|Year : 2015 | Volume
| Issue : 3 | Page : 119-124
An in vitro study to evaluate the accuracy of dies obtained from dual-arch impression trays using addition silicone impression material and tray combinations
S George1, Vidya K Shenoy2, Shobha J Rodrigues1, Thilak Shetty1, Sharon Saldanha1
1 Department of Prosthodontics, Manipal College of Dental Sciences, Manipal University, Mangalore, Karnataka, India
2 Department of Prosthodontics, A. J. Memorial Institute of Dental Sciences, Mangalore, Karnataka, India
|Date of Web Publication||28-Apr-2016|
Shobha J Rodrigues
Department of Prosthodontics, Manipal College of Dental Sciences, Manipal University, Mangalore, Karnataka
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Objectives: This study aims to evaluate and compare the accuracy of dies obtained from dual-arch impression trays using vinyl polysiloxane impression material and tray combinations. Materials and Methods: Typodont teeth were embedded in the maxillary and mandibular Dentoform model bases and mounted in an articulator using maximum intercuspation. Impressions were made with vinyl polysiloxane materials (Reprosil Putty, Aquasil Ultra Heavy, Aquasil Ultra LV [Dentsply International]) using one-step simultaneous dual viscosity technique in dual-arch plastic trays and metal trays as well as in full arch acrylic resin custom trays. These were compared for the dimensional accuracy with the dies prepared from typodont tooth as a control. Results obtained were statistically analyzed. Results: The results indicated that dies obtained from all the impression combinations showed increased dimension (acrylic resin custom trays 9.4 ± 0.048 mm, dual-arch plastic trays 9.5 ± 0.035 mm, and dual-arch metal trays 9.41 ± 0.017 mm) as compared to the dimension of control (9.39 ± 0.007 mm). Conclusion: All the tray impression material combinations showed variable accuracies. Full arch acrylic resin trays exhibited the greatest accuracy whereas dual-arch plastic trays showed the least accuracy.
CLINICAL RELEVANCE TO INTERDISCIPLINARY DENTISTRY
In fixed prosthodontics, a lower incidence of errors can be obtained using a combination of PVS impression material with metal or custom tray, thereby improving the accuracy of the subsequent restoration. Interdisciplinary dentistry necessitates good prosthodontics and as such prosthodontics is an integral part of good interdisciplinary dentistry.
Keywords: Accuracy, addition silicone, custom tray, dual-arch tray
|How to cite this article:|
George S, Shenoy VK, Rodrigues SJ, Shetty T, Saldanha S. An in vitro study to evaluate the accuracy of dies obtained from dual-arch impression trays using addition silicone impression material and tray combinations. J Interdiscip Dentistry 2015;5:119-24
|How to cite this URL:|
George S, Shenoy VK, Rodrigues SJ, Shetty T, Saldanha S. An in vitro study to evaluate the accuracy of dies obtained from dual-arch impression trays using addition silicone impression material and tray combinations. J Interdiscip Dentistry [serial online] 2015 [cited 2019 Nov 18];5:119-24. Available from: http://www.jidonline.com/text.asp?2015/5/3/119/181373
| Introduction|| |
The accuracy and dimensional stability of elastomeric materials have been the subject of numerous investigations.,, The introduction of addition silicone material in 1970 has given the dental profession a material with superior dimensional stability due to the absence of volatile reaction products such as alcohol and water.,,,,, These materials are currently available in several viscosities leading to at least three choices of general techniques. Among different techniques dual-arch technique is claimed to be accurate and a viable alternative to full-arch impressions., This technique allows simultaneous recording of tooth preparation, opposing anatomical teeth, and the occlusal registration of the relative opposing dentition within a single impression tray. Although widely accepted, the accuracy of the technique has not been verified except by Davis and Schwartz.,,
With this background, the present study aimed to compare the accuracy of impressions by using vinyl polysiloxane in custom, metal, and plastic dual-arch impression trays.
| Materials and Methods|| |
This in vitro study was conducted for comparative evaluation of dimensional accuracy of casts obtained from vinyl polysiloxane impressions (Reprosil; Heavy body and Light body, Dentsply Caulk, USA) using full arch acrylic tray, dual-arch metal tray (Quad-Tray Xtreme, Clinicians Choice, USA) and dual-arch plastic trays (Dual tray; Dispodent, Chennai, India) [Figure 1].
|Figure 1: Acrylic resin custom tray, dual-arch plastic tray, and dual-arch metal tray|
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The study was undertaken in the following steps:
- Fabrication of the samples
- Preparation of the control group
- Making the impression
- Fabrication of the dies
- Assessment of the accuracy of the impression.
