Direct Composite Resin Veneers:
Injection Moulding Technique
One of the most difficult things to perfect in dentistry is the natural shape, surface texture and morphology of teeth using direct composite resin veneers. One often feels like Michelangelo or Leonardo sculpting out custom nature-like pieces of art and when you get it right, it is amazing. The great thing with composite resin is that you can always add and remove material quite easily, yet, if you are placing 8-12 veneers it can get very time consuming.
Indirect porcelain is the most beautiful material we have, however, there are cases where composite resin veneers are more suitable. They can offer a good conservative option for cosmetic rehabilitation. We can improve aesthetics and also replace tooth structure that has been lost due to tooth wear. Modern composites have much improved physical and aesthetic properties. Using an additive wax up we can ensure that we are often using no preparation or minimal preparation of the teeth whilst achieving optimal aesthetic outcomes. Minimal treatment means the tooth undergoes less trauma and lowers the risk of the tooth requiring ongoing future treatment such as endodontic treatment.
Furthermore, if the shorter life-span is acceptable for all parties then it is also a less expensive option than porcelain.
Composite resin veneers have traditionally been either placed freehand or in conjunction with the use of templates can help guide the palatal and incisal contours. However, the labial surface texture and morphology from the wax up for the most part is lost.
The surface texture and morphology is the game changer when going to the next level in natural aesthetics. Adding surface texture and morphology can turn a denture looking tooth to something that looks like what nature created. Traditional methods either place surface texture and morphology during placement of the composite resin or during the finishing process by using burs and discs. Both of which can be time consuming.
Injection moulding is a widely used manufacturing process that is often used to produce plastic products. It is essentially a shape-forming process where material is injected into a mold that is shaped like the end product and squeezed under high pressure. We can see some big advantages injection moulding to form our veneers directly on teeth.
Replicate the surface texture and morphology quickly and precisely.
Application of a single layer of composite decreases voids, porosities and hence reduces staining.
Monolithic appearance. Case selection is important. More aesthetically demanding clinical situations can require dual-shade or multilayering technique to mimic the adjacent tooth structure.
Unable to place internal characteristics.
Cannot use rubber dam isolation.
The other problem was finding a composite resin that was flowable (low viscosity), high strength, low wear and high polishibility to be suitable for use as a veneer. To fill this void, GC released a new product, G-aenial Universal Injectable. Read more about G-aenial Universal Injectable in my reivew.
So that's the theory, how does it happen practically?
Pros and Cons
Here are our pros and cons of the injection moulding technique.
Replication of surface texture and morphology is precise and quick.
Very little air bubbles/voids.
Efficient technique that produces excellent results when restoring multiple teeth.
Monolithic appearance means matching a single tooth with the adjacent teeth would be difficult.
Removal of interproximal excess can be time consuming.
Difficult for direct visualisation to see if there is adequate fill of the tooth when injecting the composite. Natural human behaviour will often mean that we overfill and hence more excess composite over the adjacent teeth.
However, there are more advanced techniques to overcome the monolithic appearance and the excess formation over adjacent teeth and still use the injection moulding technique
Dr Andrew See is a Sydney-based dentist with advanced training in Restorative Dentistry and Implantology. He inspires and educates dentists to be the best they can be. Stay tuned for more reviews. Follow @dr.andrewsee to see more cases, tips of the trade and dental photography.