- Email: [email protected]
An evaluation of occlusal contact marking indicators
cclusal contacts are made when mandibular teeth come into contact with maxillary teeth. Occlusal contact marking indicators are used to determine the specific areas of these occlusal contacts.1 These indicators are made of special materials that on occlusal contact transfer color from the indicator to the occlusal contact area.2 It is assumed that a color Occlusal mark represents a contact and that the contact marking transfer is accurate. An occlusal contact may be formed by indicators the meeting of two blunt surfaces or of vary, and the close contact of many irregular surtheir markings faces.3 Occlusal contacts may take place may not be simultaneously or in a microsecond-long repeatable even sequence.4 Near-contacts are those that when they are appear to touch but do not. Surface friction may occur when two used alike. 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
O
1280
IO N
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PHILIP MILLSTEIN, D.M.D., M.S.; ALVARO MAYA, D.M.D., M.S.D.
T
A descriptive quantitative method
Background. Dentistry needs an accurate means of recording occlusal contacts. The authors unA D A J dertook a study to eval✷ ✷ ® uate the accuracy of occlusal contact marking indicators and the reproN C ducibility of their results. A U I N G E D U 4 R TICLE Methods. The authors recorded occlusal contact areas using occlusal indicators made of paper, film and silk. They studied 10 indicators by testing them on articulator-mounted, impact-resistant casts and measuring the surface area of the resultant contact marks made on impact using a video camera, a frame grabber and a computer-linked image analyzer. Results. All indicators differed in surface area markings between and within groups. The indicator’s thickness and color and the material from which it was made separately and interactively had an effect on the size of the markings. Measurements were evaluated at a P = .05 significance level. The authors used Bonferroni-adjusted cutoffs when computing post hoc pairwise comparisons. The data were grouped into four categories: descriptive statistics, comparison of indicators by surface area marked, indicator thickness and repeatability. Conclusions. Indicators vary, and their markings may not be repeatable even when they are used alike. Further study is required, as is the development of an indicator measuring standard. Clinical Implications. Indicators are used to determine occlusal disharmony and to establish occlusal harmony. Since the accuracy of the markings can be questioned, the interpretation of the markings may be correct but the accuracy of the markings themselves may be misleading. CON
An evaluation of occlusal contact marking indicators
ABSTRACT
T
& R E S T O R AT I V E C A R E
A
COSMETIC
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 charac-
JADA, Vol. 132, September 2001 Copyright ©1998-2001 American Dental Association. All rights reserved.
COSMETIC
& RESTORATIVE CARE
teristics allow closure without resistance. On setvaried as to thickness, color and material. These ting, the material can be removed and occlusal are the 10 indicators we tested: contacts can be noted in it. A similar procedure is darticulating film (Arti-Fol II, Bausch/Pulpdent) used in dentistry with the application of occlusal black and red, 20 micrometers thick; indicator wax.13 There is resistance to closure into darticulating silk (Bausch), blue and red, 80 μm the wax, whereas there is none to closure into the thick; darticulating nylon band (Bausch), red, 120 μm elastic impression materials. That is why an thick; occlusal-indicator type of silicon impression matedarticulating paper in two thicknesses: 40 μm rial was used to mark the occlusal recordings. (blue and red [Bausch]) and 200 μm (blue Dentists need an accurate means of recording [Bausch], referred to from this point forward as occlusal contacts. At present, clinical judgment of “blue paper 1”; blue [Rudischhauser, Sullivan the marks made by occlusal contact indicators is Schein], referred to as “blue paper 2”; and blue the only method available for assessing occlusal [Mynol, Glaxo SmithKline], referred to as “blue contacts. A review of the literature related to paper 3”). occlusion and occlusal treatment reveals few To study the markings, we used a computer articles that address the accuracy of occlusal software program (Image Analyst, Automatix) contact marking indicators.2,4,7,11 The accuracy of that can process both live and stored image files the many occlusal contact marking indicators is and can extract quantitative data.14 assumed by most practitioners despite the lack of either qualitative We validated the reliability of the The accuracy of the or quantitative evidence. test system and the marking matemany occlusal Therefore, we undertook a study to rials by measuring the positional contact marking evaluate the accuracy of occlusal conaccuracy of the dental casts on the indicators is assumed articulator, verifying hinge axis tact marking indicators and the by most practitioners repeatability and calibrating the reproducibility of their performance despite the lack of by measuring the areas of contact program using samples of known markings on occlusal contact areas. shape.15 The application of the proeither qualitative or quantitative evidence. gram for the evaluation of occlusal MATERIALS AND METHODS contact