Atypical histological presentation of bone regeneration after insertion of cryoprotected allogeneic bone graft.

BACKGROUND: To evaluate bone regenerative capacity of cryoprotected corticocancellous allogeneic bone graft performed in type II and III post-extraction sockets for ridge preservation after twelve weeks in-vivo. MATERIAL AND METHODS: Twenty-seven type II or III bony-walled extraction sockets (mandible and maxilla) were selected for this study. Following atraumatic tooth-extraction a cryoprotected corticocancellous allogeneic bone graft material and a resorbable porcine-derived collagen membrane were used for ridge preservation. During re-entry surgery at approximately 12 weeks, bone core biopsies were obtained using a 3.2 mm trephine drill and samples were histologically processed and subjected to qualitative and quantitative histomorphometric analysis. Quantitative data was analyzed using a general linear mixed model with results presented as mean values with the corresponding 95% confidence interval values. RESULTS: Healing without incident and ridge preservation allowed for the placement of dental implants after 12 weeks in 25 out of the 27 treated socket sites. Analyses yielded an average of ~21.0±7% of old/native bone, ~17±5.5% of newly regenerated bone (total of ~38±12.8% for all bone), 0.23±0.14% of new bone presenting with nucleating sites within the matrix, ~52±5.12% of soft tissue, and 3.6±2.09% of damaged bone. The average regenerated bone was statistically analogous to that of old/native bone (p=0.355). Furthermore, an atypical histological pattern of bone regeneration was observed, with newly formed bone exhibiting "infiltration-like" behavior and with new bone nucleating sites observed within the demineralized bone matrix. CONCLUSIONS: Cryoprotected corticocancellous allogeneic bone-graft demonstrated osteoconductive, osteoinductive, and osteogenic properties, yielding unique healing patterns which does warrant further investigation.

The effect of nano hydroxyapatite coating implant surfaces on gene expression and osseointegration.

BACKGROUND: Hierarchical micro-nano structured topography along with surface chemistry modifications of dental implants have been suggested to positively contribute to the osseointegration process. However, the effect of such surface modifications on the molecular response as well as bone formation rate and quality are still unclear, especially in the early healing period. This study aimed to evaluate the effect of coating a double acid etched (DAE) implant surface with nano-sized (20 nm) hydroxyapatite (Nano) with respect to gene expression, histologic parameters, and nanomechanical properties when compared to DAE control at 1 and 2 weeks after implant placement in a rodent femur model. MATERIAL AND METHODS: Expression of bone-related genes was determined by qRT-PCR (Col-I, Runx-2, Osx, Opn, Ocn, Alp). Histomorphometric evaluation of bone-to-implant contact (BIC) and bone area fraction occupancy (BAFO) within implant threads was performed using photomicrographs after histologic processing. Mechanical properties, reduced elastic modulus and hardness, were determined through nanoindentation. RESULTS: At 1 week, the Nano group demonstrated significantly higher expression of Col-I and Ocn compared to the DAE group, indicating upregulation of osteoprogenitor and osteoblast differentiation genes. At 2 weeks, Nano surface further exhibited enhanced gene expression of Col-I and Osx in comparison to the DAE surface, suggesting an increased mineralization of the newly formed bone. Nanoindentation analysis revealed that the Nano group presented no significant difference on the ranks of reduced elastic modulus and hardness compared to DAE for both timepoints. Histomorphometric analysis yielded no significant difference in the percentage of BIC and BAFO between the Nano and DAE surfaces at 1 and 2 weeks. However, Nano implants did present a higher mean value, ~50%, of BIC compared to DAE, ~30%, after 2 weeks in vivo. CONCLUSIONS: While no significant differences were observed in the amount and mechanical properties of newly formed bone, Nano surface positively and significantly increased the expression osteogenic genes compared to DAE surface at early healing periods.

Impact of implant thread design on insertion torque and osseointegration: a preclinical model.

