EFFECT OF IMMERSION AND SPRAY ATOMIZATION TECHNIQUE OF DISINFECTION ON COMPRESSION RESISTANCE OF TWO INTEROCCLUSAL RECORDING MATERIALS.

Junu Henry 1 , Basavaraj S. Salagundi 2 , Rupesh P. L 3 , Bhavana B.L 4 , Bharat Kataraki 4 and Vachan Poonacha 5 . 1. MDS III year Postgraduate, Coorg Institute of Dental Sciences, Karnataka, India. 2. MDS, Professor and Head Of Department, Coorg Institute of Dental Sciences, Karnataka, India. 3. MDS,Professor and Chair, Coorg Institute of Dental Sciences, Karnataka, India. 4. MDS, Senior Lecturer, Coorg Institute of Dental Sciences, Karnataka, India. 5. MDS, Reader, Coorg Institute of Dental Sciences, Karnataka, India. ...................................................................................................................... Manuscript Info Abstract ......................... ........................................................................ Manuscript History Received: 14 December 2018 Final Accepted: 16 January 2019 Published: February 2019


ISSN: 2320-5407
Int. J. Adv. Res. 7 (2), 1007-1020 modifications intraorally, thus reducing the chairside time. 2 Apart from the operator's clinical ability and the technique followed the material used can critically affect the accuracy of interocclusal registration. 2 Polyvinylsiloxane elastomeric materials are recently been introduced. 1 Addition silicone impression materials (polyvinylsiloxane) have been widely accepted due to excellent dimensional stability, superior recovery from deformation, and precise detail reproduction. 3 Recording and transferring of accurate existing occlusal records is of prime importance for a successful restoration. Interocclusal recording of the relationship of the mandible to the maxilla is a simple but complex procedure. The inaccuracies attributed to the interocclusal records can be divided into three main categories: 1. The biologic characteristics of stomatognathic system, 2. Manipulation of the material and 3. The properties of the interocclusal recording materials Polyvinyl siloxane have also shown to have better resistance to compression. 3 One of the most desirable characteristics of the interocclusal registration material is resistance to compression after polymerization. The material should be rigid enough to resist the distortion that might be caused from the weight of the dental casts, the components of the articulator, or other means used to stabilize the casts during the mounting procedure. The ability of an interocclusal registration material to resist compressive forces is very important because any discrepancy between the intraoral relationships of the teeth and the position of the teeth on the mounted working casts will result in restorative errors. 2 It has been shown that the compression resistance decreases as the thickness increases. 4 Interocclusal registration materials act as a significant source of cross contamination, so these must be disinfected immediately after their removal from mouth. Occupational safety and health association (OSHA) guidelines in 1996 required dentist, dental laboratory employers and other employers in health care fields to provide protection for their employees against the possibility of infection transmission by implementation of conscientious and consistent barrier controls. 8 There are two important factors to consider when choosing a disinfectant namely, its ability to eliminate microbial contamination and its effect on the resultant material. 8 Impressions are a potential vehicle in transmission of infectious agents. Moreover, cast produced from contaminated impressions may themselves be contaminated because microorganisms are able to migrate from impressions into the cast, while setting occurs. The disinfection of impressions and other laboratory fabricated material is more difficult and requires immersion. The agent chosen must not have a deleterious effect on the compression resistance and tear strength of impression materials and must act in reasonable time. So the American Dental Association in 1988, 1991 and 1996, and Council on Dental Materials, Instruments and Equipment in 1988 issued guidelines on disinfecting impressions both by immersion and spray atomization techniques. [8][9][10] Since only limited amount of data regarding the effect of immersion and spray atomization techniques on interocclusal recording materials are available in literature, this study intended to see the effect of immersion and spray atomization technique of disinfection on compression resistance of polyvinyl siloxane and polyether interocclusal recording materials.

