implants

dized radiographs in the mandible

B. J. A, Meijer, University

of Utrecht,

of the alveolar

crest

DDS,a W. H. A. Steen, DDS, PhD,b and F. Bosman, Faculty

of Medicine,

Utrecht,

The

aroun

PhD”

Netherlands

The techniques currently used for standardized longitudinal radiographic evaluation of the supporting bone around dental implants are not suitable for general application. An aiming device is described for intraoral radiography used to evaluate the crestal bone height around dental implants used as retention for overdentures. This aiming device has been tested on four different implant systems by four dentists. Error analysis of serial radiographs indicates small deviations in reproducibility. It is concluded that this method is suitable for routine evaluation of dental implants. (J PROSTHET DENT 1992;68:318-21.)

t is difficult to develop denture retention and stability in patients with severe atrophy of the mandible. One solution for this problem provides permucosal implants to which the denture can be attached. Continuous monitoring of patients to detect changes in the tissues surrounding the implants is needed. Evaluation of the status of the bone height can be made with serial reproducible radiographs.l, 2 However, obtaining radiographs of the desired quality with an easy reproducible technique is difficult to achieve (Table I). The rotational panoramic radiograph is widely used for the evaluation of bone around dental implants in the edentulous mandible. However, the rotational panoramic radiograph lacks sharpness, distorts images, and superimposes bony structures of the spine. Reproducibility with this technique is difficult to achieve. Better results can be obtained with the extraoral oblique cephalometric technique.3 This reproducible radiographic technique provides sharpness and distortion is minimal. Because of the required special radiographic equipment, however, the method can only be used at some research centers. In general practice, periapical dental films are used. Using the bisecting-the-angle technique, the patient holds the film in place. With this approach, reproducibility is often poor, making the application impossible for standardized longitudinal evaluation. The paralleling technique, with

Supported in part by the “Stichting voor Wetenschappelijk Tandheelkundigen Arbeid” (Foundation for Postgraduate Education) aAssistant Professor, Department of Oral-Maxillofacial Surgery, Prosthodontics and Special Dental Care. bAssociate Professor, Department of Oral-Maxillofacial Surgery, Prosthodontics and Special Dental Care. cProfessor, Department of Oral-Maxillofacial Surgery, Prosthodontics and Special Dental Care.

10/1/35680 318

I. Rating summary of quality and reproducibility, ease of radiography, and availability of technique for radiographs of implants in the edentulous mandible

Table

Quality

Reproducibility

-

+I-

Rotational panoramic method Oblique cephalometric method Bisecting-the-angle method Parallelling technique t,

Sufficient; +/-, moderate;

Ease of application

Availability

+

+/-

+

+

+I--

-

-

-

+

+

+

+I-

-

+

-, insufficient.

the use of a conventional intraoral film holder, assures that the central x-ray axis is perpendicular to the film. Although the quality of the radiograph is improved, the relatively high floor of the mouth in these patients and the size of the film limits the ability to keep the film holder parallel to the implant. El Charkawi4 suggested use of an individual template of autopolymerizing resin to hold the film parallel to the implant region. Although the requirements for evaluation are met, the method is difficult to use and is timeconsuming. This article discusses a technique that meets the requirements for standardized longitudinal evaluation of bone around permucosal dental implants in the interforaminal region of the mandible. It has been reported5 that the mean annual marginal bone loss around dental implants is 0.1 mm. Measurement& by a computerized digitizing

system

appear

to have

a standard

deviation

of 0.02

mm. Therefore a standard deviation of 0.02 mm, as a result of the radiographic technique, is considered acceptable to evaluate

marginal

bone

loss. AUGUST

1992

VOLUME

68

NUMBER

2

INTRAORAL

RADIOGRAPHIC

AIMING

DEVICE

Fig. 1. A, Assembled device.

