Shear-peel bond strength of orthodontic primers in wet conditions.

OBJECTIVE: The purpose of this in vitro study was to determine whether a hydrophilic primer (Transbond MIP, [MIP]) produces a significant difference in shear/peel bond strength compared with a traditional hydrophobic primer (Transbond XT, [XT]) in wet (W) or dry (D) conditions and if there is a difference in the site of bond failure. DESIGN: A randomized blinded in vitro design. SETTING AND SAMPLE POPULATION: The University of Missouri-Kansas City School of Dentistry. Forty extracted human premolars were divided into four test groups (n = 10 each): MIP-dry conditions (MIPD), MIP-wet conditions (MIPW), XT-dry (XTD) and XT-wet (XTW). EXPERIMENTAL VARIABLE: Orthodontic brackets were bonded to the teeth according to the manufacturer's directions except XTW and MIPW were exposed to moisture. OUTCOME MEASURE: Shear/peel test 24 h after bonding using an Instron at a crosshead speed of 0.5 mm/min and the adhesive remnant index to determine the site of bond failure. RESULTS: The bond strengths (X +/- SD) in MPa were XTD = 8.3 +/- 2.3; XTW = 0.8 +/- 0.7; MIPD = 7.5 +/- 1.8 and MIPW = 7.9 +/- 1.7. The shear/peel bond strengths were significantly different: XTD = MIPD = MIPW > XTW (p < or = 0.01; two-way ANOVA; Tukey HSD). The ARI scores were also significantly different: XTD = MIPD = MIPW > XTW (p < or = 0.01; Chi-square). CONCLUSIONS: Orthodontists who suspect moisture contamination should use a hydrophilic primer during bonding procedures to maintain shear/peel bond strength.

The effects of different storage conditions on polyether and polyvinylsiloxane impressions.

While being shipped to a laboratory, impressions can be exposed to excessive temperatures. This study compared the effects of different time and temperature storage conditions, including temperature extremes of 66 C and -10 C, on the accuracy of addition silicone and polyether impressions. The greatest distortion generally occurred as a result of the 66 C temperature extreme. The authors recommend that impressions be poured in stone according to manufacturers' specifications before being shipped to a dental laboratory.

Marginal ridge strength of Class II tunnel restorations.

PURPOSE: To test the strength, at the marginal ridge, of the tunnel preparation vs the Class II traditional box preparation when restored with composite or glass ionomer (GI). MATERIALS AND METHODS: Eighty-four extracted maxillary molars stored in normal saline and thymol were randomly divided into six groups of 14 each (determined by pilot study where alpha = 0.05, beta = 0.2). Group A and C were tunnel preparations. Group B and D were traditional Class II preparations. Group E-whole tooth (negative control), and Group F-tunnel preparation unrestored (positive control). Group A and B were restored with Scotchbond 2/P-50 composite. Group C and D were restored with Ketac Fil-GI. The marginal ridge of each tooth was loaded at 0.5 mm/minute on the Instron. A loading rod produced a contact point of 1.0 mm in diameter. RESULTS: The mean compressive loads (kg) required for fracture were: (A): 42.2 +/- 11.9, (B): 53.1 +/- 10.7, (C): 52.0 +/- 10.9, (D): 23.8 +/- 8.4. (E): 79.1 +/- 16.1, (F): 27.0 +/- 10.6. A significant difference was found between whole teeth (E) and all other groups (P < 0.05). The Newman-Keuls test showed a significant difference between Class II composite (B) and tunnel composite (A) (P < 0.05), between tunnel GI (C) and tunnel composite (A) (P < 0.05) but no difference between tunnel GI (C) and Class II composite (B).

Accuracy of one-step versus two-step putty wash addition silicone impression technique.

This study compared the accuracy of one-step putty wash with two-step putty wash impression techniques. Five addition silicone impression materials-Mirror 3 (MR), Mirror 3 Extrude (ME), Express (E), Permagum (P), and Absolute(A)--were tested. A stainless steel model containing two full-crown abutment preparations was used as the positive control. Five replications for one-step and two-step putty wash impressions of the master model were made for each test material. Accuracy of the materials was assessed by measuring six dimensions on stone dies poured from impressions of the master model. Accuracy of addition silicone impression material is affected more by material than technique. Accuracy of the putty wash one-step impression technique was not different from the putty wash two-step impression technique except at one of the six dimensions where one-step was more accurate than two-step. Mirror 3 putty wash two-step impression presented less distortion than Mirror 3 Extrude putty wash one-step or two-step impression.

An experimental evaluation of the effectiveness and efficiency of the leadup activity.

