Jia Kuang Liu

Effect of fluoride containing bleaching agents on enamel surface properties

OBJECTIVES To evaluate the effects of fluoridated bleaching agents and post-bleaching fluoridation treatment on the whitening efficiency and microhardness of bovine enamel. METHODS Twenty five freshly extracted bovine incisors were cut into halves, embedded and then divided into the following five groups: Group 1, untreated controls; Group 2, treatment with 10% carbamide peroxide (CP) bleaching agent; Group 3, treatment with 10% CP followed by a 0.9% sodium fluoride gel application, Group 4, treatment with 10% CP containing 0.11% fluoride; Group 5, treatment with an experimental bleaching agent consisting of 10% CP and 0.37% fluoride. Groups 2-5 were treated 8h per day for 14 days then immersed in saliva for 2 weeks. Enamel morphology changes were evaluated under SEM on Day 14. Changes in enamel color and microhardness were evaluated on Days 7 and 14, and compared with the baseline data. Additionally, microhardness was determined on post-bleaching Days 21 and 28. RESULTS After 2 weeks, an erosion pattern was noted on the specimens in Groups 2 and 3. Groups 4 and 5 showed a milder demineralized pattern. All the bleached enamel specimens revealed increased whiteness and overall color value. Groups 2 and 3 showed significantly decreased enamel microhardness compared to their baseline data. The specimens treated with fluoridated bleaching agents showed relatively less reduction in enamel microhardness than those treated with nonfluoridated agents during the bleaching treatment. CONCLUSIONS The fluoridated bleaching agents produced less demineralization of surface morphology and microhardness. The addition of fluoride did not impede the whitening effect.

Finite element analysis of miniscrew implants used for orthodontic anchorage

INTRODUCTION The miniscrew has been developed and effectively used as orthodontic anchorage, but current studies of its usage are insufficient to provide information about the underlying mechanical mechanisms. The aim of this study was to investigate the roles of bone quality, loading conditions, screw effects, and implanted depth on the biomechanics of an orthodontic miniscrew system by using finite element analysis. METHODS A 3-dimensional model with a bone block integrated with a miniscrew was constructed to simulate various cortex thicknesses, cancellous bone densities, force magnitudes and directions, screw diameters and lengths, and implanted depths of miniscrews. RESULTS Both stress and displacement increased with decreasing cortex thickness, whereas cancellous bone density played a minor role in the mechanical response. These 2 indexes were linearly proportional to the force magnitude and produced the highest values when the force was perpendicular to the long axis of the miniscrew. A wider screw provided superior mechanical advantages. The exposed length of the miniscrew was the real factor affecting mechanical performance. CONCLUSIONS The screw diameter was the dominant factor for minscrew mechanical responses. Both bone stress and screw displacement decreased with increasing screw diameter and cortex thickness, and decreasing exposed length of the screw, force magnitude, and oblique loading direction.

The DNA excision repair system of the highly radioresistant bacterium Deinococcus radiodurans is facilitated by the pentose phosphate pathway

Deinococcus radiodurans is highly resistant to radiation and mutagenic chemicals. Mutants defective in the putative glucose‐6‐phosphate dehydrogenase gene (zwf–) and the aldolase gene (fda–) were generated by homologous recombination. These mutants were used to test the cells’ resistance to agents that cause dimer formation and DNA strand breaks. The zwf – mutants were more sensitive to agents that induce DNA excision repair, such as UV irradiation and H2O2, but were as resistant to DNA strand break‐causing agents such as methylmethanesulphonic acid (MMS) and mitomycin C (MMC) as the wild‐type cells. Analysis of the cytoplasmic fraction of zwf– cells showed that the concentrations of inosine monophosphate (IMP) and uridine monophosphate (UMP) were only 30% of those found in the wild‐type cells. The fda– mutants were slightly more resistant to UV light and H2O2. Results suggested that the deinococcal pentose phosphate pathway augmented the DNA excision repair system by providing cells with adequate metabolites for the DNA mismatch repair.

