Influence of the implant abutment types and the dynamic loading on initial screw loosening

Comparison of fatigue lifetime of new generation CAD/CAM crown materials on zirconia and titanium abutments in implant-supported crowns: a 3D finite element analysis

OBJECTIVES

Due to the dynamic character of the stomatognathic system, fatigue life experiments simulating the cyclic loading experienced by implant-supported restorations are critical consideration. The aim of this study was to examine the effect of different crown and abutment materials on fatigue failure of single implant-supported crowns.

METHODS

Models were created for 10 different designs of implant-supported single crowns including two zirconia-reinforced lithium silicates (crystallized and precrystallized), monolithic lithium disilicate, polymer-infiltrated ceramic networks, and polyetheretherketone supported by zirconia and titanium abutments. A cyclic load of 179 N with a frequency of 1 Hz was applied on palatal cusp of a maxillary first premolar at a 30° angle in a buccolingual direction.

RESULTS

In the models with titanium abutments, the polymer-infiltrated ceramic network model had a lower number of cycles to fatigue failure values in the implant (5.07), abutment (2.30), and screw (1.07) compared to others. In the models with zirconia abutments, the crystallized zirconia-reinforced lithium silicate model had a higher number of cycles to fatigue failure values in the abutment (8.52) compared to others. Depending on the fatigue criteria, polyetheretherketone implant crown could fail in less than five year while the other implant crowns exhibits an infinite life on all models.

CONCLUSIONS

The type of abutment material had an effect on the number of cycles to fatigue failure values for implants, abutments, and screws, but had no effect on crown materials. The zirconia abutment proved longer fatigue lifetime, and should thus be considered for implant-supported single crowns.

The Effect of Different Abutment Designs and Materials on Stress Distribution in Implants and Peripheral Bones: A Three-Dimensional Finite Element Analysis

AIMS

To evaluate and compare the distribution of stress patterns around a single implant-supported crown with various abutment designs using different abutment materials.

SETTING AND DESIGN

This is an in vitro study to evaluate and compare stress distribution patterns.

METHODS

The three-dimensional (3D) finite element models included four stock and four customized abutments made of Titanium, Zirconia, Fibre-Reinforced Composite, and Poly Ether-Ether Ketone (PEEK) attached to an end-osseous root form implant. The models were subjected to a 300 N vertical load at the central fossa and a 150 N oblique load at the centre of the lingual inclines of the buccal cusps of the mandibular molar crown designed on the model.

STATISTICAL ANALYSIS USED

 The stress distribution within the implant and the surrounding supporting structures was evaluated using finite element analysis.

RESULTS

In all the models, stresses on the implants were observed to be concentrated in the neck of the implants in the first few threads. Irrespective of the abutment design, PEEK abutment transferred greater stresses to implants and Zirconia abutment transferred lesser stresses to implants. In the implants, the customized abutment showed lesser stress values than the stock abutment during oblique loading.

CONCLUSIONS

Stresses on implants and cortical bone can be reduced by using Zirconia as an abutment material compared to Titanium, Fibre-Reinforced Composite, and Poly Ether-Ether Ketone material. Customized abutments improve the load transfer between the prosthesis and the implant and the surrounding bone, lessen the micro-movement of the abutments, and distribute the stress more evenly across the implant's component parts.

The effect of different implant-abutment types and heights on screw loosening in cases with increased crown height space

OBJECTIVES

The stability of the abutment screw is pivotal for successful implant-supported restorations, yet screw loosening remains a common complication, leading to compromised function and potential implant failure. This study aims to evaluate the effect of different implant-abutment types and heights on screw loosening in cases with increased crown height space (CHS).

MATERIALS AND METHODS

In this in vitro study, a total of 64 abutments in eight distinct groups based on their type and height were evaluated. These groups included stock, cast, and milled abutments with heights of 4 mm (groups S4, C4, and M4), 7 mm (groups S7, C7, and M7), and 10 mm (groups C10 and M10). Removal torque loss (RTL) was assessed both before and after subjecting the abutments to dynamic cyclic loading. Additionally, the differences between initial RTL and RTL following cyclic loading were analyzed for each group (p < .05).

RESULTS

The C10 group demonstrated the highest RTL, whereas the S4 group exhibited the lowest initial RTL percentage (p < .05). Furthermore, the study established significant variations in RTL percentages and the discrepancies between initial and postcyclic loading RTL across different abutment groups (p < .05). Additionally, both abutment types and heights were found to significantly influence the RTL percentage (p < .05).

CONCLUSION

The type and height of the implant abutment affected screw loosening, and in an increased CHS of 12 mm, using a stock abutment with a postheight of 4 mm can be effective in minimizing screw loosening.

Prosthetic design and choice of components for maintenance of optimal peri-implant health: a comprehensive review

Current research has identified features of the prosthetic design with potential to significantly impact the long-term health of peri-implant tissues, while the choice of prosthetic components is also shown to be critical in an effort to reduce long-term complications of implant therapy. Overcontouring of the prosthesis emergence profile has been associated with marginal bone loss, recession and peri-implantitis, while the mucosal emergence angle is shown to have a strong association with peri-implant tissue inflammation. Further elements of interest include convexity/concavity of the restoration, the prosthetic connection and the different geometric configurations of junctions, as well as the peri-implant tissue dimensions. With regards to implant components, the choice between original and third-party-manufactured components might come with implications, as differences in material and microgeometry might impact precision of fit and overall performance, potentially leading to complications. Scrutiny of the specifications and manufacturing is essential when third-party-manufactured components are considered.The aim of this narrative review was to summarise the current evidence with regards to the restorative features of the implant prosthesis and also the selection of prosthetic components which can have implications for the long-term success of the implant therapy. Furthermore, the review aimed at interpretating current scientific evidence into meaningful strategies and recommendations to implement in clinical practice of implant dentistry.