PROCEDURE
Specimens of the polyvinyl siloxane (Orange bite Bite Registration material, Ref No:5013, Hannover, Germany) and polyether (3M ESPE Ramitec TM Penta TM , Seefeld, Germany interocclusal) recording material was prepared according to American Dental Association no 19. Specimens were prepared using a cylindrical stainless steel mold (Fig 1) of appropriate dimension (20mm height and 20mm diameter). The manipulation of polyvinyl siloxane (Fig 2) was done by spreading the material in a cartridge (Orange bite Bite Registration material, Ref No: 5013, Hannover, Germany) along with mixing tip attached to an auto-mixing (3M ESPE DS50 4:1/10:1, Seefeld, Germany) gun injected into the cylindrical mold. The manipulation of polyether specimens (Fig 3) was done in a pentamix (3M ESPE Pentmix TM 2, Seefeld, Germany) to get a homogenous mix and loaded it into the cylindrical mold. The polyvinyl siloxane and polyether specimens were divided into 3 groups consisting of a control group; a group subjected to spray atomization technique where the specimens were sprayed with the disinfectant until the complete surface of the specimens was wetted for 10 minutes; a group subjected to immersion technique where the specimens was immersed in .525% of sodium hypochlorite (Vensons India, Banglore, India) for 10minutes at room temperature.
Compression resistance of the specimens was determined using a Universal Testing Machine (Model: UTE 20, SR NO. 8/99-2546, Fuel instruments and engineers Pvt. Ltd, Maharashtra, India). Each of test specimens was loaded on a Universal Testing Machine (Fig 10) and subjected to a constant compressive force of 25N for a duration of 1min. The specimens were loaded to breakage or failure. This was the compressive load for the specimen.
The compression resistance was calculated as follows Compression resistance = compressive load (Newton) / cross-sectional area of the specimen (in mm 2 ) Compression resistance will be expressed in Megapascals.

Results:-
The Compression resistance of specimens were determined using the testing device Universal Testing Machine. The specimens were loaded on to the Universal testing machine and subjected to a constant compressive force of 25N for a duration of 1min. The compression resistance was calculated as follows Compression resistance = compressive load (Newton) / cross-sectional area of the specimen (in mm 2 ). Table 1 shows Comparison of Compression resistance between Control group, Immersion and Spray atomization technique in between polyether and polyvinylsiloxane interocclusal recording material. It was seen that, in the control group, when subjected to compression resistance Polyvinylsiloxane (11.0381MPa) showed greater resistance to compression than Polyether (19.747MPa);When subjected to compression resistance after immersion technique, Polyvinylsiloxane (8.332MPa) showed greater resistance to compression than Polyether (12.3885); When subjected to compression resistance after Spray atomization technique, polyvinylsiloxane (8.773MPa) showed greater resistance to compression than Polyether (9.708MPa). A T value of 15.585 was found to be highly significant at 0.000 level for control group. A T value of 8.712 was found to be highly significant at 0.000 level for immersion technique. A T value of 1.180 was found to be highly significant at 0.000 level for spray atomization. Table 2 shows Comparison of compression resistance of Polyvinyl siloxane interocclusal recording material between control group, immersion and spray atomization technique using one-way ANOVA and comparison of compression resistance of Polyether interocclusal recording material between control group, immersion and spray atomization technique using one-way ANOVA. Results indicated that, when subjected to compression resistance of polyether interocclusal recording material, the spray atomization technique (9.7080MPa) showed greater resistance to compression than the control group (19.7470MPa) and immersion technique (12.895MPa). An F value of 246.403 was found to be highly significant at 0.000 level. When subjected to compression resistance of polyvinyl siloxane interocclusal recording material, the immersion technique (.77334MPa) showed greater resistance to compression than control group (1.27243MPa) and spray atomization technique (2.46161MPa). An F value of 7.461 was found to be highly significant at 0.000 level. Table 3 shows significance of compression resistance of polyvinylsiloxane between the control and immersion technique, control and spray atomization technique and immersion and spray atomization technique also significant difference of compression resistance of polyether between the control and immersion technique, control and spray atomization technique and immersion and spray atomization technique using Post Hoc tukeys Test. Results showed that there was a mean difference of 7.3585MPa between control and immersion group which is highly significant; mean difference of 10.0390MPa between control and spray atomization group which is highly significant; mean difference of 2.6805MPa between immersion and spray atomization technique which is highly significant for polyether interocclusal recording material. For Polyvinyl siloxane interocclusal recording material results showed that there was a mean difference of 2.7061MPa between control and immersion group which is highly significant; mean difference of 2.2651MPa between control and spray atomization group which is significant; mean difference of -.4410MPa between immersion and spray atomization technique which is not significant.

