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Pin vs. slot retention in extensive amalgam restorations
5LCTlON f.!xrGR”>
FIXED PROSTHODONTICS OPERATIVE DENTISTRY
DAVID
E. BEAUDREAI!
SAMUEL t.. c;ULkli WILLIAM
LEFKOWI Ii’
Pin vs. slot retention in extensive amalgam restorations William C. Outhwaite, D.D.S.,* Thomas A. Garman, D.D.S., M.S.,** and David H. Pashley, D.M.D., Ph.D.*** Medical College of Georgia, School of Dentistry,
Augusta, Ga.
S
ilver amalgam can be retained in a cavity preparation only by mechanical methods. The traditional or direct method is to incorporate retentive features in the cavity preparation. Where great amounts of enamel and dentin have been lost, “man-made” or indirect retention must be used. In the past 2 decades, three types of metal pins have been developed to create indirect retention: cemented pins,’ friction-lock pins2 and self-threading pins. ’ Moffa, Razzano, and Doyle’ studied the retentive value of the three pin types and concluded that the self-threading pin was the most retentive in dentin and amalgam. Self-threading pins, however, have been shown by Standlee, Collard, and Caputos and Dilts and associates6 to produce lateral cracking in the dentin and crazing or cracking of the enamel if the pin is placed less than 0.5 mm from the dentinoenamel junction. All three pin types have the potential danger of encroaching on the pulp or perforating the periodontium if the pin channels are incorrectly drilled. Going and co-workers’ and Welk and Dilts’ showed that although the presence of pins in amalgam does not affect the compressive strength, it does adversely influence the transverse or tensile strength. It is apparent that an alternative procedure to pin retention would be desirable. This study is a comparison of the retentive value of a slot placed with an inverted-cone bur in remaining dentin vs. the placement of four self-threading pins. *Associate Professor of Dental Materials. **Associate Professor of Restorative Dentistry. ***Associate Professor of Oral Biology/Physiology. Parts of this material appeared in Abstract No. 889 in J Dent Res 55:B:284, 1976. This research was supported in part by the National Institute of Health, National Institute of Dental Research, Research Grant No. ROl DE04394.
396
APRIL 1979
VOLUME 41
NUMBER 4
METHODS AND MATERIALS Thirty-two extracted human teeth having similar crown dimensions and shape were selected and stored in 100% humidity throughout the experiment. These teeth were ground occlusally under water spray until all occlusal enamel was removed and a flat dentinal surface resulted. Where the pulp chamber was exposed, the defect was filled with autopolymerizing resin to prevent ingress of amalgam during condensation. The tooth roots were notched for retention, and the teeth were embedded in a stone base so that all ground occlusal surfaces were in the same plane. The axial walls were then slightly milled to assure a uniform vertical surface around which a matrix band could be adapted. The 32 teeth were divided at random into two groups of 16, one group to receive slot retention and the other to receive pins. All the retentive slots and all pin channels were cut with a porcelain facing drill* to ensure constant depth of cuts and vertical alignment of the drill and bur. The retentive slots were cut with a No. 33% inverted-cone friction-grip bur. Slot depth was equal to the full depth of the bur head and was continuous around the circumference of the tooth stump approximately 0.5 mm from the dentinoenamel junction. Pin channels were drilled with a 0.021-inch diameter twist drill using a 2 mm depth-limiting collar .* Self-threading pins 0.024 inches in diameter were screwed into each channel with a hand wrench.t Four pins were placed in the axial corners of the tooth stumps at least 0.5 mm from the dentinoenamel junction (Fig. 1). After all slots had been prepared and all pins placed, the teeth were separated into rows by machine-slitting the stone base. A matrix band was
*Mardell Industrial Products, Model MD-l 1, Monrovia, twhaledent International, New York, N. Y.
0022.3913/79/040396
+ 05$00.50/001979
Calif
The C. V. Mosby Cu.
PIN VS. SLOT RETENTION
Fig.
1.
