Passive Fit Research Articles

Effect of repetitive firing on passive fit of metal substructure produced by the laser sintering in implant-supported fixed prosthesis.

PURPOSEThe aim of the present study was to investigate the passive fit of metal substructure after repetitive firing processes in implant-supposed prosthesis.MATERIALS AND METHODSFive implants (4 mm diameter and 10 mm length) were placed into the resin-based mandibular model and 1-piece of screw-retained metal substructure was produced with the direct metal laser sintering (DMSL) method using Co-Cr compound (n = 10). The distance between the marked points on the multiunit supports and the marginal end of the substructure was measured using a scanning electron microscope (SEM) at each stage (metal, opaque, dentin, and glaze). 15 measurements were taken from each prosthesis, and 150 measurements from 10 samples were obtained. In total, 600 measurements were carried out at 4 stages. One-way ANOVA test was used for statistical evaluation of the data.RESULTSWhen the obtained marginal range values were examined, differences between groups were found to be statistically significant (P<.001). The lowest values were found in the metal stage (172.4 ± 76.5 µm) and the highest values (238.03 ± 118.92 µm) were determined after glaze application. When the interval values for groups are compared with pairs, the differences between metal with dentin, metal with glaze, opaque with dentin, opaque with glaze, and dentin with glaze were found to be significant (P<.05), whereas the difference between opaque with metal was found to be insignificant (P=.992).CONCLUSIONPassive fit of 1-piece designed implant-retained fixed prosthesis that is supported by multiple implants is negatively affected by repetitive firing processes.

Precision and practical usefulness of intraoral scanners in implant dentistry: A systematic literature review.

BackgroundThis systematic review aimed to evaluate the efficiency and accuracy of digital impression techniques for implant-supported restorations, and to assess their economic feasibility. Material and MethodsTwo independent electronic database searches were conducted in the Pubmed/MedLine, Cochrane Library, and Lilacs databases complimented by a manual search, selecting relevant clinical and in vitro studies published between 1st January 2009 and 28st February 2019. All type of studies (in vivo and in vitro) were included in this systematic review. ResultsTwenty-seven studies (8 in vivo and 19 in vitro studies) fulfilled the inclusion criteria. No meta-analysis was performed due to a large heterogeneity of the study protocols. The passive fit of superstructures on dental implants presented similar results between digital and conventional impression techniques. The studies considered that several factors influence the accuracy of implant impression taking: distance and angulation between implants, depth of placement, type of scanner, scanning strategy, characteristics of scanbody, and operator experience. Regarding the economic viability of intraoral scanning systems, only one study reported any benefit in comparison with conventional techniques. ConclusionsDigital impressions of dental implants can be considered a viable alternative in cases of one or two contiguous dental implants. However, more studies are needed to evaluate the accuracy of digital techniques in full-arch implant-supported restorations. Key words:Intraoral scanner, dental implant, prosthesis, misfit, systematic review.

Evaluation of Positional Accuracy of Conceptually Two Different Die Systems in the Fabrication of Fixed Partial Dentures

The success of any fixed prosthesis is multifactorial right from preparation to passive fit during cementation, various phases both in clinical and laboratory procedures. Die preparation is a procedure without which the success of any prosthesis is compromised. Different systems have been used for preparing die which serves as a platform for the construction of pattern for future prosthesis. Over the years, these die systems passed various modifications and innovations striving towards precision that governs the fit of any prosthesis. This article evaluates two such systems which evolved independently for their positional accuracy through-out a simulated laboratory procedure.

Zirconia crowns cemented on titanium bars using CAD/CAM: a five-year follow-up prospective clinical study of 9 patients

