In vitro fatigue and fracture testing of temporary materials from different manufacturing processes in implant-supported anterior crowns.

OBJECTIVES: The aim of this study was to investigate the in vitro fatigue and fracture force of temporary implant-supported anterior crowns made of different materials with different abutment total occlusal convergence (TOC), with/without a screw channel, and with different types of fabrication. MATERIALS AND METHODS: One hundred ninety-two implant-supported crowns were manufactured (4° or 8° TOC; with/without screw channel) form 6 materials (n = 8; 2 × additive, 3 × subtractive, 1 × automix; reference). Crowns were temporarily cemented, screw channels were closed (polytetrafluoroethylene, resin composite), and crowns were stored in water (37 °C; 10 days) before thermal cycling and mechanical loading (TCML). Fracture force was determined. STATISTICS: Kolmogorov-Smirnov, ANOVA; Bonferroni; Kaplan-Meier; log-rank; α = 0.05. RESULTS: Failure during TCML varied between 0 failures and total failure. Mean survival was between 1.8 × 105 and 4.8 × 105 cycles. The highest impact on survival presented the material (η2 = 0.072, p < .001). Fracture forces varied between 265.7 and 628.6 N. The highest impact on force was found for the material (η2 = 0.084, p < .001). CONCLUSION: Additively and subtractively manufactured crowns provided similar or higher survival rates and fracture forces compared to automix crowns. The choice of material is decisive for the survival and fracture force. The fabrication is not crucial. A smaller TOC led to higher fracture force. Manually inserted screw channels had negative effects on fatigue testing. CLINICAL RELEVANCE: The highest stability has been shown for crowns with a low TOC, which are manufactured additively and subtractively. In automix-fabricated crowns, manually inserted screw channels have negative effects.

Effects of storage and toothbrush simulation on Martens hardness of CAD/CAM, hand-cast, thermoforming, and 3D-printed splint materials.

OBJECTIVES: To investigate Martens hardness parameters of splint materials after storage in liquids and toothbrush simulation. MATERIALS AND METHODS: Ten specimens per material and group were fabricated (hand-cast CAST, thermoformed TF, CAD/CAM-milled CAM, 3D-printed PS, PL, PK, PV), stored in air, water, coffee, red wine, and cleaning tablets and investigated after fabrication, 24 h, 2- and 4-week storage or toothbrushing. Martens hardness (HM), indentation hardness (HIT), indentation modulus (EIT), the elastic part of indentation work (ηIT), and indentation creep (CIT) were calculated (ISO 14577-1). STATISTICS: ANOVA, Bonferroni post hoc test, between-subjects effects, Pearson correlation (α = 0.05). RESULTS: HM varied between 30.8 N/mm2 for PS (water 4 weeks) and 164.0 N/mm2 for CAM (toothbrush). HIT values between 34.9 N/mm2 for PS (water 4 weeks) and 238.9 N/mm2 for CAM (toothbrush) were found. EIT varied between 4.3 kN/mm2 for CAM (toothbrush) and 1.8 kN/mm2 for PK (water 2 weeks). ηIT was found to vary between 16.9% for PS (water 4 weeks) and 42.8% for PL (toothbrush). CIT varied between 2.5% for PL (toothbrush) and 11.4% for PS (water 4 weeks). The highest impact was identified for the material (p ≤ 0.001). CONCLUSIONS: Storage and toothbrushing influenced Martens parameters. The properties of splints can be influenced by the choice of materials, based on different elastic and viscoelastic parameters. High HM and EIT and low CIT might be beneficial for splint applications. CLINICAL RELEVANCE: Martens parameters HM, EIT, and CIT might help to evaluate clinically relevant splint properties such as hardness, elasticity, and creep.

Survival dependence of 3D-printed temporary materials on the filler content.

AIM: The aim of the present study was the evaluation of the in vitro performance and fracture force of 3D-printed anterior implant-supported temporary partial dentures (TPDs) with different filler content. MATERIALS AND METHODS: Identical anterior resin-based TPDs (tooth sites 11 to 13; n = eight per material) were 3D printed from methacrylate resins with different filler content. A cartridge polymethyl methacrylate (PMMA) material was used as a reference. After temporary cementation, combined thermal cycling and mechanical loading (TCML) was performed on all the restorations to mimic clinical application. Behavior during TCML and fracture force was determined, and failures were analyzed. Data were statistically investigated (Kolmogorov-Smirnov test, one-way ANOVA; post hoc Bonferroni, Kaplan-Meier survival; α = 0.05). RESULTS: Failure during TCML varied between three failures and total failure during loading time. Mean survival time varied between 93 ± 206 x 103 cycles and 329 ± 84 x 103 cycles. Significantly different survival cycles between the individual materials could be determined (Mantel Cox log-rank test: chi-square: 21,861; degrees of freedom (df) = 4, P < 0.001). A correlation between filler level and survival cycles could be found (Pearson: 0.186, P = 0.065). Fracture values of the surviving TPDs varied between 499 and 835 N. Failures were characterized by fracture of the connector (n = 24) followed by fractures at the abutment (n = 10). CONCLUSIONS: TDPs showed different filler-dependent survival. Individual 3D-printed materials provided comparable or even better performance than a standard cartridge system and might be sufficient for temporary application of at least half a year.

