The effect of saliva on shear bond strengths of hydrophilic bonding systems.

Failure of orthodontic bonded attachments and brackets is mostly attributed to contamination of the enamel surface. To overcome this problem, materials have been developed that purportedly overcome the moisture and contaminants present in the oral environment. This study compared the shear bond strengths of 2 lightcured hydrophilic bonding systems, Transbond XT with MIP (3M/Unitek, Monrovia, Calif) and Assure (Reliance Orthodontics, Itasca, Ill) with a hydrophobic bonding system, Transbond XT with XT primer (3M/Unitek). Comparison tests were conducted under 4 enamel surface conditions: (1) etched and dried; (2) etched and moistened with artificial saliva; (3) etched, primed, and moistened with artificial saliva; and (4) etched, primed, moistened with artificial saliva, and reprimed. In addition, an adhesive remnant index score was used to determine the amount of adhesive remaining on the tooth. Stainless steel brackets with mesh-backed pads (n = 144) were bonded to bovine teeth. Bond strength was then tested in shear using an Instron mechanical testing instrument. There were significant differences in the bond strengths among the products (P <.05), within surface treatments (P <.05), and among the different bonding materials in combination with various surface treatments (P <.05). Treatments 1 and 4 showed the highest mean bond strengths adhesive remnant index scores, whereas treatments 2 and 3 showed the lowest mean bond strengths and scores.

Interfacial bond strengths of amalgam bonded to amalgam and resin composite bonded to amalgam.

OBJECTIVE: The effects of time, surface preparation, and use of a bonding agent on the ability to bond amalgam or resin composite to amalgam were studied. METHOD AND MATERIALS: Cylindrical amalgam specimens were prepared in a split die (32 groups of 10 each). The 32 groups were divided into two groups of 16 each: amalgam bonded to amalgam and resin composite bonded to amalgam. One half of each group of 16 was bonded within 1 hour after the initial condensation (fresh) and the other half was bonded after 21 days' storage in physiologic saline (old). Four bonding methods (control [no bonding agent], Advance, All-Bond 2, or Amalgambond Plus) were each utilized on one abraded group (air abrasion with 50-microns aluminum oxide) and one unabraded group. After an additional 21 days of storage, bond strengths were measured with a three-point flexure test. Solid amalgam cylinders also tested. RESULTS: Solid amalgam control cylinders exhibited mean bond strengths 10,000 psi greater than any of the bonded specimens. Among specimens of amalgam bonded to amalgam, those that were abraded after 21 days and used no bonding agent showed a significantly greater bond strength than did specimens utilizing any of the other combinations of the selected independent variables. Among specimens of resin composite bonded to amalgam, those bonded after 21 days and utilizing a bonding agent exhibited significantly greater bond strengths than did specimens utilizing any of the other combinations of the selected independent variables. CONCLUSIONS: The results of this in vitro study suggest that the strength of a repaired amalgam is only about 40% of that of an unrepaired amalgam. They also indicate that the strongest repair of amalgam using additional amalgam material may be accomplished without the use of any bonding agents utilized in this study. When adding resin composite material to amalgam, the resin composite should be added after the amalgam has had adequate time to set, and the use of a bonding agent increases the strength of the repair.

Quantitative study of bacterial colonization of dental casts.

STATEMENT OF PROBLEM: Contamination of dental casts can occur if the record bases are improperly disinfected or inadvertently not disinfected during fabrication of a prosthesis. It is essential to develop an effective means of disinfecting dental casts from professional, medical, and legal points of view. PURPOSE: This study determined whether: (1) saliva contamination on the surface of the dental cast contributed to bacterial growth over time and (2) cleaning or disinfecting of dental casts can minimize bacterial growth. MATERIAL AND METHODS: Five dental casts were contaminated with saliva. Each cast was divided into six areas and swabbed at 15, 30, 60, 120, 180, and 240 minutes. Sheep blood agar plates were inoculated and incubated at 37 degrees C for 72 hours. Standardized dental stone cylinders were contaminated with 25 microliters of saliva and treated by rinsing in tap water, scrubbing with soap and tap water, soaking in 2% glutaraldehyde, or as controls with and without saliva contamination (n = 12). The treated dental stone cylinders were placed in individual test tubes containing 2.5 ml of sterile phosphate-buffered solution and a final dilution of 10(-4) was achieved. Sheep blood agar plates were inoculated and incubated at 37 degrees C for 24 hours. RESULTS: Contamination of dental casts did not decrease, even when allowed to sit 4 hours before handling. Results also demonstrated that rinsing saliva-treated stone cylinders for 20 seconds significantly diminished bacterial contamination. Scrubbing with soap and tap water or soaking in 2% glutaraldehyde significantly reduced the bacterial contamination of saliva-treated stone cylinders when compared with rinsing with tap water. CONCLUSION: Bacterial contamination of dental casts can occur and requires an effective method of disinfecting.

