A Clinical Evaluation of Materials for Interocclusal Registration in Centric Relation


Valéria de Oliveira PAGNANO
Osvaldo Luiz BEZZON
Maria da Glória Chiarello de MATTOS
Ricardo Faria RIBEIRO

Departamento de Materiais Dentários e Prótese, Faculdade de Odontologia de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, SP, Brasil


Braz Dent J (2000) 11(1): 41-47 ISSN 0103-6440

Introduction | Material and Methods | Results | Discussion | Conclusions | Resumo | References


Four techniques for interocclusal registrations of centric relation based on materials or combinations of materials usually utilized were tested by means of mounting of casts for a patient with partial lower edentulousness, without a free end saddle. To ensure the correct position of centric relation a Lucia jig was utilized. The following conditions for the record of posterior section were tested: registrations with wax, wax plus zinc oxide-eugenol paste, wax plus Duralay acrylic resin, and condensation silicone (putty). The evaluation was made by the measure of vertical distance between reference points in the base of the casts and calculation of variations occurring with each material. The combinations of wax plus zinc oxide-eugenol paste and wax plus Duralay acrylic resin showed the smallest variations in centric relation position.


Key Words: interocclusal registration, centric relation, cast, occlusion.


Introduction

It is a requirement of prosthetic oral rehabilitation that all stages of the process are carried out in a highly judicious manner. The success of treatment, in general, depends on many aspects that are related to the fidelity of cast mounting on the articulator.

Centric relation (CR) is the horizontal relation usually utilized for occlusion analysis, diagnosis and rehabilitation treatment, because it is a reproducible maxillo-mandibular relation important to the comfort, function and health of the stomatognathic system (Carroll et al., 1988; Dawson, 1993). Due the fact that the CR is a determined position by the temporomandibular joint, it is fundamental that no muscular activity interferes in the mandibular position and, therefore, all neuro-protector reflexes must be avoided during registration (Lucia, 1964; Calagna et al., 1973; Woelfel, 1986). The utilization of interocclusal records is necessary for the mounting of casts in CR because this gives support and stability to these casts and allows relation without contact of occlusal surfaces.

Obtaining accurate maxillo-mandibular registrations is fundamental for the appropriate relation of the casts. The clinical results depend on the exact reproduction of the interocclusal relation in the articulator from the time of diagnosis until the definitive treatment. Thus, the role of interocclusal registration in oral rehabilitation is highly relevant.

To obtain a satisfactory interocclusal registration, the materials must have the following characteristics: low viscosity, low resistance to mandibular closing, no adherence to the teeth, plasticity, appropriate working time, rigidity after setting, precision of details, dimensional stability, easy handling, acceptability to the patient, and low cost (Berman, 1960; Cohn, 1963; Wirth and Aplin, 1971; Skurnik, 1977; Luebke, 1981; Adams, 1982; Urstein et al., 1985, 1991; Warren and Capp, 1990; Tripodakis et al., 1997).

In the present study, four techniques of interocclusal registration of centric relation were compared, based on materials or combinations of materials usually utilized: with wax, wax plus zinc oxide-eugenol paste, wax plus Duralay acrylic resin, and condensation silicone (putty).


Material and Methods

The study casts were obtained from molds of irreversible hydrocolloid of a patient with partial lower edentulousness, without a free end saddle. The patient had clinically normal occlusion and no evidence of dysfunction of the temporomandibular joint or of periodontal disease.

The study casts obtained for this patient were manually articulated at maximum intercuspation position and maintained in this position by wax dripping, so that they would not become loose. The casts were then cut the same as for orthodontic casts in order to obtain lateral and posterior plane surfaces to provide stability during the measurements performed with a double coordinate ZKM 0.2-250 microscope (Carl Zeiss, Jena, Freiberg, Germany) using a 7326 accessory with precision of 0.2 µm. After cutting, draft paper was glued to the base of upper and lower casts on the right and left regions. Two reference points were selected at random on the draft paper of each region, one of them in the upper cast and the other in the lower cast, duly aligned for the measurement of vertical distance (VD). The selection of points was at random to avoid the operator tendency to repetition of values. The measurements were calculated as the difference between the readings referring to the two obtained points on the microscope dial (Figure 1A,B).

