[Properties of NiTi wires with direct electric resistance heat treatment method in three-point bending tests].

OBJECTIVE: To investigate the mechanical properties of Ni-Ti wires with direct electric resistance heat treatment (DERHT) method in three-point bending tests. METHODS: Two superelastic Ni-Ti wires (wire A: Smart SE, wire B: SENTALLOY SE, 0.406 mm × 0.559 mm) and 2 heat-actived Ni-Ti wires (wire C: Smart SM, wire D: L&H TITAN, 0.406 mm × 0.559 mm) were selected. They were heat-treated using the DERHT method by a controlled electric current (6.36 A) applied for different period of time [0 (control), 1.0, 1.5, 2.0, 2.5 seconds). Then, a three-point bending test was performed under controlled temperature (37°C) to examine the relationships between the deflection and the load in the bending of wires. RESULTS: After DERHT treatment, the plateau in the force-deflection curve of superelastic Ni-Ti wires and heat-activated Ni-Ti wires were increased. When the wires were heated for 2.0 seconds and deflected to 1.5 mm, the loading force of A, B, C and D Ni-Ti wires increased from (3.85 ± 0.11), (3.62 ± 0.07), (3.28 ± 0.09), (2.91 ± 0.23) N to (4.33 ± 0.07), (4.07 ± 0.05), (4.52 ± 0.08), (3.27 ± 0.15) N respectively. CONCLUSIONS: DERHT method is very convenient for clinical use. It is possible to change the arch form and superelastic force of NiTi wires. The longer the heating time is, the more the superelastic characteristics of the wires are altered.

[Relationship between condyle movement and disc position in patients with Class II division 1 malocclusion].

OBJECTIVE: To investigate the relationship between condyle movement and temporomandibular disorders (TMD) in patients with Class II division 1 malocclusion. METHODS: Twenty patients (from 11 to 12 years old) with Class II division 1 malocclusion before treatment were collected. Computer aided diagnosis axiograph (CADIAX) and magnetic resonance images (MRI) were used to analyze the condyle movement between disc displacement and normal groups. RESULTS: The sensitive values were found in open/close process in patients with disc displacement: Y [Left: (0.32 +/- 0.10) mm, Right: (-0.91 +/- 0.49) mm ], Z [Left: (4.20 +/- 0.70) mm, Right: (3.44 +/- 0.21) mm], sagittal condylar inclination (SCI) [Left: (32.48 +/- 7.70) degrees , Right: (33.47 +/- 12.60) degrees ] and horizontal condylar inclination (TCI) [Left: (-2.60 +/- 2.02) degrees , R: (-9.23 +/- 5.58) degrees ], and those items showed significant difference between two groups. CONCLUSIONS: The side shift of condyle movement in maximum open/close process might be the inducement of disc displacement. It was revealed that the changes in condyle movement could give useful information in early stage of functional treatment.

[Patients with anterior spaces caused by periodontal disease treated with aligner technique].

OBJECTIVE: To treat the patients with anterior spaces caused by periodontal diseases with aligners and evaluate the periodontal conditions before and after treatment. METHODS: Seven patients with anterior spaces ranged from 3.0 to 4.5 mm were randomly selected. All the patients were treated with aligner technique to close the spaces. Bleeding on probing (BOP) and probing depth (PD) were measured before treatment, 1 month, 3 months and 6 months after treatment. The CEJ-ABC distance was evaluated before treatment, 1 month, and 6 months after treatment. RESULTS: No significant differences were found in periodontal evaluation and the CEJ-ABC distance between any two evaluated stages. CONCLUSIONS: The aligners could be used in patients with anterior spaces caused by periodontal diseases. No periodontal tissue damages were found during the observation period.

Biomechanical and histomorphometric characterizations of osseointegration during mini-screw healing in rabbit tibiae.

OBJECTIVE: To evaluate effects of different healing times on integration of titanium mini-screws and bones under unloaded conditions. MATERIALS AND METHODS: Biomechanical stability measurements and histomorphometric observations were performed in a rabbit tibia model after different healing times: 0 (immediate) and 1, 2, 4, and 8 weeks. RESULTS: Biomechanical stability and both maximum torque and maximum pullout load increased with healing time but increased significantly only after 4 weeks. Maximum torque and maximum pullout load both significantly correlated with healing time and with each other. Similarly, histomorphometric analyses showed that new bone formation increased with healing time but increased dramatically only after 4 weeks. The data may provide guidance for determining optimal implant plans in clinical practice. CONCLUSION: Mini-screw healing is a continuous process, and week 4 is a critical time point in this process.

[Occlusal contacts in intercuspal position after orthodontic treatment].

OBJECTIVE: To observe the occlusal contacts in intercuspal position(ICP) in adolescent patients after orthodontic treatment. METHODS: Fourteen adolescent patients after orthodontic treatment were selected as experimental group and 17 healthy adolescents and young adults with normal occlusion were selected as control group. The occlusal contact in ICP in the two groups were recorded with T-Scan II system and compared. RESULTS: When the total of force (TOF) were 1/10 TOFmax, 1/4 TOFmax, 1/2 TOFmax, 3/4 TOFmax and TOFmax, the number of occlusal contacts in the anterior segment in the experimental group were 1.5(1.0), 3.0(1.3), 4.5(3.3), 5.5(3.0), 5.5(3.3), which were significantly larger than that in control group [0.0(0.3), 0.0(0.6), 0.3(0.5), 0.3(1.0), 0.0(1.8), P < 0.05]. There were no significant difference in the area of occlusal contacts in the posterior segment between experimental group and control group (P > 0.05). The center of force (COF) in the experimental group located significantly more mesially than that in control group. The value of ICP contact time in experimental group was 0.192(0.141) s and no significant difference was found between experimental group and control group [0.163(0.200) s]. CONCLUSIONS: Although the patients achieved normal occlusion after orthodontic treatment, their anterior teeth received more occlusal force than those in healthy adolescents and young adults with normal occlusion.

