Diamond-Like Carbon Coating Reduces Connection Screw Head Stripping After Multiple Tightening Instances.

The stability of implant-abutment joint is fundamental for the long-term success of implant rehabilitation. The screw loosening, fracture, and head deformation are among the most common mechanical complications. Several surface treatments of titanium screws have been proposed to improve their resistance and stability. Diamond-like carbon (DLC) coating of the materials is widely used to increase their wear resistance and durability. The present study aimed to evaluate the effect of carbon fiber coating on the screw head on screw removal torque and screw head stripping. One hundred titanium implant screws were used, 50 without coating (Group 1) and 50 with DLC coating of the screw head (Group 2). Each screw was tightened with a torque of 25 Ncm and unscrewed 10 times. The removal torque was measured with a digital cap torque tester for each loosening. Optical 3d measurement of the screw head surface was performed by a fully automatic machine before and after multiple tightening to investigate surface modifications. The reverse torque values decreased with repeated tightening and loosening cycles in both groups without significant differences (P > .05). Optical measurements of surface dimensions revealed average changes of 0.0357 mm in Group 1 and 0.02312 mm in Group 2, which resulted to be statistically significant (P < .001). The DLC coating of the retention screw head can prevent its distortion and wear, especially after multiple tightening.

Evaluation of Vertical Misfit and Torque Loss of Different Abutments for Tri-Channel Type Internal Connection Dental Implants After Mechanical Cycling.

The aim of this study was to evaluate the mechanical behavior of UCLA and Mini-conical abutments for implants with Tri-channel connections regarding torque loss and vertical misfit. Twenty 3-element metal-ceramic fixed partial dentures (FPD) supported by 2 implants were manufactured and divided into 2 groups (n = 10): UCLA (group 1) and Mini-conical Abutments (group 2). The evaluation of torque loss was carried out before and after mechanical cycling, while the vertical fit was evaluated throughout the different stages of manufacturing the prostheses, as well pre- and postcycling (300,000 cycles, 30 N). Statistical analyses of torque loss and vertical misfit were performed using the linear mixed effects model. Both groups showed torque loss after mechanical cycling (P < .05); however, there was no significant percentage differences between them (P = .795). Before cycling, the groups showed a significant difference in terms of vertical misfit values (P < .05); however, this difference was no long observed after cycling (P = .894). Both groups showed torque loss after the cycling test, with no significant difference (P > .05). There was no significant difference in vertical misfit after mechanical cycling; however, in group 1 (UCLA) there was accommodation of the implant-UCLA abutment interface, while group 2 (Mini-conical abutment) did not show changes in the interface with the implant after the test. Both groups behaved similarly regarding the torque loss of the prosthesis retention screws pre- and postmechanical cycling, with greater loss after the test.

In vitro assessment of internal implant-abutment connections with different cone angles under static loading using synchrotron-based radiation.

BACKGROUND: The stability of implant-abutment connection is crucial to minimize mechanical and biological complications. Therefore, an assessment of the microgap behavior and abutment displacement in different implant-abutment designs was performed. METHODS: Four implant systems were tested, three with a conical implant-abutment connection based on friction fit and a cone angle < 12 ° (Medentika, Medentis, NobelActive) and a system with an angulated connection (< 40°) (Semados). In different static loading conditions (30 N - 90º, 100 N - 90º, 200 N - 30º) the microgap and abutment displacement was evaluated using synchrotron-based microtomography and phase-contrast radioscopy with numerical forward simulation of the optical Fresnel propagation yielding an accuracy down to 0.1 µm. RESULTS: Microgaps were present in all implant systems prior to loading (0.15-9 µm). Values increased with mounting force and angle up to 40.5 µm at an off axis loading of 100 N in a 90° angle. CONCLUSIONS: In contrast to the implant-abutment connection with a large cone angle (45°), the conical connections based on a friction fit (small cone angles with < 12°) demonstrated an abutment displacement which resulted in a deformation of the outer implant wall. The design of the implant-abutment connection seems to be crucial for the force distribution on the implant wall which might influence peri-implant bone stability.