Evaluation of frictional resistance in esthetic brackets.

The purpose of this study was to measure the frictional forces generated between composite, ceramic, and metal brackets and selected wire alloy-size combinations with elastomeric and stainless steel ligatures in a dry environment. Four types of composite, one ceramic, one sapphire, and one metal bracket were tested with stainless steel, nickel-titanium, and beta-titanium wires. The testing was performed with two wire sizes in the 0.018-inch slot brackets and three wire sizes in the 0.022-inch slot bracket. The recently introduced composite brackets were found to offer lower frictional resistance than the ceramic and stainless steel brackets, regardless of the wire size, wire alloy, and type of ligation. The wire alloy with the least friction was stainless steel, followed by beta-titanium and nickel-titanium. Mean variability in friction, as reflected by the magnitude of the standard deviations, was 2.7 to 3 times more with the stainless steel ligation than the elastomeric ligation.

In vitro weathering of selected direct esthetic restorative materials.

Reflectance spectroscopy measurements were used to compare the degree of surface color shift in two classes of visible light-cured resin composites (hybrid and small-particle) and a glass-ionomer restorative. The weathering times investigated were 0, 100, 200, 300, and 400 hours. Environmental factors of heat, ultraviolet light, and moisture were used to affect the surface integrity of the restoratives. The parameter of delta E * ab (overall color difference) of the CIELAB system for measuring small color differences was used. Chroma changes [delta C * ab] and hue differences [delta H * ab] were also determined. Color shifts, chroma changes, and hue differences were observed for all restorative materials evaluated, regardless of the weathering conditions or time intervals imposed. Glass-ionomer cement demonstrated a significantly greater degree of color shift than did the resin composites. There was no significant difference in the amount of overall color change between the two resin composites, although the difference in change in lightness was significant.

In vitro evaluation of matrix-bound fluoride-releasing orthodontic bonding adhesives.

Sustained fluoride-releasing composite resins have the potential to prevent decalcification of enamel that may occur during the course of orthodontic treatment. The purpose of this study was to evaluate the potential of matrix-bound fluoride-releasing adhesives (MBF) for orthodontic use by comparing the shear bond strengths (in MPa) and remnant adhesive on debonding (ARI scores) of these resins with commercially available orthodontic adhesives. Two types of resins were evaluated in separate groups: The light-cured resins (group I) consisted of two light-cured MBF, designated resins LA and LB, and five nonfluoride releasing resins, designated LC, LD, LE, LF, and LG. The self-cured resins (group II) consisted of one MBF, designated resin SA, and six nonfluoride releasing resins, designated resins SB, SC, SD, SE, SF, and SG. These resins were used to attach upper right central incisor metal (foil mesh based) orthodontic brackets to 210 freshly extracted bovine incisors in groups of 15 each. Student-Newman-Keuls multiple comparison tests were performed at p < 0.05 to determine significant differences among the resin types. Resin LA was significantly higher in bond strength (mean = 27.4 MPa) compared with LD and LG (mean = 18.9, 10.7 MPa, respectively). Further, LA demonstrated a higher mean bond strength compared with LB, LC, LE, and LF (mean = 21.9, 24.1, 24.3, and 20.8 MPa, respectively). Resin LB had significantly lower ARI scores (mean = 0.33) compared with LF and LG (mean = 1.20 and 1.80). LA, LB, LC, LD, and LE (mean = 0.47, 0.33, 0.60, 0.73, and 0.73, respectively) were not significantly different in their ARI scores. Resin SB demonstrated significantly lower bond strength (mean = 17.2 MPa) compared with SC, SD, SE, SF, and SG (mean = 23.9, 23.7, 23.4, 23.8, and 22.9 MPa, respectively). Resin SA (mean = 19.0 MPa) was not significantly different in bond strength from SB, SC, SD, SE, SF, and SG. Resin SA demonstrated significantly lower ARI scores (mean = 0.73) compared with SD and SE (mean = 2.13 and 1.87). Resin SA had lower mean ARI scores compared with SB, SC, SF, and SG (mean = 1.00, 1.27, 1.13 and 0.87, respectively). Sustained fluoride-releasing (matrix-bound) orthodontic adhesive systems demonstrated bond strength and ARI scores that compared favorably with commercially available orthodontic adhesives.

