Patent Application: US-201113251574-A

Abstract:
the invention is directed to an improved dental composition useful in the repair of cavities , apex repairs , root perforations and root canals . disclosed is a dental composition and dental composition additive which have improved handling characteristics , for example improved viscosity and setting time . the addition of effective amounts of a modified cellulose and calcium chloride to available dental repair compounds , such as mineral trioxide compound , results in the improved dental composition without affecting the other characteristics of the dental repair compound .

Description:
the following example discloses a single preferred embodiment of the invention . it is meant merely to illustrate the invention and not to limit the invention . the skilled artisan in the practice of this invention will readily recognize that substitutions and alterations can be made while remaining within the metes and bounds of the invention , which are set forth in the claims that follow . recently , the inventors herein demonstrate improved characteristics of mta ( proroot dentsply tulsa dental , tulsa , okla .) through the addition of 1 % methylcellulose ( mc ) and 2 % calcium chloride ( cacl 2 ) into its parent cement . the inventors observed that the handling characteristics were vastly improved while the compressive strength of mta with the additives was not significantly affected and the setting time of mta with the additives was significantly shorter than the mta control . this observation also brought about questions on whether the chemical additives have significantly altered any inherent physical properties crucial to mta &# 39 ; s success as an ideal dental cement . therefore , this example describes the physical properties , ( marginal leakage , chemical shrinkage , cement solubility , and washout resistance ) of chemically modified mta ( 1 % mc + 2 % cacl 2 in mta / h 2 o ) and compare it to unaltered mta . four different tests were designed and employed to assess marginal leakage , chemical shrinkage , cement solubility , and washout resistance between the unaltered mta and chemically modified mta ( cmmta ) to ensure that the added chemicals have not deteriorated the aforementioned properties of mta . dye leakage results demonstrated no significant difference between cmmta and mta samples . in addition , there was significantly less leakage between the cmmta and mta groups compared to amalgam . chemical shrinkage results reported no significant difference between any of the groups ( 1 - 6 ) at any of the designated timeframes ( t 1 , t 2 , t 3 , t 24 , and t w ). more importantly , there was no significant difference in mean chemical shrinkage between cmmta and mta samples at any of the designated time intervals of the specimens . cement solubility results revealed no significant difference between cmmta and mta groups . furthermore , results demonstrated no significant difference between weights of the test materials at any designated time intervals ( t 1 , t 7 , t 21 ). modified washout tests indicated a significant difference observed between groups 1 - 3 . however , there were no significant differences noted between cmmta and mta groups . in conclusion , the data presented in this research confirm that the addition of 1 % mc + 2 % cacl 2 into mta does not deleteriously alter any of the parent cement &# 39 ; s physical properties ( marginal leakage , chemical shrinkage , cement solubility , and washout resistance ) and that cmmta performed as well or better than mta in all of the above tests conducted . as of 2005 , there have been some 150 articles published regarding mineral trioxide aggregate &# 39 ; s ( mta ) composition , properties , biocompatibility , and indications for use . mta has become the material of choice for an array of endodontic applications , including vital pulp therapy , apexification , perforation repair , as well as a root - end filling material . any root - end filling material should have the ability to seal the root canal from bacterial and chemical invasion as well as be biocompatible , prevent periradicular tissue irritation , and ideally favor regeneration of the involved tissues to their prediseased status ( 1 ). mta has been demonstrated to meet many of the ideal properties of a root - end filling material as described by gartner and dom ( 2 ). mta is different from other root - end filling materials currently in use , ( super - eba , irm , amalgam , and composite resin - based materials ). both in vitro and in vivo studies have consistently demonstrated this material to be equal or superior in terms of its biocompatibility ( 3 - 9 ), marginal adaptation ( 10 ) and sealing abilities , ( 11 - 13 ), even in the presence of blood and moisture ( 14 ). mta is a chemical mixture of three powder ingredients : portland cement ( 75 %), bismuth oxide ( 20 %), and gypsum ( 5 %) ( 15 ). these powders consists of fine trioxides and other hydrophilic particles , that upon mixing with sterile water , results in a wet , sandy consistency that sets in the presence of moisture in approximately 165 minutes . hydration of the powder results in the formation of a colloidal gel with an initial setting ph of 10 . 