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Post and core systems: Which one is best?
FIXED PROSTHODONTICS
. OPERATIVE
DENTISTRY
SECT I( IN i VI TOI<<
GORDON 1. CHRISTENSEN H. WILLIAM GILMORE SAMUEL E. GUYER WILLIAM LEFKOWITZ WILLIAM
Post and core systems: Which
F. I’. MALONE
one is best?
Amp W. Miller III, D.D.S.” Baylor Collegeof Dentistry. Dallas.Tex.
T
eeth with nonvital pulps demand special restorative consideration. They are more prone to fracture than vital teeth and sacrifice a substantial amount of tooth structure during endodontic therapy.‘,* An endodontically treated anterior tooth usually requires a post and core before restoration of its clinical crown. Posterior teeth may also need post reinforcement before they are restored, but this decisiondependson the amount of remaining tooth structure and/or the type of preparation and function anticipated. There are many methods of post fabrication described in the literature.3-7 Until recently most of these methods used somecombination of wax, plastic, wire, and/or wood to make a direct or indirect customized pattern. The post and core literature is a monument to the ingenuity of restorative dentists. However, there are currently more prefabricated post systems commercially available. Newer prefabricated systems do not decrease the value of previously described methods. There are advantages and disadvantages inherent in each post and core system. The purposeof this article is to categorize, compare, and describe someof the post systemscurrently being marketed. The following categories will be used: (1) threaded metal posts, (2) unthreaded metal posts, (3) plastic patterns, and (4) combination kits. THREADED
METAL
Fig. 1. F. K. G. obturation screws.Kit contains assortment of 10 sizes of posts.
POSTS
The threaded metal postsare the most controversial. They are retentive due to their threading capability.8*9 However, significant levels of stress can be induced during fitting and placement.“,” If fitting procedures are performed carefully, the risk of fracture can be minimized and thesetypes of postscan provide acceptable clinical results.‘”
Fig. 2. Close-up of obturation screw and its place-
ment wrenches. Self-threading post is made of hard alloy and has deep threads. Obturation
Prrsented brlorr the American Academy of Restorative Dentistry, lhr AI ademy of Operative Dentistry, and the American Academy 01 <:rown and Bridge Prosthodontics, Chicago, III. ‘Asscxialc PI ofeswr, Department of Fixed Prosthodontics.
IJWZ-3911
82 07002i + 12$01 20, 0 511982 The C. V. Mosby Co.
screws
A simple, relatively inexpensive kit (F. K. G., Switzerland, Union Broach, New York, N.Y. j contains over 100 hard alloy posts in 10 assortedconfigurations
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27
MILLER
Fig. 3. Dentatus placement tools.
screw posts. This kit contains
posts in 20 sizes, presizing
reamers, and
Fig. 4. Dentatus post is tapered and self-threading. Note latch-type reamer that is used to presize canal. Reamer simplifies placement and reduces some threading stress.
and two placement wrenches (Figs. 1 and 2). The posts are tapered and designedto be self-threading. There is no presizing drill or bur in the kit for shaping or tapping the canal.
Dentatus screw posts These tapered, self-threading, gold-plated posts(A. B. Dentatus, Hagersten, Sweden) are available in
28
Fig. 5. Star Radix-Anchors are available in three sizes. Top kit contains large and medium size threaded anchors. Lower kit has smaller post/cores that are used for molars and lower incisors.
either a semisoft alloy or a hard metal alloy (Figs. 3 and 4). The kit contains 60 screw posts in an assortment of 20 configurations, two placement wrenches, and several presizing rotary reamers that shape the canal to a close approximation of the dowel size. The
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Fig. 7. Kurer system is available in many combinations of sizes and core configurations. This threaded
post system includes tap, fur
left,
that is used to cut
threads into presized canal prior to fitting Four core types are shown on right.
of post.
Fig. 6. Radix-Anchor system includes presizing reamers, placement wrenches, and combination post/core unit. Post has parallel sides, widely separated threads, and venting groove. Projections on Radix-Anchor are for retention of core buildup material. Fig. 8. Kerr Endo-posts
matched reamers simplify insertion of the threaded dowel and have the advantage of decreasingthe risk of root fracture.” The Dentatus system is slightly more costly than the F. K. G. obturation screws,but it is still
are smooth
sided and slightly
tapered. They are marketed in either high-fusing noble metal alloy or lessexpensive hard alloy. Endopostsare keyed to match file sizes.
denta (Medidenta, Woodside, N.Y.) currently market threaded metal posts similar to those made by Dentatus.
Radix-Anchor is designedfor lower anterior teeth and molars. In longer teeth, the post length may not be adequateto encompasstwo thirds of the canal. A recent photoelastic study has shown that more acceptable levels of residual stressresult when this post doesnot tightly engagethe apical end of the canal.”
Radix-Anchors
Kurer posts
These self-threading post/core units (Star Dental Mfg. Co., Valley Forge, Pa.) are manufactured from a hard alloy (Figs. 5 and 6). Fig. 6 showsthe core, which contains multiple parallel projections that protrude from the central shaft. The projections are for retention of core buildup material. The post portion of the Radix-Anchor was designed to reduce threading stressesand maximize retention. The spiral threads are small, sharp, and widely separated. The post has parallel sidesand a cementation venting groove. There are three sizes available. The large/medium size kit contains six medium and six large posts, two
Kurer posts(Kurer Anchor Systems,Union Broach Co.) are designed with parallel sides, S-shaped grooves, and several different core configurations (Fig. 7). Most of the core configurations are available in four post diameters (1.6 to 2 mm). Each kit contains a starter or depth reamer, width reamer. root facer (counter-sink), thread cutter, placement driver, and 12 threaded dowels of that particular post diameter and core configuration. The placement procedure for the Kurer post is somewhat different from that for the other threaded postsdescribed.The canal is prepared to a depth with a
medium and two large presizing rotary drills, placement wrenches, and a sizing tool. The small size
drill is used to obtain the final canal width. Where
relatively
Monrovia, Calif.), Svedia (Svedia, Newport, R.I.), and Medi-
THE JOURNAL
inexpensive.
Unitek
OF PROSTHETIC
(Unitek
DENTISTRY
Corp.,
narrow
latch-type
rotary
drill.
