Influence of Ionic Liquid and Light Intensity on a Polymer Nanostructure Formed in Lyotropic Liquid Crystalline Templates.

Utilizing self-assembled lyotropic liquid crystal (LLC) templates with radical photopolymerization shows promise in controlling polymer structure on the nanometer scale This control of nanostructure allows tailoring and enhancement of material properties not attainable in traditional polymerization in applications including hydrogels and stimuli-responsive systems. However, thermodynamically driven phase separation between the polymer and LLC templates often hinders the control of local polymer order and resultant polymer properties. This study investigates an alternative method to control the hydrogel nanostructure and avoid phase separation using imidazolium ionic liquids (ILs) in the LLC template while modulating the light intensity used in photopolymerization. The addition of the IL improves the thermodynamic stability and enhances the polymerization rate in the LLC system. The degree of LLC nanostructure retention is increased by increasing light intensities during polymerization. In addition, intermediate concentrations of cross-linker allow a balance between phase stability and cross-linking to lock in LLC morphology. With enhanced retention, the maximum water uptake is significantly higher compared with isotropic controls. These results demonstrate a method to increase the structure on the nanometer scale of a polymer by combining the addition of ILs with the proper selection of light intensity and cross-link density that allows access to unique hydrogel properties. These templated polymers demonstrate enhanced swelling and a stimuli response that show promise in applications ranging from drug delivery to water remediation.

Photograftable Zwitterionic Coatings Prevent Staphylococcus aureus and Staphylococcus epidermidis Adhesion to PDMS Surfaces.

Due to its attractive mechanical properties and biocompatibility, poly(dimethyl)siloxane (PDMS) is widely used in the fabrication of biomedical materials. On the other hand, PDMS is also prone to adsorption of both proteins and bacteria, making PDMS implants susceptible to infection. Herein, we examine the use of durably cross-linked zwitterionic coatings for PDMS surfaces to mitigate bacterial adhesion. Using a single-step photografting technique, poly(sulfobetaine methacrylate) (pSBMA) and poly(carboxybetaine methacrylate) (pCBMA) thin films were covalently attached to PDMS substrates. The abilities of these coatings to resist the adhesion of Staphylococcus aureus and Staphylococcus epidermidis were tested in vitro under both wet and droplet conditions, as well as in subcutaneous and transcutaneous implantation models using Sprague-Dawley rats. Zwitterionic thin films effectively reduced bacterial adhesion in both in vitro and in vivo conditions. This was particularly true for pCBMA-coated materials, which exhibited significant reduction in bacterial adhesion and growth with respect to S. aureus and S. epidermidis for all in vitro conditions as well as the ability to resist bacterial growth on PDMS implants. The results of this study suggest that a simple and durable photografting process can be used to produce polymer thin films capable of preventing infection of implantable medical devices.

Influence of BMI percentile on craniofacial morphology and development in children and adolescents.

BACKGROUND: The prevalence of childhood and adolescent obesity is increasing worldwide. Reports suggest that elevated body mass index (BMI) is associated with larger craniofacial dimensions and advanced dental and skeletal development. Such an association is important for timing orthodontic treatment relative to pubertal growth and dental eruption. MATERIALS AND METHODS: To evaluate associations between BMI, craniofacial morphology, dental age, and cervical vertebrae maturation staging (CVMS), 400 participants were consecutively selected (8-15 years, n = 200 overweight and obese BMI >85%, 200 normal weight) from the University of North Carolina database. Records were analysed for cephalometric measures, Demirjian index values, and CVMS. Bivariate statistics and linear regression analysis evaluated whether CVMS, dental age, and cephalometric dimensions varied with BMI. RESULTS: Overweight/obese children and adolescents had a proportionally larger bimaxillary prognathic skeletal pattern compared to those of normal weight. These cephalometric measurements [articulare-gnathion (Ar-Gn), condylion-anterior nasal spine (Co-ANS), sella-gonion (S-Go), nasion-menton (N-Me), anterior nasal spine-menton (ANS-Me), sella-nasion-A point (SNA), sella-nasion-B point (SNB), and sella-nasion-pogonion (SNPg)] were significantly different [statistically (P < 0.05) and clinically (>2 mm or >2 degrees)] between the two study groups, with a linear relationship between BMI percentile and craniofacial dimension. The overweight/obese BMI group had a mean dental age 1.4 years advanced relative to the normal weight group (P < 0.05), with an advancement of nearly one CVM stage between the ages of 12 and 14 (P < 0.05). LIMITATIONS: The study is retrospective. CONCLUSIONS: Obese/overweight children and adolescents have proportionally larger antero-posterior and vertical dimensions and are more likely to experience advanced dental and skeletal maturation. Obese/overweight subjects may enter their growth spurt at a younger age and have earlier eruption of teeth, affecting treatment timing. BMI percentile should be a consideration for orthodontic treatment in growing patients.

