Stability behavior of human tibias after bone removal--comparative examination in 15 cadaver tibia pairs.

PURPOSE: To obtain scientific information on the loss of stability of tibias after removal of bone grafts, we performed a comparative study of 15 freshly preserved adult cadavers to determine the axial breaking loads of the operated and nonoperated tibial heads. MATERIALS AND METHODS: From all cadavers, 1 tibia was randomly selected from which the maximum possible amount of cancellous bone was harvested. The respective contralateral side remained untouched. After maceration, the proximal tibias of each cadaver were removed bilaterally and adjusted to precisely equal lengths. Using a Zwick universal testing machine, the tibial heads were loaded by an axial force until fracture. As the final breaking load, the force value was recorded when the first distinct decrease in the feed-force curve was observed. To compare the mean breaking loads of the operated and nonoperated control tibias, a t test for related samples at P = .05 was used. RESULTS: The mean breaking load for the donor tibias was 3,767 N and was significantly lower than that of the control side with an average of 5,126 N. This finding was independent of age and gender. CONCLUSIONS: Bone removal from the proximal tibia leads to a significant reduction of the axial load capacity. Therefore, we recommend partial loading of up to one half of the body weight during the first postoperative week. For an additional 5 weeks, patients should bear their full body weight on the affected leg only when walking normally and on flat ground.

In vitro study of adhesive polymethylmethacrylate bone cement bonding to cortical bone in maxillofacial surgery.

PURPOSE: In the treatment of midface fractures, the fragments are immobilized using screws and plates for osteosynthesis until reunion has occurred. This method involves drilling holes for the insertion of the screws, which can be associated with additional fracturing of the corresponding bone owing to the complex architecture and thin layers of facial bone. To alleviate this problem, new adhesive techniques for fixing the plates for osteosynthesis have been investigated, mitigating the detrimental effects of screw hole drilling. In the present experimental study, the strength of this adhesive bond and its resistance to hydrolysis were investigated. MATERIALS AND METHODS: To determine the adhesive bonding strength, a tension test was implemented. Osteosynthesis plates with screw holes 1.3 mm in diameter were fixed to cortical bone samples of bovine femur using ultraviolet (UV) light-curing polymethylmethacrylate bone cement. To facilitate bonding, the surface of the bone was conditioned with an amphiphilic bonding agent before cementing. UV light curing was implemented using either a conventional UV unit, such as is used in dentistry, or with a specialized UV unit with a limited emission spectrum but high luminosity. Reference control samples were prepared without application of the bone bonding agent. After this procedure, the samples were stored for 1 to 7 days at 37°C submerged in 0.9% saline solution before being subjected to the tension test. RESULTS: Without the bone bonding agent, the bonding strength was 0.2 MPa. The primary average bonding strength at day 0 was 8.5 MPa when cured with the conventional UV unit and 14 MPa for the samples cured with the specialized UV unit. An almost constant average bond strength of 8 and 16 MPa was noted for all samples stored up to 7 days after curing with the conventional and specialized UV unit, respectively. CONCLUSION: With the development of a new bone bonding agent, a method is now available to promote the bonding between the hydrophilic bone surface and the hydrophobic polymethylmethacrylate bone cement by creating an interlayer that is beneficial for adhesion. In the present in vitro study, the strength of this bond and its resistance to hydrolysis were investigated. This new method could have clinical bearing in cases in which conventional fixation with screws and plates is limited, such as can occur in comminuted fractures. The observed average bonding strengths of 8 to 16 MPa support the implementation of this technique in nonload-bearing regions such as the midface, facilitating immobilization until the bone reunion is complete.

A new adhesive technique for internal fixation in midfacial surgery.

