Evaluation of Temperature and Stress Distribution on 2 Different Post Systems Using 3-Dimensional Finite Element Analysis.

BACKGROUND The mouth is exposed to thermal irritation from hot and cold food and drinks. Thermal changes in the oral cavity produce expansions and contractions in tooth structures and restorative materials. The aim of this study was to investigate the effect of temperature and stress distribution on 2 different post systems using the 3-dimensional (3D) finite element method. MATERIAL AND METHODS The 3D finite element model shows a labio-lingual cross-sectional view of the endodontically treated upper right central incisor and supporting periodontal ligament with bone structures. Stainless steel and glass fiber post systems with different physical and thermal properties were modelled in the tooth restored with composite core and ceramic crown. We placed 100 N static vertical occlusal loading onto the center of the incisal surface of the tooth. Thermal loads of 0°C and 65°C were applied on the model for 5 s. Temperature and thermal stresses were determined on the labio-lingual section of the model at 6 different points. RESULTS The distribution of stress, including thermal stress values, was calculated using 3D finite element analysis. The stainless steel post system produced more temperature and thermal stresses on the restorative materials, tooth structures, and posts than did the glass fiber reinforced composite posts. CONCLUSIONS Thermal changes generated stresses in the restorative materials, tooth, and supporting structures.

Zirconia-parylene multilayer thin films for enhanced fracture resistance of dental ceramics.

Recent research has shown that the application of specific thin films can enhance the material properties of a laminate construct. In this study, the effect of different mono/multilayered films on the strength of a ceramic specimen is demonstrated. It is well established that cracks can initiate and/or propagate from the internal surfaces of all-ceramic dental restorations. Modifying that surface by thin-film deposition might help increase clinical longevity and applicability. Specimens were divided into the following groups according to different surface treatments received: uncoated (control group), 10 microm yttria-stabilized zirconia (YSZ) thin film, 10 microm parylene thin film, 9.75 microm YSZ + 0.25 microm parylene film, and a multilayered film (five layers of 1.25 microm YSZ + 0.75 microm parylene). Depositions were performed using a radio-frequency magnetron sputter system (working pressure 15 mT, 150 degrees C, 30:1 Ar/O2 gas ratio) to produce the YSZ layers, and a vapour deposition process was used to produce the parylene layers. Flexural strength measurements were carried out by three-point bending (span = 10 mm) in a servo-electric material testing system in deioinized (DI) water (37 degrees C). The results showed that the strength of the specimen significantly increased with the deposition of all types of coating, showing the greatest increase with the multilayered film (approximately 32 per cent). It is hypothesized that a multilayer thin film (brittle/ductile) can promote crack deflection, causing strength enhancement of the brittle construct.

Influence of leucite content on slow crack growth of dental porcelains.

OBJECTIVES: To determine the stress corrosion susceptibility coefficient, n, of seven dental porcelains (A: Ceramco I; B: Ceramco-II; C: Ceramco-III; D: d.Sign; E: Cerabien; F: Vitadur-Alpha; and G: Ultropaline) after aging in air or artificial saliva, and correlate results with leucite content (LC). METHODS: Bars were fired according to manufacturers' instructions and polished before induction of cracks by a Vickers indenter (19.6N, 20s). Four specimens were stored in air/room temperature, and three in saliva/37 degrees C. Five indentations were made per specimen and crack lengths measured at the following times: approximately 0; 1; 3; 10; 30; 100; 300; 1000 and 3000 h. The stress corrosion coefficient n was calculated by linear regression analysis after plotting crack length as a function of time, considering that the slope of the curve was [2/(3n+2)]. Microstructural analysis was performed to determine LC. RESULTS: LC of the porcelains were 22% (A and B); 6% (C); 15% (D); 0% (E and F); and 13% (G). Except for porcelains A and D, all materials showed a decrease in their n values when stored in artificial saliva. However, the decrease was more pronounced for porcelains B, F, and G. Ranking of materials varied according to storage media (in air, porcelain G showed higher n compared to A, while in saliva both showed similar coefficients). No correlation was found between n values and LC in air or saliva. SIGNIFICANCE: Storage media influenced the n value obtained for most of the materials. LC did not affect resistance to slow crack growth regardless of the test environment.

