[Interchangeability of resin composites and bonding agents based on bis-GMA or UDMA].

Recently, dentin bonding systems have been released separately from the resin composites, because the adhesive systems have been quickly improved. Since the merit of each material should be effectively utilized for each clinical case, the bonding systems and resin composites produced by different manufacturers may be combined according to the clinical purpose. The current restorative resins are basically categorized into two groups according to the main resin monomer, bis-GMA or UDMA resins. The purpose of this study was to evaluate the interchangeability between the bonding systems and resin composites, which were made by different manufacturers. Two bonding systems and five resin composites based on bis-GMA or UDMA were used in this study. The evaluation was performed by the tensile bond strength, fracture modes, and SEM observation, using the dentin surface of freshly-extracted bovine teeth. The highest bond strength (19.2 MPa) was shown by the combination of LBII sigma and AP-X. The bond strengths of nine other combinations were not statistically different (p > 0.05). There were many cohesive failures in dentin or resin composite, using all combinations. From the results, it was concluded that the interchangeability of the resin composites and bonding systems should be clinically acceptable.

Effect of citric acid concentration on dentin demineralization, dehydration, and rehydration: atomic force microscopy study.

Most current dentin bonding procedures use acid etchants to partially demineralize the dentin structure and provide pathways for resin infiltration. This study determined the recession rates of peritubular dentin and intertubular dentin as a function of pH during demineralization in citric acid solutions (0.0005-2.5M) and the effects of dehydration and rehydration on the partially demineralized dentin. Polished dentin disks were prepared with an internal reference layer and were studied at specific intervals for citric acid etching between pH 1 and 3.4 in an atomic force microscope. Peritubular dentin etched rapidly and linearly with time until it could no longer be measured. The intertubular surface began etching at nearly the same rate, but then recession slowed for all concentrations and stabilized after recession of less than 1 microm for all but the pH 1 solution. The decrease in recession was attributed to the limitation of contraction of the demineralized collagen scaffold as long as it remained hydrated. Dehydration following etching resulted in significant collapse of the surface, changes in roughness, and a slight decrease in tubule diameter for samples etched for 30 min. Measurements could not be made of the collapse for low pH samples, because shrinkage stresses disrupted the integrity of the reference layer. On rehydration, the dehydrated surfaces underwent an expansion up to the level seen after etching and tubule diameters returned to the etched values. These results indicate that the collapse of demineralized matrix is almost totally recoverable on rehydration.

Adhesion between collagen depleted dentin and dentin adhesives.

PURPOSE: To determine the influence of sodium hypochlorite treatment of dentin on shear bond strength and morphology. MATERIALS AND METHODS: Shear bond strengths of several dentin bonding agents were compared following specific surface treatments that included manufacturer's directions, etching plus sodium hypochlorite, and sodium hypochlorite alone. The treated surfaces and interfaces between bonding materials and treated surfaces were observed using an FE-SEM. RESULTS: Acetone-containing systems yielded equivalent or higher shear bond strengths when sodium hypochlorite was used following etching, as compared with normal procedures. In these cases it is proposed that the adhesive interacts strongly with the treated surface, that contains a high mineral content.

Effect of operator variability on dentin adhesion: students vs. dentists.

The purpose of this study was to evaluate the operator variability of two dentin bonding systems. Fourteen undergraduate students and ten dentists of different levels of clinical experience were selected. Tensile bond strengths between resin composite and bovine dentin using dentin adhesive systems (Clearfil Liner Bond II: LB II; Scotchbond Multi-Purpose: MP) bonding systems showed a large scatter among students and dentists. The dentists group demonstrated no statistically significant differences for mean bond strengths between LB II and MP. The student group recorded a statistically greater bond strength using LB II. The mean coefficient of variation of the dentists group showed no statistically significant difference between LB II and MP, however that of the students group was lower with LB II. When using MP, the dentist group demonstrated a lower coefficient of variation than that of the student group. In order to obtain optimal bonding performance, or when beginning the use of a new system, the operator should be aware of the technique sensitivity of some adhesive systems and sensitivity to operator variability.

Dentin demineralization: effects of dentin depth, pH and different acids.