BACKGROUND: The current surgical therapy of midfacial fractures involves internal fixation in which bone fragments are fixed in their anatomical positions with osteosynthesis plates and corresponding screws until bone healing is complete. This often causes new fractures to fragile bones while drilling pilot holes or trying to insert screws. The adhesive fixation of osteosynthesis plates using PMMA bone cement could offer a viable alternative for fixing the plates without screws. In order to achieve the adhesive bonding of bone cement to cortical bone in the viscerocranium, an amphiphilic bone bonding agent was created, analogous to the dentin bonding agents currently on the market. METHODS: The adhesive bonding strengths were measured using tension tests. For this, metal plates with 2.0 mm diameter screw holes were cemented with PMMA bone cement to cortical bovine bone samples from the femur diaphysis. The bone was conditioned with an amphiphilic bone bonding agent prior to cementing. The samples were stored for 1 to 42 days at 37 degrees C, either moist or completely submerged in an isotonic NaCl-solution, and then subjected to the tension tests. RESULTS: Without the bone bonding agent, the bonding strength was close to zero (0.2 MPa). Primary stability with bone bonding agent is considered to be at ca. 8 MPa. Moist storage over 42 days resulted in decreased adhesion forces of ca. 6 MPa. Wet storage resulted in relatively constant bonding strengths of ca. 8 MPa. CONCLUSION: A new amphiphilic bone bonding agent was developed, which builds an optimizied interlayer between the hydrophilic bone surface and the hydrophobic PMMA bone cement and thus leads to adhesive bonding between them. Our in vitro investigations demonstrated the adhesive bonding of PMMA bone cement to cortical bone, which was also stable against hydrolysis. The newly developed adhesive fixing technique could be applied clinically when the fixation of osteosynthesis plates with screws is impossible. With the detected adhesion forces of ca. 6 to 8 MPa, it is assumed that the adhesive fixation system is able to secure bone fragments from the non-load bearing midfacial regions in their orthotopic positions until fracture consolidation is complete.

Amphiphilic bonder improves adhesion at the acrylic bone cement-bone interface of cemented acetabular components in total hip arthroplasty: in vivo tests in an ovine model.

INTRODUCTION: Even following the introduction of the "third generation" cementing technique, an improvement of the fixation of the acetabular component similar to that of the femoral has not been shown in clinical studies. The goal of the present study was to achieve a better stability with the use of an amphiphilic bonder while preserving the mechanically important subchondral sclerosis. MATERIALS AND METHODS: In a total of 20 sheep, a cemented total hip replacement was implanted. In the treatment group (n = 10), the implantation was carried out following surface conditioning of the acetabular bed with an amphiphilic bonder. All the sheep were followed for 9 months. To assess the biocompatibility, the osseous ingrowth at the cement-bone interface was depicted with the help of an in vivo fluorescent marking of the osteoblasts. Additionally, conventional radiographs were obtained over the course of treatment. Finally, the ovine pelvic regions were split following a standardized technique allowing for histological evaluation of the cement-bone interfaces. RESULTS: The acetabular components of the treatment group revealed a stable cement-bone compound. In the control group, the implants were easily dislodged from their beds. This finding was consistent with the radiological and histological results, which had revealed increased, progressive lytic radiolucent lines and the interposition of fibrous tissue at the cement-bone interface in the control group compared to the treatment group. The bonder was biocompatible. CONCLUSION: Following the application of the bonder, the cemented acetabular components revealed an improved stability without signs of inflammation or neoplasia in a viable acetabular osseous bed. With the help of this technique, the in vivo longevities of cemented acetabular components can be increased in the clinical setting without sacrificing the biomechanical relevant subchondral sclerosis.

[Bone Cement Adhesion on Ceramic Surfaces - Deactivation of Surfaces and as a Consequence Inefficient Retention of Knee Prostheses Because of Adsorption of Atmospheric Water]. / Haftung von Knochenzement auf keramischen Oberflächen ­ Deaktivierung der Oberfläche als wirksame Retentionsfläche für Knieendoprothesen durch die Adsorption von atmosphärischem Wasser.