2 , which increases to 12 . 5 after 180 minutes . an elemental analysis of mta revealed an overall composition of mta as 58 . 9 % ca , 20 . 1 % bi , 9 . 4 % si , 2 . 1 % al , 2 . 7 % s , 4 . 4 % fe , with trace amounts of cr , ni , and pb ( 16 ). the unique composition of mta often makes it hard to use , especially in regions with difficult access . according to lee ( 17 ), mta is a difficult material to handle due to its granular consistency , slow setting time , and initial looseness . once the mixture starts to dry , it loses its cohesiveness and becomes unmanageable . delivery of mta has focused mainly on carrier and syringable - type devices to simplify placement of the material , however , each still has its own set of problems . the devices can become easily clogged and can be difficult to use due to location and access of the surgical site . recent modifications to mta has been studied and shown to improve the handling characteristics ( 18 ). 1 % methylcellulose ( mc ) was added as an anti - washout additive to enhance handling characteristics and provide a more cohesive user - friendly material . this additive does have drawbacks , including decreased compressive strength due to voids entrapped in the cement and longer setting times . to offset these drawbacks , 2 % cacl 2 was incorporated as an accelerator to decrease the setting time . the inventors observed that the compressive strength with the additives was not significantly affected compared to mta at 24 hours and 3 weeks ( table 1 ) while setting time of mta with the additives was significantly shorter than the mta control ( table 2 ). materials and methods — all chemically modified mta ( cmmta ) samples were prepared as described by ber ( 18 ). briefly , cacl 2 ( pcca , houston , tex .) equal to 2 % of the sample weight was added to distilled water and mixed into solution . half of the solution was placed on a hot plate were the temperature of the solution was raised to 80 ° c . 1 % mc ( sigma , st . louis , mo .) was added to the warmed solution and stirred to wet the particles . the remainder of the room temperature solution was added and then stirred until all of the powder was in solution . it was then stored at 0 ° c . for 20 minutes to allow for the mixture to thicken . the solution was then mechanically stirred for 30 minutes to create a homogenous gel . this solution was then added to mta at a 0 . 33 water / cement ratio generate a chemically modified mta cement . all conventional mta samples were mixed with distilled water according to manufacturer &# 39 ; s instructions , using a powder to water ratio of 3 : 1 . dye leakage — forty - one extracted , human , single - rooted maxillary incisors were collected and stored in 10 % formalin . the clinical crowns were decoronated at the cementoenamel junction ( cej ) with a # 557 carbide bur in a highspeed handpiece with water coolant . working length was determined by subtracting 0 . 5 mm from the length at which a # 10 k file exited the apical foramen . teeth were prepared using rotary instrumentation to a master apical file ( iaf ) size 40 / 04 with nickel - titanium ( niti ) profile ( tulsa dental products , tulsa , okla .) instruments via modified crown - down technique in conjunction with rc prep ( premier , king of prussia , pa .) and 5 . 25 % naocl − ( clorox ; clorox co ., oakland calif .). the canals were dried with paper points and samples were obturated immediately with roth root canal cement 801 elite grade ( roth international ltd ., chicago , ill .) and thermoplasticized gutta - percha utilizing an obtura ii ( obtura / spartan usa , fenton , mo .) unit set at 200 ° c . and expressed in one continuous movement . canals were then compacted with an s kondensor plugger ( obtura / spartan usa , fenton , mo .) and coronal access openings sealed with irm ( id caulk , milford , del .). all roots were then stored at 37 ° c . and 100 % humidity for 1 week . apical root resections were performed on all roots by removing 3 mm of each apex at 90 degrees to the long axis of the tooth with a # 169 fissure bur using a highspeed handpiece with water coolant . a 3 mm root - end cavity preparation was performed using