Effects of storage and toothbrush simulation on color, gloss, and roughness of CAD/CAM, hand-cast, thermoforming, and 3D-printed splint materials.

OBJECTIVES: The aim was to investigate color, gloss, or roughness of splint materials after storage in liquids and toothbrush simulation. MATERIALS AND METHODS: A total of 58 × 8 (n = 10 per material and group) specimens were fabricated (hand-cast, thermoforming, CAD/CAM-milled, 3D-printed materials); stored in air, water, coffee, red wine, and cleaning tablets; and investigated after fabrication, 24 h, two-, and four-week storage or toothbrushing. Color values (L*, a*, b*; ISO 11664-4:2008; CM-3500d, Konica-Minolta), gloss (ISO 2813:2014), and roughness values were determined (3D laser-scanning-microscope, KJ 3D, Keyence) before and after simulation or storage. STATISTICS: Levene-test, one-way ANOVA, Bonferroni post hoc test, between-subjects effects, Pearson correlation (α = 0.05). RESULTS: Color, gloss, and roughness altered due to contact with staining solutions/toothbrush simulation. Highest impact on color, gloss, and roughness presented the material followed by storage time (ΔE material (η2 = 0.239/p < 0.001), storage time (η2 = 0.179/p < 0.001); gloss (η2 = 0.751/p < 0.001) (η2 = 0.401/p < 0.001); Ra/Rz (η2 ≥ 0.801/p < 0.001) (η2 ≥ 0.416/p < 0.001)). Correlations were found between Rz and Ra (Pearson 0.887/p ≤ 0.001) or Rz and ΔE (0.517/p ≤ 0.001) or Ra and ΔE (0.460/p ≤ 0.001). CONCLUSIONS: Storage and toothbrushing were accompanied by a change in color, gloss, and roughness. Almost all materials showed visible discoloration after 4 weeks of storage. Gloss values decreased as storage time increased. The initial roughness and polishability were better with harder materials. CLINICAL RELEVANCE: Milled and 3D printed splints show good color, gloss, and roughness resistance after 4-week storage or toothbrush application.

Multilayer zirconia: Influence of positioning within blank and sintering conditions on the in vitro performance of 3-unit fixed partial dentures.

STATEMENT OF PROBLEM: Multilayer zirconia blanks comprise material layers with different optical and mechanical properties. Whether positioning within the blank, as well as variation in the sintering procedure, will lead to restorations with different properties is unclear. PURPOSE: The purpose of this in vitro study was to test the influence of sintering procedures and positioning in a multilayer blank on the in vitro performance of 3-unit zirconia fixed partial dentures. MATERIAL AND METHODS: Human molars were embedded in acrylic resin and prepared for 3-unit fixed partial dentures. Anatomic contour prostheses were milled from zirconia blanks (ZirCAD Prime 16 mm) in 3 different positions: above (cusp-top at the top of the blank), central (center of the prosthesis in the center of the blank), and bottom (margins at the lower edge of the blank). Sintering time (2:26, 4:25, 9:50 hours:minutes) was varied for the central and bottom prostheses. All prostheses were glazed and adhesively bonded. Thermocycling and mechanical loading was performed at 2×3000×5 °C/55 °C in distilled water for 1.2×106 cycles at a 50-N load. Then, fracture force was determined with a universal testing device by using central loading, a Ø12-mm steel ball, a 1-mm tin foil, and a rate of 1 mm/min. Failure was defined as 10% force drop or acoustic signal (crack). Statistical analysis was performed with 1-way ANOVA and Bonferroni correction (α=.05). RESULTS: All fixed partial dentures survived thermocycling and mechanical loading. Fracture forces varied between 1002 ±446 N (above; 9:50 hours) and 1760 ±607 N (central; 9:50 hours). The 1-way ANOVA revealed no statistically significant differences (P=.059) among the groups. Individual significant differences (P=.048) were found between prostheses from positions above, 9:50 hours, and central, 9:50 hours. For normal and long sintering times, fracture forces were highest in the central position. CONCLUSIONS: The sintering process and positioning of restorations within a multilayer zirconia blank have little effect on the mechanical properties of the prostheses.

