Mandibular Two-implant Overdentures Research Articles

Single lateral implant for mandibular overdentures as a fallback solution or a viable treatment alternative: Four case reports.

This report of four clinical cases aims to illustrate the use of a lateral implant as a solution for implant overdentures in the mandible in different clinical situations. The first two cases describe the clinical situations of patients wearing two-implant mandibular overdentures until the failure of one of the implants, one due to implant loss and the other due to a fracture of an abutment screw, and how the conditions were managed. The third case illustrates the placement of a single implant to retain an overdenture, where a midline implant, as originally planned, was not feasible due to anatomic reasons. The final case describes the use of a lateral implant to support and retain a single-implant mandibular overdenture. The four cases demonstrate that a single lateral implant can be utilized as sole retention in cases of a failing contra-lateral implant and as an alternative to a single implant in the midline.

Evaluation of Peri-Implant Parameters and Functional Outcome of Immediately Placed and Loaded Mandibular Overdentures: A 5-year Follow-up Study.

To evaluate the peri-implant parameters of immediately placed and loaded mandibular overdentures over a 5-year follow-up period. All subjects who had been advised and planned for two-implant mandibular overdenture treatment were included in this study. The peri-implant parameters -including plaque index (PI), bleeding index (BI) and peri-implant pocket depth (PIPD) as well as marginal bone loss (MBL) - were assessed. In addition, prosthodontic parameters including abutment-, implant- and denture-related complications were assessed. Patients were evaluated at follow-up visits, scheduled at 1, 12, 24, 36, 48, and 60 months. The data distribution was analysed with the Shapiro-Wilk test. Data within follow-up categories were compared using ANOVA and the Tukey-Kramer test. A p-value < 0.05 was considered statistically significant. Among the 32 participants, 19 were males and 13 were females, with a mean age of 60.5 ± 7.33. The mean plaque index (PI), bleeding index (BI) and peri-implant pocket depth (PIPD) varied over time. However, no statistically significant difference was observed in the plaque index, bleeding index and peri-implant pocket depth over time (p > 0.05). The mean value at baseline was found to be -0.9 ± 0.3. The values increased over time, with the highest value observed at 60 months 2.6 ± 0.7, which was statistically significant (p < 0.001). Immediately placed and loaded mandibular implant overdentures using two un-splinted implants with locator attachments showed acceptable PI, BI and PIPD at the 5-year follow-up. Statistically significantly greater marginal bone loss was observed from baseline to follow-up, but it was within acceptable limits. A moderate number of restorative and abutment complications were observed during the follow-up of IODs.

Retentive force and dislodgment time variations between three implant overdenture stud attachments in an acidic environment: An in-vitro pilot study

IntroductionThis in-vitro study aimed to evaluate the retentive force and dislodgment time of three stud attachment systems used for mandibular two-implant overdentures by simulating insertion/removal cycles. Materials and methodsFrom a simulation of a completely edentulous mandible with two parallel implants (Ø4.5 mm internal hex connection) (Zimmer Biomet, Warsaw, IN), 15 resin bases were fabricated and divided into three groups (n = 5 each): OT Equator (Rhein83, Bologna, IT), Locator (Zest Dental Solutions, Escondido, CA) and Locator R-Tx (Zest Dental Solutions, Escondido, CA). Pink inserts underwent 2000 cycles of thermocycling (SD MECHATRONIK GmbH, Feldkirchen-Westerham, Germany) and were soaked in citric acid for 24 days in an incubator. Each base underwent 2000 insertion/removal cycles on the Versa Test testing machine (Mecmesin Ltd., W. Sussex, UK) which was used to measure the retentive force and dislodgment time. The results were analyzed using ANOVA followed by the post-hoc Tukey test, Kruskal–Wallis test, and Pearson correlation coefficient test. A p-value of < 0.05 was considered statistically significant. ResultsThe retentive force and dislodgment time of the three systems significantly decreased over the cycles (p < 0.05). The Locator R-Tx showed significantly greater retentive force ​​than did the other systems (p < 0.05), except for the last cycles wherein no significant difference was found with the OT Equator (p > 0.05). The OT Equator had the most stable retention over the cycles (p > 0.05; cycle 1500). ConclusionThe three systems showed satisfactory retentive force ​​during the 2000 cycles. The Locator R-Tx demonstrated the best retention, while the OT Equator exhibited the most stable retention over time.

