Material and abutment selection for CAD/CAM implant-supported fixed dental prostheses in partially edentulous patients - A narrative review

Restorative material selection has become increasingly challenging due to the speed of new developments in the field of dental material science. The present narrative review gives an overview of the current indications for implant abutments and restoration materials for provisional and definitive implant-supported fixed dental prostheses in partially edentulous patients. For single implant restorations, titanium base abutments for crowns are suggested as an alternative to the conventional stock- and customized abutments made out of metal or zirconia. They combine the mechanical stability of a metallic connection with the esthetic potential of ceramics. For multiple-unit restorations, conical titanium bases especially designed for bridges are recommended, to compensate for deviating implant insertion axes and angulations. Even though titanium base abutments with different geometries and heights are available, certain clinical scenarios still benefit from customized titanium abutments. Indications for the definitive material in fixed implant restorations depend on the region of tooth replacement. In the posterior (not esthetically critical) zone, ceramics such as zirconia (3-5-Ymol%) and lithium-disilicate are recommended to be used in a monolithic fashion. In the anterior sector, ceramic restorations may be buccally micro-veneered for an optimal esthetic appearance. Lithium-disilicate is only recommended for single-crowns, while zirconia (3-5-Ymol%) is also recommended for multiple-unit and cantilever restorations. Attention must be given to the specific mechanical properties of different types of zirconia, as some feature reduced mechanical strengths and are therefore not indicated for all regions and restoration span lengths. Metal-ceramics remain an option, especially for cantilever restorations.

Flexural strength of novel glass infiltrated monochrome and multilayer high yttrium oxide containing zirconia upon various sintered cooling rates

PURPOSE

The sintering technique and cooling strategy influence the strength of zirconia. This study examined the impact of altering the cooling rate of glass-infiltrated monolayer and multilayer 5 mol% yttria-partially stabilized zirconia (5Y-PSZ) on their strength.

MATERIALS AND METHODS

One-hundred eighty (180) specimens (width × length × thickness = 10 × 20 × 2 mm) were prepared using monolayer (Mo: Cercon-xt) and multilayer (Mu: Cercon-xt ML) 5Y-PSZ. Randomly distributed specimens (n = 15/group) were sintered with traditional (T) versus glass infiltrated (G) technique and cooled down with different cooling rates: slow (S: 5°C/min), normal (N: 35°C/min), and fast (F: 70°C/min). Four-point bending test was used to measure flexural strength (σ). Microstructures were investigated by scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). Three-way ANOVA and Tamhane comparisons were determined for a significant difference of σ (p < 0.05). Weibull analysis was determined for Weibull modulus (m).

RESULTS

The highest σ (MPa) was seen for GMuS (696.8 ± 69.8). Mo-PSZ and Mu-PSZ showed no significant difference in σ. G-sintering presented significantly higher σ (659.9 ± 79.3) than T-sintering (426.0 ± 63.7). S-cooling (560.9 ± 126.1) had the highest σ. The highest m-value was observed in GMuN (12.1 ± 3.8). A significant difference in σ was indicated due to cooling rates and sintering techniques (p < 0.05).

CONCLUSIONS

Glass infiltration significantly enhanced strength through elastic gradience. F-cooling reduced grain size, impaired grain boundary integration, and increased the tetragonal to monoclinic phase transition, significantly decreasing flexural strength in traditional sintering. Nevertheless, F-cooling was recommended for glass-infiltrated 5Y-PSZ to enhance strength while reducing processing time.

Do strength of zirconia-abutment-interfaces depend on cement, zirconia type and titanium abutment dimensions?

OBJECTIVES

Part 1 of this study investigates the influence of zirconia types, chimney heights, and gingival heights on the strength of the zirconia-abutment-interface. Part 2 extends the analysis to include adhesive brands and macro-retentions.

METHODS

In Part 1, the study utilized three zirconia types (700 MPa, 1000 MPa, 1200 MPa) to fabricate 234 screw-retained zirconia crowns with varying chimney heights (3.5 mm, 4.1 mm, 5 mm) and gingival heights (0.65 mm, 1.2 mm, 3 mm) of the titanium abutments. All adherend surfaces underwent sandblasting with aluminum oxide before cementation with a specific resin cement. In Part 2, the investigation of 240 screw-retained zirconia crowns focused on a single zirconia type (1000 MPa) with chimney heights of 3.5 mm and 5 mm and a gingival height of 0.65 mm of the titanium abutments, cemented with three different resin cements. All adherent surfaces underwent sandblasting with aluminum oxide before cementation, whereas 120 out of 240 abutments received additional macro retentions. Storage in water at 37 °C for 24 h preceded the tensile test.

RESULTS

The study revealed a substantial impact of chimney height and zirconia type on the bond strength of the zirconia-abutment-interface. Neither adhesive brands nor macro retentions significantly impacted the bond strength. Fracture incidence was significantly influenced by gingival height and zirconia type in part 1, whereas in part 2 smaller chimney heights correlated with a higher fracture incidence.

SIGNIFICANCE

This study contributes insights into the complex interplay of factors influencing the zirconia-abutment-interface. The results provide a foundation for refining clinical approaches, emphasizing the importance of chimney height and zirconia type in achieving successful anterior gap implant restorations.

Fracture resistance of hybrid ceramic abutments with different restoration lengths: A pilot study

AIM

In this pilot study, the fracture resistance of hybrid abutments with different restoration lengths was investigated.

MATERIALS AND METHODS

Sixteen monolithic zirconia restorations of an upper right incisor were designed to fit a titanium base abutment. Eight central incisors had a crown length of 8 mm (T1) and the other half a length of 12 mm (T2). All crowns were cemented on the titanium base using a resin cement. After cementation, the samples were placed in a thermocycler for 5000 cycles. Fracture strength was measured using a universal test machine. Deformations and fractures of the samples were investigated.

RESULTS

The mean fracture resistance of T1 was 515 N (SD 96 N, 339-650) and 305 N (SD 57 N, 234-408) for T2 (p < 0.001). Both groups showed deformation of the titanium base, with no significant difference between both groups (p = 0.200). A difference in fracture type (p = 0.013) was observed, with significantly more screw fractures occurring in group T1 (p = 0.026).

CONCLUSION

Within the limitations of this study, hybrid restorations with standard titanium base abutments can withstand forces that have been associated with chewing, irrespective of the crown length. However, the shorter crowns demonstrated more fatal fractures.

Assessment of crestal bone loss and periodontal parameters of polymer infiltrated ceramic network versus lithium disilicate implant hybrid abutment crowns in the esthetic zone (A randomized clinical trial)

BACKGROUND

Lithium disilicate can be reliable when restoring implants in the esthetic zone. However, it has a high elastic modulus. This might increase the amount of forces transmitted to the crestal bone.

AIM OF THE STUDY

To evaluate the crestal bone loss and peri-implant periodontal parameters of polymer infiltrated ceramic network compared to lithium disilicate implant-supported hybrid abutment crowns after 12 months of follow-up.

METHODOLOGY

44 patients were enrolled. They were randomly assigned into two groups (n = 22). The first group received 22 implants restored with polymer-infiltrated ceramic network (Vitaenamic) hybrid abutment crowns. The second group received 22 implants restored with lithium disilicate (e.max) hybrid abutment crowns over immediately placed implants in the esthetic zone. Periapical radiographs were taken immediately after prosthetic placement and 1 year later utilizing a parallel technique, to assess crestal bone loss. Periodontal parameters were assessed after 1 year.

RESULTS

Regarding crestal bone loss, a comparison between group I (Vitaenamic) and group II (e.max) was made by using an Independent t-test, which showed an insignificant difference between them (p > 0.05). A comparison between groups I and II revealed insignificant differences regarding periodontal parameters (probing depth, bleeding on probing, visible plaque, and suppuration).

CONCLUSIONS

Regarding bone stability and periodontal parameters, polymer infiltrated ceramic network and lithium disilicate hybrid abutment crowns showed comparable results. Both materials showed clinically acceptable hard and soft tissue responses.

