Bonding orthodontic fond regards to composite Restorations with a composite-based orthodontic adhesive is merely known to hold been reported a few times antecedently ( Kao et al. , 1995 ; Chunhachteevachaloke and Tyas, 1997 ; Lai et al. , 1999 ) . None of these surveies investigated the effects of acerb etching or air scratch on the shear bond strength. Previous literature from the field of composite fix indicated that acerb etching of the composite surface did non significantly increase the bond strength ( Boyer et al. , 1978 ) , proposing possible riddance of this clinical process. In its topographic point, mechanical surface intervention, such as air-abrasion, appears to be more effectual in increasing composite to composite bond strengths ( Swift et al. , 1992 ; Turner and Meiers, 1993 ; Kupiec and Barkrneier, 1996 ; Bouschlicher et al. , 1997 ; Brosh et aluminum, 1997 ) .
A new cyanoacrylate adhesive ( smartbondB, Gestenco International, Goteborg, Sweden ) has been developed for orthodontic bonding. The maker claims the merchandise provides sufncient bond strength to composite renewing stuffs. A old cyanoacrylate adhesive was tested by Howells and Jones ( 1989 ) . They found the stuff to hold acceptable managing qualities ( easy mixed, satisfactory viscousness, adequate working clip ) , and comparable initial bond strength to a composite adhesive ( 124N vs. 132N ) . However, after storage in normal saline for 7 or 98 yearss, the hydrolysis of the polymerized stuff weakened the bond ( to 6N ) , rendering it unsuitable for clinical usage. At present, no unequivocal protocol is known for adhering orthodontic fond regards to restorative composite rosin.
Purpose OF THE STUDY
1. To find the consequence of six different adhesive/surface intervention combinations on the shead/peel bond strength of orthodontic fond regards to restorative rosin after 24 hours and after thennocycling.
2. To find the consequence of thermocycling on the shead/peel bond strength of orthodontic fond regards to restorative rosin of the six experimental groups.
3. To measure the form of failure after debonding of orthodontic fond regards to restorative rosin.
The void hypothesis provinces that there are no statistically important differences in the shead/peel bond strength between the six adhesive/surface intervention groups. The void hypothesis besides states that thermocycling has no consequence on the shead/peel bond strengths.
Concept OF ADHESION AND BONDING
Mechanical bonding or mechanical keeping are the simplest methods of accomplishing a strong fond regard between two substances. The first efforts at keeping in dental medicine involved the arrangement of undercuts in stuffs to ease the “ lockup in ” of later placed stuffs.
The ultimate end in dental bonding is to accomplish true adhesion. When two substances are brought into confidant contact with each other, the molecules of one substance may be attracted to molecules of the other. Such an attractive force is known as adhesion when different molecules are involved and coherence when like molecules are attracted. In dental medicine, bonding is achieved by the application of a liquid stuff ( the adhesive ) to advance adhesion to a solid substrate ( the disciple ) . For adhesion to happen, the adhesive and adherent surfaces must be attracted to one another at their interface. The surface of a stuff has greater energy than its interior. At the surface, the outermost atoms are non every bit attracted in ail waies by other atoms. While within the stuff, atoms held in the solid lattice are every bit attracted to each other. The addition in energy per unit country of surface is known as the surface energy or surface tenseness of a stuff.
The greater the surface energy, the greater the potency for adhesion ( Anusavice, 1996 ) .
In add-on to a high surface energy, the adhesive must be able to adequately wet the surface of the disciple. Wetting is the manifestation of the attractive forces between molecules of adhesive and adherent and may be defined as the procedure of obtaining molecular closeness or set uping interfacial contact The extent to which an adhesive is attracted to the surface of an adherent centimeter be determined by mensurating the contact angle. The contact angle is the angle between the adhesive and the disciple at their interface. The smaller the contact angle, the more effectual the adhesive is able to wet the surface of the disciple ( Anusavice, 1996 ) .
Historical Background of Composite Resin
Man-made rosins have evolved as renewing stuffs chiefly because of their esthetic features. The most widely used esthetic stuffs in dental medicine today are composite rosins ( Gleich, 1999 ) . The term composite means that it is a mechanical mixture of at least two different categories of stuffs that have limited common solubility. The combination of stuffs provides a merchandise with belongingss superior or intermediate to those of the single components ( Anusavice, 1996 ) . Dental complexs are composed of man-made polymers, inorganic fillers, molecules which promote the polymerisation reaction, silane matching agents to bond the inorganic filler atoms to the polymer matrix, pigments, and little sums of other additives to better colour stableness ( UV absorbers ) and prevent premature polymerisation ( eg. hydroquinone ) ( Bayne et al. , 1994 ; Ferracane, 1995 ; Anusavice, 1996 ) .
