using the data provided by testing machines. In vitro tests will be used to replicate different scenarios that may lead to overloading and fatigue. Thereafter, the possible effects of the reinforced composite implants in vivo will be investigated. Analysis Cyclic and compression stress tests will be conducted using an Instron instrument (as used by Mensor et al. [19]). A laser displacement sensor (Model: LB-1103, Keyence, Elmwood Park, NJ, USA) will be incorporated to precisely measure micro-motions (as used by Chen [7]). A Periometer (as used by Magne et al. [14]) will be used to determine the quantitative damping properties of the proposed structure and to compare them with those of the natural teeth.
[1] Misch CE, Suzuki JB, Misch-Dietsh FM, Bidez MW. A positive correlation between occlusal trauma and peri-implant bone loss: literature support. Implant Dent 2005;14(2):108–16. [2] Schwarz MS. Mechanical complications of dental implants. Clin Oral Implants Res 2000;11(s1):156–8. [3] Ddsmsc MH. Dental implants: a different perspective (Part 2). Implant Practice US Edition 2009;2(2):34–41. [4] Toms SR, Dakin GJ, Lemons JE, Eberhardt AW. Quasi-linear viscoelastic behavior of the human periodontal ligament. J Biomech 2002;35(10):1411–5. [5] Brand RW, Isselhard DE, Satin E. Anatomy of orofacial structures: a comprehensive approach. Elsevier Health Sciences; 2013. [6] Dowd FJ et al. Mosby’s review for the NBDE. Elsevier Health Sciences; 2007. [7] Chen Y-Y, Chen W-P, Chang H-H, Huang S-H, Lin C-P. A novel dental implant abutment with micro-motion capabilitydevelopment and biomechanical evaluations. Dent Mater 2014;30(2):131–7. [8] Friberg B, Jemt T, Lekholm U. Early failures in 4,641 consecutively placed branemark dental implants: a study from stage 1 surgery to the connection of completed prostheses. Int J Oral Maxillofac Implants 1990;6(2):142–6. [9] Moy PK, Medina D, Shetty V, Aghaloo TL. Dental implant failure rates and associated risk factors. Int J Oral Maxillofac Implants 2004;20(4):569–77. [10] Brunski JB. Biomaterials and biomechanics in dental implant design. Int J Oral Maxillofac Implants 1988;3(2):85–97. [11] Kanth L. Titanium plasma coated intramobile conical implants. ZWR 1982;91(12):42–4. [12] Kirsch A. The two-phase implantation method using imz intramobile cylinder implants. J Oral Implantol 1982;11(2):197–210. [13] Hillenburg K, Kosinski T, Mentag P. Control of peri-implant inflammation. Pract Periodontics Aesthet Dent 1990;3(8):11–6. [14] Magne P, Silva M, Oderich E, Boff LL, Enciso R. Damping behavior of implantsupported restorations. Clin Oral Implants Res 2013;24(2):143–8. [15] Kanth L. The cast (intramobile) screw implant. DDZ 1971;25(12):465. [16] Koch W. 2-Phasic endosseous implantation of intramobile cylindrical implants i). Die Quintessenz 1976;27(2):23. [17] Gaggl A, Schultes G. Biomechanical properties in titanium implants with integrated maintenance free shock absorbing elements. Biomaterials 2001;22(22):3061–6. [18] Carvalho L, Vaz M, Simões J. Mandibular strains induced by conventional and novel dental implants. J Strain Anal Eng Des 2004;39(3):291–7. [19] Mensor M, Ahlstrom R, Scheerer E. Compliant keeper system replication of the periodontal ligament protective damping function for implants: Part i. J Prosthet Dent 1998;80(5):565–9. [20] Goldberg AJ. Viscoelastic properties of silicone, polysulfide, and polyether impression materials. J Dent Res 1974;53(5):1033–9. [21] Drake R, Vogl AW, Mitchell AW. Gray’s anatomy for students. Elsevier Health Sciences; 2009. [22] Peters T, Smillie E. Studies on the chemical composition of the menisci of the knee joint with special reference to the horizontal cleavage lesion. Clin Orthop Relat Res 1972;86:245–52. [23] Vrancken ACT, Buma P, van Tienen TG. Synthetic meniscus replacement: a review. Int Orthop 2013;37(2):291–9. [24] Elsner JJ, Mezape Y, Hakshur K, Shemesh M, Linder-Ganz E, Shterling A, Eliaz N. Wear rate evaluation of a novel polycarbonate-urethane cushion form bearing for artificial hip joints. Acta Biomater 2010;6(12):4698–707. [25] Kurtz SM. Retrieval analysis of a polycarbonate-urethane acetabular cup: a case report. J Long Term Eff Med Implants 2008;18(1). [26] Alberts T, Xia H. Design and analysis of fiber enhanced viscoelastic damping polymers. J Vib Acoust 1995;117(4):398–404. [27] Matsushita Y, Kitoh M, Mizuta K, Ikeda H, Suetsugu T. Two-dimensional fem analysis of hydroxyapatite implants: diameter effects on stress distribution. J Oral Implantol 1989;16(1):6–11.
