Effect of accelerated aging on the fracture toughness of zirconias.

STATEMENT OF PROBLEM: Low temperature degradation (LTD) of yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) is of concern. PURPOSE: The purpose of this in vitro study was to assess the effect of accelerated aging on the Vickers hardness and fracture toughness of a newly developed Y-TZP and 2 primary Y-TZPs. MATERIAL AND METHODS: Two primary 3 mol% Y-TZP, Lava (LA), Everest Zirconium Soft (EV), and a new 3 mol% Y-TZP, ZirTough (NZ) were assessed. Specimens (n=30 each brand) of 10 × 10 × 3 mm were hydrothermally treated for accelerated aging to examine LTD. Five conditions were used (n = 5 per condition) as follows: control group (no aging); 5 hours at 134°C/0.2 MPa (5h-134°C); 100 hours at 134°C/0.2 MPa (100 h-134°C); 5 hours at 180°C/1.0 MPa (5 h-180°C); and 20 hours at 180°C/1.0 MPa (20 h-180°C). Fracture toughness was measured by using the indentation fracture (IF) method under a loading of 294 N and calculated from the obtained measurements. To observe differences in particle composition and fracture patterns, mirror-polished test specimens (n=5 each brand) were re-sintered at 1200°C for 1 hour as a thermal etching process, and a Vickers indenter was pressed into the test specimens according to the IF method. Test piece surfaces and cracks were observed with scanning electron microscopy (SEM). One-way ANOVA and the post- hoc (Scheffé test were used to examine) interlevel significant differences (α=.05). RESULTS: The Vickers hardness and fracture toughness were as follows: 1319 HV and 7.36 MPa · m(1/2) for LA, and 1371 HV and 6.76 MPa · m(1/2) for EV in no aging; 1334 HV and 7.02 MPa · m(1/2) for LA, and 1346 HV and 6.07 MPa · m(1/2) for EV in 5h-134°C. No significant differences were found between no aging and 5h-134°C for LA and EV for Vickers hardness and fracture toughness. Measurements could not be made for LA and EV for 100 h-134°C, 5h-180°C, or 20 h-180°C because of fractures in the surface layer. For NZ, Vickers hardness and fracture toughness were as follows: 1261 HV and 15.60 MPa · m(1/2) in no aging; 1217 HV and 14.98 MPa · m(1/2) in 5h-134°C; 1231 HV and 15.13 MPa · m(1/2) in 100 h-134°C; 1252 HV and 15.51 MPa · m(1/2) in 5h-180°C; 1224 HV and 15.01 MPa · m(1/2) in 20 h-180°C. No significant differences were shown in the Vickers hardness and fracture toughness. SEM observations after the thermal etching processing of NZ showed zirconia particles and scattered alumina particles. CONCLUSION: Measurements with LA and EV could only be made for no aging and 5h-134°C, and no significant differences were found in Vickers hardness and fracture toughness. Measurements were made with NZ under all conditions and no significant differences were found in Vickers hardness and fracture toughness.

Structural stability of posterior retainer design for resin-bonded prostheses: a 3D finite element study.

The purpose of this in vitro study was to compare the stress distribution and natural frequency of different shape and thickness retainer designs for maxillary posterior resin-bonded prostheses using finite element (FE) method. A 3D FE model of a three unit posterior resin-bonded prosthesis analysis model was generated. Three different shaped retainer designs, viz. C-shaped (three axial surface wraparounds), D-shaped (three axial surface wraparounds with central groove) and O-shaped (360° wraparounds), and three different thicknesses, viz., 0.4, 0.8, and 1.2 mm, resin-bonded prostheses were used in this study. The resin-bonded prosthesis analysis model was imported into an FE analysis software (ANSYS 10.0, ANSYS, USA) and attribution of material properties. The nodes at the bottom surface of the roots were assigned fixed zero displacement in the three spatial dimensions. A simulated angle of 45° loading of a 100 N force was applied to the node of the pontic lingual cusp surface. The stress distributions and corresponding natural frequencies were analyzed and resolved. The C-shaped retainer for 0.4 mm thickness recorded the greatest von Mises stresses of 71.4 MPa for all three groups. C-shaped, D-shaped and O-shaped retainer presented natural frequencies 3,988, 7,754, and 10,494 Hz, respectively. D-shaped retainer and O-shaped retainer increased natural frequencies and structural rigidity over the traditional C-shaped retainer. The maximum von Mises stresses values of the remaining tooth and prosthesis decreased with greater retainer thickness. D-shaped retainer and O-shaped retainer increased natural frequencies and structural rigidity over the traditional C-shaped retainer.

