Comparison of marginal and internal fit of three-unit implant-supported fixed prosthetic substructures fabricated using CAD/CAM systems

Clinical Oral Investigations - This study compared the marginal and internal fit of implant-supported fixed dentures fabricated using CAD/CAM systems. A lower jaw model representing partial...     

A clinical comparison of prosthetic complications of implant-supported overdentures with different attachment systems

OBJECTIVES: The objective of this clinical study was to evaluate the prosthetic complications of patients with 2 to 4 implants splinted with a round bar or with 2 to 4 unsplinted implants with ball attachments during the follow-up period. METHODS: A total of 26 patients were included in this study. Patients were randomly provided with a round bar or with ball attachments that were used to retain overdentures. During follow-up visits, the following prosthetic complications were recorded: round bar fracture, fractured overdenture, hygiene complications, abutment screw loose, worn O-ring or replacement of O-ring attachment, and fractured retention clip. The functioning period of overdentures in the round bar group ranged from 12 to 72 months (mean 49), and from 12 to 40 months (mean 23) in the ball attachment group. RESULTS: A total of 20 prosthetic complications were recorded in both groups. No differences in prosthetic complications were observed for 2 attachment systems. CONCLUSION: Implant-supported overdentures with bar or ball attachments may be considered to be reliable methods in the treatment of the edentulous individuals.     

Cement fixation and screw retention: parameters of passive fit. An in vitro study of three-unit implant-supported fixed partial dentures

It is generally assumed that passively fitting superstructures are a prerequisite for long-lasting implant success. In the study presented, the strain development of three-unit implant fixed partial dentures (FPDs) was evaluated at the bone surrounding the implant and on the superstructure using a strain gauge technique. Six groups of three-unit FPDs representing the commonly used techniques of bridge fabrication were investigated with 10 samples each, in order to quantify the influence of impression technique, mode of fabrication and retention mechanism on superstructure fit. Two ITI implants (Straumann, Waldenburg, Switzerland) were anchored in a measurement model according to a real-life patient situation and strain gauges were fixed mesially and distally adjacent to the implants and on the bridge pontics. The developing strains were recorded during cement setting and screw fixation. For statistical analysis, multivariate two sample tests were performed setting the level of significance at P=0.1. None of the investigated bridges revealed a truly passive fit without strains occurring. About 50% of the measured strains were found to be due to impression taking and model fabrication, whereas the remaining 50% were related to laboratory inaccuracies. The two impression techniques used did not reveal any significant differences in terms of precision. Both modes of fixation--i.e. cement and screw retention--provoked equally high stress levels. In the fabrication of screw-retained FPDs, similar results were obtained from the use of burn-out plastic copings and the technique of casting wax moulds to premachined components. Bonding bridge frames onto gold cylinders directly on the implants significantly reduces strain development.     

Does the retention system influence the stability of implant-supported maxillary overdentures? A comparison with fixed and conventional dentures

Purpose

The purpose of this in vitro study was to compare the stability of removable implant-supported maxillary overdentures with fixed complete dentures and conventional dentures.

Surgical and implant-supported fixed prosthetic treatment of a patient with ectodermal dysplasia: a case report

Ectodermal dysplasia (ED) is a hereditary disorder that affects ectodermal structures. The main clinical oral manifestations of ED include oligodontia and deficient alveolar ridges. This case report presents the oral rehabilitation of a 15-year-old female patient who never received an accurate diagnosis or appropriate dental care. Treatment included a combination of surgical intervention, a maxillary tooth-supported fixed detachable telescopic prosthesis, and an implant-supported mandibular fixed partial denture. The results showed a significant improvement in the esthetics, function, and psychological status of the patient. This article stresses the importance of appropriate care in providing an acceptable quality of life for patients with ED.     

Marginal fit of porcelain and indirect composite laminate veneers under in vitro conditions

The purpose of the present study was to compare the marginal adaptation of indirect composite and porcelain veneers in vitro using transmitted-light microscopy. A preparation with a marginal chamber finish for a veneer was performed on 10 extracted molars after which 5 composite and 5 porcelain veneers were made and fitted using self- and light-cured microfill composite resin. Three longitudinal and 3 horizontal sections were cut in each preparation with the light microscope. Although the absolute marginal discrepancy at the cervical location had the highest statistical significance in the composite veneer group, the composite and porcelain veneers, in general, demonstrated a similar absolute marginal discrepancy and thickness of luting agent with average values from 50 microns to 195 microns for the two parameters. A considerable amount of excess of luting agent was furthermore observed in both groups of veneers, being most pronounced in the composite veneers.     

