Dual stimuli-responsive Fe3O4 graft poly(acrylic acid)-block-poly(2-methacryloyloxyethyl ferrocenecarboxylate) copolymer micromicelles: surface RAFT synthesis, self-assembly and drug release applications.

BACKGROUND: Stimuli-responsive polymer materials are a new kind of intelligent materials based on the concept of bionics, which exhibits more significant changes in physicochemical properties upon triggered by tiny environment stimuli, hence providing a good carrier platform for antitumor drug delivery. RESULTS: Dual stimuli-responsive Fe3O4 graft poly(acrylic acid)-block-poly(2-methacryloyloxyethyl ferrocenecarboxylate) block copolymers (Fe3O4-g-PAA-b-PMAEFC) were engineered and synthesized through a two-step sequential reversible addition-fragmentation chain transfer polymerization route. The characterization was performed by FTIR, 1H NMR, SEC, XRD and TGA techniques. The self-assembly behavior in aqueous solution upon triggered by pH, magnetic and redox stimuli was investigated via zeta potentials, vibration sample magnetometer, cyclic voltammetry, fluorescent spectrometry, dynamic light scattering, XPS, TEM and SEM measurements. The experimental results indicated that the Fe3O4-g-PAA-b-PMAEFC copolymer materials could spontaneously assemble into hybrid magnetic copolymer micromicelles with core-shell structure, and exhibited superparamagnetism, redox and pH stimuli-responsive features. The hybrid copolymer micromicelles were stable and nontoxic, and could entrap hydrophobic anticancer drug, which was in turn swiftly and effectively delivered from the drug-loaded micromicelles at special microenvironments such as acidic pH and high reactive oxygen species. CONCLUSION: This class of stimuli-responsive copolymer materials is expected to find wide applications in medical science and biology, etc., especially in drug delivery system.

Application of a wireless resonance frequency transducer to assess primary stability of orthodontic mini-implants: an in vitro study in pig ilia.

PURPOSE: The aim of the study was to evaluate whether resonance frequency analysis (RFA) using a wireless transducer can be used to assess the primary stability of orthodontic mini-implants. MATERIALS AND METHODS: Fifteen orthodontic mini-implants were placed in three ilium bone segments of country pigs. The wireless resonance frequency transducer was bonded to the head of the mini-implants, and RFA values of the mini-implants in bone were detected and converted into implant stability quotient (ISQ) values by the RFA monitor. In addition, the percussion test value, peri-implant radiographic bone density, and cortical bone thickness were measured. RESULTS: The ISQ values of mini-implants correlated linearly with peri-implant radiographic bone density (r = 0.92, P < .0001), cortical bone thickness (r = 0.90, P < .0001), and percussion test values (r = -0.91, P < .0001), respectively. In addition, by means of the calculation of 99% confidence intervals, the absolute values of the three correlation coefficients ranged from 0.61 to 0.98. CONCLUSION: This in vitro animal study showed that the presented RFA method using a wireless transducer might have potential to provide an alternative noninvasive assessment of the primary stability of an orthodontic mini-implant.

Comparison of self-tapping and self-drilling orthodontic mini-implants: an animal study of insertion torque and displacement under lateral loading.

PURPOSE: The aim of this study was to compare two types of orthodontic mini-implants, self-tapping and self-drilling, by measurement of the insertion torques and the displacements under lateral loading in an animal model. MATERIALS AND METHODS: After predrilling of host sites, 27 self-tapping and 27 self-drilling mini-implants were inserted in vitro in the ilia of country pigs. The axial drilling forces at each host site and the insertion torques during placement were recorded, and the displacements applied by variable lateral force (1 to 9 N) were measured. Analyses of covariance with insertion torques or displacements under lateral loading as the main effect and average drilling forces as the covariate (at the alpha=5% level) were performed to determine statistical significance. RESULTS: There was a significant difference in peak insertion torque between the self-tapping and self-drilling group (P<.05), except when the average drilling force at host sites was less than 1.2 N (P>.05). In addition, this experiment demonstrated that the lateral displacement of the self-tapping group was comparable to that of the self-drilling group (P>.05). CONCLUSIONS: During implantation, the self-tapping implants typically had a lower insertion torque than the self-drilling implants. Based on the displacements under lateral loading, however, both the self-tapping and self-drilling implants showed similar resistance to lateral forces.

Insertion angle impact on primary stability of orthodontic mini-implants.

OBJECTIVE: To analyze the impact of the insertion angle on the primary stability of mini-implants. MATERIALS AND METHODS: A total of 28 ilium bone segments of pigs were embedded in resin. Two different mini-implant sizes (Dual-Top Screw 1.6 x 8 mm and 2.0 x 10 mm) were inserted at seven different angles (30 degrees , 40 degrees , 50 degrees , 60 degrees , 70 degrees , 80 degrees , and 90 degrees ). The insertion torque was recorded to assess primary stability. In each bone, five Dual-Top Screws were used to compensate for differences in local bone quality. RESULTS: The angle of mini-implant insertion had a significant impact on primary stability. The highest insertion torque values were measured at angles between 60 degrees and 70 degrees (63.8 degrees for Dual-Top 1.6 mm and 66.7 degrees for Dual-Top 2.0 mm). Very oblique insertion angles (30 degrees ) resulted in reduced primary stability. CONCLUSIONS: To achieve the best primary stability, an insertion angle ranging from 60 degrees to 70 degrees is advisable. If the available space between two adjacent roots is small, a more oblique direction of insertion seems to be favorable to minimize the risk of root contact.

