8. Biological Aspects Of Canal Instrumentation & Obturation

Question 1

The Kakehashi et al 1965 paper is useful in proving that bacteria is responsible for root canal infections. Briefly describe the findings and methods of this paper.

Answer 1

• This study compared pulp exposures in germ-free rats compared to conventional rats with a normally complex microflora
• It was found that pathologic changes such as pulpal necrosis and abscess formation occurred more frequently in the conventional rats group
• On the contrary, dentinal bridging indicative of healing started and completed in the group of germ-free rats, regardless of the severity of the pulpal exposure.
• This proved that the absence of a microbial flora is the major determinant in the healing of exposed rodent pulps

Question 2

The Moller et al 1981 paper is useful in proving that bacteria is responsible for root canal infections. Briefly describe the findings and methods of this paper.

Answer 2

• In this study, the pulps of monkeys were aseptically necrotized. After which, some canals were kept bacteria-free while some were infected by indigenous oral flora
• At the end of 6-7 months, the initially noninfected canals remained sterile with no inflammation in the apical tissues at the final samplings. On the contrary, teeth with infected pulp tissue showed inflammatory reactions in the periapical regions

Question 3

Asepsis is the foremost important principle of root canal success in vital tooth root canal treatment. Define asepsis.

Answer 3

It is a condition in which no living disease-causing microorganisms are present

Question 4

Bacteria in the root canals present themselves in many forms. Describe how we should go about cleaning the bacteria in following presentations:

1. Bacteria in the root canal lumen
2. As biofilms
3. Within the dentinal tubules, lateral canals and apical deltas
4. Extraradicular

Answer 4

1. Chemical irrigation and evacuation of infected material
2. Mechanical filing and chemical disruption of biolfilm
3. Chemical disinfection or entombing the bacteria
4. Apical surgery / Apicoectomy (resect 2-3mm of root tip)

Note: Apical delta refers to the branching pattern of small accessory canals and minor foramina seen at the tip or apex of some tooth roots.

Question 5

The apical deltas, lateral canals and dentinal tubules cannot be reached by mechanical instrumentation and chemical disinfection. What do we do about the bacteria found in these areas?

Answer 5

We entomb them through obturation. Obturation will trap these bacteria and their by-products, stopping their effects on periapical healing

Question 6

How long can a tooth be left with a temporary dressing?

Answer 6

3 months.

• While the zinc oxide in IRM and Cavit has bactericidal properties, this effect is neutralized by oral fluids over time
• IRM also has weak flexual and compressive strength and may fracture after prolonged occlusal stress
• If the tooth has to have a prolonged TD, we may consider using GIC instead of IRM and Cavit.