Lizymol P.P. Dental Products Laboratory Biomedical Technology Wing, Sree Chitra Tirunal Institute for Medical Sciences and Technology, Poojappura, Thiruvananthapuram.

Lizymol P.P. Dental Products Laboratory

Biomedical Technology Wing,Sree Chitra Tirunal Institute for Medical Sciences and

Technology,Poojappura, Thiruvananthapuram 695012, India

Dental bio materials

Biomedical Technology Wing

Achutha Menon Centre for Health Sciences Studies

Tertiary Care Medical Centre for Cardiac and Neuro disorders

Introduction

• Tooth anatomy• Need for restoration• Dental Caries - what is it ?• Dental erosion• Restorative materials • Controversy : amalgams• Zinc phosphate in Dentistry• Glass ionomers • Recent trends in dental restoration

Enamel: Calcium hydroxyapetite Ca10(PO4)6(OH)2 – 90% Dentine: Minerals – 70% H2O – 10%

Collagen – 18%

Non collagenous – 2%

The ToothConstituents

Organic Matrix (20%)

The hardness values found for sound enamel VHN 268 - 375 , KHN 292 - 390. VHN of dentin was 62.32., dentine-pulp interface VHN 40, Amalgam VHN 140-150

Tooth Glossary

Cementum - a layer of tough, yellowish, bone-like tissue that covers the root of a tooth. It helps hold the tooth in the socket The cementum contains the periodontal membrane. Crown - the visible part of a tooth. Dentin - the hard but porous tissue located under both the enamel and cementum of the tooth. Dentin is harder than bone. Enamel - the tough, shiny, white outer surface of the tooth. Gums - the soft tissue that surrounds the base of the teeth. Nerves - nerves transmit signals (conveying messages like hot, cold, or pain) to and from the brain. Periodontal membrane/ligament - the fleshy tissue between tooth and the tooth socket; it holds the tooth in place. The fibers of the periodontal membrane are embedded within the cementum. Pulp - the soft center of the tooth. The pulp contains blood vessels and nerves; it nourishes the dentin. Root - the anchor of a tooth that extends into the jawbone. The number of roots ranges from one to four.

Need for restoration

• Destruction of tooth substance by dental caries

• Fracture or loss of tooth substance due to accident

• Improvement in aesthetic appearance

• Abrasive wear of the tooth

Infectious microbiologic disease results in

gradual dissolution and destruction of calcified tissues (soft or bony) or teeth

Most common disorder affecting humans ( usually in children & young adults)

Dental Caries - what is it ?

Caries

Susceptible teeth

Cariogenic microorganisms

Substrate

Time

Host-agent-environmental model for dental caries.

Dental Caries

But naturally, the wholesale removal of sound tissues was not really a scientific answer to the issue of retention. Any sound tissue removal gives you less of the tooth for the next retentive treatment when recurrent caries develop. Moreover tooth tissues never remodel or grow back because there is no vascular activity in tooth structures. And developments in adhesion technology were always attracting thoughtful dentists. For materials that can be bonded to tooth tissue, unnecessary sound tissue removal for mechanical retention was unscientific.

Dental erosion

• Excessive tooth wear • Localized loss of tooth surfaces by chemical

process• Non bacterial origin• Excessive consumption of acidic food and

beverages • Softening of the enamel surface is an early

manifestation of erosion process• Indicates by a loss of surface hardness• Erosion enhances caries formation• 30-40% patients

Dental erosion

Bacterial effects.

Dental erosion

References

Journal of Dentistry 36,(2008),74-79

History of dental restoration

• Extracted teeth 3000 BC using gold bands and wires• BC 2500-Greeks & Romans: Gold structures-• BC 700 to 500- Etruia & Rome: Gold crowns and bridges

: filling Carious teeth. Some teeth found in Egyptian mummies were transplanted human teeth or tooth forms made of ivory.

