Year : 2010 | Volume
: 21 | Issue : 1 | Page : 92--97
An in vitro study to evaluate the effect of storage time and application of subsequent layers on the variation in thickness of three commercially available die spacers
Sunil J Jacob, Chethan Hegde, Krishna D Prasad, Manoj Shetty
Department of Prosthodontics, A. B. Shetty Memorial Institute of Dental Sciences, Deralakatte, Mangalore, India
Sunil J Jacob
Department of Prosthodontics, A. B. Shetty Memorial Institute of Dental Sciences, Deralakatte, Mangalore
Aims : The application of a paint-on die spacer onto the dies prior to the fabrication of cast crowns is an acceptable procedure to improve the fit of the restoration. The primary purpose of this study was to evaluate the variation in thickness of different brands of die spacer based on the effect of storage time and application of additional layers.
Materials and Methods: Dies were duplicated from a master model of ivorine teeth, with a full ceramic preparation. Dies obtained were then painted with one, two, and three coats of each brand of die-spacers separately. These dies were embedded in die stone and sectioned bucco-lingually. The same procedure was done after three and six months. The thickness of the paint on die spacer was measured at five points on the die using an optical microscope, and the data were statistically analyzed.
Results and Conclusion : There was a definite variation in the thickness of the die spacer with all the three brands and at various points on the die. Two coat thicknesses were found to be in the range of tolerance of 20-40 microns. Thickness at occlusal groove was noted to be the maximum with least at occlusoaxial line angles. Thickness also showed a very significant increase when bottles were stored for a period of three to six months and then applied.
|How to cite this article:|
Jacob SJ, Hegde C, Prasad KD, Shetty M. An in vitro study to evaluate the effect of storage time and application of subsequent layers on the variation in thickness of three commercially available die spacers.Indian J Dent Res 2010;21:92-97
|How to cite this URL:|
Jacob SJ, Hegde C, Prasad KD, Shetty M. An in vitro study to evaluate the effect of storage time and application of subsequent layers on the variation in thickness of three commercially available die spacers. Indian J Dent Res [serial online] 2010 [cited 2021 Feb 27 ];21:92-97
Available from: https://www.ijdr.in/text.asp?2010/21/1/92/62822
The success of cast restorations depends on the proper fit and cementation of the restoration onto the prepared tooth. Complete seating of full veneer restorations without excessive luting agent film thickness is often difficult to achieve because of the cement hydraulic pressure. Incomplete seating of crown may result in occlusal interference after cementation, loss of proximal contacts, reduced crown retention, discrepancy of marginal fit, secondary caries, plaque accumulation, rapid dissolution of luting agent, hypersensitivity, etc. 
Two techniques, venting and internal relief, were developed to improve the seating of castings to relieve hydrostatic pressure. Venting was documented as a superior way to accomplish complete seating but seldom used now. Methods of achieving internal relief are aqua regia or etching of the castings, electrochemical milling, mechanical grinding, carving of wax pattern, and die spacing. 
Application of die spacer involves the application of a material to the die, which results in an oversized die for the wax pattern fabrication. Application of paint-on die spacer is a commonly used technique to provide space for the luting agent between prepared tooth and the casting because of its simplicity, convenience, and cost-effectiveness. 
The optimum thickness of the die spacer has never been scientifically established. However, the generally accepted range is approximately 20-40 microns. Number of additional coats to be applied to achieve this optimum thickness is yet to be proven. The purpose of this study is to determine the variation in thickness of different die spacers on application of additional layers and the effect of storage of used bottles on the thickness of the coating.
Materials and Methods
A master model of ivorine teeth, which simulates a mandibular molar with preparation for a full ceramic restoration, was used for this study [Figure 1]. Three brands of die spacers, commonly used and easily available, selected for the study are [Figure 2]:
Heart-man die-spacer (Korea)Giroform die-spacer (Girbach, Germany)Pico-fit die-spacer (Renfert, Germany)Preparation of the die specimens
A metal perforated tray with multiple holes was fabricated to make impression. Tray adhesive was applied to the perforated metallic tray evenly and was allowed to dry for 5 minutes. Impressions were made of the master model with putty and light viscosity polyvinyl siloxane impression material (Aquasil, Aquasil LV, Dentsply).
The impression was stored at room temperature for one hour and then poured in improved die stone Type IV (Kalrock, Kalabhai Karson Pvt. Ltd. India). The measured quantity of water was taken in vacuum mixing jar and required die stone powder was sifted into the water. The powder was incorporated by 15 seconds of hand mixing with spatula, followed by 30 seconds of mechanical mixing under vacuum (Vibrator R2, Degussa). The mix was then painted and poured with fine camel hair brush no. 0 (zero) onto the impression surface, vibrated and allowed to set for one hour.