BackgroundThe purpose of this prospective clinical study was to evaluate clinical results of the passive fit of the substructure in the Toronto bridge and the chipping or delamination of the ceramic veneering on the zirconia-support, after 5 years, in nine patients rehabilitated with zirconia crowns cemented on titanium bars using CAD/CAM technology.MethodsA total of nine healthy patient fully edentulous in the upper and lower jaws with non-contributory past medical anamnesis needing full fixed total prosthesis maxilla and mandible were included in this clinical study, where a total 9 mandibles and 9 jaws were treated. The inclusion criteria in order for a patient to participate in the study were: a signed consent form, fully edentulous in the upper and lower jaws, required a full fixed total prosthesis restoration. The exclusion criteria were age limitation of less than 18 years old, chemotherapy, head and neck radiation therapy, diabetes or periodontal disease, smoking and severe illness. All patients received zirconia crowns cemented on titanium bars using CAD/CAM technology. The primary outcome of this study was to examine the survival rate of the zirconia crowns cemented on titanium bars using CAD/CAM technology during the observation period. Any chipping or delamination of the zirconia crowns of the restorations was considered as failure. The secondary outcome was to evaluate the passive fit of the substructure on the implants, loose of occlusal screws, implant survival and satisfactory occlusion.ResultsIn 5 years of follow-up no evidence of chipping or delamination of the ceramic veneering on the zirconia crown supported were observed. Fifteen finished protesis (93.75%) showed satisfactory occlusion and only one case (6.25%) required significant occlusal adjustment. During the first year recall all bars were stable (100%) no mobility of protheses was recorded. After 5 years all bars were stable (100%) and no mobility of protheses was recorded.ConclusionThe computerized workflow for the process of building bar and prosthesis ensures reproducible results and excellent adaptation and passive insertion of them, as well as conditions for avoiding mechanical complications and guarantees stability of screw-implant abutments.

Full-Arch Implant-Supported Fixed Dental Prosthesis Retained by a Combination of Galvano-Telescopic Copings and Screws: A Clinical Report.

Full-arch screw-retained implant-supported fixed dental prostheses have a high long-term success rate and are considered the gold standard by many clinicians. However, accurate fabrication of a passive fit long-span prosthesis can be challenging. A novel intraoral adhesion method using galvano-telescopic copings was proposed as a way of improving prosthetic fit for edentulous patients. This report describes the treatment of a 74-year-old female with a full-arch implant-supported dental prosthesis, supported by a combination of galvano-telescopic copings and screws to prevent retention loss. Four years have passed since this superstructure was placed, during this time she exhibited a good clinical course with no inflammation noted in surrounding tissues. Treatment with an implant-supported fixed dental prosthesis, retained by a combination of galvano-telescopic copings and screws, can be a useful alternative treatment for edentulous patients.

Combining Intraoral and Face Scans for the Design and Fabrication of Computer-Assisted Design/Computer-Assisted Manufacturing (CAD/CAM) Polyether-Ether-Ketone (PEEK) Implant-Supported Bars for Maxillary Overdentures.

Purpose To present a digital method that combines intraoral and face scanning for the computer-assisted design/computer-assisted manufacturing (CAD/CAM) fabrication of implant-supported bars for maxillary overdentures. Methods Over a 2-year period, all patients presenting to a private dental clinic with a removable complete denture in the maxilla, seeking rehabilitation with implants, were considered for inclusion in this study. Inclusion criteria were fully edentulous maxilla, functional problems with the preexisting denture, opposing dentition, and sufficient bone volume to insert four implants. Exclusion criteria were age < 55 years, need for bone augmentation, uncompensated diabetes mellitus, immunocompromised status, radio- and/or chemotherapy, and previous treatment with oral and/or intravenous aminobisphosphonates. All patients were rehabilitated with a maxillary overdenture supported by a CAD/CAM polyether-ether-ketone (PEEK) implant-supported bar. The outcomes of the study were the passive fit/adaptation of the bar, the 1-year implant survival, and the success rates of the implant-supported overdentures. Results 15 patients (6 males, 9 females; mean age 68.8 ± 4.7 years) received 60 implants and were rehabilitated with a maxillary overdenture supported by a PEEK bar, designed and milled from an intraoral digital impression. The intraoral scans were integrated with face scans, in order to design each bar with all available patient data (soft tissues, prosthesis, implants, and face) in the correct spatial position. When testing the 3D-printed resin bar, 12 bars out of 15 (80%) had a perfect passive adaptation and fit; in contrast, 3 out of 15 (20%) did not have a sufficient passive fit or adaptation. No implants were lost, for a 1-year survival of 100% (60/60 surviving implants). However, some complications (two fixtures with peri-implantitis in the same patient and two repaired overdentures in two different patients) occurred. This determined a 1-year success rate of 80% for the implant-supported overdenture. Conclusions In this study, the combination of intraoral and face scans allowed to successfully restore fully edentulous patients with maxillary overdentures supported by 4 implants and a CAD/CAM PEEK bar. Further studies are needed to confirm these outcomes.

