Intaglio Surface Research Articles

In vitro evaluation of shape-memory hydrogels for removable dental prostheses and optimization of phase-transition temperature for intraoral use

Removable dental prostheses require periodic relining with the loss of intaglio surface fit because of mucosal shape changes over time. Therefore, a new material with high adaptability to tissue changes over time would be beneficial. This study focused on a shape-memory gel (SMG) that softens when heated, retains its shape when cooled, and returns to its original shape when reheated. The purpose was to optimize SMG for intraoral use by controlling the ratio of 2 acrylate monomers and to evaluate the changes in the shape memory and physical properties of SMG with temperature and to evaluate biocompatibility. SMG specimens were synthesized using the following mixing ratios of 2 monomers, docosyl acrylate (DA) and stearyl acrylate (SA): 0:100, 25:75, 50:50, 75:25, and 100:0. SMG specimens were photopolymerized using a fluorescent light-polymerizing unit. To evaluate shape memory as a function of temperature, permanent deformation was measured based on the standardized compression set test for thermoplastic rubber. For evaluation of the physical properties and cytotoxicity, a 3-dimensionally printed denture base material was used as the control material. All assessments were compared between the groups by using 1-way analysis of variance followed by the Tukey-Kramer multiple comparison test (α=.05). SMGs with a higher amount of DA maintained their compressed shape at room and intraoral temperatures. However, the SMG matrices softened and recovered their original shapes above 60°C. SMGs showed Shore A hardness equivalent to that of the denture-base polymer material at intraoral temperatures because of the high phase-transition temperature. The low water solubility of SMGs supported the biocompatibility test results. SMG, in which the phase-transition temperature was controlled by mixing acrylate monomers with different melting points, exhibited shape memory in the intraoral environment. The results indicate the feasibility of applying SMG for the fabrication of removable dental prostheses because of its high adaptability to tissue changes over time and biocompatibility.

Oral Health-Related Quality of Life among Complete Denture Stomatitis Patients Treated with Methylene-Blue-Mediated Photodynamic Therapy

Aim: The aim was to assess the effect of antimicrobial photodynamic therapy (a-PDT) on the oral health-related quality of life (OHRQoL) of denture stomatitis patients. Methods: Forty patients were randomly selected to participate. Candidal proliferation was confirmed by using a CHROMagar culture and Gram staining. The denture surface and palatal mucosa were sprayed with a methylene blue photosensitizer prior to the photobiomodulation application. Laser therapy was applied two times a week at 72 h intervals for a period of 8 weeks. The OHIP-EDENT questionnaire was used to analyze the improvement in the OHRQoL. A Wilcoxon test was used to perform the candidal colony-forming unit’s count and comparison. A t-test was applied to evaluate the OHRQoL responses. Results: The overall CFU/mL values were higher in the dentures of the patients compared to a palatal mucosa swab. For instance, the CFU count was reduced from 5.56 ± 2.15 (baseline) to 3.17 ± 2.77 CFU/mL on day 60 on the palates. Similarly, the a-PDT application on the intaglio surface of the denture showed a reduction from 38.83 ± 14.71 to 29.05 ± 15.52 CFU/mL. A significant difference (p < 0.05) was found in function improvement as well as a reduction in physical pain, psychological discomfort, physical disability, and social interaction among the participants after photobiomodulation treatment. Conclusions: The OHRQoL was significantly improved in the DS patients. The Candida albicans abundance was radically reduced after the a-PDT application.

Biofilm accumulation on complete arch subperiosteal implant-supported prostheses: Effect of pontic type

