response to threaded pin and retentive ues: A pilot investigation D. A. Felton, DDS, C. F. Cox, MSd
MS,a
E. L. Webb,
DDS,
MS,b
B. E. Kanoy,
MS, DDS,C
slot and
University of North Carolina, Schoolof Dentistry, Chapel Hill, NC. This investigation compared pulpal response to threaded pin techniques with response to retentive slot techniques. The teeth were restored with composite resin. Twenty-four teeth were assigned to three treatment groups in one Macaca mulatta monkey. Ten teeth (group 1) received 32 TMS O.OZl-inch self-threading pins. Ten teeth (group II) received circumferential slot retention 1 mm deep, 0.5 mm inside the dentinoenamel junction. Four teeth (group III) served as controls. Groups I and II were restored with composite resin. Fourteen days later, the teeth were removed, demineralized, serially sectioned, and stained with hematoxylin and eosin. Chi-square analysis indicated more pulp inflammation when self-threading pins were used (p < 0.5). Pins placed within 0.5 mm of the pulp elicited severe inflammatory responses, and those placed further than 1 mm had minimal effect. Little correlation existed between remaining dentin thickness and adverse pulp response when slot retention was used. (J PROSTHET DENT 1991;66:597-602.)
A uxiliary
retention for materials used to restore severely broken down teeth has been discussed at length in the dental literature. Retentive pins have evolved from cemented and friction-lock pins to self-threading pins.l More recently, retentive slots placed within the dentinoenamel junction have been purported to be a more conservative approach than threaded pin retention. In vitro investigations have compared the retentive capabilities of pin and slot retention mechanisms. Slots were shown to provide retention of restorative materials comparable to the values demonstrated by pin retention.2, 3 Tbreaded pins may cause stresses in dentin.4 However, the same stresseshave not been attributed to slot retention. Both methods present the potential for violation of the pulp chamber or external surfaces of the tooth if inappropriately used. Several in vitro investigations demonstrated damage to tooth structure associated with the placement of threaded pins, usually in the form of dentinal microfractures.5-7 Amalgam pins or slots were shown by others to retain restorative materials adequately without the potential for residual stresses and microfractures.a However, there have been no in vivo investigations to evaluate the effects of threaded pin or slot retention on the pulp. This investigation histologically compared and evaluated the response of pulp tissues after placement of a composite resin restorative material retained exclusively by either threaded pin or slot retention. This research was sponsored in part by NIH/NIDR grant No. RR05333. aAssistantProfessor,Department of Prosthodontics. bAssociateProfessor,Department of Prosthodontics. ‘Clinical AssociateProfessorand Acting Chairman, Department of Prosthodontics. dResearchAssistant Professor,Department of Endodontics. 10/l/25742
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
MATERIAL
AND
METHODS
The severely abraded teeth of one adult Macaca mulatta monkey were used in this investigation. The the animal was scaled and polished with a prophylaxis cup and pumice 1 week before the initial operative procedure and again on the day of tooth preparation. The animal was sedated with 0.2 cc/kg ketamine hydrochloride (100 mglcc) (Bristol Laboratories, Division of Bristol-Meyers, Syracuse, N.Y.) by intramuscular injection. Deeper sedation was obtained by intramuscular injection of 20 mg/ml of xylazine (Rompun 1 mg/lb) (Mobay Corp., Shawnee, Kan.) to the desired effect. The teeth were isolated with cotton rolls and prepared for either pin or slot retention. A total of 24 teeth were randomly assigned to one of three treatment groups. Group 1 consisted of 10 teeth that received a total of 32 threaded pins. Group 2 consisted of 10 teeth that received circumferential slot retention. Group 3 consisted of four teeth that remained unrestored to serve as controls. All pins and slots were prepared according to accepted principals. No attempt was made to locate the pins or slots a given distance from the pulp. Instead, an attempt was made to place the retention features 0.5 mm inside the dentinoenamel junction. This technique resulted in variations in the amount of remaining dentin between the retention features and the pulp tissues. The extent of pin and slot preparation into dentin is diagramed in Fig. 1. In the teeth that received threaded pin retention, either three or four pin holes were prepared with a 0.21 inch TMS drill (Whaledent International, New York, N.Y.) to a depth of 2 mm with air spray, but without water spray. The pins holes were placed at the line angles, 0.5 mm inside the dentinoenamel junction. A 0.21-inch threaded pin was inserted with a hand wrench to depth, then reversed a l/4 turn
597
Deciir!eEname! Junctian
PULPAL
Table
RESPONSE
TO PIN
I. Distribution
AND
SLOT
METHODS
of materials for test and control procedures Inflammatory response* (N of teeth)
Treatment modality
Pins Slots
Soft
tissue response* (N of teeth)
RDT
(mm)
1
2A
2c
3
1
2
3
Mean
SD
9
10
4 2
9 4
9 18
12
11
10
4
0.52 0.60
0.48 0.38
24
2
N, number; RDT, remaining dentin thickness. *Criteria for judging pulpal inflammatory and soft tissue responses as defined by Cox et al. l2 Inflammatory response: 1, None to slight; ZA, moderate predominated with polymorphonuclear cells (PMN) as an acute lesion; ZC, moderate predominated with mononuclear leukocytes as a chonic lesion; 3, severe with infiltrate of PMNs involving a third or more of pulp. Soft tissue response: 1, Normal or close to normal morphology; 2, incomplete morphology at exposure site and affected dentin; 3, degeneration in the coronal third or more of pulp.
