A Comparative Study to Evaluate the Linear Dimensional Change and Compression Resistance of Four Elastomeric Interocclusal Recording Materials: An in vitro Study

ABSTRACT

The transfer of interocclusal data from the patient’s mouth to articulators utilizing various types of recording media is necessary for the production of dental prostheses. Occlusal errors in the final prosthesis result from any discrepancies in these interocclusal records

Materials and Methods:

The purpose of this study was to assess the linear dimensional changes in the four elastomeric interocclusal recording materials as well as the material’s resistance to compression during the cast mounting on the articulator.

Result:

All four elastomeric materials showed decreasing stability over time and 2 mm thickness showed the highest compression resistance with minimal articulation error

Conclusion:

Dimensional stability depends on material and time factors, and compressive resistance decreases with increasing thickness.

INTRODUCTION

Prosthodontics, a dental specialty, necessitates a collaborative effort between dentists and dental technicians to create prostheses that meet standards of fit, comfort, aesthetics, and function.[1] The precision in crafting indirect restorations is crucial for seamless integration within the oral cavity’s stomatognathic system. For this purpose, tooth and jaw relationships must be transferred to an articulator in indirect restorative procedures. The use of programmable adjustable and/or semi-adjustable articulators in the fabrication of complete dentures, fixed, and removable prostheses can simulate mandibular movements, potentially reducing the need for intraoral occlusal adjustments before prosthesis placement.[2,3]

However, the clinical significance of adjustable articulators in prosthesis fabrication hinges on the assumption that the interocclusal relationship of dental casts mounted on the articulator accurately represents the opposing dental arches.[4] An error in mounting could result in discrepancies in both intercuspal and excursive occlusion, while programming errors in articulators would primarily affect excursive occlusion. Maxillary and mandibular casts are affixed to the articulator to analyze functional and parafunctional contact between teeth.[5] It is often said that the “patient’s mouth is the best articulator.” The articulator aims to mimic the patient’s function. The maxillary cast is positioned on the articulator with the help of a face bow transfer from the patient, aligning it with the patient’s horizontal condylar axis. The mandibular cast’s correct alignment with the maxillary arch is achieved using an inter-occlusal record.[6] This enables the transfer of the maxillomandibular relationship from the patient to the articulator, ensuring that laboratory procedures on articulated casts correspond with the patient’s oral condition. The accuracy and quality of the occlusal record are critical; inaccuracies can lead to extensive intraoral adjustments, potentially compromising function, aesthetics, and the mechanical strength of restorations.[7]

Interocclusal records are records of the positional relationship of the jaws or teeth or prosthesis, which can be utilized as two main types: (a) centric interocclusal registrations and (b) eccentric interocclusal registrations. interocclusal record. These records serve as maxilla-mandibular records for transferring inter-arch relationships from the mouth to an articulator. They are essential in providing high-quality restoration and reducing chair-side time and cost.[8,9,10,11]

Interocclusal records are records of the positional relation of the jaws or teeth or prosthesis. They can be utilized by two main types: (a) centric interocclusal registrations and (b) eccentric interocclusal registrations. interocclusal record.

Any alteration in the dimensions of these interocclusal recording materials can result in changes in the maxillomandibular relationship, leading to flawed restorations with incorrect occlusal contacts and necessitating undesirable adjustments. In addition to the clinical skills and techniques employed, the choice of material can significantly impact the accuracy of interocclusal registration. Various materials are available, including dental plaster with modifiers, modeling compounds, waxes,[12] acrylic resins, zinc oxide-eugenol paste, and elastomeric impression materials.[4]

Currently, the most commonly used materials are elastomeric impression materials, specifically additional silicone and polyether impression materials, which have been adapted by adding plasticizers and catalysts for interocclusal recording purposes. These materials have gained popularity due to their dimensional accuracy, stability, and resistance to compression.

The linear dimensional changes that can occur due to delays in transporting materials to remote laboratories, articulation delays, or remounting of casts are crucial factors. Therefore, the dimensional stability of interocclusal impression materials over time is of utmost importance, ensuring a more precise representation of the patient’s maxillomandibular relationship. During the articulation procedure, compressive forces are commonly applied to the interocclusal recording material, which can lead to inaccuracies in cast mounting and distortion during prosthesis fabrication, affecting the accuracy of the record.[13]

This present study has been initiated to assess and compare the linear dimensional changes and compression resistance of four elastomeric interocclusal recording materials.

