NEET MDS Synopsis
Bones of the thorax
AnatomySternum
o Forms the medial part of the anterior chest wall
o Manubrium (upper part)-clavicle and first rib articulate with the manubrium .
o Body (middle blade)-second and tenth ribs articulate with the body via the costal cartilages
o Xiphoid (blunt cartilaginous tip)
Ribs (12 pairs)
o Each rib articulates with both the body and the transverse process of its corresponding
o thoracic vertebra
o The second to ninth ribs articulate with the body of the vertebra above'
o Ribs curve outward, forward, and then downward
o Anteriorly, each of the first seven ribs joins a costal cartilage that attaches to the sternum
o Next three ribs (eighth to tenth) join the cartilage of the rib above
o Eleventh and twelfth ribs do not attach to the sternum; are called "floating ribs"
Alveolar bone (process)
Dental Anatomy
Alveolar bone (process)
1. The bone in the jaws that contains the teeth alveoli (sockets).
2. Three types of bone :
a. Cribriform plate (alveolar bone proper)
(1) Directly lines and forms the tooth socket. It is compact bone that contains many holes, allowing for the passage of blood vessels. It has no periosteum.
(2) Serves as the attachment site for PDL (Sharpey’s) fibers.
(3) The tooth socket is constantly being remodeled in response to occlusal forces. The bone laid down on the cribriform plate, which also provides attachment for PDL fibers, is known as bundle bone.
(4) It is radiographically known as the lamina dura.
b. Cortical (compact) bone
(1) Lines the buccal and lingual surfaces of the mandible and maxilla.
(2) Is typical compact bone with a periosteum and contains Haversian systems.
(3) Is generally thinner in the maxilla and thicker in the mandible, especially around the buccal area of the mandibular premolar and molar.
c. Trabecular (cancellous, spongy) bone
(1) Is typical cancellous bone containing Haversian systems.
(2) Is absent in the maxillary anterior teeth region.
3. Alveolar crest (septa)
a. The height of the alveolar crest is usually 1.5 to 2 mm below the CEJ junction.
b. The width is determined by the shape of adjacent teeth.
(1) Narrow crests—found between teeth with relatively flat surfaces.
(2) Widened crests—found between teeth with convex surfaces or teeth spaced apart.
Cushings syndrome
General Pathology
Cushing’s syndrome
The symptoms and signs of Cushing’s syndrome are associated with prolonged inappropriate elevation of free corticosteroid levels.
Clinical features
- Central obesity and moon face.
- Plethora and acne.
- Menstrual irregularity.
- Hirsutism and hair thinning.
- Hypertension.
- Diabetes.
- Osteoporosis—may cause collapse of vertebrae, rib fractures.
- Muscle wasting and weakness.
- Atrophy of skin and dermis—paper thin skin with bruising tendency, purple striae.
Aetiopathogenesis — patients with Cushing’s syndrome can be classified into two groups on the basis of whether the aetiology of the condition is ACTH dependent or independent.
Classification of Cushing's syndrome
ACTH dependent- Iatrogenic (ACTH therapy) Pituitary hypersecretion of ACTH Ectopic ACTH syndrome (benign or malignant non-endocrine tumour)
Non-ACTH dependent - Iatrogenic, e.g. prednisolone Adrenal cortical adenoma , Adrenal cortical carcinoma
ACTH-dependent aetiology:
- Pituitary hypersecretion of ACTH (Cushing’s disease)—bilateral adrenal hyperplasia secondary to excessive secretion of ACTH by a corticotroph adenoma of the pituitary gland.
- Production of ectopic ACTH or corticotrophin- releasing hormone (CRH) by non-endocrine neoplasm, e.g. small cell lung cancer and some carcinoid tumours. In cases of malignant bronchial tumour, the patient rarely survives long enough to develop any physical features of Cushing’s syndrome.
