IMPLANT DENTISTRY / VOLUME 24, NUMBER 2 2015
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Biomechanical Evaluation of Resistance to Insertion Torque of Different Implant Systems and Insertion Driver Types Hugo Nary Filho, DDS, MDS,* José Luis Calvo Guirado, DDS, MDS,† Mariza Akemi Matsumoto, DDS, MDS,‡ Marco Dapievi Bresaola, MDS,§ and Roberto Aur, MDS§
n contemporary implantology, primary stability is considered the key factor for osseointegration prognostics.1 Immediate loading requires a high level of primary stability,2 which can be assessed by measuring the torque level applied during implant insertion or through resonance frequency analysis.3,4 It is known that a higher stability diminishes implant micromotion and leads to a better bone-implant interface, regardless the location it has been inserted.5–8 Easy-to-apply and readily available torque control is becoming an excellent clinical parameter for this stability. Indices greater than 35 N$m are considered acceptable. This value can be determined during drilling and fixture insertion or by means of precalibrated torque ratchets.5,6,8,9 The achievement of good primary stability depends on a number of factors: macro-geometric features of the implant system such as thread design
I
*Oral and Maxillofacial Surgeon and Coordinator, Advanced Implantology Course, P-I Brånemark Institute, São Paulo, Brazil; Coordinator, Graduate Course in Implantodontics, Universidade Sagrado Coração (USC), São Paulo, Brazil. †Professor, Clinica Odontológica Integrada de Adultos, Murcia, Spain; Senior Lecturer, General Dentistry, Faculty of Medicine and Dentistry, University of Murcia, Murcia, Spain. ‡Assistant Professor, Department of Oral and Maxillofacial Surgery, Universidade Sagrado Coração (USC), São Paulo, Brazil. §Fellow, Master Course in Implantodontics, Universidade Sagrado Coração (USC), São Paulo, Brazil.
Reprint requests and correspondence to: Hugo Nary Filho, DDS, MDS, Alameda Dr. Octávio Pinheiro Brizola, 12-67, Vila Universitária, São Paulo 17012-191, Brazil, Phone: +55 11 3018-8427, Fax: +55 14 3227-7495, E-mail: [email protected] ISSN 1056-6163/15/02402-211 Implant Dentistry Volume 24 Number 2 Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved. DOI: 10.1097/ID.0000000000000211
Purpose: The aim of this study was to quantify the resistance to torque of different implant systems and their connection devices using in vitro torsion tests. Materials and Methods: Three internal connection systems, 1 conventional system with internal torque and 1 conventional system with a mounting device used as a control group were tested on 5 groups. Results: Rupture torque (in newton meter): Biomet 3i Certain group 4 showed a statistically significant higher average (2.65 N$m), followed in order by Biomet 3i Osseotite group 5 (2.18 N$m), Bonelike group 2 (1.80 N$m). Angle deformation/rupture: all groups obtained similar values, without significant differences. Elastic
limit (in newton meter): Bonelike group 2 (1.06 N$m) showed similar behavior to group 1 (1.39 N$m) (Nobel Biocare), without significant differences, whereas Bonelike group 3 showed a significantly lower value (0.93 N$m). Maximum torque (in newton meter): Biomet 3i Certain group 4 showed significantly higher values in relation to other groups (2.80 N$m). Conclusions: The greater contact area the system is built on, the greater resistance against insertion torque, as internal hexagon implants with a greater contact area and external hexagon implants using a mounting device showed higher resistance to insertion torque. (Implant Dent 2015;24:211–216) Key Words: macroscopic analysis, internal hexagon, external hexagon
and diameter, the use of techniques for bone compression, and surgeon’s skill and experience when it comes to identify bone quality and characteristics at the implant site that aid the professional to decide the diameter of the final drill.5–7,10,11 When these factors act favorable, a situation that is not infrequent, high stability can be achieved, demanding high torque levels and making implant insertion difficult. The conventional adapters used to carry the implant to its insertion site and to proceed its screwing have been gradually replaced by adapters or drivers with
different internal connections. These systems use the internal contact with the implant walls instead of mounting devices to apply the force, which simplifies the procedure and diminishes the cost of materials. However, system mechanisms will always reach up to limited resistance, and excessive torque can cause damage to the upper part of the implant, around its head, and to the connection to which prosthetic components are attached.5,10 The aim of this study was to quantify the resistance of different implant systems and internal connection drivers when subjected to mechanical torsion
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testing. It also set out to investigate the type of damage caused by excessive force applied to each system, which was achieved by examining the samples after testing.
