Biomed. Eng.-Biomed. Tech. 2014; 59(6): 507–513
Rebecca Wilhelma, Istabrak Hasana,*, Ludger Keilig, Friedhelm Heinemann, Helmut Stark and Christoph Bourauel
Biomechanical investigations of the secondary stability of commercial short dental implants in porcine ribs Abstract: The use of short implants has increased widely within the last years. However, the stability of these implants has not yet been comprehensively investigated, in particular the difference in geometry and dimension of short implants. The aim of the present study was to investigate experimentally the difference of the secondary stability of different commercial short implants by measuring their displacements. Eleven implant geometries were investigated in this study. A total of 22 implants were inserted in porcine rib segments, two implants for each system. Implant displacements were measured using a self-developed biomechanical hexapod measurement system (HexMeS). The highest displacement was observed with Straumann BL NC 3.3 × 8.0 mm (266 μm), followed by Straumann Standard 4.1 × 6.0 mm (156 μm), while the lowest displacement of 61 μm was shown by Dentaurum type 1 implant (4.2 × 5.0 mm). No obvious difference of displacements was observed between hammered and screw-shaped implants with relevant dimensions. The experimental results were in good agreement with the a Equal authorship. *Corresponding author: Dr.rer.nat. Istabrak Hasan, Endowed Chair of Oral Technology, Rheinische Friedrich-Wilhelms University, Welschnonnenstr. 17, 53111 Bonn, Germany, Phone: +49 228 2872 2332 2388, E-mail: [email protected]; and Department of Prosthodontics, Preclinical Education and Dental Materials Science, University of Bonn, Welschnonnenstr. 17, 53111 Bonn, Germany Rebecca Wilhelm and Christoph Bourauel: Endowed Chair of Oral Technology, University of Bonn, Welschnonnenstr. 17, 53111 Bonn, Germany Ludger Keilig: Endowed Chair of Oral Technology, University of Bonn, Welschnonnenstr. 17, 53111 Bonn, Germany; and Department of Prosthodontics, Preclinical Education and Dental Materials Science, University of Bonn, Welschnonnenstr. 17, 53111 Bonn, Germany Friedhelm Heinemann: Department of Prosthodontics, Gerodontology and Biomaterials, University of Greifswald, 17475 Greifswald, Germany Helmut Stark: Department of Prosthodontics, Preclinical Education and Dental Materials Science, University of Bonn, Welschnonnenstr. 17, 53111 Bonn, Germany
numerical ones (19–42%) for Dentaurum implants. However, a difference of 70–80% was obtained for the Astra implant (4.0 × 6.0 mm) and Bicon implant (6.0 × 5.7 mm). The geometry of short implants directly affects their stability within the bone. Keywords: displacement; porcine ribs; short dental implants. DOI 10.1515/bmt-2014-0008 Received January 23, 2014; accepted July 7, 2014; online first August 5, 2014
Introduction In recent years, there was an increase in the popularity of implantology for edentulous patients who are in need of prosthesis treatment. The need for new alternatives for implant-supported prosthesis grew simultaneously to provide more possibilities for patients with insufficient bone volume. Following tooth loss, alveolar ridges typically develop severe atrophy, especially in patients who are edentulous for a long time. The bone volume of posterior areas of the jaw, in particular the maxilla, is often presenting a contraindication for the placement of implants with conventional dimensions, unless procedures such as ridge augmentation or sinus floor elevation are performed. However, these surgical procedures evoke several problems in the current aging society, especially when dealing with patients with multiple morbidities. This not only complicates the surgical operation enormously for older patients; the higher costs and morbidity and a longer treatment period are reasons for the increasing tendency of inserting short implants as well. According to the surgical protocol, short implants cannot be loaded before they reach the state of osseointegration. This process is complex and affected by different factors [3, 8, 21–23]. Some factors are related to so-called early failure, while the others are related to delayed failure. Factors
