it also causes damage to deoxyribonucleic acid ( dna ) and dna - protein cross - links and induces cellular death .
there is a direct relationship between the effects of ionizing radiation and the type of tissue receiving the radiation and the absorbed radiation dose .
dental radiology represents the most frequently applied radiological diagnostic tool , the enormous diagnostic benefits of which make its use indispensable .
however , while individual doses and risks are low , the collective dose is not inconsiderable .
patients most commonly receive ionizing radiation to the head , and several studies have shown dental radiography to be associated with an increased risk of meningioma , brain cancer and parotid gland tumors as well as breast cancer [ 59 ] .
four different types of x - ray examination techniques are commonly used in dentistry for diagnostic purposes : posterior bitewings , periapical films , lateral cephalometric radiographs and panoramic radiographs ( opg ) .
in addition , cone - beam computerized tomography ( cbct ) has recently been accepted as an emerging x - ray technology in dentomaxillofacial imaging .
all these imaging techniques have been implicated in nuclear alterations of stomatognathic system cells that are closely related to genotoxicity .
the fact that imaging may subject regions not specifically under consideration to x - ray radiation   warrants an assessment of what types of protective devices can be produced from nano - materials to shield areas of the jaw and the rest of the body outside the area of interest from the harmful effects of x - rays .
many techniques are available for evaluating the structural characteristics of materials that have metallic particles .
small angle x - ray scattering is one such technique used for the structural characterization of solid and fluid materials in the nanometer ( nm ) range .
measurements are commonly performed in transmission geometry by using a narrow , well - collimated and intense x - ray beam .
x - ray absorption is related to the thickness of the material and the atomic numbers of the elements from which it is composed .
a narrow beam of mono - energetic photons with an incident intensity of io will have a transmitted intensity of i that can be calculated using the equation ; 
 ( eq 1)i / io = exp  [ (/)x ] 
 where x represents the mass thickness ( the mass per unit area ) and  represents the density of the material through which the ray passes .
mass thickness can also be calculated by multiplying the thickness ( t ) by the density (  ) as x = t , allowing eq1 to be rewritten as 
 ( eq 2)lni = lniot 
  once io , i and t values have been established , the linear attenuation coefficient of  can be established from the slope of [ ln i - t ] .
for the evaluation of saxs data , gnom   and dammin   computer programs are used .
gnom is an indirect transform program for small - angle scattering data processing that reads one - dimensional scattering curves ( possibly smeared with instrumental distortions ) and evaluates a distance distribution function p for monodispersal systems or a size distribution function d for polydispersal systems .
gnom creates the function dmax ( indicates the nanostructures maximum overall size and can be determined using pair distance distributions of the nano - aggregates ) and the input file required for ab - initio modeling .
dammin uses small angle x - ray scattering to recreate ab - initio low - resolution shapes of randomly oriented particles in solution ( e.g. , biological macromolecules ) .
therefore , this study aimed to synthesize and compare a number of new nano - composites capable of protecting the jaw and the rest of the body from the harmful effects of ionizing radiation by absorbing x - rays with saxs analyzing method and to test the availability of designing an intraoral shield and its affect on the image quality of periapical radiography using the most promising nanocomposite ( co ) .
four different types of nano - powders [ ti , zr ( iv ) , ag and co ] ranging in size from 570 nm were obtained from chemical manufacturers [ sigma aldrich ( 578347 - 10 g , 544760 - 25 g ) ; alfa aesar ( 231 - 158 - 0 , 232 - 033 - 3 ) ] and were mixed in a polymer matrix to create nanocomposites with doping values of 8% in weight , without any additional purification .
the matrix was prepared using self - cure acrylic resin powder ( akribel , self curing denture acrylic powder , atlas - enta a. .
, izmir , turkey ) and heat - cure acrylic liquid ( paladent 20 , heraeus , kulzer , hanau , germany ) according to the manufacturers instructions .
each mixture was poured into a cylindrical plastic mold and polymerized with a special heat - pressure polymerization device ( ivomat ip3 , ivoclar vivadent ag , schaan , lichtenstein ) under 6-bar pressure at 40c for 15 minutes .
the composite cylinders were then processed and shaped in rectangular form with 42 mm dimensions and 0.50 cm thickness , using a high - speed dental hand piece ( k5plus , kavo , biberach , germany ) .
a 320-grit sic sandpaper ( norton , worchester , ma , usa ) was used for the surface correction of the samples and polishing procedures were applied with pumice paste .
saxs measurement was performed using hecus - saxs system with 50 kv- 50 ma , cuk ( =1.54  ) radiation line collimation and position sensitive detectors ( 54 m resolution , 1024 channels ) .
