Introduction

Interocclusal records are the means whereby the inter-arch relationships are transferred from the mouth to an articulator.1 For the success of all complex restorative treatment procedures exact duplication of existing relationships between opposing maxillary and mandibular arches is very important.2, 3 The success of a restoration depends on the maintenance of occlusal harmony. Thus, while providing a restoration to a patient, the objective of the treatment is to provide teeth that are in harmony with the entire stomatognathic system. Interferences are observed in a restoration when teeth are placed that are not in harmony with the masticatory apparatus.4 Thus, the goal of dentist is to provide a functional restoration without interferences that maintains the health and is in equilibrium with the entire stomatognathic system. This can only be possible if we create a mechanical equivalent on the articulator which simulates movements of mandible without any interference. Thus, we need to transfer the same relationship to articulator, which was present intraorally, so that functional restoration can be provided to the patient. This transfer requires the use of interocclusal records. Lateral interocclusal records are used to set condylar elements on articulator and protrusive interocclusal records are registered while protruding the mandible.5 All these records are required to be transferred accurately and precisely to make articulator a mechanical analog of mouth. This ensures fabrication of an accurate prosthesis with minimal discrepancy, thus, avoiding symptoms like severe hyperactivity and incoordination of masticatory muscle function intraorally.4, 5

Materials and Methods

20 samples of each interocclusal recording material were fabricated. A total of 80 samples prepared and Grouped into 4 Groups of 20 samples each. The Groups were as follows:

Group I: Modelling Wax (DPI Modelling Wax)

Group II: Combination Of Modelling Wax And Zinc Oxide Eugenol Impression Paste( DPI Impression Paste and DPI Modelling Wax)

Group III: Aluwax (Morsa, Germany)

Group IV: Addition Silicone Bite Registration Paste( Exabite II)

Measurement of dimensional change in antero-posterior and mediolateral direction

The dimensional change in antero-posterior and mediolateral direction were measured as follows:

Figure 1

Vertical dimensional change

The dimensional change in vertical direction was measured with the help of digital vernier caliper by calculating the distance between the conical point tips at 2mm of vertical separation. Now, the interocclusal record was poured with die stone on both the sides of the bite registration tray. This record poured was rearticulated Now at that specified vertical separation, the distance between the elevations on the maxillary and mandibular mesiobuccal cusp of first molar and buccal cusp of first premolar on both right and left sides was measured with digital Vernier caliper.

These measurements obtained were used as control Group and all the readings of the samples were then compared with this control Group to know the amount of dimensional change occurred with the materials.

Observation and Results

Each sample size was evaluated for the dimensional accuracy in antero-posterior and mediolateral dimensional change with travelling microscope (with accuracy of± 0.001mm) and vertical dimensional change with digital Vernier caliper (with accuracy of ±0.01mm).

The mean, range, standard deviation and standard error were measured by one way ANOVA test.

Post Hoc test and Tukey Homogeneous Subset Division Test were used for statistical analysis to know that which Groups were significant and insignificant. A p-value of less than 0.005 was considered as significant.

Table 1 represents the comparison of dimensional accuracy in antero-posterior dimension of each Group with rest of the four Groups.

Table 2 represents the comparison of dimensional accuracy in mediolateral dimension of each Group with rest of the four Groups and depicts the significance and insignificance relation in between the Groups.

Table 3 represents the comparison of dimensional accuracy in vertical dimension of each Group with rest of the four Groups and depicts the significance and insignificance relation in between the Groups.

Figure 2

Graph showing mean dimensional change in antero-posterior, medio-lateral and vertical direction

Discussion

The interocclusal relationship of mounted dental casts is an accurate representation of the opposing dental arches. The various methods advocated for recording interocclusal relationships are graphic, functional, cephalometric and direct interocclusal recordings.6 The present in vitro study was conducted to measure the dimensional accuracy of various interocclusal recording materials using direct method of measuring the dimensional accuracy. In the direct method, reference points are placed on measuring cast and actual movements can be registered directly7, 8, 9, 10 Vergos et al8 and Ghazal et al9 also used direct technique for measuring the dimension accuracy of various interocclusal recording materials as used most commonly in clinical practice.

Various materials have been used for making interocclusal records like wax, zinc oxide–eugenol paste, auto polymerizing acrylic and BisGMA resins, condensation-type silicones, polyether and vinyl polysiloxane. Ghazal et al9 used aluminium wax, modeling wax, addition silicones and polyether, Pipko et al10 used ten interocclusal recording material while Balthazar-hart et al11 compared dimensional accuracy of four different interocclusal recording materials i.e. zinc oxide eugenol, eugenol free zinc oxide, silicones and polyether.

In the present study, interocclusal recording materials used were modeling wax, aluwax, combination of modeling wax corrected with zinc oxide eugenol and addition silicones.

Modelling wax is one of the most versatile and commonly used interocclusal recording material because of its ease of manipulation. But its high coefficient of thermal expansion and release of internal stresses make it a dimensionally inaccurate material.12, 13, 14 Muller et al15 did an experimental study on 8 different interocclusal recording materials to determine three dimensional errors in mounting of casts out of which, wax recorded maximum dimensional change. Other studies performed by Shrunik,12 Millstein et al,14 Michalakis et al,13 Pipko et al10 and Assif et al also depicted the same results which were consistant with the present study.

