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Effect of surface roughness of porcelain on adhesion of bacteria and their synthesizing glucans
Effect of surface roughness of porcelain on adhesion of bacteria and their synthesizing glucans Keiji Kawai, DDS, PhD,a Masaaki Urano, DDS,b and Shigeyuki Ebisu, DDS, PhDc Osaka University Faculty of Dentistry, Osaka, Japan Statement of problem. In some instances of porcelain restoration, refinishing is inevitable. In terms of plaque accumulation on porcelain, refinishing could be a substitute method for glazing.
Purpose. This study compared the amount of adhesion of plaque components (bacterial cells and glucans) on porcelain disks with various degrees of surface roughness to assess the effects of surface roughness on the amount of plaque accumulation. Material and methods. Radiolabeled cell suspensions were incubated with porcelain disks for 3, 8, and 24 hours at 37°C, and the amounts of adhered cells and glucans were measured by using a liquid scintillation method. Results. The amount of cells and glucans adhered on porcelain increased with incubation time. The surface roughness value and the amount of plaque adhesion decreased with the increase in polishing level. However, the greatest amount of plaque was adhered on glazed surfaces, although their surfaces were smoother than the surfaces polished with 120- or 600-grit abrasive papers. Conclusion. With the exception of glazed surfaces, a positive correlation between surface roughness and the amount of plaque accumulation was observed. Repolishing with a diamond paste would not induce problems of plaque accumulation, compared with an intact glazed surface. (J Prosthet Dent 2000;83:664-7)
CLINICAL IMPLICATIONS Although the amount of plaque accumulation is minimal on porcelain, compared to other dental materials, the surface roughness significantly affects plaque accumulation. In terms of plaque accumulation on porcelain, repolishing the surface with a diamond paste could be a clinically acceptable method when a glazed surface needs adjustment such as grinding or finishing.
T
ooth-colored restorations are needed not only in the anterior regions but also in the posterior regions, because many patients want a natural-looking appearance. Although in most cases, resin composite or glass ionomer restorations are effective materials for these purposes, these restorations do not always satisfy the high level of esthetically related demands of patients for an extended time. With newly developed ceramic systems, one can easily produce sophisticated and highly esthetically pleasing ceramic restorations without much experience or need for refined technique. In addition, it has been reported that ceramic restoration can be applied to a posterior tooth if the ceramic restoration could adhere to the tooth sufficiently with adhesive luting cements.1 For these reasons, the use of ceramic restoration has recently increased extensively. However, ceramic restoration surfaces should not be adjusted at the time of the restoration trial, because aAssistant
Professor, Department of Conservative Dentistry. Fellow, Department of Conservative Dentistry. cProfessor, Department of Conservative Dentistry. bResearch
664 THE JOURNAL OF PROSTHETIC DENTISTRY
ceramics are very fragile. Thus, an occlusal check or adjustment before cementation is not ideal. Porcelain surfaces are smoothed and a final surface finish is achieved by glazing.2-5 Nevertheless, an occlusal adjustment is sometimes needed when the adaptation of restoration is not perfect. In such a case, refinishing of the adjusted ceramic surfaces should be performed intraorally.6-10 Although it is well-known that less plaque accumulates on ceramic or porcelain restorations, a rough surface accelerates plaque accumulation. Increased amount of plaque on the rough surface of ceramic restoration will exert not only caries-causing virulence, but also a harmful influence on periodontal tissue. For a full-coverage restoration, the risk of caries incidence would be negligible, but instead much attention has to be given to the gingival tissues. Poor polishing generates rougher surfaces, inducing more plaque accumulation and periodontal tissue inflammation. However, the polishing level or validity of the methods that are usually used for polishing ceramic restorations in the mouth have not been investigated sufficiently. VOLUME 83 NUMBER 6
KAWAI, URANO, AND EBISU
It has been reported that less plaque accumulates on ceramics compared with other dental materials such as resin composites or metals.11-13 Furthermore, surface roughness has been thought to be a very important factor in determining the amount of plaque accumulation.14 Thus, the amount of plaque adhered could be a good index for determining the surface roughness of the restoration. The purpose of this study was to quantitatively measure the adhesion of bacteria and their synthesizing glucans to porcelain disks treated with various finishing methods by using radioisotope-labeled bacteria and glucans. Then, the relationship between the surface roughness and the amount of plaque adhesion was determined.
