Factors influencing the progression of noncarious cervical lesions: A 5-year prospective clinical evaluation.

STATEMENT OF PROBLEM: The etiology (chemical, friction, abfraction) of noncarious cervical lesion (NCCL) progression is poorly understood. PURPOSE: The purpose of this 5-year prospective clinical trial was to measure the relationship between NCCLs and various etiologic factors. MATERIAL AND METHODS: After review board approval, 29 participants with NCCLs were enrolled. Polyvinyl siloxane impressions were made of each NCCL, and casts were poured at baseline, 1, 2, and 5 years. The casts were scanned with a noncontact profilometer, and 1-, 2-, and 5-year scans were superimposed over baseline scans to measure volumetric change in NCCLs. T-scan and Fujifilm Prescale films were used to record relative and absolute occlusal forces on teeth with NCCLs at the 5-year recall. Participant diet, medical condition, toothbrushing, and adverse oral habit questionnaires were given at the 5-year recall. Occlusal analysis was completed on mounted casts to determine the presence of wear facets and group function. Volumetric lesion progression from 1 to 5 years was correlated to absolute and relative occlusal force using mixed model analysis. The Kruskall-Wallis and Mann-Whitney analyses compared lesion progression with diet, medical condition, toothbrushing, adverse oral habits, wear facets, and group function. RESULTS: The NCCL progression rate over 5 years was 1.50 ±0.92 mm(3)/yr. The rate of progression of NCCLs was related to mean occlusal stress (P=.011) and relative occlusal force (P=.032) in maximum intercuspation position. No difference was seen in NCCL progression between participants with any other factors. CONCLUSION: Heavy occlusal forces play a significant role in the progression of NCCLs.

Influence of implant angulation on the fracture resistance of zirconia abutments.

PURPOSE: To investigate the effects of abutment design to correct for implant angulation and aging on the fracture resistance of zirconia abutments. Greater understanding of the fracture strength of the zirconia abutments under various clinical conditions may lead to improvement of clinical protocols and possibly limit potential failures of implant prosthetics. MATERIALS AND METHODS: Test specimens consisted of an implant-zirconia abutment-zirconia crown assembly with implant apex positioned at 0°, 20° to the facial (20F), and 20° to the lingual (20L) with respect to a constant crown contour. To keep the abutment design as the only variable, CAD/CAM technology was used to generate monolithic zirconia crowns identical both in external and internal dimensions and marginal contours to precisely fit all the abutments in an identical fashion. The monolithic zirconia abutments were designed to fit the constant crown contours and the internal connection of the implant at the three angulations. The customized abutments for the three implant angulations varied in emergence profile, screw hole location, and material thickness around the screw hole. Half the specimens from each group were subjected to steam autoclaving and thermocycling to simulate aging of the restorations in vivo. To mimic the off-axis loading of the central incisor, the specimens were loaded at the recommended cephalometric interincisal relationship of 135° between the long axis of the crown supported by the implant and the Instron force applicator simulating the mandibular incisor. The force applicator was positioned 2 mm from the incisal edge and loaded at a 1 mm/min crosshead speed. Data were evaluated by 2-way ANOVA (α = 0.05) and Tukey's HSD. RESULTS: The 20F group had the highest fracture values followed by the 0° group, and the 20L group had the lowest fracture values. Aging did not yield any significant difference in fracture force magnitudes. CONCLUSION: Within the limitations of this study, tilting the implant apex to the lingual significantly reduced the fracture strength of angle-corrected zirconia abutments. Accordingly, while the angle between the occlusal force application and the long axis of the implant decreases, the resistance (force) to fracture decreases.

Multilevel Assessment of Stent-Induced Inflammation in the Adjacent Vascular Tissue.