Statement of problemComplete arch subperiosteal implant-supported prostheses present challenges in terms of effective cleaning, leading to the accumulation of biofilm on their intaglio surfaces. The association between different intaglio surface morphologies and biofilm accumulation on complete arch subperiosteal implant-supported prostheses is unclear. PurposeThe purpose of this in vitro study was to investigate the correlation between the intaglio surface of complete arch subperiosteal implant-supported prostheses and biofilm accumulation. Material and methodsSixty-eight complete arch subperiosteal implant-supported prostheses were fabricated with varying interimplant distances and pontic morphologies. Four different types of pontic morphologies were included: saddle, flat, scalloped, and ovate. To simulate biofilm accumulation, a green aerosol was sprayed onto the intaglio surface. Dental floss was used to clean the colored spray from the intaglio surface. The intaglio surfaces of prostheses were then scanned with an intraoral scanner. The biofilm areas were identified and calculated by using a 3-dimensional macroscopical quantification method. The distances between adjacent implants and transmucosal height were measured. The correlation between interimplant distances and biofilm areas, and the correlation between the biofilm areas and transmucosal height, were analyzed using the Spearman test. Furthermore, a generalized estimating equation (GEE) was employed to examine the relationship between pontic morphology and biofilm area, adjusting for location, cantilever, implant distance, and transmucosal height (α=.05). ResultsA significant correlation was found between the biofilm area and transmucosal height (correlation coefficient=0.208, P<.001). A significant increase in biofilm accumulation was observed in the saddle group compared with the 3 groups in GEE Models I and II. ConclusionsFlat pontics and ovate pontics have significantly lower biofilm retention. Moreover, transmucosal height plays a significant role in biofilm accumulation in the pontic area.

Ultrathin Feldspathic Ceramic Veneers: A Pilot SEM Evaluation of Etched Intaglio Surfaces.

Ultrathin ceramic veneers are a viable therapeutic option to manage esthetic challenges in the anterior zone. Proper conditioning of the intaglio surface of porcelain veneers is essential to achieve an adequate bonding. In clinical practice, this is typically done with chemical etching using an acid-containing agent, such as hydrofluoric acid. While it is well established that the etching effect is dependent on etching time and the acid concentration, little is known about the impact of etching time and the veneer fabrication method. The purpose of this pilot study was to evaluate, using scanning electron microscopy (SEM), the effect that different etching-time protocols have on the intaglio surface characteristics of ultrathin ceramic veneers fabricated with either the platinum foil technique or the refractory die technique. Several replicas of an ultrathin feldspathic ceramic veneer for a maxillary central incisor were fabricated. Individual specimens were processed according to different intaglio surface-etching protocols: no etching, etching for 90 seconds, etching for 120 seconds, and etching for 150 seconds (9.6% hydrofluoric acid used for all etching groups). It was observed that the 120-second etching protocol resulted in a favorable microroughness surface pattern in the platinum foil group. This pattern was comparable to that obtained by etching for 90 seconds with hydrofluoric acid the intaglio surface of veneers fabricated with the refractory die technique. Increasing the etching time to 150 seconds did not result in a more favorable roughness pattern.

Comparative in-vivo bond failure rate of orthodontic brackets when bracket base is treated with micro-abrasive blasting vs. acid etching: eighteen month randomized control trial and scanning electron microscope study.

The aim of this study was threefold. Firstly, it aimed to introduce and detail a novel method for chemically etching the bases of stainless-steel orthodontic brackets. Secondly, the study sought to investigate the structural alterations within the brackets' microstructure following chemical etching compared to those with sandblasted bases, using electron microscopy analysis. Lastly, the study aimed to evaluate and compare the long-term durability and survivability of orthodontic brackets with chemically etched bases versus those with sandblasted bases, both bonded using the conventional acid etch technique with Transbond XT adhesive, over an 18-month follow-up period. The study was a randomized clinical control trial with triple blinding and split-mouth study design and consisted of two groups. The brackets in the sandblasted group were prepared by sandblasting the intaglio surface of the base of the bracket with 50 µm SiO2 particles. Hydrofluoric acid was used to roughen the base in the acid-etched group. The bases of the brackets were viewed under an electron microscope to analyze the topographical changes. A total of 5,803 brackets (3,006 acid-etch, 2,797 sandblasted) in 310 patients were bonded, in a split-mouth design by the same operator. The patients were followed for 18 months. The failure rate of 2.59% and 2.7% was noted in an acid-etched and sandblasted group, respectively. There was a close approximation of curves in the Kaplan-Meier plot, and the survival distribution of the two groups in the log-rank (Mantel-Cox) test was insignificant; x2 = 0.062 (P value = 0.804). Acid etching if the bases of the brackets can be used as an alternative to sandblasting furthermore acid etching can be performed on the chair side.

Anti-biofilm effectiveness of protocols for cleaning complete dentures in hospitalized patients: a randomized controlled trial.

