By K. Domenik. Mississippi Valley State University.
For example generic prednisolone 5 mg without prescription, but with many deeper lesions and poor oral hygiene there are two axiopulpal line angles in the mesio- that is not improving prednisolone 20 mg online, should probably have the tooth occlusodistal amalgam preparation: One is the axiop- restored prednisolone 5 mg mastercard, especially since a lesion extends deeper in the 9 ulpal line angle of the mesial box and the other is the actual tooth than it appears on the radiograph buy 5 mg prednisolone overnight delivery. Occlusal view showing the proximal box extending just through the proximal contact buccally and lingually. The mesial view showing the slight convergence toward the occlusal of the buccal and lingual walls of the box, and axiobuccal (A-B) and axiolingual (A-L) line angles where retentive grooves are placed. A cross section of this prepared tooth in the middle third of the crown showing the placement of the retentive grooves entirely within dentin at the axiobuccal and axiolingual line angles. Key for nomenclature: Walls, B, buccal; P, pulpal (red); L, lingual; A, axial (blue); G, gingival (green). Example of line angles: A-B, axiobuccal; A-L, axiolingual (location of retentive grooves). Improvements in across the occlusal surface into the occlusal grooves composite restorative materials and techniques have (Fig. In this way, the margins of the restoration can be better 29 30 evaluated by the dentist and kept clean by the patient. Note the convergence of the buccal and lingual walls toward the occlusal for retention and resistance form. When the decay process has progressed deeper and wider, the prepared walls by necessity will be farther apart than these. Conservative slot preparation involving the distal and occlusal surfaces of typo- dont tooth No. This con- servative preparation may be preferred to reach interproximal caries when there is proximal caries without any occlusal involvement. Retentive grooves may be prepared and bonding, there is less need for internal retention buccally and lingually in a proximal box as extensions grooves. These retentive grooves are designed to toward the occlusal (seen on a die for a cast metal prevent the amalgam restoration from dislodging in a onlay in Fig. They are located at the axiobuc- occlusodistal inlay preparation must converge slightly cal (A-B) and axiolingual (A-L) line angles seen best toward the occlusal. Resin restorations are generally pre- restoration can be refined outside of the mouth and then pared in a similar fashion to amalgam. The underlying lesion causes overlying enamel to appear slightly darker or more opaque than surrounding, sound enamel. These changes are most evident when a source of light (such as fiber optics) is placed lingually against the proximal enamel of the tooth, revealing the change in translucency facially (Fig. The line on the die marks the cavosurface margin that ends with a continuous bevel. Sometimes, how- ever, a more defined, traditional preparation may be incisal, and axial (as abbreviated in Fig. The three walls are the facial, lingual, and gingival walls, and the fourth wall (or floor) is the axial. Subsequently, this preparation has six inter- nal line angles: facioaxial, linguoaxial, gingivoaxial, faciolingual, linguogingival, and gingivofacial. There are only three internal point angles: faciolinguoaxial (abbreviated F-L-A in Fig. A light source is directed through the proximal surfaces of these anterior teeth to reveal a amalgam approached from the lingual on the distal of change in translucency just cervical to the proximal contact tooth No. The confusion with “L,” which is used to denote the lingual approach for removing the decay, whenever possible, is surface. Retentive grooves are evident at the cavosurface of the gingivoaxial and incisoaxial line angles. Note the slight convergence of the incisal and gingival wall toward the lingual for reten- tion. This preparation also has a retentive groove (in the shadow between G and A) at the gingivoaxial line angle, but it does not extend to the cavosurface. Retentive features are found internally at the axiogingival line angle and the faciolinguoaxial point angle. Key for nomenclature: for lingual approach (A and B): G, gingival; A, axial (blue); F, facial; I, incisal. Examples of the angles are the retentive features G-A and I-A for the gingivoaxial and incisoaxial line angles, respectively. Key for the facial approach (C): F, facial; A, axial (blue); G, gingival; L, lingual. However, the more patient’s concern for esthetics are important factors conservative method of affording retention and reduc- when deciding whether or not to restore the tooth. These two portions