Fabrication of the samples
The typodont teeth were embedded in the maxillary, and mandibular Dentoform model bases (No. 500B-1; Kilgore Intl, Coldwater, MI, USA), and the bases were mounted in a semi-adjustable articulator with the teeth in maximum intercuspation (Hanau H2; Teledyne WaterPik, Fort Collins, CO, USA) [Figure 2].
The samples were divided into following four groups of eight samples each:
Group A - Control – consisted of the prepared molar typodont tooth embedded in the maxillary Dentoform model base [Figure 3]
Group B - (PVS/PL) – consisted of dies obtained from the impressions made using vinyl polysiloxane and plastic dual-arch trays [Figure 4]
Group C - (PVS/M) – consisted of dies obtained from the impressions made using vinyl polysiloxane and metal dual-arch trays [Figure 5]
Group D - (PVS/AC) – consisted of dies obtained from the impressions made using vinyl polysiloxane and acrylic resin custom tray [Figure 6].
|Figure 6: Stone dies obtained from acrylic resin custom tray impressions|
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Preparation of the control group
The typodont maxillary left first molar was prepared to receive a complete cast crown, with approximately 1.5 mm occlusal reduction on the functional cusps and 1 mm on the nonfunctional cusps. The functional cusp bevel was placed on the lingual inclines of maxillary lingual cusps as an integral part of the occlusal reduction using the round-end tapered diamond bur (No. 856-016; Brasseler, USA). The buccal and lingual walls produced the desired axial reduction, forming a chamfer finish line approximately 0.75 mm in width placed supragingivally using torpedo diamond point (No. 877-010; Brasseler, USA).
After tooth preparation with straight fissure bur (No. 256; Brasseler, USA), the tooth was removed from the Dentoform, notches were placed in the margin buccally and lingually using the tapered fissure bur (No. 170L-010; Brasseler, USA), and the sharp corners of the notches were used as reference points. The digital caliper (Digimatic 500-321; MTI Corp., Aurora) was used to measure the buccolingual width of the tooth at the margin by using the sharp corners of the notches as reference points. The buccolingual dimensions of the preparation were recorded for comparison with the subsequent dies, and the preparations were reaffixed in the Dentoform model base.
Impressions were made with vinyl polysiloxane impression material using single-step simultaneous dual viscosity technique. Mixing time, setting time, and all other parameters were kept as per manufacturer's recommendations. The impression was held in place for the adequate amount of time to ensure that setting reaction was complete before removal. Since room temperature is lower than the mouth temperature, the tray was held in place for a longer duration than the manufacturers' recommendation to ensure complete polymerization. The impression was checked for clinical acceptability and grouped as following:
Group B, C and D were compared to control A model on which measurements were directly made on the model and in B, C, D measurements were made after impressions and compared to control A.
Group B impression
Sectional plastic dual-arch trays were used to make the impressions using the one-step technique. The trays were assessed to ensure that the typodont could be closed into the maximum intercuspation position without any interference from the tray. Impression material was syringed around the prepared tooth and loaded on the tray. The articulator was closed, and the impression was allowed to set for twice the manufacturer's recommended setting time to compensate for the temperature of the extraoral environment. A total of eight impressions were made that were rinsed under tap water for 10 s and dried.
Group C impression
Sectional metal dual-arch trays were used to make impressions using a one-step technique. The procedure was similar to that performed in Group A impressions except that the tray adhesive (Caulk Tray Adhesive, Dentsply/Caulk, USA) was applied on the walls of metal dual-arch trays. A total of eight impressions were made in this group [Figure 7].
