جستجوی مقالات مرتبط با کلیدواژه « friction » در نشریات گروه « پزشکی »

Metal brackets are the most commonly used brackets in clinical orthodontics, but the sight of color of the metal bracket can be unpleasant for some patients. Ceramic brackets offer the desired beauty but they have higher frictional resistance.  Considering that in vitro studies suggest that CO2 laser reduces the friction between the wire and slot of the bracket in the sliding mechanics, the aim of this study was to evaluate the clinical effect of CO2 laser on the speed of tooth movement using the sliding mechanics.

This randomized double-blind clinical trial was performed on 7 patients and a total of 13 half jaws in each group. These patients were candidates for bilateral extraction of the first premolars due to lack of space or dentoalveolar protrusion. After alignment and leveling, the ceramic brackets were passively bonded. The ceramic brackets of the experimental group irradiated with the CO2 laser and the brackets of the control group were bonded unchanged. The brackets were examined with an atomic force microscope (AFM) before and after irradiation. Statistical data were analyzed paired t-test to compare the rate of gap closure between the two groups at one-month intervals. ANOVA was used to examine the reduction in spacing at three-month intervals. A value of p<0.05 was considered statistically significant.

The rate of gap closure between the two groups was compared at one-month intervals, which was not statistically significant in either month. Furthermore, in the comparison between the study and control groups, the decrease in the distance between the canine and second premolars was not statistically significant after a total of three months (p=0.0918).

According to the results of this study, CO2 laser irradiation of the bracket surface has no effect on the speed of movement of the canine when sliding on the wire.

Frictional forces generation during orthodontic treatment with fixed appliances impedes appropriate tooth movement; hence, research is ongoing to explore “frictionless” techniques. This in vitro study compares Damon Q and Pactive self-ligating metallic brackets in terms of friction and surface characteristics of the bracket gates when using CuNiTi archwires during leveling and alignment stage and examines the effects of aging conditions on frictional force generation.

A total of 108 metallic self-ligating brackets (Damon Q and Pactive) were investigated for frictional resistance with round 0.014 ̋ and rectangular 0.014 ̋
0.025 ̋ CuNiTi archwires post exposure to water storage and acidic attack aging conditions. The bracket gate surface characteristics were evaluated using scanning electron microscope (SEM).

There was no statistically significant difference (P > 0.05) in friction generation between the two bracket systems when coupled with 0.014 ̋ CuNiTi archwire, but the Pactive brackets yielded significantly higher frictional forces (P < 0.05) when coupled with 0.014 ̋
0.025 ̋ archwire. The SEM findings revealed nonsignificant differences (P > 0.05) between the surface characteristics of the bracket gates.

Damon Q brackets generate low frictional forces, suggesting better performance than Pactive brackets during the first phase of orthodontic treatment. A modified scoring system was developed for an objective description of bracket surface characteristics.

Knee Osteoarthritis (OA) is one of the most important etiologies of pain and disability among adults. The effects of pulsed Ultrasound (US) on pain reduction and joint function have been proven, but its role on joint friction and inflammatory mediators is still unclear. Therefore, this study was designed to investigate the effects of US on knee joint friction and inflammation in non-traumatic experimental knee OA.

Forty-eight guinea pigs were randomly assigned into four groups: OA+US, OA+US sham, 30 days after OA induction (OA30), and normal control (n=12 for each group). OA was induced by intra-articular injection of 3 mg/kg of Mono-Iodoacetate (MIA) in the animal’s left knee. Joint circumstance and weight of the animals were measured at baseline, before (i.e., after 30 days of MIA injection), and after US treatment. Joint friction was evaluated by a pendulum friction tester system. Cytokine levels, including Tumor Necrosis Factor (TNF)-α and Interleukin (IL)-1β, were measured by the ELISA method. The Pearson correlation coefficient was calculated to study the relationships between friction and inflammation variables.

Joint circumference was increased in the OA30 group. Joint friction variables, including exponential curve fitting, cycle number, and friction coefficient, were significantly better in the US group (P<0.05). TNF-α and IL-1β cytokine levels were significantly lower in the US group. A significant positive correlation was observed between joint friction indices and TNF-α and IL-1β cytokine levels (P<0.05).

US was an effective approach for reducing joint friction and inflammation in OA30. Moreover, the relationship between knee joint friction and inflammation could help us better understand the etiology, mechanism, and treatment strategies of this disease.

We compared the effects of fluoride mouthwashes on surface topography of orthodontic wires, and static and kinetic frictional forces between stainless-steel (SS) orthodontic brackets and SS and nickel-titanium (NiTi) archwires.

This in vitro, experimental study evaluated 240 standard SS maxillary central incisor brackets and 0.018-, and 0.025×0.019-inch NiTi and SS archwires. Different combinations of wire diameters and wire types were exposed to artificial saliva (control), 0.05% sodium-fluoride (NaF) for 1 minute daily, or 0.2% NaF for 1 minute weekly (37°C) for 3 months. The wires were pulled in the bracket slots by 5mm in a universal testing machine (10mm/minute). The static and kinetic forces were measured. The surface topography of the wires was inspected under a scanning electron microscope (SEM). Three-way ANOVA followed by Bonferroni post-hoc tests were used for statistical analysis (P<0.05).

