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A d h e s i o n o f d e n t u r e t o o t h p o r c e l a i n t o h e a t - p o l y m e r i z e dd e n t u r e r e s i n

B a l d w i n W . M a r c h a c k , D D S , a Z h a o k u n Y u , b X i a o Y u Z h a o , P h D , c a n dS h a n e N . W h i t e , B D e n t S c , M A , M S dUniversity of Southern California, School of Dentistry, Los Angeles, Calif.U s e o f p o r c e l a i n d e n t u r e t e e t h m a y b e d e s ir a b l e i n m a n y c l i n ic a l s i t u a ti o n s , i n c l u d i n gi m p l a n t - s u p p o r t e d p r o s t h e s e s . H o w e v e r , l a c k o f s p a c e b e c a u s e o f f r a m e w o r k s o f t e np r e c l u d e s t h e u s e o f c o n v e n t i o n a l r e t e n t i o n b y d i a t o r i c s a n d p i n s . A d h e s i o n o fp o r c e l a i n d e n t u r e t e e t h t o d e n t u r e r e s i n c o u l d a l s o s t if f e n a n d p o s s i b l y s t r e n g t h e nd e n t u r e s a n d d e c r e a s e s t a i n i n g r e s s b e t w e e n p o r c e l a i n t e e t h a n d r e s i n d e n t u r e b a s e s .U n l i k e p r e v i o u s s t u d i e s t h a t i n v e s t i g a t e d th e b o n d b e t w e e n c o n v e n t i o n a l f e l d s p a t h i cm e t a l - c e r a m i c p o r c e l a i n a n d b i s- G M A b a s e d c o m p o s i t e r e s i n , th i s s t u d y i n v e s t i g a t e da d h e s i o n o f d e n t u r e t o o t h p o r c e l a i n t o p o l y m e t h y l m e t h a c r y l a t e ( PM M A ) . H i g h - e n e r g ya i r a b r a s i o n , h y d r o f l u o r i c a c i d e t c h i n g , a n d t h e u s e o f a g e n e r a l p u r p o s e b o n d i n ga g e n t r e s u l t e d i n a n i m p r o v e d b o n d s t r e n g th o f h e a t -c u r e d d e n t u r e P M M A b o n d e d t od e n t u r e t o o t h p o r c e l a i n . S i l a n e c o a t i n g d i d n o t i m p r o v e b o n d s t r e n g th s , a n d c o n v e n -t i o n a l a i r a b r a s i o n w a s n o m o r e e f f e c t i v e t h a n p o l i s h i n g w i t h 6 0 0 - gr it s i l i c o n c a r b i d e .S t o r a g e i n w a t e r a n d a r t i f ic i a l a g i n g s u b s t a n t i a l l y d e c r e a s e d b o n d s t r e n g t h s . T h es t r o n g e s t b o n d s t r e n g t h s w e r e a c h i e v e d b y a h i g h - e n e r g y - a b r a s i o n + e t c h i n g +m u l t i p l e - p u r p o s e b o n d i n g - a g e n t t r e a t m e n t , b u t a s i m p l e r e t c h i n g + m u l t i p l e - p u r p o s eb o n d i n g - a g e n t t r e a t m e n t a l s o p r o d u c e d r e l i a b l e r e s u lt s . A la b o r a t o r y t e c h n i q u e w a ss u g g es t ed . T h e r o l e o f s u r fa c e t r e a t m e n t i n t h e m e c h a n i s m o f a d h e s i o n w a s e x a m i n e dw i t h s c a n n i n g e l e c t r o n m i c r o s c o p y . H i g h - e n e r g y a b r a s i o n p r o d u c e d a s l ig h t l y m o r ed e t a i l e d i n i t i a l to p o g r a p h y t h a n c o n v e n t i o n a l a i r a b ra s i on , b u t a f t e r e t c h i n g , th eh i g h - e n e r g y t o p o g r a p h y b e c a m e m u c h m o r e d e t a i l ed . S u r f a c e t o p o g r a p h y a l o n e d i dn o t a c c o u n t f o r a l l d i f f e r e n c e s f o u n d . ( J P RO ST HE TDENT 1995;74:242-9 . )

Some dentists prefer porcelain denture teeth toresin- based teeth, 1"3 but they do not bond to polym ethylmetha cryla te (PMMA) de nture base resin. 4 Porcelain den-ture teeth are norma lly joined to acrylic resin dent urebases by mechanically retentive features such as metalpins or diatoric undercuts. Unfortunately, these retentivefeatures often have to be adjusted or removed because oflack of space. La ck of space may be the r esult of implan tframeworks and bars, pendulous tuberosities, overdentureabutmen ts, or lack of intera rch distance.