MATERIALS
AND
METHODS
This study evaluated 3 different internal connection systems and 2 conventional external hexagon systems. A conventional system with external hexagon was used as a control group. Samples were divided into 5 groups to evaluate the following systems: Group 1dMKIII Tiunite Nobel Biocare external hexagon implant system (3.75 mm diameter) and Stargrip driver (Nobel Biocare, Gothenburg, Sweden) (Fig. 1); Group 2dBonelike Morse taper connection implant system (4.0 mm diameter) and internal hexagon driver (Biotechnology, Rio Claro, Brazil) (Fig. 2); Group 3dBonelike Morse taper connection implant system (3.25 mm diameter) and internal hexagon driver (Biotechnology) (Fig. 2); Group 4dBiomet 3i Certain internal connection implant system (4.0 mm diameter) and internal hexagon driver (Biomet 3i, Sao Paulo, Brazil) (Fig. 3); Group 5dBiomet 3i Osseotite implant system (4.0 mm diameter) with external hexagon, adapter, and attachment adapter (Biomet 3i) (Fig. 1).
Fig. 1. Schematic illustration of Stargrip (group 1) and external hexagon with a mounting device (group 5) fixture.
Fig. 3. Schematic illustration of certain fixture (group 4).
Fig. 2. Schematic illustration of cone morse fixture (groups 2 and 3).
These implant systems were selected to evaluate a series of factors that might affect their resistance to torque forces: the type of connection, implant diameter (wall thickness), and internal connection contact area. A conventional system of
Fig. 4. Schematic illustration of set-up test. The specimen (fixture) was placed on a Cervoelectric motor testing machine providing 3.8 mm of exposure (L) and attached to the insertion key/device, which suffered the torque until the rupture of the system.
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IMPLANT DENTISTRY / VOLUME 24, NUMBER 2 2015
Table 1. Rupture Torque (in newton meter) Group 1 2 3 4 5
Average
Average Deviation
Minimum
Maximum
1.26d
0.09 0.10 0.11 0.11 0.02
1.24 1.01 1.08 2.47 2.14
1.45 1.28 1.37 2.74 2.21
1.21b 1.19c 2.69a 2.18d
Different letters indicate significant statistical difference (P , 0.05). Rupture torque (in newton meter) showed a statistically significant higher average of group 4 followed by group 5. No greater significance was detected among groups 1 to 3.
Table 2. Angle Deformation/Rupture (in degrees) Group
Average
Average Deviation
Minimum
Maximum
1 2 3 4 5
34.45d 37.97d 32.70c 118.5a 28.48b
6.9 2.29 2.71 44.34 1.28
19.69 35.16 29.53 38.67 27.77
35.86 41.48 36.21 131.5 30.59
Different letters indicate significant statistical difference (P , 0.05). Angle deformation/rupture (in degrees) showed all groups obtaining similar values, without greater significant differences, except for group 4 which also showed better behavior regarding the other variables.
Table 3. Elastic Limit (in newton meter) Group 1 2 3 4 5
Average
Average Deviation
Minimum
Maximum
1.39d
0.14 0.06 0.12 0.04 0.13
1.29 1.0 0.77 2.09 1.54
1.64 1.14 1.07 2.2 1.88
1.06b 0.93b 2.15a 1.82c
Different letters indicate significant statistical difference (P , 0.05). Elastic limit (in newton meter) showed groups 1 and 2 with similar behavior, and group 3 showed a significantly lower value.
Table 4. Maximum Torque (in newton meter) Group 1 2 3 4 5
Average
Average Deviation
Minimum
Maximum
1.4c 1.31b 1.32b 2.8a 2.23c
0.13 0.09 0.13 0.10 0.03
1.3 1.11 1.12 2.61 2.19
1.65 1.33 1.46 2.87 2.25
Different letters indicate significant statistical difference (P , 0.05). Maximum torque (in newton meter) showed group 4 with significantly higher values in relation to group 1, which did not show a significantly different result from groups 2 and 3.
implants/mounting devices that uses a torque driver with adapter for its insertion (these being the 3 elements tested) was used as a control group. For other systems, there were only 2 elements involved because the torque driver was connected directly to the implant. The study included 5 samples of each 5 types of commercially produced implants obtained from the manufacturers listed above, together with their respective insertion device. The selected implants
presented 13 mm in length, allowing a satisfactory adaptation to the torquetesting machine. Only brand new torque drivers were used in the test procedures and were discarded after testing, as indicated by the respective suppliers. In the same way, the insertion drivers were used only once, as a single torsional test that is enough to determine a resistance limit. The aim of these tests was to subject the samples to torque forces to determine the system’s resistance limit,
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following the norms of ASTM F543: 2007 (Standard Specification and Test Methods for Metallic Medical Bone Screws). The systems were applied on a Cervo-electric motor testing machine developed at the Materials and Engineering Department of Sao Carlos Federal University, UFSCar (Sao Paulo, Brazil), named Termomec Ortho, calibrated at 2 rpm speed and 23.3°C for this test. To prepare the material to be tested, all implants were placed on testing machine providing 3.8 mm of exposure. Values obtained from the test at the moment of implant system rupture were collected and subjected to statistical analysis. After the removal of samples from the test equipment (Fig. 4), the resistance limits of implants and torque drivers were analyzed, determining where rupture had taken place. Some microscopic aspects will be shown as an illustrative aspect only because the damage to samples could be visualized directly from the examination.