may join at an angle called occurs when the tooth corner fractures off due to a blow the axiogingival line angle. The loss of an incisal angle is plainly vis- A composite restoration that restores one incisal ible upon clinical examination. An alternative as always, must be analyzed to be sure that there is treatment is a veneer of porcelain bonded to the facial room for the restoration when the patient chews and surface of the tooth, replacing the fractured incisal area incises, especially in a protrusive direction. If the preparation is most commonly achieved by acid-etch techniques that permit resin tags to bond the composite to the tooth. A thin overlapping sleeve of excess composite mate- rial can cover beveled enamel that has been acid etched to maximize retention (Fig. View of the lesion showing the of curvature, adjacent to the gingiva, where the natural gingival and axial portions of the defect. After smoothing the cleansing action of the lips, tongue, and cheeks is inef- preparation and acid etching the enamel, the restored tooth with a sleeve (thin layer of bonded resin) that overlaps the fective. This area of the tooth is susceptible to plaque etched enamel surface, thus establishing maximum retention accumulation and resultant caries. Incipient (beginning) facial lesion that is seen as chalky and discolored and is flaking away. An obvious cavitated class V facial lesion that has destroyed much of the enamel on the buccal surface of the crown and adjacent cementum and dentin of the root. Class V demineralization: a chalky white area (arrows) seen in the cervical third of a maxillary lateral incisor with incisal wear is evidence of the first stages of dental caries. If this demineralization continued and did not reverse itself (through excellent oral hygiene, diet, and use of topical fluoride), this area could develop a cavitation (hole) that would need to be restored. Also, notice the inflammation of the adjacent gingiva (gingivitis), which is also caused by bacterial plaque. As with a radiograph of a class I lesion, the class V With decreased salivary flow and/or poor oral hygiene, lesion is superimposed over buccal or lingual surfaces the incidence and severity of caries increase in this area of enamel that show up whiter (radiopaque), thereby (Fig. As a class V lesion begins to form, it appears as a By the time a class V lesion is evident on radiographs, chalky white or stained surface (Fig. In these it has progressed far beyond the incipient stage and beginning (incipient) lesions, care should be taken with will require a much larger restoration than would have the explorer not to break through an area of beginning been required if it were clinically diagnosed at its earli- demineralization that has not yet cavitated since excel- est stages. Therefore, the examiner should not depend lent oral hygiene and fluoride have been shown to on radiographs for detection of these lesions. These lesions may be hid- when discovering a cervically located radiolucency den slightly apical to the level of inflamed gingiva so on a radiograph, the dentist should carefully evaluate that the use of the tactile sense obtained through the the tooth to clinically prove or disprove the presence explorer is critical for detection of cavitation9 and for distinction between these lesions (which are cavitated) and a calcified buildup of calculus (which is felt as a bump attached to the surface of the tooth). Other areas of cavitation (or depressions) located in the cervical of the crown and the adjacent root sur- face include defects formed from erosion by acids, or from abrasion (most commonly caused by abrasive toothpastes and improper tooth brushing [as seen in Fig. Maxillary anterior teeth showing cervical sion, the cementum, which is much less mineralized abrasion, possibly due to poor tooth brushing technique and than enamel, is more susceptible to caries compared abrasive pastes. Each tooth should be evaluated carefully to is occurring more frequently in our aging population determine if application of a desensitizing solution or a (Fig. Chapter 10 | Treating Decayed, Broken, and Missing Teeth 315 decay could respond to fluoride and improved oral hygiene and actually remineralize so that no restoration is required. Also, these defects could be areas of arrested (old, inactive) decay, or noncarious cavitated defects due to abrasion, erosion, or abfraction. Class V lesions require restorations when tooth structure is soft or cavi- tated (as seen in Fig. Restorations should also be considered to protect noncarious defects (like abra- sion defects) that occur in this part of the tooth if the tooth is sensitive and does not respond to desensitizing agents, if the lesion is very deep and