• First century AD Celsus- with lint ,lead etc…is the beginning of filling materials

• AD1480-Gold filling- by an Italian ,Johannes Arculanus, University of Bologna

• AD 1050 to 1122 filling with ground mastic alum and honey

Beginning of Dental Science (1600-1840)

• Foundation of science of dentistry• 1700 Wax models • 1775 Gold base to support artificial ivory teeth fixed

with gold pins• 1826 Combination of silver and mercury to form

amalgam “silver paste” by O.Taveau of Paris• 1840 first dental journal ,The Americal Journal of

Dental Science• 1855 silver –tin-mercury alloy or amalgam by Elisha

Townsend• 1878 silicates (first polymeric direct restorative

material)

Set of dentures made for George Washington by John Greenwood, 1798. The base was made of hippopotamus ivory carved to fit the jaw ridges. The upper denture contained ivory teeth and the lower denture consisted of eight human teeth fastened by gold rivets that screwed into the denture base

Dentistry evolved with materials driving innovation

Direct filling gold

• Gold foils are the oldest of all the procedures

• Malleable and ductile

• Pieces of gold are placed in the prepared cavity and are cold welded under pressure applied by a suitable condensing instrument

• High density

Restorative materials1. Silicates:

2. Amalgams : 3. Acrylics: 4. Composites

5. Glass Ionomers (Preventive materials) : 6.Compomers:

Amalgam restoration Composite restoration

For many years, dental amalgams and metals were the main materials used in dental restorative practice to treat caries. Dental amalgams were used for many years even before G.V. Black optimized the dental amalgams in 1895. The use of gold alloys also became widespread after William Taggart developed the method of centrifugal casting to make cast gold inlays in 1907. In the first half of the 20th century, amalgams and metals were the mainstay of materials used in clinical practice. Other materials such as silicate cements were also tried, but their success was poor.

For large posterior restorations, amalgams were the materials of choice in the past.

But for locations where esthetics was critical, and chewing attrition is not a danger (such as anterior restorations), composites and resin ionomers were favored.

Materials such as amalgams and composites have been known to everyone as fillings

Before After

Esthetic repair of broken tooth is another advance due to development of composites.

Bleaching teeth is becoming a big business

When tooth loss occurs, the implants are there for anchorage

Implanted support structures have been reporting great success rates.

Metal brackets

(stainless steel, Superelastic)

Ceramic brackets

Invisalign (clear plastic aligners to move teeth)

Materials are changing orthodontic practice

Materials make it possible to make esthetics a vital part of restorative treatment

Veneers have become widely accepted as the benchmark of conservative cosmetic dentistry. They have been used successfully to mask teeth which are discolored and poorly shaped. Bonding ultra-thin shells of porcelain to teeth created many of those Hollywood or Bollywood smiles that we see.

Silicates

• Based on a cement forming reaction between alumino fluoro silica glass powder and phosphoric acid based liquid.

• Anticariogenic

• Dissolve in oral fluids with loss of transluscency,surface crazing and lack of adequate mechanical properties.

Silicate cements were the first to be used as esthetic restoratives. Silicate cement is made by mixing a powder of Alumino-Fluoro-Silicate glass  with a 37% solution of phosphoric acid.  The acid partially dissolves the glass, chemically combining with it, thus creating a very hard and brittle matrix. Silicate cement was the only tooth colored material available before the advent of composite resins. But dentists who used it in posterior teeth soon found out that it wears out quickly. It was also very brittle. The glass particles readily separated from the matrix under masticatory stresses. Lack of translucency was also a problem. But fluoride release from the restorative was an advantage.

Amalgams

• Toxicity: to patient, doctor and environment

• Poor aesthetics

Dental Amalgam: Controversy• Mercury fillings can be dangerous, according to the U.S. Food and Drug Administration.Ailments.

include fatigue, depression ,heart conditions and Alzheimer's disease. • Simply chewing could release harmful mercury vapour from the fillings which could be breathed

into the lungs, the U.S. Food and Drug Administration said • More than half of an amalgam filling is made up of mercury, which is more poisonous than lead.