Denture biofilm acts as a potential reservoir for respiratory pathogens, considerably increasing the risk of lung infections, specifically aspiration pneumonia, mainly 48h after hospital admission. The establishment of a straightforward, affordable, and applicable hygiene protocol in a hospital environment for the effective control of denture biofilm can be particularly useful to prevent respiratory infections or reduce the course of established lung disease. To evaluate the anti-biofilm effectiveness of denture cleaning protocols in hospitalized patients. The maxillary complete dentures (MCDs) of 340 hospitalized participants were randomly cleaned once using one of the following 17 protocols (n=20): brushing with distilled water, toothpaste, or neutral liquid soap (controls); immersion in chemical solutions (1% sodium hypochlorite, alkaline peroxide, 0.12% or 2% chlorhexidine digluconate), or microwave irradiation (650 W for 3 min) combined or not with brushing. Before and after the application of the protocols, the biofilm of the intaglio surface of the MCDs was evaluated using two methods: denture biofilm coverage area (%) and microbiological quantitative cultures on blood agar and Sabouraud Dextrose Agar (CFU/mL). Data were subjected to the Wilcoxon and Kruskal-Wallis tests (α=0.05). All 17 protocols significantly reduced the percentage area of denture biofilm and microbial and fungal load (P<0.05). The highest percentage reductions in the area of denture biofilm were observed for 1% hypochlorite solution with or without brushing and for 2% chlorhexidine solution and microwave irradiation only in association with brushing (P<0.05). The greatest reductions in microbial and fungal load were found for the groups that used solutions of 2% chlorhexidine and 1% hypochlorite and microwave irradiation, regardless of the association with brushing (P<0.05). A single immersion for 10 min in 1% sodium hypochlorite, even in the absence of brushing, proved to be a straightforward, rapid, low-cost, and effective protocol for cleaning the dentures of hospitalized patients.

Secondary Healing of Palatal Fistula by Simple Palatal Plate Obturator after Excision of Pleomorphic AdenomaA Case Report

Pleomorphic adenomas are the most common benign mixed tumours of the salivary glands. They typically occur at the junction between the hard and soft palate, but can also be found in the upper lip, buccal mucosa, floor of the mouth, tonsils, pharynx, and retromolartrigone. The present case of a 55-year-old woman focuses on the use of a palatal plate obturator to treat a soft palatal fistula that developed after the removal of a pleomorphic adenoma from the palate. By applying a self-cure resin to the posterior border of the palatal plate obturator, the postoperative issue of a palatal fistula was successfully managed. To aid in the healing of the palatal tissue and provide a scaffold for the regeneration of the surrounding palatal tissue, relief was applied to the intaglio surface of the palatal plate.

Clinical management of vital and non-vital discolored tooth preparation stump shades: A clinical case series.

Traditional and modern-day laboratory techniques can be used to mask vital and non-vital discolored teeth. Two clinical case reports are presented showing different treatment approaches to differing clinical scenarios of partial coverage veneer and full coverage crown restorations, respectively. Feldspathic ceramics should be considered when customization of stump shade correction and equalization is required with minimum facial reduction with veneer restorations. Translucent zirconia (5 mol% Y2 O3 ) can be used to mask metal posts and core restorations on non-vital teeth using an opaquer material that is infused into the intaglio surface in the green state. Different clinical scenarios will present to the clinician in regard to discolored stump shades where understanding what laboratory material treatment options are available that will help guide definitive restoration types and ultimately tooth preparation design.

Accuracy of digital duplication scanning methods for complete dentures.

To compare the accuracy of four digital scanning methods in duplicating a complete denture. Four scanning methods were used: cone beam computed tomography (CBCT), Straumann desktop scanner (DS), Trios intraoral scanner (TIO), and Virtuo Vivo intraoral scanner (VVIO). Each method was used to duplicate all the surfaces of a printed complete denture. The denture was scanned 10 times in each group. The trueness (in root mean square, RMS) and precision (in standard deviation, SD) were calculated by comparing the combined dentition, denture extension, and intaglio surfaces with the reference file. One-way analysis of variance and F-tests were used to test statistical differences (α = 0.05). For the scanning accuracy of the whole denture, CBCT showed the highest RMS (0.249±0.020mm) and lowest trueness than DS (0.124±0.014mm p<0.001), TIO (0.131±0.006mm p<0.001), and VVIO (0.227±0.020mm p=0.017), while DS and TIO showed smaller RMS than VVIO (p<0.001). For the trueness of dentition, denture extension, and intaglio surfaces, CBCT also showed the highest mean RMS and lowest trueness among all groups (p<0.001). DS and TIO had smaller mean RMS and higher trueness among all groups in all surfaces (p<0.001, except VVIO in intaglio surface, p>0.05). TIO had significantly lower within-group variability of RMS and highest precision compared to DS (p = 0.013), CBCT (p = 0.001), and VVIO (p<0.001) in the combined surface. For dentition and denture extension surfaces, TIO showed similar within-group variability of RMS with the DS group (p>0.05) and lower than CBCT and VVIO (p<0.001). The 7 Series desktop scanner and Trios 4 intraoral scanner can duplicate dentures in higher trueness than CBCT and the Virtuo Vivo intraoral scanner. The Trios 4 intraoral scanner was more precise in the combined surfaces than other scanning methods, while the 7 Series desktop scanner and Trios 4 intraoral scanner were more precise in the denture extension surface.

