Degree of cure of orthodontic composite attachments underneath aligners.

The aim of this study was to assess the percentage degree of cure (DC%) of 2-mm-thick resin composite attachments used for aligner treatment. Three types of aligner - two thermoformed aligners (Clear Aligner [CLA], polyethylene terephthalate glycol modified; and Invisalign [INV], polyester urethane) and a three-dimensional-printed aligner (Graphy TC-85DAC [GRP], an acrylate-methacrylate copolymer) - were selected, along with two universal resin composites (3M Filtek Universal [FTU] and Charisma Topaz ONE [CTO]). Samples of each composite were placed under each aligner, and the degree of cure of each composite was evaluated on the top (facing the aligner) and the bottom (facing the substrate) attachment surfaces after curing. Five specimens were used per combination of aligner and composite, and an additional group of composites irradiated without aligners served as the control. The DC% measurements were performed using attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. The DC% across the aligners were (median values) 33.8%-44.8% for CLA, 33.6%-40.8% for INV, 32.8%-40.6% for GRP, and 40.0%-51.7% for the control group. The DC% values of the attachments cured under any aligner were significantly lower than that of the corresponding control, with the values recorded on the top surfaces being 6% higher than those on the bottom surfaces after adjusting for aligner group and composite type.

Surface alterations and compound release from aligner attachments in vitro.

AIM: The aim of the present study was to assess the alterations in morphology, roughness, and composition of the surfaces of a conventional and a flowable composite attachment engaged with aligners, and to evaluate the release of resin monomers and their derivatives in an aqueous environment. METHODS: Zirconia tooth-arch frames (n = 20) and corresponding thermoformed PET-G aligners with bonded attachments comprising two composite materials (universal-C and flowable-F) were fabricated. The morphological features (stereomicroscopy), roughness (optical profilometry), and surface composition (ATR-FTIR) of the attachments were examined before and after immersion in water. To simulate intraoral use, the aligners were removed and re-seated to the frames four times per day for a 7-day immersion period. After testing, the eluents were analyzed by LC-MS/MS targeting the compounds Bis-GMA, UDMA, 2-HEMA, TEGDMA and BPA and by LC-HRMS for suspect screening of the leached dental material compounds and their degradation products. RESULTS: After testing, abrasion-induced defects were found on attachment surfaces such as scratches, marginal cracks, loss of surface texturing, and fractures. The morphological changes and debonding rate were greater in F. Comparisons (before-after testing) revealed a significantly lower Sc roughness parameter in F. The surface composition of the aligners after testing showed minor changes from the control, with insignificant differences in the degree of C = C conversion, except for few cases with strong evidence of hydrolytic degradation. Targeted analysis results revealed a significant difference in the compounds released between Days 1 and 7 in both materials. Insignificant differences were found when C was compared with F in both timeframes. Several degradation products were detected on Day 7, with a strong reduction in the concentration of the targeted compounds. CONCLUSIONS: The use of aligners affects the surface characteristics and degradation rate of composite attachments in an aqueous environment, releasing monomers, and monomer hydrolysates within 1-week simulated use.

Development of Bi- and Tri-Layer Nanofibrous Membranes Based on the Sulfated Polysaccharide Carrageenan for Periodontal Tissue Regeneration.

Periodontitis is a microbially-induced inflammation of the periodontium that is characterized by the destruction of the periodontal ligament (PDL) and alveolar bone and constitutes the principal cause of teeth loss in adults. Periodontal tissue regeneration can be achieved through guided tissue/bone regeneration (GTR/GBR) membranes that act as a physical barrier preventing epithelial infiltration and providing adequate time and space for PDL cells and osteoblasts to proliferate into the affected area. Electrospun nanofibrous scaffolds, simulating the natural architecture of the extracellular matrix (ECM), have attracted increasing attention in periodontal tissue engineering. Carrageenans are ideal candidates for the development of novel nanofibrous GTR/GBR membranes, since previous studies have highlighted the potential of carrageenans for bone regeneration by promoting the attachment and proliferation of osteoblasts. Herein, we report the development of bi- and tri-layer nanofibrous GTR/GBR membranes based on carrageenans and other biocompatible polymers for the regeneration of periodontal tissue. The fabricated membranes were morphologically characterized, and their thermal and mechanical properties were determined. Their periodontal tissue regeneration potential was investigated through the evaluation of cell attachment, biocompatibility, and osteogenic differentiation of human PDL cells seeded on the prepared membranes.