MATERIAL AND METHODS Porcelain disks used in this study were fabricated from A3 shade porcelain blocks (9 mm diameter, Vita Celay blanks, A3M-9, Vita Zahnfabrik, Bad Sackingen, Germany). At first, the porcelain blocks were chosen and 60 disk-shaped specimens of 1 mm height were prepared with an Isomet low-speed saw (Buehler Ltd, Lake Bluff, Ill.). Next, all specimens were glazed with a glaze material (IPS Glaze, Ivoclar, Schäan, Liechtenstein) according to the manufacturer’s directions, and were then divided into 4 groups by the following surface treatments. Fifteen glazed disks were control specimens (group G). The remaining specimens (45 disks) were polished with an emery paper of 120-grit (15 disks, group R), 600-grit (15 disks, group S), and felt wheel with diamond paste (Dia-Finish, Renfert GmbH, Hilzingen, Germany) (15 disks, group D). The surface roughness (Ra) of the respective specimens was measured with a profilometer (SE-40C, Kosaka Lab, Tokyo, Japan). Ra is the arithmetic mean of the departures of the roughness profile from the profile center line.
Radiolabeling of bacteria by [3H]-thymidine Streptococcus sobrinus B13 was stored in Brain Heart Infusion (BHI, Difco Lab, Detroit, Mich.) broth that included 25% glycerin at –20°C until use. S sobrinus B13 was inoculated into 150 mL of BHI broth,2 including 18.5 Bq (0.5 mCi) of (6-[3H]-methyl)-thymidine (7.4 × 1010MBq/mmol [2.0 Ci/mmol], Amersham, LC Buckinghamshire, England) and cultured at 37°C for 18 hours. The cells were harvested by centrifugation at 1500g for 15 minutes with 0.05 mol/L phosphate buffer (pH 6.0; phosphate-buffered saline [PBS]). The washing procedure was repeated 2 more times, and finally cells were suspended in PBS at a concentration of 105 CFU/mL. These suspensions were routinely sonicated for 15 seconds in a ultrasonifer (model UP150P, Tomy, Tokyo, Japan) for eliminating bacterial chains. Cells were then washed once in PBS to remove any JUNE 2000
THE JOURNAL OF PROSTHETIC DENTISTRY
Table I. Means and SDs of Ra values for each surface finish Ra value Surface finish
Mean
(SD)
No. 120 polished surface No. 600 polished surface Diamond paste–polished surface Glazed surface
0.53 0.25 0.12 0.15
(0.09) (0.07) (0.02) (0.04)
labeled components released by ultrasonication. Cell numbers were determined by plating on BHI agar. Radioactive hot sucrose solution was prepared by mixing 50 µL of [14C]-sucrose (U) (22,274 Bq/mmol [602 mCi/mmol], New England Nuclear, Boston, Mass.) and 950 µL of distilled water. The amount of synthesized glucans over time was determined by the measurement of radiolabeled glucan.
Assay of adherence of bacterium to porcelain Adhesion test was initiated by 100 µL of washed [3H]-thymidine–labeled bacterial cell suspension in 9.8 mL BHI broth, including 3% sucrose and 100 µL of radioactive hot sucrose. Immediately after bacterial inoculation, the respective porcelain disks were suspended from orthodontic wires (0.9 mm diameter) and stored in a shaking bath adjusted to 37°C. Three, 8, and 24 hours later, the specimens were removed from test vials and were then immediately washed by PBS 3 times, and nonadhered bacteria and polysaccharide were removed. Specimens were then freeze-dried for 48 hours and then placed in liquid scintillation vials containing 10 mL of liquid scintillation fluid. Radioactivity was counted using a liquid scintillation counter (model LSC-673, Aloka, Tokyo, Japan). Values obtained were defined as the index of the total number of bacteria and glucans adhered to the porcelain disks.
Statistical analysis Two-way analysis of variance (ANOVA) was computed to determine significant differences among incubation times and surface finishing treatments for the amount of bacteria and glucans adhered. The Scheffé method of multiple comparison was used to test significant differences between the respective variables. Regression analysis was used to assess the relationship between the surface roughness and amount of plaque adhered.