BACKGROUND: Successful osseointegration of endosteal dental implants has been attributed to implant design, including the macro-, micro- and nano- geometric properties. Based on current literature pertaining to implant design, the resultant cellular and bone healing response is unknown when the thread thickness of the implants is increased, resulting in an increased contact area in implants designed with healing chambers. The aim of this study was to evaluate the effect of two implant designs with different thread profiles on the osseointegration parameters and implant stability at 3- and 6-weeks in vivo using a well-established preclinical dog model. MATERIAL AND METHODS: A total of 48 type V Ti alloy implants were divided in two groups according to their thread design (D1= +0.1x/mm and D2= +0.15x/mm) and placed in an interpolated fashion into the radii of six beagles. Insertion torque was measured at time of placement, radii were extracted for histological processing following 3- and 6-week healing intervals. Histologic and histomorphometric analyses were performed in terms of bone to implant contact (%BIC) and bone area fraction occupancy within implant threads (%BAFO). Statistical analyses were performed through a linear mixed model with fixed factors of time and implant thread design. RESULTS: Surface roughness analysis demonstrated no significant differences in Sa and Sq between D1 and D2 implant designs, which confirmed that both implant designs were homogenous except for their respective thread profiles. For insertion torque, statistically significant lower values were recorded for D1 in comparison to D2 (59.6 ± 11.1 and 78.9 ± 10.1 N⋅cm, respectively). Furthermore, there were no significant differences with respect to histological analysis and histomorphometric parameters, between D1 and D2 at both time points. CONCLUSIONS: Both thread profiles presented equivalent potential to successfully osseointegrate in the osteotomies, with D2 yielding higher mechanical retention upon placement without detrimental bone resorption.

Bone regeneration at extraction sockets filled with leukocyte-platelet-rich fibrin: An experimental pre-clinical study.

BACKGROUND: We aimed to histomorphometrically evaluate the effects of Leucocyte-Platelet-Rich Fibrin (L-PRF), with and without the combination of a bone grafting material, for alveolar ridge preservation using an in vivo canine model. MATERIAL AND METHODS: Seven dogs (Female Beagles, ~18-month-old) were acquired for the study. L-PRF was prepared from each individual animal by drawing venous blood and spinning them through a centrifuge at 408 RCF-clot (IntrasSpin, Intra-Lock, Boca Raton, FL). L-PRF membranes were obtained from XPression fabrication kit (Biohorizons Implant Systems, Inc., AL, USA). A split mouth approach was adopted with the first molar mesial and distal socket defects treated in an interpolated fashion of the following study groups: 1) Empty socket (negative control); 2) OSS filled defect 3) L-PRF membrane; and 4) Mix of Bio-Oss® with L-PRF. After six weeks, samples were harvested, histologically processed, and evaluated for bone area fraction occupancy (BAFO), vertical/horizontal ridge dimensions (VRD and HRD, respectively), and area of coronal soft tissue infiltration. RESULTS: BAFO was statistically lower for the control group in comparison to all treatment groups. Defects treated with Bio-Oss® were not statistically different then defects treated solely with L-PRF. Collapsed across all groups, L-PRF exhibited higher degrees of BAFO than groups without L-PRF. Defects filled with Bio-Oss® and Bio-Oss® with L-PRF demonstrated greater maintenance of VRD relative to the control group. Collapsed across all groups, Bio-Oss® maintained the VRD and resulted in less area of coronal soft tissue infiltration compared to the empty defect. Soft tissue infiltration observed at the coronal area was not statistically different among defects filled with L-PRF, Bio-Oss®, and Bio-Oss® with L-PRF. CONCLUSIONS: Inclusion of L-PRF to particulate xenograft did not promote additional bone heading at 6 weeks in vivo. However, we noted that L-PRF alone promoted alveolar socket regeneration to levels comparable to particulate xenografts, suggesting its potential utilization for socket preservation.

Effects of a local single dose administration of growth hormone on the osseointegration of titanium implants.

BACKGROUND: The aim of the present study was to evaluate the effect of different concentrations of growth hormone (GH) on endosteal implant's surface at the early stages of osseointegration. MATERIAL AND METHODS: Sixty tapered acid-etched titanium implants were divided into four groups: i) Collagen, used as a control group; and three experimental groups, where after collagen coating, GH was administered directly to the surface in varying concentrations: ii) 0.265 mg, iii) 0.53 mg, and iv) 1 mg. Implants were placed in an interpolated fashion in the anterior flange of C3, C4 or C5 of 15 sheep with minimum distance of 6 mm between implants. After 3-, 6- and 12-weeks of healing samples were harvested, histologically processed, qualitatively and quantitatively assessed for bone-to-implant contact (BIC) and bone area fraction occupancy (BAFO). RESULTS: Statistical analysis as a function of time in vivo and coating resulted in no significant differences for BIC and BAFO at any evaluation time point. Histological evaluation demonstrated similar osseointegration features for all groups with woven bone formation at 3 weeks and progressive replacement of woven for lamellar bone in close contact with the implant surface and within the implant's threads. CONCLUSIONS: A single local application of growth hormone to the surface of titanium implants did not yield improved implant osseointegration independent of healing time.