Adhesion of porcelain dentur e teeth to acrylic resin couldstiffen and strengthen dentures. Stresses are often con-centrated around denture teeth and result in the fracture

Presented at the Academy of Prosthodontics meeting, Orlando,Fla., May 1994.aAssociate Clinical Professor, Advanced Prosthodontics, Depart-ment of Restorative Dentistry.bAssociate Clinical Professor, Department of Restorative Dentist-ry/Biomaterials.CResearch Associate, Department of Restorative Dentistry/Biom-aterials.4Assistant Professor and Director of Clinical Research, Depart-ment of Restorative Dentistry/Biomaterials.Copyright 9 1995 by The Editorial Council of THE JOURNALOFPROSTHETIC DENTISTRY.0022-3913/95/$3.00 + 0. 10/H65513

of dentu re bases. However, a strong bond would allowstress to be transferred from resin to tooth and thusdecrease crack propagation and strengthen the dentures.Stain ingress to cracks between porcelain teeth and resindenture bases, and subsequent mouth odor, would be de-creased by adhesion of acrylic resin to th ese teeth. Masti-catory stresses are often localized to and concentratedaround retentive pins and thus increase the probability offracture. Distribution of stresses over a greater are a byadhesion of the t ooth to the resin would decrease the pos-sibility of failure.

Adhesion to porcelain teeth should be investigated.Silane coupling agents were shown to improve adhesion ofdentu re teeth to PMMA in the 1960s, 5 but the adhesi on ofPMMA to denture tooth porcelain has not been studiedcomprehensively. Recently, adhesion of bis-GMA to felds-pathic metal-ceramic porcelain has been enhanced byabrasion, etching, and bonding agents. Therefore, thisstudy a ttemp ted to find a reliable method of producing du-rable adhesion of PMMA to denture tooth porcelain.M A T E R I A L A N D M E T H O D S

Maxillary right central incisor porcelain denture teet h ofthe same mold and shade (Trubyte Bioform, mold 21J,shade B81, Dentsply Inte rnati onal Inc., York, Penn.) wereobtained. These teeth were made without pins so they

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t r e a t e d s u r f a c e

p o r c e l a i n _d e n t u r e t o o t h

v

s h e a r i n g l o a d

a c r y l i c r e s i na d h e s i v e t a p e

Fig. 1. Schematic of test specimen.

could be ground to a flat surface without exposing metaland so that stresses would not be concentrated around thepins. The teeth were embedded in epoxy resin (EpoxyResin, Hastings Plastics, Sa nta Monica, Calif.) containedin phenolic rings (Buehle r Ltd., Lake Bluff, Ill.). The epoxyresin was cured for 72 hours at room temperature. Thenthe specimens were ground with a series of abrasives (car-boru ndum g rit sizes 80 through 600) for uniform flat pol-ished porcelain surfaces (Fig. 1).

A fully rando mized block experimental design was used.Twenty-four groups were compared with respect to thefactors of surface air abrasion (none, conventional, orhigh-energy), acid-etching (none or etched), silane c oating(none or silane), and a bonding agent (none or bonding-agent).

The surfaces were abraded with either a laboratorysandbl aster (Integra l Syste ms Inc., Culver City, Calif.) (90psi N2, 50 pm alumina), with a high kinetic energy sand-blaster (KCP 2000, American Dental Technology, Troy,Mich.) (90 psi N2, 50 pm alumina), or not abraded. Thespecimens were the n either acid etched (10% hydrofluoricacid, Ultr adent Product s Inc., Salt Lake City, Utah), o r notetched.

After the surfaces were abraded and/or etched or nottreated, the areas for bonding were isolated by use of ad-hesive tape (Scotch Tape, 3M, St. Paul, Minn.) with aprepunched circular hole (4 mm diameter) (Fig. 1). A sili-cone wax mold-release agent was then carefully painte d onthe ta pe but not on the exposed dentu re tooth surfaces. Thebond test areas were isolated to prevent excess flash fromadhering to the surrounding denture tooth, which wouldproduce inflated bond strengths.