Marginal fit of porcelain and indirect composite laminate veneers under in vitro conditions

Abstract – The purpose of the present study was to compare the marginal adaptation of indirect composite and porcelain veneers in vitro using transmitted-light microscopy. A preparation with a marginal chamber finish for a veneer was performed on 10 extracted molars after which 5 composite and 5 porcelain veneers were made and fitted using self- and light-cured microfill composite resin. Three longitudinal and 3 horizontal sections were cut in each preparation with a diamond saw and were ground to a thickness of approximately 150 μm and investigated under the light microscope. Although the absolute marginal discrepancy at the cervical location had the highest statistical significance in the composite veneer group, the composite and porcelain veneers, in general, demonstrated a similar absolute marginal discrepancy and thickness of luting agent with average values from 50 μm to 195 μm for the two parameters. A considerable amount of excess of luting agent was furthermore observed in both groups of veneers, being most pronounced in the composite veneers.     

The effect of mechanical cycling and different misfit levels on Vicker's microhardness of retention screws for single implant-supported prostheses

Purpose: The aim of this study was to evaluate the effect of mechanical cycling and different misfit levels on Vicker's microhardness of retention screws for single implant‐supported prostheses. Materials and Methods: Premachined UCLA abutments were cast with cobalt‐chromium alloy to obtain 48 crowns divided into four groups (n = 12). The crowns presented no misfit in group A (control group) and unilateral misfits of 50 μm, 100 μm, and 200 μm in groups B, C, and D, respectively. The crowns were screwed to external hexagon implants with titanium retention screws (torque of 30 N/cm), and the sets were submitted to three different periods of mechanical cycling: 2×10⁴, 5×10⁴, and 1×10⁶ cycles. Screw microhardness values were measured before and after each cycling period. Data were evaluated by two‐way ANOVA and Tukey's test (p < 0.05). Results: Mechanical cycling statistically reduced microhardness values of retention screws regardless of cycling periods and groups. In groups A, B, and C, initial microhardness values were statistically different from final microhardness values (p < 0.05). There was no statistically significant difference for initial screw microhardness values (p > 0.05) among the groups; however, when the groups were compared after mechanical cycling, a statistically significant difference was observed between groups B and D (p < 0.05). Conclusions: Mechanical cycling reduced the Vicker's microhardness values of the retention screws of all groups. The crowns with the highest misfit level presented the highest Vicker's microhardness values.     

Effect of cement washout on loosening of abutment screws and vice versa in screw- and cement- retained implant-supported dental prosthesis

PURPOSE

The purpose of this study was to examine the abutment screw stability of screw- and cement-retained implant-supported dental prosthesis (SCP) after simulated cement washout as well as the stability of SCP cements after complete loosening of abutment screws.

MATERIALS AND METHODS

Thirty-six titanium CAD/CAM-made implant prostheses were fabricated on two implants placed in the resin models. Each prosthesis is a two-unit SCP: one screw-retained and the other cemented. After evaluating the passive fit of each prosthesis, all implant prostheses were randomly divided into 3 groups: screwed and cemented SCP (Control), screwed and noncemented SCP (Group 1), unscrewed and cemented SCP (Group 2). Each prosthesis in Control and Group 1 was screwed and/or cemented, and the preloading reverse torque value (RTV) was evaluated. SCP in Group 2 was screwed and cemented, and then unscrewed (RTV=0) after the cement was set. After cyclic loading was applied, the postloading RTV was measured. RTV loss and decementation ratios were calculated for statistical analysis.

RESULTS

There was no significant difference in RTV loss ratio between Control and Group 1 (P=.16). No decemented prosthesis was found among Control and Group 2.

CONCLUSION

Within the limits of this in vitro study, the stabilities of SCP abutment screws and cement were not significantly changed after simulated cement washout or screw loosening.     

