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Posts, Cores and Patient Care
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POSTS, CORES AND PATIENT CARE purred by an aging population, the need for fixed prosthodontics has increased in recent years—and with it a controversy over the best type of post and core for endodontically treated teeth. Custom cast posts and cores had been the most accepted treatm ent mode for many years, but this has changed. Prefabricated posts—followed by plastic m aterials, composite resin and amalgam—have become the most popular methods for post and core tooth buildups. This article reviews the m aterials and techniques available for this im portant one-appointment tooth recon struction procedure and draws conclusions based on research and clinical experience. ROSTS
Type o f m etal: Prefabricated posts for years have been made prim arily of nickel-chrome because of the considerable strength of these metals. In recent years, however, a movement toward titanium and titanium alloy for posts has emerged, in p art because nickel is allergenic to many patients, particularly females. Although posts are placed inside the teeth, there is com munication between 86
JADA, Vol. 124, September 1993
periodontal structures and the internal tooth through the dentinal canals. Are titanium or titanium alloy posts strong enough for connecting tooth roots to core buildup material? Nickel-chrome posts are the strongest types made today, and pure titanium posts are the weakest. Titanium alloy, usually containing small am ounts of aluminum and vanadium, are interm ediate in strength. Despite reports from a few clinicians about breakage or bending of titanium or titanium alloy posts, these m aterials have proved satisfactory when used with: "* adequate anti-rotational features in the remaining root (pins, potholes, channels); ■■ strong build-up m aterial (composite or glass ionomer)1; "■ a collar on the crown extended at least 1 mm apically beyond the interface of the core and remaining root structure. Although use of titanium and titanium alloy is growing and is encouraged, nickel-chrome posts are still very popular. Shape o f post: Many studies have been conducted on th e most acceptable shape for posts. Shapes include: ■■ parallel-sided, serrated rods; ™ slightly tapered, serrated rods; “ parallel-sided screws;
™ tapered screws and many others.2 There is disagreement over the comparative acceptability of “passive posts” (those cemented into a tooth and retained only by cementing material), and “active posts” (threaded posts th a t are held in place both by cement and threads th a t interdigitate into tooth structure). In vitro research shows th a t active posts have the most retention (a current example is Flexi-Post, Essential Dental Systems). How much retention is needed? Well-placed passive posts (current example, ParaPost, Coltene/Whaledent) do not have reports of excessive failure during service. From an empirical clinical use stand point, it appears th a t either passive or active posts are successful, and th a t clinicians should use the post concept with which they feel most comfortable. The most popular posts used in the United States are Coltene/ W haledent Para-Post or Para-Post Plus (parallel sided serrated) and the EDS Flexi-Post (active screw with vertical slot to reduce stress on root during placement). CEMENT FOR POSTS
Disagreement also surrounds
CHRISTENSEN
| the type of cement to use, the | reasons for choosing one over another and technique. Among cements include glass j ionomer, resin, zinc phosphate | and others.3Any of the three | major types listed is adequate j when used properly, but these j cements vary significantly in | compressive and tensile strength. The cement with the I greatest strength is resin,
followed by glass ionomer and zinc phosphate. Although conflicting invitro research exists, it seems logical th a t stronger cement (resin) should be used when posts are not fitted tightly to post chambers in roots, allowing potential lateral post move ment. Weaker cements (glass ionomer or zinc phosphate) should be selected when
A TECHNIQUE FOB PREFABRICATED POST AND CORE PLACEMENT USING RESIN Complete root canal therapy. ■■ Make post channel. Suggested length for channel is about one-half the length of the bony supported p art of the root, with a diameter th a t fills the majority of the most coronal aspect of the post channel. ■■ Select and fit post of choice. Cut post to length th a t allows it to extend coronally to approximate height of planned core. ■■ Place anti-rotational feature in tooth. At least one pin, “pothole,” or channel on both the mesial and distal aspect of a single rooted tooth, or on all four corners of a molar, is suggested. ■“ Place matrix band. Pre annealed copper bands are the easiest and fastest technique (Parkell). Cut the band to size slightly larger in diameter and about 1 mm higher coronally than the anticipated core height. Tighten the band on the tooth by crimping it with a hem ostat on the facial area.
