Technology and Prosthodontics

by Karen S. McAndrew, DMD, MS and Debra Haselton, DDS

Advancements in all areas of technology bombard us daily. These advancements have resulted in improved materials and innovations in computer technology: hardware, software, and digital imaging. It follows to reason that advancement in one area of technology will find merit and application in a variety of disciplines. Dentistry is no exception. The field of prosthodontics has embraced many new techniques and technologies to improve its ability to restore the oral health of patients to a level of precision and predictability that could not be previously achieved.

Ceramics

Dental ceramics have come a long way since their use in the early 1900s.1 Today there is a myriad of dental porcelains that can be used to simulate natural tooth structure.

Although the traditional porcelain-fused-to-metal crown continues to be used often, the veneering porcelains have evolved to allow technicians to mask the metal substrate and layer internal effects that more closely resemble dentin and enamel layers. Wear potential for these porcelains has also vastly improved, coming closer to mimicking the hardness of natural teeth. This advancement has diminished damage resulting from wear of the opposing dentition.

Contemporary ceramic and CAD/CAM

Early experiences with the porcelain jacket crown and other precursor ceramic systems such as Dicor promulgated development toward the all-ceramic crown systems in current use.1 The desire to eliminate a metal substructure to create the most favorable esthetics has been partnered with the need for strength. Research has shown that glass infiltrated alumina (In-Ceram Alumina, Vident) and high-strength, pure alumina (Procera AllCeram, Nobel Biocare) have demonstrated high flexural strength values and been clinically successful.2-5 The relationship of esthetics and strength may be best realized with the use of zirconium core, all-ceramic crowns such as those created with the Procera, In-Ceram Zirconia, Lava, or Everest systems. The zirconia-based crown can be considered when there is a desire for strength and esthetics in the posterior region, where occlusal forces can reach 522N.6 The zirconia core, while providing a tooth-colored substrate for the porcelain veneering material, is opaque enough that it can mask discolored tooth structure on cast or alloy core materials.7 Computer-design technology is now commonly used to fabricate the high-strength ceramic copings to which veneering porcelain can be applied.

CAD/CAM ceramic technology is not limited to the laboratory-fabricated restoration. The CEREC 3D system, a CAD/CAM manufacturing system for the fabrication of chairside, indirect restorations, now possesses 3-D software to assist clinicians with occlusal adjustment. Marginal adaptation of this third-generation technology has improved from precursor editions and is reported to be at 47.5 ± 19.5 μm.8

Implant therapy using CAD/CAM

CAD/CAM systems are also being used to fabricate implant restorations for partially and completely edentulous patients. Abutments for restoration of single units as well as multiple units can be custom fabricated and milled from titanium or zirconia (Procera, Nobel Biocare; and Atlantis Components Inc.). These abutments exhibit precision of fit, strength, and enhanced esthetics in the case of zirconia, making them a popular choice in dental-implant therapy.

Completely edentulous patients can also be restored using this milling technology. Implant bars can be fabricated, upon which either removable or fixed prostheses are supported (Cam StructSURE, 3i and Procera, Nobel Biocare). This one-piece, milled titanium technology is superior to casting when evaluated for ability to achieve passive fit - one of the most important attributes of a multi-implant prosthesis.9

Laser welding

Traditional connections between fixed partial denture segments have been accomplished using a compatible solder (i.e., a lower melting alloy) for the parent alloy. This brazing procedure has typically been applied using some type of air or gas torch. A newer method to create this connection is laser welding, which joins parts fabricated from the same alloy. Advantages of this method are that it is clean, fast, and precise.10

Laser welding is particularly useful for the repair of cast partial denture frameworks, which has typically been impossible to accomplish in many instances. It is also popular for the joining of segments of implant substructures, particularly when titanium is used as the alloy.

