post and core.pptx
- 1. POST and CORE DR. LADAN ELFATIH
- 2. post Post usually made of metal or fiber reinforced composite resin that is fitted into a prepared root canal of natural tooth. zirconia is also used as post material when combined with core ,it provide retention and resistance for an artificial crown . The Glossary of prosthodontic
- 3. CORE It is the center or base of a structure. The foundation restoration which restore sufficient coronal anatomy of vital or endodontically treated tooth . The Glossary of prosthodontic
- 4. .
- 5. PRINCIPLES OF TOOTH PREPARATION Conservation of Tooth Structure. Retention Form. Resistance Form.
- 6. Conservation of Tooth Structure Preparation of the Canal When post space is created, only minimal tooth structure should be removed from the canal. Excessive enlargement can; perforate or weaken the root may split during either cementation of the post or subsequent function.
- 7. Preparation of Coronal Tissue Endodontically treated teeth often have lost much coronal tooth structure . must have adequate structural integrity to prevent their fracture during the try-in and evaluation of the cast post and core restoration.
- 8. Retention Form Anterior Teeth An anterior post and core restoration are frequently dislodged simultaneously as a result of inadequate retention form of the prepared Tooth. The normal labiolingual convergence of anterior teeth, coupled with smaller tooth size, complicates achieving such retention form.
- 9. Post retention is affected by ; preparation geometry. post length. post diameter . post surface texture. luting agent.
- 10. Preparation Geometry. Some canals, particularly in maxillary central incisors, have a nearly circular cross section . These can be prepared with parallel walls or minimal taper. Conversely, canals with elliptical cross sections must be prepared with a restricted amount of taper .
- 12. Post Length Ideally, the post should be as long as possible without jeopardizing the apical seal or the strength or integrity of the remaining root structure. Most endodontic texts advocate maintaining a 5-mm apical seal.
- 14. Post Diameter Increasing the post diameter to increase retention is not recommended because retentive gain is minimal and weakened the root. prognosis is good when post diameter does not exceed one third of the cross-sectional root diameter.
- 15. Post Surface Texture. . A serrated or roughened post is more retentive than a smooth one, and controlled grooving of the post and root canal considerably increases the retention of a tapered post.
- 18. Luting Agent. luting agent seems to have little effect on post retention or the fracture resistance of dentin. although the choice of luting agent may become more important if the post has a poor fit within the canal.
- 19. Posterior Teeth long posts should be avoided in posterior teeth, which often have curved roots and elliptical or ribbon-shaped canals . If a reasonable amount of coronal tissue remains, use of a single metal post that is cemented in the largest canal can provide adequate retention for the core material.
- 20. Resistance Form Stress Distribution One of the functions of a post and core restoration is to improve resistance to laterally directed forces by distributing them over as large an area as possible. Post design should enable stresses to be distributed as evenly as possible.
- 21. • Glass fiber posts have an elastic modulus (flexibility) similar to that of dentin and therefore result in lower stress concentrations than do metal or ceramic posts; this concept is termed mono block.
- 22. The greatest stress concentrations are found at the shoulder margin, particularly inter proximally, and at the apex. Dentin should be conserved in these areas if possible. Stresses are reduced as post length increases. Parallel-sided posts may distribute stress more evenly than do tapered posts. However, parallel-sided posts heighten stresses at the apex.
- 23. Sharp angles should be avoided because they heighten stresses during loading. Threaded posts can heighten stress concentrations during insertion and loading.
- 24. Rotational Resistance To minimize the risk of dislodgment, it is important that preparation geometry prevents a post with a circular cross section from rotating during function . a small groove placed in the canal wall can serve as an anti rotational element. The groove is normally located where the root is bulkiest, usually on its lingual surface. auxiliary pin in the root surface. a small cavity (half in the post, half in the root) and condensing amalgam into it after the post is cemented.
- 26. PROCEDURES Tooth Preparation Tooth preparation for endodontically treated teeth is a three- stage operation: 1. Removal of the root canal filling material to the appropriate depth. 2. Enlargement of the canal. 3. Preparation of the coronal tooth structure.
- 27. Removal of the Endodontic Filling Materia Two methods are commonly used to remove guttapercha : (1) using a warmed endodontic plugger. (2) using a rotary instrument, sometimes in conjunction with chemical agents.
- 29. Although more time consuming, the warmed endodontic plugger method is preferred because it eliminates the possibility that the rotary instrument will inadvertently damage the dentin.
- 30. The procedure is as follows: 1. Before removing gutta-percha, calculate the appropriate post length. As a guide, make the post length equal to the height of the anatomic crown (or two-thirds the length of the root), but leave 5 mm of apical gutta percha. An absolute minimum of 3 mm of apical fill is needed.
- 31. 2.apply a rubber dam before preparing the post space. 3. Select an endodontic condenser large enough to hold heat well. 4. Mark it at the appropriate length (normally endodontic working length, −5 mm), heat it, and place it in the canal to soften the gutta-percha. 5. If the gutta-percha is old and has lost much of its thermo plasticity, use a rotary instrument.
