Guidelines for fiber reinforced resin composite
Grossly destructed posterior vital teeth can be restored with resin composite reinforced with fiber. The following guidelines can be kept in mind while doing such restorations.
Resin composite restorations reinforced with fiber are indicated for grossly destructed posterior vital tooth. This restorative technique is very useful to preserve the vitality of the grossly destructed tooth structure and to act as holding restorations. However there are no protocols or guidelines present in the existing literature for doing such restoration. It is assumed that the reader is already aware of the technique and guidelines to do such technique are discussed in this article.
The operator can either use glass fiber (Splint-it : Jeneric-pentron co.,/Interlig: angelus co.,/Vectris: ivoclor co.,) or polyethylene (Ribbond: ribbond co.,). The fibers are available in unidirectional or braided or woven. Fibers are included in the restorations to increase the resistance form which will allow the restorations to withstand high occlusal forces. The retention for these restorations is achieved by the bonding agents only. If additional retention is required then additional pins can be used.
The following brief guidelines will help the clinician to do such restorations in their day to day practice.
Type of fiber:
Literature states that reinforcement with glass fiber provides better improvement in physical properties than polyethylene. But the manipulation of glass fiber is very difficult and it cannot be adapted well to the different contours of the cavity preparations. On the other hand, ribbond can adapt easily and save considerable chair time. It also leads to predictable restorations. While ribbond is preferable overall, glass fibers can be effectively used in small pieces for discontinuous reinforcement.
Fibers are available in unidirectional, braided or woven. The direction of the fiber dictates the direction of reinforcement. Maximum reinforcement is obtained in the direction parallel to the fiber direction. Since restorations are subjected to occlusal stress from different directions, unidirectional fiber will not be suitable. Braided or woven fibers which can resist multi directional forces will be a good choice for chair side reinforcement -restorative technique.
Pre-impregnation of fibers with resin is very useful for laboratory reinforcement. For restorative procedure, which requires chair side manipulation, impregnation of fiber with unfilled resin (older generation bonding agent) gives the best results.
Layer of reinforcement:
Fiber can be reinforced on tension side or compression side or on neutral zone. In cavity preparations, the area near the gingival third forms the tension and the area near the occlusal surface forms the compression side. The middle zone in between is the neutral zone. Placing the fiber in neutral zone does not seem to increase the physical properties of the restorations. Earlier studies indicated that tension zone reinforcement gives the maximum strength; while the present evidence states that the compression zone reinforcement is more effective that the tension zone. Reinforcement of restorations can be done with one layer of fiber or two layers of fiber. More than two layers will compromise the biological form.
Uni-layer reinforcement with one layer of fiber can be done for cavity of depth within 3mm. Since there has to be at least 1-1.5mm of composite restorative material over the fiber, the uni- layer reinforcement can be best placed on the tension zone only.
Bi-layer reinforcement with two layers of fiber is done for cavity depth of 4-5mm. one fiber can be placed on the tension zone and one can be placed on the compression zone.
Width of the fiber:
Fibers are usually available in 2mm, 3mm and 4mm. For most of the restorative reinforcement 2mm of fiber should be ideal for all cavities. Reinforcement of pulp chamber in endodontic treated tooth for post endodontic restoration will require 3-4mm width fiber.
Direction of reinforcement:
Fibers can be placed horizontally, obliquely or circumferentially. Vertical placement is not done as oblique placement is more advantages than vertical placement. The reinforcement can be made in small pieces of fiber in specific area and can be called as “discontinuous reinforcement” or can be placed continuously along the lost structure and can be termed as “continuous reinforcement”.
1. Horizontal placement (mesio-distally/bucco-lingually)
• Usually placed as part of the bi-layer reinforcement.
•Discontinuous reinforcement in different directions across the lost cusps or marginal ridge.
•Wide proximal box reinforcement.
•Along the direction of oblique ridge (maxillary) for reinforcement of lost oblique ridge.
2. Oblique placement (cervico-occlusally)
• Reinforcement of cusps.
•Reinforcement of wide proximal box.
•Reinforcement of wide buccal or palatal extention.
3. Circumferential placement (cervico-occlusally)
• Ideal for reinforcement of pulp chamber.
•Continuous reinforcement along the lost cusp and marginal ridge in deep dentinal cavities.
The suggested guidelines can be improvised and incorporated during the restorative procedure of fiber reinforced restorations. The reader is encouraged for further reading for mastering the technique.
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