in recent years , much focus has been placed on extrinsic causes of dental erosion , such as acidic dietary beverages and citric and phosphoric acids which are often added to soft drinks .
only few studies have focused on the erosive effect of intrinsic acids such as gastric juices even though they have a higher erosive potential than soft drinks .
prolonged exposure to gastric content can cause dental erosion and in severe cases result in pathological tooth wear with loss of both function and esthetics .
it has been shown that people suffering from eating disorders or gastric reflux are at increased risk of developing dental erosion .
hence , the use of procedures such as fluoride rinses and varnishes has been recommended ; however , these are presentably ineffective because at low ph fluorapatite gets dissolved .
it was thought for many years that fluoride acted basically by its incorporation in the hydroxyapatite lattice and the reduced solubility of the so - formed fluoridated hydroxyapatite . on the contrary
, it was shown that shark enamel , which consists of solid fluorapatite , also developed carious lesion in an in situ experiment in high caries challenge regimen .
later , studies revealed that it was not the intrinsic fluoride content of tissues but rather the loosely bound fluoride present at the tooth  oral fluid interface , which was responsible for effective inhibition of lesion formation .
erosion progression can be diminished by application of fluoride preparations , such as acidic sodium , stannous , or amine fluoride preparations .
the principle of its protective effect is the precipitation of caf2-like product on the tooth surface .
one major disadvantage of this precipitate is that they readily get dissolved in acidic solutions . unlike above - mentioned agents , titanium tetrafluoride ( tif4 )
the unique interaction of tif4 with tooth structure leads to the formation of a resistant tenacious coating ( referred as a glaze - like layer ) on the tooth surface .
the advantage has been credited to the titanium group present in the compound , which synergizes the effect of fluoride .
reed and bibby 's preliminary test in children showed that the topical application of tif4 ( 1% ) was more effective in reducing enamel solubility and in preventing caries than the application of acidic phosphate fluoride ( apf ) .
these results along with stability , lack of irritating properties , and nontoxicity of titanium suggested its use in human beings .
bykyilmaz and sen observed that the glaze formed after application of 4% tif4 on the occlusal surface of deciduous enamel retained in the area of pits and fissures even after a period of 12 months despite the masticatory and abrasive forces in the oral cavity .
hence , in our present study , the effect of fluoridating agents on dentin has been evaluated .
the study described here sought to comparatively investigate the effect of 1.23% apf and 4% tif4 on human coronal dentin using vickers microhardness test .
thirty noncarious extracted premolars were collected and stored in distilled water after cleaning them out of their debris .
teeth were sectioned buccolingually with the help of diamond disk ( confident dental equipments ltd . , india ) in a micromotor straight handpiece ( nsk , nakanishi
inc , tochigi - ken , japan ) , at a speed of 20,000 rpm , using water spray as a coolant . among the two halves of the buccolingually
sectioned tooth , the one with less surface aberrations on dentin was selected to prepare the sample . exposing the sectioned surface ,
teeth were embedded in self - cure acrylic , surrounded by a plastic pipe ( sectioned to required thickness before the procedure ) to give the specimen correct shape .
exposed coronal dentin was polished with abrasive papers starting with 2205000 grit ( coarse grit to fine grit ) .
then , specimens were stored in a closed container in a dry environment to preserve the surface fineness . as a part of the evaluation of microhardness of coronal dentin , four
indentations were given 100 m apart on each specimen by vickers microhardness indenter and average of four indentations was calculated to minimize the error .
the load of 500 g was applied for 10 s. these readings stand as baseline values of microhardness of dentin .
all the specimens were treated with hydrochloric acid at a ph of 1 for 5 min , followed by the evaluation of microhardness of treated coronal dentin .
all the thirty samples were divided into two groups : 
 group a - fifteen samples in the group on coronal dentin were applied carefully with 1.23% apf gel ( dentsply , york , pa , usa ) as an approximately 2 mm thick layer in one application , with the help of the cotton pellet by tweezers and were left undisturbed .
after 4 min , it was gently removed with the help of smooth absorbent paper , followed by gentle rinsing with water and air driedgroup b - fifteen samples in the group on coronal dentin were applied carefully with freshly prepared 4% tif4 solution ( sigma - aldrich co. , st .
it was prepared by dissolving 3.4 g of tif4 powder in 100 ml deionized distilled water .
a solution of 4% tif4 was applied in drops for 4 min , the drop was left undisturbed till surface appeared dry , and the additional drops were applied in the same manner . after 4 min , the specimens were gently rinsed with water spray and air dried . 
