as noted above , the method of the present invention involves the use of cementitious filling materials to form an improved seal against migration of bacteria . this method provides a superior therapy for cavities found in the teeth of mammals , including humans , as well as other vertebrates . in another preferred embodiment , the cement composition contemplated by the present method comprises a portland cement having a blaine number falling within a certain range . however , the present invention is not limited to use of portland cement or any particular composition thereof . thus , the principal component of the present cement composition by weight is calcium , which is present in the form of calcium oxide ( cao ) on an average of about 65 weight percent . on the other hand , it is believed that a range of cement compositions having a calcium component is compatible with the present method wherein the calcium component is present by weight in an amount of about 50 - 75 %. another important component of the present composition by weight is silicon , which is present in the form of silicon dioxide ( sio 2 ) in an average of about 21 weight percent . again , it is believed that a suitable range for this component within the present cement composition is about 15 - 25 weight percent . in addition , the combination of the above calcium and silicon components is present on an average of about 86 weight percent . it appears that an acceptable range for these two components of the present cement composition is 70 - 95 weight percent . although not all of the cement compositions falling within these ranges had been utilized in test involving the present method , it is believed that such cement compositions could be effectively utilized . typically portland cement is combined with aggregate and water to form concrete . the cement and water coat and bind to the aggregate , filling the spaces between the aggregate particles to form a ceramic composite material . the cement composition of the present invention , however , does not require the use of aggregate , but utilizes portland cement with water . the process of making portland cement is well known and it can be purchased from any number of manufacturers under various trade names . the basic raw materials for portland cement are lime ( cao ), silica ( sio 2 ), alumina ( al 2 0 3 ) and iron oxide ( fe 2 o 3 ). these components are appropriately proportioned to produce various types of portland cement . in manufacturing portland cement , the selected raw materials are crushed , ground , and proportioned for the desired composition then blended . the mixture is then fed into a rotary kiln where it is heated to temperatures of up to 1400 °- 1650 ° c . in this process the mixture is chemically converted to cement clinker which is subsequently cooled and pulverized . a small amount of gypsum ( caso 4 . 2h 2 o ) is added to the cement to control the setting time of the concrete . the resulting cement consists principally of tricalcium silicate ( 3cao . sio 2 ), dicalcium silicate ( 2cao . sio 2 ), tricalcium aluminate ( 3cao . al 2 o 3 ), and tetracalcium aluminoferrite ( 4cao . al 2 o 3 . fe 2 o 3 ). calcium oxide is thus the principal component of portland cement and typically comprises in excess of 60 % by weight of the overall composition . in general , as defined for its typical use , there are five basic types of portland cement . these are identified by the standard specifications promulgated by the american society for testing of materials ( astm ). type i is called normal portland cement and is a general purpose cement suitable for all uses when the special properties of the other types are not required . type i portland cement is more generally available than are the other types of cement . type i , or ordinary , portland cement is typically used in assorted construction applications . in its normal applications , a type i cement is used when the concrete is not subject to special sulphite hazard or where the heat generated by the hydration of the cement will not cause an objectionable rise in temperature . such conditions are typical of the mouth , which would normally not necessitate the use of astm types ii through v . thus , the cement composition utilized of the present invention requires none of the special properties of type ii - v cements , and the preferred embodiment comprises an astm type i portland cement , although it is believed that such other types are within the scope of the invention as being suitable for the purposes described herein . of course , the practitioner will recognize in certain circumstances that the special characteristics of other astm types may be desirable . type ii cements are used when the cement will be exposed to moderate sulfite attacks , and where a moderate heat of hydration is desired because the cement is being used in a large structure , and may be subject to cracking due to uneven cooling . type iii portland cement is used when early strength is desired , which may be suitable for certain applications where early strength may be advantageous . type iv is a low heat of hydration cement useful when the heat of hydration is critical , for example , in extremely large structures such as dams . it would typically not be required in anatomical structures , but it may be criteria , for example , if an additive were used that may be adversely affected by a higher heat of hydration . type v is a sulfite resistent cement useful when the cement is exposed to high sulfite attack . the preferred embodiment of the present invention utilizes a type i portland cement having the following approximate composition : ______________________________________component percentage______________________________________sio . sub . 