NEET MDS Synopsis
Mechanical properties
Dental Materials
Mechanical properties
1. Resolution of forces
Uniaxial (one-dimensional) forces-compression, tension, and shear
Complex forces-torsion, flexion. And diametral
2. Normalization of forces and deformatations
Stress
Applied force (or material’s resistance to force) per unit area
Stress-force/area (MN/m2)
Strain
Change in length per unit of length because of force
Strain-(L- Lo)/(Lo); dimensionless units
3. Stress-strain diagrams
Plot of stress (vertical) versus strain (horizontal)
Allows convenient comparison of materials
Different curves for compression, tension, and shear
Curves depend on rate of testing and temperature
4. Analysis of curves
Elastic behavior
Initial response to stress is elastic strain
Elastic modulus-slope of first part of curve and represents stiffness of material or the resistance to deformation under force
Elastic limit (proportional limit)- stress above which the material no longer behaves totally elastically
Yield strength-stress that is an estimate of the elastic limit at 0.002 permanent strain
Hardness-value on a relative scale that estimates the elastic limit in terms of a material’s resistance to indentation (Knoop hardness scale, Diamond pyramid, Brinnell, Rockwell hardness scale, Shore A hardness scale, Mohs hardness scale
Resilience-area under the stress strain curve up to the elastic limit (and it estimates the total elastic energy that can be absorbed before the onset of plastic deformation)
Elastic and plastic behavior
Beyond the stress level of the elastic limit, there is a combination of elastic and plastic strain
Ultimate strength-highest stress reached before fracture; the ultimate compressive strength is greater than the ultimate shear strength and the ultimate tensile strength
Elongation (percent elongation)- percent change in length up to the point of fracture = strain x 100%
Brittle materials-<5% elongation at fracture
Ductile materials->5% elongation at fracture
Toughness-area under the stress strain curve up to the point of fracture (it estimates the total energy absorbed up to fracture)
Time-dependent behavior
the faster a stress is applied, the more likely a material is to store the energy elastically and not plastically
Creep-strain relaxation
Stress relaxation
Mylohyoid Muscle
AnatomyMylohyoid Muscle
Origin: Mylohyoid line of the mandible.
Insertion: Median raphe and body of the hyoid bone.
Nerve Supply: Nerve to mylohyoid (branch of the
trigeminal nerve, CN V3).
Arterial Supply: Sublingual branch of the lingual
artery and submental branch of the facial artery.
Action: Elevates the hyoid bone, base of the tongue,
and floor of the mouth; depresses the mandible.
Autoimmune Diseases
General Pathology
Autoimmune Diseases
These are a group of disease where antibodies (or CMI) are produced against self antigens, causing disease process.
Normally one's immune competent cells do not react against one's own tissues.
This is due to self tolerance acquired during embryogenesis. Any antigen encountered at
that stage is recognized as self and the clone of cells capable of forming the corresponding antibody is suppressed.
Mechanism of autoimmunity
(1) Alteration of antigen
-Physicochemical denaturation by UV light, drugs etc. e.g. SLE.
- Native protein may turn antigenic when a foreign hapten combines with it, e.g. Haemolytic anemia with Alpha methyl dopa.
(2) Cross reaction: Antibody produced against foreign antigen may cross react with native protein because of partial similarity e.g. Rheumatic fever.
(3) Exposure of sequestered antigens: Antigens not normally exposed to immune competent cells are not accepted as self as tolerance has not been developed to them. e.g. thyroglobulin, lens protein, sperms.
(4) Breakdown of tolerance :
- Emergence of forbidden clones (due to neoplasia of immune system as in lymphomas and lymphocytic leukaemia)
- Loss of suppressor T cells as in old age and CMI defects
Autoimmunity may be
- Organ specific.
- Non organ specific (multisystemic)
I. Organ specific.
(I) Hemolytic anaemia:
- Warm or cold antibodies (active at 37° C or at colder temperature)
- They may lyse the RBC by complement activation or coat them and make them vulnerable to phagocytosis
(ii) Hashimoto's thyroiditis:
- Antibodies to thyroglobulin and microsomal antigens.
- Cell mediated immunity.
- Leads to chronic. destructive thyroiditis.
(3) Pernicious anemia
Antibodies to gastric parietal cells and to intrinsic factor.
2. Non organ specific.
Lesions are seen in more than one system but principally affect blood vessels and connective tissue (collagen diseases).
(I) Systemic lupus erythematosus (SLE). Antibodies to varied antigens are seen. Hence it is possible that there is abnormal reactivity of the immune system in self recognition.
Antibodies have been demonstrated against:
- Nuclear material (antinuclear I antibodies) including DNA. nucleoprotein etc. Anti nuclear antibodies are demonstrated by LE cell test.
- Cytoplasmic organelles- mitochondria, rib osomes, Iysosomes.
