rapid maxillary expansion is one of the treatment options in the correction of the constriction of maxillary dental arch and jaw . maxillary constriction is a part of many deformities such as posterior crossbites , class ii and iii malocclusion . one of the reasons for relapse consequence to use of maxillary rapid palatal expander ( rpe ) is a lack of rapid and adequate bone regeneration in the midpalatal suture . long - time retention after expansion will significantly decrease the rate of relapse through bone regeneration in palatal midsuture . on the other hand , long - term use of banded or bonded rpe as retainers can cause some complications such as enamel hypocalcification , gingival irritation and dental carious . improved bone regeneration in the midpalatal suture decreases the retention time , and its complications maxillary expansion causes hyperemia , osteoblastic activity , primary bone regeneration , and calcium removal . since 1971 , studies have evaluated the effect of laser on bone regeneration in clinical conditions or cell cultures . lasers can be used in biopsy sampling , eliminating oral lesions ( aphthous ulcers , herpetic lesions ) , tuberosity reduction , coagulation , treating temporomandibular joint lesions , instrument sterilization , gingivectomies , etc . regeneration is a complicated process and laser might accelerate it . in a study , saito and shimizu investigated the effect of gallium - aluminum - arsenide ( ga - al - as ) low - power laser exposure on bone regeneration in palatal midsuture during the maxillary expansion of rats . results of histophotometric investigations showed that compared with the control group , bone regeneration increased approximately 1.21.4 times in 7 days in the experimental group . these results confirm the positive effect of laser therapy on bone regeneration in the midpalatal suture . studied effects of laser irradiation on the bone regeneration and showed increased width and depth of newly bone . . showed that areas receiving laser therapy experienced less pain and more effective dental movement . kawasaki and shimizu reported better tooth movement , greater bone regeneration and cellular proliferation , and a greater number of osteoclasts in areas exposed to the laser . in a study ozawa et al . showed that laser exposure in early stages of culture , significantly stimulates cell proliferation , alkaline phosphatase activity , and appearance of osteocalcin gene . furthermore , laser exposure in early stages of culture caused a significant increase of bone nodules in 21 day . this study was conducted to evaluate the influence of ga - al - as low - power laser exposure on bone regeneration in palatal midsuture during palatal expansion in rats . a total of 78 sprague male rats , each weighted around 200 g were randomly selected . the study was performed on six experimental groups of 12 rats , which underwent palatal expansion and one control group of six rats , which have not gone under any intervention . rats weight was monitored , and rats experiencing weight loss were kept in separate cages until reaching the normal weight of control group . rats were randomly divided into three experimental groups of 24 rats and one control group of 6 rats : 
 control group with no expansion or laser therapyexperimental group under treatment for 7 daysexperimental group under treatment for 14 daysexperimental group under treatment for 30 days . control group with no expansion or laser therapy experimental group under treatment for 7 days experimental group under treatment for 14 days experimental group under treatment for 30 days . each one of the above experimental groups was divided randomly into two groups of expansion without laser irradiation  a  and expansion with laser irradiation for maximum 14 days before placing orthodontic appliances , all experimental rats received 10% animal ketamine and 2% xylocaine intramascular injection as deep sedation . for expansion first an osteom was used to open a small space between central incisors , then a coil made of 1.5 mm stainless steel wire was used to open the midpalatal suture [ figure 1 ] . a hole was drilled using a 35,000-rpm hand - piece in the distal portion of both centrals along the gingival papillae [ figure 2 ] . the ring , was stabilized using 0.5 mm round brass wire . in the days 0 , 2 , 4 , 6 , 8 , 10 , 12 , and 14 , rats were irradiated by laser beam using a ga - al - as laser with wavelength of 810 and energy density of 4 j / cm ( photo laser , dmc , brazil ) in 4 points by placing the laser tip vertically over the mucosa as it has been described by saito and shimizu and blaya et al . stainless steel ring 1.5 mm thick , made from 0.5 mm wires , and having two extended bars for ease of use the straight handpiece ( maximum rpm : 35,000 ) with a round carbide  bur the gallium - aluminum - arsenide low - power laser device 
