NEET MDS Synopsis
Acanthosis nigricans
General Pathology
Acanthosis nigricans is a pigmented skin lesion commonly present in the axilla which is a phenotypic marker for an insulin-receptor abnormality as well as a marker for adenocarcinoma, most commonly of gastric origin.
Osteoporosis
General Pathology
Osteoporosis
is characterized by increased porosity of the skeleton resulting from reduced bone mass. The disorder may be localized to a certain bone (s), as in disuse osteoporosis of a limb, or generalized involving the entire skeleton. Generalized osteoporosis may be primary, or secondary
Primary generalized osteoporosis
• Postmenopausal
• Senile
Secondary generalized osteoporosis
A. Endocrine disorders
• Hyperparathyroidism
• Hypo or hyperthyroidism
• Others
B. Neoplasia
• Multiple myeloma
• Carcinomatosis
C. Gastrointestinal disorders
• Malnutrition & malabsorption
• Vit D & C deficiency
• Hepatic insufficiency
D. Drugs
• Corticosteroids
• Anticoagulants
• Chemotherapy
• Alcohol
E. Miscellaneous
• osteogenesis imperfecta
• immobilization
• pulmonary disease
Senile and postmenopausal osteoporosis are the most common forms. In the fourth decade in both sexes, bone resorption begins to overrun bone deposition. Such losses generally occur in areas containing abundant cancelloues bone such as the vertebrae & femoral neck. The postmenopausal state accelerates the rate of loss; that is why females are more susceptible to osteoporosis and its complications.
Gross features
• Because of bone loss, the bony trabeculae are thinner and more widely separated than usual. This leads to obvious porosity of otherwise spongy cancellous bones
Microscopic features
• There is thinning of the trabeculae and widening of Haversian canals.
• The mineral content of the thinned bone is normal, and thus there is no alteration in the ratio of minerals to protein matrix
Etiology & Pathogenesis
• Osteoporosis involves an imbalance of bone formation, bone resorption, & regulation of osteoclast activation. It occurs when the balance tilts in favor of resorption.
• Osteoclasts (as macrophages) bear receptors (called RANK receptors) that when stimulated activate the nuclear factor (NFκB) transcriptional pathway. RANK ligand synthesized by bone stromal cells and osteoblasts activates RANK. RANK activation converts macrophages into bone-crunching osteoclasts and is therefore a major stimulus for bone resorption.
• Osteoprotegerin (OPG) is a receptor secreted by osteoblasts and stromal cells, which can bind RANK ligand and by doing so makes the ligand unavailable to activate RANK, thus limiting osteoclast bone-resorbing activity.
• Dysregulation of RANK, RANK ligand, and OPG interactions seems to be a major contributor in the pathogenesis of osteoporosis. Such dysregulation can occur for a variety of reasons, including aging and estrogen deficiency.
• Influence of age: with increasing age, osteoblasts synthetic activity of bone matrix progressively diminished in the face of fully active osteoclasts.
• The hypoestrogenic effects: the decline in estrogen levels associated with menopause correlates with an annual decline of as much as 2% of cortical bone and 9% of cancellous bone. The hypoestrogenic effects are attributable in part to augmented cytokine production (especially interleukin-1 and TNF). These translate into increased RANK-RANK ligand activity and diminished OPG.
• Physical activity: reduced physical activity increases bone loss. This effect is obvious in an immobilized limb, but also occurs diffusely with decreased physical activity in older individuals.
• Genetic factors: these influence vitamin D receptors efficiency, calcium uptake, or PTH synthesis and responses.
• Calcium nutritional insufficiency: the majority of adolescent girls (but not boys) have insufficient dietary intake of calcium. As a result, they do not achieve the maximal peak bone mass, and are therefore likely to develop clinically significant osteoporosis at an earlier age.
• Secondary causes of osteoporosis: these include prolonged glucocorticoid therapy (increases bone resorption and reduce bone synthesis.)
The clinical outcome of osteoporosis depends on which bones are involved. Thoracic and lumbar vertebral fractures are extremely common, and produce loss of height and various deformities, including kyphoscoliosis that can compromise respiratory function. Pulmonary embolism and pneumonia are common complications of fractures of the femoral neck, pelvis, or spine.
