Effects of Pretreatment, Specimen Thickness, and Artificial Aging on Biaxial Flexural Strength of Two Types of Y-TZP Ceramics.

OBJECTIVES: To evaluate the effects of surface treatment, specimen thickness, and aging on the biaxial flexural strength (BFS) of two types of yttria-stabilized, tetragonal zirconia polycrystal (Y-TZP) ceramics. METHODS AND MATERIALS: Disc-shaped specimens, 0.4 and 1.3 mm thick, made from hot isostatic pressed (Denzir) and non-hot isostatic pressed (ZirPlus) Y-TZP, were sandblasted, heat treated, and autoclaved. The surface topography was assessed in accordance with European Standard 623-624:2004 and the BFS tests in accordance with International Organization for Standardization Standard 6872:2008. For statistical analyses, one-way Shapiro-Wilk test, analysis of variance (post hoc: least significant differences), Mann-Whitney U-test, and Pearson correlation tests (p<0.05) were used. RESULTS: As delivered, the BFS of the 0.4-mm ZirPlus was >1.3-mm ZirPlus (p<0.01), and the BFS of the 0.4-mm Denzir was >1.3-mm Denzir (p<0.001). Sandblasting with 0.2 MPa reduced the BFS of the ZirPlus and Denzir discs (p<0.01), whereas sandblasting with 0.6 MPa increased the BFS of the 0.4-mm Denzir (p<0.001) and reduced the BFS of the 0.4-mm ZirPlus (p<0.05). Heat treatment significantly reduced the BFS of all the groups except for the 0.6 MPa sandblasted 0.4-mm ZirPlus. Autoclaving reduced the BFS of the as-delivered ZirPlus and Denzir specimens (p<0.001), whereas autoclaving the 0.6 MPa sandblasted and heat-treated specimens had no effect (p>0.05) on the BFS. The 0.6 MPa sandblasted, heat-treated, and autoclaved 0.4-mm Denzir exhibited higher BFS than the 0.6 MPa sandblasted, heat-treated, and autoclaved 0.4-mm ZirPlus (p<0.05). CONCLUSIONS: Thickness and surface treatment of Y-TZP-based ceramics should be considered since those factors could influence the BFS of the material.

Accuracy of ceramic restorations made using an in-office optical scanning technique: an in vitro study.

The present in vitro study concerns determination of the pre-cementation gap width of all-ceramic crowns made using an in-office digital-impression technique and subsequent computer-aided design/computer-aided manufacturing (CAD/CAM) production. Two chairside video camera systems were used: the Lava Oral scanner and Cadent's iTero scanner. Digital scans were made of a first molar typodont tooth that was suitably prepared for an all-ceramic crown. The digital impressions were sent via the Internet to commercial dental laboratories, where the crowns were made. Also, an impression of the typodont tooth was made, poured, and scanned in order to evaluate the pre-cementation gap of crowns produced from scanning stone dies. These methods and systems were evaluated by creating replicas of the intermediate space using an addition-cured silicone, and the gap widths were determined using a measuring microscope. Hot-pressed leucite-reinforced glass-ceramic crowns were selected as a reference. The mean value for the marginal measuring points of the control was 170 µm, and the values for all the evaluated crowns ranged from 107 to 128 µm. Corresponding figures for the internal measuring points were 141-210 µm and 115-237 µm, respectively. Based on the findings in the present study, an in-office digital-impression technique can be used to fabricate CAD/CAM ceramic single crowns with a marginal and internal accuracy that is on the same level as that of a conventional hot-pressed glass-ceramic crown. In the present study, however, slight differences could be seen between the two types of ceramic crowns studied with respect to the internal fit obtained.

Fracture behaviour of zirconia FPDs substructures.

