Survival rate, fracture strength and failure mode of ceramic implant abutments after chewing simulation

Evaluating the Impact of Pontic Geometry on Load to Failure and Displacement in Implant-Supported Monolithic Zirconia Prostheses: An In Vitro Analysis

The pontic design may influence the load-to-failure performance of fixed implant-supported screw-retained monolithic zirconia prostheses. This study aimed to evaluate the effect of pontic geometry on the fracture resistance of such restorations. Forty restorations were designed using dental CAD software and divided into four groups (n = 10 each): (A) Flat + Wide-pontics with a flat contour, 10 mm in width and 8 mm in height; (B) Concave + Wide-pontics with a concave contour, 10 mm in width and 5.5 mm in height; (C) Flat + Narrow-pontics with a flat contour, 6 mm in width and 8 mm in height; and (D) Concave + Narrow-pontics with a concave contour, 6 mm in width and 5.5 mm in height. All specimens underwent thermal and mechanical cycling, followed by a fracture load test using a three-point bending setup. Maximum fracture loads and displacements were analyzed using one-way ANOVA. Statistically significant differences were observed among the groups for both load to failure (p = 0.001) and displacement (p = 0.002). These findings indicate that pontic geometry significantly influences the fracture resistance and deformation behavior of monolithic zirconia prostheses.

The effect of different abutment and restorative crown materials on stress distribution in single-unit implant-supported restorations: A 3D finite element stress analysis

PURPOSE

To evaluate the effect of restorative materials with or without resin content, modeled on zirconia and titanium abutment materials, on the stress distribution on the alveolar bone, implant, and prosthetic crowns with a 3D finite element stress analysis.

MATERIAL AND METHODS

Titanium and zirconia abutments were combined with three implant-supported crown materials (polymer infiltrated hybrid ceramic (PICN), lithium disilicate (LD), and zirconia-reinforced lithium silicate (ZLS)) to create six experimental groups. The 40 × 30 × 20 mm alveolar bone, 3.75 × 10 mm implant, esthetic abutment, and maxillary first premolar crown bonded over the abutment were the components of the finite element models. On the lingual cusp of the crown, the 150 N occlusal loading was applied in the buccolingual direction at a 30° angle. Equivalent von Mises stress and maximum and minimum principal stresses were used for both the qualitative and quantitative evaluation of the stress distribution of the created models.

RESULTS

The von Mises stress in implant and abutment did not differ according to the crown materials. The use of a zirconia abutment resulted in higher von Mises stress values in the abutment but lower stress values in the implant. The highest stress values were obtained in ZLS (196.65 MPa) and LD (194.05 MPa) crowns. The use of titanium abutments, regardless of crown materials, resulted in higher von Mises stress values in restorative crowns than in zirconia abutments. The principal stress values in alveolar bone showed similar distribution and concentration in all models.

CONCLUSIONS

Changes in crown material did not affect stress distribution in the implant and peripheral bone. However, the zirconia esthetic abutment resulted in a lower stress concentration on the implant.

Simultaneous Implant and Guided Bone Regeneration Using Bovine-Derived Xenograft and Acellular Dermal Matrix in Aesthetic Zone

INTRODUCTION

Implant placement in the maxillary anterior area requires sufficient quantity and quality of both soft and hard tissue. In cases where soft and hard tissues are insufficient, additional regeneration using biomaterials is recommended. Treatment using bovine-derived xenograft and acellular dermal matrix (ADM) may increase bone volume and soft tissue thickness. Case and management: A 65-year-old woman sought help for discomfort and aesthetic issues with her denture, reporting missing teeth (11, 12, 13, 14, and 21) and bone volume shrinkage due to disuse atrophy. Intraoral examination revealed 1 mm gingival thickness. CBCT showed labio-palatal bone thickness of 6.0 mm, 5.8 mm, and 4.7 mm for teeth 21, 12 and 14, respectively. Implant planning and surgical guide fabrication were carried out before the surgery. Surgery included the placement of implants 3.3 mm in diameter and 12 mm in length, with the use of xenograft and ADM. Three months post-op, improvements in soft and hard tissues were observed, with a final prosthesis being a long-span implant-supported bridge.

CONCLUSIONS

Disuse alveolar atrophy causes soft and hard tissue deficiency. The use of xenograft and ADM show favourable results even on a geriatric patient.

Fatigue and failure analysis of restored endodontically treated maxillary incisors without a dowel or ferrule

STATEMENT OF PROBLEM

Information on the survival and mode of failure of endodontically treated incisors without a ferrule and restored without dowels is lacking.

PURPOSE

The purpose of this in vitro study was to compare the survival and failure mode of endodontically treated incisors without a ferrule and restored with bonded ceramic crowns and various composite resin foundation restorations without dowels with a control group with fiber dowels.

MATERIAL AND METHODS

Forty-five decoronated endodontically treated bovine incisors without ferrule were divided into 3 experimental groups and restored with different adhesive foundation restorations without dowel: nanohybrid composite resin (Nd), bulk-fill composite resin foundation restoration (NdB), and fiber-reinforced bulk-fill composite resin (NdFR). A control group with conventional foundation restorations (glass-fiber dowel with nanohybrid composite resin foundation restoration without ferrule) (D) was included for comparison. All teeth were prepared to receive bonded lithium disilicate ceramic crowns luted with dual-polymerizing composite resin cement and were subjected to accelerated fatigue testing. Cyclic isometric loading was applied to the incisal edge at an angle of 30 degrees and a frequency of 5 Hz, beginning with a load of 100 N (5000 cycles). A 100-N load increase was applied each 15 000 cycles. Specimens were loaded until failure or to a maximum for cycles endured of 1000 N (140 000 cycles). Groups were compared by using the Kaplan-Meier survival analysis (log rank test at α=.05 and pairwise post hoc comparisons) and life table analysis for load-at-failure (followed by Wilcoxon pairwise comparison α=.05).

RESULTS

All the specimens failed before 140 000 load cycles. Even though no statistically significant differences were found between the experimental groups without dowel (P>.127), the fiber-reinforced foundation restoration yielded the highest mean ±standard deviation cycles to failure (46 023 ±4326) compared with Nd (38 899 ±2975) and NdB (39 751 ±2998). NdFR, however, outperformed the foundation restoration with glass-fiber dowel (35 026 ±2687) (P<.05). Most failure in groups without dowel were restorable, while 100% of catastrophic failure (unrestorable) were found in the group with dowels.

