Over the last several years, resin-curing lights have been introduced that cure resin in significantly less time than that in the past. Times of three seconds or less have been suggested by companies and are used by dentists. Dentists are eager to accept these fast lights, because of the significant reduction in practice time. However, there has been controversy on the subject. At almost the same time that the fast lights were introduced, several companies also introduced lights that cure at a slower rate, which is supposed to cause less resin shrinkage and stress in the tooth. Practitioners are confused.
Some dentists now use fast lights; ramp lights, which start out at lower curing power and increase over a few seconds; and phase lights, which cure at different power levels with an interval between curing periods. Allegations have been made that fast curing has significant damaging effects on the resin and on the tooth. What is correct? This article will discuss the question of light-curing speed for restorative resins from the following standpoints: influence on the practice, influence on the restorative resin, and influence on the teeth being restored.
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INFLUENCE OF FAST-CURING LIGHTS ON PRACTICE EFFICIENCY
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Although most dentists have not considered the situation to any significant degree, a major amount of time is spent each year curing resin. Clinical Research Associates, or CRA, measured the amount of time spent curing resin by typical general dentists.1 The study found that the typical dentist cured resin for about $48,000 worth of time in one year (30 eight-hour days).1 Average income per hour, as reported by the American Dental Association, was used to calculate the cost of light-curing. A typical halogen light, as used by most dentists, requires at least 30 seconds to cure a light-colored resin; assuming that a plasma arc curing, or PAC, light can cure the same resin in three seconds, the net reduction in time to cure is 90 percent. This simple math demonstrates that a dentist could save more than $40,000 worth of time in one year by changing from a typical halogen curing light to a PAC light. That should have caught your attention.
What happens to the sequence of a specific clinical procedure when changing to a fast-curing light? I will use the Class II resin as an example. With a typical curing light working at 500 milliwatts per square centimeter, each increment of resin requires about 30 seconds to cure adequately. What are the increments or steps? These steps vary from dentist to dentist, but the following steps are common:
- – cure the liner (such as Vitre-bond, 3M Dental Products), bonding agent, or both;
- – cure the first resin increment;
- – cure the second increment in the first box form;
- – cure the first increment in the second box form;
- – cure the second increment in the second box form;
- – cure the occlusal first increment;
- – cure the second occlusal increment;
- – postcure the facial surface;
- – postcure the occlusal surface;
- – postcure the lingual surface;
- – after finishing, cure the occlusal sealing resin.
There are about 11 curing steps of 30 to 40 seconds each, for a total of 5.5 to 7.33 minutes in a typical Class II resin. Change that time into dollars, and using average income numbers of $3 to $10 per minute, curing time has a value of $16.50 to $73.30. Reduce those numbers by nine-tenths if using a PAC light, and the range is $1.65 to $7.33. Fast lights represent a savings of $14.85 to $65.97 per restoration. Can we afford to stay at the slow curing times if fast curing does not cause damage?
Dentists using fast lights report that the sequential steps become much more coordinated when using a fast light, because there is so little time between the typical steps. Practitioners who have switched to the fast lights also report that they will not consider going back to using typical curing lights. These practitioners also report that they are not seeing any adverse clinical effects (G.J. Christensen, oral surveys of practitioners in continuing education series, ongoing research).
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INFLUENCE OF FAST-CURING LIGHTS ON THE RESTORATIVE RESIN AND THE TOOTH
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There have been reports that fast resin-curing lights modify the resins in a negative way. CRA has shown that resins cured with PAC lights and lasers had no properties after curing that were different from those of resins cured with typical lights.1 Other sources have reported additional restorative resin shrinkage with the fast lights. However, CRA research has not shown more shrinkage with the fast lights.1 Other sources report that there is more stress in the restored tooth after use of fast-curing lights. CRA research has not shown more stress in restored teeth when the fast lights are used.1 There have been reports that the heat generated by fast lights could injure the pulp. CRA research showed less heat in the pulp with fast lights than that with the typical halogen curing lights, assuming that both types of lights were used correctly.2
Practitioners who have switched to the fast lights report that they will not go back to using typical curing lights.