Cross-sectional analysis comparing prefabricated titanium to individualized hybrid zirconia abutments for cemented zirconia based fixed dental prostheses: a critical concept assessment.

PURPOSE: Despite the differences in material properties and shapes among the different types of prefabricated titanium (pTiA) and individualized hybrid zirconia abutments (ihZiA), the biological and clinical relevance of materials and construction features remains vague. Yet, individualized ihZiA are increasingly implemented into daily routine aiming to satisfy rising expectations. The objective was to compare these two types of abutments in fixed dental prostheses (FDP). METHODS: This cross-sectional study examined 462 implants in 102 patients comparing pTiA (52 patients) to ihZiA (50 patients) for FDP. These different treatment regimens were evaluated in terms of peri-implant health, radiographic bone loss, and oral-health related quality of life (OH-QoL) with special consideration of abutment type and superstructure design. RESULTS: ihZiA showed significantly different design features than prefabricated pTiA, but the annual bone loss in both groups did not. Visible titanium in the esthetic zone negatively impacted OHIP 14 scores. The combination of an emergence angle (EA) of < 30° and a concave emergence profile (EP) as well as gingiva thickness (p = 0.002) at the time of the prosthetic restoration significantly improved the annual peri-implant bone loss, independently of the abutment type. CONCLUSION: ihZiA showed comparable results to pTiA. To optimize the long-term outcome, not just material alone but generating adequate soft tissue thickness, minimizing the EA, and applying a concave EP seem to be the most relevant factors. To improve OH-QoL, particular attention must be paid to the esthetic zone.

Influence of screw channel angulation on reverse torque value and fracture resistance in monolithic zirconia restorations after thermomechanical cycling: an in-vitro study.

BACKGROUND: While the concept of angled screw channels has gained popularity, there remains a scarcity of research concerning the torque loss and fracture strength of monolithic zirconia restorations with various screw channel angulations when exposed to thermomechanical cycling. This in-vitro study aimed to evaluate the reverse torque value and fracture resistance of one-piece screw-retained hybrid monolithic zirconia restorations with angulated screw channels after thermomechanical cycling. METHODS: One-piece monolithic zirconia restorations, with angulated screw channels set at 0°, 15°, and 25° (n = 6 per angulation) were fabricated and bonded to titanium inserts using a dual-cure adhesive resin cement. These assemblies were then screwed to implant fixtures embedded in acrylic resin using an omnigrip screwdriver, and reverse torque values were recorded before and after thermomechanical cycles. Additionally, fracture modes were assessed subsequent to the application of compressive load. One-way ANOVA and Bonferroni post hoc test were used to compare the groups (α = 0.05). RESULTS: The study groups were significantly different regarding the fracture resistance (P = 0.0015), but only insignificantly different in the mean percentage torque loss (P = 0.4400). Specifically, the fracture resistance of the 15° group was insignificantly higher compared to the 0° group (P = 0.9037), but significantly higher compared to the 25° group (P = 0.0051). Furthermore, the fracture resistance of the 0° group was significantly higher than that of the 25° group (P = 0.0114). CONCLUSIONS: One-piece hybrid monolithic zirconia restorations with angulated screw channels can be considered an acceptable choice for angulated implants in esthetic areas, providing satisfactory fracture strength and torque loss.

The Impact of Implant Abutment Angle and Height on Peri-implant Tissue Health: Retrospective Analyses from a Randomized Controlled Clinical Trial.

