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By Y. Einar. Lees-McRae College.

Amphotericin B can affect the renal tubules buy 4mg ondansetron free shipping symptoms 6 days after iui, renal blood flow purchase ondansetron 8mg with mastercard treatment yeast infection men, or glomerular function; renal dysfunction is seen in at least 60% to 80% of patients who receive this drug (31) purchase ondansetron 8 mg visa symptoms kidney failure. However buy ondansetron 4mg on-line symptoms thyroid problems, renal dysfunction is usually transient, and few patients suffer serious long-term renal sequelae. Rarely, irreversible renal failure develops when the agent is used in high doses for prolonged periods (32). Risk factors for amphotericin B toxicity include abnormal baseline renal function, daily and total drug dose, and concurrent use of other nephrotoxic agents (e. However, some studies have not found that other drugs enhance amphotericin B-induced nephrotoxicity (22). Reversing sodium depletion and optimizing volume status prior to infusing the drug can decrease the risk of amphotericin B-induced nephrotoxicity (31,34). Liposomal preparations of amphotericin B are associated with a lower risk of nephro- toxicity compared with the parent compound. Methicillin was the first antibiotic shown to be associated with interstitial nephritis (35); nephritis can also be caused by numerous other b-lactams (36), usually following prolonged and/or high-dose therapy. Historically, renal failure was believed to be acute in onset and associated with fever, chills, rash, and arthralgias. However, the presentation of antibiotic-induced interstitial nephritis can be variable, and it should be suspected in any patient on a potentially offending agent who develops acute renal dysfunction. Urinary eosinophilia supports the diagnosis, but is present in less than half of the patients. Discontinuation of the offending agent generally reverses the process and permanent sequelae are unusual. Sulfonamides, acyclovir, and ciprofloxacin can crystallize in the renal tubules causing acute renal failure (37). Sulfonamides can also block tubular secretion of creatinine; this causes the serum creatinine to rise but glomerular filtration rate is unchanged. Patients on rifampin often develop orange-colored urine of no clinical consequence. Chloramphenicol (infrequently used in the United States) frequently causes a reversible anemia that is more common if circulating drug concentrations exceed the recommended range. In approximately 1 of every 25,000 recipients, chloramphe- nicol causes an idiosyncratic irreversible aplastic anemia (41). Patients who are glucose 6-phosphate dehydrogenase deficient are predisposed to sulfonamide- and dapsone-induced hemolytic anemia. Leukopenia Antibiotic-induced leukopenia and/or agranulocytosis are generally reversible. Anti-infectives that can cause neutropenia or agranulocytosis include trimethoprim-sulfamethoxazole (42,43), most b-lactams (44,45), vancomycin, macrolides, clindamycin, chloramphenicol, flucytosine, and amphotericin B. Severe neutropenia develops in 5% to 15% of recipients of b-lactams (45) and is associated-with duration of therapy >10 days, high doses of medication, and severe hepatic dysfunction (46,47). Likelihood of neutropenia is <1% when shorter courses of b-lactams are used in patients with normal liver function (47). Only rare patients develop infection as a result of this decrease in functioning leukocytes. Vancomycin-induced neutropenia is uncommon and generally only occurs after over two weeks of intravenous treatment (49). The etiology appears to be peripheral destruction or sequestration of circulating myelocytes. Prompt reversal of the neutropenia generally occurs after vancomycin is discontinued. Thrombocytopenia Antibiotic-related thrombocytopenia may result from either immune-mediated peripheral destruction of platelets or a decrease in the number of megakaryocytes (49). The oxazolidinone linezolid is the antimicrobial most likely to cause platelet destruction (38–40). In one study, linezolid-induced thrombocytopenia occurred in 2% of patients receiving less than or equal