NEET MDS Lessons
Conservative Dentistry
Dental Amalgam and Direct Gold Restorations
In restorative dentistry, understanding the properties of materials and the techniques used for their application is essential for achieving optimal outcomes. .
1. Mechanical Properties of Amalgam
Compressive and Tensile Strength
- Compressive Strength: Amalgam exhibits high compressive strength, which is essential for withstanding the forces of mastication. The minimum compressive strength of amalgam should be at least 310 MPa.
- Tensile Strength: Amalgam has relatively low tensile strength, typically ranging between 48-70 MPa. This characteristic makes it more susceptible to fracture under tensile forces, which is why proper cavity design and placement techniques are critical.
Implications for Use
- Cavity Design: The design of the cavity preparation should minimize the risk of tensile forces acting on the restoration. This can be achieved through appropriate wall angles and retention features.
- Restoration Longevity: Understanding the mechanical properties of amalgam helps clinicians predict the longevity and performance of the restoration under functional loads.
2. Direct Gold Restorations
Requirements for Direct Gold Restorations
- Ideal Surgical Field: A clean and dry field is essential for the successful placement of direct gold restorations. This ensures that the gold adheres properly and that contamination is minimized.
- Conservative Cavity Preparation: The cavity preparation must be methodical and conservative, preserving as much healthy tooth structure as possible while providing adequate retention for the gold.
- Systematic Condensation: The condensation of gold must be performed carefully to build a solid block of gold within the tooth. This involves using appropriate instruments and techniques to ensure that the gold is well-adapted to the cavity walls.
Condensation Technique
- Building a Solid Block: The goal of the condensation procedure is to create a dense, solid mass of gold that will withstand occlusal forces and provide a durable restoration.
3. Gingival Displacement Techniques
Materials for Displacement
To effectively displace the gingival tissue during restorative procedures, various materials can be used, including:
- Heavy Weight Rubber Dam: Provides excellent isolation and displacement of gingival tissue.
- Plain Cotton Thread: A simple and effective method for gingival displacement.
- Epinephrine-Saturated String:
- 1:1000 Epinephrine: Used for 10 minutes; not recommended for cardiac patients due to potential systemic effects.
- Aluminum Chloride Solutions:
- 5% Aluminum Chloride Solution: Used for gingival displacement.
- 20% Tannic Acid: Another option for controlling bleeding and displacing tissue.
- 4% Levo Epinephrine with 9% Potassium Aluminum: Used for 10 minutes.
- Zinc Chloride or Ferric Sulfate:
- 8% Zinc Chloride: Used for 3 minutes.
- Ferric Sub Sulfate: Also used for 3 minutes.
Clinical Considerations
- Selection of Material: The choice of material for gingival displacement should be based on the clinical situation, patient health, and the specific requirements of the procedure.
4. Condensation Technique for Gold
Force Application
- Angle of Condensation: The force of condensation should be applied at a 45-degree angle to the cavity walls and floor during malleting. This orientation allows for maximum adaptation of the gold against the walls, floors, line angles, and point angles of the cavity.
- Direction of Force: The forces must be directed at 90 degrees to any previously condensed gold. This technique ensures that the gold is compacted effectively and that there are no voids or gaps in the restoration.
Importance of Technique
- Adaptation and Density: Proper condensation technique is critical for achieving optimal adaptation and density of the gold restoration, which contributes to its longevity and performance.
Condensers/pluggers are instruments used to deliver the forces of compaction to the underlying restorative material. There are
several methods for the application of these forces:
1.
Hand pressure: use of this method alone is contraindicated except in a few situations like adapting the first piece of gold tothe convenience or point angles and where the line of force will not permit use of other methods. Powdered golds are also
known to be better condensed with hand pressure. Small condenser points of 0.5 mm in diameter are generally
recommended as they do not require very high forces for their manipulation.
2.
Hand malleting: Condensation by hand malleting is a team work in which the operator directs the condenser and moves itover the surface, while the assistant provides rhythmic blows from the mallet. Long handled condensers and leather faced
mallets (50 gms in weight) are used for this purpose. The technique allows greater control and the condensers can be
changed rapidly when required. However, with the introduction of mechanical malleting, use of this method has decreased
considerably.
3.
Automatic hand malleting: This method utilizes a spring loaded instrument that delivers the desired force once the spiralspring is released. (Disadvantage is that the blow descends very rapidly even before full pressure has been exerted on the
condenser point.
4.
Electric malleting (McShirley electromallet): This instrument accommodates various shapes of con-denser points and has amallet in the handle itself which remains dormant until wished by the operator to function. The intensity or amplitude
generated can vary from 0.2 ounces to 15 pounds and the frequency can range from 360-3600 cycles/minute.
5.
Pneumatic malleting (Hollenback condenser): This is the most recent and satisfactory method first developed byDr. George M. Hollenback. Pneumatic mallets consist of vibrating nit condensers and detachable tips run by
compressed air. The air is carried through a thin rubber tubing attached to the hand piece. Controlling the air
pressure by a rheostat nit allows adjusting the frequency and amplitude of condensation strokes. The construction
of the handpiece is such that the blow does not fall until pressure is placed on the condenser point. This continues
until released. Pneumatic mallets are available with both straight and angled for handpieces.