• It is mixed with silver, copper and tin, forming a highly durable combination to lock in the mercury.

• But it is now accepted that mercury vapour escapes and small amounts are passed into the bloodstream and organs.

• Some research suggests that this could be linked to high blood pressure, infertility, and disorders of the central nervous system.

• Amalgam has served exceptionally well for restoration of posterior tooth defects, ranging from tiny holes in teeth to amalgamfull crowns. High strength and low wear have allowed this success.

• Dental amalgam is considered a safe, affordable and durable material that has been used to restore the teeth of more than 100 million Americans. It contains a mixture of metals such as silver, copper and tin, in addition to mercury, which binds these components into a hard, stable and safe substance. Dental amalgam has been studied and reviewed extensively, and has established a record of safety and effectiveness. Depending on treatment needs, it is one material available to dentists and patients when considering restorative options. Amalgam restorations remain safe and effective.

DENTAL AMALGAM AND ALZHEIMER’S

DISEASE • The authors2 found no significant association of

AD with the number, surface area or history of having dental amalgam restorations. They also found no statistically significant differences in brain Hg level between subjects with AD and control subjects. Hg in dental amalgam restorations does not appear to be a neurotoxic factor in the pathogenesis of AD. The authors found that brain Hg levels are not associated with dental amalgam, either from existing amalgam restorations or according to subjects’ dental amalgam restoration history

References

• The amalgam controversy An evidence-based analysis, JOHN E. DODES, D.D.S. J Am Dent Assoc, Vol 132, No 3, 348-356.

© 2001 American Dental Association • Alzheimer’s disease, dental amalgam and mercury,

Stanley R. Saxe, J Am Dent Assoc, Vol 130, No 2, 191-

199. © 1999 American Dental Association

Zinc phosphate cements• Zinc phosphate cement is one of the oldest and most reliable dental

materials.  It has been used for at least two hundred years.  It is still used for cementing cast metal crowns and onlays. It is made by mixing a strong solution (37%) of phosphoric acid with zinc oxide powder.  The zinc oxide powder partially dissolves in the acid creating zinc phosphate which when dry is a very hard, waterproof matrix which bonds unreacted zinc oxide particles together.   Mixing and cementing with this material is something of an art since it must be mixed slowly or else it will harden too quickly, and the work must be kept dry until the cement is set or else it will dissolve in saliva or water.  Once set, it is still one of the most reliable and most durable cements for luting (cementing) cast metal crowns and onlays on teeth.  It is also used to cement posts in teeth and was used until quite recently as a base under amalgam fillings.  (A base is a layer of material placed under a filling to protect the nerve from hot and cold while the overlying filling is in service.  Some bases can also be useful as a method of desensitizing the nerve.)  

• Zinc oxide has an added benefit since the acidity of the phosphoric acid etches the enamel on the tooth creating the irregular surface The cement flows into these irregularities to create a tight mechanical seal with the tooth itself.  It also flows into irregularities in the structure of the casting to form a "lock and key" type of bond between the tooth and casting thus locking it in place.  With the advent of newer cements with a quicker working time and less demanding technique, zinc phosphate is used less and less today.  Note that zinc oxide is an opaque white powder.  While it can be manufactured to be any color, the set material remains perfectly opaque.  For this reason, and the fact that it lacks wear resistance, zinc oxide is not esthetic or tough enough to be used as a "tooth colored" filling restorative.

Acrylics

• Unfilled low molecular weight polymers with no reinforcement

• Polymerization Shrinkage,• High Exotherm• Early clinical failure due to recurrent caries

Composites

• 1960• Chemical• UV-curable• Visible light curable• Macro (packable) 0.2-20 µm• Micro 0.04 µm• Hybrid 0.04,0.2-3• Nano 0.002-0.075 µm

Composites: Latest additions

Nanohybrids and nanocomposites were developed in recent years. Nanoparticles have dimensions in the order of several nanometers. Generally, the nanoparticle size under favor are those with particle size < 100 nm. The nanohybrids use nanofiller particles and minifiller particles to get sufficient filler packing into the composites. The nanocomposites use nano particles and nanoclusters to do the same. Clinical evidence is yet to be demonstrated, but early reports are promising, as expected. In vitro wear studies show wear rates <10 m/year.

