International Journal of Preventive and Clinical Dental Research

: 2018  |  Volume : 5  |  Issue : 4  |  Page : 53--56

A comparative evaluation of plastic and metal impression trays on the accuracy of cast

Jiji M Edakkalathur1, Kurien Varghese2, Sony Sebastian1, Bilaal Sidhique Abubacker1,  
1 PG Student, Department of Prosthodontics and Crown and Bridge, Azeezia College of Dental Sciences and Research, Meeyannoor, Kerala, India
2 Professor and HOD, Department of Prosthodontics and Crown and Bridge, Azeezia College of Dental Sciences and Research, Meeyannoor, Kerala, India

Correspondence Address:
Dr. Jiji M Edakkalathur
Seilow, Udiyankulangara, P. P. Amaravila P.O., Thiruvananthapuram - 695 122, Kerala


Background: Defects in making an impression could affect the accuracy and fit of the final prostheses. Aims and Objectives: The present study evaluates whether the rigidity of impression trays made out of two different materials affect the accuracy of cast poured out of same impression material. Materials and Methods: For the present study, metallic perforated rim-lock tray and disposable plastic tray were selected for making the impression. Alginate (Tropicalgin™) was used as the impression material of choice. A master model constructed with stainless steel abutments at 44 and 47 and 34 and 37 region was used for making impressions using metal and plastic impression trays respectively. The cast was poured with type III dental stone and the distance between the reference points were measured using CMM (Coordinate Measuring Machine). The results obtained were compared and statistical analysis done using one sample t – test. Results: The study came out with results showing statistically significant differences (P < 0.05) between casts made out of these two different impression tray materials. Conclusions: The study concluded that rigidity of perforated metal stock trays ensured better results than perforated plastic stock trays for impressions using alginate impression material.

How to cite this article:
Edakkalathur JM, Varghese K, Sebastian S, Abubacker BS. A comparative evaluation of plastic and metal impression trays on the accuracy of cast.Int J Prev Clin Dent Res 2018;5:53-56

How to cite this URL:
Edakkalathur JM, Varghese K, Sebastian S, Abubacker BS. A comparative evaluation of plastic and metal impression trays on the accuracy of cast. Int J Prev Clin Dent Res [serial online] 2018 [cited 2020 Apr 10 ];5:53-56
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Impression as per Glossary of Prosthodontic Terms 8 is defined as a negative likeness or a copy in reverse of the surface of an object, or an imprint of the teeth and adjacent structures for use in dentistry. Many impression techniques have been advocated for obtaining clinically acceptable impressions in the fabrication of fixed partial dentures (FPDs).[1] The quality of the impression made depends on the proper selection of impression material, impression trays utilized, and appropriate manipulative techniques employed. The range of choice of impression materials varies according to the preference of the clinician. Due to cost effectiveness and easy manipulation, alginate is still preffered as the impression material.[2] The deformed trays may cause distortion of impressions, which seems to be acceptable on visual examination and is found deficient only during insertion of the final prosthesis.[3] Though custom-made impression trays minimize distortion and material wastage, clinicians prefer using stock trays owing to time constraints and to reduce patient chairside time.[4] Tray rigidity is an important parameter in FPD impressions because even slight flexing of tray causes distortion of the impression.[5]

Materials used

Metal-perforated Rim-Lock trayPerforated plastic stock trayAlgimix alginate mixerAlginate impression material (Tropicalgin™)Dental stone – type IIIMaster model made of resins.