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508 R. Wilhelm et al.: Short dental implants that can cause early failure of implants are insufficient insertion torque and poor primary stability, as well as uncontrolled loading of implants that disturb the process of osseointegration. Delayed failure is mostly associated with overloading of implants that cause bone resorption in the cervical region, or peri-implantitis due to poor oral hygiene. Han et al. [10] stated in their retrospective study that overloading and inflammation are the most common reasons for implant failure. Additionally, it is essential to have sufficient bone quality to ensure the long survival rates of the implants. Implants that are inserted in the mandible have better survival rates than those inserted in the maxilla. Moreover, non-smokers show better rates than smokers [25]. Numerous publications address the issue of implant length as a predictor of implant survival [2, 4, 9, 13, 27]. Some are indecisive about using these implants because of the perception of a higher risk of failure compared with longer implants for both fixed restorations [8, 13, 17, 19, 28] and maxillary overdentures [2, 21]. More recent studies, however, suggest that short implants (7 to 10 mm long in the posterior region with fixed partial dental prostheses. In previous studies [3, 10], eight commercial short implants were numerically analysed in posterior bone segments and investigated in the osseointegrated state at an occlusal force of 300 N. In this study, it could be shown that implant diameter and geometry had a pronounced effect on stresses in the cortical plate. The strain values obtained with the short implants were drastically higher (clearly > 10,000 μstrain) than those with the long implants (5000 μstrain, in general). The physiological strain range for the bone is defined to be between 3000 and 4000 μstrain [6].
Hence, the aim of the present study was to experimentally analyse the biomechanical characteristics of commercial short dental implants by measuring their displacements in porcine ribs, and to compare the experimental results with the numerical ones of the previous study [3, 10].
Materials and methods Nine implant systems from five manufacturers were investigated in this study (Table 1, Figure 1). Prototype short implants in four different geometries and diameters (types 1–4) were supplied by Dentaurum for this study. A total of 11 implants of different dimensions were inserted into porcine ribs as an implant bed. Porcine bone was chosen because of its anatomical and physiological similarities to the human bone regarding bone structure. It is often used in osseous courses and for studies, e.g., in dental implantology or in maxillofacial surgery [18]. Two specimens were considered for each implant, i.e., 22 specimens were measured in total. Porcine ribs were chosen because of their histological similarities to the human jaw bone (quality 3 or 4 according to the classification of Lekholm and Zarb [17]). Because of the relatively small available dimension of the specimen holder, each bone segment received one implant. The implants were inserted according to the surgical protocol of the manufacturer for each implant system. As a minimum of 2–3 mm of bone is needed around implants, the size of the segments was at least 11 mm in length and 9 mm in width. Two systems required to be inserted with hammering (OtMedical and Bicon), whereas the other implants were screw shaped. As the application of short implants followed the submerged protocol, i.e., they have to be loaded after osseointegration, the surface of the implants was coated with a resin (PalaXpress; Heraeus Kulzer GmbH & Co. KG,
Table 1 Investigated implant systems and their dimensions. Implant system
Implant type
Diameter × length (mm)
No. of specimen
Bicon dental implants (Arborway Boston, USA) ASTRA OsseoSpeed (Mölndal, Sweden) Staumann BL NC (Basel, Switzerland) Straumann S RN (Basel, Switzerland) Otmedical OT-F3 (Bremen, Germany) Dentaurum implants, type 1 (Ispringen, Germany) Dentaurum implants, type 2 Dentaurum implants, type 3 Dentaurum implants, type 4
Hammered Screw shaped Screw shaped Screw shaped Hammered Screw shaped Screw shaped Screw shaped Screw shaped
6.0 × 5.7 4.0 × 6.0, 4.0 × 8.0 3.3 × 8.0 4.1 × 6.0 5.0 × 5.0, 4.1 × 5.0 4.2 × 5.0 4.2 × 5.0 3.9 × 5.0 3.9 × 5.0
2 2, 2 2 2 2, 2 2 2 2 2
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R. Wilhelm et al.: Short dental implants 509
BiconTM 6.0×5.7 mm
Astra OssoSpeedTM 4.0×6.0 mm
Astra OssoSpeedTM 4.0×8.0 mm
Straumann® BL NC 3.3×8.0 mm
Straumann® S RN 4.1×6.0 mm
OT medical OT-F3® 5.0×5.0 mm
Dentaurum® Type 1 4.2×5.0 mm
Dentaurum® Type 2 4.2×5.0 mm
Dentaurum® Type 3 3.9×5.0 mm
OT medical OT-F3® 4.1×5.0 mm
Dentaurum® Type 4 3.9×5.0 mm
Figure 1 Overview of the investigated implant systems.
