Comparison of the effect of ball and bar attachment designs on retention and stability of mandibular implant-supported overdentures

Objectives The present study evaluated the effect of bar and ball attachment designs on retention and stability of a mandibular overdenture supported by four implants.Methods An edentulous mandibular acrylic resin model with four implants in the anterior part of the ridge (A, B, D and E) was fabricated. A metal framework simulating the overdenture was also fabricated. Totally, 30 overdentures were divided into three groups based on the attachment design; BL: Four ball attachments in A, B, D and E positions; BB: One bar attachment between B and D positions and two ball attachments at positions A and E; BR: Bar attachments between the positions A, B, D and E with two posterior extensions. To evaluate the retention and stability of the overdenture, tensile dislodging forces were applied in three directions of vertical, oblique and anterior- posterior by a universal testing machine. One-way ANOVA and Tukey’s HSD test were performed to analyze the data. All tests were carried out at 0.05 level of significance.Results There were statistically significant differences between the groups in the peak load (P < 0.001). The peak load values for vertical, oblique and anterior-posterior dislodging forces were the highest for BL with 49.38 ± 2.19 N, 52.19 ± 1.44 N, and 49.03 ± 5.89 N, respectively, while these values were the lowest for BR with 29.78 ± 2.52 N, 12.10 ± 0.45 N, and 6.26 ± 0.45 N, respectively.Conclusion The attachment designs affected the retention and stability of mandibular implant-supported overdentures

The Prevalence of Temporomandibular Disorders in Patients Referred to the Prosthodontics Department of Shahid Beheshti Dental School in Fall 2010

Objective: Temporomandibular disorders (TMDs) are among the most common disorders of the maxillofacial region and are often characterized by pain and dysfunction of the temporomandibular joint(TMJ) and muscles of mastication. Due to the presence of several diagnostic criteria for such disorders, the reported prevalence rates for TMDs have been variable in different communities. The aim of this study was to determine the prevalence of TMDs in patients presenting to the Prosthodontics Department of Shahid Beheshti Dental School (SBDS) in fall 2010.Methods: In this descriptive study, 150 patients presenting to the Prosthodontics Department of SBDS (86 females and 64 males) were randomly selected and evaluated by using a questionnaire (subjectively) and clinical examinations (objectively). Presence and prevalence of various symptoms of TMDs such as clicking and tenderness on palpation in the muscles of mastication and the TMJ were evaluated in patients. Statistical comparisons were carried out using chi-square test.Results: Clicking, masticatory muscle and joint tenderness, TMDs, and limitation of mouth opening were found in 21.3%, 18.7%, 5.3%, 18.7% and 1.3% of patients, respectively. Despite the higher prevalence of TMDs in females, the difference in this regard between males and females was not statistically significant (39.3% in men versus 60.7% in women).Conclusion: Based on the obtained results, the prevalence of TMDs and its related symptoms was 18.7% in patients presenting to the Prosthodontics Department of SBDS in fall 2010. This value was lower than the rates reported in the literature

Influence of coping and veneer thickness on the color of zirconia-based restorations on different implant abutment backgrounds

Statement of problem: The effects of coping and veneer thickness on the color of zirconia-based restorations are unknown. Purpose: The purpose of this in vitro study was to evaluate the influence of coping and veneer thickness on the color of zirconia-based restorations on different implant abutment backgrounds and to define minimum coping and veneer thicknesses for the backgrounds investigated to achieve a target color. Material and methods: Thirty zirconia disk specimens with thicknesses of 0.4, 0.6, and 0.8 mm and 30 veneering ceramic disk specimens with thicknesses of 0.8, 1.0, and 1.2 mm were fabricated. Three backgrounds were prepared: titanium alloy, zirconia ceramic, and base metal alloy. The zirconia specimens were placed on the backgrounds, and the veneering ceramic specimens were located on the zirconia specimens. Spectrophotometric measurements were made to determine CIELab values. Color difference (ΔE) values were calculated to measure color differences between the specimens and the A2 VITA classical shade tab. ΔE values were compared with a perceptibility threshold (ΔE=2.6). Repeated measures ANOVA, Bonferroni test, and 1-sample t test were used to analyze data (α=.05). Results: Mean ΔE values ranged from 2.0 to 9.8. Coping thickness, veneer thickness, and their combination significantly affected ΔE (P<.001). Conclusions: To achieve the target color with zirconia-based restorations, regardless of the backgrounds tested, the minimum thickness of zirconia coping should be 0.6 mm, and the minimum thickness of veneering ceramic should be 1.2 mm

Effect of Three Different Core Materials on Masking Ability of a Zirconia Ceramic

