Molar Abutment Research Articles

Influence of glazing and aging on the marginal, axial, axio-occlusal, and occlusal fit of 3-unit monolithic zirconia restorations fabricated using additive and subtractive techniques

Studies are sparse on how glazing and aging influence the fit of additively fabricated monolithic zirconia restorations. The purpose of this in vitro study was to assess the effect of glazing and aging on the fit of 3-unit monolithic zirconia restorations fabricated using different techniques. A total of 32 monolithic zirconia restorations were fabricated for a typodont model by using 4 distinct techniques (subtractive fabrication [SF], stereolithography [SLA], digital light processing [DLP], and lithography-based ceramic manufacturing [LCM]). The silicone replica approach was adopted to measure the discrepancy values for premolar and molar abutments after sintering, glazing, and 1 year of aging. The silicone replicas were sliced into mesiodistal and buccopalatal cross-sections, and digital micrographs of the cross-sections were made with a ×80 stereomicroscope. An inherent measuring program was run to record the discrepancy values (µm). Repeated-measures 2-way ANOVAs with the Bonferroni post hoc test were used to statistically analyze the acquired data. (α=.05). From the repeated measures 2-way ANOVAs, both the glazing×fabrication technique and the aging×fabrication technique interactions were not statistically significant (P>.05). Glazing significantly influenced premolar abutment marginal (P=.022) and occlusal (P=.007) discrepancy values, as well as molar abutment marginal discrepancy values (P=.047). Aging had a statistically significant effect on premolar abutment marginal (P=.008) and occlusal (P=.011) discrepancy values, as well as molar abutment occlusal discrepancy values (P=.039). In both the glazing and aging data, for all areas of interest, statistically significant differences were detected among the fabrication techniques (P<.05). The LCM group had the lowest discrepancy values, followed by the SLA, SF, and DLP groups. The LCM and SLA groups outperformed the other groups in terms of fit accuracy. The glazing and aging procedures altered the discrepancy values. The marginal discrepancy values of all groups were below the threshold of clinical acceptability (<120µm).

Microsurgical Management of Nonsurgical Endodontically Treated Fiasco in Natural Permanent Upper Molar Tooth – A Clinical Case Report

Abstract The maxillary first permanent molar presents wide anatomical alterations for root number and their respective canal system. The medial root (mesiobuccal) specifically has been invariably associated to treatment failures when nonsurgical endodontic procedures have been solely carried out. In endodontic treatments, the decision to retreat the failed endodontic treatment with a surgical procedure depends on multiple factors. Evidence about the enduring prognosis of conventional retreatment (nonsurgical) comparative to invasive surgery (root end) remains questionable which requires additional scrutiny. The present case report presents a case of a patient (female, age 53 years) who presented with agony in relation to the maxillary first molar (left-sided) abutment of a four-unit fixed partial denture. Routine endodontic treatment was performed for the affected tooth which showed evidence of failure at 6-month follow-up intervals. Surgical intervention as part of the desired treatment was undertaken with the sealing of the canals done by Portland cement-based repair material. A pursual (6 months) after apicoectomy showed a complete rebuilding of the lateral apical region with freshly laid bone and a complete symptom-free patient. This clinical case report is directed to highlight the prospect of nonconservative clinical procedures once a noninvasive approach produces less anticipated results.

Digital Evaluation of the Trueness and Fitting Accuracy of a Three-Unit Fixed Zirconium Bridge Fabricated from Different Types of Zirconia and Different Marginal Cement Space Thickness

