Joumal of Oral Rehabilitation, 1992, Volume 19, pages 319-327

Influence of porcelain material and composite luting resin on microleakage of porcelain laminate veneers A. ZAIMOGLU, L. KARAAGAgLIOGLU Department of Prosthodontics, Faculty of Dentistry, University of Ankara, Turkey


The microleakage beneath porcelain laminate veneers was investigated. The restoration margins were located according to the preparations made below or above CEJ of extracted maxillary central incisors. Vitadur N and Microbond porcelain materials were used to prepare laminate veneers. A light cured composite resin (Porcelite®) and a light- and chemical-cured composite resin (Porcelite Dual Cure®) were used as luting agents. The bonded specimens were thermocycled and by employing the standard dye penetration technique, the leakage was scored from cervical and incisal margins. Significantly greater microleakage was recorded at the dentine composite resin interfaces than at the enamel/composite interfaces. Statistically insignificant differences were observed with the use of the four cement/porcelain combinations studied. Introduction

The laminate veneer technique restores tooth morphology and aesthetics by bonding a thin veneer of tooth-coloured material to the labial surface of a tooth. Glazed porcelain which is used in this technique, is non-porous, resists the accumulation of debris, and is tolerated better by the soft tissues than by any other dental material. These veneers are indicated for masking discolorations and labial irregularities, for closing diastemas, for restoring fractured teeth and for contour modification of abutment teeth in removable prosthodontics (Horn, 1983). It is known that, there is a difference of thermal conductivity between tooth structure and dental restoration (Craig, 1989). This difference becomes evident between tooth structure and composite resin used to bond laminate veneers to acid-etched enamel when the teeth are exposed to temperature changes because of cold or hot beverages and food (Tjan et al.., 1989). As a result and with the addition of curing shrinkage of luting resin material some degree of microleakage can be observed at the cavosurface margins which contribute to staining, adverse pulpal response, post-operative sensitivity, and recurrent caries (Crim and Garcia-Godoy, 1987; Tjan et al.. 1989). The porcelain materials used in laminate veneers differ in handling procedures. In the past they were fired on platinum foil and this caused inaccuracy in marginal integrity. An alternative method which improves accuracy is to fire the porcelain against a tooth die made with porcelain inlay investment. The inside of laminate is Correspondence: Dr L. Karaagaflioglu, Yukari Ayranci. Ho§dere Cad. 75(79), B/I Ankara, Turkey.



A. Zaimoglu et al.

first acid-etched to create microporosities for mechanical bonding. Then, a silanization procedure takes place for chemical bonding between porcelain and the luting resin (Calamia, 1985; Lee et al., 1986). The composite resins used for bonding of porcelain laminate veneers are generally supplied as two pastes., powder and liquid, or as a single paste. The paste-paste systems are chemically initiated and the powder-liquid systems are primarily chemically initiated but can also be photoinitiated. If both initiators are present in the same material, they are said to possess an infinite depth of cure. The single paste systems are all photoinitiated (Craig, 1989). The main advantage for using a photoactivated product is a prolonged working time and a possibility of modification according to clinical requirements. In recent years, these easy handling properties rendered these resins popular in bonding porcelain laminate veneers to tooth structures (Horn, 1983). Photoactivated materials contain a light-sensitive absorber such as camphorquinone and an accelerator such as an aliphatic amine. The camphorquinone is activated by visible blue light with the wave length of 450nm (Phillips, 1982; Craig, 1989). The light cured composite resins for bonding porcelain laminate veneers are hybrid resins which consist of an optimal amount of glass and silicate fillers 3-0—0-5 um in diameter. The physical properties of this hybrid light-cured resin include a superior coefficient of thermal expansion, low water sorption, and a surface smoothness similar to microfil composite resins (Hobo and Iwata, 1985). The purpose of this study was to evaluate the microleakage of two conventional porcelain laminate veneers bonded on the labial surface of maxillary central incisors with cervical margins either above or below the CEJ. The effectiveness of a light cured and a dual cured composite luting resin on microleakage was also investigated. Materials and methods