AIM: CoCrMo alloys are contraindicated for sufferers from allergy. For these patients, uncemented and cemented prostheses made of non-allergenic titanium alloy are indicated. Knee prostheses machined from that alloy, however, may have poor tribological behaviour, especially in contact to UHMWPE inlays. Therefore, high-strength oxide ceramics may be especially suitable for knee replacement in allergy patients with mobile bearing prostheses. For adhesion to bone cement, the ceramic surface only exhibits mechanical retention spots that are less adequate than those with a textured metal surface. Generating undercuts by corundum blasting is highly efficient for mechanical adhesion to a CoCrMo surface, but is not possible on a ceramic surface, due to the brittleness of ceramics. Lack of retention of bone cement promotes micromotions of the prostheses. As a consequence of micromotions, early aseptic loosening is predictable. Silicoating (silicate and silane layering) of the ceramic surface would allow specific adhesion and hence would result in increased and hydrolytically more stable bonding between the bone cement and the prosthesis surface - thereby preventing early aseptic loosening. Silicoating, however, presupposes a chemically active surface that is not blocked by a layer of chemisorbed molecules, e.g. water. Desorption of this chemisorbed layer is mandatory and can be attained by baking out the surface. METHOD: In order to evaluate the effectiveness of surface activation via thermal treatment by baking out, with subsequent silicoating of the surface, the bond strengths of thermally treated and silicate layered ZPTA samples were compared with thermally treated surfaces that had not been silicoated. In our study of thermal surface treatment for baking out the surface, we focused on the question of whether there is a minimal "critical" temperature Ts for effective desorption of a chemisorbed water layer. The samples were prepared for the traction-adhesive strength test (sequence: ceramic disc, silicate and silane layering, protective lacquer ("PolyMA" layer), bone cement, TiAlV probes for the traction-adhesive strength test) and their traction-adhesive strengths were then measured. RESULTS: The bond strength was measured as a function of temperature for ceramic discs that had been baked out and subsequently silicoated. This was graduated, exhibits with a pronounced increase in the bond strength at a baking temperature of Ts ≈ 350 °C. The observed bond strengths before the step are ≤ 20 MPa and after the step ≥ 30 MPa. CONCLUSION: Silicoating is effective in achieving high bond strength of bone cement on surfaces of oxide ceramics and can also stabilise the long term behaviour of the bond strength, provided the surface has been thermally treated prior to silicoating. Because of the proposed migration of the silicoating layer, micromotions and debonding should be widely reduced or even eliminated.

[ Improvement of femoral bone-cement adhesion in cemented revision hip arthroplasty by application of an amphiphilic bonder in a dynamic femur expulsion testing in vitro ]. / Steigerung der femuralen Knochen-Knochenzement-Verbundfestigkeit in der zementierten Revisionshüftendoprothetik durch einen amphiphilen Knochenhaftvermittler im dynamischen in-vitro Ausstossversuch.

Cemented femoral stems have shown decreased longevity compared to cementless implants in hip revision arthroplasty. The aim of this study was to evaluate the effect of an amphiphilic bonder on bone cement stability in a biomechanical femur expulsion test. A simplified hip simulator test setup with idealised femur stem specimens was carried out. The stems were implanted into bovine femurs (group 1: no bonder, n=10; group 2: bonder including glutaraldehyde, n=10; group 3: bonder without glutaraldehyde, n=10). A dynamic loading (maximum load: 800 N; minimum load: 100 N; frequency: 3 Hz; 105 cycles) was performed. Subsequently, the stem specimens were expulsed axially out of their implant beds and maximum load at failure was recorded. The static controls showed a mean maximum load to failure of 4123 N in group 1, 8357.5 N in group 2 and 5830.8 N in group 3. After dynamic loading, the specimens of group 2 reached the highest load to failure (8191.5 N), followed by group 3 (5649.5 N) and group 1 (3462 N), respectively. In group 2, we observed nine periprosthetic fractures at a load of 8400 N without signs of interface loosening. Application of an amphiphilic bonder led to a significant improvement of bonding stability, especially when glutaraldehyde was added to the bonder. This technique might offer an increased longevity of cemented femur revision stems in total hip replacement.

[Surface pretreatment for prolonged survival of cemented tibial prosthesis components: full- vs. surface-cementation technique]. / Oberflächenkonditionierung für eine verbesserte Uberlebenswahrscheinlichkeit von Knieprothesen: Komplett- vs. Oberflächenzementiertechnik der Tibiakomponente.