[Determination and Weibull analysis of the strength of dental veneering porcelains].

OBJECTIVE: To determine the strength of the veneering porcelain stored in artificial saliva. METHODS: Standard beams with a size of 3 mm x 2 mm x 20 mm made from the body, incisal, and translucent porcelains of SHOFU Vintage were stored in the artificial saliva for 30 days. Twenty samples from each material were tested for the strength by the 3-point flexural test at a crosshead speed of 0.5 mm. The data were analyzed by the two-parameter Weibull method. RESULTS: The strength, Weibull modulus (m) and characterization strength (male0) were (75.5 +/- 5.6) MPa, 17.3, and 77.6 MPa for Body porcelain, respectively; (73.6 +/- 5.0) MPa, 16.5, and 76.0 MPa for incisal porcelain, respectively; and (72.9 +/- 4.5) MPa, 16.1, and 75. 5 MPa for translucent porcelain, respectively. CONCLUSION: There are no differences in strength between the three dental porcelains. Weibull analysis describes the strength of the porcelains better than the average and standard deviation.

Wear resistance and compression strength of ceramics tested in fluoride environments.

Dental ceramics have been widely used because of aesthetic, but wear is still questioned. There are relates that ceramic surface is prone to degradation by acidulated fluoride, that can increase wear rates. The aim of this study was to evaluate the effect of neutral and acidulated fluoride gel, used as preventive agents for professional use, at wear and compression strength of dental ceramics IPS e.max ZirPress (ZIR), IPS Empress Esthetic (EMP) e IPS Inline POM (POM). For this, 30 crowns and 30 disks were obtained by heat-pressing. Crowns and disks were submitted to two-body wear test at machine of mechanical loading, simulating occlusion, lateral movement and disocclusion. It was performed 300,000 cycles at 1Hz frequency under 20N load, to simulate 1 year of mastication. Samples were totally immersed during the test and were divided into three groups according to the gel used for immersion (n=10): control, neutral (sodium fluoride 2%) and acidulated (acidulated phosphate fluoride 1.23%). Samples (crowns and disks) were analyzed for vertical height loss after the test using, respectively, profile projector and stereomicroscope. Roughness of worn surface of crowns and disks was evaluated by laser confocal microscopy. Data of height loss and roughness were evaluated by two-way ANOVA and Bonferroni's test. A crown/disk of each group was analyzed by scanning electronic microscopy. After wear resistance tests, crowns were cemented to their abutments and submitted to compressive load at 30° angulation and 1mm/min speed. Type of failures was compared by qui-square test. Ceramic EMP worn less while ZIR worn more. Control gel worn more at crowns while acidulated gel worn more at disks. Surface roughness of samples tested at acidulated gel was significantly lower. Type of failures found at compression resistance tests was affected by ceramic type, but not by gel used. The results suggest that ceramic and fluoride gel affect wear and roughness of worn surface while type of failure is only affected by ceramic.

Effect of immediate dentine sealing on the fracture strength of lithium disilicate and multiphase resin composite inlay restorations.

