Clinical performance of posterior monolithic zirconia implant-supported fixed dental prostheses with angulated screw channels: A 3-year prospective cohort study

Mechanical and biological complications of angled versus straight screw channel implant-supported prostheses: A systematic review and meta-analysis

STATEMENT OF PROBLEM

Scientific evidence to determine the clinical performance of angled screw channel (ASC) versus straight screw channel (SC) implant-supported prostheses is lacking.

PURPOSE

This systematic review and meta-analysis investigated the mechanical and biological complications of ASC compared with those of SC implant-supported prostheses.

MATERIAL AND METHODS

A systematic search was conducted by following the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guideline in the PubMed, Embase, and Web of Science databases and was supplemented with a manual search for clinical studies reporting the mechanical and biological complications of ASC compared with those of SC implant-supported prostheses. The search was focused on porcelain fracture, screw loosening or fracture, marginal bone loss (MBL), and pink esthetic score (PES). The data were extracted from selected articles and compounded to estimate the complications with a 95% confidence interval (CI) using a random effects meta-analysis. The publication bias was assessed using the Cochrane Risk of Bias and Newcastle-Ottawa Scale (α=.05).

RESULTS

A total of 4217 records were identified, and 14 studies were selected for quantitative synthesis of 629 participants with 658 ASC and 166 SC implant-supported prostheses. The meta-analyses of comparative studies showed no statistically significant difference in mechanical complications between ASC and SC prostheses, with odds ratio (OR) of 1.75 (95% CI=0.71-4.34, P=.224). Porcelain fracture and screw loosening were the most common complications with ASC prostheses. In addition, no statistically significant difference was found between ASC and SC prostheses in the MBL (mean difference=-0.07, 95% CI=-0.15-0.01, P=.077) and PES (mean difference=-0.19, 95% CI=-0.90-0.52, P=.593).

CONCLUSIONS

The clinical performance of ASC may be comparable with that of SC implant-supported prostheses in terms of mechanical and biological complications. However, the moderate level of evidence necessitates further research to validate these findings.

Clinical outcome of monolithic zirconia on bonded or mechanically retained prefabricated titanium-base: A 4-year retrospective study

OBJECTIVE

To assess the clinical performance of monolithic screw-retained implant-supported zirconia crowns (MSI) bonded or mechanically retained on prefabricated Ti-bases using a complete digital workflow.

METHODS

A retrospective analysis was conducted on patients who underwent single dental implant procedures between January 2017 and May 2018. Inclusion criteria were: patients over 18 years of age; implants placed in posterior sites; MSI on prefabricated Ti-base realized by using a complete digital workflow; a minimum follow-up period of 2 years. Cemented crowns and fixed dental prosthesis were excluded. Mechanical complications included: fracture of Ti-base; loss of retention; loosening of Ti-base screws. Technical complications included: fracture and debonding of monolithic zirconia. Biological complication was set strictly at a probing pocket depth of 5 mm and bleeding on probing or pus secretion.

RESULTS

A total of 144 dental implants placed in 127 patients were included, 73 with a fully tapered implant system (BLX) and 71 with a conical connection system (Nobel Parallel CC). Of the 73 BLX implants, 4 experienced loosening of the Ti-base screw, while 3 Nobel Parallel CC implants experienced the same problem. In addition, 4 fractures of the Ti-base and 6 fractures of the inner surface of the monolithic zirconia were observed in the Nobel Parallel CC implants. Cumulative survival was 100 % for bonded crowns and 85 % for mechanically retained crowns. Radiographic evaluation revealed a mean CBL of 0.12 mm for the BLX and 0.13 mm for the Nobel Parallel CC implants with no statistically significant differences between the Ti-base types. There was no evidence of bleeding on probing or pus secretion. All probing pocket depths were <3 mm.

CONCLUSION

The use of a prefabricated Ti-base remains a clinically acceptable choice, however, MSIs bonded to prefabricated Ti-bases had fewer mechanical and technical complications than the MSI mechanically retained to a prefabricated Ti-base.

Optical and Mechanical Properties of the Multi-Transition Zones of a Translucent Zirconia

OBJECTIVE

To characterize the composition, flexure resistance, and optical properties of a multilayer translucent zirconia in relation to its multi-transition zones.

