porcelain bonds

294

J. Dent. 1988;

16: 294-296

Short Communication

Effect of 6-month water storage on silane-treated resin/porcelain bonds A. N. Stokes, J. A. A. Hood* and B. G. Tidmarsh Department of Restorative Dentistry Dentistry, Donedin, New Zealand

and *Department

of Oral Biology, The University of Otago School of

KEY WORDS: Composite resin, Porcelain, Bonding

J. Dent

1988;

16: 294-296

(Received 21 March 1988;

reviewed 10 May 1988;

accepted 26 June 1988)

ABSTRACT Circular mesh brackets were bonded by means of a microfilled composite resin to porcelain discs, pretreated with one of two types of silane primer. Shear bond strength determinations were undertaken after 24 h and 6 months water storage. A prehydrolysed, single-component silane primer gave consistently high bond strengths, but a two-part, operator-activated silane primer was associated with substantially lowered bond strengths after 6 months.

INTRODUCTION

MATERIALS

There have been many studies evaluating techniques and products for porcelain repair. Jochen and Caputo (1977) and Wood et al. (1986) have shown that adhesion of resin to porcelain increases with increasing porcelain roughness. The effect of silane priming agents has been tested by several means, of which the shear bond test is the most clinically relevant. Using the test Eames et al. (1977) and Newburg and Pameijer (1978) have demonstrated that silane primers give substantial short-term enhancement of composite resin/porcelain bonds. Eames and Rogers (1979), evaluating Fusion (George Taub Products, Jersey City, NJ, USA) and Dent-Mat (Den-Mat, Inc, Santa Maria, CA, USA) showed an improvement in shear bond strength with both products after water storage for 1 year. Fusion had both the higher initial and final bond strengths. A recently introduced product, Scotchprime (3M Co, St Paul, MN, USA) is stated by the manufacturer to have a longer shelf-life and to provide a more effective longterm bond than other silane primers. It comprises a single bottle of ready activated solution. This study compared the 6-month shear bond strengths of porcelain/composite resin bonds enhanced by Fusion and Scotchprime silane primers.

New samples of all products were obtained and these were handled according to manufacturers’ directions. Forty 5 mm diameter Vita Dur-N porcelain discs (Vita Zahnfabrik, Sackingen, FRG) were fired, mounted in acrylic resin blocks, and ground flat using 240 grit silicon carbide paper. Aluminous porcelain was preferred to the feldspathic porcelain denture teeth favoured by other investigators, as Semmelman and Kulp (1968) showed that the type of porcelain had an influence on the porcelain/resin bond. The discs were washed ultrasonically, cleaned and dried, after which half were coated with Fusion and half with Scotchprime. After air drying Scotchbond (3M Co.) was applied to the latter group, and 3.5 mm diameter circular mesh orthodontic brackets (TP Laboratories, La Porte, IN, USA) were bonded using Silar (3M Co.) chemically cured composite resin. Excess resin was cleared so that the circumference of the brackets delineated the bonding area. After 24 h 10 Fusion-treated and 10 Scotchprimetreated samples were mounted in a jig enabling a shear force to be applied by the cross-head of a universal testing machine (Instron Ltd, High Wycombe, UK) at 1 mm/min (Fig. 1). The remaining samples were water-stored at room

0 1988 Buttewortb & Co Publishers Ltd. 0300-57 12/88/060294-03 %03@0

AND METHODS

Communication

Short

295

S.S. wire strop to fixed anchor on lnstron head I

\ acrylic plug porcelain

disc

orthodontic

bracket

bonding resin

brass housing for tapered

/

lnstron crosshead

Fig. 1. Shear bond test system stainless-steel

showing application strap on the orthodontic bracket.

of shear force by means

of a

temperature for 6 months, after which a similar shear test

procedure was undertaken. Fracture patterns were determined by direct observation with a 10X binocular microscope, and by scanning electron microscopy.

RESULTS The 24-h shear bond strengths were 13.2 -t 2.2 MPa (Fusion) and 14.0 f 1.1 MPa (Scotchprime). Corresponding 6-month data were 1.1 f O-6 MPa and 11-l -t l-0 MPa respectively. The difference between the 6-month figures for Fusion and Scotchprime was highly significant (P< 0.001). The 24-h samples failed cohesively in the resin, at the resin/bracket interface, or within the porcelain itself. There was no difference in the distribution of mode of failure between primer types. In the 6-month specimens all those treated with Fusion failed at the resin/porcelain interface whereas Scotchprime-treated bonds failed cohesively within the resin or at the resin/bracket interface (Fig. 2).

Fig.

2.