Composites: Resin Matrix

The major problem with the light cured composite fillings is the microleakage. Who is the culprit for microleakage? We know it is a complex problem. But keeping the tissue-restoration interface intact and impermeable to external intruders is an important bioengineering problem.

Dentin

Enamel

Composite

resin

Marginal gap

Secondary Caries

Pulp

filling

Microleakage is a problem with composites The Problem in Microleakage: To keep the tissue-restoration interface

sealed to bacteria, toxins and agents that promote recurrent caries

In a dental composite (which consists of a resin matrix and a filler distribution), for example, we need to increase the modulus of elasticity and strength of the resin, decrease its shrinkage, thermal expansion coefficient etc. as well as optimize its translucency. Filler incorporation helps in all of these things.

Dental Composites

Bowen RL (1956). Use of epoxy resins in restorative materials. J Dent Res 35:361–369. Bowen RL (1963). Properties of a silica-reinforced polymer for dental restorations. J Am Dent Assoc 66:57–64.

Filler Materials

Typically silicate glass particles. Radio-opacity of the filler is an important consideration so that the composite presence in the tooth can be readily detected in radiographs for diagnosis. Heavy elements like Barium, ytterbium etc. are incorporated for this purpose. Beyond composition, the filler particle size, and its dispersion have been found to be the most important filler parameters.

Advantages of composites

• Low polymerization shrinkage

• Better mechanical properties

• High abrasion resistance

• Biologically least reactive

• Better aesthetics• Low cost• Easier clinical

handling

•Low exotherm

Chemistry

Formulation variations

Variable factors• Glass particles

– composition • basic (Al:Si:Ca:O:F), (for radiopacity add Sr:Ba:Zr)

– particle size – surface composition

• acid washing (GIC glass reactivity)

• silanisation level (composites, compomers and RMGICs)

• Methacrylate– hydrophobicity / crosslinking level

• Polyacid solution– concentration– molecular weight– acidic monomer

Silane coupling agents

Improve bond between monomer and glass to reduceviscosity, glass hydrophilicity, hydrolysis

to raise strength, wear resistance

monomerHOSi

Chemical formulas of methacrylate monomers

(hydrophilic)

Hydrophobic

Chemistry

Setting reactions

Methacrylate polymerisation reactionMethacrylate polymerisation reaction

Light and catalystinitiatedC=C

C=O

OR

H

H

CH3

C C

C=O

OR

H

H

CH 3

n

Liquid Methacrylate monomers

Crosslinked polymer

BISGMA, UDMA, TEGDMA R group contains a secondmethacrylate group

Linear polymer chainn determines molecularweight

HEMA

Hard solid polymer

n

Glass Ionomer  (polyalkenoate cement)

• Conventional glass ionomer cements were first introduced in 1972 by Wilson and Kent. They are derived from aqueous polyalkenoic acid such as polyacrylic acid and a glass component that is usually a fluoroaluminosilicate. When the powder and liquid are mixed together, an acid-base reaction occurs. As the metallic polyalkenoate salt begins to precipitate, gelation begins and proceeds until the cement sets hard.

• The mixture of poly-acrylic acid with Alumino fluro silicate glass causes a partial dissolving of the glass particles.  The poly-acrylic acid chemically combines with the dissolved glass components and produces a hard matrix material similar to that in silicate cement.  (This is essentially an acid-base reaction resulting in the formation of a "metallic polyalkenoate salt" which precipitates and begins to gel until the cement sets hard.)

• Since the filler is a glass, its esthetics can be precisely controlled.  The less brittle matrix means that the margins and surface of the restoration are less prone to chipping and crazing so there is much less staining with Glass Ionomer restorations than there is with silicates.   As a restorative, glass ionomers can be used in all esthetically sensitive areas with no reservations.  Of all the composite restoratives, glass ionomers are some of the prettiest restorations available.  

