Color stability of pressed lithium disilicate ceramics under repeated firings evaluated by different methods.

PURPOSE: The aim of this study was to determine and compare color differences of pressed lithium disilicate ceramic specimens after repeated firing cycles. An additional objective was to determine and evaluate correlation of CIEDE2000 values analyzed by X-Rite Color i5 Spectrophotometer, VITA EasyShade Advance 4.0 and Adobe Photoshop. MATERIAL AND METHODS: Tile specimens (N=36) with 8 x 10 x 1.5mm dimensions were prepared by IPS e.max Press lithium disilicate MT Monochromatic ingots and IPS e.max Multi Press lithium disilicate Multichromatic ingots. Specimens were exposed to 7 repeated firing cycles. Color analysis was performed after the 1st, 2nd, 3rd, 5th, and 7th firing cycles. CIE L*a*b* values were measured by X-Rite Color i5 Spectrophotometer, VITA EasyShade Advance 4.0 and Adobe Photoshop. CIE DE*2000 (ΔE*00) was calculated to estimate color differences. RESULTS: Linear regression and multiple comparison analysis (Tukey's HSD test) showed a statistically significant (p<.001) color difference ΔE*00 after multiple firing cycles. Statistically significant differences (p<.05) were also noted in different shade groups and between different instruments used for shade evaluation. Moreover, significant differences (p<.05) were found in interactive effects between different shades tested by different instrument, different shades tested after multiple firing cycles and different instruments after multiple firing cycles. CONCLUSIONS: Lithium disilicate material shows significant color differences after repeated firing cycles tested by three color analysis instruments. Measuring instruments used to evaluate CIE L*a*b* color values showed significant differences in color values analysis, which may lead to altered level of interpretation, particularly to determine perceptibility and clinical acceptability thresholds.

Effect of different storage conditions on dimensional accuracy of 3D-printed dental models.

PURPOSE: The objective was to determine the accuracy of 3D-printed dental models subjected to different storage conditions using six different material and printer combinations. MATERIALS AND METHODS: Three completely dentate models were designed using dental CAD software (3Shape Dental System). A horseshoe-shaped solid base with a posterior horizontal bar was used. The models were printed in a horizontal direction against the building platform without support. The models were printed using six printers with the corresponding recommended resin material: Carbon M2 (DPR10), HeyGears A2D4K (Model HP UV2.0), Stratasys J5 (MED610), Stratasys Origin One (DM200), Envision One (E-Model LightDLP), and Asiga Pro4K (VeriModel) with a standard layer thickness of 50 µm. All printed models underwent scanning using a laboratory scanner (Sirona inEOS X5) after printing. Subsequently, the models were randomly assigned into three groups of storage conditions, LT: cold environment (4 ± 1°C), HT: hot and dry environment (50 ± 2°C), and RT: room temperature (25 ± 2°C) serving as the control. Each group was kept under the designated condition and was scanned at 1, 2, 3, 4, and 8 weeks. The total number of models (N) was 72, with 6 printers producing 12 models per printer for 3 storage conditions, resulting in 4 models for each storage condition and each printer. The generated STL files were imported into a 3D inspection software for comparison with the original STL files. In-tolerance percentage, the deviation RMS, trueness, and precision were obtained and analyzed with least square mean linear regression using JMP Pro 15 to identify the significant effects (α = 0.05). RESULTS: The in-tolerance percentage as-printed was significantly different among different printers. Significant dimension deviations were observed after the first week of storage at HT and with subsequent weeks of storage. RT and LT did not show significant dimensional changes. Models printed with Carbon M2 showed the highest in-tolerance percentages compared to the other printers. CONCLUSIONS: The model deviations were affected by storage conditions and the printer used, with high-temperature storage showed least stability compared to low and room temperatures. No significant difference was observed between low and room temperature storage conditions. The Carbon M2 printer showed the highest accuracy among all printers tested. The region had a significant effect on the deviation measured, with the abutment body showing the least deviation. Among the 3D printers evaluated, A2D4K by HeyGears and Carbon M2 printers demonstrated the highest accuracy in terms of both precision and trueness.