Effect of water temperature on cyclic fatigue properties of glass-fiber-reinforced hybrid composite resin and its fracture pattern after flexural testing.

PURPOSE: To evaluate in vitro the influence of dynamic loading applied to a glass-fiber-reinforced hybrid composite resin on its flexural strength in a moist, simulated oral environment. MATERIALS AND METHODS: Three-point flexural strength specimens were subjected to cyclic loading in water at 37°C and 55°C to investigate the influence of immersion temperature on impact fatigue properties. Specimens were subjected to cyclic impact loading at 1 Hz for up to 5 × 105 cycles to obtain the number of cycles to failure, the number of unbroken specimens after 5 × 105 cycles, and the residual flexural strength of unbroken specimens. Maximum loads of 100, 200, and 300 N were chosen for both the non-reinforced and the glass-fiber reinforced hybrid composite resins. RESULTS: The mean residual flexural strength for 100 N impact loading at temperatures of 37°C and 55°C was 634 and 636 MPa, respectively. All specimens fractured at fewer than 5 × 105 cycles for loads of 200 and 300 N. CONCLUSION: Reduced numbers of cycles to fracture and lower fatigue values were observed as both the maximum load and immersion temperature increased.

Accuracy of three-dimensional finite element modeling using two different dental cone beam computed tomography systems.

The aim of this study is to evaluate the accuracy of dental ceramic object three dimensional (3D) finite element model constructed directly from two different dental cone beam computed tomography (CT) systems. CT scanned one 10.0 × 10.0 × 20.0 mm block and one 8.0 × 10.0 × 40.0 mm block of an 8-step wedge. All 3D finite element (FE) models were created from CT images. Each 3D FE model measured the length of the directions X, Y, and Z that corresponded to an original specimen using the measurement function between two points on the Mechanical Finder software package. The measurements and practical value were compared with the CT image and the accuracy of the reproduced measurements was examined. No significant differences were found between Alphard-3030 on the Z axis and ProMax 3D on the Y axis of the block. In addition, there were also no significant differences observed between Alphard-3030 on the Y axis and ProMax 3D on the X axis compared with Alphard-3030 on the Z axis and ProMax 3D on the Y axis for the step-wedge. The results suggest that measurement of the dimensions of cone beam CT images could be useful in applications where both good reproducibility and accuracy of FE models are required.

Finite element analysis to compare stress distribution of connector of lithia disilicate-reinforced glass-ceramic and zirconia-based fixed partial denture.

This study used finite element method to analyze the stress distribution in connector of ceramic-based bilayer structures, in simulation of dental crown-like structures with a functional but weak veneer layer bonded onto a strong core layer. The purpose of this study was to evaluate the stress distribution at veneer/core interface of 2 different core materials [Yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) and lithia disilicate-reinforced glass-ceramic] using three-dimensional finite element analysis. Within the limitations of this study, finite element analysis showed that stress concentrations were located at the veneer/core interface of the connector in Y-TZP core models. The general observation was that compared with Y-TZP, lithia disilicate-reinforced glass-ceramic showed a relatively stable stress value and had a minor effect on the stress concentration susceptibility.

