Temperature and humidity effects on bond strength of a dentinal adhesive.

Dentin specimens from 46 extracted human molar teeth were used in a matched-pair design examining the factors of temperature/humidity on shear bond strength of a dentinal adhesive to dentin. For one tooth-half, all procedures using restorative materials were accomplished in a controlled temperature and humidity chamber (humidity 95.0 +/- 2.0%, temperature 37.0 +/- 0.3 degrees C). For the other matched tooth-half all procedures were performed at ambient room conditions (humidity 52%, temperature 23.3 degrees C/74 degrees F). Oil-free air and water were used in all restorative procedures. Application of Scotchbond Multi-Purpose Adhesive System was followed by placement of Z100 Restorative Resin, and thermocycling 1000 cycles from 5 to 55 degrees C. Each matched specimen was tested 24 hours later in an Instron Testing Machine. A paired t-test was performed for comparison of bond strength set values, since they were obtained from matching halves of the same teeth. Paired t-test comparison showed that the average humidity/temperature chamber mean of 7.14 +/- 3.12 MPa was significantly less than the ambient conditions mean of 14.29 +/- 5.07 (P = 0.0000). Bond strength testing under simulated oral conditions may produce significantly different findings than customary bench-top laboratory experiments.

Evaluating the effect of glove coating on the shear bond strength of porcelain laminate veneers.

Gloves have become a standard tool in dentistry due to infection control concerns. But the starch powder with which many of these gloves are coated may contaminate surfaces on contact, creating potential problems during adhesive procedures such as the placement of porcelain veneers. The authors studied the powder's effect on the strength of the shear bond of etched porcelain to etched human tooth enamel and compared it to the effect of a powder-free polymer glove coating. While the starch coating led to a statistically significant decrease in shear bond strength, the powder-free coating produced no significant decrease in strength.

Influence of different etchants and etching times on shear bond strength.

This study compared the shear bond strength to enamel of Scotchbond Multi-Purpose Dental Adhesive System's bonding resin following etching of enamel with 10% maleic, 1.6% oxalic, 10% phosphoric, and 35% phosphoric acids for 15, 30, and 60 seconds. Three hundred and sixty human molar teeth were used to create 12 groups of 30 enamel specimens per group (n = 30). Flattened enamel surfaces were treated with the different etchants for the time periods indicated, the surfaces primed, and adhesive resin applied according to the manufacturer's recommendations. The specimens were completed with Silux Plus resin and subjected to 1000 thermocycles (5-55 degrees C) followed by shear stress in an Instron Testing Machine to failure within a 24-hour period. A two-way ANOVA revealed significant differences for shear bond strength values by type of etchant (10% phosphoric, 35% phosphoric > 10% maleic > 1.6% oxalic acid) (P < 0.005) and by length of application time (P < 0.005). The interaction term for these two treatments was statistically significant (P < 0.005).

Microleakage of five dentinal adhesives.

This study compared the microleakage characteristics of four dentinal adhesives against Scotchbond 2 as a control and discusses the results in light of recently reported bond strengths for these same materials. Dentin specimens from 100 caries-free extracted human molar teeth were used in a matched pair design. In each of the four test materials, 25 tooth sides were treated along with the matching control, subjected to 500 thermocycles (5 to 55 degrees C), followed by AGNO3 dye penetration, specimen sectioning, and evaluation by low-power stereomicroscopy. Mean microleakage values were as follows (microns): Scotchbond Multipurpose, 498.0; All-Bond 2, 530.8; Syntac, 748.0; X-R Bond, 844.9; and the Scotchbond 2 control (a composite score created by averaging four sets of 25 tooth sides), 1095.2. Paired t-tests showed that Scotchbond Multipurpose, Syntac, and All-Bond 2 had significantly lower microleakage than the control (P=0.0001); however, X-R Bond had no significant difference from the control (=0.4634).

The effects of sterilization on addition silicone impressions in custom and stock metal trays.

Five groups of addition silicone impressions (four made in custom autopolymerizing acrylic resin trays and one in stock metal rim-lock trays) were made of a stainless-steel master die. The first group (control group) was not sterilized. The second group was sterilized in an ethylene oxide gas autoclave, the third group in a steam autoclave, and the fourth and fifth groups by immersion for 12 hours in 2% glutaraldehyde. Casts made from each sterilization group were found to be significantly different from control impressions by multivariate analysis of variance and should not be used to fabricate prostheses.

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.

Use of a scanning laser three-dimensional digitizer to evaluate dimensional accuracy of dental impression materials.

A steel die was machined to represent a dental arch with teeth prepared for complete crowns. Impressions and casts were made from the die, and critical dimensions were measured by two methods--one using micrometers and the other a scanning laser three-dimensional (3-D) digitizer. The digitizer recorded measurements were more precise than the micrometer's and virtually eliminated operator error because the acquisition of data was automatic. The digitizer could also be useful for high-precision analyses of the dimensional accuracy of dental impression materials, but the cost and complexity of the instrument makes it less desirable for low-precision work.

Dimensional stability of a polyvinylsiloxane impression material following ethylene oxide and steam autoclave sterilization.

Polyvinlsiloxane impressions were made from a stainless steel master die machined to stimulate five full veneer crown preparations symmetrically placed in an arch form. Three groups of 10 impressions each were made. Treatment groups were sterilized using an ethylene oxide gas and a conventional steam autoclave. Casts were poured and intrapreparation, height, and diameter measurements were made using a stereomicroscope, a digital electronic caliper, and a 1-inch travel dial indicator. Analysis of dimensional changes for the two groups showed that casts made from impressions sterilized by ethylene oxide are acceptable for use in the construction of fixed or removable prostheses. Casts made from impressions sterilized in a steam autoclave can be used for the fabrication of diagnostic casts and some transitional prostheses, but not for routine construction of crowns or fixed partial dentures.

