Composite resins1/ rotary endodontic courses by indian dental academy


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Composite resins1/ rotary endodontic courses by indian dental academy

  1. 1. COMPOSITE RESINS INTRODUCTION Since the birth of dentistry, there have been numerous attempts to formulate a material and with aesthetic requirements, which would also have the expected physical, mechanical and biological properties to behave favourably in the oral environment. The basic requirement for an aesthetic restorative material is the restoration of an anterior tooth and any extra-orally visible aspect of a posterior tooth in a manner which has a similar shade and color in addition to all other visual perceptions as that of the adjacent tooth. Presently there are five groups of restorative materials under the anterior restorations banner. These 5 are in addition to the extra-orally fabricated aesthetic restoratives such as porcelain, cast moldable ceramics and the PFM restorations. The 5 anterior restoratives are in chronological order, as follows : i. Silicate cement. ii. Unfilled Resin. iii. Filled Resin. iv. Composite Resin. v. Glass Ionomer Cements. History : Certain clinical characteristics of the synthetic resins viz. tooth like appearance and insolubility in oral fluids made them superior to the silicate cements. 1
  2. 2. - However after their introduction in the late 1940s and early 1950s following their initial success, certain drawbacks such as high polymerization shrinkage and high coefficient of thermal expansion led to their clinical failures. - Thus to overcome these deficiencies, which were attributed to the resinous component, inert filler particles were added in order to reduce the volume of the resin component. These first attempts to improve the properties by decreasing shrinkage and thermal expansion did not prove fruitful as further microscopic defects resulted in the mechanically retained fillers and surrounding resin. This was because the fillers were not chemically bonded to the resin matrix. The defects were then responsible for : - Staining of resin because of fluid leakage - Therefore an unacceptable appearance. - Poor filler retention – therefore filler loss and poor wear resistance. - Then, a major advance in the resins fields occurred when BOWEN developed a new composite material. His main formulation was – a dimethacrylate resin viz. BIS-GMA, used along with silane to coat filler particles which would chemically bond to the resin. - An advantage of the dimethacrylate resin is that, since the BIS-GMA has a higher molecular weight than methyl methacrylate, the density of the methacrylate double bond groups is lower in the BIS-GMA monomer, a factor which reduces polymerisation shrinkage. The use of a dimethacrylate also improves cross-linking and thus the properties of the polymer. 2
  3. 3. 3. Definition of Composite : According to Skinners – A compound of two or more distinctly different materials with properties that are superior or intermediate to those of the individual constituents. According to DCNA – 1981 – A three-dimensional combination of atleast two chemically different materials with a distinct interface separating the components. 4. Classification of Composites : The classifications mentioned are of: i. Skinners ii. Marzouk iii. J-Dental Update 1991 (size and type of fillers) A. Skinners has classified composites based upon the average particle size as : Composite Particle size i. Traditional composite (macrofilled) 8-12µm ii. Small particle-filled composite 1-5µm iii. Microfilled composite 0.04-0.4µm iv. Hylorid composites 0.6-1.0µm B. Marzouk on the other hand has classified composites as generations depending on the order of their chronological development. 3
  4. 4. Prior to discussing the generations elucidated by Marzouk it is important to note the two main phases present in a composite resin as stated by him. So, as Marzouk states, although a variety of composite resins are now available to the dental profession they are all dependent upon the original ideal of Raphael Bowen. Composites are all reinforced materials with : 1. A continuous (dispersion/reinforced) phase. 2. An interrupted (dispersed/reinforcing) phase. a. The continuous phase – Consists of the synthetic resin macromolecules, i.e. it is a reaction product of Bisphenol A and glycidyl methacrylate. Other substitutes for BIS-GMA are : i. Modified BIS-GMA – by elimination of OH group. ii. Urethane diacrylate. iii. TEG-DMA. - Polymerization of this continuous phase brings about hardening of the material which is inturn bought about by the initiators and activators. b. The interrupted phase : This may consist of either one or combination of the following : i. MACRO- CERAMICS. ii. COLLOIDAL and MICRO-CERAMICS. iii. Fabricated macro reinforcing macro-reinforcing phases with colloidal micro-ceramic component bases. 4
  5. 5. i. Macro-Ceramics – Consists of silicate based materials (SiO4), e.g. quartz, fused silica, silicate glasses, crystalline lithium aluminium silicate, (Radio-opaque) Ba-Al-boro-Si etc. ii. Colloidal and Micro-Ceramics : Originally these consisted of colloidal silicate forms but have now been replaced by larger sized pyrogenic silica. The colloidal silica (as silicic acid) – formulated by a chemical process of hydrolysis and preparation colloidal form diameter – not more than 0.04 micrometers. Pyrogenic state – dia – 0.05 – 1 micrometer. iii. Colloidal or micro-ceramics are introduced into partially thermo- chemically polymerized spherical particles of a resin system. These highly reinforced spherical resin particles are then used as reinforces for a continuous phase resin, forming a continuous resin. The interphase between the continuous and interrupted phase is the most crucial in determining the final behaviour of these composite systems. Therefore chronologically we have: i. First Generation Composites: - Consist of macroceramic reinforce phases. - Highest surface roughness. - Highest proportion of destructive wear clinically (due to dislodging of large ceramic particles). 5
  6. 6. - Drawbacks reduced by use of smaller, soften particles of variable dimensions. ii. Second Generation Composites: - With colloidal and micro-ceramic phases. - Best surface texture of all composites. - Strength and coefficient of thermal expansion are unfavourable because of limited % age of reinforced. C. Third Generation of Composite: - Hybrid composite. - Combination of macro and microcolloidal ceramic reinforced in ratio of 75:25%. - Properties are intermediate to Ist and 2nd generations. D. Fourth Generation of Composites : - Also a hybrid composite. - But instead of macro ceramic fillers they contain heat cured, irregularly shaped highly reinforced composite macroparticles with a reinforcing phase of microceramics. - Fourth generation composites are very technique sensitive. E. Fifth Generation Composites: - Hybrid composite. 6