Then
a large diameter
29
MILLER
Fig. 9. Unitek’s Charlton crown post kit has four sizes of post/core units, numerous presizing burs, and several diamond disks. System is designed mainly for anterior teeth, as indicated by straight handpiece burs.
Fig. 11. Ellman Nu-Bond post kit includes posts, presizing reamers, and Cyanodent cement.
Fig. 12. Nu-Bond posts are tapered, serrated, and available in six sizes. Rotary reamer has depth-limiting sleeve on shank to allow operator to return to same depth with each sequentially larger drill until final canal size is reached.
UNTHREADED Fig. 10. Charlton unit has post with smooth, parallel sides and attached core with flat sides. Canal is presized with tapered fissure bur, and final sizing is completed with parallel-sided fissure bur. Diamond disk is used to place notch in orifice of canal. Notch engages flat side on core to resist antirotational forces.
applicable, a 1 mm counter-sink is then placed in the orifice of the canal. The threads are cut into the walls of the canal with a threading tap. Finally, the post is cut to length and evaluated for ,proper seating. A cement escape groove is cut into the side of the dowel and the assembly is ready to be cemented. The tapping of the canal and placement procedure must be performed carefully to minimize stresses inherent in threaded post systems.6s’o Recently, a new Kurer design called the Press Stud was marketed. The core of this threaded metal post was modified to serve as an attachment for a removable prosthesis.
30
METAL
POSTS
Unthreaded metal posts have no threads and may have parallel or slightly tapered walls. The designs vary from a simple metal dowel to an all-metal configuration that has a post and core as a single unit. From a mechanical standpoint, unthreaded metal posts with parallel sides have more retention and resistance to dislodgment than comparably sized unthreaded tapered posts of the same length. However, the chance of root perforation is greater with parallel-sided posts because they do not follow the natural apical taper of the root.
Endo-posts Kerr Endo-posts (Sybron/Kerr, Romulus, Mich.) are smooth sided, nonvented, slightly tapered dowels that can be purchased in a high-fusing noble alloy or a less expensive conventional hard alloy (Fig. 8). These posts are designed for either direct insertion, direct pattern fabrication, or indirect pattern fabrication. They are matched to endodontic file sizes ranging from 70 to 140.
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Fig. 13. Star Endowels are packaged in five sizes of color-coded plastic patterns. Therr are 10 patterns in each size.
Fig. 14. Endowels are tapered and smooth sided so they can be used for direct or indirect techniques. They are keyed to file sizes. The advantage of the system is the easeof dowel insertion, but Endo-posts are relatively expensive and the smaller post sizes have a questionable diameter to resist dislodging forces.
Charlton
crown post kit
The Charlton crown post kit (Unitek Corp.) is designedprimarily for anterior teeth (Figs. 9 and 10). The post has smooth parallel sidesand is not vented. There is a metal core attached to the postin a solid unit design. The kit contains post/core units in four sizes, straight handpiece burs, antirotational notching wheels, and a handling wrench. The canal is prepared to the desired depth with a tapered fissurebur. A parallel-sided bur is then usedto refine the canal preparation. The cross-sectionalshape of the post is circular, as is the matched canal preparation. An antirotational notch is neededin the orifice of the canal. Flat sideson the core engage the notch to prevent rotational dislodgement.The wrench simplifies
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DENTISTRY
the cumbersomehandling of the unit during shaping of the core.
Post kits The one-piece combination post/core post kits by Medidenta are similar to Unitek’s system.The kits are available in several different sizesand include matched presizing rotary drills. The hard alloy metal post/core units have slightly tapered posts with light serrations for cement retention.
Nu-Bond
post
The Nu-Bond post (Ellman Dental Mfg., Hewlett, N.Y.) is a direct insertion post system for use with Cyanodent cement (Ellman Dental Mfg.) (Figs. 11 and 12). The relatively inexpensive Nu-Bond post kit contains several sizes of posts with matched rotary reamers for each size and a 2 cc container of Cyanodent. The post is made of hard metal alloy and is tapered. There are circular cement retention notches
31
MILLER
Fig. 15. Endowels can be sprued directly out of package and cast with base metal. This is inexpensive way to fabricate various sizes of metal posts for direct insertion or temporization.
Fig. 17. Plastic-Pins are tapered and designed for direct and indirect pattern fabrication.
Fig. 16. Norm Plastic-Pins are color coded and matched to presizing rotary drills.
cut in the side of the post but no venting groove. The matched rotary reamershave a movable sleevethat can be set for a specificdepth cut. If a sizable portion of the clinical crown is missing and a core buildup is required, retentive pins are recommended to resist rotational and dislodging forces.
PLASTIC Endowels
PATTERNS
Endowels (Star Dental Mfg. Co.) are plastic post patterns that are matched to five endodontic file sizes (80 to 140) (Figs. 13 and 14). The kit contains 10 Endowels in each size. The posts are slightly tapered and smooth sided. They can be used for direct or indirect pattern fabrication. After the canal is shapedwith the appropriate file, the matching Endowel is fitted and a direct or indirect technique can proceed. If acrylic resin is usedfor a core 32
buildup, the coronal portion of the post is notched or soakedwith monomer to ensure bonding with the core acrylic resin. Endowel patterns can be sprued directly out of the package and cast unmodified with a basemetal (Fig. 15). The basemetal postsare inexpensive and can be used in a single appointment, direct insertion post technique and/or for temporization. The versatile Endowel is the most inexpensive kit described.The main disadvantageof this systemis that someof the smaller sizes do not have enough crosssectional diameter to resist dislodging forces.
Norm
Plastic-Pins
The Swiss-made plastic post shapers (H. Hader Dental Plastic Products, A. P. M. Sterngold, Stamford, Conn.) are tapered, smoothsided, and available in two sizes (Figs. 16 and 17). There are 25 pairs of colorcoded patterns in a large and small size. One of each pair is for direct post pattern fabrication with acrylic resin or wax for core additions, while the other is used in an indirect impression technique. This kit also includes two sizing rotary drills that are matched to each post size. If a direct insertion metal postis desired,the patterns can be cast in a base metal alloy. Having metal and plastic posts keyed to rotary drills is an inexpensive JULY
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modification application.
