Implant-abutment connection designs for anterior crowns: reliability and failure modes

Reliability and Failure Mode of Ti-Base Abutments Supported by Narrow/Wide Implant Systems

To assess the reliability and failure modes of Ti-base abutments supported by narrow and wide-diameter implant systems. Narrow (Ø3.5 × 10 mm) and wide (Ø5 × 10 mm) implant systems of two different manufacturers with internal conical connections (16°) and their respective Ti-base abutments (3.5 and 4.5 mm) were evaluated. Ti-base abutments were torqued to the implants, standardized metallic maxillary incisor crowns were cemented, and step stress accelerated life testing of eighteen assemblies per group was performed in three loading profiles: mild, moderate, and aggressive until fracture or suspension. Reliability for missions of 100,000 cycles at 100 and 150 N was calculated, and fractographic analysis was performed. For missions at 100 N for 100,000 cycles, both narrow and wide implant systems exhibited a high probability of survival (≥99%, CI: 94-100%) without significant differences. At 150 N, wide-diameter implants presented higher reliability (≥99%, CI: 99-100%) compared to narrow implants (86%, CI: 61-95%), with no significant differences among manufacturers. Failure mode predominantly involved Ti-base abutment fractures at the abutment platform. Ti-base abutments supported by narrow and wide implant systems presented high reliability for physiologic masticatory forces, whereas for high load-bearing applications, wide-diameter implants presented increased reliability. Failures were confined to abutment fractures.

Biomechanical efficiency of different implant-abutment connection: a systematic review of studies using photoelastic stress analysis

PURPOSE

The present review aimed to comparatively evaluate the biomechanical efficiency of different implant-abutment connections studied by photoelastic stress analysis.

MATERIALS AND METHODS

A comprehensive online literature search was conducted on Medline (Pubmed), Web of Science, and Google Scholar from 2000(Jan) to 2023(Jan). Keywords used initially to carry out the search included implant-abutment connection & photoelastic stress analysis, and stress distribution in different implant-abutment connections. 34 photoelastic stress analysis studies were screened and 30 studies were excluded after the screening of the title, abstract and full article. Finally, 4 studies were included for complete review.

RESULT

The result of this systematic review showed that the internal connection was more efficient then the external connection as there was less marginal bone loss and favorable distribution of stress in internal connection.

CONCLUSION

Crestal bone loss is more in external connection when compared to internal connection. In Internal connection, there is more intimate contact between the abutment's outer surface and implant which renders a more stable interface, which favoring uniform stress distribution and protects the retention screw.

Effect of different tightening protocols on the probability of survival of screw-retained implant-supported crowns

PURPOSE

This study evaluated the effect of different tightening protocols on the probability of survival of screw-retained implant-supported anterior crowns.

MATERIALS AND METHODS

Seventy-two implants with internal conical connections (4.0 × 10mm, Ti-6Al-4V, Colosso, Emfils) were divided into four groups (n = 18 each): 1) Manufacturer's recommendations torque (25 N.cm for abutment's screw and 30 N.cm for crown's screw) (MaT); 2) Retightening after 10 min (ReT); 3) Torque 16% below recommended to simulate an uncalibrated wrench (AgT), and; 4) Temporary crown simulation (TeT), where crowns were torqued to 13 N.cm to simulate manual tightening, subjected to 11,200 cycles to simulate temporary crown treatment time (190 N), and then retightened to manufacturer torque (TeT). All specimens were subjected to cyclic fatigue in distilled water with a load of 190 N until 250,000 cycles or failure. The probability of survival (reliability) to complete a mission of 50,000 cycles was calculated and plotted using the Weibull 2-Parameter analysis. Weibull modulus and number of cycles at which 62.3% of the specimens would fail were also calculated and plotted. The failure mode was characterized in stereo and scanning electron microscopes (SEM).

