Professor Dept. of Prosthodontics, Crown and Bridge, Sri Aurobindo College of Dentistry, Indore M.P.

Transcription

1 A COMPARATIVE EVALUATION OF DIMENSIONAL STABILITY OF POLYVINYL SILOXANE IMPRESSION MATERIAL FOLLOWINGDISINFECTION WITH 2% GLUTARALDEHYDE AND U.V. RAYS USING THREE DIMENSIONAL OPTICAL DIGITIZATION. 1 Kavita Maru, 2 3 Deshraj Jain, Rahul Maru 1 Professor Dept. of Prosthodontics, Crown and Bridge, Sri Aurobindo College of Dentistry, Indore M.P. 2 Professor and HOD, Dept. of Prosthodontics, Crown and Bridge, Govt College of Dentistry, Indore M.P. University Journal of Dental Sciences Research Article 3 Reader Department Of Periodontics, Index Dental College, Indore M.P ABSTRACT : Purpose : This study is an in-vitro evaluation of dimensional stability of polyvinyl siloxane impression material following disinfection by immersion in 2% Glutaraldehyde solution and U.V. irradiation using a three dimensional optical digitization method. Materials & Methods: 30 Impressions of the master die were made in the metal custom impression tray with polyvinyl siloxane impression material regular body by single mix-single step technique. These impressions were scanned to obtain digitized 3-D dimensional image before disinfection. Then 15 impressions were disinfected with immersion in 2% glutaraldehyde and 15 impressions with U.V. rays. These impressions were again scanned to obtain a digitized image after disinfection. The digital data of pre-disinfected image and post-disinfected image were aligned and superimposed to calculate the dimensional change. Results: Results showed that the mean value of dimensional change after disinfection with immersion in 2% Glutaraldehyde was mm and after disinfection with U.V. rays was 0.005mm. Conclusion: Disinfection of impression with 2% glutaraldehyde solution for 12 minutes and U.V. rays for 12 minutes does not affect the dimensional stability of polyvinyl siloxane impression material. Key Words : Disinfection, Optical digitization, Dimensional stability, Polyvinyl siloxane, UV disinfection Source of support : Nil Conflict of interest: None INTRODUCTION : Transmission of infectious diseases has aroused the concerns of both general public and health care workers in the past few decades because of emergence of potentially lethal infectious agents such as Hepatitis Virus, Herpes Simplex Virus, Human Immunodeficiency Virus & Mycobacterium tuberculosis etc. [1, 2] It was the Center for Disease Control in 1985 that first coined the phrase 'Universal Blood and Body Fluids Precautions' to overcome many problems that existed with the 'Identification-and-Isolation' approach. This new philosophy assumed that all patients were potentially infectious and therefore, the same precautions were required for everyone. [3, 4] Prosthodontic treatment primarily begins with impression making which may be a first link in microbial contamination during dental care. The standard procedure of rinsing impressions under running tap water immediately after removal from the mouth does not eliminate all microorganisms along with most saliva and blood. Leung & Schonfeld (1983) [5] observed the transfer of microorganisms from impression to the plaster casts, bringing about a risk of contamination to the laboratories of dental prosthesis. [6] Therefore the disinfection of impressions is a fundamental procedure in the routine dental practice. [7] It is important to weigh the effectiveness of the method/disinfectant used against the possible negative side effects on the material. Of particular interest are the dimensional accuracy, [8-16] surface details [17, 18] & wettability. [19] One of the most reliable method of disinfection, and therefore the most popular, is immersion of the impression. With this method, there is assurance that the disinfectant solution will University Journal of Dental Sciences, An Official Publication of Aligarh Muslim University, Aligarh. India 31

