Modification designed to improve instruction in intraoral dental radiography

Modification. designed to improve instruction in intraoral dental radiography S. K. Choksi, B.D.S., M.AEd.* Washington, D.C.

HOWARD UNIVERSITY COLLEGE OF DENTISTRY

A modification of the Rinn Snap-A-Ray film-holding device which facilitates more accurate visual alignment of cone and film is described. A double-blind study was undertaken to evaluate the modified instrument as compared to the standard instrument. The results indicated a reduction in the number of errors of all types by the modified instrument. The greatest reduction was observed in cone-cutting errors. (ORAL SURG. ORAL MED. ORAL PATHOL. 59~653-658, 1985)

M any different. instruments and/or aids have been developed to provide more accurate intraoral radiographs. Some of these aids fall short of the ideal requirements for a versatile instrument in providing an accurate radiograph. These instruments are either bulky, heavy, complicated to assemble or handle and time-consuming. Alignment of these instruments in the oral cavity to provide an accurate radiograph without any pain or discomfort to most of the patients is rare.

Many different instruments were selected, and a comparative study of their accuracy has been con- ducted by several authors. 1*4-6 It has been shown that the images produced with the extension cone paral- leling technique (XCP)? and Precision instru.ments$ were of higher quality, and with the Precision instru- ment the amount of radiation to the patient is reduced.2-3 The precision instrument calls for more skill than is required for use of the XCP instrument and the Snap-A-Ray? holder.’

The Snap-A-Ray instrument, which is easier to handle and in our clinical experience less painful to the patient, has one major drawback: the error of cone cutting. Since the diameter of the x-ray beam is regulated to 2.75 inches at the patient’s skin, the variables in tube alignment can result in incomplete coverage of the film by the x-ray beam (cone cutting). The cone cutting induced by this instru- ment mainly is due to the lack of a device for central locating and aiming the central beam. These errors

*Associate Professor, Department of Oral Diagnosis and Radiol-

ogy. TRinn Manufacturing Company, Elgin, Ill. *Precision Manufacturing Company, Nashville, Term.

are noticed more frequently in the posterior periapi- cal radiographs. 1,4, 5 The degree of cone cutting in this region could vary from slight to more than 50% of a single x-ray film. Once the film holder with the film is positioned in the oral cavity and the patient bites down on the block, the direct visibility of the positioned film is concealed. A cone cutting of half the area of a single x-ray film in a full-mouth series may not significantly reduce the diagnostic value of the survey, but it certainly would be of great concern when one is taking a single radiograph during an emergency or endodontic procedure. This drawback of the Snap-A-Ray instrument could be greatly improved by providing it with a beam-locating or aiming device. This modification was incorporated by the addition of a locator ring and aiming rod to the original Snap-A-Ray instrument, which was renamed Snap-A-Ray II.* Addition of the ring and the rod has enhanced the value of the device, but it has also made the device bulky, heavy, and at times difficult to manipulate and position in the oral cavity.

At Howard University College of Dentistry major errors due to cone cutting were observed on both single periapical and full-mouth series of intraoral radiographs. It was observed that the frequency of cone-cutting errors increased when the Snap-A-Ray instrument was used in comparison to other devices.

Modification of the Snap-A-Ray holder was undertaken, and the associated radiographic tech- nique was developed to improve teaching efficiency and technical accuracy in the instruction of both

*Rinn Manufacturing Company, Elgin, 111.

653

54 Choksi ~chl Surg. Line, 1985

Fig. 1. Position of film in relation to cone center.

dental and dental hygiene students and thus mini- mize the radiographic errors and the subsequent number of retakes.

