David W. Berzins

Torsion and bending properties of shape memory and superelastic nickel-titanium rotary instruments.

INTRODUCTION Recently introduced into the market are shape memory nickel-titanium (NiTi) rotary files. The objective of this study was to investigate the torsion and bending properties of shape memory files (CM Wire, HyFlex CM, and Phoenix Flex) and compare them with conventional (ProFile ISO and K3) and M-Wire (GT Series X and ProFile Vortex) NiTi files. METHODS Sizes 20, 30, and 40 (n = 12/size/taper) of 0.02 taper CM Wire, Phoenix Flex, K3, and ProFile ISO and 0.04 taper HyFlex CM, ProFile ISO, GT Series X, and Vortex were tested in torsion and bending per ISO 3630-1 guidelines by using a torsiometer. All data were statistically analyzed by analysis of variance and the Tukey-Kramer test (P = .05) to determine any significant differences between the files. RESULTS Significant interactions were present among factors of size and file. Variability in maximum torque values was noted among the shape memory files brands, sometimes exhibiting the greatest or least torque depending on brand, size, and taper. In general, the shape memory files showed a high angle of rotation before fracture but were not statistically different from some of the other files. However, the shape memory files were more flexible, as evidenced by significantly lower bending moments (P < .008). CONCLUSIONS Shape memory files show greater flexibility compared with several other NiTi rotary file brands.

Resin-modified Glass-ionomer Setting Reaction Competition

Resin-modified glass ionomers (RMGI) set by at least 2 mechanisms dependent upon reactant diffusion prior to gelation. Each reaction’s kinetics and setting mechanism may rely on and/or compete with the other. In this study, we investigated RMGI setting reaction interactions using differential scanning calorimetry (DSC) by varying light-cure initiation times. A RMGI was analyzed with isothermal and dynamic temperature scan DSC with light-curing occurring immediately, or at 5 or 10 minutes after mixing as well as without light-activation. Results show that as time allowed for the acid-base reaction increased, the light-activation polymerization exotherm decreased. Conversely, analysis of DSC data suggests that earlier light-activation may limit the acid-base reaction and result in a different structured material. During early RMGI development, acid-base and light-polymerization reactions compete with and inhibit one another.

Effect of phosphate group addition on the properties of denture base resins.

STATEMENT OF PROBLEM Acrylic resins are prone to microbial adherence, especially by Candida albicans. Surface-charged resins alter the ionic interaction between the denture resin and Candida hyphae, and these resins are being developed as a means to reduce microbial colonization on the denture surface. PURPOSE The purpose of this study was to investigate the physical and mechanical properties of phosphate-containing polymethyl methacrylate resins for their suitability as a denture material. MATERIAL AND METHODS Using PMMA with cross-linker (Lucitone 199) as a control, 4 experimental groups containing various levels of phosphate with and without cross-linker were generated. The properties examined were impact strength, fracture toughness, wettability (contact angle), and resin bonding ability to denture teeth. Impact strength was tested in the Izod configuration (n=16), and fracture toughness (n=13) was measured using the single-edge notched bend test. Wettability was determined by calculating the contact angle of water on the material surface (n=12), while ISO 1567 was used for bonding ability (n=12). The data were analyzed by 1- and 2-way ANOVA (alpha=.05). RESULTS A trend of increased hydrophilicity, as indicated by lower contact angle, was observed with increased concentrations of phosphate. With regard to the other properties, no significant differences were found when compared with the control acrylic resin. CONCLUSIONS No adverse physical effect due to the addition of a phosphate-containing monomer was found in the acrylic denture resins. Additional mechanical and physical properties, biocompatibility, and clinical efficacy studies are needed to confirm the in vivo anti-Candida activity of these novel resins.

Shear Bond Strength Comparison between Two Orthodontic Adhesives and Self-Ligating and Conventional Brackets

OBJECTIVE To evaluate and compare the shear bond strengths of two adhesives using two types of brackets: a conventional and a self-ligating bracket system. MATERIALS AND METHODS Sixty extracted human premolars were collected. The premolars were randomly divided into three groups of 20 teeth. All three groups were direct bonded. Groups 1 and 2 used light-cured adhesive and primer (Transbond XT) with a conventional (Orthos) and a self-ligating bracket (Damon 2), respectively. Group 3 used a light-cured primer (Orthosolo) and a light-cured adhesive (Blūgloo) with a self-ligating bracket (Damon 2). The specimens were stored in distilled water at 37 degrees C for 40 +/- 2 hours, after which they were debonded and inspected for Adhesive Remnant Index (ARI) scoring. RESULTS The mean shear bond strength was 15.2 MPa for group 1, 23.2 MPa for group 2, and 24.8 MPa for group 3. A one-way analysis of variance and post hoc Tukey test showed significant differences in bond strength (P < .001) between group 1 and groups 2 and 3 but no significant difference (P > .05) between groups 2 and 3. A Weibull analysis demonstrated that all three groups provided sufficient bond strength with over 90% survival rate at normal masticatory and orthodontic force levels. A Kruskal-Wallis test showed no significant difference (P > .05) in ARI scores among all three groups. CONCLUSIONS All three groups demonstrated clinically acceptable bond strength. The Damon 2 self-ligating bracket exhibited satisfactory in vitro bond strength with both adhesive systems used.

