Thank you for the opportunity to respond to this letter from my friend, Dr. Don Coluzzi. While Dr. Coluzzi takes the opportunity to promote the Academy of Laser Dentistry as a past president, I will refer the reader to my comments to the following letter from Drs. Goldstein and White regarding such promotion, and the value of expertise outside the ADL (page 706).
While I must stand corrected, and thank Dr. Coluzzi for pointing out that the diode laser (800 nanometer) has greater penetration than the Nd:YAG laser, I must also add that this is true in water and not necessarily in tissue. Since the overall penetration is a function of the structure and composition of the tissue, it can be difficult to theoretically predict the penetration in tissue with any great accuracy. For this we must turn to histology.
Such information suggests that the Nd:YAG and 805-nm diode laser are equivalent with respect to incision depth and width of thermal damage when viewed 48 hours after exposure in rat liver, muscle and porcine skin. 1 The penetration of an 850-nm diode laser in cortical bone was estimated to be between 6 and 18 millimeters, depending on the angle of incidence.2 This is an example of the kind of histologic data that we need to objectively assess any laser application with regard to the risk of collateral damage.
Dr. Coluzzi is also correct in stating that the in vivo pulp damage occurred with a perpendicular angle of incidence to the enamel surface. The two references he mentions were motivated by "tooth desensitization" using the Nd:YAG laser that had been taught for some time by Nd:YAG laser companies and their proponents. This was at a time when desensitizing was being achieved and taught without knowledge of the effect on the pulp.
The first study used several combinations of exposures: 0.68 watt, 98 seconds; 1.0 W, 48 seconds; 1.5 W, 37 seconds; 2.0 W, 25 seconds; and 3.0 W, 14 seconds. Pulpal damage occurred in all of these cases, and became worse as the power increased. These exposures are, in fact, in the range used for Nd:YAG soft-tissue surgery and sulcular débridement protocols, so it is reasonable to ask questions regarding the risk to the patient.
While the actual risk to the pulp from laser curettage may be less due to the shallow angle of incidence of the energy with the root surface, the risk to the periodontal tissue would then need to be defined with histology at multiple time intervals. It is also important to note that these references have special relevance in that perpendicular irradiation of an enamel surface occurs when the Nd:YAG laser is used to remove incipient caries.
Even though there may be a greater width of dentin protecting the pulp in a coronal area, histology is still needed to show whether damage occurs, since the two references under discussion here indicated that laser-damaged pulp tissue is typically "desensitized" and noninflamed, and, in theory, may not respond to traditional tests for pulpal hyperemia.
I must disagree with Dr. Coluzzi’s statement that the tip of a pulsed Nd:YAG laser does not heat up. Admonitions for the practitioner to remove bulk debris do not, in fact, mean that minor debris does not contribute to heat build-up. (Moreover, his reference is not peer-reviewed.3) What is remarkable, however, is that while Dr. Coluzzi recommends removing the debris, presumably to reduce the tip temperature, others are looking for ways to increase it by coating the tip with substances such as metal or carbon.4–6
These authors were seeking ways to minimize the radius of collateral damage from the laser energy, while simultaneously gaining intensity and control of the heat produced at the fiber tip. They found that not limiting the laser energy to the tip by such coatings resulted in poor cutting efficiency, and an unacceptably high number of arterial perforations from the advancing laser beam during recanalization therapy in atherosclerotic patients. These coatings not only improve the cutting efficiency of the tip, they limit the amount of actual laser energy from proceeding beyond the tip to do unwanted damage to the vessel wall (or the PDL, connective tissue and the alveolar bone, in our case).
If I may offer to Dr. Coluzzi my professional opinion as an engineer, I believe both minor cellular debris and lattice imperfections in the tip itself absorb energy. As the tip heats, the number of imperfections increases, and absorption at the tip increases, increasing the tip temperature. Once the transient temperatures reach the activation threshold, tissue vaporization begins.
With respect to the reference for the statement regarding delayed healing with the Nd:YAG laser, I must thank Dr. Coluzzi for pointing out the error. The correct citations are listed in this letter’s reference list.7–9
The comment regarding calcium:phosphorous ratios were indeed [related to] in vitro studies; however, they do in part support the FDA clearance for use on bone given to Biolase Inc., and it is this clearance that was the main reason for listing this application in the article. There are still many claims regarding the use on bone and other hard tissues that need to be scientifically verified.
The citations supporting the comfort of the Er,Cr:YSGG are also included in the reference list.10,11
Lastly, the wavelength of the diode laser should have been listed as approximately 810 nm rather than 904 nm, and again, I thank Dr. Coluzzi for the correction. I also thank him for engaging in the kind of scientific dialogue that furthers understanding. I do think that his criticism of the article as being unscientific is unfounded, especially in view of his corrections being largely limited to editorial errors (for which I take full blame), and because I believe those few scientific criticisms presented were also scientifically refuted. I also believe that Dr. Coluzzi wants the best for his patients, and that is where we are in agreement.
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