CAD/CAM-machining effects on Y-TZP zirconia.

OBJECTIVES: Computer-Aided-Design/Computer-Aided-Manufacturing (CAD/CAM) techniques are gaining importance in fabricating crowns and fixed partial dentures (FPDs) made of yttria stabilized tetragonal zirconia polycrystals (Y-TZP). The specific aims of this study were (1) to test the hypothesis that surface flaws and microcracks are induced by the grinding of crowns (2) to analyze the material removal and the grinding-induced surface layer as well as to estimate the crack size caused by machining Y- TZP under conditions simulating the grinding of crowns. METHODS: Y-TZP disks and sectioned cylinders with polished separation planes were used for the analysis of the grinding procedure. While simulating the inner surface grinding of crowns, feed and cutting depth were varied (vw = 100, 75, 50 mm/min; ap = 0.1, 0.06, 0.02 mm). SEM was used for the quantitative assessment of the machined surface. RESULTS: While the crack length is not significantly influenced by the grinding parameters, the type of material removed varied with the cutting depth as well as with the feed. Grinding induced surface flaws and microcracks were detected at the internal top surface of the crowns. Half-cylinders machined under conditions simulating the inner surface grinding of crowns showed crack lengths between 2 and 15 microm. SIGNIFICANCE: Sectioned specimens with polished section planes are suitable for the analysis of the grinding process using the face and peripheral grinding procedure. The inner surface grinding of fixed restorations is the most challenging step of CAM of crowns and FPDs. Most important appeared to be the diamond tool, especially the number and shape of the active diamond grains.     

Influence of connector design on fracture probability of ceramic fixed-partial dentures

Fracture of ceramic fixed-partial dentures (FPDs) tends to occur in the connector area because of stress concentrations. The objective of this study was to test the hypothesis that the radius of curvature at the gingival embrasure of the FPD connector significantly affects the fracture resistance of three-unit FPDs. Two three-dimensional finite element models (FEMs), representing two FPD connector designs, were created in a manner corresponding to that described in a previous experimental study (Oh, 2002). We performed fractographic analysis and FEM analyses based on CARES (NASA) post-processing software to determine the crack initiation site as well as to predict the characteristic strength, the location of peak stress concentrations, and the risk-of-rupture intensities. A good correlation was found between the experimentally measured failure loads and those predicted by FEM simulation analyses. Fractography revealed fracture initiation at the gingival embrasure, which confirms the numerically predicted fracture initiation site. For the designs tested, the radius of curvature at the gingival embrasure strongly affects the fracture resistance of FPDs.     

Reliability and Failure Modes of Implant‐Supported Y‐TZP and MCR Three‐Unit Bridges

Purpose: Chipping within veneering porcelain has resulted in high clinical failure rates for implant‐supported zirconia (yttria‐tetragonal zirconia polycrystals [Y‐TZP]) bridges. This study evaluated the reliability and failure modes of mouth‐motion step‐stress fatigued implant‐supported Y‐TZP versus palladium‐silver alloy (PdAg) three‐unit bridges. Materials and Methods: Implant‐abutment replicas were embedded in polymethylmethacrylate resin. Y‐TZP and PdAg frameworks, of similar design (n = 21 each), were fabricated, veneered, cemented (n = 3 each), and Hertzian contact‐tested to obtain ultimate failure load. In each framework group, 18 specimens were distributed across three step‐stress profiles and mouth‐motion cyclically loaded according to the profile on the lingual slope of the buccal cusp of the pontic. Results: PdAg failures included competing flexural cracking at abutment and/or connector area and chipping, whereas Y‐TZP presented predominantly cohesive failure within veneering porcelain. Including all failure modes, the reliability (two‐sided at 90% confidence intervals) for a “mission” of 50,000 and 100,000 cycles at 300 N load was determined (Alta Pro, Reliasoft, Tucson, AZ, USA). No difference in reliability was observed between groups for a mission of 50,000. Reliability remained unchanged for a mission of 100,000 for PdAg, but significantly decreased for Y‐TZP. Conclusions: Higher reliability was found for PdAg for a mission of 100,000 cycles at 300 N. Failure modes differed between materials.     