Crestal strain of two-implant mandibular overdentures with implants placed at different positions: An in vitro 3D printed simulation study

Statement of problemThe 2-implant mandibular overdenture (2IMO) is a popular treatment for patients with mandibular edentulism. However, information on the influence of implant positions on crestal strain is lacking. PurposeThe purpose of this in vitro study was to evaluate the crestal strain around 2 implants to support mandibular overdentures when placed at different positions. Material and methodsEdentulous mandibles were 3-dimensionally (3D) designed separately with 2 holes for implant placement at similar distances of 5, 10, 15, and 20 mm from the midline, resulting in 4 study conditions. The complete denture models were 3D designed and printed from digital imaging and communications in medicine (DICOM) images after scanning the patient’s denture. Two 4.3×12-mm dummy implants were placed in the preplanned holes. Two linear strain gauges were attached on the crest of the mesial and distal side of each implant (CH1, CH2, CH3, and CH4) and connected to a computer to record the electrical signals. Male LOCATOR attachments were attached, the mucosal layer simulated, and the denture picked up with pink female nylon caps. A unilateral and bilateral force of 100 N was maintained for 10 seconds for each model in a universal testing machine while recording the maximum strains in the DCS-100A KYOWA computer software program. Data were analyzed by using 1-way analysis of variance, the Tukey post hoc test, and the paired t test (α=.05). ResultsUnder bilateral loading, the strain values indicated a trend with increasing distance between the implants with both right and left distal strain gauges (CH4 and CH1). The negative (-ve) values indicated the compressive force, and the positive (+ve) values indicated the tensile force being applied on the strain gauges. The strain values for CH4 ranged between −166.08 for the 5-mm and −251.58 for the 20-mm position; and for CH1 between −168.08 for the 5-mm and −297.83 for the 20-mm position. The remaining 2 mesial strain gauges for all 4 implant positions remained lower than for CH4 and CH1. Under unilateral-right loading, only the right-side distal strain gauge CH4 indicated the increasing trend in the strain values with −147.5 for the 5-mm, −157.17 for the 10-mm, −209.33 for the 15-mm, and −234.75 for the 20 mm position. The remaining 3 strain gauges CH3, CH2, and CH1 ranged between −28.33 and −107.17. For each position for both implants, significantly higher (P<.05) strain values were observed on the distal strain gauge channels CH4 and CH1 than on the mesial channels CH3 and CH2 under bilateral loading and on the right side under unilateral loading. ConclusionsPeri-implant crestal strains in the 2IMO increased by increasing the distance of the implants from the midline. The stress values progressively increased from 5 to 10 mm to 15 to 20 mm from midline, represented as lateral incisor, canine, and premolar positions. The distal side of the implants exhibits higher strains than the mesial side of the implants.

The impact of implant-retained overdentures on type-2 diabetic and non-diabetic edentulous patients: Satisfaction and quality of life in a prospective cohort study

ObjectivesTo evaluate the benefits of implant therapy for patients with diabetes, we compared (i) healthy, (ii) well controlled T2DM and (iii) poorly controlled T2DM patients, in terms of oral health-related quality of life (OHRQoL) and satisfaction with mandibular 2-implant overdentures over 12 months following restoration. Materials and methodsThis single-center, prospective, cohort study recruited 165 edentulous adults (HbA1c<12%) to receive two endosseous implants in the anterior mandible to support mandibular overdentures. Participants were enrolled as having T2DM or not, with T2DM participants divided according to HbA1c into well-controlled (<8.1%) and poorly controlled (≥ 8.1%) groups. Participants provided responses to the OHIP-20 (OHRQoL) and the McGill Denture Satisfaction Questionnaire, before implant therapy and 6 and 12 months after overdenture insertion using Locator attachments. HbA1c was measured at the same time points. The effect of groups and time was verified using generalized estimating equations (α=0.025). ResultsAt 12 months, 137 participants provided responses. The two diabetes groups showed improvements in OHRQoL to the same extent as the non-diabetic control group at both 6 and 12 months. Patient satisfaction showed similar improvements with no between-group differences and similar increases identified at 6 and 12 months. HbA1c was not affected by time or groups. ConclusionsDental implant therapy provided significant improvements in patient-perceived benefits of mandibular two-implant overdentures for T2DM individuals, which are similar to those found for healthy edentulous individuals. Importantly, those benefits extend to those individuals with poorly controlled glycaemia. The addition of 2-implant supported mandibular overdentures did not affect glycaemic status over 12 months following insertion. Clinical SignificanceAs risks for implant therapy relative to glycaemic status are better understood, this study documents that implant therapy may offer important benefits in QoL for T2DM patients independent of glycaemic status.

