Base & Liners

Question 1

What is the single most important factor to consider, from the pulp health standpoint, when prepping a cavity?

Answer 1

Remaining dentin thickness above the pulp is the single most important factor in protecting the pulp from insult

Question 2

What does evidence suggest is the main cause of pulpal injury following restorations?

Answer 2

Bacterial growth beneath the restoration

Question 3

What induces the sensation of pulpal pain w/in teeth?

Answer 3

Pulpal Hydrodynamics. Fluid movement w/in the dentinal tubules, caused by cutting or water/air spray, results in the movement of pulp afferent nerves and the sensation of pain

Question 4

Why do hot/cold stimuli cause pain?

Answer 4

The changing size of the restorative material changes flow rates of fluid from the dentinal tubules out into marginal gaps b/t the dentin and the restoration. This change in flow rate causes the sensation of pain.

Question 5

In attempting to stop tooth pain, in theory, what is the best strategy?

Answer 5

Occlude dentinal tubules

Question 6

What is a smear layer and how does it help prevent post-op sensitivity? What kind of protection does it provide?

Answer 6

A smear layer is cutting debris from rotary instruments, which is compacted on the cut surface sealing some degree of dentin tubules (~80%). This provides Chemical Protection by limiting diffusion of potentially toxic substances to pulp.

Question 7

What are cavity sealers? Give 3 examples.

Answer 7

Cavity sealers provide a protective coat for freshly cut tooth structure of the prepared cavity. Includes varnishes, desensitizers, and dentin bonding agents.

Question 8

Gluma is a desensitizer often used in dentistry. What are Gluma’s two main ingredients and what is the purpose of each?

Answer 8

1. 35% HEMA (HydroxyEthyl MethAcrylate) - HEMA is a resin, which allows Gluma to flow into the preparation and conform to it.
2. 5% Glutaraldehyde - Antibacterial component to gluma

Question 9

What is the purpose of a liner?

Answer 9

Provides protective barrier, to protect dentin against residual reactants diffusing out of a restoration and/or oral fluids which may penetrate leaky tooth-restoration interfaces.

Question 10

Calcium Hydroxide used to be the most popular liner used in dentistry, however, more recently it has fallen out of favor. Why?

Answer 10

Calcium Hydroxide frequently will dissolve under the restoration material. Happens before amalgam can corrode and fill in the dentinal tubules. This causes microleakage & recurrent caries.

Question 11

What makes Zinc Oxide Eugenol (ZOE) such an attractive liner? What is a major problem with ZOE?

Answer 11

ZOE is believed to have a mild sedative effect on pulp thanks to the eugenol portion and it is bacteriocidal. However, ZOE inhibits polymerization of composite resins & therefore can only be used with metallic restoration products.

Question 12

What is the major use for Zinc Oxide Eugenol now?

Answer 12

ZOE is most often used as a sedative for temporary restorations.

Question 13

What is the major liner used today?

Answer 13

Glass Ionomer

Question 14

Why is Glass Ionomer such an effective liner? (3 things & result of the 3 characteristics)

Answer 14

1. Glass Ionomer chemically adheres to dentin, which physically excludes bacteria.
2. Bonds to composite, unlike ZOE
3. Releases fluoride ions in low concentrations for extended periods of time.
   RESULT = favorable post-op Pulpal response

Question 15

What is a base?

Answer 15

Bases are thick materials (1-2mm vs 0.5mm for liners) used to provide thermal protection for the pulp & to supplement mechanical support for the restoration by distributing local stresses from the restoration across the underlying dentin surface. Used when very close to pulpal chamber as a dentin replacement.

Question 16

Mechanical support provided by a base, allows resistance against disruption of thin dentin over pulp during amalgam condensation or cementation procedures, however, increased base thickness has been proven to show what negative effect in terms of restoration longevity?

Answer 16

Increased base thickness causes decreased fracture resistance of the restorative material.

Question 17

What clinical conditions call for the use of a base? What are the only two walls that base should be applied to?

Answer 17

Bases should be used clinically when dentin depth falls below 2mm, to augment dentin back to the 2mm threshold level. Apply only to pulpal & axial walls.

Question 18

Zinc Phosphate has been used successfully as a base for over 100 years thanks to its excellent physical properties and support for overlying restorations. What are 3 reasons why zinc phosphate has fallen out of favor?

Answer 18

1. Zinc phosphate is very acidic shortly after mixing, which may lead to pulpal problems
2. Zinc phosphate does not chemically bond to dentin
3. The mixing of Zinc Phosphate is very technique sensitive, making bases highly variable, and if improperly mixed will be too acidic. Operator controls properties such as strength of the base.

Question 19

ZOE liner has been modified to form a base, which is also used as a temporary restorative material. What is this base? Like ZOE what is a drawback to this modified base?

Answer 19

IRM. IRM is not compatible with composite restorations.

Question 20

What is the most common base used today?

Answer 20

Resin-modified glass ionomer. Note: Glass ionomer can be used as a liner or as a base depending on how it is mixed.

Question 21

What is the standard procedure for when there is a deep (less than 1mm) preparation?

Answer 21

1. Lay medicament, liner Calcium Hydroxide over deepest parts.
2. Lay resin-modified glass ionomer over the calcium hydroxide.
3. Add restorative material on top.