Effect of time period on biaxial strength for different Y-TZP veneering porcelains.

OBJECTIVE: To assess the influence of time period on strength for different conventional Y-TZP porcelains. MATERIALS AND METHODS: Four types of porcelain were used. Porcelain powders were pressed in a steel die and fired in a furnace as recommended by the manufacturer. The blocks were sectioned into 2 mm-thick discs. Seventy specimens were fabricated from each type of porcelain. Of six jars, three contained 40 mL of dH2 O and three were dry. Ten specimens were placed in each jar and stored in an incubator at 37°C. A biaxial flexural strength test was performed for all specimens at the baseline and each succeeding year for all groups, for 3 years, using an Instron with a crosshead speed of 0.5 mm/min. RESULTS: The data were analyzed by ANOVA and Tukey at α = .05. At the baseline, the biaxial flexural strength of VitaVM9 was significantly higher than that of NobelRondo; however, there were no significant differences among Vita VM9 and Noritake CZR or NobelRondo, Lava Ceram, and Noritake CZR. There were significant reductions in the biaxial flexural strengths of all porcelains. CONCLUSIONS: After 3 years, all porcelain groups showed a significant decrease in biaxial flexural strength. The medium used is found to have no significant effects on the mean biaxial flexural strength. CLINICAL SIGNIFICANCE: Certain commercially available Y-TZP porcelains are susceptible to decrease in strength over time, which might impact the integrity of veneered zirconia restorations. This reduction in strength is among the most common reasons for the failure of veneered zirconia as reported in several studies.

Prosthetically Driven Computer-Guided Implant Placement and Restoration Using CEREC: A Case Report.

Developments in 3-dimentional (3D) diagnostic technology and advanced digital optical imaging have improved the predictability, safety, and efficiency of restoratively driven implant dentistry. Surgical procedures may now be performed in a single visit utilizing chairside, computer-aided design/computer-aided manufacturing technology and in situations when a two-stage implant protocol is indicated as demonstrated in this case. The CEREC® GALILEOS® integration workflow system was used to prosthetically plan and place an implant in the lower right mandibular first molar site, No. 30, which had been previously grafted following tooth extraction. Preoperative planning was performed, taking into consideration all anatomic landmarks, current tissue status, and restorative needs while incorporating cone-beam computed tomography data to design and mill a stable, tooth-supported surgical guide (CEREC Guide 2.0). After placement and subsequent osseointegration, the implant was restored chairside in a pre-doctoral treatment center. The Sirona TiBase system and VITA ENAMIC® IS block were used to produce an esthetically pleasing and clinically excellent screw-retained implant crown.

Use of CAD/CAM in Second-Stage Implant Surgery to Achieve Improved Final Restoration Esthetics, Natural Gingival Appearance.

To achieve a predictable esthetic outcome when using an implant-supported crown for rehabilitation of an edentulous space, computer-aided design/computer-aided manufacturing (CAD/CAM) technology can be utilized in the second stage of implant surgery to scan, mill, and restore the implant site all in one office visit. In this case report, an implant for a first molar was restored with a CAM-fabricated hybrid ceramic crown, designed using CEREC® 4.4 software. A 3-dimensional scan was taken chairside at the time of uncovering the implant using powder-free intraoral scanning. Specific design features were implemented to control peri-implant soft-tissue growth to meet the patient's esthetic expectations and achieve an outstanding clinical outcome. This report emphasizes the value of using a CAD/CAM-milled crown in achieving an emergence profile in second-stage surgery, describes a polymer-infiltrated-ceramic-network material as a potential biomaterial for implant restoration, and discusses the importance of taking a digital impression to capture details for improved restoration esthetics and longevity.

