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PubMed2002

Titanium dioxide reinforced hydroxyapatite coatings deposited by high velocity oxy-fuel (HVOF) spray.

Hydroxyapatite (HA) coatings with titania addition were produced by the high velocity oxy-fuel (HVOF) spray process. Mechanical properties of the as-sprayed coatings in terms of adhesive strength, shear strength and fracture toughness were investigated to reveal the effect of the titania reinforcement on HA. Qualitative phase analysis with X-ray diffraction (XRD) showed that mutual chemical reaction between TiO2 and HA, that formed CaTiO3 occurred during coating formation. Differential scanning calorimetry (DSC) analysis of the starting powders showed that the mutual chemical reaction temperature was approximately 1410 degrees C and the existence of TiO2 can effectively inhibit the decomposition of HA at elevated temperatures. The positive influence of TiO2 addition on the shear strength was revealed. The incorporation of 10 vol% TiO2 significantly improved the Young's modulus of HA coatings from 24.82 (+/- 2.44) GPa to 43.23 (+/- 3.20) GPa. It decreased to 38.51 (+/- 3.65) GPa as the amount of TiO2 increased to 20 vol%. However, the addition of TiO2 has a negative bias on the adhesive strength of HA coatings especially when the content of TiO2 reached 20 vol%. This is attributed to the weak chemical bonding and brittle phases existing at the splats' interface that resulted from mutual chemical reactions. The fracture toughness exhibited values of 0.48 (+/- 0.08) MPa m0.5, 0.60 (+/- 0.07) MPa m0.5 and 0.67 (+/- 0.06) MPa m0.5 for the HA coating, 10 vol% TiO2 blended HA coating and 20 vol% TiO2 blended HA coating respectively. The addition of TiO2 in HA coating with the amount of less than 20 vol% is suggested for satisfactory toughening effect in HVOF HA coating.

Calorimetry, Differential Scanning↗
PubMed2004

Time scale for periosteal readhesion after brow lift.

OBJECTIVES/HYPOTHESIS: The objective was to determine the time interval after brow lift required to achieve periosteal readhesion to the skull with preoperative strength [corrected]. STUDY DESIGN: Randomized prospective analysis of variance with repeated measures. METHODS: Twenty-one New Zealand white rabbits, each serving as its own control, underwent subperiosteal elevation on one side of the skull. The elevated periosteum was lifted and fixed to a resorbable screw, and the contralateral periosteum was left untouched. Adhesion characteristics were subsequently examined at postoperative days 5, 6, 7, 8, 10, 12, and 17. Seven subjects were assessed histologically to determine attachment of periosteum to underlying bone. Fourteen subjects underwent biomechanical analysis of the bone-periosteum interface using the following three measures of periosteal readhesion strength: ultimate shear strength, shear stiffness, and shear energy [corrected]. RESULTS: Blinded histological analysis showed a qualitative increase in the number of markers of periosteal healing on days 8 to 12 for the operated sides. Analysis of ultimate shear strength and shear stiffness demonstrated a significant relationship to postoperative day (P <.001). The ultimate shear strength and shear stiffness of the operated side approached that of the nonoperated side by postoperative days 12 and 8, respectively. Shear energy was significantly lower for all time points on the operated side as compared with the control (P <.02). CONCLUSION: Periosteal readhesion after surgical elevation approaches preoperative strength by the twelfth postoperative day.

Absorbable Implants↗
PubMed1983

Selection of acrylic bone cements for use in joint replacement.

Commercial acrylic bone cements have been compared in terms of their mechanical, thermal and rheological properties. Significant differences have been found between the tensile strengths, shear strengths and peak polymerization temperatures of the cements tested. Large differences have been found between the viscosities of different formulations and the duration of their working periods during polymerization. Optimum cement selection is found to depend critically upon ambient conditions within the operating theatre considered in combination with the characteristics of the cements themselves. It is proposed that, at present, the only differences between commercial bone cements of relevance to successful joint replacement lie in the area of rheological properties during polymerization.

Bone Cements↗
PubMed2004

A study on the effect of drying techniques on the mechanical properties of pellets and compacted pellets.

Microcrystalline cellulose (MCC) pellets produced by a standard extrusions/spheronisation process with a 40% ethanol/water mixture as the fluid component, were dried by four different techniques, namely: freeze-drying, fluid-bed drying, hot air oven drying and desiccation with silica-gel to less than 5% (w/w) water content. A 1.0-1.18mm size fraction of the dried pellets were characterised structurally and mechanically in terms of, shape, density/porosity (open and closed), pore volume/pore volume distribution, surface area, surface tensile strength, shear strength, deformability, linear strain and elastic modulus. An amount of 600, 700 and 750mg of the same size fraction of each pellet batch were compacted to the same tablet thickness and the tensile strength and volumetric elastic recovery of the resulted compacts were determined. Analysis of variance was used to assess the significance of the drying process on the property of the pellets and their compacts. The drying process did not influence the shape of the pellets, but all the other properties were affected to some extent. Pellets dried by freeze-drying were more porous, with most of the pores open to the atmosphere and had a higher surface area than pellets dried by the other methods. Pellets dried by desiccation contained the highest proportion of closed pores. The decrease in tensile strength of the pellets, which occurred with the increase in porosity could presumably be due to ease of crack initiation and propagation between the MCC fibres. The weaker pellets broke instantly before they were subjected to appreciable strain. The porous pellets needed a higher compressing pressure and work of compaction to produce tablets of the same mass and dimensions. This reflected their compressibility, i.e. relative decrease in volume of the pellet bed during compression. The strength and volumetric elastic recovery of the compacts increased with the increase of their porosity. The drying techniques, which produced porous, deformable and weak pellets, produced stronger tablets. The value of the volumetric elastic recovery of the compacts was also observed to increase with the value of compaction pressure.

