Assessment of Effect of Different Sterilization Agents on Dimensional Accuracy of Different Impression Materials in Implant Prosthesis - An In vitro Study.

AIM: Sterilization of impression materials is of paramount importance. The present study was conducted to compare the effect of different disinfectants on dimensional accuracy of elastomeric impression materials used for implant prosthesis and other routine treatments.
MATERIALS AND METHODS: The present study was conducted with polyvinyl siloxane (PVS) (regular body), PVS (medium body), PVS (heavy body), and polyether (medium body) impression materials. Glutaraldehyde (2%) and sodium hypochlorite (NaOCl, 0.525%) were the disinfectant solutions employed in the study. After 16 h, the specimens were measured under Leica WILD stereomicroscope and dimensions were compared with master die.
RESULTS: The dimensional change in the Controls, 2% glutaraldehyde (Group I), and 0.525% NaOCl (Group II) was non significant where as Group III and Group IV showed statistically significant difference (P < 0.05). Results also showed significantly higher tear strength (newton/millimeter) in Control group followed by Group I and Group II.
CONCLUSION: PVS (heavy body) was found to be most stable, and polyether was seen to be stable of all the impression materials. Copyright:

INTRODUCTION

For successful prosthodontic therapy, impression is of paramount importance. The accuracy of impression determines the final outcome of treatment.[1] Immediately after obtaining impression, cast is made by different materials. Dental impression materials record alveolar ridges and surrounding tissues.[1]

Saliva comes in contact with impression compound, and hence, impressions need to be disinfectant. Oral cavity is the reservoir of variety of commensal. Several factors play an important role during impression that leads to dimensional change. It has been observed that different concentrations of disinfectant, composition of disinfectant, and exposure time are factors which determine the effect on impression.[1]

Based on efficacy, the disinfection process may be classified into three categories. In high-level disinfection, various microbial forms and bacterial spore activity are hampered. In intermediate-level disinfection, there is complete elimination of microorganisms such as tubercle bacilli, but spores are unaffected. Low-level disinfection has narrow antimicrobial activity. Different agents used as disinfectants are 2% glutaraldehyde, 0.525% sodium hypochlorite (NaOCl), iodophor, alcohol, phenol, and microwave irradiation.[2]

Numerous methods such as use of autoclave (steam), gas autoclave (ethylene oxide), UV light, and radiofrequency flow discharge are widely used for sterilization of impressions. Sterilization is the process in which any surface, object, or medium is free from microorganisms and spores. Sterilization is a recommended method of cross-infection control in the clinic setups. There is lack of research in this field.[3] This study aimed at comparing effect of different disinfectants on dimensional accuracy of elastomeric impression materials.

MATERIALS AND METHODS

This in vitro study was carried out in the department of prosthodontics. It comprised impression materials such as polyvinyl siloxane (PVS) (regular body), PVS (medium body), PVS (heavy body), and polyether (medium body) which were grouped into Group I, Group II, Group III, and Group IV, respectively. The approval for the study was obtained from ethical committee before the commencement of study.

Mold preparation

The preparation of mold was based on the recommendations by American Dental Association Specification No. 19. The undersurface area of die was applied by material with the help of fine-tipped impression syringe. The top surface of mold was covered with glass plate. Following this, the die was shifted to thermostatically controlled water bath (temperature of 32°C ± 2°C). 2% glutaraldehyde and 0.525% NaOCl were used for sterilization of die. Control was also included in which these impression materials were not disinfected by any solution. After 14 min, the entire assembly was recovered from the water bath. Disinfection time was 5 min.

The present study utilized thirty samples of each impression material. Ten were immersed in 2% glutaraldehyde, ten samples were put in 0.525% NaOCl solution, and remaining ten samples were allowed to dry bench cure. After 16 h, the measurement of scribed lines of impression material surface was assessed using stereomicroscope at ×10.

The assessment of tear strength was done using “trouser-method” test. Tear strength strips were prepared with a standard mold. The maximum force required to start a tear was calculated electronically as tear strength = force (Newton)/thickness (millimeters).

Statistical methods

Results were entered in MS Excel Sheet for interpretations. Tukey's multiple range test and one-way analysis of variance were used to assess tear strength. P < 0.05 was considered statistically significant.

RESULTS

Impression materials were divided into four groups; Group I comprised PVS (regular), Group II had PVS (medium), Group III had PVS (heavy), and Group IV consisted of polyether (medium body) as shown in Table 1. The dimensional change in materials disinfected with 2% Gluteraldehyde and 0.525% NaOCL compared with controls was not significant in Group I and Group II but significant change was seen in Group III and Group IV materials (P<0.05) as evident by Table 2 and Graph 1. Graph 2 and Table 3 show that there was significant higher tear strength with control group followed by Group I and Group II (Newton/millimeter).