Correction to: Temporary materials: comparison of in vivo and in vitro performance.

A Correction to this paper has been published: https://doi.org/10.1007/s00784-021-04067-4.

In vitro performance and fracture resistance of interim conventional or CAD-CAM implant-supported screw- or cement-retained anterior fixed partial dentures.

STATEMENT OF PROBLEM: Interim restorations represent an essential clinical treatment step; however, limited information is available concerning the performance of computer-aided design and computer-aided manufacturing (CAD-CAM) interim materials. PURPOSE: The purpose of this in vitro study was to evaluate the performance and fracture load of resin anterior implant-supported interim fixed partial dentures (IFPDs). MATERIAL AND METHODS: Identical anterior resin IFPDs (maxillary central incisor to canine; n=16 per material) were milled from polymethylmethacrylate (PMMA) or di-methacrylate (DMA) systems with different filler content. The IFPD groups were split to simulate a chairside (cemented implant-supported prosthesis) or laboratory procedure (screw-retained implant-supported prosthesis). A cartridge DMA material served as a control. After interim cementation, combined thermocycling and mechanical loading (TCML) was performed on all restorations to approximate a maximum of 2.5 years of clinical function. Behavior during TCML and fracture force was determined, and failures were analyzed. The data were statistically investigated (Kolmogorov-Smirnov test, 1-way-ANOVA; post hoc Bonferroni, Kaplan-Meier survival, α=.05). RESULTS: Drop out during TCML varied between no failures and complete failure during loading. For most systems, failure occurred between 120 000 and 600 000 mechanical loading cycles. For IFPDs without a screw channel fracture, values varied between 644 ±263 N and 987 ±101 N. Those with a screw channel fracture failed between 493 ±89 N and 951 ±248 N. Individual IFPDs had significantly higher mean fracture loads (P<.002), but the mean fracture values between IFPDs with and without a screw channel were not significantly different (P>.137). Failures were characterized by fracture of the connector (n=53) followed by mixed failures (n=22) or fractures at the abutment (n=21). CONCLUSIONS: These interim materials are sufficiently fracture resistant for the fabrication of implant-supported anterior IFPDs and are expected to survive between 6 months and 2 years before failure. The stability of IFPDs depended on the type of material but not on the restoration design (with or without a screw channel).

In vitro performance of CAD/CAM and conventional removable dentures.

AIM: Innovations in CAD/CAM technology and materials science offer new methodologies for removable prosthodontics. As clinical data are still rare, in vitro performance of both CAD/CAM and comparable conventional materials may help to estimate the clinical outcome. MATERIALS AND METHODS: Specimens (n = 8 per group) from teeth (CediTEC, SR VivodentCAD, Vitapan), base materials (V-Print dentbase, IvoBase CAD, Paladur), adhesives (CediTEC Primer/Adhesive, IvoBase CAD Bond), and a fully printed specimen (Try-In) were created. All specimens underwent thermal cycling and mechanical loading (TCML): 1,200,000 × 50 N; 2x3000 x 5°C/55°C; H2O. Surviving specimens were loaded to fracture. Statistical tests used were the Shapiro-Wilk test and the Kaplan-Meier survival, with the level of significance set to α = 0.05. RESULTS: Mean loading cycles until failure varied between 100 and 621,667 cycles. Up to five specimens per group failed during TCML. With one exception, all specimens of the entirely CAD/CAM-fabricated group survived TCML. The log-rank (Mantel-Cox) test showed significantly different (P = 0.000) loading cycles between the systems (chi-square test: 28,247; degree of freedom: 8). Failure of the dentures during TCML was characterized by failure of the denture base (2x), denture tooth (13x), mixed base/tooth (3x) or adhesive between base and tooth (1x). CONCLUSION: TCML and fracture testing showed different aspects of denture tooth restoration. The results indicated no correlation between fracture force, fracture pattern, and survival cycles. Denture teeth (milled, heat-pressed), bases (milled, printed, pressed), and primer should be matched up to optimize the performance of dentures.

Stability of screw-retention in two-piece zirconia implants: An in vitro study.