A mandibular arch master model was made out of self-cure orthodontic repair resin (Dentsply™) with resin teeth from canine to canine and four machined stainless steel dies simulating prepared abutment teeth embedded in 37 and 34 and 44 and 47 regions. The stainless steel dies were designed to simulate circular full-veneer crown preparations with shoulder margins. The molar die preparations having a 6° total occlusal convergence (TOC) were 7.0 mm high and had a cervical outer diameter of 9.0 mm and a shoulder width of 1.0 mm. The premolar dies had the same TOC, height, and shoulder width, but an outer diameter of 7 mm. The root portion of the stainless steel dies were 15 mm in length and had a design that well locked them inside the resin to prevent rotation and vertical displacement. Approximately 1 mm of the dies' root portion was exposed on all four dies. Diamond points (TF 21) were used to make marks on the occlusal surfaces and the shoulders of the dies. Reference points were marked on the model, at three different locations, on either side of the model, giving a total of 6 points. The two adjacent intra-abutment points were joined to obtain three locations. The model was then fixed in a wooden frame. Alginate impression material – Tropicalgin [Figure 1] – was mixed using Algimix™ [Figure 2] according to manufacturer's instructions to control the impression material thickness. Ten impressions made with both metal and plastic stock trays, respectively, were poured immediately with type III dental stone. The distance between the reference points was measured with coordinate measuring machine [Figure 3], and statistical analysis was done using one sample t-test.[6]{Figure 1}{Figure 2}{Figure 3}


The present study shows that in points A and C, metal impression tray was found to be similar to the model compared to plastic impression tray [Table 1]. In points B and D, no significant differences were found between both the metal and plastic impression trays, and values were similar to the model. In points E and F, the metal and plastic impression trays are found to be different from the model [Figure 4]. Altogether, metal impression tray was found to be similar to the model compared to plastic impression tray. P <0.05 is considered as statistically significant. Further studies are required to validate the superiority of metal trays over plastic trays.{Table 1}{Figure 4}


Many types of impression materials are available in dentistry, and the choice for an FPD impression is primarily dependent on its degree of accuracy, easy availability, and affordability.[7] Impression materials should reproduce a true measured value, and they should be dimensionally stable across time. Alginate impression materials are not as accurate as the newly introduced hydrophilic elastomeric impression materials in producing quality dental impressions due to syneresis and evaporation.[8],[9] Still, it forms the staple part of clinical practice owing to its simplicity, easy availability, and cost-effectiveness.[2]

Rigidity of an impression tray is another major factor affecting quality impressions, especially while using hydrocolloid impression material. Though there are numerous studies available regarding tray rigidity as a parameter in obtaining accurate dental impressions, they lack consensus in their results.

A study conducted by Valderhaug and Floystrand found no differences between impressions made with perforated metal stock trays and plastic trays where modulus of elasticity of metallic tray material outweighed plastic tray materials by about 50 times. Moseley et al. proved that using thick custom trays of 4 mm, the rigidity of even plastic trays was enough to withstand the forces involved in seating and removal of impressions.[10] Tjan et al. (1981) and Gordon et al. in two independent studies found that the plastic stock tray which was much less rigid consistently produced casts with greater dimensional change than the metal tray systems and concluded that the use of plastic stock trays should be limited to the reproduction of casts where great accuracy is not needed.[11] Millstein et al. and Cho and Chee did similar studies and concluded that metal stock trays produced satisfactory good results over plastic trays in producing accurate dental impressions.[12],[13] Mitchell and Damele investigated the distortion caused by various tray types with hydrocolloids and elastomers and found that the tray form had a significant impact on the amount of impression distortion by all materials tested, especially with elastomers and with irreversible hydrocolloids when nonrigid trays are employed.[14] Wasell et al. and Saunders et al. in two separate studies showed that reinforcement of stock trays improved the quality of the impression but did not eliminate completely the distortion from tray deformation.[15]

This study confirms results from previous articles that metal stock trays are preferred than plastic trays for making accurate impression. Results of the study showed more accurate linear values with metal stock tray. The differences in accuracy of details recorded were not taken into consideration. However, comparison between groups did not have any statistical significance.

Research into impression accuracy has relied heavily on in vitro tests rather than clinical evaluations. The key reason is simply that clinical studies are difficult to standardize and reproduce. For example, variables such as tray flexing/recoiling ability and differences in impression techniques are difficult to eliminate clinically. Furthermore, it is easier to make measurements in the laboratory than in the mouth. However, the drawback with most laboratory tests is that such studies do not simulate the true oral conditions very well.


The present study concluded that metal impression trays are more accurate for making impression, but it is statistically comparable with plastic impression trays.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.


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