NEET MDS Synopsis
Biomechanics of complete edentulous state
Prosthodontics
The clinical implications of an edentulous stomatognathic system are considered under the following factors:
(1) modi?cations in areas of support .
(2) functional and parafunctional considerations.
(3) changes in morphologic face height, and temporomandibular joint (TMJ).
(4) cosmetic changes and adaptive responses
Support mechanism for complete dentures
Mucosal support and masticatory loads
- The area of mucosa available to receive the load from complete dentures is limited when compared with the corresponding areas of support available for natural dentitions.
- The mean denture bearing area to be 22.96 cm2 in the edentulous maxillae and approximately 12.25 cm2 in an edentulous mandible
- In fact, any disturbance of the normal metabolic processes may lower the upper limit of mucosal tolerance and initiate in?ammation
Residual ridge
The residual ridge consists of denture-bearing mucosa, the submucosa and periosteum, and the underlying residual alveolar bone.
The alveolar bone supporting natural teeth receives tensile loads through a large area of periodontal ligament, whereas the edentulous residual ridge receives vertical, diagonal, and horizontal loads applied by a denture with a surface area much smaller than the total area of the periodontal ligaments of all the natural teeth that had been present.
There are two physical factors involved in denture retention that are under the control of the dentist
- The maximal extension of the denture base
- maximal intimate contact of the denture base and its basal seat
- The buccinator, the orbicularis oris, and the intrinsic and extrinsic muscles of the tongue are the key muscles that the dentist harnesses to achieve this objective by means of impression techniques.
- The design of the labial buccal and lingual polished surface of the denture and the form of the dental arch are considered in balancing the forces generated by the tongue and perioral musculature.
Function: mastication and other mandibular movements
Mastication consists of a rhythmic separation and apposition of the jaws and involves biophysical and biochemical processes, including the use of the lips, teeth, cheeks, tongue, palate, and all the oral structures to prepare food for swallowing.
- The maximal bite force in denture wearers is ?ve to six times less than that in dentulous individuals.
- The pronounced differences between persons with natural teeth and patients with complete dentures are conspicuous in this functional context:
(1) the mucosal mechanism of support as opposed to support by the periodontium ;
(2) the movements of the dentures during mastication;
(3) the progressive changes in maxillomandibular relations and the eventual migration of dentures
(4) the different physical stimuli to the sensor motor systems.
Parafunctional considerations
- Parafunctional habits involving repeated or sustained occlusion of the teeth can be harmful to the teeth or other components of the masticatory system.
- Teeth clenching is common and is a frequent cause of the complaint of soreness of the denture-bearing mucosa.
- In the denture wearer, parafunctional habits can cause additional loading on the denture-bearing tissues
Force generated during mastication and parafunction
Functional (Mastication)
Direction -> Mainly vertical
Duration and magnitude -> Intermittent and light diurnal only
Parafunction
Direction -> Frequently horizontalas well as vertical
Duration and magnitude -> Prolonged, possibly excessive Both diurnal and nocturnal
Changes in morphology (face height), occlusion, and the TMJs
The reduction of the residual ridges under complete dentures and the accompanying reduction in vertical dimension of occlusion tend to cause a reduction in the total face height and a resultant mandibular prognathism.
In complete denture wearers, the mean reduction in height of the mandibular residual alveolar ridge measured in the anterior region may be approximately four times greater than the mean reduction occurring in the maxillary residual alveolar process
Occlusion
- In complete denture prosthodontics, the position of planned maximum intercuspation of teeth is established to coincide with the patient’s centric relation.
-The coincidence of centric relation and centric occlusion is consequently referred to as centric relation occlusion (CRG).
- Centric relation at the established vertical dimension has potential for change. This change is brought about by alterations indenture-supporting tissues and facial height, as well as by morphological changes in the TMJs.
TMJ changes
impaired dental ef?ciency resulting from partial tooth loss and absence of or incorrect prosthodontic treatment can in?uence the outcome of temporomandibular disorders.