2 come into contact with all surfaces of the impression material & tray. However, immersion is not the method of choice for the Hydrocolloid materials, and some hydrophilic elastomeric impression materials, because they are highly hydrophilic and controversy exists whether this method should be used with polyether materials. The effect of immersion on the dimensional accuracy of impression is a critical factor and the main reason why one may choose an alternate method such as spray atomization, [20] U.V.rays [21] etc. Dental impression materials have been evaluated through analysis of the resulting dental casts of either linear or arch form configuration. There appears to be no consensus in the literature on measuring device that should be used to evaluate dental casts. Both measuring microscopes & calipers have been used. [22] These manual devices are easy to use & readily available but permit error due to operator fatigue & make linear measurements only between 2 points. These two dimensional measuring devices neglect to account for the dimensional changes that exist along a three dimensional surface. Considering the technological advancement in measuring methods and development of different disinfection procedures, this study is undertaken to elucidate possible dimensional alterations that may occur in Polyvinyl Siloxane impression material following disinfection with 2% Glutaraldehyde & U.V. rays using three-dimensional optical digitization. MATERIALS AND METHODS : A steel master die representing dental arch bearing five studs and two orientation studs was fabricated using computer aided designing by ProEngineer and computer aided machining on five axis vertical milling center. Five studs on the die represent five teeth; each was 10 mm in height and had flat circular occlusal surfaces. Three smaller anterior studs had 8.6mm diameter at base and 6 mm at top and two posterior studs had similar dimensions except the diameter were 3.1 mm greater (Figure-1). Two orientation studs were provided for the firm and steady placement of the master tray on the master die during impression making. Metal impression tray was designed and fabricated over the master die with 3 mm uniform space for impression material having five stud holes and two holes for the orientation studs by CAD- CAM technology and was used for making impressions of master die (Figure-2). Impression of custom made metal master die was made in custom made metal impression tray using polyvinyl siloxane impression material (Aquasil Monophase, dentsply) mixed according to manufacturer's instructions. Monophase viscosity was used because its pseudo plastic nature allows it to be used as both syringe as well as bulk material. This provides for a more convenient and practical technique of making impressions. A thin layer of universal tray adhesive was applied ten min. prior to impression making on the impression surface of the tray for the adherence of the impression material to the tray. Single mix single step technique was utilized for making the impression. The loaded tray was placed on the master die with the help of orientation studs and holes and pressed till it seated completely. The impression was allowed to set undisturbed for 5 minutes. And then after confirming that the impression was set (using a needle point) the impression was removed from the die. The reference points were placed on the impression tray so that the individual measurements are transformed into common coordinate system. The Digitization system used was ATOS II SO. (Advanced Topometric Sensor, SMALL object)which is an efficient 3D coordinate measuring technique for digitizing object surfaces quickly and with high local resolution. This is a non- contact and material independent three- dimensional digitizer and can digitize any arbitrary object such as work pieces, models, moulds etc (Figure-3). The fringe projection sensor ATOS is based on triangulation Principle: different fringe patterns are projected onto the object of measurement and are observed with 2 cameras. The software calculates the high precision 3-D coordinates of up to 1.3 million-object point maximum. The tray was mounted securely to a rotating platform and different fringe pattern were projected on the tray and these were observed by the two cameras on the sensor head and recorded. This process was repeated rapidly until the impression's entire topography had been mapped. The initial digital file was a collection of Points known as a "point file." The point file was converted to create a "mesh" of connected dots. These connected dots formed an image of the impression rendered through multiple triangular facets resulting "STL" files. This STL files were stored in the high performance PC as digital data (Figure-4). Ultra- violet disinfection unit used for disinfection of impression was made up of tin had two compartments upper and lower, mechanical timer and on-off switch. The upper compartment has two U.V. tubes of 8 watt, 254 nm wavelengths each and a silver-plated tray meant for keeping University Journal of Dental Sciences, An Official Publication of Aligarh Muslim University, Aligarh. India 32