PURPOSE: Limited information is available on the effect of Immediate Dentin Sealing (IDS) on the fracture strength of indirect partial posterior restorations. This study evaluated the effect of IDS on the fracture strength and failure types of two indirect restorative materials. MATERIALS AND METHODS: Standard MOD inlay preparations were made on sound molars (N=40, n=10 per group) and randomly divided into four groups to receive the inlay materials with and without the application of IDS: Group L-IDS-: Li2Si2O5 (Lithium disilicate, IPS e.max) without IDS; Group L-IDS+: Li2Si2O5 with IDS; Group MR-IDS-: Multiphase resin composite (MR, Lava Ultimate) without IDS; MR-IDS+: MR with IDS. Inlays made of L were etched with 5% hydrofluoric acid, and MR inlays were silica coated. After silanization, they were cemented using adhesive resin cement (Variolink Esthetic DC). The specimens were thermo-mechanically aged (1.2×106 cycles, 1.7Hz, 8000 cycles, 5-55°C) and then subjected to load to failure (1 mm/min). Failure types and locations of debondings were classified. Data were statistically analyzed using ANOVA, Mann Whitney U-test and Chi-square tests (α=0.05). Two-parameter Weibull distribution values including the Weibull modulus, scale (m) and shape (0), values were calculated. RESULTS: After aging conditions, no apparent changes were observed in marginal integrity but occlusal wear facets were more common with MR than with L (p<0.001). Material type and the application of IDS significantly affected the results (p=0.013). While group L-IDS- showed the lowest mean fracture strength (1358±506N) among all groups (p<0.05), application of IDS significantly increased the results significantly (L-IDS+: 2035±403N) (p=0.006). MR groups with and without IDS, did not show significant difference (MR-IDS-: 1861±423, MR-IDS+: 1702±596 N) (p=0.498). When materials without IDS are compared, L showed significantly lower results than that of MR (p=0.035). With the application of IDS, no significant difference was noted between L and MR materials (p=0.160). Weibull distribution presented the highest shape (0) for L-IDS+ (5.66) compared to those of other groups (3.01-4.76). Neither the material type (p=0.830), nor the application of IDS (p=0.54) affected the severity of the failure types. In 95% of the cases, the IDS layer left adhered on the tooth surface after fracture tests. In groups where no IDS was used, resin cement remained on the tooth surface in 44% of the cases (p=0.001). No significant differences were observed between the materials with respect to cement remnants or IDS after fracture (p=0.880). The incidence of repairable failure types (83%) was more common with L than with MR (75%) material (p>0.05). CONCLUSION: Immediate dentin sealing improves adhesion, and thereby the fracture strength of inlays made of lithium disilicate but not that multiphase resin composite.

Resistance to abrasion of extrinsic porcelain esthetic characterization techniques.

STATEMENT OF PROBLEM: A novel esthetic porcelain characterization technique involves mixing an appropriate amount of ceramic colorants with clear, low-fusing porcelain (LFP), applying the mixture on the external surfaces, and firing the combined components onto the surface of restorations in a porcelain oven. This method may provide better esthetic qualities and toothbrush abrasion resistance compared to the conventional techniques of applying color-corrective porcelain colorants alone, or applying a clear glaze layer over the colorants. However, there is no scientific literature to support this claim. PURPOSE: This research evaluated toothbrush abrasion resistance of a novel porcelain esthetic characterization technique by subjecting specimens to various durations of simulated toothbrush abrasion. The results were compared to those obtained using the conventional characterization techniques of colorant application only or colorant followed by placement of a clear over-glaze. METHOD AND MATERIALS: Four experimental groups, all of which were a leucite reinforced ceramic of E TC1 (Vita A1) shade, were prepared and fired in a porcelain oven according to the manufacturer's instructions. Group S (stain only) was characterized by application of surface colorants to provide a definitive shade of Vita A3.5. Group GS (glaze over stain) was characterized by application of a layer of glaze over the existing colorant layer as used for Group S. Group SL (stain+LFP) was characterized by application of a mixture of colorants and clear low-fusing add-on porcelain to provide a definitive shade of Vita A3.5. Group C (Control) was used as a control without any surface characterization. The 4 groups were subjected to mechanical toothbrushing using a 1:1 water-to-toothpaste solution for a simulated duration of 32 years of clinical use. The amount of wear was measured at time intervals simulating every 4 years of toothbrushing. These parameters were evaluated longitudinally for all groups as well as compared at similar time points among groups. RESULTS: In this study, the novel external characterization technique (stain+LFP: Group SL) did not significantly enhance the wear resistance against toothbrush abrasion. Instead, the average wear of the applied extrinsic porcelain was 2 to 3 times more than Group S (stain only) and Group GS (glaze over stain). Application of a glaze layer over the colorants (Group GS) showed a significant improvement on wear resistance. Despite its superior physical properties, the leucite reinforced ceramic core (Group C) showed 2 to 4 times more wear when compared with other test groups. CONCLUSION: A conventional external esthetic characterization technique of applying a glaze layer over the colorants (Group GS) significantly enhanced the surface wear resistance to toothbrush abrasion when compared with other techniques involving application of colorants only (Group S) or mixture of colorant and LFP (Group SL). The underlying core ceramic had significantly less wear resistance compared with all externally characterized specimens. The novel esthetic characterization technique showed more wear and less color stability, and is thus not advocated as the "best" method for surface characterization. CLINICAL IMPLICATIONS: Application of a glaze layer provides a more wear-resistant surface from toothbrush abrasion when adjusting or extrinsically characterizing leucite reinforced ceramic restorations. Without the glaze layer, the restoration is subjected to a 2 to 4 times faster rate and amount of wear leading to possible shade mismatch.

