Adequate Curing: What Ails Your Composite Restorations
By: Dr. Richard Price - Dalhousie University, Halifax, Canada
Dental curing lights are now used in almost every dental office to photopolymerize restorations, adhesives, luting agents, sealants, bond orthodontic brackets, and during tooth whitening procedures. Despite what you hear in many lectures about posterior composites lasting 15+ years, direct composite restorations are susceptible to failure and over half of them placed in the average dental office will fail within seven years.1-10
Among the factors contributing to failure are the formation of gaps at the margin and development of secondary decay often at the bottom of the proximal box that is furthest away from the curing light, as well as the patient’s age and caries status11, 12 (figure 1). Additionally, straying from recommended clinical techniques when placing direct restorations—such as improperly handling the bonding agent and not following the manufacturer’s instructions for use —will contribute to composite failure.
Properly curing direct composite restorations requires that you deliver sufficient light at the required wavelengths. How often do you hear, 'and then you light cure' with no additional information about how to do it? Does this not seem strange when there are detailed instructions on how to cut the cavity, use the adhesive, place the composite, and even how to polish the restoration. Dental curing lights must be used correctly for dentists to achieve in the mouth what the manufacturers and laboratory bench researchers state is possible.
Factors affecting the dental curing unit itself, and how it is used, are variables that greatly influence how well the resin is light-cured. All researchers know this fact and make every effort to ensure that their specimens are well light cured. They test the curing light to ensure that it is working correctly; wear eye protection; watch what they are doing; keep the light tip close to and directly over the specimen; and cure for the recommended time. Unfortunately, unless you are conducting a clinical trial, this rarely happens in most dental offices. 13-17 If it did, we would likely see the restorations lasting longer.
Curing Light Technology
Dental curing light technology has improved over the years in terms of size, handling, wavelength, and light output. Today's curing lights are ergonomic units that use light-emitting diode (LED) technology. This can provide dentists with portable battery-operated units and thousands of hours of predictable use. The new Bluephase G4 and Bluephase PowerCure (Ivoclar Vivadent) also include Polyvision technology that will warn the user if the curing light tip moves away from a tooth and onto the soft tissues.18 Even a small deviation will increase the exposure time, and if the tip moves entirely off the tooth, the curing light turns off. This technology also prevents the light from being accidentally shone into the eye.
Compromised Intensity & Output
Although your new dental curing light may deliver an excellent light output, this output will diminish over time due to wear and tear of both the light and the materials encasing its tip and optics; deterioration of the unit’s light, filters, or reflectors, improper maintenance; or debris on the light tip19 (figure 2). For example, if the manufacturer's instructions are not followed, and the light is not allowed to cool down between repeated exposures, this can cause the LED chip to overheat and the epoxy surrounding the LED to yellow. As a result, light output is reduced, and the curing light may then deliver insufficient light to cure the restoration adequately.
Unfortunately, it’s virtually impossible for clinicians to visually evaluate the quantity and quality of light output from dental curing units. Contributing to such difficulties is that even faulty light-curing units will produce a hard surface at the top of the restoration. Since you cannot test the bottom of the restoration, dentists may think that the light is curing the entire restoration properly and experience a false sense of security.
Monitoring Curing Light Output
Because dental curing light performance significantly affects the longevity of direct composite restorations, it is essential to monitor curing light output regularly. Dental radiometers have traditionally been used for this purpose, but, in general, they are inaccurate. Fortunately, the new Ivoclar Vivadent Bluephase Meter II features a large sensor capable of measuring the power from any curing light tip that is between 5 mm and 13 mm in diameter. The manufacturer claims that the power measurement (mW) reported by the Bluephase Meter II is accurate ±10%, and this is supported by independent research20 (figure 3).
Although dentists may not have initially considered that curing lights and the curing process as essential variables that influence the success of their restorations, the longevity of direct restorations and indirect restorations that are cemented with resin cement requires reliable light curing. The simplest and most dentist-friendly method for ensuring predictable light curing is measuring a curing light's power output using the Bluephase Meter II, (Ivoclar Vivadent). By recording the power of their curing light when new, and then to daily monitor proper output, dentists can ensure the reliability of the restorations they place, as well as address any decrease in the output from their curing light.
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