After isolation of the t est area, t he bonding procedureswere initiated. The exposed tooth surfaces were then eithertreated with a silane coupling agent (Silane, UltradentProducts Inc.) according to manufacturer's recommenda-tions or the surfaces were left untreated. The exposed toothsurfaces were then coated with a multipurpose bondingagent (Tenure S, Den-Mat, Sant a Maria, Calif.), accordingto the manu fact urer 's instr uctions, or not coated. 6 Fivespecimens were ma de for each of the 24 possible abrasion/etctdsilane/bonding agent groups.

The trea ted specimens were then placed in polyvinyl si-

loxane molds (Express, 3M) in the lower part s of brassdent ure flasks (Teledyne Hanau, Buffalo, N. Y.). The up-per pa rts of the flasks contained polyvinyl siloxane button-shaped molds (5 mm diameter, 2 mm high) tha t were cen-tered over the samples. Five specimens were placed in eachflask. Heat-polymerized PMMA denture resin (Lucitone199, Dentsply International Inc.) was mixed according tothe manufacturer's recommendations until it reached adoughy consistency. Pea-sized pieces were placed in thebutton -shape d molds and the flasks were closed slowly ina screw-type press (Teledyne Hanau). The specimens werethen cured according to manufact urer's recommendationsin a water-filled curing tank (Teledyne Hanau), and after8 hours of curing, the specimens were carefully removedfrom the polyvinyl siloxane molds and placed in water at37 ~ C for 16 hours .

After storage in water, the specimens were mounted ina servohydraulic univers al testing machin e (Instron, Can-ton, Mass.), and the resin-denture tooth interface wastested in shea r at a load rate o f 0.05 cm/minute (Fig. 1).Failure loads were plotted with a chart recorder.

Mean failure loads and their standard deviations werecalculated for each abrasion/etch/silane/bonding-agentgroup. A four-way analysis of vari ance (ANOVA) was com-puted to determine whe ther the m ain effects of abrasion,etching, silane, and bonding agent, and their interactionshad significant effects on bond str engt h (p < 0.05). If theabrasion had a significant effect, a multiple comparisonstest (Tukey's honest ly least significant difference method)was used to determine which of the thr ee abr asion sub-groups (conventional, high-energy, or none) were effective(p < 0.05).

The main effects that significantly improved bondstrength were then further evaluated with extended stor-age and artificial aging to compare the four most promis-ing treat ment combinations, with a sample size of sevenspecimens per group. Specimens were mad e as previouslydescribed, bu t stored for 7 days in 37 ~ C water after fabri-cation and t hen artificially aged by ther mal cycling (2000cycles from 5 ~ C to 50 ~ C with a dwell time of 30 secondsand a trans fer time of 20 seconds). After storage a nd aging,the specimens were tested as previously described. Thegroup means and their standard deviations were calcu-

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F i g . 2 . T h r e e - d i m e n s i o n a l b a r c h a r t o f 2 4 - h o u r m e a nb o n d s t r e n g t h s i n M P a . H A , H i g h - e n e r g y a b r a s i o n ; CA,c o n v e n t i o n a l a b r a s i o n ; E , e t c h i n g ; S , s i l a n e ; B , b o n d i n g ;NONE, n o t r e a t m e n t .T a b l e I . T w e n t y - f o u r - h o u r s h e a r b o n d s t r e n g t h s a n ds t a n d a r d d e v i a t i o n s ( S D s)

B on d i n g M eanAbras ion Etching Si lane agent (MPa) SDNone - - 02.4 0.2

- - + 16 . 7 1.6- + - 0 1 . 9 0 . 4

- + + 14.3 2.0+ - - 10.8 4.2+ - + 21.5 3.8+ + 12.4 1.2+ + + 18.9 3.8

Con vent ional - - 13.6 3.8- - + 14.6 1.6- + - 09.2 2.0- + + 12 . 7 1.4+ - 10.4 2.6+ - + 09.4 2.0+ + - 14.3 3.4+ + + 16.5 3.4

Hig h-en ergy - - - 06.3 2.0- - + 21.9 1.8- + 1 5 . 4 1 . 6

- + + 17 . 5 5. 4+ - - 20.7 2.8+ - + 22.6 2.4+ + - 23.2 6.2+ + + 10.6 2.4

F i g . 3 . T h r e e - d i m e n s i o n a l b a r c h a r t o f s t o r e d a n d a r t i f i-c i a l l y a g e d m e a n b o n d s t r e n g t h s i n M P a . S a m e k e y a s F i g .2.

l a t e d a n d a o n e - w a y A N O V A w a s c o m p u t e d t o d e t e r m i n ew h e t h e r t h e g r o u p s w e r e d i f f e r e n t ( p < 0 .0 5 ) a n d a m u l t i -p l e c o m p a r i s o n s t e s t d e t e r m i n e d w h i c h g r o u p s w e r e s i m -i la r (p < 0 .05) .

