NEET MDS Synopsis
PHYSICAL PROPERTIES OF MATERIALS
Dental Materials
PHYSICAL PROPERTIES OF MATERIALS
Definite and precise terms are used to describe the physical properties of dental materials.
a. Hardness. Hardness is the measure of the resistance of a metal to indentation or scratching. It is an indication of the strength and wearability of an alloy or metal.
b. Ductility. Ductility is the measure of the capacity of a metal to be stretched or drawn by a pulling or tensile force without fracturing. This property permits a metal to be drawn into a thin wire.
c. Malleability. Malleability is the measure of the capacity of a metal to be extended in all directions by a compressive force, such as rolling or hammering. This property permits a metal to be shaped into a thin sheet or plate.
d. Flexibility and Elasticity. These terms differ in their technical definition but they are very closely related. Flexibility is the characteristic of a metal, which allows it to deform temporarily. The elasticity of a metal is used when it returns to its original shape when the load or force is removed.
e. Fatigue. Fatigue is the property of a metal to tire and to fracture after repeated stressing at loads below its proportional limit.
f. Structure (Crystalline or Grain Structure). Metals are crystalline and many of their physical properties depend largely upon the size and arrangement of their minute crystals called grains.
(1) Grain size. The size of the grains in a solidified metal depends upon the number of nuclei of crystallization present and the rate of crystal growth. In the practical sense, the faster a molten is cooled to solidification, the greater will be the number of nuclei and the smaller will be the grain size. Generally speaking, small grains arranged in an orderly fashion give the most desirable properties.
(2) Grain shape. The shape of the grains is also formed at the time of crystallization. If the metal is poured or forced into a mold before cooling, the grains will be in a flattened state. Metal formed by this method is known as cast metal. If the metal is shaped by rolling, bending, or twisting, the grains are elongated and the metal becomes a wrought wire.
g. Crushing Strength. Crushing strength is the amount of resistance of a material to fracture under compression.
h. Thermal Conductivity. Thermal conductivity is defined as the ability of a material to transmit heat or cold. A low thermal conductivity is desired in restorative materials used on the tooth whereas a high thermal conductivity is desirable where the material covers soft tissue.
TRICYCLIC ANTIDEPRESSANTS
Pharmacology
TRICYCLIC ANTIDEPRESSANTS
e.g. amitriptyline, imipramine, nortriptyline
Belong to first generation antidepressants
ACTION:
Inhibit 5-HT(5-hydroxytryptamine) and norepinephrine reuptake
slow clearance of norepinephrine & 5-HT from the synapse
enhance norepinephrine & 5-HT neuro-transmission
MODE OF ACTIONMODE OF ACTION
TCAs also block
– muscarinic acetylcholine receptors
– histamine receptors
– 5-HT receptors
– α1 adrenoceptors
Onset of antidepressant activity takes 2-3 weeks
PHARMACOKINETICS
- Readily absorbed from the gastro-intestinal tract
- Bind strongly to plasma albumin
- Has a large volume of distribution(as a result of binding to extravascular tissues)
- Undergo liver CYP metabolism into biologically active metabolites
- These metabolites are inactivated via glucuronidation and excreted in urine
ADVERSE DRUG REACTIONS
Antimuscarinic - dry mouth, blurred vision, constipation and urinary retention
Antihistamine – drowsiness
adrenoceptor blockage(+/- central effect) postural hypotension
Reduce seizure threshold
Testicular enlargement, gynaecomastia, galactorrhoea
AV-conduction blocks and cardiac arrhythmias
TOXICITY
- Fatal in toxicity
- Most important toxic effect is, slowing of depolarisation of the cardiac action potential by blocking fast sodium channels ("quinidine-like" effect)
- delays propagation of depolarisation through both myocardium and conducting tissue
- prolongation of the QRS complex and the PR/QT intervals
- predisposition to cardiac arrhythmias
DRUG INTERACTIONS
Pharmacodynamic:
– ↑ sedation with antihistamines, alcohol
– ↑ antimuscarinic effects with anticholinergics– ↑ antimuscarinic effects with anticholinergics
– Hypertension and arrhythmias with MAOIs- should be given at least 14 days apart
Pharmacokinetic (via altering CYP metabolism)
– ↓ plasma concentration of TCA by- carbamazepine, rifampicin
– ↑ plasma concentration of TCA by- cimetidine, calcium channel blockers,fluoxetine
OTHER CLINICAL USES OF AMITRIPTYLINE
- Treatment of nocturnal enuresis in children
- Treatment of neuropathic pain
- Migraine prophylaxis
TOOTH MORPHOLOGY
Dental Anatomy
TOOTH MORPHOLOGY
Descriptive anatomy
Median sagittal plane: the imaginary plane in the center that divides right from left.