A recent U.S. Food and Drug Administration report presented the currently available scientific information related to biological response to metal implants. In this work, a multilevel approach was employed to assess the implant-induced and biocorrosion-related inflammation in the adjacent vascular tissue using a mouse stent implantation model. The implications of biocorrosion on peri-implant tissue were assessed at the macroscopic level via in vivo imaging and histomorphology. Elevated matrix metalloproteinase activity, colocalized with the site of implantation, and histological staining indicated that stent surface condition and implantation time affect the inflammatory response and subsequent formation and extent of neointima. Hematological measurements also demonstrated that accumulated metal particle contamination in blood samples from corroded-stetted mice causes a stronger immune response. At the cellular level, the stent-induced alterations in the nanostructure, cytoskeleton, and mechanical properties of circulating lymphocytes were investigated. It was found that cells from corroded-stented samples exhibited higher stiffness, in terms of Young's modulus values, compared to noncorroded and sham-stented samples. Nanomechanical modifications were also accompanied by cellular remodeling, through alterations in cell morphology and stress (F-actin) fiber characteristics. Our analysis indicates that surface wear and elevated metal particle contamination, prompted by corroded stents, may contribute to the inflammatory response and the multifactorial process of in-stent restenosis. The results also suggest that circulating lymphocytes could be a novel nanomechanical biomarker for peri-implant tissue inflammation and possibly the early stage of in-stent restenosis. Large-scale studies are warranted to further investigate these findings.

Validation of strain gauges as a method of measuring precision of fit of implant bars.

UNLABELLED: Multiple articles in the literature have used strain gauges to estimate the precision of fit of implant bars. However, the accuracy of these measurements has not been fully documented. The purpose of this study was to evaluate the response of strain gauges to known amounts of misfit in an implant bar. This is an important step in validation of this device. MATERIALS: A steel block was manufactured with five 4.0-mm externally hexed implant platforms machined into the block 7-mm apart. A 1.4-cm long gold alloy bar was cast to fit 2 of the platforms. Brass shims of varying thickness (150, 300, and 500 microm) were placed under one side of the bar to create misfit. A strain gage was used to record strain readings on top of the bar, one reading at first contact of the bar and one at maximum screw torque. Microgaps between the bar and the steel platforms were measured using a high-precision optical measuring device at 4 points around the platform. The experiment was repeated 3 times. Two-way analysis of variance and linear regression were used for statistical analyses. RESULTS: Shim thickness had a significant effect on strain (P < 0.0001). There was a significant positive correlation between shim thickness and strain (R(2) = 0.93) for strain at maximum torque, and for strain measurements at first contact (R(2) = 0.91). Microgap measurements showed no correlation with increasing misfit. CONCLUSIONS: Strain in the bar increased significantly with increasing levels of misfit. Strain measurements induced at maximum torque are not necessarily indicative of the maximum strains experienced by the bar. The presence or absence of a microgap between the bar and the platform is not necessarily indicative of passivity. These data suggest that microgap may not be clinically reliable as a measure of precision of fit.

Comparison of the passivity between cast alloy and laser-welded titanium overdenture bars.

PURPOSE: The purpose of this study was to investigate the fit of cast alloy overdenture and laser-welded titanium-alloy bars by measuring induced strain upon tightening of the bars on a master cast as well as a function of screw tightening sequence. MATERIALS AND METHODS: Four implant analogs were secured into Type IV dental stone to simulate a mandibular edentulous patient cast, and two groups of four overdenture bars were fabricated. Group I was four cast alloy bars and Group II was four laser-welded titanium bars. The cast alloy bars included Au-Ag-Pd, Pd-Ag-Au, Au-Ag-Cu-Pd, and Ag-Pd-Cu-Au, while the laser-welded bars were all Ti-Al-V alloy. Bars were made from the same master cast, were torqued into place, and the total strain in the bars was measured through five strain gauges bonded to the bar between the implants. Each bar was placed and torqued 27 times to 30 Ncm per screw using three tightening sequences. Data were processed through a strain amplifier and analyzed by computer using StrainSmart software. Data were analyzed by ANOVA and Tukey's post hoc test. RESULTS: Significant differences were found between alloy types. Laser-welded titanium bars tended to have lower strains than corresponding cast bars, although the Au-Ag-Pd bar was not significantly different. The magnitudes of total strain were the least when first tightening the ends of the bar. CONCLUSIONS: The passivity of implant overdenture bars was evaluated using total strain of the bar when tightening. Selecting a high modulus of elasticity cast alloy or use of laser-welded bar design resulted in the lowest average strain magnitudes. While the effect of screw tightening sequence was minimal, tightening the distal ends first demonstrated the lowest strain, and hence the best passivity.