T o u n d e r s t a n d t h e i n f l u e n c e of s u r f a c e t r e a t m e n t o n t h em e c h a n i s m o f a d h e r en c e , s c a n n i n g e l e c t r o n m i c r o g ra p h s( S E M s ) w e r e m a d e o f a b r a d e d a n d / o r e t c h e d d e n t u r e t o o t hs u r fa c e s . A s c a n n i n g e l e c t r o n m i c r o s c o p e w i t h a n e n e r g yd i s p e r s i v e s p e c t r o m e t e r ( E D S ) ( C a m b r i d g e 3 6 0, C a m -b r i d g e I n s t r u m e n t s , C a m b r i d g e , U . K . ) w a s u s e d t o m a k et h e i m a g e s a t a m a g n i f i c a t i o n o f w i t h a n e n e r g y o f1 0 k V a n d d i g i t a l l y s t o r e t h e m . T h e m i c r o g r a p h s w e r e l a t e rp r i n t e d o n P o l a r o i d f i l m (P o l a ro i d , C a m b r i d g e , M a s s .) .R E S U L T S

T w e n t y - f o u r h o u r m e a n s h e a r b o n d s t re n g t h s a n d t h e i rs t a n d a r d d e v i a t i o n s a r e s h o w n i n T a b l e I a n d F i g. 2. T h e yr a n g e d f r o m 1 .9 M P a f o r n o a b r a s i o n + n o e t c h i n g +s i l a n e + n o b o n d i n g - a g e n t t o 2 3 .2 M P a f o r h i g h - e n e r g ya b r a s i o n + e t c h i n g + s il a n e + n o b o n d i n g - a g e n t .

F o u r - w a y A N O V A r e v e a l e d t h a t a b r as i o n, e t c hi n g , a n db o n d i n g a g e n t a l l s i g n i f i c a n t l y i m p r o v e d 2 4 - h o u r b o n ds t r e n g t h s ( p < 0 . 0 0 0 1 ) ( T a b l e II ). H o w e v e r , t h e s i l a n e c o u -p l i n g a g e n t d i d n o t i m p r o v e 2 4 - h o u r s h e a r b o n d s t r e n g t h s( p 0 . 5 8 ) ( T a b l e I I) . A m u l t i p l e c o m p a r i s o n s t e s t i n d i c a t e dt h a t h i g h - e n e r g y a b r a s i o n w a s s u p e r i o r a n d c o n v e n t i o n a la b r a s i o n w a s s i m i l a r t o n o a b r a s i o n ( p < 0 .0 5 ).

T h e m e a n s a n d s t a n d a r d d e v i a t i o n s o f t h e f o ur a rt i f i-c i a l l y a g e d g r o u p s a r e p r e s e n t e d i n F i g . 3 a n d i n T a b l e I II .T h e y r a n g e d f r o m 3 . 0 M P a f o r h i g h - e n e r g y a b r a s i o n + n o

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Fig. 4. SEM of glazed surface of porcelain denture toothas supplied by manufacturer (original magnification All micrographs were made from perpen dicularviews without stage tilt. All black magnification bars rep-resent 10 pm.

Fig. 5. SEM of polished porcelain (original magnificatio nxlO00).

Tab l e IL Four-way ANOVA for 24-hour shear bond strengt hS o u r c e o f S u m o f D e g r e e s o f M e a n S i g n i f i ca n c ev a r i a t i o n s q u a r e s f r e e d o m s q u a r e F - r a t i o l e v e l

Main effectsAbrasion (A) 618 2 309 28.5


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Fig. 6. SEM of specimen that was polished and etchedwith 10% hydrof luoric acid for 30 seconds (original magni-fication Surface topography appears to be fairlyflat, but many grooves 2 to 3 pm wide can be seen.

Fig. 8. SEM of specimen tha t was polished, convention-ally air abraded, and etched (original magnification 1000).Surface appears to be rough and uneven, but grooves arefewer than in Fig. 4 and are now 5 to 8 ~m wide.