Development of dental complexs began in the late 1950 ‘s and early 1960 ‘s when Dr. R.L. Bowen began experiments on reenforcing epoxy rosins with filler atoms ( Bowen, 1963 ) . For the past 40 old ages, 80-90 % of complexs utilized the Bis-GMA ( 2.2-bis [ 4 – ( 2-hydroxy-3-methacryloyloxy-propoxy ) phenyl ] propane ) monomer developed by Dr. Bowen as the matrix-forming rosin ( Ruyer and Oys?d, 1987 ) . Bis-GMA is highly syrupy at room temperature because of the H adhering interactions that occur between the hydroxyl groups on the monomer molecules ( Ferracane, 1995 ) . Dilutants of a more unstable rosin such as TEGDMA ( triethylene ethanediol dimethacrylate ) , which is besides a crosslinking agent, are added to bring forth pastes of clinically useable consistences ( Ferracane, 1995 ) . Stannard ( 1993 ) reported that optimum belongingss are produced with a, 1: 1 ratio of Bis-GMA and TEGDMA.
Inorganic filler atoms are used to better the strength ( Farracane et al. , 1987 ; Eversoll and Moore, 1988 ) , addition stiffness ( Braem et al, 1989 ) , change the coefficient of thermic enlargement ( Soderholm, 1984 ; Brown, 1988 ) , cut down polymerisation shrinking ( Iga et al. , 1991 ) , and increase the radio-opacity ( van Dijken et al. , 1989 ) of composite rosins. Filler atoms are most normally produced by crunching or milling silicate atoms incorporating oxides of Ba, Sr, Zn, aluminium, or Zr ( Khan et al. , 1992 ) . Composite rosins have been classified harmonizing to their filler particulate size and per centum ( Anusavice, 1996 ) . Microfilled stuffs have filler sizes of 0.04um and filler burden of 35-60 wt % . Small particle-filled complexs have big filler sizes of 1 to 5pm and increased burden of fillers up to 80-90 wt % . Loanblends are a 3rd categorization which combines -04 and 1 autopsy atoms in weight per centums in the 75-80 wt % scope ( Anusavice, 1996 ) . Clinical Research Associates recommends intercrossed rosin usage in Class 5 Restorations where there is a high esthetic demand ( C.R.A. , 1999 ) . Their recommendation was based on an ordinal rating of 12 clinical features such as colour lucifer and surface smoothness. These are the surfaces to which orthodontic bonding will be by and large required. Therefore, it is likely that the type of composite encountered will be of the intercrossed categorization. To accomplish the optimum belongingss of the composite, matching agents are used to chemically bond the filler particles to the rosin matrix. Matching agents displace adsorbed H2O and supply a strong chemical bond between the oxide groups on the glass filler surface and the polymer molecules of the rosin ( van Noort, 1994 ) . Silane matching agents have the general expression:
where R represents an organofunctional group and the Ten groups are hydrolysable groups bonded to the silane. The Ten units are hydrolysed and a tri-hydroxy-silanol is produced.
R-Si-X3 + 3H2O — – & gt ; R-Si ( OH ) 3 + 3HX
These silanols form H bonds with other hydroxyl groups on the glass surface. Water is removed upon drying in a condensation reaction to organize a covalent bond between the yoke agent and the glass. Finally, the organofiinctional group, R, reacts with the polymer to associate the two stuffs ( van Noort, 1994 ) . The most common yoke agents are organosilanes such as 3 -methacryloxypropyl-trimethoxy-silane ( MPS ) ( Ferracane, 1995 ) .
