Quality Evaluation of Zirconium Dioxide Frameworks Produced in Five Dental Laboratories from Different Countries.

PURPOSE: The aim of this study was to assess and compare quality as well as economic aspects of CAD/CAM high strength ceramic three-unit FDP frameworks ordered from dental laboratories located in emerging countries and Switzerland. MATERIAL AND METHODS: The master casts of six cases were sent to five dental laboratories located in Thailand (Bangkok), China (Peking and Shenzhen), Turkey (Izmir), and Switzerland (Bern). Each laboratory was using a different CAD/CAM system. The clinical fit of the frameworks was qualitatively assessed, and the thickness of the framework material, the connector height, the width, and the diameter were evaluated using a measuring sensor. The analysis of the internal fit of the frameworks was performed by means of a replica technique, whereas the inner and outer surfaces of the frameworks were evaluated for traces of postprocessing and damage to the intaglio surface with light and electronic microscopes. Groups (dental laboratories and cases) were compared for statistically significant differences using Mann-Whitney U-tests after Bonferroni correction. RESULTS: An acceptable clinical fit was found at 97.9% of the margins produced in laboratory E, 87.5% in B, 93.7% in C, 79.2% in A, and 62.5% in D. The mean framework thicknesses were not statistically significantly different for the premolar regions; however, for the molar area 4/8 of the evaluated sites were statistically significantly different. Circumference, surface, and width of the connectors produced in the different laboratories were statistically significantly different but not the height. There were great differences in the designs for the pontic and connector regions, and some of the frameworks would not be recommended for clinical use. Traces of heavy postprocessing were found in frameworks from some of the laboratories. The prices per framework ranged from US$177 to US$896. CONCLUSIONS: By ordering laboratory work in developing countries, a considerable price reduction was obtained compared to the price level in Switzerland. Despite the use of the standardized CAD/CAM chains of production in all laboratories, a large variability in the quality aspects, such as clinical marginal fit, connector and pontic design, as well as postprocessing traces was noted. Recommended sound handling of postprocessing was not applied in all laboratories. Dentists should be aware of the true and factitious advantages of CAD/CAM production chains and not lose control over the process.

Three- to nine-year survival estimates and fracture mechanisms of zirconia- and alumina-based restorations using standardized criteria to distinguish the severity of ceramic fractures.

OBJECTIVES: The aims of this study were set as follows: 1. To provide verifiable criteria to categorize the ceramic fractures into non-critical (i.e., amenable to polishing) or critical (i.e., in need of replacement) 2. To establish the corresponding survival rates for alumina and zirconia restorations 3. To establish the mechanism of fracture using fractography MATERIALS AND METHODS: Fifty-eight patients restored with 115 alumina-/zirconia-based crowns and 26 zirconia-based fixed dental prostheses (FDPs) were included. Ceramic fractures were classified into four types and further subclassified into "critical" or "non-critical." Kaplan-Meier survival estimates were calculated for "critical fractures only" and "all fractures." Intra-oral replicas were taken for fractographic analyses. RESULTS: Kaplan-Meier survival estimates for "critical fractures only" and "all fractures" were respectively: Alumina single crowns: 90.9 and 68.3 % after 9.5 years (mean 5.71 ± 2.6 years). Zirconia single crowns: 89.4 and 80.9 % after 6.3 years (mean 3.88 ± 1.2 years). Zirconia FDPs: 68.6 % (critical fractures) and 24.6 % (all fractures) after 7.2 and 4.6 years respectively (FDP mean observation time 3.02 ± 1.4 years). No core/framework fractures were detected. CONCLUSIONS: Survival estimates varied significantly depending on whether "all" fractures were considered as failures or only those deemed as "critical". For all restorations, fractographic analyses of failed veneering ceramics systematically demonstrated heavy occlusal wear at the failure origin. Therefore, the relief of local contact pressures on unsupported ceramic is recommended. Occlusal contacts on mesial or distal ridges should systematically be eliminated. CLINICAL RELEVANCE: A classification standard for ceramic fractures into four categories with subtypes "critical" and "non-critical" provides a differentiated view of the survival of ceramic restorations.

Resin-bonded restorations: a strategy for managing anterior tooth loss in adolescence.

