Effects of Liner-Bonding of Implant-Supported Glass-Ceramic Crown to Zirconia Abutment on Bond Strength and Fracture Resistance.

This study was conducted to test the hypothesis that heat-bonding with a liner positively affects the bond strength and fracture resistance of an implant-supported glass-ceramic crown bonded to a zirconia abutment produced by a computer-aided design/computer-aided milling (CAD/CAM) procedure. Lithium disilicate-reinforced Amber Mill-Q glass ceramic blocks were bonded to 3 mol% yttria stabilized tetragonal zirconia polycrystal (3Y-TZP) blocks by heat-bonding with a liner or cementation with a dual-cure self-adhesive resin cement for a microtensile bond strength test. CAD/CAM implant-supported glass ceramic crowns were produced using Amber Mill-Q blocks and bonded to a milled 3Y-TZP zirconia abutments by heat-bonding or cementation for a fracture test. A statistical analysis was conducted to investigate the significant differences between the experimental results. The mode of failure was analyzed using high-resolution field emission scanning electron microscopy. Chemical bonding was identified at the interface between the zirconia ceramic and liner. The mean tensile bond strength of the liner-bonded group was significantly higher than that of the cement-bonded group. The initial chipping strength of the liner-bonded group was significantly higher than that of the cement-bonded group, although no statistically significant difference was found for the fracture strength. The mode of failure was mixed with cohesive fracture through the liner, whereas the cement-bonded group demonstrated adhesive failure at the interface of bonding.

The Principles of Functional and Mucostatic Impressions for Complete Denture Bases: A Review.

In addition to needing to be hygienic and biocompatible, the base of a complete denture (CD) should provide intimate adaptation to the mucosa of a ridge. The ridge form may differ under function than when at rest because of the compressibility of mucosa. This viscoelastic behavior of ridge mucosa has been a focus of research and a clinical challenge confronted by dentists when making impressions. This article discusses the basic principles of nonpressure mucostatic and selective-pressure functional impression concepts and provides a theoretical and scientific basis for the design of a CD base.

Impact of implantoplasty on strength of the implant-abutment complex.

PURPOSE: Implantoplasty, a procedure that is done to smooth contaminated implant surfaces, has been used in the treatment of peri-implantitis. It reduces the implant diameter, which might compromise the implant's strength. This in vitro study was designed to evaluate the effect of implantoplasty on implant strength. MATERIALS AND METHODS: Thirty-two tapered implants were used; half were 3.75 mm in diameter (narrow) and the other half were 4.7 mm in diameter (wide). All implants were connected to 20-degree angled abutments. The apical half of each implant was embedded in acrylic resin. Eight 3.75-mm- and eight 4.7-mm-diameter implants were randomly assigned to receive implantoplasty. The remaining implants did not receive implantoplasty (control group). Implantoplasty was performed with a series of diamond and polishing burs. The specimens were then loaded 30 degrees off-axis in a universal testing machine until fracture failure occurred. Bending and fracture strength values were recorded and analyzed statistically (α = .05). The fractured surfaces were evaluated under a scanning electron microscope. RESULTS: All narrow implants failed by fracture at the implant platform. The mean bending strength of narrow implants was statistically significantly reduced by implantoplasty (511.4 ± 55.9 N versus 613.9 ± 42.8 N). Implantoplasty did not affect the strength of wide implants; fracture failures occurred at the abutment screw. The fracture mode was ductile and the crack growth was oblique in direction, indicating complex stress distribution and concentration under loading. CONCLUSION: Within the limits of this study, implantoplasty appeared to weaken the strength of narrower implants. Therefore, this procedure should be performed with caution on narrower, freestanding implants that are subject to greater occlusal force (eg, posterior regions). Validation of these results is needed for different implant systems.

Optimization of maxillary obturator thickness using a double-processing technique.