Short fiber-reinforced composite resins as post-and-core materials for endodontically treated teeth: A systematic review and meta-analysis of in vitro studies.

STATEMENT OF PROBLEM: As the use of traditional posts has been associated with complications and failure outcomes, the introduction of novel materials and minimally invasive dentistry has shifted toward the use of composite resin post-and-core restorations for endodontically treated teeth. As a further process, to improve stress absorption environment in restored teeth, the invention of short fiber-reinforced composite resins (SFRCs) as post-and-core restorations has recently emerged. However, evidence regarding its performance is still scarce, and a synthesis of existing data is lacking. PURPOSE: The purpose of this systematic review and meta-analysis was to assess the performance of SFRC post-and-core restorations, regarding fracture resistance and failure mode and considering both cyclic and static loading. MATERIAL AND METHODS: An electronic search in 5 databases was conducted up to August 2022, and the protocol of the study was registered a priori. The search terms included "fiber reinforced composite," "core build-up," and "post." Studies were considered if they compared SFRC restorations with other types of conventional posts and teeth restored using bulk fill composite resin. The internal validity of the studies was assessed by using a custom-made risk of bias tool. RESULTS: A total of 1271 records were identified, of which 13 were considered for full-text assessment. Eight were ultimately included, all being in vitro studies, and 7 of them were deemed eligible for quantitative syntheses. The results varied considerably across studies with divergent fracture resistance values and percentages of catastrophic failure being reported. Standard depth (6 mm) SFRCs presented fewer repetitions until fracture on average, compared with the individually made FRCs (3 studies: mean difference (MD): -4062; 95% CI: -6148, -1975; P<.001) under cyclic loading. Under static loading, SFRCs (standard depth) presented a nearly 300 N lower fracture force compared with that of intact teeth, (3 studies: MD: -297; 95%CI: -378, -216; P<.001). CONCLUSIONS: Evidence on the laboratory fracture and failure performance of SFRCs is limited, and future studies should incorporate more standardized experimental conditions, as well as SFRCs with limited sacrifice of tooth substrate within the root canal of endodontically treated teeth.

Leaching from a 3D-printed aligner resin.

AIM: To quantitatively assess the degree of conversion and the water-leaching targeted compound from 3D-printed aligners. MATERIALS AND METHODS: 3D-printed aligners were made of photopolymerized resin (Tera Harz TC85A). The molecular structure and degree of conversion of the set resin were investigated by ATR-FTIR spectroscopy (n = 5). The aligners (n = 10) were immersed in double distilled water for 1 week at 37°C and the eluents were analysed using liquid chromatography/mass spectrometry methods (LC-ESI-MS/MS for urethane dimethacrylate [UDMA] and LC-APCI-MS/MS for bispenol-A [BPA]). RESULTS: The resin was composed of aliphatic vinyl ester-urethane monomers, with acrylate and/or methacrylate functionalization. The degree of conversion was estimated as to 83%. There was no detection of BPA in any of the assessed samples (0.25 µg/l). Quantifiable amounts of UDMA were detected in all the exposed samples, ranging from 29 to 96 µg/l. CONCLUSIONS: Although efficiently polymerized and BPA free, the great variability in the amount of UDMA monomer leached from the examined samples may raise concerns on potential health hazards after repeated intraoral exposure, which is indicated for this class of materials.

Strength of implant-supported lithium disilicate and polymer-infiltrated ceramic network restorations after thermomechanical aging.

AIM: To evaluate the fracture load and type of failure of two different monolithic restorative materials bonded to standardized titanium bases and fabricated by two different procedures regarding the bonding interface. MATERIALS AND METHODS: All screw-retained implant crown specimens (n = 40), subjected to fatigue by thermomechanical loading, differed in the restorative material (lithium disilicate [LDS] or polymer-infiltrated ceramic network [PICN], referred to as 'hybrid ceramic' [HYC]) and the interface type between the restorative material and the titanium base abutment (prefabricated ex-factory or produced during a CAM-milling procedure). This resulted in the following groups (n = 10/group): 1) LDS-M: lithium disilicate crown with a CAM-milled interface; 2) LDS-P: lithium disilicate crown with a prefabricated interface; 3) HYC-M: PICN crown with a CAM-milled interface; and 4) HYC-P: PICN crown with a prefabricated interface. Aged specimens underwent static fracture load testing. The load (N) at which the initial crack occurred was denoted as Finitial, and the maximal load (N) at which the restorations fractured as Fmax. All specimens were examined under a stereomicroscope to determine the failure mode. RESULTS: The median Finitial values were 180 N for LDS-M, 343 N for LDS-P, 340 N for HYC-M, and 190 N for HYC-P. The median Fmax values were 1822 N for LDS-M, 2039 N for LDS-P, 1454 N for HYC-M, and 1581 N for HYC-P. The intergroup differences were significant for Finitial (KW: P = 0.0042) and for Fmax (KW: P = 0.0010). The failure types also showed differences between the restorative groups. CONCLUSIONS: The choice of restorative material had a stronger influence on the fracture load than the abutment interface workflow. Lithium disilicate showed the highest load for initial crack appearance (Finitial) and for complete fracture of the restoration (Fmax).

