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PubMed2004

Appropriate radial clearance of ceramic-on-ceramic total hip prostheses to realize squeeze-film lubrication.

OBJECTIVE: Estimation of appropriate radial clearance of ceramic-on-ceramic total hip prostheses to realize squeeze-film lubrication. BACKGROUND: Some clinical results show that severe wear occurs at ceramic-on-ceramic interfaces of total hip prostheses if the design parameters are improper. Appropriate design is required to realize the optimum lubrication of joint prostheses. DESIGN: Squeeze-film thickness of total hip prostheses with different radial clearances was numerically estimated under the physiological conditions of normal walking. METHODS: The changes in the fluid film thickness between ceramic balls and a ceramic cups with radial clearances of various values from 10 to 80 microm were numerically estimated under the assumption of normal walking conditions by means of elastohydrodynamic squeeze-film lubrication theory including the three-dimensional theory of elasticity. RESULTS: The minimum film thickness remained over 0.02 microm during a few walking steps with a radial clearance under 20 microm and a head diameter of 28 mm. On the other hand, the fluid film was squeezed out during a few steps when the radial clearance was greater than 30 microm. CONCLUSIONS: Squeeze-film lubrication can be realized in a ceramic-on-ceramic total hip prosthesis if the radial clearance is smaller than 20 microm on a head of 28 mm diameter. RELEVANCE: Fluid film lubrication is necessary to prevent the severe wear of ceramic joint prostheses. The present investigation shows which radial clearance of ceramic-on-ceramic hip prostheses is appropriate for squeeze-film lubrication under physiological conditions in daily action.

Ceramics↗
PubMed1995

Flexural strength of an infused ceramic, glass ceramic, and feldspathic porcelain.

In-Ceram material is a relatively new all-ceramic restorative material with improved properties that require research. The clinical selection of restorative materials is based on a number of parameters such as esthetics, fit, and strength. This study determined the flexural strength of In-Ceram system components and compared the core material with conventional feldspathic ceramics and with Dicor all-ceramic restorative material. Four-point flexural strength values of bend bars of each ceramic were 18.39 +/- 5.00 MPa for In-Ceram sintered alumina, 76.53 +/- 15.23 MPa for In-Ceram infusion glass, and 236.15 +/- 21.94 MPa for In-Ceram infused alumina core. Flexural strength of self-glazed feldspathic porcelain was 69.74 +/- 5.47 MPa, as-cast Dicor ceramic 71.48 +/- 7.17 MPa, and polished Dicor ceramic was 107.78 +/- 8.45 MPa.

Aluminum Oxide↗
PubMedDate not supplied

Mechanical properties of In-Ceram Alumina and In-Ceram Zirconia.

PURPOSE: This study compared the mechanical properties of In-Ceram Zirconia and In-Ceram Alumina. MATERIALS AND METHODS: Ninety-four disks and six bars were prepared with the slip-casting technique. The disks were used to assess biaxial flexural strength (piston on three ball), Weibull modulus, hardness, and fracture toughness with two methods: indentation fracture and indentation strength. The bars were used to measure elastic moduli (Young's modulus and Poisson's ratio). X-ray diffraction analysis of the specimens was carried out upon every step of the specimen preparation and of the fractured surfaces. RESULTS: Mean biaxial flexure strengths of In-Ceram Alumina and In-Ceram Zirconia were 600 MPa (SD 60) and 620 MPa (SD 61), respectively. Mean fracture toughness measured according to indentation strength was 3.2 MPa.m1/2 (SD 0.34) for in-Ceram Alumina and 4.0 MPa.m1/2 (SD 0.43) for In-Ceram Zirconia. Mean fracture toughnesses of In-Ceram Alumina and In-Ceram Zirconia measured according to indentation fracture were 2.7 MPa.m1/2 (SD 0.34) and 3.0 MPa.m1/2 (SD 0.48), respectively. X-ray diffraction analysis showed that little phase transformation from tetragonal to monoclinic occurred when the specimens were fractured, supporting the existence of a modest difference of fracture toughness between the two ceramics. CONCLUSION: No statistically significant difference was found in strength. In-Ceram Zirconia was tougher (P < .01) than In-Ceram Alumina when tested according to indentation strength. However, no significant difference was found in the fracture toughness when tested with the indentation fracture technique.

