In this month’s student guide, Hannah Hook explores lube cements, their uses and the pros and cons of the different cements available.
The long-term success of an indirect fixed intention is influenced by several factors. One of them is choosing the right rubber cement.
Luting cements hold indirect restorations (such as crowns and bridges) in place indefinitely (Ladha and Verma, 2010). They also fill the gap between the tooth restoration interface.
There are certain ideal requirements that a groove cement should meet.
Ideal requirements for tensile cements (Ramaraju et al, 2014)
- Biological: it should not cause damage to the tooth or tissues
- Chemical substance: It should be chemically inert with a neutral pH and bond to enamel/dentin. It must not dissolve in liquids and remain intact
- Rheological: should have a low film thickness to allow easy flow of cement, increased mixing and working time and reduced setting time
- Engineer: it should have high compressive strength, tensile strength and modulus of elasticity. It should show minimal dimensional change during adjustment. It should be attached to the enamel/dentin
- Thermal: it should be a good thermal insulator and have a coefficient of thermal expansion similar to the tooth and a stable restoration
- Aesthetic: it should not alter the color of the tooth or the restoration. It should be radiopaque to allow detection of secondary caries or cavities.
With this extensive list, it is not surprising that there is no one cement that meets all ideal requirements. This explains why there are many cements available.
Most rubber cements will meet the ideal requirements to some degree. However, each has its own strengths and weaknesses.
A major reason for failure of crowns is that they are not cemented (Ladha and Verma, 2010). Therefore, it is important to know which rubber cement is best suited for various situations, allowing for an informed decision and increased lifespan of the restoration.
There are four main types of dental cements, which are:
- Zinc Phosphate
- Zinc polycarboxylate
- Glass ionomer cement (GIC)
- 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: Cement DEHP zinc phosphate cement, Detrey zinc phosphate cement.
Strong points: good compressive strength. Adequate film thickness. Reasonable working time. It can be used in areas of high masticatory stress or long-lasting prostheses. Long clinical history and resistant to water dissolution (Ladha and Verma, 2010; Ramaraju et al, 2014).
Weaknesses: no adhesion to the tooth. Requires mechanical restraint. Soluble in acids. It has no antibacterial properties. Very acidic (may cause pulpal sensitivity). Low tensile strength (Ladha and Verma, 2010; Ramaraju et al, 2014).
Indications: metal restorations with mechanical retainers.
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.
Strong points: no negative effect on pulp. Bonds to enamel and dentin. Connections with stainless steel. Some resistance to water dissolution. Release of fluoride. Good compressive strength (Ladha and Verma, 2010; Ramaraju et al, 2014).
Weaknesses: low adhesion. Low tensile strength. Difficult to obtain low film thickness. Soluble in acids. Manipulation is critical. Early rapid increase in film thickness (may affect proper placement) (Ladha and Verma, 2010; Ramaraju et al, 2014).
Indications: metal restorations with mechanical retainers. It can also be used for poorly retained temporary restorations.
GIC
Composition: powder (silica, alumina, fluorides) and liquid (polyacrylic acid, copolymers, tartaric acid, water).
Example: Aquacem, Ketac Cem, Fuji.
Strong points: fluoride release (anti-caries); Absorbs fluoride from the oral environment. Thermal expansion similar to tooth. Some resistance to acid dissolution. Adhesion to tooth and metal. Handy. Effective when used appropriately (Ladha and Verma, 2010; Ramaraju et al, 2014).
Weaknesses: slow setting initially. Susceptible to early moisture contamination (protect with fluoride varnish). May cause pulpal sensitivity initially. Low tensile strength. Replaced by RMGIC. Inadequate wear resistance (Ladha and Verma, 2010; Ramaraju et al, 2014).
Indications: metal restorations with mechanical retainers. Crowns with reinforced cores (where mechanically retained). Where humidity control is adequate.
RMGIC
Composition: hybrid resin and GIC formula.
Examples: Relyx luting cement, Fuji Plus, Fujicem
Strong points: Higher compressive and tensile strength than GIC. Release of fluoride. Less sensitive to early moisture during setting. Handy. High bond with dentin. Glue on tooth and metal. Low film thickness. Reduced solubility (Ladha and Verma, 2010; Ramaraju et al, 2014).
Weaknesses: cement expansion (can crack ceramic restorations); Polymerization shrinkage. The excess needs to be removed quickly. Increased water absorption due to HEMA. Excess cement is difficult to remove (Ladha and Verma, 2010; Ramaraju et al, 2014).
Indications: metal restorations with mechanical retainers. Crowns with reinforced cores (where mechanically retained).
Summary
- Luting cements are used to hold indirect prostheses such as crowns and bridges in place
- There is a list of “ideal requirements” that a groove cement should meet, however none quite manage to meet the criteria
- There are four main types of cements: zinc phosphate, zinc polycarboxylate, GIC and RMGIC
- Each rubber cement has its strengths and weaknesses, which should be considered when choosing which one to use.
bibliographical references
Ladha K and Verma M (2010) Conventional and modern lubricity 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 modern sliding agents used in dentistry. Am J Mater Sci Eng 2: 28-35
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