Biocompatibility
Dr. FARAH. L
2nd year
2013-2014
Introduction
Biocompatibility, which was the subject of a consensus conference and whose evaluation follows an ISO 10-993 standard which cancels and replaces the old biocompatibility standards.
For years, biocompatibility was synonymous with inertness, that is, a material that posed no biological problems was considered biocompatible. In fact, biocompatibility is different from tolerance to a material because it assumes an appropriate response from the host.
Biocompatibility encompasses all the body’s responses to the implementation of a biomaterial, it must be evaluated by a series of tests given by the ISO standard. This is valid for all medical devices, regardless of the field of medical application.
1. Definitions
1.1 Definition of a medical device:
Any instrument, apparatus, material or other article (such as software), used alone or in combination, intended for use solely or primarily in humans for the purpose of:
- for the diagnosis, prevention, control, treatment or mitigation of an injury or disability,
- of study, replacement or modification of anatomy or a physiological process,
- of contraception control.
The main action is not achieved by pharmacological, chemical, immunological, metabolic means, but can be assisted by such means.
A medicine, by definition, is not a medical device. Its evaluation will therefore be different from that of a medical device. Medical devices include dental devices, the evaluation of which therefore complies with the general rules applicable to medical devices.
1.2 Definition of a biomaterial:
A biomaterial is a non-living material used in a medical device, for therapeutic or non-therapeutic purposes, and intended to interact with biological systems.
According to this definition, a graft is therefore not a biomaterial. On the other hand, a headgear or a corneal lens is one.
Biomaterials are classified into class I, IIa, IIb and III, depending on the duration and nature of contact as well as the chemical origin of the biomaterial.
- Class I: non-invasive or invasive medical devices for temporary use.
- Class IIa: short-term and long-term invasive medical devices of the oropharyngeal sphere.
- Class IIb: long-term invasive medical devices other than the oropharyngeal sphere.
- Class III: Long-term invasive medical devices in contact with the heart, circulatory and nervous systems.
Depending on this classification, biomaterials will not have to undergo the same tests: dental biomaterials are classified IIa. They will therefore have to undergo the following tests: genotoxicity, cytotoxicity, sensitization and implantation.
1.3 Definition of biocompatibility:
Biocompatibility is the ability of a biomaterial to perform a specific function with an appropriate host response.
Biocompatibility has long been synonymous with material inertness, i.e. linked to the absence of host response and the absence of degradation by the host.
Gold, for example, can be defined as a biocompatible material or not depending on the purpose for which it is used: it is considered biocompatible if it is used for a coronal restoration but not if it is used as an orthopedic implant because it does not induce osseointegration like titanium.
2. Tests carried out
2.1 Chronology:
There is a timeline of the tests performed
- primary tests:
- in vitro genotoxicity tests (mandatory in dentistry),
- carcinogenicity and reproduction tests ( in vivo),
- hemolysis tests ( in vitro),
- systemic toxicity tests ( in vivo),
- cytotoxicity tests ( in vitro) mandatory in dentistry.
- secondary tests:
- mucosal irritation tests (in vivo),
- skin irritation tests ( in vivo),
- sensitization tests ( in vivo) ( mandatory in dentistry),
- implantation tests ( in vivo) ( mandatory in dentistry).
- animal use trials.
- clinical trials in humans.
2.2 Correlation between primary tests and secondary tests:
From an ethical point of view, a good correlation between primary and secondary tests is desirable. It helps to reduce the number of animals sacrificed because only products that have successfully passed the primary tests are subjected to secondary tests.
2.3 Advantages and disadvantages of in vitro tests and in vivo tests:
2.3.1. In vitro tests:
- Benefits :
- faster than in vivo tests,
- less expensive,
- reproducible,
- In vitro tests allow the biological effects of each of the material’s components to be evaluated separately.
- Disadvantages:
- they have little to do with the clinic,
- they are too sensitive.
2.3.2. In vivo tests:
- Benefits :
- they are much closer to the clinic,
- they allow to evaluate the effects of a material on organs far from the target organ,
- they allow the toxicity of metabolites to be assessed. A material can in fact prove to be biocompatible while its degradation products, once metabolized by the body, prove to be dangerous,
- Interpretation of the results is sometimes easier because the relationship with the clinic is often more obvious.