Trunnion Corrosion in Total Hip Arthroplasty-Basic Concepts.

There has been increased interest in the role of corrosion in early implant failures and adverse local tissue reaction in total hip arthroplasty. We review the relationship between the different types of corrosion in orthopaedic surgery including uniform, pitting, crevice, and fretting or mechanically assisted crevice corrosion (MACC). Passive layer dynamics serves a critical role in each of these processes. The femoral head-neck trunnion creates an optimal environment for corrosion to occur because of the limited fluid diffusion, acidic environment, and increased bending moment.

Efficacy of platelet-rich plasma on wound healing in rabbits.

BACKGROUND: The purpose of this study was to evaluate if the healing of full-thickness skin wounds was accelerated by platelet-rich plasma (PRP). METHODS: Four 2.5 x 2.5-cm full-thickness skin wounds were created on the backs of 15 New Zealand white rabbits. One wound on each animal received 0.3, 0.6, or 0.9 ml PRP, and the fourth wound served as a control. Seven and eight animals were sacrificed after 1 or 2 weeks, respectively, to determine histomorphometrically the epithelialization rate, contraction rate, healing rate, tissue fill, and volume fractions of fibroblasts, neutrophils, macrophages, and blood vessels. RESULTS: Only the 0.6- and 0.9-ml groups had significantly lower contraction rates than the controls after 2 weeks (P <0.05). Although no statistically significant differences were found in other parameters between the PRP-treated wounds and the controls, the PRP treatment led to increases in average epithelialization rates and volume fraction of blood vessels at both time periods. The PRP also seemed to have the most positive effect on healing rate, tissue fill, and volume fraction of fibroblasts during week 1 compared to week 2. CONCLUSIONS: The PRP treatment enhanced healing in full-thickness wounds by reducing the contraction rate with a trend toward acceleration of the epithelial migration and the angiogenic response. Further studies with larger sample sizes should be conducted to improve statistical sensitivity. Longer time intervals and modifications of PRP volume should also be explored to evaluate the long-term efficacy of PRP on wound healing.

Surface analysis and biocorrosion properties of nanostructured surface sol-gel coatings on Ti6Al4V titanium alloy implants.

Surfaces of biocompatible alloys used as implants play a significant role in their osseointegration. Surface sol-gel processing (SSP), a variant of the bulk sol-gel technique, is a relatively new process to prepare bioreactive nanostructured titanium oxide for thin film coatings. The surface topography, roughness, and composition of sol-gel processed Ti6Al4V titanium alloy coatings was investigated by atomic force microscopy (AFM) and X-ray electron spectroscopy (XPS). This was correlated with corrosion properties, adhesive strength, and bioreactivity in simulated body fluids (SBF). Electroimpedance spectroscopy (EIS) and polarization studies indicated similar advantageous corrosion properties between sol-gel coated and uncoated Ti6Al4V, which was attributed to the stable TiO2 composition, topography, and adhesive strength of the sol-gel coating. In addition, inductive coupled plasma (ICP) and scanning electron microscopy with energy dispersive spectrometry (SEM-EDS) analysis of substrates immersed in SBF revealed higher deposition of calcium and phosphate and low release rates of alloying elements from the sol-gel modified alloys. The equivalent corrosion behavior and the definite increase in nucleation of calcium apatite indicate the potential of the sol-gel coating for enhanced bioimplant applications.

Accelerating aging of zirconia femoral head implants: change of surface structure and mechanical properties.

Recently, alternations of zirconia ceramic femoral heads of total hip prostheses during in vivo conditions have caused concern in the medical disciplines regarding phase transformation of zirconia prosthetic components. In this paper, we have investigated the mechanical and structural properties of different laboratory aged zirconia femoral heads and correlated changes in mechanical properties with the phase compositions of the sample. From laser microscope observation, cross-sectional Scanning electron microscopy imaging, and X-ray diffraction analysis on the surface of the zirconia femoral heads, we found monoclinic to tetragonal phase transformation in zirconia prostheses over time during the aging process in the laboratory. Mechanical properties, mainly hardness (H) and Young's modulus (E) values, were measured by nanoindentation technique on the surface of these implants. The results showed that both H and E values decreased with increased monoclinic phase in zirconia, thus confirming a phase transformation over time during aging.