Radiological impact assessment to the environment due to waste from disposal of porcelain.

The present study aimed to assess the radiological parameters from gamma rays due to the uncontrolled disposal of porcelain waste to the environment. Qualitative and quantitative identification of radionuclides in the investigated samples was carried out by means of a high-purity germanium (HPGe) detector. The average activity concentrations of the local porcelain samples were measured as 208.28 Bq/kg for 226Ra, 125.73 Bq/kg for 238U, 84.94 Bq/kg for 232Th and 1033.61 Bq/kg for 40K, respectively. The imported samples had an average activity of 240.57 Bq/kg for 226Ra, 135.56 Bq/kg for 238U, 115.74 Bq/kg for 232Th and 1312.49 Bq/kg for 40K, respectively. Radiological parameters and the radium equivalent Raeq for the investigated samples were calculated. The external and internal hazard indices, representative level index (Iγ), alpha index (Iα), and the exemption level (Ix), were estimated to be higher than the recommended value (unity), while the average activity concentrations for the studied samples were higher than recommended levels. In conclusion, we are concerned that disposal of porcelain in the environment might be a significant hazard.

Component analysis of dental porcelain for assisting dental identification.

The fluorescence of porcelain crowns recovered from the mouth of an unknown murder victim, and several control porcelain samples, were examined by fluorescent examination lamps. The fluorescence from two of the control samples was quite similar to that from the porcelain crowns recovered from the victim. To increase the objectivity of the results by quantitative analysis, the composition of each porcelain crown and control sample was also evaluated by wave dispersion X-ray microanalyser. The elements detected from the porcelain crowns of the victim matched those of two of the porcelain samples. Later, the antemortem dental records and radiographs of the victim were obtained through a dentist, who had recognized the name of the porcelain manufacturer in a postmortem dental information request placed on the Japanese Dental Association web page. Although component analysis of dental porcelain may be an effective means of assisting dental identification, a more rapid and non-destructive analysis for detecting the elements is required. The energy dispersive X-ray fluorescence (EDXRF) spectrometer was used for a pilot study of identification of porcelain composition.

[Line scanning analysis of white porcelain from Gong Kiln in early Tang dynasty by energy disperse X-ray fluorescence].

Gong kiln, for its long porcelain-firing history, was one of three representative white porcelain kilns in northern China. In order to improve the quality and whiteness of white porcelain, a decorating layer or cosmetic earth was laid on the body surface in Gong kiln during early Tang dynasty, which was able to blot out rough surface and weaken the influence of fuscous body upon surface color. In this paper the main chemical composition of the white porcelain's profile was analyzed by using energy disperse X-Ray fluorescence. The result showed that different materials were used as cosmetic earth during early Tang dynasty, in accordance with the phenomenon under optical microscope. In addition, the glaze belongs to calcium glaze in which plant ash was added.

Evaluation of Zirconia-Based All-Ceramic Single Crowns and Fixed Dental Prosthesis on Zirconia Implants: 5-Year Results of a Prospective Cohort Study.

