the descriptive matter immediately hereinafter is arranged so as to describe the materials that have been referred to in respective method steps . accordingly , the first descriptive matter will be clarifying what is meant by the respective bonding resins and catalysts delineated in the summary of the invention hereinbefore . the bonding resins that are employed in this invention are those resins that will bond in the presence of a catalyst to form a firm , substantially permanent bond that resists hydrolysis , even in the presence of mouth acids and enzymes in the mouth . the bond that is formed , as well as the catalyst and bonding resin should be nontoxic so that the patient is not adversely affected during the bonding of the dental appliance onto the teeth or the retention of the appliance in the mouth . these types of bonding resins are conventionally available and include the epoxy resin , per se , or capped with hydrolysis - resistant moieties ; urethane resin ; cyano - acrylate resin ; methacrylate resin ; vinyl ester resin ; and acrylate resin . if desired , the resins that have ends that do not resist hydrolysis by their own chemical nature are capped with hydrolysis - resistant moieties such as the acrylate moiety or methacrylate moiety . both the uncapped resins such as epoxy resins and methacrylic capped epoxy resins are commercially available , as from dupont , wilmington , del . ; dow chemical company , midland , mich . ; shell chemical co . ; houston , tex . ; or rohm and haas chemical company , st . louis , mo . if desired , the resin like the methacrylate capped epoxy resin may have other monomers such as styrene incorporated into its formulation in order to block hydrolysis of the ester linkage by steric hindrance . to ensure complete understanding , the following structural formula is given to amplify the definition of the epoxy resins . these resins are defined by the structural formula i . ## str1 ## to eliminate the harmful effects of epoxy curing agents the epoxide ends are reacted with the methacrylic moiety shown in formula ii . ## str2 ## ordinarily , it is preferred to employ monomer additions , or diluents , to obtain clearer , less viscous monomer solutions . these diluents include styrene , methyl methacrylate , hydroxy methyl methacrylate , ethylene glycol dimethacrylate , diethylene glycol dimethacrylate , triethylene glycol dimethacrylate , various polyethylene glycol methacrylates individually , trimethylol propane - trimethacrylate , 1 , 4 - butane glycol dimethacrylate , 1 , 3 - butane glycol dimethacrylate , n - propyl methacrylate , n - butyl methacrylate , penta - erythritol tetra methacrylate , and the like . the preferred resin for bonding is methacrylate capped epoxy diluted with styrene constituting 40 - 55 percent of the final admixture ; but its odor is objectionable . work is being done to overcome this objection . preferably , the bonding resin that is employed with the catalyst in a layer on the teeth will have a low viscosity in the range of 250 - 5 , 000 centipoises at room temperature . the value of n in the structural formula i is selected such that the molecular weight will be in the range of 10 , 000 - 300 , 000 , although it may be even higher to obtain the desired viscosity with lesser amount of filler as described hereinafter with respect to the layer on the bracket bases . the polymerization of these types of bonding resins is ordinarily effected by free radical initiation employing suitable initiators , or accelerators , as well as catalyst . typical of the initiators are amines such as n , n - dimethyl - para - toluidine ; n , n - dimethylaniline ; and cobalt naphthenate . as is recognized , the cobalt naphthenate is ordinarily employed with methyl ethyl ketone peroxide catalyst for the epoxide type resins . the preferred initiator is n , n - dimethyl - p - toluidine . the catalyst may comprise any of those that are ordinarily employed for polymerizing these type of monomers . the preferred catalyst for this invention is either benzoyl peroxide of methyl ethyl ketone peroxide . in accordance with this invention , there is no need to mix a powdered catalyst with a resin to form an admixture that changes viscosity and consistency during application . instead , the layer of bonding resin and initiator , or accelerator , may be formulated to have the desired critical viscosity in the range of 25 , 000 - 40 , 000 centipoises measured to 50 ° c . this viscosity is unchanging , therefore , the work time of the orthodontist is essentially limitless , since there is no substantial polymerization until the layer of bonding resin and catalyst on the tooth is emplaced contiguous the layer of bonding resin and initiator on the base of the bracket . in order to obtain the viscosity as defined hereinbefore it is preferred to add an inert filler , in the form of a particulate solid . preferably , the particles of solid have a predominant size of smaller than 35 microns with no sizes so large as to interfere with proper bonding between the appliance and the teeth . the filler is selected from the group consisting of alumina , barium fluoride , calcium fluoride , glass , asbestos , and silica . of these , the colloidal silica such as formed by fumed silica is preferable . thus the optimum viscosity of the bonding resin liquid can be formulated to allow being emplaced intermediate the two layers of catalyst on the appliance and the teeth surfaces that are to be bonded together . typically the first layer of the bonding resin and catalyst that is emplaced on the teeth will have a proportion of bonding resin in the range of from 90 percent to 98 percent , the remainder being catalyst . typically , the second layer of the bonding resin and the initiator has a concentration in the range of 0 . 