Dental Cements

Fig 9-1 Classification of dental cements according to bonding mechanism. EBA = ethoxybenzoic acid.

Table 9-1 Classification of dental cements

 TYPE (MATRIX BOND) CLASS OF CEMENT FORMULATIONS

 Phosphate

Zinc phosphate

Zinc phosphate

 

 

Zinc phosphate fluoride

 

 

Zinc phosphate copper oxide/salts

 

 

Zinc phosphate silver salts

 

Zinc silicophosphate

Zinc silicophosphate

 

 

Zinc silicophosphate mercury salts

 Phenolate Zinc oxide–eugenol Zinc oxide–eugenol
    Zinc oxide–eugenol polymer
    Zinc oxide–eugenol EBA/alumina
  Calcium hydroxide salicylate Calcium hydroxide salicylate

 Polycarboxylate

Zinc polycarboxylate

Zinc polycarboxylate

 

 

Zinc polycarboxylate fluoride

 

Glass ionomer

Calcium aluminum polyalkenoate

 

 

Calcium aluminum polyalkenoate-polymethacrylate

 Resin Acrylic PMMA
  Dimethacrylate Dimethacrylate unfilled
    Dimethacrylate filled
  Adhesive 4-META

 Resin-modified

Hybrid ionomers

Self-cured

 glass ionomers

 

Light-cured

The cements based on the reaction between calcium hydroxide and a liquid salicylate also originated 35 years ago. They were primarily fluid, two-paste materials intended for the lining of deep cavities that had actual or potential exposure, thus providing an antibacterial sealing to facilitate the formation of reparative dentin. The susceptibility to acid erosion of the original formulations, both through marginal leakage of restorations and exposure to phosphoric acid during acid-etch techniques, has resulted in more resistant compositions and, recently, to a light-cured, resin-based material.

As a result of the research of the last 20 years, five basic types of cements are available, classified according to the matrix-forming species, as shown in Fig 9-1 and Table 9-1:

Table 9-2 “Permanent” luting cements

  PRODUCT TYPE MANUFACTURER

  Multilink Automix

Dual-cured resin

Ivoclar Vivadent

  Panavia F 2.0 Dual-cured resin with Fl Kuraray Dental

  Maxcem

Dual-cured resin cement

Kerr Dental

  Fuji Plus Hybrid ionomer GC America

  Vitremer Luting

Hybrid ionomer

3M ESPE

  Fleck’s Extraordinary Zinc phosphate Mizzy

  Fuji I

Glass ionomer

GC America

  Fynal Zinc oxide–eugenol Dentsply Caulk

  Hy-Bond Polycarboxylate Cement

Zinc carboxylate

Shofu Dental

  Hy-Bond Zinc Phosphate Cement Zinc phosphate Shofu Dental

  Ketac-Cem

Glass ionomer

3M ESPE

  Rely X Hybrid ionomer 3M ESPE

  Modern Tenacin

Zinc phosphate

Dentsply Caulk

  Super EBA Zinc oxide–eugenol Bosworth

  Tylok Plus

Zinc carboxylate

Dentsply Caulk

  Zinc Cement Improved Zinc phosphate Mission White Dental

 

Table 9-3 Selection of dental cements

  APPLICATION CEMENT TYPE

  Luting inlays, crown posts, multiretainers, fixed partial denture in or on:

Glass-ionomer cement, hybrid ionomers, dual-cure resin

  Nonvital teeth or teeth with advanced pulpal recession and average retention

Zinc phosphate

  Vital teeth with average retention, average pulpal recession, thin dentin, especially for single units and small-span fixed partial dentures

Zinc polycarboxylate

  Multiretainer splints on vital teeth with above-average retention, minimal dentin thickness; hypersensitive patients Zinc oxide–eugenol polymer

  Provisional cementation

Zinc oxide–eugenol polymer

 

Zinc polycarboxylate (thin mix)

  Provisional cementation and stabilization of old, loose restorations; fixation of facings and acid-etched cast restorations Dimethacrylate resin composite

  Base/liner in:

 

