Clinical performance comparison between lithium disilicate and hybrid resin nano-ceramic CAD/CAM onlay restorations: a two-year randomized clinical split-mouth study.

A total of 20 lithium disilicate glass-ceramics (IPS e.max CAD, Ivoclar Vivadent) and 20 resin nano-ceramic (Voco Grandio Blocks) onlay restorations were performed in 20 patients using a split-mouth design to compare the two-year clinical performance of lithium disilicate and resin nano-ceramic onlay restorations. Both restorations were evaluated at baseline, one-year, and two-year clinical follow-ups based on the modified United States Public Health Service (USPHS) criteria. Chi-square and Fisher's exact tests showed no statistically significant difference between Voco Grandio and IPS e.max ceramic restorations for all evaluated parameters during the different follow-up periods (p > 0.05). Cochrane's and MC-Nemar's tests indicated statistically significant differences regarding color match within the Voco Grandio group. They also indicated statistically significant differences in marginal discoloration, marginal adaptation, surface texture, and postoperative hypersensitivity within both ceramic material groups (p < 0.05). Kaplan-Meier curve indicated that the survival rate of both ceramic materials was 90%. After two years of clinical service, IPS e.max CAD and Voco Grandio onlay restorations exhibited similar clinical performance.

Influence of retainer design and number of inlay boxes on the biomechanical behavior of zirconia cantilever resin bonded fixed dental prosthesis.

OBJECTIVES: The development of dental adhesives with enhanced bond strength has assisted minimally invasive dentistry. The aim of this study was to evaluate the fracture load and stress distribution pattern of two retainer designs for posterior cantilever resin bonded fixed dental protheses (RBFDPs). MATERIALS AND METHODS: Forty human mandibular molars were divided into two groups according to the retainer design; lingual coverage (LC) and occlusal coverage (OC) retainers. Each main group was then divided according to the number of inlay boxes (n = 10); one inlay and two inlay boxes. High translucency (3Y) zirconia was used to manufacture all restorations, and a dual-polymerizing adhesive resin cement was used for bonding. All specimens underwent 10,000 cycles of thermocycling (5-55°C), 240,000 cycles of dynamic loading (50 N, descending speed v = 30 mm/second, frequency = 1.6 Hz), and failure load test. Both one-way and two-way ANOVA tests were used to analyze the data. The four models included in the in-vitro study are part of the finite element analysis (FEA). When the restorations failed, maximal principal stress values on restorations, enamel, dentin, and luting resin were investigated. RESULTS: A statistically significant (p = 0.018) higher failure load was recorded for OC1 (627.00 ± 153.4 N) than the other groups; (548.0 ± 75.6 N, 521.20 ± 11.3 N, and 509.20 ± 14.9 N for LC1, LC2, and OC2, respectively). With regard to failure mode, one inlay box designs showed more favorable failure pattern than those of two inlay boxes. FEA showed higher stress magnitude transmitted to the tooth structure in models LC2 and OC2. CONCLUSIONS: Lingual coverage and occlusal coverage retainers are promising designs capable to withstand the normal occlusal force for cantilever RBFDP in premolar area. The use of two inlay boxes decreased the fracture load of the two retainer designs and increased the stress transmitted to the tooth and resulted in high incidence of catastrophic failure. CLINICAL SIGNIFICANCE: Monolithic high translucent zirconia RBFDP could be considered as a viable treatment option to substitute missing posterior tooth, with improved esthetics and biocompatibility.

Effect of simulated intraoral adjustment on the color and translucency of gradient multilayered monolithic zirconia.

