Dentin bonding systems: a review of current products and techniques

Surface fine structure of treated dentine investigated with tapping mode atomic force microscopy (TMAFM)

OBJECTIVES

The objective of this study was to investigate the surface morphology and roughness of human dentine treated with different dentine conditioning agents with tapping mode atomic force microscopy (TMAFM).

METHODS

Dentine samples from third permanent molar teeth were prepared as flat disks. The samples were treated with different conditioning agents for 15-30 s: aqueous phosphoric acid and those supplied with three commercial adhesive products. The surface morphology and roughness was measured with tapping mode atomic force microscopy, a highly resolving method which minimises unwanted side effects of conventional AFM.

RESULTS

The tubules, the areas between the tubules and the entire surface showed variations in surface morphology and roughness, depending on the conditioning agent used. These differences might affect the bonding properties of the agents in dentine/polymer systems.

CONCLUSIONS

The surface structure, such as the tubules diameters and depths, the local height differences of the surface between the tubules and the overall mean surface roughness Ra varies between samples treated with different conditioning agents. All conditioning agents, however, led to exposed and open tubules.

CLINICAL RELEVANCE

The direct observation of effects of conditioning agents on dentine is important in order to judge their performance under clinically relevant conditions-free of desiccation artefacts. A vast number of conditioning agents is available today. The differences in their actual effects on dentine surfaces, however, are less than clear to many users.

Effect of primers on bonding agent polymerization

The aim of the present study was to evaluate the effect of primers on the polymerization of bonding agent. We measured the degree of conversion (radical production) and mechanical properties (surface hardness and direct tensile strength) of various adhesives/primers mixed at different ratios and the effect of varying the visible-light curing time. With and without primer treatment, the tensile bond strength of adhesive resin to micacious glass ceramic and human enamel was measured. After the tensile bond test, using the Image Capture System, the failure patterns of adhesive resin bonded to micacious glass-ceramic were analysed. The results show that the mixtures containing the higher amounts of primer yielded a lower degree of conversion and inferior mechanical properties when compared with the mixtures containing a lower proportion of primer, except in the experimental bonding system. The adhesive/primer mixtures inhibited free radical polymerization. The value for the Knoop hardness number and the direct tensile strength of the adhesive/primer mixtures were significantly decreased compared with those of the adhesive bonding agent alone with no primer added. The tensile bond strength of adhesive resin bonded to micacious glass-ceramic or human enamel without primer treatment was significantly greater than that of adhesive resin with primer treatment in certain cases. Most of the fractures of ceramic surfaces were cohesive (within resins) and/or interface (at the ceramic surface) failure.

Restorative therapy for erosive lesions

More needs to be learned about the etiology of erosion lesions before they can be accurately diagnosed, confidently treated and, more importantly, prevented. The treatment is dependent on the location and the degree of erosion. The decision to treat an erosion lesion should be based on careful consideration of the etiology and progression of the condition. Reasons for restoring noncarious enamel/dentin lesions are discussed and various therapeutic measures are provided. Preventive and restorative therapeutic measures for noncarious abrasive/ erosive lesions are proposed such as: a change of dietary or behavior patterns; application of desensitization products; intensive fluoride therapy with or without iontophoresis; brushing with desensitizing dentifrices; adhesive penetration with dentin bonding agents; glass ionomers and compomers; resin composites; composite or porcelain veneers; crown and bridge work; occlusal adjustments and nightguard fabrication if the abfraction factor coincides. The clinical durability of restorative therapy and important clinical factors related to the restoration of multifactorial defects are discussed.

Influence of light irradiation of dentine primers on dentine-resin bond

OBJECTIVE

The purpose of this study was to examine the influence of light irradiation of dentine primers that contain camphoroquinone (CQ) on the shear bond strength to dentine and their contact angle.

METHOD

Three dentine bonding systems which contain CQ, Imperva Bond, OptiBond and XR-Bond; and Light Bond, which does not contain CQ, were employed. Labial surfaces of freshly extracted lower bovine incisors were ground with no. 600 grit SiC paper. Dentine primers were applied to the dentine surfaces in two groups, irradiated and non-irradiated. A shear bond strength test was performed and the direct contact angle was measured.

RESULTS

Statistical analysis (Newman-Keuls multiple comparison P < 0.05) of the data indicated that light irradiation of the dentine primer for systems containing CQ resulted in increased bond strength and decreased contact angle.

CONCLUSION

This study indicates that for these dentine bonding systems containing CQ in their primers, light irradiation of the dentine primer is effective in improving wettability and increasing the bond strength to dentine.

Effects of water and carboxylic acid monomer on polymerization of HEMA in the presence of N-phenylglycine

OBJECTIVES

This research was designed to study the effect of water or carboxylic acid monomer on the polymerization of 2-hydroxyethyl methacrylate (HEMA) in order to understand the bonding mechanism of dentin bonding systems using N-phenylglycine (NPG).