Evaluation of stresses and forces in selected I-bars using the finite element method.

PURPOSE: Three-dimensional models of half-round, tapered and full-round, untapered I-bar clasps of varying configurations and material properties were constructed. The purpose of this study was to examine the stresses and reaction forces produced within each model upon deflection to 0.01 in (0.254 mm), 0.02 in (0.508 mm), and 0.03 in (0.762 mm) at 1 mm from the tip using the finite element method. MATERIALS AND METHODS: Three-dimensional computer models of half-round and full-round clasps were constructed using solid eight-node brick elements. The half-round, tapered I-bar clasp model was 2.4 and 1.4 mm in diameter at the base and tip, respectively. The full-round, untapered I-bar clasp model was 1 mm in diameter. Three design groups were created for each clasp form. Group A had 25% of the total length in the straight anchor end of the I-bar clasp, B had 35%, and C had 50%. All models were 31 mm in length and had a radius of curvature of 5 mm. Different material properties were incorporated into the models. Each model was deflected at a point 1 mm from the tip to 0.01 in (0.254 mm), 0.02 in (0.508 mm), and 0.03 in (0.762 mm). RESULTS: The stresses and forces produced as a result of the deflection applied to each clasp were viewed and displayed graphically. The maximum von Mises stresses in megapascals and the reaction force in newtons (N) were recorded. Stresses varied in each clasp in the range of 0 to 154.3 MPa for the half-round, tapered I-bar clasp models, and 0 to 100.9 MPa for the full-round I-bar clasp models at 0.01-in deflection. Reaction force measured near the tip of the clasp models was between 1.60 N and 6.31 N for the half-round, and between 0.22 N to 2.13 N for the full-round I-bar clasp models. For all clasps studied, as the deflection increased, the location of stress within each group remained the same regardless of the material properties; however, the stress and force values increased linearly. CONCLUSIONS: The location of maximum stress varied with the length of the anchor portion of the clasps studied. Maximum stresses were located on the flat side of the half-round, tapered I-bar clasp model.

Stiffness-deflection behavior of selected orthodontic wires.

Treatment of horizontal and vertical tooth discrepancies requires wires of low stiffness to produce forces as the teeth are leveled and aligned. In this investigation, the stiffness characteristics of several solid and multistrand nickel-titanium and stainless steel orthodontic wires were determined at selected clinically relevant deflections. Twenty specimens of 24 different wires were tested in both three-point and three-bracket bending modes. The unloading force deflection plot of each wire was described by a polynomial regression from which wire stiffnesses were obtained by mathematical differentiation. Graphs of the functional relationship between stiffness and deflection are presented. The results of this investigation show that wire stiffness can be altered not only by changing the size, but also by varying the number of strands and the alloy composition. An equally important finding was the dependence of stiffness on deflection for most of the wires measured. Comparisons were also made between the stiffness values obtained in three-point bending and the three-bracket bending systems.

Bond strengths of fluoride-releasing restorative materials.