The purpose of this study was to evaluate the occurrence of superficial flaws after machining and to identify fracture initiation and propagation in three-unit heat-treated machined fixed partial dentures (FPDs) substructures made of hot isostatic pressed (HIPed) yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) after loaded to fracture. Four three-unit HIPed Y-TZP-based FPDs substructures were examined. To evaluate the occurrence of superficial flaws after machining, the surfaces were studied utilizing a fluorescent penetrant method. After static loading to fracture, characteristic fracture features on both mating halves of the fractured specimens were studied using a stereomicroscope and a scanning electron microscope. Grinding grooves were clearly visible on the surfaces of the machined FPDs substructures, but no other flaws could be seen with the fluorescent penetrant method. After loading to fracture, the characteristic fracture features of arrest lines, compression curl, fracture mirror, fracture origin, hackle and twist hackle were detected. These findings indicated that the decisive fracture was initiated at the gingival embrasure of the pontic in association with a grinding groove. Thus, in three-unit heat-treated machined HIPed Y-TZP FPDs substructures, with the shape studied in this study, the gingival embrasure of the pontic seems to be a weak area providing a location for tensile stresses when they are occlusally loaded. In this area, fracture initiation may be located to a grinding groove.

Fracture resistance of all-ceramic crowns placed on a preparation with a slice-formed finishing line.

The purpose of this study was to determine the fracture resistance of all-ceramic crowns with a core of a zirconia ceramic, using various stabilizing oxides and luted on a preparation with a slice-formed finishing line. Ten cores made of HIPed yttrium-oxide partially stabilized zirconia (HIPed Y-TZP) and five cores of densely-sintered magnesia partially stabilized zirconia (Mg-PSZ) were made. The Mg-PSZ cores and five of the HIPed Y-TZP cores were made with a thickness of 0.2 mm. A further five cores 0.1-mm thick were made of HIPed Y-TZP. All 15 cores were then veneered with a feldspar ceramic and luted onto a stylized steel master die model with a slice-formed finishing line. The specimens were then loaded until fracture occurred. The HIPed Y-TZP specimens with the 0.2 mm core exhibited significantly higher fracture resistance than the Mg-PSZ specimens (P = 0.004) and the HIPed Y-TZP specimens with the 0.1 mm core (P = 0.001). The fracture resistance of the Mg-PSZ specimens was significantly (P = 0.015) higher than that of the HIPed Y-TZP specimens with the 0.1 mm core. The fracture resistance determined was equal or superior to reported values for bite forces and all-ceramic crowns. Thus, it seems likely that the type of restorations evaluated have the potential for successful use on a slice-formed preparation. However, long-term studies are essential in order to assess the performance of this ceramic system in a clinical context.

Surface roughness of five different dental ceramic core materials after grinding and polishing.

In clinical practice, core materials can be exposed after adjustments are made to previously-luted all-ceramic restorations. The purpose of this study was to evaluate the surface roughness of five different dental ceramic core materials after grinding and polishing. Five different ceramic core materials, Vita In-Ceram Alumina, Vita In-Ceram Zirconia, IPS Empress 2, Procera AllCeram, and Denzir were evaluated. Vita Mark II was used as a reference material. The surface roughness, Ra value (mum), was registered using a profilometer. The measurements were made before and after grinding with diamond rotary cutting instruments and after polishing with the Sof-Lex system. The surface of representative specimens was evaluated qualitatively using scanning electron microscopy (SEM). Results were statistically analysed using analysis of variance (anova) supplemented with Scheffè's and Bonferroni multiple-comparison tests. Before grinding, Procera AllCeram and Denzir had the smoothest surfaces, while IPS Empress 2 had the coarsest. After grinding, all materials except IPS Empress 2 became coarser. Polishing with Sof-Lex provided no significant (P > 0.05) differences between Denzir, Vita Mark II and IPS Empress 2 or between Procera AllCeram and In-Ceram Zirconia. There were no significant differences (P > 0.05) either between the ground and the polished Procera AllCeram or In-Ceram Alumina specimens. Polishing of Denzir, IPS Empress 2 and In-Ceram Zirconia made the surfaces smoother compared with the state after grinding, whereas the polishing effect on Procera AllCeram and In-Ceram Alumina was ineffective. The findings of the SEM evaluation were consistent with the profilometer readings.