Fig. 7. SEM of specimen that was polished and conven-tionally air abraded (original magnification Sur-face appears to be rough and uneven.Fig. 9. SEM of specimen tha t was polished and high- en-ergy abraded. This surface topography appears to be roughand uneven. Appearance is fairly similar to that of con-ventionally abraded specimen in Fig. 6, but surf ace topog-rap hy is more detailed and some small-sized debris typicalof shattered crystals are present.

T a b l e I V . O n e w a y A N O V A f o r fa t i g u e d s h e a r b o n d s t r e n g t h sS o u r c e o f S u m o f D e g r e e s o f M e a n S i g n i f ic a n c evar iat ion squar e s f r e e dom squar e F-r at io l e ve l

Between groups 406 03 135.5 33.7


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MARCHACK ET AL THE JOURNA L OF PROSTHETIC DENTISTRY

sizes. This "two-tier" roughness may account for the supe-rior bond strengths achieved with this surface treatment.The greater velocity high-energy abrasive particles maynot only knock out superficial grains, bu t ma y also producenarrow microcracks and shattered crystals. These cracksmay have been too narr ow to see at magnification,but may have preferentially etched and thus produced thenarrow grooves.D I S C U S S I O N

High-energy-abrasion, hydrofluoric acid-etching, anduse of a general-purpose dentin-bonding agent all im-proved bond strength of heat-polymer ized denture acrylicresin bonded to denture tooth porcelain. Therefore, thesemethods are recommended to improve the bond strengthof dentu re acrylic resin bonded to porcelain dentu re teeth.However, many dentists and laboratories may not haveaccess to high-energy abrasion equipment; but acid-etch-ing and a bonding agent, which are readily available andinexpensive, still produced reliable bonds after artificialaging.

Conventional abra sion did not effectively improve bondstrength , possibly because the velocity of the abrasive par-ticles was insufficient to cause sufficient roughn ess of thestrong dense dentur e-toot h porcelain matrix. I t is probablethat denture tooth porcelain had g reater crystalline com-ponents and a lesser g lassy component, or highe r density,than conventional feldspathic metal-ceramic porcelain,which would rend er it less susceptible to abrasion or etch-ing. 79 In addition, conventional abr asion is known to beless effective th an etching in the improve ment of bondstre ngth to feldspathic metal ceramic porcelain. 1~ Al-though etching of feldspathic metal-ceramic porcelain isknown to produce a rough micromechanically retentivesurface,S, 10-12 no ev idence for it s effectiveness on bondin gto denture tooth porcelain has been reported. This studyused 10% hydrofluoric acid with a 30-second etch time.This etch time is sufficient to dissolve surface glass, butlonger times would not dissolve the crystalli ne componentsunless stronger and much more dangerous acids wereused.

Trea tmen t with a silane coupling agent was not effectivein improving bond strengt h to heat-polymerized resin. Si-lane coupling agents react slowly to form stable covalentbonds between substrates. Heat-polymerization of denturebase resin in a wat er bath may allow early water ingressth at could cause hydrolysis, 13 in c ontras t to the immedia teautopolymerization or light-polymerization of bis-GMAbased filled composite resins a gains t ceramic restorations.In addition, unfilled PMMA is more prone to water sorp-tion than highly filled and cross-linked bis-GMA basedmaterials. Use of an auto polymerizi ng resin, or heat-poly-merizing with dry h eat or microwave energy, may negatethis problem. Previous studies of the effect of silanetreatment on bond strength to porcelain denture teethwere poorly controlled or used autopolymerized resin

Fig. 10. SEMofspecimenthatwaspolished, high-energyabraded, and etched. Surface remains rough and uneven,but unlike conventionally abraded and etched specimen,many small grooves are present.

only.7, 14-16 The delete rious effect of wate r storage and ar-tificial aging on the silane coating of porcelain denturetee th has been demonstr ated . 7,13,14, 17 Some prior studieson the adhesion of composite resin to feldspathic metal-ce-ramic porcelain demonstrated that silane coupling agentscan improve bond strength , 18,19 but other studies producedmixed results , 11,20-24 reported th at bond streng ths de-crease after storage or artificial aging, 253z or demon-strat ed tha t silane w as ineffective, s

A multipurpose bonding agent significantly improvedbond stren gths (Tables I thr ough III an d Figs. 2 and 3). 6The type of bonding agent u sed in this study consisted ofa low-viscosity mixtu re of small surface-active monomersdissolved in acet one an d alcohol. 6 Thus the monomers m aypenet rate into tiny irregularities an d copolymerize withother more viscous resins to form a strong micromechanicalbond to dentu re t ooth porcelain. It is expected that chem-ically similar bonding agents would produce similar results.

