Reliability and Failure Modes of a Hybrid Ceramic Abutment Prototype

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.

Comparative Evaluation of the Effect of Implant Crown Materials on Implant Components and Bone Stress Distribution: A 3D Finite Element Analysis

Background

Choosing implant crown materials for restoration remains challenging in clinical practice. This study assesses the impact of all-ceramic restoration instead of porcelain-fused-to-metal (PFM) restoration on the stress distribution within implant components and the surrounding bone.

Methods

Four 3D models of a mandibular second premolar were meticulously prepared. The study groups comprised zirconia, lithium disilicate, and zirconia lithium silicate monolithic ceramic crowns cemented onto a zirconia hybrid abutment. A PFM crown cemented onto a cementable abutment was chosen as the control group. A total vertical load of 583 N was applied to the occlusal contact areas. Stress distribution within the crown and implant components was analyzed using von Mises stress analysis. Principal stress analyses were employed to assess stress distribution in the peripheral bone.

Results

The PFM model exhibited the highest von Mises stress values for both the implant (428.7 MPa) and crown (79.7 MPa) compared to the other models. The all-ceramic models displayed the highest maximum von Mises stress within the abutment, approximately 335 MPa, compared to the PFM model. von Mises stresses of the abutment and implant in the all-ceramic models were 69% higher and 20% lower, respectively, than those in the PFM model. Screw stresses were relatively consistent across all groups. Principal stresses in spongy bone and minimum principal stress in cortical bone were consistent across all models.

Conclusions

All-ceramic restoration with a hybrid abutment, as opposed to traditional PFM restoration with a cementable abutment, does not adversely affect the implant and abutment screw and reduces crown stresses. Stresses within hybrid abutments were notably higher than those within cementable abutments. Spongy bone stresses remained unaffected by the type of crown or abutment.

Clinical Performance of CAD/CAM Monolithic Lithium Disilicate Implant-Supported Single Crowns Using Solid or Predrilled Blocks in a Fully Digital Workflow: A Retrospective Cohort Study With Up To 33 Months of Follow Up

PURPOSE

To assess the clinical performance of CAD/CAM monolithic implant-supported restorations manufactured using a fully digital workflow and two different types of ceramic blocks.

MATERIALS AND METHODS

One hundred and one patients received single-unit implant-supported restorations at a University predoctoral clinic. All restorations were designed and fabricated using either a predrilled LS₂ block (group P, n = 59) or a conventional solid LS₂ block with an occlusal opening drilled manually prior to crystallization (group M, n = 42). The mean follow-up time after restoration delivery was 18.4 ± 4.8 months (range 12 to 33 months). Patients with less than a 12-month follow-up were excluded. Electronic health records were reviewed to identify number and type of complications during the follow-up time. Clinical outcomes were classified as success, survival, and failure of the restoration. Chi-square tests were used to identify differences in success and survival rates between the groups. Nonparametric Mann-Whitney U tests were used to identify differences in the number of major and minor complications as well as the total number of complications that were observed among groups.

RESULTS

Overall success and survival rates were 80.2% and 97%, respectively. Seventy one restorations (70.3%) were complication-free. There were no significant differences between the groups with regards to the number of complications or success and survival rates.

CONCLUSIONS

Single-unit CAD/CAM monolithic implant-supported restorations that are fabricated in a fully digital workflow present relatively high complication rates and moderate short-term clinical outcomes. Clinical studies with longer follow-up times are needed to evaluate long-term outcomes of these restorations.

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.

Impact of Coping Veneering Techniques on the Survival of Implant-Supported Zirconia-Based-Crowns Cemented to Hybrid-Abutments: An-In-Vitro Study

