CAD/CAM Vs Rapid Prototyping: An In-Vitro Study to Assess the Accuracy, Durability and Prognosis of Implant Frameworks

CAD/CAM Vs Rapid Prototyping: An In-Vitro Study To Assess The Accuracy, Durability And Prognosis Of Implant Frameworks.

 

Dentistry is a dynamic field with constant room for evolution and innovation. This was particularly true when the first dental implants were placed back in the 1980s (1). Ever since that the field of dental implants has been revolutionized with constant innovation and progressive development. These developments range from new implant systems, the propagation of new diagnostic systems, to the introduction of novel surgical techniques and  the incorporation of multidisciplinary approach towards dental implants(2-4).

One of the recent and most iconic advancement is in the field of implant prosthodontics and involves an amalgamation of engineering principal of computer-aided design and computer-aided manufacturing (CAD/CAM) to construct implant prosthesis (5). The benefits include high precision, simpler fabrication, durability, and minimal intervention with the option of chair side manufacturing of indirect restorations (6). All these advantages make CAD/CAM ideal for quality assurance, precision and cost effective manufacturing of implant frameworks (6-8).

Ever since the introduction of CAD/CAM technology almost more than twenty years ago in dentistry (9) considerable work has been done on the subject and the novelty has appealed to numerous clinicians and researchers alike. The use of CAD/CAM in dentistry, however has flourished in the past ten years as a lot of work has been done on implant abutment and framework (10). Initially the technology was used for fixed prosthodontics only such as inlays, onlays, veneers and crowns (11) but the advancements in technology in the last few years have seen the utilization of different materials such as composite, porcelain and metallic blocks which could not be used earlier due to technical limitations and  restraint (11, 12) it has expanded the choice of material by providing a wider selection of material choices with higher dependability (13). This led to the incorporation of CAD/CAM in implant abutment and frameworks.

CAD/CAM production usually involves three steps; scanning of the specimen or data acquisition ( which records the geometry of the infrastructure), restoration design or CAD modelling  and construction of the prosthesis or CAM production (6, 14). Customized CAD/CAM products combine the benefits of stock and cast abutments (6, 15). Apart from the accuracy, durability and ease of manipulation most of the prosthesis parameters are modifiable such as the emergence profile, the external contour, the thickness and the finish line contour which were conventionally done by dental technicians with a larger margin of error (13, 15).CAD/CAM reduces the error gap and aids in providing better fitting abutment and framework (15). It is more precise as it does not incorporate small errors from impression distortions and modelling materials (16). CAD/CAM when applied to the implant surgery allows manufacturing of implant abutments and surgical guides and the production of high density and resistance crowns (11, 16).In short the CAD/CAM technology provides three major benefits in term of implant prosthesis namely accuracy, durability and simplicity of construction (6).

While considering the equilibrium of an implant prosthesis a very important factor is the passivity of fit, it helps maintain biological and mechanical stability and optimizes the load on bone, screw and abutment (17).The passivity of fit  is defined as the simultaneous and even contact of all the fitting surfaces, without the development of strains prior to functional loading (18-20).Despite all the benefits associated with CAD/CAM earlier studies suggested an inferior fit of CAD/CAM on teeth when compared to conventional fabrication methods (21, 22).Nevertheless, some recent studies observed a more progressive outcome of CAD/CAM restoration fit (23, 24) but more work needs to be done on the subject (25). Most of literature suggests CAD/CAM to be a better option as compared to conventional methods .But most studies are literature reviews and need clinical validation. Despite the benefits and advantages the fact of the matter remains that  CAD/CAM has not thrived and been utilized to its full potential in dentistry and the reason is the drawbacks associated with it (26).