Table II. Statistical analysis of pulpal responses Statistical
Responses
ChiSquare
Inflammation Soft tissue
p 0.049
p 0.011
KruskalWallis
p 0.003 p 0.015
test
ANOVA
p 0.008 p 0.015
t-Test p 0.008 p 0.041
mm or more from the pulp exhibited minimal pulpal response, whereas pins placed 0.5 mm or closer usually resulted in severe pulpal response. Specimens with pins placed between 0.5 and 1 mm from the pulp exhibited varying degrees of inflammation and soft tissue changes (Fig. Z). Representative histologic specimens of both pin and slot retention are presented in Figs. 3 and 4.
DISCUSSION tending grades of N-butyl alcohol, and embedded in Paraplast-Plus material (Monoject Scientific, Division of Sherwood Medical, St. Louis, MO.). Uninterrupted serial sections of 7 pm were cut on a rotary microtome and placed on specially prepared gelatin slides to prevent tissue loss during staining. The sections were stained with hematoxylin and eosin. Histopathologic assessment was made according to the criteria previously defined and tabulated by Cox et a1.12 Pulpal responses for pin retention were graded at the closest location of the pinhole to the pulp. Pulpal responses for slot retention were graded at 32 randomly selected locations throughout the pulp. Remaining dentin thickness (RDT) was measured from each pinhole or slot to the closest location of pulp chamber with a micrometer scale attached to tbe eyepiece of the microscope. Pulpal responses were independently graded by three investigators with 3 to 15 years’ experience. The data were compared, and responses that were judged to differ by more than one category were reevaluated by the investigators until a consensus was reached. The data from each category were analyzed by chi-square analysis, Mruskal-Wallis, analysis of variance (ANOVA), and paired t-tests.
RESUL The data collected for pulpal inflammation, soft tissue response, and RDT for all experimental groups are summarized in Table I. The statistical analysis of the data is presented in Table II. The results indicated that there was a statistically significant lesser pulpal response when slots are used instead of threaded pins (p < 0.5). In the absence of mechanical exposure, there was little correlation between RDT and adverse pulp response with slot retention. However, with threaded pin retention, the pins placed 1 THE
JOURNAL
OF ~~QST~E~IC
DENTISTRY
In this pilot investigation, the teeth of the animal were severely abraded, although secondary dentin formation had not resulted in the obliteration of the pulp chambers. In addition, the pulps of the control teeth met the criteria established for acceptable inflammatory and soft tissue response. Factors that may have resulted in the pulpal responses include (1) the composite resin material, (2) preparation trauma, (3) residual stresses and dentinal microfractures, and (4) the remaining dentin thickness (RDT). Tbe composite resin may have influenced the pulpal responses. However, because many of the experimental teeth and all of the control teeth presented normal pulpal responses, it is most likely that any adverse responses were the result of one of the other factors. Preparation trauma may have been a factor in pulpal responses, although there was little inflammation or soft tissue change noted for restorations with slot retention, regardless of proximity to the pulp. Slot retention was placed with a new carbide bur, high-speed instrumentation, and copious water spray, all of which would tend to minimize the effects of preparation trauma. Pinholes were placed with slow-speed instrumentation, new burs, and a stream of air, but with no water spray, per the manufacturer’s recommendation and accepted clinical techniques.13 There may have been sufficient heat to injure the dental pulps. In this investigation, no pinholes were prepared and left unfilled, which would have facilitated the evaluation of preparation trauma as a factor in pin placement. Further investigation into this phenomenon is needed. Residual stresses following the insertion of the threade pins should not have been a factor because the pins were inserted to full seating depth, then unthreaded a l/4 turn to release insertion stresses. Pin insertion may have resulted. in dentinal microfractures that communicated with the 599
FELTON
r 3, Typicd response n-ml from pulp. Note int fnal ~~agni~ca~io~ x400 Severe inflanmat.o.ory re ‘22: magnrfication xaoo.]