The effect of microrough surface treatment on miniscrews used as orthodontic anchors

OBJECTIVES The aim of this study was to investigate the effects of two different microrough surface treatments on miniscrews with loading over different time periods in vivo. MATERIAL AND METHODS Twenty-four New Zealand white rabbits were selected. One hundred and forty-four miniscrews with a machined (MA), sandblasted and acid-etched (SLA) or sandblasted and alkaline-etched (SL/NaOH) surface were implanted into the tibia of the rabbits. Then, orthodontic forces with Ni-Ti coils were applied immediately to two of the three miniscrews in each tibia, with the center one serving as the control. After 2, 4, 8 and 12 weeks, the rabbits were sacrificed. The removal torque value (RTV) was tested and bone-to-implant contact (BIC) was examined. RESULTS In most groups, there were no differences between the RTV in the unloaded and loaded conditions at different time periods. In the loaded condition, the RTV of the SLA groups increased significantly after 4 weeks of healing. The RTV in the SL/NaOH groups increased after 8 weeks, and reached a significant difference with the SLA groups after 12 weeks. After 12 weeks, the BIC in the SLA and SL/NaOH groups was higher than in the MA groups. A regression test revealed a moderate correlation between the BIC and the RTV. CONCLUSIONS There were no differences between the loaded and unloaded conditions in most groups. The RTV and BIC increased with time. In the loaded condition, the RTV of the SLA surface increased earlier, at 4 weeks, while the SL/NAOH group showed the highest RTV after 8 weeks.

Effect of loading force on the dissolution behavior and surface properties of nickel-titanium orthodontic archwires in artificial saliva

INTRODUCTION For orthodontic applications, equiatomic nickel-titanium (NiTi) wires are used to level and align the teeth under bending conditions in the oral environment for long periods. The aim of study was to investigate the influence of bending stress on the nickel release of commercial NiTi orthodontic wires in vitro, simulating the intraoral environment as realistically as possible. METHODS Two types of as-received orthodontic NiTi wires, free of performed internal stress, were immersed in artificial saliva. Half of the NiTi wires were exposed to continuous bending stress throughout the 14-day experimental period. RESULTS The stressed NiTi wires exhibited substantial increases in the nickel release compared with the unstressed specimens during all experimental periods. The highest dissolution rate during the 0 to 1 day incubation period was observed for all stressed specimens. However, a slight increase of nickel released as a function of time was observed in the 3 groups of stressed specimens after 3 days of immersion. For the stressed specimens, it was hypothesized that the bending stress would induce buckling or cracking of the protective oxide film of the NiTi wires. In this study, the mechanism of nickel release was the underlying metal surface reacting with the surrounding environment. CONCLUSIONS The results indicated that bending stress influences the nickel release of NiTi wires. The factor of loading condition with respect to corrosion behavior and passive film should be considered in view of the widespread use of NiTi wires for dental devices.

Shear Bond Strengths of Plastic Brackets With a Mechanical Base

This study compares the shear bond strengths of plastic brackets with a mechanical base and metal brackets using two different adhesives, and examines the modes of failure using a scanning electron microscope (SEM). Forty extracted human premolars were selected for bonding. Two types of brackets: metal and plastic-Spirit MB, and two orthodontic adhesives: System 1 + and Enlight, were used. After bonding, all samples were put into a 37 degrees C distilled water bath for 24 hours before shear bond strengths were tested. The bond strengths of the plastic brackets were significantly lower than those of the metal brackets (P < .0001). There was a statistically significant difference in bond strengths between System 1 + and Enlight for plastic brackets (P < .05), but not for metal brackets. The modes of failure predominantly occurred at the enamel/adhesive interface in the metal bracket-System 1 + group, within the adhesive in the metal bracket-Enlight and plastic bracket-System 1 + groups, and at the bracket/adhesive interface in the plastic bracket-Enlight group.

Effect of fluoridated carbamide peroxide gels on enamel microtensile bond strength

