The Role of CAD-CAM Technology in Implant-Retained Prosthodontics - Research Paper Example

The Role of CAD-CAM Technology in Implant-Retained Prosthodontics Introduction Osseointegrated dental implants are now widely accepted. They have been used as a means of supporting and retaining mandibular overdentures. Conventionally, radiographic methods were in use. Detection of changes in the distal alveolar residual ridges of the implants that are contained by the edentulous mandible are critical when implant-retained overdentures are used. This is an important area of clinical and operative dentistry since research and experience have shown that these increase satisfaction and really improve the quality live of the individuals who are edentulous (Blum and McCord, 2004). Naert et al. (2004) have indicated that these are preferred in terms of speech, stability, and function. These usually utilise the principles of CAD-CAM technologies, which employ computer-assisted design and computer-assisted machining. These have been reported to have received considerable research and clinical interest from modern dental practice. The idea of using these technologies it to produce lifelike restoration of natural dentition with consistent esthetic outputs (Naert et al., 2004). Consequently, these techniques have been welcome by the orthodontists and the patients. The CAD/CAM system may be used in different steps of implant retained dentistry such as fabrication of crowns, bridges, and telescope dentures (Sun et al., 2006). From the clinical and technological standpoints, the passivity of fit of the implant prosthesis is the most important consideration. This is an important parameter for intraoral osseointegrated and functional fixtures. Traditionally, these had been accomplished with clinical procedures and methods utilised in laboratory fabrication in both fixed and removable partial dentures used in prosthodontics. The impression making, master cast, resin verification, and other stages such as investing, casting, veneering, and finishing all potentially may lead to distortion and hence prevent passivity of fit (Raigrodski, 2003). The techniques of optical digitalisation and use of CAD-CAM technologies may bypass these stages, and as alternative strategies, they may really achieve the intended passivity of fit. If the goal is to achieve clinical logevity of the prosthesis, CAD-CAM may confer a most minimum level of distortion and acceptable level of associated stress in comparison to the other techniques. There is a growing body of literature that deals with the accuracy of these procedures with the utilisation of CAD-CAM technologies (Tan, 1995). This indicates that production stages in dental technologies are in the process of undergoing a change towards automation. This is currently recognised to be a major method in treatment planning and therapy. This has financial implications in terms of cost of therapy. These advanced computer-assisted technologies may now enable cost-effective production of individual implant pieces and are being increasingly used in dental practice. Beuer et al. (2008) have referred these to be digital dentistry and have delineated the steps which may be successfully accomplished through CAD-CAM technologies. They have highlighted the benefits of these technologies, which are "access to" defect-free "industrially prefabricated and controlled materials" with enhancement of quality and reproducibility. This definitely improves precision and planning leading ultimately to increase in efficiency of the implants and the operators. The most important benefit perhaps is data storage which comply with chain of production which can be easily standardised. These point to the necessity of an overview of the knowledge related to these CAD-CAM technologies and related available systems, since in future dentists or orthodontists will be exposed to these with increasing frequencies. This enhanced knowledge would benefit the dentists by opening areas of potentially new procedures. There is a need for updating the knowledge since continual improvement and development of computer software and hardware would lead to new treatment concepts through technological advancement (Beuer et al. 2008). Therefore, this review may be considered as a futuristic knowledge investment on the parts of dental professionals working in this area of practice. The internal as well as marginal fit is important quality indicators of fixed restorations. Many clinical trials indicated that clinical success of these restorations is related to marginal accuracy. Examinations that dealt with fit of the crowns derivatives of marginal accuracies. However, the internal fit is indicated by the measurements of sectioned teeth. A three-dimensional method of mapping of the crown fit was introduced by Kelly et al. This