Mini dental implants retaining mandibular overdentures: A dental practice-based retrospective analysis

Stress distribution of one-piece and two-piece mini-Implant overdentures with various attachment systems and diameters: A finite element analysis

PURPOSE

We investigated and compared the stress distribution within one- and two-piece mini-implants for overdentures with three different attachments (ball, Locator, and magnet) and two different diameters using three-dimensional finite element (3D FE) analysis and a monotonic bending test. The goal was to identify the most beneficial implant attachment system design for mini-implant overdentures with a lower risk of implant fracture.

METHODS

Twelve 3D FE models simulating a mandible segment with one- and two-piece mini-implants with different attachment systems, diameters, and overdentures were created using three-dimensional computer-aided design (CAD) software. Vertical and oblique forces (45° to the longitudinal axis of the implant) of 100 N were applied to the dentures. The stress distribution was analyzed. A bending test was performed on a mini-implant (Locator, 2.4 mm) using a testing machine to quantify the load at yield stress.

RESULTS

One-piece mini-implants showed lower maximum stress compared to two-piece mini-implants. Among the three designs, the magnet attachment systems showed the maximum stress. The maximum von Mises stress occurred at the neck of the implants, which was surrounded by cortical bone in all models, and under both loading conditions.

CONCLUSIONS

Focusing on the attachments and one- and two-piece designs of mini-implant overdentures using CAD models to reduce confounding factors affecting the stress distribution, we concluded that one-piece mini-implants tended to show lower stress compared to two-piece mini-implants. Mini-implant overdentures with Locator and ball attachments demonstrated lower stress within the implants compared to those with magnet attachments under vertical and oblique loading conditions.

Survival and stability of strategic mini-implants with immediate or delayed loading under removable partial dentures: a 3-year randomized controlled clinical trial

Objectives

Stability values of mini-implants (MIs) are ambiguous. Survival data for MIs as supplementary abutments in reduced dentitions are not available. The aim of this explorative research was to estimate the 3-year stability and survival of strategic MIs after immediate and delayed loading by existing removable partial dentures (RPDs).

Material and methods

In a university and three dental practices, patients with unfavorable tooth distributions received supplementary MIs with diameters of 1.8, 2.1, and 2.4 mm. The participants were randomly allocated to group A (if the insertion torque ≥ 35 Ncm: immediate loading by housings; otherwise, immediate loading by RPD soft relining was performed) or delayed loading group B. Periotest values (PTVs) and resonance frequency analysis (RFA) values were longitudinally compared using mixed models.

Results

A total of 112 maxillary and 120 mandibular MIs were placed under 79 RPDs (31 maxillae). The 1st and 3rd quartile of the PTVs ranged between 1.7 and 7.8, and the RFA values ranged between 30 and 46 with nonrelevant group differences. The 3-year survival rates were 92% in group A versus 95% in group B and 99% in the mandible (one failure) versus 87% in the maxilla (eleven failures among four participants).

Conclusions

Within the limitations of explorative analyses, there were no relevant differences between immediate and delayed loading regarding survival or stability of strategic MIs.

Clinical relevance

The stability values for MIs are lower than for conventional implants. The MI failure rate in the maxilla is higher than in the mandible with cluster failure participants.

Clinical trial registration

German Clinical Trials Register (Deutsches Register Klinischer Studien, DRKS-ID: DRKS00007589, www.germanctr.de), January 15, 2015.

Prosthetic complications and quality of life among wearers of mandibular overdenture with the Facility-Equator system

This longitudinal study aimed to assess the performance of the Facility-Equator system as mandibular overdenture (MO) retainers from a prosthetic perspective during 2 years of loading and to investigate the oral health-related quality of life (OHRQoL) and whether prosthetic events can affect the OHRQoL. Twenty-four patients (68.1 ± 7.51 years) reported their OHRQoL through the Geriatric Oral Health Assessment Index (GOHAI) and Oral Health Impact Profile (OHIP-EDENT) questionnaires before MO loading and after 1 and 2 years of usage. Prosthetic occurrences were recorded during this period. Data were analyzed using the Wilcoxon test, Mann-Whitney test, and Spearman correlation coefficients. Of the 127 prosthetic events that occurred in the first year, the most frequent events were prosthesis adjustments (16.5%), dislodgement of the Equator attachment (14.17%), and O-ring replacement (11.8%). Eighty-seven prosthetic events were recorded in the second year, the most frequent events being prosthesis adjustments (27.6%), O-ring replacement (20.7%), and recapturing the female matrix (11.5%). All domains of the GOHAI and OHIP-EDENT questionnaires exhibited a significant difference (p < 0.05) between the baseline and 1- and 2-year evaluations, except in the Social Disability and Psychological Discomfort domains (p > 0.05) of OHIP-EDENT after 1 year. Complications related to prosthetic maintenance, such as fracturing of the prosthesis, Equator dislodgement, prosthesis rebasing, and new overdenture confection, affect the OHRQoL (p < 0.05), primarily the Physical Pain and Discomfort domains, especially in the first year of MO loading.