The aim of this study was to examine the resin bond strength on enamel treated with different fluoridated bleaching agents. Forty-eight bovine incisors were divided into four groups to receive bleaching treatments, over a 14-d period, as follows: no treatment; 10% carbamide peroxide (CP) bleaching; 10% CP containing 0.11% fluoride; and 10% CP containing 0.37% fluoride. Immediately, and 7 and 14 d after bleaching, the enamel surfaces were respectively bonded with composite and sectioned to create resin-enamel beams. These beams were subjected to the microtensile bond strength (microTBS) test, then assessed for failure mode under scanning electron microscopy. The results showed that the 0.37% fluoridated group demonstrated a microTBS equivalent to that of the unbleached group at all stages. Non-fluoridated and 0.11% fluoridated groups showed a weaker microTBS after bleaching but regained the bond strength after 14 or 7 d of storage, respectively. In the non-fluoridated group, adhesive failure was the predominant fracture pattern that comprised the enamel prism demineralization change and widely dispersed voids on the resin-enamel interfaces. No evident enamel erosion and fewer microporosities were found in the 0.37% fluoridated group. Accordingly, treatment with 0.37% fluoridated CP maintained the microTBS as effectively as the unbleached enamel. Additional fluoride in the bleaching agents may facilitate subsequent restorative treatment by inhibiting enamel demineralization.

Use of the matching optimal symmetry plane method in planning surgical correction of facial asymmetry--a preliminary report of 20 patients.

PURPOSE A voxel-based median plane (optimal symmetry plane [OSP]) was developed to assess facial bone asymmetry. The purpose of the present study was to introduce a new method of planning surgical correction of facial asymmetry using the OSPs as guides and test its effectiveness. PATIENTS AND METHODS A retrospective study was conducted of 20 facial asymmetry patients with a mandibular deviation of 4 mm or greater or 4° or more that required surgical correction. In the test group (n = 8), the plans for asymmetry correction were formulated using the matching OSP method, in which the OSPs of the facial bones are tracked and matched during the model surgery setup. In the control group (n = 12), traditional planning was conducted. The traditional plans were cross-checked for symmetry through tracking and revised as needed. The symmetry results of the plans were compared between the 2 groups and within the control group. The outcome measures were the deviation distances between the OSPs of the midface and mandible at the anterior or posterior mandible, the occlusal plane cant, and the angle formed by the 2 OSPs. Surgery was performed in accordance with the final plans, and the results were assessed for symmetry. RESULTS The traditional plans left a major mandibular deviation in 5 of the 12 control subjects compared with none in the test group. The test group did significantly better than the control group. The revised plans were significantly better than the initial plans. Postoperatively, significant improvements in symmetry were observed. CONCLUSION The new method resulted in surgical plans that brought about significantly less postoperative mandibular deviation while maintaining a reasonable occlusion.

Effect of bracket bevel design and oral environmental factors on frictional resistance.

OBJECTIVE To investigate the effects of bracket bevel design and oral environmental factors (saliva, temperature) on frictional resistance. MATERIALS AND METHODS Five types of brackets, namely a conventional bracket (Omni-arch), an active self-ligating bracket (Clippy), and three passive self-ligating brackets (Carriere, Damon, and Tenbrook T1) coupled with a 0.014-inch austenitic nickel-titanium archwire were tested. In the experimental model, which used a group of five identical brackets, the center bracket was displaced 3 mm to mimic the binding effects. The friction experiments were performed at three temperatures (20°C, 37°C, 55°C) in a dry or a wet (artificial saliva) state. Finally, the surfaces of the bracket slots were observed using scanning electron microscopy (SEM) before and after the friction tests. RESULTS The sliding frictional force was significantly influenced by the bracket slot bevel and saliva whether in the active or passive configuration (P < .05). The frictional force significantly increased as the temperature increased in the active configuration (P < .01). Based on the SEM observations, a correlation was found among the level of frictional force, the bevel angle, and the depth of scratches on bracket bevels. CONCLUSION Frictional force can be reduced by increasing the bevel angle and by lowering the oral temperature, whereas the presence of saliva increases frictional resistance.

Feature subimage extraction for cephalogram landmarking

The significant features corresponding to skull structures on cephalograms are clinically useful for cephalometric diagnosis and superimposition. Accordingly the specific anatomical landmarks need to be firstly located for cephalometric measurements. In this paper, a novel method combining the multilayer perceptron and genetic algorithm is proposed to extract the specific feature areas. Thus, the useful landmarks may then be easily found from these feature areas instead of the whole image. The multilayer perceptron is used to approximate a fitness function for the genetic algorithm. In each iteration, eighty randomly selected subimages are grouped as the population for a GA search. Based on the feature characteristics, the selected subimages with the best fitness will survive to the last. From the experimental results, it is shown that the proposed algorithm does work better than our previous method of correlation.