Long-term clinical outcome of three-unit fixed-fixed posterior zirconia ceramic inlay-retained FDPs with a modified design

ObjectivesTo assess the long-term clinical outcome of posterior inlay-retained fixed dental prostheses (IRFDPs) with a modified design made from zirconia ceramic. MethodsIn 30 patients thirty 3-unit IRFDPs were placed to replace 7 premolars (4 in the maxilla, 3 in the mandible), and 23 first molars (15 in the maxilla, 8 in the mandible). Preparations were accomplished in agreement with the general principles for ceramic inlay restorations and modified with a short retainer-wing bevel preparation within the enamel at the buccal and oral sides. The frameworks were milled from 3Y-TZP ceramic, and the pontics were veneered with feldspathic ceramic. All IRFDPs were bonded with a phosphate monomer containing luting resin after air-abrasion of the intaglio surfaces. The patients were recalled 6–12 months after placement, and then annually. Kaplan-Meier analysis was used to calculate the survival and complication rates of the IRFDPs. ResultsThe mean observation time was 10.6 ± 1.5 years. The 10-year cumulative survival rate was 89% with 4 failures, two of them were due to deep secondary caries with loss of retention, one due to repeated debonding with enamel fractures, and one due to generalized progressive periodontitis. The most common complication was chipping of the veneering ceramic (20.1%). Eighteen IRFDPs were free of any type of complication up to 15.4 years, which corresponds to a 10-year cumulative success rate of 70.4%. ConclusionThe long-term clinical performance of modified IRFDPs made of veneered zirconia ceramics was favorable after 10 years, therefore, they represent a treatment alternative to replace posterior single missing teeth. Clinical significanceZirconia-based IRFDPs fabricated in the modified design may represent a substance-preserving alternative to conventional posterior FDPs to replace posterior single missing teeth, particularly in cases where implants cannot be placed, and when the adjacent teeth already have small restorations or defects.

Er:YAG laser debonding of zirconia and lithium disilicate restorations

Yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) restorations of different formulations are being used increasingly in monolithic form for a range of clinical applications. Using rotary instruments to remove such restorations for any purpose is challenging, but they can be removed conservatively with erbium lasers. However, studies on how a laser penetrates different zirconias to break the cement bond between the tooth surface and the zirconia are lacking. The purpose of this in vitro study was to evaluate and compare the time required for an erbium-doped yttrium-aluminum-garnet (Er:YAG) laser to remove different types of zirconia and lithium disilicate crowns. Forty extracted premolar teeth were prepared, scanned, designed, and milled to fabricate 40 computer-aided design and computer-aided manufacturing (CAD-CAM) crowns, which were assigned to 4 groups (n=10): 3mol% Y-TZP, 4mol% Y-TZP, 5mol% Y-TZP, and lithium disilicate as a control. All crowns were bonded to the teeth with a self-adhesive resin cement (Panavia SA Cement Universal). Each specimen was irradiated with an Er:YAG laser with the following parameters: 300mJ, 15Hz, 5.0W, and a 50-microsecond pulse duration (supershort pulse mode). The irradiation time required for crowns to be retrieved successfully was recorded for each specimen. Data were statistically analyzed using analysis of variance and the Tukey honestly significant difference post hoc test (α=.05). The intaglio surfaces of the restorations were analyzed using scanning electron microscopy (SEM). The mean ±standard deviation times in minutes needed for crown debonding were 12.46 ±4.17 for the 3mol% Y-TZP group, 10.30 ±3.33 for the 4mol% Y-TZP group, 4.03 ±1.62 for the 5mol% Y-TZP group, and 2.08 ±0.92 for the lithium disilicate group. A statistically significant difference (P<.05) in the debonding time was found for all investigated groups, expect between the 3mol% and 4mol% Y-TZP groups and between the 5mol% Y-TZP and lithium disilicate groups. SEM analysis of the ceramic surfaces showed no visual damage associated with Er:YAG laser irradiation. Zirconia crown retrieval time with the Er:YAG laser was influenced by the yttria content of the zirconia, with decreasing retrieval time with increasing yttria content. Er:YAG laser debonding of zirconia crowns is a noninvasive, efficient, and rapid approach to the removal of crowns and could be applied in clinical practice.

