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Assessment of different types of cement for base filling

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Cement that is used as a base filling is supposed to protect from micro-organisms and serve as a thermal insulator from hot and cold that would otherwise be especially well conducted through metal filling materials, such as amalgam or gold. Furthermore, it protects from toxic materials and prevents dentine discolouration. The table below assesses the requirements for a material for dentine sealing and base filling:

Requirements Assessment
  • protection from toxic materials
  • impenetrable for toxic substances
  • prevention of dentine discolouration
Irritation of, and damage to, the pulp is not mainly caused by toxic substances contained in the filling material but predominantly by the toxic effects of micro-organisms.
  • thermal insulation
  • possibly low conductivity of temperature
All currently used types of cement are suitable for thermal insulation, ie they have a thermal conductivity similar to the dental hard substance which is clearly below that of metals.
  • mechanical stability
  • sufficient resistance to pressure
  • high elasticity module (E module), and
  • high flexibility
With regard to the resistance to pressure, phosphate cement and glass ionomer cement are suitable for use as a base filling; other cements do not exhibit sufficient resistance to pressure.
Calcium hydroxide salicylate ester cement, more so than other cements, has very poor results in this regard and can therefore not be used as a final base filling.
The only cement equivalent to dental hard substance with regard to the elasticity module is phosphate cement. All other cements are inferior, even glass ionomer cements.
  • chemical durability
  • insolubility to acid, and
  • sufficient resistance to pressure
A great disadvantage of calcium hydroxide salicylate ester cement is its chemical instability.
Calcium hydroxide is dissolved from dentine tubules by moisture, forming water-filled cavities facilitating entry and proliferation of micro-organisms.
The same applies to zinc oxide eugenol cement.
Eugenol is dissolved from the dentine tubules by the ambient moisture, also causing the formation of water-filled cavities.
This is also true of carboxylate cement which is soluble in water and saliva, and again dissolution results in water-filled cavities and subsequent decomposition by bacteria. In the past decades, this has often resulted in the loss of prosthodontic preparations that were fixed with carboxylate cement.
Glass ionomer cements are least soluble to water though rather sensitive to humidity entering during their initial setting phase. Their resistance to pressure and adhesion to dentine can thus be heavily reduced.
Phosphate cement is relatively little water-soluble but more soluble in an acid than in a neutral environment.
  • no hydraulic impact on dentine tubules (pump effect)
  • thermal volume behaviour as adequate as possible for the dental hard substance, and
  • chemical and mechanical volume stability
While glass ionomer cement (2 - 4.4 percent by volume) and phosphate cement (under 3.2 percent by volume) exhibit relatively little setting shrinkage, these values are clearly exceeded by those of other cements.
Carboxylate cement is subject to shrinkage of approx. 6.7 percent by volume.
A possible pump effect, however, can be a problem of glass ionomer cements; they adhere very well to the dentinal surfaces but are very susceptible to humidity. If dentine fluid leaches out from the open dentine tubules, this may negatively influence adhesion of glass ionomer cement to the dentine surface. This impairment can result in the formation of a cleft following polymerisation of composites used as a cover filling ("nano-leakage"). Adhesion of the composite filling to the surface of the glass ionomer cement is better than that of the glass ionomer cement to the dentine surface. If polymerisation leads to shrinking of the composite material, a minimal cleft between the glass ionomer cement and the dentine surface may develop. This might explain post-operative sensitivities following placement of composite fillings. The pain is caused by what is referred to as a "pump effect" that occurs if the glass ionomer cement does not completely seal the dentine tubules and mastication results in pressure on the odontoblast processes and pain to the pulp.
  • protection from micro-organisms
  • good adhesion to dentine
  • impermeability for micro-organisms and their toxins, and
  • possibly antibacterial effects
Animal studies demonstrate that bacteria have a more damaging influence on the pulp than the actual filling material used. However, more than anything, it is not the bacteria as such that penetrate the dentine to the pulp but their toxic substances. Therefore, current belief that pulp irritation following restorative treatment is largely caused by the material used for filling or base filling is not correct.
The effect of glass ionomer cement on bacteria is controversial.
Freshly mixed phosphate cement exhibits a clearly antibacterial effect which is significantly diminished after hardening. Antibacterial add-ons to base filling cement, such as calcium hydroxide or fluorides, however, are ineffective and should not be used as it is questionable whether they are able to dissolve from the cement which is a prerequisite for their antibacterial activity. However, if they do dissolve from the cement, the mechanical stability of these base filling cements will be clearly reduced.
  • biocompatibility, no pulp damage
Acid is also released from the cement though it will usually be back to a neutral level within approx. an hour; glass ionomer cement is clearly more acid during the initial phase than phosphate cement. However, to date there has been no evidence of pulp damage being caused by this acid, even though this is the usual presumption. Pulp and dentine have sufficient buffer capacities in order to cope well with an acid attack for a short period of time.
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Summary of assessments of cements for base fillings