to two weeks of therapy, 5% of those receiving two to four weeks of therapy, and 7% of those receiving more than four weeks of drug (39). Severe linezolid-induced thrombocytopenia (and anemia) is significantly more common in patients with end-stage renal disease (51). Vancomycin can stimulate the production of platelet-reactive antibodies that can cause thrombocytopenia and severe bleeding (51). Sulfonamides, rifampin, and rarely b-lactams (including penicillin, ampicillin, methicillin, cefazolin, and cefoxitin) have also been reported to induce platelet destruction (45,52). Chloramphenicol-induced thrombocytopenia is usually dose-related and, if not associated with aplastic anemia, is reversible following discontinuation of the drug. Coagulation Malnutrition, renal failure, hepatic failure, malignancy, and medications can all predispose critically ill patients to bleeding. Although many studies have found an association between antibiotics and clinical bleeding (53), in-depth, statistically validated investigations may be necessary to establish causation in complex patients with multiple underlying diseases (54). Dysfunctional platelet aggregation, an important mechanism by which selected antibiotics may cause bleeding, is mostly noted with penicillins. Among penicillins, it is most likely with penicillin G and advanced-generation penicillins (55). The problem is dose- related, may be exacerbated by renal failure, and is additive to other factors seen in critically ill patients that could, in their own right, be associated with dysfunctional platelet aggregation (55,56). Most commonly, the reason for dysfunctional platelet aggregation is that carboxyl groups on the acyl side chain block binding sites located on the platelet surface resulting in the inability of platelet agonists such as adenosine diphosphate to affect aggregation (55). All of these products contain an N-methylthiotetrazole side chain that can interfere with hepatic prothrombin synthesis (59). Sulfonamides can displace warfarin from its binding site on albumin and thereby enhance its bioavailability. Virtually any antimicrobial agent may cause a rash, but this problem occurs most commonly with b-lactams, sulfonamides, fluoroquinolones, and vancomycin (60). Factors that should lead the clinician to suspect a serious drug reaction include facial edema, urticaria, mucosal involvement, palpable or extensive purpura, blisters, fever, or lymphaden- opathy. Maculopapular eruptions associated with antibiotics are especially common, usually occurring within one to two weeks after starting the offending agent and often becoming generalized and pruritic. In patients with thrombocytopenia or other coagulopathies, hemorrhage into the skin may modify the appearance of the rash. In some instances, the likely offending agent can be continued and the rash will stabilize or disappear. In patients with penicillin-induced mild or moderately severe maculopapular rashes, it is generally safe to use cephalosporins (61). If the rash is severe or associated with mucosal lesions or exfoliation, the offending agent should almost always be discontinued. The most commonly implicated antibiotics are the aminopenicillins and sulfonamides. Clinically, the rash can present as symmetrical target lesions, maculopapular and urticarial plaques, and/or vesicular lesions. Stevens–Johnson syndrome can involve mucosae of the eyes, mouth, entire gastrointestinal tract, and the genitourinary tract. Infections (for which the offending antibiotic may have been prescribed), including pneumococcal, mycoplasmal, and staphylococcal infections can cause a similar rash. Stevens–Johnson syndrome can evolve into toxic epidermal necrolysis; mortality of this condition is 30% (62). Sulfonamides are the antibiotics most often associated with toxic epidermal necrolysis. Although the benefits of corticosteroid therapy are unproven, these products are often used for treatment. Severe cases have been associated with angioedema, hypotension, chest pain, and rarely, severe cardiac toxicity and death (20). Incidence may be as high as 47% in patients and is substantially higher in human volunteers (64).