5 - 3 . 0 percent by weight of initiator ; the optimum concentration of initiator being about 1 . 5 - 2 . 0 percent by weight based on weight of bonding resin and initiator . the concentration of the filler in the second layer of bonding resin and initiator may vary depending upon the type of filler and bonding resin being employed . with larger filler of , for example , - 325 mesh u . s . standard sieve , up to 80 percent by weight of filler may be employed . ordinarily , with colloidal size filler , the concentration of filler will be in the range of 4 - 10 percent by weight of the bonding resin . the optimum concentration of the filler would be in the range of 6 - 7 percent of the preferred filler in the preferred resin to obtain the optimum viscosity of about 25 , 000 - 40 , 000 centipoises measured at 50 ° c . the cure time is in the range of about 10 minutes to about 2 hours for the bonding strength to develop sufficient strength in the presence of the catalyst and initiator to take the stress attendant to affixing of the remainder of the dental appliance . ordinarily about 15 - 20 minutes are allowed before the orthodontist , or dentist , begins to affix the remainder of the dental appliance . in point of fact , the bracket base may be sufficiently adhered to a tooth in as little as 20 seconds to allow moving on to the next teeth . expressed otherwise , in as little as 20 seconds , the base would be bonded sufficiently to the tooth that the bracket holder can be released and another bracket emplaced contiguous , or adjacent , another tooth with the layers of bonding resin , catalyst and initiator therebetween . ordinarily , an orthodontic appliance may comprise a series of mounting brackets that are to be bonded directly to the surfaces of the teeth and the remainder of the appliances high strength wire , connecting the brackets in a manner so as to apply torque or forces to the teeth to effect the desired movement of the teeth . the bases of the brackets are bonded to the teeth by one of two methods preparatory to affixing the remainder of the dental appliance . the first is referred to as direct bonding . the second is referred to as indirect bonding and is employed to expedite affixing the dental appliance to the teeth . in direct bonding , the method of this invention is performed independently for each tooth involved . a multiplicity of steps is involved for each of the surfaces of the teeth to which a particular and respective bracket is to be bonded . for each tooth to be treated , the method comprises the steps of : a . cleaning the surface of the tooth to which the bracket is to be affixed ; b . acidizing the surface of the tooth to which the bracket is to be affixed to create an etched surface ; c . water washing the acid - etched surface of the tooth to insure it has been thoroughly cleaned ; e . applying the first layer of bonding resin and catalyst to the cleaned , etched , dried tooth surface ; f . applying to the cleaned , dried base of the bracket a second layer of catalyst and initiator ; g . positioning the bracket base adjacent the surface of the tooth with the intermediate layer of the bonding resin , catalyst and initiator so as to obtain polymerization of the bonding resin and the necessary bonding of the bracket to the tooth ; h . repeating the above described steps for each of the several teeth involved ; i . after a predetermined cure time , affixing the remainder of the dental appliance to the brackets . the method steps may be understood completely by referring to the accompanying fig1 - 3 in conjunction with the following descriptive matter . fig1 illustrates a dental appliance 11 applied to the teeth 13 by way of brackets 15 . each of the bases of the brackets are adhered to the surface of the respective teeth by durable bond 17 , fig2 . the bond 17 , fig3 is formed by polymerization reaction between the first layer 19 of bonding resin and catalyst on the surface of the tooth 13 and a second layer 21 of catalyst and initiator on the base 23 of the bracket 15 . at the interface , denoted by dashed line 24 , the polymerization reaction expands rapidly , as shown by the intermediate layer 25 . finally , through molecular diffusion of the bonding resin , catalyst and initiator in the combined layer , a final bond 17 is formed , presumably by the mechanism of free - radical polymerization . the component of low viscosity consisting of bonding resin and catalyst ( or initiator substituted for the catalyst ) is applied to both the cleaned , dried tooth surface and to the cleaned base of the bracket ; the second component of high viscosity bonding resin containing the initiator ( or catalyst substituted therefor ) and filler is applied onto the layer already present on the base of the bracket , then the bracket is immediately applied to the layer of the first component on the tooth . in carrying out the method of the invention , the dentist , the orthodontist , or the assistant first cleans the teeth with a suitable material such as a pumice type material in the form of a toothpaste or the like . such pumices and pastes are conventionally employed and need not be described in great detail herein . the pumice type paste is then washed from the teeth with water and the teeth dried by warm clean dry air . next an acid etch is applied to the teeth . ordinarily phosphoric acid having a concentration in the range of 30 - 50 percent by weight is dabbed onto the teeth with a cotton pellet or light brush . after about a minute and a half , the teeth are rinsed with water again and dried with warm clean dry air . next the cleaned metal brackets are arrayed on an absorbent towel . preferably , a bracket is selected to have a curvature of the base to match the curvature of the surface