Comparative elasticity tests for elastomeric (non putty) impression materials P. A. H. Blomberg* S. Mahmoodt R. J. SmalesS 0. F. Makinsons
Key words: Elasticity, elastomers, impression materials. Abstract This study was conducted to evaluate the methods used for measuring the elastic recovery of various elastomeric impression materials. One brand from each chemical group was selected to allow relative ranking of the results from each deforming test mode. For compression tests, the polysulphide and silicone specimens made in metal moulds gave significantly less set than those made in acrylic moulds; this was not so for the polysiloxane and polyether specimens. For polysulphide and polyether materials, the set in compression was greater using the BSI balanced beam method than for an optical method without inertia or load effects; this was not so for silicone or polysiloxane materials. The elastic recovery of the materials did not alter significantly after ten minutes of strain release, except in tensile tests, where the elastic recovery continued to change for twenty minutes. The rank ordering of the deformation set showed a relative correlation for the compression test, a new tensile test method, and bend and torsion testing methods. Thus only one method is needed to determine set per cent.
Introduction Elastomeric impression materials are used in dentistry for their ability to reproduce the fine details of oral structures. One of the prerequisites for a successful dental impression material is its ability to recover from the deforming strain caused by external forces. This ability is clinically significant because of the presence of undercut structures. Therefore, the degree of elastic recovery or, conversely, the permanent deformation, is an important property in reflecting the accuracy of these impression materials. Several workers have conducted studies on the elastic recovery of elastomeric impression materials.'-'' Most of the research has been devoted to compression tests although tensile and shear tests have also been conducted. However, considerable variations are observed in the test conditions and methods for determining elasticity in Standards.'2-'5 The present study examines and compares several test methods (Table 1) to facilitate the selection of the most appropriate procedures.
Table 1. Summary of elasticity tests performed Test type
Source
Modelspecimen
1. Compression
(Received for publication May 1990. Revised August 7991. Accepted August 1991.)
BSI L? SA
346
I (b) Microscope [ (c) Stereomicroscope
3. Bending
BSI BSI Osborne -
4. Torsion
-
1.2 Acrylic mould 2. Tensile *Specialist practitioner, Townsville. ?Postgraduate student, Conservative Dentistry, The University of Adelaide. $Senior Lecturer, Conservative Dentistry, The University of Adelaide. $Reader, Conservative Dentistry, The University of Adelaide.
[ (a) Balanced beam
1.1 Metal mould
Microscope (a) Vertical specimen (b) Horizontal specimen (c) Horizontal specimen (a) Flat specimen (b) Rod specimen Rod specimen
Australian Dental Journal 1992;37(5):346-52.
Table 2.
Elastomers selected for the elasticity tests
Chemical group
Proprietary name
Viscosity class
Batch code
Manufacturer
Stated setting time (min)
Polysulphide
Permlastic
High
Base 12057 Catalyst 11061 Base 6547B Catalyst 6672F Base H041 Catalyst H034 Base 0 1037 Catalyst 0 1036
SybronlKerr, USA
10.0
Condensation silicone Delicron
Medium
Polyet her
Impregum
Medium
Poly (vinyl) siloxane
Reflect
Medium
Materials and methods One brand from each main chemical group of elastomers was selected to allow for relative ranking of the results from each deformation test mode. The materials used, together with the manufacturers' names and batch numbers, are listed in Table 2. All the materials were supplied as paste/paste systems requiring mixing of equal lengths of base and catalyst. The materials were stored and mixed at a room temperature of 23 & 2 "C and humidity of 55 & 10 per cent. The mixing was carried out for sixty seconds on the pads provided by the manufacturers, and according to their instructions regarding proportioning and manipulation. The specimen moulds used for the four types of tests are described in Table 3. The moulds were stored at 32°C in a constant temperature cabinet before and during polymerization of the specimens. The specimens were loaded into the moulds by means of a mixing spatula, and the loading was completed at one and one-half minutes from the start of mixing. The specimens were gently removed and placed in the test apparatus at the setting times recommended by the manufacturers. The initial length of each specimen was measured one minute after the setting time. The specimens were suddenly strained for five seconds at one and one-quarter minutes after the manufacturer's recommended setting time. The strains were then suddenly released. The specimen
Bayer, Germany
5.0
ESPE GmbH, Germany SybrodKerr, USA
5.75 6.0
length was measured every two minutes after release of the strain for 20 minutes. Five specimens of each material were studied for each test. For the compression tests, cylindrical stainless steel moulds and cylindrical acrylic moulds were constructed according to the BSI standard (Fig. 1). Both types of moulds were split vertically to allow easy removal of the material without deformation. In each case, 30 per cent strain was used. The specimens from the metal moulds were used for balanced beamYL6 depth of field and stereomicroscope'* modes. On the other hand, the specimens from the acrylic moulds were only tested by using the microscope depth of field mode. For the tensile tests, two types of Specimens were used (a) cylindrical specimens aligned vertically and free to recover without friction or load, and (b) bar specimens placed in a horizontal position to allow recovery on a plate lightly covered with talc to reduce friction. A 50 per cent strain was used in these circumstances. For the vertical mode, the specimen mould was made of stainless steel. The specimen was held by grips, integral with the mould, and transferred to the test apparatus. Following removal of the mould, the lower specimen support was lowered rapidly. After five seconds, the specimen was sectioned below the lower length mark to allow free recovery. The length of the specimen between two marks was recorded photographically initially and during elastic recovery. For the two horizontal modes, the moulds were made of aluminium. In one case, the
Table 3. Mould and data summary Type of test
Specimen shape and size
Mould material and source
Compression (Vertical) Compression (vertical) Tensile (vertical) Tensile (horizontal) Tensile (horizontal) Bend (flat) Bend (round) Torsion
Cylinder 20.0 x 12.5 mm diam Cylinder 20.0 x 12.5 mm diam Rod 50.0 x 5.0 mm diam Bar 50.0 x 3.8 x 2.0 mm Bar 50.0 x 5.0 x 3.0 mm Tongue-shaped plate 20.0 x 23.0 x 5.0 mm Rod 30.0 x 10.0 mm diam Rod 61.0 x 6.0 mm diam
Stainless steel BSI Acrylic Stainless steel Aluminium BSI Aluminium (Osbome) Acrylic Teflon Acrylic
Australian Dental Journal 1992;37:5.