RESULTS Results are shown in the following tables as averages; values were submitted to Analysis of Variance and Turkey multiple comparison tests (P . 0.05). Rupture torque (in newton meter): group 4 showed a statistically significant higher average (2.69 N$m), followed by group 5 (2.18 N$m). No greater significance was detected among groups 1 (1.26 N$m) to 3 (1.19 N$m), as shown in Table 1. Angle deformation/rupture: all groups obtained similar values, without greater significant differences, except for group 4 (Certain), which also showed better behavior regarding other variables (Table 2). Elastic limit (in newton meter): Bonelike group 2 showed similar behavior to group 1 (Nobel Biocare), without greater significant differences, whereas Bonelike group 3 showed a significantly lower value (Table 3). Maximum torque (in newton meter): Biomet 3i Certain group 4 showed significantly higher values in relation to group 1 (Nobel Biocare),
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Fig. 5. Implant hexagon fractured (A) and remained located at the mounting device (B) after testing in a sample from group 5.
which did not show a significantly different result from groups 2 and 3 (Bonelike), as presented in Table 4. Macroscopic analysis of the samples revealed a homogeneous damage pattern, dependent on the type of connection. The conventional system, group 5, which used an implant mounting device, suffered severe damage to the implant hexagon (Fig. 5, A), which fractured and separated from the length of the implant axis (Fig. 5, B). All groups with internal connection presented damage of the implant walls and wear to the active points on the driver. In group 4, all samples showed damage of the internal hexagon and the drivers’ active parts (Fig. 6, A and B), which was easily visible due to a color alteration. External hexagon system with Stargrip drivers exhibited the same damage to the drivers’ active parts and hexagons (Fig. 7, A and B). In some
Fig. 6. Damage to the internal hexagon (A) and to the driver (B) after testing in a fixture sample from group 4.
Fig. 8. Serious damage to the head of the implant with external hexagon wall ruptures after testing in a sample of group 1.
Fig. 7. Less damage to the hexagon wall (A) and to the Stargrip driver (B) after testing in some samples from group 1.
Fig. 9. Damage to the internal hexagon walls in samples from groups 2 and 3.
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IMPLANT DENTISTRY / VOLUME 24, NUMBER 2 2015
Fig. 10. Driver of samples from groups 2 (A) and 3 (B) showing wear to its edge.
samples of this group, there was serious damage to the head of the implant, with external hexagon wall ruptures (Fig. 8). Morse taper connection systems (groups 2 and 3) showed less implant deformation (Fig. 9), probably because the connection area does not suffer direct loading. The drivers did show wear to their edges (Fig. 10, A and B). Therefore, the walls of implants of smaller diameter were seen to suffer greater deformation.
DISCUSSION A large number of studies comparing implant systems also mention the primary stability produced by torquing the implants at the moment of insertion (insertion torque) and the initial implant stability quotient for different bone types.5,7,8,10,12 Manufacturers have developed a range of different connections and insertion systems accompanied by recommended techniques for drilling and bone compaction, conceived to ensure good anchorage. Failure to identify bone quality correctly can lead to the application of excessive insertion torque.13 When this happens, rupture or damage to the insertion driver and/or damage to the implant around its connection can occur. These events could compromise or even invalidate the screw-in implant insertion procedure. It is a well-known fact that the correct corono-apical positioning of an implant is essential in esthetic areas. When a high level of
torque is required, this optimal position could not be obtained. Most importantly, when implants are damaged in their platforms, this may compromise the prosthetic outcome. Nevertheless, comparative studies of the resistance of the different systems available have not determined their resistance to the torsional forces applied when they are screwed into place.5,6,8,10–12 The results of this study allow an analysis of the following variables: connection type, implant diameter, and stress zone. Regarding implant connection type, an analysis of the area that suffers the most stress revealed that all study groups displayed a homogeneous behavior, and both drivers and implant walls were seen to suffer deformation, except for the conventional system, with external hexagon and mounting device, in which the damage to the implant head was greater, perhaps due to the type of connection and the greater area of contact between implant head and mounting device, indicating greater fragility of the external hexagon walls. In comparison, implants with the same external hexagon design but with internal connection drivers suffered less deformation, although there were also alterations, including deformations and ruptures, which made prosthetic connection considerably difficult. It seems clear that external hexagon implant systems might have different levels of resistance, and the systems that
