Bridge Restorations Research Articles

Lifetime of alumina‐ and zirconia ceramics used for crown and bridge restorations

The lifetime of a ceramic is dependent on the presence of incidental cracks and their gradual propagation under the conditions of the oral cavity. The objective of this study was to examine the long-term strength of glass-infiltrated alumina- and various zirconia ceramics currently used in CAD/CAM systems to manufacture crown and bridge frameworks. Fracture mechanics were applied to determine characteristic strength (sigma(omicron)), Weibull modulus (m), fracture toughness (K(Ic)), and the subcritical crack growth parameters n and B. Based on these parameters, lifetime diagrams were generated which allowed the evaluation of the long-term behavior. The results showed that in a moist environment, the glass-infiltrated alumina- and some zirconia ceramics have a high susceptibility to subcritical crack growth. Zirconia ceramics with an alumina oxide content of 0.25 wt %, however, exhibited the highest initial and most favorable long-term strength, and should therefore be suitable for crown and bridge restorations.

The influence of simulated masticatory loading regimes on the bi-axial flexure strength and reliability of a Y-TZP dental ceramic

The purpose of the current study was to examine the influence of simulated masticatory loading regimes, to which all-ceramic crown or bridge restorations will routinely be subjected during their service-life, on the performance of a yttria-stabilised tetragonal zirconia polycrystalline (Y-TZP) dental ceramic. Ten sets of 30 Y-TZP ceramic discs (13 mm diameter, 1.48-1.54 mm thickness) supplied by the manufacturer were randomly selected. Six groups were loaded for 2000 cycles at 500 N (383-420 MPa), 700N (536-588 MPa) and 800 N (613-672 MPa) with three groups maintained dry and the remaining three groups loaded while immersed in water at 37+/-1 degrees C. A further two groups underwent extended simulated masticatory loading regimes at 80 N (61-67 MPa) for 10(4) and 10(5)cycles under dry conditions. The mean bi-axial flexure strengths, standard deviations and associated Weibull moduli (m) were determined. The surface hardness was also determined using the Vickers hardness indentation technique. No significant difference (P>0.05) was identified in the bi-axial flexure strength of the simulated masticatory loading regimes and the control specimens loaded dry or wet. A significant increase in m was identified for the Y-TZP specimens following loading while immersed in water (8.6+/-1.6, 8.5+/-1.6 and 10.3+/-1.9) compared with the control (7.1+/-1.3). However, the extended loading regime to 10(5)cycles resulted in a significant reduction in the m of the Y-TZP specimens (5.3+/-1.0) compared with the control. Localised areas of increased surface hardness were identified to occur directly beneath the spherical indenter. The occurrence of localised areas of increased surface hardness could be the result of either a transformation toughening mechanism or crushing and densification of the material beneath the indentor manifested as the formation of a surface layer of compressive stresses that counteracted the tensile field generated at the tip of a propagating crack which increased the Weibull modulus of the Y-TZP specimens. The reduced reliability of the Y-TZP specimens loaded to 80 N for 10(5)cycles was associated with the accumulation of subcritical damage as a result of the extended nature of loading.

The influence of surface modification techniques on the performance of a Y-TZP dental ceramic