347
Fig. 1 .-Stainless steel compression set moulds.
Fig. 2.-Flat specimen bend test jig.
BSI spe~ifications'~ were used while in the other case, a mould designed by Professor J. Osbornell in the Dental School, University of Birmingham, was used. Two modes of combined compressive and tensile tests were tested by bending specimens using two forms, one flat (Fig. 2) and the other round (Fig. 3). A deflection of 45 O was induced by incorporating a plunger after placing the specimens in their respective jigs. Direct measurements were made with a travelling microscope. For the torsion tests, a rod-shaped specimen was held vertically in the apparatus shown (Fig. 4). A 110O strain was employed and the elastic recovery was measured with an attached vernier gauge. IPersonal communication, 1973. 348
Results The permanent deformation results obtained at various times from the compression tests with specimens from a metal mould are given in Table 4. The comparative effect of mould material on compression set is shown graphically (Fig. 5). Table 5 shows the permanent deformation results following tensile strain. The permanent deformation results obtained with bend and torsion tests are shown in Tables 6 and 7, respectively.
Discussion Permanent deformation of elastomers is proportional to the degree of applied The degree of strain for each test in this study was based Australian Dental Journal 1992375.
Fig. 3.-Rod specimen bend test jig.
Fig. 4.-Torsion test apparatus.
on specifications (listed in Table 1) for compression and tensile tests, and on arbitrary decisions for the bend and torsion tests; the duration ofthe strain was for 5 seconds as based on the previous study (Table 1). The results indicate that the relative ranking of the materials was similar in the compression metal Australian Dental Journal 1992;37:5.
mould tests, the vertical and BSI horizontal test modes (tensile) and the bend and torsion tests: that is, Impregum >Permlastic>Delicron s Reflect (Fig. 6). Some variation was observed in the case of compression tests in the acrylic mould mode, and for the tensile horizontal mode (after Osborne). In these cases, the relative order was Permlastic >Impregum >Delicron 9 Reflect. In a separate study, it was found that the temperatures reached by the impression materials in the acrylic moulds were lower than in the metal moulds, except for Reflect. Similarly, compression set was also greater with specimens from the acrylic moulds, except Reflect (Fig. 5). These fm’khgs mean that the rapid heat transfer from the metal moulds allowed a greater degree of polymerization which does not necessarily reflect clinical conditions. As far as individual results were concerned, it was found that set in compression was greater using the BSI method, because of instrument inertia or loading effect, for polysulphide and polyether materials. This finding was not observed with the optical methods which were designed to allow elastic recovery without any load or instrument inertia. Therefore, it is evident from the ranking that the response of elastomers to all the tests is similar, provided that certain conditions of volume distribution of specimen material within the mould and mould material are accepted. It can be suggested from this study that compression tests using specimens made in acrylic moulds are required to determine the permanent deformation of these elastomers. This is in agreement with the work of Lautenschlager et al. l9 Acrylic moulds are preferred 349
-
PM PA 1DM DA IM IA RM RA Y
EII E5
0
a
15
25
5
Time (min) Fig. 5.-Comparison of compression set of specimens from metal and acrylic moulds. PM, Permlastic metal; PA, Permlastic acrylic; IM, Impregum metal; IA, Impregum acrylic; DM, Delicron metal; DA, Delicron acrylic; RM, Reflect metal; RA, Reflect acrylic.
