Measuring wear of artificial teeth with stereophotography: Part I

Measuring wear of artificial teeth with stereophotography: Part I

DENTURE-WEARING AND ORAL HEALTH care and oral hygiene for the life of the patient. Dentures and mouths need examination and care for life. Only by...

2MB Sizes 0 Downloads 13 Views

DENTURE-WEARING

AND

ORAL

HEALTH

care and oral hygiene for the life of the patient. Dentures and mouths need examination and care for life. Only by regular visits to the dentist can this be accomplished. Dentures seldom change: mouths do. Regular visits allow professional evaluation of the oral tissues and the functioning jaw-joint mechanism to detect early treatment needs of the tissue and/or the denture. This interface must be intimate, vibrant, healthy, clean, and comfortable. To this end only, the professional person with a depth of knowledge, total education, keen insight to the anatomy, physiology, total body health, and the psyche and its interrelations to the inanimate prosthesis can make the denture an integral part of the living being. The dentist can keep it that way with the patient’s cooperation. Dentures can be one of the best replacements of human body parts; but professional care and good home care are essential.

The patient is responsible for good care of his or her general health. Regular physical check-ups are essential. Proper nutritional habits and supplements are to be guided by a professional. “The food, diet and nutritional needs of the elderly patient should be considered a part of his total supportive management. It is encumbent upon the dentist to provide the patient with this nutritional information for optimal oral health, because what is good for preventing oral disease will be equally good for preventing general illness.“3 Ample sleep and general good care of the body and psyche are each individual’s responsibility. If the general health suffers, so does the whole stomatognathic system and denture-bearing tissues. Unfortunately, patients who neglect their natural teeth neglect their general health. They do not eat properly and do not follow instructions. The dentist frequently sees this in the poor health of the orofacial mechanism. Showing the patient the findings, taking a dietary history, reviewing nutritional needs, supplements, and oral health care are essential. If need be, the dentist should review his findings with the patient’s physician. ~If this stimulates better care of the patient’s total health, everyone is a winner. If the physician does not cooperate, the dentist must do the best he can for the patient as circumstances allow.

REFERENCES 1.

Lytle RC: Management of abused oral tissues in complete denture construction. J PROSTHU DENT 7~27, 1957. 2. Lytle RB: Soft tissue displacement beneath removable partial dentures and complete dentures. J PROSTHET DENT 12:34. 1962. 3. Nizel AE: Nutrition in the oral health of the aging patient. Dent Clin North Am 20:569, 1967. Refmt

A frank discussion at the beginning of treatment will inform the patient of what is possible in denture fabrication as well as in proper and responsible denture

Measuring wear of artificial stereophotography: Part I

requesb

to:

DR. DOUGLASC. WENDT FAIRFAX SQUARE 9870 MAIN ST. FAIRFAX, VA 22031

SUMMARY

teeth with

R. E. Ogle, D.D.S.,* and L. F. Ortman, D.D.S., M.S.* State University of New York, School of Dentistry, Buffalo, N.Y.

A

n apparatus that uses twin cameras for stereoimaging has been developed to measure accurately in vivo wear of artificial teeth in complete dentures. The new measuring technique is called close-range photogrammetry. The data reduction system is the same as that used by photogrammetrists for measuring and mapping the earth’s surface from aerial photographs. A general definition of stereophotogrammetry, was *Associate Professor, Department of Removable Prosthodontics THE JOURNAL

OF PROSTHETIC

DENTISTRY

given by Hallert.’ It is “the science of measurement with the aid of photographs in order to determine geometrical data such as size, shape, and position of photographed objects.” With stereophotography, a spatial or optical model that can be accurately measured is created. The principle behind the creation of the model is binocular vision. The two eyes send slightly different images of an object to the brain. These slightly different images are then interpreted in terms of depth, length, and breadth. Similarly, if two binocular or stereophotographs of an 807

OGLE AND

-AXIS

ORTMAN

OF LENS CANT -

Fig. 1. Acquisition

component of close-range stereophotogrammetric system. A = Camera bodies mounted at 17-degree angle to object plane; B = camera cradle

with adjustable

stage; C = dual release cables; D = fibe-

-43.54

roptic light sources; and E = complete denture positioned within

reference

frame.