Wasserburg, Germany) before insertion in the bone. The resin was chosen after several tests of different materials, such as the classic cement material for fixing hip implants. The PalaXpress resin had a suitable working time, stability, and radiopacity. The stability of the specimens within the holder was achieved by embedding them up to half into a resin (Technovit 4004, Heraeus Kulzer GmbH, Wehrheim, Germany). The specimens were positioned on the holder 30° from its long axis according to ISO standard 14801, 2003 [12] (Figure 2). The prepared specimen was installed in a self-developed biomechanical hexapod measurement system (HexMeS, Figure 3) [16], which has been designed especially to apply different magnitudes of force on a small object such as an implant. The system consists of three main parts: a hexapod high-precision robot (PI M-850.50; Physik Instrumente, Karlsruhe, Germany) to perform translations and rotations with high resolution ( 10 mm) implants [2, 5, 9, 15, 26]. Several publications are older than 10 years, such as the 5-year follow-up study by Jemt and Lekholm [14] and others [2, 5, 7]. The results of these studies confirmed the need for more studies to analyse the behaviour of these short implants. The present study aimed to analyse the effect of the geometry of short implants on their stability, as an additional factor to their dimensions. It was obvious that implant stability in the bone does not depend on the lengths but rather on the geometry of the implant. Experimentally, the lowest displacement in this study was registered for Dentaurum implant types 1 and 2, while the highest displacement was observed with the longest implant, Straumann Bone Level 3.3 × 8.0 mm (Table 2). In the very recent study by Anitua et al. [1], the success rate of short implants with lengths of 7.0, 7.5, and 8.5 mm and a crown-root ratio of 1.4 was investigated in a clinical 10-year follow-up. They stated that with a success rate of 98.9% and 98.2%, short implants can now be seen as a valuable treatment option in critical patient situations, which is what Kim et al. [16] proved in their 1-year followup study as well. The previous numerical studies of Hasan et al. [11] and Bourauel et al. [4] showed that strains in cancellous bone as well as stresses in cortical bone were remarkably higher with short implants than with standard ones. Compared with the numerical displacement (Table 2), it was noticeable that the experimental results showed smaller displacement values. Dentaurum types 2, 3, and 4 showed
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512 R. Wilhelm et al.: Short dental implants 500
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400 350 300 250 200 150 100 50
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Figure 5 Overview of the mean maximum displacement of the investigated implants at 30 N.
A
200
Dnum
Dentaurum type 1 (4.2×5.0 mm)
180
Dexp1
Displacement (µm)
160
Dexp2
140
Dexp3
120 100 80 60 40 20 0
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Dentaurum type 3 (3.9×5.0 mm)
180
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160 Displacement (µm)
30
Dexp2
140 120 100 80 60 40 20 0 0
5
10
15 Force (N)
20
25
30
Figure 6 Comparison of total implant displacement that were obtained at 30 N experimentally (Dexp) and numerically (Dnum). (A) Dentaurum type 1 (4.2 × 5.0 mm). (B) Dentaurum type 3 (3.9 × 5.0 mm). Dexp (1–3) refers to the number of measurements that were done for the implant system.