A comparison of fracture strength of yttrium-oxide- partially-stabilized zirconia ceramic crowns with varying core thickness, shapes and veneer ceramics.

The fracture strengths of stylized all-ceramic crowns manufactured using an yttrium-oxide-partially-stabilized (Y-TZP) zirconia ceramic core (Denzir) veneered with lithium disilicate glass-ceramics (IPS Empress 2 or IPS Eris) were evaluated. The Denzir cores were manufactured in two ways: either with different thickness in different parts of the restoration, called an 'adapted Denzir core'; or with a uniform core thickness of 0.5 mm. IPS Empress 2 all-ceramic crowns served as reference. There was no significant difference between the crowns with an 'adapted Denzir core' veneered with the two brands of glass-ceramics. No significant difference was seen between the crowns with a 0.5 mm Denzir core veneered with the two brands of glass-ceramics. The crowns with an 'adapted Denzir core' exhibited significantly higher values than those with a 0.5 mm Denzir core and than the IPS Empress 2 crowns used as reference. No significant differences were seen among the IPS Empress 2 crowns used as reference and the crowns with a 0.5 mm Denzir core. The mode of failure varied among the Empress 2 crowns and the crowns with a core of a Y-TZP zirconia ceramic. Long-term studies are necessary to assess the clinical performance of this restorative system.

A retrospective study of pre-fabricated carbon fibre root canal posts.

Although pre-fabricated carbon fibre posts have been used during the past decade clinical evaluations of the technique are still few. Using dental records and radiographs the clinical performance of 65 pre-fabricated carbon fibre posts (Composipost and Endopost) placed in 48 patients who regularly visited a general practice were evaluated in the present study. After an average time of 2.3 +/- 0.8 years (median 2.1 years, range 1-4.9 years) of clinical service the failure rate was 3%. Failure occurred in one tooth with a single crown restoration and in one tooth that was part of a cantilever fixed partial denture. Although the failure rate is lower than those mostly reported for metallic posts and cores more clinical studies are necessary to assess the suitability of pre-fabricated carbon fibre posts for routine use as an alternative to individually cast posts.

Retention of prefabricated and individually cast root canal posts in vitro.

OBJECTIVES: The aim of the study was to evaluate the retention of prefabricated root canal posts made of a variety of materials that have recently been introduced into dentistry. MATERIALS AND METHODS: The posts studied were CosmoPost, Composipost carbon fibres, Composipost Aestheti-Plus, Composipost Light-Post and Para Post Fiber White. The posts were luted in extracted human premolars and the cores were built up with the resin composites recommended by the manufacturers. The retention of individually cast gold alloy posts luted with zinc-phosphate cement were used as reference. A universal testing machine was used to determine the retention of each cemented post Data were compared using ANOVA supplemented with Fisher's PLSD at a significance level of p < 0.05. RESULTS: Only the CosmoPost system exhibited retention values that were significantly lower than for the conventionally cast gold alloy posts luted with zinc-phosphate cement The force necessary to loosen the CosmoPost specimens was significantly less than that needed to loosen the Composipost. Estheti-Plus (p < 0.05) and the Composipost Ught-Post systems (p < 0.001]. The force necessary to loosen the ParaPost Fiber White specimens was significantly less than for the Composipost Light-Post system (p < 0.01). Other combinations did not differ significantly (p > 0.05). CONCLUSIONS: When zirconium oxide ceramic posts are luted with resin composites the bonding between the ceramic and resin composite seems to be weak. Further studies are thus necessary to achieve improved retention of all-ceramic root canal posts.

Cytotoxicity of dental alloys, metals, and ceramics assessed by millipore filter, agar overlay, and MTT tests.

