A post and core restoration is used to build up tooth structure for a crown when there is not enough structure remaining. A post is placed in the root canal and a core is built up around the post to provide support and retention for the crown. Key factors in post and core design include post length and diameter, surface texture, and luting agents to provide retention, as well as post design and cement layer to provide resistance to stresses. Custom post and cores are made using direct or indirect techniques involving impression taking, while prefabricated posts are used for circular root canals.

1. Restoration of endodontically treated teeth Composite / amalgam restoration Crown – metal / ceramic

2. A post and core is a dental restoration used to sufficiently build-up tooth structure for future restoration i.e crown when there is not enough tooth structure to properly retain the crown.

3. post is placed within the body of the root of a tooth that has already treated with root canal treatment. The core is the part of the restoration that shows out in the mouth that help anchor a cap or crown

4. Principles of tooth preparation Conservation of tooth structure Retention form Resistance form

5. Conservation of tooth structure -canal preparation-enlargement of canal should exceed about 1-2 additional file sizes beyond the largest size used. Coronal part preparation- removal of undercuts and ferrule (extension of axial wall of the crown apical to the missing tooth structure)

6. Retention form Post length Post diameter Surface texture Luting agent

7. Post length Greater post length=greater retention 2/3 length of root / post length should equal crown length Maintain 3 – 5mm apical seal

8. Post diameter Shouldn't exceed 1/3 diameter of the root A minimum of 1 mm of sound dentin should be maintained circumferentially

9. SURFACE TEXTURE Serrated or roughened post is greater retentive than smooth post LUTING AGENT Znpo4,Resin and GIC are greater to other cements

10. Resistance form Post design influences the stress distribution and in turn resistance -post length -parallel posts -threaded posts produce stress conc. -cement layer results in better stress distribution -sharp angles -rotational resistance

11. Post and core systems Custom post and core – mainly used in flared canals,elliptical crossection canals ,multiple canal teeth Prefabricated – circular crossection canals

12. Steps in tooth preparation Removal of RC filling material Enlargement of the canal Preparation of coronal tooth structure

13. Prefabricated post and core system

14. Eliminate weaker residual walls, clean up the cavity, preserving all healthy dentine

15. Prepare the root canal according to your usual procedure (Gates,paesso reamers ] the post is chosen according to the canal's diameter, not to the root's.

16. Prepare the composite bonding cement, coat the post Insert it immediately into the canal

17. Fit the core form boxing system Fill up with the core composite while pressing and polymerize

18. Custom cast post system Direct technique Indirect technique

19. Remove any weak, thin, and/or unsupported tooth structure. Direct technique

20. Using progressively larger diameter Pesso reamers remove the gutta percha to the predetermined initial depth Repeat this process as necessary leaving 4-5 mm of gutta percha as an apical seal.

21. Add a keyway to resist rotation of the post/core. Place the keyway in the bulkiest part of the remaining tooth structure.

22. Try-in the preformed plastic post and be sure it goes all the way down the prepared canal without binding (a totally passive fit). Trim it as necessary. Measure the post relative to the depth of the canal with a periodontal probe

23. Lubricate the canal with Duralay lubricant Using the "bead brush" technique, fill the canal completely with Duralay resin. Use the bristles of a brush (bent at a 45 degree angle for easier access) to force acrylic down the canal and express any trapped air

24. Immediately, dip the plastic post in acrylic liquid (to soften post and enhance bond of acrylic) and seat it in the canal to its full depth. Move the post up and down in the canal 1-2 mm (only after the Duralay is nearly set) to avoid getting it "locked in."

25. Using hemostats, carefully remove the post pattern and inspect it to be sure it is fully formed (with no voids).

26. Cut off the top of the plastic post so that your patient can close completely

27. Using a large diameter coarse diamond (high speed handpiece at "near stall" speed with water spray), shape the pattern to ideal preparation form (on the tooth).

28. Using hemostats (held mesiodistally), remove the pattern from the tooth. The pattern should not be removed (except one time to check that the post portion is fully formed) until it is completed. There is the risk of breakage each additional time the pattern is removed.

29. Indirect technique of making custom post and core

30. Post and core The tooth is prepared prior to the pattern fabrication. A heated endodontic condensor is used to safely remove the gutta percha (this is best accomplished at the same time the endodontic therapy is rendered). Gates & Parapost drills are used to shape the canals to an appropriate size and depth. The most common sizes used are Brown Yellow and Red (see the table below).

31. The minimum length of the post is equal to the length of the clinical crown. The recommended length is two-thirds the length of the root in bone while maintaining 5 mm of gutta-percha at the apex. Remember chances of a perforation increase as the length of the post approaches the apex of the tooth.

32. The prefabricated posts are inserted into the canals. In this case a precious metal post is being used in the lingual canal because the canal diameter is only equivalent to a brown sized Parapost (Gates #3 - see table). The precious metal posts are issued from the Dispensing Window, and require an additional fee.

33. An assistant holds the Duralay powder, liquid, and suction - while the core portion is made in resin. First lubricate the remaining tooth structure with a water soluble lubricant (Surgilube) then apply the resin. The assistant may move the suction near the resin, evaporating monomer from its surface, thus preventing the resin from slumping or running.

34. The completed resin core is allowed to polymerize - then it is prepared to the shape of an ideal crown preparation

35. Using conventional diamond instruments, water and suction, the resin core is prepared in the same manner as a conventional preparation

36. The preparation is completed to ideal form and in this case its path of insertion is aligned with the preparation of tooth #11

37. The completed post & core pattern is submitted to the Service Laboratory for investing & casting in gold alloy.

38. The casting is cleaned and sandblasted with alumina oxide in preparation for try-in, shaping, and cementation. The canals are dried and the casting inserted using light pressure. Small shiny marks on the casting surface help indicate where adjustment should be made.

39. The completed post is cemented