In children or adolescents with anterior tooth loss, space closure with the patient's own teeth should be considered as the first choice to avoid lifelong restorative needs. Thorough diagnostics and treatment planning are required when autotransplantation or orthodontic space closure is considered. If these options are not indicated and a single tooth implant restoration is considered, implant placement should be postponed until adulthood, particularly in young women and in patients with hyperdivergent skeletal growth pattern. A ceramic resin-bonded fixed dental prosthesis with 1 retainer is an excellent treatment solution for the interim period; it may also serve as a long-term restoration, providing that sound enamel structure is present, sufficient framework dimensions have been provided, adhesive cementation techniques have been meticulously applied, and functional contacts of the cantilever pontic avoided. In contrast, a resin-bonded fixed dental prosthesis with a metal framework and retentive preparation is indicated if the palatal enamel structure is compromised, interocclusal clearance is limited, splinting (such as after orthodontic treatment) is required, or more than 1 tooth has to be replaced.

Recent advances in dental zirconia: 15 years of material and processing evolution.

OBJECTIVES: The objective was to discuss the research on zirconia published in the past 15 years to help the dental materials community understand the key properties of the types of zirconia and their clinical applications. METHODS: A literature search was performed in May/2023 using Web of Science Core Collection with the term "dental zirconia". The search returned 5102 articles, which were categorized into 31 groups according to the research topic. RESULTS: The current approach to improving the translucency of zirconia is to decrease the alumina content while increasing the yttria content. The resulting materials (4Y-, 5Y-, and above 5 mol% PSZs) may contain more than 50% of cubic phase, with a decrease in mechanical properties. The market trend for zirconia is the production of CAD/CAM disks containing more fracture resistant 3Y-TZP at the bottom layers and more translucent 5Y-PSZ at the top. Although flaws located between layers in multilayered blocks might represent a problem, newer generations of zirconia layered blocks appear to have solved this problem with novel powder compaction technology. Significant advancements in zirconia processing technologies have been made, but there is still plenty of room for improvement, especially in the fields of high-speed sintering and additive manufacturing. SIGNIFICANCE: The wide range of zirconia materials currently available in the market may cause confusion in materials selection. It is therefore imperative for dental clinicians and laboratory technicians to get the needed knowledge on zirconia material science, to follow manufacturers' instructions, and to optimize the design of the prosthetic restoration with a good understanding where to reinforce the structure with a tough and strong zirconia.

Strength-limiting damage and defects of dental CAD/CAM full-contour zirconia ceramics.

OBJECTIVE: This study aimed to compare the four-point flexural strength of CAM-milled and sintered (as-sintered, AS) specimens with those of high-polished (HP) specimens using chairside polishing systems to simulate clinical surface conditions. METHODS: Seven full-contour zirconia CAM/CAM blanks with various yttria contents (3, 4, 5 mol%) including three high-translucent groups (5Y) were selected to prepare flexural specimens. The bend bar specimens (2.0 × 4.0 × 25.0 mm3) were fabricated by using STL file and dental CAM machine with the respective zirconia blanks (98 mm ϕ and 10-14 mm in height). Twelve bar specimens were machined from one zirconia puck and a total of 24 specimens were prepared from each group. The pre-sintered bar specimens were sintered by using a dental zirconia furnace at 1530-1550 °C for 2 h according to the instructions. All sintered specimens were divided into two groups: as-sintered (AS) group and high-polished (HP) groups (n = 12). HP groups were subjected to polishing one surface of specimens using a three-step polishing system and finally finished with diamond polishing. After cleaning and drying, the flexural strength of all specimens was determined by a fully articulating four-point flexure fixture consisting of a 1/4-point test configuration with an inner/outer span of 10/20 mm. Statistical differences between AS and HP groups were conducted with Weibull analysis. The fractured surfaces of zirconia specimens were observed using a field emission SEM and EDS to detect failure origins. RESULTS: The mean AS flexural strength values were significantly lower than those of HP counterparts. However, Weibull moduli expressing the reliability of HP groups were generally decreased although not significantly in comparison to their AS. The fracture of the AS specimens mostly originated from extrinsic CAM-milling defects, while the HP specimens were fractured from intrinsic subsurface or volume defects including pores, large grain clusters, inclusions, and corner-located critical flaws. Two high-translucent (5Y) zirconia groups were not affected in their strength and reliability after polishing, whereas one 5Y zirconia significantly increased its strength but significantly lowered its reliability. SIGNIFICANCE: The extrinsic and intrinsic strength-limiting defects should be considered in evaluating the flexural strength and reliability of dental CAD/CAM zirconia ceramics for full-contour restorations. For the materials tested in this study, more optimized processing of blanks and milling protocols of pre-sintered zirconia blanks should be developed including post-sintering surface finishing to reduce the flaw population regulating strength and reliability which will affect the survivability of dental zirconia prostheses.