Abstract Objective The aim of this study was to measure the internal, marginal fitness, and trueness of a three-unit fixed zirconium bridge fabricated using two types of zirconia and different marginal cement space thicknesses. Methods and Materials Thirty-two aluminum master models, constructed by computer numerical control (CNC) milling machines using aluminum rod, representing two prepared aluminum abutments (the upper first premolar and the first molar) were chosen due to differences in shape and dimensions, which may affect adaptation. It may also be considered one of the most common cases in clinical practice and a missing second premolars were used to fabricate a three-unit fixed partial zirconium bridge. A master model was scanned with an intraoral scanner. Fixed dental prostheses (FDPs) were fabricated with two designs (single-layer high-translucent [HT] Katana and ultra-translucent multilayer (UTML] zirconia Katana) and two marginal cement space thicknesses (0 and 25μm for HT and ML). These specimens are divided according to marginal cement space and type of zirconia into four groups, each containing eight samples. Group A: 25-μm marginal cement space with single-layer HT zirconia. Group B: 25-μm marginal gap with UTML zirconia. Group C: 0 μm marginal gap single-layer HT zirconia. Group D: 0 μm marginal gap with UTML zirconia. Fitness and trueness of the fabricated three-unit FDPs were evaluated by scanning the silicone replica of the cement space and analyzing the thickness of the silicone replica in the three-dimensional inspection software (Geomagic Control X, Morrisville, North Carolina, USA). Results Highest mean value of internal gap was recorded at the molar abutment of group D (95.05, ± 3.42 μm), while the lowest was recorded at the premolar abutment of group A (57.12, ± 2.43μm). For marginal gap, the lowest marginal gap was also recorded at the premolar abutment of group A (36.14, ± 3.94μm), and the highest was at the molar abutment of group D (84.74, ± 2.98 μm).For trueness, group A showed the lowest root mean square (RMS) of mean with both abutments compared with group D, which recorded the highest RMS of mean for trueness. Conclusion The marginal cement space thickness affects the FPD internal, marginal fitness, and trueness; single-layer HT (Katana) zirconia shows better fitness and trueness than UTML (Katana).

Comparative analysis of the retention force and deformation of PEEK and PEKK removable partial denture clasps with different thicknesses and undercut depths

Statement of problemThe retentive force and deformation of milled polyetheretherketone (PEEK) and polyetherketoneketone (PEKK) removable partial denture (RPD) frameworks are not well understood. PurposeThe purpose of this in vitro study was to assess the retentive force and deformation of PEEK and PEKK Akers clasps with different designs and undercut depths. Material and methodsA master model containing the first and second molar abutments was used to design Akers clasps of different cross-sectional dimensions, undercut depths (0.5 and 0.75 mm), and materials. The components of the removable partial denture framework also included an occlusal rest and were manufactured using a milling machine (n=5). The fatigue resistance of the Akers clasps was measured before and after deformation regarding the retentive forces. ResultsThe PEEK2-U50 clasp had the largest retentive force with no significant difference among all groups before and after the insertion and removal cycle. In addition, the increased cross-sectional dimensions of the design resulted in significant differences in retentive forces between the PEEK1 and PEEK2 groups and between the PEEK and PEKK materials. ConclusionsIncreasing the clasp's cross-sectional dimensions significantly impacted retentive forces, especially between different PEEK groups and between PEEK and PEKK materials.

Fracture load of 4-unit interim fixed partial dentures using 3D-printed and traditionally manufactured materials

Statement of problemHow the fracture strength of recently introduced 3-dimensionally (3D) printed interim materials compares with that of conventional materials is unclear. PurposeThe purpose of this in vitro study was to compare the fracture load of 4-unit interim fixed partial dentures made from 3 different materials before and after mastication simulation. Material and methodsBased on a master model of a 4-unit fixed partial denture with maxillary left first premolar and second molar abutment teeth, interim restorations were fabricated from 3 different materials (3D-printed, Temporary CB Resin, milled, PMMA for brain, and manually manufactured, Luxatemp Plus). The fixed partial dentures (n=30 for each material) were cemented on 3D-printed model abutment teeth that were connected via a thin latex layer to a polyurethane base block. The fracture load of 15 fixed partial dentures of each material was tested without aging. Another 15 fixed partial dentures of each material were tested after thermomechanical aging. ResultsThe mean fracture load was between 186 N and 661 N, and all materials showed significant lower fracture loads after aging. Before and after aging (before/after ±standard deviation) milled (661 ±59/568 ±52 N) achieved the highest loads before manually manufactured (621 ±100/478 ±96 N) and 3D-printed (294 ±83/186 ±70). ConclusionsThe 3D-printed interim restoration material and the inherent manufacturing process show significant lower fracture loads than the tested alternatives. However, as the influence of geometric differences could not be quantified, whether this remains true after correcting for geometric differences remains unclear. For the tested interim materials, thermocycling and mastication simulation significantly reduced fracture loads over time, even at loads as low as 50 N.