OBJECTIVES: To compare the stability of a screw-retained connection in a novel two-piece zirconia implant to a conventional titanium-based connection in an in vitro chewing simulation including artificial ageing. MATERIAL AND METHODS: Incisor (I) and molar (M) shaped monolithic zirconia crowns were screw-retained on either two-piece zirconia (test) or two-piece titanium (control) implants resulting in 4 groups of 8 samples (titanium implants with incisor-shaped crowns (T-I), titanium implants with molar-shaped crowns (T-M), zirconia implants with incisor-shaped crowns (Z-I) and zirconia implants with molar-shaped crowns (Z-M). These were subjected to artificial ageing by thermal cycling (TC: 2 × 3000 × 5°C/55°C cycles of 2 min) and mechanical loading (ML: 1.2 × 106 cycles of 50 N, f = 1 Hz). Surviving samples additionally underwent a fracture force test. Kaplan-Meier plots were drawn, and two-way ANOVA was calculated taking anatomical localisation and material variables as factors. RESULTS: The mean corresponding survival times were lower for T-M (0.86 × 106  ± 0.31 × 106 cycles) and Z-I (0.84 × 106  ± 0.21 × 106 cycles) compared to T-I (1.14 × 106  ± 0.10 × 106 cycles) and Z-M (1.20 × 106  ± 0.10 × 106 cycles). In one-way ANOVAs for survival time dependent on either location or material, no statistically significant differences could be found (location: p = .31; material: p = .62) in one-way ANOVAs. The interaction of location and material showed significant differences (F = 21.3, p < .001). CONCLUSION: The connection of the tested screw-retained zirconia crowns in two-piece zirconia implants is comparable to standard titanium implants in the specific in vitro testing.

Temporary materials: comparison of in vivo and in vitro performance.

OBJECTIVE: The aim of this investigation was to compare clinical performance and in vitro wear of temporary CAD/CAM and cartridge crowns. This study is an approach to estimate the influence of in vivo use and laboratory simulation on temporary crowns. MATERIALS AND METHODS: A total of 90 crowns were fabricated from each temporary CAD/CAM or cartridge material. Also, 10 crowns of each material were clinically applied for 14 days, and 80 identical duplicate restorations were investigated in the laboratory after storage in water (14 days; 37 °C) and subsequent thermal cycling and mechanical loading (TCML, 240.000 × 50N ML, 600 × 5°C/55 °C). After in vivo application or in vitro aging, facture force, superficial wear (mean and maximum), surface roughness (Ra, Rz), thermal weight loss (TGA), and heat of reaction (DSC) were determined for all crowns. STATISTICS: Bonferroni post hoc test; one-way analysis of variance (ANOVA); α = 0.05). RESULTS: The fracture resistance of the temporary materials varied between 1196.4 (CAD in vivo) and 1598.3 N (cartridge crown in vitro). Mean (maximum) wear data between 204.7 (386.7 µm; cartridge in vitro) and 353.0 µm (621.8 µm; CAD in vitro) were found. Ra values ranged between 4.4 and 4.9 µm and Rz values between 36.0 and 40.8 µm. DSC and TG analysis revealed small differences between the materials but a strong influence of the aging process. CONCLUSIONS: Comparison of in vivo and in vitro aging led to no significant differences in fracture force and wear but differences in roughness, DSC, and TGA. SEM evaluation confirmed comparability. Comparison of CAD/CAM and cartridge temporary materials partially showed significant differences. CLINICAL RELEVANCE: In vitro aging methods might be helpful to estimate materials' properties before principal clinical application. CAD/CAM and cartridge temporary materials provided comparable good clinical performance.

Fracture force of CAD/CAM resin composite crowns after in vitro aging.

OBJECTIVES: The aim of this in vitro study was to investigate the influence of material, preparation, and pre-treatment on the aging and fracture force of CAD/CAM resin composite molar crowns. MATERIALS AND METHODS: CAD/CAM molar crowns (n = 80) were milled from four resin composites (Block HC, Shofu; Lava Ultimate, 3 M; Grandio Blocs, Voco; and Tetric CAD, Ivoclar Vivadent, with/without sandblasting). Extracted human teeth were prepared with optimal preparation (height 6-8 mm, angle 6-8°) or worst-case preparation (height 3.5-4 mm, angle 10-15°). Both groups were prepared with a 1-mm deep cervical circular shoulder. Crowns were adhesively bonded after corresponding tooth treatment required for the individual adhesive systems (Table 1). Specimens were aged for 90 days in water storage (37 °C) and subsequently subjected to thermal cycling and mechanical loading (TCML 3000 × 5 °C/3000 × 55 °C, 2 min each cycle, H20 distilled; 1.2 × 106 cycles à 50 N, 1.6 Hz). De-bonding and fracture force was determined. STATISTICS: one-way-ANOVA; post hoc Bonferroni, α = 0.05. RESULTS: Four crowns of Lava Ultimate with worst-case preparation de-bonded during TCML. Individual crowns without sandblasting treatment (3x Tetric CAD with optimal preparation; 1x Tetric CAD with worst-case preparation) de-bonded during water storage. One crown of Grandio Blocs with optimal preparation showed a small chipping during TCML. All other crowns survived TCML and water storage without failure. Fracture forces differed between 1272 ± 211 N (Lava Ultimate) and 3061 ± 521 N (Tetric CAD). All Grandio Blocs and Tetric CAD crowns revealed significantly (p ≤ 0.023) higher fracture forces than Block HC or Lava Ultimate crowns. No significantly different (p > 0.05) fracture forces were found between optimal or worst-case preparation/fit groups. CONCLUSIONS: De-bonding during water storage and TCML was dependent on material and crown pre-treatment. Therefore, surface roughening seems strongly required. Fracture forces were not influenced by preparation but by the type of material. CLINICAL RELEVANCE: Clinical success and de-bonding of CAD/CAM resin composite crowns is strongly influenced by the type of material and its pre-treatment.

