ORIGINAL RESEARCH

https://doi.org/10.5005/jp-journals-10063-0135
CODS Journal of Dentistry
Volume 14 | Issue 2 | Year 2022

A Comparative Evaluation of Compressive Resistance and Surface Hardness of Two Elastomeric Interocclusal Recording Materials: An In Vitro Study

Vidya S Bhat1https://orcid.org/0000-0003-4311-9557, Shifas Hameed2, Sanha Razdan3https://orcid.org/0000-0002-3288-0378, Sanath Shetty4https://orcid.org/0000-0002-6681-4168

1-4Department of Prosthodontics, Yenepoya Dental College (Deemed to be University), Mangaluru, Karnataka, India

Corresponding Author: Sanha Razdan, Department of Prosthodontics, Yenepoya Dental College (Deemed to be University), Mangaluru, Karnataka, India, Phone: +91 8178059330, e-mail: srazdan94@gmail.com

Received on: 30 April 2023; Accepted on: 22 September 2023; Published on: 29 September 2023

ABSTRACT

Aim: This study was conducted to compare and evaluate the compressive resistance at varying thicknesses and surface hardness of Exabite II and Ramitec interocclusal recording materials.

Materials and methods: In the present study, the compressive resistance and the surface hardness of Exabite II and Ramitec were studied when subjected to a constant compressive load. Various thicknesses of the interocclusal recording materials were selected. As standard cylindrical stainless steel dies with an internal diameter of 10 mm and three different heights of 2, 3, and 4 mm, a metal plate, and a metal base were prepared, fabricating 80 specimens for the study. A universal testing machine (UTI) was used and subjected to a constant compressive force of 25 N and Shore A hardness tester at 1 and 72 hrs time intervals to test the compressive resistance and surface hardness, respectively.

Results: The 2 mm thickness specimens showed the least compression, and the 4 mm thickness specimen showed maximum compression under a constant load of 25 N for both the materials tested. The independent t-test (p ≤ 0.05) indicated a significant difference in surface hardness between the materials at different time intervals. Both materials possessed higher surface hardness at 72 hours than at 1 hour.

Conclusion: The compressive resistance of both materials was inversely proportional to the thickness of the sample. This implies that the minimum thickness of the recording materials should be used for recording maxillomandibular relations without sacrificing the strength of the interocclusal record.

How to cite this article: Bhat VS, Hameed S, Razdan S, et al. A Comparative Evaluation of Compressive Resistance and Surface Hardness of Two Elastomeric Interocclusal Recording Materials: An In Vitro Study. CODS J Dent 2022;14(2):33-39.

Source of support: Nil

Conflict of interest: None

Keywords: Bite registration, Compressive resistance, Hardness, Interocclusal record material.

INTRODUCTION

It is essential to achieve harmony between the patient’s functional anatomy and the prosthesis in order to produce a suitable prosthesis and maxillomandibular connection. For the diagnosis and given treatment management, the patient’s cast must be precisely articulated. The substance chosen can significantly affect interocclusal registration accuracy, in addition to the operator’s clinical abilities and the procedure employed.1

The most common and straightforward technique of transmitting maxillomandibular connections from the mouth to the articulator is the interocclusal record, which captures the interrelationship between the opposing teeth or arches in terms of position. It is mostly utilized to attain horizontal stability and stop the castings from rotating or translating horizontally.

With or without tooth contact, the arches are brought together, and a gap is formed between the teeth. It commences as soft material that fills in the spaces between teeth before being transferred into casts that may be mounted on an articulator.2

Choosing the right materials and techniques, applying knowledge of the characteristics and varied disadvantages of the interocclusal recording mediums, and the technique used to record the relationship can reduce a significant source of mistakes when transferring registration records to the articulator.3

The materials’ properties should be as close as feasible to those of the optimal bite registration material.4

Interocclusal registration material—dental waxes, metal oxide paste (such as zinc oxide paste), acrylic resins, and elastomeric materials, such as polyethers and addition silicones.5

Silicone Elastomers: Condensation Silicone and Additional Silicone

They were shown to be dimensionally stable over a 48 hour period with little discernible weight change, and they are highly precise. They are not dependent on a carrier. However, their minimal working hours, the need to plan in advance for record space, and the set material’s susceptibility to compression make it more challenging to establish plaster casts.6

Polyether Elastomers

They may be used without a carrier, are precise, stable after polymerization and during storage, fluid, and exhibit little resistance to closure. The fact that precision and resilience may surpass those of plaster casts is a drawback. Both of these factors may prevent the plaster cast from being properly inserted into the recording medium during mounting procedures.7

Resistance to compression after polymerization is one of the interocclusal registration materials’ most favorable characteristics. The material should be sufficiently robust to withstand deformation brought on by the weight of the dental casts, the articulator’s parts, or other equipment needed to support the castings during the mounting processes.8 It is important to accurately record the incisal and occlusal surfaces of the teeth,9 easy to handle, biocompatible with the tissues involved in the procedure, and easy to verify.

