Correlations between incisor and condylar movements during lateral excursion in children with primary dentition

The purpose of this study was to look for associations between lower incisor movement and working and balancing condylar movement during lateral excursion in children with primary dentition and adults with permanent dentition. Mandibular movement was recorded using a TRI-MET (an optoelectronic analysis system with six degrees-of-freedom) at a sampling frequency of 100 Hz. The movement data was transferred to a graphics workstation for analysis. Subjects were categorized by age into two groups. The primary dentition group consisted of 19 children (mean age: 5 years and 5 months, s.d.: 8.7 months), and the permanent dentition group consisted of 22 women (mean age: 20 years and 5 months, s.d.: 26.3 months). The occlusion and TMJ in both groups were normal, with no history of orthodontic treatment. Three orthogonal excursive ranges and the 3D linear distance of the incisal and balancing and working condylar points, along with inter- and intra-individual correlations between the incisor and the balancing and working condyles during lateral excursion, were estimated by using multilevel statistical models. Lateral excursion in children with primary dentition was characterized by smaller incisor excursive ranges and 3D linear distance than in adults, and stronger inter- and intra-individual correlations between incisor and balancing condylar movements than in adults. In both children and adults the lateral excursion of the incisor was a good indicator of the extent of balancing condylar movement, but not working condylar movement.     

下颌骨与胫骨骨折愈合有机成份的免疫组化表达及对照研究

本研究选择８周龄Ｗｉｓｔａｒ白鼠４０只,造成下颌骨和胫骨人工骨折。通过软Ｘ线照像,组织学观察,免疫组化染色分析进行对比研究。结果显示两种骨骨各骨折愈合特征主要区别于原始骨痂形成阶段。下颌骨骨折是由内骨痂“膜内成骨”和外骨痂“软骨内成骨”共同修复。骨膜在骨愈合中起着重要作用。愈合过程中,Ⅰ型、Ⅱ型、Ⅲ型胶原免疫组化阳性反应高峰期分别为骨折后第２１天,７～２１天、第１４天;硫酸软骨素与硫酸角质素,硫酸软骨素Ａ和Ｃ的合成高峰期分别为第２１天,第１４～２１天。上述成分在软骨区内呈不均匀分布,强阳性细胞集中于增殖区和新成熟区。而且下颌骨反应强于胫骨一个判断级。波形蛋白和纤维连接蛋白在愈合７～２１天间呈持续中、强阳性反应,层粘蛋白仅在愈合早期骨膜增殖带和新生血管中有中度阳性反应。下颌骨与胫骨间对比差异不大。     

Effect of different filling materials in combination with intraradicular posts on the resistance to fracture of weakened roots

The preservation and restoration of severely weakened pulpless teeth is a difficult and relatively unpredictable procedure. This study evaluated the resistance to fracture of experimentally weakened bovine roots internally reconstructed with different filling materials in combination with prefabricated post compared with restored roots that were relatively intact. The roots of 75 mandibular bovine incisors with similar bulks were selected. Of these, 60 were internally prepared to standardized dimensions, thereby simulating weakness. All roots were filled with different restorative materials. The specimens were submitted to the fracture resistance testing with the application of a tangential compressive loading at an angle of 135 degrees in relation to the long axes of the roots. Results indicated statistically significant differences in relation to the root conditions. Weakened roots were less resistant to fracture than were controls. The roots restored with the resin cement demonstrated the lowest fracture resistance values, but statistically significant differences were observed only when compared with those restored by the resin-modified glass-ionomer cement. Resin-modified glass-ionomer cement, polyacid-modified resin composite and resin composite behaved similarly without statistically significant differences among them. None of the materials evaluated were capable of achieving the fracture resistance recorded for unweakened controls.     

纯钛锥状螺旋型种植体在下颌骨骨折中的应用

采用锥状螺旋型人工牙种植体时对10例下颌骨骨折患者进行了骨折内固定手术，固定骨折18处，植入牙种植体18枚，最小年龄16岁，最大年龄56岁。术后经过3—12个月随访，病例全部成功，骨折愈合良好，咬合关系恢复正常，术区无不良反应，作者讨论了固定手术方法。     

下颌骨骨折动力加压固定断面应力分析

实验采用反射光弹模拟应力分析法,通过受力模型等差线条纹图观测、分析、量化换算,对下颌骨骨折轴向和偏心动力加压固定作断面压应力比较研究.结果显示两种固定状态下骨折断面均表现为挤压应力,沿骨折线应力分布不均匀,板周区和牙槽区呈压应力高峰带,最大应力分量在轴向和偏心加压分别为1.8MPa和2.3MPa(板周区),以及0.5MPa和1.0MPa(牙槽区),中间区受力较弱.轴向动力加压总压力为100N,偏心动力加压总压力为140N,后者比前者断面应力分布稍趋合理.     