A total of 40 caries- and defect-free extracted human maxillary central incisors were used in this investigation. On the labial side of the incisors two types of preparations which include a slight chamfer (approximately 0-5 mm deep) one in enamel 0-5 mm. above the CEJ {n: 20) and the other in root dentine 0-5 mm below the junction (n: 20) were cut. The mesio and disto proximal borders of the preparation were stopped at the contact areas. A 0-5 mm incisal reduction was applied to form a slight incisal overlap (Fig. 1). The teeth were divided into eight experimental groups each of five restorations (Table 1). In this investigation, two conventional porcelain materials were used. These are Vitadur N* which contains alumina crystals, and feldspathic porcelain containing leucite crystals, Microbond natural ceramict. The composite luting resins used in this investigation were: (1) Porcelitet, a single paste light activated resin; (2) a paste/ paste, light and chemically activated hybrid resin, Porcelite Dual Cure$. As a light curing unit, Optilux 50§ was used. After the impressions of the preparations were taken using a silicone impression material^, the refractory dies were prepared using the die material provided with each porcelain kit. The teeth were stored in distilled water at 37°C in individual containers until the cementation of the restorations. Following standardized laboratory pro* Vita Zahnfabrik, Bad Sackingen, Germany. X Kerr/Sybron. Romulus. Ml, U.S.A. t Austcnal Dental hic, Switzerland. § Demetron Researeh Corp; U.S.A. H Coltex fine, Coltene AG, Altstatten, Switzerland.

Microleakage of porcelain laminate veneers



Fig. 1. The two positions of porcelain laminate veneers. Table 1. Experimental groups and restorative procedures

Experimental groups A B C D E F G H

n 5

5 5

5 5 5 5 5

Cervical margin

Eaminatc veneer material

Composite luting resin

Above Above Above Above Below Below Below Below

Vitadur N Vitadur N Microbond Microbond Vitadur N Vitadur N Microbond Microbond

Porcclitc Porcclitc Porcclitc Porcelitc Porcclitc Porcclitc Porcclite Porcclitc


Dual Cure Dual Cure Dual Cure Dual Cure

cedures, the porcelain laminate veneers were fired and glazed on dies. The internal surfaces of the veneers were etehed by means of 60s application of an acidic solution containing 10% hydrofluoric acid in the laboratory. Kerr Command etchant which contains phosporic acid was applied to the fit surface of the laminate veneers and left intact for 60s. Since its function was to acidify the surface, it was not rinsed off. Porcelain Primer* was then applied to the same surface and left for 60s; it was then washed and thoroughly dried. The enamel surfaces of all the preparations were etched with a 37% phosphoric acid etchant for 60s, they were then washed and thoroughly dried. Bondlite*, a Kerr/Sybron. Romulus, MI. U.S.A.


A. Zaimoglu et al.

dentine/enamel bonding agent was applied as a thin layer to dentine and etched enamel surfaces. It was light cured for 10 s. Veneers were cemented using either Porcelite light-cured cement or Porcelite Dual Cure. In groups where the luting agent was Porcelite Dual Cure, equal amounts of catalyst and base cement were mixed and applied to the fit surface of laminate veneers. After they were seated individually, excess resin was removed from the margins with a brush tip. The resin was light polymerized using four 30-s-light applications. The light guide tip was placed over the incisal area of the restorations for the first 30 s and then directed from cervical, mesial and distal surfaces for 30s each. The completed restorations were checked for deficiencies and polished using burs, rubber wheels and polishing paste. The bonded specimens were stored in distilled water at 37°C for 14 days. These were then sealed with two coats of nail varnish to within 1 mm of the restorations to limit dye penetrations to the margins and then subjected to 100 temperature cycles. A cycle consisted of 15 s at 37°C, 15 s at 5°C, 15 s at 37°C and 15 s at 55°C. After this procedure the teeth were placed in an aqueous solution of basic fuchsin dye (0-5%) for 24h. The teeth were retrieved, the varnish was removed, and the teeth were lightly pumiced to remove superficial dye. Each tooth was sectioned longitudinally in a buccolingual direction through the center of the restorations. The microleakage was evaluated at the following four interfaces (i) cervical tooth/ composite resin interface; (ii) cervical porcelain/composite resin interface; (iii) incisal enamel/composite resin interface; and (iv) incisal porcelain/composite resin interface (Tjan et al., 1989). Microleakage was scored (Fig. 2) under a stereomicroscope (Wild M3Z Stereozoom Microscope)*, at x40 magnification. Two examiners scored the specimens independently and the scores were compared and common score was achieved. Mean scores were calculated for each group and statistically analyzed. Results