Impact of implant design on primary stability of orthodontic mini-implants.

AIM: Skeletal anchorage with mini-implants has greatly broadened the treatment possibilities in orthodontics over the last few years. To reduce implant failure rates, it is advisable to obtain adequate primary stability. The aim of this study was to quantitatively analyze the impact of implant design and dimension on primary stability. MATERIAL AND METHODS: Forty-two porcine iliac bone segments were prepared and embedded in resin. To evaluate the primary stability, we documented insertion torques of the following mini-implants: Aarhus Screw, AbsoAnchor, LOMAS, Micro-Anchorage-System, ORLUS and Spider Screw. In each bone, five Dual Top Screws were inserted for reference purposes to achieve comparability among the specimens. RESULTS: We observed wide variation in insertion torques and hence primary stability, depending on mini-implant design and dimension; the great impact that mini-implant diameter has on insertion torques was particularly conspicuous. Conical mini-implants achieved higher primary stabilities than cylindrical designs. CONCLUSIONS: The diameter and design of the mini-implant thread have a distinctive impact on primary stability. Depending on the region of insertion and local bone quality, the choice of the mini-implant design and size is crucial to establish sufficient primary stability.

Pre-drilling force and insertion torques during orthodontic mini-implant insertion in relation to root contact.

BACKGROUND AND AIM: The use of mini-implants for skeletal anchorage has greatly broadened the therapeutic spectrum in orthodontics over the last few years. The alveolar ridge is the most frequent insertion site, which however is associated with tooth injury, a risk not to be underestimated. The objective of this study was to examine the quantitative parameters of pre-drilling and implant insertion in association with the degree of a root contact. MATERIAL AND METHODS: Eleven lower jaw bones of adult pigs were prepared and embedded in resin. At 320 sites in the toothbearing alveolar ridge a 1.3 mm pre-drilling was carried out up to the complete implant length. The vertical force exerted against the pre-drilling upon penetration of the different bone layers and at a root contact was measured at a drift-speed of 0.5 mm/s. Dual Top screws (1.6 x 8 mm) were then inserted into the prepared implant sites, the insertion torques were measured, and recorded as a function of the rotation angle. After explantation, we prepared histological slides from the level of the implant's maximum diameter. The implant's contact with cortical and cancellous bone and to the roots was measured and correlated to vertical pre-drilling forces and insertion torques. RESULTS: Vertical pre-drilling forces and insertion torques of orthodontic mini-implants varied in relation to the type of tissue penetrated and the degree of root contact. The insertion torques ranged from 32 to 345 Nmm and pre-drilling forces up to 6 N overall. CONCLUSION: Root contact can be recognized during pre-drilling by a distinct increase in resistance, and during mini-implant insertion by higher torques.

Stiffness and frictional resistance of a superelastic nickel-titanium orthodontic wire with low-stress hysteresis.

INTRODUCTION: Stress-induced martensite formation with stress hysteresis that changes the elasticity and stiffness of nickel-titanium (Ni-Ti) wire influences the sliding mechanics of archwire-guided tooth movement. This in-vitro study investigated the frictional behavior of an improved superelastic Ni-Ti wire with low-stress hysteresis. METHODS: Improved superelastic Ni-Ti alloy wires (L & H Titan, Tomy International, Tokyo, Japan) with low-stress hysteresis were examined by using 3-point bending and frictional resistance tests with a universal test machine at a constant temperature of 35 degrees C, and compared with the former conventional austenitic-active superelastic Ni-Ti wires (Sentalloy, Tomy International). Wire stiffness levels were derived from differentiation of the polynomial regression of the unloading curves, and values for kinetic friction were measured at constant bending deflection distances of 0, 2, 3, and 4 mm, respectively. RESULTS: Compared with conventional Sentalloy wires, the L & H Titan wire had a narrower stress hysteresis including a lower loading plateau and a higher unloading plateau. In addition, L & H Titan wires were less stiff than the Sentalloy wires during most unloading stages. Values of friction measured at deflections of 0, 2, and 3 mm were significantly (P <.05) increased in both types of wire. However, they showed a significant decrease in friction from 3 to 4 mm of deflection. L & H Titan wires had less friction than Sentalloy wires at all bending deflections (P <.05). CONCLUSIONS: Stress-induced martensite formation significantly reduced the stiffness and thus could be beneficial to decrease the binding friction of superelastic Ni-Ti wires during sliding with large bending deflections. Austenitic-active alloy wires with low-stress hysteresis and lower stiffness and friction offer significant potential for further investigation.

Unilateral horizontally impacted maxillary canine and first premolar treated with a double archwire technique.

A patient with a unilateral horizontally impacted upper left canine and first premolar was treated orthodontically. The use of a double archwire technique achieved the desired treatment goals. We discuss the problems associated with impacted maxillary canines and first premolars and the biomechanical interventions used for this patient.