Evaluation of strain distribution on an edentulous mandible generated by cobalt-chromium metal alloy fixed complete dentures fabricated with different techniques: An in vitro study

Statement of problemFixed complete dentures (FCDs) have been used in the treatment of completely edentulous patients for over 40 years. However, few reports have investigated misfit values and strain distribution in the context of FCDs fabricated with new technologies. PurposeThe purpose of this in vitro study was to evaluate misfit values and strain distribution in FCDs and their relation to the fabrication technique of the cobalt-chromium (Co-Cr) metal framework. Material and methodsFour implants were placed in the interforaminal region of a mandibular cast at the bone level. The Co-Cr metal alloy frameworks were fabricated using the following techniques: computer-aided design and computer-aided manufacturing (CAD-CAM), milling from hard blocks, CAD-CAM milling from soft blocks, and direct metal laser sintering (DMLS). The superstructures of equal sizes with acrylic resin bases and acrylic resin denture teeth were fabricated on the Co-Cr metal alloy framework, and a digital microscope was then used to measure the misfit between the abutments and the implants. The stress formed after the application of torque was measured with a strain-gauge stress analysis technique. Data were statistically analyzed using 1-way ANOVA and the Tukey Honestly Significant Difference test (α=.05). The correlation between the misfit and the strain values was evaluated with the Pearson Correlation test (α=.001). ResultsThe lowest mean misfit values (99 ±17 μm) were observed in the hard block group (P<.05) and the highest in the DMLS group (139 ±29 μm). A statistically significant positive relationship was found between the misfit and the stress distribution after torque application (P<.05). Moreover, the lowest misfit group, hard blocks, had the lowest mean strain values (81.1 ±54 MPa) after torque application. ConclusionsWithin the limitations of this in vitro study, the fabrication technique used for Co-Cr metal alloy frameworks appears to influence the passive fit significantly (P<.05). The hard-block technique was found to be the most precise fabrication technique for Co-Cr metal alloy frameworks. A significant relationship was observed between the amount/distribution of misfit and the strain on the FCD (P<.05).

Effect of materials and superstructure designs on the passive fit of implant-supported fixed prostheses

This study aimed to compare the passive fits of implant-supported cement-retained computer aided design/computer aided manufacturing (CAD/CAM) bridges fabricated with different implant superstructure designs from zirconia and titanium. A total of 32 cubic clods with the same dimensions and with elastic modulus similar to that of mandibles were used. Each clod received two one-stage implants to simulate a partially edentulous jaw that was missing teeth between the lower left second premolar and second molar. Four linear strain gauges were bonded on the region surrounding each implant on the mesial, buccal, distal, and lingual aspects. A total of 32 identical frameworks were fabricated through CAD/CAM after scanning. The frameworks were allocated into four different groups (n=8) in accordance with material types and superstructure designs. Group A included zirconia ceramic implant-supported fixed prostheses with regular marginal designs. Group B comprised zirconia ceramic implant-supported fixed prostheses with full circumferential zirconia-collar marginal designs. Group C consisted of titanium ceramic implant-supported fixed prostheses with regular marginal designs. Group D included titanium ceramic implant-supported fixed prostheses with full circumferential titanium-collar marginal designs. Strain development before and after ceramic veneering was recorded during cement setting. Data were statistically analyzed by using SPSS software. Before ceramic veneering, material types affected the strains of prostheses, and zirconia frameworks showed lower strain than other frameworks (P<0.01). Designs affected the strains of prostheses, and frameworks with full collar marginal design showed lower strain than other frameworks (P<0.01). These two factors showed interactions (P<0.01). The strain of decorative porcelain increased after sintering. The two groups of different materials did not significantly differ (P>0.05). Nevertheless, the full circumferential collar marginal design reduced discrepancies among groups (P<0.01). The passive fits of zirconia prostheses were better than those of titanium-based porcelain-fused-to-metal restorations. The full circumferential collar marginal design can help reduce fit inaccuracy, as well as the adverse effects of ceramic veneering.

