sistance to tensile, compression, ed by four post systems John 0. Burgess, DDS, MS,” James B. Summitt, DDS, J. William Robbins, DDS, MAb University of Texas Health Science Center, San Antonio, Tex.
and torsional
MS,a
forces
and
This study measured the force required to displace four dBerent endodontic posts (an experimental, Para-Post, Flexi-Post, and V Lock) when tensile, torsion, or compressive forces were applied. Extracted mandibular premolars were decoronated at the cementoenamel junction, the roots were divided into groups of similar size, and the pulpal tissue was removed. The canals were enlarged, cleaned, and filled with gutta percha. Post preparations were made, and the posts were cut and cemented into the post spaces with resin cement. The roots were notched with a separating disc and lowered into a metal tube filled with acrylic resin. Two Minim pins were placed into the coronal dentin paralleling the post. Composite resin cores were made around the coronal 4 mm of the posts and the two pins for 10 specimens from each group. The specimens were placed into a standardized fixture and a load applied until failure. The tensile load required to pull the experimental post and resin was significantly less than the load required to remove the threaded posts. Flexi-Posts provided the greatest resistance to torsion and tensile loading. The compressive load required to fracture the core over the V-Lock post was significantly greater than the other post systems. (J PROSTHET DENT 1992:68:899903.)
L
aboratory studies during the past decade have investigated retention of various post systems, and the variables affecting retention, post design, post length, post diameter, canal preparation, method of cementation, and luting medium.l Threaded posts are most retentive, followed by parallel posts, and tapered posts are least retentive.2-4 Longer posts are more retentive, but increased post diameter produces minimal increase in post retention.3, 5 Removal of additional dentin to increase the post diameter significantly weakens remaining tooth structure.6, 7 Several methods of preparing the post space and the effect of each on the apical seal have been investigated. These methods have included rotary instruments, heated instruments, and solvents.8-12 The literature is equivocal on post space preparation; no method has been consistently superior. Immediate post space preparation (immediately after the endodontic filling) versus delayed preparation (waiting at least 24 hours) has also been investigated.lO, 1215 Again, neither method has been consistently shown to be superior. The actual method of post cementation has been investigated, including placing the cement on the post and/or placing the cement in the canal with a lentulo spiral, a paper point, and an endodontic explorer.16,17 The lentulo spiral was the superior method of cement placement. The luting medium has also been investigated exten-
aAssociate Professor, Department bAssociate Professor, Department
of Restorative Dentistry. of General Practice.
IO/l/39317
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
Table
I.
Post systems tested
Post
Luting agent
Experimental post
Experimental resin
Experimental post with over-sized preparation Para-Post
Experimental resin
Flexi-Flow
Canal
treatment
1. Dry-paper point 2. Polyacrylic acid-20 set (Dentin prep) 3. Drying agent-10 set (Methyl ethyl ketone) 4. Cement Bis-GMA 1. Same as above
1. Dry-paper Cement 1. Dry-paper 2. Cement 1. Dry-paper 2. Cement
point
0
L.
V Lock
Flexi-Flow
Flexi-Post
Flexi-Flow
point point
sively.3, 18-33 Again, the literature does not consistently suggest that one cement is superior to another. The resistance to fracture of the tooth and post combination when placed in compression has been studied. Posts increase fracture resistance in anterior endodontically treated teeth with crowns, but do not increase fracture resistance in posterior endodontically treated teeth with cuspal coverage restorations.34-36 Although some studies
899
BURGESS,
SUMMITT,
AND
ROBBINS
Fig. 1. Tensile testing apparatus. Fig. 2. Torsion testing apparatus. Fig. 3. Pin and post arrangement in specimens prepared for compressive testing. Pi, pins; PO, post. Fig. 4. Specimen positioned for compressive loading. indicate a post strengthens an intact anterior tooth,37a38 other studies suggest that the fracture resistance of an intact anterior endodontically treated tooth is not affected or even decreases with post placement.3g-41 Posts are not generally recommended for these situations. Resistance of the post and core to torsional forces has received minimal research interest.42-44 Increased resistance to torsional forces is especially important in the restoration of endodontically treated anterior teeth. The incorporation of an antirotation device, such as a pin or keyway, into the post and core is a critical element in increasing the force required to displace the restoration.42,43 The purpose of this study was to investigate, in vitro, the retention and resistance of four post systems subjected to tensile, compressive, and torsional forces.