STATEMENT OF PROBLEM: Biocompatibility of dental materials is dependent on the release of elements from the materials. In addition, the composition, pretreatment, and handling of the materials influence the element release. PURPOSE: This study evaluated the cytotoxicity of dental alloys, metals, and ceramics, with specific emphasis on the effects of altering the composition and the pretreatment. MATERIAL AND METHODS: By using cells from a mouse fibroblast cell line and the agar overlay test, Millipore filter test, and MTT test, cytotoxicity of various metals, metal alloys, and ceramics for dental restoration were studied. Effects of altering the composition of a high noble gold alloy and of pretreatment of a ceramic-bonding alloy were also studied. In addition, the release of elements into the cell culture medium by the materials studied was measured using an inductively coupled plasma optical emission spectrophotometer. The results of the MTT test were analyzed statistically using ANOVA and Scheffé test at a significance level of P <.05. RESULTS: Specimens manufactured from materials intended for dental restorations and handled in accordance with the manufacturers' instructions were ranked from "noncytotoxic" to "mildly cytotoxic" according to the agar overlay and Millipore filter tests. For the MTT test, no significant differences were observed between these materials and controls, with the exception of JS C-gold and unalloyed titanium. The modified materials were ranked from "mildly cytotoxic" to "moderately cytotoxic" in the agar overlay and Millipore filter tests and from "noncytotoxic" to "moderately cytotoxic" in the MTT test. Thus, cytotoxicity was related to the alloy composition and treatment. The release of Cu and Zn seemed to be important for the cytotoxic effect. CONCLUSION: Alterations in the composition and the pretreatment can greatly influence the cytotoxicity, and the results stress the importance of carefully following the manufacturers' instructions when handling dental materials.

A 3-year follow-up study of preformed beta-quartz glass-ceramic insert restorations.

OBJECTIVE: The purpose of this study was to evaluate the clinical performance of preformed beta-quartz glass-ceramic insert restorations. METHODS AND MATERIALS: Nine Class I and 30 Class II beta-quartz glass-ceramic insert restorations were placed in 16 patients who were seen regularly by personnel at Umeå University Dental School. The California Dental Association criteria were used to evaluate the restorations at baseline, 6 months, and 1, 2, and 3 years after luting. The occurrence of postoperative sensitivity, the time taken to manufacture each restoration, and certain periodontal conditions were also evaluated. RESULTS: Sixty-nine percent of the restorations were rated satisfactory at the 3-year examination. During the follow-up period, 4 became loose and 7 were fractured or had flaking surfaces. Caries was registered in connection with 1 restoration. Excellent ratings were obtained for marginal integrity, anatomic form, surface, and color in 62%, 84%, 32%, and 44% of the restorations, respectively. There was no statistically significant difference in the occurrence of plaque and bleeding on probing in comparison with the controls. The mean overall time for placement was 38 minutes. The estimated survival rate (Kaplan-Meier) was 59% after 3.5 years. CONCLUSION: The quality of the beta-quartz glass-ceramic restorations in the present study was inferior to that presented in most earlier studies of ceramic or resin composite posterior restorations placed in patients treated at university clinics. Both the technique and the beta-quartz glass-ceramic inserts have to be evaluated in more long-term studies to assess the possibility of their serving as an alternative restorative technique.

Clinical examination of leucite-reinforced glass-ceramic crowns (Empress) in general practice: a retrospective study.