The antimicrobial and cytotoxic effects of a copper-loaded zinc oxide phosphate cement.

OBJECTIVES: Evidence about modifications of dental luting materials to minimize biological failure at the "marginal gap" between teeth and fixed prosthodontics is scarce. We compared a copper-modified (Co-ZOP) and a conventional zinc oxide phosphate cement (ZOP) in terms of antimicrobial and cytotoxic potentials in vitro and in vivo. MATERIALS AND METHODS: Specimens of ZOP and Co-ZOP were characterized by the mean arithmetic roughness (Ra) and surface free energy (SFE). Powder components were examined using scanning electron microscopy (SEM). Energy-dispersive X-ray spectroscopy (EDX) showed elemental material compositions. In vitro microbial adhesion was shown using SEM, luminescence, and fluorescence assays. CCK-8 assays of mouse fibroblasts (L929) and human gingival fibroblasts (GF-1) were performed after 6, 24, and 48 h of specimen incubation. In vivo, ZOP and Co-ZOP specimens were applied intraorally for 12 h; biofilm accumulation was shown using SEM. RESULTS: Ra of ZOP and Co-ZOP showed no significant differences; SFE was significantly higher for Co-ZOP. EDX exhibited minor copper radiation for Co-ZOP, none for ZOP. In vitro fungal adhesion to Co-ZOP was significantly higher than to ZOP; in vitro streptococcal adhesion, cytotoxicity, and in vivo biofilm formation were not significantly different. CONCLUSIONS: Co-ZOP showed low surface allocations of copper with no improved antimicrobial properties compared with conventional ZOP in vitro or in vivo. CLINICAL RELEVANCE: Antimicrobial effects and low cytotoxicity of biomaterials are important for the clinical outcome. Based on our in vitro and in vivo results, no clinical recommendation can be given for the tested Co-ZOP.

Polishing effects and wear performance of chairside CAD/CAM materials.

OBJECTIVES: To investigate the surface roughness of CAD/CAM materials immediately after milling and after different chairside and labside polishing procedures. A two-body wear test was performed to compare the different wear characteristics of the materials and the corresponding antagonists. MATERIALS AND METHODS: Specimens (n = 12 per series) from different CAD/CAM materials (three composites: Lava Ultimate, Cerasmart, BRILLIANT Crios; one hybrid ceramic: VITA Enamic; three ceramics: Celtra Duo, VITA Suprinity, IPS Emax.CAD) were polished according to the manufacturer's instructions. The effect of different polishing procedures was investigated by comparing surface roughness (Ra, Rmax) after labside polishing and after chairside polishing. Wear behavior (mean, volume, and maximum wear) of specimens and antagonists as well as changes in surface roughness were determined in a pin-on-block wear test. Statistical analysis was performed with a one-way analysis of variance (ANOVA)/Bonferroni multiple-comparison post hoc test and a multifactorial ANOVA/Tukey's significant difference post hoc test (α = 0.05). SEM micrographs were used for the qualitative evaluation of surfaces and wear traces. RESULTS: After chairside high-gloss polishing, ceramics and composites exhibited Ra values between 0.08 and 0.10 µm and between 0.11 and 0.13 µm, respectively. After labside high-gloss polishing, values varied between 0.02 and 0.09 µm for ceramics and between 0.06 and 0.16 µm for resin composites. No significant differences were found between labside and chairside pre- and high-gloss polishing. For the ceramics, lower mean wear depths (between - 132.2 ± 19.9 and - 137.0 ± 19.0 µm) were identified compared to the resin composites (which exhibited wear depths between - 159.1 ± 19.4 and - 176.3 ± 23.9 µm). For maximum wear depth and volume, a different ranking of the materials was found. Antagonistic wear varied between 12.0 ± 6.4% and 30.6 ± 9.9% and was higher for the ceramic materials and Lava Ultimate. For all materials, a smoothing between 0.20 and 2.70 µm (Ra) was identified after wear simulation. CONCLUSIONS: Chairside polishing is as effective as labside polishing, although surfaces were directly adjusted (roughened) only before the chairside polishing. Wear was lowest for ceramics, followed by the resin-infiltrated material and the resin composites. CLINICAL RELEVANCE: Polishing after milling or adjustment is essential to guaranteeing optimal clinical performance. Chairside polishing after adjustment leads to comparably smooth surfaces as labside polishing after milling and grinding. Ceramics are expected to exhibit lower wear than resin composites under clinical conditions.

