Operative Dentistry | Composite Resin & Glass Ionomer | INBDE, ADAT

Tooth-Colored Restorations: Composite Resin and Glass Ionomer

In this section, the focus is on tooth-colored restorations using composite resin and glass ionomer. The discussion delves into the benefits of composite resin, adhesive dentistry, and the challenges of bonding to dentin compared to enamel.

Composite Resin Bonding Process

• Adhesive dentistry originated in 1955 with Michael Bonocore's inspiration from industrial use of phosphoric acid for adhesion. Acid etching transforms enamel surface, enhancing wettability for resin.

• Acid etching creates irregular surface on enamel, aiding resin spread. Polymerization mechanically interlocks resin with enamel. Dentin bonding is challenging due to composition differences (mineral vs. organic matter).

• Enamel has higher mineral content (hydroxyapatite), making it more receptive to acid effects than dentin with collagen and water. Enamel prisms are regular, while dentinal tubules are irregular.

Challenges in Dentin Bonding

• Dentinal tubules' fluid content near pulp hinders bond strength compared to enamel. Sclerotic dentin is deeper and more resistant to acid. Smear layer reduces permeability by 90%, complicating bonding.

• Dentin's unpredictability in bonding stems from composition, structure (collagen maze), depth (fluid-filled tubules), and smear layer blocking tubules orifices.

Clinical Steps: Acid Etch & Primer

• Acid etch with phosphoric acid cleans debris, creating micro-porosity for better adhesion on both enamel and dentin surfaces.

• Optimal etching results in chalky appearance on enamel and exposes collagen layer on dentin. Proper rinsing balances moisture level for effective bonding.

Application of Primer & Bond

• Primer application involves HEMA monomer that prevents collagen collapse for retention. The bond contains bisphenol A glass ionomer methacrylate for adhesion.

• Gently air drying primer and bond post-application evaporates solvent, leaving valuable monomers inside cavity prep for curing with a light source.

Bonding Systems in Dentistry

This section delves into the intricate details of bonding systems in dentistry, emphasizing the importance of the hybrid layer for strong bond strength and explaining the process of resin tags formation.

Hybrid Layer Formation

• The hybrid layer is crucial for bond strength, formed by interprismatic enamel dissolution leaving irregular high-energy surfaces and patent dentinal tubules with collagen fibrils.

Resin Tag Formation

• Enamel and dentin provide ideal surfaces for resin tag formation where primer and adhesive flow into openings to create extensions that lock into micro porosity of etched enamel and intertubular dentin.

Micro-Mechanical Bond

• Adhesive dentistry relies on micro-mechanical bond where adhesive resins physically lock into enamel and dentin through resin tags, offering retention between tooth and other materials.

Generations of Bonding Systems

This segment explores the four generations of bonding systems commonly used in dentistry, detailing their characteristics, application methods, and considerations.

Fourth Generation - Total Etch (Etch-and-Rinse) Systems

• Fourth-generation systems like OptiBond FL involve separate syringes for acid etch, primer, and bond in a three-step process considered the gold standard.

Fifth Generation - Simplified Total Etch Systems

• Fifth-generation systems such as Prime & Bond Universal combine primer and bond in one bottle for a two-step process aiming to reduce errors compared to fourth-generation systems.

Selective Etching Technique

• Selective etching involves applying etchant selectively to enamel only in fourth or fifth-generation systems to potentially reduce post-op sensitivity while maintaining strong bonds to enamel.

Self-Etch Bonding Systems

This part focuses on self-etch bonding systems where the etchant is included in the adhesive bottle, discussing considerations like smear layer presence and enamel bond strength.

Self-Etch Characteristics

• Self-etch systems leave behind a smear layer due to less potent acid etch, leading to reduced post-op sensitivity but weaker enamel bonds compared to total etch systems.

Considerations with Self-Etch Systems

• Using carbide burrs is recommended with self-etch systems due to smear layer concerns; these materials typically need refrigeration without rinsing after etching.

Evolution of Bonding Systems: Sixth & Seventh Generations

Exploring sixth generation combining etchant-primer in one bottle & seventh generation all-in-one system simplifying bonding procedures significantly.

Sixth Generation - Combined Etch & Primer

• Sixth-generation bonding combines etchant-primer in one bottle while keeping bond separate; exemplified by Clearfil SE II offering a two-step process with altered component combination.

Seventh Generation - All-in-One System

• Seventh-generation bonding integrates etchant-primer-adhesive into one product like LP Pop providing a single-step application often utilized in orthodontics for efficiency.

Potential Adverse Health Effects of Fillers in Resin Composites

The discussion delves into the composition of resin composites, focusing on filler particles and their impact on properties.

Filler Particles in Resin Composites

• Filler particles like barium silicate, strontium silicate, zinc, or silver silicate vary in size and shape, influencing composite properties.

• Coupling agents like silane coat filler particles to enhance adhesion to the matrix, crucial for composite integrity.

• Different categories of composites based on composition: macro fill (80% filler), micro fill posit (40% filler), hybrid composite (combines properties), nano fill and nano hybrid (extremely small filler particles).

Composite Types Based on Filler Particle Size

Various composite types are discussed based on filler particle sizes and their implications.

Composite Types

• Macro fill composites have large filler particles for strength but roughness over time; micro fill posit has smaller particles for good polish and wear resistance.

• Hybrid composites combine advantages of macro fill and micro fill posit with 80% filler content and smooth surface.

• Nano fill and nano hybrid offer advanced materials with extremely small filler particles for improved properties.

Polymerization Methods: Self Cure vs. Light Cure

Exploring the two main polymerization methods for composites: self-cure and light-cure systems.

Polymerization Methods

• Self-cure system involves a base paste with benzoyl peroxide as initiator and a catalyst paste with tertiary amines as activator.

• Light-cure system uses a single paste without mixing, initiated by camphor quinone under blue visible light for free radical polymerization.

Polymerization and Shrinkage in Composites

The discussion delves into the process of polymerization in composites, highlighting how shrinkage occurs during this chemical reaction and its implications.

Understanding Polymerization and Shrinkage

• Polymerization leads to composite shrinkage of about 2-3% even if light cannot reach the chemical reaction. Free radicals break carbon-carbon double bonds to form single bonds, initiating polymerization.

• As monomers are added to the growing polymer chain, resin volume decreases, causing shrinkage. Cross-linking via covalent bonds between side groups results in a stronger material.

Exploring Configuration Factor (C Factor)

• The C factor represents the ratio of bound to unbound surfaces in composites. In Class I composites, with one unbound surface and five bound surfaces, the C factor is 5.

• Higher GV Black classes correspond to lower C factors. Increased bonding surfaces raise the risk of composite detachment during shrinkage, leading to issues like microleakage and post-operative sensitivity.

Glass Ionomer X' and Composite Resins

This segment contrasts glass ionomer x' with composite resins, outlining their compositions, advantages, limitations, and hybrid variations.

Glass Ionomer X' Characteristics

• Glass ionomer x' self-adheres to enamel and dentin through chemical bonding without requiring priming or bonding agents. Calcium chelation facilitates this bond.

• Benefits include fluoride storage/release within the material and reduced overall shrinkage compared to composite resins.

Hybrid Variations

• Resin-modified glass ionomer x' combines features of glass ionomer x' and resin matrix composite resins for enhanced properties like rapid polymerization and fluoride release.

• Compromised or poly acid modified resin composites exclude water for controlled setting by polymerization initially; later acid-base reactions occur upon water absorption.