NÚMERO 1 - 1996 - ARTÍCULO 1
NÚMERO 1 - 1996 - ARTÍCULO 1
The present study evaluates the effect produced upon conventional feldespatic ceramic used in our prostodontic restorations when these are submitted to acidulated gel-based topical fluoride application.
Our samples were submitted to study with a surface analyzer and an electronic scanning microscope in order to evaluate, quantitatively as well as qualitatively, the degree of roughness produced in the ceramic in relationship to the number of applications and the contact time of acidulated fluoride gels, and thereby confirm any damage that such applications might cause on dental ceramic surfaces.
From a clinical standpoint, we are witness to a greater demand on the part of our patients for two types of treatment: on the one hand, the preservation and conservation of their natural teeth and, on the other, the use of materials which meet and comply with optimal aesthetic standards.
With respect to indirect restorations, the ideal material is ceramic, given that it bestows our work with an extraordinary similarity to human teeth. For this reason, we have seen a growth of its use over that of other more classical materials such as gold and acrilic resins which neither obtain the desired aesthetic results nor present the smooth surface which would obviate the risk of bacterial plaque that deteriorates the restorations and causes lesions in gingival tissues. The renewal of ceramic use evidenced in recent years in applications such as laminated veneers in front teeth and ceramic inlay and onlay incrustations, this second example being cemented to teeth with mecanical retention in dental enamel and mecanic-chemical retention on the inner side of the ceramic achieved with fluorhidric acid-derived solutions at varying concentrations and application times, can be attributed to this fact.
This motivates us to reflect upon the action that acidic substances such as topically applicated acidulated fluoride gels could have on the porcelain surfaces of our restorations. The question that must be asked is the following: over time and according to the frecuency of usage, is the acid that this type of topical fluoride application contains capable of producing alterations in the outer surface of conventional or feldespatic ceramic which we employ during the glazing period of our restorations? The answer to this question is, consequently, the objective of this study.
For the experimental study of the action that acidulated gel-based fluorides have on the outer surface of conventional ceramic, 20 feldespatic ceramic (Figure 1) (ITS Ivoclar) disks measuring 10 milimeters in diameter and 3 milimeters in height, and in the glazing period, were fabricated. These were submitted to a Surface Analyzer and a graphic register was taken on each surface. Each one of the samples were tested four times in four different positions in order to obtain a more exact average. The methodology used in the current article is expressed in Figure 3.
Of the twenty experimental samples, eighty results of roughness were obtained. The corresponding graphs are shown in Figure 4.
One layer of acidulated fluoride gel at a 1,23 per cent concentration (MINUTE GEL from Oral B) was applied during a five-minute period to each one of the samples. At the end of the exposition time, the samples were carefully washed for twenty seconds with non-pressurized water and introduced one by one in an etilic acetate solution in order to obtain a higher degree of surface cleanliness and, at the same time, a lesser risk of particle contamination, thus avoiding potential alterations of surface roughness results.
Once the surfaces dried, the ceramic disks were analyzed a second time with the Surface Analyzer, and a total of eighty scores of the roughness of the surfaces, four for each sample, were once again obtained. These results were noted in the corresponding table. As before, a graphic register was taken for each one of the measurements and all registers were filed and labeled in the same manner as were the samples prior to acidulated fluoride gel treatment.
The samples, thusly treated, were placed in saline solution in a glass container in order to simulate "in vivo" conditions.
Every twenty-four hours, and during a period of seven days, the samples were removed from the container and submitted to repetition of the aforementioned procedure.
Once detailed the methodology and materials employed in the quantitative and qualitative evaluation of the effect, similar to that of clinical topical fluoride applications on patients who wear ceramic restorations, of acidulated gel-based fluoride on the surface of feldespatic ceramic, we proceed to a commentary of our results.
The four roughness scores obtained with the Surface Analyzer for each one of the conventional feldespatic ceramic samples, prior to application of the gel, as well as the arithmetical average and the standard deviation of said scores, are reflected in Table I.
The results given with the Roughmeter after one application of the gel are expressed in Table II.
Table III shows the eighty surface roughness results obtained after seven applications of the gel.
Table IV details the averages of all the scores obtained throughout the entire study.
Our transformed tables, obtained with log 10 of each roughness score, permitted us a greater graphic amplitude and delimitated our confidence range. (Tables V, VI, VII, and VIII).
Lastly, we determined the probability "p" as indicator of the degree of security in which we were working and obtained a value of p>0,02 -- in other words with a 98 per cent probability.
Study with an Electronic Scanning Microscope revealed the aggresiveness of the acidulated gel-based flouride on the surface of glazed ceramic treated with it and demonstrated that this aggresiveness is directly related to the number of gel applications. The gradual loss of the glazed surface exposes the underlying coarse ceramic mass.
