Long-term clinical evaluation of 211 two-unit cantilevered resin-bonded fixed partial dentures

Objectives

This retrospective study aims to evaluate the long term clinical performance of two-unit cantilevered resin-bonded fixed partial dentures (RBFPDs) relating to their retention, success and survival rate.

Materials and methods

Prostheses that were placed at least four years previously were clinically reviewed to evaluate retention, success and survival rate. Additional information was also collected, including patient's gender, age and satisfaction on their prosthesis, operator's experience, prosthesis service life, root canal therapy if performed, abutment mobility, bone support, the presence of shim-stock contacts on the abutment or pontic in intercuspal position, and the presence of proximal axial contacts adjacent to the prosthesis. The date of any debonding with subsequent treatment was also recorded.

Results

A total of 211 two-unit RBFPDs were placed in 153 patients, with a mean service life of 113.2 ± 33.5 months. Twenty-eight prostheses debonded, resulting in a retention rate of 86.7 percent, and another five teeth were extracted with the prostheses, resulting in a success rate of 84.4 percent. 90.0 percent prostheses were functioning (survival rate) by means of rebonding at the time of review. The location of the replaced tooth had a significant effect on the retention of RBFPDs with posterior RBFPDs lower than anterior (p = 0.020). Kaplan–Meier analysis revealed 5-, 10- and 15-year cumulative probability of surviving was 0.97, 0.91 and 0.84, respectively.

Conclusions

211 two-unit RBFPDs were observed to have a success, retention and survival rate of 84.4, 86.7 and 90.0 percent, respectively, with a mean service life of 9.4 years.

Clinical Significance

Based on the clinical results, two-unit RBFPD are shown to be a durable prosthesis over the long term with high patient satisfaction. The posterior prostheses, particularly in the lower arch appeared to have a higher failure rate, and improved design features should be considered.     

Initial bridges between two ribosomal subunits are formed within 9.4 milliseconds,as studied by time-resolved cryo-EM

Association of the two ribosomal subunits during the process of translation initiation is a crucial step of protein synthesis. The two subunits (30S and 50S) of the bacterial 70S ribosome are held together by 12 dynamic bridges involving RNA–RNA, RNA–protein, and protein–protein interactions. The process of bridge formation, such as whether all these bridges are formed simultaneously or in a sequential order, is poorly understood. To understand such processes, we have developed and implemented a class of microfluidic devices that mix two components to completion within 0.4 ms and spray the mixture in the form of microdroplets onto an electron microscopy grid, yielding a minimum reaction time of 9.4 ms before cryofixation. Using these devices, we have obtained cryo-EM data corresponding to reaction times of 9.4 and 43 ms and have determined 3D structures of ribosomal subunit association intermediates. Molecular analyses of the cryo-EM maps reveal that eight intersubunit bridges (bridges B1a, B1b, B2a, B2b, B3, B7a, B7b, and B8) form within 9.4 ms, whereas the remaining four bridges (bridges B2c, B4, B5, and B6) take longer than 43 ms to form, suggesting that bridges are formed in a stepwise fashion. Our approach can be used to characterize sequences of various dynamic functional events on complex macromolecular assemblies such as ribosomes.The ribosome is the site of protein synthesis in the cell. It is a highly complex ribonucleoprotein machine consisting of a small and a large subunit. In prokaryotes, the small (30S) subunit consists of a 16S ribosomal RNA (rRNA, 1,542 nt) and 21 ribosomal proteins (numbered S1–S21), whereas the large (50S) subunit comprises two rRNA molecules (23S [2,904 nt] and 5S [120 nt]) and 32 ribosomal proteins (numbered L1–L34 with gaps). The two ribosomal subunits associate at the final stage of the initiation step of protein synthesis, facilitated by three initiation factors (IF1, IF2, and IF3), to yield the 70S ribosome (molecular weight ∼2.5 MDa). The two subunits are joined by 12 canonical intersubunit bridges, which are formed between rRNA and rRNA, rRNA and protein, or protein and protein components (1). The kinetics of ribosomal subunit association has been a subject of great interest for the last several decades (2); however, there have been few published reports on the kinetics of specific structural elements during this process (3, 4). Time-resolved structural studies to capture subunit assembly intermediates on the order of seconds or minutes have been recently reported (5, 6). The goals of the present study are to capture structures of the association intermediates of the two ribosomal subunits on a millisecond timescale, to understand the process of subunit association, and to lay the groundwork for generalization of this technique to a wide variety of macromolecular systems.The challenge of time-resolved cryo-EM is to rapidly mix reactants and then deposit them in a thin film of solvent within a short time before flash freezing the EM grid in liquid ethane. We have found that spraying the mixture with an air atomizer can produce a thin enough aqueous film if the carbon film is freshly made and plasma-cleaned before plunging (7). The mixing, reacting, and spraying steps were accomplished by means of a monolithic, microfabricated silicon device that incorporated a mixer, incubation channel, and pneumatic sprayer in a single chip. At the flow rate used here of 3 μL/s per reactant, mixing was estimated to be complete within 0.4 ms (8). This mixer-sprayer was incorporated into a computer-controlled plunging apparatus (9). In the current configuration of the device, the mixed reactants spend 4 ms in the outlet channel, 0.4 ms in flight from the nozzle to the grid, and 5 ms on the grid while plunged into the cryogen, for a minimum reaction time of 9.4 ms. Longer reaction times are achieved by use of a meandering path between the point of initial mixing and the nozzle. 3D reconstructions, obtained from the cryo-EM data collected from the ribosomal subunit association experiments, show missing densities for specific intersubunit bridges, suggesting that the intersubunit bridges are formed in a sequential order.     

