Comparison of the accuracy and dimensional stability of interocclusal recording materials - An in- vitro study

Purpose: The purpose of this in vitro study was to compare and correlate the accuracy and dimensional stability of commonly used interocclusal recording materials. Materials and methods: A stainless steel die, made according to modified ADA specification no. 19, was loaded with different interocclusal recording materials. These materials were separated from die 3 min after their respective setting time, which resulted in disks of standard diameter with two parallel lines and three perpendicular lines (thin, medium and thick) on the surface. These lines were observed under Nikon profile projector V-12 and graded for line and shape criteria to find out the accuracy of the material. The distance between two parallel lines was measured at different time intervals to find out the dimensional stability of the material. Statistical analysis used: ANOVA followed by Mann-Whitney test for pair wise comparison Results: There was significant difference found between accuracies of different interocclusal recording materials. Zinc oxide eugenol and polyether were more accurate than silicon and Aluwax. The comparison of dimensional stability showed that zinc oxide eugenol and polyether were more dimensionally stable followed by silicon. Aluwax was least dimensionally stable of all. Conclusions: The zinc oxide eugenol is more accurate interocclusal recording material and which is followed by polyether, silicon and Aluwax respectively. Poly ether, zinc oxide eugenol and silicone possess good dimensional stability. No correlation exists between accuracy and dimensional stability of interocclusal recording materials. Key-words: Interocclusal recording material; Bite registration material; Accuracy; Dimensional stability INTRODUCTION: Diagnosis and treatment of a patient for prosthetic rehabilitation requires the clinicians to fabricate diagnostic cast, as well as master cast and articulate. In some cases, the casts can be easily mounted in maximum intercuspation by stabilizing them with cast cement after hand articulation. While in others, it is necessary to record maxillomandibular relationship and accurately transfer it to the articulator by using appropriate interocclusal recording medium (1). The use of ideal material and proper technique allows the placement of indirectly fabricated prosthesis in the patient’s mouth with minimal occlusal adjustment. Phillip Pfaff made the first interocclusal registration in 1756, since then many materials and techniques have been used for maxillomandibular relationship record. These materials are basically impression materials but that have been modified to give better handling characteristics(2). These include impression plaster, waxes, zinc oxide eugenol, acrylic resin, hydrocolloids, and newer ones include polyether and vinyl polysiloxane. Both waxes and zinc oxide eugenol are most commonly used interocclusal recording materials because of their ease of manipulation, economy, less time consuming and less skill dependent. These materials serve as base line for newer developments in the interocclusal recording materials. Requirements for ideal interocclusal registration material include; a) It should have limited resistance before setting to avoid displacement of teeth or mandible during closure. b) It should become rigid and exhibit minimal dimensional change after setting. c) It should produce accurate record of the incisal and occlusal surface of the teeth d) It should be easy to manipulate. e) It should not produce adverse effects on the tissues involved in procedure and it should allow easy verification (1). But no material has all the properties of the “ideal” interocclusal registration material. The inaccuracies attributed to the interocclusal records can be divided into three categories: the biologic characteristics of stomatognathic system, manipulation of the material, and the properties of the interocclusal recording materials (3). Many studies have been conducted to find the accuracy and dimensional stability of several bite registration materials (2-10). In an experimental study on physical properties of interocclusal recording materials, the Polyether interocclusal recording material exhibited lesser linear change than Silicon and Zinc oxide eugenol, which was not associated with their respective weight loss (2). In another study on differential accuracy of Silicon interocclusal recording materials, the authors found that a direct relationship exists between dimensional stability and percentage of weight loss (8), but no study has been done to correlate the accuracy and dimensional stability. International Journal of Scientific and Research Publications, Volume 5, Issue 7, July 2015 2 ISSN 2250-3153 www.ijsrp.org Hence, this study was planned to compare and correlate the accuracy and dimensional stability of four commonly used interocclusal recording materials. MATERIALS AND METHODS: Four commercially available interocclusal materials were evaluated. 