NEET MDS Synopsis
Cardiovascular Effects of Sevoflurane, Halothane, and Isoflurane
General SurgeryCardiovascular Effects of Sevoflurane, Halothane, and Isoflurane
Sevoflurane:
Maintains cardiac index and heart rate effectively.
Exhibits less hypotensive and negative inotropic effects compared to
halothane.
Cardiac output is greater than that observed with halothane.
Recovery from sevoflurane anesthesia is smooth and comparable to
isoflurane, with a shorter time to standing than halothane.
Halothane:
Causes significant decreases in mean arterial pressure, ejection
fraction, and cardiac index.
Heart rate remains at baseline levels, but overall cardiovascular
function is depressed.
Recovery from halothane is less favorable compared to sevoflurane and
isoflurane.
Isoflurane:
Preserves cardiac index and ejection fraction better than halothane.
Increases heart rate while having less suppression of mean arterial
pressure compared to halothane.
Cardiac output during isoflurane anesthesia is similar to that of
sevoflurane, indicating a favorable cardiovascular profile.
Periodontal ligament
Dental Anatomy
Periodontal ligament
Composition
a. Consists mostly of collagenous (alveolodental) fibers.
Note: the portions of the fibers embedded in cementum and the alveolar bone proper are known as Sharpey’s fibers.
b. Oxytalan fibers (a type of elastic fiber) are also present. Although their function is unknown, they may play a role in the regulation of vascular flow.
c. Contains mostly type I collagen, although smaller amounts of type III and XII collagen are also present.
d. Has a rich vascular and nerve supply.
Both sensory and autonomic nerves are present.
(1) The sensory nerves in the PDL differ from pulpal nerves in that PDL nerve endings can detect both proprioception (via mechanoreceptors) and pain (via nociceptors).
(2) The autonomic nerve fibers are associated with the regulation of periodontal vascular flow.
(3) Nerve fibers may be myelinated (sensory) or unmyelinated (sensory or autonomic).
Cells
a. Cells present in the PDL include fibroblasts; epithelial cells; cementoblasts and cementoclasts; osteoblasts and osteoclasts; and immune cells such as macrophages, mast cells, or eosinophils.
b. These cells play a role in forming or destroying cementum, alveolar bone, or PDL.
c. Epithelial cells often appear in clusters, known as rests of Malassez.
Types of alveolodental fibers
a. Alveolar crest fibers—radiate downward from cementum, just below the cementoenamel junction (CEJ), to the crest of alveolar bone.
b. Horizontal fibers—radiate perpendicular to the tooth surface from cementum to alveolar bone, just below the alveolar crest.
c. Oblique fibers
(1) Radiate downward from the alveolar bone to cementum.
(2) The most numerous type of PDL fiber.
(3) Resist occlusal forces that occur along the long axis of the tooth.
d. Apical fibers
(1) Radiate from the cementum at the apex of the tooth into the alveolar bone.
(2) Resist forces that pull the tooth in an occlusal direction (i.e., forces that try to pull the tooth from its socket).
e. Interradicular fibers
(1) Only found in the furcal area of multi-rooted teeth.
(2) Resist forces that pull the tooth in an occlusal direction.
Gingival fibers
a. The fibers of the gingival ligament are not strictly part of the PDL, but they play a role in the maintainence of the periodontium.
b. Gingival fibers are packed in groups and are found in the lamina propria of gingiva
c. Gingival fiber groups:
(1) Transseptal (interdental) fibers
(a) Extend from the cementum of one tooth (just apical to the junctional epithelium), over the alveolar crest, to the corresponding area of the cementum of the adjacent tooth.
(b) Collectively, these fibers form the interdental ligament , which functions to resist rotational forces and retain adjacent teeth in interproximal contact.
(c) These fibers have been implicated as a major cause of postretention relapse of teeth that have undergone orthodontic treatment.
(2) Circular (circumferential) fibers
(a) Extend around tooth near the CEJ.
(b) Function in binding free gingiva to the tooth and resisting rotational forces.
(3) Alveologingival fibers—extend from the alveolar crest to lamina propria of free and attached gingiva.
(4) Dentogingival fibers—extend from cervical cementum to the lamina propria of free and attached gingiva.
(5) Dentoperiosteal fibers—extend from cervical cementum, over the alveolar crest, to the periosteum of the alveolar bone.