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JADA, Vol. 124, September 1993
™ Place bonding system down post channel on Lentulo spiral with a small piece of cotton on it. Place same bonding material on remaining coronal portion of tooth. Check bonding system beforehand to assure th a t it does not accelerate cement set. ■■ Seat post with resin cement. A Centrix needle tube is useful to place cement in post channel. (Centrix Inc.). When post is seated, excess cement will flow onto coronal tooth portion. ■■ Place resin build-up material immediately, before resin cement has set. Excess cement will be displaced by heavier viscosity resin build up material. Popular composite resin, build-up brands are Core Paste (DenMat Corp.); Prosthodent (Lee Pharmaceuticals); Ti-Core (Essential Dental Systems, and FluoroCore (L.D. Caulk/Dentsply). ■■ Complete tooth prepara tion within a few minutes after core placement.
relatively tight-fitting posts are used, reducing potential for post lateral movement. BONDING CEMENTS AND POSTS
Bonding posts into post channels with resin cement has gained popularity.4 Dentinbonding m aterials are used before cementing with auto cure resin cements such as Panavia (J. Morita USA, Inc.), Imperva Dual/Bond (Shofu Dental Corp.) and Resiment (Septodont, Inc.). A resin cement th a t does not require a bonding agent also may be selected. Examples include C & B Metabond (Parkell). If bonding agents are used before cementing posts with resin cement, clinicians should make sure, by testing outside the mouth, th a t the bonding material does not accelerate the setting of the resin cement, which would preclude post seating. Posts may be bonded to resin cement by sandblasting m etal posts directly before placement and using an appropriate resin cement th a t bonds to metal. Panavia and C & B Metabond are popular choices. CORE MATERIALS
Strong core m aterials are necessary because many cores replace most of the coronal portions of teeth.5Although conflicting in vitro research exists, core m aterials th a t have at least the compressive strength of the tooth structure being replaced appear to be appropriate (40,000 pounds per square inch). At this time, only two types of core m aterial meet this requirement, composite resin (-40,000 psi) and silver amalgam (~65,000 psi). Glass
CHRISTENSEN
Defense Without The Dental Record, you may meet your Waterloo. Defending yourself against malpractice claims requires a dental record that doesn’t come up short. The Dental Record provides an excellent risk manage ment shield because its comprehensive de sign documents all phases of treatment. Its flexible defense system is built of 14 forms and a revolutionary folder. To add The Dental Record to your empire, call for astarter kit ($10 includes shipping), MasterCard and VISA ac cepted.
800
-
2 4 3 - 4 B7 5 The DentalRecord ByDentists, For Dentists
W isconsin Dental Association, 1 1 1 E. W isconsin Ave.. Suite 1300
ionomer (-18,000 psi) and glass ionomer-resin (-25,000 psi) make Dr. Christensen is adequate co-founder and “filler” currently senior consultant of m aterials for Clinical Research small “pot A ssociates, Provo, Utah, and is a holes,” boxes, member of JA D A ’ s previous Class editorial board. He V restorations has a m aster’s degree in restorative or other dentistry and a defects on doctorate in education and teeth. But psychology. He is long-term board certified in clinical prosthodontics. evidence is still necessary to support their use as large buildups or as core materials. BONDING CORE MATERIALS TO TEETH
Core m aterials (composite or amalgam) should be bonded to tooth structure using bonding m aterials with known accepta bility. Because of their speed of use, examples for composite resin bonding are Scotchbond Multi-Purpose (3M Dental Products), and Universal Bond 3 (L.D. Caulk/Dentsply). Bonding examples for amal gam are Amalgambond
(Parkell), and All-Bond 2 (Bisco Dental Products). Dentin bond ing materials reduce leakage and increase retention to tooth structure. Placement of other mechanical features for extra retention is still recommended (pins, potholes, channels, etc.). SUMMARY
Custom cast posts and cores are quite acceptable, with proven usefulness. However, prefabricated posts and bonded composite or silver amalgam cores are replacing them rapidly. These posts and cores are faster and easier to construct than custom cast posts and cores, and they provide acceptable strength and serviceability a t a relatively low cost to patients. ■ Further information concerning these techniques may be obtained from Dr. Gordon J. Christensen, 3707 N. Canyon Rd., Suite 7A, Provo, U tah 84604. 1. CRA News 1991;15(7):l-2. 2. Christensen GJ, Christensen RP. Post and cores—state of the art. CRA News 1990;14(2):l-3. 3. Christensen GJ, Christensen RP. Cements for fixed prosthodontics—update 1991. CRA News 1991;15(4):l-3. 4. Christensen GJ, Christensen RP. Resin cements—update ’93. CRA News 1993;17(5):l-2. 5. Christensen GJ. Should teeth be built-up before crowns? JADA 1993;124(6):93-4.
o r d o n
J .
