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Dental bio materials Lizymol P.P. Dental Products Laboratory

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1 Dental bio materials Lizymol P.P. Dental Products Laboratory
Biomedical Technology Wing, Sree Chitra Tirunal Institute for Medical Sciences and Technology, Poojappura, Thiruvananthapuram , India Biomedical Technology Wing Achutha Menon Centre for Health Sciences Studies Tertiary Care Medical Centre for Cardiac and Neuro disorders

2 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

3 The Tooth Constituents
Enamel: Calcium hydroxyapetite Ca10(PO4)6(OH)2 – 90% Dentine: Minerals – 70% H2O – 10% Collagen – 18% Non collagenous – 2% Organic Matrix (20%) The hardness values found for sound enamel VHN , KHN VHN of dentin was , dentine-pulp interface VHN 40, Amalgam VHN

4 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.

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6 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

7 Dental Caries - what is it ?
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)

8 Dental Caries Host-agent-environmental model for dental caries.
Cariogenic microorganisms Susceptible teeth Ca ri es Substrate Time

9 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.

10 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

11 Dental erosion Bacterial effects.

12 Dental erosion

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

14 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

15 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)

16 Dentistry evolved with materials driving innovation
Set of dentures made for George Washington by John Greenwood, 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

17 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

18 Restorative materials 1. Silicates:. 2. Amalgams : 3. Acrylics: 4
Restorative materials 1. Silicates: 2. Amalgams : 3. Acrylics: 4. Composites 5. Glass Ionomers (Preventive materials) : 6.Compomers: Amalgam restoration Composite restoration

19 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 The use of gold alloys also became widespread after William Taggart developed the method of centrifugal casting to make cast gold inlays in 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.

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

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

22 Bleaching teeth is becoming a big business

23 When tooth loss occurs, the implants are there for anchorage
Implanted support structures have been reporting great success rates.

24 Materials are changing orthodontic practice
Metal brackets (stainless steel, Superelastic) Ceramic brackets Invisalign (clear plastic aligners to move teeth)

25 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.

26 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.

27 Silicate cements were the first to be used as esthetic restoratives
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.

28 Amalgams Toxicity : to patient, doctor and environment Poor aesthetics

29 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.

30 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

31 References The amalgam controversy An evidence-based analysis, JOHN E. DODES, D.D.S. J Am Dent Assoc, Vol 132, No 3, © 2001 American Dental Association Alzheimer’s disease, dental amalgam and mercury, Stanley R. Saxe, J Am Dent Assoc, Vol 130, No 2, © 1999 American Dental Association

32 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.)  

33 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.

34 Acrylics Unfilled low molecular weight polymers with no reinforcement
Polymerization Shrinkage, High Exotherm Early clinical failure due to recurrent caries

35 Composites 1960 Chemical UV-curable Visible light curable
Macro (packable) µm Micro 0.04 µm Hybrid 0.04,0.2-3 Nano µm

36 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 mm/year.

37 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.

38 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                                               Composite resin Marginal gap filling Enamel Secondary Caries Dentin Pulp

39 Dental Composites 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. 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.

40 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.

41 Advantages of composites
Low polymerization shrinkage Better mechanical properties High abrasion resistance Biologically least reactive Better aesthetics Low cost Easier clinical handling Low exotherm

42 Chemistry Formulation variations

43 Variable factors Glass particles Methacrylate Polyacid solution
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 So what factors can be varied to improve the mechanical and particularly wear properties of RMGICs. First of all we can vary the ratio of the glass to acid and monomer. The elements in the glass can also be altered as can the particle size and surface properties. This can provide some control over the rates of its reaction with the polyacid solution. The concentration and molecular weight of the polyacid can also be modified as can the hydropholicity of the monomer. We can also add crosslinking groups to the methacrylate monomer as this is known to improve wear resistance in polymeric systems.

