In reply

Abstract

To the Editor: I would like to thank Dr Convissar for his valuable and interesting comments. I would like to address Dr Convissar's 3 major comments, which are:1.Choosing CO2 laser irradiation was less than ideal.2.The Er:YAG laser is the only wavelength that can remove the smear layer.3.CO2 laser irradiation is not yet approved by the Food and Drug Administration (FDA) for hard tissue application. Prior to addressing the comments, a brief discussion of laser interaction with hard tissue and the purpose of each laser system is warranted. First, when CO2 laser light strikes dental hard tissue, it can be reflected, scattered, transmitted, or absorbed (coefficient of absorption). The most efficient interaction is when laser light is highly absorbed by hard tissue. The 10.6-λ laser irradiation is the most efficiently absorbed by most hard tissue when compared to other types of lasers (Nd:YAG and Er:YAG). This high coefficient of absorption, and consequently, interaction with dental hard tissue, is primarily due to the carbonated hydroxyapatite, which has a strong absorption band in the infrared region. The Er:YAG laser is highly absorbed by the water content of hard tissue in the 2.78- to 2.94-micrometer range (in the middle infrared region). From the way the CO2 laser irradiation interacts with dentin, it produces different ultrastructural changes including melting, fusion of hydroxyapatite crystals, and smear layer removal (as observed in our scannining electron microscopy [SEM] images). This is due to the temperature gradient, which is higher in the center of the laser strike and diffuses across the dentin. These ultrastructural changes can not be achieved by the Er:YAG lasers. Second, Dr Convissar in his letter referred to several articles in the periodontal literature. In periodontal surgery, the goal is to remove the pathologic tissue and conditioning the root surface to expose collagen fibers and enhance PDL attachment. In periapical surgery, disinfecting and sealing opened dentinal tubules is the ultimate goal and conditioning the root surface is a secondary objective. For the above reasons, CO2 is the laser of choice for the purpose of our study. Third, I totally agree with Dr Convissar that CO2 lasers are not currently approved for apicoectomy procedures through the FDA 510(k) mechanism. Therefore, its use by clinicians would be “off label” for apicoectomy procedures. On the other hand, it does not mean that CO2 lasers should not be evaluated for their use in dentistry. Without performing such research projects, how can we evaluate the performance of different devices and materials in our profession? Finally, I do believe that comparing different laser systems is like comparing apples to oranges. How can we compare the results of different laser systems having different wavelengths, different laser conditions (laser mode, fluence, beam diameter, etc), and different coefficients of absorption to each other. I do believe that each study should be evaluated based on its own merits. The endodontic literature is replete with studies using the CO2 laser for apical surgery, with the latest article in the J Clin Laser Med Surg, April 2004.1.Gouw-Soares S. Stabholz A. Lage-Marques J.L. Zezell D.M. Groth E.B. Eduardo C.P. Comparative study of dentine permeability after apicectomy and surface treatment with 9.6 micron TEA CO2 and Er:YAG laser irradiation.J Clin Laser Med Surg. 2004; 22: 129-139Google Scholar CO2 laser (9.6 micrometer) and Er:YAG laser irradiation were compared after apicoectomy procedures. SEM analysis showed that CO2 laser–irradiated dentin showed smooth, clean surfaces and fusion and recrystallization sealing dentinal tubules. From the 7 references Dr Convissar reported, only 1 reference used CO2 and all 7 references referred to periodontal procedures, which wasn't the scope of our research project. The results of our study can only be related to the laser conditions used. Under different CO2 laser conditions, different results could be expected. Use of laser energy during endodontic surgical proceduresOral Surgery, Oral Medicine, Oral Pathology, Oral Radiology and EndodonticsVol. 98Issue 5PreviewTo the Editor: Full-Text PDF