Effects Of Low-Power Semiconductor Laser Irradiation On Healing Progress Of Tympanic Membrane Perforations

Objective Investigate effects at different doses of low-power 635nm semiconductor laser irradiation on healing progress of tympanic membrane perforations.Methods Thirty-nine healthy guinea pigs were randomly divided into three groups(A,B,C). Resecting the tragus and lower part of the auricle to make external acoustic meatus exposed. After wound healing, standard otomicrosurgical techniques were used to create bilateral perforations (1.5mm×2.0mm) in the posterosuperior quadrants of the tympanic membranes, leaving the fibrous annulus and the portion of the tympanic membrane covering the malleus intact. Three groups respectively received low-power semiconductor laser (635nm) irradiation at intensities of 45.11mW/cm~2 (group A), 12.38mW/cm~2 (group B) and 6.19mW/cm~2 (group C) , the doses were 27.07J/cm~2 (group A), 7.43 J/cm~2 (group B ) and 3.72 J/cm~2 (group C), once daily for 10min, 9 tunes in all. The irradiated side was selected randomly and the other side was left untreated for comparison. The ears were examined under an operating microscope and 8 of them were recorded the healing time of the tympanic membrane perforations. To examine the healing progress in different periods, the other 5 animals in each group were killed 3, 5, 7, 9 and 11 days respectively after the creation of the perforations. The intact tympanic membranes with bony annulus were harvested, stained with hematoxylin and eosin, andexamined under light microscopy. Histologically, the thickness of the tympanic membrane was measured, and neovascularization of the fibrous layer was scored.Results The mean spontaneous healing period of the tympanic membranesin control groups was 10.92 days (8-15days). The difference between the control groups was not significant (P=0.880). The mean perforation closure time of the treated sides was 11.25 days (9-14 days) in group A, 9.00days(8-12 days) in group B and 10.50 days (8-13 days) in group C. The difference between the treated sides and the control sides in group B was significant (P=0.002), and the other two groups were not. The difference between the three treated groups was significant (P=0.016), group B was different from group A and C (P < 0.05 ) , and the difference between group A and C was not significant (P>0.05) .The mean thickness of the tympanic membranes in control groups was 114.05um (43.47-255.97um). The difference between the control groups was not significant (P=0.720). The mean thickness of the tympanic membranes of the treated side was 142.89um (50.13-269.53um ) in group A, 214.28um (165.63-258.23nm) in group B and 135.02um (63.6-271.93um) in group C. The difference between the treated sides and the control sides in group B was significant (P=0.000), and the two others were not. The difference between the three treated groups was significant (P=O.O35), group B was different from group A and C (P < 0.05), and the difference between group A and C was not significant (P > 0.05 ) .The difference of neovascularization scores in control groups which were recorded from + to +++ (mean 1.375+) was not significant (P=0.265). Theneovascularization scores in group A were +-+++ (mean 1.625+), +-++++ (mean 2.375+) in group B, and +-+++ (mean 1.250+) in group C. The differences between the treated sides and the control sides in each group itself were not significant(P^=0.107;Pb=0.094;Pc=0.653), and the difference between the three treated groups was not significant(P=0.097), too.In the course of the perforations' healing, the squama epidermis had an obvious hyperplasia, a faster migration and a significant thicker fibrous layer in group B in contrast to in group A and C.Conclusions1 Low-power semiconductor laser (635nm) irradiation at intensity of 12.38mW/cm2, whose energy density was 7.43J/cm2, once daily for lOmin, 9 times in all, could accelerate the closure of acute tympanic membrane perforations of guinea pigs, promote the thickness of the healing tympanic membranes, but it was need to research whether these were the optimal stimulative parameters. Irradiation at intensities of 45.1 lmW /cm2 and 6.19mW/cm2 , whose energy densities were 27.07J/cm2 and 3.72J/cm2, could not be observed promoting the healing progress.2 According to these conclusions, we can use low-power laser irradiation to promote the healing of chronic tympanic membrane perforations or tympanic membrane perforations accompanied by impaired wound healing ability.3 The objects in our research were guinea pigs, and it had shown that low-power laser irradiation could improve the healing progress of tympanic membrane perforations of guinea pigs. It need to research that whether low-power laser irradiation can similarly improve the healing progress of tympanic membraneperforations of human beings. If this presume is true, then it should be concerned what are the optimal stimulative intensities and energy densities.