Many restorative procedures are limited by the relatively low fracture toughness of composite resins. Improving the fracture strength of these materials enables dentists to provide their patients with a possible alternative to indirect restorations that inevitably require further tissue preparation and tooth loss. Fibre reinforcing of composite resins is not a new idea and several dental manufacturers offer these materials for a range of procedures to extend the clinical applications of direct materials.
Braided white Dacron fibres are readily impregnated with resin and with a breaking strain of around 30 lb perform extremely well as fibre reinforcements for composite resins (Fig. 1). These fibres are very malleable and easy to place, do not swell when exposed to the oral environment and can be bagged and sterilized. They are available as “Fly Line Backing” either from the internet or speciality Fly Fishing retailers for less than $25 for 200 metres. A further purchase of dedicated fishing line scissors facilitates cutting the fibres to the desired length (Fig. 2).
Three clinical examples of how fibre reinforcing can extend the clinical use of composite resin in the oral environment are demonstrated below:
- Reducing the risk of marginal ridge fracture in class II composite resins
- Splinting lower incisors
- Fibre reinforced direct resin bridge
Reducing The Risk Of Marginal Ridge Fractures In Class II Composites
There are patients who always seem to fracture class II composite restorations no matter how much care is taken with the occlusion. Fractures usually occur at the isthmus between the marginal ridge and occlusal section of the restoration.
The layering of several fibres along the long axis of the cavity substantially improves the fracture toughness of the composite resin and reduces the chance of a fracture.
The placement technique is as follows:
- Determine the length of the fibres required for the restoration and cut several more than anticipated
- Sparingly wet the fibres in resin bond
- Remove the fractured restoration and prepare the cavity
- Clean the preparation, place a matrix band and prepare the cavity surfaces with an appropriate adhesive agent
- Place composite resin into the proximal box to the level of the occlusal floor and photo cure (Fig. 3)
- Place an increment of flowable resin onto the base of the cavity and apply sufficient fibres into the flowable resin to cover the cavity floor (Figs. 4 & 5)
- Place an increment of composite resin over the fibres and pack the material down so that the surface remains below the occlusal table and photo cure (Fig. 6)
- Remove the matrix band, contour the restoration
- Adjust the occlusion and polish (Fig. 8)
This technique is not a panacea for all restorative challenges however it certainly extends the clinical application of direct materials. It is always prudent to inform patients of the limitations of restorative dentistry and alternative procedures may be required if failure occurs.
Splinting Lower Incisors
The difficulties with splinting lower incisors with a composite resin on the lingual surfaces, are getting the correct occlusal contour and making the restoration smooth enough so as not to irritate the patient’s tongue.
This technique involves preparing a 1.5 mm groove along the incisal edges of the incisors and through the canines with a small diameter end cutting flat fissure bur. The age of patients presenting with chronic tooth mobility is generally such that sclerotic changes have occurred within the pulp that will have reduced the chance of an exposure. However, patients must be made aware of this possibility.
At least three fibres are required to stabilize mobile incisors.
The patient illustrated, presented with severe mobility on her lower incisors and canines.
The placement technique is as follows:
- Five fibres are cut to length so as to slightly extend beyond the distal margins of the lower canines and sparingly wet with bonding resin
- Gross interferences in the occlusion are removed
- A 1.5 mm deep groove is prepared along the incisal edges of the incisors and through the canines with a small diameter end cutting flat fissure bur (Fig. 9)
- Clean the cavity and after isolation with cotton rolls, prepare the cavity surfaces with an appropriate adhesive agent but do not cure
- Place several small increments of flowable composite resin along the preparation.
- Embed at least at least three or more pre-cut fibres into the flowable composite along the base of the groove with a periodontal probe (Fig.10)
- Sparingly place composite resin over the fibres to slightly overfill the preparation (Fig. 11)
- Place a freezer bag (3 x 1 cm) over the uncured composite and have the patient close into centric occlusion, positioning the teeth in the correct occlusal position
- While still occluded photo cure the restoration for 10 seconds, open the bite and remove the freezer bag followed by a further 10 second cure (Fig. 12).