METHODS

The polymerization of HEMA in the presence of NPG was studied by adding various amounts of water and/or 4-(2-methacryloyloxyethoxycarbonyl) phthalic acid (4-MET) and evaluated using differential scanning calorimetry (DSC).

RESULTS

The addition of water promoted the polymerization of HEMA. Polymerization was further promoted through the addition of 4-MET as a carboxylic acid monomer. Polymerization was promoted at the molar ratio of 4-MET to NPG of 1.0-7.0.

SIGNIFICANCE

Moisture on the dentin surface could contribute to improving bond strength in dentin bonding systems using NPG by promoting polymerization at the dentin interface.

SEM evaluation of the resin-dentin interface with proprietary bonding agents in human subjects

Laboratory studies on dentin bonding do not replicate physiological reality. This study examined with SEM the attachment produced in vivo under clinical conditions. Forty-four cavities were prepared in buccal/lingual surfaces of 16 premolar teeth scheduled for extraction and assigned randomly for treatment with: All-Bond 2 (Bisco) (A) with and (B) without dentin etch, (C) Scotchbond 2 (3M), (D) Scotchbond Multi-Purpose (3M), and (E) controls, using Enamel Bond (Kulzer) with dentin etch. After atraumatic extraction, restorations were split transversely by freeze-fracture and acid-treated. SEM examination of A revealed significant areas of gap-free attachment, with evidence of an acid-resistant hybrid layer (5-8 microns), often with resin tags of various lengths. Resin-reinforced collagen fibers were seen. Gap formation was coincident with lack of bonding resin layer over primed dentin. Attachment with B was less effective; a hybrid layer was infrequently seen and few resin tags. Pooled bonding resin at internal line angles appeared to favor an effective bond. Treatment C resulted in large areas of detachment, leaving an adherent primed dentin layer with short resin tags. Treatment D revealed significant areas of gap-free attachment and evidence of a hybrid layer. Controls (E) showed total bond failure. Attachment with A and D was secure, restorations remaining in situ even after freeze-fracture. This study confirmed that brief acid pre-treatment of dentin, allowing diffusion of resin-dentin primers, appeared conductive to development of an effective bond in vivo, similar to that reported in vitro.

Bond strength of six dentinal adhesives

This study compared the shear bond strengths on dentine of five dentine adhesives against Scotchbond 2 as a control. Dentine specimens from 225 extracted human permanent molar teeth were used in a matched-pair design, such that 45 tooth sides were treated along with the matching control for each of the five test materials. Shear bond strength testing was conducted 24 h after the completion of each specimen. Results showed that mean force (MPa) for the materials were: XR Bond, 17.1 +/- 5.1; Scotchbond Multi-Purpose, 15.9 +/- 6.5; Syntac, 13.5 +/- 8.6; All-Bond 2, 6.2 +/- 4.1; Scotchbond 2 (control composite score), 4.9 +/- 3.0; Denthesive, 3.4 +/- 1.7. Matched pair t-test comparisons with Scotchbond 2 control were: XR Bond, P = 0.0005; Scotchbond Multi-Purpose, P = 0.0005; Syntac, P = 0.0005; All-Bond 2, P = 0.0368; Denthesive, P = 0.005. Analysis of variance determined a statistically significant difference (P = 0.05) between the means of the bond strengths, which fell into four groups: Group A, XR Bond and Scotchbond Multi-Purpose; Group B, Syntac; Group C, All-Bond 2 and Scotchbond 2; Group D, Scotchbond 2 and Denthesive. In Group C, there was no significant difference between Scotchbond 2 and All-Bond 2. In Group D there was no significant difference between Scotchbond 2 and Denthesive, however, there was significant difference between All-Bond 2 and Denthesive. It was concluded that XR Bond and Scotchbond Multi-Purpose had significantly better shear bond strength than the other dentine adhesives.

In vitro bond strengths and SEM evaluation of dentin bonding systems to different dentin substrates

In comparison to enamel, bonding to normal dentin is a greater challenge because of its organic constituents, fluid-filed tubules, and variations in intrinsic composition. Bonding to sclerotic dentin is even more difficult. To evaluate the shear bond strengths of four adhesive systems to dentin substrates with different levels of mineralization, 120 extracted human teeth were randomly assigned to three groups (n = 40). After mid-coronal dentin was exposed, groups of specimens were artificially hypermineralized by immersion in a remineralizing solution, demineralized by means of an acetic acid demineralizing solution, or stored in distilled water to model sclerotic, carious, and normal dentin, respectively. Resin composite was bonded to dentin by use of commercial adhesive systems. After the specimens were thermocycled, shear bond strengths were determined in an Instron universal testing machine. Dentin substrates and resin/dentin interfaces were examined by SEM. For each adhesive system, the mean shear bond strength to normal dentin was significantly higher than that to either of the other substrates. Shear bond strengths to hypermineralized dentin were significantly higher than those to demineralized dentin with all adhesives except Prisma Universal Bond 3.