of the tooth to which it will be adhered . as indicated hereinbefore , the bases of the respective brackets will have been cleaned of all dirt and grease . the grease is particularly detrimental to the effecting of a durable bond by the resin , since it limits the bonding to the surfaces . a relatively thin layer of the bonding resin and catalyst is applied to the surface of the teeth to which the brackets are to be affixed , or bonded . as indicated hereinbefore , the bonding resin applied to the teeth has a lower viscosity in the range of 250 - 5 , 000 centipoises at room temperature . there is very little interaction between the catalyst and the bonding resin in the absence of an initiator , or accelerator . to promote polymerization as rapidly as possible but within the time frame permitted , the bonding resin and catalyst are also applied to the base of the bracket followed by a second layer of higher viscosity bonding resin , initiator and filler . the bonding resin having the proper amount of viscosity to prevent &# 34 ; creep &# 34 ; and the initiator are admixed together and are applied to the bases of the brackets so as to form a second layer of substantially uniform admixture thereon . preferably a desired amount of filler is included in the second layer to obtain the desired viscosity in the delineated range . the respective uniform admixtures of , respectively , the bonding resin and catalyst and , the bonding resin and initiator and filler ( if employed ) may be separate prepared admixtures specifically available commercially for bonding the bracket to the teeth . typical such prepared admixtures are readily available , as from advance dental corporation , fort worth , tex . specifically , the relatively low viscosity solution of the bonding resin and catalyst may be brushed onto the teeth and bracket , or splayed onto the teeth and bracket with a syringe or the like . the second , more viscous layer of the bonding resin and the initiator can be emplaced on the bases of the brackets with a spatula or dispensing device such as a syringe , tube or the like . thereafter , each bracket is positioned on its tooth in the exact location desired . one advantage of this invention is that it is unnecessary to hold the bracket firmly in place as required heretofore . the close contact effects molecular interdiffusion such that there is a mixture of the bonding resins , catalyst and initiator to provide rapid polymerization and finally bonding . for all practical purposes , because of the viscosity of the resin , the bracket will remain in place without creeping as soon as it has been firmly emplaced . this is one advantages of this invention -- that the orthodontist does not have to waste time holding a bracket until a conventional adhesive builds sufficient gel strength to hold the bracket in place . the next and subsequent brackets are then similarly treated and applied to the other teeth . during the emplacement of the brackets , a small amount of the bonding resin catalyst and initiator is ordinarily extruded from between the bracket base and the tooth surface around the edge of the bracket . this cement , or bonding resin , is preferably folded over and around the edge of the bracket for better mechanical locking in place . in accordance with this invention , it has been found that the simple expedient of employing only two solutions will effect a durable bond within about ten to twenty minutes sufficient to allow attaching the remainder of the dental appliance . the thin layer of resin occupies very little space between the bracket and the tooth ; and , because of the relatively small mass , there is rapid polymerization , producing strong bonds and consistent results ; in contrast to the prior art methods . the affixing of the remainder of the dental appliance is carried out by wiring with the high strength wires as has been done for many years and need not be described in great detail herein . similarly , adjustments are made as conventional . in the final step , when the orthodontic appliance is ready to be removed , the orthodontist may unwire the remainder of the appliance and employ snub - nosed gripper pliers to shear through the cement formed by the cured bonding resin . one of the advantages of this invention is that only about 5 percent of the bonding resin remains on the teeth ; whereas with a conventional mixture about 50 to 100 percent remains on the teeth . the total effect of this small residue is that much less time has to be spent polishing off the cement , or cured bonding resin , from the teeth with this invention . in the indirect bonding of the dental appliance to the teeth , a cast is made of the mouth of the patient and the brackets are temporarily affixed into the desired position onto the cast . a layer of soft plastic such as polyethylene is folded over the brackets and vacuum drawn into place so as to embed the brackets in the soft plastic . thereafter , the soft plastic containing the brackets is folded back and the embedded brackets are cleaned of the material used to temporarily affix the brackets to the cast teeth . a layer of bonding resin and catalyst is effected on the clean dry teeth , similarly as described hereinbefore . similarly as described hereinbefore , a layer of bonding resin and initiator is effected on the bases of brackets . the plastic with the brackets embedded therein is inserted into the patients mouth such that the bracket bases are suitably emplaced adjacent the surfaces of the teeth to which they will bond . the plastic with the brackets emplaced is left in the patients mouth for a suitable interval of time to bond the brackets to the teeth . this time will be a short time of from only a few minutes to as much as ten to twenty minutes . thereafter , the plastic is removed to leave the brackets in place on the teeth in the patients mouth . this technique is employed for speed in applying the brackets . after the cure time of ten to twenty minutes , the remainder of the dental appliance can be affixed . adjustments and finally removal are carried out as described hereinbefore . the following examples are given to illustrate in a very specific way this invention . in this example the orthodontist first cleaned the teeth with a pumice type toothpaste and water , and wiped clean only with cotton pellet . thereafter , the orthodontist etched the teeth with a 37 . 