Dental Implant Abutment Screw Loss: Presentation of 10 Cases

Re-tightening the loosened dental implant abutment screw is an accepted procedure, however the evidence that such screw will hold sufficiently is weak. The purpose of this study was material analysis of lost dental implant abutment screws made of the TiAlV alloy from various manufacturers, which became lost due to unscrewing or damaged when checking if unscrewed; undamaged screws could be safely re-tightened. Among 13 failed screws retrieved from 10 cases, 10 screws were removed due to untightening and 3 were broken but without mechanical damage at the threads. Advanced corrosion was found on nine screws after 2 years of working time on all surfaces, also not mechanically loaded. Sediments observed especially in the thread area did not affect the corrosion process because of no pit densification around sediments. Pitting corrosion visible in all long-used screws raises the question of whether the screws should be replaced after a certain period during service, even if they are well-tightened. This requires further research on the influence of the degree of corrosion on the loss of the load-bearing ability of the screw.

Evaluation of prosthetic screw loosening in all-on-four implant-supported restorations with two different connection systems

STATEMENT OF PROBLEM: The OT BRIDGE connection system can be an alternative to multiunit abutments (MUA) for patients with all-on-four implant-supported restorations. However, the amount of prosthetic screw loosening of the OT BRIDGE in comparison with the MUA used in all-on-four implant restorations is unclear.

PURPOSE

The purpose of this in vitro study was to compare the loss of removal torque in the absence of load and after dynamic cyclic loading between the 2 different connection systems: OT BRIDGE attachment and MUA used in all-on-four implant-supported restorations.

MATERIAL AND METHODS

Four dummy implants (Neobiotech Co Ltd) were inserted into an edentulous mandibular model according to the all-on-four concept. Sixteen screw-retained restorations were digitally fabricated and assigned to 2 groups: the OT BRIDGE group received 8 restorations connected with OT BRIDGE (Rhein 83 srl); the MUA group received 8 restorations connected with MUA (Neobiotech Co Ltd). Restorations were tightened to the abutments according to the manufacturers' recommendations by using a digital torque gauge. The removal torque value (RTV) was measured with the same digital torque gauge. After retightening, dynamic cyclic loading was applied by using a pneumatic custom cyclic loading machine. RTV after loading was measured with the same torque gauge. From the RTVs measured, the ratios of removal torque loss (RTL) before and after loading and the difference between before and after loading were calculated. Data were analyzed by using the independent samples t test, paired samples t test, and mixed model analysis of variance (α=.05).

RESULTS

The OT BRIDGE showed significantly higher RTL before loading ratio (%) than the MUA in anterior abutments (P=.002) and posterior abutments (P=.003), as well as significantly higher RTL after loading ratio (%) in anterior abutments (P=.02). The MUA showed significantly higher RTL difference between before and after loading ratio (%) than the OT BRIDGE in both anterior (P=.001) and posterior abutments (P<.001). In both systems, posterior abutments showed significantly higher RTL after loading ratio (%) than anterior abutments (P<.001).

CONCLUSIONS

Posterior abutments showed more prosthetic screw loosening than anterior ones in both systems. The OT BRIDGE showed higher total prosthetic screw loosening than the MUA, although this was not significant in posterior abutments after loading. However, the OT BRIDGE was less affected by cyclic loading than the MUA.

Clinician preferences for single-unit implant restoration designs and materials: A survey of the membership of the Pacific Coast Society for Prosthodontics

STATEMENT OF PROBLEM

Clinical research has difficulty keeping pace with the rapid evolution of materials, protocols, and designs of single-unit implant restorations. The clinical design preferences of prosthodontics for different clinical scenarios are lacking.

PURPOSE

The purpose of this cross-sectional survey was to determine the current prevalence of usage of various treatment options and materials for single-unit implant-supported restorations.

MATERIAL AND METHODS

From August to September of 2022, a survey invitation was sent to members of the Pacific Coast Society for Prosthodontics (PCSP). The survey was hosted online and asked 37 questions related to the materials, protocols, and design preferences for single-unit implant-supported restorations in various clinical scenarios. The prompts included the suggestion that answers should be based on preferences for the "ideal" treatment of a hypothetical patient seeking implant treatment for the replacement of a single missing tooth.

RESULTS

Of 133 questionnaires sent via email, 35 were returned. The results are presented with histograms that use color coding as an experience proxy metric. A total of 87% of respondents was in private practice, and 60% reported having restored more than 1000 single-unit implant restorations. For the replacement of a single maxillary central incisor under ideal conditions and angulation through the palatal surface, respondents preferred bone level implants (93%) and screw-retained restorations (80%), with 50% of those being zirconia with a titanium abutment and 21% being cast metal-ceramic. For an identical scenario, except that the angulation would be through the facial surface, respondents preferred the angled screw system (55%) and cemented (41%) restorations. For the replacement of a single missing mandibular molar under ideal conditions, respondents preferred bone level implants (79%) and screw-retained restorations (79%), with 70% of those being zirconia with a titanium abutment and 17% being cast metal-ceramic.

CONCLUSIONS

While a wide range of protocols, designs, and materials exist for the replacement of a single missing tooth, these results provide a snapshot of current single-unit implant prosthodontic preferences in the Western United States and Canada.