ET AL
of pulp tissues to retention pin piacement. in pIacement I .5 odontoblastic layer and normal soft tissue morphology. 9Pin placement 0.3 mm from pulp tissues jupper right c leucocytes. (Origis predomimted by ~~~~~~r~~~n~~~ear
from ha-l generation, microfractures, or dentinai stress is unhewn Teeth requirieg ~~xil~~~y retention where minimal RD?‘ is anticipated would beat Se suited for slot retention. A mechanism for detection of tile exact location
of the p&p charnhe~ is needed to facilitate the selection of appropriate auxiliary retention. It is rroteworthy that these were three j?lechanical exposores in each of the test groups. The mechanical exposures for the slot retention group were easily and immediately
PULPAL
RESPONSE
TO PIN
AND
SLOT
METHODS
4. Typical response of pulp tissues to retention slot placement. A, Slot placement 0.5 mm remote from pulp tissues. (Original magnification x100.) B, Slot placement 0.3 mm from pulp tissues. Favorable pulp responses are seen in both instances (Original magnification X100.)
Fig.
detectable, although no effort was made to place a sedative base over the exposure sites. In contrast, none of the three exposure sites for the threaded pins were determined before pin insertion, and all pins seated fully and securely. The exposures for this group were on the lateral borders of the pinholes (Fig. 5) instead of at the end of the pinholes, giving the clinical impression that the pins had been fully seated. In addition, one pin was found to perforate the external surface of the tooth root, but was also clinically determined to be fully and securely seated. The full seating of this pin was, however, on alveolar crestal bone.
CONCLUSIONS Within the experimental limitations of this investigations, the following conclusions can be drawn: 1. Slot retention was statistically less injurious to the pulp than threaded pins. 2. The remaining dentin thickness between the preparation and the pulp was a greater factor for threaded pins than for slots relative to the inflammatory response. 3. Threaded pins should be avoided when lessthan 1 mm of RDT is anticipated between the pinhole and the pulp.
REFERENCES 1. Moffa JP, Razzano MR, Doyle MC. Pins-a comparison of their retentive properties. J Am Dent Assoc1969;78:529-35. 2. Outhwaite WC, Garman TA, Pashley DH. Pin vs. slot retention in extensive amalgam restorations. J PROSTHET DENT 19X$41:396-400. 3. German TA, Outhwaite WC, Hawkins IK, Smith CD. A clinical comparison of dentinal slot retention with metallic pin retention. J Am Dent Assor 1983;107:762-3. THE
JOURNAL
OF PROSTI3ETIC
DENTISTRY
Fig. 5. Perforation of pulp chamber with threaded pin. Presence of ledge at bottom of pinhole (arrow) gave impression that pin had fully seated. No evidence of lateral perforation into pulp was detected clinically. Severe pulpal response is evident. (Original magnification X100.)
4. Irvin AW, Webb EL, Holland GA, White JT. Photoelastic analysis of stress induced from insertion of self-threading retentive pins. J PROS~~~~D~~~1985;53:311-6. 5. Dilts WE, Welk DA, Laswell HR, George RL. Crazing of tooth structure associated with placement of pins for amalgam restorations. J Am Dent Assoc 1970;81:387-91.
FELTQNETAL
13. Sturdevant CM, Barton RE, SockweIl CL, Strickland WD. The art and science of operative dentistry. 2nd ed. St Louis: CV Mosby Co, 1985; 382.
14. Webb EL, Straka WF, Phillips threaded pins: a three-dimensional
CL. Tooth crazing associated with model. J PRWTHET DENT 198951:
624-8. Reprint
requests
to.