areas was based on the digiMounting and contact procedure. tization of macroscopic video images We hand-articulated two impact-resistant resin that we recorded in a computer using a standard casts of opposing arches in maximal intercuspal video camera (Pulnex TM-7EX, Pulnex). The position and mounted them with stone (Mounting camera used a microchip with an array of indiStone, Whip Mix), mixed according to the manuvidual picture elements, called pixels. An optical facturer’s instructions, on an articulator (Artex, image typically consists of many pixels with gray Jensen Industries) with a fixed and repeatable levels compressed into two or more ranges. The hinge axis. The mounting plates were split cast image was divided into a large number of pixels, and magnetic, thus minimizing the possibility of and the gray level of each individual pixel was our torquing the casts on removal and placement. digitized and stored in the computer, resulting in The maxillary cast served as the control for testthe creation of a digital image.16 With the image ing the different marking media. analysis software, the number of pixels belonging We opened the articulator 90 degrees, removed to each gray level range can be quantified and the incisal guide pin, placed two identical indicacompared with the total number of pixels in the tors on either side of the mandibular dentition entire image to determine the area fraction of a and allowed the upper member of the articulator particular region of interest.14 with the maxillary cast to fall to closure. Then we Image analysis and processing. We opened the articulator, videographed the markremoved the maxillary cast from the articulator ings, discarded the indicators and cleaned the once we had marked it with the indicator and casts of any markings. A total of 50 tests were placed it occlusal side up on a stand. We placed a made this way. We repeated the procedure five photographic tent around the cast, then positimes for each indicator on the same articulator. tioned two floodlights and a video camera 12 Materials. We evaluated 10 occlusal contact inches above the cast. The image of the cast was marking indicators. All were in strip form yet projected from the camera to a frame grabber and JADA, Vol. 132, September 2001 Copyright ©1998-2001 American Dental Association. All rights reserved.
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COSMETIC
SURFACE AREA (mm2)
12
& RESTORATIVE CARE
Second molar First molar
10 8 6 4 2 0
Red Black Blue Red
Film
Paper 40 μm
Blue
Red
Silk
Red Blue 1 Blue 2 Blue 3
Nylon
Paper 200 μm
INDICATOR TYPE AND COLOR
Figure 1. Comparison of indicators by surface area markings. μm: micrometers. mm2: square millimeters.
Figure 2. Computer image of first molar markings made by 40-micrometer–thick articulating paper.
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 1282
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: ddescriptive statistics; dcomparison of indicators by surface area markings; dindicator thickness; drepeatability 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
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 nylonbased indicators (Figures 2-4). Descriptive statistics. Table 1 shows the means and standard deviations in measured surface area for the two molars. The results for both molars are highly variable. For example, with the 20-μm–thick film, the mean area for M2 differs by color (2.86 mm2 for black film vs. 2.26 mm2 for red film); the means for the red film shows greater variability for a smaller mean than does the black film. There is a great amount of variability between brands for the 200-μm–thick samples.
JADA, Vol. 132, September 2001 Copyright ©1998-2001 American Dental Association. All rights reserved.
COSMETIC
Variations in surface area range from 2.76 ± 0.27 mm2 (blue paper 3) to 7.56 ± 1.75 mm2 (blue paper 2) for M2 and from 2.57 ± 0.54 mm2 (blue paper 3) to 11.16 ± 2.57 mm2 (blue paper 2) for M1. There is great variability not only between brands, but also within brands (Table 1). Comparison of indicators by surface area marked. We used a one-way analysis of variance, or ANOVA, to compare the 10 indicators by the amount of surface area they marked. The results of the ANOVA aided us in computing the intraclass correlation coefficient, or ICC, for each indicator thickness. The ICC is the theoretical upper bound of the percentage of variation in surface area that is explainable by knowledge of the material used. For each tooth, the ANOVA test of whether the mean is the same for each indicator was rejected at the P < .00005 level (Table 2). For M1, the ICC was 0.74 (95 percent CI, 0.540.95). Whether it is acceptable to explain 74 percent of the variation, yet fail to explain 26 percent of the variation, is a subjective decision. However, the ICC was smaller than what it should be for materials that are supposed to be measuring the same thing. For M2, the ICC was 0.76 (95 percent CI, 0.560.96). 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 20μm–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
& RESTORATIVE CARE
Figure 3. Computer image of first molar markings made by 120-micrometer–thick articulating nylon band.
Figure 4. Computer image of first molar markings made by 200-micrometer–thick blue articulating paper (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
JADA, Vol. 132, September 2001 Copyright ©1998-2001 American Dental Association. All rights reserved.