Multi-energy w i n d o w operation m a d e feasible dual isotope studies and the dual or triple energy w i n d o w m e thod for scatter correc­ tion [1] discount 8mg ondansetron with visa treatment emergent adverse event. M o d e m g a m m a cameras have an intrinsic spatial reso­ lution of 3 - 4 m m full width at h a l f -maximum ( F W H M ) purchase ondansetron 4mg symptoms your dog has worms, a sensitivity uniformity of less than 3 buy 8mg ondansetron mastercard symptoms viral infection. T h e system resolution of a g a m m a camera equipped with a parallel hole colli­ mator starts from about 5 m m close to the surface of the collimator and degrades with increasing distance f r o m the collimator surface; hence the camera head must be rotated as close as possible to the patient buy ondansetron 4 mg with amex symptoms whiplash. For torso imaging, most S P E C T sys­ tems can adopt an elliptic rotation of the camera head with respect to the bod y centre. For brain or heart imaging with a L F O V camera, a fan b e a m collimator is use­ ful in improving the utilization of the large detector area. T o increase detection sensitivity, multi-headed S P E C T systems provided with t w o to four camera heads are available (see Fig. A m o n g them, a triangular S P E C T system using three camera heads [2, 3] is attractive because the system can be used for brain imaging with fan b e a m collimators, as well as for bod y imaging with parallel hole collimators (see Fig. Triangular S P E C T systems equipped with fan b e a m collimators have about five times greater sensitivity than a single headed system with a parallel hole collimator. Another merit of triangular S P E C T using fan b e a m collimators is that transmission measurement for attenuation correction can be performed with rod sources placed at the focal lines of the fan b e a m collimators, as s h o w n in Fig. Simultaneous measurement of emission and transmission data is also possible by using one rod source and rotating over 360° [4]. S P E C T with stationary detectors S P E C T systems with stationary cylindrical detectors dedicated for brain studies have been developed. T h e detector consists of a cylindrical array of a n u m b e r of Nal(Tl) crystal rods, and 96 photomultiplier tubes ( P M T s ) are coupled to the outside of the cylinder. T h e detector system is stationary, and a continuously rotating ‘turbo-fan’collimator is provided inside the crystal array. E a c h crystal views an object at various directions along with the rotation of the collimator. Another example is C E R A S P E C T (Digital Scintigraphic) [5], s h o w n in Fig. T h e detector system consists of a single annu­ lar Nal(Tl) crystal (inner diameter 31 cm, height 13 c m and thickness 8 m m ) and a rotating collimator. T h r e e dimensionally converging collimators T h e detection sensitivity of fan b e a m collimators is further improved b y the use of cone b e a m collimators. A typical cone b e a m collimator provides an increase of effi­ ciency of about 2. I m a g e reconstruction with a cone b e a m S P E C T must be handled by a 3 - D reconstruction algorithm. T h e simplest scanning m e t h o d is rotating the camera head in such a w a y that the focal point of the collimator m o v e s along a circular trajectory around the object. T h e single circular orbit, however, can provide a mathematically accurate image only in the vicinity of the plane of the circular orbit, and not in the other part distant fro m the plane. Nevertheless, a relatively simple reconstruction algorithm, the F e l d k a m p algorithm [7], is useful to obtain an approximate image w h e n the angle of the cone b e a m is not so large. T h e algorithm essentially consists of 1-D filtering of observed 2 - D projections along the transaxial direction and 3 - D back projection along the cone b e a m direction. T o acquire sufficient data for accurate 3 - D imaging with the cone b e a m geometry, the scanning trajectory of the focal point must have at least one point of intersection for any plane passing through the reconstructed region of interest [8]. Several focal point trajectories have been suggested which s e e m to be realistic. These are the circle and line orbit, dual orthogonal circular orbit, helical orbit, etc. In using cone b e a m collimators, the activity distribution must be inside the sensitive v o l u m e of the collimator. For easier positioning of an object in the F O V , astigmatic col­ limators [10], as s h o w n in Fig. O n e focal line is parallel to the axis of rotation, while the other is perpendicular. T h e geometry of the astigmatic collimator lies between a fan and a cone b e a m geometry. Recently, a variable focus collimator, the ‘Cardiofocal collimator’(Siemens) [11], has been developed for heart