Biocompatibility of dental materials

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Biocompatibility of dental materials

  1. 1. COLLEGE OF DENTAL SCIENCES DEPARTMENT OF CONSERVATIVE DENTISTRY AND ENDODONTICS SEMINAR ON “BIOCOMPATIBILITY OF DENTAL MATERIALS” Presented By : - Dr. Sharno Mathai Varghese
  2. 2. CONTENTS  INTRODUCTION  REQUIREMENTS  TESTS FOR EVALUATION  ALLERGIC RESPONSE TO DENTAL MATERIALS  PULPAL REACTIONS TO RESTORATIONS o ZINC PHOSPHATE CEMENT o ZINC POLYCARBOXYLATE CEMENT o ZINC OXIDE EUGENOL CEMENT o GLASS IONOMER CEMENTS o SILICATE CEMENTS o CALCIUM HYDROXIDE CEMENTS o VARNISHES o FILLED AND UNFILLED RESINS o AMALGAM  PULPAL RESPONSE TO VARIOUS STIMULI / CARIES  CONCLUSION
  3. 3. BIOCOMPATIBILITY OF DENTAL MATERIALS INTRODUCTION : The term biocompatible is defined as being harmonious with life and not having toxic or injurious effects on biologic function. In general, biocompatibility is measured on the basis of localized cytotoxicity (such as pulp and mucosal response), systemic responses, allergenicity and carcinogenicity. REQUIREMENTS : 1) It should not be harmful to the pulp and soft tissues. 2) It should not contain toxic diffusible substances that can be released and absorbed into the circulatory system to cause a systemic toxic response. 3) It should be free of potentially sensitizing agents that are likely to cause an allergic response. 4) It should have no carcinogenic potential. Tests for evaluation : Group I tests – consist of cytotoxic evaluation in which dental material in a fresh or cured state are placed directly on tissue culture cells or on membranes that leach through the barriers. Eg. Genotoxicity test : Mammalian and non mammalian cells. Bacteria, yeast, fungi cells are used to determine whether change in chromosome structure, gene mutation are caused by test materials. Group II : Secondary tests : The product is evaluated for its potential to create systemic toxicity. Eg. Oral median lethal dose, irritation, implantation tests. Dermal toxicity. Group III : Preclinical usage tests : Approval of the product after it has successfully pass the primary and secondary tests on the basis that the product would not be harmful to humans. 3
  4. 4. Eg. a) Pulp and dentin usage test : This test is designed to assess the biocompatibility of dental materials placed in dentin adjacent to the dental pulp (Class V is prepared to leave 1 mm or less of tubular dentin between the floor of cavity preparation anterior the pulp). b) Pulp capping and pulpotomy usage test (pulp is partially removed / pulp is merely exposed). c) Endodontic usage test (Pulp is partially or completely removed and replaced by the obtaining material. The degree of inflammation is evaluated). Allergic Responses to Dental Materials : a) Allergic contact dermatitis : Seen commonly first by primary physicians. It is a skin condition caused by simple chemical insult to the skin. An allergic contact dermatitis associated with monomers of bonding agent frequently involves the distal parts of the fingers and patman aspects of finger tips. Allergy to Latex Products : Hypersensitivity to latex containing products may represent a true latex allergy or a reaction to accelerates and an antioxidants used in latex processing. Thiuram is a chemical used in the fabrication of latex articles that has also been reported to cause allergic reactions. Polyether component : Allergy. Localized rashes, Wheezing, Anaphylaxis. Allergy Contact Stomatitis : It is the most common adverse reaction to dental material. It may be local or at distant site. Dental material contain many components known to be common allergens, such as chromium cobalt, mercury, eugenol, components of resin 4
  5. 5. based materials, formaldehyde. People who are sensitive to formaldehyde may develop enhanced tissue responses under this condition. Free residual methyl methacrylate monomer in autopolymerized acrylic dentures can cause allergic reactions (to avoid it, dentures are immersed in water for 24 hours) Allergic reaction is associated with resin based materials. The polymerization of composite materials is never complete, there is a percentage of reactive groups do not participate in polymerization. The incomplete polymerization of a resin restorative material may predispose to material degradation. Degradation and wear of the materials release components of the resin based materials and these may cause reaction both locally and systemically. Adverse Reaction : - Gingival reactions. - Lichenoid reactions. Mercury : Minamata Disaster of early 70’s in Japan. Symptom weakness, fatigue, anorexia, weight loss, insomnia, dizziness, tremors. 35 µg/mL – lowest level of total blood Hg at which non specific symptoms occur. Dental Iatrogenesis : Creation of side effects, problems or complications resulting from treatment by a physician or dentist. A favourable situation requires that the intensity of a pulp response, if any, should be higher initially and decrease with increasing postoperative time intervals. 5
