3.2 POST AND CORE RESTORATION

what is post and core restorations used for?

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

what is the principle of tooth preparation?

1. conservation of tooth structure which involves canal preparation

2. retention form (2/3 of the root)

3. resistance form

what is the Core?

substitution of the missing hard dental tissues of the tooth crown. it replaces fractured or missing coronal structure and retains the final restoration or crown.

what is the Post?

rigid restorative material that connects the core to the root inside the root canal. Placed within the body of the root of a tooth that has been treated with root canal treatment.

how does dowel length effect its retention?

• longer dowel/post length = greater retention

• Dowel length >/= crown length = success rate > 97.5%

• Dowel</= ¾ crown length = less success than no dowel

by how much does a dowel increase resistance to lateral forces on crown?

by 15-48%

what can dowels be made of?

metallic and non metallic

metallic = stainless steel, titanium, brass, chromium-containing alloy

Non metallic = carbon fiber and fiberglass used in recent years

why do we use non metallic ceramic dowels for anterior teeth?

to avoid darkening of root and gingiva

why do fiber dowels have poor torsional resistance?

due to low torsional stiffness

why do zirconia dowels have poor torsional resistance?

due to lack of bonding

what are the two types of dowel systems?

• passive (cemented) dowel system

• active (threaded) dowel system

how is the dowel secured into the root canal in passive dowel system?

by cement

how is dowel inserted into root canal in active dowel system?

with help of threads or grooves on the dowel to engage with the root canal walls. These threads create a mechanical interlock, enhancing retention

what effect does the length of the post have?

using the longest possible post ensures that the forces transmitted from the crown are distributed over as much of the root as possible giving greater retention

2/3 root/post length should equal crown length

what effect does the diameter of the post ?

• shouldn’t exceed 1/3 root diameter; maintain 1mm sound dentin circumferentially

What does a parallel post ensure?

the greatest retention of the post within the canal

what does smooth-surfaced post do?

although less retentive than serrated or threaded post surfaces, transmits the least amount of force to the tooth structure

variations in dental restoration materials of post and core?

• composite fiber reinforced

• ceramics

• metal (gold, non-precious and precious alloy)

what are the variations in manufacturing methods of post and core?

• prefabricated

• made by casting

• made by sintering

• made by polymerisation

• made by CAD/CAM

what does the canal preparation entail?

enlarging the canal beyond the largest file size used

what is the coronal part preparation?

remove undercut and ferrule (metal band or ring) to increase fracture resistance

what are some factors that affect retention?

• post length

• post diameter

• surface texture

• post shape

how does surface texture affect retention?

serrated and roughened posts have better retention than smooth posts

how does post shape affect retention?

tapered for tapered root canals, parallel for more retention and less chance of fracture

how does post design influence stress distribution and resistance?

• threaded posts may cause stress concentration, while cement layers provide better stress distribution

who introduced post and core crown?

P. Fauchard in 1746

when is post and core crown used?

when tooth have a very short crown and abutment alone cannot provide enough retention for the future restoration. It’s a way to strengthen and support devitalised teeth

what are the stages to prepare for post and core restoration?

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

2. preparation of root canal: root part of the post and core is prepped with calibrated mechanical burs. post reaches 3-5mm of the orificium, taking up 2/3 of canals length; creating the most favourable ratio of root post to crown length as 2:1

3. prep of contra rotational elements

4. removal of thin walls less than 1mm

how does the diameter differ in cervical area of root compared to middle root section?

• the width of the middle root section is 1.2-2 mm smaller than one at cervical area

• diameter of post in cervical zone must not exceed the width of the tooth wall on any side. prep for the post has a slightly ellipsoidal shape, which is preferable than the round configuration

what is direct post and core restoration?

• factory made post (metal or fibre-reinforced glass) and composite or cement; usually used for single tooth restoration

what are steps of indirect post and core restoration?

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

what materials are used for indirect post and core restoration?

• metal alloy or/and ceramics; usually used for multiple teeth or tooth for multiple canals

why is ferrule affect important?

it helps to strengthen the tooth and improve the long-term success of dental restorations. By preserving the natural tooth structure and providing support, the ferrule effect can help prevent future complications

how do you create a ferrule effect?

at least 1mm of dental tissue should be present above the preparation junction. This means that when a dental crown is placed, it acts like a ring, clamping the tooth and increasing its resistance to fracture

what is a ferrule?

a metal band or ring that is used to fit around the root or crown of a tooth, purpose is to preserve as much of the natural tooth structure as possible

what are advantages of post and core restorations?

• allows restorations of severely damaged teeth and provides support for the crown

• can be used for certain corrections of improperly inclined teeth

what are disadvantages of post and core restoration?

• can be used only endodontically treated teeth

• increase risk of root fracture

• high risk of root perforation or root resorption

why are posterior teeth more prone to fractures?

• have a naturally divided occlusal surface, making them prone to vertical fractures even without caries.

in post and core restorations what is the minimum treatment for endodontics for molars and premolars?

placing a cast restoration with occlusal coverage, like MOD onlay

when should dowel care be used on premolars?

if the roots are adequately bulky

what is the success rate in coronal coverage of molars and premolars in restorations such as post and core?

94% success rate

what are posterior teeth more prone to because of their naturally divided occlusal surface?

• prone to vertical fractures even without caries

• should be wary of this when doing post and core

post and core preparation on a phantom model

preparation of an acrylic prototype

what are basic components of post crown?

• Crown - final restoration that is placed over the core, could be a full metal, full veneer or jacket crown

• Core - coronal extension or addition to the dowel post necessary to provide the desire retention for the final crown restoration

• Post - part of the restoration that extended into the root canal

what are the two types of post - crowns?

1. two unit post crown (post and core + crown)

2. one unit post crown (post + core + crown one piece)

when is a one unit post crown used?

• when tooth has very short clinical crown (like lower incisor), there may not be enough space within the tooth to create both a retentive core and a separate crown

• so a one piece post crown can be used, where the final crown restoration is a direct extension of the dowel post, this approach allows for combined solution

can the crown restoration of two unit post crown be replaced in the future?

yes, if needed, without disturbing the dowel core part of the restoration. This is particularly beneficial for young patients under 18 years of age

when is it not necessary to prepare the post crown parallel to second abutment in two unit post crowns?

when an endodontically treated tooth has an abutment for a fixed bridge (bridge retainer)

in two unit post crown what is the marginal adaption and fit of crown restoration independent of?

• any dowel that needs to be used

when preparing a tooth for post and core what is the first step?

• clean out the crown that is already in place, if the tooth structure underneath the crown is insufficient or weakened a dowel can be fabricated. the dowel acts as a support for the restoration

how is the core portion of the restoration formed?

• the dowel is lubricated and used as a matrix, core portion is then formed around the dowel, completing the pattern in the usual manner.