Zinc oxide eugenol paste offers minimal resistance with mandibular closure owing to the fluidity of paste before setting and becomes rigid after it sets finally. It has lengthy setting time, is brittle, stick to the teeth and rigid. Vital portions of the record can be lost through breakage on removal from the mouth and cannot be reused. Corrected wax improved the detailed recording and displacement of wax but caused increase in the vertical dimension.$ Assif et al monitored the accuracy and vertical discrepancy of four interocclusal recording materials during transfer of records to an articulator with an electromechanical device.While making record with corrected wax, they used double sheet of baseplate wax and later relined it with zinc oxide eugenol and concluded that most of the distortion was caused by wax record. Corrected wax improved the detailed recording and displacement of wax but caused increase in the vertical dimension.11, 16

Fattore16 and Muller et al11 found corrected wax to be more dimensionally accurate than modeling wax alone. In the present study, wax corrected with zinc oxide eugenol showed less deviation from modeling wax anteroposteriorly (1.98±0.03mm), mediolaterally (1.97±0.04mm) and vertically (0.33±0.010mm). Thus, the results are consistent with the studies performed earlier.

The metallised wax wafer(Aluwax) has been found more accurate than non-metallised wax due to addition of metal particles (aluminium) to the modeling wax. Millstein et al17 determined the dimensional accuracy of laminated and non-laminated, metalized and non-metalized wax interocclusal wafer as a function of initial heating, intraoral withdrawal, storage environment, storage time and seating force and concluded that metalized wafers were more accurate than those of non-metalized.. A wafer should be cooled adequately so that it doesn’t distort on removal. However, abrupt withdrawal provides unnecessary additive effect to the baseline error that is already present.

In our study Aluwax showed less deviation than modeling wax i.e. anteroposteriorly (1.09±0.04mm) , mediolaterally (1.09±0.02mm) and vertically (0.22±0.01mm). These results are consistent with studies performed earlier by Millstein et al,17 Erriksson et al,7 Vergos et al8 and Michalakis et al.13

Addition silicones are the most dimensionally stable materials attributed to the fact that it sets by addition polymerization. Also, they are easy to manipulate and offer little resistance to closure, set to a consistency that makes them easy to trim without distortion, and accurately reproduce tooth details. However, spring action found in these materials may cause inaccuracies during mounting of the casts.18 Karthikeyan et al in 200419 compared the dimensional stability of three different interocclusal recording materials i.e. addition silicones, aluwax and zinc oxide eugenol at the time intervals of 1h, 24h, 48h and 72h. The addition silicones presented the minimal linear dimensional change (0.226±0.11 mm) of all the materials tested at all the time intervals followed by zinc oxide eugenol( 0.443±0.064) and aluwax (0.582±0.082).

Vergos et al in 2003[8] found elastomers to be the most dimensionally stable interocclusal recording material with addition silicones and polyether showing the minimal discrepancy of 101µm and 107µm respectively. However, wax displayed the greatest discrepancy of 168µm. acrylic resin was in between wax and elastomers.

Dua et al (2007)6 compared the linear dimensional change and compressive resistance of four commercially available elastomeric interocclusal recording media. Three were different addition silicones and the fourth was polyether material and found addition silicones to be dimensionally much more accurate than other interocclusal recording materials.

Further studies performed by Millstein et al,13 Balthazar-Hart et al11 and Ghazal et al9compared the various interocclusal recording materials with addition silicones and found addition silicones to be dimensionally much accurate than other interocclusal recording materials

The results in the study depicted that in anteroposterior and mediolateral dimension addition silicon was dimensionally most stable followed by aluwax, corrected modeling wax and modeling wax was dimensionally least stable.

In vertical plane, addition silicon was dimensionally most stable followed by aluwax,modeling wax and corrected wax was dimensionally least stable

The least dimensional accuracy of corrected modeling wax in vertical direction is attributed to the fact that though zinc oxide eugenol improved the detail of wax recording but caused increase in vertical dimension.

These results are consistent with the studies performed earlier by Dua et al in 2007,6 Karthikeyan et al in 2004,19 Michalakis et al in 2004,13 Vergos et al in 2003,8 Balthazar-Hart et al in 198111 and Ghazal et al in 2008.9

Conclusion

Based on the observations and results of this study, following conclusions were made:

Based on the results of the study, it is concluded that addition silicon as interocclusal recording material is the most accurate and modeling wax is least accurate interocclusal recording material.

It is recommended that depending on the clinical situations, different types interocclusal recording materials need to be used.

Corrective wax should be used for rechecking the record when occlusal changes are observed in the patient. Rigid materials (modeling wax, aluwax) should be used when segmental records are required and non-rigid materials (addition silicones, polyether) are found to be beneficial in accurately recording patterns of closure and avoiding mandibular deviations which is generally caused by rigid materials.

Conflict of Interest

None.

Source of Funding

None.