Calcium hydroxide cement

Calcium hydroxide cement exhibits reduced mechanical stability and consistency and is absorbed to a certain extent. Due to its poor mechanical properties, there is no indication for calcium hydroxide cement as a final base filling. Despite attempts to increase the stability of these types of cement by the addition of synthetic material, their mechanical stability is not sufficient. Furthermore, the specific benefit of calcium hydroxide is lacking.

Aqueous calcium hydroxide suspensions are clearly superior to those hardening because of their higher pH value.
However, aqueous calcium hydroxide suspensions should be applied in layers as thin as possible when they are used in indirect capping in the treatment of deep caries. If the layer is too thick, adhesion and mechanical properties of the actual base filling may be impaired.

Zinc-oxide eugenol cement

Zinc-oxide eugenol cement displays relatively high solubility and reduced stability to pressure combined with the cytotoxic and neurotoxic effects of eugenol.

There is no indication for zinc-oxide eugenol cement as a final base filling.

Furthermore, eugenol inhibits polymerisation of synthetics.
Therefore, this cement should not be used for base fillings in modern adhesives dentistry.

Ethoxybenzoic acid (EBA) and ZOE cements

EBA and ZOE cements are relatively elastic, flexible and easily shapeable, display only little retention and are soluble.
This type of cement is also not indicated for use as a base filling.

Carboxylate cement

Stability to pressure and E module are reduced in carboxylate cements; their shrinking during hardening is increased, their solubility high.
This type of cement is also not suitable for use as a base filling.

Glass ionomer cements

Glass ionomer cements display good adhesion to dentine and a colour similar to teeth and are especially suitable for use as a base filling in adhesive technology.
However, their mechanical stability and their E modules are lower than with phosphate cement.

Cermet glass ionomer cement

Adhesion of cermet glass ionomer cement to dentine is worse than that of glass ionomer cement alone. Their colour is not similar to that of teeth, their E module is lower, and there is a risk of fractures along the metal filings. Furthermore, the metal in the filling material may react with the added silver particles in cermet glass ionomer cement.
This type of cement is also not indicated for use as a base filling.

Zinc oxide phosphate cement

The mechanical stability of zinc oxide phosphate cement is clearly superior to that of all other cements used for base fillings and has been tried and tested in the field of dentistry since 1878. Handling of zinc oxide phosphate cement is uncomplicated and it is relatively cheap. Acid released from this cement will not damage the pulp.
Therefore, phosphate cement is recommended for use as a standard base filling with all types of filling materials and procedures.

Practical advice for cements used as a base filling

Amalgam fillings should always have a phosphate cement base filling; in flat cavities, cavity lacquer (e.g. Copalite) or a dentine adhesive may also be used under certain circumstances.

Composite fillings should be based on a base filling of phosphate or glass ionomer cement, at least in the deepest part of the dentine, close to the pulp. In especially flat cavities, dentine adhesives can be used.

The dentine close to the pulp should always be covered with a calcium hydroxide suspension prior to the treatment of deep caries or indirect pulp capping. In order to stabilise the calcium hydroxide, the suspension can additionally be covered with calcium hydroxide salicylate ester cement before a base filling of phosphate cement or glass ionomer cement is applied.