In-house 3D-printed aligners: effect of in vivo ageing on mechanical properties.

OBJECTIVE: To investigate alterations in the mechanical properties of in-house three-dimensional (3D) printed orthodontic aligners after intraoral ageing. MATERIALS AND METHODS: Sixteen 3D-printed aligners (TC-85DAC resin, Graphy, Seoul, Korea) were used for the purpose of the study, which were divided into 10 control (not used) aligners and 6 materials retrieved from 4 patients after 1-week service (retrieved group). Samples from the control group were analysed by attenuated total reflectance-Fourier-transform infrared (ATR-FTIR) spectroscopy. Samples from control/retrieved groups were embedded resin and subjected to instrumented indentation testing (IIT) to record force-indentation depth curves, calculating the following (as per ISO 14577-1, 2002 standard): Martens hardness (HM), indentation modulus (EIT), and elastic index (ηIT), and the indentation relaxation index (RIT). Differences between control and retrieved 3D-printed aligners were checked with Mann-Whitney/t-tests at an alpha = 5%. RESULTS: ATR-FTIR analysis showed that aligners were made of a vinyl ester-urethane material. The results of the IIT testing were: HM (control: median 91.5 N/mm2, interquartile range [IQR] 88.0-93.0/as-retrieved: median 90.5 N/mm2, IQR 89.0-93.0); EIT (control, mean 2616.3 MPa, standard deviation [SD] 107.0 MPa/retrieved, mean 2673.2 MPa, SD 149.4 MPa); ηIT (control: median 28.6%, IQR 28.2-30.9%/as-retrieved: median 29.0%, IQR 28.7-29.2%); and RIT (control: median 45.5%, IQR 43.0-47.0%/as-retrieved: median 45.1%, IQR 45.0-45.3%). No differences between as-retrieved and control aligners were found for any of the mechanical properties tested (P > 0.05 in all instances). CONCLUSION: The mechanical properties of the in-house 3D-printed aligners tested were not affected after 1 week in service period.

Roughness and wettability of aligner materials.

OBJECTIVE: The characterisation of surface roughness and energy of contemporary thermoplastic materials used in manufacturing of orthodontic aligners. DESIGN: In vitro, laboratory study. MATERIALS AND METHODS: Four commercially available thermoplastic materials were selected (CA-medium/CAM, Essix-copopyester/COP, Duran/DUR and Erkodur/ERK). Five disks from each, as received, material were tested and subjected to: (1) reflected light microscopy; (2) optical profilometry for the estimation of Sa, Sz, Sq, Sdr, Sc, Sv surface roughness parameters (n = 5); and (3) contact angle measurements with a Zisman series of liquids for the estimation of critical surface tension (γC), total work of adhesion (WA), as well as the work of adhesion due to polar (WP) and dispersion (WD) components employing the Zisman method (n = 5/liquid). Thermoformed disks were prepared against a dental stone model and the roughness parameters were calculated again Statistical analysis was performed by one-way ANOVA/ Tukey multiple comparison test and t-test (a = 0.05). RESULTS: Microscopic and profilometric analyses revealed a smooth surface texture in the as-received materials, but a very rough texture after thermoforming, with insignificant differences within each state. Significant differences in the as-received state were found in the surface energy parameters; CAM showed the lowest γC and the highest WA, WP, WD, whereas ERK with the highest γC demonstrated lower WA. COP and DUR were ranked in an intermediate group regarding γC, with a statistically significant difference in WA between them, mainly attributed to the lower WP of the former. CONCLUSION: Given the differences in surface energy parameters and the lack of roughness differences within the as received or thermoformed groups, it may be concluded that variations in the plaque retaining capacity are anticipated, determined by γC, WA and the WP, WD components.

