Intemationat Endoiontk journal (1992) 2 5.93-96
A method for experimental dental radiography J. FORSBERG Department of Oral Radiobgy, School of Dentistry, University of Bergen, Bergen, Norway
Summary An apparatus was designed for experimental dental radiography, which permitted separate a^ustment of the subject, target and film. The precision ct the apparatus was tested by radiographing a test subject, consisting erf' anall steel globes embedded in a plastic plate. The subject was placed in the apparatus and exp(Ked 30 times on dental X-ray film with different adjustments of angles and distances. Ail exposures were repeated after readjustment of the same form. Three linear distances between pairs of the projected steel globes were selected and measured on each radiogra[di. Depending on the different orientations of film, target and subject, the distances measured ranged from 9.011.1 mm, fi-om 7.0-10.7 mm and from 12.7-17.3 mm, respectively. From the measurements on the radiographs the error of method was calculated to be 0.07-0.08 mm and the error of measurement to be 0.05-0.06 mm. The precision ofthe apparatus was thus found to be adequate for measurement of differences in small, but clinically relevant, distances.
outline of the tooth apex in relation to the position of a contrasting object in the root canal, such as an instnunent or a root filling (Forsberg 1987). Walker (1986) reported a simple device for radiographic examination of teeth in vitro. However, the adjustments of the central beam and film in this apparatus appear to be limited. In order to study the effect of different angulations of central beam and film on the measurement of small distances it is necessary to use an adjustable apparatus with the capacity to record these variables in a reproducible manner. In the present paper an apparatus for experimental laboratory dental radiography is described. This apparatus permits separate adjustment ofthe subject, target and film. A series of test exposures and measurements of distances for calculating the error of method was performed. Description and use of apparatus The apparatus is shown in Fig. 1, and consists of three main parts. Device for orientation of subject
Keywords: dental radiography, endodontics. Introduction Endodontic diagnosis and treatment planning require adequate radiographic imaging of the tooth and periradicular structures. Particularly important is information about root canal morphology and the location and size of periapical bone destruction. The paralleling technique, although slightly enleirging the image of the tooth, has been found to produce less distortion than the bisecting-angle technique (Carlsson & Benkow 1964. Eggen 1969, Vande Voorde & Bjomdahl 1969, Larheim & Eggen 1979). In these studies the efficacy of the two techniques was assessed from measurements ofthe total length of tooth. In endodontic therapy it is most important to reproduce accurately the Correspondence: Dr ]. Forsberg, Department of Oral Radiology, School ot Dentistry. University ot Bergen, Arstadveien 17, N-5009, Bergen. Norway.
The subject table can be rotated in the horizontal plane (A). Two rows of canals, perpendicular to each other in the subject table, permit the fixation of the subject by means of two or more plastic-retaining pins. The subject may cdso be fixed in a bowl with thermoplastic impression material supplied with pins fitting the canals. Both methods of fixation allow repeated testing. For observation of endodontic relationships where an instrument is positioned in the root canal ofthe tooth, an extra canal is made in the centre ofthe subject table. The handle of a root canal file can be securely fixed and used as a vertical axis for the root canal. The subject may be rotated around its vertical axis by turning the subject table. The horizontal position is read on the scale at A. Device for orientation ofthe target and central beam A cone or open tube is fixed to a rangearm (B). By pushing the arm, the target-to-subject distance is altered. The movement ofthe cone in the vertical plane is 93
94
/. Forsberg (a)
Fig. 1. Apparatus for experimental dental radiography, (a) photograph, (b) diagram. Device for orientation of subject: A = subject table with scale for horizontal angulationof subject: T = test subject fixed to subject table. Device for orientation of target and central beam: B = rangearm. with fixed cone. for modifying target-subject distance: C = wheel for moving cone in verticaJ plane: D=scale for reading intersection of central beam with vertical axis of centre of subject table: E=: scale for reading vertical angle of central beam: F = aiming device for adjustment of central beam in relation to subject out of its aiming position. Device for orientation of film: G=scale for recording distance from filmsupporting plate to centre of subject tabie: H=scale for vertical angulation of film: i = scale for horizontal angulation offilm:J — scale for vertical movement of film plate.