PURPOSE: To examine the influence of abutment emergence angle and abutment height on marginal peri-implant bone stability in patients not considered susceptible to peri-implantitis. Furthermore, it was analyzed whether titanium-base (Ti-base) abutments lead to wider abutment emergence angles compared to one-piece abutments. MATERIALS AND METHODS: A total of 48 abutments (ie, 24 Ti-base and 24 one-piece abutments in 24 patients) were evaluated at abutment installation, after 1 year, and thereafter on a yearly basis for up to 5 years. Clinical and radiographic outcome variables were assessed. RESULTS: With regard to peri-implant marginal bone stability, only moderately negative, albeit significant, correlations were found on the mesial sides of the one-piece abutments after 4 and 5 years for an abutment emergence angle > 30 degrees. No statistically significant negative correlations were found for distances of ≤ 1.5 mm between the restoration margin and the crestal peri-implant bone level for either Ti-base or for one-piece abutments. Furthermore, abutments bonded to Ti-bases were not associated with larger emergence angles than one-piece abutments. CONCLUSIONS: For patients at low risk of developing peri-implantitis, it can be concluded that neither a larger abutment emergence angle (> 30 degrees) nor a distance of ≤ 1.5 mm between the restoration margin and the crestal peri-implant bone level are associated with marginal peri-implant bone loss. Furthermore, abutments bonded to Ti-bases are not associated with wider emergence angles than one-piece abutments.

Evaluation with a Coordinate-Measuring Machine of Dimensional Accuracy of the Abutment Duplication Technique in Cement- Retained Implant Restoration.

PURPOSE: To evaluate the effectiveness and accuracy of a proposed duplication technique in terms of one- and three-dimensional discrepancies between an original abutment and polyurethane duplicates obtained through a conventional workflow in single-implant rehabilitation. MATERIALS AND METHODS: A titanium, shoulderless abutment was chosen for a single-implant cemented rehabilitation. The master cast was made using a plastic-based die system, and the implant portion was separated. The implant section was consecutively duplicated eight times using a manual technique with polyvinyl siloxane and unfilled polyurethane resin as impression and die materials. The duplicates were analyzed with a coordinate-measuring machine (SmartScope Flash 200, Optical Gaging Products): one- and three- dimensional discrepancies were determined for each duplicate on 20 analysis points (A to T) located on the abutment surface. Changes in the abutment radius were also calculated to estimate the effects on cement thicknesses. RESULTS: One-dimensional discrepancies were -0.5 Å} 61.2 µm, -6.6 Å} 39.7 µm, and -19.4 Å} 47.8 µm on the X, Y, and Z axes, respectively; three-dimensional variation was -66.4 Å} 60.1 µm. Friedman test showed no significant difference between duplicates' one-dimensional variations on X (P = .059), Y (P = .156), or Z (P = .223) axes; a significant difference was found regarding three-dimensional changes (P < .001). Dunn test showed higher discrepancies on the X axis and on the abutment head. Mean variation of the abutment radius was -12.09 µm. CONCLUSIONS: The abutment duplication technique was shown to be an accurate and repeatable procedure for single cementable restorations.

Frequency of Contamination on Used Healing Abutments after Sterilization: An In Vitro Study.

PURPOSE: To determine and compare the frequency of contamination on different sites of healing abutments (HAs) after sterilization with Phloxine B dye on unused and used HAs after sterilization. MATERIALS AND METHODS: A total of 60 HAs were divided into two test groups: (1) used and sterilized and (2) a control group (unused). The test group was evaluated for contamination after sterilization; the control group did not undergo any procedure. Data were analyzed using SPSS version 22 (IBM). Descriptive statistics were used to determine the frequency of contamination in the different groups and at the different HA sites. Chi-square test was used to evaluate the association of frequency of contamination with the HA site and design. The level of significance was kept at P ≤ .01. RESULTS: The test group showed more contamination compared to the control group. The most contaminated sites were the screw thread and the screwdriver engagement location. CONCLUSIONS: HA reuse is cost-effective, but cleaning and sterilization was not effective for these components; thus, HAs need to be reused with caution because they were heavily contaminated when compared to new HAs. Among the different sites, the screw thread and screwdriver engagement sites were more prone to contamination. HA type did not influence the frequency of contamination.

Anticorrosion and Antimicrobial Tannic Acid-Functionalized Ti-Metallic Glass Ribbons for Dental Abutment.

