Measurements of the torque moment in various archwire-bracket-ligation combinations.

The torque moment generated by third-order bends is important for tooth movement. The purpose of this study was to measure the torque moment that can be delivered by various archwire and bracket combinations at the targeted tooth. Stainless steel (SS) upper brackets with 0.018 and 0.022 inch slots, two sizes of nickel-titanium (Ni-Ti) alloy wires, and three sizes of SS wires for each bracket were used. The wire was ligated with elastics or wire. The torque moment delivered by the various archwire-bracket-ligation combinations was measured using a torque gauge. Statistical analysis was undertaken using analysis of variance (multiple comparison tests and post hoc using Tukey's honestly significant difference test. The torque moment increased as the degree of torque and wire size increased. There was no significant difference in torque moment between the SS and Ni-Ti wires at lower or higher than 40 degrees torque. The torque moment with wire ligation was significantly larger than that with elastic ligation with 0.016 × 0.022 and 0.017 × 0.025 inch Ni-Ti wires in the 0.018 inch slot brackets and the 0.017 × 0.025 and 0.019 × 0.025 inch SS and Ni-Ti wires in the 0.022 inch slot brackets. However, there was no significant difference in torque moment between either ligation method when using the full slot size wires.

Orthodontic mini-implant stability and the ratio of pilot hole implant diameter.

One notable complication of mini-implants that are used to provide anchorage in orthodontic treatment is loosening. The aim of this study was to evaluate the relationship between mini-implant mobility during the healing phase and the prognosis for implant stability. Twenty male Wistar rats (aged 20 weeks) were used. Drills with diameters of 0.8, 0.9, 1.0, and 1.1 mm were used to make pilot holes in the rat tibiae. The inserted mini-implants (diameter 1.4 mm; spearhead 1.2 mm; halfway between maximum and minimum 1.3 mm; length 4.0 mm) were subjected to an experimental traction of force for 3 weeks. Bone-to-implant contact (BIC) was observed histologically. Another 20 male rats (aged 20 weeks) underwent an identical procedure, and the stability of the mini-implants was measured using the Periotest before and after traction. The data were statistically analysed using Scheffé's test. The BIC ratios of the 0.9 and 1.0 mm groups were significantly greater than those of the other groups. The Periotest values measured 3 weeks after implant insertion were significantly lower (P < 0.05) than those measured at insertion, except in the 1.1 mm group. To obtain mini-implant stability, the hole diameter should be between 69 and 77 per cent of the diameter of the mini-implant. A significant decrease in the mobility of the mini-implants 3 weeks post-insertion implies a good prognosis for the subsequent mini-implant stability.

Relationship between masseter muscle size and maxillary morphology.

The aim of this study was to investigate the relationship between masseter muscle size and craniofacial morphology, focusing on the maxilla. Twenty-four patients (11 males and 13 females; mean age 27.6 ± 5.6 years) underwent cephalometric analyses. Ultrasonography was used to measure the cross-sectional area (CSA) of the masseter muscle and bite force was measured using pressure sensitive film. The results showed that CSA-relaxed was positively correlated with upper anterior face height (UAFH)/total anterior face height (TAFH) and negatively with lower anterior face height (LAFH)/TAFH and LAFH (P < 0.05). CSA-clenched was correlated positively with SN-palatal, FH-palatal, UAFH/TAFH, and lower posterior face height (LPFH)/total posterior face height (TPFH) and negatively with LAFH/TAFH, LAFH, upper posterior face height (UPFH)/TPFH, and UPFH (P < 0.05). Bite force was positively correlated with LPFH/TPFH and negatively with UPFH/TPFH (P < 0.05). As the masseter became larger, the anterior maxillary region tended to shift downwards relative to the cranial base, whereas the posterior region tended to shift upwards. The decrease in LAFH/TAFH and increase in LPFH/TPFH as the size of the masseter muscle increases may be influenced not only by the inclination of the mandibular plane but also by the clockwise rotation of the maxilla.

Effect of Ga-Al-As laser irradiation on COX-2 and cPLA2-alpha expression in compressed human periodontal ligament cells.

BACKGROUND AND OBJECTIVE: Prostaglandin E(2) (PGE(2)), which has bone-resorptive activity, is produced by human periodontal ligament (PDL) cells in response to mechanical stress. We previously reported that low level laser (LLL) irradiation inhibited PGE(2) production in PDL cells in response to mechanical stress; however, the mechanism underlying this inhibitory effect was unclear. Thus, we sought to determine the mechanism underlying the inhibitory effect of LLL on PGE(2) production in compressed PDL cells. STUDY DESIGN/MATERIALS AND METHODS: A compressive force of 2.0 g/cm(2) was applied for 24 hours to human PDL cells obtained from premolars extracted for orthodontic treatment. LLL irradiation (Ga-Al-As laser, 830 nm, 3.82 J/cm(2)) was applied 6 hours before, 1 hour before, and immediately after the application of compressive force. The mRNA expression of COX-2 and cPLA(2)-alpha was then examined by real-time PCR. RESULTS: LLL irradiation significantly inhibited COX-2 and cPLA(2)-alpha mRNA expression, which was increased in response to the application of a compressive force. Moreover, LLL irradiation immediately after compression had the strongest inhibitory effect on the expression of these genes. CONCLUSIONS: The inhibition of PGE(2) production by LLL irradiation in compressed PDL cells may be due to the inhibition of COX-2 and cPLA(2)-alpha expression and is most pronounced immediately after the application of a compressive force.