Medical knowledge | Dentistry » Jorge Zeredo - Comparison of jaw opening reflexes

Comparison of jaw-opening reflexes evoked by Er:YAG laser versus scalpel incisions in rats Jorge L. Zeredo, DDS, PhD,a Katia M Sasaki, DDS, PhD,a Joseph H Yozgatian, DDS,a Yukio Okada, PhD,a and Kazuo Toda, DDS, PhD,a Nagasaki, Japan NAGASAKI UNIVERSITY Objective. Anecdotal remarks suggest that incisions in oral soft tissue would be less painful if performed with laser rather than with scalpel, but such an argument remains to be scientifically validated. Study design. Twelve rats received graded incisions to lip, gingiva, mucosa, and tongue with either a pulsed Er:YAG laser (65 mJ/pulse at 10 Hz) or a stainless steel scalpel. The amplitude of the jaw-opening reflex, as measured by the digastric muscle electromyogram, was used to quantify the nociceptive response evoked by the surgical incisions. Results. Except for lip, mean reflex amplitudes evoked by laser were significantly smaller (P 05) than those evoked by scalpel in all other incision sites. Conclusion. Er:YAG laser surgery

may be less painful and therefore require less use of anesthesia and sedation than conventional scalpel surgery in oral soft tissue procedures. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2005;100:31-5) The erbium-doped:yttrium-aluminum-garnet (Er:YAG) laser is one of the most promising laser systems for dental surgery because of its ability to cut soft and hard tissues without inflicting substantial thermal damage to the surrounding and underlying tissues.1-3 Er:YAG laser use has been described for a variety of clinical applications such as root surface debridement and soft tissue management.4,5 In addition, this is one of the laser systems suitable for ablation of vital teeth6,7 Clinical experiments suggest the results obtained with the Er:YAG laser to be comparable or sometimes superior to those obtained with conventional tools. The advantages associated with the use of the Er:YAG laser for dental procedures include among others bactericidal effects,8 dental ablation without

forming smear layer,9,10 less bleeding,11 and less pain from soft tissue incisions.4,11 Some of these outcomes, although well documented in the literature, remain to be scientifically validated. Particularly, remarks that laser incisions would be less painful than scalpel incisions in oral soft tissue have not been addressed in the scientific literature so far. In this study, we assessed the pain from Er:YAG laser and steel scalpel incisions in oral soft tissues by the jawopening reflex (JOR) response as measured by the a Division of Integrative Sensory Physiology, Department of Developmental and Reconstructive Medicine, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki, Japan. Received for publication May 27, 2004; returned for revision Oct 8, 2004; accepted for publication Nov 9, 2004. Available online 10 March 2005. 1079-2104/$ - see front matter Ó 2005 Elsevier Inc. All rights reserved doi:10.1016/jtripleo200411012 digastric muscle mass electromyogram (EMG).

The null hypothesis was that laser and scalpel incisions would evoke reflexes with similar amplitudes. As an alternative hypothesis, responses evoked by laser incisions would be less intense than those evoked by scalpel incisions. MATERIALS AND METHODS Twelve male Sprague-Dawley rats weighing 310 to 370 g were used in this study. The animals were lightly anesthetized with thiamylal sodium (60 mg/kg i.p, Isozol, Yoshitomi Pharmaceutical, Osaka, Japan), and after the experiment the animals were killed with an anesthetic overdose. The experimental procedures were in agreement with the Animal Care Standards of Nagasaki University, and had the approval of its Animal Welfare Committee. Surgical incisions The rats were randomly divided into laser and scalpel groups (n = 6, each). Graded incisions were made to the lip (4 mm long 3 2 mm deep), gingiva (2 3 1), mucosa (3 3 2), and tongue (4 3 2). Each rat received 12 incisions, always in the same sequence: 4 incisions (lip, gingiva, mucosa, and

