Influence of resin cement viscosity on m

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In¯uence of resin cement viscosity on microleakage of ceramic inlays

P. Hahn*, T. Attin

1

, M. GroÈfke, E. Hellwig

Department of Operative Dentistry and Periodontology, Dental Clinic, University of Freiburg, Hugstetterstrasse 55, 79106 Freiburg, Germany

Received 16 September 1999; revised 10 May 2000; accepted 1 June 2000

Abstract

Objectives.The aim of the present investigation was to evaluate the effect of the different viscosities of two resin luting cements on microleakage of ceramic inlays at dentinal margins. The effect of the width of the space between inlay and tooth, on the quality of the marginal seal was also investigated.

Methods.Mesial and distal class V cavities were prepared in 48 extracted third molars. The incisal margins of the cavities were in enamel and the cervical margins in dentin. Subsequently, Empresse_{inlays with different cervical margin gap dimensions were fabricated. The mean}

cervical gap dimensions in the respective groups were as follows: group 1 (27mm); group 2 (232mm); group 3 (406mm). Half the inlays in

each group (16) were cemented with a low viscous resin luting cement, and half (16) with a highly viscous resin luting cement. The teeth were subjected to occlusal loading with synchronized thermal cycling in a masticatory simulator. Then, the specimens were immersed in basic fuchsin solution, and dye penetration along the cavity walls was measured. In addition, marginal adaptation was analyzed in the SEM at baseline and after loading, using a replica technique.

Results.With regard to dye penetration at dentinal margins, the highly viscous cement performed statistically signi®cantly better at dentin/ composite margins than the low viscous cementp0:0158:These ®ndings are supported by SEM analysis.

Signi®cance.It is assumed that polymerization stress within the luting cement could not be completely compensated for by larger luting spaces. Highly viscous luting cements are recommended for cementing class V inlays in larger luting spaces.q_{2001 Academy of Dental}

Keywords: Viscosity; Microleakage; Ceramic inlay

1. Introduction

Composite restorative materials undergo signi®cant volu-metric shrinkage when polymerized [1]. It has been suggested that this property leads to poor margin quality in composite restorations. Various techniques have been recommended to compensate for this shortcoming, for example, acid etching and incremental technique, or the use of inlay restorations instead of direct composite ®llings [2]. Ceramic inlays are adhesively cemented using composite materials. It has been claimed that a small volume of luting composite is desirable [3] in order to reduce stress formation caused by polymeriza-tion shrinkage of the luting material [4]. However, it has also been stated [5±8] that the narrower the luting space is, the more polymerization stress occurs, due to shrinkage of the material. This stress is increased when the cavity design

shows an unfavorable con®guration factor (C-factor). With respect to adhesively cemented ceramic inlays it is important to note that the C-factor of cavities prepared for ceramic inlays is high, i.e. unfavorable [7].

Shrinkage of composite materials also depends on their composition and viscosity [9,10]. Moreover, composites with a low viscosity show better ¯ow properties thereby reducing the stress created within the material during early setting [5]. However, the opportunity for ¯ow in light cured composites is small as the material hardens quickly when exposed to the polymerization light [11]. Additionally, light polymerization is initiated at the surface of the restoration. This further prevents ¯ow of the compo-site material at the surface and prevents this portion of the ®lling from acting as a source of stress relief for deeper composite layers during polymerization [12].

To date, no adhesive technique is available which results in predictably good marginal adaptation, when margins of the restoration are located cervical to the dentin±enamel junction [13±15]. Taking the above-mentioned aspects into consideration, it is conceivable that larger luting spaces and low viscosity luting cements may improve the quality of Dental Materials 17 (2001) 191±196

dental

materials

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* Corresponding author. Tel.:149-761-270-4756; fax:149-761-270-4762.

E-mail address:hahn@zmk2.ukl.uni-freiburg.de (P. Hahn).

1 _{New address: Department of Operative and Preventive Dentistry,}

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ceramic inlay restorations at dentinal margins by producing lower stress contractions. The objective of the present study was, therefore, to investigate the in¯uence of two luting cements with different viscosities and various luting space dimensions on adaptation of ceramic inlays at dentinal margins.