The purpose of the current study was to examine the influence of the pre-cementation surface modification techniques, namely alumina abrasion and surface grinding, routinely employed by dental practitioners prior to cementation and placement of crown and bridge restorations on the performance of a Y-TZP dental ceramic. Twelve sets of 30 Lava ceramic discs (13 mm diameter, 1.5mm thickness) supplied by the manufacturer were randomly selected. Six groups were abraded utilising 25, 50 and 110 microm alumina and stored dry or in a water bath at 37+/-1 degrees C for 24 h. Four groups were ground utilising a fine or a coarse grit diamond bur, specimens were ground dry or while using water as a coolant. The mean bi-axial flexure strengths, standard deviations and associated Weibull moduli (m) were determined. The surface roughness, hardness and phase composition were assessed utilising profilometry, the Vicker's hardness indentation and X-ray diffraction, respectively. No significant difference (P > 0.05) was identified in the bi-axial flexure strength of the 25, 50 and 110 microm alumina-abraded and the control specimens stored dry and wet for 24h. However, a significant increase in m was identified for the alumina-abraded specimens stored dry (10.7+/-1.9, 10.6+/-1.9 and 10.6+/-1.9) compared with the control (7.5+/-1.3) and the specimens stored in a water bath. In addition, the alumina abrasion regimes reduced the surface roughness compared with the controls. The coarse grinding regime significantly reduced both the bi-axial flexure strength and the associated m compared with the control whilst no significant difference was identified for the fine grinding regimes. The surface modification techniques initiated a phase transformation mechanism and resulted in the formation of a layer of compressive stresses on the surface of the disc-shaped specimens. The combination of the reduced surface roughness and the formation of a surface layer of compressive stress as a result of the alumina abrasion regimes investigated increased the reliability of the bi-axial flexure strength. The presence of water in the current study did not detrimentally influence the performance of the Y-TZP ceramic under investigation. Coarse grinding significantly reduced the bi-axial flexure strength and m due to the increased surface roughness. The Y-TZP specimens in the current investigation underwent a toughening mechanism as a result of a phase transformation mechanism which generated a transformation compressive stress that opposes the externally applied, crack-propagating tensile stress.

メタルフリーレストレーションの新しい展開―エステニアC&Bの臨床的特性について

Prosthetic dental restorations began to be used more frequently in 1907 when casting was introduced as a method to make fixed prostheses. Since then, cast crown and bridge restorations have been improved significantly and continue to contribute in a major way to dental restorative treatment. To provide tooth colored restorations with the cast metal, porcelain fused to cast metal was invented and opened the way to the present esthetic dentistry transformation. During the 20th century, metal and porcelain were the main materials for fixed prosthetic restorations. The cast metal and porcelain, being hard and strong materials, were considered to be excellent for fixed restorative treatment. Recently, there have been concerns that these materials, which are harder than living tissue and are very strong, may have a detrimental influence on the abutment and antagonistic teeth. Therefore, materials that wear closer to that of tooth structure, actually the same as tooth structure, are more desirable, and would be ideal. We believe ESTENIA can measure up to this rigorous 21st century request for a better, kinder material.

In Vitro Color Stability of Provisional Crown and Bridge Restoration Materials

Discoloration of provisional restorations can be an esthetic problem, especially when the treatment plan requires long-term provisionalization. In this study, therefore, we examined the effects of staining solution on the color stability of these provisional crown and bridge restoration materials: Structur, Temdent, and Tab 2000. Treatment solutions were namely carrot juice, tea, cola, light cola, and distilled water. Thirty samples were prepared for each type of provisional material, such that a total of 90 samples were prepared. The color value of each sample was measured with a colorimeter at baseline and after one day, one week, two weeks, and four weeks of immersion in various treatment solutions. Results were determined using the CIELAB system. Color change data were calculated and subjected to two-way analysis of variance. To examine significant interactions, one-way ANOVA and Tukey's multiple comparisons test were performed to identify differences between the solutions (p < or = 0.05). After four weeks of treatment, color difference values were found to range from 0.20 to 3.99 deltaE* units. The highest color difference values were obtained in carrot juice, cola, and tea with Structur samples after four weeks, where these values were categorized as "noticeable" and "unacceptable" color change values. Based on the results of this study, we do not recommend amine-containing Structur to be used as a provisional crown and bridge restorative material for treatments of a longer duration.

Application of GA in optimal robot selection for bridge restoration

This paper further expands and tests a method for optimising construction robot's kinematic parameters using a genetic algorithm (GA) technique as a tool, proposed earlier by Navon and McCrea [J. Comput. Civ. Eng. 11 (1997) 175]. The approach to selecting an optimal robot is demonstrated on a steel bridge restoration robot. Optimising a robot's kinematic parameters is divided into a two-stage problem. Distinctions among the criteria, different ways of assessing the robot's behaviour according to these criteria and ranking the criteria according to their importance lie at the base of this division. The robot's parameters: (i) major configuration, (ii) minor configuration, (iii) optimal division of the unit length between both links in RRR (revolute configuration) option, (iv) determination of the joints' movement ranges, (v) determination of joints' velocities and accelerations are optimised simultaneously, based on: (i) collision avoidance including arm and wrist singularity avoidance, (ii) percentage of coverage, (iii) dexterity, and (iv) productivity. The procedure for analysis of the inter-relation between the task characteristics and robot design characteristics enables extensions to disparate structures. The GA general function optimisation software is customised here, to be used as the optimisation tool. Comments on the effectiveness of the method and quality of the outcome conclude the paper.