method is a noninvasive optical technique. However, a 3-D analysis of higher resolution would necessitate in this technique digital data acquisition. This can be accomplished through the CAD technique. The evolution of CAD/CAM systems for the production of machined inlays, onlays, veneers, and crowns led to the development of a new generation of ceramics that are machinable. The major advantage of this technology is cost-effective production of individual prosthetic pieces. These are accomplished through computer assistance of CAD-CAM procedures, in the practice, laboratories, or manufacturing centres. This is very possible to be compliant with laboratory work, which currently is a major way to determine treatment planning and strategy. The Cerec system is available for use for several years. Currently improved Cerec 2 system has been introduced. This equipment comprises of a computer integrated imaging followed by milling system. Consequently this is capable of designing restorations on the computer screen. The modern versions of this CAD-CAM system utilises a chairside application for restorative dentistry. The initial versions could fabricate inlays and onlays; however, modern versions are far too advanced leading to significant improvements in restorative capabilities, so the most contemporary Cerec 3 system has the advantage of fabrication of inlays, onlays, and posterior crown. Additionally, these can also fabricate anterior crown and veneers. Wittneben et al. (2009) in their systemic review determined the long-term clinical survival rates of single tooth restorations that were fabricated with CAD-CAM technology. They found that the results and failure rates of these restorations were comparable to the conventional ones. However, despite these apparent usage and success rates, there had been a number of Cerec related concerns and limitations on the parts of the dentists. As indicated in Fasbinder (2006), there were obvious concerns related to adaptation and marginal fit, when these were accomplished through the CAM processes in milled restorations. There were also issues related to clinical longevity, durability, and fracture resistance since in the Cerec systems, the ceramic materials were cemented adhesively (Fasbinder 2006). Despite appreciable success, there were limitations of results in the Cerec systems. The two important limitations were poor marginal fit of the restorations and the lack of sophistications in the machining of the occlusal surface. In the current versions, the marginal adaptations have been improved, and there are provisions for shaping the occlusal anatomy. Most of the providers now claim guaranteed precisions and reliability of their systems. These systems use state of the art CAD-CAM technologies. At present different metallic and ceramic abutments are used. Currently there has been use of zirconium dioxide as the material for implant abutment. This has outstanding fracture toughness and esthetics. Despite these, there are certain technical hurdles in this since it is difficult to achieve these faultlessly in the laboratory. Many providers offer services to facilitate these aspects, and in this way in practice, the orthodontists may get precise processing eliminating surface cracks and breakage through the use of CAD-CAM technologies. This also obviates wax modeling, casting, and grindings. Along with the provision of considerable time saving, as evident the failure risks are also eliminated. The stored data in the computer also facilitates reproducibility as the earliest with significant rapidity. From this discussion, the benefits of CAD-CAM are evident. Fabrication for dental restoration by CAD-CAM has distinct advantage since they can circumvent waxing, firing, casting, and occlusal adjustment on the articulator. Most of these systems use as indicated by Yoshida et al. (2001) complex imaging technologies and computer designs. At the outset, these were used for fabrication of full crowns. In some systems such as DentiCAD systems, crown fabrication is accomplished with a pen digitiser. This allows intraoral digitisation of the preparation. Although most systems had versions for chairside designing, the current trend is that of laboratory support. One of the greatest advantages of CAD/CAM systems is copy milling, which can produce inlays with identical types of materials used in CAD/CAM systems. One of the examples is Procera system designed to create titanium crowns through use of copy milling and Spark erosion technologies, intended primarily for milling restorations of implant systems. The advantages of the Cerec systems are ability to perform a three-dimensional cavity scanning, and with the CAD-CAM system, the data can be transformed immediately. The subsequent three-axial milling can be integrated into the mobile unit. In contrast to