Cellulose↗
PubMed2002

The effects of low-intensity pulsed ultrasound on bioabsorbable self-reinforced poly L-lactide screws.

The effects of low-intensity pulsed ultrasound on the mechanical and molecular properties of self-reinforced poly L-lactide (SR-PLLA) screws were studied in vitro. SR-PLLA screws of 4.5 mm diameter were exposed on low-intensity ultrasound for 1, 3. 6, 9, and 12 weeks. After exposure, the bending strength, shear strength, and molecular weight were investigated. There were no differences in the investigated properties between the ultrasound exposure and control groups. We found no evidence that low-intensity ultrasound has any effect on the mechanical or molecular properties of SR-PLLA screws in vitro. The present results suggest that biodegradable SR-PLLA fixation devices are compatible with low-intensity ultrasound in vitro.

Absorbable Implants↗
PubMed2001

Mechanical and histological evaluations of hydroxyapatite-coated and noncoated Ti6Al4V implants in tibia bone.

This paper evaluates the behavior of hydroxyapatite (HAP) coated and noncoated Ti6Al4V implants in dog tibia after 3 and 5 months implantation. HPA-coated implants were obtained by plasma spraying. XRD, SEM, and EPMA were employed to estimate the coating characteristics and their behavior in vivo. Investigation of material characteristics showed that the as-received coatings consisted mainly of amorphism and HAP phase. Other phases such as TCP and CaO were identified due to thermal changes of HAP particles in plasma flame. SEM micrographs showed a typical microstructure of plasma-sprayed coating. The as-received coating was formed by well-melted pancake-like splats that lead to a dense coating with a rough surface. Lamellar structure, micropores, and microcracks, observed inside the coating, are characteristic of plasma spraying. Push-out tests revealed that HAP coating had a significant promotion of interfacial shear strength. The shear strength between bone and HAP-coated implants was much higher than that between bone and noncoated implants due to the different bone-implant interfaces formed after implantation. SEM observation revealed a direct attachment between HAP coating and newly formed bone. However, noncoated implants were separated from newly formed bone by fibrous tissues. Ti ions were found to be released into the surrounding environment after long time immersion in body fluid, and thus caused low shear strength. Prolongation of implantation time had different effects on shear strength. It improved the shear strength between HAP-coated implant and newly formed bone. However, it had little effect on that between noncoated implant and surrounding tissues.

Alloys↗
PubMed1992

Revision of cemented fixation and cement-bone interface strength.

Interfacial shear strength between poly(methyl methacrylate) (PMMA) bone cement and cancellous bone was measured in bone samples from human proximal femora. Samples were prepared with fresh cement-bone, fresh cement inside a mantle of existing cement and with fresh cement-revised bone surfaces. Push-out tests to measure shear strength caused failure only at bone-cement interfaces; revised bone interfaces were 30 per cent weaker (P < 0.02) than primary interfaces. The clinical relevance is that revision of cemented joint arthroplasties may necessitate removal of components with sound cement-bone fixation. The practice of removing all traces of PMMA cement may not yield the optimal fixation; adhesion of fresh cement to freshly prepared surfaces of the existing cement might also be considered where circumstances are favourable.

Bone Cements↗
PubMed2005

Effects of hydrogen peroxide cleaning procedures on bone graft osteoinductivity and mechanical properties.

Bone allografts are frequently used during orthopaedic trauma cases or other reconstructive procedures. Most allografts are processed and cleaned before use. Our goals were to determine if an improved cleaning procedure compromises the strength or osteoinductivity of a graft. We compared our improved cleaning procedure to our standard cleaning procedure on cortical bone allograft. The cleaning procedures are generally composed of a series of chemical steps with nonionic detergents, hydrogen peroxide, and alcohol under time and temperature control, subjected to ultrasonic agitation. We tested the compressive strength, impact strength, and shear strength following the standard and improved cleaning procedures. Osteoinductivity was tested in 4 groups, using the improved cleaning procedure with four different hydrogen peroxide cleaning times: 0, 1, 3, and 5 h. Osteoinductivity was evaluated in vivo, using a 28-day implant in the hamstring muscle of an athymic, nude mouse. Results demonstrated that osteoinductivity is maintained with cleaning in hydrogen peroxide for up to 1 h, and that compressive strength, impact strength, and shear strength were all unaffected by the improved cleaning procedure. The improved cleaning procedure therefore did not compromise the strength or osteoinductivity of cortical bone allografts in comparison to the standard procedure.

