T h e e f f e c t o f th e m e t h o d o f tooth e n a m e l p r e p a r a t io n on th e b o n d s tre n g t h s o f f o u r c o m p o s it e re s to r a tiv e m a t e r ia ls w a s d e t e r m i n e d . M e t h o d s o f tooth p r e p a r a t io n i n v e s t ig a t e d w e r e u n p r e p a r e d e n a m e l, e n a m e l p r e p a r e d w ith a d ia m o n d b u r, a n d e n a m e l p r e p a r e d w ith a c a r b i d e b u r.

Effect of methods of tooth enamel preparation on the retentive strength of acid-etch composite resins Debra A. Aker John R. Aker, DDS Soren E. Sorensen, DDS, M S

m ajor goal of research on dental m aterials during the past 20 years has been to develop a fil­ ling m aterial capable of form ing strong bonds to tooth structures. F illin g m aterials that are not able to bond to tooth structure require the tooth be pre­ pared w ith u ndercuts to lock the restoration in place. Often, this requires the removal of additional am ounts of tooth structure that may weaken the tooth and m ake it more likely to fracture. M aterials that do not bond to tooth structure are more liable to allow oral fluids to penetrate the m inute gap b e­ tween the m aterial and surface of the tooth .1 T his may lead to decay or discoloration around the m ar­ gins of the restorative m aterial. A frequent problem in restorative dentistry is the Class IV restoration or fractured in cisal edges in an­ te rio r te e th . D iffic u lty in p ro v id in g re te n tiv e undercuts for these restorations initiated the devel­ opm ent of anterior restorative m aterials that are ca­ pable of form ing strong bonds to tooth structure. A lthough B u o n o co re’s original con cep t, etch in g enam el w ith phosphoric acid to promote the bond­ ing of acrylic resin to tooth structure, was pub­ lished more than two decades ago, it is still the basis for the current set of com posite resins that are

capable of bonding to tooth structure.2 Although the exact nature of the bond betw een resin and etched enam el may not be com pletely understood, it is believed to be chiefly m ech an ical in nature. Etching the enam el w ith phosphoric acid rem oves organic m aterial from the enam el surface, opens m icroscopic pores in the enam el, and thus increases the surface area for bonding. The resin flows into the pores and forms m inute tags to inter­ lock the resin and enam el surface. Tw o techniques for preparation of fractured in ­ cisors before etching have been proposed. A com ­ m only used method involves no cavity preparation at all3; rather, it relies on the m aterial being ex­ tended over the fracture onto the labial surface. T h is procedure requ ires that the resto ration be overcontoured and relies on unprepared enam el surfaces for bonding. Unprepared enam el has been resistant to the acid-etch process because of the presence of prism less or fluorosed enam el on the surface.4,5 The resulting featheredge of this restora­ tion is difficult to finish and is likely to fracture and thus increases the chance for m arginal leakage and discoloration.6,7 A second m ethod of preparing the tooth before etching has been proposed.8 T h is is JADA, Vol. 99, August 1979 ■ 185

know n as the “ cham fer sh ou ld er” preparation; it involves establishing a definite lin e of fin ish by rem oving approxim ately h alf the enam el thickness 1 mm cerv ically from the edge of the fracture, with use of a roundnosed diam ond bur. This m ethod al­ lows the restoration to be properly contoured, elim ­ inates the problem s associated w ith featheredge fin ish lin es, and rem oves any layer of prism less or fluorosed enam el on the surface. A prelim inary study reported a retention rate of 97% for a threeyear period for restoring fractured in cisal edges by use of this m ethod. The purpose of this investigation was to deter­ m ine w hether the bond strengths of several popular com p osite resin s are affected by the m ethod of to o th p re p a ra tio n . T h e co m p o site s u sed w ere A daptic acid etch ,* Concise Enam el Bond,+ NuvaSeal/N uva-Fil.t and Restodent.§ M ethods of tooth preparation were unprepared enam el, enam el pre­ pared w ith a diam ond bur, and enam el prepared w ith a carbide bur.