  6. 6. In most instances, 2 mm of dentin thickness provides an adequate insulating barrier against traumatic thermal operative techniques and irritating components of most restorative materials. At low speed handpiece 6000-20,000 rpm air water sprays a cavity preparation 2 mm from pulp elicit minimal pulp lesion. At high speed > 50,000 rpm, with adequate low pressure air H2O spray, the pulp response is greatly reduced. Pulpal reactions to restorations and various restorative materials. Some of the properties of materials that might be capable of producing injury mainly includes ; a) Acidity b) Absorption of water during setting c) Heat evolved during setting d) Poor marginal adaptation resulting in bacterial contamination. Plant and Jones (1976) found that pulpal response beneath a material is not associated with the materials, hydrogen ion concentration. The acid present in restorative material is probably neutralized by dentin and dentinal fluid. However placement of an acidic material such as ZnPO4 at luting consistency in a deep cavity may have a toxic effect on pulp since the diffusion barrier is extremely thin. They found out that ZnPO4 current showed greatest temperature rise – an increase of 2.14o C. This amount is not sufficient to produce tissue injury. Absorption of water – but compared with removal of fluid from dentin by an air stream, this injury is insignificant. In current thinking, pulpal injury is primarily due to microleakage through gaps between filling material and walls of cavity. In general, dental materials do not adapt to tooth structure well enough to provide a hermitic seal. Bacteria may penetrate the gap and create toxic 6
  7. 7. products that can diffuse through the dentinal tubules that evoke an inflammatory reaction. This has been found to be a major cause in pulpal injury. Watts A. (1979) showed that materials such as composite resins, silicates produced only a localized tissue reaction when placed directly on exposed pulp in germ free animals. Brannstrom (1979) found that bacteria did not grow when the outer portion of restorations were replaced with ZnO eugenol. When bacterial growth was inhibited, pulpal inflammation was negligible. Two important factors affecting marginal adaptation are temporary changes and masticatory forces. If a material was a different coefficient of thermal expansion than tooth structure, temperature change is likely to produce gaps between material and cavity wall. Since at present time, there is no material that can bond chemically to dentin and thus prevent leakage, the use of a cavity liner to seal dentin is highly recommended. Factors that determine whether bacterial growth injure the pulp includes ; - Pathogenicity of microorganisms. - Permeability of underlying dentin. - Ability of irritated pulps to produce reparative dentin. The antibacterial properties of filling materials may be of considerable importance (ZnO eugenol, Ca(OH)2, polycarboxylate cements). Dentin permeability increase with increasing cavity depth due to difference in size and number of dentin tubules. For most materials, 2 mm of remaining dentin affords adequate pulp protection. Coefficient of thermal expansion. 7
  8. 8. If a restoration has a different coefficient thermal expansion than tooth structure, temperature change is likely to produce gap formation between material and cavity wall. Ceramics : 1- 15 ppm/o C Metals : 10-30 ppm/o C Polymers : 30-600 ppm/o C Amalgam : 25 ppm/o C Tooth : 9-11 ppm/o C It is important that the CTE of a restorative material be as near as that of tooth structure. Microleakage : Is found to occur around all the restorative materials being used because no material truly adheres to tooth structure. The clinical symptoms are sensitivity and recurrent caries. Galvanism : Presence of metallic restoration in mouth cause galvanism. There is difference in