A jig was made on the upper cast (Lucia, 1964) with Duralay acrylic resin. The jig was placed in the patient's mouth and the patient was led to CR closure by chinpoint guidance for adjustment of the jig height. At each closure, the interposition of carbon paper indicated the site in the jig to be filled. On this basis, a separation of the posterior teeth was defined to guarantee the elimination of any interference on closure and created a space for the positioning of the registration materials. A small portion of resin was then added to the palatine surface of the jig which permitted the determination of the key of CR position. The patient was kept in the supine position throughout all registration procedures. During the work, the same jig was used and kept in a moist environment and ten registrations were obtained with each material.

Registrations with wax

Ten registrations were obtained with wax 7 sheets (Polidental, São Paulo, SP, Brazil) previously cut along the extension of the arches. The wax was then heated and placed in the oral cavity and the patient was instructed to close her mouth, with the jig in position. The registrations were obtained on double-thickness wax to compensate the posterior space created by the jig (Figure 2). The registrations were removed after the wax cooled and kept in a container with water until analysis.

Registrations with wax plus zinc oxide-eugenol paste

The registrations with wax were obtained in the same manner mentioned above and a small portion of zinc oxide-eugenol paste (Herpo, Petrópolis, RJ, Brazil) was then added in the region of the first molars, both on the upper and the lower part of the wax sheet. After paste setting, the registrations were removed and kept in a moist environment.

Registrations with wax plus Duralay acrylic resin

After the registrations with wax were obtained as cited above, two small perforations were made in the wax sheet for the addition of small portions of resin (Reliance, Worth, IL, USA) (Bezzon and Orsi, 1994). During the plastic phase of the resin, the registration was repositioned in the mouth until full polymerization. After acrylic resin polymerization, the registrations were removed and kept in a container with water.

Registrations with condensation silicone (putty)

The silicone (3M, Sumaré, SP, Brazil) was divided into two parts and placed on the right and left sides on the occlusal surface of the molars. With the jig in position, the mandible was placed in CR position. After silicone setting, the registrations were removed and kept in plastic bags in the absence of humidity.


Results

The averages, range of variation and standard deviations of CR position obtained with each material are shown in Figures 3 and 4.

Because the distribution of sample was normal, the analysis of variance and Tukey test were used, showing the right side to be statistically different at the level of 1%. As can be seen in Figure 3, on the right side silicone had a higher standard deviation and higher range of variation, followed by wax. Using analysis of variance and Tukey test, silicone showed statistically significant differences at the level of 1% compared to the other materials. The other materials were not significantly different.

On the left side, wax and silicone were the materials with the highest standard deviations and highest range of variations. According to statistical analysis, however, there was no statistically significant difference among the materials tested (Figure 4).


Discussion

The success of rehabilitation treatment is closely related to an exact reproduction of occlusal relation in the articulator during all stages of treatment. The conditions are totally dependent on procedures and materials used for the interocclusal records which should result in the installation of prosthetic restorations, with a minimal occlusal adjustment. The interocclusal registrations must be obtained with special attention to the materials and manufacturer's instructions.

In this research, we evaluated the materials in the centric relation because this is the position of choice for diagnosis and planning of oral rehabilitation.

For many years, the jig and recently, the leaf gauge, have been reliable to properly locate and maintain the condyles in this position. Both maintain the least vertical distance increase necessary to eliminate dental contact. In this research, the Lucia jig was used because it allowed obtention of a rigid and defined stopping point in the anterior region, which ensured the CR position and allowed the evaluation of registration materials used in the posterior region of the arch during measurement with the microscope.

