NEET MDS Synopsis
Velopharyngeal Insufficiency (VPI)
Oral and Maxillofacial SurgeryVelopharyngeal Insufficiency (VPI)
Velopharyngeal insufficiency (VPI) is
characterized by inadequate closure of the nasopharyngeal airway during speech
production, leading to speech disorders such as hypernasality and nasal
regurgitation. This condition is particularly relevant in patients who have
undergone cleft palate repair, as the surgical success does not always guarantee
proper function of the velopharyngeal mechanism.
Etiology of VPI
The etiology of VPI following cleft palate repair is multifactorial and can
include:
Inadequate Surgical Repair: Insufficient repair of the
musculature involved in velopharyngeal closure can lead to persistent VPI.
This may occur if the muscles are not properly repositioned or if there is
inadequate tension in the repaired tissue.
Anatomical Variations: Variations in the anatomy of the
soft palate, pharynx, and surrounding structures can contribute to VPI.
These variations may not be fully addressed during initial surgical repair.
Neuromuscular Factors: Impaired neuromuscular function
of the muscles involved in velopharyngeal closure can also lead to VPI,
which may not be correctable through surgical means alone.
Surgical Management of VPI
Pharyngoplasty: One of the surgical options for managing VPI
is pharyngoplasty, which aims to improve the closure of the nasopharyngeal port
during speech.
Historical Background: The procedure was first
described by Hynes in 1951 and has since been modified by various authors to
enhance its effectiveness and reduce complications.
Operative Procedure
Flap Creation: The procedure involves the creation of
two superiorly based myomucosal flaps from each posterior tonsillar pillar.
Care is taken to include as much of the palatopharyngeal muscle as possible
in the flaps.
Flap Elevation: The flaps are elevated carefully to
preserve their vascular supply and muscular integrity.
Flap Insetting: The flaps are then attached and inset
within a horizontal incision made high on the posterior pharyngeal wall.
This technique aims to create a single nasopharyngeal port rather than the
two ports typically created with a superiorly based pharyngeal flap.
Contractile Ridge Formation: The goal of the procedure
is to establish a contractile ridge posteriorly, which enhances the function
of the velopharyngeal valve, thereby improving closure during speech.
Advantages of Sphincter Pharyngoplasty
Lower Complication Rate: One of the main advantages of
sphincter pharyngoplasty over the traditional superiorly based flap
technique is the lower incidence of complications related to nasal airway
obstruction. This is particularly important for patient comfort and quality
of life post-surgery.
Improved Speech Outcomes: By creating a more effective
velopharyngeal mechanism, patients often experience improved speech
outcomes, including reduced hypernasality and better articulation.
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
Antiarrhythmic Drugs-Class II Beta Blockers
Pharmacology
Class II Beta Blockers
Block SNS stimulation of beta receptors in the heart and decreasing risks of ventricular fibrillation
– Blockage of SA and ectopic pacemakers: decreases automaticity
– Blockage of AV increases the refractory period
- Increase AV nodal conduction ´
- Increase PR interval
- Reduce adrenergic activity
Treatment: Supraventricular tachycardia (AF, flutter, paroxysmal supraventricular tachycardia
– Acebutolol
– Esmolol
– Propanolol
Contraindications and Cautions
• Contraindicated in sinus bradycardia P < 45
• Cardiogenic shock, asthma or respiratory depression which could be made worse by the blocking of Beta receptors.
• Use cautiously in patients with diabetes and thyroid dysfunction, which could be altered by the blockade of Beta receptors
• Renal and hepatic dysfunction could alter the metabolism and excretion of these drugs.
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
The Effects of Enzyme Inhibitors
Biochemistry
The Effects of Enzyme Inhibitors
Enzymes can be inhibited
competitively, when the substrate and inhibitor compete for binding to the same active site or
noncompetitively, when the inhibitor binds somewhere else on the enzyme molecule reducing its efficiency.
The distinction can be determined by plotting enzyme activity with and without the inhibitor present.
Competitive Inhibition
In the presence of a competitive inhibitor, it takes a higher substrate concentration to achieve the same velocities that were reached in its absence. So while Vmax can still be reached if sufficient substrate is available, one-half Vmax requires a higher [S] than before and thus Km is larger.
Noncompetitive Inhibition
With noncompetitive inhibition, enzyme molecules that have been bound by the inhibitor are taken out
enzyme rate (velocity) is reduced for all values of [S], including
Vmax and one-half Vmax but
Km remains unchanged because the active site of those enzyme molecules that have not been inhibited is unchanged.
Headgear
OrthodonticsHeadgear is an extraoral orthodontic appliance used to
correct dental and skeletal discrepancies, particularly in growing patients. It
is designed to apply forces to the teeth and jaws to achieve specific
orthodontic goals, such as correcting overbites, underbites, and crossbites, as
well as guiding the growth of the maxilla (upper jaw) and mandible (lower jaw).
Below is an overview of headgear, its types, mechanisms of action, indications,
advantages, and limitations.
Types of Headgear
Class II Headgear:
Description: This type is used primarily to correct
Class II malocclusions, where the upper teeth are positioned too far
forward relative to the lower teeth.