- Blood constituents like RBC, WBC. platelets, coagulation factors.
Mechanism. Immune complexes of body proteins and auto antibodies deposit in various organs and cause damage as in type III hypersensitivity
Organs involved
- Skin- basal dissolution and collagen degeneration with fibrinoid vasculitis.
- Heart- pancarditis.
- Kidneys- glomerulonephritis of focal, diffuse or membranous type
- Joints- arthritis.
- Spleen- perisplenitis and vascular thickening (onion skin).
- Lymph nodes- focal necrosis and follicular hyperplasia.
- Vasculitis in other organs like liver, central or peripheral nervous system etc,
2. Polyarteritis nodosa. Remittant .disseminated necrotising vasculitis of small and medium sized arteries
Mechanism :- Not definitely known. Proposed immune reaction to exogenous or auto antigens
Lesion : Focal panarteritis- a segment of vessel is involved. There is fibrinoid necrosis with initially acute and later chronic inflammatory cells. This may result in haemorrhage and aneurysm.
Organs involved. No organ or tissue is exempt but commonly involved organs are :
- Kidneys.
- Heart.
- Spleen.
- GIT.
3. Rheumatoid arthritis. A disease primarily of females in young adult life.
Antibodies
- Rheumatoid factor (An IgM antibody to self IgG)
- Antinuclear antibodies in 20% patients.
Lesions
- Arthritis which may progress on to a crippling deformity.
- Arteritis in various organs- heart, GIT, muscles.
- Pleuritis and fibrosing alveolitis.
- Amyloidosis is an important complication.
4. Sjogren's Syndrome. This is constituted by
- Kerato conjunctivitis sicca
- Xerostomia
- Rheumatoid arthritis.
Antibodies
- Rheumatoid factor
- Antinuclear factors (70%).
- Other antibodies like antithyroid, complement fixing Ab etc
- Functional defects in lymphocytes. There is a higher incidence of lymphoma
5. Scleroderma (Progressive systemic sclerosis)
Inflammation and progressive sclerosis of connective tissue of skin and viscera.
Antibodies
- Antinuclear antibodies.
- Rheumatoid factor. .
- Defect is cell mediated.
lesions
- Skin- depigmentation, sclerotic atrophy followed by cakinosis-claw fingers and mask face.
- Joints-synovitis with fibrosis
- Muscles- myositis.
- GIT- diffuse fibrous replacement of muscularis resulting in hypomotility and malabsorption
- Kidneys changes as in SLE and necrotising vasculitis.
- Lungs – fibrosing alveolitis.
- Vasculitis in any organ or tissue.
6.Wegener’s granulomatosis. A complex of:
- Necrotising lesions in upper respiratory tract.
- Disseminated necrotising vasculitis.
- Focal or diffuse glomerulitis.
Mechanism. Not known. It is classed with autoimmune diseases because of the vasculitis resembling other immune based disorders.
Types of Removable Orthodontic Appliances
OrthodonticsTypes of Removable Orthodontic Appliances
Functional Appliances:
Purpose: Designed to modify the growth of the jaw
and improve the relationship between the upper and lower teeth.
Examples:
Bionator: Encourages forward positioning of the
mandible.
Frankel Appliance: Used to modify the position
of the dental arches and improve facial aesthetics.
Retainers:
Purpose: Used to maintain the position of teeth
after orthodontic treatment.
Types:
Hawley Retainer: A custom-made acrylic plate
with a wire framework that holds the teeth in position.
Essix Retainer: A clear, plastic retainer that
fits over the teeth, providing a more aesthetic option.
Space Maintainers:
Purpose: Used to hold space for permanent teeth
when primary teeth are lost prematurely.
Types:
Band and Loop: A metal band placed on an
adjacent tooth with a loop extending into the space.
Distal Shoe: A space maintainer used in the
lower arch to maintain space for the first molar.
Aligners:
Purpose: Clear plastic trays that gradually move
teeth into the desired position.
Examples:
Invisalign: A popular brand of clear aligners
that uses a series of custom-made trays to achieve tooth movement.
Expansion Appliances:
Purpose: Used to widen the dental arch,
particularly in cases of crossbite or narrow arches.
Examples:
Rapid Palatal Expander (RPE): A device that
applies pressure to the upper molars to widen the maxilla.
Components of Removable Orthodontic Appliances
Baseplate: The foundation of the appliance, usually
made of acrylic, which holds the other components in place.
Active Components: Springs, screws, or other mechanisms
that exert forces on the teeth to achieve movement.
Retention Components: Clasps or other features that
help keep the appliance securely in place during use.
Adjustable Parts: Some appliances may have adjustable
components to fine-tune the force applied to the teeth.
Indications for Use
Correction of Malocclusions: Removable appliances can
be used to address various types of malocclusions, including crowding,
spacing, and crossbites.