Standard
SYSTEMS
Fig. 18. F. K. G. Standard Plastic-Pins described system in Figs. 16 and 17.
are similar
Fig. 19. C-I kit 1 has three latch-type that are matched to sizing burs.
burs, plastic
to the Hader
post kit and permits
JOURNAL
patterns,
and function
and stainless
to previously
steel dowels
broader
Plastic-Pins
F. K. G. plastic post patterns (Union Broach Co.) are similar to those of the Hader system (Fig. 18). There are two sizes of paired post patterns: one for direct and one for indirect post and core fabrication. There is a matched rotary drill for each post size. The tapered Standard Plastic-Pins are comparable to the Hader pins and can be modified in a similar fashion. THE
in design
OF PROSTHETIC
DENTISTRY
Fig. 20. Parke11 percha, presize, and metal posts tion and direct
C-I kit buns are used to remove guttaand finally size canal, Plastic Patterns are tapered and used for direct inseror indirect pattern fabrication. 33
MILLER
Fig. 21. PD system is packaged in vials that contain either stainless steel posts, acrylic resin post patterns, or tapered reamers in one of six sizes.
Fig. 22. Metal PD posts are serrated and tapered while acrylic resin post patterns are tapered and smooth sided so they can be used for direct or indirect patterns. Reamer has depth-limiting sleeve.
spiral-bladed reamers, acrylic resin post patterns, and metal posts are the components. The metal posts are stainless steel, tapered, and serrated, but not vented. The plastic patterns are smooth sided and tapered so that they can be used for direct or indirect techniques. The matched spiral reamers have a depth-limiting “distance piece” that is adjustable and designed for a contra-angle latch-type handpiece. The PD system is moderately priced and well designed. The components of the system are available in vials of 12 metal or plastic posts per size. The wide variety of post sizes makes this system versatile. Colorama
COMBINATION
KITS
These types of post and core kits have more application than the previously described systems. They contain canal sizing drills, metal direct insertion posts, and plastic patterns. C-I kit The C-I kit (Parkell, Farmingdale, N.Y.) is a relatively inexpensive system that contains tapered metal dowels, plastic patterns, and three burs (Figs. 19 and 20). The first bur is used for gutta-percha removal, the second preshapes the canal, and the third completes the canal preparation. The steel posts can be used in a temporary role or for direct insertion; however, there is no venting groove in the side of the post. The plastic patterns have a predesigned core attached to the post that can be modified to the desired shape. The C-I kit is simple to manipulate and inexpensive. PD posts This Swiss-made post system (Union Broach Co.) is available in six sizes (Figs. 21 and 22). Matched 34
This post and core system is also produced in Switzerland (Metaux Precieux, Switzerland; J. Aderer, Inc., Long Island City, N.Y.). Like the other combination kits described, it includes metal posts and plastic patterns that are keyed to rotary sizing drills (Figs. 23 and 24). The stainless steel posts and plastic patterns are smooth sided, nonvented, and available in five sizes. The shape of the post has been well designed. Parallel-sided posts generally have a greater chance of perforating root structure than do tapered posts due to the apical taper of the natural root structures. Tapered posts have less perforation potential but less retention and resistance to dislodging forces than parallel-sided posts. Metaux Precieux has marketed a post that is parallel sided in its coronal half and tapered in its apical portion (Fig. 25). This design combines the safety of a tapered post with the retention of parallel walls. Another post system with a similar design is the Schenker step pivot.* The Schenker design has parallel walls of a standard (1.4 or 1.9 mm) diameter in its coronal two thirds. ‘However, in its apical one third the diameter steps JULY
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Fig. 23. Five sizes of metal and plastic posts and matched contra-angle reamers comprise the Colorama kit. Posts and reamers are neatly organized and color coded.
Fig. 24. Colorama metal and plastic posts are smooth sided and can be used directly or indirectly. down to a smaller size but still has parallel walls to maximize retention. The Colorama post kit is moderate to high in price but has a multitude of direct and indirect uses. Each component is color coded and precisely matched. These advantages, coupled with its ingenious post design, make it a popular kit. Medidenta markets a similar system.
Para-post
Fig. 25. Close-up view of Colorama post reveals unique design. Apical portion is tapered to reduce risk of perforation, and coronal end is parallel sided to maximize retention.
The Para-post system (Whaledent, Int., New York, N.Y.) is unique when compared to other combination kits. This system contains metal and color-coded plastic posts that are matched to drill sizes and also makes available pins, paralleling jigs, and twist drills (Figs. 26 and 27). The metal posts are parallel sided, serrated for cement retention, and vented for cement release. They
are made of either stainless steel or a high-fusing noble metal alloy and are available in five sizes (diameters 0.9 to 1.75 mm). Direct technique plastic posts, identical to the stainless steel direct insertion dowels, are also available. For indirect post fabrication, parallel, nonserrated
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35
MILLER
Fig. 26. Whaledent’s Para-post is available in complete version (right) and smaller size for direct post placement.
Fig. 27. Close-up view equipment (righf side).