FINITE ELEMENT EVALUATION OF THE EFFECT OF ADHESIVE CREAMS ON THE STRESS STATE OF DENTURES AND ABUTMENT TEETH

The appropriate fit of removable partial dentures (RPDs) is hypothesized to lead to lower tooth mobility. An adhesive layer between the denture and oral mucosa can facilitate better denture retention and therefore increased stability. Study objectives were to model and compare the response of abutment structures with and without the application of a denture adhesive and to observe the stress response of abutment periodontal ligaments (PDLs) during the application of occlusal force on the RPD. A 3D finite element (FE) model was developed from computer tomography datasets of the mandibular region and the RPD. An adhesive layer was developed by extending the denture surface and using the Prony series approximation of rheological data to implement a viscoelastic material model. FE simulations were performed by applying a bite force on one of the denture segments, with the resulting deformation in PDL compared between the model with the adhesive layer and the base model without. The maximum deformation of 15[Formula: see text][Formula: see text]m was observed in the 2nd molar abutment PDL with the implementation of the adhesive, as compared to 42[Formula: see text][Formula: see text]m for the model without. The lower impact of RPDs on the supporting abutment teeth could potentially reduce the discomfort of denture wearers.

Comparative Evaluation of Stress Acting on Abutment, Bone, and Connector of Different Designs of Acid-Etched Resin-Bonded Fixed Partial Dentures: Finite Element Analysis.

Background: Finite element analysis (FEA) is one of the best methods for evaluating the stress distribution of restorations, such as fixed partial dentures. The development of resin cement has transformed prosthesis bonding and retention properties. Resin-bonded fixed partial dentures (RBFPD) have been considered minimally invasive treatment options for the prosthetic rehabilitation of single missing teeth. Objectives: The aim of this study was to evaluate the stress load and distribution in four different designs of acid-etched RBFPDs using FEA. Materials and Methods: The designs included standard tooth preparation principles and additional features. The first premolar and first molar abutments replaced the missing second premolar. Designs 1, 2, 3, and 4 included (1) lingual wings and occlusal rests; (2) wings and proximal slices; (3) wings, rests, and grooves; and (4) wings, rests, grooves, and occlusal coverage. The prepared models were restored with RBFPDs. A load of 100 N was applied to the central groove of the pontic to simulate occlusal forces. The materials used in the models were considered to be isotropic, homogeneous, and linearly elastic. FEA was used to reveal stresses acting on the abutment, bone, and connector in all prosthesis designs. Results: The stresses transmitted to the abutment and bones were lowest for design 3, using wings, rests, and grooves. The stresses acting on the connector were the weakest in design 2. The stresses transmitted to the abutment and bone were highest in designs 1 and 4. The stresses transmitted to the connector were highest in design 3. Conclusion: The wings, rests, and grooves design is possibly the ideal and conservative tooth preparation design to receive a posterior RBFPD. This design transmits less stress to the abutments and less bone resorption in the FEA. It is most likely to be successful in the clinical provision and ensures the longevity of the prosthesis.

Residual stress estimated by nanoindentation in pontics and abutments of veneered zirconia fixed dental prostheses.

Glass ceramics’ fractures in zirconia fixed dental prosthesis (FDP) remains a clinical challenge since it has higher fracture rates than the gold standard, metal ceramic FDP. Nanoindentation has been shown a reliable tool to determine residual stress of ceramic systems, which can ultimately correlate to failure-proneness.Objectives:To assess residual tensile stress using nanoindentation in veneered three-unit zirconia FDPs at different surfaces of pontics and abutments.Methodology:Three composite resin replicas of the maxillary first premolar and crown-prepared abutment first molar were made to obtain three-unit FDPs. The FDPs were veneered with glass ceramic containing fluorapatite crystals and resin cemented on the replicas, embedded in epoxy resin, sectioned, and polished. Each specimen was subjected to nanoindentation in the following regions of interest: 1) Mesial premolar abutment (MPMa); 2) Distal premolar abutment (DPMa); 3) Buccal premolar abutment (BPMa); 4) Lingual premolar abutment (LPMa); 5) Mesial premolar pontic (MPMp); 6) Distal premolar pontic (DPMp); 7) Buccal premolar pontic (BPMp); 8) Lingual premolar pontic (LPMp); 9) Mesial molar abutment (MMa); 10) Distal molar abutment (DMa); 11) Buccal molar abutment (BMa); and 12) Lingual molar abutment (LMa). Data were assessed using Linear Mixed Model and Least Significant Difference (95%) tests.Results:Pontics had significantly higher hardness values than premolar (p=0.001) and molar (p=0.007) abutments, suggesting lower residual stress levels. Marginal ridges yielded higher hardness values for connectors (DPMa, MMa, MPMp and DPMp) than for outer proximal surfaces of abutments (MPMa and DMa). The mesial marginal ridge of the premolar abutment (MPMa) had the lowest hardness values, suggesting higher residual stress concentration.Conclusions:Residual stress in three-unit FDPs was lower in pontics than in abutments. The outer proximal surfaces of the abutments had the highest residual stress concentration.