Rehabilitation of edentulous jaws with zirconia complete-arch fixed implant-supported prostheses: An up to 4-year retrospective clinical study

Statement of problemLimited data are available on the clinical outcomes of patients with edentulism treated with zirconia complete-arch fixed implant-supported prostheses (CAFIPs). PurposeThe primary purpose of this retrospective clinical study was to study the failure rate of dental implants as well as the fracture rate of zirconia CAFIPs. The secondary purpose was to study the survival outcomes of patients with edentulism treated with zirconia CAFIPs as well as the rate of technical complications. Material and methodsThis retrospective clinical study from private practice included 128 patients rehabilitated between January 1, 2013, and December 31, 2016, with 1072 implants supporting 191 zirconia CAFIPs for single-jaw as well as double-jaw rehabilitations. All zirconia prostheses were of 1-piece design and were veneered with feldspathic porcelain only at the gingival region and therefore considered as predominantly monolithic. Additionally, all prostheses were bonded to implant manufacturer’s titanium cylinders that provided an intimate contact with the implants. The primary outcome measures were implant failure rate and prosthesis fracture rate. The secondary outcome measures were prosthodontic treatment survival rate and the incidence of technical complications with respect to monolithic zirconia CAFIPs. Cumulative survival rate (CSR) for implants and prostheses was calculated after a life-table survival analysis. ResultsOf the analyzed samples over a 4-year period, at least 288 implants and 49 prostheses had a minimum of 4 years of follow-up. A total of 18 implant failures were noted (13 in maxilla, 5 in mandible), yielding a CSR of 97.6% for implants. One fracture of the zirconia prosthesis was recorded, yielding a CSR of 99.4% for the prostheses over the 4-year period. Another 3 prostheses required remaking because the supporting implants failed, and 1 prosthesis was remade because the lack of passive fit resulted in a CSR of 96.8% for the prosthodontic treatment itself. During the 4-year period, 1 zirconia prosthesis had a technical complication related to the debonding of titanium cylinders, and 2 prostheses had fractured screws, which were resolved successfully. No zirconia prostheses had chipping of the veneered gingival porcelain. ConclusionsFindings from this retrospective clinical study from private practice showed that prosthodontic treatment of edentulous patients with a 1-piece, complete-arch fixed implant-supported zirconia prosthesis with veneered porcelain restricted to the gingival region had high survival rates for implants and prostheses. Minimal technical complications related to this type of treatment for edentulous jaws and no chipping of the veneered gingival porcelain were encountered.

Precision and Accuracy of a Digital Impression Scanner in Full-Arch Implant Rehabilitation.

To evaluate the accuracy and precision of a digital scanner used to scan four implants positioned according to an immediate loading implant protocol and to assess the accuracy of an aluminum framework fabricated from a digital impression. Five master casts reproducing different edentulous maxillae with four tilted implants were used. Four scan bodies were screwed onto the low-profile abutments, and a digital intraoral scanner was used to perform five digital impressions of each master cast. To assess trueness, a metal framework of the best digital impression was produced with computer-aided design/computer-assisted manufacture (CAD/CAM) technology and passive fit was assessed with the Sheffield test. Gaps between the frameworks and the implant analogs were measured with a stereomicroscope. To assess precision, three-dimensional (3D) point cloud processing software was used to measure the deviations between the five digital impressions of each cast by producing a color map. The deviation values were grouped in three classes, and differences were assessed between class 2 (representing lower discrepancies) and the assembled classes 1 and 3 (representing the higher negative and positive discrepancies, respectively). The frameworks showed a mean gap of < 30 μm (range: 2 to 47 μm). A statistically significant difference was found between the two groups by the 3D point cloud software, with higher frequencies of points in class 2 than in grouped classes 1 and 3 (P < .001). Within the limits of this in vitro study, it appears that a digital impression may represent a reliable method for fabricating full-arch implant frameworks with good passive fit when tilted implants are present.

