On the interfacial fracture of porcelain/zirconia and graded zirconia dental structures

Porcelain fused to zirconia (PFZ) restorations are widely used in prosthetic dentistry. However, their susceptibility to fracture remains a practical problem. The failure of PFZ prostheses often involves crack initiation and growth in the porcelain, which may be followed by fracture along the porcelain/zirconia (P/Z) interface. In this work, we characterized the process of fracture in two PFZ systems, as well as a newly developed graded glass-zirconia structure with emphases placed on resistance to interfacial cracking. Thin porcelain layers were fused onto Y-TZP plates with or without the presence of a glass binder. The specimens were loaded in a four-point-bending fixture with the thin porcelain veneer in tension, simulating the lower portion of the connectors and marginal areas of a fixed dental prosthesis (FDP) during occlusal loading. The evolution of damage was observed by a video camera. The fracture was characterized by unstable growth of cracks perpendicular to the P/Z interface (channel cracks) in the porcelain layer, which was followed by stable cracking along the P/Z interface. The interfacial fracture energy G_C was determined by a finite-element analysis taking into account stress-shielding effects due to the presence of adjacent channel cracks. The resulting G_C was considerably less than commonly reported values for similar systems. Fracture in the graded Y-TZP samples occurred via a single channel crack at a much greater stress than for PFZ. No delamination between the residual glass layer and graded zirconia occurred in any of the tests. Combined with its enhanced resistance to edge chipping and good esthetic quality, graded Y-TZP emerges as a viable material concept for dental restorations.     

单节段内固定术治疗胸腰椎骨折的手术方法与临床疗效分析

目的 研究单节段内固定术治疗胸腰椎骨折的手术方法与临床疗效.方法 将90例胸腰椎骨折患者按随机数字表法分为观察组（单节段内固定术）和对照组（双节段内固定术）,每组45例,比较两组手术情况、术后疼痛程度、矫正情况、伤椎相邻椎关节病变情况等.结果 观察组手术时间、出血量、切口长度、术后疼痛发生率、上节段和下节段间盘退变发生率明显少于对照组[（107.93±2.75） min比（132.68±2.81） min、（198.44±9.17）ml比（314.18±8.73）ml、（8.36±1.15）cm比（12.33±1.08） cm、8.89％（4/45）比26.67％（12/45）、6.67％（3/45）比22.22％（10/45）和4.44％（2/45）比20.00％（9/45）],差异有统计学意义（P＜0.01）.两组矫正情况比较差异无统计学意义（P＞0.05）.结论 在症状适宜的情况下,单节段内固定术治疗胸腰椎骨折效果突出,术后患者恢复状况好,术后并发症少,远期不良影响轻微,建议在临床中推广应用.     

Inferior alveolar and mental nerve injuries associated with open reduction and internal fixation of mandibular fractures: A Seven Year retrospective study

PurposeTo document adverse neurosensory changes in the inferior alveolar nerve (IAN) and mental nerve (MN) after surgical mandibular fracture treatment and to identify risk factors associated with these changes.Materials and methodsA retrospective study of patients surgically treated for mandibular fractures. The primary study variable was the postoperative change in IAN/MN neurosensory examination after fracture fixation. Risk factors were categorized as demographic, anatomic, experience of the operator, fracture displacement and number of miniplates placed at each fracture site. Appropriate statistics were computed.Results209 patients with 293 fractures were analysed. One hundred twenty fractures (41%) were located between the lingula and mental foramen, and 173 fractures (59%) were located distal to the mental foramen. Two hundred seventeen (41%) were displaced by 5 mm or more. In 38 fractures (13%), the IAN/MN neurosensory status worsened after treatment. In a multivariate model, fracture displacement, operator inexperience and two plate fixation were associated with a statistically significant risk (P ≤ 0.05) for postoperative deterioration of IAN/MN sensation.ConclusionFixation with two miniplates, fracture displacement of 5 mm or more and operator inexperience were associated with an increased risk for deterioration of the IAN/MN neurosensory status after treatment of mandibular fractures.     

(iii) Cervical spine trauma

Cervical spine trauma frequently accompanies major trauma, and its presence should be assumed until proved otherwise. It is important to recognize whether an injury is stable or not, and if there is instability then stabilization should be achieved either by nonoperative or operative means. This article considers the injury patterns seen in the cervical spine and how these should be evaluated and managed.     

老年髋部骨折患者家庭照顾者照顾负荷的研究进展

髋部骨折通常是指股骨颈及股骨转子间骨折，它的病残率和致死率高，严重威胁老年人的生命及生存质量。相关研究报道显示：老年髋部骨折患者术后3个月是患者功能锻炼和肢体功能恢复的最佳时间。在我国，家庭照顾者是老年髋部骨折患者的主要照顾力量，而由于人口老龄化的问题和核心家庭比例的增加，家庭照顾问题和照顾者负荷显得愈加严重。     

The mandibular symphysis as a starting point for the occlusal-level reconstruction of panfacial fractures with bicondylar fractures and interruption of the maxillary and mandibular arches: Report of two cases

Panfacial fractures represent a challenge, even for experienced maxillofacial surgeons, because all references for reconstructing the facial skeleton are missing. Logical reconstructive sequencing based on a clear understanding of the correlation between projection and the widths and lengths of facial subunits should enable the surgeon to achieve correct realignment of the bony framework of the face and to prevent late deformity and functional impairment. Reconstruction is particularly challenging in patients presenting with concomitant fractures at the Le Fort I level and affecting the palate, condyles, and mandibular symphysis. In cases without bony loss and sufficient dentition, we believe that accurate fixation of the mandibular symphysis can represent the starting point of a reconstructive sequence that allows successful reconstruction at the Le Fort I level. Two patients were treated in our department by reconstruction starting in the occlusal area through repair of the mandibular symphysis. Both patients considered the postoperative facial shape and profile to be satisfactory and comparable to the pre-injury situation.     

Sliding contact fracture of dental ceramics: Principles and validation

Ceramic prostheses are subject to sliding contact under normal and tangential loads. Accurate prediction of the onset of fracture at two contacting surfaces holds the key to greater long-term performance of these prostheses. In this study, building on stress analysis of Hertzian contact and considering fracture criteria for linear elastic materials, a constitutive fracture mechanics relation was developed to incorporate the critical fracture load with the contact geometry, coefficient of friction and material fracture toughness. Critical loads necessary to cause fracture under a sliding indenter were calculated from the constitutive equation, and compared with the loads predicted from elastic stress analysis in conjunction with measured critical load for frictionless normal contact—a semi-empirical approach. The major predictions of the models were calibrated with experimentally determined critical loads of current and future dental ceramics after contact with a rigid spherical slider. Experimental results conform with the trends predicted by the models.