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present disposable mounting devices are more effective, probably because of the greater contact area where the insertion torque is applied to the fixture. Besides, the fact that those systems have another key, an insertion driver that matches the mounting device with a certain clearance, can imply in one more resistance factor to the system. However, both systems are most affected by overload, and deformations on fixtures occur in the prosthetic abutment contact area. Any deformity on external hexagon can derail prosthetic rehabilitation, especially in single crowns. A comparison of the different systems (external hexagon, internal connection, and Morse connection) demonstrated that all of them showed similar results. If a greater contact area exists, as in external hexagon with mounting device and internal connection key (Certain), high levels of torque are needed due to deformation (over 200 N$cm). All the remaining systems have a lower contact area between insertion key and implant wall, which reduces those values (between 100 and 130 N$cm), except at the sites where deformations occur. Additionally, these deformations are much more severe compared with external hexagon systems. Regarding internal connection systems, the Morse taper implant systems analyzed in this study do not use the Morse connection area to receive the torque required for insertion. Morse taper groups (2 and 3) did not show any alteration at the area of abutment adaptation. However, the other type of internal connection system, Certain system, may show damage to the hexagon. It is important to note that the deformation occurs in the angles of the hexagon, keeping the walls intact. When external hexagons are used, the use of an internal connection driver restricts the contact area between driver and implant. In comparison with internal hexagon implants, systems such as the Stargrip offer less contact area, a fact that may explain the great difference found between the Certain system and other internal connection systems. In particular, the insertion driver’s support is much greater, which seems to affect Morse taper connection because of its
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particular design, the driver does not attach to the Morse connection area, reducing its internal connection dimension. For this reason, this system showed similar values to those of the group 1. Thus it may be inferred that the greater the contact area between insertion torque driver and internal implant walls, the more effective the system will be in terms of offering greater resistance during insertion and so making higher torque values possible. Nevertheless, care must be taken to avoid the possible deformation of implant walls. The study tested implants of different diameters (3.25, 3.75, and 4 mm) and platform designs. The larger implant body diameter was not found to offer any significant advantage in terms of resistance to insertion torque. In groups 2 and 3, the same torque driver diameter was used on implants of different diameter. Thus the contact area was the same, with hardly any variation in the thickness of the implant walls. Even so, fixtures of 4.0 mm diameter showed advantages over 3.25 mm implants, which suffered critical dimensional alterations to the abutment connection area, indicating the necessity of avoiding overloading the more narrow systems. This premise can also be applied to external hexagon designs using the Stargrip system. The importance of these comparative mechanical studies lies on the collection of information concerning the limitations of different system types, information of great clinical relevance. Obviously, the minimum resistance values obtained in this kind of research are higher than the maximum torque insertion forces indicated by each manufacturer. Excessive torque is not recommended, mainly to avoid the possibility of deformation of implant seating platforms and connection areas. This study was based on a series of technical norms and applied axial force to the implant, through insertion drivers (mainly internal connection drivers) using a test machine. In clinical practice, where there may be limited access to the limitations of each system, the force values likely to produce deformation may be lower as a result of shear forces, given that the implant has variable insertion axes. Thus, knowledge and
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experience in the manipulation of bone tissues and a correct diagnosis of bone density will allow the surgeon to select the optimal drill/implant diameter, producing good stability and avoiding mechanical overloading and the risk of deformation.
CONCLUSIONS Test results for resistance to torsion in different implant systems found that: • The contact area between the device used for insertion of the fixture and implant head influences the system resistance. Internal hexagon implants with a greater contact area and external hexagon implants using a mounting device showed higher resistance to insertion torque compared with other systems with smaller hexagon connections or internal connections. • For internal connection systems, resistance is influenced by implant wall thickness. The more fragile this is, the greater the possibility of deformation and the lower the system resistance. • Excessive torque must be avoided because of the risk of deformation of the seating platform and of connection areas.
DISCLOSURE The authors claim to have no financial interest, either directly or indirectly, in the products or information listed in the article.
ACKNOWLEDGMENTS The authors thank Biomet 3i (Brazil) for supplying all the materials used in this study. Also, we thank M. M. S. Juliana Burigo for the relevant contribution to this study. Study testing was carried out at the laboratory of the Centre for Materials Characterization and Development (CCDM) Federal University of São Carlos, São Paulo, Brazil.