potential between dissimilar fillings resulting in pain. Thermal Conductivity : If tooth structure is replaced with metallic restorations, which tend to be thermal conductors, then it is important to place additional thermal insulator to protect the pulp from rapid increase or decrease of temperature in the mouth. Generally, dental cements are used as bases. Dental pulp can withstand small temperature changes (37o C – 42o C) for relatively short periods (30-60 seconds0 without any permanent damage. Pulpal reactions to various restorative materials. ZnPO4 cement : Acts as a luting agent. Commonly used to retain crowns, inlays, onlays, bridges, orthodontic bands, used as base and temporary restorative material. ZnPO4 is considered to be the most irritating of all the intermediary base materials. 8
  9. 9. a) Acidity during setting : pH of ZnPO4 liquid is approximately 2. As soon as powder and liquid are combined, the pH level begins to rise 3 minutes after start of mixing, the pH is approximately 3.5 – 4. The pH then increases rapidly, but still is only 5.5 at 24 hours, it may take 24 hours before neutrability (7) is attained. The pH is lower and remains lower for a longer period when thin mix is employed. Acidity can be reduced by increasing P:L ratio, increasing surface area of contact with dentin to take full advantage of buffering capacity of dentin. The others are microleakage, exothermic heat, depletion underlying dentin from part of its calcium content. Studies have shown that in young teeth in wide open dentinal tubules, the acid from cement can penetrate a dentin thickness as great as 1.5 mm and result in an intense inflammatory response. Polycarboxylate Cement : Uses : Permanent cementation of crowns and bridges, orthodontic bands, stainless steel crowns and for root canal fillings, cement base. It has excellent biocompatibility, potential adhesion to tooth structure. Although polycarboxylate cement liquid, is more acidic than ZnPO4 liquid (1.7), it is neutralized more rapidly during setting process. Polyacrylic acid has relatively high molecular weight, it is restricted from diffusing through the dentinal tubules. Histological studies reveal that the polycarboxylate cements cause a pulpal response similar to that caused by ZnO eugenol, with a slight to moderate response after 3 days and only mild, chronic inflammation after 5 weeks, regenerative dentin formation is minimal, they are recommended in cavities with intact dentin in the floors of the cavity preparation. 9
  10. 10. Zinc Oxide Eugenol : Used as temporary and permanent luting agent, root canal sealer, thermal insulating base, temporary restorative material, periodontal pack. The reason that ZnO eugenol is a good temporary cement and causes only a mild reaction in pulp is that ; a) pH is approximately 7 at the time, they are inserted into the tooth. b) It adapts very close to dentin, thus providing a good marginal seal. c) Its antibacterial properties inhibits bacterial growth on cavity walls. When ZnO eugenol comes in direct control with the pulp tissues, following reaction takes place. 1) Chronic inflammation may remain limited, the area will be walled off by fibrous tissues followed by matrix formation, mineralization and bridging of the exposure. 2) Chronic inflammation may propogate to involve all pulp and root canal tissues with slow, symptomless necrosis. 3) Chronic inflammation may lead to complete fibrosis of pulp and root canal tissues leaving pulp dentin organ susceptible to any irritation and with little or no defense. 4) Chronic inflammation may change to acute inflammation leading to necrosis of pulp and root canal tissues. Eugenol is slightly acidic and produces palliative or obtundant actions on the pulp in low concentration. Since eugenol injures cells, one must use Ca(OH)2 cavity liner in very deep cavity preparation where there is risk of pulp exposure. Glass Ionomer Cements : Used both as luting agent and as a restorative material. They elicit greater pulp reaction than ZnO eugenol but less than ZnPO4. It contains polyacrylic acids which are weaker than phosphoric acid and possess higher molecular weight that may limit their diffusion through the dentinal tubules. 10