5 % solution of phosphoric acid . this solution was debbed carefully onto the teeth with cotton pellets . this effected a clean acid etch . after allowing about one and a half minutes , the acid was thoroughly rinsed from the teeth and the teeth were again dried with dry air . a first layer was formed on the teeth by brushing thereonto a substantial uniform admixture of monomer resin and catalyst . another layer of the same material was brushed onto the base of the bracket . the monomer resin was methacrylate - capped epoxy resin containing styrene and having a viscosity of about 500 centipoises at 77 ° f . the catalyst was benzoyl peroxide . the bracket bases had applied to them a second layer of bonding resin and the initiator . the bonding resin contained 1 . 2 % by weight initiator and 6 . 7 % by weight a filler . the initiator was n , n - dimethyl - p - toluidine . the filler was fumed colloidal silica , cabosil from cobot corp ., billerica , mass . the resin employed was a methacrylate - capped epoxy resin containing styrene amounting to about 45 % of the mixute . the admixture had the desired viscosity of about 32 , 000 centipoises measured at 50 ° c . the admixture was applied by spatula to the base of each metal bracket . each metal bracket was firmly affixed to each tooth by means of tweezers , applying a firm force against each bracket in the exact position desired . after placement of the bracket on the tooth , the resin held the bracket in the position without allowing the bracket to creep . the excess bonding resin that was exuded from between the base of the bracket and the tooth was folded around the edge of the bracket with a small spatula . sufficient curing time was allowed ; for example about 20 minutes ; and the remainder of the appliance was affixed into place against each of the brackets to apply the desired force to affect the movement of the teeth in the desired way . the orthodontist was thereafter able to make adjustments on the appliances that were applied to pull the teeth into the position desired . the teeth may be pushed or pulled with this method by using an external appliance . when ready to be removed , the orthodontist employed snub - nosed gripper pliers and sheared through the cement formed by the cured resin . only about 5 % of the total cement remained in place on the teeth . this cement was polished from the teeth and no ill effects were observed . the same procedure and steps were carried out in this example as were carried out in example i except that the methacrylate capped epoxy resin contained diluent monomers other than styrene . one reactive diluent monomer was substituted for styrene in a series of resins with different reactive diluent monomers . for example reactive diluents used in the series were methyl methacrylate , hydroxy methyl methacrylate , ethylene glycol dimethylacrylate , diethylene glycol dimethacrylate , triethylene glycol dimethylacrylate , various polyethylene glycol methacrylates individually , trimethylol propane - trimethacrylate , 1 , 4 - butane glycol dimethacrylate , 1 , 3 - butane glycol dimethacrylate , n - propyl methacrylate , n - butyl methacrylate , penta - erythritol tetramethacrylate , and a few other methacrylate monomers . each of these resins was found to provide a satisfactory bonding job . while the method of this invention has been described hereinbefore directed primarily to the practice of orthodontia , it should be remembered that it may be employed for adhering directly to the teeth other dental appliances or the like . specifically , such things as metal crowns , protective sheaths , space maintainers , bridges , peridontal splints , and other such dental appliances of a similar nature may be adhered directly to the teeth through the use of the respective layers of bonding resin and initiator on the respective tooth and dental appliance . having thus described the invention , it will be understood that such description has been given by way of illustration and example and not by way of limitation , reference for the latter purpose being had to the appended claims .
a method for affixing a dental appliance to teeth characterized by effecting a layer of bonding resin and catalyst on the teeth , effecting a layer of a substantially uniform admixture of only two reactants of a three - reactant system , the two reactants including the bonding resin and one of the other reactants , on the teeth ; effecting a second layer of a substantially uniform admixture of a second two reactants of said three reactant system , said second two reactants including the bonding resin and the other of the reactants , on the dental appliance to be affixed to the teeth ; positioning the portion of the dental appliance adjacent the teeth with the bonding resin , catalyst , and initiator in situ to effect polymerization and bonding on the surface of each of the teeth . after a predetermined cure time , the remainder of the dental appliance is affixed . also disclosed are the preferred bonding resins , catalysts and initiators , as well as the preferred viscosity and fillers for obtaining the desired viscosity ; and an indirect bonding method .