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Dental/ rotary endodontic courses by indian dental academy

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Indian Dental Academy: will be one of the most relevant and exciting training center with best faculty and flexible training programs for dental professionals who wish to advance in their dental practice,Offers certified courses in Dental implants,Orthodontics,Endodontics,Cosmetic Dentistry, Prosthetic Dentistry, Periodontics and General Dentistry.

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  • 1. T 3 days the response ranges from slight to moderate; at 5 and 8 weeks the inflammatory process is slight and a zone of reparative dentin has formed underlying the cavity. Inflammatory cells may still persist at the later time periods, presumably because of stimulation caused by the continued release of some calcium ions. Typical responses are shown in Figs. 7-11 and 7-12. One function of calcium hydroxide liners is to serve as a contact dressing in the event of exposure of the pulp. At.3 days the response of an exposed of the pulp to calcium hydroxide may range from slight to severe, and these same responses may be maintained at 5 and 8 weeks. The reason for the range or response to various Ca (OH)2 compounds is that the cement may be in a water-soluble form or the solubility may be restricted by the cement bin compounded in a resin. Formulations using a water-base carrier of calcium hydroxide may cause a zone of necrosis adjacent to the compound. Beyond the zone of necrosis, healing occurs and a dentinal bridge forms (Fig 7-13 A). The resigned salicylate Ca (OH)2 liners stimulate healing with no zone of necrosis; therefore dentin is laid down adjacent to the liner (Fig 7-13 B) an indication that the formative cells, the odontoblasts, began forming dentin in contact with the liner. Calcium gydroxide is the most effective liner now available for treating pulp exposures with subsequent formation of a reparative dentin bridge. Adder exposure the pulp organ goes through a relatively uncomplicated wound-healing process in manner similar to that of skin if the tissue is not infected. Usually in a deep carious lesion the Helen process is complicated by the presence of bacteria. When a pulp is exposed, hemorrhage initially occurs and a blood clot forms at the expenses of the connective tissue at the site. Healing then progresses with resolution of the clot by homeless, and proliferating fibroblasts of dentin. The resin-filled Ca (OH)2 liners offer a major advance in pulp-would management. Healing takes place with minimal inflammation, and reparative dentin forms at the initial site of exposure with minimal loss of pulp size (Fig.7-13,B) There is evidence that these materials break down in time and create a gape between the rest ration and the cavity wall. Varnishes. Numerous investigators have analyzed the effects of the application of “thin layer” liners such as copal varnishes and polystyrenes under silicates and zinc phosphate cements. These liners are used in such thin layers that they do not provide thermal insulation, but they serve to isolate the tubule contains from the cavity. They also inhibit penetration of bacteria of chemical subnstancex resulting from the setting of a restoration. They should prevent penetration of components of amalgam into dentin and reduce marginal leakage. Several applications may be nbeccssary to prevent penetration of bacteria or acids Composites. Chemically accelerated composites placed in cautious with approximately 0.5 mm of remaining dentin generally show a moderate response ate 3 days (Fig 7-14.) The response to ultraviolet (UV) accelerated composites after 3 days is moderate to slight. The milder response to the UV-accelerated materials may be a result of the lack of chemical acceleration, which provides fewer chemicals to affect the tissue.
  • 2. The inflammatory response diminishes as the postoperative time increases to 5 to 8 weeks, with an increase in the quantity of reparative dentin. The response to both chemical-and UV accelerated composites cause reparative dentin to from underlying the cavity floor. This dentin appears to be regular, containing dentinal tubules and few if any cell inclusions (Fig.7-15) Because of the moderate initial response to these materials, it is recommended that a protective line such as calcium drooled be used. With a liner, the pulp response to the composite system is minimal. Amalgams. Since amalgam is the most commonly seed restorative material, the pulpal response it produces has received a great deal of attention. Investitures agree that in cavities of average depth, the pulp is affected mainly by the cold and hot stimuli that result from the thrall conductive properties of the amalgam. In deep cavities, pain is a characteristic of unlined cavities and 5 weeks. Aspiration of obontoblasts into dentinal tubules underlying the cavity has en seen. The response to amalgam is minimal in shallow cavities. There is a significant difference in pulpal response in the unlined cavity and those lined with cluclum hydroxide, sine oxide- eugenol, or varnishes. Several reasons are advanced for the presence of pulpal damage soon after the placement do an unlined amalgam. Marginal leakage has been reported to cause some damage to the pulp after the placement do amalgam restorations. The margins of newly placed amalgam restorations show significant microleakage (Fig.7-16) In summary, puple response to silver amalgam restorations occurs shortly after their placement and is probably a result of cavity preparation and marginal leakage. Leaching of toxins from amalgams that may penetrate dentin is dependent on the size o the molecules and the patience of the tubules. There is a significantly improved response when the cavity is lined, and the patebct if the tubules. There is a significantly improved response when the cavity is lined, and the amalgam rarely causes irreversible damage to the pulp. A number of silver amalgams with high copper contents are currently in clinical use. These have been introduced because their resistance to corrosion and creep is higher than that for the conventional silver amalgams containing the y2 phase. At 3 days the pulpal responses elicited by these highcopper amalgams appeared similar to those of conventional amalgams in unlined cavities. At 5 weeks they elicited only slight pulpal response. AT 8 weeks the inflammatory response was again reduced.. bacterial tests on the high-copper amalgam pellets revalued little inhibitory effect on stereotypes of S. Mutants, which indicates that the elements are firmly incorporated in the amalgam and thus unlikely to be released into the oral environment. Although the newly introduced high-copper amalgams appear to be biologically acceptable, it is suggested that liners be used in all deep cavities. Gold. Cast gold restorations very widely in size because of tooth- coverage requirement . it has been said that pulp reaction to cast gold crowns is a dressily of the type of cement used to retain the restoration. In shallow cavities Sine