Effect of connector design on the fracture resistance of all-ceramic fixed partial dentures

STATEMENT OF PROBLEM: Fracture of all-ceramic fixed partial dentures (FPDs) tends to occur in the connector area. PURPOSE: The objective of this study was to test the hypothesis that the radii of curvature at the connector affects the fracture resistance of 3-unit FPDs. MATERIAL AND METHODS: With the use of a standardized silicone mold, 40 three-unit FPD wax patterns were fabricated with the same dimensions and divided into 4 groups of 10 specimens per group. Each pattern was modified at the connector areas of the occlusal embrasure (OE) and the gingival embrasure (GE); 2 wax carvers with radii of curvature at their tips of 0.90 mm and 0.25 mm were used. The dimensions of the connectors were standardized with an electronic caliper to 4 +/- 0.12 mm in height and 5 +/- 0.13 mm in width. Connector designs were as follows: Design I: OE and GE 0.90 mm; Design II: OE 0.90 mm and GE 0.25 mm; Design III: OE 0.25 mm and GE 0.90 mm; and Design IV (control): OE and GE 0.25 mm. An experimental hot-pressed core ceramic was used to make the FPD frameworks, which were consequently cemented on epoxy dies with dual-polymerizing composite (Variolink II) and loaded to fracture in a universal testing machine at a crosshead speed of 0.5 mm/min. The failure load data were analyzed with analysis of variance (ANOVA; P=.05) and Duncan's test (alpha=.01). RESULTS: The mean failure loads and standard deviations were as follows: 943 +/- 151 N for Design I; 746 +/- 106 N for Design II; 944 +/- 144 N for Design III; and 673 +/- 55 N for Design IV. ANOVA revealed a significant difference (P< or = .0001) between the mean failure loads of different connector designs. The mean loads to failure for Designs I and III were significantly higher than those for Designs II and IV (Duncan's test). CONCLUSION: Within the limitations of this study and for the experimental ceramic tested, as the radius at the gingival embrasure increased from 0.25 to 0.90 mm, the mean failure load increased by 140%. The radius of curvature at the occlusal embrasure had only a minor effect on the fracture susceptibility of 3-unit FPDs.     

Effect of pontic height on the fracture strength of reinforced interim fixed partial dentures

OBJECTIVES: This in vitro study evaluated the fracture load of interim FPDs made with various materials and pontic heights. The hypothesis was that different materials and pontic heights result in different fracture resistance. METHODS: Groups of interim FPDs were fabricated with prosthodontic resin materials on two abutments with two different pontic heights (4.3 and 5.8 mm) and a pontic width of 4 units (19 mm) (n = 3). The following materials were tested: (1) a thermoplastic polymer (Promysan Star), (2) Promysan Star with a veneering composite (Vita Zeta), (3) a non-impregnated polyethylene fiber reinforced resin (Ribbond) with a veneering composite (Sinfony), (4) an impregnated fiber reinforced composite system (Targis/Vectris), and (5) a conventional poly methyl methacrylate (PMMA) (Biodent K+B, control group). After 5000 thermocycles, the FPDs were temporarily fixed with a provisional cement on the corresponding abutments and tested for fracture strength. One-way and two-way ANOVA and Bonferroni-Dunn's multiple comparison tests were performed for the statistical analysis (alpha = 0.05). RESULTS: The mean fracture strength ranged from 83.0 to 625.9 N for a pontic height of 4.3 mm and from 97.2 to 893.7 N for a pontic height of 5.8 mm. Vectris/Targis FPDs of both pontic heights exhibited significantly superior fracture resistance compared to the corresponding Promysan, Promysan/Vita Zeta, Ribbond/Sinfony and Biodent groups. Except Biodent FPDs, fracture resistance of FPDs with a pontic height of 4.3 mm showed no significant differences compared to a pontic height of 5.8 mm for each material. SIGNIFICANCE: Material type of the FPDs has a significant influence on the fracture strength, whereas pontic height has no significant effect (except control group).     

