An occlusal contact may be formed by the meeting of two blunt surfaces or of the close contact of many irregular surfaces.³ Occlusal contacts may take place simultaneously or in a microsecond-long sequence.⁴ Near-contacts are those that appear to touch but do not.

Surface friction may occur when two surfaces rub over each other.⁵ Enamel may be smooth or rough, depending on its character and occlusal wear.⁶ Ceramic may be smooth or rough, depending on the specific ceramic, its glaze and the amount of wear.⁶ An indicator surface may be smooth or coarse, depending on the material and its thickness.⁷ Articulating film is thin and smooth, and it does not engage the many irregularities in an occlusal contact. Articulating paper may be thick and coarse, and it may create friction and resistance on occlusal contact.⁸

Tooth movement relates to positioning of the tooth in the periodontal housing.⁹ Movement may occur on occlusal contact or increase on resistance to an occlusal indicator. Implants do not move on occlusal contact.¹⁰ Recording occlusal contact of implants and vital teeth may require the use of a nonresistant indicator such as thin articulating film.¹¹

Impression materials have been used to record occlusal contacts.¹² Their flow characteristics allow closure without resistance. On setting, the material can be removed and occlusal contacts can be noted in it. A similar procedure is used in dentistry with the application of occlusal indicator wax.¹³ There is resistance to closure into the wax, whereas there is none to closure into the elastic impression materials. That is why an occlusal-indicator type of silicon impression material was used to mark the occlusal recordings.

Dentists need an accurate means of recording occlusal contacts. At present, clinical judgment of the marks made by occlusal contact indicators is the only method available for assessing occlusal contacts. A review of the literature related to occlusion and occlusal treatment reveals few articles that address the accuracy of occlusal contact marking indicators.^2,4,7,11 The accuracy of the many occlusal contact marking indicators is assumed by most practitioners despite the lack of either qualitative or quantitative evidence.

The accuracy of the many occlusal contact marking indicators is assumed by most practitioners despite the lack of either qualitative or quantitative evidence.

Therefore, we undertook a study to evaluate the accuracy of occlusal contact marking indicators and the reproducibility of their performance by measuring the areas of contact markings on occlusal contact areas.

	MATERIALS AND METHODS

TOP ABSTRACT MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSION REFERENCES

 
Mounting and contact procedure. We hand-articulated two impact-resistant resin casts of opposing arches in maximal intercuspal position and mounted them with stone (Mounting Stone, Whip Mix), mixed according to the manufacturer’s instructions, on an articulator (Artex, Jensen Industries) with a fixed and repeatable hinge axis. The mounting plates were split cast and magnetic, thus minimizing the possibility of our torquing the casts on removal and placement. The maxillary cast served as the control for testing the different marking media.

We opened the articulator 90 degrees, removed the incisal guide pin, placed two identical indicators on either side of the mandibular dentition and allowed the upper member of the articulator with the maxillary cast to fall to closure. Then we opened the articulator, videographed the markings, discarded the indicators and cleaned the casts of any markings. A total of 50 tests were made this way. We repeated the procedure five times for each indicator on the same articulator.

Materials. We evaluated 10 occlusal contact marking indicators. All were in strip form yet varied as to thickness, color and material. These are the 10 indicators we tested:

– articulating film (Arti-Fol II, Bausch/Pulpdent) black and red, 20 micrometers thick;

– articulating silk (Bausch), blue and red, 80 µm thick;

– articulating nylon band (Bausch), red, 120 µm thick;

– articulating paper in two thicknesses: 40 µm (blue and red [Bausch]) and 200 µm (blue [Bausch], referred to from this point forward as "blue paper 1"; blue [Rudischhauser, Sullivan Schein], referred to as "blue paper 2"; and blue [Mynol, Glaxo SmithKline], referred to as "blue paper 3").

