Ceramics in dentistry: historical roots and current perspectives

Correlation of surface texture with the stainability of ceramics

STATEMENT OF PROBLEM

Stainability is an important factor in the long-term clinical success of ceramic restorations. Contour adjustments on restoration surfaces cause differences in ceramic texture that may be affected differently by the staining agent.

PURPOSE

The purpose of this study was to evaluate the surface texture obtained by different surface treatments relevant to the stainability of heat-pressed leucite-reinforced ceramic disk-shaped specimens.

MATERIAL AND METHODS

Sixty-six ceramic disks (IPS Empress Esthetic) (15 × 2 mm) were prepared, glazed, and then assigned to 6 groups. All disks were abraded with a diamond rotary cutting instrument except group GG (control), which was not subjected to any procedure. Group R (rotary diamond cutting instrument) was left untreated after abrasion. Group PB was polished with an abrasive stone, a round polishing brush, and paste with felt wheels. Group PU was polished with 1.0- to 0.5-μm polishing pastes with a goat-hair brush. Group PS was polished with abrasive stone, silicon carbide polishers, and polishing paste with polishing disks. Group GR was reglazed. Surface roughness was measured with a profilometer and evaluated with scanning electron microscopy. A spectrophotometer was used before and after 12 days of immersion in a coffee solution to assess color difference. Data were analyzed by 1-way ANOVA, the Tukey honestly significant difference test, and the Pearson rank correlation tests (α=.05).

RESULTS

Ra values of groups from highest to lowest were, in order, R, PB, PU, PS, GR, and GG (P<.01). Scanning electron microscope images and Ra values were compatible. The color difference (ΔE) values of groups from highest to lowest were, in order, R, PB, PU, PS, GR, and GG. A positive significant relationship of 65.6% between the Ra and ΔE values was found (P<.01).

CONCLUSIONS

Ceramic staining may be related to surface texture. The use of appropriate polishing materials with compatible porcelain may reduce stainability.

Digital imaging and fabrication

Bioceramics have been adopted in dental restorations for implants, bridges, inlays, onlays, and all-ceramic crowns. Dental bioceramics include glass ceramics, reinforced porcelains, zirconias, aluminas, fiber-reinforced ceramic composites, and multilayered ceramic structures. The process of additive manufacturing is ideally suited to dentistry. Models are designed using data from a computed tomography scan or magnetic resonance imaging. Since its development in 2001, direct ceramic machining of presintered yttria tetragonal zirconia polycrystal has become increasingly popular in dentistry. There are wide variety commercially available cements for luting all-ceramic restorations. However, resin cements have lower solubility and better aesthetic characteristics.

The effect of coloring liquids on the translucency of zirconia framework

PURPOSE

Translucency of all-ceramic restorations is an important factor which affects the final appearance and esthetic outcome of the restoration. The aim of this study was to evaluate the effect of the shade of coloring liquid on the translucency of zirconia framework.

MATERIALS AND METHODS

Thirty zirconium oxide core plate (15 × 12 × 0.5 mm) were divided into 6 groups of 5 plates each. Each group was classified according to the shade of coloring liquid based on Vita Classic Scale (A2, A3, B1, C2, and D2), and each sample was immersed in coloring liquid for 3 seconds as recommended by the manufacturer, except for the control group. Contrast ratio, as a translucency parameter, was calculated using a spectrophotometer and the data were analyzed with oneway analysis of variance (ANOVA) and Tukey's honestly significant differences (HSD) tests (α=.05).

RESULTS

Significant differences in translucency among the control and test groups, and the B1 shaded group and other shades was observed. There were no significant differences among A2, A3, C2, and D2 shaded groups.

CONCLUSION

The translucency of the zirconium oxide cores was affected by the coloring procedure and significant differences in the translucency measurements were identified between specific shades.

Influence of coping design on the cervical color of ceramic crowns

STATEMENT OF PROBLEM

The replication of natural teeth, especially with single-tooth restorations, represents a challenge. Similar to metal ceramic crowns, different designs of zirconia substructures have been suggested to improve the esthetic results of zirconia ceramic crowns.

PURPOSE OF STUDY

The purpose of the study was to analyze the color of the cervical portion of single zirconia ceramic crowns fabricated with different zirconia coping designs.

MATERIAL AND METHODS

The color, measured on the CIELAB color scale, of 3 different groups of restorations (n=10) fabricated with zirconia coping (Lava) and feldspathic porcelain (Noritake Super Porcelain) was analyzed with a spectrophotometer. Conventional zirconia crowns with zirconia facial margins were compared with ceramic crowns with porcelain facial margins and either a horizontal reduction of the zirconia coping (1.0 mm reduction) or an additional vertical reduction (1.0 mm additional reduction). The 3 groups, each with a different coping extension, were examined with a 1-way ANOVA and the Fisher exact test, and the differences of the groups were evaluated by applying ΔE thresholds (α=.05).

RESULTS

The mean color difference among all the groups was not clinically significant (ΔE<3.7). Reduced color differences were present between the 2 porcelain butt margin groups of crowns (ΔE=1.06, between group H and V). Increased differences were present between the zirconia margin group and the porcelain butt margin group (ΔE=2.54 between group C and H; ΔE=2.41 between group C and V). Lab* values were examined in all the groups of crowns to determine the clinical implications.

CONCLUSIONS

Within the limitation of the study, no significant differences were present among the tested groups of crowns. Nevertheless, although some differences were present between the zirconia margin group and the porcelain butt margin group, reduced differences were present between the 2 different cutback designs.