Shear bond strength of an experimental composite bracket.

OBJECTIVE: The in vitro shear bond strength of MZ100 brackets (an experimental composite bracket developed by the Dental Biomaterial Laboratory at Boston University) and the effect of different treatment methods on these brackets were evaluated. MATERIALS AND METHODS: As the bonding substrates, 80 Vitablocs® Mark II (Vident, Brea, CA, USA) were chosen. Three treatment methods were employed on 60 MZ100 bracket bases (20 brackets per treatment): silane coupling agent (Porcelain Primer; Ormco, Orange, CA, USA), sandblasting (Basic Professional Model Sandblaster; Renfert GmbH, Germany), and non-treatment. Two different orthodontic adhesives were also used: Blugloo™ (Ormco, Orange, CA, USA) and Enlight™ (Ormco, Orange, CA, USA). Twenty metal brackets were used as controls. Shear bond strength tests were performed after sample preparation and bracket bonding. RESULTS: The mean shear bond strength of non-treated MZ100 brackets bonded with Enlight™ had the lowest value (7.9 MPa), while that of sandblasted MZ100 brackets bonded with Blugloo™ showed the highest value (17.9 MPa). The mean shear bond strength of non-treated MZ100 brackets was significantly lower than that of the other groups (p<0.05). The mean shear bond strength of sandblasted MZ100 brackets bonded with Blugloo™ was significantly higher than that of those bonded with Enlight™ (p<0.05). With the exception of the silane-Blugloo™ group, the treated MZ100 brackets demonstrated shear bond strengths that did not significantly differ from metal brackets. CONCLUSION: The use of sandblasting and silane coupling agent significantly increases the shear bond strength of the MZ100 brackets to values resembling those of metal brackets.

Zirconia: a proven, durable ceramic for esthetic restorations.

In dental ceramics, zirconia has proven to be a durable, reliable framework material capable of inhibiting crack growth and preventing catastrophic failure. Zirconia, which is the oxidized form of zirconium, can exist in several phases, depending on temperature. Used in combination with CAD/CAM technology, zirconia enables the fabrication of esthetic all-ceramic restorations in all areas of the mouth.

The use of light/chemically hardened polymethylmethacrylate, polyhydroxyethylmethacrylate, and calcium hydroxide graft material in combination with polyanhydride around implants in minipigs: part I: immediate stability and function.

BACKGROUND: The present study is designed as a proof-of-concept study to evaluate light/chemical hardening technology and a newly formulated polymethylmethacrylate, polyhydroxyethylmethacrylate, and calcium hydroxide (PPCH) plus polyanhydride (PA) (PPCH-PA) composite graft material as a bone substitute compared to positive and negative controls in a minipig model. METHODS: PPCH-PA (composite graft); PPCH alone (positive control), PA alone (positive control), and no graft (negative control) were compared. Four mandibular premolar teeth per quadrant were extracted; a total of 48 implants were placed into sockets in three minipigs. Abutments were placed protruding into the oral cavity 4 mm in height for immediate loading. Crestal areas and intrabony spaces were filled with PPCH-PA, PPCH, or PA using a three-phase delivery system in which all graft materials were hardened by a light cure. In the negative control group, implant sites were left untreated. At 12 weeks, block sections containing implants were obtained. Evaluations included periodontal probing, pullout-force load, and stability measurements to determine implant stability, radiographs to examine bone levels, and scanning electron microscopy (SEM)-energy-dispersed spectroscopy to determine bone-to-implant contact. RESULTS: Probing measurements did not reveal any pathologic pocket formation or bone loss. Radiographs revealed that immediate implant placement and loading resulted in bone at or slightly apical to the first thread of the implant in all groups at 12 weeks. Stability test values showed a relative clinical stability for all implants (range: -7 to +1); however, implants augmented with PPCH-PA exhibited a statistically significantly greater stability compared to all other groups (P <0.05). The newly formed bone in PPCH-PA-treated sites was well organized with less marrow spaces and well-distributed osteocytes. SEM revealed a tighter implant-socket interface in the PPCH-PA group compared to other groups with reduced microfissures and implant-bone interface fractures during pullout testing, whereas implants treated with PA or no graft showed ≈ 10-µm microfissures between the implant and bone with fractures of the intrathread bone. CONCLUSIONS: The newly formulated chemically hardened graft material PPCH-PA was useful in immediate implant placement after tooth extraction and resulted in greater stability and a well-organized implant-bone interface with immediate loading, especially in those areas where cancellous bone was present. The results of this proof-of-concept study warranted further research investigating different healing times and longer durations.