To study the markings, we used a computer software program (Image Analyst, Automatix) that can process both live and stored image files and can extract quantitative data.¹⁴ We validated the reliability of the test system and the marking materials by measuring the positional accuracy of the dental casts on the articulator, verifying hinge axis repeatability and calibrating the program using samples of known shape.¹⁵ The application of the program for the evaluation of occlusal contact areas was based on the digitization of macroscopic video images that we recorded in a computer using a standard video camera (Pulnex TM-7EX, Pulnex). The camera used a microchip with an array of individual picture elements, called pixels. An optical image typically consists of many pixels with gray levels compressed into two or more ranges. The image was divided into a large number of pixels, and the gray level of each individual pixel was digitized and stored in the computer, resulting in the creation of a digital image.¹⁶ With the image analysis software, the number of pixels belonging to each gray level range can be quantified and compared with the total number of pixels in the entire image to determine the area fraction of a particular region of interest.¹⁴

Image analysis and processing. We removed the maxillary cast from the articulator once we had marked it with the indicator and placed it occlusal side up on a stand. We placed a photographic tent around the cast, then positioned two floodlights and a video camera 12 inches above the cast. The image of the cast was projected from the camera to a frame grabber and video screen. The information then was stored on a computer disk. Using the computer program, we blocked out extraneous areas such as shadows and measured areas of occlusal contact within the outlined area. We used the image analysis software to extract the quantitative data.

Evaluation of indicator marks. We made calculations using the data collected for surface area markings. Measurements were obtained for all contact indicator markings on the first and second molars on the right side. We made comparisons to determine changes in surface area.

It should be noted that the tests were not independent of one another, because we used the same dental casts throughout the investigation. We tested the measurements at a P = .05 significance level. We used Bonferroni-adjusted cutoffs in computing post hoc pairwise comparisons. Data for surface area were grouped into four categories:

– descriptive statistics;

– comparison of indicators by surface area markings;

– indicator thickness;

– repeatability of indicator performance.

For thickness comparisons, we used films 20 µm thick, silk 80 µm thick, and papers 40 µm and 200 µm thick.

	RESULTS

TOP ABSTRACT MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSION REFERENCES

 
Indicators differed in size of surface area markings. The thickness of the indicator and the material from which it was made had an effect on the size of the markings (Figure 1). Figure 1 shows the difference between the 20-µm–thick red articulating film and the 200-µm–thick blue paper 2. The first molar, or M1, and second molar, or M2, contact areas for the film are in the range of 2 square millimeters, or mm², whereas the M1 and M2 contact areas for the blue paper 2 are 11 mm² and 7.5 mm², respectively. The M1 markings with blue paper 2 are disproportionate to the M2 markings, whereas the M1 and M2 markings are equivalent for the 20-µm–thick film. Silk 80 µm thick produced significantly greater contact areas for the molars than did the 20-µm–thick articulating film. Blue paper 2 and blue paper 3, although of the same thickness and color, produced surface area markings that were significantly different from tooth to tooth and from marking to marking. Note the visual differences in M1 markings made from paper- and nylon-based indicators (Figures 2–4).

View larger version (53K): [in this window] [in a new window]   Figure 1. Comparison of indicators by surface area markings. µm: micrometers. mm2: square millimeters.

View larger version (134K): [in this window] [in a new window]   Figure 2. Computer image of first molar markings made by 40-micrometer–thick articulating paper.

View larger version (149K): [in this window] [in a new window]   Figure 3. Computer image of first molar markings made by 120-micrometer–thick articulating nylon band.

View larger version (124K): [in this window] [in a new window]   Figure 4. Computer image of first molar markings made by 200-micrometer–thick blue articulating paper (blue paper 2).

For M2, the ICC was 0.76 (95 percent CI, 0.56–0.96). This is marginally better than the result for M1, but the CI still is very wide, and there remains a substantial amount of variation that is not explained by the material used.

Comparisons by thickness of the indicator. Next, we compared the area marked by different indicators that were the same thickness. In other words, we compared the two 20-µm–thick indicators, the two 40-µm–thick indicators, the two 80-µm–thick indicators and the three 200-µm–thick indicators in four tests with each tooth. Table 2 presents a summary of all tests, as well as ICCs in each case.

