By F. Varek. Institute for Transpersonal Psychology.
However discount vardenafil 10 mg without a prescription, the eruption of the first permanent molars largely goes unnoticed until there is a problem buy 20mg vardenafil. The first permanent molars are teeth that commonly exhibit disrupted enamel; the reported incidence of defects range from 3 discount vardenafil 10 mg with mastercard. The occlusal surfaces of these molar teeth account for about 90% of caries in children. Restoration of the young permanent dentition is part of a continuum and cannot be regarded in isolation. It does nothing to cure the disease and must form part of a much wider treatment modality, which includes identification of the risk factors contributing to the disease followed by introduction of specific prevention counter measures. Efforts must be applied to all of these areas to attempt to provide the optimum conditions for future tooth survival. These risk factors and preventive measures are addressed in other chapters, such that the authors can confine themselves to appraisal of methods of treatment of caries in the young permanent dentition. They cannot hope to completely cover every aspect of operative treatment in one chapter; there are other texts that should be read to give a fuller account of the available techniques (see sections 9. The idea of a caries risk assessment for each child patient is to ensure that the chosen diagnostic tests, preventive treatment, and any provided restorations, are geared specifically to the need of that patient. Factors requiring consideration are: (1) present caries activity; (2) past caries activity; (3) parent /sibling caries activity; (4) sugar consumption; (5) oral hygiene; (6) fluoride exposure; (7) teeth morphology; (8) Streptococcus mutans levels; (9) saliva characteristics, flow rate, and consistency. Factors (1)-(7) will become clear when a full history and examination are carried out; while (8) and (9) will only come into play if there is rampant caries, which the dentist cannot explain from the history (Fig. The operator must keep this to a minimum, consistent with complete caries eradication. Every time an operator places a restoration, he or she destroys more of the original tooth structure, thereby weakening the tooth. Even though the occlusion in a young person changes as growth occurs and teeth erupt, it is important to realize, that when the operator places restorations, he or she must replicate the original occlusal contacts in the tooth. Although, it may be tempting to keep the restoration totally out of the occlusion, teeth will move back into the occlusion, which will thereafter be slightly different and the cumulative effect of a lot of little changes can severely disrupt the occlusion in the long term. When treating an approximal lesion on one tooth with an adjacent neighbour, the operator will almost certainly damage the latter. The important surface layer of the neighbouring tooth, which contains the highest level of fluoride is the most resistant, so damage inflicted increases the chances of the adjacent surface of the neighbouring tooth becoming carious. It also creates an area of roughness on that surface, which in turn will accumulate more plaque, thereby increasing the risk of further decalcification. When placing an interproximal restoration it is inevitable that there is some damage to the periodontal tissues. There is the transient damage caused by placement of the matrix band and wedge, and there is also an enduring effect caused by the presence of the restoration margin. The very presence of the new restoration results in a contour change of the interstitial space. However smooth the operator attempts to make it, the altered state will increase plaque accumulation. Key Point Every time a restoration is placed, more of the original tooth structure will be destroyed, thereby weakening the tooth. There is little evidence to suggest that remineralization occurs in lesions already into dentine. The rate of caries progression is usually slow but can be rapid in some individuals, particularly younger children. In general, the older the child is at diagnosis of a carious lesion the slower the progress of the lesion, assuming constancy of other risk factors. Small restorations are generally more successful than large, so a balance has to be struck, allowing preventive procedures adequate time to function, against the risk of lesion enlargement. The progression rate of approximal caries can vary from tooth to tooth within the same mouth. Remineralization sources available are: • fluoride rinse, • fluoride varnish, • chlorhexidine thymol varnish, • oral hygiene measures, • adjacent glass ionomer restorations. Determination of the most effective method to retard the progression of approximal caries requires not only identification of the most effective remineralizing agent but also the frequency with which to employ it. Key Point The remineralized tissue of early caries is less susceptible to further caries. Existing studies indicate that fluoride varnishes, solutions, and toothpastes all provide a significant effect on the progression of approximal caries in permanent molars when assessed radiographically. It would be interesting to know what happened after the completion of the studies and poses the following questions: • Would the lesions have developed to the restorative stage? Progress of caries through the enamel seems to be fairly slow but once the dentine is reached it accelerates. So as a rule of thumb, restore approximal surfaces once the lesion reaches the enamel/dentine interface. Where there is no overt or open cavity, diagnosing the status of a discoloured or stained fissure can be incredibly difficult if not impossible on occasions. These include: • visual methods (dry tooth); • probe/explorer; • bitewing radiographs; • electronic; • fibre optic transillumination; • laser diagnosis. When two or three methods are used in combination, there is greater accuracy and higher rates of detection of caries. The most widely used combination is visual inspection under a good light, to examine a dry tooth for stains, opacities, etc. Drying the tooth to be examined is essential as early lesions will only become visible, where the demineralization is minimal, when there is a dry surface. Different recommendations are made for the timing of bitewing radiographs and these are discussed in Chapter 3414H. Bitewing radiographs will show dentinal caries in teeth that are designated as clinically sound but there will also be teeth visually designated as carious in which there are no radiological signs of caries, hence the need for more than one method of diagnosis. In making a diagnosis of caries, the operator has to decide, not only that there is a lesion present but also: • Whether or not demineralization is present. Measurements of electrical conductance and laser fluorescence have the potential to chart lesion progression/retardation as they provide a quantitative record, which if repeated over several appointments will demonstrate whether the lesion is active or arresting. However, it should be remembered that the electrical conductance and laser fluorescence methods would incorrectly interpret hypomineralization as caries and that similarly the laser-based instrument will routinely interpret staining to be caries. Key Point Diagnosis of early caries is important to be able to plan the whole treatment package. Toothbrush bristles cannot access the pit and fissure system because the dimensions of the fissures are too small. The tooth is most susceptible to plaque stagnation during eruption, that is, a period of between 12 and 18 months. During this time, children need extra parental help in maintaining their oral hygiene. Lesion formation takes place in the plaque stagnation area at the entrance to the fissure and commences with subsurface demineralization.