The rosins themselves polymerize by an add-on mechanism initiated by free groups ( Anusavice, 1996 ) . No by-products are formed in add-on polyrnerization reactions ; the construction of the monomer is merely repeated legion times. An external stimulation is used to trip the add-on reaction ( Anusavice, 1996 ) . In self-cured rosins the initiation system is chemically activated by blending two separate pastes. Typically, one paste contains benzoyl peroxide ( the instigator ) and the other paste contains an aminoalkane, dihydroxyethyl-p-toluidine ( DHEPT ) which works as an activator ( Anusavice, 1996 ) . The most popular complex rosins are now light-activated ( C.R.A. , 1999 ) . The instigator in these merchandises is camphoroquinone ( CQ ) which generates free groups when exposed to blue visible radiation in the 470nm scope of the electromagnetic spectrum ( Ferracane, 1995 ) . These merchandises are popular because they are one-part systems, and working clip is slightly controlled by the operator.
Aging and Water Sorption
Composite rosins are non inert stuffs. They have been shown to be soluble in H2O and in organic dissolvers such as ethyl alcohol ( Craig and Payton, 1975 ; Pearson, 1979 ; Ferracane and Condon, 1990 ; Soderholm, 1990 ; Ferracane, 1994 ) . The leaching of constituents has a possible impact on both the structural stableness and biocompatibility of the stuff ( Ferracane, 1994 ) . Of class, the former is of concern to this survey, as the structural stableness of the complex may be a factor in the shear bond strength of orthodontic fond regards.
It has been estimated by infrared spectrometry that merely 50-75 % of the rosin monomer dual bonds are really polymerized after light bring arounding ( Eliades et al. , 1987 ; Ferracane, 1990, 1994 ; Ferracane and Condon, 1992 ) . As mentioned antecedently, the Bis-GMA and TEGDMA monomers polymerize by a free extremist add-on reaction affecting significant cross-linking. The cross-linking reaction produces a gel construction which badly reduces molecular mobility and greatly slows the rate of polymerisation ( Ferracane, 1994 ) . Most of the unreacted carbon-carbon dual bonds are on molecules which have reacted at one terminal and are therefore bound to the polymer concatenation and are non free to elute ( Ferracane, 1994 ) . However, the polymer mom & A ; does incorporate a part of wholly free monomer molecules. Surveies have verified that virtually all of the constituents in complexs may be leached into solution- Bis-GMA and TEGDMA have been identified in solution by many different beginnings ( Inoue and Hayashi, 1982 ; Thompson et al. , 1982 ; Ferracane and Condon, 1990 ; Rathbum et al- , 1991 ; Tanaka et al. , 1991 ) .
Approximately 5-10 % of the unbound monomer elutes into an aqueous solution. This equals approximately 2 % of the weight of the rosin constituent for most complexs ( Ferracane, 1994 ) . Filler atoms are besides known to leach ions such as Si, Ba, Sr and Na when stored in H2O ( Soderholm, 1983, 1990 ; Soderholm et al. , 1984 ; 0ys?d and Ruyter, 1986 ) .
Fluoride has besides been shown to be released from composite rosins ( Teminnd Csuriz, 1988 ; Swift, 1989 ; Wiltshire and new wave Rensburg, 1995 ) . The efficaciousness of such fluoride release as an anticariogenic agent is still under probe ( Swift, 1989 ) .
The loss of constituents and subsequent H2O sorption is rapid during the initial soakage period and slows well within hours. Approximately 75 % of the elutable species are extracted within the first several hours ( Pham and Ferracane, 1989 ; Ferracane and Condon, 1990 ; Wiltshire and new wave Rensburg, 1995 ) .
Water consumption has been reported to be 2-3 % of the weight of the composite ( Fan et al. , 1985 ; Ferracane and Condon, 1990 ) . Such H2O sorption may impact the, mechanical belongingss of the complex and has been explained by filler-matrix debonding and hydrolytic debasement of the fillers ( Soderholm et al. , 1984 ) . Soderholm et Al. ( 1984 ) hypothesized that the dislocation of the filler articles raised internal osmotic force per unit area within the composite construction and microcracks formed dong the matrix-filler interfaces. These clefts propagated until they reached the surface of the composite, as evidenced in S.E.M. surveies ( Solderholm, 1984 ) .