CONCLUSIONS

Based on the present in vitro study, dowels did not improve the performance of the adhesive restoration of endodontically treated incisors without a ferrule. The use of a short fiber-reinforced composite resin foundation restoration without a dowel was able to not only improve the resistance of the restorations compared with adhesive foundation restorations with dowels but also minimize catastrophic failures.

Influence of monolithic restorative materials on the implant-abutment interface of hybrid abutment crowns: An in vitro investigation

Purpose This in vitro study aimed to investigate the long-term performance, stability, and fracture mode of monolithic hybrid abutment crowns, and the effect of different materials on the implant-abutment interface (IAI).Methods Eighty monolithic hybrid abutment crowns luted on titanium bases were manufactured from 3Y-TZP zirconia (ZY3), "Gradient Technology" zirconia (ZY35), 5Y-TZP zirconia (ZY5), lithium disilicate ceramic (LDS), zirconia-reinforced lithium silicate ceramic (ZLS), polymer-infiltrated ceramic network (MHY), polymethylmethacrylate (PMA), and 3D-printed hybrid composite (PHC) (n = 10 for each material). Eighty implants (Camlog Progressive-Line, diameter: 3.8 mm) were embedded in accordance with ISO standard 14801, and crowns were mounted. After artificial aging (1.2 × 10⁶ cycles, 50 N, thermocycling), intact specimens were loaded 30° off-axis in a universal testing machine until failure.Results Seven specimens in the PHC group failed during artificial aging, and all the others survived. There were two subgroups based on the one-way analysis of variance and Dunnett's test (P < 0.05) of the mean fracture load values. The first comprised Z3Y, ZY35, Z5Y, and LDS, with mean fracture loads between 499.4 and 529.7 N, while the second included ZLS, MHY, and PMA, with values in the 346.2-416.0 N range. ZY3, ZY35, ZY5, and LDS exhibited irreversible, visible deformations of the implant shoulders with varying dimensions after load-to-fracture tests.Conclusions Crowns made of LDS, ZLS, MHY, and PMA may act as potential stress breakers, and prevent possible deformation at IAIs. Further clinical studies need to assess if these materials also withstand relevant loads in-vivo.

Fracture load of 4-unit interim fixed partial dentures using 3D-printed and traditionally manufactured materials

STATEMENT OF PROBLEM

How the fracture strength of recently introduced 3-dimensionally (3D) printed interim materials compares with that of conventional materials is unclear.

PURPOSE

The purpose of this in vitro study was to compare the fracture load of 4-unit interim fixed partial dentures made from 3 different materials before and after mastication simulation.

MATERIAL AND METHODS

Based on a master model of a 4-unit fixed partial denture with maxillary left first premolar and second molar abutment teeth, interim restorations were fabricated from 3 different materials (3D-printed, Temporary CB Resin, milled, PMMA for brain, and manually manufactured, Luxatemp Plus). The fixed partial dentures (n=30 for each material) were cemented on 3D-printed model abutment teeth that were connected via a thin latex layer to a polyurethane base block. The fracture load of 15 fixed partial dentures of each material was tested without aging. Another 15 fixed partial dentures of each material were tested after thermomechanical aging.

RESULTS

The mean fracture load was between 186 N and 661 N, and all materials showed significant lower fracture loads after aging. Before and after aging (before/after ±standard deviation) milled (661 ±59/568 ±52 N) achieved the highest loads before manually manufactured (621 ±100/478 ±96 N) and 3D-printed (294 ±83/186 ±70).

CONCLUSIONS

The 3D-printed interim restoration material and the inherent manufacturing process show significant lower fracture loads than the tested alternatives. However, as the influence of geometric differences could not be quantified, whether this remains true after correcting for geometric differences remains unclear. For the tested interim materials, thermocycling and mastication simulation significantly reduced fracture loads over time, even at loads as low as 50 N.

Prosthetic complications with monolithic or micro-veneered implant-supported zirconia single-unit, multiple-unit, and complete-arch prostheses on titanium base abutments: A single center retrospective study with mean follow-up period of 72.35 months

BACKGROUND

The influence of prosthetic design on prosthetic complications when monolithic or micro-veneered zirconia prostheses are supported with titanium base (ti-base) abutments is not well-known.

PURPOSE

The purpose of this single center, retrospective study was to assess the prevalence of prosthetic complications with monolithic or micro-veneered single-unit, multi-unit, and complete-arch zirconia prostheses supported with ti-base abutments (implant level or multi-unit abutment level).

MATERIAL AND METHODS

This study retrospectively evaluated the electronic health record (EHR) of participants who received either monolithic or micro-veneered implant-supported single-unit, multi-unit, and/or complete-arch prostheses supported by ti-base or zirconia-ti-base hybrid abutments delivered between the years 2010 and 2021. Data were analyzed by using logistic regression and Exact Mantel-Haenszel chi-square test (α = 0.05) to assess the clinical performance of prostheses and complications including crown decementation, feldspathic porcelain chipping, prosthesis fracture, zirconia-ti-base hybrid abutment decementation, abutment screw loosening, screw fracture, abutment fracture, implant loss, and prosthesis remake.

RESULTS

The study included 94 participants (50 female, 44 male) with a mean age of 59.5 years (range: 24-101 years of age). The retrospective EHR evaluation yielded 82 single-unit, 51 multi-unit, and 20 complete-arch prostheses on 325 implants. Among 153 prostheses delivered, 108 were micro-veneered (47 single-unit, 41 multi-unit, and 20 complete-arch prostheses) and 45 were monolithic. The average duration was 72.35 months (6.02 years) with a follow-up period of 5-132 months. From the time of insertion to the time of EHR review, of 153 prostheses, 78.43% did not exhibit any prosthetic complication. However, 33 prostheses (21.57%) from 29 participants (30.85%) had at least one prosthetic complication. Only four patients (4.25%) experienced two or more prosthetic complications. Prosthetic design affected the probability of having a complication (p = 0.005); complete-arch prostheses had higher probability (p ≤ 0.028). Single-unit prostheses had lower probability of complication than multi-unit prostheses (p = 0.005). The most commonly observed complication was fracture of veneering material (5.88%) followed by prosthetic screw loosening (4.57%) and decementation between the zirconia and the ti-base abutment (2.61%). Micro-veneered complete-arch prostheses had higher probability of having chipping than that of not having (p < 0.001), and other micro-veneered prosthetic designs had similar probability of chipping with that of complete-arch prostheses (p ≥ 0.082). Frequency of chipping was affected by veneering (p < 0.001). Monolithic prostheses had lower probability of chipping than micro-veneered prostheses, regardless of the prosthetic design (p < 0.001).