  11. 11. However the luting agents pose a greater hazard because of lower powder : liquid ratio 1.25 – 1.5 g/ml of liquid and a slower setting reaction. Post operative sensitivity has been associated with cementation of full cast crowns. It has been suggested that the hydraulic pressure generated during seating may force some of liquid into the dentinal tubules. At the time of initial mixing, the cement is highly acidic and have the potential to produce post operative sensitivity and pulpal irritation. The final pH value reaches 6-7. Pulpal studies indicate that glass ionomer cements cause a mild, inflammatory response which is normally resolved in 30 days. Silicate Cements : The pH of the liquid is less than 2 and may be as low as 1. After the liquid and powder are mixed and material is ready for insertion, the pH is less than 3 and remains below 7 even after 1 month. Silicate cement is highly irritating to pulp. The pulps of younger persons are more likely to react severely to these cements than the pulp of older persons. A non-irritating base, such as ZnO eugenol should be used under silicates. Ca(OH)2 can be an irritant to the pulp if it comes in contact with it. The irritating ingredients and characteristics could be the forces with which the material is introduced into the pulp tissue and high alkalinity of the material. If the effective depth is 100 micrometer or more, a healthy reparative reaction can be expected. When Ca(OH)2 comes in contact with the pulp tissues, the layer of tissue that its contacts directly will undergo chemical necrosis (Coagulation). To anticipate a favourable pulpal reaction, the following criteria must be met ; 11
  12. 12. a) the pulpal tissue must exhibit no signs of degeneration and have sufficient vascularity, cellularity. b) Ca(OH)2 must not be pushed inside the pulp chambers and root canal space, thereby increase the area to be bridged by reparative dentin. c) The microbial status at exposure site cannot be controlled. If these criteria are fulfilled, the pulp tissue next to coagulated surface area in contact with Ca(OH)2 will deposit an organic matrix which will mineralize within 4-6 weeks. If Ca(OH)2 comes in contact with degenerating pulp tissue, the degeneration will be converted to a calcific type of degeneration that will lead to multiple local isolation of pulp and root canal tissues which will be devitalized. Varnishes : Is a solution of one or more resins form natural gums, synthetic resin. The volatile solvents evaporate quickly when varnish is applied to the prepared tooth surface, thus leaving a thin resin film. To attain a uniform continuous coating on all surfaces of prepared cavity, several thin layers should be applied where the first layer dries. The varnish must be applied in thin consistency using a brush or a small pledget of cotton. Varnish produces a positive effect on reducing the pulpal irritation. It provides a barrier against the passage of irritants from cements or other restorative materials. Varnish aid in reduction of post-operative sensitivity when applied to dentinal surfaces. This could be attributed to the reduced infiltration of oral fluids at restoration tooth interface into underlying dentin. It prevents penetration of corrosion products of amalgam into dentinal tubules. (NB) Not employed under composites it may soften resin and its coating prevents proper wetting of prepared cavity by bonding agents. Not indicated when GIC are used. 12
  13. 13. Filled and Unfilled Resin : Irritating agents 1) Residual monomer 2) Exothermic heat of polymerization 3) Leakage, especially when accompanied by marginal percolation 4) High coefficient of thermal expansion 5) Enamel etching acids acidulating applied on dentin. Although, they produce a less severe inflammatory reaction of the pulp, they require use of Ca(OH)2 or GI cavity liner as resins are irritants. The acid etchant appears to open dentinal tubules and permits greater penetration of low viscosity bonding agent with potentially irritating low molecular weight monomer. Amalgam : Residual mercury can diffuse form the restoration to the surrounding dentin. Use of radioactive mercury in silver amalgam has also revealed that some mercury might even reach pulp. Such mercury has been reported to poison odontoblasts, subsequently reducing predentin and secondary dentin formation. Endodontic Procedures : As a consequence of pathologic changes in dental pulp, the root cement system can harbour numerous irritants. As irritants are released form the root canal system into the periradicular tissue, granulation tissue proliferates and replaces normal periradicular tissue. An ideal root canal filling material should meet the following requirements : a) It should seal the canal laterally as well as apically. b) Should not shrink after being inserted. 13