An In Vitro Evaluation of the Effects of Air-Polishing Powders on Sound and Demineralised Enamel.

AIM: To evaluate the effects of two air-polishing powders, during orthodontic treatment, on the surface roughness of sound and demineralised enamel. MATERIALS AND METHODS: Forty-two caries-free human molars were collected, and the enamel surfaces were flattened and polished. Teeth were assigned to two groups (n = 21 each), a sound- and a demineralised-enamel group (subjected to pH-cycling over 2 weeks to create artificially induced white spot-like lesions). Within each group, teeth were further assigned to three groups (n = 7 each), air polished with either sodium bicarbonate, erythritol, or a negative control (water). Each sample was treated for 5 and 150 s. The average surface roughness (Ra) for each sample was measured using white-light-sensor profilometry. RESULTS: On sound enamel, the Ra was roughly 0.17 ± 0.07 µm. After 150 s of air polishing, the Ra increased with erythritol (by 0.28 µm), and even more so with bicarbonate treatment (by 0.68 µm) (p < 0.01). On demineralised enamel, the Ra was roughly 0.79 ± 0.56 µm. The Ra increased after 5 s of air-polishing treatment similarly with erythritol and bicarbonate powders (by 1.03 µm and 1.04 µm, respectively) (p = 0.025), and even more after 150 s (by 2.48 µm and 2.49 µm, respectively) (p < 0.001). CONCLUSIONS: On white spot lesions, one should be aware that enamel surface roughness will increase with both erythritol and bicarbonate air-polishing powders, especially with longer exposure times.

Implementation of the "loaded implant" model in the rat using a miniaturized setup--description of the method and first results.

OBJECTIVE: To miniaturize the "loaded implant" model to permit its application to small rodents. In this model, two titanium implants are placed 8 mm apart with their heads protruding from the skin and are forced together by a dedicated actuator. To assess the effect of (i) the post-implantation healing period and the duration of stimulation and (ii) the intratissular strain level on the microtomographical bone parameters BV/TV, Tb.N., Tb.Th. and BIC. MATERIALS AND METHODS: Implants, 1 × 8 mm, were machined, inserted into the tibiae of rats and activated. A total of 123 animals were used. In series 1, the implants were left to heal for 2/4 weeks and then loaded to generate intratissular strains of 1125 ± 5% µÎµ for 4/8 weeks. Series 2 had their implants loaded to 750, 1500 and 2250 ± 5% µÎµ, respectively. RESULTS: Bone to implant contact increased upon loading. In series 1, no difference was observed regarding the duration of healing or the stimulation period. In series 2, at 750 µÎµ, the bone parameters did not differ from baseline. At 1500 µÎµ, all four parameters increased. At 2250 µÎµ, three of four parameters decreased relative to 1500 µÎµ. CONCLUSIONS: (i) The loaded implant model can be miniaturized to the millimeter range; (ii) in the present model, implant activation beyond 4 weeks did not affect the bone parameters; (iii) mechanical stimulation increased bone to implant contact by up to 20%; (iv) the results obtained are consistent with the concept of an anabolic effect from 750 to 1500 µÎµ and deleterious effects at strains in the 2250 µÎµ range; and (v) strains at 2250 µÎµ did not lead to implant dis-integration.

Preferences of dental care providers in maintaining compromised teeth in relation to their professional status: implants instead of periodontally involved maxillary molars?