Aesthetic, behavioral, and adaptive response
Aesthetic changes associated with the edentulous state.
- Deepening of nasolabial groove
- Loss of labiodentals angle
- Narrowing of lips
- Increase in columellae philtral angle
- Prognathic appearance
Parvoviruses
General Pathology
Parvoviruses
- smallest DNA virus
- erythema infectiosum (fifth disease) is characterized by a confluent rash usually beginning on the cheeks ("slapped face") which extends centripetally to involve the trunk; fever, malaise and respiratory problems; and arthralgias and joint swelling (50%).
other associations:
- aplastic anemia in patients with chronic hemolytic anemias (e.g., sickle cell disease, spherocytosis).
- repeated abortions associated with hydrops fetalis.
- pure RBC aplasia by involving the RBC precursors (no reticulocytes peripherally).
-chronic arthritis
Cement Applications
Dental Materials
Root canal sealers
Applications
Cementation of silver cone gutta-percha point
Paste filling material
Types
Zinc oxide-eugenol cement types
Noneugenol cement types
Therapeutic cement types
properties
Physical-radiopacity
Chemical-insolubility
Mechanical-flow; tensile strength
Biologic-inertness
Gingival tissue packs
Application-provide temporary displacement of gingival tissues
Composition-slow setting zinc oxide-eugenol cement mixed with cotton twills for texture and strength
Surgical dressings
1.Application-gingival covering after periodontal surgery
2. Composition-modified zinc oxide-eugenol cement (containing tannic, acid. rosin, and various oils)
Orthodontic cements
Application-cementation of orthodontic bands
Composition-zinc phosphate cement
Manipulation
Zinc phosphate types are routinely mixed with cold or frozen mixing slab to extend the working time
Enamel bonding agent types use acid etching for improved bonding
Band, bracket, or cement removal requires special care
Marsupialization
Oral and Maxillofacial SurgeryMarsupialization
Marsupialization, also known as decompression, is a surgical
procedure used primarily to treat cystic lesions, particularly odontogenic
cysts, by creating a surgical window in the wall of the cyst. This technique
aims to reduce intracystic pressure, promote the shrinkage of the cyst, and
encourage bone fill in the surrounding area.
Key Features of Marsupialization
Indication:
Marsupialization is indicated for large cystic lesions that are not
amenable to complete excision due to their size, location, or proximity
to vital structures. It is commonly used for:
Odontogenic keratocysts
Dentigerous cysts
Radicular cysts
Other large cystic lesions in the jaw
Surgical Technique:
Creation of a Surgical Window:
The procedure begins with the creation of a window in the wall
of the cyst. This is typically done through an intraoral approach,
where an incision is made in the mucosa overlying the cyst.
Evacuation of Cystic Content:
The cystic contents are evacuated, which helps to decrease the
intracystic pressure. This reduction in pressure is crucial for
promoting the shrinkage of the cyst and facilitating bone fill.
Suturing the Cystic Lining:
The remaining cystic lining is sutured to the edge of the oral
mucosa. This can be done using continuous sutures or interrupted
sutures, depending on the surgeon's preference and the specific
clinical situation.
Benefits:
Pressure Reduction: By decreasing the intracystic
pressure, marsupialization can lead to the gradual reduction in the size
of the cyst.
Bone Regeneration: The procedure promotes bone fill
in the area previously occupied by the cyst, which can help restore
normal anatomy and function.
Minimally Invasive: Compared to complete cyst
excision, marsupialization is less invasive and can be performed with
less morbidity.
Postoperative Care:
Patients may experience some discomfort and swelling following the
procedure, which can be managed with analgesics.
Regular follow-up appointments are necessary to monitor the healing
process and assess the reduction in cyst size.
Oral hygiene is crucial to prevent infection at the surgical site.
