NEET MDS Synopsis
Zygomatic Bone Reduction
General SurgeryZygomatic Bone Reduction
When performing a reduction of the zygomatic bone, particularly in the
context of maxillary arch fractures, several key checkpoints are used to assess
the success of the procedure. Here’s a detailed overview of the important
checkpoints for both zygomatic bone and zygomatic arch reduction.
Zygomatic Bone Reduction
Alignment at the Sphenozygomatic Suture:
While this is considered the best checkpoint for assessing the
reduction of the zygomatic bone, it may not always be the most practical
or available option in certain clinical scenarios.
Symmetry of the Zygomatic Arch:
Importance: This is the second-best checkpoint and
serves multiple purposes:
Maintains Interzygomatic Distance: Ensures that
the distance between the zygomatic bones is preserved, which is
crucial for facial symmetry.
Maintains Facial Symmetry and Aesthetic Balance:
A symmetrical zygomatic arch contributes to the overall aesthetic
appearance of the face.
Preserves the Dome Effect: The prominence of
the zygomatic arch creates a natural contour that is important for
facial aesthetics.
Continuity of the Infraorbital Rim:
A critical checkpoint indicating that the reduction is complete. The
infraorbital rim should show no step-off, indicating proper alignment
and continuity.
Continuity at the Frontozygomatic Suture:
Ensures that the junction between the frontal bone and the zygomatic
bone is intact and properly aligned.
Continuity at the Zygomatic Buttress Region:
The zygomatic buttress is an important structural component that
provides support and stability to the zygomatic bone.
Zygomatic Arch Reduction
Click Sound:
The presence of a click sound during manipulation can indicate
proper alignment and reduction of the zygomatic arch.
Symmetry of the Arches:
Assessing the symmetry of the zygomatic arches on both sides of the
face is crucial for ensuring that the reduction has been successful and
that the facial aesthetics are preserved.
Stages of anesthesia
Pharmacology
Stages of anesthesia
Stage I
Analgesia
Still conscious but drowsy
Stage II
Excitement stage
Loss of consciousness, however, irregular ventilation may be present which affects absorption of inhalation agents.
Reflexes may be exaggerated.
This is a very dangerous stage
Stage III
Surgical anesthesia
Loss of spontaneous movement
Regular, shallow respiration
Relaxation of muscles
Stage IV
Medullary paralysis
Death
Liners
Conservative DentistryLiners
Liners are relatively thin layers of material applied to the cavity
preparation to protect the dentin from potential irritants and to provide a
barrier against oral fluids and residual reactants from the restoration.
Types of Liners
1. Solution Liners
Composition: Based on non-aqueous solutions of acetone,
alcohol, or ether.
Example: Varnish (e.g., Copal Wash).
Composition:
10% copal resin
90% solvent
Setting Reaction: Physical evaporation of the solvent,
leaving a thin film of copal resin.
Coverage: A single layer of varnish covers
approximately 55% of the surface area. Applying 2-3 layers can increase
coverage to 60-80%.
2. Suspension Liners
Composition: Based on aqueous solvents (water-based).
Example: Calcium hydroxide (Ca(OH)₂) liner.
Indications: Used to protect dentinal tubules and
provide a barrier against irritants.
Disadvantage: High solubility in oral fluids, which can
limit effectiveness over time.
3. Importance of LinersA. Smear Layer
The smear layer, which forms during cavity preparation, can decrease
dentin permeability by approximately 86%, providing an additional protective
barrier for the pulp.
B. Pulp Medication
Liners can serve an important function in pulp medication, which helps
prevent pulpal inflammation and promotes healing. This is particularly
crucial in cases where the cavity preparation is close to the pulp.
Dextromethorphan
Pharmacology
Dextromethorphan
O-methylated dextrorphan, Excellent oral antitussive, No analgesic effect, No GI effects, No respiratory depression
Rotational Speeds of Dental Instruments
Conservative DentistryRotational Speeds of Dental Instruments
1. Measurement of Rotational Speed
Revolutions Per Minute (RPM)
Definition: The rotational speed of dental instruments
is measured in revolutions per minute (rpm), indicating how many complete
rotations the instrument makes in one minute.
