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Print version ISSN 0103-0663
Rev Odontol Univ São Paulo vol.13 n.3 São Paulo July/Sept. 1999
In vitro evaluation of the marginal microleakage of class II amalgam restoration associated with dentin adhesive*
Avaliação in vitro da microinfiltração marginal de restauração de amálgama classe II associada a adesivos dentinários
OLIVEIRA, F. S.; SILVA, S. M. B.; BIJELLA, M. F. T. B.; LIMA, J. E. O. In vitro evaluation of the marginal microleakage of class II amalgam restoration associated with dentin adhesive. Rev Odontol Univ São Paulo, v. 13, n. 3, p. 263-268, jul./set. 1999.
The marginal microleakage of class II amalgam restorations (Dispersalloy) associated with copal varnish (Copalite) and with two dentin bonding agents (Scotchbond Multi-uso Plus and Multi Bond Alpha) was evaluated in vitro and compared by two methods: scores and linear measurements. Forty-five sound premolars were used, on which two separated class II cavities were prepared on the M and D surfaces. After the restoration, the specimens were thermocycled and stored in a solution of 0.5% basic fuchsin during 24 hours. The analysis allowed to conclude that none of the three restorative systems were able to eliminate the marginal microleakage. Nevertheless, the leakage was significantly smaller on the restorations associated with dentin bonding agents when compared to copal varnish. The linear measurement method was more sensitive than the score criteria.
UNITERMS: Dental leakage; Dental amalgam; Dentin bonding agents; Dental cavity lining.
Although there are several options of restorative materials for posterior teeth, the dental amalgam remains as the main choice. It is highly resistant, insoluble in oral fluids, inexpensive, of easy handling and not technique sensitive13,15,16,18,20,21. However, one of the biggest disadvantages of this material is the lack of adhesion to the dental structure, due to the formation of a gap in the tooth/restoration interface measuring about 2-25 micrometers. It allows marginal microleakage, which is the penetration of buccal fluids and bacteria that can provoke secondary decay and pulpar irritation5,8,16,17,20.
Since the complete sealing of the cavity margins is important to the success of the restoration, the application of a sealing agent is necessary before the condensation of the amalgam, whose sealing capacity is defective. The copal varnish has been used for many years. It's purpose is to prevent the initial marginal microleakage until the corrosion products of the amalgam that had been formed within some months after the accomplishment of the restoration, seal the interface of tooth/restorative material.
The dentin adhesives have been evaluated as an alternative to the conventional varnish since VARGA et al.30 (1986) related a new technique, associating the dentin adhesive to the dental amalgam. A great number of studies1,3,4,7,8,9,13,25,27 showed that this material, when used under the amalgam restorations, decreases the marginal microleakage when compared to the conventional varnish.
The qualitative microleakage of the adhesive systems is generally determined through an in vitro23 study, being the use of the dye the more frequent technique14,28. According to KIDD14 (1976), the value of the in vitro tests has been questioned, because those experiments eliminate the effect of the pulpal hydrostatic pressure and the bacterial plaque on the restauration's surface.
Nevertheless these tests play an important role in clinical researches because they allow a previous evaluation of the material's sealing capacity in the tooth/restoration interface. As a consequence of the constant evolution of the dentin adhesives, it is interesting, that they are initially evaluated in vitro.
Considering the control importance of the marginal microleakage due to its deleterious consequences to the restoration, the aim of the present study was to evaluate the capacity of the cavity varnish and the influence of dentin adhesives to the marginal microleakage comparing two different evaluation methods.
MATERIAL AND METHODS
Forty-five premolars, free from decay or other enamel defects, removed for orthodontic reasons, were selected. Each tooth received two independent standardized class II cavities, on mesial and distal surfaces. They were prepared with a carbide burr number 245 (JET Dental Beavers). The cavities were 4mm wide, with the vestibular and lingual walls parallel to each other and slightly expulsive on the axio-proximal direction. The axial walls were flat with rounded internal angles; the cervical walls were 1 mm wide, flat and perpendicular to the longitudinal axis of the tooth, extending themselves 1 mm after the enamel-cementum junction.