Aluminum Oxide↗
PubMed1985

[Antigenicity of alumina ceramic and calcium phosphate ceramics--genetic control of the immune response].

Antigenicity of alumina ceramic, hydroxyapatite ceramic and tricalcium phosphate ceramic was studied by induction of footpad swelling in C57BL/6 mice immunized by ceramics with Freund's complete adjuvant. Significant footpad swelling was observed in mice immunized with tricalcium phosphate ceramic at 2 and 4 weeks after immunization. Antigenic specificity was demonstrated between tricalcium phosphate ceramic and fetal bovine serum in crisscross. Time course of the reaction suggested that delayed-type hypersensitivity played an important role in footpad swelling. These results indicate that tricalcium phosphate ceramic has antigenicity to C57BL/6 mice. Antigenicity of alumina ceramic and hydroxyapatite ceramic was not demonstrated in this study. A positive footpad reaction to tricalcium phosphate ceramic was shown in C57BL/10 (H-2b) and C57BL/10 X BR (H-2k), but was not observed in C57BL/10 X D2(H-2d). These results suggest that this response to tricalcium phosphate ceramic was under control by a gene located within the major histocompatibility complex.

Aluminum↗
PubMed2005

Marginal fit of leucite-glass pressable ceramic restorations and ceramic-pressed-to-metal restorations.

STATEMENT OF PROBLEM: Fabricating a feldspathic porcelain margin on a metal-ceramic restoration with a clinically acceptable marginal fit has proven to be a technique-sensitive procedure. Pressable ceramics are advocated to solve this problem. PURPOSE: The purpose of this in vitro study was to compare the marginal adaptation of a pressable ceramic system when used with both all-ceramic and metal-ceramic crowns, with a traditional metal-ceramic restoration. MATERIAL AND METHODS: A 1.5-mm, 360-degree chamfer margin was prepared on a typodont maxillary central incisor. Polyether impressions were made and poured in a Type IV dental stone, and the following crowns were fabricated on individual dies: 15 metal ceramic restorations (MCR) (Ceramco II, Ceramco, and Argelite 60), 15 pressed-to-metal restorations (PTM) (CPC-MK, and Argelite 60), and 15 pressed ceramic restorations (PCR) (CPC-MK). The marginal fit of the crowns was evaluated every 90 degrees around the crown margin circumference under a microscope at original magnification x 45. A 1-way analysis of variance (ANOVA) was used to compare data (alpha=.05). RESULTS: The mean marginal discrepancy for MCRs was 94 +/- 41 microm, for PTMs, 88 +/- 29 microm, and for PCRs, 81 +/- 25 microm. The 1-way ANOVA showed no significant difference between groups ( P =.568). CONCLUSION: The marginal fit of pressed-to-metal (PTMs) and pressed all-ceramic crowns (PCRs) was similar to that of traditional metal-ceramic crowns (MCRs).

Aluminum Silicates↗
PubMed2003

The effect of investment material and ceramming regime on the surface roughness of two castable glass-ceramic materials.

OBJECTIVE: To assess the surface roughness (R(a)) of two castable glass-ceramic materials, cast using four different investment materials and employing different ceramming regimes. METHODS: Forty discs, each 12 mm diameter and 2 mm thick were produced from two castable glass-ceramic materials, one a glass ionomer derivative based on 1.5SiO(2)-1Al(2)O(3)-0.53P(2)O(5)-1CaO-0.67CaF(2) (LG112), the other a fluorcanasite material based on 0.60SiO(2)-0.05K(2)O-0.10Na(2)O-0.15CaO-0.10CaF(2) (SG3). The discs were made using four dental investments, two gypsum-bonded (Whip-Mix Cristobalite (WMC), Degussa California (DC)) and two phosphate-bonded (Fujivest Super (FS), Techceram Glass (TG)). A Ni-Cr metal/ceramic alloy (Wiron 99) was also used as a control. Each investment was used to produce 10 discs for each glass-ceramic material, five left in the as-cast, glass state, the other five cerammed. Ceramming was carried out either within the investment mold or after de-vesting from the investment mold. The discs had their surface roughness values measured using a stylus, surface contact measuring instrument. RESULTS: For the Ni-Cr alloy the phosphate-bonded investments produced discs significantly smoother than those produced by the two gypsum-bonded investments (p<0.05). The FS investment produced the smoothest discs (p<0.05), but there was no significant difference between the discs produced by the two gypsum-bonded investments (p>0.05). For the SG3 material no significant differences were seen between the as-cast glass and cerammed discs (p>0.05), with the WMC investment producing the smoothest discs (p<0.05), and the TG investment the roughest (p<0.05). The LG112 material showed a significant difference between glass and cerammed discs for the gypsum-bonded investments (p<0.05) but not when using phosphate-bonded investments (p>0.05). With LG112 the WMC investment produced smoother discs than the DC and TG investments (p<0.05). The DC investment produced rougher discs than the two phosphate-bonded investments (p<0.05). SIGNIFICANCE: The selection of investment material can have a significant effect on the as-cast surface finish of castable glass-ceramic materials. A gypsum-bonded investment material gave smoother surface finishes compared to phosphate-bonded investments. The ceramming process significantly increases surface roughness.