Failure loads of all-ceramic cantilever fixed dental prostheses on post-restored abutment teeth: influence of the post presence and post position.

The influence of a fiber post-restored abutment tooth on the load capability of a three-unit zirconia framework cantilever fixed dental prosthesis (cFDP) was evaluated after simulated clinical function. Human lower sound premolars (n = 64) were distributed, in equal numbers, to four experimental groups: two vital abutment teeth (group I; control); mesial abutment tooth post-restored (group II); distal abutment tooth post-restored (group III); and mesial and distal abutment teeth post-restored (group IV). All specimens received an adhesively luted three-unit cFDP of veneered zirconia. Simulated clinical function was performed by two subsequent sequences of thermal-cycling (2 × 3,000 cycles) and mechanical loading (1.2 × 106 load cycles from 0 to 50 N) (TCML). Four specimens failed during TCML (one in each of groups I and IV and two in group II). The maximum load capability ranged from 365 to 538 N and was not significantly different between groups. Specimens with post-restored abutments failed mainly because of abutment tooth fracture of the distal abutment. The presence or position of post-restored abutment teeth has no significant impact on load capability of all-ceramic three-unit cFDPs. The risk of tooth fracture of the distal abutment teeth of a cFDP was significantly increased when one abutment tooth, irrespective of its position, was post-and-core restored.

Direct or Indirect Restoration of Endodontically Treated Maxillary Central Incisors with Class III Defects? Composite vs Veneer or Crown Restoration.

PURPOSE: The aim of this ex-vivo study was to evaluate the load capacity of direct or indirect endodontically restored maxillary central incisors with Class III defects, with or without glass-fiber posts. MATERIALS AND METHODS: Seventy-two extracted human maxillary central incisors were endodontically treated and bi-proximal Class III cavities were prepared. Specimens were randomly allocated to six groups (n = 12): direct restoration with composite (C); direct restoration with composite and additional glass-fiber post (CP); ceramic veneer restoration (V), ceramic veneer restoration and additional glass-fiber post (VP), ceramic crown restoration (Cr), ceramic crown restoration and additional glass-fiber post (CrP). Specimens were exposed to thermomechanical loading (TML: 1.2 million cycles, 1 to 50 N; 6000 thermal cycles between 5°C and 55°C for 1 min each), and subsequently linearly loaded until failure (Fmax [N]) at an angle of 135 degrees 3 mm below the incisal edge on the palatal side. Statistical tests were performed using the Kruskall-Wallis and Mann-Whitney U-Test. RESULTS: During dynamic loading by TML, one early failure occurred in group C, CP, and CrP. Subsequent linear loading resulted in mean fracture load values [N] of C = 483 ± 219, CP = 536 ± 281, V = 908 ± 293, VP = 775 ± 333, Cr = 549 ± 258, CrP = 593 ± 259. The Kruskal-Wallis test showed significant differences of load capacity between groups (p < 0.05). Mann-Whitney U-test revealed significantly lower maximum fracture load values of group C compared to group V (p = 0.014), after Bonferroni-Holm correction. Non-restorable root fracture was the most frequent type of failure. CONCLUSION: Endodontically treated maxillary central incisors with Class III defects directly restored with composite are as loadable as indirect crown restorations. Compared to full-coverage restorations, less invasive veneers appear to be more beneficial. Additional placement of glass-fiber posts shows no positive effect.

Roughness, surface energy, and superficial damages of CAD/CAM materials after surface treatment.

