Micromotion of implant-abutment interfaces (IAI) after loading: correlation of finite element analysis with in vitro performances

Biomechanical evaluation of abutment stability in morse taper implant connections in different times: A retrospective clinical study compared with an in vitro analysis

Objectives

Micromotion between a dental implant and abutment can adversely affect clinical performance and compromise successful osseointegration by creating a bacterial harbor, enabling screw loosening, and imparting disruptive lateral forces on the cortical bone. Thus, the aim of the present study was to measure the abutment stability evolution using resonance frequency analysis (RFA) in vivo at four different times (baseline, 3, 4, and 12 months), and compare these data obtained with the RFA measured after mechanical cycling (in vitro) corresponding to the proposed times in numbers of cycles.

Methods

To evaluate the abutment stability, RFA was performed in 70 sets of implant/abutment (IA) with a total of 54 patients (31 women, 23 men). These IA sets were divided into three groups, according to the abutment angulation: straight abutment (Abt1 group), 17-degree angled abutment (Abt2 group), and 30-degree angled abutment (Abt3 group). Abutment stability was measured immediately at implant placement and the abutment installation (T1), 3 (T2), 4 (T3), and 12 months (T4) later. For the in vitro analysis, ten sets of each group were submitted to mechanical cycling: T1 = 0 cycles, T2 = 90,000 cycles, T3 = 120,000 cycles, and T4 = 360,000 cycles. All data collected were statistically evaluated using the GraphPad Prism 5.01 software, with the level of significance was α = 0.05.

Results

In vivo, the overall data of implant stability quotient (ISQ) values obtained for all groups in each evaluation time were 61.5 ± 3.94 (95% CI: [60-63]) at T1, 62.8 ± 3.73 (95% CI, [61-64]) at T2, 63.4 ± 3.08 (95% CI: [61-64]) at T3, and 65.5 ± 4.33 (95% CI: [63-68]) at T4. Whereas in vitro, the ISQ were 61.5 ± 2.66 (95% CI: [59-63]) at T1, 63.2 ± 3.02 (95% CI, [61-65]) at T2, 63.9 ± 2.55 (95% CI: [62-66]) at T3, and 66.5 ± 2.97 (95% CI: [64-68]) at T4. In both evaluations (in vivo and in vitro), the data showed a significant difference (ANOVA test with p < 0.0001).

Conclusions

The RFA to measure the abutment stability used in this study showed that there was a progressive increase in stability among the predetermined times for the measurements, in both analysis (in vivo and in vitro). Furthermore, the values at each time point were similar, with no statistical difference between them.

Stress distribution and microgap formation in angulated zirconia abutments with a titanium base in narrow diameter implants: A 3D finite element analysis

PURPOSE

This in vitro study aimed to use failure stress and implant abutment interface (IAI) microgap size to find the compromised axial angle range of angulated zirconia abutments with a titanium base in narrow diameter implants in the esthetic region.

MATERIALS AND METHODS

A three-dimensional (3D) finite element model of maxillary central incisor implant prosthesis was reconstructed. Angulated zirconia abutments (0°, 15°, 30°, and - 15°) with a titanium base in narrow diameter implants (3.3*12 mm, Bone level, Roxolid SLActive, Straumann AG, Switzerland) were designed to simulate clinical scenarios of buccal inclination 0°, 15°, and 30°, and palatal inclination 15° of the implant long axis. Straight titanium abutment and pure titanium implant were used as two control groups. An oblique force at 30° inclination to the long axis of the crown was applied 3 mm below the incisal edge on the palatal surface of the prosthesis. Under simulated dynamic chewing force, the stress distribution of the implant components and surrounding bone were investigated. The relative micromotion displacement between the implant and abutment models at the IAI area was recorded, and the influence of tightening torque on the IAI microgap was evaluated.

RESULTS

The angulation of the zirconia abutment could affect the stress value and IAI microgap of implant restorations. When the zirconia abutment angle increased from -15 °to 30°, the stress on the central screw, titanium base, and surrounding bone tissue gradually increased by 9%, 20%, and 23%, respectively. The stress levels of the 30° zirconia abutment group showed the risk of exceeding the threshold. When the long axis of the implant was inclined in the palatal direction, the -15° angle abutment reduced the stress by 3% and reduced the strain level of the implant system by 17% and the surrounding bone tissue by 26%. Under simulated dynamic chewing load, the displacement between the implants and the abutment occurred in each group of the implant system, and the amplitude of the micromotion fluctuated with the change in the load. The horizontal displacement caused a 0.075-1.459 μm palatal microgap and 0.091-0.945 μm distal microgap in the IAI. The microgap between the lip and palate was more evident, and the vertical displacement difference was manifested as the abutment sliding down the implant.

CONCLUSIONS

In cases of upper implant restoration with difficulties such as small gaps and axial defects in the esthetic zone, the abutment angle is highly recommended to be in a slightly palatal-inclined direction or to not exceed 15° when the implant is inclined to the labial side to avoid mechanical damage and leakage caused by the appearance of excessively large micromotion gaps. This article is protected by copyright. All rights reserved.