Composite To Composite Bonding
The bulk of the literature on rosin to resin adhering trades with the fix of antecedently placed composite rosin Restorations. The interfacial bond strength of composite to fresh ( i.e. , merely a few proceedingss old ) complex has been reported to be the same as the cohesive strength of the stuff ( Lloyd et al. , 1 980 ; Boyer et al. , 1984 ) . Boyer et Al. ( 1984 ) reported cross bond strength of between 53.2 and 109.4 MPa, depending on the type of composite rosin. However, the bond strength to smooth, untreated composite surfaces is in the scope of 20 % to 75 % of the cohesive strength of the several substrate ( Lloyd et al. , 1980 ; Vankerckhoven et al. , 1982 ; Chan and Boyer, 1983 ; Boyer et al. , 1984 ; Azarbal et al. , 1986 ; Pounder et al. , 1987 ; Kao et al. , 1988b ; Puckett et al. , 1991 ) . Absolute values for the cohesive and adhesive shear bond strengths reported in the above mentioned surveies ranged from every bit low as 5.74 MPa to every bit high as 11 1.6 MPa depending on legion factors such as substrate, surface interventions, adhesives, storage conditions, and bond strength proving methods.
There are three possible mechanisms of a ‘new ” composite rosin adhering to an “ old ” composite rosin. Chemical bonds may organize with the rosin matrix ( Brosh et al. , 1997 ) , chemical bonds may organize with the exposed filler atoms ( Brosh et al. , 1997 ) , and micromechanical keeping may be gained by incursion of rosin monomer into undercuts on the Restoration surface and possibly even into microcracks in the matrix ( Brosh et al. , 1997 ) . This micromechanical bonding may be farther enhanced by dissolver bonding. Solvent adhering occurs as the methylmethacrylate monomer diffuses into the “ old ” rosin, ensuing in swelling of the set rosin, and leting incursion of the “ new ” rosin ( Powers et al. , 1997 ) . Upon polymerisation, the “ new ” rosin is automatically locked onto the surface of the “ old ” rosin.
Chemical bonding between rosin matrices is dependent upon the concentration and handiness of unreacted methacrylate groups in the substrate rosin ( Vankerckhoven et al. , 1982 ; Puckett et al. , 1991 ; Tumer and Meiers, 1993 ; Li, 1997 ) . The concentration of such unreacted methacrylate groups decreases from 100 % to about 50 % as the rosin polymerizes, so the potency for chemical bonding diminishes as the rosin ages ( Vankerckhoven et al. , 1982 ; Swifi et al. , 1992 ) . Besides, when the Restoration surface is polished, inorganic filler atoms are exposed and the grade of unsaturated methacrylate groups is, decreased to 25 % . This limits the chemical bonding between rosin matrices ( Vankerckhoven et al. , 1982 ) .
Chemical bonding to the filler atoms would necessitate the usage of a silane matching agent, much like the organosilane incorporated into single composite stuffs as discussed in subdivision 2.2.1. Silane matching agents have been shown to better the bond of composite to etched, sandblasted and roughened porcelain by up to 3 MPa ( Stangel et al. , 1987 ; Andreasen and Stieg, 1988 ; Kao et al. , 1988a ; Major et al. , 1995 ; Roulet et al. , 1995 ) . However, silanes have failed to predictably increase the bond strength of new and old complexs compared with dentine/enamel adhering agents ( Azarbal et al. , 1986 ; Saunders, 1990 ; Soderholm and Roberts, 1991 ; Swift et al. , 1994 ; Bouschlicher et al. , 1997 ; Brosh et al. , 1997 ) . This may propose that mechanical engagement is the most important factor lending to mend strength, and therefore, silanes are non recommended for clinical application of composite to composite bonding ( Soderholm and Roberts, 199 1 ; Swift et al. , 1994 ; Bouschlicher et al. , 1997 ; Brosh et al. , 1997 ) .
Numerous surface interventions and adhering agents have been advocated to better the fix strength of complexs. Most interventions attempt to increase the micromechanical bonding between the substrates ( Brosh et al. , 1997 ) . Weting of the Restoration surface by the fix stuff is a major factor commanding the fix bond strength as discussed in subdivision 2.1. Unfilled rosins better the bonding of fresh stuff to smooth composite surfaces by up to 6 to 25 MPa after 24 hours ( Boyer et al. , 1984 ; Azarbal et al. , 1986 ; Puckett et al. , 1991 ; Swift et al. , 1992 ) .
