1. Bonding to Enamel and Dentin
Dr. Elaheh Habibi

2. Introduction

3. Indications for Use of Adhesives
To treat carious and fractured tooth structure
To restore erosion or abrasion defects in cervical areas
To correct unaesthetic contours, positions, dimensions, or shades of teeth
For the repair of fractured porcelain, amalgam and resin restorations

5. Indications for Use of Adhesives (con’t)
For pit and fissure sealants
Bond composite restorations
Bond amalgam restorations
Lute crowns
Bond orthodontic brackets

6. Advantages of Bonding Techniques
Minimizes removal of sound tooth structure
Management of dentin hypersensitivity
Adhesion reduces microleakage at tooth restoration interface
Adhesion expands the range of esthetic possibilities
Reinforces weakened tooth structure

7. ADHESIVE DENTISTRY

8. Factors Affecting Adhesion
Clean Surface
Wetting
Contact Angel
Surface Energy
Surface Contamination
Water

9. Factors Affecting Adhesion

10. Factors Affecting Adhesion

11. Factors Affecting Adhesion

14. ENAMEL BONDING Enamel the hardest tissue in the human body
consists of 95 percent mineralized inorganic substance
hydroxyapatite arranged in a dense crystalline structure and a small amount of protein and water

16. Buonocore developed acid etching of the enamel.
showed that when enamel is treated with a dilute acid for 30 seconds, it results in a microscopically roughened, porous surface into which the resin forms retentive tags

17. ENAMEL BONDING Percentage of etchants used: %37 Acid application time

18. Enamel etch Pattern
I: central II : peripheral III : mix

20. Dentin Bonding

21. Dentin Bonding
Bonding to dentin has been proven more difficult and less reliable and predictable than to enamel. This is basically because of difference in morphologic, histologic and compositional differences between enamel and dentin

22. Enamel vs Dentin
In enamel, it is 86 percent inorganic hydroxyapatite by volume, in dentin it is 50 percent. Dentin contains more water than does enamel

24. Enamel vs Dentin Hydroxyapatite crystals
have a regular pattern in enamel whereas in dentin, hydroxyapatite crystals are randomly arranged in an organic matrix
The presence of the smear layer
makes wetting of the dentin by the adhesive more difficult
Dynamic structure of dentin
shows changes due to aging, caries or operative procedures.

25. Enamel vs Dentin
Dentin contains dentinal tubules which contain vital processes of the pulp, odontoblasts.
Fluid present in dentinal tubules constantly flows outwards which reduces the adhesion of the composite resin.
This makes the dentin a sensitive structure

26. Dentinal tubules

29. Dentinal tubules
Peritubular dentin
Intertubular dentin

30. SMEAR LAYER

31. SMEAR LAYER
Basically, when a tooth surface is altered using hand or rotary instruments, cutting debris are smeared on the enamel and dentin surface, this layer is called the smear layer

32. Structure
smear layer has an amorphous, irregular and granular appearance.
smear layer consists of two separate parts:
1. One superficial and loosely attached to the underlying dentin
2. The other consisting of plugs of dentinal debris in the orifices of dentinal tubules

33. Depth
The smear layer has an average depth of 1 to 5 µm but in the dentinal tubules, it may go up to 10 µm. The depth of the smear layer depends on following factors:
Dry or wet-cutting of the dentin
Type of instrument used
Chemical composition of irrigating solution.

35. Components of the Smear Layer
The inorganic material
The organic components : collagen , necrotic or viable pulp tissue and odontoblastic processes, saliva, blood cells and microorganisms

36. Role of the Smear Layer The smear layer is apparently responsible for:
Acting as a physical barrier for bacteria and bacterial products
Restricting the surface area available for diffusion of both small and large molecules
Resistance to fluid movement

37. Disadvantages of the Smear Layer
Bonding to the smear layer forms a weak union because the smear layer can be torn away from the underlying matrix.
Since this layer is nonhomogeneous and a weakly adherent structure, it may slowly disintegrate, dissolving around a leaking filling material, thus creating a void

38. Disadvantages of the Smear Layer
Smear layer on root canal walls acts as an intermediate physical barrier and may interfere with adhesion and penetration of sealers into dentinal tubules
The prescence of a smear layer causes possibility for leakage of microorganisms and a source of substrate for bacterial growth
Presence of viable bacteria which may remain in the dentinal tubules and make use of the smear layer for sustained growth and activity

40. DENTIN BONDING AGENT Mechanism of Bonding
M R X
Where, M is the double bond of methacrylate which copolymerizes with composite resin.
R is the spacer which makes the molecule large.
X is a functional group for bonding which bonds to inorganic or organic portion of dentin

42. Mechanism of Bonding
Ideally a dentin bonding agent should have both hydrophilic and hydrophobic ends. The hydrophilic end displaces the dentinal fluid, to wet the surface. The hydrophobic end bonds to the composite resin.

43. Classification of Dental Adhesives
Based on generations
First generation bonding agent
Second generation bonding agent
Third generation bonding agent
Fourth generation bonding agent
Fifth generation bonding agent
Sixth generation bonding agent
Seventh generation bonding agent

44. Classification of Dental Adhesives
Based on smear layer treatment
Smear layer modifying agents
Smear layer removing agents
Smear layer dissolving agents.

45. Classification of Dental Adhesives
Based on number of steps
Three step
Two step
Single step.

46. Evolution of Dentin Bonding Agents

47. Fourth Generation Dentin Bonding Agents
They were made available in the mid 1990s. Fourth generation bonding agents represent significant improvements in the field of adhesive dentistry. These agents are based on total etch technique and moist bonding concept.