Discussion:-
An interocclusal record is a precise recording of a maxillomandibular position. 1 An interocclusal record is a registration of the positional relationship of the opposing teeth or arches. (GPT-9). 11 Inaccurate interarch registration leads to errors in diagnosis and treatment. 11 Interocclusal recording of the relationship of the mandible to the maxilla is a simple but complex procedure. The inaccuracies attributed to the interocclusal records can be divided into three main categories: (1) The biologic characteristics of stomatognathic system, (2) Manipulation of the material and (3) The properties of the interocclusal recording materials .2 To prevent clinical error, the procedure used to record, and fix interocclusal relations should be performed with the utmost care and understanding. 1 The various methods of recording interocclusal relationships are graphic, functional, cephalometric and direct interocclusal recordings. Recording maxillomandibular relationships is an important step in oral rehabilitation. This relationship is transferred to the articulator, so that the laboratory procedures done on the casts will correspond with the patient's mouth. 1 The forces exerted on these records during removal from mouth or articulation depends on the thickness, properties of the material, the storage, the time interval between making the records, and articulation time affects these changes. Hence, the selection of interocclusal recording material is critical, depending on the situation. 1 Interocclusal recording materials are partly responsible for accurate precision and occlusal quality of final prosthetic restorations when used for mounting casts on the articulators. Accurate mountings can lead to restorations that require minimal occlusal modifications intraorally, thus reducing the chairside time. 2 Apart from the operator's clinical ability and the technique followed the material used can critically affect the accuracy of interocclusal registration. For making a successful prosthesis, it is important to achieve a harmony between the maxillomandibular relationship and functional anatomy of the patient. 2 The ideal interocclusal recording material should be easy to handle, exhibit minimal dimensional changes during and after setting. It should offer adequate resistance to closure during the mounting of casts. 11 Polyether and polyvinylsiloxane elastomeric materials are recently been used. 1 Addition silicone impression materials (polyvinylsiloxane) have been widely accepted due to excellent dimensional stability, superior recovery from deformation, and precise detail reproduction. 3 Addition silicone and polyether impression materials have been modified by adding plasticizers and catalyst in order to be used as interocclusal recording media. 2 From the previous studies, it is concluded that wax and zinc oxide eugenol impression paste are not reliable as interocclusal registration materials, because of the great linear changes these materials present even from the first hour and there are possible mounting inaccuracies that may develop if they are not used immediately after the interocclusal registration procedure. 2 Direct interocclusal records are commonly used to record maxillomandibular relationships. The recording material, which is soft initially fills the spaces between teeth, hardens, and records the specific relationship of the arches. The set material is then transferred onto casts to be mounted on an articulator. 1 It is essential that the interocclusal record material used for recording centric relation position provides limited resistance before setting to avoid displacing the mandible during closure. 12 Fattore et al compared polyethers with and without a carrier, pink baseplate wax, reinforced wax, and zinc oxide-eugenol paste, and concluded that the polyether without a carrier was the most reliable interocclusal material in his study. 12 Addition silicones (polyvinyl siloxanes) exhibit the least amount of distortion when compared with other elastomeric impression materials. 12 Accuracy, stability after setting, minimal resistance to closure, and easy manipulation (because there is no need for a carrier) are the main advantages of addition silicones as interocclusal record materials. 12 There is no material, however, that has all the properties of the ideal interocclusal registration medium. These properties have been described as having: 1. Limited initial resistance to closure (in order to avoid the displacement of mobile teeth or of the mandible during record making). 2. Dimensional stability after setting. 3. Resistance to compression after polymerization. 4. Ease of manipulation. 5. Absence of any adverse effects on the tissues involved in the recording procedures. 6. Accurate recording of the incisal or occlusal surface of the teeth. 7. Ease of verification. 13 In clinical practice it seems that the polyether will display less resistance during the interocclusal registration procedures. As a result, displacement of mobile teeth or of mandible should be less frequent. A lengthy setting time is not a desired property for the registration of maxillomandibular relations, because it can affect the precision due to possible movement of the mandible. This movement can occur because of the patient's inability to maintain the mandible in one position. 