imaging to avoid truncation artefacts (see Fig. T h e focusing of this collimator is strongest at the centre of the collimator and gradually relaxes to nearly parallel hole collimation at the edge of the collimator. S P E C T with pinhole collimators There is an expanding need to localize radiopharmaceuticals in vivo in small laboratory animals such as rats and mice in pre-clinical studies. T h e spatial resolu­ tion achieved with conventional S P E C T imaging with multihole collimators is not adequate for such small animals, and a rotating g a m m a camera equipped with a pin­ hole collimator having an aperture diameter of 1-3 m m can yield significantly better resolution, provided a short imaging distance is used so as to obtain large image magnification. S P E C T i maging of positron emitters It has been well recognized that P E T imaging of 18F-deoxyglucose (18F D G ) is useful for the diagnosis of cardiac, oncological and neurological diseases. Recently, several groups have reported the usefulness of S P E C T imaging of 18F D G with g a m m a camera rotating S P E C T systems using ultrahigh energy collimators designed for 511 keV. For example, with a dual head S P E C T system, a spatial resolution of 17 m m F W H M and a v o lume sensitivity of 2 7 0 (counts/min)/mCi were obtained [13]. In addition, the 18F D G S P E C T system allows simultaneous dual isotope studies, such as " T c m - M I B I / 18F D G tests. P E T with multiple detector rings T h e principle of P E T is based on the coincidence detection of each pair of p h o ­ tons emitted from the annihilation of positrons. T h e most c o m m o n detector configu­ ration is a cylindrical array of small scintillation crystals forming stacked multiple detector rings. Bismuth germanate ( B G O : Bi4G e 30 12) is most widely used as a scin­ tillator by virtue of its high stopping p o w e r for 511 k e V annihilation photons. T h e spatial resolution of P E T has been improved from 10-15 m m to 3-5 m m F W H M in the last t w o decades, mainly by reducing the size of the crystal elements. A s the crystals b e c o m e smaller, one-to-one coupling between the crystals and P M T s be c o m e s difficult and, at present, a block detector configuration, as s h o w n in Fig. Recently, a compact P S - P M T ( H a m a m a t s u model R5600), packaged in a 28 m m square by 20 m m high metal can, w a s developed. T h e P M T has ten stages of metal channel dynodes and crossed wire anodes, four wires each in the X and Y directions. A n animal P E T scanner using block detectors, each consisting of the P S - P M T coupled to an 8 X 4 B G O element array, is n o w under development [14]. Slice septa (shields) are usually placed between the detector rings to reduce the incidence of photons f rom oblique angles to the slices, thereby reducing unwanted 11 curie (Ci) = 3. T h e coincidence detection is conventionally performed between t w o detectors belonging to the s a m e detector ring to form ‘direct plane images’, and between t w o detectors belonging to adjacent rings to f orm ‘cross-plane images’. In m o d e r n high resolution systems, coincident events occurring in several contiguous rings are accepted as ‘enhanced’direct plane or ‘enhanced’cross-plane events. T h e sampling density in the projections has been increased by a certain scanning motion (typically wobbling) of the detector gantry for full utilization of the detector resolution. Recent developments, however, tend to result in the discarding of the scanning motion to avoid the mechanical complexity of m o v i n g a heavy gantry by using a sufficiently fine arrangement of detectors. T h r e e dimensional P E T In conventional P E T , in which v o l u m e imaging has been performed slice by slice, the detection sensitivity decreases with increasing axial resolution. T o over­ c o m e this drawback, the fully 3 - D data acquisition technique has been developed [15], in which slice septa are r e m o v e d (or retracted) and all coincidence events occurring along lines at an oblique angle to the slices are accepted (see Fig. In the 3 - D P E T , 2 - D projection data are accepted in various oblique angles from the slice plane. If the axial acceptance angle is assumed to be constant for a whole imaging volume, a 3 - D filtered back projection algorithm can be utilized, in which the 2 - D projections are filtered by a certain 2 - D filter function and the filtered 2 - D projections are back projected onto the imaging volume. In practical 3 - D P E T scanners, however, the cylindrical detector is truncated axially and the m a x i m u m axial acceptance angle varies throughout the v o lume being imaged. O n e solution in this situation, which has been successfully implemented, is the ‘reprojection m e t h o d ’, described as follows [17].