Myocardial bridges in man: Clinical correlations and angiographic accentuation with nitroglycerin

Little is known of the clinical significance of myocardial bridges, which may be recognized angiographically as systolic coronary artery narrowing (SCAN). A retrospective review of a 1 year's experience (313 consecutive coronary arteriograms) revealed 5 patients with SCAN, an incidence of 1.6%. SCAN involved the proximal and/or middle segments of the left anterior descending coronary artery in all patients. It is of particular note that the administration of nitroglycerin noticeably accentuated the SCAN phenomenon in each of 3 patients to whom it was administered. Four of the 5 patients had left ventricular hypertrophy due to hypertrophic car-diomyopathy (2), aortic stenosis (1), and hypertension (1). All 5 patients with the SCAN phenomenon had anginal chest pains, and critical obstructive coronary atherosclerosis was observed in only 2 cases. The other 3 patients showed, otherwise, normal coronary arteriograms. Thus, myocardial bridges appear to be angiographically manifest predominantly in patients with cardiac hypertrophy. Nitroglycerin, which accentuates SCAN, might be useful as a provocative test to enhance the angiographic recognition of this phenomenon. The possible role of myocardial bridges in the production of myocardial ischemia warrants further investigation.     

神经桥接材料与周围神经修复

周围神经损伤的长段缺损需要神经移植修复。自体神经移植一直被认为是桥接周围神经缺损最好的方法，但其来源有限，且存在供区并发症。 最近研究表明，神经移植可以通过不同的桥接材料来完成。这些周围神经桥接体，作为一种调节和改变神经再生的细胞和分子环境的载体，对周围神经损伤的修复有不同影响。     

Facilitated Cement Removal Technique Between Splinted Crowns

A technique for facilitating cement removal between splinted crowns is described. The technique involves tying dental floss with the large-diameter yarn portion around the embrasure of the splinted crown before cementing, and pulling it through before the cement has reached a final set. This simple, quick technique achieves removal of cement without damage to the interproximal crown surface.     

Comparing Rubber Bearings and Eradi-Quake System for Seismic Isolation of Bridges

Seismic isolation systems have been used worldwide in bridge structures to reduce vibration and avoid collapse. The seismic isolator, damper, and Shock Transmission Unit (SUT) are generally adopted in the seismic design of bridges to improve their seismic safety with economic efficiency. There are several seismic isolation systems, such as Natural Rubber Bearing (NRB), Lead Rubber Bearing (LRB), and the Eradi-Quake System (EQS). EQS as a new technology is expected to effectively reduce both seismic force and displacement, but there is still some need to verify whether it might provide an economical and practical strategy for a bridge isolation system. Moreover, it is important to guarantee consistent performance of the isolators by quality control. A comparative evaluation of the basic properties of the available seismic isolators is thus necessary to achieve a balance between cost-effectiveness and the desired performance of the bridge subjected to extreme loading. Accordingly, in this study, the seismic response characteristics of the seismic isolation systems for bridges were investigated by conducting compressive test and compressive-shear test on NRB, LRB, and EQS.     

