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Medicine and Health

The Effects of Prosthetic Material on Stress Distribution

Abstract

This research is a finite element analysis, which involved the evaluation of dental implant systems characterized by prostheses of a different material. The study sought to determine the difference in stress distribution on the crowns, abutments, implants, and bones, as determined by the material used in designing the crowns. For clarity and distinction, the setups were named system 1 and 2. System 1 consisted of metal-ceramic crowns, while zirconia crowns were used in system 2. In both setups, titanium abutments were used. An equal load of 50 N was applied in both systems, and the stress distribution on the bone, crown, implant, and abutment determined and recorded. The length and diameter of the implants were constant, 10 mm and 3.3 mm respectively. There was a significant difference in stress distribution between the two systems, as far as the bone, crown, and abutment were concerned. Therefore, the dental implant systems with metal-ceramic prostheses produce less stress on the alveolar bone and the abutment complex, and greater stress on the prosthesis. On the other hand, dental implant systems having zirconia prostheses produce higher levels of stress on the alveolar bone and the abutment complex and less stress on the prosthesis.

Introduction

Over the years, scientists have invested many resources in research aimed at improving dental care. For many years, patients with tooth loss had to rely on therapeutic techniques like bridges and dentures. With the advent of more advanced options like dental transplant, dentists are now capable of managing dental problems more efficiently. It is estimated that the success rate of dental implant is as high as 98% (Kim, Eo, Nguyen, & Kim, 2019). However, the success rate is dependent on the specific part of the jaw in which the implant is placed, the length of the implant, implant diameter, the quality of the bone and the age of the patient (Kim, Eo, Nguyen, & Kim, 2019). Studies have shown that the part of the jaw, which produces the highest rate of dental implant success is the mandibular anterior.

However, there is still a debate as to whether all these factors affect implant success and failure. Whereas some studies claim that all these factors play a significant role in determining the success rate of implants, some studies have provided evidence showing that most of these factors have zero or insignificant influence on implant success rate.   Despite its higher effectiveness in dental care, dental implantation is still subject to improvement due to technical issues arising from its use. The issues include but are not restricted to loosening of screws, breakage of screws, bone, and crown displacement (Quaresma, Cury, Sendyk, & K, 2008). The abutment-implant connection micro-displacement is also another problem common in patients who have undergone dental transplant (Quaresma, Cury, Sendyk, & K, 2008). These problems are mainly attributed to excessive occlusal force and the type of material used in the design of the implants (Quaresma, Cury, Sendyk, & K, 2008). Another key factor linked with the issues arising from the use of dental implants is the geometrical properties of the implants.

Studies have provided evidence showing that the diameter and shape of an implant affect stress distribution on the implant and the surrounding areas. For example, conical-shaped implants have a better stress distribution than stepped cylindrical implants. As a result, conical implants have a lower risk of developing mechanical complications, compared to stepped cylindrical implants (Quaresma, Cury, Sendyk, & K, 2008). Research has also shown that cylindrical implants produce better results than both conical and stepped cylindrical implants (Quaresma, Cury, Sendyk, & K, 2008). This is mainly due to its ability to offer maximum resistance to shear stress (Elias, 2011).

Intensive research on the materials used in designing some parts of the dental implants systems has also revealed other risks. For instance, studies suggest that titanium and zirconium could be associated with peri-implant disease (Shwarz, et al., 2019). A few studies suggest that titanium and zirconia particles can induce cytotoxicity, enhancing pro-inflammatory responses (Shwarz, et al., 2019). However, there are not enough studies to prove the association of titanium and zirconia with the mentioned health complications. The available studies have some loopholes which can be used to disapprove their hypotheses. For instance, metal particles can also be found in healthy transplants. This means that their presence in peri-implant conditions does not necessarily mean that they are the cause of the disease.

The implant-abutment connection is also a major point of focus due to its influence in stress distribution (Sadowsky, 2019). Therefore, the design of implants has been extensively studied due to its role in load transmission at both the bone-implant and implant-abutment interfaces (Quaresma, Cury, Sendyk, & K, 2008). This research aimed to investigate two systems, both made of titanium abutments. However, system 1 used metal-ceramic crowns, contrary to system 2, which used zirconia crowns. The study sought to examine the stress distribution on the prostheses, bones, abutments, and six implants.

Materials and Methods

A finite element model of the mandible, implants, abutments, and crowns was made. The setup consisted of a mandible, six implants, and titanium abutments. Some of the implants were filled with metal-ceramic crowns while others were filled with zirconia crowns. Six implants were placed in the mandible. Abutments were then placed over them, after which the crowns were added on top of the titanium abutments. The face-face angle tolerance was set at 75o and the trim tolerance at 0.71709mm. A 10 mm length and 3.3 mm diameter were maintained in all the implants. Considering that the project was in vitro osseointegration, direct contact between the bone and the implant was assumed. This assumption was made for consistency with the notion that there was a direct transmission of the load from the occlusal surface to the alveolar bone. AUTOMAP, AUTOCAD, and MSC PATRAN software were used to process the data and generate results. Data showing the level of deformation, elastic strain and stress were recorded and analyzed for both the setups. In the finite element model, the total nodes were 1053272, while the elements were 601933. After the application of the 50 N loads, the values for the stress exerted on the alveolar bone, prosthesis, implant, and abutment were noted.

