By: Dr. Murtaza Najabat Ali (CEng MIMechE P.E.)

1. Dental materials, Dental amalgam alloys, noble metals and base metals used in dentistry and alloys for Dental implants, complications of Dental implants By: Dr. Murtaza Najabat Ali (CEng MIMechE P.E.)

2. Biomaterials for dental Applications

3. Biomaterials for dental Applications Caries---a destructive process of decalcification of the tooth enamel and leading to continued destruction of enamel and dentin, and cavitation of the tooth

4. Biomaterials for dental Applications

5. Biomaterials for dental Applications • These materials must withstand forces during either fabrication or mastication, • Retain their strength and toughness, and be resistant to • Corrosion, • Friction and • Wear • Similar to implantable devices for non-dental applications, they must also be biocompatible • Biocompatibility is defined as the ability of a material to elicit an appropriate biological response in a given application in the body

6. Biomaterials for dental Applications Biocompatibility is defined as the ability of a material to elicit an appropriate biological response in a given application in the body • Inherent in this definition is the concept that a single material will not be biologically acceptable in all applications • For example, a material that is acceptable as a full cast crown may not be acceptable as a dental implant • In a bone implant, the material is expected to allow the bone to integrate with the implant. Therefore, an appropriate biological response for the implant is Osseointegration (i.e. close approximation of bone to the implant material) • Whereas in a full cast crown, the material is expected to not cause inflammation of pulpal or periodontal tissues. Osseointegration, however, is not expected

7. Types of Dental Materials Three main groups, which are Metals Polymers Ceramics

8. Classification of Dental Materials Dental biomaterials fall into three classes, which are Preventive Dental Materials Restorative Dental Materials Auxiliary Dental Materials

9. Classification of Dental Materials Preventive Dental Materials • Pit and Fissure Sealants • Sealing agents that prevent leakage • Materials used primarily for their antibacterial effects • Liners, bases, cements and restorative materials that are used primarily because they release fluoride • Chlorhexidine (antiseptic/antimicrobial agent) or other therapeutic agents ( such as tooth paste, mouth wash (anti-caries)) used to prevent or inhibit the progression of tooth decay

10. Classification of Dental Materials 2. Restorative Dental Materials Dental restorative materials are specially fabricated materials, designed for use as dental restorations (fillings), which are used to restore tooth structure loss, usually resulting from dental caries (dental cavities) which include bonding agents, liners, cement bases, amalgams, resin-based composites, cast metals, metal-ceramics, ceramics, and denture polymers. Direct restorative materials • The chemistry of the setting reaction for direct restorative materials is designed to be more biologically compatible. Heat and byproducts generated cannot damage the tooth or patient, since the reaction needs to take place while in contact with the tooth during restoration • Used intraorally to fabricate restoration or prosthetic devices directly on the teeth Indirect restorative materials • Indirect restorations are fabricated outside of the mouth and therefore made extraorally in which the materials are formed indirectly on the teeth or tissues • Temporary restorative materials

11. Classification of Dental Materials 3. Auxiliary Dental Materials • Substances used in the construction of dental prostheses and appliances but do not become part of these devices. • Impression materials, casting investments, gypsum cast, and model materials, dental waxes, acrylic resins for impression, bleaching trays, mouth guards, and occlusion aids, finishing and polishing abrasives. Gypsum cast Mouth guard (braces) Dental impression materials Dental wax model

12. Dental Biomaterials Dental Amalgam Alloys • Dental Amalgam is a metallic restoration made by mixing mercury and a powdered alloy containing silver, tin and copper and sometimes zinc, palladium, indium and selenium • The amalgamation reaction produces a solidified alloy over a short time range, allowing the dentist to manipulate the pasty amalgam in tooth cavity • Dental amalgam is used to restore chewing surfaces and is subject to heavy forces • The aim of the amalgam is to develop an acceptable compressive strength in the restoration within several hours • The dimensional stability of the amalgam during setup is important for its clinical application Amalgamator is used to mix and to make a pliable mass of Dental amalgam alloy. It mixes the liquid and powder components and the reaction begins after mixing Amalgam Capsules; one capsule contains powdered amalgam alloy and the other capsule contains liquid mercury

13. Dental Biomaterials Dental Amalgam Alloys • When a tooth cavity is restored by using an amalgam, there is no adhesion between the amalgam and the tooth material. This can cause marginal leakage of the restoration (filling) • The dimensional stability of the amalgam during setup and its ability to reproduce the convolutions of the cavity walls, along with the technique of the dentist in mixing and applying the amalgam, affect leakage • Dental amalgam is brittle, which can lead to failure in tension or creep. Dentists avoid this by feathering edges and minimizing chances for high tensile loads