Table 4. Permanent deformation from compression tests with specimens from a metal mould: per cent mean and standard deviation Material
~
Time/test
6 min
10 min
16 min
20 min
T1 T2 T3 T1 T2 T3 T1 T2 T3 T1 T2 T3
2.21 iO.06 1.93f 0.03 1.95f 0.12 1.61 fO.10 1.49 k 0.08 1.65 f 0.09 2.51 fO.05 2.25 k 0.06 2.14f0.09 0.21 k 0.06 0.2 1 k 0.05 0.16f0.04
2.17f0.06 1.91 k 0.05 1.60i0.16 1.60 f 0.10 1.46 k 0.08 1.68k 0.09 2.52 i 0.05 2.28 i 0.04 2.11 f0.07 0.2 1 k 0.07 0.2 1 i 0.05 0.17 f 0.09
2.15 i 0.05 1.89 f 0.05 1.83k 0.19 1.60 i 0.10 1.44 k 0.08 1.63 f 0.05 2.54 k 0.06 2.28 k 0.04 2.15f0.09 0.2 1 k 0.07 0.21 iO.05 0.15 i0.06
2.14f0.05 1.88 k 0.04 1.73 i 0.1 1 1.61 fO.09 1.44 f 0.08 1.63 i 0.12 2.54 f 0.05 2.26 f 0.05 2.15 i 0.10 0.21 k 0.06 0.20 k 0.06 0.17 f 0.06
~
P = Permlastic, I = Impregum, D = Delicron, R =Reflect, T1 = Balanced beam, T2 =Depth of field microscope, T3 = Stereomicroscope.
Table 5. Permanent deformation following tensile tests: Per cent mean and standard deviation Material
Timeltest
6 min
Vertical BSI Osborne Vertical BSI Osborne Vertical BSI Osborne Vertical
2.56 f 0 . 2 7 1.69 k 0.23 2.78 k 0.29 2.41 fO.30 1.46 k 0.25 1.85 k 0.37 2.87f0.31 1.82 i 0.42 1.89 f 0.32 0.05 f 0 . 2 6 0.10f0.55
BSI Osborne
10 min
16 min
2.46 f 0.20 1.97 k 0.19 1.29 k 0.32 1.23i0.39 2.62 f 0.22 1.90 f 0.12 1.91 f0.54 1.87 k 0.51 1.16f0.25 1.OO f 0.24 1.22 f 0.17 1.46 f 0.18 2.53 i 0.35 2.29 f 0.36 1.41 i 0 . 4 1 1.66 f 0.40 1.99 k 0.12 1.78i0.45 - 0.15 f 0.28 - 0.15 f 0.22 - 0.05 f 0.22 0.16 i 0.30 Fracture on 50% tensile strain
20 min 1.68 f 0.23 1.03 k 0.18 2.05 f 0.28 1.52k0.36 0.94 f 0.24 0.93 k 0.21 2.05 i 0.39 1.30k0.33 1.70 i 0.25 -- 0.19 f 0.20 0.00 f 0.26
P = Permlastic, I = Impregum, D = Delicron, R =Reflect.
350
Australian Dental Journal 1992;37:5.
*O
1
1
W Permlastic Delicron Impregum Reflect
%
a -5
1
2
3
5
4
6
7
8
9 1 0
Fig. 6. -Comparison of results of elasticity tests. 1, British Standards Institution balanced beam (compression, metal); 2, Field microscope (compression, metal); 3, Stereomicroscope (compression, metal); 4, Microscope (compression, acrylic); 5, Vertical (tensile); 6, British Standards Institution horizontal (tensile); 8, Flat (bend); 9, Round (bend); 10, Torsion.
Table 6. Permanent deformation following bending tests: Per cent mean and standard deviation Material
Timeltest
6 min
10 min
16 min
20 min
Flat Rod Flat Rod Flat Rod Flat Rod
13.88 f 0.77 12.40k0.51 8.88 f0.66 10.76 f 0.48 15.04k 1.11 12.76 f 0.52 0.10 f 0.04 0.23 f 0.05
13.56 k 0.20 11.68 f 0.52 8.68 k 0.76 10.64 f 0.50 15.04 f 1.1 1 12.52 k 0.50 1.10 k 0.04 0.22 f 0.06
13.56k0.57 11.44 k0.57 8.44 k 0.74 10.64 k 0.50 15.04k1.11 12.52 k 0.50 O.lOkO.04 0.20 f 0.06
13.56k0.57 11.32 f 0.61 8.44 k 0.74 10.64k0.50 15.04k1.11 12.52k0.50 0.10 f 0.04 0.20 k 0.06
P = Permlastic, I = Impregum, D = Delicron, R = Reflect.