C
h r is t e n s e n
,
d
.d .s . ,
m
.s .
d
.,
p h
.d .
POSTS, CORES AND PATIENT CARE purred by an aging population, the need for fixed prosthodontics has increased in recent years—and with it a controversy over the best type of post and core for endodontically treated teeth. Custom cast posts and cores had been the most accepted treatm ent mode for many years, but this has changed. Prefabricated posts—followed by plastic m aterials, composite resin and amalgam—have become the most popular methods for post and core tooth buildups. This article reviews the m aterials and techniques available for this im portant one-appointment tooth recon struction procedure and draws conclusions based on research and clinical experience. ROSTS
Type o f m etal: Prefabricated posts for years have been made prim arily of nickel-chrome because of the considerable strength of these metals. In recent years, however, a movement toward titanium and titanium alloy for posts has emerged, in p art because nickel is allergenic to many patients, particularly females. Although posts are placed inside the teeth, there is com munication between 86
JADA, Vol. 124, September 1993
periodontal structures and the internal tooth through the dentinal canals. Are titanium or titanium alloy posts strong enough for connecting tooth roots to core buildup material? Nickel-chrome posts are the strongest types made today, and pure titanium posts are the weakest. Titanium alloy, usually containing small am ounts of aluminum and vanadium, are interm ediate in strength. Despite reports from a few clinicians about breakage or bending of titanium or titanium alloy posts, these m aterials have proved satisfactory when used with: "* adequate anti-rotational features in the remaining root (pins, potholes, channels); ■■ strong build-up m aterial (composite or glass ionomer)1; "■ a collar on the crown extended at least 1 mm apically beyond the interface of the core and remaining root structure. Although use of titanium and titanium alloy is growing and is encouraged, nickel-chrome posts are still very popular. Shape o f post: Many studies have been conducted on th e most acceptable shape for posts. Shapes include: ■■ parallel-sided, serrated rods; ™ slightly tapered, serrated rods; “ parallel-sided screws;
™ tapered screws and many others.2 There is disagreement over the comparative acceptability of “passive posts” (those cemented into a tooth and retained only by cementing material), and “active posts” (threaded posts th a t are held in place both by cement and threads th a t interdigitate into tooth structure). In vitro research shows th a t active posts have the most retention (a current example is Flexi-Post, Essential Dental Systems). How much retention is needed? Well-placed passive posts (current example, ParaPost, Coltene/Whaledent) do not have reports of excessive failure during service. From an empirical clinical use stand point, it appears th a t either passive or active posts are successful, and th a t clinicians should use the post concept with which they feel most comfortable. The most popular posts used in the United States are Coltene/ W haledent Para-Post or Para-Post Plus (parallel sided serrated) and the EDS Flexi-Post (active screw with vertical slot to reduce stress on root during placement). CEMENT FOR POSTS
Disagreement also surrounds
CHRISTENSEN
| the type of cement to use, the | reasons for choosing one over another and technique. Among cements include glass j ionomer, resin, zinc phosphate | and others.3Any of the three | major types listed is adequate j when used properly, but these j cements vary significantly in | compressive and tensile strength. The cement with the I greatest strength is resin,
followed by glass ionomer and zinc phosphate. Although conflicting invitro research exists, it seems logical th a t stronger cement (resin) should be used when posts are not fitted tightly to post chambers in roots, allowing potential lateral post move ment. Weaker cements (glass ionomer or zinc phosphate) should be selected when
A TECHNIQUE FOB PREFABRICATED POST AND CORE PLACEMENT USING RESIN Complete root canal therapy. ■■ Make post channel. Suggested length for channel is about one-half the length of the bony supported p art of the root, with a diameter th a t fills the majority of the most coronal aspect of the post channel. ■■ Select and fit post of choice. Cut post to length th a t allows it to extend coronally to approximate height of planned core. ■■ Place anti-rotational feature in tooth. At least one pin, “pothole,” or channel on both the mesial and distal aspect of a single rooted tooth, or on all four corners of a molar, is suggested. ■“ Place matrix band. Pre annealed copper bands are the easiest and fastest technique (Parkell). Cut the band to size slightly larger in diameter and about 1 mm higher coronally than the anticipated core height. Tighten the band on the tooth by crimping it with a hem ostat on the facial area.