higher values for displacement in the experimental study (Table 2). When comparing experimental and numerical results, the standard deviation ranges from small values (smallest for Dentaurum type 1 with 6.9 μm) to significantly higher ones (the highest being Astra OsseoSpeed 4.0 × 6.0 mm with 185 μm). The present results confirm the influence of the quality of the bone bed around implants and the stability of the implant in the bone on the numerical results, which is ideal in the numerical analysis. Additional limitations are the different bone structure in both studies and the attempt to imitate osseointegration with PalaXpress in the experimental study. Moreover, the way of insertion seems to have a major effect on implant mobility. The highest variation was observed with the hammered implant systems OtMedical and Bicon. The numerical results showed that OtMedical (5.0 × 5.0 mm) and Bicon implants (6.0 × 5.7 mm) were among the implants with the highest displacement (410 and 370 μm), whereas the experimental results verified them as more stable with displacements of only 141 μm for the OtMedical one and 113 μm for Bicon. This was similar to the observation of Venuleo et al. [28] in their retrospective 5-year follow-up study. They investigated patients who had at least one 6.0 × 5.7 mm implant as well as at least one non-6.0 × 5.7 mm implant. They observed that bone loss around the implants does not vary between the conventional and short implants in this period, which would rather favour the experimental results here.
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R. Wilhelm et al.: Short dental implants 513
The experimental results confirm the influence of implant geometry and insertion protocol on the mobility of short implants. For all investigated implants, the displacement was around 150 μm experimentally, which can predict good clinical outcomes.
References [1] Anitua E, Piñas L, Begoña L, Orive G. Long-term retrospective evaluation of short implants in the posterior areas: clinical results after 10–12 years. J Clin Periodont 2014; 41: 404–411. [2] Bernard JP, Belser UC, Martinet JP, Borgis SA. Osseointegration of Brånemark fixtures using a single-step operating technique. A preliminary prospective one-year study in the edentulous mandible. Clin Oral Implants Res 1995; 6: 122–129. [3] Blaszczyszyn A, Heinemann F, Gedrange T, Kawala B, G erber H, Dominiak M. Immediate loading of an implant with fine threaded neck – bone resorption and clinical outcome of single tooth restorations in the maxilla. Biomed. Eng.-Biomed. Tech. 2012; 57: 3–9. [4] Bourauel C, Aitlahrach M, Heinemann F, Hasan I. Biomechanical finite element analysis of small diameter and short dental implants: extensional study of commercial implants. Biomed. Eng.-Biomed. Tech. 2012; 57: 21–32. [5] Chan MF, Nähri TO, de Baat C, Kalk W. Treatment of the atrophic edentulous maxilla with implant-supported overdentures: a review of the literature. Int J Prosthodon 1998; 11: 7–15. [6] Frost HM. Bone “mass” and the “mechanostat”: a proposal. Anat Rec 1987; 219: 1–9. [7] Fugazzotto PA. Shorter implants in clinical practice: rationale and treatment results. Int J Oral Maxillofac Implants 2008; 23: 487–496. [8] Götz W, Gedrange T, Bourauel C, Hasan I. Clinical, biomechanical and biological aspects of immediately loaded dental implants: a critical review of the literature. Biomed. Eng.Biomed. Tech. 2010; 55: 311–315. [9] Griffin TJ, Cheung WS. The use of short, wide implants in posterior areas with reduced bone height: a retrospective investigation. J Prosthet Dent 2004; 92: 139–144. [10] Han HJ, Kim S, Han DH. Multifactorial evaluation of implant failure: a 19-year retrospective study. Int J Oral Maxillofac Implants 2014; 29: 303–310. [11] Hasan I, Heinemann F, Aitlahrach M, Bourauel C. Biomechanical finite element analysis of small diameter and short dental implants. Biomed. Eng.-Biomed. Tech. 2010; 55: 341–350. [12] ISO 14801. Fatigue test for endosseous dental implants 2003. [13] Jaffin RA, Berman CL. The excessive loss of Brånemark fixtures in type IV bone: a 5-year analysis. J Periodont 1991; 62: 2–4.