Comparison of the Accuracy of Intraoral Scanners Based on the Type of Tooth Preparation for a Single Crown

The purpose of this study was to evaluate the accuracy of intraoral scanners in 10 abutments (five premolars and five molars) obtained in a dental clinic and to analyze the impacts of the volume and area of abutments on scanning accuracy. Abutment casts were scanned five times with a 3D contact scanner (DS10; Renishaw plc). The five scan files were lined up and then merged, and one high-resolution computer-aided design reference model (CRM) was obtained. To obtain a computer-aided design test model (CTM), three types of intraoral scanners (CS3600 (Carestream Dental), i500 (Medit), and EZIS PO (DDS)) and one type of laboratory scanner (E1; 3Shape) were employed. Using 3D analysis software (Geomagic control X; 3D Systems), the accuracy of the scanners was evaluated, including optimal overlap by optimal alignment. The conformity of the overlapped data was calculated by the root mean square (RMS) value, using the 3D compare function for evaluation. As for statistical analysis, testing was conducted, using one-way and two-way ANOVA and the Tukey HSD test (α = 0.05) for the comparison of the groups. To analyze the correlations of the volume and area of the abutments with accuracy, Pearson’s correlation analysis was conducted (α = 0.00625). Both premolar and molar abutments showed a lower RMS value on the laboratory scanner than on the intraoral scanners, and the RMS value was lower in premolars than in molars (p &lt; 0.001). In the intraoral scanner group, CS3600 showed the best accuracy (p &lt; 0.001). There were significant positive correlations for the volume and area of the abutments with accuracy (p &lt; 0.001). The type, volume, and area of the clinically applicable abutments may affect the accuracy of intraoral scanners; however, the scanners used in the present study showed a clinically acceptable accuracy range, regardless of the type of abutment.

Analysis of the relationship between the surface topography of prepared tooth surfaces and data quality of digital impressions from an intraoral scanner

Background/purposeWith the rise of digitalization in dentistry, intraoral scanners and digital impressions have recently been adopted by many clinicians. The aim of this study was to investigate surface topography of prepared teeth and the accuracy of digital impressions. Materials and methodsTwenty mandibular typodonts, containing left first premolar and left first molar abutment teeth manufactured by using CAD/CAM, were used in this study. An intraoral scanner was used to scan each typodont, and each STL file generated was exported in high resolution (Group H), moderate resolution (Group M), and low resolution (Group L). All 60 files were inspected in a 3-D mesh processing software. For each file, the number of triangulation points in the meshwork were obtained for both abutment teeth. ResultsThe measurements obtained from the 3-D mesh processing software revealed that the mean number of triangulation points on the 3-D surface of the abutment teeth (20 premolars + 20 M) were 790,625 ± 98,890 dots in Group H, 592,283 ± 74,881 dots in Group M, and 198,067 ± 19,328 dots in Group L. Significant differences were found between Group H and M (p < 0.05), Group H and L (p < 0.001), and Group M and L (p < 0.01). ConclusionThe outcomes of this study reveal that there are strong correlations between the data quality of digital impressions and surface topography of prepared teeth. Therefore, the utilization of STL files in high resolution format is the recommended choice for clinicians engaging in a digital workflow process.