Mechanical behavior of titanium and zirconia abutments at the implant-abutment interface: A systematic review

STATEMENT OF PROBLEM

Zirconia has become popular for dental implant abutments in the esthetic zone but can damage the implant connection interface. Studies have been conducted to compare zirconia abutments with conventional titanium abutments; however, a consensus or systematic review is lacking.

PURPOSE

The purpose of this systematic review was to evaluate the performance of abutments made of zirconia and titanium in relation to wear and misfit at the implant-abutment interface.

MATERIAL AND METHODS

Electronic databases (PubMed/MEDLINE, Embase, Web of Science) were independently searched by 2 researchers for relevant studies published up to June 2021. The population, intervention, comparison, outcome (PICO) question was "Do zirconia abutments cause greater wear at the implant-abutment interface than titanium abutments under occlusal forces?" Eligible studies included in vitro studies that evaluated changes in the surface of external and/or internal connections and single and/or multiple, screwed and/or cemented prostheses rehabilitated with titanium and zirconia abutments submitted to mechanical cycling.

RESULTS

Nine studies were included for qualitative analysis. A total of 172 specimens were analyzed, 86 zirconia and 86 titanium abutments. In terms of wear on the implant connection surface, zirconia abutments caused more severe wear, more scratches, and more rounding of the hexagonal angles at the implant connection interface than titanium abutments. In terms of misfit at the connection interface, zirconia abutments showed greater misfit than titanium abutments.

CONCLUSIONS

Zirconia abutments produce more wear at the titanium implant connection interface, titanium abutments showed better fit to the implant connection interface, and the fit can be influenced by the abutment manufacturing method.

The natural CAD/CAM anterior implant single tooth restoration: A novel digital workflow

OBJECTIVE

To report a novel digital workflow to replace an anterior maxillary tooth lost due to trauma with an implant multilayer restoration by using the patient's extracted tooth as a final crown restoration using computer-aided design/computer-aided manufacturing (CAD/CAM) technology.

CLINICAL CONSIDERATIONS

Instead of using the patient's natural tooth as an immediate provisional restoration to achieve predictable results in terms of esthetics and soft tissue structure, a novel digital strategy was performed to obtain a natural final crown restoration by using the patient's tooth associated with a lithium disilicate customized implant abutment.

CONCLUSIONS

The perspective of using this strategic approach for implant restorative dental treatments in patients with traumatic root fractures in the anterior region has great potential as it helps to maintain the emergence profile of the natural dentition and esthetics.

CLINICAL SIGNIFICANCE

Optimal esthetic outcomes are challenging in implant dentistry regarding soft tissue structure and morphology factors. Using natural teeth from surgery to deliver the final restoration might be beneficial when an anterior tooth is lost due to trauma.

Biomechanical behavior of different designs of hybrid abutment-restoration on the posterior crown: a finite element analysis

This study aimed to evaluate the influence of material and crown design on the biomechanical behavior of implant-supported crowns with hybrid abutment (HA) through three-dimensional (3D) finite element analysis. The study factors were the type of material used as the mesostructure or crown (zirconia, lithium disilicate, and hybrid ceramic) and the crown design cemented to the titanium base (mesostructure cemented to the titanium base and a crown cemented on it (HaC); hybrid crown-abutment, the abutment and crown are manufactured as a single piece and cemented to the titanium base (HC); monolithic crown cemented on the titanium base and screwed to the implant (CS); and monolithic crown cemented on the titanium base (CC). Four 3D models were constructed using an implant with an internal connection, and an oblique load of 130 N was applied at 45° to the long axis of the implant. The models were evaluated using the von Mises stress for crown, abutment, screw, and implant and maximum principal stress for bone tissues. The lowest stresses occurred in the groups with a lower elastic modulus material, mainly hybrid ceramics, considered a material with greater resilience. The cemented crown group presented the lowest stress values. The stresses were concentrated in the cervical region of the crown at the titanium crown/base interface. Mesostructures made of materials with a higher elastic modulus exhibited a higher concentration of stress. The presence of a screw hole increased the stress concentration in the ceramic crown. Cemented ceramic crowns exhibited better biomechanical behavior than screw-retained crowns.

Implant deformation and implant-abutment fracture resistance after standardized artificial aging: An in vitro study

BACKGROUND AND PURPOSE

Zirconia abutments have been widely adopted in clinical implant practice. The unique mechanical properties of zirconia may significantly affect the long-term prognosis of implant treatments. The purpose of this study was to investigate the influence of abutment material on implant deformation and fracture resistance of internal conical connection implant-abutment complexes of two diameters after standardized artificial aging.

MATERIALS AND METHODS

Thirty original abutments (one-piece titanium, one-piece zirconia, zirconia with alloy base) with two diameters (regular, narrow) were connected to internal conical connection implants and subjected to a standardized artificial aging process consisting of thermal cycling and mechanical cyclic loading. Microcomputed tomography (μCT) scans of implant bodies were performed before and after aging. 3-dimensional images of implant bodies were generated from the μCT scans and aligned for before and after aging to calculate the volumetric deformation amount. Finally, fracture resistance was measured using a mechanical static loading test for the surviving aged and 30 brand-new specimens.

RESULTS

All specimens survived artificial aging. No significant difference in implant deformation was found in the regular groups (p = 0.095). In narrow groups, the one-piece zirconia group showed significantly less deformation (p < 0.0001). For fracture resistance, no significant decrease was observed after aging in any group (p > 0.05). One-piece zirconia abutments showed significantly lower strength than the other two materials for both diameters (p < 0.0001).

CONCLUSIONS

In the regular diameter system, abutment material had no significant influence on the tested mechanical property degradation after simulated long-term oral use. The mechanical performance of narrow diameter one-piece zirconia abutments differed from the other two materials. For optimal performance, one-piece zirconia abutments should be adopted only in anterior regions.

Physical and mechanical changes on titanium base of three different types of hybrid abutment after cyclic loading

PURPOSE

This study investigated the physical and mechanical changes in the titanium base of three different hybrid abutment materials after cyclic loading by estimating the post-load reverse torque value (RTV), compressive side fulcrum wear pattern of titanium base, and surface roughness.

MATERIALS AND METHODS

A total of 24 dental implants were divided into three groups (n = 8 each): Group Z, LD, and P used zirconia, lithium disilicate, and polyetheretherketone, respectively, for hybrid abutment fabrication. RTV was evaluated after cyclic loading with 50 N for 1.2 × 10⁶ chewing cycles. The compressive sides of the titanium bases were analyzed using a scanning electron microscope, and the roughness of the affected areas was measured using an optical profilometer after loading. Datasets were analyzed using Kruskal-Wallis test followed by Mann-Whitney tests with the Bonferroni correction (α = .05).

RESULTS

Twenty-three samples passed the test; one LD sample fractured after 770,474 cycles. Post-load RTV varied significantly depending on the hybrid-abutment material (P = .020). Group P had a significantly higher median of post-load RTVs than group Z (16.5 and 14.3 Ncm, respectively). Groups LD and P showed minor signs of wear, and group Z showed a more pronounced wear pattern. While evaluating compressive side affected area roughness of titanium bases, lower medians were shown in group LD (Ra 0.16 and Rq 0.22 µm) and group P (Ra 0.16 and Rq 0.23 µm) than in group Z (Ra 0.26 and Rq 0.34 µm); significant differences were found only among the unaffected surface and group Z.

CONCLUSION

The hybrid abutment material influences the post-load RTV. Group Z had a more pronounced wear pattern on the compressive side of titanium base; however, the surface roughness was not statistically different among the hybrid-abutment groups.

Abutment removal torque and implant conical surface morphological changes after standardized artificial aging: An in vitro study

STATEMENT OF PROBLEM

Zirconia abutments have become popular as they provide favorable esthetic outcomes. However, studies investigating how abutment material affects abutment screw torque performance and implant conical surface morphological changes in internal conical connection systems are scarce.