Median line: an imaginary line on that plane that bisects the dental arch at the center.
Mesial: toward the center (median) line of the dental arch.
Distal: away from the center (median) line of the dental arch.
Occlusal plane: A plane formed by the cusps of the teeth. It is often curved, as in a cylinder. We will speak often of the occlusal surface of a tooth.
Proximal: the surface of a tooth that is toward another tooth in the arch.
Mesial surface: toward the midline.
Distal surface: away from the midline.
Facial: toward the cheeks or lips.
Labial: facial surface of anterior teeth (toward the lips).
Buccal: facial surfaceof anterior teeth (toward the cheeks).
Lingual: toward the tongue.
Occlusal: the biting surface; that surface that articulates with an antagonist tooth in an opposing arch.
Incisal: cutting edge of anterior teeth.
Apical: toward the apex, the tip of the root.
Muscles of the Pharynx
AnatomyMuscles of the Pharynx
This consists of three constrictor muscles and three muscles that descend from the styloid process, the cartilaginous part of the auditory tube and the soft palate.
External Muscles of the Pharynx
The paired superior, middle, and inferior constrictor muscles form the external circular part of the muscular layer of the wall.
These muscles overlap each other and are arranged so that the superior one is innermost and the inferior one is outermost.
These muscles contract involuntarily in a way that results in contraction taking place sequentially from the superior to inferior end of the pharynx.
This action propels food into the oesophagus.
All three constrictors of the pharynx are supplied by the pharyngeal plexus of nerves, which lies on the lateral wall of the pharynx, mainly on the middle constrictor of the pharynx.
This plexus is formed by pharyngeal branches of the glossopharyngeal (CN IX) and vagus (CN X) nerves.
The Superior Constrictor Muscle
Origin: pterygoid hamulus, pterygomandibular raphe, posterior end of the mylohyoid line of the mandible, and side of tongue.
Insertion: median raphe of pharynx and pharyngeal tubercle.
Innervation: though the pharyngeal plexus of nerves.
The pterygomandibular raphe is the fibrous line of junction between the buccinator and superior constrictor muscles.
The Middle Constrictor Muscle
Origin: stylohyoid ligament and greater and lesser horns of hyoid bone.
Insertion: median raphe of pharynx.
Innervation: through the pharyngeal plexus of nerves.
The Inferior Constrictor Muscle
Origin: oblique line of thyroid cartilage and side of cricoid cartilage.
Insertion: median raphe of pharynx.
Innervation: through the pharyngeal plexus of nerves.
The fibres arising from the cricoid cartilage are believed to act as a sphincter, preventing air from entering the oesophagus.
Gaps in the Pharyngeal Musculature
The overlapping arrangement of the three constrictor muscles leaves 4 deficiencies or gaps in the pharyngeal musculature.
Various structures enter and leave the pharynx through these gaps.
Superior to the superior constrictor muscle, the levator veli palatini muscle, the auditory tube, and the ascending palatine artery pass through a gap between the superior constrictor muscle and the skull.
Superior to the superior border of the superior constrictor, the pharyngobasilar fascia blends with the buccopharyngeal fascia to form, with the mucous membrane, the thin wall of the pharyngeal recess.