Effect of feldspathic porcelain layering on the marginal fit of zirconia and titanium complete-arch fixed implant-supported frameworks

Statement of problemVeneering with porcelain may adversely affect the marginal fit of long-span computer-aided design and computer-aided manufacturing (CAD-CAM) implant-supported fixed prostheses. Moreover, data regarding the precision of fit of CAD-CAM–fabricated implant-supported complete zirconia fixed dental prostheses (FDPs) before and after porcelain layering are limited. PurposeThe purpose of this in vitro study was to evaluate the effect of porcelain layering on the marginal fit of CAD-CAM–fabricated complete-arch implant-supported, screw-retained FDPs with presintered zirconia frameworks compared with titanium. Material and methodsAn autopolymerizing acrylic resin–fixed complete denture framework prototype was fabricated on an edentulous typodont master model (all-on-4 concept; Nobel Biocare) with 2 straight in the anterior and 2 distally tilted internal-hexagon dental implants in the posterior with multiunit abutments bilaterally in canine and first molar locations. A 3-dimensional (3D) laser scanner (S600 ARTI; Zirkonzahn) was used to digitize the prototype and the master model by using scan bodies to generate a virtual 3D CAD framework. Five presintered zirconia (ICE Zirkon Translucent - 95H16; Zirkonzahn) and 5 titanium (Titan 5 - 95H14; Zirkonzahn) frameworks were fabricated using the CAM milling unit (M1 Wet Heavy Metal Milling Unit; Zirkonzahn).The 1-screw test was applied by fixing the frameworks at the location of the maxillary left first molar abutment, and an industrial computed tomography (CT) scanner (XT H 225 - Basic Configuration; Nikon) was used to scan the framework-model complex to evaluate the passive fit of the frameworks on the master model. The scanned data were transported in standard tessellation language (STL) from Volume Graphics analysis software to PolyWorks analysis software by using the maximum-fit algorithm to fit scanned planes in order to mimic the mating surfaces in the best way. 3D virtual assessment of the marginal fit was performed at the abutment-framework interface at the maxillary right canine (gap 3) and right first molar (gap 4) abutments without prosthetic screws. The facial or buccal aspects of the teeth on frameworks were layered with corresponding porcelain (Initial Dental Ceramic System; GC) and CT-scanned again using the same protocol. Marginal fit measurements were made for 4 groups: titanium (Ti) (control), porcelain-layered titanium (Ti-P) (control), zirconia (Zir), and porcelain-layered zirconia (Zir-P). 3D discrepancy mean values were computed and calculated, and the results were analyzed with a repeated measures 3-way ANOVA using the maximum likelihood estimation method and Bonferroni adjustments for selected pairwise comparison t-tests (α=.05). ResultsThe 3D fit was measured at gap 3 and gap 4. Statistically significant differences in mean 3D discrepancies were observed between Zir-P (175 μm) and Zir (89 μm) and between Zir-P and Ti-P (71 μm) (P<.001). ConclusionsPorcelain layering had a significant effect on the marginal fit of CAD-CAM–fabricated complete-arch implant-supported, screw-retained FDPs with partially sintered zirconia frameworks. 3D marginal discrepancy mean values for all groups were within clinically acceptable limits (<120 μm), except for the layered zirconia framework.

Accuracy of fit of implant-supported bars fabricated on definitive casts made by different dental stones.