RESULTS

The probability of survival was 69.3% for MaT, 70% for ReT, 54.8% for AgT, and 40.3% for TeT, all with no statistically significant difference. Weibull modulus was approximately 1.0 for all groups. The characteristic number of cycles for failure was 105,000 cycles for MaT, 123,000 for ReT, 82,000 cycles for AgT, and 54,900 cycles for TeT, with no significant difference between groups. The chief failure mode for MaT, ReT, AgT groups was crown screw fracture, whereas abutment screw fracture was the chief failure mode for the TeT group.

CONCLUSION

Tightening protocol did not influence the probability of survival of the screw-retained anterior crowns supported by internal conical implants (Ti-6Al-4V, Colosso, Emfils).

Hydrothermal aging affects the three-dimensional fit and fatigue lifetime of zirconia abutments

OBJECTIVE

Evaluate the effect of aging using two different methods on the three-dimensional fit of zirconia abutments at the implant-abutment connection and estimate the probability of survival of anterior crowns supported by straight and 17-degree angled abutments.

MATERIALS AND METHODS

Two different zirconia abutment designs, straight and 17-degree angled abutments (n = 63/group), were evaluated in the current study. The abutments were randomly allocated into three experimental groups according to laboratory aging condition (134°C, 2.2 bar, 20 h): (i) control, (ii) autoclave aging, and (iii) hydrothermal reactor aging. Crystalline content was determined by X-Ray diffraction (XRD) and Raman spectroscopy, and microstructure was analyzed using field-emission gun scanning electron microscope (FEG-SEM). Implant-abutment volume misfit was determined in the straight abutments by micro-computed tomography using the silicone replica technique. For fatigue testing, abutments were torqued to the implants and connected to standardized maxillary incisor zirconia crowns. The assemblies were subjected to step-stress accelerated life testing (SSALT) in water until fracture or suspension. The use level probability Weibull curves and probability of survival for a mission of 50,000 cycles at 50, 100, 150 and 200 N were calculated and plotted. Fractured samples were analyzed using a stereomicroscope and scanning electron microscope.

RESULTS

The crystalline spectra depicted a zirconia system primarily composed of the tetragonal phase. Laboratory aging yielded a 20%- and 37%-increase in the monoclinic content for abutments aged in autoclave and hydrothermal reactor relative to control, respectively. A fully crystalline matrix with a regular grain size was observed in the FEG-SEM for control abutments, with a considerable presence of intergranular defects. While autoclave aging triggered no significant alteration to the microstructure, defect population was reduced after hydrothermal reactor aging. Control abutments presented a significantly higher volume misfit (2.128 ± 0.54 mm3) relative to aged abutments using autoclave (1.244 ± 0.48 mm3) or hydrothermal reactor (1.441 ± 0.41 mm3). The beta (β) values indicated that failures were predominantly controlled by material strength rather than fatigue damage accumulation for all groups, except for straight control abutments. Irrespective of aging, the probability of survival of straight and angled zirconia abutments was up to 95% (95-100%) at 50 and 100 N. A 50N-increase in the load resulted in wider range of survival estimate, with straight autoclave abutments percentage significantly lower probability of survival (77%) than angled hydrothermal reactor abutments (99%). At 200N, angled hydrothermal reactor (97%) or autoclave (82%) aged abutments demonstrated the highest probability of survival, angled control (71%) and straight hydrothermal reactor (69%) abutments intermediate values, and straight autoclave (23%) and control (7%) abutments the lowest estimate. The failure mode predominantly involved abutment and/or abutment screw fracture for both straight and angled abutments.

CONCLUSIONS

Hydrothermal aging significantly influenced volume misfit, as well as the probability of survival of zirconia abutments at higher loads for both angled and straight abutments.