  7. 7. - Continuous phase is reinforced with microceramics and macro, spherical, heat cured highly reinforced composite particles. - The spherical shape of these macro ceramics improves their wettability and consequently their chemical bonding to the continuous phase of the final composite. F. Sixth Generation Composites: - Hybrid type. - Continuous phase is reinforced with a combination of micro-ceramics and agglomerates of sintered microceramics. C. Classification of Composites based on Sizes and type of fillers (G.J. Pearson : Dent Update 1991). Composites are divided into 3 categories determined by the size and type of their fillers: They are: i. Conventional composites. ii. Microfine. iii. Hybrid. i. Conventional composites: - The fillers in these is now usually radiopaque barium or strontium glass with particle sizes in range between 2.5-5µm. 7
  8. 8. - (Disadvantages poor union to resin and therefore breakdown of restoration). ii. Microfine composites: - The filler particles here viz. Colloidal silica are about 200 times smaller than the conventional products. (These composites have a higher proportion of resin therefore increased polymerisation shrinkage and potentially more bulk wear). iii. Hybrid composites: - The filler particle size here is carefully defined and graded to give varying proportion of large, medium and fine sized particles. - The merit of this gradation is to provide maximum packing of the filler (vol fraction 70%). iv. Another classification based on size of fillers is mentioned by Sturdevant as: (K. Leinfelder). 1. Megafill composites - Megafillers – β quartz, very large size. 2. Macrofill composites - Macrofillers – 10-100µ. 3. Midifill composites - Midifillers – 1-10µ. 4. Minifill composites - Minifillers – 0.1-1µ. 5. Microfill composites - Microfillers – 0.01-0.1µ. 6. Nanofill composites - Nanofillers – 0.005-0.01µ. 8
  9. 9. Composition : - As I’ve stated earlier on in this seminar, the development of modern dental composite resins started as for back as the early 60s when Raphael Bowen had begun experiments to reinforce epoxy resins with filler particles. These epoxy systems (with fillers) had certain drawbacks : - Slow curing rate and - Tendency to discolor, and thus these prompted him to combine the advantages of epoxies and acrylates which culminated in the development of the BIS-GMA molecule. - So as of today majority of the composites contain a common formula with the following major components : 1. An (organic) resin matrix. 2. Inorganic fillers. 3. Coupling agent. 4. Activator – Initiatior. 5. Inhibitors. 6. Pigments. 1. Organic Resin Matrix: - Most of the composite resin matrix contain utilize alphatic or aromatic diacrylate monomers. - Hence we have the BIS-GMA, VEDMA and TEGDMA resin which are amongst these commonly employed. 9
  10. 10. - The original high molecular weight resin viz. BIS-GMA has a very high viscosity and thus since early times efforts to reduce this high room temperature viscosity have been made by the addition of TEGDMA (which is a diluent dimethacrylate monomer). - The reduction in viscosity of BIS-GMA on addition of TEGDMA is quite significant. - However the addition of TEGDMA or other dimetharcylate monomers leads to an increased polymerization shrinkage. - The use of a urethane diacrylate base reduces the risk of shrinkage, since this resin has a lower viscosity and so less diluent resin is needed. 2. Inorganic Fillers: - The inorganic filler particles generally constitute 30-70 vol% or 50-85 wt% of the composite. - A proper bonding done by a coupling agent of the filler particles to the resin matrix is essential for optimal properties of the composite. - The fillers reduce the resin components of the composite and thus in turn reducing the % age of polymerization shrinkage (compared to unfilled resins). - The shrinkage should be of the order of 3 vol% for 24 hours. - In filled resins thus, 10
  11. 11. 1. Water sorbtion and coefficient of thermal expansion are less. 2. Compressive strength, tensile strength and modulus of elasticity are improved. - A classification of composites based on fillers has already been stated. - Quartz and silica are the most commonly employed inorganic fillers. - These obtained from grinding or milling procedures are usually of 0.1- 100µm in size. - The silica fillers (0.04µm size) – colloidal size usually referred to as microfillers are produced by a pyrolytic / precipitation process. - In this process, low molecular weight, Silicone compounds viz. SiCl4 are polymerized by burning SiCl4 in an O2 & H2 atmosphere. - During this process macromolecules of colloidal sizes are formed and constitute the fillers. - On the other hand, quartz has been used extensively as a filler (specially in the 1st generation). - Quartz is available in 4 forms viz: 1. Crystalline quartz. 2. Crystalline crystoballite crystalline trigidymite. 3. Non-crystalline fused quartz. 11
  12. 12. - Quartz has an advantage of being chemically inert and extremely hard with clinically makes the restoration difficult to polish and may cause more abrasion of opposing teeth/restorations. - To ensure acceptable aesthetics of a composite restoration. The translucency of the filler must be similar to the tooth structure, therefore the R.I. of the filler and resin should be III. - Regarding index Similar - [BIS-GMA + TEGDMA – together R.I. – 1.5, Quartz R.I. = 1.5] 1.55 1.46 - Additional fillers for all heavy metals, for all Ba, St and Zr provide the necessary radiopacity to the material (Zirconium  Z-100 – 3M). 3. Coupling Agent: - The bond between the two phases of the composite viz. The resin matrix and the inorganic filler is provided by the coupling agent. - This bonding allows the more flexible polymer matrix to transfer stresses to the stiffer filler particles. - Though titanates and Zirconates can be employed it is the Organosilanes which are most commonly used with agents. 12
  13. 13. Method of Coupling: - In their hydrolysed state the silanes contain silanods groups that can bond with silanods on the filler surface by formation of siloxane bonds (S-O-Si). - The methacrylate group of the coupling agent forms covalent bonds with the resin when polymerized. 4. Activator – Initiator systems: The methacrylate monomers used in dental composites polymerize by an Addition Polymerization reaction mechanism which is initiated by free radicals. - These free radicals in turn are generated either by: i. Chemical activation or. ii. External energy activation (light/heat activation). (And therefore we have the chemically and light cured composites). i. Chemically activated composites: - Usually supplied as 2 pastes. 1. Contains benzyol peroxide initiator. 13 S-O-S1 Organic Resin Matrix Coupling Agent Filler (Inorgan)
