DENTAL MATERIALSCHAPTER 16

MICROLEAKAGE AND BIOLOGIC CONSIDERATIONS

Leakage- the greatest deterrent to the development of an ideal restorative material that occurs along the restoration-tooth surface

No restorative dental material exactly duplicates the physical properties of tooth structure

Changes in temperature and mechanical stress can result in the development of gaps atthe tooth-material junction

Overwhelming evidence shows that all restorative materials permit ingress of deleterious agents such as acid, food debris and microorganisms, between the walls of the prepared cavity and the restoration

Microleakage- may be the precursor of:

Secondary caries Marginal detoriaration Postoperative sensitivity Pulp pathology

With restorations, microleakage often results in unslightly marginal discoloration and necessities replacement of the restoration

Microleakage poses a particular problem for teeth in the pediatric patient because the floor of the cavity preparation may be close to the pulp

The added insult to the pulp caused by the seepage of irritants that penetrate around the restoration and through the thin layer of dentin, or a microscopic pulpal exposure, may produce irreversible pulp damage

Acid etching- is commonly used to accomplish bonding of a

restorative resin to enamel by the formation of resin tags into etched enamel

Bonding- true adhesion to occur, it must take place at a

molecular level and must involve a chemical interaction between the molecules of the adhesive and the adherend

Polycarboxylate and Glass Ionomer Cements- the only dental materials currently use that

have the potential for true adhesion to tooth structure and an established clinical record for success

CAVITY VARNISHES

Used for many years as a liner for cavity preparations

Leaves a thin resin film

Reduce microleakage

May reduce initial microleakage around amalgam

CEMENT BASES Promote recovery of the injured pulp and to protect it

against further insult

Serves as thermal insulator and replaces missing dentin

The base should be of sufficient thickness to provide effective insulation (0.5 mm is required)

ZINC PHOSPAHATE, HARD SETTING CALCIUM HYDROXIDE, ZINC OXIDE-EUGENOL and GLASS IONOMER CEMENTS have sufficient strength to serve effectively

In certain cases, such as a class II preparation that involves the restoration of an angle or of a deep depression, it may be necessary to cover a calcium hydroxide base with a layer of stronger zinc phosphate or glass ionomer cement

AMALGAM

No longer the most commonly employed material for restoring posterior carious lesions

The unique clinical success of amalgam during 150 years of use has been associated with many characteristics

Excellent clinical service Least technique and time required replacement Lack of dimensional change during hardening

FAILURES OF AMALGAM

Form recurrent caries

Fracture

Dimensional change or involvement of the pulp or periodontal membrane

3 FACTORS THAT LEAD TO SUCH CLINICAL FAILURES ARE:

Improper design of the prepared cavity

Faulty manipulation

Choice of the alloy used

SELECTION OF THE ALLOYS

1. The alloy should meet the requirements of the ADA specification No. 1 or the corresponding ISO specification for dental amalgam alloys

The manipulative characteristics of dental amalgam are extremely important and a matter of subjective preference

Rate of hardening Smoothness of the mix Ease of condensation Finishing vary with the alloy

Dental amalgam alloys generally are available as either small fillings called LATHE-CUT or spherical particles called SPHERICAL ALLOYS

SPHERICAL ALLOYS

Tend to amalgamate very readily

Require less condensation pressure

HIGHER COPPER ALLOYS The original dental amalgam alloys were alloys of silver and tin

with maximum of 6% copper

Alloys that contain enough copper to eliminate the formation of the tin-mercury phase (11% to 30% are called HIGH COPPER AMALGAM ALLOYS

ADMIXED SYSTEM- first alloy type  Creep- the tendency of a material to deform continuously

under a constant applied stress- this property has been associated with the marginal breakdown (ditching) commonly noted with amalgam restoration

Choice of amalgam alloy today should be limited to high copper alloy systems

MERCURY / ALLOY RATIO Most of the amalgam alloy sold today is in the form of

prefilled, disposable mixing capsules containing the proper amounts of alloy and mercury

The alloy/mercury ratio is accurately proportioned

The need for disinfection procedures is minimized because the capsule system is discarded after use

Exposure of dental personnel and environmental contamination by mercury vapour is minimized

These prefilled capsules are usually available for different size mixes, often called single or double spill capsules

TRITURATION Second manipulative variable

Can significantly influence both consistency and working timed of the mixed amalgam

The correct trituration time varies depending on the composition of the alloy, the mercury, alloy ration, the size of mix and other factors

The most serious error in amalgamation generally is UNDERTRITURATION

An undertriturated mix appears dry and sandy and does not cohere into a single mass