- Disadvantages:
- tests carried out on laboratory animals (two species of mammals) may not be relevant to humans,
- the harmful effect may go unnoticed if it is not sought and therefore not assessed,
- incorrect timing of the trial (the deleterious effect manifests itself after the observation periods) evaluation and interpretation of the results may be difficult,
- It may be difficult to simulate pre-existing pathology (caries, periodontal lesion).
3. Primary tests
3.1 Genotoxicity tests:
They assess the effects of medical devices and their degradation products on gene mutations, changes in chromosomal structure or any other modification of genes and DNA. The best known is the Ames test. Mutants of Salmonella Typhimurium, very sensitive to gene mutations, do not know how to synthesize histidine. If this strain undergoes a mutation, it sooner or later becomes capable of synthesizing histidine and can thus develop on a medium without histidine. We then observe formations on the surface whose number is proportional to the genotoxic effect.
3.2 Cytotoxicity test:
The material is brought into contact with the target cells and then their viability is assessed.
Three questions must be asked to judge the validity of the cytotoxicity test:
– which target cells to choose?
– what criterion should be chosen to assess cell viability?
– is the method of bringing the cells and the material together judicious?
- ؤ
3.2.2. Cytotoxicity assessment criteria:
There are two possibilities:
- Basal toxicity test : valid on all cells. It answers the question: is the cell alive or not, or better: is the cell alive but are its cellular functions intact (study of mitochondrial function)?
- Specific toxicity test: valid on primary cultures. It answers the question whether the cell fulfills the function for which it exists.
3.2.3. The different tests:
- Direct contact tests: The material is placed using a biological glue at the bottom of a cell culture dish. Cells suspended in culture medium are then seeded in the dish. The target cells then adhere to the bottom of the dish and after a given time, the distance separating the cells from the material is measured, the cells coming into contact with the material if it is non-toxic while they stay away from it if it releases cytotoxic products.
- Agarose overlay: Cells are seeded at the bottom of a culture dish. The culture medium is replaced with agarose. After the agarose has gelled on the cells, the material to be tested is placed on the surface of the hardened agar and the whole is returned to the incubator for 24 hours. The cytotoxic products released by the material diffuse through the agarose to reach the target cells.
- Natural dentin interposition: A slice of dentin cut with a diamond saw is interposed between the target cells and the material to be tested. The material is placed on the dentin following the manufacturer’s recommendations.
4. Secondary tests
4.1. The awareness test:
The reference test is the Guinea Pig Maximization Test (GPMT) carried out on guinea pigs. The animals are put in contact with the biomaterial twice at 15-day intervals.
The skin is observed at 24, 48 and 72 hours and the skin reaction is assessed. The animal is not sacrificed and there is no histological evaluation of the results.
4.2 Implantation test:
After intraosseous implantation of the material into the rabbit mandible or femur, the animals are sacrificed at 1 month (short term) or 3 months (long term). After histological preparation, the results are analyzed according to the following criteria of the ISO 10-993 standard:
– presence of inflammatory cells,
– fibrous interposition,
– bone marrow degeneration,
– bone necrosis,
– presence of debris,
– granuloma.
This allows reactions to be classified as absent, mild, moderate and severe.
5. Usage (biofunctionality) tests:
During usability testing, materials are used on animals under real conditions of placement and function. They are not mandatory and remain the responsibility of the manufacturer who must decide whether or not to sacrifice laboratory animals. This may involve, for example, testing a coronal restorative material by filling class V cavities in monkeys, or testing an endodontic material by performing a complete root canal treatment in monkeys or dogs.
These tests are few in number because they are expensive and difficult to justify.
6. Clinical trials:
They are carried out on humans after advice from the departmental ethics committee. They are initiated by a “promoter”, carried out in the clinic by an “investigator” and the results are verified by an independent “monitor”.
Conclusion :
The assessment of biocompatibility can only be made from a set of tests. These must be carried out but above all interpreted by specialists according to the future clinical use of the biomaterial.
To assess the biocompatibility of a given biomaterial, some tests are more suitable than others depending on the type of material. Minister of Higher Education and Scientific Research
University of ANNABA
Faculty of Medicine
Department of Dental Surgery
Biomaterials module
Biocompatibility
Dr. FARAH. L
2nd year
2013-2014
Introduction
Biocompatibility, which was the subject of a consensus conference and whose evaluation follows an ISO 10-993 standard which cancels and replaces the old biocompatibility standards.
