Intracoronal Attachments
Intracoronal attachments can be prefabricated as well as made in a laboratory.
tNJey Dental International: Bloom field. Conn
Use of Ceka extracoronal attachments to retain a distal extension RPD. A to C, The female attachment is positioned in relation to the wax pattern by means of a mandrel in the dental surveyor. D, Substructures are cast directly onto the attachments. E, Anterior prosthesis assembled. Porcelain has been applied. F, Fixed splint and RPD at try-in. G, Male attachments in place. H, Attachments bonded to the RPD base. 1, The completed prosthesis.
Use of Ceka extracoronal attachments to retain a distal extension RPD. A to C, The female attachment is positioned in relation to the wax pattern by means of a mandrel in the dental surveyor. D, Substructures are cast directly onto the attachments. E, Anterior prosthesis assembled. Porcelain has been applied. F, Fixed splint and RPD at try-in. G, Male attachments in place. H, Attachments bonded to the RPD base. 1, The completed prosthesis.
Prefabricated Types (Fig. 21-31). The more commonly used prefabricated intracoronal attachments (e.g., Stern* or Ney-Cheyes no. 9t) typically consist of a precision-milled male-female assembly similar to the dovetail configuration described for nonrigid connectors (see Chapter 28).
The tolerance between accurately fitting components of an intracoronal precision attachment is so fine that retention results from the frictional fit. An intracoronal attachment RPD is not readily dislodged, because it can be removed only in one direction, which may become a liability in patients with limited dexterity. However, retention can be significantly reduced after wear of the retentive sur-
tNey Dental International: Bloomfield, Conn.
faces. Most precision attachments are made of platinum-palladium alloys, which withstand the high temperature associated with casting of metal-ceramic alloys.
The female attachment is incorporated in a wax pattern, and the assembly is invested. After wax elimination the restoration is cast directly onto the attachment. Although multiple parallel attachments can be fabricated in this manner, most technicians prefer to solder a second or third attachment to the respective retainer(s). This allows for verification of alignment with the attachment in the first retainer.
A tray may be incorporated in the secondary retainer for added flexibility during positioning of the second attachment parallel to the first attachment. The secondary retainer is luted into place, invested, and soldered. Male components can then be in
- Fig. 21-31. Prefabricated intracoronal attachments. A, The Ney-Cheyes no. 9. B, The Stern.
Fig. 21-32. Intracoronal attachment technique. A, The female attachment is tried in the proximal tray, which has been luted to the anatomic contour wax pattern. B, Sprued wax patterns. The extruding portion of the tray provides retention for the investment. C, The retainers have been cast directly on the tray. Casting directly onto the female attachment is also possible. D, Retainers seated on the master cast. E, After preliminary finishing, the female attachment is positioned and luted in the tray. Note the lingual channel (arrow) through which solder will be fed. F, A carbon insert is placed in the female attachment, and sprue wax is added to create airways in the soldering assembly.
Continued
Fig. 21-32. Intracoronal attachment technique. A, The female attachment is tried in the proximal tray, which has been luted to the anatomic contour wax pattern. B, Sprued wax patterns. The extruding portion of the tray provides retention for the investment. C, The retainers have been cast directly on the tray. Casting directly onto the female attachment is also possible. D, Retainers seated on the master cast. E, After preliminary finishing, the female attachment is positioned and luted in the tray. Note the lingual channel (arrow) through which solder will be fed. F, A carbon insert is placed in the female attachment, and sprue wax is added to create airways in the soldering assembly.
Continued serted. After the RPD framework has been made, the male attachments are either soldered to the frame or attached to the acrylic resin denture base with autopolymerizing resin (see Fig. 21-30 and Fig. 21-32).
The preceding paragraph condenses an intricate sequence of technically demanding steps. The less experienced operator is strongly cautioned not to underestimate the high level of skill and meticulous attention to detail that are required.
The biggest advantage of intracoronal attachments is they eliminate the need for an often unes-thetic facial clasp. Simultaneously the size of most precision intracoronal attachments limits their application, especially on vital teeth. To facilitate maintaining the health of supporting tissues, the proximal surface of the restoration should not be overcontoured. Therefore the optimum placement of attachments is within the normal contours of the restoration. However, this is usually possible only
Fig. 21-32, cont'd. G, After investing and burnout, the female is soldered to the tray. Note that the carbon rod provides positional stability of the female attachment. H, Master cast with completed retainers ready for duplicating the refractory cast. I, Removable partial denture waxed. Note the plastic patterns incorporated adjacent to the attachments (arrows). J, The partial denture cast and seated. The females have been positioned and their locator wires bent to extrude through the proximal plate (arrows). K, RPD invested. It is now ready for burnout. However, before soldering, the locator wires (connected to the female attachments with low-fusing solder) should be removed. L, Solder is fed in through the slot in the proximal plate. M, The completed RPD ready for try-in. (Courtesy Ney Dental International.)