cannot be kept clean, or if it appears that it will continue to advance due to poor oral hygiene or parafunctional habits. Root caries (arrow) on an area of exposed consists of five walls: distal, occlusal, mesial, gingival, cementum after gingival recession. These preparations have eight line angles: axiomesial, axiogingival, axiodistal, axio-occlusal, of class V caries. Darker (radiolucent) areas of cervical mesiogingival, distogingival, mesio-occlusal, and disto- abrasion, as well as older types of radiolucent restor- occlusal. The axio-occlusal and axiogingival line angles ative materials, can appear like class V or root surface are prepared with retentive grooves labeled as A-O and caries on radiographs.
Two ways to survive infection: What resistance and tol- erance can teach us about treating infectious diseases order 10mg prednisolone. Functional genetic screen of human diversity reveals that a methionine salvage enzyme regulates infammatory cell death proven 20 mg prednisolone. Integrating poverty and gender into health programmes: A sourcebook for health pro- fessionals (module on noncommunicable diseases) buy prednisolone 5mg visa. Sepsis: Stimulation of energy-dependent protein break- down resulting in protein loss in skeletal muscle discount prednisolone 20mg with mastercard. Appropriate protein provision in critical illness: A system- atic and narrative review. The acute phase response of plasma protein synthesis during experi- mental infammation. Albumin synthesis rates in post-surgical infants and septic ado- lescents; infuence of amino acids, energy, and insulin. Vitamin A sup- plementation for preventing morbidity and mortality in children from 6 months to 5 years of age. Respiratory infec- tions reduce the growth response to vitamin A supplementation in a randomized con- trolled trial. Substantial reduction in severe diarrheal morbidity by daily zinc supplementation in young north Indian children. Zinc with oral rehydration therapy reduces stool output and dura- tion of diarrhea in hospitalized children: A randomized controlled trial. Short-course prophylactic zinc supplementation for diarrhea morbidity in infants of 6 to 11 months. Effect of micronutrient supplementation on diarrhoeal disease among stunted children in rural South Africa. Zinc or multiple micronutrient supplementation to reduce diarrhea and respiratory disease in South African children: A randomized controlled trial. The role of vitamin E and selenium on arachidonic acid oxidation by way of the 5-lipoxygenase pathway. Vitamin E supplementation enhances cell-mediated immunity in healthy elderly subjects. Vitamin E supplementation and in vivo immune response in healthy elderly subjects. Seleno-organic compounds and the therapy of hydroperoxide- linked pathological conditions. Selenium and inter- leukins in persons infected with human immunodefciency virus type 1. Supplementary vitamin E, selenium, cysteine and ribofavin for preventing kwash- iorkor in preschool children in developing countries. Alterations of serum selenium concentrations in the acute phase of pathological conditions. New assay for the measurement of selenoprotein P as a sepsis biomarker from serum. The role of selenium in infammation and immunity: From molecular mechanisms to therapeutic opportunities. Assessment of whole body protein metabolism in criti- cally ill children: Can we use the [15N]glycine single oral dose method? Current recommended parenteral protein intakes do not support protein synthesis in critically ill septic, insulin-resistant adolescents with tight glucose control. Despite a general decrease in infectious disease mortality during the 20th century, increases in the infectious disease mortality among persons aged >65 years have been reported during the 1980s and 1990s due to increases in pneumonia and infuenza deaths. Multiple factors, including decline of immune function, comorbidities, changes in nutritional status due to alterations in intake and metabolism of nutrients, contribute to the increased susceptibility to infection in the elderly. In this chapter, we discuss the changes in immunity and nutritional status that accompany aging and the interaction between nutrient and infection. We review how nutritional status infuences susceptibility to infectious diseases and the impact of nutritional supplementation on infectious diseases in the elderly. Improvement in medical care, vaccination, living condition, and sanitation, contributed to the overall decline in infectious diseases mortality during the last century. Among the infectious diseases, infuenza and pneumonia contributed the most to the infectious disease mortality, averaging 44. Pronounced year-to-year fuctuation in infectious disease mortality