Application of die-spacer
The models were allowed to dry for at least 48 hours. Die- spacer was applied with the manufacturer's brush, which was cleaned frequently with thinner before application of each coat, the die spacer bottles were kept on a vibrator to ensure that there is no settling of the metallic oxides. Each coat was allowed to dry for at least two minutes before application of the next coat. 36 dies were duplicated to be divided into three groups of 12 dies each. The die spacers were applied to the dies in the following manner:
Pico-fit die-spacer (Renfert, Germany) was applied using manufacturers brush with strokes in one direction. Twelve dies were divided into three subgroups of four dies each. First subgroup had one coat of die spacer while second subgroup had two and third had three coats of the die spacer. Care was taken not to let excess material accumulate.
Giroform die-spacer (Girbach, Germany) was applied using manufacturers brush with strokes in one direction for the three subgroups. First subgroup had one coat of die spacer while second subgroup had two and third had three coats of the spacer.
Heart-man die-spacer (Korea) was applied with manufacturers brush with strokes in one direction. First subgroup had one coat of die spacer while second subgroup had two and third had three coats of the spacer.
Measuring the thickness of the die spacer
These dies were then embedded in die stone. The dies were then sectioned bucco-lingually [Figure 3]. Each section was measured at x 100 magnification with an optical microscope connected to a computer with software to measure the thickness of die spacer [Figure 4]. The thickness of the die spacer was measured at five different positions: a) buccal cusp, b) buccal surface, c) lingual surface, d) occlusal fossa, and e) lingual cusp.
The same procedures were repeated after three and six months of storage of the used die spacers. The results were then statistically analyzed using Post Hoc Tukey HSD, multiple comparisons with least significant difference (LSD) test and using paired samples test to compare the variation in thickness at different time period.
The data collected were subjected to statistical analysis. On application of single coat, Pico-fit die spacer showed mean thickness of 13.628 μm, while Giroform die spacer was 9.056 μm and Heart-man was 14.11 μm. Two coats of application of Pico-fit die spacer showed mean thickness of 25.83 μm, while Giroform die spacer was 20.570 μm and Heart-man die spacer was 35.91 μm thick. Mean thickness for Pico-fit die spacer was 51.91 μm, whereas Giroform die spacer was 40.9440 μm and Heart-man was 55.313 μm thick in three coat applications [Table 1].
Thickness of each die-spacer coating was compared with other brands and subjected to statistical analysis using Post Hoc Tukey HSD. On single coat application, the disparity in the thickness was found to be highly significant (P=0.002 sig and 0.001) between Pico-fit and Giroform and between Heart-man and Giroform, respectively; but when Pico-fit and Heart-man were compared, no significant (P=0.862 sig) difference was noted. Two coat applications also showed the same disparity in the thickness. On application of three coats the disparity in the thickness was found to be very highly significant (P=0.000 sig) when Heart-man and Giroform were compared and a high significance (P=0.001 sig) between Pico-fit and Giroform, but when Pico-fit and Heart-man were compared, no significant (P=0.231) changes were noted [Table 2].
Thickness of die spacer was evaluated at different points on the die. Mean thickness at buccal cusp was 22.7611μm, while buccal surface was 31.3147 μm, lingual surface 31.829μm, occlusal surface 39.1011 μm, and at lingual cusp was 23.475μm. Multiple comparisons with LSD test was used to compare of thickness of die spacer at each point on the die to various other points. A very highly significant (P=0.000sig) increase in thickness was noted at occlusal surface when compared to all other surfaces. The disparity in thickness showed a very high significant difference (P=0.000 sig and 0.000 sig) between the buccal surface to buccal cusp and lingual surface to lingual cusp while between buccal cusp to lingual cusp and buccal surface to lingual surface, no significant (P=0.631 sig and 0.394 sig) difference was noted [Table 3] and [Table 4].
Thickness of die spacer has also been evaluated after storing the bottles for three and six months. Pico-fit die spacer showed a thickness of 21.91350 μm and 50.8615 μm after storing the closed bottles for three and six months. Mean thickness of Pico-fit die spacer on two coat application was 50.2850 μm and 87.7620 μm after three and six months, respectively. On three coat application it was 68.87750 μm and 121.7685 μm after three and six months, respectively. Results show a very high significant increase in thickness after three and six months when compared to initial thickness especially on two and three coat application [Table 5].