CAD/CAM Abutments versus Stock Abutments: An Update Review

With the evolution of CAD/CAM technology, custom titanium and/or zirconia abutments are increasingly being used, leading to several comparisons in the literature, both mechanical and aesthetic, to evaluate performance differences between these two types of abutments. Therefore, the aim of this comprehensive review is to present the most recent data on the latest comparisons between CAD/CAM and stock abutment applications. The PICO model was used to perform this review, through a literature search of the PubMed (MEDLINE) and Scopus electronic databases. CAD/CAM abutments allow individualization of abutment parameters with respect to soft tissue, allow increased fracture toughness, predict the failure mode, show no change in the fracture toughness over time, reduce the prosthetic steps, and reduce the functional implant prosthesis score and pain perceived by patients in the early stages. The advantages associated with the use of stock abutments mainly concern the risk of corrosion, time spent, cost, and fit, evaluated in vitro, in the implant–abutment connection. Equal conditions are present regarding the mechanical characteristics during dynamic cycles, screw loss, radiographic fit, and degree of micromotion. Further randomized controlled clinical trials should be conducted to evaluate the advantages reported to date, following in vitro studies about titanium and/or zirconia stock abutments.

Marginal Bone Level Evaluation of Fixed Partial Dental Prostheses Using Preformed Stock versus CAD/CAM Customized Abutments

Background: The maintenance of marginal bone levels around dental implants is an important criterion for evaluating the success of implants. Although computer-aided design/computer-aided manufacturing (CAD/CAM) customized abutments (CAs) provide more flexible solutions, compared with the original preformed stock abutments (PAs), there are dimensional tolerances and underlying drawbacks in the production of CAD/CAM CAs, which may change the tightness and seamless connection between fixtures and abutments set by the manufacturer and then affect the long-term stability of the abutments. This study aimed to examine the change in both mesial and distal bone levels using digital periapical radiographs to evaluate the difference between CAD/CAM CAs and original PAs.Material and methods: Radiographs were taken before delivery; after functional loading for 1 month; and after 3, 6, and 12 months; and the vertical marginal bone levels (vMBLs) of both the mesial and distal surrounding implant bones were measured. All data are presented as means ± standard errors and were analyzed using Student’s t-test. A p-value < 0.05 was judged to represent a significant difference. Results: A total of 57 implants in 50 patients were divided into 22 CAD/CAM CAs and 35 original stock abutments. The PAs appeared to have a more stable bone level. By contrast, the amount of bone level change in the CAs was higher than that in the PAs. The change in the vMBL of the CAs was significantly more than that of the PAs after functional loading for 1 month (p = 0.006), 3 months (p = 0.013), 6 months (p = 0.014), and 12 months (p = 0.002). In contrast, the distal marginal bone level was lower than the mesial marginal bone level in any period. Nevertheless, the bone levels of the CAs and PAs in any period were comparable with no significant difference. Conclusions: Significant differences were found between the mesial and distal bone levels in the PAs. The CAD/CAM CAs showed a significantly greater bone level change than the original stock abutments after functional loading.

Evaluation of Viability and Cell Proliferation in Bone and Gingival on Dental Implant Fixtures with Active Sandblasted and Sandblasted Surfaces by the Cytotoxicity Test Method

In recent years, the technology of dental implants has advanced a lot and this has become one of the main reasons for dentists to refer to implants immediately after tooth extraction. Evaluation of cell survival in implantology studies to determine cell sensitivity determines the outcome of treatment. This study aimed to investigate the bone integration properties as well as the cytotoxicity between the implant surface and the jaw bone. In this study, cytotoxicity test was used to evaluate the toxicity and viability of sandblasted large grit acid etched, and sandblasted large grit acid etched active surfaces in 3A brand dental implants with G292 osteoblastic cells and human gingival fibroblasts cells are discussed. This operation was performed using a laboratory incubator of the German company MEMMERT for 24 hours, by neubauer lam cells counting for one hundred thousand cultured cells in each test at a temperature of 37 °C, a pressure of 1 atmosphere and 90% humidity. Based on the scanning electron microscopy images and the cytotoxicity test results, it can be seen that the bone graft of the implant, with the sandblasted large grit acid etched active surface treatment, is much better and also one week faster than the implant with the sandblasted large grit acid etched one. However, the viability of the implant with the sandblasted large grit acid etched active surface treatment for both G292 osteoblastic cells and human gingival fibroblasts cells samples was equal to 98.4% and 97.3%, respectively, and is lower than the sandblasted large grit acid etched surface treatment. The results show that the viability of the sandblasted large grit acid etched implant is about 1.5 to 2% higher than the sandblasted large grit acid etched active one, but the surface integrity of sandblasted large grit acid etched active is better than sandblasted large grit acid etched in all samples, and the treatment process is reduced by one week.

Accuracy of Original vs. Non-original Abutments Using Various Connection Geometries for Single Unit Restorations: A Systematic Review

PURPOSE

To ascertain whether the compatibility of non-original abutments (NOAs) with dental implants is influenced by the type of implant connection i.e. internal or external, and whether certain combinations of componentry may be as compatible as the original components.

METHODS

A structured literature search was conducted using 3 electronic databases (MEDLINE®, The Cochrane Library, and Web of Science Core Collection) for studies reporting on the use of non-original abutments published between 1995 and 2020. This was supplemented with hand searching in relevant journals and references, as well as searching grey literature. Relevant studies were selected according to specific inclusion criteria. Data was collected for the following parameters: precision of fit, microleakage, micromorphological differences, micromotion, rotational misfit, screw loosening, maximum load capacity, fracture resistance, tensile strength, compressive strength and in-vivo implant and prosthesis outcomes.