Atraumatic Restorative Treatment (ART) is a minimally invasive approach to
dental cavity management and restoration. Developed as a response to the
limitations of traditional drilling and filling methods, ART aims to preserve as
much of the natural tooth structure as possible while effectively managing
caries. The technique was pioneered in the mid-1980s by Dr. Frencken in Tanzania
as a way to address the high prevalence of dental decay in a setting with
limited access to traditional dental equipment and materials. The term "ART" was
coined by Dr. McLean to reflect the gentle and non-traumatic nature of the
treatment.
ART involves the following steps:
1. Cleaning and Preparation: The tooth is cleaned with a hand instrument to
remove plaque and debris.
2. Moisture Control: The tooth is kept moist with a gel or paste to prevent
desiccation and maintain the integrity of the tooth structure.
3. Carious Tissue Removal: Soft, decayed tissue is removed manually with hand
instruments, without the use of rotary instruments or drills.
4. Restoration: The prepared cavity is restored with an adhesive material,
typically glass ionomer cement, which chemically bonds to the tooth structure
and releases fluoride to prevent further decay.
Indications for ART include:
- Small to medium-sized cavities in posterior teeth (molars and premolars).
- Decay in the initial stages that has not yet reached the dental pulp.
- Patients who may not tolerate or have access to traditional restorative
methods, such as those in remote or underprivileged areas.
- Children or individuals with special needs who may benefit from a less
invasive and less time-consuming approach.
- As part of a public health program focused on preventive and minimal
intervention dentistry.
Contraindications for ART include:
- Large cavities that extend into the pulp chamber or involve extensive tooth
decay.
- Presence of active infection, swelling, abscess, or fistula around the tooth.
- Teeth with poor prognosis or severe damage that require more extensive
treatment such as root canal therapy or extraction.
- Inaccessible cavities where hand instruments cannot effectively remove decay
or place the restorative material.
The ART technique is advantageous in several ways:
- It reduces the need for local anesthesia, as it is often painless.
- It preserves more of the natural tooth structure.
- It is less technique-sensitive and does not require advanced equipment.
- It is relatively quick and can be performed in a single visit.
- It is suitable for use in areas with limited resources and less developed
dental infrastructure.
- It reduces the risk of microleakage and secondary caries.
However, ART also has limitations, such as reduced longevity compared to amalgam
or composite fillings, especially in large restorations or high-stress areas,
and the need for careful moisture control during the procedure to ensure proper
bonding of the material. Additionally, ART is not recommended for all cases and
should be considered on an individual basis, taking into account the patient's
oral health status and the specific requirements of each tooth.
Caridex System
Caridex is a dental system designed for the treatment of root canals, utilizing the non-specific proteolytic effects of sodium hypochlorite (NaOCl) to aid in the cleaning and disinfection of the root canal system. Below is an overview of its components, mechanism of action, advantages, and drawbacks.
1. Components of Caridex
A. Caridex Solution I
- Composition:
- 0.1 M Butyric Acid
- 0.1 M Sodium Hypochlorite (NaOCl)
- 0.1 M Sodium Hydroxide (NaOH)
B. Caridex Solution II
- Composition:
- 1% Sodium Hypochlorite in a weak alkaline solution.
C. Delivery System
- Components:
- NaOCl Pump: Delivers the sodium hypochlorite solution.
- Heater: Maintains the temperature of the solution for optimal efficacy.
- Solution Reservoir: Holds the prepared solutions.
- Handpiece: Designed to hold the applicator tip for precise application.
2. Mechanism of Action
- Proteolytic Effect: The primary mechanism of action of Caridex is based on the non-specific proteolytic effect of sodium hypochlorite.
- Chlorination of Collagen: The N-monochloro-dl-2-aminobutyric acid (NMAB) component enhances the chlorination of degraded collagen in dentin.
- Conversion of Hydroxyproline: The hydroxyproline present in collagen is converted to pyrrole-2-carboxylic acid, which is part of the degradation process of dentin collagen.
3. pH and Application Time
- Resultant pH: The pH of the Caridex solution is approximately 12, which is alkaline and conducive to the disinfection process.
- Application Time: The recommended application time for Caridex is 20 minutes, allowing sufficient time for the solution to act on the root canal system.
4. Advantages
- Effective Disinfection: The use of sodium hypochlorite provides a strong antimicrobial effect, helping to eliminate bacteria and debris from the root canal.
- Collagen Degradation: The system's ability to degrade collagen can aid in the removal of organic material from the canal.
5. Drawbacks
- Low Efficiency: The overall effectiveness of the Caridex system may be limited compared to other modern endodontic cleaning solutions.
- Short Shelf Life: The components may have a limited shelf life, affecting their usability over time.
- Time and Volume: The system requires a significant volume of solution and a longer application time, which may not be practical in all clinical settings.
