SECTIONEDITORS
one-step versus ression technique
two-step
H. Hung, DDS, MS,” John H. Purk, DDS, MS,b Daniel. and J. David. Eick, PhDd University of Missouri-Kansas City, School of Dentistry, Kansas City, MO. Shirley
E. Tira,
PhD,C
This study compared the accuracy of one-step putty wash with two-step putty wash impression techniques. Five addition silicone impression materials-Mirror 3 (MR), Mirror 3 Extrude (ME), Express (E), Permagum (P), and Absolute(A)-were tested. A stainless steel model containing two full-crown abutment preparations was used as the positive control. Five replications for one-step and two-step putty wash impressions of the master model were made for each test material. Accuracy of the materials was assessed by measuring six dimensions on stone dies poured from impressions of the master model. Accuracy of addition silicone impression material is affected more by material than technique. Accuracy of the putty wash one-step impression technique was not different from the putty wash two-step impression technique except at one of the six dimensions where one-step was more accurate than two-step. Mirror 3 putty wash two-step impression presented less distortion tham Mirror 3 Extrude putty wash one-step or two-step impression. (J PROSTHET DENT 1992;67:583-9.)
he putty wash (P/W) impression technique was originally recommended to overcome the problems associated with polymerization shrinkage of the condensation silicone impression materials. The P/W technique has been recommended for addition silicone impression materials even though these materials appear t.o be dimensionally stable.? The P/W impression technique can be made as a one-step2 or as a two’-step technique. The working time of some addition silicone putty materials has been lengthened, so it is now possible to make P/W impressions using a one-step technique. Advantages of the P/W one-step technique include reduced chairside time and savings of impression material. A disadvantage is that there are occasional ledges at the junction of the putty and wash material. An advantage of the P/W two-step impression technique is that the impression of the teeth can be captured with the wash material. Disadvantages of the P/W two-step impression technique are distortions, extra chairside time, and extra material needed. Ideally, wash material should cover the entire preparation for both techniques. However, clinically it is not always possible to accomplish this procedure.
Presented at the American Association for Dental Research/ International Association for Dental Research, Cincinnati, Ohio. aAssociate Professor, Department of Fixed Prosthodontics. bAssistant Professor, Department of Operative Dentistry. cProfessor, Department of Behavioral Sciences. dCurator’s Professor, Department of Oral Biology. POllI
THE JOURNAL
OFPROSTHETICDENTISTRY
This study had two objectives. The first objective was to compare the accuracy of the P/W one-step technique with the P/W two-step impression technique for four different addition silicone impression materials. The second objective was to compare the accuracy of all of the materials tested (either one-step or two-step) with the accuracy of a standard stainless steel model (positive control) and with the accuracy of stone dies produced from impressions made from Mirror 3 P/W two-step technique (negative control). The null hypotheses to be tested were as follows: 1. There will be no significant difference in accuracy between the one-step putty wash impression technique and the two-step putty wash impression technique. 2. There will be no significant difference in accuracy between the materials tested compared with the positive control of the standard stainless steel model and between the materials tested compared with the negative control of Mirror 3PiW two-step impression technique at six different measurement locations.
METHODS
AND MATERIAL
A stainless steel model containing two full-crown fixed partial denture abutment preparations with six measurement locations was made.3 One abutment had a V-shaped undercut below the gingival margin and the other abutment did not. For measuring purposes a post was built between the two abutment crown preparations as a reference point (Figs. 1 and 2, Table I). Five addition silicone impression materials were evaluated. Table II lists the respective viscosities and manufac-
m3
Fig. 1. Diagram of stainless steel model with reference marks. Numbers cations measured.
Fig.
2. Stainless steel model.
turing dates for each impression material tested. Each material, except Mirror 3 (MR), was used with a PW one-step technique and a PW two-step technique. Mirror 3 material was used with only the PW two-step impression technique because of its shorter working time. Mirror 3 material was also used as one control for comparison with the longer working-time putty materials presently available, including Mirror 3 extrude. The stainless steel model was used as the other control. The same size of perforated metal tray (XL21, Coe Laboratories, Inc., Chicago, Ill.) was used to make impressions of the stainless steel model. The tray adhesive supplied by each impression material manufacturer was applied evenly over the surface of the tray. For the PW two-step impression technique, a plastic spacer supplied by the manufacturer was placed over the stainless steel model when the preliminary putty impression was made. This procedure was followed to sirnulate clinical practice. The preliminary impression was allowed to set for 10 minutes. The light-body wash was then added. For PW one-step impressions, the putty and wash impressions were mixed simultaneously. All wash material was dispensed
584
Fig.
indicate six lo-
3. Stainless steel model wit.h positioning
device.