Space Maintenance: To hold space for permanent teeth
when primary teeth are lost prematurely.
Tooth Movement: To move teeth into desired positions,
particularly in growing patients.
Retention: To maintain the position of teeth after
orthodontic treatment.
Jaw Relationship Modification: To influence the growth
of the jaw and improve the relationship between the dental arches.
Advantages of Removable Orthodontic Appliances
Patient Compliance: Patients can remove the appliance
for eating, brushing, and social situations, which can improve compliance.
Hygiene: Easier to clean compared to fixed appliances,
reducing the risk of plaque accumulation and dental caries.
Flexibility: Can be adjusted or modified as treatment
progresses.
Less Discomfort: Generally, removable appliances are
less uncomfortable than fixed appliances, especially during initial use.
Aesthetic Options: Clear aligners and other aesthetic
appliances can be more visually appealing to patients.
Disadvantages of Removable Orthodontic Appliances
Compliance Dependent: The effectiveness of removable
appliances relies heavily on patient compliance; if not worn as prescribed,
treatment may be delayed or ineffective.
Limited Force Application: They may not be suitable for
complex tooth movements or significant skeletal changes.
Adjustment Period: Some patients may experience
discomfort or difficulty speaking initially.
Antimania Drugs
Pharmacology
Antimania Drugs
MANIC SYMPTOMSMANIC SYMPTOMS
Elevated or irritable mood
Increased activity or psychomotor agitation
Reduced need for sleep
Inflated self esteem or grandiosity
Increased or pressure of speech
Flight of ideas
These drugs are used to treat manic-depressive illness.
1. Lithium
2. Carbamazepine
3. Valproic acid
Mechanisms of action
1. Lithium works inside the cell to block conversion of inositol phosphate to inositol.
2. Carbamazepine blocks sodium channels
3. Valproic acid blocks sodium and calcium channels
PHARMACOKINETICS
Absorbed readily and almost completely from the GI tract; peak concentrations in 1-2 hrs
Lithium toxicity
1. Nausea, diarrhea, convulsions, coma, hyperreflexia, cardiac arrhythmias, hypotension.
2. Thyroid enlargement; increases thyroid stimulating hormone (TSH) secretion; may cause hypothyroidism.
3. Polydipsia, polyuria (lithium inhibits the effect of antidiuretic hormone on the kidney).
Clinical applications concerning lithium
- Patients must be warned against sodium-restricted diets because sodium restriction leads to greater retention of lithium by the kidney.
- Patients must have regular (e.g., monthly) blood checks because the margin of safety is narrow.
Endocrine Effects – Goitre and hypothyroidism commonly
Cardiac Effects:– ECG changes(common) - T-wave flattening/inversion and appearance of U wavesflattening/inversion and appearance of U waves
Li and Pregnancy -1st Trimester:Cardiovascular anomalies of the newborn, especially Ebstein's malformation
- 3rd Trimester: Neonatal goiter, CNS depression, hypotonia ("floppy baby" syndrome)
Drug–drug interactions of lithium
Diuretics and newer nonsteroidal anti-inflammatory drugs (NSAIDs) reduce lithium excretion and may cause lithium toxicity.
HERPES SIMPLEX
General Pathology
HERPES SIMPLEX
An infection with herpes simplex virus characterized by one or many clusters of small vesicles filled with clear fluid on slightly raised inflammatory bases.
The two types of herpes simplex virus (HSV) are HSV-1 and HSV-2. HSV-1 commonly causes herpes labialis, herpetic stomatitis, and keratitis; HSV-2 usually causes genital herpes, is transmitted primarily by direct (usually sexual) contact with lesions, and results in skin lesions
Primary infection of HSV-1 typically causes a gingivostomatitis, which is most common in infants and young children. Symptoms include irritability, anorexia, fever, gingival inflammation, and painful ulcers of the mouth.
Primary infection of HSV-2 typically occurs on the vulva and vagina or penis in young adults
Herpetic whitlow, a swollen, painful, and erythematous lesion of the distal phalanx, results from inoculation of HSV through a cutaneous break or abrasion and is most common in health care workers.
Functions in Different Regions of the Cortex
Physiology
Sensory:
Somatic (skin & muscle) Senses:
Postcentral gyrus (parietal lobe). This area senses touch, pressure, pain, hot, cold, & muscle position. The arrangement is upside-down (head below, feet above) and is switched from left to right (sensations from the right side of the body are received on the left side of the cortex). Some areas (face, hands) have many more sensory and motor nerves than others. A drawing of the body parts represented in the postcentral gyrus, scaled to show area, is called a homunculus .
Vision:
Occipital lobe, mostly medial, in calcarine sulcus. Sensations from the left visual field go to the right cortex and vice versa. Like other sensations they are upside down. The visual cortex is very complicated because the eye must take into account shape, color and intensity.