Statistical norms, reflected in each of the corresponding tables, were applied to every sample, with a total of 240 graphic registers of roughness -- eighty for each of the stated cases. The arithmetic average, as well as the standard deviation, were calculated for each one of the twenty samples prior to acidulated fluoride gel application, after a single application, and after the seven applications. A Gaussian Curve, made accordingly for each of the three stages of our study, reflects, in virtue of its homegeneity, the regularity of our measurements.
After this first study, we transformed the data obtained for each sample and thus obtained three Transformed Roughness Tables (V, VI, VII) in which each datum was the log 10 of the original datum.
Following this, we proceeded to a comparative study of the three treatment patterns (prior to gel application, after one and after seven applications) in order to determine the confidence limits in which we were working and concrete the probability which we could count upon (Figure 7).
Lastly, a small subgroup of samples from each one of the three study patterns -- prior to fluoride gel application, after one five-minute application, and after seven five-minute applications -- were analyzed with an Electronic scanning Microscope.
One of the main difficulties which we found to perform the study was the design of our samples. Based on the studies done by COPPS (1984), we fabricated samples which later had to be rejected, firstly, because their two millimeter-size coincided with the limit of our roughmeter and, secondly, due to the presence of a metal window-like band around the ceramic which caused errors in the readings of our surface analyzer. We opted to increase the size of the samples but later realized that the polishing was less than perfect in the area where the ceramic joins the metal band and thus ended up fabricating ten-millimeter samples which, while larger than those used by COPPS, lacked the metal band which caused jumps in the register.
In an initial phase we observed the roughness of the surface of the ceramic with the surface analyzer when the samples were in the biscuit stage, and thus obtained visual orientation for the topographical variations that transpire when the ceramic is in the glazed phase. These observations served as a basis for our experiment.
The twenty samples of glassed conventional feldespatic ceramic in the aforementioned group, groundwork for our experiment in keeping with the studies done by WUNDERLICH and YAMAN (1986) and JONES (1985), were given a cylindric form with a 10 millimeter diameter, but whereas these authors used half of the samples covered with wax as a control, we were unable to do so given that our roughmeter entered into error due to the structural differences between the ceramic surface and that of the wax in the same way that it did when it encountered the metalic band.
Based on the studies of KATZ (1982) in reference to the effect of topical applications of fluoride gels with determined exposition times and periodicness and those of WUNDERLICH and YAMAN (1982), COPPS ( 1984), and JONES (1985) in vitro, we decided to submit our experimental samples to topically-applicated acidulated gel-based fluoride (MINUTE GEL from ORAL B) during a five minute exposition time -- the average time indicated for topical treatments in the clinic. This was analized quantitatively and qualitatively with the Surface Analyzer and graphic registers for each one of the samples were taken. Likewise, an in vitro study of surface changes that occur when the gel is applicated for five minutes daily over seven consecutive days which, according to JONES (1985), is equivalent to the clinical treatment undergone by a patient submitted to bi-annual or annual fluorizations for five years, was also perfomed.
Statistically, the roughness results obtained when the topical acidulated gel-based fluoride was applicated once, as well as seven times, did not present a significant variation in the degree of roughness of the three samples given that all the scores were within the confidence limits calculated according to a statistical probability of 98 per cent (p.< 0.02) as is shown in the results tables.
Therefore, our results differ from those of JONES who did, in fact, find a qualitative difference when treated and untreated samples were inspected with the human eye, despite the fact that he did not perform a quantitative roughmeter analysis. Conversely, COPPS (1984) did perform a roughmeter study on 1.5 millimeter samples which were, therefore, of a higher resolution than ours, but did not find quantitative differences in the degree of roughness. If we review the studies of WUNDERLICH and YAMAN in which different fluoride gels with varying exposition times and concentrations are used, we find that there does not appear to be any direct correlation between the increment of exposition time and the degree of roughness when analyzed with the roughmeter nor with an electronic scanning microscope. This contrasts with the present study in which, while significant differences in the average degree of roughness of treated ceramic surfaces are not found, a loss of glaze and the subsequent appearance in the surface of a ceramic mass which is irregular, and therefore causes a lack of shine and greater plaque retention, are observed with the Electronic Scanning Microscope.
1. There do not exist significant differences with respect to the changes in surface roughness in glazed feldespatic ceramic before and after being treated with acidulated gel-based fluoride.
2. Likewise, there are no statistical differences among results obtained when the aforementioned surface is treated with the gel one time during five minutes or five minutes a day during seven consecutive days.
3. When the surfaces are studied with an Electronic Scanning Microscope before and after one and seven applications of the fluoride gel, a gradual agression to the glaze layer of the ceramic is evidenced.
More exhaustive microscopic studies should be undertaken in order to confirm the present findings.
