1. BIOCOMPATIBILITY OF DENTAL MATERIALS
DR.RAMASHANKER
Associate professor
Deptt. of prosthodontic
3rd nov2014 time-10-11am

2. CONTENTS Introduction History Definition Requirements
Tests for evaluation
Allergic responses to dental materials
Materials considered for biocompatibility
Physical factors affecting pulp health
Summary
References

3. Introduction Biocompatibility :- interaction between body & material
Placement of material creates interface : dynamic
Interface activity depends on:
- location of material
- its duration in body
- its properties
- health of host

4. History
Mid 1800’ s dentists tried new materials for first time by directly putting them in patient’s mouth
eg. Fox : fusible metal-bismuth, lead & tin-melted & poured in cavity preparation at appx.100o C
G.V. Black tried his new ideas of restorative materials, like early amalgams in patients’ mouth

5. Concept of protecting patients- early 1960’s
Regulations & ethics introduced
Organisations like FDA,ANSI,ADA and ISO .

6. Definition
Being harmonious with life & not having toxic or injurious effects on biologic function.
(G.P.T. 8th edn.-2005)
Ability of the material to elicit an appropriate biological response in a given application in the body (Kenneth J.A).

7. Requirements for Dental Material Biocompatibility
Should not be harmful to pulp & soft tissues
Should not contain toxic diffusible substances
Should not produce allergic responses
Should not be carcinogenic

8. Biomaterial
Any substance, other than a drug, that can be used for any period as a part of a system that treats, augments, or replaces any tissue, organ or function of the body.
(G.P.T. 8th edn.-2005)

9. Classification of Biomaterials from perspective of Biocompatibility
Those which contact soft tissues within the oral cavity
eg. Acrylic resin
Those which could affect health or vitality of pulp
eg. Liner, bases
Those which are used as root canal filling materials
eg. Gutta percha

10. Classification of Biomaterials from perspective of Biocompatibility
Those which affect hard tissues of oral cavity
eg. Implants
Those used in dental laboratory
eg. Nickel, chromium, cobalt

11. ADVERSE EFFECTS FROM DENTAL MATERIALS
Classical biological reactions to materials are :
TOXICITY
INFLAMMATION
ALLERGY
MUTAGENICITY

12. TOXICITY Earliest response studied
Earlier material containing LEAD posed a risk to patient due to toxic property of lead

13. INFLAMMATION Involves activation of the host immune system
Histologically it is characterized by edema of the tissue with infiltration of acute & chronic inflammatory cells

15. ALLERGY
Most common response that occurs when the body recognizes a material as foreign
Reactions involves all dimensions of immune system
An allergic reaction results histologically in an inflammatory response that can be difficult to differentiate between non allergic inflammation or low grade toxicity .

16. Allergy

17. Allergic Responses to Dental Materials
Allergic Contact Dermatitis
Allergic Contact Stomatitis
Allergy to Latex products

18. Allergic Contact Dermatitis
Most common occupational disease
Susceptibility & prior sensitization necessary
Dose independent

19. Allergic Contact Dermatitis
Usually occurs where body surface makes direct contact with allergen.
eg. Monomers of bonding agent-
distal part of fingers & palmer aspect
of fingertips
Acrylic component of dental cements, nickel & resin monomers-allergic contact sensitizers.

20. Patch Test Most definitive diagnostic test
Suspected allergen applied to skin to produce small area of allergic contact dermatitis
After 48 to 96 hrs
hyperemia, edema, vesicle formation & itching
Positive reaction
(Slavin and Ducomb,1989)

21. Allergic Contact Stomatitis
Most common adverse reaction to Dental Materials
A) Local/contact type lesions
B) Systemic/distant lesions

22. Allergic Contact Stomatitis
Common allergens :- chromium, cobalt, mercury, eugenol, components of resin based materials, & formaldehyde
Mouthwashes, dentifrices, lozenges, & cough drops cause burning, swelling & ulceration of oral tissues.
Lichenoid reactions :- Long-term effect in oral mucous membrane adjacent amalgam & composite resins.
(Bratel and Johntell,1994)