1 . effective radius of the nano - aggregations , forms , most probable ab - initio shape and pair - distance distributions of the samples were obtained through analyses of the experimental data .
saxs profiles of polymer - based ag , co , zr and ti nano - composites ( 0.50 cm thick ) measured according to q ( magnitude of transmitted scattering vector ) .
the x - ray absorbance values of the nano - composites were calculated using the eq 1 ( i /io = exp[ ( /)x ] ) and eq2 ( lni = lnio t ) . ti nano - composites ( ti - pnm ) yielded the most promising values of the four nano - composites tested in terms of x - ray absorption followed by co nano - composites ( co - pnm ) and ti - pnm ( fig .
2 ) . nanoparticle atomic number ( z ) ; the differences in total transmitted intensities ( i ) of nano - composites . in this study , co - pnm samples of different thicknesses ( 0.20 , 0.50
, 0.57 and 0.60 cm ) were prepared , and saxs analysis was performed in order to assess the effects of material thickness on x - ray absorption . prior to saxs testing , sample thickness was confirmed using a digital caliper ( tresna , guanglu europa gmbh , essen , germany ) .
an experimental shield was constructed from co - pnm to act as an x - ray protector for the human mandible surrounding tooth # 36 ( fig .
two layers of pink wax were adapted over teeth # 35 , 36 and 37 , and the acrylic resin - based mass was adapted directly over the wax .
the resin mass was shaped with the aid of a spatula , and the polymerization procedure was completed using a heat - polymerization device .
surface correction was performed using laboratory hand - pieces to obtain a uniform thickness of 0.50 cm , as measured by a digital caliper .
the prepared matrix was then cut into three pieces , two of which were shortened to provide a clear view of the mesial and distal parts of tooth # 36 .
the remaining part was adapted to fit over tooth # 36 and the two other parts of the shield to create an easily adaptable , multi - unit stent ( fig .
four different types of nano - powders [ ti , zr ( iv ) , ag and co ] ranging in size from 570 nm were obtained from chemical manufacturers [ sigma aldrich ( 578347 - 10 g , 544760 - 25 g ) ; alfa aesar ( 231 - 158 - 0 , 232 - 033 - 3 ) ] and were mixed in a polymer matrix to create nanocomposites with doping values of 8% in weight , without any additional purification .
the matrix was prepared using self - cure acrylic resin powder ( akribel , self curing denture acrylic powder , atlas - enta a. .
, izmir , turkey ) and heat - cure acrylic liquid ( paladent 20 , heraeus , kulzer , hanau , germany ) according to the manufacturers instructions .
each mixture was poured into a cylindrical plastic mold and polymerized with a special heat - pressure polymerization device ( ivomat ip3 , ivoclar vivadent ag , schaan , lichtenstein ) under 6-bar pressure at 40c for 15 minutes .
the composite cylinders were then processed and shaped in rectangular form with 42 mm dimensions and 0.50 cm thickness , using a high - speed dental hand piece ( k5plus , kavo , biberach , germany ) .
a 320-grit sic sandpaper ( norton , worchester , ma , usa ) was used for the surface correction of the samples and polishing procedures were applied with pumice paste .
saxs measurement was performed using hecus - saxs system with 50 kv- 50 ma , cuk ( =1.54  ) radiation line collimation and position sensitive detectors ( 54 m resolution , 1024 channels ) .
1 . effective radius of the nano - aggregations , forms , most probable ab - initio shape and pair - distance distributions of the samples were obtained through analyses of the experimental data .
saxs profiles of polymer - based ag , co , zr and ti nano - composites ( 0.50 cm thick ) measured according to q ( magnitude of transmitted scattering vector ) .
the x - ray absorbance values of the nano - composites were calculated using the eq 1 ( i /io = exp[ ( /)x ] ) and eq2 ( lni = lnio t ) .
ti nano - composites ( ti - pnm ) yielded the most promising values of the four nano - composites tested in terms of x - ray absorption followed by co nano - composites ( co - pnm ) and ti - pnm ( fig .
2 ) . nanoparticle atomic number ( z ) ; the differences in total transmitted intensities ( i ) of nano - composites . in this study , co - pnm samples of different thicknesses ( 0.20 , 0.50
, 0.57 and 0.60 cm ) were prepared , and saxs analysis was performed in order to assess the effects of material thickness on x - ray absorption . prior to saxs testing , sample thickness was confirmed using a digital caliper ( tresna , guanglu europa gmbh , essen , germany ) .
an experimental shield was constructed from co - pnm to act as an x - ray protector for the human mandible surrounding tooth # 36 ( fig .
two layers of pink wax were adapted over teeth # 35 , 36 and 37 , and the acrylic resin - based mass was adapted directly over the wax .
the resin mass was shaped with the aid of a spatula , and the polymerization procedure was completed using a heat - polymerization device .
surface correction was performed using laboratory hand - pieces to obtain a uniform thickness of 0.50 cm , as measured by a digital caliper .
the prepared matrix was then cut into three pieces , two of which were shortened to provide a clear view of the mesial and distal parts of tooth # 36 .
the remaining part was adapted to fit over tooth # 36 and the two other parts of the shield to create an easily adaptable , multi - unit stent ( fig .
saxs profiles calculated using the magnitude of the transmitted scattering vector showed ti to have the highest absorbance value , followed by zr , co and ag , respectively ( fig .
these findings indicate that ti absorbs the majority of transmitted x - rays , whereas ag scatters the x - rays .