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TABLE 1
thickness, surface deposition of inks, transferring media, MEAN CONTACT AREAS MARKED BY INDICATOR size of indicator, plastic MATERIALS TESTED. deformation and hygienic manufacturing procedures. MEAN AREA MARKED (mm2†) TYPE AND THICKNESS However, there is no mea± STANDARD DEVIATION (μm*) OF INDICATOR suring or marking standard First Molar Second Molar for dentistry. An occlusal contact may Film—20 2.16 ± 0.56 2.26 ± 0.48 Red be defined by its shape, size 2.61 ± 0.50 2.86 ± 0.30 Black and position and by whether Paper it actually makes occlusal or 40 near-occlusal contact. Near4.46 ± 1.22 3.63 ± 0.50 Blue 3.69 ± 1.62 3.36 ± 0.35 Red occlusal contacts may appear 200 as actual contact areas, 4.84 ± 1.79 4.53 ± 1.28 Blue paper 1 11.16 ± 2.57 7.56 ± 1.75 Blue paper 2 depending on the type of 2.57 ± 0.54 2.76 ± 0.27 Blue paper 3 marking indicator that is Silk—80 used. In this study, there 4.48 ± 1.54 4.02 ± 0.83 Blue were many variations of the 5.01 ± 0.98 4.14 ± 0.47 Red same contact. There was Nylon—120 variation even when we used 2.86 ± 1.42 2.55 ± 1.05 Red the same indicator. Such * μm: Micrometers. variation may indicate sig† mm : Square millimeters. nificant differences in what some clinicians view as an occlusal contact. One clinician may remove tooth (Table 3). If a clinician would make a different structure during an occlusal equilibration, decision based on the minimum than he or she whereas another may choose not to. The clinical would make based on the maximum, then there judgment may depend on the choice of occlusal clearly is a serious problem with the repeatability contact marking indicator. of these measures (Table 3). The dental literature is replete with case DISCUSSION studies concerning occlusal interferences that create obstructions that, in turn, cause the There are many different kinds of occlusal contact mandible to deviate on closure. Clinicians use marking indicators. They vary in thickness, color indicators to find such interferences. However, if and type of transferring medium used (paper vs. the indicator interferes with closure, a false confilm, marking ink vs. wax). The manufacture of tact may occur. A false contact as defined in this these materials is controlled for uniformity of 2
TABLE 2
EFFECTS OF INDICATOR THICKNESS, BY TOOTH. INDICATOR THICKNESS (μm*)
SECOND MOLAR
FIRST MOLAR P Value
ICC † (95% CI ‡)
20
.21
0.14 (0.0-0.94)
.046
0.48 (0.0-1.00)
40
.42
0.0 (0.0-0.59)
.34
0.005 (0.0-0.60)
80
.53
0.0 (0.0-0.59)
.79
0.0 (0.0-0.59)
< .00005
0.85 (0.57-1.00)
.0002
0.78 (0.39-1.00)
200
P Value
ICC (95% CI)
* μm: Micrometers. † ICC: Intraclass correlation coefficient, the theoretical upper bound of the percentage of variation in surface area that is explainable by knowledge of the material used. ‡ CI: Confidence interval.
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JADA, Vol. 132, September 2001 Copyright ©1998-2001 American Dental Association. All rights reserved.
COSMETIC
& RESTORATIVE CARE
TABLE 3
MAXIMUM AND MINIMUM SURFACE CONTACT AREAS (mm2*). INDICATOR—THICKNESS
FIRST MOLAR
SECOND MOLAR Minimum Contact Area
Maximum Contact Area
Minimum Contact Area
Maximum Contact Area
1.24 2.01
2.70 3.10
1.52 2.57
2.66 3.26
2.76 1.63
6.22 5.60
2.95 2.91
4.29 3.79
1.72 6.68 2.02
6.25 13.25 3.28
2.37 4.63 2.45
5.71 9.12 3.05
Silk—80 Blue Red
2.72 4.10
6.35 6.54
3.03 3.65
5.02 4.83
Nylon—120 Red
1.82
5.31
1.76
4.39
Film—20 Red Black Paper 40 Blue Red 200 Blue 1 Blue 2 Blue 3
* mm2: Square millimeters.
