Biocompatibility of materials for use in the body Flashcards
Definition of a biomaterial
- Materials (synthetic or natural) that are used in medical devices that are in contact with tissues
- Augments or replaces partially or totally any tissue, organ or function of the body, in order to maintain or improve the quality of life of the individual
Biomaterial application examples
-Medical implants
Heart valves, artificial joints, dental implants
-Repair and healing of human tissues
Sutures, clips, staples, stents
-Cellular scaffolds for regenerating tissues
Biomaterials incorporating cells
Bioactive molecules
-Molecular probes and nanoparticles
Used in imaging for cancer and to deliver therapies at a molecular level
-Biosensors
Devices that convert biologic responses into electrical signals
Blood glucose monitoring devices and brain activity sensors
-Drug delivery systems
Chemotherapy devices for cancer patients
Implantable birth control
Biocompatibility definition
-Ability of a material to perform with an appropriate host response in a specific application (must be beneficial to the host)
Examples of materials that interact in oral cavity but still have a beneficial response
- Monomers in denture base materials
- Allergic reactions to alloys containing nickel
- Mercury in dental amalgam
- Phosphoric acid used as an etchant on enamel
Ideal properties of dental materials
- Non-toxic to patient and staff
- Non-irritant in mouth and other tissues
- Minimal inflammation (acute, not chronic)
- Tissue integration (implants)
- Physical and mechanical properties (for intended application)
- Not mutagenic or carcinogenic
Effects the body has on the implant material
-Protein adsorption
Dependent on material properties
-Environmental
Body fluids, pH, cells, proteins
-Degradation
Breakdown products
-Corrosion
Metals eg. cobalt-chrome alloys
Effects the implant has on the body
-Blood clot-equilibrium disturbed
Coagulation (platelets)
-Inflammatory response
Acute (neutrophils)
-Chronic inflammation
Chronic (lymphocytes and monocytes)
-Evokes immune response (activation of macrophages, lymphocytes)
-Wound healing (repair/regeneration)
Fibroblasts, endothelial cells
Evaluation of biocompatibility
-In vitro tests
Cytotoxicity screening tests provide an indication of cell death (by material itself or its extracts)
Many tests can assess cell number, growth rate, metabolism, gene up regulation
-Evaluating biocompatibility of a material in vitro allows prediction of in vivo oral tissues
- In vitro allows the prediction of in vivo oral tissues
- Not always comparable tho
Pros of in vitro testing and guidelines
- Social pressure to reduce animal experimentation
- Advance in vitro testing
- More sophisticated technology
-International Standardization Organisation (ISO) provides guidelines
-European Centre Validation Alternative Methods (ECVAM)- 3 R’s
Reduction, Refinement, Replacement
Pro(s) and cons of in vivo testing
- Need to identify a relevant mammalian model
- Addressing ethical concerns
- Expensive and time consuming
- Not always reproducible response
BUT
-Can obtain a more comprehensive biological response
Pros and cons of clinical trials
- Most relevant test
- Needs ethical approval and patient consent
- All other tests can be measured against this
- Expensive and logistically complicate
- Lots of variables, difficult to interpret results
ISO’s guidelines for testing cytotoxicity in vitro
-Material to be tested should be representative of either the final product or a component of the final product
3 requirements for biocompatibility testing methods:
-Specificity (ability of a test to correctly identify those with a disease)
Appropriate cells for a material being tested
-Sensitivity (ability of test to correctly identify those without a disease)
Methods used should be sensitive and suitable for cell culture medium
-Quality controls
Both negative and positive and also, material and cell culture control
Biocompatiblity broken down
- Ability of a material to perform with an appropriate host response in a specific application
- Involves 2 components:
-Biosafety
Deals with the exclusion of deleterious effects of a biomaterial on the organism itself
-Biofunctionality
Concerns and addresses the need of a material not only to be free from damaging effects on the host, but also to elicit a beneficial host-response, for optimal functioning of the medical device
Regulatory bodies for dental materials
- American National Standard Institute/American Dental Association
- International Standards Organization
- These regulatory bodies do not require specific biological tests but are guidelines for approval of materials
- Responsiblity is therefore placed on the manufacturer to present evidence for approval
Requirements of biomaterials before release into the market
-Any material or device that is to be used or placed within the body must be tested for biocompatibility to ensure it is safe for human use
- Dental materials used in the oral cavity should be harmless to all oral tissue: gingiva, mucosa, pulp and bone
- Materials should contain no toxic, leachable or diffusible substance that can be absorbed into the circulatory system, causing systemic toxic responses/toxicity (including teratogenic or carcinogenic effects)
- Materials should be free of agents that could elicit sensitization or an allergic response in a sensitized patient
How common are side effects of dental materials and how would they manifest
- Rare
- Those reported in resorative materials may show toxic, irritative or allergic reactions
- Often greater risk to the practicioner than the patient
- Effects range from cumulative irritation to severe allergenic responses
- Manifested as local and/or systemic
- Local reactions involve the gingiva, mucosal tissues, pulp and hard tooth tissues
- Systemic reactions are expressed generally as allergic skin reactions
- Side effects may be acute or chronic
Biocompatibility of dental amalgam
- No major adverse responses
- Lichenoid episodes reported
- Thermal conduction to pulp tissue may cause some tissue damage
Biocompatibility of GICs
- Few documented systemic adverse effects
- Minor irritant effect on the pulp
- Hydraulic pressure/etching during placement may irritate pulp
- Good adhesion, minimal leakage at margins and no gingival reactions reported
- Overall excellent biocompatibility
Biocompatibility of resin-based composites
- Few systemic adverse affects documented
- Incomplete polymerisation leads to degradation, leaching and imperfect bonding
- Polymerisation shrinkage
- Adverse local pulp and dentine reactions, development of recurrent caries and pain
- Increased plaque adhesion and lichenoid episodes reported
Biocompatiblity of ceramics
- Critical to the long term success of dental prosthesis
- No known severe reactions
- Except wear on opposing dentition and resoteation
- Strong, wear resistant
- Aesthetically pleasing
- Good biocompatibility
Difference between direct and indirect toxicity
- Direct toxicity is when a material should be free of substances that cause sensitisation or allergic responses
- Indirect toxicity should contain no toxic, leachable or diffusable substances
