Innovative subtractive production of a digital removable complete denture from start to finish: a JPD Digital video presentation.

This JPD Digital video presentation presents the clinical treatment from start to finish in which a dual-shaded bi-coloured monolithic disk was used for the fabrication of an immediate digital complete denture followed by the delivery of a definitive digital complete denture. The treatment plan included extraction of the remaining maxillary and mandibular teeth followed by an esthetic evaluation with digital smile design. The digital definitive complete dentures were milled from a monolithic dual-shaded disk.

Effect of indenter material on reliability of all-ceramic crowns.

OBJECTIVES: Controversy exists about whether the elastic modulus (E) mismatch between the loading indenter and ceramic materials influences fatigue testing results. The research hypotheses were that for porcelain veneered Y-TZP crowns 1) A low modulus Steatite indenter (SB) leads to higher fatigue reliability compared to a high modulus tungsten carbide indenter (WC); 2) Different surface damage patterns are expected between low and high modulus indenters after sliding contact fatigue testing. All ceramic crowns will exhibit similar step-stress accelerated life testing (SSALT) contact fatigue reliability (hypothesis 1) and failure characteristics (hypothesis 2) when using high stiffness tungsten carbide (WC, E = 600 GPa) vs. enamel like steatite (SB, E = 90 GPa) indenters. METHODS: Manufacturer (3M Oral Care) prepared Y-TZP-veneered all-ceramic molar crowns were bonded to aged resin composite reproductions of a standard tooth preparation and subjected to mouth-motion SSALT fatigue (n = 18 per indenter type). Failure was defined either as initial inner cone crack (IC), or final fracture (FF) when porcelain fractured (chipping). Selected IC specimens that did not progress to FF were embedded in epoxy resin and sectioned for fractographic analysis. RESULTS: The distribution of failures across the load and cycle profiles lead to similar calculated Weibull Use Level Probability Plots with overlap of the 2-sided 90% confidence bounds. The calculated reliability for IC and FF was equivalent at a mission of 300 N or 700 N load and 50,000 cycles, although the WC indenter had a trend for lower reliability for IC at 700 N. Both indenters produced similar patterns of wear and cracking on crown surfaces. Fractographic landmarks showed competing failure modes, but sliding contact partial inner cone cracks were the most dominant for both groups. SIGNIFICANCE: The more compliant Steatite indenter had similar veneered crown fatigue reliability and failure modes to those found with use of a high stiffness tungsten carbide indenter (hypotheses 1 and 2 rejected).

CAD/CAM Beyond Intraoral Restorations: Maxillofacial Implant Guide.

With a digital revolution impacting nearly all industries and disciplines, the incorporation of digital technologies into dental offices and laboratories appears to be inevitable. Highlighting the use of computer-aided design/computer-aided manufacturing (CAD/CAM) technology, this case report demonstrates the development of a maxillofacial prosthesis after creation of a 3-dimensional printed surgical guide to enable accurate and predictable implant positioning to enhance overall facial prosthetic retention and comfort for the patient. The management of lost craniofacial hard and soft tissues due to congenital abnormalities, trauma, or, in this case, cancer treatment poses a multifaceted challenge to not only oral and maxillofacial surgeons but also general dentists, prosthodontists, dental laboratory technicians, and other dental and medical professionals. CAD/CAM technology may be viewed beyond its use for teeth reconstructions and intraoral implants and become an important tool for success when implant-supported maxillofacial prosthetic components are needed.

Esthetic planning with a digital tool: A clinical report.

This clinical report describes digital planning and execution using a novel software tool to enhance digital workflow. The proposed treatment, integrated with the face of the patient, was presented before clinical treatment. The patient was rehabilitated with ceramic veneers. The virtual design contributed to a satisfactory and predictable esthetic outcome.

A new classification system for all-ceramic and ceramic-like restorative materials.

