NEET MDS Synopsis
Tooth eruption Theories
Dental Anatomy
Tooth eruption Theories
Tooth eruption occurs when the teeth enter the mouth and become visible. Although researchers agree that tooth eruption is a complex process, there is little agreement on the identity of the mechanism that controls eruption. Some commonly held theories that have been disproven over time include: (1) the tooth is pushed upward into the mouth by the growth of the tooth's root, (2) the tooth is pushed upward by the growth of the bone around the tooth, (3) the tooth is pushed upward by vascular pressure, and (4) the tooth is pushed upward by the cushioned hammock. The cushioned hammock theory, first proposed by Harry Sicher, was taught widely from the 1930s to the 1950s. This theory postulated that a ligament below a tooth, which Sicher observed on under a microscope on a histologic slide, was responsible for eruption. Later, the "ligament" Sicher observed was determined to be merely an artifact created in the process of preparing the slide.
The most widely held current theory is that while several forces might be involved in eruption, the periodontal ligaments provide the main impetus for the process. Theorists hypothesize that the periodontal ligaments promote eruption through the shrinking and cross-linking of their collagen fibers and the contraction of their fibroblasts.
Although tooth eruption occurs at different times for different people, a general eruption timeline exists. Typically, humans have 20 primary (baby) teeth and 32 permanent teeth. Tooth eruption has three stages. The first, known as deciduous dentition stage, occurs when only primary teeth are visible. Once the first permanent tooth erupts into the mouth, the teeth are in the mixed (or transitional) dentition. After the last primary tooth falls out of the mouth—a process known as exfoliation—the teeth are in the permanent dentition.
Primary dentition starts on the arrival of the mandibular central incisors, usually at eight months, and lasts until the first permanent molars appear in the mouth, usually at six years. The primary teeth typically erupt in the following order: (1) central incisor, (2) lateral incisor, (3) first molar, (4) canine, and (5) second molar. As a general rule, four teeth erupt for every six months of life, mandibular teeth erupt before maxillary teeth, and teeth erupt sooner in females than males. During primary dentition, the tooth buds of permanent teeth develop below the primary teeth, close to the palate or tongue.
Mixed dentition starts when the first permanent molar appears in the mouth, usually at six years, and lasts until the last primary tooth is lost, usually at eleven or twelve years. Permanent teeth in the maxilla erupt in a different order from permanent teeth on the mandible. Maxillary teeth erupt in the following order: (1) first molar (2) central incisor, (3) lateral incisor, (4) first premolar, (5) second premolar, (6) canine, (7) second molar, and (8) third molar. Mandibular teeth erupt in the following order: (1) first molar (2) central incisor, (3) lateral incisor, (4) canine, (5) first premolar, (6) second premolar, (7) second molar, and (8) third molar. Since there are no premolars in the primary dentition, the primary molars are replaced by permanent premolars. If any primary teeth are lost before permanent teeth are ready to replace them, some posterior teeth may drift forward and cause space to be lost in the mouth. This may cause crowding and/or misplacement once the permanent teeth erupt, which is usually referred to as malocclusion. Orthodontics may be required in such circumstances for an individual to achieve a straight set of teeth.
The permanent dentition begins when the last primary tooth is lost, usually at 11 to 12 years, and lasts for the rest of a person's life or until all of the teeth are lost (edentulism). During this stage, third molars (also called "wisdom teeth") are frequently extracted because of decay, pain or impactions. The main reasons for tooth loss are decay or periodontal disease.
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
Streptomycin
Pharmacology
Streptomycin
Streptomycin was the first of a class of drugs called aminoglycosides to be discovered, and was the first antibiotic remedy for tuberculosis. It is derived from the actinobacterium Streptomyces griseus.
Streptomycin cannot be given orally, but must be administered by regular intramuscular injection.
Phospholipids Functions
Biochemistry
- There are two important phospholipids, Phosphatidylcholine and Phosphatidylserine found the cell membrane without which cell cannot function normally.
- Phospholipids are also important for optimal brain health as they found the cell membrane of brain cells also which help them to communicate and influence the receptors function. That is the reason food stuff which is rich in phospholipids like soy, eggs and the brain tissue of animals are good for healthy and smart brain.
- Phospholipids are the main component of cell membrane or plasma membrane. The bilayer of phospholipid molecules determine the transition of minerals, nutrients, and drugs in and out of the cell and affect various functions of them.
- As phospholipids are main component of all cell membrane, they influence a number of organs and tissues, such as the heart, blood cells and the immune system. As we grown up the amount of phospholipids decreases and reaches to decline.
- Phospholipids present in cell membrane provide cell permeability and flexibility with various substances as well its ability to move fluently. The arrangement of phospholipid molecules in lipid bilayer prevent amino acids, carbohydrates, nucleic acids, and proteins from moving across the membrane by diffusion. The lipid bi-layer is usually help to prevent adjacent molecules from sticking to each other.
- The selectivity of cell membrane form certain substances are due to the presence of hydrophobic and hydrophilic part molecules and their arrangement in bilayer. This bilayer is also maintained the normal pH of cell to keeps it functioning properly.
- Phospholipids are also useful in the treatment of memory problem associated with chronic substances as they improve the ability of organism to adapt the chronic stress.