RESULTS Table I presents the mean centric linear roughness (Ra) of the respective specimens. The surface obtained by polishing with diamond paste was the smoothest, followed by the glazed surface, and then the surface polished by 600-grit abrasive paper. Polishing by 120-grit emery paper produced the roughest surface. 665
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KAWAI, URANO, AND EBISU
Fig. 1. Effects of various porcelain finishing treatments on number of bacteria adhered at 3, 8, and 24 hours. Asterisk indicates values that are significantly different (P<.05).
Fig. 2. Effects of various porcelain finishing treatments on amount of glucan adhered at 3, 8, and 24 hours. Asterisk indicates values that are significantly different (P<.05).
When the bacteria were grown in a test tube, the number of bacteria increased exponentially from 3 to 10 hours, and then reached a plateau after 10 hours. On the basis of this finding, 3, 8, and 24 hours were adopted as incubation times for plaque component adhesion tests. The amount of bacteria and glucans adhered is illustrated in Figures 1 and 2, respectively. The amount of plaque components, such as cells and glucans, increased with incubation time. The diamond paste-polished surface giving the smallest Ra value exhibited the smallest amount of adhered cells and glucans. The greatest amount of plaque was adhered on the glazed surfaces, though it was not the roughest among all the finishing surfaces. From the statistical analysis, it was confirmed that there were no significant differences at any incubation time in the amount of the bacteria or glucans adhered among the various finishing surfaces, except between diamond paste–polished and glazed surfaces. The Scheffé test revealed significant differences of bacteria and glucans adhesion between glazed and diamond paste–polished surfaces at 24 hours (P=.015 and P=.021, respectively). However, there were significant differences (P<.0001) among the respective incubation times for any finishing surfaces. Although the relationship between the Ra value and the amount of bacteria and glucans adhered was significant for 3 polished surfaces (regression analysis, P<.05, r=0.990 and 0.996, respectively), there were no significance for all 4 surfaces, taking into account the results for the glazed surfaces (P>.1, r=0.794 and 0.802, respectively).
the eye,15 polishing of porcelain, in particular, is usually done to obtain an esthetically pleasing appearance and to prevent a roughened surface from abrading an opposing tooth. Another reason may be derived from the fact that less plaque could accumulate on a smooth surface obtained by polishing. However, it is often believed that a glazed surface of porcelain restoration would be the ideal.2-5 Some reports have claimed that glazed surfaces are not always the smoothest, and in most cases, polishing with a fine-particle–size abrasive would be necessary for obtaining a smoother surface.6-10 Our study confirmed that glazed surfaces were not the smoothest, based on the measurement of Ra values. The results of our study exhibited that more plaque was adhered on glazed surfaces, compared with other polished surfaces. This means that a glazed surface would not be clinically acceptable from a biologic point of view. Glazing can produce an undulating and rough surface that usually has irregularities, inducing more adhesion of bacteria and other substances. Although polished surfaces have been reported to have voids and microcracks on the subsurface of porcelain,9 these superficial defects did not contribute to the Ra values or the amount of plaque adhesion. Contrary to previous reports, polishing with diamond paste is helpful for obtaining a smoother surface that will prevent plaque from accumulating. Although 600- or 120-grit emery papers are usually not used clinically, these abrasive papers were adopted in this study for obtaining flat, uniform surfaces with no undulations. However, it was found from the preliminary experiment that the roughness of 600- or 120-grit paper polished surface is almost equivalent to that ground by a fine (Ra=.65) or super-fine grain finishing bur (Ra=.29), respectively.
DISCUSSION Although polishing is defined as the process of making a rough surface smooth to the touch and glossy to 666
VOLUME 83 NUMBER 6
KAWAI, URANO, AND EBISU
The bacterium used in our study is considered to be cariogenic because it has the capacity to synthesize adhesive glucans.16 With the help of these adhesive glucans, these bacteria can adhere even to a smooth surface such as enamel or restoration.17 Because this test enabled the measurement the adhesion of 2 important plaque components quantitatively, it revealed the characteristics of the surfaces made by the various methods of finishing. Unfortunately, besides the use of the naked eye, we do not have a method of determining whether the objective surface would be clinically smooth or not. A smooth surface is glossy, and its reflection coefficient is usually large. Taking this into consideration, less plaque adhesion might suggest a clinically smoother surface. Therefore, measuring the amount of plaque accumulation on the restoration could be a good index for judging whether the respective polishing method can achieve less plaque adhesion. Because this test method used radiolabeled bacteria and sucrose, the amount of grown bacteria and in situ products synthesized from sucrose could be precisely counted. Thus, this test could simulate the actual mouth sufficiently by reproducing the adhesion process as accurately as possible. However, there still remain some problems in this method. First, the specimen disks were not treated with saliva. Secondly, this artificial mouth used only 1 kind of bacterium, and the actual mouth was not reproduced completely. These are problems to be addressed in further studies.
