ADHESIVE CEMENTS

CONTENTS

Introduction to cements

Adhesion

Zinc poly-carboxylate cements

Glass Ionomer Cements and its advances

Resin Cements

Recent Advances of resin cements

Conclusion

What is a dental cement?

Dental cements are hard, brittle materials formed by mixing powder and liquid together.

They are either resin cements or acid-base cements. In the latter the powder is a basic metal oxide or silicate and the liquid is acidic.

An acid base reaction occurs with the formation of a metal salt which acts as the cementing matrix.

Applications of Dental Cements:

Cementing agent for permanent restorations.

Temporary restorations.

Liners and bases.

Cementing agents for orthodontic appliances.

Root canal fillers and sealers.

Pulp capping agents.

Restorations.

Requirement of Dental Cements

Adequate mechanical properties.

Non-irritating & non-toxic.

Insoluble.

Insulating the pulp from thermal, electrical and chemical irritants.

Adhesive properties.

Esthetic properties.

Easy to manipulate.

Form a strong bond with enamel and dentin.

Provide good marginal sealing to prevent marginal leakage.

Be resistant to dissolution in saliva, or in any oral fluid.

Classification

Cements are classified on the basis of their components. Generally, they can be classified into categories:

Water-based acid-base cements:

Zinc phosphate (Zn3(PO4)2),

Zinc Polyacrylate(Polycarboxylate)

Glass ionomer (GIC)

Non-aqueous acid-base cements:

Zinc oxide eugenol

Non-eugenol zinc oxide

Resin-based:

Acrylate or methacrylate resin cements, including the latest generation of self-adhesive resin cements which contain silicate or other types of fillers in an organic resin matrix.

Adhesive dentistry

Adhesion

Adhesion is a process by which two bodies are held together at an interface by ionic or covalent bonding between molecules on either side of the interface.

Adhesive dentistry is a branch of dentistry which mainly deals with adhesion or bonding of the adhesive material or cements to the natural substance of teeth, enamel and dentin.

Dental Bonding

Dental bonding is the process in which tooth colored materials are adhered to the tooth. This is a procedure that can be used to repair or improve the appearance of a tooth that has been badly stained, broken or chipped.

Tooth bonding techniques have various clinical applications including operative dentistry and preventive dentistry as well as cosmetic and pediatric dentistry, prosthodontics, and orthodontics.

In modern science, adhesive dentistry studies the nature and strength of the adhesion to dental hard tissues, properties of adhesive materials, causes and mechanisms of failure of the bonds, clinical techniques for bonding and newer applications for bonding such as bonding to the soft tissue.

There's also direct composite bonding which uses tooth-colored direct dental composites to repair various tooth damages such as cracks or gaps.

Manipulation

The proper powder /liquid ratio mixed on paper bad (1:1 or 2:1)

Dispensing of the liquid should be done immediately before mixing.

Cooled glass slap to extend working time.

The consistency of the mix is creamy .

The Viscosity decreases as the shear rate increase,i.e.the flow increases as the spatulation increases

Should be used only as long as it still has a glossy surface.

Setting Reaction of Zinc Polycarboxylate Cement

ZnO + Polyacrylic Acid Zinc polacrylate+ ZnO

Setting Reaction

Unlike zinc phosphate cement, the setting reaction of polycarboxylate cement produces little heat.

This has made it a material of choice. Manipulation is simpler, and trauma due to thermal shock to the pulp is reduced.

The rate of setting is affected by the powder-liquid ratio, the reactivity of the zinc oxide, the particle size, the presence of additives, and the molecular weight and concentration of the polyacrylic acid.

The strength can be increased by additives such as alumina and fluoride.

The zinc oxide reacts with the polyacrylic acid forming a cross-linked structure of zinc polyacrylate. The set cement consists of residual zinc oxide bonded together by a gel-like matrix.

Zinc Polycarboxylate Cement

Uses :

Used for cementation of crowns and inlays.

Used as base under restorations .