tongue) ipsilateral to the digastric EMG recording side; 4 incisions to the contralateral side. For paired comparisons, the last 4 incisions were made to the ipsilateral side with the opposite tool (ie, rats in the laser group received scalpel incisions and vice versa). Laser incisions were made with a pulsed Er:YAG laser system (Dentlite, Hoya Photonics, Tokyo, Japan; wavelength 2.94 mm) using a contact tip without water spray and the irradiation parameters suggested by the 31 32 Zeredo et al OOOOE July 2005 Fig 1. Macroscopic view of the surgical incisions Graded incisions were made with either A, Er:YAG laser or B, stainless steel scalpel in the (L) lip, (G) gingiva, (M) mucosa, and tongue (not shown). Laser incisions had a characteristic roughness not observed in scalpel incisions. Nociceptive reflex recording JOR recordings were made from the anterior belly of the right digastric muscle. An incision was made in the ventral neck to expose the jaw-depressing musculature for

the placement of a bipolar recording electrode. The recording electrode consisted of 2 Teflon-coated stainless steel wires (no. 791400, A-M Systems, Carlsborg, Wash) with 4 mm of insulation removed at the tip and inserted into the muscle about 4 mm apart from each other. The recording electrode was connected to a high-impedance amplifier (DAM-80, WPI, Sarasota, Fla; 31000 gain, 300 Hz and 3 kHz for low and high filters, respectively), and the amplified signal was displayed and stored in a computer system through a Cambridge Electronic Design interface (CED1401, Cambridge Electronic Design, Cambridge, UK). Fig 2. Representative examples of digastric EMG recordings From the same rat, jaw-opening reflexes evoked by A, Er:YAG laser and B, scalpel incisions on gingiva. manufacturer for soft tissue surgery (65 mJ/pulse at 10 Hz). Scalpel incisions were made with a stainless steel microsurgery scalpel (no. 7628B, Feather Safety Razor, Osaka, Japan). A new blade was opened for each rat Data

analysis Digastric EMG waveforms were analyzed with the software Spike2 version 4.19 (Cambridge Electronic Design). To allow for the comparison of EMG data between different rats, the absolute values of the average JOR amplitudes were standardized into a percentage of the reflex amplitude evoked by 1.5-T tooth-pulp electrical stimulation according to the method described by Toda et al.12 Rectangular constant current pulses (01 ms OOOOE Volume 100, Number 1 Zeredo et al 33 Fig 3. JOR amplitudes evoked by surgical incisions in each site Except for the ipsilateral and contralateral lip, reflex amplitudes evoked by laser incisions were significantly smaller than those evoked by scalpel incisions in all other sites. Absolute values were standardized into a percentage of the reflex amplitude evoked by 1.5-T tooth-pulp stimulation Displayed values are mean 6 SEM *P .05 in the Mann-Whitney U test duration at 1 Hz) were used for electrical stimulation (SEN7203 and SS202, Nihon Kohden,

Tokyo, Japan). Comparisons between laser and scalpel groups were made by the Mann-Whitney U test. Reflex amplitudes from laser and scalpel incisions in the same rats were compared by the Wilcoxon signed rank test. In each test, P .05 was considered statistically significant The software Statview version 5.0 (SAS Institute, Cary, NC) aided in statistical analyses. RESULTS From the macroscopic aspect of the surgical incisions, we observed that laser incisions had a characteristic roughness with whitish borders in some regions of gingiva, mucosa, and tongue, whereas scalpel incisions were sharp and smooth (Fig 1). In addition, laser incisions produced considerably less bleeding than scalpel incisions. The digastric EMG responses were lower during laser cutting (Fig 2). Except for the lip, the JOR amplitudes evoked by laser were significantly smaller than those evoked by scalpel in all other incision sites (Fig 3). The mean JOR amplitudes were also smaller in lip incisions with laser;