Mean marginal leakage scores and standard errors of the four interface sites of each veneer with cervical margin above CEJ are presented in Table 2; those with cervical margin below CEJ are present in Table 3. After square root transformation V^ + ^'^- the data of the investigation was analyzed in factorial order by analysis of variance (ANOVA). According to Table 2, statistical analysis indicated no significant difference in microleakage for Vitadur N and Microbond porcelain laminate veneers with any of the two kinds of composite luting resin tested. Likewise, no significant differences in microleakage at the four interface sites were found among groups E, F, G, and H (Table 3), however, significantly greater microleakage was recorded at the dentine/ composite interface sites than at the enamel/composite ones at F < 0-01. (Figs 3 and 4). Discussion

Marginal leakage is an important factor that risks the longevity of dental restorations. This concerns not only percolation of fluids but also the invasion by a variety of molecules, ions, enzymes, acids and bacteria. The bonding of porcelain laminate veneers to tooth substrates by using composite * Wild Heerbrugg Ltd, Heerbrugg, Switzerland.

Microleakage of porcelain laminate veneers


Porcelain laminate veneer

Composite luting agent

Fig. 2. Marginal leakage scoring diagram.

Table 2. Mean leakage scores of laminate vcnccrs with ccr\ ical margin above CEJ Experimental group A B C D

5 5 5 5

Interface 1 (X±Sx)

Interface 2 (X±Sx)

Interface 3 (X±Sx)

Interface 4 (X±Sx)

0-50 0-60 0-50 0-30

()•(»() ± 0-00 0-10 ±0-10 O-OO ± 0-00

0-00 ± 0-00 0-00 ± 0-(X) 0-10±0-10 0 20 ±0-12

0-00 ± 0-00 0-00 ±0-00 0-(X) ± 0-00 0-20 ±0-12

±0-16 ±0-19 ± 0-22 ±0-16


Interfaces: 1: Cervical enamel/composite resin; 2; Cervical porcelain/composite resin; 3; Incisal cnamel/compositc resin; 4; Incisal porcelain/composite resin.

Table 3. Mean leakage scores of laminate veneers with cervical margin below CEJ Interface 1 (X±Sx)

Interface 2 (X±Sx)

Interface 3 (X ± Sx)

Interface 4 (X±Sx)


1-40 1-70 1-80 1-60

0 -00 ± 0-(K) 0 -00 ± 0-CXJ 0 -10 ± 0 - 1 0 0-20 ± 0 - 1 2

0-20 0-00 0-0(J 0-00

0-20 ± 0 - 1 2 O-(XJ ± 0-00 OCX) ± 0-00 0-00 ± 0-(X)


Experimental group

3 3 3

±0-24 ±0-37 ±0-20 ±0-24

±0-12 ± 0-CXJ ±0-00 ±0-00

Interfaces; 1; Cervical dentine/composite resin; 2; Cervical porcelain/composite resin; 3; Incisal enamel/composite resin; 4; Incisal porcelain/composite resin.