among the old age group suggested large contributions of pneumonia and infuenza to mortality in this group. Infectious disease hospitalization rate was highest among those aged >80 years, followed by those <1 year, >70 years, and then >60 years. These mortality and hospitalization rates clearly show that infectious disease is a major health issue in the elderly. In addition to pneumonia and infuenza, certain infections, including urinary tract infection, diverticulitis, endocarditis, and bactere- mia, are more prevalent in the elderly compared with younger adults. Impaired adaptive immunity with aging has been well described; however, how aging affects innate immunity has been less clear. Age-related changes in effector functions such as decreased chemotaxis, phagocytosis of microbes, and generation of reactive oxygen species in response to stimulation have been reported in human neutrophils. However, excessive infammatory response due to increased infltration of neutrophils and excessive chemokine production after infection have been observed in aged animals. Macrophages play a key role in innate immunity by phagocytosing intracellular pathogens and in infammatory responses through the release of a variety of infam- matory mediators, including prostaglandins and proinfammatory cytokines. Age-associated changes in T cells occur at multiple levels, including changes in population, functionality, signal transduction, and gene transcription. These age-associated changes in T cells were only observed within naive T-cell subpopulations. Aged T cells cannot effectively form immunologic synapses or recruit signaling molecules. Physiological changes that occur with aging or associated with comorbidities contribute to the alteration in nutrient metabolism. Various factors, such as inability to purchase enough foods, poor appetite, and decreased capability to absorb nutrients, can contribute to insuffcient dietary intake. Lower status of several nutrients is a particular problem among the older population. Protein–energy malnutrition and lower plasma levels of zinc, vitamin D, and vitamin B have been reported to be more common in the elderly. Dietary intake analysis using National Health and Nutrition Examination Survey between 1988 and 1994 revealed that population >71 years old were at a greater risk of inadequate zinc intake. Nevertheless, decline in plasma selenium concentration with age was evident in the elderly population. A signifcant inverse correlation between plasma selenium and age was observed in both free-living and institutional- ized elderly. Of homebound elderly in Baltimore, 54% of com- munity dwellers and 38% of nursing home residents had the serum 25-hydroxyvita- min D levels < 25 nmol/L (10 ng/mL). Prospective studies that investigated nutritional changes after infection in humans, especially in the elderly, are limited. Cross-sectional studies that compared infectious disease patients with the healthy controls reported lower plasma nutrient concentrations in the patients. Among hospitalized patients, those with respiratory disease had the highest percentage of patients with <70 μg/dL zinc concentrations. Vitamin D defciency was associated with an increased risk of intensive care unit admission and 30-day mortality. Vitamin D levels were determined from the blood samples taken within 24 h of admission. Overall, 44% of patients had vitamin D levels < 50 nmol/L, and 15% of the patients were severely vitamin D defcient (<30 nmol/L). Patients with severe vitamin D defciency had signifcantly higher 30-day mortality compared with patients with mildly defcient (30–49 nmol/L) or suffcient vitamin D (≥50 nmol/L) levels. The unadjusted 30-day mortality was 5 of 17 among severely vitamin D–defcient patients, while it was 2 of 32 among mildly vitamin D–defcient and 2 of 63 among vitamin D–suffcient patients. Keshan disease seemed to be caused by multiple factors, and infections may be one of the etiologies. Coxsackievirus has been isolated from the blood and tissues of persons with Keshan disease.