fastener and film holder of aiming device. B, Three parts of aiming

MATERIAL AND METHODS Design and construction of the aiming device The principles of design of an aiming device7 include (1) parallelism of the film to the long axis of the implant, with the central x-ray axis perpendicular to the film to avoid image distortion; (2) reproducible images that permit comparison of measurements on series of radiographs; (3) ease of use in reasonable time; and (4) cost-effective equipment available for private practice. The aiming device developed consists of a fastener, a film holder, and an indicator rod (Fig. 1). The fastener is attached to the implant abutment. The implant abutment fits into the opening and the fastener is secured to the lingual surface of the implant with two labial screws. The fastener fits all implant abutments with a diameter between 3.5 mm and 5 mm and a minimum height of 3.5 mm. To obtain reproducibility, the fastener must be attached to the implant abutment in the same position. Reproducible positioning can be achieved by placing one of the screws in an abutment hole placed in the superstructure for the overdenture. The film holder is placed parallel to the fastener so that the film will be parallel to the implant. Three different horizontal positions of the film holder are possible. Depending on the anatomy of the mandible and the resistance of the soft tissues of the floor of the mouth, the film holder can be set at 8,12, or 16 mm from the center of the implant. Film size 0, 1, or 2 can be used to obtain as much information as possible dependent upon the resilience of the floor of the mouth. The short side of the film is placed parallel to the implant axis. The indicator rod, aligning the x-ray tube, is attached to the film holder extension, which is parallel to the fastener. In this way the central x-ray axis will be perpendicular to the implant and the film. The indicator rod is constructed of polyvinylchloride so there is little torque that could be harmful to the anchorage of the implant. A prototype of this aiming device was tested by four opTHE

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DENTISTRY

Table II. Standard deviations in position device on implant abutment in horizontal and in vertical plane (SD,)

SD,

of aiming plane (SD,) SD,

(degrees)

(degrees)

Bonefit system (n = 20) IMZ system (n = 20) Bmnemark system (n = 20) Bosker TM1 system (n = 20)

0.18 0.17 0.14 0.15

0.19 0.14 0.18 0.13

Test after 2 months (n = 10)

0.09

0.14

Test by another examiner (n = 10)

0.16

0.10

erators on a simulation head, of which the mandible was provided with different types of implants. The aiming device was tested for the Bonefit (Institut Straumann AG, Waldenburg, Switzerland), the IMZ (Friedrichsfeld, Mannheim, Germany), Branemark (Nobelpharma, Goteborg, Sweden), and the Bosker TM1 (Krijnen Medical, Beesd, The Netherlands) implant systems.

Error

analysis

The errors inherent in the method can be separated into radiographic errors and measuring errors.” Radiographic errors are related to the making of the radiograph and can be divided in nongeometric errors such as processing of the radiograph, and geometric errors such as magnification and distortion.8 Measuring errors are the result of differences in the interpretation of the radiographs by examiners.g Error analysis of radiographs made with this aiming device was restricted to geometric errors. Nongeometric errors and measuring errors are not specificially related to this aiming device and will not differ from those occurring in other studies. Analyzing geometric errors in successive radiographs indicates (1) magnification caused by the object-film distance and the focus-object distance, (2) differences in the posi319

MEIJER,

Table

III.

Standard

deviation SD,

Position of x-ray (n = 10) SD,,

Horizontal

plane;

tube

in position (degrees)

of x-ray tube SD,.

0.35

SD,, vertical

(degrees) 0.16

plane.

Talble IV. Mean difference (x, y) and standard deviation (SD,, SD,) in position of the patient after aligning x-ray tube and before depressing exposure switch SD, Motion of patient (n = 10)

(degzees)

(degrees)

(deg:ees)

0.09

0.04

0.19

SD (degries)

0.11

tion of the aiming device on the implant abutment, (3) differences in aligning the x-ray tube with the indicator rod, and (4) motion of the patient after aligning the x-ray tube. 1. Image magnification (m) depends on the object-film distance (D) and the focus-object distance (L): m=-