CONCLUSIONS Within the results of this study, the following conclusions were drawn: 1. Although the amount of bacteria and glucans adhered increased with incubation time, at 24 hours, the plaque adhesion reached a plateau. 2. For surface roughness of each finishing method, the diamond paste–polished surfaces were smoother (smaller Ra), compared with glazed surfaces. 3. Diamond paste–polished surfaces exhibited the least amount of plaque adhesion (bacteria, glucans). 4. Although the surface roughness of the glazed surface was clinically acceptable, glazing did not exhibit the best result: the least amount of plaque adherence. Therefore, it was suggested that diamond paste polishing would be the most clinically acceptable finishing method from the perspective of minimization of plaque adhesion.
JUNE 2000
THE JOURNAL OF PROSTHETIC DENTISTRY
REFERENCES 1. Pratt RC, Burges JO, Schwartz RS, Smith JD. Evaluation of bond strength of six porcelain repair systems. J Prosthet Dent 1989;62:11-3. 2. Barghi N, Alexander L, Draughn RA. When to glaze—an electron microscope study. J Prosthet Dent 1976;35:648-53. 3. Sulik WD, Plekavich EJ. Surface finishing of dental porcelain. J Prosthet Dent 1981;46:217-21. 4. Raimond RL Jr, Richardson JT, Wiedner B. Polished versus autoglazed dental porcelain. J Prosthet Dent 1990;64:553-7. 5. Patterson CJ, McLundie AC, Stirrups DR, Taylor WG. Refinishing of porcelain by using a refinishing kit. J Prosthet Dent 1991;65:383-8. 6. Klausner LH, Cartwright CB, Charbeneau GT. Polished versus autoglazed porcelain surfaces. J Prosthet Dent 1982;47:157-62. 7. Newitter DA, Schlissel ER, Wolff MS. An evaluation of adjustment and postadjustment finishing techniques on the surface of porcelain-bondedto-metal crowns. J Prosthet Dent 1982;48:388-95. 8. Jacobi R, Shillingburg HT, Duncanson MG. A comparison of the abrasiveness of six ceramic surfaces and gold. J Prosthet Dent 1991;66: 303-9. 9. Patterson CJ, McLundie AC, Stirrups DR, Taylor WG. Efficacy of a porcelain refinishing system in restoring surface finish after grinding with fine and extra-fine diamond burs. J Prosthet Dent 1992;68:402-6. 10. Jagger DC, Harrison A. An in vitro investigation into the wear effects of unglazed, glazed, and polished porcelain on human enamel. J Prosthet Dent 1994;72:320-3. 11. Adamczyk E, Spiechowicz E. Plaque accumulation on crowns made of various materials. Int J Prosthodont 1990;3:285-91. 12. Olsson J, van der Heijde Y, Holmberg K. Plaque formation in vivo and bacterial attachment in vitro on permanently hydrophobic and hydrophilic surfaces. Caries Res 1992;26:428-33. 13. Harn R, Weiger R, Netuschil L, Bruch M. Microbial accumulation and vitality on different restorative materials. Dent Mater 1993;9:312-6. 14. Quirynen M. The clinical meaning of the surface roughness and the surface free energy of intraoral hard substrata on the microbiology of the supra- and subgingival plaque: results of in vitro and in vivo experiments. J Dent 1994;22:S13-6. 15. O’Brien WJ. Dental materials and their selection. 2nd ed. Chicago: Quintessence Publishing Co; 1997. p. 115-22. 16. Kohler B, Krasse B. Human strains of mutans streptococci show different cariogenic potential in the hamster model. Oral Microbiol Immunol 1990;5:177-80. 17. Gibbons RJ, van Houte J. On the formation of dental plaque. J Periodontol 1973;44:347-60. Reprint requests to: DR KEIJI KAWAI DEPARTMENT OF CONSERVATIVE DENTISTRY OSAKA UNIVERSITY FACULTY OF DENTISTRY 1-8 YAMADAOKA, SUITA OSAKA 565-0871 JAPAN FAX: (81)6-6879-2928 E-MAIL: [email protected] Copyright © 2000 by The Editorial Council of The Journal of Prosthetic Dentistry. 0022-3913/2000/$12.00 + 0. 10/1/107442 doi:10.1067/mpr.2000.107442
667