Effect of cyclic impact load on shear bond strength of zirconium dioxide ceramics.

PURPOSE: To investigate the influence of cyclic impact load and the number of load cycles on compressive shear bond strength under the three different cements. MATERIALS AND METHODS: The following materials were used: Super Bond C&B (SB) and Panavia Fluoro Cement (PF) as adhesive resin cements, Fuji Luting (FL) as a resin-modified glass-ionomer cement, and zirconium dioxide ceramics as adherend. Before the shear bond test, three different impact loading conditions (compressive direction, shear direction, and no impact) and the number of load cycles (1 to 106 cycles), were performed. A total of 189 specimens (n = 3/group) were randomly assigned to groups and tested. A cyclic impact test was performed by applying a load of 98N at a distance of 40 mm and a loading cycle frequency of 1 Hz. All results were statistically analyzed with two-way ANOVA and Tukey's multiple comparison test. RESULTS: Shear bond strengths of SB, PF, and FL subjected to no cyclic impact load were 21.6 to 53.8 MPa in SB, 27.0 to 63.6 MPa in PF, and 20.0 to 35.9 MPa in FL. The shear bond strength of SB and PF increased to a certain degree from one to 105 cycles, while FL did likewise from one to 104 cycles. CONCLUSION: The shear bond strengths of SB, PF, and FL were greatest without cyclic impact, followed by compressive and then shear cyclic impact.

Stress and strain analysis of the bone-implant interface: a comparison of fiber-reinforced composite and titanium implants utilizing 3-dimensional finite element study.

This study analyzed stress and strain mediated by 2 different implant materials, titanium (Ti) and experimental fiber-reinforced composite (FRC), on the implant and on the bone tissue surrounding the implant. Three-dimensional finite element models constructed from a mandibular bone and an implant were subjected to a load of 50 N in vertical and horizontal directions. Postprocessing files allowed the calculation of stress and strain within the implant materials and stresses at the bone-to-implant interface (stress path). Maximum stress concentrations were located around the implant on the rim of the cortical bone in both implant materials; Ti and overall stresses decreased toward the Ti implant apex. In the FRC implant, a stress value of 0.6 to 2.0 MPa was detected not only on the screw threads but also on the implant surface between the threads. Clear differences were observed in the strain distribution between the materials. Based on the results, the vertical load stress range of the FRC implant was close to the stress level for optimal bone growth. Furthermore, the stress at the bone around the FRC implant was more evenly distributed than that with Ti implant.

The Effect of Implant Length and Diameter on Stress Distribution around Single Implant Placement in 3D Posterior Mandibular FE Model Directly Constructed Form In Vivo CT.

A three-dimensional (3D) finite element (FE) model of the mandibular bone was created from 3D X-ray CT scan images of a live human subject. Simulating the clinical situation of implant therapy at the mandibular first molar, virtual extraction of the tooth was performed at the 3D FE mandibular model, and 12 different implant diameters and lengths were virtually inserted in order to carry out a mechanical analysis. (1) High stress concentration was found at the surfaces of the buccal and lingual peri-implant bone adjacent to the sides of the neck in all the implants. (2) The greatest stress value was approximately 6.0 MPa with implant diameter of 3.8 mm, approx. 4.5 MPa with implant diameter of 4.3 mm, and approx. 3.2 MPa with implant diameter of 6.0 mm. (3) The stress on the peri-implant bone was found to decrease with increasing length and mainly in diameter of the implant.

Studies on mechanical strength, thermal expansion of layering porcelains to alumina and zirconia ceramic core materials.

The aim of this study was to evaluate and clarify the various mechanical properties and behavior of layering porcelains (Tokuyama Dental Ceramic, IPS Empress 2, Cerabien, Vitadura, Creation) used for veneering high-strength ceramic core materials. The layering porcelains studied exhibited the following range of mechanical properties: compressive strength at 586-1091 MPa, bending strength at 30-97 MPa, diametral tensile strength at 16-28 MPa, Vickers hardness at 481-647 Hv, and fracture toughness at 1.36-2.05 MPa x m1/2. Results of this study indicated that the mechanical shortcomings of conventional porcelain, such as brittleness and hardness, have been overcome by the enhanced mechanical properties of layering porcelain, resulting in improved fracture toughness.

