Fracture analysis of randomized implant-supported fixed dental prostheses

Implant-supported prosthesis under progressive loading protocol stimulates alveolar bone growth in patients with severe alveolar bone atrophy. Retrospective case series

Introduction

The jaw with severe bone atrophy is a difficult challenge when rehabilitating with dental implants. To be able to place dental implants in the most severe cases and to achieve an increase in bone volume by means of the tension transmitted by the load is a novelty. This work provides data on the alveolar bone changes in a severely atrophic mandible that has been treated with implant supported prosthesis under progressive loading protocol.

Material and methods

This study reported on 3 patients with completely edentulous mandible. In all cases, implants were inserted in the anterior region of the mandible and progressive loading was carried out with an increase in the distal cantilever. The length of the cantilever extension was adapted to growth of the residual alveolar bone at the mandible body. The increase in bone height was controlled in the area of implant placement as well as in the area distal to the implants (1 cm behind the last implant).

Results

This case series described 3 patients where 13 implants were placed. The patients were followed for 17, 19 and 20 years after implants insertion. The mean mandibular residual height of the alveolar bone was 7.8 ± 2.7 mm at the implant site. The mean mandibular body height at 1.0 cm distal to the last implant was 7.0 ± 3.9 mm in the third quadrant and 8.1 ± 4.4 mm in the fourth quadrant. The mean height at the last follow-up was 11.0 ± 3.2 mm (±3.2) in the third quadrant and 11.20 ± 4.4 mm in the fourth quadrant.

Conclusions

Implant-supported prosthesis and progressive loading have resulted in vertical bone growth in a series of patients with extreme atrophy of the mandible. The long-term follow-up indicated that bone growth is confined to the dental implants but has been extended to distant regions resulting in the thickening of the mandibular body and the creation of the absent mandibular canal.

Zirconia-ceramic versus metal-ceramic implant-supported multiunit fixed dental prostheses: A systematic review and meta-analysis

Implant-supported prostheses could serve as a reliable restorative option for partial edentulism. Various restorative materials have been utilized in fabricating these prostheses, impacting both esthetics and peri-implant health. The present systematic review aimed to assess the survival rate and mechanical complications of zirconia ceramic compared to metal-ceramic implant-supported multiunit fixed dental prostheses (FDPs). We conducted searches in online databases such as MEDLINE (PubMed), Scopus, and Cochrane up until December 2022. A risk-of-bias assessment was done for all the included studies. Data extraction was performed based on the following parameters: author, year, study design, number of implants, abutment material, age range, observation period, incidence of mechanical complications, and survival rate. This systematic review included six studies (four randomized controlled trials and two retrospective studies). The meta-analysis significantly favored metal-ceramic restorations regarding mechanical complications with a risk ratio (RR) value of 1.64 and P = 0.001. Meta-analysis showed no difference in metal-ceramic FDPs in prostheses survival rate (P = 0.63; RR: 1.27, 95% confidence interval: 0.52-3.37; heterogeneity: P = 0.65; I2: 0%). While metal-ceramic multiunit implant-supported prostheses exhibited fewer mechanical complications compared to zirconia-ceramic prostheses, there was no significant difference in terms of prosthesis survival rate between the two. Hence, both treatments appear to be viable options for long-term implant-supported prostheses.

Proof testing to improve the reliability and lifetime of ceramic dental prostheses

OBJECTIVES

Ceramic dental prostheses exhibit increasing failure rates with service time. In particular, veneered crowns and bridges are susceptible to chipping and other fracture modes of failure. The purpose of this manuscript is to introduce a computational methodology and associated software that can predict the time-dependent probability of failure for ceramic prostheses and subsequently design proof test protocols to significantly enhance their reliabilities and lifetimes.

METHODS

Transient reliability and corresponding proof testing theories are introduced. These theories are coded in the Ceramic Analysis and Reliability Evaluation of Structures (CARES/Life) code. This software will be used to demonstrate the predictive capability of the theory as well as its use in designing proof test protocols to significantly improve the reliability (survival probability) and lifetime for dental prostheses. A three-unit fixed dental prosthesis (FDP) with zirconia core (ZirCAD) and veneering ceramic (ZirPress) are used to compare the predicted probabilities of failure to general clinical results. In addition, the capability to use proof testing to significantly improve the performance (reliability and lifetime) for this restoration is demonstrated.