13 Guidelines set by the American Dental Association (ADA) and the Centers for Disease Control (CDC) suggest that all surfaces that have been splashed or touched by human body fluids be disinfected with a hospital-grade disinfectant with the Environmental registered Protection Agency. The surface of elastomeric impressions, routinely made in restorative dentistry, generally contact saliva and blood, allowing transfer of viruses to the stone cast. 14 Interocclusal registration materials acts as a significant source of cross contamination, so these must be disinfected immediately after their removal from mouth. There are two important factors to consider when choosing a disinfectant namely, its ability to eliminate microbial contamination and its effect on the resultant material. 8 So the American Dental Association in 1988, 1991 and 1996, and Council on Dental Materials, Instruments and Equipment in 1988 issued guidelines on disinfecting impressions both by immersion and spray atomization techniques. [8][9][10] The performance of sodium hypochlorite is based on cell oxidation. A study by Silva and Salvador Frederick et al and Drennon et al showed that disinfection of impression by spray appeared to be as efficacious as immersion and unlike the immersion method, it does not cause any dimensional changes. 14 Guidelines suggested that addition silicone impression can be disinfected by immersion without affecting accuracy and detail reproduction. Times for disinfection vary, so information supplied with the disinfectant should be consulted to determine the proper time. Polyether impressions may be adversely affected with disinfection by immersion. To minimize dimensional change with polyether impressions, a chlorine compound product with a short disinfection time should be selected or the impressions should be disinfected with a spray. 9 Since the compatibility of an impression material with a disinfectant varies, manufacturer's recommendations for proper disinfection should be followed. The use of disinfectants requiring times of no more than 30 minutes for disinfection is recommended. 10 One of the most desirable characteristics of the interocclusal registration material is resistance to compression after polymerization. 2 The resistance to compression after setting is a very desirable property for interocclusal recording media. Maxillomandibular relationships that were registered correctly in the patient can be erroneously transferred in the mounting procedures because of the compressibility of the materials. If a material is compressible, it can be distorted by faulty manipulation by the operator or by the weight of the cast to be mounted. The clinicians should choose interocclusal registration materials that display the least possible elastic or torsion due to compression from a load. Of all the materials tested, polyvinylsiloxane presented the greatest resistance to compression. 15 The ability of an interocclusal registration material to resist compressive forces is very important because any discrepancy between the intraoral relationships of the teeth and the position of the teeth on the mounted working casts will result in restorative errors. 2 A compressive force is commonly exerted on the recording material during the articulation procedure which may cause inaccuracies during mounting of casts. Each of these interocclusal recording materials exhibits a degree of deformation when compressed under a load. The deformation may vary with the thickness and the properties of the recording materials used. 4 The testing of the resistance to compression after setting was performed following a modification of the method described in A.D.A specification no 19 for the elastomeric impression materials. 1,15 For standardization, the specimens were stored at room temperature for 24hrs to simulate the time between clinical and laboratory phases. 2 Rubber bands are commonly used to sustain the contact of opposing casts during mounting procedures. The maximal force exerted by use of one office standard rubber band (No.19) to a position a maxillary cast to a mandibular cast mounted on an articulator was approximately 25 N, so this value was selected in the investigation. 2 A limited thickness of recording material is usually indicated between prepared teeth on one arch opposing an unprepared dental arch compared with a thickness of material between two opposing edentulous arches. 16 It has been stated that if these interocclusal recordings are used for mounting working cast in fabrication of prosthesis, the casts should be secured in a record, in a manner that ensures complete seating but exerts a minimal compressive force. 16 Thickness of interocclusal record is lesser in fixed partial denture cases. It is more in complete denture cases. 11 Proper interocclusal records minimizes preinsertion adjustments to the restorations and saves chair side time or repetition of some clinical and technical stages. 1 In the present study, polyvinylsiloxane interocclusal recording material showed the greatest resistance to compression when compared with polyether interocclusal recording material when subjected to immersion technique (8.332MPa) and spray atomization technique (8.773MPa) and the control group (11.0381MPa). The reason for greater compression resistance of polyvinylsiloxane may be because of its low dimensional change when compared to other bite registration material. 1,2 This observation was in correlation with the studies of Breeding LC, Dixon DL who showed that Blue Mousse polyvinylsiloxane displayed the greatest resistance to compression as compared to other elastomeric interocclusal recording materials in their study. 