CONCLUSIONS

The frequency of prosthetic complications varied depending on prosthetic design. Complete-arch prostheses had the highest probability of complications while the single-unit prostheses had the lowest. Micro-veneered prostheses had higher probability for chipping than monolithic prostheses. Probability of chipping was similar for micro-veneered single-unit, multi-unit, and complete-arch zirconia prostheses.

Comparing the Fracture Resistance and Modes of Failure in Different Types of CAD/CAM Zirconia Abutments with Internal Hexagonal Implants: An In Vitro Study

Three groups of zirconia abutments (n = 5) consisting of different connection designs or manufacturers were investigated (All-Zr, ASC-Zr, and AM-Zr groups). All-electric dynamic test instruments were used to place static loading on a specimen with a crosshead speed set at 1 mm/min. A Kruskal-Wallis test and a post hoc Mann-Whitney U test were used for statistical evaluation. The mean fracture resistance was 252.37 ± 82.79 N for the All-Zr group, 384.62 ± 45.24 N for ASC-Zr group, and 361.83 ± 90.31 N for the AM-Zr group. The difference of fracture resistance between the three groups was marginally significant (Kruskal-Wallis test, p = 0.054), with the ASC zirconia abutment tending to have higher fracture resistance than the full zirconia abutment. The modes of failure among the three types of abutments are different. The All-Zr group showed an oblique fracture line starting from the buccal aspect at the region of the implant platform. While the ASC-Zr and AM-Zr groups showed a relatively horizontal fracture line with a greater distance from the implant platform. The titanium inserts cannot significantly improve the fracture resistance of the zirconia abutment. However, they may alter the modes of failure, allowing buccal fracture surfaces of the zirconia abutments to be placed away from the implant platform, thereby protecting the implant-abutment connection.

Original vs compatible stock abutment- implant connection. An in vitro analysis of the internal accuracy and mechanical fatigue behaviour

PURPOSE

To assess the internal accuracy and mechanical behaviour under cyclic loading after artificial aging of implantsupported crowns restored with original stock abutments and two compatible non-original stock abutments.

METHODS

Forty-eight original internal hexagon connection implants were connected to different stock abutments. The samples were divided into three groups depending on the manufacturer of the abutment components (one original, two non-originals).Firstly, samples were cross-sectioned and observed by using Scanning Electron Microscope (SEM) to evaluate the internal accuracy in three different implant-abutment interface locations (platform, internal and screw). Further, cyclic fatigue loading was carried out according to the ISO Norm 14801 using dynamic testing machine under sinusoidal loads for 2,000,000 cycles at test frequencies of 2 Hz in air after thermocycling with 10,000 cycles at 5 °C and 55 °C in artificial saliva for aging simulation.

RESULTS

Original abutment components presented the highest percentage of surface with tight contact with the implant in the three implant-abutment interfaces studied. Additionally, original configuration showed highest fatigue limit value and fatigue strength exponent (280 N and -0.054) than non-original 1 (225 N and -0.109) and non-original 2 (200 N and -0.101).

CONCLUSION

Original abutment components provide better fit and mechanical results under cyclic loading than nonoriginal configurations. The results obtained in this study seem to suggest that the use of the original stock abutments to implants leads to a more homogeneous load distribution between the components that can influence the long-term success of the restorations.

Performance of different abutment/implant joints as a result of a sealing agent

Purpose This in vitro study aimed to evaluate the effectiveness of a sealing agent in sealing the abutment/implant interface and the preload maintenance of retaining screws after mechanical cycling.Methods Six groups (n = 12) were evaluated according to the abutment/implant system (external-hexagon implant and UCLA abutments, EHU; Morse taper implant and UCLA abutments, MTU; and Morse taper implant and flexcone abutments, MTF) and the presence of an anaerobic gel sealing agent (control group, no sealing agent; experimental group, sealing agent). Toluidine blue (0.7 μL) was inserted into each implant and the abutments were attached to the implants using a digital torque wrench to evaluate the sealing of the abutment/implant interface. The specimens were tested through mechanical cycling (1 × 10⁶ cycles, 2 Hz, and 130 N). Dye release from the abutment/implant interface was analyzed using a spectrophotometer, and the reverse torque values were obtained using a digital wrench. Reverse torque and dye release data were measured after mechanical cycling and analyzed using ANOVA and Tukey's test (α =.05).Results All experimental groups showed higher reverse torque values than the control groups (P <.05). In general, the MTU and MTF experimental groups, as well as the MTF control group, showed no significant dye release at different periods (P >.05).Conclusions The use of a sealing agent improved the preload maintenance of screw-retained implant-supported prostheses. The sealing agent was effective in sealing the Morse taper connection.

Influence of butt joint connections with long guiding areas on the stability of single crowns and 3-unit bridges - an in-vitro-study

PURPOSE

The aim of this study was to evaluate the stability of single crowns and 3-unit bridges in relation to the implant-abutment complex with and without tube in tube connection.

METHODS

60 specimens with a total of 90 implants (diameter 3.8 mm) were fabricated and distributed into 4 groups: CST (Crown with short tube), CLT (crown with long tube), BNT (Bridge without tube) and BLT (bridge with long tube). All superstructures consisted of one-piece hybrid abutment restorations out of monolithic zirconia, bonded on prefabricated titanium bases and were directly screwed into the implants. Specimen underwent artificial aging (2.000.000 cycles, 120 N, 30° off axis) and were subsequently loaded in an universal testing machine at an angle of 30° until failure. The specimens were examined for damage during and after artificial aging.

RESULTS

During artificial aging, one test specimen of group CLT and two test specimens of group BNT failed. The average failure load was 498.8 (± 34.4) N for CLT, 418.8 (± 41.5) N for CST, 933.1 (± 26.2) N for BLT and 634.4 (± 29.0) N for BNT, with a statistical differences (p ˂ 0.001) between the crown and bridge groups. All tested samples exhibited macroscopic deformations at the implant shoulder, which were more pronounced in the specimens without a tube in tube connection.

CONCLUSIONS

Single crowns and 3-unit bridges with a long tube in tube connection showed significantly higher fatigue fracture strength compared to restorations with short or without tube in tube connection.

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.