Composite Resin Surface Treatments
Many different surface intervention protocols have been recommended. Possibly the most of import process in composite to composite bonding is the roughening of the mature rosin surface ( Swift et al. , 1992 ; Turner and Meiers, 1993 ; Kupiec and Barkmeier, 1996 ) . Turner and Meiers ( 2993 ) compared the shear bond strengths achieved with assorted surface interventions and with different adhesives. In a bipartisan ANOVA, they found the surface intervention to be extremely important ( p & lt ; 0.0001 ) and the adhesive to be less important ( p=0.643 ) . Etching with 37 % phosphorous acid, while critical in adhering to enamel ( Abdullah and Rock, 1993 ; Johnston et al. , 1996 ; Olsen et al. , 1996 ; Powers et al. , 1997 ) , appears to be comparatively uneffective in composite bonding ( Boyer et al. , 1978 ) . Boyer et Al. ( 1997 ) reported no important difference in tensile bond strength between rosin beds with the usage of 37 % phosphorous acid. Hydrofluoric acid ( HF ) is used to etch porcelain surfaces for indirect Restorations, inraoral fix, or orthodontic bonding ( Zachrkson and BuyukyiImaz, 1993 ; Kem and Thompson, 1994 ; Major
et al. , 1995 ) . HF can etch the glass filler atoms in intercrossed and little atom, complexs. HF has been shown to do some little surface alterations such as minor roughening ( Kula et al. , 1983 ; Kula et al. , 1986 ) ; nevertheless, research does non uncover important additions of bond strength with the usage of HF for composite fix ( Cnimpler et al. , 1989 ; Swift et al. , 1992 ; Swift et al. , 1994 ; Brosh et al- , 1997 ) . Mitchem et Al. ( 1991 ) even recommended against the usage of HF with intercrossed complexs as etching softens the rosin surface. This alteration is likely as a consequence of the remotion of the difficult filler atoms, as it has been shown that there is no alteration in hardness in unfilled rosins after exposure to 15 % HF for 6 months ( Al-Jezairy and Williams, 1996 ) .
Mechanical intervention of the composite surface may be accomplished with rotary instruments such as diamond or green carborundum rocks or through the usage of air scratch with aluminium oxide atoms. Brosh et Al. ( 1997 ) descnbed the surface intervention of complexs with diamonds or green rocks as supplying “ macro ” retentive characteristics which are controlled by the operator. Air scratch resulted in “ micro ” recollective characteristics that are under the control of the instrument. In the same survey ( Brosh et al. , 1997 ) the writers concluded that the “ micro ” recollective characteristics demonstrated superior shear bond strengths over the ”macro ” recollective characteristics in combination with a bonding agent. Smdblasting increased the shear bond strength by 4.19 MPa and roughening with a diamond rock increased the bond strength by 0.64 MPa ( Brosh et aL, 1997 ) . Microetching with air scratch is less invasive of the composite Restoration than roughening with handpieces ( Brosh et al. , 1997 ) . Besides, it is a comparatively simple and speedy process, and does non affect the usage of strong acids intraorally. Recent surveies have reported air scratch as an effectual agencies for surface readying of aged complexs ( Swift et al. , 1992 ; Turner and Meiers, 1993 ; Kupiec and Barkmeier, 1996 ; Bouschlicher et al. , 1997 ) .
Arguably, the most important accomplishment in dental medicine in the twentieth century was the acerb etch technique developed by Buonocore ( 1955 ) . Using assorted acidic mixtures, of which 30 % to 40 % phosphorous acid seems to be the most effectual ( Moin and Dogon, 1974 ; Retief, 1974 ; Legler et al. , 1990 ; Wang et al. , 1994 ; Olsen et al- , 1996 ) , enamel surfaces are “ engraved, ” a procedure in which the acid preferentially dissolves the centres or fringes of the enamel rods. The etching clip has besides been debated and studied legion times. Britton et Al. ( 1990 ) compared bond strengths between 15- 2nd and 60-second etch times. Their consequences indicated increased bond strengths in the 15-second group. Gorelick ( 1977 ) evaluated the effects of 60- and 90-second etching times, Barbier et Al. ( 1985 ) compared 15- and 60-seconds of etching, and Beech and Jalaly ( 1980 ) evaluated 5- , 15, 60- , and 120-second intervals. They all reported no lessening in bond strength as the consequence of shortened etching times. The most recent reappraisals on the topic of etching clip ( Olsen et al. , 1996 ) besides concluded there was no important consequence on bond strength between 10- or 30-second etching intervals. Etched enamel allows a bonding agent of low viscousness to perforate into the microscopic undercuts as evidenced by “ rosin tickets ” when seen under S.E.M. ( Pahlavan et al. , 1976 ) . Once polymerized, a micromechanical bond is established.