14. Dental Biomaterials Mercury Dose from Amalgam Dental Amalgam Alloys • Person with average number of fillings would absorb ~1.6 µg/day • Person with a moderately high number of fillings would absorb ~3 µg/day • According to EPA, absorbed dose of mercury from food, water, and air is 5.7 µg/day

15. Dental Biomaterials Noble and Base Metals • In addition to the Amalgam alloy, dental alloys can be placed into two broad categories, i.e. Noble Metals Base Metals Noble Metals ----- are elements with a good metallic surface that retain their surface in dry air. Their resistance to oxidation, tarnish and corrosion during heating, casting, soldering and use in the mouth is very good. The noble metals include: • Gold • Platinum • Palladium • Iridium • Rhodium etc.

16. Dental Biomaterials Noble and Base Metals • Gold, in either pure or alloyed form, is the most commonly used Noble metal used for dental restorations • Gold casting alloys are typically used for crowns and bridgework and ceramic-metal restorations • Some Palladium-base alloys are also used for similar applications • Although many in the metallurgical field also consider silver a Noble metal, it is not considered a Noble metal in dentistry because it corrodes considerably in the oral cavity

17. Dental Biomaterials Noble and Base Metals Base (Non-Noble) Metals ---- and their alloys for dental restorations include; • Cast Cobalt-chromium alloys used for partial dentures and porcelain-metal restorations • Cast Nickel-chromium alloys used for partial dentures, crowns and bridges, and porcelain-metal restorations • Cast Titanium and titanium alloys used for implants, crowns and bridges, and orthodontic wires • Stainless steels used for dental instruments, orthodontic wires and brackets, and reformed crowns Dental Cast Partial Denture Titanium crowns Orthodontic Bridges and Wires

18. Dental Biomaterials Noble and Base Metals • Because of the significant increases in the price of noble metals during the past few decades, alloys with considerably less noble metal content have been developed • In addition, base metal alloys have replaced noble metals systems in many applications • The metals and alloys used as substitutes for Gold alloys in dental applications must have the following fundamental characteristics, such as • The chemical nature of the alloy should not produce harmful toxicologic or allergic effects in the patient • The chemical properties of the appliance should provide resistance to corrosion and physical changes when in the oral environment • The base metals and alloys for fabrication should be plentiful, relatively inexpensive and readily available • The physical and mechanical properties such as Thermal Conductivity, Coefficient of Thermal Expansion and Strength, should all be satisfactory and meet specified values of the application

19. Dental Biomaterials Porcelain-Fused-to-Metal (PFM) Alloys • All-ceramic anterior (front teeth) restorations can appear very natural • Unfortunately, the ceramics used in these restorations are brittle and subject to fracture • Conversely, All-metal restorations are strong and tough, but from an aesthetic viewpoint are acceptable only for posterior restorations • Fortunately, the aesthetic qualities of ceramic materials can be combined with the strength and toughness of metals to produce restorations that have both a natural tooth like appearance and very good mechanical properties • The ceramic used for these restorations are porcelains, hence it is named as Porcelain-Fused-to-Metal (PFM) restorations

20. Dental Biomaterials Fabrication of PFM Restorations • PFM restorations consist of a cast pre-oxidized metallic coping on which at least two layers of ceramic are baked • The first layer applied is the opaque layer, consisting of a ceramic rich in opacifying oxides • Its role is to mask the darkness of the oxidized metal core to achieve adequate aesthetics, and as a first layer it also provides a ceramic-metal bond • The next step is the buildup of mostly translucent dentin and enamel ceramics to obtain an aesthetic appearance similar to the natural tooth • After building up the porcelain powders, the ceramic-metal crown is sintered in a porcelain furnace

21. Dental Biomaterials Fabrication of PFM Restorations

22. Dental Biomaterials Types of PFM Alloys • Both noble and base metals and alloys are used for PFM restorations • There are five types of Noble Metal Alloys for PFM restorations. In chronological order, they are: • Gold-platinum-palladium (Au-Pt-Pd) alloys • Gold-palladium-silver (Au-Pd-Ag) alloys • Palladium-silver (Pd-Ag) • Gold-palladium (Au-Pd) alloys • Palladium-copper (Pd-Cu) alloys • These alloys have noble metal contents ranging from about 50% to nearly 100%

23. Dental Biomaterials Types of PFM Alloys • In Base Metal PFM Alloys for PFM restorations, there is a range of compositions available of Base metal alloys for ceramic-metal restorations, which are • Nickel-chromium • Cobalt-chromium • Titanium etc.