Bonding of Composite to Base Materials: Effects of Adhesive Treatments on Base Surface Properties and Bond Strength.

PURPOSE: To evaluate the effects on the surface properties (morphology, roughness, microhardness, composition) and bond strength to composite of four types of base cements (Equia-Fil/EQF, Angelus white MTA/MTA, Biodentin/BDN and IRM/IRM) when treated with phosphoric acid etching (PAE) or two self-etch adhesives (Select One Prime & Bond and Clearfil S3 Bond). MATERIALS AND METHODS: Disk-shaped specimens were prepared and stored until complete setting. The surfaces before and after treatments were examined by stereomicroscopy, optical profilometry, ATR-FTIR, and LV-SEM/EDX. Interfacial bond strength with composite was evaluated under shear loading (SBS) using a conventional bonding resin (Heliobond) on silane treated (SIL) specimens as a reference. Failure mode was evaluated using stereomicroscopy. RESULTS: PAE induced compositional changes on MTA and BDN, forming a phosphate-rich surface layer, probably composed of Ca-P salts. Dissolution of the amorphous cement fractions was evident in all materials. SPB and CSB did not show remarkable changes apart from an increase in Si content on MTA. On all bases, PAE resulted in the highest values for most of the roughness parameters. SPB and CSB showed lower or equal average roughness (Sa) and percentage of additional surface area contributed by the texture (Sdr) compared to the control in MTA and EQL. In terms of SBS, the highest ß (Weibull shape parameter) in MPa were MTA-SIL = 5.79, BDN-PAE = 3.67, and MTA-PAE = 3.46, whereas the highest α (Weibull scale parameter) were EQF-CSB = 9.08, BDN-PAE = 5.13, and BDN-SIL = 4.67. Adhesive failures with less than 20% of the bonding area were encountered in IRM-PAE and SIL, EQF-CBS and MTA-SIL. CONCLUSION: Each base material requires a different procedure for optimal bonding with composite. Phosphoric acid etching and application of the conventional bonding resin Heliobond is the preferred procedure for composite bonding to MTA, BDN, IRM, but for composite bonding to CSB for EQF, the mild self-etch adhesive is preferable.

Does long-term intraoral service affect the mechanical properties and elemental composition of multistranded wires of lingual fixed retainers?

Purpose: The aim of this study was to evaluate the elemental and mechanical alterations of stainless steel (SS) multistranded orthodontic wires used in fixed retention after intraoral ageing. Materials and Methods: Two types of 0.022-inch, seven-stranded wires, Lingual Retainer Wire (LRW) and Tru-Chrome (TCH), from the same manufacturer (Rocky Mountain Orthodontics, Denver, Colo, USA) were tested. Thirty-three samples from LRW group and thirty-seven from TCH were collected, whereas three unused wires from each package were used as controls. The median ageing time for LRW was 7.4 years and 8.4 for TCH. All samples were subjected to scanning electron microscope/X-ray energy dispersive spectroscopy analysis. Three spectra were taken from the surface of each wire and then all samples were used for the assessment of Martens hardness, indentation modulus (EIT), and elastic index (ηIT) with the instrumented indentation testing method (IIT). The intraoral ageing time was statistically compared between the two groups by Mann-Whitney rank sum test and the compositional and mechanical properties were compared by unpaired t-test. The Spearman correlation between elemental content and ageing time was carried out for all elements (a = 0.05). Results: No significant differences were found for both the elemental content and for the mechanical properties between the wires tested. Spearman analysis revealed no correlation between elemental content and intraoral time while two groups share statistically equal intraoral ageing times (P > 0.05). Conclusions: Both wires seemed to maintain their mechanical and elemental integrity within a period of 14-year intraoral exposure, whereas no measurable ionic release could be identified.

Enamel gloss changes induced by orthodontic bonding.