Osteoblast adhesion and matrix mineralization on sol-gel-derived titanium oxide.

The biological events occurring at the bone-implant interface are influenced by the topography, chemistry and wettability of the implant surface. The surface properties of titanium alloy prepared by either surface sol-gel processing (SSP), or by passivation with nitric acid, were investigated systematically using X-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy and contact angle metrology. The bioreactivity of the substrates was assessed by evaluating MC3T3-E1 osteoblastic cell adhesion, as well as by in vitro formation of mineralized matrix. Surface analysis of sol-gel-derived oxide on Ti6Al4V substrates showed a predominantly titanium dioxide (TiO(2)) composition with abundant hydroxyl groups. The surface was highly wettable, rougher and more porous compared to that of the passivated substrate. Significantly more cells adhered to the sol-gel-coated surface, as compared with passivated surfaces, at 1 and 24h following cell seeding, and a markedly greater number of mineralized nodules were observed on sol-gel coatings. Collectively our results show that the surface properties of titanium alloy can be modified by SSP to enhance the bioreactivity of this biomaterial.

In vivo monitoring of the inflammatory response in a stented mouse aorta model.

The popularity of vascular stents continues to increase for a variety of applications, including coronary, lower limb, renal, carotid, and neurovascular disorders. However, their clinical effectiveness is hindered by numerous postdeployment complications, which may stimulate inflammatory and fibrotic reactions. The purpose of this study was to evaluate the vessel inflammatory response via in vivo imaging in a mouse stent implantation model. Corroded and noncorroded self-expanding miniature nitinol stents were implanted in mice abdominal aortas, and novel in vivo imaging techniques were used to assess trafficking and accumulation of fluorescent donor monocytes as well as cellular proliferation at the implantation site. Monocytes were quantitatively tracked in vivo and found to rapidly clear from circulation within hours after injection. Differences were found between the test groups with respect to the numbers of recruited monocytes and the intensity of the resulting fluorescent signal. Image analysis also revealed a subtle increase in matrix metalloproteinase activity in corroded compared with the normal stented aortas. In conclusion, this study has been successful in developing a murine stent inflammation model and applying novel in vivo imaging tools and methods to monitor the complex biological processes of the host vascular wall response.

A comparison of torque required to fracture rotary files with tips bound in simulated curved canal.

The purpose of this study was to compare torque force and rotation needed to fracture three types of nickel titanium alloy rotary instruments in a simulated curved root canal space that were bound at the file tip. Files of similar size tips were studied. The files studied were ProFiles with 0.04 taper diameters of 15, 20, 25, 30, 35, 40, 45; 0.04 ProFile GT sizes 20, 30, 40; and ProTaper files sizes S1, S2, F1, F2, and F3. All files were 25 mm in length. Unwinding was defined as the rotation in degrees it took for a file to fracture after the first evidence of permanent deformation. All files exhibited permanent deformation before breaking, with the ProFile GT files demonstrating the greatest unwinding. The #45 0.04 ProFile withstood the most force while the #20 ProFile GT required the least amount of force before beginning to exhibit permanent deformation. The S1 and S2 ProTaper files fractured with so little rotation that no extended data were recorded. Generally, as the file diameter increased, the force needed to begin unwinding also increased. Also, as the file diameter increased, the force needed to fracture also increased.

Quasi-linear viscoelastic behavior of the human periodontal ligament.

Previous studies have not produced a comprehensive mathematical description of the nonlinear viscoelastic stress-strain behavior of the periodontal ligament (PDL). In the present study, the quasi-linear viscoelastic (QLV) model was applied to mechanical tests of the human PDL. Transverse sections of cadaveric premolars were subjected to relaxation tests and loading to failure perpendicular to the plane of section. Distinct and repeatable toe and linear regions of stress-strain behavior were observed. The amount of strain associated with the toe region differed as a function of anatomical location along the tooth root. Stress relaxation behavior was comparable for different anatomical locations. Model predicted peak tissue stresses for cyclic loading were within 11% of experimental values, demonstrating that the QLV approach provided an improved, accurate quantification of PDL mechanical response. The success of the QLV approach supports its usefulness in future efforts of experimental characterization of PDL mechanical behavior.