achie\'ed by turning wheel C. The intersection of the central beam with the vertical axis of the centre of the subject table is recorded on scale D. The vertical angle is adjusted by rotating the rangearm, and is read on scale E. The adjustment ofthe central beam in relation to the subject is performed by means of an aiming device which
is fixed to the rangearm (F). The central beam passes through the tip of the aiming device. The beam centre coincides with the point where the tip touches the subject. In the present experimental system the Siemens Roentgenkugel (Siemens, Erlangen, Germany) was used.
A method for experimental dental radiography 1 40
95
_
3 30
I
•s S 20
-
5
Numtier
•5
1—1
1— Difference (mm)
Fig. i. Error of method. Graphical representation ofthe di^ribution of the differences by measurements of pairs of radiographs, exposed in the same way.
50
40
Fig. 2, Radiograph of the test subject showing the three distances measured for calculations of the error of method.
30
Table 1. The error of method in experimental radiography of a test subject
Reference point
Real distance (mm)
Projected distance, range (mm)
Error of method (mm)
Error of measurement (mm)
AB AC DE
9.1 6.0 12.7
9.0-11.1 7.0-10.7 12.7-17.3
0.08 0.08 0.07
0.06 0.05 0.05
The apparatus may also be used in combination with other X-ray machines.
Device for orientation of the film Thefilmis positioned relative to the subject by means of a film holder, which is moved along two parallel tubes. Films with dimensions up to 50 x 70 mm may be used. The films are supported by a metal plate and fixed with double-sided adhesive tape. The distance from the centre of the film-supporting plate to the centre ofthe subject table is recorded on scale
iber of dupl leal
a>
20
t Z
10
Difference (mm) Fig, 4. Error Fig. Erroi of measurement. Graphical representation of the distribution 1 ofthe Dfthi paired differences by repeated measurements on the same fflms.
G. The vertical anguiation of the film is read from (H) as well as the horizontal anguiation (I). To facilitate orientation ofthe film, the film piate may also be moved vertically (J). Eccentric exposures can be performed by rotating the subject in the horizontal plane. Test of error of method A test subject consisting of 12 steel globes each of diameter 0.5 mm embedded in a plastic plate was used to study the efficacy ofthe apparatus. The steel globes were arranged in four horizontal rows with three globes in
96
/. Forsberg
each row (Fig. la, T). The test subject was fixed to the subject table with four pins. Thirty exposures were performed on Kodak Ultraspeed film, DF5 7 (Eastman Kodak Co., Rochester, NY, USA). The expcKureparameters were 72 kV and 12 mA. Between exposures, the angles and distances between the target, subject and film were changed. Angles were read to an accuracy of one degree. The distance between target and subject was adjusted to an accuracy of 5 mm. Adjustment of all other scales of distance was performed to within 1 mm. Each adjustment was performed independently and the devices were fixed in their positions. All exposures were repeated a second time with adjustment of film, target and subject identical to those of the first series. Three linear distances were selected and measured on each radiograph (Fig. 2). Measurements were made from centre to centre of the projected globes. To calculate the error inherent in the measuring procedure, the films of the second series were measured twice. The measurements were performed in a room specifically designed for radiographic analysis. The radiographs were placed over a viewing box masked to the size of one flkn and examined with a x 5 magniiying glass to 0.1 mm.
