Journal of Oral Rehabilitation, 1990, Volume 17, pages 3 0 3 - 3 1 0
Accuracy of impression materials measured with a vertical height gauge I. L E W I N S T E I N and R . G . C R A I G * Department of Restorative Dentistry and Biomaterials, The Hebrew University, Hadassah School of Dental Medicine, Jerusalem, Israel and *Biological and Materials Sciences Department, School of Dentistry, The University of Michigan, Michigan, U.S.A. .
Summary
The objectives of this study were to introduce a different method for evaluating the accuracy of impression materials using a vertical height gauge, and to determine the vertical (axial) and horizontal (transversal) changes of four impression materials. Comparison of means demonstrated the changes for addition and condensation type silicones, and larger changes for the agar/alginate combination and the visible hght cured (polyetherurethanedimethacrylate) impression material. The results were in agreement with an earlier study of the agar/alginate combination, and the values for the condensation and addition silicones were about half those reported in previous studies. These small changes might indicate the use of a mandibular stock tray for the upper jaw when a putty/wash technique is employed. The findings suggest that, when the horizontal changes (AX) of impressions taken with a mandibular stock tray have a negative sign (contraction), then the vertical changes (AL) will have a positive value (expansion), and vice versa. Thus the pattern of distortion can be formulated as AX AL' Introduction
The accuracy of impression materials has been extensively investigated. In previous studies (Reisbick & Matyas, 1975; Eames et al, 1979; Augsburger et al, 1981), the accuracy of impression materials was evaluated by comparing the elevation of a master coping when seated on a stone die with that when seated on a master die. The elevation of the coping is a result of horizontal distortions and is not affected by the vertical changes. By excluding the latter, this method provides only partial information regarding the accuracy of impression materials. Johnson and Craig (1985) determined the accuracy of four types of rubber impression material by measuring the changes of vertical and horizontal lines which were marked on a two-abutment master model. In a three-dimensional study (Linke & Nicholls, 1985), the distortions of stone casts made from impression materials were analysed using a full-arch master model with five cylindrical-shaped abutments. In the latter two studies, changes of certain points or lines were assessed with a travelling microscope, assuming that these points and lines represented the entire distortion pattern.
Correspondence: Dr I. Lewinstein, Department of Restorative Dentistry and Biomaterials, The Hebrew University, Hadassah School of Dental Medicine, P.O. Box 1172, Jerusalem, Israel. 303
304
/. Lewinstein and R.G. Craig
'
' •
, • •
The aims of the present study were as follows: (1) to introduce a different method for evaluating the accuracy of impression materials using a vertical height gauge, and (2) using this method, to determine the vertical and horizontal changes of stone dies produced from four impression materials. Materials and methods
A special stainless steel master model consisting of a master die, a base-plate, a baseblock, and a template-coping, was machined and highly polished (Fig. 1). The master die was 10 mm wide at the base and 8 mm high. The convergence angle of the axial walls was 29=10-36° for both the die and the template-coping. The die, which simulated a full extracoronal preparation, was attached to the base plate with a screw. Impressions of the die were taken using a perforated mandibular stock tray*. Two alignment pins attached to the base-plate (Fig. 1) were used to position an acrylic resin jig, on which the stock tray was seated when the impression was made. With the exception of the agar/alginate combination, the impression materials were mixed at room temperature (23±1°C). The impression materials that were used are hsted in Table 1. For the putty-wash technique, a sheet of polyethylene was placed over the master die prior to the preliminary impression. The putty impression was made 1 min
. . ' • : ? • .
Fig. 1. Components of the master model: (A) base plate with two alignment pins (arrow); (B) master die; (C) base block; (D) template-coping. * No. 21, Coe Laboratories, Chicago, IL, U.S.A!
Accuracy of impression materials
305
Table 1. Impression materials tested Product
Symbol
Supplier
Type
Citricon
CN
Kerr/Sybron, Romulus, MI 48174, U.S.A. Caulk/Dentsply, Milford, DE 19963, U.S.A. Brasseler USA, Savannah, GA 31419, U.S.A. Caulk/Dentsply, Milford, DE 19963, U.S.A. Kerr Mgf. Co., Romulus, MI 48174, U.S.A.