RESULTS

The electronic searching and hand search yielded titles and abstracts of 5617 studies following de-duplication; 40 studies were finally selected. Overall, original abutments showed better precision of fit, ability to resist microleakage, prevention of rotational misfit and micromotion, and fatigue strength compared with non-original abutments. Some non-original abutments on external connections were comparable with original abutments in terms of precision of fit and resistance to screw loosening and may be associated with less catastrophic failures than those on internal connections.

CONCLUSION

Original abutments present more predictable outcomes than non-original abutments with regards to the parameters investigated. However, it seems that external connections can provide some level of compatibility in terms of precision of fit and may also exhibit less catastrophic failures than NOAs on internal connections. This may be due to increased rotational freedom external connections provide. There is a lack of information regarding the influence of connection geometry on many aspects of compatibility and therefore the current clinical recommendation should be to use original abutments. More laboratory studies comparing non-original abutments on different implant connections are required. In addition, there is a need for long-term in vivo studies providing data on the clinical performance of non-original abutments. This article is protected by copyright. All rights reserved.

Oral reconstruction with hybrid implant-supported fixed prostheses in cases of mandibular defect using two methods along with 3 years of follow-up: A case report

Ameloblastoma is an invasive odontogenic tumor, and for reconstruction, iliac graft and dental implants play an important role. This article evaluates the application of hybrid prostheses, clinical steps, and complications related to this treatment.

Investigation of the Effect of Abutment Angle Tolerance on the Stress Created in the Fixture and Screw in Dental Implants Using Finite Element Analysis

Today, an artificial tooth root called a dental implant is used to replace lost tooth function. Treatment with dental implants is considered an effective and safe method. However, in some cases, the use of dental implants had some failures. The success of dental implants is influenced by several biomechanical factors such as loading type, used material properties, shape and geometry of implants, quality and quantity of bone around implants, surgical method, lack of rapid and proper implant surface's integration with the jaw bone, etc. The main purpose of functional design is to investigate and control the stress distribution on dental implants to optimize their performance. Finite element analysis allows researchers to predict the stress distribution in the bone implant without the risk and cost of implant placement. In this study, the stresses created in the 3A.P.H.5 dental implant's titanium fixture and screw due to the change in abutment angles tolerance have been investigated. The results show that although the fixture and the screw's load and conditions are the same in different cases, the change of the abutment angle and the change in the stress amount also made a difference in the location of maximum stress. The 21-degree abutment puts the fixture in a more critical condition and increases the chance of early plasticization compared to other states. The results also showed that increasing the abutment angle to 24 degrees reduces the stress in the screw, but decreasing the angle to 21 degrees leads to increased screw stress and brings it closer to the fracture.

Clinical outcomes of single implant supported crowns versus 3-unit implant-supported fixed dental prostheses in Dubai Health Authority: a retrospective study

Background

This study assessed retrospectively the clinical outcomes of single implant-supported crowns and implant-supported fixed dental prostheses (FDPs).

Methods

This case series compared biological and technical complications in single implant-supported crowns and implant-supported bridges in a time framed sample of all patients who received dental implants between 2009 and 2016 in Dubai Health Authority. Only 3-unit implant-supported prostheses (FDPs) with one intervening pontic and an implant each end were included for comparison to single crown supported implants. Cantilevered implants, implant-supported dentures and cases involving bone grafts or sinus lifts were excluded. The primary outcome measure was marginal bone loss, measured on digital radiographs taken after prosthesis placement at baseline and one year after implant loading, whilst peri-implantitis and technical complications were secondary outcomes. Mixed regression models adjusted for clustering of implants within patients was used for patient and implant factor associations.

Results

A total of 454 patients (152 males; 302 females) had 1673 implants. The mean age of males (53.7 years, SD 14.6) was significantly greater than females (49.3 years, SD 12.9, p < 0.001). Mean mesial bone loss on the FDPs was significantly greater at 1 year (1.14 mm, SD 0.63) compared with the mesial surface of single implant-supported crowns (0.30 mm, SD 0.43, p < 0.001). Mean distal bone loss was also significantly greater at 1 year on the distal surfaces of implants supporting bridgework (1.29 mm, SD 0.71) compared with distal surfaces on single implant-supported crowns (0.36 mm, SD 0.54, p < 0.001). Mean marginal bone loss mesially and distally around implants placed in the lower anterior sextant was significantly greater compared to all other sites (p < 0.001). Bone loss by gender, patient’s age and medical condition was not different between the 2 implant groups. Screw loosening was the main technical complication (11.5%) whilst peri-implantitis occurred rarely (0.5%). The 66 cement retained implants had significantly more complications compared to the 1607 screw retained implants (p < 0.001).

Conclusions

Mean marginal bone loss around the supporting implants of FDPs (3-unit fixed bridgework) was greater than on single implant-supported crowns at one year after implant loading. Position in the mouth was associated with bone loss. Biological and technical complications occurred rarely.

In vitro assessment of PEEK and titanium implant abutments: Screw loosening and microleakage evaluations under dynamic mechanical testing

STATEMENT OF PROBLEM

Polyetheretherketone (PEEK) has been advocated to replace metal components in dentistry. Although PEEK is a high-performance polymer with a white color, adequate biological response, and resistance to fracture, data to support PEEK as an alternative material for implant abutments are lacking.

PURPOSE

The purpose of this in vitro study was to assess the mechanical and functional properties of PEEK implant abutments as a nonmetallic alternative to titanium abutments, which presents esthetic limitations and greater difficulty to customize clinically.