How successful are maxillary implant-retained overdentures on two or four implants?

Design A randomised crossover clinical trial was designed to determine survival and success of four-implant overdentures in the edentulous maxilla, in participants with mandibular two-implant overdentures. Participants received four implants in the maxilla, two anteriorly and two posteriorly, then were randomly allocated into two treatment groups. The prosthetic phase included alternate loading of anterior and posterior implants for three months each, followed by loading of all four implants for another three months. Participants were then followed up in the recall phase for a mean period of 2.2 years.Case selection Four participants were taken from the authors' previous clinical study, meeting the inclusion criteria for a two-implant overdenture in the mandible. Another 21 participants were recruited from study calls after a widening of inclusion criteria. These patients were all pre-treated in accordance with the previous study protocol, so there was standardisation before maxillary implant placement.Data analysis A sample size calculation was performed and a Kaplan-Meier curve was used to demonstrate implant survival over time.Results Twenty-four patients were included in the study. Three implants were lost during the prosthetic phase and two during the recall phase; all were anterior implants. Implant survival after loading was 93.8% after a mean period of 3.1 years. There were 27 maxillary prosthetic complications overall. Denture success was 95.8% after a mean period of 2.2 years.Conclusions Implant survival of four asynchronously loaded implants in implant-supported overdentures in the edentulous maxilla was good and is a recommendable treatment option for patients with two-implant mandibular overdentures. Implant and prosthetic complications are common but mostly straightforward to manage. Two posterior implants are not superior to two anterior implants, but the majority of patients prefer the four-implant maxillary overdenture.

Circumferential bone level and bone remodeling in the posterior mandible of edentulous mandibular overdenture wearers: influence of mandibular bone atrophy in a 3-year cohort study.

Evaluate circumferential bone level and morphological alterations in the posterior mandibular ridge of atrophic (AP) and non-atrophic (NAP) patients using implant-retained mandibular overdentures (MO) over 3years. Twenty-six edentulous patients categorized according to mandibular atrophy (AP = 13/NAP = 13) received two narrow diameter implants (Facility, 2.9 × 10mm) in the anterior region of mandible. The vertical and horizontal bone level was measured along with bone remodeling at 4 distances from the mental foramen in the posterior region of the mandible (L1-L4) via CBCT. NAP showed significantly higher total height and medullary height in all posterior regions at 1 and 3years (p ≤ 0.01). Cortical height and width were significantly higher (p ≤ 0.05) in this group at distances L1 and L4, respectively, in year 1. NAP shows a significantly higher % of medullary height at distances L1 (p ≤ 0.05), L2 (p ≤ 0.01), and L3 (p ≤ 0.05) after 1year, and at all distances (p ≤ 0.05) after 3years. Bone remodeling in the groups differed significantly (p ≤ 0.05) in terms of cortical width and % medullary width at L3. AP and NAP showed similar vertical and horizontal bone level. Bone resorption in the posterior ridge was stabilized by MO over 3years; however, AP are more susceptible to the long-term substitution of medullary bone by cortical bone. This study is the first to longitudinally evaluate bone dimensions in atrophic and non-atrophic two-implant MO users by CBCT and revealed that MO is a predictable treatment based on the stabilization of the posterior bone resorption.