Importance: Understanding the rpm is essential for
selecting the appropriate instrument for specific dental procedures, as
different speeds are suited for different tasks.
2. Speed Ranges of Dental Instruments
A. Low-Speed Instruments
Speed Range: Below 12,000 rpm.
Applications:
Finishing and Polishing: Low-speed handpieces are
commonly used for finishing and polishing restorations, as they provide
greater control and reduce the risk of overheating the tooth structure.
Cavity Preparation: They can also be used for
initial cavity preparation, especially in areas where precision is
required.
Instruments: Low-speed handpieces, contra-angle
attachments, and slow-speed burs.
B. Medium-Speed Instruments
Speed Range: 12,000 to 200,000 rpm.
Applications:
Cavity Preparation: Medium-speed handpieces are
often used for more aggressive cavity preparation and tooth reduction,
providing a balance between speed and control.
Crown Preparation: They are suitable for preparing
teeth for crowns and other restorations.
Instruments: Medium-speed handpieces and specific burs
designed for this speed range.
C. High-Speed Instruments
Speed Range: Above 200,000 rpm.
Applications:
Rapid Cutting: High-speed handpieces are primarily
used for cutting hard dental tissues, such as enamel and dentin, due to
their ability to remove material quickly and efficiently.
Cavity Preparation: They are commonly used for
cavity preparations, crown preparations, and other procedures requiring
rapid tooth reduction.
Instruments: High-speed handpieces and diamond burs,
which are designed to withstand the high speeds and provide effective
cutting.
3. Clinical Implications
A. Efficiency and Effectiveness
Material Removal: Higher speeds allow for faster
material removal, which can reduce chair time for patients and improve
workflow in the dental office.
Precision: Lower speeds provide greater control, which
is essential for delicate procedures and finishing work.
B. Heat Generation
Risk of Overheating: High-speed instruments can
generate significant heat, which may lead to pulpal damage if not managed
properly. Adequate cooling with water spray is essential during high-speed
procedures to prevent overheating of the tooth.
C. Instrument Selection
Choosing the Right Speed: Dentists must select the
appropriate speed based on the procedure being performed, the type of
material being cut, and the desired outcome. Understanding the
characteristics of each speed range helps in making informed decisions.
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
ENDOCRINE
Anatomy
ENDOCRINE
Endocrine glands have no ducts
They secrete into the blood from where the secretion (hormone) reaches a target cell
The following is a list of endocrine glands:
Hypophysis
Thyroid
Parathyroid
Adrenals
Islets of Langerhans
Pineal
Gonads
Hypophysis: Develops from oral ectoderm and nerve tissue, The oral part forms an upgrowth with an invagination (Rathke's pouch) The nervous part grows from the floor of the diencephalon - staying intact .The oral part separates from the mouth
Ectoderm – adenohypophysis - pars tuberalis
- pars distalis
- pars intermedia .
Diencephalon – neurohypophysis - pars nervosa .
- infundibulum
- median eminence
Rathke's pouch remains as Rathke's cysts
Pars Distalis: Forms 75% of the gland, The cells form cords, with fenestrated capillaries in-between
2 Cell types:
Chromophobes : 50% of the cells, do not stain lie in groups, they are resting chromophils
granules have been used
Chromophils: Stain
They can be subdivided according to their reaction with different stains
Acidophils (40%) :Cells have acidophilic granules in their cytoplasm. The cells are secretory.
