NEET MDS Synopsis
Angle's Classification of Malocclusion
OrthodonticsAngle's Classification of Malocclusion
Developed by Dr. Edward Angle in the early 20th century, this classification
is based on the relationship of the first molars and the canines. It is divided
into three main classes:
Class I Malocclusion (Normal Occlusion)
Description: The first molars are in a normal
relationship, with the mesiobuccal cusp of the maxillary first molar fitting
into the buccal groove of the mandibular first molar. The canines also have
a normal relationship.
Characteristics:
The dental arches are aligned.
There may be crowding, spacing, or other dental irregularities, but
the overall molar relationship is normal.
Class II Malocclusion (Distocclusion)
Description: The first molars are positioned such that
the mesiobuccal cusp of the maxillary first molar is positioned more than
one cusp width ahead of the buccal groove of the mandibular first molar.
Subdivisions:
Class II Division 1: Characterized by protruded
maxillary incisors and a deep overbite.
Class II Division 2: Characterized by retroclined
maxillary incisors and a deep overbite, often with a normal or reduced
overjet.
Characteristics: This class often results in an
overbite and can lead to aesthetic concerns.
Class III Malocclusion (Mesioocclusion)
Description: The first molars are positioned such that
the mesiobuccal cusp of the maxillary first molar is positioned more than
one cusp width behind the buccal groove of the mandibular first molar.
Characteristics:
This class is often associated with an underbite, where the lower
teeth are positioned more forward than the upper teeth.
It can lead to functional issues and aesthetic concerns.
2. Skeletal Classification
In addition to Angle's classification, malocclusion can also be classified
based on skeletal relationships, which consider the position of the maxilla and
mandible in relation to each other. This classification is particularly useful
in assessing the underlying skeletal discrepancies that may contribute to
malocclusion.
Class I Skeletal Relationship
Description: The maxilla and mandible are in a normal
relationship, similar to Class I malocclusion in Angle's classification.
Characteristics: The skeletal bases are well-aligned,
but there may still be dental irregularities.
Class II Skeletal Relationship
Description: The mandible is positioned further back
relative to the maxilla, similar to Class II malocclusion.
Characteristics: This can be due to a retruded mandible
or an overdeveloped maxilla.
Class III Skeletal Relationship
Description: The mandible is positioned further forward
relative to the maxilla, similar to Class III malocclusion.
Characteristics: This can be due to a protruded
mandible or a retruded maxilla.
3. Other Classifications
In addition to Angle's and skeletal classifications, malocclusion can also be
described based on specific characteristics:
Overbite: The vertical overlap of the upper incisors
over the lower incisors. It can be classified as:
Normal Overbite: Approximately 1-2 mm of overlap.
Deep Overbite: Excessive overlap, which can lead to
impaction of the lower incisors.
Open Bite: Lack of vertical overlap, where the
upper and lower incisors do not touch.
Overjet: The horizontal distance between the
labioincisal edge of the upper incisors and the linguoincisal edge of the
lower incisors. It can be classified as:
Normal Overjet: Approximately 2-4 mm.
Increased Overjet: Greater than 4 mm, often
associated with Class II malocclusion.
Decreased Overjet: Less than 2 mm, often associated
with Class III malocclusion.
Crossbite: A condition where one or more of the upper
teeth bite on the inside of the lower teeth. It can be:
Anterior Crossbite: Involves the front teeth.
Posterior Crossbite: Involves the back teeth.
Ampicillin
Pharmacology
Ampicillin offered a broader spectrum of activity than either of the original penicillins and allowed doctors to treat a broader range of both Gram-positive and Gram-negative infections. Ampicillin is often used in molecular biology as a test for the uptake of genes (e.g., by plasmids) by bacteria (e.g., E. coli)
COMPOSITE RESINS -ACID ETCH TECHNIQUE
Dental Materials
ACID ETCH TECHNIQUE
Cavities requiring added retention (to hold firmly) are treated with an acid etching technique. This technique improves the seal of the composite resin to the cavity wall. The enamel adjacent to the margins of the preparation is slightly decalcified with a 40 to 50 percent phosphoric acid solution. This etched enamel enhances the mechanical retention of the composite resin. In addition, the acid etch technique is used to splint unstable teeth to adjacent teeth. The acid is left on the cut tooth structure only 15 seconds, in accordance with the directions for one common commercial brand. The area is then flushed with water for a minimum of 30 seconds to remove the decalcified material. Etched tooth structure will have a chalky appearance.
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.
The Transition from the Deciduous to the Permanent Dentition.
Dental Anatomy
The Transition from the Deciduous to the Permanent Dentition.
1. The transition begins with the eruption of the four first permanent molars, and replacement of the lower deciduous central incisors by the permanent lower central incisors.
2. Complete resorption of the deciduous tooth roots permits exfoliation of that tooth and replacement by the permanent (successional) teeth
3. The mixed dentition exists from approximately age 6 years to approximately age 12 years. In contrast, the intact deciduous dentition is functional from age 2 - 2 /2 years of age to 6 years of age.
4. The enamel organ of each permanent anterior tooth is connected to the oral epithelium via a fibrous cord, the gubernaculum. The foramina through which it passes can be seen in youthful skulls
The deciduous second molars are particularly important. It is imperative that the deciduous second molars be preserved until their normal time of exfoliation. This prevent mesial migration of the first permanent molars.