As with any technology CAD/CAM has its fair share of obstacles, despite the fact that the idea of CAD/CAM is very lucrative and intriguing the ground reality remains that the entire setup is pretty expensive and almost impossible for small dental setups to purchase the scanner, the milling units and the soft wares (11). Apart from the cost of the setup there is also a learning curve involved with using the CAD component as the clinician needs to learn how to use and work the computer aided designing and associated soft wares which are difficult for some people and hiring a skilled person just adds onto the overall cost again. Similarly at the modelling stage, margin placement and restoration contour are prone to error and were proven to suffer from more discrepancies (18, 22).Furthermore, the accuracy of the milling procedure is dictated by the diameter of the smallest bur surface details less than the diameter of the smallest bur will not be produced successfully (18, 27). The CAD/CAM technology in itself is a subtractive method wherein the material is subtracted from an initial block of material to acquire the desired shape such as an implant abutment or framework (28, 29). This subtractive method can produce a complete shape but at the expense of material being wasted .As a considerable amount of raw material is wasted as the unused portion of the mono block is discarded after  milling and recycling of the ceramic is not feasible (28). The milling tools are exposed to heavy abrasions and wear and microscopic cracks can form in the ceramic due to milling of brittle materials. The entire process is neither easy nor economical for big, full undercuts or complex milling parts (30-32).

Alternatively additive fabrication is a process by which the final product is manufactured by adding multiple layers of materials on top of one another (28, 33).The idea is that the model is sliced into many thin layers and the manufacturing equipment uses the geometric data to build each layer sequentially until its completed (28). It is also known as 3D-printing or layered manufacture (33, 34). This 3D printing or rapid prototyping or “generative manufacturing technique “exhibits the potential to overcome the shortages of CAD/CAM techniques (32, 35-37).

Rapid prototyping or 3D printing consist of two phases only, the virtual phase (this includes modelling and simulating) and the physical phase (this involves the fabrication or printing). Virtual prototyping is development of the model by dynamic and interactive simulation (28, 33). The benefits and  advantages  have  led to its introduction in the biomedical field almost a decade ago (38). And according to Wohler and Wohler several advances have been made to incorporate it into the field of dentistry (39).A combination of dental science and the manufacturing technologies is the notion behind  the use of 3D printing in dentistry and prosthodontics (28). With new innovations the system is already being used for pre surgical planning in dentistry, treatment planning and implant placement, fabrication of facial prosthesis and fabrication of cranioplasty  prosthesis and a range of other purpose (38).

The are many benefits associated with rapid prototyping, primarily one being speed (40). Printing can also reproduce complex shapes without requiring special strategies or use of special parameters to compensate for the size of the cutting tool. Curves, holes and more complex shapes are easier and more accurately reproduced with 3D printing. Printers do not require burs. The nature of the printing itself gives excellent detail without the constraints of the size of the smallest bur. There is nothing to break or change. Printing reproduces the object to be printed exactly as designed without waste.
Multiple parts can be printed at the same time. It is easy to learn and operate. It requires very little training time therefore the idea of incorporation of 3D printing or rapid prototyping for implant abutment seems too lucrative.

But since this is a fairly new technology in dentistry there seems to be a lack of research on the subject to prove the efficacy and benefits in implant abutments or framework. Also no study was found that actually compared the CAD/CAM technology to rapid prototyping (3D printing) to demonstrate the superiority of one technique over the other. With the advancements in the digital field the manufacturers tend to showcase their product as being the best and aim to market it but as researchers we should try to identify which technology is better and more user friendly with superior results in terms of accuracy and clinical fit.

Therefore the aim of the project will be to compare the CAD/CAM technology with rapid prototyping and perform further tests on the printed and milled specimens to check the accuracy and durability of the implant framework.

AIM:

• To compare and analogize the use of CAD/CAM with 3D printing (rapid prototyping)

• To find out which digital technology yields a more accurate and stable implant framework which is durable enough to withstand the in vitro testing.

• To provide a recommendation for future researchers and clinicians about the efficacy of the two systems.

OBJECTIVE:

1. To investigate the methods to produce metallic implant framework for implants using CAD/CAM and rapid prototyping.

2.  To identify and measure the vertical misfit at the implant framework interface using a scanning electron microscope for both the groups.

3. To evaluate the mechanical properties of final products using a universal testing machine.

4. To evaluate and compare the accuracy of fit of the products.

5- To identify and calculate the degree of distortion of the frameworks.

6- To evaluate the effect of natural and artificial weathering conditions on the products.

