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Absorbed radiation doses in transcranial temporomandibular joint radiography
MEDIAL
PTERYGOID
MUSCLE
ACTIVITY
CO and PC for the two subjects with Class II, division II malocclusion can be attributed not to a high PC but rather to a low CO activity. The palatally inclined incisors may have forced a posteriorly directed effort during the CO clench, which, as has been demonstrated, caused a drop to 20% of CO medial pterygoid muscle activity. This low level of activity in the COP was in agreement with the findings of Siirila et al6 The direction of applied effort is almost at right angles to the direction of the medial pterygoid muscle fibers for this act, whereas in the COA the two directions are parallel and the muscle is recruited to its maximum to contribute to the act. In any event it appears from the types of intercuspal clenches performed in this study that the medial pterygoid is sensitive to changes in the direction of effort, whatever the cause.
SUMMARY AND CONCLUSIONS Specific activity of the human medial pterygoid muscle in relation to jaw movements and occlusion during mastication and clenching tasks is unclear. EMG activity of the medial pterygoid, masseter, anterior, and posterior temporal muscles was recorded simultaneously with three dimensional incisor point movement of the mandi; ble. Data were sampled and analyzed by an on-line computer system. Patterns of medial pterygoid muscle activity were consistent for ipsilateral chewing and demonstrated activity of the muscle on the chewing side that peaked near the onset of intercirspation. The muscle on the contralateral side was active at the onset of intercuspation for subjects with a chopping stroke and inactive for those with a more lateral stroke guided into intercuspation on cuspal inclines. Activity in the early part of the
AbsoM radition temporomandibtilar
closing phase was associated with a marked jaw movement toward the chewing side. There was generally less activity in protrusive than intercuspal clenching when occlusion was normal but more activity if marked incisal wear was present or multiple tooth contacts could be attained on protrusion. Intercuspal clenching initiated less activity when force was directed posteriorly and more activity when directed anteriorly than vertical intercuspal clenching. The author wishes to thank Mrs. J.D. Scott and Mr. R.E. DeCou for their technical assistance in this study.
REFERENCES 1. Moller E: The chewing apparatus: An electromyographic study of the action of the muscle of mastication and its correlation to facial morphology. Acta Physiol &and 69(Suppl):280, 1966. 2. Hannam AG, Wood WW: Medial pterygoid muscle activity during the closing and compressive phases of human mastication. Am J Phys Anthropol 55~359, 1981. 3. MacDonald JWC, Hannam AG: Relationship between occlusal contacts and jaw-closing muscle activity during tooth clenching: Part II. J PROSTHET DENT 52:862, 1984. 4. Carlsoo S: Nervous co-ordination and mechanical function of mandibular elevators. Acta Odontol Stand iO(Supp1. 1 l):l, 1952. 5. Hannam AG, DeCou RE, Scott JD, Wood WW: The kinesiographic measurement of jaw displacement. J PROSTHET DENT 44~88, 1980. 6. Siirila HS, Ekholm A, Aula S: An electromyographic study of the function of the medial pterygoid muscle. Suom Hammaslaak Toim 56:421, 1960. Reprint requests to: DR. W. W. Wool FACULTY OF DENTISTRY UNIVERSITY OF BRITISH COLUMBIA VANCOWER, B.C. CANADA V6T 127
doses in transcranial joint radiography
Tarnjit S. Ssrini, B.D.S., M.S.,* Willard G. Fischer, D.D.S., M.S.,** and Robert S. Verbin, D.M.D., Ph.D.*** University of Pittsburgh, School of Dental Medicine, Pittsburgh, Pa.
T
emporomandibular joint (TMJ) radiography provides vital information concerning the status and dynam*Assistant Professor, Department of Diagnostic Services. **Associate Professor, Department of Diagnostic Services. ***Professor and Chairman, Department of Diagnostic Services. THE JOURNAL
OF PROSTHmC
DENTISTRY
ic relationship of joint components. Because of the anatomic location and morphologic diversities between patients and between joints in the same patient, imaging of this region is difficult.’ Various specialized radiagraphic techniques such as cephalometric corrected conventional tomography2-’ and computerized axial tomog621
SAINI,
FESCWER, AND
VBRBIN
faster screen-film combinations and a strict collimation of the beam.