object are juxtaposed so that the left eye sees the left photograph and the right eye sees the right photograph in proper relation, the perception of depth can be as clear as if the object were seen directly.* To capture and create the stereoscopic model, two components are needed: (1) an acquisition component to obtain the stereophotographs and (2) a reduction component to generate measurement data. There are two basic types of acquisition. The more common type uses two camera axes that are parallel to each other and perpendicular to the object plane. This type of stereophotography is used principally for aerial and terrestial surveying. The other type is that of convergent stereophotography. In this type, the two camera axes interact at an external conjugate of the fixed-focus lenses to form an isosceles triangle of known dimensions. The use of convergent photography allows greater access into the oral cavity. This system also provides 100% overlap between stereopairs, which accentuates the impression of depth and provides greater accuracy in measuring depth (the z component). The data reduction component projects the acquired stereophotographs so that the optical model can be viewed and measured. Jt is designed to be compatible with the acquisition component. The angular relationships of the isosceles triangle formed by the camera system are duplicated by the projections of the data reduction component. In the close-range system, in which the object being photographed is small, the base separation of the projectors is increased eight times that of the cameras. The resulting stereomodel is thereby

t

----

---I - 87.08

-.---_

----I

Fig. 2. Buffalo dental camera system interior and exterior geometry. Dimensions are in millimeters.

enlarged over its natural size by eight times and is easier to view and more precise to measure.

REVIEW OF THE LITERATURE Stereophotogzaatmetry Since its beginning with the development of photography, stereophotogrammetry has become a sophisticated and precise method of measurement. For many years, medicine and dentistry have used it in a limited capacity to obtain quantitative data. Nyquist and Than? measured volumetric changes of impressions, casts, and prosthetic base materials. Savara’,s drew contours of individual teeth as photographed from plaster casts. He also presented a method to quantitatively measure tissues of the face and bones of the face uia stereoadiographs. Zeller’ and Gruner et al.’ demonstrated mechanical wear and chemical erosion of teeth and restorative materials from stereophotographs. A specially designed dental system using convergent photogrammetry was developed to provide data concerning the changes in gingival tissue contours after periodontal surgery. R-10Its accuracy in the + dimension (depth) was approximately 140 pm at the 95% confidence interval. Eick et al.“,‘* developed a similar convergent system known as the Buffalo close-range system to measure the deterioration of restorative materials in vivo in anterior teeth. The Buffalo system was later refined and adopted to measure washout of Class III restorations, compare wear and deterioration of composite JUNE 1985

VOLUMI?

53

NUMBER

6

STEREOPHOTOGRAPHY

FOR MEASURING

WEAR

Fig. 3. Evaluation component of close-range stereophotogrammetric system (Balplex 760 plotter). A = Double projector heads at 17-degree angle to object plane; B = projector support with leveling adjustors; C = ultraflat slate tracing table; and D = tracing table with micron counter.-

resins with that of amalgam restorations in Class II cavity preparations, measure the thickness of labially bonded veneers, and measure calculus formation on the lingual surfaces of mandibular anterior teeth. The Buffalo system was able to distinguish a difference of 50 pm between two points in the z dimension at the 95% confidence level.13

Altemkte measuring systems Other instruments have been developed to measure artificial tooth wear. HarrisonI designed an instrument that used a dial gauge with interchangeable styli supported by a rigid-horizontal arm to measure in vivo wear of artificial teeth on complete dentures. The instrument used a micrometer-controlled work table and a mounting jig to ensure repeatable denture positioning. Steel balls embedded into the denture base with cold-curing acrylic resin served as reference points. His tests indicate that dentures removed and replaced on the instrument are accurate to within 0.01 mm at the occlusal surfaces of the teeth. Winkler et a1.15measured in vitro processing changes in complete dentures from pour resins with a dial gauge supported by a modified Ney (J. M. Ney Co., Bloomfleld, Conn.) surveyor. With the use of this method and gypsum casts with perfectly flat bottoms, readings were made at the maximum vertical height of each cusp tip to the nearest 0.01 mm. Beall”j evaluated clinical wear of acrylic resin teeth by measuring stone replicas of complete dentures on reference casts. MeaTHE JOURNAL