Analysis of Variance↗
PubMed1990

Massive wear of a steel ball head by ceramic fragments in the polyethylene acetabular cup after revision of a total hip prosthesis with fractured ceramic ball.

The purpose of this case study of severe metallosis is to draw the attention of orthopedic surgeons to extremely serious results of this kind in the event of the fracture of the ceramic ball in a total hip prosthesis. Eleven months after implantation of a KJF hip prosthesis with an aluminum oxide ceramic ball in combination with a polyethylene acetabular cup, fracture of the ceramic ball was observed. After examining the polyethylene cup during the revision operation, the operating orthopedic surgeon merely replaced the fractured ceramic ball with a metal ball head made of stainless steel. Twenty-five months after this procedure, radiography revealed massive wear of the steel ball head with resulting severe metallosis of the surrounding tissues. All prosthetic components therefore had to be removed. Careful examination of the removed prosthetic components clearly showed that sharp-edged ceramic particles originating from the fractured ceramic ball had become embedded in the bearing surface of the polyethylene cup. These tiny ceramic fragments, ranging from 0.05 to 2 mm, were too small to be seen by the operating surgeon's unaided eye. It is these extremely hard ceramic fragments that were responsible for the massive wear of the steel ball head, the hardness of which is approximately ten times less than that of aluminum oxide ceramic. The fracture of the ceramic ball further resulted in damage to the metal taper of the stemmed femoral component. In cases of this kind it is consequently absolutely essential to remove both the polyethylene cup and the ball head, and--if necessary--the femoral component as well.

Acetabulum↗
PubMed2004

Strength, fracture toughness and microstructure of a selection of all-ceramic materials. Part I. Pressable and alumina glass-infiltrated ceramics.

OBJECTIVE: The present study, divided into two parts, aimed to compare the strength, fracture toughness and microstructure of a range of all-ceramic materials. In part I, three hot-pressed glass-ceramics (IPS-Empress, Empress 2 and a new experimental ceramic) and alumina glass-infiltrated ceramics (In-Ceram Alumina), processed by both slip casting and dry pressing, were compared. METHODS: Tensile strength was appraised on 10 bar-shaped specimens (20 x 4 x 1.2 mm3) for each material with the three-point bending method; the fracture toughness was measured from 20 specimens (20 x 4 x 2 mm3), by using the indentation strength technique. Data were compared with ANOVA and the Sheffé post hoc test (p = 0.05). The volume fraction of each phase, the dimensions and shapes of the grains, porosity and the crack patterns were investigated using SEM. RESULTS: The average and standard deviation in strength (MPa) and fracture toughness (MPa m(1/2)) were: IPS-Empress 106(17)1, 1.2(0.14)1; Empress 2 306(29)2, 2.9(0.51)2, new experimental ceramic 303(49)2, 3.0(0.65)2, In-Ceram Alumina dry-pressed 440(50)2, 3.6(0.26)2, In-Ceram Alumina slip 594(52)3, 4.4(0.48)3. Values with the same superscript number showed no significant statistical difference. Microscopy revealed the relationship between the glass matrix and the crystalline phase and the characteristics of the latter were correlated to the strengthening and toughening mechanisms of these glass-ceramics. SIGNIFICANCE: The mechanical properties and microstructure of core materials have been advocated as crucial to the clinical long-term performance of all-ceramic dental restorations. This investigation provides the clinician with data regarding strength, fracture toughness and microstructure of a broad range of current materials.