The acerb etch technique provided the background for direct orthodontic bonding. Direct bonding eliminates the demand for sets. This has several advantages such as enhanced ability for plaque remotion by the patient ( Zachrisson, 1976 ) minimising soft tissue annoyance and hyperplastic gum ( Zachrisson, 1976 ) minimising the danger of decalcification with loose sets ( Zachrisson, 1976 ) riddance of the demand for separation, absence of post-treatment set infinites, and improved esthetics during intervention. There is some contention over who should acquire recognition for the fist direct orthodontic bonding. Most mentions, and the American Association of Orthodontists, seem to back up the claim of George Newman ( Newman, 1992 ) . He reported a bonding technique utilizing acrylic rosins in 1965 ( Newman, 1965 ) . The early rosins had a 15-minute scene clip, which limited their credence in clinical pattern ( Retief and Sadowsky, 1975 ) .
Orthodontic Adhesive materials
Presently, there are legion stuffs available for direct orthodontic bonding. These include diacrylate composite resin-based merchandises and glass-ionomer adhesives, which are available in either chemical or dual-cured systems ( Powers, 1997 ) , and cyanoacrylate systems ( Ortendahl and Ortengren, 2000 ) . The composite rosin adhesives are largely based on the Bis-GMA rosin ( Bowen, 1963 ) modified to suited viscousness for clinical usage. The new chemically-cured rosins have a reduced scene clip of three to eight proceedingss ( Wang and Meng, 1992 ; Mitchell, 1994 ; Lloyd and Scrimgeour, 1995 ) . In vitro bond strengths do non look to be affected by whether the composite is chemically-cured, light-cured, or dual-cured ( Bradburn and Pender, 1992 ; Wang and Meng, 1992 ; Smith and Shivapuja, 1993 ; Whitlock et al. , 1994 ; Eliades et al. , 1995 ; Kao et al. , 1995 ; Chamda and Stein, 1996 ) .
Glass ionomer stuffs are besides now available as either chemically or light-cured systems for orthodontic bonding ( Powers et al. , 1997 ) . They have non replaced composite rosins, as they have lower in vitro bond strengths to either etched or non-etched enamel ( Rezk-Lega and Ogaard, 1991 ; Oen et al. , 199 1 ; Wiltshire, 1994 ; Powers et al. , 1997 ) . For illustration, Wiltshire ( 1994 ) recorded average shear bond strength of an orthodontic fond regard bonded to etched enamel with a chemically-cured glass ionomer cement to be 5.5 MPa, and the comparative bond strength with a composite cement was 26 MPa. A new group of resin-modified glass-ionomer ( RMGI ) cements do supply for increased bond strengths over conventional GI cements ( Enckson and Glasspoole, 1994 ) . Erickson and Glasspoole ( 1994 ) reported shear bond strength of 20.5 MPa for a RMGI compared to 7.2 MPa for a conventional GI. Powers et Al. ( 1997 ) besides reported tensile bond strengths of 8 MPa to 25 MPa for five different RMGI ‘s to unetched enamel. However, a recent publication reported low initial bond strength ( after 30 proceedingss ) for an orthodontic RMGI cement of 0.4 MPa vs. 5.2 MPa for rosin cement ( Bishara et al. , 1999 ) . Recently, a cyanoacrylate adhesive system- has been developed for direct, orthodontic bonding. The maker, Gestenco Int. , claims equal adhering to many surfaces including enamel, porcelain, and composite ( Gestenco Int. , 1999 ) . Previous cyanoacrylate adhesives have failed to derive credence in the orthodontic community because of their hapless lastingness in a wet environment. Crabb and Wilson ( 1971 ) studied three cyanoacrylate adhesives ( Cyanodont, Eastman 9 10, and Permabond ) . After storage in 37 ” C saline for 24 hours, al1 of the bond strengths were reduced to near nothing. More late, Howells and Jones ( 1989 ) reported on another cyanoacrylate adhesive developed entirely for orthodontic bonding. Again in their survey, the stuff proved to be excessively susceptible to impairment after storage in H2O. Bond strengths went from a mean of 124 N after one hr to 26 N after seven yearss and decreased to merely 6 N after 98 yearss.