[14] Jemt T, Lekholm U. Oral implant treatment in posterior partially edentulous jaws: a 5-year follow-up report. Int J Oral Maxillofac Implants 1993; 8: 635–640. [15] Keilig L, Bourauel C, Grüner M, et al. Design and testing of a novel measuring set-up for use in dental biomechanics – measuring principle and exemplary measurements with the hexapod measuring system. Biomed. Eng.-Biomed. Tech. 2004; 49: 208–215. [16] Kim YK, Yun PY, Yi YJ, Bae JH, Sung SB, Ahn GJ. One-year prospective study of 7 mm long implants in mandible: installation technique and crown/implant ratio of 1.5 or less. J Oral Implantol 2013 [Epub ahead of print]. [17] Lekholm U, Zarb GA, Albrektsson T. Patient selection and preparation. Tissue integrated prostheses. Chicago: Quintessence Publishing Co. Inc. 1985: 199–209. [18] Mardas N, Dereka X, Donos N, Dard M. Experimental model for bone regeneration in oral and cranio-maxillo-facial surgery. J Invest Surg 2014; 27: 32–49. [19] Naert I, Koutsikakis G, Duyck J, Quirynen M, Jacobs R, van Steenberghe D. Biologic outcome of implant-supported restorations in the treatment of partial edentulism. Part I: a longitudinal clinical evaluation. Clin Oral Implants Res 2002; 13: 381–389. [20] Naert I, Koutsikakis G, Quirynen M, Duyck J, van Steenberghe D, Jacobs R. Biologic outcome of implant-supported restorations in the treatment of partial edentulism. Part 2: a longitudinal radiographic study. Clin Oral Implants Res 2002; 13: 390–395. [21] Nedir R, Bischof M, Briaux JM, Beyer S, Szmukler-Moncler S, Bernard JP. A 7-year life table analysis from a prospective study on ITI implants with special emphasis on the use of short implants. Results from a private practice. Clin Oral Implants Res 2004; 15: 150–157. [22] Parithimarkalaignan S, Padmanabhan TV. Osseointegration: an update. J Indian Prosthodont Soc 2013; 13: 2–6. [23] Rahimi A, Bourauel C, Jager A, Gedrange T, Heinemann F. Load transfer by fine threading the implant neck – a FEM study. J Physiol Pharmacol 2009; 60(Suppl 8): 107–112. [24] Renouard F, Nisand D. Short implants in the severely resorbed maxilla: a 2-year retrospective clinical study. Clin Implant Dent Rel Res 2005; 7: 104–110. [25] Sharan A, Madjar D. Maxillary sinus pneumatisation following extractions: a radiographic study. Int J Oral Maxillofac Implants 2008; 23: 48–56. [26] Telleman G, Raghoebar GM, Vissink A, den Hartog L, Huddleston Slater JJ, Meijer HJ. A systematic review of the prognosis of short (
Rebecca Wilhelma, Istabrak Hasana,*, Ludger Keilig, Friedhelm Heinemann, Helmut Stark and Christoph Bourauel
Biomechanical investigations of the secondary stability of commercial short dental implants in porcine ribs Abstract: The use of short implants has increased widely within the last years. However, the stability of these implants has not yet been comprehensively investigated, in particular the difference in geometry and dimension of short implants. The aim of the present study was to investigate experimentally the difference of the secondary stability of different commercial short implants by measuring their displacements. Eleven implant geometries were investigated in this study. A total of 22 implants were inserted in porcine rib segments, two implants for each system. Implant displacements were measured using a self-developed biomechanical hexapod measurement system (HexMeS). The highest displacement was observed with Straumann BL NC 3.3 × 8.0 mm (266 μm), followed by Straumann Standard 4.1 × 6.0 mm (156 μm), while the lowest displacement of 61 μm was shown by Dentaurum type 1 implant (4.2 × 5.0 mm). No obvious difference of displacements was observed between hammered and screw-shaped implants with relevant dimensions. The experimental results were in good agreement with the a Equal authorship. *Corresponding author: Dr.rer.nat. Istabrak Hasan, Endowed Chair of Oral Technology, Rheinische Friedrich-Wilhelms University, Welschnonnenstr. 17, 53111 Bonn, Germany, Phone: +49 228 2872 2332 2388, E-mail: [email protected]; and Department of Prosthodontics, Preclinical Education and Dental Materials Science, University of Bonn, Welschnonnenstr. 17, 53111 Bonn, Germany Rebecca Wilhelm and Christoph Bourauel: Endowed Chair of Oral Technology, University of Bonn, Welschnonnenstr. 17, 53111 Bonn, Germany Ludger Keilig: Endowed Chair of Oral Technology, University of Bonn, Welschnonnenstr. 17, 53111 Bonn, Germany; and Department of Prosthodontics, Preclinical Education and Dental Materials Science, University of Bonn, Welschnonnenstr. 17, 53111 Bonn, Germany Friedhelm Heinemann: Department of Prosthodontics, Gerodontology and Biomaterials, University of Greifswald, 17475 Greifswald, Germany Helmut Stark: Department of Prosthodontics, Preclinical Education and Dental Materials Science, University of Bonn, Welschnonnenstr. 17, 53111 Bonn, Germany