STATEMENT OF PROBLEM: The use of multilayered monolithic zirconia ceramics is becoming popular because it simplifies the production of esthetic restorations. The effect of clinical adjustment on the optical properties of these ceramics, especially strength-gradient zirconia, remains unclear. PURPOSE: The purpose of this in vitro study was to evaluate the color and translucency of gradient multilayered zirconia brands after grinding and polishing. MATERIAL AND METHODS: Sixty 10×10×1-mm monolithic zirconia specimens were milled from 6 zirconia brands (Ceramill Zolid HT White, Ceramill Zolid HT Preshade, Ceramill Zolid FX Multicolor, VITA YZ XT Multicolor, IPS e.max ZirCAD Prime, and KATANA YML). The zirconia specimens were milled to include all layers of A2 preshaded multilayered zirconia blanks (A2 shade) except Ceramill Zolid HT White and Ceramill Zolid HT Preshade. Ceramill Zolid HT White specimens were milled from a white zirconia blank with subsequent shading. The color coordinates and the relative translucency parameter after glazing and after grinding and polishing were determined with a reflectance spectrophotometer, and the relative translucency parameter and contrast ratio were measured. The differences in color and translucency were calculated. The data were analyzed using 2-way ANOVA and 1-way ANOVA tests followed by the post hoc Tukey test (α=.05). RESULTS: Statistically significant changes (P<.001) in the color coordinates measured before and after grinding and polishing were detected for each zirconia brand except for the KATANA YML that showed no significant difference (P=.686) in lightness. The highest color difference after grinding and polishing was detected in group KATANA YML. The 2-way ANOVA test showed a statistically significant interaction (P<.001) between the zirconia brand and the grinding and polishing regarding the relative translucency parameter. The zirconia brand had a significant impact on the relative translucency parameter before and after grinding and polishing (both P<.001). CONCLUSIONS: Except for KATANA YML, the color change in multilayered zirconia after clinical adjustment with polishing was not beyond the clinically acceptable limit of the color difference. Although clinical adjustment with polishing reduced the translucency of gradient zirconia, the change in translucency was below the clinically detectable threshold value of the translucency difference.

A microcomputed tomography analysis of adaptation in premolars with flared root canals restored with different digitally custom fabricated post materials.

STATEMENT OF PROBLEM: Preserving and strengthening the remaining tooth structure of compromised flared root canals after endodontic treatment is challenging. PURPOSE: The purpose of this in vitro study was to compare the adaptation of milled polymer- infiltrated ceramic, fiber-reinforced composite resin, and high-performance semicrystalline thermoplastic resin posts as used to restore mandibular premolars with flared root canals. MATERIAL AND METHODS: Forty sound mandibular premolars were randomly divided into 4 groups: custom Vita Enamic (CV), custom fiber-reinforced composite resin (CF), custom polyetherketoneketone (CP), and prefabricated fiber (RF) posts. After endodontic treatment, each tooth was sectioned 1.5 mm occlusal to the cementoenamel junction. Then, the post space was prepared and flared, except the RF group, to a depth of 9 mm. The post space in RF group was prepared with a post drill. For the CV, CF, and CP groups, the posts were milled, finished, and cemented to their corresponding teeth. Each tooth was scanned using a microcomputed tomography device, and the reconstructed images were analyzed in mesiodistal, buccolingual, and horizontal planes. The cement thickness, cement volume, and volume of voids were measured. The data were analyzed using 3-way ANOVA (cement thickness) and 2-way ANOVA (cement volume and voids volume) tests followed by the post hoc Tukey test (α=.05). RESULTS: The 3-way ANOVA test revealed a significant interaction (P<.001) between material type, section, and surface on the cement thickness. The mean cement thickness in the RF group was significantly higher than in the CV group (P=.001) and CF group (P=.005). The least mean cement thickness was at the apical section followed by the cervical and middle sections. Regarding cement volume, the 2-way ANOVA test showed statistically significant interaction between material type and section. The mean cement volume in the RF group was significantly lower than in the CV group (P=.001), CF group (P=.001), and CP group (P=.001). The highest mean cement volume was in the cervical section followed by the middle and apical sections. The 2-way ANOVA test showed statistically significant interaction (P<.001) between material type and section on the volume of voids. Significant differences were found between the mean volume of voids at the cervical and middle sections (P=.001) and the cervical and apical sections (P=.002). CONCLUSIONS: Compared with prefabricated fiber posts, digitally fabricated polymer-infiltrated ceramic and fiber-reinforced composite resin posts had a thinner cement layer with minimal thickness at the apical section. The digitally fabricated posts had higher cement volume, especially at the cervical section, than prefabricated fiber posts. High volumes of voids were related to the cervical section of all tested posts.

Effect of different preparation designs and material types on fracture resistance of minimally invasive posterior indirect adhesive restorations.

