NEET MDS Synopsis
CASTING
Dental Materials
CASTING: casting is the process by which the wax pattern of a restoration is converted to a replicate in a dental alloy. The casting process is used to make dental restorations such as inlays, onlays, crowns, bridges and removable partial dentures.
Objectives of casting
1) To heat the alloy as quickly as possible to a completely molten condition.
2) To prevent oxidation by heating the metal with awell adjusted torch .
3) To produce a casting with sharp details by having adequate pressure to the well melted metal to force into the mold.
STEPS IN MAKING A CAST RESTORATION
1. TOOTH PREPARATION
2. IMPRESSION
3. DIE PREPARATION
4. WAX PATTERN FABRICATION
5. SPRUING
Miconazole
Pharmacology
Miconazole
Miconazole is an imidazole antifungal agent commonly used in topical sprays, creams and ointments applied to the skin to cure fungal infections such as Athlete's foot and Jock itch. It may also be used internally to treat vaginal yeast infection.
When used by a person taking the anticoagulant medication warfarin, Miconazole may cause an adverse reaction which can lead to excessive bleeding or bruising.
Propofol
Pharmacology
Propofol -Intravenous Anesthetics
- A nonbarbiturate anesthetic
- It is very lipid-soluble, acts rapidly and has a short recovery time.
- It is associated with less nausea and vomiting than some of the other IV anesthetics.
- Propofol is very similar to thiopental in its effects on the cardiorespiratory system.
- It does not have any analgesic properties but lowers the dose of opioid needed when the two agents are used in combination.
- The most significant adverse cardiovascular effect associated with propofol administration is hypotension. It should be used with caution in patients with cardiac disease.
Ridge Augmentation
Oral and Maxillofacial SurgeryRidge Augmentation Procedures
Ridge augmentation procedures are surgical techniques used to increase the
volume and density of the alveolar ridge in the maxilla and mandible. These
procedures are often necessary to prepare the site for dental implants,
especially in cases where there has been significant bone loss due to factors
such as tooth extraction, periodontal disease, or trauma. Ridge augmentation can
also be performed in conjunction with orthognathic surgery to enhance the
overall facial structure and support dental rehabilitation.
Indications for Ridge Augmentation
Insufficient Bone Volume: To provide adequate support
for dental implants.
Bone Resorption: Following tooth extraction or due to
periodontal disease.
Facial Aesthetics: To improve the contour of the jaw
and facial profile.
Orthognathic Surgery: To enhance the results of jaw
repositioning procedures.
Types of Graft Materials Used
Ridge augmentation can be performed using various graft materials, which can
be classified into the following categories:
Autografts:
Bone harvested from the patient’s own
body, typically from intraoral sites (e.g., chin, ramus) or extraoral
sites (e.g., iliac crest).
Advantages: High biocompatibility, osteogenic
potential, and lower risk of rejection or infection.
Disadvantages: Additional surgical site, potential
for increased morbidity, and limited availability.
Allografts:
Bone grafts obtained from a human donor
(cadaveric bone) that have been processed and sterilized.
Advantages: No additional surgical site required,
readily available, and can provide a scaffold for new bone growth.
Disadvantages: Risk of disease transmission and
potential for immune response.
Xenografts:
Bone grafts derived from a different
species, commonly bovine (cow) bone.
Advantages: Biocompatible and provides a scaffold
for bone regeneration.
Disadvantages: Potential for immune response and
slower resorption compared to autografts.
Alloplasts:
Synthetic materials used for bone
augmentation, such as hydroxyapatite, calcium phosphate, or bioactive
glass.
Advantages: No risk of disease transmission,
customizable, and can be designed to promote bone growth.
Disadvantages: May not integrate as well as natural
bone and can have variable resorption rates.
Surgical Techniques
Bone Grafting:
The selected graft material is placed in the deficient area of the
ridge to promote new bone formation. This can be done using various
techniques, including:
Onlay Grafting: Graft material is placed on top
of the existing ridge.