PURPOSE: To compare the shear bond strengths to dentin of four tooth-colored fluoride-releasing restorative materials that utilize different mechanisms of dentin-bonding. MATERIALS AND METHODS: Four materials were tested: a chemically-cured glass ionomer (Ketac-Fil); a light-cured resin-modified glass ionomer (Photac-Fil); a light-cured resin-modified glass ionomer in conjunction with a resin dentin-bonding agent (Vitremer); and a light-cured resin composite in conjunction with a resin dentin-bonding agent (Tetric). The enamel was removed from four sides of the twenty human noncarious extracted molars which had their roots embedded in acrylic blocks. Cylindrical samples of the materials were prepared in plastic molds and bonded to the dentin surface according to the manufacturers' instructions. After 24 hours of storage in a humidor, the samples were sheared with an Instron testing machine at a crosshead speed of 0.5 mm/minute. RESULTS: Statistical evaluation (ANOVA and Duncan's test) suggests that the fluoride-releasing resin composite material utilizing a resin dentin-bonding agent provided a significantly greater mean shear bond strength (16.5 MPa) after 24 hours storage than any of the selected glass ionomer materials. Of the three glass ionomer materials compared, the light-cured resin-modified material with a resin dentin-bonding agent provided a significantly greater mean shear bond strength (6.7 MPa) than the light-cured resin-modified material without a resin dentin-bonding agent (3.0 MPa) or the chemically-cured material (3.8 MPa).

Uses and properties of current glass ionomer cements: a review.

Glass ionomer cements have been used for a variety of restorative purposes. Recently, the formulation of these and other restorative materials has changed rapidly, so it is difficult to keep pace with the literature concerning effective use. A major modification to glass ionomer cements has been incorporation of resin components. This and other modifications over the years have changed some handling characteristics and physical properties of glass ionomer cements. A general review of some changes is reported here.

Frictional resistances in stainless steel bracket-wire combinations with effects of vertical deflections.

This research evaluated the effects of different bracket-wire combinations and second-order deflections on kinetic friction. Thirteen different brackets, six with 0.018 x 0.025 inch slots and seven with 0.022 x 0.028-inch slots were evaluated with six different sizes and shapes of stainless steel orthodontic wire, i.e., 0.016, 0.016 x 0.022, 0.017 x 0.025, 0.018, 0.018 x 0.025 and 0.019 x 0.026 inch for four second order deflections of 0.00, 0.25, 0.50, and 0.75 mm. The wires were ligated into the brackets with elastomeric modules. Bracket movement was implemented by means of an Instron universal testing instrument (RMO, Denver, Colo.), and frictional forces were measured by a tension load cell and recorded on an X-Y recorder (Hewlett-Packard, Anaheim, Calif.). Second-order deflection was created by a specially designed and machined testing apparatus that allowed two alternate pairs of the four total brackets to be offset in increments of 0.25 mm. The kinetic frictional force increased for every bracket-wire combination tested as the second-order deflection increased. Friction also increased with an increase in wire size, whereas rectangular wires produced greater friction than round wires. Bracket designs that limited the force of ligation on the wire generated less friction at low second-order deflections (0.00 and 0.25 mm).

Fracture strength of ceramic brackets during arch wire torsion.

This study evaluated the fracture strengths of eight new vintage ceramic brackets with application of torsional forces. Palatal root torque was applied at the distal side of right maxillary central incisor brackets with 0.022-inch slots by means of a 0.0215 x 0.027-inch rounded edge stainless steel arch wire. A specially designed apparatus that attached to an Instron machine was used to test the ceramic brackets. The amount of torque, degrees of torsion at failure, and fracture locations were measured. The monocrystalline bracket did not break when the torquing test was applied; the portion of the wire outside the slot of the bracket twisted on itself. The mean torquing forces at failure ranged from 5755.2 gm-mm to 9316.5 gm-mm and could be separated into three statistically different groups. The mean torsional rotation at fracture ranged from 32.7 degrees to 68.1 degrees for the polycrystalline brackets. The results suggested that all the brackets studied were sufficiently strong to withstand the commonly accepted magnitudes of arch wire torquing forces. The present investigation showed higher angulation values for all the brackets than those reported by Holt who used the same apparatus with older style brackets.

Ceramic bracket design: an analysis using the finite element method.