In this study, a recently reported Ti-based metallic glass (MG), without any toxic element, but with a significant amount of metalloid (Si-Ge-B, 18 atom %) and minor soft element (Sn, 2 atom %), was produced in ribbon form using conventional single-roller melt-spinning. The produced Ti60Zr20Si8Ge7B3Sn2 ribbons were investigated by differential scanning calorimetry and X-ray diffraction to confirm their amorphous structure, and their corrosion properties were further investigated by open-circuit potential and cyclic polarization tests. The ribbon's surface was functionalized by tannic acid, a natural plant-based polyphenol, to enhance its performance in terms of corrosion prevention and antimicrobial efficacy. These properties can potentially be exploited in the premucosal parts of dental implants (abutments). The Folin and Ciocalteu test was used for the quantification of tannic acid (TA) grafted on the ribbon surface and of its redox activity. Fluorescent microscopy and ζ-potential measurements were used to confirm the presence of TA on the surfaces of the ribbons. The cytocompatibility evaluation (indirect and direct) of TA-functionalized Ti60Zr20Si8Ge7B3Sn2 MG ribbons toward primary human gingival fibroblast demonstrated that no significant differences in cell viability were detected between the functionalized and as-produced (control) MG ribbons. Finally, the antibacterial investigation of TA-functionalized samples against Staphylococcus aureus demonstrated the specimens' antimicrobial properties, shown by scanning electron microscopy images after 24 h, presenting a few single colonies remaining on their surfaces. The thickness of bacterial aggregations (biofilm-like) that were formed on the surface of the as-produced samples reduced from 3.5 to 1.5 µm.

Removal of broken abutment screws using ultrasonic tip - a heat development in-vitro study.

BACKGROUND: Dental implants can cause complications, including the loosening of the abutment screw or fracture. However, there is no standardized technique for removing broken abutment screws. This necessitates further research. OBJECTIVE: This study aimed to measure heat generation during screw removal to better understand its implications for dental implant procedures. MATERIAL AND METHODS: The experimental setup involved using synthetic bone blocks and titanium implants. An ultrasonically operated instrument tip was utilized for screw removal. Infrared thermometry was employed for accurate temperature measurement, considering factors such as emissivity and distance. Statistical analysis using linear regression and ANOVA was conducted. RESULTS: The findings revealed an initial rapid temperature increase during the removal process, followed by a gradual decrease. The regression model demonstrated a strong correlation between time and temperature, indicating the heat generation pattern. CONCLUSION: Heat generation during screw removal poses risks such as tissue damage and integration issues. Clinicians should minimize heat risks through an intermittent approach. The lack of a standardized technique requires further research and caution. Understanding the generated heat optimizes implant procedures.

Repositioning accuracy of the implant- and abutment-level prosthetic components used in conventional and digital workflows.

OBJECTIVES: To evaluate the repositioning accuracy of the implant- and abutment-level impression components (impression abutments and implant scan bodies) and implant abutments (with and without anti-rotational hex index); also, to estimate the tightening torque influence on the positional stability of abutments. METHODS: Seven types of prosthetic components (n = 7) [impression pick-up copings (PC), implant scan bodies (ISB), non­hex and hex titanium base implant abutments (TB H and TB NH), multi-unit impression copings (MU PC), multi-unit implant scan bodies (MU ISB), and multi-unit caps (MU C) (Medentika GmbH)] were tested. For repositioning accuracy tests a coordinate measuring machine (CMM) was used. During assembly 15 Ncm torque for all components was applied. After measurement, only hex and non­hex abutments were torqued to 25 Ncm and their coordinates were again recorded to assess torque influence. The procedure was repeated 7 times for each component. Linear and 3D deviations, angulation to the vertical axis, and axial rotation were calculated. The Kruskal-Wallis test was used to compare the measurements between the groups. A post-hoc test (Mann-Whitney U test) was used for pairwise comparison to determine the influence of the torque (α=0.05). RESULTS: Implant- and abutment-level components used for digital scans showed different positional discrepancies compared to ones used for conventional impressions and ranged from 10 to 37 µm. Hex abutments demonstrated statistically significantly lower 3D deviations (4.4 ± 7.1 µm) compared to non­hex abutments (8.7 ± 6.1 µm). Torque influence was significantly lower for hex abutments than for non­hex abutments. CONCLUSIONS: Repositioning inaccuracies were found in all implant- and abutment-level impression components (impression abutments and implant scan bodies) and all abutments (with and without anti-rotational hex index) tested. Final tightening of the components could cause further positional discrepancies. CLINICAL SIGNIFICANCE: The misfit of the prosthetic components used in conventional and digital workflows stays in the clinically acceptable range. Even when multiple connections and disconnections on the track of the laboratory preparation is needed, it should not have a negative influence for single teeth reconstructions. However, in the complex cases with multiple implants, repetitive repositioning of the prosthetic components may lead to the accumulation of vertical, horizontal and rotational errors leading to the clinical problems with the passive fit of the final framework.