2 In this study polyvinylsiloxane showed greater resistance to compression when compared to polyether at 20mm thickness. It exhibited minimal distortion during compression and hence can give the clinician the opportunity to make only minimal adjustments to the restoration that will be delivered from the laboratory and avoid unnecessary use of chair time or repetition of some clinical and technical stages. 2 Studies done by Craig RG and Sun Z, Chai J, Tan E and Pang IC, Campos AA and Nathanson D have also shown that PVS interocclusal recording material was more accurate and dimensionally stable than polyether interocclusal recording material. 1 Tripodakis et al suggests that these records should possess adequate rigidity to resist deformation by the casts (compression resistance). Excessive forces cause the casts to be placed too close and inadequate forces cause the casts to be mounted too far apart. Researchers have suggested a force of 20-25 Newton for one minute for evaluating the compressive resistance. 4 These results also suggested that if these interocclusal recordings are used for mounting working casts in fabrication of the prosthesis the casts should be secured in a manner that ensures complete seating but exerts a minimal compressive force. 16 In this study polyether has been shown less compression resistance than polyvinylsiloxane may be because of a "Spring" to this elastomer that can cause articulated casts to "open" in the centric closure position. If polyether is not trimmed and carefully seated on the casts, it can be more inaccurate than any other material examined in the study. 11 Nevertheless, the potential error introduced by the use of more compression resistant materials would be acceptable if casts were mounted for diagnostic evaluation of partially edentulous patients. 16 On the basis of result seen in Table 1, in the control group, when subjected to compression resistance polyvinylsiloxane (11.0381MPa) showed greater resistance to compression than polyether (19.747MPa); When subjected to compression resistance after immersion technique, polyvinylsiloxane (8.332MPa) showed greater resistance to compression than polyether (12.3885MPa); When subjected to compression resistance after spray atomization technique, polyvinylsiloxane (8.773MPa) showed greater resistance to compression than polyether (9.708MPa). A T value of 15.585 was found to be highly significant at 0.000 level for control group. A T value of 8.712 was found to be highly significant at 0.000 level for immersion technique. A T value of 1.180 was found to be highly significant at 0.000 level for spray atomization.
When polyvinylsiloxane interocclusal recording material was subjected to compression resistance, the immersion technique (.77334MPa) showed better than control group (1.27243MPa) and spray atomization technique (2.46161MPa). An F value of 7.461 was found to be highly significant at 0.000 level. It might be due to the addition of surfactants to improve its ability to reproduce details. The presence of these agents improves the compatibility with water and increases the sorption of water when impressions are immersed. 8 Impressions can be disinfected by immersion in any compatible disinfecting product. Since the compatibility of an impression material with a disinfectant varies, manufacturer's recommendations for proper disinfection should be followed. The use of disinfectants requiring time of not more than 30 minutes for disinfection is recommended according to JADA. 10 Current ADA guidelines state that the impression should be rinsed to remove saliva, blood, and debris, followed by immersion in a disinfecting product, such as hypochlorite, iodophor, glutaraldehyde, or phenol. According to the Organization for Safety and Asepsis Procedures, the recommended exposure time for most surface disinfectants is 10-15 minutes. 17 Also it has been seen that the surface quality of polyvinlysiloxane will not be much affected by sodium hypochlorite after 10 minutes or 1 hour immersion, in contrast polyether surface quality was significantly affected by sodium hypochlorite immersion with a mottled surface on 30% of the impressions after 10 minute immersion and a matte/sticky surface on 100% of the polyether impressions after 1hr immersion. This would suggest that in addition to NaOCl absorption by polyether, there might be an adverse interaction between NaOCl and polyether resulting in impression surface degradation. 17 Merchant also warns that polyether should be disinfected for short periods with the disinfectants accepted by the ADA, which in turn recommends immersion not exceeding 30 minutes. 18 The performance of sodium hypochlorite is based on cell oxidation. A study by Silva and Salvador, Frederick et al. and Drennon et al. showed that disinfection of impression by spray appeared to be as efficacious as immersion and unlike the immersion method, it does not cause any dimensional changes. 14 Polyether shows varied dimension with sodium hypochlorite when immersed for more than 10min. Since sodium hypochlorite is both an oxidizing and hydrolyzing agent they are strongly alkaline, hypertonic, and typically have normal concentrations of 10 to 14% available chlorine. They deteriorate with time, exposure to light, temperature, and contamination with metallic ions. Chlorine compound is highly reactive and could react and fix on the material. The dimensional change might be due to reaction of chlorine compound with sulfonic ether which interferes with the polymerization reaction and produces distortion. 