Classification systems for all-ceramic materials are useful for communication and educational purposes and warrant continuous revisions and updates to incorporate new materials. This article proposes a classification system for ceramic and ceramic-like restorative materials in an attempt to systematize and include a new class of materials. This new classification system categorizes ceramic restorative materials into three families: (1) glass-matrix ceramics, (2) polycrystalline ceramics, and (3) resin-matrix ceramics. Subfamilies are described in each group along with their composition, allowing for newly developed materials to be placed into the already existing main families. The criteria used to differentiate ceramic materials are based on the phase or phases present in their chemical composition. Thus, an all-ceramic material is classified according to whether a glass-matrix phase is present (glass-matrix ceramics) or absent (polycrystalline ceramics) or whether the material contains an organic matrix highly filled with ceramic particles (resin-matrix ceramics). Also presented are the manufacturers' clinical indications for the different materials and an overview of the different fabrication methods and whether they are used as framework materials or monolithic solutions. Current developments in ceramic materials not yet available to the dental market are discussed.

Reliability and failure modes of two Y-TZP abutment designs.

Fracture strength and accelerated fatigue reliability of two zirconia abutment systems were tested. Thirty-six implants with a Morse taper (MT; n = 18) or cone (C; n = 18) design were restored with metallic crowns. Loads were applied as single load to failure (SLF) or mouth-motion cycles using a step-stress accelerated life testing (SALT) method. SLF mean values were 690 ± 430 N and 209 ± 25 for MT and C groups, respectively. In terms of the SALT results, 8 specimens survived (50,000 cycles) and 7 failed (maximum load 400 N) in the MT group; whereas for the C group all abutments failed before the maximum number of cycles. Failure mode was fracture of the Y-TZP abutments for both groups. Higher reliability for a mission of 50,000 cycles at 175 N for MT versus C designs was determined, and significant differences in fracture modes were observed.

Slow cooling protocol improves fatigue life of zirconia crowns.

OBJECTIVE: To compare the fatigue life and damage modes of zirconia crowns fabricated with and without framework design modification when porcelain veneered using a fast or slow cooling protocol. METHODS: Composite resin replicas of a first molar full crown preparation were fabricated. Zirconia copings were milled as conventional (0.5mm even thickness, Zr-C, n=20,) or modified (lingual margin of 1.0mm thickness, 2.0mm height connected to two proximal struts of 3.5mm height, Zr-M, n=20). These groups were subdivided (n=10 each) according to the veneer cooling protocol employed: fast cooling (Zr-CFast and Zr-MFast) and slow cooling (Zr-CSlow and Zr-MSlow). Crowns were cemented and fatigued for 10(6) cycles in water. The number of cycles to failure was recorded and used to determine the interval databased 2-parameter probability Weibull distribution parameter Beta (ß) and characteristic life value Eta (η). RESULTS: 2-parameter Weibull calculation presented ß=5.53 and ß=4.38 for Zr-MFast and Zr-CFast, respectively. Slow cooled crowns did not fail by completion of 10(6) cycles, thereby Weibayes calculation was applied. Increased fatigue life was observed for slow cooled crowns compared to fast cooled ones. Groups Zr-MFast and Zr-MSlow presented no statistical difference. Porcelain cohesive fractures were mainly observed in fast cooled groups. Slow cooled crowns presented in some instances inner cone cracks not reaching the zirconia/veneer interface. SIGNIFICANCE: Improved fatigue life in tandem with the absence of porcelain fractures were observed in slow cooled crowns, regardless of framework design. Crowns fast cooled chiefly failed by porcelain cohesive fractures.

Influence of abutment-to-fixture design on reliability and failure mode of all-ceramic crown systems.

OBJECTIVE: Evaluate the effect of implant connection designs on reliability and failure modes of screw-retained all-ceramic crowns. METHODS: Central incisor ceramic crowns in zirconia abutments were screwed and torqued down to external hexagon (EH), internal hexagon (IH) and Morse taper (MT) implant systems. Single-load-to-fracture (SLF) test (n=4 per group) determined three step-stress fatigue profiles with specimens assigned in the ratio of 3:2:1. Fatigue test was performed under water at 10 Hz. Use level probability Weibull curves and reliability for missions of 50,000 cycles at 400 N and 200 N were calculated (90% confidence bounds-CB). Weibull probability distribution (90% CB) was plotted (Weibull modulus vs characteristic strength) for comparison between the groups. Fractographic analyses were conducted under polarized-light microscopy and SEM. RESULTS: Use level Weibull probability calculation indicated that failure was not associated with fatigue in groups EH (ß=0.63), IH (ß=0.97) and MT (ß=0.19). Reliability data for a mission of 50,000 cycles at 400 N revealed significant reliability differences between groups EH (97%), IH (46%) and MT (0.5%) but no significant difference at 200 N between EH (100%) and IH (98%), and IH and MT (89%). Weibull strength distribution (figure) revealed ß=13.1/η=561.8 for EH, ß=5.8/η=513.4 for IH and ß=5.3/η=333.2 for MT. Groups EH and IH exhibited veneer cohesive and adhesive failures. Group IH also presented adhesive failure at zirconia/titanium abutment insert while MT showed fracture at abutment neck. SIGNIFICANCE: Although group EH presented higher reliability and characteristic strength followed by IH and MT, all groups withstood reported mean anterior loads.