REVIEW OF THE LITERATURE

The study conducted by Mourshed and McKin- ney’ with groups of students at various levels of experience (junior, senior, and dental hygiene) with Precision, XCP, and Snap-A-Ray instruments showed that students who used the Precision instru- ment demonstrated the largest reduction in cone- cutting errors. Students using the XCP instrument showed slightly more errors in cone cutting as compared to those using the Precision instrument. The largest number of cone-cutting errors occurred when students used the Snap-A-Ray instrument. The reduction in cone cutting observed with the Precision and XCP instruments was due to the fact that these devices allowed easy alignment of the beam with and external ring centered over the film. The study also found that students made fewer film-packet-placing and horizontal-overlap errors when the Snap-A-Ray instrument was used. It appears from the study that the Precision instrument calls for more skill in film-packet placement than is required by either the XCP or the Snap-A-Ray device. The Precision instrument was found to be least comfortable to the patient and not as well tolerated as the other two devices.

Patel,5 using a hemostat with bite block and a tongue blade as a film-holding device, found a higher percentage of errors. In descending order of frequen- cy, they were incorrect film placement (41.8%), cone cutting (26.1%), incorrect horizontal angulation (20.6%), incorrect vertical angulation (9.1%), and miscellaneous errors (2.4%). This study also indi- cated that the second most predominant error was cone cutting in the mandibular molar region. These

results indicate that, in the absence of direct film visibility and external !ocating devices, there is an increase in frequency of errors caused by incorrect film placement and cone cutting in the mandibular region as compared to the maxillary region

In MourshedV study, dental students made a far from satisfactory number of errors. Cone-cutting errors were seen most frequently in the molar areas and, to a lesser degree, in the premolar areas of both jaws. The study also revealed the difficulty faced by students using the XCP instrument in comparison to the Snap-A-Ray instrument.

The data presented by Mourshed and revealed that cone cutting was reduced to one half when the long, open-ended transparent plastic cones were used instead of the long open-ended opaque plastic cones.

Crandel14 suggests that cone cutting is a substan- tial cause of x-ray errors when a beam that is 2.75 inches in diameter at the film surface is used.

Bean’ compared the radiographs taken by the bisecting angle technique and the paralleling tech- nique. In this study the XCP instrument was used for the paralleling technique, while the patient’s finger was used for the bisecting angle technique. The result indicated that 25% of the bisecting angle radiographs were unsatisfactory, while 11% of the radiographs taken by the paralleling technique were unsatisfactory. In both techniques failure to include the apex was the most frequent error.

METHOD AND MATERIAL Part 1. Instrument modification

A piece of white paper was taken and a circle 2.75 inches in diameter was drawn to represent the diameter of the beam of radiation and the position- indicating device (cone) (Fig. 1). Next a vertical (AB) and a horizontal (XY) axis, intersecting at the right angle to each other within the center of the circle, were drawn. An ANSI 1.2 size x-ray film was placed within the circle, with the center point of the

coinciding with the center of the circle and the axis of the film along the XY axis. The outline

of the film was traced on the paper. The jaws of the Snap-A-Ray instrument were

opened and the film was inserted horizontally to the end of the jaws and then locked in position with the help of the sliding friction ring (Fig. 2). The film, with the instrument attached, was then centered over the traced outline on the paper with the instrument lying parallel to the XY axis. Two marks (b in Fig. 2) were made on the edge of the instrument, corre- sponding to the anterior position of the film and the edge of the beam of radiation. Grooves about 0.5 mm

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Modijied film-holding device 655

Fig. 2. Markings in relation to film placement to the tube.

deep were then cut into the instrument at the marks and filled with blue quick-set acrylic.*

With the same film holder, the anterior edge of the film was repositioned to the middle of the jaws and relocked. Once again the film was centered over the traced outline with the instrument parallel to the XY axis. Two additional marks (r in Fig. 2) were then made on the edge of the instrument, coinciding with the anterior edge of the film and the edge of the beam of radiation. Two shallow grooves about 0.5 mm deep were cut at these marks and filled with red quick-set acrylic.?