Influence of Connection Type and Platform Diameter on Titanium Dental Implants Fatigue: Non-Axial Loading Cyclic Test Analysis

Two-pieces dental implants must provide stability of the implant-abutment-interface. The connection type and platform diameter could influence the biomechanical resistance and stress distribution. This study aims to evaluate the fatigue for different types of connections, external and internal, and different platform diameters. Three implant designs with the same length were used: (a) external hexagon/narrow platform; (b) internal double hexagon/narrow platform; (c) internal octagon/regular platform. A fatigue test was developed to establish the number of cycles needed before fracture. A 30º oblique load with a sinusoidal function of fatigue at a frequency of 15 Hz and 10% stress variation was applied to each system. The fatigue load limit (FLL) for design (a) was 190 N, being the nominal-curvature-moment (NCM) = 1.045; FLL = 150 N, with a NCM = 0.825 for (b), and FLL = 325 N, with a NCM = 1.788 for (c). The platform diameter affects the FLL, obtaining lower FLL on a narrow platform. The connection type interferes with the implant walls’ width, especially in narrow implants, making internal connections more unstable at this level. Long-term clinical studies to assess the restoration’s success rate and survival are mandatory.

Failure Modes and Survival of Anterior Crowns Supported by Narrow Implant Systems

The reduced hardware design of narrow implants increases the risk of fracture not only of the implant itself but also of the prosthetic constituents. Hence, the current study is aimed at estimating the probability of survival of anterior crowns supported by different narrow implant systems. Three different narrow implant systems of internal conical connections were evaluated (Ø3.5 × 10 mm): (i) Active (Nobel Biocare), (ii) Epikut (S.I.N. Implant System), and (iii) BLX (Straumann). Abutments were torqued to the implants, and standardized maxillary incisor crowns were cemented. The assemblies were subjected to step-stress accelerated life testing (SSALT) in water through load application of 30 degrees off-axis lingually at the incisal edge of the crowns using a flat tungsten carbide indenter until fracture or suspension. The use level probability Weibull curves and reliability for completion of a mission of 100,000 cycles at 80 N and 120 N were calculated and plotted. Weibull modulus and characteristic strength were also calculated and plotted. Fractured samples were analyzed in a stereomicroscope. The beta (β) values were 1.6 (0.9-3.1) and 1.4 (0.9-2.2) for BLX and Active implants, respectively, and 0.5 (0.3-0.8) for the Epikut implant, indicating that failures were mainly associated with fatigue damage accumulation in the formers, but more likely associated with material strength in the latter. All narrow implant systems showed high probability of survival (≥95%, CI: 85-100%) at 80 and 120 N, without significant difference between them. Weibull modulus ranged from 6 to 14. The characteristic strength of Active, Epikut, and BLX was 271 (260-282) N, 216 (205-228) N, and 275 (264-285) N, respectively. The failure mode predominantly involved abutment and/or abutment screw fracture, whereas no narrow implant was fractured. Therefore, all narrow implant systems exhibited a high probability of survival for anterior physiologic masticatory forces, and failures were restricted to abutment and abutment screw.

The biological width around implant

PURPOSE

The concept of biological width has been proposed and widely used in oral implantation. This review aimed to summarize the biological width around implant in detail.

STUDY SELECTION

An electronic search of the literature prior to March 2019 was performed to identify all articles related to biological width in periimplant soft tissue. The search was conducted in the MEDLINE (National Library of Medicine) database accessed through PubMed with no date restriction. The following main keywords were used: "implant", "biological width", "soft tissue", "junctional epithelium", "peri-implant epithelium", "connective tissue", "gingiva", "mucosa" (connecting multiple keywords with AND, OR).

RESULTS

The identified researches focused on several aspects related to biological width in oral implantation, namely the concept, formation, remodeling, dimension, structure and function.

CONCLUSIONS

Based on of the reviewed literature, the concept, formation, remodeling, structure, dimension, and functional significances of periimplant biological width are explored in this narrative review. The formation of biological width around implant is a complex process after several weeks of healing. The biological width around implant is a 3-4mm distance from the top of the peri-implant mucosa to the first bone-to-implant contact or the stabilized top of the adjacent bone, consisting of sulcular epithelium, junctional epithelium and fibrous connective tissue between the epithelium and the first bone-to-implant contact or the stabilized top of the adjacent bone. The biological width forms a biological barrier against the bacteria, influences the remodeling of soft and hard tissue around implant and has implications for clinical aspects of dental implantation.

