_{Wedging Techniques}

_{Various wedging methods are employed to achieve optimal results, especially in cases involving gingival recession or wide proximal boxes. Below are descriptions of different wedging techniques, including "piggy back" wedging, double wedging, and wedge wedging.}

_{1. Piggy Back Wedging}

_{A. Description}

• _{Technique: In piggy back wedging, a second smaller wedge is placed on top of the first wedge.}
• _{Indication: This technique is particularly useful in patients with gingival recession, where there is a risk of overhanging restoration margins that could irritate the gingiva.}

_{B. Purpose}

• _{Prevention of Gingival Overhang: The additional wedge helps to ensure that the restoration does not extend beyond the tooth surface into the gingival area, thereby preventing potential irritation and maintaining periodontal health.}

_{2. Double Wedging}

_{A. Description}

• _{Technique: In double wedging, wedges are placed from both the lingual and facial surfaces of the tooth.}
• _{Indication: This method is beneficial in cases where the proximal box is wide, providing better adaptation of the matrix band and ensuring a tighter seal.}

_{B. Purpose}

• _{Enhanced Stability: By using wedges from both sides, the matrix band is held securely in place, reducing the risk of material leakage and improving the overall quality of the restoration.}

_{3. Wedge Wedging}

_{A. Description}

• _{Technique: In wedge wedging, a second wedge is inserted between the first wedge and the matrix band, particularly in specific anatomical situations.}
• _{Indication: This technique is commonly used in the maxillary first premolar, where a mesial concavity may complicate the placement of the matrix band.}

_{B. Purpose}

• _{Improved Adaptation: The additional wedge helps to fill the space created by the mesial concavity, ensuring that the matrix band conforms closely to the tooth surface and providing a better seal for the restorative material.}

Beveled Conventional Preparation

Characteristics

• External Walls: In a beveled conventional preparation, the external walls are perpendicular to the enamel surface.
• Beveled Margin: The enamel margin is beveled, which helps to create a smooth transition between the restoration and the tooth structure.

Benefits

• Improved Aesthetics: The beveling technique enhances the aesthetics of the restoration by minimizing the visibility of the margin.
• Strength and Bonding: Beveling can improve the bonding surface area and reduce the risk of marginal leakage, which is critical for the longevity of the restoration.

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.

Glass ionomer cement is a tooth coloured material 
Material was based on reaction between silicate glass powder & polyacrylicacid.
They bond chemically to tooth structure & release fluoride for relatively long period

CLASSIFICATION 

Type I. For luting

Type II. For restoration 

Type II.1 Restorative esthetic 

Type II.2 Restorative reinforced

Type III. For liner & bases

Type IV. Fissure & sealent

Type V. As Orthodontic cement

Type VI. For core build up

Physical Properties

1. Low solubility
2. Coefficient of thermal expansion similar to dentin
3. Fluoride release and fluoride recharge
4. High compressive strengths
5. Bonds to tooth structure
6. Low flexural strength
7. Low shear strength
8. Dimensional change (slight expansion) (shrinks on setting, expands with water sorption)
9. Brittle
10.Lacks translucency
11.Rough surface texture

Indications for use of Type II glass ionomer cements 

1) non-stress bearing areas 

2) class III and V restorations in adults 

3) class I and II restorations in primary dentition 

4) temporary or “caries control” restorations 

5) crown margin repairs 

6) cement base under amalgam, resin, ceramics, direct and indirect gold 

7) core buildups when at least 3 walls of tooth are remaining (after crown preparation)

Contraindications 

1) high stress applications I. class IV and class II restorations II. cusp replacement III. core build-ups with less than 3 sound walls remaining

Composition

Factors affecting the rate or setting

1. Glass composition:Higher Alumina – Silica ratio, faster set and shorter working time.
2. Particle Size: finer the powder, faster the set.
3. Addition of Tartaric Acid:-Sharpens set without shortening the working time.
4. Relative proportions of the constituents: Greater the proportion of glass and lower the proportion of water, the faster the set.
5. Temperature

Setting Time

Type 1 - 4-5 min
type II - 7 min

PROPERTIES 

Adhesion :

- Glass ionomer cement bonds chemically to the tooth structure->reaction occur between carboxyl group of poly acid & calcium of hydroxyl apatite.
 
- Bonding with enamel is higher than that of dentin ,due to greater inorganic content. 

Esthetics :
-GIC is tooth coloured material & available in different shades.
Inferior to composites.
They lack translucency & rough surface texture.
Potential for discolouration & staining.

Biocompatibilty :

- Pulpal response to glass ionomer cement is favorable. 
- Pulpal response is mild due to 
- High buffering capacity of hydroxy apatite. 
- Large molecular weight of the polyacrylic acid ,which prevents entry into dentinal tubules. 

a) Pulp reaction – ZOE < Glass Ionomer < Zinc Phosphate 

b) Powder:liquid ratio influences acidity 

c) Solubility & Disintegration:-Initial solubility is high due to leaching of intermediate products.The complete setting reaction takes place in 24 hrs, cement should be protected from saliva during this period.

Anticariogenic properties :
- Fluoride is released from glass ionomer at the time of mixing & lies with in matrix.
Fluoride can be released out without affecting the physical properties of cement.

ADVANTAGE DISADVANTAGE

Effects of Acid Etching on Enamel

Acid etching is a critical step in various dental procedures, particularly in the bonding of restorative materials to tooth structure. This process modifies the enamel surface to enhance adhesion and improve the effectiveness of dental materials. Below are the key effects of acid etching on enamel:

1. Removal of Pellicle

• Pellicle Removal: Acid etching effectively removes the acquired pellicle, a thin film of proteins and glycoproteins that forms on the enamel surface after tooth cleaning.
• Exposure of Inorganic Crystalline Component: By removing the pellicle, the underlying inorganic crystalline structure of the enamel is exposed, allowing for better interaction with bonding agents.

2. Creation of a Porous Layer

• Porous Layer Formation: Acid etching creates a porous layer on the enamel surface.
• Depth of Pores: The depth of these pores typically ranges from 5 to 10 micrometers (µm), depending on the concentration and duration of the acid application.
• Increased Surface Area: The formation of these pores increases the surface area available for bonding, enhancing the mechanical retention of restorative materials.

3. Increased Wettability

• Wettability Improvement: Acid etching increases the wettability of the enamel surface.
• Significance: Improved wettability allows bonding agents to spread more easily over the etched surface, facilitating better adhesion and reducing the risk of voids or gaps.

4. Increased Surface Energy

• Surface Energy Elevation: The etching process raises the surface energy of the enamel.
• Impact on Bonding: Higher surface energy enhances the ability of bonding agents to adhere to the enamel, promoting a stronger bond between the tooth structure and the restorative material.