Mercury Release in Dental Procedures Involving Amalgam
Mercury is a key component of dental amalgam, and its release during various dental procedures has been a topic of concern due to potential health risks. Understanding the amounts of mercury released during different stages of amalgam handling is essential for dental professionals to implement safety measures and minimize exposure.
1. Mercury Release Quantification
A. Trituration
- Amount Released: 1-2 µg
- Description: Trituration is the process of mixing mercury with alloy particles to form a homogenous amalgam. During this process, small amounts of mercury can be released into the air, which can contribute to overall exposure.
B. Placement of Amalgam Restoration
- Amount Released: 6-8 µg
- Description: When placing an amalgam restoration, additional mercury may be released due to the manipulation of the material. This includes the handling and packing of the amalgam into the cavity preparation.
C. Dry Polishing
- Amount Released: 44 µg
- Description: Dry polishing of amalgam restorations generates the highest amount of mercury release among the listed procedures. The friction and heat generated during dry polishing can vaporize mercury, leading to increased exposure.
D. Wet Polishing
- Amount Released: 2-4 µg
- Description: Wet polishing, which involves the use of water to cool the restoration during polishing, results in significantly lower mercury release compared to dry polishing. The water helps to capture and reduce the amount of mercury vapor released into the air.
Ariston pHc Alkaline Glass Restorative
Ariston pHc is a notable dental restorative material developed by Ivoclar Vivadent in 1990. This innovative material is designed to provide both restorative and preventive benefits, particularly in the management of dental caries.
1. Introduction
- Manufacturer: Ivoclar Vivadent (Liechtenstein)
- Year of Introduction: 1990
2. Key Features
A. Ion Release Mechanism
- Fluoride, Hydroxide, and Calcium Ions: Ariston pHc releases fluoride, hydroxide, and calcium ions when the pH within the restoration falls to critical levels. This release occurs in response to acidic conditions that can lead to enamel and dentin demineralization.
B. Acid Neutralization
- Counteracting Decalcification: The ions released by Ariston pHc help neutralize acids in the oral environment, effectively counteracting the decalcification of both enamel and dentin. This property is particularly beneficial in preventing further carious activity around the restoration.
3. Material Characteristics
A. Light-Activated
- Curing Method: Ariston pHc is a light-activated material, allowing for controlled curing and setting. This feature enhances the ease of use and application in clinical settings.
B. Bulk Thickness
- Curing Depth: The material can be cured in bulk thicknesses of up to 4 mm, making it suitable for various cavity preparations, including larger restorations.
4. Indications for Use
A. Recommended Applications
- Class I and II Lesions: Ariston pHc is recommended for use in Class I and II lesions in both deciduous (primary) and permanent teeth. Its properties make it particularly effective in managing carious lesions in children and adults.
5. Clinical Benefits
A. Preventive Properties
- Remineralization Support: The release of fluoride and calcium ions not only helps in neutralizing acids but also supports the remineralization of adjacent tooth structures, enhancing the overall health of the tooth.
B. Versatility
- Application in Various Situations: The ability to cure in bulk and its compatibility with different cavity classes make Ariston pHc a versatile choice for dental practitioners.
Primary Retention Form in Dental Restorations
Primary retention form refers to the geometric shape or design of a prepared cavity that helps resist the displacement or removal of a restoration due to tipping or lifting forces. Understanding the primary retention form is crucial for ensuring the longevity and stability of various types of dental restorations. Below is an overview of primary retention forms for different types of restorations.
1. Amalgam Restorations
A. Class I & II Restorations
- Primary Retention Form:
- Occlusally Converging External Walls: The walls of the cavity preparation converge towards the occlusal surface, which helps resist displacement.
- Occlusal Dovetail: In Class II restorations, an occlusal dovetail is often included to enhance retention by providing additional resistance to displacement.
B. Class III & V Restorations
- Primary Retention Form:
- Diverging External Walls: The external walls diverge outward, which can reduce retention.
- Retention Grooves or Coves: These features are added to enhance retention by providing mechanical interlocking and resistance to displacement.
2. Composite Restorations
A. Primary Retention Form
- Mechanical Bond:
- Acid Etching: The enamel and dentin surfaces are etched to create a roughened surface that enhances mechanical retention.
- Dentin Bonding Agents: These agents infiltrate the demineralized dentin and create a hybrid layer, providing a strong bond between the composite material and the tooth structure.
3. Cast Metal Inlays
A. Primary Retention Form
- Parallel Longitudinal Walls: The cavity preparation features parallel walls that help resist displacement.
- Small Angle of Divergence: A divergence of 2-5 degrees may be used to facilitate the seating of the inlay while still providing adequate retention.
4. Additional Considerations
A. Occlusal Dovetail and Secondary Retention Grooves
- Function: These features aid in preventing the proximal displacement of restorations by occlusal forces, enhancing the overall retention of the restoration.
B. Converging Axial Walls
- Function: Converging axial walls help prevent occlusal displacement of the restoration, ensuring that the restoration remains securely in place during function.