Prepared specimens showing pin and slot reten-
titrn.
secured around each tooth with a matrix retainer.* Silver amalgam? was then condensed into all 32 test teeth using a mechanical condenserx to aid in uniformity of condensation. All samples were allowed to harden for 24 hours. The amalgam crowns were then milled down with a No. 558 bur (Fig. 2) to the same occlusogingival height of 4 mm. The peripheral walls of the restorations were also milled to conform to the dimensions of the crown and to be parallel to the long axis of the tooth. During mastication the main forces exerted on amalgam foundations or definitive restorations are not purelv tensile. They are rather a combination of forces, including compression and shear forces as cusps are forced to ride up and down opposing cusp slopes. For this reason, the rows of teeth were remounted at a 45-degree angle by embedding their stone bases in a new pour of stone. Flat surfaces were milled on the amalgam crowns (parallel to the new base), simulating the angle of cusp slopes. This bevel was of sufficient area to insure that the compressive strength of the amalgam was not exceeded. Each sample tooth was placed in a compression testing machine8 at a 45-degree angle, and a test load was applied to the beveled face of the amalgam crown at a constant crosshead speed 0.02 inch per minute until failure of the specimen occurred. Load diagrams were recorded for each of the specimens.
*‘The William Getz Corp., Chicago, Ill. ~Dispersallo);, Johnson & ,Johnson Dental Windsor. ICondensairr
N. .J. Model
$Instron (hrp..
THE JOURNAL
No. 8’20 Standard,
Densco,
Model ‘IYY-C, Canton, Mass.
OF PROSTHETIC
Products
DENTISTRY
Co.,
Denver,
East
Cola.
Fig. 2. The amalgam crowns were millet! to constant heights. The axial walls were alreadv m~ileii E
7000
’ E
6000
2 5000 LL !zj 4000 VI w” 3000 f v) 2000
I I I6 PI N-RETAINED CROWNS
16 SL.CF-RETAINEK CROWNS
Fig. 3. Breaking stresses of individu
RESULTS Since the sample teeth were not all the same size, the cross-sectional area of each tooth stump was calculated in square, inches before resting. The results were recorded in pounds per square inch of stress needed to cause failure of the amalgam crown. The actual breaking loads varied from 120 to 270 pounds, which is within the physiologic range of mastlcatory forces of the human dentition. Fig. 3 shows the breaking stress for each specimen. The bars are arranged in two groups representing the pin and slot retained specimens. ‘The ruean stress at failure of the slot-retained amalgam crowns was 392 1 psi, with a standard deviation of 865 psi. The mean stress required for failure of th.e pin-retained crowns was 3453 psi, with a standard deviation of 679 psi.
397
OUTHWAITE,
GARMAN,
AND
PASHLEl
500 I bw 450
-
400
-
350-
a 16
17
I8
19
Fig. 5. Load diagrams of four specimens
Fig. 4. Typical failure of pin-retained specimens. A, Arrows show hairline fractures in the amalgam. B, The amalgam has fractured along the plane of the pins. 0, Amalgam. f, Tooth.
The difference between the means was tested using the t-test for independent means. The value oft was 1.70, which is not significant at the 0.05 confidence level. It can therefore be assumed that there was no significant difference between the amount of force needed to cause failure in the slot-retained and pin-retained amalgam crowns. DISCUSSION The purpose of this study was to compare direct retention using a circumferential slot prepared in dentin with that of indirect retention using selfthreading pins. Under the conditions of this study, the slots in dentin were as retentive as the selfthreading pins. There are some important points to mention about both techniques concerning the failure patterns of the amalgam crowns. Fig. 4 shows typical failures of the experimental pin-retained amalgam crowns. Fig. 4, B shows a large portion of the amalgam fractured along the vertical plane of the pins. This is an expected result, since the presence of
398
vertical pins lessens the tensile strength of the amalgam in that area. The pins have been bent, and the entire remaining bulk of amalgam has shifted laterally. Clinical failures of this type are easily detectable due to the gross fractures of the amalgam and its partial dislodgement from the cavity preparation. Fig. 4, A shows a pin-retained failure with very minor fracture of the amalgam and very little slippage or dislodgement of the restoration. It is this type of failure which may be very difficult to detect clinically, especially if the pin-retained amalgam is used as a foundation for a complete veneer crown. In Fig. 5, four typical load diagrams from the Instron machine are shown. Plots 16 and 18 are of slot-retained and 17 and 19 of pin-Iztained specimens. The first point of departure from linearity is shown by the arrows on plots 17 and 19. This point was taken as the point of failure for all specimens. When studied, this departure from linearity was present in 11 of the 16 pin diagrams at an average of 75% of the peak load. This feature was less pronounced in the slot diagrams, being present in only seven of the 16 and at an average of 85% of their peak load. Since the cross-head speed and chart speed were constant, it may be concluded that there was a greater tendency for the pin restorations to slip on their bases at the higher load levels than was the case with the slots. If this occurs clinically, the slippage may be so minute as to be undetected immediately