Non-ACTH-dependent aetiology
Iatrogenic steroid therapy—most common cause of Cushing’s syndrome.
Adrenal cortical adenoma—well-circumscribed yellow tumour usually 2–5 cm in diameter.
Extremely common as an incidental finding in up to 30% of all post-mortem examinations. The yellow colour is due to stored lipid (mainly cholesterol) from which the hormones are synthesised. The vast majority have no clinical effects (i.e. they are non-functioning adenomas), with only a small percentage producing Cushing’s syndrome.
Adrenal cortical carcinoma—rare and almost always associated with the overproduction of hormones, usually glucocorticoids and sex steroids.
Cushing’s syndrome mixed with androgenic effects which are particularly noticeable in women. Tumours are usually large and yellowish white in colour. Local invasion and metastatic spread are common.
Irrespective of the aetiology, the diagnosis is based on clinical features and the demonstration of a raised plasma cortisol level.
The aetiology of the disorder is elucidated through:
- Raised urinary cortisol in the first instance, but further testing is required.
- Low-dose dexamethasone suppression test (suppression of cortisol levels in Cushing’s disease due to suppression of pituitary ACTH secretion, but a lack of suppression suggests ACTH-independent Cushing’s syndrome).
- MRI and CT scan visualisation of pituitary and adrenal glands.
- Analysis of blood ACTH (high = pituitary adenoma or ectopic ACTH source; low = primary adrenal tumour due to feedback suppression).
- Treatment of the underlying cause is essential as untreated Cushing’s syndrome has a 50% 5-year mortality rate.
The therapeutic administration of glucocorticosteroids (e.g. prednisolone) is a common cause of the features of Cushing’s syndrome.
CASTING
Dental Materials
CASTING
Melting & Casting Technique Melting & Casting requires Heat source to melt the alloy Casting force, to drive the alloy into the mould
Casting Torch Selection Two type of torch tips: Multi-orifice Single-orifice Multi-orifice tip is widely used for metal ceramic alloys. Main advantage is distribution of heat over wide area for uniform heating of the alloy. Single-orifice tip concentrate more heat in one area.Three fuel sources are used for Casting Torch; Acetylene ,Natural Gas ,Propane
CASTING CRUCIBLES
Four types are available ;
1) Clay .
2) Carbon .
3) Quartz .
4) Zirconia –Alumina .
Casting Machines
It is a device which uses heat source to melt the alloy casting force .
Heat sources can be :
1) Reducing flame of a torch .( conventional alloys & metal ceramic alloys )
2) Electricity .(Base metal alloys )
Advantages of electric heating :
-heating is evenly controlled .
-minimal undesirable changes in the alloy composition .
- Appropriate for large labs .
Disadvantage :
Expensive .
Casting machines use :
1) Air pressure .
2) Centrifugal force .
3) Evacuation technique .
Alloys can be melted by :
1) Alloy is melted in a separate crucible by a torch flame & is cast into the mold by centrifugal force .(centrifugal C M )
2) Alloy is melted by resistance heating or by induction furnace & then cast centrifugally by motor or spring action (springwound CM electrical resistance )
3) Alloy is melted by induction heating cast into mold centrifugally by motor or spring action .(Induction CM )
4) Alloy is vacum melted by an argon atmosphere
Torch melting / Centrifugal casting machine
Electrical resistance /Heated casting machine
Melting of the alloy should be done in a graphite or ceramic crucible .
Advantage :
-Oxidation of metal ceramic restorations on
overheating is prevented .
-Help in solidification from tip of the casting to the button surface .
Induction casting machine
Commonly used for melting base metal alloys.
Advantage :
- Highly efficient .
- Compact machine withlow power consumption
-No pre heating needed ,
- safe & reliable.
Direct current arc melting machine
A direct current arc is produced between two electrodes :
The alloy & the water cooled tungsten electrode .Temp used is 4000 degrees .
Disadvanage :
High risk of overheating the alloy .