Outcomes:
Marsupialization can be an effective treatment for large cystic
lesions, leading to significant reduction in size and promoting bone
regeneration. In some cases, if the cyst does not resolve completely,
further treatment options, including complete excision, may be
considered.
Phenytoin
Pharmacology
Phenytoin (Dilantin): for tonic-clonic and all partial seizures (not effective against absence seizures)
Mechanism: ↓ reactivation of Na channels (↑ refractory period, blocks high frequency cell firing, ↓ spread of seizure activity from focus)
Side effects: ataxia, vertigo, hirsutism (abnormal hair growth), gingival hyperplasia, osteomalacia (altered vitamin D metabolism and ↓ Ca absorption), blood dyscrasias (rare; megaloblastic anemia, etc)
Drug interactions: induces hepatic microsomal enzymes (can ↓ effectiveness of other drugs); binds tightly to plasma proteins and can displace other drugs
Guardsman Fracture
Oral and Maxillofacial SurgeryGuardsman Fracture (Parade Ground Fracture)
Definition: The Guardsman fracture, also known as the parade
ground fracture, is characterized by a combination of symphyseal and bilateral
condylar fractures of the mandible. This type of fracture is often associated
with specific mechanisms of injury, such as direct trauma or falls.
Fracture Components:
Symphyseal Fracture: Involves the midline of the
mandible where the two halves meet.
Bilateral Condylar Fractures: Involves fractures of
both condyles, which are the rounded ends of the mandible that
articulate with the temporal bone of the skull.
Mechanism of Injury:
Guardsman fractures typically occur due to significant trauma, such
as a fall or blunt force impact, which can lead to simultaneous
fractures in these areas.
Clinical Implications:
Inadequate Fixation: If the fixation of the
symphyseal fracture is inadequate, it can lead to complications such as:
Splaying of the Cortex: The fracture fragments
may open on the lingual side, leading to a widening of the fracture
site.
Increased Interangular Distance: The splaying
effect increases the distance between the angles of the mandible,
which can affect occlusion and jaw function.
Symptoms:
Patients may present with pain, swelling, malocclusion, and
difficulty in jaw movement. There may also be visible deformity or
asymmetry in the jaw.
Management:
Surgical Intervention: Proper fixation of both the
symphyseal and condylar fractures is crucial. This may involve the use
of plates and screws to stabilize the fractures and restore normal
anatomy.
TRICYCLIC ANTIDEPRESSANTS
Pharmacology
TRICYCLIC ANTIDEPRESSANTS
e.g. amitriptyline, imipramine, nortriptyline
Belong to first generation antidepressants
ACTION:
Inhibit 5-HT(5-hydroxytryptamine) and norepinephrine reuptake
slow clearance of norepinephrine & 5-HT from the synapse
enhance norepinephrine & 5-HT neuro-transmission
MODE OF ACTIONMODE OF ACTION
TCAs also block
– muscarinic acetylcholine receptors
– histamine receptors
– 5-HT receptors
– α1 adrenoceptors
Onset of antidepressant activity takes 2-3 weeks
PHARMACOKINETICS
- Readily absorbed from the gastro-intestinal tract
- Bind strongly to plasma albumin
- Has a large volume of distribution(as a result of binding to extravascular tissues)
- Undergo liver CYP metabolism into biologically active metabolites
- These metabolites are inactivated via glucuronidation and excreted in urine
ADVERSE DRUG REACTIONS
Antimuscarinic - dry mouth, blurred vision, constipation and urinary retention
Antihistamine – drowsiness
adrenoceptor blockage(+/- central effect) postural hypotension
Reduce seizure threshold
Testicular enlargement, gynaecomastia, galactorrhoea
AV-conduction blocks and cardiac arrhythmias
TOXICITY
- Fatal in toxicity
- Most important toxic effect is, slowing of depolarisation of the cardiac action potential by blocking fast sodium channels ("quinidine-like" effect)
- delays propagation of depolarisation through both myocardium and conducting tissue
- prolongation of the QRS complex and the PR/QT intervals
- predisposition to cardiac arrhythmias
DRUG INTERACTIONS
Pharmacodynamic:
– ↑ sedation with antihistamines, alcohol
– ↑ antimuscarinic effects with anticholinergics– ↑ antimuscarinic effects with anticholinergics
– Hypertension and arrhythmias with MAOIs- should be given at least 14 days apart
Pharmacokinetic (via altering CYP metabolism)
– ↓ plasma concentration of TCA by- carbamazepine, rifampicin
– ↑ plasma concentration of TCA by- cimetidine, calcium channel blockers,fluoxetine
OTHER CLINICAL USES OF AMITRIPTYLINE
- Treatment of nocturnal enuresis in children
- Treatment of neuropathic pain
- Migraine prophylaxis
EMBOLISM
General Pathology
EMBOLISM
An embolus is a detached intravascular solid, liquid, or gaseous mass that is carried by the blood to a site distant from its point of origin
99% due to dislodged thrombus
Types:
1. Thrombo-embolism
2. Fat embolism
3. Air embolism
4. Nitrogen embolism
Emboli result in partial or complete vascular occlusion.