Preservation of remaining structures is a primary goal of prosthetic rehabilitation. Continuously applied stresses on the remaining tissues from a large, heavy obturator jeopardize the health of the tissues, compromise the function of the prosthesis, and affect patient comfort. Various techniques have been described for hollowing the bulb of an obturator after processing to reduce its weight; however, access to the inner aspects of the bulb is limited, preventing adequate control of thickness of the walls. This article describes a double-processing technique for an obturator to optimize the weight and thickness of the bulb.

Prosthodontic management of abnormal tooth development secondary to chemoradiotherapy: a clinical report.

Late effects of chemoradiotherapy for childhood cancer treatment include developmental disturbances of the maxillofacial and dentoalveolar structures. Prosthodontic rehabilitation of these patients presents a significant challenge in restoring function, esthetics, and comfort. This clinical report describes the prosthodontic management of a young patient who received chemoradiotherapy for neuroblastoma and subsequently developed tooth abnormalities. Osseointegrated implants and an implant-connecting bar along with an attachment system were used to provide retention, support, and stability of a removable mandibular overdenture opposing a conventional maxillary complete denture.

Effect of heat treatment on fracture toughness K(IC) and microstructure of a fluorcanasite-based glass-ceramic.

PURPOSE: The purpose of this study was to test the hypothesis that the increase in fracture toughness of a fluorcanasite-based glass-ceramic is a linear function of crystal volume fraction. MATERIALS AND METHODS: A total of 60 specimen bars (20 x 5 x 2 mm(3)) were cut from parent glass blocks, polished, annealed, randomly divided into six groups, nucleated at 680 degrees C/4 hr, and crystallized at the following temperatures and times: (1) 850 degrees C/0.5 hr, (2) 850 degrees C/1 hr, (3) 850 degrees C/3 hr, (4) 750 degrees C/6 hr, (5) 800 degrees C/6 hr, or (6) 850 degrees C/6 hr. Indentation flaws were produced by a microhardness indenter at the center of one surface, and the prepared specimens were subjected to three-point flexure loading with the severely flawed surface under tension at a crosshead speed of 0.5 mm/min. Flexural strength and fracture toughness (K(IC)) were calculated based on the indentation-strength technique. Crystal volume fraction (V(c)) was determined by quantitative stereology of scanning electron images of each group of ceramic specimens. Statistical analysis was performed using ANOVA and Duncan's multiple comparison test (alpha= 0.05). RESULTS: The mean K(IC) and V(c) values ranged from 2.7 to 3.9 MPa m(1/2) and 37% to 71% within the crystallization temperature range of 750 to 850 degrees C. Five statistical subsets of groups 1, 2/4, 3, 5, and 6 were determined as a function of crystallization temperature and holding time (Duncan's multiple comparison analysis; alpha= 0.05). The lowest and highest K(IC) and V(c) values were associated with Groups 1 (850 degrees C/0.5 hr) and 6 (850 degrees C/6 hr), respectively. Fracture toughness increased linearly as a function of crystal volume fraction (correlation coefficient R(2)= 0.67). The fracture toughness increased by 45% when the crystal volume fraction increased by 92%. CONCLUSIONS: Mean K(IC) values increased as a linear function of crystal volume fraction in a fluorcanasite-based glass-ceramic within the crystallization temperature range of 750 to 850 degrees C and at isothermal crystallization time range of 0.5 to 6 hours. The control of crystallization temperature and isothermal holding time should be optimized to generate tougher, more reliable ceramic prostheses in the shortest period of time.

Maxillofacial restoration after head and neck tumor therapy.

Oral and pharyngeal cancers are among the leading cancer sites. Surgery, radiation, chemotherapy, or combination therapies are common treatment modalities. Radiotherapy and chemotherapy cause significant morbidity and long-term irreversible sequelae in the oral cavity. Surgical resection can be mutilating, disfiguring, and deeply affect self-image. Orofacial defects have unique limitations and challenges for both the surgeon and the maxillofacial prosthodontist. Microvascular surgical techniques and the use of osseointegrated implants improve the rehabilitation potential of the various head and neck defects. This article reviews current treatment modalities of tumor therapy, their consequences, and the restoration of maxillofacial defects.

