Australian Dental Journal, December, 1975 Volume 20, No. 6

Bases for gold inlays and crown restorations* Roland W. Bryant, M.D.S.(Syd.) Lecturer, Department of Operative Dentistry, University of Sydney AND

George Wing, M.D.S., D.D.Sc.(Syd.), F.A.C.D., F.R.A.C.D.S.

Associate Professor, Department of Operative Dentistry, University of Sydney

ABsnucr-Modified zinc oxide-eugenol and calcium hydroxide cements are frequently used as bases beneath restorations. Investigation reveals that the bond strength between different types of cement may be less than that between dif€erent consistencies of the same type of dental cement. In some clinical situations, the choice of the type of cement as a base forming material beneath inlays and crowns should be made bearing in mind the type of luting material to be used. (Received for publication February, 1975)

Introduction

In recent years, clinical dentists and research workers have displayed considerable concern for the health of the dental pulp, following restorative dental treatment. Attempts at maintaining a vital healthy pulp and reducing post operative pain have led to the introduction of many new and modified dental cements. Acceptance of quicksetting zinc oxide-eugenol and calcium hydroxide cements, as bases for amalgam restorations has led to an almost universal use of these materials by many operators, including the use of such materials as base forming materials for gold inlay and crown restorations. To eliminate completely the use of zinc phosphate cement, a more recent trend has been the development of

* This

research was suppoited by the University of Sydney Research Grant.

modified zinc oxide-eugenol cements and polycarboxylate or polyacrylate cements as luting agents, for the final cementation of inlays and crown restorations. The retention of a gold inlay or crown restoration depends on its frictional fit, the resistance and retention forms given to the cavity preparation, and the bonding of the luting agent to the cavity walls and the restoration. To provide adequate pulp protection, the application of a base material is frequently indicated in teeth to be restored subsequently, with a crown or an inlay. Although, ideally, the cavity walls should be sound dentine, in badly broken down teeth a considerable proportion of the prepared surface may be base forming cement. The aim of this investigation was to determine the strength of the bond between various cements used as luting agents and a number of base forming materials.

393

Australian Dental Journal, December, 1975 TABLE

1

Base forming materials and luting agents investigated and the proportions of powder and liquid employed Material

Base consistency

Luting consis(cncy

Manufacturer andlor Distributor

S. S. White Zinc Cement Improved

2.30 gm/O.S ml

l.lOgm/O.S ml

S. S. White Dental Mfg. Co.

Zinc oxide (1 yo zinc acetate-eugenol Kalsogen

2.25 g d 0 . S ml 2.70 gm/O.S ml

-

Opotow EBA Cement

One scoop of powder to four drops of liquid*

Fynal

One scoop of powder to eight drops of liquid

Durelon

Equal lengths of base and catalyst

-

1.10gm/O.S ml

1.10gm/0.5 ml

(G.B.) Ltd., London

Non commercial product A.D. International Ltd., London Surgident, Ltd., Los Angeles, Calif. L. D. Caulk Co., Milford, Del.; Toronto, Ont. L. D. Caulk Co., Milford, Del.; U.S.A. Espe Gmbh, Seefeld/ Oberbay, West Germany

2.50 p powder/0.5 ml liquid

1

cements. Fynal and Opotow are both intended I primarily as luting agents but some use is made

Fig. 1-Diagrammatic reprcscntation of completed cylindrical specimen in position for tsstins of diametral compressive strength: A, base consistency material; B, luting consistency material.

Experimental methods Table 1 lists the cementing materials studied. The materials included one zinc phosphate cement, S.S. mite Zinc Cement Improved, and two quick-setting zinc oxide-eugenol cements one of which, Kalsogen was a commercial product and the other was a non-commercial product. The powder of the non-commercial cement contained 99 per cent zinc oxide and 1 per cent zinc acetate crystals by weight. This powder was mixed with eugenol. Dycal, a calcium hydroxide cement, has found considerable favour with clinicians both because of its ease of manipulation and its palliative effects on the pulp and is representative of the quick-setting calcium hydroxide