Stress patterns of two-implant mandibular overdentures depending on the types of attachments

Stress patterns of two-implant mandibular overdentures depending on the types of attachments

Evaluation of Oral Health Related Quality of Life in Different Telescopic Two-implant Supported Mandibular Overdenture

AIM: The purpose of the study was to evaluate patient’s oral health related quality of life using oral health impact profile (OHIP14) in rigid and non-rigid telescopic two-implant supported mandibular overdenture patients. METHODS: Twelve completely edentulous patients received two mandibular interforaminal implants to retain telescopic overdenture opposed by maxillary complete denture. Group I (six patients) had rigid telescopic connection and Group II (six patients) received non-rigid telescopic attachments. OHIP14 questionnaire was translated in Arabic and orally asked the patients, answers were collected soon after denture insertion and use (within 1 week), 6 and 12 months after using the overdenture to assess patient’s quality of life. RESULTS: There was no statistical significant difference regarding quality of life using OHIP14 questionnair between the two groups. CONCLUSION: Telescopic two-implant mandibular overdenture showed high quality of life, great satisfaction, and acceptance among patients; regardless to the type of attachments rigid or non-rigid.

Maxillary implant overdentures on two or four implants. A prospective randomized cross-over clinical trial of implant and denture success and survival.

To determine implant survival and success of four conventionally but initially asynchronously loaded implants in implant-supported overdentures for the edentulous maxilla, in participants with opposing mandibular two-implant overdentures. Twenty-six participants received four implants in the region of the maxillary canines and molars. After healing, 24 of these participants (mean age: 68.3years) were randomly allocated to one of two treatment groups, and the adapted overdenture was attached to two unsplinted cylindrical attachments. The other two matrixes remained unattached to the implants for 3months. After this period, the other two implants were loaded for 3months (cross-over design). Then, all four implants were loaded for another 3months. Kaplan-Meier curves were used to evaluate survival and success of implants and dentures. During the active prosthetic study phase, three participants lost one implant. Two participants lost three implants during the recall period. Implant survival after loading was 93.8% after a mean observation period of 3.1years. Denture survival was 100%, but denture success was 95.8%, due to major prosthetic complications. Most participants preferred four implants to two. Within the limitations of the study, it can be concluded that maxillary implant overdentures on two or four implants are both recommendable treatment options. Two posterior implants are not superior to two anterior implants under overdentures retained by unsplinted cylindrical attachments. Implant and prosthetic complications and aftercare measures are common but are mostly easy to handle. However, 23 of the 24 participants preferred the 4-implant maxillary overdenture.

An 8-10 Year Follow-up of Denture Satisfaction and Oral Health-Related Quality of Life with Implant-Retained Mandibular Overdentures.

To report changes in denture satisfaction and oral health-related quality of life (OHRQoL) in edentulous patients treated with two-implant mandibular overdentures (IODs) over a follow-up of 8 to 10 years. This is a follow-up of a previous study carried out between 1997 and 2005. The patients were originally randomly divided into one group receiving IODs and another group who had their conventional mandibular dentures relined (RCD group). The RCD group was offered and received IODs at the 2-year follow-up. The participants completed a self-administered questionnaire containing demographics, 15 variables related to denture satisfaction, and 20 questions from the Oral Health Impact Profile (OHIP-20). Changes over time were analyzed using multilevel linear models for denture satisfaction and multilevel ordinal regression analyses for OHIP-20 variables. Comparisons between groups were analyzed using Mann-Whitney U test for ordinal and t test for metric data. Disregarding patients who passed away during follow-up, the 29 responders represented a response rate of 76%. The degree of denture satisfaction and the OHIP-20 scores remained high and stable in the IOD group over the 10-year observation period for all but one variable. The same factors showed only a modest improvement in the RCD group for the first 2 years; however, during the subsequent 8 years of the observation period (after receiving IODs), denture satisfaction and OHIP-20 scores improved to the same level as the original IOD group. The positive effect on denture satisfaction and OHRQoL of edentulous patients treated with two-implant mandibular overdentures remained unchanged 8 to 10 years after treatment.

Patient-reported outcome measures of edentulous patients restored with single-implant mandibular overdentures: A systematic review.