Effect of Number and Location on Stress Distribution of Mini Dental Implant-Assisted Mandibular Kennedy Class I Removable Partial Denture: Three-Dimensional Finite Element Analysis

Purpose. To investigate effects of number and location on patterns of von Mises stress distribution and volume average stress on abutment tooth, edentulous ridge, mini dental implant, and surrounding bone of mini dental implant-assisted mandibular Kennedy class I removable partial denture. Materials and Methods. Eight three-dimensional finite element models of mandibular Kennedy class I with different numbers and locations of mini dental implants were constructed. Mini dental implants were generated in the area of second premolar, first molar, and second molar, respectively. A static load of 400 N was applied on all models. The von Mises stress and volumetric average stress were calculated by three-dimensional finite element analysis. Result. The minimum volumetric average stress of abutment tooth was found in the model, where there was one mini dental implant at the second molar position and 2 mini dental implants at first molar and second molar positions. The model with three mini dental implants had reduced volumetric average stress of abutment tooth, which was not different from the model with two mini dental implants. However, the minimum volumetric average stress of mini dental implant and surrounding bone were found when three mini dental implants were applied, followed by two and one mini dental implants, respectively. Conclusion. Placing at least one mini dental implant at a second molar position can help reduce stress transferred to the abutment tooth. Stresses around each implant and surrounding bone reduced with increased numbers of mini dental implants.

Prospective clinical implementation of optional implant treatment into pregraduate dental education-mini implants for retention and support of mandibular overdentures

Background

The primary aim of the study was to evaluate mini implant (MDI) survival, prosthodontic maintenance, and patient-reported outcome measures after conducting an optional pregraduate academic course on patients with mandibular edentulism including fabrication of overdentures and MDI planning and placement as well as chair-side incorporation of the respective restauration. In a prospective clinical study, 20 patients received 80 MDIs that were restored with mandibular overdentures. All treatment steps including placement of 40 MDIs were conducted by undergraduate students under strict guidance of a consultant. Next to students’ perceptions after participation, survival of MDIs, and prosthodontic maintenance, patients’ perceptions as well as peri-implant parameters were assessed after 4 weeks and 3 and 12 months.

Results

Three MDIs fractured (two during insertion and one after 3 months; total survival 96.25%). Two overdentures fractured and a total of 23 cases of minor prosthodontic maintenance were required. Over time, patients’ satisfaction significantly increased. Besides, questionnaires showed a high rate of students’ positive perception and high self-confidence to include MDI therapy into own practice.

Conclusions

The results are in accordance to those reported by postgraduate dentists. In accordance, therapy with MDI-retained mandibular overdentures seems to be feasible and successful at pregraduate level if the students receive guidance.

Maintenance and risk factors for fractures of overdentures using immediately loaded conventional diameter or mini implants with Locator abutments: A cohort study

BACKGROUND

Fractures in mandibular implant-retained overdentures are a common complication. However, little is known on the related risk factors and outcome differences when using two conventional diameter or two mini implants.

PURPOSE

The purpose of this study was first, to evaluate the required maintenance and complications with the overdentures and second, to analyze risk factors for overdenture fractures.

MATERIALS AND METHODS

This cohort study was conducted in edentulous patients with complete dentures. Patients received either two conventional (4.1 mm in diameter) and two mini (2.9 mm or less in diameter) implants, based on available buccal-lingual ridge width. All implants were immediately loaded with mandibular overdentures retained by Locator abutments. The number of prosthodontic after care visits (scheduled and unscheduled) were recorded and compared between the two implant diameter groups. Fracture occurrence was the primary outcome variable. Risk estimates were presented as odds ratios (ORs) with 95% confidence intervals (CIs). The ORs were adjusted for potential clinical confounders (ie, necessity of relining, matrix recapture, abutment loosening, implant diameter, height of the Locator, and retention force).

RESULTS

A total of 50 edentulous patients were analyzed. One conventional diameter and three mini implants failed within a 1-year follow-up period. Prosthetic maintenance requirements for overdentures on both implant diameter groups were comparable. A total of 12 overdenture fractures (four in the mini implant group and eight in the conventional diameter group) occurred. Adjusted OR (AOR) analysis showed a significant association between abutment loosening and overdenture fracture (AOR = 12.00, 95% CI = 1.11-129.45; P = .041).