PURPOSE: The purpose of this study was to retrospectively evaluate leucite reinforced-glass ceramic crowns (Empress) placed in patients who regularly visit general practices. MATERIALS AND METHODS: One hundred ten Empress crowns, placed in 29 patients who visited a general practice on a regular basis, were evaluated according to the California Dental Association's (CDA) quality evaluation system. In addition, the occurrence of plaque and certain gingival conditions was evaluated. All crowns were luted with resin composite cement. The mean and median years in function for the crowns were 3.6 and 3.9 years, respectively. RESULTS: Based on the CDA criteria, 92% of the 110 crowns were rated "satisfactory." Eighty-six percent were given the CDA rating "excellent" for margin integrity. Fracture was registered in 6% of the 110 crowns. Of the remaining 103 crowns, the CDA rating excellent was given to 74% for anatomic form, 86% for color, and 90% for surface. No significant differences (P > 0.05) were observed regarding fracture rates between anterior and posterior crowns. With regard to the occurrence of plaque and bleeding on probing, no significant differences (P > 0.05) were observed between the Empress crowns and the controls. CONCLUSION: Most of the fractured crowns had been placed on molars or premolars. Although the difference between anterior and posterior teeth was not statistically significant with respect to the fracture rates obtained, the number of fractured crowns placed on posterior teeth exceeded that of those placed on anterior teeth. The difference between the fracture rates may have clinical significance, and the risk of fracture has to be taken into consideration when placing crowns on teeth that are likely to be subjected to high stress levels.

Clinical evaluation of all-ceramic crowns (Dicor) in general practice.

STATEMENT OF PROBLEM: There are few studies regarding all-ceramic full crowns placed by general practitioners; however, most dental restorations are carried out by general practitioners, and their clinical performance may be of particular interest. PURPOSE: Ninety-eight all-ceramic Dicor crowns placed in 46 patients regularly visiting a general practice were evaluated with the California Dental Association's (CDA) criteria. Mean and median ages of the crowns were 6.1 and 5.8 years, respectively (range 1.4 to 10. 9 years). Crowns were luted with either a glass ionomer, zinc phosphate, or resin composite cement. RESULTS: Of the 98 crowns, 82% were rated satisfactory. For marginal integrity, 51% were rated excellent. Fracture was registered in 14 all crowns, and 1 endodontically treated tooth with a Dicor crown was extracted because of root fracture; of the remaining 83 crowns, 55% were rated excellent for color. Corresponding figures for surface and anatomic form were 46% and 23%, respectively. The most common finding was slightly rough surfaces (64%). No statistically significant difference was observed for fracture rates obtained when the crowns luted with different luting agents were compared (P >.05). There was no more plaque or bleeding on probing (P >.05) in connection with the Dicor crowns than in the control surfaces.

A 5-year clinical evaluation of ceramic inlays (Cerec) cemented with a dual-cured or chemically cured resin composite luting agent.

Sixty-six class-II CAD/CAM-manufactured ceramic inlays (Cerec) were placed in 27 patients. Each patient received at least one inlay luted with a dual-cured resin composite and one inlay luted with a chemically cured resin composite. The inlays were examined 5 years after luting using the California Dental Association (CDA) criteria. Eighty-nine percent of the 66 inlays were rated 'satisfactory'. During the follow-up period replacement was required for 3 inlays because of inlay fractures (4.5%) and 1 inlay because of fracture of the tooth substance (1.5%). All those inlays were luted with the dual-cured resin composite luting agent. Of the remaining 62 inlays the CDA rating 'excellent' was given to 84% for color, 97% for surface, and 81% for anatomic form. 'Excellent' margin integrity was seen in 52% of the dual-cured resin composite luted inlays and in 61% of the chemically cured resin composite luted inlays. No statistically significant (P> 0.05) difference was observed between the two luting agents.

Filler content and gap width after luting of ceramic inlays, using the ultrasonic insertion technique and composite resin cements. An in vitro study.

The effect of ultrasonic insertion on the filler content and the gap width for two brands of composite resin luting agents, intended for luting with the ultrasonic insertion technique, were studied after MOD ceramic inlays (Cerec) had been placed. In addition, the internal and marginal gap widths were determined after MOD ceramic inlays (Celay) bad been luted on extracted premolars with this technique. No statistically significant differences (P > 0.05) were observed for either brand between the filler content obtained from the internal surfaces, from the excess luting agent, or from the luting agent as delivered. There were no statistically significant differences (P > 0.05) between the final internal and marginal gap widths when the two brands of luting agent were compared with each other. Except for the final occlusal and internal gap widths obtained for the inlays luted with the Sono-Cem luting agent, no statistically significant differences (P > 0.05) were observed between the gap widths at the different locations determined. Thus, the ultrasonic insertion technique used did not significantly influence the filler ratio of the hybrid luting agents studied. Judged by the findings in this study, the properties of luting agents seem to greatly influence the final marginal and internal gap widths.