REFERENCES 1. Duyck J, Roesems R, Cardoso MV, et al. Effect of insertion torque on titanium
implant osseointegration: An animal experimental study. Clin Oral Implants Res. 2015;26:191–196. 2. Rea M, Botticelli D, Ricci S, et al. Influence of immediate loading on healing of implants installed with different insertion torques: An experimental study in dogs. Clin Oral Implants Res. 2015;26:90–95. 3. Barikani H, Rashtak S, Akbari S, et al. The effect of shape, length and diameter of implants on primary stability based on resonance frequency analysis. Dent Res J (Isfahan). 2014;11:87–91. 4. Shokri M, Daraeighadikolaei A. Measurement of primary and secondary stability of dental implants by resonance frequency analysis method in mandible. Int J Dent. 2013;2013:506968. 5. Alsaadi G, Quirynen M, Michiels K, et al. A biomechanical assessment of the relation between the oral implant stability at insertion and subjective bone quality assessment. J Clin Periodontol. 2007;34: 359–366. 6. Fanuscu MI, Chang TL, Akca K. Effect of surgical techniques on primary implant stability and peri-implant bone. J Oral Maxillofac Surg. 2007;65:2487– 2491. 7. Irinakis T, Wiebe C. Clinical evaluation of the NobelActive implant system: A case series of 107 consecutively placed implants and a review of the implant features. J Oral Implantol. 2009;35:283–288. 8. Maeda Y, Satoh T, Sogo M. In vitro differences of stress concentrations for internal and external hex implant-abutment connections: A short communication. J Oral Rehabil. 2006;33:75–78. 9. Neugebauer J, Scheer M, Mischkowski RA, et al. Comparison of torque measurements and clinical handling of various surgical motors. Int J Oral Maxillofac Implants. 2009;24:469–476. 10. Sakoh J, Wahlmann U, Stender E, et al. Primary stability of a conical implant and a hybrid, cylindric screw-type implant in vitro. Int J Oral Maxillofac Implants. 2006;21:560–566. 11. Trisi P, Perfetti G, Baldoni E, et al. Implant micromotion is related to peak insertion torque and bone density. Clin Oral Implants Res. 2009;20:467–471. 12. Degidi M, Perrotti V, Strocchi R, et al. Is insertion torque correlated to bone-implant contact percentage in the early healing period? A histological and histomorphometrical evaluation of 17 human-retrieved dental implants. Clin Oral Implants Res. 2009;20:778–781. 13. Trisi P, Berardi D, Paolantonio M, et al. Primary stability, insertion torque, and bone density of conical implants with internal hexagon: Is there a relationship? J Craniofac Surg. 2013;24:841–844.
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Biomechanical Evaluation of Resistance to Insertion Torque of Different Implant Systems and Insertion Driver Types Hugo Nary Filho, DDS, MDS,* José Luis Calvo Guirado, DDS, MDS,† Mariza Akemi Matsumoto, DDS, MDS,‡ Marco Dapievi Bresaola, MDS,§ and Roberto Aur, MDS§
n contemporary implantology, primary stability is considered the key factor for osseointegration prognostics.1 Immediate loading requires a high level of primary stability,2 which can be assessed by measuring the torque level applied during implant insertion or through resonance frequency analysis.3,4 It is known that a higher stability diminishes implant micromotion and leads to a better bone-implant interface, regardless the location it has been inserted.5–8 Easy-to-apply and readily available torque control is becoming an excellent clinical parameter for this stability. Indices greater than 35 N$m are considered acceptable. This value can be determined during drilling and fixture insertion or by means of precalibrated torque ratchets.5,6,8,9 The achievement of good primary stability depends on a number of factors: macro-geometric features of the implant system such as thread design
I
*Oral and Maxillofacial Surgeon and Coordinator, Advanced Implantology Course, P-I Brånemark Institute, São Paulo, Brazil; Coordinator, Graduate Course in Implantodontics, Universidade Sagrado Coração (USC), São Paulo, Brazil. †Professor, Clinica Odontológica Integrada de Adultos, Murcia, Spain; Senior Lecturer, General Dentistry, Faculty of Medicine and Dentistry, University of Murcia, Murcia, Spain. ‡Assistant Professor, Department of Oral and Maxillofacial Surgery, Universidade Sagrado Coração (USC), São Paulo, Brazil. §Fellow, Master Course in Implantodontics, Universidade Sagrado Coração (USC), São Paulo, Brazil.
Reprint requests and correspondence to: Hugo Nary Filho, DDS, MDS, Alameda Dr. Octávio Pinheiro Brizola, 12-67, Vila Universitária, São Paulo 17012-191, Brazil, Phone: +55 11 3018-8427, Fax: +55 14 3227-7495, E-mail: [email protected] ISSN 1056-6163/15/02402-211 Implant Dentistry Volume 24 Number 2 Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved. DOI: 10.1097/ID.0000000000000211
Purpose: The aim of this study was to quantify the resistance to torque of different implant systems and their connection devices using in vitro torsion tests. Materials and Methods: Three internal connection systems, 1 conventional system with internal torque and 1 conventional system with a mounting device used as a control group were tested on 5 groups. Results: Rupture torque (in newton meter): Biomet 3i Certain group 4 showed a statistically significant higher average (2.65 N$m), followed in order by Biomet 3i Osseotite group 5 (2.18 N$m), Bonelike group 2 (1.80 N$m). Angle deformation/rupture: all groups obtained similar values, without significant differences. Elastic
limit (in newton meter): Bonelike group 2 (1.06 N$m) showed similar behavior to group 1 (1.39 N$m) (Nobel Biocare), without significant differences, whereas Bonelike group 3 showed a significantly lower value (0.93 N$m). Maximum torque (in newton meter): Biomet 3i Certain group 4 showed significantly higher values in relation to other groups (2.80 N$m). Conclusions: The greater contact area the system is built on, the greater resistance against insertion torque, as internal hexagon implants with a greater contact area and external hexagon implants using a mounting device showed higher resistance to insertion torque. (Implant Dent 2015;24:211–216) Key Words: macroscopic analysis, internal hexagon, external hexagon
and diameter, the use of techniques for bone compression, and surgeon’s skill and experience when it comes to identify bone quality and characteristics at the implant site that aid the professional to decide the diameter of the final drill.5–7,10,11 When these factors act favorable, a situation that is not infrequent, high stability can be achieved, demanding high torque levels and making implant insertion difficult. The conventional adapters used to carry the implant to its insertion site and to proceed its screwing have been gradually replaced by adapters or drivers with
different internal connections. These systems use the internal contact with the implant walls instead of mounting devices to apply the force, which simplifies the procedure and diminishes the cost of materials. However, system mechanisms will always reach up to limited resistance, and excessive torque can cause damage to the upper part of the implant, around its head, and to the connection to which prosthetic components are attached.5,10 The aim of this study was to quantify the resistance of different implant systems and internal connection drivers when subjected to mechanical torsion
Copyright © 2015 Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited.