Aseptic loosening of tibial components due to degradation of the interface between bone cement and metallic tibial shaft component is still a persistent problem, particularly for surface-cemented tibial components. The surface cementation technique has important clinical meaning in case of revision and for avoidance of stress shielding. This study was done to prove crack formation in the bone cement near the metallic surface when this is not coated. We propose a newly developed coating process by SiOx-PVD layering to avoid crack formation. A biomechanical model for a vibration fatigue test was done to prove that crack formation can be significantly reduced in the case of coated surfaces. It was found that coated tibial components showed a highly significant reduction of cement cracking near the metal/bone cement interface (p < 0.01) and a significant reduction of gap formation in the metal-to-bone cement interface (p < 0.05). Coating dramatically reduces hydrolytic- and stress-related crack formation at the prosthesis metal/bone cement interface. This leads to a more homogenous load transfer into the cement mantle which should reduce the frequency of loosening in the metal/bone cement/bone interfaces. With surface coating of the tibial component it should become possible that surface-cemented TKAs reveal similar loosening rates as TKAs both surface- and stem-cemented. This would be an important clinical advantage since it is believed that surface cementing reduces metaphyseal bone loss in the case of revision and stress shielding for a better bone health.

[PVD-layering for increased retention of glass fibre reinforced endodontic posts]. / PVD-beschichtung für verbesserte Retention glasfaserverstärkter Wurzelkanalstifte.

For esthetical and biomechanical reasons root canal posts made of fibre-reinforced composite (FRC) have gained an important role in clinical application. Additionally, in contrast to metal or ceramic posts, FRC-posts offer the option of removal. Prior to adhesive placement of FRC-posts the root canal dentin of the non vital tooth and the post surface have to be preconditioned. Up to now the post preconditioning has to be proceeded in the chair side technique. This leads to an additional time expense in the clinical treatment schedule. Also a certain risk of errors in application during chair side conditioning procedure is of concern. Modern PVD-technologies can help to make the treatment by the manufacturer well in advance of the clinical use more efficient and reliable, as well as saving clinicians valuable chair-time. For this reason the apical surfaces of the posts were intensively cleaned and activated, PVD-layered and coated by a conserving transparent layer. This coating has the meaning to protect the surface against environmental contamination and allows the try-in of the posts without any risk of damage of the preconditioned surface. To prove the stability of the layer system under simulated clinical conditions pull out tests after 180 days'storage in physiological saline solution have been performed.

Fracture Forces of Dentin after Surface Treatment with High Speed Drill Compared to Er:YAG and Er,Cr:YSGG Laser Irradiation.

Dental tooth restorative procedures may weaken the structural integrity of the tooth, with the possibility of leading to fracture. In this study we present findings of coronal dentin strength after different techniques of surface modification. The fracture strength of dentin beams after superficial material removal with a fine diamond bur high speed drill hand piece, Er:YAG (2.94 µm, 8 J/cm(2)), and Er,Cr:YSGG (2.78 µm, 7.8 J/cm(2)) laser irradiation slightly above the ablation threshold was measured by a four-point bending apparatus. Untreated dentin beams served as a control. A total of 58 dentin beams were manufactured from sterilized human extracted molars using the coronal part of the available dentin. Mean values of fracture strength were calculated as 82.0 ± 27.3 MPa for the control group (n = 10), 104.5 ± 26.3 MPa for high speed drill treatment (n = 10), 96.1 ± 28.1 MPa for Er,Cr:YSGG laser irradiation (n = 20), and 89.1 ± 36.3 MPa for Er:YAG laser irradiation (n = 18). Independent Student's t-tests showed no significant difference between each two groups (p > 0.05). Within the parameter settings and the limits of the experimental setup used in this study, both lasers systems as well as the high speed drill do not significantly weaken coronal dentin after surface treatment.

Bioactivation of inert alumina ceramics by hydroxylation.

