Dental Cement

DENTAL CEMENTS

       1. INTRODUCTION

       2. HISTORY

         3.      TERMINOLOGIES

      4.      CLASSIFICATION 

   5.       DEVELOPMENT OF DENTAL CEMENTS

   6.      IDEAL PROPERTIES OF DENTAL CEMENTS

   7.      RESTORATIVE CEMENTS

   8.      LUTING CEMENTS

   9.      AGENTS FOR PULP PROTECTION

   10.  ZINC PHOSPHATE CEMENT

   11.  SILICATE CEMENT

   12.  ZINC SILICOPHOSPHATE CEMENT

   13.  ZINC POLYCARBOXYLATE CEMENT

   14.  ZINC OXIDE EUGENOL CEMENT 

  15.GLASS IONOMER CEMENT

15. RESIN CEMENTS
16. CALCIUM HYDROXIDE
17. FLUORIDES IN DENTAL MATERIALS
18. SOLUBILITY AND DISINTEGRATION OF CEMENTS
19. SUMMARY
20. REFERENCES

Introduction

In Dentistry, the term “cement” has been applied, traditionally to powder / liquid materials which are mixed to a paste consistency set to a hardness, and used clinically to restore teeth and attach preformed restorations, in or on the teeth.

Dental cements, in the recent years has become  restricted to those materials which are employed to bond inlays, crowns, bridges, posts and facings in or on the tooth and to retain orthodontic bands and  retainers, however secondary applications of these cements include cavity linings, bases and temporary fillings.

These different applications  make varying demands on manipulative properties, working and setting time, and resistance to mechanical  breakdown  and dissolution.

Thus some materials are  better suited to some application than others.

 Many of these materials are supplied in powder/liquid form and set by an acid-base reaction, but this is not universally true.

The word `cement’as used in this context, conveys the idea not only of a bonding agent but also the concept implied in the word `lute’ that is , the additional requirement of gap filling and sealing.

HISTORY

1.  1873- Silicate cement by Fletcher

2. 1873- Zinc oxide and clove oil by Chisolm

3.  1879- Zinc phosphate cement by Dr Pierce

4.1930- Calcium hydroxide paste by Hermann

5. 1968-Polycarboxilic cement by Dennis Smith

6.1971-Glass ionomer cement by Wilson and Kent

DEFINITION

Cement

Substance that hardens to act as a base, liner, filling material or adhesive to bind devices and prosthesis to tooth structure or to each others.                

                             Kenneth j. Anusavice 

A cement is  commonly considered as a substance that holds two surfaces together, it also serves as an agent as esthetic restorative  material, thermal  insulator, temporary restorative material and medicament for pulpal protection under larger restorations.

                             Karl. F. and Jack Moons

Cement :-A non metallic material  used for luting, filling permanent or temporary restorative purposes, made by mixing components into a plastic mass that sets or as an adherent sealer in attaching various dental restorations in or on the tooth .

CRAIG

Classification

The following is a classification of dental cements based on their chief chemical ingredients and application.  By Craig

Zinc Phosphate	Retention of restorations, retention of orthodontic bands, higher strength base, temporary restoration.
Zinc Oxide- Eugenol	Bases, temporary restorations, temporary and permanent retention of restoration, root canal sealer, gingival tissue pack, surgical dressing
Zinc Polyacrylate	Retention of restoration, retention of orthodontic bands, high strength base.
Glass Ionomer	Class-v  restoration, retention of restorations and orthodontic bands, composite and adhesive resin cements. retention of conventional crowns and bridges, retention of ceramic and composite inlays ,onlays, retention of  orthodontic brackets
Calcium Hydroxide	Low strength base.

Classification based on setting reaction                                                                                

 (kenneth J.Anusavice)

1. Acid Base Reaction –Zinc Phosphate cement

                                              -Zinc polycarboxylate cement

                                              -Zinc oxide- eugenol cement

                                              -Glass ionomer cement

2.      Light / Chemical – activated polymerization and acid base reaction    

                                                         

3.       Resin modified glass ionomer cement

4.       Light / Chemical – activated polymerization

5. Compomers

6.      Resin cement.

7. Polymerizing cements
8. Cyanoacrylates
9. Dimethacrylate polymers
10. Polymer ceramic composites
11. Other materials
12.                         ♦ Calcium hydroxide
13.                         ♦ Varnishes.

Classification based on: Uses of Dental cements
by Skinner

Cement	Principal uses	Secondary Uses
Zinc phosphate	Luting agent for restorations and orthodontic appliances	Intermediate restoration, thermal insulating base
Zinc oxide- eugenol	Temporary restoration, cavity liner, pulp capping agent.	Root canal sealer, Periodontal surgical dressing
Zinc         Polycarboxylate	Luting, thermal insulating bases	Luting for orthodontic appliances.