Fig 1 ■ Enamel prepared with coarse diamond bur, then etched (original m agnification, X100).

Method A total of 120 extracted perm anent hum an teeth were obtained from the departm ent of oral surgery, State U niversity of New York at Buffalo Sch oo l of Dentistry. The teeth had been stored in 5% Form alin solution since extraction. They were cleaned of all tissue, bone, and calculus and were placed in a 1% so lu tion of Coe GermicideH to prevent b acterial grow th. Each tooth was embedded in a cylinder of dental stone that was 1.25 inch in diam eter and 1 in ch in length w ith the facial surface of the crow n perpendicular to the base of the cylinder. Ten sam ­ ples w ere used for each of the 12 com binations of m ethods of tooth preparation and com posite m ate­ rials. O f these, 4 0 teeth did not have the enam el surface prepared. The facial surfaces of 40 m ounted sam ­ ples were prepared using a coarse diam ond b u r** to rem ove su fficient enam el to leave a flat area at least 4 mm in diam eter. The surface of the prepared area w as perpendicular to the base of the stone cyl­ inder. The rem aining 40 sam ples were sim ilarly prepared w ith a carbide fissure b u r .t t Photographs taken with a scanning electron m i­ croscope (Fig 1-3) illustrate the topography of the typical enam el surface produced by these prepara­ tion procedures. A resin m olding fixture was constructed (Fig 4). T h is device was designed to m old a resin rod 2 mm in diam eter on the tooth surface; the long axis of the rod was parallel to the base of the stone cylinder. 186 ■ JADA, Vol. 99, August 1979

Fig 2 ■ Enam el prepared w ith carbide fissure bur, then etched (original m agnification, xlOO).

The device clam ped a split section of Teflon-coated tubing, 4 mm in length (inside diam eter, 2 mm), and held the tubing directly over the previously prepared area of the tooth. A 500-m g w eight was used to put pressure on the resin as it polym erized. Resin rods were m olded to the facial surfaces of ten teeth for each com bination of m ethods of tooth

Fig 3 ■ U nprepared enam el surface, etched (original m agnification,

Fig 5 ■ Test fixture with specim en, ram in place, ready for testing.


Fig 4 ■ Resin molding fixture with specim en, weight in place. Completed specim en with resin rods is on left.

preparation (unprepared enam el, diamond bur, and carbide bur) and com posite resin (Concise Enam el Bond, A daptic acid etch, Nuva-Seal/Nuva-Fil, and Restodent). In each case, the tooth was etched using the m anufacturer’s etchant and follow ing the rec­ ommended procedure. The m anufacturer’s unfilled

resin was applied to the bonding area before Con­ cise, A daptic, and Nuva-Seal/Nuva-Fil were used. A layer of unfilled resin is not used under the R e­ stodent com posite resin. After the specim en was prepared to receive the com posite resin , it was placed in the m olding fixture w ith the m old placed directly over the center of the prepared area. W hen the self-curing resins (Concise, A daptic, and Resto­ dent) were used, the resin was m ixed according to the m anufacturer’s instructions, the m aterial was loaded into a clean amalgam carrier and was in ­ jected into the m old cavity. An excess of m aterial was used and the w eight was placed over the mold to com press the resin against the surface of the tooth. After the resin had set undisturbed for ten m inutes, the m olding fixture w as disassem bled carefully and the sp lit T eflon-coated sleeve was rem oved from the resin rod. B ecause N uva-Fil re­ quires exposure to ultraviolet ligh t for polym er­ ization and the opacity of the m aterial only perm its penetration of approxim ately 1.5 mm by the ultra­ violet light, this m aterial required a different tech ­ nique. T he Nuva-Fil com posite was placed, in in ­ crem ents 1 mm thick, into the m old, tam ped into place w ith an amalgam condenser, and polym er­ ized w ith a N uva-Litet for two m inutes. Four in ­ crem ents were required to fill the mold. The specim ens were stored in a m oist environ­ m ent for 24 hours before testing. T h e specim ens were placed in the test fixture (Fig 5) so that the chisel-shaped ram cam e in contact w ith the resin rod 0.01 inch from the surface of the tooth. T he test


Table I ■ Mean retentive strength and standard deviation as a function of brand of composite resin and method of surface preparation.