with an automatic-mixing syringe with the exception of Mirror 3 wash material, which was m.ixed by hand. The final impression was allowed to set on the stainless steel model for 12 minutes from the start of mixing. The manufacturer’s setting time was doubled to compensate for a delayed polymerization reaction compared with one at mouth temperature. All impressions were stored at room temperature, 25” C, for 1 hour before being poured in improved stone (Die Keen, Columbus Dental, St. Louis, MO.). The improved stone was first mixed by hand to incorporate the water and then mechanically mixed under vacuum for 15 seconds. All mixes were vibrated into the impressions and allowed to set for 1 hour before separation from the impression. A positioning device (Figs. 3 and 4) was made so that the measurements made from the six locations on the stainless steel model and the stone dies could be reproduced. Each measurement of the stainless steel model at the six measurement locations was taken 10 times. The mean and standard deviation at each measurement location was used as the standard measurement for comparison to test the first null hypothesis. The test samples at each measure-
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~abIe I. Description of locations measured and corresponding means and standard deviations ef meas~reme~t$ for standard die Location
Description
ml m2
Distance between preparations Mesiodistal dimension of nonundercut preparation Mesiodistal dimension of undercut preparation Diameter of undercut area Occlusogingival height of nonundercut preparation Occlusogingival height of undercut preparation
m3 m4 m5 m6
Mean (mm)
SD (mm)
Measurement error (%)
28.934 10.069
0.009 0.016
0.03 0.16
9.762
0.010
0.10
8.497 9.589
0.023 0.014
0.21 0.15
9.118
0.004
0.04
Table II. List of addition silicone impression materials evaluated Batch Product
Symbol
Mirror 3
MR
Extrude
ME
Express
E
Permagum
P
Absolute
A
Manufacturer
Kerr/Sybron Romulus, Mich. Kerr/Sybron 3M Dental Products Div. St. Paul, Minn. Premier/Premier ESPE Norristown, Pa. COE Laboratories, Inc. Chicago, Ill.
ment location were measured with a traveling microscope (Unitron Instruments, Inc., Woodbury, N.Y.) capable of measuring to 0.001 mm (Fig. 5). Each measurement of the stone dies was repeated three times. The difference between the mean of the stone model (msm) and the mean of the stainless steel model (mss) divided by the mean of the stainless steel model multiplied by 100 was expressed as the percent of deviation from the stainless steel model for each impression material at each measurement location. Percent of deviation =
msm - mss x 100 mss
A pilot study to determine sample size was performed. Fifteen Mirror 3 material P/W two-step impressions of the stainless steel model were made and poured in die stone. With the mean and standard deviation at each measurement location, the experimental design parameters of alpha = 0.05 and with a power of 0.8, a test sample size of five for each group was calculated. Therefore, five replications of each material and impression technique were used for all test conditions. The investigator’s coefficient of variability ranged from 0.03 % to 0.27 % for this study (Table I-measurement error). A two-factor ANOVA was used to test the first null hypothesis. A one-factor ANOVA with
THE
JOURNAL
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DENTISTRY
Viscosity
putty Wash Putty Wash putty Low Putty Low Putty Low
date
9-8-83 3-26-86 10-27-88 11-04-88 4-20-86 l-10-86 8-8-88 8-8-63 4-18-39 3-16-89
the stainless steel model as the positive control and the Mirror 3 P/W material two-step impression technique as the negative control were used to test the second null hypothesis. If significant differences were found, a comparison of individual means was performed by the StudentNewman-Keuls method.4 All hypotheses were tested at the 95% level of confidence 03 I 0.05). RESULTS The means and standard deviations for the stainless steel model and the stone dies at each measurement location are listed in Table III. Graphic results are presented in Figs. 6 and 7 as percent deviations of the stone dies from the stainless steel model for each material and measurement (ml to m6). The graphs in Figs. 8 and 9 present percent deviations of the stone dies from the Mirror 3 P/W material two-step impression for measurements ml to m6. Means that were shown to differ significantly (p 5 0.05) are indicated with asterisks on Figs. 6 through 9. The interabutment distance (ml) increased for all materials compared with the stainless steel model except for Permagum material P twostep impression technique, which decreased 0.1%. The measurements of all the stone dies at m2, m3, and m4 were generally larger than the standard dies except for the stone
585
IIUNG
ig. 4. Stone dies with positioning device.
a significant difference; the one-step impression technique was more accurate than the two-step impression technique e, I 0.05). To test the second null hypothesis, a one-factor ANOVA revealed a statistically significant difference between groups (p I 0.05) with the standard stainless steel model used as the control. The error term generated from the ANOVA was used with the Student Newman-Keuls sequential range test to compare group means. Only Mirror 3 Extrude P/W material (one and two step), Express P/W material (one and two step) and Absolute P/W material (two step) for ml and Mirror 3 Extrude P/W material (two step) for m2 and m5 were found to be statistically different from the standard stainless steel model 0, I 0.05). To test against the negative control, a one-factor ANQVA using Mirror 3 P/W material (two step) as the control found a significant difference between the control and Mirror 3 Extrude P/W material (one and two step) at ml and m2 (p 5 0.05). There was no significant difference at the other measurements m3, m4, m5, and m6 for both materials.