Cavity with remaining dentin greater than about 0.5mm

Glass-ionomer cement, resin ionomer

 

Zinc polycarboxylate

 

Zinc phosphate (low-acid type)

Cavity with minimal dentin or exposure

Calcium hydroxide salicylate

 

Zinc oxide–eugenol polymer

 

Table 9-4 Properties of dental luting cements

Image

1. Phosphate bonded

2. Phenolate bonded

3. Polycarboxylate bonded

4. Dimethylacrylate bonded

5. Polycarboxylate and dimethylacrylate combinations

Numerous brands of each type are available, and there is some overlap between properties. Examples of current widely used brands of permanent luting cements are presented in Table 9-2. Since clinical and in vivo evaluation of cements is still very limited, the predictive value of laboratory data for assessment of clinical performance requires knowledgeable interpretation, especially because generalizations about specific types of cement cannot be made based on the behavior of one or two brands. The applications of the different types of cements are presented in Table 9-3. Typical properties of luting cements are presented in Table 9-4.

Image Phosphate-Based Cements

Zinc phosphate cement

Applications

Because of their long history, these materials have the widest range of applications, from the cementation (luting) of fixed cast alloy and porcelain restorations and orthodontic bands (see Table 9-2) to their use as a cavity liner or base to protect pulp from mechanical, thermal, or electric stimuli.

Composition and setting

The powder is mainly zinc oxide with up to 10% magnesium oxide and small amounts of pigments. It is fired at high temperature (> 1,000°C) for several hours to reduce its reactivity. The liquid is an aqueous solution of phosphoric acid containing 45% to 64% H3PO4 and 30% to 55% water. The liquid also contains 2% to 3% aluminum and 0% to 9% zinc. Aluminum is essential to the cement-forming reaction, whereas zinc is a moderator of the reaction between powder and liquid, allowing adequate working time and permitting a sufficient quantity of powder to be added for optimum properties in the cement.

Some zinc phosphate cements have modified compositions. One material, widely used as a cavity liner, has 8% aluminum and only 25% H3PO4 in the liquid and a powder that contains calcium hydroxide. Others may contain fluoride and have as much as 10% stannous fluoride.

The amorphous zinc phosphate formed binds together the unreacted zinc oxide and other components of the cement. The set cement consists of a cored structure of residual zinc oxide particles in a phosphate matrix:

zinc oxide + phosphoric acid → amorphous zinc phosphate

Manipulation

The mixing slab must be thoroughly dried before use. A chilled (5°C) thick glass slab will slow the initial reaction and allow incorporation of more powder, giving superior properties in the set cement.

The measurement of the components and the timing of mixing are necessary. The powder is added to the liquid in small portions to achieve the desired consistency. Increasing the powder/liquid ratio gives a more viscous mix, shorter setting time, higher strength, lower solubility, and less free acidity. Dissipation of the heat of reaction by mixing over a large area on a cooled slab will allow a greater incorporation of powder in a given amount of liquid. The cement must be undisturbed until the end of the setting time. It is kept sealed with a stopper to prevent changes in the water content. Cloudy liquid should be discarded.

Properties

Zinc phosphates have been used in clinical practice for many years. Under routine conditions, they can be easily manipulated, and they set sharply to a relatively strong mass from a fluid consistency. Although the properties are far from ideal, they are usually regarded as a standard against which to compare newer cements (see Table 9-4).

For a given brand, the properties are a function of the powder/liquid ratio. For a given cementing consistency, the higher the powder/liquid ratio, the better the strength properties and the lower the solubility and free acidity. At room temperature (21°C to 23°C) the working time for most brands at luting consistency is 3 to 6 minutes, and the setting time is 5 to 14 minutes. Extended working times and shorter setting times can be achieved by use of a cold mixing slab, which permits up to an approximate 50% increase in the amount of powder, improving both strength and resistance to dissolution.