2 21 % al . sub . 2 o . sub . 3 4 % fe . sub . 2 o . sub . 3 5 % cao 65 % mgo 2 % so . sub . 3 2 . 5 % alkalies ( na . sub . 2 o , k . sub . 2 o ) 0 . 5 % ______________________________________ this preferred portland cement is commercially available as the colton fast - set brand of the california portland cement company . the suitability of a particular cement composition for a given purpose is typically determined by a combination of its chemical composition and its physical attributes , i . e . the manner and degree to which the cement is ground ( granulation ) and the resulting particle size . the fineness of a cement is indicated by the cement &# 39 ; s blaine number , which represents the ratio of the cement &# 39 ; s particle surface area to its weight ( square centimeters of surface per gram ). portland cements generally have a blaine number in the range of 3 , 200 to 5 , 500 cm 2 / g or greater . faster setting cements , like that preferably utilized in the present invention , have a blaine number in the range of 4 , 000 - 5 , 500 cm 2 / g . the most preferable cement utilized in the present invention has a blaine number in the range of 4 , 500 - 4 , 600 cm 2 / g . in this formulation , the cement composition comprises a powder consisting of fine particles which are hydrophilic and which set in the presence of moisture . hydration of the powder results in a colloidal gel which solidifies to a hard rock - like substructure in less than four hours . the characteristics of the cement composition depend upon the size of the particles , the powder - water ratio , temperature , presence of water , and entrained air . after setting , the composition has compressive strength equal to that of amalgam . portland cement is combined with water to form the cement composition of the present invention . depending on the particular application , various amounts of water may be utilized to form the cement composition . enough water is added to the cement to give it a putty consistency , which then solidifies to a rock - like hardness . in using the preferred cement composition as a retrograde filling material , the water content is in the range of 10 to 40 weight percent , and most preferably three parts cement are used with one part water , or 25 weight % of the cement composition is water . the fact that water is the principal reactant in the hardening reaction offers a significant advantage over many of the filling materials commonly used by allowing the cement to set in the moist environment of the body . portland cement hardens by reactions with water , which are called hydration reactions . these reactions are complex , but principally involve the reaction of tricalcium silicate ( 3cao . sio 2 ) and dicalcium silicate ( 2cao . sio 2 ) with water . when these compounds react with water during the hardening of the cement , the principal hydration product is tricalcium silicate hydrate . this material is a colloidal gel of extremely small particles ( less than 1 micron ). the tricalcium silicate hardens rapidly and is most responsible for the early strength of portland cement . the dicalcium silicate has a slower hydration reaction and is mainly responsible for strength increases beyond one week . tricalcium aluminate , which plays a lesser role in the hardening process , hydrates rapidly also and contributes to early strength of development . portland cement is not radiopaque , but a radiopaque component may be added to render it radiopaque for purposes of dental diagnostics . bismuth oxide ( bi 2 o 3 ) has been found to be a suitable such compound . depending on the degree of radiopaqueness desired , various ratios of additive may be used . in the preferred form of the cement composition , one part bismuth oxide is used per four parts portland cement . in addition , other additives or adjuvants could also be combined with the present cement composition to help facilitate and modify its beneficial therapeutic behavior . for example , small amounts of preservatives could be added , as well as stabilizers and desensitizers . in many dental applications , the ultimate success of the treatment often depends on the adaption of the filling material to the tooth walls , and the resultant seal between the filler and the remaining tooth structure . an ideal seal will prevent the migration of bacteria and other byproducts into the cavity . the