NEET MDS Lessons
Conservative Dentistry
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.
Sterilization in Dental Practice
Sterilization is a critical process in dental practice, ensuring that all forms of life, including the most resistant bacterial spores, are eliminated from instruments that come into contact with mucosa or penetrate oral tissues. This guide outlines the accepted methods of sterilization, their requirements, and the importance of biological monitoring to ensure effectiveness.
Sterilization: The process of killing all forms of life, including bacterial spores, to ensure that instruments are free from any viable microorganisms. This is essential for preventing infections and maintaining patient safety.
Accepted Methods of Sterilization
There are four primary methods of sterilization commonly used in dental practices:
A. Steam Pressure Sterilization (Autoclave)
- Description: Utilizes steam under pressure to achieve high temperatures that kill microorganisms.
- Requirements:
- Temperature: Typically operates at 121-134°C (250-273°F).
- Time: Sterilization cycles usually last from 15 to 30 minutes, depending on the load.
- Packaging: Instruments must be properly packaged to allow steam penetration.
B. Chemical Vapor Pressure Sterilization (Chemiclave)
- Description: Involves the use of chemical vapors (such as formaldehyde) under pressure to sterilize instruments.
- Requirements:
- Temperature: Operates at approximately 132°C (270°F).
- Time: Sterilization cycles typically last about 20 minutes.
- Packaging: Instruments should be packaged to allow vapor penetration.
C. Dry Heat Sterilization (Dryclave)
- Description: Uses hot air to sterilize instruments, effectively killing microorganisms through prolonged exposure to high temperatures.
- Requirements:
- Temperature: Commonly operates at 160-180°C (320-356°F).
- Time: Sterilization cycles can last from 1 to 2 hours, depending on the temperature.
- Packaging: Instruments must be packaged to prevent contamination after sterilization.
D. Ethylene Oxide (EtO) Sterilization
- Description: Utilizes ethylene oxide gas to sterilize heat-sensitive instruments and materials.
- Requirements:
- Temperature: Typically operates at low temperatures (around 37-63°C or 98.6-145°F).
- Time: Sterilization cycles can take several hours, including aeration time.
- Packaging: Instruments must be packaged in materials that allow gas penetration.
Considerations for Choosing Sterilization Equipment
When selecting sterilization equipment, dental practices must consider several factors:
- Patient Load: The number of patients treated daily will influence the size and capacity of the sterilizer.
- Turnaround Time: The time required for instrument reuse should align with the sterilization cycle time.
- Instrument Inventory: The variety and quantity of instruments will determine the type and size of sterilizer needed.
- Instrument Quality: The materials and construction of instruments may affect their compatibility with certain sterilization methods.
Biological Monitoring
A. Importance of Biological Monitoring
- Biological Monitoring Strips: These strips contain spores calibrated to be killed when sterilization conditions are met. They serve as a reliable weekly monitor of sterilization effectiveness.
B. Process
- Testing: After sterilization, the strips are sent to a licensed reference laboratory for testing.
- Documentation: Dentists receive independent documentation of monitoring frequency and sterilization effectiveness.
- Failure Response: In the event of a sterilization failure, laboratory personnel provide immediate expert consultation to help resolve the issue.
Types of fillers:
- Silica: Common in microfilled and hybrid composites, providing good aesthetics and polishability.
- Glass particles: Used in macrofill and microfill composites for high strength and durability.
- Ceramic particles: Provide excellent biocompatibility and wear resistance.
- Zirconia/silica: Combined to improve the strength and translucency of the composite.
- Nanoparticles: Enhance the resin's physical properties, including strength and wear resistance, while also offering improved aesthetics.
Filler size:
- Macrofillers: 10-50 μm, suitable for class I and II restorations where high strength is not essential but a good seal is required.
- Microfillers: 0.01-10 μm, used for fine detailing and aesthetic restorations due to their ability to blend with the tooth structure.
- Hybrid fillers: Combine macro and microfillers for restorations requiring both strength and aesthetics.
Filler loading: The amount of filler in the resin affects the material's physical properties:
- High filler loading: Increases strength, wear resistance, and decreases shrinkage but can compromise the resin's ability to adapt to the tooth structure.
- Low filler loading: Provides better flow and marginal adaptation but may result in lower strength and durability.
Filler-resin interaction:
- Chemical bonding: Improves the adhesion between the filler and the resin matrix.
- Mechanical interlocking: Larger filler particles create a stronger mechanical bond within the resin.
- Polymerization shrinkage: The filler can reduce shrinkage stress, which is crucial for minimizing marginal gaps and microleakage.
Selection criteria:
- Clinical requirements: The filler should meet the specific needs of the restoration, such as strength, wear resistance, and aesthetics.
- Tooth location: Anterior teeth may require more translucent fillers for better aesthetics, while posterior teeth need stronger, more opaque materials.