The cement must have the ability to wet the tooth and restoration, flow into the irregularities on the joining surfaces, and fill in and seal the gaps between the restoration and the tooth. The minimum value of film thickness is a function of powder particle size, powder/liquid ratio, and mix viscosity. As measured by ISO and ANSI/ ADA specifications,13 acceptable cements give film thicknesses of less than 25 µm. In practice, the cement fills in the inaccuracies between the restoration and the tooth and allows most castings to seat satisfactorily. Unless escapeways or vents are provided with full crowns, separation of powder and liquid may occur, with marginal defects in the cement film.

At the recommended powder/liquid ratio (2.5 to 3.5 g/mL), the compressive strength of the set zinc phosphate cement is 80 to 110 MPa (11,000 to 16,000 psi) after 24 hours. The minimum strength for adequate retention of restorations is about 60 MPa (8,500 psi). The strength is strongly and almost linearly dependent on powder/liquid ratio. The tensile strength is much lower than the compressive strength, 5 to 7 MPa (700 to 900 psi), and the cement shows brittle characteristics. The modulus of elasticity (stiffness) is about 13 GPa (1.8 × 106 psi).

According to the standard method, the solubility and disintegration in distilled water after 23 hours may range from 0.04% to 3.3% for inferior material. The standard limit is 0.2%. The solubility in fluoride-containing cements is about 0.7% to 1.0% because of the leaching of fluoride. The solubility in organic acid solutions, such as lactic or citric acid, is 20 to 30 times higher. These data are only a rough guide to solubility under oral conditions. The comparative evaluation of cement solubility under clinical conditions has shown significant loss but conflicting results. Dissolution contributes to marginal leakage around restorations and bacterial penetration. This occurrence may be facilitated by dimensional change. The cement has been found to contract about 0.5% linearly, giving rise to slits at the tooth-cement and cement-restoration interfaces.

Biologic effects

The freshly mixed zinc phosphate is highly acidic, with a pH between 1 and 2 after mixing, and, even after setting 1 hour, the pH may still be below 4. After 24 hours, the pH is usually between 6 and 7. Pain on cementation is due not only to the free acidity of the mix but also to osmotic movement of fluid through the dentinal tubules. Hydraulic pressure developed during seating of the restoration may also contribute to pulpal damage. Prolonged pulpal irritation, especially in deep cavities that necessitate some form of pulpal protection, may be associated with prolongation of the low pH. Irritation is minimized by a high powder/liquid ratio and rapid setting. A material that has a low acid content and incorporates calcium hydroxide has little effect on pulp when used as a liner. Very thin mixes will also lead to etching of the enamel.

Advantages and disadvantages

The main advantages of zinc phosphate cements are that they can be mixed easily and that they set sharply to a relatively strong mass from a fluid consistency. Unless the mix is extremely thin (for instance, with a very low powder/liquid ratio), the set cement has a strength that is adequate for clinical service, so manipulation is less critical than with other cements.

However, zinc phosphates’ distinct disadvantages include pulpal irritation, lack of antibacterial action, brittleness, lack of adhesion, and solubility in oral fluids.

Modified zinc phosphate cements

Copper and silver cements

Black copper cements contain cupric oxide (CuO), and red copper cements contain cuprous oxide (Cu2O). Others may contain cuprous iodide or silicate. Because a much lower powder/liquid ratio is necessary to obtain satisfactory manipulation characteristics with these cements, the mix is highly acidic, resulting in much greater pulpal irritation. Their solubility is higher and their strength is lower than zinc phosphate cements. Their bacteriostatic or anticariogenic properties seem to be slight. Silver cements generally contain a small percentage of a salt such as silver phosphate. Their advantages over zinc phosphate cement have not been substantiated.

Fluoride cements

Stannous fluoride (1% to 3%) is present in some orthodontic cements. These materials have a higher solubility and lower strength than zinc phosphate cement due to dissolution of the fluoride-containing material. Fluoride uptake by enamel from such cements results in reduced enamel solubility and potentially anticariogenic effects. Fluoride is found in some hybrid iononomer and dualcured resin cements.

Silicophosphate cements

These materials have been available for many years as a combination of zinc phosphate and silicate cements. The presence of the silicate glass provides a degree of translucency, improved strength, and fluoride release.