The same basic technique was used to mark the instrument for anterior periapical radiographs, except that the film was positioned in the anterior portion of the film holder. The film in the holder was centered within the beam outline and the hol.der was marked where it overlapped the circle (r’ in Fig. 2). The groove was cut and filled with red acrylic,

There are several advantages to the use of color coding on the modified instrument:

1. The color-coded markings coincide with the exact film position and cone positioning in a horizon- tal plane when the instrument is positioned in the oral cavity.

2. Different color codes are provided to relate different film positions useful in radiographing vari- ous segments of the posterior teeth and to facilitate insertion and alignment of the instrument. For the premolar exposure, the film is positioned completely within the jaws (that is, up to the blue mark). This placement provides rigidity to the film, helping displace the tongue and mylohyoid muscle while facilitating the gentle positive placement of the film

*Caulk Trayresin, LD Caulk Company, Milford, Del. tRed acrylic, Duralay, Inaly Pattern Resin, Reliance Dental Mfg. co.

in its proper position. For the molar exposure the film is inserted halfway within the jaws of the holder (that is, up to the red mark). This placement provides a triple advantage in placing and positioning the film within the oral cavity because (1) it extends the film distally approximately 10 mm to cover the most distally placed third molars, especially horizon- tal impactions; (2) it reduces discomfort in the retromolar pad area upon closure because the bite- block portion of the instrument is positioned mesially from the anterior border of the ramus and does not impinge on the tissue; and (3) the free cantilevered extension of the film provides more flexibility to the film and allows easy adaptation in the highly sensi- tive retromylohyoid space area.

The modified instrument may be used for both bisecting angle and paralleling techniques.

Part II. Instrument comparison

A full-month radiographic survey consisted of sixteen periapical and four bitewing films. For the purpose of this study, only the sixteen periapical radiographs were considered. The technique employed was the paralleling technique using the Snap-A-Ray film holder and the modified technique with the modified Snap-A-Ray film holder (Part 1).

A standard GE-1000 intraoral x-ray unit equipped with a 16-inch-long open-ended transparent plastic cone, with a beam diameter at cone tip of 2.15 inches, was used. Only standard surveys of dentulous adult patients were included in this study.

First-year dental hygiene students are taught intraoral radiographic technique in a series of lec- tures during their first semester. As second-year students, they are assigned to five clinic sessions in the radiology clinic per semester. During their first- semester rotation these students were trained to take

Oral Snrg. June. 1985

Fig. 3. Tube position in relation to holder and ala- canthus line. (Black thread indicates ala-canthus line.)

Table 1. Distribution of radiogra

Regular Modified I film holder film holder Total I

With errors 220 120 340 (38.5%) (30.5%) (35.2%)

Without errors 351 274 625 (61.5%) (69.5%) (64.8%) I -

571 394 965

X2 = 6.859 with 1 degree of freedom. P 0.01.

full-mouth series radiographs by the paralleling tech- nique and with XCP instruments.

During the second semester, thirteen second-year students were assigned in groups of two to three to take full-mouth surveys. Alternate groupsg epending on their assignment to the clinic, were

given a thorough demonstration of the use of the two Snap-A-Ray instruments on a technique manikin DXTTR.* The first assigned group was given a demonstrating on the use of the unmodified Snap-

*Alderson Research Laboratories, Inc., Stamford, Conn

Table il. umber of ~adiogra~bs with errors per sixteen-film periapical radiographic survey

No. of radiographs Modified Regular

per c‘wx instrument instrument

1 5 1 2 2 1 3 1 3 4 4 2 5 2 4 6 6 I 7 - 6 8 2 4 9 2 4

10 1 2

12 z 2 Survey with errors 25 36 Mean 4.1 6.6 Standard deviation 2.4 3.8 t value 2.31*

*Significant at 5% level.