C o m p osite resin C o n cise En am el Bond A d aptic acid etch R estoden t

N uva-Seal/ N uva-Fil

M ethod o f surface preparation

M ean retentive strength (lb / in )

SD (lb / in )

D iam ond bur C arb id e bur U nprepared D iam ond bur C arb id e bur U nprepared D iam ond bur C arb id e bur U nprepared D iam ond bur C arb id e bur U nprepared

7471 6022* 5841* 8105 5343* 5569* 4574* 4800* 4754* 4573 2943* 2490*

715 838 715 571 1028 403 1001 874 1087 439 575 489

*No significant difference between these values (for that resin) at the 95% level of confidence.

Table 2 ■ Percent increase in retentive strength as a func­ tion of methods of preparation of material and tooth. M eth od s of su rfa ce p reparation M aterial C oncise

A d aptic R estodent

Nuva Seal/ N uva-Fil

H igher m ean, p si

Low er m ean, psi

In crease in retentiv e stren gth* (%)

D iam ond D iam ond C arbide D iam ond D iam ond U nprepared U nprepared C arbide C arbide D iam ond D iam ond C arbide

U nprepared C arbide U nprepared U nprepared C arbide C arbide D iam ond D iam ond U nprepared U nprepared C arbide U nprepared

28 24 N St 46 52 NS NS NS NS 84 55 NS

‘ Percent increase in retentive strength = Higher mean — lower mean

;--------------------- A 1UU.

Lower mean

+NS, not statistically significant at P < .05 (95% confidence level), therefore no comparisons could be made.

/ fixture was placed in an Instron Universal Testing m a c h in e tt that was operated at a crosshead speed of 0.05 cm/min. The force required to break the co m p o site rod from the tooth su rface w as re ­ corded. The retentive strength in psi was deter­ mined by dividing the force required to rem ove the resin rod by the cross-sectional area of the rod.

Results The mean retentive strength and standard devia­ tion of the m ean for each brand of com posite resin and m ethod of tooth preparation are sh ow n in Table 1. Preparing the enamel surface with a diam ond bur resulted in significantly higher retentive strengths for Concise, Adaptic, and Nuva-Fil. There was no significant difference in retentive strengths of these materials when the surface of the tooth was unpre­ pared or prepared with a carbide bur. Different pro­ cedures of preparation of the tooth did not affect the retentive strength of Restodent. T able 2 sh ow s the in crease in p ercen t in reten tive stren gth as a fu n ction of m eth od s of m aterial and tooth p rep aratio n . M ean reten tive stren gth s of the three p ossib le pairs of tooth prep aratio n m eth od s w ere co m p a re d for each m aterial. T h e eq u ation u sed w as: in crease in % in reten tive stren g th = h ig h er m ean — low er m ean I low er m ean x 10 0 .

Table 2 indicates that preparing the surfaces with a diamond bur before etching resulted in 24% to 84% higher retentive strengths than preparing the tooth with a carbide bur or leaving the tooth unpre­ pared w hen Concise, Adaptic, or Nuva-Fil com po­ site resins were used. Significance was determined by using an analysis of variance and Scheffe Test. 188 ■ JADA, Vol. 99, August 1979