Zirconia: material background and clinical application.

Zirconia is the oxidized form of zirconium and can exist in several phases, depending on the temperature. In dental ceramics, zirconia can inhibit crack growth and prevent catastrophic failure. The following case report demonstrates the use of zirconia as a framework material. Overall, zirconia has proven to be a strong and reliable framework material. In combination with CAD/CAM, this material allows for the fabrication of esthetic all-ceramic restorations in all areas of the mouth.

Ceramics overview: classification by microstructure and processing methods.

The plethora of ceramic systems available today for all types of indirect restorations can be confusing--and overwhelming--for the clinician. Having a better understanding of them is key. The authors use classification systems based on the microstructural components of ceramics and the processing techniques to help illustrate the various properties and uses.

The effect of different powder particle size on mechanical properties of sintered alumina, resin- and glass-infused alumina.

In this study, the compaction and sintering behavior of fine alumina powders of different particle sizes and the effect of matrix particle size on biaxial strength and fracture toughness of infused matrices were investigated. Three different alumina powders, In-Ceram alumina, A16SG, and RC172 were selected, representing a range of particle size and shape. RC172 and A16SG were dry-pressed. In-Ceram alumina was slip-cast following manufacturer's recommendations. Dry-pressed ceramic blocks were sectioned into disks with a thickness of 1.5-mm. Uninfused disks were sintered at four temperatures between 1250 degrees C and 1400 degrees C. For glass or resin infused specimens, alumina disks were sintered at 1250 degrees C for 2 h and separated into two groups for glass infusion and resin (UDMA/TEGDMA) infusion. Disks were tested for biaxial flexural strength with a universal testing machine (Instron) at 0.5-mm/min crosshead speeds. One-way ANOVA and Duncan's multiple range tests revealed that alumina disks with different smaller particle sizes have significantly higher biaxial strength (p < 0.05). The strength of the alumina matrix was greatly increased by glass and resin infusion. The biaxial strength of resin-infused alumina increased as particle size decreased, whereas strength of glass-infused alumina was constant.

The effect of hydrofluoric acid surface treatment and bond strength of a zirconia veneering ceramic.