DKDAVIDAFELTON SCHOOLOFDENTISTRY ROOM 302 BHAUER WALL CB No.1450 UNIVERSITY DF NORTH CAROLINA CHAPEL HILL,NC 27599-7450
ented wit glass ionomer and conditioning
with
MS,a
E. L. Webb,
DDS,
MS,b
B. E. Kanoy,
MS, DDS,C
slot and
University of North Carolina, Schoolof Dentistry, Chapel Hill, NC. This investigation compared pulpal response to threaded pin techniques with response to retentive slot techniques. The teeth were restored with composite resin. Twenty-four teeth were assigned to three treatment groups in one Macaca mulatta monkey. Ten teeth (group 1) received 32 TMS O.OZl-inch self-threading pins. Ten teeth (group II) received circumferential slot retention 1 mm deep, 0.5 mm inside the dentinoenamel junction. Four teeth (group III) served as controls. Groups I and II were restored with composite resin. Fourteen days later, the teeth were removed, demineralized, serially sectioned, and stained with hematoxylin and eosin. Chi-square analysis indicated more pulp inflammation when self-threading pins were used (p < 0.5). Pins placed within 0.5 mm of the pulp elicited severe inflammatory responses, and those placed further than 1 mm had minimal effect. Little correlation existed between remaining dentin thickness and adverse pulp response when slot retention was used. (J PROSTHET DENT 1991;66:597-602.)
A uxiliary
retention for materials used to restore severely broken down teeth has been discussed at length in the dental literature. Retentive pins have evolved from cemented and friction-lock pins to self-threading pins.l More recently, retentive slots placed within the dentinoenamel junction have been purported to be a more conservative approach than threaded pin retention. In vitro investigations have compared the retentive capabilities of pin and slot retention mechanisms. Slots were shown to provide retention of restorative materials comparable to the values demonstrated by pin retention.2, 3 Tbreaded pins may cause stresses in dentin.4 However, the same stresseshave not been attributed to slot retention. Both methods present the potential for violation of the pulp chamber or external surfaces of the tooth if inappropriately used. Several in vitro investigations demonstrated damage to tooth structure associated with the placement of threaded pins, usually in the form of dentinal microfractures.5-7 Amalgam pins or slots were shown by others to retain restorative materials adequately without the potential for residual stresses and microfractures.a However, there have been no in vivo investigations to evaluate the effects of threaded pin or slot retention on the pulp. This investigation histologically compared and evaluated the response of pulp tissues after placement of a composite resin restorative material retained exclusively by either threaded pin or slot retention. This research was sponsored in part by NIH/NIDR grant No. RR05333. aAssistantProfessor,Department of Prosthodontics. bAssociateProfessor,Department of Prosthodontics. ‘Clinical AssociateProfessorand Acting Chairman, Department of Prosthodontics. dResearchAssistant Professor,Department of Endodontics. 10/l/25742
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
MATERIAL
AND
METHODS
The severely abraded teeth of one adult Macaca mulatta monkey were used in this investigation. The the animal was scaled and polished with a prophylaxis cup and pumice 1 week before the initial operative procedure and again on the day of tooth preparation. The animal was sedated with 0.2 cc/kg ketamine hydrochloride (100 mglcc) (Bristol Laboratories, Division of Bristol-Meyers, Syracuse, N.Y.) by intramuscular injection. Deeper sedation was obtained by intramuscular injection of 20 mg/ml of xylazine (Rompun 1 mg/lb) (Mobay Corp., Shawnee, Kan.) to the desired effect. The teeth were isolated with cotton rolls and prepared for either pin or slot retention. A total of 24 teeth were randomly assigned to one of three treatment groups. Group 1 consisted of 10 teeth that received a total of 32 threaded pins. Group 2 consisted of 10 teeth that received circumferential slot retention. Group 3 consisted of four teeth that remained unrestored to serve as controls. All pins and slots were prepared according to accepted principals. No attempt was made to locate the pins or slots a given distance from the pulp. Instead, an attempt was made to place the retention features 0.5 mm inside the dentinoenamel junction. This technique resulted in variations in the amount of remaining dentin between the retention features and the pulp tissues. The extent of pin and slot preparation into dentin is diagramed in Fig. 1. In the teeth that received threaded pin retention, either three or four pin holes were prepared with a 0.21 inch TMS drill (Whaledent International, New York, N.Y.) to a depth of 2 mm with air spray, but without water spray. The pins holes were placed at the line angles, 0.5 mm inside the dentinoenamel junction. A 0.21-inch threaded pin was inserted with a hand wrench to depth, then reversed a l/4 turn
597
Deciir!eEname! Junctian
PULPAL
Table
RESPONSE
TO PIN
I. Distribution
AND
SLOT
METHODS
of materials for test and control procedures Inflammatory response* (N of teeth)
Treatment modality
Pins Slots
Soft
tissue response* (N of teeth)
RDT
(mm)
1
2A
2c
3
1
2
3
Mean
SD
9
10
4 2
9 4
9 18
12
11
10
4
0.52 0.60
0.48 0.38
24
2
N, number; RDT, remaining dentin thickness. *Criteria for judging pulpal inflammatory and soft tissue responses as defined by Cox et al. l2 Inflammatory response: 1, None to slight; ZA, moderate predominated with polymorphonuclear cells (PMN) as an acute lesion; ZC, moderate predominated with mononuclear leukocytes as a chonic lesion; 3, severe with infiltrate of PMNs involving a third or more of pulp. Soft tissue response: 1, Normal or close to normal morphology; 2, incomplete morphology at exposure site and affected dentin; 3, degeneration in the coronal third or more of pulp.