Effects of build orientation on adaptation of casting patterns for three-unit partial fixed dental prostheses fabricated by using digital light projection

Statement of problemThe lost-wax technique is commonly used for fabricating partial fixed dental prostheses. The casting patterns can be fabricated by using vat photopolymerization (a type of additive manufacturing), but the adaptation of these casting patterns has not been elucidated. PurposeThe purpose of this in vitro study was to evaluate the effect of build orientation on the adaptation of casting patterns fabricated by digital light projection (DLP). Material and methodsA 3-unit partial fixed dental prosthesis with mandibular left second premolar and second molar abutment teeth was scanned and virtually designed with a computer-aided design software program. The cement space was designed to be 30 μm. Specimens were fabricated with 3 build orientations: 0 degrees (with the occlusal surface parallel to the platform), 30 degrees, and 45 degrees (by rotating the file along the long axis). The casting patterns were fabricated by using DLP (Cara Print 4.0) with a photopolymerizable monomer (dima Print Cast Q). Photopolymerization, cleaning, and postpolymerization processes were performed according to the manufacturer’s instructions. The adaptation of the specimens was examined by using a silicone replica method. The vertical marginal discrepancy and axial wall, occlusal, and marginal gaps were measured by using a digital measuring microscope. The effect of build orientation at each cross-sectional area was statistically analyzed by using the Kruskal-Wallis test followed by the pairwise Wilcoxon rank sum test with Bonferroni correction (α=.05). ResultsExcess polymerized resin was observed along the intaglio buccal wall at build orientations of 30 degrees and 45 degrees. Vertical marginal discrepancies in the buccolingual section ranged from −50 to 248 μm, while those in the mesiodistal section ranged from −25 to 182 μm. The gaps in the buccolingual section ranged from 0 to 236 μm, while those in the mesiodistal section ranged from 0 to 177 μm. According to the observation of vertical marginal discrepancies and gaps, the 30-degree specimens inclined during insertion, and the 45-degree specimens were not completely seated. However, the marginal gaps of the 0- and 30-degree specimens were within the clinically acceptable limit of 120 μm. ConclusionsThe limited data indicated that the build orientation influenced the adaptation of casting patterns for 3-unit partial fixed dental prostheses fabricated by using DLP. A build orientation of 0 degrees is recommended for fabricating casting patterns for 3-unit partial fixed dental prostheses because no excess polymerization of the intaglio buccal wall was observed.

Effect of layer thickness on the flexural strength of multiple-unit laser-sintered metal frameworks

Statement of problemLaser sintering devices have been increasingly used to fabricate the metal frameworks of metal–ceramic restorations. In the fabrication process, the sintering layer thickness is an important parameter; however, information on how it may affect the flexural strength of metal frameworks remains limited. PurposeThe purpose of this in vitro study was to evaluate the flexural strength of 3-unit and 4-unit cobalt-chromium (Co-Cr) metal frameworks laser sintered with 20-μm, 30-μm, and 40-μm layer thicknesses. Material and methodsThree-unit and 4-unit master metal die models with premolar and molar abutments were prepared through direct metal laser sintering (DMLS). A total of 40 metal frameworks (n=10 for each metal die model) were fabricated by the lost-wax technique (group C, served as the control group) and through DMLS with 20-μm, 30-μm, and 40-μm layer thickness (experimental groups LS20, LS30, and LS40, respectively). Each metal framework was cemented to a master die with a polyvinyl siloxane impression material and then subjected to a 3-point bend test at a crosshead speed of 1 mm/min. The yield force of each metal framework was used to calculate the flexural strength. Data were statistically analyzed by using 1-way ANOVA followed by a Tukey honestly significant difference (HSD) test and an independent-samples t test (α=.05) The microstructure of the fracture surface was evaluated by scanning electron microscopy. ResultsGroup C reported the lowest mean flexural strength (P<.05), whereas group LS20 reported the highest mean flexural strength, although no significant difference (P>.05) in flexural strength was observed among the DMLS groups. The 3-unit metal frameworks exhibited a statistically significant higher mean flexural strength than the 4-unit metal frameworks (P<.05). ConclusionsThe sintering layer thickness did not significantly affect the flexural strength of the laser-sintered metal frameworks. However, the DMLS groups reported a higher mean flexural strength than the cast group.

Managing Tilted Molar Abutment Using a Digitally Fabricated Split-Pontic Fixed Dental Prosthesis—A Case Report

Prosthetic rehabilitation of a missing tooth with tilted abutments is yet an enigmatic and less unconventionally sought-after treatment strategy. Many methods have been previously reviewed over the years. This clinical report aims to integrate the principles of the segmented fixed dental prosthesis into a digital workflow. It elucidates the rehabilitation using a split-pontic design that mitigates the issue of developing a common path of insertion without much compromise to the tooth preparation to derive parallel prepared walls. This prosthetic design rather incorporates a common path of insertion into the pontic in the form of a key-keyway non-rigid connector design.

