|Year : 2014 | Volume
| Issue : 2 | Page : 50-55
Effect of low power diode laser on mandibular growth (experimental study)
Ali Saafan1, Ahmed Abd-El-Fattah2, Adel Bakeer3, Shereen Mohammed Khattab4
1 Department of Dental Laser Applications, National Institute of Laser Enhanced Sciences, Cairo University, Giza, Egypt
2 Department of Orthodontic, Suez Canal University, Ismailia, Egypt
3 Department of Pathology, Faculty of Veterinary Medicine, Cairo University, Giza, Egypt
4 Department of Orthodontics, Cairo University, Giza, Egypt
|Date of Web Publication||21-Nov-2014|
Shereen Mohammed Khattab
Medical Laser Applications, National Institute of Laser Enhanced Sciences, Cairo University, Giza
Source of Support: None, Conflict of Interest: None
Introduction: Low laser level therapy (LLLT) has a stimulatory effect on bone formation. The aim of this study was to assess the effect of the low laser therapy LLLT on the condylar growth in rabbits. Materials and Methods: The sample consisted of 24 male white New Zealand rabbits with the mean age of 5 weeks and the mean weight of 1.5 kg. LLLT was used for radiation. The sample was divided into two groups: The first group was the control group, which was not subjected to any laser irradiation. The second group was irradiated unilaterally (right side) with was CW 870 nm with power output of 300 mW, energy of 180 J. The spot size was 4 mm circle. The exposure was performed on the temporomandibular joint (TMJ) (a total of 10 min) for 3 sessions/week for 4 weeks. The rabbits in both groups were sacrificed, and the histological evaluation of TMJ was performed to compare the fibro cartilaginous layer, chondrogenic layer and newly formed bone trabeculae. Results: Hyperplasia was observed in the fibro cartilaginous layer associated with hypertrophy in the chondroblasts with excessive newly formed bony trabeculae in the underlying bony structure. Conclusion: Low-level laser (diode) in rabbits enhances mandibular growth by condylar endochondreal bone growth while no increase in the fibrous tissues. The results of this study encourage the use of LLLT during orthodontic treatment as it would provide benefit to patients, allowing them to shorten prolonged treatment.
Keywords: Condyle, growth, low-level laser, rabbit
|How to cite this article:|
Saafan A, Abd-El-Fattah A, Bakeer A, Khattab SM. Effect of low power diode laser on mandibular growth (experimental study). J Dent Lasers 2014;8:50-5
|How to cite this URL:|
Saafan A, Abd-El-Fattah A, Bakeer A, Khattab SM. Effect of low power diode laser on mandibular growth (experimental study). J Dent Lasers [serial online] 2014 [cited 2020 Jun 7];8:50-5. Available from: http://www.jdentlasers.org/text.asp?2014/8/2/50/145139
| Introduction|| |
The mandibular condyle is a growth center of the mandible that contributes to its length and height. Proliferation of pre chondroblasts, followed by synthesis of the extracellular matrix and hypertrophy of the chondroblasts, governs the major part of condylar growth. 
It is known that orthopedic treatment of Class II malocclusions is a matter of ongoing controversy regarding the possibility of stimulating mandibular growth in a predictable manner. Apparently, the effectiveness of mandibular orthopedic treatments depends on the synergy between treatment and growth, especially in individuals who are undergoing their pubertal growth spurt. 
The Class II malocclusion has been called the most frequent skeletal problem in the orthodontic practice. The solution can involve the use of functional or fixed orthodontic appliances, or both.  It has been claimed that the most frequent skeletal problem in Class II patients is mandibular retrognathia. 
Recently, low-level laser was used to enhance bone healing after fracture, after mandibular distraction osteogenesis, , and also for condylar growth stimulation.  The results suggest that low-level laser therapy (LLLT) had a positive effect on the percentage of newly formed bone. Better-quality bone sites may allow early healing, thus shortening total treatment time.
The development of technologies capable of accentuating the growth potential of mandibular cartilage could allow our profession to predictably intervene in the development of growing tissues.
In the orthopedic field, the repair of articular cartilage is still a difficult problem, due to the physiological characters of cartilaginous tissues and chondrocytes.  To find an effective method of stimulating their regeneration, this in vitro study focuses on the biostimulation of rabbit articular chondrocytes.
Considering the positive effects of LLLT on bone regeneration. The objective of this study was to assess the effect of the low laser therapy LLLT on the condylar growth in rabbits.
| Materials and Methods|| |
This study was approved by and performed at Faculty of Veterinary Medicine Cairo University, Pathology Department. A 24 male white New Zealand rabbits with the mean age of 5 weeks and the mean weight of 1.5 kg were selected. Appropriate permissions were secured from institutional review board, and appropriate animal care was provided as per guidelines.