DISCUSSION Interabutment
Fig. 5. Unitron microscope. dies produced from the Mirror 3 material P-W two-step, Permagum material P/W one-step, and Absolute material P/W two-step impression techniques for m2. Most cases were not statistically significant (p 10.05). To test the first null hypothesis, a two-factor ANOVA evaluating technique versus material was performed. A statistically significant difference was found among all impression materials tested at all measurements (ml to m6). There was no significant difference between the P/w onestep impression technique and the P/W two-step impression technique at ml, m3, m4, m5, and m6. At m2 there was 586
ET AL
distance
The interabutment distance increased for all materials except with Permagum P/W material two-step impressions, which decreased 0.1% . This increase of ml was also reported by Linke et a1.5The six types of impression materials studied by Linke et aL5 were polyvinyl siloxane, silicone-irreversible hydrocolloid, light/regular silicone irreversible hydrocolloid, irreversible hydrocolloid, modified reversible-irreversible hydrocolloid, and reversible hydrocolloid. Linke et a1.5reported that the perimeter of the arch of the test cast was larger than the standard reference model. However, Johnson and Craig3 and Craigs reported that there were no significant differences for addition silicones between techniques for measurements between preparations. Gordon et aL7 reported that interabutment distances were greater for all dies using polysulfide, polyether, and addition silicone impression materials, especially when the stock tray was used; a linear change of 45 pm to 100 pm greater than the standard was observed. Clinically, this change may result in fixed ps.rtial dentures that are too long mesiodistally when constructed on casts made from stock tray impressions. Similar results were found in our study with Mirror 3 Extrude, Express, and Absolute materials. Permagum material produced interabutment distances with the most accuracy. Individual abutment Horizontal measurements m2, m3, and m4). The diameters of all the stone dies were generally larger than the standard model except the stone dies produced from Mirror 3 P/W material two-step impressions, Permagum P/W material one-step, and Absolute P/w material one-step impressions for m2. These dies were smaller and this decreasewould need to be compensated for on a stone die by a die relief method. Permagum P/W material one-step and two-step impressions produced dies MAY
1992
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ACCURACY
OF PUTTY
Table III.
WASH
IMPRESSIONS
Die measurements,
corresponding
means, and standard
ml Technique (putty wash)
Product Stainless steel model Mirror 3 Extrude Extrude Express Express Permagum Permagum Absolute Absolute
Two-step One-step Two-step One-step Two-step One-step Two-side One-step Two-step
deviations
m2
(mm)
m3
m4
m5
m6
x
SD
ii
SD
ii
SD
:
SD
;;
SD
ii
SD
28.984 29.053 29.317 29.316 29.289 29.289 28.992 28.983 29.090 29.221
0.009 0.018 0.033 0.029 0.027 0.013 0.038 0.016 0.149 0.111
10.069 10.048 10.105 10.128 10.100 10.100 10.040 10.079 10.047 10.082
0.016 0.024 0.012 0.013 0.022 0.013 0.016 0.010 0.047 0.024
9.762 9.794 9.781 9.803 9.785 9.791 9.750 9.761 9.789 9.792
0.010 0.034 0.018 0.019 0.027 0.033 0.027 0.023 0.033 0.021
8.497 8.494 8.534 8.540 8.479 8.514 8.473 8.473 8.501 8.505
0.023 0.050 0.047 0.029 0.026 0.034 0.044 0.055 0.031 0.028
9.589 9.607 9.632 9.650 9.616 9.619 9.607 9.598 9.615 9.624
0.014 0.050 0.032 0.019 0.009 0.019 0.018 0.007 0.022 0.027
9.118 9.148 9.143 9.146 9.106 9.134 9.121 9.101 9.139 9.130
0.004 0.026 0.010 0.011 0.027 0.008 0.021 0.004 0.023 0.020
N = 5 for each group.