3 impressions for disinfection. The lower compartment had the circuit of the unit. The tray was reoriented three times, so as to achieve a total of four exposures of 3 minutes each and thus complete cycle of disinfection (Figure-5). Two disinfection procedures were used. Group I: 15 impressions were disinfected by immersion in 2% glutaraldehyde solution for 12 minutes. Group II: 15 impressions were disinfected by placing the impression in U.V disinfection unit for 12 minutes. The disinfected impression was again placed on the rotating platform and a digitized image was obtained as described before. The digital data of postdisinfected impression was aligned and superimposed with digital data of predisinfected impression using common coordinate, which was determined by uncoded markers placed on the periphery of the impression tray before the scanning process. This alignment and superimposition was done by the ATOS application software. When these image data were superimposed on each other, deviation of each and every point of postdisinfected impression data from each and every point of predisinfected impression data was calculated in X, Y and Z direction and a contour map was created. This contour map helped in the easy visualization of differences in volume of the impressions due to disinfection process (Figure-6 & 7). The null Hypothesis was that there is no significant dimensional change in polyvinyl siloxane impression material after disinfection with 2% Glutaraldehyde and U.V. rays. Alternative Hypothesis (H1) was that there is significant dimensional change in polyvinyl siloxane impression material after disinfection with 2% Glutaraldehyde and U.V. rays. The above hypothesis was tested at 0.1% () level of significance (p0.001) for t-test for dimensional change in Polyvinyl Siloxane impression material after disinfection with 2% Glutaraldehyde and U.V. rays. To obtain the numerical data of the dimensional change, a point was selected from the digital data of predisinfected impression and its position in the X, Y and Z direction in the common coordinate system was determined. The position of the same point on postdisinfected impression in the same common coordinate system was also determined. The distance between these points gave the value of dimensional change on that particular location. Similarly thirty points were picked randomly from the entire scanned data at different locations and mean value of dimensional change was determined. 1. Ax, AY and AZ were distances between point on postdisinfected impression image and predisinfected impression image. 2. Ax + AY + AZ = A (general) 3. Average dimensional change in each sample A A2 A3... A RESULTS 1. The mean value for dimensional change of polyvinyl siloxane impression material after disinfection with 2% glutaraldehyde was mm with standard error (Table 1) 2. The mean value for dimensional change of polyvinyl siloxane impression material after disinfection with U.V. rays was 0.005mm with standard error (Table 2) 3. The value of 't' in t-test of difference of means for dimensional change of polyvinyl siloxane impression material after disinfection with 2% glutaraldehyde and with U.V. rays was calculated to be 2.87 insignificant at 0.1% level of significance. (Table 3) DISCUSSION : A complete elimination of all microorganisms is not possible by rinsing impressions under running tap water. Surface disinfection of impressions is highly desirable to inactivate infectious agents to reduce the potential risk of transmission of disease to dental personnel. Linear dental casts are not similar in shape to the dental arch and therefore are not subjected to the same strains that are produced when clinical dental impressions are made. Therefore a steel Master die was machined like a dental arch with 5 metal studs resembling teeth prepared for a fixed prosthesis. The white light 3-D digitizer can delineate X, Y and Z coordinates from a specimen without actually contacting the surface. The digitizer automatically tracks coordinates with precision and stores data from an inordinate number of points on a surface. These exacting features suggest that the white light digitizer might accurately and reliably measure the dimension of dental impressions while avoiding subjective errors. Ultraviolet rays are a powerful bactericidal [21] and fungicidal [23] agent and an effective means to disinfect polyvinyl impressions. R. K. Samra and S. V. Bhide [24]conducted a study to check persistence of microflora qualitatively and quantitatively on the untreated (control University Journal of Dental Sciences, An Official Publication of Aligarh Muslim University, Aligarh. India 33