23. Allergy to Latex Products
Polyether component-main causative agent
…March,1988
Dermatitis of hand (eczema) most common adverse reaction
Localized rashes & swelling to wheezing & anaphylaxis

24. Repeated exposure & duration plays important role.
Most serious systemic reactions occur when gloves or rubber dam contact mucous membrane - generalized angioneurotic edema, chest pain, rash on neck or chest region and respiratory distress
…Blinkhorn and Leggate,1984

25. Prevention: Use Vinyl gloves or gloves made of other synthetic polymer gloves:-
Polythene gloves.
Powder free gloves.
Nitrile gloves.

26. MUTAGENIC REACTIONS
Mutagenicity results when the components of the material alter the base pair sequences of the DNA in cells
Dental materials or components such as nickel, copper, beryllium, some components of root canal sealers & resin based materials are mutagens

27. KEY PRINCIPLES THAT DETERMINE ADVERSE EFFECTS
Two key factors have paramount importance :
Metal Corrosion or Metal degradation
Surface Characterstics

28. CORROSION Biocompatibility depends on degradation process
Biological response of corrosion products depends on:
Amount
Composition
Form
Location in tissues

29. CORROSION
Biological environment in contact also determines the corrosion property
for eg:
salivary esterases accelerate breakdown of dental resins
Ingestion of acidic substances may alter corrosion of alloys or ceramics

30. SURAFCE CHARATERISTICS
Surface different from the Interior region
For eg: casting alloy
sealant
EFFECTS OF SURFACE :
Ti alloys promote osseointegration
Rough surface promotes corrosion

31. Tests for Evaluation of Biocompatibility
Aim
To eliminate any potential harm or damage to oral or maxillofacial tissues from a product or any component of a product
To modify or control the use by manufacturer & operator to prevent cytotoxicity.

32. Tests for Evaluation of Biocompatibility
Biocompatibility tests are classified on three levels (tiers) :-
Group I : Primary tests
Group II : Secondary tests
Group III : Usage tests

33. Group I : Primary Tests Advantages :-
in vitro test, done in controlled experimental condition
Most rapid, economical & easily standardized
Large scale screening
Disadvantages :-
Lack of relevance to in vivo use of material
Lack of immune, inflammatory & circulatory system

34. Cytotoxicity Tests
Material in a fresh or cured state → placed directly on tissue culture cells or on membranes overlying them.
e.g.. Agar (Agar overlay technique)
Barriers like dentin disks

35. Genotoxicity Tests Determines carcinogenic/mutagenic potential
Carried out on mammalian or non-mammalian cells, bacteria, yeasts, or fungi.
Evaluates gene mutations, changes in chromosomal structure & other DNA or genetic changes caused by dental materials.

36. Genotoxicity Tests Ames Test :-
-Material is tested with mutant histidine dependant bacteria
-Agent is added to culture medium consisting salmonella typhimurium mutant gene which cannot produce histidine
-If carcinogenic :- salmonella species reversed to original state, i.e.... start producing histidine again

37. Group II : Secondary Tests
Advantages :-
Intact biologic system to respond to a material
Provide important bridge between in vitro environment & clinical use of material
Disadvantages :-
More expensive & difficult to control
Time consuming
Ethical concerns

38. Group II : Secondary Tests
1. Systemic toxicity test :-
Material administered to test animals e.g.. Rats- orally or i.v.
If > 50% animals survive material is safe

39. Group II : Secondary Tests
2. Skin irritation test :-
Irritation is inflammation without intervention of antibody or immune system.
Material held in contact with shaved skin of rats for 24 to 90 days
Erythema & edema are examined & confirmed.

