WHAT ARE EFFECTS OF ENDODONTIC TREATMENT ON THE TOOTH?
• Structural changes
Tooth weakening caused by:
– Caries – Trauma
– Access cavity preparation – Radicular preparation
Compromised structural integrity.
• Changes in dentin
A reduced amount of moisture in nonvital teeth.
• Aesthetic considerations
– Loss of tooth structure
– Change in appearance because of alteration in biochemical properties of dentin.
WHAT ARE REQUIREMENTS OF A TOOTH TO ACCEPT A POST AND CORE?
• Optimal apical seal
• Absence of active inflammation • No sensitivity to percussion
• Absence of associated periodontal disease • Sufficient bone support around the root.
WHAT SHOULD BE THE PROPERTIES OF AN IDEAL POST?
Post is relatively rigid restorative material placed in the root of a nonvital tooth. It extends coronally to anchor the core material which supports the crown (Fig. 20.1).
A Post should
• Provide maximum protection of the root to resist root fractures.
• Provide maximum retention of the core and crown. • Be easy to place.
• Be less technique sensitive.
• Have high strength and fatigue resistance. • Be visible radiographically.
• Be biocompatible.
GIVE CLASSIFICATION OF POSTS. WHAT ARE ADVANTAGES AND DISADVANTAGES OF VARIOUS POST SYSTEMS?
A. Posts can be classified as
Prefabricated Post
1. Metal prefabricated posts are made up of • Gold alloy
• Stainless steel
• Titanium and titanium alloys 2. Carbon fiber post
3. Quartz fiber post 4. Zirconia posts 5. Glass fiber post
Custom Made Posts
They can be cast from a direct pattern fabricated in patient’s month or indirect pattern fabricated in the lab.
These can be of two types:
a. Custom cast metal post and core are usually made
up of:
• Gold alloys • Base metal alloys • Ni-Cr alloys.
b. Ceramic custom made posts are made up of all
ceramic.
B. Posts can also be classified as:
1. Active post: Active posts mechanically engage the canal walls.
2. Passive or cemented posts: Passive posts don’t engage the canal walls.
Custom Cast Metal Post
Advantages
• Adaptable to large irregularly shaped canals. • Very strong.
• Better core retention because core is an inherent part of the post.
• In multirooted teeth, they are cost effective. Disadvantages
• Requires more chair side time.
• Very rigid so lead to greater stress concentration in root causing root or post fracture.
• Poor aesthetics.
• Require temporization. • Prone to corrosion.
All Ceramic Post and Cores
Advantages
• Excellent aesthetics • Biocompatibility • Good radiopacity
Disadvantages
• Brittle, so not indicated in high stress conditions like bruxism.
• Very rigid, so more risk of root or post fracture. • Gross undercuts in root canals make pattern
fabrication for cast posts difficult.
Prefabricated Metal Posts
Advantages • Simple to use.
• Less time consuming.
• Retentive with in the root specially serrated and parallel sided posts.
• Radiopaque. • Cost effective. Disadvantages
• Not conservative because root is designed to accept the post.
• Cannot be placed in tortuous canals. • Poor aesthetics.
• Very rigid.
Carbon Fiber Posts
Carbon fiber post consists of bundle of stretched carbon fibers embedded into an epoxy matrix.
Advantages
• Clinical procedure is less time consuming.
• Strong but low stiffness and strength than ceramic and metal posts.
• Easily retrievable. • Less chair side time.
• Modulus of elasticity similar to dentin. Disadvantages
• Black in color, so unaesthetic.
• Radiolucent, so impossible to detect radiographically.
Glass Fiber Post
It consists of unidirectional glass fibers embedded in a resin matrix which strengthens the dowel without compromising the modulus of elasticity.
Restoration of Endodontically Treated Teeth 87
Advantages
• Aesthetically acceptable.
• Modulus of elasticity similar to dentin. • Biocompatible.