MATERIALS AND METHODS

A multilayer zirconia (5Y/4Y) and a conventional 3 mol% yttria partially stabilized zirconia (3Y) were investigated. Bar-shaped specimens were obtained from the enamel and dentin layers, and the vertical cross-section of 5Y/4Y (N = 10). A four-point flexural (σf) test was performed using a universal testing machine (1.0 mm/min). Plate-shaped specimens (N = 6) were also produced from the enamel, transition 1, transition 2, and dentin layers. Translucency parameters (TPab and TP00) were determined using a dental spectrophotometer (N = 6). X-ray fluorescence and X-ray diffraction techniques were used to analyze elemental (N = 2) and phase compositions (N = 2), respectively. Data were analyzed using analysis of variance (ANOVA) and Tukey's test (α = 0.05).

RESULTS

The yttrium content and σf varied between layers of 5Y/4Y. 3Y had the highest σf, followed by dentin. Enamel and cross-section showed lower and statically similar σf. 3Y and dentin groups had similar but statistically lower TPab and TP00 than the enamel.

CONCLUSIONS

Different layers of multilayered zirconia have distinct compositions, which affect their mechanical and optical properties. The weak enamel layer compromises the mechanical properties of cross-sectional specimens.

CLINICAL SIGNIFICANCE

The development of novel cubic-containing multilayer zirconia ceramics to produce monolithic restorations brings new challenges to dental clinicians and laboratory technicians. The CAD/CAM design of multilayered 5Y/4Y restorations should consider the esthetic and mechanical requirements of each clinical case, as different properties are found in the different layers of these materials.

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.

The mechanical complications and behavior of angulated dental implant abutment systems versus conventional abutments, a narrative review

Background

Angulated screw channel (ASC) abutment allows off-axis dental implants to be used in dental restorations without the need for cementation. As this is a relatively new system, research on its clinical performance is limited.

Objectives

To summarize the available in-vitro and in-vivo studies on the mechanical and technical issues associated with the ASC system and compare its clinical performance with that of conventional implant-supported abutments.

Methods

A comprehensive literature search in PubMed, Web of Science, and ScienceDirect databases was performed, focusing on articles about angulated (angled) screw channel (ASC) systems published in English between January 2015 and November 2023. Only in-vitro and in-vivo studies were included.

Results

After analyzing the recorded articles, 26 studies (11 in vivo and 15 in vitro) were included in the final discussion and review.

Conclusion

Although the ASC system is still relatively new, and is presently outperformed by conventional abutment systems in terms of technical and mechanical properties, in short- and medium-term in-vivo studies, it was shown reliable for retaining single or multiple-unit implant restorations in both posterior and anterior zones. Still, further long-term clinical research is needed to fully elucidate the risk factors associated with ASC failures.

Clinical performance of implant-supported single hybrid abutment crown restoration: A systematic review and meta-analysis

PURPOSE

To investigate survival rates and technical and biological complications of one-piece screw-retained hybrid abutments in implant-supported single crowns (SCs).

STUDY SELECTION

An electronic search was performed on five databases for clinical studies involving implant-supported single hybrid abutment crowns constructed using titanium-base (Ti base) abutments, with at least 12 months of follow-up. The RoB 2, Robins-I, and JBI tools were used to assess the risk of bias for the different study types. Success, survival, and complication rates were calculated, and a meta-analysis was performed to obtain a pooled estimate. Peri-implant health parameters were extracted and analyzed.

RESULTS

22 records (20 studies) were included in this analysis. Direct comparisons between screw-retained hybrid abutment SCs and cemented SCs showed no significant differences in the 1-year survival and success rates. For SCs using a hybrid abutment crown design, their 1-year survival rate was 100% (95% CI: 100%-100%, I2 = 0.0%, P = 0.984), and a success rate of 99% (95% CI: 97%-100%, I2 = 50.3%, P = 0.023) was calculated. No confounding variables significantly affected the estimates. The individual technical complication rate was low at 1-year follow-up. The estimated incidence of all types of complications in hybrid abutment SCs is less than 1%.

CONCLUSIONS

Within the limitations of this study, implant-supported SCs using a hybrid abutment crown design showed favorable short-term clinical outcomes. Additional well-designed clinical trials with at least a 5-year observation period are required to confirm their long-term clinical performance.

Influence of straight versus angulated screw channel titanium bases on failure loads of two-piece ceramic and titanium implants restored with screw-retained monolithic crowns: An in-vitro study

OBJECTIVE

To analyze the influence of titanium-base (straight [SSC]/angulated-screw-channel [ASC]) on failure-loads and bending-moments of two-piece ceramic and titanium-zirconium implants restored with monolithic-zirconia crowns after fatigue.