  14. 14. 2. Contains tertiary (N,N dimethyl p-toludine) amine activator. - When 2 pastes are spatulated the amine reacts with the benzoyl peroxide to form free radicals and addition polymerization is initiated. ii. Light Activated composites: - Initially, the U-V light was used to cure composites which was later replaced by the visible light. - These had an advantage of increased penetration depth of upto 2mm. - The light curable composites are supplied as a single paste system consisting of the photo initiator viz. Camphoroquinone and an amine activator. - Exposure of these components to light of correct wavelength usually on the blue zone (approx 468nm) causes excitation of the photoinitiator and a following interaction with the amine to form free radicals which initiate polymerization. - The light source required should be in the range of 400-500nm (for the photo initiator) which is in the blue region of visible light). - An alternative to the visible light is the Argon Ion laser source. In a study conducted, it was seen that the argon-ion laser beam though of a similar wavelength i.e. 420-480nm has a greater depth of penetration i.e. 14
  15. 15. upto 5mm which also improved physical properties of the composite materials of both microfilled and hybrid. The depth of cure is greater for hybrid composition as a result of increased particle size and increased dispersion (and increased depth of cure). 5. Inhibtors: - A characteristic feature of the incorporated inhibitors is that they prevent spontaneous polymerization of the composite by reacting with the free radical formed (during a brief exposure of the composite) and thus inhibiting chain propagation. Eg: butylated hydroxytoluene  0.01 wt%. 6. Optical Modifiers and Pigments: - These are added to imitiate the shade and translucency of the original tooth structure. - The shading / coloring is achieved by the addition of various metal oxides. - The opacifiers which affect the translucency, actually dictate the amount of light transmitted / reflected from the restoration and thus have a final word as far as the appearance of the restoration is concerned. - A limited amount of opacifier makes the restoration too translucent while it’s excess makes the restoration appear “too white” as excess light is scattered back. 15
  16. 16. Opacifiers used – Titanium dioxide and Al.oxide - (0.001-0.007wt%). - It is noticed that all optical modifiers affect the light transmission ability of a composite. - As most composites are light cured, this suggests that different shades and opacities have a different depth of cure. - Studies have suggested that darker shades and opacifiers should be placed in thinner layers to optimize polymerization. Manipulation and Placement of Composite Systems: Here, we would be discussing at length in relation to the manipulation and placement of the 2 paste and single paste systems: - However prior to placement of the composite restoratin, the pulp may be protected using a cavity liner and Ca(OH2) placed at the deepest portion of the cavity. - The enamel is then etched with an acid solution. Acid – Etch Technique : - One of the most effective ways of improving the marginal seal and mechanical bonding is by the use of the acid etch technique, developed and introduced by Bunocore 1955. - The process of achieving a bond between enamel and resin restorative systems includes discrete etching of the enamel in order 16
  17. 17. to provide selective dissolution with resultant micro-porosity (microtags). - The etched enamel has a high surface energy unlike the normal enamel surface, and allows the resin to wet readily the surface and penetrate into the microporosity. - These resin tags may go as for as 10-20µm into the microporosities, (the length is however dependant on the etching time). - The most commonly employed acid is the H3PO4 at a concentration of 30-50% (DCNA 81) Chow & Brown have shown that concentration below 30% were unacceptable because the pdt. from the action of phosphoric acid on enamel was insoluble and would remain as a contaminant on the surface. - Concentrations greater than 50% result in the formation of a Monocalcium Phosphate Monohydrate which inhibits further dissolution. - Therefore an optimum concentration i.e. of 37% is provided. - In other situations we have. ALL ETCH – 10% UNI ETCH – 37% - Although aqueous solutions are present, generally the etchant is supplied in a gel form (increased silica content) to allow control over the area of placement. - Can be applied with brushes / syringe system. 17
  18. 18. Regarding the GEL Application time : Originally 60 seconds was recommended but studies have revealed that 15 secs provides a strong bond. - However application time varies with the history of the tooth for eg: a tooth with high fluoride content requires a longer etch time. It is said that the fluorides react with etched surfaces to produce reaction pdt that may interfere with bonding. - The bond strengths achieved with etched enamel range from 16Mpa (2300psi) – 22Mpa (3200psi). - Clinically, the etchant should be thoroughly rinsed off and the tooth surface dried completely such that the enamel should have a white, frosted appearance. - Drying the enamel with warm air or with an ethanol rinse also increases the bond strength. - The etched enamel should be kept free of contaminants and saliva, blood, moisture which would affect bond strengths. - If contaminated, the tooth should be rinsed and the enamel dried and etched again for 10 seconds. Manipulation of the composite systems: As spoken of before, the composite systems may be a 2 paste or a single paste system, therefore we have their respective manipulation techniques: 18
  19. 19. A. 2-paste system : (chemically cured) : - The pastes are supplied as: i. Universal paste and ii. Catalyst paste. - The two pastes are mixed (20-30 seconds M.T.) using a plastic, wooden or agate spatula. - Metal spatulas are not recommended as the inorganic particles are abrasive and abraded metal particles could discolor the metal. - Care also should be taken during manipulation to avoid incorporation of air bubbles which contain O2 and these could lead to O2 inhibition during polymerization. - The W.T. (or insertion time) is about 1-1/2 min. - The S.T. is about 4-5 min. - The material may be placed into the cavity by: A. Plastic instruments : Advantages are i. Do not stick to composite during insertion. ii. Avoid discoloration of composite by metal instruments. B. Plastic tip of syringe : Advantages for this are: i. Syringe allows use of small mixes. ii. Reduces problem of void incorporation. 19
  20. 20. iii. Facilitates placement of material in areas of retention. - Materials employed for matrces for these composites include : Polyster or polyethelene plastic strips. To overcome 2 potential problems of the 2-paste system viz. - Incorporation of air bubbles. - No control of W.T. after mixing of materials. Materials which did not require mixing, were developed viz. The light composites. Their advantages included: - Control over the manipulation time (sp. W.T.) and it took only about 40 secs to cure a 2mm thick increment. - The light cure systems were not sensitive to the O2 inhibition. However certain disadvantages association with these light cured composites include : - Shrinkage of composites towards the light source. - Complicating factors association with the light souce. In the single paste system, thus, the paste, available in many shades is held in a syringe or compule that contains all of the necessary ingredients which is placed or injected into the prepared cavity. - The composite is then cured, when exposed to a visible light source of the wavelength between 400-500nm. 20