Fig. 1. A, Rando “average man” head and neck phantom. B, Condy-ray system. C, Accurad system. D, AXA system. E, Farrar system.
raphy5 have been developed in the effort to eliminate these difficulties. Conventional radiographic techniques, especially lateral transcranial radiography, continue to be used to demonstrate both the structural and functional relationships of the joint. The quality of the images produced by these conventional techniques, however, is limited by the “clutter” of intervening anatomic structures and image distortion.6S* In spite of the reduced clarity, these teehniques demonstrate the functional relationship of the joint components? Presently, many TMJ positioners are commercially available that assist in standardizing the geometry of images and facilitate localization of the region of interest (Fig. l).‘O The purpose of this study is to measure and compare the radiation dose distribution to the head and neck when using four of these positioners. In the dental literature, Brooks and Lanzetta” recently reported the first comprehensive study on dose distribution by using dental x-ray generators. Although other authors reported on head and neck radiation doses, they did not work with dental x-ray generators or the image receptor combinations did not permit extrapolation of their data to this study. 12-14Using lateral transcranial radiography, Rrooks and Lannetta’~~~ m&surements of skin entrance doses varied from &SOto 850 rr&iradsper exposure. Because of the high exposure, they recommend 622
A Rando “averageman” (Machlett-Alderson Company, Springdale, Corm.) head and neck phantom was used for measuring the absorbed dose distribution in 17 locations (Table I). This phantom includes a dry skdl covered by a tissue-simulating synthetic material- It is horizontally sectioned into 10 equal segments 1 inch thick. Thirty-four holes are drilled into the phabtom at various intervals to house thermoluminscent -dosimeters (TLDs). The loaded phantom was placed on a block of lead to prevent back scatter. Each of the four TMJ positioners was placed according to the manufacturer’s instructions for imaging the right TMJ region of the phantom. The positioners had collimators of various dimensions to restrict the size of the x-ray beam. Each positioner was iocated at a different collimator-to-skin distance (Table II). A calibrated GE 900 (Gendex Corpor&on, Milwaukee, Wis.) dental x-ray unit fitted with a 12-inch lead-lined positioning cone was used in this study. The positioning cone had a beam-restricting lead collimator with an aperture 1 cm in diameter located on the end of. the tube. The x-ray unit was filtered with 2.7 nun of aluminum. A preliminary study was done to find a single exposure time applicable to all four- positioners to provide the most readable diagnostic image. Kodak Lanex Regular intensifying screens and Kodak .OL screen films (Eastman Kodak Co., Roehester, N.Y.) were used with all exposures. Optimum diagnost& images were produced when the unit was oper&ed at 9Q kVp, 15 mA, and 18 impulses. The loaded phantom was exposed 10 times with each of the four techniques. An arithmetic average was calculated to find the dose received at each selected location. This procedure was repeated three times with each positioner. A new TLD was used with each l&exposure series and-a totalof 44!$ TLDs were exposed. The do&meters .werc read -in a Harshaw 2000 series T.L.D. reader (Ha&raw Chemical Co., Cleveland, Ohio).‘5
RESULTS Absorbed doses were measured at vs&&~ locations (Table I). The radiatian-absorbed ~dosesat the-point of entrance (left side of phantom) varied from i75 to 161 millirads per exposure. Measured doses at exit over the right TMJ varied from 2;s to 3.2 milli~ds. The TLDs located in the thytx&d -arp, the. .bone marrow of the sixth to the seeond eer&&
1986
VOLUME
55
NUMBER
5
Table I. Radiation projection
absorbed doses to different
locations
in skull phantom
from a single transcranial
TM J positioners
1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17.