OF PROSTHETIC

DENTISTRY

surements were made with a dial indicator and a vertical stylus with truncated cone tip. He reported the accuracy of this method as ? 0.005 inch or ? 0.13 mm at the occlusal surfaces of the teeth. Christensen* used photographic interferometry to measure in vivo wear of artificial teeth. His system requires sophisticated laboratory apparatus, high resolution film, and long exposure times; but it yields promising results for detecting small changes. DESIGN

OF MEASURING SYSTEM

An acquisition component was used to acquire the stereophotographs. It consisted of two camera bodies, special close-range lens, camera cradle, and support as designed by Eick et a1.“-‘3 (Fig. 1). The camera housings are modified Honeywell Pentax Spotmatic (HoneywellPentax, Minneapolis, Minn.) camera bodies that accommodate 35 mm film (Ektachrome 200, Eastman Kodak Co., Rochester, N.Y.) and have a mirror reflex viewing system and focal plane shutter. Dual release cables are attached to provide simultaneous shutter release. The cameras use a six-element symmetric lens designed for close-range photography (Bausch and Lomb Inc., Rochester, N.Y.). The camera cradle and support fix the geometric relationships of the camera system (Fig. 2). The evaluation component is the Balplex 760 plotter (Bausch and Lomb Inc.) (Fig. 3). It is a direct reviewing *Christensen G: Personal communication, 1983.

809

OGLE AND

ORTMAN

within selected fossae of the artificial teeth. All reference points must coincide with the standard model before successive recordings can be made. MATERIAL

Fig. 4. Superior view of reference frame. A = Base; B = support shelf; C = fixed wall of custom matrix; D = buccal index; E = dental stone base; F = complete

denture with random dot pattern; and G = removable wall of custom matrix. double-projection stereoplotting instrument. The stereopairs obtained by the cameras are precisely centered in special plate holders and then placed in the projectors of the Balplex plotter. The projectors are adjusted so that hey have the same relative geometric orientation as the camera system.I2 After orientation, the stereomodel can be viewed, traced, measured, and plotted. A tracing table is used to plot the x-y components and measure the z dimension of any point or feature in the stereomodel data. Changes in the z dimension are read from a counter on the tracing table, the graduations of which permit recording to a least reading of 10 pm (0.01 mm). Contour lines can be traced by lowering the pencil chuck and moving the tracing table throughout all points of similar height. A reference frame is used to ensure that each denture is in exactly the same position when placed before the camera system (Fig. 4). The reference frame consists of a white horizontal plexiglass base 26 cm square supported by clear plexiglass shelves to elevate the base to the correct focal distance from the camera lens. The custom denture matrix is 9 cm square with two permanently fixed vertical plexiglass walls and two removable walls 25 mm high. The removable walls fit accurately into a 6 mm square channel in the base. Dental stone is used to form the base of the matrix, which is a replica of the internal tissue surface of the denture. Two dental stone buccal indexes of the external denture border and teeth lock the denture within the matrix and serve as a platform for several reference points. The reference points aid in repositioning or leveling the model with the Balplex plotter. Other reference points are located 810

AND

METHODS

Accuracy of the camera system is checked during the period of photographing dentures by also photographing an ultraflat precision glass grid at the initial, 12-, 24-, and 36-month recall examinations. When the grid exposures are placed in the Balplex projectors, the relative orientation of the projectors and cameras can be verified. If the resulting orientation is the same, it can be assumed there has been no change in the relative orientation of the cameras in the holding cradle. A reference frame is used to assure exact repositioning of the denture for successive future recordings. This step is essential for accurate measurement of tooth wear. The first steps involved in preparing the denture for mounting require the fabrication of a dental stone base to support the borders and tissue-bearing surface. Blockout material is placed into undercuts and dental stone is vibrated into place on the base of the custom matrix. The denture is inverted, placed within the wet stone mass, and aligned for parallelism of the occlusal surfaces of the teeth and the superior border of matrix wall. Parallelism of the occlusal and incisal surfaces to the buccal matrix wall reduces plotter recovery time. A second dental stone matrix is poured on the buccal surface of the denture to the height of cusps of the teeth, and six to eight 14-gauge Williams (Williams Gold Co., Buffalo, N.Y.) plastic sprues are inserted into the wet dental stone approximately 3 mm from the buccal surfaces of the teeth. When the matrix is set, the outer surface is ground horizontal to the base on a model trimmer. The matrix is inscribed with the patient’s initials, disassembled, and checked for accuracy of fit with the denture. A random pattern of opaque dots is sprayed onto the teeth with a solution containing a water-soluble pigment to improve contrast and texture on the teeth and make cusp inclines easier to read. The pigment is easily washed off after the denture is photographed. After the denture is repositioned in the dental stone matrix and set in position before the cameras, three pictures are made at different exposure times to bracket the subject into light, medium, and dark exposures. This procedure is performed at each time interval during the course of the study. RESULTS The accuracy of the photogrammetry system used in this study was determined by grid-model flatness tests conducted over 3 years. The grid models indicated that the system accuracy, exclusive of operator reading errors, was -to.01 mm over the usable format of the camera system. Grid tests indicated that the cameras JUNE 1985