numerical ones (19–42%) for Dentaurum implants. However, a difference of 70–80% was obtained for the Astra implant (4.0 × 6.0 mm) and Bicon implant (6.0 × 5.7 mm). The geometry of short implants directly affects their stability within the bone. Keywords: displacement; porcine ribs; short dental implants. DOI 10.1515/bmt-2014-0008 Received January 23, 2014; accepted July 7, 2014; online first August 5, 2014
Introduction In recent years, there was an increase in the popularity of implantology for edentulous patients who are in need of prosthesis treatment. The need for new alternatives for implant-supported prosthesis grew simultaneously to provide more possibilities for patients with insufficient bone volume. Following tooth loss, alveolar ridges typically develop severe atrophy, especially in patients who are edentulous for a long time. The bone volume of posterior areas of the jaw, in particular the maxilla, is often presenting a contraindication for the placement of implants with conventional dimensions, unless procedures such as ridge augmentation or sinus floor elevation are performed. However, these surgical procedures evoke several problems in the current aging society, especially when dealing with patients with multiple morbidities. This not only complicates the surgical operation enormously for older patients; the higher costs and morbidity and a longer treatment period are reasons for the increasing tendency of inserting short implants as well. According to the surgical protocol, short implants cannot be loaded before they reach the state of osseointegration. This process is complex and affected by different factors [3, 8, 21–23]. Some factors are related to so-called early failure, while the others are related to delayed failure. Factors
Brought to you by | Simon Fraser University Authenticated Download Date | 6/13/15 10:03 AM
508 R. Wilhelm et al.: Short dental implants that can cause early failure of implants are insufficient insertion torque and poor primary stability, as well as uncontrolled loading of implants that disturb the process of osseointegration. Delayed failure is mostly associated with overloading of implants that cause bone resorption in the cervical region, or peri-implantitis due to poor oral hygiene. Han et al. [10] stated in their retrospective study that overloading and inflammation are the most common reasons for implant failure. Additionally, it is essential to have sufficient bone quality to ensure the long survival rates of the implants. Implants that are inserted in the mandible have better survival rates than those inserted in the maxilla. Moreover, non-smokers show better rates than smokers [25]. Numerous publications address the issue of implant length as a predictor of implant survival [2, 4, 9, 13, 27]. Some are indecisive about using these implants because of the perception of a higher risk of failure compared with longer implants for both fixed restorations [8, 13, 17, 19, 28] and maxillary overdentures [2, 21]. More recent studies, however, suggest that short implants (7 to 10 mm long in the posterior region with fixed partial dental prostheses. In previous studies [3, 10], eight commercial short implants were numerically analysed in posterior bone segments and investigated in the osseointegrated state at an occlusal force of 300 N. In this study, it could be shown that implant diameter and geometry had a pronounced effect on stresses in the cortical plate. The strain values obtained with the short implants were drastically higher (clearly > 10,000 μstrain) than those with the long implants (5000 μstrain, in general). The physiological strain range for the bone is defined to be between 3000 and 4000 μstrain [6].