- Remove excess composite from the preparation (Fig. 13).
- Adjust the occlusion.
- Contour and finish the restoration (Fig. 14).
These splints are relatively easy and predictable to fabricate as they position the teeth in the correct occlusal position. Patients find them very acceptable as, unlike lingually bonded splints, they are unaware of these splints in their mouths.
If a periodontal abscess occurs under one of the splinted teeth, the root can be sectioned from the crown and removed. After initial healing, a sectional matrix can be used as a template to build up the gingival floor beneath the crown with a resin modified glass ionomer that will minimize plaque growth and re-establish aesthetics (Fig. 15).
Fibre Reinforced Direct Resin Bridge
There are a wide range of clinical and personal circumstances for patients that will make this prosthesis a preferred treatment option and a great practice builder.
Fibre reinforced direct resin bridges can be made in a single appointment, are relatively easy to fabricate, position mobile teeth, and with correct occlusal adjustment and fibre reinforcing, provide patients with a long-term clinical solution.
The placement technique is as follows:
- Determine that a resin bridge can be accommodated within the occlusion (Fig. 16).
- Remove existing pellicle and restorations from the pontic abutment interface and after isolation with cotton rolls, prepare the cavity surfaces with an appropriate adhesive agent and photo cure.
- Place an increment of composite resin against the abutment and after placing a 3×1 cm strip of freezer bag over the uncured composite resin, ask the patient to close in centric occlusion (Fig. 17).
- With the mouth in centric occlusion, photo cure for 10 seconds to create the lingual surface of the pontic.
- Using a sectional matrix to form the gingival contour, place resin modified glass ionomer to build up the cervical section of the pontic (Fig.18).
- Place a direct resin laminate over the labial section of the pontic to form a cantilever abutment (Fig. 19).
- Adjust the occlusion to clear any interferences and prepare a slot 3 mm wide and about 1.5 mm deep (depth of enamel) about two thirds across the lingual surfaces of the abutment and the pontic.
- Measure the length of the slot and cut about five fibres to fit within the slot, wetting them sparingly with resin bond.
- Clean the slot and prepare the cavity surfaces with an appropriate adhesive agent and photo cure (Fig. 20).
- Insert several small increments of flowable composite into the slot and place a sufficient number of fibres to fill the preparation.
- Place an increment of composite resin over the fibres, ask the patient to bite once again into the freezer bag in centric occlusion
- Photo cure in the occluded position for 10 seconds, then remove the freezer bag and photo cure for another 10 seconds (Fig. 21).
- Adjust the occlusion so that there are no interferences over the full envelope of occlusal movement.
- Contour and finish the restoration (Fig. 22).
This has been a long-term restoration solution (18 years) for patients in my practice (Fig. 23) who are sceptical about implants, don’t want their teeth prepared for a conventional bridge or to suffer with a removable prosthesis.
Getting the occlusion correct is essential as occlusal forces, at the limits of movements, will often fracture even the strongest pontic from an abutment.
Cantilever bridges are far more successful than bonding to both sides, as occlusal forces will often shear the pontic from one abutment. Furthermore, it is much easier to clean under the bridge with floss if it is a cantilever.
These three procedures will certainly not fit comfortably into every dental practice. However, dentists who are looking for a new generation of minimally invasive procedures will find them a valuable addition to the services they are looking to provide to their patients and a useful way to grow their patient base.
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About the Author
Geoffrey Knight is a general dentist from Melbourne, Australia with interests in aesthetic and minimal intervention dentistry. He has introduced a number of innovative clinical techniques and is named on several dental patents. He speaks internationally with a focus on highly efficient, minimally invasive dentistry. He has been State President of his Dental Association and has extensive political and economic experience within the profession.