  21. 21. - More specifically the blue zone (468nm), produces excitation of the photoinitiator molecule and an interaction with the amine ensures to form free radicals that initiate addition polymerization. - This mentioned light source is usually a tungsten halogen bulb. - The light is transmitted to the hose by means of a fiber-optic. - The exposure times of the composite for polymerization depend upon: - The type of lamp. - The depth of the composite – 20-60 secs for a restoration 3mm thick. - Shade of the composite – darker shades more time. - Type of the composite – Microfilled composites require longer time than fine particle because the smaller filler particles scatter the light more. - Caution – although the light is filtered to provide only blue light, one should not look at the tip or the reflected (from enamel) light because of the high intensity, with could affect the color vision (affect rods and cones)?. - Some lamps may even produce considerable heat which could lead to pulpal irritation. Properties of the Composites and Clinical Considerations : - The physical properties are exhibited by the following chart. - Coming next to the clinical considerations of the individual composites. 21
  22. 22. 1. Traditional Composites : - A major clinical disadvantages of the traditional composites is the rough surface that develops during the abrasive wear of the soft-resin matrix that leaves the more wear resistance filler particles elevated. - This rough surfaced texture also pre-disposes the restoration with a tendency to discolor. - The poor wear resistance thus makes traditional composites as inferior materials for posterior composites. - The high filler content decreases polymerisation shrinkage and coefficient of T.E. the resin matrix however doesn’t bond chemically to the tooth structure. 2. Microfilled Composites: - Their use in stress bearing areas has been questioned because of their potential for chipping. - This chipping observed more commonly at the restoration margins has been attributed to the debonding of the pre-polymerized composite filler. - To minimize this marginal chipping, diamond bur rather than fluted tungsten carbides have been recommended for trimming microfilled composites. However due to their smooth surface texture. Physical Properties of Composite Restorative Materials: 22
  23. 23. Some of the important physical properties I would be discussing here, are as follows: i. Inorganic filler content. 1. Compressive and Tensile strengths. 2. Polymerization shrinkage. 3. Water sorption. 4. Coefficient of thermal expansion. 5. Fracture Resistance. 6. Wear resistance. 7. Radio-opacity. 8. Bond strengths to enamel and dentin. i. Inorganic filler content: As the filler content primarily affects the previously mentioned physical properties, it is thus imperative to have an ideal about the actual inorganic filler content of the individual varieties of composites : 1. Compressive and tensile strengths : The compressive and tensile strengths of small particles and hybrid composites are clearly superior to the traditional and microfilled composites. (Craig) – The particles of the microfilled composites increase the viscosity of the materials so that only ICW volume fractions of filler are possible and thus their compressive strengths are lower. 2. Polymerization shrinkage: 23
  24. 24. The fine (small) particle composites shrink less during polymerization than microfilled, since the shrinkage is a direct function of the amount of organic matrix. - It has been shown that even with acid etching of enamel and the use of bonding agents, stresses from polymerization shrinkage can exceed bond strengths of the composites to tooth structure and as a result marginal leakage is not prevented. - Thus 2 techniques have been proposed to overcome or minimize this polymerisation shrinkage. 1. To insert and polymerize the composite in layers (incremental build up) thus reducing the effective shrinkage). 2. To prepare a composite inlay in the mouth or die and then to cement the inlay to the tooth with a thin layer of a low-viscosity composite cement. These composite inlays are usually heated outside the mouth after curing which increases polymerization and wear resistance. 3. Water sorption The higher values for microfilled compressive are apparent. These results occur because the organic matrix is mainly responsible for the absorption of water. Clinically therefore, the microfilled composites have a greater potential for being discolored by water soluble stains. - Also, the effect water sorption on the degradation of properties of composites is irreversible. 24
  25. 25. 4. Coefficient of thermal expansion: - As seen from the table the microfilled have the highers coefficient of thermal expansion, reason being. - Higher the amount of organic matrix, higher the linear coefficient of thermal expansion, since the polymer has a higher value than the filler. - Therefore clinically, restorations with microfilled composite will have a greater change in dimension with changes in oral temperature. 5&6. Fracture resistance: - The KHN of comosites is exponentially related to the volume fraction of the filler (filler density) and is less related to the hardness of the filler. The wear resistance of any composite is also a function of the interparticle spacing called the “Protection Hypothesis”. - As seen from the table the small particle and hybrid composites have a superior hardness and wear resistance in comparison with the other systems. 7. Radioopacity: For a composite to be radio-opaque it must contain an element with a high atomic number, Ba, Str, Bromins, Zinc, Zr, Since carbon, hydrogen, oxygen and silicone are not sufficiently high in the atomic series to alternuate x-rays. 25
  26. 26. - The small particle or hybrid composites usually contain these elements (i.e. the heavy metal glasses) and are this advertised as radio-opaque by the manufacturers. - However, Craig points out that not all composites appear radio-opaque on dental radiographs. 8. Bond strengths: The maxillary bond strengths of composites to acid etched enamel are about twice as high as the bond strengths to dentin. - The difference exists based on the increased inorganic content of enamel and also the compositional and morphological differences in dentin. Biocompatibility of Composites: Composite resins have found to: i. Produce more cytotoxicity than amalgam in comparative in vitro tests. ii. Be classifiable as a toxic restorative material. iii. Produce inflammatory response in the pulp when placed in test cavities in animals. iv. Be strongly allergenic. v. Inhibit RNA synthesis of cells. The peroxides in composites are used to generate free radicals in the polymerization of composite resins and the peroxides are known to be promotes of skin tumours. The peroxides may be mainly responsible for the toxicity of composites. 26