MATERIAL
AND
METHODS
Four post systems (Flexi-Post, V Lock, Para-Post, and an experimental post) were evaluated in torsion, compression, and tension. In addition, the experimental post sys-
900
tem was evaluated in an oversized post preparation producing a fifth test group. Table I lists the luting agents and the canal treatments for each test group. One hundred twenty extracted mandibular premolar teeth were stored in normal saline solution, except during testing and specimen manipulation. The teeth were sized and divided into 12 groups with similar mean faciolingual dimensions. The coronal portion of the tooth was removed at the cementoenamel junction with a separating disk, the pulpal tissue was removed, and the canals were enlarged with Peeso reamers (Union Broach Co., Long Island City, N.Y.) and endodontic files (Kerr, Romulus, Mich.). The canals were irrigated with diluted (2.6 %) sodium hypochlorite solution, dried with paper points, and filled with gutta-percha (Hygienic Corp., Arkon, Oh.) and Proco-Sol sealer (Den-Tal-EZ, Inc., Lancaster, Pa.) with lateral condensation. The canal space was prepared to a standardized depth of 9 mm with the use of drills supplied by the appropriate manufacturer. The posts were cut if necessary to provide a uniform 13 mm length. This length allowed a 4
DECEMBER
1982
VOLUME
68
NUMBER
6
RESISTANCE
PROVIDED
BY FOUR
POST
SYSTEMS
.
_
-
80
0 Experimental
* Experimental
Para-Post
Reeirtance
To
Tensile
Load
m ExperImental Fig.
Table
Post-
Oversized
5. Resistance
and Ming
agent
Canal
to tensile
Tension
Experimental post and resin Oversized experimental and Resin Para-Post & Flexi-Flow V Lock & Flexi-Flow Flexi-Post & Flexi-Flow that
loading
provided
are not statistically different
are connected
(kg)
by four post systems.
Tensile
DENTISTRY
Compression 50.86* 46.99% 51.51* 68.28** 59.12**
(kg) *** *** ***
with the same symbol.
test
OF PROSTHETIC
(kg-cm2) 3.54** 3.63** 1.98*** 3.40** 5.85*
98.6****
Ten specimens of each of the five test groups were mounted in orthodontic resin within metal cylinders and
JOURNAL
Torsion
36.7** 27.4* 35.6** 56.0***
mm extension of the post coronal to the entrance to the post preparation. Two resin luting agents were used. One, a newly developed experimental resin cement, was used to lute the posts in the new experimental post system. The other, Flexi-Flow cement, was used to lute the remaining post systems. The appropriate cement was mixed and placed in the post preparation with a lentulo spiral. The post was coated with cement and inserted into the preparation, A uniform weight was applied to the post until the resin polymerized. Excess cement was removed and the roots were notched with a separating disk. The posts were aligned with a paralleling device and the roots were mounted in metal cylinders filled with orthodontic resin (Caulk, Milford, Del.). After the resin polymerized, the specimens were stored in normal saline solution at room temperature until testing. The posts were then tested with tensile, torsion, and compression loading.
THE
Flexi-Post
Loads to failure
II.
Post
Groups
V-Lock
placed in a fixture that grasped the base of the metal cylinders. The 4 mm portion of the post extending from the post preparation was grasped by a Jacob’s chuck attached to an Instron testing machine (Instron, Canton, Mass.) (Fig. 1). The retention of each post was determined by tensile loading of the post at a crosshead speed of 5 mm/min until failure.
Torsion
test
An additional 10 specimens of each of the five test groups were placed in a fixture that grasped the base of the metal cylinders. A constant clockwise torque was applied to each post with an Instron torsion load cell (Fig. 2). The torque at failure was recorded.