Microtomographic reconstruction of mandibular defects treated with xenografts and collagen-based membranes: A pre-clinical minipig model.

BACKGROUND: The goal of this study was to evaluate hard tissue response following guided bone regeneration using commercially available bovine bone grafts and collagen membranes; bilayer collagen membrane and porcine pericardium-based membrane, by means of a non-destructive three-dimensional (3D) computerized volumetric analysis following microtomography reconstruction. MATERIAL AND METHODS: Bone regenerative properties of various bovine bone graft materials were evaluated in the Göttingen minipig model. Two standardized intraosseous defects (15mm x 8mm x 8mm) were created bilaterally of the mandible of eighteen animals (n=72 defects). Groups were nested within the same subject and randomly distributed among the sites: (i) negative control (no graft and membrane), (ii) bovine bone graft/bilayer collagen membrane (BOB) (iii) Bio-Oss® bone graft/porcine pericardium-based membrane (BOJ) and (iv) cerabone® bone graft/porcine pericardium-based membrane (CJ). Samples were harvested at 4, 8, and 12-week time points (n=6 animal/time point). Segments were scanned using computerized microtomography (µCT) and three dimensionally reconstructed utilizing volumetric reconstruction software. Statistical analyses were performed using IBM SPSS with a significance level of 5%. RESULTS: From a temporal perspective, tridimensional evaluation revealed gradual bone ingrowth with the presence of particulate bone grafts bridging the defect walls, and mandibular architecture preservation over time. Volumetric analysis demonstrated no significant difference between all groups at 4 weeks (p>0.127). At 8 and 12 weeks there was a higher percentage of new bone formation for control and CJ groups when compared to BOB and BOJ groups (p<0.039). The natural bovine bone graft group showed more potential for graft resorption over time relative to bovine bone graft, significantly different between 4 and 8 weeks (p<0.003). CONCLUSIONS: Volumetric analysis yielded a favorable mandible shape with respect to time through the beneficial balance between graft resorption/bone regenerative capacity for the natural bovine bone graft.

Assessing osseointegration of metallic implants with boronized surface treatment.

BACKGROUND: Modification of endosteal implants through surface treatments have been investigated to improve osseointegration. Boronization has demonstrated favorable mechanical properties, but limited studies have assessed translational, in vivo outcomes. This study investigated the effect of implant surface boronization on bone healing. MATERIAL AND METHODS: Two implant surface roughness profiles (acid etched, machined) in CP titanium (type II) alloy implants were boronized by solid-state diffusion until 10-15µm boron coating was achieved. The surface-treated implants were placed bilaterally into 5 adult sheep ilia for three and six weeks. Four implant groups were tested: boronized machined (BM), boronized acid-etched (BAA), control machined (CM), and control acid-etched (CAA). Osseointegration was quantified by calculating bone to implant contact (BIC) and bone area fraction occupancy (BAFO). RESULTS: Both implant types treated with boronization had BIC values not statistically different from machined control implants at t=3 weeks, and significantly less than acid-etched control (p<0.02). BAFO values were not statistically different for all 3-week groups except machined control (significantly less at p <0.02). BAFO had a significant downward trend from 3 to 6 weeks in both boronized implant types (p<0.03) while both control implant types had significant increases in BIC and BAFO from 3 to 6 weeks. CONCLUSIONS: Non-decalcified histology depicted intramembranous-like healing/remodeling in bone for controls, but an absence of this dynamic process in bone for boronized implants. These findings are inconsistent with in vitro work describing bone regenerative properties of elemental Boron and suggests that effects of boron on in vivo bone healing warrant further investigation.

Osteogenic parameters surrounding trabecular tantalum metal implants in osteotomies prepared via osseodensification drilling.

