Operative One -- Dental Composite Material- Biocompatibility: Vidal

Biocompatibility: Craig's textbook

Ability of a material to elicit an appropriate biological response in a given application in the body

Biocompatibility: Schmalz and Arenholt-bindslev

Ability of a material to perform with an appropriate host response when applied as intended

A single material may not be

biologically acceptable in all applications

Measuring Biocompatibility

In Vitro tests

Animal Tests

Usage tests or clinical trials

In vitro tests

Require placement of a material in contact with a cell, enzyme, or some other isolated biological system

Primary cells or cell lines

Direct or indirect (barrier) contanct

Direct:

- Material physically present with the cells

- Extract of the material contacts the cell system

Primary cells

Taken directly from an animal/tissue and cultured

Grow for a limited time

Retain many characteristics of cells in vivo

More relevant to measureing cytotoxicity of materials

Limited genetic variability, may harbor viral or bacterial agents that alter their behavior, loose their in vivo functionality once placed in culture

Cell lines

Have been transformed to allow them to grow indefinitely in culture

Do not retain all in vivo characteristics but consistently exhibit retained features

Genetically and metabolically stable, contribute for standardizing assay methods

Examples: HeLa (cancer cells- 1st cell line, obtained in 1951)

Examples of in vitro tests

Cell cytoxicity tests, membrane permeability tests, cell immune function test, changes in cell cycle or activation of complement systems

Mutagenesis tests: assess the effect of a biomaterial on a cell's genetic material

Animal tests

Involve mammals (mice, rats, hamsters, guinea pigs, etc)

Material is NOT placed in the animal with regards to its final use

WHY?

Allow for the complex interactions between a material and functioning, complete biological system to occur

More comprehensive and relevant than in vitro tests

Disadvantages in animal tests

More expensive, time consuming, often involve significant ethical concerns and oversight, difficult to interpret and quantify

Example of animal tests:

Mucous membrane irritation test

Determine whether a material causes inflammation to mucous membrane or skine

Example of animal tests:

Skin sensitization

Materials are injected intradermally, followed by secondary treatment with adhesive patches containing the test substance

Example of animal tests:

Implantation test

Evaluate materials that will contact the subcutaneous tissue or bone (common for periodontal and endodontic treatment materials)

Usage tests

Involve animals (dog, min-swine, monkeys) or humans

Material is placed in a situation IDENTICAL to its intended clinical use

Ability to mimic the clinical use of the material in every regard, including time, location, environment, and placement techniques

usually employ larger animals (similar oral environment to humans)

When human is used = clinical trial

Gold stand tests, highly relevant

VERY expensive, time consuming, ethical/legal concerns, difficult to interpret and quantify results

Usage tests:

Dental pulp irritation tests

Materials are placed in Class V cavity preparation in intact non-carious teeth

Teeth are extracted and sectioned for microscopic examination

Necrosis and inflammation are classified according to their intensity

Usage tests:

Intraosseous implant test

Materials are inserted into the jaw of test animals

Primates, dogs, miniature pigs, guinea pigs, and rats

Tissue reaction is assessed histologically as well as the tissue in contact with the implant

Usage test:

Mucosa and gingival usage tests

Material is placed in cavity preparation with subgingival extensions

Responses are characterized according to the number of mononuclear inflammatory cells in the epithelium and adjacent connective tissues

- Difficulties: Presence of existing inflammation, rough margins of restorative materials, over- or under- contour of the restoration

Correlation among tests?

- Not always possible

- Test conditions affect the results

- Most accurate and cost effective = in vitro + animal + usage

- No single test can completely characterize biocompatibility

Biocompatibility is assessed by

various experts according to specific guidelines in which a comparison with products already on the market plays an important role

there are lots of different ways to assess biocompatibility, thus

evaluations may not generate identical results

- it is the dentists obligation to not rely on these assessments blindly but rather to question them critically

Standards that regulate biocompatibility tests

Regulatory agencies require biocompatibility testing and provide guidance on how the tests should be performed

International organization for standardization (ISO), the US Food and drug administration (FDA) and the conformité Européenne (CE)

The FDA recognized human health substances as what

only two categories

- drugs or devices

Dental restorative materials are classified as

devices

Preclinical evaluation of biocompatibility of medical devices used in dentistry - Test methods for dental materials

Initial tests:

- Assess biological reaction to materials (cytotoxicity, sensation, and systemic toxicity). Some done in vitro, other in animals

Supplementary tests:

- Assess chronic toxicity, carcinogenicity, biodegradation (many in animals)