AIM: The purpose of this study was to evaluate the dentists' decision making in the maxillary molar region to find out how it is influenced by general practitioners' and specialists' characteristics as well as by the external evidence. MATERIAL AND METHODS: A questionnaire was developed containing clinical cases and statements to assess practitioners' opinions on the treatment of periodontally involved maxillary molars and implant therapy with sinus grafting. Data were analysed with respect to the dentists' age and specialty. RESULTS: Three hundred and forty questionnaires were evaluated (24% from universities, 76% from educational courses, overall response rate 35.1%). Forty six per cent of all participants indicated they had specialised, 52% placed dental implants, while 33% performed sinus grafting and 64% periodontal surgeries. Forty six per cent were against or were indecisive about having sinus grafting performed on themselves. The treatment proposals given for the clinical cases revealed a preference among older dentists and general practitioners for regenerative treatments even when these were not evidence based in through-and-through furcation involvements. Resective therapies were most often selected by periodontists. Prosthodontists tended to prefer more invasive treatment options with extractions and augmentations. More experienced general practitioners favoured conventional fixed dental prostheses in free-end situations or no treatment rather than the complicated augmentation procedures, which were preferred by younger dentists. CONCLUSIONS: Implant placement seems to be widely accepted by almost all subjects, who may either place implants themselves or refer patients. More information seems to be needed on the indications for regenerative therapies for furcation involved maxillary molars, and guidelines required for decision making in complex clinical situations.

Fractography of clinical failures of indirect resin composite endocrown and overlay restorations.

OBJECTIVES: Compare failure modes and fracture origins using fractography on recovered clinically fractured parts of indirect resin composite endocrowns and overlay restorations on endodontically treated teeth (ETT). METHODS: Four endocrowns (3 molars, 1 premolar) and one overlay (molar) adhesively luted on ETT were recovered after fracturing during function. The time in service ranged between 4 and 48 months. The composite materials were (i) CAD/CAM LAVA Ultimate (N = 1), (ii) Premise Indirect (N = 2), and (iii) Colombus (N = 2). Fractography was performed by means of digital microscopy and SEM. Occlusal surfaces were checked for signs of fatigue degradation and contact wear. Cuspal plane angles were measured from profiles obtained from 3D digital microscope images with respect to the horizontal plane of the occlusal central crown groove. RESULTS: All five cases showed a wedge-opening mode I fracture, splitting the crown and tooth in two parts through the crown's central groove. Classic brittle fracture features (arrest lines, twist and wake hackle) were easily identified on the fracture surfaces. Multiple origins were located along the central groove in conjunction with the presence of fatigue cracks. Contact wear surfaces showed pitting and cracking. Cuspal plane angles were around 30-35°, except a 50° palatal cusp slope for the Lava Ultimate overlay. SIGNIFICANCE: Fractography on clinical fractures of resin composites was enlightening. Occlusal surface fatigue degradation from cyclic loading, mode I fracture from applied mastication forces on cuspal planes, and stress concentration within the crown's central groove, indicate limitations of use of these materials for endocrowns in posterior teeth.

Fractal analysis at varying locations of clinically failed zirconia dental implants.

OBJECTIVES: Previous studies have shown that the fracture toughness of ceramics can be determined from the fractal dimensions (D) of their fracture surfaces and that the surface should be leveled to obtain an accurate D measurement. This study was to determine the effects of leveling operations and distance from the failure origin on the D values. METHODS: Twelve clinically failed zirconia implants from four different manufacturers: Axis Biodental (n=7), Z-Systems (n=3), Straumann (n=1), and Swiss Dental Solutions (n=1) were obtained from one of the authors and thoroughly cleaned. Epoxy replicas were made of three locations along the crack path in the center region of each fracture surface (near origin (O), hackle (H), and near compression curl (CC)) using a light body polyvinyl siloxane impression material. Surfaces were scanned in ScanAsyst mode with a scan size of 5µm×5µm and a scan rate of 0.592Hz using the atomic force microscope. The surface scans were then leveled using 1st order flattening operation in the AFM analysis software. The height data before and after the operation were imported into a custom MathCAD script, and FRACTALS software was used to determine the D value by Minkowski Cover algorithm, which was shown previously to be the algorithm with the highest precision. A Wilcoxon signed-rank test, two-way repeated-measures ANOVA, and one-way repeated-measures ANOVA were performed as detailed below. RESULTS: The data were not normally distributed (S-W p≤0.05), so a non-parametric repeated measures test (Wilcoxon signed-rank test) was selected. The median D values before and after leveling were 2.161 and 2.174, respectively. There was a significant difference before and after leveling (p<0.001). The two-way repeated-measures ANOVA showed no significant difference among the D values for different implant brands (p=0.66) and scanning locations on the fracture surface (p=0.83). After eliminating the implant brand as a factor, the data passed normality and equal variance tests (S-W p=0.88, BF p=0.15). The mean D values and standard deviations from the three locations (O, H, CC) were 2.183±0.031, 2.179±0.024, and 2.175±0.018, respectively. One-way repeated measures ANOVA showed no significant effect of scanning location (p=0.74). SIGNIFICANCE: The leveling operation successfully removed the tilt without decreasing surface tortuosity, as it increased the D values significantly. The fractal dimension was the same at the three locations on the fracture surfaces. This means that hackle and compression curl regions can be used to determine fracture toughness when the failure origin has been lost.