 
group a - fifteen samples in the group on coronal dentin were applied carefully with 1.23% apf gel ( dentsply , york , pa , usa ) as an approximately 2 mm thick layer in one application , with the help of the cotton pellet by tweezers and were left undisturbed . after 4 min
, it was gently removed with the help of smooth absorbent paper , followed by gentle rinsing with water and air dried group b - fifteen samples in the group on coronal dentin were applied carefully with freshly prepared 4% tif4 solution ( sigma - aldrich co. , st .
it was prepared by dissolving 3.4 g of tif4 powder in 100 ml deionized distilled water .
a solution of 4% tif4 was applied in drops for 4 min , the drop was left undisturbed till surface appeared dry , and the additional drops were applied in the same manner . after 4 min , the specimens were gently rinsed with water spray and air dried .
change in microhardness of the dentin in both groups a and b after application of 1.23% apf gel and 4% tif4 , respectively , was evaluated .
it was followed by exposure of both group a and b specimens to the acidic protocol as mentioned above , and microhardness readings were recorded to evaluate the ability of 1.23% apf gel and 4% tif4 to resist demineralization in an acidic environment .
table 1 represents the result of paired t - test between groups a and b after application of apf gel and 4% tif4 to demineralized dentin . represents result of paired t - test between group a and group b after application of apf gel and 4% tif4 to demineralized dentin table 2 represents the result of paired t - test between groups a and b after exposure of 1.23% apf gel- and 4% tif4-treated dentin to an acidic environment . represents result of paired t - test between group a and group b after exposure of apf gel and 4% tif4 treated dentin to low ph statistical analysis
was performed using ( graphpad prism , version 5 , la jolla , ca , usa ) .
paired t - test was used to compare the vickers microhardness values between groups a and b. group a has shown greater increase in microhardness of coronal dentin ( p < 0.001 ) , followed by application of apf gel than group b. greater resistance to decrease in microhardness of coronal dentin ( p < 0.05 ) followed by exposure to acidic protocol was shown by group b.
according to buyukyilmaz , 4% tif4-treated enamel surface is more resistant to crack formation and the glaze appears to be more tenacious and thicker , than with 1% tif4 .
few studies that evaluated the impact of tif4 solution on dentin in vitro have confirmed it was effective in reducing erosive dentin loss .
jones et al . have demonstrated that concentrated fluoride gels were able to provide some degree of protection to enamel against endogenous erosion .
mok et al . have demonstrated that these fluoride gels have shown the same level of protection against exogenous erosion . in both the studies
wefel and wei have stated in their study that 4-min application time of 1.23% apf gel is better over 1-min application time . while ten cate jm et al have found no difference in application time of 1.23% apf gel . however , in the case of 4% tif4 , various time periods of application have been used .
reed and bibby , von rijkom et al . , and exterkate and ten cate have considered 1- , 4- , 5-min application time , respectively , in their studies to evaluate the effect of tif4 . hence , to standardize the application time of both fluoridating agents in the present study , 4-min application time was considered . in the case of endogenous erosion ,
the teeth exposed to acids from the gastrointestinal tract are most likely intermittent and for short periods but , on the other hand , may last for weeks or months .
thus , the present direct acid exposure model is presumably more severe than exposure in the oral cavity .
the relationship between microhardness and mineral structure of teeth has been documented as directly proportional .
