dental implantation and fixation of screws for any reason are performed by drilling the bone and the success of these operations depend on many factors . through these factors , thermal injuries occurring due to temperature raise during drilling ,
the threshold level for thermal injuries on the bone is the 47c for a minute and the temperature can raise that level easily during drilling by rotational burs 1,3 . as a consequence of thermal injury ,
bone is not only resorbed but also replaced with fat cells 4 . as a result ,
the mechanical structure of the bone is weaken 5 . to prevent the bone from the temperature raise during drilling ,
various irrigation systems are used and mostly , sterile saline solutions are the material of choice 6,7 . although , to our knowledge , there is not a scientific data in the literature , there is a belief among the surgeons that cooled saline irrigation is more effective than the uncooled saline irrigation to protect the bone from the thermal injuries .
the purpose of the present study was to investigate the effect of the irrigation temperature on the bone healing .
for this aim , standardized drilling and miniscrew placement was performed in the tibias of 18 sprague dawley rats with rotating bur uncooled , cooled with 25c and 4c saline irrigation .
experiments were designed to determine the effect of irrigation temperature on the bone after osteotomy and miniscrew placement . for this aim 3 months old weighing approximately 350 to 450 g 18 sprague - dawley rats were maintained at 22 0.5 c on a 12-h light/12-h dark cycle with free access to water and standartized food in pathogen free separate cages .
all of the experiments were performed at the istanbul university , institutes of experimental science laboratories ( istanbul , turkey ) .
maintenance and all experimental procedures performed were fully in accordance with principles established by the existing governmental acts and approved by the university institutional animal welfare committee .
animals were divided randomly in to 3 groups of 6 animals and 3 experiments were performed .
anesthesia was induced with ketamine hcl ( 100 mg / kg i.p . , ketalar  , parke davis ) by the injection through the peritonium of the rats and maintained with xylozin hcl ( 23.32 mg / ml i.p . , rompun , bayer ) . after the induction of anesthesia , operation sites were shaved and the rats were placed and stabilized on the operation table .
skin incision was performed parallel to the long axis of the right femurs and the bone was exposed by the dissection of hamstring and quadriceps femoris muscles .
the drill speed was set to be 20,000 rpm , which is similar to that used during osteotomies by rotational systems and saline irrigation speed was standartized by using saline - dispencer .
all of the holes were drilled with standard burs manufactured for 2 mm miniscrews and standart 2 mm wide 5 mm length titanium miniscrews ( bone screw kit , biohorisons , usa ) were inserted . in the group one , holes were drilled without irrigation ( figure 1 ) . in the group two ,
holes were drilled with 25c ( 2c ) saline irrigation and in the group three , holes were drilled with 4c ( 2c ) saline irrigation ( figure 2 ) . after the drilling and the miniscrew placement ( figure 3 ) , muscle and fascia layers were closed with simple resorbable 4.0 sutures ( vicryl 4 - 0 , ethicon ) and finally the skin incisions were closed with continious 3.0 sutures ( silk 3.0 , dogsan ) .
postoperative antibiotics ( gentamicin , 0.5 mg / kg ) and analgesics ( xylocaine 0,5 mg / kg ) were given subcutaneously .
the positions of the miniscrews were controlled by cone beam ct scanning . during post - operative period ,
all of the animals were controlled day by day and none of them were lost . at the end of three weeks , animals were killed and right femurs of them were harvested .
then , the specimens were sent to the pathology laboratory ( istanbul university , institute of oncology , department of pathology , istanbul , turkey ) for the histopathological evaluation .
the cutting line was started parallel to the transverse axis of femurs at about 4 mm apart from femoral heads , where the first hole preparation was made .
the specimens were fixed in 10% formalin for one week and decalcified in 10% formic acid solution ( merck , darmstadt , germany ) for 25 days .
the decalcified specimens were embedded in paraffin and cut into 3 m thick sections on charged slides using a microtome ( leica microsystemic rm 2125 , germany ) , and routine hematoxylin and eosin ( h&e ) staining was performed .
the sections were examined with a light microscope ( olympus bx60 microscope ) attached to a digital camera ( olympus e-330 ) which connected to a computer .
a histomorphological review was performed by a single blinded oral pathologist to evaluate the presence of infection , necrosis , fibrosis and new bone formation .
all screw hole surroundings were evaluated by histopathologically with light microscope under 20 , 40 , 100 and 200x magnifications .
the score was made up of 0 - 5% as ( - ) , 5 - 30% as ( + ) , 30 - 60% as ( + + ) and 60% and over as ( + + + ) to evaluation of new bone formation and fibrosis according to their surface covering at 40x magnification .
the scores for infection and necrosis were determined by occurring in a standardized area at 20x magnification .
the infection was determined if inflammatory cells were observed in the healing area the ( + ) score and if there were no inflammatory cells the ( - ) score were given .
for necrosis the ( - ) score was given , if there was no necrosis whereas the ( + ) score was given if there was .