The prepared teeth were mounted on a block of gypsum, being fixed with wax (Duradent), with one tooth on each side, to simulate the proximal contacts. The teeth were divided at random in three groups with 15 premolars each. The mesial and distal surfaces of the same tooth received different restorative systems, according to the following distribution:
Group I (GI): control - Copalite varnish (Cooley & Cooley Ltda.) - (CP);
Group II (GII): dentin adhesive Scotchbond Multi-uso Plus (3M Dental Products) - (SMP); and
Group III (GIII): dentin adhesive Multi Bond Alpha (DFL Ind. and Com. Ltda.) - (MBA).
The 45 teeth were restored with Dispersalloy (Dentsply Ind. and Com.), an alloy of dispersed phase enriched with copper. All materials were used according to their manufacturer's instructions.
Welded individual metallic matrixes, stabilized with wood wedge, were used. The amalgam was condensed manually, carved with Hollenback 3S and smoothed with a cotton ball. Then, the teeth were stored in deionized water at 37°C for 24 hours, their apices sealed with two varnish layers and amalgam (Velvalloy - S. S. White), and to identify each group, the whole tooth except for 1 mm around the restorations, was covered with two layers of nail polish of different colors. Soon after, the specimens were submitted to a termocycling under 5°C and 55°C in distilled water, during 15 seconds in each bath, through a total of 500 cycles. The teeth were then stored in a 0.5% basic fuchsin solution at 37°C over 24 hours and maintained in the water for an equal period. Thus, each one was sectioned (A Nevoni buffer, ¼ HP, 20000 rpm, type F56) with a double face diamond disk at high speed and under abundant water refrigeration. On the average, three slices per tooth were obtained for an evaluation with an optical microscope.
For the analysis of the marginal microleakage the scores and linear measurement methods were used. Three calibrated examiners gave the scores based on color slides obtained with a surgical optical microscope (D. F. Vasconcelos S. A., S. P., Brazil) with a magnification of 40x.
The extension of the dye penetration was evaluated on the cervical wall, using the following criterion:
- no dye penetration;
- dye penetration up to half of the cervical wall;
- dye penetration over more than half of the cervical wall, but not reaching the axial wall, and
- dye penetration extending along the axial wall.
Each available section received a score for both restorations and faces of each slice. In case of disagreement concerning the infiltration degree, a consensus was obtained among the examiners.
The two faces of the slices were also analysed using a 30 fold magnification in an optical microscope (Mitutoyo MFG. Co. Ltd., Japan). The dye penetration in the tooth/restoration interface was assessed in micrometers.
For statistical analysis purposes, both sides of each slice were considered. The variance analyses test of Kruskal-Wallis (H = 113.7; P = 2.00.10-25) and the Dunn test for comparisons among the study groups (P < 0.05) were performed for the score method. The linear measurements method was analysed through ANOVA (P = 1.67.1031) and the Student-Newman-Keuls comparisons among the groups test (P < 0.0001).
Referring to the scores:
Tables 1 and 2 present the numeric and percentual occurrence of each score and the medium score for the marginal microleakage of the three tested restorative systems. The Kruskal-Wallis and Dunn tests were performed (Tables 3 and 4). The results were significant only within the control group when it was compared with the dentin adhesive group.
Referring to linear measurements:
The mean values for the linear measurements of the marginal microleakage of the three tested restoring systems are evidenced on Table 5. These results were analysed using the ANOVA and the Student-Newman-Keuls tests (Tables 6 and 7). The results among all the groups were significant.
The marginal microleakage around the amalgam restorations associated to dentin adhesives was evaluated in all forty-five selected teeth, without any loss of specimens or slice during the sectioning. Nevertheless it was not possible to achieve the same number of slices in all groups.
The size of the tooth and the difficulty of manipulation of the device were the limitating factors. The objective of this kind of analysis was to allow a more accurate evaluation of the degree of marginal microleakage. If only one section was made and analysed, it could happen that, coincidentally in that face, there would not occurr the maximum dye infiltration degree. Besides, this analysis is already being used by other authors4,7,16,25,30.
The dental amalgam has a tendency to decrease the marginal microleakage over time, due to the deposition of corrosion products in the space between the tooth and the restoration. However, since this is not a immediate posttreatment phenomenon, there is a variable time period in which the new restorations are subject to this pernicious effect.
The cavity varnish has been used for many years with the aim of decreasing the early marginal microleakage of the amalgam restorations2,3,12,19,26. However, this material presents solubility and is not so effective in the reduction of the marginal microleakage around the cervical walls as it is at the enamel margins.