SEM and energy dispersive X-ray surface analysis of the interfacial region of selected porcelain-metal systems.

Comparative bond strength data of Ceramco and Vita opaque and body porcelains when fired to high noble, medium noble, and base metal porcelain-fused-to-metal alloys were recently published. In the present study SEM and energy dispersive X-ray (EDX) microanalyses were undertaken--using the same specimens after debonding--to relate the bond strengths reported for 12 different porcelain-metal composites to morphology and chemistry at fracture sites. SEM examination revealed intimate contact between the different porcelains and the metal oxide substrates. On Olympia, a medium noble alloy, bubbles trapped in porcelain at or near fracture sites appeared to decrease the potential interaction. Area scan semiquantitative EDX analysis of the interfacial fracture sites detected high concentrations of metal oxides thought to be essential for a successful chemical bond. Multi-spot surface spectroscopy on similar traces of porcelain residuals revealed significant differences in the amount of particular back scattering activity. Further examination with cross sectional quantitative EDX analysis is suggested for a more precise characterization of element concentration within all components of the porcelain-metal interface.

Use of a scanning laser three-dimensional digitizer for analysis of dental materials.

A scanning laser 3-D digitizer was used to measure dimensions in dental impression materials, and its performance was compared with that of micrometer-based measuring instruments. It was found that the digitizer was precise enough to detect dimensional changes on the order of 40 microns, and it was automated enough to be convenient and almost eliminate operator errors. However, its operation required the services of an engineer for maintenance and a programmer for data analysis.

Bond strength of a light-cured and two auto-cured glass ionomer liners.

Ninety-nine extracted human molar teeth were used in this study comparing the shear bond strengths on dentine of one light-cured and two auto-cured polyalkenoate (glass ionomer) cements. Bond strength can be influenced by differences in tooth structure. A balanced-incomplete block design (Hull and Nie, 1981) was used to reduce variation attributable to such differences. Cements were applied to paired dentine surfaces in combinations such that 66 tooth sides were treated with each material. A light-cured dentinal adhesive and composite resin restorative material were then placed and shear bond strength testing was conducted exactly 24 h after the completion of each specimen. Mean forces (MPa) for the three materials were compared using an appropriate analysis of variance model (balanced-incomplete-blocks) The shear bond strengths (MPa) of the light-cured liner (Espe, Seefeld/Oberbay, FRG) was 4.71 +/- 1.16. Vitrabond showed the greatest variance of all three materials tested, however this material's average bond strength was greater than the maximum achieved for the other materials. Student-Newman-Keuls comparison of means showed that all cements differed significantly from each other (alpha = 0.05). It is concluded that the light-cured glass ionomer liner exhibited significantly better shear bond strength performance than the two auto-cured glass ionomers tested.

Microleakage and marginal placement of a glass-ionomer liner.

Glass-ionomer cements, with their ability to bond to dentin, have been reported to produce less microleakage than several other restorative resin materials. This matched-pair study reports the effect on microleakage of placement of a light-curing glass-ionomer cement used as a liner when extended out to the dentinal cervical cavosurface margin or held short of that margin. Pairs of circular Class V cavities involving 50% enamel, with bevel, and 50% cementum were cut in 31 extracted third molars. After placement of the glass-ionomer cement, etching of the bevel, and placement of a resin bonding system, microfilled resin was placed over the bonding agent in one increment, light-cured, finished, and given 500 thermocycled 500 times between 5 and 55 degrees C. A silver nitrate staining technique was used to evaluate microleakage measured in graticular units (gu) along the dentinal interface under stereomicroscopy. The extension of the glass-ionomer liner out to the dentinal cavosurface margin did not significantly improve microleakage performance compared to performance of the liner when it was placed short of that margin and covered by a resin veneer. From other considerations, such as the potential for mechanical breakdown of the glass-ionomer cement when exposed to the oral environment and abrasion, and the possibility for improved esthetics, the clinician should consider holding the glass-ionomer liner short of the dentinal cavosurface margin and covering it with a composite resin veneer of a thickness consistent with structural integrity.

Technical note: fluoride pre-treatment effects on microleakage of a resin bonding agent.

This pilot study reports the effect of fluoride pre-treatment of dentin and enamel on microleakage of a resin bonding agent. Pairs of circular class V cavities involving 50% enamel and 50% cementum were cut in 12 extracted third molars. Each tooth contained a control and a treatment cavity (matched-pair design). A stannous fluoride solution (0.717% SnF2, Gel-Kam, Scherer Laboratories, Dallas, TX) was applied to the entire treatment preparation of each tooth. A dentin resin bonding system (Scotchbond 2 with Scotchprep, a dentin primer, 3M Dental Products Div., St. Paul, MN) was applied per manufacturer's instructions. Silux resin (3M) was placed over the resin bonding agent, light-cured, and finished. The teeth were subjected to 500 temperature cycles between 5 and 55 degrees C. A silver nitrate staining technique was used for evaluation of microleakage. The mean leakage for the control was 2235 +/- 1146 microns, and 2105 +/- 1052 microns for the fluoride treatment sites. It is concluded, from this pilot study with small sample size, that pre-treatment with fluoride of dentin and enamel prior to the placement of a resin bonding agent produced no significant change in microleakage (Student's t test for paired samples, p = 0.6492).