document: a biodegradao de materiais que ocorre na cavidade bucal pode interferir na resistncia de unio entre o braquete e o esmalte , causando baixos valores de resistncia de unio in vivo , em comparao aos valores in vitro . 
   o objetivo do presente estudo foi desenvolver um prottipo para mensurar , in vivo , a fora de descolagem de braquetes e avaliar , in vitro , a resistncia de unio obtida com o uso do prottipo . 
   um alicate ( 3 m unitek ) foi modificado por meio da adio de um extensmetro diretamente conectado  garra do alicate . um circuito eletrnico realizou a leitura do extensmetro , e um software instalado em um computador registrou os valores de fora de descolagem do braquete em kgf . 
   os braquetes ortodnticos foram colados com material adesivo na face vestibular de 30 dentes incisivos bovinos . no grupo 1 ( n = 15 ) , a descolagem foi realizada com o prottipo , enquanto no grupo 2 ( n = 15 ) foi realizado teste de resistncia de unio  trao , utilizando - se uma mquina universal de ensaios . 
   de acordo com o teste de t de student (  = 0,05 ) , os grupos 1 ( 2,96 mpa ) e 2 ( 3,08 mpa ) no foram estatisticamente diferentes 
   o prottipo mostrou - se confivel para se obter , in vivo , os valores de resistncia de unio dos braquetes ortodnticos . 
   a stable interface between the bonding material and the bracket , as well as between the bonding material and the enamel , is important to withstand the loads generated by an activated arch 
   . 
  
    using universal testing machines , direct bracket bonding to dental enamel and the forces required to debond the brackets have been studied , in vitro , by means of shear or tensile strength . 
   regardless of the precision obtained in the measurement of the debonding forces , the universal testing machines are expensive , large and complex to handle . 
   due to the proportions , it may be impossible to use it for in vivo studies . 
   furthermore , the complex interaction processes that exist in the oral cavity can not be completely reproduced by in vitro studies . 
   the oral cavity is a challenging environment for dental materials , especially regarding the adhesion process . 
   the contact of adhesive systems and composite resins with the oral medium is associated with an ageing pattern , which may alter the composition and the mechanical properties of the polymers . 
   material biodegradation may interfere in the bonding between the bracket and the enamel , 
    causing lower bond strength values in vivo , in comparison with in vitro values . 
   because in vitro bond strength can not be correlated with clinical failure indexes , 
    and facing the necessity of creating a method to test the effects of the oral medium on the composite resins used in orthodontics , different devices have been developed to measure the bracket debonding force in vivo . 
   usually , strain gauges are bonded to the handle 
    or to the arm of the pliers . 
   the force obtained is a measure of the deformation that occurs in the handle or arm of the pliers during the bracket debonding procedure , and the results can be influenced by the way pliers are holded . 
    no study has developed a device using strain gauges connected directly to the part of the pliers where the bracket is attached for the debonding procedure .   thus , the aim of the present study was to develop a prototype to measure the bracket debonding force in vivo , using a strain gauge connected directly to the extremity of the pliers where the bracket debonding occurs . 
   the bond strength obtained with the prototype was also compared in vitro by using the tensile bond strength test in a universal testing machine . 
   a polypropylene plier ( debracketing instrument - 444 - 761 , instrument kit - 3m / unitek , monrovia , ca , usa ) was modified to develop the prototype ( fig 1a ) , which consists of three basic parts :  
   figure 1a ) original plier . 
   b ) exploded image of the intermediate part of the prototype ( the arrow indicates the localization of the strain gauges ) . 
   1 ) modified plier : the pliers have undergone changes from its original design . to install the strain gauge , 
   the original pliers were cut to receive an intermediate part positioned between the active arm of the pliers and the claw ( fig 1b ) . 
   one strain gauge ( 45% ni ; 55% cu ) with 10 mm of a sheet type grid and with temperature compensation for steel ( kyowa , chofu , tokyo , japan ) was directly connected to the claw . 
   figure 1c shows a photograph of the prototype.2 ) measurement and control circuit : corresponds to the electronic circuit that performs the reading of the strain gauge mounted on the intermediate part of the prototype and changes the obtained value into an 8-bit binary number . 
   the value 0 ( zero ) represents a strength of 0 kgf , and the value 255 ( 8 bits ) is the maximum measured force of 6.8 kgf . 
   prior adjustments are necessary for the required performance of the circuit ( wheatstone bridge , amplifier gain and the ad converter range ) . 