OBJECTIVE: The purpose of this study was to assess enamel gloss changes induced by orthodontic bracket bonding with a light-cured composite or a light-cured resin-reinforced glass ionomer cement. SETTING: The Department of Biomaterials, School of Dentistry, National and Kapodistrian University of Athens, Greece. DESIGN: Laboratory study. METHODS: A total of twenty extracted upper human first premolars were included in this study and each tooth served as a control for itself. Their buccal surfaces were subjected to 60o-angle gloss measurement (G%60) with a standardized and secure repeated analysis of the same site. After baseline evaluation, a bracket was bonded on the buccal surface of each tooth. Half of the specimens were bonded with acid-etching and a light-cured composite whereas the other half with a light-cured resin-reinforced glass ionomer cement without prior enamel conditioning. Gloss measurements were repeated after bracket debonding and removal of the composite/glass ionomer cement with an 18-fluted carbide bur. Gloss differences between the two measurement conditions (baseline and post-debonding) were analyzed through linear regression with standard errors derived using the bootstrap method. Level of significance was set at a < 0.05. RESULTS: A statistically significant difference was detected between the tested groups for the outcome of interest. Teeth bonded with light-cured composite exhibited larger enamel gloss changes as compared to resin-reinforced glass ionomer cement (ß = 0.74; 95% CIs: 0.10, 1.38; p = 0.02). CONCLUSIONS: Bracket bonding with two common bonding protocols (acid-etching with a light-cured composite vs. no etching with resin reinforced glass-ionomer cement) and subsequently debonding and adhesive removal with an 18-fluted carbide bur induced enamel gloss changes.

Structural, morphological, compositional, and mechanical changes of palatal implants after use: a retrieval analysis.

PURPOSE: The aim of this study was to characterize the surface, elemental, and mechanical alterations of orthodontic palatal implants after intraoral aging. MATERIALS AND METHOD: Nineteen consecutively retrieved implants (RET) after orthodontic treatment and three unused implants used as control (CON) were included in this study. Both groups were characterized non-destructively by Stereomicroscopy, Optical Profilometry (Sa, Sq, Sz, Sc), and SEM/EDX analysis and then destructively after metallogaphic preparation employing instrumented indentation testing (HM, EIT, ηIT, and HV) and SEM/EDX at bone-implant interface. RESULTS: All retrieved implants showed a loss of gloss with the formation of bone-like formation on the majority of them. However, no differences in surface roughness parameters were identified between macroscopically intact and retrieved regions of implants. The elements precipitated on the surface were O, C, Ca, and P while traces of Na, K, Al, S, Cl, and Mg were also identified. The surface of control sample is characterized by small pits while only Ti and Al traces were identified by EDX analysis. The presence of all the aforementioned elements apart from Ti and Al on the retrieved implants' surface should be appended to the contact of implant with bone and biological fluids while Interfacial analysis revealed a well-formed bone-implant interface. However, no significant differences were found for all mechanical properties tested between RET and CON groups. CONCLUSIONS: The results of this study indicate that retrieved palatal implant surface has undergone morphological and elemental alterations probably associated with the osseointegration process during service. Insertion and functional loading did not affect the mechanical properties of implants tested.

Development and testing of novel bisphenol A-free adhesives for lingual fixed retainer bonding.

AIM: To comparatively evaluate the properties of two BPA-free experimental adhesives (EXA, EXB) for lingual fixed retainer bonding versus a commercially available reference material (Transbond LR-TLR) based on BPA-compound. MATERIALS AND METHODS: The experimental materials were a flowable 60 per cent glass filler-filled UEDMA/TEGDMA flowable composite (EXB) and a 70 per cent glass filler-filled paste composite with PCDMA/UEDMA/TEGDMA co-monomers. The properties tested were degree of conversion (DC%), mechanical properties (Martens hardness-MH, elastic modulus-EIT, elastic index-nIT), effect of prolonged (6 months) water storage (changes in Vickers microhardness-VHN) and pull-out strength employing a multi-stranded wire. RESULTS: EXB showed the highest DC% (63.6 per cent), followed by EXA (50.5 per cent) and TRL (44.1 per cent), with all means differences being statistically significant (P < 0.05). The statistical rankings of MH (MPa) and EIT (GPa) means were TLR (76.1MPa; 17.3GPa) > EXA (53MPa; 12.9GPa) > EXB (12.9MPa; 6.7GPa), whereas for nIT, EXB (40 per cent) > EXA (34.9 per cent), TLR (33.6 per cent). All materials were affected by prolonged water storage with significant differences among them in VHN. TLR was the most affected material (ΔVHN = -11 per cent), followed by EXA (ΔVHN = -6.8 per cent) and EXB (ΔVHN = -4.2 per cent). No statistically significant differences were found in the pull-out strength testing (24-24.2 N range) and failure mode (70-77 per cent mixed). CONCLUSION: Considering the differences between the two experimental materials, it may be concluded that the material containing the PCDMA/UEDMA/TEGDMA co-monomers may be used as an alternative to the control.

