2 - Auxillary retention systems in vital and non-vital teeth

What is an auxiliary retention system?

Elements that are used to improve the retention of a restoration

What are the auxiliary retention systems?

Pins, posts, post and core

What are the indications for auxillary retention systems?

Retain a core in teeth with extensive loss of coronal structure.

When we dont have enough retention with cavity preparation.

When are pins used?

Vital teeth

ALWAYS in dentin NEVER enamel or pulp. (cemented or driven in)

When are posts or post and core used?

In non-vital teeth after root canal treatment

When are pin Contraindicated?

• Significant malocclusions

• If direct restoration isnt possible (anatomic/functional reasons)

What are the rules for placing pins?

1. PA xray to evaluate:

   • Pulp chamber size + position

   • Dentin thickness

   • Relative crown/root inclination

   • Tooth axis respective of neighbouring teeth.

2. Location or distribution of pins:

   • Midway between pulp and tooth surface

   • Safe distance from pulp and periodontum (2mm)

   • Cervical third of posterior teeth

   • Close as possible to line angles

   • 0.5mm away from axial or vertical wall cavity

   • Always on flat surfaces

3. 2-2-2 rule

   • Length of pin inside and outside dentin should be the same (2mm)

   • 2mm inside - 2mm outside - 2mm covered in restoration material

   • IF length outside larger, lever forces can fracture/disinsert pin

What must you avoid when placing pins?

• Interferance with cavitary walls and matrices

• Pulp

• Isthmus area

• Furcation area

• Small amounts of dentin

• Mesiofacial corners of molars

What are the 4 types of pin systems?

1. Cemented pins

2. Friction-locked pins

3. Self threading pins

4. Cyanoacrylate pins

How are cemented pins used?

Drill 0.05mm wider than pin leaving room for cement

How do friction lock pins work and why are they in disuse?

Slot in dentin cut slightly lower than that of pin, which is inserted with force to reach bottom of prepared slot.

Drawbacks: dentine cracks, little retention

How do self-threading pins work?

Slot in dentin with 0.1 mm diameter, lower than pin. Pin works it’s own thread into slot wall.

How do cyanoacrylate pins work?

4mm pin, drill can only penetrate 2mm. (For 2-2-2 rule)

What are the disadvantages of pins?

1. Decreases strength of restorative materials, induce stresses in dentin which may cause:

   • Cracks in teeth

   • Microleakage

   • Pulpal damage

2. External or pulpal perforation

3. Perforation of periodontum (can cause tooth loss)

4. Chance of microleakage around pins

5. Looseness in duct (Laterally placed or defective drill) - issue with threaded pins, not cemented

6. Fracture of drill in slot - impossible to extract, leave it in place, put pin in another slot

Where are the body and head of a post positioned in the tooth?

Body - inside canal

Head - in crown

What procedural accidents are a risk when preparing and placing posts?

Strip perforation

Root fracture

According to what 5 things are posts classified?

1. Modulus of elasticity

2. Technique of clinical use

3. Manufacturing method

4. Shape

5. Composition

What is the desired modulus of elasticity (and hence material) for posts?

Elasticity similar to dentin (18GPa)

Fibreglass (20-40GPa) and carbon fiber

Ceramic and metal posts too ridgid - can cause fractures

What happens when two materials with different modulus of elasticity are joined?

Force is concentrated on more fragile material

What are the 3 different post techniques of clinical use (and manufacturing technique)?

1. Direct - Prefabricated

2. Indirect - Anatomical, canal impression needed, manufactured in lab, made in ceramic, noble metal or glass fibre

3. Semidirect - Anatomical, canal impression needed, made in clinic, with Prefabricated fibre and composite post

What is an endocrown?

For rtc teeth with significant structure loss, where normal crown not possible. Anchored within remaining tooth.

What are the different post shapes?

Conical (tapered) - Less retentive, more anatomical, dont thin root walls much, less clinical complcations

Cylindrical (parallel) - Good retention, need apical preparation, fracture and perforation risk

Double taper (parallel tapered) - good adaptation, better retention than conical. Most commonly used. Usually quartz fiber.

3 parts:

• Coronal - cylindrical, retains filling material

• Middle - conical (tapered)

• Apical - another minor taper

Accesories - Conical, bundle of posts of 0.3mm, filling in wide canals to reduce amount of cement. When sleeve removed they spread and cover entire canal. Adapt to any canals morphology.

What is the composition of glass fiber posts?

• Longitudinal glass fibers (42%)

• Epoxy resin (29%)

• Inorganic particles (29%)

Some are phototransmitters (cant be seen in xray), and some are opaque.

Can be direct or indirect. Manufactured in lab

What are the morphological and root requirements to place a post?

• No cavites, fractures or resorption

• Adequate length and thickness and morphology

• Straight root without curvatures, with round and wide canal

• Select thickest, longest and straighest root in multiradicular teeth

Where shoud you place the post in Upper/lower molars and premolars?

Maxillary molars - Palatine root

Upper premolar - Palatine root

Mandibular molars - Distal root

What are the clinical evaluation requirements for post placement?

• Radiography showing correct RTC, good apical sealing, and no radiological lesions or symptoms. If necesarry, do reendo to avoid future failures.

• 2mm supragingival ferrule (for retention)

• Periodontal status - periodontal disease must always be treated before restoration. (bone crest must be above post level)

How should you determine post length?

Should enter up to 2 thirds of the root, and be at least 4mm from the apex, and 2mm from dentin at root.

Length greater than or equal to clinical crown

In cases of periodontal teeth - length equal to half the length of root surrounded by bone

What is the clinical protocol of the placement of a direct prefabricated glass fiber 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

Potential oxidizing effect of NaOCl

Increased volume of luting cement to fill in space between post and root dentin wall

High C-factor (ratio of bonded to unbonded surfaces) May result in greataer polymerization stress

Variations in tubule density