For years, biocompatibility was synonymous with inertness, that is, a material that posed no biological problems was considered biocompatible. In fact, biocompatibility is different from tolerance to a material because it assumes an appropriate response from the host.
Biocompatibility encompasses all the body’s responses to the implementation of a biomaterial, it must be evaluated by a series of tests given by the ISO standard. This is valid for all medical devices, regardless of the field of medical application.
1. Definitions
1.1 Definition of a medical device:
Any instrument, apparatus, material or other article (such as software), used alone or in combination, intended for use solely or primarily in humans for the purpose of:
- for the diagnosis, prevention, control, treatment or mitigation of an injury or disability,
- of study, replacement or modification of anatomy or a physiological process,
- of contraception control.
The main action is not achieved by pharmacological, chemical, immunological, metabolic means, but can be assisted by such means.
A medicine, by definition, is not a medical device. Its evaluation will therefore be different from that of a medical device. Medical devices include dental devices, the evaluation of which therefore complies with the general rules applicable to medical devices.
1.2 Definition of a biomaterial:
A biomaterial is a non-living material used in a medical device, for therapeutic or non-therapeutic purposes, and intended to interact with biological systems.
According to this definition, a graft is therefore not a biomaterial. On the other hand, a headgear or a corneal lens is one.
Biomaterials are classified into class I, IIa, IIb and III, depending on the duration and nature of contact as well as the chemical origin of the biomaterial.
- Class I: non-invasive or invasive medical devices for temporary use.
- Class IIa: short-term and long-term invasive medical devices of the oropharyngeal sphere.
- Class IIb: long-term invasive medical devices other than the oropharyngeal sphere.
- Class III: Long-term invasive medical devices in contact with the heart, circulatory and nervous systems.
Depending on this classification, biomaterials will not have to undergo the same tests: dental biomaterials are classified IIa. They will therefore have to undergo the following tests: genotoxicity, cytotoxicity, sensitization and implantation.
1.3 Definition of biocompatibility:
Biocompatibility is the ability of a biomaterial to perform a specific function with an appropriate host response.
Biocompatibility has long been synonymous with material inertness, i.e. linked to the absence of host response and the absence of degradation by the host.
Gold, for example, can be defined as a biocompatible material or not depending on the purpose for which it is used: it is considered biocompatible if it is used for a coronal restoration but not if it is used as an orthopedic implant because it does not induce osseointegration like titanium.
2. Tests carried out
2.1 Chronology:
There is a timeline of the tests performed
- primary tests:
- in vitro genotoxicity tests (mandatory in dentistry),
- carcinogenicity and reproduction tests ( in vivo),
- hemolysis tests ( in vitro),
- systemic toxicity tests ( in vivo),
- cytotoxicity tests ( in vitro) mandatory in dentistry.
- secondary tests:
- mucosal irritation tests (in vivo),
- skin irritation tests ( in vivo),
- sensitization tests ( in vivo) ( mandatory in dentistry),
- implantation tests ( in vivo) ( mandatory in dentistry).
- animal use trials.
- clinical trials in humans.
2.2 Correlation between primary tests and secondary tests:
From an ethical point of view, a good correlation between primary and secondary tests is desirable. It helps to reduce the number of animals sacrificed because only products that have successfully passed the primary tests are subjected to secondary tests.
2.3 Advantages and disadvantages of in vitro tests and in vivo tests:
2.3.1. In vitro tests:
- Benefits :
- faster than in vivo tests,
- less expensive,
- reproducible,
- In vitro tests allow the biological effects of each of the material’s components to be evaluated separately.
- Disadvantages:
- they have little to do with the clinic,
- they are too sensitive.
2.3.2. In vivo tests:
- Benefits :
- they are much closer to the clinic,
- they allow to evaluate the effects of a material on organs far from the target organ,
- they allow the toxicity of metabolites to be assessed. A material can in fact prove to be biocompatible while its degradation products, once metabolized by the body, prove to be dangerous,
- Interpretation of the results is sometimes easier because the relationship with the clinic is often more obvious.