PURPOSE

The purpose of this in vitro study was to investigate the influence of abutment material on abutment removal torque and implant conical surface morphological changes in internal conical connection implant-abutment assemblies of 2 diameters after simulated long-term oral use.

MATERIAL AND METHODS

Thirty abutments of 3 materials (1-piece titanium, 1-piece zirconia, zirconia with alloy base) and 2 diameters (regular, narrow) made by the original manufacturer were connected to internal conical connection implants and subjected to a standardized artificial aging process consisting of thermal cycling and mechanical cyclic loading with parameters corresponding to anterior and posterior mastication scenarios simulating long-term oral use. An abutment removal torque test was done before and after aging. Morphological changes in the implant conical contact surface were observed with a scanning electron microscope (SEM). Initial and after-aging torque loss values were calculated and analyzed separately with 1-way ANOVA and Tukey HSD post hoc tests (α=.05).

RESULTS

All specimens survived artificial aging. For initial and after-aging torque loss, the 1-piece zirconia groups showed significantly greater values (P<.001) for both diameters. In the SEM observation, the 1-piece zirconia groups showed distinct widespread surface damage while the other groups exhibited only minor damages.

CONCLUSIONS

Regardless of diameter, 1-piece zirconia abutments tend to induce more abutment removal torque loss and implant conical surface morphological changes than those with metal connections, both initially and after simulated long-term oral use. Zirconia abutments with an alloy base performed similarly to 1-piece titanium abutments.

Clinical assessment of different implant-supported esthetic crown systems fabricated with semi-digital workflow: Two-year prospective study

OBJECTIVE

To assess the clinical outcome of three esthetic implant-supported crown systems fabricated with semi-digital workflow and their influence on the clinical outcome of dental implants.

MATERIAL AND METHODS

A total of 30 participants had received dental implants restoring missing maxillary first/second premolars. After 6 weeks, customized zirconia abutments were early loaded. Two months later, the definitive crowns were fabricated using semi-digital workflow and cemented. According to the crown material, 3 groups were randomly allocated; group (Z): ultrahigh-translucent monolithic zirconia, group (C): resin-matrix ceramic and group (P): polyetherketoneketone veneered with light-cured composite resin. Clinical outcomes including the survival and success rates were evaluated at baseline, 6, 12, 18, and 24 months.

RESULTS

The survival rate for all studied groups was 100%, while their success rate was 100% for group (Z) and 90% for group (C) and group (P). Based on the functional implant prosthodontic score, a statistically significant difference was detected between group (Z) and group (P) (p < 0.001) as well as between group (C) and group (P) (p = 0.01).

CONCLUSIONS

The zirconia group had the most favorable clinical behavior, while the polyetherketoneketone had the least. All crown systems had comparable success rates with similar values of the peri-implant marginal bone loss.

CLINICAL SIGNIFICANCE

Using semi-digital workflow, ultrahigh-translucent monolithic zirconia, resin-matrix ceramic and polyetherketoneketone veneered with light-cured composite resin can be considered as favorable implant-supported crowns. The implant-supported crown system based on polyetherketoneketone veneered with light-cured composite resin is counted as a promising esthetic and restorative option.

Evaluation of The Fracture Resistance and Failure Types of Different CAD/CAM Ceramic Crowns Supported by Angled Titanium Abutment

PURPOSE

To evaluate the fatigue resistance of CAD-CAM single-ceramic crowns which were applied on angled implant abutments after thermomechanical aging.

MATERIALS AND METHODS

Titanium abutments (N = 72, MODE Medical Dental Implant, Turkey) with three different angles [0˚, 15°, 25°] were restored using different materials [Monolithic zirconia (Zir), lithium silicate ceramic reinforced by zirconia (VS), and Hybrid ceramic (VE)]. Crowns in the maxillary first premolar form were cemented to abutments using resin cement (Panavia 2.0 Introkit). Dynamic loading and thermomechanical aging were applied to the specimens (120,000 cycles, 49 N, 5°C to 55°C). Fracture resistance values were measured in the universal test machine and fracture types were determined. Two-way ANOVA and Tukey test were used for statistical analysis (Jamovi version 2.3.5).

RESULTS

Both the abutment angle and the type of material had a significant effect on fracture resistance (F = 3.295, p<0.05). The highest fracture resistance was obtained in the Group 0˚-Zir, and the lowest fracture resistance was obtained in the Group 15˚-VE. Fracture resistance showed significant differences between Group 0˚-Group15˚ for the Zir and VE materials, and between Group0˚-Group25˚ for VS (p<0.05), and no statistical significance was determined between the other groups (p>0.05). When failure types were evaluated they were seen to be full or partial crown fractures, and abutment deformation was found in some samples.

CONCLUSION

Monolithic crowns may be preferred on angled abutments. The fracture resistance of CAD-CAM materials decreases as the angle of abutments increases. Monolithic zirconia has higher fracture resistance than other materials. This article is protected by copyright. All rights reserved.

Masking ability of implant abutment substrates by using different ceramic restorative systems

STATEMENT OF PROBLEM

Information regarding the masking ability of ceramic crowns over different implant abutment materials is scarce.

PURPOSE

The purpose of this in vitro study was to evaluate the masking ability of different monolithic or bilayer ceramic materials with different thicknesses over substrates indicated for implant restorations by using opaque and translucent evaluation pastes.

MATERIAL AND METHODS

Disk-shaped specimens, shade A1 (VITA Classic; Ø10×1.5 to 2.5 mm), of different ceramics (a bilayer system [yttria-stabilized zirconia infrastructure+porcelain veneer: Zir+Pc] and monolithic systems [lithium disilicate under low, medium, or high translucency: LtLD, MtLD, or HtLD, respectively, and a high-translucent yttria-stabilized zirconia: HtZir]) were made (n=4). The color difference (ΔE₀₀) was assessed by using the CIEDE2000 formula and considering the different ceramic systems over 5 implant abutment materials (A1 shade Zir [Zir A1]; white Zir [White Zir]; A1 low-translucency lithium disilicate [LD]; polyetheretherketone [PEEK]; and titanium [Ti]) when using 2 different evaluation pastes (translucent or opaque). The control comparison was the restorative material positioned over the Zir A1 substrate with a translucent evaluation paste. Statistical analysis was made by using a 2-way ANOVA and Tukey post hoc tests (α=.05) for ΔE₀₀ data considering the restorative material and luting agent factors as their association. Additionally, ΔE₀₀ data were qualitatively analyzed considering the acceptability and perceptibility thresholds. The translucency parameter (TP₀₀) of each restorative material was evaluated, and data were submitted to 1-way ANOVA and Tukey post hoc tests (α=.05).

RESULTS

The most predictable masking ability was seen with Zir+Pc regardless of the evaluation paste used. Nevertheless, under 1.5-mm thickness, Zir+Pc did not adequately mask Ti (ΔE₀₀>1.77). Most monolithic ceramics did not mask discolored substrates (PEEK or Ti, ΔE₀₀>1.77). The exception was HtZir, which presented acceptable masking ability over PEEK at 2.5-mm thickness with both evaluation pastes (ΔE₀₀<1.77). Regardless of the restorative material thickness, Zir+Pc showed the lowest (P<.05) TP₀₀ values (TP₀₀=3.45 at 1.5-mm thickness; TP₀₀=2.00 at 2.5-mm thickness), and HtLD presented the highest (P<.05, TP₀₀=23.50 at 1.5-mm thickness; TP₀₀=13.36 at 2.5-mm thickness). HtZir showed similar TP₀₀ to MtLD at 1.5-mm thickness and similar TP₀₀ to Zir+Pc when used at 2.5-mm thickness (P>.05).

CONCLUSIONS

Monolithic ceramics should be used with caution over discolored implant abutments. Bilayer systems (Zir+Pc) were the most predictable approach to adequately masking discolored substrates such as PEEK or Ti. An increased restoration thickness provided higher masking ability for all restorative materials tested.