ultrasonics ( spartan usa , fenton , mo .) and kis tips ( obtura / spartan usa , fenton , mo .) under surgical microscope ( global surgical corp ., st . louis , mo .) at 9 . times . magnification . two coats of nail polish were applied to the entire surface of each root except where the root - end filling was to be placed . teeth were randomly assigned to two groups of 15 roots each . group 1 was retrofilled with mta ( proroot , dentsply tulsa dental , tulsa , okla .). group 2 with chemically modified mta , ( 1 % mc + 2 % cacl 2 in mta ). an additional 5 roots ( group 3 ) were filled with high copper amalgam ( tytin amalgam , kerr mfg . co ., romulus , mich .) without cavity varnish . each material was condensed into their respective preparation sites using an s kondensor plugger . three instrumented roots with retrograde preparations and no root - end fillings served as positive controls while three roots were instrumented and obturated with gutta - percha and sealer . entire root surfaces covered with two coats of nail polish were used as negative controls . all roots were then stored in 1 % methylene blue for 72 hours . the roots were rinsed with distilled water and nail polish removed . teeth were sectioned buccolingually using a 169 tapered fissure bur in a highspeed handpiece and fractured using a woodson instrument . dye penetration was evaluated under surgical microscope ( global surgical corp ., st . louis , mo .) at 9 × magnification . the presence of dye penetration through the material / dentin interface was scored on a four - point scale as shown in fig1 , in which 0 = no dye penetration observed , 1 = dye penetration observed up to 1 of the root - end filling material , 2 = dye penetration observed between ½ but not beyond the root - end filling material , 3 = dye penetration observed beyond the root - end filling material and into the canal system . results were recorded and submitted to non - parametric kruskal - wallis and mann - whitney u - tests . chemical shrinkage — the chemical shrinkage methodology was based on the original work performed by geiker ( 19 ). modification to geiker &# 39 ; s original work is currently under proposal as the protocol designated to determine chemical shrinkage of portland cement for the cement industry , ( astmcxxxx test method for chemical shrinkage of hydraulic cement paste ) ( 20 ). all cement pastes were prepared in accordance to manufacturer &# 39 ; s instructions at a 0 . 33 water / cement ratio for groups 1 - 6 ( group 1 = pc / h 2 o , group 2 = cmmta , group 3 = mta / h 2 o , group 4 = 2 % cacl 2 in mta , group 5 = 2 % cacl 2 in portland cement , and group 6 = 1 % mc + 2 % cacl 2 in portland cement ). the mass of each empty glass vial ( diameter = 2 . 5 cm and height = 6 cm ) was determined to the nearest 0 . 01 g . ten grams of cement paste was placed in the bottom of each vial using a vibrating table to achieve a paste height between 5 mm and 10 mm in the vial . mass of the glass vial was determined with the consolidated cement paste to the nearest 0 . 0001 g . the remainder of the glass vial was then filled to the top with de - aerated water and sealed with a rubber stopper encasing a pipette graduated in 0 . 01 ml increments . the respective graduated pipette was then filled to the top with de - aerated water with the addition of 1 - 2 drops of hydraulic oil to minimize the evaporative process over the 1 - week timeframe ( fig2 ). mass of the vial + capillary tube filled with water and cement paste was immediately determined to the nearest 0 . 0001 g . the vial was then transferred and placed in a constant temperature water bath of 23 . 0 ± 0 . 5 ° c . at 30 minutes ( t 30 m ), the glass vial was then removed from the water bath , wiped dry , capillary tube filled to excess with de - aerated water , and mass determined to the nearest 0 . 0001 g . additional weight measurements were taken at hourly intervals for the first 8 hours ( t 1 h - t 8 h ) followed by additional measurements at 24 hours ( t 24 h ) and 1 week ( t 168 h ) respectively . calculation of the mass sample was determined as follows : the mass of cement powder in the vial is given by : m vial + paste = mass of the glass vial with the added cement paste ( g ) once the mass of the cement was calculated , this weight in grams was incorporated into the following formula to determine the chemical shrinkage per unit mass at the specific time interval . the chemical shrinkage per unit mass of cement at time t is computed as : cs ( t )=([ m ( t )− m ( 30 min )]/ m cement )/ ρ w to briefly summarize , two 10 gram specimens were run for each cement group ( group 1 = pc / h 2 o , group 2 = cmmta , group 3 = mta / h 2 o , group 4 = 2 % cacl 2 in mta , group 5 = 2 % cacl 2 in portland cement and group 6 = 1 % mc + 2 % cacl 2 in pc ) at a 0 . 