with a smaller m3 measurement. Express P/W material one-step, Permagum P/W material one-step and two-step impressions produced dies with smaller m4 measurements (Fig. 6). A one-way AMOVA showed no statistically significant difference (p i 0.05). The only statistically significant difference (p 2 0.05) was shown for m2 with Mirror 3 Extrude P/W material two-step impression. The deviation was a 60 pm increase in diameter, which could adequately provide the die space needed for the fabrication of crowns without the need of applying die spacer. No obvious effect of undercut on the horizontal measurements (m3, m4) was found. The deviation related more to the material than the technique used. Impressions with Permagum material consistently yielded undersized dies whether the P/W one-step or two-step technique was used
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DENTISTRY
(Fig. 6). This finding is in agreement with the results of Tjan et a1.8 Figs. 8 and 9 show the results using Mirror 3 P/W material (two-step) as the negative control. Mirror 3 P/W two-step material provided impressions that were statistically significantly better than Mirror 3 Extrude P/W material one and two-step impressions at ml and m2. When the working time of Mirror 3 Extrude putty material was lengthened, the accuracy of the impression material might have been affected, compared with the Mirror 3 P/W material two-step. Vertical measurements m5 and Individual abutment m6). The changes in vertical height are listed under m5 and m6. Our study showed an increase in vertical heights with all impression materials tested. Impression technique and
587
KUNG ET AL
Fig.
8.
undercut of the die showed no effect on the vertical height. In the study by Gordon et al.,7 a slight increase of vertical heights for addition silicone impression with stock tray was reported. Craig,6 Linke et al. 5 and Johnson and Craig,g reported shorter vertical heights in their studies. de AraujoiO
588
to m4).
also reported that the increase in thickness of the impression material from 1 to 4 mm caused a greater distortion than height increase of the undercut from 1 mm to 3 mm. Valderhaug and Flgiystrandli reported that although an ample amount of impression material (2 to 9 mm) was al-
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Fig. 9. Percent deviation from Mirror 3 P/W material two-step stone dies (m5 and m6).
lowed, the linear dimensional stability of the impressions made in stock trays was not inferior to the stability of impressions made in custom-made trays. During this experiment, the separation of impressions from the standard stainless steel dies was much more difficult than in clinical practice. This separation might have contributed to the greater incisal-gingival dimension of the stone die, since PW impressions may not recover well. The putty material will be displaced if the tray is not seated passively and the putty material will show through after the wash impression i.smade. It then may rebound to cause deformation. The wash material may hydraulically displace the putty during seating of the impression so that the putty could then exhibit some elastic recovery on removal of the impression. Overall Mirror 3 P/w material two-step and Permagum P/W material ane or twa-step produced the most accurate dies at all six measurements compared with the stainless steel model. CONCLUSIONS 1. The accuracy of the addition silicone impression materials tested was affected more by the material than by technique. 2. The accuracy of the putty wash one-step technique was not different from that of the putty wash two-step technique except at measurement 2; where the onestep impression technique was more accurate than the two-step impression technique. 3. Mirror 3 putty wash material two-step impressions
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DENTISTRY
(using putty material with a shorter working time) presented less distortion than Mirror 3 Extrude putty wash material one-step or two-step impressions (using putty material with a longer working time). REFERENCES 1. Craig RG. Review of dental impression materials. Adv Dent Res 1988;2:51-64. 2. Pameijer CH. A one-step putty-wash impression technique utilizing vinyl polysiloxanes. Quintessence Intl 1983;8%1-3. Johnson GH, Craig RG. Accuracy of addition silicones as a function of technique. J PROSTHETDENT 1986;55:197-203. Kirk RE. Experimental design: procedures for the behavorial sciences. Belmont, Calif’z Brooks/Cole Pub1 Co, 1968:91-3. Liuke BA, Nicholls JI, Faucher RR. Distortion analysis of stone casts made from impression materials. J PROSTHETDENT 1985;54:794-802. 6. Craig RG. Evaluation of au automatic mixing system for an addition silicone impression material. J Am Dent Assoc 1985;110:213-5. I. Gordon GE, Johnson GH, Drennor DG. The effect of tray selection on the accuracy of elastomeric impression materials. J PROSTHETDENT 1990;63:12-5. 8. Tjau AHL, Whang SB, Tjan AH, Sarissian R. Clinically oriented evaluation of the accuracy of commonly used impression mat.erisls. J PRO+ THET DENT 1986$%4-S. 9. Johnson GH, Craig RG. Accuracy of four types of rubber impression materials compared with time of pour aud a repeat pour of models. J PROSTHETDENT 1985;53:484-90. 10. de Araujo PA. Effect of material bulk and undercuts on the accuracy of impression materials. J PROSTHETDENT 1985;54:791-4. 11. Valderhaug J, Fl$ystraud F. Dimensional &ability of elastomeric impression materials in custom-made and stock trays. J PROSTHET DENT 1984;52:514-7. Reprint requests to: DR. SHIRLEY H. HUNG UNIV!ARSITY OF MISSOURI-KANSAS CITY SCHOOL OF DENTISTRY KANSAS CITY, MISSOURI 64108
589
one-step versus ression technique
two-step
H. Hung, DDS, MS,” John H. Purk, DDS, MS,b Daniel. and J. David. Eick, PhDd University of Missouri-Kansas City, School of Dentistry, Kansas City, MO. Shirley
E. Tira,
PhD,C
This study compared the accuracy of one-step putty wash with two-step putty wash impression techniques. Five addition silicone impression materials-Mirror 3 (MR), Mirror 3 Extrude (ME), Express (E), Permagum (P), and Absolute(A)-were tested. A stainless steel model containing two full-crown abutment preparations was used as the positive control. Five replications for one-step and two-step putty wash impressions of the master model were made for each test material. Accuracy of the materials was assessed by measuring six dimensions on stone dies poured from impressions of the master model. Accuracy of addition silicone impression material is affected more by material than technique. Accuracy of the putty wash one-step impression technique was not different from the putty wash two-step impression technique except at one of the six dimensions where one-step was more accurate than two-step. Mirror 3 putty wash two-step impression presented less distortion tham Mirror 3 Extrude putty wash one-step or two-step impression. (J PROSTHET DENT 1992;67:583-9.)