Please cite this article in press as: Sheikhhassani R et al. Potential use of a polycarbonate-urethane matrix reinforced with polyethylene fibers for shockabsorbing dental implants. Med Hypotheses (2015), http://dx.doi.org/10.1016/j.mehy.2015.05.003
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[28] Mailath G, Stoiber B, Watzek G, Matejka M. Part Bone resorption at the entry of osseointegrated implants – a biomechanical phenomenon. Finite element study. Z Stomatol 1989;86(4):207–16. [29] Lum LB. A biomechanical rationale for the use of short implants. J Oral Implantol 1990;17(2):126–31. [30] Holmgren EP, Seckinger RJ, Kilgren LM, Mante F. Evaluating parameters of osseointegrated dental implants using finite element analysisa twodimensional comparative study examining the effects of implant diameter, implant shape, and load direction. J Oral Implantol 1998;24(2): 80–8.
[31] Nishihira M, Yamamoto K, Sato Y, Ishikawa H, Natali A. 2 mechanics of periodontal ligament. Dent Biomech 2003:20. [32] Cook S, Weinstein A, Klawitter J. Materials science a three-dimensional finite element analysis of a porous rooted co–cr–mo alloy dental implant. J Dent Res 1982;61(1):25–9. [33] J. McGarry, Dynamic evaluation of forces during mastication (Ph.D. thesis), Worcester Polytechnic Institute. [34] Chun H-J, Cheong S-Y, Han J-H, Heo S-J, Chung J-P, Rhyu I-C, Choi Y-C, Baik H-K, Ku Y, Kim M-H. Evaluation of design parameters of osseointegrated dental implants using finite element analysis. J Oral Rehabil 2002;29(6):565–74.
Please cite this article in press as: Sheikhhassani R et al. Potential use of a polycarbonate-urethane matrix reinforced with polyethylene fibers for shockabsorbing dental implants. Med Hypotheses (2015), http://dx.doi.org/10.1016/j.mehy.2015.05.003
Contents lists available at ScienceDirect
Medical Hypotheses journal homepage: www.elsevier.com/locate/mehy
Potential use of a polycarbonate-urethane matrix reinforced with polyethylene fibers for shock-absorbing dental implants Ramtin Sheikhhassani a,⇑,1, Pasha Anvari b,2, Simin Taei d,3, Yasmin Sheikhhassani c,3 a
Department of Aerospace and Mechanical Engineering, University of Southern California, Los Angeles, CA 90089, USA Department of Ophthalmology and Ophthalmic Research Center, Farabi Eye Hospital, Tehran University of Medical Sciences, Tehran, Iran c School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran d Private Practice, Tehran, Iran b
a r t i c l e
i n f o
Article history: Received 4 February 2015 Accepted 2 May 2015 Available online xxxx
a b s t r a c t The absence of a shock-absorbing mechanism in commercial dental implants is a likely factor in the resulting bone loss and possible implant failure. The aim of the current study is to generate a shock-absorbing dental implant that resembles the periodontal ligament, which naturally absorbs occlusal overloading forces. To achieve this, a polycarbonate-urethane composite reinforced with polyethylene fibers will be constructed. Tests based on finite element analysis and mechanical testing are proposed to further examine this novel implant type. Ó 2015 Elsevier Ltd. All rights reserved.
Introduction The ideal dental implant should closely mimic the biomechanical properties of a natural tooth. In the presence of overloading, a shock-absorption mechanism should be implemented within or around the implant to help dissipate the impacting forces. However, most commercially available dental implants do not have such overload absorption advancements. It has been reported that occlusal overloading can be destructive for implants and can cause bone loss [1], screw loosening, fracture, or implant failure [2]. In the event of excessive loading, the periodontal ligament (PDL) serves as a shock absorber for the natural tooth [3]. The primary function of the PDL is to connect the teeth to the alveolar bone. The PDL displays both viscous and elastic behavior and is thus considered a viscoelastic material [4]. In completely elastic materials, all stored energy is recovered once the applied force is removed. However, in viscous materials, the stored energy is not recovered. In a viscoelastic system, some of the energy is recovered and the remainder is dissipated. From an anatomical viewpoint, intra- and extravascular fluids in the PDL resist light and moderate forces, while the principal fibers resist heavier forces. The PDL consists mainly of collagenous fibers, including alveolar crest, horizontal, oblique, apical, and interradicular fibers [5].