Vacuum or pressure assisted casting machine
Molten alloy is drawn into the evacuated mold by gravity or vacuum & subjected to aditional pressure
For Titanium & its alloys vacuum heated argon pressure casting machines are used .
Accelerated casting method
This method reduces the time of both bench set of the investment & burnout .
Uses phosphate bonded investments which uses 15 mnts for bench set & 15mnts for burnout by placing in a pre – heated furnace to 815 degrees .
Effect of burnout on gypsum bonded investments
Rate of heating has influence on smoothness & on overall dimensions of the investment
Rapid heating causes cracking & flaking which can cause fins or spines .
Avoid heating gypsum bonded investment above 700 degrees .Complete the wax elimination below that temp .
Effect of burnout on phosphate bonded investments
Usual burnout temp is 750 -1030 degrees.
Although they are strong they are brittle too .
Since the entire process takes a long time two stage burnout & plastic ring can be used .
OCCLUSION AND DENTAL DEVELOPMENT- Variation in Development
Dental Anatomy
1. Errors in development. These are usually genetic.
a. Variability of the individual teeth. In general, the teeth most distal in any class are the most variable.
b. Partial or total anodontia. missing teeth in children,
c. Supernumerary teeth.
d. Microdontia
e. Macrodontia
F. Microdontia
2. Errors in skeletal alignment. Malpositioned jaws disrupt normal tooth relationships.
3. Soft tissue problems.
-Ocasionally, the proper eruption of a tooth is prevented by fibrous connective tissue over the crown of the tooth.
-In the mixed dentition, the deciduous second molars have a special importance for the integrity of the permanent dentition. Consider this: The first permanent molars at age six years erupt distal to the second deciduous molars.
-Permanent posterior teeth exhibit physiological mesial drift, the tendency to drift mesially when space is available. If the deciduous second molars are lost prematurely, the first permanent molars drift anteriorly and block out the second premolars.
An incisor diastema may be present. The plural for diastema is diastemata.
-Important: The deciduous anteriors--incisors and canines are narrower than their permanent successors mesiodistally.
-Important: The deciduous molars are wider that their permanent successors mesiodistally.
-This size difference has clinical significance. The difference is called the leeway space.
The leeway space in the lower arch is approximately 3.4 mm.
-The leeway space in the upper arch is approximately 1.8 mm. In normal development, the leeway space is taken up by the mesial migration of the first permanent molars.
Principles of cutting, polishing, and surface cleaning
Dental Materials
Principles of cutting, polishing, and surface cleaning
Surface mechanics for materials
Cutting-requires highest possible hardness materials to produce cutting
Finishing-requires highest possible hardness materials to produce finishing, except at margins of restorations where tooth structure may be inadvertently affected
Polishing- requires materials with Mohs ./ hardness that is 1 to 2 units above that of substrate
Debriding-requires materials with Mohs hardness that is less than or equal to that of substrate to prevent scratching
Factors affecting cutting, polishing. and surface cleaning
Applied pressure
Particle size of abrasive
Hardness of abrasive
Hardness of substrate
Precautions
During cutting heat will build up and change the mechanical behavior of the substrate from brittle to ductile and encourage smearing
Instruments may transfer debris onto the cut surface from their own surfaces during cutting, polishing, or cleaning operations (this is important for cleaning implant surfaces)
Classical Conditioning in Pedodontics
PedodonticsPrinciples of Classical Conditioning in Pedodontics
Acquisition:
Definition: In the context of pedodontics,
acquisition refers to the process by which a child learns a new response
to dental stimuli. For example, a child may learn to associate the
dental office with positive experiences (like receiving a reward or
praise) or negative experiences (like pain or discomfort).
Application: By creating a positive environment and
using techniques such as positive reinforcement (e.g., stickers, small
prizes), dental professionals can help children acquire a positive
response to dental visits.