The mechanical characteristics of additional silicone (A-silicone) bite recording materials, including dimensional stability and accuracy, have been examined in several articles. Some key traits, including elasticity, have not yet been studied. Any compressive force given to elastomers during the mounting of the castings may result in errors, which is the major potential drawback of incorporating them in clinical use.10

The thickness, storage properties, the forces applied to these records after removal from the mouth or articulation depend on the time between making the records as well as the amount of time for the articulation.11,12 The resistance to compression of an interocclusal recording material. All of these factors will lead to improper cast articulation and inaccurate restorations.13

A Shore A durometer is an established method of testing the surface rigidity or hardness of elastomeric polymeric materials. It registers surface hardness by recording the resistance to indentation of the elastomeric material tested. The Shore hardness units are quantified on a scale from 0 to 100.12

Also, it would be valuable to understand the effect of time on the rigidity of interarch registration materials. When choosing appropriate materials for use in clinical sections, dental materials’ viscoelasticity is critical.13

To compare the compression resistance of more advanced elastomeric interocclusal recording materials is the objective of this study like Exabite II [vinylpolysiloxane (VPS)] and Ramitec (polyether) bite registration material at varying thicknesses when a constant compressive force is applied, as well as the surface hardness at varying intervals.

AIMS

To compare and evaluate the compressive resistance at the varying thicknesses and surface hardnesses of Exabite II and Ramitec interocclusal recording materials.

Objectives of the Study

  • To compare the effect of variations in the thickness of 2, 3, and 4 mm of Exabite II and Ramitec interocclusal recording materials on the compression resistance.

  • To evaluate and compare the surface hardness of the Exabite II and Ramitec recording materials at 1 hour and after 72 hours intervals.

MATERIALS AND METHODS

The instruments used in this study were:

Fig. 1: Shore A hardness tester

Fig. 2: Universal testing machine

Materials used in this study were:

Ramitec (Fig. 3) is a polyether occlusal registration material for manual mixing. It includes two tubes of base material, 120 mL each; two tubes of catalyst, 60 mL each; one mixing pad; one Ramitec syringe.

Fig 3: Ramitec bite registration material

Exabite II (Fig. 4) NDS is an advanced VPS material and was developed specifically for occlusal registration. It was supplied in the form of a cartridge containing base and accelerator paste.

Fig 4: Exabite II NDS bite registration material

Methods followed in this study were as follows.

Preparation of Mold

  • According to the updated ADA standard number 19 for nonaqueous elastic impression materials, a research mold was constructed.

  • A standard cylindrical stainless steel die, a metal plate of 500 mg, and a metal base were fabricated for the study (Fig. 5).

  • Cylindrical stainless steel dies were created as hollow, open-ended cylinders with three different heights of 2, 3, and 4 mm and an interior diameter of 10 mm (Fig. 6).

  • This die was used for the fabrication of specimens for the measurement of both compressive resistance and surface hardness.

Fig. 5: Stainless steel dies consisting of a metal plate of 500 mg, hollow cylindrical die, and metal base (ADA specification no. 19)

Fig 6: Cylindrical stainless steel dies of 4, 3, and 2 mm (from left to right)

Selection and Manipulation of Materials

Two commercially available interocclusal recording materials [polyether (Ramitec, 3M ESPE), VPS (Exabite II NDS, GC products)] were used for this study.

Polyether (Ramitec 3M):

  • The ratio of base paste to catalyst is 8.3–1 gm.

  • The paste was dispensed to a mixing pad and swirled with a mixing spatula to produce a uniform mass of one single color.

  • The Ramitec syringe was filled with the paste mixture, which was then injected into the cylindrical die.

Vinylpolysiloxane (VPS) (Exabite II NDS, GC):

  • The dispensing gun was used to inject the cartridge into the cylindrical die once it had been loaded with the automixing tip.

Preparation of Samples (Fig. 7)

Figs 7A and B: (A) Ramitec samples of 2, 3, and 4 mm (from bottom to top); (B) Exabite II NDS samples of 2, 3, and 4 mm (from bottom to top)

For Measurement of Compressive Resistance

The material was injected into a 10 mm diameter die of different heights (2, 3, and 4 mm) and then covered with a metal plate weighing 500 mg on the top and the material was allowed to be set for one minute before removing from the cylinder. Cylindrical specimens made were divided into two groups of 30 specimens each.