A Comparative Analysis of Implants Presenting Different Diameters: Extra-Narrow, Narrow and Conventional

This study aimed at performing a comparative analysis of the fracture resistance of implants, evaluating extra-narrow, narrow, and regular implants. Four groups containing 15 implants each were evaluated. Group 1 (G1): single-piece extra-narrow implants; Group 2 (G2): single-piece narrow implants; Group 3 (G3): Morse taper narrow implants with solid abutments; Group 4 (G4): Morse taper conventional implants with solid abutments. The implants were tested using a universal testing machine for their maximum force limit and their maximum bending moment. After obtaining the data, the Shapiro–Wilk, ANOVA, and Tukey (p < 0.05) statistical tests were applied. Samples from all the groups were analyzed by scanning electron microscopy and Groups 3 and 4 were analyzed by profilometry. The means and the standard deviation values for the maximum force limit (N) and the maximum bending moment (Nmm) were respectively: G1:134.29 N (10.27); G2:300.61 N (24.26); G3:360.64 N (23.34); G4:419.10 N (18.87); G1:1612.02 Nmm (100.6); G2:2945 Nmm (237.97); G3:3530.38 Nmm (228.75); G4:4096.7 Nmm (182.73). The groups behaved statistically different from each other, showing that the smallest diameter implants provided less fracture resistance, both in the tensile strength tests and in the maximum bending moment between all groups. Furthermore, single-piece implants, with 2.5 mm and 3.0 mm diameters, deformed in the implant body region area, rather than in the abutment region.

Influence of Abutment Collar Height and Implant Length on Stress Distribution in Single Crowns

Abstract This in silico study evaluated the influence of the abutment collar height and implants length on the biomechanical behavior of morse taper single dental implants with different crown-to-implant ratio. Six virtual models were constructed (S11, M11, L11, S13, M13 and L13) by combining short (S: 2.5 mm), medium (M: 3.5 mm) or long (L: 4.5 mm) abutment collar heights with different implant lengths (11 or 13-mm). An upper central incisor of 11-mm height was constructed on top of each abutment. Each set was positioned in a virtual bone model and exported to analyze mathematically. A 0.60-mm mesh was created after convergence analysis and a 49 N load was applied to the cingulum of the crown at an angle of 45°. Load-generated stress distribution was analyzed in the prosthetic components according to von Mises stress criteria (σvM) and in the cortical and cancellous bone by means of shear stress (εmax). The use of longer collar abutments (L11) increased the stress on the abutment by 250% and resulted in 40% higher stresses on the screw and 92% higher cortical shear stresses compared to short collared abutments (S11). Increasing the implant length produced a slight stress reduction on cortical bone. Cancellous bone was not affected by the crown-to-implant ratio. Longer abutment collars concentrate stresses at the implant level and cortical bone by increasing the crown-to-implant ratio.

Implant fracture failure rate and potential associated risk indicators: An up to 12-year retrospective study of implants in 5,124 patients

OBJECTIVES

This study investigated fracture rates and risk indicators for fractures in internal connection dental implants.

MATERIAL AND METHODS

We performed a retrospective analysis of 19,006 internal connection implants used in fixed restoration in 5,124 patients (4,570 males, 554 females) at the Dental Hospital of Veterans Health Service Medical Center between 2006 and 2015. Patients were followed through June 2018 (0.03-12.39 years post-installation). Clinical factors (age, sex, implant diameter, implant length, placement site, bone graft, fixture material, cervical feature, abutment connection, microthread, and platform switching) were recorded. Kaplan-Meier survival analysis identified risk indicators associated with an implant fracture. Cox regression models elucidated potential fracture risks.