Effect of different surface treatments on the retention force of additively manufactured interim implant-supported crowns.

To compare the effect of different pre-cementation surface treatments and bonding protocols on the retention force of additively manufactured (AM) implant-supported interim crowns. A total of 50 AM interim crowns (Temporary CB resin) were cemented on implant abutments. Five groups (n = 10) were established based on the different surface pre-treatments performed in the intaglio surface of the specimens: no surface pre-treatment (Group C or control), air-abraded with 50-μm aluminium oxide particles (Group AP), air-abraded with 50-μm aluminium oxide particles followed by the application of silane (Group AMP), silane (Group MP), and air-abraded with 30μm silica-coated aluminum oxide particles followed by the application of silane (Group CMP). Each specimen was cemented into an implant abutment using a composite resin cement (Rely X Unicem2). Afterward, the specimens underwent retention testing with a Universal Instron machine. Pull-off forces (N) and modes of failure were registered. Statistical analysis was performed using Mann-Whitney U tests with Bonferroni corrections for multiple tests (α = .05). The median retention force values were 233.27 ±79.28 N for Group Control, 398.59 ±68.59 N for Group MP, 303.21 ±116.80 N for Group AMP, 349.31 ±167.73 N for Group CMP, and 219.85 ± 55.88 N for Group AP. The pull-off forces were significantly greater for Group MP, while the differences between the remaining groups were not statistically significant (P>0.05). Group AP showed the lowest retention force values among all the groups. Failure modes after the pull-off testing were predominantly adhesive and substrate failure of the AM interim material. The surface treatment of the intaglio AM crown tested significantly influenced the retention force values measured. Pre-treatment with an MDP-containing silane improved the retentive force values computed, whereas pre-treatment with 50-μm Al2 O3 air-particle abrasion alone is not recommended prior to cementation on a titanium-based implant abutment. This article is protected by copyright. All rights reserved.

Comparison of retention of monolithic zirconia crowns with alumina airborne-particle abraded and nonabraded intaglio using three different cements: A clinical simulation

The necessity of roughening the intaglio surface of zirconia crowns to achieve adequate retention is unclear. The purpose of this clinical simulation study was to evaluate the retention of airborne-particle-abraded and nonabraded monolithic zirconia crowns using 3 different cement types. Extracted human molars were used and prepared with a 10-degree taper. Impressions were made of the prepared teeth with a polyvinyl siloxane (PVS) material, and dies were made with Type 4 gypsum. Each die was scanned with a NobelProcera 1G Scanner, and the standard tessellation language (STL) files were transferred electronically to the Nobel Biocare production site, where a bar was added virtually on top of each crown and parameters were set for milling. Seventy-two Procera zirconia crowns were generated, of which half were airborne-particle abraded on the intaglio surface with 50-µm alumina particles at 400 to 500 kPa for 15 seconds. The other 36 received no intaglio treatment other than cleaning. Both groups of 36 crowns were divided into 3 subgroups of 12 specimens. The area of each preparation was calculated using a computer-aided design software program. The specimens were distributed to attain similar mean surface areas among the cementation groups. The crowns were cemented onto the specimen with a controlled force of 196N. The 3 cements used were self-adhesive, modified resin RelyX Unicem Aplicap, resin-modified glass ionomer RelyX Luting, and a composite resin, Panavia F2.0 with ED Primer A & B. All specimens were thermocycled (5 °C to 55 °C) for 5000 cycles and then removed axially with a universal testing machine (Instron Model 5585H) at a crosshead speed of 0.5mm/min. The removal force was recorded, and stress of dislodgement was calculated for each crown. A 2-way analysis of variance was used for statistical analyses. The type of failure was analyzed with the chi-squared test of association for independent samples (α=.05 for all tests). The mean dislodging force for crowns with airborne-particle abraded intaglio was 5.4MPa, which was statistically greater than the mean of 3.2MPa for nonabraded specimens (P<.001). No significant differences related to the dislodging stresses were detected among the 3 cements (P=.109). The mode of failure was similar whether abraded or not, with 50% of specimens retaining cement in the crown after separation. Alumina airborne-particle abrasion of the intaglio of zirconia to create surface roughness is beneficial in retaining the crowns, regardless of the cement type. The nonabraded crowns demonstrated significantly lower retentive stress with crown removal. The principal mode of failure was similar whether the zirconia intaglio was airborne-particle abraded or not. The most common mode of failure (>50% of specimens) was at least three-fourths of the cement remaining within the crown.

