Cast Core Jacket Crown Notes

Cast Core Jacket Crown

Post crown/Radicular retainers/Endodontically restored tooth/Dowel crowns/Coronal radicular stabilization.

Classification of radicular retainers/Endodontically restored tooth

• Single-rooted teeth to be restored require dowels: 80% of remaining tooth structure
• Restoration without dowels for multi-rooted teeth only: 75% remaining tooth structure – Pin-retained complete crown
• Cast dowels
  • Single-rooted teeth:
    • Direct technique
    • Indirect technique (multiple dowel and cores and overdenture abutments).
  • Multi-rooted teeth:
    • Single dowel or multiple parallel dowels.
    • Nonparallel dowels:
      Interlocking castings
      Nonparallel dowel(s) fitted through primary dowel and core casting.
• Preformed dowels
  • Smooth sided tapered:
    • Unitek Kerr Endo Post
    • Minimal retention hence, used for 90% remaining tooth structure.
  • Parallel sided with serrations or grooves for retention (Parapost)
  • Tapered threaded post:
    • E.g. Dentatus
      Threads for retention post are not screwed in.
      Core retention in multi-rooted teeth.
• Tapered and threaded posts:
  • E.g. Flexi Post Brasseler
    • Maximum retention
    • Useful with short roots to retain core.
• Core retention with pins.

Advantages of cast post to preformed dowels

• Custom fit to irregularly shaped canals and not cylindrical as preformed dowels
• Cast as one unit rather than two separate units
• Do not require auxiliary retention as in prefabricated systems.

Custom (Cast) Dowel and Core/Custom cast post and cores

Read And Learn More: Fixed Partial Denture Short Essay Question And Answers

For single-rooted teeth

Techniques

• Direct Technique:
  • Commonly used.
• Indirect technique:

For multiple dowels and cores, overdenture attachments.

Direct Technique

Preparation of tooth
The remaining tooth structure is reduced to the buccal and lingual surface to produce a ferrule effect (360° collar) with the dowel and core.

Preparing the root canal

• Correct sized files, Pesso reamers and Gates Glidden drills are used to prepare the canal to the approximate size of a No 30 file
• The coronal end of the canal is funnelled.

Placement of anti-rotational groove

• If the canal is elliptical in shape, an anti-rotational notch is not required
• If it is circular an anti-rotational notch is placed with a tapered bur.

Impression of the canal

• Plastic dowels of the canal size, Kerr Endo Post, toothpicks, nails, paper clips can be used to carry acrylic or wax to form the pattern of the canal. The plastic dowel is roughened and canal is lubricated

• A resin, such as Duralay is applied to the dowel. After the resin reaches the doughy stage, the dowel is inserted into the canal and the dowel is moved up and down to prevent it being locked in an undercut in the canal
• After the resin has set, the pattern is removed and checked for accuracy.

Shaping of coronal aspect
Coronal aspect is next shaped to resemble an ideal tooth preparation.

Investing and casting in Shaping of coronal aspect
The pattern is then invested and cast in a metal of choice.

Indirect Technique
For multiple dowels and cores, overdenture attachments.

Cast Core Jacket Crown Advantages

• Reduced chair time
• Accurate fitting of the coping margin in the gingival crevice
• Can accurately align the overdenture attachment
• Can accurately parallel the coping.

Cast Core Jacket Crown  Technique

Impression of the canal

• A loose-fitting plastic or metal dowel with the coronal end bend is used to make the impression
• The dowel is coated with impression material adhesive and the selected elastomeric impression material is injected into the canal with a lentulospiral
• The dowel is also coated with the impression material before placing into the canal. Additional impression material is injected around the tooth and into the gingival crevice and the loaded impression tray is seated.

Removing the impression

• The impression tray is removed along with the dowel carrying the impression of the canal
• The impression is poured in die stone.

Trimming of dies

Dies are trimmed to expose the margins.

Forming pattern of the die

• The dowel pattern is formed by adding molten soft wax on the loose-fitting dowel and inserting it into the canal
• Procedure is repeated until a satisfactory pattern is obtained.

Forming coronal portion
The coronal portion is made with inlay wax to replicate a prepared tooth.

Investing and casting
The pattern is sprued and invested as in the direct technique and cast.

For Multi-rooted teeth

First technique
The larger, longer canal is selected for the primary post, e.g., the palatal canal of maxillary molars or the distal canal of mandibular molars, while the other canal is made parallel to the primary canal for the secondary post, which is not more than 3 or 4 mm in length.

Second technique
Is to make an interlocking post and core for divergent canals so that the length of the secondary canal can be made long.

Third technique
Is to use two or even three canals when they are not parallel with the primary post in the larger, longer canal, while the other canal or canals are used for the secondary dowels.

Procedure (mandibular molar)

• A plastic dowel of last file size used is seated in the distal canal
• A stainless steel dowel is placed in the mesial canal
• The plastic dowel is notched, roughened, and coated with resin which is pumped up and down to prevent locking.

Forming the coronal aspect

After the resin is almost set, the dowel is inserted back into the distal canal and coronal portion is made to resemble an ideal tooth preparation with resin, embedding the lubricated stainless steel post in the pattern.

Removing stainless steel dowel

• After the resin has set the stainless steel dowel is removed with a plier and is heated until it is oxidized (turning cherry red)
• After it cools, it is reinserted into the pattern to maintain the patency of the hole for the post in the mesial canal during casting.

Investing and casting

• The pattern is invested and cast with a metal of choice
• The oxidation of the stainless steel dowel prevents it from becoming an integral part of the casting.

Removing stainless steel dowel

• The dowel is removed from the casting with a plier
• When fitting the post and core, a new stainless steel dowel of the same size is placed in the hole in the casting.

Seating the casting in the tooth
A cast dowel should be at least the size of a No. 90 endodontic file.

Fitting and cementing custom dowel and cores

• Casting is seated passively
• Occlusal clearance and axial contour are examined
• Final corrections are made and the dowel and core are ready for cementation
• The canal is cleaned with a solvent to remove residual lubricant, dried with absorbent points and luted with an appropriate cement (zinc phosphate, resin or glass ionomer)
• The cement is mixed and placed into the canal with a lentulo spiral, the dowel and core is also coated with cement and then placed into the tooth under finger pressure until the cement sets
• The crown needs to be made separately after impression procedure to be cemented over the core
• A minimum of 1–2 mm of sound tooth structure apical to the gingival margin of the dowel (post) and core is required.

Note: For question on radicular retainers details of prefabricated dowels also need to be included.

Prefabricated Dowels

Shape
Cylindrical.

Design

• Matched with a specific size endodontic file, Pesso reamer or Gates-Glidden drill
• Have an escape channel for the cement.

Cast Core Jacket Crown Disadvantages

• Cannot resist rotation because of their cylindrical shape, hence threaded or serrated dowels need to be used
• Core material need to be made of amalgam or composite resin.

Available systems

Para-Post
It is a parallel-sided post with a threaded or spiral fluted surface. The amalgam core is retained by the screw-in pins.

Dentatus Screw Post
It is a tapered, threaded rectangular-headed post that retains the core, which can be screwed-in or passively fitted with the threads, providing retention for the cement.

Flexi-post
Prevents root fracture with its split shank that closes during insertion, absorbing stresses.

Brasseler–Vlock Drill and Post System
Is a parallel-sided micro-threaded post with a posthole that can be precisely cut to match the micro-threaded post, reducing stress and improving retention.

Cementing and core fabrication

• Luting is similar to other techniques
• The core is fabricated with composite resin or amalgam in posterior teeth which is pin retained
• The gingival margin should not terminate on the core build up.