Crown and bridge restorations

Crown and bridge restorations

Seismic performance of repaired hollow-bridge piers

To develop an effective repair technique for rapid bridge restoration after an earthquake, four hollow bridge columns were cyclically loaded to failure, repaired and retested. The repair process includes using dog-bone shape bars to replace the fractured longitudinal bars in plastic hinges and using FRP (Fiber Reinforced Plastic) wraps to enhance the deformation capacity of columns. The repair aims to restore seismic capacity in terms of strength and ductility. Test results indicate that the fractured longitudinal bars can be completely repaired and the deformation capacities of the columns were enhanced by FRP wraps. However, due to concrete deterioration and the buckling of the longitudinal bars in the inner layer of the hollow sections, the test results also indicate the repaired column strengths are less than anticipated.

The three-dimensional finite element analysis of fixed bridge restoration supported by the combination of teeth and osseointegrated implants.

This study investigated the designs of osseointegrated prostheses in cases of free-end partial edentulism using comparative stress interpreted with the three-dimensional finite element method. Three free-end fixed osseointegrated prostheses models with various connection designs (i.e., rigidly connected to an abutment tooth and an implant, rigidly connected to an implant and two abutment teeth, and rigidly connected to an implant and three abutment teeth) were studied. The stress values of the three models loaded with vertical, buccolingual, and linguobuccal directions at 30 degrees angled to vertical axis forces were analyzed. When the fixed partial denture was connected to the three natural abutment teeth and an implant, the lowest levels of stress in the bone were noted.

Effect of thermal cycling on whisker-reinforced dental resin composites.

The mechanical properties of dental resin composites need to be improved in order to extend their use to high stress-bearing applications such as crown and bridge restorations. Recent studies used single crystal ceramic whiskers to reinforce dental composites. The aim of this study was to investigate the effects of thermal cycling on whisker-reinforced composites. It was hypothesized that the whisker composites would not show a reduction in mechanical properties or the breakdown of whisker-resin interface after thermal cycling. Silicon carbide whiskers were mixed with silica particles, thermally fused, then silanized and incorporated into resin to make flexural specimens. The filler mass fraction ranged from 0% to 70%. The specimens were thermal cycled in 5 degrees C and 60 degrees C water baths, and then fractured in three-point bending to measure strength. Nano-indentation was used to measure modulus and hardness. No significant loss in composite strength, modulus and hardness was found after 10(5) thermal cycles (family confidence coefficient=0.95; Tukey's multiple comparison test). The strength of whisker composite increased with filler level up to 60%, then plateaued when filler level was further increased to 70%; the modulus and hardness increased monotonically with filler level. The strength and modulus of whisker composite at 70% filler level were significantly higher than the non-whisker controls both before and after thermal cycling. SEM revealed no separation at the whisker-matrix interfaces, and observed resin remnants on the pulled-out whiskers, indicating strong whisker-resin bonding even after 10(5) thermal cycles. In conclusion, novel dental resin composites containing silica-fused whiskers possessed superior strength and modulus compared to non-whisker composites both before and after thermal cycling. The whisker-resin bonding appeared to be resistant to thermal cycling in water, so that no loss in composite strength or stiffness occurred after prolonged thermal cycling.

Cytotoxicity of provisional crown and bridge restoration materials: an in vitro study.