An amalgam will set too rapidly, which results in a high residual mercury content, reduced strength, and the increased likelihood of fracture or marginal breakdown

Properly mixed amalgam is SHINY, coherent mass that can be readily removed from the capsule

CONDENSATION

The purpose of condensation is to adapt the amalgam to the walls of the cavity preparation as closely as possible to minimize the formation of internal voids and to express mercury from the amalgam

The greater the condensation pressure, the lower the amount of residual mercury in the restoration and the greater the strength of the restoration

MOISTURE Moisture contamination of an amalgam restoration can

promote failure

If zinc is present in the alloy, it will react with water and hydrogen gas will be formed

As gas builds up within the amalgam, a significant delayed expansion can occur and may cause protrusion of the amalgam from the cavity preparation, which enhances the possibility of fracture at the margins

Exposure to saliva after the amalgam has been completely condensed is not harmful

It is only moisture incorporated within the amalgam as it is being prepared or inserted that must be avoided

MARGINAL BREAKDOWN AND BULK FRACTURE If the restoration is improperly finished by the dentist, a

thin ledge of amalgam may be left that extends slightly over the enamel at the margins

These thin edges of such a brittle material cannot support the forces of mastication. In time they fracture, leaving an opening at the margin

Bulk fracture of amalgam is much less common with high-copper amalgam alloys

Those cases that do occur likely have one of two causes:

Poor cavity design resulting in an insufficient bulk of material across the isthmus can lead to failure of even a high-strength alloy

Premature loading of the restoration

Unlike a resin matrix composite, amalgam gains strength slowly over the first 24 hours

The use of rapid setting amalgam with a high 1-hour compressive strength should be considered when treating a pediatric patient in whom compliance with instructions to refrain from biting down hard on the freshly placed amalgam

BONDED AMALGAM RESTORATIONS

Dental amalgam does not adhere to tooth structure, it must be retained mechanically by the design of the cavity preparation and or mechanical devices such as pins

The placement of an amalgam does not strengthen the compromised remaining tooth structure and subsequent fracture may occur, particularly in molar teeth with relatively large mesiodistocclusal amalgam restorations

The use of dental adhesive systems serves as lining materials for amalgam

It is important to distinguish the application from use of a dental adhesive to seal the dentin surface and reduced early microleakage

When dental adhesives are used to seal the dentin surface, the adhesive should be polymerized before the amalgam is placed

At the present time, amalgam bonding should be considered only as an adjunct for conventional, accepted practices of cavity preparation and mechanical retention of amalgam

CEMENTS Serve as luting agent to fill the space between a

restoration fabricated outside the mouth and tooth structure.

  FUNCTIONS:

Provides mechanical retention. Serves as a filling material for either permanent or temporary

restorations. Used as bases for other restorative materials.

* Silicate Cement – early tooth colored filling material. Although is no longer used today, has the ability to reduce development of secondary caries. Because of the presence of fluoride in the silicate cement powder. Fluoride ion is released slowly and reacts with the adjoining tooth throughout the life of the restoration, the protective mechanism is undoubtedly a continuous one.

TYPES:

Advantages: Excellent handling

characteristics. (setting time,fluidity,film thickness)

Long history of successful permanent cementation.

Does not have carcinogenic effects.

Disadvantages: Is an irritant. Moderate degree of

intraoral solubility. Does not adhere to

tooth structure. Sensitivity and Pulp

response are most likely to be problems

ZINC PHOSPATE CEMENT

- most widely used luting agent.

LUTING CEMENT

Several types of cements can be used as luting agents. Thus the selection depends on the individual situation presented by the patient.

POLYCARBOXYLATE CEMENT

Advantages:

Excellent biologic properties.

Useful as base or luting agent, particularly if the restoration is already close to the pulp.

A chemical bond is formed between the cement and the calcium in the hydroxyapatite in enamel and dentin.

Disadvantages:

Leakage and loss of retention may occur along the cement restoration.

Low tensile strength. No significant fluoride

release. Modest intraoral

solubility.

- one of few dental materials that demonstrate true adhesion to the tooth surface.

As a luting agent, several factors affect the wetting of the tooth by the cement and thereby the retention and the restoration. After cavity preparation the enamel and dentin surfaces are covered with thin layer of tenacious debris referred to as smear layer.

The preparation may also be covered with a thin film material such as zinc oxide eugenol,if a provisional restoration was placed.

10-15 second swabbing with 10% polyacrylic acid to clean the prepared surface.

HANDLING:• Liquid should not be dispensed until just before the

mix is to be made.

• Powder and liquid should be mixed rapidly. And completed within 30 seconds.

