Stainless Steel Reinforced Resin Retained Bridges

Provisional restorations are an important and desirable restoration in today’s practice. The advent of implant dentistry, total mouth cosmetic restorations, increased tooth life due to periodontal therapy advances, and the public’s demand for cost-effective restorative alternatives all place the provisional prosthesis in the forefront of the modern dental practice.

Every practitioner has faced the situation where an effective provisional prosthesis would make the difference in the long-term scheme of treatment. In addition, certain patients, such as the medically compromised or those with financial concerns, may require an alternative treatment to conventional fixed bridges or implant-retained restorations. The design of a provisional prosthesis must consider the following requirements:

(1) Minimal invasiveness. Any provisional restoration must be capable of change or modification. The treatment plan is ongoing, and change is often indicated in the long term. Minimal invasiveness allows this to take place with relative ease.

(2) Durability and serviceability. Any provisional restoration must be durable enough to withstand the functional forces of the dentition being treated. It must also be easily repairable, especially when long-term applications are considered. 

(3) Aesthetics. With reasonable aesthetics, patient acceptance and compliance are assured.
These factors, coupled with a prefabricated universal design, can give the practitioner a distinct advantage in executing long-term treatment plans and treating medically compromised or financially challenged patients.

Stainless steel reinforced resin retained fixed bridge techniques take advantage of several physical and biological principles to provide a lasting fixed provisional prosthesis. To understand the use of this technique one must understand the histological and physical principles at work in the contact areas of teeth. The density per unit area of enamel rods is largest in the contact areas.1 The dentin-enamel interfaces in these areas also show a convergence angle of less than 45º. This convergence angle provides a greater resistance to compression mathematically than convergence angles of higher values.2 These two histological factors give the areas approximating the contact point the strongest dentin-enamel etched bond.

The mechanical design of the reinforcing steel is the second factor in the success of the steel reinforced bonded bridge (Figures 1 and 2). A double axis of rotation provides a better resistance than a single axis of rotation. Components designed with a double axis of rotation not only have greater resistance to rotation and dislodgment, but also have greater surface area for bond adhesion. Studies show that this system has a resis­tance of 1,200 psi.3 Load testing of “split wing” or double axis metal components demonstrated failure at the pontic facing, but not at the attachment point. This demonstrates the strength of the attachment bond.

 

Figure 1. The stainless steel component of the reinforced resin retained fixed bridge. Figure 2. The mechanical design of the reinforcing steel component.
Figure 3. The zone of attachment, which is the placement for the steel component.

The preparations are standard class III preparations. Their placement is in the zone of attachment.4 The zone of attachment is described in Figure 3. It is determined by statistical analysis of surveyed patient models. The preps should be placed as close to the axial height of contour of the tooth as possible. Their width should be at least 2 mm and deep enough to incorporate the steel component. Survey studies reveal that the difference between the axial height of contours of anterior teeth is 2 mm. This measurement is what is used to determine the width of the double axis retention wing. Furthermore, stainless steel when freshly micro-etched increases bond adhesion. This further adds to the strength of the total restoration.

THE DIRECT EASTFLEX BRIDGE TECHNIQUE
The technique for fabricating a stainless steel reinforced resin bridge utilizes Eastflex bridge components. These components allow the fabrication and placement of single pontic bridges without the need for laboratory support. When the procedure is followed, a durable fixed prosthesis can be fabricated that can withstand a minimum of 1,200 psi. Armamentarium consists of the Eastflex bridge component selected to fit the space; appropriate handpiece(s) and bur(s) for tooth preparation; 35% phosphoric acid etchant gel; bonding agent and composite resin; curing light if light-cured resin is used; and suitable plastiform crown contoured to fit the space.

Figure 4. Make the necessary cavity and tooth preparations to receive the steel component. Figure 5. Prepare the space of the missing tooth.
Figure 6. Contour and fit the steel component into the prepared space.

Figures 7 and 8. Prepare the plastiform crown.

Figures 9 and 10. Invest the crown form and place it onto the space making sure it is also completely invested to the supporting steel component.
Figure 11. Final restoration has been finished with appropriate composite finishing equipment.

The technique consists of the following steps:


(1) Examine the patient’s dentition and prepare the teeth to accept the Eastflex component (Figures 4 and 5). 

(2) Contour and fit the component into the prepared space (Figure 6).

(3) Prepare the plastiform crown (Figures 7 and 8).

(4) Bond the component into the teeth preparations. Remove excess resin from the component that will interfere with the investment of the crown form to the component.
Invest the crown form and place it onto the space, making sure it is also completely invested to the supporting component (Figures 9 and 10).

(5) Finish with appropriate composite finishing equipment (Figure 11).

 

CLINICAL RESULTS 
The author and Dr. Maris J. Lans (a practitioner in Lanham, Md) have placed 150 stainless steel reinforced resin bridges and followed them from 3 months to 5 years.5 They produced the following data: 28 posterior bridges; 57 premolar bridges; and 65 anterior bridges. The total repair rate was 8%. The breakdown was: 2 posterior repairs; 4 premolar repairs; and 6 anterior repairs. 

Stress studies performed on these bridges gave the following results6: the anterior bridges can withstand over 1,200 psi before breaking. The posterior bridges can withstand over 2,000 psi before breaking. Breakage occurred at the resin portion of the pontic. The metal component remained intact. These results are well within the average masticatory forces, which are 600 psi and 1,200 psi, respectively.7

CONCLUSION

Properly designed stainless steel micro-etched components can provide a reinforcement to resin retained bridges that rivals conventional single tooth bridge procedures. This technique is less invasive than conventional cast bridges. It is also more cost-effective than conventional bridgework and requires minimal lab work. This is a viable treatment option that the dentist can do in his/her office.

This technique will provide a tooth replacement for many patients who otherwise cannot afford a fixed procedure, or a provisional restoration during long-term treatment.

 


References

  1. Leeson, DF. History of the Oral Structures. St. Louis, Mo: Mosby; 1987:326-328. 

  2. Travis DF, Glimacher MJ. Structure and relationship of bovine enamel to dentine. J of Cell Biol. 1964;23:447.

  3. Lab Report No. a68347, 1999, RambleTest Labs Inc, Cinnaminson, NJ.

  4. Eastflex Scientific Report 1997, Eastflex Inc, Indianapolis, Ind. 

  5. Eastflex Case Files 1994-1999, Indiana­polis, Ind.

  6. Lab report No.A68347, Ramble Test Labs Inc, Cinnaminson, NJ.

  7. RG Craig. Restorative Dental Ma­terials. 7th ed. St Louis, Mo: Mosby; 1985: 61.

Dr. Purvis is a general dentist and full-time practitioner in Indianapolis, Ind. He can be contacted at (317) 545-6011.

Disclosure: Dr. Purvis is Vice President and on the Board of Directors of Eastflex Inc.



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