⇑ Corresponding author. 1 2 3
E-mail address: [email protected] (R. Sheikhhassani). PhD. MD, MPH. DDS.
Oblique fibers withstand the occlusal forces along the long axis of the tooth. Apical and interradicular fibers (which are only present in multi-rooted teeth) withstand forces in the occlusal direction [6]. When masticatory force is exerted, the tooth rapidly moves apically, and the adjoining teeth support this loading. As the masticatory force grows larger, tooth movement slowly decreases. The tooth will gradually return to its primary position as the force dissipates. These biomechanical actions distribute the force and absorb the shock received by the tooth [7]. Significance/Prevalence Conventional implants lack the potential to be supported by a cushion-like structure. Therefore, these implants are more vulnerable to traumatic overloading, which has been shown to be a major reason for implant failure [8]. Because the failure rate of implants is 4.93% for the mandible and 8.16% for the maxilla [9], a robust damping system designed to minimize traumatic overloading may help to prevent such failures. Background literature The issue of shock absorption by implants has been theoretically discussed in previous literature [10]. To reduce tension on the bone, some studies [11,12] have suggested using a silicone-based abutment (connecting element). Moreover, some of the newly designed prototypes [7] use silicone for part of the model (e.g., the resilient ring). Nonetheless, silicone is not an appropriate bio-inert material for direct contact with the
http://dx.doi.org/10.1016/j.mehy.2015.05.003 0306-9877/Ó 2015 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Sheikhhassani R et al. Potential use of a polycarbonate-urethane matrix reinforced with polyethylene fibers for shockabsorbing dental implants. Med Hypotheses (2015), http://dx.doi.org/10.1016/j.mehy.2015.05.003
2
R. Sheikhhassani et al. / Medical Hypotheses xxx (2015) xxx–xxx
Table 1 Various shock-absorbing materials used in the past. Application
Inventor
Material/Mechanism
Dental
Kanth [15], [11] Koch [16], Kirsch [12]
Dental
Mobile-implant (SIS-Inc., Klagenfurt, Austria) Gaggl and Schultes [17] Carvalho [18]
Silicon abutments, direct contact with gingiva, inflammation Conic implant with three silicon rings enclosed in center Silicone rubber between abutment and crown Selectively controlled progressive loading, silicone O- rings Partial cannular cylinder, resilient silicone ring
Dental Dental
Compliant Keeper (CK) system Mensor et al. [19]
Dental
Chen, et al. [7]
pre-implant tissue region, and it may induce a host immune reaction [13]. In addition, the finite element methods used to analyze and verify the aforementioned model have been restricted to isotropic and homogenous materials, whereby the assumption is that the materials have a consistent structure in all directions. This assumption does not reflect the actual mechanical properties of biological tissues. Recently, the shock-absorption capacity of a zirconia implant abutment was assessed using the PeriometerÒ, a percussion device that measures damping [14]. The inclusion of composite resin components (e.g., an abutment or restoration) has demonstrated shock-absorbing characteristics that mimic natural teeth. It was suggested that further studies should be conducted to evaluate the long-term and fatigue behavior of the implant. Advantages and disadvantages All of the shock-absorption solutions in the dental implants listed in Table 1 use silicone. When in direct contact with the gingiva, silicone causes inflammation. For implants that use silicone in an enclosed chamber, there is concern that an accident leading to implant breakage would result in the silicone contacting oral tissue. Although plain silicone is viscoelastic, it demonstrates linear behavior [20]. The PDL has a non-linear characteristic. The PDL consists of collagenous fibers. A mechanism for mimicking the fibers is absent in all previously described techniques.