Bond Strength of an Amorphous Calcium Phosphate–Containing Orthodontic Adhesive

OBJECTIVE To determine whether an amorphous calcium phosphate (ACP)-containing adhesive has an acceptable level of shear bond strength to be used as an orthodontic adhesive. MATERIALS AND METHODS Sixty extracted premolars were randomly divided into three groups for orthodontic bonding. Group 1 used a composite resin adhesive (Transbond XT), group 2 was bonded with an ACP-containing adhesive (Aegis Ortho), and group 3 used a resin-modified glass ionomer (Fuji Ortho LC). All bonded teeth were stored in distilled water at 37 degrees C for 40 +/- 2 hours prior to debonding. Shear bond strength and adhesive remnant index (ARI) were recorded for each specimen. RESULTS The mean shear bond strengths for the three test groups were: group 1 (15.2 +/- 3.6 MPa), group 2 (6.6 +/- 1.5 MPa), and group 3 (8.3 +/- 2.8 MPa). A one-way analysis of variance showed a significant difference in bond strengths between the groups. A post hoc Tukey test showed group 1 to be significantly (P < .001) greater than groups 2 and 3. A Kruskal-Wallis test and a Mann-Whitney U-test showed groups 1 and 3 exhibited lower ARI scores than group 2, but a majority of specimens in each group had greater than 50% of the cement removed along with the bracket during debonding. CONCLUSIONS The ACP-containing adhesive demonstrated a low, but satisfactory bond strength needed to function as an orthodontic adhesive.

Bond Strength of Direct and Indirect Bonded Brackets After Thermocycling

Thermocycling simulates the temperature dynamics in the oral environment. With direct bonding, thermocycling reduces the bond strength of orthodontic adhesives to tooth structure. The purpose of this study was to evaluate the shear bond strengths (SBS) of one direct and two indirect bonding methods/adhesives after thermocycling. Sixty human premolars were divided into three groups. Teeth in group 1 were bonded directly with Transbond XT. Teeth in group 2 were indirect bonded with Transbond XT/Sondhi Rapid Set, which is chemically cured. Teeth in group 3 were indirect bonded with Enlight LV/Orthosolo and light cured. Each sample was thermocycled between 5 degrees C and 55 degrees C for 500 cycles. Mean SBS in groups 1, 2, and 3 were not statistically significantly different (13.6 +/- 2.9, 12.3 +/- 3.0, and 11.6 +/- 3.2 MPa, respectively; P > .05). However, when these values were compared with the results of a previous study using the same protocol, but without thermocycling, the SBS was reduced significantly (P = .001). Weibull analysis further showed that group 3 had the lowest bonding survival rate at the minimum clinically acceptable bond-strength range. The Adhesive Remnant Index was also determined, and group 2 had a significantly (P < .05) higher percentage of bond failures at the resin/enamel interface.

Electrochemical characteristics of high-Pd alloys in relation to Pd-allergy

OBJECTIVE The aim of this study was to determine whether the Pd-Cu-based dental ceramic alloys possess any electrochemical characteristics distinguishable from that of other Pd-containing alloys. Of all Pd-containing alloys, this particular alloy group has been linked to frequent incidence of allergy and hypersensitivity reactions. Electrochemical corrosion may instigate these reactions. METHODS Four groups of alloys, Pd-Cu, Pd-Ga-(with and without Ag), Pd-Ag, and Au-Pd, were evaluated by traditional corrosion measurement techniques in a phosphated buffer saline solution at 20 degrees C. The electrochemical characteristics measured were: (1) 20 h open circuit potential (OCP); (2) 20 h corrosion rate (Icorr); and (3) anodic polarization (E-i) curves. RESULTS The OCP values (232 +/- 25 mV) of the Ag-free Pd-Ga and Pd-Cu-based alloys were higher than and distinctly different from that (144 +/- 52 mV) of the Ag-containing alloys. The Icorr values of different alloys, despite varied compositions, were indistinguishable from one another. The E-i curves of all alloys were essentially similar, with the Ag-containing (> 5 wt%) alloys showing a subtle difference in their anodic slope within 100 mV above their corrosion potentials. SIGNIFICANCE The OCP values of Pd-Cu alloys and the Ag-free Pd-Ga alloy are comparable to that reported for pure Pd (239 +/- 21 mV), which indicates that during corrosion these alloys undergo dealloying and consequent Pd-enrichment on their surface. Such a condition is conducive to the release of allergenic Pd++ ions and offers a plausible explanation for the frequent incidence of hypersensitivity reactions associated with the Pd-Cu alloys. The OCP values in other alloys are attributed to dealloying followed by surface enrichment with Ag and/or Au and the possible formation of an insoluble AgCl surface film on the respective alloy surfaces. These events have the potential to suppress or prevent Pd++ ion release. Alloys showing these characteristics have seldom been linked to allergic reactions.

