- Email: [email protected]
Radiographic detection of porosities in removable partial denture castings
Radiographic detection of porosities in removable partial denture castings Elamin A. Elarbi, B.D.S, M.D.S.,* Yahia H. Ismail, D.M.D., Ph.D.,** Mohsen Azarbal, D.M.D., M.D.!&,*** and Tarnjit S. Saini, B.D.S., M.S.**** University of Pittsburgh, School of Dental Medicine, Pittsburgh, Pa.
M
any chrome-cobalt castings contain internal and external defects of varying size and shape, which can cause failure of the prosthesis. Previous investigations have shown that industrial and dental radiograph machines can be used to detect such structural defects.lw6 Since the radiograph machine is readily available in most dental offices, this study was designed to determine its usefulness in detecting flaws in removable partial denture frameworks. Although two alloys were used, no comparison was made as to the superiority of one over the other.
MATERIAL
AND METHODS
Seventy-seven removable partial denture frameworks were obtained from two dental laboratories that used standardized induction casting techniques. The 30 Ticonium (Ticonium Division, CMP Industries, Albany, N.Y.) castings provided by one laboratory and the 47 Nobilium (Nobilium Division, CMP Industries) castings provided by the other were frameworks for patients seeking treatment at the University of Pittsburgh. A GE 900 X-ray machine (General Electric Co., Milwaukee, Wis.) with a 2.7 mm aluminum equivalent half-layer was operated at 15 mA and 90 kV(p). The exposure time was set at 3/5 second (36 impulses) to produce a good quality radiograph of the castings. Kodak dental film group D (Eastman Kodak Co., Rochester, N.Y.) size 1.2 (31 X 41 mm) was used, because trials indicated that the periapical film was easy to position in critical regions of the casting because of its size. During each radiographic exposure, the central beam was perpendicular to the specimen surface. The castings were radiographed with different angulations to record various components and to obtain better visibility of casting defects (Fig. 1). Each casting was given a code
*Clinical Fellow, Department of Prosthodontics. **Professor and Chairman, Department of Prosthodontics. ***Assistant Professor, Department of Prosthodontics. ****Assistant Professor and Supervisor, Radiology Section, Department of Diagnostic Services.
674
Fig. 1. Casting is positioned and supported by wax for radiographic exposure of I-bar. Note that central beam is perpendicular to specimen surface.
Fig. 2. Semicircular defect at center of T-clasp is indidot is shown by cated by arrow a. Film identification arrow b.
number, and similar lead numerals were included in the exposure so that cross-identification could be made. The films were processed in a Xonics 4%-minute automatic processor (Xonics Radiographs, Inc., Arlington Heights, Ill). All of the radiographs were viewed independently in a semidark room with a variable
NOVEMBER
1985
VOLUME
54
NUMBER
5
RADIOGRAPHIC
DETECTION OF POROSITIES
Fig. 4. Large void at origin of retentive arm is indicated by arrow a. Circular radiolucent areas indicated by arrow b are framework mesh. Relative radiolucent area shown by arrow c is thinness of casting.
Fig. 3. Two semicircular defects are visible at junction of retentive arms of embrasure clasp indicated by arrow a. Arrow b points to radiolucency on base of occlusal rest caused by thinness of casting.
Table I. Distribution
of radiolucencies
indicative
of defects according
to sites of occurrences
in two
alloys Occurrence of defects
Maxillary Ticonium
Clasp unit Major connector bars and lingual plates
Mandibular Nobilium
4
high-intensity illuminator (CGR Medical Corp., Baltimore, Md.) and a magnifier (x5). The results are presented in absolute values and percentages.
Ticonium
17 11
9 7
The findings of the radiographic examination indisites of casting defects in the two different alloys are listed in Table I. Table II exhibits the number and percent of defects in the various components of castings studied. In total, 47 of 77 castings (61.04%) exhibited structural defects in clasp units, major connectors, or both. Twenty castings (25.97%) contained one flaw; seven castings (9.09%) had three flaws. There were four or more flaws in four castings (5.19%), and cracks were readily detected with good contrast in nine frameworks (11.69%). Well defined voids were found in nine castings (11.69%).