• If the mix is too thick, insufficient acid is present to produce bond in the tooth.

• If there is excess liquid, intraoral solubility is increases significantly.

• Glossy appearance is produced when the mix is properly prepared and can be extruded into a thin film.

GLASS IONOMER CEMENT-

another type of cement that is based on polyacrylic acid most widely used cement.

Powder: Fluoro-aluminosilicate glass Liquid: Polyacrylic acid or ( alkenoic

acid, itaconic acid, or maleic with tartar acid)

Advantages:

Biologic kindness Fluoride release Potential adherence

to tooth structure. Possesses anti-

carcinogenic potential.

Lower intra-oral solubility.

Disadvantages: Reported post-

operative sensitivity in cases of deep preparations.

Low initial pH of cement.

Slow setting

HANDLING:

Material is pre-proportioned in a disposable capsule mixed in the amalgamator.

In cases of type I GIC the liquid acid may be freeze-dried and combined in the powder.

The freeze-dried products have lower viscosity.

The mix can be made either in a disposable, moisture resistant paper pad or on a glass slab.

The liquid the same as polycarboxylate cement, is not dispensed until just before the start of the mix.

Large increments of the powder are rapidly incorporated into the liquid.

Mix should be completed in 40 seconds.

Working time is short, not more than 3 minutes from the start of mix.

It should no longer be used if the mix has already lost its gloss or a skin is formed on the surface.

After setting of the cement it is brittle than a polycarboxylate cement and can be trimmed and finished.

*The cut dentin surface can be cleaned mechanically with pumice, but the smear layer should not be removed.

  *Most commonly employed luting cements for metallic restorations.

*Employed for bonding orthodontic brackets.

RESIN-MODIFIED GLASS IONOMER CEMENTS

most recent addition to the cement field. Also referred to as hybrid glass ionomers.

  Advantage:

Longer working time.

Much less sensitive to dehydration or moisture.

  Disadvantage:

Reported fracture of all-ceramic crowns.

Less well-established.

ZINC OXIDE-EUGENOL

can be used as both luting and restorative material.

Advantage: Kind biologic behavior.

Used as base material,

temporary luting cement,

temporary restorative material

Disadvantage: Low strength

High oral solubility.

RESIN CEMENTS although not new to dentistry have now just been extensively used.

Major clinical application was in direct bonding of orthodontic attachments to acid-etched enamel.

  Advantage:

High strength, low film thickness. Very low oral solubility. Can be bonded to etched enamel, ceramics, resins and etched or treated

metal surfaces.

Types:

Two component- chemically activated curing system.

Single component ( Visible light-activated)- used with translucent restorative materials.

Dual activated materials- chemical and light activated, for thick restorations and locations where geometry can limit access.

TEMPORARY AND PERMANENT RESTORATIONS

TEMPORARY RESTORATIONS Must have minimal solubility. Must be rigid, strong and resistant to abrasion resistance.

* Zinc-oxide eugenol is the most commonly used for holding or for intermediate restorations, because of its excellent tissue tolerance and ability to minimize initial microleakage.

*Type II glass ionomer cements or the new modified GICs are also useful as long term, temporary restoratives, for example in eroded areas in patients when exposed areas of cementum and dentin are present.

*As mentioned earlier the resin modified glass ionomer is the best choice for both temporary and semi-permanent restorations.

RESTORATIVE RESINS 

Conventional Composites Composite material refers to a combination of at least two

chemically different materials with a distinct interface separating the components.

They are composed of inorganic filler and a resin matrix.

Some types of resin matrix are bis-GMA or urethane dimethacrylate resin.

Some types of macro fillers are ground particles of fused silica, crystalline quartz, and soft glasses. These make-up 70-80% of the material.

Filler and resin must be bonded by a coupling agent such as silane product on the surface of the filler.

The higher filler content the more the coefficient of thermal expansion is reduced compared with unfilled acrylic resin.

  Despite the use of the coupling sytem the filler particles do

become dislodged during cutting and finishing and under abrasive action that affects the softer resin matrix which becomes worn away.

The higher filler content the more the coefficient of thermal expansion is reduced compared with unfilled acrylic resin.

  Despite the use of the coupling sytem the filler particles do

become dislodged during cutting and finishing and under abrasive action that affects the softer resin matrix which becomes worn away.

MICROFILLED COMPOSITES

improved surface smoothness and polishablity of composite resins.

  The composite is based on the use of

extremely small silica filler particles sizes 0.02 to 0.04 um hence are called microfine, microfilled, or polishable resins.

May be dispensed directly into the paste but only in a limited manner. Addition to amounts in excess of 20% results in a viscous paste.