Generalization:
Definition: Generalization occurs when a child
responds to stimuli that are similar to the original conditioned
stimulus. In a dental context, this might mean that a child who has
learned to feel comfortable with one dentist may also feel comfortable
with other dental professionals or similar dental environments.
Application: If a child has a positive experience
with a specific dental procedure (e.g., a cleaning), they may generalize
that comfort to other procedures or to different dental offices,
reducing anxiety in future visits.
Extinction:
Definition: Extinction in pedodontics refers to the
process by which a child’s conditioned fear response diminishes when
they are repeatedly exposed to dental stimuli without any negative
experiences. For instance, if a child has a fear of dental drills but
experiences several visits where the drill is used without pain or
discomfort, their fear may gradually decrease.
Application: Dental professionals can facilitate
extinction by ensuring that children have multiple positive experiences
in the dental chair, helping them to associate dental stimuli with
safety rather than fear.
Discrimination:
Definition: Discrimination is the ability of a
child to differentiate between similar stimuli and respond only to the
specific conditioned stimulus. In a dental setting, this might mean that
a child learns to respond differently to various dental tools or sounds
based on their previous experiences.
Application: For example, a child may learn to feel
anxious only about the sound of a dental drill but not about the sound
of a toothbrush. By helping children understand that not all dental
sounds or tools are associated with pain, dental professionals can help
them develop discrimination skills.
Cardiac Output
Physiology
Cardiac Output:
Minute Volume = Heart Rate X Stroke Volume
Heart rate, HR at rest = 65 to 85 bpm
Each heartbeat at rest takes about .8 sec. of which .4 sec. is quiescent period.
Stroke volume, SV at rest = 60 to 70 ml.
Heart can increase both rate and volume with exercise. Rate increase is limited due to necessity of minimum ventricular diastolic period for filling. Upper limit is usually put at about 220 bpm. Maximum heart rate calculations are usually below 200. Target heart rates for anaerobic threshold are about 85 to 95% of maximum.
Terms:
End Diastolic Volume, EDV - the maximum volume of the ventricles achieved at the end of ventricular diastole. This is the amount of blood the heart has available to pump. If this volume increases the cardiac output increases in a healthy heart.
End Systolic Volume, ESV - the minimum volume remaining in the ventricle after its systole. If this volume increases it means less blood has been pumped and the cardiac output is less.
EDV - ESV = SV
SV / EDV = Ejection Fraction The ejection fraction is normally around 50% at rest and will increase during strenuous exercise in a healthy heart. Well trained athletes may have ejection fractions approaching 70% in the most strenuous exercise.
Isovolumetric Contraction Phase - a brief period at the beginning of ventricular systole when all valves are closed and ventricular volume remains constant. Pressure has risen enough in the ventricle to close the AV valves but not enough to open the semilunar valves and cause ejection of blood.
Isovolumetric Relaxation Phase - a brief period at the beginning of ventricular diastole when all valves are closed and ventricular volume is constant. Pressure in the ventricle has lowered producing closure of the semilunar valves but not opening the AV valves to begin pulling blood into the ventricle.
Dicrotic Notch - the small increase in pressure of the aorta or other artery seen when recording a pulse wave. This occurs as blood is briefly pulled back toward the ventricle at the beginning of diastole thus closing the semilunar valves.
Preload - This is the pressure at the end of ventricular diastole, at the beginning of ventricular systole. It is proportional to the End Diastolic Volume (EDV), i.e. as the EDV increases so does the preload of the heart. Factors which increase the preload are: increased total blood volume, increased venous tone and venous return, increased atrial contraction, and the skeletal muscular pump.
Afterload - This is the impedence against which the left ventricle must eject blood, and it is roughly proportional to the End Systolic Volume (ESV). When the peripheral resistance increases so does the ESV and the afterload of the heart.
The importance of these parameters are as a measure of efficiency of the heart, which increases as the difference between preload and afterload increases