MicroCT analysis of a retrieved root restored with a bonded fiber-reinforced composite dowel: a pilot study.

PURPOSE: This evaluation aimed to (1) validate micro-computed tomography (microCT) findings using scanning electron microscopy (SEM) imaging, and (2) quantify the volume of voids and the bonded surface area resulting from fiber-reinforced composite (FRC) dowel cementation technique using microCT scanning technology/3D reconstructing software. MATERIALS AND METHODS: A fiberglass dowel was cemented in a condemned maxillary lateral incisor prior to its extraction. A microCT scan was performed of the extracted tooth creating a large volume of data in DICOM format. This set of images was imported to image-processing software to inspect the internal architecture of structures. RESULTS: The outer surface and the spatial relationship of dentin, FRC dowel, cement layer, and voids were reconstructed. Three-dimensional spatial architecture of structures and volumetric analysis revealed that 9.89% of the resin cement was composed of voids and that the bonded area between root dentin and cement was 60.63% larger than that between cement and FRC dowel. CONCLUSIONS: SEM imaging demonstrated the presence of voids similarly observed using microCT technology (aim 1). MicroCT technology was able to nondestructively measure the volume of voids within the cement layer and the bonded surface area at the root/cement/FRC interfaces (aim 2). CLINICAL SIGNIFICANCE: The interfaces at the root dentin/cement/dowel represent a timely and relevant topic where several efforts have been conducted in the past few years to understand their inherent features. MicroCT technology combined with 3D reconstruction allows for not only inspecting the internal arrangement rendered by fiberglass adhesively bonded to root dentin, but also estimating the volume of voids and contacted bond area between the dentin and cement layer.

Mechanical testing of implant-supported anterior crowns with different implant/abutment connections.

PURPOSE: This study evaluated the reliability and failure modes of anterior implants with internal-hexagon (IH), external-hexagon (EH), or Morse taper (MT) implant-abutment interface designs. The postulated hypothesis was that the different implant-abutment connections would result in different reliability and failure modes when subjected to step-stress accelerated life testing (SSALT) in water. MATERIALS AND METHODS: Sixty-three dental implants (4 × 10 mm) were divided into three groups (n = 21 each) according to connection type: EH, IH, or MT. Commercially pure titanium abutments were screwed to the implants, and standardized maxillary central incisor metallic crowns were cemented and subjected to SSALT in water. The probability of failure versus number of cycles (95% two-sided confidence intervals) was calculated and plotted using a power-law relationship for damage accumulation. Reliability for a mission of 50,000 cycles at 150 N (90% two-sided confidence intervals) was calculated. Polarized-light and scanning electron microscopes were used for failure analyses. RESULTS: The beta values (confidence intervals) derived from use-level probability Weibull calculation were 3.34 (2.22 to 5.00), 1.72 (1.14 to 2.58), and 1.05 (0.60 to 1.83) for groups EH, IH, and MT, respectively, indicating that fatigue was an accelerating factor for all groups. Reliability was significantly different between groups: 99% for MT, 96% for IH, and 31% for EH. Failure modes differed; EH presented abutment screw fracture, IH showed abutment screw and implant fractures, and MT displayed abutment and abutment screw bending or fracture. CONCLUSIONS: The postulated hypothesis that different implant-abutment connections to support anterior single-unit replacements would result in different reliability and failure modes when subjected to SSALT was accepted.

Low temperature degradation and reliability of one-piece ceramic oral implants with a porous surface.