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testing. It also set out to investigate the type of damage caused by excessive force applied to each system, which was achieved by examining the samples after testing.
MATERIALS
AND
METHODS
This study evaluated 3 different internal connection systems and 2 conventional external hexagon systems. A conventional system with external hexagon was used as a control group. Samples were divided into 5 groups to evaluate the following systems: Group 1dMKIII Tiunite Nobel Biocare external hexagon implant system (3.75 mm diameter) and Stargrip driver (Nobel Biocare, Gothenburg, Sweden) (Fig. 1); Group 2dBonelike Morse taper connection implant system (4.0 mm diameter) and internal hexagon driver (Biotechnology, Rio Claro, Brazil) (Fig. 2); Group 3dBonelike Morse taper connection implant system (3.25 mm diameter) and internal hexagon driver (Biotechnology) (Fig. 2); Group 4dBiomet 3i Certain internal connection implant system (4.0 mm diameter) and internal hexagon driver (Biomet 3i, Sao Paulo, Brazil) (Fig. 3); Group 5dBiomet 3i Osseotite implant system (4.0 mm diameter) with external hexagon, adapter, and attachment adapter (Biomet 3i) (Fig. 1).
Fig. 1. Schematic illustration of Stargrip (group 1) and external hexagon with a mounting device (group 5) fixture.
Fig. 3. Schematic illustration of certain fixture (group 4).
Fig. 2. Schematic illustration of cone morse fixture (groups 2 and 3).
These implant systems were selected to evaluate a series of factors that might affect their resistance to torque forces: the type of connection, implant diameter (wall thickness), and internal connection contact area. A conventional system of
Fig. 4. Schematic illustration of set-up test. The specimen (fixture) was placed on a Cervoelectric motor testing machine providing 3.8 mm of exposure (L) and attached to the insertion key/device, which suffered the torque until the rupture of the system.
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IMPLANT DENTISTRY / VOLUME 24, NUMBER 2 2015
Table 1. Rupture Torque (in newton meter) Group 1 2 3 4 5
Average
Average Deviation
Minimum
Maximum
1.26d
0.09 0.10 0.11 0.11 0.02
1.24 1.01 1.08 2.47 2.14
1.45 1.28 1.37 2.74 2.21
1.21b 1.19c 2.69a 2.18d
Different letters indicate significant statistical difference (P , 0.05). Rupture torque (in newton meter) showed a statistically significant higher average of group 4 followed by group 5. No greater significance was detected among groups 1 to 3.
Table 2. Angle Deformation/Rupture (in degrees) Group
Average
Average Deviation
Minimum
Maximum
1 2 3 4 5
34.45d 37.97d 32.70c 118.5a 28.48b
6.9 2.29 2.71 44.34 1.28
19.69 35.16 29.53 38.67 27.77
35.86 41.48 36.21 131.5 30.59
Different letters indicate significant statistical difference (P , 0.05). Angle deformation/rupture (in degrees) showed all groups obtaining similar values, without greater significant differences, except for group 4 which also showed better behavior regarding the other variables.
Table 3. Elastic Limit (in newton meter) Group 1 2 3 4 5
Average
Average Deviation
Minimum
Maximum
1.39d
0.14 0.06 0.12 0.04 0.13
1.29 1.0 0.77 2.09 1.54
1.64 1.14 1.07 2.2 1.88
1.06b 0.93b 2.15a 1.82c
Different letters indicate significant statistical difference (P , 0.05). Elastic limit (in newton meter) showed groups 1 and 2 with similar behavior, and group 3 showed a significantly lower value.