Table 7. Permanent deformation following torsional tests: Per cent mean and standard deviation Timel material
P D I R
6 min
10 min
16 min
20 min
15.72f0.30 13.64f0.65 16.20k0.75 0.72f0.23
15.32 k0.50 13.20f0.45 16.16k0.68 0.72f0.23
15.08 f0.48 13.04k0.39 16.12f0.73 0.72k0.23
15.08 f0.48 13.04k0.36 16.12k0.73 0.72k0.23
P = Permlastic, I = Impregum, D = Delicron, R = Reflect
to metal moulds, because the rapid heat transfer from metal moulds may not reflect the setting characteristics found in the clinical situation. The negative value of up to 0.5 per cent reached in the vertical mode of tensile test (Table 5) indicates a slight contraction. Lacy et d Z 0 have also found curing shrinkage of up to 0.5-1.0 per cent at 30 minutes after mixing. Australian Dental Journal 1992;37:5.
The differences shown in Fig. 6 for the last three tests compared with the first seven, could be that in deformation for these three tests the strain was not evenly distributed within the specimens. From the results obtained in this study (Tables 4-7), it was shown that for non-tensile tests, the elastic recovery of the materials did not alter much after ten minutes after strain release. For tensile tests, the elastic recovery continued over the 20 minutes. The observed delay may be due to the relatively large strain as shown by Makinson.” Overall, Impregum and Reflect did not change much after six minutes, but Permlastic and Delicron did alter although the change was not significant after ten minutes. It is therefore suggested that a delay of ten minutes following strain release should be allowed for standard testing of permanent deformation. For clinical purposes, casts could be poured from Impregum and Reflect after six minutes, while 351
in the case of Permlastic and Delicron, the time allowed should be ten minutes. Conclusions 1. When assessing the elasticity of elastomeric impression materials, the tensile, bend and torsion tests did not add to the information obtained from the compression tests for the materials selected in this study. 2. Compression tests with specimens made in acrylic rather than metal moulds are sufficient. The effect of mould material on the temperature of the polymerizing material must be accounted for, when comparing test results. 3. The optical systems which are without inertia and loading effects can be recommended for the compression tests. 4. A delay of ten minutes following strain release should be allowed before conducting standard elasticity tests. Acknowledgements The authors would like to acknowledge the support and guidance provided by Associate Professor G. C. Townsend, Department of Dentistry, The University of Adelaide. References 1. Cresson J. Physical properties of elastic duplicating materials. J Dent Res 1949;28:573-82. 2. Wilson HJ. Elastometric impression materials: I. The setting material. Br Dent J 1966;121:277-83. 3. Wilson HJ. Elastomeric impression materials: 11. The set material. Br Dent J 1966;121:322-8. 4. Chong MP, Docking AR. Some setting characteristics of elastomeric impression materials. Aust Dent J 1969;14:295-301. 5. Mansfield MA, Wilson HJ. A new method of determining the tension set of elastomeric impression materials. Br Dent J 1973;135:101-5. 6. Inoue K, Wilson HJ. Visco-elastic properties of elastomeric impression materials: 111. The elastic recovery after removal of strains applied at the setting time. J Oral Rehabil 1978;5:323-7.
352
7. McCabe JF, Storer R. Elastomeric impression materials. The measurement of some properties relevant to clinical practice. Br Dent J 1980;121:73-9. 8. Habu H, Uchida H, Hashimoto K. Permanent deformation of elastic impression materials. J Dent Res 1985;64:275 Abstr 902. 9. DeArujo PA, Jorgensen KD, Finger W. Viscoelastic properties of setting elastomeric impression materials. J Prosthet Dent 1985;54:633-6. 10. Finger W, Komatsu M. Elastic and plastic properties of elastic dental impression materials. Dent Mater 1985;l: 129-34. 11. Jamani KD, Harrington E, Wilson HJ. The determination of elastic recovery of impression materials at the setting time. J Oral Rehabil 1989;16:89-100. 12. American Dental Association Council on Dental Materials and Devices. Revised American Dental Association Specification No. 19 for non-aqueous elastomeric dental impression materials. J Am Dent Assoc 1977;94:733-41. 13. Standards Australia. Elastomeric dental impression materials. Australian Standard 1185, 1984. 14. International Organization for Standardization. Elastomeric dental impression materials. I S 0 4823, 1984. 15. British Standards Institution. Specification for dental elastic impression materials. British Standard 4269: 1,1968. 16. Wilson HJ. Tissue conditioners and functional impression materials. Br Dent J 1966;121:9-16. 17. Makinson OF. Elastic recovery from compression strains in some alginate impression materials. International Association for Dental Research Meeting (Australia and New Zealand Division) 1970: Abstr 14. 18. Menz J. Three dimensional surfaces measuring with the SMXX stereomicroscope VEB Carl Zeiss JENA. JENA Review 1969;4:238-41. 19. Lautenschlager EP, Miyomoto P, Hilton R. Elastic recovery of polysulphide base impressions. J Dent Res 1972;51:773-9. 20. Lacy AM, Fukui H, Bellman T, Jendersen MD. Time dependent accuracy of elastomer impression material. 11. Polyether, polysulphide, polysiloxane. J Prosthet Dent 1981;45:329-33.
Address for correspondenceheprints: 0. F. Makinson, Department of Dentistry, The University of Adelaide, GPO Box 498, Adelaide, South Australia, 5001.