APRIL 1979
VOLUME
41
NUMBER
4
PIN VS. SLOT RETENTION
by either the patient or the dentist. However, even minute movements of a restoration must be considered a failure. ‘I’he amalgam crowns retained by dentinal slots showed a different failure pattern (Fig. 6). In both Fig. 6. if and Fig. 6, B, the entire crown had separated from the tooth. The fractures usually occurred at the occlusal portion of the slot. This is a predictable failure pattern, since the rigidity of amalgam does not allow slight deformation or bending such as is seen in the crowns retained by stainless steel pins. The failure pattern in the slot-retained crowns could be described as “all or none.” This type of failure would be dramatic and easily detectable in a clinical situation. It would, however, reduce the possibility of clinically undetected failures that may occur in pin-retained restorations. The slot-retained amalgams were somewhat sensitive to slight movement of the matrix during condensation or during matrix removal. In some instances, slot-retained amalgam crowns separated at the time of matrix removal and required recondensation. It is suspected that the fractures occurred during condensation. This could be due to heavy condensation pressure near the edges causing a slight tipping movement of the matrix band when it was almost full. t\lthough none of the pin-retained crowns showed this type of failure, they clearly could have been weakened in the same manner. Clinically the ad,jacenr teeth \vould help prevent this in the mesiodistal dir-ection, and thr use of modeling plastic to stabilize the band would eliminate the risk. Usually there are irregularities in the tooth surface and wall height that would reduce the risk of matrix movement considerably. Another suggestion that would improve the strength of slot-retained crowns is to remove the sharp edges of the slot with a chisel. This was not done in this particular study. The t);pe of slot described may be used clinically in almost any situation where pins could be used down to single cusp replacements. Contraindication would be when the slot would have to be made so close to the enamel that either slot or enamel would be inadequately supported. The incisal edge of a Class IV preparation may fall into this category. Slots are versatile and may follow irregular tooth surfaces. They may be made at any convenient angle, including in the vertical wall. They need not be continuous, and several short parallel ones may be better in some circumstances. Further study is now in progress using more
THE fOURNAL
OF PROSTHETIC
DENTISTRY
Fig. 6. Typical failure of slot-retained
specimens. Arrows show slots with parts of the amalgam remainmg in them. A, Lower wall of slot is fractured off. 15, ‘T‘he crown is separated from the tooth. a, Amalgam. i ^i i~~~~th.
elaborate methods of evaluation. i ‘*chewing machine” has been developed which \\fll test ietention in amalgam crowns comparing k/o: -in..dentin with pin retention. Using this machinc:. the number of chewing cycles needed to cause faiiurc‘ under a given load will be electronically monir )I.&. CONCLUSIONS Under the conditions of this study, ihr following conclusions were made: 1. Slot-in-dentin retention was comparable to retention by self-threading pins. 2. In pin-retained amalgams, there was a greater tendency for slippage to take place hefore catastrophic failure than with the slot-retained pins. 3. Slot-retained amalgams were more scnsitivr to matrix movement during condensaticrn and rough handling during matrix removal than those with self-threading pins.
399
OUTHWAITE,
GARMAN,
AND
PASH1.6f
Crazing of tooth structure associated with placetntrl: <)I Q~!L% for amalgam restorations. J Am Dent Assoc 81:X7. i:i;iI. 7. Going, R. E.. Moffa, J. P.. Nostranr. iZ W.. and J&nxr,r.. ii E.: The strength of dental amalg.im as inNurnct:ri h\ pi;,\ ] Am Dent Assoc 77:1331. 1968. 8. Welk. D. A.. and Dilts, W. E Influence of pin, ~~~~11w compressive and transverse strength of dental amalgam .md retention of pins in amalgam. .J Am Dent Aw: 78:iOl, 1969.