MATERIALS AND METHODS

Thirty-two anterior monolithic-screw-retained zirconia crowns were divided into four groups (n = 8/group) according to the factors: (1) type of implant material: two-piece titanium-zirconium implant (Ti-Zr; control-group) versus two-piece ceramic implant (CI; test-group) and (2) type of titanium-base: SSC (0° angle) versus ASC (25°). An intact implant was used for field emission gun-scanning electronic microscopy (FEG-SEM) characterization and Raman spectroscopy for phase analyses and residual stress quantification. All samples were exposed to fatigue with thermodynamic loading (1.2-million-cycles, 49 N, 1.6 Hz, 5-55°C) at a 30° angle. Surviving specimens were loaded until failure (SLF) and bending moments were recorded. Failed samples were examined using light microscope and SEM. Statistical analyses included ANOVA and Mann-Whitney U-test.

RESULTS

Raman-spectroscopy revealed the presence of residual compressive stresses. FEG-SEM revealed a roughened surface between threads and polished surface at the cervical-collar of the ceramic implant. All samples survived fatigue and were free of complications. Mean bending-moments (±SD) were: Ti-Zr-0: 241 ± 45 N cm, Ti-Zr-25: 303 ± 86 N cm, CI-0: 326 ± 58 N cm, CI-25: 434 ± 71 N cm. Titanium-base and implant-material had significant effects in favor of ASC titanium bases (p = .001) and ceramic-implants (p < .001). Failure analysis after SLF revealed severe fractures in ceramic implants, whereas titanium implants were restricted to plastic deformation.

CONCLUSIONS

Ceramic and titanium implants exhibited high reliability after fatigue, with no failures. From a mechanical perspective, titanium bases with ASC can be recommended for both ceramic and titanium implants and are safe for clinical application.

Comparative evaluation of biological, mechanical, and patient-reported outcomes of angulated screw channel abutments versus multi-unit abutment-retained single-unit implant restorations in the anterior esthetic zone: An-in vivo study

Aims

The study aimed to evaluate biological, mechanical, and patient reported parameters associated with ASC abutments and MU abutments for the fabrication of screw retained implant crowns in the anterior esthetic zone.

Setting and Design

For the study, 20 patients were selected and implants were placed within the constraints of prosthetic envelope. Later, the screw retained crown was fabricated.

Materials and Methods

Biological parameters (including implant survival rate, marginal bone levels using cone beam computed tomography, and soft tissue assessment using periodontal indices) were measured at the time of crown placement and 1 year follow up. Mechanical parameter (screw loosening) was calculated using removal torque loss (RTL) values obtained at the time of crown placement and 1 year follow up. Patient reported parameters were evaluated using a questionnaire at 1 year follow up.

Statistical Analysis Used

All data were tabulated, statistically analyzed, and compared using SPSS version 23 IBM Corporation, Armonk, NY, USA.

Results

Implant survival was found 100% in both the groups. The marginal bone level reduced considerably in both the groups from baseline to 1 year follow up. The MU abutment group had slightly less marginal bone loss than the ASC abutment group. Additionally, there was no statistically significant difference between the two groups' periodontal indices at baseline and 1-year follow-up values. At baseline, the RTL value was substantially lower (P <0.003) in the ASC abutment group than in the MU abutment group, however at the 1-year follow-up, there was no statistically significant difference in RTL or screw loosening between the two groups. Patient-reported data showed no statistically significant difference.

Conclusion

Within the constraints of this study, it was suggested that both ASC and MU abutments provide equally promising results in terms of biological, mechanical, and patient-reported parameters in the anterior esthetic region for single screw-retained crowns.

Monolithic hybrid abutment crowns (screw-retained) versus monolithic hybrid abutments with adhesively cemented monolithic crowns

OBJECTIVES

The objective of this study is to compare monolithic hybrid abutment crowns (screw-retained) versus monolithic hybrid abutments with adhesively cemented monolithic single-tooth crowns.