44 Silane coupling agents
HOSi monomer Improve bond between monomer and glass to reduce viscosity, glass hydrophilicity, hydrolysis to raise strength, wear resistance

45 Chemical formulas of methacrylate monomers
(hydrophilic) Hydrophobic

46 Chemistry Setting reactions

47 Methacrylate polymerisation reaction
Liquid Methacrylate monomers Hard solid polymer C C C=O OR H CH 3 n Light and catalyst initiated C=C C=O OR H CH 3 n Linear polymer chain n determines molecular weight HEMA This shows the chemical structure of the methacrylate monomer. When this monomer polymerises in RMGICs this carbon carbon double bond splits into 2 single carbon carbon bonds joining the monomer molecules together in a long linear polymer chain. We can increase its hydrophobicity by making this R group more hydrophobic. We can also add a second double bond onto the end of the R group to enable the linear polymer to become crosslinked to a second chain through the R group. Such a process is known to improve wear resistance in polymers. If we change any of the properties of an RMGIC, however we have to be able to quantify and thereby control the level and rates of the methacrylate polymerisation. In the next part of this talk I shall go on to describe some of the new Raman and IR methods we have devised to quantify setting reactions in complex dental restoratives. Since much of our work is commercially sensitive I shall, however, focus largely upon data for commercial systems. BISGMA, UDMA, TEGDMA R group contains a second methacrylate group Crosslinked polymer

48 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.

49 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.)

50 Since the filler is a glass, its esthetics can be precisely controlled
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.  

51 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. 

52 Polyacids (hydrophilic and reactive)
Acrylic Itaconic Maleic

53 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

54 Recent trends in Restoration
Ormocers resin-modified glass ionomers compomers Tissue engineering

55 Organically modified ceramics
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.

56 Ormocer synthesis Sol-gel type reaction
Formation of additional organic net work or cross linking after the build up of the inorganic net work

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58

59 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.

60 Tissue engineering

61 Advantages of organically modified ceramics composites
Low shrinkage during curing Good mechanical properties Good abrasion resistance Adhesion to the teeth Good toxicological data

62 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..

63 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 A second type of hybrid material is the resin modified glass ionomer cement. These RMGICS consist of all the GIC components plus a hydrophilic monomer called HEMA (That is hydroxyethylmethacrylate). In both composites and compomers the monomer is hydrophobic (ie repels water) Such materials can set via both a polymerisation and aicd glass reaction. Generally like GICs Resin modified GICs adhere to tooth structure and can release significant levels of fluoride. The hydrophilicity of the polymerised monomer also encourages water sorption which can cause swelling to compensate for the polymerisation shrinkage. The major disadvantages of RMGICs are their strength which is intermediate between that of GICs and composites and their generally low wear resistance.

64 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 Companies, therefore, have more recently produced hybrid materials of composites and GICS that can potentially undergo both a polymerisation and acid glass reaction. One class of such materials are the acid modified composites or compomers for short. Compomers consist of fluoride containing glass and acidic hydrophobic monomers. Such materials set largely by the polymerisation reaction although some acid glass reaction can occur at the material surface. The main advantages of Compomers is their resonable strength combined with fluoride release. Unfortunately the levels of release achieved with compomers are generally much lower than seen with GICs. The disadvantages of compomers are the same as those for composites IE they require an separate adhesive and shrink during cure.

65 Commercial examples of the various classes of restorative materials
Decreasing strength Material type Commercial name Company Composition Composite Z100 (Z1) 3M glass (80%) BISGMA/ TEGDMA 50/50(20%) Compomer Dyract (DY) Dentsply glass (72%) UDMA (18%) acidified monomer(9%) RMGIC Fuji II LC (Imp) (F2) Fuji GC glass (76%) HEMA(10%) polyacid water GIC Fuji ix (F9) Fuji GC glass (78%) polyacid water

66 Future Developments More emphasis on preventive treatment
Tissue regeneration Tissue engineering A fully integrated tissue engineered organ.

67 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.

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

69 Thank you “We smile not because we are happy
We are happy because we smile”


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