- 32. 6. If you are using a rotary instrument, choose one that is slightly narrower than the canal. 7. Ensure that the instrument follows the center of the gutta- percha and does not cut dentin. 8. When the gutta-percha has been removed to the appropriate depth, shape the canal as needed. This can be accomplished with an endodontic file or a low-speed drill.
- 33. Canal Enlargement Before the canal is enlarged, the type of post system that will be used for fabrication of the post and core restoration must be chosen.
- 35. Prefabricated Posts. Many prefabricated posts are available in kits that include rotary instruments for post space preparation that correspond in size to the posts. Alternatively, some of these posts are manufactured to match standard sizes of endodontic files.
- 36. procedure 1. Enlarge the canal one or two sizes with a drill, an endodontic file, or a reamer that matches the configuration of the post. 2. Use a prefabricated post that matches standard endodontic instruments. A tapered post conforms better to the canal than does a parallel-sided post and requires less removal of dentin to achieve an adequate fit. 3. Be especially careful not to remove more dentin at the apical extent of the post space than is necessary.
- 38. Posts Custom-Made Use custom-made posts in canals that have a noncircular cross section or extreme taper. Often very little preparation is needed for a custom-made post. Any undercuts within the canal must be removed. some additional shaping is usually necessary.
- 39. A custom-made post and core restoration can be made of; 1. cast metal . 2. zirconia fabricated with CAD/CAM technology.
- 40. A cast metal post and core restoration can be made from; a direct pattern fabricated in the patient’s mouth or from an indirect pattern fabricated in the dental laboratory.
- 41. Direct Pattern Procedure 1. Fit a prefabricated plastic dowel to the root canal. For a flared canal, the fit will only be adequate in the apical half of the prepared post space.
- 42. 2. Lightly lubricate the canal and dry the canal.
- 43. 3. Use the “brush-bead” technique to add resin to the occlusal half dowel, and seat it in the prepared canal
- 44. 4. Push the resin into the canal with a small condenser . Do not allow the resin to harden fully within the canal. Loosen and reseat it several times while it is still rubbery.
- 45. 5.Once the resin has polymerized, remove the pattern. 6. Form the core part of the post by adding additional auto polymerizing resin or light polymerized resin .
- 46. Pattern Fabrication with Thermoplastic Resin
- 47. Indirect Procedure 1. Cut pieces of orthodontic wire to length and shape them like the letter J . 2. Verify the fit of the wire in each canal. 3. Coat the wire with tray adhesive.
- 48. 4. Using a Lentulo spiral , fill the canals with elastomeric impression material. 5. Seat the wire reinforcement to the full depth of each post space, and insert the impression tray. Remove the impression, evaluate it, and pour the definitive cast .
- 49. CAD/CAM ZIRCONIA POST AND CORE RESTORATION Strong, esthetic post and core restorations can be fabricated from strong zirconia with CAD/CAM technology. Typically, the dentist makes an impression of the prepared tooth. which is scanned and digitized by the dental laboratory. before the zirconia is milled and sintered.
- 50. disadvantage of a custom-milled zirconia system ; difficulty of removal if an endodontic re-treatment is indicated.
- 51. Core Fabrication The core of a post and core restoration replaces missing coronal tooth structure and, in combination with the remaining coronal tissue. It can be shaped in resin or wax. It is cast directly onto a prefabricated post. It make from a plastic restorative material, such as amalgam, composite resin or glass ionomer.
- 52. Plastic Filling Materials The advantages of amalgam, glass ionomer, or resin include the following: Maximum tooth structure can be conserved. Treatment requires one fewer patient visit. There are fewer laboratory procedures. Testing has generally revealed good resistance to fatigue testing and good strength characteristics.
- 53. Disadvantages include the following: Long-term success may be affected by 1. corrosion of amalgam cores, 2. the low strength of glass ionomer , 3. or the continued polymerization and high thermal expansion coefficients of composite resin cores.
- 54. Microleakage with temperature fluctuations (thermocycling) . Difficulty may be encountered with certain operative procedures such as rubber dam or matrix application (particularly on badly damaged teeth).
- 55. Cast Metal They can be cast directly onto a prefabricated post , which will provide the restoration with good strength characteristics. Conventional high noble-metal content alloys can be used. An indirect procedure can be used, which will facilitate restoration of posterior teeth.
- 56. Pattern Fabrication with Auto polymerizing Resin
- 57. Investing and Casting Evaluation
- 58. Cementation The luting agent must fill all space within the root canal system . Voids may be a cause of periodontal inflammation via lateral canals.
- 59. Thanks
- 60. Disadvantages to the Routine Use of a Cemented Post require additional operative procedure. Require additional removal of tooth structure It may be difficult to restore the tooth later. It may be difficult for future endodontic re-treatment