The specimens were produced in the way described below:

Group A: Ramitec polyether bite registration material

  • Subgroup IA: 10 specimens of 2 mm thickness.

  • Subgroup IIA: 10 specimens of 3 mm thickness.

  • Subgroup IIIA: 10 specimens of 4 mm thickness.

Group B: Exabite II NDS VPS bite registration material

  • Subgroup IB: 10 specimens of 2 mm thickness.

  • Subgroup IIB: 10 specimens of 3 mm thickness.

  • Subgroup IIIB: 10 specimens of 4 mm thickness.

Samples were stored in sealed containers and kept for 24 hours before testing.

Measurement of Surface Hardness

The material was injected into a die with a diameter of 10 mm and a height of 4 mm covered with a riser that weighed 500 mg on top and allowed to set before being removed from the cylinder.

Measurement of Compressive Resistance

  • A universal testing machine was used to measure the compressive resistance.

  • Every test sample was loaded into a UTI machine and subjected to a constant 25 N compressive force.

Measurement of Surface Hardness

  • The Shore A durometer’s depth indication was set to zero before testing the specimens.

  • The device was lowered onto the sample until the presser foot was fully in contact after 3 seconds of gently pressing the indenter with the index finger.

  • On the hardness tester, the hardness value was presented and noted.

Statistical Analysis

For Compression Resistance

  • A two-way analysis of variance (ANOVA) test was used to compare the results obtained from the samples between the groups.

  • Post hoctest was used to compare the results obtained from the samples within the groups.

For Surface Hardness

  • An independent t-test was used to compare the surface hardness between the groups at two-time points.

  • To compare the two-time points within the group, a paired t-test was performed.

RESULTS

The results are elaborated as follows:

Tables 1 and 2 show the average data of compressive resistance during the study of Exabite and Ramitec, respectively.

Table 1: Comparison of surface hardness between two interocclusal recording materials at different time intervals using independent t-test
Time Groups Mean Standard deviation Coefficient of variation p-value 1 vs 2
After 1 hour Ramitec 76.80 1.135 0.015 <0.001
Exabite II 86.60 1.265 0.015
After 72 hours Ramitec 81.10 0.876 0.012 <0.001
Exabite II 94.70 1.252 0.013

p≤ 0.05, significant; p ≤ 0.001, highly significant; p ≥ 0.05, not significant, The time factor affects the surface hardness of both interocclusal record materials.

Table 2: Two-way ANOVA comparison of compression distance values in mm of group A specimens (Ramitec) and group B (Exabite) at various thicknesses
Material Thickness Mean Standard deviation p-value
Exabite II NDS 2 mm 0.016 0.001 0.002
3 mm 0.034 0.001
4 mm 0.016 0.008
Total 0.039 0.021
Ramitec 2 mm 0.017 0.001 0.002
3 mm 0.036 0.011
4 mm 0.027 0.007
Total 0.041 0.023

p ≤ 0.05, significant; p ≤ 0.001, highly significant; p ≥ 0.05, not significant

Fig. 8: Comparison of surface hardness of Ramitec and Exabite at different time intervals

Table 3: Post hoc test comparison of compression of different thicknesses of interocclusal recording materials
(I) Thickness (J) Thickness Mean difference (I−J) Standard error p-value
2 mm 3 mm −0.018 0.002 0.000
4 mm −0.051 0.002 0.000
3 mm 2 mm 0.018 0.002 0.000
4 mm −0.033 0.002 0.000
4 mm 2 mm 0.051 0.002 0.000
3 mm 0.033 0.002 0.000

p ≤ 0.05, significant; p ≤ 0.001, highly significant; p ≥ 0.05, not significant, Exabite II interocclusal record material has a mean surface hardness that is higher than Ramitec, Compression rises together with the thickness

DISCUSSION

The positional relationship between the opposing teeth or arches is recorded in the interocclusal record. The intraoral placement of restorations is made possible by the excellent interocclusal record without the need for significant changes.

Various interocclusal recording materials, including waxes, acrylic resin, zinc oxide eugenol paste, modeling compound, and dental plaster with modifiers, all deform to varying degrees when compressed under strain. In order to be employed as the interocclusal recording medium, plasticizers and catalysts have recently been added to silicone and polyether impression materials. Because of their dimensional precision, stability, and compression resistance, these materials have gained popularity.