Structural and torque changes in implant components of different diameters subjected to mechanical fatigue.

OBJECTIVES: To evaluate torque maintenance and structural damage in implant components of different diameters subjected to a fatigue challenge. METHODS: Thirty 10-mm-long, morse taper connection, titanium dental implants and their corresponding one-piece abutments were divided into three groups (n = 10) according to implant diameter: 4.3 mm (I4.3), 3.5 mm (I3.5), and 2.9 mm (I2.9). The implants were placed into a load-bearing fixture simulating bone tissue (modified G10), and the abutments were screwed into the implants to a final torque of 20 Ncm for the I4.3 and I3.5 and 15 Ncm for I2.9. The torque was secured by a digital torque meter. Cone-beam computed tomography (CBCT) scans were acquired and post-processed (e-Vol DX software) for all implant/abutment sets before and after subjecting them to fatigue in 37 °C distilled water (2 million cycles, constant load and frequency). The removal torque was measured using the same digital torque meter to calculate the difference in torque before and after fatigue. RESULTS: I2.9 showed substantial structural deformation compared with the other implant diameters (I3.5 and I4.3). However, the experimental groups did not show statistical differences for abutment loosening. SIGNIFICANCE: Implants smaller than 3.5 mm in diameter have a higher probability of structural deformation than standard-diameter implants. The association between tomographic scans and e-Vol DX software showed satisfactory consistency with the direct assessment using the digital torque meter, offering an additional tool to evaluate implant component loosening and structural deformations.

Implant-supported single all-ceramic crowns made from prefabricated (stock) or individualized CAD/CAM zirconia abutments: A 5 year randomized clinical trial.

AIM: The aim of this randomized, prospective, and clinical multicenter study was to compare the overall clinical performance of two restorative options over a 5-year period: individualized CAD/CAM abutments veneered with a hand-layered ceramic, and prefabricated zirconium dioxide abutments veneered with press ceramic and inserted into a single edentulous gap in the anterior maxilla. MATERIALS AND METHODS: Forty subjects were recruited from two universities: 20 from the University of XX and 20 from the University of XY. Each subject received an implant to restore a single edentulous gap in the maxillary anterior region (14-24 FDI). 20 patients were randomized into each Group. Group A received a one-piece single crown produced from a prefabricated zirconia abutment with pressed ceramic and Group B received an individualized CAD/CAM zirconia abutment with a hand-layered technique. After 5 years, the aesthetic and radiographic parameters were assessed. RESULTS: Group A had four dropouts and one failure, resulting in a 95% survival rate and 95% success rate. Group B had two dropouts and two failures which resulted in a 90% survival rate and 90% success rate. No crestal bone level changes were observed, with a mean DIB of 0.06 mm in Group A and 0.09 mm in Group B. No statistically significant differences were present at baseline, 6 months, 1 year, 3 years, or 5 years for DIB values between time points and groups. Pink aesthetic score/white aesthetic score, Peri-Implant and Crown Index, and Implant Crown Aesthetic Index values were stable over time at all five points for both groups. CONCLUSION: Both implant-supported restorative options represent a valuable treatment option for the restoration of implant crowns in the anterior maxilla. CLINICAL SIGNIFICANCE: In general, the use of ceramic abutments in the anterior zone represents a valuable treatment procedure with both standardized and CAD/CAM individualized abutments and following the recommendations from the respective manufacturer(s).