Objectives: Masking ability of a restorative material plays a role in hiding colored substructures; however, the masking ability of zirconia ceramic (ZRC) has not yet been clearly understood in zirconia-based restorations. This study evaluated the effect of three different core materials on masking ability of a ZRC. Materials and Methods: Ten zirconia disc samples, 0.5mm in thickness and 10mm in diameter, were fabricated. A white (W) substrate (control) and three substrates of nickel-chromium alloy (NCA), non-precious gold alloy (NPGA), and ZRC were prepared. The zirconia discs were placed on the four types of substrates for spectrophotometry. The L*, a*, and b* values of the specimens were measured by a spectrophotometer and color change (ΔE) values were calculated to determine color differences between the test and control groups and were then compared with the perceptual threshold. Randomized block ANOVA and Bonferroni test analyzed the data. A significance level of 0.05 was considered. Results: The mean and standard deviation values of ΔE for NCA, NPGA, and ZRC groups were 10.26±2.43, 9.45±1.74, and 6.70±1.91 units, respectively. Significant differences were found in the ΔE values between ZRC and the other two experimental groups (NCA and NPGA; P<0.0001 and P=0.001, respectively). The ΔE values for the groups were more than the predetermined perceptual threshold. Conclusions: Within the limitations of this study, it was concluded that the tested ZRC could not well mask the examined core materials.

Masking ability of a zirconia ceramic on composite resin substrate shades

Background: Masking ability of a restorative material plays an important role to cover discolored tooth structure; however, this ability has not yet been well understood in zirconia-based restorations. This study assessed the masking ability of a zirconia ceramic on composite resin substrates with different shades. Materials and Methods: Ten zirconia disc specimens, with 0.5 mm thickness and 10 mm diameter, were fabricated by a computer-aided design/computer-aided manufacturing system. A white substrate (control) and six composite resin substrates with different shades including A1, A2, A3, B2, C2, and D3 were prepared. The substrates had a cylindrical shape with 10 mm diameter and height. The specimens were placed onto the substrates for spectrophotometric evaluation. A spectrophotometer measured the L*, a*, and b* values for the specimens. ΔE values were calculated to determine the color differences between the groups and the control and then were compared with a perceptional threshold (ΔE = 2.6). Repeated measures ANOVA and Bonferroni tests were used for data analysis (P < 0.05). Results: The mean and standard deviation of ΔE values for A1, A2, A3, B2, C2, and D3 groups were 6.78 ± 1.59, 8.13 ± 1.66, 9.81 ± 2.64, 9.61 ± 1.38, 9.59 ± 2.63, and 8.13 ± 1.89, respectively. A significant difference was found among the groups in the ΔE values (P = 0.006). The ΔE values were more than the perceptional threshold in all the groups (P < 0.0001). Conclusion: Within the limitations of this study, it can be concluded that the tested zirconia ceramic could not thoroughly mask different shades of the composite resin substrates. Moreover, color masking of zirconia depends on the shade of substrate

Dipping Impact on the Bond Strength between Zirconia Ceramic and a Resin Cement

Introduction: Dipping technique is commonly used by dental technicians to color zirconia ceramics; however, its impact on the bond between zirconia and resin cements is unclear. This in vitro study aimed to evaluate the microtensile bond strength (µTBS) between a zirconia ceramic and Panavia F2.0 resin cement after dipping in coloring liquids with different shades.Materials and Methods: Twenty zirconia blocks were dipped in four different shades of coloring liquids including A3, B2, C1, and D4, while five blocks were not colored for the control. All zirconia blocks were cemented to corresponding composite blocks using Panavia F2.0 resin cement. Zirconia-cement-composite blocks were cut into one hundred microbar specimens (1×1×10 mm). The specimens were divided into five studied groups according to their shade (A3, B2, C1, D4, control) and were subjected to an aging process. A microtensile tester applied tensile forces to the specimens, till the fracture occurred, and measured the µTBS values. One-way ANOVA and Tukey’s Post Hoc were used to analyze the data (P&lt;0.05). Optical microscopy and scanning electron microscopy were employed to evaluate failure modes and surface structure. Results: The µTBS values for the groups showed significant differences (P&lt;0.0001). D4 had the highest, and B2 had the lowest µTBS values. C1 (P=0.69) and A3 (P=0.89) showed no significant differences in the µTBS values compared with the control. Failure modes evaluation represented the lowest rate of adhesive failure for D4 (10%), and the highest in this respect for B2 (80%).Conclusion: Depending on the shade of coloring liquids, dipping had positive, negative, or no effects on the µTBS of zirconia ceramic to Panavia F2.0 resin cement

The effect of inter-implant distance on retention and resistance to dislodging forces for mandibular implant-tissue-supported overdentures.