Table 1

Different types of material used in the study

Group I	Group II	Group III	Group IV
Polyvinyl siloxane (regular)	Polyvinyl siloxane (medium)	Polyvinyl siloxane (heavy)	Polyether (medium body)

Table 2

Comparison of dimensional change of four elastomeric impression materials with different agents

Groups	Control	2% glutaraldehyde	0.525% sodium hypochlorite	Percentage change in 2% glutaraldehyde	Percentage change in 0.525% sodium hypochlorite	P
Group I	24.68	24.60	24.48	0.42	0.31	NS
Group II	24.62	23.56	24.74	0.16	0.19	NS
Group III	24.78	24.76	24.86	0.31	6.12	S
Group IV	24.72	23.42	24.32	6.82	6.78	HS

One-way ANOVA test, Tukey’s multiple range test. S: Significant, NS: Nonsignificant, HS: Highly significant

Graph 1

Comparison of dimensional change of four elastomeric impression materials with different agents

Graph 2

Tear strength of different groups

Table 3

Tear strength of different groups

Groups	Control	2% glutaraldehyde	0.525% sodium hypochlorite	P
Group I	0.8	0.9	0.7	NS
Group II	0.7	0.8	0.6	NS
Group III	0.6	0.7	0.4	S
Group IV	0.3	0.5	0.2	HS

S: Significant, NS: Nonsignificant, HS: Highly significant

DISCUSSION

The process of cross-infection control involves various stages such as identification of high-risk populations by judicious anamnesis and also use of a technical barrier consisting of masks, gloves, eyeglasses, and caps, both on the part of the professional and of his assistants; proper technique of disinfection and sterilization of instruments, other surfaces, and equipment with disinfectant solutions (2% glutaraldehyde, NaOCl, and quaternary ammonium compounds); and further sterilization in an oven or by autoclaving.[4]

Glutaraldehyde is a chemical agent (colorless liquid) which possesses high-level killing ability. It is present in various forms such as acidic, neutral, and alkaline. It is potent disinfectant, also known as chemosterilizer. It can act both thermophilic and thermostatic and capable of killing all types of bacterial and fungal spores, tubercle bacilli, and viruses.[5]

Other useful disinfectant such as 5% NaOCl is potent bactericidal in nature. It has additional advantage of stability, noninflammable, solubility, and nontoxicity. It is nonstaining and colorless. It has been observed that the chances of irritation to mucous membrane and corrosion of metals are common. It has limited effectiveness in organic environment.

Immersion of elastomers in water for longer period can lead to dimensional changes, owing to its hydrophilic nature.[6] This study aimed at comparing effect of different disinfectants on elastomeric impression materials.

We used different impression materials such as PVS (regular), PVS (medium), PVS (heavy), and polyether (medium body). We found that in Group I, 2% glutaraldehyde and 0.525% NaOCl exhibited nonsignificant change in dimensions whereas statistically significant difference of P < 0.05 was evident in Group III and Group IV. Khinnavar et al.[7] in their study assessed the effect of cold sterilization on dimensional changes of elastomers. Authors found that out of four impression materials, PVS (heavy body) was the most dimensionally stable, and polyether was the least dimensionally stable in both the groups.

We found that there was significant higher tear strength with control group followed by Group I and Group II (Newton/millimeter). Forrester-Baker et al.[8] assessed dimensional stability using ten impressions which were made of three addition-cured silicone impression materials. The shoulder region dimension values for each group of impression materials were significantly different from dimension of metal abutment in the original form. However, the use of gypsum-based die material for casting showed that no significant changes in dimensions were seen from those taken from the original metal abutment.

Abado et al.[9] assessed dimensional stability of six elastomeric materials based on disinfection methods used. Impression materials were immersion in 5.25% sodium hypochlorite solution for 10 min and 2% glutaraldehyde solution for 30 min, and there was control group in which no immersion was done. When the impressions were poured after treatment procedures, the measurement of stone casts with a Nikon Profile projector was done and compared with the master model. It showed no difference in disinfection in either of the group, and it was comparable with control.

Badrian et al.[10] studied 66 alginate impressions for the effect of three different types of disinfectant agents. Samples were contaminated with species such as Staphylococcus aureus, Candida albicans, and Pseudomonas aeruginosa. NaOCl (0.525%), Deconex, and Epimax were disinfecting materials used. Later, all those impressions were kept in plastic bags with humid rolled cotton for the period of 5 and 10 min. Disinfecting solution Epimax showed the highest disinfection action on S. aureus. The disinfection capacity of different agents can be increased as time elapses except for P. aeruginosa which was removed completely in both 5 and 10 min. Mahalakshmi et al. stated that the disinfection of impression material is essential to prevent infection.[11]

CONCLUSION

Authors concluded that among different elastomers used for the study, maximum stability was achieved with PVS (heavy body) and least stability was obtained with polyether.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.