|Year : 2021 | Volume
| Issue : 1 | Page : 53-60
The effect of sterilization and disinfection on the physical-mechanical properties of preformed crowns
Shital Kiran Davangere Padmanabh, Vaidehi Patel
Department of Pediatric and Preventive Dentistry, Karnavathi School of Dentistry, Gandinagar, Gujarat, India
|Date of Submission||29-Nov-2020|
|Date of Decision||20-Feb-2021|
|Date of Acceptance||02-Mar-2021|
|Date of Web Publication||22-Apr-2021|
Dr. Shital Kiran Davangere Padmanabh
Karnavathi School of Dentistry, A/907, Uvarsad, Gandinagar - 382 422, Gujarat
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Introduction: Different sizes of crowns may be tried on children since there is no universal crown size because of distinctions in tooth morphology from one child to other. During the process of trial and error, the crown gets contaminated which needs to be sterilized for reuse of crown. This study was carried out to evaluate the physical–mechanical outcome after the sterilization and disinfection of pediatric preformed crowns. Materials and Methods: In total, sixty crowns consisted of 20 each, stainless steel crowns (SSCs) (3M ESPE), preveneered stainless steel (Kinder Krowns), and Zirconia crowns (Kinder Krowns) which were divided into four groups. G1 in which crowns did not undergo any sterilization, G2 consisted of fast sterilization, similarly G3 was slow sterilization, and G4 underwent chemical disinfection using Korsolex Plus for 15 min. Following sterilization, all the crown samples were observed under a stereomicroscope at ×200 magnification and assessed for color change, crazing, dimensional stability, and fracturing. Post hoc Tukey test and two-way ANOVA were performed for comparison between types of crowns and sterilization methods, with a significance level was set at P < 0.05. Results: There was no color change or fracturing following sterilization among crowns in any of the groups. Highest crazing was noted in stainless steel and the least in Zirconia crowns. Preveneered stainless steel was the most dimensionally stable and SSCs was the least. Conclusion: No color changes and fracture were noted in any type of crowns. Preveneered stainless steel was most dimensionally stable followed by Zirconia and SSCs. Maximum crazing was seen in SSCs and nil in Zirconia.
Keywords: Chemical disinfection, korsolex plus, preveneered stainless steel crowns, stainless steel crowns, zirconia crowns
|How to cite this article:|
Davangere Padmanabh SK, Patel V. The effect of sterilization and disinfection on the physical-mechanical properties of preformed crowns. J Indian Soc Pedod Prev Dent 2021;39:53-60
|How to cite this URL:|
Davangere Padmanabh SK, Patel V. The effect of sterilization and disinfection on the physical-mechanical properties of preformed crowns. J Indian Soc Pedod Prev Dent [serial online] 2021 [cited 2021 May 16];39:53-60. Available from: https://www.jisppd.com/text.asp?2021/39/1/53/314367
| Introduction|| |
Dental caries is the utmost prevalent disease involving primary teeth in children. Following pulpal treatments of carious primary teeth, they need to be restored using full coronal restorations as following pulp therapy teeth become more prone to fracture. Other indications for such restorations include an abutment for space maintainer, teeth with extensive wear restorations for multi-surface caries, fractured teeth, developmental defects, and patients at high risk for dental caries. Full coronal restorations comprise preveneered stainless steel, zirconia, stainless steel, open faced stainless steel, polymers such as strip, acrylic resin, and polycarbonate crowns, etc.
Stainless steel crown (SSC) is exceptionally durable, subjected to least sensitivity to technique during the procedure and provides the benefit of complete coronal coverage. To overcome the disadvantage of metallic appearance which is disliked by children and parents and due to demand for improvement, preveneered esthetic crown was introduced with the same durability and strength as SSC.
Prefabricated zirconia crowns are reasonably newer which provides to the patients with highly polished, esthetic, and superior results in comparison to the SSCs., Before fitting any sort of crown, tooth needs to be prepared by reducing its proximal, occlusal, and peripheral surfaces. During the fit of any preformed crowns to the abridged tooth, the designated preformed crown would not always be suitable for prepared tooth, therefore, to achieve appropriate fit one has to attempt differently sized crowns.
