Doctoral thesis by DMD MSc Scott R. Dyer, April 22, 2005:

Fibre-reinforced composite bridges stronger than conventional porcelain fused to metal bridges

The academic dissertation of DMD MSc Scott R. Dyer’s doctoral thesis* on fibre-reinforced composite bridges’ (FRC) mechanical properties of the composite and load bearing capacity of the prosthesis was held on April 22, 2005 in Turku, Finland. The doctoral thesis points out the strength characteristics of FRC bridges as compared to conventional porcelain fused to metal (PFM) bridges. According to the study results FRC bridges can be made as strong as PFM bridges. It is to note that everStick® fibre reinforced composite (Stick Tech Ltd) as a material proved to be stronger than PFM.

"When we surveyed all the available FRC systems for dental use, we found that the Stick system yielded the highest performing composite. I think this is due to the reinforcement and unique matrix polymers. The everStick system was stronger than the conventional ceramic-metal structure that dentistry considers to be the ultimate standard", Scott R. Dyer said.

"We found that the Stick (and especially everStick) system allowed for a highly designable composite structure. This will be important for present and future applications. One emerging and important application is the use of this FRC system for fabricating definitive prostheses in situ. For some clinical situations, we can make crowns and bridges with the everStick system without significant tooth reduction. This represents a potentially significant advancement in prosthetic dentistry", Scott R. Dyer continued.

The study evaluated fiber-reinforcement composite design in sizes and modalities useful in dentistry, with particular emphasis on the fixed partial denture (FPD). The study results on fiber-reinforced composites’ strength highlight the usability of this material in bridges as compared to conventional PFM bridges that have existed in dentisty for over 30 years. The three fixed partial denture experiments indicated the great significance of the FRC structure when evaluating the failure performance of the bridge.

In the first experiment(1) bridges with varying fibre substructure amounts were evaluated (0%, 18 %, 43 %, 66 %). The load to IF indicated that earlier fracture was evident in the unidirectional R-glass system than in E-glass systems. Another study (4)was completed comparing the usefulness of changing tooth abutment design, allowing for addition of an interproximal box in the FPD. The measurements of load to initial failure showed that the addition of interproximal boxes rated the fiber-reinforced composite bridges in a load range that was not significantly different than PFM. One unidirectional E-glass group had significantly higher load to IF than PFM specimens. In the fifth study5 directly fabricated bridges were constructed with different retainer designs. The control, a full crown preparation, did not fracture earlier than two of the experimental groups requiring less tooth preparation.

everStickC&B fibre reinforced bridges resisted breakage much better than the others

In one of the studies(4) everStickC&B fiber-reinforced IPN-bondable laboratory-made Gradia-composite bridges were compared to other fiber-reinforced composite bridges. According to the results the everStickC&B fiber-reinforced Gradia bridge resisted breakage statistically significantly better than the other fiber-reinforced composite bridges. Another study(5) revealed that everStickC&B surface retained fiber-reinforced bridges endure mechanical stress as well as conventionally manufactured bridges.

Scott R. Dyer employed the principles of composite design used in engineering in his doctoral studies to understand the fracturing mechanism and to reinforcing structures. "A fiber-reinforcing frame for bearing the load of a bridge need to be designed and manufactured to optimum measures. The correct measurements of the bridge structure and placement of load bearing components are crucial factors for a sound bridge – whether used in dentistry or in highway bridge construction", Scott R. Dyer says.

The results of this doctoral thesis will surely increase the interest toward fiber-reinforced prosthodontics among clinicians and material researchers," said professor Bengt Öwall from the University of Copenhagen, Denmark, the opponent for Scott R. Dyer’s dissertation.

Dr. Scott R. Dyer is an Assistant Professor at Oregon Health & Science University in the Department of Restorative Dentistry in the divisions of Biomaterials and Biomechanics, and Prosthodontics. He received his DMD from Oregon Health & Science University and a Certificate in Prosthodontics with a Master's of Science from the University of Texas Health Science Center at San Antonio.

* Scott R. Dyer. Fiber-reinforced composite fixed partial denture design: Mechanical properties of the composite and load bearing capacity. Annales Universitatis Turkuensis, Ser.D Tom. 651, ISBN 951-29-2845-0, ISSN 0355-9483. Painosalama Oy, Turku, 2005.

Publications:
1)Scott R. Dyer, Johan A.Sorensen, Lippo VJ Lassila, Pekka K.Vallittu: Damage mechanics and load facture of fiber-reinforced composite fixed partial dentures. Accepted Dental Materials, March 2005.

2)Scott R. Dyer, Lippo VJ Lassila, Mikko Jokinen, Pekka K.Vallittu: Effect of fiber position and orientation on fracture load of fiber-reinforced composite. Dental Materials (2004) 20; 947-955.

3)Scott R. Dyer, Lippo VJ Lassila, Mikko Jokinen, Pekka K.Vallittu: Modulus of elasticity and toughness of fiber-reinforced composite. Accepted Journal of Prosthetic Dentistry, July 2004.

4)In vitro static strength of porcelain-fused-to-metal and fiber-reinforced composite fixed partial dentures. Submitted to Journal of Prosthodontics, March 2005.

5)Scott R. Dyer, Lippo VJ Lassila, Mikko Jokinen, Pekka K.Vallittu:Static strength of molar region direct technique glass fibre-reinforced composite fixed partial dentures. Journal of Oral Rehabilitation 2005 32; 351-357.

Further information:
Scott R. Dyer, dyers(@)ohsu.edu (Please note: write e-mail address without the parenthesis)
Oregon Health Sciences University