Adult↗
PubMed2026

Clinical performance of two lithium disilicate CAD/CAM materials in posterior Class II inlay restorations: A 48-month randomised split-mouth clinical trial.

OBJECTIVES: To compare the clinical performance of Amber Mill (AM) and IPS e.max CAD (EM) lithium disilicate computer-aided design/computer-aided manufacturing (CAD/CAM) materials in posterior Class II inlay restorations and characterise their baseline properties. METHODS: Thirty-four adults received paired AM and EM posterior Class II inlays (68 restorations) in a triple-blind randomised split-mouth trial followed for 48 months. Restorations were evaluated at baseline and annually using revised World Dental Federation (FDI) criteria, with fracture and retention as the primary endpoint. Baseline characterisation included flexural strength, shear bond strength, translucency parameter, and scanning electron microscopy. McNemar, Wilcoxon signed-rank, Friedman, one-way analysis of variance, Tukey post hoc, and inter-rater agreement analyses were used. RESULTS: At 48 months, 18 paired participants were available for primary analysis. Failures occurred in 2 of 18 AM restorations and in 3 of 18 EM restorations, corresponding to success rates of 88.9% and 83.3%, respectively, with no significant between-material difference (McNemar p = 1.000). No catastrophic bulk ceramic fracture was observed. Secondary FDI scores remained mostly within the clinically acceptable range; marginal staining deteriorated over time in both groups (p < .001) without significant between-material differences. Baseline material testing showed significant material- and translucency-dependent differences in flexural strength, shear bond strength, and translucency. CONCLUSIONS: Within the limitations of the 48-month follow-up and the tested Class II inlay indication, AM showed clinical performance comparable to EM. Observed clinical complications were related to retention or marginal/interface behaviour. CLINICAL SIGNIFICANCE: For posterior Class II lithium disilicate CAD/CAM inlays, medium-term complications were mainly retention/interface-related, suggesting adhesive-interface durability may be as important as baseline ceramic strength.

Humans↗
PubMedDate not supplied

Effects of dentin air abrasion with aluminum oxide and hydroxyapatite on adhesive bond strength.

Shear bond strengths to dentin were determined with six current-generation resin adhesive systems following air abrasion of the dentin surface with aluminum oxide and hydroxyapatite. In addition, scanning electron microscopy was used to examine the effects of air abrasive techniques and conditioners/primers on the dentin surfaces. Altering the dentin surface with air abrasion using aluminum oxide and hydroxyapatite did not enhance dentin bond strengths with current-generation adhesive systems. Air abrasion of dentin with aluminum oxide created more surface irregularity than hydroxyapatite. Dentin surfaces air abraded with aluminum oxide and the treated with conditioners that removed the smear layer appeared more irregular than flat ground dentin surfaces treated with the same conditioners.

Acid Etching, Dental↗
PubMedDate not supplied

Retention and shear bond strength of two post systems.

The purpose of this study was to compare the retention and shear strength of teeth restored with the Para Plus post (P) and the C post (C1 and C2) systems. Twenty-four P, C1, and C2 posts each were placed 7 mm into recently extracted and endodontically treated maxillary anterior roots and luted with Ketac-Cem and Bis-Core respectively. In addition, 13 samples of each post type had a Bis-Core composite core placed. The tensile retention strength of the post and the shear strength of the post and core restorations when the core was loaded buccolingually at 45 degrees to the roots' long axis were determined at a strain rate of 1.3 mm/min. The C2 posts required significantly more tensile force (P < 0.0001) to remove them than the P or C1 posts. The shear strength of the post/core restorations was not significantly different (P < 0.04). The C1 restorations had 12 root fractures, the C2 restorations had 11 root fractures, and the P samples had six root fractures. It was concluded that the lack of stiffness of the C posts adversely affected the success of these restorations.

Dental Bonding↗
PubMed2003

[Study on bonding strength of TF adhesive compounded with nanograde hydroxyapatite].

TF no-mix orthodontic adhesive was compounded in different weight proportion of nanograde hydroxyapatite as 10%, 20% and 30%, for use in this comparative study on composites. 80 orthodontic brackets were cemented and divided into 8 experimental groups, and TF adhesive was set as the control group. The tensile strength and shear strength were tested respectively. The results showed that the group of 10% nanograde hydroxyapatite obtained the greatest bonding strength (9.668 +/- 1.0649 MPa in tensile strength and 11.991 +/- 1.4135 MPa in shear strength), and there was significant difference between the 10% group and the other groups (P < 0.05, one-way ANAOV). It is concluded that the bonding strength can be enhanced when TF adhesive is compounded in suitable proportion of nanograde hydroxyapatitie.

Animals↗