Laboratory Fracture Resilience of Hybrid Abutments Used in Oral Rehabilitation: A Systematic Review

When implants are required in prosthodontics treatment, one of the most important decisions is the choice of the final crown and the type of connection to the implant through the abutment. Hybrid abutments are becoming a primary choice. They are projected and produced with materials whose properties guarantee the required mechanical features (including resistance) and take advantage of the hybrid abutment crown retention between screw and cement. However, a review of the mechanical resistance of the different abutment types and associated materials is still lacking. This review aimed to study the in vitro mechanical efficiency of the hybrid abutments used in oral rehabilitation. Methods: A systematic review was conducted using the PubMed, B-on, and Google Scholar databases according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Results: 75 articles were identified from all databases, and 33 were selected after abstract screening. Thus, 21 studies were included in the review after full-text reading. Among the materials used for crowns, lithium disilicate was, aesthetically, the primary choice for its aesthetic and moderate strength. On the other hand, zirconia showed the best fracture resistance. Regarding the different kinds of abutments, there is still some lack of knowledge about the best design. Conclusions: Within the limitations of this systematic review, we can conclude that hybrid pillars are an excellent choice for oral rehabilitation through implants, showing improved resistance when including materials such as zirconia and lithium disilicate.

Effect of Different Customized Abutment Types on Stress Distribution in Implant-Supported Single Crown: A 3D Finite Element Analysis

PURPOSE

The purpose was to investigate stress distribution among 4 different customized abutment types: titanium abutment (Ti), titanium hybrid-abutment-crown (Ti-Hybrid), zirconia abutment with titanium base (Zir-TiBase), and zirconia hybrid-abutment-crown with titanium base (Zir-Hybrid-TiBase).

MATERIALS AND METHODS

To achieve this purpose, 4 types of abutment configurations were simulated. A static load of 200 N (vertical) and 100 N (oblique) were applied to the models. The volume average, maximum, and stress distribution of von Mises stress, including percentage difference, were analyzed with three-dimensional finite element analysis.

RESULTS

According to the volume average von Mises stress, the Ti and Zir-TiBase comparison group showed that the Zir-TiBase group dominantly generated the higher value at Ti-base (22.57 MPa) and screw (17.68 MPa). To evaluate the effect of the hybrid-abutment-crown on volume average von Mises stress by comparing the Ti-Hybrid and Zir-Hybrid-TiBase groups, it was revealed that the combination of abutment and crown in the Ti-Hybrid group generated the worst stress concentration at the screw (12.42 MPa), while in the Zir-Hybrid-TiBase group presented stress concentration at the implant (8.90 MPa).

CONCLUSIONS

A titanium base improved stress distribution at implant in zirconia abutment with titanium base by absorbing stress itself. Customized titanium hybrid-abutment-crown and zirconia hybrid-abutment-crown with titanium base created concentrated stress at screw and implant; respectively. Both abutment types should be cautiously used and maintenanced regularly. This article is protected by copyright. All rights reserved.

Fatigue Loading Test on Screw-Retained Lithium Disilicate Crowns Adhesively Cemented on Titanium Abutment

The aim of this study was to assess the mechanical behavior and the microleakage of crown abutments made of lithium disilicate (LDS), adhesively bonded to preconditioned titanium bonding base under dynamic loading considering the type of teeth incisors, premolars, and molars. Thirty-three monolithic LDS implant supra-structures, representing a copy of natural tooth morphology (central incisor, second premolar, or first molar) were fabricated and bonded to titanium bases, screw-retained on the implant, and subjected to dynamic loading of 250,000 loading cycles at 2 Hz. After mechanical cycling, specimens were immersed in 5% methylene blue solution for 24 h at 37 °C. Microleakage was evaluated under magnification. The presence or absence of the following parameters were also evaluated: abutment screw deformation, abutment deformation, crack or craze line on the ceramic structure, adhesive failure between titanium base and ceramic superstructure, failures in ceramic superstructure or titanium base, and remaining cement around titanium base and ceramic superstructure. Considering the type of teeth, there are eight defects in relation to the group of central incisors, whereas the group of first molars accounts for seven defects. The second premolar is the worst performer with eleven defects. Significant accumulation of dye was registered in all teeth groups, i.e., grade 2 (staining around hexagonal area of the connection), according to the applied scale. Failure of hybrid abutments could be related to the correct seal between the titanium base and the ceramic restorations. The type of teeth could also be related to the presence of failures.

Fatigue Resistance of Cast-on Implant Abutment Fabricated with Three Different Alloys

OBJECTIVES

 This study aimed to evaluate fatigue resistance of cast-on implant abutment using three alloys.

MATERIALS AND METHODS

 Forty specimens of implant-supported crowns were prepared; Group 1 (TA) stock titanium abutments, Group 2 (GS) abutment cast with 40% gold alloy, Group 3 (GP) abutment cast with palladium alloy, and Group 4 (CN) abutment cast with nickel-chromium alloy. Specimens were cyclic loaded at 20 Hz, starting from 200 N (5,000 cycles), followed by stepwise loading of 400, 600, 800, 1,000, 1,200, 1,400, 1,600, and 1,800 N (30,000 cycles/step). Specimens were loaded until failure or reached 245,000 cycles.

STATISTICAL ANALYSIS

 The withstand cycles were analyzed using one-way analysis of variance and Weibull survival analysis. Fracture surfaces were examined using scanning electron microscopy.

RESULTS

 The results of withstand cycles were TA (189,883 ± 22,734), GS (195,028 ± 22,371), GP (187,662 ± 22,555), and CN (200,350 ± 30,851). The statistical analysis showed no significant difference between the groups (p = 0.673).

CONCLUSION

 Although CN has higher Weibull characteristic strength which means greater durability, its lower Weibull modulus demonstrated less structural reliability. Consistent failures at implant fixture level were also found in CN group.

Enhancing the esthetics of a maxillary central implant crown with a hybrid-abutment: A case report

Reducing the fabrication time and costs involved in classical methods of implant crown production are goals being constantly pursued. Consequently, computer-aided design and computer-aided manufacturing technologies have evolved considerably, offering improved and predictable outcomes in terms of esthetics and function. The aim of this case report is to demonstrate how hybrid-abutments can provide optimum esthetics and biomechanical foundations. A 57-year-old woman had a non-restorable tooth #8, which was indicated for extraction and immediate implant placement. Lithium disilicate (LD) crowns were used to restore the adjacent teeth #7, 9, and 10. A zirconia abutment was used to block the gray color of the titanium base. The zirconia abutment finish line was designed to be placed 1-mm apical to the free marginal gingiva of the adjacent tooth, and an LD implant crown was cemented on the hybrid-abutment. The technique demonstrated promising results, and after more than 18 months of follow-up following the implant placement, the surrounding soft tissue was well adapted around the implant crown. The hybrid-abutment enhanced the esthetics of the definitive restoration as well as saved time and cost by elimination of the casting step.

Investigation of the Type of Angled Abutment for Anterior Maxillary Implants: A Finite Element Analysis

PURPOSE

The optimal abutment material and design for an angled implant-abutment connection in the esthetic zone is unclear. The purpose of this finite element analysis (FEA) study was to compare different abutment models by evaluating the stress values in the implant components and strain values on the simulated bone around an anterior maxillary implant with different angled abutment models and loading conditions.

MATERIALS AND METHODS

One Ø3.5×12-mm implant was placed in 3D FEA models representing the anterior left lateral segment of the maxilla. Three different contemporary implant models were created with 17° or 25° angled abutments (Ti base abutment, zirconia abutment, and titanium abutment) and 3D-modeled. The implant abutment model was an angled Ti base abutment (TIB), an angled zirconia abutment (ZIR), or an angled titanium abutment (TIT). Vertical and oblique loads of 100 N for the central incisors were applied as boundary conditions to the cingulum area and incisal area in a nonlinear FEA.