Influence of sterilization on the retention forces of lithium disilicate and polymer-infiltrated ceramic-network crowns bonded to titanium base abutments: An in-vitro study.

OBJECTIVES: The aim of this study was to evaluate the effect of sterilization on the retention forces of lithium disilicate (LD) and polymer-infiltrated ceramic network (PICN) crowns bonded to titanium base (Ti-base) abutments. MATERIALS AND METHODS: Forty LD and 40 PICN crowns were milled and then bonded to 80 Ti-bases with two resin composite cements: Multilink Hybrid Abutment (mh) and Panavia V5 (pv) for a total of 8 groups (n = 10). Half of the specimens (test) underwent an autoclaving protocol (pressure 1.1 bar, 121°C, 20.5 min) and the other half not (control). Restorations were screw-retained to implants, and retention forces (N) were measured with a pull-off testing machine. The surfaces of the Ti-bases and the crowns were inspected for the analysis of the integrity of the marginal bonding interface and failure mode. Student's t-test, chi-square test, and univariate linear regression model were performed to analyze the data (α = 0.05). RESULTS: The mean pull-off retention forces ranged from 487.7 ± 73.4 N to 742.2 ± 150.3 N. Sterilized groups showed statistically significant overall higher maximum retention forces (p < .05), except for one combination (LD + mh). Sterilization led to an increased presence of marginal gaps and deformities compared to no-sterilization (p < .001), while no statistically significant relationship was found between failure mode and sterilization (p > .05). CONCLUSIONS: Sterilization may have a beneficial effect on the retention forces of LD and PICN crowns bonded to titanium base abutments, although it may negatively influence the integrity of the marginal bonding interface.

Clinical performance of implant-supported single hybrid abutment crown restoration: A systematic review and meta-analysis.

PURPOSE: To investigate survival rates and technical and biological complications of one-piece screw-retained hybrid abutments in implant-supported single crowns (SCs). STUDY SELECTION: An electronic search was performed on five databases for clinical studies involving implant-supported single hybrid abutment crowns constructed using titanium-base (Ti base) abutments, with at least 12 months of follow-up. The RoB 2, Robins-I, and JBI tools were used to assess the risk of bias for the different study types. Success, survival, and complication rates were calculated, and a meta-analysis was performed to obtain a pooled estimate. Peri-implant health parameters were extracted and analyzed. RESULTS: 22 records (20 studies) were included in this analysis. Direct comparisons between screw-retained hybrid abutment SCs and cemented SCs showed no significant differences in the 1-year survival and success rates. For SCs using a hybrid abutment crown design, their 1-year survival rate was 100% (95% CI: 100%-100%, I2 = 0.0%, P = 0.984), and a success rate of 99% (95% CI: 97%-100%, I2 = 50.3%, P = 0.023) was calculated. No confounding variables significantly affected the estimates. The individual technical complication rate was low at 1-year follow-up. The estimated incidence of all types of complications in hybrid abutment SCs is less than 1%. CONCLUSIONS: Within the limitations of this study, implant-supported SCs using a hybrid abutment crown design showed favorable short-term clinical outcomes. Additional well-designed clinical trials with at least a 5-year observation period are required to confirm their long-term clinical performance.

Effect of argon plasma abutment activation on soft tissue healing: RCT with histological assessment.

OBJECTIVE: To assess the peri-implant soft tissue profiles between argon plasma treatment (PT) and non-treated (NPT) healing abutments by comparing clinical and histological parameters 2 months following abutment placement. MATERIALS AND METHODS: Thirty participants were randomly assigned to argon-plasma treatment abutments group (PT) or non-treated abutments (NPT) group. Two months after healing abutment placement, soft peri-implant tissues and abutment were harvested, and histological and clinical parameters including plaque index, bleeding on probing, and keratinized mucosa diameter (KM) were assessed. Specialized stainings (hematoxylin-eosin and picrocirious red) coupled with immunohistochemistry (vimentin, collagen, and CK10) were performed to assess soft tissue inflammation and healing, and the collagen content keratinization. In addition to standard statistical methods, machine learning algorithms were applied for advanced soft tissue profiling between the test and control groups. RESULTS: PT group showed lower plaque accumulation and inflammation grade (6.71% vs. 13.25%, respectively; p-value 0.02), and more advanced connective tissue healing and integration compared to NPT (31.77% vs. 23.3%, respectively; p = 0.009). In the control group, more expressed keratinization was found compared to the PT group, showing significantly higher CK10 (>47.5%). No differences in KM were found between the groups. SIGNIFICANCE: PT seems to be a promising protocol for guided peri-implant soft tissue morphogenesis reducing plaque accumulation and inflammation, and stimulating collagen and soft tissue but without effects on epithelial tissues and keratinization.