2. Materials and methods

Forty-eight extracted caries free third molars of compar-able dimension were selected for the experiments. The teeth were cleaned, using scalers and rotating brushes to comple-tely remove soft tissue remnants, and stored in Ringer's solution (Delta-Pharma, Pfullingen, Germany). The teeth were then randomly divided into three groups. Each tooth was ®xed in a custom-made specimen holder. Box-shaped non-beveled class V cavities were prepared in the mesial and distal aspects of each tooth, using a 6-degree conical diamond bur (30mm, No.: 8959KR.314.016, Gebr.Brasse-ler, Lemgo, Germany) in a high-speed handpiece with air± water spray. The bur was renewed after 16 preparations. The preparation extended incisally to enamel and cervically to dentin. Standardization of the cavity size was accomplished by ®xing the handpiece in a parallelometer during prepara-tion. The handpiece was carried along using a template with the corresponding preparation form. The cavity had an asymmetric design, which ensured correct positioning of the inlay after fabrication with different cervical luting spaces (Fig. 1). Subsequently, Empresse inlays were produced using plaster casts and the lost wax technique. In group 1, the control group, Empresseinlays were fabri-cated according to the manufacturer's instructions. In order to reproduce the dentinal margin gap in the remaining groups, tin foil was placed at the cervical cavity wall before wax modulation. The thickness of the tin foil (Fino, DT Dental Trading, Bad Kissingen, Germany) used in group 2 amounted to 200mm and in group 3 to 400mm. The remain-ing fabrication steps were in accordance with group 1.

Before luting, the ®t of the inlays was checked by measur-ing the discrepancy between cavity wall and inlay usmeasur-ing a light microscope (40£, Zeiss, Oberkochen, Germany). Measurements were performed at three locations along the enamel margins. Five measurements were taken at dentinal margins (Fig. 1).

Prior to cementation, the ceramic inlays were etched with 10% ammonium hydrogen di¯uoride (Biodent Retention Gelw, DeTrey Dentsply, Dreieich, Germany) and silanised (Monobond Sw, Vivadent, Schaan, Liechtenstein). The enamel margins of the cavities were etched with phosphoric acid for 60 s (DeTrey Conditioner 36w, DeTrey Dentsply, Dreieich, Germany). Afterwards, dentin was treated with the dentin bonding agent Syntac classicw (Vivadent, Schaan, Liechtenstein) according to the manufacturer's instructions. A thin layer of the un®lled resin (Heliobondw, Vivadent, Ellwangen, Germany) was then applied to dentin,

enamel and the bottom of the inlays. In each group 16 inlays were cemented into 8 teeth with a low viscous composite luting cement (Variolink IIw, Vivadent, Schaan, Liechten-stein) and 16 inlays into 8 teeth with a highly viscous composite luting cement (Variolink ultraw, Vivadent, Schaan, Liechtenstein). The inlays ®xed with the low viscous cement were positioned conventionally by ®nger pressure only, while the inlays luted with the highly viscous cement were inserted using an ultrasonic insertion technique [16]. Excess highly viscous cement was removed with scalers, and low viscous material with foam pellets. In order to avoid oxygen inhibition, glycerin gel was applied to the margins. The luting cement was then light cured for 60 s from the inlay surface. The margins of the restorations were ®nished and polished using ®nishing diamonds (Gebr.-Brasseler, Lemgo, Germany) and ¯exible discs of decreas-ing grain (So¯ex discs, 3M Dental Products, St. Paul, USA). The materials used in this study are listed in Table 1.

After the inlays were placed, teeth were subjected to arti-®cial aging by exposing them to a chewing simulator (Kausimulator N6C41/N6W26, Willytec, Munich, Germany). This simulator mimics occlusal loading and ther-mal cycling simultaneously. The device is more precisely speci®ed by Kern et al. [17]. The loading procedure comprised 120 000 cycles with 100 N (frequency 1.6 Hz). The parameters of the 520 thermal cycles were: 60 s at either 5 or 558C, with 12 s break in between. After arti®cial aging, the specimens were stored in Ringer's solution for nine months.

A quantitative scanning electron microscope (SEM) analysis of margin adaptation at the restoration surface was carried out [18]. For this purpose epoxy resin replicas of the cemented inlays were fabricated before and after processing in the chewing simulator, and after water storage, respectively. The margins were evaluated in incre-ments of 200mm each at 100£ magni®cation. The inter-faces between ceramic and luting composite, and between luting composite and dentin were evaluated separately. A clearly visible loss of adhesion was described as a gap and expressed as a percentage of the entire length of the eval-uated interface.