Purpose. This study compared the amount of adhesion of plaque components (bacterial cells and glucans) on porcelain disks with various degrees of surface roughness to assess the effects of surface roughness on the amount of plaque accumulation. Material and methods. Radiolabeled cell suspensions were incubated with porcelain disks for 3, 8, and 24 hours at 37°C, and the amounts of adhered cells and glucans were measured by using a liquid scintillation method. Results. The amount of cells and glucans adhered on porcelain increased with incubation time. The surface roughness value and the amount of plaque adhesion decreased with the increase in polishing level. However, the greatest amount of plaque was adhered on glazed surfaces, although their surfaces were smoother than the surfaces polished with 120- or 600-grit abrasive papers. Conclusion. With the exception of glazed surfaces, a positive correlation between surface roughness and the amount of plaque accumulation was observed. Repolishing with a diamond paste would not induce problems of plaque accumulation, compared with an intact glazed surface. (J Prosthet Dent 2000;83:664-7)
CLINICAL IMPLICATIONS Although the amount of plaque accumulation is minimal on porcelain, compared to other dental materials, the surface roughness significantly affects plaque accumulation. In terms of plaque accumulation on porcelain, repolishing the surface with a diamond paste could be a clinically acceptable method when a glazed surface needs adjustment such as grinding or finishing.
T
ooth-colored restorations are needed not only in the anterior regions but also in the posterior regions, because many patients want a natural-looking appearance. Although in most cases, resin composite or glass ionomer restorations are effective materials for these purposes, these restorations do not always satisfy the high level of esthetically related demands of patients for an extended time. With newly developed ceramic systems, one can easily produce sophisticated and highly esthetically pleasing ceramic restorations without much experience or need for refined technique. In addition, it has been reported that ceramic restoration can be applied to a posterior tooth if the ceramic restoration could adhere to the tooth sufficiently with adhesive luting cements.1 For these reasons, the use of ceramic restoration has recently increased extensively. However, ceramic restoration surfaces should not be adjusted at the time of the restoration trial, because aAssistant
Professor, Department of Conservative Dentistry. Fellow, Department of Conservative Dentistry. cProfessor, Department of Conservative Dentistry. bResearch
664 THE JOURNAL OF PROSTHETIC DENTISTRY
ceramics are very fragile. Thus, an occlusal check or adjustment before cementation is not ideal. Porcelain surfaces are smoothed and a final surface finish is achieved by glazing.2-5 Nevertheless, an occlusal adjustment is sometimes needed when the adaptation of restoration is not perfect. In such a case, refinishing of the adjusted ceramic surfaces should be performed intraorally.6-10 Although it is well-known that less plaque accumulates on ceramic or porcelain restorations, a rough surface accelerates plaque accumulation. Increased amount of plaque on the rough surface of ceramic restoration will exert not only caries-causing virulence, but also a harmful influence on periodontal tissue. For a full-coverage restoration, the risk of caries incidence would be negligible, but instead much attention has to be given to the gingival tissues. Poor polishing generates rougher surfaces, inducing more plaque accumulation and periodontal tissue inflammation. However, the polishing level or validity of the methods that are usually used for polishing ceramic restorations in the mouth have not been investigated sufficiently. VOLUME 83 NUMBER 6
KAWAI, URANO, AND EBISU
It has been reported that less plaque accumulates on ceramics compared with other dental materials such as resin composites or metals.11-13 Furthermore, surface roughness has been thought to be a very important factor in determining the amount of plaque accumulation.14 Thus, the amount of plaque adhered could be a good index for determining the surface roughness of the restoration. The purpose of this study was to quantitatively measure the adhesion of bacteria and their synthesizing glucans to porcelain disks treated with various finishing methods by using radioisotope-labeled bacteria and glucans. Then, the relationship between the surface roughness and the amount of plaque adhesion was determined.