UNLABELLED: Low temperature degradation of zirconia (3Y-TZP) oral implants and its effect on fatigue reliability is poorly documented. OBJECTIVE: The aim of this investigation was to follow the aging process occurring at the surface of implants exhibiting a porous coating and to assess its influence on their mechanical (fatigue) properties. METHODS: Tetragonal to monoclinic transformation (t-m) was evaluated during accelerated aging tests up to 100h in autoclave (134°C, 2 bars) by X-ray diffraction (XRD) and focused ion beam (FIB). A series of implants were steam-aged for 20h before fatigue testing. Such temperature-time conditions would correspond roughly to 40 years in vivo. The aged specimens and a non-aged control group were step-stress fatigued until failure or survival. RESULTS: The evolution of XRD surface monoclinic content was slow, i.e. 16% and 35% for 20 and 100h respectively. However, FIB revealed a significant transformation, initiated at the interface between the porous layer and the bulk, preferentially growing towards the bulk. FIB is therefore better indicated than XRD to follow aging in such implants. Higher average fatigue strength (aged 1235N versus non-aged 826N) and reliability levels were observed for the 20h aged group. SIGNIFICANCE: After aging for durations compatible with clinical use, 3Y-TZP with porous surface presented higher fatigue performance. This is in contrast to previous studies where loss of strength due to aging was often reported. Generalizations must therefore be avoided when considering aging of zirconia dental products and every new material/process combination should be tested before drawing conclusions.

Effect of core design and veneering technique on damage and reliability of Y-TZP-supported crowns.

OBJECTIVES: To evaluate the effect of framework design modification and veneering techniques in fatigue reliability and failure modes of veneered Yttria-Stabilized Tetragonal Zirconia Polycrystals (Y-TZP) crowns. METHODS: A CAD-based mandibular molar crown preparation served as a master die. Y-TZP crown cores (VITA-In-Ceram-YZ, Vita-Zahnfabrik, Bad Säckingen, Germany) in conventional (0.5mm uniform thickness) or anatomically designed fashion (cusp support) were porcelain veneered with either hand-layer (VM9) or pressed (PM9) techniques. Crowns (n=84) were cemented on 30 days aged dentin-like composite dies with resin cement. Crowns were subjected to single load to fracture (n=3 each group) and mouth-motion step-stress fatigue (n=18) by sliding a WC indenter (r=3.18 mm) 0.7 mm buccally on the inner incline surface of the mesio-lingual cusp. Stress-level curves (use level probability lognormal) and reliability (with 2-sided 90% confidence bounds, CB) for completion of a mission of 50.000 cycles at 200 N load were calculated. Fractographic analyses were performed under light-polarized and scanning electron microscopes. RESULTS: Higher reliability for hand-layer veneered conventional core (0.99, CB 0.98-1) was found compared to its counterpart press-veneered (0.50 CB 0.33-65). Framework design modification significantly increased reliability for both veneering techniques (PM9 [0.98 CB 0.87-0.99], VM9 [1.00 CB 0.99-1]) and resulted in reduced veneer porcelain fracture sizes. Main fracture mode observed was veneer porcelain chipping, regardless of framework design and veneering technique. SIGNIFICANCE: Hand-layer porcelain veneered on conventional core designs presented higher reliability than press-veneered with similar core designs. Anatomic core design modification significantly increased the reliability and resulted in reduced chip size of either veneering techniques.

Effect of microthread presence and restoration design (screw versus cemented) in dental implant reliability and failure modes.

OBJECTIVES: This study evaluated the reliability and failure modes of implants with a microthreaded or smooth design at the crestal region, restored with screwed or cemented crowns. The postulated null hypothesis was that the presence of microthreads in the implant cervical region would not result in different reliability and strength to failure than smooth design, regardless of fixation method, when subjected to step-stress accelerated life-testing (SSALT) in water. MATERIALS AND METHODS: Eighty four dental implants (3.3 × 10 mm) were divided into four groups (n = 21) according to implant macrogeometric design at the crestal region and crown fixation method: Microthreads Screwed (MS); Smooth Screwed (SS); Microthreads Cemented (MC), and Smooth Cemented (SC). The abutments were torqued to the implants and standardized maxillary central incisor metallic crowns were cemented (MC, SC) or screwed (MS, SS) and subjected to SSALT in water. The probability of failure versus cycles (90% two-sided confidence intervals) was calculated and plotted using a power law relationship for damage accumulation. Reliability for a mission of 50,000 cycles at 150 N (90% 2-sided confidence intervals) was calculated. Differences between final failure loads during fatigue for each group were assessed by Kruskal-Wallis along with Benferroni's post hoc tests. Polarized-light and scanning electron microscopes were used for failure analyses. RESULTS: The Beta (ß) value (confidence interval range) derived from use level probability Weibull calculation of 1.30 (0.76-2.22), 1.17 (0.70-1.96), 1.12 (0.71-1.76), and 0.52 (0.30-0.89) for groups MC, SC, MS, and SS respectively, indicated that fatigue was an accelerating factor for all groups, except for SS. The calculated reliability was higher for SC (99%) compared to MC (87%). No difference was observed between screwed restorations (MS - 29%, SS - 43%). Failure involved abutment screw fracture for all groups. The cemented groups (MC, SC) presented more abutment and implant fractures. Significantly higher load to fracture values were observed for SC and MC relative to MS and SS (P < 0.001). CONCLUSION: Since reliability and strength to failure was higher for SC than for MC, our postulated null hypothesis was rejected.

