Infrared laser and bone metabolism: A pilot study

hTt. J. Oral Maxillq/iu'. Surg. 1994; 23. 54-56 Priztted in Denmark. All rights reserved

Copyright (© M u n k s g a a r d 1994

IntemadonalJoumalof

Oral & MaxillofacialSurgery I S S N 0901-5027

Infrared laser and bone metabolism: a pilot study

M. G o r d j e s t a n i ~, L. D e r m a u t 1, H. T h i e r e n s 2 1Department of Orthodontics and 2Institute of Medical Physics, University of Ghent, Belgium

M. Gordjestani, L. Dermaut, HI Thierens. Infrared laser and bone metabolism." a pilot study. Int. J. Oral Maxillofac. Surg. 1994," 23." 54-56. © Munksgaard, 1994

Abstract. A circular defect in each parietal bone of six Wislander rats was created. The animals were divided into two three-unit subgroups. The experimental group received infrared laser radiation on the left defect. The control group was sham irradiated. After 28 days, the bone metabolism was evaluated by technetium-99m methylene diphosphonate scintigraphy. The obtained results revealed no differences in bone metabolic activity between the laser-treated and the control defects.

Since the discovery of the laser in 1960 by MAIMAN, the use of this form of radiation has gained considerable attention in various medical areas. With respect to laser therapy, a distinction should be made between high- and low-energy lasers. The use of low-intensity lasers (soft laser) has gained much attention in the last few years 1,3,4&16. Soft-laser therapy has been introduced to promote the healing of superficial wounds ~. MESTER~3 maintained that laser radiation increases blood circulation within regenerating tissue. In a histologic study, LIEVENS et al. ~ described a rapid reorganization of the lymphatic and capillary system in wound healing after the application of laser therapy in mice. TAKEDA16 showed in vivo that rat fibroblast cells, after being exposed to the laser beams, proliferate more rapidly than tissue not exposed to the laser. HAAS et al. 8 observed a higher motility of cultured h u m a n keratinocytes. BOSATRA et al. 2 showed by electron microscopy that, after the application of laser beams, ergastoplasm in human fibroblast cells increases in volume, suggesting a greater protein production. Increased collagen production after stimulation of cells by laser beams has been demonstrated by various scientists 1,3. Some authors 7,18 suggest that stimulation of nerve fibers

by laser therapy might result in an analgesic effect. However, the biostimulating effects Of soft lasers remain a matter of debate, since other authors have not found any effect from soft-laser therapy. BRAVERMAN et al. 4 did not notice any change in the speed of the healing process of skin wounds in rabbits after laser therapy. In an in vitro study, DE RIDDER et al. 6 could not detect any change in cellular activity and division of embryonic chick heart cells. Although laser therapy is being used in some fields of medicine, the soft laser as a biostimulating device is not universally accepted because of lack of scientific evidence 9,~s,~7. The aim of this study was to investigate the effect of soft lasers on bone metabolism, since ossification might be stimulated by laser treatment as a result of increased collagen production and accelerated cell division 12'16. Material and methods

Six male Wislander albino rats were chosen for the experiment. The animals were mature (90 days old) and from the same parents. Their average weight was 387 g. The rats were divided at random into two three-unit subgroups: an experimental group and a control group. The rats were kept in one cage (18°C) in which they could move freely and eat and drink from the same source.

Key words: bone healing; low-energy laser. Accepted for publication 27 August 1993

Production of standard defects in the skull General anesthesia was achieved by intraper-

itoneal injection of pentobarbiturate (40 mg/ kg body weight). After the heads had been shaved, the periost of the parietal bones was dissected by an incision of the scalp. In each parietal bone, a circular bone defect was created (Fig. 1). The diameter of the circular defect was 2.7 mm. The choice of this diameter was based on the dimension of the infrared beam emitted by the laser device (3 ram) and the fact that spontaneous healing of the defect could be expecteds. Because of deep drilling and possible damage to the brain, the piercing drill was equipped with a safety ring to control precisely the depth of the hole. Registration of the position of the created bone defects in the parietal bones

The determination of the position of the bone defects, which were covered by the scalp, was very important for the application of laser rays during the experimental period and for the measurement of bone metabolism, registered by a scintillation detector, at the end of the experimental period. Therefore, the following two devices were developed to position the laser beam and the scintillation detector accurately above the covered defect. 1) A Plexiglas plate was used to determine the center of the bone defect in the experimental group (left defect) for application of laser rays. After the creation of the bone defects, the Ptexiglas plate was placed on the surgery field, and the center of the left bone defect and three anatomic points (two in-

I R laser and bone

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The laser beams might stimulate osteogenic activity in situ, but they might also have an effect on the contralateral side by stimulation of the blood circulation of the region j3. Therefore, the experimental group was composed of animals in which only the left defects received laser rays during the experimental period. The control group, on the contrary, was not stimulated by any laser application in an attempt to evaluate the healing process itself. For equal treatment of both groups, the control group was also sham irradiated. Immediately after surgery, the experimental animals were exposed to the laser beam for 5 min twice a day for a period of 28 days. While the rays were beamed at the experimental defect, the control defect was covered with a 0.15-mm-thick a l u m i n u m sheet, to protect the defect against the emitted laser rays.

Bone scintigraphy

Fig. 1. Two circular defects 2.7 m m in diameter were created in each parietal bone of animals.

