Laser Light-Curing Unit Key Element in Deep Composite Restoration
Alireza Sadr, DDS, PhD
A patient presented with an old and failing amalgam restoration on a first molar that showed signs of dentin cracking. The patient was anesthetized, rubber dam isolation was achieved, and the amalgam and any secondary decay was removed and dentin cracks prepared. A sectional matrix was placed, and a deep gingival proximal margin was formed. Because an attempt was made to remove any crack as deeply as possible supragingivally in the mesial box, the gingival margin was at least 6-mm deep from the top of the matrix. The proximal margin was bonded and sealed using a multistep adhesive system, and circumferential walls and a marginal ridge were formed using a universal hybrid composite in a single step after bonding. Light-curing was accomplished with a laser light-curing unit (Monet®, CAO Group, Inc., caogroup.com). Because of the depth of the preparation, an ultra-high molecular weight polyethylene continuous fiber material was used to bridge the pulpal floor cracks, mitigate stresses, and reinforce the composite. Proximal and buccolingual walls were created with composite, and a polyethylene fiber mesh was wetted with a bonding agent and placed over the tooth with a thin layer of the hybrid composite. Close adaptation of the fiber material against the cracked dentin was achieved, the fiber-reinforced composite was light-cured, and a final occlusal layer of the hybrid composite was placed and light-cured.
Dental light-curing units have evolved to improve the degree of polymerization that can be achieved in deep preparations. Unlike light from other sources, laser light is collimated, which means that all of the rays are parallel to each other-an important characteristic, as the light beam does not diverge over longer distances in the way that light from an LED source does.
The Monet laser light-curing unit, in unpublished optical coherence tomography experiments by the author, demonstrated effective curing of a 4-mm deep composite restoration from as far away from the surface as 8 mm in 3 seconds, and the restorations exhibited less debonding than those cured by a standard LED light-curing unit for 20 seconds. The Monet demonstrated the capability to cure composite restorations to their depth, regardless of its distance from them.
In this case, the Monet laser light-curing unit helped ensure a predictable bond and complete polymerization of the adhesive and composite that were placed to create a proximal wall and marginal ridge as well as the fiber-reinforced composite that was placed in the deepest part of the preparation. The consistent energy delivered by this light-curing unit is a "game changer" not only for thick increments of bulk-fill composites but also for thinner increments of light-cure resins and base materials used in deeper preparations.
About the Author
Alireza Sadr, DDS, PhD
Associate Professor and Vice Chair, Department of Restorative Dentistry, School of Dentistry, University of Washington, Seattle, Washington