Image quality and res- the models of critical anatomy were directly dis- olution differ widely generic prednisolone 20 mg fast delivery, with older technology using played as a transparent overlay in the stereo- image intensifers to newer technology using scopic viewport buy 5 mg prednisolone. However discount 40 mg prednisolone otc, in contrast to the motor-actuated fat-panel detectors that are syn- preoperative data and manual updates used by chronized with an X-ray source 5mg prednisolone otc. In designing a hybrid dered a virtual transparent sphere at an offset to operating room, the “free” or available the tip. The color of the sphere changed from workspace, after surgical setup, shared between green, to yellow, to red, when the estimated dis- an imaging system and a surgical robotic system, tance from tracked sphere was <=2 mm outside of must be evaluated. For otolaryngology, work- the margin, inside the margin by 2 mm, and inside space ergonomics were explored in a 2015 pre- the margin by 4 mm, respectively (Fig. Results 20 Intraoperative Imaging and Navigation in Robotic Surgery 207 from ex vivo and in vivo porcine models measur- real-time planar projection of the resection ing resection ratios showed improved resection throughout the procedure but also stereotactic tri- effciency, when comparing current practice to angulation, which is useful for tool localization their proposed dynamic visual navigation with . More confdence can be achieved by visual- explicit stereoscopic depth information. In a follow-up study, guidance in 3D in the primary visual feld for workspace ergonomics of the single-port da robotics in otolaryngology. Vinci® Sp and the zeego were investigated further The limitation from this experiment is the lack using a confguration for transoral intervention of continuous imaging updates to capture defor- (Fig. In these experiments, a cadaveric mation from resection as the intervention pro- model was injected with synthetic tumors, and gressed. From these images, the carotid the robotic arms positioned for intervention, they arteries were identifed (Fig. A superfcial cancer lesion, about superior constrictor muscle and medial to the 1. For this patient, the cancer lesion was Aloka Alpha 7 ultrasound system (Hitachi Aloka not recognizable by computed tomography, mag- Medical, Ltd. For applications in the posterior and metastasis nor distant metastasis was found on lateral oropharynx (e. The lesion was clinically diag- ryngeal space), a neuro-spine straight ultrasound nosed as T1N0M0. The extent of the lesion of tongue, a liver ultrasound probe was used was confrmed by iodine staining. This probe is aligned at a 90° angle and markings of the lesion and an incision line at the has a small tab on its backside that could be lower boundary of the lesion were made with the grasped with the Maryland dissector on the electric needle knife, and the procedure was robotic arm. For example, in a case involving a using the 8 mm Maryland dissector and 8 mm 210 W. No neck dissection was per- patients (group A) and using fuorescence navi- formed. The detection extent of the superfcial lesion precisely, which rate of sentinel nodes was 83 % (29/35 in group was benefcial in determining the extent of A) and 95 % (36/38 in group B), while the false- resection. Their results patients were identifed based on comorbid con- show that ultrasound could be used to character- ditions that resulted in a higher risk of fap fail- ize adjacent site involvement, midline, and ure, as well as the need for a locoregional fap for endophytic extent, in addition to visualizing the reconstruction. Following a vascular delay of In optical imaging for otolaryngology, research- 3 weeks, repeat measurements were substantially ers have shown extensive interest in the applica- improved. At 10–30 min after ical use of such promising agents has been dif- injection, they confrmed the visibility of bright fcult to achieve . Sahani D, Mehta A, Blake M, Prasad S, Harris G, shown added value for localization during neck Saini S. Cheng L, Cao R, Meng G, Huang Q, Hou D, Hu their use in routine clinical practice. Application of computer assisted navigation sys- tem in endoscopic sinus and skull base surgery. Hypoglossal technical advances over the last decade in nerve stimulation and airway changes under fuoros- copy. Skull Base: Off J North Am imaging can identify and preserve adjacent Skull Base Soc [et al]. Sonography-assisted geal and parapharyngeal spaces while maxi- cutting needle biopsy in the head and neck for the diagnosis of lymphoma: can it replace lymph node mizing and the adequacy of resection. Helbig M, Krysztoforski K, Krowicki P, Helbig S, the ability to treat pathology with greater pre- Gstoettner W, Kozak J. Wakasugi-Sato N, Kodama M, Matsuo K, Yamamoto including the use of very large robotic systems N, Oda M, Ishikawa A, Tanaka T, Seta Y, Habu M, without haptic feedback while operating in the Kokuryo S, Ichimiya H, Miyamoto I, Kito S, narrow, deep confnes of the head and neck, Matsumoto-Takeda S, Wakasugi T, Yamashita Y, Yoshioka I, Takahashi T, Tominaga K, Morimoto which can be disorienting. Advanced clinical usefulness of ultrasonography igation offers a promising tool to overcome for diseases in oral and maxillofacial regions. Clearly, researchers phy in the follow-up of patients with clinical N0 stage are pushing to adapt and evaluate diagnostic neck disease and oral