According to Urstein et al. (1985), elastomers are not rigid materials, thus raising doubts about the seating of the casts on the registrations. This can explain the fact that silicone was statistically different compared to the other materials. It is important to note that there was no intention to pattern the strength for seating of casts, because the objective was to simulate clinical practice, i.e., to apply sufficient pressure for the casts to articulate properly, with the jig in position, without causing elastic deformations in the material, as is normally done by the clinicians.

Despite the opinion of several investigators that wax is unfavorable as a material for interocclusal registration (Millstein et al., 1971, 1973; Scott, 1978; Lassila and McCabe, 1985; Urstein et al., 1985), it was evaluated because it is the most utilized material in the dental clinic, because of its easy handling, clinical versatility, ease of corrections and low cost (Wirth and Aplin, 1971; Scott, 1978; Urstein et al., 1991).

In this study, the current alterations of wax utility can be due to insufficient pressure applied to promote the correct positioning of the casts, without causing perfuration of wax sheets. Thus, it was verified that the wax also did not provide security to the operator in terms of the pressure that should be applied to provide correct cast relation. On this basis, the plastic or elastic deformations of wax and silicone were responsible for the higher variations shown in Figures 3 and 4.

By analyzing the results, it was possible to verify that the combinations of wax with rigid materials such as zinc oxide-eugenol paste and Duralay acrylic resin provided the smallest variations around the average. In these cases, the wax acted only as a support for these rigid materials. According Lassila and McCabe (1985), the major problem with the use of zinc oxide-eugenol paste is that it is a brittle material that tends to adhere to teeth and, when used in excess, it may become distorted and provoke vertical dislocation. Furthermore, by being above the wax it is subjected to its deformation, contrary to acrylic resin which was placed in the space obtained by perforation of the wax. Thus, the use of acrylic resin provided more security to the operator at the time of seating the casts on the registrations.

Therefore, it is necessary to emphasize that not only is the choice of material important to obtain interocclusal registrations, but the technique of the material manipulation and the selection and execution of the correct mounting technique for each case are also important.


Conclusions

1. Silicone and wax were the materials that provided the highest standard deviations and the highest range of variation.

2. The smallest variation ranges were obtained with the combinations of wax plus the rigid materials zinc oxide-eugenol paste and Duralay acrylic resin.

3. On the right side, silicone was significantly different at the level of 1% compared to the other materials tested.


Resumo

Pagnano VO, Bezzon OL, Mattos MGC, Ribeiro RF: Avaliação clínica de materiais de registro interoclusal em relação cêntrica. Braz Dent J 11(1): 41-47, 2000.

Quatro técnicas de registro interoclusal da posição de relação cêntrica fundamentadas em materiais ou combinações de materiais comumente utilizados, foram avaliadas por meio da montagem de modelos de um paciente com desdentamento parcial inferior, sem extremidade livre. Para assegurar a posição correta da relação cêntrica foi utilizado o jig de Lucia. As seguintes condições para o registro do segmento posterior foram avaliadas: registros com cera, cera mais pasta zincoenólica, cera mais resina acrílica Duralay e silicona de condensação (pesada). A avaliação foi realizada pela medida da distância vertical entre pontos referenciais nas bases dos modelos e cálculo das variações ocorridas com cada material. As combinações de cera mais pasta zincoenólica e cera mais resina acrílica Duralay apresentaram menores variações na posição de relação cêntrica.


Unitermos: registro, relação cêntrica, modelos, oclusão.


References

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Correspondence: Prof. Dr. Osvaldo Luiz Bezzon, Departamento de Materiais Dentários e Prótese, Faculdade de Odontologia de Ribeirão Preto, Universidade de São Paulo, Av. do Café s/n, 14040-904 Ribeirão Preto, SP, Brasil. E-mail: OLBezzon@usp.br


Accepted November 17, 1999
Eletronic publication July, 2000


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