Fiber-reinforced onlay composite resin restoration: a case report.

AIM: The purpose of this case report is to describe the clinical procedure for fabricating fiber-reinforced composite (FRC) onlay composite resin restorations using a FRC as the substructure. BACKGROUND: A variety of therapeutic modalities are available to restore teeth with moderate coronal defects in the posterior region of the mouth. For patients who refuse complete crown restorations or when minimal tooth reduction is preferred, a FRC restoration can be a good alternative to conventional restorative techniques. CASE REPORT: A 42-year-old female patient presented with an endodontically treated mandibular right first molar with extensive destruction of the coronal tooth structure. To conserve the remaining tooth structure a FRC resin core substructure was fabricated and veneered with Ceramage dentin and enamel hybrid composite to create the final restoration. SUMMARY: FRC restorations using adhesive technology appears to be a promising restorative option. However, further clinical investigation will be required to provide additional information on this technique. Based on the clinical and radiographic findings in the present case, the fabrication of a conventional crown was avoided in order to conserve the remaining tooth structure. CLINICAL SIGNIFICANCE: The restoration of badly damaged teeth is a challenge for clinicians when cast crown restorations are not an option for the patient. The use of FRC restorations along with adhesive technology may be a rational restorative alternative in the near future.

Three-dimensional finite element analysis of posterior fiber reinforced composite fixed partial denture: framework design for pontic.

This study investigated the effects of two types of loading conditions on mechanical behavior of the pontic of composite fixed partial denture (C-FPD) and fiber reinforced composite fixed partial denture (FRC-FPD). Two types of FE model of posterior bridge were developed. Two types of loading conditions, i.e. vertical 629 N, and lateral of 250 N, were used. In lateral load, displacement was showed a similar behaviours. However in vertical load, displacement of FRC-FPD was less than C-FPD. These results clarified the magnitude, distribution of stress and displacement generated in C-FPD and FRC-FPD of pontic caused by two different loading conditions.

Three-dimensional finite element analysis of metal and FRC adhesive fixed dental prostheses.

PURPOSE: The aim of this study was to evaluate stress distribution in anterior adhesive fixed dental prostheses (FDP) and at the tooth/framework interface. Metal (M-FDP) and glass fiber-reinforced composite (FRC-FDP) frameworks were compared. MATERIALS AND METHODS: The design of the FDP consisted of retainers on a maxillary central incisor and canine with a pontic of a lateral incisor. Two different framework materials were compared: isotropic Au-Pd alloy and anisotropic continuous unidirectional E-glass FRC. Veneers in both cases were made of isotropic veneering hybrid composite. A 3-dimensional finite element model of a 3-unit FDP loaded with 154 N (at a 45-degree angle to the incisal edge of the pontic) was used to analyze stress distribution in the FDP and at the adhesive interface. A finite element analysis was used in calculation of the maximum principal stress and displacement. RESULTS: The maximum displacement of FRC-FDP was higher than that of M-FDP. Stress concentrations were located equally in the connectors and at the occluding contact points in both framework types. Maximum principal stress of FRC-FDP was lower than that of M-FDP. Stress analysis further indicated that the maximum stress in the luting cement interface of FRC-FDP was located at the middle part of the retainers, whereas in the M-FDP, the maximum stress was located at the marginal edge of the retainers. CONCLUSION: The FE model revealed differences in displacement and stress distribution between metal and FRC frameworks of FDP. The general observation was that FRC-FDP provided more even stress distribution from the occluding contact point to the cement interface than did M-FDP.