cancer. Ultrasonographic demonstration but limited preclinical studies and clinical of retropharyngeal lymph nodes: preliminary report. Use of and cost-effectiveness of such technology transoral sonography with an endocavitary trans- ducer in diagnosis, fne-needle aspiration biopsy, and remain to be seen. Transoral carotid ultrasonography for evaluating T, Funakoshi M, Aoyama I, Hirano S, Kitamura M, internal carotid artery occlusion. Comparison of different computer-aided surgery guided fne-needle aspiration of the tongue base: a systems in skull base surgery. Imaging and visualization in the modern robotic surgery using an image guidance system. Intraoperative image- rescence imaging in robotic urologic surgery: a sys- guided transoral robotic surgery: pre-clinical stud- tematic review and critical analysis of the literature. Muto M, Nakane M, Katada C, Sano Y, Ohtsu A, transforms of binary images in arbitrary dimensions. Insight into effcient image registration techniques Murayama T, Kishimoto Y, Hayashi T, Funakoshi and the demons algorithm. Intraoperative ultrasonography during transoral online in Insight (Online Journal) [http://www. Impact of indocyanine green of da Vinci Si-assisted cochlear implant with aug- fuorescent image-guided surgery for parapharyn- mented visual navigation for otologic surgery. Contextual anatomic mimesis hybrid in-situ visu- lymph node biopsy using real-time fuorescence navi- alization method for improving multi-sensory depth gation with indocyanine green in head and neck skin perception in medical augmented reality. Ultrasound-guided methylene blue dye surgery and surgeon-performed trans-oral ultrasound injection for parathyroid localization in the reopera- for intraoperative location and excision of an isolated tive neck. Additionally, rele- the morbidity of these therapies while not com- vant complications of neck dissection and pre- promising oncologic outcome. Level V (posterior triangle) is the zone bounded by the anterior border of the trapezius An understanding of oropharyngeal lymphatic muscle and the posterior border of the sterno- drainage patterns is critical to the selection of cleidomastoid muscle. Level I posed, the medial border of the common carotid is divided into levels Ia (submental) and Ib (sub- artery . Level Ia is bounded by the digastric Lymphatic drainage patterns vary signif- muscles laterally, the mandible superiorly, and cantly from patient to patient, but in general the hyoid bone inferiorly. Level Ib is bounded by oropharyngeal tumors frst drain to the retro- the anterior and posterior bellies of the digastric pharyngeal and internal jugular nodal basins. It is posteri- nodal metastasis patterns of oropharyngeal and orly bounded by the posterior edge of the sterno- oral cavity squamous tumors was performed by cleidomastoid muscle and anteriorly by the Shah who reviewed 1,119 elective and therapeu- stylohyoid muscle. It is infrequently performed today; radical surgery is usually nec- essary for therapeutic neck dissection if key Fig. Furthermore, the cystic nature of tion and can be safely performed for appropriate oropharyngeal nodal metastases has also been cases. The precise reasons for the occurrence of cystic metastases in oropharyngeal carcinoma are unclear but have 21. Regardless of the precise mecha- metastases from these two distinct cancer sub- nism of formation of cystic nodal metastases in types have different characteristics and behavior. It should be approximately 50 %; however, recent analysis noted, however, that the presence of cystic cervi- has shown that this percentage has dramatically cal node metastases also occurs in other diseases increased to as high as 80 % currently in North processes as well, such as papillary thyroid carci- America and Europe . As a management strategy of the neck should differ result, elective neck dissection is usually offered between these two cancer subtypes. Here, we to patients with a clinically and radiographically outline our clinical practice in regard to the surgi- negative neck.