Translational research on clinically failed zirconia implants.

OBJECTIVES: To provide fractographic analysis of clinically fractured zirconia implants recovered with their cemented crown. To calculate bending moments, corresponding stress and crack onset location on the implant's fracture surface using a mathematical model integrating spatial coordinates of the crown-implant part and occlusal loading obtained from 2D and 3D images. METHODS: 15 fractured zirconia implants parts (11 posterior and 4 anterior) with their all- ceramic crowns still cemented on it were recovered. The implants were first generations from four manufacturers (AXIS Biodental, Z-Systems, Straumann, Swiss Dental Solutions). The time-to-failure varied between 2weeks and 9years. Fractography was performed identifying the failure origin and characteristic surface crack features. From 2D and 3D digital images of the crown-implant part, spatial coordinates anchoring the crown's occlusal contacts with the implant's central axis and reference plane were integrated in a mathematical model spreadsheet. Loads of 500 N in total were selectively distributed over identified occlusal contacts from wear patterns. The resultant bending and torsion moments, corresponding shear, tensile, maximum principal stress and von Mises stress were calculated. The fracture crack onset location on the implant's fracture surface was given by an angular position with respect to an occlusal reference and compared with the location of the fracture origin identified from fractographic analysis. RESULTS: Implants fractured from the periphery of the smaller inner diameter between two threads at the bone-entrance level except for one implant which failed half-way within the bone. The porous coating (AXIS Biodental) and the large grit alumina sandblasting (Z-System) created surface defects directly related to the fracture origin. The model spreadsheet showed how occlusal loading with respect to the implant's central axis affects bending moments and crack onset. Dominant loads distributed on contacts with important wear pattern provided a calculated crack onset location in good agreement with the fractographic findings of the fracture origin. SIGNIFICANCE: Recovered broken zirconia implant parts with their restorative crowns can provide not only information regarding the failure origin using fractography but also knowledge regarding occlusal crown loading with respect to the implant's axis. The mathematical model was helpful in showing how occlusal loading affects the location of the fracture initiation site on clinical zirconia implant fracture cases.

Calvarial Model of Bone Augmentation in Rabbit for Assessment of Bone Growth and Neovascularization in Bone Substitution Materials.

The basic principle of the rabbit calvarial model is to grow new bone tissue vertically on top of the cortical part of the skull. This model allows assessment of bone substitution materials for oral and craniofacial bone regeneration in terms of bone growth and neovascularization support. Once animals are anesthetized and ventilated (endotracheal intubation), four cylinders made of polyether ether ketone (PEEK) are screwed onto the skull, on both sides of the median and coronal sutures. Five intramedullary holes are drilled within the bone area delimited by each cylinder, allowing influx of bone marrow cells. The material samples are placed into the cylinders which are then closed. Finally, the surgical site is sutured, and animals are awaken. Bone growth may be assessed on live animals by using microtomography. Once animals are euthanized, bone growth and neovascularization may be evaluated by using microtomography, immune-histology and immunofluorescence. As the evaluation of a material requires maximum standardization and calibration, the calvarial model appears ideal. Access is very easy, calibration and standardization are facilitated by the use of defined cylinders and four samples may be assessed simultaneously. Furthermore, live tomography may be used and ultimately a large decrease in animals to be euthanized may be anticipated.

Bone reactions to controlled loading of endosseous implants: a pilot study.