The mean static and kinetic frictional forces of 0.025×0.019- inch NiTi wired in the 0.05%NaF group were significantly greater than the SS wire. The mean kinetic frictional force in the 0.05%NaF group was significantly greater than the 0.2%NaF and artificial saliva groups for all wires. The mean static and kinetic forces in 0.2%NaF were significantly greater than in artificial saliva. In all groups, larger wires showed higher mean frictional forces. SEM results revealed higher wire surface roughness in the 0.05%NaF group followed by the 0.2%NaF group.

Weekly use of 0.2%NaF mouthwash is recommended during sliding mechanics to minimize frictional forces between SS and NiTi wires and SS brackets.

The aim of this study was to compare the effect of chlorhexidine‑ and Persica‑containing mouthrinses on the surface characterization of orthodontic appliance and friction between the orthodontic stainless steel wires and brackets.

In this randomized controlled trial, 75 orthodontic patients (aged 13–30) were allocated (n = 25) into two experimental groups (prescribed by Persica‑ or chlorhexidine‑containing mouthrinse) and one control group (no prescription). The ovoid stainless steel archwires were placed, and the maxillary first premolar stainless steel edgewise brackets were ligated to wires by elastomeric rings. The patients were recalled after 2 weeks, and then, the archwires were removed and replaced. The surface analysis of archwires and brackets was evaluated using scanning electron microscopy and atomic force microscopy. The frictional forces between the archwires and brackets were measured using a universal testing machine. The data for surface roughness were analyzed by the nonparametric Kruskal–Wallis and Mann–Whitney tests. The frictional forces data were analyzed using a two‑way analysis of variance and Tukey’s post hoc test using SPSS software. The level of significance was P < 0.05.

The retrieved brackets showed minor changes in their surface topography. The surface roughness of archwires after the intervention was significantly greater for the chlorhexidine than that of Persica (P < 0.05). The friction force between the archwires and brackets was also significantly higher for the chlorhexidine than that of Persica (P < 0.05).

The Persica‑containing mouthrinse from the biomechanical and biochemical standpoints may be a better option for oral hygiene in orthodontic patients compared with the chlorhexidine.

In sliding mechanics, archwires should slide easily during the retraction of anteriors. Round wires slide well, but the torque control is a significant problem. Rectangular wires produce effective torque expression but pose a challenge to free sliding due to factors like friction and force used to overcome friction, etc. To utilize the properties of both wires, the wire should be bi-dimensional. Dual-dimensional wire is one such wire with different dimensions in the anterior and posterior sections. This study aimed to compare the amount of space closure and anchorage loss of molars between the rectangular and dual-dimensional wire groups during retraction with mini-implants.

Forty patients were randomly allocated to two groups (n=20). Patients with rectangular wires formed the control group, and those with dual-dimensional wires formed the experimental group. Mini-implants and NiTi coil springs were used for retraction. Model and cephalometric analyses were carried out to calculate the amount of space closure and anchor loss, before and four months after the study. Statistical significance was set at P<0.05.

The average amount of space closure was higher with DDW (3.98 mm) than rectangular wire (3.22 mm). The difference was statistically significant. No significant difference was found with anchorage loss. Conclusion. DDW can be used as an alternative to rectangular wires during retraction with mini-implants; however, it cannot replace the rectangular wires completely. Anchorage control was effective with both wires.

Friction is defined as the force that resists a movement when objects move tangentially against each another. Various forces arise, when two surfaces which are in contact slide against one another. An orthodontist has various difficulties related to friction specially with sliding mechanics and has to deals with it successfully to provide effective tooth movement. During Orthodontic treatment, sliding mechanics is used widely. Friction generated at the bracket/archwire interface is one of the disadvantages of this mechanics, which reduces the quality of desired orthodontic movement acquired. Both clinicians and scientists have an interest in the role of friction in Orthodontics, due to its application. As per clinical studies, the resistance to bodily tooth movement by sliding has far too less to do with friction. It is mainly a binding-and-release situation that is similar to conventional and self-ligating brackets.

The present study aimed to evaluate an experimental herbal mouthwash, as compared to sodium fluoride mouthwash on the frictional resistance and surface roughness between brackets and two rectangular archwire types.

A total of 60 premolar׳s brackets engaged with 0.019×0.025 archwires made of stainless steel and nickel-titanium alloys were used in this study. The samples were assigned into three groups, each group contained ten stainless steel archwires-brackets and ten nickel titanium archwires-brackets combination. Thereafter, these samples were immersed in herbal mouthwash, sodium fluoride mouthwash (study groups) and artificial saliva (control group) for 90 minutes. Universal testing machine was used to test the friction resistance in the three groups. Atomic force and scanning electron microscopes were used to evaluate the surface roughness of wires and bracket surface topography, respectively.

The samples immersed in sodium fluoride mouthwash illustrated the highest mean friction resistance and mean surface roughness, followed by herbal mouthwash and the least was for artificial saliva.

The 90-minute immersion in herbal mouthwash did not exert any significant effect on frictional resistance or surface roughness among orthodontic brackets and archwires made of stainless steel and nickel titanium. Based on the results, herbal mouthwash may be prescribed as a non-destructive prophylactic agent on materials evaluated in the present study for the orthodontic patient.