A. Zaimoglu et al.

Fig. 3. Porcelain laminate veneer (Microbond) with cervical margin above CEJ. (Composite luting resin: Porcclitc Dual Cure)

Fig. 4. Ecakagc at cervical dcntinc/compositc interface in Vitadur N porcelain laminate veneer bonded with Porcclitc.

resin cement produces two bonded interfaces, one between the tooth and the composite, and the other between the porcelain and the composite resin (Tjan et aL, 1989). High polymerization shrinkage and thermal dimensional changes of composite resin cause an interfacial gap to form along margins of restoration (Craig, 1989; Tjan

Microleakage of porcelain laminate veneers


et al., 1989). With the addition of 50% volume of inorganic phase and the use of the higher molecular weight BIS-GMA oligomer, the volumetric dimensional change of composite resin during polymerization is 1 — 1-7%. This shrinkage creates tensile stresses as high as 13MPa at the interface between resin and tooth. Thermal stresses place an additional strain on the acid-etched bond, which further compounds the detrimental effect of the polymerization contraction. Thermal changes are also cyclic in nature and their effect can lead to material fatigue and early bond failure (Craig, 1989). These properties are also effective at the interface between composite and porcelain laminate veneer. A competition may always occur between the adhesive forces of the two bonded interfaces. As a result, it is logical that the weaker link may break (Tjan et al., 1989). As seen in our results, at the cervical margin (especially below CEJ), the leakage was more than the leakage at the incisal margin. This supports the opinion of different authors about poor bonding at this margin (Fayyad and Shortall, 1987; Shortall et al., 1989; Tjan et al., 1989). In specimens with cervical margins above the CEJ, the reason for this failure is the deviation in the orientation of enamel prisms and also the thin enamel at this part of a tooth. When the cervical margin lies on root dentine, the problem of leakage becomes more prominent. The bonding of composite to dentine by acid etching, as is done with enamel, is not recommended (Craig, 1989). 30% of dentine is composed of low surface energy protein, and its tubule-like structure has a flow of protein aqueous fluid. Thus, retention cannot be effectively developed by acid etching dentine and by placing a low viscosity resin to penetrate the tubules (Falian et al., 1989). In addition, because the dentine tubules extend to the dental pulp, with acid etching, there is a possibility of damaging pulpal health. For this reason, there is a need to use an agent which reacts chemically with the organic and inorganic components of dentine, or with a combination of both element and with composite material (Asmussen and Munksgaard, 1988). But according to Craig (1989) despite the significant advances the dentine bonding agents produce moderate bonds between dentine and composite and higher bonds between enamel and composites, but the magnitude of even the best is not enough to eliminate marginal leakage as a result of the polymerization shrinkage of the composite. Light cure had great advantages, but one disadvantage had to do with being able to cure deep areas or areas that the curing light could not easily reach. It is known that incomplete polymerization of composite resin can damage the pulp and lead to inadequate retention. The degree of polymerization of the composite luting cements may be influenced by the porcelain material placed between the curing light and the resin (Blackman et al., 1990). Because the porcelain absorbs 40-50% of the radiation (Strang et al., 1987), the thickness, shade and opacity of porcelain laminate veneer are important factors for curing the composite luting agent. In our investigation, the thickness of the laminate veneers were held between 0-5—0-8 mm which were claimed to be the optimal thickness for these restorations (Hobo and Iwata, 1985). The shade of laminates was also standardized (Vita Lumin A3 porcelain shade). But, because of the use of two different porcelains one of which is a feldspathic porcelain with leucyte crystals and the other with alumina crystals, the opacity levels of porcelain laminate veneers may be different. In spite of this difference, the leakage values beneath laminate veneers were found to be similar. This result is in accordance with the results of the study by Linden et al. (1990) in which it is stated that unlike thickness and shade, porcelain opacity level has little effect on polymerization of the com-