  • 3. phosphate cement serves to stimulate reparative dentin. In deep cavities the pulp should be protected from the zinc pjhospjhate cement mix because of the free acid available, as discussed previously. The pulp responds more favorable to the improved zinc oxideeugenol cements. The condensation of cohesive gold is a factor in pulp response. A moderate to severe inflammation was reported at 10 to 20 days, but after 35 days spoons. Condensation of gold thus causes a short-term severe response that stimulates reparative dention formation. If a base is required, pulpal inflammation is reduced. There are no irreversible changes, and the use of cohesive gold thus causes a shortterm severe response that stimulates reparative denotation is reduced . there are no irreversible changes, and the use of dchoesive gold may be considered biologically sound. Among all restorations evaluated, gold foil showed the least marginal leakage; however, the leakage does not decrease with age. Usage tests on inflamed teeth Pulps used for the testing of dental materials are usually normal (noninflamed ) pulps from intactnoncarios teeth. There is concern that liners, cements, and restorative agents will respond differently to an inflamed rather than a normal pulp. After all, this is the situation in which most materials must function in human teeth. To gain information about this factor, a number of investigators have propose developing a model of inflamed teeth for testing these materials. The several methods proposed are as follows (1) soft carious dentin from freshly exrtracted human teeth is placed in the floor of cavities and covered with cment for 4 to 7 days (Fig 7-17) (2) a gutta-percha temporary filling is placed in the cavity for 4 to 7 days, or (3) the cavity is left open to the oral enviroment for 4 to 7 days. Days . After this time the carious dentin or gutta-percha is removed, the the cavities are dried with cotton pellects. And the test material is placed on the floor of the cavity and sealed with amalgam. The carious dentin produces a sever localized pulp reaction the gutta-percha causes a slight to moderate one, and the open cavities produce varied responses. Thus the carious dentin and gutta-percha rechnics are the ones widely used today in animal research to produce pulpitis before a material is tested. Efforts have been made to quantify and qualitfy the technic of bacterial insult. For example, recent studies in which 1 u1 each of lactobacillus casei and Streptococcus mutans were sealed in cavities resulted in sevr pulpitis in soe cases and less in others. This variability in response has resulte in the continued use of human carious dentin. A further advanc in technology is the use of a Brown and Bren stain for determining the presence of bcteria. This stain clarly demonstrates the personce and location of both gram positive and gram-begative bacteria after routine histological preparation. Thew presence of bacteria in the dentinal tubules an dpulp can be corrclated with pulp response. Serapings from a cavity can also be cultured by routine microbiological procedures to ascertain the presence and identity of bacteria at the site.
  • 4. The use of the inflamed pulp in the evaluation of dental material is gaining popularity since this closely resembles the situation in which thse materials will be used in man. Not onl is the pulp evaluated, but also the type of reparative dntin. The pulp evaluated, but also the type of reoaratuve debtin. The idealk response is regular tubular dentin. Other types of irregular entin may form that may contain few tubules or osteodentin or a combinatiuon of these (Fig 7-18) irregular dentin or osteodentin with cell inclusion indicates a more severe response to the dental material. GINGIVAL RESPONSE Since usage tests in man and animals are carried out at sites that are appropriate for their intended use, various dental materials have been placed in subgnigival cavities and the response of the gingiva evaluated in manner similar to pulpal eveluations. One of the difficulties of this type o study is nthe normal presence of some degree of inflammation in the giviva. To avoid this condition, a prophylaxis is performed before the cavity preparation and placement of the material in a sunbgingival cavity. It has been shown that bacterial plaque is the most important factor in gingival inflammation, and surface roughness of the restorative material, open or overhanging margins, plaque accumulation retained by rough surfaces or marins is also an important factor. Operative Procedures Trauma caused by rotatidng instruments is a reversible condition. Even prophylaxis with a rubber cup and pumice will cause loss of the sulcal epithelium, which will beal completely in 8 to 14 days. If subgingival margins exist, inflammation may occur ;and time for healing must be allowed before assessment of the effects of the restorative ageents is made. It has been suggested that subgingival is made. It has been suggested that subgingival cavity preparations be raised to a level even with the crest of the gingiva since this causes the least inflammatory response. Even the best operative procedures produce some degree of gingival margins. Before restorative evaluation, good oral hygiene and normal-appearing gingiva must be attained. Restorative materials After oral prophylaxis and cavity preparation (class V test Cavities) the material, mixed accordin to the manufacturer’s recommendations, is placed in a subgingival cavity, and its effects are onserved after short (7-da7) and long (30-day) terms.Responses are categorized as slight, moderate, or severe. A slight response is characterized by a few rond cells in the epithelium and abjacent connective tissues. A moderate response is indicated by numerous round cells in the connective tissue and a few ncutorphils in the epithelium A severe reaction is evidenced by an increase in the responses in each category and thinned or absent epithelium.