Langerhans cell disease associated with pathological fracture of the mandible

A 27-year-old male suffered a fractured mandible following extraction of a tooth. It was subsequently found that the fracture occurred in an area pathologically weakened by a localized lesion of Langerhans cell disease. Since lesions of the jaws may be seen either as the first manifestation or as a complication of widespread Langerhans cell disease, the dentist has a major role in the diagnosis and management of such cases.     

预防性选磨防止后牙牙折临床观察

目的 探讨预防性选磨对防止后牙牙折发生的作用。方法 对临床30例牙齿磨耗不均患者的227颗后牙进行预防性选磨，经过为期6、12、18个月的随访，对选磨后牙折发生的状况进行跟踪观察。结果 选磨的227颗牙在随访期内均未出现牙折。结论 初步观察表明预防性选磨对防止牙折发生具有一定的作用。     

Can poly(acrylic) acid molecular weight mixtures improve the compressive fracture strength and elastic modulus of a glass-ionomer restorative?

Objectives

To optimize the compressive fracture strength (σ) and elastic modulus (E) of a glass-ionomer (GI) restorative using poly(acrylic) acid (PAA) weight average molecular weight (M_w) mixtures.

Methods

174 PAA solutions were prepared (four control PAA M_ws at three PAA concentrations (25, 35 and 45%) (n = 12) and six M_w mixtures (Groups A-F at nine blend ratios and three PAA concentrations (n = 162))). The viscosity (η) of each PAA solution was determined using a digital viscometer. The PAA solutions were hand-mixed with a commercial GI restorative powder (Ionofil Molar; Voco, Cuxhaven, Germany) and σ and E were determined using cylindrical (6 mm height, 4 mm diameter) specimens (n = 20) at 24 h. Data were analyzed using analyses of variance (ANOVA) (three-, two- and one-way) and regression analyses at p < 0.05.

Results

The three- and two-way ANOVAs highlighted significant effects of M_w mixture, blend ratio and PAA concentration (all p < 0.0001) on the η, σ and E data. Regression analyses showed significant increases in η, σ and E (p < 0.0001) with increasing M_w from Groups A to F. There was no significant effect of blend ratio on the σ data for Groups A (p = 0.178), D (p = 0.747) and F (p = 0.107) and on the E data (p > 0.083).

Significance

The current approach to improving the mechanical properties of GI restoratives using PAA M_w mixtures is encouraging, however, further manipulation of the GI restorative system by optimizing PAA M_w mixtures, blend ratios and PAA concentrations is required to elicit further improvements in σ and E without impacting upon the η of the PAA solution.     

Mandibular condyle movement during mastication of foods

This study evaluated the mandibular condyle displacement on the working side while masticating certain foods with different textures. For referencing the mandibular condyle movement, the range of voluntary border movement of the mandibular condyle was determined based on the analysis of the sagittal, left lateral and right lateral border motion using Posselt's figure. The test foods consisted of cheese, peanuts, and beef jerky. During mastication of cheese and peanuts, the amount of displacement of the mandibular condyle in all directions was within the range of border movement. Significant posterior and superior shifts of the mandibular condyle were observed during mastication of beef jerky, compared with the findings obtained during border movement. Accordingly, it is suggested that prolonged mastication of hard fibrous foods, may stimulate the temporomandibular joint structure and mandibular dysfunction patients should limit their intake of such foods.     

Fracture reasons in ceramic-fused-to-metal restorations

Ceramic-fused-to-metal restorations are widely used in dentistry with a high degree of general success. Fracture of the ceramic veneers as a result of oral function or trauma is not an uncommon problem in clinical practice. Although fractures of such restorations do not necessarily mean the failure of the restoration, the renewal process is both costly and time consuming and therefore remains a clinical problem. Fractures in the anterior region pose an aesthetic problem but when they are in the posterior, chewing function could also be affected. The published literature reveals that reasons for failures cover a wide spectrum from iatrogenic factors to laboratory mistakes or because of factors related to the inherent structure of the ceramics or simply to trauma.