A retrospective study of 12,538 internal conical connection implants: focused on the long-term integrity of implant-abutment complexes

OBJECTIVES

To evaluate the long-term integrity of implant-abutment complexes in implant systems with two internal conical angles.

MATERIAL AND METHODS

12,538 bone-level implants of two systems placed between January 2012 and December 2018 were retrospectively analyzed. Cumulative abutment/implant fracture rates in systems with larger (LA, 7.5°) and smaller (SA, 5.7°) internal conical angles were estimated using Kaplan-Meier analysis and compared between groups. The association between implant systems and jammed abutment retrievability was evaluated by multivariable generalized estimating equation logistic regression modelling.

RESULTS

For LA, the 8-year cumulative incident rate was 0.10% (95% confidence interval (CI): 0-0.24%) for implant fracture and 0.26% (95% CI: 0.11%-0.41%) for abutment fracture, demonstrating a significant difference in gender (p = 0.03), implant diameter (p = 0.01), jaw (p = 0.006) and antagonist tooth (p < 0.001). For SA, the 8-year cumulative incident rate was 0.38% (95% CI: 0-0.79%) for implant fracture and 2.62% (95% CI: 0.05%-5.13%) for abutment fracture, which was influenced by implant diameter (p < 0.001) and site (p = 0.03). The cumulative implant/abutment fracture rate was lower for LA implants, particularly for LA implant-supported single crowns (SCs) (p < 0.05). The abutment-retrieval success rate was 92.8% for LA, and 57.1% for SA (p = 0.055).

CONCLUSION

LA implants exhibited a lower incidence of fracture in abutment-implant complexes and a relatively higher retrievability success rate for jammed abutments.

Biomechanical effects of dental implant diameter, connection type, and bone density on microgap formation and fatigue failure: A finite element analysis

BACKGROUND AND OBJECTIVE

Understanding fatigue failure and microgap formation in dental implants, abutments, and screws under various clinical circumstances is clinically meaningful. In this study, these aspects were evaluated based on implant diameter, connection type, and bone density.

METHODS

Twelve three-dimensional finite element models were constructed by combining two bone densities (low and high), two connection types (bone and tissue levels), and three implant diameters (3.5, 4.0, and 4.5 mm). Each model was composed of cortical and cancellous bone tissues, the nerve canal, and the implant complex. After the screw was preloaded, vertical (100 N) and oblique (200 N) loadings were applied. The relative displacements at the interfaces between implant, abutment, and screw were analyzed. The fatigue lives of the titanium alloy (Ti-6Al-4V) components were calculated through repetitive mastication simulations. Mann-Whitney U and Kruskal-Wallis one-way tests were performed on the 50 highest displacement values of each model.

RESULTS

At the implant/abutment interface, large microgaps were observed under oblique loading in the buccal direction. At the abutment/screw interface, microgap formation increased along the implant diameter under vertical loading but decreased under oblique loading (p < 0.001); the largest microgap formation occurred in the lingual direction. In all cases, the bone-level connection induced larger microgap formation than the tissue-level connections. Moreover, only the bone-level connection models showed fatigue failure, and the minimum fatigue life was observed for the implant diameter of 3.5 mm.

CONCLUSIONS

Tissue-level implants possess biomechanical advantages compared to bone-level ones. Two-piece implants with diameters below 3.5 mm should be avoided in the posterior mandibular area.

Prospective randomized clinical trial evaluating the effects of two different implant collar designs on peri-implant healing and functional osseointegration after 25 years

OBJECTIVES

Evaluate the effects of two different machined-collar lengths and designs on peri-implant healing.

MATERIAL AND METHODS

An implant with a microtextured surface and 3.6mm-long internal-connection machined collar was compared to two implants that had an identical 1.2mm-long external-connection machined collar, but one had the microtextured surface while the other's was machined. Participants received the three implants, with microgap at the crest, alternately at five sites between mental foramen, and a full-arch prosthesis. Peri-implant bone levels were measured after 23 to 26 years of function. Keratinized tissue height, plaque, probing depth, bleeding, and purulence were also evaluated. Descriptive and mixed models for repeated\measures analyses were used, with Bonferroni correction for pairwise comparisons.

RESULTS

Twenty-two participants (110 implants) were evaluated at the 25-year examination. Microtextured implants with the longer machined collar had significantly greater mean marginal bone loss (-1.77mm ± 0.18, mean ± SE) than machined (-0.85mm ± 0.18, p < .001) and microtextured (-1.00 ± 0.18mm, p < .001) implants with the shorter machined collar. Keratinized tissue height was greater for internal-connection (0.74mm ± 0.10) versus external-connection (0.51 ± 0.08, p =  0.01) microtextured implants. No differences were observed for plaque (p = 0.78), probing depth (p = 0.42), bleeding (p  = 0.07), and purulence (p = 1.00). Implant survival rate was 99%.

CONCLUSIONS

Implants with the 1.2mm machined collar limited bone loss to 1mm, while those with the longer machined collar showed > 1.5mm loss after 25 years of function with microgap at the crest. Internal-connection design and fixture surface microtexturing did not result in greater bone preservation. ClinicalTrials.gov Identifier: NCT03862482.