心肌桥和壁冠状动脉的多层螺旋CT诊断及其临床意义

目的探讨心肌桥-壁冠状动脉(MB-MCA)的多层螺旋CT(MSCT)诊断和与冠脉硬化的关系。方法应用64层螺旋CT对可疑冠心病(CHD)者,行冠状动脉血管成像(CTA),3名CT诊断医师独立判断MB-MCA的存在,结果一致时确定为MB-MCA。测量壁冠状动脉(MCA)长度、肌桥(MB)厚度,结果用平均数±标准差表示,记录MB-MCA近、远段血管形态变化。根据这三项指标,提出载MB-MCA冠脉积分计算方法。确定载MB-MCA冠脉硬化情况,应用秩和统计分析,判断血管硬化与MB-MCA的关系。结果900例可疑CHD者,冠脉CTA发现MB-MCA167例(18.56%,167/900),180处。MB-MCA位于左前降支者占92.78%(167/180)。MSCT显示MCA可被心肌完全包绕(36.11%,65/180)或不完全包绕(63.89%,115/180)。MCA长度为18.7mm±10.2mm。MB厚度为1.7mm±1.2mm。70%的MCA前段和/或远段邻近血管走行迂曲成角。载MB-MCA冠脉积分评分方法MCA长度<10mm、MB不全包绕血管、邻近血管平滑,每项1分;MCA长度10~20mm、MB<1mm、邻近血管一侧成角,每项2分;MCA程度>20mm、MB>1mm、邻近血管近、远段两侧成角,每项3分。167例中,88例可见冠状动脉硬化征象(52.69%),统计学结果提示载MB-MCA冠脉硬化与MB-MCA形态积分无明显相关(u=1.234,P>0.05)。结论64层螺旋CT可用于判断MB-MCA和载MB-MCA冠脉的结构特征;临床怀疑CHD者MB-MCA检出率为18.56%;载MB-MCA冠脉硬化与MB-MCA形态积分无明显相关。     

A retrospective clinical evaluation of resin-bonded bridges inserted at the Adelaide Dental Hospital

The clinical performance of resin-bonded Rochette and Maryland bridges inserted by various operators at the Adelaide Dental Hospital is reported. Thirty-four Rochette bridges (30 anterior, 4 posterior) and 228 Maryland bridges (150 anterior, 78 posterior) were assessed. Clinical data were compiled on types of bridge failure, factors influencing bridge retention, and the effects of the prostheses on abutment teeth and supporting tissues. The failure rate for Rochette bridges over 6 years was 75 per cent with a median survival of 2.14 years. Debonding occurred in 70 per cent of bridge failures. The failure rate for Maryland bridges over 5 years was 42 per cent with a median survival of 2.60 years. Pontic fracture (29 per cent) and debonding (20 per cent) were the main failures observed. Porcelain pontics performed significantly better than the processed hybrid resin pontics (P<0.01). The main reasons for debonding included occlusal stresses, non-retentive bridge designs and resin cement failure. A life-table analysis showed no significant difference in the overall cumulative survival rates between Rochette and Maryland bridges. Bridge design and the choice of pontic material and resin cement emerged as significant factors influencing the success rate of the bridges examined.     

Intercellular bridges between megalospermatocytes in the human testis

The occurrence of intercellular bridges connecting megalospermatocytes in the human testis has been documented by means of light and electron microscopy. Thereby, the clonal character of this special form of male germ cell degeneration has been substantiated. In the course of the cellular degeneration, the intercellular bridges themselves enter a degenerative process. This process, involving the invagination and subsequent internalization of the bridge into the cytoplasm of one of the megalospermatocytes concerned, finally leads to disconnection of the cells and thus to the termination of the former clonal condition. Several clones of megalospermatocytes include additional cells which, while being bridge-connected to typical megalospermatocytes, exhibit a considerably different but likewise degenerative morphology. The cause of this occasionally occurring intraclonal heterogeneity of the megalospermatocyte morphology is discussed.     

Formation of cytotoxic transthyretin is not dependent on inter-molecular disulphide bridges commonly found within the amyloid form

Familial amyloidotic polyneuropathy (FAP) is linked to destabilising point mutations in the human plasma protein transthyretin (TTR). Consistent with similar amyloid disorders, low molecular weight TTR oligomers have been shown to exert the major cytotoxic effect. The amyloid structure of TTR contains non-native inter-molecular disulphide linkages via the cysteine at position 10 (Cys10). Moreover, substitution of Cys10 in a mouse model for TTR-amyloidosis abolishes TTR deposits, indicating an important role of Cys10 in FAP pathogenesis. However, the role of disulphide bridges in TTR cytotoxicity has not been elucidated. By probing Cys10Ser TTR variants to the human neuroblastoma SH-SY5Y cell line, we have addressed this question, and our results clearly show that formation of an inter-molecular disulphide bridge is not a pre-requisite for TTR cytotoxicity. This finding suggests that prevention of inter-molecular TTR disulphide bridges as a therapeutic intervention will not impair the cytotoxic potential of TTR.