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dental implantation is a treatment method in which fixtures are implanted in the jawbone , followed by prosthetic implantation after a resting period of approximately 36 months , at which time new bone is formed around the fixtures .
bone modeling and remodeling processes are important ( 1 ) to induce long - term stability of the implants ; ( 2 ) to develop osseointegration between implant materials and the bone ; ( 3 ) to allow the maturation of new bone around the implants .
it has been reported that the maximum occlusal force in adults with a natural dentition is 430  n , and similar loads are likely to be applied to implants as well as normal prostheses
. therefore , to achieve long - term retention and stability of implants under such conditions , the quality of newly formed bone around implants is important .
many studies have reported that newly formed bone around implants is spongy bone . however , although the morphology of newly formed bone is reportedly like spongy bone , it is difficult to discriminate whether the bone quality is mature like cortical bone , or immature like spongy , osteoid , or cartilaginous bone ; therefore , evaluation of the bone quality is required .  
nakano et al .   evaluated bone density and alignment of biological apatite ( bap ) , and boskey and pleshko   used fourier - transform infrared ( ftir ) imaging to assess bone and cartilage quality and composition .
in addition , our group has reported on the use of polarized microscopy   and scanning electron microscopy ( sem )   to evaluate new bone and cortical bone quality , as well as microscopic raman spectroscopy to analyze phosphate peaks of bone apatite , and microcomputed tomography ( micro - ct ) to assess trabecular microarchitecture and bone mineral density ( bmd ) [ 810 ] .
however , basic research on new bone formation has been sparse , and molecular and elemental characterization of bap , the basic building block of bone , has generally been overlooked .
moreover , responses to early dynamic loading in implants , with analysis of changes in new bone quality associated with mineralization , remain an important issue for further research . in this study
, differences in the bone quality between newly formed bone and cortical bone formed around titanium ( ti ) alloy implants were investigated using x - ray photoelectron spectroscopy ( xps ) .
six 18-week - old new zealand white rabbits ( sankyo labo service co. , tokyo , japan ) were used in experiments .
the rabbits were housed in individual metal cages at a room temperature of 23  1c and humidity of 50  1% , with ad libitum access to food and water .
the experimental protocol was approved by an animal experimentation ethics committee ( approval number eca 07 - 0016 ) .
all experiments were conducted according to the guidelines for the treatment of animals , nihon university , chiba , japan .
implants ( diameter , 3.0  mm ; length , 7.0  mm ) were fabricated using ti-15%zr-4%nb-4%ta ( ti-15 - 4 - 4 ) alloy [ 1115 ] ( table 1 displays its chemical composition ) .
surface treatment of implants consisted of sulfuric acid - etching and grit - blasting with apatitic abrasive ( particle size 250  m , himed co. , ny , usa ) ( figure 1 ) .
rabbits underwent general anesthesia with 2.0  mg / kg of intravenous ketalar ( daiichi sankyo , tokyo , japan ) .
implant cavities were surgically created in the tibia 10  mm distal to the knee joint , one each bilaterally , by using a 1.0  mm and 3.0  mm diameter round bar , while irrigating the area with sterile saline .
implants were inserted into the right tibia , with each rabbit receiving one implant ( 8 implants were used in total ) .
rabbits were sacrificed by anesthesia overdose at 4 or 8 weeks after - implantation , and the tibias were resected .
for xps analysis , newly formed bone in close proximity to implants and cortical bone ( control ) which not in close proximity to implants were analyzed using thin - cut nondecalcified histological specimens . since both bone resorption by osteoclasts and bone formation by osteoblasts progress concurrently , differences in measurement of bone tissue results are apt to occur
; therefore , it is difficult to specify the measurement area . in the present study ,
more than 3 areas of newly formed bone close to implants and those of cortical bone were measured , and sites within which appropriate average values were obtained were determined as the measurement areas ( figure 2 ) .
an xps analysis was performed under the following conditions : x - ray source : monochromatic alk ( 1,486.6  ev ) , detection region : 20  m , and detection depth : approximately 4 - 5  nm ( take - off angle : 45 ) . qualitative analysis was performed using wide scan measurement , and the chemical bonding conditions of detected elements were analyzed using narrow scan measurement .
hydroxyapatite powders were used as the standard specimens , followed by performance of measurements with a correction for relative sensitivity factors ( rsfs ) .
qualitative analysis of the peak strengths on newly formed bone around implants and cortical bone at 4 and 8 weeks is shown in figure 3 .
although peaks of ca , o , p , c , mg , n , and na were detected , a marked unevenness in these peaks was observed at 4 weeks , in contrast to 8 weeks .
based on the results of wide scan measurement , narrow scan measurement of elements related to ca10(po4)6oh2 was performed .
the resulting overlap of c1s , o1s , ca2p , and p2p of newly formed and cortical bone at 4 weeks is shown in figures 3 and 4 , respectively ; the results at 8 weeks are shown in figure 5 .