Artificial aging by water storage and thermocyclingdramatically reduced bond strengths (Tables I and III,Figs. 2 and 3). Studies on the ad hesion of composite resinby adhesive resins to feldspathic metal-ceramic porcelainalso demonstrated that extended thermocycling decreasedbond streng th. 32-34

The SEMs of the glazed surface of porcelain dentureteeth (Fig 4) were similar to previously published micro-graphs of denture teeth made by the same manufacturer.16As expected, the surface of he 600-grit polished specimens(Fig 5) was of interm ediate roughn ess between t hat of pre-viously published micrographs of diamond paste-polishedporcelain a nd 240-gri t polished porcelain. 15,16 One previ-ously published micrograp h clearly shows the fine narrowgrooves produced by polishing + etching (Fig 6) or bypolishing + high ener gy abrasion + etching (Fig 10) in thisstudy; however, that study did not identify the specifictre atm ent tha t produced the fine grooves. 16

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The results clearly show that complex interactionsbetween different surface trea tmen ts affect bond streng ths(Table I). An interaction between high-energy abrasionand etching produced the most favorable micromechani-cally retentive surface, namely the two-tier roughness.However, surface topography is not the only factor influ-encing adhesion. For example, the difference in bondstrengths produced by conventional and high-energy abra-sion cannot be accounted for by their slight difference insurface detail produced by preparatory abrasion (Figs. 7and 8). Therefore, changes in surface ene rgy and wettabil-ity produced by different tre atments may also be impor-tant.

The negative control, no abrasion + no etching + nosilane + no bonding agent group, recorded a 24-hour bondstre ngth of 2.4 MPa, but this bond would not be expectedto survive prolonged storage or aging. The bond strengthvalues for the most favorable groups after storage and ag-ing ranged from 3.0 to 13.4 MPa. These are lower thantypically achieved for bonding bis-GMA based compositesto porcelain veneers, 11, 18-34 but may still be sufficient toretain denture teeth, strengthen denture bases, and pre-vent stain ingress around denture teeth. Differences informulation, processing, microstructure, and surface en-ergy between PMMA and bis-GMA resins and betweenfeldspathic metal ceramic and denture tooth porcelainsprobably account for the lower bond strengths.

In this experiment, low failure stresses produced adhe-sive bond failure, but internal cohesive cracking of theporcelain was noted at shear stre sses of approxima tely 10MPa. High failure stresses, in the order of 20 MPa or more,produced catastrophic cohesive failure and shattering ofdenture teeth. Intermediate failure stresses produced amixture of adhesive and cohesive failure similar to that ofa previous study. 35 Even after storage a nd aging, threeporcelain teeth in the high-energy abrasion + etching +bonding-agent group failed cohesively. Therefore, thisstudy underestimated shear bond strengths of the strongergroups.

Adhesion can be examined in many different ways, butthis s tudy was successful in the comparat ive evaluation ofdifferent techniques and treatments. The specimens weretested in shear, but the thickness of the isolating tape andflexure of he PMMA buttons probably introduced complextensile forces to the bond interface. This test configurationwas more demanding than routine clinical situationswhere some mechanical engagement of the denture toothwould occur and where the larger bulk of resin would al-low greater relief of strain, thus protecting the bond. Theartificial aging test simulated oral conditions by storingthe specimens in water to ensure full water sorption, andthen subjecting them to rigorous mechanical forces be-cause of repeated expansion and contraction caused bythermocycling. However, the exact relationship betweennormal usage and thermocycling is unknown, and the ex-

act bond stre ngth necessa ry for clinical success is also un-known. 17 Norma l chewing forces are unlikely to reach thefailure pressures recorded for the best tr eatment groups. 36However, clinical failures produced by slow crack growth,namely fatigue, could be produced by many repetitions ofsmall chewing forces. The low variances and the completerandomized block design allowed intergroup comparisonsto be made with confidence, despite the small sample size.The experimen tal methodology was reliable, because nobonds in any test groups failed spontaneous ly during stor-age or aging before testing.

Adhesion between denture teeth and denture baseswould stiffen the dentu re because the porcelain teeth havea much higher elastic modulus that the PMMA denturebase material. The stre ngth of the denture might also beincreased because strength is not only dependent onmicroscopic surface flaws, bu t a lso on macroscopic discon-tinuities and decreased base thickness around teeth. Thusdenture base fractures that involve the base and teethwould be expected to be decreased. However, bases alsofracture through other susceptible areas such as fraenalnotches, and t hese types of fractures would not be affectedby adhesion.L A B O R A T O R Y T E C H N I Q U E

The following labora tory technique is suggested for sit-uations where re tentive element s have been lost, increasedstrength of the denture is needed, or enhanced preventionof stain ingress is desired.