RESULTS

The probability of failure, Pf, after five years without proof testing is predicted to be 0.337. This compares to clinical studies showing the failure rate to be between 0.2 and 0.23 after 5 years. After 10 years, reference 18 found the clinical failure rate for similar bridges (but not the same) to be up to 0.28 compared to the predicted Pf of 0.38. The difference may be due to the analysis applying the load at an inclination of 75° which is more critical than vertical loading. In addition, clinical studies often report a simple survival rate instead of using Kaplan-Meier analysis to properly account for late enrollees. Therefore, true clinical failure rates may be higher than reported and may more closely match the predictions of this manuscript. The effectiveness of proof testing increases with selecting materials less susceptible to slow crack growth (higher SCG exponent, N). For example, proof testing the ZirPress glass-veneered bridges with N = 43.4 analyzed in this manuscript at 400 N bite force for 1 s which induces a failure rate during proof testing of 0.31, reduces the Pf of bridges not proof tested from 0.45 to an attenuated-proof-tested probability of failure Pfa of 0.21 after 20 years of usage. If another material is selected with improved resistance to SCG of N = 60 and the same loading conditions, the failure rate for the proof tested bridges after 20 years of service drops to 2 in 10,000 from 2.4 in 100 had they been not proof tested. The failure rate during proof testing for this material would be 5.1 in 100. Proof testing a material with absolutely no susceptibility to SCG at the same service load (in this case 285 N, not even the 400 N load used above) results in 0 % failure rate and is of course independent of time.

SIGNIFICANCE

The transient reliability and proof test theory presented in this paper and associated computational software CARES/Life were successful in predicting the performance of ceramic dental restorations when compared to clinical data. Well-designed proof test protocols combined with proper material selection can significantly enhance the reliabilities and lifetimes of ceramic prostheses. This proof test capability can be a translational technology if properly applied to dental restorations.

Finite Element Analysis of an Implant-Supported FDP with Different Connector Heights

All-ceramic fixed dental prostheses (FDPs) tend to fracture in the connector areas, due to the concentration of tensile stresses. This study aimed to evaluate the role of connector height on the stress distribution of a posterior three-unit implant-supported all-ceramic FDP using finite element analysis (FEA). Two titanium dental implants, their abutments, screws, and a three-unit all-ceramic FDP were scanned using a micro-CT scanner. Three 3D models with altered distal connector heights (3, 4, and 5 mm) were generated and analyzed on ABAQUS FEA software. The maximum principal stress values in MPa observed for each model with different connector heights and their respective locations (MA = mesial abutment; DA = distal abutment; F = framework; V = veneer) were: 3 mm—219 (MA), 88 (DA), 11 (F), 16 (V); 4 mm—194 (MA), 82 (DA), 8 (F), 18 (V); 5 mm—194 (MA), 80 (DA), 8 (F), and 18 (V). All the assembled models demonstrated the peak stresses at the neck area on the mesial abutments. The connector height had a significant influence on the stress distribution of the prosthesis. The models with higher distal connectors (4 and 5 mm) had a lower and more uniform distribution of maximum principal stresses (except for the veneer layer) when compared with the model with the smallest distal connector.

Fracture strength of monolithic and glass-soldered ceramic sub-components of 5-unit fixed dental prosthesis

PURPOSE

Zirconium dioxide ceramic has been successfully introduced as a framework material for fixed dental prostheses. To reduce manufacturing constraints, joining of sub-components could be a promising approach to increase the mechanical performance of long-span fixed dental prostheses. In this experimental study, the biomechanical behavior of monolithic and soldered framework specimens for fixed dental prostheses made of Y-TZP was investigated.