   3 ) pc : a specific software was developed to record the values ( in kgf ) of the bracket debonding force . 
   the software was programmed in c ( programming language ) and was designed to enable appropriate use in a research environment . 
   the software has a calibration system , and calibration was performed with weights ranging from 0.5 kg to 6 kg . a known load ( kg ) 
   a simple linear regression analysis was applied to adjust the data ( r = 0.99 ) . 
    ) 
   modified plier : the pliers have undergone changes from its original design . to install the strain gauge , 
   the original pliers were cut to receive an intermediate part positioned between the active arm of the pliers and the claw ( fig 1b ) . 
   one strain gauge ( 45% ni ; 55% cu ) with 10 mm of a sheet type grid and with temperature compensation for steel ( kyowa , chofu , tokyo , japan ) was directly connected to the claw . 
   measurement and control circuit : corresponds to the electronic circuit that performs the reading of the strain gauge mounted on the intermediate part of the prototype and changes the obtained value into an 8-bit binary number . 
   the value 0 ( zero ) represents a strength of 0 kgf , and the value 255 ( 8 bits ) is the maximum measured force of 6.8 kgf . 
   prior adjustments are necessary for the required performance of the circuit ( wheatstone bridge , amplifier gain and the ad converter range ) .   ) 
   pc : a specific software was developed to record the values ( in kgf ) of the bracket debonding force . the software was programmed in c ( programming language ) and was designed to enable appropriate use in a research environment . 
   the software has a calibration system , and calibration was performed with weights ranging from 0.5 kg to 6 kg . 
   a known load ( kg ) was applied to the claw , and the measurements were recorded in kgf . a simple linear regression analysis was applied to adjust the data ( r = 0.99 ) . 
   figure 2a ) prototype after electronic instrumentation ; b ) measurement and control circuit ; c ) usb communication cable . 
   figure 3representative diagram of the parts of the prototype . 
    to measure the accuracy and precision of the prototype , 
   the following weights were used : 1 , 2 , 3 , 4 , 5 , and 6 kg . 
   each weight was connected to the claw of the prototype by a stainless steel wire , and the measurement was done by means of displacing the active arm and lifting the weight . 
   the measurements were undertaken by two examiners , who did not standardize the position of the hand on the pliers . 
   twenty repetitions were performed for each weight . the numerical value recorded by the software installed on the computer was noted , and the arithmetic mean was calculated . 
   the mean temperature in the laboratory during the experiments was 23  2c and the humidity was 70% . 
   the exposed enamel surface was lightly abraded with # 600 grain silicon carbide abrasive paper in a polisher to obtain a flat enamel surface . 
   the maxillary central incisor brackets ( eurodonto , curitiba , pr , brazil ) were bonded to the enamel using the following procedure : a ) prophylaxis with pumice stone and water ; b ) etching with phosphoric acid at 37% for 15 s , followed by washing and drying ; c ) application of scotchbond multi - purpose adhesive ( bond ) ( 3 m , st . 
   paul , mn , usa ) on the enamel ; d ) application of z100 composite resin ( 3 m , st . 
   paul , mn , usa ) at the base of the bracket and positioning on the tooth with light manual pressure , followed by removal of the excess with a periodontal scaler ; e ) light curing for 40 s ( 10 seconds on each side ) with the optilight plus appliance ( gnatus , ribeiro preto , brazil ) . 
   the specimens were stored in 100% relative humidity at 37c for 24 hours . after storage 
   , specimens were divided into two equal groups : group 1 - bracket debonding with the prototype : each specimen was placed on a bench lathe . 
   a single operator held the prototype , which was placed on the bracket with the supports aligned in an occlusal - gingival direction in contact with the enamel . 
   with the claw hitched onto one of the bracket wings , the prototype was activated by moving the active arm until bracket debonding occurred . 
   the value of the force necessary to remove the bracket was recorded by the software in kgf , transformed into newtons and divided by the bracket area ( 14.12 mm ) , to obtain resistance values in mpa . 
   group 2 - bracket debonding by tensile testing in a universal testing machine : the specimen was fixed in a metal sleeve on the bottom part of the emic - dl 2000 universal testing machine ( so jos dos pinhais , paran , brazil ) . for tensile testing 
   , a claw made of stainless steel wire , 0.40 mm in diameter and 5 cm in length , was connected to one of the bracket wings . at the top part of the claw , a 2 mm thick and 20 mm long wire segment 
   was welded , which was hitched onto the top part of the universal testing machine . 