8 Bustos et al revealed that patient-derived silicone specimens showed complete elimination of bacteria after being subjected to 2% GA and 0.5% SH for 10 minutes. 19 A study done by Matyas et al showed that there was no significant changes when the silicone or vinylpolysiloxane impressions were sprayed or immersed in five viricidal agents. 20 When subjected to compression resistance of polyether interocclusal recording material, the spray atomization technique (9.7080MPa) showed better resistance to compression than the control group (19.7470MPa) and immersion technique (12.895MPa). An F value of 246.403 was found to be highly significant at 0.000 level. Immersion technique of disinfection is not usually indicated for polyether material as there are chances for a mottled surface/matte or a sticky surface to form because of the presence of chlorine compounds which could react and fix on material. 6,17 Hence sodium hypochlorite had significantly affected polyether. Therefore, spray atomization technique can be recommended for polyether disinfected with sodium hypochlorite, to preserve dimensional stability, whereas both spray or immersion technique can be safely used with addition silicone. For polyether interocclusal record, restrictions based on type, duration, and method of disinfection must be applied to preserve the accuracy of the impression and effective microbial elimination. 8 Significance of compression resistance of polyvinylsiloxane between the control and immersion technique and spray atomization technique and immersion and spray atomization technique also significant difference of compression resistance of polyether between the control and immersion technique, control and spray atomization technique and immersion and spray atomization technique using Post Hoc tukeys test was seen. Results showed that there was a mean difference of 7.3585Mpa between control and immersion group which is highly significant; mean difference of 10.0390MPa between control and spray atomization group which is highly significant; mean difference of 2.6805MPa between immersion and spray atomization technique which is highly significant for polyether interocclusal recording material. For Polyvinyl siloxane interocclusal recording material results showed that there was a mean difference of 2.7061MPa between control and immersion group which is highly significant; mean difference of 2.2651MPa between control and spray atomization group which is significant; mean difference of -.4410MPa between immersion and spray atomization technique which is not significant. Graph 1 shows that polyvinyl siloxane interocclusal recording material is least resistant to compression than polyether interocclusal recording material when subjected to compression resistance after immersion and spray atomization technique of disinfection. Graph 2 indicates that immersion technique of disinfection proved to be better for polyvinylsiloxane interocclusal recording material and spray atomization technique of disinfection was shown to be better for polyether interocclusal recording material.
A few limitations of the study are 1. There was no simulation of intra-oral mouth temperature during the setting of the materials. 2. It should be mentioned that in clinical practice the thickness of material is never 20mm. It ranges between 2-4mm, depending on whether occlusal clearance was provided to one or both arches.11,12 Since it has shown that thicker elastomeric interocclusal occlusal registration material are generally more compressible, it should be noted that further research is needed in order to evaluate the compressibility of interocclusal recording material in thickness similar to those of simulated clinical conditions. 12 3. Another point of interest is the ongoing polymerization reaction of the elastomeric materials, even after 30mins. This continued setting process may result in increased surface hardness as shown by Chai et al and may affect the resistance to compression as well.
Conclusion:- 1. Immersion technique could be indicated for polyvinylsiloxane interocclusal recording material when subjected to compression resistance because its low dimensional change when compared to other bite registration material. 2. Immersion technique is not indicated for polyether interocclusal recording material when subjected to compression resistance as polyether showed varied dimension with sodium hypochlorite when immersed for 10min.
3. Spray atomization technique can be indicated for polyether interocclusal recording material when subjected to compression resistance as it helps in preserving the dimensional stability. 4. Spray atomization technique can be indicated for polyvinylsiloxane interoclusal recording material when subjected to compression resistance because of its greater dimensional stability. 5. When subjected to compression resistance after the immersion and spray atomization technique of disinfection between the polyvinyl siloxane and polyether interocclusal recording material, the polyvinyl siloxane showed greater resistance to compression with immersion technique when compared to polyether interocclusal recording material. Immersion technique was shown to be better for polyvinylsiloxane interocclusal recording material while spray atomization technique proved to be better for polyether interocclusal recording material.