P. Hahn et al. / Dental Materials 17 (2001) 191±196

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For dye penetration analysis, tooth surfaces (except for the area of the restoration) were covered with nail varnish. Specimens were immersed in 0.5% basic fuchsin solution, at 378C for 24 h. Then, the teeth were embedded in acrylic resin (Technovit 4071, Heraeus Kulzer, Hanau, Germany) and bisected bucco-orally resulting in two halves containing one inlay each. These samples were sectioned twice mesio-distally using a band saw (EXAKT 300 CL, Exakt Appara-tebau GmbH, Germany). Cutting the specimens resulted in sections, which allowed for evaluation of dye penetration depths along the cavity walls. Thus, four interface sites per inlay were evaluated (Fig. 1). The extension of the dye penetration (inmm) was measured with a light microscope at 40_£ magni®cation (Zeiss, Oberkochen, Germany).

Analysis of variance (ANOVA) was used to detect differences between the experimental groups. Signi®cance was set at a level of a0:05. Luting space and luting composite material were chosen as ªinter-specimen factorsª for variables in the ANOVA test. Time of measurement (SEM analysis: before and after loading) and interface were regarded as ªintra-specimen factorsª. Repeated measures of ANOVA tested the hypothesis of effects between different variables. One way ANOVA and Kruskal Wallis tests were used to detect for differences at dentinal margins.

3. Results

The gap between inlay and enamel cavity margin prior to cementation was 47mm^8;In group 1 the dentin cavity margin gap was 27mm^8;in group 2 (with the 200mm

tin foil) the gap was 232mm^26and in group 3 (with the 400mm tin foil) the gap was 406mm^38:

3.1. Dye penetration analysis

The results of the dye penetration analysis (mm) are summarized in Fig. 2. The values are plotted separately with regard to the different luting cements, the cervical composite/ceramic interface and the composite/dentin inter-face.

Assessing penetration data for all groups together, pene-tration depths at dentin/composite interfaces 221mm^ 166were higher as compared to ceramic/composite inter-faces53mm^68:The in¯uence of the interface location was signi®cantp0:0001:

Luting space and kind of luting cement had no signi®cant in¯uence on dye penetration at the ceramic/composite inter-faces. However, at dentin/composite interfaces the variable luting cement signi®cantly in¯uenced margin quality.

When inlays had ideal luting spaces (group 1), luting cements did not signi®cantly in¯uence marginal seal at the dentin/composite interface. However, dye penetration depths for larger luting spaces were deeper for inlays cemented with low viscous material than for those cemented with highly viscous material at the dentinal margins. The in¯uence of luting cement on dye penetration depths was signi®cant for the 400mm luting spacep0:0106:

3.2. SEM analysis

Results of SEM analysis concerning the parameter gap are summarized in Figs. 3a and b. Means and standard deviations are recorded with regard to the interfaces P. Hahn et al. / Dental Materials 17 (2001) 191±196

Table 1

Materials used for the restorations

Material Manufacturer Essential ingredients (batch numbers)

Empressw

Ivoclar, Ellwangen, Germany

Leucite strengthened glass cermaic (920838)

Biodent Retention Gelw

Germany Tetraethylene glycol dimethacrylate, maleic acid in aqueous aceton solution (730193)

Adhesive:

Polyethylene glycol dimethacrylate, glutaraldehyde 50% in aqueous solution (902168)

Heliobondw Vivadent, Ellwangen, Germany

Bispheylglycidyl methacrylate, triethylene glycol dimethacrylate (904711)

Variolink IIw

Vivadent, Schaan, Liechtenstein

Bis-GMA, urethane dimethacrylate, triethylene glycol dimethacrylate, barium glass, ytterbium tri¯uoride. Ba±Al-¯uorosilicate glass, spheriod mixed oxide (Base 824319, Catalyst 918863)

Variolink Ultraw

Vivadent, Schaan, Liechtenstein

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(composite/ceramic interface, composite/dentin interface), the time before and after arti®cial loading, and the different luting spaces for both resin cements used.

Repeated measures of variance were performed for the factors; localization of interface, luting space, luting cement, and time. This analysis revealed that the location of the interfacep0:001;the luting cementp0:001; and time p0:001 in¯uenced gap formation signi®-cantly. Luting space had no signi®cant in¯uence.

Luting cement was found to have an in¯uence at the ceramic margin after loadingp0:0496;Fig. 3a). Inlays cemented with low viscous cement showed greater gap formation than inlays cemented with the highly viscous cement at the composite/ceramic interfaces.

In accordance with these results, larger gap values were found at dentin/composite interfaces after luting inlays with low viscous cement. This was signi®cant before p

0:0037and after loadingp0:0085;Fig. 3b).

