NEET MDS Synopsis
Composite Materials- Mechanical Properties
Conservative DentistryComposite Materials- Mechanical Properties and Clinical
Considerations
Introduction
Composite materials are essential in modern dentistry, particularly for
restorative procedures. Their mechanical properties, aesthetic qualities, and
bonding capabilities make them a preferred choice for various applications. This
lecture will focus on the importance of the bond between the organic resin
matrix and inorganic filler, the evolution of composite materials, and key
clinical considerations in their application.
1. Bonding in Composite Materials
Importance of Bonding
For a composite to exhibit good mechanical properties, a strong bond must
exist between the organic resin matrix and the inorganic filler. This bond is
crucial for:
Strength: Enhancing the overall strength of the
composite.
Durability: Reducing solubility and water absorption,
which can compromise the material over time.
Role of Silane Coupling Agents
Silane Coupling Agents: These agents are used to coat
filler particles, facilitating a chemical bond between the filler and the
resin matrix. This interaction significantly improves the mechanical
properties of the composite.
2. Evolution of Composite Materials
Microfill Composites
Introduction: In the late 1970s, microfill composites,
also known as "polishable" composites, were introduced.
Characteristics: These materials replaced the rough
surface of conventional composites with a smooth, lustrous surface similar
to tooth enamel.
Composition: Microfill composites contain colloidal
silica particles instead of larger filler particles, allowing for better
polishability and aesthetic outcomes.
Hybrid Composites
Structure: Hybrid composites contain a combination of
larger filler particles and sub-micronsized microfiller particles.
Surface Texture: This combination provides a smooth
"patina-like" surface texture in the finished restoration, enhancing both
aesthetics and mechanical properties.
3. Clinical Considerations
Polymerization Shrinkage and Configuration Factor (C-factor)
C-factor: The configuration factor is the ratio of
bonded surfaces to unbonded surfaces in a tooth preparation. A higher
C-factor can lead to increased polymerization shrinkage, which may
compromise the restoration.
Clinical Implications: Understanding the C-factor is
essential for minimizing shrinkage effects, particularly in Class II
restorations.
Incremental Placement of Composite
Incremental Technique: For Class II restorations, it is
crucial to place and cure the composite incrementally. This approach helps
reduce the effects of polymerization shrinkage, especially along the
gingival floor.
Initial Increment: The first small increment should be
placed along the gingival floor and extend slightly up the facial and
lingual walls to ensure proper adaptation and minimize stress.
4. Curing Techniques
Light-Curing Systems
Common Systems: The most common light-curing systems
include quartz/tungsten/halogen lamps. However, alternatives such as plasma
arc curing (PAC) and argon laser curing systems are available.
Advantages of PAC and Laser Systems: These systems
provide high-intensity and rapid polymerization compared to traditional
halogen systems, which can be beneficial in clinical settings.
Enamel Beveling
Beveling Technique: The advantage of an enamel bevel in
composite tooth preparation is that it exposes the ends of the enamel rods,
allowing for more effective etching compared to only exposing the sides.
Clinical Application: Proper beveling can enhance the
bond strength and overall success of the restoration.
5. Managing Microfractures and Marginal Integrity
Causes of Microfractures
Microfractures in marginal enamel can result from:
Traumatic contouring or finishing techniques.
Inadequate etching and bonding.
High-intensity light-curing, leading to excessive polymerization
stresses.
Potential Solutions
To address microfractures, clinicians can consider:
Re-etching, priming, and bonding the affected area.
Conservatively removing the fault and re-restoring.
Using atraumatic finishing techniques, such as light intermittent
pressure.
Employing slow-start polymerization techniques to reduce stress.
NBDE Test 1
NBDE TestTYPES OF TEETH
Dental Anatomy
TYPES OF TEETH
The human permanent dentition is divided into four classes of teeth based on appearance and function or position.
Incisors, Canines, Premolars & Molars
The Walls of the Orbit
AnatomyThe Walls of the Orbit
Each orbit has four walls: superior (roof), medial, inferior (floor) and lateral.
The medial walls of the orbit are almost parallel with each other and with the superior part of the nasal cavities separating them.
The lateral walls are approximately at right angles to each other
The Optic Nerve
Anatomy
This is the second cranial nerve (CN II) and is the nerve of sight.
Manipulation of Acrylic Resins
Dental Materials
Manipulation
Mixture of powder and liquid is painted onto working cast to create shape for acrylic appliance à After curing of mixture, the shape and fit are adjusted by grinding with burrs and stones with a slow-speed handpiece .Acrylic dust is irritating to epithelial tissues of nasopharynx and skin and may produce allergic dermatitis or other reactions. Grinding may heat polymer to temperatures that depolymerize and release monomer vapor. which may be an irritant
TetricEvoFlow
PedodonticsTetricEvoFlow
TetricEvoFlow is an advanced nano-optimized flowable composite developed by
Ivoclar Vivadent, designed to enhance dental restorations with its superior
properties. As the successor to Tetric Flow, it offers several key benefits:
Optimum Surface Affinity: TetricEvoFlow exhibits
excellent adhesion to tooth structures, ensuring a reliable bond and
minimizing the risk of microleakage.
Penetration into Difficult Areas: Its flowable nature
allows it to reach and fill even the most challenging areas, making it ideal
for intricate restorations.
Versatile Use: This composite can serve as an initial
layer beneath medium-viscosity composites, such as TetricEvoCeram, providing
a strong foundation for layered restorations.
Stability for Class V Restorations: TetricEvoFlow
maintains its stability when required, making it particularly suitable for
Class V restorations, where durability and aesthetics are crucial.
Extended Applications: In addition to its use in
restorations, TetricEvoFlow is effective for extended fissure sealing and
can be utilized in adhesive cementation techniques.
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.