the results of narrow scan measurement at 4 weeks ( figure 4 ) indicate that , although the peak strengths of newly formed and cortical bone were almost equal at o1s , the half - width became smaller in newly formed bone . at p2p and c1s , although a shifting of the peak in newly formed bone was observed , the half - width became smaller in newly formed bone ; the peak strength of newly formed bone at c1s were lower than that of cortical bone . at ca2p ( ca2p 3/2 ) , although the peak strengths of newly formed bone was lower than that of cortical bone , the half - width became smaller in newly formed bone , and a shifting of the peak was observed .
the chemical bonding condition observed for each element in newly formed bone differed from that of cortical bone . as a result of narrow scan measurement at 8 weeks ( figure 5 ) , the half - width and strength of newly formed bone were almost equal to those of cortical bone at c1s , p2p , and ca2p . at o1s ,
the half - width became small in newly formed bone , and a shifting of the peak was observed .
the chemical bonding condition observed for each element of newly formed bone was similar to that of cortical bone . 

table 2 shows the results of the quantitative analysis of each element and the ca / p ratio .
the results for newly formed bone were ca : 15.07  2.83 weight percent and p : 7.83  1.56 weight percent at 4 weeks ; ca : 17.33  2.393 weight percent and p : 8.90  0.80 weight percent at 8 weeks .
these values gradually became similar to those of cortical bone at 4 weeks ( ca : 17.33  2.39 weight percent and p : 8.90  0.80 weight percent ) and at 8 weeks ( ca : 21.33  1.88 weight percent and p : 11.03  0.70 weight percent ) .
the use of xps analysis in the present experiment has been employed in industry since the 1960s and is now being clinically applied to the qualitative analysis of several nanometer - sized areas on material surfaces .
changes in spectra reveal alterations in chemical bonds based on changes in interatomic transition and valence - band state density . in the present study , newly formed bone at 4 weeks showed differences in the ca / p ratio ( table 2 ) , and in peak position , peak height , and half - width on the narrow scan measurement of each element ( figures 4 and 5 ) .
many mineral elements were present in newly formed bone at 4 weeks , suggesting that the arrangement of chemical bonding and element composition in newly formed bone differed from those in cortical bone .
furthermore , the peak position , peak height , and half - width on narrow scan measurement at 8 weeks in newly formed and cortical bone showed similar traces , and the quantitative analysis of new and cortical bone at 8 weeks ( table 2 ) showed similar results .
these results suggest that newly formed bone at 8 weeks showed a similar bone quality to that of cortical bone , due to progressive bone maturation and bone metabolism of minerals .
each element showed a complex spectrum with changes in the arrangement of chemical bonding regarding the peak and element composition .
the spectrum is related to changes in the chemical bonding of elements caused by interatomic transition and changes in the density or state of the valence band . under the atomic arrangement of bap crystals in immature new bone , various minor and trace elements , including co3 , na , and mg , were substituted for ca , po4 , and oh . such substitutions have been shown to affect the properties of bap crystals .
for example , substitution of co3 for po4 in the apatite lattice can cause changes in chemical bonding that leads to strain and reduced crystallite size in bap [ 16 , 17 ] .
such changes in chemical bonds can result in changes in binding energy in the magnitude of several electron volts ( ev ) . in chemical bonds ,
trace element peaks shift to higher energy as differences in the electronegativity of bond - forming elements and the electron valence of elements increase .
peak shifts are easily influenced by the surrounding molecular environment , and peak shift and half - width variations signify the presence of compounds with different molecular weights and atomic arrangement .
the peak value in a chemical bond is clear with many reports [ 1821 ] .
the main combined states of each element and a corresponding peak are shown in table 3 . in the present study , differences were observed in xps spectra between new bone at 4 weeks postimplantation and cortical bone , indicating immature bone quality due to bap imperfection . in the chemical bonds of each spectrum , changes in the order of 0.1  ev affected bap crystallinity .
the xps spectra of new bone at 8 weeks postimplantation resembled those of cortical bone , and quantitative analysis showed higher ca and p in newly formed bone compared to 4 weeks .
this indicated that the composition of newly formed bone was closer to that of cortical bone at 8 weeks .
osseointegration around implants occurs as mineralization progresses , involving the accumulation of mineral components or bap nanocrystals .
however , the present study was unable to analyze in detail the chemical bonding present in bap nanocrystals , a subject for future analysis .
the aim of this study was to evaluate differences in bones quality between newly formed bone and cortical bone formed around titanium alloy implants by using x - ray photoelectron spectroscopy . 
 as a result of narrow scan measurement at 4 weeks , the newly formed bone of c1s , p2p , o1s , and ca2p were observed at a different peak range and strength compared with a cortical bone . at 8 weeks 
 , the peak range and strength of newly formed bone were similar to those of cortical bone at c1s , p2p , and ca2p , but not o1s . 
 the results from this analysis indicate that the peaks and quantities of each element of newly formed bone were similar to those of cortical bone at 8 weeks , suggestive of a strong physicochemical resemblance .