Effect of Silane Reaction Time on the Repair of a Nanofilled Composite Using Tribochemical Treatment.

PURPOSE: To investigate the influence of silane reaction time on the repair strength of an aged nanofilled composite and to characterize the bonding mechanism. MATERIALS AND METHODS: Nanofilled composite disks (n = 110, Filtek Supreme XT) were aged for 90 days in water. After tribochemical treatment (CoJet-Sand), the specimens were assigned to 5 groups (n = 22), primed with silane (Espe-Sil), and left to react for 1, 2, 3, 4, and 5 min. A thin layer of adhesive (Visio-Bond) was applied and a new composite with the same dimension was placed and cured. Non-aged specimens immediately layered and cured using the incremental technique served as controls. After aging (30 days in water plus 5000 thermal cycles), the interface was subjected to a shearing force until failure. Failure mode was evaluated under a stereomicroscope and scanning electron microscopy (SEM). Additional aged and treated surfaces were evaluated for morphology as well as elemental and molecular composition using SEM/EDX and ATR-FTIR. RESULTS: The mean shear bond strength (SBS) of the repaired specimens was 53.9 ± 8.6 MPa, with no significant difference among the various reaction times, but significantly lower compared to the control (88.1 ± 12.5 MPa). Tribochemical treatment created an irregular surface morphology with particles imbedded in the aged surface. Interfacial SEM/EDX analysis showed a 5-µm non-uniform high atomic number zone rich in Al and Si. CONCLUSION: Tribochemical treatments for repairing composite using a short silane reaction period (1 min) are equally effective as the prolonged reaction periods (2 to 5 min), yielding interfacial shear strength of ~60% of unrepaired material.

Cyclic Loading Effect on Color Stability of Unshaded versus Shaded Zirconia.

STATEMENT OF PROBLEM: Shaded versions of dental zirconia may improve initial color matching to teeth, but might change color with cyclic mechanical loading. PURPOSE: The purpose of this study was to measure the color of unshaded and shaded zirconia dental ceramic before and after cyclic mechanical loading and calculate color differences (ΔE). MATERIAL AND METHODS: Disk-shaped specimens (N = 30, Nobel Procera, 0.8 mm thick, 12 mm diameter) of unshaded or shaded zirconia (intrinsically shaded by small oxide modifications) were fabricated by the Nobel Biocare using standard CAD-CAM processing. Milled surfaces were polished. CIE L*a*b* values were measured (Konica Minolta spectrophotometer) before and after mechanical cycling (custom modified Leinfelder test machine, biaxial flexure loading, load = 80 N × 500,000 cycles, dry), and L*a*b* individual differences and ΔE color differences were calculated and compared (ANOVA, p < 0.05). RESULTS: Mean L*a*b* values for the unshaded group before (U1 = 86.165, -0.887, 0.372) and after (U2 = 84.860, -0.805, 0.097) cyclic loading were compared to the shaded group before (S1 = 75.281, -0.679, 23.251) and after (S2 = 74.961, -1.233, 22.439) cyclic loading. All color variables for both unshaded and shaded groups were significantly different between before and after cyclic loading (p < .004) except for the L* value of the shaded group. The ΔE for unshaded (1.441 ± 0.495) versus shaded (1.252 ± 0.363) were statistically different but clinically the change would not be detectable at this point. CONCLUSIONS: The color of the unshaded and shaded zirconia specimens was influenced by cyclic loading (p < 0.05). Color changes were detectable but small at levels up to 500,000 cycles, and remained clinically acceptable at that point. CLINICAL SIGNIFICANCE: It is important to acknowledge any possible color changes that might occur in zirconia restorations, especially in the esthetic zone. Minor color changes that are individually imperceptible to the human eye within different restorative components may be compounded to produce clinically significant color change that is not aesthetically acceptable.

Porosity of maxillofacial silicone elastomers and microleakage pattern of the commercially pure Ti-silicone elastomer interface after hydrothermal cycling.