88
JADA, Vol. 124, September 1993
™ Place bonding system down post channel on Lentulo spiral with a small piece of cotton on it. Place same bonding material on remaining coronal portion of tooth. Check bonding system beforehand to assure th a t it does not accelerate cement set. ■■ Seat post with resin cement. A Centrix needle tube is useful to place cement in post channel. (Centrix Inc.). When post is seated, excess cement will flow onto coronal tooth portion. ■■ Place resin build-up material immediately, before resin cement has set. Excess cement will be displaced by heavier viscosity resin build up material. Popular composite resin, build-up brands are Core Paste (DenMat Corp.); Prosthodent (Lee Pharmaceuticals); Ti-Core (Essential Dental Systems, and FluoroCore (L.D. Caulk/Dentsply). ■■ Complete tooth prepara tion within a few minutes after core placement.
relatively tight-fitting posts are used, reducing potential for post lateral movement. BONDING CEMENTS AND POSTS
Bonding posts into post channels with resin cement has gained popularity.4 Dentinbonding m aterials are used before cementing with auto cure resin cements such as Panavia (J. Morita USA, Inc.), Imperva Dual/Bond (Shofu Dental Corp.) and Resiment (Septodont, Inc.). A resin cement th a t does not require a bonding agent also may be selected. Examples include C & B Metabond (Parkell). If bonding agents are used before cementing posts with resin cement, clinicians should make sure, by testing outside the mouth, th a t the bonding material does not accelerate the setting of the resin cement, which would preclude post seating. Posts may be bonded to resin cement by sandblasting m etal posts directly before placement and using an appropriate resin cement th a t bonds to metal. Panavia and C & B Metabond are popular choices. CORE MATERIALS
Strong core m aterials are necessary because many cores replace most of the coronal portions of teeth.5Although conflicting in vitro research exists, core m aterials th a t have at least the compressive strength of the tooth structure being replaced appear to be appropriate (40,000 pounds per square inch). At this time, only two types of core m aterial meet this requirement, composite resin (-40,000 psi) and silver amalgam (~65,000 psi). Glass
CHRISTENSEN
Defense Without The Dental Record, you may meet your Waterloo. Defending yourself against malpractice claims requires a dental record that doesn’t come up short. The Dental Record provides an excellent risk manage ment shield because its comprehensive de sign documents all phases of treatment. Its flexible defense system is built of 14 forms and a revolutionary folder. To add The Dental Record to your empire, call for astarter kit ($10 includes shipping), MasterCard and VISA ac cepted.
800
-
2 4 3 - 4 B7 5 The DentalRecord ByDentists, For Dentists
W isconsin Dental Association, 1 1 1 E. W isconsin Ave.. Suite 1300
ionomer (-18,000 psi) and glass ionomer-resin (-25,000 psi) make Dr. Christensen is adequate co-founder and “filler” currently senior consultant of m aterials for Clinical Research small “pot A ssociates, Provo, Utah, and is a holes,” boxes, member of JA D A ’ s previous Class editorial board. He V restorations has a m aster’s degree in restorative or other dentistry and a defects on doctorate in education and teeth. But psychology. He is long-term board certified in clinical prosthodontics. evidence is still necessary to support their use as large buildups or as core materials. BONDING CORE MATERIALS TO TEETH
Core m aterials (composite or amalgam) should be bonded to tooth structure using bonding m aterials with known accepta bility. Because of their speed of use, examples for composite resin bonding are Scotchbond Multi-Purpose (3M Dental Products), and Universal Bond 3 (L.D. Caulk/Dentsply). Bonding examples for amal gam are Amalgambond
(Parkell), and All-Bond 2 (Bisco Dental Products). Dentin bond ing materials reduce leakage and increase retention to tooth structure. Placement of other mechanical features for extra retention is still recommended (pins, potholes, channels, etc.). SUMMARY
Custom cast posts and cores are quite acceptable, with proven usefulness. However, prefabricated posts and bonded composite or silver amalgam cores are replacing them rapidly. These posts and cores are faster and easier to construct than custom cast posts and cores, and they provide acceptable strength and serviceability a t a relatively low cost to patients. ■ Further information concerning these techniques may be obtained from Dr. Gordon J. Christensen, 3707 N. Canyon Rd., Suite 7A, Provo, U tah 84604. 1. CRA News 1991;15(7):l-2. 2. Christensen GJ, Christensen RP. Post and cores—state of the art. CRA News 1990;14(2):l-3. 3. Christensen GJ, Christensen RP. Cements for fixed prosthodontics—update 1991. CRA News 1991;15(4):l-3. 4. Christensen GJ, Christensen RP. Resin cements—update ’93. CRA News 1993;17(5):l-2. 5. Christensen GJ. Should teeth be built-up before crowns? JADA 1993;124(6):93-4.