|Year : 2017 | Volume
| Issue : 4 | Page : 193-197
Effect of cyclic loading on marginal fit of implant–abutment interface for three different connections with telescopic attachment: in-vitro study
Wafaa Y El-Ashry, Eman A Shakal, Mohamed M El-Sheikh
Department of Prosthodontics, Faculty of Dentistry, Tanta University, Tanta, Egypt
|Date of Web Publication||21-Dec-2017|
Wafaa Y El-Ashry
Department of Prosthodontics, Faculty of Dentistry, Tanta University, Tanta
Source of Support: None, Conflict of Interest: None
The objective of this article was to evaluate the effect of dynamic cyclic loading on marginal fit at implant–abutment interface with three different implant connections using scanning electron microscope.
Materials and methods
Thirty implant fixtures were divided equally into three groups (N = 10): group I external hex fixture, group II internal hex fixture, group III conical hybrid fixture. Each fixture was vertically placed in the center of epoxy resin block using modified dental surveyor. Matched prefabricated titanium abutments were screwed to the implant and metal coping was adapted onto abutment. The samples were subjected to eccentric cyclic loading (at a distance 2–3 mm) away from center of abutment at three different intervals 10 000, 100 000, 500 000 cycles. Marginal fit was evaluated before and after each cycles by measuring microgap size in (μm) using scanning electron microscope with a magnification ×700. The values of microgap size in um before and after each cyclic loading were collected, tabulated and statistically analyzed using analysis of variance and Tukey's post-hoc test at 0.05 level of significance.
After cyclic loading the microgap size was measured in all groups and high value was recorded to group I external hex connection 60.64 ± 4.3μm, while minimum value recorded to group III internal conical connections 0.94 ± 0.11 μm and internal hex connection in between 17.98 ± 2.07 μm. Two way analysis of variance showed significant effect upon marginal fit for both connection and cyclic loading.
The geometric factors of implant–abutment connection and dynamic cyclic loading have effect on marginal fit at implant–abutment interface. Internal conical connections showed a better marginal fit than internal and external hex connection so use of conical implants can be promoted as it has better sealing abilities compared to other systems.
Keywords: dynamic loading, implant connection, implant–abutment interface, microgap, scanning electron microscope
|How to cite this article:|
El-Ashry WY, Shakal EA, El-Sheikh MM. Effect of cyclic loading on marginal fit of implant–abutment interface for three different connections with telescopic attachment: in-vitro study. Tanta Dent J 2017;14:193-7
|How to cite this URL:|
El-Ashry WY, Shakal EA, El-Sheikh MM. Effect of cyclic loading on marginal fit of implant–abutment interface for three different connections with telescopic attachment: in-vitro study. Tanta Dent J [serial online] 2017 [cited 2018 Apr 19];14:193-7. Available from: http://www.tmj.eg.net/text.asp?2017/14/4/193/221385
| Introduction|| |
Dental implant restoration has been widely accepted as one of the treatment modalities to replace missing teeth and to restore human masticatory function , and considered an alternative not only for the treatment of total edentulism but also for the replacement of one or more dental element . For this reason it become one of the most successful rehabilitation techniques among medical and dental specialties with success rates reported above 90% over the last 30 years .
Most dental implant systems consist of two components; endosteal component (implant) which is placed in a first surgical phase, and a transmucosal connection (abutment) which is typically attached after successful implant osseointegration to support the prosthetic restoration and connected to the implant body by a screw in a process assisted by external or internal geometries (the most typical has a hexagon geometry) for alignment. Following sitting and adaptation of abutment on the implant top, a clamping force between components is achieved by means of torquing the screw to values predetermined by the implant manufacturer. During chewing and biting, the prosthetic restoration and implant–abutment connection is affected by various physiological forces .
Different types of implant–abutment connections are available and they may be external or internal. The geometry of implant connection is further described as octagonal, hexagonal, cone screw, cone hex, cylinder hex, tube, or combination. Most companies tended to manufacture connection design of conical features with other features such as internal hex this type named hybrid conical in attempt to achieve higher stability, tight contact and decrease microgap as possible. The manufacturers try to develop new designs of implant–abutment connection with high degree of precision fit and more stability to improve longevity of implant and to reduce prosthetic and biological complications .
Successful implant therapy requires a dynamic equilibrium between biological and mechanical factors. The biologic factors are generally considered multifactorial, mechanical factors such as the implant–abutment precise fit and the abutment screw preload are involved in the success of implant rehabilitation. The preload loss during occlusal load with the prosthesis in function favors a lack of stability and misfit of the implant–abutment connection and this can result in stress increase in the implant and connection components, and consequently in the surrounding bone ,.