33 water / cement ratio . weight measurements ( 0 . 0001 g ) were taken from the shrinkage apparatus initially at 30 minutes ( t 30m ) followed by hourly intervals for the first 8 hours ( t 1 h - t 8 h ). subsequent weighing of samples were taken at 24 hours ( t 24 h ) and 1 week ( t 168 h ) respectively with the resulting average of each group being reported and statistically examined for differences in chemical shrinkage per unit mass between groups at the aforementioned specified time intervals ( t 1 h , t 2 h , t 3 h , t 24 h , and t 168 h ). solubility — degree of solubility of the test samples was determined by the modified method of ada / ansi specification # 30 ( 21 ) as performed by torabinejad et al . ( 22 ). briefly , the materials were prepared in accordance to manufacturer &# 39 ; s recommendations . individual mta and cmmta samples were hand - mixed and transferred into a small disc approximately 20 mm × 1 5 mm by use of a plastic former and two glass slabs . mixing and weighing of the samples were performed by a single operator at 23 . 0 ± 2 ° c . and a relative humidity of 50 ± 5 %. 6 discs of mta and 8 discs of cmmta were prepared and tested . following fabrication , discs were placed in 100 % humidity for 21 hours . discs were removed and stored individually in glass jars containing 50 ml of distilled water at 37 ° c . the specimens were then desiccated for 1 hour at 37 ° c . individual discs were weighed to the nearest 0 . 0001 g and placed back into their respective glass jars . the water in glass jars were neither changed nor added during the test periods . desiccation and weighing of samples were performed at : 1 day ( t 1 ), 7 days ( t 7 ) and at 21 days ( t 21 ). mean weights of the specimens were recorded and submitted to non - parametric kruskal - wallis and mann - whitney u - tests to determine statistical differences between weights of the test materials at different time intervals . dispersion resistance / washout — the percentage of cement washout of the test samples was determined by a modified method based on concrete standard test ( crd - c 61 - 89a ) ( 24 ). the receiving container and washout apparatus is shown in fig3 . briefly , two representative 10 gram samples from each group ( group1 = portland cement , group2 = mta , group3 = cmmta ) were prepared in accordance to manufacturer &# 39 ; s instructions at a 0 . 33 water / cement ratio . each sample was hand - mixed and placed into a separate receiving container . the cement mixture was tamped down with the handle of a cement spatula 10 - 15 times to allow the cement to adhere to the walls of the container . extruded cement was removed from the outside of the receiving container allowing the mass of the cement and container to be obtained and recorded to the nearest 0 . 0001 g ( m i ) immediately following weight measurement , the receiving container with cement sample was allowed to freely fall through the h 2 o to the bottom of a 1000 ml graduated cylinder and sit for 15 seconds . the receiving container was then slowly raised to the top of the graduated cylinder in 5 ± 1 seconds , allowed to drain for 2 minutes , air dried carefully to remove excess h 2 o but not disrupt the cement , and weighed to the nearest 0 . 0001 g . mass of the cement remaining in the receiving container was recorded as m f . repeated testing was performed three times on the same cement sample , determining a new m f each time . the m f after the final sequence was then calculated as the cumulative loss in mass qualifying as the percent washout of the cement ( d ) demonstrated below . the washout of the cement is computed as : d =( m i − m f / m i ) 100 dye leakage — microleakage results of all groups are presented in table 1 . results from group 1 ( mta ) showed that 14 of 15 samples ( 93 %) showed an evaluation score of 0 ( no leakage ) ( fig5 ). from group 2 ( cmmta ), 100 % of the specimens displayed an evaluation score of 0 ( no leakage ) ( fig6 ). in contrast , 100 % of the samples from group 3 ( amalgam ) displayed an evaluation score of 3 ( dye penetration throughout the entire canal ). the kruskal - wallis test was used to compare differences between all groups . this test revealed a significant difference between the groups ( p & lt ; 0 . 05 ). when examining differences within groups , the mann - whitney u - test showed that leakage observed in group 1 ( mta ) was significantly less ( p & lt ; 0 . 05 ) than group 3 ( amalgam ). likewise , group 2 ( cmmta ) displayed significantly less leakage ( p & lt ; 0 . 05 ) than group 3 . there was no significant difference noted between groups 1 ( mta ) and 2 ( cmmta ) ( p & lt ; 0 . 