BackgroundThe purpose of this study was to evaluate the accuracy of fitting of an implant supported screw-retained bar made on definitive casts produced by 4 different dental stone products.Material and MethodsThe dental stones tested were QuickRock (Protechno), FujiRock (GC), Jade Stone (Whip Mix) and Moldasynt (Heraeus). Three external hexagon implants were placed in a polyoxymethylene block. Definitive impressions were made using monophase high viscosity polyvinylsiloxane in combination with custom trays. Then, definitive models from the different types of dental stones were fabricated. Three castable cylinders with a machined non-enganging base were cast and connected with a very small quantity of PMMA to a cast bar, which was used to verify the marginal discrepancies between the abutments and the prosthetic platforms of the implants. For that purpose special software and a camera mounted on an optical microscope were used. The gap was measured by taking 10 measurements on each abutment, after the Sheffield test was applied. Twelve definitive casts were fabricated for each gypsum product and 40 measurements were performed for each cast. Mean, minimum, and maximum values were calculated. The Shapiro-Wilk test of normality was performed. Mann-Whitney test (P<.06) was used for the statistical analysis of the measurements.ResultsThe non-parametric Kruskal-Wallis test revealed a statistically significant effect of the stone factor on the marginal discrepancy for all Sheffield test combinations: 1. Abutment 2 when screw was fastened on abutment 1 (χ2=3, df=35.33, P<0.01), 2. Abutment 3 when the screw was fastened on abutment 1 (χ2=3, df=37.74, P<0.01), 3. Abutment 1 when the screw was fastened on abutment 3 (χ2=3, df=39.79, P<0.01), 4. Abutment 2 when the screw was fastened on abutment 3 (χ2=3, df=37.26, P<0.01).ConclusionsA significant correlation exists between marginal discrepancy and different dental gypsum products used for the fabrication of definitive casts for implant supported bars. The smallest marginal discrepancy was noted on implant supported bars fabricated on definitive casts made by Type III mounting stone. The biggest marginal discrepancy was noted on implant supported bars fabricated on definitive casts made by Type V dental stone. The marginal discrepancies presented on implant supported bars fabricated on definitive casts made by two types of Type IV dental stone were not significantly different. Key words:Dental implant, passive fit, dental stones, marginal discrepancy.

Factors Affecting the Decision to Use Cemented or Screw-Retained Fixed Implant-Supported Prostheses: A Critical Review.

This review aimed to compile and enumerate all the factors described in the literature that may affect the decision to use either cemented or screw-retained restorations and to determine the relative weights of each factor by type of retention and prosthesis. The literature was reviewed, and the factors were classified as either determining (present in a clinical situation in which one of the retention mechanisms was clearly more suitable than the other) or conditioning (present in clinical situations in which one type of restoration was not clearly more advantageous than the other). Three determining factors (esthetic outcome, retention, and biologic risk) and five conditioning factors (passive fit, fracture strength, occlusal area, complications, and retrievability) were identified. Although there is not a clearly better alternative for all clinical situations, determining factors in certain scenarios can render one of the two approaches more recommendable. For esthetic reasons, when the implant angle cannot be corrected to conceal the access hole, cementation is more suitable; however, screw retention is the better option when the occlusal space is under 6 mm or margins cannot be located supra- or equigingivally. In the absence of determining factors, the decision should be based on conditioning factors, which carry different weights depending on the type of prosthesis.

Zinc phosphate as a definitive cement for implant-supported crowns and fixed dentures.

Implant-supported dental prostheses can be retained by a screw or cement. Implant-supported fixed partial dentures have a passive fit. A passive fit means there is an internal gap between the abutment surface and the intaglio of the retainer to insure that there is no lateral pressure on the supporting implants or friction upon seating of the prosthesis. This gap is filled with cement for retention of the prosthesis. Any lateral pressure may cause marginal bone loss or periimplantitis. Also, there is usually a microscopic gap at the margin of a crown retainer that exposes the cement to oral fluids. The solubility of zinc phosphate (ZOP) cement is a definite liability due to the risk for cement dissolution. In fixed prostheses, the dissolution of the cement of one or more retainers would cause a transfer of the occlusal load to the retained unit(s). The resulting rotation and lifting of the cement-retained implants from occlusal and parafunctional loads could cause loss of osseointegration of the abutment-retained implant(s). ZOP cement may not be indicated for implant-supported fixed partial dentures or splints. Cement dissolution in single unit probably only involves re-cementation, if the patient does not swallow or aspirate the crown.

A Protocol for Screw-Retrievable, Cement-Retained, Implant-Supported Fixed Partial Dentures.

Longevity of implant-supported fixed partial dentures (ISFPDs) may be associated with multiple clinical complications, irrespective of whether retention is achieved via screws or cement. While use of screws ensures ease of prosthesis retrievability and elimination of the inherently risky cementation process, more mechanical strains are induced in this design. A combined screw-retrievable and cement-retained ISFPD is designed to achieve the best passive fit and strain reduction while allowing complete excess cement removal and maintaining ease of retrievability. Moreover, this approach suggests better protection of the cement layer from oral environment degradation and offers scope for an alternative retention protocol. This paper outlines aspects of the clinical indications and fabrication of a screw-retrievable, cement-retained ISFPD. A diagnostic assessment method that provides tactile resistance guidance for selection is also proposed.