In vitro quality testing of dentin adhesives

A tensile and a shear bond strength test are compared, using two well-known and two more recently marketed dentin adhesive systems: Gluma (Bayer), Scotchbond 2 (3M), Scotchbond Multi-Purpose (3M), and Syntac (Vivadent). The adhesives were used to bond composite resins to the buccal surface of human third molars. Specimens stored for 24 h before testing did not show significant differences between bond strength values obtained by either the tensile or the shear test method for any of the materials. The bond strength of thermocycled specimens did not differ for Gluma, was significantly lower for Scotchbond 2, and significantly higher for Scotchbond Multi-Purpose and Syntac. SEM observations showed increasing amounts of cohesive failure in resin with increasing bond strength values. Cohesive fractures in dentin were also observed. It is concluded that either the tensile or the shear test method can be used for quality testing of dentin adhesives. Thermocycling may provide interesting information about the quality of a bond.

Noncarious cervical lesions: the decision to ignore or restore

A variety of unusual noncarious cervical lesions (NCL) are depicted that appear to negate W.D. Miller's toothbrush/dentifrice abrasion theory and demonstrate that other factors may be involved in their etiology. Confusion exists in the designation of NCL ever since G.V. Black stated in 1908 that toothbrush/dentifrice abrasion is an erosive effect. Since abrasion and erosion are two distinct activities, it is suggested that dentistry adopt the same terminology as chemical engineering in order to foster improved communication between the sciences. The term "abfraction" has been used to supplant erosion because it seems more appropriate when describing the loss of tooth substance attributable to effects of occlusal loading forces as well as the physiochemical breaking that occurs during stress corrosion. Numerous reasons, based on accepted engineering principles, indicate that NCL should be restored. It is incumbent on dentists to become cognizant of these reasons, since this would help them inform patients of the benefits to be gained by restoring such deficient areas.

Shear bond strengths of ten dentin adhesive systems

This in vitro study tested the shear bond strengths of nine third-generation dentin bonding systems. All of these systems had higher bond strengths than the control, a second-generation agent. Amalgambond and All-Bond had the strongest bonds to dentin, 23.3 +/- 5.7 and 19.3 +/- 5.6 MPa, respectively. Clearfil Photo Bond and Prisma Universal Bond 3 had intermediate bond strengths (approximately 13 MPa). Gluma, PowerBond, Scotchbond 2, Tenure, and XR-Bond all had mean shear bond strengths of less than 8 MPa.

Morphological aspects of the resin-dentin interdiffusion zone with different dentin adhesive systems

Cross-sections of resin-dentin interfaces were etched with an argon-ion beam to make their substructure detectable by scanning electron microscopy. The dentin adhesive systems were categorized morphologically into three groups, and an attempt was made to clarify their adhesive mechanism. The first group of products removed the smear layer. The argon-ion bombardment clearly disclosed a hybrid or resin-impregnated dentin layer. It is hypothesized that conditioning with acidic or chelating agents demineralized the dentin surface-layer to a certain depth, leaving behind a collagen-rich mesh-work. Hydrophilic monomers are then believed to alter this collagen-fiber arrangement in a way that facilitates penetration of the adhesive resin, resulting in a mechanical, intermingled link between collagen and the adhesive resin. The second group preserved the smear layer. In this case, the dentinal tubules were obliterated with globular particles at their orifices and remained patent underneath these smear plugs. This type of adhesive system aims at the incorporation of the smear layer into the hydrophilic monomers, which have an affinity for the organic and/or inorganic components of the underlying dentin. Finally, a third, small group only partly dissolved the smear layer, creating a thin resin-impregnated dentin layer and a resin-impregnated smear plug. This study clearly showed that the application of recent adhesive systems induced structural changes in the dentin surface morphology, creating a retentive interface, called the inter-diffusion zone, between the deep, untouched dentin layers and the composite filling material. This resin-dentin interdiffusion zone offers bonding sites for copolymerization with the resin composite and, concurrently, might have protective potential for the pulp tissues.

Report of the Committee on Scientific Investigation of the American Academy of Restorative Dentistry

The committee screened several hundred articles, citing 518 published papers. Some are present quality in research, others provide clinical interest, and some are identified as misleading. New techniques in pulp physiology and pathology are reported. Laser use and techniques in prevention, restorative dentistry, and materials use are reported. Epidemiology of selected diseases and the results of various formulations for treatment are cited. Diagnosis of craniomandibular dysfunction is well represented as well as references to literature reviews and other sophisticated scientific investigation. Research on adhesives is presented in respect to bonding agents for dentin and enamel. Several clinical studies are included, along with customary laboratory reports on several materials.