MATERIAL AND METHODS Porcelain disks used in this study were fabricated from A3 shade porcelain blocks (9 mm diameter, Vita Celay blanks, A3M-9, Vita Zahnfabrik, Bad Sackingen, Germany). At first, the porcelain blocks were chosen and 60 disk-shaped specimens of 1 mm height were prepared with an Isomet low-speed saw (Buehler Ltd, Lake Bluff, Ill.). Next, all specimens were glazed with a glaze material (IPS Glaze, Ivoclar, Schäan, Liechtenstein) according to the manufacturer’s directions, and were then divided into 4 groups by the following surface treatments. Fifteen glazed disks were control specimens (group G). The remaining specimens (45 disks) were polished with an emery paper of 120-grit (15 disks, group R), 600-grit (15 disks, group S), and felt wheel with diamond paste (Dia-Finish, Renfert GmbH, Hilzingen, Germany) (15 disks, group D). The surface roughness (Ra) of the respective specimens was measured with a profilometer (SE-40C, Kosaka Lab, Tokyo, Japan). Ra is the arithmetic mean of the departures of the roughness profile from the profile center line.
Radiolabeling of bacteria by [3H]-thymidine Streptococcus sobrinus B13 was stored in Brain Heart Infusion (BHI, Difco Lab, Detroit, Mich.) broth that included 25% glycerin at –20°C until use. S sobrinus B13 was inoculated into 150 mL of BHI broth,2 including 18.5 Bq (0.5 mCi) of (6-[3H]-methyl)-thymidine (7.4 × 1010MBq/mmol [2.0 Ci/mmol], Amersham, LC Buckinghamshire, England) and cultured at 37°C for 18 hours. The cells were harvested by centrifugation at 1500g for 15 minutes with 0.05 mol/L phosphate buffer (pH 6.0; phosphate-buffered saline [PBS]). The washing procedure was repeated 2 more times, and finally cells were suspended in PBS at a concentration of 105 CFU/mL. These suspensions were routinely sonicated for 15 seconds in a ultrasonifer (model UP150P, Tomy, Tokyo, Japan) for eliminating bacterial chains. Cells were then washed once in PBS to remove any JUNE 2000
THE JOURNAL OF PROSTHETIC DENTISTRY
Table I. Means and SDs of Ra values for each surface finish Ra value Surface finish
Mean
(SD)
No. 120 polished surface No. 600 polished surface Diamond paste–polished surface Glazed surface
0.53 0.25 0.12 0.15
(0.09) (0.07) (0.02) (0.04)
labeled components released by ultrasonication. Cell numbers were determined by plating on BHI agar. Radioactive hot sucrose solution was prepared by mixing 50 µL of [14C]-sucrose (U) (22,274 Bq/mmol [602 mCi/mmol], New England Nuclear, Boston, Mass.) and 950 µL of distilled water. The amount of synthesized glucans over time was determined by the measurement of radiolabeled glucan.
Assay of adherence of bacterium to porcelain Adhesion test was initiated by 100 µL of washed [3H]-thymidine–labeled bacterial cell suspension in 9.8 mL BHI broth, including 3% sucrose and 100 µL of radioactive hot sucrose. Immediately after bacterial inoculation, the respective porcelain disks were suspended from orthodontic wires (0.9 mm diameter) and stored in a shaking bath adjusted to 37°C. Three, 8, and 24 hours later, the specimens were removed from test vials and were then immediately washed by PBS 3 times, and nonadhered bacteria and polysaccharide were removed. Specimens were then freeze-dried for 48 hours and then placed in liquid scintillation vials containing 10 mL of liquid scintillation fluid. Radioactivity was counted using a liquid scintillation counter (model LSC-673, Aloka, Tokyo, Japan). Values obtained were defined as the index of the total number of bacteria and glucans adhered to the porcelain disks.
Statistical analysis Two-way analysis of variance (ANOVA) was computed to determine significant differences among incubation times and surface finishing treatments for the amount of bacteria and glucans adhered. The Scheffé method of multiple comparison was used to test significant differences between the respective variables. Regression analysis was used to assess the relationship between the surface roughness and amount of plaque adhered.
RESULTS Table I presents the mean centric linear roughness (Ra) of the respective specimens. The surface obtained by polishing with diamond paste was the smoothest, followed by the glazed surface, and then the surface polished by 600-grit abrasive paper. Polishing by 120-grit emery paper produced the roughest surface. 665
THE JOURNAL OF PROSTHETIC DENTISTRY
KAWAI, URANO, AND EBISU
Fig. 1. Effects of various porcelain finishing treatments on number of bacteria adhered at 3, 8, and 24 hours. Asterisk indicates values that are significantly different (P<.05).