PURPOSE: To evaluate the impact of various preparation designs and the material type on fracture resistance of minimally invasive posterior indirect adhesive restorations after aging using a digital standardization method. MATERIALS AND METHODS: One-hundred sixty human maxillary premolars free from caries were assigned into 16 groups (n = 10): bevel design on enamel substrate with mesial box only (VEM), butt joint design on enamel substrate with mesial box only (BEM), bevel design on enamel substrate with mesial and distal box (VED), butt joint design on enamel substrate with mesial and distal box (BED), bevel design on dentin substrate with mesial box only (VDM), butt joint design on dentin substrate with mesial box only (BDM), bevel design on dentin substrate with mesial and distal box (VDD), and butt joint design on dentin substrate with mesial and distal box (BDD). Each group was restored with pressable lithium disilicate (LS2) or disperse-filled polymer composite (DPC) materials. Adhesive resin cement was used to bond the restorations. The specimens were aged for 10,000 thermal cycles (5°C and 55°C), then 240,000 chewing cycles. Each specimen was subjected to compressive axial load until failure. A two-way analysis of variance (ANOVA) test followed by a post hoc Tukey test was used to analyze the data (α = 0.05). RESULTS: The two-way ANOVA test revealed a significant difference among designs (p < 0.001) and materials (p < 0.001) with no interaction effect (p = 0.07) between the variables. The Post hoc Tukey test revealed that the VEM group exhibited the highest mean fracture resistance value, while the BDM group had the lowest. The LS2 groups showed the highest mean fracture resistance values. The DPC groups showed a restorable fracture pattern compared to the LS2 groups. CONCLUSIONS: Bevel and butt joint designs with mesial or distal boxes are recommended for conservative posterior indirect adhesive restorations in premolar areas. Enamel substrate improved load distribution and fracture resistance. DPCs have restorable failure patterns, while pressed LS2 may harm underlying structures.

Biomechanical behavior of posterior metal-free cantilever fixed dental prostheses: effect of material and retainer design.

OBJECTIVE: To study the fracture resistance and stress distribution pattern of translucent zirconia and fiber-reinforced composite cantilever resin-bonded fixed dental prostheses (RPFDPs) with two retainer designs. MATERIALS AND METHODS: Forty human mandibular molars were divided into two groups according to the retainer design. The restorations included a premolar pontic and 2 retainer designs: (D1) inlay ring retainer and (D2) lingual coverage retainer. Each main group was then divided according to the material used (n = 10): zirconia (Z) or fiber-reinforced composite (FRC) (F). Restorations were cemented using dual polymerizing adhesive luting resin. All specimens were thermo-cycled (5-55 °C for 10,000 cycles), then subjected to dynamic loading (50 N, 240,000, and 1.6 Hz) and fracture resistance test. The finite element analysis includes the two models of retainer designs used in the in vitro test. Modified von Mises stress values on enamel, dentin, luting resin, and restorations were examined when the restorations failed. RESULTS: A significantly higher failure load was recorded for zirconia groups (505.00 ± 61.50 and 548.00 ± 75.63 N for D1Z and D2Z, respectively) than for FRC groups (345.00 ± 42.33 and 375.10 ± 53.62 N for D1F and D2F, respectively) (P = 0.001). With regard to failure mode, D2 showed a more favorable failure pattern than D1. Model D2 resulted in lower stresses in tooth structure than model D1, and zirconia transmitted more stresses to the tooth structure than FRC. CONCLUSIONS: The lingual coverage retainer (D2) enhanced the biomechanical performance of the restoration/tooth complex. Considering the failure mode and tooth stress, FRC is a promising treatment option when constructing a cantilever RPFDP. CLINICAL RELEVANCE: Dentists should be aware of the biomechanical behavior during the selection of the material and for the replacement of a single missing mandibular premolar tooth with minimally invasive RBFDP.

Fracture resistance of monolithic translucent zirconia crown bonded with different self-adhesive resin cement: influence of MDP-containing zirconia primer after aging.