Reliability and failure modes of internal conical dental implant connections.

OBJECTIVE: Biological and mechanical implant-abutment connection complications and failures are still present in clinical practice, frequently compromising oral function. The purpose of this study was to evaluate the reliability and failure modes of anterior single-unit restorations in internal conical interface (ICI) implants using step-stress accelerated life testing (SSALT). MATERIALS AND METHODS: Forty-two ICI implants were distributed in two groups (n = 21 each): group AT-OsseoSpeed(™) TX (Astra Tech, Waltham, MA, USA); group SV-Duocon System Line, Morse Taper (Signo Vinces Ltda., Campo Largo, PR, Brazil). The corresponding abutments were screwed to the implants and standardized maxillary central incisor metal crowns were cemented and subjected to SSALT in water. Use-level probability Weibull curves and reliability for a mission of 50,000 cycles at 200 N were calculated. Differences between groups were assessed by Kruskal-Wallis along with Bonferroni's post-hoc tests. Polarized-light and scanning electron microscopes were used for failure analyses. RESULTS: The Beta (ß) value derived from use level probability Weibull calculation was 1.62 (1.01-2.58) for group AT and 2.56 (1.76-3.74) for group SV, indicating that fatigue was an accelerating factor for failure of both groups. The reliability for group AT was 0.95 and for group SV was 0.88. Kruskal-Wallis along with Bonferroni's post-hoc tests showed no significant difference between the groups tested (P > 0.27). In all specimens of both groups, the chief failure mode was abutment fracture at the conical joint region and screw fracture at neck's region. CONCLUSIONS: Reliability was not different between investigated ICI connections supporting maxillary incisor crowns. Failure modes were similar.

Surface characterisation and bonding of Y-TZP following non-thermal plasma treatment.

OBJECTIVES: (1) To chemically characterise Y-TZP surface via X-ray photoelectron spectroscopy (XPS) and evaluate the surface energy levels (SE) after non-thermal plasma (NTP). (2) To test the microtensile bond strength (MTBS) of Y-TZP bonded to cured composite disks, after a combination of different surface conditioning methods. METHODS: Twenty-four Y-TZP discs (13.5mm×4mm) were obtained from the manufacturer and composite resin (Z-100) discs with similar dimensions were prepared. All discs were polished to 600 grit and divided into 8 groups (n=3 disks each), four control (non-NTP treated) and four experimental (NTP treated for 10s) groups. All groups received one of the four following treatments prior to cementation with Rely×Unicem cement: sand-blasting (SB), a Clearfil ceramic primer (MDP), sand-blasting+MDP (SBMDP), or baseline (B), no treatment. SE readings and surface roughness parameters were statistically analysed (ANOVA, Tukey's, p<0.05). Mixed model and paired samples t-tests were used to compare groups on MTBS. RESULTS: XPS showed increase in O and decrease in C elements after NTP. The polar component increased for BP (42.20mN/m) and SBP (43.77mN/m). MTBS values for groups BP (21.3MPa), SBP (31MPa), MDPP (30.1MPa) and SBMDPP (32.3MPa) were significantly higher in specimens treated with NTP than their untreated counterparts B (9.1MPa), SB (14.4MPa), MDP (17.8MPa) and SBMDP (24.1MPa). CONCLUSIONS: (1) Increase of O and decrease of C led to higher surface energy levels dictated by the polar component after NTP; (2) NTP application increased MTBS values of Y-TZP surfaces.