BACKGROUND: Surgical fixation of implants into bone for the correction of bone deformities or defects is a traditional approach for skeletal stabilization. Important measures of efficacy of implants include implant stability and osseointegration-the direct interaction between living bone and an implant. Osseointegration depends on successful implant placement and subsequent bone remodeling. This study utilized osseodensification drilling (OD) in a low bone density model using trabecular metal (TM) implants. MATERIAL AND METHODS: Three osteotomy sites, Regular, OD-CW (clockwise), and OD-CCW (counterclockwise), were prepared in each ilium of three female sheep. Drilling was performed at 1100rpm with saline irrigation. Trabecular metal (TM) (Zimmer, Parsippany, NJ, USA) implants measuring 3.7mm in diameter x 10mm length were placed into respective osteotomies. A three-week period post-surgery was given to allow for healing to take place after which all three sheep were euthanized and the ilia were collected. Samples were prepared, qualitatively and quantitatively analyzed using histology micrographs and image analysis software (ImageJ, NIH, Bethesda, MD). Bone-to-implant contact (BIC) and bone area fraction occupancy (BAFO) were quantified to evaluate the osseointegration parameters. RESULTS: All implants exhibit successful bone formation in the peri-implant environment as well as within the open spaces of the trabecular network. Osseointegration within the TM (quantified by %BIC) as a function of drilling technique was more pronounced in OD samples(p>0.05). The %BAFO however shows a significant difference (p=0.036) between the CCW and R samples. Greater bone volume and frequency of bone chips are observed in OD samples. CONCLUSION: The utilization of OD as a design for improved fixation of hardware was supported by increased levels of stability, both primary and secondary. Histological data with OD provided notably different results from those of the regular drilling method.

Effect of implant placement depth on the peri-implant bone defect configurations in ligature-induced peri-implantitis: An experimental study in dogs.

BACKGROUND: The subcrestal placement of implant platform has been considered a key factor in the preservation of crestal bone, but the influence of implant placement depth on bone remodeling combined with peri-implantitis is not fully understood. The aim of this study was to assess the effect of the crestal or subcrestal placement of implants on peri-implant bone defects of ligature-induced peri-implantitis in dogs. MATERIAL AND METHODS: Eight weeks after tooth extraction in six beagle dogs, two different types of implants (A: OsseoSpeed(TM), Astra, Molndal, Sweden; B: Integra-CP(TM), Bicon, Boston, USA) were placed at either crestal or subcrestal (-1.5 mm) positions on one side of the mandible. Ligature-induced peri-implantitis was initiated four weeks after the installation of the healing abutment connections. After 12 weeks, tissue biopsies were processed for histological analyses. RESULTS: Supra-alveolar bone loss combined with a shallow infrabony defect was observed in crestal level implants while deep and wide infrabony defects were present in subcrestal level groups. Subcrestal groups showed significantly greater ridge loss, depths and widths of infrabony defects when compared to crestal groups (P <0.001). CONCLUSIONS: Within the limitations of the animal study, it can be stated that the implants at subcrestal position displayed greater infra-osseous defect than implants at crestal position under an experimental ligature-induced peri-implantitis.

A Critical Perspective on Mechanical Testing of Implants and Prostheses.

The degree of interplay among variables in dental implant treatment presents a challenge to randomized clinical trials attempting to answer questions in a timely, unbiased, and economically feasible fashion. Further adding complexity to the different scenarios is the varied implant designs and related bone response, area of implantation, implant bulk material, restoration, abutments and related screws, fixation mode (screwed, fixed, or a combination), and horizontal implant-abutment matching geometry. This article critically appraises the most common mechanical testing methods used to characterize the implant-prostheses complex. It attempts to provide insight into the process of construction of an informed database of clinically relevant questions regarding preclinical evaluation of implant biomechanics and failure mechanisms. The use of single load to failure, fatigue life, fatigue limit, and step-stress accelerated life testing is discussed with emphasis on their deliverables, weaknesses, and strengths. Fractographic analysis and challenges in the correlation between laboratory- and in-service-produced failures of dental ceramics, resin composites, and titanium are introduced. In addition, examples are presented of mechanical characterization studies used in our laboratory to assess some implant-supported rehabilitation variables.

Effect of calcination on minimally processed recycled zirconia powder derived from milling waste.