A comparison of torque required to fracture three different nickel-titanium rotary instruments around curves of the same angle but of different radius when bound at the tip.

Instrument fracture is an unfortunate but possible sequela of instrumentation of canals, especially when the instrument is bound at the tip. The purpose of this study was to compare the torque required to fracture three file sizes of three different rotary file types around two simulated canal curvatures, gradual or acute, when the tip of the working end of the file was bound. Profile Series 29 0.04 and 0.06 taper and Profile 0.06 ISO rotary files were placed passively into simulated canal curvatures of the same angle but of different radii. The file tips were bound 2 mm from the working end and a measurable torque was applied until fracture. ANOVA with Tamhane post-hoc comparison showed that the 0.06 Series 29 did not differ from the ISO 0.06 taper or the 0.04 Series 29 but there was statistical difference (p < 0.01) showing that the 0.04 Series 29 broke with less force than did the 0.06 ISO files. Statistical tests (p < 0.01) also showed smaller files failed with less torque, as did files in more acute canal curvatures.

Nanostructured ceramics for biomedical implants.

Recent progress in the synthesis, characterization, and biological compatibility of nanostructured ceramics for biomedical implants is reviewed. A major goal is to develop ceramic coating technology that can reduce the friction and wear in mating total joint replacement components, thus contributing to their significantly improved function and longer life span. Particular attention is focused on the enhancement of mechanical properties such as hardness, toughness, and friction coefficient and on the bioactivity as they pertain to the nanostructure of the material. The development of three nanostructured implant coatings is discussed: diamond, hydroxyapatite, and functionally graded metalloceramics based on the Cr-Ti-N ternary system. Nanostructured diamond produced by chemical vapor deposition (CVD) techniques and composed of nano-size diamond grains have particular promise because of the combination of ultrahigh hardness, improved toughness over conventional microcrystalline diamond, low friction, and good adhesion to titanium alloys. Nanostructured processing applied to hydroxyapatite coatings is used to achieve the desired mechanical characteristics and enhanced surface reactivity and has been found to increase osteoblast adhesion, proliferation, and mineralization. Finally, nanostructured metalloceramic coatings provide continuous variation from a nanocrystalline metallic bond at the interface to the hard ceramic bond on the surface and have the ability to overcome adhesion problems associated with ceramic hard coatings on metallic substrates.

Biomaterials, biomechanics, tissue healing, and immediate-function dental implants.

Selected factors and opinions are reviewed specific to immediate function of dental implants in terms of biomaterial and biomechanical properties and how they might influence postsurgical tissue healing. Comparisons are made among plate, rod, and screw vs plateau, finn, and porous geometry endosteal dental-implant designs with and without alterations in device body-surface microchemistry and microtopography. Available information introduces more questions than answers, and recommendations are made for ongoing studies of bone responses specific to the implant fit and fill parameters focused on the kinetics of postsurgical osteotomy healing and applied loading. The clinical literature supports opportunities for immediate function; however, proposals about pathways for bone healing need further investigation. The current trends within the discipline of implant dentistry offer opportunities to reevaluate current vs previous immediate-function systems.

Bone Formation Under the Elevated Sinus Membrane Using Venous Coagulum.

INTRODUCTION: Insufficient bone height is a common obstacle to placing dental implants in the posterior maxilla. Sinus grafts have been shown to be a highly predictable way to increase bone height in the posterior maxilla. This case series illustrates a technique using venous coagulum and simultaneous implant placement under the elevated sinus. Bone formation is demonstrated clinically, radiographically, and histologically. To the best of our knowledge, this is the first report of histomorphometric results and microcomputed tomography (micro-CT) using this technique. CASE SERIES: A total of five sinus elevations with simultaneous placement of two dental implants were performed with venous blood coagulum as the sole filling biomaterial. At the time of uncovering, after 8 to 9 months of healing, biopsies were harvested from the lateral wall of the maxilla. This study illustrates bone formation under five elevated sinuses, with simultaneous placement of dental implants, using venous coagulum as the sole filling material. Results showed significant gains in bone height adjacent to the implant. Micro-CT showed well-structured trabecular bone. Histomorphometry of biopsies showed 38% to 74% vital bone. CONCLUSIONS: This case series illustrates that bone-grafting materials in the subsinus cavity are not required for successful placement of implants. Use of one's own blood as filling material removes any objections to grafting, including religious, ethical, or fear of disease transmission. Venous coagulum is a simple, inexpensive biomaterial, and its systematic use during a sinus lift may be a relevant option, ultimately leading to increased access to implant treatment options for patients.