Thyroid gland Sixth to second cervical vertebrae First cervical vertebrae (midline) Body and ramus of mandible Parotid gland Maxillary antrum Condyle Skin TMJ region Eyes Sella turcica (midline) Petrous portion of temporal bone Squamous portion of temporal bone Junction of temporal and parietal bone Skin of the junction of temporal and parietal bone Parietal bone Frontal bone Occipital bone
Condy-ray’ millirads dose
Accuradt millirads dose
Entry side
Entry side
Exit side
7.0
-
-
2.7
4.8 2.9
-
17.7 3.5 7.4 6.6
7.0 -
3.0
-
Entry side
2.5
3.4
191.2
Exit side
AXAS millirads dose Exit side
2.9
3.4 3.2
16.2 3.0 10.6
3.2
205.2
-
-
Farrar system IQ millirads dose Entry side
Exit side
2.8
3.2 2.6
13.4 3.2 4.0
4.9 -
186.1
-
2.8
-
2.6 2.5 4.5 2.7 9.3 4.0 175.8
- = Dose undetectable. *Rinn Corp., Elgin, Ill. tDenar Corp., Anaheim, Calif. $Teledyne Dental-Hanau, Buffalo, N.Y. $Brell Mar Products, Clinton, Mass.
The pituitary gland received 4.5 millirads with the Farrar system (Brell Mar Products, Clinton, Mass.) and 17.7 millirads with the Condy-ray device (Rinn Corp., Elgin, Ill.) No measurable dose was detected in the parotid gland region on the entrance side, but on the exit side the parotid gland received 3.8 millirads when the Condy-ray device (Rinn Corp.) was used. The dose to the anterior part of the first cervical vertebra varied from 2.5 to 2.8 millirads with all positioners except the Condy-ray in which it was 7 millirads. DISCUSSION The ionizing radiation dose used for diagnostic purposes in maxillofacial radiology has not been demonstrated to produce any perceptible deleterious biologic effect. The statistical data accumulated from groups exposed to high dosages have been intrapolated to the lower dosages to provide quantitative estimation of biologic risks. Because of the lack of definite proof of assumed risks, prudence demands that the so-called risk should be kept at a minimum. The profession must strive to further reduce the minimum assumed risk to attain public confidence Radiation hygiene emphasizes the THE JOURNAL
OF PROSTHETIC
DENTISTRY
Table II. Types and characteristics of TMJ positioners used in transcranial projections TMJ positioners ‘Condy-ray t Accurad #AXA tjFarrar system
Collimator dimensions 4.1 2.7 1.8 2.9
cm cm cm cm
X 3.3 cm x 2.7 cm
diameter X 3.3 cm
Collimatorskin distance 5 3.7 7.5 5.8
cm cm cm cm
*Rinn Corp., Elgin, Ill. tDenar Corporation, Anaheim, Calif. *Teledyne Dental-Hanau, Buffalo, N.Y. §Brell Mar Products, Clinton, Mass.
importance of curtailing the size of the x-ray beam to include only the area of interest. This can be readily achieved by using a TMJ positioner. This study demonstrates that introduction of fast screen-film combinations such as rare earth screens and orthochromatic films can markedly reduce skin entrance doses to 175 to 200 millirads. This is approximately one third the dose reported by Brooks and Lanzetta” in their 623
SAINI,
study involving lateral transcranial projections. The radiation dose measured at the exit area over the TMJ varied from 2.5 to 3.2 millirads. Brooks and Lanzetta” mentioned that skin exit exposure was detectable in their study but was too low to be measured accurately. WeinbergI has stated that in exposing three pairs of TMJ radiographs (one each with the jaws closed, jaws opened, and with the mandible in the rest position) the amount of radiation exposure is approximately equal to that found in exposing 54 periapical films. That study was conducted using 65 kVp for intraoral and 68 kVp for extraoral projections. WeinbergI used par speed intensifying screens and Blue-Brand medical x-ray films (Eastman Kodak Co., Rochester, N.Y.) with the recommended exposure time of 2 seconds for a single TMJ projection. The 200 millirads measured at the skin entrance in this study is approximately equal to the reported exposure for a single intraoral periapical projection. ” However, this comparison is not valid because of the quantitative difference in bone marrow radiated in these differing types of projections. During the making of a complete-mouth radiographic survey, the thyroid gland receives radiation estimated to range from 6 millirads using a rectangular collimator to 23 millirads using an open shielded cylindrical cone.‘* By comparison, the thyroid may receive undetectable, low amounts in TMJ radiography as both this study and the one conducted by Brooks and Lanzetta indicate. Exposure data obtained relative to the Accurad (Denar Corp., Anaheim, Calif.), AXA (Teledyne Dental, Hanau, Buffalo, N.Y.), and Farrar (Brell Mar Products) systems are remarkably close. However, data obtained in use of the Condy-ray (Rinn Corp.), particularly with reference to the bone marrow of the first cervical vertebra, condyle on the entrance side, and parotid gland on the exit side, indicated greater absorbed doses. This may be accounted for by the wider collimahr used with this device and the shorter-than-recommended positioning cone used in this study.