Mechanism: It typically consists of a facebow that
attaches to the maxillary molars and is anchored to a neck strap or a
forehead strap. The appliance applies a backward force to the maxilla,
helping to reposition it and/or retract the upper incisors.
Class III Headgear:
Description: Used to correct Class III
malocclusions, where the lower teeth are positioned too far forward
relative to the upper teeth.
Mechanism: This type of headgear may use a
reverse-pull face mask that applies forward and upward forces to the
maxilla, encouraging its growth and improving the relationship between
the upper and lower jaws.
Cervical Headgear:
Description: This type is used to control the
growth of the maxilla and is often used in conjunction with other
orthodontic appliances.
Mechanism: It consists of a neck strap that
connects to a facebow, applying forces to the maxilla to restrict its
forward growth while allowing the mandible to grow.
High-Pull Headgear:
Description: This type is used to control the
vertical growth of the maxilla and is often used in cases with deep
overbites.
Mechanism: It features a head strap that connects
to the facebow and applies upward and backward forces to the maxilla.
Mechanism of Action
Force Application: Headgear applies extraoral forces to
the teeth and jaws, influencing their position and growth. The forces can be
directed to:
Restrict maxillary growth: In Class II cases,
headgear can help prevent the maxilla from growing too far forward.
Promote maxillary growth: In Class III cases,
headgear can encourage forward growth of the maxilla.
Reposition teeth: By applying forces to the molars,
headgear can help align the dental arches and improve occlusion.
Indications for Use
Class II Malocclusion: To correct overbites and improve
the relationship between the upper and lower teeth.
Class III Malocclusion: To promote the growth of the
maxilla and improve the occlusal relationship.
Crowding: To create space for teeth by retracting the
upper incisors.
Facial Aesthetics: To improve the overall facial
profile and aesthetics by modifying jaw relationships.
Advantages of Headgear
Non-Surgical Option: Provides a way to correct skeletal
discrepancies without the need for surgical intervention.
Effective for Growth Modification: Particularly useful
in growing patients, as it can influence the growth of the jaws.
Improves Aesthetics: Can enhance facial aesthetics by
correcting jaw relationships and improving the smile.
Limitations of Headgear
Patient Compliance: The effectiveness of headgear
relies heavily on patient compliance. Patients must wear the appliance as
prescribed (often 12-14 hours a day) for optimal results.
Discomfort: Patients may experience discomfort or
soreness when first using headgear, which can affect compliance.
Adjustment Period: It may take time for patients to
adjust to wearing headgear, and they may need guidance on how to use it
properly.
Limited Effectiveness in Adults: While headgear is
effective in growing patients, its effectiveness may be limited in adults
due to the maturity of the skeletal structures.
Dental Implants
Dental Materials
Dental Implants
Applications/Use
Single-tooth implants
Abutments for bridges (freestanding, attached to natural teeth)
Abutments for over dentures
Terms
Subperiosteal- below the periosteum -but above the bone (second most frequently used types)
Intramucosal-within the mucosa
Endosseous into the bone (80%of all current types)
Endodontics-through the root canal space and into the periapical bone
Transosteal-through the bone
Bone substitutes -replace. Long bone
Classification by geometric form
Blades
Root forms
Screws
Cylinders
Staples
Circumferential
Others
Classification by materials type
Metallic-titanium, stainless steel, and .chromium cobalt
Polymeric-PMMA
Ceramic hydroxyapatite, carbon, and sapphire
Classification by attachment design
Bioactive surface retention by osseointegration
Nonative porous surfaces for micromechanical retention by osseointegration
Nonactive, nonporous surface for ankylosis. By osseointegration
Gross mechanical retention designs (e.g.. threads, screws, channels, or transverse holes)
Fibrointegration by formation of fibrous tissue capsule
Combinations of the above
Components
a. Root (for. osseointegration)
b. Neck (for epithelial attachment and percutancaus sealing)
c. Intramobile elements (for shock absorption)
d. Prosthesis (for dental form and function)
Manipulation
a. Selection-based on remaining bone architecture and dimensions
b. Sterilization-radiofrequency glow discharge leaves biomaterial surface uncontaminated and sterile; autoclaving or chemical sterilization is contraindicated for some designs
Properties
1. Physical-should have low thermal and electrical conductivity
2. Chemical
a. Should be resistant to electrochemical corrosion
b. Do not expose surfaces to acids (e.g.. APF fluorides).
c. Keep in mind the effects of adjunctive therapies (e.g., Peridex)
3. Mechanical
a. Should be abrasion resistant and have a high modulus
b. Do not abrade during scaling operations (e.g.with metal scalers or air-power abrasion systems like Prophy iet)
4. Biologic-depend on osseointegration and epithelial attachment
Ketorolac
Pharmacology
Ketorolac
Mechanism of action
primary action responsible for its anti-inflammatory/antipyretic/analgesic effects is inhibition of prostaglandin synthesis through inhibition of the enzyme cyclooxygenase (COX). Ketorolac is not a selective inhibitor of COX enzymes
Indications: short-term management of pain
Contraindications
hypersensitivity to ketorolac, and against patients with the complete or partial syndrome of nasal polyps, angioedema, bronchospastic reactivity or other allergic manifestations to aspirin or other non-steroidal anti-inflammatory drugs (due to possibility of severe anaphylaxis).