he putty wash (P/W) impression technique was originally recommended to overcome the problems associated with polymerization shrinkage of the condensation silicone impression materials. The P/W technique has been recommended for addition silicone impression materials even though these materials appear t.o be dimensionally stable.? The P/W impression technique can be made as a one-step2 or as a two’-step technique. The working time of some addition silicone putty materials has been lengthened, so it is now possible to make P/W impressions using a one-step technique. Advantages of the P/W one-step technique include reduced chairside time and savings of impression material. A disadvantage is that there are occasional ledges at the junction of the putty and wash material. An advantage of the P/W two-step impression technique is that the impression of the teeth can be captured with the wash material. Disadvantages of the P/W two-step impression technique are distortions, extra chairside time, and extra material needed. Ideally, wash material should cover the entire preparation for both techniques. However, clinically it is not always possible to accomplish this procedure.
Presented at the American Association for Dental Research/ International Association for Dental Research, Cincinnati, Ohio. aAssociate Professor, Department of Fixed Prosthodontics. bAssistant Professor, Department of Operative Dentistry. cProfessor, Department of Behavioral Sciences. dCurator’s Professor, Department of Oral Biology. POllI
THE JOURNAL
OFPROSTHETICDENTISTRY
This study had two objectives. The first objective was to compare the accuracy of the P/W one-step technique with the P/W two-step impression technique for four different addition silicone impression materials. The second objective was to compare the accuracy of all of the materials tested (either one-step or two-step) with the accuracy of a standard stainless steel model (positive control) and with the accuracy of stone dies produced from impressions made from Mirror 3 P/W two-step technique (negative control). The null hypotheses to be tested were as follows: 1. There will be no significant difference in accuracy between the one-step putty wash impression technique and the two-step putty wash impression technique. 2. There will be no significant difference in accuracy between the materials tested compared with the positive control of the standard stainless steel model and between the materials tested compared with the negative control of Mirror 3PiW two-step impression technique at six different measurement locations.
METHODS
AND MATERIAL
A stainless steel model containing two full-crown fixed partial denture abutment preparations with six measurement locations was made.3 One abutment had a V-shaped undercut below the gingival margin and the other abutment did not. For measuring purposes a post was built between the two abutment crown preparations as a reference point (Figs. 1 and 2, Table I). Five addition silicone impression materials were evaluated. Table II lists the respective viscosities and manufac-
m3
Fig. 1. Diagram of stainless steel model with reference marks. Numbers cations measured.
Fig.
2. Stainless steel model.
turing dates for each impression material tested. Each material, except Mirror 3 (MR), was used with a PW one-step technique and a PW two-step technique. Mirror 3 material was used with only the PW two-step impression technique because of its shorter working time. Mirror 3 material was also used as one control for comparison with the longer working-time putty materials presently available, including Mirror 3 extrude. The stainless steel model was used as the other control. The same size of perforated metal tray (XL21, Coe Laboratories, Inc., Chicago, Ill.) was used to make impressions of the stainless steel model. The tray adhesive supplied by each impression material manufacturer was applied evenly over the surface of the tray. For the PW two-step impression technique, a plastic spacer supplied by the manufacturer was placed over the stainless steel model when the preliminary putty impression was made. This procedure was followed to sirnulate clinical practice. The preliminary impression was allowed to set for 10 minutes. The light-body wash was then added. For PW one-step impressions, the putty and wash impressions were mixed simultaneously. All wash material was dispensed
584
Fig.
indicate six lo-
3. Stainless steel model wit.h positioning
device.