1. Shape the denture teeth to their expected final form.2. Abrade the denture teeth with a high-energy systemif available.3. Complete the wax-up.4. Flask the denture.5. Boil out, washing the exposed parts of the teeth withdetergent and hot water.6. Etch the exposed parts of the tee th with a 10 hydro-fluoric acid gel for 30 seconds.7. Wash vigorously and dry.8. Paint two coats ofsepara ting medium on the stone, noton the teeth, and let dry fully.9. Apply a multipurpose bonding agent to the exposedparts of the teeth and li ght cure.

10. Mix and pack with resin as normal.11. Continue routine procedures.Although, on the basis of the re sults of this study, theabove protocol is expected to produce the best adhesion,many other combinations of surface trea tment and bond-ing agent will also improve bond strength (Tables Ithrough III, Figs. 2 and 3). If the equipment or materialsmentioned are not available, others may be substituted,but bond strengths may be lower.C L I N I C A L I M P L I C A T I O N S

This study showed that routine adhesive proceduresmay strengthen the bond between denture teeth and den-

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M A R C H A C K E T AL THE JOURNAL OF P R O S T H E T I C D E N T I S T R Y

tu r e base r es in . Th is may s t r eng then and s t i f f en den tu rebases and d ecrease den t u re too th loss , s ta in ing ress , andmou th odo r .C O N C L U S I O N

Rel iab le m ethods of bonding porce la in denture tee th toheat -polymer ized polymethyl methacrylate denture baseres in hav e been identif ied, described, a nd their mechan isminves t igated .

We thank Drs. Mark Latta and Ron Zentz of Dentsply Interna-tional Inc., York Division, for providing the porcelain dentureteeth used in this study. We also thank Drs. Winston Chee andTerry Donovan for their advice.R E F E R E N C E S

1. Dirksen LC. Plastic teeth: their advantages, disadvantages and limi-tations. J Am Dent Assoc 1952;44:265-8.2. Appelbaum M. Theories of posteri or tooth selection: porcelain ve rsusacrylic. Dent Clin North Am 1984;28:299-306.3. Shimoyama K, Uchida T, Nagao M, Odagiri K, Shirasaki Y, TateishiT. Mechanical properties of artificial teeth. Bulletin of Tokyo Medicaland Dental Universi ty 1993;40:13-6.4. Suzuki S, Sakoh M, Shiba A. Adhesive bonding of dentu re base resinsto plastic dentu re teeth. J Biomed Mate r Res 1990;24:1091-103.5. Paffenbarger GC, Sweeney WT, Bowen RL. Bonding porcelain teeth toacrylic resin dentu re bases. J Am Dent Assoc 1967;74:1018-23.6. Bowen RL, Cobb EN, Rapson JE. Adhesive bonding of various mat eri-als to hard tooth tissues: improvement in bond strengt h to dentin. JDent Res 1982;61:1070-6.7. Semmelman JO, Kulp PR. Silane bonding porcelain t eeth to acrylic. JAm Dent Assoc 1968;76:69-73.8. Sorensen JA, Engelman MJ, Torres TJ, Avera SP. She ar bond strengt hof composite resin to porcelain. In t J Prosthodont 1991;4:17-23.9. Kern M, Neikes MJ, St rub JR. HafLfestigkeit des klebeverbundles au fIn-Ceram nach unterschi edlicher Oberflachenkonditionierung. [Ten-sile s trengt h of the bond to In-Ceram after varying models of surfaceconditioning.] Deutsche Zahnarztliche Zeitschrii~ 1991;46:758-61.10. Suliman AH, Swift EJ J r, Perdigao J. Effects of surface treat ment andbonding agents on bond stren gth of composite resin to porcelain. JProsthet Dent 1993;70:118-20.11. Stangel I, Nathanson D, Hsu CS. Shea r strength of he composite bondto etched porcelain. J Dent Res 1987;66:1460-5.12. A1 Edr is A, A1 Jabr A, Cooley RL, Barghi N. SEM evaluation of etchpatterns by three etchants on three porcelains. J PROSTHET DENT1990;64:734-9.13. Steas A, Picard B, Ogolnik R. Adhesion of artificial tee th to poly-methacrylate resins. [French] Rev Odontostomatol Paris 1990;19:61-7.14. Meyerson RL. Effects of silane bonding of acrylic re sins to porcelain onporcelain st ructure . J Am Dent Assoc 1969;78:113-9.15. Eames WB, Rogers LB, Feller PR, Price WR. Bonding agents forrepairing porcelain and gold: an evaluation. Oper Dent 1977;2:118-124.