DISCUSSION This study demonstrated that a 90 kVp radiograph machine provides an adequate source to detect large or small defects in base-metal removable partial denture castings. The desirable removable partial denture framework
THE JOURNAL OF PROSTHETIC DENTISTRY
Total
36 24
66 42
Table II. Number and percent of incidence of defects in total casting componenlts both alloys*
RESULTS cated a total of 108 internal defects. The frequency and
Nobilium
Castings
Clasp units Retentive arms Reciprocal arms Occlusal rests Minor connectors Major connectors Lingual bars/plates Anterior/posterior palatal bars
No. studied
No. showing defects
of
Percent
232 230 146 233 140 69 57
43 33 9 9 11 15 10
18.53 14.35 6.16 3.86 7.86 21.74 17.54
12
5
41.67
*Total defects regardless of degree of acceptability.
should show no sizeable defects within its structure to be able to fulfill its function. In Figs. 2 to 8, distinctive defects of varying size and shape, which may jeopardize the quality of the castings, are seen in the structure of different components. According to Strandman and Lockowandt,’ defects such as fissures and microporosities with surface connec-
675
ELARBI
Fig. 5. Visible defect exists at origin of I-bar and is seen on casting (arrow).
rig. 6. Uetect on occlusal rest (arrow a) not visible on casting. Arrow b shows visible defect on casting close to proximal supporting plate.
tions may result in increased corrosion of the alloy. Based on this finding, the cracks at the inferior border of the lingual plate in Fig. 8 may lead to corrosion and subsequent failure of the removable partial denture. The presence of a radiolucent area in a radiograph does not necessarily represent a critical structural defect. However, radiolucent areas in dental castings may indicate less than optimum thickness that endanger the casting to the extent that the entire structure becomes susceptible to fracture. This may explain the higher rate of fractures of flawless castings while they are in use. Accordingly, special attention must be given during the waxing of a removable partial denture framework. Radiographs of the Nobilium castings demonstrated a greater number of defects than those of Ticonium castings. Although both were cast by an induction casting machine, only fresh alloy ingots were used for the Ticonium frameworks, whereas portions of sprue buttons and previously cast alloy were mixed with these
676
ET AL
Fig. 7. Four distinct defects exist in minor and major connectors not visible on casting. General radiolucenties on casting indicate thin metal.
Fig. 8. Two cracks at inferior (arrows).
edge of lingual
plate
ingots for the Nobilium castings. This might account for the greater number of defects of the Nobilium castings, although the number of defects may also have been due to a difference in attenuation of the polychromatic* beams. Nevertheless, the fact that the two alloys were of similar density (Ticonium, 7.95 gm/cc; Nobilium, 8.38 gm/cc) and average atomic number would negate this possibility. Therefore, for any given thickness of each alloy, the attenuation of the polychromatic beam would be almost identical. By examining such radiographs, the dentist can evaluate the presence of defects and determine how critical such defects are based on the factors of shape, size, location, number of defects, and thickness of metal base. Structural defects may not cause fracture of a removable partial denture framework, but they will increase the
*A beam composed of photons of greatly varied wavelength.
NOVEMBER
1985
VOLUME
54
NUMBER
5
RADIOGRAPHIC
DETECTION
OF POROSITIES
possibility of plastic deformation of certain components leading to casting misfit. This, of course, may be related to overall tissue adaptation, fit on the supporting teeth, or both. SUMMARY
REFERENCES
3.
AND CONCLUSION
The purpose of this study was to discern the existence of structural defects in removable partial denture frameworks by means of radiographs. A simple technique was described using a dental radiograph unit and routine periapical dental films. All components of removable partial denture castings were radiographed with different angulations. The visibility of defects was clear. Structural defects were located and classified in two brands of removable partial denture base metal alloys (Ticonium and Nobilium) commonly used in fabrication of removable partial denture castings. The technique described is simple, inexpensive, not time-consuming, and can be implemented with minimum instrumentation. Future studies with this radiogaphic method for investigation of internal defects in fixed prostheses or dental implants are recommended.