Dental implant-assisted prosthetic rehabilitation of a patient with a bilateral maxillectomy defect secondary to mucormycosis.

Prosthodontic rehabilitation of patients with bimaxillary resection involving the maxillae, hard and soft palates, and paranasal sinuses presents a significant challenge in restoring speech, deglutition, mastication, and respiration. This clinical report describes the prosthodontic management of a young girl treated for leukemia who required a bilateral maxillectomy secondary to mucormycosis. Distraction osteogenesis, bone grafts, osseointegrated implants, and magnet attachments were used to provide retention, support, and stability of a large definitive obturator.

Effect of post-silanization drying on the bond strength of composite to ceramic.

STATEMENT OF PROBLEM: The temperature reported for thermally treating silanated ceramics to improve composite-ceramic bonding is often too high for chairside applications. PURPOSE: This study investigated whether post-silanization drying with a stream of warm air could enhance the composite/ceramic tensile bond. MATERIAL AND METHODS: Thirty-two ceramic blocks (6 x 6 x 9 mm), 16 of each ceramic, were fabricated and divided into 8 subgroups using 4 roughening procedures and 2 silanization protocols per ceramic (Eris and IPS Empress). Roughening included polishing to 1200 grit as control (P), airborne-particle abrasion (A), hydrofluoric acid etching (E), or a combination of abrasion and etching (AE). Silanated surfaces were dried with room-temperature air (SR) or 45+/-5 degrees C warm air (SH). An adhesive (Heliobond) was applied and light-polymerized before adding composite (Tetric Ceram). Thirty-three specimens (0.9 x 0.9 x 18 mm) were cut from a pair of blocks and stored in 37 degrees C distilled-water for 3 weeks. Each specimen was loaded under tension until failure in a universal testing machine (n=33). Strength (MPa) was calculated by dividing the failure load by the cross-sectional area. Mode of failure was investigated with scanning electron microscopy (SEM). Statistical analyses were performed with ANOVA and the Tukey HSD test (alpha=.05). RESULTS: The mean tensile bond strength values (SD) in MPa for P, A, E, and AE procedures were, respectively, 11.4 (5.4), 11.9 (5.4), 9.9 (2.6), and 15.8 (4.3) for Eris/SR; 17.8 (6.2), 20.4 (7.1), 18.0 (6.7), and 18.8 (3.9) for Eris/SH; 9.3 (2.8), 14.0 (4.0) 17.1 (3.7), and 23.2 (6.8) for IPS-Empress/SR; and 14.8 (4.5) 22.6 (4.8), 22.7 (5.0), and 28.7 (4.4) for IPS Empress/SH. ANOVA indicated the influence of ceramic material, roughening, and postsilanization drying was significant (P<.0001). The Tukey HSD test showed mean strength values higher for IPS Empress than for Eris, SH greater than SR, and AE producing the highest mean strength values. SEM examination showed there were greater areas of cohesive failure with SH specimens. CONCLUSION: Silane drying by a stream of warm air was effective in enhancing tensile bond strength of composite to ceramic.

Effect of nucleation temperature on fracture toughness (KIC) of fluorcanasite-based glass-ceramic.