MATERIALS AND METHODS

Framework specimens (n  =  80) of 5-unit fixed dental prostheses made of Y-TZP were prepared and divided into 10 equal groups. The specimens were monolithic or composed of sub-components, which were joined using a silicate-based glass solder. Thereby, three joint geometries (diagonal, vertical with an occlusal cap, and dental attachment-based) were investigated. Moreover, the groups differed based on the mechanical test (static vs. dynamic) and further processing (veneered vs. unveneered). The framework specimens were cemented on alumina-based jaw models, where the canine and second molar were acting as abutments, before a point-load was applied. In addition, μCT scans and microscopic fractography was used to evaluate the quality of soldered joints and to determine the causes of fracture.

RESULTS

The determined fracture loads of the different unveneered framework specimens in static testing did not vary significantly (p  =  1). Adding a veneering layer significantly increased the mechanical strength for monolithic framework specimens from 1,196.29 ±203.79 N to 1,606.85 ±128.49 N (p  =  0.008). In case of soldered specimens with a dental attachment-based geometry the mechanical strength increased from 1,159.42 ±85.65 N to 1,249.53 ±191.55 N (p  =  1). Within the dynamic testing, no differences were observed between monolithic and soldered framework specimens. μCT scans and fractography proved that the dental attachment-based joining geometry offers the highest quality.

CONCLUSION

Using glass soldering technology, sub-components of 5-unit framework specimens made of Y-TZP could be joined with mechanical properties comparable to those of monolithic frameworks. This article is protected by copyright. All rights reserved.

Fracture of Lithia Disilicate Ceramics under Different Environmental Conditions

The objective of this research was to quantify the effect of surface degradation and abrasion separately and in combination on the flexural strength of lithia disilicate ceramics. Lithia disilicate disks were fabricated using the lost wax technique and pressing in vacuum. The eight groups in this pilot experiment were (i) reference, hydrated in distilled water for 24 h prior to fracture; (ii) reference, non-hydrated group; (iii) 28-day pH cycling group; (iv) 125K chewing cycle group; (v) combined pH cycling + 125K chewing cycle; (vi) constant pH 2 solution for 28 days; (vii) constant pH 7 solution for 28 days; and (viii) constant pH 10 solution for 28 days. pH cycling is a method that alternates between pH 2, 7 and 10 over 28 days. A total of 15 disks were used for each group. All the groups were tested using the biaxial piston and a three-ball flexural strength test to obtain their biaxial flexural strength. pH 2 constant immersion demonstrated the highest fracture strength and was significantly greater than all other groups (p < 0.0001). Chewing and pH cycling + chewing groups exhibited the lowest fracture strengths and were significantly lower than all other groups (p < 0.0001). The damage observed from the chewing simulator does not represent apparent clinical fractures.

Three-Dimensional Finite Element Analysis of Different Connector Designs for All-Ceramic Implant-Supported Fixed Dental Prostheses

All-ceramic fixed dental prostheses (FDPs) tend to fracture at the connector regions due to high stress concentration at these areas influenced by their design. This study was performed as an adjunct to an existing clinical study to evaluate the influence of the different radii of curvature of gingival embrasure on the stress distribution of a three-unit all-ceramic implanted supported FDP. Three three-dimensional (3D) models were created by scanning two titanium dental implants, their suitable zirconia abutments, and a patient-retrieved dental prosthesis using a micro-CT scanner. The radius of curvature of the gingival embrasure for the distal connector of the FDP was altered to measure 0.25 mm, 0.50 mm, and 0.75 mm. A finite element analysis (FEA) software (ABAQUS) was used to evaluate the impact of different connector designs on the distribution of stresses. Maximum Principal Stress data was collected from the individual components (veneer, framework, and abutments). The radius of curvature of gingival embrasure had a significant influence on the stress distribution at the assessed components. The tensile peak stresses at all structures were highest in the 0.25 mm model, while the 0.50 mm and 0.75 mm models presented similar values and more uniform stress distribution.