Group D impression
Impressions were made using the acrylic resin custom trays that were prepared by placing uniform thickness of 2 mm of the wax spacer. The fit of the trays was confirmed. The tray adhesive was painted on the walls and borders of the trays and was allowed to dry for 5 min. Light body material was mixed and loaded in a syringe that was injected around and over the prepared tooth. Heavy-body material was loaded in the custom tray, and the tray was positioned over the maxillary arch. After 10 min from the start of the mix, the impression was removed by applying equal pressure bilaterally, and the impression was evaluated, rinsed under tap water and air dried. A total of eight impressions were made in this group.
Preparation of the die
All the impressions above were poured with type IV dental stone (Kalrock, Kalabhai Karson, Mumbai, India). To standardize the effect of the setting expansion of the improved stone, the water powder ratio was critically matched with manufacturer's recommendation and a product of similar batch number was used to pour all the impressions. The opposing arch was not poured in the dual-arch impressions. The stone dies were retrieved from the impressions after a setting time of 2 h examined for clinical acceptability and labeled.
Assessment of accuracy
The casts were allowed to air dry for at least 48 h before measurements were obtained. The dimensions of the original preparation were compared with the dimensions of the dies measured with digital caliper (Digimatic 500-321; MTI Corp., Aurora, USA). Each measurement of the stone die was repeated 3 times to ensure its reproducibility and a mean was recorded for a particular dimension. To eliminate individual variability, all measurements were made by the same individual. The data were statistically analyzed using software Statistical Package for Social Sciences SPSS (USA) version 11.5. One-way ANOVA and post hoc Tukey test was used. P < 0.05 was considered to be statistically significant.
| Results|| |
The mean buccolingual dimension was 9.4 ± 0.048 mm for acrylic resin custom trays, 9.5 ± 0.035 mm for dual-arch plastic trays, and 9.41 ± 0.017 mm for dual-arch metal trays as compared to the dimension of control (9.39 ± 0.007 mm) [Table 1]. Statistically significant difference (P < 0.001) was seen between the dimensions of control and the dies produced using dual-arch plastic trays. Similarly, statistically significant difference was seen between the dimensions of acrylic custom trays and dual-arch plastic trays [Table 2].
|Table 1: Descriptive statistics of buccolingual dimensions of control and dies|
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|Table 2: Post hoc test showing statistical difference between dual-arch plastic tray, control, custom, and metal dual-arch tray|
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| Discussion|| |
Custom trays improve the accuracy of an elastomeric impression by limiting the volume of the material, thus reducing stresses during removal and polymerization contraction increasing accuracy. Autopolymerizing acrylic resin, thermoplastic resin as well as photopolymerized resins are used to construct custom trays. The custom trays should be rigid, dimensionally stable, and at the same time easy to fabricate. The advantages of custom trays include the use of less quantity of material, no need of sterilization and relatively small amount of distortion. However, the time consumed for fabrication and the need to store them for at least 24 h to minimize the distortion of autopolymerized resin are the disadvantages.
Dual-arch trays, also known as quad trays or triple trays are made of metal or plastic with or without side walls. Metal trays are rigid and will not deform during the impression procedure. Plastic dual-arch trays are flexible to varying degrees, depending on the shape and dimensions of the side wall.
The dual- or double-arch impression technique as described by Wilson and Werrin  is convenient in that it makes the maxillary and mandibular impressions, as well as the interocclusal record in one procedure. The dual-arch impression technique allows the impression to be made in closed mouth position. This position provides two benefits: (1) The mandibular flexure that occurs after 28% of the maximum opening is eliminated, and (2) teeth are placed near maximum intercuspation.
However, the decision to use the dual-arch impression technique must be based on sound physical principles. These impression techniques are contraindicated in long-span fixed partial dentures, as well as in Braly's Class III, as in these patients the breakdown of the dentition is so extensive that reliable guides for tooth form or occlusal position do not remain. These patients require full mouth reconstruction procedures.