RESULTS

One hundred and seventy-four implants fractured in 135 patients, for an incidence rate of 0.92% after an average of 4.95 ± 2.14 years of use. Kaplan-Meier estimates showed that the 3-, 5-, and 10-year survival rates of implants were 99.8%, 99.2%, and 97.7%, respectively. In the multivariable Cox regression model, the diameter, location, history of bone graft, and microthread presence were significantly correlated with implant fractures. Wide-diameter implants had a reduced fracture risk within 90 months, after which the diameter did not correlate with fractures. Implants placed in the anterior mandible had a lower fracture risk within 90 months; mandibular premolar implants corresponded with a lower risk after 90 months. Implants without a history of bone graft or microthreads were more likely to fracture throughout the follow-up time.

CONCLUSIONS

These results elucidate risk indicators for implant fractures and facilitate their reduction in clinical practice.

Peri-Implant Bone Loss of External Hexagon and Morse Taper in Patients Wearing Immediately Loaded Overdentures

The aim of this study was to evaluate the peri-implant bone loss of External Hexagon (EH) and Morse Taper (MT) implants in patients wearing immediately loaded mandibular overdentures during a 1-year follow-up. This is a non-randomized controlled clinical trial including 18 MT and 22 EH implants. Periapical radiographs were taken after overdentures insertion and following 1 year. The peri-implant bone loss was assessed through digitalization and analysis of the radiographs in the software Corel DRAW X7. For this, measurement from implant platform to residual ridge at mesial and distal surfaces of each implant was conducted. The results showed high success rate in the groups EH (100%) and MT (94.4%). For peri-implant bone levels, it was found significant difference between the groups (p=0.032) and greater bone loss was observed in the group EH. In general, bone loss was 0.85mm (±0.82) for EH and 0.10mm (±1.0) for MT. It was concluded that greater bone loss occurred in the group EH in comparison to the group MT after a 1-year follow-up.

Influence of platform diameter in the reliability and failure mode of extra-short dental implants

PURPOSE

To evaluate the influence of implant diameter in the reliability and failure mode of extra-short dental implants.

MATERIALS AND METHODS

Sixty-three extra-short implants (5mm-length) were allocated into three groups according to platform diameter: Ø4.0-mm, Ø5.0-mm, and Ø6.0-mm (21 per group). Identical abutments were torqued to the implants and standardized crowns cemented. Three samples of each group were subjected to single-load to failure (SLF) to allow the design of the step-stress profiles, and the remaining 18 were subjected to step-stress accelerated life-testing (SSALT) in water. The use level probability Weibull curves, and the reliability (probability of survival) for a mission of 100,000 cycles at 100MPa, 200MPa, and 300MPa were calculated. Failed samples were characterized in scanning electron microscopy for fractographic inspection.

RESULTS

No significant difference was observed for reliability regarding implant diameter for all loading missions. At 100MPa load, all groups showed reliability higher than 99%. A significant decreased reliability was observed for all groups when 200 and 300MPa missions were simulated, regardless of implant diameter. At 300MPa load, the reliability was 0%, 0%, and 5.24%, for Ø4.0mm, Ø5.0mm, and Ø6.0mm, respectively. The mean beta (β) values were lower than 0.55 indicating that failures were most likely influenced by materials strength, rather than damage accumulation. The Ø6.0mm implant showed significantly higher characteristic stress (η = 1,100.91MPa) than Ø4.0mm (1,030.25MPa) and Ø5.0mm implant (η = 1,012.97MPa). Weibull modulus for Ø6.0-mm implant was m = 7.41, m = 14.65 for Ø4.0mm, and m = 11.64 for Ø5.0mm. The chief failure mode was abutment fracture in all groups.

CONCLUSIONS

The implant diameter did not influence the reliability and failure mode of 5mm extra-short implants.

In vitro fatigue tests and in silico finite element analysis of dental implants with different fixture/abutment joint types using computer-aided design models

PURPOSE

The aim of this study was to evaluate fatigue resistance of dental fixtures with two different fixture-abutment connections by in vitro fatigue testing and in silico three-dimensional finite element analysis (3D FEA) using original computer-aided design (CAD) models.

