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NEET MDS Synopsis - Lecture Notes
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📖 Conservative Dentistry

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Light-Cure Composites
Conservative Dentistry

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.
Dental Burs
Conservative Dentistry

Dental Burs

Dental burs are essential tools used in restorative dentistry for cutting, shaping, and finishing tooth structure. The design and characteristics of burs significantly influence their cutting efficiency, vibration, and overall performance. Below is a detailed overview of the key features and considerations related to dental burs.

1. Structure of Burs

A. Blades and Flutes

  • Blades: The cutting edges on a bur are uniformly spaced, and the number of blades is always even.
  • Flutes: The spaces between the blades are referred to as flutes. These flutes help in the removal of debris during cutting.

B. Cutting Action

  • Number of Blades:
    • Excavating Burs: Typically have 6-10 blades. These burs are designed for efficient removal of tooth structure.
    • Finishing Burs: Have 12-40 blades, providing a smoother finish to the tooth surface.
  • Cutting Efficiency:
    • A greater number of blades results in a smoother cutting action at low speeds.
    • However, as the number of blades increases, the space between subsequent blades decreases, which can reduce the overall cutting efficiency.

2. Vibration and RPM

A. Vibration

  • Cycles per Second: Vibrations over 1,300 cycles/second are generally imperceptible to patients.
  • Effect of Blade Number: Fewer blades on a bur tend to produce greater vibrations during use.
  • RPM Impact: Higher RPM (revolutions per minute) results in less amplitude and greater frequency of vibration, contributing to a smoother cutting experience.

3. Rake Angle

A. Definition

  • Rake Angle: The angle that the face of the blade makes with a radial line drawn from the center of the bur to the blade.

B. Cutting Efficiency

  • Positive Rake Angle: Generally preferred for cutting efficiency.
  • Radial Rake Angle: Intermediate efficiency.
  • Negative Rake Angle: Less efficient for cutting.
  • Clogging: Burs with a positive rake angle may experience clogging due to debris accumulation.

4. Clearance Angle

A. Definition

  • Clearance Angle: This angle provides necessary clearance between the working edge and the cutting edge of the bur, allowing for effective cutting without binding.

5. Run-Out

A. Definition

  • Run-Out: Refers to the eccentricity or maximum displacement of the bur head from its axis of rotation.
  • Acceptable Value: The average clinically acceptable run-out is about 0.023 mm. Excessive run-out can lead to uneven cutting and discomfort for the patient.

6. Load Applied by Dentist

A. Load Ranges

  • Low Speed: The load applied by the dentist typically ranges from 100 to 1500 grams.
  • High Speed: The load is generally lower, ranging from 60 to 120 grams.

7. Diamond Stones

A. Characteristics

  • Hardness: Diamond stones are the hardest and most efficient abrasive tools available for removing tooth enamel.
  • Application: They are commonly used for cutting and finishing procedures due to their superior cutting ability and durability.
Ariston pHc Alkaline Glass Restorative
Conservative Dentistry

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.
Instrument formula
Conservative Dentistry

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.