Compression
test
In the final 10 specimens of each of the five test groups, two Minim pins (Whaledent Inc., New York, N.Y.) (Fig. 3) were placed as antirotational devices, and composite resin cores (Herculite XR, Romulus, Mich.) were placed over the post with the use of a standard core former. The composite resin was polymerized for 2 minutes with an Optilux 400
901
BURGESS,
SUMMITT,
AND
ROBBINS
7-J 6-. 6 -. 4321 -.
I
Experimental
* Experimental
Pam-Post
V-Lock
Resistance m 0 Exporlmontal
Fig.
Poet-
6. Resistance
Ovwsixod
To
Toreion
Loading
Canal
to clockwise
torsion
loading
provided
by four post systems.
70 60 60 40 30 20 10 0 Experimental
* Experimental
Para-Post Load
m * Experimental
Fig.
Poet-
‘7. Resistance
Overalxed
Flexi-Past
To
Displace
Core
Canal
to compressive
visible light-curing unit (Demetron Research Corp., Danbury, Conn.) with a new 100 watt bulb. The specimens were stored in a fixture positioned at 45 degrees (Fig. 4), and a compressive load was applied to the lingual surface of the composite resin core at a crosshead speed of 5 mm/min until failure. The peak failure load was recorded as the first dip in the stress strain curve.
RESULTS Mean failure loads for the compression, tensile, and torsion tests of each post system were evaluated for signifi-
902
V-Lock
loading
provided
by four post systems.
cance with three separate one-factor analysis of variance tests. A least significant difference multiple range post hoc analysis was used to determine individual differences between each group. Results are presented in Table II and Figs. 5 through 7.
CONCLUSIONS The experimental post system tested, with its resin adhesive, polyacrylic acid conditioner, and drying agent did not provide a significant improvement over posts cemented with a conventional nonadhesive resin cement. Failure in
DECEMBER
1992
VOLUME
68
NUMBER
6
RESISTANCE
PROVIDED
BY FOUR
POST
SYSTEMS
almost all instances occurred at the dentin-resin interface; that is, failure was primarily adhesive at the dentinal surface. Because failures occurred at the cement-dentin interface, it is not surprising that the tensile values for nonthreaded post systems were similar. Threaded post systems provided significantly higher tensile resistance than the cemented post systems. REFERENCES 1. Robbins JW. Guidelines for the restoration of endodontically treated teeth. J Am Dent Assoc 1990;120:558-66. 2. Cooney JP, Caputo AA, Trabert KC. Retention and stress distribution of tapered-end endodontic posts. J PROSTHET DENT 1986;55:540-6. 3. Standlee JP, Caputo AA, Hanson EC. Retention of endodontic dowels: effects of cement, dowel length, diameter, and design. J PROSTHET DENT
1978;39:401-5. 4. Johnson
JK, Sakamura
JS. Dowel form
and tensile
force.
J PROSTHET
D~~~1978;40:645-9. 5. Assif D, Bleicher S. Retention of serrated endodontic posts with a composite luting agent: effect of cement thickness. J PROSTHET DENT
1986;56:689-91. 6. Mattison GD, van Fraunhofer JA. Angulation loading effects on castgold endodontic posts: a photoelastic stress analysis. J PROSTHET DENT
