4. Obturation And Coronal Restorations

Question 1

What are the biological and mechanical objectives of obturation?

Answer 1

In general, obturation is done to create a 3-dimensional seal along the length of the root canal system from the coronal opening to the apical termination. There are biological and mechanical objectives for doing this:

Biological:

•To provide an effective seal in the root canal system against bacteria and their products

Mechanical:

• To create a root-fill that resists dislodgement during subsequent coronal restoration
• To create a root-fill that may be removed completely if and when it becomes necessary
• To create a hermetic (complete & airtight) root-fill within the confines of the instrumented root canal

Question 2

What are the desirable qualities of Gutta Percha which allows it to be used as an obturation material?

Answer 2

1. Easy to insert and remove
2. Seals the canal 3-dimensionally
3. Dimensionally stable after insertion
4. Impervious to moisture
5. Radio-opaque
6. Non-staining

Note: GP cannot be used alone, must be used with a sealant

Question 3

What are some sealers used in obturation?

Answer 3

• Resin-based sealers such as AH Plus (however, can cause acute inflammation if extruded into PA tissues)
• Contemporary sealers such as calcium silicate. Calcium silicate has high pH during setting which gives it a bactericidal effect. It also has superior flowability and hydrophilic properties that allow it to set in liquid

In the past, eugenol-based sealers were popular

Question 4

What is the technique used for obturation? Describe all the steps in obturation.

Answer 4

Cold Lateral Condensation Technique

1. Select a GP cone which is the same size as the MAF. Place this cone at WL and check for fit (Tug-back). Then take out this master GP cone
2. Use a file one size smaller than MAF and coat the file with sealer. Insert file to WL then rotate anticlockwise as the file is withdrawn to deposit sealer on the canal walls. Do this twice to apply 2 coats
3. Coat the apical half of the master GP cone then seat cone to WL
4. Insert spreader in a watchwinding motion with apical pressure till within 1-2mm from WL. Insert accessory GP cones at the spreader’s length
5. Repeat process till apical 5mm is well obturated. Take mid-ob radiograph to confirm good obturation. Continue obturation past the 5mm till canal orifice is reached
6. To complete obturation, heat one end of a plugger. Place this end near to the canal orifice and sear off the excess GP in one clean sweep. Use a cold plugger to vertically condense the warm GP. Repeat till the GP is flushed with the orifice (for multi-rooted teeth) or 2mm below CEJ (single-rooted teeth)
7. Place a cotton pellet and seal the opening with a temporary coronal restoration such as Cavit (dressing must be at least 3mm thick!!). Expose a final obturation radiograph

Question 5

There are different spreaders: MF, F, FM, M. How do we determine which spreaders to use for the cold lateral condensation technique?

Answer 5

It depends on the taper, apical size and length of the canal we are about to obturate. In general:

• MF for MAF Sz30 and curved canals
• F for most of the large, straight and long canals (upper and lower anteriors)
• FM and M for large and straight canals that are shorter (palatal canals of upper molars and distal canals of lower molars)

Question 6

What are the 3 things we need to check before we start obturating a canal? Why are these important?

Answer 6

1. Adequate flare and apical stop: To allow dense and proper obturation. Apical stop prevents gross extrusion into the periapical tissues
2. Presence of debris at apical terminus: Place MAF and turn 1-2 full turns clockwise at length and pull
3. Spreader size and accessory cones: Select correct spreader and corresponding accessory cones (use the largest spreader that would go within 1mm of the WL without binding any canal walls)

Question 7

Why do we obturate to 2mm below CEJ for single-rooted teeth?

Answer 7

It is the ideal position to prevent labial discolouration of the tooth

Question 8

What are interim restorations and how are they classified?

Answer 8

Interim restorations are low-cost restorations with a limited period of function. They are of easily placed and removed and their removal will not compromise tooth integrity

• There are classified as Eugenol-based and Non-Eugenol based

Question 9

Name a Eugenol-based interim restoration material. What are its properties?

Answer 9

IRM (Intermediate Restorative Material)

• Zinc oxide-eugenol cement with polymer reinforcement
• Comes in a powder and liquid form
• High compressive strength, excellent abrasion resistance, good sealing properties and low solubility

Question 10

Name a Non-eugenol-based interim restoration material. What are its properties?

Answer 10

Cavit

• Self-cure, moisture hastens setting
• Contains zinc oxide, calcium sulfate, zinc sulfate, glycol acetate, polyvinyl acetate etc
• Easy to use with relatively low cost
• Setting expansion creates a good seal

Note: Low abrasion resistance means that Cavit cannot be used for high loading areas!!