Condensation silicone
Reprosil
JLB/JLB plus
RL
JJ
Genesis
GS
Permlastic
PS
Addition silicone Aginatc/
agar
Viscosity
;-
Putty ; Light
05/13/87 05/13/87
Putty Light
; •••
01/07/88 -• 12/01/87
—i.
:
V.L.C. (polyetherurethanedimethacrylate) Polysulphide
-•-
•
Batch date
;.
12/-/86 01/31/86
Heavy Light
02/05/88 03/23/88 -,;
Heavy Light
12/15/88 10/07/87
following the start of mixing, and was removed 7 min later. The polyethylene spacer was removed and the putty was stored undisturbed for 8 min to simulate the time required for gingival retraction. The wash impression was then mixed and placed within lmin from the start of mixing. The final impression remained on the master model for an additional 10 min and was poured 60 min later. The putty-wash technique was used with both the condensation and addition silicones. The agar/alginate hydrocolloid impression technique was carried out according to the procedure described by Johnson and Craig (1986a). When the visible light curing (VLC) impression material was used, the Hght body was injected to cover the master die, followed by visible-light curing of the buccal, lingual, occlusal and proximal aspects for 20 s each. A transparent mandibular stock tray loaded with heavy body was then placed on the master die. Adhesive was painted on the surfaces of the tray prior to loading. The final impression was cured for 30s from each aspect. After removal, the impression was stored for 60 min before the model was poured. All impressions were poured in improved stone* using a ratio of 20 ml water to 100 g powder. The casts were removed after l h and allowed to dry for 24 h before measurements were made. The stone dies were examined at a magnification of x20. Stone protuberances, when present, were removed with a scalpel. For measuring purposes the master die was removed from the base-plate and inserted into the base-block under a load of 100 g. The template-coping was then seated on the master die and the heights of the points Am, Bm, Cm, and Dm (Fig. 2A & B, and Fig. 3) were recorded. Similarly, the stone die, with the template-coping above, was placed in the base-block and measurements of the points As, Bs and Cs were made. These measurements were taken with a vertical height gauge. It must be pointed out that the base-block was perpendicular to the axis of the dial gauge. The geometric relationship (Fig. 4) between the elevation of the template-coping
* Fujirock, G-C International Inc., Tokyo, Japan.
306
/. Lewinstein and R.G. Craig
Fig. 2. System for measurement with a vertical height gauge: (A) height of the template coping (Am); (B) oeclusal height of the master die (Bm).
(AH) and half of the horizontal changes ( AX
1 can be expressed as follows:
= AH tan 6
(1)
Consequently, the total horizontal changes (of both axial walls) that elevate the template-coping will be: AX = 2AH tan 9
Fig. 3. Schematic view of the different measuring points of the master and stone dies.
(2)
Accuracy of impression materials
307
Template coping
Fig. 4. Elevation of the template coping (AH) due to horizontal changes (AX).
According to Fig. 3 the elevation of the template-coping due to horizontal changes is given by: AH = [(As-Dm)-(Cs-Dm)]-[(Am-Dm)-(Cm-Dm)] = (As-Cs)-(Am-Cm) = Hs-Hm
(3)
where Hs and Hm are the distances between the upper part of the template-coping and the shoulder for the stone and master die, respectively. By substituting Equation (3) into Equation (2), the horizontal change (AX) is obtained: = 2[(As-Cs)-(Am-Cm)] tan 9
(4)
Figure 3 demonstrates that vertical deviation of the stone die from the master die may be computed using the following equation: AL = Ls-Lm = (Bs-Cs)-(Bm-Cm)
(5)
where Ls and Lm are the distances between the shoulder and the occlusal portion for the stone and the master die, respectively. The data were analysed by one-way analysis of variance (ANOVA). Comparison of means was conducted using the Scheffe multiple comparison test. All hypothesis testing was performed at the 95% level of confidence. Results
The accuracy of stone dies produced from different impression materials is illustrated in Fig. 5, and is expressed as the horizontal (AX) and vertical (AL) deviations of the stone dies from the master die. The ANOVA demonstrated significant differences for the
308
/. Lewinstein and R. G. Craig 30r
19(5)
20 10
14(5) 7(8)
-10 o o
-20
E
-30
-32(5) -40
n-6
n-6
n-6
-50 CN
JJ
RL
GS
Type of impression material
Fig. 5. Horizontal (AX) and vertical (AL) changes of four impression materials. CN = condensation silicone, RL = addition silicone, JJ = agar/alginate, GS = VLC polyetherurethanedimethacrylate. (Numbers in parentheses represent standard deviations).