Fracture resistance of fiber-reinforced composite restorations with different framework design

OBJECTIVES. Veneer fracture and bond deficiency between framework and veneer are typical failures of fiber-reinforced inlay fixed partial dentures (FPD). An eccentric load point on the pontic was used in this study to investigate the fracture resistance of FPDs with different framework designs. As null hypothesis, it was assumed that fracture resistance was not influenced by the fiber framework supporting the veneer. METHODS. Four groups of Vectris/Adoro FPDs (4 x n=10 each) were manufactured. Beams (25 mm length) of Vectris Pontic (parallel aligned) with (a) rectangular (3 x 3) sectional view and (b) circular sectional view (theta 3 mm) were directly veneered using Adoro. (c) Circular beams like "b" were modified, i.e. those on the upper side were coated with two layers of the cross-sectioned fiber mat Vectris frame. (d) Vectris Pontic fibers were "anatomically" placed in the pontic area and wrapped using Vectris Frame. The frameworks were constructed in a vacuum/pressure process. All FPDs were mounted in a restrained-end apparatus and thermally cycled and mechanically loaded (TCML: 6000 x 5 degrees C/55 degrees C; 1.2 x 10(6) x 50 N, 1.66 Hz). After TCML, the FPDs were loaded to fracture. RESULTS. All FPDs surpassed TCML, with no visible damage to the veneer or framework. Without transversal enlargement of the framework, additional cross-sectioned fiber mats alone did not improve resistance to fracture (a: 573+/-158 N (mean, standard deviation given); b: 737+/-66 N; c: 694+/-93 N; d: 902+/-149 N). Fracture lines occurred only in the veneer; the fiber frameworks were never affected. CONCLUSIONS. Anatomical enlargement of the fiber framework at the pontic area (height, width) to support the veneer material improves the fracture resistance of fiber-reinforced FPDs.     

Comparison of load-bearing capacity of direct resin-bonded fiber-reinforced composite FPDs with four framework designs

OBJECTIVES: This in vitro study was aimed to compare the fracture resistance of directly fabricated inlay-retained fiber-reinforced composite (FRC) fixed partial dentures (FPDs) with four types of framework designs. METHODS: Forty-eight directly fabricated inlay retained FPDs were made of FRC and particulate resin composite (everStick/Tetric flow and Ceram). Extracted human mandibular first premolars and first molars were as abutments. The following framework designs were tested: in the Group A (control group), the framework was made of two prepregs of unidirectional glass FRC; the Group B, two prepregs in pontic portion were covered with one layer of multidirectional fiber veil FRC; the Group C, the FRC prepregs were covered in pontic portion with four short unidirectional FRC pieces along the main prepregs; in Group D, one short unidirectional FRC prepregs were placed on the main prepregs in 90 degrees angle to the main framework. After thermal cycling, FPDs of each group (n=12) were randomly divided into two subgroups (n=6). Fracture test was performed at the universal testing machine (1mm/min) where FPDs were loaded from the occlusal direction to the occlusal fossa or to the buccal cusp. Failure patterns were observed with stereomicroscope. Median and 25%/75% percentile values were calculated and nonparametric analysis was performed. RESULTS: Compared with three other framework designs, the FPDs in Group D showed the highest resistance when loading to the occlusal fossa, with maximum load of 2,353.8N (25%/75%: 2,155.5/2,500.0) (p=0.000, 0.000, and 0.005 for compared with Group A, B, and C). The same group showed also higher resistance when loaded to the buccal cusp (1,416.3N (1,409.2/1,480.8)) if compared to the FPDs of the Group A and Group C (p=0.044, 0.010). In general the FPDs showed higher resistant to loading at the occlusal fossa (p<0.05). CONCLUSIONS: This in vitro study showed that inlay-retained FRC FPD constructed with direct technique provided high fracture resistance. The framework design that provided support for the veneering composite of the pontic contributed to the highest load-bearing capacity even when loaded to the buccal cusp.     

Structural optimization of the fibre-reinforced composite substructure in a three-unit dental bridge