4. Discussion

The marginal integrity of the ceramic inlay/composite resin system was assessed according to the hypothesis that gap formation, and therefore also dye penetration are in¯uenced by the degree of contraction stress within the composite luting cement, which itself is modulated by polymerization shrinkage and compensation phenom-ena [20]. It has been debated, that this stress can be compensated for when low viscous composite cements and wider luting spaces between inlay and tooth are

used [5±8]. The in¯uence of these parameters on marginal quality of ceramic inlays at dentinal margins should be evaluated.

Class V cavities have an unfavorable C-factor, resulting in high contraction stress within an adhesively ®xed resin material. For this reason, ceramic inlays in class V cavities were evaluated, to simulate a particularly disadvantageous situation and also because it is easier to standardize the preparation of class V cavities than class II cavities. The cavities were prepared on both approximal sides of the teeth to reduce the number of the teeth needed for the experi-ments. Since the morphology of buccal and oral surfaces is often very different, mesial and distal approximal surfaces were prepared. The box-shaped preparation design without beveling is related to the geometrical form of the proximal portion of class II inlay preparations. For this reason, the results of the present study should, in principle, also be applicable for the proximal parts of class II inlays.

Occlusal forces may cause tooth de¯ections and vertical tooth deformations resulting in tensile ¯exure stresses and shear stresses at the margins of restorations [19]. Therefore, a chewing simulator was chosen to age the restorations in the present investigation.

Only the results referring to the gap formation aspect were reported, facilitating the comparison between SEM analysis and the results of dye penetration.

As expected, dye penetration and SEM analysis revealed better restoration margin quality at ceramic/composite inter-faces than at dentin/composite interinter-faces. Additionally, arti-®cial loading resulted in a signi®cant increase in gap formation and penetration depths.

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Larger cervical luting spaces created higher penetration depths at margins below the dentin±enamel junction, when inlays were cemented with low viscous luting material, but not when luted with highly viscous cement. According to the present results, further studies could demonstrate that low viscous luting cements are unfavorable in combination with ceramic inlays with larger luting spaces for class II cavities surrounded by enamel. Additionally, larger luting spaces had no in¯uence on marginal quality at enamel margins when inlays were cemented with highly viscous luting cement [21,22].

In contrast to these results Dietschi et al. [20] found no interaction between cement thicknesses, different luting cements and marginal seal, in a model of simply shaped bonded ceramic onlays with dentinal margins. It is

conceiva-ble that free vertical movement of onlay restorations compen-sated for polymerization stress within luting cement, while for class V inlays this movement is restrained by the high ratio of bonded to unbonded surfaces [20,23,24]. In the clin-ical situation free vertclin-ical movement of class II inlays for polymerization stress relaxation is unlikely, therefore inter-action between cement viscosity and luting space should be similar to the results found in the present investigation.

Larger luting spaces did not increase marginal leakage when inlays were luted with highly viscous luting cement. This is in agreement with Alster et al. [25] who found a decreased contraction stress with increasing cement layer thickness of a highly viscous, chemically hardening compo-site (Clear®l F2, Kuraray, Japan). Moreover, compocompo-site cements, which are mixed from two pastes, have an P. Hahn et al. / Dental Materials 17 (2001) 191±196

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additional effect on remaining contraction stress. They contain air voids increasing ¯ow capacity [24]. In highly viscous materials this porosity may be greater than in low viscous materials contributing to a higher ¯ow and therefore, a better marginal seal in inlays with larger luting spaces.

Therefore, in the present investigation bond strength between dentin and highly viscous cement was suf®cient to compensate for the remaining polymerization stress and to withstand the aging procedure. For inlays cemented with low viscous composite resin, the increased polymerization shrinkage in larger luting spaces resulted in loss of adhesion at dentinal margins under the present experimental conditions.

5. Conclusions

With well ®tting inlays viscosity of luting cements had no signi®cant in¯uence on marginal quality at dentinal margins. If inlays extend beyond the dentin±enamel junction, good marginal ®t is still desirable. For inlays with larger luting spaces extending into dentin, for example Cerec inlays or prefabricated ceramic inlays, luting composites with higher viscosities should be preferred.

Acknowledgements

We acknowledge gratefully the support of Professor JuÈrgen Schulte-MoÈnting, Department of Medical Biometrics, University of Freiburg, who did the statistical analysis of the results of this study.