A. Zaimoglu et al.

posite resin cement. However, further studies are suggested to determine the leakage values with the use of porcelain laminate veneers having different thicknesses and shades, and also composite luting agents having different shades. In our investigation, two different cured composite luting agents were used. When a composite material requires the mixing of two components, typically 2 - 5 % porosity is inevitable. The porosity is introduced during mixing. The non-porous products have a higher fatigue limit and longer fatigue life than the porous ones. This may have some bearing on the durability of materials in certain applications (McCabe, 1990). Strang etal. (1987) found also that a visible light-curing resin cement performed better than a light- and chemical-curing (dual curing) resin. In the light of these opinions and our results, we suggest that the single paste system, Porcelite, seems to be more advantageous than the two paste system for bonding porcelain laminate veneers. Conclusions

Results of the study indicated the following: (i)

A greater microleakage was observed at tooth/composite resin interface, when the cervical margins were located below CEJ. (ii) Similar leakage patterns were observed at the tooth/composite interface when light- and dual-cured luting agents were used. (iii) Because of the easy handling and the non-porous structure of light-cured material, the use of this material for bonding laminate veneers is suggested, (iv) Regarding the leakage scores beneath all porcelain laminate veneers, it can be said that the two porcelain materials used are satisfactory for these restorations.

References AsMUSSBN, E. & MuNKSGAARD. E.C. (1988) Bonding of restorative resins to dentine: Status of dentine adhesives and impact on cavity design and filling techniques. International Dental Journal. 38, 97. BLACKMAN, R . , BARGHI. N . & DUKH. E . (1990) Influence of ceramic thickness on the polymerization of light cured resin cement. Journal of Prosthetic Dentistry, 63. 295. CALAMIA. J . R . (1985) Etched porcelain veneers: the current state of the art. Qmntessence International,


R.G. (1989) Restorative Dental Materials, 8th edn. p. 255. CV Mosby Company. St Louis. CRIM, G . A . & GARCIA Godov. F. (1987) Microleakage; The effeet of storage and eyeling duration. Journal of Prosthetic Dentistry, 57. 574. FAUAN, H . , DEXIN, Z . & WEIZHONG. J. (1989) Bonding of resinous filling materials to acid-etched teeth: a scanning electron microseobie observation. Quintessence International, 20. 27. FAYYAD, M . A . &. SHORTAI,L. A.C. (1987) Microleakage of dentine-bonded posterior composite restorations. Journal of Dentisty, 15, 67. HOBO, S. & \wata, T. (1985) A new laminate veneer technique using a eastable apatite ceramic material. II: Practical procedures. Quintesence International, 16. 509. HORN, H . R . (1983) Porcelain laminate veneers bonded to etched enamel. Dental Clinics of North Ameriea, 27, 671. LEE, J.G., MOORE, B.K.. AVERY, D.R., & HOVUITRA, T . S . (1986) Bonding strengths of etched porcelain discs and three different bonding agents. Journal of Dcnttstry for Children, 6, 409. LINDEN, J.J., Swin, E.J. & DAVIS, B . K . (1990) Effect of porcelain opacity on curing of composite resin cements. Journal of Dental Research, 29 (Abstract No. 806), 209. MccABE, J.F. (1990) Applied Dental Materials, 7th edn, p. 157. Blaekwell Scientific Publications, Oxford. PHILLIPS, R.W. (1982) Skinner's Science of Dental Materials, 8th edn, p. 216. W.B. Saundcrs Company, Philadelphia.


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R.L., BAYLIS, M . A . & GRUNDY, J . R . (1989) Marginal seal comparisons between resin-bonded class II porcelain inlays, posterior composite restorations and direct composite resin inlay. Internaiional Journal of Prosthodontics, 2. 217. STRANG, R . , MCCROSSON, J., MUIRHKAD, G . M . & RICHARDSON, S.A. (1987) The setting of visible-lightcured resins beneath etched porcelain veneers. British Dental Journal. 163, 149. TJAN, A.H.L., DUNN, J.R. & SANDERSON, I . R . (1989) Microleakage patterns of porcelain and castable ceramic laminate veneers. Journal of Prosthetic Dentistry., 61, 276.


Influence of porcelain material and composite luting resin on microleakage of porcelain laminate veneers.

The microleakage beneath porcelain laminate veneers was investigated. The restoration margins were located according to the preparations made below or...
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