Effect of commercially available bonding agents impregnated with fibers on bending strength of hybrid resin.

To clarify the mechanical properties of fiber-reinforced hybrid resin bridges, this study evaluated the influence of various bonding agents ((Modeling Liquid (ML), DE Resin (DE), Bell Bond (BE), Mega Bond (MG), Durafil Bond (DU), Fluoro Bond (FB), Mac-Bond (MC), EG Bond (EG), Unifill Bond (UN), Single Bond (SN)) impregnated with fibers on bending strength. FB attained the highest bending strength of 570 MPa, whereas SN exhibited the lowest value of 224 MPa, which meant that the bending strength of FB was 2.5 times higher than that of SN. Results of this study suggested that the bending strength of fiber-reinforced hybrid resin was significantly affected by bonding agents impregnated with fibers. Therefore, selection of bonding agent for hybrid resin restoration requires careful consideration of product composition to ensure an optimal bonding agent-fiber combination, thereby imparting improved mechanical properties to the resultant dental restoration.

Treated enamel surface patterns associated with five orthodontic adhesive systems--surface morphology and shear bond strength.

The chief aim of this study was to evaluate the influence of three different types of pretreatment solutions (phosphoric acid, self-etching primers, and polyacrylic acid) on enamel surfaced when used in association with one of the five orthodontic adhesive systems. In the same vein, the shear bond strength of orthodontic metal brackets was also measured to evaluate the influence of bonding procedure. After the enamel surfaces of extracted human maxillary incisors were pretreated with the five adhesive systems, scanning electron microscopy (SEM) was used to observe the effects of pretreatment on enamel. Additionally, the shear bond strength of metal brackets bonded with the five adhesives was measured (n=6). SEM observation revealed different etching patterns on the enamel surface after pretreatment. As for shear bond strength, no statistically significant differences were observed among the five different adhesives (p>0.05). It was found that self-etching primers and polyacrylic acid produced a less aggressive etching pattern than phosphoric acid. Nonetheless, all the five adhesive systems provided acceptable bond strength and attachment of orthodontic brackets.

Effects of dental adhesive cement and surface treatment on bond strength and leakage of zirconium oxide ceramics.

To evaluate the interactive influence of adhesive materials and surface treatments on bond strength of zirconium oxide ceramics, six types of adhesive resin cements (RelyX ARC (RA), Super-Bond C & B (SB), Linkmax (LM), Panavia Fluoro Cement (PF), Bistite II (BT), and Imperva Dual (ID)), three types of resin-reinforced glass ionomer cements (Xeno Cem Plus (XC), Vitremer Luting (VR), and Fuji Luting (FL)), as well as four types of surface treatments (# 600 polishing, sandblasting, silane, and Rocatec system) were used in this study. Results of this study indicated that all the tested adhesive materials treated with Rocatec system achieved the highest shear bond strength (31.9-67.1 MPa). In particular, the highest shear bond strength value of 67.1 MPa was found for Linkmax and Rocatec treatment combination, while the lowest shear bond strength value of 5.4 MPa was found for RelyX and # 600 polishing combination. Furthermore, results showed that Rocatec treatment was an effective way to prevent marginal leakage.

Hybrid type anterior fibre-reinforced composite resin prosthesis: a case report.

A variety of therapeutic modalities, from implant to conventional Maryland prosthesis, can be used for the replacement of a missing anterior tooth. In patients refusing implant treatment, when minimal teeth reduction is preferred, a fibre reinforced composite (FRC) prosthesis can be a good alternative to conventional prosthetic techniques. The purpose of this case report is to describe the clinical procedure for fabricating hybrid type FRC prosthesis with pre-impregnated unidirectional E-glass fibres. Fibre-reinforced composite, in combination with adhesive technology, appears promising treatment option for replacing missing teeth. However, further clinical investigation will be required to provide additional information on this technique.

[Planning guidelines for prosthodontic treatment].