   , tokyo , japan ) at 10x magnification to assess the adhesive remnant index ( ari ) : score 0 = no composite resin left on the tooth ; score 1 = less than half of the composite resin left on the tooth ; score 2 = more than half of the composite resin left on the tooth ; score 3 = all composite resin left on the tooth , with a distinct impression of the bracket mesh . 
   student s t test (  = 0.05 ) for paired samples was used for comparison between the examiners . 
   student s t test (  = 0.05 ) was performed to compare the groups . 
   a polypropylene plier ( debracketing instrument - 444 - 761 , instrument kit - 3m / unitek , monrovia , ca , usa ) was modified to develop the prototype ( fig 1a ) , which consists of three basic parts :  
   figure 1a ) original plier . 
   b ) exploded image of the intermediate part of the prototype ( the arrow indicates the localization of the strain gauges ) . 
   1 ) modified plier : the pliers have undergone changes from its original design . to install the strain gauge , 
   the original pliers were cut to receive an intermediate part positioned between the active arm of the pliers and the claw ( fig 1b ) . 
   one strain gauge ( 45% ni ; 55% cu ) with 10 mm of a sheet type grid and with temperature compensation for steel ( kyowa , chofu , tokyo , japan ) was directly connected to the claw . 
   figure 1c shows a photograph of the prototype.2 ) measurement and control circuit : corresponds to the electronic circuit that performs the reading of the strain gauge mounted on the intermediate part of the prototype and changes the obtained value into an 8-bit binary number . 
   the value 0 ( zero ) represents a strength of 0 kgf , and the value 255 ( 8 bits ) is the maximum measured force of 6.8 kgf . 
   prior adjustments are necessary for the required performance of the circuit ( wheatstone bridge , amplifier gain and the ad converter range ) . 
   3 ) pc : a specific software was developed to record the values ( in kgf ) of the bracket debonding force . 
   the software was programmed in c ( programming language ) and was designed to enable appropriate use in a research environment . 
   the software has a calibration system , and calibration was performed with weights ranging from 0.5 kg to 6 kg . a known load ( kg ) 
   a simple linear regression analysis was applied to adjust the data ( r = 0.99 ) . 
    ) 
   modified plier : the pliers have undergone changes from its original design . to install the strain gauge , 
   the original pliers were cut to receive an intermediate part positioned between the active arm of the pliers and the claw ( fig 1b ) . 
   one strain gauge ( 45% ni ; 55% cu ) with 10 mm of a sheet type grid and with temperature compensation for steel ( kyowa , chofu , tokyo , japan ) was directly connected to the claw . 
   measurement and control circuit : corresponds to the electronic circuit that performs the reading of the strain gauge mounted on the intermediate part of the prototype and changes the obtained value into an 8-bit binary number . 
   the value 0 ( zero ) represents a strength of 0 kgf , and the value 255 ( 8 bits ) is the maximum measured force of 6.8 kgf . 
   prior adjustments are necessary for the required performance of the circuit ( wheatstone bridge , amplifier gain and the ad converter range ) .   ) 
   pc : a specific software was developed to record the values ( in kgf ) of the bracket debonding force . the software was programmed in c ( programming language ) and was designed to enable appropriate use in a research environment . 
   the software has a calibration system , and calibration was performed with weights ranging from 0.5 kg to 6 kg . 
   a known load ( kg ) was applied to the claw , and the measurements were recorded in kgf . a simple linear regression analysis was applied to adjust the data ( r = 0.99 ) . 
   figure 2a ) prototype after electronic instrumentation ; b ) measurement and control circuit ; c ) usb communication cable . 
   to measure the accuracy and precision of the prototype , the following weights were used : 1 , 2 , 3 , 4 , 5 , and 6 kg . 
   each weight was connected to the claw of the prototype by a stainless steel wire , and the measurement was done by means of displacing the active arm and lifting the weight . 
   the measurements were undertaken by two examiners , who did not standardize the position of the hand on the pliers . 
   twenty repetitions were performed for each weight . the numerical value recorded by the software installed on the computer was noted , and the arithmetic mean was calculated . 
   the mean temperature in the laboratory during the experiments was 23  2c and the humidity was 70% . 
   the exposed enamel surface was lightly abraded with # 600 grain silicon carbide abrasive paper in a polisher to obtain a flat enamel surface . 
   the maxillary central incisor brackets ( eurodonto , curitiba , pr , brazil ) were bonded to the enamel using the following procedure : a ) prophylaxis with pumice stone and water ; b ) etching with phosphoric acid at 37% for 15 s , followed by washing and drying ; c ) application of scotchbond multi - purpose adhesive ( bond ) ( 3 m , st . 
