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Microleakage in Class II Resin Composite Restorations with Various Adhesive/ Liner Combinations: An In Vitro Study

April 1, 2003
by Ann-Marie L. Neme, DDS, MS; Diane C. Hoelscher, DDS, MS and Barbara B. Maxson, DDS, MS


Resin composite is currently the material of choice for direct aesthetic restorations. The properties of contemporary composites have improved considerably generating predictable, aesthetic, durable and biologically compatible posterior restorations. However, posterior composite restorations remain technique sensitive.

A concern of clinicians when placing any posterior restoration is the potential for poor adaptation of the material to the tooth structure. The ability of a material to seal a cavity preparation can be influenced by composition, plastic deformation, flow, coefficient of thermal expansion, modulus of elasticity, and mechanical stresses caused by cavity preparation shape.1 The importance of the handling characteristics of a restorative material during condensation has long been recognized.2

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According to many studies, there are a variety of potential causes for failure of composite restorations at the cavosurface margin of class II restorations.3 Studies investigating microleakage have shown that selection and handling of materials are the most significant factors influencing marginal adaptation and subsequent microleakage.4

Clinicians have a variety of materials to choose from that not only have unique chemistries (resin, glass ionomer, and/or combinations) but also unique viscosities leading to different handling characteristics.

Flowable resin-based materials have been recommended as liners beneath posterior composites due to their low viscosity, increased elasticity and wettability. The handling characteristics and unique delivery system make flowables an ideal choice for use as a liner beneath a more viscous resin composite material. However lower physical properties and increased polymerization shrinkage associated with flowable resins should be considered as potentially detrimental.

Research has demonstrated that the polymerization shrinkage associated with resin composite, especially in the deepest part of the proximal box of class II restorations, can result in poor marginal adaptation.5 In vitro microleakage studies using thermocycling to stress the marginal seal have demonstrated a superior marginal seal at the cementum/dentin margin with a resin-modified glass ionomer (RMGI) compared to both resin composite and compomer materials.6-7

Clinical evaluation of class V non-carious lesions restored with a resin composite and a RMGI bonding agent demonstrated positive results comparable to the in vitro findings.8

Sandwich techniques have been described which are intended to take advantage of the differences in sealing capability of glass ionomer and resin materials. Sandwich techniques, using alternative materials at the cementum margin of class II resin composite restorations, have been tested both in vitro9-12 and in vivo.13-16 Results have varied with materials and techniques. It was the purpose of this in vitro investigation to compare the extent of microleakage in class II resin composite restorations with and without a low-viscosity liner placed at the cervical margin using both a resin and RMGI adhesive system.

MATERIALS AND METHODS

Twenty extracted non-carious third molar teeth stored in 0.2% sodium azide at room temperature for less than one month were used in this study. All teeth were cleaned with a slurry of flour of pumice and water prior to preparation. Samples were stored in distilled water at room temperature following cleaning and throughout the experiment.

Tooth Preparation

Two class II preparations were made in each tooth, one on the mesial surface and one on the distal surface, with a high-speed handpiece using water spray and a #256 carbide bur (Brassler USA, Savannah, GA). At least 1.5 mm of sound tooth structure was left between the two cavities occlusally. Pulpal floor depth was 2 mm and the proximal boxes were approximately 4.0 mm high, 4.0 mm wide, and 1.0 to 1.5 mm deep. The cervical margin was placed on cementum 1.0 to 1.5 mm apical to the CEJ. Twenty teeth with two preparations per tooth were randomly assigned to one of four treatment groups of five teeth (ten preparations).

Restoration placement

The restorations were placed by a single operator according to manufacturer’s instructions. The adhesive/liner combination (treatment groups) and manufacturers are listed in Table 1. Per manufacturer’s instructions, each tooth was etched or conditioned and adhesive material was applied.

A stainless steel matrix (Tofflemire, Teledyne Water Pik, Ft. Collins, CO) was then adapted to the prepared tooth before incremental insertion and light curing of the resin composite material (Gradia, GC America, Inc.). Where a liner application was randomized, it was placed in 0.5-mm thickness prior to the composite from axial wall to gingival margin and light cured.