Effect of Different Implant-Abutment Connection Materials on the Fracture Resistance of Zirconia Abutments

The aim of the present in vitro study was to assess the modes of failures under static load among titanium (Ti) and 1- and 2-piece zirconia abutments. The 1- and 2-piece zirconia abutment specimens were fabricated from prescanned Ti abutments. Twenty-one implant abutments and 21 implant replicas were equally divided into 3 groups as follows: (a) Group 1 (Titanium group); (b) Group 2 (1-piece zirconia abutment group); and (c) Group 3: 2-piece zirconia abutment group). A 250 000-cycle linear fatigue load ranging between 10 N and 210 N was applied to all specimens using an all-electric dynamic test instrument. The specimens were loaded until they fractured. In all groups, assessment of mode of fracture was done on visual assessment by a trained and calibrated investigator. Prior sample-size estimation was performed; and sample distribution was assessed using the Kolmogorov and Shapiro tests. Screw fracture (n = 7) and abutment bending at the apical part (n = 7) occurred in the Ti group. In the 1-piece zirconia group, screw and abutment fractures occurred in 7 and 7 cases, respectively. In the 2-piece zirconia screw fracture (n = 7) above the Ti zirconia junction (transgingival segment) and abutment fracture (n = 7) were determined as the failure modes. In vitro, the 1-piece zirconia abutments are more fracture resistant than titanium and 2-piece zirconia abutments. From a clinical perspective, further studies are needed to determine the minimum static load value required to induce fracture of the 1- and 2-piece zirconia abutments.

Two-part implant abutments with titanium and ceramic components: Surface modification affects retention forces-An in-vitro study

OBJECTIVES

Two-part abutments consist of titanium base and ceramic coping. Their long-term success is largely determined by the mechanical stability. The aim of the present study was to investigate the retention forces of two-part implant abutments. The study included zirconia and lithium disilicate ceramics copings, with different surface treatments and resin-based luting agents.

MATERIAL AND METHODS

The analysis of retention forces was based on a total of 70 test specimens. Seven surface modifications and three resin-based luting agents were employed for the bonding of components in the seven groups (n = 70). All surfaces of titanium bases-except for a control-were pretreated with aluminum oxide blasting, either alone or in combination with surface activating primers. Surfaces of ceramic copings were also treated mechanically by sandblasting, either alone or with acid etching or different primers. All specimens underwent thermal aging (10⁴ cycles, 5°C/55°C). The retention forces between the two parts were measured with a pull-off test. The results were analyzed by two-way ANOVA statistics. Fracture patterns were evaluated by light and scanning electron microscopy.

RESULTS

No mechanical pretreatment of the titanium (group 2) base resulted in the lowest retention. The combination with Monobond plus leads to the highest pull-off forces for both ceramic materials.

CONCLUSIONS

Surface modifications and resin-based agents influence the retention of components of two-part abutments. Lithium disilicate ceramic copings reached comparable results of retention to the typically used zirconia copings.

Fatigue survival and failure resistance of titanium versus zirconia implant abutments with various connection designs

STATEMENT OF PROBLEM

Data regarding the effect of connection design and abutment material on the fatigue survival and failure resistance of implant abutments are scarce.

PURPOSE

The purpose of this in vitro study was to investigate the effect of connection design and abutment material on the fatigue survival and failure resistance of implant abutment assemblies.

MATERIAL AND METHODS

Three types of implants (n=18, N=54) and 6 groups of abutments (n=9, N=54) with different connection designs-internal conical (IC), internal tri-channel (IT), and external hexagonal (EH)-and abutment materials-titanium (T) and zirconia (Z)-were investigated. All the abutments were restored with identical central incisor crowns. Fatigue testing, including thermal and mechanical aging, was performed in a mastication simulator (Esetron Smart Robotechnologies) for up to 1.2×10⁶ cycles with a load of 50 N at an angle of 45 degrees. Then, the surviving specimens were subjected to failure resistance testing in a universal testing machine (Shimadzu AG-IS; Shimadzu Corp) at a crosshead speed of 1.0 mm/min. The maximum loads to failure (N) were recorded. Survival performance of the specimens throughout the fatigue testing was examined by the Kaplan-Meier survival analysis. The failure loads were analyzed by using the Kruskal-Wallis test followed by the Mann-Whitney U tests with Bonferroni-Holm correction (α=.05).

RESULTS

All the specimens of groups ICT, ITT, ITZ, and EHT survived fatigue testing, whereas 2 specimens from group ICZ and 3 specimens from EHZ failed. Statistically significant differences were found among the groups, based on the results of maximum failure loads (P<.05). The highest mean failure load was obtained in the ICT group (1069 ±182 N), followed by the ITT (926 ±197 N), EHT (873 ±126 N), ITZ (568 ±81 N), EHZ (311 ±45 N), and ICZ (287 ±63 N) groups.

CONCLUSIONS

Abutment material and connection design affected the fatigue survival of implant abutment assemblies. Implant abutment assemblies with a titanium-titanium interface revealed higher failure resistance than the implant abutment assemblies with a titanium-zirconia interface.

Contact analysis of gap formation at dental implant-abutment interface under oblique loading: A numerical-experimental study

PURPOSE

To develop numerical and experimental methods for investigating the formation of micro-gaps and the change in contact area at the implant-abutment interface of two different connector designs under oblique cyclic loading.

MATERIALS AND METHODS

Samples (n = 10 per group) of two-piece implant systems with the conical connection (group A) and the external hexagonal connection (group B) were subjected to cyclic loading with increasing load amplitudes up to 220 N. After loading, the samples were scanned using micro-CT, with silver nitrate as a high-contrast penetrant, and the level of leakage was assessed using a discrete scoring system. Three-dimensional finite element (FE) analyses of the two implant systems were also conducted to reveal the micro-gap formation process, especially bridging of the internal abutment screw space. The experimental and numerical results for the bridging load were then compared.

RESULTS

90% of the samples in group A showed leakage into the internal implant space at a load of around 100 N; while over 80% of those in group B did so at a load of around 40 N. This agreed with the FE analysis, which showed bridging of the internal implant space at loads similar to those measured for the two implant systems. Residual gaps of less than 1.49 μm were predicted for group A only after unloading.

CONCLUSIONS

The FE-predicted loads for bridging agreed well with those found experimentally for leakage to occur. The conical connection showed more resistance against formation of micro-gaps at the implant-abutment interface than the external hexagonal connection. Although the minimum load required to bridge the internal implant space was within the range of human biting force, the relation between bacterial invasion and micro-gaps needs further research.

A systematic review of the influence of the implant-abutment connection on the clinical outcomes of ceramic and metal implant abutments supporting fixed implant reconstructions

OBJECTIVES

The objective of this systematic review was to assess the influence of implant-abutment connection and abutment material on the outcome of implant-supported single crowns (SCs) and fixed dental prostheses (FDPs).

