Braz Dent J (1998) 9(2): 85-90 ISSN 0103-6440
| Introduction | Material and Methods | Results and Discussion | Conclusions | References |
The objective of the present study was to submit specimens with amalgam restorations to 4 different polishing techniques and one control group without polishing. The specimens were then submitted to rugosimetric analysis and the differences compared.
Key Words: amalgam restorations, conventional alloy, polishing techniques, superficial rugosimetric values.
Dental amalgam is a restorative material that has been used for more than a century (Goldfogel et al., 1976; Reavis-Scruggs, 1982; Jordan et al., 1985). During the last decades, modifications introduced in amalgam alloys have provided significant development in terms of structural and mechanic stability. However, dental amalgam exhibits several vulnerable points, among them low resistance to oxidation and corrosion (Marshall et al., 1980; Dinelli et al., 1983) and marginal deterioration (Wing, 1965; O'Brien et al., 1977). Classical authors agree that corrosion in structural degradation of filling (Charbeneau, 1965; Letzel and Vrijhoef, 1984) interferes directly in the clinical performance of restorations.
Trying to clinically minimize oxidation and corrosion of amalgam fillings and their early substitution (Bryant and Collins, 1989), researchers have pointed out the importance of the finishing procedure in order to achieve a longer shelf life (Leinfelder et al., 1978; Reavis-Scruggs, 1982; Paarman and Christie, 1986). Unfortunately, finishing as a routine clinical procedure has not been considered by clinicians in general, and has often been neglected. It is important to point out the real objective that clinicians attempt to achieve with amalgam filling finishing, and although it is difficult to define what is really a polished surface, generally the objective is a maximum smooth and homogenous surface.
Nadal (1962), Heath and Wilson (1976), Huysmans and Nieuwenhuysen (1979), and Reavis-Scruggs (1982) suggest different instruments to polish amalgam restorations, and this shows the multiplicity of techniques that may be used to achieve the objective.
Thus, the objective of this investigation was to study the effect of 4 standard techniques (Nascimento, 1992) for polishing conventional amalgam alloy fillings at 24 and 168 h, and submitting the specimens to rugosimetric analysis.
Material and Methods
A total of 60 specimens were prepared in a steel matrix with a circular cavity 8 mm in diameter and 2 mm in depth.
The amalgam to be condensed in this cavity was prepared using a conventional alloy (Novo True Dentalloy, SS White). Trituration was performed with a high frequency mechanic amalgamator (Silamat type) using a Deltronix non-screwing capsule, in the proportion indicated by the manufacturer. The mass of amalgam was condensed in the metallic matrix, with manual pressure, using a Hollenback nº 2 condenser.
Five minutes after condensation, excess was removed with a steel blade and burnishing was performed. After 25 minutes, using the screw of the matrix, the amalgam filling, as a tablet, was removed and stored in a clean recipient.
After condensation, carving and burnishing, specimens were stored in a sterilizer at 37ºC, and were submitted to the following polishing techniques 24 h (N = 6 of each group) and 168 h (N = 6 of each group) after condensation.
Group I (12 specimens) - Control group which was only carved and burnished.
Group II (12 specimens) - Initial finishing with smooth polishing rubber and pumice, followed by polishing with a Sweeney brush and zinc oxide paste. This was performed at conventional speed, approximately 18,000 rpm, using a smooth rubber cup and pumice paste, over the surface of the restoration with intermittent movements. Pumice paste was then removed with water spray and polishing was completed with a Sweeney brush and zinc oxide paste, and subsequently irrigated with water until total elimination.
Group III (12 specimens) - Initial finishing with abrasive polishing rubber points (brown, green and blue), followed by polishing with a smooth rubber cup and pumice paste, and with a Sweeney brush and zinc oxide paste. The abrasive rubber points were used in decreasing order, according to manufacturer instructions (brown, green and blue). This was performed at conventional speed, with intermittent movements and suave pressure, until the surface appeared smooth to the naked eye. After the abrasive rubber points and abundant water spray, the filling received the same treatment as group II.
Group IV (12 specimens) - Finishing procedure with silicone (white stone) carbide points, polishing with smooth rubber cup and pumice paste, plus a Sweeney brush with zinc oxide paste. The silicone carbide point was used as a first step in this procedure, at conventional speed, approximately 18,000 rpm, and intermittent movements. The point was passed over the entire restoration until all superficial scratches, which appear after carving and burnishing, were removed. All samples were then treated as in group II.