They have a well developed EPR and Golgi apparatus.They have secretory granules.
subdivided into:
- Somatotropin cells: secrete somatotropin (growth hormone)
- Mammotropic cells: secrete prolactin
Basophils (10%) : These cells have basophilic granules in their cytoplasm and can be subdivided into:
Thyrotropin cells: secrete thyroid - stimulating hormone (TSH)
Corticotrophin cells: secrete adrenocorticotropic (ACTH)
Gonadotropic cells: secrete two hormones: Follicle stimulating hormone (FSH):
Stimulate follicle development and spermatogenesis
Luteinizing hormone (LH): Stimulate the formation of the corpus luteum and Leydig cells
Pars Tuberalis: Cells lie around the infundibulum . It is continuous with the pars distalis
Cells are cuboidal with no granules. Their function is unknown
Pars Intermedia: Poorly developed in the human. Follicles lined by cuboidal cells and filled with colloid are found Known as Rathke's cysts .There are also a few big basophilic cells
Their function is unknown
Pars Nervosa: Contains: - myelinated axons pituicytes, blood vessels
Axons:
The cell bodies of the axons lie in the supra-optic and paraventricular nuclei of the hypothalamus .From the cell bodies the axons go through the infundibulum forming the hypothalamohypophyseal tract to end in the pars nervosa
The axons have dilated blind endings filled with hormones (Herring bodies) coming from the cell bodies.
Two hormones are secreted:
Oxytoxin: - Cause contraction of the uterus
- Cause contraction of the myoepithelial cells of the milkgland
- The hormone is secreted by the paraventricular nuclei
Vasopressin :- Cause reabsorption of H2O in the kidney (also known as antidiuretic hormone ADH) The hormone is secreted by the supraoptic nuclei. A hypophyseal portal system exists
A primary capillary plexus of fenestrated capillaries form around the median eminence. Inhibitory hormones are secreted into these capillaries
The capillaries rejoin to form the portal veins that traverse the pituitary stalk
The portal veins break up into a secondary capillary plexus which lies close to the cells of the adenohypophysis
This portal system regulates the functions of the anterior pituitary function.
Pineal
Surrounded by pia which sends septae into the gland Cells are mainly pinealocytes and astroglial cells
Pinealocytes:Irregular shaped cells. with processes ending in flattened dilatations
Have a well developed smooth surfaced endoplasmic reticulum, Also a rough EPR not well developed, Lots of microtubules
Astroglial Cells: Elongated nucleus, Cells have long processes, They perform a supporting function
Hormones:
Melatonin - secreted during the night .suppress the onset of puberty
Serotonin - secreted during the day
In humans the pineal form concretions of calcified material called brain sand
Brain sand vary in size and number with age and is visible on X-rays
Mast cells are also found in the pineal and cause the high histamine contend of the gland
THYROID
Has a CT capsule that sends septae into the gland to divide it up into incomplete lobes and lobules. In the lobules are follicles, Follicles vary in size, They are surrounded by surrounded by reticular CT and capillaries
Cells of the Follicle:
Follicular Cells : Single layer of cuboidal cells, lie around the colloid, Follicular cells can become columnar when very active, Nucleus central, EPR has wide cisternae ,Golgi present
microvilli on the free surface
Parafollicular Cells: Also known as C-cells, Form part of the epithelium or form clusters between the follicles
- They never come into contact with the colloid
- Larger and stain less intensely than the follicular cells, Form 2% of the cells, Secrete calcitonin
Hormones: Thyroxine and thyriodothyronine - stimulate the metabolic rate, Calcitonin - lower the blood calcium
Parathyroid:
Has a CT capsule which send septae into the gland to divide it up into incomplete lobules, The CT contains fat which increase with age - may eventually be 50% of the gland, Glandular cells are arranged in cords
Glandular Cells:
Chief Cells: Small cells so their nuclei lie close together, Rich in glycogen, Biggest omponent
Secrete parathyroid hormone - essential for life
Oxyphil Cells:Develop at puberty, Bigger than the chief cells, Nuclei are smaller, Acidophilic
Hormones:
Parathyroid hormone - regulate calcium and phosphate ions in the blood
ADRENAL
- Thick CT capsule that do not send septae into the gland
Cortex:
Has 3 layers
Zona glomerulosa: 15% of the cortex, Directly under the capsule, Cells are columnar or pyramidal, Arranged in small groups or clusters, Wide fenestrated capillaries surround the clusters, Cells have an extensive smooth EPR
Zona Fasciculata: 78% of the cortex, Cells are arranged in cords ,1 to 2 cells wide perpendicular to the surface, Sinusoids lie between the cords, Cells are polyhedral with a central nucleus which is bigger than that of the zona glomerulosa, Lots of lipid in the cytoplasm cause the cells to stain lightly, Cells have a well developed smooth and rough EPR
The mitochondria in the cells are round with tubular or vesicular cristae
Zona Reticularis: 7% of the cortex, Cells form a network of cords with wide capillaries in-between The mitochondria in the cells are more ofte6n elongated than that in the zona fasciculate Degenerating cells with pyknotic nuclei are found. Cells contain numerous large lipofuscin granules. Cells of the cortex do not store their secretions but form and secrete on demand.