OBJECTIVE

To compare elastomeric interocclusal impression material and to find the best among them, which exhibits the least linear dimensional change and the highest resistance to a constant compressive load and will give the least inaccuracies.

MATERIALS AND METHODS

Die coated for easy material removal; assembled with metallic cylinder. Placed in 37°C water bath to simulate oral temperature; 5.564 N force applied for registration. Fifteen specimens of each material (total 60) were made in 2, 4, and 6 mm lengths. Tests conducted: (1) compression resistance: samples subjected to 25 N force for 1 min after 24-hour room temperature storage. (2) Linear dimensional change: measured at 1 hour and 24 hours using a 10x magnification microscope, following ADA specification No. 19.

Data were analyzed using SPSS 22.0 with analysis of variance (ANOVA) and Tukey’s honestly significant difference (HSD) tests (0.05 significance level) for all 60 samples in four groups.

RESULT

In all groups (A, B, C, D), significant differences were found in compression values among different thicknesses using one-way ANOVA. Post hoc Tukey’s HSD tests showed weak evidence that 4 mm had higher values than 2 mm (P > 0.05). Very strong evidence that 6 mm had higher values than 2 mm (P < 0.001). Very strong evidence that 6 mm had higher values than 4 mm (P < 0.01/0.001/0.001, depending on the group) [Table 1].

Table 1.

Master chart for data in terms of compression of all four elastomeric interocclusal recording materials at 2 mm, 4 mm, and 6 mm thickness

Thickness	Group A	Group B	Group C	Group D
2 mm	0.065	0.056	0.108	0.109
	0.076	0.058	0.179	0.105
	0.062	0.080	0.165	0.101
	0.072	0.050	0.201	0.098
	0.081	0.062	0.194	0.101
4 mm	0.097	0.078	0.186	0.101
	0.092	0.073	0.226	0.108
	0.093	0.074	0.189	0.120
	0.095	0.092	0.180	0.146
	0.117	0.112	0.246	0.129
6 mm	0.120	0.105	0.292	0.182
	0.173	0.098	0.282	0.171
	0.122	0.112	0.296	0.168
	0.128	0.094	0.318	0.176
	0.171	0.108	0.322	0.169

In Group A, Group B, Group C, and Group D, comparing linear dimensional changes between 1 hr and 24 hrs at different thicknesses (sample t-test) showed that for 2 mm thickness, at 24 hrs, there was strong evidence of higher change (P < 0.05). For 4 mm thickness, at 24 hrs, there was weak/strong evidence (P > 0.05/P < 0.05). For 6 mm thickness, at 24 hrs, there was very strong evidence of higher change (P < 0.01). However, for 6 mm thickness in Group D, we could not calculate statistical significance due to a standard error of 0 [Table 2].

Table 2.

Master chart for data in terms of linear dimensional change of all four elastomeric interocclusal recording materials at 2 mm, 4 mm, and 6 mm thickness at 1-hour and 24-hour intervals

Thickness	Group A		Group B		Group C		Group D
	1 hour	24 hour	1 hour	24 hour	1 hour	24 hour	1 hour	24 hour
2 mm	24.71	24.70	24.79	24.77	24.77	24.75	24.81	24.79
	24.73	24.73	24.76	24.76	24.7	24.69	24.79	24.78
	24.74	24.73	24.73	24.72	24.73	24.72	24.73	24.72
	24.78	24.77	24.71	24.7	24.76	24.75	24.74	24.73
	24.79	24.77	24.74	24.73	24.74	24.73	24.69	24.68
4 mm	24.78	24.78	24.73	24.72	24.71	24.7	24.8	24.79
	24.71	24.71	24.75	24.75	24.74	24.73	24.74	24.72
	24.74	24.74	24.8	24.78	24.74	24.73	24.8	24.78
	24.71	24.69	24.7	24.69	24.72	24.72	24.7	24.69
	24.80	24.79	24.74	24.73	24.77	24.76	24.71	24.71
6 mm	24.71	24.71	24.74	24.73	24.72	24.71	24.76	24.75
	24.74	24.74	24.78	24.76	24.74	24.73	24.73	24.72
	24.78	24.78	24.73	24.72	24.75	24.74	24.74	24.73
	24.74	24.74	24.74	24.73	24.74	24.72	24.81	24.8
	24.76	24.76	24.71	24.7	24.71	24.71	24.69	24.68

DISCUSSION

This in-vitro study was designed to compare the dimensional stability and compression resistance over time of four different interocclusal recording materials at varying thicknesses. The aim was to provide clear guidance to clinicians regarding the practical use of these materials and make recommendations for their application in different situations. Additionally, the study aimed to determine the optimal timeframe for accurately articulating elastomeric interocclusal recording materials.

