Luting agents & Cementation Flashcards
An ideal luting agent should
- has a long working time.
- adheres well to both tooth structure and cast alloys. provides a good seal.
- is nontoxic to the pulp.
- has adequate strength properties.
- is compressible into thin layers.
- has low viscosity and solubility.
- and exhibits good working and setting characteristics.
- In addition, any excess can be easily removed.
Most luting agents traditionally used for cast restorations are dental cements.
These consist of an acid combined with a metal oxide base to form a salt and water.
The setting mechanism results from the binding of unreacted powder particles by a matrix of salt to harden the mass.
They are somewhat soluble in oral fluids.
Talk about zinc phosphate attributes
- This traditional luting agent continues to be popular forcast restorations.
- It has reasonable working time.
- a film thickness (thickness of the layer) of about 25 um (which is within the tolerance limits required for making cast restorations),
- It has adequate strength,
- Excess material can be easily removed.
- The toxic effects of zinc phosphate, or, more specifically, phosphoric acid, are well documented. However, the success of the use of this material over many years suggests that its effect on the dental pulp is clinically acceptable as long as normal precautions are taken and the preparation is not too close to the pulp.
Talk about Zinc polycarboxylate cement
Viscosity
Working time
One advantage of this luting agent is its relative biocompatibility, which may stem from the fact that the polyacrylic acid molecule is large and therefore does not penetrate into the dentinal tubule.
- Zinc polycarboxylate cement also exhibits specific adhesion to tooth structure because it chelates the calcium
- At manufacturers’ recommended powder/liquid ratios, mixed polycarboxylate cement is very viscous.
- Because of its high viscosity, zinc polycarboxylate cement can be difficult to mix, but this problem can be overcome by using encapsulated products.
- Some dentists may prefer a more fluid working consistency for reliable seating during cementation.
- However, polycarboxylate cements have different rheologie or flow properties than zinc phosphate,
- polycarboxylate cements exhibiting thinning with increased shear rate.
- This means that they are capable of forming low film thicknesses despite their viscous appearance. When the dentist unnecessarily reduces the powder/liquid ratio, the solubility (how susceptible something is to being dissolved) of the cement increases dramatically (as much as three fold).
- This may be the cause of increased clinical failures.
- The working time of polycarboxylate is much shorter than that of zinc phosphate (about 2.5 minutes, in comparison with 5 minutes). This may be a problem when multiple units are being cemented.
- Residual zinc polycarboxylate is more difficult to remove than zinc phosphate, and there is some evidence that it provides less crown retention than zinc phosphate.
- And its use as a base material.
its selection therefore should probably be limited to restorations with good retention and resistance form where minimum pulp Irritation is wanted e.g., in children with large pulp chambers, also its use to block out minor undercuts in preparations on vital teeth may also be worth considering.
Talk about Zinc oxide-eugenol with ethoxybenzoic acid
- The ethoxybenzoic acid (EBA) modifier replaces a portion of the eugenolin conventional ZOE cement, this is to improve its compressive strength
- Reinforced ZOE cement is extremely biocompatible and provides an excellent seal.
- However, its mechanical and physical properties are generally inferior to those of other cements, which limits its use. In terms of compressive strength, solubility, and film thickness, phosphate) should be used.
The EBA cement has a relatively short working time, and excess material is difficult to remove. another luting agent (e.g., zinc
Although Reinforced ZOE cement with improved compressive strength; the cement should be used only in restorations with good inherent retention form.
Talk about glass monomer
Glass ionomer cement
This cement adheres to enamel and dentin And exhibits good biocompatibility. In addition, Because it releases fluoride, it may have an anticariogenic effect, although this has not been documented clinically.
The mechanical properties of glass ionomer cement are generally superior compared with zinc phosphate or polycarboxylate cements.
Also it has good working properties, and is more translucent than zinc phosphate.
Glass ionomer cement has become a popular cement for luting cast restorations.
What’s dis advantage of Glass ionomer cement
disadvantage is that during setting, glass ionomer appears particularly susceptible to moisture contamination and should be protected with a foil or resin coat. The water changes the setting reaction of the glass ionomer.
Glass ionomers should not be allowed to desiccate during this critical initial setting period. The newer resin modified glass ionomers are less susceptible to early moisture.