Applications

Their principal applications have been for the cementation of fixed restorations and orthodontic bands (type I), as a provisional posterior restorative material (type II), and as a dual-purpose material (type III).

Composition and setting

The powder in these materials consists of a blend of 10% to 20% zinc oxide (zinc phosphate cement powder) and silicate glass (silicate cement powder) mechanically mixed or fused and reground. The silicate glass usually contains 12% to 25% fluoride. Some materials have been labeled “germicidal” because of the presence of small amounts of mercury or silver compounds. The liquid is a concentrated orthophosphoric acid solution containing about 45% water and 2% to 5% aluminum and zinc salts.

The setting reaction has not been fully investigated, but may be represented as follows:

zinc oxide/aluminosilicate glass + phosphoric acid → zinc aluminosilicate phosphate gel

The set cement consists of unreacted glass and zinc oxide particles bonded together by the aluminosilicophosphate gel matrix.

Manipulation

The mixing is analogous to that for a phosphate cement; a nonabradable spatula and a cooled mixing slab should be used. The filling mix should be glossy, with putty-like consistency.

Properties

At cementing consistency, the setting time is 5 to 7 minutes; working time is about 4 minutes and may be increased by using a cold mixing slab. These cements generally have shorter working times and a coarser grain size, leading to a higher film thickness than with zinc phosphate cements. One material is improved in these respects, and film thickness is adequate for cementation of cast gold and porcelain restorations.

The compressive strength of the set cement ranges from 140 to 170 MPa (20,000 to 25,000 psi); the tensile strength is considerably lower at 7 MPa (1,000 psi) (see Table 9-4). The toughness and abrasion resistance are higher than those of phosphate cements. The durability in bonding orthodontic bands to teeth is greater, and less decalcification is observed.

The solubility in distilled water after 7 days is about 1% by weight. Solubility in organic acids and in the mouth is less than for phosphate cements. In the presence of oral fluids, fluoride will leach out

The glass content gives considerably greater translucency than phosphate cements, making silicophosphate cements useful for cementation of porcelain restorations.

Biologic effects

Because of the acidity of the mix and the prolonged low pH (4 to 5) after setting, pulpal protection is necessary on all vital teeth. Fluoride and other ions are leached out from the set cement by oral fluids, resulting in increased enamel fluoride and probable anticariogenic action.

Advantages and disadvantages

Silicophosphate cements have better strength, toughness, and abrasion-resistance properties than zinc phosphate cements and show considerable fluoride release, translucency, and, under clinical conditions, lower solubility and better bonding.

However, the initial pH and total acidity are greater than those for zinc phosphate cements; thus, pulpal sensitivity may be of longer duration. Manipulation with these cements is more critical than with zinc phosphate cements.

Image Phenolate-Based Cements

The main types of phenolate-bonded cements are:

1. Simple zinc oxide–eugenol combination that may contain setting accelerators

2. Reinforced zinc oxide–eugenol

3. Ortho-ethoxybenzoic acid (EBA)

Cements have also been formulated using other phenolic liquids, but have seen little use except for those materials containing calcium hydroxide and a salicylate.

Zinc oxide–eugenol cements

Applications

The basic combination of zinc oxide and eugenol finds its principal applications in the provisional cementation of crowns and fixed partial dentures, in the provisional restoration of teeth, and as a cavity liner in deep cavity preparations.

Composition and setting

The powder is pure zinc oxide (United States Pharmacopeia or equivalent, arsenic-free). Commercial materials may contain small amounts of fillers, such as silica. About 1% of zinc salts, such as acetate or sulfate, may be present to accelerate the setting. The liquid is purified eugenol or, in some commercial materials, oil of cloves (85% eugenol). One percent or less of alcohol or acetic acid may be included to accelerate setting together with small amounts of water, which is necessary for the setting reaction.