Some people have suggested that because of the alleged negative aspects of curing resin rapidly, teeth could have more postoperative sensitivity. This suggested phenomenon has no basis in fact; rather, the reverse has been reported by clinicians in the field (G.J.C., oral surveys of practitioners, ongoing research). Both scientific and empirical evidence support the use of fast-curing lights.
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ARE THERE NEGATIVE ASPECTS TO THE FAST-CURING LIGHTS?
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The current generation of PAC lights has some negative characteristics that may persuade some practitioners to wait before purchasing one. In my opinion, the following are negative characteristics of PAC lights.
The cost is high, but some may not consider it to be high when the time savings are considered. PAC lights currently cost about $2,600 to $5,000. Typical halogen curing lights range from about $800 to $1,000. The cost of fast-curing lights needs to be reduced.
Fast-curing lights are large and take up significant space on countertops. They need to be significantly reduced in size.
Foot controls, to date, have consisted of the "off-on" switch. Although a few manufacturers have now placed hand-activated controls on their devices, they have been poorly received, because of their large size and uncertain activation. Manufacturers need to develop easy-to-use hand controls as soon as possible.
Heat generation in some of the devices is excessive. The heat is not damaging to the pulp if the devices are used correctly, but it is potentially damaging to the lips or gingiva if the devices are inadvertently held on these soft tissues. Manufacturers need to reduce the amount of heat generated.
The curing-tip diameter is too narrow to cure some large posterior restorations or large veneers. A curing-tip diameter of about 11 millimeters would be desirable for these large restorations. The current 6- to 7-mm tips are not adequate for many situations. Tip diameter needs to be increased, which some manufacturers are now doing.
Some manufacturers have not made the curing wavelength wide enough to activate some restorative resins, bonding agents or flowables at the recommended times.3 All curing lights should have curing capability for all current brands of restorative resins.
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CHOICES FOR PRACTITIONERS IN 2000
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At this time, there are several choices in regard to curing restorative resin. Each practitioner has different concerns about light-curing, and a universal decision will not satisfy everybody. All of the following choices are acceptable, but significantly different amounts of money will be saved or lost in each situation.
Continue as you have been in the recent past.
You may be getting along well, and you do not wish to change. This option may cost you up to $40,000 per year. Most dentists will want to change to faster lights within the next few years.
Purchase a special curing tip.
This simple device (Turbo Tip, SDS Kerr/Demetron) fits many curing lights and will increase the curing potential of your old light up to 2x power (decreasing the curing time by one-half). I suggest that you talk with SDS Kerr to find out if your light will accept a Turbo Tip. This option will save a significant amount of money by cutting the curing time in half and costs only about $200.
Purchase a new halogen light.
A new halogen light (model Optilux 501, SDS Kerr/Demetron) that is more powerful than earlier lights has been introduced, and it comes with a Turbo Tip.4 This option will decrease, by more than three-fourths, the time spent curing with a standard light. This light costs far less than a PAC light and only slightly more than a high-quality halogen light of a few years ago.
Purchase a PAC light.
This option will save you the most money initially and will make dentistry much easier and faster. Some of these lights cure in only a few seconds, saving as much as nine-tenths the time previously spent on resin curing. Because these lights are changing constantly, a PAC light purchased now will probably need upgrading or replacement. Here are some representative brands: Apollo 95 E, Dental/Medical Diagnostics; ARC Light, Air Techniques; PAC Light, ADT; Virtuoso, Den-Mat Corp.; and Wavelight, New Wave Dental.
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CONCLUSIONS
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Numerous curing lights have been introduced to the market during the last few years. Some of them represent new concepts, and they claim to produce better resin restorations. Others are modifications of the current halogen light concept. The fastest of the new lights have the potential to save a significant amount of money over time by reducing the time needed for resin curing. Some companies and continuing education speakers have criticized the fast lights. Other sources show the fast lights to be acceptable, without negative characteristics. Opinions of clinicians are favorable toward the fast-curing lights. Clinicians do not appear to observe any negative clinical characteristics. Faster curing of resin restorations appears to be the preferred technique for the near future. However, the exact technology needed to achieve fast curing is still in evolution.
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INFLUENCE OF FAST-CURING LIGHTS...
INFLUENCE OF FAST-CURING LIGHTS...