SUMMARY Lateral transcranial radiographs are commonly used to evaluate TMJ morphology and function. This study evaluated the use of four TM J positioners in controlling the amount of radiation absorbed at predetermined sites on a phantom head. Use of positioners and collimators can reduce the amount of radiation exposure.
624
FISCHER ANzt VERBIN
1. Yale SH, Allison BD, Hauptfuehrer JD: An epidemiological assessment of mandibular condyles morphology. Oral Surg 21:169,
2. 3. 4.
5.
6. 7. 8.
9. 10.
11. 12. 13.
14.
15.
16. 17.
18.
1966.
Rosenberg HM: Laminagraphy methods and application in oral diagnosis. J Am Dent Assoc 7488, 1967. Dunn M J, Rabinov K, Hayes C: Polycycloidal corrected tomography of temporomandibular joint. Oral Surg 51:375, 1981. Williamson H, Wilson CW: The use of submental vertex analysis for producing quality temporomandibular joint laminagraphs. Am J Orthod i’&2CKJ, 1976. Roberts D, Pettigrew J, Udupa J, Ram C: Three-dimensional imaging and display of the temporomandibutar joint. Oral Surg 58:461, 1984. Berry DC, Chick AO: Temporomandibular joint: interpretation of radiographs. Dent Pratt Dent Ret 7:18. 1956. Jones GL, Harris SD: Transcranial radiographs of temporomandibular joint. J Dent Res 59~152, 1979. Rosenberg HM, Silha RE: Temporomandibuiar joint radiography with emphasis on tomography. Dent Radiogr Photogr 551, 1982. Weinberg LA: Correlation of temporomandibular dysfunction with radiographic finding. J PROSTHET DENT Z&519, 1972. Donovan W: A method of temporomandibular joint roentgenography for serial or multiple records. J Am Dent Assoc 49:4Ql; 1954. Brooks SL, Lanzetta M: Absorbed doses from temporomandibular joint radiography. Oral Surg 59:647, 1985. Hollender L, Lyskll G: Radiation doses during roentgenography of the head. Odont Revv 1515, 1964. Affolter A, Graf H, Poretti G: Radiation exposure of teeth and temporomandibular joints by radiography. Schwiez Monatsschr Zahnheilkd 89:1221, 1979. Rother U, Hildebrandt KH, Konig W: Somatic radiation load by radiography of temporomandibuiar joint. ~Stomatol DDR 29~49, 1979. White WB, Tanner BK, Wood RE, Palms JIM: Use of the Harshaw Model 2000 for thermoluminescence analvsis of environmental b&ground level dose measurements, April, 1973. (Information provided with operating instructions for the Haeshaw Model 2000). Weinberg LA: Radiographic investigation into temporomandibular joint function. J PR~STHET DENT 33:672, 19% Langland GE, Sippy FH, Langlais RP: Textbook of Dental Radiology, ed 2. Springfield, III., 1984, Chart& C. Thomas, Publisher, chap 6, p 188. Smith QW, Preece JW, Hefley DC, Easser CE: Radiation exposure in the dental setting: An update. Radio1 Tech1101 55:546, 1983.