STATEMENT OF PROBLEM: Clinicians are frequently faced with a challenge in selecting materials for adjacent restorations, particularly when one tooth requires a zirconia-based restoration and the next requires a veneer. While it may be desirable to use the same veneering ceramic on adjacent teeth, little information is available about the use of veneering ceramics over a zirconia-based material. PURPOSE: The purpose of this study was threefold: (1) to study the influence of hydrofluoric acid-etched treatment on the surface topography of the zirconia veneering ceramic, (2) to test the bond strength of zirconia veneering ceramic to enamel, and (3) to evaluate the flexural strength and the elemental composition of ceramic veneers. MATERIAL AND METHODS: Three zirconia veneering ceramics (Cerabien CZR (CZ), Lava Ceram (L), and Zirox (Z)) and 4 conventional veneering ceramics (Creation (C), IPS d.Sign (D), Noritake EX-3 (E), and Reflex (R)) were evaluated. Twenty ceramic bars of each material were fabricated and surface treated with hydrofluoric acid according to the manufacturer's recommendations. Ten specimens from each group of materials were examined with a profilometer, and a sample of this group was selected for quantitative evaluation using a scanning electron microscope (SEM). Another 10 acid-etched specimens from each group of materials were treated with silane prior to cementing with resin cement (Variolink II) on enamel surfaces. These luted specimens were loaded to failure in a universal testing machine in the shear mode with a crosshead speed of 0.05 mm/min. The data were analyzed with a 1-way ANOVA, followed by Tukey's HSD test (alpha=.05). An additional 10 ceramic bars from each material group were fabricated to evaluate flexural strength and elemental composition. The flexural strength (MPa) of each specimen was determined by using a 4-point-1/4-point flexure test. A Weibull statistic tested the reliability of the strength data; pairwise differences among the 7 groups were evaluated at confidence intervals of 95%. The chemical composition of each bar was determined by energy dispersive spectroscopy (EDS). RESULTS: There was a significant difference in the surface roughness in all testing groups. Conventional veneering ceramics (groups C and R) had a mean surface roughness higher than the groups of zirconia veneering ceramics (P<.001). Group D showed no difference in surface roughness compared with the groups of zirconia veneering ceramics. The SEM micrographs revealed differences in the acid-etched surfaces of ceramics. Zirconia veneering ceramics were smooth, with some groove formations, while conventional veneering ceramics had an amorphous, spongy-like structure with numerous microporosites. The mean bond strength (SD) of zirconia veneering ceramics to enamel revealed a significant difference. Group R (25.16 (3.40) MPa) followed by group C (22.51 (2.82) MPa) had significantly higher mean bond strength than the groups of zirconia veneering ceramics (P<.001, P=.009 respectively). Groups D (16.54 (2.73) MPa) and E (17.92 (3.39) MPa) showed no differences. Only group L (9.45 (1.62) MPa) exhibited significantly lower mean bond strength when compared with conventional veneering ceramics (P<.001). For flexural strength, only 1 group, group CZ, had a significantly lower flexural strength than all other groups (P<.001). CONCLUSIONS: Effective ceramic interface management, such as acid etching and enamel bonding, is essential for successful ceramic laminate veneer restorations. Not all zirconia veneering ceramics display the same quality of surface roughness after hydrofluoric acid etching and the same bond strength to enamel when used as laminate veneer materials.

In vitro evaluation of low-temperature aging effects and finishing procedures on the flexural strength and structural stability of Y-TZP dental ceramics.

STATEMENT OF PROBLEM: Yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) ceramic material has been reported to possess exceptionally high flexural strength; however, the strength of Y-TZP ceramics can be affected by surface treatments performed by dental laboratory technicians and by intraoral conditions. PURPOSE: This study investigated the influence of low-temperature-degradation (LTD) treatment, airborne-particle abrasion, and polishing on the flexural strength and structural stability of a Y-TZP ceramic material. MATERIAL AND METHODS: By sectioning zirconia ceramic blocks (Vita In-Ceram YZ blocks) into 25 x 4 x 2-mm bars, 310 specimens were fabricated and divided into 9 groups: Group C, as-sintered (control); group B24h, boiled in water for 24 hours; group B7d, boiled in water for 7 days; group H6h, stored in humidified air at 250 degrees C for 6 hours; group H24h, stored in humidified air at 250 degrees C for 24 hours; group H7d, stored in humidified air at 250 degrees C for 7 days; group P, polished; group A, airborne-particle abraded; and group AB, airborne-particle abraded and boiled for 7 days. The flexural strengths (MPa) of all specimens were determined by using a 3-point bending test. The variability was analyzed by using Weibull statistics. Pairwise differences among the 9 groups were evaluated by using confidence intervals (95%) for scale and shape parameters. From every block used, 8 specimens were obtained and every specimen was marked according to the location of its origin from the original block. Surfaces of the specimens were evaluated by using scanning electron microscopy (SEM) at various magnifications. X-ray diffraction analysis was performed to identify possible tetragonal-to-monoclinic phase transformations. Energy dispersive spectroscopy (EDS) was used to obtain information on the chemical composition. RESULTS: Aging or "finishing" treatments had no significant negative effects on flexural strengths. Mean flexural strengths ranged from 796.7 to 950.2 MPa. Group A exhibited the highest mean flexural strength (950.2 MPa). Weibull modulus values ranged between 5.6 and 9.3. Tetragonal-to-monoclinic phase transformation was detected for a specimen boiled for 24 hours. More tetragonal-to-monoclinic phase transformation was detected for specimens boiled for 7 days and stored in humidified air at 250 degrees C for 7 days. The SEM examination of fractured surfaces revealed sintering defects, and EDS analysis showed less yttria concentration on Y-TZP specimens that were boiled for 7 days. CONCLUSION: Within the limitations of this study, the results suggested that the LTD procedures and the polishing treatment used did not reduce the flexural strengths of zirconia bars. Airborne-particle abrasion increased the flexural strength of specimens. CLINICAL IMPLICATIONS: Although polishing, airborne-particle abrasion, and various low-temperature degradation (LTD) treatments did not significantly degrade the strength of the Y-TZP ceramic material, LTD resulted in loss of yttria. Over time, gradual dissolution of yttria could decrease the tetragonal-phase stability and long-term clinical serviceability of this dental ceramic material.