1983;49:636-8. 7. Mat&on GD. Photoelastic stress analysis of cast-gold endodontic posts. J PROSTHET D~~~1982;48:407-11. 8. Kwan EH, Harrington GW. The effect of immediate post preparation on apical seal. J Endodont 1981;7:325-9. 9. Mattison GD, Delivanis PD, Thacker RW, Hassell KJ. Effect of post preparation on the apical seal. J PROSTHET DENT 1984;51:785-9. 10. Madison S, Zakariasen KL. Linear and volumetric analysis of apical leakage in teeth prepared for posts. J Endodont 1984;10:422-7. 11. Sucbina JA, Ludington JR. Dowel space preparation and the apical seal. J Endodont 1985;11:11-7. 12. Dickey DJ, Harris GZ, Lemon RR, Luebke RG. Effect of post space preparation on apical seal using solvent techniques and Peeso reamers. J Endodont 1982;8:351-4. 13. Porte11 FR, Bernier WE, Lorton L, Peters DD. The effect of immediate versus delayed dowel space preparation on the integrity of the apical seal. J Endodont 1982;8:154-60. 14. Schnell FJ. Effect of immediate dowel space preparation on the apical seal of endodontically filled teeth. Oral Surg Oral Med Oral Path01 1978;45:470-4. 15. Bourgeois RS, Lemon RR. Dowel space preparation and apical leakage. J Endodont 1981;7:66-9. 16. Goldman M, DeVitre R, Tenca J. Cement distribution and bond strength in cemented posts. J Dent Res 1984;63:1392-5. 17. Goldstein GR, Hudis SI, Weintraub DE. Comparison of four techniques for the cementation 0fposts.J PROSTHET DENT 1986;55:209-11. 18. Goldman M, DeVitre R, White R, Nathanson D. An SEM study of posts cemented with an unfilled resin. J Dent Res 1984;63:1003-5. 19. Chapman KW, Worley JL, von Fraunhofer JA. Retention of prefabricated posts by cements and resins. J PROSTHET DENT 1985;54:649-52. 20. Young HM, Shen C, Maryniuk GA. Retention of cast posts relative to cement selection. Quintessence 1985;16:357-60. 21. Krupp JD, Caputo AA, Trabert KC, Standlee JP. Dowel retention with glass-ionomer cement. J PROSTHET DENT 19'79;41:163-6. 22. Ben-Amar A, Gontar G, Fitzig S, Urstein M, Liberman R. Retention of
THE JOURNAL
OF PROSTHETIC
DENTISTRY
prefabricated
posts with
dental
adhesive
and composite.
J PROSTHET
D~~~1986;56:681-4. 23. Gontar
G, Liberman R, Urstein M, Fitzig S, Ben-Amar A. Retention of dowels using Conclude composite resin as a luting medium. Dent Mater
1986;2:118-20. 24. Hill GL, Zidan
0, Duerst L. Retention of etched based metal dowels with resin cement and bonding agent. J PROSTHET DENT 1986;55:691-3. 25. Nasr HH, Eskander ME, Zake AM. The luting efficacy of cements in bonding dowels of different metals. Egypt Dent J 1987;33:155-71. 26. Brown JD, Mitchem JC. Retentive properties of dowel post systems. Oper Dent 1987;12:15-9. 27. Tjan AHL, Tjan AH, Greive JH. Effects of various cementation methods on retention of prefabricated posts. J PROSTHET DENT 1987;58:309-
13. 28. Chapman
KW, Worley JL, van Fraunhofer JA. Effect of bonding agents on the retention of posts. Gen Dent 1985;33:128-30. 29. Goldman M, DeVitre R, Pier M. Effect of the dentin smeared layer on tensile strength of cemented posts. J PROSTHET DENT 1984;52:485-8. 30. Assif DA. Retention of dowels using a composite resin as a cementing medium.J PROSTHET D~~~1982;48:292-6. RA, Podesta RE. Retention of cast endodontic 31. Radke RA, Barkhordar posts: comparison of cementing agents. J PROSTHET DENT 1988;59:318-
20. 32. Coleman
RA, Corcoran JF, Powers JM, Sloan KM, Lorey RE, LaTurno SAL. Dentin-bonded post and cores: an in vitro failure analysis [Abstract]. J Dent Res 1987;66(Special issue):135. 33. Wolff MS, Breuer J, Shiu A, Osborne JW. A comparison of three cements in retaining posts in teeth [Abstract]. J Dent Res 1987;66(Special issue):135. 34. Sorensen JA, Martinoff MD. Intracoronal reinforcement and coronal coverage: a study of endodontically treated teeth. J PROSTHET DENT
1984;51:780-4. evaluation of three post and core 35. Hoag EP, Dwyer TG. A comparative techniques.J PROSTHETDENT 1982;47:177-81. 36. Zakhary SY, Nasr HH. In vitro assessment of intact endodontically
31. 38. 39. 40.