Inlay Grafting: Graft material is placed within
the ridge.
Guided Bone Regeneration (GBR):
A barrier membrane is placed over the graft material to prevent soft
tissue infiltration and promote bone healing. This technique is often
used in conjunction with grafting.
Sinus Lift:
In the maxilla, a sinus lift procedure may be performed to augment
the bone in the posterior maxilla by elevating the sinus membrane and
placing graft material.
Combination with Orthognathic Surgery:
Ridge augmentation can be performed simultaneously with orthognathic
surgery to correct skeletal discrepancies and enhance the overall facial
structure.
Anchorage
OrthodonticsAnchorage in orthodontics refers to the resistance to unwanted tooth movement
during orthodontic treatment. It is a critical concept that helps orthodontists
achieve desired tooth movements while preventing adjacent teeth or the entire
dental arch from shifting. Proper anchorage is essential for effective treatment
planning and execution, especially in complex cases where multiple teeth need to
be moved simultaneously.
Types of Anchorage
Absolute Anchorage:
Definition: This type of anchorage prevents any
movement of the anchorage unit (the teeth or structures providing
support) during treatment.
Application: Used when significant movement of
other teeth is required, such as in cases of molar distalization or when
correcting severe malocclusions.
Methods:
Temporary Anchorage Devices (TADs): Small
screws or plates that are temporarily placed in the bone to provide
stable anchorage.
Extraoral Appliances: Devices like headgear
that anchor to the skull or neck to prevent movement of certain
teeth.
Relative Anchorage:
Definition: This type allows for some movement of
the anchorage unit while still providing enough resistance to achieve
the desired tooth movement.
Application: Commonly used in cases where some
teeth need to be moved while others serve as anchors.
Methods:
Brackets and Bands: Teeth can be used as
anchors, but they may move slightly during treatment.
Class II or Class III Elastics: These can be
used to create a force system that allows for some movement of the
anchorage unit.
Functional Anchorage:
Definition: This type utilizes the functional
relationships between teeth and the surrounding structures to achieve
desired movements.
Application: Often used in conjunction with
functional appliances that guide jaw growth and tooth positioning.
Methods:
Functional Appliances: Such as the Herbst or
Bionator, which reposition the mandible and influence the growth of
the maxilla.
Factors Influencing Anchorage
Tooth Position: The position and root morphology of the
anchorage teeth can affect their ability to resist movement.
Bone Quality: The density and health of the surrounding
bone can influence the effectiveness of anchorage.
Force Magnitude and Direction: The amount and direction
of forces applied during treatment can impact the stability of anchorage.
Patient Compliance: Adherence to wearing appliances as
prescribed is crucial for maintaining effective anchorage.
Clinical Considerations
Treatment Planning: Proper assessment of anchorage
needs is essential during the treatment planning phase. Orthodontists must
determine the type of anchorage required based on the specific movements
needed.
Monitoring Progress: Throughout treatment,
orthodontists should monitor the anchorage unit to ensure it remains stable
and that desired tooth movements are occurring as planned.
Adjustments: If unwanted movement of the anchorage unit
occurs, adjustments may be necessary, such as changing the force system or
utilizing additional anchorage methods.
INVESTING
Dental Materials
INVESTING
Mixing investment with distilled water is done according to the manufacturers ratio in a clean dry bowl without entrapment of the air into the mix.
Mixing methods:
a. Hand mixing and the use of the vibrator to remove air bubbles.
b. Vacuum mixing- This is the better method because it removes air bubbles as well as gases that are produced and thus produces a smoother mix.
Methods of investing:
a. Hand investing
b. Vacuum investing
Hand investing:
First the mixed investment is applied on all the surfaces of the pattern with a soft brush. Blow off any excess investment gently, thus leaving a thin film of investment over the pattern, then apply again.
Then the coated pattern can be invested by two methods;
1. Placing the pattern in the ring first and then filling the ring full with investment.
2. Filling the ring with the investment first and then force the pattern through into it.
Vacuum investing :
Vacuum investing unit: This consists of the chamber of small cubic capacity from which air can be evacuated quickly and in which casting ring can be placed.