of various
Para-post components
plastic shapes in the five corresponding sizes are included. These are intended to be inserted into the canal and removed with an impression. After the working cast is made, a matched metal or plastic dowel is placed in the die canal spaceand the post and core is fabricated indirectly. Parallel antirotational pins can be incorporated into a direct or indirect pattern with the paralleling jig and combinations of 0.7 mm diameter plastic and high-
(left side) and paralleling
fusing alloy pins. The jig allows pin holesto be placed parallel to the primary post canal, which was shaped with the appropriate color-coded Para-post drill. The canal should be prepared by starting with the smallest drill and successivelyusing the next largest until the desired post size is attained. After the canal and pin holes are completed, direct or indirect pattern fabrication can proceed. Direct pattern techniques use various combinations
JULY
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of plastic and/or metal posts and pins. The post is inserted into the canal and the pins placed in the pin holes. Duralay (Reliance Dental Mfg. Co., Chicago, Ill.) or wax is used to build the core and retain the pins in their positions in the core. The pattern is then sprued, cast, and inserted. The stainless steel posts can be used for single appointment, direct insertion techniques. They are fitted, cut to length, and cemented. If a core is required, pins are inserted into the root face and either alloy or composite resin is used for the core buildup. However, crown margins should never terminate on composite resin. If marginal termination is anticipated on the core buildup, the core should either be cast or restored with amalgam. Composite resin core buildups have been the object of continued research. These materials appear adequate but merit further study as core materials. The Para-post system also includes aluminum posts and pins that are matched and color coded with the Para-post drills. These are used to simplify temporization procedures. Slight modification of the Para-post system eliminates the need for several components of the kit and decreases its expense. If a cast core is desired, the canal. is prepared with increasingly larger Para-post drills as described earlier. However, rather than use the jig and parallel pins to develop antirotational features, a U-shaped notch is placed in the canal orifice. This simple technique effectively keys the post and core to prevent rotation without extra materials. Duralay is a popular core material when placed around the metal Para-posts for fabricating a direct pattern (Fig. 28). By casting the core directly to a notched prefabricated metal Para-post, casting and fitting problems are minimized. It can be time consuming to seat a full cast post and core with slight expansion and minor inaccuracies resulting from casting procedures. In addition, if the core requires maximal expansion for an extracoronal fit around the remaining root structure, the post may expand excessively. This causes binding as the post is inserted into the canal. By casting the core to a prefabricated, prefitted metal post, the expansion of the core is the only factor to consider during investment of the pattern. This technique simplifies and accelerates seating procedures. Some clinicians have expressed concern about casting noble metals directly to stainless steel. Further research is needed to clarify the compatibility of noble and base metal alloys with stainless steel posts. Because of its wide range of application, the Para-
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Fig. 28. Post and core pattern fabricated with metal Para-post and Duralay acrylic resin to establish core in “cast-on” technique.
Fig. 29. Customized post and core pattern with endo-
dontic file ascarrier. Core is made of Duralay, and post is comprised of sprue wax with sticky wax to hold it to file.
post systemhas a greater number of componentsand is slightly more expensive than the simpler systems. However, smaller kits and individual componentscan be purchased to reduce the cost. The primary components are the stainless steel posts,the plastic serrated post patterns, and the Parapost drills. Whaledent has recently marketed a superior Parapost that is tapered at its apical end. This altered post shape is designed to reduce the risk of perforation during canal preparation and cementation.
37
MILLER
DISCUSSION Prefabricated post and core systems can simplify and accelerate restorative procedures on nonvital teeth. Each system has its own inherent advantages and disadvantages. The threaded designs have maximal retention, but the risk of root fracture is greater than with the nonthreaded types. The nonthreaded posts with parallel sides have greater retention than the tapered shapes, but the risk of root perforation is increased in the parallel-sided designs. Post systems that have matched sizing drills for canal preparation can simplify fitting procedures; however, these drills can also increase the risk of perforation if they are not carefully aligned and manipulated. There are many clinical situations in which a single appointment, direct insertion metal post with a composite resin or amalgam core is an acceptable restoration. However, this procedure is not always the treatment of choice. For example, teeth with thin labiolingual preparations might be prone to fracture with a pin-retained composite resin or amalgam core. In this instance a cast core is indicated. Another tooth may have an exceptionally large canal with minimal root structure surrounding the canal. It is not wise to place pins in the thin tooth structure surrounding the canal. Sizing drills would be contraindicated in preparation of the canal, because it would be ludicrous to remove additional tooth structure from a weakened root. If a prefabricated post system is not indicated, a custom technique is recommended.” This customized approach uses a combination of endodontic files, Duralay, sticky wax, and sprue wax to fabricate a post and core pattern (Fig. 29). Post patterns, whether they are customized or built from prefabricated components, can be cast with base metal alloys, making them less expensive than gold castings. In addition, many of the physical properties of base metal posts are superior to those of gold post and core castings. Although base metals are somewhat harder to adjust, the results are satisfactory.
SUMMARY
AND
for these teeth can be handled in many ways. This article has described some of the prefabricated post systems currently available. The relative advantages and disadvantages have been compared. Prefabricated post systems in many instances can simplify and expedite restorative dentistry. Which system is best? The answer varies according to the restorative situation and the skills and preference of the dentist. A post and core should not jeopardize the remaining tooth structure, and the particular system must be manageable. REFERENCES 1.
2.
3. 4.
Sommer, R. F., Ostrander, F. D., and Crowley, M. C.: Clinical Endodontics, ed 2. Philadelphia, 1961, W. B. Saunders Co, p 549. Johnston, J. F., Phillips, R. W., and Dykema, R. W.: Modern Practice in Crown and Bridge Prosthodontics, ed 3. Philadelphia, 1971, W. B. Saunders Co, p 608. Frederick, D. R.: An application of the dowel and composite resin core technique. J PROSTHET DENT 32420, 1975. Abadie, F. R.: Plastic stopping-Its multiple uses. J PROSTHET DENT
5. 6. 7.
8. 9.
10. 11.
24:103,
J PROSTHET Re‘brinl
1970.
McPherson, J. L.: A simplified dowel crown technique. J South Calif State Dent Assoc 39:115, 1971. Cooley, I. T., Hampson, E. L., and Lenman, M. L.: Retention of post crowns. Br Dent J 12463, 1968. Tylman, S. D.: Theory and Practice of Crown and Fixed Partial Prosthodontics, ed 6. St. Louis, 1970, The C. V. Mosby Co., pp 580-605. Brewer, A. A., and Morrow, R. M.: Overdentures. St. Louis, 1975, The C. V. Mosby Co., p 166. Standlee, J. P., Caputo, A. A., Halcomb, J., and Trabert, K. C.: The retentive and stress-distributing properties of a threaded endodontic dowel. J PROSTHET DENT 44402, 1980. Zmener, 0.: Adaptation of threaded dowels to dentin. J PROSTHET DENT 43~530, 1980. Miller, A. W.: Direct pattern technique for posts and cores.
requests
DENT
40~392,
1978.
lo:
DR. AMP W. MILLER
III BAYLOR COLLEGE OF DENTISTRY 3302 GASTON AVE. DALLAS, TX 75246
CONCLUSIONS
Teeth with nonvital pulps or pulpless teeth demand special restorative attention. Post and core fabrication
38
JULY
1982
VOLUME
48
NUMBER
1
. OPERATIVE
DENTISTRY
SECT I( IN i VI TOI<<
GORDON 1. CHRISTENSEN H. WILLIAM GILMORE SAMUEL E. GUYER WILLIAM LEFKOWITZ WILLIAM
Post and core systems: Which
F. I’. MALONE
one is best?