Dimensional accuracy and clinical adaptation of ceramic crowns fabricated with the stereolithography technique

Statement of problemThe stereolithography technique has been a promising method of fabricating fracture-resistant ceramic restorations efficiently. However, studies on the dimensional accuracy and clinical adaptation of ceramic crowns fabricated with the technique are lacking. PurposeThe purpose of this in vitro study was to evaluate the dimensional accuracy and clinical adaptation of ceramic crowns fabricated with the stereolithography technique. Material and methodsA typodont maxillary right first molar abutment tooth was scanned by using an extraoral scanner, and a crown was designed by using 3Shape Dental System CAD software. Ten ceramic crowns were fabricated with 2 different stereolithography systems, CeraFab7500 (CF) alumina and CSL150 (CL) zirconia, and a conventional computer-aided design and computer-aided manufacturing system, X-MILL500 (XM) zirconia. The crowns were scanned, and the digital casts were exported. Dimensional accuracy was measured by superimposing the digital casts with the reference model by using Geomagic Qualify software. The silicone replica method was applied to measure clinical adaptation. Results were statistically analyzed by using a 1-way analysis of variance (α=.05). ResultsCeraFab7500 reported better dimensional accuracy (41 ±11 μm) than CSL150 (65 ±6 μm) or X-MILL500 (72 ±13 μm) (P<.001). No significant difference was found between the CSL150 and X-MILL500 groups (P>.05). X-MILL500 reported significantly better adaptation in the marginal, corner, and occlusal areas but inferior adaptation in the axial area compared with CeraFab7500 and CSL150 (P<.05). Significant differences were only apparent in the axial and occlusal areas between CeraFab7500 and CSL150 (P<.05). No significant difference was found in the marginal or corner area between CeraFab7500 and CSL150 (P>.05). ConclusionsBoth CeraFab7500 and CSL150 can fabricate ceramic crowns with high dimensional accuracy and marginal adaptation within clinically acceptable limits. The results indicate that the fabrication of ceramic crowns by using the stereolithography technique seems to be promising.

The Influence of Split Pontic Designs on The Fracture Resistance Of CAD/CAM Fabricated Monolithic Zirconia FDPs Under Simulating Aging Conditions

Purpose: The purpose of the study was to evaluate the fracture resistance of CAD/CAM fabricated monolithic zirconia FDPs with differently designed split pontics under simulating ageing conditions. Methods: A total of 21 FDPs with split pontics were constructed over 21 dental epoxy resin casts representing missing mandibular first molar with a second premolar abutment of 0° angulation and a tilted second molar abutment of 25° angulation. The FDPs were divided into three groups (n=7) according to the split pontic design; Group (K): Keyhole, Group (B): Bone, Group (R): Relief cut. The cemented FDPs were subjected to thermocycling and mechanical loading in a chewing simulator equivalent to one-year clinical service. Fracture resistance of aged specimens was measured by a universal testing machine and followed by fracture mode detection by scanning electron microscope. One-way ANOVA and Bonferroni post-hoc tests were utilized to compare among groups. The significance level was set at P ≤ 0.05. Results: There was a statistically significant difference among groups (P-value <0.001, Effect size =0.852). Pair-wise comparisons among the groups revealed that group (K) showed the statistically significantly highest mean fracture resistance (2148.6 ± 193 N), and followed by group (R) (1605.4 ± 286.2 N). While group (B) showed statistically significantly lowest mean fracture resistance (1027.6 ± 91.8 N). Conclusions: The tested different split pontic designs of monolithic zirconia FDPs for tilted molar abutments demonstrated clinically acceptable fracture load values.

Chairside fabrication of provisional crowns on FDM 3D-printed PVA model

PurposeThe purpose of this study was to evaluate the dimensional accuracy of crowns fabricated using a polyvinyl alcohol (PVA) dental model. MethodsAn intraoral scanner (LAVA TDS) was used to scan a prepared molar abutment as a master model. The STL file obtained from the scanning process was transferred into the FDM 3D printer (Value 3D Magix MF-1000) and then models were fabricated with PVA filament. In order to compare with the conventional method, an impression of the master model was taken using silicone impression material to fabricate the conventional stone cast model (Conv). An indirect resin composite (Gradia) and self-cured acrylic resin (Curergrace) were used to fabricate crowns (n = 20) according to the manufacturer's instructions. Surface accuracy of the Conv and PVA models and internal accuracy of the crowns set on the models were measured using two methods; 3D digital analysis and silicon-fitting evaluation. Statistical analysis of the results was done using t-test and Willcoxon signed rank test with Bonferroni correction at 5% significance. ResultsDigital analysis showed the Root Mean Square (RMS) value of PVA model surface was higher than that of Conv, while there was no significant difference between the two crown materials. However, the silicon-fitting analysis showed marginal discrepancy of crowns fabricated on PVA model were within 100 µm. Conclusion3D printed PVA model can be used for chairside crown fabrication with an acceptable accuracy.