  • 5. Cements Zonc polycarboxylate cement produces the mildest gingival reaction of all cements tested, with mainly slight but a few moderate responses. Gew inflammatory cells are present in epithelium and connective tissue. Zinc oxide-eugenol cements cause slight to moderate response with a few severe responses and thinned epithelium. This wide range or responmse is of interest and may be a result of variations in damage to the tissue. Ethoxybenzoic acid cements show slight to moderate responses, with more moderae than slight. To modeerate response with a few severe responses and thinned eithelium. This wide range of response is of interest and may be a result of variations in damage to the tissue. Ethoxybenzoic acid cements show slight to moderate responses, with more moderate than slight. Silicates In general, silicates elicit moderate gingival responses, with a few slight and severe responses. Epithelial cell proliferation occurred in some arease epithelial cells polit away, and there were a few instances of dense cellular infiltration. Most of these changes pesisted at 30 days. Again, the wide range of response may be a result of thin or think mixes; the think mixes allow more free acid to afect the adjcent tissue. Surface irregularity is an important factor and should be eliminated. Composites Composite resins placed sunbgingivally in class V cavity preparations in subjects withpreviously normal gingiva developed marginal gingivitis. It was found that plaque forms more readiluy on the surface of composite resins than on tooth enamel, even though the resins are finished and polished according to the manufacturer’s directions. It is he importance of develping materials for dental use that are well tolerated by the oralk tissues cannot be overstated. Testing regimens have involved manuy different methods including: tissue culture studies; subdermal implantation in animals; and in-use testing methods in nboth methods there have been variations in technique and widely different results have been ontained in differefnt centres which the samd material has been evaluated. Recently, nboth the british Standards institutre (BSI) have set our protocols for the nbiological testing of dental materials. These include general systemic toxicity tests as well as in-use dental evaluiation. The propocols are complex and demand the use of different animal models. To date there is no record of any material being sunjected to the complete protocol in one laboratory. The major biologifcal concern with restorative materials has been their efect on the dental pulp. Much of the early wsork concentrated on the chemical toxicity of materials caused by, by for example, the acidity of cements or free monomer in resin
  • 6. systems. Recent reports have demonstrated that bacterial contamination(see below) may modify the response of the pulp to these aspects of materials. Indeed, it has been shown that much of the damage kpreviously attributed to the chemical toxicity of materials such as silicate and phosphate cement was caused by bacterial action. Potential sources of bacterial contaminiation of the floors of cavities are: (a) the original carious lesion; (b) saliva and/or plaque which may become smeared over the cavity walls and floors duridng cavity preparation; (c) bacterial ingrowth which may occur down cavity walls following insertion of the restoration. At present there is no restortive material which gives a perfect marginal seal and it sis accepted that all restorative materials sufer from some degree of marginal leakage. With careful technique, this is least with the modern adhesive restorative materials and most marked where there is a setting contraction. Removed by normal cavity cleasing, i,e by hand instruments and water-spray. It may be divided into an outer layer which follows the contour of the cavity wall, and an inner layer which forms plugs’ in the ends of the dentinal tunbules (Fig 17.3; see also Fig 18.2p, 363). DENTINE CLEANSERS AND CONDITIONERS (SEE ALSO Chptter 18) After cavity preperation with rotary instruments the Dentine walls and floor of the cavity will be covered with the Dentine ‘Smer Layer’ (see Chpter 16) this consists of a layer. Irregurally shaped hrd tissue particles of dentine (& perhapes animal) debris ranging in size from beolow 0.5 um to more than 15 um. Which are not removed by normal cavity cleansing. i.i., by hand instrument and water spray. It may be devided into an outer layer which follows the contour of the cavity wall. And an iner layer which forms “Plugs” in the ends of the dentinal tubuls (fig. 17.3 & fig 18.2 p 363) There is considerable debate as to how much of the smear layer should be removed. Some authorities advocate its totald removal (With lower molecular weight acids.)but this can be criticized because it ipens up and widens the ends of the dentinal tubules, with three possile significant disadvantages. (a) It renders the tubules much more susceptibnle to invasion b bacteria and their toxins: this will invariably produce and adverse pulp response. (b) It increases the permeability of the dentine to certain irritant dental materials. (c) It allows an outflow of fluid from the dentinal tunbules which will wet the dentine surface, this in turn making it more difficult to achieve an adequate seald with any lining or base.tuibwe’ to prepare the dntine in abrasion avities to receive galss- ionomer cements. In these cavities, the dentine, as a result of exposure to saliva, will be coated with a thin film of mucins which, if left, act as a separating agent threrby preventing the bonding of the alassinomer cement to the dntine. In this sitution, shorr apliction times (of a few seconds) would remove the mucns Pulp irritation is
  • 7. not usually a problem because the coronal pulp is normally completely onbliterated by repartive dentine in theeth with abrasion cavities. However, such adids hould not be applied to freshly cut dentine. (d) More recently, polycrylic acid has been sunbstituted for the citric acid is some demtome pmdotopmers supplied with glss-ionomer cements. This has a much hiher molecular weight than citric acid, and a 25-second application of a 10% solution of polyacrylic acid is recommended for conditioning freshly cut dentine. The effects of polyacrylic acid on the smear layer have yet to be investiated fully. LINING MATERIALS The trditional view of the function of a lining is that it is necessary promarily to protect the pulp from thermal and/ or chemical injury and hence also from postoperative pain. The mechanisms of pin sensation in dentine do, however, remain incomopletely understood. Some authorities associate it with the movement. It has been demonstrated in the laboratory that to achieve ideal thermal instulation wtih dental lining materials and cements, a thickness of 1.0-1.5 mm is necessary (Fig.17.6) There authors and others have advocated lining thicknesses of 0.5- 0.75mm (Fig.17.6) However, these orders of thickness appear to be only rerely achieved with some materials (e.g clacim hydroxidesee below), yet patients arely complain of thermal sensitivity when well adapted thin linings are placed. The current view is that much of the pupal damage kproveiously attributed to the chemical composition of lining and filling materials (e.g. silicate cement and resin) was in fact caus by tjhe ingrowth of bacteria at the margind if these restorations. It appears, therefore that the most important function of a lining is to seal the dentinal tubules, thus preventing pulp damage caused by any bacteril ingroth sich occus at the restoration margins as a result of mucroleakage. The following are the important features of lining material. Ideally, it should. (a) seal dentine; (b) be bactericida; (c) non-toxic and bland to the pulp; (d) have adequate physical proprties-mecgabucal;thermal etc; (e) induce remineralizatio or huyperminewralization of dentine on cavity floors (this reduces the permebility of the dntine to any bacteria dwhich do gain access); (f) be adhesive to dentine and major restdorative materials. Calcium hydroxide Whilist tis precese mode of action is unclera, clacium hydroxide is the material of choice for both pulop capping and lining the deep cavity. The proprietary hard-setting clacium hydroxice materials seve well as universal lining materials. As a pulp-capping material, calcium hdroxide fis unique in its ability to rormite dentine