REFERENCES Markley, M. R.: Pin reinforcement and retention of amalgam foundations and restorations. J Am Dent Assoc 56:675. 1958. 2. Goldstein, P. M.: Retention pins are friction locked without use of cement. J Am Dent Assoc 73:1103, 1966. 3. Going, R. E.: Pin-retained amalgam. J Am Dent Assoc 73:619, 1966. 4. Moffa, J. P., Razzano, M. R., and Doyle, M. G.: Pins-A comparison of their retentive properties. .J Am Dent Assoc 78:529, 1969. 5. Standlee, J. P., Collard, E. W., and Caputo, A. A.: Dentinal defects caused by some twist drills and retentive pins. J PROSTHET DENT 24:185, 1970. 6. Dilts, W. E., Welk, D. A., Laswell, H. R., and George, L.: 1.
Reprint requeststo: DR. WILLIAM C. OUTHWAITE MEDICAL COLLEGE OF GEORGIA SCHOOL OF DENTISTRY .kJGUSTA, GA. 30901
ARTICLES TO APPEAR IN FUTURE ISSUES Temperature rise in pulp chamber during fabrication of temporary self-curing resin crowns Rafael
Grajower,
Ph.D.,
Sasson Shaharbani,
D.M.D.,
and Eliezer
Kaufman,
D.M.D.
The influence of the loss of teeth and attrition on the articular eminence Jose I. Granados,
D.D.S.,
M.S.
In vitro comparison of intact endodontically treated teeth with and without endo-post reinforcement Gary
E. Guzy, D.D.S.,
and Jack I. Nicholls,
Ph.D.
An anatomic study of the temporomandibular investigation Tore
Hansson,
D.D.S.,
Odont.
Dr., William
K. Solberg,
joints of young adults. A pilot D.D.S.,
M.S.D.,
and Mary
Kay
Penn
Distortions in indexing methods and investing media for soldering and remount procedures R. J. Harper,
D.D.S.,
M.S.D.,
and J. I. Nicholls,
Ph.D.
Physical properties of an experimental composite resin liner John
H. Hembree,
Jr., D.D.S.
Fabricating cone locating devices for radiation treatment of tumors of the soft palate Phillip
400
E. Hutcheson,
D.D.S.,
M.S.D.,
and Thomas
E. Daly,
D.D.S.
APRIL 1979
VOLUME
41
NUMBER
4
FIXED PROSTHODONTICS OPERATIVE DENTISTRY
DAVID
E. BEAUDREAI!
SAMUEL t.. c;ULkli WILLIAM
LEFKOWI Ii’
Pin vs. slot retention in extensive amalgam restorations William C. Outhwaite, D.D.S.,* Thomas A. Garman, D.D.S., M.S.,** and David H. Pashley, D.M.D., Ph.D.*** Medical College of Georgia, School of Dentistry,
Augusta, Ga.
S
ilver amalgam can be retained in a cavity preparation only by mechanical methods. The traditional or direct method is to incorporate retentive features in the cavity preparation. Where great amounts of enamel and dentin have been lost, “man-made” or indirect retention must be used. In the past 2 decades, three types of metal pins have been developed to create indirect retention: cemented pins,’ friction-lock pins2 and self-threading pins. ’ Moffa, Razzano, and Doyle’ studied the retentive value of the three pin types and concluded that the self-threading pin was the most retentive in dentin and amalgam. Self-threading pins, however, have been shown by Standlee, Collard, and Caputos and Dilts and associates6 to produce lateral cracking in the dentin and crazing or cracking of the enamel if the pin is placed less than 0.5 mm from the dentinoenamel junction. All three pin types have the potential danger of encroaching on the pulp or perforating the periodontium if the pin channels are incorrectly drilled. Going and co-workers’ and Welk and Dilts’ showed that although the presence of pins in amalgam does not affect the compressive strength, it does adversely influence the transverse or tensile strength. It is apparent that an alternative procedure to pin retention would be desirable. This study is a comparison of the retentive value of a slot placed with an inverted-cone bur in remaining dentin vs. the placement of four self-threading pins. *Associate Professor of Dental Materials. **Associate Professor of Restorative Dentistry. ***Associate Professor of Oral Biology/Physiology. Parts of this material appeared in Abstract No. 889 in J Dent Res 55:B:284, 1976. This research was supported in part by the National Institute of Health, National Institute of Dental Research, Research Grant No. ROl DE04394.