MATERIAL AND METHODS

Implant abutments manufactured by using PEEK (n=24) or titanium grade 5 (n=24) were attached to MIS Implants type M4 3.75×16 mm with an internal screw tightened to 25 Ncm. Screw loosening and microleakage was assessed by submersion in a 2% methylene blue solution for 48 hours at 37 °C. Both groups were compared with and without applying dynamic loading; fatigue testing was performed following the International Organization for Standardization (ISO) 14801:2016 standard. All specimens were observed under a stereomicroscope at ×8 magnification. Statistically significant differences among the PEEK and titanium implant abutments were tested with 2-factor ANOVA and the chi-square analysis for nonpaired and paired data, respectively (α=.05).

RESULTS

The implant abutments made of titanium were better in all mechanical tests. The torque loss of titanium abutments was approximately 10%, while PEEK showed a significantly higher (P<.05) torque loss of up to 50%. Moreover, 91.6% of the titanium abutments did not present microleakage, while there was no specimen of PEEK abutments without microleakage, once subjected to dynamic loading (P<.05).

CONCLUSIONS

Titanium implant abutments (Ti6Al4V) were better in all tests performed. However, PEEK abutments may be suitable for long-term interim restorations, especially in the anterior area, in patients without parafunction.

Effect of Serrating Abutment-Implant Mating Surface on Torque Stability of Implant-Abutment Connection, Before and After Cyclic Loading

This study evaluated the effect of adding serration to the abutment-implant connection on torque maintenance before and after loading. Two implant systems with the same dimensions and connection design (internal 8° Morse taper octagon) were selected: one with nonserrated abutments (Simple line II) and the other one with serrated abutments (F & B). The removal torque value (RTV) was measured in 2 groups for each system: one group with one-piece abutments and the other group with 2-piece abutments, before and after cyclic loading (n = 10 in each group). The initial RTV of the abutment screw was measured with a digital torque meter. Each abutment received a cement-retained metal crown with 30° occlusal surface. Cyclic axial peak load of 75 ± 5 N was applied to the implants for 500 000 cycles at 1 Hz. The post-load RTV was then measured. Two-way and repeated-measures analysis of variance (ANOVA), and independent t test were applied to assess the effects of cyclic loading, connection design, abutment type, and their interaction on the percentage of torque loss (α = .05). Two-way ANOVA showed that serration of mating surfaces had a significant effect on torque maintenance before (P < .001) and after (P = .004) cyclic loading. Repeated-measures ANOVA also showed that loading had a significant effect on the torque loss percentage (P < .01). Comparison of the groups with t test showed that the torque loss of the serrated groups was lower than that of non- serrated groups. Despite the limitations of this study, the stability of the implant-abutment connection in the serrated design was higher than that of non-serrated group.

Effect of aging on fracture resistance and torque loss of restorations supported by zirconia and polyetheretherketone abutments: An in vitro study

STATEMENT OF PROBLEM

New materials have been developed for digital processing, including implant abutments, but studies on their mechanical properties are lacking.

PURPOSE

The purpose of this in vitro study was to compare the effect of aging on the fracture resistance, failure mode, and torque loss of restorations made of zirconia and ceramic-reinforced polyetheretherketone (PEEK) abutments with titanium bases.

MATERIAL AND METHODS

Titanium-based PEEK and zirconia abutments were milled and veneered with composite resin or feldspathic porcelain in the form of maxillary first premolars (n=10). All the specimens were subjected to an aging process and were assessed after every 250 000 cycles under a stereomicroscope, and torque loss was recorded with an electronic torque meter. Fracture resistance was measured under static load (crosshead speed of 1 mm/min), and failure modes and final torque were determined. A t test was conducted for statistical analyses (α=.05).

RESULTS

The fracture resistance of the zirconia restorations was significantly greater than the PEEK-based restorations (P=.001). Torque losses were not significantly different after aging (P=.18); however, significant difference was recorded after the fracture test (P=.007). The effect of fracture load was significantly greater for the zirconia group (P<.001). Unlike with the zirconia group, the failure mode in the PEEK-based restorations was mainly adhesive and favorable (9 of 10 specimens).

CONCLUSIONS

Ceramic-reinforced PEEK abutments had acceptable resistance to fracture, a favorable failure mode, and successfully sustained the aging process.

Effect of dynamic cyclic loading on screw loosening of retightened versus new abutment screw in both narrow and standard implants (in-vitro study)

BACKGROUND

The purpose of this in-vitro study was to evaluate the effect of dynamic cyclic loading on screw loosening of retightened abutment screw versus new abutment screw in both narrow and standard implants.

METHODS

Separate acrylic resin blocks containing implant assembly (fixture, abutment, abutment screw, metal tube capping the abutment). Samples were divided into two main groups according to the diameter of implant: group 1 (GI 4.5-mm diameter) and group 2 (GII 3-mm diameter). Each group is subdivided into two subgroups according to the suggested option to manage screw loosening either by retightening (GIA, GIIA) or using new screws (GIB, GIIB). One hundred thousand cycles of eccentric dynamic cyclic loading (DCL) were applied before and after retightening or replacing the screw; then, removal torque loss (RTL) ratio was calculated, tabulated, and analyzed by t-student, ANOVA, pair wise Tukey's tests.

RESULTS

There were differences between GI and GII regarding the incidence of screw loosening process. Removal torque loss ratio was higher in GIB and GIIB where the old abutment screws were replaced by new screws for both standard implants (SIs) and narrow diameter implants (NDIs). There was significant effect of retightening and replacing the abutment screws after exposure to DCL.