Results

From the results generated from the project, stress was most concentrated at the point of application of the force. System one recorded higher stress levels on the prostheses, and lower on the bones and abutments. The maximum stress on the bones for system 1 was 194.05 Mpa, whereas the maximum for system 2 was 458.8 Mpa. Regarding the prostheses, system 1 recorded a maximum stress level of 6.7301 Mpa, while system 2 registered 8.6184 Mpa. However, the average stress for system 1 was higher than that of system 2, at 0.84615 Mpa compared to 0.16066 Mpa. Concerning the abutments, system 1 registered a maximum of 54.499 Mpa, against 126.07 Mpa for system 2. In both systems, the highest stress levels were concentrated on the abutments, averaging to 4.1371 MPa and 9.6273 MPa respectively. Also, the lowest stress levels were on the prostheses for both systems, averaging to 0.84615 MPa and 0.16066 MPa respectively. As far as the implants are concerned, there was no variation regarding the stress concentration. This is probably because the implant particles used were made of the same material. Below is a graph showing the difference in stress distribution between the setup with metal-ceramic crowns and that with zirconia crowns:

Discussion

Among the key findings of this research was that system one can produce lower stress levels on the alveolar bone and the abutment, in comparison to system 2. However, when it comes to the prosthesis, system 2 produces less stress than system 1. Even though both systems exhibit the highest stress levels at the prostheses, the stress associated with system 1 is significantly higher than that of system 2. This could mean that implant systems with zirconia crowns are more efficient for reducing the risk of complications like prosthetic micro-displacement, compared to metal-ceramic crowned implant systems. This is because of the lower the stress levels on the occlusal surface, the lower the risk of mechanical complications (Quaresma, Cury, Sendyk, & K, 2008). However, this notion cannot be said to be 100% accurate or reliable because this level of stress might not be detrimental to the implant system. Studies have shown that there is a threshold load, below which stress can be beneficial (Sadowsky, 2019). Below the threshold, stress is said to improve bone density, boosting the success of the implantation process (Sadowsky, 2019). Above the threshold, problems such as bone loss in the form of saucerization or other forms may occur. Overloading the occlusal surface could also result in mechanical issues such as screw loosening. Considering that the threshold stress is not known precisely, it is not possible to tell whether the stress amount in this system can or cannot be detrimental.

This study also showed that metal-ceramic crowned dental implant systems are characterized by lower stress on the alveolar bone, relative to the zirconia crowned systems. This could insinuate that system 1 is a better option for lowering the risk of clinical complications. An example of the complications is marginal bone resorption, usually caused by pressure accumulation on the bone (Quaresma, Cury, Sendyk, & K, 2008). This property also lowers the risk of bone loss through saucerization. This allows the easy growth of other tooth components around the implant, enabling the implant to last for a long time. Some studies suggest that dental transplants can last for a lifetime. Considering the vital role played by the jawbones in dental health, it is correct to say that within the limitations of this study, that system 1 is likely to be a more effective and efficient option than system 2. The lower stress produced by the metal, ceramic crowned system on the abutment complex could also make it a better option, compared to a zirconia crowned system. This is because there would be a reduced risk for problems like screw loosening or fracture, as well as micro-motion-associated issues.

This research showed that in general, a metal-ceramic crowned dental implant system is better than the zirconia crowned dental implant system, as far as addressing the clinical issues is concerned. Using system one would reduce complications associated with dental implant systems. As a result, it would be less costly for both the patients and the health practitioners. On the contrary, the use of system two would increase the risk of patients experiencing dental implant-related complications. This would make it necessary for the patients to spend more money to take care of the problems arising. As a result, the cost of dental care will be increased. Some patients may also lose confidence in the therapeutic technique itself, reducing the number of patients managed by the doctors concerning tooth loss. Some patients might also avoid this method if they perceive it to be financially straining. However, more research is required to prove this hypothesis.

In conclusion, the dental implant systems with metal-ceramic prostheses produce less stress on the alveolar bone and the abutment complex, and greater stress on the prosthesis. On the other hand, dental implant systems having zirconia prostheses produce higher levels of stress on the alveolar bone and the abutment complex and less stress on the prosthesis.

References

Elias, C. N. (2011). Factors affecting the success of dental implants. London: IntechOpen.

Kim, K. T., Eo, M. Y., Nguyen, T. T., & Kim, S. M. (2019). General review of titanium toxicity. International Journal of Implant Dentistry.

Quaresma, S. E., Cury, P. R., Sendyk, W. R., & K, C. S. (2008). A finite element analysis of two different dental implants: stress distribution in the prosthesis, abutment, implant, and supporting bone. Journal of Oral Implantology, 1-6.

Sadowsky, S. J. (2019). Occlusal overload with dental implants: a review. International Journal of Implant Dentistry.

Shwarz, F., Langer, M., Hagena, T., Hartige, B., Sader, R., & Becker, J. (2019). Cytotoxicity and proinflammatory effects of titanium and zirconia perticles. International Journal of Implant Dentistry.

 

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