396
APRIL 1979
VOLUME 41
NUMBER 4
METHODS AND MATERIALS Thirty-two extracted human teeth having similar crown dimensions and shape were selected and stored in 100% humidity throughout the experiment. These teeth were ground occlusally under water spray until all occlusal enamel was removed and a flat dentinal surface resulted. Where the pulp chamber was exposed, the defect was filled with autopolymerizing resin to prevent ingress of amalgam during condensation. The tooth roots were notched for retention, and the teeth were embedded in a stone base so that all ground occlusal surfaces were in the same plane. The axial walls were then slightly milled to assure a uniform vertical surface around which a matrix band could be adapted. The 32 teeth were divided at random into two groups of 16, one group to receive slot retention and the other to receive pins. All the retentive slots and all pin channels were cut with a porcelain facing drill* to ensure constant depth of cuts and vertical alignment of the drill and bur. The retentive slots were cut with a No. 33% inverted-cone friction-grip bur. Slot depth was equal to the full depth of the bur head and was continuous around the circumference of the tooth stump approximately 0.5 mm from the dentinoenamel junction. Pin channels were drilled with a 0.021-inch diameter twist drill using a 2 mm depth-limiting collar .* Self-threading pins 0.024 inches in diameter were screwed into each channel with a hand wrench.t Four pins were placed in the axial corners of the tooth stumps at least 0.5 mm from the dentinoenamel junction (Fig. 1). After all slots had been prepared and all pins placed, the teeth were separated into rows by machine-slitting the stone base. A matrix band was
*Mardell Industrial Products, Model MD-l 1, Monrovia, twhaledent International, New York, N. Y.
0022.3913/79/040396
+ 05$00.50/001979
Calif
The C. V. Mosby Cu.
PIN VS. SLOT RETENTION
Fig.
1.
Prepared specimens showing pin and slot reten-
titrn.
secured around each tooth with a matrix retainer.* Silver amalgam? was then condensed into all 32 test teeth using a mechanical condenserx to aid in uniformity of condensation. All samples were allowed to harden for 24 hours. The amalgam crowns were then milled down with a No. 558 bur (Fig. 2) to the same occlusogingival height of 4 mm. The peripheral walls of the restorations were also milled to conform to the dimensions of the crown and to be parallel to the long axis of the tooth. During mastication the main forces exerted on amalgam foundations or definitive restorations are not purelv tensile. They are rather a combination of forces, including compression and shear forces as cusps are forced to ride up and down opposing cusp slopes. For this reason, the rows of teeth were remounted at a 45-degree angle by embedding their stone bases in a new pour of stone. Flat surfaces were milled on the amalgam crowns (parallel to the new base), simulating the angle of cusp slopes. This bevel was of sufficient area to insure that the compressive strength of the amalgam was not exceeded. Each sample tooth was placed in a compression testing machine8 at a 45-degree angle, and a test load was applied to the beveled face of the amalgam crown at a constant crosshead speed 0.02 inch per minute until failure of the specimen occurred. Load diagrams were recorded for each of the specimens.
*‘The William Getz Corp., Chicago, Ill. ~Dispersallo);, Johnson & ,Johnson Dental Windsor. ICondensairr
N. .J. Model
$Instron (hrp..
THE JOURNAL
No. 8’20 Standard,
Densco,
Model ‘IYY-C, Canton, Mass.
OF PROSTHETIC
Products
DENTISTRY
Co.,
Denver,
East
Cola.
Fig. 2. The amalgam crowns were millet! to constant heights. The axial walls were alreadv m~ileii E
7000
’ E
6000
2 5000 LL !zj 4000 VI w” 3000 f v) 2000
I I I6 PI N-RETAINED CROWNS
16 SL.CF-RETAINEK CROWNS
Fig. 3. Breaking stresses of individu
RESULTS Since the sample teeth were not all the same size, the cross-sectional area of each tooth stump was calculated in square, inches before resting. The results were recorded in pounds per square inch of stress needed to cause failure of the amalgam crown. The actual breaking loads varied from 120 to 270 pounds, which is within the physiologic range of mastlcatory forces of the human dentition. Fig. 3 shows the breaking stress for each specimen. The bars are arranged in two groups representing the pin and slot retained specimens. ‘The ruean stress at failure of the slot-retained amalgam crowns was 392 1 psi, with a standard deviation of 865 psi. The mean stress required for failure of th.e pin-retained crowns was 3453 psi, with a standard deviation of 679 psi.