This ondansetron 8 mg cheap medicine keychain, in turn purchase ondansetron 4 mg symptoms ruptured ovarian cyst, has a pro- found effect on definition of illness and society’s expectation and demands placed on the medical profession cheap ondansetron 8 mg with mastercard treatment h pylori. The losses in economic terms are substantial 8mg ondansetron sale medicine zithromax, at a correction is used when the subject is older than 18 years. This exposure of 100 dB for 8 hours a day over 30 years gives a amount includes direct and indirect costs related to production. The factors affecting quality of life include social iso- to attempt to explain the variance, such as inadequate evalua- lation, increased unemployment, and difficulties in family life tion of the noise exposure, pitfalls in the equal energy principle, due to communication difficulties related to hearing handicap. As 80 dB controls 97 subjects not exposed to noise were included in the 80 85 dB 90 dB study. This model introduced the 105 dB energy principle to enable the combination of different sound 20 110 dB levels (15). After correcting the 5 model for age and gender, the distribution of hearing loss was Time (years) calculated by using the specific formulas. Passchier-Vermeer (17) summarised the results of 19 of deterioration of hearing in individual cases and may cause smaller studies, 12 of which have 50 or fewer cases. A deeper analysis of con- agree well with Robinson’s data at some frequencies, but, at founding factors might reduce the uncertainty in evaluation of other frequencies, large differences were found. A database should include all this information if its purpose Robinson (12) and Passchier-Vermeer (17). The data of is to evaluate total exposure for assessing hearing loss risk in Baughn (10,11) was also used in evaluating hearing loss in the individual cases. For this reason, the hearing loss of the nonexposed population is somewhat less in this report than in the work by Burns and Robinson (12) or Passchier- Historical databases used in Vermeer (17). The study consisted of an otologi- risk criterion is derived from a group of curves that were based cally screened normal population of 792 noise-exposed subjects on laboratory experiments on the development of temporary and 380 controls. The committee on hearing, bio- control values from hearing threshold values measured in noise- acoustics, and biomechanics (9) used the data to express the exposed subjects. The information on which this standard is based is not iden- between noise exposure and hearing loss was made by Baughn tified, but, according to Suter (16), the data of Baughn (10,11) (10). His studies from the early 60s involved a large worker pop- form the basis of this standard. Baughn (10) recommended that the hearing loss of and Sutton (21) demonstrated a 10% and U. Burns and Robinson (12) studied 759 subjects, of whom The problem with historical data is that subjects were not 422 males were exposed to four classes of noise ranging from 87 screened for genetic factors and with few exceptions the Noise-related hearing impairment 93 workers were exposed to the same type of noise. In today’s on workers belonging to particularly sensitive risk groups during society, the noise exposure sources vary and free-time noise has their whole working career. For all subjects, noise immission of individual working introduced on protection against noise. This includes noise characteristics (duration, after by performing noise dosimetry in selected workers. The impulsiveness, and level) and the effect of combined exposure noise immission in forest work was evaluated by determining with vibration and ototoxic chemicals. Finally, the employer the average noise level of the chain saws and by performing must give particular attention when carrying out risk assessment noise dosimetry in selected forest workers. At different work Accuracy of measurement sites, 10 minute samples were recorded for the analysis of A- weighted noise equivalent level and impulsiveness (27). The The detailed noise exposure measurements are necessary to measurements showed that the protector attenuation is about improve the understanding of exposure–response relationships. The exposure period, A is the effective attenuation of hearing pro- observed hearing levels were very consistent with the model for tectors, Ti is the length of the ith work period in years, and forest workers, where the noise was not impulsive. The dif- A L L L 10 L O G 10 1 c ((L A )/10) ference could not be explained by the small change in exposure. Use rates were elicited for all work periods in steps 0, 25, 50, 75, and 100, where 0 means no use at all and 100 means The most frequent exposure to noise in free time is exposure to regular use. The highest music exposure rates are from rock The contribution of occupational, free-time, and military music. Noise levels in a concert or a disco often exceed 100 dB noise and use of hearing protectors can also be evaluated. Thus, only one attendance a week causes an exposure Although the 3 dB equal-energy rule is not universally accepted exceeding the occupational exposure limit value. Similar levels as a method for characterising exposures that consist of both are reported in the users of portable cassette recorders (31). In impulsive and continuous-type noises, the evaluation of cumu- classical music, the levels are lower, but the musicians still have lative lifetime noise exposure might be based on the concept of a risk of hearing loss (32). In studies conducted among young people, Noise-related hearing impairment 95 exposure to loud music causes no changes in the audiogram. It 10 20 30 40 50 60 has