The objective of this study is to investigate the influence of veneering technique (hand-layering vs. milling) on the fracture resistance of bi-layer implant-supported zirconia-based hybrid-abutment crowns. Mandibular molar copings were anatomically designed and milled. Copings were then veneered by hand-layering (HL) (n = 20) and milling using the Cad-On technique (LD) (n = 20). Crowns were cemented to zirconia hybrid-abutments. Ten samples of each group acted as a control while the remaining ten samples were subjected to fatigue in a chewing simulator. Crowns were loaded between 50 and 100 N for 1.2 million cycles under simultaneous temperature fluctuation between 5 and 55 °C. Crowns were then subjected to static load a to fracture test. Data were statistically analysed using the one-way ANOVA. Randomly selected crowns from each group were observed under scanning electron microscopy to view fractured surfaces. Study results indicate that during fatigue, LD crowns had a 100% survival rate; while HL crowns had a 50% failure rate. Fracture resistance of LD crowns was statistically significantly higher than that of HL crowns at the baseline and after fatigue (p ≤ 0.05). However, fatigue did not cause a statistically significant reduction in fracture resistance in both LD and HL groups (p > 0.05). Copings fractured in the LD crowns only and the fracture path was different in both LD and HL groups. According to the results, it was concluded that milled veneer implant-supported hybrid-abutment crowns exhibit significantly higher fracture resistance, and better withstand clinical masticatory loads in the posterior region compared to the hand-layered technique. Also, fatigue application and artificial aging caused no significant strength reduction in both techniques. Clinical significance: Different veneering techniques and materials (hand-layering or milling) act differently to clinical forces and environment and may be prone to early chipping during service. Therefore, practitioners are urged to consider the appropriate veneering protocol for posterior implant-supported hybrid-abutment restorations.

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.

Load-Bearing Capacity of Zirconia Crowns Screwed to Multi-Unit Abutments with and without a Titanium Base: An In Vitro Pilot Study

The static and dynamic load-bearing capacities and failure modes of zirconia crowns screwed to multi-unit abutments (MUAs) with and without a titanium base (T-base) were determined. Thirty-six monolithic zirconia crowns screwed to straight MUAs torqued to laboratory analogs (30 Ncm) were assigned to two groups (n = 18). In group A, the zirconia crowns were screwed directly to the MUAs; in group B, the zirconia crowns were cemented to the T-base and screwed to the MUAs. All specimens were aged in 100% humidity (37 °C) for one month and subjected to thermocycling (20,000 cycles). Afterwards, the specimens underwent static and dynamic loading tests following ISO 14801. The failure modes were evaluated by stereomicroscopy (20×). There was an unequivocally similar trend in the S-N plots of both specimen groups. The load at which the specimens survived 5,000,000 cycles was 250 N for both groups. Group A failed mainly within the metal, and zirconia failure occurred only at a high loading force. Group B exhibited failure within the metal mostly in conjunction with adhesive failure between the zirconia and T-base. Zirconia restoration screwed directly to an MUA is a viable option, but further studies with larger sample sizes are warranted.

Fracture resistance of implant- supported monolithic crowns cemented to zirconia hybrid-abutments: zirconia-based crowns vs. lithium disilicate crowns

PURPOSE

The aim of this in vitro study was to investigate the fracture resistance under chewing simulation of implant-supported posterior restorations (crowns cemented to hybrid-abutments) made of different all-ceramic materials.

MATERIALS AND METHODS

Monolithic zirconia (MZr) and monolithic lithium disilicate (MLD) crowns for mandibular first molar were fabricated using computer-aided design/computer-aided manufacturing technology and then cemented to zirconia hybrid-abutments (Ti-based). Each group was divided into two subgroups (n=10): (A) control group, crowns were subjected to single load to fracture; (B) test group, crowns underwent chewing simulation using multiple loads for 1.2 million cycles at 1.2 Hz with simultaneous thermocycling between 5℃ and 55℃. Data was statistically analyzed with one-way ANOVA and a Post-Hoc test.

RESULTS

All tested crowns survived chewing simulation resulting in 100% survival rate. However, wear facets were observed on all the crowns at the occlusal contact point. Fracture load of monolithic lithium disilicate crowns was statistically significantly lower than that of monolithic zirconia crowns. Also, fracture load was significantly reduced in both of the all-ceramic materials after exposure to chewing simulation and thermocycling. Crowns of all test groups exhibited cohesive fracture within the monolithic crown structure only, and no abutment fractures or screw loosening were observed.

CONCLUSION

When supported by implants, monolithic zirconia restorations cemented to hybrid abutments withstand masticatory forces. Also, fatigue loading accompanied by simultaneous thermocycling significantly reduces the strength of both of the all-ceramic materials. Moreover, further research is needed to define potentials, limits, and long-term serviceability of the materials and hybrid abutments.