To review the literatures concerning the effect of the single-implant mandibular overdenture (SIMO) on patient-reported outcome measures (PROMs) and masticatory function in the fully edentulous patients. Electronic databases (PubMed, Cochrane Library, EMBASE and Web of Science) were searched, complemented with manual resources. Prospective studies published in English up to February 2020 reporting the effect of SIMO on PROMs and masticatory function in the edentulous patients were included. This review focused on oral health-related quality of life (OHRQoL), satisfaction and masticatory function outcomes. Of 1157 initially screened articles, 9 randomised controlled trials (RCTs) and 8 prospective studies involving 551 subjects fulfilled the inclusion criteria. Two RCTs were graded as high risk of bias or some concern, while others were low risk. All prospective studies had adequate representativeness and assessment, but only one study had a controlled cohort. In general, the edentulous patients restored with SIMOs had improved OHRQoL and general satisfaction compared to those with conventional complete dentures (CCDs), but the outcome of masticatory function was controversial. Compared with two-implant mandibular overdenture (TIMO), SIMO showed no significant differences regarding general satisfaction and satisfaction with speech, comfort, chewing ability, aesthetics and social life. Conflicting results were observed in OHRQoL and satisfaction with retention and stability. Better masticatory performance was observed in TIMO group than SIMO group. Within the limitation of this review, SIMO is featured with better OHRQoL and satisfaction than CCD. SIMO and TIMO rendered similar patient satisfaction, but TIMO had better masticatory performance.

Mandibular two-implant overdentures with CAD-CAM milled bars with distal extensions or retentive anchors: A randomized controlled trial.

This randomized controlled trial (RCT) aimed to demonstrate the non-inferiority of mandibular 2-implant overdentures (IODs) on a CAD-CAM milled bar with long distal extensions (MBDE) against IODs on retentive anchors (RA). Forty edentulous participants rehabilitated with a maxillary conventional denture and a mandibular 2-IOD participated in this trial. They were randomized into two groups [Control group (CG): RA+gold matrices; Experimental group (EG): MBDE+gold clip]. The outcomes included implant survival rate (ISR), chewing efficiency [quantitative (VoH) and subjective (SA) assessments], peri-implant marginal bone levels (PI-MBL), maximum bite force (MBF), and patient-reported outcomes [oral health impact profile (OHIP-EDENT), and denture satisfaction index (DSI)]. Outcomes were recorded at baseline (BL), two weeks (T0 ), 6months (T1 ), and at 1year (T2 ) after the intervention. Intra- and inter-group analyses were performed using regression models with ⍺=0.05. 38 participants completed the T2 visit (CG: n=19, age=74.7±7.8years; EG: n=19, age=70.3±10.7years). At T2 , there was no implant loss in either of the groups (ISR=100%). There were no significant differences between the groups for the PI-MBL changes (p=.754). Improvements occurred faster in the EG than in the CG, but over the observation time, there were no differences between the trial groups for VoH, MBF, OHIP-EDENT, and the DSI, except for SA being significantly better in the EG group (p=.022). The results of this RCT confirm that mandibular 2-IODs with a CAD-CAM milled bar with long distal extensions are not an inferior treatment to the conventional IODs on retentive anchors in the short term (1year).

In vitro retention force changes during cyclic dislodging of three novel attachment systems for implant overdentures with different implant angulations.

This in vitro study aimed to compare changes in retentive force due to cyclic dislodging of three novel un-splinted attachments. Experimental models simulating a mandibular two-implant overdenture situation, with implants positioned with various interimplant discrepancies (0°, 20°, 40°, and 60°) were fabricated. Three attachment systems were tested, "N": a straight or 15°-angulated stud; "L": a sole straight stud; and "C": a straight or individually angulated stud. All models underwent wet testing and were subjected to 10,000 insertion-removal cycles in a universal testing machine. The mean retentive forces were calculated for cycles 10, 100, 1,000, 5,000, and 10,000. Multiple mixed-effects linear regression models were applied for statistical analyses (⍺<0.05). "N" demonstrated an increasing retention until 1,000 cycles, which subsequently diminished back to its initial retention at 10,000 cycles, showing no significant loss during the entire experiment. Statistical models demonstrated no effect of implant angulation on retention, except for 60° after 10,000 cycles (p<.05). "L" showed an early peak at 100 cycles and did not significantly lose retentive force before 5,000 cycles. Angulations of 40° or higher were shown to lead to lower retentive forces (0° vs. 40° cycle 5,000: p<.05; 0° vs. 60° cycle 100: p<.05, ≥cycle 1,000: p<.001). "C" showed stable retentive forces with no significant loss only at 10,000 cycles (all angles: p<.001) or 5,000 cycles (0° vs. 60°: p<.05). All systems showed retentive forces promising successful clinical use in implant overdentures, even in situations with extremely angulated implants. Specific abutments compensating interimplant angulation maintain retention longer in situations with high axe divergencies.

