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Brazilian Journal of Oral Sciences
Piracicaba Dental School - UNICAMP
EISSN: 1677-3225
Vol. 5, Num. 16, 2006, pp. 963-966

Brazilian Journal of Oral Sciences, Vol. 5, No. 16, Jan - March, 2006, pp. 963-966

Surface roughness analysis of ceramic systems after disinfection andsterilization procedures

Vinícius Carvalho Porto1* Rafael Balsalobre1** Luiz Fernando Pegoraro1 Acácio Lins do Valle1*

1DDS, MS *Professor, Department of Prosthodontics, Faculty of Dentistry of Bauru, University of São Paulo, Brazil **Graduate Student, Faculty of Dentistry of Bauru, University of São Paulo, Brazil
Correspondence to: Vinícius Carvalho Porto Rua Octávio Pinheiro Brisolla, n-9-75, Vila Universitária, Bauru São Paulo CEP-17012-901 Fax: 14 235-8277 E-mail: Vcporto@fob.usp.br

Received for publication: September 01, 2005
Accepted: February 02, 2006

Code Number: os06006

Abstract

The surface roughness of prosthodontic materials is an important factor that influences the amount of microbial plaque accumulation, thereby increasing the risk of caries and periodontal inflammation of abutment or adjacent teeth. Few studies exist that have investigated the influence of disinfectant materials on the surface roughness of prosthodontic materials. The purpose of this study is to evaluate the roughness changes in metal-ceramic and IPS Empress 2 ceramic structures, finished by either manual-polishing or glazing, followed by immersion in 2% glutaraldehyde solution for either 30 minutes (disinfection procedure) and 10 hours (sterilization procedure). The study consisted of 26 metalceramic specimens and 26 Empress 2 specimens measuring 10 x 10 x 2 mm. One-half of each group of specimens was polished by using rotatory instruments and the other half was glazed in a glazing oven (subgroups). Afterwards, the specimens were submitted to sterilization and disinfection in 2% glutaraldehyde for either 30 minutes or 10 hours, respectively. 3 specimens from each group were sterilized in autoclave, and for control group, the initial measurement of each specimen before the disinfection and sterilization procedures was obtained. The surface roughness was determined by a Hommel Tester T-1000, using the mean arithmetic Ra as roughness parameter. The results were statistically analyzed using a 4-way analysis of variance (ANOVA) method for individual comparisons among the means and the Tukey test at a significance level of p<.05. The results showed that there were no statistically significant differences of roughness in both groups, after immersion in chemical solution and sterilization in autoclave (p<.05). The mean of ceramic materials ranged from .631mm to 1.687mm in surface roughness. There was a statistically significant difference only among final polishing of ceramics (F=19.00; p<.001) and in the interaction between polishing and material used (F=18.83; p<.001). No significant changes in surface roughness of tested ceramic materials occurred after completion of the disinfection and sterilization procedures used in this study. Clinical implications: Infection control procedures are indispensable steps before cementation of prostheses. Based on the results of this study, prosthodontic materials can be disinfected or sterilized without causing significant changes in surface roughness.

Key Words: fixed partial denture, infection control, all ceramic, disinfection

Introduction

In clinical prosthodontics, there are many reasons for being concerned about infection control. In every procedure, the dentist comes into contact with materials that may be a source for transmitting infectious microorganisms. Dental impressions and prostheses represent potential contamination hazards that could transmit infections such as hepatitis B and Herpetic whitlow1. Previous studies have reported the presence of microorganisms transmitted to dental laboratories2-3. Pathogenic microorganisms can be cultured in laboratory pumice and other instruments4. The American Dental Association (ADA)5 recommends guidelines for cleaning, disinfecting, and handling impressions of dental prostheses transported between dental offices and laboratories3. However, a clinician may not know whether a disinfecting procedure might alter dental prosthetic surfaces. It has been shown that chemical disinfectants may promote alterations in the physical and mechanical properties of denture resins6-8 Other studies have demonstrated that materials such as topical fluoride preparations can affect the glaze and surface roughness of metal-ceramic restorations9-10. If disinfectants do promote surface roughness, restoration esthetics as well as periodontal health may be harmed. The surface roughness of ceramic would play an important role in initial plaque adhesion11-13.