Influence of dentin and core porcelain thickness on the color of fully sintered zirconia ceramic restorations

STATEMENT OF PROBLEM

The influence of the thickness of dentin and core porcelain, and the glazing procedure on the color of computer-aided design and computer-aided manufacturing ceramic restorations has not been investigated.

PURPOSE

This study evaluated the influence of the thickness of dentin and core porcelain and glazing on the color of fully sintered zirconia ceramic restorations.

MATERIAL AND METHODS

Fully sintered zirconia core material was cut into 90 specimens of 0.3 mm (n=30, group ZC1), 0.4 mm (n=30, group ZC2), and 0.5-mm thickness (n=30, group ZC3). On a dentin disk obtained from an extracted molar, the L*, a*, b* values of the specimens were measured at different steps in the laboratory procedures (Zirconia core, Effect Bonder, Effect Liner, dentin porcelain, glazing) with a spectrophotometer. One millimeter dentin porcelain was applied on half of the specimens of each group and 1.5-mm dentin porcelain on the rest. To assess the ability of porcelain substructures to mask the underlying dark colored tooth structure, color difference (ΔE) values between the steps were calculated. Results were statistically analyzed with ANOVA.

RESULTS

Glazing caused a decrease in the L* values and an increase in the a* and b* values (P<.05). Increasing the thickness of dentin porcelain decreased the L*, a*, and b* values (P<.05). Increasing the zirconia core thickness resulted in an increase in the L* values and a decrease in the a* and b* values (P<.05). Increasing the dentin porcelain thickness from 1 mm to 1.5 mm resulted in a color change below the perceptibility threshold (ΔE<2.6). In the ZC1 group, glazing resulted in a color change perceptible to 50% of observers, whereas, in the ZC2 and ZC3 groups with 1-mm dentin porcelain, the ΔE value was higher than 5.5. However, the color change was perceptible to 50% of the observers in all of the groups with 1.5-mm dentin porcelain.

CONCLUSIONS

Although the thicknesses of the dentin and core porcelain did not influence the final shade of the restoration, glazing resulted in a perceptible color difference.

Clinical performance of a new biomimetic double network material

BACKGROUND

The development of ceramics during the last years was overwhelming. However, the focus was laid on the hardness and the strength of the restorative materials, resulting in high antagonistic tooth wear. This is critical for patients with bruxism.

OBJECTIVES

The purpose of this study was to evaluate the clinical performance of the new double hybrid material for non-invasive treatment approaches.

MATERIAL AND METHODS

The new approach of the material tested, was to modify ceramics to create a biomimetic material that has similar physical properties like dentin and enamel and is still as strong as conventional ceramics.

RESULTS

The produced crowns had a thickness ranging from 0.5 to 1.5 mm. To evaluate the clinical performance and durability of the crowns, the patient was examined half a year later. The crowns were still intact and soft tissues appeared healthy and this was achieved without any loss of tooth structure.

CONCLUSIONS

The material can be milled to thin layers, but is still strong enough to prevent cracks which are stopped by the interpenetrating polymer within the network. Depending on the clinical situation, minimally- up to non-invasive restorations can be milled.

CLINICAL RELEVANCE

Dentistry aims in preservation of tooth structure. Patients suffering from loss of tooth structure (dental erosion, Amelogenesis imperfecta) or even young patients could benefit from minimally-invasive crowns. Due to a Vickers hardness between dentin and enamel, antagonistic tooth wear is very low. This might be interesting for treating patients with bruxism.

All-ceramic prosthetic rehabilitation of a worn dentition: Use of a distal cantilever. Two-year follow-up

The rehabilitation of heavily abraded occlusion in patients with parafunctional habits is a restorative challenge to the dentist. Use of all-ceramic systems in such cases is widely considered, but uncertainty over their resistance hinders their broad use. The authors would like to illustrate a possible approach by mixing two all-ceramic systems based on zirconium dioxide and lithium disilicate. A 48-year-old female patient attended with reduced vertical dimension in a full dentition. She suffered from craniomandibular (CMD) pain and desired an esthetic rehabilitation. Prosthodontic treatment was started in a pain-free condition, after correction of the vertical dimension with an occlusal splint, over four months. Determination of the treatment was based on the clinical findings: IPS e.max^® ZirCAD frameworks veneered with IPS e.max^® Ceram were used for discolored retainers or subgingival finishing lines. All the rest received IPS e.max^® Press crowns. A zirconia-based, single-tooth-retained distal cantilever reconstruction was used to replace a missing second molar. No technical or biological complication was observed 24 months after treatment. The patient was highly satisfied and pain-free.

The effect of resin cements and primer on retentive force of zirconia copings bonded to zirconia abutments with insufficient retention

PURPOSE

The purpose of this study was to investigate the effect of resin cements and primer on the retentive force of zirconia copings bonded to zirconia abutments with insufficient retention.

MATERIALS AND METHODS

Zirconia blocks (Lava, 3M ESPE, St. Paul, MN, USA) were obtained and forty sets of zirconia abutments and copings were fabricated using CAD/CAM technology. They were grouped into 4 categories as follows, depending on the types of resin cements used, and whether the primer is applied or not:Panavia F2.0 (P), Panavia F2.0 using Primer (PRIME Plus, Bisco Inc, Schaumburg, IL, USA) (PZ), Superbond C&B (S), and Superbond C&B using Primer (SZ). For each of the groups, the cementation was conducted. The specimens were kept in sterilized water (37℃) for 24 hours. Retentive forces were tested and measured, and a statistical analysis was carried out. The nature of failure was recorded.

