By Parsa T. Zadeh, DDS, FAGD, FICOI
In the last few years, there has been much publicity about use of lasers in dentistry and medicine. There seems to be a fascination about use of this form of energy to achieve various results in the healing sciences. Lasers are claimed to be useful in variety of situations from removal of unwanted body hair to repairing the detached retina.
The public’s attraction to this new tool combined with the dentists’ and dental patients’ demand for faster, more comfortable and more efficient way of performing dental procedures has created an extremely fertile ground for manufactures of such equipment.
Many dental procedures are performed by modifying or removal of part of dental hard and soft tissues. These procedures were traditionally performed by the dental drill and scalpel. There are now two types of lasers in the American market which are claimed to perform these procedures with superior results.
The focus of this study is on the Argon laser which is recommended to be used for curing of light activated composite resins and whitening of teeth. Most of the current data is either the result of manufactures’ in house studies or studies sponsored by manufactures in one way or another. It is very difficult for the progressive technophilic dentist to get unbiased information about these products before spending thousands of dollars.
The purpose of this study is to evaluate the efficiency of Argon lasers for curing of composite resins as compared to the visible light curing without any influence by manufactures of these products. This study was done without the knowledge of any manufacturer and no solicitation was made for any incentives.
The purpose of light curing of composite resins is to activate the polymerization reaction of the material and preferably bring it to a completion. Clinically the ideal curing is the one that:
A) Occurs within seconds of exposure to light.
B) Occurs completely and uniformly throughout the thickness up to 6-7 MM. and through the thickness of enamel and dentin
C) Occurs without any shrinkage.
Materials and Methods
All three of these criteria are evaluated using three different methods.
Extreme care is taken to maintain the uniformity of testing conditions. Individual comparative tests are done alternating the laser with light to ensure comparable room temperature, moisture and ambient light leaking from window shades. Each test is performed twice, once with laser first and once with light first. The average of the two tests is reported when different, even though the difference is very minor. The composite resins were freshly ordered and kept refrigerated until 4 hours before testing. Temperature of the room that the instruments and materials were stored and tests were performed was kept at 70 degrees F. Each comparative test sets are done using the material from the same tube after discarding the “lead” material. Two popular composites which are used by the author namely Charisma by Kulzer, a hybrid material and Heliomolar by Ivoclar a microfilled material is used which in the opinion of the author is a good representation of composite restorative materials.
The light unit and laser were connected to a UPS 450 to ensure uniform input voltage to the units in spite of fluctuations in the city power supply.
The light output of the curing light which is powered by a 110 volt, Watts bulb and uses a liquid optic wand, was measured before and after tests were completed. The reading was ……
The laser has a self calibrating feature which ensures uniform pre-determined out put for each test.
The diameter of composite cylinder was measured on the tested materials to ensure uniform thickness. Those cylinders that varied from one test to the other, were discarded and new samples were tested. A Miltex Bowley gage with 1/10th of a MM accuracy was used for measurements.
To test the relative hardness
As the notes and tables in the attached PDF document suggests, there was not only no advantage of using Argon Laser for curing composites but the Laser takes longer time to achieve the same hardness of the composites.
We know from experience that faster curing rate equals higher polymerization shrinkage of composites. Now that Laser is “slower” in curing the composite, does it mean that it causes less polymerization shrinkage? More studies need to be done to find out if this happens to be true.