During the initial fit test, crowns can covertly contaminate with saliva and blood which might carry numerous microorganisms and viruses such as human immunodeficiency or hepatitis B which may possibly cause cross infection if the same crown is used in an alternative patient. Hence, for the same reason, the indirect and direct contact surfaces of crowns need to be disinfected and sterilized before re-use in another patient.
The exercise of re-use and re-circulation of these tried-in crowns is extensively established and practiced. Due to increased professional awareness and public concern, official rules from associated organizations and statutory bodies have steered to the standardization of infection control techniques for all patients which are termed as universal precautions. It is a professional responsibility and legal right of practicing clinicians to safeguard all equipment which is likely to contact with body fluids or oral cavity; therefore, they are liable to follow the recommended guidelines. In case, the same material needs to be re-used, it needs to endure an acceptable sterilization practice to aid in complete obliteration or denaturation of dangerous microorganisms and other contaminants.
Several authors have published articles regarding disinfection/sterilization of dental prosthesis,, and also a study has been carried out to know the physical properties of dental restorative materials changes on effect of sterilization techniques before antimicrobial testing.
Although a microbiological study regarding tried-in preformed metal crowns of five different decontamination methods have been carried out, no study is published regarding the effect of physical–mechanical properties of preformed crowns; therefore, this study was planned to compare and evaluate three types of crowns, namely, preveneered, zirconia, and SSCs on different decontamination methods.
| Materials and Methods|| |
As it was the policy of institution, that every study protocol should go through the institutional review board and ethical committee and get clearance, this study was submitted to obtain ethical clearance in accordance with the Central Ethics Committee on Human Research, India. This study was designed as a laboratorial investigation, which was carried out in the Department of Paediatric and Preventive Dentistry in association with Facilitation Center for Industrial Plasma Technologies.
A total of sixty crowns was obtained which included twenty SSCs from 3M ESPE and twenty each preveneered SSCs and zirconia crowns from Kinder Krowns. The sixty crowns (SSCs from 3M ESPE- Maplewood, Minnesota, USA) Preveneered SSCs from(Kinder Krowns-St. Louis Park, Minnesota, USA)Zirconia crowns from (Kinder Krowns-St. Louis Park, Minnesota, USA were divided into no disinfection application or sterilization which was control group (G1), and three experimental groups consisted of (G2) fast sterilization with steam autoclaving at 134°C, 30 psi pressure for 4 min, (G3) slow sterilization with steam autoclaving at 121°C, 15 psi pressure for 20 min, and (G4) chemical disinfection at room temperature for 15 min using ultrasonication bath containing korsolex plus from BODE Chemie. Each of the four groups consisted of 15 crowns, in which five crowns were randomly picked from each of the three crown types.
The crowns in groups G2 and G3 were packed in sterilization pouches and placed in front-loading Runyes autoclave having a capacity of 22 l for sterilization. For G4 group having 15 crowns including five crowns from all three types, chemical disinfection using Korsolex Plus was performed. Korsolex plus is an aldehyde-free instrument disinfectant concentrate. 100 g of this solution contains 9.2 g of dodecyl-bispropyltriamine and 13 g of didecyldimethyl ammonium chloride. To prepare 1 l solution, 20 ml korsolex plus was added into 980 ml of potable drinking water. The prepared solution was placed in the ultrasonic cleaner, and the crowns were put into the cleaner containing the solution and sonicated for 15 min, and then crowns were taken out and packed in a sterilization pouch. The procedure described for the disinfection of crowns was already validated in previous studies.,
All samples of crowns were studied under a stereomicroscope (Leica DMRM) at ×200 magnification with the positioner measurement gauge of 50 μm placed in a slot provided on the microscope. Proximal surfaces of SSCs, zirconia crowns, and preveneered SSCs were used for the stereomicroscopic study because these surfaces are flatter as compared to other surfaces, hence blurring of vision due to curvatures under microscope was minimized.
Stereomicroscopic images of G1 were used as the locus data for evaluating any changes on the crowns after sterilization or disinfection which was to be performed on the crowns belonging to experimental groups. Crown surfaces were scored for the absence or presence of any changes observed using the norms of Wickersham et al. with modifications. The parameters assessed were color change, crazing, dimensional stability and fracturing by the principal investigator, and finally scoring criteria for each of the parameters were evaluated. A single examiner was trainer for calibration for the determination of all the parameters in our study. In our study, the same examiner assed all micrographs for the re-evaluation after a week to validate the reproducibility for assessing each criterion.