RESULTS

The means and standard deviations of retentive force in Newton for each group were 265.15 ± 35.04 N (P), 318.21 ± 22.24 N (PZ), 445.13 ± 78.54 N (S) and 508.21 ± 79.48 N (SZ). Superbond C&B groups (S & SZ) showed significantly higher retentive force than Panavia F2.0 groups (P & PZ). In Panavia F2.0 groups, the use of primer was found to contribute to the increase of retentive force. On the other hand, in Superbond C&B groups, the use of primer did not influence the retention forces. Adhesive failure was observed in all groups.

CONCLUSION

This study suggests that cementation of the zirconia abutments and zirconia copings with Superbond C&B have a higher retentive force than Panavia F2.0. When using Panavia F2.0, the use of primer increases the retentive force.

Effects of the sintering conditions of dental zirconia ceramics on the grain size and translucency

PURPOSE

This study aimed to identify the effects of the sintering conditions of dental zirconia on the grain size and translucency.

MATERIALS AND METHODS

Ten specimens of each of two commercial brands of zirconia (Lava and KaVo) were made and sintered under five different conditions. Microwave sintering (MS) and conventional sintering (CS) methods were used to fabricate zirconia specimens. The dwelling time was 20 minutes for MS and 20 minutes, 2, 10, and 40 hours for CS. The density and the grain size of the sintered zirconia blocks were measured. Total transmission measurements were taken using a spectrophotometer. Two-way analysis of variance model was used for the analysis and performed at a type-one error rate of 0.05.

RESULTS

There was no significant difference in density between brands and sintering conditions. The mean grain size increased according to sintering conditions as follows: MS-20 min, CS-20 min, CS-2 hr, CS-10 hr, and CS-40 hr for both brands. The mean grain size ranged from 347-1,512 nm for Lava and 373-1,481 nm for KaVo. The mean light transmittance values of Lava and KaVo were 28.39-34.48% and 28.09-30.50%, respectively.

CONCLUSION

Different sintering conditions resulted in differences in grain size and light transmittance. To obtain more translucent dental zirconia restorations, shorter sintering times should be considered.

Effect finishing and polishing procedures on the surface roughness of IPS Empress 2 ceramic

OBJECTIVE

To evaluate the surface roughness of IPS Empress 2 ceramic when treated with different finishing/polishing protocols.

MATERIALS AND METHODS

Sixteen specimens of IPS Empress 2 ceramic were made from wax patterns obtained using a stainless steel split mold. The specimens were glazed (Stage 0-S0, control) and divided into two groups. The specimens in Group 1 (G1) were finished/polished with a KG Sorensen diamond point (S1), followed by KG Sorensen siliconized points (S2) and final polishing with diamond polish paste (S3). In Group 2 (G2), the specimens were finished/polished using a Shofu diamond point (S1), as well as Shofu siliconized points (S2) and final polishing was performed using Porcelize paste (S3). After glazing (S0) and following each polishing procedure (S1, S2 or S3), the surface roughness was measured using TALYSURF Series 2. The average surface roughness results were analyzed using ANOVA followed by Tukey post-hoc tests (α = 0.01) RESULTS: All of the polishing procedures yielded higher surface roughness values when compared to the control group (S0). S3 yielded lower surface roughness values when compared to S1 and S2.

CONCLUSIONS

The proposed treatments negatively affected the surface roughness of the glazed IPS Empress 2 ceramic.

Influence of surface treatment on the wear of solid zirconia

OBJECTIVE

Recently there has been talk of the use of full-contour solid zirconia crowns or bridge restorations with no porcelain overlay. This could be a useful solution for patients with bruxism or limited interocclusal space. However, the hardness of zirconia could affect the opposite natural dentition. The aim of this in-vitro study was to investigate the role of surface treatments on the wear of a zirconia material and its antagonist.

MATERIALS AND METHODS

Fifty plates (10 × 10 × 1 mm) made of zirconia (LavaMulti(™) ZrO2, 3M ESPE), divided into five equal groups, were sandblasted and ground under standardized conditions with a fine-grit diamond bur (Komet Brasseler, Germany) to simulate clinical conditions. Group (a) was only fired, (b) was fired and sandblasted, (c) only ground, (d) was ground and additionally polished (EVE Ceramic Polishing-Set, Pforzheim) and (e) was ground and glazed. Wear behavior was measured with a pin-on-disk apparatus ABREX against 6 mm steatite balls as antagonists (45°, 5 N load, 5000 cycles, water). The amount of wear was determined topographically using a 3-D profilometer (Concept 3D, Mahr, Germany) by measuring the height loss of the antagonist and the depth of wear Pt of the zirconia.

RESULTS

In groups (a), (b), (c) and (d) the wear value Pt could not be determined (<1 μm). Wear values of the antagonists (steatite balls) revealed a similar outcome in contact with (b), (c) and (e) in the range of 81-85 μm, whereas (e) was more abrasive but not significantly. A noticeable difference in the wear of the antagonist showed group (d) to have the smallest value.

CONCLUSION

Polished zirconia seems to have the lowest wear on the antagonists, in contrast with the other kinds of surface treatment.

