Adhesive Materials in Dentistry

• Adhesive materials have revolutionized restorative and preventive dentistry.
• These techniques help conserve tooth structure and reduce microleakage, which is a major cause of secondary caries.
• Adhesives are crucial for the success of aesthetic materials in modern dentistry.

Advantages and Clinical Significance of Adhesion

• Allows for long-term retention of restorations.
• Improves the transmission and distribution of forces.
• Reinforces weakened tooth structures.
• Reduces microleakage.
• Expands the possibilities for aesthetic restorations, including direct, indirect, and repair options.

Definitions for Adhesion and Cohesion

• Adhesion refers to the attachment of one substance to another when they come into close contact.
• Adhesion involves an "adherend" with an applied "adhesive/adherent" creating an "interface," resulting in an "adhesive joint."
• Cohesion involves intermolecular attractions between like molecules or atoms.
• Cohesion is often reported as the cohesive strength of a material or tissue.

Mechanisms of Adhesion in Conservative Dentistry

• Chemical adhesion: involves the formation of atomic or molecular bonds across the interface between the adhesive and the substrate.
• Mechanical adhesion: occurs when the substrate has undercuts or irregularities that allow the material to interlock.
• Dental adhesion is primarily based on mechanical retention.
• Macro-mechanical: refers to retention undercuts.
• Micro-mechanical: retention on a microscopic level, where the adhesive flows into the pores of the adherend, hardens, and interlocks.

Requirements for Creating Good Adhesion

• Clean Surfaces:
  • The surface must be clean and in a high-energy state.
  • Water, organic debris, or biofilms in clinical situations can interfere with wetting and spreading.
• Surface Roughness:
  • Wettability is enhanced by the presence of microsurface roughness.
• Proper Contact Angle and Good Wetting:
  • An adhesive or adherent should easily flow over the adherend to produce good wetting for good bonding.
  • Wetting is measured by the contact angle.
  • The contact angle is determined by the angle formed by the adhesive with the adherend at their interface, or the internal angle in a liquid droplet in contact with a solid.
  • 0 degrees indicates maximum adhesion.
  • Less than 90 degrees indicates moderate adhesion.
  • More than 90 degrees indicates poor adhesion.
• Low Viscosity Adhesives and Adequate Flow:
  • Adhesives must have a low viscosity to flow sufficiently over the adherend surface.
• Adhesive Solidification:
  • Enamel and dentin adhesive systems require polymerization of the liquid components as their final stage.

Requirements for Successful Wetting of Adhesive

• Intimate molecular contact between the adhesive and tooth tissues (adherend) must be achieved.
• The tooth tissues must be clean.
• The tooth tissues need a high surface energy to attract the atoms of the adhesive.
• The adhesive material should have low surface tension to properly wet the adherend.
• The adhesive must have low viscosity to penetrate into the microporosities.
• The adhesive must be able to displace air and moisture during the bonding process.

Adhesion to Tooth Structure

• The requirements for adhesion to tooth structure include:
  • Removal of calcium phosphate to expose microporosities in enamel and dentin (conditioning/etching).
  • Hybridization phase with infiltration and subsequent polymerization of resin within the created microporosities.

Bonding to Enamel

• Mature enamel is composed of 96% hydroxyapatite and 4% organic content and water.
• Crystallites are enveloped in enamel prisms, and the outer surface has prismless or aprismatic enamel.
• Adhesion to enamel is achieved through conditioning/etching and infiltration/polymerization of adhesive resin.

Conditioning / Etching of the Enamel Surface

• The goals of enamel etching are:
  • To remove the organic pellicle and prismless enamel.
  • To clean the enamel surface.
  • To remove the enamel smear layer.
  • To create micropores (5-50 µm).
  • To increase surface-free energy from 28 dynes/cm to 72 dynes/cm.

Successful Etching Via Selective Demineralization

• Achieved using:
  • Chemical Conditioners (Acid Etching):
  • 37% Phosphoric acid over 20 seconds is the most widely used etchant.
  • EDTA is a strong decalcifying agent that doesn't etch effectively and yields low bond strength.
  • Nitric, Citric, Maleic, and Oxalic acids can be used.
  • 15% Hcl acid with icon treatment, (resin infiltration tx white spot lesions).
  • Physical Conditioners (Laser)
    • Leads to desensitized dentin by occluding dentinal tubules.
  • Mechanical Conditioners (Microabrasion)
    • Microabrasion with aluminum oxide particles is useful in self-etching systems.
• The effect of acid etching depends on:
  • The type of acid used.
  • The acid concentration.
  • The form of etchant, gel being preferred for its control.
  • The rinsing time.
  • The chemical composition of the enamel.
  • Whether a primary or permanent tooth.
  • Whether the enamel is fluoridated.

Patterns of Etching

• Type I: Predominate dissolution of prism cores (Honeycomb appearance) (Figure 2).
• Type II: Predominate dissolution of prism peripheries and core left intact (Cobblestone appearance) (Figure3).
• Type III: Not related to enamel morphology. On etching of enamel turns dull and appears Frosty white.