A comparison of bond strength between direct- and indirect-bonding methods.

The purpose of this study was to evaluate and compare the shear bond strength and the sites of bond failure for brackets bonded to teeth, using two indirect-bonding material protocols and a direct-bonding technique. Sixty extracted human premolars were collected and randomly divided into three groups. The direct-bonded group (group 1) used a light-cured adhesive and primer (Transbond XT). One indirect-bonded group (group 2) consisted of a chemical-cured primer (Sondhi Rapid Set) and light-cured adhesive (Transbond XT), whereas the other group (group 3) used a light-cured primer (Orthosolo) and adhesive (Enlight LV). Forty hours after bonding, the samples were debonded. Mean shear bond strengths were 16.27, 13.83, and 14.76 MPa for groups 1, 2, and 3, respectively. A one-way analysis of variance showed no significant difference in mean bond strength between groups (P = .21). Furthermore, a Weibull analysis showed all three groups tested provided over a 90% survival rate at normal masticatory and orthodontic force levels. For each tooth, an Adhesive Remnant Index (ARI) score was determined. Group 2 was found to have a significantly lower ARI score (P < .05) compared with groups 1 and 3. In addition, Pearson correlation coefficients indicated no strong correlation between bond strength and ARI score within or across all groups.

A differential scanning calorimetry study of the setting reaction of MTA

AIM To evaluate the setting of mineral trioxide aggregate (MTA) at various time intervals using differential scanning calorimetry (DSC). METHODOLOGY Hydrated MTA and Portland cement were examined with DSC at the following intervals: immediate (0 h), 2 h, 4 h, 12 h, 24 h, 1 week, 1 month, 3 months and 1 year. DSC analysis consisted of a temperature scan from 37 to 640 degrees C, resulting in thermograms with reaction product decomposition endotherms. The thermogram peak attributed to calcium hydroxide product formation was identified and quantified to serve as an indicator of reaction product formation over time. Unmixed powders of both cements and individual components of MTA were also studied using DSC. The results were analysed with repeated measures anova between time intervals and a t-test between cements. RESULTS A low temperature endotherm attributed to various calcium silicate hydrates showed continual maturation of MTA up to 1 year. The rate of calcium hydroxide formation was greatest between 4 and 24 h after mixing with maximum amounts present at 7 days. Specimens aged greater than 1 month showed a decrease in calcium hydroxide content, presumably because of carbonation reactions. Portland cement had similar thermogram peaks, although the amount of calcium hydroxide formed was generally smaller compared to MTA. The endothermic peaks from the various powders and components were helpful in corroborating the peaks formed in the hydrated cements. CONCLUSIONS Hydration reactions and structure maturation in MTA continue well beyond clinically observed setting times.

Thermal Analysis of As-received and Clinically Retrieved Copper-nickel-titanium Orthodontic Archwires

OBJECTIVE To compare as-received copper-nickel-titanium (CuNiTi) archwires to those used in patients by means of differential scanning calorimetry (DSC). Also, the thermal or phase properties of 27 degrees C, 35 degrees C, and 40 degrees C CuNiTi archwires were studied to ascertain if their properties match those indicated by the manufacturer. MATERIALS AND METHODS Six wires of 27 degrees C, 35 degrees C, and 40 degrees C CuNiTi were tested as-received, and six each of the 27 degrees C and 35 degrees C wires were examined after use in patients for an average of approximately 9 and 7 weeks, respectively. Segments of archwire were investigated by DSC over the temperature range from -100 degrees C to 150 degrees C at 10 degrees C per minute. RESULTS There were no significant differences between as-received and clinically used 27 degrees C and 35 degrees C wires for all parameters (heating onset, endset, and enthalpy and cooling onset, endset, and enthalpy), except the 27 degrees C wires exhibited a significant decrease in the heating enthalpy associated with the martensite-to-austenite transition after clinical use. The heating endsets (austenite finish temperatures) of the 27 degrees C and 35 degrees C wires were within 2 degrees C of those claimed by the manufacturer, but the 40 degrees C wires were found to be nearer to 36 degrees C than 40 degrees C. CONCLUSIONS Clinical use of CuNiTi wires resulted in few differences when compared with as-received wires analyzed by DSC. Two temperature varieties of CuNiTi are reasonably within the parameters of those identified by the manufacturer.