In particular, surface roughness promotes the adhesion and retention of Candida albicans, which is of specific importance in denture-induced stomatitis pathogenesis14. Cannon et al.15 have suggested that Candida albicans has great affinity for adhering to saliva-coated hydroxiapatite. The production of collagenolytic enzymes by C. albicans can hydrolyze and degrade dentinal collagen fibers16. These enzymes could be involved not only with caries, but also with periodontal diseases, since previous studies have shown severe periodontitis in relation to Candida albicans17-18. Studies have been conducted to assess the surface roughness and methods for disinfecting fixed prosthodontics materials prior to their cementation19-20 Diamond burs and rubber wheels that are used for developing grooves in porcelain materials and for manual polishing21-22 can be associated with cross-contamination. Based on pertinent literature, the effects of antimicrobial chemical solutions on metal and ceramic materials used in clinical prosthodontics still remain unclear. This study evaluated the roughness of dental porcelain, finished by manual polishing or glazing, before and after submission to chemical solutions for disinfection and 2 sterilization methods.

Material and Methods

A circular stainless steel master model was machined, measuring 30mm in diameter and 7mm in the vertical dimension. An inner cavity measuring 10 x 10 x 2mm was prepared. This device was calibrated for steps of waxing to two dimensions: 0.5mm (nickel-chromium for metal-ceramic) and 2mm (waxing for all-ceramic specimens). Fifty-two (52) specimens, 26 of all-ceramic IPS Empress 2 (Ivoclar-Vivadent, Schaan, Liechtenstein) reinforced with lithium disilicate and orthosilicate crystals, and 26 of metal-ceramic (Duceram Plus-Degudent – Hanau-Germany), were fabricated for the two groups in this study.

Each group was divided into two categories, representing the way that the ceramic materials were polished: Polished by using rotatory instruments (13) or glaze (13). Of these 13 specimens of each material, five were immersed in a glutaraldehyde (Anti-G Plus 2% - Dentsply) for 30 minutes (disinfection procedure), five were immersed in the same chemical solution for 10 hours (sterilization procedure), and three was sterilized in an autoclave (Horizontal autoclave, HA 22 Model – SERCOM), representing the positive control group (Figure 1). The temperature of autoclave was 127 °C, for 15’, and a pressure of 1.5 Kgf/cm2.

Fabrication and polishing of specimens

Metal-ceramic specimens. Metal-ceramic specimens were made in square form, 1mm in diameter and 2mm thick (0.5mm metal alloy, 1.5mm ceramic). The first step was to fabricate 0.5mm of nickel-chromium alloy (DAN Ceramalloy – Osaka -Japan) by adjusting it to the master model to the desired thickness. The specimens were waxed-up and alloys were cast following the manufacturer’s directions. After the metal specimens were cast, the specimens were finished and polished. To simulate natural conditions, two thin layers of opaque porcelain were applied on each metal surface. Each metal plus opaque porcelain specimen (Duceram Plus - shade D3 - Degudent – Hanau-Germany) was set in the initial master model to ensure the porcelain (Duceram Plus – Shade -DC2 -Degudent – Hanau-Germany) buildup of each specimen. Excesses were removed and the specimens were then fired according the manufacturer’s instructions.

After this step, the specimens were divided into two subgroups. In one subgroup (n=13), the porcelain restoration was polished by using rotatory instruments. Progressively smoother diamond burs (Renfert –Hilzimgen - Germany) followed by progressively less abrasive rubber wheels (Labordental 0301/0306 Edenta AG Dental – labordental produkte – Haupstrasse -Switzerland) were used. The other subgroup (n=13) was submitted to a glazing procedure. All specimens were made in a calibrated furnace (Centurion Q 200, Ney dental –Bloomsield), according to the manufacturer’s instructions.