the hardness number is based on the surface area of the indent itself divided by the applied force , giving hardness units in kgf / mm .
microindentation tests typically have forces of < 2 n and produce indentations of about 50 m .
in addition , microhardness values vary with load and work - hardening effects of materials .
the indentation has two measurements of the length of the diagonal ( d1 and d2 ) which are measured in an optical microscope and reading of microhardness appears on the screen .
results obtained were statistically evaluated by paired t - test ; all at p < 0.05 to find statistical significance of microhardness values .
a t - test is any statistical hypothesis test in which the test statistic follows a student 's t - distribution if the null hypothesis is supported .
it can be used to determine if two sets of data are significantly different from each other and are most commonly applied when the test statistic would follow a normal distribution if the value of a scaling term in the test statistic was known .
comparison of results obtained between groups a and b after application of 1.23% apf gel and 4% tif4 solution to demineralized dentin has shown statistically significant ( p < 0.001 ) difference in the increase of microhardness .
the amount of increase in microhardness of group b less than group a was probably due to low ph of 4% tif4 solution ( ph - 1.5 ) .
however , the mineral loss was considered partial and limited to outermost 810 m . on the other side
, apf gel has a ph range of 33.5 , which is comparatively less acidic to 4% tif4 , thereby causes less surface mineral loss .
comparison of results obtained between groups a and b after exposure of 1.23% apf gel- and 4% tif4-treated dentin to the acidic environment has shown statistically significant difference in the decrease in microhardness .
the results confirmed that 4% tif4- and 1.23% apf gel - treated dentin was resistant to demineralization in an acidic environment .
this might be due to glaze - like layer formed on the surface of dentin , which is a product of interaction between 4% tif4 and proteins on the surface of dentin .
another explanation for this acid - resistant glaze - like layer includes ti ion reacts with oxygen groups on the tooth surface , i.e. , phosphate - bound oxygen .
this mechanism would provide covalently bound titanium on the enamel surface properties of the glaze .
the protective action of 1.23% apf gel is the precipitation of caf2-like product on the eroded tooth surface and its major disadvantage is that they possibly readily dissolve in acidic solution , so the effectiveness of 1.23% apf gel in preventing dentinal erosion is limited .

 within confines of the study , it can be stated that both 1.23% apf gel and 4% tif4 solution are effective in resisting the demineralization of dentin in acidic environmenthowever , 4% tif4 has shown better efficacy than 1.23% apf gel . 
  within confines of the study
, it can be stated that both 1.23% apf gel and 4% tif4 solution are effective in resisting the demineralization of dentin in acidic environment however , 4% tif4 has shown better efficacy than 1.23% apf gel .
 aim : the aim of this study was to comparatively evaluate the effect of 4% titanium tetrafluoride ( tif4 ) and 1.23% acidic phosphate fluoride ( apf ) gel on the microhardness of human coronal dentin.materials and methods : thirty noncarious extracted premolars were collected and sectioned buccolingually with the help of diamond disk . exposing the sectioned surface , 
 teeth were embedded in self - cure acrylic . 
 exposed coronal dentin was polished with abrasive papers starting with 2205000 grit . 
 microhardness was evaluated by vickers microhardness evaluator , at four different stages as follows - stage 1 : baseline values , stage 2 : exposure of specimens to acidic environment at a ph 1 for 5 min , stage 3 : application of 1.23% apf gel and 4% tif4 ( after dividing the specimens into two groups , i.e. , group a and b , respectively ) , and stage 4 : followed by exposure of fluoridated specimens to acidic protocol as mentioned above.results:paired t - test was used to compare the readings between groups a and b. group b has shown greater resistance to decrease in microhardness of coronal dentin ( p < 0.05 ) on exposure to acidic protocol.conclusion:due to acidic ph ( 1.5 ) of 4% tif4 , amount of increase in microhardness of dentin is < 1.23% apf gel . 
 4% tif4 was more effective in resisting demineralization than 1.23% apf gel . 
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
CONCLUSION
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