Materials for chairside CAD/CAM-produced restorations.

BACKGROUND: and Overview. Although the use of computer-aided design/computer-aided manufacturing (CAD/CAM) seems to be a recent addition to the dental restorative armamentarium, this concept was first investigated more than 35 years ago. CEREC (Sirona Dental Systems GmbH, Bensheim, Germany) was the first and is the only available chairside system, and it has more than 20 years of use in the dental office. The initial concept had three tenets: esthetic ceramic reconstruction, a single patient visit and minimal tooth reduction (inlays and onlays instead of crowns). The author reviews the materials used for CAD/CAM-fabricated restorations. The structure, properties and clinical success of the materials for full-contour chairside restorations, as well as laboratory-based high-strength all-ceramic restorations are presented. RESULTS: CAD/CAM restorations have demonstrated clinical success owing to a combination of improvements in materials with advances in CAD/CAM systems. Full-contour ceramic restorations fabricated chair-side may reinforce the tooth, providing good long-term clinical success. High-strength milled restorations allow for the use of all-ceramic restorations for multiple-unit posterior and anterior bridges. CLINICAL IMPLICATIONS: Examination of the structure, properties and clinical results of CAD/CAM materials supports their use in routine dental practice.

An evaluation of the effects of handpiece speed, abrasive characteristics, and polishing load on the flexural strength of polished ceramics.