  27. 27. In addition free radicals produced during polymerization may be responsible for the development of some cancers. The dimethacrylates can be enzymically degraded by the enzymes present in the saliva and gingival crevicular fluid and this can influence the rate of wear. As far as the pulpal response is concerned the polymerized composites are more / less biocompatible, however uncured composites serve as reservoir of diffusable components that can induce long term pulp-inflammation. - The second biologic concern is associated with the shrinkage of the composite during polymerization and subsequent marginal leakage. - The emitted light from the VL unti can cause retinal damage, microfilled have become the resins of choice for anterior restorations and subgingival restorations. III. Small Particle Filled Composites: - Due to their better strengths and high filler content these are more suitable for regions where higher and abrasion may be encountered for all Class I and II sites. - They have a reasonably good surface smoothness but not as much as microfilled or hybrid. IV. Hybrid Composites: 27
  28. 28. - As a result of their surface smoothness and reasonably good strength these composites are widely used for anterior restorations including Class IV sites. - Though their mechanical properties are slightly inferior to the small particle filled composites the hybrid composites are widely used for stress bearing restorations. Posterior Composites  To be discussed as under A relatively newer topic for discussion, the post composites, is dealt with as follows: A. Controversies in development of alternatives to amalgam. B. The advances of posterior tooth colored restorations (compressive inlays). C. More recent advances - Flowable composites. - Condensable composites. A. Controversies in development of alternatives to amalgam: - Dissension in some form has always has a role in dentistry. The posterior composite resin restorations present the practitioners with a number of uncertainties and because of this the dental profession finds itself in the middle of an emotional duel. - As a result of the misleading media, Cosmetics has become a chief priority for patients today. - These advertisings have led to almost a large % age of patients who refuse metallic restorations in their mouth. 28
  29. 29. - To add to the problems, these advertisers have joined hands with the Zealots of dental community who cry about the never ending controversely of “Mercury Toxicity”. - However to date, as stated by Ronald Jordan (JADA 91) there has not been a shred of evidence directly linking dental amalgam with a systemic disease of any kind for all multiple scelerosis, anthritis etc, though some very rare instances are reported. - Thus condemning the use of these time honored metallic restorations, the zealots now replace them with the esthetic posterior composite restorations. - I say “time honoured” metallic restorations because these restorations, amalgam in particular had cutain advantage’ to withstand the test of time advantages were: 1. Ease of placement. 2. Good mechanical properties. 3. Excellent wear resistance. 4. Self-sealing ability with aging of restorations. The amalgam restorations I feel would enjoy successful use in the future too, since recently developed materials actually bond dental amalgam to both enamel and dentin. However then, due to an increased in aesthetic consciousness, posterior composites developed. The ideal requirements of a posterior test material (as published in the D.C.N.A. Jan 1990 include. 1. Esthetics. 2. High resistance to clinical wear. 29
  30. 30. 3. Permanent marginal integrity. 4. Minimal cavity preparation. 5. Provision of a sealing bond and retentive bond to tooth structure. 6. Non-brittle mateial with adequate tensile and compressive strength. 7. Radiopacity. 8. Self bonding properties should additional restorations become necessary. 9. Ease of manipulation. 10.Non-toxicity. 11.Resistance to formation of secondary caries. 12.Minimal galvanic and thermal shock properties. History: of direct posterior composite restorations: The use of directly placed posterior composites for Class I and II preparations dates back to the mid 1960s. - Desirable features of these new alternatives to amalgam included : Naturally : - Better aesthetics. - Marginal integrity. - Low thermal conductivity. - Resistance to T&C - However, at the beginning, the initial claims for their success were based on short term clinical studies and laboratory tests. - Failures of these materials, in the form of color changes, wear, microleakage and rec., caries began to appear in approx 2 years, major 30
  31. 31. reasons being the dynamic forces of mastication associated with other factors in the oral environment which were not included in the short term and laboratory studies. - Thus the composites underwent compositional improvements from the 70s to 90s. - Thus as of today materials, with : a. Improved color stability. b. Resistance to microleakage. c. Reduced wear and d. A lower incidence to rec caries are made available which are encouraging for the clinician. Selection criteria for direct posterior composite restoration materials: The important features on the tooth restored to be with posterior composite restorations are: A. The location of the centric stops – In general the location of centric stops on the occlusal surface of the proposed restoration must be avoided. Failure to comply with this could lead to serious problems for all wear from the antagonistic cusp or bulk fracture as in certain composite resins when subjected to concentrated occlusal stresses. As for as the wear pattern is concerned, altogether 5 types of wear patterns could be exhibited, which I would be dealing with later on. 31
  32. 32. B. Anticipated depth of the gingival floor on the proximal surface. - In this context, the deeper the gingival floor the thinner would be the enamel wall in cross-section and as the enamel becomes thinner the potential for adequate bonding of the composite decreases. - When the gingival margins are located in the dentin or cementum or both and the resin is firmly anchored to the etched enamel at the other margins, the material tends to shrink away from the gingival margins during polymerization. - This leads to a gap formation and ensuring marginal leakage. C. Location and Size of the Restoration: - In general the more distal the location the greater is the rate of wear. - As a general rule posterior composite resins in molars commonly wear away approx twice as fast as those in premolars as reported by Skinners the best composites designed for posterior restorations still wear more than natural enamel under identical conditions. - Bucco-lingual width of the restorations – is also an important consideration. 32
  33. 33. - The greater the dimension of the isthmus the faster rate of wear. Advantages of Bonded Direct Composite Restorations for class I, II, III and IV preparations (Vs amalgam in general). 1. Esthetics 2. Conservation of tooth structure. 3. Improved resistance to microleakage. 4. Strengthening of tooth structure. 5. Low thermal conductivity. 6. Completion in one appointment. 7. Economics – less expensive than gold /ceramics. 8. No corrosion. Disadvantages : 1. Very technique sensitive. - One of the by pdts of this drawback according to Karl Leinfelder is secondary caries. - Also due to salivary contamination (if any) decreased bond strengths and thus ensuring reduction in other properties would ensure. - In Class II restorations care should be observed in placing and positioning the matrix bonds because posterior composites are almost entirely dependent upon the contour and position of the matrix for proximal contact establishment also pre-wedging is required (explain). 33