VOLUME

53

NUMBER

6

STEREOPHOTOGRAPHY

FOR MEASURING

WEAR

were in good internal adjustment and calibration and remained stable over the 36-month course of the study. When the differences between the mean of the entire grid and the actual recording at each grid intersect in millimeters were subjected to t test analysis, the results showed no significant difference in the numbers and therefore that the system was accurate (Table I). The reliability of the system was determined by means of Pearson correlation coefficients on the raters. Three raters measured a test denture at three or four different times over the course of 3 years to obtain the ratings. All test denture recordings were blind; that is, the raters were not aware of the test denture or of their previous recordings on this denture at successivetime intervals. At each time interval, the test denture was mounted and photographed for analysis. The inter-rater reliabilities at each time point were equal to or greater than 0.9998; that is, the raters were nearly identical in their recordings and agreed within kO.01 mm on occlusal surface measurements.

DISCUSSION The close-range stereophotogrammetric system was selected as the measuring tool to record and evaluate clinical artificial tooth wear for several reasons. The primary reason was its accuracy. No other device has been reported to match the accuracy and precision of this system for measuring in vivo artificial tooth wear. The importance of reproducibly detecting small changes in tooth contours is obvious. The system is also direct. Wear is measured from the image (stereomodel) of the clinical denture itselt, not from a cast of the denture. Errors due to impression and cast preparation that are necessary for stylus type measuring are thereby eliminated. Stylus systems that generate data from the actual clinical dentures cannot remeasure points of wear or measure additional points once the denture is returned to service. The stereomodel, once captured and aligned, can be remeasured at the data points or any other point throughout the course of the study. Furthermore, the eightfold enlargement of the stereomodel produced by the close-range system allows more accurate identification of points of wear and other areas of interest. Periodic measurements on test denture models oriented to the same reference frame resulted in rater agreement within 0.01 mm. When readings from the same model are compared, the minor differences would be largely due to how the points were interpreted and read. The differences between the same points read in different models would be a combination of how the denture was seated in the custom matrix of the reference frame, slight variations in the orientation of each of the models, and variations caused by the appearance of the point in models. The ability of the operator to repeat a reading on the same point in the same model varies according to the THE JOURNAL

OF PROSTHETIC

DENTISTRY

Table I. Grid model t-test data showing significant numbers*

difference

Time (months) Initial 12 24 36

no between grid intersect t-tests (intersects) t37 t3s ha 134

p value -0.50 1 .oo 0.00 0.00

*p > .05.

appearance of the point due primarily to lighting conditions, image quality, and dirt on the film emulsion. Image quality was reduced in a few circumstances when dirt or foreign matter became embedded within the film emulsion. The problem was believed to be due to dirty developing solutions and rollers used in processing the film. This was overcome by requiring the processors to use clean solutions and equipment. Another problem occasionally encountered was an uneven distribution of the random dot pattern from spraying the pigment more intensely on one side of the dental arch than the other. The undersprayed side was more difficult to read accurately. This problem was overcome by carefully controlling spray density on both sides of the arch. In addition, lighting conditions and/or surface reflectivity in some areas created glare on the enlarged image and made recording more difficult. Uniform spraying helped to correct this condition.