with an automatic-mixing syringe with the exception of Mirror 3 wash material, which was m.ixed by hand. The final impression was allowed to set on the stainless steel model for 12 minutes from the start of mixing. The manufacturer’s setting time was doubled to compensate for a delayed polymerization reaction compared with one at mouth temperature. All impressions were stored at room temperature, 25” C, for 1 hour before being poured in improved stone (Die Keen, Columbus Dental, St. Louis, MO.). The improved stone was first mixed by hand to incorporate the water and then mechanically mixed under vacuum for 15 seconds. All mixes were vibrated into the impressions and allowed to set for 1 hour before separation from the impression. A positioning device (Figs. 3 and 4) was made so that the measurements made from the six locations on the stainless steel model and the stone dies could be reproduced. Each measurement of the stainless steel model at the six measurement locations was taken 10 times. The mean and standard deviation at each measurement location was used as the standard measurement for comparison to test the first null hypothesis. The test samples at each measure-
MAY1992
VOLUMEW
NUMBERS
ACCURACY
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WASH
IMPRESSIONS
~abIe I. Description of locations measured and corresponding means and standard deviations ef meas~reme~t$ for standard die Location
Description
ml m2
Distance between preparations Mesiodistal dimension of nonundercut preparation Mesiodistal dimension of undercut preparation Diameter of undercut area Occlusogingival height of nonundercut preparation Occlusogingival height of undercut preparation
m3 m4 m5 m6
Mean (mm)
SD (mm)
Measurement error (%)
28.934 10.069
0.009 0.016
0.03 0.16
9.762
0.010
0.10
8.497 9.589
0.023 0.014
0.21 0.15
9.118
0.004
0.04
Table II. List of addition silicone impression materials evaluated Batch Product
Symbol
Mirror 3
MR
Extrude
ME
Express
E
Permagum
P
Absolute
A
Manufacturer
Kerr/Sybron Romulus, Mich. Kerr/Sybron 3M Dental Products Div. St. Paul, Minn. Premier/Premier ESPE Norristown, Pa. COE Laboratories, Inc. Chicago, Ill.
ment location were measured with a traveling microscope (Unitron Instruments, Inc., Woodbury, N.Y.) capable of measuring to 0.001 mm (Fig. 5). Each measurement of the stone dies was repeated three times. The difference between the mean of the stone model (msm) and the mean of the stainless steel model (mss) divided by the mean of the stainless steel model multiplied by 100 was expressed as the percent of deviation from the stainless steel model for each impression material at each measurement location. Percent of deviation =
msm - mss x 100 mss
A pilot study to determine sample size was performed. Fifteen Mirror 3 material P/W two-step impressions of the stainless steel model were made and poured in die stone. With the mean and standard deviation at each measurement location, the experimental design parameters of alpha = 0.05 and with a power of 0.8, a test sample size of five for each group was calculated. Therefore, five replications of each material and impression technique were used for all test conditions. The investigator’s coefficient of variability ranged from 0.03 % to 0.27 % for this study (Table I-measurement error). A two-factor ANOVA was used to test the first null hypothesis. A one-factor ANOVA with
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
Viscosity
putty Wash Putty Wash putty Low Putty Low Putty Low
date
9-8-83 3-26-86 10-27-88 11-04-88 4-20-86 l-10-86 8-8-88 8-8-63 4-18-39 3-16-89
the stainless steel model as the positive control and the Mirror 3 P/W material two-step impression technique as the negative control were used to test the second null hypothesis. If significant differences were found, a comparison of individual means was performed by the StudentNewman-Keuls method.4 All hypotheses were tested at the 95% level of confidence 03 I 0.05). RESULTS The means and standard deviations for the stainless steel model and the stone dies at each measurement location are listed in Table III. Graphic results are presented in Figs. 6 and 7 as percent deviations of the stone dies from the stainless steel model for each material and measurement (ml to m6). The graphs in Figs. 8 and 9 present percent deviations of the stone dies from the Mirror 3 P/W material two-step impression for measurements ml to m6. Means that were shown to differ significantly (p 5 0.05) are indicated with asterisks on Figs. 6 through 9. The interabutment distance (ml) increased for all materials compared with the stainless steel model except for Permagum material P twostep impression technique, which decreased 0.1%. The measurements of all the stone dies at m2, m3, and m4 were generally larger than the standard dies except for the stone
585
IIUNG
ig. 4. Stone dies with positioning device.
a significant difference; the one-step impression technique was more accurate than the two-step impression technique e, I 0.05). To test the second null hypothesis, a one-factor ANOVA revealed a statistically significant difference between groups (p I 0.05) with the standard stainless steel model used as the control. The error term generated from the ANOVA was used with the Student Newman-Keuls sequential range test to compare group means. Only Mirror 3 Extrude P/W material (one and two step), Express P/W material (one and two step) and Absolute P/W material (two step) for ml and Mirror 3 Extrude P/W material (two step) for m2 and m5 were found to be statistically different from the standard stainless steel model 0, I 0.05). To test against the negative control, a one-factor ANQVA using Mirror 3 P/W material (two step) as the control found a significant difference between the control and Mirror 3 Extrude P/W material (one and two step) at ml and m2 (p 5 0.05). There was no significant difference at the other measurements m3, m4, m5, and m6 for both materials.
