A randomized clinical trial comparing the clinical fit and chairside adjustment time for implant-supported crowns fabricated by fully digital and partially digital techniques.

STATEMENT OF PROBLEM: Implant-supported crowns made in both fully and partially digital workflows have been evaluated, but these studies have been mainly performed in vitro. Moreover, data on the comparison of clinical fitting and adjustment time for implant-supported crowns are limited. PURPOSE: The purpose of this randomized clinical trial was to evaluate the clinical fit and adjustment time for implant-supported crowns produced by a partially and fully digital workflow in partially edentulous participants. MATERIAL AND METHODS: Twenty-eight participants who had received 2 adjacent implants in posterior sites were enrolled, each receiving 2 custom titanium abutments and a splinted monolithic zirconia restoration. Restorations of the control group (n=14) were produced from a digital scan and a cast-free digital workflow, while the restorations of the test group (n=14) were from a conventional impression and a partially digital workflow. A blinded investigator delivered the restorations. The clinical adjustment was performed incrementally, and a digital chronometer recorded the time required for the evaluation and adjustment at each step. An independent t test, Mann-Whitney U test, and the Fisher exact test were used to evaluate the results (α=.05). RESULTS: The total mean adjustment time in the control group (12.49 minutes) was significantly longer than that of the test group (11.27 minutes) (P<.001). For the occlusal contact points, significantly less clinical adjustment time was required with the cast-free digital workflow (5.31 minutes) than with the model-based partially digital workflow (6.06 minutes) (P=.001). On other surfaces, no significant difference was found between the 2 groups (P>.05). All crowns could be successfully delivered after 2 clinical appointments (impression and delivery). Remakes were not necessary for any restorations in the test or control group. CONCLUSIONS: The parameters of occlusal adjustment time and total adjustment time of the fully digital workflow were significantly shorter than those of the partially digital workflow.

Comparison of Tensile Bond Strength of Soft Liners to an Acrylic Resin Denture Base with Various Curing Methods and Surface Treatments.

PURPOSE: To compare the bond strengths of three types of permanent silicone and acrylic resin soft liners to the denture-base acrylic resin by employing both synchronous and asynchronous processing methods and different surface treatments. MATERIALS AND METHODS: A total of 198 cylindrical samples were fabricated from denture-base acrylic resin and a 3-mm soft liner. Surface treatments of the samples were classified into five groups (n = 33 each): no treatment (control); erbium:yttrium-aluminum-garnet (Er:YAG) laser; grit-blasting with 150-µm particles; monomer application; and phosphoric acid application. In addition, synchronous processing (n = 33) of the acrylic resin denture base and the soft liner was performed. Each group was divided into three subgroups (n = 11 each) based on the type of soft liner: Group M (Molloplast-B [silicone]), Group P (PermaFlex [silicone]), and Group A (AcroSoft [acrylic resin]). The samples were processed and thermocycled for 5,000 cycles between 5°C and 55°C, and the tensile strength test was then performed. The maximum tensile strength to failure and the type of failure were recorded, and Dunn statistical analysis and Kruskal-Wallis tests were used for comparison of the groups. The surface treatments were assessed using scanning electron microscopy. RESULTS: Irrespective of the method of processing or surface treatment, Group A had a significantly higher bond strength (8.1 ± 1.1 MPa) than the other two soft liners (Group M: 1.9 ± 0.3 MPa, Group P: 1.1 ± 0.2 MPa; P < .001). Moreover, in Group A, the synchronous processing method produced a significantly higher tensile strength (P < .001), while in Group P (P = .112) and Group M (P = .993), synchronous processing had no significant effect on bond strength. Bond strength after surface treatment in Group M was lowest after grit blasting (0.7 ± 0.2 MPa) and highest after monomer application (3.1 ± 0.5 MPa) (P < .001). The same was observed for Group P in grit blasting (0.5 ± 0.2 MPa) and monomer application (2.1 ± 0.3 MPa) (P < .001). For Group A, grit blasting (4.8 ± 0.7 MPa) was also the lowest and the monomer application (8.1 ± 0.8 MPa) the highest ± (P < .001), while the bond strength resulting from the synchronous processing method was higher than that of the other methods (14.7 ± 2.1 MPa). CONCLUSION: Within the limitations of this in vitro study, the acrylic resin soft liner showed the best bond strength. In all types of soft liners, surface treatment with the monomer resulted in higher bond strengths. Synchronous processing exhibited a significantly higher bond strength for the acrylic resin soft liner, but not for the silicone soft liners.