Primarily for luting permanent alloy restorations

Properties of Zinc Polycorboxylate Cements

1-Consistency and Film thickness :

25 – 48 µm

Poly-carboxylate cement mixed with white portland cement at concentrations of 1.8% and 2.4% has reduced setting time and increased flowability of cement.

[Wongo Kornchaowalit n, Lert chirakarn U]

[J Endod – 2011 March]

2-Strength :

Compressive strength : 57 – 99 MPa

Tensile strength : 3.6 -6.3 Mpa

In an invitro study,retentive strength of zinc phosphate and GIC is higher than that of zinc poly-carboxylate cement.

[Raghunath Reddy, Subba Reddy VV]

[J Indian Pedod Prev Dent - 2010 Oct]

3- Bonding to tooth structure :

It bonds chemically to the tooth structure.

The polyacrylic acid is believed to react with calcium ions via carboxyl groups on the surface of enamel or dentin.

Thus bond strength to enamel is greater than that to dentin.

4-Biological properties :

Pulp response is mild when compared with silicate cement.

The pH of Zinc polycarboxylate cement is higher than that of a zinc phosphate cement.

Its mild irritation is due to that, the larger size of the polyacrylic acid molecule compared with phosphoric acid molecule may limit its diffusion through the dentinal tubules.

Zinc poly-carboxylate cement is similar to GIC in controlled release of active organic compounds.

[Ali MN, Edwards M]

[J Mater Sci Mater Med – 2010 April]

Advantages :

1. Adhesion to tooth structure.

2. Less irritation.

3. Easy manipulation.

4. Strength.

5. Film thickness properties.

Disadvantages:

1. Critical proportioning.

2. Lower compressive strengths.

3. Requires clean surface.

Types of GIC :

Type I :

Luting cement for crowns and inlays.

Type II :

Restorative material

TYPE III:

• Liner or Base Material

MANIPULATION

1.Preparation of tooth surface :-

The enamel & dentin are first cleaned with pumice slurry followed by swabbing with polyacrylic acid for 5 sec. After conditioning & rinsing ,tooth surface should isolate & dry.

2.Proportioning & mixing :-

Powder & liquid ratio is 3:1 bywt. Powder & liquid is dispensed just prior to mixing.

First increment is incorporated rapidly to produce a homogenous milky consistency.

Mixing done in folding method preserves gel structure.

Finished mix should have a glossy surface.

3. Protection of cement during setting :-

Glass ionomer cement is extremely sensitive to air & water during setting.

Immediately after placement into cavity, preshaped matrix is applied to it.

4. Finishing :-

Excess material should be trimmed from margins.

Hand instruments are preferred to rotary tools to avoid ditching.

Further finishing is done after 24hrs.

5.Protection of cement after setting :-

Before dismissing the patient ,restoration is again coated with the protective agent to protect trimmed area.

Failure to protect for first 24hrs from moisture results in weaken cement.

In an invitro study, it has been proved that early water exposure does not affect the strength of glass ionomer restoratives.

[XY Wang, AUJ Yap]

[operative Dentistry 2006]

SETTING REACTION

When the powder & liquid are mixed, Surface of glass particles are attacked by acid. then Ca, Al, sodium, & fluoride ions are leached into aqueous medium.

Calcium poly salts are formed first, then followed by aluminum poly salts which cross link with poly anion chain.

Set cement consist of unreacted powder particle surrounded by silica gel in amorphous matrix of hydrated calcium & aluminum poly salts.

Calcium poly salts are responsible for initial set.

Aluminum poly salts form the dominant phase.

Water plays an important role in structure of cement.

After hardening, fresh cement is extremely prone to the cracking & crazing, due to drying of loosely bound water .

Hence these cements must be protected by application of varnish.

The structure of the set GIC

SETTING TIME

Type I 4 - 5 minutes

Type II 2.5-6 minutes

PROPERTIES

Compressive strength - 150 mpa

Tensile strength - 6.6 mpa.

Hardness - 49 KHN.

Solubility & Disintegration:-

Initial solubility is high due to leaching of intermediate products.