treated anterior teeth with different restorative procedures. Egypt Dent J 1986;32:221-39. Kantor ME, Pines MS. A comparative study of restorative techniques for pulpless teeth. J PROSTHET DENT 1977;38:405-12. Trabert KC, Caputo AA, Abou-Rass M. Tooth fracture-a comparison of endodontic and restorative treatments. J Endodont 1978,4:341-5. Trope M, Malts DO, Tronstad L. Resistance to fracture of restored endodontically treated teeth. Endodont Dent Traumatol 1985;1:108-11. Guzy GE, Nicholls JI. In vitro comparison of intact endodontically treated teeth with and without endo-post reinforcement. J PROSTHET
DENT 1979;42:39-44. 41 Lovdahl PE, Nicholls JI. Pin-retained amalgam cores vs cast-gold dowel-cores.J PROSTHETDENT 1977;38:507-14. 42 Ruemping DR, Lund MR, Schnell RJ. Retention of dowels subjected to tensile and torsional forces. J PROSTHET DENT 19'79;41:159-62. 43. Newburg RE, Pameijer CH. Retentive properties of post and core systems.J PROSTHET DENT 1976;36:636-43. 44. Tjan AHL, Miller GD. Comparison of retentive properties of dowel forms after application of intermittent torsional forces. J PROSTHET DENT 1984;52:238-42. Reprint
DR.JOHN
requests
to:
O.B~RGESS,DDS,
MS
UT HSC
7703 FLOYD CURLDRIVE SAN ANTONIO,TEXAS 78284-7890
903
and torsional
MS,a
forces
and
This study measured the force required to displace four dBerent endodontic posts (an experimental, Para-Post, Flexi-Post, and V Lock) when tensile, torsion, or compressive forces were applied. Extracted mandibular premolars were decoronated at the cementoenamel junction, the roots were divided into groups of similar size, and the pulpal tissue was removed. The canals were enlarged, cleaned, and filled with gutta percha. Post preparations were made, and the posts were cut and cemented into the post spaces with resin cement. The roots were notched with a separating disc and lowered into a metal tube filled with acrylic resin. Two Minim pins were placed into the coronal dentin paralleling the post. Composite resin cores were made around the coronal 4 mm of the posts and the two pins for 10 specimens from each group. The specimens were placed into a standardized fixture and a load applied until failure. The tensile load required to pull the experimental post and resin was significantly less than the load required to remove the threaded posts. Flexi-Posts provided the greatest resistance to torsion and tensile loading. The compressive load required to fracture the core over the V-Lock post was significantly greater than the other post systems. (J PROSTHET DENT 1992:68:899903.)
L
aboratory studies during the past decade have investigated retention of various post systems, and the variables affecting retention, post design, post length, post diameter, canal preparation, method of cementation, and luting medium.l Threaded posts are most retentive, followed by parallel posts, and tapered posts are least retentive.2-4 Longer posts are more retentive, but increased post diameter produces minimal increase in post retention.3, 5 Removal of additional dentin to increase the post diameter significantly weakens remaining tooth structure.6, 7 Several methods of preparing the post space and the effect of each on the apical seal have been investigated. These methods have included rotary instruments, heated instruments, and solvents.8-12 The literature is equivocal on post space preparation; no method has been consistently superior. Immediate post space preparation (immediately after the endodontic filling) versus delayed preparation (waiting at least 24 hours) has also been investigated.lO, 1215 Again, neither method has been consistently shown to be superior. The actual method of post cementation has been investigated, including placing the cement on the post and/or placing the cement in the canal with a lentulo spiral, a paper point, and an endodontic explorer.16,17 The lentulo spiral was the superior method of cement placement. The luting medium has also been investigated exten-
aAssociate Professor, Department bAssociate Professor, Department
of Restorative Dentistry. of General Practice.
IO/l/39317
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
Table
I.
Post systems tested
Post
Luting agent
Experimental post
Experimental resin
Experimental post with over-sized preparation Para-Post
Experimental resin
Flexi-Flow
Canal
treatment
1. Dry-paper point 2. Polyacrylic acid-20 set (Dentin prep) 3. Drying agent-10 set (Methyl ethyl ketone) 4. Cement Bis-GMA 1. Same as above
1. Dry-paper Cement 1. Dry-paper 2. Cement 1. Dry-paper 2. Cement
point
0
L.