OBJECTIVES: To validate an experimental setup designed to apply load onto bone tissue using osseointegrated implants in a rabbit model. Specifically, (1) to design an apparatus capable of generating controlled forces, (2) to assess implant placement, maintenance and loading and (3) to evaluate outcome variables using three radiological methods. MATERIAL AND METHODS: New Zealand White rabbits were used. Two dental implants were inserted 15-18 mm apart in the animals' tibiae. After 3 months of healing, the implants were loaded normal to their long axes using a pneumatically activated device. A 15 min load regimen at 1 Hz was applied 5 days per week. Every week the applied load was increased by 5 N up to week 8 and by 10 N up to 100 N by week 14. Groups of animals (n=3) were sacrificed at load levels 25, 50 and 100 N. One unloaded controlateral implant in each group provided the baseline data. The rabbits were computer tomography (CT) scanned and radiographed using conventional frames every 4-5 weeks. After sacrifice, a volume of interest (VOI) located in the inter-implant zones and a VOI set as a ring surrounding the distal implant were analyzed using micro computer tomography (microCT). RESULTS: A variety of osseous responses was observed, ranging from minor alterations to significant increases in porosity and lamelling of the cortical layer. microCT data of the inter-implant VOI demonstrated an initial increase in total volume (upto 50 N) followed by stabilization. Concomitantly, bone volumetric density first decreased and then augmented until the end of the experiment. This phenomenon was not observed in the peri-implant VOI, for which volumetric density augmented from the beginning to the end of the experiment. CONCLUSIONS: 1. In future trials the loading devices must be constructed so as to sustain heavy cyclic loads over prolonged periods. 2. When properly handled, rabbits are cooperative animals in this application. In a third of the sites, signs of inflammation were observed. 3. In the inter-implant VOI, the cortical bone tended to react in two phases: first, as an increase in porosity and lamelling and second, as an augmentation of bone volumetric density. The peri-implant VOI adapted only by augmenting volumetric density.

Fractographic failure analysis of a Procera AllCeram crown using stereo and scanning electron microscopy.

OBJECTIVES: Presentation of a methodological approach using stereo and scanning electron microscope examination for the failure analysis of an alumina all-ceramic premolar crown (Procera AllCeram). METHODS: The recovered part of a fractured Procera alumina crown was examined utilizing first a stereomicroscope and second a scanning electron microscope (SEM). The stereomicroscope analysis was performed at low magnifications with oblique lighting in order to enhance spatial relationships and gross detection of crack features. A preliminary fracture surface map of the stereo observations was drawn and used as a guide for the SEM analysis that followed. Specific sites of interest identified under the stereo microscope were analyzed using the SEM at high magnifications searching for small fracture features such as wake hackle and twist hackle within the veneering ceramic in order to confirm the direction of crack propagation. RESULTS: At low magnifications and oblique illumination, the stereomicroscope analysis provided an excellent overview of the fractured topography, showing sites of major interest such as a primary edge chip at a margin, a compression curl indicating the end of the fracture event as well as larger hackle lines distributed over the cracked surface. The greater magnifications with the SEM analysis of the sites of interest showed the presence of wake and twist hackle, indicators of the crack propagation direction. A general map of the fracture events could be reconstructed starting with a primary veneer edge chip at the mesial margin. Hackle and wake hackle of the crack front emanating from this margin arose from hoop stresses and propagated through the full crown thickness towards the distal end of the restoration where the compression curl was located. Additional occlusal surface damage in the form of veneer chipping containing arrest lines and twist hackle running in the opposite direction as the main crack path were observed, but occurred as a secondary event without penetrating the alumina core material. SIGNIFICANCE: Stereo and scanning electron microscopy are complementary analysis techniques useful for the mapping and interpretation of the fracture surface. This case examination is intended to guide the clinical researcher in using qualitative (descriptive) fractography as a tool for understanding the failure process in brittle restorative materials, as well as for assessing possible design inadequacies.

Microstructural characterization and fracture behavior of a microhybrid and a nanofill composite.