OBJECTIVES: The aim of this study was to examine the effects of surface pre-treatment on CAD/CAM materials including ceramics, zirconia, resin-infiltrated ceramic, and resin-based composite. MATERIALS AND METHODS: Specimens were made of ten CAD/CAM materials (Celtra Duo, Degudent, D; Vita Suprinity, Vita, D; E.max CAD, Ivoclar-Vivadent, FL; E.max ZirCAD, Ivoclar-Vivadent, FL; Vita Enamic, Vita, D; Cerasmart, GC, B; LAVA Ultimate, 3M, D; SHOFU Block HC, SHOFU, US; Grandio Blocs, VOCO, D; BRILLIANT Crios, Coltene, CH) and pretreated to represent clinical procedures (Hf 20 s/5%; phosphoric acid 20 s/37%; Monobond etch and prime (Ivoclar-Vivadent, FL); water-cooled diamond bur (80 µm; 4 µm); Al2O3-blasting (50 µm/1 bar, 50 µm/2 bar, 120 µm/1 bar, 120 µm/2 bar); untreated; manufacturer's instructions). SEM-analysis (Phenom, FEI, NL) of the surfaces was performed (magnifications ≤ 10,000×). Roughness values Ra, Rz (KJ 3D, Keyence, J), and surface energy SE (OCA15 plus, SCA20, DataPhysics, D) were determined (statistics: non-parametric Mann-Whitney U test/Kruskal-Wallis test for independent specimen, α = 0.05). RESULTS: Kruskal-Wallis revealed significant (p < 0.001) differences for all materials with different surface treatments. Roughness ranged from Ra = 0.05 µm (VS; D4)/Rz = 0.41 µm (VS; D4) to Ra = 1.82 µm (EMA; SB120/2)/Rz = 12.05 µm (CS; SB 120/2), SE from 22.7 mN/m (VE; M) to 52.8 mN/m (CD; M). SEM analysis showed material-dependent damages after pre-treatment. CONCLUSION: Different CAD/CAM materials require individual pre-treatment for optimized and protective surface activation. CLINICAL RELEVANCE: Cementation is a key factor for clinical success. Given the variety of available CAD/CAM materials, specific procedures are needed.

Interim rehabilitation of occlusal vertical dimension using a double-crown-retained removable dental prosthesis with polyetheretherketone framework.

Polyetheretherketone (PEEK) is a polymeric material that has recently been introduced in dentistry and can be used as framework material for fixed and removable dental prostheses. This clinical report describes the fabrication of a double-crown-retained prosthesis with a PEEK framework in a patient with a substantially diminished occlusal vertical dimension. The insertion of the removable dental prosthesis with a PEEK framework resulted in the functional and esthetic rehabilitation of the patient; however, removable dental prostheses fabricated from PEEK should currently be regarded as interim restorations because of the limited available scientific evidence.

In-vitro performance of CAD/CAM-fabricated implant-supported temporary crowns.

OBJECTIVES: The aim of this study was to investigate the in-vitro performance and fracture resistance of a temporary computer-aided designed and computer-aided manufactured polymethylmethacrylate (CAD/CAM-PMMA) material as implant or tooth-supported single crown with respect to the clinical procedure (permanently bonded/temporarily cemented). MATERIALS AND METHODS: Sixty-four crowns were fabricated on implants or human molar teeth simulating (a) labside procedure on prefabricated titanium-bonding base ([TiBase] implant crown bonded in laboratory, screwed chairside), (b) labside procedure ([LAB] standard abutment and implant crown bonded in laboratory, screwed chairside), (c) chairside procedure ([CHAIR] implant crown bonded to abutment), and (d) reference ([TOOTH] crowns luted on prepared human teeth). Crowns were made of a CAD/CAM-PMMA temporary material (TelioCAD, Ivoclar-Vivadent). For investigating the influence of fixation, half of the crowns were permanently (P) or temporarily (T) bonded. Combined thermal cycling and mechanical loading (TCML) was performed simulating a 5-year clinical situation. Fracture force was determined. Data were statistically analyzed (Kolmogorov-Smirnov test, one-way ANOVA; post hoc Bonferroni, α = 0.05). RESULTS: All restorations survived TCML without visible failures. Fracture results varied between 3034.3 (Tooth-P) and 1602.9 N (Tooth-T) [TOOTH], 1510.5 (TiBase-P) and 963.6 N (TiBase-T) [TiBase], 2691.1 (LAB-P) and 2064.5 N (LAB-T) [LAB], and 1609.4 (Chair-P) and 1253.0 N (Chair-T) [CHAIR]. Tested groups showed significantly (p < 0.001) different fracture values. Failure pattern was characterized by fractures in mesial-distal, buccal-oral, or mixed (mesial-distal/buccal-oral) directions, with differences for the individual groups. CONCLUSIONS: Temporary CAD/CAM crowns showed no different in-vitro performance but provided different fracture results that depended on cementation, screw channel, and type of abutment. CLINICAL RELEVANCE: All bonded and screwed PMMA crowns were in a range where clinical application seems not restricted.