CONCLUSION

Within the limitations of this study, the present findings suggest that implant diameter does not affect number of prosthetic maintenance and complications, and that abutment loosening is a risk factor for overdenture fractures, regardless of the implant diameter used.

Definition of a drilling protocol for mini dental implants in different bone qualities

Mini dental implants (MDI) have proven to be a good alternative of the conventional implants to support lower overdentures in elderly edentulous patients with narrow residual ridge. The aim of the present study was to define drilling protocols for each diameter of the MDI in each bone quality. The number and the diameter of the drilling bur and the drilling depth was investigated. A total of 48 MDIs with a ball head and transgingival collar were used to the drilling protocol in four different bone qualities (Q1-Q4). All available four diameters of the implants were included: 1.8mm, 2.1mm, 2.4mm, and 2.9mm. The length of all implants was 15mm. Three different protocols were prepared for each of the four bone qualities and for each implant diameter. The insertion torques and the primary stability of the implants were measured in their final position. Regardless of implant diameter and bone quality, the insertion torque was significantly higher using drilling protocol 1 than 3 and using drilling protocol 2 than 3 as well. The insertion torque was significantly higher in bone quality Q1 than in Q2-Q4. The unscrewing resulted in considerably increase in the torque, which exceeded the insertion torques by up to two times. This repeatedly led to the bending and fractures of implants.

Evolution of in vivo assessed retention forces in one-piece mini dental implant-retained mandibular overdentures: 5-Year follow-up of a prospective clinical trial

BACKGROUND

The evolution of retention forces in one-piece mini dental implants (MDIs) retaining implant overdentures (IODs) is of major importance, as the male parts cannot be exchanged, due to the implant design.

PURPOSE

To report the evolution of retention forces of one-piece MDIs, retaining mandibular IODs with ball/ O-ring attachments during 5 years assessed in vivo.

MATERIALS AND METHODS

Four MDIs were installed in the interforaminal region and immediately loaded using the existing mandibular complete denture. Directly post-op, at the 1-year and the 5-year follow-up, the retention forces were assessed with a validated strain gauge at each implant site separately.

RESULTS

At the male part, changes could only be observed at implant site 34: During the first year, there was a statistically significant increase, whereas the retention forces were decreased at the 5-year follow-up. At the female part, retention forces decreased significantly over time. Baseline values could be reestablished by exchanging the O-rings. The changes of the retention forces were more obvious in the posterior, compared to the anterior implants.

CONCLUSIONS

Retention forces at the female part decrease significantly over time, when retaining mandibular IODs by MDIs with ball/ O-ring attachments. Baseline values can be reestablished by exchanging the O-rings. At the male part, changes of retention forces depend on the implant location.

Comparison of Three Prosthodontic Treatment Modalities for Patients with Periodontally Compromised Anterior Mandibular Teeth: A 2-year follow-up study

OBJECTIVES

To prospectively assess self-perceived chewing function (CF) and oral health-related quality of life (OHRQoL) in geriatric patients after receiving three different treatment modalities in the mandible: removable partial denture (CD-RPD), complete denture (CDs), or complete overdenture supported by mini dental implants (CD-MDI). At baseline, all patients had mobile anterior teeth (1 mm or >) and missing posterior teeth in the mandible. Patients were completely edentulous in the maxilla. After treatment, patients were recalled at the 3-month and the 2-year post-treatment period.

MATERIALS AND METHODS

A total of 176 patients participated (CD group, n=68; CD-RPD group, n=58; CD-MDI group, n=50). Self-reported CF was assessed using the Chewing Function questionnaire (CFQ), The OHRQoL was evaluated using the OHIP14 questionnaire, which the patients completed 1. before treatment, 2. three months after treatment, and 3. at the 2-year post-treatment stage.

RESULTS

The OHRQoL and the self-perceived CF significantly improved in all groups after treatment (p<0.01). The highest improvement of a CF was recorded in the CD-MDI group. The OHRQoL was significantly higher in the CD-MDI group in comparison to the CDs group after treatment (p<0.01). At the 2-year post-treatment stage, self-perceived CF significantly further improved in the CD-MDI group, while it worsened in the CD and the CD-RPD groups (p<0.01). The same pattern was recorded for the OHIP14 summary scores. The highest amount of denture repairs and adjustments was recorded in the CD-RPD group, although maintenance was also demanding in the CD-MDI group.