Evaluation of the surface roughness in dental ceramics submitted to different finishing and polishing methods

Ceramic restorations have been widely used in dentistry. These restorations often require intraoral adjustment with diamond burs after their cementation causing increasing roughness of the ceramic surface. Consequently some finishing and polishing methods have been used to minimize this occurrence. The aim of this study is to evaluate the roughness of the ceramic surfaces submitted to different finishing and polishing methods. 144 specimens of VITAVM(®)7, VM(®)9 and VM(®)13 (VITA Zahnfabrik) ceramics were fabricated and submitted to grinding using diamond burs. They were then divided into 15 groups (five of each ceramic type). Groups 1, 6 and 11-positive control (Glaze); Groups 2, 7 and 12-negative control (no polishing); Groups 3, 8 and 13-polished with abrasive rubbers (Edenta), felt disc and diamond polishing past; Groups 4, 9 and 14-polished with abrasive rubbers (Shofu), felt disc and diamond polishing past; Groups 5, 10 and 15-polished with aluminum oxide discs (Sof-Lex, 3M-ESPE), felt disc and diamond polishing paste. The roughness of the samples surfaces were measured using the rugosimeter Surfcorder SE 1700 and the data were submitted to statistical analysis using ANOVA and Tukey test at a level of significance of 5 %. There was statistically significance difference between the positive control groups and the other groups in all the ceramic types. Mechanical finishing and polishing methods were not able to provide a surface as smooth as the glazed surface for the tested ceramics. To assist dental practitioners to select the best finishing and polishing methods for the final adjustment of the ceramic restorations.

A comparative evaluation of wear of enamel caused by ceramics with different fusion temperatures

Dental ceramics are the most used esthetic fixed Prosthodontic restorative material today. However, dentists remain suspicious about their potential abrasivity. Lower-fusing ceramic materials developed, are claimed to be wear friendly. This study was conducted to compare the wear of enamel of extracted teeth against one conventionally used ceramic VMK-95 (fusing temperature 930 °C) and two new lower-fusing ceramics-Omega 900 and Finesse with fusing temperatures 900 and 760 °C respectively, used for metal-ceramic restorations. Metal disks were prepared from ceramic alloy and divided into three groups of 10 disks each on which VMK-95, Omega 900 and Finesse ceramics were applied respectively. Ceramic disks and tooth specimen were mounted on custom-made wear simulator and subjected to predefined masticatory test. Each tooth specimen was profiled by laser triangulation sensor before and after masticatory test. Difference in height was calculated. The results showed that mean loss of height of tooth was least against Finesse (0.3431 + 0.0177 mm) followed by Omega 900 (0.4076 + 0.0135 mm) and VMK-95 (0.6177 + 0.014 mm). Statistical analysis revealed statistically significant difference between VMK-95 & Omega 900 and VMK-95 & Finesse. The difference in loss of height of tooth against Finesse & Omega 900 is statistically insignificant (P < 0.001). The results of this study indicate that lower-fusing dental ceramics cause less wear of opposing enamel.

Evaluation of the effect of surface preparation using phosphoric acid and luting cement on the flexural strength of porcelain laminate veneering material

BACKGROUND

Conventionally HF acid has been used for etching ceramic veneer restorations before their cementation. Studies are lacking regarding the effectiveness of phosphoric acid as a substitute for HF acid for etching the ceramic veneers. The purpose of this study was to evaluate the effectiveness of surface preparation of porcelain laminate veneers using phosphoric acid, as compared to HF acid etching in providing the necessary surface roughness conducive to development of an effective bond between the ceramic laminate and the resin luting cement.

METHODS

210 porcelain discs of 15 mm diameter and 0.9 mm thickness were prepared. These study samples were divided into seven groups of thirty samples each. Surfaces of the first (control) and the second group of samples were not prepared. The surfaces of other five groups were prepared with different surface treatments. Further all the groups of specimens were coated with a layer of resin luting cement. Flexural strength of each specimen was determined using universal testing machine and the results were compared.

RESULTS

The combination surface treatment using alumina surface abrasion followed by etching with phosphoric acid provided the highest flexural strength with the mean flexural strength of 101.11 MPa, followed by alumina surface abrasion (95.41 MPa), and phosphoric acid surface etching (81.68 MPa).

CONCLUSION

Laminate veneers surface treated using 50 μm alumina abrasion followed by etching with phosphoric acid showed the highest flexural strengths after resin coating compared to other groups.

Detection of artificial demineralization bordering different types of laminate veneers using visual inspection and storage phosphor radiography

OBJECTIVE

The objective of this study is to compare the diagnostic accuracy of visual inspection (VI) and storage phosphor plate (SPP) radiography for the detection of artificial demineralization bordering different laminate veneers.

MATERIALS AND METHODS

Twenty human maxillary canine teeth were prepared. All-ceramic (A) and hybrid ceramic (H) laminate veneers were fabricated and luted. Veneered teeth were covered except for a circular window on the proximal surface bordering restorations. Teeth were kept in acetic acid buffer to create demineralization and imaged with a SPP system. Ten observers evaluated all teeth first visually then with SPP images for the presence/absence of demineralization. Teeth were examined using scanning electron microscopy (SEM) as well. The accuracy was expressed as the area under the ROC curves (A(z)). Pair-wise comparisons were performed using two-way ANOVA and post hoc t test (p = 0.05). Fleiss kappa (κ) was used for agreement.

RESULTS

SPP radiography was better than the VI for both veneers (p = 0.004). The A(z)s of two veneers were different for both VI (p < 0.005) and SPP (p < 0.005). SEM evaluation revealed lesions confined to enamel. κ was fair for H, and fair to moderate for A. Agreement was higher for the radiographic evaluation for both veneers.