Procedure: Preliminary design, material selection, finite element analysis (FEA), prototype generation, and mechanical testing. Materials: Possible materials that can be used to absorb stress include fiber-enhanced viscoelastic damping polymers [26] and PCU with PE fibers. Devices: Fiber-reinforced polymers are prepared by molding processes that generate the correct shape. Measurements: The size, dimension, and thickness of the damping structure required for shock resistance must be computed. Design parameters To develop an optimal design, the following suggestions, based on FEA available from the literature, will be considered. Size In larger diameter implants, the stress distribution becomes more uniform [27,28], and the magnitude of cortical bone stresses decreases [28]. To protect the bone and dissipate occlusal forces over a larger area, it has been recommended to avoid short implants. Lum et al. [29] showed that occlusal forces are primarily distributed to the crestal bone rather than being evenly distributed throughout the surface area of the implant-bone interface. The typical diameter (D) and length (L) for the implant are as follows: D = [3.5 mm, 4 mm, 4.5 mm, 5 mm, 6 mm]; and, L = [9 mm, 10 mm, 11 mm, 12 mm, 13 mm]. Here, mid-range values of D = 4.5 mm and L = 11 mm are selected. Shape Mailath et al. [28] reported that implants with cylindrical shapes are more suitable than cone-shaped implants. Holmgren et al. [30] showed how, in terms of distribution, stepped cylindrical implants are preferable. Mechanical properties The data available in the literature offer contradictory measures for the elastic modulus of the PDL [31]. The ultimate tensile strength of Bionate PCU 55D is 60.5, which is close to the PDL strength reported by Cook et al. [32]. Although masticatory and bruxing forces may reach 500 N in females and 700 N in males [33], some FEA reports have only considered forces up to 100 N [34].
Hypothesis In the search for a biocompatible dental implant material, an approach similar to that for an orthopedic problem was adopted. The meniscus is a C-shaped, bi-phasic piece of cartilage [21] that cushions the knee and acts as a shock-absorber; it consists of water (63–75%) and collagenous fibers [22]. The meniscus may undergo tears during traumatic events. In 85% of cases, surgical intervention (i.e., meniscectomy) is required to remove all or part of the torn meniscus [23]. A synthetic meniscus replacement made from a polycarbonate-urethane (PCU) matrix reinforced with polyethylene fibers (PE) was recently developed to treat patients who suffer from post-meniscectomy syndrome [23]. Importantly, PCU shows a low wear rate [24] and good compatibility with natural tissues [25]. Proposed materials and methods Objective: Conceptual design of a mechanism for shock absorption in dental implants that is biologically safe for patients.
Fig. 1. Suggested design. A cylindrical implant with squared threads is depicted.
Please cite this article in press as: Sheikhhassani R et al. Potential use of a polycarbonate-urethane matrix reinforced with polyethylene fibers for shockabsorbing dental implants. Med Hypotheses (2015), http://dx.doi.org/10.1016/j.mehy.2015.05.003
R. Sheikhhassani et al. / Medical Hypotheses xxx (2015) xxx–xxx
3
Summary In summary, commercially available implants do not have a mechanism for shock absorption. Although silicone has been previously suggested for use in a shock-resistant implant, its bio-incompatibility in the oral cavity is a major concern. Implementation of PCU-PE reinforced composites for shock-resistant components provides a better design for improving the shock-absorbing properties of dental implants. In addition, an ideal geometric shape to minimize the effects of stress on the implant is provided. Conflict of interest None declared. References
Fig. 2. Cross-section view. Cross section of the proposed shock-absorber implant is shown. The blue parts represent three O-rings made of PCU-PE placed inferiorly, laterally, and superiorly, in the areas that are most likely to have stress concentrations. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Chun et al. [34] reported that an elevated stress concentration occurs in the region of the jaw bone and in the uppermost thread of the implant. They also demonstrated that stress is more evenly distributed for implants that have a square thread. Thus, our suggested design is as follows (Fig. 1). To increase the area for osseointegration, a slit will be placed through the implant to create a hollow region. The threads will be square-shaped, as suggested in previous studies. The composite shock absorber (Fig. 2) will be placed in three regions throughout the implant: inferiorly, laterally, and superiorly, where the stress is most concentrated. Evaluation of the hypothesis Computations will be performed for a preliminary design. Von Misses stress criteria will be used to show resistance against overloading in implants with and without damping. The strength of the implant will be compared with that of natural teeth. FEA software (ANSYS, ABAQUS) will be used to simulate the forces applied to the damping system. After successfully passing these criteria, a prototype will be created. Force–displacement curves for the prototype will be obtained using the data provided by testing machines. In vitro tests will be used to replicate different scenarios that may lead to overloading and fatigue. Thereafter, the possible effects of the reinforced composite implants in vivo will be investigated. Analysis Cyclic and compression stress tests will be conducted using an Instron instrument (as used by Mensor et al. [19]). A laser displacement sensor (Model: LB-1103, Keyence, Elmwood Park, NJ, USA) will be incorporated to precisely measure micro-motions (as used by Chen [7]). A Periometer (as used by Magne et al. [14]) will be used to determine the quantitative damping properties of the proposed structure and to compare them with those of the natural teeth.
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Please cite this article in press as: Sheikhhassani R et al. Potential use of a polycarbonate-urethane matrix reinforced with polyethylene fibers for shockabsorbing dental implants. Med Hypotheses (2015), http://dx.doi.org/10.1016/j.mehy.2015.05.003