V Lock
Flexi-Flow
Flexi-Post
Flexi-Flow
point point
sively.3, 18-33 Again, the literature does not consistently suggest that one cement is superior to another. The resistance to fracture of the tooth and post combination when placed in compression has been studied. Posts increase fracture resistance in anterior endodontically treated teeth with crowns, but do not increase fracture resistance in posterior endodontically treated teeth with cuspal coverage restorations.34-36 Although some studies
899
BURGESS,
SUMMITT,
AND
ROBBINS
Fig. 1. Tensile testing apparatus. Fig. 2. Torsion testing apparatus. Fig. 3. Pin and post arrangement in specimens prepared for compressive testing. Pi, pins; PO, post. Fig. 4. Specimen positioned for compressive loading. indicate a post strengthens an intact anterior tooth,37a38 other studies suggest that the fracture resistance of an intact anterior endodontically treated tooth is not affected or even decreases with post placement.3g-41 Posts are not generally recommended for these situations. Resistance of the post and core to torsional forces has received minimal research interest.42-44 Increased resistance to torsional forces is especially important in the restoration of endodontically treated anterior teeth. The incorporation of an antirotation device, such as a pin or keyway, into the post and core is a critical element in increasing the force required to displace the restoration.42,43 The purpose of this study was to investigate, in vitro, the retention and resistance of four post systems subjected to tensile, compressive, and torsional forces.
MATERIAL
AND
METHODS
Four post systems (Flexi-Post, V Lock, Para-Post, and an experimental post) were evaluated in torsion, compression, and tension. In addition, the experimental post sys-
900
tem was evaluated in an oversized post preparation producing a fifth test group. Table I lists the luting agents and the canal treatments for each test group. One hundred twenty extracted mandibular premolar teeth were stored in normal saline solution, except during testing and specimen manipulation. The teeth were sized and divided into 12 groups with similar mean faciolingual dimensions. The coronal portion of the tooth was removed at the cementoenamel junction with a separating disk, the pulpal tissue was removed, and the canals were enlarged with Peeso reamers (Union Broach Co., Long Island City, N.Y.) and endodontic files (Kerr, Romulus, Mich.). The canals were irrigated with diluted (2.6 %) sodium hypochlorite solution, dried with paper points, and filled with gutta-percha (Hygienic Corp., Arkon, Oh.) and Proco-Sol sealer (Den-Tal-EZ, Inc., Lancaster, Pa.) with lateral condensation. The canal space was prepared to a standardized depth of 9 mm with the use of drills supplied by the appropriate manufacturer. The posts were cut if necessary to provide a uniform 13 mm length. This length allowed a 4
DECEMBER
1982
VOLUME
68
NUMBER
6
RESISTANCE
PROVIDED
BY FOUR
POST
SYSTEMS
.
_
-
80
0 Experimental
* Experimental
Para-Post
Reeirtance
To
Tensile
Load
m ExperImental Fig.
Table
Post-
Oversized
5. Resistance
and Ming
agent
Canal
to tensile
Tension
Experimental post and resin Oversized experimental and Resin Para-Post & Flexi-Flow V Lock & Flexi-Flow Flexi-Post & Flexi-Flow that
loading
provided
are not statistically different
are connected
(kg)
by four post systems.
Tensile
DENTISTRY
Compression 50.86* 46.99% 51.51* 68.28** 59.12**
(kg) *** *** ***
with the same symbol.
test
OF PROSTHETIC
(kg-cm2) 3.54** 3.63** 1.98*** 3.40** 5.85*
98.6****
Ten specimens of each of the five test groups were mounted in orthodontic resin within metal cylinders and
JOURNAL
Torsion
36.7** 27.4* 35.6** 56.0***
mm extension of the post coronal to the entrance to the post preparation. Two resin luting agents were used. One, a newly developed experimental resin cement, was used to lute the posts in the new experimental post system. The other, Flexi-Flow cement, was used to lute the remaining post systems. The appropriate cement was mixed and placed in the post preparation with a lentulo spiral. The post was coated with cement and inserted into the preparation, A uniform weight was applied to the post until the resin polymerized. Excess cement was removed and the roots were notched with a separating disk. The posts were aligned with a paralleling device and the roots were mounted in metal cylinders filled with orthodontic resin (Caulk, Milford, Del.). After the resin polymerized, the specimens were stored in normal saline solution at room temperature until testing. The posts were then tested with tensile, torsion, and compression loading.