Australian Dental Journal 1992;37:5.
Key words: Elasticity, elastomers, impression materials. Abstract This study was conducted to evaluate the methods used for measuring the elastic recovery of various elastomeric impression materials. One brand from each chemical group was selected to allow relative ranking of the results from each deforming test mode. For compression tests, the polysulphide and silicone specimens made in metal moulds gave significantly less set than those made in acrylic moulds; this was not so for the polysiloxane and polyether specimens. For polysulphide and polyether materials, the set in compression was greater using the BSI balanced beam method than for an optical method without inertia or load effects; this was not so for silicone or polysiloxane materials. The elastic recovery of the materials did not alter significantly after ten minutes of strain release, except in tensile tests, where the elastic recovery continued to change for twenty minutes. The rank ordering of the deformation set showed a relative correlation for the compression test, a new tensile test method, and bend and torsion testing methods. Thus only one method is needed to determine set per cent.
Introduction Elastomeric impression materials are used in dentistry for their ability to reproduce the fine details of oral structures. One of the prerequisites for a successful dental impression material is its ability to recover from the deforming strain caused by external forces. This ability is clinically significant because of the presence of undercut structures. Therefore, the degree of elastic recovery or, conversely, the permanent deformation, is an important property in reflecting the accuracy of these impression materials. Several workers have conducted studies on the elastic recovery of elastomeric impression materials.'-'' Most of the research has been devoted to compression tests although tensile and shear tests have also been conducted. However, considerable variations are observed in the test conditions and methods for determining elasticity in Standards.'2-'5 The present study examines and compares several test methods (Table 1) to facilitate the selection of the most appropriate procedures.
Table 1. Summary of elasticity tests performed Test type
Source
Modelspecimen
1. Compression
(Received for publication May 1990. Revised August 7991. Accepted August 1991.)
BSI L? SA
346
I (b) Microscope [ (c) Stereomicroscope
3. Bending
BSI BSI Osborne -
4. Torsion
-
1.2 Acrylic mould 2. Tensile *Specialist practitioner, Townsville. ?Postgraduate student, Conservative Dentistry, The University of Adelaide. $Senior Lecturer, Conservative Dentistry, The University of Adelaide. $Reader, Conservative Dentistry, The University of Adelaide.
[ (a) Balanced beam
1.1 Metal mould
Microscope (a) Vertical specimen (b) Horizontal specimen (c) Horizontal specimen (a) Flat specimen (b) Rod specimen Rod specimen
Australian Dental Journal 1992;37(5):346-52.
Table 2.
Elastomers selected for the elasticity tests
Chemical group
Proprietary name
Viscosity class
Batch code
Manufacturer
Stated setting time (min)
Polysulphide
Permlastic
High
Base 12057 Catalyst 11061 Base 6547B Catalyst 6672F Base H041 Catalyst H034 Base 0 1037 Catalyst 0 1036
SybronlKerr, USA
10.0
Condensation silicone Delicron
Medium
Polyet her
Impregum
Medium
Poly (vinyl) siloxane
Reflect
Medium
Materials and methods One brand from each main chemical group of elastomers was selected to allow for relative ranking of the results from each deformation test mode. The materials used, together with the manufacturers' names and batch numbers, are listed in Table 2. All the materials were supplied as paste/paste systems requiring mixing of equal lengths of base and catalyst. The materials were stored and mixed at a room temperature of 23 & 2 "C and humidity of 55 & 10 per cent. The mixing was carried out for sixty seconds on the pads provided by the manufacturers, and according to their instructions regarding proportioning and manipulation. The specimen moulds used for the four types of tests are described in Table 3. The moulds were stored at 32°C in a constant temperature cabinet before and during polymerization of the specimens. The specimens were loaded into the moulds by means of a mixing spatula, and the loading was completed at one and one-half minutes from the start of mixing. The specimens were gently removed and placed in the test apparatus at the setting times recommended by the manufacturers. The initial length of each specimen was measured one minute after the setting time. The specimens were suddenly strained for five seconds at one and one-quarter minutes after the manufacturer's recommended setting time. The strains were then suddenly released. The specimen
Bayer, Germany
5.0
ESPE GmbH, Germany SybrodKerr, USA
5.75 6.0
length was measured every two minutes after release of the strain for 20 minutes. Five specimens of each material were studied for each test. For the compression tests, cylindrical stainless steel moulds and cylindrical acrylic moulds were constructed according to the BSI standard (Fig. 1). Both types of moulds were split vertically to allow easy removal of the material without deformation. In each case, 30 per cent strain was used. The specimens from the metal moulds were used for balanced beamYL6 depth of field and stereomicroscope'* modes. On the other hand, the specimens from the acrylic moulds were only tested by using the microscope depth of field mode. For the tensile tests, two types of Specimens were used (a) cylindrical specimens aligned vertically and free to recover without friction or load, and (b) bar specimens placed in a horizontal position to allow recovery on a plate lightly covered with talc to reduce friction. A 50 per cent strain was used in these circumstances. For the vertical mode, the specimen mould was made of stainless steel. The specimen was held by grips, integral with the mould, and transferred to the test apparatus. Following removal of the mould, the lower specimen support was lowered rapidly. After five seconds, the specimen was sectioned below the lower length mark to allow free recovery. The length of the specimen between two marks was recorded photographically initially and during elastic recovery. For the two horizontal modes, the moulds were made of aluminium. In one case, the
Table 3. Mould and data summary Type of test
Specimen shape and size
Mould material and source
Compression (Vertical) Compression (vertical) Tensile (vertical) Tensile (horizontal) Tensile (horizontal) Bend (flat) Bend (round) Torsion
Cylinder 20.0 x 12.5 mm diam Cylinder 20.0 x 12.5 mm diam Rod 50.0 x 5.0 mm diam Bar 50.0 x 3.8 x 2.0 mm Bar 50.0 x 5.0 x 3.0 mm Tongue-shaped plate 20.0 x 23.0 x 5.0 mm Rod 30.0 x 10.0 mm diam Rod 61.0 x 6.0 mm diam
Stainless steel BSI Acrylic Stainless steel Aluminium BSI Aluminium (Osbome) Acrylic Teflon Acrylic
Australian Dental Journal 1992;37:5.