Evaluation of marginal discrepancy in metal frameworks fabricated by sintering-based computer-aided manufacturing methods.

PURPOSEThe aim of this in vitro study was to evaluate the effect of sintering procedures on marginal discrepancies of fixed partial metal frameworks fabricated using different sintering-based computer-aided design and computer/aided manufacturing (CAD/CAM) techniques.MATERIALS AND METHODSForty resin die models of prepared premolar and molar abutment teeth were fabricated using a three-dimensional (3D) printer and divided into four groups (n = 10) according to the fabrication method of metal frameworks used: HM (via hard milling), SM (via soft metal milling), L25 (via direct metal laser melting [DMLM] with a 25 µm layer thickness), and L50 (via direct DMLM with a 50 µm layer thickness). After the metal frameworks were fabricated and cemented, five vertical marginal discrepancy measurements were recorded in each site (i.e., buccal, facing the pontic, lingual, and facing away from the pontic) of both abutment teeth under a stereomicroscope (×40). Data were statistically analyzed at a significance level of 0.05.RESULTSNo statistically significant differences (P>.05) were found among the four axial sites of metal frameworks fabricated by sintering-based CAD/CAM techniques. The HM and L25 groups showed significantly (P<.001) lower marginal discrepancy values than the SM and L50 groups.CONCLUSIONMarginal discrepancy in the sites facing the pontic was not influenced by the type of sintering procedure. All fabrication methods exhibited clinically acceptable results in terms of marginal discrepancies.

Influence of margin location and luting material on the amount of undetected cement excess on CAD/CAM implant abutments and cement-retained zirconia crowns: an in-vitro study

BackgroundThe flexibility in designing the submucosal part of CAD/CAM customized implant abutments and the individual positioning of its shoulder line has been suggested to reduce the risk of leaving undetected cement residues, thus preventing adverse effects on peri-implant tissues. A high correlation between excess cement left in the soft tissues and the occurrence of increased biofilm accumulation with sulcular bleeding and/ or suppuration has been reported. This in turn may cause peri-implant inflammation and peri-implant marginal bone loss. The aim of this study was to assess the frequency of cement remnants after the luting of zirconia crowns on CAD/CAM custom molar abutments with different margin levels and to evaluate the impact of the luting material.Material and methodsA total of 20 titanium molar CAD/CAM implant abutments (BEGO Medical GmbH) with internal taper connection/ internal hex anti-rotation protection, and a convex emergence profile with different margin positions (0, 1, 2 and 3 mm below the mucosa), were virtually designed (Implant Studio, 3Shape) and manufactured. A master cast was scanned, duplicated by a 3D printer and individual gingival masks were produced to simulate peri-implant soft tissues. 20 corresponding zirconia crowns were designed (Cerec 3D, Dentsply Sirona), produced and cemented to the abutments with two different luting materials; a zinc oxide non-eugenol cement (Temp Bond NE) or a methacrylate cement (Panavia V5). To ensure retrievability of the crown/abutment connection, occlusal openings providing access to the abutment screws were designed. Excess cement was thoroughly removed and the crown/abutment units were unscrewed to evaluate the occurrence of cement residues. All the quadrants of each specimen were evaluated for calculation of the ratio between the cement remnant area and the total specimen area using Adobe Photoshop. Spearman analysis was performed to detect correlations between different variables. A two-sided t-test, ANOVA, Mann–Whitney, and Kruskal–Wallis tests were applied to detect differences between the groups.ResultsCement remnants were found in every depth of the crown abutment complex and in almost every area investigated. The amount of cement residues increased as the crown-abutment margin was located more submucosally. Lingual areas were more prone to cement remnants than other surface areas (p = 0.0291). Excess cement was not only found at the margins of the crown-abutment complex, but also underneath (basal) the abutment itself, where cleaning was impossible. No statistical difference in the effect of zinc oxide non-eugenol- and methacrylate cement on the frequency of excess material at the lateral abutment surfaces could be demonstrated in vitro. The proportion of basal abutment aspects covered with cement residues was, however, significantly smaller in Panavia V5 samples with an average of 4.9 ± 3.7% compared to Temp Bond samples with an average of 8.6 ± 5.5%.ConclusionsGiven the results obtained in the present investigation the margin of CAD/CAM molar abutments should be located as coronally as possible to minimize the amount of cement remnants. If an epigingival or supragingival margin location is not feasible due to esthetic concerns, it cannot be recommended to place the margin of molar CAD/CAM abutments deeper than 1.5 mm in the proximal and oral regions.