A chemical reaction occurs between zinc oxide and eugenol, with the formation of zinc eugenolate (eugenate):

Image

The precise mechanism is not fully understood, but the set mass contains residual zinc oxide particles bonded by a matrix of zinc eugenolate and some free eugenol. Water is essential to the reaction, which is also accelerated by zinc ions. The reaction is reversible because the zinc eugenolate is easily hydrolyzed by moisture to eugenol and zinc hydroxide. Thus, the cement disintegrates rapidly when exposed to oral conditions. The rate of reaction between the zinc oxide and eugenol depends on the nature, source, reactivity, and moisture content of the zinc oxide and on the purity and moisture content of the eugenol.

Manipulation

The zinc oxide is slowly wetted by the eugenol; therefore, prolonged and vigorous spatulation is required, especially for a thick mix. A powder/liquid ratio of 3:1 or 4:1 must be used for maximum strength.

Properties

The working time is long because moisture is required for setting. Variable results are obtained with different samples of zinc oxide, depending on their mode of preparation and reactivity. For a given oxide, set time is controlled by moisture availability, accelerators, and the powder/liquid ratio. Mixes of cementing consistency set very slowly unless accelerators are used and/or a drop of water is added. Commercial materials set in 2 to 10 minutes, resulting in adequate strengths at 10 minutes for amalgam restorations to be placed (see Table 9-4).

The particle size of the zinc oxide and the viscosity of the mix govern the film thickness. Use of a fluid mix gives values of about 40 µm.

Because of the weak nature of the binding agent, the compressive strength is low, in the range of 7 to 40 MPa (1,000 to 6,000 psi). The tensile strength is very low also.

The solubility is high, about 1.5% by weight in distilled water after 24 hours. Eugenol is extracted from the set cement by the hydrolytic decomposition of the zinc eugenolate/eugenate. The cement disintegrates rapidly when exposed to oral conditions.

Biologic effect

The presence of eugenol in the set cement under clinical conditions appears to lead to an anodyne and obtundent effect on the pulp in deep cavities. At the same time, eugenol is a potential allergen. When exposed directly to oral conditions, the material maintains good sealing characteristics despite a volumetric shrinkage of 0.9% and a thermal expansion of 35 × 10–6/°C. The sealing capacity and antibacterial action appear to facilitate pulpal healing; however, when in direct contact with connective tissue, the material is an irritant. Reparative dentin formation in exposed pulp is variable.

Advantages and disadvantages

The main advantage of these materials is their bland and obtundent effect on the pulpal tissues, together with their good sealing ability and resistance to marginal penetration.

Disadvantages include low strength and abrasion resistance, solubility and disintegration in oral fluids, and little anticariogenic action.

Reinforced zinc oxide–eugenol cements

Applications

These materials have been used as cementing agents for crowns and fixed partial dentures, cavity liners and base materials, and provisional restorative materials.

Composition and setting

The powder consists of zinc oxide with 10% to 40% finely divided natural or synthetic resins (eg, colophony [pine resin], PMMA, polystyrene, or polycarbonate) together with accelerators. The liquid is eugenol, which may also contain dissolved resins as mentioned earlier and accelerators such as acetic acid, as well as antimicrobial agents such as thymol or 8-hydroxyquinoline.

The setting reaction is similar to zinc oxide–eugenol cements. Acidic resins such as colophony (abietic acid) may react with the zinc oxide, strengthening the matrix.

Manipulation

More powder is required for a cementing mix than with other cements. Measures are provided for some commercial materials, and the proper ratio must be adhered to for adequate strength properties. The mixing pad or slab should be thoroughly dry. The powder is mixed into the liquid in small portions with vigorous spatulation until the correct amount has been incorporated. Adequate time should be allowed for setting without disturbance of the cement. Both powder and liquid containers should be kept closed and stored under dry conditions.

Properties

These cements may have a long working time because moisture is needed for setting. Some commercial materials contain moisture and, therefore, have working and setting times in the same range as zinc phosphate cements, that is, 7 to 9 minutes in oral conditions. Setting time is also lengthened by reducing the powder/liquid ratio.

At cementing consistency, values of film thickness from 35 to 75 µm have been obtained with commercial materials (see Table 9-4). Clinical trials have shown satisfactory performance in seating castings for cements with the lowest values.