Fractured unaffected

An example of cohesive-adhesive resin; b, dish-shaped porcelain porcelain surface. x 25.

failure. fracture;

a, c,

DISCUSSION A previous study (Eames and Rogers, 1979) showed that the shear strength of the silane-treated resin/porcelain interface increased after 1 year’s water storage and that Fusion gave the highest shear bond strength. The results of this study differ in that while both Fusion- and Scotchprime-enhanced bonds became weaker with 6 months water storage, those associated with Fusion became clinically unacceptable while those associated with Scotchprime remained at a level not significantly different from the 24-h specimens. Culler et al. (1986) showed a correlation between the degree of hydrolysis of the silane coupling agent and

the bond strength of composite resin to silane-primed porcelain. As the 24-h bond strengths of the two commercial products were similar in the present study it is unlikely that the degree of hydrolysis of the silane at placement was a caustive factor for the decreased 6month bond strength of Fusion. Amore likely explanation is time-dependent bond failure. Silane primers are also used as coupling agents between the ceramic/glass filler particles and the resin matrix of

296

J. Dent. 1988; 16: No. 6

composite resin restorative materials (Bowen, 1963), and it is suggested that hydrolysis of the Si-0 bonds of the silane (Siklerhohn, 198 1) due to the ingress of water may be responsible for the time-dependent degradation of composite resin under clinical conditions (Bowen and Cleek, 1972; Sijderholm, 1981, 1983). As the degradation of bond strength noted in the present study is also time dependent it is likely that it is also occurring as a result of hydrolysis of the Si-0 bonds at the porcelain/silane interface. While no conclusion can be drawn as to the reasons for the difference in susceptibility between the products, it is possible that the permeability of the silane layer or its degree of polymerization may be involved. A major advantage of Scotchprime is that it is ready for immediate use as presented by the manufacturer. This eliminates the potential for operator error during activation, and the potential for waste inherent in the 2-week shelf-life of the mixed components of Fusion.

CONCLUSION Porcelain will continue to fracture in service, and products which enhance the adhesion of dental resins to prepared porcelain surfaces with the assurance of a continuing resin/porcelain bond have a useful place in clinical practice. This study suggests that the single-component silane primer Scotchprime is superior to the dual-

component Fusion with respect porcelain bond enhancement.

to long-term

resin/

References Bowen R L. (1963) Properties of silica-reinforced polymer for dental restorations. J. Am. Dent. Assoc. 66, 57-64. Bowen R L. and Cleek G. W. (1972) A new series of X-ray opaque reinforcing fillers for composite materials. J. Dent. Res. 51, 177-182.

Culler S. R, Kreuger D. D. and Joos R W. (1986) Investigation of silane priming solutions to repair fractured crowns. .I Dent. Res. (Special Issue) 65, (Abstr. 193),

191. Eames W. B. and Rogers L. B. (1979) Porcelain repairs: retention after one year. Oper. Dent. 4, 75-77. Eames W. B., Rogers L. B., Feller P. R et al. (1977) Bonding agents for repairing porcelain and gold: an evaluation. Oper. Dent. 2, 118-124. Jochen D. G. and Caputo A. A. (1977) Composite resin repair of porcelain denture teeth. .I Prosthet. Dent. 38, 673-679. Newburg R and Pameijer C. H. (1978) Composite resins bonded to porcelain with silane solution. J. Am. Dent. Assoc. 96,288-291.

Semmelman J. 0. and Kulp P. R (1968) Silane bonding porcelain teeth to acrylic. J. Am. Dent. Assoc. 76,69-73. Sbderhohn K. experimental Soderholm K. composites.

J. (1981) Degradation of glass tillers in composites. J. Dent. Res. 60, 1867-1875. J. (1983) Leaking of fillers in dental J. Dent. Res. 62, 126-130.

Wood D. P., Jordan R E., Way D. C. et al. (1986) Bonding to porcelain and gold. Am. J. Orthod. 89, 194-205.

Correspondence should be addressed to: Mr A. N. Stokes, Department of Restorative Dentistry, University of Otago School of Dentistry, PO Box 647, Dunedin, New Zealand.

Book Reviews The Acid Etch Retained Bridge. D. J. Eldridge. 32 min. 1987. Manchester, Manchester University TV. Videotape, f50 (individuals f35). The Cosmetic Treatment of Patients with Missing Anterior Teeth. D. H. Lewis, D. J. Eldridge and C. Asher. 33 min. 1987. Manchester, Manchester University TV. Videotape, f 50 (individuals f35). Despite the obvious appeal of videotapes to the hardpressed dental teacher, few seem willing to take the plunge, no doubt because it is both technically demanding and time-consuming. The two under review here have been made by members of the staff of Manchester University Dental Hospital in conjunction with the highly experienced university TV service whose previous credits include the Open University. The topics chosen are not unattractive and focus on the treatment of three different patients, all requiring cooperation between an orthodontist and a restorative dentist. The first concerns a patient with spaced upper anterior teeth. A fixed appliance is used to move the adjacent teeth so that a missing lateral incisor can be replaced by an acid-etch

retained bridge. In the second, the first part describes the treatment of a patient with a missing central incisor: following movement of the lateral with a fixed appliance, the tooth is built up in composite: in the second part, the patient has a peg lateral and after orthodontic alignment a cosmetic result is again achieved by the use of composite resin. The outcome is less satisfactory. In the first programme although the commentary stresses the importance of ensuring wide interproximal spaces for cleansing, the camera does not demonstrate them: further, and more damaging, the teeth are not isolated with rubber dam before the bridge is bonded. In both such is the rate of change in dentistry today that the authors apologize at the outset for the absence of masks and gloves. The commentary is spasmodic and the background sounds and asides by the operator to both the patient and DSA a distraction. Several of the sequences were tedious and would have been improved by judicious editing, particularly the prolonged finishing sequence in the first tape. Finally, it is not clear who constitutes the intended audience. S. L. Pearson