COMPARISON OF PERI-IMPLANT CLINICAL INFLAMMATORY PARAMETERS AMONG SCREW RETAINED CAD/CAM METAL BAR AND ZIRCONIA BAR FOR PATIENTS WITH RECONSTRUCTED MANDIBLES

Background: Segmental resection of the mandible results in severe disturbance of chewing function. Advances in microvascular surgeries and CAD/CAM technology helped with the prosthetic rehabilitation of reconstructed mandibles.Purpose: The aim of this study was to assess metal bar versus zirconia bar in patients with reconstructed mandibles that were rehabilitated with implant retained mandibular removable partial overdenture concerning the peri implant gingival index and probing depth.Materials and methods: fourteen patients were selected according to the inclusion criteria, the participants were stratified equally into two groups, patients were assigned to receive either metal bar or zirconium bar. Preparation of implant sites started with pilot drill followed by sequential drilling under copious refrigerated irrigation. Monthly follow up appointments were scheduled for each patient. After second stage surgery, abutments were secured to implant fixtures. Open top impression technique was used for bar fabrication using CAD/CAM technology. The bar was screwed in the patient’s mouth and checked for passive fit. Construction of the implant assisted removable partial overdenture took place in the conventional way. Female part were picked up directly in the patient’s mouth. Patients were recalled one week, 3,9 and 12 months after delivery for assessment of gingival index and probing depth. Results: Mann-Whitney U test was used to analyze the gingival index score between the two groups metal bar and zirconium bar. The metal bar group mean and standard deviation was 0.40±0.48 after 1 week and 0.36±0.32 after 3 months, 0.30±0.42 after 9 months, 0.20±0.42 after 12 months. While for zirconium group 0.30 ± 0.70, 0.28± 0.42 ,0.25±0.32, 0.10±0.32 respectively after 1 week,3 months ,9 months and 12 months. There was a statistical significance between the groups in 9 and 12 months, where P value was Conclusion: Within the limitation of this study, zirconia metal bar is considered more biocompatible than the metal bar.

In vitro fit of CAD-CAM complete arch screw-retained titanium and zirconia implant prostheses fabricated on 4 implants

Statement of problemComputer-aided designed and computer-aided manufactured (CAD-CAM) titanium and zirconia implant-supported fixed implant prostheses on 4 implants have become popular. The precision and accuracy of their interface fit has not been widely researched. PurposeThe purpose of this in vitro study was to compare the marginal fit of zirconia and titanium implant-supported screw-retained CAD-CAM complete fixed dental prostheses (CFDP) fit with a standardized cast simulating the all-on-4 implant distribution. Material and methodsRepresentation of an edentulous maxilla with 4 multiunit replicas embedded in sites corresponding to the positions of the maxillary first molars and canines was chosen. Multiunit abutments were digitally scanned using scan bodies and a laboratory scanner. CAD software was used to design screw-retained implant-fixed complete prostheses framework, and the file was sent to a milling machine for CAM. Titanium (n=5) and zirconia (n=5) frameworks were milled on 4 implants, and the frameworks were scanned with an industrial computed tomography (CT) scanner while applying the 1-screw test. The direct CT scans were reconstructed to generate a standard tessellation language (STL) file from the voxel data set and transported to volume graphics analysis software from which measurements were extracted. The circular mating surfaces of the corresponding framework interfaces to their representative multiunit abutment replicas on the standard were measured for implant position left maxillary canine (LMC), implant position right maxillary canine (RMC) and implant position right maxillary first molar (RMFM). In addition, color maps were generated to show the marginal discrepancy between the mating surfaces using ±0.500 mm color scale ranges. ResultsThe material type (zirconia or titanium) was not significant for 3D discrepancy measurements (P=.904). However, 3D discrepancy measurement values were significantly different between RMC and RMFM within each group (P<.001). The mean 3D ±SD discrepancy measurement for LMC for titanium was 48.2 ±2.6 μm. The mean ±3D discrepancy measurement for RMC for titanium was 74 ±15 μm and 84.4 ±12.1 μm for zirconia. The mean 3D discrepancy measurement for RMFM for titanium was 102 ±26.7 μm and 93.8 ±30 μm for zirconia. All 3D discrepancy measurements showed values <135 μm. ConclusionsWithin the limitations of the present in vitro study, implant-supported CAD-CAM fabricated titanium and zirconia complete fixed dental prosthesis frameworks showed comparable marginal fit. Three-dimensional microgap measurements of frameworks showed clinically acceptable misfit values. Absolute passive fit was not achieved.

