Strong, reliable and esthetic

March 21, 2012

Patients presenting with limited vertical space, cross bite, parafunctional habits, or especially implant supported and retained prosthetics provide challenges to dental professionals. Patients will break or fracture prosthetics, leading to a loss of faith in the restorative team as well as non-revenue time. 

Patients presenting with limited vertical space, cross bite, parafunctional habits, or especially implant supported and retained prosthetics provide challenges to dental professionals. Patients will break or fracture prosthetics, leading to a loss of faith in the restorative team as well as non-revenue time. 

The shift from teeth to implants and abutments needs to be taken into consideration. Teeth have periodontal ligament and proprioseption so patients know when they have exceeded physiological limits. Implants do not, thus today’s implant supported and retained prosthetics allow patients to generate greater destructive forces to acrylic, teeth and opposing dentition. Today’s patients are very image conscious and don’t want to see unsightly metal mesh or braided fiber in their prosthesis.

The introduction of modern reinforcement materials, such as impregnated e-glass fibers, allows the dental professional to provide a light, thin, strong, highly esthetic prosthesis. No longer does reinforcement require esthetic trade-offs or rough surfaces. Reinforcing new prosthetics using unidirectional e-glass fibers is a simple but effective way to increase both flexural strength and fatigue resistance in removable and fixed polymer prosthetics.

The three major factors of reinforcement are bonding, position/placement and direction.

The goal of dental polymer reinforcement is to stop fractures before they begin. The strongest metal, or Kevlar, will stop bullets, but because they don’t bond to dental polymers, these materials create a “sandwich” effect wherein the thin layers of polymer are actually weaker than before and do not stop the stress fractures from starting. These materials simply hold a prosthesis together after it breaks. Pre-impregnation of the fiber matrix is key and allows for covalent adhesion bonding and a successful integration of fiber and polymer.

The reinforcement should be placed on the tension side of the prosthesis, as close to the surface as possible. This strategic placement of reinforcement on the side in tension stops the fracture before it begins and increases the load to initial and final failure.

When the direction of forces or loads is known, unidirectional fibers are placed perpendicular to these forces to provide the highest tensile strength. Weaker multi-directional fibers, such as mesh, are used when the forces are parallel or unknown. Because the direction of forces on a full denture is usually known, unidirectional fiber is the best option.

The technique

In this example, eFiber is used because its unique characteristics allow for maximum strength and esthetics as well as strategic and intelligent placement. eFiber is a BIS-GMA and PMMA impregnated e-glass fiber that bonds to all acrylics and composites. The material is translucent, easy to grind, adjust and polish, and easy to handle with no special tools required.

01 The technique to reinforce a new denture is very simple. Grooves are cut in the ridgelap of the acrylic or composite denture teeth to receive the fiber reinforcement.

02 eFiber is bonded to the denture teeth. Bonding the fiber to the acrylic or composite denture teeth places the fiber in the proven optimal position-the tension side of the prosthesis-at the junction of denture teeth and acrylic. eFiber is impregnated with both BIS-GMA and PMMA and will therefore bond with any acrylic or composite denture tooth. A secondary benefit of bonding the fiber to the denture teeth is increasing the bond strength of the denture base resin to the bonded denture teeth. The PMMA in eFiber allows for great bond strength with denture base resin. Another benefit of bonding eFiber to the denture teeth is splinting the denture teeth together for increased denture tooth retention.

03 The grooves in the denture teeth may be cut during denture tooth setup (preferred), or after the denture is invested, boiled out and wax is removed.

04 For traditional dentures, preparing the six anterior teeth for reinforcement is recommended because most fractures occur in the midline area. The reinforcement grooves should be extended to the posterior teeth for removable dentures with posterior attachments, for all fixed detachable cases, or when maximum strength is indicated (Fig. A). Ideally, the groove should be cut so the eFiber 1.6 mm may be fully placed inside the contours of the denture tooth (Fig. B).

05 Place one continuous piece of wax rope or dental floss into the grooves in the teeth to measure the length of eFiber needed. Remove the fiber from the protective foil, and cut a length of the eFiber and clear silicone matrix. Protect the fiber from the light.

06 After investment and wax removal, and the grooves are in the denture teeth, paint eFiber bonding agent on the bonding surfaces of the denture teeth. Wait for the bonding to dry (Fig. C).

07 Prior to curing, eFiber is very flexible and pliable (Fig. D). It’s easy to adapt eFiber to accommodate each individual patient’s arch. Start with the most posterior tooth, and press the fiber into the groove in the denture tooth. The clear silicone matrix may be used to hold the fiber in place when curing. Use a hand-held light to quickly (3-5 seconds) bond the fiber to each tooth. A wax spatula or eFiber Stepper tool is used to protect the uncured fiber from prematurely curing (Fig. E).

08 If multiple pieces of eFiber are needed, gently overlap the two sections and press together before curing. Take care to have one continuous piece of eFiber in the midline/incisal notch area.

09 If Perma Mesh hoods are indicated to reinforce any attachment areas, bond the cured Mesh hoods to the eFiber at this time (Fig. F). Alternatively, Perma Mesh may be placed in the two tension areas of the (anterior and posterior) palate at this time as well.

10 Once the fiber has been initially bonded to all the teeth, fully cure the fiber, either with a hand held light or curing unit.

11 Proceed with normal acrylic processing procedure of choice.

The result

The final result is an extremely strong, esthetic patient pleasing prosthesis.

About the author

Chris Bormes graduated from Gonzaga University prior to attending the Dental Laboratory Technology program at City College of San Francisco. Chris has earned both ICOI Fellowship and Mastership in Dental Technology; graduated from both Ticonium’s and BEGO’s Partial Denture Programs; is a candidate for CDT in Complete Dentures; and wrote the PREAT Corporation Technical Manual. Chris joined PREAT Corporation in 1997 and was named President in 2010.