RESULTS

The TIB model resulted in reduced stress conditions. According to the von Mises stresses occurring on the screw, abutment, crown, and implant, especially under oblique loads, the TIB model was exposed to less stress than the ZIR or TIT models. Strain values in simulated cortical and trabecular bones were obtained lower in the TIB model.

CONCLUSIONS

When a standard implant was placed in the esthetic zone at an increased angle, the implants, abutments, and screws had more unfavorable stress levels; therefore, using a Ti-base abutment may reduce stress. The amount of contact surface of the implant with the simulated cortical bone is also an important factor affecting stress and strain.

Titanium Base Abutments in Implant Prosthodontics: A Literature Review

Implant abutments are essential components in restoring dental implants. Titanium base abutments were introduced to overcome issues related to existing abutments, such as the unesthetic appearance of titanium abutments and the low fracture strength of ceramic abutments. This study aimed to comprehensively review studies addressing the mechanical and clinical behaviors of titanium base abutments. A search was performed on PubMed/MEDLINE, Web of Science, Google Scholar, and Scopus databases to find articles that were published in English until December 2020 and that addressed the review purpose. A total of 33 articles fulfilled the inclusion criteria and were included for data extraction and review. In vitro studies showed that titanium base abutments had high fracture strength, adequate retention values, particularly with resin cement, and good marginal and internal fit. Although the clinical assessment of titanium base abutments was limited, they showed comparable performance with conventional abutments in short-term evaluation, especially in the anterior and premolar areas. Titanium base abutments can be considered a feasible treatment option for restoring dental implants, but long-term clinical studies are required for a better assessment.

Screwmentable implant-supported prostheses: A systematic review

STATEMENT OF PROBLEM

Screwmentable prostheses were developed to combine the benefits of screw retention and cement retention. However, data are limited on the clinical performance of this type of prosthesis.

PURPOSE

The purpose of this systematic review was to collect scientific evidence on screwmentable prostheses and evaluate their long-term clinical behavior.

MATERIAL AND METHODS

An electronic search was conducted by 2 independent reviewers for articles published in scientific dental journals in English from 2004 to April 2020. The search strategy followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Inclusion criteria were scientific studies concerning the screwmentable type of prosthesis.

RESULTS

The search provided 494 records. Of these, 24 studies fulfilled the inclusion criteria and were included in the review. The included articles presented significant heterogeneity concerning the manufacturing process and the materials used. One randomized clinical trial, 2 prospective clinical studies, 14 in vitro studies, 3 protocol descriptions, 1 case series, and 3 case reports were included.

CONCLUSIONS

Based on the systematic search of the literature, it is concluded that the screwmentable prosthesis combines advantages of both cement-retained and screw-retained restorations, including passive fit, retrievability, excess cement control, tissue-friendly emergence profile, and improved esthetics. Nevertheless, data from well-designed clinical trials are limited, and further research is required to provide evidence on their long-term clinical behavior.

Fracture Resistance of Single-Unit Implant-Supported Crowns: Effects of Prosthetic Design and Restorative Material

PURPOSE

To evaluate the fracture resistance and fracture patterns of single implant-supported crowns with different prosthetic designs and materials.

MATERIALS AND METHODS

One hundred and forty-four identical crowns were fabricated from zirconia-reinforced lithium silicate (ZLS), leucite-based (LGC), and lithium disilicate (LDS) glass-ceramics, reinforced composite (RC), translucent zirconia (ZR), and ceramic-reinforced polyetheretherketone (P). These crowns were divided into 3 subgroups according to restoration design: cementable crowns on a prefabricated titanium abutment, cement-retained crown on a zirconia-titanium base abutment, and screw-cement crown (n = 8). After adhesive cementation, restorations were subjected to thermal-cycling and loaded until fracture. The fracture patterns were evaluated under a stereomicroscope. Statistical analysis was performed by using 2-way ANOVA/Bonferroni multiple comparison post hoc test (α = 0.05).

RESULTS

For each prosthetic design, ZR presented the highest fracture resistance (p ≤ 0.005). Other than the differences with ZLS and RC for screw-cement crowns (p > 0.05) and RC for crowns on zirconia-titanium base abutments (p > 0.05), LGC showed the lowest fracture resistance. P endured higher loads than LDS (p < 0.001), except for the crowns on zirconia-titanium base abutments (p > 0.05). Cementable crowns presented the highest fracture resistance (p < 0.001), other than LGC and LDS. The differences between LGC crowns (p > 0.05) or LDS crowns on prefabricated titanium and zirconia-titanium abutments were nonsignificant (p = 0.133). Fragmented crown fracture was predominant in most of the restorations. Screw and abutment fractures were observed in ZR screw-cement crowns, and all P crowns were separated from the abutments.

CONCLUSIONS

Restorative material and restoration design affect the fracture resistance and fracture pattern of implant-supported single-unit restorations. Clinicians may restore single-unit implants in premolar sites with the materials and prosthetic designs tested in the present study.

Mechanical behavior of nano-hybrid composite in comparison to lithium disilicate as posterior cement-retained implant-supported crowns restoring different abutments

OBJECTIVE

Resin-based materials are gaining popularity in implant dentistry due to their shock absorption capacity. Therefore, the aim of this study was to evaluate the fracture strength and failure mode of resilient materials for both crowns and abutments and compare them to the most widely used materials in different combinations after subjection to long-term fatigue loading.

METHODS

Forty-eight cement-retained implant-restorations were assembled on titanium implants. Identical custom-made CAD/CAM abutments were milled out of 3 different materials (n = 16); T: titanium, Z: zirconia and P: ceramic-reinforced PEEK. Each group was subdivided, according to the restorative crown material, into two subgroups (n = 8); C: nano-hybrid composite and L: Lithium disilicate. Specimens were subjected to dynamic load of 98 N for 1,200,000 cycles with integrated thermal cycling. The surviving specimens were subjected to quasi-static loading until failure. Shapiro-Wilk test was used to test for normality. One-way ANOVA followed by Tukey's post-hoc test was used to detect statistically significant differences between groups.

RESULTS

All specimens withstood 1,200,000 load cycles. The fracture strength values varied from a minimum of 1639 ± 205 N for group PL to a maximum of 2949 ± 478 N for group ZL.

SIGNIFICANCE

The abutment material influenced the fracture strength and failure mode of the restoration. A combination of zirconia abutments and nano-hybrid composite showed the most favorable mode of failure within the test groups. Therefore, this combination might be recommended as an alternative for restoring single implants in the posterior area.

Effect of fatigue loading and failure mode of different ceramic implant abutments

STATEMENT OF PROBLEM

Currently many options are available for restoring a dental implant, although the ideal implant abutment for withstanding the occlusal load and the restorative material for fulfilling the esthetic need remains unclear. Zirconia (Zir) abutments offer good esthetics, but concerns still remain regarding their fracture strength, complex fabrication, and higher cost as compared with those of titanium (Ti) base abutments offering lower cost, acceptable esthetics, and a straightforward procedure.

PURPOSE

The purpose of this in vitro study was to evaluate the fracture strength and failure mode of single-tooth Zir and Ti base implant abutments with fatigue loading.

MATERIAL AND METHODS

Forty restorations were included using 4 different types of abutment-restorations. Zir abutments with lithium disilicate crowns (ZirLd); titanium base abutments with custom Zir abutments and lithium disilicate crowns (TiZirLd); titanium base abutments with monolithic lithium disilicate abutment-crowns (TiLd); titanium base abutments with monolithic polymer-infiltrated ceramic abutment-crowns (TiEn). Specimens were subjected to a progressive cyclic loading by using a custom-made mastication simulator at a frequency of 1.4 Hz starting with a load of 88 N followed by stages of 170, 210, 250, and 290 N for a maximum of 20 000 cycles each or until fracture occurred. The number of cycles, maximum load, and failure modes were recorded. Statistical analysis was done by using the Mann-Whitney U test (α=.05).

