JOHN KANOA III, D.M.D.

estorative dentistry needs a dentin-enam el bonding system th a t can: " provide gapfree composite restorations; ™ achieve rapidly developing high-bond strengths; ■■ be biocompatible; «■ function in the presence of m oisture; ™ tre a t dentin and enamel sim ultaneously; “ tre a t m ultiple types of in traoral surfaces. Producing a gapfree resto ra­ tion is critical, especially in composite resin restorations. B rannstrom has shown th a t bacteria can rapidly colonize the gaps betw een composite resin restorations and the tooth interface.1Bergenholtz and others found th a t bacteria are directly correlated to pulpal pathosis.2 Bonding system s need to generate high-bond strengths in a short tim e. Typically, 24-hour bond strengths are the reported values, but no one w aits 24 : hours to begin inserting com­ posite resins. Davidson and others showed th a t the poly: m erization shrinkage of : composite resins places stress on bonding system s.3 To resist the contraction force of polymerizing composites, bond strengths m ust develop rapidly. The need for biocompatibility is

ABSTRACT

A bonding system using moisture on the tooth surface can be an enormous benefit as obtaining dentin dryness in the mouth is nearly impossible. The author describes a system that bonds to both wet and dry surfaces. obvious, but it’s likely th a t all current bonding system s are biocompatible. Since dentin is inherently a wet substrate, the bonding system m ust function in the presence of m oisture. The need for a common tre a tm e n t of dentin and enam el is again obvious to the practicing dentist, who well knows there really is no other way to tre a t. Often it’s very difficult to recognize w here enam el ends and dentin begins. Keeping an enam el etchant off dentin all the tim e is not practical. Rem ember this when considering a bonding system th a t is detrim entally affected by the enam el etchant contacting th e dentin surface.4 Finally it would be most convenient to the practitioner if one bonding system could be

used to bond all types of surfaces. R ath er th a n purchase one k it to bond enam el, another for m etal and yet another for porcelain, it would be highly desirable to be able to use the the sam e bonding system for all surfaces w ith only sm all alterations. For th is reason we should consider not dentin enam el bonding system s but ra th e r adhesive system s. P erhaps the m ost intriguing need is function on m oist or w et dentin surfaces. Freshly cut dentin presents a difficult restorative m edium for adhesive resin system s. The dentin su b stra te is inherently m oist because of the tu b u la r fluid. Reports have dem on­ strated th a t m oisture typically deters the ability of resin bonding system s to adhere to dentin. Terkla and others5 showed th a t two dentin bonding resin system s tested could not seal m oist dentin. M itchem and o thers6 noted th a t the bond strengths of Scotchbond (3M Dental Products), T enure (Den-M at) and Glum a (Columbus Dental) fell w hen tested under sim u­ lated physiological conditions. A ndreaus and o thers7 reported th a t w ater in dentinal tubules interfered w ith th e adhesion of dentin adhesives. Tao and Pashley8 reported th a t the bond JADA, Vol. 123, September 1992

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Figure 1. Maxillary left central incisor before restoration of dentin.

Figure 2. Cord is packed in gingival sulcus to prevent fluid contamination.

strength of G lum a and Scotchbond fell significantly when sm ear layers were removed and pulpal pressure was applied to a dentin surface. P ra ti and others9 found th a t storage in sim ulated pulpal pressure caused a significant reduction in the bond stren g th of Clearfil Photobond (J. M orita) and Scotchbond 2 in deep dentin. M itchem and G ronas10 and Glasspoole and o thers11 reported th a t the bond stren g th of Scotchbond 2 w as dim inished in the presence of dentinal 36

JADA, Vol. 123, September 1992

m oisture. This report presents data dem onstrating the improve­ m ent in bond strengths obtained w ith a particular bonding system when dentin is acid-etched and the prim ers are applied to w et dentin surfaces. The clinical technique is also illustrated.

defects and used w ithin two weeks of harvest. They were cleaned w ith a soap containing chlorhexidine and placed in a 3 percent glutaraldehyde solution for 24 hours. They were then rinsed and stored in tap w ater a t 4 C until tim e of usage. For the experim ent the teeth were embedded in an autopolymerizing acrylic resin in a stainless ring w ith an inside diam eter of one inch. The teeth were ground on a model trim m er to expose adequate facial dentin surface for bonding. The sam ples were stored in w ater a t 37 C for 24 hours. After storage, the exposed dentin surfaces were wetsanded w ith 320 g rit sandpaper ju st before treatm en t. The teeth were random ly divided into three equal groups, each of which was divided into two subgroups. The dentin-enam el bonding system exam ined w as the All Bond 2 system (Bisco Dental). The system has available two concentrations of phosphoric acid semigel etchant condi­ tioners: a 10 percent and a 32 percent concentration. The system also contains a Prim er A and Prim er B and a dual-cure capability unfilled bonding resin. Prim er A is m ade up of NTG-GMA(N-tolyl glycine TABLE 1

LIST OF MATERIALS A ll-E tc h (10% p h o s p h o ric a c id s e m ig e l e t c h a n t ) U n i- E tc h (32% p h o s p h o ric acid, se m ig e l