context as one that does not exist even though it ences in thickness.18 The thickness of a marking may be replicated. Practitioners must determine indicator should be considered for two reasons: the validity of the indicator material. da patient may not perceive the Crown construction has saved excessive thickness, but it will be Many clinicians many teeth and sustained the manifest in the occlusal markings; place restorations mandibular posture of countless dthe use of various indicators will patients. Yet many clinicians place produce different results (films may that prove to be restorations that prove to be underocdeform readily or resist cuspal underoccluded cluded because a thick indicator regdeformation; paper can be brittle because a thick istered a false contact. and not compressible), and the indicator registered The results of this study indicate degree to which an indicator a false contact. differences between and within samdeforms will affect its marking ples tested. A single type of indicator status. may show extreme variation. The The marking ingredients on indisame indicator may present different markings on cators may contain waxes, oils, pigments and soleach closure. This does not take into account that, vents. The indicators contain compounds to clinically, closures also may vary.12 soften, harden or wet the surface and to release In an ideal sense, all posterior teeth should the pigment. The components and their formulae contact simultaneously and the occlusal contacts are proprietary.2 All or some of these components should be evenly distributed. In a clinical sense, come into play on tooth contact. cuspal interferences create uneven distributions Occlusal contacts vary. They may be flat, sharp of pressure on occluding teeth that often do not or round. Contact on closure is force-dependent. contact simultaneously.17 An ideal indicator The force of closure and the shape of the opposing should mark only the designated contacts. It cusps can create extreme forces on the indicator, should be thin enough to negate positional errors resulting in an explosion of the small ink capsules induced by tooth displacement and extended jaw that compose the colorants on the marking film movements. (Figure 4). Paper can compress and fragment. There are significant differences in thickness, Furthermore, closing force differs for each person. color and plastic deformation of articulating paper Repeatability is important because a lack of it and films. Patients can perceive minimal differcan be clinically misleading. Our data show that JADA, Vol. 132, September 2001 Copyright ©1998-2001 American Dental Association. All rights reserved.
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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 20μm–thick articulating film and the 200-μm–thick blue paper 3 produced the least aberrations for a film and a paper. CONCLUSION
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. ■ Dr. Millstein is a clinical professor, Tufts University School of Dental Medicine, Boston. Address reprint requests to Dr. Millstein at 15 Langdon St., Cambridge, Mass. 02138, e-mail “[email protected]”. Dr. Maya is in private practice in Westford, Mass. The authors acknowledge the help of Richard Goldstein, Ph.D., for sharing his statistical expertise in integrating the data. The results of this study were presented first at the 74th General Session and Exhibition of the International Association for Dental Research, San Francisco, March 1996. 1. Millstein PL. An evaluation of occlusal contact marking indicators: a descriptive, qualitative method. Quintessence Int 1983;14:813-36. 2. Schelb E, Kaiser DA, Brukl CE. Thickness and marking characteristics of occlusal registration strips. J Prosthet Dent 1985;54(1):122-6.
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3. Millstein PL. A method to determine occlusal contact and noncontact areas: preliminary report. J Prosthet Dent 1984;52(1):106-10. 4. Zuccari AG, Oshida Y, Okamura M, Paez CY, Moore BK. Bulge ductility of several occlusal contact measuring paper-based and plasticbased sheets. Biomed Mater Eng 1997;7:265-70. 5. O’Brien WJ, Ryge G. An outline of dental materials and their selection. Philadelphia: Saunders; 1978:395. 6. Leinfelder KF. Porcelain esthetics for the 21st century. JADA 2000;131:1186-7. 7. Millstein PL, Alibrandi S. Occlusal contact marking indicators for improved dentist-technician communication. Quintessence Dent Technol 1984;8(4):247-8. 8. Millstein PL, Alibrandi S. The dual effect of articulating film for improved dentist-technician communication. Quintessence Dent Technol 1984;8:495-6. 9. Bien SM. The mechanism of tooth movement: an investigative approach. N Y J Dent 1966;36(6):191-2. 10. Pesun IJ. Intrusion of teeth in the combination implant-to-natural-tooth fixed partial denture: a review of the theories. J Prosthodont 1997;6:268-77. 11. Halperin GC, Halperin AR, Norling BK. Thickness, strength, and plastic deformation of occlusal registration strips. J Prosthet Dent 1982;48:575-8. 12. Molligoda MA, Berry DC, Gooding PG. Measuring diurnal variations in occlusal contact areas. J Prosthet Dent 1986;56(4):487-92. 13. Millstein PL. An evaluation of occlusal indicator wax. J Prosthet Dent 1985;53:570-2. 14. Russ JC. The image processing handbook. Boca Raton, Fla.: CRC Press; 1992:1-53. 15. Hatzi P, Millstein P, Maya A. Determining the accuracy of articulator interchangeability and hinge axis reproducibility. J Prosthet Dent 2001;85(3):236-45. 16. Sakaguchi RL, Anderson GC, DeLong R. Digital imaging of occlusal contacts in the intercuspal position. J Prosthodont 1994;3(4): 193-7. 17. Korioth TW. Number and location of occlusal contacts in intercuspal position. J Prosthet Dent 1990;64:206-10. 18. Karlsson S, Molin M. Effects of gold and bonded ceramic inlays on the ability to perceive occlusal thickness. J Oral Rehabil 1995;22(1): 9-13.