DISCUSSION Interabutment
Fig. 5. Unitron microscope. dies produced from the Mirror 3 material P-W two-step, Permagum material P/W one-step, and Absolute material P/W two-step impression techniques for m2. Most cases were not statistically significant (p 10.05). To test the first null hypothesis, a two-factor ANOVA evaluating technique versus material was performed. A statistically significant difference was found among all impression materials tested at all measurements (ml to m6). There was no significant difference between the P/w onestep impression technique and the P/W two-step impression technique at ml, m3, m4, m5, and m6. At m2 there was 586
ET AL
distance
The interabutment distance increased for all materials except with Permagum P/W material two-step impressions, which decreased 0.1% . This increase of ml was also reported by Linke et a1.5The six types of impression materials studied by Linke et aL5 were polyvinyl siloxane, silicone-irreversible hydrocolloid, light/regular silicone irreversible hydrocolloid, irreversible hydrocolloid, modified reversible-irreversible hydrocolloid, and reversible hydrocolloid. Linke et a1.5reported that the perimeter of the arch of the test cast was larger than the standard reference model. However, Johnson and Craig3 and Craigs reported that there were no significant differences for addition silicones between techniques for measurements between preparations. Gordon et aL7 reported that interabutment distances were greater for all dies using polysulfide, polyether, and addition silicone impression materials, especially when the stock tray was used; a linear change of 45 pm to 100 pm greater than the standard was observed. Clinically, this change may result in fixed ps.rtial dentures that are too long mesiodistally when constructed on casts made from stock tray impressions. Similar results were found in our study with Mirror 3 Extrude, Express, and Absolute materials. Permagum material produced interabutment distances with the most accuracy. Individual abutment Horizontal measurements m2, m3, and m4). The diameters of all the stone dies were generally larger than the standard model except the stone dies produced from Mirror 3 P/W material two-step impressions, Permagum P/W material one-step, and Absolute P/w material one-step impressions for m2. These dies were smaller and this decreasewould need to be compensated for on a stone die by a die relief method. Permagum P/W material one-step and two-step impressions produced dies MAY
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Table III.
WASH
IMPRESSIONS
Die measurements,
corresponding
means, and standard
ml Technique (putty wash)
Product Stainless steel model Mirror 3 Extrude Extrude Express Express Permagum Permagum Absolute Absolute
Two-step One-step Two-step One-step Two-step One-step Two-side One-step Two-step
deviations
m2
(mm)
m3
m4
m5
m6
x
SD
ii
SD
ii
SD
:
SD
;;
SD
ii
SD
28.984 29.053 29.317 29.316 29.289 29.289 28.992 28.983 29.090 29.221
0.009 0.018 0.033 0.029 0.027 0.013 0.038 0.016 0.149 0.111
10.069 10.048 10.105 10.128 10.100 10.100 10.040 10.079 10.047 10.082
0.016 0.024 0.012 0.013 0.022 0.013 0.016 0.010 0.047 0.024
9.762 9.794 9.781 9.803 9.785 9.791 9.750 9.761 9.789 9.792
0.010 0.034 0.018 0.019 0.027 0.033 0.027 0.023 0.033 0.021
8.497 8.494 8.534 8.540 8.479 8.514 8.473 8.473 8.501 8.505
0.023 0.050 0.047 0.029 0.026 0.034 0.044 0.055 0.031 0.028
9.589 9.607 9.632 9.650 9.616 9.619 9.607 9.598 9.615 9.624
0.014 0.050 0.032 0.019 0.009 0.019 0.018 0.007 0.022 0.027
9.118 9.148 9.143 9.146 9.106 9.134 9.121 9.101 9.139 9.130
0.004 0.026 0.010 0.011 0.027 0.008 0.021 0.004 0.023 0.020
N = 5 for each group.