Amp W. Miller III, D.D.S.” Baylor Collegeof Dentistry. Dallas.Tex.
T
eeth with nonvital pulps demand special restorative consideration. They are more prone to fracture than vital teeth and sacrifice a substantial amount of tooth structure during endodontic therapy.‘,* An endodontically treated anterior tooth usually requires a post and core before restoration of its clinical crown. Posterior teeth may also need post reinforcement before they are restored, but this decisiondependson the amount of remaining tooth structure and/or the type of preparation and function anticipated. There are many methods of post fabrication described in the literature.3-7 Until recently most of these methods used somecombination of wax, plastic, wire, and/or wood to make a direct or indirect customized pattern. The post and core literature is a monument to the ingenuity of restorative dentists. However, there are currently more prefabricated post systems commercially available. Newer prefabricated systems do not decrease the value of previously described methods. There are advantages and disadvantages inherent in each post and core system. The purposeof this article is to categorize, compare, and describe someof the post systemscurrently being marketed. The following categories will be used: (1) threaded metal posts, (2) unthreaded metal posts, (3) plastic patterns, and (4) combination kits. THREADED
METAL
Fig. 1. F. K. G. obturation screws.Kit contains assortment of 10 sizes of posts.
POSTS
The threaded metal postsare the most controversial. They are retentive due to their threading capability.8*9 However, significant levels of stress can be induced during fitting and placement.“,” If fitting procedures are performed carefully, the risk of fracture can be minimized and thesetypes of postscan provide acceptable clinical results.‘”
Fig. 2. Close-up of obturation screw and its place-
ment wrenches. Self-threading post is made of hard alloy and has deep threads. Obturation
Prrsented brlorr the American Academy of Restorative Dentistry, lhr AI ademy of Operative Dentistry, and the American Academy 01 <:rown and Bridge Prosthodontics, Chicago, III. ‘Asscxialc PI ofeswr, Department of Fixed Prosthodontics.
IJWZ-3911
82 07002i + 12$01 20, 0 511982 The C. V. Mosby Co.
screws
A simple, relatively inexpensive kit (F. K. G., Switzerland, Union Broach, New York, N.Y. j contains over 100 hard alloy posts in 10 assortedconfigurations
THE
JOURNAL
OF PROSTHETK
DENTfSTRY
27
MILLER
Fig. 3. Dentatus placement tools.
screw posts. This kit contains
posts in 20 sizes, presizing
reamers, and
Fig. 4. Dentatus post is tapered and self-threading. Note latch-type reamer that is used to presize canal. Reamer simplifies placement and reduces some threading stress.
and two placement wrenches (Figs. 1 and 2). The posts are tapered and designedto be self-threading. There is no presizing drill or bur in the kit for shaping or tapping the canal.
Dentatus screw posts These tapered, self-threading, gold-plated posts(A. B. Dentatus, Hagersten, Sweden) are available in
28
Fig. 5. Star Radix-Anchors are available in three sizes. Top kit contains large and medium size threaded anchors. Lower kit has smaller post/cores that are used for molars and lower incisors.
either a semisoft alloy or a hard metal alloy (Figs. 3 and 4). The kit contains 60 screw posts in an assortment of 20 configurations, two placement wrenches, and several presizing rotary reamers that shape the canal to a close approximation of the dowel size. The
JULY
1982
VOLUME
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SYSTEMS
Fig. 7. Kurer system is available in many combinations of sizes and core configurations. This threaded
post system includes tap, fur
left,
that is used to cut
threads into presized canal prior to fitting Four core types are shown on right.
of post.
Fig. 6. Radix-Anchor system includes presizing reamers, placement wrenches, and combination post/core unit. Post has parallel sides, widely separated threads, and venting groove. Projections on Radix-Anchor are for retention of core buildup material. Fig. 8. Kerr Endo-posts
matched reamers simplify insertion of the threaded dowel and have the advantage of decreasingthe risk of root fracture.” The Dentatus system is slightly more costly than the F. K. G. obturation screws,but it is still
are smooth
sided and slightly
tapered. They are marketed in either high-fusing noble metal alloy or lessexpensive hard alloy. Endopostsare keyed to match file sizes.
denta (Medidenta, Woodside, N.Y.) currently market threaded metal posts similar to those made by Dentatus.
Radix-Anchor is designedfor lower anterior teeth and molars. In longer teeth, the post length may not be adequateto encompasstwo thirds of the canal. A recent photoelastic study has shown that more acceptable levels of residual stressresult when this post doesnot tightly engagethe apical end of the canal.”
Radix-Anchors
Kurer posts
These self-threading post/core units (Star Dental Mfg. Co., Valley Forge, Pa.) are manufactured from a hard alloy (Figs. 5 and 6). Fig. 6 showsthe core, which contains multiple parallel projections that protrude from the central shaft. The projections are for retention of core buildup material. The post portion of the Radix-Anchor was designed to reduce threading stressesand maximize retention. The spiral threads are small, sharp, and widely separated. The post has parallel sidesand a cementation venting groove. There are three sizes available. The large/medium size kit contains six medium and six large posts, two
Kurer posts(Kurer Anchor Systems,Union Broach Co.) are designed with parallel sides, S-shaped grooves, and several different core configurations (Fig. 7). Most of the core configurations are available in four post diameters (1.6 to 2 mm). Each kit contains a starter or depth reamer, width reamer. root facer (counter-sink), thread cutter, placement driver, and 12 threaded dowels of that particular post diameter and core configuration. The placement procedure for the Kurer post is somewhat different from that for the other threaded postsdescribed.The canal is prepared to a depth with a
medium and two large presizing rotary drills, placement wrenches, and a sizing tool. The small size
drill is used to obtain the final canal width. Where
relatively
Monrovia, Calif.), Svedia (Svedia, Newport, R.I.), and Medi-
THE JOURNAL
inexpensive.
Unitek
OF PROSTHETIC
(Unitek
DENTISTRY
Corp.,
narrow
latch-type
rotary
drill.