the other milling systems mentioned above, the main disadvantage of this system is requirement of inlays, onlays, and veneers. However, this appears to be miniscule when the comparable advantage of ability to design and fabricate a chairside ceramic restoration in a single appointment. Studies have indicated minimal detectable marginal cement loss, the long-term outcome in terms of clinical appearance and marginal integrity of Cerec inlays and onlays are excellent (Yoshida et al. 2001). The more advanced systems in the recent times also used CAD-CAM systems through the use of more sophisticated 5-dimensional noncontacting laser sensors with the facility of free and easy designs of restorations. Despite these advantages, these indirectly fabricated restorations have problems with marginal exposure. This is one of the disadvantages of these systems. It is considered that with these technologies, the weakest part of the restorations is the marginally exposed resin luting agent layer. As an alternative and as a solution to this problem, the provision of indirect resin composites and porcelain with silane coupling agents was made in such systems with the thought that these would improve the bond strength between the cured resin composite or porcelain and the resin luting agent. This led to changes in the systems in the recently developed CAD/CAM composites where cementing is done using a resin luting agent. However, despite wide usage, the use of prefabricated systems in the CAD-CAM techniques has been criticised. This system uses prefabricated ceramic blocks which are adhesively luted with resin composite cements, and usually dual cured composites are in use. A number of clinical trials have evaluated these systems. However, the basis of the criticism is the finding from in vitro studies that curing of light and dual-cured resin composite cements and their durabilities are time dependent, making them unsuitable for a chairside process. Moreover, the intensity of the light source is another important parameter. The other factors dictating the durability of the implant are the thickness and shade of the ceramic. These all lead to a lower conversion rate in the resin composite luting agents, and these may reduce the durability of the ceramic agents. It is evident that risk of failures in dental restorations increase with time. Therefore, the studies which investigate the 10-year results would be a better method to investigate the long-term durability. Despite these advantages, literature has demonstrated deficits in these systems which may be termed as disadvantages. It has been reported that some patients suffer intermittent postoperative symptoms that are related to endodontic problems. Fractured inlays are also reported in relation to luting with dual-cured resin composite cement, although there had been no demonstrated fault in the cavity design. Although these postoperative symptoms were related to region of inlays cemented with dual-cured luting agents, there were no problems related to occlusal stress or temperature changes. In some cases, inlays luted with dual-cured resin cement or chemically cured resin, both demonstrated minor marginal fracture or fracture of the marginal ridge. Despite these and exposure of the dentin, their functions remained well even after 10 years. These inlays did never demonstrate caries, although 24% patients were at risk of caries. It was demonstrated that at 10 years, survival rate was in the range of 89%. The use of dual-cured resin-composite luted inlays had a 77% survival as opposed to chemically cured resin-composite luted inlays. However, in these systems there are certain design issues that may not be in conformity to the required standards. The fit and/or congruence of the of the inner surface of the restorative material coping and the corresponding surface of the prepared tooth had been an issue with all CAD-CAM systems. In this regard the problem is interface discrepancy or gap, which can be internal and/or marginal. Internal discrepancy is defined as the misfit of the coping at the occlusal or incisional and axial surfaces. In contrast, marginal discrepancy is said to exist in the vertical dimension from the finish line of the preparation to the cervical margin of the restoration. Problems with crown restorations may lead to such problems even with CAD-CAM systems, if the crowns are too short and the seating of the crowns are too short. On the other hand of the crowns are too wide, these may also lead to marginal gaps through horizontal discrepancy perpendicular to the axis of the restored tooth. Postoperative sensitivity has been reported following these restorations, which ranged from immediate to remote. Most of these cases resolve within three months, and only a few persisted beyond that, needing endodontic treatments. The ideas of