Fig. 2. Effects of various porcelain finishing treatments on amount of glucan adhered at 3, 8, and 24 hours. Asterisk indicates values that are significantly different (P<.05).
When the bacteria were grown in a test tube, the number of bacteria increased exponentially from 3 to 10 hours, and then reached a plateau after 10 hours. On the basis of this finding, 3, 8, and 24 hours were adopted as incubation times for plaque component adhesion tests. The amount of bacteria and glucans adhered is illustrated in Figures 1 and 2, respectively. The amount of plaque components, such as cells and glucans, increased with incubation time. The diamond paste-polished surface giving the smallest Ra value exhibited the smallest amount of adhered cells and glucans. The greatest amount of plaque was adhered on the glazed surfaces, though it was not the roughest among all the finishing surfaces. From the statistical analysis, it was confirmed that there were no significant differences at any incubation time in the amount of the bacteria or glucans adhered among the various finishing surfaces, except between diamond paste–polished and glazed surfaces. The Scheffé test revealed significant differences of bacteria and glucans adhesion between glazed and diamond paste–polished surfaces at 24 hours (P=.015 and P=.021, respectively). However, there were significant differences (P<.0001) among the respective incubation times for any finishing surfaces. Although the relationship between the Ra value and the amount of bacteria and glucans adhered was significant for 3 polished surfaces (regression analysis, P<.05, r=0.990 and 0.996, respectively), there were no significance for all 4 surfaces, taking into account the results for the glazed surfaces (P>.1, r=0.794 and 0.802, respectively).
the eye,15 polishing of porcelain, in particular, is usually done to obtain an esthetically pleasing appearance and to prevent a roughened surface from abrading an opposing tooth. Another reason may be derived from the fact that less plaque could accumulate on a smooth surface obtained by polishing. However, it is often believed that a glazed surface of porcelain restoration would be the ideal.2-5 Some reports have claimed that glazed surfaces are not always the smoothest, and in most cases, polishing with a fine-particle–size abrasive would be necessary for obtaining a smoother surface.6-10 Our study confirmed that glazed surfaces were not the smoothest, based on the measurement of Ra values. The results of our study exhibited that more plaque was adhered on glazed surfaces, compared with other polished surfaces. This means that a glazed surface would not be clinically acceptable from a biologic point of view. Glazing can produce an undulating and rough surface that usually has irregularities, inducing more adhesion of bacteria and other substances. Although polished surfaces have been reported to have voids and microcracks on the subsurface of porcelain,9 these superficial defects did not contribute to the Ra values or the amount of plaque adhesion. Contrary to previous reports, polishing with diamond paste is helpful for obtaining a smoother surface that will prevent plaque from accumulating. Although 600- or 120-grit emery papers are usually not used clinically, these abrasive papers were adopted in this study for obtaining flat, uniform surfaces with no undulations. However, it was found from the preliminary experiment that the roughness of 600- or 120-grit paper polished surface is almost equivalent to that ground by a fine (Ra=.65) or super-fine grain finishing bur (Ra=.29), respectively.
DISCUSSION Although polishing is defined as the process of making a rough surface smooth to the touch and glossy to 666
VOLUME 83 NUMBER 6
KAWAI, URANO, AND EBISU
The bacterium used in our study is considered to be cariogenic because it has the capacity to synthesize adhesive glucans.16 With the help of these adhesive glucans, these bacteria can adhere even to a smooth surface such as enamel or restoration.17 Because this test enabled the measurement the adhesion of 2 important plaque components quantitatively, it revealed the characteristics of the surfaces made by the various methods of finishing. Unfortunately, besides the use of the naked eye, we do not have a method of determining whether the objective surface would be clinically smooth or not. A smooth surface is glossy, and its reflection coefficient is usually large. Taking this into consideration, less plaque adhesion might suggest a clinically smoother surface. Therefore, measuring the amount of plaque accumulation on the restoration could be a good index for judging whether the respective polishing method can achieve less plaque adhesion. Because this test method used radiolabeled bacteria and sucrose, the amount of grown bacteria and in situ products synthesized from sucrose could be precisely counted. Thus, this test could simulate the actual mouth sufficiently by reproducing the adhesion process as accurately as possible. However, there still remain some problems in this method. First, the specimen disks were not treated with saliva. Secondly, this artificial mouth used only 1 kind of bacterium, and the actual mouth was not reproduced completely. These are problems to be addressed in further studies.