Discussion When Concise Enamel Bond, Adaptic acid etch, and N uva-Seal/N uva-Fil com posite resins w ere applied to surfaces prepared with a coarse diamond bur, retentive strengths were significantly (24% to 84% ) greater than when the tooth surfaces were prepared with a carbide bur or left unprepared. The different procedures of preparation of the tooth did not affect the retentive strength of ^Restodent com ­ posite resin. Preparing enamel surface with a coarse diamond bur results in a surface that is noticeably rough and striated when seen with unaided eye. The surface of unprepared enamel and enamel prepared using a carbide bur are m uch smoother. Preparing enam el with a coarse diamond bur may provide a m acros­ co p ic rou gh n ess th at adds to the m icro sco p ic roughness of the etching process and provide addi­ tional surface area for bonding Concise, Adaptic, and Nuva-Fil com posites. This increased rough­ ness did not affect the retentive strength of Resto­ dent. Restodent differs from the other composites in this study because an intermediary unfilled resin is not used but the viscosity of its bonding material is relied on to enter the surface irregularities and pro­ vide bonding. The bonding material also contains the filler particles that may prevent it from deeply penetrating the roughened surface. This could be caused if the particles block entrance to the cre­ vices or if not enough free liquid bonding agent is available to penetrate the crevices.


T he authors thank the Calspan Corporation, Cheektowaga, NY, for the use of their scanning electron microscope.

The effect of three procedures of preparing the enamel surface on the retentive strengths of Con­ cise Enam el Bond, Adaptic acid etch, Restodent, and Nuva-Seal/Nuva-Fil was investigated. Resins using an unfilled-filled resin com bination (Concise Enamel Bond, A daptic acid etch, and Nuva-Fil) had a significantly higher retentive strength when the enamel was prepared with a coarse diamond bur than when the surface was unprepared or prepared w ith a carbide bur. The different procedures of tooth p re p a ra tio n did not affect the rete n tiv e strength of the resin when only a filled resin was used (Restodent).

*Johnson & Johnson Dental Products Division, East W indsor, NJ 08520. +3M Company, St. Paul, M inn 55101. tL . D. Caulk Co., Division o f Dentsply International, Inc., M ilford, Del 19963. §Lee Pharm aceuticals, South El M onte, Calif 91733. HCoe Laboratories, Inc., Chicago, 60658. **T eled yn e Dental Products Co., Densco Div., Denver 80207. ++S. S. W hite Co., Division Pennw alt Corp., Philadelphia, 19102. itln str o n Corp., Canton, Mass 02161.

Debra Aker is a student at Calasanctius Preparatory School, Buffalo, NY. Dr. Aker is clin ical instructor, department of operative dentistry, and Dr. Sorensen is chairman, department of dental m aterials, State Univer­ sity of New York at Buffalo, Buffalo, 14114. Address requests for reprints to Dr. Aker. 1. Skinner, E.W ., and Phillips, R.W. The science of dental materials. Philadelphia, W. B. Saunders Co., 1967. 2. Buonocore, M.G. Sim ple method of increasing the adhesion of acrylic filling m aterials to enam el surfaces. J Dent Res 3 4 :8 4 9 -8 5 3 ,1 9 5 5 . 3. Buonocore, M.G., and Davila, J. Restoration of fractured anterior teeth with ultraviolet-light-polym erized bonding m aterials: a new tech­ nique. JADA 86(6):1349-1354, 1973. 4. Brudevold, F.; Steadm an, L.T.; and Sm ith, F.A. Inorganic and or­ ganic components of tooth structures. Ann NY Acad S c 8 5 :1 1 0 -1 3 2 ,1 9 6 0 . 5. Gwinnett, A.J. The ultrastructure o f the “prism less” enam el o f per­ manent teeth. Arch Oral B io l 12 :3 8 1 -3 8 8 ,1 9 6 7 . 6. Sturdevant, C.M.; Barton, R.E.; and Brauer, J.C. (eds.). T he art and science of operative dentistry. New York, McGraw-Hill Book Co., 1968. 7. Bell, B.H., and Grainger, D.A. Basic operative dentistry procedures, ed 2. Philadelphia, Lea & Febiger, 1971. 8. Jordan, R.E., and others. Restoration of fractured and hypoplastic in­ cisors by th e acid etch resin tech n iqu e: a three year report. JADA 95(4):795-803, 1977.


Effect of methods of tooth enamel preparation on the retentive strength of acid-etch composite resins.

T h e e f f e c t o f th e m e t h o d o f tooth e n a m e l p r e p a r a t io n on th e b o n d s tre n g t h s o f f o u r c o m p o s it e re s to...
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