OBJECTIVE: To assess the influence of calcination process on the properties of minimally processed recycled 3Y-TZP, and to compare it with its commercial counterpart. METHODS: Non-milled 3Y-TZP waste was collected, fragmented and ball-milled to a granulometric < 5 µm. Half of the recycled powder was calcined at 900 °C. Recycled 3Y-TZP disks were uniaxially pressed and sintered to create two recycled groups: 1) Calcined and 2) Non-calcined to be compared with a commercial CAD/CAM milled 3Y-TZP. The microstructure of experimental groups was assessed through density (n = 6), scanning electron microscopy (n = 3) and energy-dispersive X-ray spectroscopy (n = 3); and the crystalline content was evaluated through X-ray diffraction (XRD) (n = 3). Optical and mechanical properties were investigated through reflectance tests (n = 10), and Vickers hardness, fracture toughness (n = 5), and biaxial flexural strength tests (n = 16), respectively. Fractographic analysis was performed to identify fracture origin and crack propagation. Statistical analyses were performed through ANOVA followed by Tukey´s test, and by Weibull statistics. RESULTS: Particle size distribution of recycled powder revealed an average diameter of ∼1.60 µm. The relative density of all experimental groups was > 98.15 % and XRD analysis exhibited a predominance of tetragonal-phase in both recycled groups, which were similar to the crystallographic pattern of the control group. Cross-section micrographs presented flaws on the non-calcined group, and a more homogeneous microstructure for the calcined and commercial groups. Commercial samples showed lower contrast-ratio and higher translucency-parameter than the recycled groups, where non-calcined presented higher translucency-parameter and lower contrast-ratio than its calcined counterpart. The commercial group presented higher fracture toughness and characteristic strength than the recycled groups. Moreover, the calcined group exhibited higher hardness, characteristic strength, and probability of survival at higher loads than the non-calcined group. Fractographic analysis depicted the presence of microstructural flaws in the non-calcined group, which may have acted as stress-raisers and led to failures at lower flexural strengths values. SIGNIFICANCE: The calcination process improved the microstructure, optical, and mechanical properties of the recycled 3Y-TZP.

Effect of High-radiant Emittance and Short Curing Time on Polymerization Shrinkage Vectors of Bulk Fill Composites.

PURPOSE: To evaluate the effect of short curing time using a high-radiant emittance light on polymerization shrinkage vectors in different consistency bulk-fill composites (BFRCs) using micro-computed tomography. METHODS AND MATERIALS: Radiopaque zirconia fillers were homogeneously incorporated and functioned as radiopaque tracers into two regular-paste: TBFill (Tetric EvoCeram Bulk Fill) and TPFill (Tetric PowerFill), and two flowable (n=6): TBFlow (Tetric EvoFlow Bulk Fill) and TPFlow (Tetric PowerFlow) resin composites. Class I cavities (4 mm depth × 4 mm length × 4 mm width) were 3D-printed and filled in a single increment: TBFill and TBFlow were light-activated using a Bluephase Style 20i (10 seconds in high-mode); TPFill and TPFlow were light-activated using a Bluephase PowerCure (three seconds). The same adhesive system (Adhese Universal) was used for all groups. Microcomputed tomography scans were obtained before and after light-activation. Filler particle movement was identified by polymerization shrinkage vectors at five depths (from 0-4 mm): top, top-middle, middle, middle-bottom and bottom. RESULTS: TPFlow showed the lowest total vector displacement, followed by TBFlow, TBFill and TPFill, significantly different among each other (p<0.05). Generally, BFRCs showed decreased vector displacement with increased depth, and higher displacement at the top-surface (p<0.05). Qualitative analysis showed a similar pattern of vector magnitude and displacement for groups TBFill and TPFill, with displacement vectors on occlusal (top) surfaces toward the center of the restoration from the top to middle areas, and relatively limited displacement at the bottom. TBFlow and TPFlow showed more displacement on the occlusal (top). CONCLUSIONS: Short curing time with high-radiant emittance on fast-curing BFRCs was shown to be a feasible option in terms of vector displacement. Flowable BFRCs presented lower vector displacement than their regular-viscosity versions.

Characteristics of implant-CAD/CAM abutment connections of two different internal connection systems.

Titanium or zirconium computer-aided design/computer-aided manufacturing abutments are now widely used for aesthetic implant treatments; however, information regarding microscopic structural differences that may influence the biological and mechanical outcomes of different implant systems is limited. Therefore, the characteristics of different connection systems were investigated. Optical microscopic observation and scanning electron microscopy showed different characteristics of two internal systems, namely the Astra Tech and the Replace Select system, and for different materials. The scanning electron microscopic observation showed for the Astra Tech that the implant-abutment interface seemed to be completely sealed for both titanium and zirconium abutments, both horizontally and sagittally; however, the first implant-abutment contact was below the fixture top, creating a microgap, and fixtures connected with titanium abutments showed significantly larger values (23·56µm±5·44 in width, and 168·78µm±30·39 in depth, P<0·001). For Replace Select, scanning electron microscopy in the sagittal direction showed that the sealing of titanium and zirconium abutments differed. The seal between the implant-titanium and implant-zirconium abutments seemed to be complete at the butt-joint interface; however, the displacement of the abutment in relation to the fixture in the lateral direction was evident for both abutments with no statistical differences (P>0·70), creating an inverted microgap. Thus, microscopy evaluation of two commonly used internal systems connected to titanium or zirconium abutments showed that the implant-abutment interface was perfectly sealed under no-loading conditions. However, an inverted microgap was seen in both systems, which may result in bacterial accumulation as well as alteration of stress distribution at the implant-abutment interface.