however, the lip was the site where not only Fig 4. Comparison of reflex amplitudes evoked by laser or scalpel incisions in the same rats. Absolute values were standardized into a percentage of the reflex amplitude evoked by 1.5-T tooth-pulp stimulation Incisions were made ipsilateral to the electrical stimulation and EMG recording side. *P .05 in the Wilcoxon signed rank test laser incision was most effective, but also scalpel incision was least effective in evoking JOR. As for the other incision sites, the greatest difference in reflex amplitude was found in the gingiva. In scalpel incisions, ipsilateral sites evoked larger reflex amplitudes than contralateral ones. Such effect was not observed in laser incisions. OOOOE July 2005 34 Zeredo et al Table I. JOR amplitudes evoked by laser or scalpel in each incision site Incisions Area Laser Scalpel Ipsilateral (n = 6) Lip Gingiva Mucosa Tongue 53.9 11.2 28.1 31.8 6 6 6 6 16.2 1.5 7.7 8.2 104.4 149.6 141.1 159.2 6 6 6 6

47.4 25.9* 48.7* 50.3* Contralateral (n = 6) Lip Gingiva Mucosa Tongue 34.3 12.6 29.7 39.8 6 6 6 6 11.7 3.5 15.0 9.1 71.3 107.5 125.4 119.5 6 6 6 6 42.3 62.7* 46.5* 30.4* Second ipsilateral (n = 6) Lip Gingiva Mucosa Tongue 28.1 20.9 23.5 35.5 6 6 6 6 6.4 7.1 8.8 10.2 77.2 175.8 140.2 115.3 6 6 6 6 33.7 58.8* 68.4* 42.6* Values are mean 6 SEM (%); n is the number of incisions. *P # .05 (Mann-Whitney U test) Comparison of JOR amplitudes from laser and scalpel incisions in the same rats showed results similar to that of groups (Fig 4). Statistically significant differences were found in all incision sites except lip (P = .09 in the Wilcoxon signed rank test) Similarly, the greatest difference in mean reflex amplitudes was found in the gingiva. The JOR amplitudes evoked by Er:YAG laser or steel scalpel from all 144 incisions are summarized in Table I. DISCUSSION The JOR is a nocifensive reflex that follows a stimulusresponse relationship,13 and was thus used in this

study as an index of nociceptive response or sensation. Under normal conditions, both the JOR magnitude and the degree of pain experienced increase with increasing stimulus intensity.14 It is well known that noxious orofacial stimulation evokes JOR responses15 The reflex can also be evoked by stimulation of the inferior alveolar nerve below sensory thresholds or by innocuous tapping of teeth and intraoral tissues16,17; nevertheless, under normal conditions (ie, not under analgesic treatments) the reflex magnitude reliably indicates the degree of pain experienced.14 Clinical experience indicates that oral soft tissue surgery with the Er:YAG laser would cause minimal pain and discomfort. Although anesthesia is mandatory for conventional scalpel surgery, Aoki et al11 were able to treat 61 patients with a variety of surgical procedures, such as gingivectomy and frenectomy, under no infiltrative anesthesia. In that study, the patients’ subjective pain assessment using a visual analogue

scale (VAS) ranged only from slight to moderate. Although there have been anecdotal remarks that cutting oral soft tissue with a laser would be less painful than with a scalpel,4,18,19 the mechanisms behind this phenomenon are not understood. One theory states that protein coagulation caused by laser cutting would seal the ends of peripheral sensory nerves and thus reduce pain sensation.20 From the point of view of nerve fiber activation, it is known that laser stimulation below tissue ablation threshold effectively excites Ad and C mechano-heat nociceptors in the orofacial region (the so-called laser evoked potentials).21 Therefore, highpower laser irradiation could be expected to evoke pain Despite the obvious mechanical effect of the incisions, and hence the noxious nature of tissue ablation (with both laser and scalpel), the comparatively lower mean amplitudes of JOR observed during laser incisions may be due to analgesic mechanisms inherent to the laser irradiation. As for the

