Post And Core Flashcards
Definition
A post and core is a prosthetic device that is utilized when there is inadequate tooth structure remaining to support a traditional restoration or an artificial crown.
Structure
A post and core consists of two parts :
- The post
The post is a small rod, usually metal, that is inserted into the root space of the tooth and protrudes from the root a couple of millimetres. The post is then used to hold the core or a filling in place.
Because the post is inserted into the root canal, a post and core can only be made for a tooth that has had root canal treatment. - Core
The core replaces missing tooth structure in preparation for making a new dental crown. Normally, a dental core can be directly built up from composite materials without a post to hold it in place.
The core is then utilized to hold a dental crown in place. The crown can be a single unit crown or a retainer crown for a dental bridge.
Procedure
- Examination, Raiographs (periapical)
Principles of post and core
Rule #1: The post should be longer than the height of the clinical crown. 2/3
Rule #2: There should be 4-5 mm of GP remaining apically
Rule #3: There should be at least 2mm of circumferential ferrule
Rule #4: The tip of the post should be no more than 1/3 of the diameter of the root
Rule #5: The post diameter should ideally not exceed the diameter of the shaped and disinfected canal
INDICATIONS FOR POST AND CORE
• Where the natural crown of root-filled teeth either has been lost or is extensively damaged.
• Where the root-filled tooth is to be used as bridge abutment.
• Where a change in axial position greater than 1mm is required.
• In a crowned anterior endodontically involved tooth, to reinforce the crown covered tooth at cervical area susceptible to fracture.
CONTRAINDICATIONS
• Severe curvature of the root-eg: Dilacerations of the root.
• Persistent periapical lesion
• Poor periodontal health
• Poor crown to root ratio
• Weak / fragile roots
• Teeth with heavy occlusal contacts
• Patients with unusual and occupational habits
• Economic factors
• Inadequate skill.
An ideal post system according to Wagnild et (2002) should have the following features
• Provide maximal retentiveness to the core.
• Physical properties compatible to core
• Maximum retention with minimum removal of dentin
• Even distribution of functional stresses along root surfaces
Esthetic compatibility
Minimal stress during placement and cementation
• Resistance to displacement.
• Easy retrievability
• Ease of use
• Reasonable cost
Grossman
According to Cohen
Posts should provide as many of the following clinical features as possible:
• Maximal protection of the root from fracture
• Maximal retention within the root and retrievability
• Maximal retention of the core and crown
• Maximal protection of the crown margin seal from coronal leakage
• Pleasing esthetics, when indicated
• High radiographic visibility
• Biocompatibility
Classification of posts
- Metallic Posts
• Custom-cast Posts
• Prefabricated Posts
і.Passive Tapered Posts
ii.Passive Parallel Posts
іії.Active Posts
- Non-metallic Posts
• Carbon Fiber Posts
• Tooth Colored Posts
• Woven fiber composite
Ferrule
• FERRULE(EISSMAN & RADKE): A band of metal that protectively encircles the remaining tooth structure
Root - Retain the post
Post - Retain the core
Core - Retain the crown
Indications and Contraindications of a cast post
Indications
• Moderate to severe loss of tooth structure
• Smaller teeth
• Multiple cores in the same arch
• Angles of cores to be changed
• Tapered canals
• Single rooted teeth
Contraindications
• Sufficient tooth structure for prefabricated post
• Short roots, thin roots
• Flared canals
• When esthetics is a major concern
ADVANTAGES OF CAST POST OVER
PREFABRICATED CORE SYSTEMS
• High strength
• Custom fit to the root configuration
• Minimal alteration of canal anatomy
• Adaptable to large irregularly shaped canals and orifices
• Changes in core angulation is possible
Disadvantages of cast post
• Rigidity - Root fracture
• Tapered canals - wedging effect
• Expensive
• Two or more appointments
Temporization between appointments - more difficult
• Risk of casting inaccuracies
• Unesthetic appearance
Difficult to retrieve
ADVANTAGES OF PREFABRICATED
POSTS OVER CAST POST SYSTEMS
• Simple to use
• Requires less chair side time
Completed in one appointment
Easy to temporize
DISADVANTAGES OF
PREFABRICATED POST OVER CAST
POST SYSTEMS
• Root is designed to accept the post rather than the post being designed to fit the root
• Application - limited - considerable coronal tooth structure is lost
• Chemical reactions - post and core - dissimilar metals
Principles of tooth preparation
• CONSERVATION OF TOOTH STRUCTURE
- Preparation of the canal
- Preparation of coronal tissue
• RETENTION FORM
- Anterior teeth
- Posterior teeth
• RESISTANCE FORM
- Stress distribution
- Rotational resistance