These materials have compressive strengths in the range from 35 to 55 MPa (5,000 to 8,000 psi). The tensile strength is 5 to 8 MPa (700 to 1,000 psi) (see Table 9-4). The strength is adequate as a lining material and for luting single restorations and retainers with good retention form. The modulus of elasticity is 2 to 3 GPa (300,000 to 400,000 psi). The mechanical properties of these cements are reduced by immersion in water, which results in loss of eugenol, although this appears to be slower than with simple zinc oxide–eugenol materials. This tendency seems less pronounced with the polymer-reinforced materials.

Because of the presence of the resin, the solubility of these cements appears to be lower than that of zinc oxide–eugenol materials.

Biologic effects

Polymer-reinforced zinc oxide–eugenol cements have biologic effects similar to basic materials, although there is some variation in inflammatory reaction in connective tissue with the brand of material. There may be softening and discoloration of some resin restorative materials.

Advantages and disadvantages

The main advantages of these materials are the minimal biologic effects, good initial sealing properties, and adequate strength for final cementation of restorations. The principal disadvantages are the lower strength, higher solubility, and higher disintegration compared with zinc phosphate cements; hydrolytic instability; and the softening and discoloration of some resin restorative materials.

EBA and other chelate cements

To further improve on the basic zinc oxide–eugenol system, many researchers have investigated mixtures of zinc and other oxides with various liquid chelating agents. The only system that has received extensive commercial exploitation for luting and lining is that containing ortho-EBA. (Noneugenol cements have also been developed in which fatty acids or low-odor phenolic derivatives are used to overcome the smell and taste of eugenol.)

Applications

These materials have been used for the cementation of inlays, crowns, and fixed partial dentures; for provisional restorations; and as base or lining materials.

Composition and setting

In EBA materials, the powder is mainly zinc oxide containing 20% to 30% aluminum oxide or other mineral fillers. Polymeric reinforcing agents, such as PMMA, may also be present. The liquid consists of eugenol and 50% to 66% EBA.

The setting mechanism has not been fully elucidated, but it appears to involve chelate salt formation between EBA, eugenol, and zinc oxide. The setting is accelerated by the same factors that are operative for zinc oxide–eugenol cements.

Manipulation

In general, the manipulation is similar to that of reinforced zinc oxide–eugenol cements. The cement mixes readily to a very fluid consistency even at a high powder/liquid ratio. To obtain optimal properties, it is important to use as high a powder/liquid ratio as possible—about 3.5 g/mL for cementation and 5 to 6 g/mL for liners or bases. Vigorous spatulation is required for about 2 minutes to incorporate all of the powder. The correct mix flows readily under pressure because of the long working time. Adequate setting time in the mouth should be allowed. Several days may be required to reach maximum strength.

Properties

The working time at room temperature is long because of the dependence on moisture. The setting time ranges between 7 and 13 minutes under oral conditions (see Table 9-4).

The film thickness may be between 40 and 70 µm depending on the brand, but for permanent cementation of restorations, the lower level is preferable.

At cementing consistency, the compressive strength of these materials is in the range of 55 to 70 MPa (8,000 to 10,000 psi); higher values, similar to those of zinc phosphate cements, can be obtained by increasing the powder/liquid ratio. The tensile strength is considerably lower, about 3 to 6 MPa (500 to 900 psi), and the modulus of elasticity is about 5 GPa (700,000 psi). The viscoelastic properties of EBA cements show very low strength and slow rates of large plastic deformation (0.1 mm/min) at oral temperature (37°C). These characteristics may explain why the retention values for crowns and orthodontic bands are considerably below those for zinc phosphate cements.

The solubility is similar to that of the polymer-reinforced zinc oxide–eugenol materials in distilled water, although loss of eugenol also occurs. The resistance to solubility in organic acids appears to be greater than that of the zinc phosphate cements. When exposed to moisture, greater oral dissolution occurs than for other cements. However, a clinical survey by Silvey and Myers4 of the performance of an EBA-alumina cement during 3 years showed only slightly worse results than for zinc phosphate and polycarboxylate cements. Oral breakdown may thus depend on the precise brand and manipulation.