后牙区螺丝固位与黏结固位种植义齿修复效果的比较研究

目的探讨后牙区螺丝同位与黏结固位种植固定义齿临床修复效果的差异。方法选择上下颌后牙区牙列缺损患者42例共70枚种植体．其中24枚采用螺丝固位修复体．46枚采用黏结周位修复体。分别于修复后1年复诊．检测种植体周围边缘骨吸收量、改良菌斑指数（mPLI）、改良出血指数（mSBI）等临床指标以及患者对种植义齿的美观满意度。结果螺丝固位组及黏结固位组平均种植体周围边缘骨吸收量分别为0．78mm和0．68mm：螺丝组与黏结组mPLI平均水P50均为1，mSBI平均水平P50亦均为1：两组美观满意度平均得分P50为1。统计结果显示螺丝固位组与黏结固位组间种植体周围边缘骨吸收量、mPLI、mSBI以及患者满意度的差异均无统计学意义（P〉0．05）。结论后牙区螺丝固位与黏结固位种植义齿短期临床修复效果差异无统计学意义。     

The fit of cobalt-chromium three-unit fixed dental prostheses fabricated with four different techniques: A comparative in vitro study

Objectives

This study sought to evaluate and compare the marginal and internal fit in vitro of three-unit FDPs in Co-Cr made using four fabrication techniques, and to conclude in which area the largest misfit is present.

Methods

An epoxy resin master model was produced. The impression was first made with silicone, and master and working models were then produced. A total of 32 three-unit Co-Cr FDPs were fabricated with four different production techniques: conventional lost-wax method (LW), milled wax with lost-wax method (MW), milled Co-Cr (MC), and direct laser metal sintering (DLMS). Each of the four groups consisted of eight FDPs (test groups). The FDPs were cemented on their cast and standardised-sectioned. The cement film thickness of the marginal and internal gaps was measured in a stereomicroscope, digital photos were taken at 12× magnification and then analyzed using measurement software. Statistical analyses were performed with one-way ANOVA and Tukey's test.

Results

Best fit based on the means (SDs) in μm for all measurement points was in the DLMS group 84 (60) followed by MW 117 (89), LW 133 (89) and MC 166 (135). Significant differences were present between MC and DLMS (p < 0.05). The regression analyses presented differences within the parameters: production technique, tooth size, position and measurement point (p < 0.05).

Significance

Best fit was found in the DLMS group followed by MW, LW and MC. In all four groups, best fit in both abutments was along the axial walls and in the deepest part of the chamfer preparation. The greatest misfit was present occlusally in all specimens.     

Location of main occluding areas and masticatory ability in patients with implant-supported prostheses

Background: The purpose of this study was to locate the main occluding area when the reduced posterior occlusal support was treated with an implant‐supported prosthesis and to evaluate the subsequent improvement in the masticatory ability as compared with removable partial dentures. Methods: Twenty‐six patients with implant prostheses and 24 patients with removable partial dentures were recruited for this study. All patients had partially lost their posterior occlusal support. The first molar region in any quadrant was always included in the prosthetic region. Each subject was instructed to clench a piece of temporary stopping as a test food on the occluding area that was preferably used during mastication. The main occluding area was judged by locating the tooth on which the temporary stopping rested during clenching. Subjective masticatory ability was self‐assessed by means of a questionnaire. Results: The main occluding area of the subjects in the implant group was located more posterior compared with the removable partial denture group. The level of masticatory ability in the implant group was the same as that in the control group. Conclusions:  The location of the main occluding area and the masticatory ability of the subjects with implants were equivalent to those with healthy natural dentition.     

动态载荷下不同骨质对天然牙-种植体联合修复应力分布的影响

目的 利用有限元方法探索下颌后牙区天然牙-种植体联合修复在不同骨质内的应力分布情况,以评定出适宜行联合修复所需的骨质类型。方法 采用三维有限元分析法,分别对骨质为Ⅰ、Ⅱ、Ⅲ、Ⅳ类颌骨类型中的天然牙-种植体联合修复体施加动态载荷,并对各界面所承受的Von Mises应力进行分析。结果 皮质骨所受最大Von Mises应力值从Ⅰ类骨到Ⅳ类骨逐渐增大,最大等效应力分别为89.229、91.860、125.840、158.420 MPa。松质骨所受最大Von Mises应力值从Ⅰ类骨到Ⅳ类骨均逐渐减小,最大等效应力分别为58.584、43.645、21.688、18.249 MPa。在同一类模型中,松质骨和皮质骨的最大Von Mises应力值均为舌颊向加载>颊舌向加载>垂直向加载。结论 骨质的类型对修复体周围骨的应力分布有重要的影响,Ⅰ、Ⅱ类骨较Ⅲ、Ⅳ类骨更适合行种植体-天然牙联合修复。     