Between the superior and middle constrictor muscles, the gateway to the mouth, though which pass the stylopharyngeus muscle, the glossopharyngeal nerve (CN IX), and the stylohyoid ligament.
Between the middle and inferior constrictor muscles, the internal laryngeal nerve and the superior laryngeal artery and vein pass to the larynx.
Inferior to the inferior constrictor muscles, the recurrent laryngeal nerve and inferior laryngeal artery pass superiorly into the larynx.
MICROBIAL VIRULENCE FACTORS
General Microbiology
MICROBIAL VIRULENCE FACTORS
Microbial virulence factors are gene products required for a microbial pathogen to establish itself in the host. These gene products are located on the bacterial chromosome, or on mobile genetic elements, such as plasmids or transposons.
Primary pathogens express virulence factors that allow them to cause disease in the normal host.
Opportunistic pathogens are environmental organisms or normal flora that lack the means to overcome normal host defense mechanisms. They cause disease only when the normal host defenses are breached or deficient.
Virulence factors can be divided into several categories.
Skin - Propionibacterium acnes, Staphlococcus epidermis , diptheroids; transient colonization by Staphlococcus
aureus
Oral cavity - Viridans Streptococci, Branhamella species, Prevotella melaninogenicus, Actinomyces species, Peptostreptococcus species, other anaerobes
Nasopharynx Oral organisms; transient colonization by S. pneumoniae, Haemophilus species, N. meningitidis
Stomach Rapidly becomes sterile
Small intestine Scant
Colon - Bacteroides species, Clostridium species, Fusobacterium species, E. coli, Proteus species, Pseudomonas aeruginosa, Enterococcus species, other bacteria and yeasts
Vagina - Childbearing years:Lactobacillus species, yeasts, Streptococcus species
Prepuberty / Postmenopause: colonic and skin flora
A. Enzyme production can be of several types depending on the needs of the organism, its requirements for survival, and the local environment.
1. Hyaluronidase breaks down hyaluronic acid to aid in the digestion of tissue.
2. Protease digests proteins to enhance the spread of infections.
3. Coagulase allows coagulation of fibrinogen to clot plasma.
4. Collagenase breaks down collagen (connective tissues).
B. Toxins
1. Exotoxins are heat-labile proteins with specific enzymatic activities produced by many Gram-positive and Gram-negative organisms. Exotoxins are released extracellularly and are often the sole cause of disease.
a. Some toxins have several domains with discrete biological functions that confer maximal toxicity. An example is A-B exotoxin, where the B subunit binds to host tissue cell glycoproteins and the A subunit enzymatically attacks a susceptible target.
b. Many toxins are ADP-ribosylating toxins
2. Endotoxin is the heat-stable lipopolysaccharide moiety found in the outer membrane of Gram-negative organisms. when released by cell lysls, the lipid A portion of lipopolysaccharide can induce septic shock characterized by fever, acidosis, hypotension, complement consumption, and disseminated intravascular coagulation (DIC).
C. Surface components
may protect the organism from immune responses such as phagocytosis or aid in tissue invasion. For example, the polysaccharide capsules of H. influenzae type b and the acidic polysaccharide capsule of Streptococcus pneumoniae interfere with phagocytosis. Other surface proteins, such as adhesins or filamentous appendages (fimbriae, pili), are involved in adherence of invading microorganisms to cells of the host.