JADA, Vol. 132, September 2001 Copyright ©1998-2001 American Dental Association. All rights reserved.
O
1280
IO N
I
PHILIP MILLSTEIN, D.M.D., M.S.; ALVARO MAYA, D.M.D., M.S.D.
T
A descriptive quantitative method
Background. Dentistry needs an accurate means of recording occlusal contacts. The authors unA D A J dertook a study to eval✷ ✷ ® uate the accuracy of occlusal contact marking indicators and the reproN C ducibility of their results. A U I N G E D U 4 R TICLE Methods. The authors recorded occlusal contact areas using occlusal indicators made of paper, film and silk. They studied 10 indicators by testing them on articulator-mounted, impact-resistant casts and measuring the surface area of the resultant contact marks made on impact using a video camera, a frame grabber and a computer-linked image analyzer. Results. All indicators differed in surface area markings between and within groups. The indicator’s thickness and color and the material from which it was made separately and interactively had an effect on the size of the markings. Measurements were evaluated at a P = .05 significance level. The authors used Bonferroni-adjusted cutoffs when computing post hoc pairwise comparisons. The data were grouped into four categories: descriptive statistics, comparison of indicators by surface area marked, indicator thickness and repeatability. Conclusions. Indicators vary, and their markings may not be repeatable even when they are used alike. Further study is required, as is the development of an indicator measuring standard. Clinical Implications. Indicators are used to determine occlusal disharmony and to establish occlusal harmony. Since the accuracy of the markings can be questioned, the interpretation of the markings may be correct but the accuracy of the markings themselves may be misleading. CON
An evaluation of occlusal contact marking indicators
ABSTRACT
T
& R E S T O R AT I V E C A R E
A
COSMETIC
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 charac-
JADA, Vol. 132, September 2001 Copyright ©1998-2001 American Dental Association. All rights reserved.
COSMETIC
& RESTORATIVE CARE
teristics allow closure without resistance. On setvaried as to thickness, color and material. These ting, the material can be removed and occlusal are the 10 indicators we tested: contacts can be noted in it. A similar procedure is darticulating film (Arti-Fol II, Bausch/Pulpdent) used in dentistry with the application of occlusal black and red, 20 micrometers thick; indicator wax.13 There is resistance to closure into darticulating silk (Bausch), blue and red, 80 μm the wax, whereas there is none to closure into the thick; darticulating nylon band (Bausch), red, 120 μm elastic impression materials. That is why an thick; occlusal-indicator type of silicon impression matedarticulating paper in two thicknesses: 40 μm rial was used to mark the occlusal recordings. (blue and red [Bausch]) and 200 μm (blue Dentists need an accurate means of recording [Bausch], referred to from this point forward as occlusal contacts. At present, clinical judgment of “blue paper 1”; blue [Rudischhauser, Sullivan the marks made by occlusal contact indicators is Schein], referred to as “blue paper 2”; and blue the only method available for assessing occlusal [Mynol, Glaxo SmithKline], referred to as “blue contacts. A review of the literature related to paper 3”). occlusion and occlusal treatment reveals few To study the markings, we used a computer articles that address the accuracy of occlusal software program (Image Analyst, Automatix) contact marking indicators.2,4,7,11 The accuracy of that can process both live and stored image files the many occlusal contact marking indicators is and can extract quantitative data.14 assumed by most practitioners despite the lack of either qualitative We validated the reliability of the The accuracy of the or quantitative evidence. test system and the marking matemany occlusal Therefore, we undertook a study to rials by measuring the positional contact marking evaluate the accuracy of occlusal conaccuracy of the dental casts on the indicators is assumed articulator, verifying hinge axis tact marking indicators and the by most practitioners repeatability and calibrating the reproducibility of their performance despite the lack of by measuring the areas of contact program using samples of known markings on occlusal contact areas. shape.15 The application of the proeither qualitative or quantitative evidence. gram for the evaluation of occlusal MATERIALS AND METHODS contact areas was based on the digiMounting and contact procedure. tization of macroscopic video images We hand-articulated two impact-resistant resin that we recorded in a computer using a standard casts of opposing arches in maximal intercuspal video camera (Pulnex TM-7EX, Pulnex). The