Primary Bone Healing and Rigid Fixation
Oral and Maxillofacial SurgeryPrimary Bone Healing and Rigid Fixation
Primary bone healing is a process that occurs when bony
fragments are compressed against each other, allowing for direct healing without
the formation of a callus. This type of healing is characterized by the
migration of osteocytes across the fracture line and is facilitated by rigid
fixation techniques. Below is a detailed overview of the concept of primary bone
healing, the mechanisms involved, and examples of rigid fixation methods.
Concept of Compression
Compression of Bony Fragments: In primary bone healing,
the bony fragments are tightly compressed against each other. This
compression is crucial as it allows for the direct contact of the bone
surfaces, which is necessary for the healing process.
Osteocyte Migration: Under conditions of compression,
osteocytes (the bone cells responsible for maintaining bone tissue) can
migrate across the fracture line. This migration is essential for the
healing process, as it facilitates the integration of the bone fragments.
Characteristics of Primary Bone Healing
Absence of Callus Formation: Unlike secondary bone
healing, which involves the formation of a callus (a soft tissue bridge that
eventually hardens into bone), primary bone healing occurs without callus
formation. This is due to the rigid fixation that prevents movement between
the fragments.
Haversian Remodeling: The healing process in primary
bone healing involves Haversian remodeling, where the bone is remodeled
along the lines of stress. This process allows for the restoration of the
bone's structural integrity and strength.
Requirements for Primary Healing:
Absolute Immobilization: Rigid fixation must
provide sufficient stability to prevent any movement (interfragmentary
mobility) between the osseous fragments during the healing period.
Minimal Gap: There should be minimal distance (gap)
between the fragments to facilitate direct contact and healing.
Examples of Rigid Fixation in the Mandible
Lag Screws: The use of two lag screws across a fracture
provides strong compression and stability, allowing for primary bone
healing.
Bone Plates:
Reconstruction Bone Plates: These plates are
applied with at least three screws on each side of the fracture to
ensure adequate fixation and stability.
Compression Plates: A large compression plate can
be used across the fracture to maintain rigid fixation and prevent
movement.
Proper Application: When these fixation methods are
properly applied, they create a stable environment that is conducive to
primary bone healing. The rigidity of the fixation prevents interfragmentary
mobility, which is essential for the peculiar type of bone healing that
occurs without callus formation.
Berkson's Bias
Public Health DentistryBerkson's Bias is a type of selection bias that occurs in
case-control studies, particularly when the cases and controls are selected from
a hospital or clinical setting. It arises when the selection of cases
(individuals with the disease) and controls (individuals without the disease) is
influenced by the presence of other conditions or factors, leading to a
distortion in the association between exposure and outcome.
Key Features of Berkson's Bias
Hospital-Based Selection: Berkson's Bias typically
occurs in studies where both cases and controls are drawn from the same
hospital or clinical setting. This can lead to a situation where the
controls are not representative of the general population.
Association with Other Conditions: Individuals who are
hospitalized may have multiple health issues or risk factors that are not
present in the general population. This can create a misleading association
between the exposure being studied and the disease outcome.
Underestimation or Overestimation of Risk: Because the
controls may have different health profiles compared to the general
population, the odds ratio calculated in the study may be biased. This can
lead to either an overestimation or underestimation of the true association
between the exposure and the disease.
Example of Berkson's Bias
Consider a study investigating the relationship between smoking and lung
cancer, where both cases (lung cancer patients) and controls (patients without
lung cancer) are selected from a hospital. If the controls are patients with
other diseases that are also related to smoking (e.g., chronic obstructive
pulmonary disease), this could lead to Berkson's Bias. The controls may have a
higher prevalence of smoking than the general population, which could distort
the perceived association between smoking and lung cancer.
Implications of Berkson's Bias
Misleading Conclusions: Berkson's Bias can lead
researchers to draw incorrect conclusions about the relationship between
exposures and outcomes, which can affect public health recommendations and
clinical practices.