Bound Bound volumes of the pubiisher
I.
volumes
available
3.
4.
5
6.
7.
Lewis AJ: Radiographic evaluaGon of porosi&s in removable partial denture castings. J PROSTHETDENT .39:278, 1978. Pascoe DF, Wimmer J: A radiographic technique for d&&n of in~~n;d defects in drntal casCngs. J PKOTHE.I. I)ENT 39:lSO. 1978. I lrnrikaon (:O. IYiwwin L, Oslerberg J: Kadiographic detection of defects in soldered joinr$ of dental gold alloys. Odonr Rev 24:161, 1973. 1l;r~Gla K: .\ roencgenolw$cal study 01 internal defecrs in (hrome-cobalt implants with partial denturrs. :\r~a Odoncol Stand 22:215, 1904. \Yise IIB. Kaiser DA: ‘2 radiographic techniclue for examination 01 inwnal drlects in metal frameworks. 1 PROSTIIET DENT 42:594, 1979 Wicwrin L. Julin P. Mollers~en L: RoemgtmAogical detection of casting defects in cobalt-chromium alloy frameworks. J Oral RrhAil 6: 137, 1979. Strandman E, LockowandL P: Equipment for standardizing casting of Co-0 alloys in dentistry. Odont Revy 27:145. 1976.
to subscribers
are available to subscribers (only) for the 1985 issues from the for Vol. 53 (January-June) and Vol. 54 (July-December). Shipping
JOURNALOF PROSTHETIC DENTISTRY
at a cost of $40.95 ($51.75 international)
charges are included. Each bound volume contains a subject and author index, and all advertising is removed. Copies are shipped within 30 days after publication of the last issue in the volume. The binding is durable buckram with the journal name, volume number, and year stamped in gold on the spine. Payment must accompany all orders. Contact The C. V. Mosby Co., Circulation Department, 11830 Westline Industrial Drive, St. Louis, MO 63146, USA; phone (800) 325417’7, ext. 351.
Subscriptions
must be in force to qualify.
Bound volumes
are not available
in place of a regular
JOURNAL subscription.
THE JOURNAL
OF PROSTHETIC
DENTISTRY
677
M
any chrome-cobalt castings contain internal and external defects of varying size and shape, which can cause failure of the prosthesis. Previous investigations have shown that industrial and dental radiograph machines can be used to detect such structural defects.lw6 Since the radiograph machine is readily available in most dental offices, this study was designed to determine its usefulness in detecting flaws in removable partial denture frameworks. Although two alloys were used, no comparison was made as to the superiority of one over the other.
MATERIAL
AND METHODS
Seventy-seven removable partial denture frameworks were obtained from two dental laboratories that used standardized induction casting techniques. The 30 Ticonium (Ticonium Division, CMP Industries, Albany, N.Y.) castings provided by one laboratory and the 47 Nobilium (Nobilium Division, CMP Industries) castings provided by the other were frameworks for patients seeking treatment at the University of Pittsburgh. A GE 900 X-ray machine (General Electric Co., Milwaukee, Wis.) with a 2.7 mm aluminum equivalent half-layer was operated at 15 mA and 90 kV(p). The exposure time was set at 3/5 second (36 impulses) to produce a good quality radiograph of the castings. Kodak dental film group D (Eastman Kodak Co., Rochester, N.Y.) size 1.2 (31 X 41 mm) was used, because trials indicated that the periapical film was easy to position in critical regions of the casting because of its size. During each radiographic exposure, the central beam was perpendicular to the specimen surface. The castings were radiographed with different angulations to record various components and to obtain better visibility of casting defects (Fig. 1). Each casting was given a code
*Clinical Fellow, Department of Prosthodontics. **Professor and Chairman, Department of Prosthodontics. ***Assistant Professor, Department of Prosthodontics. ****Assistant Professor and Supervisor, Radiology Section, Department of Diagnostic Services.