qualitative aspects of the surgical incisions, we noticed a few advantages of the Er:YAG laser over scalpel. For instance, less bleeding may provide ‘‘cleaner’’ surgical fields. In addition, it is not necessary to apply pressure to incise tissue, which improves the precision of tissue ablation. These features are particularly useful in the case of the highly vascular and resilient oral tissues. On the other hand, scalpel cutting was somewhat swifter and produced sharper incisions. Some studies indicate that Er:YAG laser would be superior to scalpel in terms of postoperative pain and wound healing.11,22,23 Noxious stimulation produces the phenomenon of neurogenic inflammation (axon reflex).24 Activation of a nociceptive receptor by a noxious stimulus causes the release of several peptides, including substance P and other tachykinins, that increase the local blood flow, resulting in vasodilation, plasma extravasation, and edema. This reaction activates adjacent nociceptors, which

leads to the spread of the response. Noxious stimulation may also cause functional changes in the central nervous system that result in sensitization to pain. Therefore, one could expect that decreased noxious stimulation during surgery would result in less postoperative pain and tissue inflammation. Our results indicate that oral incisions made with Er:YAG laser may produce significantly less pain than similar incisions made with a steel scalpel, suggesting that considerably less use of local anesthesia and sedation would be required for Er:YAG lasereassisted oral surgery. We thank Mr Youji Yamaguchi from HOYA Photonics Corporation, Osaka, Japan, for kindly providing the laser system used in this study. REFERENCES 1. Ross EV, McKinlay JR, Sajben FP, Miller CH, Barnette DJ, Meehan KJ, et al. Use of a novel erbium laser in a yucatan minipig: a study of residual thermal damage, ablation, and OOOOE Volume 100, Number 1 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. wound healing

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jaw-opening reflex a valid model of pain? Brain Res 1985;357:137-46. Hannam AG, Matthews B. Reflex jaw opening in response to stimulation of periodontal mechanoreceptors in the cat. Arch Oral Biol 1969;14:415-9. Zeredo et al 35 16. Sessle BJ Presynaptic excitability changes induced in single laryngeal primary afferent fibres. Brain Res 1973;53: 333-42. 17. Cadden SW, Newton JP A comparison of reflex depressions of activity in jaw-closing muscles evoked by intra- and peri-oral stimuli in man. Arch Oral Biol 1988;33:863-9 18. White JM, Goodis HE, Rose CL Use of the pulsed nd:Yag laser for intraoral soft tissue surgery. Lasers Surg Med 1991;11: 455-61. 19. Arnabat-Dominguez J, Espana-Tost AJ, Berini-Aytes L, Gay-Escoda C. Erbium:Yag laser application in the second phase of implant surgery: a pilot study in 20 patients. Int J Oral Maxillofac Implants 2003;18:104-12. 20. Schuller DE Use of the laser in the oral cavity Otolaryngol Clin North Am 1990;23:31-42. 21. Romaniello A, Iannetti GD,

Truini A, Cruccu G Trigeminal responses to laser stimuli: reponses a la stimulation trigeminale par laser. Neurophysiologie Clinique/Clinical Neurophysiology 2003;33:315-24. 22. Tal H, Oegiesser D, Tal M Gingival depigmentation by erbium: Yag laser: clinical observations and patient responses. J Periodontol 2003;74:1660-7. 23. Watanabe H, Ishikawa I, Suzuki M, Hasegawa K Clinical assessments of the erbium:Yag laser for soft tissue surgery and scaling. J Clin Laser Med Surg 1996;14:67-75 24. Meyer RA, Campbell JN, Raja SN Peripheral neural mechanisms of nociception In: Wall PD, Melzack R, editors Textbook of pain. London: Churchill Livingstone; 1994 p 13-44 Reprint requests: Jorge L. Zeredo, DDS, PhD Division of Integrative Sensory Physiology Department of Developmental and Reconstructive Medicine Graduate School of Biomedical Sciences Nagasaki University 1-7-1 Sakamoto Nagasaki 852-8588, Japan jorge@net.nagasaki-uacjp