Generalizability Issues: Findings from studies affected
by Berkson's Bias may not be generalizable to the broader population,
limiting the applicability of the results.
Mitigating Berkson's Bias
To reduce the risk of Berkson's Bias in research, researchers can:
Select Controls from the General Population: Instead of
selecting controls from a hospital, researchers can use population-based
controls to ensure a more representative sample.
Use Multiple Control Groups: Employing different control
groups can help identify and account for potential biases.
Stratify Analyses: Stratifying analyses based on
relevant characteristics (e.g., age, sex, comorbidities) can help to control
for confounding factors.
Conduct Sensitivity Analyses: Performing sensitivity
analyses can help assess how robust the findings are to different
assumptions about the data.
Piezosurgery
Oral and Maxillofacial SurgeryPiezosurgery
Piezosurgery is an advanced surgical technique that utilizes
ultrasonic vibrations to cut bone and other hard tissues with precision. This
method has gained popularity in oral and maxillofacial surgery due to its
ability to minimize trauma to surrounding soft tissues, enhance surgical
accuracy, and improve patient outcomes. Below is a detailed overview of the
principles, advantages, applications, and specific uses of piezosurgery in oral
surgery.
Principles of Piezosurgery
Ultrasonic Technology: Piezosurgery employs ultrasonic
waves to create high-frequency vibrations in specially designed surgical
tips. These vibrations allow for precise cutting of bone while preserving
adjacent soft tissues.
Selective Cutting: The ultrasonic frequency is tuned to
selectively cut mineralized tissues (like bone) without affecting softer
tissues (like nerves and blood vessels). This selectivity reduces the risk
of complications and enhances healing.
Advantages of Piezosurgery
Strength and Durability of Tips:
Piezosurgery tips are made from high-quality materials that are
strong and resistant to fracture. This durability allows for extended
use without the need for frequent replacements, making them
cost-effective in the long run.
Access to Difficult Areas:
The design of piezosurgery tips allows them to reach challenging
anatomical areas that may be difficult to access with traditional
surgical instruments. This is particularly beneficial in complex
procedures involving the mandible and maxilla.
Minimized Trauma:
The ultrasonic cutting action produces less heat and vibration
compared to traditional rotary instruments, which helps to preserve the
integrity of surrounding soft tissues and reduces postoperative pain and
swelling.
Enhanced Precision:
The ability to perform precise cuts allows for better control during
surgical procedures, leading to improved outcomes and reduced
complications.
Reduced Blood Loss:
The selective cutting action minimizes damage to blood vessels,
resulting in less bleeding during surgery.
Applications in Oral Surgery
Piezosurgery has a variety of applications in oral and maxillofacial surgery,
including:
Osteotomies:
LeFort I Osteotomy: Piezosurgery is particularly
useful in performing pterygoid disjunction during LeFort I osteotomy.
The ability to precisely cut bone in the pterygoid region allows for
better access and alignment during maxillary repositioning.
Intraoral Vertical Ramus Osteotomy (IVRO): The
lower border cut at the lateral surface of the ramus can be performed
with piezosurgery, allowing for precise osteotomy while minimizing
trauma to surrounding structures.
Inferior Alveolar Nerve Lateralization:
Piezosurgery can be used to carefully lateralize the inferior alveolar
nerve during procedures such as bone grafting or implant placement,
reducing the risk of nerve injury.
Bone Grafting:
Piezosurgery is effective in harvesting bone grafts from donor
sites, as it allows for precise cuts and minimal damage to surrounding
tissues. This is particularly important in procedures requiring
autogenous bone grafts.
Implant Placement:
The technique can be used to prepare the bone for dental implants,
allowing for precise osteotomy and reducing the risk of complications
associated with traditional drilling methods.
Sinus Lift Procedures:
Piezosurgery is beneficial in sinus lift procedures, where precise
bone cutting is required to elevate the sinus membrane without damaging
it.
Tumor Resection:
The precision of piezosurgery makes it suitable for resecting tumors
in the jaw while preserving surrounding healthy tissue.