STATEMENT OF PROBLEM: Delamination of the maxillofacial silicone elastomer away from the commercially pure titanium (cpTi)-encapsulated magnets affects the long-term performance of the facial restoration. PURPOSE: The purposes of this in vitro study were to investigate the interfacial microleakage patterns of 2 maxillofacial silicone elastomers with cpTi when 3 different primers were used and to evaluate the porosity of the 2 elastomers tested. MATERIAL AND METHODS: To test the interfacial microleakage patterns of the 2 elastomers MDX4-4210 (EL1) and A-2006 (EL2) with cpTi when 3 metal primers, A-304 (PR1), A-320 bonding enhancer (PR2), Super-Bond C&B monomer (PR3), and ethyl-cyanoacrylate (Super Glue) were used, the bonded interfaces were observed using reflected light microscopy, and the percentage of the linear extent of leakage along the interface (%microleakage) was measured. High-resolution x-ray computed microtomography scanning was used to investigate the percentage of void volume fraction (%VF) for both silicone EL1 and EL2. The data were analyzed with 2-way ANOVA and post hoc tests (α=.05). RESULTS: No statistically significant differences were found among the percentages of PR1, PR2, and PR3 microleakage, whereas ethyl-cyanoacrylate showed a statistically significant higher percentage of microleakage than either of the silicone elastomers (P<.001). EL1 medical grade elastomer groups have always had a statistically significantly higher percentage of microleakage than the EL2 platinum silicone elastomer groups (P<.001). For both elastomers, no statistically significant differences were found in %VF (P=.056). CONCLUSIONS: Differences in mechanical properties, chemical composition, and manipulations during handling of the maxillofacial silicone elastomers can affect the linear microleakage along the cpTi-silicone elastomer bonding interface and the porosity of the silicone elastomer.

Composition, phase analysis, biaxial flexural strength, and fatigue of unshaded versus shaded Procera zirconia ceramic.

STATEMENT OF THE PROBLEM: Recent interest in shaded zirconia has raised questions about the relative stability of the tetragonal phase after colorant oxide additions. PURPOSE: The purpose of this in vitro study was to evaluate the effects of fatigue cycling on the stability of a commercially available dental zirconia (Procera) in both unshaded and shaded compositions by measuring the change in biaxial flexural strength (BFS) after 500 000 cycles at 80-N loads and in phase composition as detected by x-ray diffraction (XRD). MATERIAL AND METHODS: Partially stabilized zirconia disks (NobelProcera) were fabricated in unshaded and shaded forms (12 mm diameter × 0.8 mm thick). Specimens were analyzed by energy-dispersive x-ray spectroscopy (EDS) and by wavelength-dispersive x-ray spectroscopy (WDS) for oxide compositions which indicated the presence of small amounts of Fe-O (0.13 ±0.10 wt %) in the shaded specimens. XRD focused on the tetragonal (T) and monoclinic (M) peaks in the 20 to 40 degrees 2θ range. The disks were polished on 1 side, cyclically loaded (80N, 500 000 cycles, custom 4-station fatigue test machine), and tested for residual BFS after cycling. Unshaded (U) and shaded groups (S) were compared before (U1, S1) and after (U2, S2) load cycling with XRD and residual BFS. RESULTS: Residual BFS (MPa) for specimens before (U1=856 ±99 versus S1= 842 ±40) and after fatigue (U2=772 ±65 versus S2= 718 ±68) were statistically different (U1 versus U2; S1 versus S2; U2 versus S2, P<.05). The XRD of U1 and S1 specimens revealed tetragonal and cubic zirconia. U2 and S2 specimens contained tetragonal zirconia, with the initial appearance of small amounts of monoclinic zirconia after fatigue cycling. Monoclinic detection was measured on the tension side of the tested specimens and varied between tests at the center and radially at 4 mm. CONCLUSIONS: The results indicated shaded materials more readily transform the tetragonal to the monoclinic phase during load cycling than unshaded ones. However, extrapolating the effects of any shortening of the service life of zirconia compositions is difficult. The potential mitigating effects of other factors such as the thermal postprocessing of porcelain veneers, stains on zirconia, or effects of water have yet to be investigated.

Retrieval analysis of lingual fixed retainer adhesives.