Group V (12 specimens) - Finishing procedure with multi-blade bur, polishing with smooth rubber cup and pumice paste, plus a Sweeney brush with zinc oxide paste. The bur was used as a first step at conventional speed (18,000 rpm) with intermittant movements. The bur was passed over the entire restoration until all superficial scratches, which appear after carving and burnishing, were removed. All samples were then treated as in group II.
After polishing, all samples were analyzed in a rugosimetric device (Prazis Rug 03).
The original data consisted of 180 values of superficial rugosity, measured in micrometers, resulting from the crossing of 5 groups, 2 polishing times, 6 repetitions and 3 measurements of each sample. The mean of the 3 measurements of each sample for a total of 60 data were analyzed statistically (Table 1). Statistical analysis showed abnormal and not homogenous distribution of the samples; thus, data were transformed into square root values. The data were analyzed using the analysis of variance (ANOVA) method and the Tukey test.
Results and Discussion
Analysis of the data showed that rugosity at 24 and 168 hours was not significantly different. In relation to finishing techniques there was a significant difference. The Tukey test (T = 0.232) showed that group I (µ = 1.053) had a greater rugosity when compared with groups II (µ = 0.707), III (µ = 0.517), VI (µ = 0.591) and V (µ = 0.540), which had similar rugosity values.
The four polishing techniques were analyzed comparatively between themselves, so that the great variability observed in group I had no influence on the statistical analysis of the other groups. We performed ANOVA between the 4 polishing groups and obtained a statistically significant difference between the 4 groups. Tukey's test (µ = 0.232) showed that group II (µ = 0.707) had greater rugosity than group III (µ = 0.517) while group IV (µ = 0.591) and V (µ = 0.540) had statistically intermediate rugosity values that were not statistically different from the results of groups II and III.
A surface free of irregularities is achieved more easily when, in a previous operative step, burnishing is performed on the surface of the amalgam restoration, allowing it to be more compact and consequently less porous (Charbeneau, 1965; Teixeira and Denehy, 1976; Marzouk et al., 1985; Baratieri et al., 1989).
Leitão (1982) reported that mechanical polishing always induces scratches and irregularities, but the contribution of these to rugosity values depends on the polishing technique and also the size of abrasive grain used in the final stage of the polishing procedure.
Charbeneau (1965) reported that filling rugosity can be detected by the method and instruments used in the polishing procedure.
The objective of polishing procedures is to remove scratches and irregularities, although polishing itself induces some scratches on the surface of the amalgam restoration. According to Leitão (1982), the restoration can be polished indefinitely and one can still find some superficial irregularity.
When clinical polishing is achieved, the failure of the amalgam due to the cyclic movements of mastication will be minimized (Marzouk et al., 1985). A polished surface reduces the corrosion concentration that can start at the superficial irregularities or scratches, preventing the adherence of plaque and its consequent problems.
When the groups with different polishing techniques were compared, group II showed greater rugosity values which can be explained because neither burs nor points were used to perform this technique. The use of only a smooth polishing rubber with pumice was insufficient to remove irregularities.
Group III showed the smallest rugosity values; the polishing techniques were performed with abrasive rubber points. These rubber points were used in a sequence of 3 points, with decreasing abrasiveness, which led to a more regular amalgam surface.
Groups IV and V exhibited intermediate rugosity values because the white stone and multi-blade bur have abrasiveness or a cutting effect more evident than the smooth polishing rubber used in group II and rougher than the sequential rubber points. These two, white stone and multi-bladed burs, must have a complement in the polishing procedure to make the amalgam surface smoother.
We can see that polishing is necessary to allow a longer shelf life to amalgam restorations (Leinfelder et al., 1978; Reavis-Scruggs, 1982; Paarman and Christie, 1986; Nascimento, 1992), because group I (no polishing technique) showed a greater superficial rugosity value than any of the groups with the different polishing techniques.
1 - There were no statistical differences between specimens polished with the different polishing techniques at 24 and 168 hours.
2 - Group I (control) exhibited the greatest rugosimetric values.
3 - Group II (smooth polishing rubber) show greater rugosimetric values than group III (sequential rubber points).
4 - Group IV (white stone) and V (multi-blade bur) exhibited intermediate rugosimetric values, not statistically different from groups II and III.
Marco Antonio Pereira was the recipient of a CNPq fellowship.
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Correspondence: Dr. Marco Antonio Pereira, Departamento de Odontologia Restauradora, Faculdade de Odontologia de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, SP, Brasil.
Accepted March 15, 1998
Electronic publication: April, 1999