Digital tooth shade matching

Shade matching can be a significant challenge for restorative dentists. Although devices have been developed to assist with this challenge, many variables still exist in the translation and application of the data to the actual restoration. Technology such as EasyShade, combined with the use of the VITA 3D Master Tooth shade system, may help practitioners better understand hue, value, and chroma and generate a closer estimation of the shade of the natural tooth and its relationship to its imitation, the crown.11,12

Three-dimensional imaging and computer-guided, dental-implant surgery

One of the most exciting technological advances in implant dentistry is computer-aided surgery and guided-implant placement. Using conventional or computed tomography, 3-D images of the edentulous sites can be used to evaluate bone quality, quantity, and anatomic structures in concert with a desired proposed tooth position.

A virtual implant surgery then allows for planning of the exact location of implant placement dictated by the parameters of the desired prosthetic design (Nobel Guide, Nobel Biocare; and Materialise, SimPlant). The implant surgery is planned according to the co-localization of the bone and desired prosthesis. A surgical guide can also be fabricated from computer-based planned allowing for placement with the highest level of predictability and precision in conjunction with the virtually planned placement. Diminished postoperative discomfort is a result of more conservative surgical placement when the need to reflect a surgical flap has been eliminated.

Implant design and surface-texture technology coupled with precision of fit has allowed for earlier load and, in given cases, immediate load of the implant fixtures with the definitive prostheses. Through CAD/CAM milling technology and specialized abutments, the Teeth-in-an-Hour protocol (Nobel Biocare) can provide a definitive prosthesis that is delivered via an immediate load protocol at the time of implant placement.

Conclusion

It is an exciting and rapidly progressing time in dentistry and the application of technology has advanced the specialty of prosthodontics and the services rendered to patients. Current trends in technology have propagated an evolution in the art and science of dentistry resulting in direct improvements and benefits to patients.

There will be continued improvements of materials, techniques, and technology used in dentistry, especially in prosthodontics. Advancements in esthetics and computer software will also enhance all areas of dentistry.

References

1. McLean JW. Evolution of dental ceramics in the twentieth century. J Prosthet Dent 2001;85:61-66.
2. Konstantinos P, Griggs JA, Woody RD, Guillen GE, Miller AW. Fracture resistance of three all-ceramic restorative systems for posterior applications. J Prosthet Dent 2004;91:561-569.
3. Potliket, N, Chiche G, Finger IM. In vitro fracture strength of teeth restored with different all-ceramic crown systems. J Prosthet Dent 2004;92:491-495.
4. Segal BS. Retrospective assessment of 546 all-ceramic anterior and posterior crowns in a general practice. J Prosthet Dent 2001;85:544050.
5. Haselton DR, Diaz-Arnold AM, Hillis SL. Clinical assessment of high strength all-ceramic crowns. J Prosthet Dent 2000;83:396-401.
6. Bakke M, Holm B, Jensen BL, Michler L, Miller E. Unilateral, isometric bite force in 8-68 year old women and men, related to occlusal factors. Scand J Dent Res 1009;98:149-158.
7. Heffernan MJ, Aquilino SA, Diaz-Arnold AM, Haselton DR, Stanford CM, Vargas MA. Relative translucency of six all-ceramic systems. Part I: core materials. J Prosthet Dent 2002;88:4-9.
8. Ellingsen LA, Fasbinder DJ. In vitro evaluation of CAD/CAM ceramic crowns. J Dent Res 2002;81:331.
9. Brudvik JS, Chigurupati. The milled implant bar: an alternative to spark erosion. J Can Dent Assoc 2002;68:485-488.
10. Longoni S, Sartori M, Ariello F, Anzani M, Baldoni M. Passive definitive fit of bar-supported implant overdentures. Implant Dent 2006;15:129-134.
11. Baltzer A, Kaufman-Jinoian V. Shading of ceramic crowns using digital tooth shade matching devices. Int J Comput Dent 2005;8:129-152.
12. Wee AG, Kang EY, Jere D, Beck FM. Clinical color match of porcelain visual shade-matching systems. J Esthet Restor Dent 2005;17:351-357.