Classification of cysts of the orofacial region
Oral Pathology
Epithelial cysts
Developmental odontogenic cysts
Odontogenic keratocyst
Dentigerous cyst (follicular cyst)
Eruption cyst
Lateral periodontal cyst
Gingival cyst of adults
Glandular odontogenic cyst (sialo-odontogenic)
Inflammatory odontogenic cysts
Radicular cyst (apical and lateral)
Residual cyst
Paradental cyst
Non-odontogenic cysts
Nasopalatine cyst
Nasolabial cyst
Non-epithelial cysts (not true cysts)
Solitary bone cyst
Aneurysmal bone cyst
ISO-ENZYMES
Biochemistry
ISO-ENZYMES
Iso-enzymes are physically distinct forms of the same enzyme activity. Higher organisms have several physically distinct versions of a given enzyme, each of which catalyzes the same reaction. Isozymes arise through gene duplication and exhibit differences in properties such as sensitivity to particular regulatory factors or substrate affinity that adapts them to specific tissues or circumstances.
Isoforms of Lactate dehydrogenase is useful in diagnosis of myocardial infarction. While study of alkaline phosphatase isoforms are helpful in diagnosis of various bone disorder and obstructive liver diseases.
Cavernous sinus thrombosis
Oral Maxillofacial Surgery
Initial symptoms
- pain in the eye and tenderness to pressure.
- high fluctuating fever, chills, rapid pulse, and sweating.
- Venous obstruction subsequently causes edema of the eyelids, lacrimation, and proptosis, and chemosis and retinal hemorrhages
There is also cranial nerve involvement (oculomotor, trochlear, abducens, ophthalmic division of the trigeminal, and carotid sympathetic plexus),
- It results in ophthalmoplegia, diminished or absent corneal reflex, ptosis, and dilatation of the pupil.
- terminal stages bring signs of advanced toxaemia, and meningitis
CASTING DEFECTS
Dental Materials
CASTING DEFECTS
Classification :
1) Distortion.
2) Surface roughness .
3) Porosity .
4)Incomplete casting .
5) Oxidation .
6) Sulfur contamination .
Distortion
It is usually due to the distortion of wax pattern.
To avoid this :
Manipulation of the wax at its softening temp
Invest the pattern at the earliest .
If storage is necessary store it in a refrigerator .
Surface roughness
May be due to :
Air bubbles on the wax pattern .
Cracks due to rapid heating of the investment .
High W/P ratio .
Prolonged heating of the mold cavity .
Overheating of the gold alloy .
Too high or too low casting pressure .
Composition of the investment .
Foreign body inclusion.
POROSITY
May be internal or external .
External porosity causes discolouration .
Internal porosity weakens the restoration .
Classification of porosity .
I .Those caused by solidification shrinkage :
a) Localised shrinkage porosity .
b) Suck back porosity .
c) Microporosity .
They are usually irregular in shape .
II ) Those caused by gas :
a) Pin hole porosity .
b) Gas inclusions .
c) Subsurface porosity .
Usually they are spherical in shape .
III ) Those caused by air trapped in the mold :
Back pressure porosity .
Localised shrinkage porosity
Large irregular voids found near sprue casting junction.
Occurs when cooling sequence is incorrect .
If the sprue solidifies before the rest of the casting , no more molten metal is supplied from the sprue which can cause voids or pits (shrink pot porosity )
This can be avoided by -
- using asprue of correct thickness .
- Attach the sprue to the thickest portion of the pattern .
-Flaring of the sprue at the point of atttachment .
-Placing a reservoir close to the pattern .
Suck back porosity
It is an external void seen in the inside of a crown opposite the sprue .
Hot spot is created which freezes last .
It is avoided by :
Reducing the temp difference between the mold & molten alloy .
Microporosity :
Fine irregular voids within the casting .
Occurs when casting freezes rapidly .
Also when mold or casting temp is too low .
Pin hole porosity :
Upon solidification the dissolved gases are expelled from the metal causing tiny voids .
Pt & Pd absorb Hydrogen .
Cu & Ag absorb oxygen .
Gas inclusion porosities
Larger than pin hole porosities .
May be due to dissolved gases or due to gases Carried in or trapped by molten metal .
Apoorly adjusted blow torech can also occlude gases .
Back pressure porosity
This is caused by inadequate venting of the mold .The sprue pattern length should be adjusted so that there is not more than ¼” thickness of the investmentbetween the bottom of the casting .
This can be prevented by :
- using adequate casting force .
-use investment of adequate porosity .
-place the pattern not more than 6-8 mm away from tne end of the casting .