The Inhibition of Radial and Axial Micromovement of Bone Scaffold with Gelfoam® and Titanium Mesh Fixation and Its Effects on Osteointegration.

A major drawback of nanocomposite scaffolds in bone tissue engineering is dimensional shrinkage after the fabrication process. Shrinkage yields gaps between the scaffold and host bone in the defect site and eventually causes failure in osteointegration by micromovement. The present study was conducted using titanium (Ti) mesh and Gelfoam® to prevent radial and axial micromovement, respectively. A critical-sized defect (CSD) was created in the center of the calvarium of Sprague Dawley rats to implant porous polydopamine-laced hydroxyapatite collagen calcium silicate (HCCS-PDA), a novel nanocomposite scaffold. Gelfoam® was applied around the edge of the defect, and then the HCCS-PDA scaffold was inserted in the defect area. Ti mesh was placed between the periosteum and skin right, above the inserted scaffold site. There were two test groups, with a fixture (Gelfoam® and Ti mesh) and without a fixture, each group contained five animals. The rats were sacrificed after three months post-operation. The explanted calvaria underwent micro-CT scanning and a push-out test to quantify osteointegration and mechanical strength between the scaffold and host bone. Histological analysis of undecalcified bone was performed by grinding resin infiltrated calvaria blocks to prepare 10 µm slices. Osteointegration was higher in the group with fixation than without fixation. Movement of the HCCS-PDA scaffold in the gap resulted in diminished osteointegration. With fixation, the movement was inhibited and osteointegration became prominent. Here we present a successful method of preventing axial and radial movement of scaffolds using Gelfoam® and Ti mesh. Applying this fixture, we expect that an HCCS-PDA scaffold can repair CSD more effectively.

The effect of orthodontic clinical use on the mechanical characteristics of nickel-titanium closed-coil springs.

OBJECTIVE: To examine the effect of clinical use on both force retention and the deactivation of closed-coil nickel-titanium (NiTi) springs in a 16-week trial. METHODS: The force-activation curves for NiTi springs were determined before and after clinical use. The rate of tooth movement and maximum force (MF), hysteresis between activation and deactivation, and mean force of the deactivation plateau (MDF) were examined and correlated as a function of 4, 8, 12 and 16 weeks of clinical use. To recover the force properties, the springs were heat treated at 100°C and the results were compared with the preceding data. RESULTS: A total of 36 springs were analysed. The MF loss after use was 60, 74, 55, and 48 g for the 4-, 8-, 12- and 16-week springs, respectively. Heat treating had little effect on the MF. Clinical use lowered hysteresis by a mean of 180 g*mm compared with the pre-clinical use data, and heat treating increased the hysteresis by a mean of 59 g*mm above the post clinic testing data. The MDF was nominally 100 g less than the MF. Teeth moved approximately 1 mm/month, independent of the force loss. CONCLUSIONS: The loss of MF and the lowering of the MDF was not time dependent. Heat treating can partially recover the mechanical properties of the used springs.

Influence of interbracket distances on the resistance to sliding of orthodontic appliances.