OBJECTIVES: This investigation sought to determine: 1) if dentin demineralization rates are proportional to acid concentration for demineralization in phosphoric acid (10% or 1.76 M, 0.025 M, 0.0001 M, with pH = 0.95, 2.0, 4.0 respectively); 2) if the etching characteristics are independent of dentin depth; and 3) if the etching characteristics for phosphoric acid were comparable to those for citric acid over a similar pH range. METHODS: Highly polished dentin disks from freshly extracted, non-carious, third molars were prepared with a reference layer. Samples were prepared from either superficial or deep coronal dentin. The samples were etched for periods of up to 30 min using phosphoric acid solutions (pH = 0.95, 2.0, 4.0) in a wet cell of an atomic force microscope (AFM). Depth changes with respect to the reference layer were determined for the intertubular and peritubular dentin to quantify structural changes. The results were compared with similar studies using citric acid (pH = 1.0, 2.15 or 3.4). Etching characteristics were statistically compared using 2-way repeated measures ANOVA at p < 0.05 and the Tukey's multiple comparison test. RESULTS: The relation between time and recession for peritubular dentin was initially linear. The intertubular dentin recession started rapidly but then reached a plateau within a very short interval for etching solutions at pH = 2.0 and 4.0. At the highest concentration, the recession decreased with time, but a clear plateau was not established. There was no statistical difference between peritubular etching rates of superficial and deep dentin surfaces with phosphoric acid at any concentration. There was also no difference in the intertubular dentin recession at the location of the plateau that depended on dentin depth. Etching rates increased dramatically with decreased pH for both phosphoric and citric acids, but were higher for citric acid than for phosphoric acid. SIGNIFICANCE: The AFM allowed quantification of changes during etching of wet dentin. Peritubular dentin etching rates increased with decreasing pH, as expected, but changes were not linear and were different for the two acids studied over a similar pH range. Intertubular dentin surface recession was small and plateaued for low concentrations. The peritubular etching rate and intertubular dentin recession did not depend on dentin depth.

[Report of dental treatment for an island of Okinawa].

Dental treatment was performed on the the inhabitants of Iriomote Island, which is a non-dentist island at present, in Okinawa; two hundred forty-five patients received the treatment for 647 man-days during the period from July 6 through 28, 1994. Since completion of the treatment plan was considered to be necessary during that period, treatments for many teeth had to be done simultaneously because a large number of dental caries and periodontal disease were found. Dental hygienic education such as brushing instruction was made but the long-term educational program is considered to be important so as to prevent dental disease as well. It is to be desired that many dentists become interested in the treatment in non-dentist areas.

Influence of temperature and relative humidity on early bond strengths to dentine.

The effect of temperature and relative humidity (RH) on the early tensile bond strengths to bovine dentine of two bonding systems (Liner Bond System, and Scotchbond Multi-purpose), and an experimental system (KB-110) were tested. Two environmental conditions, room temperature (23 degrees C/50% RH) and oral temperature (30 degrees C/80% RH), were used in a controlled temperature and humidity chamber. Bond strengths were recorded immediately after, 10 min and 24 h following light curing. The tensile bond strengths did not vary between the two test conditions, but the mode of fracture was observed to change. The 30 degrees C/80% RH condition exhibited a slightly greater degree of adhesive type failures compared with the 23 degrees C/50% RH group. This was particularly so for the experimental system, indicating that different bonding systems may be more or less sensitive to changes in RH and temperature. Failures occurred partially or totally within the resin composite at the early test times, and it was concluded that the bond strengths of the systems tested tended to exceed the early cohesive strengths of the resin composite.

The influence of age and depth of dentin on bonding.

OBJECTIVES: The purpose of this study was to investigate what influence the two variables of dentin depth and age may have on the tensile bond strengths of three bonding systems. METHODS: Dentin discs prepared from human molars were divided into young and old, superficial and deep surfaces. Three bonding systems, Scotchbond Multi-purpose (3M Dental Products), Superbond D-liner (Sun Medical Co.), and Liner Bond II (Kuraray Co.) were the materials tested for tensile bond strength. In addition, the structural variation of the resin-impregnated, or hybrid, layer was compared among the two variables and three bonding systems. RESULTS: Tensile bond strengths exceeding 10 MPa were obtained for all materials. After ANOVA, an effect on tensile bond strength could be attributed to dentin age or depth for only Superbond D-liner used on deep-young dentin as compared with old-superficial dentin. All other group comparisons failed to show any variation between dentin depth or age. However, specimens bonded to deeper dentin showed slightly lower strengths. SEM observations showed thicker resin-impregnated layers for Scotchbond MP and Superbond D-liner compared with Liner Bond II. Liner Bond II exhibited a thinner and more diffuse resin-impregnated layer, believed to be due to the different dentin conditioning method. SIGNIFICANCE: Dentin age or depth may not show as great an influence on bond strengths with the newer type of bonding systems. The resin-impregnated layer quality, rather than thickness, is believed to be the most important factor for obtaining high tensile bond strengths.