Post-insertion Posterior Single-implant Occlusion Changes at Different Intervals: A T-Scan Computerized Occlusal Analysis.

AIM: The aim of this prospective cohort study was to evaluate the postinsertion posterior single-implant occlusion changes at 3- and 6-month intervals using T-Scan computerized occlusal analysis. MATERIALS AND METHODS: A total of 21 patients received single implant, opposed by natural dentition, in posterior regions of the maxilla or mandible (13 premolar, 8 molar) and were finally restored with cemented-retained metal-ceramic crowns. The occlusal contacts were equilibrated according to the implant-protective occlusion concept to develop light contact with heavy occlusion and no contact with light occlusion in maximum inter-cuspation. The percentage of force applied to the implant crowns (POFI) and contralateral teeth (POFT) was evaluated using T-Scan computerized occlusal analysis at prosthesis insertion, 3- and 6-month follow-up appointments. The data were statistically analyzed using Friedman test and Wilcoxon post hoc test (α = 0.05). RESULTS: The POFI values at the 6- and 3-month follow-up appointments were significantly higher than those at prostheses insertion (p = 0.001 and p = 0.005 respectively). In addition, there were significant differences between the POFI at 3- and 6-month follow-up (p = 0.020). However, the POFT values at 3- and 6-month follow-up appointments were significantly lower than those at baseline (p < 0.001). CONCLUSION: The intensity of occlusal contacts of implant-supported prostheses opposed by natural dentition gradually increased after prosthesis insertion. Placement of single posterior implant-supported restoration decreased the percentage of occlusal force applied to contralateral arch. CLINICAL SIGNIFICANCE: A periodic occlusal adjustment of implant-supported prostheses is necessary to prevent potential overloading from the movement of opposing natural dentition.

Effect of technique and impression material on the vertical misfit of a screw-retained, three-unit implant bridge: An in vitro study.

INTRODUCTION: A dental impression is a negative imprint of an oral structure that can be used to produce a positive cast of a patient's teeth as a permanent record. The accuracy of the impression affects the accuracy of the cast, and a precise impression is needed in order to create prosthesis with optimal fitting. Minimization of misfit is an important aim in prosthesis science and dental implants. The aim of this study was to evaluate the effects of the materials and techniques used to take an impression on the vertical misfit of implant-supported, screw-retained, three-unit bridges. MATERIALS AND METHODS: The principal model used was an acrylic block with two ITI implants. A 1.5-mm abutment was attached to fixtures with torque of 25 N.cm. A base-metal framework was built on the abutment in the acrylic block. The abutments of the acrylic model were unscrewed and fixture-level impressions were made. The impression techniques included open/closed-tray techniques and the impression materials were polyether and polyvinyl siloxane. Forty acrylic custom trays were built for each impression. The marginal gap in the framework at three points (buccal, lingual, and distal) was measured using an optical microscope with ×250. RESULTS: It is demonstrated that in all 360 evaluated samples, the mean vertical misfit in polyether samples of molar and premolar teeth was significantly lower than in polyvinyl siloxane (P < 0.001 and P = 0.017, respectively) in all three locations of the molar and lingual premolar examined (buccal, lingual, and distal), the mean vertical misfit of the polyether samples was significantly lower than those of polyvinyl siloxane (P < 0.01). On the other hand, although the mean vertical misfit using the open-tray technique in the molar teeth was significantly lower than with the closed-tray method (P = 0.002), no statistical difference was seen between the open-tray and closed-tray technique in general (P = 0.87). CONCLUSION: Within the limitations of this study, the following conclusions can be drawn: The impression method had no effect on marginal discrepancy of 3-unit screw retained fixed partial dentures. A higher marginal accuracy was obtained using polyether impression material compared to polyvinyl siloxane.

Three-dimensional accuracy of different impression techniques for dental implants.