- Disadvantages:
- tests carried out on laboratory animals (two species of mammals) may not be relevant to humans,
- the harmful effect may go unnoticed if it is not sought and therefore not assessed,
- incorrect timing of the trial (the deleterious effect manifests itself after the observation periods) evaluation and interpretation of the results may be difficult,
- It may be difficult to simulate pre-existing pathology (caries, periodontal lesion).
3. Primary tests
3.1 Genotoxicity tests:
They assess the effects of medical devices and their degradation products on gene mutations, changes in chromosomal structure or any other modification of genes and DNA. The best known is the Ames test. Mutants of Salmonella Typhimurium, very sensitive to gene mutations, do not know how to synthesize histidine. If this strain undergoes a mutation, it sooner or later becomes capable of synthesizing histidine and can thus develop on a medium without histidine. We then observe formations on the surface whose number is proportional to the genotoxic effect.
3.2 Cytotoxicity test:
The material is brought into contact with the target cells and then their viability is assessed.
Three questions must be asked to judge the validity of the cytotoxicity test:
– which target cells to choose?
– what criterion should be chosen to assess cell viability?
– is the method of bringing the cells and the material together judicious?
- ؤ
3.2.2. Cytotoxicity assessment criteria:
There are two possibilities:
- Basal toxicity test : valid on all cells. It answers the question: is the cell alive or not, or better: is the cell alive but are its cellular functions intact (study of mitochondrial function)?
- Specific toxicity test: valid on primary cultures. It answers the question whether the cell fulfills the function for which it exists.
3.2.3. The different tests:
- Direct contact tests: The material is placed using a biological glue at the bottom of a cell culture dish. Cells suspended in culture medium are then seeded in the dish. The target cells then adhere to the bottom of the dish and after a given time, the distance separating the cells from the material is measured, the cells coming into contact with the material if it is non-toxic while they stay away from it if it releases cytotoxic products.
- Agarose overlay: Cells are seeded at the bottom of a culture dish. The culture medium is replaced with agarose. After the agarose has gelled on the cells, the material to be tested is placed on the surface of the hardened agar and the whole is returned to the incubator for 24 hours. The cytotoxic products released by the material diffuse through the agarose to reach the target cells.
- Natural dentin interposition: A slice of dentin cut with a diamond saw is interposed between the target cells and the material to be tested. The material is placed on the dentin following the manufacturer’s recommendations.
4. Secondary tests
4.1. The awareness test:
The reference test is the Guinea Pig Maximization Test (GPMT) carried out on guinea pigs. The animals are put in contact with the biomaterial twice at 15-day intervals.
The skin is observed at 24, 48 and 72 hours and the skin reaction is assessed. The animal is not sacrificed and there is no histological evaluation of the results.
4.2 Implantation test:
After intraosseous implantation of the material into the rabbit mandible or femur, the animals are sacrificed at 1 month (short term) or 3 months (long term). After histological preparation, the results are analyzed according to the following criteria of the ISO 10-993 standard:
– presence of inflammatory cells,
– fibrous interposition,
– bone marrow degeneration,
– bone necrosis,
– presence of debris,
– granuloma.
This allows reactions to be classified as absent, mild, moderate and severe.
5. Usage (biofunctionality) tests:
During usability testing, materials are used on animals under real conditions of placement and function. They are not mandatory and remain the responsibility of the manufacturer who must decide whether or not to sacrifice laboratory animals. This may involve, for example, testing a coronal restorative material by filling class V cavities in monkeys, or testing an endodontic material by performing a complete root canal treatment in monkeys or dogs.
These tests are few in number because they are expensive and difficult to justify.
6. Clinical trials:
They are carried out on humans after advice from the departmental ethics committee. They are initiated by a “promoter”, carried out in the clinic by an “investigator” and the results are verified by an independent “monitor”.
Conclusion :
The assessment of biocompatibility can only be made from a set of tests. These must be carried out but above all interpreted by specialists according to the future clinical use of the biomaterial.
To assess the biocompatibility of a given biomaterial , some tests are more suitable than others depending on the type of material.
Biocompatibility
Early cavities in children need to be treated promptly.
Dental veneers cover imperfections such as stains or cracks.
Misaligned teeth can cause difficulty chewing.
Dental implants provide a stable solution to replace missing teeth.
Antiseptic mouthwashes reduce bacteria that cause bad breath.
Decayed baby teeth can affect the health of permanent teeth.
A soft-bristled toothbrush preserves enamel and gums.