Color change was evaluated by keeping the crowns belonging to control group and experimental groups side by side against green background. No change and change in color were given 0 and 1, respectively.
“Crazing is defined as internal cracks visible under ×10 magnification, but not detectable with an explorer gently moved over the surface.” Crazing was evaluated by checking for fine lines (internal cracks) under the stereomicroscope at ×200 magnification for reconfirmation. Score 0 was noted when no crazing was observed, whereas score 1 indicated few isolated cracks relating to less than one-third of surface, score 2 indicated cracks relating to one-third to one-half of the surface, and score 3 indicated cracks involving greater than> one half of the surface.
“Changes in surface contour are defined as deformation consistent with melting or flow of surface veneer and visible as dipping-in or flattening of the surface relative to contour of the crown.” Dimensional stability was evaluated by checking for irregularities such as dipping in or flattening of any part visible under the field at ×200 magnification. Score 0 was no changes, where score 1 indicated few isolated irregularities involved less than< one third of the surface. Score 2 consisted of irregularities restricted to one-third to one-half of the surface similarly score 3 was irregularities relating to >1 half of the surface.
“Fracturing is defined as cracks detectable both visually under ×10 magnification and manually when the tip of an explorer was moved gently over the surface detected roughness.” Score 0 indicated no fracturing. Score 1 was cracks detected visually and manually relating to <1 third of surface. Score 2 implicated cracks detected visually and manually from one third to one half of the surface and score 3 was cracks detected visually and manually >1 half of the surface.
The three criteria, crazing, dimensional stability, and fracturing were scored as 0, 1, 2, and 3 as per the scoring done for crazing and dimensional stability by Wickersham et al. Kolmogorov–Smirnov normality test was applied to verify the distribution of data before choosing the statistical test. Data were analyzed using SPSS version 23. Tests performed were descriptive statistics, two-way post hoc Tukey's test, and ANOVA for comparison among types of crowns and types of sterilization methods were employed. The perilous assessment for statistical connotation was set at P < 0.05.
| Results|| |
Micrographs of the results for preveneered crowns, Zirconia crowns, and SSCs in the control and experimental groups for crazing and dimensionally stability [Figure 1], [Figure 2], [Figure 3].
|Figure 1: Control group for (a) preveneered crowns (b) stainless steel crowns and (c) zirconia crowns|
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|Figure 2: Crazing group for (a) preveneered crowns (b) stainless steel crowns and (c) zirconia crowns|
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|Figure 3: Dimensional stability for (a) preveneered crowns (b) stainless steel crowns and (c) Zirconia crowns|
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No color changes were observed in any type of sterilization, either in control or experimental group [Chart 1].
Among preveneered crowns group G1, score 1 and 2 was 40% and 20% for score 3. In G2 group, score 3 was for score 0, 2, and 3 it was 40%. Internal cracks were not seen for G3 group. In case of G4 group, 40% was noted for score 2 and 3 and for G1, G2, G3, and G4 groups, score 3 was 100% and score 0 was 100% for stainless steel and zirconia crowns, respectively [Chart 2].
After sterilization, a statistically highly significant difference between crazing among crowns P < 0.001 and among sterilization methods P = 0.006. Taking various types of crowns and sterilization methods into consideration, a statistically highly significant variation was noted between crazing among the different crown groups P = 0.001 [Table 1].
|Table 1: Two-way ANOVA test for crazing and dimensional stability (dependent variable)|
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No significant result was observed from post hoc Tukey analysis for crazing which was compared among the various types of crowns [Table 2], however when compared among different groups statistically significant difference was established in sterilization methods when G1 was compared with G3 and also G3 with G4 [Table 3].
|Table 2: Post hoc Tukey test for crazing and dimensional stability for comparison among types of crowns|
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|Table 3: Post hoc Tukey test for crazing and dimensional stability for comparison among various groups|
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Among preveneered crowns in G1 group, score 1 and 3 was 20% and 80%, respectively, whereas for G2, score 1 was 20% and 40% for score 2 and 3. In case of G3 and G4, score 3 was 100%. For the SSCs, in G1, G2, G3, and G4 score 3 was 100% and for zirconia group G1 score 2 and 3 was 40% and 60%, respectively, similarly in G2, G3, and G4 score 3 was 100% [Chart 2].