INTRODUCTION: The influence of interbracket distance (IBD) on the resistance to sliding (RS) was evaluated. METHODS: Commercially pure titanium brackets (CP-Ti; 0.018- and 0.022-in slots, width = 0.14-in) were tested against 0.016 x 0.022-in rectangular stainless steel (SS), nickel titanium (Ni-Ti), and beta-titanium (beta-Ti) archwires in the dry and wet (human saliva) states. With a custom testing apparatus that simulated a 3-bracket system, the RS was measured at a normal force of 300 cN and at second-order angles (theta) ranging from -9 degrees to +9 degrees. Twenty-three pairs of IBDs (written as IBD1_IBD2) were varied to simulate clinically relevant biomechanical scenarios with IBD ranging from 16 to 7 mm. RESULTS: In the dry state, the kinetic frictional coefficients (micro(k)) were equal to 0.12, 0.23, and 0.24 for the SS, Ni-Ti, and beta-Ti archwires against the CP-Ti brackets, respectively. The presence of saliva slightly increased micro(k). The RS was inversely proportional to the total IBD (IBD(T) = IBD1 + IBD2) regardless of archwire alloy or bracket slot. Elastic binding (BI = RS - frictional force in the passive region) did not depend on the order of the IBDs in the IBD1_IBD2 pair. CONCLUSIONS: For a specific archwire-bracket couple, the BI of an IBD1_IBD2 pair is equal to any other pair with an equal IBD(T). Although no significant difference was found between the coefficients of binding (micro(BI)) for SS and beta-Ti archwires, the micro(BI)'s of Ni-Ti archwires were lower and significantly different. The micro(BI) was linearly related (P<.01) to IBD(T) and total archwire beam length (L(T)).

Resistance to sliding of titanium brackets tested against stainless steel and beta-titanium archwires with second-order angulation in the dry and wet states.

INTRODUCTION: With the increased awareness of Ni allergies, alternative alloys for orthodontic products must be identified. The properties of these new products must be determined. METHODS: Rectangular (0.017 x 0.025 in) stainless steel (SS) and beta-titanium (beta-Ti) archwires were tested against commercially pure titanium brackets (CP-Ti, 0.018-in slot) in the dry state and with whole human saliva. Resistance to sliding (RS) was measured as a function of 5 normal forces (N, 200 to 950 cN), 32 angles (theta, -12 degrees to +12 degrees), and 1 interbracket distance (IBD, 18 mm). RESULTS: With clearance between the archwire and the bracket (passive region, theta < or =theta(c)), the frictional coefficients (mu) of the SS archwire and the CP-Ti bracket couples were 0.12 and 0.13 for the dry and wet tests, respectively; for the beta-Ti archwire and the CP-Ti bracket couples, the mu values were 0.29 and 0.28 for the dry and wet tests, respectively. For an theta without clearance (active region, theta > or =theta(c)), RS increased as a function of theta and N. To examine the rates of binding (mu(BI)) in this active region, the value of classical friction (mean of the passive region data) was subtracted from RS to yield BI, and the value of theta(c) was subtracted from each theta to yield relative contact angles (theta(r)). Because of the unique relationship between the frictional and mechanical properties of these SS and beta-Ti archwires tested against the CP-Ti brackets at a large IBD, the mu(BI) values for these archwire-bracket couples were nominally equivalent (24 to 30 cN per degree). Clinical outcomes would be unaffected by this 6 cN per degree (approximately 0.2 oz-force per degree) difference. When all kinetic data in the elastic region (theta(r) < or =5 degrees ) were combined, mu(BI) equaled 28 cN per degree. Above this region (theta(r) > or =5 degrees ), the data for the SS archwire and CP-Ti bracket couples were less scattered than those for the beta-Ti archwire and the CP-Ti bracket couples. This demarcation from linearity was designated as theta(z) and indicated the end of the elastic region and the beginning of the plastic region, above which sliding can eventually cease. This region (theta > or =theta(z)), the binding region (theta(c) < or =theta < or =theta(z)), and the classical friction region (theta < or =theta(c)) were described in a model. CONCLUSIONS: This model explains, in part, the equivalent values of mu(BI) for SS and beta-Ti archwires tested against CP-Ti brackets.

Thermal and mechanical characteristics of stainless steel, titanium-molybdenum, and nickel-titanium archwires.