Table 4. Maximum Torque (in newton meter) Group 1 2 3 4 5
Average
Average Deviation
Minimum
Maximum
1.4c 1.31b 1.32b 2.8a 2.23c
0.13 0.09 0.13 0.10 0.03
1.3 1.11 1.12 2.61 2.19
1.65 1.33 1.46 2.87 2.25
Different letters indicate significant statistical difference (P , 0.05). Maximum torque (in newton meter) showed group 4 with significantly higher values in relation to group 1, which did not show a significantly different result from groups 2 and 3.
implants/mounting devices that uses a torque driver with adapter for its insertion (these being the 3 elements tested) was used as a control group. For other systems, there were only 2 elements involved because the torque driver was connected directly to the implant. The study included 5 samples of each 5 types of commercially produced implants obtained from the manufacturers listed above, together with their respective insertion device. The selected implants
presented 13 mm in length, allowing a satisfactory adaptation to the torquetesting machine. Only brand new torque drivers were used in the test procedures and were discarded after testing, as indicated by the respective suppliers. In the same way, the insertion drivers were used only once, as a single torsional test that is enough to determine a resistance limit. The aim of these tests was to subject the samples to torque forces to determine the system’s resistance limit,
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following the norms of ASTM F543: 2007 (Standard Specification and Test Methods for Metallic Medical Bone Screws). The systems were applied on a Cervo-electric motor testing machine developed at the Materials and Engineering Department of Sao Carlos Federal University, UFSCar (Sao Paulo, Brazil), named Termomec Ortho, calibrated at 2 rpm speed and 23.3°C for this test. To prepare the material to be tested, all implants were placed on testing machine providing 3.8 mm of exposure. Values obtained from the test at the moment of implant system rupture were collected and subjected to statistical analysis. After the removal of samples from the test equipment (Fig. 4), the resistance limits of implants and torque drivers were analyzed, determining where rupture had taken place. Some microscopic aspects will be shown as an illustrative aspect only because the damage to samples could be visualized directly from the examination.
RESULTS Results are shown in the following tables as averages; values were submitted to Analysis of Variance and Turkey multiple comparison tests (P . 0.05). Rupture torque (in newton meter): group 4 showed a statistically significant higher average (2.69 N$m), followed by group 5 (2.18 N$m). No greater significance was detected among groups 1 (1.26 N$m) to 3 (1.19 N$m), as shown in Table 1. Angle deformation/rupture: all groups obtained similar values, without greater significant differences, except for group 4 (Certain), which also showed better behavior regarding other variables (Table 2). Elastic limit (in newton meter): Bonelike group 2 showed similar behavior to group 1 (Nobel Biocare), without greater significant differences, whereas Bonelike group 3 showed a significantly lower value (Table 3). Maximum torque (in newton meter): Biomet 3i Certain group 4 showed significantly higher values in relation to group 1 (Nobel Biocare),
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Fig. 5. Implant hexagon fractured (A) and remained located at the mounting device (B) after testing in a sample from group 5.
which did not show a significantly different result from groups 2 and 3 (Bonelike), as presented in Table 4. Macroscopic analysis of the samples revealed a homogeneous damage pattern, dependent on the type of connection. The conventional system, group 5, which used an implant mounting device, suffered severe damage to the implant hexagon (Fig. 5, A), which fractured and separated from the length of the implant axis (Fig. 5, B). All groups with internal connection presented damage of the implant walls and wear to the active points on the driver. In group 4, all samples showed damage of the internal hexagon and the drivers’ active parts (Fig. 6, A and B), which was easily visible due to a color alteration. External hexagon system with Stargrip drivers exhibited the same damage to the drivers’ active parts and hexagons (Fig. 7, A and B). In some
Fig. 6. Damage to the internal hexagon (A) and to the driver (B) after testing in a fixture sample from group 4.
Fig. 8. Serious damage to the head of the implant with external hexagon wall ruptures after testing in a sample of group 1.
Fig. 7. Less damage to the hexagon wall (A) and to the Stargrip driver (B) after testing in some samples from group 1.
Fig. 9. Damage to the internal hexagon walls in samples from groups 2 and 3.
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IMPLANT DENTISTRY / VOLUME 24, NUMBER 2 2015
Fig. 10. Driver of samples from groups 2 (A) and 3 (B) showing wear to its edge.
samples of this group, there was serious damage to the head of the implant, with external hexagon wall ruptures (Fig. 8). Morse taper connection systems (groups 2 and 3) showed less implant deformation (Fig. 9), probably because the connection area does not suffer direct loading. The drivers did show wear to their edges (Fig. 10, A and B). Therefore, the walls of implants of smaller diameter were seen to suffer greater deformation.