05 ). positive control samples showed dye leakage throughout the entire canal system , while the negative control samples displayed no signs of dye penetration . chemical shrinkage — results from the kruskal - wallis test confirmed our rationale and revealed that there was no significant difference noted between groups 1 - 6 ( p & lt ; 0 . 05 ). furthermore , statistical analysis employed with median tests to compare groups at the designated time intervals ( t 1 h , t 2 h , t 3 h , t 24 h , and t 168 h ) were unable to show a statistically significant difference in mean chemical shrinkage between the specimens at the previously mentioned time frames ( p & lt ; 0 . 05 ). in this experiment , we were interested in the amount of shrinkage that would occur from time t 30 m to time intervals t 1 h , t 2 h , t 3 h , t 24 h , and t 168 h . reasoning for these timeframes was that the recommended setting time for mta is 165 minutes ( 22 ). thus , it is expected that the majority of hydration would be occurring during the initial three hours for mta and therefore , chemical shrinkage of the cement would be anticipated to be at its greatest . astm guidelines for this experiment require hourly measurements for the first 8 hours , a 24 hour reading , and finally at 1 week . solubility — the mean weights ( g ) of the specimens and standard deviation for each test material at various time intervals ( t 1 h , t 7 h , t 21 h ) are shown in tables 2 and 3 . the change in mass for each of the samples revealed that there was a tendency for a positive gain in total mass (+ 0 . 024 %−+ 2 . 46 %) with a mean gain in mass of 1 . 14 % over the 21 day period for cmmta samples . likewise , half of the mta samples ( 1 - 3 ) revealed a positive change in mass (+ 1 . 04 %−+ 2 . 18 %) while samples 4 - 6 showed a negative change in mass (− 0 . 135 %−− 0 . 58 %) with an overall mean gain in mass of 0 . 57 % over the 21 day period for the mta samples . when examining differences between the two groups , the mann - whitney u - test displayed no significant differences between mta and cmmta in solubility ( p & lt ; 0 . 05 ). furthermore , statistical analysis with the wilcoxon signed ranks test was unable to show a statistical significant difference when the mean weight of the specimens were compared at different time intervals ( t 1 h , t 7 h , t 21 h ) ( p & lt ; 0 . 05 ). dispersion resistance / washout — weights ( g ) of each test group with corresponding repeated measures on washout for portland cement , mta , and cmmta is shown in tables 4 - 6 respectively . results from the friedman test used to analyze the amount of cumulative washout revealed a significant difference observed between groups ( p & lt ; 0 . 05 ). however , due to the small sample size , post hoc analysis ( median test ) was unable to identify significant differences within groups . dye leakage — an apicoectomy followed by a root - end filling material is a common endodontic procedure used to rectify recalcitrant periapical pathosis in teeth where orthograde endodontic therapy has failed and nonsurgical treatment is not an option . one of the properties of an ideal root - end filling material is the ability to seal the root canal system ( 2 ). dye leakage studies are a quick an effective method to evaluate the sealing ability of root - end filling materials ( 22 ). in 1989 , kersten and moorer determined the leakage of methylene blue to be comparable to that of a small bacterial metabolic product of similar molecular size . thus , when a filling material does not allow the penetration of small molecules such as methylene blue , it has the potential to prevent leakage of larger substances such as bacteria and their by - products ( 24 ). under the parameters of this study , leakage was quantified with the use of a likert four - point scale in which 0 = no dye penetration observed , 1 = dye penetration observed up to 1 of the cavity depth , 2 = dye penetration observed between 1 / 2 but not beyond root - end filling material placement , and 3 = dye penetration observed beyond the filling material and into the canal system . thus , greater disparity from a score of zero directly reflects the ability of the root - end filling to adequately seal the dentin / material interface . graphical representation of leakage scores obtained over 72 hours is presented in table 1 . from this table , we were able to conclude that the greatest disparity occurred between amalgam and cmmta groups . a similar contrast was also evident between the mta and amalgam groups . however , there was no significant difference noted in leakage between mta and cmmta groups . our results indicate that the cmmta ( 1 % methylcellulose + 2 % cacl 2 in mta ) was comparable to the unaltered mta ( mta / h 2 o ) in preventing dye penetration beyond the extent of the material . therefore , the additives placed into mta had no significant effect on its sealing properties . in fact , the chemically modified mta showed no evidence of leakage in all 15 specimens . chemical shrinkage — numerous properties of cementitious materials are controlled by their initial hydration rate ( early - age strength development , heat release , and crack resistance ). a direct method for analysis of the cement &# 39 ; s initial hydration rate is by quantifying the chemical shrinkage of the cement paste during its hydration . as cement hydrates , the hydration products occupy less volume than the initial reacting materials ( cement and water ). as a result of this volume change , a hydrating cement paste will absorb water , if available from its immediate surroundings . at early times this water absorption is in direct proportion to the amount of hydration that has occurred ( 25 ). it has been generally considered that a potential root - end filling material should set as soon as it is placed in a root - end cavity without significant shrinkage . this would allow for dimensional stability of the material after placement and less time for an unset material to be in contact with periapical tissues . the incorporation of 1 % methylcellulose + 2 % cacl 2 into mta by ber . ( 18 ) has demonstrated to show promise to rectify some of mta &# 39 ; s potential shortcomings as a root - end filling material ( long setting time and poor handling characteristics ). a detrimental effect of calcium chloride is drying shrinkage ( 26 ). this study was undertaken to determine if the incorporated additives ( namely cacl 2 ) into mta significantly affected the chemical shrinkage properties of mta . statistical analysis in the mean amount of chemical shrinkage occurring over 1 week ( 168 hours ) for each of the six groups revealed no significant difference between groups at any of the determined time intervals ( p & lt ; 0 . 05 ). as illustrated in fig8 , specimens with the greatest to the least amount of chemical shrinkage displayed over 1 week is represented as follows : group 5 ( 2 % cacl 2 in pc )& gt ; group 6 ( 1 % mc + 2 % cacl 2 in pc )& gt ; group 1 ( pc / h 2 o )& gt ; group 4 ( 2 % cacl 2 in mta )& gt ; group 2 ( cmmta )& gt ; group 3 ( mta / h 2 o ). we expanded the graph to provide a clearer representation of specific trends for each specimen tested relative to early age shrinkage ( t 0 - t 8 ) ( fig9 ). both figures illustrate a consistent increase in chemical shrinkage for each of the specimens tested over time . likewise , the addition of 2 % calcium chloride revealed a propensity to increase the chemical shrinkage rate . this is expected , since calcium chloride is used as an accelerant to increase the hydration process and provide early - age strength . nonetheless , statistical analysis was able to demonstrate no significant amount of shrinkage between mta and cmmta mean samples . these results have demonstrated that unique to the dental sector and unlike in the cement industry , small quantities ( usually & lt ; 1 gram ) of mta mixed at a 3 : 1 w / c ratio placed in intimate contact with periapical tissues which provides 100 % humidity within an aqueous environment will enable and maintain saturation of the material and prevent a significant amount of autogenous or drying shrinkage . solubility — root - end filling materials used during periapical surgery are routinely placed in intimate contact with inflamed or infected areas of the periodontium . it is therefore essential that the root - end filling material be given every opportunity to maintain its apical seal and resist dissolution while in the presence of moisture / blood or lowered ph of the involved area . torabinejad et al . was able to demonstrate that mta leaked significantly less than amalgam , super eba and irm in the presence of blood , and they observed that the presence or absence of blood had no significant effect on the amount of leakage of the material ( 27 ). the rationale for this is that mta beneficial properties are realized with the added moisture from blood within the surgical site during the hydration process to initiate the initial seal . the literature states the presence of periradicular inflammation may provide an acidic ph of 5 . 5 and this lowered ph may alter the physical properties of mta to inhibit setting reactions , affect adhesion , or increase solubility of the material ( 28 ). a study performed by roy et al . was able to demonstrate that the sealing ability of freshly mixed mta was not affected in an acidic environment ( ph 5 . 