Evacuation of air can be done by electrically or water driven vacuum pump.
Procedure:
The ring filled with investment is placed in the vacuum chamber. Air entry tube is closed. Then the vacuum is applied. The investment will rise with froth vigorously for about 10-15 sec and then settles back. This indicates that air has been extracted from the ring. The pressure is now restored to atmospheric by opening the air entry tap gradually at first and then more rapidly as the investment settles back around the pattern. Then the ring is removed from the chamber and the investment is allowed to set. Modern investing unit does both mixing and investing under vacuum and is considered better than hand mixing and pouring.
Then there are two alternatives to be followed depending upon what type of expansion is to be achieved in order to compensate for metal shrinkage. They are:
1. If hygroscopic expansion of the investment is to be achieved then immediately immerse the filled ring in water at the temperature of 37C.
Or “under controlled water adding technique”. A soft flexible rubber ring is used instead of usual lined metal ring. Pattern is invested as usual. Then specified amount of water is added on top of the investment in the rubber ring and the investment is allowed to set at room temperature. In this way only enough water is added to the investment to provide the desired expansion.
2. If thermal expansion of the investment is to be achieved, then investment is allowed to set by placing the ring on the bench for 1 hour or as recommended by the manufacturer.
SPECIAL VISCERAL AFFERENT (SVA) PATHWAYS
Physiology
SPECIAL VISCERAL AFFERENT (SVA) PATHWAYS
Taste
Special visceral afferent (SVA) fibers of cranial nerves VII, IX, and X conduct signals into the solitary tract of the brainstem, ultimately terminating in the nucleus of the solitary tract on the ipsilateral side.
Second-order neurons cross over and ascend through the brainstem in the medial lemniscus to the VPM of the thalamus.
Thalamic projections to area 43 (the primary taste area) of the postcentral gyrus complete the relay.
SVA VII fibers conduct from the chemoreceptors of taste buds on the anterior twothirds of the tongue, while SVA IX fibers conduct taste information from buds on the posterior one-third of the tongue.
SVA X fibers conduct taste signals from those taste cells located throughout the fauces.
Smell
The smell-sensitive cells (olfactory cells) of the olfactory epithelium project their central processes through the cribiform plate of the ethmoid bone, where they synapse with mitral cells. The central processes of the mitral cells pass from the olfactory bulb through the olfactory tract, which divides into a medial and lateral portion The lateral olfactory tract terminates in the prepyriform cortex and parts of the amygdala of the temporal lobe.
These areas represent the primary olfactory cortex. Fibers then project from here to area 28, the secondary olfactory area, for sensory evaluation. The medial olfactory tract projects to the anterior perforated substance, the septum pellucidum, the subcallosal area, and even the contralateral olfactory tract.
Both the medial and lateral olfactory tracts contribute to the visceral reflex pathways, causing the viscerosomatic and viscerovisceral responses.
Paget Disease
General Pathology
Paget Disease (Osteitis Deformans)
This unique bone disease is characterized by repetitive episodes of exaggerated, regional osteoclastic activity (osteolytic stage), followed by exuberant bone formation (mixed osteoclastic-osteoblastic stage), and finally by exhaustion of cellular activity (osteosclerotic stage). The net effect of this process is a gain in bone mass; however, the newly formed bone is disordered and lacks strength. Paget disease usually does not occur until mid-adulthood but becomes progressively more common thereafter. The pathognomonic histologic feature is a mosaic pattern of lamellar bone (likened to a jigsaw puzzle) due to prominent cement lines that haphazardly fuse units of lamellar bone. (Fig. 12-5) The axial skeleton and proximal femur are involved in the majority of cases. In patients with extensive disease, hypervascularity of the marrow spaces can result in high-output congestive heart failure. Cranial nerves impingement also occurs and can lead to head ache and auditory disturbances. Rarely Paget disease is complicated by bone sarcoma (usually osteogenic).