OBJECTIVE: The objective of this 5-year cohort investigation was to determine the survival and success rate of all-ceramic reconstructions on zirconia oral implants. MATERIAL AND METHODS: Ninety-three patients received 122 one-piece zirconia implants. One hundred seventeen implants were restored with 63 single crowns (SCs) and 27 three-unit bridges (fixed dental prostheses, FDPs) fabricated using zirconia frameworks (Procera(®) Zirconia, Nobel Biocare(®), Göteborg, Sweden) hand-layered with a silicate ceramic (NobelRondo(™) Zirconia, Nobel Biocare(®)). With any occurrence of chipping regarded as an event, Kaplan-Meier success curves were plotted. Covariates (gender, location, manufacturing date) were estimated by the use of log-rank tests. RESULTS: Eighty-nine patients received prosthetic reconstructions. Sixty-three of them were seen at the 5-year follow-up, with a mean observation time of 58.2 months (47 patients with SCs, 16 patients with FDPs). Reasons for the decreasing number of patients at the follow-up sessions included dropouts due to implant loss (n = 21), moving (n = 3), missed appointments (n = 1), and severe illness (n = 1). Over half of the SCs (57.2%) and 38% of the FDPs were successful after an observation time of 5 years (overall success rate of 51.7%). The performed log-rank tests revealed no statistically significant differences for the success curves regarding the above-mentioned covariates. Among the 63 restorations that completed the study, 11 of 47 SCs and one of 16 FDPs had to be replaced due to the severity of the observed chipping. This results in survival rates of 76.6% for the SCs and 93.8% for the FDPs. No framework fractures or decementations were observed in any group. CONCLUSION: Hand-layering of zirconia-based SCs and FDPs with NobelRondo(™) Zirconia restoring one-piece zirconia implants did not show acceptable survival and success rates. Meanwhile, the material has been recalled from the market. It is advised that new materials should undergo adequate preclinical evaluation before coming to the market.

Estimation of radiation dose from porcelain teeth containing uranium compound.

Uranium concentrations of porcelain teeth were determined using the fission track method. The uranium contents of each brand range 0.33-10 ppm, 0.69-81 ppm, 2.5-14 ppm, and 11-205 ppm, respectively. In addition, corresponding dose equivalents to the oral mucosa were calculated.

Topography and distribution of trace surface metals (Sn, In) on alloys for porcelain-metal restoration: influence of surface treatment.

Gold alloys were given five different conditioning treatments prior to porcelain firing. The alloys were examined with a scanning electron microscope and energy dispersive X-ray analyzer. Only two of the alloys had tin and indium present; these were concentrated in particles partially fused to the alloy's surface.

Microstructures in non-precious alloys near the procelain-metal interaction zone.

The chemistry of microstructures near the interfacial reaction zones of four non-precious alloys and two different brands of dental porcelain has been analyzed. It was found that most non-precious dental alloys contain second phases which can alter elemental concentration profiles. Recommendations for assessing interfacial reaction zone chemistry in dental non-precious alloys are offered.

Dental porcelain/Ni alloy interface reactions and their effective prevention.

In a Be-bearing Ni alloy porcelainized without preoxidation, Be diffuses to the interface, oxidizes, and oxygen is supplied by the atmosphere at the porcelain surface and by reduction of SiO2 at the porcelain-alloy interface. On the alloy side of the interface, pits develop locally and near them Ni and Cr oxidize. In the oxide, Ni and Si are reduced to form nickel silicides. Preoxidation of the alloy prevents Be oxidation and Si reduction for several hours of porcelainization.

Be, Li, and Na redistribution near a porcelain/Ni alloy interface shown by ion microprobe mass analysis.

During porcelainization the non-preoxidized alloy develops a Be-rich reaction zone in the interface which separates a Be-depleted alloy from a Li and (to a lesser extent Na) depleted region of the ceramic. Thus, Be diffuses to the interface through the alloy Be degrees leads to Be++ + 2 e- occurs at the interface; some of the electrons are electronically conducted to the porcelain-air interface where they are consumed as 2 e- + 1/2 O degrees 2 leads to O=, and the resulting negatively charged porcelain surface attracts Li+ (and Na+).