CONCLUSION

Enamel demineralizations bordering hybrid and ceramic laminate veneers can be detected better with SPP radiography than VI and detectability was better for all-ceramic veneers than the hybrid ceramic ones.

CLINICAL RELEVANCE

Early detection of enamel demineralizations bordering laminate veneers would result in time-saving and less-invasive treatment methods; therefore, SPP radiography may be recommended in clinically suspicious cases since it provides better diagnostic accuracy.

Color management of the cervical region using different framework materials

BACKGROUND

  Color-matching of the cervical area between natural teeth and different crown prostheses is a common clinical problem.

PURPOSE

  The purpose of this study was to compare the color of the cervical region of five commercially available crown systems to an extracted natural tooth and to each other.

MATERIALS AND METHODS

  The color of the cervical region of an extracted maxillary incisor was measured by means of a colorimeter (ShadeVision, X-Rite). Fifty master dies were fabricated, divided into five groups (N=10) according to the framework material; group 1: high-noble gold alloy, group 2: same as group 1 but treated with gold paste material, group 3: precious reinforced alloy, group 4: white zirconium oxide substructure (Lava 3M ESPE), and group 5: shaded zirconium oxide (Lava). A direct comparison of L*, a*, and b* parameters was accomplished between the control natural tooth and the five crown systems, and the mean color differences (ΔE) was calculated. The data were statistically analyzed with one-way analysis of variance and post hoc multiple comparison (α=0.05).

RESULTS

  Compared to the natural tooth, the mean color differences (ΔE) values were clinically unacceptable for all groups (ΔE > 3.7). The detected color differences, among different porcelain systems, were not visually perceptible (ΔE < 3.7).

CONCLUSIONS

  Within the limitations of this study, the cervical color of an extracted natural tooth could not be duplicated using different crowns systems.

CLINICAL SIGNIFICANCE

Color-matching of the cervical region of different crown systems with natural tooth remains a difficult task.

Comparative radiopacity of ceramics and metals with human and bovine dental tissues

STATEMENT OF PROBLEM

Ceramics should be radiopaque enough to be seen on radiographs and to be distinguishable from tooth structures. Information on the radiopacity of different ceramics used in restorative dentistry is limited.

PURPOSE

The purpose of this study was to investigate the radiopacity of ceramics in comparison with human and bovine dental hard tissues and metals.

MATERIAL AND METHODS

A total of 128 disk-shaped specimens, 6 × 1 mm (n=8), were prepared from dental ceramic materials and metals. The optical densities of each material, along with 2 tooth sections (canine and molar teeth), bovine dentin and enamel specimens, and 2 different aluminum step wedges, were measured from radiographic images using a transmission densitometer. The optical densities of the specimens were used to determine the equivalent aluminum thicknesses. The data were analyzed by nonparametric 1-way ANOVA (Kruskal-Wallis) and Student-Newman-Keuls multiple range tests for post hoc comparison (α=.05).

RESULTS

Among ceramic materials, Cercon Zirconia had the highest and the Cergo Pressable Ceramic had the lowest radiopacity values. Cergo Pressable Ceramic, Noritake Super Porcelain EX3 dentin, IPS Empress e.max Press, Cercon Kiss dentin, IPS Empress 2, Cercon Ceram dentin, bovine dentin, human canine, and molar tooth dentin radiopacity measurements were not significantly different. The radiopacity measurements of In-Ceram Alumina, In-Ceram Spinell, Celay Alumina, Titanium alloy (Ti-6Al-4V), Celay Zirconia, In-Ceram Zirconia, NiCr alloy, Wieland Zirconia, Cercon Zirconia, and 22-carat gold were significantly higher than that of bovine enamel (P<.05).

CONCLUSIONS

Significant differences in radiopacity were found among ceramic materials, when compared to metals, bovine enamel and human and bovine dentin. Cercon and Wieland Zirconia had high radiopacity values, which were similar to metals.

Effects of sintering temperature and particle size on the translucency of zirconium dioxide dental ceramic

The aim of this study was to evaluate the effects of sintering temperature and particle size on the translucency of yttrium stabilized tetragonal zirconia polycrystals (Y-TZP) dental ceramic. Eighty disc-shaped and cylindrical specimens were fabricated from zirconia powers of particle size 40 and 90 nm. These specimens were sintered densely at the final sintering temperature 1350, 1400, 1450 and 1500°C, respectively. The visible light transmittance, sintered density and microstructure of the sintered block were examined. The results showed that the sintered densities and transmittances increased with the temperature from 1,350 to 1,500°C. Y-TZP could gain nearly full density and about 17-18% transmittance at the final sintering temperature of 1,450-1,500°C. The 40-nm powders had higher sintered density and transmittance than the 90-nm. The translucency of Y-TZP dental ceramic could be improved by controlling the final sintering temperature and primary particle size.

Influence of framework design on the cervical color of metal ceramic crowns

STATEMENT OF PROBLEM

The replication of natural teeth, especially for single tooth restorations in patients with high esthetic needs, represents a challenge.

PURPOSE

The purpose of the study was to analyze the color of the cervical portion of single metal ceramic crowns fabricated with different metal framework designs.

