NEET MDS Synopsis
Contractility
Physiology
Contractility : Means ability of cardiac muscle to convert electrical energy of action potential into mechanical energy ( work).
The excitation- contraction coupling of cardiac muscle is similar to that of skeletal muscle , except the lack of motor nerve stimulation.
Cardiac muscle is a self-excited muscle , but the principles of contraction are the same . There are many rules that control the contractility of the cardiac muscles, which are:
1. All or none rule: due to the syncytial nature of the cardiac muscle.There are atrial syncytium and ventricular syncytium . This rule makes the heart an efficient pump.
2. Staircase phenomenon : means gradual increase in muscle contraction following rapidly repeated stimulation..
3. Starling`s law of the heart: The greater the initial length of cardiac muscle fiber , the greater the force of contraction. The initial length is determined by the degree of diastolic filling .The pericardium prevents overstretching of heart , and allows optimal increase in diastolic volume.
Thankful to this law , the heart is able to pump any amount of blood that it receives. But overstretching of cardiac muscle fibers may cause heart failure.
Factors affecting contractility ( inotropism)
I. Positive inotropic factors:
1. sympathetic stimulation: by increasing the permeability of sarcolemma to calcium.
2. moderate increase in temperature . This due to increase metabolism to increase ATP , decrease viscosity of myocardial structures, and increasing calcium influx.
3. Catecholamines , thyroid hormone, and glucagon hormones.
4. mild alkalosis
5. digitalis
6. Xanthines ( caffeine and theophylline )
II. Negative inotropic factors:
1. Parasympathetic stimulation : ( limited to atrial contraction)
2. Acidosis
3. Severe alkalosis
4. excessive warming and cooling .
5. Drugs ;like : Quinidine , Procainamide , and barbiturates .
6. Diphtheria and typhoid toxins.
Phenytoin-Induced Gingival Overgrowth
PedodonticsPhenytoin-Induced Gingival Overgrowth
Phenytoin (Dilantin):
An anticonvulsant medication primarily used in the treatment of
epilepsy.
First introduced in 1938 by Merrit and Putnam.
Gingival Hyperplasia
Gingival hyperplasia refers to the overgrowth of gum tissue, which
can lead to aesthetic concerns and functional issues, such as difficulty
in maintaining oral hygiene.
Historical Context:
The association between phenytoin therapy and gingival hyperplasia
was first reported by Kimball in 1939.
In his study, 57% of 119 patients taking phenytoin for seizure
control experienced some degree of gingival overgrowth.
Mechanism of Gingival Overgrowth
Fibroblast Activity:
Early research indicated an increase in the number of fibroblasts in
the gingival tissues of patients receiving phenytoin.
This led to the initial terminology of "Dilantin hyperplasia."
Current Understanding:
Subsequent studies, including those by Hassell and colleagues, have
shown that true hyperplasia does not exist in this condition.
Findings indicate:
There is no excessive collagen accumulation per unit of tissue.
Fibroblasts do not appear abnormal in number or size.
As a result, the term phenytoin-induced gingival overgrowth is
now preferred, as it more accurately reflects the condition.
Clinical Implications
Management:
Patients on phenytoin should be monitored for signs of gingival
overgrowth, especially if they have poor oral hygiene or other risk
factors.
Dental professionals should educate patients about maintaining good
oral hygiene practices to minimize the risk of gingival overgrowth.
In cases of significant overgrowth, treatment options may include:
Improved oral hygiene measures.
Professional dental cleanings.
Surgical intervention (gingivectomy) if necessary.
Patient Education:
It is important to inform patients about the potential side effects
of phenytoin, including gingival overgrowth, and the importance of
regular dental check-ups.
Nephrosclerosis
General Pathology
Nephrosclerosis
Disease of the renal arteries.
Clinical manifestations:
(1) Benign (arterial) nephrosclerosis → Caused by the formation of atherosclerotic plaques in the renal artery. Results in narrowing of the arterioles.
(2) Malignant nephrosclerosis → Caused by malignant hypertension. Common signs of malignant hypertension include severe hypertension, retinal hemorrhages, and hypertrophy of the left ventricle. Results in inflammatory changes in the vascular walls, which may lead to rupture of the glomerular capillaries.
FUNCTIONS OF PERIODONTIUM
Dental Anatomy
FUNCTIONS OF PERIODONTIUM
Tooth support
Shock absorber
Sensory (vibrations appreciated in the middle ear/reflex jaw opening)
Caries Risk Assessment Tool
PedodonticsThe American Academy of Pediatric Dentistry (AAPD) Caries Risk Assessment
Tool is designed to evaluate a child's risk of developing dental caries
(cavities). The tool considers various factors to categorize a child's risk
level as low, moderate, or high.