1) Bite registration wax (Aluwax, Aluwax Dental Product Co., Michigan USA). 2) Polyether bite registration paste (Ramitec, 3M ESPE, AG Dental Products, Germany Lot 268467). 3) Vinylpolysiloxane bite registration cream (Exabite II NDS, GC America Inc, ALSIP, IL, Lot 0602061). 4) Zinc–oxide eugenol bite registration paste (Superbite, Bosworth Company, Skokie, IL lot 0608-395). Materials and method followed in this study has been discussed under the following headings. 1) Preparation of mold. 2) Selection and manipulation of materials. 3) Preparation of samples. 4) Observation made for scoring the samples for accuracy. i) Observation of continuity of lines. ii) Observation of shape of the thick line. 5) Measurement of the distance between lines for determining dimensional stability. 1) Preparation of mold: A mold was prepared according to revised American Dental Association specification no. 19 for non-aqueous elastic dental impression materials (11). It was consist of a ruled block AA, test material mold BB and a riser CC. All parts were made up of stainless steel except raiser, which was made up of brass. The ruled block was having three horizontal lines of different widths; small Y -line (width-24mm), medium X-line (width-57 mm) and a thick Z line (width –83mm). And two vertical lines CD and C’D’ of 82mm each. The lines CD and C’D’ were separated from each other by 25mm approx. (24.740mm) (fig.1&2). The test material mold was a cylinder of inner diameter 30mm and depth of 6mm. The riser was a brass disc of diameter 29.9mm and thickness of 3mm. 2) Selection and Manipulation of materials:Four commonly used interocclusal recording materials were selected for the purpose of this study. All the materials were purchased from local market through regular commercial channels. The materials used for the study were divided into four groups of 10 samples each. Group 1: Bite registration wax (Aluwax) Group2: Polyether registration paste (Ramitec) Group 3: Polyvinyl siloxane bite registration cream (Exabite II NDS) Group 4: Zinc oxide eugenol bite registration paste (Superbite) Altogether, a total of forty samples were prepared. All the study materials were conditioned to ambient room temperature for at least 24 hrs before manipulation and the individual materials were manipulated following the manufacturers’ instructions. 3) Preparation of samples:Each material was manipulated as mentioned above and the total force of 5.56 N (weight of glass plate 67g + external weight 500g = 567g) was applied. This is the average pressure required to compensate initial resistance of interocclusal material which may vary between 0.5 N to 13.8 N (12). The whole assembly was then submerged in water bath of temperature 32 ± 1 0 C resembling mouth temperature. Each assembly remained in the bath for the setting time suggested by manufacturer plus 3 min to ensure polymerization in case of elastomeric materials. After removal from the water bath, the material was separated from the die by using the brass disk (riser). The excess flash was trimmed using a Bard Parker knife. Thus prepared specimens were measuring 30 mm in diameter, 3mm in thickness and had the lines X, Y, Z, CD and C I D I lines on it. Similarly, all the 40 bite registration record samples were obtained. (fig. 3) In between days of observation, the samples were stored in a moisture free polyethylene bags at room temperature of 28 ± 2 0 C. Dimensional changes of elastomers can be reduced by storage in a sealed dry container (12, 13) and at room temperature air (12). 4) Observation made for scoring the samples for accuracy:  Accuracy of different interocclusal recording materials was determined by observing each sample under Nikon Profile Projector V-12 (Nikon inc., Japan) with the accuracy of 0.001mm. (fig 4) Observations for accuracy were made immediately after obtaining the samples only on the day 1.  Each sample was graded group wise according to line criteria and shape criteria. Following criteria were used for grading the samples. (i) Observation for continuity of lines reproduced (line criteria): Thinnest continuous line produced by each material was observed by using Nikon Profile Projector V-12 with 50 X magnification and the scores were noted. International Journal of Scientific and Research Publications, Volume 5, Issue 7, July 2015 3 ISSN 2250-3153 www.ijsrp.org Score Observation 0 No continuous line 1 Continuous thick line (Z-line) 2 Continuous medium line (Xline) 3 Continuous thin line (Yline) (ii) Observation for the shape of the line reproduced (shape criteria): The shape of ‘Z’ line reproduced on the surface of the sample was observed by using Nikon profile Projector V-12 with 50 X magnification, compared with V-shaped line on the master die and scores were noted to check the accuracy.