This investigation was designed to generate finite element models for selected ceramic brackets and graphically display the stress distribution in the brackets when subjected to arch wire torsion and tipping forces. Six commercially available ceramic brackets, one monocrystalline and five polycrystalline alumina, of twin bracket design for the permanent maxillary left central incisor were studied. Three-dimensional computer models of the brackets were constructed and loading forces, similar to those applied by a full-size (0.0215 x 0.028 inch) stainless steel arch wire in torsion and tipping necessary to fracture ceramic brackets, were applied to the models. Stress levels were recorded at relevant points common among the various brackets. High stress levels were observed at areas of abrupt change in geometry and shape. The design of the wire slot and wings for the Contour bracket (Class One Orthodontic Products, Lubbock, Texas) and of the outer edges of the wire slot for the Allure bracket (GAC, Central Islip, N.Y.) were found to be good in terms of even stress distribution. The brackets with an isthmus connecting the wings seemed to resist stresses better than the one bracket that did not have this feature. The design of the isthmus for the Transcend (Unitek/3M, Monrovia, Calif.) and Lumina (Ormco, Glendora, Calif.) brackets were found to be acceptable as well. The Starfire bracket ("A" Company, San Diego, Calif.) showed high stresses and irregular stress distribution, because it had sharp angles, no rounded corners, and no isthmus. The finite element method proved to be a useful tool in the stress analysis of ceramic orthodontic brackets subjected to various forces.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation of the temporomandibular joint to altered mandibular function.

This pilot study describes responses of Sprague Dawley rats to mandibular retrusion. Lingually overcontoured crowns were cemented onto maxillary incisors to produce 3.5 mm of autoretrusion. Monitoring data indicate that activity was suppressed and nutritional intake was reduced. Histological evaluation of the 2-, 4-, 7-, and 59-day test specimens detected only a monocytic infiltrate response in the 4-day group.

Bond strengths and remnant adhesive resin on debonding for orthodontic bonding techniques.

Bond strengths and remnant adhesive resin on the tooth surface after debonding for three bonding techniques used to attach foil mesh orthodontic brackets to 315 freshly extracted bovine incisor teeth were compared in an in vitro study. Each method of bonding used 105 teeth in groups of 15, bonded with seven different (bis-GMA type) two-paste chemically cured resins. The direct method comprised bonding the attachments directly to the incisors with the composite resin. The indirect-1 method comprised securing attachments to die-stone models of the teeth with a water soluble glue, making silicone positioners to transfer the brackets from the models to the teeth, and bonding to the teeth with the use of the two-paste composite resin system. The indirect-2 method comprised bonding the attachments to die-stone models of the teeth with composite resin, making silicone positioners to transfer the brackets from the models to the teeth, and bonding to the teeth with the use of unfilled sealant resin. Significant differences in bond strength existed among the groups evaluated. The direct technique had statistically significant (p < 0.05) higher bond strength as compared with the indirect-1 and indirect-2 techniques in four of the seven groups evaluated. The indirect-1 and indirect-2 techniques were not significantly different (p < 0.05) in bond strength in six of seven groups tested. The indirect-2 technique had significantly lower adhesive remnant index scores (ARI) compared with the direct and indirect-1 techniques.(ABSTRACT TRUNCATED AT 250 WORDS)

Relative kinetic frictional forces between sintered stainless steel brackets and orthodontic wires.

The level of kinetic frictional forces generated during in vitro translation at the bracket-wire interface were measured for two sintered stainless steel brackets as a function of two slot sizes, four wire alloys, and five to eight wire sizes. The two types of sintered stainless steel brackets were tested in both 0.018-inch and 0.022-inch slots. Wires of four different alloy types, stainless steel (SS), cobalt chromium (Co-Cr), nickel-titanium (Ni-Ti), and beta-titanium (beta-Ti), were tested. There were five wire sizes for the 0.018-inch slot and eight wire sizes for the 0.022-inch slot. The wires were ligated into the brackets with elastomeric ligatures. Bracket movement along the wire was implemented by means of a mechanical testing instrument, and time dependent frictional forces were measured by a load cell and plotted on an X-Y recorder. For most wire sizes, lower frictional forces were generated with the SS of Co-Cr wires than with the beta-Ti or Ni-Ti wires. Increase in wire size generally resulted in increased bracket-wire friction. There were no significant differences between manufacturer for the sintered stainless steel brackets. The levels of frictional force in 0.018-inch brackets ranged from a low of 46 gm with 0.016-inch Co-Cr wire to a high of 157 gm with 0.016 x 0.025-inch beta-Ti wire. In comparing the data from a previous study by Kapila et al. 1990 performed at OUHSC with the same apparatus, the friction of sintered stainless steel brackets was approximately 40% to 45% less than the friction of the conventional stainless steel brackets.