24. Dental Biomaterials Alloys for Dental Implants • Dental implants are intended to support various dental appliances in the mouth • Dental implant designs can be separated into two categories called • Endosteal (endosseous), which enter the bone tissue • Subperiosteal systems, which contact the exterior bone surfaces

25. Dental Biomaterials Alloys for Dental Implants • The Endosteal implant designs such as cylinders, screws, blades etc., are placed into the bone • In contrast, the Subperiosteal devices are fitted to the bone surface and fixed with Endosteal screws

26. Introduction to ceramics, their structure, tissue attachment mechanisms, classification of ceramics and non-absorbable or relatively bioinert bioceramics

27. Ceramics • Ceramics are inorganic materials composed of non-directional ionic bonds between electron-donating and electron-accepting elements • Ceramics may contain crystals like metals, or may be non-crystalline (amorphous glasses) • Ceramics are very hard and brittle because of the nature of ionic bonds Articulating surfaces in several implants

28. Ceramics • Due to the similarity between the chemistry of ceramics and that of native bone, ceramics are most often used as a part of orthopedic implants or as dental materials • Their aesthetic quality and appearance is closer to natural bone/tooth • These materials are attractive as biological implants because bone bonds well to them, and they exhibit minimum foreign body reaction (implying inertness within the body), high stiffness, and low friction/wear as articulating surfaces Implantable skull fixators

29. Ceramics • Their main drawback is their brittle nature and resultant low impact resistance • Although dozens of compositions have been explored in the past, relatively few have achieved human clinical application • Ceramics due to their non-ductile nature, are very susceptible to notches or microcracks because instead of undergoing plastic deformation (or yield) they will fracture elastically on initiation of a crack Excellent Aesthetics

30. Ceramics • In order to be classified as a Bioceramic, the ceramic material must meet or exceed the following properties: • If a ceramic is flawless, it is very strong even when subjected to tension • Flawless glass fibers have twice the tensile strengths of high strength steel • Non-toxic • Non-carcinogenic • Non-allergenic • Non-inflammatory • Biofunctional for its lifetime in the host

31. Ceramics Structure of Ceramics • Since the bonds in ceramics are partially to totally ionic in nature (i.e. Pure ionic bonding cannot exist: all ionic compounds have some degree of covalent bonding. Thus, an ionic bond is considered a bond where the ionic character is greater than the covalent character) • Crystal structures in ceramic materials are thought of as being composed of ions rather than atoms • The variety of chemical compositions of ceramic materials results in a wider range of crystal structures than with metals • Ceramic crystal structure is affected by two parameters that are not concerns in metallic structures; (i) the magnitude of the electrical charge on the constituent ions, and (ii) the particle size of these ions

32. Ceramics Ceramics Ceramics Structure of Ceramics • The magnitude of the electrical charge is important because the crystal must remain electrically neutral (i.e. Sum of cation and anion charges in unit cell should be zero) • The second characteristic requires the knowledge of the radii of both the cations (rc) and anions (ra) composing a ceramic material • Cations are generally smaller, positively charged and usually metals • Anions are usually O, C, N, larger and negative charge • For an optimally stable structure, cations prefer to contact the maximum allowable number of anions (and vice versa for the anions) Certain ratios does not allow close contact between cations and anions and thus produce unstable structures

33. Ceramics Ceramics Ceramics Structure of Ceramics

34. Ceramics Structure of Ceramics • In this case, ion’s coordination number refers to the number of nearest neighbors with opposite charge and it depends on the rc/raratio • This ratio of ionic radii dictates the coordination number of anions around each cation • As the ratio gets larger, the coordination number gets larger • For example, for a coordination number of 4, the cation is found at the center of a tetrahedron, with anions at each corner • The most common coordination numbers for ceramics are 4,6 and 8 Silicate Structure

35. Ceramics Structure of Ceramics • AX Crystal Structures • For ceramics in which both the cation and anion have the same charge, an equal number of each is required for a stable crystal structure • These are called AX crystals, with A representing the cation and X representing the anion • The most common AX structure is the Sodium Chloride (NaCl) structure, and the coordination number for both cations (Na+) and anions (Cl-) is 6 The NaCl structure can be thought of as two interpenetrating FCC-type crystals, one composed of anions and the other of cations