Considering the crown types, sterilization methods, and both, there was no statistically significant difference in the dimensional stability [Table 1]. To confirm the results of two-way ANOVA test, post hoc Tukey test was done to compare various crowns and groups which was found to be statistically highly significant difference present between dimensional stability among preveneered and SSCs (P = 0.047) while no statistically significant differences were found on comparing dimensional stability among preveneered and zirconia crowns as well as stainless steel and zirconia crowns [Table 2]. In case of dimensional stability in crowns among various groups no statistically significant difference was obtained [Table 3].
No fracturing was seen after any type of sterilization in the various crowns among different groups.
| Discussion|| |
Pediatric dentist has a responsibility of superior disinfection for all the clinical procedures. With the advent of disposable articles, a secure situation in been created for both patients and dentist. Preformed metal crowns are used by pediatric dentist worldwide. Contaminated crowns which have come in contact with the blood and saliva cannot be discarded due to the expenditure involved; however, it can be reused after the proper effective sterilization without any changes to physical properties of the crown.
Usually, crowns are manufactured in such a fashion that circumferential and mesiodistal measurement is proportional to its length. After tooth preparation, selected preformed crown may not always acceptably fit the prepared tooth correctly during trial fitting of these preformed crowns to the reduced tooth. Majority of the clinicians select the crown after the tooth preparation, even some of them may use trial method; therefore, in these cases, crown should be properly sterilized before putting it back into the kit. Furthermore, during test fitting, undesirable crowns becomes contaminated with blood and saliva leading to infection if used in another patient. Hence, indirect and direct contact surfaces of such crowns require sterilized and/or disinfected prior their re-use in another patient. Whatever sterilization or disinfection method is used should not alter the material composition and must be effective.
The fast and slow sterilization procedures are routinely practiced for most of the dental instruments used in daily dental practice. Front loading autoclave with digital display was used for autoclaving procedures due to the ease of use, and most dental clinics prefer to use these types of autoclaves. Chemical disinfection was carried out in ultrasonic cleaner using disinfectant (Korsolex Plus) which is an aldehyde-free disinfectant concentrate hence metal corrosion was nil. A solution of chlorhexidine or chlorine, hypochlorite was considered, but it has been found that disinfectants encompassing sodium hypochlorite are reasonably cytotoxic, chlorine-based disinfectants are not cytotoxic; however, it may produce metal corrosion and chlorhexidine gluconate can modify the mechanical properties of the restorative materials.
Manufacturers have recommended various sterilization methods for different crowns like autoclaving for SSCs, zirconia crowns and cold sterilization for preveneered SSCs. The manufacturer's directives do not precisely advise the user not to subject their crowns for the heat sterilization; however, they advocate cold sterilization. Wickersham et al. initiated the project for couple of reasons.
First, the investigators believed that, due to the potential for bloody contamination of these crowns, cold sterilization was insufficient because it cannot be routinely verified for effectiveness. Second, anecdotal reports are that dentists are using heat to sterilize these crowns. They unknowingly might be weakening the facing bond and subsequently using a crown with an increased potential for failure of the facings.
To begin with, the specialists accepted that because of the potential for bleeding sullying of these crowns, cold disinfection was inadequate in light of the fact that it can't be regularly checked for adequacy. Second, narrative reports are that dental specialists are utilizing warmth to clean these crowns. They unconsciously may be debilitating the confronting bond and in this way, utilizing a crown with an expanded potential for disappointment of the facings.
To begin with, investigators accepted that because of the potential for bloody contamination of these crowns, cold disinfection was inadequate in light of the fact that it cannot be regularly checked for adequacy. Second, anecdotal reports are that dental specialists are utilizing heat to sterilize the crowns which could be weakening the bond and resulting in using a crown with a bigger possibility for breakdown of the facings.
Color change was assessed by keeping the crowns belonging to control and experimental groups side by side on a green cloth as a background to have good contrast to identify changes in color of crowns following sterilization since human eye can identify things clearer against green color background. No color change was observed in any types of crowns which contradict to Wickersham et al., wherein the only technique that caused color change of a magnitude noticeable by the human eye was the chemiclave using glutaraldehyde vapor. The probable reason could be that glutaraldehyde might have leached and come in contact with both sides of composite resin, the inner incisal and outer incisal which might have affected the strength of the veneer bond. Even if the colour changes was significant as in case of Wickersham et al. then in those cases the degree of color change would jeopardize the use of those crowns in pediatric dentistry.