Then
a large diameter
29
MILLER
Fig. 9. Unitek’s Charlton crown post kit has four sizes of post/core units, numerous presizing burs, and several diamond disks. System is designed mainly for anterior teeth, as indicated by straight handpiece burs.
Fig. 11. Ellman Nu-Bond post kit includes posts, presizing reamers, and Cyanodent cement.
Fig. 12. Nu-Bond posts are tapered, serrated, and available in six sizes. Rotary reamer has depth-limiting sleeve on shank to allow operator to return to same depth with each sequentially larger drill until final canal size is reached.
UNTHREADED Fig. 10. Charlton unit has post with smooth, parallel sides and attached core with flat sides. Canal is presized with tapered fissure bur, and final sizing is completed with parallel-sided fissure bur. Diamond disk is used to place notch in orifice of canal. Notch engages flat side on core to resist antirotational forces.
applicable, a 1 mm counter-sink is then placed in the orifice of the canal. The threads are cut into the walls of the canal with a threading tap. Finally, the post is cut to length and evaluated for ,proper seating. A cement escape groove is cut into the side of the dowel and the assembly is ready to be cemented. The tapping of the canal and placement procedure must be performed carefully to minimize stresses inherent in threaded post systems.6s’o Recently, a new Kurer design called the Press Stud was marketed. The core of this threaded metal post was modified to serve as an attachment for a removable prosthesis.
30
METAL
POSTS
Unthreaded metal posts have no threads and may have parallel or slightly tapered walls. The designs vary from a simple metal dowel to an all-metal configuration that has a post and core as a single unit. From a mechanical standpoint, unthreaded metal posts with parallel sides have more retention and resistance to dislodgment than comparably sized unthreaded tapered posts of the same length. However, the chance of root perforation is greater with parallel-sided posts because they do not follow the natural apical taper of the root.
Endo-posts Kerr Endo-posts (Sybron/Kerr, Romulus, Mich.) are smooth sided, nonvented, slightly tapered dowels that can be purchased in a high-fusing noble alloy or a less expensive conventional hard alloy (Fig. 8). These posts are designed for either direct insertion, direct pattern fabrication, or indirect pattern fabrication. They are matched to endodontic file sizes ranging from 70 to 140.
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1982
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Fig. 13. Star Endowels are packaged in five sizes of color-coded plastic patterns. Therr are 10 patterns in each size.
Fig. 14. Endowels are tapered and smooth sided so they can be used for direct or indirect techniques. They are keyed to file sizes. The advantage of the system is the easeof dowel insertion, but Endo-posts are relatively expensive and the smaller post sizes have a questionable diameter to resist dislodging forces.
Charlton
crown post kit
The Charlton crown post kit (Unitek Corp.) is designedprimarily for anterior teeth (Figs. 9 and 10). The post has smooth parallel sidesand is not vented. There is a metal core attached to the postin a solid unit design. The kit contains post/core units in four sizes, straight handpiece burs, antirotational notching wheels, and a handling wrench. The canal is prepared to the desired depth with a tapered fissurebur. A parallel-sided bur is then usedto refine the canal preparation. The cross-sectionalshape of the post is circular, as is the matched canal preparation. An antirotational notch is neededin the orifice of the canal. Flat sideson the core engage the notch to prevent rotational dislodgement.The wrench simplifies
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JOURNAL
OF PROSTHETIC
DENTISTRY
the cumbersomehandling of the unit during shaping of the core.
Post kits The one-piece combination post/core post kits by Medidenta are similar to Unitek’s system.The kits are available in several different sizesand include matched presizing rotary drills. The hard alloy metal post/core units have slightly tapered posts with light serrations for cement retention.
Nu-Bond
post
The Nu-Bond post (Ellman Dental Mfg., Hewlett, N.Y.) is a direct insertion post system for use with Cyanodent cement (Ellman Dental Mfg.) (Figs. 11 and 12). The relatively inexpensive Nu-Bond post kit contains several sizes of posts with matched rotary reamers for each size and a 2 cc container of Cyanodent. The post is made of hard metal alloy and is tapered. There are circular cement retention notches
31
MILLER
Fig. 15. Endowels can be sprued directly out of package and cast with base metal. This is inexpensive way to fabricate various sizes of metal posts for direct insertion or temporization.
Fig. 17. Plastic-Pins are tapered and designed for direct and indirect pattern fabrication.
Fig. 16. Norm Plastic-Pins are color coded and matched to presizing rotary drills.
cut in the side of the post but no venting groove. The matched rotary reamershave a movable sleevethat can be set for a specificdepth cut. If a sizable portion of the clinical crown is missing and a core buildup is required, retentive pins are recommended to resist rotational and dislodging forces.
PLASTIC Endowels
PATTERNS
Endowels (Star Dental Mfg. Co.) are plastic post patterns that are matched to five endodontic file sizes (80 to 140) (Figs. 13 and 14). The kit contains 10 Endowels in each size. The posts are slightly tapered and smooth sided. They can be used for direct or indirect pattern fabrication. After the canal is shapedwith the appropriate file, the matching Endowel is fitted and a direct or indirect technique can proceed. If acrylic resin is usedfor a core 32
buildup, the coronal portion of the post is notched or soakedwith monomer to ensure bonding with the core acrylic resin. Endowel patterns can be sprued directly out of the package and cast unmodified with a basemetal (Fig. 15). The basemetal postsare inexpensive and can be used in a single appointment, direct insertion post technique and/or for temporization. The versatile Endowel is the most inexpensive kit described.The main disadvantageof this systemis that someof the smaller sizes do not have enough crosssectional diameter to resist dislodging forces.
Norm
Plastic-Pins
The Swiss-made plastic post shapers (H. Hader Dental Plastic Products, A. P. M. Sterngold, Stamford, Conn.) are tapered, smoothsided, and available in two sizes (Figs. 16 and 17). There are 25 pairs of colorcoded patterns in a large and small size. One of each pair is for direct post pattern fabrication with acrylic resin or wax for core additions, while the other is used in an indirect impression technique. This kit also includes two sizing rotary drills that are matched to each post size. If a direct insertion metal postis desired,the patterns can be cast in a base metal alloy. Having metal and plastic posts keyed to rotary drills is an inexpensive JULY
1982
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NUMBER
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modification application.