INTRODUCTION: Our objective was to analyze the surface and bulk properties alterations of clinically aged composites used for fixed retention. METHODS: Twenty-six lingual retainers bonded for different time periods (2.2-17.4 years) were retrieved from postorthodontic patients. Fifteen lingual retainers had been cemented by a chemically cured adhesive (Maximum Cure, Reliance Orthodontic Products, Itasca, Ill), and 11 were treated with a photo-cured adhesive (Flow-Tain, Reliance Orthodontic Products). The first group was in service for 2.8 to 17.4 years and the second for 2.2 to 5.4 years. Five specimens from each material were prepared and used as the control (or reference) group. The debonded surfaces from enamel were studied by attenuated total reflectance Fourier transform infrared spectroscopy (n = 3 per material per group), low-vacuum scanning electron microscopy, and energy dispersive x-ray microanalysis (n = 3 per material per group). All specimens were used for the assessment of Vickers hardness, indentation modulus, and elastic index with the instrumented indentation testing method. The values of Vickers hardness, indentation modulus, and elastic index were compared between the retrieved and the reference groups with 1-way analysis of variance and the Student-Newman-Keuls multiple comparison test (α = 0.05). RESULTS: The attenuated total reflectance Fourier transform infrared spectroscopy analysis showed that both retrieved composites demonstrated reduced unsaturation in comparison with the corresponding reference specimens. Some bonded surfaces showed development of organic integuments. All retrieved specimens showed reduced silicon content. Barium was identified only in the photo-cured group. No significant differences were found between the reference and retrieved groups in Vickers hardness, indentation modulus, and elastic index. CONCLUSIONS: Despite the changes in composition, the mechanical properties of the materials tested remained unaffected by intraoral aging.

Disease and functional loading effect on the structural conformation and mechanical properties of the mandibular condyle in a transgenic rheumatoid arthritis murine model: an experimental study.

AIM: The aim of the present study was to investigate the effect of rheumatoid arthritis (RA) and functional loading through diet modification on the structural conformation and the mechanical properties of the mandibular condyle in a transgenic mouse model and compare to healthy littermates. MATERIALS AND METHODS: Four-week-old hybrid male mice from mixed background CBAxC57BL/6 were used. Four groups of animals were formed consisting of five animals each, either presenting RA (transgenic line hTNF 197), or wild-type (control), half receiving ordinary (hard) diet and half receiving soft diet within each category. Following sacrifice, resin-embedded and metallographically polished condylar specimens were evaluated employing scanning electron microscopy/ Energy dispersive x-ray spectroscopy and also tested for mechanical properties, through Vickers microhardness (HV100) measurements. RESULTS: The multivariable analysis revealed significantly lower HV100 values for the RA groups after adjusting for diet (ß = -10; 95% confidence interval: -16, -4; P = 0.001), while functional loading through diet modification did not appear as a significant predictor of the outcome. CONCLUSIONS: There was evidence of compromised mechanical properties of the mandibular condylar bone for the diseased animals, whereas no association between functional loading and mechanical properties of the condyle could be established.

Do the mechanical and chemical properties of InvisalignTM appliances change after use? A retrieval analysis.

AIM: To investigate the mechanical and chemical alterations of Invisalign appliances after intraoral aging. MATERIALS AND METHODS: Samples of Invisalign appliances (Align Technology, San Jose, California, USA) were collected following routine treatment for a mean period of 44±15 days (group INV), whereas unused aligners of the same brand were used as reference (group REF). A small sample from the central incisors region was cut from each appliance and the buccal surface was analysed by attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy (n = 5). Then the appliances were cut (n = 25) and embedded in acrylic resin, ground/polished in a grinding polishing machine, and the prepared surfaces were subjected to Instrumented Indentation Testing under 4.9 N load. Force-indentation depth curves were recorded for each group and the following parameters were calculated according to ISO 14577-1; 2002 specification: indentation modulus (E IT), elastic to total work ratio also known as elastic index (ηIT), Martens Hardness (HM), and indentation creep (C IT) The mean values of the mechanical properties were statistically analysed by unpaired t-test (a = 0.05). RESULTS: ATR-FTIR analysis confirmed the urethane based structure of the appliances, without important chemical differences attributed to the aging process. INV group showed significantly lower E IT (REF: 2466±20, INV: 2216±168MPa), HM (REF: 119±1, INV: 110±6 N mm-2) and higher ηIT (REF: 40.0±0.3, INV: 41.5±1.2%), and C IT (REF: 3.7±0.2 INV: 4.0±0.1%). The increase in ηIT indicates that INV is a more brittle than REF, whereas the increase in C IT, a decrease in creep resistance. CONCLUSION: Despite the lack of detectable chemical changes, intraoral aging adversely affected the mechanical properties of the Invisalign appliance.