For an interocclusal recording medium, the resistance to compression after loading is a highly desirable quality.14 If a material is compressible, improper operator handling or the weight of the cast that must be mounted might cause it to become deformed.14,15

According to Chai et al., the elastomeric materials’ continuous polymerization process may improve surface hardness even after 30 minutes16 and may also have an impact on compression resistance.17 Setting time hardness progression is crucial since it may provide distortion-free interocclusal recordings. Due to low setting shrinkage and great resistance to deformation, hard, fully filled interocclusal recording materials are anticipated to display fewer vertical discrepancies, providing a more precise match with the stone models. When more stiffness is needed, such as in interocclusal registrations, these materials are employed in certain clinical conditions. Therefore, the interocclusal recording materials’ compressive resistance and surface hardness were examined in this study.

According to Lassila et al., the force required to overcome the interocclusal material’s initial resistance to closure ranges from 0.5N to 13.8N. As a result, the specimens were created with a force of 500 mg (5.56N).18

Depending on whether occlusal clearance was given to one or both arches, the materials’ thickness in clinical practice ranges between 2 and 4 mm.19 Hence specimens of the thickness of 2, 3, and 4 mm of the interocclusal recording materials were used to measure the compressive resistance. Rubber bands are widely used during mounting procedures to keep the contact of opposing casts. A number of 19 rubber bands, which are frequently used to stabilize the casts during mounting operations, create a force of around 25 N on the castings and the interocclusal registration material; as such, this figure was employed for the investigation. Breeding and Dixon 20 recognized this, and this value was used.

The 30 specimens of each material were divided into three groups of 10, with thicknesses of 2, 3, and 4 mm. Each specimen was evaluated using the universal testing machine under a continuous compression load of 25 N in accordance with the manufacturer’s recommendations.

The findings of this study revealed that there was a significant difference between the compressive resistance of the two interocclusal materials, with a p-value of 0.05 indicating this. According to Table 2, Exabite II NDS bite registration material had a lower compression value (0.039 mm) than Ramitec polyether bite registration material (0.041 mm).

A considerable variation in the size of all the samples at different thicknesses of 2, 3, and 4 mm specimens derived from the two interocclusal bite registration materials under constant compressive pressure was another crucial finding. According to the study’s findings, under a continuous load of 25 N for both materials, specimens with a 2 mm thickness exhibited the least compression, while those with a 4 mm thickness showed the most compression, as shown in Fig. 9. This finding means that when thickness increases, compression likewise does as well. This was in line with research by Breeding and Dixon that demonstrated the compressibility of thicker elastomeric interocclusal recording materials.

Fig. 9: Bar graph showing the comparison of compressive resistance of Ramitec and Exabite II NDS at various thicknesses

Bite registration materials made of VPS and polyether are distinguished by their rapid setup and working times, high stiffness, minimal compression strain, and low flow.20,21 In this investigation, polyether bite registration material showed more compression than VPS (Exabite II) bite registration material, whereas VPS bite registration material demonstrated greater compression resistance. The lower dimensional change of VPS bite registration material as compared to polyether bites registration material 22 may be the source of its higher compression resistance.22

Studies conducted by Craig and Sun, Chai et al., and Campos and Nathanson have further demonstrated the superior accuracy and dimensional stability of VPS bite registration material.23

In this study, the surface hardness of the interocclusal record materials was assessed over time.

The time intervals mentioned above were computed utilizing either the delay in the cast’s articulation in the laboratory or the time required to transport the interocclusal record material to a laboratory that is far.24

Surface hardness was more than 75 units for all samples. At 72 hours, two-bite registration materials exhibited noticeably higher surface hardness. At both time intervals, Exabite II had a higher hardness value than Ramitec.

The continuous polymerization process could be responsible for the continual increase in surface hardness. The increased surface hardness of one of these two materials after a few hours may lead one to hypothesize that comparing dental casts with registrations created with that material will be more accurate since the dimensional stability of those two materials is not affected after 72 hours. A minimum thickness of these materials should be used to prevent deformation brought on by compression since it has been proven that thicker elastomeric occlusal registration materials are often more compressible.

Correct interocclusal records would result in castings with accurate occlusal contacts on the articulator, which would allow the clinician to make only minor adjustments to the restorations that were delivered from the laboratory and prevent sitting in the chair for unnecessary lengths of time or repeating some clinical and technical steps. The time required for articulation and the clinical situation must be taken into consideration when choosing a material. Working casts should be mounted on elastomeric interocclusal recording materials with the least amount of pressure applied to the articulated casts while mounting, the thinnest record possible, and the least amount of distortion possible during compression of the recording material.

CONCLUSION

Based on the observation of this study, the following conclusion was drawn:

ORCID

Vidya S Bhat https://orcid.org/0000-0003-4311-9557

Sanha Razdan https://orcid.org/0000-0002-3288-0378

Sanath Shetty https://orcid.org/0000-0002-6681-4168

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