Aluminum Silicates↗
PubMedDate not supplied

[Computer-based motion simulation of total hip prostheses with ceramic-on-ceramic wear couple. Analysis of implant design andorientation as influence parameters].

OBJECTIVE: In THA, ceramic-on-ceramic wear couples are increasingly used. A restricted range of motion (ROM) due to unfavourable implant design or positioning may cause impingement or dislocation, which can result in failure of ceramic inserts. METHODS: By means of a 3-D CAD program different hip joint movements were simulated and the effects of ceramic hip implant design and position on the range of motion were analysed. RESULTS: To offer sufficient ROM and to minimise risk of impingement and dislocation, inclination angle of the acetabular cup should be 45 degrees, cup anteversion 15 degrees and stem antetorsion 0 degrees to 10 degrees. In regard to implant design, acetabular cups with slightly- recessed ceramic inserts should be used. Prosthetic systems with an elevated liner or with a mushroom-shaped femoral head are associated with limited ROM and increased risk of mechanical failure. The ratio of head to neck diameter should never be less than 2 : 1. Larger heads not only increase ROM, but also the stability of the prosthesis against dislocation. Thereby, the wear rate of ceramic-on-ceramic couples is not increased, in contrast to polyethylene. CONCLUSION: Considering certain criteria for ceramic hip implants regarding implant positioning, design and handling, ceramic-on-ceramic couples can be used with low risk of revision surgery and they can also reduce the prosthesis loosening associated with wear in young and active patients.

Ceramics↗
PubMed2000

Modern ceramic-on-ceramic total hip systems in the United States: early results.

In 1997, two manufacturers began Food and Drug Administration approved investigations of a ceramic-on-ceramic (alumina) articulation total hip replacement in the United States. Osteonics (Allendale, NJ) and Wright Medical Technology (Arlington, TN) enrolled more than 500 and 300 patients, respectively, when their studies ended in the middle part of 1998. The author presents detailed early results of the series by Wright Medical Technology. Three hundred thirty-three patients were enrolled in 11 centers around the country in a prospective series. All patients received the Transcend ceramic-on-ceramic articulation and have a minimum of 18 months followup with a range of 18 to 36 months. Harris hip scores increased on average from 44 to 97 points. Four patients underwent revision surgery; one for deep infection, one for early migration of the cup, one for dislocation, and one for liner malplacement. Overall, there were 42 complications. Seven were systemic and 35 were related to the total hip replacement. Four of the 35 complications were ceramic related and included three chipped liners and one eccentric seating of the cup liner. To date, no patient underwent revision surgery for aseptic loosening. Seven technical guidelines are suggested to enhance the quality of the intraoperative and postoperative results: a conservative femoral neck cut; horizontal cup placement (< 45 degrees); increased anteverted cup placement (> 20 degrees); use of trial liners; impaction of ceramic pieces; hand placement of the liner; and removal of osteophytes and/or part of the anterior wall of the acetabulum to avoid impingement. Alternate bearing articulations, particularly ceramics, have important technical aspects to be considered at the time of implantation to minimize intraoperative and postoperative complications. To date, there have been no postoperative fractures of the ceramic pieces in any of the completed or ongoing ceramic-on-ceramic investigations by all involved manufacturers. These preliminary results are satisfactory at this time. One can look to the future with cautious optimism.

Arthroplasty, Replacement, Hip↗
PubMed2000

Effect of a ceramic and a non-ceramic hydroxyapatite on cell growth and procollagen synthesis of cultured human gingival fibroblasts.