Hqml reyue.sls to: DR. WILLARD G. FISCHER C-174 SALK HALL UNIVERSITY OF P~~EURGH Scnoo~ OF DENTAL MEDICINE PITKSBIJRGH, PA 15261
MAY
1966
VOLUME55
NWbHSFiR5
PTERYGOID
MUSCLE
ACTIVITY
CO and PC for the two subjects with Class II, division II malocclusion can be attributed not to a high PC but rather to a low CO activity. The palatally inclined incisors may have forced a posteriorly directed effort during the CO clench, which, as has been demonstrated, caused a drop to 20% of CO medial pterygoid muscle activity. This low level of activity in the COP was in agreement with the findings of Siirila et al6 The direction of applied effort is almost at right angles to the direction of the medial pterygoid muscle fibers for this act, whereas in the COA the two directions are parallel and the muscle is recruited to its maximum to contribute to the act. In any event it appears from the types of intercuspal clenches performed in this study that the medial pterygoid is sensitive to changes in the direction of effort, whatever the cause.
SUMMARY AND CONCLUSIONS Specific activity of the human medial pterygoid muscle in relation to jaw movements and occlusion during mastication and clenching tasks is unclear. EMG activity of the medial pterygoid, masseter, anterior, and posterior temporal muscles was recorded simultaneously with three dimensional incisor point movement of the mandi; ble. Data were sampled and analyzed by an on-line computer system. Patterns of medial pterygoid muscle activity were consistent for ipsilateral chewing and demonstrated activity of the muscle on the chewing side that peaked near the onset of intercirspation. The muscle on the contralateral side was active at the onset of intercuspation for subjects with a chopping stroke and inactive for those with a more lateral stroke guided into intercuspation on cuspal inclines. Activity in the early part of the
AbsoM radition temporomandibtilar
closing phase was associated with a marked jaw movement toward the chewing side. There was generally less activity in protrusive than intercuspal clenching when occlusion was normal but more activity if marked incisal wear was present or multiple tooth contacts could be attained on protrusion. Intercuspal clenching initiated less activity when force was directed posteriorly and more activity when directed anteriorly than vertical intercuspal clenching. The author wishes to thank Mrs. J.D. Scott and Mr. R.E. DeCou for their technical assistance in this study.
REFERENCES 1. Moller E: The chewing apparatus: An electromyographic study of the action of the muscle of mastication and its correlation to facial morphology. Acta Physiol &and 69(Suppl):280, 1966. 2. Hannam AG, Wood WW: Medial pterygoid muscle activity during the closing and compressive phases of human mastication. Am J Phys Anthropol 55~359, 1981. 3. MacDonald JWC, Hannam AG: Relationship between occlusal contacts and jaw-closing muscle activity during tooth clenching: Part II. J PROSTHET DENT 52:862, 1984. 4. Carlsoo S: Nervous co-ordination and mechanical function of mandibular elevators. Acta Odontol Stand iO(Supp1. 1 l):l, 1952. 5. Hannam AG, DeCou RE, Scott JD, Wood WW: The kinesiographic measurement of jaw displacement. J PROSTHET DENT 44~88, 1980. 6. Siirila HS, Ekholm A, Aula S: An electromyographic study of the function of the medial pterygoid muscle. Suom Hammaslaak Toim 56:421, 1960. Reprint requests to: DR. W. W. Wool FACULTY OF DENTISTRY UNIVERSITY OF BRITISH COLUMBIA VANCOWER, B.C. CANADA V6T 127
doses in transcranial joint radiography
Tarnjit S. Ssrini, B.D.S., M.S.,* Willard G. Fischer, D.D.S., M.S.,** and Robert S. Verbin, D.M.D., Ph.D.*** University of Pittsburgh, School of Dental Medicine, Pittsburgh, Pa.
T
emporomandibular joint (TMJ) radiography provides vital information concerning the status and dynam*Assistant Professor, Department of Diagnostic Services. **Associate Professor, Department of Diagnostic Services. ***Professor and Chairman, Department of Diagnostic Services. THE JOURNAL
OF PROSTHmC
DENTISTRY
ic relationship of joint components. Because of the anatomic location and morphologic diversities between patients and between joints in the same patient, imaging of this region is difficult.’ Various specialized radiagraphic techniques such as cephalometric corrected conventional tomography2-’ and computerized axial tomog621
SAINI,
FESCWER, AND
VBRBIN
faster screen-film combinations and a strict collimation of the beam.
