|Year : 2014 | Volume
| Issue : 3 | Page : 163-169
Effect of disinfection on gypsum casts retrieved from addition and condensation silicone impressions disinfected by immersion and spray methods
SC Ahila1, C Thulasingam2
1 Department of Prosthodontics, SRM Dental College, Ramapuram, India
2 Department of Prosthodontics, Government Dental College, Chennai, Tamil Nadu, India
|Date of Web Publication||14-Aug-2014|
S C Ahila
Department of Prosthodontics, SRM Dental College, Ramapuram, Chennai, Tamil Nadu
Source of Support: None, Conflict of Interest: None
Introduction: The standard procedure of rinsing impressions under running tap water immediately after removal from the mouth eliminates cross contamination along with most saliva and blood. However not all micro-organisms are removed, they can be a source of infection. Surface disinfection to inactivate infectious agents would reduce the potential for disease transmission to dental personnel from contaminated impressions. Aim and Objectives: The objective was to evaluate the effect of disinfection on gypsum casts retrieved from disinfected addition and condensation silicone impressions by spray and immersion methods using various disinfectants. Materials and Methods: Twenty four impressions of each type of silicone material were made from a master model. In each group, 18 of the impressions were disinfected, while the other 6 impressions were considered as a control. The impressions were then rinsed for approximately 10 s under cold tap water and disinfected by an immersion or spray method for 10 min. All impressions were poured in Type IV die stone using a double-pour technique. Results: The dimensional stability of the impressions was evaluated using a travelling microscope and the surface roughness (Ra) was assessed using a perthometer (M1 - Mahs). The means of dimensions and surface roughness were calculated and statistically analyzed using ANOVA. Conclusion: The disinfection procedure didn't show significant changes on dimensional stability and surface roughness of gypsum casts retrieved from disinfected addition and condensation silicone impressions by immersion and spray methods.
Keywords: Disinfection, immersion, silicone impression, spray
|How to cite this article:|
Ahila S C, Thulasingam C. Effect of disinfection on gypsum casts retrieved from addition and condensation silicone impressions disinfected by immersion and spray methods. SRM J Res Dent Sci 2014;5:163-9
|How to cite this URL:|
Ahila S C, Thulasingam C. Effect of disinfection on gypsum casts retrieved from addition and condensation silicone impressions disinfected by immersion and spray methods. SRM J Res Dent Sci [serial online] 2014 [cited 2022 May 16];5:163-9. Available from: https://www.srmjrds.in/text.asp?2014/5/3/163/138724
| Introduction|| |
Public awareness of the potential for spread of micro-organisms and infectious diseases in the dental office among the dental practitioners,  auxiliaries and laboratory personnel has increased significantly. Some micro-organisms, are not normally pathogenic, but may cause opportunistic infections in immuno compromised individuals, such as those with hepatitis, tuberculosis, herpes and AIDS. , Saliva and blood contaminated dental impressions serve as a source of infectious micro-organisms to dental personnel who handle the impressions or cast made from them. ,,
Impression disinfection is now considered as a routine procedure in dental offices and laboratories.  Different methods of disinfection have been suggested including argon radiofrequency, glow discharge,  however, the use of a disinfectant solution in some form is a more common procedure.
Spray disinfection of the gypsum cast is a reliable method but it is not a practical method in avoiding cross contamination within the dental team.  Spray disinfection of the impression  is very convenient and is therefore a very popular method of disinfection. Immersion however is the most reliable method  because it guarantees that all surfaces of the impression and impression tray will come into contact with the disinfectant solution. Durr and Novak  found that an improvement in the quality of stone casts from irreversible hydrocolloid impressions that had been disinfected by immersion.
Sterilization of impressions is expensive,  time consuming and potentially damaging to the materials, since surface disinfection with various chemicals by spray or immersion has become a practical alternative. ,
A wide variety of disinfectants are commercially available, but specific recommendations about which one to use are primarily based on the disinfection characteristics of individual disinfectants.  Chemical agents suitable for the disinfection of dental impressions routinely used are chlorine compounds, glutaraldehydes, phenols and iodophors. They have been shown to be effective against viruses, spores and bacteria. ,,
Important factors to be considered when a disinfection protocol for dental impressions is being considered include the effectiveness of the disinfection procedures, then chemical stability of the disinfecting solution and the influence of the disinfectant procedure on the dimensional stability and surface reproduction of the impression materials and resultant casts. 