BACKGROUND: Ceramic hydroxyapatites and non-ceramic hydroxyapatites have been used extensively as alloplastic materials for bone reconstruction. However, different forms of hydroxyapatite induce different types of tissue response. METHODS: Human gingival fibroblasts (FMM1 cells) were used to analyze ceramic and non-ceramic hydroxyapatite biocompatibility. The cells were grown on surfaces covered either by collagen (control group), collagen plus ceramic hydroxyapatite, or collagen plus non-ceramic hydroxyapatite. Scanning electron microscopy, growth and cell viability curves, and procollagen immunoprecipitation were obtained. For the growth and viability curves, 10(4) cells were seeded on 60 mm dishes. Cells from each group were counted, in triplicate, at 1, 3, 4, 5, and 6 days after seeding using the Trypan blue dye exclusion assay. RESULTS: The cells grew in close contact with both types of hydroxyapatite particles. No differences were found in the amount of procollagen synthesis among any experimental group. The cultures treated with ceramic hydroxyapatite had a growth delay for the first 5 days. There was no difference in cell viability between the control group and the non-ceramic hydroxyapatite group. However, cultures treated with ceramic hydroxyapatite showed significantly lower viability percentages than the other groups. CONCLUSIONS: Hydroxyapatite supports cell growth and fibroblast metabolism including collagen production, and hence is biocompatible. Cell viability and structural studies showed that non-ceramic hydroxyapatite has relevant physical and biological properties as an implant material.

Algorithms↗
PubMedDate not supplied

Flexural strength of In-Ceram alumina and In-Ceram zirconia core materials.

PURPOSE: The study compared the flexural strength of In-Ceram alumina and In-Ceram zirconia systems. The probability of failure of the two glass-infiltrated ceramic core materials was analyzed with and without lamination with Vitadur-alpha porcelain. MATERIALS AND METHODS: Ten uniform beams of core materials as well as 10 beams of laminated core materials were fabricated for In-Ceram alumina and In-Ceram zirconia. The samples were subjected to three-point bending tests. Flexural strength for both ceramic core materials was determined with and without their porcelain laminations. The strength data were analyzed using the Weibull method. Modes of failure for both systems were determined using scanning electron micrography. RESULTS: The strength of the In-Ceram zirconia system was significantly higher than In-Ceram alumina when comparing their core materials with and without porcelain lamination. The failure mode for both systems was predominantly transgranular fracture of alumina platelets. CONCLUSION: In-Ceram zirconia demonstrated higher flexural strength than In-Ceram alumina.

Aluminum Oxide↗
PubMed2004

Strength, fracture toughness and microstructure of a selection of all-ceramic materials. Part II. Zirconia-based dental ceramics.

OBJECTIVE: The present study is the second part of an investigation of strength, fracture toughness and microstructure of nine all-ceramic materials. In the present study, DC Zirkon, an experimental yttria partially stabilized zirconia, In-Ceram Zirconia slip and In-Ceram Zirconia dry-pressed were compared. METHODS: Strength was appraised on ten bar-shaped specimens for each material (20 x 4 x 1.2 mm) with the three-point bending method. The fracture toughness (Indentation Strength) was measured on twenty specimens (20 x 4 x 2 mm) for each ceramic. The volume fraction of each phase, the dimensions and shapes of the grains and the crack pattern were investigated with SEM. Phase transformation was investigated with X-ray diffraction. Data were compared with an ANOVA and Sheffé post hoc test (p = 0.05). RESULTS: Means of strength (MPa) and fracture toughness (MPa m(1/2)) values and their standard deviation were: In-Ceram Zirconia dry-pressed 476 (50)1, 4.9 (0.36)1; In-Ceram Zirconia slip 630 (58)2, 4.8 (0.50)1; the experimental yttria partially stabilized zirconia 680 (130)2, 5.5 (0.34)2; DC-Zirkon 840 (140)3, 7.4 (0.62)3. Values with the same superscript number showed no significant statistical difference. Microscope investigation and X-ray diffraction revealed the important role played by the tetragonal to monoclinic phase transformation and by the relationship between the glassy matrix and the crystalline phase in the strengthening and toughening mechanisms of these ceramics. SIGNIFICANCE: the zirconia-based dental ceramics are stronger and tougher materials than the conventional glass-ceramics. Better properties can have positive influence on the clinical performance of all-ceramic restorations.

Analysis of Variance↗
PubMed2002

Ceramic-on-ceramic bearings in total hip arthroplasty.