MATERIAL AND METHODS

The color, as measured on the CIELAB color scale, of 3 different groups of restorations (n=10) fabricated with a high noble metal alloy (V-Deltaloy) and feldspathic porcelain (Noritake Super Porcelain) was analyzed with a colorimeter. Conventional metal ceramic crowns with metal facial margins were compared to metal ceramic crowns with porcelain facial margins and a horizontal reduction of the metal framework (1.0 mm reduction) or an additional vertical reduction (1.0 mm reduction). In all specimens, the finish line was positioned at a subgingival or equigingival level. The 6 groups obtained by the combination of the levels of the 2 factors (framework extension and finish line location) were examined with an ANOVA Fisher's F-test and a post hoc Tukey's HSD test (α=.05).

RESULTS

The mean color difference for all the groups was clinically acceptable (ΔE<3.7). Conventional metal ceramic crowns showed higher differences in relation to finish line location (ΔE=2.34), while a vertical reduction of the framework was related to lower values (ΔE=0.96). Mean Lab* values were reported for all the groups of crowns. Statistically significant differences were present for L*, a*, and b* values when related to framework extension. Considering each value in relation to the interaction between framework extension and finish line location factors, significant differences were present only for L* and a* values.

CONCLUSIONS

No significant differences in base shade were present among the investigated crowns. Nevertheless metal ceramic crowns with vertical cut-back and porcelain facial margins presented more consistent results that tended to be closer to those of natural teeth.

Single visit fabrication of a porcelain laminate veneer with CAD/CAM technology: a clinical report

Computer-assisted design and computer-assisted milling (CAD/CAM) technology has been shown to be an effective dental treatment adjunct. This article demonstrates its use in the fabrication of an in-office, one visit, porcelain laminate veneer.

The effect of ceramic thickness and number of firings on the color of a zirconium oxide based all ceramic system fabricated using CAD/CAM technology

PURPOSE

Ceramics have a long history in fixed prosthodontics for achieving optimal esthetics and various materials have been used to improve ceramic core strength. However, there is a lack of information on how color is affected by fabrication procedure. The purpose of this study was to evaluate the effects of various dentin ceramic thicknesses and repeated firings on the color of zirconium oxide all-ceramic system (Lava™) fabricated using CAD/CAM technology.

MATERIALS AND METHODS

Thirty disc-shaped cores, 12 mm in diameter with a 1 mm thickness were fabricated from zirconium oxide based all ceramic systems (Lava™, 3M ESPE, St Paul, MN, USA) and divided into three groups (n = 10) according to veneering with dentin ceramic thicknesses: as 0.5, 1, or 1.5 mm. Repeated firings (3, 5, 7, or 9) were performed, and the color of the specimens was compared with the color after the initial firing. Color differences among ceramic specimens were measured using a spectrophotometer (VITA Easyshade, VITA Zahnfabrik, Bad Säckingen, Germany) and data were expressed in CIELAB system coordinates. A repeated measures ANOVA and Bonferroni post hoc test were used to analyze the data (n = 10, α=.05).

RESULTS

L*a*b* values of the ceramic systems were affected by the number of firings (3, 5, 7, or 9 firings) (P<.001) and ceramic thickness (0.5, 1, or 1.5 mm) (P<.001). Significant interactions were present in L*a*b* values between the number of firings and ceramic thickness (P<.001). An increase in number of firings resulted in significant increase in L* values for both 0.5 mm and 1.5 mm thicknesses (P<.01, P=.013); however it decreased for 1 mm thickness (P<.01). The a* values increased for 1 mm and 1.5 mm thicknesses (P<.01), while it decreased for 0.5 mm specimens. The b* values increased significantly for all thicknesses (P<.01, P=.022). As the dentin ceramic thickness increased, significant reductions in L* values (P<.01) were recorded. There were significant increases in both a* and b* values (P<.01) as the dentin ceramic thickness increased.

CONCLUSION

The number of firings and dentin ceramic thickness have a definite effect on the final color of all ceramic system tested. The mean ΔE value increased as the dentin ceramic thicknesses increased for zirconium-oxide based all ceramic specimens tested. However, the mean ΔE values were less than 3.7ΔE units which is rated as a match in the oral environment.

Color match of two different ceramic systems to selected shades of one shade guide

STATEMENT OF PROBLEM

There are no consistent indications given by dental manufacturers on how to layer ceramics to achieve a color match to a shade selected from a dental shade guide. The technique for ceramic layering relies primarily on the skill and experience of ceramists and is not easily predictable.

PURPOSE

The purpose of this study was to evaluate, using a clinical spectrophotometer, the ability to color match shades selected with the 3D-Master shade guide using 2 different ceramic systems.

MATERIAL AND METHODS

Two ceramic systems were selected for this study, the VITA Omega 900 and VITA VM 13. For both systems, shades 2M3, 3M2, 4M2 of the VITA 3D-Master shade guide were selected. Thirty ceramic discs, 15 mm in diameter, were fabricated with different layer thickness ratios of opaque dentin, dentin, and enamel, maintaining a constant overall thickness. A clinical spectrophotometer (VITA Easyshade) was used for color comparison. The measured ΔE values were statistically analyzed with a 3-way ANOVA and the Tukey HSD test (α=.05).

RESULTS

The 3-way ANOVA showed that the ceramic system (P<.001), the selected shade (P<.001), and the layering scheme all significantly influenced the ΔE values (P<.001).

CONCLUSIONS

Both VITA VM 13 and VITA Omega 900 ceramic systems showed a color match with the shades 2M3, 3M2, and 4M2 of the VITA 3D-Master shade guide to be within the limits for clinical acceptability (ΔE≤ 3.3). VM 13 showed a statistically better color match. The layering scheme influenced the definitive color of the restoration.