Hence, the aim of the present study was to experimentally analyse the biomechanical characteristics of commercial short dental implants by measuring their displacements in porcine ribs, and to compare the experimental results with the numerical ones of the previous study [3, 10].
Materials and methods Nine implant systems from five manufacturers were investigated in this study (Table 1, Figure 1). Prototype short implants in four different geometries and diameters (types 1–4) were supplied by Dentaurum for this study. A total of 11 implants of different dimensions were inserted into porcine ribs as an implant bed. Porcine bone was chosen because of its anatomical and physiological similarities to the human bone regarding bone structure. It is often used in osseous courses and for studies, e.g., in dental implantology or in maxillofacial surgery [18]. Two specimens were considered for each implant, i.e., 22 specimens were measured in total. Porcine ribs were chosen because of their histological similarities to the human jaw bone (quality 3 or 4 according to the classification of Lekholm and Zarb [17]). Because of the relatively small available dimension of the specimen holder, each bone segment received one implant. The implants were inserted according to the surgical protocol of the manufacturer for each implant system. As a minimum of 2–3 mm of bone is needed around implants, the size of the segments was at least 11 mm in length and 9 mm in width. Two systems required to be inserted with hammering (OtMedical and Bicon), whereas the other implants were screw shaped. As the application of short implants followed the submerged protocol, i.e., they have to be loaded after osseointegration, the surface of the implants was coated with a resin (PalaXpress; Heraeus Kulzer GmbH & Co. KG,
Table 1 Investigated implant systems and their dimensions. Implant system
Implant type
Diameter × length (mm)
No. of specimen
Bicon dental implants (Arborway Boston, USA) ASTRA OsseoSpeed (Mölndal, Sweden) Staumann BL NC (Basel, Switzerland) Straumann S RN (Basel, Switzerland) Otmedical OT-F3 (Bremen, Germany) Dentaurum implants, type 1 (Ispringen, Germany) Dentaurum implants, type 2 Dentaurum implants, type 3 Dentaurum implants, type 4
Hammered Screw shaped Screw shaped Screw shaped Hammered Screw shaped Screw shaped Screw shaped Screw shaped
6.0 × 5.7 4.0 × 6.0, 4.0 × 8.0 3.3 × 8.0 4.1 × 6.0 5.0 × 5.0, 4.1 × 5.0 4.2 × 5.0 4.2 × 5.0 3.9 × 5.0 3.9 × 5.0
2 2, 2 2 2 2, 2 2 2 2 2
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R. Wilhelm et al.: Short dental implants 509
BiconTM 6.0×5.7 mm
Astra OssoSpeedTM 4.0×6.0 mm
Astra OssoSpeedTM 4.0×8.0 mm
Straumann® BL NC 3.3×8.0 mm
Straumann® S RN 4.1×6.0 mm
OT medical OT-F3® 5.0×5.0 mm
Dentaurum® Type 1 4.2×5.0 mm
Dentaurum® Type 2 4.2×5.0 mm
Dentaurum® Type 3 3.9×5.0 mm
OT medical OT-F3® 4.1×5.0 mm
Dentaurum® Type 4 3.9×5.0 mm
Figure 1 Overview of the investigated implant systems.