All-ceramic specimens. Empress castable porcelain specimens were fabricated from wax patterns (Proart Wax; Williams, Ivoclar-Vivadent, Amherst, N.Y). Ceramic specimens were pressed after investment. All procedures were performed with IPS Empress 2 materials and protocol. Finally, the all-porcelain group was glazed in a porcelain oven (n=13) or submitted to a polishing by using rotatory instruments (n=13), as carried out in the other group.

Surface texture

Only one examiner evaluated the surface texture after rigorous calibration. The mean surface roughness of each test specimen was obtained before immersion and after each period of autoclaving and immersion time: 10 minutes and 10 hours. Although various surface parameters were recorded, the mean arithmetic (Ra) was used to analyze surface changes. In this study, Ra values were obtained using a Hommel Tester T-1000 (HOMMEL Werke, Germany). This machine was used to record data to the nearest 0.01µm. For each specimen, 3 passes were carried out, and the mean Ra of these 3 readings was used for the statistical analysis.

Statistical analysis

A four-way analysis of variance (ANOVA) at p = .05 was used to assess statistical difference among methods for treatment of the specimens before and after disinfection and sterilization. Significance was determined by a Tukey multiple comparisons test at p=.05

Results and Discussion

In this study, the disinfection or sterilization method used at each time interval did not alter surface roughness (p<.05). There was a statistically significant difference only among final polishing of ceramics (F=19.00; p<.001) and in the interaction between polishing and material used (F=18.83; p<.001). Tukey’s test of multiple comparisons was used to identify significant difference among the respective variables. For both groups, the mean roughness values were lower for ceramics polished by using rotatory instruments than glazed ceramics. However, the surface roughness was significantly reduced only in metal-ceramic with manual polishing when compared with the others subgroups (p<.05), irrespective of the infection control method. Mean and standard deviation values of all groups before and after each treatment are shown in the Table 1. The metal structures ranged from .292mm to 1.139mm in surface roughness. There was no statistically significant difference between before and after immersion or autoclaving in the tested metal specimens either (p<.05).

Material surface roughness is considered to be an important factor in determining the amount of plaque accumulation. Bollen, Lambrechts and Quirynen12 stated that values of Ra equal to 0.2 mm were considered as the surface roughness threshold for dental plaque retention, and based on this review of literature, only Vita VMK 68 porcelain had a surface roughness of 0.2 mm. Polishing with successively finer abrasives such as tungsten-carbide burs, abrasive points, diamond tips and polishing discs resulted in little surface roughness, but not below the threshold surface roughness13 The surface roughness of a porcelain restoration is still an important aspect since it directly or indirectly affects resistance, patient comfort, periodontal health, and surface color. Ma and Johnson19 found that when using Dicor systems and precious casting alloys, even after immersion in disinfectant solution, the surface textures did not show significant changes. The results of their study are similar to those of the present work, although the infection control methods and porcelain used were different.

Manual polishing has been shown to produce smoother porcelain surfaces than oven-glazing21-22. This phenomenon may provide improvements in wear and lessen plaque retention. The roughness values found in this study were statistically significant when comparing the method of polishing the porcelain materials, with manual polishing producing the smoothest surfaces. These results do not imply that disinfection or sterilization procedures could alter surface roughness and consequently the clinical performance of porcelain and metal prosthodontic materials.

In summary, considering the possibility of plaque accumulation, the infection control is very important because the prostheses may present a risk of inducing gingival inflammatory responses. The infection control procedures applied to metallic or ceramic restorations are an indispensable process before cementation of a prosthesis. Based on the results of this study, prosthodontic materials can be disinfected in 2% glutaraldehyde for 30 minutes or sterilized either in 2% glutaraldehyde for 10 hours or an autoclave for15 minutes, without promoting changes in surface roughness.

References

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Copyright 2006 - Piracicaba Dental School - UNICAMP São Paulo - Brazil


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