of these materials as bases so they have been investigated in this category. Fynal may be considered as a typical resin reinforced zinc oxideeugenol cement, and Opotow is a zinc oxideeugenol EBA fortified cement. hrelon is a typical polycarboxylate cement. S.S. White Zinc Cement Improved, Fynal, Opotow and Durelon have been studied as both a base forming material and luting agent at consistencies considered to be clinically acceptable, for each purpose. Materials of base forming consistency were packed into a cylindrical mould (8mm high, 4mm diameter). The cylinders of base consistency cement were allowed to set for twenty-four hours. When set, the cylindrical specimens were ground in a longitudinal plane using 220 and 400 grade silicon carbide abrasive papers under a stream of running water, to produce a hemi-cylindrical specimen. The hemi-cylindrical specimens were replaced in the lubricated mould which was then filled with one of the materials of luting consistency. The completed cylindrical specimens were stored for one week at 37'C in an environment of 100 per cent humidity and tested for tensile strength using a diametral compression test as illustrated in Fig. 1, using a Hounsfield Tensometer*. * Tensometer Limited, Croydon.

England

394

Australian Dental Journal, December, 1975 TABLE 2

Tensile “Bond strengths” (diametral compression) between combinations of base forming materials and luting agents “Bond strength” kg/cm2 Base fonninn material

S. S. While Zinc Cement Improved 97 fa)

Zinc oxide (1% zinc acetate) -eugenol 25 fa)

KPLsogen 17 (a)

Opotow 73 (a)

Fynal 56 (a)

Dycal 28 (a)

Dudon 92(a)

bonding

No

No bonding

66 (1.0)

49 (3.9)

N? bonding

59 (3.8)

S. S. White Zinc Cement Improved 77 (b)

74(3.5)

2

Fynal 56 (b)

bonding

31 (1.8)

34(3.2)

**

38 (2.5)

30 (3.5)

43 (3.4)

3

Opotow 73 (b)

56 (3.2)

26 (2.5)

33 (3.5)

53 (3.2)

**

27 (2.8)

63 (4.2)

Durelon 92 (b)

*

No bonding

bonding

No

**

**

*

c)

E

a3

.-*c“

No

No

bonding

Standard deviation: figures in brackets of material at base forming consistency (b) Ultimate tensile strength of material at luting consistency * Valid test not possible because of bending. (See Fig. 2 and discussion) ** Not tested (a) Ultimate tens3e strength

Cylindrical specimens prepared from only base forming consistency or luting consistency material were tested so that a comparison could be made between the tensile strength of the base material, luting material, and the bond between these. In some specimens, after grinding the original base consistency cements and before the addition of the luting material, two thin layers of copal varnish were applied to the ground surface to investigate the influence of this material on the bond strength. Some ground surfaces were similarly coated liberally with free eugenol before the addition of the luting consistency cement.

Results Table 2 presents the results when different base forming materials and luting agents are combined. With seven combinations of base and luting materials there was n o bonding. These specimens separated during storage or during handling to place them in the Hounleld Tensometer for testing. From Table 2 it can be seen that zinc phosphate cement, used as a luting agent produced a high bond strength with base consistency zinc phosphate cement. A good bond is also exhibited between luting consistency zinc phosphate cement and Fynal and Opotow when these materials are used as base materials. No bonding was exhibited between luting consistency zinc phosphate cement

and the accelerated zinc oxide-eugenol cement or Kalsogen or Dycal. Fynal produced interesting results when used as a luting material. This material is primarily intended for the final cementation of inlays and crowns. It exhibits no bonding to set zinc phosphate cementing materials such as S.S. White Zinc Cement Improved, but does bond to other products including a Fynal base. The strength of each of these bonds is significantly lower than the bond between two consistencies of zinc phosphate cement. Opotow EBA Cement bonds well to itself, a zinc phosphate cement base and a polycarboxylate cement base. Like Fynal, however, the bond strength of Opotow with Kalsogen, Dycal and zinc oxide (1 per cent zinc acetate)-eugenol was considerably lower than the strength of the Opotow luting agent when a cylinder of this material was tested. Whereas Opotow has a tensile strength of approximately 73 kg/cmZ the bond strengths of Opotow to the Kalsogen, Dycal, and quicksetting zinc oxide-eugenol cement were in the range 26 to 33 kg/cm2. Durelon, typical of the polycarboxylate cements which were developed principally because of their ability to bond to tooth structure and highly favoured because of their compatibility with the pulp, exhibited variable properties of bonding to base forming materials. No bonding was exhibited