PURPOSE: The purpose of this study was to test the hypothesis that nucleation temperature significantly affects the fracture toughness of a fluorcanasite-based glass-ceramic. MATERIALS AND METHODS: Sixty specimens were cut from a glass bar, polished, and randomly divided into six groups for nucleation treatment at temperatures of (1) 520 degrees C, (2) 550 degrees C, (3) 580 degrees C, (4) 610 degrees C, (5) 640 degrees C, and (6) 670 degrees C for 4 hours and a crystallization temperature of 850 degrees C for 6 hours. A precrack was produced at the center of each bar, and the prepared specimens were subjected to three-point flexural loading with the cracked surface under tension using an Instron machine at a cross-head speed of 0.5 mm/min. Fracture toughness was calculated based on the indentation strength technique, and crystal volume fraction was determined by quantitative stereology of SEM images of each group of ceramic specimens. RESULTS: The mean fracture toughness and crystal volume fraction ranged from 2.6 to 3.5 MPa x m1/2 and from 65% to 81%, respectively, within the limits of the nucleation temperatures investigated. ANOVA showed statistically significant differences among the test groups. Based on Duncan's multiple comparison test, significant differences in mean fracture toughness and crystal volume fraction were found among the following statistical subsets: groups 1 to 4, group 5, and group 6. CONCLUSION: Fracture toughness and crystal volume fraction of a fluorcanasite-based glass-ceramic were strongly influenced by nucleation temperature; the crystals precipitated during thermal processing are thought to be an important factor in increasing fracture toughness.

Effect of surface topography on the bond strength of a composite to three different types of ceramic.

STATEMENT OF PROBLEM: Mechanical retention based on the surface topography is critical for the success of chairside repair of chipped or fractured ceramic prostheses with a composite. PURPOSE: The purpose of this study was to investigate whether the tensile bond strength of a composite to 3 dental ceramics was affected by surface roughening procedures on the ceramics. MATERIAL AND METHODS: Three ceramics, Eris (ERV), Empress 1 (E1C), and an experimental ceramic (EXC), were used to fabricate 12 rectangular blocks (5 x 5 x 10 mm). After polishing with a series of SiC papers (120 through 1200 grit size), 4 surfaces were created on each ceramic as follows: 1) as-polished (P); 2) airborne-particle abraded with 50 microm Al(2)O(3) (A); 3) etching with 5% hydrofluoric acid gel (E); and 4) a combination of airborne particle abrasion and etching (A/E). An adhesive (Heliobond) was applied on the roughened ceramic surface and a composite (Tetric Ceram) was built-up incrementally. Twelve groups of different ceramic/surface treatment combinations were prepared. Twenty ceramic/composite specimens per group (0.9 x 0.9 x 20 mm) were obtained from each block with a slow speed diamond saw. Each specimen was subjected to a tensile force at a crosshead speed of 0.5 mm/min using a universal testing machine until failure. The mode of failure was determined by scanning electron microscopy. ANOVA and Duncan's multiple range test (alpha=.05) were used to analyze the bond strength values. RESULTS: Specimens of all as-polished groups and EXC(A) group separated during sectioning. The mean bond strength values (SDs) in MPa for the remaining groups were as follows: ERV(A): 2.6 (0.8); E1C(A): 2.8 (1.1); ERV(E): 3.1 (1.3); ERV(A/E): 9.3 (1.3); E1C(E): 10.5 (1.5); E1C(A/E):13.5 (3.3); EXC(E): 19.2 (4.7); and EXC(A/E): 23.1 (5.4). ANOVA showed statistically significant differences in the bond strength for both ceramics (P<.0001) and surface treatments (P<.0001). Duncan's analysis yielded following statistical subsets of the bond strength values: EXC > E1C > ERV by ceramic; A/E > E > A by surface treatment. The mode of failure was a combination of adhesive and cohesive failures. CONCLUSION: The tensile bond strength of a composite to ceramic was significantly different depending on the surface topography of ceramic. Among the surfaces investigated, combined surface roughness was the most effective surface topography in terms of the bond strength increase.

Fracture toughness (K(IC) of a hot-pressed core ceramic based on fractographic analysis of fractured ceramic FPDs.

