A dental student’s guide to…luting cements

Luting CementsIn this month’s student’s guide, Hannah Hook explores luting cements, their uses and the pros and cons to the different cements available.

The long-term success of an indirect fixed prosthesis is influenced by a variety of factors. One of these is the selection of a suitable luting cement.

Luting cements hold indirect restorations (such as crowns and bridges) in place for an indefinite amount of time (Ladha and Verma, 2010). They also fill the void between the tooth-restoration interface.

There are certain ideal requirements that a luting cement should meet.

Ideal requirements of luting cements (Ramaraju et al, 2014)

  1. Biological: it should not cause harm to the tooth or tissues
  2. Chemical: it should be chemically inert with a neutral pH and bond to enamel/dentine. It should not dissolve in fluids and stay intact
  3. Rheological: it should have a low film thickness enabling easy flow of the cement, an increased mixing and working time, and a decreased setting time
  4. Mechanical: it should have high compressive strength, tensile strength, and modulus of elasticity. It should exhibit minimal dimensional change on setting. It should bond to enamel/dentine
  5. Thermal: it should be a good thermal insulator and have a coefficient of thermal expansion similar to the tooth and fixed restoration
  6. Aesthetic: it should not alter the colour of the tooth or restoration. It should be radiopaque to enable detection of secondary caries or voids.

With this extensive list, it is not surprising to hear that there is no single luting cement that meets all the ideal requirements. This explains why there are multiple cements available.

Most luting cements will satisfy the ideal requirements to a certain extent; however, each has their own strengths and weaknesses.

A major reason for failure of crowns is due to them becoming uncemented (Ladha and Verma, 2010). Therefore, it is important to know which luting cement is best suited to various situations enabling an informed decision and increased longevity of the restoration.

There are four main types of dental luting cements, these are:

  1. Zinc phosphate
  2. Zinc polycarboxylate
  3. Glass ionomer cement (GIC)
  4. Resin modified glass ionomer cement (RMGIC).

Zinc phosphate

Composition: powder (zinc oxide, magnesium oxide, silicon dioxide, bismuth trioxide, calcium oxide, barium oxide) and liquid (phosphoric acid, water, buffering agents).

Example: DEHP zinc phosphate cement, Detrey zinc phosphate cement.

Strengths: good compressive strength. Sufficient film thickness. Reasonable working time. Can be used in regions of high masticatory stress or long span prosthesis. Long clinical history and resistant to water dissolution (Ladha and Verma, 2010; Ramaraju et al, 2014).

Weaknesses: no adhesion to tooth. Requires mechanical retention. Dissolves in acids. Lacks antibacterial properties. Highly acidic (can cause pulpal sensitivity). Low tensile strength (Ladha and Verma, 2010; Ramaraju et al, 2014).

Indications: metal supported restorations with mechanically retentive preparations.

Contraindications: composite and all ceramic crowns due to lack of adhesion. Non-retentive preparations (Ladha and Verma, 2010; Ramaraju et al, 2014).

Zinc polycarboxylate

Composition: powder (zinc oxide, magnesium oxide) and liquid (polyacrylic acids, copolymer).

Example: Poly-F Plus, DEHP polycarboxylate cement, Detrey zinc polycarboxylate cement.

Strengths: no adverse effect on the pulp. Bonds to enamel and dentine. Bonds to stainless steel. Some resistance to water dissolution. Fluoride release. Good compressive strength (Ladha and Verma, 2010; Ramaraju et al, 2014).

Weaknesses: low adhesion. Low tensile strength. Difficult to obtain low film thickness. Dissolves in acids. Manipulation is critical. Early rapid rise in film thickness (may interfere with proper seating) (Ladha and Verma, 2010; Ramaraju et al, 2014).

Indications: metal supported restorations with mechanically retentive preparations. Can also be used for poorly retentive provisional restorations.

GIC

Composition: powder (silica, alumina, fluorides) and liquid (polyacrylic acid, copolymers, tartaric acid, water).

Example: Aquacem, Ketac Cem, Fuji.

Strengths: fluoride release (anti-cariogenic). Absorbs fluoride from the oral environment. Thermal expansion similar to tooth. Some resistance to acid dissolution. Adhesion to tooth and metal. Easy to use. Effective when used appropriately (Ladha and Verma, 2010; Ramaraju et al, 2014).

Weaknesses: slow setting initially. Sensitive to early moisture contamination (protect with fluoride varnish). Can cause pulpal sensitivity initially. Low tensile strength. Superseded by RMGIC. Inadequate wear resistance (Ladha and Verma, 2010; Ramaraju et al, 2014).

Indications: metal supported restorations with mechanically retentive preparations. Crowns with strengthened cores (where mechanically retentive). Where moisture control is adequate.

RMGIC

Composition: hybrid formula of resin and GIC.

Examples: Relyx luting cement, Fuji Plus, Fujicem

Strengths: Superior compressive and tensile strength to GIC. Fluoride release. Less sensitive to early moisture during setting. Easy to use. High bond to dentine. Adhesive to tooth and metal. Low film thickness. Decreased solubility (Ladha and Verma, 2010; Ramaraju et al, 2014).

Weaknesses: cement expansion (can crack ceramic restorations). Polymerisation shrinkage. Excess needs removing quickly. Increased water absorption due to HEMA. Excess cement is difficult to remove (Ladha and Verma, 2010; Ramaraju et al, 2014).

Indications: metal supported restorations with mechanically retentive preparations. Crowns with strengthened cores (where mechanically retentive).

Summary

  • Luting cements are used to hold indirect prosthesis such as crowns and brides in place
  • There is a list of ‘ideal requirements’ that a luting cement should meet, however none manage to completely fulfil the criteria
  • There are four main types of luting cements: zinc phosphate, zinc polycarboxylate, GIC and RMGIC
  • Each luting cement has its strengths and weaknesses, which should be considered when selecting which one to use.

References

Ladha K and Verma M (2010) Conventional and contemporary luting cements: An overview. J Indian Prosthodont Soc 10: 79-88

Ramaraju DV S, Krishna Alla R, Ramaraju Alluri V and Makv R (2014) A Review of Conventional and Contemporary Luting Agents Used in Dentistry. Am J Mater Sci Eng 2: 28-35


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