Australian Dental Journal, December, 1975

395 TABLE 3

The effect of c o p 1 varnish on the bonding between luting consistency zinc phosphate cement and two materials of base forming consislency ~

Base forming material

“Bond strength” kglcm2 No coml varnish Copal varnish

S. S. White Zinc Cement Improved

74 (3.5)

0

Zinc oxide (1% zinc acetate)-eugenol

0

0

Standard deviation: figures in brackets

TABLE 4

The effect of surface eugenol on the “Bond strength” between base consistency zinc phosphate cement and luting consistency zinc DhosDhate cement No eugenol

S. S. White Zinc Cement Improved

74 (3.5)

“Bond strength” kglcm2 Eugenol

76 (4.8)

Standard deviation: figures in brackets

Fig. 2 . 4 m week specimen showing marked bending and n o apparent separation of: A , zinc phosphate base material (showing cracks); B, Dunlon luting agent. Magnification X 12.5.

between Durelon and either of the quick setting zinc oxide-eugenol cements, or Dycal, Fynal or w o w . Shrinkage of the Durelon, with the characteristic behaviour of this material to bend on setting, caused fracture and bending of the set zinc phosphate portion of the cylinder without obvious separation of the two materials (Fig. 2). This bending invalidated testing of the specimens for “bond strength”. A similar although slightly less marked fracturing and bending occurred of the previously set portion of a cylinder composed of Durelon as base forming material and luting agent.

Table 3 shows the effect of coating base materials with copal varnish before the addition of luting consistency zinc phosphate cement. Where a zinc oxide (1 per cent zinc acetate)eugenol cement was used as a base no bonding occurred with or without copal varnish. The application of copal varnish to the zinc phosphate base material inhibited the previously good bonding. Specimens where copal varnish was used, fell apart after one week’s storage. It has been suggested by interested colleagues that the lack of bonding between luting consistency zinc phosphate cement and quick-setting zinc oxide-eugenol base material may be due to the presence of free eugenol. When eugenol was applied to the surface of base forming consistency zinc phosphate cement, so that a generous amount of this oily substance was present during the addition of the luting consistency zinc phosphate cement, there was no reduction in the bond strength v a b l e 4). Conclusions As a result of this investigation, it is possible to offer recommendations regarding the selection of base materials for clinical use in gold inlay and crown restorations. A luting agent of zinc phosphate cement is indicated when use is made of a zinc phosphate base forming material and it is intended to utilise the base in helping to retain the crown or inlay.

3 96

Ideally retention should be obtained by long, nearly parallel walls of sound dentine, but practically this is not always possible. In preparations, where the depth of the cavity necessitates the use of a zinc oxide-eugenol or calcium hydroxide material for pulp protection, this material should be covered by a zinc phosphate cement preferably retained by undercuts in the cavity walls. Cementation of the restoration should then be effected using zinc phosphate cement. It is difficult to understand why no bonding takes place between thin zinc phosphate cement with free phosphoric acid present, and zinc oxideeugenol type materials in which unreacted zinc oxide should be present. When a polycarboxylate cement was used as the luting agent, no bonding took place to the zinc oxide-eugenol and calcium hydroxide types of materials. The occurrence of fracture lines and bending of the cylindrical specimen when

Australian Dental Journal, December, 1975 the previously set material was a zinc phosphate or polycarboxylate cement was probably indicative of good bonding between these materials. The clinical relevance, of the bending of the set base forming material, to the clinical situation is not known. The use of a copal resin varnish prior to cementation will normally result in some loss of retention, probably due to the elimination of surface irregularities in the base forming material. It is likely that a similar mechanism may reduce retention when copal resin varnish is applied to dentine, prior to cementation. The benefit provided by the copal varnish, in the form of pulp protection, may outweigh the resultant loss of retention. Department of Operative Dentistry, University of Sydney, 2 Chalmers Street, Surry Hills, N.S.W., 2010.

Bases for gold inlays and crown restorations.

Australian Dental Journal, December, 1975 Volume 20, No. 6 Bases for gold inlays and crown restorations* Roland W. Bryant, M.D.S.(Syd.) Lecturer, Dep...
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