 one point with buccal : 0.5 mm apically to the edge of bone crestthree points in palatal:1 mm apically to the edge of bone crest2 mm apically to the edge of bone crest3 mm apically to the edge of the bone crest . one point with buccal : 0.5 mm apically to the edge of bone crest three points in palatal : 1 mm apically to the edge of bone crest 2 mm apically to the edge of bone crest 3 mm apically to the edge of the bone crest . after expansion and irradiation in 3 times intervals ( 7 , 14 , and 30 days ) , exposed ( n12 ) and unexposed ( n12 ) rats were anesthetized by injection of sodium pentobarbital and stored in 10% formalin with volume ratio of 1:20 and then sacrificed [ figure 4 ] . for histological evaluation , optical microscopy and computer software it was stored in 10% formalin with volume ratio of 1:20 surface areas were measured on digital images using adobe photoshop cs3 distribution of weight mean changes in irradiated groups and nonirradiated groups with their living days are given in table 1 . distribution of mean weight changes in exposed ( a ) and unexposed ( b ) groups during 7 days , weight changes of rats in group this decrease occurred after appliance placement and using the first dose of anesthesia , but weight loss in all laser - treated groups b  was significantly less than weight loss of no - laser experimental groups  a.  while most rats in experimental groups  b  showed weight loss only for 2 days , rats in experimental groups with no laser therapy  a  continued losing weight until 4 day , and many of them were not able to recover their initial weight after 7 days . b  started gaining weight at a rate equal to control , in a way that after 7 days , most of them could recover their weight loss in the first 2 days . weight gain in groups continued during days 6 , 8 , 10 , 12 and 14 until the group without laser therapy  a  completely recovered in the 9 day . 3a  were also significant during 2 to 6 days . during 10 to 14 days , b  was more , but we did not observe any significant difference between two groups . changes in mean weight ( g / day ) of experimental groups are compared in diagram 1 . mean weight changes of control group and study groups ( g / day ) quantitative bone changes [ table 2 ] : the mean of bone regeneration in study groups the extent of bone regeneration in group  2a  was 37.6  1.7  10 inches , while it was 40.2  3.15  10 inches in group  2b . 2a  and  2b  was not significant ( p > 0.05 ) [ figure 6 and diagram 2 ] histological view of midpalatal suture , 7 days after expansion ( a ) without laser therapy and ( b ) with laser therapy mean bone regeneration ( in 0.001 inch ) after 7 days . 3b  and  3a  were 41.7  2.8  10 and 38.8  1.85  10 inches , respectively . statistically significant differences between two exposed and unexposed groups were observed ( p = 0.032 ) [ figure 7 and diagram 3 ] . histological view of midpalatal suture , 14 days after expansion ( a ) without laser therapy and ( b ) with laser therapy mean bone regeneration ( in 0.001 inch ) after 14 days . the difference was significant however , radiation were stopped in 15 days but after 30 days bone regeneration in unexposed group (  4a  ) was 37.6  1.7  10 inches , while it was 40.2  3.15  10 inches in exposed group (  4b  ) . this difference was statistically significant ( p = 0.001 ) [ figure 8 and diagram 4 ] . histological view of midpalatal suture , 30 days after expansion ( a ) without laser therapy and ( b ) with laser therapy during the first 14 days mean bone regeneration ( in 0.001 inch ) after 30 days . the difference was significant in each day of 1 week after expansion , mean of bone regeneration for group 2b  was 5.7  10 inches while this amount was 5.3  10 inches for group mean of bone regeneration during next 7 days in group without laser therapy was 1.2  10 inches and was 0.4  10 inches in the laser group . it means that the mean of bone regeneration in each day of 2 week for group 3a  was 0.1  10 inches and for group  3b  was 0.06  10 inches that showed a drastic decrease . in 3 and 4 week , bone regeneration decreased for 0.4  10 inches in rats not treated with the laser , while it increased for about 2.8  10 inches in rats , which received laser irradiation . according to this statistics , the greatest amount of bone regeneration in first 7 days was in group 2b while the greatest effect on bone regeneration in groups with laser therapy against groups without laser therapy were observed during second 15 days . 2a  was 37.6  1.7  10 inches , while it was 40.2  3.15  10 inches in group  2b . 2a  and  2b  was not significant ( p > 0.05 ) [ figure 6 and diagram 2 ] histological view of midpalatal suture , 7 days after expansion ( a ) without laser therapy and ( b ) with laser therapy mean bone regeneration ( in 0.001 inch ) after 7 days . mean bone regeneration in groups  3b  and  3a  were 41.7  2.8  10 and 38.8  1.85  10 inches , respectively . statistically significant differences between two exposed and unexposed groups were observed ( p = 0.032 ) [ figure 7 and diagram 3 ] . histological view of midpalatal suture , 14 days after expansion ( a ) without laser therapy and ( b ) with laser therapy mean bone regeneration ( in 0.001 inch ) after 14 days . however , radiation were stopped in 15 days but after 30 days bone regeneration in unexposed group (  4a  ) was 37.6  1.7  10 inches , while it was 40.2  3.15  10 inches in exposed group (  4b  ) . this difference was statistically significant ( p = 0.001 ) [ figure 8 and diagram 4 ] . histological view of midpalatal suture , 30 days after expansion ( a ) without laser therapy and ( b ) with laser therapy during the first 14 days mean bone regeneration ( in 0.001 inch ) after 30 days . the difference was significant in each day of 1 week after expansion , mean of bone regeneration for group 2b  was 5.7  10 inches