been suggested that the effect of music exposure would 120 Shooting 32 show up later. In this case Lex,8hi 16 should be replaced with the equivalent continuous A-weighted 14 sound pressure level. Effective time exposure per day (or week 20 30 40 50 60 or year) will be also taken into consideration. The shipyard worker starts working at the age of 20 years in an impulsive (in Pa s) might be calculated from the equation (4): noise environment of 98dB(A). Additionally, in the case of occupa- nominal attenuation is obtained is often questioned (34,35). The difference could not be explained by the small Nonoccupational noise exposure interacts with occupa- change in exposure. In addition to occupational noise, questioned by the several studies, suggesting that 3 to 18 dB other noise sources such as military noise, vehicle noise, and, should be subtracted from the protection values given by the especially, exposure to free-time noise have become increas- manufacturer. This is due to the high content of high frequencies in impulses (36) that are attenuated effec- tively by earmuffs. If earplugs are used, 40 special attention must be paid to the proper installation technique (34,37). Also sound pressure levels for workers exposed to occupational noise showed on average 5 dB speech and music are indicated. The emitted sounds originate from the electri- must be repeated consistently (38). In practice, we recommend that the audiometry test stimuli such as clicks or tone pips. When two signals are aver- starts at 1 kHz and that the tester evaluates the threshold in aged and compared, the repeatability of the signal can be ascer- descending order. As parameters for hair cell damage, the amplitude of the correctly hears two out of three tone peeps at the lowest thresh- signal over a specified frequency range and its repeatability can olds. Transient emissions are normally present when hearing test frequency is repeated, and after that higher frequencies of loss is 20 dB or less. These all cause variability in the audiometric tudes at different frequencies are used for comparison (44). There are various ways by which the recording and responses, resulting in an unreliable audiogram. They are absent with cochlear hearing loss greater these instances, the 0-dB threshold values cannot be measured. These are attractive for use as a screening booth to allow 0-dB threshold values to be measured. In indus- procedure as the test procedure is short and no cooperation of try, screening audiometry is performed for 20-dB hearing level at the subject is needed. No shifts in workplace audiometric monitoring, the “15 dB twice” changes in the audiogram are to be expected at speech frequen- criterion. This is defined as 15 dB worsening at any frequency, cies if the A-weighted equivalent noise level is less than 80 dB.

Varnishes Duraphat 5% by wt fluoride = 22 order 4 mg ondansetron amex symptoms diabetes,600 ppm fluoride is the main fluoride varnish order ondansetron 8 mg otc symptoms 7dpiui. It is supplied in a small tube purchase ondansetron 8 mg without prescription symptoms colon cancer, but used lavishly by most dentists as if it were toothpaste generic ondansetron 4mg on-line medicine 94. It should be used sparingly with a cotton bud, a small pea-size amount is sufficient for a full mouth application in children up to 6 years. Slow-release fluoride devices Many dental materials like amalgam, composites, cements, acrylics, and fissure sealants have had fluoride added, but the fluoride release was either short term or the properties of the materials were adversely affected, to make them of any use to provide a long-term source of intraoral fluoride. Glass ionomer cements are a group of materials that have fluoride, but long-term release is debatable. That is when the fluoride is released from the material it later takes up fluoride from other dental products that are used by the patient, for example, fluoride toothpaste or mouth rinse, and this fluoride is released at a later time. The objective is to develop an intraoral device that will release a constant supply of fluoride over a period of at least a year. Studies in Leeds demonstrated that there were 67% fewer new carious teeth and 76% fewer new carious surfaces in high caries-risk children after 2 years in a clinical caries trial for children with the fluoride devices in comparison to the control group with placebo devices. There were 55% fewer new occlusal fissure carious cavities showing that occlusal surfaces were also protected by the fluoride released from the devices. The fluoride glass devices have been patented and commercial development is now under progress. The provision of fluoride for each individual must be tailor-made to suit varying social and working circumstances. Slow-release fluoride devices seem ideal for targeting the high caries- risk groups who are notoriously bad dental attenders with very poor oral hygiene and motivation. This is a very promising development with application for use in numerous high-risk groups including the medically compromised. Deciding which fluoride preparation to use for differing clinical situations: This will depend on: (1) Which groups of children? In addition, the expected patient/parent motivation and compliance is very important in deciding what to use. Initially developed to prevent caries their use has been developed further and they now have a place in the treatment of caries. The decline in caries observed in industrialized countries over recent decades has affected all tooth surfaces but has been greatest on smooth surfaces. Therefore the pit and fissured surfaces, particularly of the molars have the greatest disease