人牙釉质酸蚀过程中三维形貌的原子力显微镜观察

目的 比较不同酸蚀时间处理后牙釉质表面的三维形貌并分析粗糙度的改变,探讨酸蚀对牙釉质微观形貌的影响.方法 将15颗新鲜前磨牙包埋、切割、打磨后得到光滑牙釉质切片,按单纯随机法分为5组,用37％磷酸凝胶分别酸蚀0(对照组)、5、10、20和30s,原子力显微镜观察釉质表面形貌,分析轮廓改变,计算图像的算术平均粗糙度(Ra)、均方根粗糙度(Rq)、十点高度平均差(Rz)值及表面积、容积并对5组的结果数据进行单因素方差分析,用Turkey's法进行组间两两比较,以P＜0.05为差异有统计学意义.结果 镜下形貌观察显示,0～20 s内釉质的釉柱结构逐渐明显,釉质表面由较光滑逐渐变为典型鱼鳞状;20 s后表面形态变化不明显.表面轮廓观察显示,随着酸蚀时间由0s增加至30 s,釉柱间隙首先被溶解,酸蚀深度逐渐增加到2.8μm,30 s后釉柱顶部宽度减小至1.8μm,且高度略降低.从0s到30 s,Ra值由(19.69±3.42) nm增加到(359.51±75.79)nm,Rq值由(22.02±5.57) nm增加到(431.02±83.09) nm,Rz值由(0.24±0.08) μm增加到(2.38±0.26) μm;组间比较显示,Ra和Rq值的20s组与30 s组和Rz值的10、20和30 s组差异无统计学意义(P＞0.05),其余各组间差异均有统计学意义(P＜0.05).同时釉质表面积由(406.77±3.88) μm2 (0 s)增大到(546.69±84.02) μm2 (30 s),容积由(65.73±14.46) μm3 (0 s)增大到(474.63±52.50)μm3(30 s).结论 随着酸蚀时间的增加,釉质表面酸蚀深度不断增大,表面粗糙度增加,表面积及容积增大,酸蚀会造成釉质微观形貌的明显改变.     

人工楔状缺损牙颈部硬组织应力分布的有限元接触分析

目的:分析人工楔状缺损患牙颈部硬组织的应力分布。方法:在下颌前磨牙沿釉牙本质界建立三角形缺损,设计楔状缺损模型,模拟紧咬和咀嚼运动中牙的受力情况,对下颌前磨牙颈部硬组织进行非线性接触分析。结果:模拟紧咬和咀嚼运动中牙的受力情况,釉牙本质界缺损的下颌前磨牙缺损区尖端均存在明显的拉应力集中,应力集中区沿釉牙本质界向方延伸,其中尤以侧方运动工作侧一点接触载荷下的应力集中最为明显,应力值最大。结论:釉牙本质界破坏改变了缺损区牙颈部的应力分布。     

心理干预在下颌升支矢状劈开截骨术后肌功能康复训练中的作用

目的:探讨心理干预在下颌升支矢状劈开截骨术(sagittal split ramus osteotomy,SSRO)矫治下颌前突畸形术后肌功能康复训练中的作用。方法:60例接受下颌升支矢状劈开术的患者随机分为实验组和对照组,2组均接受系统治疗和肌功能康复训练,实验组在此基础上增加心理干预,测量术前、术后2、4周的张口度;术前、术后4、8周的焦虑自评评分和力。结果:实验组术后4周时张口度已接近术前水平,术后8周时力接近术前水平,焦虑情绪改善,实验组各方面参数相比对照组都有明显提高。结论:系统地心理干预能有效地提高患者健康知识水平,改善认知态度,使焦虑情绪得以改善,医患配合度提高,从而提高治疗有效率。     

Comparison of immediate complete denture, tooth and implant-supported overdenture on vertical dimension and muscle activity

PURPOSE

To compare the changes in the occlusal vertical dimension, activity of masseter muscles and biting force after insertion of immediate denture constructed with conventional, tooth-supported and Implant-supported immediate mandibular complete denture.

MATERIALS AND METHODS

Patients were selected and treatment was carried out with all the three different concepts i.e, immediate denture constructed with conventional (Group A), tooth-supported (Group B) and Implant-supported (Group C) immediate mandibular complete dentures. Parameters of evaluation and comparison were occlusal vertical dimension measured by radiograph (at three different time intervals), Masseter muscle electromyographic (EMG) measurement by EMG analysis (at three different positions of jaws) and bite force measured by force transducer (at two different time intervals). The obtained data were statistically analyzed by using ANOVA-F test at 5% level of significance. If the F test was significant, Least Significant Difference test was performed to test further significant differences between variables.