sufficiency of the seal is particularly important where the pulp chamber is to be sealed . the clinician will recognize that adaption and sealing ability of a filling material can be measured in various ways . any test of adaption and sealing ability attempts to determine the filling material &# 39 ; s ability to seal the cavity from bacteria and other organisms that can promote further decay . therefore , the filling material &# 39 ; s effectiveness can also be directly determined by clinical studies ; however , these are subject to many variables and require significant time and expense . to simulate the clinical function , the filling material can be evaluated by a dye penetration test . various dyes have been used to measure the sealing ability of materials to tooth structure , including the use of rhodamine - b fluorescent dye as a tracer . a tandem scanning reflected light microscope (&# 34 ; sem &# 34 ;) is used to determine the degree of dye penetration . this method of measuring the adaption and sealing ability is well known to the clinician . see , e . g ., tronstad , l ., trope , m ., doering , a . and hasselgren , g . ( 1983 ), sealing ability of dental amalgams as retrograde fillings and endodontic therapy , j . endodontics 9 : 551 - 53 ; chung , b . s ., pitt ford , j . r . and watson , t . f . ( 1991 ) the adaptation and sealing ability of light - cured glass ionomer retrograde root fillings , int &# 39 ; l endodontic j . 24 : 223 - 32 . in dye penetration tests , the cavity is first prepared and filled with the material to be tested . this test allows a comparison , under controlled conditions , between the sealing ability of standard filling materials , such as amalgam , and the cement composition contemplated by the method of the present invention . after the outside of the tooth is coated to prevent dye leakage through anywhere but the cavity being tested , the tooth is immersed in a solution of the dye . the tooth is then sectioned and examined under the sem , and the degree of dye leakage along cavity walls measured . such leakage is expressed in terms of the distance ( millimeters ) travelled by the dye . in one such test , root canals for thirty single - rooted extracted human teeth were prepared using the standard step - back technique . the canals were obturated with gutta percha and grossman sealer using the lateral condensation technique . the roots were then wrapped in moist gauze pads and kept in 100 % humidity for a week prior to root end preparations . nail varnish was then applied to the entire external surface of each root and allowed to dry . about 3 - 4 millimeters of the apical segment of each root was removed at a 90 ° angle to the longitudinal axis of the root . the resected surface was acid etched , and a thin layer of pitting and fissure sealant was applied to prevent dye penetration through the exposed dentinal tubules . the roots were then divided into three groups of ten , and the retrograde cavities were filled with one of the three retrograde filling materials : amalgam , eba and the cement composition of the preferred embodiment . the roots were then placed in wet pieces of gauze and allowed to remain in 100 % humidity for 24 hours . next , the roots were totally immersed in an aqueous solution of rhodamine b fluorescent dye for 24 hours . by using a slow - speed diamond saw , each root was sectioned into two halves parallel to the longitudinal axis of the tooth . the extent of leakage along cavity walls was then observed under the sem . the results , expressed in millimeters , are shown in table i below . table i______________________________________initial leakage dye penetration test results : highest score offluorescent dye leakage ( mm ) along cavity walls ofretrograde filling . sample amalgam eba cement composition______________________________________1 3 3 02 3 2 03 3 1 04 3 3 & lt ; 1 * 5 3 2 06 3 2 07 3 1 & lt ; 18 3 1 & lt ; 19 3 1 010 3 1 & lt ; 1______________________________________ * less than onethird of root end cavity depth . thus , in the case of retrograde cavities , the cement composition of the present invention performed significantly better than either amalgam or super eba cement . in various tests on retrograde fillings , amalgam allowed dye penetration all the way to the end of the retrograde cavity , which is typically 2 - 3 millimeters . such cavities filled with super eba cement leaked less than those filled with amalgam , but significantly more than the cement composition of the present invention . thus , based on this dye penetration test and associated visualization , the cement composition associated with the present invention performs excellently as a filling and sealing material . although direct extrapolation and relevance of such dye leakage studies to clinical practice has been questioned , such tests are the oldest and easiest method to test new restorative filling materials . furthermore , when the filling material does not allow penetration of small molecules , such as those exhibited in the dye , it logically has the potential to prevent