• On the plus side, these restorations not only look good, but they bond to tooth structure quite well.   Bonding between the cement and dental hard tissues is achieved through an ionic exchange at the interface.  Polyalkenoate chains enter the molecular surface of enamel and dentin, 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. 

Polyacids (hydrophilic and reactive)

Acrylic

Itaconic

Maleic

Glass ionomers

• Preventive material• Powder is an ion leachable fluro

aluminosilicate glass• Liquid is aq.soln. of polymers and

copolymers of acrylic acid• Cross linked gel formation followed by an

aluminum ion exchange strengthening the cross linking in the final set

• Calcium ion chelation occurs at the exposed surface creating an adhesive bond

Poor Strength, High Porosity

Recent trends in Restoration

• Ormocers

• resin-modified glass ionomers

• compomers

• Tissue engineering

Ormocer

Organically modified ceramics

or

Inorganic organic hybrid materials produced from liquid precursors using the sol gel

process. They form strong covalent bonds with the organic and inorganic components. The cross linking of organic and inorganic

moieties lead to 3D network with significant chemical and thermal stability.

Ormocer synthesis

• Sol-gel type reaction

• Formation of additional organic net work or cross linking after the build up of the inorganic net work

www.fraunhofer.jp

www.fraunhofer.jp

Organically modified Ceramics resin

• Binder for the filler• Continuous phase• Does not form the major part of the

composite• Its properties and chemistry contributing

much greater proportion to the acceptability and biocompatibility of the restoration.

www.fraunhofer.jp

Tissue engineering

Advantages of organically modified ceramics composites

• Low shrinkage during curing

• Good mechanical properties

• Good abrasion resistance

• Adhesion to the teeth

• Good toxicological data

resin-modified glass ionomers

• In the 1990s manufacturers improved shortcomings of GIC 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. Importantly, 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, however, to discolor over time..

Resin-modified glass-ionomer cements (RMGICs)

Consist of– F containing glass

– polyacrylic acid solution

– HEMA (hydrophillic monomer)

• Main advantages– adhere to tooth

– high fluoride release

– water sorption induced swelling

• Setting reactions– polymerisation – acid / base reaction

• Main disadvantages– intermediate strength– low wear resistance– polymerisation

shrinkage

Acid -modified composites (compomers)

• Consist of– F containing glass– acidic hydrophobic

methacrylate monomers

• Main advantages– reasonable strength– low fluoride release

• Setting reactions– monomer

polymerisation– limited acid /glass

reaction (catalysed by water sorption)

• Main disadvantages– Require adhesive– polymerisation

shrinkage

Commercial examples of the various classes of restorative materials

Material type

Commercial name

Company

Composition

RMGIC

Fuji II LC (Imp) (F2)

Fuji GC

glass (76%)HEMA(10%)polyacidwater

GIC

Fuji ix (F9)

Fuji GC

glass (78%)

polyacidwater

Compomer

Dyract(DY)

Dentsply

glass (72%)UDMA (18%)acidifiedmonomer(9%)

Composite

Z100 (Z1)

3M

glass (80%)BISGMA/ TEGDMA50/50(20%)

Decreasing strength

Future Developments

• More emphasis on preventive treatment

• Tissue regeneration

• Tissue engineering

• A fully integrated tissue engineered organ.A fully integrated tissue engineered organ.

Tissue engineering

• The research is lead by Professor Paul Sharpe at King’s College London Dental Institute. His team has demonstrated that tooth development can be initiated in stem cells, and that fully formed teeth can be created in developmental models. This is pioneering in that it represents one of the very few examples of a fully integrated tissue engineered organ.

• The technology opens the potential for the

implantation of cultured cells in patients to grow and replace damaged or missing teeth.

Conclusion

• History of dental restoration started with natural teeth and reaches to cultured normal teeth

“We smile not because we are happyWe are happy because we smile”