RESULTS

Comparison between mean differences in occlusal vertical dimension for tested groups showed that it was only statistically significant at 1 year after immediate dentures insertion. Comparison between mean differences in wavelet packet coefficients of the electromyographic signals of masseter muscles for tested groups was not significant at rest position, but significant at initial contact position and maximum voluntary clench position. Comparison between mean differences in maximum biting force for tested groups was not statistically significant at 5% level of significance.

CONCLUSION

Immediate complete overdentures whether tooth or implant supported prosthesis is recommended than totally mucosal supported prosthesis.     

Analysis of Occlusal Stresses Transmitted to the Inferior Alveolar Nerve by Multiple Threaded Implants

Background : Potential nerve injury or loss of sensation can occur after mandibular implant placement or loading. To avoid this type of damage, it is critical to determine the proper distance from implants to the mandibular nerve. Hence, the purpose of this study is to use biomechanical analyses to determine the safe distance from multiple implants to the inferior alveolar nerve. Methods: Using the boundary element method, a numerical mandibular model was designed to simulate a mandibular segment containing multiple threaded fixtures. This model allows assessment of the pressure, as induced by occlusal loads, on the trigeminal nerve. Such pressure distribution was evaluated against different distances from the fixtures to the mandibular canal, against the possible lack of the central fixture in a three‐abutment configuration, and against different levels of implant osseointegration. All the simulations considered a canal that is orthogonal to the implant axis. Results: Nerve pressure increased quickly when the implant–canal distance decreased in the range studied. Lack of the central implant to support the central abutment caused major increases in nerve pressure. Conclusions: This study suggests a minimal implant–canal distance of 1 mm to prevent inferior alveolar nerve damage caused by three connected implants. For clinical safety, an additional 0.5 mm is recommended as a cushion, so a 1.5‐mm minimal distance should be planned to avoid potential nerve injury.     

Evaluation of acoustic radiation force impulse imaging for determination of liver stiffness using transient elastography as a reference

AIM: To evaluate cut-off values and performance of acoustic radiation force impulse imaging (ARFI) using transient elastography [FibroScan^© (FS)] as a reference.METHODS: Six hundred and six patients were enrolled in this study. All patients underwent liver stiffness measurement with FS (FS-LS) and ARFI (with shear wave velocity quantification; ARFI-SWV) and the performance of ARFI in comparison to FS was determined. Sixty-eight patients underwent liver biopsy.RESULTS: Significantly higher success rates for the determination of liver stiffness were found using ARFI as compared to FS [604/606 (99.7%) vs 482/606 (79.5%), P < 0.001]. ARFI-SWV correlated significantly with FS-LS (r = 0.920, P < 0.001). ARFI-SWV increased significantly with the stage of fibrosis (1.09 ± 0.13 m/s for patients with no significant fibrosis (FS-LS < 7.6 kPa); 1.46 ± 0.27 m/s for patients with significant liver fibrosis (7.6 < FS-LS ≤ 13.0 kPa); and 2.55 ± 0.77 m/s for patients with liver cirrhosis (FS-LS > 13.0 kPa)). ARFI-SWV cut-off values were identified for no significant fibrosis (1.29 m/s; sensitivity 91.4% and specificity 92.6%) and for liver cirrhosis (1.60 m/s; sensitivity 92.3% and specificity 96.5%). The optimal cut-off value for predicting liver fibrosis (F ≥ 2) was 1.32 m/s (sensitivity 87.0% and specificity 80.0%) and for liver cirrhosis (F4) 1.62 m/s (sensitivity 100% and specificity 85.7%), for patients who underwent liver biopsy. An excellent inter-and intraobserver reproducibility was observed for ARFI-SWV determinations.CONCLUSION: An ARFI-SWV cut-off value of 1.29 m/s seems to be optimal for patients with no significant liver fibrosis and 1.60 m/s for patients with liver cirrhosis.     