Stereophotogrammetric impression making for polyoxymethylene, milled immediate partial fixed dental prostheses

Immediate post-extraction and same-day placement of interim prostheses have increased patient acceptance of implant-supported prostheses. However, for immediate prostheses supported by multiple implants, meeting passive fit and esthetic standards is often challenging. In this clinical report, implant photogrammetry was combined with conventionally obtained digitized casts to prepare an interim, milled prosthesis from a polyoxymethylene (POM) disk, using computer-aided design and computer-aided manufacturing techniques. The following 2 conclusions were drawn. First, stereophotogrammetric scanning appears to be a reliable method for making impressions of immediate, implant-supported partial prostheses, and second, POM is suitable for preparing immediate interim screw-retained prosthetic implants.

Use of Intraoral Welding to Increase the Predictability of Immediately Loaded Computer-Guided Implants.

Inaccuracy of computer-guided implant placement may lead to complications when combined with an immediately loaded prefabricated prosthesis. The aim of this case series was to describe the use of an intraoral welding technique to increase the predictability of immediately loaded implants supporting a fixed full-arch prosthesis after computer-guided flapless implant placement. A total of 60 Ankylos plus implants (Dentsply) with a width of 3.5 mm and a length of 8 to 14 mm were placed consecutively in 10 patients. The implants were functionally loaded using the intraoral welding technique on the day of surgery. The accuracy of guided implant placement was assessed by matching the planning cone beam computed tomography (CBCT) scans with postoperative CBCT scans. No mechanical or biologic complications were registered at the 1-year follow-up. The global coronal deviation of implant placement from the guide plan ranged from 0.25 to 2.84 mm (SD: 0.6 mm), with a mean of 1.28 mm. Average angle deviation was 3.42 degrees (range 0.38-7.82 degrees; SD: 1.52 degrees). The global apical deviation ranged between 0.36 and 3.85 mm (SD: 0.71 mm), with a mean of 1.65 mm. Despite the inaccuracy registered, this guided-welded approach allowed successful achievement of a passive fit of the full-arch prosthesis on the inserted implants the same day of the surgery and provided a high implant and prosthetic survival rate at the 1-year follow-up.

Assessing different patterns of laser welding with Nickel-Chromium (Ni-Cr) alloy for structures applicable to fixed prosthesis

Among all desired requirements to dental prosthesis, marginal adaptation and passive fit are the most important. In some cases, in order to achieve these goals, it is necessary to cut and weld the teeth / implant-supported framework. Nowadays, the laser welding process shows a great advantage in comparison to other methods. The aim of this study was to evaluate the optimal laser welds point that is more appropriate to Ni-Cr prosthetic framework. A total of 60 specimens of Ni-Cr (35 mm x 4 mm) were designed and welded using a Nd:YAG laser device model EV 900. They were fixed in a metal piece 0.27 mm between the ends to be welded. All specimens were welded with 21 laser pulses diametrically opposed (frequency of 1.0Hz, load time 3.0 ms and 0.5 mm of diameter pulse). They were divided into three groups according to the electric current of the laser weld: A – 180A; B – 200A and C – 220A. To determinate the flexural mechanic strength, all specimens were submitted to a three-point bending test. The results obtained were: Group A = 553 Mpa; B = 751 Mpa and C = 802.1 Mpa. The control group was 1040.9 Mpa. ANOVA and Tukey’s test were performed and statistical significance differences were observed between group A and B as well as between group A and C. However, no significant difference was observed between B and C.