CONCLUSION A highly accurate method for measuring in vivo wear of artificial teeth in complete dentures has been developed. The component parts of the system have been described and evaluated. Grid tests and standard test denture recordings indicate that a high degree of accuracy and precision are obtainable by using this system. Appreciation is expressed to Mr. Robert McGivern of LaFave. White & McGivern, Rochester, N. Y. for helping develop, test, record, plot, and evaluate this close-range photogrammetry system. Appreciation is also expressed to Mr. Frank Hall for consistent recordings over a 3-year period.

REFERENCES 1. Hallert B: Photogrammetry, Basic Principles and General Survey. New York, 1960, McGraw-Hill Book Co., Inc. 2. Hertzberg HTE, Dupertrus CW, Emanuel I: Stereophotogrammetry as an anthropometric tool. Photogrammetric Eng 23:924, 1957. 3. Nyquist G, Tham P: Method of measuring volume movements of impressions, model, and prosthetic base materials in a photogrammetric way. Photogrammetric Eng 19:670, 1953. 4. Savara BS: Applications of photogrammetry for quantitative study of tooth and face morphology. Am J Phys Anthropol 23~427, 1965. 5. Savara BS: Application of photogrammetry for growth and volumetric studies of premature infants. In: Proceedings of the

811

OGLE AND

6. 7.

8. 9. IO. 11.

12.

Symposium on Close-Range Photogrammetry. Urbana, Ill., 197 1, University of Illinois Press, p 365. Zeller M: Textbook of Photogramr,.Stry. London, H.K. I,ewla and Co., Ltd.. 1952. Gruner H, Zulqar-Nain J, Zander II: A short range photogrammetric system for dental surgery. Photogrammetric Eng 33:1240, 1967. Zeller M: Microphotogrammetrical examination ot thr wriaces of tooth fillings. Photogrammetric Eng 19:660, 1953 Zulqar-Nain J, Burgess G, Zander HA: Photogr,lmmetry. ,J Periodontol 38:677, 1967. Burgess GH. ‘Zulqar-Nain J: Dental research using a &se range system. Photogrammetric Eng 34:677, 1968. Eick JD, McCivern NF, Sorensen SE: A photogrammetrlc system for measuring topographical changes of anterior restorations. J Dent Res 50 (Special issue) 1971 (Abstr No. 747). Rick JD, Woods RB, Pranitoff HI,, McGivcrn NF, Sorensen SE: The evaluation of photogrammetric system for measuring topographical changes of anterior restorations under clinical

James A. Stackhouse,

ORTMAN

Rrjmt wque,/s III. DR. ROBERT E. OGLE STATE ‘CIN~WWTV w NEW YORK SCHOOL OF DENTIWRY

BUFFALO, NY 14214

Jr., D.D.S., MS.*

University of Medicine and Dentistry of New Jersey, New Jersey Dental School, Newark, N.J.

A

syringe is frequently used in restorative dentistry to apply impression material around teeth prepared for crowns to eliminate or minimize bubbles in the finished impression. Every restorative dentist has occasionally (or perhaps frequently) experienced bubbles in critical places which necessitated remaking the impression. A previous study reported some reasons for such bubbles and that, in all probability, a bubble-free syringe of impression material is a rarity.’ Others have compared syringes and report that “operator skill is a more important factor in bubble entrapment than is the syringe or the material used.“’ One aspect that has received little study is the effect of the syringe-tip size on the included bubbles as they are extruded along with the impression material through the syringe opening. The present article reports the relationship between the syringe-tip diameter and the number and distribution of bubbles in extruded strips of impression material. MATERIAL

AND METHODS

Two medium-viscosity polyvinyl silicone elastomers, Reflect (Sybron/Kerr Mfg. Co., Romulus Mich.), *Professor, Dental Materials

and Fixed Prosthodontics.

Fig. 1. “Stropping” technique has been shown to minimize number of bubbles in mixed elastomer.’ labeled A, and Cinch-Vinyl (Parke& Farmingdale, N.Y.), labeled B, were used throughout the investigation. For each test, 8 g-mof catalyst was mixed with 8 gm of base. Spatulation was done with a flexiblespatufa for 30 seconds under standardized conditions until- the mass was uniform in color (Fig. 1). The mixed material was loaded into a syringe by a series of scooping motions across the mixing pad until the syringe barrel was completely filled (Fig. 2). Within 2 minutes of the start of mix, the impression material was totally extruded in JUNE 1985

VOLUME

53

NUMBER

6