different materials in the dimensional changes between master dies and stone dies. These differences were significant in both the horizontal and vertical aspects. Scheffe comparison of means ranked the deviations as follows: GS, JJ>CN, RL for the horizontal changes and GS>JJ>CN, RL for the vertical changes, where underlining indicates means that were not different at a=0-05.
Discussion By using the template-coping technique it is possible to detect the warpage and irregularities of dies that may affect the fit of crown castings. It is well known that the contraction of impression materials depends on the bulk of the material in the stock tray, and this will vary at different locations around a tooth (Lacy et al, 1981; de Araujo & Jorgensen, 1985). Because of its circumferential characteristic, the coping responds to the largest protuberances on the entire die surface, and does not detect changes at various locations. Thus the vertical height of the coping is originated only from the largest horizontal dimension of the die. Equation (2) demonstrates that the use of a template-coping increases the measuring sensitivity by AH = 0-5 cot AX for the horizontal changes. If the convergence angle of the axial walls is 26 = 10°, then a horizontal change of 1 ^m will cause a displacement of 0-5 cot 5 = 5-7|im to the vertical rod of the height gauge. In addition, the use of a vertical height gauge instead of a travelling microscope provides a simpler method with consistent results. It can be seen from Fig. 5, and was evident in previous studies (Johnson & Craig, 1985; Johnson & Craig, 1986a; Johnson & Craig, 1986b) that, when the horizontal changes (AX) have a negative sign (contraction), then the vertical changes (AL) will have a positive value (expansion), and vice versa. Thus the pattern of distortion can
; -
,,
,
,
be formulated as follows:
Accuracy of impression materials
309
< .
; •
••
•••
^
x
AL
Accuracy of impression materials measured with a vertical height gauge I. L E W I N S T E I N and R . G . C R A I G * Department of Restorative Dentistry and Biomaterials, The Hebrew University, Hadassah School of Dental Medicine, Jerusalem, Israel and *Biological and Materials Sciences Department, School of Dentistry, The University of Michigan, Michigan, U.S.A. .
Summary
The objectives of this study were to introduce a different method for evaluating the accuracy of impression materials using a vertical height gauge, and to determine the vertical (axial) and horizontal (transversal) changes of four impression materials. Comparison of means demonstrated the changes for addition and condensation type silicones, and larger changes for the agar/alginate combination and the visible hght cured (polyetherurethanedimethacrylate) impression material. The results were in agreement with an earlier study of the agar/alginate combination, and the values for the condensation and addition silicones were about half those reported in previous studies. These small changes might indicate the use of a mandibular stock tray for the upper jaw when a putty/wash technique is employed. The findings suggest that, when the horizontal changes (AX) of impressions taken with a mandibular stock tray have a negative sign (contraction), then the vertical changes (AL) will have a positive value (expansion), and vice versa. Thus the pattern of distortion can be formulated as AX AL' Introduction
The accuracy of impression materials has been extensively investigated. In previous studies (Reisbick & Matyas, 1975; Eames et al, 1979; Augsburger et al, 1981), the accuracy of impression materials was evaluated by comparing the elevation of a master coping when seated on a stone die with that when seated on a master die. The elevation of the coping is a result of horizontal distortions and is not affected by the vertical changes. By excluding the latter, this method provides only partial information regarding the accuracy of impression materials. Johnson and Craig (1985) determined the accuracy of four types of rubber impression material by measuring the changes of vertical and horizontal lines which were marked on a two-abutment master model. In a three-dimensional study (Linke & Nicholls, 1985), the distortions of stone casts made from impression materials were analysed using a full-arch master model with five cylindrical-shaped abutments. In the latter two studies, changes of certain points or lines were assessed with a travelling microscope, assuming that these points and lines represented the entire distortion pattern.