In vitro performance and fracture resistance of CAD/CAM-fabricated implant supported molar crowns.

OBJECTIVES: The aim of this study is to investigate the performance and fracture resistance of different CAD/CAM ceramic and composite materials as implant- or tooth-supported single crowns with respect to the clinical procedure (screwed/bonded restoration). MATERIALS AND METHODS: One hundred twenty crowns were fabricated on implants or human molar teeth simulating (a) chairside procedure ([CHAIR] implant crown bonded to abutment), (b) labside procedure ([LAB] abutment and implant crown bonded in laboratory, screwed chairside), and (c) reference ([TOOTH] crowns luted on human teeth). Four materials were investigated: ZLS (zirconia-reinforced lithium silicate ceramic; Celtra Duo, Degudent: polished (P)/crystallized (C)), RB (resin-based composite; Cerasmart, GC), and RIC (resin-infiltrated ceramic; Enamic, Vita-Zahnfabrik). LiS (lithiumdisilicate; Emax CAD, Ivoclar-Vivadent) served as reference. Combined thermal cycling and mechanical loading (TCML) was performed simulating a 5-year clinical situation. Fracture force was determined. Data were statistically analyzed (Kolmogorov-Smirnov test, one-way ANOVA; post hoc Bonferroni, α = 0.05). RESULTS: One crown of ZLS_C[LAB] (1,200,000 cycles) and RB[CHAIR] (890 cycles) failed during TCML. Fracture values varied between 977.7 N(RB) and 3070.4 N(LiS)[CHAIR], 1130.6 N(RB) and 2998.1 N(LiS)[LAB], and 1802.4 N(ZLS) and 2664.3 N(LiS)[TOOTH]. Significantly (p < 0.003) different forces were found between the materials in all three groups. ZLS_C, RIC, and RB showed significantly (p < 0.014) different values for the individual groups. CONCLUSIONS: Partly ceramic and resin-based materials performed differently on implant or tooth abutments. The insertion of a screw channel reduced the stability for individual crown materials. Insertion of the screw channel should be performed carefully. CLINICAL RELEVANCE: All restorations were in a range where clinical application seems not restricted, but insertion of a screw channel might reduce stability of individual materials.

Comparison of flowable bulk-fill and flowable resin-based composites: an in vitro analysis.

OBJECTIVES: Flowable bulk-fill resin bonded composites (RBCs) are supposed to show improved abrasion resistance and fracture toughness in comparison to flowable conventional RBCs. MATERIALS AND METHODS: Specimens of eight flowable RBCs (5× flowable conventional, 3× flowable bulk-fill) were fabricated for testing relative fracture toughness (SENB), relative three-body wear, the Vickers hardness, glass transition Tg (differential scanning calorimetry; DSC) and filler mass fraction (thermal gravimetric analysis; TGA). A laboratory veneering composite was used as a reference. Fracture toughness and wear values were related to this reference. Scanning electron microscope images were evaluated for fraktographical and microstructural investigations. Statistical analyses were performed using one-way Anova, the Bonferroni post hoc test and the Pearson correlation test (α =0.05). RESULTS: Relative fracture toughness varied between 0.64 and 1.34 (1.00 = 1.69 MPam½) and relative wear rates between 1.24 and 0.55 (1.00 = 134 µm). The Vickers hardness ranged between 14.4 and 57.2 HV. TGA showed filler fractions between 55 and 77 wt.%. Tg values varied between -67.8 and -40.9 °C. None of the tests identified clear differences between flowable bulk-fills or conventional flowable RBCs. The Pearson correlation coefficient (cc) showed significant correlations (cc > 0.583; p < 0.001) between relative fracture toughness and hardness or filler content. There was a significant correlation (cc = 0.757; p = 0.005) between relative wear and glass transition temperature or between filler fraction and the Vickers hardness (cc > 0.702; p < 0.001). For all filler sizes breakdown was found, where clusters and pre-polymerized particles were partly disintegrated. CONCLUSIONS: Flowable bulk-fill RBCs showed no improved abrasion resistance and fracture toughness in comparison to flowable conventional RBCs. CLINICAL RELEVANCE: Differences in the properties were higher between the individual materials than between the material groups. Therefore the appropriate material selection may be essential for a clinical success.