Zirconium Oxide Three-Unit Fixed Partial Denture Frameworks Supported by Dental Implants in Acceptable and Reduced Interocclusal Space Possibilities: Pilot In Vitro Fracture Strength and Fractographic Analyses.

This study investigated the effect of fracture strength and fracture mode characteristics related to reduced interocclusal space on computer-aided design/computer-aided manufacturing (CAD/CAM). ZrO2 fixed partial denture (FPD) frameworks subjected to quasi-static loads. First, two dental implants (4 × 10 mm) were positioned simulating a three-unit FPD (second premolar and second molar abutments). The implants were distributed into two groups: control group (n = 10), positioned at the same level; and the test group (n = 10), where the interocclusal space corresponding to the second molar was reduced by 3 mm in relation to the second premolar to simulate a clinical situation. After FPD wax-up (25-mm long; connector height = 5 mm; connector width = 3 mm, proximal and lingual collar reinforcement), casting was made in a Co-Cr alloy to serve as a prototype. Upon scanning, screw-retained CAD/CAM ZrO2 FPDs were fabricated for each group. Then, FPDs were subjected to quasi-static axial loading until fracture in the mid-occlusal pontic area using a universal testing machine at the crosshead speed of 0.5 mm/min. Next, the samples were analyzed by scanning electronic microscopy (SEM) to describe the fracture characteristics. The mean fracture strength values for the control group (1,747.4 ± 122.3 N) and test group (1,817.7 ± 158.9 N) showed no significant difference (Student t test, P < .124). The SEM images of the fracture sites revealed two cleavage areas in the test group, providing representative sites with increased fracture energy storage in this group compared with the control group. Within the limitations of this study, the results showed that reduced interocclusal space and reduced length did not decrease the fracture strength of the ZrO2 FPD frameworks.

Effect of layer thickness on the marginal and internal adaptation of laser-sintered metal frameworks

Statement of problemLaser sintering is commonly used for fabricating metal-ceramic restorations. The layer thickness of the sintering process may affect restoration adaptation. However, limited information is available regarding its impact. PurposeThe purpose of this in vitro study was to compare the marginal and internal adaptation of laser-sintered cobalt-chromium single crown frameworks sintered with layer thicknesses of 25 and 50 μm. Material and methodsThirty resin dies that represented prepared single molar abutment teeth were prepared by using a 3-dimensional printer and were divided into 3 groups (n=10) according to the method used for fabricating metal frameworks: group C, metal frameworks fabricated by using the lost-wax method (control); group L25, metal frameworks fabricated by using direct metal laser melting with a layer thickness of 25 μm; and group L50, metal frameworks fabricated by using direct metal laser melting with a layer thickness of 50 μm. After fabricating the metal frameworks, 15 vertical marginal discrepancy measurements were made in each axial region (mesial, distal, buccal, and lingual) using a stereomicroscope. Next, all the specimens were sectioned from the midline, and 5 internal discrepancy measurements were made in each internal region (inner marginal, axial, and occlusal). The data were analyzed statistically by using 1-way ANOVA, the Tukey honestly significant difference, and Tamhane T2 tests (α=.05). ResultsThe highest marginal and internal discrepancy values were obtained for metal frameworks in group C, and these values were significantly different (P<.001) from those obtained for metal frameworks in the other 2 groups. No significant difference was observed in the marginal and internal discrepancy values of metal frameworks in groups L25 and L50. ConclusionsThese results indicate that layer thickness does not affect the adaptation of laser-sintered metal frameworks, yet both sintering parameters yielded significantly lower mean marginal discrepancy values than the cast group.