Evaluation of the Influence of Acid Etching Technique on Surface Roughness and Fracture Strength of Heat-Pressed Lithium-disilicate Veneers

Abstract Background Metal-free ceramic veneers exhibit many desirable properties. However, low fracture strength is a major disadvantage. The success of the veneers depends on optimal tooth preparation and intaglio surface preparation techniques for bonding porcelain substrates to the tooth to ensure clinical success. This study was conducted to evaluate the influence of acid etching technique on surface roughness and fracture strength of veneers. Methods The in vitro study was conducted on maxillary central incisors that were prepared to receive the veneers; the specimens were divided into two groups—group A and group B. The intaglio surface of veneer in both groups was etched with 4.6 % of the hydrofluoric acid solution for 30 seconds, in group B specimens were further treated with 33% sodium hypochlorite solution treatment following which the surface roughness was measured and calculated with scanning electron microscope at a magnification of 3000X and profilometer, respectively. The fracture strength of the specimens in both groups was determined by subjecting the tooth with veneer to a universal testing machine; the force was applied until the fracture occurred. Results There was a significant difference observed in the surface roughness, fracture strength, and bond strength of the heat-pressed lithium-disilicate veneers treated solely with hydrofluoric acid and samples treated with hydrofluoric acid and phosphoric acid. Conclusion Optimizing porcelain surfaces before treatment with various adhesives and luting resins requires an understanding of the involved substrates and materials, as well as a logical and systematic methodology in their manipulation. The intaglio surface of the veneers treated with hydrofluoric acid followed with phosphoric acid has no significant difference observed in the properties of the veneers but has better bonding with the tooth structure.

Effect of high-speed sintering on the marginal and internal fit of CAD/CAM-fabricated monolithic zirconia crowns

This study compared the marginal and internal fit of zirconia crowns fabricated using conventional and high-speed induction sintering. A typodont mandibular right first molar was prepared and 60 zirconia crowns were fabricated: 30 crowns using conventional sintering and 30 crowns using high-speed sintering. We presented a new evaluation methodology to measure the marginal and internal fit of restorations through digital scanning, aligning the two datasets, and measuring the distance between two arbitrary point sets of the datasets. For the marginal fit, we calculated the maximum values of the shortest distances between the marginal line of the prepared tooth and that of the crown. The calculated values ranged from 359 to 444 μm, with smaller values for the high-speed sintered crowns (P < 0.05). For the internal fit, we employed mesh sampling and computed the geodesic distances between the prepared tooth surface and the crown intaglio surface. The measured values ranged from 177 to 229 μm with smaller values for the high-speed sintered crowns, but no significant difference was found (P > 0.05). Based on our results, the high-speed sintering method can be considered a promising option for single-visit zirconia treatment in dental practice.

Verification of a digital approach for three-dimensional evaluation of marginal and internal fit