  • 8. bridge formation. In the deep cavity it induces some remineralization of any softened dentine remaining on the cavity floor. Studies with labelled calcium hydroxide have demonstrated that calcium ions do not move from the dmaterial itself, but they dcome from the bloodstream. The proprietary calcium hdroxide lining materials appear to seal the dentine adequatcly, and they are bacteicidal. Certinly they are active against many microorganisms, but there are resistant strains. Many authorities attach improtance to the alkaline PH. Which is considered to counteract the acidity in the deeper parts of carious lesions in dentine. Propriearty calcim hydroxide materials are presented in combination with a number of different setting rsins, which appears to be bound into the resin and not released. The film thickness chieved with thes proprietary materials is usually less than 0.5 mm (Fig.17.7) and though they are the weakest of all the standard lining materials, they are adequately strong to withstand the packing of amalgam. However, they re not suitabfle for use in thick sections or to block out undercuts under gold or procelain in restorations. Care should be taken to use an acid-resistant calcium hydroxide material if acid etching dof the enamel parts of the cavity walls is to take place; some propritary clacium hdroxide liners are solunble in phosphoric acid (fid.17.8.) Zinc oxide/eugenol-based cement The resin-bonded frofms of these are physically stronger cements and they also induc remineralization of softened dentine. They from the best seal of any of the dental cements and they are truly bnactericidal to may oral bacyteria. However, the phenolic group in the eugenol are pulpal irritants and they produce persistent chronci inflammation (Fig 17.9) if placed on a pulp exposre. There is some evidence to suggest that a similar effect occurs nin very deep cavities even where there is no exposure, and a sublining of calcium hydroxide is there for desirable in these situations. In cavities with a reasonable residual dentine thickness, zinc koxide/ eugenol is a excellent lining material. It is also a satisfactory material for building up a thick base over calcium hydroxide when required. It should not be used under composite resin restorations, as the eugenol may inhibit polmerzation. Any excess engenol will also stain the dentine, which is a cosmetic pronblem in anterior teeth. The ethoxydenzoic acid (EBA) cements are modified zince oxide/eugenol cements with superior mechanical properties, achieved buy sunstituting two-thirds of the zinc oxide with fused quartz. zinc phosphate cements. These were the first widely used lining and luting materials in dentistry and in this latter role they are still pupuilar. However, they are irritant to the pulp- dentine complex, early reports attrinbutig this to their very acidec settfing pH of 2. This is only transient, and they rapidly become neutral after setting. Their toxicity is now
  • 9. consideted to be caused largely nby bacterial ingrowth at the margins, following a settifng contraction. Zinc polycarboxylate cements These cements were introduced in 1968 as the first materials which adhered to both enamel and dentine. They are presented as both linin and luting cementsf. However, presented as both lining and luting cements. However, they are didfficult to manipulate well and in use they adsorb water, which leads to a deterioration of their mechanical properties, including their bond strentth. Studies of their effect on the pulp have produced variabfle results, with sosme relports of sever inflammation and others which fdemonstrate an apparentluy mild response. In any but the shallowest cavity, a calcium hydroxide sunblining should be placed. The polycarboxylate cements play a useful role as materials to replace lost dentine or block ot undercuts in preparations which are to receive cast or cermic restorations. Glass-ionomer cements (Polyalkenoate cements) Glass-inomer cements are now availabfle for use as lining and luting cements, as well as being restortive materials their proncipal advatage lies in their forming a molecular bond with the dentine (and the enamel), though the seal produced is not necessaril perfect; nbcteria have been demonstrated in the interface between glassionomer restorations and the tooth (Fig 17.10) This probably reflects the difficulty in the clinical situation of bringing the material into even contact with the cavity surface. This ingrowth of bacteria appeas to be responsinble for at least part sdof the pulpal damage that has been reported after placefment of glss-ionomer cements in deep cavities. Recent reports have sugested that glass-ionomers applied to dentine may also produce chemical damage in the pilp. This is manifested b damage to pulp cells and an inhinbition of calcific repair, rather than by inflammation. It is therefore necessary to place a sunlining (calcium hydroxide) in the deepest parts of all cavities that are to receive glass-ionomer cement where dentine has been freshly cut. In abrasion cavidties the cornal pulp is normally completely obliterated by calcific material and a lining is not required. There have been reports of pulpal hypersensitivity following the use of glass- ionomer lutin cement for crowns. Now of the glass-ionomer materials has physical properties suitable for the long-term restoration of occlusal surfaces, though they have a number of useful indidcation (see p.367.) As a straight glass-ionomer centnt or in the form of a cement (see p. 368), the material appears to hve an improtant role in building up dentine prior to the application of composite resion (see Gig 14.57). Used in this manner it protects the pulp and dentine tubules from the effects of the acid used to etch the enmel prior to composite bonding. This acid treatment also serves to roughen the surface fof the glass- ionomer, so enabling an effective bond with the composite. Although there have been criticisms regardifng disrupation of the surface integrity of glass-ionomer cments
  • 10. following acid application and treatment with acid cannot be recommended. Fortunateluy restorative suystems have become availabfle in which acid treatment dof the glass-ionomer ‘lining’ is no longer necessary. Varnishes Varnishes are apploed sparingly to cavity perparations (inclding the cavity walls and margins) for amalgam, as they reduce the intial microleakage which occurs with amalgam restorations. Some clinicians use then routineluy, especially in the USA They have a special place in sealing the cavity walls and dentine din minimal cavities where there is insufficiefnt depth to fwarrant a cemfent lining . The majority of varnishes consist of natural resine, e.g copla or shellac dissoved in n organic solvent sucjh as ether dor ethl acetate. Whenapplied, the solvent evaporates leaving a resion coating on the dentine and enamel. It is necessary to apply at least two coats of the varnish to achivee fa viod-free films and hence a seal (Fig.17.11). Most varnishes are clear liquids. It is important to replace the cap on the bottle to prevent evaporation of the solvent leadifng to thickening of the varnisjh which makes it impossinle to apply in thin layers. It is necessary to add thinner to the bottle from time to time . FURTHER READING Amussen E., jorgenson K.D. (1972) A microscopic investigation of the adaption of some plastic filling materials to dental cavity walls. Acta odont. Scand 30-3-21. Brannxstron M (1981) Dentine and pulp in restorative dentistry Nacka: Dental Therepeutics AB (Also London Wolfe Medical Publications, 1982) Causton B.E. (1984) Improved bonding of composite restorative to dentine brit dent J; 156: 93-95. Morrandt G. (1977) Dental instrumentaion and pulpal injury.1 Biological and physical factors. L Brit. Endodont Soc., 10:55-63. Pateson R.C. Watts A. (1981) Dental instrumentation and pulpal injury.2 Clinical considentations J.brit Endodont. 10:55-63. Paterson R.C. Watts A kinner’s science of dental materials, 7th edn. Philadephia:W.B Saunders.