while this amount was 5.3  10 inches for group mean of bone regeneration during next 7 days in group without laser therapy was 1.2  10 inches and was 0.4  10 inches in the laser group . it means that the mean of bone regeneration in each day of 2 week for group 3a  was 0.1  10 inches and for group  3b  was 0.06  10 inches that showed a drastic decrease . in 3 and 4 week , bone regeneration decreased for 0.4  10 inches in rats not treated with the laser , while it increased for about 2.8  10 inches in rats , which received laser irradiation . according to this statistics , the greatest amount of bone regeneration in first 7 days was in group 2b while the greatest effect on bone regeneration in groups with laser therapy against groups without laser therapy were observed during second 15 days . this study has evaluated changes in different timescales using the histomorphometric method . furthermore , in this study , samples were standardized . weight loss of rats in initial days after placing appliance is probably due to pain and trauma of rapid maxillary expansion . according to previous studies , laser can reduce inflammation and pain by different mechanisms including increasing levels of some prostaglandins , decreased infection , affecting sensory receptors , and proper coagulation and hemostasis . a significant difference in weight changes during 1 days after placing the appliance in all groups can verify it . according to findings of this study , a difference of the extent of regenerated bone during the 1 week was not significant between laser - included and laser - free groups . based on a study of saito and shimizu on the same timescale , there is a significant difference in the bone regeneration of groups that received laser therapy compared with control groups . probably , laser power and exposure time can affect the amount of bone regeneration as well . difference in bone regeneration in laser - included and laser - free experimental groups was significant in the 14 day , which was consistent with another study . pretel et al . reported an advanced tissue response and bone formation in the laser group , shortened initial inflammatory reaction and promoted rapid new bone matrix formation in 15 and 45 days . however , they did not find any significant differences between the groups in 60 day . they concluded that aiming infrared low - level laser directly at the wound showed a biostimulating effect on bone remodeling by stimulating the modulation of the initial inflammatory response and enhancing the recovery . as well concluded that low - level laser can affect the bone regeneration process of the suture and accelerate healing . as well observed a greater and accelerated amount of bone regeneration after rapid palatal expansion . the difference in bone regeneration extent in laser - treated and laser - free experimental groups was significant as well . during days of 1430 , 4  10 inches of regenerated bone the reason may be the gradual elimination of inflammatory factors and replacement by osteoblastic phase . laser exposure can increase amount of atp , that is , intracellular energy , during primary and secondary cellular reactions . in this process , light energy along primary reactions in oxidation cycle activates the intracellular reactions and enhances the bone healing . low - power laser irradiation can increase and accelerate bone regeneration in the midpalatal suture during and after rapid palatal expansion . while the highest extent of bone regeneration was seen in the first 7 days , the highest efficacy of laser was observed in 3 and 4 week .
background : rapid palatal expansion is one of the most important orthopedic treatments that correct the dental and palatal constriction . 
 stability of the changes partly depend on the rapidity of new bone formation in affected sutures after expansion . 
 the purpose of this study was to investigate the effect of laser irradiation on the healing of midpalatal suture concurrent to the expansion of midpalatal suture in rats.materials and methods : a total of 78 male sprague rats in seven groups were evaluated : a control group of six rats without any treatments and three experimental groups of 24 which underwent palatal expansion for different time periods ( 7 , 14 , and 30 days ) , and each divided into two groups of with and without laser irradiation . 
 laser therapy was done by gallium - aluminum - arsenide diode laser with 810 nm wavelength and 4 j / cm2 irradiation in days 0 , 2 , 4 , 6 , 8 , 10 , 12 , 14 in 4 points ( 1 labial and 3 palatal points ) . after sacrificing , 
 the sections were evaluated by histomorphometric and quantitative analysis and results were statistically investigated by independent samples t-test.results:the results in 7 days , 14 days , and 30 days show that laser therapy can increase the rate of osteogenesis in palatal suture during rapid palatal expansion but the differences in 7 days groups were not significant ( p = 0.117 ) while in 14 days groups ( p = 0.032 ) and 30 days groups were significant ( p = 0.001 ) . most of effectiveness of low - power laser was seen between 14 and 30 days while the laser therapy was stopped.conclusion:these findings suggest that low - level laser irradiation can increase and accelerate bone regeneration in the midpalatal suture after rapid palatal expansion , hence , reduce retention time .