 

Advantage: Ability to be finished to an extremely smooth surface. Surface irregularities caused by the dislodgement of small silica

particles are not visible or detected by the eye.

Disadvantage:

Softer and have a slightly higher coefficient of thermal expansion.

Higher water absorption. More polymerization and shrinkage. Lower mechanical properties.

Because of the disadvantages of microfilled resins it should be used where esthetics are the main concern such as in class III or class V restorations, and should not be used in restorations that are subjected to stress.

SMALL- PARTICLE AND HYBRID COMPOSITE

Small- particle composites are recommended for stress bearing applications such as Class IV and class II restorations.

Their surface finish is inferior to that of a microfill resin but much better than that of a conventional composite.

Small particle composites have an average filler sizes

This permits higher filler loading than in the conventional composites and results in the best combination of physical properties of all currently available composites.

Small particle composites are recommended for stress- bearing applications such as class Iv and class II restorations.

Hybrid composites are the most recent step toward smaller particle size.

They contain radiopaque glass particle with an average size of 0.6 to 1.0 in addition to 10% to 20% colloidal silica.

The total filler level, 70% to 80%, is lower than in a small-particle composite but higher than in microfill resin.

Because these combine two types of fillers, the result is called a hybrid composite.

One of the primary motivations in the development of these hybrid materials was to find a material that could compare favorably with dental amalgam in wear resistance in class I and II restorations.

LIGHT- CURED COMPOSITE

Composite resins were chemically activated, which required the mechanical mixing of two pastes to initiate the chemical reaction.

Have largely supplanted the chemically activated composites.

Light curing provides an advantage in working time and other handling characteristics.

One major disadvantage of light- cured composites must be emphasized.

Polymerization will only occur if the resin is exposed to light of sufficient intensity for an adequate length of time.

The curing time should at least 40 seconds, and the depth of resin to be cored should not exceed 2.5 mm.

Larger restorations and dark shades of resin require an incremental placement technique.

Dual- activated resins are available that combine both light and chemical activation.

Dark shades of composites resin may require longer curing times.

The most commonly used visible light activation units employ a quartz-tungsten-halogen lamp (QTH) as a light source.

This light is filtered to retain the wavelengths between 400 and 500 nm (blue light).

A more recent addition to activation units uses a blue light- emitting diode (LED).

LEDs are nearly 100% efficient at generating light over a relatively narrow wavelength band (460 to 480 nm).

The advantage of LED lights appears to be convenience , because they do not require a fixed power cord to a base unit.

POSTERIOR COMPOSITE RESTORATION

Composite Restoration were originally used for anterior or non- stress- bearing locations such as:

Class III Class V

Class IV

The improved strength, hardness, and modulus of elasticity of some of the newer composite resins, with their low thermal conductivity and superior esthetics, indicate that they may serve as alternatives for amalgam in the restoration of occlusal and proximal surfaces in posterior teeth.

Class I Class II

RESIN INLAYS

The resin inlay restoration addresses some of the short comings of composite resins, particularly the difficulties with the placement and light curing.

Indirect Inlay restoration – is fabricated in the laboratory on a die poured from an impression of the prepared tooth like a wax pattern for a cast restoration.

Finished inlay is cemented in the mouth using a resin cement.

It is more time consuming and expensive than direct resin restorations.

ACID- ETCHING TECHNIQUE

One of the most satisfactory methods for mechanical bonding of resin to enamel is the use of acid-etch technique.

The enamel is etched with a solution of phosphoric acid ( usually about 35% ) for approximately 15-20 seconds.

Both liquid and gel etching agents are available;

Placement is more readily controlled with the gel.

The acid cleans the enamel to provide better wetting of the resin and creates pores into which the resin flows to produce “tags” that greatly increase retention.

BONDING AGENTS

The bonding agent consisted of bis-GMA resin matrix material diluted with low-viscosity methacrylate monomer.

After acid- etching of the enamel, the bonding agent was applied.

The success of the acid-etch, enamel- bond technique led to attempts to do the same for bonding to dentin.

For the past 20 years, researched has focused on the development of agents that will bond adhesively to dentin. This has led to the introduction of dentin-bonding agents, which are either chemically activated or light cured.

They are applied to the dentin before placement of the composite.

GIC has been recommended for use as dentin- bonding agent in the so-called sandwich technique.

Dental resins are no more or less irritating to the pulp than are several other commonly used restorative materials.

Whenever, the cavity preparation is deep, the same precautions should be taken with resins as with other restorative materials.

THANK YOU & GOOD DAY

Dasco, Danica Amor

Lim, Shiela Marie

Juan, Faye Anna