2- Auxiliary Retention Systems

what are auxillary retention systems?

elements that provide retention to the restoration

they retaina core in a tooth with loss of coronal structure

What are the types of auxiliary retention systems?

Pins- vital

Posts- non vital

what are pins?

Small metal rod driven into dentin on one side, other is embedded in sealing material to aid retention

When is the use of pins indicated?

significant loss of coronal structure due to caries or trauma

when preparation design alone doesnt provide enough retention

always in dentin, never enamel or pulp

Vital teeth

When is the use of pins not indicated?

For restoring teeth with severe malocclusion

If direct resto not possible due to anatomy or functional considerations

What should we evaluate on the periapical x ray to correctly place the pins?

location of position and size of the pulp chamber

thickness of dentin

inclination of crown axis relative to root axis and adjacent tooth

What should we evaluate on the location of pins to correctly place the pins?

place midway between pulp and tooth surface

keep 2mm away from pulp and periodontium

at cervical third of molars and premolars

as close as possible to line angles

0.5mm away from axial or vertical wall cavity

on flat surfaces

which areas should we not interfere with when inserting pins?

cavity walls or matrix

pulp chamber

isthmus

furcation areas

small amounts of dentin

mesiofacial corners of molars

222 rule

length of pin inside dentin and remains outside should be 2mm- if not- fractures or disinserts pin

what are disadvantages of pins?

doesn’t increase the strength of restorative materials- may even decrease- induces stress- cracks, microleakage, pulpal damage

external or pulpal perforation

perforation in periodontium

chance of microleakage

looseness in duct- due to drill defects

fracture of drill

what are posts?

only placed in teeth that have RCT with large portions of tooth missing- one part inside canal other protrudes into crown

what procedural accidents may occur during the post space preparation?

strip perforation- in apical portion of root

increased risk of root fracture if oversized channel

how are posts classified? (5) according to…

modulus of elasticity

technique of clinical use

manufacturing method

its shape

composition

How are posts classified according to the modulus of elasticity?

Higher MOE- rigid- e.g metallic and ceramic

Lower- flexible- fiberglass and carbon fiber- MOE similar to dentin- this avoids stress and root fractures

How is force distributed in posts with different modulus of elasticity?

When materials with different mechanical properties are combined

Stresses concentrate in the weaker one at the root apex- causes fracture

If both have similar elasticity- act as a monoblock- distributing forces evenly

In what 3 techniques are posts used?

Direct- ready made in diff sizes, shapes and compositions

Indirect- made in lab using impression of root canal

Semi direct- mix impression of root canal and prefabricated fiber post and composite

What is an emdocrown?

Type of crown designed for a tooth that’s undergone RCT or has significant structure loss

endocrowns are anchored within tooth structure extends in pulp chamber for stability

How are posts classified by shape?

Conical (tapered)- less retentive than cylindrical but more anatomical in apical zone- don’t thin in roots

Cylindrical (parallel)- good retention but need to prep apical zone of canal for adaptation- risk of fractures and perforation

Double taper- more ret than conical, has 3 parts- coronal- cylindrical so retains filling material, middle- conical, has taper, apical- minor taper- usually made of quartz fiber  

What are accessories?

Bundled glass fiber reinforced composite

Many fine individual posts 0.3mm diameter

Remove sleeve- fibers spread inside the root canal, adapting to its exact shape- translucent so aesthetic

How can posts be classified according to its composition?

Metallic 

Ceramic

Carbon fibre 

Glass fibre- 42% longitudinal glass fiber, 29% epoxy resin, 29% inorganic particles, can either transmit lighti or not  

What are morphological requirements to place a post?

No cavities, fractures or resorption

Enough length and thickness

Straight root, round wide canal

In multi radicular teeth- choose thickest, longest most straight root

In which root should posts be placed?

Upper molars- palatine

Lower molar- distal 

Upper premolar- palatine 

Lower premolar- single 

What are the clinical requirements to place a post?

X ray

Correct RCT

Good apical sealing

No radiolucent lesions

2mm of supragingival ferrule

If bone crest is below post due to bone loss- no resto

What are the requirement of the post length in order to place a post?

Post enters up to 2/3 of root, leaves 4mm to apex, 2mm to dentin wall

Longer post- greater retention 

Length equal or more than clinical crown 

In periodontal teeth- length=half length of root surrounded by bone

How do you place a direct prefabricated glass fibre post?

X ray, clinical eval, isolation- only use rubber dam when inserting post not when removing gap to avoid perforations

Post space preparation- create a correct entry, then use Gates-Glidden drills #2, #3 to remove GP, drill corresponding to the chosen post size, insert post, adjust and cut to desired length

Surface treatment of post and canal with acid etch and alcohol 

Dual adhesive system inside canal

Apply fluid composite and place post, polymerise

Manufacture cure with same composite or hybrid 

What are the challenges when a direct fibreglass post bonds to root dentin?

Limited vision and access

Residual GP 

Hard to apply and cure adhesives in root canal 

Hard to rinse etchings

Solvent may not completely evaporate