METHODS

Dental implant fixtures with external connection (EX) or internal connection (IN) abutments were fabricated from original CAD models using grade IV titanium and step-stress accelerated life testing was performed. Fatigue cycles and loads were assessed by Weibull analysis, and fatigue cracking was observed by micro-computed tomography and a stereomicroscope with high dynamic range software. Using the same CAD models, displacement vectors of implant components were also analyzed by 3D FEA. Angles of the fractured line occurring at fixture platforms in vitro and of displacement vectors corresponding to the fractured line in silico were compared by two-way ANOVA.

RESULTS

Fatigue testing showed significantly greater reliability for IN than EX (p<0.001). Fatigue crack initiation was primarily observed at implant fixture platforms. FEA demonstrated that crack lines of both implant systems in vitro were observed in the same direction as displacement vectors of the implant fixtures in silico.

CONCLUSIONS

In silico displacement vectors in the implant fixture are insightful for geometric development of dental implants to reduce complex interactions leading to fatigue failure.

Fatigue Failure of Narrow Implants with Different Implant-Abutment Connection Designs

PURPOSE

To evaluate the reliability of narrow diameter dental implants (NDIs) with similar macrogeometry and 3 implant-abutment connection designs.

MATERIALS AND METHODS

Eighty-four NDIs (3.5 × 10 mm) were selected and divided into 4 groups (n = 21/group) according to implant-abutment connection design, as follows: EH - external hexagon, IH - internal hexagon, IC - internal conical, and IC-M - internal conical connected to a monolithic titanium abutment. Identical abutments were torqued to the implants, and standardized maxillary incisor crowns were cemented and subjected to step-stress accelerated life testing (SSALT) in water. Use of level probability Weibull curves, and reliability for a mission of 50,000 cycles at 75 N and 200 N were calculated.

RESULTS

The beta (β) values were: 1.48 for IC, 1.40 for IC-M, 8.54 for EH, and 1.98 for IH, indicating that damage accumulation was an acceleration factor for failure of all groups. At 75 N the probability of survival was not significantly different between groups. A decrease in reliability was observed for all groups at 200 N with no significant differences between IC (81.71%) and IC-M (94.28%), or between EH and IH (0%) which presented the lowest values. EH failures were primarily restricted to the screw, while IH involved screw and implant fracture. IC and IC-M were restricted to prosthetic failures (fracture and bending).

CONCLUSIONS

Narrow implants with external or internal hexagon connections presented the lowest reliability at high loads compared to internal conical connections. Failure modes differed among connections.

Is the internal connection more efficient than external connection in mechanical, biological, and esthetical point of views? A systematic review

PURPOSE

This systematic review aimed to evaluate if the internal connection is more efficient than the external connection and its associated influencing factors.

METHODS

A specific question was formulated according to the Population, Intervention, Control, and Outcome (PICO): Is internal connection more efficient than external connection in mechanical, biological, and esthetical point of views? An electronic search of the MEDLINE and the Web of Knowledge databases was performed for relevant studies published in English up to November 2013 by two independent reviewers. The keywords used in the search included a combination of "dental implant" and "internal connection" or "Morse connection" or "external connection." Selected studies were randomized clinical trials, prospective or retrospective studies, and in vitro studies with a clear aim of investigating the internal and/or external implant connection use.

RESULTS

From an initial screening yield of 674 articles, 64 potentially relevant articles were selected after an evaluation of their titles and abstracts. Full texts of these articles were obtained with 29 articles fulfilling the inclusion criteria. Morse taper connection has the best sealing ability. Concerning crestal bone loss, internal connections presented better results than external connections. The limitation of the present study was the absence of randomized clinical trials that investigated if the internal connection was more efficient than the external connection.

CONCLUSIONS

The external and internal connections have different mechanical, biological, and esthetical characteristics. Besides all systems that show proper success rates and effectiveness, crestal bone level maintenance is more important around internal connections than external connections. The Morse taper connection seems to be more efficient concerning biological aspects, allowing lower bacterial leakage and bone loss in single implants, including aesthetic regions. Additionally, this connection type can be successfully indicated for fixed partial prostheses and overdenture planning, since it exhibits high mechanical stability.