The complete setting reaction takes place in 24 hrs, cement should be protected from saliva during this period.

Film Thickness

The film thickness of GICs is similar to or less than that of zinc phosphate cement and is suitable for cementation and luting.

Luting : 15µm

Restorative : 50 µm

Adhesion

By bonding a restorative material to tooth structure, the cavity is theoretically sealed, protecting the pulp, eliminating secondary caries and preventing leakage at the margins.

This also allows cavity forms to be more conservative and, to some extent, reinforces the remaining tooth by integrating restorative material with the tooth structures.

Bonding between the cement and dental hard tissues is achieved through an ionic exchange at the interface.

Polyalkenoate chains enter the molecular surface of dental apatite, replacing phosphate ions.

Calcium ions are displaced equally with the phosphate ions so as to maintain electrical equilibrium.

This leads to the development of an ion-enriched layer of cement that is firmly attached to the tooth.

The shear bond strength of conventional glass ionomer cements to conditioned enamel and dentin is relatively low, varying from 3 to 7 MPa.

Hydroxy Apatile Particles functions as an adsorbent and an ion exchangeable agent, resulting in improved mechanical and chemical properties of GIC.

[Arita K, Yamamoto A]

[Dent mater J – 2011 Sept]

However, this bond strength is more a measure of the tensile strength of the cement itself, since fractures are usually cohesive within the cement, leaving the enriched residue attached to the tooth.

In an invitro study by Guglielmi et al,

The use of ultrasound affects the marginal sealing of GIC with enamel.

[Int J Pediatr Dent – 2011 Aug]

Comparisons between resin-modified glass ionomer cements and conventional materials reveal that the shear bond strength of the former is generally greater, but that they show very low bond strength to unconditioned dentin compared to conventional materials.

Conditioning therefore plays a greater role in achieving effective bonding with the resin-modified glass ionomer cements.

Esthetics :-

GIC is tooth coloured material & available in different shades.

Inferior to composites.

They lack translucency & rough surface texture.

Potential for discolouration & staining.

Heat curing GIC, lead to long lasting and bio-compatible posterior GIC restorations which is not only mechanically equal in strength and wear but also in esthetics compete with posterior composites

[Van Duinen RN]

[Refaut Hapeh Vehashinavim – 2011 July]

Biocompatibilty :-

Pulpal response to glass ionomer cement is favorable.

Pulpal response is mild due to

- High buffering capacity of hydroxy apatite.

- Large molecular weight of the polyacrylic

acid ,which prevents entry into dentinal tubules.

Anticariogenic properties :-

• Fluoride is released from glass ionomer at the time of mixing & lies with in matrix. Fluoride can be released out without affecting the physical properties of cement.

Initial release is high. But declines after 3 months.

After this, fluoride release continuous for a long period.

Fluoride can also be taken up into the cement during topical fluoride treatment and released again ,thus GIC act as fluoride reservoir.

Advantages:-

♣ Inherent adhesion to the tooth surface.

♣ Good marginal seal.

♣ Anticariogenic property.

♣ Biocompatibilty

♣ Minimal cavity preparation required.

Disadvantages :-

♦ Low fracture resistance.

♦ Low wear resistance.

♦ Water sensitive during setting phase .

♦ Less esthetic compared to composite.

Uses :-

1. Anterior esthetic restoration material for class III & V restorations.

2. For luting.

3. For core build up.

4. For eroded area .

5. For atraumatic restorative treatment.

6. As an orthodontic bracket adhesive.

7. As restoration for deciduous teeth.

8. Used in lamination/ Sandwich technique.

9. In an invitro study by Jefferies SR et al, a new bio active luting cement which is a combination of calcium aluminate and glass ionomer showed no loss of retention, no secondary caries, no marginal dis- colourations and no subjective sensitivity after 2 years in tooth with fixed partial dentures.

[Jefferies SR, Pameijer CH]

[J Prosthodont 2011 Oct]

SANDWICH TECHNIQUE(GIC As Adhesive Cavity Liners)

Devolped by Mclean,

To combine the beneficial properties of GIC & composite.