BACKGROUND: Accurate impression making is an essential prerequisite for achieving a passive fit between the implant and the superstructure. The aim of this in vitro study was to compare the three-dimensional accuracy of open-tray and three closed-tray impression techniques. MATERIALS AND METHODS: Three acrylic resin mandibular master models with four parallel implants were used: Biohorizons (BIO), Straumann tissue-level (STL), and Straumann bone-level (SBL). Forty-two putty/wash polyvinyl siloxane impressions of the models were made using open-tray and closed-tray techniques. Closed-tray impressions were made using snap-on (STL model), transfer coping (TC) (BIO model) and TC plus plastic cap (TC-Cap) (SBL model). The impressions were poured with type IV stone, and the positional accuracy of the implant analog heads in each dimension (x, y and z axes), and the linear displacement (ΔR) were evaluated using a coordinate measuring machine. Data were analyzed using ANOVA and post-hoc Tukey tests (α = 0.05). RESULTS: The ΔR values of the snap-on technique were significantly lower than those of TC and TC-Cap techniques (P < 0.001). No significant differences were found between closed and open impression techniques for STL in Δx, Δy, Δz and ΔR values (P = 0.444, P = 0.181, P = 0.835 and P = 0.911, respectively). CONCLUSION: Considering the limitations of this study, the snap-on implant-level impression technique resulted in more three-dimensional accuracy than TC and TC-Cap, but it was similar to the open-tray technique.

Effect of denture cleansers on color stability and surface roughness of denture base acrylic resin.

BACKGROUND: Color stability of acrylic resin is one of the most important feature for denture wearers. Many patients use detergent solutions to remove denture stains. The purpose of this study was to evaluate color stability and surface roughness of two common acrylic resins in different detergent and tea solutions. MATERIALS AND METHODS: 112 acrylic resin blocks of Meliodent and Acropars (each 56 blocks) were divided into seven groups of different treatment: 1% sodium hypochlorite for 10 min a day for 1 month (H10m), 1% sodium hypochlorite for 8 hours a day for 1 week (H&h), Correga tabs solution for 8 hours a day for 1 month (C&H), tea bag for 2 hours a day for 1 month (T2 h), tea bag for 2 hours a day then 10 min in 1% sodium hypochlorite for 1 month (T-H), tea bag for 2 hours then 8 hours in the Correga tab solution a day for 1 month (T-C), and finally distilled water for 1 month as a control group (con). After specimen's treatment, color (CIE Lab) and surface roughness (Ra, µm) of samples were measured. The results were analyzed by analysis of variance (ANOVA), followed by Tukey's HSD and Dunnett T3. RESULTS: Group T2h exhibited a significant (P<;0.05) color change and control specimens exhibited the lowest color change. Sodium hypochlorite caused a significant (P<0.05) color change in the Acropars group in comparison with the Meliodent group. In the Correga tab solution the difference was not significant (P=0.155). There was a significant (P<0.05) color change in the T-H treatment. The Acropars and Meliodent acrylic resin did not a show significant difference in surface roughness after different treatments. CONCLUSION: Sodium hypochlorite 1% for 10 minutes a day in a month is the recommended hygiene protocol. The color stability of acryl is brand-type dependent but surface roughness is not.

The microbiology of the peri-implant sulcus following successful implantation of oral prosthetic treatments.

BACKGROUND: Oral implants are widely used in partially and fully edentulous patients; however, the integration of an implant can be endangered by factors such as intraoral bacteria or inflammatory reactions. The purpose of this study was to evaluate the microbial flora present in the sulcus around dental implants and to assess the relationship between gingival health and microbial flora present. MATERIALS AND METHODS: Twenty patients who had received oral implants with no complications were followed for a period of 9 months. Assessment of probing depth, the presence of bleeding on probing and microbial sampling from the peri-implant sulcus were performed at three different time points- 4 weeks after surgery, 1 month and 6 months after loading. The samples were taken by paper points and transferred to the microbiology lab in thioglyocolate cultures. In order to do a colony count and isolate the aerobic capnophilic and anerobic bacteria the samples were cultured and incubated on laboratory media. The colonies were also identified using various diagnostic tests. Alterations in the presence of various bacterial species over time and gum health were tested using analysis of variance (ANOVA) with Tukey's test post hoc. RESULTS: The average pocket depth for each patient ranged from 1.37 ± 0.39 mm to 2.55 ± 0.72 mm. The bacteria isolated from the cultured samples included aerobic, facultative anerobic, obligate anerobic and capnophilic bacteria. CONCLUSION: The anerobic conditions created in the peri-implant sulcus might with time enhance the number of anerobic bacteria present following dental implant loading.