Results Depending on the different orientations of film, target and subject, the distances which were measured varied {Table 1). The error of method calculated from pairs of radiographs was low. A graphical representation of the distribution is shown in Fig. 3. The error of measurement calculated from repeated reading of identical films is illustrated in Fig. 4. Discussion With the present equipment it was possible to make repeated exposures with a geometrical arrangement
nearly identical to that of the ordinal. Ofaviousiy, the independent adjustments of angles and distances eind the ability to fix the separate devices in the chosen positions made handling of the apparatus secure. During endodontic treatment the distance from the tip of a root canal imtrument, masteipoint or root filling to the apex is usually within the range 0-5 mm. The precision of measurements obtained with the apparatus will therefore permit experimental radiography of extracted teeth to elucidate the effects of varying geometrical arrangement on structures in the apical area. The effect of geometry on the imaging of periapical lesions has been little investigated. Clinical studies should be preceded by laboratory investigations, which permit controlled variation of angles and distances. The present apparatus or a similar construction would thus be suitable for comparison of the efficacy of the bisecting angle and the paralleling principles exposing extracted teeth with simulated periapical lesions. Research now in progress will compare the advantages and limitations of these techniques in endodontic diagnosis and therapy.
References CARLSSON G.E. & BENKOW H.H. (1964) JamfSrande undersokning melian en standardiserad pro)ektionstekn& och Instalining enltgt isometriregeln vid intraoral rontgenfotografering (English summary). Svensk TawSdkare Tidskrift. 6 1 . 1 3 3 - 1 4 2 . EGGEN S. (1969) Standardiserad intraoral rontgenteknik. Sveriges Tandldkarforbunds Tidning. 6 1 , 8 6 7 - 8 7 2 . FORSBERO J. (1987) A comparison of the paralleling and bisectingangle radiographic techniques in endodontics. International Endodontic journal. 20, 177-182. LARHHM T.A. & EOOEN S. (1979) Determination of tooth length with a standardized paralleling technique and calibrated radiographic film. Oral Surgery, Oral Medicine and Oral Pathology. 4 8 , 3 7 4 - 3 78. VANDB VOORDE H.E. & BJORNDAHL A. (1969) Estimating endodontic working length' with paralleling radiographs. Oral Surgery. Oral Medicine and Oral Pathology, 2 7 , 1 0 6 - 1 1 0 . WALKER R.T. (19 66) Device for the radiographic examination of teeth in vitro. Intemationai Endodontic journal 19, 315-317.
A method for experimental dental radiography J. FORSBERG Department of Oral Radiobgy, School of Dentistry, University of Bergen, Bergen, Norway
Summary An apparatus was designed for experimental dental radiography, which permitted separate a^ustment of the subject, target and film. The precision ct the apparatus was tested by radiographing a test subject, consisting erf' anall steel globes embedded in a plastic plate. The subject was placed in the apparatus and exp(Ked 30 times on dental X-ray film with different adjustments of angles and distances. Ail exposures were repeated after readjustment of the same form. Three linear distances between pairs of the projected steel globes were selected and measured on each radiogra[di. Depending on the different orientations of film, target and subject, the distances measured ranged from 9.011.1 mm, fi-om 7.0-10.7 mm and from 12.7-17.3 mm, respectively. From the measurements on the radiographs the error of method was calculated to be 0.07-0.08 mm and the error of measurement to be 0.05-0.06 mm. The precision ofthe apparatus was thus found to be adequate for measurement of differences in small, but clinically relevant, distances.
outline of the tooth apex in relation to the position of a contrasting object in the root canal, such as an instnunent or a root filling (Forsberg 1987). Walker (1986) reported a simple device for radiographic examination of teeth in vitro. However, the adjustments of the central beam and film in this apparatus appear to be limited. In order to study the effect of different angulations of central beam and film on the measurement of small distances it is necessary to use an adjustable apparatus with the capacity to record these variables in a reproducible manner. In the present paper an apparatus for experimental laboratory dental radiography is described. This apparatus permits separate adjustment ofthe subject, target and film. A series of test exposures and measurements of distances for calculating the error of method was performed. Description and use of apparatus The apparatus is shown in Fig. 1, and consists of three main parts. Device for orientation of subject
Keywords: dental radiography, endodontics. Introduction Endodontic diagnosis and treatment planning require adequate radiographic imaging of the tooth and periradicular structures. Particularly important is information about root canal morphology and the location and size of periapical bone destruction. The paralleling technique, although slightly enleirging the image of the tooth, has been found to produce less distortion than the bisecting-angle technique (Carlsson & Benkow 1964. Eggen 1969, Vande Voorde & Bjomdahl 1969, Larheim & Eggen 1979). In these studies the efficacy of the two techniques was assessed from measurements ofthe total length of tooth. In endodontic therapy it is most important to reproduce accurately the Correspondence: Dr ]. Forsberg, Department of Oral Radiology, School ot Dentistry. University ot Bergen, Arstadveien 17, N-5009, Bergen. Norway.