OBJECTIVES: To characterize the microstructure and composition of two different composites, and to determine their influence on the physical properties and fracture behavior. METHODS: The microstructure and composition of a microhybrid (Filtek Z250-Z2) and a nanofill (Filtek Supreme-SU) composite were analyzed using scanning electron microscopy (SEM) and electron dispersive spectroscopy (EDS). Filler wt% was determined by thermogravimetric analysis. Hardness (H) and degree of conversion (DC) were evaluated at top and bottom surfaces of 2-mm thick specimens, and the dynamic elastic modulus (E) was determined with ultrasonic waves. Bar specimens (n=30) were subjected to flexure loading and flexural strength (sigmaf) was calculated (MPa). Fractographic analysis (FA) was performed to determine the fracture origin (c) for calculation of fracture toughness (KIc), and these results were compared to those from the single edge notch beam (SENB) method. Results were statistically analyzed using two-way ANOVA, Student's t-test and Weibull analysis (alpha=0.05). RESULTS: Z2 had higher filler wt%, H, E and DC at 2-mm depth as compared with SU. The fracture behavior (sigmaf and KIc) and the structural reliability (m) of the composites were similar. Results of KIc tested by SENB or calculated from fracture surfaces from flexure testing were similar. SIGNIFICANCE: The microstructural organization of the composites determines their physical properties, in spite of the similar filler content. In contrast, the microstructure did not influence the fracture behavior and the structural reliability of these highly filled composites. FA was shown to be a reliable method for determining the KIc of composites.

Resistance of internal-connection implant connectors under rotational fatigue loading.

PURPOSE: To aid in developing mechanically optimized implant-abutment connectors, the fatigue resistance of 5 connector configurations of the Replace Select system (Easy abutment, Easy abutment without antirotational mechanism, Multi-unit abutment, Esthetic Alumina abutment, Esthetic Zirconia abutment) was investigated. Other purposes of the study were to determine whether the connector's antirotational mechanism participates in fatigue resistance and to compare the results with previous data on Straumann connectors. MATERIALS AND METHODS: The repetitive, alternating, and multivectorial intraoral force pattern was reproduced by subjecting the test specimens to the rotating cantilever beam test. To this end, the samples were spun around their long axis while clamped into a revolving collet on one end and loaded normal to their long axis on the other end. The aim was to determine the load level at which 50% of the specimens survived and 50% fractured before 106 cycles. Means were determined using the staircase procedure. They were fitted with 95% confidence intervals for intergroup comparisons. RESULTS: In the chosen testing configuration, 2 statistical groups emerged. The Easy abutments with and without antirotational mechanism were statistically similar, with mean failure loads in the 70 to 72 N range. Both ceramic and the Multi-unit abutments belonged to the second group, with mean failure loads in the 53 to 58 N range. CONCLUSIONS: (1) The fatigue resistance of ceramic and the Multi-unit abutments was approximately 20% less than that of the Easy Abutments. (2) The antirotational mechanism did not participate in mechanical resistance. (3) The fatigue strength of the Easy abutment connectors was approximately 20% greater than the equivalent abutments in the Straumann system.

Rotational fatigue-resistance of seven post types anchored on natural teeth.

PURPOSE: To develop a laboratory model aimed at duplicating the failure process of post and core restorations. The load pattern applied was to be repetitive (fatigue) and multivectorial. To determine and compare the resistance under fatigue loading of seven endodontic post/natural root combinations: stainless steel-, titanium-, ceramic-, composite-fiber/epoxy-, two glass-fiber/epoxy- and glass-fiber/acrylic posts. MATERIALS AND METHODS: The repetitive, alternating and multivectorial intraoral force pattern was reproduced by subjecting the specimens to the rotating cantilever beam test. To this end, the samples were designed as rotation-symmetric structures comprising a root, a post, periodontal ligament- and bone analogs and a restoration analog. The following posts were tested: Unimetric-Ti, Unimetric-SS, Biopost, Composipost, Easypost, DT Lightpost, Everstickpost. The samples were spun around their long axes while being clamped into a revolving collet on one end and loaded normal to their long axis on the other end. The aim was to determine the load level at which 50% of the specimens survived- and 50% fractured before 10E6 cycles. The 50% means were determined using the staircase procedure. RESULTS: In increasing order of magnitude, the resistances to fatigue loading were as follows: Biopost, Unimetric-Ti, Unimetric-SS, Composipost, Easypost, Everstickpost, DT Lightpost. SIGNIFICANCE: The fatigue resistance of the two fibrous posts with the highest fatigue resistance was twice that of any of the ceramic or metal posts.

Using implant connectors to support clinical abrasion probes: a methodological study.

