Placing dental bonding - The procedure. (Part 2)
F) Acid etching the tooth's surface.
In preparation for the bonding process, the tooth's surface (both enamel and dentin) needs to be etched with an acidic "tooth conditioner."
Current bonding protocol involves the use of a tooth conditioner (typically a gel) that contains a 30 to 40 percent concentration of phosphoric acid. The conditioner is usually left on the tooth's surface for at least 15 seconds and then thoroughly washed off.
At this point the tooth's surface (both tooth enamel and dentin) has been etched and is ready to receive the dental bonding. If the dentist were to dry the tooth its etched enamel surface would reveal a frosted appearance, much like the appearance of etched glass. In the past a dentist might actually do this so to evaluate the effectiveness of the etching process. However, with today's understanding of dental bonding technique (especially as it relates to tooth dentin) a dentist will usually minimize the extent to which they dry a tooth for fear of desiccating it.
G) Applying the bonding agent.
On our pages that describe the science of dental bonding we detail the fact that in order to create a bond with tooth structure, a dentist needs both an etched tooth surface and also the application of a (curable) liquid plastic resin on this surface. Dentists term this liquid resin "bonding agent."
A dentist will paint or dab the bonding agent onto the etched tooth surface using a small brush or equivalent applicator. The dentist may agitate the resin during the application process so to insure a thorough coating of the tooth's surface. They might also gently blow air over the tooth so to disperse the bonding agent into a thin even layer.
H) Curing the bonding agent.
Once the bonding agent has been applied the dentist will initiate its set by way of exposing it to the output of a "curing light." Bonding agents contain a catalyst that is used to triggers their set. The activation of this catalyst is, in turn, triggered by the light emitted from a curing light.
Once the dentist has shined the curing light on the bonding agent for about 10 to 20 seconds the bonding agent will have become fully hardened. At this point a bond to the tooth has been created. The bonding agent has established a micromechanical bond with the etched tooth's surface.
[ Dentistry is undergoing fairly rapid change in the way tooth etchants and bonding agents (now collectively termed "adhesive systems") are formulated and used. One of the main reasons why these changes are taking place is because dental researchers now understand the science of creating a bond with tooth dentin much better than before.
Some of these new adhesive systems incorporate the tooth conditioner (acidic etchant) right in with the bonding agent itself. This means that there is no "etch then wash" step but instead the bonding agent is applied on the tooth without prior etching and then hardened using a curing light. ]
I) Creating the restoration. / Applying composite restorative.
Now that an initial bond has been established with the tooth's surface (by way of the bonding agent), successive layers of dental bonding restorative (dental composite) are added so to give the restoration being created its needed bulk and shape. Dental composite is capable of creating a chemical bond with both the bonding agent layer and also other, subsequently placed, layers of dental composite.
Most of the dental composite that the dentist will use to create the restoration will have a consistency of putty, although some of the internal layers of the restoration may be composed of a liquid "flowable" dental composite. The firmer putty-like form of dental composite typically has good wear and strength characteristics, whereas the flowable form is used because it can easily adapt and conform to the shape of the tooth surface on which it is placed. Both types of dental composite come in a variety of shades of white so they can closely mimic the color of the particular type of tooth structure they replace.
Flowable dental composite is applied by way of squirting it out of a small syringe. In contrast, the firmer putty-like form of dental composite is applied to the tooth in small portions, each of which are then patted with hand tools until they have taken their needed shape.
Curing the restoration.
Once the dentist is satisfied with the positioning of the dental composite, they will initiate its set using a curing light. In most cases 20 to 40 seconds of exposure time are needed to fully harden the dental composite.
So to complete the formation of the bonded restoration, the dentist will continue to add more layers of dental composite (usually each layer will be no more than 2 mm thick or so). As each individual layer is placed, it is hardened using the curing light before the next layer is added. Dental composite is added in layers because the light emitted from a curing light can only penetrate through only so much thickness of dental composite at a time. Another reason dental composite is added in thin layers is because as composite sets it shrinks (on a microscopic level). Keeping each application of composite thin means that the cumulative effects of this distortion will be less problematic than if the composite was placed and cured as a single lump.