METHODS

An electronic Medline search complemented by manual searching was conducted to identify randomized controlled clinical trials, prospective and retrospective studies with a mean follow-up time of at least 3 years. Patients had to have been examined clinically at the follow-up visit. Failure and complication rates were analyzed using robust Poisson regression, and comparisons were made with multivariable Poisson regression models.

RESULTS

The search provided 1511 titles and 177 abstracts. Full-text analysis was performed for 147 articles resulting in 60 studies meeting the inclusion criteria. Meta-analysis of these studies indicated an estimated 5-year survival rate of 97.6% for SCs and 97.0% for FDPs supported by implants with internal implant-abutment connection and 95.7% for SCs and 95.8% for FDPs supported by implants with external connection. The 5-year abutment failure rate ranged from 0.7% to 2.8% for different connections with no differences between the types of connections. The total number of complications was similar between the two connections, yet, at external connections, abutment or occlusal screw loosening was more predominant. Ceramic abutments, both internally and externally connected, demonstrated a significantly higher incidence of abutment fractures compared with metal abutments.

CONCLUSION

For implant-supported SCs, both metal and ceramic abutments with internal and external connections exhibited high survival rates. Moreover, implant-supported FDPs with metal abutments with internal and external connections for also showed high survival rates.

The Use of a Hybrid Pillar and Its Importance for Aesthetic Rehabilitation and Tissue Stability: A Clinical Report

In the past, aesthetics had a secondary role in implant rehabilitation. Nowadays, the search for a perfect and harmonious aesthetic has stimulated the development of new materials and techniques. Due to this aesthetic requirement, the hybrid abutment (titanium link + zirconia) emerged as an alternative to metallic pillars. The hybrid abutment made a more favorable aesthetic possible, provided reliable mechanical properties, and increased biocompatibility to the surrounding tissues. Additionally, the individual zirconia abutment improves the emergency profile and the final white aesthetics. The objective of this paper is to report a clinical case with a manufactured individualized hybrid abutment for a metal-free indirect restoration, showing the applicability, mechanical properties, and biocompatibility of the hybrid abutment.

Dislodgement Resistance of Zirconia Copings Cemented onto Zirconia and Titanium Abutments

PURPOSE

To determine the effect of the cement type and abutment material on the tensile strength required to dislodge zirconia copings.

MATERIALS AND METHODS

Two experimental groups of abutments were prepared: (1) titanium abutments (n = 30) and (2) zirconia abutments (n = 30). Sixty zirconia copings (custom designed) were fabricated using 3-dimensional computer-assisted design to have a 6-mm projection above the abutment to accommodate a hole, through which a wire was inserted to attach the zirconia coping to a universal testing machine. Each abutment was placed onto an implant analog embedded in acrylic resin blocks to fit onto the universal testing machine. The zirconia copings were cemented onto the abutments with a provisional luting agent, zinc phosphate (ZP) cement, and adhesive resin cement, and after 5500 thermocycles, a tensile force was applied at a crosshead speed of 0.5 mm/min. The removal force was recorded for each specimen. Two-way analysis of variance (ANOVA) and 1-way ANOVA were used for the statistical analysis (P < 0.05).

RESULTS

The mean forces necessary to remove the zirconia copings from titanium abutments were 6.52, 83.09, and 251.18 N for temporary cement, ZP cement, and resin cement, respectively. For zirconia abutments, the required forces were 17.82, 116.41, and 248.72 N.

CONCLUSIONS

The abutment material had no effect on retention, but the cement type affected the retention of the zirconia copings.

Compressive Resistances and Failure Modes of Abutments With Different Transgingival Heights and Types on Internal Conical Connected Implants

PURPOSE

This study aimed to research the effect of different transgingival heights (THs) and types of abutments on performances including the compressive resistances and fracture modes of abutments on internal conical connected implants.

MATERIALS AND METHODS

Three groups were established: a 1-piece zirconia abutment group (group A), a 2-piece zirconia abutment group (group B), and a 1-piece titanium abutment group (group C). Three THs (2, 3.5, and 5 mm, n = 6) were set as the subgroups of each group. All groups were subjected to a compressive resistance test at a 30 degree angle. The main failure modes were analyzed using scanning electron microscopy and a stereomicroscope.

RESULTS

The compressive resistances of the abutments on the internal conical connected implants were significantly related to the TH (P = 0.004), the type of abutment (P < 0.0001), and the combined effect (P < 0.0001). All of the subgroups in group C exhibited the greatest compressive loads at the same TH. Different types of abutments had different failure modes.

CONCLUSIONS

Both the TH and the type of abutments influenced compressive resistances of the implant-abutment complexes.

Comparison of fit accuracy and torque maintenance of zirconia and titanium abutments for internal tri-channel and external-hex implant connections

PURPOSE

This in vitro study aimed to evaluate the effect of implant connection design (external vs. internal) on the fit discrepancy and torque loss of zirconia and titanium abutments.

MATERIALS AND METHODS

Two regular platform dental implants, one with external connection (Brånemark, Nobel Biocare AB) and the other with internal connection (Noble Replace, Nobel Biocare AB), were selected. Seven titanium and seven customized zirconia abutments were used for each connection design. Measurements of geometry, marginal discrepancy, and rotational freedom were done using video measuring machine. To measure the torque loss, each abutment was torqued to 35 Ncm and then opened by means of a digital torque wrench. Data were analyzed with two-way ANOVA and t-test at α=0.05 of significance.

RESULTS

There were significant differences in the geometrical measurements and rotational freedom between abutments of two connection groups (P<.001). Also, the results showed significant differences between titanium abutments of internal and external connection implants in terms of rotational freedom (P<.001). Not only customized internal abutments but also customized external abutments did not have the exact geometry of prefabricated abutments (P<.001). However, neither connection type (P=.15) nor abutment material (P=.38) affected torque loss.

CONCLUSION

Abutments with internal connection showed less rotational freedom. However, better marginal fit was observed in externally connected abutments. Also, customized abutments with either connection could not duplicate the exact geometry of their corresponding prefabricated abutment. However, neither abutment connection nor material affected torque loss values.

A device for testing the durability and exploitation reliability of dental prostheses

PURPOSE

The aim of this work was to develop the design of the construction of a stand for testing the operational stability of dental prostheses, designed on the basis of an own idea. There are no devices that would make it possible to test complete structures, including the actual kinematics of motion and the influence of the environment of the oral cavity.