The positive effects of a leadup activity on the production of intracoronal operative preparations have been documented in earlier studies. However, an absence of certain controls may have jeopardized the validity of the earlier study, and an adequate test of the innovation's efficiency was not undertaken. The purpose of this investigation was to evaluate the effects of a leadup activity implemented as part of the scheduled laboratory course, when the amount of supervision provided to the experimental subjects during the entire course was reduced significantly, and when subjects were assigned randomly to the two conditions. Calibrated raters, blind to group affiliation of products, graded all preparations. Mean scores for the experimental group (n = 35) were superior to those of the control group (n = 29) for all five preparations, and were statistically significantly (p less than .05) higher on three. Self-evaluations were equivalent to rater evaluations for subjects in the experimental group but not for those in the control group. Self-reports suggest that students receiving leadup training used fewer teeth to practice each of the preparation styles. Anecdotal data indicate that instructors in the experimental group may have found their job no more difficult than it had been in the past. It is concluded that the leadup activity improves performance and increases efficiency as measured by the faculty-student ratio and amount of practice required by students.

The effect of storage and thermocycling on the shear bond strength of three dentinal adhesives.

The purpose of this investigation was to evaluate the effects of time of storage and thermocycling on the shear bond strength of three dentinal adhesives. The shear bond strength of Mirage Bond was significantly greater than that of Scotchbond 2, which was significantly greater than that of Scotchbond Dual Cure (P less than or equal to .05). Thermocycling significantly lowered the shear bond strength of Scotchbond Dual Cure and Scotchbond 2, but not that of Mirage Bond (P less than or equal to .05). Time of storage did not affect the shear bond strength of the other adhesives, but Mirage Bond had a significantly greater shear bond strength after 1 month of storage (P less than or equal to .05). Scanning electron microscopic observations showed that the fracture patterns were all at the smear layer-adhesive interface for Scotchbond Dual Cure, the majority of the fractures were at the primer-adhesive interface for Scotchbond 2, and most of the fractures were cohesive in the bonding agent for Mirage Bond.

The effect of time on the adhesion of light-body to heavy-body Express in the two-step reline polyvinylsiloxane impression technique.

Often times light-body wash (LB) cannot be added to the heavy-body putty (HB) within 30 minutes when utilizing the two-step reline impression technique. The purpose of this study was to add the LB to the HB at times greater than 30 minutes and test the tensile bond strength. A split aluminum mold which created a bonding area of 1.13 cm2 and tray were filled with Express HB. After HB set the Express LB in a tray was added at varying times. The split molds were then separated and samples tested on the Instron. Ten groups with five samples/group (determined by a pilot study) were made. The times which the LB was added to the set HB and tested were: A) Immediately (one-step procedure); B) 10 minutes and contaminated with saliva (negative control); C) 10 minutes; D) 30 minutes; E) 45 minutes; F) 1 hour; G) 3 hours; H) 24 hours; I) 115 hours; and J) Freshened after 3 months. The results of this study indicate that saliva-contaminated samples were weaker than all other groups (P less than or equal to 0.01) and as far as tensile bond strength between materials is concerned, there appears to be no detrimental effect in tensile bond strength between HB and LB when delaying the application of the light-body material (P less than or equal to 0.01).

Fracture strength of Class I versus Class II restored premolars tested at the marginal ridge. 2. Cavosurface bonding and cavosurface plus internal enamel bonding.

The purpose of this study was to test the difference between the strength of the marginal ridge of extracted teeth with a Class I composite resin restoration and the strength of the marginal ridge of teeth with a Class II amalgam restoration with retention grooves. A statistically significant difference in fracture strengths was found among groups. No statistically significant difference was found among restored preparations, beveling technique, and restorative material. Statistically significant differences in fracture strength were found between the whole tooth group and treatment groups; between the whole tooth group and Class II amalgam restoration group; and between the unrestored tooth preparation group and all other tooth groups.

Fracture strength of Class I versus Class II restored premolars tested at the marginal ridge. I. Standard preparations.

Two groups of maxillary premolars with Class I cavities were prepared with one marginal ridge thickness to a width of 1.0 mm. One group was restored with amalgam and the other group with composite resin. Two groups of Class II cavities also were prepared and restored with amalgam and composite resin. The teeth in the four treatment groups were subjected to a centric load at the marginal ridge until fracture occurred. A two-factor analysis of variance revealed a statistically significant difference between the class of preparation (Class I preparations were weaker than were Class II preparations) but differences in strength between restorative materials (composite resin versus amalgam) and the interaction effect (class of preparation x restorative materials) were not found to be statistically significant (alpha = .05). A Newman-Keuls sequential range test found no statistically significant differences in strength between groups (alpha = .05). Fracture patterns were observed under scanning electron microscope. Fractures extended into the enamel and into the material in the Class I composite resin, Class I amalgam, and Class II composite resin restorations. Fractures extended only into the material in Class II amalgam restorations.