There are numerous materials used to provide temporary coverage for teeth while permanent restorations are being fabricated. The biocompatibility of these materials is important for the protection of teeth and gingiva, but there is little information on this subject. This study aimed to examine possible time-dependent toxic effects of provisional crown and bridge restoration materials, manipulated intraorally or extraorally, on epithelia cells. A total of 20 discs, 4 sample discs from each product having dimensions of 4 mm diameter and 2 mm thickness, were prepared. After sterilization, toxicity of these discs was evaluated in the Madin Darby Bovine Kidney (MDBK) cell line. Morphological cell changes were observed microscopically at the 3rd, 6th, 12th, and 24th hours by the filter diffusion test method. After the 3rd hour, Artglass and Structur produced cytotoxic symptoms. Temdent had the least toxic effects at the end of the 12th hour. However, after the 24th hour, the toxic values were similar for all materials. The results of this study show that although the toxicity response of chemically and light curing materials had changed in different time periods, all of them had the same toxic effects at the end of the 24th hour.

Adhesive Dentistry Thus Improved Crown and Bridge Restoration Peculiarity Existing in Adhesive Dentistry

Adhesive Dentistry Thus Improved Crown and Bridge Restoration Peculiarity Existing in Adhesive Dentistry

The influence of the impression tray on the accuracy of impressions for crown and bridge work--an investigation and review.

To evaluate the accuracy of working casts for crown and bridge restorations made from twin mix putty/wash silicone elastomeric impression materials using different types of stock tray. A master cast was made from ivorine teeth in a mandibular model. Three teeth were prepared for full crown restorations to simulate a single unit and a three unit bridge. Impressions were taken using four different types of impression tray and two different viscosities of silicone putty, together with a wash. Full metal crowns were constructed and seated on duplicate master casts and measurements made of the marginal discrepancies. The work was carried out in a dental technology laboratory in a university department of restorative dentistry in 1995/1996. Metal and rigid plastic impression trays showed the least discrepancy (about 50 microns), the latter slightly greater with the normal putty than the soft one. Impressions taken with flexible plastic trays produced considerable discrepancy with both putties, approximately 210 microns and 180 microns respectively. Metal and rigid plastic stock trays give greater accuracy in the putty/wash silicone twin mix impression technique compared with flexible plastic ones for crown and bridge work. Those using the latter should be aware of their shortcoming in this respect.

Colour stability of provisional crown and bridge restoration materials.

In an in vitro study to determine the colour stability of provisional restoration materials, the PMMA synthetics Trimm and Cronsin and the bis-acrylic composites Protemp Garant, Protemp Garant NF, Protemp II and Provipont DC were investigated. The colour changes of the cylindrical untreated samples were measured in comparison with samples after 24 and 72 hours of artificial ageing in a Suntest CPS+ UV ageing device using the Minolta CM 3500d spectrophotometer according to the CIE-L*a*b* system. Trimm (light), Cronsin (brown, yellow and universal), Provipont DC (yellow) and Protemp Garant NF (extra light) displayed the greatest discoloration with values > or = 4-21 delta E, where discoloration toward yellow could be discerned. The remaining materials showed lower luminance reflectance values of < or = 1-4 delta E, and therefore greater colour stability. Because of their colour stability the materials Cronsin (grey), Protemp Garant (yellow), Protemp II (light), Protemp Garant NF (yellow, light and extra light) could also be used as long-term interim prosthetics.

Reduced plaque accumulation on hydrocarbon thin film deposited on restorative acrylic polymers.

The deposition of a thin polymeric film from ethylene plasma was used to modify the surface properties of acrylic teeth, commonly used in the dental practice for crown and bridge restorations. The effects of the surface modification process on the surface composition, morphology, and energetics were evaluated by electron spectroscopy for chemical analysis, atomic force microscopy, and contact angle measurement respectively. Plaque accumulation on the plasma-coated and untreated material was evaluated in in vivo experiments, in which the same patient received conventional and plasma-coated restorations. The hydrocarbon-like surface of the plasma-coated restoration remained remarkably free from plaque, even in the absence of brushing. On the other hand, plaque accumulation was observed on the unmodified restoration. Results are discussed according to recent theories on bioadhesive phenomena.