position and mounted them with stone (Mounting camera used a microchip with an array of indiStone, Whip Mix), mixed according to the manuvidual picture elements, called pixels. An optical facturer’s instructions, on an articulator (Artex, image typically consists of many pixels with gray Jensen Industries) with a fixed and repeatable levels compressed into two or more ranges. The hinge axis. The mounting plates were split cast image was divided into a large number of pixels, and magnetic, thus minimizing the possibility of and the gray level of each individual pixel was our torquing the casts on removal and placement. digitized and stored in the computer, resulting in The maxillary cast served as the control for testthe creation of a digital image.16 With the image ing the different marking media. analysis software, the number of pixels belonging We opened the articulator 90 degrees, removed to each gray level range can be quantified and the incisal guide pin, placed two identical indicacompared with the total number of pixels in the tors on either side of the mandibular dentition entire image to determine the area fraction of a and allowed the upper member of the articulator particular region of interest.14 with the maxillary cast to fall to closure. Then we Image analysis and processing. We opened the articulator, videographed the markremoved the maxillary cast from the articulator ings, discarded the indicators and cleaned the once we had marked it with the indicator and casts of any markings. A total of 50 tests were placed it occlusal side up on a stand. We placed a made this way. We repeated the procedure five photographic tent around the cast, then positimes for each indicator on the same articulator. tioned two floodlights and a video camera 12 Materials. We evaluated 10 occlusal contact inches above the cast. The image of the cast was marking indicators. All were in strip form yet projected from the camera to a frame grabber and JADA, Vol. 132, September 2001 Copyright ©1998-2001 American Dental Association. All rights reserved.
1281
COSMETIC
SURFACE AREA (mm2)
12
& RESTORATIVE CARE
Second molar First molar
10 8 6 4 2 0
Red Black Blue Red
Film
Paper 40 μm
Blue
Red
Silk
Red Blue 1 Blue 2 Blue 3
Nylon
Paper 200 μm
INDICATOR TYPE AND COLOR
Figure 1. Comparison of indicators by surface area markings. μm: micrometers. mm2: square millimeters.
Figure 2. Computer image of first molar markings made by 40-micrometer–thick articulating paper.
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 1282
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: ddescriptive statistics; dcomparison of indicators by surface area markings; dindicator thickness; drepeatability 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
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 nylonbased indicators (Figures 2-4). Descriptive statistics. Table 1 shows the means and standard deviations in measured surface area for the two molars. The results for both molars are highly variable. For example, with the 20-μm–thick film, the mean area for M2 differs by color (2.86 mm2 for black film vs. 2.26 mm2 for red film); the means for the red film shows greater variability for a smaller mean than does the black film. There is a great amount of variability between brands for the 200-μm–thick samples.
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COSMETIC
Variations in surface area range from 2.76 ± 0.27 mm2 (blue paper 3) to 7.56 ± 1.75 mm2 (blue paper 2) for M2 and from 2.57 ± 0.54 mm2 (blue paper 3) to 11.16 ± 2.57 mm2 (blue paper 2) for M1. There is great variability not only between brands, but also within brands (Table 1). Comparison of indicators by surface area marked. We used a one-way analysis of variance, or ANOVA, to compare the 10 indicators by the amount of surface area they marked. The results of the ANOVA aided us in computing the intraclass correlation coefficient, or ICC, for each indicator thickness. The ICC is the theoretical upper bound of the percentage of variation in surface area that is explainable by knowledge of the material used. For each tooth, the ANOVA test of whether the mean is the same for each indicator was rejected at the P < .00005 level (Table 2). For M1, the ICC was 0.74 (95 percent CI, 0.540.95). Whether it is acceptable to explain 74 percent of the variation, yet fail to explain 26 percent of the variation, is a subjective decision. However, the ICC was smaller than what it should be for materials that are supposed to be measuring the same thing. For M2, the ICC was 0.76 (95 percent CI, 0.560.96). 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 20μm–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
& RESTORATIVE CARE
Figure 3. Computer image of first molar markings made by 120-micrometer–thick articulating nylon band.