16. Wood DP, Jordan RE, Way DC, Galil KA. Bonding to porcelain and gold.Am J Orthod 1986;89:194-205.17. Duhane y HN. A clinical and labora tory study of silane bond ing of por-celain teeth to the auto-curing methyl methacrylate base [MS Thesis].Boston: Boston Univer sity, 1970.

18. Hsu CS, Stangel I, Nathans on D. Shear bond strength ofresin to etchedporcelain [Abstract]. J Den t Res 1985;64:296.19. Stokes AN, Hood JA. Thermocycling, si lane priming, and resin/porce-lain in ter face s--a n electrical leakage study. Dent Mater 1989;5:369-70.20. Newburg R, Pameijer CH. Composite re sins bonded to porcelain withsilane solution. J Am Dent Assoc 1978;96:288-91.21. Fer rando JM, Graser GN, TaUents RH, Jarvis RH. Tensile st reng thand microleakage of porcelain repair systems. J PROSTHET DENT1983;50: 44-50.22. Lacy AM, Laluz J , Watanabe LG, Dellinges M. Effect of poreelain sur-face t reatment on the bond to composite. J PROSTHET DENT 1988;60:288-91.23. Nath anson D. Dental porcelain technology. In: Garber DA, GoldsteinRE, Feinma n RA, eds. Porcelain laminate veneers. Chicago: Quintes-sence Publ Co, Inc, 1988:24-35.24. Lu R, Harcourt JK, Tyas MJ, Alexander B. An investigation of thecomposite resin/porcela in interface. Aust Dent J 1992;37:12-9.

25. Gregory WA, Hagen CA, Power s JM. Composite resin repai r of porce-lain using different bonding materials. Oper Dent 1988;13:114-8.26. Pra tt RC, Burgess JO, Schwartz RS, Smith JH. Evalua tion of bondstrength ofsix porcelain repa ir systems. J I~OSTHETDENT 1989;62:11-3.27. Bailey JH. Porcelain-to-composite bond streng ths usi ngfo ur organosi-lane materials. J PROSTHET DENT 1989;61:174-7.28. Diaz-Arnold AM, Aquilino SA. An evaluation of the bond stre ngth s offour organosilane ma teria ls in response to therma l s tres s. J PROSTHETDENT 1989;62:257-60.29. Diaz-Arnold AM, Schneider RL, Aquilino SA. Bond steng ths of in-tra oral porcelain repair materials . J PROSTHET DENT 1989;61:305-9.30. Llobel A, Nicholls JI, Kois JC, Daly CH. Fatigue life of porcelain repairsystems. Int J Prosthodon t 1992;5:205-13.31. Appeldoorn RE, Wilwerding TM, Barkmeier WW. Bond strength ofcomposite resin to porcelain wi th newe r generation porcelain repairsystems. J PROSTHET DENT 1993;70:6-11.32. Nowlin TP, Barghi N, Norling BK. Evaluation of the bonding of three

porcelain repair systems. J PROS~-mT DENT 1981;46:516-8.33. Cooley RL, Tseng EY, Evans JG. Evaluati on ofa 4-META porcelain re-pair syst em. J Esthe t Dent 1991;3:11-3.34. Wolf DM, Powers JM, O'Keefe KL. Bond str eng th of composite to por-celain treate d wit h new porcelain repa ir agents. Dent Mat er 1992;8:158-61.35. Matsumu ra H, Kawaba ra M, Tana ka T, Atsuta M. A new porcelain re-pair system with a silane coupler, ferric chloride, and adhesive opaque

resin. J Dent Res 1989;69:813-8.36. HaraldsonT. Comparisons ofchewingpatternsinpatie ntswithbridgessupported on osseointegrated implants and subjects wit h natur al den-titions. Acta Odontol Scand 1983;41:203-8.Reprint requests to:DR. BALDWINW. MARCHACKPINCUS BIOMATERIALSRESEARCH LABORATORYU.S.C. SCHOOLOF DENTISTRY# 4112LOS ANGELES, CA 90089-0641

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