   paul , mn , usa ) on the enamel ; d ) application of z100 composite resin ( 3 m , st . 
   paul , mn , usa ) at the base of the bracket and positioning on the tooth with light manual pressure , followed by removal of the excess with a periodontal scaler ; e ) light curing for 40 s ( 10 seconds on each side ) with the optilight plus appliance ( gnatus , ribeiro preto , brazil ) . 
   after storage , specimens were divided into two equal groups : group 1 - bracket debonding with the prototype : each specimen was placed on a bench lathe . 
   a single operator held the prototype , which was placed on the bracket with the supports aligned in an occlusal - gingival direction in contact with the enamel . 
   with the claw hitched onto one of the bracket wings , the prototype was activated by moving the active arm until bracket debonding occurred . 
   the value of the force necessary to remove the bracket was recorded by the software in kgf , transformed into newtons and divided by the bracket area ( 14.12 mm ) , to obtain resistance values in mpa . 
   group 2 - bracket debonding by tensile testing in a universal testing machine : the specimen was fixed in a metal sleeve on the bottom part of the emic - dl 2000 universal testing machine ( so jos dos pinhais , paran , brazil ) . for tensile testing , a claw made of stainless steel wire , 0.40 mm in diameter and 5 cm in length , was connected to one of the bracket wings . at the top part of the claw , a 2 mm thick and 20 mm long wire segment was welded , which was hitched onto the top part of the universal testing machine . 
   tokyo , japan ) at 10x magnification to assess the adhesive remnant index ( ari ) : score 0 = no composite resin left on the tooth ; score 1 = less than half of the composite resin left on the tooth ; score 2 = more than half of the composite resin left on the tooth ; score 3 = all composite resin left on the tooth , with a distinct impression of the bracket mesh . 
   student s t test (  = 0.05 ) for paired samples was used for comparison between the examiners . student s t test (  = 0.05 ) was performed to compare the groups . 
   table 1 compares the mean values obtained by the two examiners , with each weight , during the gauging procedure of the prototype . according to student s t test for paired samples 
   , there were no significant differences ( p < 0.05 ) between the examiners at any weight . 
   table 1comparison between the examiners in each weight.comparisonnmean ( kgf)standard deviationp valuea - 1 kg 201.040.080.30b - 1 kg 201.070.08a - 2 kg 202.030.070.20b - 2 kg 
   202.060.09a - 3 kg 202.950.060.08b - 3 kg203.010.09a - 4 kg 204.080.080.44b - 4 kg 204.040.09a - 5 kg205.010.090.16b - 5 kg 205.050.07a - 6 kg 206.080.080.32b - 6 kg 206.050.09*p > 0.05 indicates no significant difference between the examiners a - examiner a.b - examiner b. 
    * p > 0.05 indicates no significant difference between the examiners   according to student s t test , the mean bond strength obtained in group 1 ( 2.96 mpa ) and in group 2 ( 3.08 mpa ) were statistically similar ( table 2 ) . 
   table 2comparison of mean bond strength ( mpa ) obtained in each group.groupnmeansdpgroup 1152.960.32 > 0.05group 2153.080.40group 1 : prototype.group 2 : tensile test in a universal testing machine . 
   adhesive remnant index score 3 was predominant in the two groups ( table 3 ) . 
   score 0score 1score 2score 3group 1 - 1 ( 7%)1 ( 7%)13 ( 86%)group 2- -2 ( 13%)13 ( 86%)group 1 : prototype.group 2 : tensile test in a universal testing machine . 
   the prototype of the present study was an evolution of a device which had two strain gauges bonded to the anterior and posterior 2/3 surfaces of the active arm of the pliers . 
   because the strain gauges were placed in the active arm of the pliers , they suffered from the influence of the operator s hand . 
   the present prototype has been developed in order to control this problem by placing the strain gauge near the claw , and not in the active arm of the pliers . 
   strain gauges are defined as localized mechanical deformation sensors , since all and any phenomenon responsible for mechanical deformation can be analyzed . 
   therefore , strain gauges are transducers that convert mechanical displacement into a range of electrical resistance . 
   strain gauges are very sensitive and temperature alterations are able to influence the measurements . 