Fig. 21-32, cont'd. G, After investing and burnout, the female is soldered to the tray. Note that the carbon rod provides positional stability of the female attachment. H, Master cast with completed retainers ready for duplicating the refractory cast. I, Removable partial denture waxed. Note the plastic patterns incorporated adjacent to the attachments (arrows). J, The partial denture cast and seated. The females have been positioned and their locator wires bent to extrude through the proximal plate (arrows). K, RPD invested. It is now ready for burnout. However, before soldering, the locator wires (connected to the female attachments with low-fusing solder) should be removed. L, Solder is fed in through the slot in the proximal plate. M, The completed RPD ready for try-in. (Courtesy Ney Dental International.)
on large teeth. On small teeth, few intracoronal precision attachments can be kept within the confines of normal tooth contour without endodontic treatment. Additionally, sufficient clinical crown must exist for adequate cervicoocclusal length to allow a positive friction fit (4 mm or more is recommended).
Laboratory-made Types. Many laboratory-made (semiprecision) attachments are in use today. Often they are referred to as dovetails because of the shape of their interlocking components. They can be made by incorporating a prefabricated plastic insert in the wax pattern, which is then invested and eliminated, and the pattern is cast (Fig. 21-33). The fe male dovetail also can be milled, after which the male component is waxed and cast.
An alternative method of fabrication is to use a tapered metal mandrel (e.g., Ticon*) that is heated and inserted in the wax pattern. When the wax is eliminated after investing, the exposed portion of the mandrel in the mold oxidizes. The crown is then cast directly onto the mandrel, which is later removed. A male attachment can be waxed and cast separately. After seating, the attachment is soldered to the RPD (Fig. 21-34).
Fig. 21-34. A, Ticon mandrels for intracoronal rests. B, The mandrel is positioned with a dental surveyor. C, Mandrel luted to the wax pattern. The assembly (pattern and mandrel) is invested, and the metal is cast directly against the mandrel. The mandrel is then removed, creating the intracoronal rest, after which porcelain is applied in the conventional manner. D, Fixed prosthesis at try-in. E, The male attachment is waxed and cast independently. F, Framework and male attachment at try-in. After this, the components are soldered together. (B to D and F courtesy Dr. F. Hsu.)
Fig. 21-34. A, Ticon mandrels for intracoronal rests. B, The mandrel is positioned with a dental surveyor. C, Mandrel luted to the wax pattern. The assembly (pattern and mandrel) is invested, and the metal is cast directly against the mandrel. The mandrel is then removed, creating the intracoronal rest, after which porcelain is applied in the conventional manner. D, Fixed prosthesis at try-in. E, The male attachment is waxed and cast independently. F, Framework and male attachment at try-in. After this, the components are soldered together. (B to D and F courtesy Dr. F. Hsu.)
Because of the inaccuracies inherent in their fabrication, most laboratory-made attachments have a limited amount of frictional retention compared to the commercially available precision attachments. The majority are tapered for ease of fabrication and therefore require the use of lingual clasps for positive retention.
When attachments are used with a metal-ceramic restoration, adequate metal must remain between the female component and the facial veneer of dental porcelain. A minimum material thickness of 1 mm is recommended between any intracoronal at tachment and the metal-ceramic interface (Fig. 21-35).
BARS, STUDS, AND MAGNETS FIG. 21-36) Stud attachments and magnets are sometimes used to retain overdentures. They are incorporated in post-retained castings or implant abutments and offer the advantage of allowing increased occlusal forces' (Fig. 21-37). A bar-retained RPD or over-denture can be very stable while it braces individual abutment teeth. The bar should attach to the retainer without interfering with oral hygiene.
- Fig. 21-35. Female intracoronal rest incorporated in a metal-ceramic restoration. The attachment should be at least 1 mm from the metal-ceramic junction. Retention is provided by a lingual undercut into which a clasp engages. Reciprocation is provided internally by the rest seat.
Fig. 21-36. A, The Stern stud attachment. 1, Female component; 2, male component. B, Stud attachment assembled. C and D, The Stern bar attachment. 1, Sleeve; 2, spacer; 3, bar.
Fig. 21-37. A, Post-retained casting incorporating a male component of a stud attachment. The design allows for slightly different paths of insertion (arrows) of the post and overdenture. B, The female component is attached to the overdenture with acrylic resin.
Fig. 21-36. A, The Stern stud attachment. 1, Female component; 2, male component. B, Stud attachment assembled. C and D, The Stern bar attachment. 1, Sleeve; 2, spacer; 3, bar.
Fig. 21-37. A, Post-retained casting incorporating a male component of a stud attachment. The design allows for slightly different paths of insertion (arrows) of the post and overdenture. B, The female component is attached to the overdenture with acrylic resin.
Generally this means considerable coronal length is necessary for the bar to produce an acceptable result. The bar should not be placed in contact with an edentulous ridge (Fig. 21-38).
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