M A T E R IA L S A N D M ETHODS

Sixty extracted hum an m olars were selected for th is study. They were free of obvious

e t c h a n t) P r i m e r A. ( b a tc h 129161) P r i m e r B ( b a tc h 129171) D e n tin - e n a m e l bond, ( b a tc h 12 9 09 1 )

glycidylm ethacrylate)/acetone and P rim er B is BPDM (biphenyl dim ethacrylate)/ acetone (Table 1). The teeth were divided into th re e equal groups and were treated in the following m anner: ■■ Group 1. The sm ear layer was not removed. Dentin surfaces in 10 teeth were airdried for 3 seconds w ith the tip of the a ir syringe about 3 centim eters from the tooth surface. A drop each of Prim er A and Prim er B were mixed together in a well. The prim er m ixture was applied to the dentin surface in a m inim um of five consecutive coats. The surfaces were not dried between coats. Each application was able to spread out on the surface before the next was made. After the fifth application, the prim ed surface rem ained undisturbed for 5 seconds and then was airdried for 5 seconds. A layer of the dentin-enam el unfilled bonding resin (Bisco) was applied to the prim ed surface, air-thinned for 1 to 2 seconds and light-polymerized for 20 seconds w ith a Dem etron 401 light-curing u n it (Demetron Research). A Teflon mold 2.5 m illim eters thick w ith a cylindrical m atrix 4 mm in diam eter was then clam ped to the embedded tooth so th a t the m atrix was over the treated dentin. The m atrix was filled w ith a single increm ent of All­ purpose composite (universal shade, Bisco Dental), and the composite was light-activated for 40 seconds. On the second 10 teeth, the sm ear layer was rinsed but left visibly wet, or moist. The m oisture presence was obvious, I in th a t the dentin surface was

Figure 3. Cavity is prepared with light bur treatment to enhance retention.

Figure 4. Preparation is treated with semigel etchant and rinsed with air-water-

shiny w ith m oisture. A facial tissue was sprayed with airw ater until it was wet and wiped the surface of the sam ples, removing only the excess w ater. (For a patient, sim ply use a disposable brush to rew et the dentin surface should it become dry.) A drop each of Prim er A and B were mixed together in a well and applied to the wet dentin surface in a m inim um of five consecutive coats as described The prim ed surface was dried

and the dentin-enam el bond applied. Composite cylinders were bonded to the treated dentin surface. ™ Group 2. The dentin was treated with 10 percent phosphoric acid gel etchant (AllEtch, Bisco D ental Products) for 30 seconds and rinsed for 5 seconds w ith an air-w ater m ixture. On 10 teeth, the dentin was dried for 3 seconds w ith an a ir syringe a t full blast a t a distance of about 2 cm. On the rem aining 10 teeth, the JADA, Vol. 123, September 1992

37

Figure 5. M atte appearance of surface shows area too dry to be treated.

and dried. Prim er A and B and the bonding resin were applied as in group 3. Composite cylinders were applied as previously described. The m atrices were removed from the teeth and the sam ples were stored for 24 hours in w ater a t 37 C. Shear bond strength was m easured on an Instron m achine (Model no. 1123) w ith a crosshead speed of 5 m m /m inute and recorded. We used a sharp blade to shear the sam ples w ith the blade parallel and im m ediately adjacent to the bonded dentin surface. RESULTS

dentin was left w et as described in group 1. P rim er A and B and the dentin-enam el bonding resin were applied as described. It som etim es took more th an five coats of the Prim er A and B i m ixture to produce a glossy coating of dentin. We placed j enough applications of the A and B m ixture to achieve this appearance. Composite cylinders were bonded to the dentin surfaces as previously described. ™ Group 3. The dentin in this group was tre a te d with 32 percent phosphoric acid gel J etchant (Uni-Etch, Bisco Dental) for 20 seconds and rinsed for 5 seconds w ith an air-

The best results were obtained when the dentin was acidetched and the prim er m ixture applied to wet dentin surfaces (Table 2). The lowest bond strengths occurred when the prim er m ixture was applied to a dry sm ear layer. In all cases, we obtained higher bond strengths when the prim er m ixture was applied to a w et dentin surface. Failure modes were exam ined with a light microscope. In the 10 percent etch/wet and 32 percent etch/wet groups, all samples failed cohesively w ithin the body of th e dentin. In the 10 percent etch/dry and 32 percent etch/dry groups, four of 10 samples failed cohesively in the dentin. All sam ples bonded to a sm ear layer experienced SURFACE adhesive W ET failure CV CV M p a (S.D .) betw een the 8.8%; 46.3% 24.1 (2.1) resin and the 7.0% 21.4% 34.3 (2.4) sm ear layer. 4.4% 36.5 ( 1.6) 52.2% Two-way 15.0% ANOVA analysis of each of the

w ater m ixture. On 10 teeth, the dentin was dried for 3 seconds with an air syringe as in group 2. On the rem aining 10, we wiped the dentin w ith a wet tissue to remove only the excess w ater as in group 1. P rim er A and B and the dentin-enam el unfilled bonding resin were applied to the dentin as described in group 2. Composite cylinders were bonded to the sam ples as above. For a control group, 10 incisors were embedded in acrylic and ground to produce adequate enam el surface for bonding. The enam el was treated with the 32 percent etchant for 20 seconds, rinsed

TABLE 2

BONO STRENGTHS W ill VARIOUS SURFACE TREATMENTS DRY GROUP

3 2 0 g r i t sm ear- la y e r

11.7 (4.8)

10% H 3 P 0 4 3 0 s

24.3 (5.2)

32% H 3 P 0 4 2 0 s

2 0 .7 ( 10.8)

32% H 3 P 0 4 2 0 s ( e n a m e l)

3 1 .9 ( 4 .8 )

All g r o u p s N = 10. C V = c o e ffic ie n t o f v a r ia n c e .

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M p a (S .D .)

JADA, Vol. 123, September 1992

Figure 6. Preparation surface must be wet for higher bond strength.

Figure 7. Primers are applied directly on wet dentin.

groups (etch vs. no etch, wet vs. dry) shows th a t in each case the bond strength of m aterials was significantly higher to the wet th a n th e dry dentin surface (P