these treatments were to complete in a single appointment. These sensitivities were reported to be related to premature occlusal contact, and legitimately, these sensitivities would be related to occlusal interferences, and hence would need an after treatment for equilibration of these occlusal contacts. With the development of better adhesive material and luting techniques, recent reports indicate less post restoration of sensitivity. In the chairside CAD/CAM restorations, careful isolation is used to accomplish optical imaging of the preparation, thus ensuring isolated cavity for adhesive cementation, ensuring the maximized predictability of adhesive luting. A single sitting restoration also prevents sensitivity due to less likelihood of tooth contamination during the phase of temporisation due to fracture or loss of the temporary restoration or contamination or leakage under the temporary cement. The main disadvantage had been restoration fractures. Most occur through the occlusal isthmus. This occurs due to less thickness of the ceramic. Porcelain fractures were reported to be the most common mechanism of failures of some inlays. Although fractures have been reported, the fracture rates were low. The consistent reports of low failure rates and restoration fracture rates in CAD-CAM Cerec restorations make them preferable in clinical practice. Conclusion The main disadvantage had been restoration fractures. Most occur through the occlusal isthmus. This occurs due to less thickness of the ceramic. Porcelain fractures were reported to be the most common mechanism of failures of some inlays. Although fractures have been reported, the fracture rates were low. The consistent reports of low failure rates and restoration fracture rates in CAD-CAM Cerec restorations make them preferable in clinical practice. The primary purpose in recommending an all ceramic restoration is to achieve the best possible esthetic result. Typically this will be at the risk of reduced restoration longevity due to the potential for fracture of the ceramic, and the restoration may have a slightly inferior marginal adaptation than a metal-ceramic crown. Most hazards of restoration failure will be removed if these restorations are confined to lower-stress anterior teeth, and patients are carefully evaluated for evidence of para-functional activity. A knowledge of the available ceramic systems is needed to select a material that will provide the best esthetics for a particular patient. This is especially important when matching a single maxillary incisor to an adjacent tooth. Careful consideration should also be given to the availability of laboratory support, because no dental laboratory invests in the expensive equipment needed for all the various systems. The marginal adaptation of the system is very important, even when resin bonding is used. When selecting a system, the dentist should carefully evaluate the internal and marginal adaptation using an elastomeric detection paste. One concern with ceramic restorations is the potential for abrasion of the opposing enamel, particularly in patients with parafunctional habits. Whenever possible, a low-abrasion material should be considered. References Beuer, F., Schweiger, J., and Edelhoff, D., (2008). Digital dentistry: an overview of recent developments for CAD/CAM generated restorations. Br Dent J; 204(9): 505-11. Blum, IR. and McCord, JF., (2004). A clinical investigation of the morphological changes in the posterior mandible when implant-retained overdentures are used. Clin Oral Implants Res; 15(6): 700-8. Fasbinder, DJ., (2006). Clinical performance of chairside CAD/CAM restorations. J Am Dent Assoc: 137, 1; 22S-31S Naert, I., Alsaadi, G., Quirynen, M., (2004). Prosthetic aspects and patient satisfaction with two-implant-retained mandibular overdentures: a 10-year randomized clinical study. Int J Prosthodont 17:401-410. Raigrodski, AJ., (2003). Clinical and laboratory considerations for the use of CAD/CAM Y-TZP-based restorations. Pract Proced Aesthet Dent; 15(6): 469-76 Sun, F., Zhang, GR., Zhang, F., Liu, F., Mao, H., Huang, L., and Wang, PF., (2006). The use of CAD/CAM system with zirconia in modern prosthodontics. Shanghai Kou Qiang Yi Xue; 15(4): 337-44. Tan, KB., (1995). The clinical significance of distortion in implant prosthodontics: is there such a thing as passive fit? Ann Acad Med Singapore; 24(1): 138-57. Wittneben, JG., Wright, TF., Weber, HP., and Gallucci, GO., (2009). A systematic review of the clinical performance of CAD/CAM single-tooth restorations. Int J Prosthodont; 22(5): 466-71. Yoshida, K., Kamada, K., and Atsuta, M., (2001). Effects of two silane coupling agents, a bonding agent, and thermal cycling on the bond strength of a CAD/CAM composite material cemented with two resin luting agents. J Prosthet Dent; 85(2): 184-9. Read More