IntroductionFailures of fixed partial dentures (FPDs) made of fibre-reinforced composites (FRC) have been reported in many clinical and in vitro studies. The types of failure include debonding at the composite-tooth interface, delamination of the veneering material from the FRC substructure and fracture of the pontic. The design of the FRC substructure, i.e. the position and orientation of the fibres, will affect the fracture resistance of the FPD.ObjectivesThe purpose of this study was to find an optimal arrangement of the FRC substructure, by means of structural optimization, which could minimize the failure-initiating stresses in a three-unit FPD.MethodsA structural optimization method mimicking biological adaptive growth was developed for orthotropic materials such as FRC and incorporated into the finite element (FE) program ABAQUS. Using the program, optimization of the fibre positions and directions in a three-unit FPD was carried out, the aim being to align the fibre directions with those of the maximum principal stresses. The optimized design was then modeled and analyzed to verify the improvements in mechanical performance of the FPD.ResultsResults obtained from the optimization suggested that the fibres should be placed at the bottom of the pontic, forming a U-shape substructure that extended into the connectors linking the teeth and the pontic. FE analyses of the optimized design indicated stress reduction in both the veneering composite and at the interface between the veneer and the FRC substructure.SignificanceThe optimized design obtained using FE-based structural optimization can potentially improve the fracture resistance of FPDs by reducing some of the failure-initiating stresses. Optimization methods can therefore be a useful tool to provide sound scientific guidelines for the design of FRC substructures in FPDs.     

The Effect of Incorporation, Orientation and Silane Treatment of Glass Fibers on the Fracture Resistance of Interim Fixed Partial Dentures

Fracture of interim fixed partial dentures (FPD) is of important concern to the dental surgeon, especially with long-span fixed partial dentures or areas of heavy occlusal stress. Polymers used in interim FPDs, reinforced with glass fibers have shown to have a positive effect on the fracture resistance of interim FPDs. Since little research has been done on the influence of silane treated glass fibers on the fracture resistance of interim FPDs, this study was conducted to evaluate the effect of silane treatment of glass fibers on the fracture resistance of interim FPDs and its correlation with the position of fiber reinforcement and length of the span of the interim FPD. Interim FPDs were fabricated from an autopolymerizing polymethyl methacrylate (PMMA) resin. Seven FPDs were made in each group. The FPDs in the control group were unreinforced, and in the other groups the FPDs were reinforced either with non silane treated glass fiber or with silane treated glass fiber. The fibers were placed in two different locations in the FPDs. Three length of span of FPDs were tested. The load was applied to the FPD by a steel ball placed in the center of the pontic space. One Way Anova, Two Way Anova, Studentized range test (Scheffe’s). Results showed that the load required for fracturing the unreinforced FPDs varied from 272 to 998 N. Mean fracture load of reinforced FPDs varied from 536 to 1642 N. One-way analysis of variance showed that the position of fibers and the silane treatment fibers significantly affected the fracture load. The results of this study suggested that the silane treatment of glass fibers had a marked improvement in the fracture resistance of FPDs as compared to untreated glass fibers. Selective placement of the glass fibers at the undersurface of the pontic and the occlusal surface of the interim fixed partial denture showed more increase in the fracture resistance as compared to the randomly distributed glass fibers. The glass fiber reinforcement is effective in increasing the fracture resistance with the effectiveness most evident in interim FPDs with long spans. With increase in the length of span of interim fixed partial denture the fracture resistance was shown to decrease significantly in all the groups.     

Fracture load of CAD/CAM-generated slot-inlay FPDs

PURPOSE: This study investigated fracture load of computer-aided design/manufacturing (CAD/CAM)-generated slot-inlay fixed partial dentures (FPD) machined from ceramic and composite. MATERIALS AND METHODS: Ninety slot-inlay FPDs were machined in groups of 15 specimens each using the same design on a Cerec 3 unit. Materials were assigned to groups: (1) Mk II feldspathic ceramic, (2) ProCAD glass-ceramic, (3) glass-ceramic 1, (4) glass-ceramic 2, (5) composite 1, and (6) composite 2. The slot-inlay FPDs were placed on models with two abutment teeth without cementation and loaded to fracture. For control, test bars (n = 15) were machined from each of the materials, and flexural strength was examined using three-point bending. Data were statistically analyzed using ANOVA and Scheffé tests. RESULTS: Fracture load of groups 4 (1,557 N, SD 236), 5 (1,048 N, SD 77), and 6 (1,512 N, SD 106) was significantly higher than that of groups 1 (652 N, SD 53) and 2 (773 N, SD 65). Flexural strength of group 4 (256 MPa, SD 20) was significantly higher than that of groups 1 (103 MPa, SD 6), 2 (127 MPa, SD 15), 3 (162 MPa, SD 32), 5 (178 MPa, SD 18), and 6 (170 MPa, SD 20). CONCLUSION: Fracture loads of glass-ceramic 2 and composite 2 appear adequate for CAD/CAM slot-inlay FPDs.     