Silicate	Anterior restorations
Glass ionomer	Anterior restorations, cavity liners, luting  agent for restorations	Pit& fissure sealant, thermal insulating bases
Calcium   hydroxide	Pulp capping, thermal insulating bases.	Temporary restorations

Silicate	Anterior restorations
Glass ionomer	Anterior restorations, cavity liners, luting  agent for restorations	Pit& fissure sealant, thermal insulating bases
Calcium   hydroxide	Pulp capping, thermal insulating bases.	Temporary restorations

Ideal properties of dental cements

1.     Should be strong and hard.                              

2.     Should be insoluble in saliva .                         

3.     Should be dimensionally stable.                   

4.     Should be adhesive .                                                    

5.     Should be non porous .                                     

6.     Should be biocompatible and non irritant.    

7.     Co-efficient of thermal expansion(CTE) should   be equal to the tooth structure.

8.     Should not be affected by thermal changes and moisture.

9.     Should be easy to manipulate.

Restorative cements

Dental cements are employed for

i.       Temporary restorations

ii.     Intermediate restorations

iii.  Esthetic restorations/ fluoride releasing cements for direct filling restorations

Temporary restorations

        Materials used for temporary restorations are expected to last for only a short period of time, a few days or few weeks

They may serve as a treatment while the pulp heals

Cement used

-  Zinc oxide-eugenol

Also called holding type restorations

Duration – several months or longer

Particularly used in pedodontics

 Rampant caries

Material used          :type II zinc phosphate

                   type II and type III zinc silicophosphate

  

Fluoride releasing cements for direct filling restorations

The use of dental cement as a restorative material began with silicate cement

Cements used

1.    Silicate cement

2.    Glass ionomer cement

LUTING CEMENTS

Numerous dental treatments necessitate attachment of prostheses and appliances to the teeth by means of a luting agent.

These include metal, metal-ceramic, composite and ceramic restorations, provisional or interim acrylic restorations, laminate veneers for anterior teeth, orthodontic appliances, and pins and posts used for retention of restorations

Definition : The word `luting’ implies the use of a moldable substance to seal a space or to cement two components together; hence the term is descriptive of dental cementing agents.

Luting agent: A viscous material placed between tooth structure and a prosthesis that hardens through chemical reaction to firmly attach the prosthesis to the tooth structure.

As luting agent, the most important clinical requirements are-

1.    Flow/viscosity

2.    Wetting

3.    Film thickness

4.    Setting time

5.    solubility

To enhance flow and wetting, the materials are mixed at relatively low powder-to-liquid ratios.

To produce a film thickness of less than 25 micro meter, cement particles of 5 micro meter or less in diameter should be used.

Indications  for use of  luting cements 

1.    Because cements are much more soluble than the overlying restorative material, the accurate fit of the resin to be luted is critical. 

2.    Poor fitting margins increase solubility of the cement that can lead to recurrent decay.

3.    Examples for luting Cements :

4.    Zinc phosphate, zinc oxide eugenol, zinc  polycarboxylate, glass ionomer, resin modified glass ionomer, compomer and resin cements .

AGENTS FOR PULP PROTECTION 
(LINERS , BASES  AND CAVITY VARNISHES)

Many restorative dental materials that provide excellent properties for the bulk of a dental restoration may not protect the dental pulp during setting or during cyclic, thermal or mechanical stressing.

Pulp protection requires considerations of

a) Chemical protection

b) Electrical protection

     c) Thermal protection

          d) Mechanical protection

        e) Pulpal medication

CAVITY VARNISHES

·       Definition :

Cavity varnishes are principally natural gums, such as copals or rosins, or synthetic resins dissolved in an organic solvent such as acetone, chloroform or ether.

}  They form a coating on the tooth by evaporation of the solvent and are not generally  applied in a  sufficient thickness to provide the required thermal insulation.

COMPOSITION, STRUCTURE & PROPERTIES OF TYPICAL VARNISH	COPAL RESIN VARNISH
COMPONENTS
Solid	10% Copalresin
Solvent	90% ether, acetone, alcohol.
Setting Reaction	Physical (by solvent evaporation)
STRUCTURE
Arrangement	Amorphous film
Bonding	Covalently bonded organic material
Phases	Single phase
Defects	Pores & Cracks

          LINERS

“ Liners” are relatively thin layers of material used primarily to provide a barrier to protect the dentin from residual reactants diffusing out of restoration and/or oral fluids that may penetrate leaky tooth- restoration interfaces.

USES:

u They also contribute initial electrical insulation; generate some thermal protection; and , in some formulations, provide pulpal treatment as well.

u The need for liners is greatest with pulpally extended metallic restorations that are

ànot well bonded to tooth structure

ànot insulating such as amalgam and cast gold

àwith  other indirect restorations.

Calcium hydroxide

 Accelerates formation of  reparative dentin.

 Formulated by dispensing calcium hydroxide in aqueous or resin carrier solutions to facilitate application to the walls of a cavity  preparation.

The carrier evaporates and leaves a thin layer of calcium hydroxide on the cavity walls.

 In addition a film of calcium hydroxide with a pH of 11 can neutralize or react with acid released from adjacent phosphoric acid containing cements.

 Other hard setting materials are also available such as  low viscosity ZoE  and glass ionomers liner.

BASES

Cement bases are used to provide thermal protection for the pulp and to supplement mechanical support for the restoration by distributing local stresses from the restoration across the underlying dentin surface.

A layer of cement, called base, is placed under a permanent restoration to encourage recovery of the pulp and to protect it against several types of insults.

That insult may come from thermal shock and/or chemical irritation.

The base, in essence, serves as a replacement for the dentin that has been damaged by caries and removed during cavity preparation

Properties

1.   In contrast to liners, bases are applied in much thicker layers (0.5-1mm) under restorations to protect the pulp against thermal injury, galvanic shock and chemical irritation, depending on the particular restorative material.

2.   In addition, the material should be strong enough to withstand condensation forces during placement of restorations and to resist fracture under any masticatory forces.

3.   Examples : Cements used as bases are zinc phosphate, glass ionomer cement, zinc polycarboxylate.