A-Ray holder. The next group was given a demon- stration on the use of the modified Snap-A-Ray holder with its modified technique (Fig. 3). The demonstration was followed by assignment of patients for radiographs. Each student completed between four and six full-mouth series, each consist- ing of sixteen periapical radiographs. Technical errors observed in the radiographs were identified and suggestions as to how these errors could be corrected or avoided were made,

Only errors due to film/cone-placement tech- niques were counted. Errors due to incorrect expo- sure time or improper film processing were not included. In counting the radiographic errors, each radiograph was evaluated individually and all techni- cal errors were counted. At the end of the study, all radiographs were evaluated by double-blind methods (that is, without knowledge of whether the standard technique or the modified technique ws used).

RESULTS

The number of periapical radiographic errors made by dental hygiene students is shown in Table I. A total of 965 periapical radiographs were made. Students using the regular Snap-A-Ray holder took 571 radiographs of 36 patients; those using the modified film holder with its modified technique took 394 radiographs of 25 patients. Variations in the total number of surveys performed by each student were due mostly to limitations in availability of patients and the number of students assigned per block.

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Table 111. Types of radiographic errors

Percentage

Regular

Improper film positioning P 71 57 13.5 Incorrect vertical angulation V 47 23 8.2 Incorrect horizontal angulation H 8 2 1.4 Slight cone cutting (less than CS 57 29 10.0

25% of x-ray film) Large cone cutting (over 25% CL 36 6 6.3

of x-ray film) Improper film positioning (and PC 13 I 2.3

cone cutting in third molar region

No. of radiographs without 251 EL 61.5 error

Total No. of radiographs 571* 394*

*These totals do not equal column total because of more than one error in some radiographs. tChi-square for each category has been calculated against the number of radiographs without errors.

Modi’ed

14.5 5.8 0.51 7.4

1.5

1.8

69.5

Chi-square?

0.076 3.103 2.276 3.165

14.113** (P 0.01) 0.616

Table IV. Percentage of cone-cutting errors according to arch and side

Regular “‘“; Modified pk Regular Rigy sideMadi$ed Regular “‘: ‘jde Modified

Maxilla 13.2 7.1 16.7 10.2 14.9 8.9 (19)* (7) (24) (10) (43) (17)

Mandible 16.1 8.1 19.3 10. 17.7 9.1 (23) (8) (27) (10) (50) (18)

Total 14.6 7.6 18.0 10.2 16.3 8.9 (42) (15) (51) (20) (93) (35)

*The numbers in parenthesis denote the number of radiographs with cone-cutting errors.

Table V. Cone-cutting errors according to anatomic region

‘i Crror~odijed /---%egular

Total radiographs

Regular Modified

Molars 47 16 144 99 Premolars 31 14 144 96 Cuspids 6 2 142 99 incisors 9 3 141 100

Percentage errors

Regular Modified

32.6 16.2 21.5 14.6

4.2 2.0 6.4 3.0

Of the 571 radiographs taken by the regular method, 38.5% had at least one technical error (Table I). With the modified instrument, only 30.5% of the 394 radiographs had at least one technical error. Eight percent fewer errors were produced with the modified instrument and technique. The reduc- tion in number of all types of errors was statistically significant (P < 0.01).

The frequency of errors per patient for both techniques is indicated in Table II. The table indi- cates the lowest (1) and highest (12) numbers of radiographic errors among the sixteen radiographs per individual patient. The mean number of errors

per patient was 4.7 with the modified method and 6.6 with the standard method. The t test was statistically significant at the 0.05 level of confidence.

The frequency and significance of difference for various types of radiographic errors between regular and modified methods are shown in Table III. Except for improper film positioning, all the other errors were reduced in the modified method. The reduction in large cone-cutting error (1.5%) with the modified method compared to the regular method (6.3%) was highly significant at the 0.01 level. This reduction in the frequency of cone-cutting errors was similar, irrespective of the location of the tooth or the

Choksi

type of tooth (Tables IV and Vj. In general, the reduciion in cone cutting was 40% to 50%, depending upon the quadrant.