  • 11. Wats A. (1979) Bacterial contamination and the toxicity of sillicate andc zinc phosphate cement. Brit.dent J., 146:7-13.use a clear plastic matrix band to enhance curidng in the less accessinle regions of the cavity while the band is till in place. Unfortunately, however, the handing properties of plastic matrix bands somethimes make them awkward to use. Clear plastic wedges can be used to transmit the light to the cervi cal region of the restoration. The maximum reliabfle depth of cure that cn nbe achieved with light is about 2mm This means that an incremental techniquer is usually necessary to ensure complete curing (Fig.18.5) Most opertors limit themselves to a thickness of 1.5 mm for each application. The composite should be applied first to exposed parts of the dentine, because the bond to dentine is fweaker thand to enanel; if resin is applied across enamel and dentine, the disparity in strenght of the bond, togerther with the more repid cure achieved in contact with the enamel, may cause the resin to pull away from the dentine. In general, the material should fbe applied to the more remote parts of the cavity first. As the resin shrinks towards the curidng light, placement dof the light against the baccal and lingual tooth surfaces is advised prior to curing from the occlusal direction. This will assist the increments of resin shrinking towards the cavity floor. Finishuing of composite restorations Any gross excesses should be trimmed with tungsten carbide or find diamond bursm usifng water spray as a coolant. High or low speed can nbe used, the latter allowing more control where only small amounts of excent material dare present. Fine abrasive strips and/or discs have been developed for final dshaping and polishing and these are veruy effective. Asmussen’s wsorks suggests that only gross excesses should fbe removed immediately. Since all composites absorb some water over the first 24 hours after their insertion and undergo hygroscopic expansion, his argument is that if the final dfinishing is delayed until this reduced to a minimum. Nevertheless, many practitioners go against this advice, for they feel that the practicalities of the situatioin demand that finishing and polishing should fbe undertaken at the same visit at which the restoration is placed. Certainly, it can be argued that once the rubber dam has been removed, attention to detail (e.g. that of achieving the final approximal contour) becomes more difficult; and the cervical margin is then likely to relate to moist gingival tissues and therefore be less accessile.f The hybrids can be polished, but a high gloss will not be achieved. The danger of leakage at the gingival margins of class ii restorations makes regular checks essential Disadvadntages and contraindications of composites The main drawacks of the posterior composites are: (a) polymerization shrinkage; (b) possinly unsatisfactory were characteristics; (c) difficulty in achieving anatomical form. (d) Polymerization shrinkage
  • 12. This is inevitable by the very nature sof the material and it will tend fto be greater in bigger cavities where larger volumes of resin are used. When the acid etch technique is used, polymerization shrinkage can lead to inward bendifng of the cusps. The long-term implications of this are unknown, but it certainly seems reasonabfle to tae all steps to minimize it (sewe ‘Dynamics of the restored tooth P.3569). Leakage is a likely consequence of polymerizqtion shrinkage and this is especially liabfle to occur at the cervical dmargins of restorations where there is tlittle or no enamel for bonding purposes. Such leakage may be the reason for the sensitivity to hot and cold which sometimes follows the placing of these restorations. It certainly contraindicates their use in patinents whose caries is not properly controlled, or where there is poor oral hygiene. Wear The newer posterior composites appear to wear favourably. Though it fis pruudent to avoid their use in patients with marked attriotion. The consequences of wer of the opposing and adjacent teeth hve still to be evaluated in the long term. GLASS-IONOMER CEMENTS Glass-ionomer centnts consist of aluminosilicate glass mixed with an aqqueous solution of polyacrllic acid and related polyacids. This forms a set mass of unconsumed glass particles embedded in a matirxx of poluacrylate gel. Some of the moe recently inrroduced glass-ionomer cements contain other acids such as polymaleic acid and itaconic acid. Glass-ionomer cenents dhave the ability to bond chemically to both enamel and dentine. Theyu were first introduced in the 1970.s when dthey found thedir greatest clinical use in the restoration, without mechanical preparation, of cervical erosion/abrasion lesions. The adhesion of glass-ionomer cements has been attributed to penetration of carboxylate grops into the huydroxyapatite of the senamel and dentine, with displacement o phosphate ions. Electrical neutrality is maintained by the displacement dof calcium ions along with the phosphate ions. As restorative materials, the glass-ionomer cements have the distinctly bebeficial characteristic of leaching flouried; this should help to prevent secondary caries. The al;so pick up fresh fluoride ions from the moth, e.g from fluoride toothpaste; these ions then become available to the adjacent enamel. Co,pared with the composites, certain of the mechanical; properties of the glassionomer cemefnts are poorer. Clinical lhandling properties Glass-ionomer cements require particular care during handling. They tend to stick to metal instruments and to pull away from cavity walls during manipulation. Thus, while being contoured they tend to ‘drag’ away from the cavity margins. These materials are moisture sensitive and the cavity must be kept completely dry during placement. After placement they should be kept dry for several hours by coating with varnish or restorative resin (polymerized), to prevent disruption of the gel. The earlier materials