36. Ceramics Structure of Ceramics • AmXp Crystal Structures • Ceramic materials are often composed of cations and anions that do not have equal charges, leading to compounds with the formula AmXp • A common example is found in Fluorite (CaF2) • The coordination number for Ca2+ is 8, and the system exhibits a cubic coordination geometry • The cations are at the center of the cube, with the anions at the corners

37. Ceramics Structure of Ceramics • Carbon-based Materials • Although carbon-based materials do not neatly fall into any of the classes of materials (metals, ceramic or polymers) • One common form, Graphite, is sometimes considered a ceramic • Even though it does not possess a standard unit cell, Graphite is crystalline Crystal structure of Graphite

38. Ceramics Structure of Ceramics • Carbon-based Materials • The structure consists of planes of hexagonally arranged carbon atoms • Within the planes, each carbon atom is bonded covalently to three neighbors • While the fourth valence electron participates in van der Waals interactions with plane above it

39. Ceramics Structure of Ceramics • Carbon-based Materials • A property of graphite that is important to the biomaterialist is its ability to adsorb gases • This is used in the formation of Pyrolytic carbon, in which carbon in the gaseous state is deposited onto another material (such as graphite) • Pyrolytic carbon has been used in a number of cardiovascular devices, including replacement heart valves

40. Ceramics Structure of Ceramics • Carbon-based Materials • An additional synthetic form of carbon can be found in Single-walled nanotubes (SWNT) and Multi-walled nanotubes (MWNT) • A single-walled nanotube can be visualized as a single sheet of graphite rolled to form a tube • Similarly, a multi-walled nanotube can be visualized as a tube rolled from multiple layers of graphite sheets • These carbon nanotubes are generally a few nanometers in diameter and on the order of a micron in length

41. Ceramics Tissue Attachment Mechanisms • No one material is suitable for all biomaterial applications • As a class of biomaterials, ceramics, glasses and glass-ceramics are generally used for repair or replacement of musculoskeletal hard connective tissues • Their use depends on achieving a stable attachment to connective tissue • Carbon-base ceramics are also used for replacement heart valves, where resistance to blood clotting and mechanical fatigue are essential characteristics Diamond-like carbon (DLC) coated

42. Ceramics Tissue Attachment Mechanisms • The mechanism of tissue attachment is directly related to the type of tissue response at the implant interface • No material implanted in living tissues is practically inert; all materials elicit a response from living tissues • Four types of possible tissue responses to biomedical implants, given below

43. Ceramics Tissue Attachment Mechanisms • These types of tissue responses (mentioned in the previous slide) allow four different means of achieving attachment of prostheses to the musculoskeletal system • Therefore, tissue attachment mechanisms for bioceramic implants, are

44. Ceramics Tissue Attachment Mechanisms • When biomaterials are nearly inert and the interface between an implant and bone is not chemically or biologically bonded • There is relative movement and progressive development of a fibrous capsule in soft and hard tissues • The presence of movement at the biomaterial-tissue interface eventually leads to deterioration in function of the implant or the tissue at the interface or both

45. Ceramics Tissue Attachment Mechanisms

46. Ceramics Classification of Ceramics • Ceramics used in fabricating implants can be classified as • Nonabsorbable (relatively inert) • Bioactive or Surface Reactive (semi-inert) • Biodegradable or Resorbable (non-inert) Calcium phosphate Putty for coating/filling purpose of various Grafts (which enables excellent cell infiltration, vascularization and resorption) • Alumina, zirconia, silicone nitrides and carbons are inert bioceramics • Certain glass ceramics and dense hydroxyapatite are semi-inert (bioreactive/bioactive) • Calcium phosphates and calcium aluminates are resorbable ceramics Collagen ceramic osteoconductive scaffolds are engineered to mimic the composition and pore structure of natural bone

47. Ceramics Classification of Ceramics

48. Ceramics Classification of Ceramics

49. Ceramics Classification of Ceramics

50. Ceramics Nonabsorbable (Relatively inert) Ceramics • Relatively bioinert ceramics maintain their physical and mechanical properties while in the host • They resist corrosion and wear have properties, such as • Non-toxic • Non-carcinogenic • Non-allergenic • Non-inflammatory • Biofunctional for its lifetime in the host • Examples of relatively bioinert ceramics are dense and porous Alumina (Aluminium oxides) and Zirconia (Zirconium dioxides) etc. • Relatively bioinert ceramics are typically used as structural-support implants, such as bone plates, bone screws and femoral heads • Examples of non-structural support uses are ventilation tubes, sterilization devices and drug delivery devices