Wasserburg, Germany) before insertion in the bone. The resin was chosen after several tests of different materials, such as the classic cement material for fixing hip implants. The PalaXpress resin had a suitable working time, stability, and radiopacity. The stability of the specimens within the holder was achieved by embedding them up to half into a resin (Technovit 4004, Heraeus Kulzer GmbH, Wehrheim, Germany). The specimens were positioned on the holder 30° from its long axis according to ISO standard 14801, 2003 [12] (Figure 2). The prepared specimen was installed in a self-developed biomechanical hexapod measurement system (HexMeS, Figure 3) [16], which has been designed especially to apply different magnitudes of force on a small object such as an implant. The system consists of three main parts: a hexapod high-precision robot (PI M-850.50; Physik Instrumente, Karlsruhe, Germany) to perform translations and rotations with high resolution ( 10 mm) implants [2, 5, 9, 15, 26]. Several publications are older than 10 years, such as the 5-year follow-up study by Jemt and Lekholm [14] and others [2, 5, 7]. The results of these studies confirmed the need for more studies to analyse the behaviour of these short implants. The present study aimed to analyse the effect of the geometry of short implants on their stability, as an additional factor to their dimensions. It was obvious that implant stability in the bone does not depend on the lengths but rather on the geometry of the implant. Experimentally, the lowest displacement in this study was registered for Dentaurum implant types 1 and 2, while the highest displacement was observed with the longest implant, Straumann Bone Level 3.3 × 8.0 mm (Table 2). In the very recent study by Anitua et al. [1], the success rate of short implants with lengths of 7.0, 7.5, and 8.5 mm and a crown-root ratio of 1.4 was investigated in a clinical 10-year follow-up. They stated that with a success rate of 98.9% and 98.2%, short implants can now be seen as a valuable treatment option in critical patient situations, which is what Kim et al. [16] proved in their 1-year followup study as well. The previous numerical studies of Hasan et al. [11] and Bourauel et al. [4] showed that strains in cancellous bone as well as stresses in cortical bone were remarkably higher with short implants than with standard ones. Compared with the numerical displacement (Table 2), it was noticeable that the experimental results showed smaller displacement values. Dentaurum types 2, 3, and 4 showed
Brought to you by | Simon Fraser University Authenticated Download Date | 6/13/15 10:03 AM
512 R. Wilhelm et al.: Short dental implants 500
Numerical
450
Experimental
Displacement (µm)
400 350 300 250 200 150 100 50
4 e
e ru m
-ty p
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8
6
0
Figure 5 Overview of the mean maximum displacement of the investigated implants at 30 N.
A
200
Dnum
Dentaurum type 1 (4.2×5.0 mm)
180
Dexp1
Displacement (µm)
160
Dexp2
140
Dexp3
120 100 80 60 40 20 0
B
0
200
5
10
15 Force (N)
20
25
Dnum
Dentaurum type 3 (3.9×5.0 mm)
180
Dexp1
160 Displacement (µm)
30
Dexp2
140 120 100 80 60 40 20 0 0
5
10
15 Force (N)
20
25
30
Figure 6 Comparison of total implant displacement that were obtained at 30 N experimentally (Dexp) and numerically (Dnum). (A) Dentaurum type 1 (4.2 × 5.0 mm). (B) Dentaurum type 3 (3.9 × 5.0 mm). Dexp (1–3) refers to the number of measurements that were done for the implant system.
higher values for displacement in the experimental study (Table 2). When comparing experimental and numerical results, the standard deviation ranges from small values (smallest for Dentaurum type 1 with 6.9 μm) to significantly higher ones (the highest being Astra OsseoSpeed 4.0 × 6.0 mm with 185 μm). The present results confirm the influence of the quality of the bone bed around implants and the stability of the implant in the bone on the numerical results, which is ideal in the numerical analysis. Additional limitations are the different bone structure in both studies and the attempt to imitate osseointegration with PalaXpress in the experimental study. Moreover, the way of insertion seems to have a major effect on implant mobility. The highest variation was observed with the hammered implant systems OtMedical and Bicon. The numerical results showed that OtMedical (5.0 × 5.0 mm) and Bicon implants (6.0 × 5.7 mm) were among the implants with the highest displacement (410 and 370 μm), whereas the experimental results verified them as more stable with displacements of only 141 μm for the OtMedical one and 113 μm for Bicon. This was similar to the observation of Venuleo et al. [28] in their retrospective 5-year follow-up study. They investigated patients who had at least one 6.0 × 5.7 mm implant as well as at least one non-6.0 × 5.7 mm implant. They observed that bone loss around the implants does not vary between the conventional and short implants in this period, which would rather favour the experimental results here.
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R. Wilhelm et al.: Short dental implants 513
The experimental results confirm the influence of implant geometry and insertion protocol on the mobility of short implants. For all investigated implants, the displacement was around 150 μm experimentally, which can predict good clinical outcomes.
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