  • 13. could not be trimmed during the initial 24 hours, though some of the newer materials have been modified and can be trimmed during the visit at which they are placed. However, a better surface finish is obtrained if final finishing is delayed for 24 hours. Indications and uses 1. Erosion/abration lesions in permanent teeth. Provision of mechanical retention in these cavities is difficult and glass-ionomer cements cements can be used without this. 2. Class I and II and V cavities in deciduous teeth. Recent clinical trials have demonstrated that glass-ionomer cements can be used satisfactorily to restore these lesions in deciduous teeth. 3. Class III and V cavities, especially in caries-prone individuals. 4. Repair cavities. The fluoride leaching properties of the glass-ionomer cements make them a fist-choice material for repairing restorations in regions where future secondary caries is a realistic possibiliy, such as at the cervical margins of crowns 5. Deep cervical and root cavities. In cavities which extend towards the edge of the anatomical crown, the cervical margin often consists of thin and friable enamel with a prism direction that is complex and not conducive to good etching. If composite resin is placed against such a margin there wilkl be a very real risk of an unsatisfactory seal. Similarly a seal could not e expected when the cavity margin is entirel in cementum or dentine. Subject to satisfacytory isolation(usually with rubber dam,) glassionomercompositre sandwich restoration (Fig. 18.6). With this laytter m,ethod thefirst=placed glass-ionomer material is addapterd against the vulnerable cervical margin to achieve the best p[osible seal. In the coronal part of the cavity tyhe glass- inomer cemnt forms a lining onluy. This can then be coated with a bonding agent consistintg of a halophoshorus ester of Bis-gma.This will bond chemically both ytop the glas-inomer and to the compsite resin which completes the restoration. This twopart restoration provides the hbbest possible marinasl seal aesthertis and function that can be achived with a plastic restoration in these difficult cavities. 6. Fissure sealing in deciduous and permanent teeth. Because of the turgid nature of the material this use is onl;u recommended where the vfissure is well opened up either naturallu or by a bur(as when investigation the extent of the caries present in a sealantrestoration technique; see chapter 13) 7. As luting cements. Thisa had been made possible y a reduction in the particle size. The materialxs have the advantage that they adher to enamel, dentine and metalic ions.They will therefore adhere to metal cast9ings. CERMET CEMENTS The term cermet derives form ceramic plus metal. These materials are made by mixing metalllic fillers of silver or gold with moltern glass and sintering them. The resultant poiwder is mixed with a sloution of polumaleic acid. Suyccessful
  • 14. clinicasl trial result jhave been had prevented its commercial introduction.However expense had prevented its copmmercial introdution. The silve-based material had been mark eted and the following remarks refer to this. Clinical handling properties The materiual is presented in capsules for mechanical mixing and a special applicator allows the capsule contents toi be syringed directly into the cavity.It is difficult to work with:the cemtn sticks to metal; inmstruments;and it had a relatively short settint toime of 1.5minutes. It is difficult to achieve any packin pressure and carvinmg and contouroing require special care as the material tends to draw away form, the cavituy margins. Once set the cement must not be left esposed to air, or large cracks will form as it dries oit: it should bre varinisjhed to prevent moisture contmination. It can only be poli9shed to a dull lustre finish. Examination of finished restorations reeveals a pitted and cracked surface and there are frequent voids at the margins presumaly caused by a setting contraction. Indications and uses Wheres further development work is necessary before the use of cemt cement can be supporyted without reservartion the following uses have been suggested. 1. Restorations in deciduous teeth. 2. Class I restorations in permanent molars. 3. Building up lost dentine under composite restorations including in insrtances where an internal or tunnerl preparation had been made to restore a posterior tooth with apporoximal caries. 4. As a core material for crowns in broken down permanent teeth. FUTURE DEVELOPMENTS In view of the considerable amount of pulp damager that can be produced by bacterial ingrowth at restoration marins the following areas should be seen as improtant for development with respect to both composite resins and glass- ionomer cements. 1. Techniques to improve the wetting of the cavity walls Inflammation:
  • 15. The defense elements of the body that are mobilized to the site of injury are present in the blood. To achieve this mobilization a series of changes occurs in the microcirculation of the injured area. These changes are dominated by arteriolar vasodilatation and increased permeability through contraction of the endothelial cells of the post capillary venules. These vascular and hemodynamic changes are mediated by a variety of chamecal mediatrors realsed in the injured area: histamine (from the granuales of mast cells and baspohil leukocytes); serotonin (in humans, from the dense granuales of blood platelets); kinins (pep0tides formed through cleavage of kinigonens of by kininogensses): anaphylatoxins (peptides formed through cleavage of the third and fifth complemlent components releasing the anaphylatoxins C3a and C5a, which in induce degranulation of mast cells and basophils); and prostaglandins and leukotrienes (arachidonic acid derivatives) Exudation develops as a result of increased vascular permeability Leukocytes that have marginated adjacent to the vascular endothelium and adhered to the endothelial cells and pseudopods through the gaps between the endothelial cells and escape from the vascular lumen. Once outside the endothelial cells,d they migrate toward the site of injury under the influence of chemotactice factors (both bacterial and endogenous in origin; the latter include C5a, the activaterial and endogenous in origin; the latter include C5a the activated triple complex C567, and certain lymphokines secreated by T and B lymphocytes)
  • 16. Neutrophils are the first leukocytes to arrive at the site of injury. They are the predominant cells of acute inflammation. However, virtually nany type of injury results in initial accumulation of neutrophils. 30 These involves a sespiratory burst with increase in oxygen consumption and generation of reactive oxygen radicals that the are bactericidal but can also induce tissue injury. Whereas the neutrophils are the predominant cells of acute inflammation, macrophages, lymphocytes, and plasma cells are the predominant cells of chronic inflammation. What leads to chronicity is persistence of the irritant, and this is often accompanined by the development of a cell- mediated immune reaction. Macrophages are derived from the mamocytes of blood. Monocytes are not end cells. Their half-life in the circulatin is about I day. They leave the circulatioun to form different components of the mono nuclear phyagocyte system. Macrophagea are efficient phagocytes. Not only do they phagocytose bacterial, buyt also they ingest tissue debrise to clean up the area in preparation for repair. They also play an essential role in the development of immune reactions through antigen processing aznd antigen presentation to lymphocytes. Among their secretory products are lysoszyme, certain components of the complement system, interferon, collagenase, fibronectin, fibroblast- activating factor, and angiogenesis factor. Lymphocytes are the essential cells of the immune system. Two major types are recognized , T and B cells. Lymphocytes are the essential cells of cell- mendiated immune reactions. B lymphocytes are the essential cells of humoral immunity. Intricate interactions take place between macrophagea and T and B lymphocytes, and T helper
