Probing nano-scale adhesion force between AFM and acid demineralized intertubular dentin: Moist versus dry dentin

Objective

The aim of this study was to investigate the effect of dentin dryness on the variation in the probed nano-scale adhesion force between an AFM silicon nitride tip and demineralized intertubular dentin collagen fibrils network surface.

Methods

Dentin specimens were etched with 37% phosphoric acid for 15 s and then divided into three groups. Specimens of the first two groups were air-dried for 5 or 10 s (DH5s and DH10s), respectively, whereas specimens of the third group were left in the hydrated condition (H). For each group, Force curves were characterized by contact-mode AFM and the adhesion force (Fad) was calculated. The structure of the demineralized collagen fibrils network was characterized by tapping mode AFM. The tensile bond strength (TBS) to dentin was evaluated using one alcohol-based dentin self-priming adhesive. The dentin/resin interface was investigated by SEM.

Results

Dentin specimens in the wet-hydrated condition (H) showed significantly higher adhesion force and TBS values than dry-dehydrated specimens (DH5s and DH10s). AFM images showed open collagen fibrils network structure in wet-hydrated specimens (H), while the dry-dehydrated specimens (DH5s and DH10s) showed a collapsed appearance to varying degrees. SEM images revealed minimum resin infiltration in dry-dehydrated specimens.

Significance

The nano-scale adhesion force between the AFM probe and demineralized intertubular dentin surface was shown to be sensitive to surface air-drying. The decrease in the nano-scale adhesion force with the increase in the time of air-dryness is related to dehydration of the demineralized collagen fibrils network surface.     

楔状缺损与咬合力关系的研究

目的 临床研究楔状缺损与He力的关系。方法 将123例患不同程度楔状缺损的中老年患者，按楔状缺损的程度分为无、轻、中、重度4组；使用电阻应变式咬合力计测量上颌尖牙、第一、二双尖牙、第一磨牙牙齿咬合力；用光He法测定上颌牙齿最高He接触强度。结果 楔状缺损患牙的咬合力低于无楔状缺损牙。上颌第一双尖牙的楔状缺损患牙的最高He接触强度高于未患牙、楔状缺损组中的第一磨牙和第一双澡牙相对于其邻牙的最高He接触强度增高。结论 He力与楔状缺损的发生有关。     

楔状缺损深度与合面磨损指数的Spearman等级相关分析

目的　探讨楔状缺损与牙合面磨损发病率的相关性及二者程度的相关性 ;分析二者在发生和加重方面的共同因素。方法　随机选取口腔内科就诊的患者 393例 ,调查活髓双尖牙 ,记录年龄、性别、刷牙习惯、咀嚼习惯、疲劳微裂、楔状缺损深度 (mm)与磨损指数 (TWI) ,进行统计学分析。结果　楔状缺损与牙合面磨损的发病率具有相关性 ,楔状缺损深度与牙合面磨损指数在一定范围内呈正相关 ,等级相关系数有极显著性意义。楔状缺损与磨损同时发生的患者中 ,喜用力刷牙并长期使用横刷法的占 74 % ;喜爱咀嚼耐磨食物或硬物的占 6 7% ;疲劳微裂发生率为 95 % ;男性发病率与病损程度均高于女性 ;随年龄增加 ,楔状缺损与磨损的发病率与程度均有所增加。结论　牙合力与机械摩擦是二者发生的共同因素。时间因素 ,机械摩擦与牙合力积累是二者共同的加重因素     

牙周炎患者的合力,肌功能及下颌运动轨迹描记

本研究对４０例牙周炎患者的合力、咀嚼肌肌电和下颌运动轨迹作了检查，结果表明，患者的超、覆合值异常且个体差异很大，但ＩＣＰ后移者仅２例。下颌从肌位到牙位发生偏斜者少，这与牙齿的松动有关，ＭＫＧ显示合间隙＜１ｍｍ者２０例。下颌姿势位肌电值明显升高。表明牙周炎患者的咀嚼肌处于较紧张状态。最大紧咬肌电值及平均每牙合力值明显减小，这与牙周组织的炎性破坏密切相关。     

高性能固定矫治用磁体与橡皮圈组合力的评价

目的:分析与托槽大小相近的高性能固定矫治用磁体与橡皮圈形成的组合力的稳定性及有效工作距离。方法:将形状及体积与托槽相近的N48型钕铁硼,分别与1/8、3/16、1/4、3/8inch正畸弹力橡皮圈组合成超长距离移动牙齿的组合力,使用万能材料实验机对磁体磁力、橡皮圈弹力和组合力进行测试,并绘制力的变化曲线,分析组合力的特征、磁力与橡皮圈弹力的互补作用、不同拉伸距离的组合力中磁力及弹力的构成比,对组合力与橡皮圈弹力的差异进行t检验。结果:随着拉伸间距的加大,磁体磁力急剧下降,而橡皮圈弹力呈线性增大,组合后力的变化较为平缓,力较为恒定,4种组合力分别达到86、138、163、192g超长工作距离(1.25～20mm)稳恒矫治力。拉伸距离为3mm时,磁力占各组合力的百分比范围是34.94%～93.98%。拉伸距离为6mm时,占组合力的12.60%～37.89%。拉伸距离为12mm时,磁力降到仅占组合力的2.69%～5.98%。统计结果显示,拉伸距离为3mm(P<0.01)、6mm(P<0.01)、9mm(P<0.05)时,4种组合力与单独的橡皮圈弹力的差异有显著性。结论:磁体与橡皮圈形成的组合力是一种新型、理想、超长工作距离的稳恒矫治力。     