Early Childhood Caries (ECC) Classification
Conservative DentistryEarly Childhood Caries (ECC) Classification
Early Childhood Caries (ECC) is a significant public health concern
characterized by the presence of carious lesions in young children. It is
classified into three types based on severity, affected teeth, and underlying
causes. Understanding these classifications helps in diagnosing, preventing, and
managing ECC effectively.
Type I ECC (Mild to Moderate)
A. Characteristics
Affected Teeth: Carious lesions primarily involve the
molars and incisors.
Age Group: Typically observed in children aged 2
to 5 years.
B. Causes
Dietary Factors: The primary cause is usually a
combination of cariogenic semisolid or solid foods, such as sugary snacks
and beverages.
Oral Hygiene: Lack of proper oral hygiene practices
contributes significantly to the development of caries.
Progression: As the cariogenic challenge persists, the
number of affected teeth tends to increase.
C. Clinical Implications
Management: Emphasis on improving oral hygiene
practices and dietary modifications can help control and reverse early
carious lesions.
Type II ECC (Moderate to Severe)
A. Characteristics
Affected Teeth: Labio-lingual carious lesions primarily
affect the maxillary incisors, with or without molar caries, depending on
the child's age.
Age Group: Typically seen soon after the first tooth
erupts.
B. Causes
Feeding Practices: Common causes include inappropriate
use of feeding bottles, at-will breastfeeding, or a combination of both.
Oral Hygiene: Poor oral hygiene practices exacerbate
the condition.
Progression: If not controlled, Type II ECC can
progress to more advanced stages of caries.
C. Clinical Implications
Intervention: Early intervention is crucial, including
education on proper feeding practices and oral hygiene to prevent further
carious development.
Type III ECC (Severe)
A. Characteristics
Affected Teeth: Carious lesions involve almost all
teeth, including the mandibular incisors.
Age Group: Usually observed in children aged 3
to 5 years.
B. Causes
Multifactorial: The etiology is a combination of
various factors, including poor oral hygiene, dietary habits, and possibly
socio-economic factors.
Rampant Nature: This type of ECC is rampant and can
affect immune tooth surfaces, leading to extensive decay.
C. Clinical Implications
Management: Requires comprehensive dental treatment,
including restorative procedures and possibly extractions. Education on
preventive measures and regular dental visits are essential to manage and
prevent recurrence.
Second Generation Cephalosporins
Pharmacology
Second Generation Cephalosporins
Prototype drug is CEFUROXIME (IV) and CEFUROXIME AXETIL (oral). CEFOXITIN has good activity vs. anaerobes.
1. Expanded activity against gram negative bacilli. Still have excellent activity against gram positive (Staph. and Strep.) bacteria.
Activity for Gram negative bacteria
Neisseria sp. (some gonococci resistant)
H. influenzae (including some ampicillin-resistant strains)
Moraxella catarrhalis (some resistance esp. to cefaclor)
E. coli
Proteus mirabilis
Indole + Proteus (some strains resistant)
Morganella morganii (some strains resistant)
Klebsiella pneumoniae
Serratia sp. (many strains resistant)
2. Anaerobic infections - CEFOXITIN & CEFOTETAN only
Moderate activity against Bacteroides fragilis group.
Good activity for other Bacteroides sp., Peptostreptococcus, Fusobacterium, Clostridium sp
Uses
1. Community-acquired pneumonia - Cefuroxime is widely used for empiric therapy. Has activity vs. many ampicillin-resistant H. influenzae strains.
2. Skin and soft tissue infection
3. Urinary tract infections
4. Upper respiratory tract infections (otitis media, sinusitis). Some resistance to H.influenzae to cefaclor (20-30%).
5. Mixed aerobic & anaerobic infections - Cefoxitin & Cefotetan. Resistance to B.fragilis is increasing.
6. Surgical prophylaxis - Cefoxitin or cefotetan are widely used in cases where mixed aerobic & anaerobic infections may occur, esp. intra-abdominal, colorectal, and gynecologic operations. For cardiovascular and orthopedic procedures, cefuroxime and others may be used, but cefazolin is cheaper and appears to work well.
Glasgow Coma Scale
Oral and Maxillofacial SurgeryGlasgow Coma Scale (GCS): Best Verbal Response
The Glasgow Coma Scale (GCS) is a clinical scale used to
assess a patient's level of consciousness and neurological function,
particularly after a head injury. It evaluates three aspects: eye opening,
verbal response, and motor response. The best verbal response (V) is one of the
components of the GCS and is scored as follows:
Best Verbal Response (V)
5 - Appropriate and Oriented:
The patient is fully awake and can respond appropriately to
questions, demonstrating awareness of their surroundings, time, and
identity.
4 - Confused Conversation:
The patient is able to speak but is confused and disoriented. They
may answer questions but with some level of confusion or incorrect
information.
3 - Inappropriate Words:
The patient uses words but they are inappropriate or irrelevant to
the context. The responses do not make sense in relation to the
questions asked.
2 - Incomprehensible Sounds:
The patient makes sounds that are not recognizable as words. This
may include moaning or groaning but does not involve coherent speech.
1 - No Sounds:
The patient does not make any verbal sounds or responses.
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