Casting with gas blow holes
This is due to any wax residue in the mold .
To eliminate this the burnout should be done with the sprue hol facing downwards for the wax pattern to run down.
Incomplete casting
This is due to :
- insufficient alloy .
-Alloy not able to enter thin parts of the mold .
-When the mold is not heated to the casting temp .
-Premature solidification of the alloy .
-sprues blocked with foreign bodies .
-Back pressure of gases .
-low casting pressure .
-Alloy not sufficiently molten .
Too bright & shiny casting with short & rounded margins :
occurs when wax is eliminated completely ,it combines with oxygen or air to form carbon monoxide .
Small casting :
occurs when proper expansion is not obtained & due to the shrinkage of the impression .
Contamination of the casting
1) Due to overheating there is oxidation of metal .
2) Use of oxidising zone of the flame .
3) Failure to use a flux .
4) Due to formation sulfur compounds .
Black casting
It is due to :
1) Overheating of the investment .
2) Incomplete elimination of the wax .
Inlay Preparation
Conservative DentistryInlay Preparation
Inlay preparations are a common restorative procedure in dentistry,
particularly for Class II restorations.
1. Definitions
A. Inlay
An inlay is a restoration that is
fabricated using an indirect procedure. It involves one or more tooth
surfaces and may cap one or more cusps but does not cover all cusps.
2. Class II Inlay (Cast Metal) Preparation Procedure
A. Burs Used
Recommended Burs:
No. 271: For initial cavity preparation.
No. 169 L: For refining the cavity shape and creating the proximal
box.
B. Initial Cavity Preparation
Similar to Class II Amalgam: The initial cavity
preparation is performed similarly to that for Class II amalgam
restorations, with the following differences:
Occlusal Entry Cut Depth: The initial occlusal
entry should be approximately 1.5 mm deep.
Cavity Margins Divergence: All cavity margins must
diverge occlusally by 2-5 degrees:
2 degrees: When the vertical walls of the
cavity are short.
5 degrees: When the vertical walls are long.
Proximal Box Margins: The proximal box margins
should clear the adjacent tooth by 0.2-0.5 mm, with 0.5 ± 0.2 mm being
ideal.
C. Preparation of Bevels and Flares
Primary and Secondary Flares:
Flares are created on the facial and lingual proximal walls, forming
the walls in two planes.
The secondary flare widens the proximal box, which initially had a
clearance of 0.5 mm from the adjacent tooth. This results in:
Marginal Metal in Embrasure Area: Placing the
marginal metal in the embrasure area allows for better
self-cleansing and easier access for cleaning and polishing without
excessive dentin removal.
Marginal Metal Angle: A 40-degree angle, which
is easily burnishable and strong.
Enamel Margin Angle: A 140-degree angle, which
blunts the enamel margin and increases its strength.
Note: Secondary flares are omitted on the
mesiofacial proximal walls of maxillary premolars and first molars for
esthetic reasons.
D. Gingival Bevels
Width: Gingival bevels should be 0.5-1 mm wide and
blend with the secondary flare, resulting in a marginal metal angle of 30
degrees.
Purpose:
Removal of weak enamel.
Creation of a burnishable 30-degree marginal metal.
Production of a lap sliding fit at the gingival margin.
E. Occlusal Bevels
Location: Present on the cavosurface margins of the
cavity on the occlusal surface.
Width: Approximately 1/4th the depth of the respective
wall, resulting in a marginal metal angle of 40 degrees.
3. Capping Cusps
A. Indications
Cusp Involvement: Capping cusps is indicated when more
than 1/2 of a cusp is involved and is mandatory when 2/3 or more is
involved.
B. Advantages
Weak Enamel Removal: Helps in removing weak enamel.
Cavity Margin Location: Moves the cavity margin away
from occlusal areas subjected to heavy forces.
Visualization of Caries: Aids in visualizing the extent
of caries, increasing convenience during preparation.
C. Cusp Reduction
Uniform Metal Thickness: Cusp reduction must provide
for a uniform 1.5 mm metal thickness over the reduced cusps.
Facial Cusp Reduction: For maxillary premolars and
first molars, the reduction of the facial cusp should be 0.75-1 mm for
esthetic reasons.
D. Reverse Bevel (Counter Bevel)
Definition: A bevel given on the margins of the reduced
cusp.
Width: Varies to extend beyond any occlusal contact
with opposing teeth, resulting in a marginal metal angle of 30 degrees.