  • 17. cells are essential for the induction of a humoral immune response to certain agigens. T suppressor cells regulate both humoral and cellmediated immune reactions. Plasma cells, which are derived from B lymphocytes, synthesize and secrete immugoglobulins. Eosinophils may be encountered in inflamed tissues, including inflamed pulp. They phagocytose antigen antibody complexes and contain enzymes that inactivate some of the chemical mediators released in areas of injury. Undetected microscopic exposure of the pulp is of utomost importance. Each of these causes of iatrogenic pulp injury will be briefly considered. Preparation of the Cavity: Dentin is a vital tissue. That fact the dentin is a hard tissue and that it does not bleed on cutting may give rise to a false sense of security. Avoide heat generation and dentin desiccation during cavity preparation. Heat dissiopation and prevention of desiccation can both be accomplished through the use of a water coolant. With the present day high –speed instrumention, the use of a water coolant with collant is mandatory. A simple rule to follow to eliminate two sources of iatrogenic pulp injury (heat and desiccation) is “never cut dry. Insertion of the Restorative Material: Physical forces generated during condensation of amalgam and direct gold restorations can lead to pulp injury 26, 27 This is particularly. The major requirements of a cement base with such me tallic restorations are as follows:
  • 18. A hard – shtting calcium hydroxide preparation or a reinforced zinc oxide and eugenol cement, a calcium hy-droxide liner or a stronger base. Howeer, with this cement , a calcium hydroxide liner or a caviry varnsh should be applied prior to the insertion of the cement to protect the pulp from chemical irritation. Irritational Qualities of Restorative Materials. A major cause of iatrogenic pulp injury is chemical irritation by the restorative material. According to their irritational qualities, restorative materials can be classified into three major groups: Group I -- Low irritaitonal potential : gold, amalgam, zincoxide and eugenol cement, polycarboxylate cements, and glass ionomer cements. Group II -- Moderate irritational potential : zinc phosphate cements, and glass ionomer cement. Group III – High irritaitonal potential : silicate cement and resins. Group I. Biologically, gold and amalgam are relatively insert. Any primary from physical forces incident to condensation and possibly from thermal shock and electrogalvanism caused by the high conductive qualities of these materials. Measures to protect the pulp from such injury have already been outlined. Zine oxide and eugenol (ZOE) has a low irritational potential. Its pH, when freshly mixed, is 7. 19 The low irritational potential of ZOE makes it ideal as a negative control in stuies that evaluate pulp reaction to restorative materals. Zinc oxide and eugenol also has an obtundent effect on the pulp. Eugenol inhibits the synthsis of prostaglandin; it will of ionglammation and also contribnute to pain sensation in areas of
  • 19. injury. Furthermore, the hygroscopic qualities of ZOE may result in withdrawal of fuild from the pulp through the dentinal tubules thus reliving pressure on sensory nerve endings of the pulp. Zinc oxide and placed over an exposed pulp, ZOE dies not stimulate reparative dentinogenesis ; on the contrary, it elicits a low-grade inflame-matory response. Polycarboxylate cements have a low irritational potential . 9 They are remarkabluy innicucous, despite a pH of 1.7 of the rapid rise of the pH during setting of the cement. Furthermore, the large molecular proteins would limit its diffusion through the tissues. Group II. Zinc phosphate cement has an irritaional potential that ios intermediate between ZOE and silicate cement. Three minutes after thereafter, approaching neutrality in 24 hours. 19 Thus, damage to the pulp would occur during the first few hours after insertion of the cement. This damage could be prevented by application of a calcium hydroxide liner or a cavityvarnish prior to placement of the cement. Group III. Silicate cements have ahigh irritational potential. These cements have a pH below 3 at the time of insertion ; the pH remains below neutrality even after one month. 19 The high irritational potential of silicate cement makes it ideal as a materials. A calcium hydroxide liner or a cavity varnish prior to placement of the cement. Resins, whether unfilled or coposits, and the latter, whether conventional or microfilled,autopolymerizing or photoactivated with ulraviolet or visible light are irritating to the pulp. Their irritational potential is comparable to that of silicate cement. Which component of the composite resin elicits pulp injury? In a study of pulp reactions to eight components of composite resins, none of the components tested elicited
  • 20. significant pulp injury 24 It appears likely that reactive radicals generated during the polymerization of the resin are responsible for pulp injury by these materials. Pulp injury by the resin resto ration can be totally abrogated through the application of a hardsetting calcium hydroxide base beneath the resin. FACTORS THAT INFLUENCE PULP REACTIONS TO RESTORATIVE MATERIALS The most important single factor in determining the intensity of pulp reaction to restorative materials is the thickness of remaining dentin. With most materials, 2 mm of remaining dentin affords adequate pulp protection 22 The presence of reparative dentin is influential; materials –laced ever freshly cut dentin are more damaging. The undetected microscopic exposure of the pulp is of utomost importance. Numerous studies have shown that pulp exposure can occur without climnically detectable bleeding. Only through examination of serial histologic sections of the cavity and the underlying pulp. Because it is impossible to determine cavity floor thickness clipically and because microscopic exposure of the pulp may occur without being clinically detectable, these two simple rules should be followed to protect the pulp from iatrogenic injury due to the inherent irritation of restorative materials and the clinically undetected undetected microscopic exposure; 1. Use a protective base or liner with materials in groups II and III regardless of cavity depth.