CONCLUSION

Within the limitations of this study, rehabilitation with mandibular MDI retained overdenture can be considered as preferred treatment with the constant improvement of OHRQoL and a chewing function in comparison to mandibular CD or mandibular RPD option in patients with mobile anterior mandibular teeth.

Clinical outcome of removable prostheses supported by mini dental implants. A systematic review

INTRODUCTION

For many years, edentulous patients have had no other option than conventional dentures to reestablish their oral function. To avoid the need for bone graft surgery, some professionals have suggested the use of mini dental implants (MDIs) to support prostheses. The MDIs are narrow implants, ranging approximately from 1.8 to 2.9 mm in diameter. Recently, the promising results of mini implants regarding osseointegration and patient satisfaction have led clinicians to accept them as a definitive treatment option.

OBJECTIVE

Therefore, the proposition of this systematic review was to assess information on the outcomes of MDIs supporting removable prostheses.

METHODS

The PubMed and Cochrane databases were searched for articles published before September 2017, which yielded a total of 774 studies for analysis. After exclusion and inclusion criteria, 22 prospective studies were included in this systematic review.

RESULTS

Most mini implants were placed in a flapless single-stage surgery and loaded immediately. Most studies reported failures in the first year and prosthetic complications. The mean survival rate of the selected studies was 95.6%, and mean follow-up was 22.8 months.

CONCLUSION

The MDI-supported removable prostheses successfully improved patients' chewing and speaking ability, quality of life, and satisfaction, suggesting that MDIs are a viable and safe option to support removable prostheses in the mandibular arch.

Mini Dental Implant-Retained Removable Partial Dentures: Treatment Effect Size and 6-Months Follow-up

Objective

The aim was to compare esthetic outcomes, masticatory performance and a comfort of removable partial denture (RPD) wearing after receiving: clasp-retained RPD (C-RPD) or mini dental implant-retained RPD (MDI-RPD) in the mandible.

Materials and Methods

A sample of 88 patients (Kennedy Class I) with all posterior teeth missing and a linear support for a RPD participated. A total of 52 patients (36 females, 16 males; 56 to 84 years old) participated in the C-RPD group and 36 patients (26 females, 10 males; 43 to 81 years old) in the MDI-RPD group. All MDIs were placed adjacent to the last remaining mandibular anterior tooth or one tooth length posteriorly. The new RPDs had Co-Cr frameworks with lingual plate major connectors; the MDI-RPDs were retained by O-ball matrices and the C-RPDs with clasps. Patients answered questions at pre-treatment and post-treatment stages and after 6-months follow-up: how satisfied they had been with esthetic appearance, how confident they were while chewing hard food, how satisfied they were with food comminution and they also evaluated a comfort of RPD wearing. The 0-10 visual-analogue scale was used. Statistics included descriptive methods, t-tests and the standardized effect-size calculation.

Results

The MDI-RPD wearers were more satisfied with their post-treatment esthetics, food comminution, a comfort with RPDs and had better confidence while chewing than the C-RPD wearers. The MDI-RPD wearers reported larger positive effect of the treatment. The results were consistent throughout the first 6-months period.

Conclusion

The MDI-RPD patients showed superior outcomes than the C-RPD patients after the treatment and over the 6-month period.

The role of IL-1 gene polymorphisms (IL1A, IL1B, and IL1RN) as a risk factor in unsuccessful implants retaining overdentures

PURPOSE

Implant-supported overdentures are an alternative predictable rehabilitation method that has a high impact on improving the patient's quality of life. However, some biological complications may interfere with the maintenance and survival of these overdenture implants. The goal of this article was to assess the factors that affect peri-implant success, through a hypothetical prediction model for biological complications of implant overdentures.

METHODS

A retrospective observational, prevalence study was conducted in 58 edentulous Caucasian patients rehabilitated with implant overdentures. A total of 229 implants were included in the study. Anamnestic, clinical, and implant-related parameters were collected and recorded in a single database. "Patient" was chosen as the unit of analysis, and a complete screening protocol was established. The data analytical study included assessing the odds ratio, concerning the presence or absence of a particular risk factor, by using binary logistic regression modeling. Probability values (p values) inferior to 0.05 were considered as representing statistically significant evidence.

RESULTS

The performed prediction model included the following variables: mean probing depth, metal exposure, IL1B_allele2, maxillary edentulousness, and Fusobacterium nucleatum. The F. nucleatum showed significant association with the outcome. Introducing a negative coefficient appeared to prevent complications or even boost the biological defense when associated with other factors.

CONCLUSIONS

The prediction model developed in this study could serve as a basis for further improved models that would assist clinicians in the daily diagnosis and treatment planning practice of oral rehabilitation with implant overdentures.