Department of Prosthodontics, Faculty of Dentistry, Hacettepe University, Ankara, Turkey
Correspondence: Assoc. Prof. Dr. Filiz Keyf, Department of Prosthodontics, Faculty of Dentistry, Hacettepe University, Ankara, Turkey. Fax: +90-312-311-3741. e-mail: firstname.lastname@example.org
Braz Dent J (2001) 12(1): 43-46 ISSN 0103-6440
INTRODUCTION | MATERIAL AND METHODS | RESULTS | DISCUSSION | RESUMO | REFERENCES
Many materials are used for making interocclusal records to mount casts on dental articulators. The strength of these materials during the compressive forces encountered in the mounting process is important because any deformation will cause incorrect occlusal relationships. This investigation compared the deformation of 4 thicknesses (2 mm, 5 mm, 10 mm, 20 mm), when subjected to 25 N compressive force, of 3 interocclusal recording materials: condensation silicone, recording wax, and rubber-based polyvinylsiloxane. Significant differences were recorded for all materials of 20 mm, 10 mm and 2 mm thickness. However, there was no significant difference among the 5 mm groups. Interocclusal records should be made of a minimal thickness, using a recording material which exhibits minimal distortion during compression.
Key Words: compressive strength, interocclusal recording materials.
The determination of a repeatable centric relationship is necessary for the dentist. Various materials are used for interocclusal registration of the occlusal relationship between natural and/or artificial teeth for planning occlusal rehabilitation and for construction of removable and fixed partial dentures. Numerous studies have investigated the repeatability of specific interocclusal registration techniques (1-5).
Many materials available for occlusal registration have been analyzed for accuracy in the mounting of casts (6-13). Plaster, impression compound, wax, zinc oxide-eugenol paste, zinc oxide eugenol-free paste, acrylic resin and elastomeric materials are products routinely used for the registration of the occlusal relationship. Recently, polyether and polyvinylsiloxane elastomeric materials for interdental records have been used (5,12-14).
Casts must be secured together with the recording material positioned between them for mounting on an articulator. A rubber band is used to securely approximate the cast during mounting procedures, but even a rubber band applies undesired compressive force. The resistance of these recording materials to compressive forces is important, because any deformation during removal from the mouth or mounting process will result in inaccurate articulation of casts and faulty restorations.
This investigation compared the deformation of various thicknesses of three interocclusal recording materials when subjected to a constant compressive force.
MATERIAL AND METHODS
Three commonly used interocclusal recording materials were selected for this study: 1) a condensation silicone elastomeric material (Durosil L, Centradent, Germany); 2) a recording wax (Dentsply Detrey, England); c) a polyvinylsiloxane elastomeric material (Flex, Bite registration regular set, Benlioglu, Turkey). Cylindrical specimens (2 mm, 5 mm, 10 mm and 20 mm thickness) were prepared in a split brass mould for testing. Ten specimens were fabricated in the four thicknesses of each material for a total of 120 specimens. The tested materials were prepared and mixed according to the manufacturers' instructions. Each mixed material was placed in a 10 mm diameter split brass mould and allowed to set for 5 min before removal from the mould. Specimens were stored dry at room temperature for 12 h before testing.
Each specimen was subjected to a constant compressive force of 25 N (2.55 kg) using a Hounsfield Tensometer (W7584, Tensometer Limited 81, Morland Road Croydon, England) with a cross-head speed of 3.3 mm/min.
The thickness of each specimen was measured after 60 s of force application and was compared by the SPSS statistical software program. The Kruskal-Wallis one-way ANOVA and Mann-Whitney U test were used for statistical analysis.
The mean thickness of each material during compression by the 25 N force is shown in Table 1. The Kruskal-Wallis one-way ANOVA test indicated that there was a significant difference in compressive strength between the different thicknesses of materials (p=0.00001 and p=0.0185) except for the 5 mm thickness. There was no difference in accuracy of the three materials tested at 5 mm thickness (p>0.05) (Table 2). In the paired comparison using the Mann-Whitney U test, a significant difference was found between groups except between the 2 mm thick recording wax and polyvinylsiloxane (p>0.05) (Table 3).
Jaw registration materials should be accurate, easily manipulated, and economical (7). We selected condensation silicone, recording wax and polyvinylsiloxane elastomeric material as best matching these requirements. These three materials are commonly used to record maxillomandibular relations.
The various thicknesses of the recording materials were selected to simulate clinical situations. The thin specimens would match the limited space between prepared teeth on one arch opposing unprepared teeth compared with the large thickness of material used between two opposing edentulous arches (12). The specimens were stored for 12 h to simulate the time between clinical and laboratory phases (registration and mounting) (8,13).
Rubber bands are commonly used to sustain the contact of opposing casts and registration material during mounting procedures. Because the maximal forces exerted by the use of one rubber band to position a maxillary cast to a mandibular cast mounted on an articulator is approximately 25 N (12), this value was selected.
Lassila and McCabe (8) evaluated compressibility of several recording materials and concluded that the tendency for the interocclusal registration to deform was more common with elastomeric materials. Breeding and Dixon (12) concluded that elastomeric interocclusal recording materials become distorted as a result of compressive forces during the mounting of casts on an articulator.
One of the materials used to record jaw relations is wax. Wax has the advantage in registration that it rapidly stiffens when it cools. However, Millstein and Clark (6) determined that wax was unreliable in interocclusal registration because of its considerable cooling contraction. Lassila (9) reported that wax was a reliable material only when it was left at the site of registration, for example, on removable dentures.
Breeding and Dixon (12) and Breeding et al. (13) reported polyvinysiloxane to have high dimensional accuracy and ease of manipulation and also reported that polyvinylsiloxane is more resistant to compression than other materials at thickness of 5, 10 and 20 mm.
In the present study, recording wax exhibited the greatest strength to compression for all designated thickness in vitro. The values for silicone were significantly lower than those of the other recording materials. Polyvinylsiloxane had less strength than recording wax but more than silicone. However, wax would undoubtedly distort significantly more than either elastomeric material from body temperature to room temperature. Therefore, jaw registrations made with wax may not necessarily be more accurate.
The ability of an interocclusal registration material to resist compressive forces is very important. Any discrepancy between the intraoral relationships of the teeth and the position of the teeth on the mounted working casts will result in restorative errors.
Keyf F, Altunsoy S. Resistência à compressão de materiais de registro interoclusal. Braz Dent J 2001;12(1):43-46.
Muitos materiais são utilizados para confecção de registros interoclusais para montagem de modelos no articulador. A resistência desses materiais durante a força de compressão existente durante o processo de montagem no articulador é muito importante no processo de montagem pois qualquer deformação pode causar relações interoclusais incorretas. Esse estudo comparou a deformação de diferentes espessuras (2 mm, 5 mm, 10 mm, 20 mm) de materiais (silicona de condensação, cera e polivinilsilicona) quando submetidos a uma força de compressão de 25 N. Entretanto não houve diferença estatisticamente significante entre os grupos cuja espessura era 5 mm. Os registros interoclusais devem ser realizadas com o mínima espessura, usando um material que apresente pequena distorção durante a compressão.
Unitermos: resistência à compressão, materiais de registro interoclusal.
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Accepted July 17, 2000
Braz Dent J 12(1) 2001