Reliability evaluation of alumina-blasted/acid-etched versus laser-sintered dental implants.

Step-stress accelerated life testing (SSALT) and fractographic analysis were performed to evaluate the reliability and failure modes of dental implant fabricated by machining (surface treated with alumina blasting/acid etching) or laser sintering for anterior single-unit replacements. Forty-two dental implants (3.75 × 10 mm) were divided in two groups (n=21 each): laser sintered (LS) and alumina blasting/acid etching (AB/AE). The abutments were screwed to the implants and standardized maxillary central incisor metallic crowns were cemented and subjected to SSALT in water. Use-level probability Weibull curves and reliability for a mission of 50,000 cycles at 200 N were calculated. Polarized light and scanning electron microscopes were used for failure analyses. The Beta (ß) value derived from use-level probability Weibull calculation of 1.48 for group AB/AE indicated that damage accumulation likely was an accelerating factor, whereas the ß of 0.78 for group LS indicated that load alone likely dictated the failure mechanism for this group, and that fatigue damage did not appear to accumulate. The reliability was not significantly different (p>0.9) between AB/AE (61 %) and LS (62 %). Fracture of the abutment and fixation screw was the chief failure mode. No implant fractures were observed. No differences in reliability and fracture mode were observed between LS and AB/AE implants used for anterior single-unit crowns.

Conventional and modified veneered zirconia vs. metalloceramic: fatigue and finite element analysis.

PURPOSE: The purpose of this study was to test the hypothesis that all-ceramic crown core-veneer system reliability is improved by modifying the core design and as a result is comparable in reliability to metal-ceramic retainers (MCR). Finite element analysis (FEA) was performed to verify maximum principal stress distribution in the systems. MATERIALS AND METHODS: A first lower molar full crown preparation was modeled by reducing the height of proximal walls by 1.5 mm and occlusal surface by 2.0 mm. The CAD-based preparation was replicated and positioned in a dental articulator for specimen fabrication. Conventional (0.5 mm uniform thickness) and modified (2.5 mm height, 1 mm thickness at the lingual extending to proximals) zirconia (Y-TZP) core designs were produced with 1.5 mm veneer porcelain. MCR controls were fabricated following conventional design. All crowns were resin cemented to 30-day aged composite dies, aged 14 days in water and either single-loaded to failure or step-stress fatigue tested. The loads were positioned either on the mesiobuccal or mesiolingual cusp (n = 21 for each ceramic system and cusp). Probability Weibull and use level probability curves were calculated. Crack evolution was followed, and postmortem specimens were analyzed and compared to clinical failures. RESULTS: Compared to conventional and MCRs, increased levels of stress were observed in the core region for the modified Y-TZP core design. The reliability was higher in the Y-TZP-lingual-modified group at 100,000 cycles and 200 N, but not significantly different from the MCR-mesiolingual group. The MCR-distobuccal group showed the highest reliability. Fracture modes for Y-TZP groups were veneer chipping not exposing the core for the conventional design groups, and exposing the veneer-core interface for the modified group. MCR fractures were mostly chipping combined with metal coping exposure. CONCLUSIONS: FEA showed higher levels of stress for both Y-TZP core designs and veneer layers compared to MCR. Core design modification resulted in fatigue reliability response of Y-TZP comparable to MCR at 100,000 cycles and 200 N. Fracture modes observed matched with clinical scenarios.

Biomechanical evaluation of internal and external hexagon platform switched implant-abutment connections: An in vitro laboratory and three-dimensional finite element analysis.