INTRODUCTION: In recent years, nickel-titanium (Ni-Ti) archwires have been developed that undergo thermal transitions. Before the practitioner can fully utilize these products, the effect of those transitions within the clinical application must be understood. METHODS: The transitional temperatures and mechanical stiffnesses of 3 archwire alloys--stainless steel, beta-titanium, and Ni-Ti--were investigated were for 7 products. Among the nickel-titanium alloys, 2 were thought to represent classic Ni-Ti products and 3 copper (Cu)-Ni-Ti products. By using 2 techniques, differential scanning calorimetry to measure heat flow and dynamic mechanical analysis to measure storage modulus, transition temperatures were evaluated from -30 degrees C to +80 degrees C. RESULTS: With regard to the first technique, no transitions were observed for the stainless steel alloy, the beta-titanium alloy, and 1 of the 2 classic Ni-Ti products. For the other classic Ni-Ti product, however, a martensitic-austenitic transition was suggested on heating, and a reverse transformation was suggested on cooling. As expected, the Cu-Ni-Ti 27, 35, and 40 products manifested austenitic finish temperatures of 29.3 degrees C, 31.4 degrees C, and 37.3 degrees C, respectively, as the enthalpy increased from 2.47 to 3.18 calories per gram. With regard to the second technique, the storage modulus at a low frequency of 0.1 Hz paralleled static mechanical tests for the stainless steel alloy (183 gigapascal [GPa]), the beta-titanium alloy (64 GPa), and the Nitinol Classic (3M Unitek, Monrovia, Calif) product that represented a stable martensitic phase (41 GPa). The remaining 4 Ni-Ti products generally varied from 20 to 35 GPa when the low-temperature or martensitic phase was present and from 60 to 70 GPa after the high-temperature or austenitic phase had formed. CONCLUSIONS: From the clinical viewpoint, the Orthonol (Rocky Mountain Orthodontics, Denver, Colo), Cu-Ni-Ti 27, Cu-Ni-Ti 35, and Cu-Ni-Ti 40 (SDS/Ormco, Glendora, Calif) products increased at least twofold in stiffness as temperature increased, best emulating the stiffness of Nitinol Classic below the transformational temperature and the stiffness of TMA (SDS/Ormco, Glendora, Calif) above the transformational temperature. Of the 3 Cu-Ni-Ti products, the least differences were found between Cu-Ni-Ti 27 and Cu-Ni-Ti 35, thereby questioning the justification for 3 similar products.

The congenitally missing maxillary lateral incisor. Part 1: esthetic judgment of treatment options.

AIM: To determine how general dentists, orthodontists, combined dental specialists, and laypeople judged the relative attractiveness of a series of photographs of teeth that included cases with congenitally missing incisors to compare the esthetic appeal of various treatment options. METHODS: The photographs included cases with Maryland bridges, dental implants, and orthodontic substitution of the lateral incisors with the canines. Cases with no missing teeth were included as controls. The subjects rated each photograph independently, assigning a number between 1 and 5 for each of a series of 7 bipolar adjectives. Each photograph was given an overall score from 7 (best) through 35 (worst) for use in statistical analysis (ANOVA). RESULTS: Results indicated that general dentists, orthodontists, combined dental specialists, and laypeople differed in their evaluations of the photographs, which represented multiple treatment options for congenitally missing maxillary lateral incisors. CONCLUSIONS: Including esthetics of the finished result as an advantage or disadvantage for either restoration or canine substitution of the lateral incisors could be misleading to the patient because the judgment of esthetics of a smile can vary from one person to another or from one dental professional to another, as indicated in this study.

The congenitally missing maxillary lateral incisor. Part 2: assessing dentists' preferences for treatment.

AIM: To (1) determine if there are different preferences among general dentists, a combined group of dental specialists, and orthodontists concerning whether a patient with congenitally missing lateral incisors should have the teeth restored or if the canines should be orthodontically moved into the position of the missing teeth; (2) determine the role that esthetics and function of the final result has on the respondents' treatment preferences; and (3) compare the respondents' opinions about treatment preferences to their rankings of esthetics reported in part 1. METHODS: The questionnaire accompanied the photographic evaluation in part 1. Percentages were computed and chi-squares were used to compare response patterns. RESULTS: Compared to orthodontists, a significantly greater percentage of general dentists and combined dental specialists would restore the lateral incisors and would do so primarily for esthetic reasons. Interestingly, for those dental professionals who responded that the missing teeth should be restored, many did not rank any photograph of a restorative option as the best option. CONCLUSIONS: Dental professionals should attempt to eliminate their personal opinions when recommending treatment options for a congenitally missing maxillary lateral incisor because discrepancies exist between the treatment result judged as most esthetic and the one most likely to be recommended.