Note that the results are not statistically significant, except at the 200-µm thickness. The low ICCs indicate that there is a great deal of variability within each indicator’s measures. Thus, looking again at Table 1, we see that the standard deviations generally are quite large compared with the differences in the means. We also see that at the 200-µm thickness, the differences are much larger than they are at other thicknesses and are large even compared with the standard deviations. For the comparisons at the 200-µm thickness, we also computed Bonferroni-adjusted post hoc pairwise comparisons. For each tooth, these showed that blue paper 1 and blue paper 2 differed from blue paper 3, but not from each other. Thus, even at 200 µm, the statistically significant result primarily is due to one particular material (blue paper 2).

Repeatability. There is no generally accepted, or generally useful, measure of repeatability in this situation. Instead, for each tooth, we present the minimum and maximum contact surface area for each of the 10 indicators (Table 3). If a clinician would make a different decision based on the minimum than he or she would make based on the maximum, then there clearly is a serious problem with the repeatability of these measures (Table 3).

	DISCUSSION

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An occlusal contact may be defined by its shape, size and position and by whether it actually makes occlusal or near-occlusal contact. Near-occlusal contacts may appear as actual contact areas, depending on the type of marking indicator that is used. In this study, there were many variations of the same contact. There was variation even when we used the same indicator. Such variation may indicate significant differences in what some clinicians view as an occlusal contact. One clinician may remove tooth structure during an occlusal equilibration, whereas another may choose not to. The clinical judgment may depend on the choice of occlusal contact marking indicator.

The dental literature is replete with case studies concerning occlusal interferences that create obstructions that, in turn, cause the mandible to deviate on closure. Clinicians use indicators to find such interferences. However, if the indicator interferes with closure, a false contact may occur. A false contact as defined in this context as one that does not exist even though it may be replicated. Practitioners must determine the validity of the indicator material.

Crown construction has saved many teeth and sustained the mandibular posture of countless patients. Yet many clinicians place restorations that prove to be underoccluded because a thick indicator registered a false contact.

Many clinicians place restorations that prove to be underoccluded because a thick indicator registered a false contact.

The results of this study indicate differences between and within samples tested. A single type of indicator may show extreme variation. The same indicator may present different markings on each closure. This does not take into account that, clinically, closures also may vary.¹²

In an ideal sense, all posterior teeth should contact simultaneously and the occlusal contacts should be evenly distributed. In a clinical sense, cuspal interferences create uneven distributions of pressure on occluding teeth that often do not contact simultaneously.¹⁷ An ideal indicator should mark only the designated contacts. It should be thin enough to negate positional errors induced by tooth displacement and extended jaw movements.

There are significant differences in thickness, color and plastic deformation of articulating paper and films. Patients can perceive minimal differences in thickness.¹⁸ The thickness of a marking indicator should be considered for two reasons:

– a patient may not perceive the excessive thickness, but it will be manifest in the occlusal markings;

– the use of various indicators will produce different results (films may deform readily or resist cuspal deformation; paper can be brittle and not compressible), and the degree to which an indicator deforms will affect its marking status.

The marking ingredients on indicators may contain waxes, oils, pigments and solvents. The indicators contain compounds to soften, harden or wet the surface and to release the pigment. The components and their formulae are proprietary.² All or some of these components come into play on tooth contact.

Occlusal contacts vary. They may be flat, sharp or round. Contact on closure is force-dependent. The force of closure and the shape of the opposing cusps can create extreme forces on the indicator, resulting in an explosion of the small ink capsules that compose the colorants on the marking film (Figure 4). Paper can compress and fragment. Furthermore, closing force differs for each person.

Repeatability is important because a lack of it can be clinically misleading. Our data show that throughout the study, maximum and minimum results differed. If the differences are small, then they most likely are clinically acceptable; however, if the differences are large, they may reflect faulty indicator materials or use. The 20-µm–thick articulating film and the 200-µm–thick blue paper 3 produced the least aberrations for a film and a paper.

	CONCLUSION

TOP ABSTRACT MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSION REFERENCES

 
Occlusal contact indicators vary. Since there are no specific directions for their use, nor any standards for measuring their results, clinicians may want to test indicators before using them.