Thickness, Strength, Plastic Deformation And Marking

Characteristics Of Occlusal Registration Strips

Ink, silk paper, plastic strips and wax have been used for a long time in dentistry to determine occusal contacts. These materials indicate different thickness, tensile strength, plastic deformation and marking ability. The manufacturers have not standardized the specification of these materials. Moreover, the articulation strips sold in the market- be they thick, thin or extra thin, differ from each other due to the trademarks. Thus, properties of these materials should be known to the dentist. If the material is unsuitable, it may show contact areas inaccurately and thickness will affect the precision of the restoration. In this study, 11 articulation strips (3 plastics, 8 papers) have been tested and results are presented. 

Registration of occlusal contact is very important for diagnosis and treatment because its accuracy is essential for the success of the treatment.⁸ For example, the different thicknesses of articulating papers may display false markings and, thus, cause confusion.²⁹¹⁰

Manufacturer's designation of registration strip thickness which is presently not standardized, such as micro thin, extra thin and thick, has only rough qualitative relationships to the true strip thickness or marking size.⁷

The purpose of this study was to compare the thickness, strength, plastic deformation and marking characteristics of 11 different occlusal registration strips under dry laboratory conditions.

In this study, 11 different occlusal registration strips (8 papers and 3 plastics) were tested for thickness, strength, plastic deformation and marking characteristics. These were Black-Check/¹ Ash Improved,¹³ Polydental,⁰ Bausch (blue and red),^d Bausch Dental,^d Betch,^e Hanel GHM^f (red and blue), David Scottlander§ and Sensicolor.^h

Thickness:

Micrometer¹ and PassameteH were used to measure the thickness of the occlusal registration strips. Five measurements were made for each type and mean values were calculated.

Strength:

An lnstron^k universal testing machine was used. The distance between the crossheads was 1.5 cm, loading was 10 kg, crosshead speeds for arti- culating papers were 10 mm/min and 100 mm/min for plastic strips. Four strips from each brand were tested to determine the mean values.

Plastic Deformation:

The   percentage   of  plastic   deformation   was calculated by dividing the increase in length at tear point by the original length of the strips.

Approximately 10N of force was applied five times for each strip on the stone block, which was located on a parallelometer [Fig. 1]. The load was applied by a 1 cm diameter steel ball [Fig. 2] which was tied to the parallelometers vertical arm [Fig. 3]. Photographs were taken and magnified (6x) to compare their sizes in mm² [Fig. 4]. The measurement was done by placing a transparent paper with millimeter squares onto the photographs, magnified to standard scales.

The thickness of the tested materials ranged between 22- 203 microns and strength values ranged between 0.85-2.75 kg/cm²; percentage of plastic deformation ranged between 3-124%, and marking characteristics ranged between 15-104 mm² as shown in Table 1. 

Hollstein¹¹ stated that the perception of occlusal thickness for a patient with natural teeth was 58 micron. The thickness of occlusal registration materials should be below the patient's perception. Therefore, selecting thinner articulating papers is important in producing accurate registration. Only five strips in this study met this demand.

Using a thicker articulating strip has two major disadvantages of which (1) it may display false markings and smears, and (2) the patient becomes astutely aware of the presence of a foreign substance between teeth, which may result in a false intercuspal relationship.

Tensile strength is the resistance in kilogram to the breakage of occlusal registration strip. Therefore, it is unrelated to thickness but is directly related to the plastic deformation of the material. In this study, the three thinnest strips showed the maximum tensile strengths.

The strips had varying percentages of plastic deformation. Although the deformation of plastic strips ranged between 52-124%, the plastic deformation of various articulating papers was only 10%. Occlusal registration strips that have lower plastic deformation are more brittle and, thus, they break long before the occlusal contact can be evaluated. All paper strips are brittle and are, therefore, not recommended as they tear when wet, which makes it an impractical material for evaluating occlusion intraorally.⁹ Plastic strips have another advantage of being unaffected by wetness.⁹

The results of this study supported that of Shelb⁷, who stated that the increase in thickness also increases      the      marking      ability.      Marking characteristics of the two strips, tested under the same conditions, were highly deviant with 20- 25% standard deviations (Table 1). Such high standard deviations, with the same articulating strip markings, suggests limited reliability of these two materials and that careful checking during handling is needed.

The selection and appropriate handling of occlusal articulating strips are important. Their thickness should be below 58 micron, and they should have adequate plastic deformation. Brittle materials, such as paper, are not desirable.

The thickness of the strips affected the size of the markings. Standard deviation in the marking characteristics of some materials suggested large variation. Therefore, even if the most appropriate articulating strip is chosen, markings should be checked several times before grinding.

Based on this study, Hanel GHM (blue and red) and Sensicolor seemed to meet optimal requirements.