4 ) were calculated according to eq 1 using the i , io and  values given in table 1 .
logarithmic distributions of the transmitted intensity values ( i ) showed that 0.20 cm co - pnm had the highest transmission value ( 16.05 ) followed by 0.50 cm co - pnm ( 15.44 ) , 0.57 cm co - pnm ( 15.07 ) and 0.60 cm co - pnm ( 15.06 ) .
experimental results about the x - ray absorbance of cobalt nanocomposite logarithmic transmitted intensity as a function of thickness for co nanocomposite . figures 5 and 6 show , respectively , the graphs of the effective radius of the nano - aggregation values and the dmax values for co - pnm of different thicknesses . as seen in fig . 5 , the 0.2 cm co - pnm had an effective radius of the nano - aggregation value ( 77.44  ) higher than that of the other thicknesses ( 0.50 , 0.57 and 0.60 cm ) of co - pnm , which had similar values ranging from 66.2266.34 .
6 , the 0.20 cm co - pnm had the highest dmax value of the different thicknesses of co - pnm tested .
saxs patterns ( blue circles ) and ab - initio fitting scatter curves of co nano - composites of different thicknesses .
standard periapical x - ray radiograph showed that the co - pnm stent appeared as a radiopacity over the occlusal surface of the teeth and did not affect subjective image quality .
saxs profiles calculated using the magnitude of the transmitted scattering vector showed ti to have the highest absorbance value , followed by zr , co and ag , respectively ( fig .
these findings indicate that ti absorbs the majority of transmitted x - rays , whereas ag scatters the x - rays .
4 ) were calculated according to eq 1 using the i , io and  values given in table 1 .
logarithmic distributions of the transmitted intensity values ( i ) showed that 0.20 cm co - pnm had the highest transmission value ( 16.05 ) followed by 0.50 cm co - pnm ( 15.44 ) , 0.57 cm co - pnm ( 15.07 ) and 0.60 cm co - pnm ( 15.06 ) .
experimental results about the x - ray absorbance of cobalt nanocomposite logarithmic transmitted intensity as a function of thickness for co nanocomposite .
figures 5 and 6 show , respectively , the graphs of the effective radius of the nano - aggregation values and the dmax values for co - pnm of different thicknesses . as seen in fig .
5 , the 0.2 cm co - pnm had an effective radius of the nano - aggregation value ( 77.44  ) higher than that of the other thicknesses ( 0.50 , 0.57 and 0.60 cm ) of co - pnm , which had similar values ranging from 66.2266.34 .
6 , the 0.20 cm co - pnm had the highest dmax value of the different thicknesses of co - pnm tested .
saxs patterns ( blue circles ) and ab - initio fitting scatter curves of co nano - composites of different thicknesses .
standard periapical x - ray radiograph showed that the co - pnm stent appeared as a radiopacity over the occlusal surface of the teeth and did not affect subjective image quality .
x - rays have been widely used for decades as diagnostic tools in the field of dentistry .
studies have clearly shown that ionizing radiation induces cellular death by karyorrhexis , pyknosis and karyolysis .
individuals continually exposed to x - rays ( for endodontic , orthodontic , implant and other purposes ) may later develop cancer as a result of genotoxic / cytotoxic cell differentiation .
the literature contains insufficient information regarding the use of nano - materials in providing regional protection from the harmful effects of x - rays on areas of the body and jaw outside the area of consideration . in the field of nanotechnology ,
both small- and wide - angle x - ray scattering methods have been effectively used to study polymer matrix - based nano - composites .
the present study used ti , zr , co and ag nanoparticles in the synthesis of nano - composites .
co , ag and ti are transition metals that do not form binary phases in polymeric media and demonstrate negligible solubility .
zirconia is a white amorphous powder that shows a homogeneous distribution in a composite matrix .
other materials with high mass attenuation coefficients , such as lead ( pb ) , are also widely used to protect biological tissue from the harmful effects of high energy x - rays for many years [ 2325 ] .
the low brittleness , hardness and oxidation characteristics of pb make it very difficult to synthesize nanoparticles from this element .
the main reason of using nanoparticles in this study was their low weight in any composite material .
thus , ti , zr , co and ag have low weights as in nano - powder form and the materials that will be produced from these materials will not be affected by the nanoparticles of metallic alloys
. however , the traditional x - ray protectors that contain pb are very heavy for use [ 2326 ] . as fig
. 1 shows , ti and zr matrixes had lower x - ray scattering angle to transmitted scattering vector ratios than the co and ag matrixes of similar thicknesses . however , as fig .