Effect of Framework Shape on the Fracture Strength of Implant-Supported All-Ceramic Fixed Partial Dentures in the Molar Region

Purpose: The aim of the present study was to clarify the effects of the shape of the zirconium framework of implant-supported, all-ceramic fixed partial dentures (FPDs) on the fracture strength and fracture mode.
Materials and Methods: This study consisted of mechanical strength testing and 3D finite element analysis (FEA). The three framework shapes used in this study were: (1) conventional shape (control); (2) convex shape: 1.0-mm curve in the direction of the occlusal surface; and (3) concave shape: 1.0-mm curve in the direction of the gingival surface. Five frameworks were made for each condition (total: 15). A load (N) was applied until the FPD fractured. For FEA, a 3D model consisting of cortical bone, cancellous bone, implant bodies, and superstructure was constructed.
Results: The results of the mechanical strength test showed that fracture load was 916.0 ± 150.1 N for the conventional shape, 1690.5 ± 205.3 N for the convex shape, and 1515.5 ± 137.0 N for the concave shape. The mean final fracture load for the FPDs with frameworks was the highest for the convex shape; however, a critical crack in the veneer porcelain (736.5 ± 145.2 N) was confirmed during loading for the convex shape. Stress distribution maps for all conditions showed that tensile stress was generated at the veneer porcelain on the gingival side of the mesial and distal connectors of the pontic; however, there were differences in the maximum value and stress distribution within the framework.
Conclusion: The shape of the framework, particularly the shape of the pontic–connector interface, affects the stress distribution, fracture strength, and fracture mode of all-ceramic FPDs, and stress concentration inside a framework may induce cracking of layering porcelain.     

Fracture resistance of lithium disilicate-, alumina-, and zirconia-based three-unit fixed partial dentures: a laboratory study

PURPOSE: The purpose of this study was to determine the fracture resistance of three-unit fixed partial dentures (FPD) made of new core ceramics. MATERIALS AND METHODS: A base metal three-unit master FPD model with a maxillary premolar and molar abutment was made. Tooth preparation showed 0.8-mm circumferential and 1.5-mm occlusal reduction and a chamfer margin design. FPDs were constructed with a uniform 0.8-mm-thick core ceramic and a porcelain veneer layer. In-Ceram Alumina, In-Ceram Zirconia, and DC-Zirkon core ceramics were machined by a computer-aided design/manufacturing system, whereas IPS Empress 2 core ceramic was indirectly built up using the fabrication technology of waxing and heat pressing. FPDs of IPS Empress were heat pressed as complete restorations without core material. To ensure standardized dimensions, the FPDs were controlled at different points. All FPDs were cemented with ZnPO4 on the master model and loaded on a universal testing machine until failure. The failure load and mode of failure were recorded. RESULTS: The highest failure loads, exceeding 2,000 N, were associated with FPDs of DC-Zirkon. FPDs of IPS Empress and In-Ceram Alumina showed the lowest failure loads, below 1,000 N, whereas intermediate values were observed for FPDs of IPS Empress 2 and In-Ceram Zirconia. Differences in mean values were statistically significant. CONCLUSION: The high fracture resistance evaluated for FPDs made of DC-Zirkon underscores the remarkable mechanical properties of high-performance ceramic, which could be useful for highly loaded all-ceramic restorations, especially in the molar region.     