Although distortion of an impression is a three-dimensional problem that is inherent in all of the steps involved in fabricating an indirect dental restoration, the buccolingual dimension of the gingival margin was chosen because this is one of the least supported areas of an impression in most of the dual-arch impression trays. Any flexure or rebound of the impression in the buccolingual direction would result in a corresponding error in the mesiodistal direction; however, this dimension was not measured in this study.
The result of this study showed increased buccolingual dimension in all the series of dies prepared (9.4 mm, standard deviation [SD] - 0.048 in case of acrylic custom tray, 9.5 mm, SD - 0.035 in case of dual-arch plastic tray and 9.407 mm, SD - 0.017 in case of dual-arch metal tray as compared to the 9.39 mm, SD - 0.007 of control). The altered dimensions might be attributed to the polymerization shrinkage in the vinyl polysiloxane impression material. This material shrinks toward the center of mass during polymerization. The use of tray adhesive would redirect this shrinkage toward the wall of the tray, resulting in an increase in the buccolingual dimension. Hence, these findings of the study are in agreement with the results obtained by Breeding and Dixon and Ceyhan et al. in that the buccolingual dimensions increased and mesiodistal dimensions decreased.
The difference in the mean buccolingual dimensions of control, as well as the dies obtained from various impressions, revealed that the increased dimension of dies from dual-arch plastic trays were statistically significant as compared to all other three types. The findings were in agreement with the work done by Breeding and Dixon, Ceyhan et al., and Cox et al. This variation in dimension can be attributed to the relative flexibility of the plastic dual-arch trays in comparison to the metal dual-arch trays and the full arch acrylic custom tray. The more flexible plastic trays provided less rigid support at the borders, and these were flexed outward by the impression material during seating on the prepared tooth. Another possible explanation for the increased dimension seen with the plastic dual-arch trays may be a distortion caused by the weight of the stone when the impression was poured. Only the side of the tray with the prepared tooth was poured in this study. The metal tray and acrylic custom tray would resist any flexure due to the weight of the stone, but the flexible plastic tray may distort.
However, the study conducted by Larson et al. revealed that the flexed dual-arch impression trays produced significantly undersized dies compared to the custom trays and to passively seated dual-arch trays, which is not in agreement with the findings of the present study. However, the above study measured the mesiodistal dimension and hence it cannot be merely compared with this study where buccolingual dimension was measured to draw any conclusion.
Measurements made on the stone casts are potentially affected not only by the impression materials and tray type but also by the expansion of dental stone used. In this study, improved die stone with a reported low-expansion of 0.10% was used.
The significant difference (P < 0.001) between the measurements recorded at different points on the preparation margins may possibly relate to the pattern of distortion in the impression, and particularly when the distorted tray relaxes upon removal of the impression.
The results of the study showed that the dies obtained from plastic dual-arch tray impressions had least accurate buccolingual dimension. This supported the theory that “it is advantageous to use a more rigid tray to make an accurate impression.”
Limitations of the study
- The change in dimension was measured only in one direction, i.e., buccolingual and not the mesiodistal
- The possibility of change in dimension of the control and dies produced by these various impression/tray combinations might be different in other direction than buccolingual. Hence, the change in dimensions in mesiodistal direction also should be considered while studying for the accuracy of impression techniques
- Impressions were poured only on the side of interest that is on the side of prepared tooth
- Due to a load of die stone poured, the impression may flex in various amounts especially when the contralateral side of the arch is not poured. This flexing of the impressions may be more in case of flexible tray materials such as plastic dual-arch trays.
| Conclusion|| |
The study indicates that impressions made with rigid tray had acceptable die dimensions. Full arch acrylic custom tray produced the most accurate dies as compared with those produced by using metal or plastic dual-arch trays. Acrylic custom tray and metal dual-arch tray produced significantly more accurate dies as compared to those produced by plastic dual-arch trays. Further, the results of the study also indicated that flexure of the plastic dual-arch tray during impression making appeared to adversely affect the accuracy of dies.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]
[Table 1], [Table 2]