purpose : The purpose of this review is to organize this topic into its component parts and provide evidence-based principles that are sound from a restorative as well as an endodontic perspective
ARE ENDODONTICALLY TREATED TEETH DIFFERENT?
•It was thought that the dentin in endodontically treated teeth was more brittle because of water loss and loss of collagen cross-linking .
•Huang et al. compared the physical and mechanical properties of dentin specimens from teeth with and without endodontic treatment at different levels of hydration. They concluded that neither dehydration nor endodontic treatment caused degradation of the physical or mechanical properties of dentin.
•More recent studies showed that it is the loss of structural integrity associated with the access preparation, rather than changes in the dentin, that lead to a higher occurrence of fractures in endodontically treated teeth compared with “vital” teeth
RESTORATIVE FACTORS THAT AFFECT THE PROGNOSIS OF ENDODONTIC TREATMENT:
•Coronal leakage is a potential cause of endodontic failure.
•Dental restorations must withstand repeated exposure to physical, chemical, and thermal stressors.
•Once RCT is completed, immediate restoration of the tooth is recommended whenever possible.
•The quality of the restorative dentistry performed after root-canal treatment directly impacts the prognosis of the endodontically treated tooth. Post spaces, in particular, should be restored immediately.
•There is a strong evidence that cuspal coverage should be provided for posterior teeth.
•Endodontically treated teeth with cuspal coverage are six times more likely to survive than those with intracoronal restorations
•Coronal tooth structure should be preserved to provide resistance and retention form for the crown
INDICATIONS FOR A POST:
•The primary purpose of a post is to retain a core in a tooth with extensive loss of coronal tooth structure.
The placement of posts also may increase the chances of root fracture and treatment failure , especially if an oversized post channel is prepared •Anterior teeth: with minimal loss of tooth structure can be restored with bonded restoration only. if teeth that are to receive crowns , a post usually is indicated.
•Molars: should receive at least cuspal coverage. posts are not always indicated unless the destruction of coronal structure is extensive, the post should be placed in the largest, straightest canal, which is the palatal canal in the maxillary molars and a distal canal in the mandibular molars.
•Premolars: require posts more often than molars. They are more likely than molars to be subjected to lateral forces during mastication
IMPORTANT PRINCIPLES FOR POSTS:
•Post retention refers to the ability of a post to resist vertical dislodging forces.
•Retention is influenced by the post’s length, diameter and taper, the luting cement used, and whether a post is active or passive.
•Increasing the length and diameter of the post can increase retention •Resistance refers to the ability of the post and tooth to withstand lateral and rotational forces.
•It is influenced by the remaining tooth structure, the post’s length and rigidity, the presence of anti-rotation features, and the presence of a ferrule • Restoration lacking resistance form is not likely to be a long-term success, regardless of the retentiveness of the post
it is important that posts can be retrieved if endodontic retreatment becomes necessary. In most cases, metal posts can be removed effectively and safely. Most fiber posts also are reported to be easy to retrieve . In contrast, ceramic and zirconium posts are considered to be very difficult and sometimes impossible to retrieve.
Types of posts:
•Active Versus Passive Posts : active posts are more retentive than passive posts, but introduce more stress into the root. Their use should be limited to short roots in which maximum retention is needed.
•Parallel Versus Tapered Posts: Parallel metal posts are more retentive than tapered posts, induce less stress into the root, because there is less of a wedging effect. Tapered posts, on the other hand, require less dentin removal because most roots are tapered. They are primarily indicated in teeth with thin roots and delicate morphology
•Prefabricated Post and Cores: Prefabricated posts are typically made of stainless steel, nickel chromium alloy, or titanium alloy. They are very rigid, and with the exception of the titanium alloys, very strong.
•Custom Cast Post and Cores: they offer advantages in certain clinical situations. For example, when multiple teeth require posts, it is sometimes more efficient to make an impression and fabricate them in the laboratory rather than placing a post and buildup in individual teeth as a chair-side procedure.
•Ceramic and Zirconium Posts: esthetic but weaker, does not bound to resin, difficult to retrieve.
•Fiber Posts: more flexible, relatively easy to remove and had approximately the same modulus of elasticity (stiffness) as dentin.
PREPARING THE POST SPACE:
•There should be minimal enlargement of the canal beyond the shape that was developed during root-canal instrumentation. In most cases, it is best that the clinician who performs the root-canal treatment also prepares the post space.
•GP can be removed with the aid of heat or chemicals, but most often the easiest and most efficient method is with rotary instruments.
•A review article by Goodacre and Spolnik (1995), recommends post length equal to 3⁄4 of root canal length, if possible, or at least equal to the length of the crown. They caution that 4 to 5 mm of gutta-percha should remain apically to maintain an adequate seal.
•According to Neagley, 8 mm is the minimum length required for a post.
Do Bonded Posts Really Strengthen Roots?
•Bonded posts are reported to strengthen the root initially , but this strengthening effect is probably lost with time, because of the repeated thermal, chemical, and mechanical stresses of the oral cavity
Principles to be followed in the restoration of endodontically treated teeth, to achieve high levels of clinical success:
1. Avoid bacterial contamination of the root-canal system
2. Provide cuspal coverage for posterior teeth
3. Preserve radicular and coronal tooth structure
4. Use posts with adequate strength in thin diameters
5. Provide adequate post length for retention
6. Maximize resistance form including an adequate ferrule
7. Use posts that are retrievable.