397
OUTHWAITE,
GARMAN,
AND
PASHLEl
500 I bw 450
-
400
-
350-
a 16
17
I8
19
Fig. 5. Load diagrams of four specimens
Fig. 4. Typical failure of pin-retained specimens. A, Arrows show hairline fractures in the amalgam. B, The amalgam has fractured along the plane of the pins. 0, Amalgam. f, Tooth.
The difference between the means was tested using the t-test for independent means. The value oft was 1.70, which is not significant at the 0.05 confidence level. It can therefore be assumed that there was no significant difference between the amount of force needed to cause failure in the slot-retained and pin-retained amalgam crowns. DISCUSSION The purpose of this study was to compare direct retention using a circumferential slot prepared in dentin with that of indirect retention using selfthreading pins. Under the conditions of this study, the slots in dentin were as retentive as the selfthreading pins. There are some important points to mention about both techniques concerning the failure patterns of the amalgam crowns. Fig. 4 shows typical failures of the experimental pin-retained amalgam crowns. Fig. 4, B shows a large portion of the amalgam fractured along the vertical plane of the pins. This is an expected result, since the presence of
398
vertical pins lessens the tensile strength of the amalgam in that area. The pins have been bent, and the entire remaining bulk of amalgam has shifted laterally. Clinical failures of this type are easily detectable due to the gross fractures of the amalgam and its partial dislodgement from the cavity preparation. Fig. 4, A shows a pin-retained failure with very minor fracture of the amalgam and very little slippage or dislodgement of the restoration. It is this type of failure which may be very difficult to detect clinically, especially if the pin-retained amalgam is used as a foundation for a complete veneer crown. In Fig. 5, four typical load diagrams from the Instron machine are shown. Plots 16 and 18 are of slot-retained and 17 and 19 of pin-Iztained specimens. The first point of departure from linearity is shown by the arrows on plots 17 and 19. This point was taken as the point of failure for all specimens. When studied, this departure from linearity was present in 11 of the 16 pin diagrams at an average of 75% of the peak load. This feature was less pronounced in the slot diagrams, being present in only seven of the 16 and at an average of 85% of their peak load. Since the cross-head speed and chart speed were constant, it may be concluded that there was a greater tendency for the pin restorations to slip on their bases at the higher load levels than was the case with the slots. If this occurs clinically, the slippage may be so minute as to be undetected immediately
APRIL 1979
VOLUME
41
NUMBER
4
PIN VS. SLOT RETENTION
by either the patient or the dentist. However, even minute movements of a restoration must be considered a failure. ‘I’he amalgam crowns retained by dentinal slots showed a different failure pattern (Fig. 6). In both Fig. 6. if and Fig. 6, B, the entire crown had separated from the tooth. The fractures usually occurred at the occlusal portion of the slot. This is a predictable failure pattern, since the rigidity of amalgam does not allow slight deformation or bending such as is seen in the crowns retained by stainless steel pins. The failure pattern in the slot-retained crowns could be described as “all or none.” This type of failure would be dramatic and easily detectable in a clinical situation. It would, however, reduce the possibility of clinically undetected failures that may occur in pin-retained restorations. The slot-retained amalgams were somewhat sensitive to slight movement of the matrix during condensation or during matrix removal. In some instances, slot-retained amalgam crowns separated at the time of matrix removal and required recondensation. It is suspected that the fractures occurred during condensation. This could be due to heavy condensation pressure near the edges causing a slight tipping movement of the matrix band when it was almost full. t\lthough none of the pin-retained crowns showed this type of failure, they clearly could have been weakened in the same manner. Clinically the ad,jacenr teeth \vould help prevent this in the mesiodistal dir-ection, and thr use of modeling plastic to stabilize the band would eliminate the risk. Usually there are irregularities in the tooth surface and wall height that would reduce the risk of matrix movement considerably. Another suggestion that would improve the strength of slot-retained crowns is to remove the sharp edges of the slot with a chisel. This was not done in this particular study. The t);pe of slot described may be used clinically in almost any situation where pins could be used down to single cusp replacements. Contraindication would be when the slot would have to be made so close to the enamel that either slot or enamel would be inadequately supported. The incisal edge of a Class IV preparation may fall into this category. Slots are versatile and may follow irregular tooth surfaces. They may be made at any convenient angle, including in the vertical wall. They need not be continuous, and several short parallel ones may be better in some circumstances. Further study is now in progress using more
THE fOURNAL
OF PROSTHETIC
DENTISTRY
Fig. 6. Typical failure of slot-retained
specimens. Arrows show slots with parts of the amalgam remainmg in them. A, Lower wall of slot is fractured off. 15, ‘T‘he crown is separated from the tooth. a, Amalgam. i ^i i~~~~th.