  34. 34. - This technique of composite placement is a more time consuming and tedious compared to amalgam. 2. Higher coefficient of thermal expansion than tooth structure. 3. Low modulus of elasticity. 4. Biocompatibility of some components unknown. 5. Limited wear resistance in high stress areas. Polymer shrinkage Indications for direct posterior composite restorations: 1. Aesthetics. 2. Class I and II cavities which can be properly isolated and where some centric contact(s) on the tooth structure is (are) present. 3. Class V defects – hypoplasia, hypomineralization. - Cavitated carious lesions. - Abrasion and erosion lesions which are excessively sensitive or deep. 4. Class VI cavities (faulty pits on selected occlusal cusps). 5. Veneers for metal restorations. 34
  35. 35. 6. Repair of #’d areas (teeth and or restorations). 7. Restoration of a weakened tooth that can be strengthened by a bonded restorations. 8. Where gingival cavosurface margin is in intact enamel. 9. Where bucco-lingual width is less than 1/3 intercuspal distance. 10. Where centric stops are on sound enamel surface. Contra indications: 1. Operating site cannot be well isolated. 2. When all occlusal contact will be on the composite. 3. Therefore heavy occlusal stresses for all bruxism. 4. Deep subgingival areas difficult to prepare or restore. 5. High caries index. Clinically loss of material caused with 1. Functional Contact Area Wear – Related to sliding contacts. 2. Proximal Contact Area Wear – at interproximal contact regions. 3. Tooth brush abrasions wear – From tooth brushes and dentifrices. Studies reveal that the best composites for posterior restorations. Still wear more than natural enamel under identical conditions. - The nature of wear has said to have two principle mechanism viz: 35
  36. 36. 1. Based on direct contact of restorations with opposing cusp (Direct Contact Area Wear). 2. Loss of material in non-contact areas must probably caused by contact with a food bolus. (Contact Free Area Wear). A classification of these composite inlays is according to: A. Method of construction – Direct Technique. – Indirect technique. B. Method of curing – Super cured – Secondary cured – Cured by conventional V.L.C. unit of ambient temperature. C. Type of composite – Microfilled (according to filler type) – Fine hybrid – Coarse Hybrid Advances in posterior composites: - Although the posterior composites have increased in popularity and appear to be well accepted by patients and also improved materials and accessories have helped maximise their potential, the direct placement posterior composites still have some limitations viz: (as mentioned) 1. Polymerization shrinkage. 36
  37. 37. 2. Difficulty in achieving adequate polymerization in deep interproximal areas with leads to a partially cured interphase susceptible to a wash out and subsequent bacterial ingress. 3. Lack of stability in anatomic form and susceptibility to damage in load bearing areas. 4. Water sorbtion and resultant hydrolytic instability. 5. Technique sensitivity. - Thus to overcome some of these drawbacks composite inlays systems were introduced. They are defined as : (BDJ 1991 Burke and Watts). - “A composite inlay is a restoration which is cemented into a dental cavity as a solid mass that has been fabricated from composite resin with a form established either by an indirect or direct procedure. Classifications in Detail: A. Method of construction : 1. Direct Technique: - Inlays are constructed in the prepared cavity in the mouth, prior to removal for additional curing, finishing and polishing. Eg. Brilliant direct inlay system (Coltene Whal‘dent); True vitality system (Dent Mat Corp). 2. Indirect Techniques (Clearfil CR inlay (Kuraray) – in India by Tracom Services – may be chairside fabricated or lab fabricated. B. Method of curing : 37
  38. 38. 1. Super cured: - One stage cure at elevated temperature under pressure. - The composite is heat cured, rather than light cured as in sec cured and conventional cured systems. - The inlays here are cured at 120° C at 6 bar pressure under water. Eg. SR- ISOSIT System contains homogenously filled compressive material with 55% wt% colloidal silica + 20% radiopaque lanthanum fluoride in 7 shades + 6 mix in colors. 2. Secondary cured : - After initial light curing at room or body temperature additional curing is effected by heat and light. Eg: a. Coltene Brilliant Aesthetic Line System in which the inlay is sec cured in high intensity light system upto 120°C for 7 mins. b. Kulzer Inlay System – Inlay is sec cured in high intensity light in an enclosed light activating unit attachment with internal narrowed surfces. Glass ceramic filled material which 80% filler by mass. 3. Conventional Cure – Normal mechanism Eg. EOS system. Short note on: 1. Indication for composite inlays: a. Good oral hygiene status. 38
  39. 39. b. Teeth with adequate remaining tooth structure for bonding. c. Cavities where occlusal function of the restoration is limited. d. Restorations of particularly root filled teeth, which are ultimately destined for crowning. e. Where there is no evidence of excessive wear. f. Patients who are prepared to receive and accept a restoration with unknown life expectancy. 2. Contra indications for composite inlays: a. Poor oral hygiene. b. Less tooth structure for adequate bonding and retention and resistance form. c. Situations where there is evidence of atypical loss of tooth substance from the surfaces of teeth to be restored. d. Where moisture control for optimal bonding cannot be maintained. 3. Advantages of Composite inlays: - High esthetics. - Better control of contact areas. Excellent marginal adaptation. - Reduced or no lab fee (therefore decreased cost) if done in the office. - Ready reparability of the material intraorally. 39
  40. 40. - Cross splinting of compromised tooth and easy removal if replacement becomes necessary. - Compensation for polymerization shrinkage by curing materials outside the mouth. - Increased composite resins strength because of the heat curing process. Prosthodontic Resins (Veneering Resins) - The initial resins, veneering materials employed were basically heat cured polymethyl methacrylate. - There were subsequently improved by the addition of fillers and cross linking agents. - So then we had microfilled resins with resin matrices of either BIS-GMA, UDMA etc. - These resins were polymerized using light of wavelength between 320- 520nm or by a combination of heat and pressure. As far as the bonding of these resins to the underlying metal substrates is concerned, these resins were initially bonded Mechanically using wire loops or retention bends. The recent improvements in bonding mechanisms have included micromechanical retention created by acid etching the basal metal alloy and the use of chemical bonding systems for all 4-META. Phosphorylated methacrylate or epoxy resins. 40