Materials were light cured per manufacturer’s instructions with the Astralis 7 (Ivoclar Vivadent) light-curing unit. The curing unit was tested per manufacture’s suggestion for light intensity. Within fifteen minutes following placement, the occlusal aspects of each restoration were grossly contoured and all cavosurface margins finished flush using a gold shank football finishing bur (#7406; Brassler).

The restored specimens were stored in room temperature distilled water for a minimum of 24 hours. The specimens were then thermocycled in 5C and 55C water with a one-minute dwell time for 1000 cycles. Following thermocycling, the apex of each tooth was sealed with epoxy cement and the tooth was painted with two coats of fingernail varnish to within 1mm of the restoration margins. Specimens were placed in a solution of 0.5% fuschin dye for 24 hours. Following dye exposure, the teeth were rinsed with distilled water and embedded in self-curing clear orthodontic resin (DENTSPLY/ Caulk). Specimens were stored in distilled water until sectioning.

Embedded specimens were sectioned longitudinally through the centers of both restorations from mesial to distal using a water-cooled, slow-speed diamond saw (Isomet, Buehler Ltd., Lake Bluff, IL) to produce multiple sections (Fig. 1). Dye penetration was measured at both the cervical and occlusal margins of all restorations. The extent of microleakage was determined visually under a light microscope at 40X.

Two examiners scored extent of dye penetration using an ordinal scale (0-4) (Fig. 2) by consensus. Examiners were blind to material and/or technique used. Ranked data were analyzed using the Kruskal-Wallis test for nonparametric data and the Wilcoxon Signed Rank test for paired non-parametric comparisons (a=0.05).

RESULTS

Table 2 lists the median microleakage scores for each of the systems at both the occlusal and cervical margins. There was a significant difference in the amount of leakage between the cervical and occlusal margin for all systems. Rank sum analysis revealed significantly more leakage with the RMGI adhesive compared with the resin adhesive at the occlusal margin of resin composite restorations (Table 3). However, the RMGI adhesive systems both with and without a liner yielded significantly less microleakage at the cervical margin than the resin systems.

At the occlusal margin of resin restorations placed with either resin or RMGI adhesives, there was no significant difference in leakage based on liner placement. Also at the cervical margin of resin restorations placed with a resin adhesive there was no significant difference in restorations with or without a flowable liner (Fig. 3). However, at the cervical margins of the restorations placed with a RMGI adhesive there was significantly less leakage in the systems where the flowable liner was placed (Fig. 3).

DISCUSSION

Both in vivo and in vitro studies have shown that in resin composite restorations where the cervical margin is in dentin, the quality of the margin is suspect.17,18 Findings from this study support previous studies demonstrating that gingival margins are potentially a greater source of marginal leakage in class II composite restorations compared to occlusal margins.19-21 Although the resin adhesive in this study demonstrated superior seal c
ompared to the RMGI adhesive at the occlusal (enamel) margin, it could be argued that more attention should be placed on the material that better seals the cervical margin.

Low-viscosity materials such as flowable composite or RMGI cements have been suggested as liners in class II composite restorations due to their increased elasticity, wettability and adaptability to cavity walls. This rationale for the sandwich technique utilizing placement of a flowable resin composite to better seal the cervical margins in posterior composite restorations was not supported by this in vitro investigation. In this study the RMGI liner with the corresponding adhesive resulted in the best seal at the cervical margin.

Researchers have sought not only to determine differences among techniques and materials for reduction in microleakage at the cavosurface margins but also attempt to explain the reason for these differences. It has been suggested that a higher ratio of resin matrix to filler particles in a material placed at the cavosurface margin might influence the degree of microleakage. As the ratio of resin to filler increases, so does the polymerization shrinkage.7 This would support the use of an alternative material such as RMGI at the cervical margin of a composite restoration to reduce leakage.