The promising results showed by the dentin adhesives when used with the composite, have stimulated their association with the amalgam in substitution of the cavity varnish. A great number of studies4,7,8,11,16,25,27,29 is unanimously reporting the superiority of the dentin adhesives in the reduction of the marginal microleakage of amalgam restorations when compared with the conventional varnish. It is supposed that the adhesives may promote a micromechanic union with the dentine by bonding chemically to the calcium ions in the dentin and in the smear layer, and filling the existent gap in the tooth/restoration interface. This is a different mechanism from that of the varnish which only works as a mechanical barrier and doesn't bond to either the amalgam or the tooth structure.
The data of this study relative to the marginal microleakage are in agreement with the data of other studies which compared the use of cavity varnish and the association between dentin adhesive and amalgam. In this study, it was observed that GII and GIII, although they didn't totally eliminate the dye infiltration, presented smaller scores and medium linear values for the marginal microleakage than GI (Tables 1, 2 and 5).
The superiority of the MBA adhesive in relation to the SMP may be understood through its form of application. It employs 5 sequential layers of the material, each of which could have appropriately impermeabilized the floor of the cavities, while SMP uses only 2 layers. As the manufacturers didn't supply the components of that material, it was impossible to compare it with the other one used.
The method of scores is more used in the literature4,6,7,8,9,10,11,16,24,25,27,29 , but it only gives a qualitative appreciation. Although this type of evaluation (Tables 1, 2, 3 and 4) showed the superiority of dentin adhesives in the control of marginal microleakage, it is not accurate enough to demonstrate a significant difference between GII and GIII. However, for the linear measurements method (Tables 5, 6, and 7), a significant difference was revealed among all groups. This type of result has a very important meaning, because it clearly shows the sensibility of the used analysis method, in spite of neither being the ideal one.
Longitudinal in vivo studies should be done aiming to verify clinically if in fact the dentin adhesive should substitute the conventional varnish, without any damage to the amalgam restoration and with the actual advantages of its adhesive properties. It will be of interest if the studies consider the application on the sclerotic or carious dentine, because these represent a challenge for the adhesion22 and also the clinical situations that still wait for an effective long term solution.
Our results within the experimental conditions of this research allowed us to conclude that:
- none of the three restoring systems was capable to eliminate the marginal microleakage;
- the amalgam restorations associated to dentine adhesive presented a smaller and significant marginal microleakage, when compared with those associated to the cavity varnish, with better results for Multi Bond Alpha, and
- the evaluation through the linear measurements method was more sensitive than the one through scores. It was able to show a significant difference about the degree of marginal microleakage among the three restoring systems.
OLIVEIRA, F. S.; SILVA, S. M. B.; BIJELLA, M. F. T. B.; LIMA, J. E. O. Avaliação in vitro da microinfiltração marginal de restauração de amálgama classe II associada a adesivos dentinários. Rev Odontol Univ São Paulo, v. 13, n. 3, p. 263-268, jul./set. 1999.
A microinfiltração marginal de restaurações de amálgama classe II (Dispersalloy), associada ao verniz convencional (Copalite) e a dois adesivos dentinários (Scotchbond Multi-uso Plus e Multi Bond Alpha), foi avaliada e comparada in vitro através de dois métodos: escores e medidas lineares. Foram utilizados 45 pré-molares hígidos que receberam duas cavidades independentes M e D. Após a restauração, foram submetidos à termociclagem e armazenados em uma solução de fucsina básica a 0,5% durante 24 horas. A análise da infiltração do corante permitiu concluir que nenhum dos três sistemas restauradores foi capaz de eliminar a microinfiltração marginal. No entanto, ela foi menor e estatisticamente significante para as restaurações associadas aos adesivos dentinários, quando comparadas àquelas com o verniz cavitário. O método das medidas lineares foi mais sensível do que o de escores.
UNITERMOS: Infiltração dentária; Amálgama dentário; Adesivos dentinários; Forramento da cavidade dentária.
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Recebido para publicação em 29/09/98
Enviado para reformulação em 05/12/98
Aceito para publicação em 18/04/99
* Part of the Dissertation Master of Science in Pediatric Dentistry.
** Master of Science.
*** Professors and **** Associated Professor of Pediatric Dentistry, Bauru School of Dentistry of the University of São Paulo - USP.