  41. 41. Another method is by the use of silicone dioxide that is flame sprayed to the metal surface followed by the application of a silane coupling agent (Silicoating). These prosthodontic resin veneering materials have several advantages and even certain disadvantages over ceramics. The advantages are: i. Ease of fabrication. ii. Predictable intraoral repairability. iii. Less wear of opposing teeth ore restorations. The disadvantages include: i. Low proportional limit and pronounced plastic deformation that contribute to distortion on occlusal loading therefore resin must be protected with metal occlusal surfaces. ii. Another disadvantage – leakage of oral fluids and staining below the veneers, particularly those attached mechanically are caused by the : - Dimension change during thermal cycling and - Water sorption - Surface staining and intrinsic discoloration of the resins has also been reported. On the clinical front: 41
  42. 42. - The prosthodontic resins have been utilized as an alternative to conventional prosthodontic restorations. Such as for masking tooth discoloration or teeth malformations. - In this, the resins aer used as preformed laminate veneers where resin shells are adjusted by grinding and the contoured facing is boded to tooth structure using acid –etch technique or dual cure luting cements. - These resins are susceptible to wear during tooth brushing and thus part of the clinician it is important for him to advise proper cleansing procedures and also the use of a soft toothbrush with a mild abrasive toothpaste. Pit and Fissure Sealants: The prevention of caries in deep grooves and fissures of teeth is more difficult than is the prevention of caries on the smooth surfaces. The susceptibility of occlusal pits and fissures to caries is related to the physical size and morphology of the individual pit and fissure. (may be v- shaped / bottle neck shaped). Treatment options for pit and fissure canines include: 1. When there is no evidence of a “explorer catch” at the bottom of the groove – to be kept under observation. 2. To run a bur through the fissure so as to open up the groove and provide a more self cleansing effect “Prophylactic Odontomy”. 42
  43. 43. 3. Another option is to cut a larger groove and restore with dental amalgam (Jack L. Ferracane). However a more conservative approach than the last one mentioned is the use of the Pit and fissure sealants. Although filling pits and fissures with chemicals and other materials dates back almost to the turn of the 20th century, it was the development in the 1960s (1955 Dr. Buconocore – concept of acid etching), of the acid etch technique for bonding resins to enamel with made this option available. Materials used: - The pit and fissure sealants may be supplied as a : - 2 component system or - Single Essential Component- Organic monomer – BIS-GMA 1. 2 component system – (also called amine accellerated) The polymerization here can be bought about by mixing equal drops of two liquids containing essential chemical activators (amines and initiators (peroxides). - The resin liquid hardens in 1.5 – 2 mins providing an ample W.T. to brush or pour material onto the etched tooth surface. - The reaction is exothermic but clinically insignificant until used in bulk. 43
  44. 44. 2. Single component : A more popular method, of polymerizing the resin is the use of a blue light source. The advantages of this method are: i. Longer W.T. (W.T. under control of operators). ii. No mixing, therefore no air bubbles. iii. Studies reveal L.C. P&F sealants have increased surface hardness (because of less air inhibition during polymerization). A drawback observed was that polymer resin sealants wear under occlusal forces studies have shown this loss as 15% by volume over period of 6 months. The chemistry of the BISGMA resin types is essentially same as those described for composites. The principle difference is that the BIS-GMA sealants must be much more fluid to penetrate into P and F etched tags 3 parts of BIS-GMA are mixed with 1 part of MMA to obtain a low viscosity sealant. The photoinitiated resins are activated by the inclusion of benzoin methyl ether in a carrier o pthalate ester when the operture of the source is held 1mm from the sealant curing time of 20 secs is sufficient. Technique of Application: 1. Enamel surface preparation: Other than usual steps followed important points remember are: 44
  45. 45. a. The wettability of enamel surface is improved by etching 1min for normal enamel. b. Entire depth of the fissure should be etched and subsequently penetrated by resin which may be prevented by air entrapped / debris. c. Penetration of resin leads to resin tag formation (25-50µm). d. Isolation is essential. Poly Acid Modified Composite Resin: According to Jay (Dent Update Sept 95) these are – materials that may contain either or both of the essential components of a glass ionomer cement but at levels insufficient to promote the acid/ base reaction in the dark. Eg. Dyract – where the resin is TCB – a reaction pdt of butane tetracarboxylic acid + HEMA. The filler is a silicate glass containing fluoride. C. More Recent Advances in Posterior Composites: 1. Flowable Composites : The traditional composite resins are densely loaded with reinforcing filler particles for strength and wear resistance. Generally all mechanicalproperteis improve with filler loading. 45
  46. 46. Despite the numerous refinements made in traditional composites over the past decade, two desirable clinical handling characteristics for composites have not existed until very recently : They are: i. Non-Stickiness – so that materials could be packed or condensed like amalgam. ii. Fluid injectability. The first generation of flowable composites was thus introduced in 1996, just before the condensable composites. So date a very limited information is available on either type of new composites. The flowable composites have been created by retaining the same small particle size of traditional hybrid composite, but reducing the filler content, thus allowing the increased resin to reduce the viscosity of the mixture. Therefore these flowable composites fitted into the range of resin based restoratives with variations in filler content. This range from least to most filled is as follows: 1. Pit and fissure sealants. 2. Microfil composite resins. 3. Flowable composites. 4. Hybrid composite. 5. Condensable / packable composit. The early success, then associated with the flowable composite pdts was more as a result of marketingthan of any properties beyond flow. - Thus several companies so on had their own flowable composite pdts out in the market. 46