RESULTS

Group TiEn showed a lower resistance to fatigue, with a mean ±standard deviation of 5054 ±123.3 cycles subjected to a mean force of 170 N. Groups ZirLd and TiLd resisted higher forces without fracture 13452.6 ±7094.3 cycles, and load of 178 ±16.9 N, followed by the TiLd group with a mean ±standard deviation of 25798.6 ±5498.7 cycles, and load of 202 ±16.9 N, while the TiZirLd group showed a mean of 48235.4 cycles subjected to a mean force of 258 N. The failure mode observed in the TiEn occurred only in the ceramic, whereas in the ZirLd and TiLd group, it was above the shoulder level of the Ti base abutment. Even though the TiZirLd group was able to withstand higher loads and a higher number of cycles, the failures were catastrophic and presented fractures of the titanium-base abutment and prosthetic screw.

CONCLUSIONS

The TiZirLd, ZirLd, and TiLd abutment-restorations have the potential to withstand the average physiological occlusal forces that occur in the anterior region. The group with the higher fatigue resistance was TiZirLd, although care should be taken with patients presenting parafunctional habits since the failure mode can be catastrophic. Also, polymer-infiltrated ceramic is not suitable for a Ti base abutment when subjected to oblique loading.

Mechanical stability and technical outcomes of monolithic CAD/CAM fabricated abutment-crowns supported by titanium bases: An in vitro study

OBJECTIVES

To evaluate mechanical stability (survival and complication rates) and bending moments of different all-ceramic monolithic restorations bonded to titanium bases (hybrid abutment-crowns) or to customized titanium abutments compared to porcelain-fused-to-metal crowns (PFM) after thermo-mechanical aging.

MATERIAL AND METHODS

Sixty conical connection implants (4.3 mm-diameter) were divided in five groups (n = 12): PFM using gold abutment (GAbut-PFM), lithium disilicate crown bonded to customized titanium abutment (TAbut+LDS), lithium disilicate abutment-crown bonded to titanium base (TiBase+LDS), zirconia abutment-crown bonded to titanium base (TiBase+ZR), polymer-infiltrated ceramic-network (PICN) abutment-crown bonded to titanium base (TiBase+PICN). Simultaneous thermocycling (5°-55°C) and chewing simulation (1,200,000-cycles, 49 N, 1.67 Hz) were applied. Catastrophic and non-catastrophic events were evaluated under light microscope, and survival and complication rates were calculated. Specimens that survived aging were loaded until failure and bending moments were calculated.

RESULTS

Survival rates after aging were 100% (TAbut+LDS, TiBase+LDS), 91.7% (GA-PFM), 66.7% (TiBase+ZR) and 58.3% (TiBase+PICN) and differed among the groups (p = .006). Non-catastrophic events as screw loosening (GA-PFM) and loss of retention or micro-/macro-movement (TiBase groups) were observed. Complication rates varied among the groups (p < .001). TiBase+PICN had lower bending moment than all the other groups (p < .001).

CONCLUSIONS

Hybrid abutment-crowns made of lithium disilicate can be an alternative to PFM-based restorations, although concerns regarding the bonded interface between the titanium base and abutment-crown can be raised. PICN and zirconia may not be recommended due to its inferior mechanical and bonding outcomes, respectively. Titanium customized abutment with bonded lithium disilicate crown appears to be the most stable combination.

Fatigue fracture resistance of titanium and chairside CAD-CAM zirconia implant abutments supporting zirconia crowns: An in vitro comparative and finite element analysis study

STATEMENT OF PROBLEM

Zirconia abutments with a titanium base are promising candidates to substitute for titanium abutments based on clinical studies reporting good short-term survival rates. However, information on the long-term performance of zirconia abutments supporting ceramic crowns is scarce.

PURPOSE

This in vitro comparative and finite element analysis study compared the fatigue life performance of ceramic computer-aided design and computer-aided manufacturing (CAD-CAM) monolithic restorations and zirconia abutments fabricated with a chairside workflow connected to a titanium interface versus titanium abutments.

MATERIAL AND METHODS

Twenty-two internal connection implants were divided into 2 groups, one with a zirconia abutment and monolithic ceramic zirconia crown (ZZ) and the other with a titanium abutment and zirconia crown (TiZ). They were subjected to a fatigue test to determine the fatigue limit and fatigue performance of each group as per International Organization for Standardization (ISO) 14801. Microstructural analysis of the fracture surfaces was conducted by using a scanning electron microscope (SEM). Simulations of the in vitro study were also conducted by means of finite element analysis (FEA) to assess the stress distribution over the different parts of the restoration.

RESULTS

The fatigue limit was 250 N for the TiZ group and 325 N for the ZZ group. In both groups, the screw was the part most susceptible to fatigue and was where the failure initiated. In the zirconia abutment models, the stress on the screw was reduced.

CONCLUSIONS

Chairside CAD-CAM zirconia abutments with a titanium base supporting zirconia crowns had higher fatigue fracture resistance compared with that of titanium abutments.

Mechanical Behavior and Fracture Loads of Screw-Retained and Cement-Retained Lithium Disilicate Implant-Supported Crowns

PURPOSE

To evaluate the fatigue survival, fracture loads and failure modes of monolithic lithium disilicate screw-retained crowns, attached to titanium insert, and cement-retained crowns.

MATERIALS AND METHODS

Internal tapered connection implants, embedded in acrylic resin at 30° inclination, were restored with lithium disilicate restorations, simulating a maxillary premolar (n = 20), with different designs: screw-retained titanium base abutment-crowns, and cement-retained crowns. The specimens were submitted to cyclic mechanical loading (1.2 × 10⁶ cycles with a load of 0-250 N at 2 Hz). Surviving specimens were subjected to single load to fracture in a universal testing machine and failure modes were determined with the aid of an optical microscope. Maximum load values were analyzed statistically using the t-test and differences in failure modes were analyzed using the chi-squared test (α = 0.05).

RESULTS

All specimens survived the cyclic mechanical loading. Fracture load was significantly higher for screw-retained crowns (821.69 ±196.71 N) than the cement-retained crowns (577.03 ± 137.75 N) (p = 0.005). Ceramic failure was the predominant mode, with no statistical difference between groups.

CONCLUSIONS

Screw-retained and cement-retained lithium disilicate crowns survived the cyclic mechanical loading. The use of titanium inserts to support a monolithic restoration enhances the fracture strength of the crown/abutment system.

Fracture strength of various titanium-based, CAD-CAM and PFM implant crowns

OBJECTIVE

CAD-CAM has dramatically advanced dental restorative procedures to include implant-supported crowns. The purpose of this study was to compare the fracture resistance following mechanical loading and thermocycling of various screw-retained and cement-retained ceramic and polymethylmethacrylate material combinations using the TiBase abutment compared to PFM implant-supported crowns.

OVERVIEW

Twelve implant restorations were fabricated for each of eight groups. Three groups were screw-retained and five groups were cement-retained implant restorations. The ceramic and polymethylmethacrylate restorations were fabricated on the TiBase abutment while the PFM restorations were fabricated on an UCLA abutment. Data were analyzed with a one way Analysis of Variance and Tukey's post-hoc test to evaluate the effect of abutment and crown type on fracture load (alpha = 0.05). A significant difference was found in the maximum fracture load between groups (P < 0.001).

CONCLUSIONS

The screw-retained implant restorations demonstrated higher fracture loads than their cement-retained counterparts. The TiBase abutment compared favorably to the UCLA abutment.

CLINICAL SIGNIFICANCE

The TiBase abutment is a titanium insert which combines the esthetics of a ceramic abutment with the mechanical properties of a titanium abutment and should be considered a viable clinical alternative to the conventional implant-supported PFM crown based on theses in vitro results and in context of in vivo studies. The lithium disilicate hybrid abutment/crown implant-supported restoration utilizing the TiBase abutment may be an ideal clinical choice due to simplicity, single appointment CAD-CAM, and esthetics.

