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.     

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.     

Root fracture in immature anterior teeth followed for 15 years

Abstract –  We report a case of injury to an immature tooth, observed over a period of 15 years. In 1987, a 9-year-old boy fell down in a schoolyard. The right central incisor demonstrated palato-version and radiographic observations revealed that the roots of both central incisors were incomplete. Further, a root fracture in the apical region of the central incisors was observed. During the first treatment visit, the right central incisor was repositioned and both teeth splinted. After confirming that the line of fracture was aligned, the fixation was continued for 2 months. The teeth were examined periodically for the next 15 years. Both teeth had favorable outcomes with continued root development of both the apical and coronal segments with good apposition of the fracture lines.     

Chronic osteomyelitis: 20 years after mandible fracture

Abstract  – Chronic osteomyelitis is a persistent abscess of the bone that is characterized by the usual complex of inflammatory processes, including necrosis of mineralized and marrow tissues, suppuration, resorption, sclerosis, and hyperplasia. The purpose of this paper is to report a case of chronic osteomyelitis seen 20 years after mandible fracture.     

正畸钢丝冠内固定治疗磨牙纵折的应用

目的:改进磨牙纵折保留治疗的固定方法.方法:对56颗磨牙纵折采用正畸钢丝冠内固定、牙体牙髓治疗加全冠修复的综合治疗,保留患牙.结果:56颗磨牙纵折成功49颗,失败7颗,有效率为87.5%.结论:在磨牙纵折的保留治疗中,正畸钢丝冠内固定是一种较佳的固定方法.     

In vivo fractures of endodontically treated posterior teeth restored with amalgam

Abstract The cumulative survival rate (retention of both cusps) and the fracture pattern of 1639 endodontically treated posterior teeth were assessed in a retrospective study. All teeth had an MO/DO or an MOD cavity restored with amalgam without cuspal overlays. The 20-year survival rate of teeth with an MO/ DO cavity was markedly higher than that of teeth with an MOD cavity. The lowest survival rate was found for the upper premolars with an MOD cavity: 28% of these teeth fractured within 3 years after endodontic therapy, 57% were lost after 10 years, and 73% after 20 years. Generally, the cusp most prone to fracture was the lingual one, and lingual fractures caused significantly more damage to the periodontal tissues than did facial or total crown fractures. The severity of periodontal damage increased with posterior location of the tooth. By far the most serious failures, irrespective of the cavity type, were found for the upper second molar, as 10 of 29 fractures led to extraction. It is concluded that amalgam, especially in MOD cavities, is an unacceptable material for restoration of endodontically treated posterior teeth if used without cuspal overlays.     

Correlation between fracture properties and clinical performance of composite resins in Class IV cavities

One hundred and two Class IV cavities were restored randomly with four composite resins. The restorations were assessed at six months, one year, two years and three years for surface chipping, bulk fracture and incisal wear. The data were correlated with various mechanical properties of the materials. A significant correlation was found between surface chipping/bulk fracture and fracture toughness (P = 0.002), elastic modulus (P = 0.006) and tensile strength (P = 0.045). There was a trend towards an association between incisal wear and both elastic modulus and inherent flaw size. Fracture toughness may be a useful indicator of the clinical performance of composites in Class IV cavities.     

A comparison of fracture strength of yttrium-oxide- partially-stabilized zirconia ceramic crowns with varying core thickness, shapes and veneer ceramics

The fracture strengths of stylized all-ceramic crowns manufactured using an yttrium-oxide-partially-stabilized (Y-TZP) zirconia ceramic core (Denzir) veneered with lithium disilicate glass-ceramics (IPS Empress 2 or IPS Eris) were evaluated. The Denzir cores were manufactured in two ways: either with different thickness in different parts of the restoration, called an 'adapted Denzir core'; or with a uniform core thickness of 0.5 mm. IPS Empress 2 all-ceramic crowns served as reference. There was no significant difference between the crowns with an 'adapted Denzir core' veneered with the two brands of glass-ceramics. No significant difference was seen between the crowns with a 0.5 mm Denzir core veneered with the two brands of glass-ceramics. The crowns with an 'adapted Denzir core' exhibited significantly higher values than those with a 0.5 mm Denzir core and than the IPS Empress 2 crowns used as reference. No significant differences were seen among the IPS Empress 2 crowns used as reference and the crowns with a 0.5 mm Denzir core. The mode of failure varied among the Empress 2 crowns and the crowns with a core of a Y-TZP zirconia ceramic. Long-term studies are necessary to assess the clinical performance of this restorative system.     

Crown-root fracture of lower molar – restorative procedures

Abstract Endodontically treated teeth may undergo crown, crown-root, or root fractures. The treatment of fractured teeth can be complicated, sometimes because of difficulties with the final restoration. This case report describes a case of crown-root fracture of a left lower first molar in which endodontic treatment and rapid orthodontic eruption of the tooth made a good prosthetic restoration possible.