Table II. Statistical analysis of pulpal responses Statistical
Responses
ChiSquare
Inflammation Soft tissue
p 0.049
p 0.011
KruskalWallis
p 0.003 p 0.015
test
ANOVA
p 0.008 p 0.015
t-Test p 0.008 p 0.041
mm or more from the pulp exhibited minimal pulpal response, whereas pins placed 0.5 mm or closer usually resulted in severe pulpal response. Specimens with pins placed between 0.5 and 1 mm from the pulp exhibited varying degrees of inflammation and soft tissue changes (Fig. Z). Representative histologic specimens of both pin and slot retention are presented in Figs. 3 and 4.
DISCUSSION tending grades of N-butyl alcohol, and embedded in Paraplast-Plus material (Monoject Scientific, Division of Sherwood Medical, St. Louis, MO.). Uninterrupted serial sections of 7 pm were cut on a rotary microtome and placed on specially prepared gelatin slides to prevent tissue loss during staining. The sections were stained with hematoxylin and eosin. Histopathologic assessment was made according to the criteria previously defined and tabulated by Cox et a1.12 Pulpal responses for pin retention were graded at the closest location of the pinhole to the pulp. Pulpal responses for slot retention were graded at 32 randomly selected locations throughout the pulp. Remaining dentin thickness (RDT) was measured from each pinhole or slot to the closest location of pulp chamber with a micrometer scale attached to tbe eyepiece of the microscope. Pulpal responses were independently graded by three investigators with 3 to 15 years’ experience. The data were compared, and responses that were judged to differ by more than one category were reevaluated by the investigators until a consensus was reached. The data from each category were analyzed by chi-square analysis, Mruskal-Wallis, analysis of variance (ANOVA), and paired t-tests.
RESUL The data collected for pulpal inflammation, soft tissue response, and RDT for all experimental groups are summarized in Table I. The statistical analysis of the data is presented in Table II. The results indicated that there was a statistically significant lesser pulpal response when slots are used instead of threaded pins (p < 0.5). In the absence of mechanical exposure, there was little correlation between RDT and adverse pulp response with slot retention. However, with threaded pin retention, the pins placed 1 THE
JOURNAL
OF ~~QST~E~IC
DENTISTRY
In this pilot investigation, the teeth of the animal were severely abraded, although secondary dentin formation had not resulted in the obliteration of the pulp chambers. In addition, the pulps of the control teeth met the criteria established for acceptable inflammatory and soft tissue response. Factors that may have resulted in the pulpal responses include (1) the composite resin material, (2) preparation trauma, (3) residual stresses and dentinal microfractures, and (4) the remaining dentin thickness (RDT). Tbe composite resin may have influenced the pulpal responses. However, because many of the experimental teeth and all of the control teeth presented normal pulpal responses, it is most likely that any adverse responses were the result of one of the other factors. Preparation trauma may have been a factor in pulpal responses, although there was little inflammation or soft tissue change noted for restorations with slot retention, regardless of proximity to the pulp. Slot retention was placed with a new carbide bur, high-speed instrumentation, and copious water spray, all of which would tend to minimize the effects of preparation trauma. Pinholes were placed with slow-speed instrumentation, new burs, and a stream of air, but with no water spray, per the manufacturer’s recommendation and accepted clinical techniques.13 There may have been sufficient heat to injure the dental pulps. In this investigation, no pinholes were prepared and left unfilled, which would have facilitated the evaluation of preparation trauma as a factor in pin placement. Further investigation into this phenomenon is needed. Residual stresses following the insertion of the threade pins should not have been a factor because the pins were inserted to full seating depth, then unthreaded a l/4 turn to release insertion stresses. Pin insertion may have resulted. in dentinal microfractures that communicated with the 599
FELTON
r 3, Typicd response n-ml from pulp. Note int fnal ~~agni~ca~io~ x400 Severe inflanmat.o.ory re ‘22: magnrfication xaoo.]
