Journal of Prosthodontics

Introduction : Overdentures supported and retained by endosteal implants depend upon mechanical components to provide retention. Ball attachments are frequently described because of simplicity and low cost, but retentive capacity of these components may be altered by a lack of implant parallelism.

Purpose : The aim of this in vitro study was to investigate the retention of gold and titanium overdenture attachments when placed on ball abutments positioned off‐axis.

Methods and Materials : Four ball abutments were hand‐tightened onto ITI dental implants and placed in an aluminum fixture that allowed positioning of the implants at 0°, 10°, 20°, and 30° from a vertical reference axis. Gold and titanium matrices were then coupled to the ball abutments at various angles and then subjected to pull tests at a rate of 2 mm/second; the peak loads of release (maximum dislodging forces) were recorded and subjected to statistical analyses. A balanced and randomized factorial experimental design testing procedure was implemented.

Results : Statistically significant differences in retention of gold matrices were noted when ball abutments were positioned at 20° and 30°, but not at 0° and 10°. Statistically significant differences were noted among the titanium matrices employed for the testing procedure, as well as for the 4 ball abutments tested. Angle was not a factor affecting retention for titanium matrices.

Conclusions : (1) The gold matrices employed for the testing procedures exhibited consistent values in retention compared to titanium matrices, which exhibited large variability in retention. (2) Angle had an effect upon the retention of gold matrices, but not for titanium matrices.

Purpose: The aim of this study was to examine early changes in retentive values of implant overdenture attachments during multiple pulls.

Materials and Methods: Two implant attachment systems (Hader bar and clip, Locator system) were used in this study. The experimental groups were divided into yellow Hader clips, white Locator attachments, and green Locator attachments. Each group consisted of 21 matrix attachments. The attachments were placed into a custom‐made acrylic resin block seated passively on another acrylic block containing a Hader bar or two Locator abutments with different angulations. Each attachment was subjected to 20 consecutive pulls using a universal testing machine. The peak load‐to‐dislodgement of the attachments after each pull was documented, and the percent reduction of the peak load‐to‐dislodgement was calculated. One‐way ANOVA and Tukey's honestly significant difference test were used for data analyses. A p≤ 0.05 was considered significant.

Results: There was a significant difference in the percent reduction in peak load‐to‐dislodgement between the attachments after the first pull (p= 0.005) and after the final pull (p= 0.0001). The yellow Hader clips exhibited the least percent reduction in peak load‐to‐dislodgement (6.50 ± 3.59%) after the first pull, followed by the white Locator attachments (8.60 ± 4.42%); the green Locator attachments exhibited the greatest reduction (11.05 ± 4.94%).

Conclusion: The results of this in vitro study demonstrate that retentive values of the Locator attachments are reduced significantly after multiple pulls. Although this reduction might not be noticeable to the patient, it is recommended that the clinician place and remove the overdenture multiple times before delivery.

Purpose: To evaluate the changes in retention of pink Locator attachments after exposure to various denture cleansers.

Materials and Methods: Six groups (20 pairs each) of pink Locator attachments (3.0 lb. Light Retention replacement patrix attachments) were soaked for the equivalent of 6 months of clinical use in the following solutions: Water (control), Polident Regular, Efferdent, 6.15% sodium hypochlorite (NaOCL, 1:10 dilution), Polident Overnight, and Cool Mint Listerine mouthwash. A universal testing machine set at a crosshead speed of 2 in/min was used to perform one pull. The peak load‐to‐dislodgement was recorded to reflect changes in the retention of the Locator attachments after soaking. Data were analyzed by one‐way ANOVA followed by Tukey's Honestly Significant Difference test. A p≤ 0.05 was considered significant.

Results: Denture cleansing solutions significantly affected the retentive values of pink Locator attachments (F = 344.3, p≤ 0.0001). Cool Mint Listerine mouthwash increased the retentive values of the attachments (51.10 ± 5.31 N) when compared to the control group (45.25 ± 3.49 N). There was no significant difference in the retentive values of attachments soaked in Polident Regular or Polident Overnight when compared to the control group. Efferdent caused a small reduction in the retentive values (40.81 ± 2.56 N) and most importantly, diluted NaOCl caused a large reduction in the retentive values (7.83 ± 2.50 N) of pink Locator attachments. In addition, Cool Mint Listerine mouthwash caused blue discoloration of the Locator attachments, and NaOCl caused whitening and softening of the pink Locator attachments.

Conclusion: Cool Mint Listerine and Efferdent's small effect on the retentive values of the Locators might be clinically unimportant; however, NaOCl caused a large reduction in the retentive values of the attachments. Because of their effect on retentive values and on the color of the Locator attachments, NaOCl and Cool Mint Listerine are not recommended. These results should be interpreted clinically with caution, realizing that different results may be obtained when fatigue stress during function and multiple pulls (in vivo) are combined with the chemical action of denture cleansers.

Purpose: To evaluate the retention of yellow Hader clips after exposure to various denture cleansers.

Methods: Seven groups of 18 yellow Hader clips each were soaked for the equivalent of 6 months of clinical use in the following denture cleansing solutions: Polident Regular, Polident Overnight, Efferdent, 5.25% Sodium Hypochlorite (NaOCl, 1:10 dilution) 15 min/day, NaOCl (1:10 dilution) 8 hours/day, water and dry (control) group. A Universal Testing Machine, set at a crosshead speed of 2 in/min, pulled each clip once, and the peak load‐to‐dislodgement was recorded and used as a measure to reflect changes in the retention of the Hader clips. Data were analyzed by a one‐way analysis of variance followed by Tukey's HSD test. A p value ≤ 0.05 was considered significant.