Classification
Pharmacology
Classification
1. Natural Alkaloids of Opium
Phenanthrenes -> morphine, codeine, thebaine
Benzylisoquinolines -> papaverine, noscapine
2. Semi-synthetic Derivatives
diacetylmorphine (heroin) hydromorphone, oxymorphone hydrocodone, oxycodone
3. Synthetic Derivatives
phenylpiperidines pethidine, fentanyl, alfentanyl, sufentnyl
benzmorphans pentazocine, phenazocine, cyclazocine
propionanilides methadone
morphinans levorphanol
Osteoporosis
General Pathology
Osteoporosis
is characterized by increased porosity of the skeleton resulting from reduced bone mass. The disorder may be localized to a certain bone (s), as in disuse osteoporosis of a limb, or generalized involving the entire skeleton. Generalized osteoporosis may be primary, or secondary
Primary generalized osteoporosis
• Postmenopausal
• Senile
Secondary generalized osteoporosis
A. Endocrine disorders
• Hyperparathyroidism
• Hypo or hyperthyroidism
• Others
B. Neoplasia
• Multiple myeloma
• Carcinomatosis
C. Gastrointestinal disorders
• Malnutrition & malabsorption
• Vit D & C deficiency
• Hepatic insufficiency
D. Drugs
• Corticosteroids
• Anticoagulants
• Chemotherapy
• Alcohol
E. Miscellaneous
• osteogenesis imperfecta
• immobilization
• pulmonary disease
Senile and postmenopausal osteoporosis are the most common forms. In the fourth decade in both sexes, bone resorption begins to overrun bone deposition. Such losses generally occur in areas containing abundant cancelloues bone such as the vertebrae & femoral neck. The postmenopausal state accelerates the rate of loss; that is why females are more susceptible to osteoporosis and its complications.
Gross features
• Because of bone loss, the bony trabeculae are thinner and more widely separated than usual. This leads to obvious porosity of otherwise spongy cancellous bones
Microscopic features
• There is thinning of the trabeculae and widening of Haversian canals.
• The mineral content of the thinned bone is normal, and thus there is no alteration in the ratio of minerals to protein matrix
Etiology & Pathogenesis
• Osteoporosis involves an imbalance of bone formation, bone resorption, & regulation of osteoclast activation. It occurs when the balance tilts in favor of resorption.
• Osteoclasts (as macrophages) bear receptors (called RANK receptors) that when stimulated activate the nuclear factor (NFκB) transcriptional pathway. RANK ligand synthesized by bone stromal cells and osteoblasts activates RANK. RANK activation converts macrophages into bone-crunching osteoclasts and is therefore a major stimulus for bone resorption.
• Osteoprotegerin (OPG) is a receptor secreted by osteoblasts and stromal cells, which can bind RANK ligand and by doing so makes the ligand unavailable to activate RANK, thus limiting osteoclast bone-resorbing activity.
• Dysregulation of RANK, RANK ligand, and OPG interactions seems to be a major contributor in the pathogenesis of osteoporosis. Such dysregulation can occur for a variety of reasons, including aging and estrogen deficiency.
• Influence of age: with increasing age, osteoblasts synthetic activity of bone matrix progressively diminished in the face of fully active osteoclasts.
• The hypoestrogenic effects: the decline in estrogen levels associated with menopause correlates with an annual decline of as much as 2% of cortical bone and 9% of cancellous bone. The hypoestrogenic effects are attributable in part to augmented cytokine production (especially interleukin-1 and TNF). These translate into increased RANK-RANK ligand activity and diminished OPG.
• Physical activity: reduced physical activity increases bone loss. This effect is obvious in an immobilized limb, but also occurs diffusely with decreased physical activity in older individuals.
• Genetic factors: these influence vitamin D receptors efficiency, calcium uptake, or PTH synthesis and responses.
• Calcium nutritional insufficiency: the majority of adolescent girls (but not boys) have insufficient dietary intake of calcium. As a result, they do not achieve the maximal peak bone mass, and are therefore likely to develop clinically significant osteoporosis at an earlier age.
• Secondary causes of osteoporosis: these include prolonged glucocorticoid therapy (increases bone resorption and reduce bone synthesis.)
The clinical outcome of osteoporosis depends on which bones are involved. Thoracic and lumbar vertebral fractures are extremely common, and produce loss of height and various deformities, including kyphoscoliosis that can compromise respiratory function. Pulmonary embolism and pneumonia are common complications of fractures of the femoral neck, pelvis, or spine.
Diphenoxylate
Pharmacology
Diphenoxylate (present in Lomotil)
A meperidine congener
Not absorbed very well at recommended doses.
Very useful in the treatment of diarrhea.