In recent years "practice guidelines" based on EBM techniques have even been attracting attention at a societal level, and guidelines modeled after the procedure for preparing practice guideline (described at http://www.niph.go.jp/glgl-4.3rev.htm) have begun to be drafted and made public. With the aim of ensuring the quality and presenting the basic concepts of prosthodontic therapy, the Japan Prosthodontic Society, which bears a great obligation and responsibility toward society and the Japanese public, has decided to undertake the formulation of guidelines related to prosthodontic therapy, and decided to first undertake the formulation of "Practice guideline for denture relining and rebasing", and to prepare a guideline model. We tried to prepare the guidelines according to the "Procedure for preparing practice guidelines", but because of the scientific uniqueness of prosthodontic treatment and dentistry, research to elucidate the basis of treatment has been insufficient, and we ultimately reconfirmed the current state of affairs in which it is difficult to perform. We therefore prepared the guidelines based on the limited evidence obtained in a search of the scientific literature and on the consensus of experts. The Japan Prosthodontic Society has investigated and prepared a Society guideline "model" to the extent possible at the present time, and it has prepared "Guidelines for adhesion bridge" and "Practice guidelines for denture prosthodontics" based on it. Nevertheless, the fact of the matter is that we are faced with numerous problems, and we think that in the future new bases and clinical knowledge will be accumulated by promoting scientific clinical research, and that the guidelines should be revised regularly based on them.

Durability of diamond burs for the fabrication of ceramic crowns using dental CAD/CAM.

The diamond burs of two dental CAD/CAM systems (GN and CD) were examined if they could be used to fabricate up to 21 ceramic full crowns without fracture. After one, 11, and 21 machining times, the surfaces of the diamond burs were observed and the number of particles captured on SEM pictures was counted. The average surface roughness of the crowns was also measured. All diamond burs could be used to fabricate 21 ceramic crowns without fracture. A significant decrease in the number of diamond particles was found on the surfaces of GN burs after 11 and 21 machining times, but not on those of CD burs. The average surface roughness of GN crowns significantly increased with increase in the number of machining times. A significant positive correlation was found between the average surface roughness and the number of diamond particles.

Durability of tungsten carbide burs for the fabrication of titanium crowns using dental CAD/CAM.

The purpose of this study was to evaluate the durability of tungsten carbide burs for the fabrication of titanium crowns using two dental CAD/CAM systems (DECSY, Digital Process, Japan and Cadim, Advance, Japan). A tungsten carbide bur in each system was examined and used without fracture to fabricate 51 titanium crowns. For both systems tiny chips were found on the bur blade at the 11th machining. These chips gradually enlarged as the number of machining times increased. At the first machining no significant difference in the average surface roughness was found on the crown between the two systems (1.6 microm for DECSY and 1.2 microm for Cadim). The cutting grooves became dull and the average surface roughness increased as the number of machining times increased. It is concluded that the tungsten carbide burs for both systems can be used to fabricate up to 51 titanium crowns.

Three-dimensional finite element analysis of Aramany Class IV obturator prosthesis with different clasp designs.

The purpose of this study was to evaluate the stress distribution on the alveolar bone surrounding abutment teeth and the displacement of the Aramany Class IV obturator prosthesis with two different clasp designs. Three-dimensional finite element models of an Aramany Class IV maxillary defect were constructed. Two different clasp designs on an obturator prosthesis (double Akers clasps and multiple Roach clasps) and two different load conditions (vertical and horizontal) were compared. Finite element analysis was used to calculate the equivalent stress. The difference in the clasp design of the Aramany Class IV obturator prosthesis affected the stress distribution of the alveolar bone surrounding the abutment teeth and the displacement of the obturator prosthesis. Multiple Roach clasps reduced the stress distribution on the alveolar bone surrounding the abutment teeth and the displacement of the Aramany Class IV obturator prosthesis compared to double Akers clasps.