DISCUSSION A large number of studies comparing implant systems also mention the primary stability produced by torquing the implants at the moment of insertion (insertion torque) and the initial implant stability quotient for different bone types.5,7,8,10,12 Manufacturers have developed a range of different connections and insertion systems accompanied by recommended techniques for drilling and bone compaction, conceived to ensure good anchorage. Failure to identify bone quality correctly can lead to the application of excessive insertion torque.13 When this happens, rupture or damage to the insertion driver and/or damage to the implant around its connection can occur. These events could compromise or even invalidate the screw-in implant insertion procedure. It is a well-known fact that the correct corono-apical positioning of an implant is essential in esthetic areas. When a high level of
torque is required, this optimal position could not be obtained. Most importantly, when implants are damaged in their platforms, this may compromise the prosthetic outcome. Nevertheless, comparative studies of the resistance of the different systems available have not determined their resistance to the torsional forces applied when they are screwed into place.5,6,8,10–12 The results of this study allow an analysis of the following variables: connection type, implant diameter, and stress zone. Regarding implant connection type, an analysis of the area that suffers the most stress revealed that all study groups displayed a homogeneous behavior, and both drivers and implant walls were seen to suffer deformation, except for the conventional system, with external hexagon and mounting device, in which the damage to the implant head was greater, perhaps due to the type of connection and the greater area of contact between implant head and mounting device, indicating greater fragility of the external hexagon walls. In comparison, implants with the same external hexagon design but with internal connection drivers suffered less deformation, although there were also alterations, including deformations and ruptures, which made prosthetic connection considerably difficult. It seems clear that external hexagon implant systems might have different levels of resistance, and the systems that
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present disposable mounting devices are more effective, probably because of the greater contact area where the insertion torque is applied to the fixture. Besides, the fact that those systems have another key, an insertion driver that matches the mounting device with a certain clearance, can imply in one more resistance factor to the system. However, both systems are most affected by overload, and deformations on fixtures occur in the prosthetic abutment contact area. Any deformity on external hexagon can derail prosthetic rehabilitation, especially in single crowns. A comparison of the different systems (external hexagon, internal connection, and Morse connection) demonstrated that all of them showed similar results. If a greater contact area exists, as in external hexagon with mounting device and internal connection key (Certain), high levels of torque are needed due to deformation (over 200 N$cm). All the remaining systems have a lower contact area between insertion key and implant wall, which reduces those values (between 100 and 130 N$cm), except at the sites where deformations occur. Additionally, these deformations are much more severe compared with external hexagon systems. Regarding internal connection systems, the Morse taper implant systems analyzed in this study do not use the Morse connection area to receive the torque required for insertion. Morse taper groups (2 and 3) did not show any alteration at the area of abutment adaptation. However, the other type of internal connection system, Certain system, may show damage to the hexagon. It is important to note that the deformation occurs in the angles of the hexagon, keeping the walls intact. When external hexagons are used, the use of an internal connection driver restricts the contact area between driver and implant. In comparison with internal hexagon implants, systems such as the Stargrip offer less contact area, a fact that may explain the great difference found between the Certain system and other internal connection systems. In particular, the insertion driver’s support is much greater, which seems to affect Morse taper connection because of its
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particular design, the driver does not attach to the Morse connection area, reducing its internal connection dimension. For this reason, this system showed similar values to those of the group 1. Thus it may be inferred that the greater the contact area between insertion torque driver and internal implant walls, the more effective the system will be in terms of offering greater resistance during insertion and so making higher torque values possible. Nevertheless, care must be taken to avoid the possible deformation of implant walls. The study tested implants of different diameters (3.25, 3.75, and 4 mm) and platform designs. The larger implant body diameter was not found to offer any significant advantage in terms of resistance to insertion torque. In groups 2 and 3, the same torque driver diameter was used on implants of different diameter. Thus the contact area was the same, with hardly any variation in the thickness of the implant walls. Even so, fixtures of 4.0 mm diameter showed advantages over 3.25 mm implants, which suffered critical dimensional alterations to the abutment connection area, indicating the necessity of avoiding overloading the more narrow systems. This premise can also be applied to external hexagon designs using the Stargrip system. The importance of these comparative mechanical studies lies on the collection of information concerning the limitations of different system types, information of great clinical relevance. Obviously, the minimum resistance values obtained in this kind of research are higher than the maximum torque insertion forces indicated by each manufacturer. Excessive torque is not recommended, mainly to avoid the possibility of deformation of implant seating platforms and connection areas. This study was based on a series of technical norms and applied axial force to the implant, through insertion drivers (mainly internal connection drivers) using a test machine. In clinical practice, where there may be limited access to the limitations of each system, the force values likely to produce deformation may be lower as a result of shear forces, given that the implant has variable insertion axes. Thus, knowledge and
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experience in the manipulation of bone tissues and a correct diagnosis of bone density will allow the surgeon to select the optimal drill/implant diameter, producing good stability and avoiding mechanical overloading and the risk of deformation.
CONCLUSIONS Test results for resistance to torsion in different implant systems found that: • The contact area between the device used for insertion of the fixture and implant head influences the system resistance. Internal hexagon implants with a greater contact area and external hexagon implants using a mounting device showed higher resistance to insertion torque compared with other systems with smaller hexagon connections or internal connections. • For internal connection systems, resistance is influenced by implant wall thickness. The more fragile this is, the greater the possibility of deformation and the lower the system resistance. • Excessive torque must be avoided because of the risk of deformation of the seating platform and of connection areas.
DISCLOSURE The authors claim to have no financial interest, either directly or indirectly, in the products or information listed in the article.
ACKNOWLEDGMENTS The authors thank Biomet 3i (Brazil) for supplying all the materials used in this study. Also, we thank M. M. S. Juliana Burigo for the relevant contribution to this study. Study testing was carried out at the laboratory of the Centre for Materials Characterization and Development (CCDM) Federal University of São Carlos, São Paulo, Brazil.
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