MATERIALS AND METHODS

Twenty subjects in need of an implant-borne restoration were randomly assigned to receive either a cement-retained (CRR) or a screw-retained (SRR) implant-supported monolithic lithium disilicate (LS₂ ) reconstruction. Each patient received a titanium implant with in internal conic connection. After osseointegration and second-stage surgery, healing abutments were placed for about 10 days. The type of restoration (CRR vs. SRR) was randomly assigned, and the restorations were manufactured of monolithic LS₂ . Both types of restorations, CRR and SRR, were based on a titanium component (Ti-base) that was bonded to the abutment (CRR) or the crown (SRR). The follow-up period for all restoration was 36 months. Clinical outcome was evaluated according to Functional Implant Prosthetic Score (FIPS). Quality of live (OHIP) and patient's satisfaction were assessed using patient-reported outcome measures (PROMs). Primary endpoint was loss of restoration for any reason. Kaplan-Meier curves were constructed and log-rank testing was performed (p < .05).

RESULTS

One restoration of group CRR failed after 6 months due to loss of adhesion between Ti-base and individual abutment. No further biological or technical failures occurred. Kaplan-Meier analysis showed no significant difference between both treatment options (p = .317). There was no statistically significant difference between both types of restoration, neither for FIPS, OHIP, treatment time nor patient satisfaction (p > .05).

CONCLUSION

Monolithic hybrid abutment crowns (screw-retained) and monolithic hybrid abutment with adhesively cemented monolithic crowns using lithium disilicate showed no statistically significant difference for implant-based reconstructions in this pilot RCT setting.

Survival and prosthetic complications of monolithic ceramic implant-supported single crowns and fixed partial dentures: A systematic review with meta-analysis

STATEMENT OF PROBLEM

Monolithic ceramic implant-supported restorations have been used to rehabilitate partially edentulous patients. However, knowledge of the survival and prosthetic complications of single crowns (SCs) and fixed partial dentures (FPDs) is limited.

PURPOSE

The purpose of this systematic review with meta-analysis was to evaluate the clinical performance of monolithic ceramic implant-supported SCs and FPDs in terms of survival and prosthetic complication rates.

MATERIAL AND METHODS

The systematic review was registered on the prospective register of systematic reviews (PROSPERO) (CRD42017078568). Five electronic databases were independently searched by 2 authors for articles published until May 2022. In addition, a hand search was performed in the nonpeer-reviewed literature, specific journals, and reference lists of included articles. A single-arm meta-analysis was performed by using the R program. The risk of bias and quality were assessed using the Cochrane risk of bias tools and the Newcastle-Ottawa scale.

RESULTS

Twenty-eight studies were included in the quantitative synthesis. A total of 1298 monolithic ceramic implant-supported restorations (1116 SCs and 182 FPDs) were evaluated in 1193 participants, with a median observation time of 24 months (range: 12 to 72 months). Meta-analysis indicated the proportion of failures and prosthetic complication rates of 2% (95% confidence interval [CI]: 1% to 4%) for SCs. No difference was observed for monolithic zirconia and lithium disilicate SCs. In the FPDs, only monolithic zirconia was considered, with 1 failure reported totaling the proportion of failures of 0% (0% to 1%) and complication rates of 4% (0% to 12%). The most complications reported for both types of restorations were screw loosening, debonding, and minor chipping and were considered repairable. The included studies showed a low risk of bias and good quality.

CONCLUSIONS

The use of monolithic ceramic implant-supported SCs, independent of ceramic material, and monolithic zirconia implant-supported FPDs should be considered an effective and safe treatment option because of favorable short-term survival and low prosthetic complications. However, additional well-conducted studies with a longer-term follow-up and direct comparison between veneered restorations are recommended to reassess clinical performance.

Failure Load and Fatigue Behavior of Monolithic and Bi-Layer Zirconia Fixed Dental Prostheses Bonded to One-Piece Zirconia Implants

No evidence-based prosthetic treatment concept for 3-unit fixed-dental-prostheses (FDPs) on ceramic implants is currently available. Therefore, the aim of this in vitro study was to investigate the failure load and fatigue behavior of monolithic and bi-layer zirconia FDPs supported by one-piece ceramic implants. Eighty 3-unit FDPs supported by 160 zirconia-implants (ceramic.implant; vitaclinical) were divided into 4 groups (n = 20 each): Group Z-HT: 3Y-TZP monolithic-zirconia (Vita-YZ-HT); Group Z-ST: 4Y-TZP monolithic-zirconia (Vita-YZ-ST); Group FL: 3Y-TZP zirconia (Vita-YZ-HT) with facial-veneer (Vita-VM9); Group RL (Rapid-layer): PICN “table-top” (Vita-Enamic), 3Y-TZP-framework (Vita-YZ-HT). Half of the test samples (n = 10/group) were fatigued in a mouth-motion chewing-simulator (F = 98 N, 1.2 million-cycles) with simultaneous thermocycling (5−55 °C). All specimens (fatigued and non-fatigued) were afterwards exposed to single-load-to-failure-testing (Z010, Zwick). Statistical analysis was performed using ANOVA, Tukey’s post-hoc tests and two-sample t-tests (p < 0.05, Bonferroni-corrected where appropriate). All specimens withstood fatigue application. While the effect of fatigue was not significant in any group (p = 0.714), the choice of material had a significant effect (p < 0.001). Material FL recorded the highest failure loads, followed by Z-ST, Z-HT and RL, both with and without fatigue application. Taken together, all tested FDP material combinations survived chewing forces that exceeded physiological levels. Bi-Layer FL and monolithic Z-ST showed the highest resilience and might serve as reliable prosthetic reconstruction concepts for 3-unit FDPs on ceramic implants.