Nanoscale physico-mechanical properties of an aging resistant ZTA composite.

OBJECTIVE: To characterize the effects of aging on the nanomechanical properties and 3D surface topographical parameters of an experimental Zirconia Toughened Alumina (ZTA) composite compared to its respective individual counterpart materials. METHODS: Disk-shaped specimens comprised of three material groups were processed: 1) ZTA 70/30 (70% alumina reinforced with 30% second-generation 3Y-TZP); 2) Zpex (Second-generation 3Y-TZP), and; 3) Al2O3 (High purity Alumina) (n = 10/material, 12 × 1 mm). After synthesis, ceramic powders were pressed, the green-body samples were sintered and polished. Nanoindentation testing was performed to record elastic modulus (E) and hardness (H). Interferometry was utilized to assess 3D surface roughness parameters (Sa, Sq), while X-ray diffraction (XRD) and scanning electron microscope (SEM) assessed the crystalline content and microstructure. All tests were performed before and after simulated aging (134°C, 2.2 bar, 20 h). Statistical analyses were performed using linear mixed-model and least square difference pos-hoc tests (α = 5%). RESULTS: XRD spectra indicated increase of monoclinic peaks for Zpex (~18%) relative to ZTA 70/30 (~2.5%) after aging. Additionally, aging did not affect the surface roughness parameters of ZTA 70/30 and Al2O3, although a significant increase in Sa was recorded for Zpex following aging (~90 nm) (p < 0.001). Al2O3 yielded the highest H and E values (H:21 GPa, E: 254 GPa), followed by ZTA 70/30 (H: 13 GPa, E: 214 GPa) and Zpex (H:11 GPa, E: 167 GPa), all significantly different (p < 0.03). CONCLUSION: ZTA 70/30 and Al2O3 presented high hydrothermal stability with respect to all evaluated variables, where artificial aging significantly increased the monoclinic content and surface roughness of Zpex.

Microstructural, mechanical, and optical characterization of an experimental aging-resistant zirconia-toughened alumina (ZTA) composite.

OBJECTIVE: To evaluate the effect of aging on the microstructural, mechanical, and optical properties of an experimental zirconia-toughened alumina composite with 80%Al2O3 and 20%ZrO2 (ZTA Zpex) compared to a translucent zirconia (Zpex) and Alumina. METHODS: Disc-shaped specimens were obtained by uniaxial and isostatic pressing the synthesized powders (n = 70/material). After sintering and polishing, half of the specimens underwent aging (20 h, 134 °C, 2.2 bar). Crystalline content and microstructure were evaluated using X-ray diffraction and scanning electron microscopy, respectively. Specimens underwent biaxial flexural strength testing to determine the characteristic stress, Weibull modulus, and reliability. Translucency parameter (TP) and Contrast ratio (CR) were calculated to characterize optical properties. RESULTS: ZTA Zpex demonstrated a compact surface with a uniform dispersion of zirconia particles within the alumina matrix, and typical alumina and zirconia crystalline content. ZTA Zpex and alumina exhibited higher CR and lower TP than Zpex. ZTA Zpex and Zpex showed significantly higher characteristic stress relative to alumina. While aging did not affect optical and mechanical properties of ZTA Zpex and alumina, Zpex demonstrated a significant increase in translucency, as well as a in characteristic stress. Alumina reliability was significantly lower than others at 300 MPa, ZTA Zpex and Zpex reliability decreased at 800 MPa, except for aged Zpex. SIGNIFICANCE: While aging did not affect the mechanical nor the optical properties of ZTA Zpex and alumina, it did alter both properties of Zpex. The results encourage further investigations to engineer ZTA as a framework material for long span fixed dental prostheses specially where darkened substrates, such as titanium implant abutments or endodontically treated teeth, demand masking.

Aging resistance of an experimental zirconia-toughened alumina composite for large span dental prostheses: Optical and mechanical characterization.

