60 - post and core crowns

sections

• what is post and core

• post and core variations in materials

• post and core variations in manufacturing

• conservation of tooth structure

• effect of posts

• stages of post and core prep

• ferrule

• direct and indirect post and core

• advantages + disadvanatges

• what is post and core

• used to stabilize a weakened/broken down tooth that may have been damaged by fracture or decay or to provide tooth structure to retain a crown.

• Core - is a substitution of the missing hard dental tissues of the tooth crown. It replaces fractured or missing coronal structure and retains the final restoration or crowns.

• Dowel/post – is a rigid restorative material that connects the core to the root inside the root canal. It is placed within the body of the root of a tooth that has been treated with root canal treatment (non-vital).

• post and core variations in materials

• Composite-fiber reinforced

• Ceramics

• Metals-gold, non-precious and precious alloys

• post and core variations in manufacturing

• Prefabricated

• Made by casting

• Made by sintering

• Made by polymerization

• Made by CAD/CAM

• conservation of tooth structure

• Canal preparation: where the enlargement of the canal should exceed 1-2 additional file sizes beyond the largest size used.

• Coronal part preparation: involves the removal of the undercut and ferrule.

• effect of posts

• greater the post length is the better the retention will be.There should be a 2/3 length of root/ post length that should be equal to the crown length. A 3-5mm apical seal must be maintained.

• Post-diameter: shouldn’t exceed 1/3 diameter of the root and minimum of 1mm sound dentin circumferentially

• The surface texture: serrated and roughened post have a greater retention than smooth post.

• shape of posts come in two forms parallel and tapered:

  • tapered form have less tooth structure removed and are used in tapered root canals.

  • Parallel post shape is more beneficial as more tooth structure is removed. It has more retention and decreases the chance of tooth fracture.

• Resistance form: post design influences the stress distribution and in turn resistance where threaded posts produce stress concentration, the cement layers result in better stress distribution

• stages of post and core prep

1. Preparation of the margins (a crown preparation): weaker residual walls are eliminated; the cavity is cleaned up and all healthy dentin is preserved.

2. Preparation of the root canal: Root part of the post-and-core is prepared with calibrated mechanical burs. The post reaches 3-5mm of the orificium, taking up 2/3 of canal’s length; thus, creating the most favorable ratio of root post to crown length as 2:1. Post diameter – the width of the middle root section is 1.2-2.0mm smaller than the one at the cervical area. The diameter of the post in the cervical zone must not exceed the width of the tooth wall on any side. The preparation for the post has a slightly ellipsoidal shape, which is preferable than the round configuration.

3. Preparation of the contrarotational elements.

4. Removal of the thin walls less than 1mm.

• ferrule

• is a metal band or a ring used to fit the root or crown of a tooth;

• At least 1mm of dental tissues should be above the preparation junction in order for a ferrule effect. When there is a ferrule effect, the artificial crown clamps the tooth as a ring and increases its fracture resistance.

• direct and indirect post and core

• Direct post-and-core restoration:

  • Factory made post (metal or fibre-reinforced glass) and composite or cement

  • usually used for single tooth restoration.

• Indirect post-and-core restoration:

  • Preparation, impression is taken → sent to dental lab→undergoes process of cementation.

  • Materials used are metal alloy or/and ceramics; usually used for multiple teeth or tooth with multiple canals.

• advantages + disadvanatges

• +

  • Allows restoration of severely damaged teeth and provides support for the crown.

  • Can be used for certain corrections of improperly inclined teeth.

• -

  • Can be used only in endodontically treated teeth.

  • Increase the risk of root fractures.

  • High risk of root perforation or root resorption.