Fracture strength of zirconia implants after artificial aging

Background: Zirconia (ZrO₂) might be an alternative material to titanium (Ti) for dental implant fabrication. However, no data are available on the fracture strength of one‐piece ZrO₂ oral implants. Purpose: The objective of this study was to evaluate the fracture strength of ZrO₂ implants after exposure to the artificial mouth. Materials and Methods: One hundred twenty ZrO₂ and Ti implants were used. The Ti implants were divided into two control groups (A and B). ZrO₂ implants manufactured from yttria‐stabilized tetragonal ZrO₂ polycrystal (Y‐TZP) in group C, from Y‐TZP dotted with alumina (Y‐TZP‐A) in group D, and from Y‐TZP‐A with a modified surface in groups E and F were used. In group F, the implant heads were prepared, and in group G, the implants were restored with ZrO₂ crowns. Each group included 16 samples with the exception of group D, which included 24 samples. A subgroup of each implant type (eight implants) was subjected to thermomechanical cycling in a chewing simulator prior to fracture testing. Test specimens were then loaded until a fracture occurred. Results: Seven of the 120 samples failed in the chewing simulator. ZrO₂ implant fracture occurred at 725 to 850 N when the implants were not prepared, and at 539 to 607 N when prepared. The samples in group A fractured at the level of the abutment screw. All ZrO₂ implants fractured at the level of the Technovit® resin (Heraeus Kulzer GmbH & Co., Wehrheim, Germany). No fracture of the ZrO₂ crowns in group G was observed. Conclusion: Mean fracture strength values obtained were all within the limits of clinical acceptance. However, implant preparation had a statistically significant negative influence on the implant fracture strength. Long‐term clinical data are necessary before one‐piece ZrO₂ implants can be recommended for daily practice.     

In vitro resistance of reinforced interim fixed partial dentures

STATEMENT OF PROBLEM: Comprehensive restorative dental treatment often necessitates the use of interim fixed partial dentures (FPDs) with high stiffness, especially in long-span restorations or areas of heavy occlusal stress. PURPOSE: This in vitro study evaluated the fracture load of interim FPDs made with various materials and span lengths. MATERIAL AND METHODS: Groups (n = 3) of interim FPDs were fabricated with prosthodontic resin materials on 2 abutments with 3 different pontic widths of 3 units (12 mm), 4 units (19 mm), and 5 units (30 mm). The following materials were tested: (1) a thermoplastic polymer (Promysan Star), (2) Promysan Star with a veneering composite (Vita Zeta), (3) a nonimpregnated polyethylene fiber reinforced resin (Ribbond) with a veneering composite (Sinfony), (4) an impregnated fiber reinforced composite system (Targis/Vectris), and (5) a conventional polymethyl methacrylate, Biodent K+B, (control group). After 5000 thermocycles in 2 water baths at 5 degrees and 55 degrees C, the FPDs were temporarily fixed with a provisional cement on the corresponding abutments and subjected to 3-point bending until fracture by a universal testing machine. Statistical analysis consisted of an analysis of variance (ANOVA, 1-way, 2-way) and Bonferroni-Dunn's multiple comparisons post hoc analysis for test groups (alpha = .05). RESULTS: Fracture resistance (N) differed significantly for 3 (mean: 640 +/- 146 N), 4 (626 +/- 229 N), and 5 unit (658 +/- 98 N) Targis/Vectris FPDs compared with the corresponding Promysan (284 +/- 21 N to 125 +/- 73 N), Biodent K+B (247 +/- 91 N to 218 +/- 85 N), and Promysan/Vita Zeta (95 +/- 15 N to 82 +/- 6 N) groups (P < .05). Significant differences were obtained for the 4 and 5 unit Targis/Vectris FPDs compared with the Sinfony/Ribbond FPDs (281 +/- 25 N - 252 +/- 74 N) for the corresponding pontic spans. CONCLUSION: Within the limitations of this in vitro study the impregnated fiber reinforcement may considerably enhanced the fracture resistance of interim FPDs of different span lengths.     

Disparity in embrasure fill and papilla height between tooth‐ and implant‐borne fixed restorations in the anterior maxilla: a cross‐sectional study

Purpose

The objective of the present study was to compare inter‐proximal fill and papilla height between different embrasures.

Material & Methods

One hundred and fifty non‐smoking consecutive patients (mean age 54, range 32–73; 63 males and 87 females) without periodontal disease were selected in a multidisciplinary practice during regular supportive care. All had been treated for multiple tooth loss in the anterior maxilla at least 1 year earlier by means of a fixed restoration on teeth (n = 50) or implants (n = 100) using straightforward procedures (without hard and/or soft tissue augmentation). Embrasure fill was assessed by means of Jemt's papilla index and papilla height was registered following local anaesthesia by means of bone sounding by one clinician.