CONCLUSIONS

Within the limitations of this in-vitro study, it can be conclude that screw loosening process occurred in both SIs and NDIs but with higher values in NDIs. It is better to retighten the screw of NDIs and SIs than replacing it with a new screw.

Hybrid-abutment-restoration: effect of material type on torque maintenance and fracture resistance after thermal aging

Purpose

To evaluate the tightening torque maintenance with zirconia, lithium disilicate, and polyetheretherketone (PEEK) hybrid-abutment-crowns after thermal aging, in addition to assess the fracture resistance of hybrid-abutment-crowns fabricated with different materials.

Materials and methods

Thirty implants were restored with identical hybrid-abutment-crowns, resembling the maxillary first premolar, fabricated from zirconia (Zr), lithium disilicate (L2), or ceramic-reinforced PEEK (PE). The three groups (n = 10) were constructed utilizing a Ti-base. After bonding, each restoration was secured in its respective implant with a torque of 25 Ncm. All restorations were subjected to thermal aging for 7000 cycles. The loosening torque was assessed utilizing the digital torque meter. Each restoration was subjected to fracture testing and the mode of failure was determined.

Results

Zr group displayed the highest mean torque loss value (2.70 ± 0.59 Ncm) with the mean loosening torque value of 22.38 ± 0.68 Ncm. PE group displayed the lowest mean torque loss (2.55 ± 0.50 Ncm) with mean loosening torque value of 22.61 ± 0.59 Ncm. There was no significant difference between study groups regarding loosening torque (p = 0.68), torque loss (p = 0.80), and percentage of torque loss (p = 0.79). There was significant difference regarding the mean fracture load value between Zr and PE groups. However, there was no significant difference (p = 0.05) regarding mean fracture load value between L2 and PE groups.

Conclusion

The hybrid-abutment-crown material does not affect the torque maintenance after thermal aging. Based on fracture load, zirconia hybrid-abutment-crown can be used, while lithium disilicate and PEEK hybrid-abutment-crowns may cautiously serve in premolar region.

Retrospective comparison of posterior fixed dental prostheses supported by two different titanium abutments on tissue level implants

STATEMENT OF PROBLEM

Clinical studies comparing compatible computer-aided design and computer-aided manufacturing (CAD-CAM) titanium abutments (CAs) and original prefabricated 1-piece titanium abutments (PAs) for posterior fixed dental prostheses (FDPs) on Straumann Tissue Level (STL) implants are sparse.

PURPOSE

The purpose of this retrospective clinical study was to compare the performance of posterior FDPs supported by CAs and PAs on STL implants after a mean observation period of 7.2 years.

MATERIAL AND METHODS

Patients who received STL implants and posterior FDPs by using CAs or PAs between January 2002 and December 2012 and returned for follow-up between January 2017 and September 2018 were included in this study. Technical and biological complications of FDPs were examined and recorded. Radiographs were used for the measurement of marginal bone loss (MBL) of each implant. Variables, complication rates, and MBL of the 2 groups were analyzed by using a generalized estimating equation and multivariable linear mixed model.

RESULTS

Ninety-nine patients with 195 implants in the CA group and 75 patients with 143 implants in the PA group were included. The mean functional time of FDPs was 6.5 ±1.1 years for the CA group and 8.1 ±2.6 years for the PA group. No implant failure was noted in either group. The technical complication rate was 20.8% in the CA group and 26.3% in the PA group. Abutment screw loosening (ASL) was noted in the CA group (8.5%). The decementation rate was significantly higher in the PA group (14.1%) than that in the CA group (3.1%) (adjusted odds ratio=4.40, confidence interval=1.41 to 13.69, P=.011). No significant differences were found between the 2 groups in terms of the rates of ceramic chipping, peri-implantitis, peri-implant mucositis, or mean MBL.

CONCLUSIONS

Using CAs or PAs to support posterior FDPs on STL implants has no significant effect on the incidence rate of biological complications. However, a higher ASL rate and a lower decementation rate were noted with CAs than with PAs.

Effect of implant abutment connection designs, and implant diameters on screw loosening before and after cyclic loading: In-vitro study

AIMS

The purpose of this in-vitro study was to evaluate the screw loosening of two different forms of implant abutment connection designs, and two implant diameters by measuring removal torque value (RTV) before and after cyclic loading.

MATERIALS AND METHODS

Twenty implant fixtures were divided equally into 2 groups (N=10): group I fixture with conical hybrid connection (CH), and group II fixture with internal hex connection (IH). Each group was divided equally into two subgroups according to implant diameters: subgroup A (3.3mm), and subgroup B (4.2mm). Each fixture was vertically placed in the center of an acrylic resin block. The samples were fixed to the jig, and an implant abutment connected it with a 20 Ncm tightening torque. The samples were subjected to eccentric cyclic loading (at a distance of 5mm) away from center of abutment at 100,000 cycles. A digital torque gauge was used to evaluate screw loosening by measuring RTVs in (Ncm) before and after cyclic loading. The removal torque loss ratio before and after cyclic loading and the removal torque loss ratio between before and after cyclic loading were calculated and analyzed using the SPSS statistical analysis.

RESULTS

For GI the initial removal torque loss ratio measurement was (14.45±3.18) and decreased significantly after loading, it was (11.47±3.64). For GII the initial removal torque loss ratio measurement was (20.47±4.99) and increased significantly after loading, being (35.35±4.26). There is no significant effect upon screw loosening for two implant diameters.

