Introduction and History to acid etching
During the last decades clinicians have been confronted with a continuous and fairly rapid turnover in adhesive materials. It started in the mid- ‘60s with the advent of first commercialized restorative resin composites, followed in the early ‘70s with the introduction of the acid etch technique in clinical practice. [Operative dentistry supplement 2001: 6 ; 119-144]
The bonding of restorative materials to teeth typically involves the use of acids to demineralize their surfaces. Changes in the surface due to acid treatment include the gross removal of smear layer, an increase in both permeability, micro porosity and chemical modifications of the surface composition. [Dental material 2002; 18; 26-35]
Bonding to enamel is now considered a durable and predictable clinical procedure. The acid etch technique relies on the micro mechanical retention obtained on the enamel surface by an acidic etchant and subsequent penetration of a blend of polymerizable monomers into the interprismatic spaces to form enamel resin tags (Gwinnett and matsui 1967)
In contrast, dentin bonding has become one of the most challenging topics of restorative dentistry. Recent developments in dentin bonding technology involve the simultaneous etching of enamel and dentin with acids. Dentin etching has become most common in Japan since the late ‘70s [Operative dentistry; 2000;25; 144-186].
A significant advance in dentin bonding was made by kanca who reasoned that if appropriate, chemically compatible, resin formulation was added following a total etch of the mineralized dental tissues [Esthetics].The evolution of adhesive systems has resulted in bond strengths to dentin that are very close to that of the celebrated union of enamel.
Possibly, in the not too distant future, dental adhesion will involve only one application of a self-etching system capable of satisfactorily bonding both to enamel and to dentin [Quintessence Int 2002; 33; 213 – 214]
HISTORY:
Adhesive dentistry originated from a simple clinical experiment and the vision and dedication of a unique dental scientist. In 1955, Buonocore reported the self-curing, methyl-methacrylate resin could be durably bonded to the enamel of human incisor teeth. Phosphoric acid was the agent of choice and was applied to the enamel surface for 30 seconds at a concentration of 85%.
The first clinical trails of the method were concerned with the sealing of pits and fissures of molar teeth to prevent their decay. (Dental adhesives – John Gwinneth)
FUSAYAMA et al [1979] introduced the concept of ‘Total etching’ advocating the treatment of both enamel and dentin with phosphoric acid prior to bonding. This technique has become relatively popular in Japan, but initially met with resistance in the USA. (Esthetics dentistry and ceramic restoration, Bernaud Touati]
Between 1982 and 1985, Nakabayashi described micro mechanical bonding mechanism of dentin bonding agents. He introduced the concepts of hybridization (Operating Dentistry 2003 28; (3); 287- 295). A significant step in improving the bond to dentin through smear layer removal came from the work of Bowen. He showed an improvement in bond strength of dentin with a combination of ferric oxalate conditioning and resin priming of the dentin surface.
The primers consisted of a comonomer of N- Tolyl glycineglycidil metharylate (NTG-GMA) and a coupling agent derived from an addut of pyromellitic acid dianhydriate and 2 hydroxyethyl methacrylate (PMDM). The oxalate was changed to the Aluminium salt to avoid staining invivo associated with the ferricion. The bonding procedure was clinically demanding and has since been simplified.
Further more, it has been documented that the presence of nitric acid in the oxalate conditioner was responsible for the improvements in bond strengths. Other products entered the market place were designed to remove dentin smear layer. The conditioning agents ranged from the chelation of EDTA (Gluma, Bayer) to the incorporation of maleic acid in a resin primer. (Scotchbond 2, 3m (Dental adhesives)
Perdiago and others (1998), found the application of Aqua – Prep to dried dentin surfaces to restore the bond strengths of acetone-based water free dentin adhesives to the same level as bonding to moist substrates. They have shown that rewetting the etched dentin with an aqueous HEMA solution re-established the level of bond strength obtained to moist dentin and severed as an effective means to reopen the interfibrillar spaces for penetration of resin.
Pilo and others (2001) concluded that pretreatment of etched dentin with either a disinfectant (2% chlorhexidise gluconate, tubulicid [2% EDTA and 1% benzylkonium chloride] or rewetting (Aquaprep 35% Hema) may have a positive effect on the shear bond strength of resin to dentin. Duke and Rhodes (2001) evaluated the effect of desensitizers (vivadent and Gluma) used as rewetting agents on dentin shear bond strength.
Vivadent –> 5% Glutaraldehyde and 35% polyethylene glycol dimethacrylate
Gluma –> Solution of glutaraldehyde and HEMA [Operative dentistry; 2003;28-3; 287-296].
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