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

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.

A comprehensive biomechanical evaluation of length and diameter of dental implants using finite element analyses: A systematic review

Background

With a wide range of dental implants currently used in clinical scenarios, evidence is limited on selecting the type of dental implant best suited to endure the biting force of missing teeth. Finite Element Analysis (FEA) is a reliable technology which has been applied in dental implantology to study the distribution of biomechanical stress within the bone and dental implants.

Purpose

This study aimed to perform a systematic review to evaluate the biomechanical properties of dental implants regarding their length and diameter using FEA.

Material and methods

A comprehensive search was performed in PubMed/MEDLINE, Scopus, Embase, and Web of Science for peer-reviewed studies published in English from October 2003 to October 2023. Data were organized based on the following topics: area, bone layers, type of bone, design of implant, implant material, diameter of implant, length of implant, stress units, type of loading, experimental validation, convergence analysis, boundary conditions, parts of Finite Element Model, stability factor, study variables, and main findings. The present study is registered in PROSPERO under number CRD42022382211.

Results

The query yielded 852 results, of which 40 studies met the inclusion criteria and were selected in this study. The diameter and length of the dental implants were found to significantly influence the stress distribution in cortical and cancellous bone, respectively. Implant diameter was identified as a key factor in minimizing peri-implant stress concentrations and avoiding crestal overloading. In terms of stress reduction, implant length becomes increasingly important as bone density decreases.

Conclusions

The diameter of dental implants is more important than implant length in reducing bone stress distribution and improving implant stability under both static and immediate loading conditions. Short implants with a larger diameter were found to generate lower stresses than longer implants with a smaller diameter. Other potential influential design factors including implant system, cantilever length, thread features, and abutment collar height should also be considered in future implant design as they may also have an impact on implant performance.

Biomechanical influence of narrow-diameter implants placed at the crestal and subcrestal level in the maxillary anterior region. A 3D finite element analysis

PURPOSE

To evaluate the tendency of movement, stress distribution, and microstrain of single-unit crowns in simulated cortical and trabecular bone, implants, and prosthetic components of narrow-diameter implants with different lengths placed at the crestal and subcrestal levels in the maxillary anterior region using 3D finite element analysis (FEA).

MATERIALS AND METHODS

Six 3D models were simulated using Invesalius 3.0, Rhinoceros 4.0, and SolidWorks software. Each model simulated the right anterior maxillary region including a Morse taper implant of Ø2.9 mm with different lengths (7, 10, and 13 mm) placed at the crestal and subcrestal level and supporting a cement-retained monolithic single crown in the area of tooth 12. The FEA was performed using ANSYS 19.2. The simulated applied force was 178 N at 0°, 30°, and 60°. The results were analyzed using maps of displacement, von Mises (vM) stress, maximum principal stress, and microstrain.

RESULTS

Models with implants at the subcrestal level showed greater displacement. vM stress increased in the implant and prosthetic components when implants were placed at the subcrestal level compared with the crestal level; the length of the implants had a low influence on the stress distribution. Higher stress and strain concentrations were observed in the cortical bone of the subcrestal placement, independent of implant length. Non-axial loading influenced the increased stress and strain in all the evaluated structures.

CONCLUSIONS

Narrow-diameter implants positioned at the crestal level showed a more favorable biomechanical behavior for simulated cortical bone, implants, and prosthetic components. Implant length had a smaller influence on stress or strain distribution than the other variables.

Marginal Bone Level and Biomechanical Behavior of Titanium-Indexed Abutment Base of Conical Connection Used for Single Ceramic Crowns on Morse-Taper Implant: A Clinical Retrospective Study

The goal of this retrospective clinical study was to evaluate the behavior of Morse-taper indexed abutments by analyzing the marginal bone level (MBL) after at least 12 months of function. Patients rehabilitated with single ceramic crowns between May 2015 and December 2020 received single Morse-taper connection implants (DuoCone implant) with two-piece straight abutment baseT used for at least 12 months, presenting periapical radiograph immediately after crown installation were enrolled. The position of the rehabilitated tooth and arch (maxilla or mandible), crown installation period, implant dimensions, abutment transmucosal height, installation site (immediate implant placement or healed area), associated with bone regeneration, immediate provisionalization, and complications after installation of the final crown were analyzed. The initial and final MBL was evaluated by comparing the initial and final X-rays. The level of significance was α = 0.05. Seventy-five patients (49 women and 26 men) enrolled had a mean period of evaluation of 22.7 ± 6.2 months. Thirty-one implant-abutment (IA) sets had between 12–18 months, 34 between 19–24 months, and 44 between 25–33 months. Only one patient failed due to an abutment fracture after 25 months of function. Fifty-eight implants were placed in the maxilla (53.2%) and 51 in the mandible (46.8%). Seventy-four implants were installed in healed sites (67.9%), and 35 were in fresh socket sites (32.1%). Thirty-two out of these 35 implants placed in fresh sockets had the gap filled with bone graft particles. Twenty-six implants received immediate provisionalization. The average MBL was −0.67 ± 0.65 mm in mesial and −0.70 ± 0.63 mm in distal (p = 0.5072). The most important finding was the statistically significant difference comparing the values obtained for MBL between the abutments with different transmucosal height portions, which were better for abutments with heights greater than 2.5 mm. Regarding the abutments’ diameter, 58 had 3.5 mm (53.2%) and 51 had 4.5 mm (46.8%). There was no statistical difference between them, with the following means and standard deviation, respectively, −0.57 ± 0.53 mm (mesial) and −0.66 ± 0.50 mm (distal), and −0.78 ± 0.75 mm (mesial) and −0.746 ± 0.76 mm (distal). Regarding the implant dimensions, 24 implants were 3.5 mm (22%), and 85 implants (78%) had 4.0 mm. In length, 51 implants had 9 mm (46.8%), 25 had 11 mm (22.9%), and 33 implants were 13 mm (30.3%). There was no statistical difference between the abutment diameters (p > 0.05). Within the limitations of this study, it was possible to conclude that better behavior and lesser marginal bone loss were observed when using abutment heights greater than 2.5 mm of transmucosal portion and when placed implants with 13 mm length. Furthermore, this type of abutment showed a little incidence of failures within the period analyzed in our study.

A randomized clinical study to compare implant stability and bone loss using early loading protocol in two implant systems with different design

Aims

The study compared changes in implant stability and bone loss of implants with different designs using early loading at 6 weeks.

Setting and Design

In vivo-comparative study.

Materials and Methods

Forty subjects were selected and divided randomly by sealed envelope method in Group X and Group A for early loading for missing single posterior tooth in mandible. Implants in Group X had flared crest module and buttress thread design, whereas implants in Group A had parallel crest module and V-shaped thread design. All subjects were evaluated by Ostell for implant stability at the interval of baseline, 6 weeks, 3 months, and 6 months. ImageJ software was used for measurement of crestal bone loss in intraoral periapical radiographs at the interval of 6 weeks, 3 months, and 6 months.

Statistical Analysis Used

Unpaired t test, repeated ANOVA, Tukey post hoc test.

Results

The mean bone loss values of Group X at predetermined interval were 1.51 ± 0.20 mm, 2.11 ± 0.21 mm and 2.13 ± 0.21 mm. The mean bone loss values of Group A were 1.79 ± 0.16 mm, 2.92 ± 0.23 mm and 2.95 ± 0.23 mm. The mean bone loss was statistical significant (P < 0.05) at 6 weeks, 3 months and 6 months. It was highly significant in Group A at 6 months (P < 0.001).

Conclusions

It was concluded that Group X implants design showed better implant stability and less bone loss when compared to Group A implants design.