CONCLUSION

Within the limitations of this study, the results suggested that conical hybrid connections showed a better screw stability than an internal hex connection. Therefore, the use of conical implants can be promoted as they have better screw stability compared to other systems.

Incidence of abutment screw failure of single or splinted implant prostheses: A review and update on current clinical status

Osseointegrated implants have been widely used for decades with high survival and success rates. However, mechanical complications continue to be reported in the literature, and their clinical management can be often very challenging for the clinician while there is no consensus on the ideal management. The aim of this manuscript was to review the risk factors of abutment screw complications, to identify the most recent incidence of screw failure in the clinical setting and report on the methodology used and the outcome of intervention. Clinical studies and reports were reviewed that reported on abutment screw looseness and/or fracture. A search of the electronic database PUBMED was conducted in November 2018, including manuscripts published in English from 2004 to 2018. Study selection: animal studies, narrative reviews, expert opinions and communications/letters were excluded. Further exclusion criteria included reports on occlusal prosthetic screws and fracture of abutments, and reports that did not provide adequate data. A total of 12 manuscripts were finally included that reported on single implant crowns or 2-unit implant fixed dental prosthesis. To conclude, the most current abutment screw loosening incidence ranges between 7% and 11%, while the abutment screw fracture incidence was found to be 0.6%. The majority reported on fracture of the screw body. Screw loosening or fracture was often located at the first molar restored area, while the maxillary central incisor area was also reported as an area that presented screw fracture. No single abutment screw failure management can be identified as the ideal treatment approach.

Mechanical Outcomes, Microleakage, and Marginal Accuracy at the Implant-Abutment Interface of Original versus Nonoriginal Implant Abutments: A Systematic Review of In Vitro Studies

Purpose

Instead of original abutments, compatible abutments are often selected for financial reasons. The present study aimed to evaluate mechanical outcomes, microleakage, and marginal accuracy at the implant-abutment interface of original versus nonoriginal implant abutments.

Study Selection

Search strategy encompassed literature from 1967 up to March 2017 to identify relevant studies meeting the inclusion criteria. The following electronic databases were consulted: PubMed database of the U.S. National Library of Medicine, Embase (Excerpta Medica dataBASE), and the Grey Literature Database (New York Academy of Medicine Grey Literature Report). Quality assessment of the full-text articles selected was performed. Abutments were classified in original (produced by the same implant manufacturer), nonoriginal certified (produced by a third-party milling center, certified by implant companies), and nonoriginal compatible (produced by a third-party milling center for similar connections).

Results

A total of 16 articles fulfilled inclusion criteria and quality assessment and were selected for the qualitative analysis. All of the included studies were in vitro research with high or moderate risk of bias and reported data from 653 implant abutments. Original and nonoriginal certified abutments showed better results in terms of mechanical outcomes, microleakage, and marginal accuracy compared to nonoriginal compatible abutments.

Conclusions

Following the clear warnings coming from the present systematic review, clinical suggestions regarding the effect of a nonoriginal abutment can be drawn. However, in vivo, long-term, randomized controlled trials are needed to provide definitive clinical conclusion about the long-term clinical outcomes of original and nonoriginal abutments.

Retention failures in cement- and screw-retained fixed restorations on dental implants in partially edentulous arches: A systematic review with meta-analysis

PURPOSE

This systematic review aimed to evaluate retention failures in cement- and screw-retained fixed restorations on dental implants in partially edentulous arches.

METHODS

The relevant articles were retrieved from MEDLINE (PubMed), Cochrane Library, and EBSCO electronic databases for articles published from January 1995 to January 2016 and were restricted to randomized controlled trials and retrospective and prospective studies on human subjects that were reported in English. A further hand search was conducted on individual journals and reference list of the articles found. Reviewed studies which reported retention failures in fixed implant-supported prostheses using screw and cement retention mechanism. Information on the type and nature of restoration, as well as different luting cement, were also collected.

RESULTS

Thirty-three articles were finalized, 20 short-term clinical studies (up to 5 years) and 13 long-term studies (≥5 years). Out of 33 studies, 16 studies were included in meta-analysis, 8 in short-term and 8 in long-term studies. The results of the meta-analysis for short-term studies showed statistically significant difference between cement-retained and screw-retained prosthesis, with the forest plot favoring cement-retained prostheses (risk ratio [RR]: 0.26; confidence interval [CI]: 0.09-0.74; P < 0.0001; I2 = 79%). In long-term studies, the forest plot revealed statistically significant difference between both retention systems favoring cement-retained prostheses (RR: 0.31; CI: 0.13-0.76; P = 0.03; I2 = 56%).

CONCLUSION

Analysis of the short- and long-term studies shows lesser retention failures with cement-retained prostheses when compared to screw-retained prostheses. Further, multicentric, high-quality randomized controlled studies with long-term observations and modified cementation protocols can yield higher grades of recommendation to avoid retention failures.

Influence of Abutment Surface Treatments on Screw Loosening of Morse Taper Implants

PURPOSE

To evaluate the effect of blasting and bonding on abutment surface to prevent screw loosening in Morse taper connections.

MATERIAL AND METHODS

Twenty-eight Morse taper connection implants were divided into 4 groups: no treatment (G1), blasting (G2), bonding (G3), and blasting + bonding (G4). In groups G2 and G4, the abutments were blasted with aluminum oxide granules; in groups G3 and G4, the conical abutment region was covered with a thin layer of bond thread lock agent. In all implants, the abutment-implant joint was tightened at a torque of 35 Ncm. The specimens were submitted to the mechanical cycling, under an oblique load for 1.0 × 10 cycles. The torque was measured with a digital torque meter. Data were analyzed by the t test, one-way analysis of variance, and Tukey tests (95%).