with a smaller m3 measurement. Express P/W material one-step, Permagum P/W material one-step and two-step impressions produced dies with smaller m4 measurements (Fig. 6). A one-way AMOVA showed no statistically significant difference (p i 0.05). The only statistically significant difference (p 2 0.05) was shown for m2 with Mirror 3 Extrude P/W material two-step impression. The deviation was a 60 pm increase in diameter, which could adequately provide the die space needed for the fabrication of crowns without the need of applying die spacer. No obvious effect of undercut on the horizontal measurements (m3, m4) was found. The deviation related more to the material than the technique used. Impressions with Permagum material consistently yielded undersized dies whether the P/W one-step or two-step technique was used
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(Fig. 6). This finding is in agreement with the results of Tjan et a1.8 Figs. 8 and 9 show the results using Mirror 3 P/W material (two-step) as the negative control. Mirror 3 P/W two-step material provided impressions that were statistically significantly better than Mirror 3 Extrude P/W material one and two-step impressions at ml and m2. When the working time of Mirror 3 Extrude putty material was lengthened, the accuracy of the impression material might have been affected, compared with the Mirror 3 P/W material two-step. Vertical measurements m5 and Individual abutment m6). The changes in vertical height are listed under m5 and m6. Our study showed an increase in vertical heights with all impression materials tested. Impression technique and
587
KUNG ET AL
Fig.
8.
undercut of the die showed no effect on the vertical height. In the study by Gordon et al.,7 a slight increase of vertical heights for addition silicone impression with stock tray was reported. Craig,6 Linke et al. 5 and Johnson and Craig,g reported shorter vertical heights in their studies. de AraujoiO
588
to m4).
also reported that the increase in thickness of the impression material from 1 to 4 mm caused a greater distortion than height increase of the undercut from 1 mm to 3 mm. Valderhaug and Flgiystrandli reported that although an ample amount of impression material (2 to 9 mm) was al-
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Fig. 9. Percent deviation from Mirror 3 P/W material two-step stone dies (m5 and m6).
lowed, the linear dimensional stability of the impressions made in stock trays was not inferior to the stability of impressions made in custom-made trays. During this experiment, the separation of impressions from the standard stainless steel dies was much more difficult than in clinical practice. This separation might have contributed to the greater incisal-gingival dimension of the stone die, since PW impressions may not recover well. The putty material will be displaced if the tray is not seated passively and the putty material will show through after the wash impression i.smade. It then may rebound to cause deformation. The wash material may hydraulically displace the putty during seating of the impression so that the putty could then exhibit some elastic recovery on removal of the impression. Overall Mirror 3 P/w material two-step and Permagum P/W material ane or twa-step produced the most accurate dies at all six measurements compared with the stainless steel model. CONCLUSIONS 1. The accuracy of the addition silicone impression materials tested was affected more by the material than by technique. 2. The accuracy of the putty wash one-step technique was not different from that of the putty wash two-step technique except at measurement 2; where the onestep impression technique was more accurate than the two-step impression technique. 3. Mirror 3 putty wash material two-step impressions
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DENTISTRY
(using putty material with a shorter working time) presented less distortion than Mirror 3 Extrude putty wash material one-step or two-step impressions (using putty material with a longer working time). REFERENCES 1. Craig RG. Review of dental impression materials. Adv Dent Res 1988;2:51-64. 2. Pameijer CH. A one-step putty-wash impression technique utilizing vinyl polysiloxanes. Quintessence Intl 1983;8%1-3. Johnson GH, Craig RG. Accuracy of addition silicones as a function of technique. J PROSTHETDENT 1986;55:197-203. Kirk RE. Experimental design: procedures for the behavorial sciences. Belmont, Calif’z Brooks/Cole Pub1 Co, 1968:91-3. Liuke BA, Nicholls JI, Faucher RR. Distortion analysis of stone casts made from impression materials. J PROSTHETDENT 1985;54:794-802. 6. Craig RG. Evaluation of au automatic mixing system for an addition silicone impression material. J Am Dent Assoc 1985;110:213-5. I. Gordon GE, Johnson GH, Drennor DG. The effect of tray selection on the accuracy of elastomeric impression materials. J PROSTHETDENT 1990;63:12-5. 8. Tjau AHL, Whang SB, Tjan AH, Sarissian R. Clinically oriented evaluation of the accuracy of commonly used impression mat.erisls. J PRO+ THET DENT 1986$%4-S. 9. Johnson GH, Craig RG. Accuracy of four types of rubber impression materials compared with time of pour aud a repeat pour of models. J PROSTHETDENT 1985;53:484-90. 10. de Araujo PA. Effect of material bulk and undercuts on the accuracy of impression materials. J PROSTHETDENT 1985;54:791-4. 11. Valderhaug J, Fl$ystraud F. Dimensional &ability of elastomeric impression materials in custom-made and stock trays. J PROSTHET DENT 1984;52:514-7. Reprint requests to: DR. SHIRLEY H. HUNG UNIV!ARSITY OF MISSOURI-KANSAS CITY SCHOOL OF DENTISTRY KANSAS CITY, MISSOURI 64108
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