    to compensate for any possible temperature alterations , 
   the following procedures were adopted : a ) use of an electrical resistance strain gauge with temperature compensation for steel that self - compensates eventual temperature variations , and ; b ) control of the laboratory mean temperature during the experiments .   in the present study , 
   the strain gauges were bonded in the intermediate part positioned between the active arm of the plier and the claw . 
   one strain gauge was directly connected to the claw . when the plier was used to debond the brackets , the strain gauge metal grid resistance generated a tension ( mv ) . 
   the small amount of tension generated was multiplied by an amplifier circuit in the electronic circuit , which performed the reading of the strain gauge , into binary numbers that were converted into kgf . 
   the mode of holding the prototype was not standardized between the two examiners , and there was no statistically significant difference in the values obtained between the examiners at any weight . 
   this means that the prototype was not influenced by the way that it was held - as in another study 
   - , confirming that the new prototype is superior to the previous one .   after gauging the prototype , in vitro orthodontic bracket debonding 
   the bracket debonding performed with a universal testing machine is not dependent on operator variation , the values obtained with this method were compared to the values obtained with the prototype to evaluate its reliability . 
   the tensile test on the universal testing machine ( group 2 ) tried to reproduce the same conditions as debonding with the prototype . for this purpose 
   , a 0.40 mm in diameter stainless steel wire claw was made reproducing the same thickness as the prototype claw ( group 1 ) . 
   along with that , the claw made for the test machine was also connected on a single wing of the bracket at the testing time , reproducing the same position used by the prototype claw at the debonding moment . 
   although it is named tensile test , it is known that not only tensile forces occur at the debonding moment of the bracket , but that there is also an interaction of tensile , shear and compressive forces . 
   debonding of the bracket was performed under a constant crosshead speed of 0.5 mm / min in the universal testing machine . 
   this load speed is generally used in spite of not corresponding to clinical conditions due to the fact that in vivo debonding occurs at a higher speed . 
   therefore , when the prototype was applied , a speed higher than 0.5 mm / min was probably used for bracket removal . despite the fact that differences existed between the methodologies used for debonding 
   , the bond strength did not differ statistically between the prototype ( 2.96 mpa ) and the tensile test on the universal testing machine ( 3.08 mpa ) . 
   this suggests that the prototype might be a useful tool for measuring bond strength in vivo . 
   orthodontic bracket bonding to teeth requires that the bond system applied must provide sufficient bond strength to withstand the forces that occur during the orthodontic mechanics and chewing . for clinical situations 
   bond strength values above 10 mpa are potentially dangerous since they may cause enamel fractures during bracket debonding . 
   however , it is difficult to establish a numerical value because these values depend on several factors , such as the condition of the substrate , 
    the material involved , 
    the devices chosen for the test , 
    cure time , 
    and the location where force is applied to the bracket . 
  
    due to the difficulty of comparing and extrapolating the results obtained from in vitro studies to the clinical situation , it remains unknown what minimum bond strength values are required for safe clinical performance of orthodontic bonding procedures . 
   thus , it would be useful to determine the bracket bond strength values in vivo , by using a device to measure the bracket debonding force directly in the oral cavity . 
   the ari scores showed that the fracture pattern was predominantly score 3 in both groups . 
   the composite resin remained completely bonded to the enamel after bracket debonding , which is advantageous since score 3 has the least probability of harming the enamel . 
   therefore , debonding with the prototype was shown to be a safe method for preserving the enamel surface . 
   
summary: abstractintroduction : material biodegradation that occurs in the mouth may interfere in the bonding strength between the bracket and the enamel , causing lower bond strength values in vivo , in comparison with in vitro studies . objective : to develop a prototype to measure bracket debonding force in vivo and to evaluate , in vitro , the bond strength obtained with the prototype.methods : a original plier ( 3 m unitek ) was modified by adding one strain gauge directly connected to its claw . 
   an electronic circuit performed the reading of the strain gauge , and the software installed in a computer recorded the values of the bracket debonding force , in kgf . 
   orthodontic brackets were bonded to the facial surface of 30 bovine incisors with adhesive materials . in group 1 
   ( n = 15 ) , debonding was carried out with the prototype , while tensile bond strength testing was performed in group 2 ( n = 15 ) . 
   a universal testing machine was used for the second group . the adhesive remnant index ( ari ) 
   was recorded.results : according to student s t test (  = 0.05 ) , group 1 ( 2.96 mpa ) and group 2 ( 3.08 mpa ) were not significantly different . 
   ari score of 3 was predominant in the two groups.conclusion : the prototype proved to be reliable for obtaining in vivo bond strength values for orthodontic brackets .