The occlusalgraph: A graphic representation of photocclusion data

The occlusalgraph: A graphic photocclusion data

representation

Morton Amsterdam, D.D.S., D.Sc.,* Lyle C. Purdum, Katherine L. Purdum, B.A.***

M.S.,**

University

of Pennsylvania,

School

of Dental

Medicine,

Philadelphia,

liotocclusion is a relatively new dental technology that permits in vivo peak pressures of occlusion to be permanently recorded for comparison, analysis, diagnosis, and therapy. The objective of this preliminary report is the description of a graphical method of representing photocclusal data.

METHOD

DESCRIPTION

The recording device is a thin (0.1 mm) polymer sheet (memory wafer) of photoplastic material that records and maintains, in the form of birefringent strain patterns, the intensity of occlusal contacts (Fig. 1). To register the occlusal contacts, the wafer, which is light and designed to fit easily, is inserted into the patient’s mouth and the patient is asked to bite it in a normal (not clenching) manner for 10 seconds. After the wafer is removed, a specially designed polariscope is used to evaluate the occlusally recorded birefringent patterns. This optical instrument permits circularly polarized light to pass through the wafer and, in areas where it has been deformed by occlusal pressures, to obtain isochromatic colored stress (or birefringent) patterns as the indentations split the light into a color spectrum (Fig. 2). By relating these color patterns to a color calibration chart (Fig. 3) and a conversion scale (Table I), the patient-recorded occlusal contacts can be evaluated for different levels of intensity and strain. These birefringent patterns are similar to topographic ones and similar colors (or singular regions of color) represent equivalent retained contact strains. Although the bite force may not remain constant for separate recordings of the same occlusion, the locations of the peaks will remain in the same relative position and the ratio of their values will not change. For the photoplastic material used in the memory wafers (an olefin polymer), the recorded occlusal birefringent patterns have been shown experimental*Professor, Department of Periodontics. **Consultant in microwave and electromagnetics, Philadelphia, ***Administrator, Technical Projects Coordination, RCA Moorestown, N. J.

Pa. Corp.,

of

and

Pa.

Table I. Correlation of birefringent color patterns with percent of photocclusion wafer deformation Birefringent, (dimensionless)

Color Black Gray White Yellow Orange Red Tint of passage Blue Blue-Green Green-yellow Orange Red Tint of passage Blue-green Green

6.

Applied contact strain, em (%)

0 0.28 0.45 0.60 0.79 0.90 1.00 1.06 1.20 1.38 1.62 1.81 2.00 2.20 2.33

1

2

0 25 29 33 38 40 43 45 48 53 60 63 68 75 80

ly to be quantitatively related to the total applied strain of deformation in vivo (Table I).’ A recent study also established the theoretic basis for the memory wafer calibration and conversion data.2 This study used the inplane principal stress/strain constants and the inplane principal indices of refraction to correctly predict the relationship of the retained contact strain, t,, and the retained birefringent, 6,. The two contact geometries previously used in the experimental calibration study, that is, a static cylinder and a dynamic sphere, were also used for the theoretic analysis. The close agreement between the theoretic and experimental results obtained by this study indicates that a high degree of confidence can be placed in occlusal contact data obtained by this photocclusion method. Because the polariscope displays essentially all of the full arch occlusal data obtained when the patient bites on the wafer, it may be difficult for the dentist to quantify quickly (except in a very general manner) the viewed information. Several recent studies have shown that it is exceedingly difficult for most people to assimilate, coor-

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THE

OCCLUSALGRAPH

AND

PHOTOCCLUSION

Fig. 1. Birefringent patterns for occlusal contact intensities. patterns. B, Magnified view of contacts on a single tooth.

A, Wafer-recorded

contact

81TRARV ANGLE W VERTICAL

PLANE

NTEGER OTHER T”AlN TIPLES OF A/2 I I LEFT

POLARIZED

LIGHT

CIRCULAR

POLARIZER

hi&Xi~~*~ LINEAR POLARIZER EXTINCTION FOR GREEN I SzOO A I -RED OBSERVED MIXTURE FOR 0T”ER WAVELENGTHS

POLARISCOPE

SCREEN

Fig. 2. Operation of photocclusion

dinate, and understand more than three to five separate pieces of any type of information at any one time. For each recorded wafer of interest, the peak retained contact strain, as displayed on the polariscope screen, is recorded and plotted for pairs of occluding teeth on both sides of the dental arch. In accordance with the nomenclature adopted in a previous article,3 pairs of teeth (maxillary and mandibular) are identified as indicated in Table II. A sample occlusalgraph is shown in Fig. 4 and the recorded polariscope data from which it was plotted are given in Table III.

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polariscope.

The difference between the retained strain for each of the complementary pairs of teeth can be expressed in terms of the absolute value of the difference between the recorded strain on the right (E,J and the recorded strain on the left (E& or

and the magnitude of this difference gives at least a more quantified indication of the amount of unbalance as can be seen (Fig. 4). The average strain difference, Davg, is given by the

95

AMSTERDAM,

Table II. Nomenclature Position

Identification

First incisor Second incisor Canine First premolar Second premolar First molar Second molar

Table III.