4 group) and the disinfected impression surface after 24 h and used immersion systems like glutaraldehyde, sodium hypochlorite and the ultraviolet chamber. the disinfection systems were effective in reducing the microbial load with ultraviolet chamber as the most effective. Ultraviolet disinfection unit may more safely disinfect materials that might be harmed or altered by prolonged exposure to chemical solutions. Few limitations of Ultraviolet rays as a disinfectant are that they allow survival of microorganisms that are shielded in some or the other way on impressions and loss of UV radiation with time requires replacement of UV tubes. In this study the Ultraviolet disinfection unit is so designed (by giving the inner silver plated tray) to reflect the UV rays emitted so that items within the unit will be exposed to UV radiation from many directions. This can help in preventing the shadowing effect and also increases the effectiveness of UV rays. [21] Quick et al [25] reported an accuracy of 40 µm when stone casts were examined with a 3-dimensional digitizer. When dimensional changes of dental materials are evaluated, use of a digitizer has several advantages. The instrument is more reliable and precise than manual devices; is highly automated, thereby reducing operator error; and is able to record more data points, thereby allowing for more statistical analyses. However, the digitizer is expensive to purchase and maintain and requires custom software. The 3-dimensional optical digitizer allowed measurement of distortion across the surface of a dental impression. This characteristic combined with the digitizer's high accuracy, reliability, and low operator error made it an excellent measuring device. It was chosen to measure dimensional change on the impression itself to avoid the other factors associated with making a cast. Thus other variables the water powder ratio, temperature involved during manipulation of gypsum products the setting reaction setting expansion etc. were all brought to nil. The only variable that could cause dimensional change i.e. the disinfection procedure was considered. The results of this in-vitro study show that the dimensional change following disinfection with 2% Glutaraldehyde and U.V. rays when measurement are done along the three dimensional surface is in the range of 5-10 microns. These minute discrepancies are not considered clinically significant because crystalline structure of die stone does not reproduce detail to that magnitude [26] and the margin of error of the optical digitizer is within this range. Marginal discrepancies of cemented crowns as large as 50 microns are considered clinically acceptable [27]. This study is in general agreement with previous studies that appropriate disinfectants have little effect on the dimensional accuracy of impression materials. Merchant et al[28] found no dimensional change in polysulphide and vinylpolysiloxane after disinfection in various disinfectants. Johansen and Stackhouse[29] observed no change in addition silicone, polysulphide and condensation reaction silicone after 16 hours of immersion. Godbole and others[30] in a comparative study evaluated the effect of 10 minutes UV light disinfection on the dimensional stability of rubber base impressions and concluded that UV light treatment of these impressions do not exhibit any significant dimensional change when compared to controls. This indicates the value of the 3-dimensional optical digitizer as a method to evaluate dental materials. CONCLUSION : Within the limitations of this study it was found that disinfection with immersion in 2% glutaraldehyde solution for 12 minutes and U.V. rays exposure for minutes does not affect the dimensional stability of polyvinyl siloxane impression material. There is no statistically significant difference between the dimensional changes caused by either of both disinfection procedures. The disinfectants used in this study can be used for disinfection of polyvinyl siloxane impression material without distorting the impression. Table-1- Dimensional change following disinfection with 2% Glutaraldehyde solution. University Journal of Dental Sciences, An Official Publication of Aligarh Muslim University, Aligarh. India 34

5 Figure-3- ATOS II optical digitizer Table-2 Dimensional change following disinfection with U.V. Rays. Figure-4- Digitization process with fringe projection. Figure-5- UV Disinfection Unit Table-3- Statistical analysis of data collected after evaluating dimensional change of Polyvinyl Siloxane impression material after disinfection with 2% Glutaraldehyde and U.V. rays. Figure-6- Contour map of impression following disinfection with 2%Glutaraldehyde solution. Figure-1 - Metal master die and custom tray. Figure-2- Die and tray assembly. Figure-7- Contour map of impression following disinfection with U.V. rays University Journal of Dental Sciences, An Official Publication of Aligarh Muslim University, Aligarh. India 35

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7 27. Abbate MF, Tjan AH, Fox WM. Comparision of the marginal fit of various ceramic crown systems. J Prosthet Dent 1989; 61: Merchant VA, McNeight MK, Ciborowski CJ, Molinari JA. Preliminary investigation of a method for disinfection of dental impressions. J Prosthet Dent.1984; 52: Johansen RE, Stackhouse JA. Dimensional changes of elastomers during cold sterilization. J Prosthet Dent.1987; 57: Godbole S, Dahane TM, Patidar NA, Nimonkar SV. Evaluation of the Effect of Ultraviolet Disinfection on Dimensional Stability of the Polyvinyl Silioxane Impressions. an in-vitro Study. J Clin Diagn Res. 2014; 8:ZC73 ZC76. CORRESPONDING AUTHOR : Dr. Kavita Maru M.D.S. Prosthodontics Professor, Department of Prosthodontics Sri Aurobindo College of Dentistry Indore (M.P.) F-75 LIG Colony, Near Asian Hospital Indore Madhya Pradesh Contact No drkavitamaru@gmail.com University Journal of Dental Sciences, An Official Publication of Aligarh Muslim University, Aligarh. India 37