Fig. 2. After fixation of animal's head, center of each defect was exactly registered on graph paper. ner eye corners and the nose of the animals) were indicated on the plate. After this procedure, laser rays could be aimed at the center o f the defect by reorienting the plate on the three anatomic points. 2) For measuring the ossification activity with a scintillation detector device, the center of the bone defect in all rats was determined with a fixator. The skull of the animal was fixed in the device by inserting two metal pins in its ears and attaching nose clips. Once the animal was fixed, the center of the defect in the skull was pinpointed, a n d the coordinates were registered on graph paper s. By this procedure, the position of the skull bone defect under the skin could be precisely determined to measure the emission of g a m m a rays at the end of the experiment (Fig. 2).

After determination of the position of the skull defects, the operation field was disinfected and the scalp was stitched.

Laser beam application procedure An infrared laser type G a - A s (wavelength 904 nm) was used. The power density of the device was 33.3 m W / c m 2, and an energy density equivalent to 20 J / c m 2 was administered daily 15. The infrared laser rays were chosen for their deep penetration into subcutaneous tissues, because of low absorption in water or skin pigments. The choice of an experimental and a control group was based on the consideration that laser application on a well-defined area m a y have a local as welt as a general effect.

After 28 days of treatment with laser rays, the bone metabolism of the bone defects was measured by bone scintigraphy. One mCi (37 MBq) of technetium-99m methylene diphosphonate was injected intraperitoneally ~°,~4. The diphosphonate uptake adsorbed onto the surface of hydroxyapatite crystals in areas of active bone tissue. Within 5 h, the excess radioactive substance was removed from blood a n d connective tissues through urinary excretion. After this period, the rats were anesthesized by an intraperitoneal injection of pentobarbiturate (40 m g / k g ) and were placed in the fixator. The center of the bone defect was registered in the fixating device according to the previously registered coordinates on the graph paper, as explained before. For measuring the bone metabolism, a scintillation detector (Bicron 1.5 x M 1/2 NaI crystal) was placed in a collimator made of lead to prevent side radiation. The 3-mm orifice of the collimator was aimed precisely at the center o f the bone defect. In this manner, only the parallel beam of emitted g a m m a rays from the defect could reach the detector and be registered. The a m o u n t of registered radiation indicated the activity of bone metabolism of the 12 bone defects.

Results T h e r e s u l t s s h o w t h a t n o d i s t i n c t differe n c e s in b o n e m e t a b o l i s m d e v e l o p e d b e tween the left-side (laser-treated) and t h e r i g h t - s i d e d e f e c t s ( c o n t r o l side) in t h e e x p e r i m e n t a l g r o u p (Fig. 3). T h e u p t a k e v a l u e s in t h e e x p e r i m e n t a l g r o u p did not show any significant difference from the control group.

Discussion Reviewing the literature on the biostim u l a t i n g e f f e c t s o f soft laser o n c o l l a g e n

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Fig. 3. Registered counts by scintillation detector show no significant differences between the created bone defects in either experimental or control group.

p r o d u c t i o n a n d the increase in cellular division o f fibroblasts, we consider t h a t studies on the effects o f laser b e a m s o n bone m e t a b o l i s m are still lacking. In this study, the infrared laser was used because of its k n o w n p e n e t r a t i o n into s u b c u t a n e o u s tissues. T h e experimental defects received a n i n f r a r e d b e a m with a n energy density equal to 20 J / c m 2 per day at a power density o f 33.3 r o W / cm 2. It has to be emphasized t h a t the effect of different intensities of laser rays on b o n e m e t a b o l i s m is, as yet, n o t well known. M o r e research is required to test this variable. With the e q u i p m e n t developed, a precise positioning of the laser b e a m could be obtained. After 28 days, each animal's skull was repositioned in the fixator very precisely to measure the emitted g a m m a rays from the skull defects by b o n e scintigraphy. T h e reliability of the repositioning of the animals in the fixator has been e x a m i n e d by DE BIE et al. 5. Fig. 3 shows t h a t differences in registered c o u n t s were f o u n d a m o n g the animals in b o t h groups. I n t e r i n d i v i d u a l differences in the general m e t a b o l i s m can explain these results. The b o n e metabolism was m e a s u r e d by b o n e scintigraphy, which reflects the activity of osteoblasts as well as osteoclasts. T h e question o f w h e t h e r osteoblast activity was the cause of increased b o n e m e t a b olism was n o t investigated because n o laser effects could be detected. F r o m this experiment, it can be c o n c l u d e d t h a t infrared laser b e a m s with a power den-

sity of 33.3 m W / c m 2 a n d a n energy density of 20 J / c m 2, a d m i n i s t e r e d daily for 28 days, have neither stimulating n o r inhibiting effects on the b o n e m e t a b olism activity of the skull surface o f rats. Because o f the limited n u m b e r o f animals in this pilot study, the results Should be interpreted with caution. F o r more precise conclusions, m o r e experiments with a higher n u m b e r of a n i m a l s a n d with varied powers o f laser are required. F r o m this pilot study, however, there is n o indication to introduce infrared soft-laser therapy (20 J / c m 2 p e r day) to accelerate bone healing. Acknowledgment. The author kindly thanks Mr Abbas Gordjestani for his support.

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