674
Fig. 1. Casting is positioned and supported by wax for radiographic exposure of I-bar. Note that central beam is perpendicular to specimen surface.
Fig. 2. Semicircular defect at center of T-clasp is indidot is shown by cated by arrow a. Film identification arrow b.
number, and similar lead numerals were included in the exposure so that cross-identification could be made. The films were processed in a Xonics 4%-minute automatic processor (Xonics Radiographs, Inc., Arlington Heights, Ill). All of the radiographs were viewed independently in a semidark room with a variable
NOVEMBER
1985
VOLUME
54
NUMBER
5
RADIOGRAPHIC
DETECTION OF POROSITIES
Fig. 4. Large void at origin of retentive arm is indicated by arrow a. Circular radiolucent areas indicated by arrow b are framework mesh. Relative radiolucent area shown by arrow c is thinness of casting.
Fig. 3. Two semicircular defects are visible at junction of retentive arms of embrasure clasp indicated by arrow a. Arrow b points to radiolucency on base of occlusal rest caused by thinness of casting.
Table I. Distribution
of radiolucencies
indicative
of defects according
to sites of occurrences
in two
alloys Occurrence of defects
Maxillary Ticonium
Clasp unit Major connector bars and lingual plates
Mandibular Nobilium
4
high-intensity illuminator (CGR Medical Corp., Baltimore, Md.) and a magnifier (x5). The results are presented in absolute values and percentages.
Ticonium
17 11
9 7
The findings of the radiographic examination indisites of casting defects in the two different alloys are listed in Table I. Table II exhibits the number and percent of defects in the various components of castings studied. In total, 47 of 77 castings (61.04%) exhibited structural defects in clasp units, major connectors, or both. Twenty castings (25.97%) contained one flaw; seven castings (9.09%) had three flaws. There were four or more flaws in four castings (5.19%), and cracks were readily detected with good contrast in nine frameworks (11.69%). Well defined voids were found in nine castings (11.69%).
DISCUSSION This study demonstrated that a 90 kVp radiograph machine provides an adequate source to detect large or small defects in base-metal removable partial denture castings. The desirable removable partial denture framework
THE JOURNAL OF PROSTHETIC DENTISTRY
Total
36 24
66 42
Table II. Number and percent of incidence of defects in total casting componenlts both alloys*
RESULTS cated a total of 108 internal defects. The frequency and
Nobilium
Castings
Clasp units Retentive arms Reciprocal arms Occlusal rests Minor connectors Major connectors Lingual bars/plates Anterior/posterior palatal bars
No. studied
No. showing defects
of
Percent
232 230 146 233 140 69 57
43 33 9 9 11 15 10
18.53 14.35 6.16 3.86 7.86 21.74 17.54
12
5
41.67
*Total defects regardless of degree of acceptability.
should show no sizeable defects within its structure to be able to fulfill its function. In Figs. 2 to 8, distinctive defects of varying size and shape, which may jeopardize the quality of the castings, are seen in the structure of different components. According to Strandman and Lockowandt,’ defects such as fissures and microporosities with surface connec-
675
ELARBI
Fig. 5. Visible defect exists at origin of I-bar and is seen on casting (arrow).
rig. 6. Uetect on occlusal rest (arrow a) not visible on casting. Arrow b shows visible defect on casting close to proximal supporting plate.
tions may result in increased corrosion of the alloy. Based on this finding, the cracks at the inferior border of the lingual plate in Fig. 8 may lead to corrosion and subsequent failure of the removable partial denture. The presence of a radiolucent area in a radiograph does not necessarily represent a critical structural defect. However, radiolucent areas in dental castings may indicate less than optimum thickness that endanger the casting to the extent that the entire structure becomes susceptible to fracture. This may explain the higher rate of fractures of flawless castings while they are in use. Accordingly, special attention must be given during the waxing of a removable partial denture framework. Radiographs of the Nobilium castings demonstrated a greater number of defects than those of Ticonium castings. Although both were cast by an induction casting machine, only fresh alloy ingots were used for the Ticonium frameworks, whereas portions of sprue buttons and previously cast alloy were mixed with these
676
ET AL
Fig. 7. Four distinct defects exist in minor and major connectors not visible on casting. General radiolucenties on casting indicate thin metal.