Orthodontic Bonding to Various Materials
The primary surface to which orthodontic brackets are straight bonded is enamel. The acid-etch process allowed for direct orthodontic bonding to be possible, and is discussed in subdivision 2.3.1. Application of 30 % to 40 % phosphorous acid for at least 10 seconds seems to be the most effectual in fixing enamel surfaces. Shear bond strengths of metal brackets bonded to etched, dry enamel with composite rosin adhesives may achieve values near 26 MPa ( Wiltshire, 1994 ) . Although glass ionomer cements can be bonded in a wet environment, the bond strengths are merely 5-8 MPa ( Chung et al. , 1999 ) . Even when bonded prohibitionist, glass ionomers still produce lower bond strengths than composite rosins ( 3-10 MPa vs. 26 MPa ) ( Rezk-Lega and Ogaard, 1991 ; Oen et al. , 199 1 ; Wiltshire, 1994 ; Powers et al. , 1997, Chung et al. , 1999 ) . The new RMGI cements are assuring as they had similar shear bond strengths compared to a composite cement in a recent article ( 8.8 MPa vs. 10.4 MPa ) ( Bishara et al. , 1999 ) .
Bonding orthodontic fond regards straight to porcelain or ceramic Restorations has besides been extensively studied. Major et Al. ( 1995 ) compared adhesion boosters and recommended the usage of a silanating agent. Use of a silane produced bond strengths of 6-14 MPa, whereas bond strengths without the primer ranged from 0.4 to 4 MPa ( Whitlock et al. , 1994 ; Major et al. , 1995 ; Zachrisson et al. , 1996 ) . Porcelain prepared with acidulated phosphate fluoride solutions produced low bond strengths of less than 5 MPa ( Barbosa et al. , 1995 ; Zachrisson et al. , 1996 ) . Roughening of the porcelain surface seems to be by and large contraindicated, as bond strengths become inordinate and porcelain breaks occur upon debonding. Cochran et Al. ( 1997 ) reported bond strengths of 28-39 MPa with sandblasting and silanization, and Barbosa et Al. ( 1995 ) obtained bond strengths of 28-47 MPa with diamond bur surface readying and silanization.
Buyukyilmaz et Al. ( 1995 ) compared sandblasting the gold surface to roughening with a diamond bur and found that sandblasting produced better bond strengths ( 20 MPa ) than the diamond bur intervention ( 10 MPa ) . Superbond C & A ; BTM ( Sun Medical, Kyoto, Japan ) , a 4-META metal-bonding adhesive rosin besides produced superior bond strengths compared to a conventional composite rosin ( BuyiiSilmaz et al. , 1995 ; Nollie et al. , 1997 ) .
Bond strengths of both conventional and 4-META adhesives to amalgam are by and large low ( 3-6 MPa ) ( Zachrisson et al. , 1995 ) . Sperber et Al. ( 1999 ) late sandblasted an amalgam surface and produced shear bond strengths similar to adhering to etched enamel with a rosin cement ( 1 1.77 MPa vs. 10.76 MPa ) .
Bonding of orthodontic brackets to composite rosin surfaces is merely known to hold been reported a few times. Newman et Al. ( 1984 ) studied orthodontic bonding to a heat-cured composite rosin ( Isosit TM, Vivadent Corp. , Buffalo, N.Y. ) . They compared the shear bond strengths between brackets bonded with Concise TM, ( 3M, St. Paul, MN ) with or without silane application to brackets bonded to etched, natural dentition. No important differences existed between the three groups, and their bond strengths were 1120-1300 lbs/in2 ( 7.7 – 8.9 MPa ) .
Schwartz et Al. ( 1990 ) studied the tensile bond strengths of metal brackets to resin substrates utilizing three composite rosin adhesives. They bonded to either untreated surfaces or surfaces treated with 37 % phosphorous acid, reduced with a diamond bur, coated with silane agent, or coated with a dentine bonding agent. Though most of their consequences were non reported, they did describe bond strengths of 4.3 +/- 2.0 MPa utilizing Contacto on untreated rosin surfaces. It was besides reported that the usage of Mono-Lok 2 and Unite produced tensile bond strengths of 10.5 +/- 3.2 MPa and 10.3 +/- 2.6 MPa. Kao et Al. ( 1995 ) compared the torsional bond strength of ceramic brackets bonded to composite rosin veneer laminates and enamel. Silux Plus TM ( 3M, St. Paul, MN ) veneers were fabricated and ceramic brackets were bonded with either a light-cured or chemically-cured composite adhesive. All samples were acid-etched before adhering and later thermocycled. Torsional bond strengths of between 30 MPa and 60 MPa were recorded for both the chemically- and light-cured adhesives.