Charges extracted from dental ceramics: an indication of piezoelectric activity?

A method was established for demonstrating charge generation on the surfaces of dental materials by means of mechanical loading with different forces. With this experimental set-up charges could be extracted both from the surfaces that were mechanically loaded and from the surfaces perpendicular to the applied force. When specimens of certain ceramics were subjected to mechanical loading and the charges extracted were related to the applied force, charges of up to 3 x 10(-3) pC/N were recorded from the surfaces perpendicular to the applied force and charges of up to 8 x 10(-3) pC/N from the surfaces that were mechanically loaded. The results from this study indicate support for the hypothesis that the extracted charges were created by direct piezoelectricity. However, further studies are necessary for decisive proof that true piezoelectricity occurs in these materials.

Ceramic inlays (Cerec) cemented with either a dual-cured or a chemically cured composite resin luting agent. A 2-year clinical study.

On the basis of the criteria of the California Dental Association (CDA), 66 CAD/CAM-manufactured ceramic class-II inlays (Cerec) were compared intraindividually after they had been cemented with either a chemically cured or a dual-cured composite resin luting agent in 27 patients. Plaque and gingival conditions, the overall time consumption for producing each inlay, and the frequency of postoperative sensitivity were also evaluated. There was no statistically significant difference between the two luting agents with regard to the properties evaluated. One inlay was replaced owing to fracture of the restored tooth just before the 24-month re-examination. After 2 years excellent CDA ratings were obtained for color in 92% of the remaining 65 inlays. The corresponding figures for surface and for anatomic form were 100% and 85%, respectively. For margin integrity 85% of the 33 inlays cemented with the dual-cured luting agent and 88% of the 33 inlays cemented with the chemically cured luting agent were rated excellent after 2 years.

Marginal and internal fit of four different types of ceramic inlays after luting. An in vitro study.

The marginal and internal fit of four different types of ceramic inlays--Cerec, Celay, Empress, and Vita In-Ceram Spinell--was determined after they had been luted on extracted premolars. For the Cerec inlays sharp and U-shaped proximal box shapings were also compared. There was no statistically significant difference either in the proximal fit or in the gingivoproximal fit between the four inlay systems studied, with the exception of the Cerec inlays made for preparations with sharp proximal boxes, which had wider marginal gaps. At the occlusal margins a significant-principle order of the gap width was established. The best internal fit was recorded for the Celay inlays, whereas there was no significant difference in the internal fit between the other systems. For the Cerec inlays the U-shaped proximal box shaping improved the marginal accuracy all around the restoration.

Piezoelectricity in dental materials, a conceivable cause of postrestorative sensitivity.

With the increased use of tooth-colored posterior inlays reports of postrestorative sensitivity have also increased. One of the symptoms the patients complain of is a sharp pain when the inlays are loaded through chewing and biting. Many explanations for the causes of dissimilar types of postrestorative sensitivity have been offered, but one conceivable explanation that has not hitherto been studied is the direct piezoelectric effect in dental materials. Direct piezoelectric effect means that when certain anisotropic crystals are mechanically loaded, a charge is generated on the surface. The aim of the present study was to examine whether this physical phenomenon occurs in certain materials intended for dental use. Specimens of four different dental ceramics and one indirect composite resin for inlays were mechanically loaded with various forces, and the current was directly recorded. Currents of up to 0.9 microA with a pulse duraton of 0.4 msec were extracted, and it cannot be excluded that the piezoelectric phenomenon and related properties may cause postrestorative sensitivity. This has to be taken into consideration when posterior inlays of the types concerned are used.