An extension-distraction injury of the thoracic spine with traumatic partial correction of thoracic kyphosis.

Study Design The study is a case report. Objective The authors aim to report an unusual injury pattern in a patient previously treated for thoracic kyphoscoliosis. Methods A postoperative (computed tomography) CT of a healthy 24-year-old man who underwent posterior instrumentation and fusion for a kyphoscoliosis deformity was compared with a CT performed after a motor vehicle accident (MVA) 1 year later, which resulted in an extension-distraction injury of T8 with no neurologic deficit. Cobb angles of the thoracic sagittal images of both CTs were measured using a digital measuring device and the values were recorded. Results Initial postoperative sagittal CT images demonstrate a 67-degree residual thoracic kyphosis compared with the post-MVA sagittal CT images, which reveal a 54-degree thoracic kyphosis, a 13-degree improvement in sagittal alignment. Conclusion It is unusual for a patient with long posterior instrumentation of the spine to sustain a spinal fracture without breakage of the rods, which were 6-mm nickel-titanium alloy with two crosslinks. Although sustaining plastic deformation, the rods maintained their integrity to the degree that the patient required no subsequent treatment to his spine at 12 months follow-up. It is rare to sustain a vertebral fracture without implant failure, which occurred in this case.

Stent overlapping and geometric curvature influence the structural integrity and surface characteristics of coronary nitinol stents.

Preliminary studies have revealed that some stents undergo corrosion and fatigue-induced fracture in vivo, with significant release of metallic ions into surrounding tissues. A direct link between corrosion and in-stent restenosis has not been clearly established; nonetheless in vitro studies have shown that relatively high concentrations of heavy metal ions can stimulate both inflammatory and fibrotic reactions, which are the main steps in the process of restenosis. To isolate the mechanical effects from the local biochemical effects, accelerated biomechanical testing was performed on single and overlapping Nickel-Titanium (NiTi) stents subjected to various degrees of curvature. Post testing, stents were evaluated using Scanning Electron Microscopy (SEM) to identify the type of surface alterations. Fretting wear was observed in overlapping cases, in both straight and curved configurations. Stent strut fractures occurred in the presence of geometric curvature. Fretting wear and fatigue fractures observed on stents following mechanical simulation were similar to those from previously reported human stent explants. It has been shown that biomechanical factors such as arterial curvature combined with stent overlapping enhance the incidence and degree of wear and fatigue fracture when compared to single stents in a straight tube configuration.

The role of vascular calcification in inducing fatigue and fracture of coronary stents.

Traditional approaches for in-vitro pulsatile and fatigue testing of endovascular stents do not take into consideration the pathologies of the stented vessel and their associated biomechanical effects. One important pathology is calcification, which may be capable of inducing changes in the vessel wall leading to inhomogeneous distribution of stresses combined with wall motion during the cardiac cycle. These local property changes in the region adjacent to stents could directly influence in-vivo stent performance. Seven cases containing a total of 18 stents were obtained from autopsy. Radiographs were evaluated and vessels were sectioned for histology and stent topographical analysis. Stents were retrieved by chemical removal of surrounding tissue and surfaces were evaluated using 3D digital optical and scanning electron microscopy for biomechanical abrasion and fracture features. Pathologic complications such as restenosis and thrombus formation were assessed from histological sections. Direct evidence of fracture was found in 6 of the 7 cases (in 12 out of 18 stents; 9 drug eluting and 3 bare metal). The degree of stent alterations was variable, where separation of segments due to fracture occurred mostly in drug-eluting stents. All fracture surfaces were representative of a high cycle fatigue mechanism. These fractures occurred in complex lesions involving the presence of diffuse calcification alone, or in combination with vessel angulations and multiple overlapping stents. Morphologic analysis of tissue at or near some fracture sites showed evidence of thrombus formation and/or neointimal tissue growth.