|Year : 2018 | Volume
| Issue : 3 | Page : 180-183
Comparison of biomechanical properties of different implant-abutment connections
Kalpana Devaraju, Sanjana J Rao, Joel Koshy Joseph, Sampath Raju Kumara Kurapati
Department of Prosthodontics, Dayananda Sagar College of Dental Sciences and Hospital, Bengaluru, Karnataka, India
|Date of Web Publication||12-Sep-2018|
Dr Joel Koshy Joseph
Department of Prosthodontics, Dayananda Sagar College of Dental Sciences and Hospital, Kumaraswamy Layout, Bengaluru, Karnataka
Source of Support: None, Conflict of Interest: None
Implant abutment connection has proven to have a significant impact on the success of the prosthetic rehabilitation for an implant-supported restoration. This connection not only provides the base on which the restoration is supported but also maintains the integrity of the hard and the soft tissues surrounding the implant. In this review, we describe the performances of different implant-abutment connections that are the external implant connections, internal implant connections, and the Morse taper connections in terms of their mechanical properties, biological properties, and its biomechanical effects.
Keywords: Abutment connection, implant, Morse taper, systematic review
|How to cite this article:|
Devaraju K, Rao SJ, Joseph JK, Kurapati SK. Comparison of biomechanical properties of different implant-abutment connections. Indian J Dent Sci 2018;10:180-3
|How to cite this URL:|
Devaraju K, Rao SJ, Joseph JK, Kurapati SK. Comparison of biomechanical properties of different implant-abutment connections. Indian J Dent Sci [serial online] 2018 [cited 2018 Dec 9];10:180-3. Available from: http://www.ijds.in/text.asp?2018/10/3/180/241053
| Introduction|| |
In the late 1970s, we saw the advent of modern implantology with the accidental discovery of osseointegration of titanium within the bone by Professor Per-Ingvar Branemark. Since then, prosthodontic rehabilitation with osseointegrated implant turned out to be the therapeutic solution of choice for treating partially or completely edentulous arches. However, for a long time, “osseointegration” was the only criteria taken into account for the evaluation of implant success. This has changed with time and technology. Now, esthetics and functional results also serve as important criteria to be fulfilled for a successful implant treatment.
Even with a successful placement of implant, if it fails to serve the very purpose of esthetics, the treatment is a failure. Similarly, an osseointegrated implant if not able to withstand occlusal forces and maintain its stability and rigidity, the treatment is again considered to be a failure.
Under these circumstances, the implant abutment connection plays the crucial role to maintain the biomechanical criteria. The strength of the implant connections determines whether it can withstand the occlusal loads, whereas the rigidity of the implant connections aims to minimize the micromovements. Implant abutment connections could be external or internal depending on the distinct projection; external or recessed into the implant body.
Branemark's original implant-abutment connection was an external hexagon [Figure 1], which later on underwent manymodifications to counter the demerits of the former, for example, tapered hexagon, external octagon, and spline  dental implant.
Internal implant-abutment connections were introduced to overcome the clinical complications associated with external connections. They are further subdivided depending on the type of joint which is passive fit or frictional fit. These connections also underwent several modifications which gave them specific clinical advantages such as, 12-point internal hex connections, internal tripod connections, and internal octagon.
In 1864, Stephen A. Morse an enterprising mechanic invented the Morse taper connection which was used to connect two rotating machine components in drilling machines. This connection was later used by the orthopedic industry under the generic name of “Morse tapers” as means of reliably joining modular components of total joints directly for hip arthroplasty.
The principle of Morse taper is that, of the cone in the cone [Figure 2], where the trunnion (the male portion) and the bore (the female portion) both are uniformly tapered. The bone is tapped into the trunnion as they come in intimate contact; thus, the stresses inside the materials keep both components fixed together.
In the recent decade, the biomechanics of this connection favored the requirements of implant abutment connections not only in the physical terms but also at microscopic levels, as they were able to counter the demerits of traditionally used abutment connections.
| Mechanical Strength|| |
Generally, internal connections initially showed increased fragility compared to the external connections, especially for the small diameters. This fragility is due to the recess in the body of the implant destined to provide space for the implant abutment.
This thinned the walls of the implant and decreased its strength. However, in vitro studies suggest that internal connections showed greater resistance than external connections under heavy torque stresses.
Chun et al., 2006, demonstrated that internal hexagon connections distributed stress better within the implant and further redistributed within bone. This was possible due to larger implant abutment contact area. In external hexagon connection, highest strain concentration was found between the implant platform and the abutment which indirectly led to compromised biological width.
| Stress/load Performance|| |
Implant abutment designs show different degrees of peri-implant crestal bone remodeling after subjected to functional loading.
In a histological and histomorphological evaluation of marginal bone resorption around implants in dogs, Resende et al. demonstrated the smaller amount of bone loss for Morse taper implants, both on the buccal and lingual sides, whereas external hex implants showed a larger bone loss.