Rabbits were randomly divided into two groups: The first group was the control group, which was not subjected to any laser irradiation; the second group was irradiated unilaterally on the right side . The rabbits were kept in room temperature with heating the room at nights at average 20°C. The exposure site was marked with a unerasable pen The exposure site was shaved prior to the exposure process; this was to allow direct laser exposure with no hair obstacles.
Low-level laser therapy radiation
Radiation was performed via low power diode laser device locally manufactured (Photon Scientific, Industrial Area, Qaliub, Egypt), which was CW 870 nm with power output of 300 mW (at the end of the tip in contact mode), energy of 180 J, and the total exposure time was 10 min/session. The spot size was 4 mm circle so; the power density was 0.6 W/cm 2 , and the energy density was 180 J/cm 2 .
Statistical analysis was performed with IBM ® (IBM Corporation, NY, and USA.) Statistical Package for Social Sciences (SPSS) ® (SPSS, Inc., an IBM Company) statistics version 20 for windows, and the significance level was set at P ≤ 0.05.
Exposure was performed on the right sided temporomandibular joint (TMJ), through the skin. Exposure was a total of 10 min for 3 sessions/week for 4 weeks. Eye goggles were worn as protective measurement for the physician.
The rabbits in both groups were sacrificed by vital perfusion, the right-sided hemi mandibles (control and radiated) were dissected and fixed in formaldehyde 4%, decalcified in ethylenediaminetetraacetic acid for 60 days and then embedded in paraffin. Serial sections from TMJ including condyle and glenoid fossa were cut sagittally with 4-5 μm diameter and stained with hematoxylin and eosin. The sections were evaluated blindly under a light microscope Durable Educational Microscope with Superior Optics Leica BME with different powers magnifications.
The photograph of each section was taken and saved as a digital file, and then analyzed by image software analysis (Leica Q win Plus). Each slide was viewed under ×100 optical microscope, and images were acquired using a digital camera connected with microscope. The bone interconnected to cartilage considered as new bone. The power calculation for different variables to confirm the reliability of the study was performed.
The present study was concerned of studying the fibro cartilaginous layer and newly formed bone trabeculae.
The lengths of the right sides of the mandibular halves were measured with a measuring device with a precision of 0.01 mm, on the line connecting the ear hole and the tip of the gingival papilla between the mandibular incisors. This was done by two independent examiners. These measurements were on soft tissue and performed on days 0, 30 days.  After scarification, denuded mandibles were measured from the level of the cranial extremity of the alveolar root of the incisor to the level of the caudal border of the mandible. This protocol was based on hard tissue.
T-test and three-way analysis of variance were performed for both histological and mandibular measurements.
| Results|| |
Statistical analysis showed a significant difference between mandibular length of the control and radiated groups. Enlarged condyle and increased ramal height were clearly observed in treated sides compared with the nontreated sides. Moreover, canting of the occlusal plane could also be seen in [Table 1] and [Figure 1].
|Figure 1: Line chart comparing the mandibular length of the radiated and control groups (in relation to the baseline represented by the zero line)|
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|Table 1: The mandibular length of right sides of the mandible (control and radiated), the mean difference and the P value. *Significant difference P≤0.0001|
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In all the control groups: Tissue sections of the condyle of normal rabbits revealed a thin fibrous layer, which covered the articular surface, a thin fibro cartilaginous layer, and well-organized bony trabeculae with areas of marrow tissue while the articular surfaces of the condyle of all control (normal) sides showed a dense fibrous layer, which covered a fibro cartilaginous layer, and thin arcades of calcified cartilage under which there were well-organized bony trabeculae, lined with inactive osteoblasts, and encircled with wide areas of vascularized marrow tissue. There was no histopathological alteration and the normal histological structure of the fibro cartilaginous layer and the underlying bony structure [Figure 2]; while, in the exposed groups: The condyle of the radiated group revealed hyperplasia of the fibro cartilaginous layer, hypertrophy of the chondroblasts of the chondrogenic layers, and endochondreal ossification (bone replacement) on the mineralized cartilaginous layer. Excessive bony trabeculae lined with prominent active osteoblasts and dilated blood capillaries were also detected [Figure 3] and [Figure 4].