Figure 4. Computer image of first molar markings made by 200-micrometer–thick blue articulating paper (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
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TABLE 1
thickness, surface deposition of inks, transferring media, MEAN CONTACT AREAS MARKED BY INDICATOR size of indicator, plastic MATERIALS TESTED. deformation and hygienic manufacturing procedures. MEAN AREA MARKED (mm2†) TYPE AND THICKNESS However, there is no mea± STANDARD DEVIATION (μm*) OF INDICATOR suring or marking standard First Molar Second Molar for dentistry. An occlusal contact may Film—20 2.16 ± 0.56 2.26 ± 0.48 Red be defined by its shape, size 2.61 ± 0.50 2.86 ± 0.30 Black and position and by whether Paper it actually makes occlusal or 40 near-occlusal contact. Near4.46 ± 1.22 3.63 ± 0.50 Blue 3.69 ± 1.62 3.36 ± 0.35 Red occlusal contacts may appear 200 as actual contact areas, 4.84 ± 1.79 4.53 ± 1.28 Blue paper 1 11.16 ± 2.57 7.56 ± 1.75 Blue paper 2 depending on the type of 2.57 ± 0.54 2.76 ± 0.27 Blue paper 3 marking indicator that is Silk—80 used. In this study, there 4.48 ± 1.54 4.02 ± 0.83 Blue were many variations of the 5.01 ± 0.98 4.14 ± 0.47 Red same contact. There was Nylon—120 variation even when we used 2.86 ± 1.42 2.55 ± 1.05 Red the same indicator. Such * μm: Micrometers. variation may indicate sig† mm : Square millimeters. nificant differences in what some clinicians view as an occlusal contact. One clinician may remove tooth (Table 3). If a clinician would make a different structure during an occlusal equilibration, decision based on the minimum than he or she whereas another may choose not to. The clinical would make based on the maximum, then there judgment may depend on the choice of occlusal clearly is a serious problem with the repeatability contact marking indicator. of these measures (Table 3). The dental literature is replete with case DISCUSSION studies concerning occlusal interferences that create obstructions that, in turn, cause the There are many different kinds of occlusal contact mandible to deviate on closure. Clinicians use marking indicators. They vary in thickness, color indicators to find such interferences. However, if and type of transferring medium used (paper vs. the indicator interferes with closure, a false confilm, marking ink vs. wax). The manufacture of tact may occur. A false contact as defined in this these materials is controlled for uniformity of 2
TABLE 2
EFFECTS OF INDICATOR THICKNESS, BY TOOTH. INDICATOR THICKNESS (μm*)
SECOND MOLAR
FIRST MOLAR P Value
ICC † (95% CI ‡)
20
.21
0.14 (0.0-0.94)
.046
0.48 (0.0-1.00)
40
.42
0.0 (0.0-0.59)
.34
0.005 (0.0-0.60)
80
.53
0.0 (0.0-0.59)
.79
0.0 (0.0-0.59)
< .00005
0.85 (0.57-1.00)
.0002
0.78 (0.39-1.00)
200
P Value
ICC (95% CI)
* μm: Micrometers. † ICC: Intraclass correlation coefficient, the theoretical upper bound of the percentage of variation in surface area that is explainable by knowledge of the material used. ‡ CI: Confidence interval.
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TABLE 3
MAXIMUM AND MINIMUM SURFACE CONTACT AREAS (mm2*). INDICATOR—THICKNESS
FIRST MOLAR
SECOND MOLAR Minimum Contact Area
Maximum Contact Area
Minimum Contact Area
Maximum Contact Area
1.24 2.01
2.70 3.10
1.52 2.57
2.66 3.26
2.76 1.63
6.22 5.60
2.95 2.91
4.29 3.79
1.72 6.68 2.02
6.25 13.25 3.28
2.37 4.63 2.45
5.71 9.12 3.05
Silk—80 Blue Red
2.72 4.10
6.35 6.54
3.03 3.65
5.02 4.83
Nylon—120 Red
1.82
5.31
1.76
4.39
Film—20 Red Black Paper 40 Blue Red 200 Blue 1 Blue 2 Blue 3
* mm2: Square millimeters.