7. To evaluate the microbial contamination of the implant framework based on the process of production.

STATEMENT OF PROBLEM:

Computer aided manufacturing continues to undergo significant and regular improvements and it is highly possible that it will be highly acceptable in dentistry pretty soon however with the recent advances in the manufacturing component there are other options for additive manufacturing such as the 3D printer. No such study was found that actually compared the two methods of fabrication with each other and performed different tests on the product. Therefore this study shall be one of the very few to actually compare the implant framework formed by CAD/CAM and 3D printing and evaluate them.

MATERIALS AND METHOD:

The study will be divided into 3 parts the first part being the production of the implant framework, the second part will be the mechanical testing and the third part will deal with the prognosis or biological aspects of the implant framework.

 

1. Production:

In the first phase a master edentulous model with 3 implants at the position of mandibular second premolar, first molar and second molar will be used. Multiunit abutments will be secured to the model and will be digitally scanned.

Twelve frameworks will be evaluated in this study. Six frameworks will be fabricated with cobalt chromium for the CAD/CAM fabrication group and six frameworks will be fabricated with cobalt chromium for the 3D printing group.

Three external hexagon implants with regular platform (4.1 mm diameter x 9mm bone depth) implants will be inserted in an aluminum matrix. The implants will be positioned in the region of the left mandibular second premolar (implant A), first molar (implant B) and second molar (implant C). Three direct copings will be used for implant impression in the matrix.  A medium body polyether impression will be taken to get a working cast. Three abutments will be attached to the analogues and the frame work will be milled using CAD/CAM (17). The same process will be repeated for the other group but the framework will be produced using 3D printing. Everything else apart from the mode of production will be kept same so as to standardize the study.

2. Accuracy of Fit:

After the two sets of implant frameworks are produced they will be checked for precision of fit using a scanning electron microscope. The values will be measured from both the groups and an average will be taken for each group so as to standardize the result. Therefore for the CAD/CAM group a total of 6 values will be available which will be averaged and same goes for the 3D printing group.

3. Mechanical Testing:

A total of 12 implant supported frameworks will be fabricated between the two groups, 06 by means of CAD/CAM and 06 by means of 3D printing. These will be cyclically loaded under three different loading conditions; anterior region, unilaterally on posterior cantilever and bilaterally on posterior cantilever. A cyclical load of 200N will be applied to each framework for 200,000 cycles. The abutment and framework will be returned to the definitive casts for measurements. Linear measurements of the gap between the prosthetic cylinder and implant supported abutments at 04 predetermined reference points will be made. The cycled abutments will be replaced with as- manufactured abutments and the gaps will be measured at the same reference points (41).

Data will be collected and analyzed.

 

4. Biological Considerations:

Identification of microorganisms inhabiting the peri implant crevices and internal parts  of implants  have been of relevance  an importance  with respect to the success pf of the dental implants, as several studies  have shown a correlation between bacterial and candidal infiltration and failure of implants (42).

Staphylococcus aureus identified with Grams stain and biochemical reactions (catalase and coagulase tests) will be used for this study. A bacterial suspension will  be prepared by cultivating S.aureaus in brain heart infusion (BHI) broth and incubating for 24hours at 37C. Thereafter the suspension will be diluted in nutrient broth to obtain a density of 0.5 mc farlands standards (1 x 10⁸   colony forming units per milliliter).

The implant frameworks  will be immersed in sterile beakers containing BHI for 30s to determine whether there was any external contamination. The beakers will be incubated at 37C for 14 days.

After 14 days the specimen will be removed  and immersed in 70% alcohol for 3min to prevent external contamination and dried with sterile gauze. The inner surface of the specimen  will be sampled with sterile paper points for bacterial contamination. The paper points  will then be immersed in test tubes containing BHI from the broth culture will be done on blood agar plates and incubated at 37C for 24 hours. thereafter the resulting colonies will be identified and stain and biochemical reaction (43).

PROPOSED TIME LINE:

It is hoped and anticipated that the entire research component should be done within the first two years of the tenure leaving the last year free to write down the thesis and also to take into account any delays.

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