E. Retention Considerations
Retention Form: Cusp reduction decreases the retention
form due to reduced vertical wall height. Therefore, proximal retentive
grooves are usually recommended.
Collar and Skirt Features: These features can enhance
retention and resistance form.
Dental Practice Considerations
Conservative DentistryImplications for Dental Practice
A. Health and Safety Considerations
Mercury Exposure: Understanding the amounts of mercury
released during these procedures is crucial for assessing potential health
risks to dental professionals and patients.
Regulatory Guidelines: Dental practices should adhere
to guidelines and regulations regarding mercury handling and exposure limits
to ensure a safe working environment.
B. Best Practices
Use of Wet Polishing: Whenever possible, wet polishing
should be preferred over dry polishing to minimize mercury release.
Proper Ventilation: Ensuring adequate ventilation in
the dental operatory can help reduce the concentration of mercury vapor in
the air.
Personal Protective Equipment (PPE): Dental
professionals should use appropriate PPE, such as masks and gloves, to
minimize exposure during amalgam handling.
C. Patient Safety
Informed Consent: Patients should be informed about the
materials used in their restorations, including the presence of mercury in
amalgam, and the associated risks.
Monitoring: Regular monitoring of dental practices for
mercury exposure levels can help maintain a safe environment for both staff
and patients.
1. Noise Levels of Turbine Handpieces
Turbine Handpieces
Ball Bearings: Turbine handpieces equipped with ball
bearings can operate efficiently at air pressures of around 30 pounds.
Noise Levels: At high frequencies, these handpieces may
produce noise levels ranging from 70 to 94 dB.
Hearing Damage Risk: Exposure to noise levels exceeding
75 dB, particularly in the frequency range of 1000 to 8000 cycles per second
(cps), can pose a risk of hearing damage for dental professionals.
Implications for Practice
Hearing Protection: Dental professionals should
consider using hearing protection, especially during prolonged use of
high-speed handpieces, to mitigate the risk of noise-induced hearing loss.
Workplace Safety: Implementing noise-reduction
strategies in the dental operatory can enhance the comfort and safety of
both staff and patients.
2. Post-Carve Burnishing
Technique
Post-Carve Burnishing: This technique involves lightly
rubbing the carved surface of an amalgam restoration with a burnisher of
suitable size and shape.
Purpose: The goal is to improve the smoothness of the
restoration and produce a satin finish rather than a shiny appearance.
Benefits
Enhanced Aesthetics: A satin finish can improve the
aesthetic integration of the restoration with the surrounding tooth
structure.
Surface Integrity: Burnishing can help to compact the
surface of the amalgam, potentially enhancing its resistance to wear and
marginal integrity.
3. Preparing Mandibular First Premolars for MOD Amalgam Restorations
Considerations for Tooth Preparation
Conservation of Tooth Structure: When preparing a
mesio-occluso-distal (MOD) amalgam restoration for a mandibular first
premolar, it is important to conserve the support of the small lingual cusp.
Occlusal Step Preparation: The occlusal step should
be prepared more facially than lingually, which helps to maintain the
integrity of the lingual cusp.
Bur Positioning: The bur should be tilted slightly
lingually to establish the correct direction for the pulpal wall.
Cusp Reduction
Lingual Cusp Consideration: If the lingual margin of
the occlusal step extends more than two-thirds the distance from the central
fissure to the cuspal eminence, the lingual cusp may need to be reduced to
ensure proper occlusal function and stability of the restoration.
4. Universal Matrix System
Overview
Tofflemire Matrix System: Designed by B.R. Tofflemire,
the Universal matrix system is a commonly used tool in restorative
dentistry.
Indications: This system is ideally indicated when
three surfaces (mesial, occlusal, distal) of a posterior tooth have been
prepared for restoration.
Benefits
Retention and Contour: The matrix system helps in
achieving proper contour and retention of the restorative material, ensuring
a well-adapted restoration.
Ease of Use: The design allows for easy placement and
adjustment, facilitating efficient restorative procedures.
5. Angle Former Excavator
Functionality
Angle Former: A special type of excavator used
primarily for sharpening line angles and creating retentive features in
dentin, particularly in preparations for gold restorations.
Beveling Enamel Margins: The angle former can also be
used to place a bevel on enamel margins, enhancing the retention of
restorative materials.
Clinical Applications
Preparation for Gold Restorations: The angle former is
particularly useful in preparations where precise line angles and retention
are critical for the success of gold restorations.
Versatility: Its ability to create retentive features
makes it a valuable tool in various restorative procedures.