Results

Tooth‐pontic and tooth‐implant embrasures demonstrated comparable inter‐proximal fill and papilla height (≥58% Jemt's score 3; mean papilla height ≥4.1 mm). Between missing teeth, embrasure fill and papilla height were lower regardless of the embrasure type. The implant‐implant and implant‐pontic embrasure demonstrated comparable outcome (≤42% Jemt's score 3; mean papilla height ≤ 3.3 mm; p ≥ 0.416), which was significantly poorer when compared to the pontic‐pontic embrasure (82% Jemt's score 3; mean papilla height 3.7 mm; p ≤ 0.019). Overall, papilla index and papilla height demonstrated a weak correlation (Spearman's correlation coefficient: 0.198; p = 0.002).

Conclusions

The re‐establishment of a papilla is difficult when there is no tooth involved. In that scenario a short papilla should be expected and implant‐borne restorations demonstrate the poorest outcome. Moreover, an implant with a pontic may not perform better than adjacent implants.     

Experimental design of FPD made of all-ceramics and fibre-reinforced composite.

OBJECTIVES: This study was carried out to combine flexural properties of FRC materials with aesthetic values of ceramics. METHODS: The bonding strength of fibre-reinforced composite to ceramic was determined. Afterwards, 8 three unit and 8 four unit FPDs (fixed partial dentures) were manufactured based on the experimental design and were then adhesively luted onto human molars. After thermal cycling and mechanical loading in an artificial environment, the fracture strength and marginal adaptation was determined. FPDs made of FRC (fibre-reinforced composite) materials were used as a control. RESULTS: The most reliable bonding strength of ceramic to FRC material was achieved using acid etching in combination with adhesive luting techniques. Median fracture strength values of 575 N for three unit FPD and 876 N for four unit FPD were established. More than 85% of the experimental FPDs showed a perfect margin while less than 15% revealed a marginal gap, even after thermal cycling and mechanical loading (TCML). The strongest influence of TCML on the marginal adaptation of the experimental design FPD was determined within the four unit system showing approximately a 10% change in marginal gap and perfect margin. SIGNIFICANCE: Assuming an improvement in adhesive bonding between the ceramic and the FRC material and, in addition, an enhancement of the contact surface between pontic and abutment, the hybrid technique could represent an interesting procedure for further investigations and, eventually, clinical implication.     

金瓷桥对口腔局部细菌的影响

目的：探讨金瓷桥戴人口腔对局部细菌的影响。方法：采用经典细菌培养鉴定及菌落形成单位计数(CFU／ml)的检测方法观测临床病例。结果：戴牙后龈沟及桥体组织面以产黑色素普氏菌增多显著。结论：金瓷桥戴入可能对口腔生态环境产生较长时间的影响。     

Local Injection of Hyaluronic Acid Filler Improves Open Gingival Embrasure: Validation Through a Rat Model

Background: The open gingival embrasure, the so‐called black triangle, is one of the unsolved dilemmas in adult dentistry. Although various techniques have been introduced to improve black triangles, the lack of reproducible experimental models has prevented development of successful protocols to regenerate or to compensate loss of the interdental papilla. Therefore, the objective of this study is first to develop a reliable animal model of open gingival embrasure and then to validate a minimally invasive injection technique using hyaluronic acid (HA) filler to augment the interdental papilla. Methods: To reproduce open gingival embrasure in rats, rapid space opening was induced between the mandibular incisors by attachment of a compression spring. Loss of interdental papilla height was morphologically evaluated and calculated using standardized serial photographs, microcomputed tomography, and histologic sections. Afterward, HA fillers or phosphate‐buffered saline (PBS) was locally injected, and changes in the interdental papilla were evaluated. Results: After 7 days of space opening, the margin of the interdental papilla between the mandibular incisors gradually became irregular and flat, indicating a condition similar to the open gingival embrasure (P <0.05). Local injection of HA filler induced an augmentation effect of the interdental papilla compared with injection of PBS (P <0.05). Interdental papilla became convex, and inner granules containing HA were detected within the submucosal layer after its injection. Conclusions: Open gingival embrasure was reproduced reliably in vivo. Local injection of HA filler was validated as a meaningful minimally invasive procedure to improve open gingival embrasure.     