Correspondence: Dr I. Lewinstein, Department of Restorative Dentistry and Biomaterials, The Hebrew University, Hadassah School of Dental Medicine, P.O. Box 1172, Jerusalem, Israel. 303
304
/. Lewinstein and R.G. Craig
'
' •
, • •
The aims of the present study were as follows: (1) to introduce a different method for evaluating the accuracy of impression materials using a vertical height gauge, and (2) using this method, to determine the vertical and horizontal changes of stone dies produced from four impression materials. Materials and methods
A special stainless steel master model consisting of a master die, a base-plate, a baseblock, and a template-coping, was machined and highly polished (Fig. 1). The master die was 10 mm wide at the base and 8 mm high. The convergence angle of the axial walls was 29=10-36° for both the die and the template-coping. The die, which simulated a full extracoronal preparation, was attached to the base plate with a screw. Impressions of the die were taken using a perforated mandibular stock tray*. Two alignment pins attached to the base-plate (Fig. 1) were used to position an acrylic resin jig, on which the stock tray was seated when the impression was made. With the exception of the agar/alginate combination, the impression materials were mixed at room temperature (23±1°C). The impression materials that were used are hsted in Table 1. For the putty-wash technique, a sheet of polyethylene was placed over the master die prior to the preliminary impression. The putty impression was made 1 min
. . ' • : ? • .
Fig. 1. Components of the master model: (A) base plate with two alignment pins (arrow); (B) master die; (C) base block; (D) template-coping. * No. 21, Coe Laboratories, Chicago, IL, U.S.A!
Accuracy of impression materials
305
Table 1. Impression materials tested Product
Symbol
Supplier
Type
Citricon
CN
Kerr/Sybron, Romulus, MI 48174, U.S.A. Caulk/Dentsply, Milford, DE 19963, U.S.A. Brasseler USA, Savannah, GA 31419, U.S.A. Caulk/Dentsply, Milford, DE 19963, U.S.A. Kerr Mgf. Co., Romulus, MI 48174, U.S.A.
Condensation silicone
Reprosil
JLB/JLB plus
RL
JJ
Genesis
GS
Permlastic
PS
Addition silicone Aginatc/
agar
Viscosity
;-
Putty ; Light
05/13/87 05/13/87
Putty Light
; •••
01/07/88 -• 12/01/87
—i.
:
V.L.C. (polyetherurethanedimethacrylate) Polysulphide
-•-
•
Batch date
;.
12/-/86 01/31/86
Heavy Light
02/05/88 03/23/88 -,;
Heavy Light
12/15/88 10/07/87
following the start of mixing, and was removed 7 min later. The polyethylene spacer was removed and the putty was stored undisturbed for 8 min to simulate the time required for gingival retraction. The wash impression was then mixed and placed within lmin from the start of mixing. The final impression remained on the master model for an additional 10 min and was poured 60 min later. The putty-wash technique was used with both the condensation and addition silicones. The agar/alginate hydrocolloid impression technique was carried out according to the procedure described by Johnson and Craig (1986a). When the visible light curing (VLC) impression material was used, the Hght body was injected to cover the master die, followed by visible-light curing of the buccal, lingual, occlusal and proximal aspects for 20 s each. A transparent mandibular stock tray loaded with heavy body was then placed on the master die. Adhesive was painted on the surfaces of the tray prior to loading. The final impression was cured for 30s from each aspect. After removal, the impression was stored for 60 min before the model was poured. All impressions were poured in improved stone* using a ratio of 20 ml water to 100 g powder. The casts were removed after l h and allowed to dry for 24 h before measurements were made. The stone dies were examined at a magnification of x20. Stone protuberances, when present, were removed with a scalpel. For measuring purposes the master die was removed from the base-plate and inserted into the base-block under a load of 100 g. The template-coping was then seated on the master die and the heights of the points Am, Bm, Cm, and Dm (Fig. 2A & B, and Fig. 3) were recorded. Similarly, the stone die, with the template-coping above, was placed in the base-block and measurements of the points As, Bs and Cs were made. These measurements were taken with a vertical height gauge. It must be pointed out that the base-block was perpendicular to the axis of the dial gauge. The geometric relationship (Fig. 4) between the elevation of the template-coping
* Fujirock, G-C International Inc., Tokyo, Japan.