Probably m ore im portant than the route of delivery is peri-partum planning and team w ork: delivery m ust be planned in advance discount vardenafil, and the patient intensively m onitored discount vardenafil amex, kept w ell hydrated and not allow ed to drop her system ic vascular resistance cheap vardenafil express. Consultant obstetric and anaesthetic staff experienced in these conditions should be present, and the cardiologist readily available. Rachael James All anticoagulant options during pregnancy are associated w ith potential risks to the m other and fetus. Any w om an on w arfarin w ho w ishes to becom e pregnant should ideally be seen for pre- pregnancy counselling and should be involved in the anti- coagulation decision as m uch as possible. Potential risks to the fetus need to be balanced against the increased m aternal throm - botic risk during pregnancy. Anticoagulation for m echanical heart valves in pregnancy rem ains an area of som e controversy. The use of w arfarin during pregnancy is associated w ith a low risk of m aternal com plications1 but it readily crosses the placenta and em bryopathy can follow exposure betw een 6–12 w eeks’ gestation, the true incidence of w hich is unknow n. A single study has reported that a m aternal w arfarin dose 5m g is w ithout this em bryopathy risk. Conversion to heparin in the final few w eeks of pregnancy is recom m ended to prevent the delivery of, w hat is in effect, an anticoagulated fetus. Studies have been criticised for the use of inadequate heparin dosing and/or inadequate therapeutic ranges4 although a recent prospective study w hich used heparin in the first trim ester and in the final w eeks of pregnancy reported fatal valve throm boses despite adequate anticoagulation. Use in pregnancy is m ainly for throm boprophylaxis rather 100 Questions in Cardiology 201 than full anticoagulation but experience is increasing. M anagement W om en w ho do not w ish to continue w arfarin throughout preg- nancy can be reassured that conceiving on w arfarin appears safe but conversion to heparin, to avoid the risk of em bryopathy, needs to be carried out by 6 w eeks. Possible regim es include: • W arfarin throughout pregnancy until near term and then conversion to unfractionated heparin. Coum arin anticoagulation during pregnancy in patients w ith m echanical valve prostheses. Guidelines on the prevention, investi- gation and m anagem ent of throm bosis associated w ith pregnancy. Failure of adjusted doses of subcutaneous heparin to prevent throm boem bolic phenom ena in pregnant patients w ith m echanical cardiac valve prostheses. Matthew Streetly M echanical heart valves are associated w ith an annual risk of arterial throm boem bolism of <8%. This constitutes an unacceptable risk for patients undergoing m ajor surgery, and it is necessary to tem porarily institute alternative anticoagulant m easures. If surgery cannot be delayed, the effect of w arfarin can be reversed by fresh frozen plasm a (2–4 units) or a sm all dose of intravenous vitam in K (0. Recom m encing intravenous heparin in the im m ediate post- operative period m ay increase the risk of haem orrhage to greater levels than the risk of throm boem bolism w ith no anticoagulation. Heparin is usually restarted 12–24 hours after surgery, depending on the type of surgery and the cardiac reason for w arfarin. W arfarin should be restarted as soon as the patient is able to tolerate oral m edication. Marc R Moon The indications for surgical m anagem ent of endocarditis fall into six categories. Congestive heart failure Patients w ith m oderate-to-severe heart failure require urgent surgical intervention. W ith m itral regurgitation, afterload reduction and diuretic therapy can im prove sym ptom s and m ay m ake it possible to postpone surgical repair until a full course of antibiotic therapy has been com pleted. In contrast, acute aortic regurgitation progresses rapidly despite an initial favourable response to m edical therapy, and early surgical intervention is im perative. Persistent sepsis