40. Group II : Secondary Tests
3. Skin Sensitization test :-
Sensitization is inflammatory response requiring participation of an antibody system specific for material allergen.
Done similar to irritation tests

41. Group II : Secondary Tests
4. Inhalation toxicity test :-
Performed on rats, rabbits or guinea pigs in exposure chamber with aerosol preparations by releasing spray material around head & upper trunk of animals.
Death within 2 to 3 min very toxic
No death safe for human application

42. Group II : Secondary Tests
5. Implantation test :-
Only used for testing implants & endodontic materials.
Material placed subcutaneously,intramuscularly, or as a bone implant at lateral cortex of femur or tibia or both
Histopathological examination has to be done
Observation period may be upto 1 year.

43. IMPLANTATION TEST

44. Group III : Usage Tests Advantage :-
Material placed in an environment clinically relevant to its use in clinical practice
Disadvantages :-
Extremely complex & difficult to perform
Exceptionally expensive & very time consuming
Ethical concerns
In animals : usage tests
In humans : clinical trials

45. Classical progression of biocompatibility tests

46. Newer schemes for progression of biocompatibility tests

47. VARIOUS DENTAL MATERIALS CONSIDERED FOR BIOCOMPATIBILITY

48. Metals : Amalgam & mercury
Nickel
Beryllium
Gold
Resins : Acrylic Resins
Chemically cured composite resins
Light cured composite resins

49. Cements : Silicate cement
Zinc Phosphate cement
Glass ionomer cement
Zinc oxide Eugenol cement
Miscellaneous : Impression materials
Implant materials

50. Amalgam & Mercury Mercury itself has no effect on pulp
Pulp response related to condensation pressure
Rate of diffusion into enamel & dentin-inversely related to degree of mineralization.

51. Mercury Elemental mercury, Inorganic ion & Methyl mercury
Methyl mercury :-formed by biologic action of
elemental mercury; Absorbed 100% in gut; Most toxic
Elemental mercury absorbed less than 0.01%
65% to 85% mercury vapor that is inhaled is retained in body

52. Mercury Levels in Blood
Subjects with amalgam restoration ng/mL
Subjects without amalgam restoration ng/mL
Lowest level at which earliest ng/mL
non-specific symptoms occur

53. Mercury Hazard to Dental Personnel
Via inhalation & skin contact (allergic contact dermatitis)
Accidental spillage
Handling with bare fingers
Improper storage
Improper retrieval of spilled mercury or waste amalgam
Faulty equipment

54. Acute mercury poisoning :- Rare; stomatitis & diarrhoea
Chronic mercury poisoning :-
Weakness, fatigue, anorexia, wt. loss, insomnia,
irritability, shyness, dizziness & tremors in extremities.
Methyl mercury poisoning :-
Paresthesia of extremities, lips & tongue; ataxia (gait disturbance), & concentric constriction of visual fields (Tunnel Vision)

55. Recommendations in Mercury Hygiene
Store in unbreakable tightly sealed containers
Clean-up spilled mercury immediately
Do not handle with bare hands
Salvage all amalgam scrap & store it under water
Use water spray & suction while grinding
Do not use ultrasonic condensers
Periodic mercury vapor level determination in clinic
Alert health personnel about hazards of mercury
Use of rubber dam
Provide adequate ventilation

56. Nickel Most common cause of allergic dermatitis
Female : Male :: 10 : 1
Intraorally : little chance of allergy
Nasal & sinus cancer among nickel refinery workers due to nickel carbonyl

57. Beryllium Component of base metal alloys
Highest risk to dental technicians during melting & trimming of alloy
Berylliosis : inflammatory lung disease due to inhalation of beryllium dust or fumes

58. Beryllium Prevention : Confirm allergy by Patch test
Avoid base metal restorations in patients with known allergy
Good ventilation & exhaust

60. Gold
Pure gold is inert
Allergy to gold is very rare
(1 in 1 million)

61. Cements

62. Acrylic Resin
Cause allergic reactions (denture stomatitis) when used as denture base material or provisional fixed partial denture resin
Highest risk for dental professionals due to frequent exposure to unpolymerized monomer

63. Chemically Cured Resin Composites
Require use of matrix pressure to enhance adaptation to
cavity walls : Potential pulp irritant
Chronic pulpitis : persists for indefinite period, after
2 to 3 weeks, develop massive pulp lesion
Thin coating of hard setting Ca(OH)2 cement recommended for deep cavities