PURPOSE: To synthesize a zirconia-toughened alumina (ZTA) composite with 85% alumina matrix reinforced by 15% zirconia and to characterize its optical and mechanical properties before and after artificial aging, to be compared with a conventional dental zirconia (3Y-TZP). MATERIAL AND METHODS: After syntheses, ZTA and 3Y-TZP powders were uniaxially and isostatically pressed. Green-body samples were sintered and polished to obtain 80 disc-shaped specimens per group (12 × 1 mm, ISO 6872:2015). The crystalline content and microstructure were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). Optical properties were determined by the calculation of contrast ratio (CR) and translucency parameter (TP) using reflectance data. Mechanical properties were assessed by Vickers hardness, fracture toughness and biaxial flexural strength test (BFS). All analyses were conducted before and after artificial aging (20h, 134 °C, 0.22 MPa). Optical parameters and microhardness differences were evaluated through repeated-measures analysis of variance (p < 0.05). BFS data were analyzed using Weibull statistics (95% CI). RESULTS: The synthesis of the experimental ZTA composite was successful, with 98% of theoretical density, as shown in the SEM images. XRD patterns revealed typical zirconia and alumina crystalline phases. ZTA optical properties parameters showed no effect of aging, with a high CR and low TP values denoting a high masking-ability. 3Y-TZP presented lower masking-ability and aging significantly affected its optical properties. ZTA Vickers hardness, fracture toughness and Weibull parameters, including characteristic stress and Weibull modulus were not influenced by aging, while 3Y-TZP presented a significant decrease in characteristic stress and increase in fracture toughness after aging. The ZTA probability of survival for missions of 300 and 500 MPa was estimated at ~99% validating its use for 3-unit posterior fixed dental prostheses (FDP), and no different from conventional 3Y-TZP. At high-stress mission (800 MPa) a significant decrease in probability of survival was observed for aged 3Y-TZP (84%) and for immediate and aged ZTA (73 and 82% respectively). CONCLUSION: The ZTA composite presented a dense microstructure, with preservation of the crystalline content, optical and mechanical properties after artificial aging, which encourages future research to validate its potential use for large span FDP.

Effect of Thermocycling on Biaxial Flexural Strength of CAD/CAM, Bulk Fill, and Conventional Resin Composite Materials.

New resin-based restorative materials have been developed, such as computer-aided design/computer-aided manufacturing (CAD/CAM) and bulk-fill composites, as an alternative to traditional layering techniques. This study evaluated the biaxial flexural strength (BFS) before and after thermocycling of five different resin composites: one hybrid resin/ceramic CAD/CAM indirect material, Lava Ultimate CAD-CAM Restorative (LU, 3M Oral Care); a conventional composite, Filtek Z350 XT (Z350, 3M Oral Care); two bulk-fill composites, Tetric N-Ceram Bulk Fill (TBF, Ivoclar Vivadent) and Filtek Bulk Fill (FBF, 3M Oral Care); and one bulk-fill flow resin composite, Filtek Bulk Fill Flow (FBFF, 3M Oral Care). Three hundred disc-shaped specimens (6.5 mm in diameter and 0.5 mm thick) were fabricated and divided into five groups (n=30 for each composite and condition). The BFS test was performed in a universal testing machine at a crosshead speed of 0.5 mm/min immediately (i, 24 hours) and after thermocycling (a, 500 thermal cycles of 5°C to 55°C with a 30-second dwell time). The Weibull modulus (m) and characteristic stress (η) were calculated, and a contour plot was used (m vs η) to detect differences between groups (95% two-sided confidence intervals). Significantly higher characteristic stress was observed for LUi (286.6 MPa) and Z350i (248.8 MPa) compared to the bulk-fill groups (FBFi=187.9 MPa, FBFFi=175.9 MPa, TBFi=149.9 MPa), with no differences between LUi and Z350i. Thermocycling significantly decreased the characteristic stress of all groups with the highest values observed for LUa (186.7 MPa) and Z350a (188.9 MPa) and the lowest for FBFFa (90.3 MPa). Intermediate values were observed for FBFa (151.6 MPa) and TBFa (122.8 MPa). The Weibull modulus decreased only for FBFa compared to FBFi. Composition and thermocycling significantly influenced the biaxial flexural strength of resin composite materials.

Laboratory and FEA evaluation of dentin-to-composite bonding as a function adhesive layer thickness.