ET AL
of pulp tissues to retention pin piacement. in pIacement I .5 odontoblastic layer and normal soft tissue morphology. 9Pin placement 0.3 mm from pulp tissues jupper right c leucocytes. (Origis predomimted by ~~~~~~r~~~n~~~ear
from ha-l generation, microfractures, or dentinai stress is unhewn Teeth requirieg ~~xil~~~y retention where minimal RD?‘ is anticipated would beat Se suited for slot retention. A mechanism for detection of tile exact location
of the p&p charnhe~ is needed to facilitate the selection of appropriate auxiliary retention. It is rroteworthy that these were three j?lechanical exposores in each of the test groups. The mechanical exposures for the slot retention group were easily and immediately
PULPAL
RESPONSE
TO PIN
AND
SLOT
METHODS
4. Typical response of pulp tissues to retention slot placement. A, Slot placement 0.5 mm remote from pulp tissues. (Original magnification x100.) B, Slot placement 0.3 mm from pulp tissues. Favorable pulp responses are seen in both instances (Original magnification X100.)
Fig.
detectable, although no effort was made to place a sedative base over the exposure sites. In contrast, none of the three exposure sites for the threaded pins were determined before pin insertion, and all pins seated fully and securely. The exposures for this group were on the lateral borders of the pinholes (Fig. 5) instead of at the end of the pinholes, giving the clinical impression that the pins had been fully seated. In addition, one pin was found to perforate the external surface of the tooth root, but was also clinically determined to be fully and securely seated. The full seating of this pin was, however, on alveolar crestal bone.
CONCLUSIONS Within the experimental limitations of this investigations, the following conclusions can be drawn: 1. Slot retention was statistically less injurious to the pulp than threaded pins. 2. The remaining dentin thickness between the preparation and the pulp was a greater factor for threaded pins than for slots relative to the inflammatory response. 3. Threaded pins should be avoided when lessthan 1 mm of RDT is anticipated between the pinhole and the pulp.
REFERENCES 1. Moffa JP, Razzano MR, Doyle MC. Pins-a comparison of their retentive properties. J Am Dent Assoc1969;78:529-35. 2. Outhwaite WC, Garman TA, Pashley DH. Pin vs. slot retention in extensive amalgam restorations. J PROSTHET DENT 19X$41:396-400. 3. German TA, Outhwaite WC, Hawkins IK, Smith CD. A clinical comparison of dentinal slot retention with metallic pin retention. J Am Dent Assor 1983;107:762-3. THE
JOURNAL
OF PROSTI3ETIC
DENTISTRY
Fig. 5. Perforation of pulp chamber with threaded pin. Presence of ledge at bottom of pinhole (arrow) gave impression that pin had fully seated. No evidence of lateral perforation into pulp was detected clinically. Severe pulpal response is evident. (Original magnification X100.)
4. Irvin AW, Webb EL, Holland GA, White JT. Photoelastic analysis of stress induced from insertion of self-threading retentive pins. J PROS~~~~D~~~1985;53:311-6. 5. Dilts WE, Welk DA, Laswell HR, George RL. Crazing of tooth structure associated with placement of pins for amalgam restorations. J Am Dent Assoc 1970;81:387-91.
FELTQNETAL
13. Sturdevant CM, Barton RE, SockweIl CL, Strickland WD. The art and science of operative dentistry. 2nd ed. St Louis: CV Mosby Co, 1985; 382.
14. Webb EL, Straka WF, Phillips threaded pins: a three-dimensional
CL. Tooth crazing associated with model. J PRWTHET DENT 198951:
624-8. Reprint
requests
to.
DKDAVIDAFELTON SCHOOLOFDENTISTRY ROOM 302 BHAUER WALL CB No.1450 UNIVERSITY DF NORTH CAROLINA CHAPEL HILL,NC 27599-7450
ented wit glass ionomer and conditioning
with