Optimizing the esthetic outcome by using screw-retained implant abutment crowns: A 3-year clinical follow-up

This clinical report describes a ceramic complete-mouth rehabilitation with screw-retained implant abutment crowns, optimizing esthetics by combining the properties of ceramic materials. The abutments connected a titanium insert to a computer-aided design and computer-aided manufacturing (CAD-CAM) monolithic zirconia framework, offering improved esthetics and biologic response without negatively affecting the implant abutment interface. Lithium disilicate crowns were cemented extraorally on the abutments, resulting in a screw-retained restoration.

Resistance to Fracture of Zirconia Abutments with Different Angulations: Impact of Implant Platform Diameter

Objective  The aim of this study was to assess the impact of implant platform diameters on ultimate force to failure of zirconia abutments with different angulation.

Materials and Methods  Forty-two zirconia abutments with either 0 degree (ST) or 15-degree (AN) angulation were assembled on tapered internal connection titanium implants (Direct's Legacy; 13 mm Implant Direct, LLC, Las Vegas, United States) with a platform diameter of Ø3.0, Ø3.5, and Ø4.5 mm (14 per group). Zirconia crowns (Ceramill Zolid; Amann Girrbach GmbH) were fabricated and cemented using self-adhesive resin cement (MaxCem Elite, Kerr). The specimens were thermomechanically loaded (TCML= 6,000 cycles of 5 to 50°C for 2 minutes/cycle followed by cyclic loading 600,000 cycles) followed by static loading until fracture. The data of load (N) at which fracture occurred were statistically analyzed by using Kruskal–Wallis analysis of variance and Mann–Whitney U tests at 5% significance level.

Results  Higher load to fracture was reported for zirconia crowns in straight abutments groups and a platform of 4.5, 3.5, and 3 mm diameter was 438.2± 85.4, 345.5± 71.3, and 331.1± 59.1 N, respectively. However, the groups restored with zirconia crowns in angulated abutments groups and a platform of 4.5, 3.5, or 3 mm diameter showed a fracture load of 411.4 ± 49.8, 354.2 ± 52.5, and 302.8 ± 52.5 N, respectively.

Conclusion  Straight and angulated zirconia abutments presented similar load to fracture on 3 and 3.5 mm platform diameters yet being significantly less for 4.5 mm diameter.

Hybrid-abutment-restoration: effect of material type on torque maintenance and fracture resistance after thermal aging

Purpose

To evaluate the tightening torque maintenance with zirconia, lithium disilicate, and polyetheretherketone (PEEK) hybrid-abutment-crowns after thermal aging, in addition to assess the fracture resistance of hybrid-abutment-crowns fabricated with different materials.

Materials and methods

Thirty implants were restored with identical hybrid-abutment-crowns, resembling the maxillary first premolar, fabricated from zirconia (Zr), lithium disilicate (L2), or ceramic-reinforced PEEK (PE). The three groups (n = 10) were constructed utilizing a Ti-base. After bonding, each restoration was secured in its respective implant with a torque of 25 Ncm. All restorations were subjected to thermal aging for 7000 cycles. The loosening torque was assessed utilizing the digital torque meter. Each restoration was subjected to fracture testing and the mode of failure was determined.

Results

Zr group displayed the highest mean torque loss value (2.70 ± 0.59 Ncm) with the mean loosening torque value of 22.38 ± 0.68 Ncm. PE group displayed the lowest mean torque loss (2.55 ± 0.50 Ncm) with mean loosening torque value of 22.61 ± 0.59 Ncm. There was no significant difference between study groups regarding loosening torque (p = 0.68), torque loss (p = 0.80), and percentage of torque loss (p = 0.79). There was significant difference regarding the mean fracture load value between Zr and PE groups. However, there was no significant difference (p = 0.05) regarding mean fracture load value between L2 and PE groups.

Conclusion

The hybrid-abutment-crown material does not affect the torque maintenance after thermal aging. Based on fracture load, zirconia hybrid-abutment-crown can be used, while lithium disilicate and PEEK hybrid-abutment-crowns may cautiously serve in premolar region.

Survival Probability, Weibull Characteristics, Stress Distribution, and Fractographic Analysis of Polymer-Infiltrated Ceramic Network Restorations Cemented on a Chairside Titanium Base: An In Vitro and In Silico Study

Different techniques are available to manufacture polymer-infiltrated ceramic restorations cemented on a chairside titanium base. To compare the influence of these techniques in the mechanical response, 75 implant-supported crowns were divided in three groups: CME (crown cemented on a mesostructure), a two-piece prosthetic solution consisting of a crown and hybrid abutment; MC (monolithic crown), a one-piece prosthetic solution consisting of a crown; and MP (monolithic crown with perforation), a one-piece prosthetic solution consisting of a crown with a screw access hole. All specimens were stepwise fatigued (50 N in each 20,000 cycles until 1200 N and 350,000 cycles). The failed crowns were inspected under scanning electron microscopy. The finite element method was applied to analyze mechanical behavior under 300 N axial load. Log-Rank (p = 0.17) and Wilcoxon (p = 0.11) tests revealed similar survival probability at 300 and 900 N. Higher stress concentration was observed in the crowns’ emergence profiles. The MP and CME techniques showed similar survival and can be applied to manufacture an implant-supported crown. In all groups, the stress concentration associated with fractographic analysis suggests that the region of the emergence profile should always be evaluated due to the high prevalence of failures in this area.

In Vitro Comparison of Modes of Failures among Titanium and One- and Two-piece Zirconia Abutment under Static Load

Objectives  The objective was to assess modes of failures under static load (SL) among titanium (Ti) and one- and two-piece zirconia abutment (ZA) in vitro .

Materials and Methods  The Ti abutments were digitally scanned for the fabrication of the one- and two-piece zirconia abutment specimens. This was done to standardize the design of the one-piece abutment and make it the blueprint of the Ti abutment. Twenty-one implant abutments and 21 implant replicas were categorized into three groups as follows: group 1 (Titanium group), group 2 (one-piece ZA group), and group 3 (two-piece ZA group). A 250K-cycle, linear fatigue-load, reaching 10 to 210 Newton (N), was put on all specimens using an all-electric dynamic test instrument and the specimens were loaded until fracture.

Statistical Analysis  Assessment of mode of fracture among the groups was done visually. Significance was based below 0.05.

Results  Screw fracture ( n = 7) and abutment bending at the apical part ( n = 7) occurred in the Ti group. In the one-piece zirconia group, screw and abutment fractures occurred in seven and seven cases, respectively. In the two-piece zirconia group, screw fracture ( n = 7) above the Ti zirconia junction (transgingival segment) and abutment fracture ( n = 7) were determined as the failure modes.

Conclusion  In conclusion, all abutments underwent failures under SL in vitro ; and the mode of failure modes varied among the different abutment designs used.

Effect of Various Surface Treatments on Ti-Base Coping Retention

Clinical Relevance

Mechanical surface roughening of the titanium-abutment base is necessary to increase the pull-off bond strength of the lithium disilicate abutment material. Additional chemical surface treatment may further increase the bond strength, but the effects are product specific.

SUMMARY

Objective:

The titanium-cement interface of a Ti-Base implant crown must be able to resist intraoral pull-off forces. The purpose of this study was to evaluate the effect of mechanical and chemical surface treatments of a titanium-abutment base (Ti-Base, Dentsply/Sirona) on the pull-off bond strength of a lithium disilicate abutment coping.