[Preliminary clinical application of Chinese-made invisible orthodontic technique].

OBJECTIVE: To treat simple malocclusions preliminarily using Chinese-made invisible orthodontic aligners and discuss the indications, problems existed and future development. METHODS: Forty-one cases with different malocclusions were selected, including crowding, spaces and spaces due to periodontal problems. Invisible aligners were made and worn by patients and they were changed every 2 - 3 weeks. RESULTS: Acceptable treatment results were obtained in all cases, with nice alignments and good overbite and overjet. Treatment time ranged from 6 - 25 months. CONCLUSIONS: Indications of this technique were still limited and the technique needed to be further developed in the future.

[Relationships between MRI image changes of lateral pterygoid muscle, disc position and condylar mobility in Class II patients].

OBJECTIVE: To analyze the relationships between MRI image changes of lateral pterygoid muscle (LPM), disc position and condylar mobility. METHODS: Twenty Class II patients were chosen and MRI images of LPM were taken. The relationships between MRI image changes of LPM, disc position and condylar mobility were analyzed. RESULTS: The rate of MRI image changes of LPM in Class II patients was about 45%. No significant correlations were found between MRI image changes of LPM, condylar mobility and disc position. CONCLUSIONS: MRI image changes of LPM in Class II patients was common but no significant correlations were found between MRI image changes of LPM, condylar mobility and disc position.

[Condyle movement in class II division 1 malocclusion patients after functional appliance treatment].

OBJECTIVE: To record and analyze the characteristics of condyle movement before and after functional treatment in Angle class II division 1 malocclusion (II(1)) patients. METHODS: Twenty Angle II(1) patients were included in the study and 20 Angle I patients without temporomandibular disorders symptoms served as controls. Computer aided diagnosis axiograph (CADIAX) was used to record the condyle movement in Angle II(1) patients and that caused by functional appliance treatment during mouth opening and closing. RESULTS: The tracing were vertically displayed. Value Z [L: 2.21 (1.01) mm, R: 1.12 (1.02) mm] and sagittal condylar inclination [L: 12.89 (9.12) degrees, R: 12.12 (8.89) degrees] were increased significantly in Angle II(1) patients compared with those in control group (P < 0.05). After functional treatment, the condyle movement in Angle II(1) patients was close to normal (P > 0.05). CONCLUSIONS: Typical characteristics of condyle movement were found in Angle II(1) patients and it was stable and repeatable. Functional therapy had a positive effect on temporomandibular joint function in Angle II(1) patients.

[Opportunities and challenges during the development of the orthodontic invisible aligner technique].

The bracketless invisible aligner technique has been considered as a new developed orthodontic technique since its appearance during the period of late 1990s. It is characterized with the advantages of more aesthetic, comfortable, simple, high-efficient and predictable compared with current traditional orthodontic techniques depending on brackets and wires for orthodontic tooth movements. There have been many opportunities for further development and clinical application for the technique with the developments of material sciences, computer software and hardware technology, rapid prototyping techniques, et al. Nevertheless, kinds of difficulties and challenges have been and should be met either at present or in the future for this relatively new technique which just occurred around 10 years ago. The histories, developments with opportunities and challenges and prospects of the technique will be reviewed and discussed in this paper.

[Stability of the miniscrew implant during healing period].

OBJECTIVE: To evaluate the stability of mini-screw implant during different healing periods in the unloaded conditions. METHODS: Sixty titanium mini-screws were used in this study. A total of 10 New Zealand white rabbits were randomly divided into 5 groups according to different healing periods. The stability was evaluated biomechanically at different time points. One-way ANOVA and correlation analyses were used. RESULTS: (1) After 4 weeks and 8 weeks of healing, maximal pull-out loads were (179.68 +/- 24.65) N and (212.06 +/- 42.51) N, respectively. The maximal torques were (0.47 +/- 0.13) N.m and (0.61 +/- 0.16) N.m, respectively. (2) Significant difference in maximal torque was found between 4 week and 8 week healing groups. (3) Both reverse torque and pull-out load significantly correlated with healing time. CONCLUSIONS: Fourth-week is a critical time point in the progress of osseointegration. Within 8 weeks of healing process, the stability of implant was significantly correlated with healing time.

[Single nucleotide polymorphisms of growth hormone receptor gene in Chinese Han ethnic population].

OBJECTIVE: To analyze the distribution of single nucleotide polymorphisms (SNP) of growth hormone receptor (GHR) gene in Chinese Han ethnic population. METHODS: The sample of 106 unrelated healthy Chinese Hans was studied by sequencing exons of the GHR gene to detect SNP. RESULTS: There were 6 SNP spots identified in exon 6 and exon 10. Five of them were found in exon 10, and one in exon 6. There were differences between the allele frequencies of the SNP we found and those in the NCBI database. The highest heterozygosity of the SNP was found at 1630 A > C (I526L), which was 47.6%. The SNP 1483 A > C (P477T), 1735 A > C (P561T) and 1319 G > T (C422F) had polarity change. The SNP 536 A > G in exon 6 from the NCBI database was not detected in this population. The allele distribution of SNP was in good unity with the Hardey-Weinberg equilibrium. CONCLUSION: It is suggested that the SNP of GHR are unevenly distributed and different in different ethnic populations.