MATERIALS AND METHODS

Presented were several devices used for testing both fixed and removable prostheses. Attention was paid to their limited possibilities in the area of the tested friction node, kinematics of motion, and the assessment of the influence of the environment of the oral cavity on the tested functional quality. The construction was based on the author's own ideas as well as on a review of the available literature.

RESULTS

As the final result of the research, simplified images of the stand were presented along with their descriptions.

CONCLUSIONS

The experimental verification of the stand allowed concluding that the research aims have been achieved. First of all, the device allows testing prosthetic structures of different sizes and it is possible to load the tested prostheses in randomly chosen points.

Comparison of mechanical and biological properties of zirconia and titanium alloy orthodontic micro-implants

OBJECTIVE

The aim of this study was to compare the initial stability as insertion and removal torque and the clinical applicability of novel orthodontic zirconia micro-implants made using a powder injection molding (PIM) technique with those parameters in conventional titanium micro-implants.

METHODS

Sixty zirconia and 60 titanium micro-implants of similar design (diameter, 1.6 mm; length, 8.0 mm) were inserted perpendicularly in solid polyurethane foam with varying densities of 20 pounds per cubic foot (pcf), 30 pcf, and 40 pcf. Primary stability was measured as maximum insertion torque (MIT) and maximum removal torque (MRT). To investigate clinical applicability, compressive and tensile forces were recorded at 0.01, 0.02, and 0.03 mm displacement of the implants at angles of 0°, 10°, 20°, 30°, and 40°. The biocompatibility of zirconia micro-implants was assessed via an experimental animal study.

RESULTS

There were no statistically significant differences between zirconia micro-implants and titanium alloy implants with regard to MIT, MRT, or the amount of movement in the angulated lateral displacement test. As angulation increased, the mean compressive and tensile forces required to displace both types of micro-implants increased substantially at all distances. The average bone-to-implant contact ratio of prototype zirconia micro-implants was 56.88 ± 6.72%.

CONCLUSIONS

Zirconia micro-implants showed initial stability and clinical applicability for diverse orthodontic treatments comparable to that of titanium micro-implants under compressive and tensile forces.

Effect of screw access hole preparation on fracture load of implant-supported zirconia-based crowns: an in vitro study

Background. Fracture load of implant-supported restorations is an important factor in clinical success. This study evaluated the effect of two techniques for screw access hole preparation on the fracture load of cement-screw-retained implant-supported zirconia-based crowns.

Methods. Thirty similar cement-screw-retained implant-supported zirconia-based maxillary central incisor crowns were evaluated in three groups of 10. Group NH: with no screw access holes for the control; Group HBS: with screw access holes prepared with a machine before zirconia sintering; Group HAS: with screw access holes prepared manually after zirconia sintering. In group HBS, the access holes were virtually designed and prepared by a computer-assisted design/computer-assisted manufacturing system. In group HAS, the access holes were manually prepared after zirconia sintering using a diamond bur. The dimensions of the screw access holes were equal in both groups. The crowns were cemented onto same-size abutments and were then subjected to thermocycling. The fracture load values of the crowns were measured using a universal testing machine. Data were analyzed with ANOVA and Tukey test (P < 0.05).

Results. The mean fracture load value for the group NH was 888.37 ± 228.92 N, which was the highest among the groups, with a significant difference (P < 0.0001). The fracture load values were 610.48 ± 125.02 N and 496.74 ± 104.10 Nin the HBS and HAS groups, respectively, with no significant differences (P = 0.44).

Conclusion. Both techniques used for preparation of screw access holes in implant-supported zirconia-based crowns decreased the fracture load.

The role of prosthetic abutment material on the stress distribution in a maxillary single implant-supported fixed prosthesis

PURPOSE

Evaluate the influence of abutment's material and geometry on stress distribution in a single implant-supported prosthesis.

MATERIALS AND METHODS

Three-dimensional models were made based on tomographic slices of the upper middle incisor area, in which a morse taper implant was positioned and a titanium (Ti) or zirconia (ZrN) universal abutments was installed. The commercially available geometry of titanium (T) and zirconia (Z) abutments were used to draw two models, TM1 and ZM1 respectively, which served as control groups. These models were compared with 2 experimental groups were the mechanical properties of Z were applied to the titanium abutment (TM2) and vice versa for the zirconia abutment (ZM2). Subsequently, loading was simulated in two steps, starting with a preload phase, calculated with the respective friction coefficients of each materials, followed by a combined preload and chewing force. The maximum von Mises stress was described. Data were analyzed by two-way ANOVA that considered material composition, geometry and loading (p<0.05).

RESULTS

Titanium and zirconia abutments showed similar von Mises stresses in the mechanical part of the four models. The area with the highest concentration of stress was the screw thread, following by the screw body. The highest stress levels occurred in screw thread was observed during the preloading phase in the ZM1 model (931MPa); and during the combined loading in the TM1 model (965MPa). Statistically significant differences were observed for loading, the material×loading interaction, and the loading×geometry interaction (p<0.05). Preloading contributed for 77.89% of the stress (p<0.05). There were no statistically significant differences to the other factors (p>0.05).

CONCLUSION

The screw was the piece most intensely affected, mainly through the preload force, independent of the abutment's material.

Fracture Resistance of Molar Crowns Fabricated with Monolithic All-Ceramic CAD/CAM Materials Cemented on Titanium Abutments: An In Vitro Study

PURPOSE

To assess the fracture resistance of single-tooth implant-supported crown restorations made with different CAD/CAM blocks.

MATERIALS AND METHODS

Thirty-six titanium abutments were put on dental implant analogs (Mis Implant). For each of three test groups (n = 12/group), implant-supported, cement-retained mandibular molar single crowns were produced. Crowns were made of lithium disilicate glass (LD) IPS e.max CAD, feldspathic glass ceramic (FEL) Vita Mark II, and resin nano-ceramic (RNC) Lava Ultimate. The crowns were cemented with self-adhesive resin cement RelyX Unicem 2. After chewing cycling, crowns were tested to failure in a universal testing machine. Fracture values were calculated as initial (F-initial) and maximum fracture (F-max).

RESULTS

The study groups were ranked, in order of having highest value, (LD > FEL) > RNC for F-initial load value and (LD > RNC) > FEL for F-max load value. This demonstrated that there was no parallel change in the F-initial and F-max values presenting the fracture resistance of specimens.