OBJECTIVES: To validate a procedure aimed at assessing the clinical wear rate of full crown veneering materials. To confirm its clinical applicability and alignment capacity in the ancillary profiling apparatus. To quantify the wear rate of a full crown veneering composite (Sinfony, 3M-ESPE) as compared to that of a ceramic (negative control) and an unfilled resin (positive control). METHODS: The technique consisted in utilizing implant supported crowns which were either screw-fastened to endosseous implants via ITI-Straumann Octa connectors or to an Octa analog on an x-y measuring table. After initial contour profiling, 14 crowns were placed in the mouths of seven patients. Six crowns were veneered with composite, four with ceramic and four with an unfilled resin. The crowns were removed at 3, 6, 9, 12, 15, 18 and 24 months and digitalized contour profiles were obtained. Contour profiling consisted in securing the restorations to the x-y table and assessing the z-coordinate using an LVDT stylus. At the end of the experimental period, loss of material was computed as the differences between the initial- and subsequent measurements. RESULTS: The total error of the method was estimated at +/-10 microm. The composite's annual wear rate was 75 microm/year, the ceramic wore at ca. 6 microm/year and the unfilled resin wore at 160 microm/year. Wear was unevenly distributed and concentrated on occlusal contact areas. SIGNIFICANCE: (1) A technique utilizing ITI-Straumann octagonal implant connectors is suitable for clinical use. (2) The veneering composite wears at a rate that is superior to ADA guidelines for composites intended for direct fillings.

Fractographic ceramic failure analysis using the replica technique.

OBJECTIVES: To demonstrate the effectiveness of in vivo replicas of fractured ceramic surfaces for descriptive fractography as applied to the analysis of clinical failures. METHODS: The fracture surface topography of partially failed veneering ceramic of a Procera Alumina molar and an In-Ceram Zirconia premolar were examined utilizing gold-coated epoxy poured replicas viewed using scanning electron microscopy. The replicas were inspected for fractographic features such as hackle, wake hackle, twist hackle, compression curl and arrest lines for determination of the direction of crack propagation and location of the origin. RESULTS: For both veneering ceramics, replicas provided an excellent reproduction of the fractured surfaces. Fine details including all characteristic fracture features produced by the interaction of the advancing crack with the material's microstructure could be recognized. The observed features are indicators of the local direction of crack propagation and were used to trace the crack's progression back to its initial starting zone (the origin). Drawbacks of replicas such as artifacts (air bubbles) or imperfections resulting from inadequate epoxy pouring were noted but not critical for the overall analysis of the fractured surfaces. SIGNIFICANCE: The replica technique proved to be easy to use and allowed an excellent reproduction of failed ceramic surfaces. It should be applied before attempting to remove any failed part remaining in situ as the fracture surface may be damaged during this procedure. These two case studies are intended as an introduction for the clinical researcher in using qualitative (descriptive) fractography as a tool for understanding fracture processes in brittle restorative materials and, secondarily, to draw conclusions as to possible design inadequacies in failed restorations.

Grinding damage assessment for CAD-CAM restorative materials.

OBJECTIVES: To assess surface/subsurface damage after grinding with diamond discs on five CAD-CAM restorative materials and to estimate potential losses in strength based on crack size measurements of the generated damage. METHODS: The materials tested were: Lithium disilicate (LIT) glass-ceramic (e.max CAD), leucite glass-ceramic (LEU) (Empress CAD), feldspar ceramic (VM2) (Vita Mark II), feldspar ceramic-resin infiltrated (EN) (Enamic) and a composite reinforced with nano ceramics (LU) (Lava Ultimate). Specimens were cut from CAD-CAM blocs and pair-wise mirror polished for the bonded interface technique. Top surfaces were ground with diamond discs of respectively 75, 54 and 18µm. Chip damage was measured on the bonded interface using SEM. Fracture mechanics relationships were used to estimate fracture stresses based on average and maximum chip depths assuming these to represent strength limiting flaws subjected to tension and to calculate potential losses in strength compared to manufacturer's data. RESULTS: Grinding with a 75µm diamond disc induced on a bonded interface critical chips averaging 100µm with a potential strength loss estimated between 33% and 54% for all three glass-ceramics (LIT, LEU, VM2). The softer materials EN and LU were little damage susceptible with chips averaging respectively 26µm and 17µm with no loss in strength. Grinding with 18µm diamond discs was still quite detrimental for LIT with average chip sizes of 43µm and a potential strength loss of 42%. SIGNIFICANCE: It is essential to understand that when grinding glass-ceramics or feldspar ceramics with diamond discs surface and subsurface damage are induced which have the potential of lowering the strength of the ceramic. Careful polishing steps should be carried out after grinding especially when dealing with glass-ceramics.