Results: Denture cleansing solutions affected the retentive values of yellow Hader clips (F= 6.102, p≤ .0001). Sodium hypochlorite solution, 15 min/day for 6 months, caused an increase in the retentive values of the clips tested with a mean peak load‐to‐dislodgement of 22.63 ± 1.29 N. In addition, clips soaked in water showed no difference in retentive values when compared with all other groups. Furthermore, Polident Regular, Polident Overnight, Efferdent, and NaOCl (8 hours/day) had no effect on the retentive values of yellow Hader clips.

Conclusion: This in vitro study demonstrated that the retention of yellow Hader clips used in implant overdentures is unaffected when soaked in commercial effervescent denture cleansers (Polident 5 Minute, Polident Overnight, and Efferdent) for six simulated months. Sodium hypochlorite statistically increased the single‐pull retentive values of the clips, an effect that may not be beneficial. Increased retentive values may be associated with reduced durability of clips; further research is needed to address this issue.

Purpose: The introduction of yttrium partially stabilized zirconia polycrystals (Y‐TZP) has pushed the application limits of all‐ceramic restorations. The mechanical properties of these materials can be further improved by the addition of a secondary dopant phase. The aim of this work was to evaluate the properties of a new nano‐composite ceramic used as a dental framework material.

Materials and Methods: The properties of a new ceria‐stabilized tetragonal zirconia polycrystal co‐doped with alumina (Ce‐TZP‐Al) were investigated. Y‐TZP was used as control. Sixty bars (20 × 2.5 × 1.5 mm³) from each material were prepared by cutting CAD/CAM milling blocks. Twenty specimens were used to measure the 4‐point flexural strength and the modulus of elasticity of the tested materials. The remaining specimens were used to measure the fracture toughness using indentation strength (IS), single edge notched beam (SENB), and fractography (FR). The thermal expansion coefficient (TEC) was measured using temperature expansion diagrams. The bond strength of the two framework materials to two esthetic veneer ceramics was tested using the microtensile bond strength test (MTBS). Finally, scanning electron microscopy (SEM) and energy dispersive X‐ray microanalysis (EDX) were used to analyze the internal structure of the materials. One‐ and two‐way analysis of variance (ANOVA) and Bonferroni post hoc tests were used to analyze the data (α= 0.5).

Results: The flexural strength and modulus of elasticity of Ce‐TZP‐Al (856 MPa, 170 GPa) were significantly weaker (p < 0.001) than those of Y‐TZP (1003 MPa, 215 GPa). The (IS) fracture toughness of the former (19.02 MPa m^1/2) was significantly higher (p < 0.001) than SENB (12.6 MPa m^1/2) or FR (12.8 MPa m^1/2) values. These values were significantly higher (p < 0.001) than the fracture toughness of Y‐TZP (7.4 MPa m^1/2), which showed statistically similar values using the same three techniques. The measured TEC for the two materials was relatively similar, 10.1 μm/°C and 10.4 μm/°C, respectively. Regarding MTBS values, Ce‐TZP‐Al had significantly lower bond strength values (p < 0.001) and a higher percentage of interfacial failure than Y‐TZP, which failed completely cohesively with the two used veneer ceramics. SEM analysis revealed zirconia grains pull out and structural defects at the core–veneer interface for Ce‐TZP‐Al material, which explained its weak bond to the two used veneers.

Conclusion: Despite the promising mechanical properties of Ce‐TZP‐Al nano‐composite ceramic, its very low bond strength to esthetic veneers leaves such layered restorations highly susceptible to delamination and chipping under function. Further studies are needed to enhance the surface stability of this high fracture toughness ceramic.

Purpose : The purpose of this study was to compare the dentin/adhesive interfacial characteristics when bonding to noncarious as well as caries‐affected dentin.

Materials and Methods : Seven extracted, unerupted, third molars were sectioned into halves. Artificial caries was created on one‐half of each tooth, leaving the other half as a control. Dentin surfaces were treated with UNO adhesive according to the manufacturer's instructions for the wet‐bonding technique and under environmental conditions present in the oral cavity. Dentin/adhesive interface sections of each half‐tooth were stained with Goldner's trichrome, a classic bone stain, and examined using light microscopy. The width of exposed collagen was measured directly from photomicrographs, and adhesive penetration was analyzed qualitatively.

Results: The degree and extent to which the adhesive encapsulated the demineralized dentin matrix were reflected in the color difference in the stained sections with the noncarious dentin sections showing a degree of collagen encapsulation superior to that of the caries‐affected dentin sections. The overall mean widths of exposed collagen were significantly (p≤ .05) greater at the caries‐affected dentin/adhesive interface, 8.6 (1.7) μm, as compared with those at the noncarious dentin/adhesive interface, 6.0 (1.5) μm.

Conclusions: The morphologic characteristics of the caries‐affected dentin/interface suggest an increase in the exposed collagen zone and a decrease in the quality of the adhesive infiltration when compared with noncarious dentin. The evidence suggests that dentin substrate characteristics have a significant effect on the dentin/adhesive interface structure.