Fig. 1. A, Rando “average man” head and neck phantom. B, Condy-ray system. C, Accurad system. D, AXA system. E, Farrar system.
raphy5 have been developed in the effort to eliminate these difficulties. Conventional radiographic techniques, especially lateral transcranial radiography, continue to be used to demonstrate both the structural and functional relationships of the joint. The quality of the images produced by these conventional techniques, however, is limited by the “clutter” of intervening anatomic structures and image distortion.6S* In spite of the reduced clarity, these teehniques demonstrate the functional relationship of the joint components? Presently, many TMJ positioners are commercially available that assist in standardizing the geometry of images and facilitate localization of the region of interest (Fig. l).‘O The purpose of this study is to measure and compare the radiation dose distribution to the head and neck when using four of these positioners. In the dental literature, Brooks and Lanzetta” recently reported the first comprehensive study on dose distribution by using dental x-ray generators. Although other authors reported on head and neck radiation doses, they did not work with dental x-ray generators or the image receptor combinations did not permit extrapolation of their data to this study. 12-14Using lateral transcranial radiography, Rrooks and Lannetta’~~~ m&surements of skin entrance doses varied from &SOto 850 rr&iradsper exposure. Because of the high exposure, they recommend 622
A Rando “averageman” (Machlett-Alderson Company, Springdale, Corm.) head and neck phantom was used for measuring the absorbed dose distribution in 17 locations (Table I). This phantom includes a dry skdl covered by a tissue-simulating synthetic material- It is horizontally sectioned into 10 equal segments 1 inch thick. Thirty-four holes are drilled into the phabtom at various intervals to house thermoluminscent -dosimeters (TLDs). The loaded phantom was placed on a block of lead to prevent back scatter. Each of the four TMJ positioners was placed according to the manufacturer’s instructions for imaging the right TMJ region of the phantom. The positioners had collimators of various dimensions to restrict the size of the x-ray beam. Each positioner was iocated at a different collimator-to-skin distance (Table II). A calibrated GE 900 (Gendex Corpor&on, Milwaukee, Wis.) dental x-ray unit fitted with a 12-inch lead-lined positioning cone was used in this study. The positioning cone had a beam-restricting lead collimator with an aperture 1 cm in diameter located on the end of. the tube. The x-ray unit was filtered with 2.7 nun of aluminum. A preliminary study was done to find a single exposure time applicable to all four- positioners to provide the most readable diagnostic image. Kodak Lanex Regular intensifying screens and Kodak .OL screen films (Eastman Kodak Co., Roehester, N.Y.) were used with all exposures. Optimum diagnost& images were produced when the unit was oper&ed at 9Q kVp, 15 mA, and 18 impulses. The loaded phantom was exposed 10 times with each of the four techniques. An arithmetic average was calculated to find the dose received at each selected location. This procedure was repeated three times with each positioner. A new TLD was used with each l&exposure series and-a totalof 44!$ TLDs were exposed. The do&meters .werc read -in a Harshaw 2000 series T.L.D. reader (Ha&raw Chemical Co., Cleveland, Ohio).‘5
RESULTS Absorbed doses were measured at vs&&~ locations (Table I). The radiatian-absorbed ~dosesat the-point of entrance (left side of phantom) varied from i75 to 161 millirads per exposure. Measured doses at exit over the right TMJ varied from 2;s to 3.2 milli~ds. The TLDs located in the thytx&d -arp, the. .bone marrow of the sixth to the seeond eer&&
1986
VOLUME
55
NUMBER
5
Table I. Radiation projection
absorbed doses to different
locations
in skull phantom
from a single transcranial
TM J positioners
1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17.