PURPOSE: The objective of this study was to test the hypothesis that there is no significant difference between the fracture toughness (K(IC)) of an experimental hot-pressed core ceramic measured by fractographic analysis of failed ceramic prostheses and the values determined by other standard methods. MATERIALS AND METHODS: Four groups were subjected to one of four test methods: group 1 = indentation strength technique (standard numerical calculation); group 2 = indentation strength technique (fractographic analysis); group 3 = flexure test of precracked specimens (fractographic analysis); and group 4 = fractographic analysis of failed three-unit fixed partial dentures (FPD). For groups 1 to 3, 20 ceramic bar specimens were subjected to three-point flexure at a cross-head speed of 0.5 mm/min until fracture occurred. For group 4, 10 failed FPDs were collected from a previous study. Stress values at failure were calculated from either a flexure stress equation (groups 1 to 3) or from finite element analyses (group 4). K(IC) values were calculated from an equation and fractographic measurement data. RESULTS: Mean fracture toughness ranged from 3.1 MPa x m1/2 (SD 0.2) (group 1) to 3.4 MPa x m1/2 (SD 0.2) (group 4). The mean K(IC) value for group 1 was significantly different from that of group 4; however, no significant differences were found between groups 1, 2, and 3, or between groups 2, 3, and 4. CONCLUSION: Fracture toughness for an experimental hot-pressed core ceramic measured by fractographic analysis in combination with finite element analysis was comparable with the values determined with other standard fractographic methods.

Wetting characteristic of ceramic to water and adhesive resin.

STATEMENT OF PROBLEM: Maximum wetting of ceramic by adhesive resin is required to achieve optimal adhesion of the resin to ceramic. It is unknown whether the adhesion of the resin to the ceramic is affected by the surface topography and wetting by water or the adhesive resin. PURPOSE: This study was designed to characterize the effect of surface topography on the wetting of ceramics by water and adhesive resin. MATERIALS AND METHODS: Three materials, a veneering ceramic, Eris (ERV), and 2 core ceramics, Empress 1 core ceramic (E1C) and an experimental core ceramic (EXC), were used. Four surface-roughening procedures were used. They included polishing through 1200-grit SiC paper (P), air abrasion with 50 microm Al(2)O(3) (A), etching with 5% hydrofluoric acid gel (E), and a combination of airborne particle abrasion and etching (A/E). Forty bar specimens (15 x 10 x 1.5 mm) were prepared from each material (N=120). Twelve groups of 10 specimens each were prepared for the 4 surface-roughening procedures. Advancing (theta(A)) and receding (theta(R)) contact angles were measured with a CAHN Dynamic Contact Analyzer, on the basis of the Wilhelmy plate technique, with water and adhesive resin. The work of adhesion (W(A)) by the probing media was calculated by use of advancing contact angle data. The data were analyzed by t testing, analysis of variance, and Duncan's tests (alpha=0.05) to determine the statistical significance of differences in the contact angles between ceramic and water or resin as a function of surface roughening. RESULTS: In general, the mean theta(A) values were higher than the mean theta(R) values except for groups of E or A/E specimens with water used as a probing medium. E and A/E treatments yielded the lowest contact angle values, followed by A and P treatments (P<.001). The E1C exhibited the highest mean contact angles, whereas EXC exhibited the lowest mean contact angle except for the theta(R) with resin. The corresponding values for ERV were between those of E1C and EXC except for theta(R) values with resin. The resin medium yielded higher mean contact angles than the water medium for the same surfaces. W(A) ranged from 62.9 to 145.2 mJ/m(2). CONCLUSIONS: Within the limitations of this study, etching or a combination of air abrasion and etching were comparably effective in increasing the surface area for bonding. The most wettable surface as measured by the resin medium was EXC, followed by ERV and E1C.

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.

Factors affecting enamel and ceramic wear: a literature review.

Enamel wear by ceramics may adversely affect maintenance of the vertical dimension of occlusion and can increase the potential for thermal sensitivity. In this article, factors related to the abrasion of enamel by dental ceramics are critically reviewed. Concepts of physical, microstructural, chemical, and surface characteristics of dental ceramics on wear are presented based on research published since 1950. A PubMed search for key words (wear of enamel and ceramic) was supplemented with a hand search to identify relevant peer-reviewed articles published in English. Based on the literature, it can be concluded that material factors, their proper handling, and control of the patient's intrinsic risk factors related to wear are critically important to the reduction of enamel wear by dental ceramics.