Degradation of plastic polyoxymethylene brackets and the subsequent release of toxic formaldehyde.

PURPOSE: Heat, acids, alkalis, oxygen, abrasion, enzymes, and radiation are all viable mechanisms for the chemical breakdown of polyoxymethylene (POM), a plastic material used in some esthetic orthodontic brackets. The aim of this study was to establish the thermal characteristics of POM brackets and the chemical by-products in the as-received bracket, during thermal analyses of the bracket, and after abrasion of the slot and base of the bracket. MATERIAL: Plastic brackets and control rods made of POM were evaluated ex vivo by thermal and chemical analyses. RESULTS: POM brackets produce toxic formaldehyde gas whether heated or mechanically abraded. Patients who wear these brackets are being exposed to, at the very least, a potential irritant. Thermal analyses showed that the melting temperature of a POM bracket was approximately 178 degrees C, comparable to that for a commercial rod of POM. Both POM products started to degrade at approximately 250 degrees C, and, by 420 degrees C, both products had completely decomposed into their fundamental molecular structure, formaldehyde. A colorimetric assay with a fuchsin-aldehyde reagent (Schiff's reagent) showed that aldehydes were present in the effluent from thermal heating, from mechanical abrasion of the bracket's slot or base, and even from the as-received bracket. The only difference between the 6 to 8-week assays and the 12 to 14-week assays was the intensification of the color, which occurred because of an increase in aldehyde formation and the concomitant increase in double-bond formation. These observations are consistent with a report in the tribologic (ie, friction and wear) literature, which documented the degradation of POM when it rubs against steel. CONCLUSIONS: Because formaldehyde's inherent uses as a disinfectant base and embalming fluid preclude its beneficial presence in the human body, further use of POM for orthodontic brackets, crowns for children, and other prosthetic appliances is contraindicated because even radiography will promote its degradation.

Comparisons of surface roughnesses and sliding resistances of 6 titanium-based or TMA-type archwires.

Six titanium-based or TMA-type archwires (Beta III, Resolve, CNA, TMA, low-friction ion-implanted TMA or TMAL, and TiMolium) were studied as functions of composition, morphology, surface roughness, and sliding mechanics by using a scanning electron microscope, an x-ray energy dispersive wavelength analyser, a laser specular reflectometer, and a frictional testing machine. In the last instrument, all wires were coupled with 0.022-in stainless steel brackets in which normal forces were applied by 0.010-in stainless steel ligatures. With regard to composition, 5 wires were true beta-titanium alloys having nominal compositions of 80% titanium, 10% molybdenum, 6% zirconium, and 4% tin, and 1 was an alpha-beta alloy having a nominal composition of 90% titanium, 6% aluminum, 3% vanadium, and 1% other. Morphologies varied from surfaces with striations, scale, or layers of drawn material that suggested surface steps or fissures. Specular reflectance and optical roughness measurements divided the archwires into 2 groups of 3: Beta III, Resolve, and CNA had an overall mean value of 0.148 microm; and TMA, TMAL, and TiMolium had a mean overall value of 0.195 microm. These roughness measurements and their accompanying details of the compositional analyses suggested that there could be as few as 2 vendors manufacturing the 5 beta-titanium products. For 6 different values of angulation that embraced the passive and active regions of sliding, the coefficients of friction varied rather narrowly from 0.17 to 0.27 and were independent of surface roughnesses. Although these contemporary products are better than their predecessors of over a decade ago, other issues might be more important than surface finishes or frictional resistances because all products appear fairly comparable.

Carpal tunnel syndrome.

Preview Data entry, bar-code scanning at a grocery store checkout, playing the drums-these are all activities that may precipitate carpal tunnel syndrome, the most common entrapment neuropathy. Beyond cessation of repetitive wrist motions, treatment options range from corticosteroid injection to surgical intervention. Which form of therapy is best for your patient? Which tests are most useful in clinical evaluation? The authors address these questions in this overview of diagnosis and treatment.