Biologic effects

The biologic properties of these materials appear to be similar to those of zinc oxide–eugenol materials.

Advantages and disadvantages

EBA cements are very easy to mix and have a long working time, good flow characteristics, and low irritation to pulp. Strength and film thickness can be comparable with those of zinc phosphate cements (see Table 9-4).

The main disadvantages are the critical proportioning, hydrolytic breakdown in oral fluids, liability to plastic deformation, and poorer retention than zinc phosphate cements. These materials seem best suited for luting restorations with good fit and retention where there is no undue stress and as cavity bases.

Calcium hydroxide chelate cements

The value of calcium hydroxide as a pulp-capping material that facilitates the formation of reparative dentin has long been recognized. This action appears to be largely attributable to its alkaline pH and consequent antibacterial and protein-lyzing effect. Although a number of aqueous paste materials based on calcium hydroxide are available, they are not easy to manipulate, and the dried films tend to crack. In the early 1960s, phenolate-type cements based on the setting reaction between calcium hydroxide and other oxides and salicylate esters were introduced.

Applications

These cements are used as liners in deep cavity preparations.

Composition and setting

Usually, two pastes are used: One contains calcium hydroxide, zinc oxide, and zinc salts in ethylene toluene sulphonamide; and the other contains calcium sulfate, titanium dioxide, and calcium tungstate (a radiopacifying agent) in a liquid disalicylate ester of butane-1,3-diol. An intentional excess of calcium hydroxide produces an alkaline pH to effect an antibacterial and remineralization action. There is some variation among the materials in this respect. At least one material contains fluoride.

Calcium and zinc oxide react with the salicylate ester to form a chelate similar to the zinc oxide–eugenol reaction. Likewise, the reaction is greatly accelerated by moisture and accelerators.

Manipulation

Equal lengths of the two pastes are mixed to a uniform color.

Properties

Working time may be 3 to 5 minutes, depending on the availability of moisture. In the mouth, setting is rapid, about 1 or 2 minutes.

The compressive strength at 7 minutes is about 6 MPa (900 psi), and the tensile strength is 1.5 MPa (200 psi); at 1 hour the corresponding values are about 10 MPa (1,500 psi) and 1.5 MPa (200 psi); at 24 hours the values are 14 to 20 MPa (2,000 to 3,000 psi) and 1.7 to 2.0 MPa (250 to 300 psi). Thin films become resistant to an 8 MPa (1,100 psi) penetration force in 90 seconds. Plastic flow without fracture occurs at 37°C.

The solubility in 50% phosphoric acid during acidetching procedures is significant. These cements seem to be subject to hydrolytic breakdown. When continued marginal leakage takes place, complete dissolution of the linings of these materials can occur.

Biologic effects

These cements appear to exert a strong antibacterial action when free calcium hydroxide is available and to assist in remineralization of carious dentin. They facilitate the formation of dentin bridges when used for pulp capping on exposures. Their effect on exposed pulp is superior to that of zinc oxide–eugenol materials. These materials can also exert a pulpal protective action by neutralizing and preventing the passage of acid and by acting as a barrier to the penetration of other agents, such as methyl methacrylate.

Advantages and disadvantages

These cements are easy to manipulate, they rapidly harden in thin layers, and they have good sealing characteristics and beneficial effects on carious dentin and exposed pulp.

However, they show low strength even when fully set, exhibit plastic deformation, are weakened by exposure to moisture, and will dissolve under acidic conditions and if marginal leakage occurs. The data on physical properties and clinical experience suggest that further improvements in these materials are required before they can be used as the sole liner in deep cavity preparations.

More recently, polymerizable resin compositions containing calcium hydroxide have been introduced as alternatives to these materials.

Image Polycarboxylate (Carboxylate)-Based Cements

Zinc polycarboxylate cements

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May 28, 2016 | Posted by in Dental Materials | Comments Off on Dental Cements
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