The so called sandwich technique involves using GIC as dentine replacement and a composite to replace enamel.

These purpose designed lining materials set quickly and can be made receptive for the bonding of composite resins simply by washing the material surface if the material is freshly placed.

Excess water results in some of the GIC matrix being washed out from around the filler particles giving a microscopically rough surface to which the composite wall will attach in an analogous manner to etched enamel.

This surface should be coated either with an unfilled resin or a DBA to optimize attachment.

It is only necessary to etch a GIC with acid if the restoration has been in place for some time and has fully matured.

The sandwich technique has a number of attractions but it should be undertaken as planned procedure rather than as method to improve the appearance of unsatisfactory GIC restoration.

Clinical steps:-

After cavity preparation,

condition the cavity to develop good adhesion with GIC.

Place Type III GIC into prepared cavity.

After setting, etch the enamel & GIC with orthophosphoric acid for 15 seconds.

This will improve micromechanical bond to composite resin.

Apply a thin layer of low viscosity enamel bonding agent & finally place the composite resin over GIC & light cure it.

Advantages of sandwich technique:-

♣ Polymerization shrinkage is less, due to reduced bulk of composite.

♣ Favorable pulpal response.

♣ Chemical bond to the tooth.

♣ Anti-cariogenic property.

♣ Better strength, finishing, esthetics of overlying composite resin.

Modification of GIC :

A. Metal Reinforced GIC .

1. Silver alloy admix.

2. Cermet cement.

B. Hybrid Ionomer (Resin-Modified GIC)

Dual cure .

Tricure .

C. Compomer (Polyacid modified resin composite materials ).

D. Giomer

Metal Reinforced Glass Ionomer Cements

Metal-reinforced glass ionomer cements were first introduced in 1977.

The addition of silver-amalgam alloy powder to conventional materials increased the physical strength of the cement and provided radiodensity.

Silver alloy admix / miracle mix:-

This is made by mixing of spherical silver amalgam alloy powder with glass ionomer powder and liquid.

Cerment:-

Bonding of silver particles to glass ionomer particles by fusion through high temperature sintering.

Nowadays these materials are considered as old-fashioned as the conventional glass ionomer cements have comparable physical properties and far better aesthetics.

The clinical performance of cerments is considered to be inferior to other restorative materials, so much so that their use is now discouraged.

Metal - Reinforcement Of Glass Ionomers

Glass Cermets (Ketac Silver)

Amalgam Alloy (Miracle Mix)

Problems with Metal-Reinforced Glass Ionomer Cements

Poor esthetics.

Less Fluoride Release.

Low increase in strength due to lack of bonding of metals to the matrix

Hybrid Ionomer (Resin-Modified GIC)

Dual- cure :

These combine an acid-base reaction of the traditional glass ionomer with a self-cure amine-peroxide polymerization reaction.

These light-cured systems have been developed by adding polymerizable functional methacrylate groups with a photo-initiator to the formulation.

Such materials undergo both an acid-base ionomer reaction as well as curing by photo-initiation and self cure of methacrylate carbon double bonds or in other words their acid-base reactions are supplemented by a second resin polymerization initiated (usually) by a light-curing process.

For this reason they’re also called Dual-Cured GIC which was Developed in 1992. The resin-modified glass ionomer cements in their simplest form are glass ionomer cements that contain a small quantity of a water-soluble, polymerizable resin component.

More complex materials have been developed by modifying the polyalkenoic acid with side chains that could polymerize by light-curing mechanisms in the presence of photo initiators, but they remain glass ionomer cements by their ability to set by means of the acid-base reaction.

Tri-cure :

Some systems have also incorporated a chemical curing tertiary amine-peroxide reaction to polymerize the methacrylate double bonds along with the photo-initiation and acid-base ionic reaction.

These materials are known as tri-cure glass ionomer cements.

The chemical cure component of tri-cure cements has been shown to have a significant effect on their overall strength.

Photo-initiated cements cannot be used in cases involving opaque structures such as metal substrates.

