Materials Used in Pulp Protection

Varnishes and other surface treatments

(a) Varnishes:

Properties Very low viscosity containing a relatively large proportion by volume of a volatile solvent
Purpose of use For application to dentine in order to decrease permeability
Disadvantages ®  Because of the high proportion of solvent, and subsequently the large volume reduction on drying, the ultimate film is relatively porous and therefore not very effective

®  Relies, to a degree, on presence of an intact smear layer, with which it may combine, to reduce permeability

Limited uses They were originally used to decrease early microleakage around amalgam restorations and then wash out to be replaced by corrosion products, and this remains their best use

(b) Resin sealants:

Properties Light-activated, Unfilled resins. Most are relatively viscous and do not set through loss of solvent but by either chemical or light activation.
Purpose of use ®  Used as cavity primers or bonding agents with composite resins;

®  They seal dentin more effectively after smear layer has been removed;

®  They reduce the potential for ingress of bacteria or their byproducts.

Disadvantages Whether or not the brief, chemical risk they pose to odontoblasts is outweighed by their possible longer term benefits, by enhancing seal against microleakage, has yet to be determined.

(c) Remineralising solutions:

Properties Chemical treatments using topical fluoride or oxalate salts
Purpose of use ®  Designed to reduce dentinal permeability à lowered risk of ingress of bacteria and their products;

®  Successfully reduce dentinal sensibility.

Drawbacks The long-term benefits of such treatments for pulp health have not yet been established.

(d) Liners and bases:

The main differences between liner and base are the thickness and strength.

LINER BASE
The term liner is used for a thin wash A base is a relatively thick material strong enough to provide resistance form and to become an intrinsic part of the ultimate restoration. A base can be regarded as a dentin substitute.

 Calcium hydroxide (Ca[OH]2):

Mechanism of action During Direct Pulp Capping, Ca[OH]2is placed on the exposed pulp àBecause it is strongly alkaline [pH = 12-13] à there will be a degree of necrosis in adjacent soft tissue but, at the same time, bacteria fail to thrive in its presence à it will counter bacterial microleakage and, as it is not unduly toxic, exposed and relatively healthy pulp tissue in the vicinity usually survives à Calcific scar tissue may be laid down beyond any area of necrosis and may successfully bridge the lesion if no bacteria remain.

 

(Previously, it was believed that Ca[OH]2 provides Ca++ ions, thus aiding remineralisation but this has since been discounted).

Drawbacks Over time, Ca[OH]2 is likely to be washed out from under any restoration which does not have a complete marginal seal, so its effect may be transitory. Because of this it is not recommended as a liner or base. Its use should be limited to protection of an actual pulp exposure only. A very small quantity of an autocure cement should be placed over the area of soft tissue exposure, then a seal created over it with a glass-ionomer.

Zinc phosphate cement:

Properties ·     Despite its acid nature, it is well tolerated by the pulp if placed on intact dentin because of buffering of the unreacted acid by hydroxyapatite.

·     There may be immediate and short-term pain if placed on the dentin, due to osmotic effects on dentin tubule fluid.

Current use ® Used for many decades as an insulating base material beneath metallic restorations, and also as a luting agent.

® As it has no therapeutic effect upon the pulp there seem to be few indications for its use as a lining or base material.

Zinc oxide-eugenol (ZOE):

Purpose of use ®    Management of deep, active carious lesions (pulp Therapy);

®    Used as lining and base material.

Relevant Properties ·     When ZOE is placed on intact dentin, it is unlikely to harm pulp cells;

·     It is possible for ZOE to develop local anaesthetic and anti-inflammatory reactions in adjacent pulp tissue (obtundant/ soothing/ anodyne effect).

·     Like GIC, it provides an effective antibacterial seal – Any gap between the cement and dentine will contain a high concentration of eugenol, which is strongly bactericidal.

·     Any available eugenol may also inhibit bacterial metabolism within dentin.

Drawbacks ·  Despite these therapeutic benefits, the cement slowly hydrolyses with time, leaving a residue of soft zinc hydroxide;

·  Eugenol inhibits the polymerization of composite resin, so it must not be used anywhere prior to, or in relation to, resin restorations or resin luting cements.

·  Should NOT be used in direct contact with exposed pulp tissue, since the release of eugenol by hydrolysis is markedly greater due to the wetness of the tissue. A concentration of eugenol sufficient to kill pulpal cells may develop rapidly in adjacent vital tissue, and the level may be sustained for several days.

Limited Indications ®  Used in situations where the dentin is intact and some form of indirect pulp therapy or caries therapy is required.

®  It is an effective temporary restoration in those situations where it is intended to remove infected surface caries and leave demineralized affected caries behind. Generally, within three weeks it will be safe to proceed with a permanent restoration.

®  Due to the problem of long term hydrolysis, its use should be limited to less than three months as a temporary restoration.

Glass-ionomer Cement:

Properties ®    Glass-ionomer, when placed without pressure on intact dentin, poses no chemical risk to the pulp.

®    With the development of an ion-exchange layer, it creates an effective antibacterial seal.

®    It shows very low solubility à material of choice for use as base, or dentin substitute, beneath all plastic restorations.

®    GIC will adhere to remaining tooth structure through the ion exchange mechanism.

®    It is apparently mildly antibacterial because of fluoride release.

Uses ®  GIC has potential as long-term temporary, or provisional, restoration in the treatment of active caries. Following removal of infected dentin, a strong mix of GIC is placed in the cavity over the remaining affected dentin and allowed to set. In the presence of dentinal fluid from the affected dentin there is likely to be a reasonable release of fluoride as well as calcium and phosphate ions from the cement and these will be useful in the remineralizing process.

®  Glass-ionomer is the material which has been recommended for Atraumatic Restorative Technique (A.R.T.) technique and it has been shown to be very effective in stimulating remineralization of affected dentin over a short period of time, providing it is used with a high powder content.

In Summary:

Amalgam

 

o   Very low toxicity to pulp;

o   Marginal seal through: copal varnish, remineralising solution, or glass-ionomer resin bond.

Luting crowns & bridges

 

Leave smear layer intact, or Seal surface with –

o mineralising  solution

o two layers of  varnish

o resin-dentin bond

Calcium hydroxide

 

o   Very high pH;

o   Highly toxic to bacteria;

o   Causes necrosis to living tissue;

o   Use in very small quantities only;

o   Seal with glass- ionomer.

Zinc phosphate cement o   Very limited use as a lining only.
Zinc oxide and eugenol o   Anti-inflammatory;

o   Antibacterial;

o   Mildly anesthetic;

o   Good seal against microleakage.

Glass-ionomer cement o   Ion-exchange adhesion;

o   No microleakage;

o   Antibacterial;

o   Stimulates remineralization.