elaborate methods of evaluation. i ‘*chewing machine” has been developed which \\fll test ietention in amalgam crowns comparing k/o: -in..dentin with pin retention. Using this machinc:. the number of chewing cycles needed to cause faiiurc‘ under a given load will be electronically monir )I.&. CONCLUSIONS Under the conditions of this study, ihr following conclusions were made: 1. Slot-in-dentin retention was comparable to retention by self-threading pins. 2. In pin-retained amalgams, there was a greater tendency for slippage to take place hefore catastrophic failure than with the slot-retained pins. 3. Slot-retained amalgams were more scnsitivr to matrix movement during condensaticrn and rough handling during matrix removal than those with self-threading pins.
399
OUTHWAITE,
GARMAN,
AND
PASH1.6f
Crazing of tooth structure associated with placetntrl: <)I Q~!L% for amalgam restorations. J Am Dent Assoc 81:X7. i:i;iI. 7. Going, R. E.. Moffa, J. P.. Nostranr. iZ W.. and J&nxr,r.. ii E.: The strength of dental amalg.im as inNurnct:ri h\ pi;,\ ] Am Dent Assoc 77:1331. 1968. 8. Welk. D. A.. and Dilts, W. E Influence of pin, ~~~~11w compressive and transverse strength of dental amalgam .md retention of pins in amalgam. .J Am Dent Aw: 78:iOl, 1969.
REFERENCES Markley, M. R.: Pin reinforcement and retention of amalgam foundations and restorations. J Am Dent Assoc 56:675. 1958. 2. Goldstein, P. M.: Retention pins are friction locked without use of cement. J Am Dent Assoc 73:1103, 1966. 3. Going, R. E.: Pin-retained amalgam. J Am Dent Assoc 73:619, 1966. 4. Moffa, J. P., Razzano, M. R., and Doyle, M. G.: Pins-A comparison of their retentive properties. .J Am Dent Assoc 78:529, 1969. 5. Standlee, J. P., Collard, E. W., and Caputo, A. A.: Dentinal defects caused by some twist drills and retentive pins. J PROSTHET DENT 24:185, 1970. 6. Dilts, W. E., Welk, D. A., Laswell, H. R., and George, L.: 1.
Reprint requeststo: DR. WILLIAM C. OUTHWAITE MEDICAL COLLEGE OF GEORGIA SCHOOL OF DENTISTRY .kJGUSTA, GA. 30901
ARTICLES TO APPEAR IN FUTURE ISSUES Temperature rise in pulp chamber during fabrication of temporary self-curing resin crowns Rafael
Grajower,
Ph.D.,
Sasson Shaharbani,
D.M.D.,
and Eliezer
Kaufman,
D.M.D.
The influence of the loss of teeth and attrition on the articular eminence Jose I. Granados,
D.D.S.,
M.S.
In vitro comparison of intact endodontically treated teeth with and without endo-post reinforcement Gary
E. Guzy, D.D.S.,
and Jack I. Nicholls,
Ph.D.
An anatomic study of the temporomandibular investigation Tore
Hansson,
D.D.S.,
Odont.
Dr., William
K. Solberg,
joints of young adults. A pilot D.D.S.,
M.S.D.,
and Mary
Kay
Penn
Distortions in indexing methods and investing media for soldering and remount procedures R. J. Harper,
D.D.S.,
M.S.D.,
and J. I. Nicholls,
Ph.D.
Physical properties of an experimental composite resin liner John
H. Hembree,
Jr., D.D.S.
Fabricating cone locating devices for radiation treatment of tumors of the soft palate Phillip
400
E. Hutcheson,
D.D.S.,
M.S.D.,
and Thomas
E. Daly,
D.D.S.
APRIL 1979
VOLUME
41
NUMBER
4