347
Fig. 1 .-Stainless steel compression set moulds.
Fig. 2.-Flat specimen bend test jig.
BSI spe~ifications'~ were used while in the other case, a mould designed by Professor J. Osbornell in the Dental School, University of Birmingham, was used. Two modes of combined compressive and tensile tests were tested by bending specimens using two forms, one flat (Fig. 2) and the other round (Fig. 3). A deflection of 45 O was induced by incorporating a plunger after placing the specimens in their respective jigs. Direct measurements were made with a travelling microscope. For the torsion tests, a rod-shaped specimen was held vertically in the apparatus shown (Fig. 4). A 110O strain was employed and the elastic recovery was measured with an attached vernier gauge. IPersonal communication, 1973. 348
Results The permanent deformation results obtained at various times from the compression tests with specimens from a metal mould are given in Table 4. The comparative effect of mould material on compression set is shown graphically (Fig. 5). Table 5 shows the permanent deformation results following tensile strain. The permanent deformation results obtained with bend and torsion tests are shown in Tables 6 and 7, respectively.
Discussion Permanent deformation of elastomers is proportional to the degree of applied The degree of strain for each test in this study was based Australian Dental Journal 1992375.
Fig. 3.-Rod specimen bend test jig.
Fig. 4.-Torsion test apparatus.
on specifications (listed in Table 1) for compression and tensile tests, and on arbitrary decisions for the bend and torsion tests; the duration ofthe strain was for 5 seconds as based on the previous study (Table 1). The results indicate that the relative ranking of the materials was similar in the compression metal Australian Dental Journal 1992;37:5.
mould tests, the vertical and BSI horizontal test modes (tensile) and the bend and torsion tests: that is, Impregum >Permlastic>Delicron s Reflect (Fig. 6). Some variation was observed in the case of compression tests in the acrylic mould mode, and for the tensile horizontal mode (after Osborne). In these cases, the relative order was Permlastic >Impregum >Delicron 9 Reflect. In a separate study, it was found that the temperatures reached by the impression materials in the acrylic moulds were lower than in the metal moulds, except for Reflect. Similarly, compression set was also greater with specimens from the acrylic moulds, except Reflect (Fig. 5). These fm’khgs mean that the rapid heat transfer from the metal moulds allowed a greater degree of polymerization which does not necessarily reflect clinical conditions. As far as individual results were concerned, it was found that set in compression was greater using the BSI method, because of instrument inertia or loading effect, for polysulphide and polyether materials. This finding was not observed with the optical methods which were designed to allow elastic recovery without any load or instrument inertia. Therefore, it is evident from the ranking that the response of elastomers to all the tests is similar, provided that certain conditions of volume distribution of specimen material within the mould and mould material are accepted. It can be suggested from this study that compression tests using specimens made in acrylic moulds are required to determine the permanent deformation of these elastomers. This is in agreement with the work of Lautenschlager et al. l9 Acrylic moulds are preferred 349
-
PM PA 1DM DA IM IA RM RA Y
EII E5
0
a
15
25
5
Time (min) Fig. 5.-Comparison of compression set of specimens from metal and acrylic moulds. PM, Permlastic metal; PA, Permlastic acrylic; IM, Impregum metal; IA, Impregum acrylic; DM, Delicron metal; DA, Delicron acrylic; RM, Reflect metal; RA, Reflect acrylic.