The ideal bearing surface for total hip arthroplasty still is being sought. This bearing would be durable, cost-effective, easy to implant, inert, and produce minimal wear debris. Ceramic-on-ceramic bearings have continued to evolve and have enjoyed success in many European centers throughout the past 3 decades. A limited number of early reports from the United States discouraged widespread acceptance and use of ceramic-on-ceramic total hip arthroplasty. Once critically analyzed most of the failures from the early reports are attributable to design and material specific flaws. Vast improvements have been made in ceramic manufacturing leading to even more superior wear characteristics and higher burst strengths. The case for alumina-on-alumina ceramic bearings is becoming stronger as data accumulate clinically and in vitro. In a multicenter, prospective and randomized study, an alumina-on-alumina ceramic bearing is compared with a cobalt chrome-on-polyethylene bearing. After as many as 48 months there has been no significant difference in clinical performance between the two study groups. No ceramic head fracture or ceramic bearing failure has occurred. Therefore, this new alumina-on-alumina ceramic bearing is a safe option for total hip arthroplasty and may provide a more durable prosthesis especially in young and active patients.

Aluminum Oxide↗
PubMed2004

In vitro fracture resistance of posterior metal-ceramic and all-ceramic inlay-retained resin-bonded fixed partial dentures.

STATEMENT OF PROBLEM: Inlay-retained resin-bonded fixed partial dentures (RBFPDs) are conservative prosthetic restorations; however, their resistance to fracture is not clear. PURPOSE: The purpose of this study was to compare fracture loads of posterior complete coverage metal-ceramic restorations with all-ceramic inlay-retained RBFPDs. MATERIAL AND METHODS: Thirty-two posterior ceramic RBFPD restorations were divided into 4 groups (n=8): (1) Complete metal-ceramic fixed partial dentures (MC-FPDs) fabricated of Ni-Cr-based alloy (Wirolloy) and veneered with a ceramic (IPS d.SIGN) as the control group; (2) inlay-retained metal-ceramic (MC RBFPDs) with the same materials as the control; (3) inlay-retained lithium disilicate (LD) glass-ceramic (IPS Empress 2) RBFPDs; and (4) inlay-retained zirconia-based (Z) ceramic (Cercon) RBFPDs. Control specimens were prepared to receive conventional complete MC-FPDs designed to include a 1.3-mm-circumferential, 90-degree flat shoulder with rounded angles. Inlay-retained RBFPD specimens were prepared with 2-mm occlusal reduction but without bevels at the occlusal or gingival margins. Specimens were loaded and fracture loads (N) measured at fracture with a universal testing machine at a crosshead speed of 1.0 mm/min and 250 kgf load cell. Data were analyzed with 1-way ANOVA and Duncan test (alpha=.001). RESULTS: Fracture loads (mean +/- SD) were greatest for control specimens (1318.43 +/- 211.00 N) and Z-RBFPD (1247.70 +/- 262.51 N) specimens as compared to MC-RBFPD or LD-RBFPD (P < .001). MC-RBFPD exhibited the next highest fracture loads (958.01 +/- 194.29 N), and LD-RBFPD exhibited the significantly lowest values (303.23 +/- 92.54 N) of the materials tested (P < .001). CONCLUSION: Inlay-retained zirconia-based ceramic RBFPDs demonstrated the greatest fracture resistance among all inlay-retained restorations tested.

Ceramics↗
PubMed1994

In vitro fracture behavior of ceramic and metal-ceramic restorations.

PURPOSE: Failed crowns and failure load data were studied to gain insights into the fracture behavior of prostheses under incisal-directed, load-to-failure testing. MATERIALS AND METHODS: Incisor crowns (n = 68) were fabricated: two all-ceramic groups (feldspathic veneer on high-strength core), differing in core design, and two metal-ceramic groups, differing in metal oxidation time (30 seconds v 3 minutes). Crowns were loaded to failure on their incisal edge. Gross visual, microscopic, and elemental microprobe analyses of failed crowns were coupled with Weibull analysis of the failure load data. RESULTS: Failure loads were higher for the normal oxidation time (TN) than for the extended oxidation time (TE) metal-ceramic crowns (P < .02), but both groups had indistinguishable Weibull moduli indicating the possibility of a common failure origin. Fracture behavior and Weibull results both implicated the oxide layer as being the origin of failure. The ratio of fracture loads (TE/TN) corresponded well with calculated oxide-volume ratios. Failure loads were lower for the all-ceramic than for the metal-ceramic crowns (P < .001). Fifty percent of the all-ceramic crowns failed by delamination of veneering glass alone, leaving a thin layer of residual glass on the core surface. Scanning electron microscope views showed that delamination occurred 10 to 50 microns away from the core-veneer interface. Electron microprobe elemental analysis of the core-veneer interface showed that residual core infiltration glass was not present on the core surface and that chemical alterations in the veneering glass were apparently limited to less than a 2- to 3-microns thick layer. CONCLUSIONS: Failure for both restorative systems involved interfacial stresses with crack propagation occurring at or near the core-veneer interface. The weaker interface in the metal-ceramic system probably resulted from an increase in surface oxide volume, irrespective of any change in its adherence or physical properties. For the ceramic crowns, delamination crack fronts appeared to propagate through chemically unaltered veneering porcelain. Both the Weibull moduli and characteristic strengths were indistinguishable between either of the two ceramic core designs or between groups failing from delamination with or without core cracking/failure. This is consistent with delamination being the primary fracture process during failure. Clinical implications should not be drawn from results of this study because no correlation is known to have ever been established between clinical behavior and incisal load-to-failure results.