Standard
SYSTEMS
Fig. 18. F. K. G. Standard Plastic-Pins described system in Figs. 16 and 17.
are similar
Fig. 19. C-I kit 1 has three latch-type that are matched to sizing burs.
burs, plastic
to the Hader
post kit and permits
JOURNAL
patterns,
and function
and stainless
to previously
steel dowels
broader
Plastic-Pins
F. K. G. plastic post patterns (Union Broach Co.) are similar to those of the Hader system (Fig. 18). There are two sizes of paired post patterns: one for direct and one for indirect post and core fabrication. There is a matched rotary drill for each post size. The tapered Standard Plastic-Pins are comparable to the Hader pins and can be modified in a similar fashion. THE
in design
OF PROSTHETIC
DENTISTRY
Fig. 20. Parke11 percha, presize, and metal posts tion and direct
C-I kit buns are used to remove guttaand finally size canal, Plastic Patterns are tapered and used for direct inseror indirect pattern fabrication. 33
MILLER
Fig. 21. PD system is packaged in vials that contain either stainless steel posts, acrylic resin post patterns, or tapered reamers in one of six sizes.
Fig. 22. Metal PD posts are serrated and tapered while acrylic resin post patterns are tapered and smooth sided so they can be used for direct or indirect patterns. Reamer has depth-limiting sleeve.
spiral-bladed reamers, acrylic resin post patterns, and metal posts are the components. The metal posts are stainless steel, tapered, and serrated, but not vented. The plastic patterns are smooth sided and tapered so that they can be used for direct or indirect techniques. The matched spiral reamers have a depth-limiting “distance piece” that is adjustable and designed for a contra-angle latch-type handpiece. The PD system is moderately priced and well designed. The components of the system are available in vials of 12 metal or plastic posts per size. The wide variety of post sizes makes this system versatile. Colorama
COMBINATION
KITS
These types of post and core kits have more application than the previously described systems. They contain canal sizing drills, metal direct insertion posts, and plastic patterns. C-I kit The C-I kit (Parkell, Farmingdale, N.Y.) is a relatively inexpensive system that contains tapered metal dowels, plastic patterns, and three burs (Figs. 19 and 20). The first bur is used for gutta-percha removal, the second preshapes the canal, and the third completes the canal preparation. The steel posts can be used in a temporary role or for direct insertion; however, there is no venting groove in the side of the post. The plastic patterns have a predesigned core attached to the post that can be modified to the desired shape. The C-I kit is simple to manipulate and inexpensive. PD posts This Swiss-made post system (Union Broach Co.) is available in six sizes (Figs. 21 and 22). Matched 34
This post and core system is also produced in Switzerland (Metaux Precieux, Switzerland; J. Aderer, Inc., Long Island City, N.Y.). Like the other combination kits described, it includes metal posts and plastic patterns that are keyed to rotary sizing drills (Figs. 23 and 24). The stainless steel posts and plastic patterns are smooth sided, nonvented, and available in five sizes. The shape of the post has been well designed. Parallel-sided posts generally have a greater chance of perforating root structure than do tapered posts due to the apical taper of the natural root structures. Tapered posts have less perforation potential but less retention and resistance to dislodging forces than parallel-sided posts. Metaux Precieux has marketed a post that is parallel sided in its coronal half and tapered in its apical portion (Fig. 25). This design combines the safety of a tapered post with the retention of parallel walls. Another post system with a similar design is the Schenker step pivot.* The Schenker design has parallel walls of a standard (1.4 or 1.9 mm) diameter in its coronal two thirds. ‘However, in its apical one third the diameter steps JULY
1982
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Fig. 23. Five sizes of metal and plastic posts and matched contra-angle reamers comprise the Colorama kit. Posts and reamers are neatly organized and color coded.
Fig. 24. Colorama metal and plastic posts are smooth sided and can be used directly or indirectly. down to a smaller size but still has parallel walls to maximize retention. The Colorama post kit is moderate to high in price but has a multitude of direct and indirect uses. Each component is color coded and precisely matched. These advantages, coupled with its ingenious post design, make it a popular kit. Medidenta markets a similar system.
Para-post
Fig. 25. Close-up view of Colorama post reveals unique design. Apical portion is tapered to reduce risk of perforation, and coronal end is parallel sided to maximize retention.
The Para-post system (Whaledent, Int., New York, N.Y.) is unique when compared to other combination kits. This system contains metal and color-coded plastic posts that are matched to drill sizes and also makes available pins, paralleling jigs, and twist drills (Figs. 26 and 27). The metal posts are parallel sided, serrated for cement retention, and vented for cement release. They
are made of either stainless steel or a high-fusing noble metal alloy and are available in five sizes (diameters 0.9 to 1.75 mm). Direct technique plastic posts, identical to the stainless steel direct insertion dowels, are also available. For indirect post fabrication, parallel, nonserrated
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
35
MILLER
Fig. 26. Whaledent’s Para-post is available in complete version (right) and smaller size for direct post placement.
Fig. 27. Close-up view equipment (righf side).