the statistical differences between the control and test groups were compared by ki - square and fisher tests .
in this research , all of the statistical evaluations were performed by using the ncss software ( ncss inc . , 2007 , usa ) .
ki - square and fisher tests were performed for the evaluation of the definitive statistical methods and also qualitative datas .
the distribution difference of the new bone formation between 4c , 25c and control groups were observed as statistically significant ( p=0,031)(table 1 ) .
the new bone formation of the control group was evaluated significantly lower than the 4c and 25c groups ( p=0,020 , p=0,049 ) , however , there was no statistically significant difference evaluated between the 4c and 25c groups statistically(p=0,637)(table 2 ) .
statistically significant difference was observed between 4c , 25c and control groups regarding the distribution of the infection presence ( p=0,0001)(table 3 ) .
the presence of the infection in the control group 9 ( % 75 ) , was observed as significantly higher than the 4c and 25c groups ( p=0,0001 ) , but no statistically significant difference was seen between the 4c and 25c groups ( p=1)(table 4 ) .
the distribution of the bone necrosis existence between 4c , 25c and control groups were observed significantly different ( p=0,0001 ) ( table 5 ) .
the existence of the bone necrosis in the control 11 ( % 91,7 ) , group was evaluated significantly higher than the 4c and 25c groups ( p=0,0001 ) , but , no statistically difference was observed between the 4c and 25c groups ( p=1 ) ( table 6 ) .
no statistically significant difference was observed between 4c , 25c and control groups regarding the distribution of the fibrosis existence ( p=0.355)(table 7 ) .
the fibrosis distribution of the control group was not significantly different than the 4c and 25c groups ( p=0,334 , p=0,164 ) , and also , no statistically significant difference was observed between the 4c and 25c groups ( p=0,232 ) ( table 8) .
the temperature rise on the bone during osteotomies performed by rotational systems is affected by various factors 8 - 10 .
some of these factors are bone density , and the location of the osteotomy , in particular the amount of cortical versus cancellous bone , which may be influential .
other important factors pertain to the drilling , including the speed at which the drill rotates , the sharpness of the margins on the drill , the thickness of the drill , and the force with which the drills applied to the bone 11 . regardless of the reason for , this temperature rise can cause damage or impaired healing on the bone 1,3 .
as previously mentioned , the accepted threshold level that is required for the thermal injury on the bone is 47c for a period of 1 minute 1,3 .
for the protection of the bone from the thermal damage during osteotomy , saline solution is routinely applied to the drill and the osteotomy site in surgical practice . and also ,
most of the surgeons prefer cool saline solutions and they believe that it is more effective than the normal solutions for the reduction of the temperature . in the literature , there are some studies indicating the effect of the saline application on temperature rise 11 , on the contrary , others indicate that application of saline solution to the rotational system to bone interface during osteotomy do not reduce the temperature during the osteotomy to any significant degree 12,13 . in the authors ' knowledge , this is the first study focuses on the effect of the irrigation temperature to reduce thermal rise . at the same time
, it is evaluated in this study that application of saline solution is effective or not for the reduction of the thermal damage . in the present study we evaluated the specimens in terms of new bone formation , presence of infection , necrosis and fibrosis
our study demonstrated significant difference regarding the necrosis values between control group ( without irrigation ) and the group irrigated with 25c and 4c saline ( figures 4 - 6 ) .
however copious saline irrigation was useful for cleaning the operation area from any remnants of the drill .
although there was no statistically significant difference between the group irrigated with 25c and 4c saline for new bone formation , latter group had numerous osteoblasts and more prominent osteoblastic rim around the trabeculae of new bone ( figures 4,5 ) .
these results indicate that there is no disadvantage to use 25c saline irrigation , but it may be better to use 4c saline irrigation for rapid healing . in this study , it is verified that the use of saline irrigation is not only useful to reduce temperature rise on the bone during osteotomy , but also effective for cleaning the osteotomy site from any bony remnants .
 objective : osteotomies , performed by rotational instruments , can cause temperature rise on the bone and elevated temperature can disrupt the bone healing . when the osteotomies are performed for the insertion of miniscrews , the bone healing disruption may cause stability loosening or failures . 
 saline irrigation is mostly used for the prevention of the heat generation during osteotomy.purpose : the purpose of this study was to evaluate the effect of the saline irrigation temperature on bone healing.material and method : standardized drilling and miniscrew placement was performed in the tibias of 18 sprague dawley rats with rotating bur uncooled , cooled with 25c and 4c saline irrigations . 
 after the 21 days , the difference in healing was observed between the uncooled and cooled groups.results : although there was no statistically significant difference between the group irrigated with 25c and 4c saline for newly bone formation , osteoblasts were seen more active and bone marrow was more dynamic in group 4c than group 25c . 
 there is no disadvantage to use 25c , but it may be better to use 4c for rapid healing . 
Introduction
Material and Method
Results
Discussion