CONCLUSIONS

There was no accordance between the F-initial and F-max values of the LD, RNC, and FEL after chewing simulation with thermocycling resembling 5 years of clinical functional use. LD had the highest fracture resistance during the fracture test. RNC had low fracture resistance; however, it had considerably high fracture resistance during the fracture test. FEL had considerably low fracture resistance values.

Comparative Evaluation of Fracture Resistance and Mode of Failure of Zirconia and Titanium Abutments with Different Diameters

AIM

The purpose of the current study was to compare the fracture resistance and mode of failure of zirconia and titanium abutments with different diameters.

MATERIALS AND METHODS

Fourteen groups of abutments including prefabricated zirconia, copy-milled zirconia and titanium abutments of an implant system (XiVE, Dentsply) were prepared in different diameters. An increasing vertical load was applied to each specimen until failure occurred. Fracture resistance was measured in each group using the universal testing machine. Moreover, the failure modes were studied and categorized as abutment screw fracture, connection area fracture, abutment body fracture, abutment body distortion, screw distortion and connection area distortion. Groups were statistically compared using univariate and post-hoc tests. The level of statistical significance was set at 5%.

RESULTS

Fabrication method (p = 0.03) and diameter (p < 0.001) had significant effect on the fracture resistance of abutments. Fracture resistance of abutments with 5.5 mm diameter was higher than other diameters (p < 0.001). The observed modes of failure were dependent on the abutment material as well. All of the prefabricated titanium abutments fractured within the abutment screw. Abutment screw distortion, connection area fracture, and abutment body fracture were the common failure type in other groups.

CONCLUSION

Diameter had a significant effect on fracture resistance of implant abutments, as abutments with greater diameters were more resistant to static loads. Copy-milled abutments showed lower fracture resistance as compared to other experimental groups.

CLINICAL SIGNIFICANCE

Although zirconia abutments have received great popularity among clinicians and even patients selecting them for narrow implants should be with caution.

Influence of preparation depths on the fracture load of customized zirconia abutments with titanium insert

PURPOSE

This study evaluated the fracture load of customized zirconia abutments with titanium insert according to preparation depths, with or without 5-year artificial aging.

MATERIALS AND METHODS

Thirty-six identical lithium disilicate crowns (IPS e.max press) were fabricated to replace a maxillary right central incisor and cemented to the customized zirconia abutment with titanium insert on a 4.5×10 mm titanium fixture. Abutments were fabricated with 3 preparation depths (0.5 mm, 0.7 mm, and 0.9 mm). Half of the samples were then processed using thermocycling (temperature: 5-55℃, dwelling time: 120s) and chewing simulation (1,200,000 cycles, 49 N load). All specimens were classified into 6 groups depending on the preparation depth and artificial aging (non-artificial aging groups: N5, N7, N9; artificial aging groups: A5, A7, A9). Static load was applied at 135 degrees to the implant axis in a universal testing machine. Statistical analyses of the results were performed using 1-way ANOVA, 2-way ANOVA, independent t-test and multiple linear regression.

RESULTS

The fracture loads were 539.28 ± 63.11 N (N5), 406.56 ± 28.94 N (N7), 366.66 ± 30.19 N (N9), 392.61 ± 50.57 N (A5), 317.94 ± 30.05 N (A7), and 292.74 ± 37.15 N (A9). The fracture load of group N5 was significantly higher than those of group N7 and N9 (P<.017). Consequently, the fracture load of group A5 was also significantly higher than those of group A7 and A9 (P<.05). After artificial aging, the fracture load was significantly decreased in all groups with various preparation depths (P<.05).

CONCLUSION

The fracture load of a single anterior implant restored with lithium disilicate crown on zirconia abutment with titanium insert differed depending on the preparation depths. After 5-year artificial aging, the fracture loads of all preparation groups decreased significantly.

Microscopical and chemical surface characterization of CAD/CAM zircona abutments after different cleaning procedures. A qualitative analysis

PURPOSE

To describe and characterize the surface topography and cleanliness of CAD/CAM manufactured zirconia abutments after steaming and ultrasonic cleaning.

MATERIALS AND METHODS

A total of 12 ceramic CAD/CAM implant abutments of various manufacturers were produced and randomly divided into two groups of six samples each (control and test group). Four two-piece hybrid abutments and two one-piece abutments made of zirconium-dioxide were assessed per each group. In the control group, cleaning by steam was performed. The test group underwent an ultrasonic cleaning procedure with acetone, ethyl alcohol and antibacterial solution. Groups were subjected to scanning electron microscope (SEM) analysis and Energy-dispersive X-ray spectroscopy (EDX) to verify and characterize contaminant chemical characterization non-quantitatively.

RESULTS

All zirconia CAD/CAM abutments in the present study displayed production-induced wear particles, debris as well as organic and inorganic contaminants. The abutments of the test group showed reduction of surface contamination after undergoing an ultrasonic cleaning procedure. However, an absolute removal of pollutants could not be achieved.

CONCLUSION

The presence of debris on the transmucosal surface of CAD/CAM zirconia abutments of various manufacturers was confirmed. Within the limits of the study design, the results suggest that a defined ultrasonic cleaning process can be advantageously employed to reduce such debris, thus, supposedly enhancing soft tissue healing. Although the adverse long-term influence of abutment contamination on the biological stability of peri-implant tissues has been evidenced, a standardized and validated polishing and cleaning protocol still has to be implemented.

Retention Forces between Titanium and Zirconia Components of Two-Part Implant Abutments with Different Techniques of Surface Modification

BACKGROUND

The adhesive connection between titanium base and zirconia coping of two-part abutments may be responsible for the failure rate. A high mechanical stability between both components is essential for the long-term success.

PURPOSE

The aim of the present in-vitro study was to evaluate the influence of different surface modification techniques and resin-based luting agents on the retention forces between titanium and zirconia components in two-part implant abutments.

MATERIALS AND METHODS

A total of 120 abutments with a titanium base bonded to a zirconia coping were investigated. Two different resin-based luting agents (Panavia F 2.0 and RelyX Unicem) and six different surface modifications were used to fix these components, resulting in 12 test groups (n = 10). The surface of the test specimens was mechanically pretreated with aluminium oxide blasting in combination with application of two surface activating primers (Alloy Primer, Clearfil Ceramic Primer) or a tribological conditioning (Rocatec), respectively. All specimens underwent 10,000 thermal cycles between 5°C and 55°C in a moist environment. A pull-off test was then conducted to determine retention forces between the titanium and zirconia components, and statistical analysis was performed (two-way anova). Finally, fracture surfaces were analyzed by light and scanning electron microscopy.