susceptibility. This means that the potential benefits of effectively used sealants continue to increase. The technique for placement of sealants is relatively simple but is technique sensitive. Salivary contamination of as little as half a second can affect the bond and therefore the retention of the sealant. Current resin materials are either autopolymerizing or photo-initiated, and most operators prefer the advantages of demand set offered by photo-initiation. Although there are theoretical advantages to chemically cured materials in terms of retention, as these materials have longer resin tags extending into the etched surface. Filled and unfilled resins are available, the filled materials being produced to provide greater wear resistance. However, this is not clinically relevant and clinical trials demonstrate superior efficacy for unfilled materials. Irrespective of the presence of fillers some materials are opaque or tinted to aid evaluation. This is an advantage but means the clinician is unable to view the enamel surface to assist with caries detection and to detect the presence of restorations such as sealant restorations. Key Points Fissure sealing technique • Prophylaxis before etching does not enhance retention but is advisable if abundant plaque is present. A dry brush should be used rather than paste as these are retained in the depths of the fissures preventing penetration of the resin. Operator and assistant must act as a team as it is impossible for single operators to apply sealant effectively. The vast majority of trials have demonstrated cotton wool and suction to be an effective means of isolation. Rubber dam is advocated by some because of the superior isolation offered by this material. This is probably true but its use is frequently not possible because of the stage of eruption of the tooth or level of co-operation of the patient. It would be inappropriate to delay sealant application to allow further eruption to permit the application of rubber dam. The application of sealant is a relatively non-invasive technique, frequently used to acclimatize a patient. It is difficult to justify the use of rubber dam with the associated use of local anaesthetic and clamps for the majority of patients, on both clinical and economic grounds. Glass ionomers have also been used as sealants, the application technique is less sensitive, than that for resins. It is suggested that the fluoride release from glass ionomers provides additional protection but the clinical relevance of this remains doubtful. The addition of fluoride to resin sealants has been demonstrated to provide no additional benefit. Glass ionomer sealants only have a place as temporary sealants during tooth eruption, when adequate isolation to permit the application of resin is not possible or in patients whose level of anxiety or co-operation similarly prevent placement of resin. Glass ionomers have been developed specifically for this role but clinical evidence of their effectiveness is not yet available. Key Points Application of glass ionomer sealants • Clean the surface • Isolate the tooth • Run the glass ionomer into the fissures • Protect the material during initial setting • Apply unfilled resin, petroleum jelly, or fluoride varnish to protect the material. For anxious patients application can be done with a gloved finger until the material is set. Resin fissure sealants are effective; a recent systematic review has demonstrated 57% caries reductions at 4 years, with retention of 71-85% at 2 years falling to 52% at 4 years (Ahovuo-Saloranta et al. To gain the full caries preventive benefit sealants should be maintained, that is, sealants with less than optimal coverage identified and additional resin applied. Since the development of sealants there has been a question regarding the effect of sealing over caries, the concern being that caries will progress unidentified under the sealant. Given the difficulty in diagnosing caries this must be a frequent occurrence in daily practice. A number of trials have examined this by actively sealing over caries, and all have shown that sealants arrest or slow the rate of caries progression. We are not at the point where sealing of active caries is recommended by most authorities but the maxim if in doubt seal is good advice. The surface should then be monitored clinically and radiographically at regular intervals until its status is confirmed. One instance where actively sealing over caries is to be recommended is in the pre- cooperative patient where the placement of sealant may help acclimatization of the patient, with the added benefit of controlling the caries, until a definitive restoration can be placed. Sealants are also effective at preventing pit and fissure caries in primary teeth. Primary teeth have more aprismatic enamel than permanent teeth, and doubt about the effectiveness of etching deciduous enamel lead to a belief that they required prolonged etching times. This has been demonstrated not to be the case and the technique for sealant application to primary teeth is identical to that employed with permanent teeth. Although the effectiveness of fissure sealants is beyond doubt, to be used cost effectively their use should be targeted. Guidelines for patient selection and tooth selection have been published by the British Society for Paediatric Dentistry, and these are summarized below. Fissure sealing of all occlusal surfaces of permanent teeth should be considered for those who are medically compromised, physically or mentally disabled, or have learning difficulties, or for those from a disadvantaged social background.

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