The subject table can be rotated in the horizontal plane (A). Two rows of canals, perpendicular to each other in the subject table, permit the fixation of the subject by means of two or more plastic-retaining pins. The subject may cdso be fixed in a bowl with thermoplastic impression material supplied with pins fitting the canals. Both methods of fixation allow repeated testing. For observation of endodontic relationships where an instrument is positioned in the root canal ofthe tooth, an extra canal is made in the centre ofthe subject table. The handle of a root canal file can be securely fixed and used as a vertical axis for the root canal. The subject may be rotated around its vertical axis by turning the subject table. The horizontal position is read on the scale at A. Device for orientation ofthe target and central beam A cone or open tube is fixed to a rangearm (B). By pushing the arm, the target-to-subject distance is altered. The movement ofthe cone in the vertical plane is 93
94
/. Forsberg (a)
Fig. 1. Apparatus for experimental dental radiography, (a) photograph, (b) diagram. Device for orientation of subject: A = subject table with scale for horizontal angulationof subject: T = test subject fixed to subject table. Device for orientation of target and central beam: B = rangearm. with fixed cone. for modifying target-subject distance: C = wheel for moving cone in verticaJ plane: D=scale for reading intersection of central beam with vertical axis of centre of subject table: E=: scale for reading vertical angle of central beam: F = aiming device for adjustment of central beam in relation to subject out of its aiming position. Device for orientation of film: G=scale for recording distance from filmsupporting plate to centre of subject tabie: H=scale for vertical angulation of film: i = scale for horizontal angulation offilm:J — scale for vertical movement of film plate.
achie\'ed by turning wheel C. The intersection of the central beam with the vertical axis of the centre of the subject table is recorded on scale D. The vertical angle is adjusted by rotating the rangearm, and is read on scale E. The adjustment ofthe central beam in relation to the subject is performed by means of an aiming device which
is fixed to the rangearm (F). The central beam passes through the tip of the aiming device. The beam centre coincides with the point where the tip touches the subject. In the present experimental system the Siemens Roentgenkugel (Siemens, Erlangen, Germany) was used.
A method for experimental dental radiography 1 40
95
_
3 30
I
•s S 20
-
5
Numtier
•5
1—1
1— Difference (mm)
Fig. i. Error of method. Graphical representation ofthe di^ribution of the differences by measurements of pairs of radiographs, exposed in the same way.
50
40
Fig. 2, Radiograph of the test subject showing the three distances measured for calculations of the error of method.
30
Table 1. The error of method in experimental radiography of a test subject
Reference point
Real distance (mm)
Projected distance, range (mm)
Error of method (mm)
Error of measurement (mm)
AB AC DE
9.1 6.0 12.7
9.0-11.1 7.0-10.7 12.7-17.3
0.08 0.08 0.07
0.06 0.05 0.05
The apparatus may also be used in combination with other X-ray machines.
Device for orientation of the film Thefilmis positioned relative to the subject by means of a film holder, which is moved along two parallel tubes. Films with dimensions up to 50 x 70 mm may be used. The films are supported by a metal plate and fixed with double-sided adhesive tape. The distance from the centre of the film-supporting plate to the centre ofthe subject table is recorded on scale
iber of dupl leal
a>
20
t Z
10
Difference (mm) Fig, 4. Error Fig. Erroi of measurement. Graphical representation of the distribution 1 ofthe Dfthi paired differences by repeated measurements on the same fflms.