Masticatory function of immediately loaded two-implant mandibular overdentures: A 5-year prospective study.

To treat mandibular edentulous patients by fitting immediately loaded two-implant overdentures via guided flapless surgery and evaluate their masticatory performance. Nineteen patients who presented with edentulous mandibles (mean age: 69.8 years; range: 60 to 85 years) at the Dental Hospital, Tokyo Medical and Dental University, were enrolled in this study. A newly fabricated complete denture was used as a radiographic guide. Computer planning followed the design procedure, and surgical guides were fabricated for each patient. Flapless surgery was performed using this guide, and two implants were placed in the canine positions. On the day of surgery, a removable overdenture supported by two ball attachments was fitted. Masticatory function was evaluated on the basis of masticatory performance with a color-changeable chewing gum, maximum occlusal force with an occlusal force meter, and occlusal contact area with an occlusal diagnostic system. The masticatory performance significantly improved from 48 months after surgery. The maximum occlusal force significantly increased 24 months after surgery. The occlusal contact area significantly increased from 6 months after surgery. This prospective study indicated that maximum occlusal force and occlusal contact area significantly improved at a comparatively earlier period after implant surgery and were maintained for up to 5 years with the immediate loading of two-implant overdentures with stud attachments. However, masticatory performance took more time to improve than maximum occlusal force and occlusal contact area. According to this 5-year prospective study, masticatory performance, maximum occlusal force, and occlusal contact area showed significant improvement after 4 to 5 years, 2 years, and 6 months postsurgery, espectively.

Mandibular single-implant overdenture as an alternative for full arch rehabilitations

Oral rehabilitation with mandibular single-implant overdentures (SIO) has been characterized as a solution to improve retention and stability of conventional complete dentures (CD). Among the benefits of this therapy, it can be mentioned minimally invasive surgery, simple prosthetic technique, better retention, and significantly reduced costs. However, the application of this protocol in daily clinic is still not widespread. Aim: Thus, this study aimed to perform a literature review to address the clinical characteristics of this rehabilitation, when compared to two-implant mandibular overdentures and CD. Methods: For this, a search was conducted in the PubMed database, considering articles published in English language, without date limitation. Results: It was found 243 manuscripts, of which 20 were compatible with the aim of this study after title/abstract reading. The selected papers focused on masticatory muscles function, satisfaction levels and self-reported quality of life, as well as surgical and prosthetic outcomes, such as maintenance, repair and implant failure rates. All evaluated manuscripts showed similar masticatory function and patient's satisfaction with SIO and two-implant overdenture, while results for a SIO were greater when compared to rehabilitations with CD. In addition, SIO have proven to do not damage the implant, being implant loss close to zero. However, the prosthesis fracture adjacent to the implant was a recurrent clinical outcome, which requires further studies to solve this impairment. Conclusion: Thus, it can be concluded that SIO represents an alternative treatment for frail elders or low-income patients, leading to higher masticatory function, as well as improved quality of life.

Dental-Implant Retained Mandibular Overdenture: A Case Report

The prosthetic management of the patient with resorbed ridge has long been a major challenge for dentistry. Conventional complete denture for long was the standard of care for all such patients. However, most patients find it difficult to adapt to mandibular denture due to lack of retention and stability. Recent scientific studies carried out over the past decade have determined that the benefits of a mandibular two-implant overdenture are sufficient to propose the two-implant overdenture-rather than the conventional denture - as the first treatment option. BJHS 2018;3(2)6:488-491.

Retentive Properties of Two Stud Attachments with Polyetherketoneketone or Nylon Insert in Mandibular Implant Overdentures.