• High resistance to fracture. • Easy retrieval.
Disadvantages
• Poor radiographic visibility. • Expensive.
• Technique sensitive.
WHAT FACTORS ARE TO BE CONSIDERED WHILE PLANNING POST AND CORE?
• Retention and the resistance form • Preservation of tooth structure • Ferrule effect
• Mode of failure • Retrievability.
Retention and the Resistance Form
Post retention refers to the ability of post to resist vertical dislodging forces. Post resistance refers to the ability of the post and the tooth to with stand the lateral and rotational forces.
Factors affecting post retention
• Post length • Post diameter
• Post taper and design • Luting agent
• Luting method
• Canal shape
• Post position in dental arch.
Factors affecting post resistance
• Post length • Rigidity
• Presence of antirotational features • Presence of ferrule.
Post Length
Accepted guidelines for determining post length include: • Post should be equal to clinical crown length. • Post should end halfway between the crestal bone
and the root apex.
• Post should be as long as possible without disturbing the apical seal.
Post Diameter
It has been seen that post diameter has little difference in the retention of post, but increase in post diameter increases the resistance form but it also increases the risk of root fracture.
Post Design
Different types of post designs available are (Fig. 20.2): • Tapered, smooth sided
• Tapered, serrated type • Parallel smooth sided • Parallel serrated type
*Generally parallel sided are more retentive than tapered ones.
Luting Agents
Commonly used dental cements for luting the posts are zinc phosphate, polycarboxylate, glass ionomer cement, resin-based composite.
Luting Method
Luting method also affects the retention of post. Since luting agents are susceptible to moisture present in the canal so canal should be absolute dry.
Preservation of the Tooth Structure
One should try to preserve maximum of the coronal and radicular tooth structure whenever possible.
Ferrule Effect
Ferrule is encircling collar of metal band or ring used to fit the root or crown of a tooth (Fig. 20.3). Basically, it braces the tooth and protects it against the wedging stresses and vertical root fracture.
Fig. 20.3: Ferrule effect
Mode of Failure
All post systems show some percentage of failure but with variable range.
Failures of posts and core can occur in form of: • Post fracture
• Root fracture • Core fracture • Post dislodgement
Retrievability
Ideally a post system selected should be such that if an endodontic treatment fails, or failure of post and core occurs, it should be retrievable.
WHAT ARE STEPS OF PREPARATION OF THE CANAL SPACE AND THE TOOTH FOR
ACCEPTING POST AND CORE?
1. Plan for the length and diameter of the post according to the tooth type.
2. Remove the gutta-percha filling.
3. Prepare the canal space using Gates-Glidden drills or Peeso reamers.
4. Following the preparation of canal space, preparation of coronal tooth structure is done (Fig. 20.4).
5. Remove all the unsupported tooth structure (Fig. 20.5).
6. Place an antirotational notch with the help of cylindrical diamond or carbide bur.
7. Ferrule effect is provided thereafter. Ferrule ensures that the final restoration encircles the tooth apical to the core and rests on sound tooth structure. It also presents the vertical root fracture by posts.
8. Finally eliminate all the sharp angles, undercuts and establish a smooth finish line (Fig. 20.6).
Restoration of Endodontically Treated Teeth 89
WHAT SHOULD BE THE IDEAL PROPERTIES OF A CORE MATERIAL? ENLIST VARIOUS CORE MATERIALS
Core is the supragingival portion that replaces the missing coronal tooth structure and forms the center of new restoration.
Ideal Requirements for a Core Material
• Biocompatibility • Ease of manipulation
• Ability to bond to tooth structure and post
• Coefficient of thermal expansion similar to dentin • Minimal water absorption
• Dimensionally stable • No reaction with chemicals • Low cost
• Easily available.
Various Core Build-up Materials Available
• Dental amalgam
• Resin modified glass ionomers • Composite resin
• Reinforced glass ionomers cement.