306
/. Lewinstein and R.G. Craig
Fig. 2. System for measurement with a vertical height gauge: (A) height of the template coping (Am); (B) oeclusal height of the master die (Bm).
(AH) and half of the horizontal changes ( AX
1 can be expressed as follows:
= AH tan 6
(1)
Consequently, the total horizontal changes (of both axial walls) that elevate the template-coping will be: AX = 2AH tan 9
Fig. 3. Schematic view of the different measuring points of the master and stone dies.
(2)
Accuracy of impression materials
307
Template coping
Fig. 4. Elevation of the template coping (AH) due to horizontal changes (AX).
According to Fig. 3 the elevation of the template-coping due to horizontal changes is given by: AH = [(As-Dm)-(Cs-Dm)]-[(Am-Dm)-(Cm-Dm)] = (As-Cs)-(Am-Cm) = Hs-Hm
(3)
where Hs and Hm are the distances between the upper part of the template-coping and the shoulder for the stone and master die, respectively. By substituting Equation (3) into Equation (2), the horizontal change (AX) is obtained: = 2[(As-Cs)-(Am-Cm)] tan 9
(4)
Figure 3 demonstrates that vertical deviation of the stone die from the master die may be computed using the following equation: AL = Ls-Lm = (Bs-Cs)-(Bm-Cm)
(5)
where Ls and Lm are the distances between the shoulder and the occlusal portion for the stone and the master die, respectively. The data were analysed by one-way analysis of variance (ANOVA). Comparison of means was conducted using the Scheffe multiple comparison test. All hypothesis testing was performed at the 95% level of confidence. Results
The accuracy of stone dies produced from different impression materials is illustrated in Fig. 5, and is expressed as the horizontal (AX) and vertical (AL) deviations of the stone dies from the master die. The ANOVA demonstrated significant differences for the
308
/. Lewinstein and R. G. Craig 30r
19(5)
20 10
14(5) 7(8)
-10 o o
-20
E
-30
-32(5) -40
n-6
n-6
n-6
-50 CN
JJ
RL
GS
Type of impression material
Fig. 5. Horizontal (AX) and vertical (AL) changes of four impression materials. CN = condensation silicone, RL = addition silicone, JJ = agar/alginate, GS = VLC polyetherurethanedimethacrylate. (Numbers in parentheses represent standard deviations).
different materials in the dimensional changes between master dies and stone dies. These differences were significant in both the horizontal and vertical aspects. Scheffe comparison of means ranked the deviations as follows: GS, JJ>CN, RL for the horizontal changes and GS>JJ>CN, RL for the vertical changes, where underlining indicates means that were not different at a=0-05.
Discussion By using the template-coping technique it is possible to detect the warpage and irregularities of dies that may affect the fit of crown castings. It is well known that the contraction of impression materials depends on the bulk of the material in the stock tray, and this will vary at different locations around a tooth (Lacy et al, 1981; de Araujo & Jorgensen, 1985). Because of its circumferential characteristic, the coping responds to the largest protuberances on the entire die surface, and does not detect changes at various locations. Thus the vertical height of the coping is originated only from the largest horizontal dimension of the die. Equation (2) demonstrates that the use of a template-coping increases the measuring sensitivity by AH = 0-5 cot AX for the horizontal changes. If the convergence angle of the axial walls is 26 = 10°, then a horizontal change of 1 ^m will cause a displacement of 0-5 cot 5 = 5-7|im to the vertical rod of the height gauge. In addition, the use of a vertical height gauge instead of a travelling microscope provides a simpler method with consistent results. It can be seen from Fig. 5, and was evident in previous studies (Johnson & Craig, 1985; Johnson & Craig, 1986a; Johnson & Craig, 1986b) that, when the horizontal changes (AX) have a negative sign (contraction), then the vertical changes (AL) will have a positive value (expansion), and vice versa. Thus the pattern of distortion can
; -
,,
,
,
be formulated as follows:
Accuracy of impression materials
309
< .
; •
••
•••
^
x
AL