D+L L

2. Errors caused by malpositioning of the aiming device were calculated using two markers in the midsection of the mandible of the simulation head. One marker was placed at the labial side of the mandible and one marker was placed at the lingual side. The four implant systems and their specific superstructures for overdentures were tested. From each system an implant in the left and right side of the mandible was used. Each implant was radiographed 10 times. During the series of 10 radiographs, the x-ray tube was fixed. After making a radiograph, the aiming device was removed carefully, the film was changed, and the aiming device was repositioned. After 2 months, 10 radiographs were made of one of the implants to detect long-term reproducibility. To detect the influence of the operator, a second operator not familiar with this aiming device also made 10 radiographs of one of the implants. The coordinates of the markers were registered. The horizontal deviation of each radiograph related to the ideal position of the aiming device was calculated using the equation: Ly = (XbII - x111)- (XbI - XII) x $1 . m where ax = angular deviation in the horizontal plane between the ideal position of the aiming device (I) and the actual position during making of a radiograph (II); xbn = x coordinate of the buccal marker in position II; XIII = x coordinate of the lingual marker in position II; xbl = x coordinate of the buccal marker in position I; xt = x coordinate of the lingual marker in position I; db, 1= distance between the buccal and lingual marker, measured parallel to the central x-ray beam; m = magnification caused by the focus-object distance and the object-film distance. 320

STEEN,

AND

BOSMAN

A similar equation for the y coordinates was used to calculate the vertical deviation. Because the ideal position (I) of the aiming device is not known, the mean value of the 10 coordinates of each series was taken as the ideal position. Subsequently, the angular deviation of each radiograph of a series and the standard deviation (SD) from the ideal position were calculated. 3. Errors caused by positioning the x-ray tube were calculated using the same two markers, but now the aiming device was fixed. A series of 10 radiographs was made of two implants. After making a radiograph, the angle of the x-ray tube was distorted in all directions. The film in the holder was changed without moving the aiming device and the x-ray tube was aligned again with the indicator rod. 4. Geometric errors caused by motion of the patient after aligning the x-ray tube with the indicator rod and before depressing the exposure switch were, for x-ray protection reasons, calculated with a Selspot movement recording system.lO One light-emitting diode (LED) was attached in front of the test subject as a reference point and one LED was attached to the lower incisors of a test subject, simulating the position of the aiming device. The time between aligning the x-ray tube and depressing the exposure switch was estimated to be 6 seconds. Differences in position of the two LEDs between starting and after 6 seconds were registered. The recording was repeated 10 times.

RESULTS 1. Three different film-object distances are possible (position 1, 2, and 3; D = 8 mm, D = 12 mm, and D = 16 mm, respectively). Because the end of the x-ray tube is always positioned at a colored marker on the indicator rod, the focus-object distance is constant (L = 381 mm). (GE 1000 x-ray machine, long cone, General Electric, Milwaukee, Wise.). Therefore the image magnification (m) was 1.02 for position 1, 1.03 for position 2, and 1.04 for position 3. 2. The standard deviation (SD, and SD,) from the ideal position for all systems appeared to be between 0.13 and 0.19 degrees (Table II). After 2 months, SD, was 0.09 degrees and SD, was 0.14 degrees (Table II). The 10 radiographs made by the other examiner showed a standard deviation of 0.16 degrees in the horizontal plane and 0.10 degrees in the vertical plane (Table II). 3. The standard deviation from the ideal position of the x-ray tube was 0.35 degrees in the horizontal plane and 0.16 degrees in the vertical plane (Table III). 4. When the motion of the patient was recorded, the mean difference in the horizontal plane was 0.09 degrees (standard deviation, 0.04 degrees) and the mean difference in the vertical plane was 0.19 degrees (standard deviation, 0.11 degrees) (Table IV).

DISCUSSION The radiographic method presented, using the long cone technique with the help of a newly designed aiming device, meets the requirements previously formulated. The intraoral dental film is kept parallel to the implant and the AUGUST

1992

VOLUME

68

NUMBER

2

INTRAORAL

RADIOGRAPHIC

Pig.