Experimental/intervention Studies Randomized Clinical trial Patients Controlled studies Field trial Healthy persons Community trial Community Communities intervention studies Non-Randomized — Patients The main aim of various study designs: 1 prednisolone 40mg online. Based on the existing state of knowledge about a problem that is being studied buy prednisolone 10mg on-line, different types of research questions may be asked which require different study designs (Table 6 buy prednisolone 5 mg low price. Descriptive (case studies/ not much known • How do the affected people cross-sectional studies) behave? Suspecting that certain • Do certain factors Analytical studies factors contribute to the really associate with Case-control/cohort stud- problem the problem? Case control/cohort studies Having adequate knowledge What is the effect of a Randomized/non- about a factor to develop and particular intervention? Exploratory studies gain in explanatory value if we approach the problem from different angles at the same time generic prednisolone 5mg with mastercard. In a study that is looking for causes of the low percentage of supervised deliveries, it may be very useful to include observations and interviews with health staff in the maternity centers that should serve the mothers in question and interviews with their supervisors, as well as with the mothers themselves. In this manner, information from different independent sources can be cross-checked. If the problem and its contributing factors are not well defined, it is always advisable to do an exploratory study before planning a large-scale descriptive or comparative study. Descriptive Studies A descriptive study involves describing the characteristics of a particular situation, event or case. The descriptive study can answer the research question by asking what, when, where, who, and how for an event (Table 6. Case Studies Case studies describe in-depth the characteristics of one or a limited number of ‘cases’. Case studies are common in social sciences, management sciences, and clinical medicine. For example, in clinical medicine the characteristics of a hitherto unrecognized illness may be documented as a case study. This is often the first step toward building up a clinical picture of that illness. Case Report Series Objective and brief report of a clinical characteristic or outcome from a group of clinical subjects. Generalization is not possible due to biased selection or unrepresentativeness of subjects, lack of control group, etc. Correlation Studies This study uses data from entire populations to compare disease frequency between different groups during the same period of time or in the same population at different points in time. The study showed that the higher intake of meat was associated with increased risk of colon cancer. It cannot estimate the individual’s risk but helps in stimulating hypothesis for under-taking analytic studies. It can be done quickly and less expensively as data are readily available on demography product, consumption which can be related to disease incidence, mortality or utilization of health services, etc. However, if one wishes to test whether the findings pertain to a larger population, a more extensive, cross-sectional survey has to be designed. Cross-Sectional Studies Cross-sectional study is also known as instantaneous study, Prevalence study and Simultaneous study. Study Design Options in Medical and Health Research 47 A cross-sectional study is an observational study and the investigator has no control over the exposure of interest (e. It includes identifying a defined population at a particular point in time, measuring a range of variables on an individual basis and at the same time measuring outcome of interest. There is no in-built directionality as both exposure and outcome are present in the study subject for quite some time. It deals with the situation existing at a given time (or during a given period) in a group or population. These may be related with the presence of disorders such as diseases, disabilities and symptoms of ill-health, dimensions of positive health, such as physical fitness, other attributes relevant to health such as blood pressure and body measurements, factors about health and disease such as exposure to specific environmental exposure or defined social and behavioral attributes and demographic attributes, determining the workload of personnel in a health program as given by prevalence, etc. A cross-sectional survey may be repeated in order to measure changes over time in the characteristics that were studied. In these cases only a limited number of variables will usually be included, in order to avoid problems with analysis and report writing. Small surveys can reveal interesting associations between certain variables, such as between having tuberculosis and socio- economic status, sex, and ways of coping. Cross-sectional surveys of morbidity and the health services utilization in different countries often give varying results, usually reflecting variations in survey methods as well as true difference between populations. Comparisons of morbidity and utilization rates can be masked by the absence of standardization in survey methods. Attention must be given to the purpose of the surveys; questionnaires must be well designed and sample chosen must be appropriate and representative. They include cases (people with disease of interest) and