Hormones:
3 Groups:
Glucocorticoids (e.g. cortisol) - have an affection on carbohydrate metabolism
Mineralocorticoid (e.g. aldosterone) - control water and electrolyte balans
Androgens (e.g. dehyroepiandrosterone) - not very important
Medulla:
- Cells are big and oval and lie in groups and cords around bloodvessels
- Oxidising agents stain the granules in these cells brown - cells are therefore called chromaffin cells
- Granules contain adrenaline or non-adrernalin
- A few parasympathetic ganglion cells are also present
Hormones:
- Adrenaline - increase oxygen uptake
- increase blood pressure
- Noradrenaline - maintain blood pressure
Blood Supply:
- Blood vessel enter from the capsule to form the wide capillaries
- They flow into venules that form a central vein
- Between the endothelium of the capillaries and the glandular cells there is a subendothelial
- space.
- The glandular cells have microvilli protruding into this space.
ISLES OF LANGERHANS
Endocrine part of pancreas. The isles are round clusters in the exocrine tissue
- 100 - 200 µm
Islands consists of slightly stained polygonal or rounded cells, The cells are separated by fenestrated capillaries
- Autonomic nerve fibres innervate the blood vessels and the island cells
- 4 different cell types have been described
A cells : 20% of the cells, Bigger than B cells, Lie at the periphery, Have secretory granules ,Contain glucagon
B cells : 80%, Lie in the centre of the island, The cells are small with granules which are crystals, Granules are formed by insulin
D cells : Not numerous, Membrane bound granules, Store somatostatin (inhibit somatotropin)
F cells : Have membrane bound granules, Store pancreatic polypeptide, The hormone inhibits pancreatic exocrine secretion
CHRONIC INFLAMMATlON
General Pathology
CHRONIC INFLAMMATlON
When the inflammatory reaction instead of subsiding after the acute phase (or without entering an acute phase), persists as a smouldering lesion, it is called chronic inflammation. .
Characteristics
Predominantly mononuclear response.
Inflamation.and..repair going on simultaneously.
Usually results in more prominent-scarring.
Causes:
Chronicity may be due to :
- Defective defence mechanisms.
- Persistence of injurious agent.
(a) Certain organisms resist phagocytosis and destruction e.g tubercle bacillus, fungi
(b) insoluble particulate matter e.g., crystals. fibres suture materials.
(c) Constants supply of causative agent as in autoimmune disease where body reacts against its own tissues.
- Defective healing.
Granulomatous inflammation
It is a type of chronic inflammation characterised by localised collections of histiocytes.
These cells are usually accompanied by lymphocytes, fibroblasts and giant cells also.
Granulomas are characteristically seen in diseases like tuberculosis. syphilis, leprosy, sarcoidosis, fungal infections etc. In some of these, the lesion is morphologically distinct enough to point to the type of underlying disease. These are sometimes called' specific' granulomas. Granulomas can also be elicited by particulate, insoluble foreign material e.g. granuloma, suture granuloma, cholesterol granuloma (organising haemorrhages).