Mean thickness of Giroform die spacer on application of single coat application was 11.43450 μm and 13.1815 μm after three and six months, respectively, with statistical significance (P=0.037 sig and 0.010 sig). On two coat application, Giroform die spacer thickness was 20.57 μm and 36.89 μm after three and six months, respectively, with high significance (P=0.001 sig). Mean thickness of Giroform die spacer on three coat application after three months and six months were 38.876μm and 59.28 μm, respectively. The disparity in thickness showed no significance (P=0.0383 sig) when compared from initial to three months and a high significance (P=0.001) from initial to six months on application of three coats [Table 6].
Mean thickness of Heart-man die spacer on single coat application was 25.14 μm after three months and 34.11μm after six months with high significance (P=0.005 sig and 0.001 sig) when compared with initial thickness. On two coat application after three months the thickness was 47.76μm with high significance (P=0.001 sig) and after six months it was 83.77 μm with very high significance (P=0.000 sig). Three coat applications showed a thickness of 60.98 μm and 112.74 μm after three and six months, respectively, with very high significance [Table 7].
Application of die spacer is a commonly used technique to provide cement space between the internal surfaces of a cast restoration and the prepared tooth surface. Die spacing involves the application of a material onto a die in multiple coats within 0.5-1mm short of the margins which results in production of an over sized die for wax pattern fabrication.
The variation in thickness per brush application in literature is quite large varying from 6 to 19.8 microns per layer and probable is due to variation in clinical and experimental technique as well as differing positions on the die, compositions, brushes and substrate.  An optimum thickness of 20-40 μm is generally specified to facilitate complete seating of the casting and to allow for the film thickness of the cement. Considering these observations and suggestions this study was planned to determine the variation in thickness of different die spacers and their effect on thickness after using the stored bottles for a period of three and six months. ,
Several factors may affect the thickness of the paint-on die spacer, application of die-harder to the die prior to spacer application prevents the first layer being absorbed by the gypsum die, settling of the metallic pigments necessitates vigorous shaking before and during application, the brush attached to the inside of the cap, bottles left open during use allow volatile ingredients to evaporate, and tend to show variation in die-spacer thickness at different areas of the preparations. 
From the observations of this study it was seen that on single coat application mean thickness of die-spacers varied from 9 to 14 μm, while on two coat application the thickness varied from 20 to 35 μm and on three coat application it was 40 to 55 μm. The reported ideal thickness ranges from 25 to 40 microns. ,, Results recommend that application of two coats of die spacer is sufficient to provide internal relief.
Results further showed that the thickness of die spacer application varies from 20 to 40 μm at different points on the die and thickness was found to be very high at occlusal surface and least at buccal and lingual cusp region. Variation in thickness on the buccal and lingual surfaces may be due to the overlapping of the coats of the die spacer, absorption of the first layer by the die stone, merging of the layers, settling of the die spacer in the grooves, etc.
Results also showed a marked increase in die spacer thickness after the bottles were stored for three to six months. A highly significant difference in thickness for Pico-fit and heart-man die spacer were observed. Giroform die spacer responded well without much significance even after three and six months without a thinner solution.
Evaporation of die spacer components tends to produce larger die spacer thickness. Granjower et al. found a 140% increase in True fit die-spacer thickness for six months old bottles versus new.  Larger die spacer thickness can cause excessive film thickness of luting agent, which can lead to lower restoration retention and higher luting agent solubility at the margins. Greater die-spacer thickness is probably caused by subsequent higher concentration of metal-oxide particles in solution, which tends to settle down added by the evaporation of the volatile solvent. Thus, it is recommended to avoid use of stored bottles or it can be used with a thinner, but further studies are required to determine the thickness on application after the addition of thinner.
From the results of this study the following conclusion can be drawn:
On single coat application, mean thickness of die-spacer varied from 9 to 14μm, while on two coat application the thickness varied from 20 to 35μm and on three coat applications it was 40 to 55μm.Application of two coats of die spacer was within the required range of 20-40μm, which is the ideal thickness according to earlier researchers.The thickness of die spacer varied from different points on the die. Maximum thickness was noted in the occlusal groove, while least on the buccal and lingual cusp tips, and thus, it is recommended to pre-coat the cusp tips and occluso-axial line angles with an additional layer.Application of die spacer showed marked variation in thickness after using the stored bottles for a period of three to six months. Thickness tends to increase three or four times than the normal thickness, when new open bottle was used and so it is recommended to avoid usage of stored bottles or use thinner solutions to reduce the thickness.
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