CONCLUSIONS Within the results of this study, the following conclusions were drawn: 1. Although the amount of bacteria and glucans adhered increased with incubation time, at 24 hours, the plaque adhesion reached a plateau. 2. For surface roughness of each finishing method, the diamond paste–polished surfaces were smoother (smaller Ra), compared with glazed surfaces. 3. Diamond paste–polished surfaces exhibited the least amount of plaque adhesion (bacteria, glucans). 4. Although the surface roughness of the glazed surface was clinically acceptable, glazing did not exhibit the best result: the least amount of plaque adherence. Therefore, it was suggested that diamond paste polishing would be the most clinically acceptable finishing method from the perspective of minimization of plaque adhesion.
JUNE 2000
THE JOURNAL OF PROSTHETIC DENTISTRY
REFERENCES 1. Pratt RC, Burges JO, Schwartz RS, Smith JD. Evaluation of bond strength of six porcelain repair systems. J Prosthet Dent 1989;62:11-3. 2. Barghi N, Alexander L, Draughn RA. When to glaze—an electron microscope study. J Prosthet Dent 1976;35:648-53. 3. Sulik WD, Plekavich EJ. Surface finishing of dental porcelain. J Prosthet Dent 1981;46:217-21. 4. Raimond RL Jr, Richardson JT, Wiedner B. Polished versus autoglazed dental porcelain. J Prosthet Dent 1990;64:553-7. 5. Patterson CJ, McLundie AC, Stirrups DR, Taylor WG. Refinishing of porcelain by using a refinishing kit. J Prosthet Dent 1991;65:383-8. 6. Klausner LH, Cartwright CB, Charbeneau GT. Polished versus autoglazed porcelain surfaces. J Prosthet Dent 1982;47:157-62. 7. Newitter DA, Schlissel ER, Wolff MS. An evaluation of adjustment and postadjustment finishing techniques on the surface of porcelain-bondedto-metal crowns. J Prosthet Dent 1982;48:388-95. 8. Jacobi R, Shillingburg HT, Duncanson MG. A comparison of the abrasiveness of six ceramic surfaces and gold. J Prosthet Dent 1991;66: 303-9. 9. Patterson CJ, McLundie AC, Stirrups DR, Taylor WG. Efficacy of a porcelain refinishing system in restoring surface finish after grinding with fine and extra-fine diamond burs. J Prosthet Dent 1992;68:402-6. 10. Jagger DC, Harrison A. An in vitro investigation into the wear effects of unglazed, glazed, and polished porcelain on human enamel. J Prosthet Dent 1994;72:320-3. 11. Adamczyk E, Spiechowicz E. Plaque accumulation on crowns made of various materials. Int J Prosthodont 1990;3:285-91. 12. Olsson J, van der Heijde Y, Holmberg K. Plaque formation in vivo and bacterial attachment in vitro on permanently hydrophobic and hydrophilic surfaces. Caries Res 1992;26:428-33. 13. Harn R, Weiger R, Netuschil L, Bruch M. Microbial accumulation and vitality on different restorative materials. Dent Mater 1993;9:312-6. 14. Quirynen M. The clinical meaning of the surface roughness and the surface free energy of intraoral hard substrata on the microbiology of the supra- and subgingival plaque: results of in vitro and in vivo experiments. J Dent 1994;22:S13-6. 15. O’Brien WJ. Dental materials and their selection. 2nd ed. Chicago: Quintessence Publishing Co; 1997. p. 115-22. 16. Kohler B, Krasse B. Human strains of mutans streptococci show different cariogenic potential in the hamster model. Oral Microbiol Immunol 1990;5:177-80. 17. Gibbons RJ, van Houte J. On the formation of dental plaque. J Periodontol 1973;44:347-60. Reprint requests to: DR KEIJI KAWAI DEPARTMENT OF CONSERVATIVE DENTISTRY OSAKA UNIVERSITY FACULTY OF DENTISTRY 1-8 YAMADAOKA, SUITA OSAKA 565-0871 JAPAN FAX: (81)6-6879-2928 E-MAIL: [email protected] Copyright © 2000 by The Editorial Council of The Journal of Prosthetic Dentistry. 0022-3913/2000/$12.00 + 0. 10/1/107442 doi:10.1067/mpr.2000.107442
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