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Endodontics


Author: Dr. Siddhrth Sisodia, Sr. Lecturer, Dept. of Prosthodontics, K. D. Dental College Hospital, Mathura

Abstract:
Adhesive dentistry has revolutionized restorative dental practice during the past 30 years. Improved adhesive materials have made resin-based composite restorations more reliable and long-standing.
This article reviews the evolution of bonding from the first generation to current bonding materials. The principles of adhesive dentistry date back to 1955 when Buonocore, using techniques of industrial bonding when he referred to Dr. Bowen’s attempts to investigate substances that will displace water from tooth surfaces with the idea that they could be used as pretreatment for enamel or dentin.
Early dentin bonding was further complicated by the presence of the smear layer. The smear layer blocks the dentinal tubules and acts as a "diffusion barrier." As dentin bonding improved, the removal of the smear layer became necessary, but not without controversy.
Several factors characterize the change in bonding systems from the Buonocore era to today.

KEY WORDS: Bonding agent, Adhesive dentistry, dentin bonding,

 

INTRODUCTION:
Adhesion is defined as state in which two surfaces are held together by interfacial forces which may consist of valance forces or interlocking forces or both.
Word adhesion comes from latin word “adhere” means “to stick”.
Restorative dentistry plays an important role in the field of dentistry in restoring the tooth tissue to its form, function esthetics and in maintaining the physiologic integrity in harmony with the surrounding hard and soft tissues.
Many of the restorative material used did not adhere to enamel to dentin by physical and / or clinical interactions thus increasing the chances of microleakage at restoration tooth interface.
The production of a stable long term bond to the tooth substance is an ideal requirement for the success of all restorations.
An adhesion permits the placement of a more conservative restoration, reduces microleakage and dentin sensitivity.

History

  1. 1955-Buonocore – introduced “acid etch technique.
  2. 1979- fusayama- “total ecth technique”.
  3. 1982- nakabayashi et al- revealed formation of “hybrid layer”.
  4. 1990- kanca & gwinett- “wet bonding technique”.
  5. When dentin is etched collagen fiber network is exposed into which adhesion can seap in.

REQUIREMENTS OF DENTIN BONDING AGENTS
(Dental Update 2000, 27: 85-93)
When developing a clinically acceptable dentin bonding agent following goals must be met.

 

  • Bond strength – The adhesive should be capable of achieving an acceptable bond strength to withstand the stresses caused by polymerization contraction of composites. Optimum bond strength à 17Mpa – 20Mpa.
  • Biocompatibility of the material. The adhesion used should be biocompatible with structures in contact with it.
  • Long-term durability of the bond it is a highly desired factor.
  • Prevents microleakage by reduced gap formation between tooth structure and restorative material.
  • Prevents recurrent caries and marginal staining.
  • Be easy to use and minimally  technique sensitive.
  • Have a reasonable shelf-life.
  • Have no potential for sensitization of patients or operators.
  • Be compatible with a wide range of resins.
  • Show no reduction in bond strength when applied to moist surface.

CLASSIFICATION OF DENTIN BONDING AGENTS:
I) On the basis of chemistry
II) On the basis of smear layer:
Removed
EDTA
Mirage bond
Clearfil liner bond system.
Phosphoric acid and oxalates.
Removes the smear layer and opens the dentinal tubules to allow penetration of resin tags for first generation DBA.

Reversed
Prisma universal
Bond lite
The smear layer is partially removed or left intact. Here the phosphate – calcium bond is used but methacrylate is replaced with BIS-GMA, which will bond to both enamel and dentin.
Used for second generation bonding agents.

Modified
Tenure
Gluma
Scotch bond-2
Smear layer is either fixed with glutaraldehyde tannic acid or ferric chloride.
Or
Smear layer is removed, and replaced with an artificial crystalline precipitate.

III) On the basis of chronology, chemistry and shear bond strength:

It was stated by Erick et al (Quintessence Int. 1993; 22 : 967-977).

Category I

Include dentinal adhesives which produces shear bond strength values of 5-7Mpa.

Examples:

Scotchbond dual cure.
Dentin adhesit.
Gluma.
The failures occurred at the interface or in the resin adhesive.

Category II

Included the experimental and commercial products derived from Bowen’s work with ferric and aluminium oxalates and have produced shear bond strength values between 8-14 Mpa.
Examples:
Tenure.
Mirage bond.

As the strength increased, wetability also increased.

Category III:
Included dentinal adhesives which produced shear bond strength values of about 17-20Mpa

Examples:

Superbond
Scotchbond-2
Scotchbond multipurpose.
All bond
The failure is mainly cohesive in nature. This result is attributed to a combination of factors that include effective wetting and penetration of dentinal tubules as well as tendency to leave collagen fibres at the adhesive dentin interface in an apparently structurally intact state (Quintessence Int. 1993; 24: 571-582).

IV) On the basis of Generations:
There are six generations of dentin bonding agents:
First generation dentin bonding agents. The agents used in this generation are as follows:
Glycophosphoric acid dimethacrylate.
Cyanoacrylates.
N-phenyl glycine and glycidyl methacrylate (NPG-GMA).
Polyurethane.

This mainly consisted of a surface active compomer viz. NPG-GMA, added to BIS-GMA resin to facilitate adhesion.
The NPG-GMA acted as an adhesion promoter between the tooth structure and resin material by chelating with surface calcium.

DISCUSSION

Many patients demand an attractive provisional solution immediately after the extraction of the anterior tooth. To replace a missing tooth immediately following extraction, a long-term interim fixed prosthesis may be the treatment of choice before fixed partial denture prosthesis. This allows the surgically altered tissues to fully mature in preparation for the definitive fixed prosthesis. Reinforcement fibers have been shown to increase the flexural strength and fracture toughness of composite resin restorations and thus help prevent fracture due to high stresses associated with mastication. The fibers are made for chairside use in a single appointment procedure that requires no special treatment preparation or instrumentation.

CONCLUSION

The chairside fiber-reinforced composite resin prostheses described in this clinical report offers a fast, minimally invasive approach for esthetic, interim tooth replacement that combines the benefits of the fiber-reinforced composite resin material for a functional and durable result.

REFERENCES

1) Neslihan l, Selim E. An Innovative Approach to ChairsideProvisional Replacement an Extracted Anterior Tooth: Use of Fiber-Reinforced Ribbon-Composites and a Natural Tooth
2) Go¨hring TN, Mo¨rmann WH, Lutz F. Clinical and scanning electron microscopic evaluation of fibre-reinforced inlay fixed partial dentures: preliminary results after one year. J Prosthet Dent 1999;82:662-8.
3) Vallittu PK, Sevelius C. Resin-bonded glass fiber-reinforced composite fixed partial dentures: a clinical study. J Prosthet Dent 2000; 84: 413-8.
4) Valittu PK: A review of fiber-reinforced denture base resins. J Prosthodont 1996;5:270-276

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