The effect of slurry preparation methods on biaxial flexural strength of dental porcelain

STATEMENT OF PROBLEM

One-step and incremental mixing procedures are currently used to produce dental ceramic pastes. In the ceramic industry, high quality is obtained using one-step mixing, but in dentistry, the best method has not been yet determined.

PURPOSE

The purpose of this study is to evaluate the effects of 2 mixing techniques on the biaxial flexural strength and microstructure of dental porcelain.

MATERIAL AND METHODS

Feldspathic porcelain discs (2 × 15 mm in diameter) were produced and divided according to the ceramic paste preparation method, powder-liquid incremental mixing group (n=50) or one-step mixing, as a control group (n=50). Specimens were tested for biaxial flexural strength and characterized using porosimetry, relative humidity, SEM/EDS, XRD, and FT-IR analyses. Statistical analysis was conducted using Weibull statistics. The Weibull modulus, characteristic strength and relative humidity were compared between groups, using Student's t-test and Mann-Whitney U test (α=.05).

RESULTS

The powder-liquid incremental mixing group showed significantly higher values (SD) of Weibull modulus (6.74 (0.70), P<.001) and characteristic strength (79.87 (2.01) MPa, P<.001) when compared to the one-step mixing group (4.94 (0.94) and 75.95 (2.61) MPa). Significantly lower mean (SD) relative humidity values (P=.009) were found for powder-liquid incremental mixing group (20% (0.5%)) compared to one-step mixing group (22% (1%)). XRD spectra showed that the one-step mixing group produced higher amounts of the amorphous phase.

CONCLUSIONS

Specimens produced by the incremental mixing technique showed higher biaxial flexural strength than one-step mixing.

Novel glass-ceramics for dental restorations

BACKGROUND

There are many different ceramic systems available on the market for dental restorations. Glass-ceramics are a popular choice due to their excellent esthetics and ability to bond to tooth structure allowing a more conservative approach. However, at present, these materials have insufficient strength to be used reliably in posterior regions of the mouth.

PURPOSE

The aim of this review article is to discuss the types of novel glass-ceramic currently be investigated including composition, microstructure and properties.

CONCLUSION

Current research in glass-ceramics focuses on the quest for a highly esthetic material along with sufficient strength to enable crowns and bridgework to be reliably placed in these areas.

CLINICAL SIGNIFICANCE

There is a gap in the market for a machinable resin bonded glass-ceramic with sufficient strength as well as excellent esthetics.

Functional and esthetic rehabilitation with in-ceram alumina and zirconia system: a multidisciplinary approach

The development of all-ceramic systems following metalceramics restorations allowed simulation of natural dentition due to favorable esthetics and resistance. In-Ceram is an alternative when esthetics is primordial as well as resistance required in rehabilitation. However, an ideal smile is associated to not only shape, color, texture and translucency but also harmony with gingival tissue. So, the aim of this study is to report a clinical case based on periodontal and fixed partial dentures principles to perform periodontal plastic surgery followed by esthetic rehabilitation. A female patient, 40-year-old, presented complaint about dental esthetics. After clinical and radiographic exams, metal-ceramics crowns (teeth 11, 12, 13, 21, 22 and 23) were considered unsatisfactory due to marginal leakage, color change in gingival tissue associated to metallic margin, and gummy smile. So, a crown lengthening surgery of anterior teeth was performed followed by rehabilitation of superior teeth with In- Ceram single crowns.

CLINICAL SIGNIFICANCE

The interaction between periodontics and fixed prosthodontic area is the key of an adequated treatment planning which involves gingival smile to provide function and an esthetic condition in association with an esthetic, resistant and predictable material.

Transient and residual stresses induced during the sintering of two dentin ceramics

OBJECTIVES

To characterize the stress induced deformation of bi-axial flexure strength (BFS) test specimens during processing to provide an insight into sintering effects and associated BFS determination.

METHODS

40 Vitadur-Alpha and 80 IPS e.max Ceram disc-shaped specimens were condensed and a sintered on a silicon nitride refractory tray under controlled firing and cooling parameters. The mean of the maximum deflection (μm) and Ra values (μm) were determined using a high resolution profilometer and were related to the orientation of the measured surface within the furnace. BFS testing of the subsequent groups (n = 20) was performed and the data related to the measured deformation of the sintered specimens. A two-way analysis of variance (ANOVA) where factors were identified as surface state and firing orientation with post hoc Tukey's tests was complemented by pair-wise comparisons with a Student's t-test for each measurement (P < 0.05).

RESULTS

The mean of the maximum deflection values and the mean BFS for Vitadur Alpha discs were not significantly influenced by firing orientation (P = 0.248 and P = 0.284, respectively). However, the Ra values were significantly different (P < 0.001). The two-way ANOVA revealed a significant impact on the mean of the maximum deflection measurements for surface state (P < 0.001) and firing orientation (P < 0.001) during sintering (P < 0.001). The mean Ra values were not significantly influenced. The BFS of sintered IPS e.max Ceram discs was sensitive to firing orientation (P < 0.001).

SIGNIFICANCE

Conventional glass theory explains that residual thermal stress gradients induced during sintering can cause test specimen deformation which can alter the expected BFS data. The study demonstrates that variability such as firing orientation during sintering which is very rarely reported in the literature can have a significant impact on the reported BFS data and can confound its interpretation.