RESULTS

The loosening strength was significantly higher in group G4 (35.83 ± 3.02 Ncm). There was no significant difference among groups G1 (25.86 ± 1.96 Ncm), G2 (25.86 ± 3.29 Ncm), and G3 (26.14 ± 2.12 Ncm).

CONCLUSION

The association of blasting and bonding on abutment surface can be used to prevent screw loosening in Morse taper implants.

In Vitro Laser Treatment Platform Construction with Dental Implant Thread Surface on Bacterial Adhesion for Peri-Implantitis

This study constructs a standard in vitro laser treatment platform with dental implant thread surface on bacterial adhesion for peri-implantitis at different tooth positions. The standard clinical adult tooth jaw model was scanned to construct the digital model with 6 mm bone loss depth on behalf of serious peri-implantitis at the incisor, first premolar, and first molar. A cylindrical suite connected to the implant and each tooth root in the jaw model was designed as one experimental unit set to allow the suite to be replaced for individual bacterial adhesion. The digital peri-implantitis and suite models were exported to fulfill the physical model using ABS material in a 3D printer. A 3 mm diameter specimen implant on bacterial adhesion against Escherichia coli was performed for gram-negative bacteria. An Er:YAG laser, working with a chisel type glass tip, was moved from the buccal across the implant thread to the lingual for about 30 seconds per sample to verify the in vitro laser treatment platform. The result showed that the sterilization rate can reach 99.3% and the jaw model was not damaged after laser irradiation testing. This study concluded that using integrated image processing, reverse engineering, CAD system, and a 3D printer to construct a peri-implantitis model replacing the implant on bacterial adhesion and acceptable sterilization rate proved the feasibility of the proposed laser treatment platform.

Load Fatigue Performance Evaluation on Two Internal Tapered Abutment–Implant Connection Implants Under Different Screw Tightening Torques

This study evaluates the load fatigue performance of different abutment–implant connection implant types—retaining-screw (RS) and taper integrated screwed-in (TIS) types under 3 applied torque levels based on the screw elastic limit. Three torque levels—the recommended torque (25 Ncm), 10% less, and 10% more than the ratio of recommended torque to screw elastic limits of different implants were applied to the implants to perform static and dynamic testing according to the ISO 14801 method. Removal torque loss was calculated for each group after the endurance limitation was reached (passed 5 × 106 cycles) in the fatigue test. The static fracture resistance results showed that the fracture resistance in the TIS-type implant significantly increased (P &lt; .05) when the abutment screw was inserted tightly. The dynamic testing results showed that the endurance limitations for the RS-type implant were 229 N, 197 N, and 224 N and those for the TIS-type implant were 322 N, 364 N, and 376 N when the screw insertion torques were applied from low to high. The corresponding significant (P &lt; .05) removal torque losses for the TIS-type implant were 13.2%, 5.3%, and 2.6% but no significant difference was found for the RS-type implant. This study concluded that the static fracture resistance and dynamic endurance limitation of the TIS-type implant (1-piece solid abutment) increased when torque was applied more tightly on the screw. Less torque loss was also found when increasing the screw insertion torque.

Marginal Vertical Fit along the Implant-Abutment Interface: A Microscope Qualitative Analysis

The aim of this study was to qualitatively evaluate the marginal vertical fit along two different implant-abutment interfaces: (1) a standard abutment on an implant and (2) a computer-aided-design/computer-aided-machine (CAD/CAM) customized screw-retained crown on an implant. Four groups were compared: three customized screw-retained crowns with three different “tolerance” values (CAD-CAM 0, CAD-CAM +1, CAD-CAM −1) and a standard titanium abutment. Qualitative analysis was carried out using an optical microscope. Results showed a vertical gap significantly different from both CAD-CAM 0 and CAD-CAM −1, while no difference was found between standard abutment and CAD-CAM +1. The set tolerance in producing CAD/CAM screw-retained crowns plays a key role in the final fit.

Effect of abutment screw length and cyclic loading on removal torque in external and internal hex implants

PURPOSE

The purpose of this study was to evaluate the effects of abutment screw length and cyclic loading on the removal torque (RTV) in external hex (EH) and internal hex (IH) implants.

MATERIALS AND METHODS

Forty screw-retained single crowns were connected to external and internal hex implants. The prepared titanium abutment screws were classified into 8 groups based on the number of threads (n = 5 per group): EH 12.5, 6.5, 3.5, 2.5 and IH 6.5, 5, 3.5, 2.5 threads. The abutment screws were tightened with 20 Ncm torque twice with 10-minute intervals. After 5 minutes, the initial RTVs of the abutment screws were measured with a digital torque gauge (MGT12). A customized jig was constructed to apply a load along the implant long axis at the central fossa of the maxillary first molar. The post-loading RTVs were measured after 16,000 cycles of mechanical loading with 50 N at a 1-Hz frequency. Statistical analysis included one-way analysis of variance and paired t-tests.

RESULTS

The post-loading RTVs were significantly lower than the initial RTVs in the EH 2.5 thread and IH 2.5 thread groups (P<.05). The initial RTVs exhibited no significant differences among the 8 groups, whereas the post-loading RTVs of the EH 6.5 and EH 3.5 thread groups were higher than those of the IH 3.5 thread group (P<.05).

CONCLUSION

Within the limitations of this study, the external hex implants with short screw lengths were more advantageous than internal hex implants with short screw lengths in torque maintenance after cyclic loading.