Crazing which is termed as internal cracks was observed under ×10 magnification and no rough surface was evident on moving the explorer on the surface. Highest crazing was observed in SSCs and the least in zirconia crowns. Among different groups, highest crazing was seen in G4 (chemical disinfection) and the least in G3 (slow sterilization). Crazing might be due to the manufacturing process of crowns, and since it is not an external defect, it can be considered normal. The findings of this study agree Wickersham et al. and Kopel who testified that usage of methylmethacrylate causes crazing and color changes in polycarbonate crowns and also crazing can cause plaque development.
Dimensional stability was evaluated by checking for irregularities such as dipping in or flattening of any part visible under the field at ×200 magnification. Highest dimensional stability was observed in preveneered SSCs and the least in SSCs. Among various groups, dimensional stability was almost the same following any sterilization techniques.
Fracturing is defined as cracks detectable both visually under ×10 magnification and manually when the tip of an explorer moved gently over the surface detected roughness. Fracturing was evaluated both visually and manually. No fracturing was observed in any type of crowns which is in agreement with Wickersham et al. where no fracture or flattening or concavity was evident in the surfaces of the crowns following any sterilization procedure. Similar results were observed by Yilmaz and Guler when the crowns were examined under stereomicroscope at ×60 magnification, they did not discovery any variations in any of the valuation criteria (crazing, contour alterations, fracturing, vestibular surface changes). In contrast, they noted surface variations in crowns examined by scanning electron microscope (SEM). Van Dijken et al. have revealed that surfaces which are rough may develop alterations of the hybrid composite resin over a period of time of preveneered SSCs, resulting in the plaque formation.
Yilmaz and Guler observed that sterilizing and/or disinfecting NuSmile crowns and Kinder Krowns (preveneered) caused in irregular surfaces of the esthetic constituent and assists in the growth of dental plaque. He also found that, in SEM micrographs, as per the entire evaluation criteria, the slightest surface change was found by means of combination of chemical disinfection and ultrasonication. Chemical disinfection of SSCs with glutaraldehyde had disadvantages such as color change (for NuSmile crowns, Kinder Krowns), marked decrease in fracture resistance of Kinder Krowns. The time required for effective disinfection is more and also it is costly, the solution dynamically drops disinfectant power over a 14 days duration and leads to corrosion of selective metals, also it is a mucosal and skin irritant. Yilmaz and Guler experimented lysetol AF as a chemical disinfectant for the reason of aldehyde-free, metallic corrosion free and rapid action of the disinfection.
Yilmaz and Guler also observed surface changes of NuSmile and Kinder Krowns crowns and also vestibular surface changes and crazing to the amount that these variations were almost similar. All the procedures of steam autoclaving can actually cause deviations in the esthetic elements of the preveneered crowns vestibular surface. While autoclaving, degradation of resin may happen which could be the cause for consequential surface change.
Wickersham et al. noted significant decrease in fracture resistance in Kinder Krowns subjected to cold sterilization method as recommended by the manufacturer. The lower fracture resistance exhibited by the Kinder Krowns following soaking in glutaraldehyde could be associated with manufacturer's veneering process. Steam may play some part in changing the fracture resistance. In this study, steam techniques produced neither significant changes in fracture resistance nor color changes which were clinically detectable which indicated that steam techniques tested can be safely used by clinicians to sterilize either Kinder Krowns or NuSmile preveneered SSCs.
| Conclusion|| |
Within the limits of this study, it can be observed that there was no change in color and fracture noted following sterilization in stainless steel, preveneered stainless, steel and zirconia crowns. Preveneered SSCs were the most dimensionally stable followed by zirconia crowns and SSCs were the least dimensionally stable and also dimensional stability was almost same regardless of any sterilization technique.
Highest amount of crazing was seen in SSCs followed by preveneered SSCs and almost nil in zirconia crowns following sterilization. Chemical disinfection showed the highest crazing followed by control group and by steam autoclaving at 134°C, 30 psi pressure for 3 min. Least crazing was seen in steam autoclaving at 121°C, 15 psi pressure kept for 20 min.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3]