Fig. 8. Two cracks at inferior (arrows).
edge of lingual
plate
ingots for the Nobilium castings. This might account for the greater number of defects of the Nobilium castings, although the number of defects may also have been due to a difference in attenuation of the polychromatic* beams. Nevertheless, the fact that the two alloys were of similar density (Ticonium, 7.95 gm/cc; Nobilium, 8.38 gm/cc) and average atomic number would negate this possibility. Therefore, for any given thickness of each alloy, the attenuation of the polychromatic beam would be almost identical. By examining such radiographs, the dentist can evaluate the presence of defects and determine how critical such defects are based on the factors of shape, size, location, number of defects, and thickness of metal base. Structural defects may not cause fracture of a removable partial denture framework, but they will increase the
*A beam composed of photons of greatly varied wavelength.
NOVEMBER
1985
VOLUME
54
NUMBER
5
RADIOGRAPHIC
DETECTION
OF POROSITIES
possibility of plastic deformation of certain components leading to casting misfit. This, of course, may be related to overall tissue adaptation, fit on the supporting teeth, or both. SUMMARY
REFERENCES
3.
AND CONCLUSION
The purpose of this study was to discern the existence of structural defects in removable partial denture frameworks by means of radiographs. A simple technique was described using a dental radiograph unit and routine periapical dental films. All components of removable partial denture castings were radiographed with different angulations. The visibility of defects was clear. Structural defects were located and classified in two brands of removable partial denture base metal alloys (Ticonium and Nobilium) commonly used in fabrication of removable partial denture castings. The technique described is simple, inexpensive, not time-consuming, and can be implemented with minimum instrumentation. Future studies with this radiogaphic method for investigation of internal defects in fixed prostheses or dental implants are recommended.
Bound Bound volumes of the pubiisher
I.
volumes
available
3.
4.
5
6.
7.
Lewis AJ: Radiographic evaluaGon of porosi&s in removable partial denture castings. J PROSTHETDENT .39:278, 1978. Pascoe DF, Wimmer J: A radiographic technique for d&&n of in~~n;d defects in drntal casCngs. J PKOTHE.I. I)ENT 39:lSO. 1978. I lrnrikaon (:O. IYiwwin L, Oslerberg J: Kadiographic detection of defects in soldered joinr$ of dental gold alloys. Odonr Rev 24:161, 1973. 1l;r~Gla K: .\ roencgenolw$cal study 01 internal defecrs in (hrome-cobalt implants with partial denturrs. :\r~a Odoncol Stand 22:215, 1904. \Yise IIB. Kaiser DA: ‘2 radiographic techniclue for examination 01 inwnal drlects in metal frameworks. 1 PROSTIIET DENT 42:594, 1979 Wicwrin L. Julin P. Mollers~en L: RoemgtmAogical detection of casting defects in cobalt-chromium alloy frameworks. J Oral RrhAil 6: 137, 1979. Strandman E, LockowandL P: Equipment for standardizing casting of Co-0 alloys in dentistry. Odont Revy 27:145. 1976.
to subscribers
are available to subscribers (only) for the 1985 issues from the for Vol. 53 (January-June) and Vol. 54 (July-December). Shipping
JOURNALOF PROSTHETIC DENTISTRY
at a cost of $40.95 ($51.75 international)
charges are included. Each bound volume contains a subject and author index, and all advertising is removed. Copies are shipped within 30 days after publication of the last issue in the volume. The binding is durable buckram with the journal name, volume number, and year stamped in gold on the spine. Payment must accompany all orders. Contact The C. V. Mosby Co., Circulation Department, 11830 Westline Industrial Drive, St. Louis, MO 63146, USA; phone (800) 325417’7, ext. 351.
Subscriptions
must be in force to qualify.
Bound volumes
are not available
in place of a regular
JOURNAL subscription.
THE JOURNAL
OF PROSTHETIC
DENTISTRY
677