G. The vertical anguiation of the film is read from (H) as well as the horizontal anguiation (I). To facilitate orientation ofthe film, the film piate may also be moved vertically (J). Eccentric exposures can be performed by rotating the subject in the horizontal plane. Test of error of method A test subject consisting of 12 steel globes each of diameter 0.5 mm embedded in a plastic plate was used to study the efficacy ofthe apparatus. The steel globes were arranged in four horizontal rows with three globes in
96
/. Forsberg
each row (Fig. la, T). The test subject was fixed to the subject table with four pins. Thirty exposures were performed on Kodak Ultraspeed film, DF5 7 (Eastman Kodak Co., Rochester, NY, USA). The expcKureparameters were 72 kV and 12 mA. Between exposures, the angles and distances between the target, subject and film were changed. Angles were read to an accuracy of one degree. The distance between target and subject was adjusted to an accuracy of 5 mm. Adjustment of all other scales of distance was performed to within 1 mm. Each adjustment was performed independently and the devices were fixed in their positions. All exposures were repeated a second time with adjustment of film, target and subject identical to those of the first series. Three linear distances were selected and measured on each radiograph (Fig. 2). Measurements were made from centre to centre of the projected globes. To calculate the error inherent in the measuring procedure, the films of the second series were measured twice. The measurements were performed in a room specifically designed for radiographic analysis. The radiographs were placed over a viewing box masked to the size of one flkn and examined with a x 5 magniiying glass to 0.1 mm.
Results Depending on the different orientations of film, target and subject, the distances which were measured varied {Table 1). The error of method calculated from pairs of radiographs was low. A graphical representation of the distribution is shown in Fig. 3. The error of measurement calculated from repeated reading of identical films is illustrated in Fig. 4. Discussion With the present equipment it was possible to make repeated exposures with a geometrical arrangement
nearly identical to that of the ordinal. Ofaviousiy, the independent adjustments of angles and distances eind the ability to fix the separate devices in the chosen positions made handling of the apparatus secure. During endodontic treatment the distance from the tip of a root canal imtrument, masteipoint or root filling to the apex is usually within the range 0-5 mm. The precision of measurements obtained with the apparatus will therefore permit experimental radiography of extracted teeth to elucidate the effects of varying geometrical arrangement on structures in the apical area. The effect of geometry on the imaging of periapical lesions has been little investigated. Clinical studies should be preceded by laboratory investigations, which permit controlled variation of angles and distances. The present apparatus or a similar construction would thus be suitable for comparison of the efficacy of the bisecting angle and the paralleling principles exposing extracted teeth with simulated periapical lesions. Research now in progress will compare the advantages and limitations of these techniques in endodontic diagnosis and therapy.
References CARLSSON G.E. & BENKOW H.H. (1964) JamfSrande undersokning melian en standardiserad pro)ektionstekn& och Instalining enltgt isometriregeln vid intraoral rontgenfotografering (English summary). Svensk TawSdkare Tidskrift. 6 1 . 1 3 3 - 1 4 2 . EGGEN S. (1969) Standardiserad intraoral rontgenteknik. Sveriges Tandldkarforbunds Tidning. 6 1 , 8 6 7 - 8 7 2 . FORSBERO J. (1987) A comparison of the paralleling and bisectingangle radiographic techniques in endodontics. International Endodontic journal. 20, 177-182. LARHHM T.A. & EOOEN S. (1979) Determination of tooth length with a standardized paralleling technique and calibrated radiographic film. Oral Surgery, Oral Medicine and Oral Pathology. 4 8 , 3 7 4 - 3 78. VANDB VOORDE H.E. & BJORNDAHL A. (1969) Estimating endodontic working length' with paralleling radiographs. Oral Surgery. Oral Medicine and Oral Pathology, 2 7 , 1 0 6 - 1 1 0 . WALKER R.T. (19 66) Device for the radiographic examination of teeth in vitro. Intemationai Endodontic journal 19, 315-317.