OBJECTIVES: Successful ceramic restorations depend on the strong bonding with resin cement and even stress distribution. The aim of this study was to evaluate the impact of adding MDP-containing zirconia primer before self-adhesive resin cements with different functional acidic monomers on fracture resistance of monolithic zirconia crown. MATERIALS AND METHODS: Eighty defect-free human maxillary premolars were divided according to the cement type and application of MDP-containing zirconia primer into eight groups (n = 10): Calibra Universal (C), Calibra Universal combined with zirconia primer (CZ), RelyX U200 (R), RelyXU200 combined with zirconia primer (RZ), Panavia SA Cement Plus (P), Panavia SA Cement Plus combined with zirconia primer (PZ), Multilink Speed (M), and Multilink Speed combined with zirconia primer (MZ). After teeth preparation and fabrication of zirconia crowns, each crown was bonded to its corresponding tooth. All specimens were subjected to 10,000 thermocycles between 5 and 55°C, followed by cyclic load (50 N) for 240,000 cycles. Each specimen was subjected to a static axial load until fracture using universal testing machine and the fracture load was recorded. The fracture mode studied and recorded. The fracture load results were analyzed using two-way ANOVA test (α = 0.05). RESULTS: A significant interaction (P = 0.038) of combining MDP-containing zirconia primer and cement type on fracture resistance of monolithic zirconia crown was detected. The mean fracture load values of zirconia crown were significantly influenced by the combined application of the MDP-containing zirconia primer with Calibra Universal (P = 0.01), RelyX U200 (P < 0.001), and Multilink Speed (P = 0.038), while there was no significant difference with Panavia SA Cement Plus (P = 0.660). There was significant difference (F = 20.69, P < 0.001) between the mean fracture loads of groups with self-adhesive cements (C, R, P, and M groups). The highest fracture load was recorded with RZ group (2446.90 ± 126.72 N) while the lowest fracture load was recorded with C group (1623.18 ± 149.86 N). CONCLUSIONS: The self-adhesive resin cement with different acidic functional monomer affects the fracture resistance of monolithic zirconia crown. Application of MDP-containing primer could improve the fracture resistance of monolithic zirconia crown with most self-adhesive cements. The application of an MDP-containing primer had no impact on the fracture resistance of monolithic translucent zirconia crown bonded by MDP-containing self-adhesive resin cement.

Retention of hybrid-abutment-crowns with offset implant placement: influence of Crown materials and Ti-base height.

BACKGROUND: The purpose of the current study was to assess the impact of three esthetic CAD/CAM material, titanium base height and their interaction on the retention strength of a hybrid-abutment-crown. METHODS: A total of 42 hybrid-abutment crowns with identical external geometries were designed in CAD software to fit two different Ti-Base abutment heights (n = 42/abutment height): either short (S) with 4 mm (n = 21) or long (L) 7 mm (n = 21) height. Each main group was divided into 3 subgroups (n = 7), according to esthetic crown material, Zirconia (Z), Lithium disilicate (L) and Hybrid ceramic (V). A universal primer and an adhesive resin cement were used for bonding according to the manufacturer instructions. Artificial aging in form of water storage (30 days), chewing simulation (50,000-cycles, 49 N, 1.67 Hz) and thermal cyclic (5000 cycles at 5-55 °C) were applied, specimens were pulled-out under tension load in (N) using a universal testing machine. Two and one-way ANOVA and Post Hoc Tukey test were used for statistical analysis. RESULTS: Long lithium disilicate (LL) group showed the highest retention (738.7 ± 178.5) followed by short lithium disilicate (LS) group (688.6 ± 169.9). Meanwhile, short zirconia (ZS) showed the lowest retention strength (231.1 ± 86.9). CONCLUSION: CAD/CAM fabricated lithium disilicate hybrid-abutment-crown can be used instead of conventional crowns over implant abutment. Etchable ceramics are recommended as a material of choice for CAD/CAM fabricated hybrid-abutment-crowns instead of zirconia in terms of retention durability.

A micro-computed tomography analysis of internal and marginal fits of fixed partial dentures: Effect of preparation finish line designs on monolithic zirconia and heat-pressed zirconia-reinforced lithium disilicate.