Antibacterial activity of dental composites containing zinc oxide nanoparticles

The resin-based dental composites commonly used in restorations result in more plaque accumulation than other materials. Bacterial biofilm growth contributes to secondary caries and failure of resin-based dental composites. Methods to inhibit biofilm growth on dental composites have been sought for several decades. It is demonstrated here that zinc oxide nanoparticles (ZnO-NPs) blended at 10% (w/w) fraction into dental composites display antimicrobial activity and reduce growth of bacterial biofilms by roughly 80% for a single-species model dental biofilm. Antibacterial effectiveness of ZnO-NPs was assessed against Streptococcus sobrinus ATCC 27352 grown both planktonically and as biofilms on composites. Direct contact inhibition was observed by scanning electron microscopy and confocal laser scanning microscopy while biofilm formation was quantified by viable counts. An 80% reduction in bacterial counts was observed with 10% ZnO-NP-containing composites compared with their unmodified counterpart, indicating a statistically significant suppression of biofilm growth. Although, 20% of the bacterial population survived and could form a biofilm layer again, 10% ZnO-NP-containing composites maintained at least some inhibitory activity even after the third generation of biofilm growth. Microscopy demonstrated continuous biofilm formation for unmodified composites after 1-day growth, but only sparsely distributed biofilms formed on 10% ZnO-NP-containing composites. The minimum inhibitory concentration of ZnO-NPs suspended in S. sobrinus planktonic culture was 50 microg mL(-1). ZnO-NP-containing composites (10%) qualitatively showed less biofilm after 1-day-anaerobic growth of a three-species initial colonizer biofilm after being compared with unmodified composites, but did not significantly reduce growth after 3 days.

Effect of veneering techniques on color and translucency of Y-TZP

PURPOSE

This study compared the color parameters and total luminous transmittance of disc specimens by different veneering techniques in order to examine the effect of veneering technique on esthetics of yttria-stabilized tetragonal zirconia polycrystalline (Y-TZP) all-ceramic restorations.

MATERIALS AND METHODS

Thirty disc specimens (10-mm diameter, 0.50 +/- 0.01 mm thick) were fabricated of IPS e.max ZirCAD core material, and ZL1 IPS e.max ZirLiner (0.10-mm thick) was layered. The specimens were randomly divided into three groups (n = 10/group). Group ZP (fully anatomical technique) was veneered 0.60 mm by heat-pressing IPS e.max ZirPress fluorapatite glass-ceramic ingots; Group ZC (traditional layering technique) was veneered 0.60 mm by condensing and sintering IPS e.max Ceram low-fusing nano-fluorapatite veneering porcelain; Group ZPC (cutback technique) was veneered by partially pressed ingots and subsequently layered 0.30 mm with veneering porcelain. Color parameters (L*, a*, b*) and total luminous transmittance (tau) of zirconia core discs and core and veneer specimens were measured with ShadeEye NCC dental colorimeter and spectrophotometer, respectively. Color saturation (C*ab) and color difference (DeltaE) were calculated using color difference formula. One-way analysis of variance (ANOVA) combined with a Tukey multiple-range test were used to analyze the data (alpha= 0.05).

RESULTS

As to ZP, ZPC, and ZC groups, the value of a* increased (-1.35 +/- 0.07, -0.64 +/- 0.06, -0.36 +/- 0.05, respectively) (p < 0.05); b* decreased (27.01 +/- 0.07, 25.48 +/- 0.11, 23.28 +/- 0.25, respectively) (p < 0.05); and C*ab decreased (27.04 +/- 0.08, 25.49 +/- 0.11, 23.28 +/- 0.25, respectively) (p < 0.05). L* value and total luminous transmittance were highest in ZP group (87.53 +/- 0.48, 1.64 +/- 0.03, respectively), and lowest in ZPC group (82.14 +/- 0.18, 1.47 +/- 0.01, respectively) (p < 0.05).

CONCLUSIONS

Y-TZP all-ceramic restoration veneered by fully anatomical technique was the most transparent and lightest, while restorations veneered by cutback technique were the least translucent and the darkest.

The effect of acidic agents on surface ion leaching and surface characteristics of dental porcelains

STATEMENT OF PROBLEM

Acidic food and sour fruits and drinks have been investigated for their destructive effects on enamel. However, their effect on porcelain restorations has not been widely examined.

PURPOSE

The purpose of this study was to evaluate the ion leaching of porcelains immersed in acidic agents.

MATERIAL AND METHODS

Fifty-five discs (12.0 mm in diameter and 2.0 mm in thickness) were made from each of 4 types of porcelain (VITA VMK 95, Vitadur Alpha, IPS Empress Esthetic, and IPS e.max Ceram). Baseline data of elemental compositions of all storage agents were recorded. Four groups of discs (n=10) were then immersed in acidic agents (citrate buffer solution, pineapple juice, and green mango juice) and deionized water (control) at 37 degrees C for 168 hours. One group was immersed in 4% acetic acid at 80 degrees C for 168 hours. After immersion, fluids from all specimens for each acidic agent were measured for ion leaching with an inductively coupled plasma optical emission spectroscopy. Surface characteristics of specimens were examined using scanning electron microscopy (SEM). Data were analyzed using 3-way repeated ANOVA and Tukey HSD multiple comparisons (alpha=.05).

RESULTS

This study revealed that each type of porcelain had significantly leached the various ions to varying degrees after being immersed in acidic agents (P<.001 for all comparisons). SEM photomicrographs showed surface destruction of all porcelains.

CONCLUSIONS

Acidic agents used in this study affected elemental dissolution of the 4 types of porcelains evaluated.