Forensic and reliability analyses of fixed dental prostheses

This article describes the protocol for determining the cause of failure for retrieved failed implant supported fixed dental prostheses (FDPs) in a clinical study of three-unit bridges. The results of loading of flexure bars of different veneer compositions at different stress rates were presented for two veneer materials (leucite reinforced and fluorapatite glass-ceramic veneers) and a Y-TZP core zirconia ceramic used in the clinical study. From these results, the strengths of the fast loading conditions were used to determine the fracture toughness of these materials. Fractal dimension measurements of the flexure bars and selected FDPs of the same materials demonstrated that the values were the same for both the bars and the FDPs. This allowed the use of fracture toughness values from the flexure bars to determine the strengths of the FDPs. The failure analysis of clinically obtained FDP replicates to determine the size of the fracture initiating cracks was then performed. Using the information from the flexure bars and the size of the fracture initiating cracks for the failed FDPs, the strengths of the FDPs were determined. The clinical failures were determined to be most likely the result of repeated crack growth due to initial overload and continuous use after initial cracking.

Factors influencing the survival of implant-supported ceramic-ceramic prostheses: A randomized, controlled clinical trial

OBJECTIVE

The goals of this research are: (1) to determine the clinical survival of ceramic-ceramic 3-unit implant supported fixed dental prostheses (FDPs) compared with control metal-ceramic and; (2) to analyze the effects of design parameters such as connector height, radius of curvature of gingival embrasure, and occlusal veneer thickness.

MATERIALS AND METHODS

This randomized, controlled clinical trial enrolled 96 participants with 129 3-unit implant-supported FDPs. Participants were randomized to receive different design combinations to include FDP material, thickness of occlusal veneer ceramic, radius of curvature of gingival embrasure and connector height. Participants were recalled for 6 months, 1year and yearly thereafter for the next 5 years. FDPs were examined for evidence of fracture and radiographs were made to assess viability of implants. Fractographic analyses and Kaplan Meier survival analysis was used to analyze the data.

RESULTS

27 FDPs, representing 21%, exhibited chipping fractures of the veneer during the 5-year observation period. There was no statistically significant effect of type of material, veneer thickness, radius of curvature of gingival embrasure and connector height on occurrence of fracture. Fractographic and occlusal analyses reveal that fractures originated from the occlusal surface and that occlusion was the most important factor in determining survival. Stresses calculated at failure demonstrated lower values compared with in vitro data.

CONCLUSION

Implant-supported ceramic-ceramic prosthesis is a viable alternative to metal-ceramic. Survival analysis for both materials were comparable and design parameters employed in this study did not affect survival as long as zirconia was used as the core material.

Clinical outcomes of partial and full-arch all-ceramic implant-supported fixed dental prostheses. A systematic review and meta-analysis

OBJECTIVE

To assess the survival and technical complication rate of partial and full-arch all-ceramic implant-supported fixed dental prostheses (P-FDP/FA-FDP) and supporting implants.

MATERIALS AND METHODS

An electronic search through three databases (MEDLINE/Pubmed, Cochrane Library, Embase) was conducted to identify relevant clinical studies with an observation period of at least 12 months, including ≥15 patients. Reconstruction and implant survival rates, technical complications and confounding variables such as processed/installed materials, retention mode and location in the mouth were obtained. Failure and complication rates were analyzed using standard Poisson regression models to calculate 5-year survival and complication estimates.

RESULTS

A total of five studies for the P-FDP group and seven studies for the FA-FDP group were included, throughout evaluating veneered zirconia reconstructions. In the P-FDP group, reconstructions were located in posterior regions. Meta-analysis indicated survival estimates on the reconstruction level of 98.3% and 97.7% for P- and FA-FDPs after 5 years. However, chipping of the veneering ceramic was frequent, resulting in estimated 5-year complication rates of 22.8% (P-FDPs) and 34.8% (FA-FDPs). Five-year survival estimates of implants supporting P-FDPs and FA-FDPs of 98.5% and 99.4% were calculated, respectively. Including a total of 540 FDPs, one screw-loosening and 11 de-cementations were reported. Confounding variables were not found to have a significant influence on survival and complication rates.

CONCLUSIONS

All-ceramic implant-supported P- and FA-FDPs comprising veneered zirconia frameworks showed high survival but clinically inacceptable fracture rates of the veneering ceramic. Their suitability with regard to this indication and a successful long-term outcome needs to be further evaluated.

Ceramic versus metal-ceramic implant-supported prostheses: A systematic review and meta-analysis

STATEMENT OF PROBLEM

There is insufficient evidence to recommend the restorative material for implant-supported prostheses.