鋳造歯冠用結晶化ガラスの色調再現性に関する研究 結晶析出量と透過率について

In recent years, castable glass ceramics have been used clinically as material in crown and bridge restorations. Materials used in such restorations must be not only strong enough to withstand masticatory and biting forces but also aesthetically close to the color of natural teeth.In order to establish a technique for enhancing the color reproducibility of castable glass ceramics, which is an essential factor for clinical application, the relationship between the amount of crystalline phase and total light transmission of the crystal was investigated. The results were as follows:1. Castable glass ceramics showed a high degree of translucency. A crystallization temperature of 910°C was found to be the most appropriate for the amount of HAP crystal, which has a translucency close to that of enamel.2. For enhancement of the color reproducibility of castable glass ceramics, consideration must be given not only to the color of the glass and the stain but also to the influence of the tooth substance and metal as well as the color of the cement.

CAD/CAM system to fabricate dental prostheses--CAD for bridge restoration.

An original CAD process for bridge restoration was developed, and CAD for a maxillary left three unit bridge was attempted. The measured shape data of the standard crown of a second premolar and molar were deformed, and were applied on the dies. The measured pontic data were inserted between two molars. Here, bite data of the opposing teeth were introduced, and the occlusal relationship with the applied molars was adjusted. The bite data were then replaced by the FGP data, and the occlusal surface interference with FGP data was eliminated. Connection processes were then carried out. The clearances between the pontic and molars were filled with interpolation, and the ends of the applied second molar and premolar were connected with the margin of each die. Finally, the data above the margin of each die were extracted, and used as the inner crown data for the bridge. The whole bridge was designed using a newly developed computer program.

Etiologic aspects and orthodontic treatment of unilateral localized arrested tooth development combined with hearing loss

In this study a case has been presented involving localized, arrested maxillary tooth development, asymmetric maxillary development, and unilateral loss of hearing. No similar case seems to have been described before. The orthodontic treatment comprised extraction of four permanent tooth germs in the maxilla and autotransplantation of mandibular teeth, followed by the use of fixed orthodontic appliances and a one-unit bridge restoration. Etiologic aspects are discussed. It is suggested that a severe attack of mumps that involved massive swelling of the parotid glands immediately after chicken pox and measles at the age of 4 to 5 years, may have resulted in a neurologic reduction of hearing and arrested tooth development. The teeth in which root development was arrested seemed to have developed normally up to 4 to 5 years of age. Arrested tooth development in relation to mumps does not appear to have been reported previously, whereas hearing loss after mumps has been reported. In the search for verification of this possible connection, children with arrested tooth development should be examined for reduction of hearing, and children with hearing loss after mumps ought to have their dental development checked. (A M J O RTHOD D ENTOFAC O RTHOP 1995;108:154-61.)

Condylar element modification of a semiadjustable articulator: Flat condylar path to curved condylar path

The Denar Mark II semiadjustable articulator (Denar Corporation, Anaheim, Calif.) is an excellent articulator for crown and bridge restorations. The dentist can improve on this articulator by modifying the flat superior-wall condylar guide with a curved superior-wall condylar guide. The dentist will find that less time is spent in chair-side occlusal adjustments when a 314 inch curved superior-wall condylar guide is used.

Use of shell crowns in Hong Kong dental hospital attenders.

In 1984 an oral health survey of Hong Kong adults aged 35-44 years revealed that 15% of subjects presented with metal shell crown restorations, often as components of fixed-bridge reconstructions. The aim of this study was to describe the patterns and means of use of shell crowns, and to describe the patterns of tooth loss in patients who presented with such restorations, attending for treatment at the dental teaching hospital in Hong Kong over a 2-year period. A total of 1563 such patients attended. The records, which included radiographs, of 165 of these patients aged 35 years and above, obtained by means of a systematic sampling frame, were studied by one trained examiner. On initial presentation each patient was found to have a mean of 4.0 shell crowns, 77% of these being components of bridge restorations. The bridges involved a mean of only 3.9 units (retainers and pontics). The tooth type most commonly replaced by a bridge of this type was the first molar. It was concluded that most shell crowns used in this patient group are abutment retainers for predominantly short-span bridge restorations.