Resin Modified Glass Ionomer Cements

Resin Modified Glass Ionomer Cements are conventional glass ionomer cements with addition of HEMA.

Properties of Resin-Modified GIC

1. Superior mechanical properties.

2. Better optical properties.

3. Prolonged working time and rapid set.

4. Adhesion to tooth structure.

5. Less moisture sensitivity.

6. Polymerization shrinkage.

7. Microleakage.

Setting reaction of resin – modified auto cure material

Mixing of powder + liquid

Usual acid base reaction initiated

Catalyst in powder will initiate polymeristaion of HEMA & cross-linkable monomers

Ultimately, there will be cross-linking between 2 systems & the entire mass will set hard with uniform physical properties

Criticisms against RMGI

1. HEMA – monomer – toxic – relative lack of biocompatibility, potential for allergic response

2. HEMA – hydrophilic – set material takes up water – expansion + less resistance to wear & erosion

3. Potential for color change over time (Doray 1994)

4. HEMA – low molecular weight monomer – more polymerisation shrinkage .

Applications of Resin-Modified GIC

1) Restoration.

2) Liners and bases.

3) Fissure sealants.

4) Core buld up.

5) Cementation of orthodontic brackets.

6) Retrograde root filling material.

According to Chitnis D et al, RMGIC provides more bond strength when compared to composite resin and giomer adhesive systems.

[Am J orthod DentoFacial orthopaedics 2006 March]

Compomer :-

Compomer is a composite resin that uses an ionomer glass which is the major component of glass ionomer as the filler.

Small quantity of dehydrated polyalkenoic acid incorporated with filler particles.

Setting reaction is light activated.

Adhesive system used with compomer is based on acid etch found with all composite resin.

Features of compomer

Fluoride release

Compomers do show a fluoride ion release, like a glass ionomer cement.

The level of this fluoride release however is only around 10% of that released by a glass ionomer, and therefore its usefulness in preventing recurrent caries is questionable

And it is shown to have no advantage over an amalgam restoration which releases silver, not fluoride.

Immersion in distilled water for the resin composite and poly acid modified resin composite caused a significant decrease in fracture toughness as the time interval increased

[Bagheri R, Azar MR]

[Am J Dent – 2010 June]

Compomers also do not have the ability to 'recharge' with topically applied fluoride from toothpaste etc., like glass ionomer cements do which again will limit their efficacy.

Handling

Handling and ease of use of composites is generally seen as good by dental professionals.

Compomers are available in both normal and flowable forms, with the manufacturers of the flowable compomers claiming that they have the ability to shape to the cavity without the need for hand instruments.

Aesthetics

Compomers are tooth coloured materials, and so their aesthetics can immediately be seen as better than that of dental amalgams.

According to Gross LC et al,

Compomers are a suitable alternative to amalgam or other, tooth colored materials when used as class II restorations in primary teeth.

[Pediatr Dent 2001 Jan]

It has been shown that ratings in various aesthetic areas are better for compomers than resin modified glass ionomer cements.

Compomers are also available in various non-natural colours from various dental companies for use in deciduous teeth.

Giomer

Giomers are a relatively new type of restorative material.

The name "giomer" is a hybrid of the words "glass ionomer" and "composite", which pretty well describes what a giomer is claimed to be.

Although glass-ionomer restorative materials such as Ketac-Fil (3M ESPE) and Fuji Type II (GC America) have some very important properties, such as fluoride release, fluoride rechargeability, and chemical bonding to tooth structure, they also have well-known shortcomings.

They are sensitive to moisture contamination and desiccation, which can present the clinician with challenges during their placement.

In the 1990s manufacturers improved these shortcomings by adding resins to glass ionomers to produce resin-modified glass ionomers.

These products (e.g., Fuji II LC, GC America; Vitremer, 3M ESPE; Photac-Fil Quick, 3M ESPE) have much better esthetics and handling characteristics than glass ionomers.

They also retain many of the glass ionomer's beneficial properties, such as long-term fluoride release and the ability to be recharged with topically applied fluoride.