PURPOSE

The purpose of this systematic review and meta-analysis was to evaluate studies that compared ceramic and metal-ceramic restorations for implant-supported prostheses (within the same study to avoid indirect comparison) in terms of the mechanical and biological complication rates, prosthesis survival rate, and marginal bone loss.

MATERIAL AND METHODS

Two independent reviewers performed a comprehensive search in databases (PubMed/MEDLINE, Web of Science, and Cochrane Library) for articles indexed until March 31, 2018. The search was performed in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement and methods were registered in the International Prospective Register of Systematic Reviews (PROSPERO). The focused question was "Do ceramic restorations have mechanical/biological complication rates, prosthesis survival rates, and marginal bone loss similar to those of metal-ceramic restorations?"

RESULTS

The search identified 949 references. The interinvestigator agreement using kappa values was 0.87 for PubMed/MEDLINE, 0.93 for Scopus, and 1.0 for the Cochrane Library. After analysis, 12 studies were selected for qualitative and quantitative analysis. The mechanical complication rate did not differ between ceramic and metal-ceramic restorations (P=.89), independent of the type of prostheses (single crown: P=.63; fixed partial denture: P=.65). The biological complication rate was also not significantly different between ceramic and metal-ceramic restorations (P=.21). The prosthesis survival rate showed no significant differences between the 2 types of restorations (P=.56). Marginal bone loss was also similar for both types of restorations (P=.12).

CONCLUSIONS

This systematic review indicated that ceramic and metal-ceramic implant-supported prostheses have similar mechanical and biological complication rates, prosthesis survival rates, and marginal bone loss. Thus, both treatments are appropriate options for long-term rehabilitation treatment.

Metal-free materials for fixed prosthodontic restorations

BACKGROUND

Fixed prosthodontic treatment (crowns, fixed dental prostheses (FDPs), complete arch prostheses) involves the use of several different materials to replace missing tooth structure. Traditionally full metal or metal frameworks veneered with ceramic (metal-ceramic (MC)) have been used. In recent years several different metal-free systems have become available to clinicians and patients. In general, metal-free restorations should allow practitioners to better reproduce natural tooth colour, avoiding shortcomings of MC restorations. The comparative in service clinical performance of fixed prosthodontic treatments of different materials is unclear.

OBJECTIVES

To assess the effects of metal-free materials for prosthodontic restorations compared to metal-ceramic or other conventional all-metal materials.

SEARCH METHODS

Cochrane Oral Health's Information Specialist searched the following databases: Cochrane Oral Health's Trials Register (searched 3 May 2017), Cochrane Central Register of Controlled Trials (CENTRAL; 2017, Issue 4) in the Cochrane Library (searched 3 May 2017), MEDLINE Ovid (1946 to 3 May 2017), and Embase Ovid (1980 to 3 May 2017). The US National Institutes of Health Trials Registry (ClinicalTrials.gov) and the World Health Organization International Clinical Trials Registry Platform were searched for ongoing trials (searched 3 May 2017). No restrictions were placed on the language or date of publication when searching the electronic databases.

SELECTION CRITERIA

Randomised controlled trials (RCTs) in which the clinical performance of metal-free fixed prosthodontic restorations was compared with metal-ceramic (MC) or other conventional restorations in adult patients requiring prosthodontic treatment. RCTs in which the clinical performance of different kinds of metal-free systems were compared among themselves were also considered.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures expected by Cochrane. Screening of eligible studies, assessment of the methodological quality of the trials and data extraction were conducted independently and in duplicate. Trial authors were contacted for missing information. Available results for the outcomes of interest of the systematic review of the studies included were tabulated as they could not be included in a formal meta-analysis.