Some researchers have promoted this sandwich-type restoration, using RMGI materials to decrease the amount of polymerization shrinkage of large composite fillings, reducing the potential for leakage at the tooth restoration interface.22-23

Additionally researchers have hypothesized that the difference in the coefficient of thermal expansion and/or elastic modulus between restorative material and tooth structure may result in stress at the interfacial gap, resulting in microleakage.19

In the current investigation the RMGI bonding agent and liner resulted in the least amount of microleakage at the cervical margin. In fact, the coefficient of thermal expansion for RMGI better matches that of tooth structure compared to the resin materials. This property may be important for the maintenance of marginal integrity following thermal stressing (thermocycling).

Although this in vitro investigation did not demonstrate a reduction in marginal leakage at the cervical with the use of a flowable resin composite in class II composite restorations, clinical handling characteristics may play a more important role in vivo. Samples evaluated in this investigation were prepared on bench top with adequate visualization, moisture control and ideal access.

The ability to place a liner via syringe application as is available for flowable composite, but not for RMGI, prior to placing a more viscous material may significantly improve marginal adaptation in vivo regardless of material factors.

CONCLUSIONS

Results of this in vitro study indicate significantly more leakage in cervical margins than occlusal margins for class II resin composite restorations.

At the occlusal margin (enamel) the best seal resulted when the resin adhesive was used.

At the cervical margin (cementum; root surface dentin) the best material combination for resistance to leakage was attained when restorations were placed with a RMGI liner and adhesive combination.

CLINICAL SIGNIFICANCE

Although the RMGI system used in the current study yielded a better seal at the cervical margin in class II resin composite restorations, the traditional resin adhesive continues to provide a superior seal at the enamel margin.

Acknowledgements

The authors would like to thank Dr. Mert Aksu for his assistance during the preparation of the samples and Dr. Frank E. Pink for statistical support. This study was supported in part by GC America Inc.

Ann-Marie L. Neme, DDS, MS, Associate Professor, Operative Restorative Dentistry; Diane C. Hoelscher, DDS, MS, Associate Professor and Interim Chair, Operative Restorative Dentistry; and Barbara B. Maxson, DDS, MS, Associate Professor and Interim Chair, Prosthodontic Restorative Dentistry, University of Detroit Mercy.

Oral Health welcomes this original article.

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ABSTRACT

Various materials have been suggested as a liner beneath composite restorations to improve marginal integrity. It was the purpose of this in vitro investigation to evaluate the extent of microleakage in class II resin composite restorations with various liner/bonding agent combinations. Ten class II cavities were prepared on the mesial and distal surfaces of extracted third molars for each of 4 material combinations; 2 resin modified glass ionomers (RMGI), Fuji Bond and Fuji Bond with liner Fuji LC, and 2 resins, Optibond Solo Plus and Optibond Solo Plus with liner Revolution. Preparations were restored with a resin composite per manufacturer’s suggestion following adhesive and/or liner placement. Samples were finished, stored in distilled water for * 24 hrs and thermocycled for 1000 cycles between 5 and 55C with a 1-min dwell time. Apices were sealed and teeth varnished to within 1-mm of the margins. Samples were placed in 0.5% basic fuschin dye for 24-hrs, rinsed, embedded in resin and sectioned to produce multiple sections. Microleakage was rated (0-4 ordinal scale) at both the occlusal and cervical margins by consensus of 2 evaluators at 40X. Data were analyzed with Kruskal-Wallis ANOVA for main effect and ranked sums analysis for pairwise testing (a=0.05). Cervical microleakage was significantly greater than occlusal leakage for all systems. A significant difference was determined among materials both at the occlusal and cervical margins. Median scores at occlusal margins were F (1.0), F with liner (1.0) > O (0), O with liner (0) and at cervical margins were O with liner (4.0), O (3.0) > F (2.5) > F with liner (1.0) (@ p* 0.05). In conclusion, the RMGI systems yielded greater occlusal leakage and less cervical leakage compared to the resin systems in class II composite restorations.


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