Although success and good survival rates for implant supported reconstructions have been reported, technical and biologic complications are frequent . Microgaps between the implant–abutment interface as a biological complication may cause microbial leakage in which microorganisms penetrate through a gap as small as 10 μm, resulting in bacterial colonization and peri-implantitis, peri-implant mucositis, halitosis, swelling and/or fistula formation, difficulty in chewing and marginal bone resorption as a results of a poor fit in the interface zone of the prosthesis and the implant . Mechanical complications include loosening and fracture of the maintaining screw, micro movements, implant fracture, abutment fracture, and fracture of overstructure (ceramic and/or metal) .
The main challenge in the development of implant–abutment connection designs relies on reducing/eliminating the incidence of mechanical failures in the implant–prosthetic devices and improving the response of bone and soft tissues  Thus, the evaluation of reliability and failure modes could provide insight into the mechanical behavior of different configurations of implant–abutment connections .
Methods that have been used to measure microgap at implant–abutment interface include the direct view, cross-sectional measurement after sectioning, the impression technique, and use of an explorer with a visual examination, scanning electron microscopy (SEM) , optical microscopy scanning , laser microscopy or theoretical approaches through finite-element modeling , as well as different forms of radiographic applications  such as microcomputed tomography  and synchrotron based radiography .
| Material and Methods|| |
Distribution of groups
Total of thirty implant fixtures (4.2 mm diameter × 11.5 mm length) with straight prefabricated titanium abutment (4.2 mm diameter × 6 mm length) were selected for this in-vitro study and divided into three equal groups, 10 each according to types of implant–abutment connection: group I (external hex): an external hexagonal connection (MicroDent System, Barcelona, Spain) geometry. Group II (internal hex): an internal hexagonal connection (Schütz Dental GmbH, Rosbach, Germany) geometry. Group III (conical hybrid): conical hybrid connection geometry. All implant fixtures were vertically installed in the center of epoxy resin blocks with the aid of modified dental surveyor. Luting resin cement (self-adhesive resin cement, translucent; GC Corporation, Tokyo, Japan) was applied in the prepared site in resin block before implant placement. The implant placement was completed with torque wrench until the implant top became ~1 mm above the resin level. For each selected abutment (6 mm length and 1 mm gingival height) metal coping was fabricated using lost wax technique according to the manufacturer's recommendations to fit accurately on abutment simulating telescopic attachment. Implant–abutments were screwed to the implants with 30 Ncm torque, as recommended by manufacturer.
Application of cyclic loading
The cyclic loading test was performed on the specimens using a universal testing machine (Model 3345; Instron Industrial Products, Norwood, Massachusetts, USA), with an axial load of 133 N, was applied eccentrically (at a distance of 2–3 mm) away from the center of abutment using a metallic rod with round tip at a frequency of 1 Hz. The load was applied at three intervals of 10 000,100 000,500 000 cycles to simulate values found in human mastication as shown in [Figure 1].
Measurement of microgap at implant–abutment interface
Marginal fit of each assembly (implant–abutment) was analyzed by measuring the size of microgap between the implants and abutments before and after each cyclic load by using a SEM (JSM-5500 LV; JEOL, Tokyo, Japan) with ×700 magnification, digital image software. The size of microgap of each assembly before and after dynamic loading was measured at four locations to the outer parts of the interfacial zone in viewing angle perpendicular to the long axis of each implant–abutment complex, each assembly had four measures.
Analysis of variance (ANOVA, Super ANOVA; Abacus Concepts, Berkeley, California, USA) was used to compare mean of microgaP values between different groups and between different loading periods followed by pair-wise Tukey's post-hoc tests at 0.05 level of significance.
Statistical analysis was performed using Assistat 7.6 statistics software for Windows (Campina Grande, Paraiba State, Brazil). P values less than or equal to 0.05 are considered to be statistically significant in all tests.
| Results|| |
The mean and SD values of microgap distance measured in micrometer at implant–abutment interface for three tested groups.