Although glass ionomers have been reported to cause sensitivity, there appears to be little pulpal response at the histologic level, particularly if the remaining dentin thickness exceeds 1 mm.
• Side effects such as post treatment sensitivity thought to result from a lack of biocompatibility may actually be a result of desiccation or bacterial contamination of the dentin rather than irritation by the cement. A desensitizing agent may prevent sensitivity, although it may also reduce retention, at least with some luting cements.
Some formulations of glass ionomer and resin cements are radiolucent ,which may prevent the practitioner from distinguishing between a cement line and recurrent caries, as well as detecting cement overhangs.
Talk about Resin-modified glass ionomer luting agents
- These materials are less susceptible to early moisture exposure than is glass ionomer and are currently among the most popular materials in general practice. The popularity of these materials is derived mainly from the perceived benefit of reduced post cementation sensitivity, although this benefit has not been confirmed in clinical studies.
- Have adhesion, low solubility and low microleakage.
- Exhibit higher strength than the conventional cements; values are similar to the resin luting agents.
- Resin modified glass ionomers should be avoided with all-ceramic restorations because some brands have been associated with fracture, which is probably caused by their water absorption and expansion
Talk about Resin luting agents?
- are available with adhesive properties (i.e., they are capable of bonding chemically and lack of solubility.
- Resin luting agents are less biocompatible than cements such as glass ionomer, especially if they are not fully polymerized.
- They also tend to have greater film thickness
- Long-term evaluations of these materials are not yet available, and so they cannot be recommended for routine use; however, they are indicated forall-ceramic and laboratoryprocessed composite restorations.
- Laboratory testing yields high retention strength values, but there is concern that stresses caused by polymerization shrinkage, magnified in thin films, lead to marginal leakage
Talk a bout Preparation of the Restoration and Tooth Surface for Cementation
- The performance of all luting agents is degraded if the material is contaminated with water, blood, or saliva. Therefore, the restoration and tooth must be carefully cleaned and dried
- So before the initiation of cement mixing, isolating the area of cementation and cleaning and drying the tooth is mandatory.
Talk about Cementation with nonadhesive cement (zinc phosphate)
- Tooth should be cleaned, gently dried, and coated with cavity varnish or dentin-bonding resin. .
- Dry the tooth again with a light blast of air and push the restoration into place.
- Final seating is achieved by rocking with an orange wood stick until all excess cement has escaped
Seating the restoration firmly with a rocking, dynamic seating force is important.
Talk about Cementation with Resin luting agents
Cementation with Resin luting agents
- Resin luting agents are available in a wide range of formulations. These can be categorized on the basis of polymerization method (chemical-cure, light-cure, or dual-cure).
- Metal restorations require a chemically cured system, whereas a light- or dual cure system is appropriate with ceramics
- Manipulative techniques vary widely, depending on the brand of resin cement
Banding in CERAMIC VENEERS AND INLAYS is achieved by
- Etching the fitting surface of the ceramic with hydrofluoric acid.
- Applying a silane coupling agent to the ceramic material
- Etching the enamel with phosphoric acid.
- Applying a resin-bonding agent to etched enamel.
- Seating the restoration with a composite resin luting agent
Talk about cementation of temporary cement
- After the zinc oxide-eugenol cement has been mixed to a thick, creamy consistency,
- an amount of petrolatum equal to 5% to 10% of the cement volume is incorporated to slightly reduce the strength of the cement. This will facilitate removal of the provisional restoration at a subsequent appointment.
- If the preparation is short or otherwise lacking in retention, the petrolatum should not be added.
- It is not necessary to keep zinc oxide-eugenol cement dry while it is setting. In fact, moisture will accelerate the hardening.
Interim luting agents are available in various formulations. A non-eugenol-containing product is recommended for bonded restorations; the clear luting agent is used for improved esthetics.
In terms of placing crown all type of cementation:
The casting is best prepared by airborne particle abrading the fitting surface with 50- um alumina. Ceramic restoration treated with etching……..
Coating the outside of the restoration with a thin film of petrolatum prior to cementation will aid in the removal of excess cement.
After the cement has hardened, all excess must be removed from the gingival crevice. Use an explorer in accessible areas and knotted dental floss interproximally • Protect the setting cement from moisture by covering it with an adhesive foil
• Cements take at least 24 hours to develop their final strength. Therefore, the patient should be cautioned to chew carefully for a day or two.