Aluminum Oxide↗
PubMed2006

Influence of ceramic surface conditioning and resin cements on microtensile bond strength to a glass ceramic.

STATEMENT OF PROBLEM: It is not clear how different glass ceramic surface pretreatments influence the bonding capacity of various luting agents to these surfaces. PURPOSE: The purpose of this study was to evaluate the microtensile bond strength (microTBS) of 3 resin cements to a lithia disilicate-based ceramic submitted to 2 surface conditioning treatments. MATERIAL AND METHODS: Eighteen 5 x 6 x 8-mm ceramic (IPS Empress 2) blocks were fabricated according to manufacturer's instructions and duplicated in composite resin (Tetric Ceram). Ceramic blocks were polished and divided into 2 groups (n=9/treatment): no conditioning (no-conditioning/control), or 5% hydrofluoric acid etching for 20 seconds and silanization for 1 minute (HF + SIL). Ceramic blocks were cemented to the composite resin blocks with 1 self-adhesive universal resin cement (RelyX Unicem) or 1 of 2 resin-based luting agents (Multilink or Panavia F), according to the manufacturer's instructions. The composite resin-ceramic blocks were stored in humidity at 37 degrees C for 7 days and serially sectioned to produce 25 beam specimens per group with a 1.0-mm(2) cross-sectional area. Specimens were thermal cycled (5000 cycles, 5 degrees C-55 degrees C) and tested in tension at 1 mm/min. Microtensile bond strength data (MPa) were analyzed by 2-way analysis of variance and Tukey multiple comparisons tests (alpha=.05). Fractured specimens were examined with a stereomicroscope (x40) and classified as adhesive, mixed, or cohesive. RESULTS: The surface conditioning factor was significant (HF+SIL > no-conditioning) (P<.0001). Considering the unconditioned groups, the microTBS of RelyX Unicem was significantly higher (9.6 +/- 1.9) than that of Multilink (6.2 +/- 1.2) and Panavia F (7.4 +/- 1.9). Previous etching and silanization yielded statistically higher microTBS values for RelyX Unicem (18.8 +/- 3.5) and Multilink (17.4 +/- 3.0) when compared to Panavia F (15.7 +/- 3.8). Spontaneous debonding after thermal cycling was detected when luting agents were applied to untreated ceramic surfaces. CONCLUSION: Etching and silanization treatments appear to be crucial for resin bonding to a lithia disilicate-based ceramic, regardless of the resin cement used.

Ceramics↗
PubMed2002

Influence of abutment substrate and ceramic thickness on the colour of heat-pressed ceramic crowns.

All-ceramic crowns made of leucite-based heat-pressed ceramics are widely used to restore non-vital teeth in conjunction with various post and core materials. However, as some light passes through the ceramic, the colour of the abutment substrate can negatively affect the final aesthetic appearance of the all-ceramic crown. In this study, we made background specimens simulating gold-alloy cast posts and other simulating porcelain veneered cast posts, overlaid different thickness of heat-pressed ceramic on these background specimens, and measured the shifts in colour. We found that, when the background specimen was a gold alloy, the background colour had an effect on the apparent colour, unless the ceramic was more than 1.6 mm thick. When the background specimen was porcelain veneered, the background colour had no evident effect, even when the ceramic was not very thick. Therefore, when making a restoration using a leucite-based heat-pressed ceramic crown, it is advisable to use tooth-coloured materials such as a porcelain veneered cast post, if you will not be able to make the ceramic more than 1.6 mm thick.

Aluminum Oxide↗