The study selected time intervals that considered factors like the time needed to transport recording materials to distant labs or potential delays in articulating or remounting casts. The findings revealed that 15.2% of clinicians performed the mounting themselves and 62.9% of records were transferred to articulators within 24 hours [Table 2]. This highlighted the importance of dimensional stability in interocclusal records before their use in articulating casts.

To assess these aspects, the study compared four groups of interocclusal recording materials (Groups A-D) using samples of different thicknesses (2 mm, 4 mm, and 6 mm) [Table 1]. Each group consisted of five samples. The samples were fabricated following ADA specification No. 19. A total of 60 circular samples were created, measuring 30 mm in diameter.

The samples were subjected to a water bath at 37 ± 0.1°C to simulate oral temperature. A force of 5.564 N (500 g external weight + 67 g glass plate) was applied during the interocclusal registration, chosen to compensate for the initial resistance of the material to closure.[9] Dimensional changes were measured at various time intervals (1 hour and 24 hours) using a traveling microscope with 10x magnification, following ADA specification No. 19 testing methodology. For compression resistance, each sample was compressed at a 25 N force for 1 minute using a Universal testing machine, and the readings were recorded.

The collected data from all 60 samples were subjected to statistical analysis using SPSS 22.0 software, involving ANOVA and Tukey’s HSD tests at a 0.05 significance level.

The study’s findings showed that, in the thickness groups of 2 mm, 4 mm, and 6 mm, the Virtual Refill (Group B) polyvinylsiloxane bite registration material outperformed the other interocclusal recording materials in terms of compression resistance. This result was in line with earlier studies by Breeding LC and Dixon DL that revealed Blue Mousse polyvinylsiloxane had the maximum compression resistance of all elastomeric interocclusal recording materials.

Furthermore, the study observed significant differences in the dimensions of samples from all four interocclusal bite registration materials under a constant compressive load, particularly as thickness increased. This aligned with previous research studies by Maj P Dua,[14] Breeding LC, Dixon,[15] and Rahul Nagrath,[16] which demonstrated that thicker elastomeric interocclusal registration materials tend to be more compressible. This higher compression strength of additional silicones might be attributed to their lower dimensional changes compared to condensation silicones and waxes. Konstantinos X.[17] Konstantinos X Michalakis et al.[18] also investigated compression resistance after material setting and found that polyvinyl siloxane displayed the highest resistance to closure compared to zinc oxide-eugenol paste and wax.

In summary, achieving accurate interocclusal records is crucial for creating dental restorations with proper occlusal contacts. Clinicians should choose materials based not only on clinical needs but also on the timing of articulation. When using elastomeric interocclusal recording materials, it is advisable to use a 2 mm thickness and perform articulation within 24 hours to minimize occlusal discrepancies in the final prosthesis.

Limitations of study included

The study focused solely on linear dimensional change; vertical variation was not explored. Apart from dimensional stability, factors like working and setting time should be investigated for material selection, especially at oral cavity temperatures. Time-related aspects require additional investigation. Expanding the sample size is advisable for more robust testing. The study examined only four brands of elastomeric bite registration materials.

CONCLUSION

The results were put to statistical analysis using ANOVA and then Tukey’s HSD tests for comparison among groups at the 0.05 level of significance. Within the limitation of the study, the following conclusions can be drawn: dimensional stability depends on material and time factors. All four elastomeric materials showed decreasing stability over time. Changes within ADA recommended limits (0.5% at 24 hours). Polyether (Ramitec) had the highest stability, followed by the addition of silicone materials. Articulation delay of up to 24 hours is possible. Thickness did not significantly impact dimensional stability—significant compressive resistance differences between materials. Compressive resistance decreased with increasing thickness. Virtual refill vinyl poly-siloxane was significantly more resistant to compression. 2 mm thickness showed the highest compression resistance with minimal articulation error.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.