References

[1] Feilzer AJ, De Gee AJ, Davidson CL. Curing contraction of compo-sites and glass-ionomer cements. J Prosthet Dent 1988;59:297±300. [2] Gary SP, Cheung BDS. Reducing marginal leakage of posterior

composite resin restorations: a review of clinical techniques. J Prosthet Dent 1990;63:286±8.

[3] Kunzelmann KH, Hickel R, Meister C, Petschelt A. Curing contrac-tion in thin bonding composite resin layers. In: MoÈrmann WH, editor. Proceedings of the International Symposium on Computer Restora-tions. The state of art of the Cerec method. Berlin, Quintessence, 1991. p. 577±90.

[4] Lutz F, Krejci I, Barbakow F. Quality and durability of marginal adaptation in bonded composite restorations. Dent Mater 1991;7:107±13.

[5] Davidson CL, De Gee AJ. Relaxation of polymerization contraction stresses by ¯ow in dental composites. J Dent Res 1984;63:146±8. [6] Davidson CL. Resisting the curing contraction with adhesive

compo-sites. J Prosthet Dent 1986;55:446±7.

[7] Feilzer AJ, De Gee AJ, Davidson CL. Setting stress in composite resin in relation to con®guration of restoration. J Dent Res 1987;66:1636±9. [8] Feilzer AJ, De Gee AJ, Davidson CL. Increased wall-to-wall curing

contraction in thin bonded resin layers. J Dent Res 1989;68:48±50. [9] Lambrechts P, Inokoshi S, Van Meerbeek B, Willems G, Braem M,

Van Herle G. Classi®cation and potential of composite luting materials. In: MoÈrmann WH, editor. Proceedings of the International Symposium on Computer Restorations. The state of art of the Cerec method. Berlin, Quintessence, 1991, p. 61±90.

[10] Inokoshi S, Willems G, Van Meerbeek B, Lambrechts P, Braem M, Van Herle G. Dual cure luting composites. Part 1: ®ller particle distribution. J Oral Rehab 1993;20:133±46.

[11] Feilzer AJ, De Gee AJ, Davidson CL. Quantitative determination of stress reduction by ¯ow in composite restorations. Dent Mater 1990;6:167±71.

[12] Kemp-Scholte CM, Davidson CL. Marginal integrity related to bond strength and strain capacity of composite resin restorative systems. J Prosthet Dent 1990;64:658±64.

[13] Retief DH. Do adhesives prevent microleakage? Int Dent J 1994;44:19±26.

[14] Davidson CL, Feilzer AJ. Polymerization shrinkage and polymerization shrinkage stress in polymer-based restoratives. J Dent 1997;25:435±40.

[15] Van Meerbeek B, Perdigao J, Lambrechts P, Vanherle G. The clinical performance of adhesives. J Dent 1998;26:1±20.

[16] Ebert J, Petschelt A. The Ultrasonic Insertion Technique without the use of a bonding agent. Dtsch ZahnaÈrztl Z 1996;51:96±100. [17] Kern M, Strub JR, LuÈ XY. Wear of composite resin veneering

mate-rials in a dual axis chewing simulator. J Oral Rehab 1999;26:372±8. [18] Roulet JF, Reich T, Blunck U, Noack M. Quantitative margin analysis in the scanning electron microscope. Scanning Microsc 1989;3:147±58. [19] Al-Salehi SK, Burke FJT. Methods used in dentin bonding tests: an

analysis of 50 investigations on bond strength. Quintessence Int 1997;28:717±23.

[20] Dietschi D, Magne P, Holz J. An in vitro study of parameters related to marginal and internal seal of bonded restorations. Quintessence Int 1993;24:281±91.

[21] Schmalz G, Federlin M, Reich E. Effect of dimension of luting space and luting composite on marginal adaptation of a class II ceramic inlay. J Prosthet Dent 1995;73:392±9.

[22] Hahn P, Schaller HG, MuÈllner U, Hellwig E. Marginal leakage in class II-restorations after use of ceramic-inserts in combination with different luting cements. J Oral Rehab 1998;25:567±74.

[23] Davidson CL, De Gee AJ, Feilzer AJ. The competition between composite±dentin bond strength and the polymerization contraction stress. J Dent Res 1984;63:1396±9.

[24] Davidson CL, Van Zaghbroek L, Feilzer AJ. Destructive stress in adhesive luting cements. J Dent Res 1991;70:880±2.

[25] Alster D, Feilzer AJ, De Gee AJ, Davidson CL. Polymerization contraction stress in thin resin composite layers as a function of layer thickness. Dent Mater 1997;13:146±50.