Quaresma et al. in 2008 showed that the stress is better distributed at the alveolar bone but more concentrated at the abutment itself in Morse taper implant. Whereas internal hex abutments produce greater stresses on the alveolar bone and the prosthesis but lower stresses on the abutment system.
| Load Fatigue Performance/resistance|| |
Failure of the abutments was system dependent and occurred primarily in the region of the weakest point, the screws, respectively, the threaded parts, or between the threaded or unthreaded parts of the abutment. Khraisat et al. reported a significant difference between the Morse taper and external hexagonal connection systems; in that no fractures were noted for the Morse taper group, while the mean fractures' rate for the external hexagonal groups was between 1733 and 1778 cycles.
| Bending Moment/Maximal Load Resistance|| |
Higher maximal load resistance values were seen for the internal conical implant abutment as compared to the internal hexagonal connections with a two-piece abutment. Fractures only occurred in the internal hexagonal group at the weakest point; the threaded part of the screw. Internal conical implant-abutment connections' systems showed higher resistance to bending forces than other internal connections.
| Microgap|| |
Microgap within external and internal implant-abutment connections was always evident. In addition, the micro-movements act like a pumping effect, which draws in intraoral fluids within the spaces making them a harbor site for the bacterial growth. Numerous studies demonstrated the presence of bacterial growth within these spaces which directly affect the continuity of the biological width and may lead to marginal bone loss and peri-implantitis.
Within Morse taper abutment connection, a cold-welded interface is seen between the implant and the abutment, which considerably reduced the presence of any microgaps and micromovements between the fixtures.
A comparative study conducted by Jaworski et al., 2012, demonstrated significant lower bacterial penetration within Morse taper (30% of cases) against external connections (60%).
When compared between Morse tapers and internal connections, Tripodi et al. in 2012 demonstrated that 2 out of the 10 Morse taper implants were contaminated against 5 of the internal hexagon connection implants.
| Platform Switching|| |
The concept of platform switching was introduced by Lazzara and Porter based on the hypothesis that a narrower abutment can increase the distance between the implant-abutment microgap contamination and the crestal bone and may allow the establishment of an adequately dimensioned biological width, thus reducing bone resorption [Figure 3].
|Figure 3: Illustration of bone morphology in Morse taper implant with platform switching|
Click here to view
Siffert and Etienne et al. in 2011 stated in a review that platform-switched implants showed biological and biomechanical consequences which led to decreased bone resorption. Biologically, they observed horizontal repositioning of the biologic width toward the implant abutment junction which repositioned the inflammatory infiltrates and created a mucosal joint. Under biomechanical consequence, they observed that forces were concentrated more toward the center of the implant which was further redistributed harmoniously into the bone. Thus, the tissues at the junction-abutment are in less stress.
Since internal connections are often associated to platform switching which gives them an added benefit against external connections. Zipprich et al. in 2007 showed that the Morse taper connections did not show microgap opening during micromovements in relation to other internal connections (without platform switching).
| Biological Width|| |
The periodontal tissue around an implant ought to acts as a barrier against the oral environment, which prevents the bacterial infiltrates contaminating the implant surfaces [Figure 4].
Tomasi et al. in 2013 conducted an experimental study on humans for morphogenesis of peri-implant mucosa. It was seen among 21 patients receiving implant-supported single tooth that the presence of connective tissue and epithelial attachment on to the implant surface about 8 weeks.
Although obtaining biological width depends on many other factors such as the presence of parafunctional habits such as bruxism, gingival biotype, and position of the implant, but the type of implant abutment connection also plays a crucial role. The presence of microgap, bacterial infiltrated, and existence of abutment micromovement all predisposes to bacterial contamination and hampers the biological width. If the biological width is invaded and is reduced to < 3 mm, there would be pocket formation or gingival recession depending on the gingival biotype and ultimately lead to implant failure.
When compared with external abutment connections, internal connections show superior performance in terms of mechanical strength, stress distribution, microgap, and bacterial penetration; thus implants supported with internal abutment connections preserve biological width better than external connections.
When compared between other internal abutment connections, Morse tapered connections distributed stress better at the alveolar bone level and better resistance to bacterial leakage. Morse taper connections with platform switching showed reduced inflammation and bone loss. Hence, Morse taper connection preserves the biological width better than other internal connections.
| Conclusion|| |
Within the limitations, this review concludes that, biomechanically, Morse taper connections showed better performance against external and internal connections, this was possible because of their geometry, as they were able to redistribute the forces and stresses evenly through the implant body, thereby ensuring reduced deleterious forces to the surrounding bone.
In terms of mechanical and structural integrity, conical abutment connection systems are more resistant to micromovements and microgaps.
They have better torque resistance and higher resistance to fatigue loading and maximum bending. No connections have absolute perfect bacterial seal; however, conical connection systems proved themselves to be better when compared with internal hex and external connections.
Clinically, Morse taper connections produced lower stress over the surrounding bone resulting to reduced marginal bone loss and therefor the vital biological width.
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Conflicts of interest
There are no conflicts of interest.
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