The aim of this study was to compare the retentive properties of an attachment with a nylon insert and an attachment with a polyetherketoneketone (PEKK) insert on two-implant mandibular overdentures during simulated masticatory loadings and insertion/removal cycles. Two attachment systems with nylon inserts or PEKK inserts were investigated, including nylon/low, nylon/medium, nylon/high, PEKK/x-low, PEKK/low, PEKK/medium, and PEKK/high. The canine region of edentulous mandibular overdenture models was retained with two implant analogs through two different stud attachments at interimplant angulations of 0 and 20 degrees. The simulated mastication and insertion/removal cycles were 400,000 cyclic loadings and 1,080 times of insertion/removal. Wear patterns and deformations on the attachment surface were analyzed with scanning electron microscopy. At 0 and 20 degrees, initial retentive force was highest in nylon/high and lowest in PEKK/x-low. Final retentive force was highest in PEKK/high and PEKK/medium at 0 and 20 degrees, respectively, and PEKK/x-low was lowest at both angulations. At 0 degrees, nylon/low, nylon/medium, PEKK/x-low, and PEKK/low displayed a significant increase in retention (P < .05), and nylon/high and PEKK/medium showed a significant decrease in retention (P < .05), except PEKK/high, which exhibited no significant decrease (P > .05). At 20 degrees, nylon/low and PEKK/x-low increased retention significantly (P < .05), and nylon/medium, nylon/high, PEKK/low, PEKK/medium, and PEKK/high decreased retention significantly (P < .05). Patrices of both attachment systems barely showed detectable abrasion, while matrices revealed severe wear and surface deformation. Nylon inserts particularly displayed more noticeable wear and deformation than PEKK inserts. Within the limitations of this investigation, the attachment system with a PEKK insert indicated less abrasion and retention change than the attachment system with a nylon insert on both paralleled implants and axially tilted implants under 400,000 cyclic loadings and 1,080 insertion/removal cycles for 1 year.

Three-dimensional finite element analysis of mandibular overdentures with different implant positions and attachment types

OBJECTIVE: This 3-D FEA study compared the stress distribution in two-implant mandibular overdentures as a function of implant position and attachment system (LA: locator attachment vs. BA: ball attachment).METHODS: Four models of mandibular overdentures were tested: M1-LA – with implants at the canine regions (standard implant position) and LA; M2-LA – with implants placed at the first premolar regions (distalized implant position) and LA; M1-BA – with standard implant position and BA; and M2-BA – with distalized implant position and BA. The geometric models were converted into finite element models. A 100 N axial load was applied at the first molar region. The von-Mises stress distribution was compared in selected points.RESULTS: The models with BA had pattern of stress distribution was more uniform along the implant axis than the ones with LA, although the stress magnitude was larger. The largest area of von Mises stresses on the alveolar ridge was in the models with standard implant distribution.CONCLUSION: The findings showed that the models with BA had better biomechanical behavior than the ones with LA. For both types of attachment, the models with increased inter-implant distance presented a smaller area of stress distribution in the perimplant cortical bone tissue than the standard implant position.

Effect of Different Degrees of Mesial Implant Inclination on the Retention and Stability of Two-Implant Mandibular Overdentures Retained with Stud Attachments: An In Vitro Study.

To evaluate the effect of different degrees of mesial implant inclinations on the retention and stability of two-implant mandibular overdentures retained with stud attachments. Four experimental mandibular acrylic models were constructed. Two laboratory implants were inserted in the canine areas of each model with the following degrees of mesial inclinations: 0, 5, 10, and 20 degrees. Experimental overdentures were connected to the implants with Locator extra-light retention (Le), Locator light retention (Ll), and Locator medium retention (Lm). Vertical (retention) and oblique (stability) dislodging forces (anterior, posterior, and lateral) were measured at the beginning of the study (initial retention) and after 540 cycles of denture insertion and removal (final retention). The final retention was not significantly affected by small (5 degrees) and large (20 degrees) implant inclinations, but decreased with a moderate (10 degrees) inclination. For a small implant inclination (5 degrees), Lm showed the highest final retention/stability and Le showed the lowest, while for moderate and large inclinations (10 and 20 degrees), Le showed the highest final retention/stability and Lm showed the lowest. Vertical dislodging recorded the highest final stability, and lateral dislodgment recorded the lowest stability. Within the limitations of this in vitro study, only moderate implant angulation (10 degrees) negatively affects the final retention and stability of Locator-retained overdentures. Locator medium retention for small angulation (5 degrees) and Locator extra-light retention for moderate (10 degrees) and large (20 degrees) angulations are recommended to maintain high retention and stability after 540 cycles of denture insertion and removal.