Etching Procedure

• Concentration of Acid:
  • 30-50% phosphoric acid is utilized, but 37% is commonly preferred.
  • Concentrations above 50% can create monocalcium phosphate monohydrate which could inhibit dissolution and cannot be rinsed off.
  • Concentrations below 27% generate dicalcium phosphate monohydrate, which can't be easily rinsed off.
• Time:
  • Fifteen seconds, Fluorosis lesions need a lot more time.
• Rinsing:
  • For ~20 seconds to remove <calcium phosphate and drying post rinsing.
• Form:
  • Gels- preferred via syringes, narrow tips for gels.
• Contamination;
  • Avoid saliva contamination, rinse, dry and re-etch.

Important Points

• Conditioning:
  • Altering Surface (No Calcium removal).
• Etching:
  • "Preferential Demineralization."
• Differences:
  • Etching = Resin Restorations - Conditioning = Glass Ionomer.

Infiltration of Resin:

• Resin tags have tiny extensions into enamel microporosities.
• The tags get interlocked via irregularties after etching.
• 2 types:
  • Macrotags: Form in-between Enamel Prisms.
  • Microtags: Form at cores of enamel prisms when hydroxyapatite crystals are removed (Larger area, Stronger Bonds).
• Bisphenol Glycidyl Methacrylate and Urethane Dimethacrylate Resins: Base for Adhesives.
• HEMA and TEGDMA: hydrophilic monomers aid wetting.

Bonding to Dentin

• Complex histological structure is challenging when bonding to Dentin
• It is comprised of heterogenous composition.
• It has very high organic and water content
• It has a decrease percentage of hydroxyapatite that is randomly arranged in organic matrix (collagen mainly)
• There is Divergence of dentinal tubules from the pulp.
• The fluid in the tubules is under a slight consistent pressure.
• And there's a smear layer

Hybridization

• Processes form layer (resin interdiffusion of 5-8 (um)), acid conditioner and collagen fibril network + porosities = inter diffused by viscocity monomers
• "Hybrid Layer/Zone: = Dentin Collagen, system Interlocks
• Hybridoid Layer:" Resin failed to penetrate.
• Microtags: Interlocking via intertubular dentin
• Macrotags: dentinal tubules.

Principles of bonding

• Demineralization, alterations- priming, Resin impregnation.

Dentin Hybridization

• 3 step: Etching, Priming, and Resin Impregnation
• 2 Step: Etch -> prime -> resin
• 1: Together, self-etching primer

Dentin Etching

• Objectives:
  • Get rid of the smear layer and demineralize.

Rinsing and Etching

• Rinse: 5-10 secs, water remnants
• Time: 10 Seconds (Low innorganic content)
• Using air for 10s; could lead to dryeness and collagen fail
• Decreased volume and rewetting

Problems

• A hard --> "soft collagen" after.
• High protein, responsible for low surface energy (44.8 dynes/cm), increase wetness
• Acid etching of dentin, removes collagen, high sensitivity
• Inducing pulp irritation

Primers needed

• Proper surface of wetting promotes agents

Priming : (Adhesive Promoting Agents)

• HEMA: Collagen Affinity
• Hydrophobic part: dissolved volatile solvent to displace water, collager
• Strategy:
  • Increased penetration with demineralization and penetration.
  • Diffusion and demineralization , bonds later

Wet/Dry Bonding

• Surface Moisture is important
• Dry --> Enamel
• Moisture -> Dentin, avoids collapse.
• Collagen Re expansion = primer balance
• Too little, too much - decrease bond strength

Alchohol

• Water chasing capacity of etch dentin
• Acetone/Ethanol in wet bonding
  • Deffuse, Dissolve, Increase elasticity.
• Too fast= Proper water dissolving and collagen issue = Acetone

Priming - Success

• MULTIPLE COATS! For penetration for penetration of the hydrpohlic monomer
• "not over dried or wet" = Collagen issues Extend the time for solvent ranges from 10-30 seconds
• Rub primer, improve diffusion/agitaiton
• wet and glossy "the structure formed in dental hard tissues such as (enamel, dentin, cementum) by SURFACE demineralization and subsurface

Dentine Bonding Agents

• Hybrid layer between the resin and dentine substrate referred to as.
• Organic components, bonded by resin
• Without a hybrid layer a bond will not be formed to the dentine. ideal agent:
• Hydrophillic for wet dentin, -hydrophbic for applied resin
• low viscocity, film, biocompatible, strenght, mini leakage, easy to apply, good shelf life

Impregnation

• Bonding agents made of hybrophobic monomers (Bis, UDMA)

Hydrophillic Monomers

• To regulat viscosity
• Main goal is to seal , and biologic tissue for crystal and collagen.
• resin to tissues.
• The resin intertubular dentin is hybrid, the resin ones are Resin Tags.
• superficial = hybrid
• deep = resin

Notes:

• Abundant interubular = no resin tag importance.
• Adhesice is chemically cured or photo (poly)
• Brush, no air (thin)
• 30-40 secs, allow material
• the manufacrere setting

Smear Layer

• Debris, 1-2um
• Tubules obstructed
• Deep 1-10 Smear Plug
• Crushed hydroxyapatite, collagen, blood, saliva

Layer Advantages and and disadvantages

• Ddecrease permeability is key!!
• Minimises the chance of contamination to keep strengths high.
• High opertative sensitivity
• Weakens bond to dentin from brittle nature, saliva and bacteria

Classification of Modern Adhesives

• Smear layer treatment, gen , Van Beerbeck

Smear Treatment

• Modifying, dissolving, Removing
• Smear: Natural barrier
• Modifying in situ- compomers

Dissolving - acidic

• self etching primers
• Don't remove plug