Effects of low dose X‐ray irradiation on porcine articular cartilage explants

Ionizing radiation therapy is a crucial treatment for cancer, but can damage surrounding normal tissues. Damage to articular cartilage leading to arthropathy can occur at irradiated sites. It is unclear whether this response is due to damaging surrounding skeletal structures or direct effects on cartilage. In this study, we showed that irradiation with 2 Gy of X‐rays causes a significant reduction in the stiffness of porcine explants 1 week post‐irradiation. By using both microindentation and indentation‐type atomic force microscopy, ionizing radiation reduces stiffness in both the superficial zone, and throughout the entire thickness of the tissue. Young's modulus values were 75% and 60% lower in 2 Gy irradiated samples when compared with controls using microindentation and nanoindentation, respectively. Glycosaminoglycans (GAGs) released into the culture media of irradiated samples was nearly 100% greater at 24 h after exposure. While collagen content in the tissue is similar between groups, GAG content is 55% lower in irradiated explants compared with controls 7 days after exposure. Therefore, the irradiated explants are unable to recover from the initial loss of GAGs by 1 week. This acute loss of GAGs is a likely contributor to the reduction in modulus seen after exposure to ionizing radiation. © 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 31:1780–1785, 2013     

Displacement of the Hip Center of Rotation After Arthroplasty of Crowe III and IV Dysplasia: A Radiological and Biomechanical Study

To study the direction and biomechanical consequences of hip center of rotation (HCOR) migration in Crowe type III and VI hips after total hip arthroplasty, post-operative radiographs and CT scans of several unilaterally affected hips were evaluated. Using a three-dimensional model of the human hip, the HCOR was moved in all directions, and joint reaction force (JRF) and abductor muscle force (AMF) were calculated for single-leg stance configuration. Comparing to the normal side, HCOR had displaced medially and inferiorly by an average of 23.4% and 20.8%, respectively, of the normal femoral head diameter. Significant decreases in JRF (13%) and AMF (46.13%) were observed in a presumptive case with that amount of displacement. Isolated inferior displacement had a small, increasing effect on these forces. In Crowe type III and IV hips, the HCOR migrates inferiorly and medially after THA, resulting in a decrease in JRF, AMF, and abductor muscle contraction force.     

Masticatory performance in older subjects with varying degrees of tooth loss

Objectives

The purpose of this study was to establish the factors influencing the masticatory performance of older subjects with varying degrees of tooth loss and associated numbers of posterior occlusal contacts.

Methods

The subjects consisted of 1274 independently living people aged 60 years and over. Individuals with partially or fully edentulous arches without a denture replacement or those having any symptoms related to an oral problem were excluded from the study participants. Masticatory performance, maximal occlusal force and stimulated whole saliva were measured. Subjects were grouped into three categories by posterior occlusal contact, according to the Eichner Index. Group A had contacts in four support zones; group B had one to three zones of contact or contact in the anterior region only; and group C had no support zones at all, although a few teeth could still remain.

Results

The masticatory performance in groups B and C was found to be 81% and 50% of that of group A, respectively. The multiple linear regression analysis showed that in all the groups, occlusal force was significantly associated with masticatory performance. In groups A and B, the number of residual teeth was significantly associated with masticatory performance, whereas in group C, it had no significant relationship with masticatory performance. Salivary flow rate had a significant correlation with masticatory performance only in group C.

Conclusions

Declines in occlusal contact, occlusal force and salivary flow appear to be associated with reduction of masticatory performance in older adults. However, the crucial factors for masticatory performance varied, depending on the phase of occlusal collapse.     

Gender differences in maximum voluntary lip-closing force during lip pursing in healthy young adults

The objectives of this study were to quantitatively evaluate the gender differences in the lip-closing force (LCF) generated during pursing-like lip-closing movement using a multidirectional LCF measurement system in healthy young adults. In 40 healthy subjects (20 women, 20 men; median age = 26·5 years, range = 22-41 years), LCF was recorded in eight directions during the performance of a voluntary pursing-like lip-closing task in four measurement sessions. The correlations between the total sum of the forces generated in all eight directions [total LCF (TLCF)] and each directional LCF (DLCF) and those between opposing DLCF were statistically analysed. The TLCF obtained from the highly reproducible measurements acquired in the four different sessions was normally distributed in both genders. The TLCF in men was significantly greater than that in women. Among the eight pairs of opposing DLCF, seven pairs of opposing DLCF showed significant correlations in men, while five pairs were significantly correlated in women. In men, no significant difference was observed between opposing DLCF; however, three pairs of opposing DLCF were significantly different in women. The present results quantitatively indicate that there are gender differences in the magnitude and directional specificity of the LCF produced during pursing-like lip-closing movement in healthy young adults.