Model-free digital workflow and immediate functional loading of implant-supported monolithic glass-ceramic crowns: A case series

OBJECTIVES

The aim of this study is to evaluate surgical and prosthetic outcomes of immediate functional loading of implants with glass-ceramic screw-retained single crowns.

METHODS

A total of 22 implants were placed. Within 24 hours, functional full-contour glass ceramic crowns were delivered to patients. The amount of attached gingiva, Simplified Oral Hygiene Index Score, bleeding on probing, time after extraction, bone type, implant size, soft tissue thickness, primary stability, a general fit of the restoration, occlusal and proximal contacts were recorded. Restorations were followed-up at 1, 3, and 6 months tracking marginal bone loss (MBL), noting changes in occlusal and interproximal contacts, checking other possible complications.

RESULTS

One implant failed and was removed after 4 weeks (95.5 % survival rate). The rest of the implants and crowns functioned with no complications during the follow-up period of 6 months. Factors such as time after extraction, bone type, implant size, soft tissue thickness, and primary stability recorded in Ncm and implant stability quotient (ISQ) values, were not associated with MBL (p<0.05). Mean MBL was found to be 0.3 mm (standard deviation = 0.42) mesially and 0.4 mm (standard deviation = 0.66) distally. One distal and one mesial proximal contact were found to be missing at the 6-month check-up appointment.

CONCLUSIONS

Within the limits of this study, fully digital workflow without a 3D printed model could be successfully employed for immediate functional loading with single-unit implant-supported crowns. Further studies are needed to obtain long-term results with a larger sample of patients.

CLINICAL SIGNIFICANCE

Model-free digital workflow and immediate functional loading of implant-supported monolithic glass-ceramic crown might be viable option to restore a single tooth defect.

Alveolar ridge preservation reduces the need for ancillary bone augmentation in the context of implant therapy

Background

There is limited information on the need for bone augmentation in the context of delayed implant placement whether alveolar ridge preservation (ARP) is previously performed or not. The primary aim of this retrospective cohort study was to evaluate the efficacy of ARP therapy after tooth extraction compared with unassisted socket healing (USH) in reducing the need for ancillary bone augmentation before or at the time of implant placement.

Methods

Adult subjects that underwent non‐molar single tooth extraction with or without simultaneous ARP therapy were included in this study. Cone beam computed tomography scans obtained before tooth extraction and after a variable healing period were used to record the baseline facial bone thickness and to virtually plan implant placement according to a standard method. A logistic regression model was used to evaluate the effect of facial alveolar bone thickness upon tooth extraction and baseline therapy (USH or ARP) on the need for additional bone augmentation, adjusting for several covariates (i.e., age, sex, baseline KMW, and tooth type).

Results

One hundred and forty subjects that were equally distributed between both baseline therapy groups constituted the study population. Implant placement was deemed virtually feasible in all study sites. Simultaneous bone augmentation was considered necessary in 60% and 11.4% of the sites in the USH and ARP group, respectively. Most of these sites (64.2% in the USH group and 87.5% in the ARP group) exhibited a thin facial bone phenotype (<1 mm) at baseline. Logistic regression revealed that the odds of not needing ancillary bone augmentation were 17.8 times higher in sites that received ARP therapy. Furthermore, the need for additional bone augmentation was reduced 7.7 times for every 1 mm increase in facial bone thickness, regardless of baseline therapy.

Conclusions

Based on a digital analysis, ARP therapy, compared with USH, and thick facial alveolar bone largely reduce the need for ancillary bone augmentation at the time of implant placement in non‐molar sites.