Adherence controlling elements in ceramic-metal systems. II. Nonprecious alloys.

Nickel-chromium alloy-ceramic couples used in this study exhibited Cr, Ni-Cr, and Ti-Cr interactions with bonding agent-ceramic complexes. Bonding agents may broaden or suppress the width of interaction zones. Metal oxides such as NiO, Cr2O3, or more complex forms such as TiO-Cr2O3 and NiCr2O4 may play a prominent role in controlling ceramic-metal adherence.

Enhanced chemical strengthening of feldspathic dental porcelain.

Previous studies on ion exchange of dental ceramics have shown that the biaxial flexural strength can be improved by exchanging potassium for sodium ions at temperatures below the strain point. The rubidium ion is bigger than the potassium ion and can also be considered as a candidate for replacing smaller ions, i.e., sodium or potassium, although it has not been used for dental ceramics. The double-step method uses the exchange of a small ion for a large ion (Li for Na) above the strain point, and the further exchange of a large ion for a small ion (K for Li) below the strain point. The purpose of this study was to compare the effect of rubidium-for-potassium ion exchange with that of potassium-for-sodium exchange (Tuf-Coat, G-C International Corp., Japan) on the flexural strength of a feldspathic dental porcelain and to test the hypothesis that a double-step ion exchange can lead to greater strengthening than potassium ion exchange alone. Weight measurements were performed before and after treatment. Qualitative chemical analyses allowed the rubidium, potassium, and sodium concentration profiles to be determined along cross-sections of the specimens. The maximum biaxial stresses were calculated after specimens were fractured in water on a ball-on-ring fixture at 0.5 mm/min. Relative to the untreated control group, the flexural strength of the potassium-exchanged groups was significantly increased, except for those treated at 400 or 500 degrees C. All the groups treated with RbNO3 exhibited a significant increase in flexural strength, with a maximum for the group treated at 450 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

Flexural strength and fracture toughness of Dicor glass-ceramic after embedment modification.

Previous studies on the surface properties of Dicor castable glass-ceramic have shown the formation of a specific crystalline phase at the glass-ceramic/embedment interface. If this phase is not removed by grinding, it leads to an undesirable strength decrease. The aims of this study were: (1) to determine the nature of this surface layer, (2) to promote the formation of a different crystalline phase at the surface with the intention of improving the properties of the glass-ceramic, by modification of the composition of the Dicor ceramming embedment, and (3) to evaluate the fracture toughness and flexural strength of Dicor glass-ceramic after embedment modification. Modifications were made to the embedment by incorporation of 2.5 wt% of lithium fluoride and ceramming at various temperatures. X-ray diffraction was used to determine the crystalline nature of the surface layer. Fracture toughness was investigated by the indentation technique. The maximum bi-axial stresses were calculated after the samples were fractured in water on a ball-on-ring fixture at 0.5 mm/min. With the recommended embedment and ceramming cycle, the crystalline phase constituting the ceram layer was a calcium magnesium silicate CaMg(SiO3)2 (diopside). The crystalline composition of the ceram layer was successfully modified by addition of 2.5 wt% lithium fluoride to the embedment. This promoted the crystallization of mica in the ceram layer and increased the fracture toughness of the glass-ceramic when the ceramming temperature was 950 or 975 degrees C. The flexural strength was significantly increased when the ceramming temperature was 1000 degrees C.

Strengthening of feldspathic porcelain by ion exchange and tempering.

This study investigated the effectiveness of tempering and ion-exchange treatments on crack growth and bi-axial flexural strength of seven feldspathic porcelains. The results showed that tempering treatment was more effective in strengthening porcelain than was the ion-exchange process as measured by the bi-axial flexural strength. However, the results of initial crack size induced by a microhardness tester showed that ion-exchange yielded a surface that was more resistant to crack initiation than was that yielded by the tempering treatment. EDX and microprobe analyses showed that there was evidence of exchange between Na+ within the porcelain surface and K+ from the ion-exchange agent applied on the surface.