OBJECTIVE: The aim of this study was to test the hypothesis that microtensile bond strength values are inversely proportional to dentin-to-composite adhesive layer thickness through laboratory mechanical testing and finite element analysis. METHOD: Eighteen noncarious third molars were obtained, and occlusal enamel removed perpendicular to the tooth long axis. Two different adhesive systems were utilized as follows (n=3): (1) application of a single layer of Single Bond (3M ESPE Co.) and Clearfil SE Bond (Kuraray Co.) following the manufacturer's directions; (2) application of one layer of both adhesive systems followed by one additional layer; (3) application of one layer of both adhesive systems followed by two additional layers. A 4mm build up was fabricated in increments on each tooth sample (Z 100 composite, 3M ESPE). Section measurements were performed and specimens were separated into three adhesive thickness groups per material (40, 40-80 and 80-120 microm) for microtensile testing. The bond strength data (MPa) were analyzed by one-way ANOVA and Tukey test. Maximum principal stresses (MPS) were determined through FEA for three different adhesive layer thicknesses (20, 50 and 100 microm). RESULTS: The bond strength data obtained for Single Bond at 0-40 microm presented significantly higher values compared to higher adhesive layer thickness groups. There were no statistical differences among bond strength values for all Clearfil SE Bond adhesive layer thicknesses. FEA modeling indicated that MPS increased as adhesive layer increased. The hypothesis was accepted for the Single Bond only. SIGNIFICANCE: Correspondence (not tested statistically) between microtensile laboratory testing and FEA model was only observed for Single Bond as increased adhesive layer thickness did not reduce Clearfil SE Bond strength.

In vitro evaluation of the implant abutment connection sealing capability of different implant systems.

This study sought to evaluate the sealing capability of the implant abutment connection of different dental implant systems. Five Nobel Replace select, Straumann and Intra-lock implants of approximately 4.5 mm diameter with their respective abutments were provided by the manufacturers. A calibration curve was determined by placing toluidine blue (TB) increments of 0.1 microL into 1.5 mL of distilled water and recording its absorbance in a spectrophotometer until reaching 0.7 microL. Then, 0.7 microL of TB was placed in the deepest portion of each implant's internal screw, the abutments were adapted to the implant according to the manufacturer's instructions and the specimens were placed in vials with 1.5 mL of distilled water. Spectrophotometric analysis was performed at 1, 3, 6, 24, 48, 72, 96 and 144 h. Statistical analysis was performed by One-way anova at 95% level of significance. The calibration curve was linear with respect to the TB amount in 1.5 microL distilled water (R(2) = 0.9961). All implant abutment systems presented an increase in absorbance as a function of time. As time elapsed in vitro, significantly higher amounts of TB was released from the Straumann and Nobel Replace Select connection systems (P < 0.0001). Leakage was significant between the groups. Despite controlled torquing, the seal between the implant body and the abutment could not be maintained in all three of the systems tested.

Effect of Sonic Resin Composite Delivery on Void Formation Assessed by Micro-computed Tomography.

OBJECTIVES: The aim of this study was to quantify the internal void volume formation in commercially available, resin composites inserted using conventional or sonic insertion methods, and analyzed using three-dimensional (3D) micro-computed tomography (µCT). METHODS AND MATERIALS: Four resin composites were evaluated: one conventional (Herculite, Ultra, Kerr Corporation, Orange, CA, USA), one flowable bulk fill (SureFil SDR Flow, Dentsply International, York, PA, USA), and two packable bulk fill (SonicFill, Kerr Corporation, and Tetric EvoCeram Bulk Fill, Ivoclar Vivadent Inc, Schaan, Liechtenstein). Eight groups were evaluated according to each resin composite type and insertion method (conventional or sonic; n=5). Forty ABS 3D-printed cylindrical molds, 5.0 mm in diameter and 4.0 mm in depth, were fabricated. For the conventional resin composite, the mold was filled incrementally (two layers), while for bulk-fill resin composites, insertion was performed in a single increment. The sonic insertion method was performed using a specific handpiece (SonicFill Handpiece, Kerr Corporation). Resin composites were light cured using a multipeak light-emitting diode light-curing unit (VALO, Ultradent Products Inc, South Jordan, UT, USA) in its regular mode. Samples were evaluated by µCT, and data were imported into software (Amira, version 5.5.2, VSG, Burlington, MA, USA) for 3D reconstruction, from which the percentage of void volume was calculated. Data were analyzed using two-way analysis of variance and Tukey post hoc test at a preset alpha of 0.05. RESULTS: The conventional insertion method resulted in reduced porosity, compared with sonic insertion, for SureFil SDR Flow and Tetric EvoCeram bulk fill. The sonic insertion method did not demonstrate any influence on void formation for Herculite Ultra or SonicFill. CONCLUSION: Results suggest that the sonic insertion method might increase void formation during resin composite delivery, depending on restorative material brand.