|Figure 2: Optical micrograph of a condyle of a rabbit showing normal histological structure (H and E, ×40)|
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|Figure 3: Optical micrograph showing the hypertrophy of the chondroblasts in the radiated condyle of a rabbit (H and E, ×40)|
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|Figure 4: Optical micrograph showing newly formed bony trabeculae in the radiated condyle of a rabbit (H and E, ×40)|
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Histological and histomorphometric analyses
The results show that the fibrous tissue mean thickness in condylar region is statistically greater in control groups as compared to lased groups, while the mean thickness of new condylar bone as well as chondrogenic layers is statistically greater which shows more bone formation in the lased group in relation to the control one [Table 2], [Figure 5] and [Figure 6].
|Figure 5: Line chart comparing the newly formed bone thickness of the radiated and control groups (in relation to the baseline represented by the zero line)|
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|Figure 6: Line chart comparing the cartilaginous layer thickness of the radiated and control groups (in relation to the baseline represented by the zero line)|
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| Discussion|| |
In this study, the stimulatory effects of 870 nm low-level diode laser irradiation on bone formation in the condylar region in rabbits were clarified. The data of this study suggest that newly formed bone increased by 3 weeks irradiation around TMJ. Miloro et al. found that LLL accelerates the process of bone regeneration in the mandibles during the consolidation phase after distraction osteogenesis as compared with control animals,  Jia and Guo demonstrated a biostimulatory effect of the He-Ne laser on articular chondrocytes. They believed that their results would be of clinical relevance and need further verification in the clinic. Moreover, further laboratory research work is required to understand the mechanisms leading to the stimulation of that cell line.  Liu believes that LLL may accelerate the process of fracture repair or increases the callus volume and bone mineral density, in the early stages of fracture healing. ,
Stein's studies indicate that LLLT has a biostimulatory effect on human osteoblast-like cells  and it could promote proliferation and maturation of human osteoblasts in vitro. 
Khadra et al. claimed that the application of LLL with a gallium-aluminum-arsenides diode laser device can promote bone healing and formation in skeletal defects. ,
Pinheiro and Gerbi concluded that the bone irradiated mostly at infrared wavelengths showed increased osteoblastic proliferation, collagen deposition, and new bone formation. 
It is reported that LLLT facilitates differentiation and activation of osteoclasts, which supports bone remodeling and cartilage differentiation of the bone.  Moreover, literature has demonstrated stimulative effects of laser irradiation in active sites such as bone fracture, bone lesions, and extraction sockets. ,,
Similar conclusions have been obtained by Dφrtbudak about the effect of soft diode lasers on osteoblasts derived mesenchymal cells. 
Findings of improved bone healing in animal models with adjunctive laser therapy are consistent with other research on the effects of laser. It is supposed that if LLLT increases bone and cartilage formation, the treatment might be easier and more stable. Since no side effects on children have been reported. ,,
Serial sections of all condyle of the US-treated group exhibited the hyperplasia of the fibro cartilaginous layer, hypertrophy of the chondroblasts of the chondrogenic layers, and endochondreal ossification on the mineralized cartilaginous framework. Excessive bony trabeculae lined with prominent active osteoblasts and dilated blood capillaries. ,
Since the initial large changes in cartilaginous proliferation are progressively diminished when restoration of functional equilibrium is obtained,  authors recommend immediate intervening with treatment immediately after laser exposure for fruitful results.
Jia and Guo demonstrated that little differences in energy density are able to have different action on cell growth and that LPL can stimulate cell proliferation, but only within combination of exposition parameters, in a narrow energy and power density bands. 
Although the mechanism of laser irradiation on ossification is unknown, increase of ossified nodules, fibroblast formation, and calcium and phosphorous aggregation. Vascular responses to laser therapy were also suggested as one of the possible mechanisms responsible for the positive clinical results observed following laser therapy. 
El-Bialy et al. demonstrated that LLL, when has a stimulatory effect on the mandibular surface area, as evaluated by histomorphometric analysis compared with no treatment or functional appliances (FAs). Their study did not support the hypothesis that a combination of more than one treatment modality (LLL, or FAs) can stimulate mandibular growth more than each treatment modality by itself when evaluated by histomorphometric analysis. 
| Conclusion|| |
Regarding the findings of this study, irradiation of LLLT (diode) in rabbits enhances mandibular growth by condylar endochondreal bone growth and consequently mandibular ramus growth, while no increase in the fibrous tissues. This study is strongly encouraging result of employing LLLT as a potential bio-stimulator. This would provide great benefit to patients, allowing them to shorten prolonged treatment.
| Acknowledgments|| |
We thank Institute of Statistical Studies and Research-Cairo University for their great effort in the statistical analysis.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]
[Table 1], [Table 2]