  47. 47. - Thus eg of commercially available flowable composites with respective filler information is as follows: Type of F.C. Manufacturer Filler information 1. Eliteflo BISCO INC. Type : Barium glass colloidal silica. Avg size: 0.7µm wt% 60% 2. Flo-Restore DEN-MAT Corp. Type : Silica; barium glass barium fluoride silicate Avg size : 0.7µm wt% 50% 3. Revolution KERR-Corp. Type : Barium glass synthetic silica Avg size : 1µm et% 62% 4. Ultraseal XT Plus Ultra dent Pdts Type : Glass Ionomer Glasses Avg size – 1.0-1.5µm wt % 60% - Recently it has been suggested that one key mechanical property for clinical prediction of performance may be toughness. - This property of toughness could co-relate with both wear and % resistance. - Since these flowable composite are more resin inch than traditional composites one might expect their toughness values to be better than those of conventional composite. - The flowable composite might also have higher # toughness values because of their low elastic module. Therefore finally, because of a lack of substantiating research these flowable composites should not be used in situations involving high stress or associated with wear. 47
  48. 48. Range of applications for flowable composites as suggested by manufacturers: - Amalgam margin repair. - Class I, II, III, IV and V restorations particularly gingival increments. - Composite repair. - Core build up. - Pit and fissure sealant. - Porcelain repair. - Restorations of air abrasion preparatus. - Tunnel preparation restorations. - Veneers. 5. Condensable Composites: As noticed, the early formulations of composites (as developed by Bowen) has a number of drawbacks for all inadequate wear resistance, shrinkage etc. - Though considerable progress has been made regarding the wear problems, comparatively little research has been directed in improving the handling of these materials. Recently a new concept was developed that provides the basis for fabricating a packable or condensable posterior composite resins. 48
  49. 49. - This innovative system also consists of a resin and a ceramic component (filler) (together known as PRIMM) Polymeric rigid inorganic matrix material. - The ceramic filler, not an inorganic one consists of a continuous network of or scaffold of ceramic fibers. - These fibres are individually composed of alumina (Al2O3) and silicon dioxide (SiO2). - The individual fibres are superficially fused together at selected sites which then generates a continuous network of small chamber or cavities. - The diameter of these individual ceramic fibres is 2.0µm or smaller, while the 3-dimensional interface interfacial chambers approximate to 25µm. - After silanation these chambers / spaces are then filled by the manufacturer with BISGMA or UDMA. - The use of PRIMM in conjunction with BISGMA or UDMA has a profound effect on a number of important properties associated with the clinical performance of posterior composites. Handling characteristics : - The consistency of the resin infused PRIMM material is very similar to that of a freshly triturated mass of amalgam. - Upon completion of cavity preparation the clinician inserts the composite in the same manner as that for an amalgam. 49
  50. 50. - However since the alumina fibres are hard they have the potential to scratch the nozzle of the amalgam carrier for this reason the tip should be coated or made from a wear resistance polymer (Teflon). Each ejected material is then condensed in a conventional manner. - The cavity is then filled to a point slightly beyond the cavosurface margin + excess removed with a cleoid discoid / hollenback cawer. - The restorations is then cured for 30 secs. - This restorations can be cured to a depth of 6mm using conventional light curing unit. This increased depth is possibly related to the light conducting properties of the individual ceramic fibres. - Regarding the shrinkage, since the surface of the ceramic fibres is silanated, the polymerising resin does not pull away from the surface. Any defects that occur as a result of polymer shrinkage will be localized in the small chambers of space formed by the surrounding ceramic fibres. Technique for placement of composites: - The light activated composites have certain manipulative advantages for all: i. No mixing required therefore eliminating certain manipulative variables. ii. W.T. is chosen by the clinician. - However during placement of the mateial into the prepared cavity avoiding void formation is essential. 50
  51. 51. - The voids can be minimized by wiping the material onto one side and then filling the cavity from the bottom outward. - To prevent material from sticking to the instument wip the instrument with a gauze dipped in alcohol. - To avoid polymerization shrinkage and also an adequate depth of cure, an incremental technique is essential. - In the curing procedure, the light tip should be positioned as closely as possible to the resin surface. Ideally, curing should be initiated at the tooth resin interface so that the resin shrinks towards the cavity walls rather than away from these walls. - This can be achieved by curing through the tooth structure adjacent to the proximal margins. Finishing and Polishing of Composites : - The smoothest surface on freshly inserted composites can be obtained by allowing polymerization to occur against an inserted mylar matrix. - The use of green /carbide stones / 12 blade carbide burs is also accepted for removal of excess, near the enamel margins. - This is followed by the use of: i. Aluminium oxide disks – for accessable areas finishing. ii. White stones – of suitable shapes – inaccessible areas. iii. Fine and microfine diamonds – finishing of microfilled resins. 51
  52. 52. Chemically by application of DBA and curing (for glazing) Repair of composites: - The composites may be repaired by placing new material over the old. - This addition procedure depends upon whether the restoration is freshly polymerized or an old restoration. - When a restoration has been freshly polymerized, it may still have the O2 inhibited layer of resin on the surface. Additions can be made directly to this layer because this represents, in essence, an excellent bonding substrate. - A restoration which has been just cured and polished may still have more than 50% of unreacted methacrylate groups to copolymerize with the newly added material. - As this restoration ages, fewer unreacted methacrylate groups remain and greater crosslinking, reduces the ability of fresh monomer to penetrate into the matrix. - Thus, the strength of the bond between the original material the added resin decreases in direct proportion to the time that has elapsed between polymerization and addition of new resin. - Under ideal condensations the strength of repaired composites is less than half of the strength of the original material. 52
  53. 53. Conclusion: “All that glitters is not gold” could be a maximum which can be evenly associated with the composite resin materials. What one would interpret with this is that though the composite materials show much promise for replacing all aesthetic and posterior restoratives in the near future, certain drawbacks associated with them viz. Wear resistance strength, polymerisation shrinkage etc. do resist their clinical usage to some extent. However, we could be sure than once these hurdles are overcome this material would surely be one of the favourites in dentistry in the years to come. 53