Methods and Materials:

Ti-Bases were divided into nine groups of 10 copings each that varied in both mechanical surface treatment (none; Al2O3 air abrasion; CoJet silicoating, 3M ESPE) and chemical treatments (none; Monobond Plus, Ivoclar Vivadent; Alloy Primer, Kuraray). Lithium disilicate abutment copings (IPS e.max CAD, Ivoclar Vivadent) were designed and milled. After crystallization, the copings were cemented onto the Ti-Bases with a resin cement (MultiLink Hybrid-Abutment Cement, Ivoclar Vivadent) according to the manufacturer's recommendations. The copings were torqued to a mounted implant, and the access channel was sealed with composite. After 24-hour storage and 2000 thermal-cycles in distilled water, the copings were subjected to a removal force parallel to the long axis of the interface until fracture. Data were analyzed with multiple one-way analyses of variance and Tukey post hoc tests (α=0.05).

Results:

Significant differences were found between groups based on type of surface treatment (p&lt;0.05).

Conclusions:

Chemical surface treatment with Monobond Plus and mechanical surface treatment with CoJet silicoating or Al2O3 air abrasion resulted in the greatest pull-off bond strength. Alloy Primer did not provide a statistically significant increased pull-off bond strength when the surfaces were mechanically treated with Al2O3 air abrasion or CoJet silicoating. The lack of any mechanical surface treatment resulted in the lowest pull-off bond strength regardless of the type of chemical surface treatment.

Monolithic Zirconia FPD on Modified Titanium Bonding Bases in Limited Interocclusal Distance: A Case Report

A 62-year-old male patient sought treatment for missing maxillary teeth. A diagnostic cast demonstrated that the interocclusal distance was insufficient. A 5-unit screw-retained implant-supported fixed partial denture (FPD) was used to restore missing maxillary teeth. The restoration of multiple missing teeth using an implant-supported FPD is challenging when the interocclusal distance is limited due to lack of retention and inadequate esthetics. In this case, a hexagonal, screw-retained, and subgingivally located titanium-based zirconia implant-supported FPD with a conical abutment base was used for restoration to overcome the limited interocclusal distance. This implant-supported FPD, consisting of CAD/CAM-designed monolithic zirconia cemented to a titanium bonding base in the laboratory, is expected to facilitate predictable retention and adequate esthetics as well as provide ease of retrieval.

Comparative evaluation of the wear resistance of two different implant abutment materials after cyclic loading – An in vitro study

Purpose:

To comparatively evaluate the wear resistance of two different implant abutment materials with titanium implants after cyclic loading.

Methodology:

Two groups utilizing 20 titanium implants secured in resin blocks, in which 10 titanium implants are connected with titanium abutments (Group I, n = 10) and the other 10 titanium implants are connected with Polyether ether Ketone (PEEK) abutments (Group II, n = 10). Abutments are cyclically loaded for 550,000 cycles. Surface profilometry, scanning electron microscopy (SEM), and energy-dispersive X-ray spectrometry (EDS) are carried out for all the abutment in both Group I and Group II before and after cyclic loading. The abutment surface at the implant-abutment interface is analyzed for wear.

Results:

On comparison using independent “t”-test, it was found that the mean difference values of pre- and post-cyclic loading surface roughness (Ra value) of Group I (premachined titanium straight abutments) (−0.073 μm) was lower than the Group II test samples (premachined PEEK straight abutments) (−0.0004 μm), and this was found to be statistically insignificant (P = 0.272). SEM micrographs and EDS results also corroborate with the results of surface profilometry.

Conclusion:

The new concept in this study is Group II (PEEK abutments) are connected with titanium implants, to prove its compatibility and aesthetics. Within the limitations of the study, the surface roughness values before and after cyclic loading of two different abutment materials revealed that the wear resistance of titanium abutments is more than PEEK abutments, but the difference was found to be statistically insignificant.

Effect of Implant Platform Connection and Abutment Material on Removal Torque and Implant Hexagon Plastic Deformation

Objectives  The aim of this study was to evaluate the plastic deformation of the hexagonal connection, and the removal torque of the implant-abutment joint of two dental implants combined with internal or external hexagonal connection implants after mechanical cycling.

Materials and Methods  Twenty-four dental implants were used in the study. Half of the implants had internal hexagonal connections (IH; Titamax II Plus) and the other half had external hexagonal connections (EH; Titamax Ti Ex). Four groups of two types of dental implant abutments (titanium: Ti, UCLA II Plus and zirconia: Zr, fabricated by CAD/CAM; n = 6) were investigated. The abutments received a metallic crown and the settings were submitted to mechanical cycling (MC; 10 ⁶ cycles, axial load, 120N). The connection surface area was measured by scanning electron microscope (SEM) images. The removal torque was evaluated and the plastic deformation of the hexagonal surface of the implant was measured by comparing the images before and after MC.

Statistical Analysis  Paired- t test was used to analyze the data statistically at a significance level of α = 0.05.

Results  The torque values decreased for all groups after MC, and the hexagonal surface area decreased due to plastic deformation for IH and EH associated with Zr abutments.

Conclusions  Zirconia abutments showed the worst plastic deformation of the implant connection surface and torque loosening when associated with IH implant.

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.

Fracture resistance and the mode of failure produced in metal-free crowns cemented onto zirconia abutments in dental implants

The purpose of the investigation was to analyze fracture resistance and mode of failure of zirconium oxide (zirconia) abutments placed on dental implants bearing crowns of different esthetic materials: zirconia, lithium disilicate (LDS), and nano-ceramic resin, for replacing single teeth in the anterior sector. Eighty implant-abutment-crown units were divided into four groups: Group T-MC (control): 20 metal-ceramic crowns cemented onto titanium abutments; Group Z-Z: 20 zirconia crowns on zirconia abutments; Group Z-LD: 20 lithium disilicate crowns on zirconia abutments; and Group Z-NCR: 20 nano-ceramic resin crowns on zirconia abutments. Specimens underwent a fatiguing process (dynamic loading and thermocycling), followed by static loading to evaluate mechanical fracture resistance, and the mode of failure produced. Mean fracture resistance values were: Control Group T-MC, 575.85±120.01 N; Group Z-Z 459.64±66.52 N; Group Z-LD, 531.77±34.10 N; and Group Z-NCR, 587.05±59.27 N. In Group T-MC, fracture occurred in the prosthetic fixing screw in 100% of specimens. In Group Z-Z, 80% of fractures occurred in the fixing screw, 15% in the abutment, and 5% in the abutment and crown. In Group Z-LD, 60% of fractures were produced in the fixing screw and 40% in the abutment. In Group Z-NCR, 70% of fractures were produced in the fixing screw and 30% in the abutment. All the abutments and crowns analyzed have the potential to withstand the physiological occlusal forces to which they would be subject in the anterior region. Lithium disilicate and nano-ceramic resin crowns cemented onto zirconia abutments are a good restoration alternative for single implants in the anterior sector.

Fracture resistance of different implant supported ceramic abutment/crown systems

Purpose

The purpose of this study was to investigate the fracture resistance and failure modes of different non-aged and aged abutment/crown systems.

Materials and methods

One hundred dental implants (diameter 4.3 mm and length 11.5 mm) were restored with five abutment/crown systems: G1: a lithium disilicate hybrid abutment crown, G2: a lithium disilicate crown cemented on a lithium disilicate hybrid abutment, G3: a lithium disilicate crown cemented on a zirconia hybrid abutment, G4: a direct veneer porcelain layering on a zirconia hybrid abutment, and G5: a lithium disilicate crown cemented on a prefabricated all-zirconia abutment. Each group was divided into two groups (n=10) as control (non-aged) and thermomechanically aged. The fracture resistance test was performed. Failures during the aging process and after the fracture resistance test were examined.

Results

Both of the factors (restoration type and aging) affected the fracture resistance values and there was not an interaction between the factors (p>0.05). When fracture resistance values were compared regardless of aging, the highest values were observed in G3 and G4, respectively (p<0.05). When comparing the fracture resistance values, regardless of the restoration type, the aged group showed a significant lower fracture resistance value than control group (p<0.05).

Conclusion

A titanium base enhanced the fracture resistance of zirconia abutments. Thermomechanical aging decreased the fracture resistance of the tested ceramic abutment/crown systems. The major failure mode was the abutment fracture.