STATEMENT OF PROBLEM: Many studies on the strengthening effects of grinding and polishing, as well as heat treatment on ceramics, are not well standardized or use commercially available industrial polishing systems. The reported effectiveness of these strengthening mechanisms on ceramics may not be applicable to clinical dentistry. PURPOSE: The purpose of this study was to evaluate the effects of controlled polishing on the flexural strength of dental ceramics by using a custom-made machine that applied standardized loads and speeds that coincided with the mean loads and speeds used by experienced prosthodontists. MATERIAL AND METHODS: A total of 140 aluminous dental ceramic bar-shaped specimens (Vitadur Alpha Enamel) measuring 1.5 x 2.0 x 25 mm were fabricated and divided into 12 groups (for most groups, n=10). Specimens were untreated, polished with different polishing systems, polished at different speeds, ground and autoglazed, polished and autoglazed, autoglazed and polished, polished with loose (paste) and bonded abrasives, or overglazed. Simulated clinical polishing was performed on the ceramic specimens by using a customized polishing apparatus that allowed independent control over the relevant polishing parameters (abrasive hardness, applied load, linear speed, rotational velocity, and wheel stiffness). Flexural strength (MPa) was measured with a 4-point bending test, and subjective surface roughness was assessed with scanning electron microscopy. Autoglazing was performed at various stages of the polishing sequence to determine the effects of polishing on surface stresses. Mean values, standard deviations, independent-sample t tests, 1-way and 2-way analyses of variance, Dunnett t tests and Kruskal-Wallis tests were applied to the data (alpha=.05). RESULTS: Under a clinical load of 0.6 N for a coarse polishing wheel, 1.0 N for a medium polishing wheel, and 1.3 N for a fine polishing wheel, a linear speed of 499 mm/min, and a rotational velocity of 10,000 rpm, the use of clinical polishing instruments did not affect the flexural strength of the aluminous ceramics studied (P=.274). At higher rotational velocity (20,000 rpm), specimens polished with the diamond polishing system produced statistically weaker specimens compared with those that had been polished at 10,000 rpm (P=.019). Autoglazing treatment of the diamond-polished specimens did not reverse the strength degradation (P=.125). Conversely, diamond polishing of the autoglazed specimens resulted in significant flexural strength reduction (P=.029). Fine-diamond-bonded abrasive significantly reduced flexural strength (P=.025). CONCLUSIONS: Simulated clinical polishing at 10,000 rpm did not appear to substantially strengthen or weaken the ceramic specimens. Polishing at 20,000 rpm reduced flexural strength of the ceramic bars.

Effects of acid hydrolysis and mechanical polishing on surface residual stresses of low-fusing dental ceramics.

STATEMENT OF PROBLEM: Cracks may arise in a ceramic restorative material over time, resulting in sudden fractures at stresses well below the yield stress. PURPOSE: This study evaluated by means of indentation technique the effects of acid hydrolysis and mechanical polishing on the surface residual stresses of low-fusing ceramic materials. MATERIAL AND METHODS: A total of 64 ceramic bars were formed to produce 4 groups of 16 bars each for 4 ceramic materials (Duceram-LFC Dentin, Duceram-LFC Enamel, Finesse Dentin, and Finesse Enamel). Four surface-treatment groups (n=4) were then formed for each of the 4 materials. The 4 surface treatments were control (autoglaze), hydrolysis, glaze/polish, and polish/glaze. A Vickers indenter contacted the Duceram-LFC specimens with a 5-N load and the Finesse specimens with a 3-N load for 10 seconds. Scanning electron microscope (SEM) was used to study surface texture before and after hydrolysis and polishing. Differences in mean crack lengths were analyzed with 1-way analysis of variance and least significant difference test (alpha=.05.) RESULTS: SEM showed obvious surface flaws as a result of hydrolysis on Duceram-LFC Enamel and Dentin specimens. However, statistical analysis of the resulting crack lengths revealed no significant differences between values for the control groups (58.16 +/- 3.88) (53.53 +/- 2.67) and hydrolysis groups (57.11 +/- 4.09) (54.54 +/- 3.15) for Enamel (P=.081) and Dentin (P=.093) respectively. When comparing polished groups and nonpolished groups, the mean crack lengths were significantly shorter for polished specimens of Duceram-LFC Enamel (53.76 +/- 3.17), Finesse Enamel (40.56 +/- 3.31), and Finesse Dentin (39.76 +/- 3.81) porcelains compared with their control groups (58.16 +/- 3.88) (43.54 +/- 4.12) (41.19 +/- 3.47), respectively (P<.0001). The mean crack lengths were significantly longer for polished specimens of Duceram-LFC Dentin (59.16 +/- 3.52) porcelain compared with the control group (53.53 +/- 2.67) (P<.0001). CONCLUSION: Within the limitations of this study, hydrolysis did not improve surface residual stresses of Duceram-LFC and Finesse ceramic materials. Mechanical polishing improved surface residual stresses of all materials tested, except Duceram-LFC Dentin porcelain.