Internal fit is an important aspect of indirect restorations, but methods for the 3-dimensional (3D) measurement of absolute marginal and intaglio fit are sparse. The purpose of this in vitro study was to evaluate an innovative 3D measurement method (AIXFit) based on intraoral scanning data for analyzing the fit of dental restorations. For the evaluation of AIXFit, 12 monolithic zirconia crowns were fabricated on typodont preparations. The fit was measured digitally with the AIXFit system and compared with the results obtained from an established 2-dimensional (2D) sectional procedure. To compare the values of both methods at identical locations, a common reference system was developed, with each die fixed in a gypsum stand with reference points. Using an intraoral scanner (True Definition), each die with its reference points and the intaglio surface of the finished crown were digitalized as standard tessellation language files. The AIXFit software program, with a specially developed best-fit algorithm, was used to match the intaglio surface of the crown with the surface of the preparation. The virtual cement gap was calculated over the entire surface and returned values for x≥0µm. A 2D comparison method involved adhesively fixing the crown to the die and sectioning it into 4 parts with a diamond band saw. The thickness of the cement gap was determined under a light microscope at ×100 magnification at 5 defined measuring points per quarter, so that a total of 240 measurements were available for comparison. A software program (Blender Foundation) was used to superimpose the data from the AIXFit system with the data from the 2D method and to compare the cement gaps at the same locations. The agreement between these methods was verified using paired t tests and determine correlation coefficients (α=.05). The mean ±standard deviation difference between the AIXFit and 2D methods was 6.7 ±29µm). Two 1-sided tests showed statistical equivalence between the methods of measurement when considering an interval between -20 and +20µm. The correlation coefficients showed a positive association for both methods (r=.931). The AIXFit software program appeared to be accurate for the digital measurement of internal fit when using the True Definition scanner. It enabled a cast-free workflow and allowed the analysis of the entire intaglio surface.

Intaglio Surface Adaptation of Removable Partial Denture Framework Fabricated by Various Data Acquisition Techniques and Fabrication Approaches.

The aim of this study was to compare intaglio surface adaptation of the removable partial denture framework among various data acquisition techniques and fabrication approaches using three-dimensional comparison by metrology software. The partial edentulous typodont model with five digital superimposition landmarks was duplicated and scanned for the digital reference model. Three approaches were the conventional lost-wax (group I; LWT, n = 5), intraoral digital impressions combined with PolyJet printing and lost-wax (group II; IP-LWT, n = 5), and extraoral digital impressions combined with PolyJet printing and lost-wax (group III; EP-LWT, n = 5). Each framework was scanned and superimposed with the reference model. The misfits at 53 locations were measured. Data were statistically analyzed by one-way analysis of variance, followed by Tukey's honestly significant difference for pairwise comparisons (p < 0.05). Significant differences were found between three approaches at the reciprocal arm, terminal part of the retentive arm, rest, and major connector (p < 0.05). In the LWT group, the reciprocal arm and palatal vault region of major connector had the lowest misfits, but the highest misfit was found in the midline region (p < 0.001). In the IP-LWT group revealed the most excessive contact at the terminal part of the retentive arm (-0.111 ± 0.038 mm, p = 0.031), with the highest misfit at the rest area (p < 0.001). A difference in adaptation was found in several removable partial denture framework components among three approaches. The LWT group had a better adaptation than other groups. Nevertheless, a clinically acceptable adaptation was seen in all three approaches.

Ultrathin lithium disilicate and translucent zirconia crowns for posterior teeth: Survival and failure modes.

To evaluate the reliability and failure modes of ultrathin (0.5 mm) lithium disilicate, translucent and ultra-translucent zirconia crowns for posterior teeth restorations. Fifty-four mandibular first molar crowns of three ceramic materials: (1) Lithium disilicate (e.max CAD, Ivoclar Vivadent), (2) 3Y-TZP (Zirconn Translucent, Vipi), and (3) 5Y-PSZ (Cercon XT, Dentsply Sirona), with 0.5 mm of thickness were milled and cemented onto composite resin abutments. Eighteen samples of each group were tested under mouth-motion step-stress accelerated life testing in a humid environment using mild, moderate, and aggressive profiles. Data was subjected to Weibull statistics. Use level curves were plotted and reliability was calculated for a given mission of 100,000 cycles at 100, 200, and 300 N. Fractographic analyses of representative samples were performed in scanning electron microscope. Beta (β) values suggest that failures were dictated by material's strength for lithium disilicate and by fatigue damage accumulation for both zirconias. No significant differences were detected in Weibull modulus and characteristic strength among groups. At a given mission of 100,000 cycles at 100 N, lithium disilicate presented higher reliability (98% CB: 95-99) regarding 3Y-TZP and 5Y-PSZ groups (84% CB: 65%-93% and 79% CB: 37&-94%, respectively). At 200 N, lithium disilicate reliability (82% CB: 66%-91%) was higher than 5Y-PSZ (20% CB: 4%-44%) and not significantly different from 3Y-TZP (54% CB: 32%-72%). Furthermore, at 300 N no significant differences in reliability were detected among groups, with a notable reduction in the reliability of all materials. Fractographic analyses showed that crack initiated at the interface between the composite core and the ceramic crowns due to tensile stress generated at the intaglio surface. Ultrathin lithium disilicate crowns demonstrated higher reliability relative to zirconia crowns at functional loads. Lithium disilicate and zirconia crown's reliability decreased significantly for missions at higher loads and similar failure modes were observed regardless of crown material. The indication of 0.5 mm thickness crowns in high-load bearing regions must be carefully evaluated. Ultraconservative lithium disilicate and zirconia crowns of 0.5 mm thickness may be indicated in anterior restorations and pre-molars. Their clinical indication in high-load requirement regions must be carefully evaluated.