RESULTS

No significant differences were found between Panavia F 2.0 and RelyX Unicem. However, the retention forces were significantly influenced by the surface modification technique used (p < 0.001). For both luting agents, the highest retention forces were found when adhesion surfaces of both the titanium bases and the zirconia copings were pretreated with aluminium oxide blasting, and with the application of Clearfil Ceramic Primer.

CONCLUSION

Surface modification techniques crucially influence the retention forces between titanium and zirconia components in two-part implant abutments. All adhesion surfaces should be pretreated by sandblasting. Moreover, a phosphate-based primer serves to enhance long-term retention of the components.

Mechanical behavior of single-layer ceramized zirconia abutments for dental implant prosthetic rehabilitation

Objectives: This study was undertaken to characterize the mechanical response of bare (as-received) and single-layer ceramized zirconia abutments with both internal and external connections that have been developed to enhanced aesthetic restorations. Material and Methods: Sixteen zirconia implant abutments (ZiReal Post®, Biomet 3i, USA) with internal and external connections have been analyzed. Half of the specimens were coated with a 0.5mm-thick layer of a low-fusing fluroapatite ceramic. Mechanical tests were carried out under static (constant cross-head speed of 1mm/min until fracture) and dynamic (between 100 and 400N at a frequency of 1Hz) loading conditions. The failure location was identified by electron microscopy. The removal torque of the retaining screws after testing was also evaluated. Results: The average fracture strength was above 300N for all the abutments, regardless of connection geometry and coating. In most of the cases (94%), failure occurred by abutment fracture. No significant differences were observed either in fatigue behavior and removal torque between the different abutment groups. Conclusions: Mechanical behavior of Zireal zirconia abutments is independent of the type of internal/external connection and the presence/absence of ceramic coating. This may be clinically valuable in dental rehabilitation to improve the aesthetic outcome of zirconia-based dental implant systems.

Key words:Dental implant, zirconia, ceramic structure, mechanical properties.

Cellular viability and genetic expression of human gingival fibroblasts to zirconia with enamel matrix derivative (Emdogain®)

PURPOSE

The objective of this study was to investigate the biologic effects of enamel matrix derivative (EMD) with different concentrations on cell viability and the genetic expression of human gingival fibroblasts (HGF) to zirconia surfaces.

MATERIALS AND METHODS

Immortalized human gingival fibroblasts (HGF) were cultured (1) without EMD, (2) with EMD 25 µg/mL, and (3) with EMD 100 µg/mL on zirconia discs. MTT assay was performed to evaluate the cell proliferation activity and SEM was carried out to examine the cellular morphology and attachment. The mRNA expression of collagen type I, osteopontin, fibronectin, and TGF-β1 was evaluated with the real-time polymerase chain reaction (RT-PCR).

RESULTS

From MTT assay, HGF showed more proliferation in EMD 25 µg/mL group than control and EMD 100 µg/mL group (P<.05). HGFs showed more flattened cellular morphology on the experimental groups than on the control group after 4h culture and more cellular attachments were observed on EMD 25 µg/mL group and EMD 100 µg/mL group after 24h culture. After 48h of culture, cellular attachment was similar in all groups. The mRNA expression of type I collagen increased in a concentration dependent manner. The genetic expression of osteopontin, fibronectin, and TGF-β1 was increased at EMD 100 µg/mL. However, the mRNA expression of proteins associated with cellular attachment was decreased at EMD 25 µg/mL.

CONCLUSION

Through this short term culture of HGF on zirconium discs, we conclude that EMD affects the proliferation, attachment, and cell morphology of HGF cells. Also, EMD stimulates production of extracellular matrix collagen, osteopontin, and TGF-β1 in high concentration levels.

CLINICAL RELEVANCE

With the use of EMD, protective barrier between attached gingiva and transmucosal zirconia abutment may be enhanced leading to final esthetic results with implants.

Pre-fabricated zirconium dioxide implant abutments for single-tooth replacement in the posterior region: success and failure after 3 years of function

OBJECTIVE

Zirconia implant abutments have gained a much broader clinical use over the past few years. The aim of the present study was to assess the clinical performance of a pre-fabricated zirconium dioxide implant abutment for single-tooth replacement in the posterior region.

MATERIALS AND METHODS

Forty implants of the XiVE(®) S plus screw type (DENTSPLY Friadent, Mannheim, Germany) were inserted in the posterior region of 24 patients and provided with zirconium dioxide abutments (FRIADENT(®) CERCON(®) Abutment, DENTSPLY Friadent). The following parameters were used to document the state of soft tissue: modified plaque index, modified sulcus bleeding index and pocket depth. Mesial and distal bone levels were determined on radiographs during the prosthetic treatment and at the 36-month recall.

RESULTS

Thirty-seven implants could be followed up after 36 months in function. One patient wearing two abutments was lost to follow-up. One abutment exhibited a rotational misfit after 2 years in function. A further abutment showed the same failure at the 36-months recall appointment. In the remaining 36 implants the soft and hard tissue parameters were indicative of a low inflammatory status. Compared to the baseline situation, a partly significant bone apposition could be observed. Chipping of parts of the veneering ceramic was registered in 22% of the remaining implant restorations.

CONCLUSIONS

The use of zirconia abutments in this study lead to mainly healthy peri-implant hard and soft tissue conditions but, considering the observed failures after 3 years in function, clinical long-term results should be awaited before recommending full zirconia implant abutments in a posterior indication.

FEA and microstructure characterization of a one-piece Y-TZP abutment

OBJECTIVES

The most important drawback of dental implant/abutment assemblies is the need for a fixing screw. This study aimed to develop an esthetic one-piece Y-TZP abutment to suppress the use of the screw.

METHODS

Material characterization was performed using a bar-shaped specimen obtained by slip-casting to validate the method prior to prototype abutment fabrication by the same process. The mechanical behavior of the prototype abutment was verified and compared with a conventional abutment by finite element analysis (FEA). The abutment was evaluated by micro-CT analysis and its density was measured.

RESULTS

FEA showed stress concentration at the first thread pitch during installation and in the cervical region during oblique loading for both abutments. However, stress concentration was observed at the base of the screw head and stem in the conventional abutment. The relative density for the fabricated abutment was 95.68%. Micro-CT analysis revealed the presence of elongated cracks with sharp edges over the surface and porosity in the central region.

SIGNIFICANCE

In the light of these findings, the behavior of a one-piece abutment is expected to be better than that of the conventional model. New studies should be conducted to clarify the performance and longevity of this one-piece Y-TZP abutment.