Thyroid gland Sixth to second cervical vertebrae First cervical vertebrae (midline) Body and ramus of mandible Parotid gland Maxillary antrum Condyle Skin TMJ region Eyes Sella turcica (midline) Petrous portion of temporal bone Squamous portion of temporal bone Junction of temporal and parietal bone Skin of the junction of temporal and parietal bone Parietal bone Frontal bone Occipital bone
Condy-ray’ millirads dose
Accuradt millirads dose
Entry side
Entry side
Exit side
7.0
-
-
2.7
4.8 2.9
-
17.7 3.5 7.4 6.6
7.0 -
3.0
-
Entry side
2.5
3.4
191.2
Exit side
AXAS millirads dose Exit side
2.9
3.4 3.2
16.2 3.0 10.6
3.2
205.2
-
-
Farrar system IQ millirads dose Entry side
Exit side
2.8
3.2 2.6
13.4 3.2 4.0
4.9 -
186.1
-
2.8
-
2.6 2.5 4.5 2.7 9.3 4.0 175.8
- = Dose undetectable. *Rinn Corp., Elgin, Ill. tDenar Corp., Anaheim, Calif. $Teledyne Dental-Hanau, Buffalo, N.Y. $Brell Mar Products, Clinton, Mass.
The pituitary gland received 4.5 millirads with the Farrar system (Brell Mar Products, Clinton, Mass.) and 17.7 millirads with the Condy-ray device (Rinn Corp., Elgin, Ill.) No measurable dose was detected in the parotid gland region on the entrance side, but on the exit side the parotid gland received 3.8 millirads when the Condy-ray device (Rinn Corp.) was used. The dose to the anterior part of the first cervical vertebra varied from 2.5 to 2.8 millirads with all positioners except the Condy-ray in which it was 7 millirads. DISCUSSION The ionizing radiation dose used for diagnostic purposes in maxillofacial radiology has not been demonstrated to produce any perceptible deleterious biologic effect. The statistical data accumulated from groups exposed to high dosages have been intrapolated to the lower dosages to provide quantitative estimation of biologic risks. Because of the lack of definite proof of assumed risks, prudence demands that the so-called risk should be kept at a minimum. The profession must strive to further reduce the minimum assumed risk to attain public confidence Radiation hygiene emphasizes the THE JOURNAL
OF PROSTHETIC
DENTISTRY
Table II. Types and characteristics of TMJ positioners used in transcranial projections TMJ positioners ‘Condy-ray t Accurad #AXA tjFarrar system
Collimator dimensions 4.1 2.7 1.8 2.9
cm cm cm cm
X 3.3 cm x 2.7 cm
diameter X 3.3 cm
Collimatorskin distance 5 3.7 7.5 5.8
cm cm cm cm
*Rinn Corp., Elgin, Ill. tDenar Corporation, Anaheim, Calif. *Teledyne Dental-Hanau, Buffalo, N.Y. §Brell Mar Products, Clinton, Mass.
importance of curtailing the size of the x-ray beam to include only the area of interest. This can be readily achieved by using a TMJ positioner. This study demonstrates that introduction of fast screen-film combinations such as rare earth screens and orthochromatic films can markedly reduce skin entrance doses to 175 to 200 millirads. This is approximately one third the dose reported by Brooks and Lanzetta” in their 623
SAINI,
study involving lateral transcranial projections. The radiation dose measured at the exit area over the TMJ varied from 2.5 to 3.2 millirads. Brooks and Lanzetta” mentioned that skin exit exposure was detectable in their study but was too low to be measured accurately. WeinbergI has stated that in exposing three pairs of TMJ radiographs (one each with the jaws closed, jaws opened, and with the mandible in the rest position) the amount of radiation exposure is approximately equal to that found in exposing 54 periapical films. That study was conducted using 65 kVp for intraoral and 68 kVp for extraoral projections. WeinbergI used par speed intensifying screens and Blue-Brand medical x-ray films (Eastman Kodak Co., Rochester, N.Y.) with the recommended exposure time of 2 seconds for a single TMJ projection. The 200 millirads measured at the skin entrance in this study is approximately equal to the reported exposure for a single intraoral periapical projection. ” However, this comparison is not valid because of the quantitative difference in bone marrow radiated in these differing types of projections. During the making of a complete-mouth radiographic survey, the thyroid gland receives radiation estimated to range from 6 millirads using a rectangular collimator to 23 millirads using an open shielded cylindrical cone.‘* By comparison, the thyroid may receive undetectable, low amounts in TMJ radiography as both this study and the one conducted by Brooks and Lanzetta indicate. Exposure data obtained relative to the Accurad (Denar Corp., Anaheim, Calif.), AXA (Teledyne Dental, Hanau, Buffalo, N.Y.), and Farrar (Brell Mar Products) systems are remarkably close. However, data obtained in use of the Condy-ray (Rinn Corp.), particularly with reference to the bone marrow of the first cervical vertebra, condyle on the entrance side, and parotid gland on the exit side, indicated greater absorbed doses. This may be accounted for by the wider collimahr used with this device and the shorter-than-recommended positioning cone used in this study.