  14. 14. c) Should be impervious to moisture d) Should be bacteriostatic e) Should not irritate periradicular tissue. f) Should not provoke an immune response. g) Should not be carcinogenic or mutagenic. Percolation of periradicular exudates into incompletely filled canals is the greatest cause of endodontic failure. It is presently speculated that the transudate constantly leaking no partially filled canals arises indirectly from blood serum. The serum is trapped in cul de-sac of poorly filled canal, away from influence of blood stream in which it undergoes degradation. Later when the degradated serum slowly diffuses into periradical tissue, it acts as an irritant to produce periapical inflammation. Pulpal Response to Various Stimuli / Caries / Restorative Dental Procedures : Tertiary dentin also referred as reactive, reparative or irregular secondary dentin is produced in reaction to various stimuli such a attrition, caries or restorative dental procedures. Unlike primary or secondary dentin, which forms along the centre pulp-dentin border, tertiary dentin is produced only by cells directly affected by the stimulus. Tertiary dentin may have regular tubules continuous with those of secondary dentin, tubules sparse in number and irregularly arranged, or no tubules at all. 14
  15. 15. Management of Dermatitis Associated with Wearing of Protective Gloves in Dental Practice : Dermatitis developed in hands Allergic contact Irritant contact Contact dermatitis Dermatitis Urticaria Pattern of hand eczema Itchy, dry, Immediate Is suggestive of rubber fissured skin type reaction Glove allergy and chapping Itching, odema and wheal within 1 hour Try alternative brand Check handcare Of glove regimen Immediate referral and avoid contact Check gloves with rubber Frequently (Emergency Treatment needed) Try alternative Brand If Dermatitis persist Consult dermatologist 15
  16. 16. Pulpal Reaction to Caries and Dental Procedures : Dental Caries Reaction of pulp to caries • Decrease in permeability of dentin. • Formation of new dentin • Inflammatory and immune reactions Inward diffusion of toxic substances form caries occurs through dentinal tubules. The most common response to caries is dentin sclerosis. The ability of pulp to produce reparative dentin below carious lesion is another mechanism of limiting diffusion of toxic substances to the pulp. The formation of a dead tract in dentin is yet another reaction that occur in response to caries. But this is not a defensive reaction. It is an area of dentin where dentinal tubules are devoid of odontoblast process. The rate of attack may be influenced by any of the following. • Age of host • Composition of the tooth • Nature of bacterial flora • Salivary flow • Buffering capacity of saliva • Antibacterial substance in saliva • Oral hygiene • Cariogenicity of the diet • Caries inhibiting factors in diet When the lesions reached to within 0.5 mm of pulp, there is significant increase in extend of inflammation. 16
  17. 17. When all of pulp’s defense systems are overwhelmed, a pulpal abscess may develop. The exudate associated with this reaction is called pus. The pus is formed when neutrophils release their lysosomal enzymes and surrounding tissue is digested. If drainage is not present, it can result in pulpal necrosis. In some cases, accumulation of neutrophils may produce surface ulceration called as chronic ulcerative pulpitis. In primary and immature permanent teeth, caries exposure can result in chronic hyperplastic pulpitis or pulp polyp. Effect of Local Anaesthesia on the Pulp : Decreases the pulpal blood flow with higher concentration of vasoconstrictor. Irreversible pulp damage resulting from tooth preparation is caused by release of vasoactive agents. Under normal circumstances, these vasoactive agents are quickly removed from pulp by blood stream. However when blood flow is reduced, then it can result in accumulation of these agents which result in permanent damage to the pulp. Therefore use of vasoconstrictor free LA for restorative procedure on vital teeth. Effect of Cavity and Crown Preparation : “Cooking the pulp in its own juice” is how Bodecker described tooth preparation without water coolant. The pulpal response depends on various factors – thermal injury, transaction of the odotoblastic process, crown preparation, vibration, desiccation of dentin, pulp exposure, smear layer, remaining dentin thickness, acid etching. Cutting of dentin with a rotating bur or stone produces a considerable amount of frictional heat. The thermal conductivity of dentin is relatively low. Heat generated during cutting of cavity in shallow preparation is less. Brushing of teeth seen during cavity preparation or crown preparation due to frictional heat. It 17