Low Risk:
- No carious (cavitated) teeth in the past 24 months
- No enamel white spot lesions (initial stages of tooth decay)
- No visible dental plaque
- Low incidence of gingivitis (mild gum inflammation)
- Optimal exposure to fluoride (both systemic and topical)
- Limited consumption of simple sugars (at meal times only)
Moderate Risk:
- Carious teeth in the past 12 to 24 months
- One area of white spot lesion
- Gingivitis present
- Suboptimal systemic fluoride exposure (e.g., not receiving fluoride
supplements or living in a non-fluoridated water area)
- One or two between-meal exposures to simple sugars
High Risk:
- Carious teeth in the past 12 months
- More than one area of white spot lesion
- Visible dental plaque
- Suboptimal topical fluoride exposure (not using fluoridated toothpaste or
receiving professional fluoride applications)
- Presence of enamel hypoplasia (developmental defect of enamel)
- Wearing orthodontic or dental appliances that may increase caries risk
- Active caries in the mother, which can increase the child's risk due to oral
bacteria transmission
- Three or more between-meal exposures to simple sugars
Buffers
Biochemistry
Buffers
• Biological systems use buffers to maintain pH.
• Definition: A buffer is a solution that resists a significant change in pH upon addition of an acid or a base.
• Chemically: A buffer is a mixture of a weak acid and its conjugate base
• Example: Bicarbonate buffer is a mixture of carbonic acid (the weak acid) and the bicarbonate ion (the conjugate base): H2CO3 + HCO3 –
• All OH- or H+ ions added to a buffer are consumed and the overall [H+ ] or pH is not altered
H2CO3 + HCO3 - + H+ <- -> 2H2CO3
H2CO3 + HCO3 - + OH- <- -> 2HCO3 - + H2O
• For any weak acid / conjugate base pair, the buffering range is its pKa +1.
It should be noted that around the pKa the pH of a solution does not change appreciably even when large amounts of acid or base are added. This phenomenon is known as buffering. In most biochemical studies it is important to perform experiments, that will consume H+ or OH- equivalents, in a solution of a buffering agent that has a pKa near the pH optimum for the experiment.
Most biologic fluids are buffered near neutrality. A buffer resist a pH change and consists of a conjugate acid/base pair.
Important Physiological Buffers include carbonate (H2CO3/HCO3-),
Phosphate (H2PO-4 /HPO2-4) and various protiens
Dental Terms
Dental Anatomy
CONTACT POINT.:-The point on the proximal surface where two adjacent teeth actually touch each other is called a contact point.
INTERPROXIMAL SPACE.:-The interproximal space is the area between the teeth. Part of the interproximal space is occupied by the interdental papilla. The interdental papilla is a triangular fold of gingival tissue. The part of the interproximal space not occupied is called the embrasure.
EMBRASURE. :-The embrasure occupies an area bordered by interdental papilla, the proximal surfaces of the two adjacent teeth, and the contact point (fig 4-18). If there is no contact point between the teeth, then the area between them is called a diastema instead of an embrasure.
OCCLUSAL
The occlusal surface is the broad chewing surface found on posterior teeth (bicuspids and molars).
OCCLUSION.:-Occlusion is the relationship between the occlusal surfaces of maxillary and mandibular teeth when they are in contact. Many patterns of tooth contact are possible. Part of the reason for the variety is the mandibular condyle's substantial range of movement within the temporal mandibular joint.
Malocclusion occurs when any abnormality in occlusal relationships exist in the dentition. Centric occlusion, is the centered contact position of the chewing surfaces of mandibular teeth on the chewing surface (occlusal) of the maxillary teeth.
OCCLUSAL PLANE.:-Maxillary and mandibular teeth come into centric occlusion and meet along anteroposterior and lateral curves. The anteroposterior curve is called the Curve of Spee in which the mandibular arch forms a concave (a bowl-like upward curve). The lateral curve is called the Curve of Wilson . The composite (combination) of these curves form a line called the occlusal plane, and is created by the contact of the upper and lower teeth
VERTICAL AND HORIZONTAL OVERLAP. :-Vertical overlap is the extension of the maxillary teeth over the mandibular counterparts in a vertical direction when the dentition is in centric occlusion Horizontal overlap is the projection of maxillary teeth over antagonists (something that opposes another) in a horizontal direction.
KEY TO OCCLUSION.:-The occlusal surfaces of opposing teeth bear a definite relationship to each other. In normal jaw relations and when teeth are of normal size and in the correct position, the mesiofacial cusp of the maxillary first molar occludes in the facial groove of the mandibular first molar. This normal relationship of these two teeth is called the key to occlusion.
PERMANENT DENTITION
The permanent dentition consists of 32 teeth. Each tooth in the permanent dentition is described in this section. It should be remembered that teeth show considerable variation in size, shape, and other characteristics from one person to another. Certain teeth show a greater tendency than others to deviate from the normal. The descriptions that follow are of normal teeth.
Temporary Filling Materials
Dental Materials
Temporary Filling Materials
Applications / Use
While waiting for lab fabrication of cast restoration
While observing reaction of pulp tissues
Objectives
Provide pulpal protection
Provide medication to reduce pulpal inflammation
Maintain the tooth position with an aesthetic restoration
Classification
Temporary filling cements
Temporary filling resins
Components
Temporary filling cements
1. Zinc oxide-eugenol cement with cotton fibers added
2. Polyme r powder-reinforced zinc oxide eugenol cement
Temporary filling resins
• MMA / PMMA filling materials
• Polyamide filling materials
• BIS-GMA filling materials