In vitro retention force changes of prefabricated attachments for overdentures

Changes in the retention force of six prefabricated spherical and cylindrical attachments were examined in vitro under continuous loading. The testing machine permitted insertion-separation cycles to be tested under reproducible conditions while a calibrated measuring device determined the insertion and retention forces. At the beginning, during the so-called run-in period, all anchoring elements showed a very unstable behaviour characterized by a varying marked increase and subsequent decrease in the retention force. During the ensuing functional period, the retention force followed a more stable course. In this phase, the frictional attachments having lamellae for activation proved more stable than did the spring-loaded retention attachments. Furthermore, in two of five cylindrical anchors by Gerber, the spring broke. This provides support to the concept that prefabricated attachments should be constructed as robust elements composed of as few individual parts as possible. This would help to ensure that service and repairs remain at a minimum. Frictional attachments with lamellae for activation are to be preferred for use in matrices and patrices over attachments having spring-loaded retention.     

Attachment systems for implant overdenture: influence of implant inclination on retentive and lateral forces

Objective: To evaluate the retentive force and lateral force of an implant with various types of attachments for overdentures in relation to implant inclination. Material and methods: An implant (3.75 × 13 mm) was embedded into an acrylic resin block, simulating the edentulous ridge. Four different attachment systems were used, including: (1) Locator black and blue, (2) a ball attachment, (3) a flat‐type magnetic attachment and (4) a self‐adjusting magnetic attachment, which has vertical and rotational movement. All of the attachments were under a constant dislodging force with an angle of the implant at 0°, 15°, 30° and 45°, and the experiments were repeated 10 times using a universal testing machine to measure the retentive force. The lateral force to the implant was measured by strain gauges attached on the implant surface. Statistical analysis was performed by multiple comparisons with Bonferroni's correction. P<0.05 was considered statistically significant. Results: At 0°, the significantly highest retentive force was observed in the Locator blue, followed by the Locator black, ball, flat‐type and self‐adjusting magnetic attachments. The Locator blue and ball attachment maintained the retentive force until a 30° inclination; however, the lateral force increased significantly, especially with the ball attachment. The retentive force of the magnetic attachment was significantly lower at 0°, as well as the lateral force in the self‐adjusting magnetic attachment. Conclusion: Within the limitations of this study, we conclude that the retentive force decreases with an increase in implant inclination, whereas the lateral force increases, except for in magnetic attachments. To cite this article:
Yang T‐C, Maeda Y, Gonda T, Kotecha S. Attachment systems for implant overdenture: influence of implant inclination on retentive and lateral forces.
Clin. Oral Impl. Res. 22 , 2011; 1315–1319.
doi: 10.1111/j.1600‐0501.2010.02137.x     

微机化多功能力仪的研制及应用

介绍具有多功能、多通道及多参数测试特点的微机化力测试仪的研制方法，并用其进行了无牙颌患者戴全口义齿后咀嚼不同食物时的咀嚼力测试研究。测试表明，仪器性能稳定，灵敏度高，重复性好，数据可靠，测试结果满意     

颞下颌关节髁突软骨的三维微观区域形貌及其纳米弹性性能

目的:探讨颞下颌关节(temporomandibular joint,TMJ)髁突纤维软骨在纳米量级的区域形貌及其材料性能分布的特点。方法:采用原子力显微镜(atomic force microscope,AFM)及纳(诺)压痕测量法,对9只6周龄正常新西兰白兔双侧TMJ的18侧下颌髁突软骨不同区域的三维微观形貌及其纳米弹性模量进行测量和分析。结果:兔下颌髁突关节软骨的不同区域具有明显不同的三维微观形貌和弹性材料性能。髁突前部和内侧表现出更显著的三维微观形貌特征。正常TMJ左、右侧髁突软骨相对应各区域具有相同的弹性模量,髁突不同部位软骨的弹性模量〔前内侧:(2.83±0.33)MPa,前外侧:(1.68±0.15)MPa,后内侧:(1.17±0.08)MPa,后外侧:(0.91±0.06)MPa〕则存在明显差异(P<0.01)。结论:正常TMJ左、右侧髁突软骨的材料力学性能对称一致。在咀嚼过程中,具有最大弹性模量的髁突前内侧软骨可能在TMJ中承担最大的压力,为关节的功能承载区。TMJ髁突软骨表面的三维微观区域形貌和纳米弹性性能的不同或许反映了关节的不同功能需要。     

Residency Training in Dental Public Health: Assessment of Status, Needs, and Issues

The opportunities for public health training have declined over the years while the need for public health skills is likely to increase. This paper reports the results of a project, sponsored by the Health Resources and Services Administration, which answers the question of "how best to invest in the dental public health education system so as to fulfill the profession's responsibilities to protect and improve the oral health of individuals and society.' An information base on dental public health education, practice, and specialization was developed from an extensive review of the literature and a survey of dentists concerning employment and practice requirements for public health dentists. An advisory group considered this information, met to discuss the issues involved in dental public health training, and provided advice to the project staff. Based on the information gathered as part of the project, recommendations were made to: (1) develop a grant program to support advanced education in dental public health; (2) increase the competencies of dentists who are working in public health positions and not eligible for board certification via off-site residencies; (3) develop model programs in areas of great need, such as general public health, management, policy, prevention, environmental health and research, that in conjunction with a basic public health core, could satisfy the eligibility requirements of the American Board of Dental Public Health; (4) develop student loan forgiveness programs for dentists and dental hygienists working in public health; and (5) develop additional credential recognition programs for dental public health workers.