SUMMARY Lateral transcranial radiographs are commonly used to evaluate TMJ morphology and function. This study evaluated the use of four TM J positioners in controlling the amount of radiation absorbed at predetermined sites on a phantom head. Use of positioners and collimators can reduce the amount of radiation exposure.
624
FISCHER ANzt VERBIN
1. Yale SH, Allison BD, Hauptfuehrer JD: An epidemiological assessment of mandibular condyles morphology. Oral Surg 21:169,
2. 3. 4.
5.
6. 7. 8.
9. 10.
11. 12. 13.
14.
15.
16. 17.
18.
1966.
Rosenberg HM: Laminagraphy methods and application in oral diagnosis. J Am Dent Assoc 7488, 1967. Dunn M J, Rabinov K, Hayes C: Polycycloidal corrected tomography of temporomandibular joint. Oral Surg 51:375, 1981. Williamson H, Wilson CW: The use of submental vertex analysis for producing quality temporomandibular joint laminagraphs. Am J Orthod i’&2CKJ, 1976. Roberts D, Pettigrew J, Udupa J, Ram C: Three-dimensional imaging and display of the temporomandibutar joint. Oral Surg 58:461, 1984. Berry DC, Chick AO: Temporomandibular joint: interpretation of radiographs. Dent Pratt Dent Ret 7:18. 1956. Jones GL, Harris SD: Transcranial radiographs of temporomandibular joint. J Dent Res 59~152, 1979. Rosenberg HM, Silha RE: Temporomandibuiar joint radiography with emphasis on tomography. Dent Radiogr Photogr 551, 1982. Weinberg LA: Correlation of temporomandibular dysfunction with radiographic finding. J PROSTHET DENT Z&519, 1972. Donovan W: A method of temporomandibular joint roentgenography for serial or multiple records. J Am Dent Assoc 49:4Ql; 1954. Brooks SL, Lanzetta M: Absorbed doses from temporomandibular joint radiography. Oral Surg 59:647, 1985. Hollender L, Lyskll G: Radiation doses during roentgenography of the head. Odont Revv 1515, 1964. Affolter A, Graf H, Poretti G: Radiation exposure of teeth and temporomandibular joints by radiography. Schwiez Monatsschr Zahnheilkd 89:1221, 1979. Rother U, Hildebrandt KH, Konig W: Somatic radiation load by radiography of temporomandibuiar joint. ~Stomatol DDR 29~49, 1979. White WB, Tanner BK, Wood RE, Palms JIM: Use of the Harshaw Model 2000 for thermoluminescence analvsis of environmental b&ground level dose measurements, April, 1973. (Information provided with operating instructions for the Haeshaw Model 2000). Weinberg LA: Radiographic investigation into temporomandibular joint function. J PR~STHET DENT 33:672, 19% Langland GE, Sippy FH, Langlais RP: Textbook of Dental Radiology, ed 2. Springfield, III., 1984, Chart& C. Thomas, Publisher, chap 6, p 188. Smith QW, Preece JW, Hefley DC, Easser CE: Radiation exposure in the dental setting: An update. Radio1 Tech1101 55:546, 1983.
Hqml reyue.sls to: DR. WILLARD G. FISCHER C-174 SALK HALL UNIVERSITY OF P~~EURGH Scnoo~ OF DENTAL MEDICINE PITKSBIJRGH, PA 15261
MAY
1966
VOLUME55
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