of various
Para-post components
plastic shapes in the five corresponding sizes are included. These are intended to be inserted into the canal and removed with an impression. After the working cast is made, a matched metal or plastic dowel is placed in the die canal spaceand the post and core is fabricated indirectly. Parallel antirotational pins can be incorporated into a direct or indirect pattern with the paralleling jig and combinations of 0.7 mm diameter plastic and high-
(left side) and paralleling
fusing alloy pins. The jig allows pin holesto be placed parallel to the primary post canal, which was shaped with the appropriate color-coded Para-post drill. The canal should be prepared by starting with the smallest drill and successivelyusing the next largest until the desired post size is attained. After the canal and pin holes are completed, direct or indirect pattern fabrication can proceed. Direct pattern techniques use various combinations
JULY
1982
VOLUME
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NUMBER
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CORE
SYSTEMS
of plastic and/or metal posts and pins. The post is inserted into the canal and the pins placed in the pin holes. Duralay (Reliance Dental Mfg. Co., Chicago, Ill.) or wax is used to build the core and retain the pins in their positions in the core. The pattern is then sprued, cast, and inserted. The stainless steel posts can be used for single appointment, direct insertion techniques. They are fitted, cut to length, and cemented. If a core is required, pins are inserted into the root face and either alloy or composite resin is used for the core buildup. However, crown margins should never terminate on composite resin. If marginal termination is anticipated on the core buildup, the core should either be cast or restored with amalgam. Composite resin core buildups have been the object of continued research. These materials appear adequate but merit further study as core materials. The Para-post system also includes aluminum posts and pins that are matched and color coded with the Para-post drills. These are used to simplify temporization procedures. Slight modification of the Para-post system eliminates the need for several components of the kit and decreases its expense. If a cast core is desired, the canal. is prepared with increasingly larger Para-post drills as described earlier. However, rather than use the jig and parallel pins to develop antirotational features, a U-shaped notch is placed in the canal orifice. This simple technique effectively keys the post and core to prevent rotation without extra materials. Duralay is a popular core material when placed around the metal Para-posts for fabricating a direct pattern (Fig. 28). By casting the core directly to a notched prefabricated metal Para-post, casting and fitting problems are minimized. It can be time consuming to seat a full cast post and core with slight expansion and minor inaccuracies resulting from casting procedures. In addition, if the core requires maximal expansion for an extracoronal fit around the remaining root structure, the post may expand excessively. This causes binding as the post is inserted into the canal. By casting the core to a prefabricated, prefitted metal post, the expansion of the core is the only factor to consider during investment of the pattern. This technique simplifies and accelerates seating procedures. Some clinicians have expressed concern about casting noble metals directly to stainless steel. Further research is needed to clarify the compatibility of noble and base metal alloys with stainless steel posts. Because of its wide range of application, the Para-
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JOURNAL
OF PROSTHETIC
DENTISTRY
Fig. 28. Post and core pattern fabricated with metal Para-post and Duralay acrylic resin to establish core in “cast-on” technique.
Fig. 29. Customized post and core pattern with endo-
dontic file ascarrier. Core is made of Duralay, and post is comprised of sprue wax with sticky wax to hold it to file.
post systemhas a greater number of componentsand is slightly more expensive than the simpler systems. However, smaller kits and individual componentscan be purchased to reduce the cost. The primary components are the stainless steel posts,the plastic serrated post patterns, and the Parapost drills. Whaledent has recently marketed a superior Parapost that is tapered at its apical end. This altered post shape is designed to reduce the risk of perforation during canal preparation and cementation.
37
MILLER
DISCUSSION Prefabricated post and core systems can simplify and accelerate restorative procedures on nonvital teeth. Each system has its own inherent advantages and disadvantages. The threaded designs have maximal retention, but the risk of root fracture is greater than with the nonthreaded types. The nonthreaded posts with parallel sides have greater retention than the tapered shapes, but the risk of root perforation is increased in the parallel-sided designs. Post systems that have matched sizing drills for canal preparation can simplify fitting procedures; however, these drills can also increase the risk of perforation if they are not carefully aligned and manipulated. There are many clinical situations in which a single appointment, direct insertion metal post with a composite resin or amalgam core is an acceptable restoration. However, this procedure is not always the treatment of choice. For example, teeth with thin labiolingual preparations might be prone to fracture with a pin-retained composite resin or amalgam core. In this instance a cast core is indicated. Another tooth may have an exceptionally large canal with minimal root structure surrounding the canal. It is not wise to place pins in the thin tooth structure surrounding the canal. Sizing drills would be contraindicated in preparation of the canal, because it would be ludicrous to remove additional tooth structure from a weakened root. If a prefabricated post system is not indicated, a custom technique is recommended.” This customized approach uses a combination of endodontic files, Duralay, sticky wax, and sprue wax to fabricate a post and core pattern (Fig. 29). Post patterns, whether they are customized or built from prefabricated components, can be cast with base metal alloys, making them less expensive than gold castings. In addition, many of the physical properties of base metal posts are superior to those of gold post and core castings. Although base metals are somewhat harder to adjust, the results are satisfactory.
SUMMARY
AND
for these teeth can be handled in many ways. This article has described some of the prefabricated post systems currently available. The relative advantages and disadvantages have been compared. Prefabricated post systems in many instances can simplify and expedite restorative dentistry. Which system is best? The answer varies according to the restorative situation and the skills and preference of the dentist. A post and core should not jeopardize the remaining tooth structure, and the particular system must be manageable. REFERENCES 1.
2.
3. 4.
Sommer, R. F., Ostrander, F. D., and Crowley, M. C.: Clinical Endodontics, ed 2. Philadelphia, 1961, W. B. Saunders Co, p 549. Johnston, J. F., Phillips, R. W., and Dykema, R. W.: Modern Practice in Crown and Bridge Prosthodontics, ed 3. Philadelphia, 1971, W. B. Saunders Co, p 608. Frederick, D. R.: An application of the dowel and composite resin core technique. J PROSTHET DENT 32420, 1975. Abadie, F. R.: Plastic stopping-Its multiple uses. J PROSTHET DENT
5. 6. 7.
8. 9.
10. 11.
24:103,
J PROSTHET Re‘brinl
1970.
McPherson, J. L.: A simplified dowel crown technique. J South Calif State Dent Assoc 39:115, 1971. Cooley, I. T., Hampson, E. L., and Lenman, M. L.: Retention of post crowns. Br Dent J 12463, 1968. Tylman, S. D.: Theory and Practice of Crown and Fixed Partial Prosthodontics, ed 6. St. Louis, 1970, The C. V. Mosby Co., pp 580-605. Brewer, A. A., and Morrow, R. M.: Overdentures. St. Louis, 1975, The C. V. Mosby Co., p 166. Standlee, J. P., Caputo, A. A., Halcomb, J., and Trabert, K. C.: The retentive and stress-distributing properties of a threaded endodontic dowel. J PROSTHET DENT 44402, 1980. Zmener, 0.: Adaptation of threaded dowels to dentin. J PROSTHET DENT 43~530, 1980. Miller, A. W.: Direct pattern technique for posts and cores.
requests
DENT
40~392,
1978.
lo:
DR. AMP W. MILLER
III BAYLOR COLLEGE OF DENTISTRY 3302 GASTON AVE. DALLAS, TX 75246
CONCLUSIONS
Teeth with nonvital pulps or pulpless teeth demand special restorative attention. Post and core fabrication
38
JULY
1982
VOLUME
48
NUMBER
1