MAIN RESULTS

Nine trials involving a total of 448 participants were included. We judged two trials to be at unclear risk of bias and seven to be at high risk of bias. The majority of items of risk of bias were evaluated to be at unclear or high risk level in more than 50% of the included trials. Each trial except two was addressing a different type of intervention. All evidence was rated as being of very low quality due to problems with risk of bias and imprecision of results, the latter being due to very small sample sizes, low event rates, 95% confidence intervals including the possibility of benefit for both the test and control groups, or combinations of these problems. This means that we are very uncertain about all of the results presented in this review.One trial compared metal-free single crowns (full contour zirconia) to cast gold single crowns in 224 participants and found insufficient evidence of a difference in failure rate after one year, but after five years there was some evidence of a benefit for the gold crowns. There was insufficient evidence of a difference for crown complications at either time of assessment.One trial compared three-unit metal-free FDPs (lithium disilicate) to three-unit metal-ceramic FDPs in 37 participants. There was insufficient evidence of a difference in bridge failure at one and six years, but some evidence of a benefit for the lithium disilicate group in terms of bridge complications at six years. One trial compared zirconia-ceramic FDPs to metal-ceramic FDPs in 34 participants but found insufficient evidence of a difference in bridge failures (i.e. no failures in either treatment group), bridge complications or patients' aesthetic evaluation at any time of assessment up to three years.One trial compared metal-free cantilevered FDPs to metal-ceramic cantilevered FDPs in 21 participants. There was insufficient evidence of a difference for any primary outcome: bridge failures (i.e. no failures in either treatment group), bridge complications, or patients' aesthetic evaluation at any time of assessment up to three years.One trial compared metal-free implant-supported screw retained single crowns (zirconia veneered with feldspathic ceramic) to metal-ceramic implant-supported screw-retained single crowns in 20 participants. There was insufficient evidence of a difference for any primary outcome: crown failures (i.e. no failures in either treatment group), crown complications, or satisfaction/aesthetic evaluation at any time of assessment up to two years.Two trials compared metal-free implant abutments (zirconia) to metal implant abutments both supporting single crowns in 50 participants. There was insufficient evidence of a difference in abutment failure at one year.One trial compared metal-free implant-supported FDPs made of two different types of zirconia ceramic in 18 participants. There was insufficient evidence of a difference in failures at any time of assessment up to 10 years (i.e. no failures in either treatment group). There was some evidence of a benefit for the zirconia-toughened alumina group in terms of complications (chipping).One trial compared metal-free tooth-supported FDPs made with two different veneering techniques (pressed versus layered) in 40 participants. There was insufficient evidence of a difference for failures (i.e. no failures in either treatment group) or complications at any time of assessment up to three years.

AUTHORS' CONCLUSIONS

There is insufficient evidence to support or refute the effectiveness of metal-free materials for fixed prosthodontic treatment over metal-ceramic or other type of standard restorations. The overall quality of existing evidence was very low, therefore great caution should be exercised when generalising the results of the included trials. Until more evidence becomes available clinicians should continue to base decisions on which material to use for fixed prosthodontic treatment on their own clinical experience, whilst taking into consideration the individual circumstances and preferences of their patients. There is urgent need of properly designed RCTs.

Effects of two grading techniques of zirconia material on the fatigue limit of full-contour 3-unit fixed dental prostheses

OBJECTIVE

This study evaluated the effects of two grading techniques of zirconia material on the fatigue limit of full-contour 3-unit fixed dental prostheses (FDPs).

METHODS

Presintered blocks of 3Y-TZP were milled to obtain sixty-nine 3-unit FDPs, which were divided into three groups (n=23). The control group (CTL) was sintered and glazed following manufacturer's instructions. In the two experimental groups presintered FDPs received a surface silica/glass infiltration treatment before the sintering process. Silica sol-gel group (SSG) was graded by the sol-gel processing route, while the glass-zirconia-glass group (GZG) was graded by an enameling technique. Graded groups did not receive a glaze layer after sintering. All FDPs were then luted with a dual-curing resin cement on composite abutments, embedded in polyurethane and stored in water for five days. The initial load of the fatigue test was calculated based on the results of the monotonic testing applied on three specimens of each group. To determine the fatigue limit, 20 samples of each group were subjected to staircase testing (100,000 cycles/5Hz).

RESULTS

The fatigue limits (in Newtons) were CTL=1607.27, SSG=1824.31, and GZG=2006.57, and the Dixon and Mood test indicated statistically significant differences among groups (95% confidence interval) (GZG > SSG > CTL).

SIGNIFICANCE

The infiltration of silica and glass on bulk zirconia, by two different grading methods, increased the fatigue limits of monolithic zirconia FDPs.