The consequences of thromboembolism include ischemic necrosis (infarction) of downstream tissue
PULMONARY THROMBOEMBOLISM
- 95% originate from deep veins of L.L
Special variants: - Saddle embolus: at bifurcation of Pulmonary artery
Paradoxical embolus: Passage of an embolus from venous to systemic circulation through IAD, IVD
CLINICAL CONSEQUENCE OF PULMONARY THROMBOEMBOLISM :
Most pulmonary emboli (60% to 80%) are clinically silent because they are small
a. Organization: 60 – 80 %
b. Sudden death, Right ventricle failure, CV collapse when more than 60 % of pulmonary vessels are obstructed.
c. Pulmonary hemorrhage: obstruction of medium sized arteries.
d. Pulmonary Hypertension and right ventricular failure due to multiple emboli over a long time.
Systemic thromboembolism
Emboli traveling within the arterial circulation
80% due to intracardiac mural thrombi
2/3 Lt. ventricular failure
The major targets are:
1. Lower limbs 75%
2. Brain 10%
3. Intestines
4. Kidneys
5. Spleen
Fat embolism
Causes
1. Skeletal injury (fractures of long bones )
2. Adipose tissue Injury
Mechanical obstruction is exacerbated by free fatty acid release from the fat globules, causing local toxic injury to endothelium. - In skeletal injury, fat embolism occurs in 90% of cases, but only 10% or less have clinical findings
Fat embolism syndrome is characterized by
A. Pulmonary Insufficiency
B. Neurologic symptoms
C. Anemia
D. Thrombocytopenia
E. Death in 10% of the case
Symptoms appears 1-3 days after injury
Tachypnea, Dyspnea, Tachycardia and Neurological symptoms
Air Embolism
causes: 1. Obstetric procedures
2. Chest wall injury
3. Decompression sickness: in Scuba and deep-sea divers ((nitrogen ))
More then 100ml of air is required to produce clinical effect.
Clinical consequence
1. Painful joints: due to rapid formation of gas bubbles within Sk. Muscles and supporting tissues.
2. Focal ischemia in brain and heart
3. Lung edema, Hemorrhage, atelectasis, emphysema, which all lead to Respiratory distress. (chokes)
4. caisson disease: gas emboli in the bones leads to multiple foci of ischemic necrosis, usually the heads of the femurs, tibias, and humeri
Amniotic fluid embolism
- Mortality Rate = 20%-40%
- Very rare complication of labor
- due to infusion of amniotic fluid into maternal circulation via tears in placental membranes and rupture of uterine veins.
- sudden severe dyspnea, cyanosis, and hypotensive shock, followed by seizures, DIC and coma
- Findings: Squamous cells, languo hair, fat, mucin …..etc within the pulmonary microcirculation