In the dental literature, numerous studies investigating different disinfection products, procedures, contact times and disinfectant agents suggest that there are no universally recognized disinfection protocols for dental impressions. Therefore, individual analysis of impression materials is required. Hence, this study was conducted with the objectives of evaluating the effect of disinfection on gypsum casts retrieved from disinfected addition and condensation silicone impressions by spray or immersion methods.
| Materials and methods|| |
The dimensional stability of the impressions was assessed indirectly by measuring several clinically relevant dimensions on gypsum casts recovered from impressions of a mandibular typodont. The typodont contained stainless steel inserts on the occlusal surface of both mandibular first molars and on the lingual surface of the mandibular central incisors, these inserts had positive grooves on the occlusal surface which served as reference marks for making measurements. In addition, the mandibular right premolar was modified to include a stainless steel premolar complete veneer crown preparation with a 6° taper. It had a groove on the facial surface to evaluate the surface quality [Figure 1].
The impression materials used are listed in [Table 1]. From each impression material, 24 impressions were made in which 18 were disinfected, while the other 6 were considered as control group. A total of 126 samples were made for this study.
Single and dual mix elastomeric materials were used to make impressions within a minute from start of mixing, the material to be injected was mixed and loaded into a 2 ml disposable syringe (DISPOVAN, Hindustan Syringes and Medical Devices Ltd., India) and injected onto the master model, then the tray material was mixed and placed. After a setting time 10 min, impressions were removed from the master model [Table 2] and [Table 3]. All impressions were rinsed for approximately 10 s under cold tap water to simulate saliva removal. The controls were air-dried and left to bench set for 30 min while the test impressions were immersed or sprayed in appropriate disinfectant (glutaraldehyde 2.45%, NaOCl 4%, povidone iodine 5%) at room temperature for 10 min.
After disinfection, both control and test impressions were rinsed again for 10 s under cold tap water and dried with air. All impressions were cast in die stone using a double-pour technique. Type IV die stone gypsum (Ultra Rock, Kalabhai Karson Pvt. Ltd., India) with a ratio of 16 ml of water to 70 g of improved stone used for the first pour. The improved stone was mixed by hand then mechanically mixed under vacuum. All mixes were vibrated into boxed impressions and allowed to set for 1 h. Later, the premolar die was prepared after 24 h.
A measuring microscope (Suswax Optik Travelling Microscope, India) capable of measuring up to 1 μm was used to measure five clinically important features of the gypsum casts including:
- Molar to molar
- Molar to incisor
- Bucco-lingual width
- Mesio distal width
- Occluso gingival height.
The measurements were taken 3 times of each cast and the mean of the three values were taken for this study.
The surface quality of disinfected impressions and controls was assessed by recording the surface roughness of the facial surface of the premolar die. A surface analyzer instrument (Perthometer - M1 - Mahs) [Figure 2] was used for this purpose with Ra in μm (the arithmetic mean deviation of roughness profile) being the roughness parameter selected for the presentation of results. Three passes of the stylus were recorded on slightly different areas of the facial surface of each gypsum die and again the mean value used in data analysis. The test conditions were: Cut off length (Lc) 0.250 mm, drive speed 0.25 mm/s, sample length 1 mm, traverse length (LT - 2.90 mm) and cutting depth (Rz) 7.35 μm. Surface quality of gypsum casts retrieved from disinfected Provil impression by spray method is shown in [Figure 3] and [Figure 4].
| Results|| |
For this study, Reprosil, Provil and Speedex silicone impression materials were taken for evaluation. The values were statistically analyzed using one-way ANOVA at 5% level of confidence and Tukey's-HSD test for multiple group comparison. On comparing the dimensional stability and surface roughness of the gypsum casts retrieved from disinfected addition and condensation silicone impressions by the immersion and spray method, the statistical analysis didn't show any significant difference (P > 0.05) between both methods [Table 4],[Table 5] and [Table 6].
|Table 4: Comparison of disinfectant solutions and sprays-Reprosil 10 min|
Click here to view
Graphs 1-6 [Additional file 1] show the dimensions measured at 5 sites from casts obtained from Reprosil, Provil and Speedex after treatment via immersion or spray method with glutaraldehyde, povidone and NaOCl for 10 min with their control. On statistical analysis the P value is <0.01. Hence the results found to be insignificant. Sodium hypochlorite had the least adverse effect on the accuracy, but it had little effect on the surface quality when compared with other solutions.
The null hypothesis tested was that the different types of disinfectants used would produce similar effects on the dimensional accuracy and surface quality of the various impression materials evaluated and the resultant casts.
| Discussion|| |
The potential for cross contamination is exacerbated in dental procedures as exposure to blood and saliva could provide a significant source of micro-organisms.  Interestingly, the results from the previous study indicated that there were more bacterial colonies on corresponding dental cast compared with the source impression.  The previous study results showed that gypsum does not have any inherent antibacterial property in them. Hence, proper impression disinfection procedure to be done to control the cross infection from dental clinic to laboratory. 