This is defined as failure to achieve bloodstream sterility after 3–5 days of appropriate antibiotic therapy or a lack of clinical im provem ent after one w eek. Recognised virulence of the infecting organism • W ith native valve endocarditis, streptococcal infections can be cured w ith m edical therapy in 90%. Fungal infections invariably require surgical intervention • W ith prosthetic valve endocarditis, streptococcal tissue valve infections involving only the leaflets can be cleared in 80% w ith antibiotic therapy alone; how ever, m echanical or tissue valve infections involving the sew ing ring generally require valve replacem ent. If echocardiography dem onstrates a perivalvular leak, annular extension, or a large vegetation, early operation is necessary 100 Questions in Cardiology 205 4. Extravalvular extension Annular abscesses are m ore com m on w ith aortic (25-50% ) than m itral (1-5% ) infections; in either case, surgical intervention is preferred (survival: 25% m edical, 60-80% surgical). Peripheral embolisation This is com m on (30-40% ), but the incidence falls dram atically follow ing initiation of antibiotic therapy. Surgical therapy is indicated for recurrent or m ultiple em bolisation, large m obile m itral vegetations or vegetations that increase in size despite appropriate m edical therapy. Cerebral embolisation O peration w ithin 24 hours of an infarct carries a 50% exacerbation and 67% m ortality rate, but the risk falls after tw o w eeks (exacer- bation <10% , m ortality <20% ). Follow ing a bland infarct, it is ideal to w ait 2–3 w eeks unless haem odynam ic com prom ise obligates early surgical intervention. Follow ing a haem orrhagic infarct, operation should be postponed as long as possible (4–6 w eeks). Peter Wilson Despite progress in m anagem ent, m orbidity and m ortality rem ain m ajor problem s for the patient w ith endocarditis, both during the acute phase and as the result of long term com plications after a bacteriological cure. Im provem ents in m icrobiological diagnosis, types of antibiotic treatm ent and tim ing of surgical intervention have im proved the outlook for som e patients but the im pact has been m inor w ith som e of the m ore invasive pathogens. Healed vegetations m ay leave valvular function so com prom ised that surgery is required. In 140 patients w ith acute infective endocarditis, 48 (34% ) required valve replacem ent during treatm ent. Recurrence w as observed in 5 (4% ) patients betw een 4 m onths and 15 years after the first episode. In the follow up period, another 16 patients died of cardiac causes, m ost w ithin five years. O f 34 patients w ith late prosthetic valve endocarditis, 27 (79% ) survived their hospital adm ission but 11 had further surgery during the next five years, usually follow ing cardiac failure. Effects of changes in m anagem ent of active infective endocarditis on outcom e in a 25 year period. Peter Wilson The great m ajority of patients w ith endocarditis have positive blood cultures w ithin a few days of incubation and only a few cases w ill becom e positive on further incubation for 1–2 w eeks. The proportion of culture-negative cases depends on the volum e of blood and m ethod of culture but a com m on estim ate is 5% w ith a range from 2. If antibiotics have been given, w ith- draw al of treatm ent for four days and serial blood cultures w ill usually dem onstrate the pathogen. Nutritionally-deficient streptococci m ay fail to grow in ordinary m edia and yet are part of the norm al m outh flora and can cause endocarditis. After four negative cultures there is only a 1% chance of an organism being identified by later culture. Endocarditis due to nutritionally deficient strepto- cocci: therapeutic dilem m a. Peter Wilson There is little firm scientific evidence for present advice on antibiotic prophylaxis for endocarditis, m ainly because of the rarity of the disease. Prevention of endocarditis in patients w ith abnorm al heart valves can be achieved by m any general m easures, for exam ple, regular dental care.