The effect of inter-implant distance on retention and resistance of implant-tissue-supported overdentures is lacking in the literature. An in vitro study was performed to evaluate this effect for mandibular implant-tissue-supported overdentures retained by two ball attachments.An acrylic cast of an edentulous mandible was fabricated. Three pairs of implants were symmetrically placed at both sides of the midline. The inter-implant distance was 10, 25, and 35 millimeters in positions A, B and C, respectively. A framework simulating the overdenture was fabricated on the cast. Six attachment housings were placed within the overdenture. For each sample, two ball abutments were screwed onto the implant pairs and two pink nylon inserts were seated in their respective attachment housings. The samples were tested in three groups of 15 (A, B, and C). The testing machine applied tensile dislodging forces and peak loads were measured in three directions: vertical, oblique, and anterior-posterior. A one-way ANOVA followed by Tukey's HSD was used to determine groups that were significantly different. Tests were carried out at 0.05 level of significance.Peak loads for the anterior-posteriorly directed dislodging forces were significantly the highest for group C (P0.05).Inter-implant distance did not affect the vertical retention and oblique resistance of mandibular implant-tissue-supported overdentures; however, it affected anterior-posterior resistance

Effect of screw access hole preparation on fracture load of implant-supported zirconia-based crowns: an in vitro study

Background. Fracture load of implant-supported restorations is an important factor in clinical success. This study evaluated the effect of two techniques for screw access hole preparation on the fracture load of cement-screw-retained implant-supported zirconia-based crowns. Methods. Thirty similar cement-screw-retained implant-supported zirconia-based maxillary central incisor crowns were evaluated in three groups of 10. Group NH: with no screw access holes for the control; Group HBS: with screw access holes prepared with a machine before zirconia sintering; Group HAS: with screw access holes prepared manually after zirconia sintering. In group HBS, the access holes were virtually designed and prepared by a computer-assisted design/computer-assisted manufacturing system. In group HAS, the access holes were manually prepared after zirconia sintering using a diamond bur. The dimensions of the screw access holes were equal in both groups. The crowns were cemented onto same-size abutments and were then subjected to thermocycling. The fracture load values of the crowns were measured using a universal testing machine. Data were analyzed with ANOVA and Tukey test (P < 0.05). Results. The mean fracture load value for the group NH was 888.37 ± 228.92 N, which was the highest among the groups, with a significant difference (P < 0.0001). The fracture load values were 610.48 ± 125.02 N and 496.74 ± 104.10 Nin the HBS and HAS groups, respectively, with no significant differences (P = 0.44). Conclusion. Both techniques used for preparation of screw access holes in implant-supported zirconia-based crowns de-creased the fracture load

Effect of Coloring–by-Dipping on Microtensile Bond Strength of Zirconia to Resin Cement

Objectives: Studies on the effect of coloring procedures on the bond strength of zirconia to resin cement are lacking in the literature. This study evaluated the effect of dipping of zirconia ceramic in different liquid color shades on the microtensile bond strength (MTBS) of zirconia ceramic to resin cement. Materials and Methods: This in vitro study was conducted on 100 microbar specimens divided into five groups of B2, C1, D4, A3 and control (not colored). To prepare the microbars, 20 white zirconia ceramic blocks, measuring 5×11×11 mm, were dipped in A3, B2, C1 or D4 liquid color shades for 10 seconds (five blocks for each color shade) and five blocks were not colored as controls. All the zirconia blocks were sintered in a sintering furnace. Composite blocks of similar dimensions were fabricated and bonded to zirconia ceramic blocks using Panavia F 2.0 resin cement. Zirconia-cement-composite blocks were sectioned into microbars measuring 1×1×10 mm. The MTBS of microbars was measured by a testing machine. Data were analyzed using one-way ANOVA and Tukey’s test. All tests were carried out at 0.05 level of significance. Results: Statistically significant differences were found among the groups in MTBS (P<0.001). The D4 group had the highest MTBS value (39.16 ± 6.52 MPa). Conclusion: Dipping affected the MTBS of zirconia ceramic to Panavia F 2.0 resin cement; however, a similar pattern of change was not seen due to the different liquid color shades

Prosthetic Reconstruction for a Child with a Congenital Bilateral Ear Deformity: Case Report

Objectives: Microtia is the most commonly seen congenital ear defect, and involves an auricular deformity either unilaterally or bilaterally. The aim of this study was to fabricate silicone prostheses for a child with bilateral microtia using an innovative technique. Methods: This method involved the construction of bilateral ear prostheses using clips, which were located within the layers of the silicone superstructure.&nbsp; Results: Surgical reconstruction was not indicated due to the patient&rsquo;s age; so prosthetic reconstruction was advised in this case. Discussion: Two prosthetic ears were manufactured, with one being attached using an adhesive method and the other by a self suspension method. The child and his parents were very satisfied by the cosmetic and aesthetic appearance of the prostheses fitted. This technique has been proven to be suitable for pediatric patients with microtia