They tend to discolor over time. In another attempt to "better" the glass ionomer restorative materials, compomers were also developed.

They were touted as being similar to glass ionomers but having much better esthetics and being easier to place and polish.

Although they handled better than GICs, they released much less fluoride and could not be recharged.

In the continuing quest for improved glass ionomer-like restoratives, manufacturers have developed and introduced a new class of materials called "giomers.“

Giomers are similar to compomers and resin composites in being light activated and requiring the use of a bonding agent to adhere to tooth structure.

It is available in 13 shades and is supplied in syringes.

According to Dhull KS et al, fluoride release was found to be higher in giomer when compared to compomer

The fluoride release from giomer and compomer was significantly higher in the acidic de-mineralizing solution than in the neutral remineralizing solution.

[J Indian Soc Ped Prev Dent- 2011 Jan-March]

On a 2 year clinical performance ,

-- The success rate of giomer in class 5 cavities is 80%, whereas in class I it is 100%

[Sunic MC, Shinkai K]

[operativeDent- 2005]

Almost assuredly, many other giomer products will become available in the future. This will continue to assess the results of the published literature and perform evaluations of these products as they become available.

Resin Cements

Material with two or more distinct substances

metals, ceramics or polymers

Most frequently used

esthetic-restorative material

Leinfelder 1993

Composition

Resin matrix

monomer

initiator

inhibitors

pigments

Inorganic filler

glass

quartz

colloidal silica

Coupling Agent

Phillip’s Science of Dental Materials 2003

Properties:

1. Insoluble in oral fluids.

2. Low viscosity.

3. Thin film thickness (<25µm).

4. Easily manipulated.

5. Early setting.

6. Good bond strength to dentin.

7. Radiopacity.

8. High wear resistance.

9. Low polymerization shrinkage.

10. Biological compatibility.

Types of resin-based cements

Self cure or auto-cure resin cements.

Light cure resin cements.

Dual-cure resin cements.

Indications

Anterior restorations

Posterior restorations

preventive resin

conservative class 1 or 2

Contraindications

Large posterior restorations

Bruxism

Poor isolation

Advantages

Esthetics

Conservation of tooth structure

Adhesion to tooth structure

Low thermal conductivity

Alternative to amalgam

Disadvantages

Technique sensitivity

Polymerization shrinkage

marginal leakage

secondary caries

postoperative sensitivity

Decreased wear resistance

Uses of Resin Cements

Cementation of ceramic or resin inlays and onlays.

Cementation of ceramic veneers.

Cementation of orthodontic bands.

Direct bonding of orthodontic brackets.

Cementation of all metal castings.

Supply of Resin Cements

Powder and liquid mix

Syringe-type applicator

Base and catalyst

Light cure/dual cure system

SELF ADHESIVE CEMENTS

The proliferation of dental cements on the market today makes it important for dentists to have a solid understanding of their capabilities and indications.

Traditional materials can offer challenges, but in recent years, the introduction of the self-adhesive resin cement category has offered advantages in many different types of cases.

The Challenges of Traditional Materials

Conventional resin cements have been a popular choice in the past and a technique-sensitive one.

Because traditional resin cements typically necessitate the use of a bonding agent, it is not uncommon for the material to penetrate the dentin tubules and result in post-operative sensitivity.

Resin modified glass ionomer (RMGI) cements, while not associated with the same sensitivity issues as resin cements, come with their own drawbacks.

These materials do not offer the same level of strength as resin cements, and also are not appropriate for some types of ceramic restorations due to the fact that they expand when seated and some can cause breakage of the restoration.

In an invivo study by Vaz RR et al, it has been proved that self-adhesive resin cement was able to promote reliable adhesion with the underlying dentin.

[J Prosthodont 2011-Nov]

In fact, the rate at which sensitivity was reported in the 1990s was cause for concern in the dental community, with one survey finding 37 percent of patients reporting sensitivity in the first year after crown placement.

Even more concerning, up to 11 percent of the teeth treated in this study required endodontic treatment within the first year.