Manufatueres evaluate the device to

determine if it could cause an adverse biological response

Manufactures perform

biocompatibility testing

The FDA reviews the testing results before

authorizing the device for market sale

Biocompatibility of dental materials

Reactions of pulp

Reactions of other soft tissues to restorative materials

Reactions of bone and soft tissues to implant materials

Reactions of pulp

Dentin bonding/bonding agents

Resin-based materials

Amalgam and casting alloys

Glass ionomers

Liners, varnishes, and non-resin cements

Bleaching agents

Reactions of pulp: Dentin bonding/bonding agents

Factors that determine/affect the biocompatibility of adhesive material

1. Smear layer is removed in etch and rinse protocol --> increases dentin permeability --> acids used for etching can be irritating (etch and rinse vs self etch)

2. Toxicity of monomers: HEMA and Bis-GMA

- High cytotoxicity when applied in contact with cells

- Less cytotoxicity when dentin barrier is present (at least 05 mm)

- In vivo evidence of HEMA cytotoxicity when <0.1 mm of dentin

- HEMA diffuses through dentin (via dentinal tubules) --> may cause pulpal irritation

Reactions of pulp: Resin-based materials

reduced cytotoxicity reported in test using dentin barrier

low pulpal inflammatory response when RBC is placed in cavities with at least 0.5 mm of remaining dentin. Reactions are diminished within 5-8 weeks

Factors that determine/affect biocompatibility of resin-based materials

Incomplete polymerization of adhesives

Resin-based restorative materials release unbound free monomers immediately after setting and later (degradation/hydrolysis) -> cytotoxic for pulp and gingival cells

Reactions of pulp: Resin-based materials

Microleakage and nanoleakage =

adhesive interfaces do present permeability and/or gaps-> bacterial infiltration --> pulp irritation

Good _____ _____ is key to avoid pulpal irritation, but material selection is also important

marginal sealing

restorative materials can alter

pulpal responses and dentin repair

Concerns about biocompatibility resin-based materials

Estrogenicity of biphenol A (BPA)

BPA can be a degradation product of some methacrylate used in resin composite and sealants, but levels of BPA release are extremely low (diet is the main source of BPA exposure in most countries)

BPA release can be minimized by proper light curing the material, using rubber dam isolation, remove

3M clinpro dental sealant does not contain BPA

Amalgam and Casting alloys: Cell culture tests

High-copper amalgam is toxic, low-copper amalgam that has set for 24h does not inhibit cell growth

Amalgam and Casting alloys: Implantation tests

low-copper amalgam are well tolerated, high-copper amalgam causes severe reactions

Amalgam and Casting alloys: Usage tests

Minimal pulpal irritation when placed in shallow cavities or in deep cavities using a liner

Amalgam and Casting alloys: when used in deep cavities with no liner =

pain (thermal and electric conductivity)

Amalgam and Casting alloys: Alloys used for restorations crown and dentures may have

adverse effects on cells if released

Metal ions released from alloys are likely to

contact the gingival and mucosal tissues than the pulp (more likely to affect by the cement retaining the restoration)

Pulp biocompatibility to Glass ionomers is attributed to

the weak nature of and high molecular weight of the polyacrylic acid - unable to diffuse through detnin

Pulp biocompatibility is pretty good

Glass ionomers: usage tests

mild pulp reactions, absent after 1 month

Glass ionomers: sensitivity to pain is increased after placing GI in cervical cavities possibly related to

increased permeability after conditioning the dentin

Alkaline liners

Used in exposed pulps but caused necrosis, coagulation of hemorrhagic exudate of the superficial pulp

After necrosis, neutrophils infiltrate the subnecrotic zone, which undergoes dystrophic calcification after week/months

not used anymore

Calcium hydroxide-based materials containing resin

less irritating and able to stimulate dentin bridge formation quicker than calcium hydroxide (no zone of necrosis)

Common brands:

- TheraCal LC = resin-modified calcium silicate cement

- Biodentine= tricalcium silicate-based material

MTA

Calcium silicate-based cement

Calcium hydroxide is the main soluble component in MTA

Stimulates formation of a thick compact dentin bridge with no inflammatory response

Stimulates dentin remin through solubilization of non-collagenous proteins from the dentin

Induces cell proliferation, migration, and differentiation to odontoblast-like cells

SUMMARY: Biocompatibility depends on the

material composition, location, and interactions with the oral cavity

SUMMARY: Diverse reactions can occur if

Material release their components and whether those components are toxic, immunogenic, or mutagenic