a suitable control group (people without that disease or outcome variable). Case control studies are also called as retrospective studies since the investigator is looking backwards from the disease to a possible cause (Fig. For example, in a hospital based case-control study where cases are being sought in the hospital, controls should normally be selected from patients attending the same hospital. If controls are selected from another hospital, they might not be from the same source population because the referral pathways may be different, and therefore they would not really be comparable to the cases. For example, in a study of the causes of neonatal death, the investigator will first select the ‘cases’ (children who died within the first month of life) and ‘controls’ (children who survived their first month of life). An important aspect of case-control study is the determination of the start and duration of exposure for cases and controls. In the case-control design, the exposure status of the cases is usually by direct questioning of the affected person or relative or friend. Exposure is sometimes determined by the biochemical measurement, which can be affected by the diseases. The predictor variable and outcome variable can be presented in a standard 2 × 2 contingency table and measurement of exposure can be calculated. The design of the same is given below: Standard 2 × 2 Table contingency Table Outcome variable/Effect/Disease Total Present(cases) Absent (control) Predictor Variable: Present a b a + b Cause Absent c d c + d Total a + c b + d a + b + c + d Cohort Studies The word ‘cohort’ has its origin in the Latin ‘cohors’ which refers to a group of warriors and gives notion of a group of persons proceeding together in time, i. Cohort study is also known as Follow-up, Longitudinal, Prospective and Incidence study. The cohort study is an observational epidemiological study which, after the manner of an experiment, attempts to study the relationship between a purported cause (exposure) and the subsequent risk of developing disease. Characteristics of cohort design • Groups are exposure based: The group or groups of persons to be studied are defined in terms of characteristics manifest prior to the appearance of the disease under investigation. Types of cohort studies • Historical/Retrospective/Non-concurrent • Prospective/Concurrent • Combined The distinction between retrospective and prospective cohort studies depends on whether or not the diseases have occurred in the cohort at the time the study begins. In a retrospective cohort study, all the relevant exposures and health outcomes have already occurred when the study is initiated. In a prospective cohort study, the relevant causes may or may not have occurred at the time the study begins, but the cases of disease have not yet occurred, and, following selection of the study cohort, the investigator must wait for the disease to appear in the cohort members. Design of cohort study Types of cohort studies Study Design Options in Medical and Health Research 51 Steps in conducting cohort study • Select suitable study and control cohorts • Data collection and measurement of exposure • Follow-up of cohort and outcome measurement. Study Cohorts There are various types of cohorts, following are some of the cohorts used for the studies. Special Exposure Cohorts: Samples are chosen on the basis of a particular exposure e. General Population Cohorts: Population groups offering special resources for follow-up or data linkage are chosen, and the individuals are subsequently allocated according to their exposure status, e. Closed or Fixed Cohorts: Fixed group of persons followed from a certain point in time until a defined endpoint, starting point-exposure defining event, endpoint—occurrence of the disease, loss to follow-up and death. Open or Dynamic Cohorts: Subjects may enter or leave the study at any time and exposure status may change over time. Control Cohort Selection of the control/comparison cohort depends on the type of comparison, e. Internal Comparison: Only one cohort identified and later on, classified into study and comparison cohort based on exposure, e. External comparison: More than one cohort in the study for the purpose of comparison, e. Comparison with general population rates: If no comparison group is available we can compare the rates of study cohort with general population, e. Exposure measurement Exogenous and/ or endogenous are important in a cohort study but there are challenges of prospective data collection with reference to choice of reference period, frequency of exposure update, changes in instrument over time, use of repeated measures and data collection costs (cost- efficient measurement methods).