OBJECTIVES: The aim of this study was to assess the effect of abutment's diameter shifting on reliability and stress distribution within the implant-abutment connection for internal and external hexagon implants. The postulated hypothesis was that platform-switched implants would result in increased stress concentration within the implant-abutment connection, leading to the systems' lower reliability. METHODS: Eighty-four implants were divided in four groups (n=21): REG-EH and SWT-EH (regular and switched-platform implants with external connection, respectively); REG-IH and SWT-IH (regular and switched-platform implants with internal connection, respectively). The corresponding abutments were screwed to the implants and standardized maxillary central incisor metal crowns were cemented and subjected to step-stress accelerated life testing. Use-level probability Weibull curves and reliability were calculated. Four finite element models reproducing the characteristics of specimens used in laboratory testing were created. The models were full constrained on the bottom and lateral surface of the cylinder of acrylic resin and one 30° off-axis load (300N) was applied on the lingual side of the crown (close to the incisal edge) in order to evaluate the stress distribution (s(vM)) within the implant-abutment complex. RESULTS: The Beta values for groups SWT-EH (1.31), REG-EH (1.55), SWT-IH (1.83) and REG-IH (1.82) indicated that fatigue accelerated the failure of all groups. The higher levels of σ(vM) within the implant-abutment connection observed for platform-switched implants (groups SWT-EH and SWT-IH) were in agreement with the lower reliability observed for the external hex implants, but not for the internal hex implants. The reliability 90% confidence intervals (50,000 cycles at 300N) were 0.53(0.33-0.70), 0.93(0.80-0.97), 0.99(0.93-0.99) and 0.99(0.99-1.00), for the SWT-EH, REG-EH, SWT-IH, and REH-IH, respectively. SIGNIFICANCE: The postulated hypothesis was partially accepted. The higher levels of stress observed within implant-abutment connection when reducing abutment diameter (cross-sectional area) resulted in lower reliability for external hex implants, but not for internal hex implants.

Residual thermal stress simulation in three-dimensional molar crown systems: a finite element analysis.

PURPOSE: To simulate coefficient of thermal expansion (CTE)-generated stress fields in monolithic metal and ceramic crowns, and CTE mismatch stresses between metal, alumina, or zirconia cores and veneer layered crowns when cooled from high temperature processing. MATERIALS AND METHODS: A 3D computer-aided design model of a mandibular first molar crown was generated. Tooth preparation comprised reduction of proximal walls by 1.5 mm and of occlusal surfaces by 2.0 mm. Crown systems were monolithic (all-porcelain, alumina, metal, or zirconia) or subdivided into a core (metallic, zirconia, or alumina) and a porcelain veneer layer. The model was thermally loaded from 900°C to 25°C. A finite element mesh of three nodes per edge and a first/last node interval ratio of 1 was used, resulting in approximately 60,000 elements for both solids. Regions and values of maximum principal stress at the core and veneer layers were determined through 3D graphs and software output. RESULTS: The metal-porcelain and zirconia-porcelain systems showed compressive fields within the veneer cusp bulk, whereas alumina-porcelain presented tensile fields. At the core/veneer interface, compressive fields were observed for the metal-porcelain system, slightly tensile for the zirconia-porcelain, and higher tensile stress magnitudes for the alumina-porcelain. Increasingly compressive stresses were observed for the metal, alumina, zirconia, and all-porcelain monolithic systems. CONCLUSIONS: Variations in residual thermal stress levels were observed between bilayered and single-material systems due to the interaction between crown configuration and material properties.

Argon-based atmospheric pressure plasma enhances early bone response to rough titanium surfaces.

This study investigated the effect of an Argon-based atmospheric pressure plasma (APP) surface treatment operated chairside at atmospheric pressure conditions applied immediately prior to dental implant placement in a canine model. Surfaces investigated comprised: rough titanium surface (Ti) and rough titanium surface + Argon-based APP (Ti-Plasma). Surface energy was characterized by the Owens-Wendt-Rabel-Kaelble method and chemistry by X-ray photoelectron spectroscopy (XPS). Six adult beagles dogs received two plateau-root form implants (n = 1 each surface) in each radii, providing implants that remained 1 and 3 weeks in vivo. Histometric parameters assessed were bone-to-implant contact (BIC) and bone area fraction occupancy (BAFO). Statistical analysis was performed by Kruskall-Wallis (95% level of significance) and Dunn's post-hoc test. The XPS analysis showed peaks of Ti, C, and O for the Ti and Ti- Plasma surfaces. Both surfaces presented carbon primarily as hydrocarbon (C-C, C-H) with lower levels of oxidized carbon forms. The Ti-Plasma presented large increase in the Ti (+11%) and O (+16%) elements for the Ti- Plasma group along with a decrease of 23% in surface-adsorbed C content. At 1 week no difference was found in histometric parameters between groups. At 3 weeks significantly higher BIC (>300%) and mean BAFO (>30%) were observed for Ti-Plasma treated surfaces. From a morphologic standpoint, improved interaction between connective tissue was observed at 1 week, likely leading to more uniform and higher bone formation at 3 weeks for the Ti-Plasma treated implants was observed.