Effect of print orientation, storage conditions, and storage time on intaglio surface accuracy of implant surgical guides fabricated by using a stereolithography technology

The accuracy of printed implant surgical guides can be affected by different factors that negatively impact the planned implant position. How print orientation, storage time, and conditions influence manufacturing accuracy remains uncertain. The purpose of this in vitro study was to evaluate the influence of print orientation, storage conditions, and storage time on the intaglio surface accuracy of implant surgical guides manufactured by using a stereolithography (SLA) printer. A tooth-supported maxillary implant surgical guide design (control file) was used to fabricate the specimens (N=40, n=10). Four groups were created based on the print orientation used: 0 (Group 0), 45 (Group 45), 70 (Group 70), and 90 degrees (Group 90). The specimens were fabricated using an SLA printer (Form 3B+) and a biocompatible dental resin (Surgical Guide Resin V1) following the manufacturer's recommended protocol. Each group was divided into 2 subgroups based on the storage conditions: light (L subgroup) and dark (D subgroup) settings. Each specimen was digitized by using a desktop scanner (Medit T710) at days 0, 1, 7, and 14. The control file and each digitized specimen were superimposed by using the best-fit technique with a metrology program (Geomagic Control X). The root mean square (RMS) error was used to calculate the discrepancies between the control files and specimen files. Three-way ANOVA and pairwise comparison Tukey tests were used to analyze trueness. The Levene test was used to assess precision (α=.05). Significant trueness discrepancies were found among the groups tested (P<.001), but no significant differences were found among the subgroups (P=.100) and the storage times analyzed (P=.609). Additionally, the Tukey test showed significant RMS error mean value discrepancies between Group 0 and Group 45 (P<.001), Group 0 and Group 90 (P<.001), Group 45 and Group 70 (P<.001), and Group 70 and Group 90 (P<.001). The Levene test revealed significant SD discrepancies among the groups tested (P<.05). The trueness and precision of the intaglio surface of the implant surgical guides manufactured by using the printer and material tested were affected by the print orientation. However, storage conditions over a 14-day period did not impact the intaglio accuracy of the specimens.

The effect of crowding on the accuracy of 3-dimensional printing

The purpose of this study was to evaluate the accuracy of 3-dimensional (3D) printed aligners compared to conventional vacuum-formed thermoplastic aligners with varying levels of dental crowding. Digital intraoral scans of 10 cases were assigned to their respective groups (n = 10, each, 30 total) as follows: no crowding (control), moderate crowding, and severe crowding. Digital images of these models were created in standard tessellation language (STL) file format using 3Shape software and randomly 3D printed. The STL files of each case were also sent to a dental laboratory to fabricate vacuum-formed samples, the current technology used for manufacturing aligners. The intaglio surfaces of fabricated aligners in both groups were scanned using cone beam computed tomography to create STL files, which were then compared to the original STL files of the cases using Geomagic Control X software. Absolute deviations from the original file and root mean square values were recorded. A Kruskal-Wallis test was conducted to analyze the difference in average deviation, and a t-test was repeated for the RMS measure. The significance level was set at 0.05. The crowding did not affect the trueness of aligners manufactured using 3D printing or conventional vacuum-forming techniques (P = 0.79). 3D-printed aligners showed less deviation than the vacuum-formed samples (0.1125 mm vs 0.1312 mm; P <0.01). Aligners manufactured with the vacuum-forming technique had significantly higher variation than those with the 3D printing process (P = 0.04). 3D aligners printed directly from an STL file exhibited better precision and trueness than those fabricated using the conventional vacuum-forming technique. Since accuracy is defined as a combination of precision and trueness, it is concluded that direct printing from an STL file can be used to manufacture aligners.