0 ) ( 29 ). conversely , a study performed by lee et al . was able to make evident that an acid environment of ph 5 adversely affected the physical properties and the hydration behavior of mta by retarding the dissolution of reactants , ( c 3 s , c 2 s , and c 3 a ) therefore decreasing the production of portlandite crystals . furthermore , sem and xrd analysis also revealed that the lowered ph had potentiated a decreased hardness value of mta with dissolution of surface crystals ( 30 ). the inventors observed that the addition of 1 % mc and 2 % cacl 2 into mta had no detrimental effects on the material &# 39 ; s solubility . under the parameters used in this example , all specimens were immersed in distilled h 2 o for 21 days to provide an adequate timeframe to identify trends in the initial solubility that may affect long - term results . thus , if the material would show any initial dissolution , there would be a chance that the marginal seal has been disrupted and the potential for leakage to occur . from the observations , it appears that specimens from both cmmta and mta groups showed no or minimal signs of solubility in water over the observation time . in fact , cmmta and mta groups both demonstrated mean increases in water absorption over the 21 day period respectively (+ 1 . 14 % and + 0 . 57 %). our results were somewhat surprising to see a positive change in mean mass for both groups over this timeframe . one may direct this discrepancy to standard measuring error where the specimens were weighed to 0 . 0001 grams . it is also plausible , methylcellulose , which is traditionally used as a bulking agent in the marketplace , may have potentially absorbed additional water into the cement during the hydration process adding to the higher mean increase in weight of cmmta . nonetheless , these results are in agreement with a study performed by torabinejad , ( 22 ) who concluded that mta , super - eba , and amalgam showed no signs of solubility at 21 days . clinically , there is no standard method for predictably measuring the manufacturer &# 39 ; s recommended 3 : 1 w / c ratios for mta . fridland ( 31 ) was able to demonstrate that the degree of solubility in mta increased as w / c ratio increased . therefore , the amount of water used in preparing the mix has a direct effect on solubility when the material is in contact with an aqueous environment . this increase in solubility has the potential to affect the long - term seal that can essentially lower the overall success of the endodontic procedure . our data is in opposition to a recent study performed by fridland ( 32 ). this long - term study measured solubility over 78 days with varying w / c ratios . the authors concluded that mta with a 0 . 33 w / c ratio over 78 days revealed a 24 . 04 % cumulative solubility of the material &# 39 ; s initial dry weight . the disparity in solubility results between studies could have resulted from differences in measurement methodology . fridland et al . calculated solubility according to an amalgamation of iso 6876 standard ( 33 ) and ada specification # 30 ( 34 ). in essence , fridland et al . used an indirect weight measurement to determine the solubility of mta . these authors used values from the weighted residues as a percentage of the initial dry weight of the specimens . in contrast , our methodology mirrored a study performed by torabinejad , ( 22 ) who used a modification to ada specification # 30 using direct measurement of the specimens at the dedicated time intervals . dispersion resistance / washout — during periapical surgery , root - end filling materials are inevitably exposed to periapical tissues and fluids . this continuous moisture contamination may complicate the placement of an effective seal and place the material at risk to washout of the material . this is particularly relevant for freshly placed mta because of its lengthy setting time ( 165 minutes ) ( 22 ). mta seems to have similar vulnerabilities to washout as portland cement when placed in aqueous environments with prolonged setting times . the cement industry routinely deals with wet conditions ( underwater concrete placement ) that can potentially affect the properties of the material , not unlike conditions encountered during periapical surgery . for a discussion of how the cement industry addresses problems of wet conditions , see concrete construction engineering handbook , e . nawy , ed ., new york , crc press , 1997 ; concrete construction handbook , j . dobrowski , 4th ed ., new york , mcgraw - hill , inc ., 1998 ; and kosmatka and panarese , design and control of concrete mixtures , 13th ed ., portland cement association , skokie , ill ., 1988 , all