AIMING

DEVICE

2. Radiograph

of bone around

transmandibular

central x-ray axis is perpendicular to the film. In this way, distortion of the images is avoided. The standard deviations of reproducibility are acceptable. If the largest standard deviation in the horizontal plane and the largest standard deviation in the vertical plane are taken, the image magnification is 1.00004. Since the distances measured are not more than 20 mm, the accepted standard deviation of 0.02 mm corresponds with an image magnification of 1.001. The image magnification of 1.00004 lies below this value. The technique is not difficult to use. Once the hole in the ring of the superstructure is made to aid positioning of the device, it is not time-consuming. The simple design of the aiming device, its construction of stainless steel and polyvinylchloride, and the use of a long cone x-ray machine make the procedure time-efficient and usable in private practice. Stability of the fastener on the implant abutment is best if the walls of the implant abutment are parallel to each other. If a conical-shaped implant abutment is used with its smallest diameter located incisally (in this study the abutment of the IT1 implant), it is suggested that the implant abutment be adjusted to one with more congruent wails. A radiograph (Fig. 2) made with this aiming device confirms that the height of the floor of the mouth and the need for parallelism of film to the implant limits the amount of the implant seen on the film. However, we do not believe that this ,limitation is a serious problem, since pathologic changes begin around the neck of the implant. Therefore the amount of bone loss and the anchorage function of the implant can be adequately assessed, even if the apical part is omitted in the radi0graph.l’

CONCLUSION A new aiming device has been developed for radiographic evaluation of the mandibular crestal bone surrounding different types of implants. The only limitation to its use

THE

JOURNAL

OF PKOSTHETIC

DENTHSTRY

implant

made with aiming

device.

is that the height of the implant abutment above the marginal gingiva must be more than 3.5 mm and the diameter must be between 3.5 and 5 mm. We thank E. Botter for constructing the aiming device. REFERENCES

1. Schnittman PA, Sculman LB, eds. Dental implants: Benefit and risk. An

2. 3. 4. 5.

6.

NIH-Harvard Consensus Development Conference 1978. U.S. Department of Health and Human Services. Washington: U.S. Government Printing Office, 1979. Schulman LB. Surgical Considerations in implant dentistry. J Dent Educ 1988;52:712-20. Steen WHA. Measuring mandibular ridge reduction. Dissertation. University of Utrecht, The Netherlands, 1984. El Charkawi HG. Residual ridge changes under titanium plasma sprayed screw implant systems. J PROSTHET DENT 1989;62:576-80. Adell R, Lekholm B, Rockier B, Brdnemark P-I. A 15.year study of osseointegrated implants in the treatment of the edentulous jaw. Int J Oral Surg 1981;10:387-416. Steffensen B, Weber H-P. Relationship between the radiographic periodontal defect angle and healing after treatment. J Periodontol 1989; 60:248-54.

7. Manson-Hing LR. Radiographic quality and artifacts. Chap 3. In: Fundamentals of dental radiography. 2nd ed. Philadelphia: Lea & Febiger, 1985. 8. Duckworth JE, Judy PF, Goodson JM, Socransky SS. A method for the geometric and densitometric standardization of intraoral radiographs. J Periodontol 1983;54:435-40. 9. Ramstad T, Hensten-Pettersen 0, Mohn E, Ibrahim SI. A methodological study of errors in vertical measurements of edentulous ridge height on orthopantomographic radiograms. J Oral Rehabil 1978;5:403-12. 10. Jemt R, Karlsson S. Computer-analysed movement in three dimensions recorded by light-emitting diodes. J Oral Rehabil 1982;9:317-26. 11. Strid K-G. Radiographic results. Chap. 11. In: Brinemark P-I, Zarb GA, Albrektsson T, eds. Tissue-integrated prostheses. Osseointegration in clinical dentistry. Chicago: Quintessence Publishing Co Inc, 1985. Reprint requests to: DR. H. J. A. MEIJER DEPARTMENT OF ORAL-MAXILLOFACIAL PROSTHODONTICS AND SPECIAL DENTAL UNIVERSITY HOSPITAL GROP~INGEN P.O. Box 30.001 9700 R B GRONINGEN THE NETHERLANDS

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