  18. 18. presents with pinkish hue which is irreversible. However dark purplish color indicates thrombosis. Effect of Lasers on the Pulp : Lasers can remove caries, modify the dentin surface for stronger bonding, eliminate pits and fissures, anaesthetize and treat hypersensitive teeth. Two requirements critical for effectiveness of cases is laser must provide superior results over traditional procedures and it must not damage the vital pulp in the process. The interaction between laser light and substrate is expressed in terms of reflection, absorption and transmission which are wavelength dependent. Clinically CO2 laser and Gr:Yag will do less harm to pulp than Nd:YAG and diode laser system. CO2 Laser : Is known for cutting soft tissue without bleeding used in periodontal and oral surgery procedures. It is not applicable for hard tissue procedures. Nd:YAG : has wavelength of 1.06 mm. They have beneficial effect on dentin but not on the pulp. The pulp damage includes nerve injury and haemorrhage leading to irreversible damage. Identifying an energy level at given dentin thickness that provides desired effect on dentin without harming the pulp is an important step in laser research. Er :YAG : Can ablate dental hard tissue with minimal damage to dental pulp. The mechanism is based on its high absorption into the water component of hard tissue. This may cause a quick temperature increase within a small volume of the tissue. Thus both enamel and dentin are partly removed by continuous vaporization process and partly by microexplosion. Hypersensitive Teeth : 18
  19. 19. Mechanism : The enamel and cementum covers the dentin when these protective layer is removed, dentinal tubules are exposed (eg, scaling, caries, #), the teeth often become hypersensitive. Dentin sensitivity is due to a δ fibres present in dentinal tubules. It is characterized by sharp, transient and well localized pain to cold, air and heat. It can be confused with pulpal pathology. In the latter, it is because of excitation of C fibres. Management of Hypersensitive Dentin : - Agents that block exposed dentinal tubules. Oxalate Salts : - Agents that reduce intradental nerve excitability. Potassium nitrate, potassium bicarbonate, potassium oxalate, silver nitrate, calcium fluoride. Current thinking on cense of pulpal reaction to restoration. Pulpal injury is due to microleakage through gaps between filling materials and walls of the cavity. There are 3 possible counts for microleakage. a) Within or through smear layer. b) Between smear layer and cavity varnish or cement. c) Between cavity varnish or cement and restorative material. Prevention : • Cutting procedures : Use light, intermittent cutting, efficient cooling system and high speed of rotation. • Avoid dentin desiccation. • Do not apply irritating chemicals to dentin. • Use cavity liner / base whenever necessary. • Do not use excessive force when inserting a restoration. 19
  20. 20. • Avoid excessive polishing procedure. • Choose restorative material carefully. • Do not use caustic cavity sterilizing agents. CONCLUSION : Tests to evaluate the biological response to dental materials can be divided into initial, secondary and usage test. Each test level gives additional information about the biocompatibility of the material. In this way, the initial tests, which are quicker and less expensive to perform, can screen potential materials before more complex secondary and usage tests are used. The initial tests can also delineate the components of materials that might be causing adverse reactions in the invivo tests. Although there are problems with the correlation among initial, secondary and usage tests, and although one type of test cannot be substituted or another at present, each type of test gives important information about the effect of materials on cell and tissue function. Continuing efforts to develop further correlations between screening and usage tests are in progress. 20

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