THE
Flexi-Post
Loads to failure
II.
Post
Groups
V-Lock
placed in a fixture that grasped the base of the metal cylinders. The 4 mm portion of the post extending from the post preparation was grasped by a Jacob’s chuck attached to an Instron testing machine (Instron, Canton, Mass.) (Fig. 1). The retention of each post was determined by tensile loading of the post at a crosshead speed of 5 mm/min until failure.
Torsion
test
An additional 10 specimens of each of the five test groups were placed in a fixture that grasped the base of the metal cylinders. A constant clockwise torque was applied to each post with an Instron torsion load cell (Fig. 2). The torque at failure was recorded.
Compression
test
In the final 10 specimens of each of the five test groups, two Minim pins (Whaledent Inc., New York, N.Y.) (Fig. 3) were placed as antirotational devices, and composite resin cores (Herculite XR, Romulus, Mich.) were placed over the post with the use of a standard core former. The composite resin was polymerized for 2 minutes with an Optilux 400
901
BURGESS,
SUMMITT,
AND
ROBBINS
7-J 6-. 6 -. 4321 -.
I
Experimental
* Experimental
Pam-Post
V-Lock
Resistance m 0 Exporlmontal
Fig.
Poet-
6. Resistance
Ovwsixod
To
Toreion
Loading
Canal
to clockwise
torsion
loading
provided
by four post systems.
70 60 60 40 30 20 10 0 Experimental
* Experimental
Para-Post Load
m * Experimental
Fig.
Poet-
‘7. Resistance
Overalxed
Flexi-Past
To
Displace
Core
Canal
to compressive
visible light-curing unit (Demetron Research Corp., Danbury, Conn.) with a new 100 watt bulb. The specimens were stored in a fixture positioned at 45 degrees (Fig. 4), and a compressive load was applied to the lingual surface of the composite resin core at a crosshead speed of 5 mm/min until failure. The peak failure load was recorded as the first dip in the stress strain curve.
RESULTS Mean failure loads for the compression, tensile, and torsion tests of each post system were evaluated for signifi-
902
V-Lock
loading
provided
by four post systems.
cance with three separate one-factor analysis of variance tests. A least significant difference multiple range post hoc analysis was used to determine individual differences between each group. Results are presented in Table II and Figs. 5 through 7.
CONCLUSIONS The experimental post system tested, with its resin adhesive, polyacrylic acid conditioner, and drying agent did not provide a significant improvement over posts cemented with a conventional nonadhesive resin cement. Failure in
DECEMBER
1992
VOLUME
68
NUMBER
6
RESISTANCE
PROVIDED
BY FOUR
POST
SYSTEMS
almost all instances occurred at the dentin-resin interface; that is, failure was primarily adhesive at the dentinal surface. Because failures occurred at the cement-dentin interface, it is not surprising that the tensile values for nonthreaded post systems were similar. Threaded post systems provided significantly higher tensile resistance than the cemented post systems. REFERENCES 1. Robbins JW. Guidelines for the restoration of endodontically treated teeth. J Am Dent Assoc 1990;120:558-66. 2. Cooney JP, Caputo AA, Trabert KC. Retention and stress distribution of tapered-end endodontic posts. J PROSTHET DENT 1986;55:540-6. 3. Standlee JP, Caputo AA, Hanson EC. Retention of endodontic dowels: effects of cement, dowel length, diameter, and design. J PROSTHET DENT
1978;39:401-5. 4. Johnson
JK, Sakamura
JS. Dowel form
and tensile
force.
J PROSTHET
D~~~1978;40:645-9. 5. Assif D, Bleicher S. Retention of serrated endodontic posts with a composite luting agent: effect of cement thickness. J PROSTHET DENT
1986;56:689-91. 6. Mattison GD, van Fraunhofer JA. Angulation loading effects on castgold endodontic posts: a photoelastic stress analysis. J PROSTHET DENT
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