leakage of large molecules such as bacteria and / or by - products . the adaption and sealing ability of a filling material can also be examined microscopically using the sem to observe voids and gaps between the filling material and the tooth structure without the benefit of the dye leakage . when examined under the microscope , teeth filled with the preferred cement composition exhibited virtually no gaps or voids , and significantly less than that exhibited by either amalgam or super eba . the application of the cement composition in filling and sealing teeth are numerous . the practitioner will realize that there are many suitable applications which fall within the method of the present invention . examples are shown in fig1 through 7 and discussed below . fig1 shows an example of an anatomical structure with which the present invention may be used . fig1 depicts a longitudinal section of a healthy single - rooted tooth 10 with pulp tissue 12 , dentin 14 and enamel 16 . fig2 depicts root canal therapy in a single - rooted tooth after apicoectomy and retrograde filling . the retrograde cavity 18 is shown filled with the cement composition . substantially all of the remainder of the pulp chamber 20 is filled with standard obturating material such as gutta percha . in order to provide additional sealing , the pulp chamber may also be sealed at the coronal end 22 with the cement composition as shown in fig2 . the remainder of the tooth cavity is filled with a standard amalgam 24 or other permanent filling material . the retrograde filling is performed in the standard manner , and the cement composition is applied using a suitable dental carrier . the preferred length of a filling or seal provided by the present cement composition is 2 - 3 mm , although other dimensions are possible . the incision may be closed upon completion of the retrograde filling , and the cement composition will harden sufficiently in vivo . prior to preparation of the cement composition , the portland cement to be used therein may be sterilized , including gas sterilization , autoclaving or other suitable method . when the cement composition is used as an orthograde cavity filler , as well as a pulp sealer , as shown in fig2 the preferred method is to utilize a temporary filler for the remainder of the cavity 24 for twenty four hours to allow the cement composition to harden sufficiently . the temporary filling can then be replaced with the desired permanent filling material . fig3 is a further example of the environment in which the present invention may be used . fig3 depicts a longitudinal section of a healthy lower molar tooth 27 with pulp tissue 26 , dentin 28 and enamel 30 . use of the cement composition to seal a tooth where decay has penetrated through the enamel and dentin is shown in fig4 . the decay has been removed , and the cement composition has been used as a base 32 for a permanent filling 34 of any suitable material . again , a temporary filling should be used for at least 24 hours to allow the cement to harden . fig5 shows a longitudinal section of a molar tooth 27 where the decay 36 has reached the pulp 26 . use of the portland cement composition to seal a tooth where decay has reached the pulp is shown in fig6 . the decay 36 has been removed , and the portland cement composition has been used to cap 38 the pulp 26 , and the filling is completed with a permanent filling 40 of any suitable material . the portland cement composition is also useful to repair any perforations which may occur during endodontic treatment . for example , fig7 shows a perforation 42 in the furcation 44 which has occurred during root canal therapy . as seen in fig8 the perforation 42 has been repaired with the present portland cement composition 46 after root canal therapy . the remainder of the root canal therapy is standard wherein the canals have been obturated with gutta percha 48 or other suitable material , and the filling has been completed with a permanent filling material 50 . in conclusion , the present invention , through the use of the cement composition of the invention , embodies a novel method of filling and sealing human and veterinarian teeth . the described examples of how the dentist or endodontist can use the cement composition to seal teeth is illustrative , and not meant to be restrictive . the scope of the invention is , therefore , indicated by the claims rather than the foregoing description . furthermore , the present invention may utilized in other specific forms without departing from its spirit or essential characteristics .
an improved method for filing and sealing tooth cavities involves the use of a cement composition which exhibits several advantages over existing orthograde and retrograde filling materials , including the ability to set in an aqueous environment . in a preferred embodiment , the cement composition comprises portland cement , or variations in the composition of such cement , which exhibit favorable physical attributes sufficient to form an effective seal against reentrance of infectious organisms .