Table 4. Permanent deformation from compression tests with specimens from a metal mould: per cent mean and standard deviation Material
~
Time/test
6 min
10 min
16 min
20 min
T1 T2 T3 T1 T2 T3 T1 T2 T3 T1 T2 T3
2.21 iO.06 1.93f 0.03 1.95f 0.12 1.61 fO.10 1.49 k 0.08 1.65 f 0.09 2.51 fO.05 2.25 k 0.06 2.14f0.09 0.21 k 0.06 0.2 1 k 0.05 0.16f0.04
2.17f0.06 1.91 k 0.05 1.60i0.16 1.60 f 0.10 1.46 k 0.08 1.68k 0.09 2.52 i 0.05 2.28 i 0.04 2.11 f0.07 0.2 1 k 0.07 0.2 1 i 0.05 0.17 f 0.09
2.15 i 0.05 1.89 f 0.05 1.83k 0.19 1.60 i 0.10 1.44 k 0.08 1.63 f 0.05 2.54 k 0.06 2.28 k 0.04 2.15f0.09 0.2 1 k 0.07 0.21 iO.05 0.15 i0.06
2.14f0.05 1.88 k 0.04 1.73 i 0.1 1 1.61 fO.09 1.44 f 0.08 1.63 i 0.12 2.54 f 0.05 2.26 f 0.05 2.15 i 0.10 0.21 k 0.06 0.20 k 0.06 0.17 f 0.06
~
P = Permlastic, I = Impregum, D = Delicron, R =Reflect, T1 = Balanced beam, T2 =Depth of field microscope, T3 = Stereomicroscope.
Table 5. Permanent deformation following tensile tests: Per cent mean and standard deviation Material
Timeltest
6 min
Vertical BSI Osborne Vertical BSI Osborne Vertical BSI Osborne Vertical
2.56 f 0 . 2 7 1.69 k 0.23 2.78 k 0.29 2.41 fO.30 1.46 k 0.25 1.85 k 0.37 2.87f0.31 1.82 i 0.42 1.89 f 0.32 0.05 f 0 . 2 6 0.10f0.55
BSI Osborne
10 min
16 min
2.46 f 0.20 1.97 k 0.19 1.29 k 0.32 1.23i0.39 2.62 f 0.22 1.90 f 0.12 1.91 f0.54 1.87 k 0.51 1.16f0.25 1.OO f 0.24 1.22 f 0.17 1.46 f 0.18 2.53 i 0.35 2.29 f 0.36 1.41 i 0 . 4 1 1.66 f 0.40 1.99 k 0.12 1.78i0.45 - 0.15 f 0.28 - 0.15 f 0.22 - 0.05 f 0.22 0.16 i 0.30 Fracture on 50% tensile strain
20 min 1.68 f 0.23 1.03 k 0.18 2.05 f 0.28 1.52k0.36 0.94 f 0.24 0.93 k 0.21 2.05 i 0.39 1.30k0.33 1.70 i 0.25 -- 0.19 f 0.20 0.00 f 0.26
P = Permlastic, I = Impregum, D = Delicron, R =Reflect.
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Australian Dental Journal 1992;37:5.
*O
1
1
W Permlastic Delicron Impregum Reflect
%
a -5
1
2
3
5
4
6
7
8
9 1 0
Fig. 6. -Comparison of results of elasticity tests. 1, British Standards Institution balanced beam (compression, metal); 2, Field microscope (compression, metal); 3, Stereomicroscope (compression, metal); 4, Microscope (compression, acrylic); 5, Vertical (tensile); 6, British Standards Institution horizontal (tensile); 8, Flat (bend); 9, Round (bend); 10, Torsion.
Table 6. Permanent deformation following bending tests: Per cent mean and standard deviation Material
Timeltest
6 min
10 min
16 min
20 min
Flat Rod Flat Rod Flat Rod Flat Rod
13.88 f 0.77 12.40k0.51 8.88 f0.66 10.76 f 0.48 15.04k 1.11 12.76 f 0.52 0.10 f 0.04 0.23 f 0.05
13.56 k 0.20 11.68 f 0.52 8.68 k 0.76 10.64 f 0.50 15.04 f 1.1 1 12.52 k 0.50 1.10 k 0.04 0.22 f 0.06
13.56k0.57 11.44 k0.57 8.44 k 0.74 10.64 k 0.50 15.04k1.11 12.52 k 0.50 O.lOkO.04 0.20 f 0.06
13.56k0.57 11.32 f 0.61 8.44 k 0.74 10.64k0.50 15.04k1.11 12.52k0.50 0.10 f 0.04 0.20 k 0.06
P = Permlastic, I = Impregum, D = Delicron, R = Reflect.
Table 7. Permanent deformation following torsional tests: Per cent mean and standard deviation Timel material
P D I R
6 min
10 min
16 min
20 min
15.72f0.30 13.64f0.65 16.20k0.75 0.72f0.23
15.32 k0.50 13.20f0.45 16.16k0.68 0.72f0.23
15.08 f0.48 13.04k0.39 16.12f0.73 0.72k0.23
15.08 f0.48 13.04k0.36 16.12k0.73 0.72k0.23
P = Permlastic, I = Impregum, D = Delicron, R = Reflect
to metal moulds, because the rapid heat transfer from metal moulds may not reflect the setting characteristics found in the clinical situation. The negative value of up to 0.5 per cent reached in the vertical mode of tensile test (Table 5) indicates a slight contraction. Lacy et d Z 0 have also found curing shrinkage of up to 0.5-1.0 per cent at 30 minutes after mixing. Australian Dental Journal 1992;37:5.