Collimator efﬁciency varies with different types of colli- mators buy line vardenafil, and the values are shown as a function of source-to-collimator dis- tance in Figure 10 buy 20 mg vardenafil amex. Uniformity It is always expected that a gamma camera should yield a uniform response throughout the ﬁeld of view purchase 10 mg vardenafil fast delivery. That is, a point source counted at different locations in the ﬁeld of view should give the same count rate by the detec- tor at all locations. However, even properly tuned and adjusted gamma cameras produce nonuniform images with count density variations of as much as 10%. Such nonuniformity adds to the degradation of the spatial resolution of the system. Although factor (c) is preventable as discussed below, factors (a) and (b) are the leading causes of deterioration in uniformity and special attention is needed to remedy them. An intrinsic image (without the col- limator) is acquired using the appropriate window and stored in a 128 × 128 matrix. The pulse height in each (X, Y) pixel is determined and stored in a 128 × 128 look-up table. In subsequent patient studies, a microprocessor compares the pulse height in each pixel of the patient image with the cor- responding value in the look-up table, and then either moves the energy 130 10. Performance Parameters of Gamma Cameras window or adjusts the pulse height to compensate for the variations. This is performed in real-time during the data collection in patient studies and should be carried out for each radionuclide. Nonlinearity The spatial nonlinearities are systematic errors in the positioning of X-, Y-coordinates of pulses in the image and result from local count compres- sion or expansion. The spatial distortions due to nonlinearity are corrected by micro- processors built into modern cameras that use correction matrices. Nonlin- earity correction factors are generated by calculating the spatial shift of the observed position of an event from its actual position. The test pattern is placed directly on the detector, and an image is stored in a 128 × 128 matrix. The actual location (X, Y) of each pixel is known and the corresponding location on the image is measured. These variations in X, Y for all pixels are calculated as correction factors and are normally supplied by the manufacturer in the form of a look-up table. These correction factors are subsequently applied in real-time to each detected event to move it to the actual position during patient imaging. As stated above, modern cameras include two look-up matrices, the pulse-height correction and the linearity correction, to compensate for vari- ations in the overall uniformity of images. As the camera slowly drifts over time, the correction tables have to be updated for proper correction of the patient scan. The exact frequency of reacquiring the correction tables depends on stability of the camera and varies with the manufacturer. The pulse-height correction tables require more frequent acquisitions, whereas the linearity correction tables are typically performed by a service engineer. Different manufacturers recommend monthly to quarterly acquisition of these correction factor maps. Even though the uni- formity corrections at times can correct for large nonuniformities, frequent retuning of the gamma camera is essential as these corrections affect lin- earity, resolution, and overall sensitivity of the camera. Gamma Camera Tuning 131 Edge Packing Edge packing is seen around the edge of an image as a bright ring and results in nonuniformity of the image. Normally a 5-cm wide lead ring is attached around the edge of the colli- mator to mask this effect. The source of radiation can be either the radi- ation from the patient or an external radioactive source, for example, 99mTc. Performance Parameters of Gamma Cameras Effects of High Counting Rates As discussed in Chapter 8, the scintillation cameras suffer count losses at high counting rates due to pulse pileup. Pulse pileup results from the detec- tion by the camera of two events simultaneously as one event with ampli- tude different from that of either original event. If one or both of the events are photopeaks, then the amplitude of the new event will be outside the pulse-height window setting and so the event will be rejected resulting in a loss of counts. If, however, two Compton scattered photons are processed together to produce an event equivalent to the photopeak in amplitude, then the event will be counted within the window setting. But the X, Y posi- tion of the event will be misplaced on the image somewhere between the locations of the two events. Both count rate loss and image distortion at high count rates must be taken into consider- ation in evaluating the performance of different cameras. Several techniques are employed to improve the high count rate performance of a gamma camera. In modern cameras, buffers (or deran- domizers) are used in which pulses are processed one at a time, and over- lapping events are kept on “hold” until the processing of the preceding event is completed. Other cameras use pulse pileup rejection circuits to minimize the count loss and image dis- tortion and thus to improve images, although they tend to increase the dead time of the camera. Recent developments include high-speed electronics that reduce the number of misplaced events and improve the image quality signiﬁcantly. Contrast Contrast of an image is the relative variations in count densities between adjacent areas in the image of an object. Contrast (C) gives a measure of detectability of an abnormality relative to normal tissue and is expressed as A − C = (10. Lesions on the image are seen as either “hot” or “cold” spots indicating increased or decreased uptakes of radioactivity in the corresponding areas in the object. Several factors affect the contrast of the image, namely, count density, scattered radiation, pulse pileup, size of the lesion, and patient motion, and each contributes to the contrast to a varying degree. Quality Control Tests for Gamma Cameras 133 Statistical variations of the count rates give rise to noise that increases with decreasing information density or count density (counts/cm2) and is given by (1/ N ) × 100, where N is the count density. For a given imaging setting, a minimum number of counts need to be collected for rea- sonable image contrast. Even with adequate spatial resolution from the imaging device, lack of sufﬁcient counts may give rise to poor contrast due to increased noise, so much so that lesions may be missed. This count density depends on the amount of activity administered and the uptake in the organ of interest. Contrast is improved with increasing administered activity and also with the differential uptake between the normal and abnormal tissues. However, due consideration should be given to the radiation dose to the patient from a large amount of administered activity. Sometimes, high count density is achieved by counting for a longer period of time in the case of low administered activity. It should be emphasized that spatial resolution is not affected by the increased count density from increased administered activity or longer counting. Background in the image increases with scattered radiations and thus degrades the image contrast. As discussed above, at high count rates, pulse pileup can degrade the image contrast. Image contrast to distinguish a lesion depends on its size relative to system resolution and its surrounding background.
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