Taste:
Postcentral gyrus, close to lateral sulcus. The taste area is near the area for tongue somatic senses.
Smell:
The olfactory cortex is not as well known as some of the other areas. Nerves for smell go to the olfactory bulb of the frontal cortex, then to other frontal cortex centers- some nerve fibers go directly to these centers, but others come from the thalamus like most other sensory nerves
Hearing:
Temporal lobe, near junction of the central and lateral sulci. Mostly within the lateral sulcus. There is the usual crossover and different tones go to different parts of the cortex. For complex patterns of sounds like speech and music other areas of the cortex become involved.
Motor:
Primary Motor ( Muscle Control):
Precentral gyrus (frontal lobe). Arranged like a piano keyboard: stimulation in this area will cause individual muscles to contract. Like the sensory cortex, the arrangement is in the form of an upside-down homunculus. The fibers are crossed- stimulation of the right cortex will cause contraction of a muscle on the left side of the body.
Premotor (Patterns of Muscle Contraction):
Frontal lobe in front of precentral gyrus. This area helps set up learned patterns of muscle contraction (think of walking or running which involve many muscles contracting in just the right order).
Speech-Muscle Control:
Broca's area, frontal lobe, usually in left hemisphere only. This area helps control the patterns of muscle contraction necessary for speech. Disorders in speaking are called aphasias.
Perception:
Speech- Comprehension:
Wernicke's area, posterior end of temporal lobe, usually left hemisphere only. Thinking about words also involves areas in the frontal lobe.
Speech- Sound/Vision Association:
Angular gyrus, , makes connections between sounds and shapes of words
Barbiturates
Pharmacology
Barbiturates (BARBS):
were used for antianxiety, sedation but now replaced by BZs; for IV sedation & oral surgery
Advantages: effective and relatively inexpensive (common in third world countries), extensively studied so have lots of information about side effects/toxicity
Peripheral effects: respiratory depression (with ↑ dose), CV effects (↓ BP and HR at sedative-hypnotic doses), liver effects (bind CYP450 → induction of drug metabolism and other enzymes → ↑ metabolism of steroids, vitamins K/D, cholesterol, and bile salts)
General mechanisms: potently depress neuron activity in the reticular formation (pons, medulla) and cortex
o Bind barbiturate site on GABAA receptor → enhanced inhibitory effect and ↑ Cl influx; → ↓ frequency of Cl channel opening but ↑ open time of Cl channels (in presense of GABA) so more Cl enters channel (at high [ ] they directly ↑ Cl conductance in absence of GABA- act as GABA mimetics)
Metabolism: liver microsomal drug metabolizing enzymes; most are dealkylated, conjugated by glucoronidation; renal excretion
Uses: anticonvulsant, preoperative sedation, anesthesia
Side effects: sedation, confusion, weight gain, N/V, skin rash
Contraindications: pain (can ↑ sensitivity to painful situations → restlessness, excitement, and delirium) and pulmonary insufficiency (since BARBS → respiratory depression)
Drug interactions: have additive depressant affects when taken with other CNS depressants, enhance depressive effects (of antipsychotics, antihistamines, antiHTNs, ethanol, and TCAs), and accelerates metabolism (of β blockers, Ca-channel blockers, corticosteroids, estrogens, phenothiazines, valproic acid, and theophylline; occurs with chronic BARB ingestion)
Acute toxicity: lower therapeutic index; can be fatal if OD; BARB poisoning a major problem (serious toxicity at only 10x hypnotic dose; → respiratory depression, circulatory collapse, renal failure, pulmonary complications which can be life-threatening)
Symptoms: severe respiratory depression, coma, severe hypotension, hypothermia
Treatment: support respiration and BP, gastric lavage (if recent ingestion)
Tolerance: metabolic (induce hepatic metabolic enzymes, occurs within a few days), pharmacodynamic (↓ CNS response with chronic exposure occurs over several weeks; unknown mechanism), and cross tolerance (tolerance to other general CNS depressants)
Physical dependence: develops with continued use; manifest by withdrawal symptoms (mild = anxiety, insomnia, dizziness, nausea; severe = vomiting, hyperthermia, tremors, delirium, convulsions, death)
Other similar agents: meprobamate (Equanil; pharmacological properties like BZs and barbiturates but mechanism unknown) and chloral hydrate (common sedative in pediatric dentistry for diagnostic imaging; few adverse effects but low therapeutic index)
Other drugs for antianxiety: β-adrenoceptor blockers (e.g., propranolol; block autonomic effects- palpitations, sweating, shaking; used for disabling situational anxiety like stage fright), buspirone (partial agonist at serotonin 1A receptor, produces only anxiolytic effects so no CNS depression, dependence, or additive depression with ethanol but onset of action is 1-3 weeks), lodipem (not a BZ but does act at BZ receptors)