The effect of surface treatment of the interfacial surface on fatigue-related microtensile bond strength of milled zirconia to veneering porcelain

Purpose: The success of zirconia‐reinforced all‐ceramic crowns depends on the formation of a stable bond between the zirconia core and the veneering porcelain. The purpose of this study was to test the effects of liner application and airborne particle abrasion of a postsintered Y‐TZP core on the bond strength between the zirconia core and veneering porcelain with or without cyclic loading. Materials and Methods: Kavo Everest® Y‐TZP blank disks were sintered and divided into three treatment groups: airborne particle abrasion, IPS e.max® Ceram Zirliner application, or no surface treatment. The disks were then veneered with IPS e.max® ZirPress veneering porcelain. Half the veneered disks from each group were cyclically loaded. This created six experimental groups: three surface treatment groups cyclically loaded and three not loaded. The disks were then sectioned into microbars for microtensile bond strength (MTBS) testing (40 specimens per group). Specimens were luted to a fixture mount and loaded to failure using a universal testing machine (MTS Insight). The maximum force was measured and bond strength computed. Data were analyzed with a two‐way ANOVA and Tukey's HSD test (α= 0.05). Results: Airborne particle abrasion significantly decreased MTBS values (p= 0.043), and ZirLiner application did not have a significant effect on MTBS values compared to control. Cyclic loading did not have a significant effect on MTBS values. The predominant failure mode in all groups was mixed. Conclusions: Airborne particle abrasion of the interfacial surface of the Everest® Y‐TZP core significantly decreased the MTBS to ZirPress veneering porcelain when compared to no interfacial surface treatment. Application of ZirLiner to the interfacial surface of the Everest® Y‐TZP core did not significantly increase or decrease the MTBS to ZirPress veneering porcelain, compared to the other surface treatments. Cyclic loading did not affect bond strengths in any of the groups, regardless of surface treatment. Neither cyclic loading nor surface treatment affected the failure mode of the specimens.     

Evaluation of a High Fracture Toughness Composite Ceramic for Dental Applications

Purpose: The introduction of yttrium partially stabilized zirconia polycrystals (Y‐TZP) has pushed the application limits of all‐ceramic restorations. The mechanical properties of these materials can be further improved by the addition of a secondary dopant phase. The aim of this work was to evaluate the properties of a new nano‐composite ceramic used as a dental framework material. Materials and Methods: The properties of a new ceria‐stabilized tetragonal zirconia polycrystal co‐doped with alumina (Ce‐TZP‐Al) were investigated. Y‐TZP was used as control. Sixty bars (20 × 2.5 × 1.5 mm³) from each material were prepared by cutting CAD/CAM milling blocks. Twenty specimens were used to measure the 4‐point flexural strength and the modulus of elasticity of the tested materials. The remaining specimens were used to measure the fracture toughness using indentation strength (IS), single edge notched beam (SENB), and fractography (FR). The thermal expansion coefficient (TEC) was measured using temperature expansion diagrams. The bond strength of the two framework materials to two esthetic veneer ceramics was tested using the microtensile bond strength test (MTBS). Finally, scanning electron microscopy (SEM) and energy dispersive X‐ray microanalysis (EDX) were used to analyze the internal structure of the materials. One‐ and two‐way analysis of variance (ANOVA) and Bonferroni post hoc tests were used to analyze the data (α= 0.5). Results: The flexural strength and modulus of elasticity of Ce‐TZP‐Al (856 MPa, 170 GPa) were significantly weaker (p < 0.001) than those of Y‐TZP (1003 MPa, 215 GPa). The (IS) fracture toughness of the former (19.02 MPa m^1/2) was significantly higher (p < 0.001) than SENB (12.6 MPa m^1/2) or FR (12.8 MPa m^1/2) values. These values were significantly higher (p < 0.001) than the fracture toughness of Y‐TZP (7.4 MPa m^1/2), which showed statistically similar values using the same three techniques. The measured TEC for the two materials was relatively similar, 10.1 μm/°C and 10.4 μm/°C, respectively. Regarding MTBS values, Ce‐TZP‐Al had significantly lower bond strength values (p < 0.001) and a higher percentage of interfacial failure than Y‐TZP, which failed completely cohesively with the two used veneer ceramics. SEM analysis revealed zirconia grains pull out and structural defects at the core–veneer interface for Ce‐TZP‐Al material, which explained its weak bond to the two used veneers. Conclusion: Despite the promising mechanical properties of Ce‐TZP‐Al nano‐composite ceramic, its very low bond strength to esthetic veneers leaves such layered restorations highly susceptible to delamination and chipping under function. Further studies are needed to enhance the surface stability of this high fracture toughness ceramic.