PURPOSE: To evaluate the effect of finish line design (chamfer and feather-edge) and ceramic type on the internal and marginal fits of fixed partial dentures on abutment teeth. MATERIALS AND METHODS: Two typodont mandibular casts, missing right first premolar tooth, received tooth preparation on canine and second premolar abutments (one cast with chamfer finish line and the other cast with feather-edge finish line). The preparation segment of each typodont model was scanned, 3D printed in resin, and then invested and casted in metal to obtain two metal models. Polyvinyl siloxane impressions were made for the metal models and poured in type IV stone. The stone models (n = 40) were randomly assigned into four groups (n = 10): chamfer finish line with heat-pressed zirconia reinforced lithium disilicate fixed partial denture (CL), chamfer finish line with monolithic zirconia fixed partial denture (CZ), feather-edge finish line with heat-pressed zirconia-reinforced lithium disilicate fixed partial denture (FL), and feather-edge finish line with monolithic zirconia fixed partial denture (FZ). After the fabrication of ceramic restoration, micro-computed tomography was used to evaluate the internal and marginal fits of each fixed partial denture. Data were statistically analyzed with three-way ANOVA (α = 0.05). RESULTS: There were no significant interactions between preparation type, material type, and tooth type at any of the areas assessed. There was significant difference (p = 0.01) between CZ (59.15 ± 4.6 µm) and FZ (73.6 ± 17.1 µm) groups at the finish line area. Regarding the horizontal marginal discrepancy area, there were significant differences between CZ (62.65 ± 10.5 µm) and FZ (90.05 ± 5.6 µm) groups (p < 0.001), CL (77.45 ± 8.1 µm) and CZ (62.65 ± 10.5 µm) groups (p < 0.001), and FZ (90.05 ± 5.6 µm) and CL (77.45 ± 8.1 µm) groups (p < 0.001). At finish line area, there was a significant difference (p = 0.018) between feather-edge with canine (72.75 ± 13.3 µm) and chamfer with canine (59.05 ± 5.8 µm); however, there was no significant difference (p = 0.774) between feather-edge with premolar (69.45 ± 12 µm) and chamfer with premolar (65.1 ± 7.4 µm). Moreover, there was no significant difference (p = 0.886) between feather-edge with canine and feather-edge with premolar. CONCLUSIONS: The internal and marginal fits of the ceramic fixed partial dentures can be affected by the finish line design and ceramic type. The feather-edge finish line had a negative impact on the marginal and internal fits of ceramic fixed partial dentures at certain measurement points. Regarding the effect of finish line design on abutment teeth, the difference in fit was only detected at the finish line area of the anterior abutment (canine) with the feather-edge finish line.

Effect of different designs of minimally invasive cantilever resin-bonded fixed dental prostheses replacing mandibular premolar: Long-term fracture load and 3D finite element analysis.

PURPOSE: To evaluate the fracture load and stress magnitude of different retainer designs of minimally invasive cantilever resin-bonded fixed dental prostheses (RBFDPs) after artificial aging. MATERIALS AND METHODS: Fifty caries-free human mandibular molars were prepared as abutments for cantilever fixed dental prostheses using different retainer designs: one wing (OW), two wings (TW), inlay ring (IR), lingual coverage (LC), and occlusal coverage (OC). Computer-aided design and computer-aided manufacturing were used for milling the RBFDPs using fiber-reinforced composite (FRC), and the restorations were adhesively bonded. The specimens were then subjected to thermomechanical aging and loaded until failure. The 3D finite element analysis (FEA) was performed with five models of retainer designs similar to the in vitro test. Modified von Mises stress values on enamel, dentine, luting resin, and restorations were examined. Data were analyzed with Kruskal-Wallis and Mann-Whitney U tests (p < 0.001). RESULTS: A statistically significant difference (p < 0.001) was found between all groups except between IR and LC and between OW and TW designs, with the highest mean failure load detected for OC (534.70 N) and the lowest detected for OW (129.80 N). With regard to failure mode, OW, TW, and LC showed more incidences of favorable failure patterns than IR and OC designs. FEA showed that FRC transmitted low stresses in tooth structure and high stresses to the luting resin. CONCLUSIONS: LC and OC designs can be used to design cantilever RBFDPs in premolar area. IR design transmitted more stresses to the tooth structure and resulted in 30% catastrophic failure. OW and TW were below the normal occlusal force and should be carefully used.