Elastic energy/stiffness ratios for selected orthodontic wires.

This investigation determined the ratio of the energy available for orthodontic tooth movement to the stiffness and flexibility of a given wire. Twenty-five specimens each of five brands of orthodontic wire were tested in tension in the as-received condition. Force versus elongation diagrams were obtained and then converted into stress-strain data. Mean values were determined for the yield strength and yield strain for each brand of wire. The modulus of elasticity (E), modulus of resilience (R), and elastic compliance (C) were then calculated. Two ratios were established by using the three mechanical properties: (1) the modulus of resilience/modulus of elasticity (R/E) ratio and (2) the modulus of resilience/elastic compliance (R/C) ratio. The results confirmed that the use of these two ratios in combination permitted one to differentiate among the various types of orthodontic wires, with respect to stored energy and its relationship to the stiffness or flexibility of the wire.

Effect of luting media on the compressive strengths of two types of all-ceramic crown.

This study evaluated the effect of selected luting media on the compressive strength of two types of all-ceramic crown. Tooth preparation was standardized; each preparation had a shoulder width of approximately 1.2 mm, and all internal preparation angles were rounded. Hi-Ceram and Dicor all-ceramic crowns were fabricated and cemented into the preparations with zinc phosphate, glass-ionomer, or composite resin cement. Coronal compressive fracture strengths were determined, using a set of unrestored teeth as a control. There were no statistically significant differences among the mean compressive strengths of the three luting media, and there was no statistically significant difference between the mean compressive strength of Dicor and that of the natural tooth control.

Variables affecting silicone-polymethyl methacrylate interfacial bond strengths.

PURPOSE: This study investigated the effects of various polymerization methods and of various types of silane coupling agents on the interfacial bond strengths of Molloplast-B and of two types of heat-processed polymethyl methacrylate (PMMA). MATERIALS AND METHODS: Standardized blocks of PMMA were processed and stored in 100% humidity for 14 days. Silicone of equal dimensions was flasked and processed with premixed and fresh-mixed silane coupling agents interposed. Processing utilized both a typical heated-water system and a dry-heat oven. Following recovery, the specimens were peel-tested at an angle of 180 degrees in an Instron machine. RESULTS: There was no significant difference between the test variables of Lucitone (Dentsply/York Division, York, PA) versus Lucitone 199 (Dentsply/York Division), nor with wet versus dry heat polymerization methods. However, the mean bond strengths for premixed silane improved slightly in a wet polymerization environment. Conversely, fresh-mixed silane's mean bond strength increased slightly with dry-heat polymerization. CONCLUSIONS: The bond strength between a methyl methacrylate denture base and a silicone soft liner varies only slightly when either Lucitone, Lucitone 199, or polymerization in a wet or dry environment is used. Under the conditions of this study, a fresh-mixed silane coupling agent produced a distinctly superior bond strength.

Force degradation of closed coil springs: an in vitro evaluation.

This in vitro study was designed to determine the force degradation of closed coil springs made of stainless steel (SS), cobalt-chromium-nickel (Co-Cr-Ni) and nickel-titanium (Niti) alloys, when they were extended to generate an initial force value in the range of 150 to 160 gm. The specimens were divided into two groups. Group I included SS, Co-Cr-Ni, and two nickel-titanium spring types (Niti 1 and Niti 2), 0.010 x 0.030 inch with an initial length of 12 mm. Group II was comprised of SS, Co-Cr-Ni, and Niti 3 0.010 x 0.036-inch springs, with an initial length of 6 mm. A universal testing machine was used to measure force. A pilot study determined the extension required for each spring type, so that the initial force was in the range of 150 to 160 gm. Initial force was recorded, and then the springs were extended to the respective distances at 4 hours, 24 hours, 3 days, 7 days, 14 days, 21 days, and 28 days resulting in a total of eight time periods. Between the time intervals, all springs were extended to the same initial extension on specially designed racks and stored in a salivary substitute at 37 degrees C. Means and standard deviations of force values, percent force loss, and mean extension were statistically analyzed. All springs showed a force loss over time. Of the total, the major force loss for most springs was found to occur in the first 24 hours.(ABSTRACT TRUNCATED AT 250 WORDS)