  • 21. 2. Use a protective base or liner in all deep cavities where the possibility of microscopic exposure exists, regardless of the material to be used for restoration. Bacteria Another potential source of pulp injury is bacteria, either residual microorganisms left on the cavity floor or bacteris that gain access to the cavity after restoration3. While bacteria may contribute to pulp injury when cavities are deep, they cannot be considered solely responsible for pulp irritation to exclusion of the inherent irritational potential of the restorative materials. In the past, highly irritating chemicals were used for sterilization of the cavity. Because vital Wheledentin has been shown to resist bacterial invasion and deep cavities should have a protective base of calcium hydroxide preparation or ZOE, and both have been shown to have antibacterial properties, the need for cavity sterilization is highly questionable.7,16 A safe and effective means for cavity cleansing is simply rinsing the cavity with warm water.22 ACID ETCHING Resin restorations leak badly. The acid-etch technique was developed to improve the marginal seal between the cavity and the restoration. Acid etching of enamel is safe, provided a protective base of a calcium hydroxide preparation is applied over exposed
  • 22. dentin prior to etching. Acid etching of dentin markedly increases its permeability. 18 Not only does it remove the amorphous smear layer over cut dentin, which plugs the orifices of the dentinal tubules, but it also demineralizes the peritunbular dentin resulting in increased tubular diameter. Such patent tubules provide easy access of irritants to the pule.24 PROTECTIVE BAES The ideal protective base should be well tolerated by the dental pulp. It should stimulate reparative dentinogenesis in case an undetected microscopic exposure of the pulp exists. It should provide adequate protection of the pulp from irritant components of the restorative material. It should have an obtundent effect on the pulp. It should have an antibacterial effect to eliminate bacteria in residual carious dentin when used with indirect pulp from thermal shock and electric conductivity to protect the pulp from thermal shock and electrogalvanism when used with metallic restorations. It should exhibit low acid solubility so that it will not disintegrate when used with the acid etching technique in case the acid accidentally comes in contact with the material. I t should not be affected by the restorative material nor should it in any way affect the restorative material. A protective base which fulfills all of these criteria remains to be developed. However, ZOE and hard-setting calcium hydroxide bases fulfill many of these criteria. With resin restorations, used with or without the acid- etching technique, calcium
  • 23. hydroxide bases should be used. Zinc oxide and dugenol cement obviously is unsuitable, as it interferes with resin polymerization. With other restorative materials, either ZOE or calcium hydroxide bases are satisfactory. However, if there is the slightest chance of a microscopic exposure of pulp, a calcium hydroxide base should be used because ZOE does not enhance reparative dentinogenesis. On the contrary, when placed in contact with an exposed pulp, ZOE elicits a low- grade chronic inflammatory reaction. PULP CAPPING Numerous materials have been investigated as pulp-capping agents- However, calcium hydroxide preparations have best withstood the test of time. There has been a widespread concern among dentists that calcium hydroxide exerts a persistent stimulating effect on the pulp that results in eventual obliteration of the pulp. Some also believe. That calcium hydroxide may, on occasion, cause persistent inflammation of the pulp or internal resorption. Pulp reactions to three capping agents were investigated in mon keys at intervals ranging from 15 to 880 days 13-15 with a calcium hydroxide preparation, there was initially a high rate of reparative dentinogenesis. The rate, however diminished with time, and there was no evidence of pulp obliteration in any of the specimens, even at 880 days after capping. A polycarboxylate cement was specimens, even at 880 days after coapping a polycarboxylate many of the pupls capped with it should pulp necrosis or severe inflammation. Interestingly, the pulp that survived showed persistent
  • 24. inflammation with areas of obliteration of the radicular pulp. It was apparent that the stimulus for eventual obliteration of the pulp is persistence of inflammation rather than a direct effect of any medicament applied over the pulp. BIOLOGIC EVALUATION OF DENTAL MATERIALS. Historically, biologic evaluation of dental materials lagged behind evaluation of their physical properties. It should be obvious that the biologic properties of dental materials are just as important as their physical, chemical, and mechanical properties. In 1972, the Council of Dental Materials and Devices of the American Dental Association published a series of guidelines for biologic evaluation of dental materials. 4 In 1979 the American National Standard Institute/American Dental Association Document No. 41 was approved by the ADA counable guidelines for biologic testing of dental materials. Tests for biologic testing of dental materials. Can be classified into screening tests and usage test. In the usage tests, the dmaterials are evaluated in suitable laboratory animals, show that the material is safe, the material is then ready for evaluation in humans.
  • 25. It is through such extensive biologic testing along with tests that evaluate the physical chemical, and mechanical properties of dental materials, that the dentist will be assured that the material he uses are both safe and effective. REFERENCES 1) Avery, J.K : Dentin.In Bhaskar, S.N. (ed) Orban’s Oral Histology Embryology, Edition 9. St. Louis, C.V. Mosby Co., 1980. 2) Brannstrom M., and Lind, P.O. Pulpal response to early dental caries JU. Dent. Res 44:1045, 1965. 3) Brannstrom, M and Nyborg, H: Cavity treatment with a microbicidal fluoride solution: Growth of bacteria and effect on the pulp. J prostht. Dent., 30:303 1973. 4) Council on Dental Materials and Devices: Recommended standard practices for biological evaluation of dental materials: J Am Dent. Assoc., 84:382, 1972.
  • 26. 5) Council on Dental Materials and devices: Amercian National Standards Institute/ Amercian Dental Association document No. 41 Recommended standard practices for biological evaluatin of dental materials J Am Dent Assoc. 99.897,1979. 6) Dickey, D.M., Kafrawy, A.H. and Mitchel, D.F. Clinical and microscopic pulp response to a composite restoration material J Am Dent Assoc., 88:108, 1974. 7) Fairbourn, D.R. Charbenau, G.T., and Loesche, W.J Effect of improved dycal and IRM on bacteria in deep carious lesions J Am dent Assoc 100:547,1974. 8) Fischer, F.M. Karraway, A.H. Mitchel, D.F. Studies of reparative dentin in monkey teeth using vital dyes J. Dyes J Dent Res 49:1537,1970. 9) Kafrawy, a.H. and Mitchel, D.F. Pulp reactions to open cavities later restored with silicate cement J Dent. Res., 53:15, 1970. 10) Kafrawy, A.H. and Mitchel, D.F., pulp reactions to open cavities later restored with silicate cement. J Dent Res ., 42:874, 1963. 11) Kuttler, Y: Classification of dentine into primary, secondary and tertiary, Oral surg 12:996, 1959. 12) Langeland, K., Dowden, W.E Tronstad L., et al: Human pulp changes of iatrogenic origin oral surg., 32:943,1971.
  • 27. 13) MeWalter, G.M. Kafrawy, A.H. and Mitchel, D.F. Rate of reparative dentiogenesis under a pulp capping agent in moneys.J. Dent Res., 56:93,1977. 14) MeWa;ter.G.M. Kafrawy, A.H., and Mitchell, D.F. pulp capping in Monkeys J, Dent. 36:90, 1973. 15) MeWalter, G.M. Kafrawy, A.H. and Mitchell, D.F. Rate of reparative dentiogenesis under a pulp capping agent in monkeys J Dent Res., 56:93, 1977. 16) Mjor, I,A. the penetration of bacteria into experimentally exposed human coronal dentin Scand. J. Dent Res. 82:191, 1974. 17) Mohammed. Y.R. Van Huysen, G.V and Boyd, D.A. Filling base materials and the unexposed and exposed tooth pulp. J Prosthet Dent. 11:503.1961.

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