The differences shown in Fig. 6 for the last three tests compared with the first seven, could be that in deformation for these three tests the strain was not evenly distributed within the specimens. From the results obtained in this study (Tables 4-7), it was shown that for non-tensile tests, the elastic recovery of the materials did not alter much after ten minutes after strain release. For tensile tests, the elastic recovery continued over the 20 minutes. The observed delay may be due to the relatively large strain as shown by Makinson.” Overall, Impregum and Reflect did not change much after six minutes, but Permlastic and Delicron did alter although the change was not significant after ten minutes. It is therefore suggested that a delay of ten minutes following strain release should be allowed for standard testing of permanent deformation. For clinical purposes, casts could be poured from Impregum and Reflect after six minutes, while 351
in the case of Permlastic and Delicron, the time allowed should be ten minutes. Conclusions 1. When assessing the elasticity of elastomeric impression materials, the tensile, bend and torsion tests did not add to the information obtained from the compression tests for the materials selected in this study. 2. Compression tests with specimens made in acrylic rather than metal moulds are sufficient. The effect of mould material on the temperature of the polymerizing material must be accounted for, when comparing test results. 3. The optical systems which are without inertia and loading effects can be recommended for the compression tests. 4. A delay of ten minutes following strain release should be allowed before conducting standard elasticity tests. Acknowledgements The authors would like to acknowledge the support and guidance provided by Associate Professor G. C. Townsend, Department of Dentistry, The University of Adelaide. References 1. Cresson J. Physical properties of elastic duplicating materials. J Dent Res 1949;28:573-82. 2. Wilson HJ. Elastometric impression materials: I. The setting material. Br Dent J 1966;121:277-83. 3. Wilson HJ. Elastomeric impression materials: 11. The set material. Br Dent J 1966;121:322-8. 4. Chong MP, Docking AR. Some setting characteristics of elastomeric impression materials. Aust Dent J 1969;14:295-301. 5. Mansfield MA, Wilson HJ. A new method of determining the tension set of elastomeric impression materials. Br Dent J 1973;135:101-5. 6. Inoue K, Wilson HJ. Visco-elastic properties of elastomeric impression materials: 111. The elastic recovery after removal of strains applied at the setting time. J Oral Rehabil 1978;5:323-7.
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7. McCabe JF, Storer R. Elastomeric impression materials. The measurement of some properties relevant to clinical practice. Br Dent J 1980;121:73-9. 8. Habu H, Uchida H, Hashimoto K. Permanent deformation of elastic impression materials. J Dent Res 1985;64:275 Abstr 902. 9. DeArujo PA, Jorgensen KD, Finger W. Viscoelastic properties of setting elastomeric impression materials. J Prosthet Dent 1985;54:633-6. 10. Finger W, Komatsu M. Elastic and plastic properties of elastic dental impression materials. Dent Mater 1985;l: 129-34. 11. Jamani KD, Harrington E, Wilson HJ. The determination of elastic recovery of impression materials at the setting time. J Oral Rehabil 1989;16:89-100. 12. American Dental Association Council on Dental Materials and Devices. Revised American Dental Association Specification No. 19 for non-aqueous elastomeric dental impression materials. J Am Dent Assoc 1977;94:733-41. 13. Standards Australia. Elastomeric dental impression materials. Australian Standard 1185, 1984. 14. International Organization for Standardization. Elastomeric dental impression materials. I S 0 4823, 1984. 15. British Standards Institution. Specification for dental elastic impression materials. British Standard 4269: 1,1968. 16. Wilson HJ. Tissue conditioners and functional impression materials. Br Dent J 1966;121:9-16. 17. Makinson OF. Elastic recovery from compression strains in some alginate impression materials. International Association for Dental Research Meeting (Australia and New Zealand Division) 1970: Abstr 14. 18. Menz J. Three dimensional surfaces measuring with the SMXX stereomicroscope VEB Carl Zeiss JENA. JENA Review 1969;4:238-41. 19. Lautenschlager EP, Miyomoto P, Hilton R. Elastic recovery of polysulphide base impressions. J Dent Res 1972;51:773-9. 20. Lacy AM, Fukui H, Bellman T, Jendersen MD. Time dependent accuracy of elastomer impression material. 11. Polyether, polysulphide, polysiloxane. J Prosthet Dent 1981;45:329-33.
Address for correspondenceheprints: 0. F. Makinson, Department of Dentistry, The University of Adelaide, GPO Box 498, Adelaide, South Australia, 5001.
Australian Dental Journal 1992;37:5.