2 shows , the total transmitted intensities of the nanocomposite matrixes varied in line with their atomic numbers of their constituent nano - composites , so that the ti matrix had the lowest total transmitted intensity , followed by the co matrix .
the saxs analysis conducted in this study found ti to have the best x - ray absorption values ; however , due to the high cost of obtaining ti nano - powder , detailed examinations were conducted using the nanocomposite containing co , which was also found to have adequate protective properties .
gnom   and dammin   software analyses used to evaluate the findings of saxs showed that the tested 0.6 cm thick co - pnm sample absorbed the greatest amount of x - ray radiation ( figs .
45 ) or transmitted the lowest x - ray radiation . however , although the maximum absorbance was found for 0.6 cm thickness , 0.5 cm thickness was chosen because in this thickness , the shapes , pair distance distributions and numbers of the nano - aggregations , and surface morphology of the plate are well optimized to cause bigger absorbance .
the weight of the protective shield did not increase with an increase in the thickness . with the advances in technology ,
economical and disposable materials that contain co nano - powder may be produced to protect the health of patients . in this study ,
an experimental intraoral co - pnm shield was constructed and tested over a human mandible to check the formability of resin matrix after the addition of metallic nano - powder .
although the shield appeared as a radiopacity over the occlusal surface of the teeth , this did not affect the visibility of periapical or surrounding tissue .
similar shields may be constructed specifically for other parts of the stomatognathic system or any part of the body using co or other nano - powders and may be used for a variety of diagnostic and/or treatment purposes .
as the technology advances , shields may be fabricated in thin - film coating , in rubber - dam like form or in plastic mouth guard form , in the future .
the co - pnm shield was fabricated only to observe the manipulative property of the acrylic resin and any effect on the diagnosis made based on periapical intraoral films .
it was designed over a human mandible that has surrounding soft tissue of the stomatognathic system .
in conclusion , the co nanocomposite fabricated in this study was found to have a linear absorption coefficient value (  ) of 2.510.06 cm , indicating that it may be used as a shield material to protect against the harmful effects of x - rays during diagnosis and dental rehabilitation .
moreover , the co nanocomposite was found to have an effective radius of the nano - aggregation ranging from 66.22 to 77.94  , demonstrating a uniform distribution that can be adequately controlled . in light of these findings
, further studies may be undertaken to examine new applications for cobalt nanocomposite in dentomaxillofacial radiology and radiotherapy .
 objectives : this study aimed to compare a number of new nano - composites capable of protecting the jaw from ionizing radiation.materials and methods : four different types of nano - powders [ ti , zr ( iv ) oxide , ag and co ] were mixed in a polymer matrix to create nano - composites with doping values of 8% in weight . 
 small - angle x - ray scattering ( saxs ) analysis was performed using a hecussaxs system with 50 kv- 50 ma . 
 co nano - composites ( co - pnm ) yielded the most promising values of the four nanocomposites tested in terms of x - ray absorption . 
 thus , 42 cm co - pnm samples of different thicknesses ( 0.20 , 0.50 , 0.57 and 0.60 cm ) were prepared , and saxs analysis was performed in order to assess the effects of material thickness on xray absorption . 
 an experimental multi part shield was constructed from co - pnm around tooth # 36 to test the effect of nanomaterial on the image quality under x - ray beam.results:logarithmic distributions of the transmitted intensity values ( i ) showed that 0.20 cm co - pnm had the highest transmission value ( 16.05 ) followed by 0.50 cm co - pnm ( 15.44 ) , 0.57 cm co - pnm ( 15.07 ) and 0.60 cm co - pnm ( 15.06 ) . 
 the 0.2 cm co - pnm had an effective radius of the nano - aggregation value ( 77.44  ) lower than that of the other thicknesses ( 0.50 , 0.57 and 0.60 cm ) of co - pnm , which had similar values ranging from 66.22 to 66.34  . 
 the 0.50 cm co - pnm had the lowest dmax value of the different thicknesses of co - pnm tested.conclusion:co nanocomposite can be used as a protection shield for the harmful effects of dental x - ray . 
INTRODUCTION
MATERIALS AND METHODS
Synthesis of nano-composites:
SAXS analysis:
X-ray absorbance calculation of the synthesized nano-composites:
Preparation of experimental shield:
RESULTS
Absorbance
SAXS results:
X-ray analysis of shield:
DISCUSSION
CONCLUSION