- Patient's preferences: Some patients may prefer more natural-looking restorations.
- Clinician's skill: Different fillers may require varying application techniques and curing times.
Continuous Retention Groove Preparation
Purpose and Technique
- Retention Groove: A continuous retention groove is prepared in the internal portion of the external walls of a cavity preparation to enhance the retention of restorative materials, particularly when maximum retention is anticipated.
- Bur Selection: A No. ¼ round bur is used for this procedure.
- Location and Depth:
- The groove is located 0.25 mm (half the diameter of the No. ¼ round bur) from the root surface.
- It is prepared to a depth of 0.25 mm, ensuring that it does not compromise the integrity of the tooth structure.
- Direction: The groove should be directed as the bisector of the angle formed by the junction of the axial wall and the external wall. This orientation maximizes the surface area for bonding and retention.
Clinical Implications
- Enhanced Retention: The continuous groove provides additional mechanical retention, which is particularly beneficial in cases where the cavity preparation is large or when the restorative material has a tendency to dislodge.
- Consideration of Tooth Structure: Care must be taken to avoid excessive removal of tooth structure, which could compromise the tooth's strength.
Instrument formula
First number : It indicates width of blade (or of primary cutting edge) in 1/10 th of a millimeter (i.e. no. 10 means 1 mm blade width).
Second number :
1) It indicates primary cutting edge angle.
2) It is measured form a line parallel to the long axis of the instrument handle in clockwise centigrade. Expressed as per cent of 360° (e.g. 85 means 85% of 360 = 306°).
3)The instrument is positioned so that this number always exceeds 50. If the edge is locally perpendicular to the blade, then this number is normally omitted resulting in a three number code.
Third number : It indicates blade length in millimeter.
Fourth number :
1)Indicates blade angle relative to long axis of handle in clockwise centigrade.
2) The instrument is positioned so that this number. is always 50 or less. It becomes third number in a three number code when
2nd number is omitted.
Light-Cure Composites
Light-cure composites are resin-based materials that harden when exposed to specific wavelengths of light. They are widely used in dental restorations due to their aesthetic properties, ease of use, and ability to bond to tooth structure.
Key Components:
- Diketone Photoinitiator: The primary photoinitiator used in light-cure composites is camphoroquinone. This compound plays a crucial role in the polymerization process.
- Visible Light Spectrum: The curing process is activated by blue light, typically in the range of 400-500 nm.
2. Curing Lamps: Halogen Bulbs and QTH Lamps
Halogen Bulbs
- Efficiency: Halogen bulbs maintain a constant blue light efficiency for approximately 100 hours under normal use. This consistency is vital for reliable curing of dental composites.
- Step Curing: Halogen lamps allow for a technique known as step curing, where the composite is first cured at a lower energy level and then stepped up to higher energy levels. This method can enhance the properties of the cured material.
Quartz Tungsten Halogen (QTH) Curing Lamps
- Irradiance Requirements: To adequately cure a 2 mm thick specimen of resin-based composite, an irradiance value of at least 300 mW/cm² to 400 mW/cm² is necessary. This ensures that the light penetrates the composite effectively.
- Micro-filled vs. Hybrid Composites: Micro-filled composites require twice the irradiance value compared to hybrid composites. This is due to their unique composition and light transmission properties.
3. Mechanism of Visible Light Curing
The curing process involves several key steps:
Photoinitiation
- Absorption of Light: When camphoroquinone absorbs blue light in the 400-500 nm range, it becomes excited and forms free radicals.
- Free Radical Formation: These free radicals are essential for initiating the polymerization process, leading to the hardening of the composite material.
Polymerization
- Chain Reaction: The free radicals generated initiate a chain reaction that links monomers together, forming a solid polymer network.
- Maximum Absorption: The maximum absorption wavelength of camphoroquinone is at 468 nm, which is optimal for effective curing.
4. Practical Considerations in Curing
Curing Depth
- The depth of cure is influenced by the type of composite used, the thickness of the layer, and the irradiance of the light source. It is crucial to ensure that the light penetrates adequately to achieve a complete cure.
Operator Technique
- Proper technique in positioning the curing light and ensuring adequate exposure time is essential for achieving optimal results. Inadequate curing can lead to compromised mechanical properties and increased susceptibility to wear and staining.
Mercury Exposure and Safety
Concentrations of Mercury in Air
- Typical Levels: Mercury concentrations in air can vary
significantly:
- Pure air: 0.002 µg/m³
- Urban air: 0.05 µg/m³
- Air near industrial parks: 3 µg/m³
- Air in mercury mines: 300 µg/m³
- Threshold Limit Value (TLV): The generally accepted TLV for exposure to mercury vapor for a 40-hour work week is 50 µg/m³. Understanding these levels is crucial for ensuring safety in dental practices where amalgam is used.