An up to 43-year longitudinal study of fixed prosthetic restorations retained with 4-META/MMA-TBB resin cement or zinc phosphate cement

Statement of problemAdhesive resin cement has been the preferred choice for the placement of prosthetic restorations, but evidence-based studies supporting this selection are sparse.PurposeThe purpose of this study was to test the hypothesis that restoration placement with the adhesive 4-methacryloxyethyl trimellitate anhydride/methyl methacrylate-tributylborane (4-META/MMA-TBB) resin cement is associated with better longevity of teeth than zinc phosphate cement up to 43 years.Materials and methodsStudy participants were individuals who had been visiting the clinic regularly for more than 20 years from their first visit between November 1970 and April 1985. The vital teeth with prosthetic restorations (N=454), including cast inlays, onlays, crowns, and fixed partial dentures, of 53 patients were assessed from dental charts and radiographs. Most of the bonding surfaces were precious metal alloy, excluding 4 restorations cemented with zinc phosphate and 6 ceramic crowns cemented with 4-META/MMA-TBB resin cement. The Kaplan-Meier method and log-rank test (α=.05) were used to compare longevity between the 2 materials. Chi-squared tests (α=.001) were also used to examine the occurrence rates of events such as secondary caries, endodontic treatment, and the dislodgement of restorations affecting the longevity of the 2 cements.ResultsClinical review examination demonstrated that 55.4% of teeth retained with 4-META/MMA-TBB resin cement had been in service for 30 years compared with 43.5% of those retained with zinc phosphate cement, with a significant difference (P=.006). 4-META/MMA-TBB resin cement also demonstrated lower event occurrence rates than zinc phosphate cement for 3 assessed types of events (P<.001).ConclusionsWithin the limitations of this study, 4-META/MMA-TBB resin adhesive cement demonstrated a higher survival rate than conventional zinc phosphate cement in service for 30 years with a lower occurrence of critical events.     

Mechanical stability of all-ceramic abutments retained with three different screw materials in two-piece zirconia implants—an in vitro study

To measure the abutment rotation and fracture load of two-piece zirconia implants screwed with three different abutment screw materials. Thirty-six zirconi     

Torque removal evaluation of prosthetic screws after tightening and loosening cycles: an in vitro study

Objectives: The aim of this study was to evaluate the variation in removal torque of implant prosthetic abutment screws after successive tightening and loosening cycles, in addition to evaluating the influence of the hexagon at the abutment base on screw removal torque. Material and methods: Twenty hexagonal abutments were tightened to 20 regular external hex implants with a titanium alloy screw, with an insertion torque of 32 N cm, measured with a digital torque gauge. The implant/abutment/screw assemblies were divided into two groups: (1) abutments without hexagon at the base and (2) abutments with a hexagon at the base. Each assembly received a provisional restoration and was submitted to mechanical loading cycles. After this, the screws were removed and the removal torque was measured. This sequence was repeated 10 times, then the screw was replaced by a new one, and another cycle was performed. Linear regression analysis was performed. Results: Removal torque values tended to decrease as the number of insertion/removal cycles increased, for both groups. Comparisons of the slopes and the intercepts between groups showed no statistical difference. There was no significant difference between the mean values of last five cycles and the 11th cycle. Within the limitations of this in vitro study, it was concluded that (1) repeated insertion/removal cycles promoted gradual reduction in removal torque of screws, (2) replacing the screw with a new one after 10 cycles did not increase resistance to loosening, and (3) removal of the hexagon from the abutment base had no effect on the removal torque of the screws. To cite this article :
Cardoso M, Torres MF, Lourenço EJV, de Moraes Telles D, Rodrigues RCS, Ribeiro RF. Torque removal evaluation of prosthetic screws after tightening and loosening cycles: an in vitro study.
Clin. Oral Impl. Res. 23 , 2012 475–480.
doi: 10.1111/j.1600‐0501.2011.02165.x