Pouring the Final Impression
Conservative DentistryPouring the Final Impression
Technique
Mixing Die Stone: A high-strength die stone is mixed
using a vacuum mechanical mixer to ensure a homogenous mixture without air
bubbles.
Pouring Process:
The die stone is poured into the impression using a vibrator and a
No. 7 spatula.
The first increments should be applied in small amounts, allowing
the material to flow into the remote corners and angles of the
preparation without trapping air.
Surface Tension-Reducing Agents: These agents can be
added to the die stone to enhance its flow properties, allowing it to
penetrate deep into the internal corners of the impression.
Final Dimensions
The impression should be filled sufficiently so that the dies will be
approximately 15 to 20 mm tall occluso-gingivally after trimming. This
height is important for the stability and accuracy of the final restoration.
Finger Rests in Dental Instrumentation
PeriodontologyFinger Rests in Dental Instrumentation
Use of finger rests is essential for providing stability and control during
procedures. A proper finger rest allows for more precise movements and reduces
the risk of hand fatigue.
Importance of Finger Rests
Stabilization: Finger rests serve to stabilize the hand
and the instrument, providing a firm fulcrum that enhances control during
procedures.
Precision: A stable finger rest allows for more
accurate instrumentation, which is crucial for effective treatment and
patient safety.
Reduced Fatigue: By providing support, finger rests
help reduce hand and wrist fatigue, allowing the clinician to work more
comfortably for extended periods.
Types of Finger Rests
Conventional Finger Rest:
Description: The finger rest is established on the
tooth surfaces immediately adjacent to the working area.
Application: This is the most common type of finger
rest, providing direct support for the hand while working on a specific
tooth. It allows for precise movements and control during
instrumentation.
Cross Arch Finger Rest:
Description: The finger rest is established on the
tooth surfaces on the other side of the same arch.
Application: This technique is useful when working
on teeth that are not directly adjacent to the finger rest. It provides
stability while allowing access to the working area from a different
angle.
Opposite Arch Finger Rest:
Description: The finger rest is established on the
tooth surfaces of the opposite arch (e.g., using a mandibular arch
finger rest for instrumentation on the maxillary arch).
Application: This type of finger rest is
particularly beneficial when accessing the maxillary teeth from the
mandibular arch, providing a stable fulcrum while maintaining visibility
and access.
Finger on Finger Rest:
Description: The finger rest is established on the
index finger or thumb of the non-operating hand.
Application: This technique is often used in areas
where traditional finger rests are difficult to establish, such as in
the posterior regions of the mouth. It allows for flexibility and
adaptability in positioning.
Beta - Adrenergic Blocking Agents
Pharmacology
Beta - Adrenergic Blocking Agents
Mechanisms of Action
- Initial decrease in cardiac output, followed by reduction in peripheral vascular resistance.
- Other actions include decrease plasma renin activity, resetting of baroreceptors, release of vasodilator prostaglandins, and blockade of prejunctional beta-receptors.
Advantages
- Documented reduction in cardiovascular morbidity and mortality.
- Cardioprotection: primary and secondary prevention against coronary artery events (i.e. ischemia, infarction, arrhythmias, death).
- Relatively not expensive.
Considerations
- Beta blockers are used with caution in patients with bronchospasm.
- Contraindicated in more than grade I AV, heart block.
- Do not discontinue abruptly.
Side Effects
- Bronchospasm and obstructive airway disease.
- Bradycardia
- Metabolic effects (raise triglyerides levels and decrease HDL cholesterol; may worsen insulin sensitivity and cause glucose intolerance). Increased incidence of diabetes mellitus.
- Coldness of extremities.
- Fatigue.
- Mask symptoms of hypoglycemia.
- Impotence.
Indications
- First line treatment for hypertension as an alternative to diuretics.
- Hypertension associated with coronary artery disease.
- Hyperkinetic circulation and high cardiac output hypertension (e.g., young hypertensives).
- Hypertension associated with supraventricular tachycardia, migraine, essential tremors, or hypertrophic cardiomyopathy.
Beta adrenergic blocker Drugs
Atenolol 25-100
Metoprolol 50-200
Bisoprolol 2.5-10