The microgap measurements before and after cyclic loading for three tested groups were statistically significant as indicated by one way ANOVA test (P ≤ 0.0001) followed by pair-wise Tukey's post-hoc tests (P < 0.05) as shown in [Table 1].
|Table 1: Microgap distance results (mean±SD) for the three different implant–abutment connections before and after cyclic loading|
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The SEM pictures for group I (external hexagonal connection geometry) showed significant increase in microgap size before and after three different cyclic loading as demonstrated in [Figure 2].
|Figure 2: Scanning electron photographs of the marginal fit of external hex I-A interfaces before and after dynamic loading. (a) Group I before Cyclic loading (b) Group I after 500000 cycles.|
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The SEM pictures for group II (internal hexagonal connection geometry) showed increase in microgap size before loading then decreased after 500 000 cycle as demonstrated in [Figure 3].
|Figure 3: (a and b) Scanning electron photographs of the marginal fit of internal hex I-A interfaces before and after dynamic loading. Group II (a) before cyclic loading Group II (b) after 500000 cycles.|
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The SEM pictures for group III (conical hybrid connection geometry) showed little increase in microgap size before loading then decreased after 500 000 cycle as demonstrated in [Figure 4].
|Figure 4: (a and b) Scanning electron photographs of the marginal fit of internal conical hybrid I-A interfaces before and after dynamic loading. Group III (a)before cyclic loading Group III (b) after 500000 cycles.|
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Interaction between variables
The difference between the three different implant–abutment connection groups was statistically significant as indicated by one way ANOVA test (P ≤ 0.0001) followed by pair-wise Tukey's post-hoc test (P ≤ 0.05) before aging, after each interval of dynamic cyclic loading as shown in [Figure 5].
|Figure 5: Mean values of microgap (μm) measurement for the three different implant/abutment connections after 500000 cycle cyclic loading.|
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| Discussion|| |
Our study compared the effect of cyclic loading on marginal fit at implant–abutment interface of external, internal hex and conical hybrid implant system. In addition, it assessed the influence of using different geometry of implant connection.
In our study, specific blocks were constructed by epoxy resin material because has appropriate elastic modulus (~20 GPa) mimic to bone. Modified dental surveyor was used for drilling to allow all fixtures were placed vertically and perpendicular to the center of blocks for standardization.
The implant platform was set ~1 mm above the resin level to allow the abutment connection and the microgap size assay.
In current study resin cement was packed in each prepared implant holes before implant installation to secure the implant to epoxy resin block. This was done to simulate osseointegration between implant and bone.
When comparing the three different connections there was a significant difference in microgap size before and after application of dynamic cyclic loading, the highest value of microgap was recorded for external hex connection, this may attributed to the back off theory and this in agreement with Cibirka et al.  who described the abutment screw as a spring stretched by preload that is maintained by the frictional fit of the threads. External forces can create a vibratory movement and cause the threads to 'back off' which leads to a reduction in effective preload and diminishes the ability of the screw to maintain the joint stability thereby increasing the implant–abutment interface gap space.
While conical connection (conical hybrid) recorded minimal values of microgap size due to cold welding and internal hex in between because of most of the tensile force may be transferred to the internal wall instead of the abutment screw and the abutment screw can be subjected to little force .
On the other hand, our data was in disagreement with those of Piermatti et al. , Steinebrunner et al. , Ribeiro et al. who evaluated the influence of long-term dynamic loading on the fracture strength of different implant–abutment connectors. And demonstrated that external hex interface had better results and superior fatigue resistance compared with internal hex connections.
Our results showed significant difference between external hex and internal hex which did not agree with those of Feitosa et al. . Who stated no significant difference between external and internal hex.
The previously mentioned findings came supported with the findings of Sutter et al. and Squier et al. who stated that conical connection provide higher stability and more predictable rehabilitation with great longevity and success rate than external hex due to cold welding on the implant–abutment interface and this condition arise from the friction between two surfaces, the pressure created by insertion force determines the maintenance of the connection even stopping the applied force of insertion.
Our results supported by the tightening torque in the internal-cone connection is driven by not only the screw height but also the wedge effect due to the conical abutment sinking, and the load is mainly supported by the internal slope of the fixture. Therefore, the stress that occurs in the abutment screws has been known to be relatively smaller than that in the external butt joint .
On the contrary, our results were in disagreement with Blum et al. , who stated that micromotion of abutment during cyclic loading can induce wear and wear particles in conical implant system and this accompanied with the formation of microgap at implant–abutment interface.
| Conclusion|| |
Within the limitation of this in-vitro study, it was concluded that:
- The conical and internal hexagonal implant–abutment connection designs provide more biomechanically suitable prosthetic options than other systems.
The mechanical aging increased the vertical misfit on external and internal hex connection but did not affect the marginal fit of the conical connections.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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