context as one that does not exist even though it ences in thickness.18 The thickness of a marking may be replicated. Practitioners must determine indicator should be considered for two reasons: the validity of the indicator material. da patient may not perceive the Crown construction has saved excessive thickness, but it will be Many clinicians many teeth and sustained the manifest in the occlusal markings; place restorations mandibular posture of countless dthe use of various indicators will patients. Yet many clinicians place produce different results (films may that prove to be restorations that prove to be underocdeform readily or resist cuspal underoccluded cluded because a thick indicator regdeformation; paper can be brittle because a thick istered a false contact. and not compressible), and the indicator registered The results of this study indicate degree to which an indicator a false contact. differences between and within samdeforms will affect its marking ples tested. A single type of indicator status. may show extreme variation. The The marking ingredients on indisame indicator may present different markings on cators may contain waxes, oils, pigments and soleach closure. This does not take into account that, vents. The indicators contain compounds to clinically, closures also may vary.12 soften, harden or wet the surface and to release In an ideal sense, all posterior teeth should the pigment. The components and their formulae contact simultaneously and the occlusal contacts are proprietary.2 All or some of these components should be evenly distributed. In a clinical sense, come into play on tooth contact. cuspal interferences create uneven distributions Occlusal contacts vary. They may be flat, sharp of pressure on occluding teeth that often do not or round. Contact on closure is force-dependent. contact simultaneously.17 An ideal indicator The force of closure and the shape of the opposing should mark only the designated contacts. It cusps can create extreme forces on the indicator, should be thin enough to negate positional errors resulting in an explosion of the small ink capsules induced by tooth displacement and extended jaw that compose the colorants on the marking film movements. (Figure 4). Paper can compress and fragment. There are significant differences in thickness, Furthermore, closing force differs for each person. color and plastic deformation of articulating paper Repeatability is important because a lack of it and films. Patients can perceive minimal differcan be clinically misleading. Our data show that JADA, Vol. 132, September 2001 Copyright ©1998-2001 American Dental Association. All rights reserved.
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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 20μm–thick articulating film and the 200-μm–thick blue paper 3 produced the least aberrations for a film and a paper. CONCLUSION
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. ■ Dr. Millstein is a clinical professor, Tufts University School of Dental Medicine, Boston. Address reprint requests to Dr. Millstein at 15 Langdon St., Cambridge, Mass. 02138, e-mail “[email protected]”. Dr. Maya is in private practice in Westford, Mass. The authors acknowledge the help of Richard Goldstein, Ph.D., for sharing his statistical expertise in integrating the data. The results of this study were presented first at the 74th General Session and Exhibition of the International Association for Dental Research, San Francisco, March 1996. 1. Millstein PL. An evaluation of occlusal contact marking indicators: a descriptive, qualitative method. Quintessence Int 1983;14:813-36. 2. Schelb E, Kaiser DA, Brukl CE. Thickness and marking characteristics of occlusal registration strips. J Prosthet Dent 1985;54(1):122-6.
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3. Millstein PL. A method to determine occlusal contact and noncontact areas: preliminary report. J Prosthet Dent 1984;52(1):106-10. 4. Zuccari AG, Oshida Y, Okamura M, Paez CY, Moore BK. Bulge ductility of several occlusal contact measuring paper-based and plasticbased sheets. Biomed Mater Eng 1997;7:265-70. 5. O’Brien WJ, Ryge G. An outline of dental materials and their selection. Philadelphia: Saunders; 1978:395. 6. Leinfelder KF. Porcelain esthetics for the 21st century. JADA 2000;131:1186-7. 7. Millstein PL, Alibrandi S. Occlusal contact marking indicators for improved dentist-technician communication. Quintessence Dent Technol 1984;8(4):247-8. 8. Millstein PL, Alibrandi S. The dual effect of articulating film for improved dentist-technician communication. Quintessence Dent Technol 1984;8:495-6. 9. Bien SM. The mechanism of tooth movement: an investigative approach. N Y J Dent 1966;36(6):191-2. 10. Pesun IJ. Intrusion of teeth in the combination implant-to-natural-tooth fixed partial denture: a review of the theories. J Prosthodont 1997;6:268-77. 11. Halperin GC, Halperin AR, Norling BK. Thickness, strength, and plastic deformation of occlusal registration strips. J Prosthet Dent 1982;48:575-8. 12. Molligoda MA, Berry DC, Gooding PG. Measuring diurnal variations in occlusal contact areas. J Prosthet Dent 1986;56(4):487-92. 13. Millstein PL. An evaluation of occlusal indicator wax. J Prosthet Dent 1985;53:570-2. 14. Russ JC. The image processing handbook. Boca Raton, Fla.: CRC Press; 1992:1-53. 15. Hatzi P, Millstein P, Maya A. Determining the accuracy of articulator interchangeability and hinge axis reproducibility. J Prosthet Dent 2001;85(3):236-45. 16. Sakaguchi RL, Anderson GC, DeLong R. Digital imaging of occlusal contacts in the intercuspal position. J Prosthodont 1994;3(4): 193-7. 17. Korioth TW. Number and location of occlusal contacts in intercuspal position. J Prosthet Dent 1990;64:206-10. 18. Karlsson S, Molin M. Effects of gold and bonded ceramic inlays on the ability to perceive occlusal thickness. J Oral Rehabil 1995;22(1): 9-13.
JADA, Vol. 132, September 2001 Copyright ©1998-2001 American Dental Association. All rights reserved.