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Objective: To investigate the three-dimensional structural features of three types of mechanically retentive ceramic bracket bases. Materials and Methods: One type of stainless steel (MicroArch, Tomy, Tokyo, Japan) and three types of ceramic maxillary right central incisor brackets--Crystaline MB (Tomy), INVU (TP Orthodontics, La Porte, Ind), and Inspire Ice (Ormco, Glendora, Calif)--were tested to compare and quantitatively analyze differences in the surface features of each ceramic bracket base using scanning electron microscopy (SEM), a three-dimensional (3D) optical surface profiler, and microcomputed tomography (micro-CT). One-way analysis of variance was used to find differences in bracket base surface roughness values and surface areas between groups according to base designs. Tukey's honestly significant differences tests were used for post hoc comparisons. Results: SEM revealed that each bracket exhibited a unique surface texture (MicroArch, double mesh; Crystaline MB, irregular; INVU, single mesh; Inspire Ice, bead ball). With a 3D optical surface profiler, the stainless steel bracket showed significantly higher surface roughness values. Crystaline MB had significantly higher surface roughness values than Inspire Ice. Micro-CT demonstrated that stainless steel brackets showed significantly higher whole and unit bracket base surface areas. Among ceramic brackets, INVU showed significantly higher whole bracket base surface area, and Crystaline MB showed a significantly higher unit bracket base surface area than Inspire Ice. Conclusion: Irregular bracket surface features showed the highest surface roughness values and unit bracket base surface area among ceramic brackets, which contributes to increased mechanically retentive bracket bonding strength. [ABSTRACT FROM AUTHOR]

Objective: To determine the variation in the insertion torque of orthodontic miniscrews according to the screw length, diameter, and shape. Materials and Methods: The maximum insertion torque (MIT) was measured using a torque tester at a constant speed of 3 rotations per minute. Cylindrical and taper type of miniscrews (Biomaterials Korea Inc, Seoul, Korea) with different lengths, diameters, and pitches were tested. Results: The results showed that the insertion torque significantly increased with increasing screw length (P < .01). In particular, there was a significant increase in torque with increasing screw length and diameter (P < .01). An analysis of the serial insertion torque of miniscrews revealed the cylindrical type screw to have much higher insertion torque at the incomplete screw thread, while the taper type screw showed a much higher insertion torque at the final inclination part of the screw thread. The insertion torque was affected by the outer diameter, length, and shape in that order. Conclusions: An increase in screw diameter can efficiently reinforce the initial stability of the miniscrew, but the proximity of the root at the implanted site should be considered. [ABSTRACT FROM AUTHOR]

Objective: To evaluate the effect of cortical bone thickness on the maximum insertion and removal torque of different types of self-drilling mini-screws and to determine if torque depends on the screw design. Materials and Methods: Three different types of self-drilling mini-screws (cylindrical type [Cl], taper type [Ta], taper type [Tb]) were inserted with the use of a driving torque tester at a constant speed of 3 rotations per minute. Experimental bone blocks with different cortical bone thicknesses were used as specimens. Results: Differences in the cortical bone thickness had little effect on the maximum insertion and removal torque in Cl. However, with Ta and Tb, the maximum insertion torque increased as the cortical bone thickness increased. The maximum insertion torque of Tb was highest in all situations, followed by Ta and Tb, in that order. Cl showed less torque loss in all cortical bone thicknesses and a longer removal time compared to Ta or Tb. There were significant relationships between cortical bone thickness, maximum insertion and removal torque, and implantation time in each type of self-drilling mini-screw. Conclusion: Since different screw designs showed different insertion torques with increases in cortical bone thickness, the suitable screw design should be selected according to the cortical thickness at the implant site. [ABSTRACT FROM AUTHOR]

Objective: To compare the level of friction resistance (FR) of conventional and silica-insert ceramic brackets using various bracket-wire combinations and angulations. Materials and Methods: Four types of ceramic brackets were examined: (1) polycrystalline alumina bracket (PCA-C), (2) polycrystalline alumina bracket with a stainless steel (SS) slot (PCA-M), (3) polycrystalline alumina bracket with a silica layer (PCA-S), and (4) monocrystalline sapphire bracket (MCS). A conventional SS bracket was used as the control. The static and kinetic FR in four bracket-wire angulations (0°, 5°, 10°, and 15°) was examined using SS and β-titanium (β-Ti) orthodontic wires, 0.019 x 0.025 inches in size, under elastic ligature in the dry state. Results: The FR generated by the PCA-S bracket was significantly lower than that generated with the other ceramic brackets, and was similar to that of the SS bracket. The PCA-S bracket showed the lowest FR with both the SS and the β-Ti wires at zero bracket angulation. The FR to sliding increased rapidly and nonlinearly when the bracket wire angulation was >5°. The PCS-S bracket showed the lowest FR from 5° to 15° of angulation. The MCS bracket demonstrated the highest increase in FR from 0° to 15° of angulation, showing the highest FR at 15° of angulation. Conclusion: PCA-S showed minimal FR among the ceramic brackets, and was comparable to the conventional SS bracket. The silica layer and rounded edges of the ceramic slot lowered FR considerably. [ABSTRACT FROM AUTHOR]