iSCUSSlON

As indicated by the Mom-shed and McKinney’ study, the frequency of improper film positioning was lower with the Snap-A-Ray instrument than with the other two devices evaluated. On the other hand, Mourshed and McKinney found an increase in cone-cutting and vertical-angulation errors. The reduction in the number of large and small cone cuts when the modified Snap-A-Ray instrument was used was highly significant. In Mourshed and McMinney’s study the Snap-A-Ray was used with a bisecting angle technique; hence, incorrect vertical angulation (11.8%) was high because of limitations associated with this technique. In this study incorrect vertical angulation occurred 8.2% of the time when the paralleling technique with the standard Snap-A-Ray holder was used and only 5.8% of the time when the modified instrument and technique were used. The improved accuracy in vertical alignment between this and the previous study may reflect the improved accuracy of the paralleling technique over the bisect- ing angle method.

Improper film positioning and cone cutting (PC) in the third molar region were separated from other errors for special consideration because of innately difficult anatomy, variations in local tooth position, accessibility, and at times lack of direct visibility. There was some reduction of error with the modified technique, although it did not reach statistical signif- icance because of the small number of radiographs.

Horizontal-angulation errors were reduced by nearly 1% with the modified technique as compared to the regular technique. When compared to the Mourshed and McKinney study, this type of error occurred infrequently. Mourshed and McKinney noted most horizontal overlap in relation to maxil- lary cuspid areas. In this study the cuspid tooth was considered as a corner tooth, and difficulty in obtain- ing a perfect radiograph of this region was taken into consideration so that slight overlapping was not considered an error. Errors of overlapping in this study occurred most frequently in the posterior region of the arch.

The frequency of cone-cutting errors according to h and side is quite interesting (Table IV), ardless of dental quadrant, the modified device

G-al Surg. June, 1985

reduced the error by 40% to 50%. It is also interest- ing to note that the left side showed a higher percentage of cone-cutting errors than the right side. Similarly, more errors occurred in the mandibular arch than in the maxillary arch. This is probably related to the patient/operator chairside relationship as well as the operator’s ability to directly visualize film placement and alignment of the cone. Cone- cutting errors, in descending order according to the anatomic region, irrespective of method used were in the molar, premolar incisor, and cuspid regions (Table V).

SUMMARY AND CONCLUSlOM

The modified film holder was designed to simplify beam alignment in order to avoid cone cutting; in addition, there was an 8% reduction in all types of technical error, compared to the regular (unmodi- fied) instrument. The mean number of errors per patient was also reduced by nearly 2.0% in the modified technique. A 40% to 50% reduction in cone-cutting errors with the modified technique occurred, irrespective of the side, arch, or region radiographed.

Modification of the Snap-A-Ray is easy and simple.

REFERENCES

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6.

I.

Mourshed F, McKinney L: A comparison of paralleling and bisecting radiographic techniques as experienced by dental students. ORAL SURC ORAL MED ORAL PATHOL 33: 284-296, 1972. Winkler KG: Influence of rectangular colhmation and intra- oral shielding on radiation dose in dental radiography. J Am Dent Assoc 77: 95-101, 1968. Weissman DD, Feinstein RB: X-ray beam profiles and oral radiography. ORAL SURC ORAL MED ORAL PATHOL 31: 546-555, 1971. Crandell CE: Cause and frequency of intraoral x-ray errors by dental and dental hygiene students. J Dent Educ 22: 189-196, 1958. Pate1 JR: Intraoral radiographic errors. ORAL SURG ORAL

MED ORAL PATHOL 48: 479-483. 1979. Mourshed F: A study of intraoral radiographic errors made by dental students. ORAL SURG ORAL MED ORAL PATHOL 32: 824-828, 1971. Bean LR: Comparison of bisecting angle and paralleling methods of intraoral radiology. J Dent Educ 33: 441-445, 1969.

Reprint requests to:

Dr. SK. Choksi Department of Oral Diagnosis and Radiology College of Dentistry Howard University Washington, DC 20059