64. Light-Cured Resin Composites
Visible light cured systems : greater depth of cure, shorter curing time, less porosity & more wear-resistant restorations than UV light cured systems less pulp response
Use twice the recommended time exposure to light
Conservative cavity preparation & incremental curing;
no need for matrices & pressure, to gain adaptation
less toxicity to pulp

65. Impression Materials
Irreversible hydrocolloids :- Inhaling fine airborne particles (dust) can cause silicosis & pulmonary hypersensitivity.
Dustless/Dustfree alginate is preferred
Elastomers :- Cellular toxicity levels
Polyether > Addition Silicone > Polysulphide

66. Implant Materials
Commercially pure Titanium & its alloys are the most biocompatible restorative materials
Bio-glass ceramics used as implant materials also exhibit good biocompatibility

67. Implant Materials
Osseointegration :- Materials have very low degradation rates, & tend to form surface oxides that promote bony approximation within 100Ao space
eg. Titanium, tantalum, several forms of ceramics
Biointegration :- Materials undergo degradation to promote bone formation without any intervening space
eg. Bio-glass ceramics

68. PHYSICAL FACTORS AFFECTING PULP HEALTH

69. Microleakage
Free penetration of fluids, micro-organisms & oral debris along interface between restoration & tooth, progressing down the walls of cavity preparation
It can result in :-
Secondary/Recurrent caries acute/chronic pulpitis, pulp abscess, etc.
Staining or discoloration
Sensitivity due to continuing Pulpal irritation

70. Nanoleakage vs Microleakage

71. Prevention:-
Use bonding/adhesive techniques for better adaptation of restoration to tooth surface
Regular monitoring of restoration
Use cavity varnish below amalgam restoration
(leakage space filled by corrosion products thereby sealing cavity : but requires much time)

72. Thermal Changes
Temperature fluctuations in oral cavity may crack restorative material or produce undesirable dimensional changes Microleakage
Thermal conductivity & coefficient of thermal expansion
Metals are good conductors of heat, causing sensitivity with large metallic restorations
eg. Amalgam or gold inlays
Provide suitable base

73. Galvanism
Flow of current when two dissimilar metallic restorations oppose each other in oral cavity
Due to different electromotive potentials of opposing metals
Saliva acts as electrolyte
Contact Short-circuit current flows through pulp Pain & Discomfort

74. Galvanism Current falls off if fillings are maintained in contact
due to polarization of cell
Pain perception depends on patient sensitivity rather than magnitude of current
Magnitude of current depends on composition & surface area of metals
eg. Alloy of stainless steel develop higher current density than gold or cobalt-chromium alloys when in contact with amalgam

75. Galvanism
As size of cathode (eg. gold alloy) increase relative to anode (eg. Amalgam), current density increases
Larger cathode enhances corrosion of smaller anode
Current density in non-gamma2 containing amalgam is less than gamma2 containing amalgam
Prevention :-
Placement of insulating base
Applying varnish on cavity walls
Proper planning of restoration

76. Estrogenicity
Ability of a chemical to act in the body in a manner similar to that of an estrogen.
Bisphenol A –xenoestrogen may act on estrogenic receptors in cells.
E-screen assay –relies on growth response of breast cancer cells that are estrogen sensitive .

77. Summary Clinical Guidelines for selecting biocompatible materials :
Define the use of material
Define how the material has been tested
Think in terms of Risk & Benefit

78. Conclusion
Risks
Benefits
Clinical
Judgement

79. References:- 1) Philips’ Science of Dental Materials
- Kenneth J. Anusavice
2) Dental Material Sciences
- Combe
3) Dental Materials – Properties & Manipulation
- Craig
4) Color Atlas of Oral Pathology – 4th Edition
- Robinson & Miller
5) Essentials of Oral Pathology & Oral Medicine
- Cawson & Odell

80. Thank You
For a Patient
Listening