of which are herein incorporated by reference . to address these problems for dental application , an anti - washout mixture ( methylcellulose ) is added to the cement to facilitate a more cohesive cement . the addition of this additive increases the viscosity of the water used in the mixture , therefore , producing a more thixotropic material to resist washout . clinically , most of the disintegration of the cement will initially occur during the placement of the material and not once it has set . that is why the addition of this cohesive antiwashout material may inhibit the dispersion of material from the cavity both during placement and as well as the first few hours of setting . the inventors ( 18 ) have adopted the cement industry &# 39 ; s solutions to these problems with the addition of 1 % methylcellulose + 2 % cacl 2 in mta . the inventors evaluated in this example whether the chemically modified mta has provided added benefits to the parent cement ( mta ) in terms of washout resistance . the results obtained in this study landed within the typical performance requirements for allowable washout (& lt ; 6 - 12 %) of underwater concrete for all of the specimens tested ( 34 ). indeed , our results from the friedman test used to analyze cumulative washout revealed a significant difference observed between groups ( p & lt ; 0 . 05 ). when evaluating the data mathematically , one could arrive at a conclusion that the significant difference in mean cumulative washout was between group 2 ( mta =− 3 . 57 %) and group 3 ( cmmta =+ 1 . 34 %). as in the solubility study , we would expect to see a negative washout value for cmmta . the positive cumulative washout for cmmta could possibly be explained by standard measuring error of the materials during the weight measurement process or inadequate removal of h 2 o from the receiving container prior to measurement . in conclusion , the data presented in this example support our position that the addition of 1 % mc + 2 % cacl 2 into mta has not deleteriously altered any of the parent cement &# 39 ; s additional physical properties ( marginal leakage , chemical shrinkage , cement solubility , and washout resistance ). on the contrary , the results from the four studies testing the physical properties of cmmta have concluded : dye leakage results demonstrated that there was no statistically significant difference noted between cmmta and mta samples ( p & lt ; 0 . 05 ). in addition , we were able to demonstrate significantly less leakage between the cmmta and mta groups compared to amalgam ( p & lt ; 0 . 05 ). chemical shrinkage results reported no statistically significant difference noted between any of the groups at any of the designated timeframes ( t 1 , t 2 , t 3 , t 24 , t w ). more importantly , we were able to show no statistically significant difference in mean chemical shrinkage between cmmta and mta samples at any of the designated time intervals of the specimens ( p & lt ; 0 . 05 ). cement solubility results revealed no statistically significant difference between cmmta and mta groups ( p & lt ; 0 . 05 ). furthermore , we were able to show no significant difference between weights of the test materials at different time intervals . modified washout tests indicated a significant difference observed between groups 1 - 3 ( p & lt ; 0 . 05 ). data obtained from the study demonstrated cmmta as having the most mean cumulative washout resistance while mta displayed the least cumulative washout resistance . however , there were no significant differences noted between these two groups ( p & lt ; 0 . 05 ). the following references are cited throughout this section using the related parenthetical numbering system . the references are incorporated herein by reference . applicant reserves the right to challenge the veracity of statements made therein . 1 ) sarkar n k , caicedo r , ritwik p , moiseyeva r , kawashima i . physicochemical basis of the biologic properties of mineral trioxide aggregate . j endod . 2005 ; 31 : 97 - 100 . 2 ) gartner a h , dom s o . advances in endodontic surgery . dent clin north am 1992 ; 36 : 357 - 78 . 3 ) koh e t , torabinejad m , pitt ford t r , brady k , mcdonald f . mineral trioxide aggregate stimulates a biological response in human osteoblasts . j biomed mater res . 1997 ; 37 : 432 - 9 . 4 ) koh e t , mcdonald f , pitt ford t r , torabinejad m . cellular response to mineral trioxide aggregate . j endod 1998 ; 24 : 543 - 7 . 5 ) torabinejad m , hong c u , pitt ford t r , kaiyawasama s p . tissue reaction to implanted super - eba and mineral trioxide aggregate in the mandible of guinea pigs : a preliminary report . j endod 1995 ; 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