Chunhacheevachaloke and Tyas ( 1997 ) besides studied adhering to resin composite. Again, they compared two types of ceramic brackets and the consequence of roughening R the composite surface with a harsh Soflex TM disc ( 3M, St. Paul, MN ) . All samples were acid-etched and bonded with Transbond TM ( 3MNnntek, Monrovia, CA ) . No important differences were found with their shear bond strengths which ranged from 17.1 MPa to 19.2 MPa. Nineteen of the 40 composite samples had cohesive failures upon debonding. The most recent and thorough survey of orthodontic bonding to composite rosin was reported by Lai et Al. ( 1999 ) . They bonded metal, ceramic and polycarbonate brackets to Silux Plus TM ( 3M, St. Paul, MN ) samples ( roughened with Soflex TM phonograph record ) utilizing either a light-cured rosin modified glass ionomer cement, a chemical-cured complex, or a light-cured composite system. One-half of the samples were tested after 24 hours and half were thermocycled. They concluded all groups to hold clinically acceptable bond strengths ( 10.0 to 30.1 MPa ) except the polycarbonate/chemically-cured group ( 3.58 MPa ) . 210 of 288 samples had damaged rosin surfaces after debonding.
Chemical bond Strength in Orthodontics
The bond strength of orthodontic fond regards must be able to defy both functional emphasiss ( from occlusion and chew ) and operator emphasiss ( from the orthodontic contraptions ) ( Powers et al. , 1997 ) . Newman et Al. ( 1994 ) stated that “ maximal strength is needed to counterbalance for the unfavourable, damp environment in which the polymer adhesive system operates, every bit good as fluctuations in pH, thermic alterations, impact forces from gluey, chewy, or difficult nutrients, and athleticss accidents. ” However, the direct bonding of orthodontic fond regards is a impermanent process ; after intervention, the fond regards must be removed with minimum or no harm to the substrate and this is best achieved with low bond strength ( Powers et al. , 1997 ) . Although it has been attempted, it is hard to measure orthodontic bond strengths in vivo ( Voss et al. , 1993 ) . Laboratory proving allows for improved standardisation of proving processs and the usage of more sensitive equipment.
Different types of bond strengths are reported in the literature including shear, shead/peel, tensile, and torsion ( Ostertag et al. , 1991 ; Powers et al. , 1997 ) . In shear bond strength testing, the debonding force is applied straight and parallel to the junction of the bracket and adhesive ( Fox et al. , 1994 ) . True shear bond strength is impossible to find practically. Using a 3D finite component analysis, Thomas et Al. ( 1999 ) found the tensile and compressive emphasiss exceeded the shear constituent. The term shear/peel is used in the literature to reflect this phenomenon ( Katona, 1994 ) . Most surveies describing shear bond strength are really proving the shead/peel bond strength ( Katona, 1997 ) . In tensile strength testing, the debonding force is applied sheer to the substrate surface. Up P to 15 % of the emphasiss are in fact shear and compressive in nature, once more directing the consequences to a tensile/peel force ( Thomas et al. , 1999 ) . A concluding method of bond strength testing is torsion lading, in which the fond regard is “ distorted ” away. This method is less favoured because most mechanical proving machines can non execute it ( Katona, 1997 ) . Besides, the consequences of a tortuosity trial are reported in N/m and can non be straight compared to trials of shear, tensile, or Peel strength which are reported in MPa ( Katona, 1997 ) .
A bond strength is merely relevant if it can be correlated clinically. The absolute value for clinically equal shear bond strength most frequently quoted is from the work of Reynolds ( Reynolds, 1975 ; Reynolds and von Fraunhofer, 1976 ) . They recommend bond strength of 60-80 kg/cm2 ( 5.9-7.9 MPa ) . However, the original paper does non province any scientific method for ciphering this value. Just every bit of import as the lower limit recommended bond strength is the maximal recommended bond strength. Retief s work ( 1974a ) must besides be considered when accessing bond strengths, as he demonstrated enamel breaks on specimens with bond strengths every bit low as 9.7 MPa.