December 10, 2019
by Geoffrey Knight, BDSc, MSc, MBA, PhD
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).
Braided Dacron “Fly Backing Line” is a useful fibre for use in restorative dentistry.
Dedicated fishing line scissors will successfully cut Dacron line.
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 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:
Build up the composite resin in the proximal boxes level with that of the occlusal floor.
Apply a small amount of flowable over the composite base
Fibres laid across cavity floor embedded in flowable composite
Layer of composite resin over fibres below occlusal table
Final increment of composite resin prior to contouring.
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.
Mobile lower incisors and canines with 1.5 mm slot along incisal edges.
Packing fibres into slot.
Composite resin sparingly placed over fibres.
After placement of freezer bag, patient closes into centric and restoration photo cured.
Following photo curing mobile teeth splinted in correct occlusal position.
Completed splint following occlusal adjustment and finishing.
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).
If a splinted tooth requires removal, section the root and build up a resin modified glass ionomer (RMGIC) cervical base to improve aesthetics.
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.
Missing central incisor prior to placing a direct fibre reinforced bridge.
Bond composite to abutment tooth and occlude using a freezer bag to create lingual contour.
Create gingival margin with a sectional matrix and build up with RMGIC
Construct a labial facing cantilevered onto the abutment tooth.
After adjusting occlusion prepare a slot 1.5 mm deep, 3 mm wide, 2/3 across the lingual portions of the abutment and pontic.
Lingual surface after fibres have been embedded and the occlusion adjusted, contoured and polished
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.
Direct Fibre Reinforced Composite Resin Bridge 18 years after placement.
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.
Oral Health welcomes this original article.
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.
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