48. Fourth Generation Dentin Bonding Agents
Mechanism of bonding: The fourth “generation” is characterized by the process of hybridization at the interface of the dentin and the composite resin.
Hybridization is the phenomenon of replacement of the hydroxyapatite and water at the dentin surface by resin. This resin, in combination with the collagen fibers, forms a hybrid layer.
In other words, hybridization is the process of resin interlocking in the demineralized dentin surface
This concept was given by Nakabayashi in 1982.

49. Fourth Generation Dentin Bonding Agents

50. Fourth Generation Dentin Bonding Agents

51. Fourth Generation Dentin Bonding Agents

52. Components of Fourth Generation Dentin Bonding Agents
The fourth generation adhesives consist of:
Conditioner (Etchant):
Commonly used acids are 37 percent phosphoric acid, nitric acid, maleic acid, oxalic acid, pyruvic acid, hydrochloric acid, citric acid or a chelating agent
Use of conditioner/etchant causes removal or modification of the smear layer, demineralizes peritubular and intertubular dentin and exposes collagen fibrils

53. Components of Fourth Generation Dentin Bonding Agents
2. Primer: consist of monomers like HEMA (2-Hydroxyethyl methacrylate) and 4-META (4-Methacryloxyethyl trimellitate anhydride) dissolved in acetone or ethanol
they have both hydrophilic as well as hydrophobic ends which have affinity for the exposed collagen and resin respectively
primer increases wettability of the dentin surface, bonding between the dentin and resin, and encourages monomer infiltration of demineralized peritubular and intertubular dentin.

54. Components of Fourth Generation Dentin Bonding Agents
3.Adhesive: The adhesive resin is a low viscosity, semi filled or unfilled resin which flows easily and matches the composite resin. Adhesive combines with the monomers to form a resin reinforced hybrid layer and resin tags to seal the dentin tubules

55. Advantages
Disadvantages

57. Fifth Generation Dentin Bonding Agents
Developed in mid 1990s
Uses two steps, i.e. Total etching + Application of primer and bonding agent
Primer + Bonding agent are available in single bottle
High bond strength
Easy to use

58. Fifth Generation Dentin Bonding Agents
The basic differences between the fourth and fifth generation dentin bonding agents is the number of basic components of bottles.
The fourth generation bonding system is available in two bottles, one consisting of the primer and the other the adhesive, the fifth generation dentin bonding agents are available in one bottle only.
This makes the fifth generation bonding agents simpler and faster than the fourth generation systems

60. Sixth Generation Dentin Bonding Agents
Self-etching primer and adhesive:
Available in two bottles:
Primer
Adhesive
Primer is applied prior to the adhesive
A drop from each bottle is taken, mixed and applied to the tooth surface
Water is the solvent in these systems.

61. Sixth Generation Dentin Bonding Agents
Mechanism of bonding: In these agents as soon as the decalcification process starts, infiltration of the empty spaces by the dentin bonding agent is initiated

64. Advantages of Self Etching Primers
Reduces postoperative sensitivity because they etch and prime simultaneously
Since they do not remove the smear layer, the tubules remain sealed, resulting in less sensitivity
They etch the dentin less aggressively than total etch products

65. Advantages of Self Etching Primers
Much faster and simpler technique
Less technique sensitive as fewer number of steps are involved for the self etch system

66. Disadvantages of Self Etching Primers
Enamel bonding
Hydrolytic degradation
Technique is more important in post operative sensitivity

68. Seventh Generation Bonding Agents
Developed in late 2000s
All in one concept, i.e. components available as single component
Uses self etch primer

69. Seventh Generation Bonding Agents
Uneven covering of the dentine surface
Hydrolytic degradation
Water sorption and water solubility
Marginal staining, marginal adaptation

70. Seventh Generation Bonding Agents
They achieve the same objective as the sixth generation systems except that they simplified the multiple sixth generation materials into a single component, single bottle one-step self-etch adhesive, thus avoiding any mistakes in mixing.

72. Seventh Generation Bonding Agents

73. 1 or 2

74. HYBRID LAYER AND HYBRIDIZATION
A dentin bonding agent is a low viscosity unfilled or semifilled resin for easy penetration and formation of a hybrid layer.
When a bonding agent is applied, part of it penetrates into the collagen network, known as intertubular penetration and the rest of it penetrates into dentinal tubules called intratubular penetration.
In intertubular penetration, it polymerises with primer monomers forming a hybrid layer/resin reinforced layer

75. Hybridization (Given by Nakabayachi in 1982)
Hybridization is the process of formation of a hybrid layer.
The hybrid layer is the phenomenon of formation of a resin interlocking in the demineralized dentin surface. The hybrid layer is responsible for micromechanical bonding between tooth and resin

76. Hybridization (Given by Nakabayachi in 1982)
Diagrammatic representation of hybrid layer

77. Wet Bonding
primers consisting of hydrophilic resin monomers dissolved in water miscible organic solvents like ethanol and acetone are used
Acetone-based primers are dependent on a moist dentin surface for hybridization because the acetone displaces water present in the interfibrillar spaces of the collagen network and carry hydrophilic resin along with it for hybridization

78. Dry Bonding water-based primers are used.
Water-based primers are not dependent on moist dentin because of their ability to self-wet a dried dentin surface and thus separating the collapsed collagen fibers.

79. Dry Bonding
Studies show that moist dentin is friendly with all primer types, it is advisable to have moist dentin for resin-dentin bonding.
To get moist dentin after etching, do not dry the dentin with compressed air after rinsing away etchant.
Instead use high-volume evacuation to remove excess water and then blot the remaining water present on the dentin surface using gauze or cotton to leave dentin optimally moist.

83. Moist vs Dry Dentin

85. Universal bondings