Use a space maintainer in the event that a second deciduous molar is lost prematurely
Transpalatal Arch
PedodonticsTranspalatal Arch
The transpalatal arch (TPA) is a fixed orthodontic appliance used primarily
in the maxillary arch to maintain or regain space, particularly after the loss
of a primary molar or in cases of unilateral space loss. It is designed to
provide stability to the molars and prevent unwanted movement.
Indications
Unilateral Loss of Space:
The transpalatal arch is particularly effective in cases where there
is unilateral loss of space. It helps maintain the position of the
remaining molar and prevents mesial movement of the adjacent teeth.
It can also be used to maintain the arch form and provide anchorage
during orthodontic treatment.
Contraindications
Bilateral Loss of Space:
The use of a transpalatal arch is contraindicated in cases of
bilateral loss of space. In such situations, the appliance may not
provide adequate support or stability, and other treatment options may
be more appropriate.
Limitations/Disadvantages
Tipping of Molars:
One of the primary limitations of the transpalatal arch is the
potential for both molars to tip together. This tipping can occur if the
arch is not properly designed or if there is insufficient anchorage.
Tipping can lead to changes in occlusion and may require additional
orthodontic intervention to correct.
PROPERTIES OF TRIACYLGTYCEROLS
Biochemistry
PROPERTIES OF TRIACYLGTYCEROLS
1. Hydrolysis : Triacylglycerols undergo stepwise enzymatic hydrolysis to finally liberate free fatty acids and glycerol.
The process of hydrolysis, catalysed by lipases is important for digestion of fat in the gastrointestinal tract and fat mobilization from the adipose tissues.
2. Saponification : The hydrolysis of triacylglycerols by alkali to produce glycerol and soaps is known as saponification.
3.Rancidity: Rancidity is the term used to represent the deterioration of fats and oils resulting in an unpleasant taste. Fats containing unsaturated fatty acids are more susceptible to rancidity.
Hydrolytic rancidity occurs due to partial hydrolysis of triacylglycerols by bacterial enzymes.
Oxidative rancidity is due to oxidation of unsaturated fatty acids.
This results in the formation of unpleasant products such as dicarboxylic acids, aldehydes, ketones etc.
Antioxidants : The substances which can prevent the occurrence of oxidative rancidity are known as antioxidants.
Trace amounts of antioxidants such as tocopherols (vitamin E), hydroquinone, gallic acid and c,-naphthol are added to the commercial preparations of fats and oils to prevent rancidity. Propylgallate, butylatedhydroxyanisole (BHA) and butylated hydroxytoluene (BHT) are the antioxidants used in food preservation.
Lipid peroxidation in vivo: In the living cells, lipids undergo oxidation to produce peroxides and free radicals which can damage the tissue. .
The free radicals are believed to cause inflammatory diseases, ageing, cancer , atherosclerosis etc
Iodine number : lt is defined as the grams (number) of iodine absorbed by 100 g of fat or oil. lodine number is useful to know the relative
unsaturation of fats, and is directly proportional to the content of unsaturated fatty acids
Determination of iodine number will help to know the degree of adulteration of a given oil
Saponification number : lt is defined as the mg (number) of KOH required to hydrolyse (saponify) one gram of fat or oiL
Reichert-Meissl (RM) number: lt is defined as the number of ml 0.1 N KOH required to completely neutralize the soluble volatile fatty acids distilled from 5 g fat. RM number is useful in testing the purity of butter since it contains a good concentration of volatile fatty acids (butyric acid, caproic acid and caprylic acid).
Acid number : lt is defined as the number of mg of KOH required to completely neutralize free fatty acids present in one gram fat or oil. In normal circumstances, refined oils should be free from any free fatty acids.
Digital Radiology
Radiology
Digital Radiology
Advances in computer and X-ray technology now permit the use of systems that employ sensors in place of X-ray ?lms (with emulsion). The image is either directly or indirectly converted into a digital representation that is displayed on a computer screen.
DIGITAL IMAGE RECEPTORS
- charged coupled device (CCD) used
- Pure silicon divided into pixels.
- Electromagnetic energy from visible light or X-rays interacts with pixels to create an electric charge that can be stored.
- Stored charges are transmitted electronically and create an analog output signal and displayed via digital converter (analog to digital converter).
ADVANTAGES OF DIGITAL TECHNIQUE
Immediate display of images.
Enhancement of image (e.g., contrast, gray scale, brightness).
Radiation dose reduction up to 60%.
Major disadvantage: High initial cost of sensors. Decreased image resolution and contrast as compared to D speed ?lms.
DIRECT IMAGING
- CCD or complementary metal oxide semiconductor (CMOS) detector used that is sensitive to electromagnetic radiation.
- Performance is comparable to ?lm radiography for detection of periodontal lesions and proximal caries in noncavitated teeth.
INDIRECT IMAGING
- Radiographic ?lm is used as the image receiver (detector).
- Image is digitized from signals created by a video device or scanner that views the radiograph.
Sensors
STORAGE PHOSPHOR IMAGING SYSTEMS
Phosphor screens are exposed to ionizing radiation which excites BaFBR:EU+2 crystals in the screen storing the image.
A computer-assisted laser then promotes the release of energy from the crystals in the form of blue light.
The blue light is scanned and the image is reconstructed digitally.
ELECTRONIC SENSOR SYSTEMS
X-rays are converted into light which is then read by an electronic sensor such as a CCD or CMOS.
Other systems convert the electromagnetic radiation directly into electrical impulses.
Digital image is created out of the electrical impulses.