Impressions need to be treated with disinfectants, which do not affect their dimensional stability.  Surface roughness of gypsum casts was adversely affected using the disinfectant solution as mixing water substitutes.  The incorporation of a quaternary ammonium compound into an irreversible hydrocolloid impression material resulted in a greater incidence of dermal and mucosal irritation. 
Gypsum combined with iodophor, neutral glutaraldehyde, phenol, or sodium hypochlorite solutions reduced the number of organisms to the level of the negative control
within 1 h.  NaOCl is one of the original and most widely used disinfectants  The results of the previous study showed that alginate impression disinfected with sodium hypochlorite found to be highly effective than iodophor against both aerobic and anaerobic bacteria. The literature showed that is effective against HIV, hepatitis bas well as numerous other bacterial species and their spores, viruses and fungi. , Although the addition of sodium hypochlorite to gypsum appears capable of providing a disinfected cast, the effect it has on the physical properties is a concern.  Ivanovski et al.  have reported a decrease in the compressive strength with the addition of sodium hypochlorite to the stone. The results of the immersion disinfection of hypochlorite showed little or no deterioration of surface detail, compressive strength, and dimensional accuracy of gypsum cast.
The stone casts produced from condensation silicone impressions that were disinfected by sodium hypochlorite, gluteraldehyde, povidone iodine demonstrated slight expansion as a result of shrinkage that took place in the condensation silicone material upon disinfection. Whereas, casts produced by pouring condensation silicon impressions following disinfection by 4% sodium hypochlorite displayed marginal addition in dimension compared with other disinfectant. These differences may be attributed to the nature of the setting reaction of the condensation silicone rather than to the disinfectant itself. These results confirming the results of the previous studies. ,
The changes in the dimensions of the resultant casts produced by pouring disinfected addition-cured silicone impressions were extremely minimal, clinically insignificant and within the range of changes that is acceptable by the standard specifications.  The effect of disinfectants on the surface quality of impressions indicated that the silicones, both addition and condensation-cured types, were superior in terms of surface integrity to the other impression materials. This is due to the hydrophobic nature of silicones, which made the surface of these impressions highly resistant to the attack by the aqueous disinfectants regardless of their types or the length of exposure period.
The stone casts poured from condensation-cured silicone impressions that were disinfected by each of sodium hypochlorite, 2% gluteraldehyde and povidine iodine demonstrated slight expansion as a result of shrinkage that took place in the condensation-cured silicone impression material upon disinfection. These differences may be attributed to the nature of the setting reaction of the condensation-cure silicone rather than to the disinfectant itself. This is consistent with previous studies, [33-36] which pointed that care should be taken when working with condensation-cured silicone impression, which may uncontrollable contraction due to the loss of byproducts.
Sterilizing elastomers by autoclave and microwave is associated with mild linear dimensional changes. Elastomeric impressions should be safely sterilized using autoclave and microwave because chemical disinfection alone is less lethal and does not eliminate all micro-organism.  A newly formulated, fast-setting, ring-opening metathesis-polymerization impression material was shown to possess accuracy similar to that of polyether and vinyl polysiloxane impression materials, with intermediate and high-level disinfection. ,
The dimensional changes were significant both as a function of time and the applied disinfectant. The results of the study showed that sodium hypochlorite had the least adverse effect on the accuracy and it had little effect on surface quality of the casts retrieved from disinfected addition and condensation silicone impressions when compared to povidone iodine and glutaraldehyde. When comparing the dimensional stability and surface roughness of gypsum casts retrieved from disinfected addition and condensation silicone as a result of either the immersion or spray method there was no significant difference.
The impression material was mixed manually by one author even though the uniformity of the mix and the penetrability of the disinfectant solution are unpredictable. Impression materials that do not absorb disinfecting solutions may not be adequately disinfected if micro-organisms become entrapped within the material when impression is taken.
Impression disinfection becomes a mandatory procedure in dental offices and laboratories. The disinfection procedure should be prescribed for all types of impression materials for the recommended time. By following infection control procedures, the transmission of infections through impressions can be prevented.
| Conclusion|| |
Within the limitations of the study, it was concluded that there was no significant difference on dimensional stability and surface roughness of the gypsum casts retrieved from disinfected addition and condensation silicone impressions by immersion and spray methods.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]