Sample occlusal contact data Before

Tooth

After

Right

Left

D

Right

Left

D

48 38 0 -

0 0 45 -

48 38 45 -

53 48 53 53

53 45 0 48

0 3 53 5

PI pz M, M2

sum of the strain differences for each pair of teeth divided by the total number of contacts, or

D, + D, + ......D, N

n = 1,2,3.....N

The average peak strain value, Pavg,is also given by

N

I: P” =

P, + P, + .....P. N

n=123) ) ).....N

On the basis of these assumptions,and to further illustrate the simplicity of the method, some occlusal studies of patients previously described in the literature> 4together with a patient not previously presented, were graphed to show occlusalcontacts before and after therapy. As can be seen, the graphs clearly show the specific balance of complementary teeth acrossthe arch as well as their relationship to other teeth on the same side of the arch. This information can be applied to augment (not supplant) decisionsby the dentist as to whether occlusal adjustments are required or whether muscle spasm is involved. It may also provide direct comparisonsof the longitudinal effects of any therapeutic endeavors.Four clinical examples are included in an effort to clarify the application of this technique.

Patient control

I: Occlusal changes related of marginal inflammation

to the

The patient was diagnosedas having gingivitis with localized early periodontitis. No other pathologic condition was found. The initial occlusal imbalance of two 96

AND

PURDUM

high (deflective occlusal)right premolar contactsand one deflective occlusal left first molar contact is shown and, after nonocclusaltherapy, a dramatic changecan be seen (Fig. 4). The three double pairs are seento be closeto being balanced and the first molar deflective occlusal contact has switched from the left to the right side. Davg has decreasedfrom 44 to 15. The therapy up to this time consisted only of curettage, root scaling, and plaque control, with no occlusal adjustment. At this time a dental occlusal adjustment was made that raised the contact strain on the left and brought all four double contacting pairs very nearly into balance acrossthe whole dental arch (Fig. 5). As can be seen,the average difference was reduced from the 15 shown after nonocclusaltherapy (Fig. 4) to three (Fig. 5). That the Pavgincreasedto 62 from the initial 44 does not necessarily have any significance, inasmuch as the final relative distribution showslittle change from that obtained after the initial nonocclusal therapy (Fig. 5). The change, in fact, is probably due to the patient exerting more force while occluding on the wafer, indenting it more in the final measurement.

Patient II: Disharmonies related spasm and occlusal imbalance

N

pavg= !+

PURDUM,

to muscle

In this patient the initial deflective occlusal right contact of the canine and the first premolar and the deflective occlusal left contact of the secondpremolar is replacedafter therapy by closeto perfect balanceon both sidesof the arch (Fig. 6). Not only is the Davgreduced from 15 to six, but the overall peak values from anterior to posterior are generally more level aswell. The average peak value has only slightly changedfrom 40 to 47. Therapy for this patient consistedof ethyl chloride, Hawley bite plane treatment, jaw exercises,and occlusal adjustments.

Patient III: Pain in posterior muscle tenderness

teeth and bilateral

The overall musclebalance in this patient was significantly improved by lowering the right and raising the left contacts of the first molar (Fig. 7). The raised right contact of the secondpremolar also contributes to the improved equilibration. Therapy for this patient consistedof occlusal adjustments. The Davgin right and left contacts has decreased dramatically after treatment from 22 to four and the peaks from anterior to posterior have obviously become similar. The changein the Pavg, from 53 to 44 is, again, of relatively little significance.

Patient IV: Pain due to occlusal imbalance interference

and

The patient complainedof pain in the right ear during mastication as well as pain in the right temporomandibular joint. JANUARY

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Black

0

Tint of pasage ikf

of DclswDe

I I

Green 80% Peak Strain

Tint of passage Tint of passage Black

White

29% u,

0

u, 1ccrn

pa PcslTlcN

8

4

22;3”1

6

-

OJ M¶

I MI

1 T h

I 9

TOOTH POSITION

I c

4Pml

I Ia

0 -WONT LWT

A--

lwanl APTm

Fig. 3. Birefringent color pattern calibration chart. Fig. 4. Sample occlusalgraph. Patient I, marginal inflammation, before and after nonocclusal therapy. Fig. 5. Patient I after occlusal adjustment. Fig. 6. Patient II, muscle spasm and occlusal imbalance, before and after therapy. Fig. 7. Patient III, pain in posterior teeth and bilateral muscle tenderness, before and after occlusal adjustments. Fig. 8. Patient IV, pain due to occlusal imbalance and interference, before and after occlusal adjustments. THE

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PURDUM

The extreme initial imbalance of the deflective occlusal contacts on the right side was almost totally eliminated by occlusal adjustments that increased the contact strain on the left first molar, two premolars, and canines (Fig. 8). The Davg across the arch changed, in this instance, from 26 to three. The anterior to posterior peak values are similar, and the Pavgchanged slightly, probably as a result of increased biting pressure by the patient while making the wafer record.

CONCLUSION A simple graphic method (occlusalgraph) of representing memory wafer-recorded photocclusal data has been described. This method permits the dentist to easily quantify differences in occlusal contacts at a particular instant in time and makes it easier to compare changes in occlusal factors as a result of other therapeutic endeavors performed over a period of time. The method also

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permits patient occlusal data to be reviewed quickly and promises to greatly simplify long-term longitudinal studies and comparisons. REFERENCES Arcan M, Zandman F: Mechanics of contact and memorized birefringence. Seances Acad Sci 29&B-17, 1980. Amsterdam M, Purdum L, Purdum K: An occlusal indicating method based on photoplasticity. Science (in press). Amsterdam M, Baumgarten H, Rakocz M: Clinical use of an occlusal indicating method based on photoplasticity. Compend Contin Educ Gen Dent 111:126, 1982. Dawson P, Arcan M: Attaining harmonic occlusion through visualized strain analysis. J PROSTHET DENT 46~615, 1981. Reprint requests.. DR. MORTON AMSTERDAM 1601 WALNUT ST., 12~~ FLOOR MEDICAL ARTS BLDG. PHILADELPHIA, PA 19102

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