Outcomes of resin-bonded attachments for removable dental prostheses.

PURPOSE: This clinical study aimed to evaluate the outcomes of resin-bonded attachments (RBAs) for precision-retained removable dental prostheses (RDPs) after at least two years of clinical maintenance. METHODS: Since December 1998, 205 RBAs (44 bonded to posterior teeth, 161 to anterior teeth) have been inserted in 123 patients (62 females and 61 males; mean age, 63.6 ± 9.6 years) who were recalled annually. The abutment teeth underwent a minimally invasive preparation limited to the enamel. RBAs were cast in a cobalt-chromium alloy with a minimum thickness of 0.5 mm and adhesively luted with a luting composite resin (Panavia 21 Ex or Panavia V5, Kuraray, Japan). We evaluated caries activity, plaque index, periodontal condition, and tooth vitality. The Kaplan-Meier survival curves were used to account for the reasons for failure. RESULTS: The mean observation time of RBAs until the last recall visit was 84.5 ± 51.3 months (range, 3.6-270.6). During the observation period, 33 RBAs debonded in 27 patients (16.1%). The 10-year success rate according to the Kaplan-Meier analysis was 58.4%, which dropped to 46.2% after 15 years of observation if debonding was considered a failure. If rebonded RBAs were regarded as surviving, the 10- and 15-year survival rates would be 68.3% and 61%, respectively. CONCLUSIONS: The use of RBAs for precision-retained RDPs appears to be a promising alternative to conventionally retained RDPs. As reported in the literature, the survival rate and frequency of complications were comparable with those of conventional crown-retained attachments for RDPs.

Effect of Thermomechanical Dynamic Loading on the Retention of Metallic and Nonmetallic Telescopic Mandibular Overdentures.

PURPOSE: To evaluate the effect of thermomechanical dynamic loading on the retention of telescopic mandibular overdentures with different metallic and nonmetallic material combinations. MATERIALS AND METHODS: Four groups were tested: (1) ZP (zirconia abutments/PEEK framework); (2) PP (PEEK abutments/PEEK framework); (3) TP (titanium abutments/PEEK framework); and (4) TG (titanium abutments/gold copings/cobalt-chromium framework). Each specimen contained four implants positioned over a polyvinylchloride-cylindrical base. After 10,000 removal/insertion cycles, the specimens were subjected to thermomechanical dynamic load in a chewing simulator for 1,200,000 loading cycles, corresponding to 5-year clinical fatigue. A screw was used to receive the chewing load, and 0.5 mm was permitted between the screw and the metal top fixed into the base to simulate the resilience of the posterior residual ridge tissues. Vertical chewing loads of 60 N were applied at a speed of 30 mm/second. Thermocycling was applied with a temperature ranging between 5°C and 55°C. The retentive force was measured using a universal testing machine 10 times before and after the thermomechanical dynamic loading test with a speed of 8 mm/second. RESULTS: The mean retentive force increased significantly from 13.2 (± 4.6) N to 16.4 (± 6.1) N in group ZP (P = .002), while in group TP, it decreased significantly from 4.9 (± 2.1) N to 3.3 (± 1.7) N (P = .046). There was no statistically significant change in the retentive force for groups PP and TG. CONCLUSIONS: The investigated metallic and nonmetallic combinations of double-crown-retained mandibular overdentures maintained acceptable levels of retention after thermomechanical dynamic loading. Further laboratory and clinical studies are needed before their routine clinical use can be recommended.