Alumina ceramics (Al(2)O(3)) are frequently used for medical implants and prostheses because of the excellent biocompatibility, and the high mechanical reliability of the material. Inauspiciously alumina is not suitable for implant components with bone contact, because the material is bioinert and thereby no bony ongrowth, and subsequently loosening of the implant occurs. Here, we present a new method to bioactivate the surface of the material. Specimens made of high purity alumina were treated in sodium hydroxide. Cell culture tests with osteoblast-like cells as well as spectroscopical and mechanical tests were performed. Aluminium hydroxide groups were detected on the surface of the treated specimens. Enhanced cell adhesion, proliferation and secretion of osteocalcin were determined after hydroxylation. The bioactivating treatment had no deteriorating effect on the short- and long-term strength behaviour. Our results indicate that the described surface technique could be used to develop a new class of osseointegrative high-strength ceramic implants.

Surface pretreatment for prolonged survival of cemented tibial prosthesis components: full- vs. surface-cementation technique.

BACKGROUND: One of few persisting problems of cemented total knee arthroplasty (TKA) is aseptic loosening of tibial component due to degradation of the interface between bone cement and metallic tibial shaft component, particularly for surface cemented tibial components. Surface cementation technique has important clinical meaning in case of revision and for avoidance of stress shielding. Degradation of the interface between bone cement and bone may be a secondary effect due to excessive crack formation in bone cement starting at the opposite metallic surface. METHODS: This study was done to prove crack formation in the bone cement near the metallic surface when this is not coated. We propose a newly developed coating process by PVD layering with SiOx to avoid that crack formation in the bone cement. A biomechanical model for vibration fatigue test was done to simulate the physiological and biomechanical conditions of the human knee joint and to prove excessive crack formation. RESULTS: It was found that coated tibial components showed a highly significant reduction of cement cracking near the interface metal/bone cement (p < 0.01) and a significant reduction of gap formation in the interface metal-to-bone cement (p < 0.05). CONCLUSION: Coating dramatically reduces hydrolytic- and stress-related crack formation at the prosthesis interface metal/bone cement. This leads to a more homogenous load transfer into the cement mantle which should reduce the frequency of loosening in the interfaces metal/bone cement/bone. With surface coating of the tibial component it should become possible that surface cemented TKAs reveal similar loosening rates as TKAs both surface and stem cemented. This would be an important clinical advantage since it is believed that surface cementing reduces metaphyseal bone loss in case of revision and stress shielding for better bone health.

Suppression of subcritical crack growth in a leucite-reinforced dental glass by ion exchange.

Glass-ceramic materials are frequently used in prosthetic dentistry because of their excellent esthetics. Problematic aspects of glass ceramics are their limited strength, the scatter in their strength data, and their time-dependent strength decrease due to subcritical crack growth effects. The short-term strength level can be significantly increased by an ion-exchange process in a potassium salt. A dual ion-exchange process in KNO3/NaNO3 can additionally improve the scatter-in-strength. The objective of the present study was to examine the effect of a single and a dual ion-exchange process on the characteristic time-dependent strength decrease of a leucite-reinforced dental glass. The parameters of subcritical crack growth were evaluated by using the constant stress rate flexural strength test. Both ion-exchange processes showed a pronounced effect on the subcritical crack growth of the glass-ceramic material. The exponential crack parameter n was increased from 25 to 52 by the single-exchange and to 107 by the dual-exchange process, respectively. We conclude that the time-dependent strength decrease of a dental glass-ceramic material can be significantly limited by the ion-exchange process. This could improve the clinical reliability of dental restorations made from this class of materials.

Threshold intensity factors as lower boundaries for crack propagation in ceramics.

BACKGROUND: Slow crack growth can be described in a v (crack velocity) versus KI (stress intensity factor) diagram. Slow crack growth in ceramics is attributed to corrosion assisted stress at the crack tip or at any pre-existing defect in the ceramic. The combined effect of high stresses at the crack tip and the presence of water or body fluid molecules (reducing surface energy at the crack tip) induces crack propagation, which eventually may result in fatigue. The presence of a threshold in the stress intensity factor, below which no crack propagation occurs, has been the subject of important research in the last years. The higher this threshold, the higher the reliability of the ceramic, and consequently the longer its lifetime. METHODS: We utilize the Irwin K-field displacement relation to deduce crack tip stress intensity factors from the near crack tip profile. Cracks are initiated by indentation impressions. The threshold stress intensity factor is determined as the time limit of the tip stress intensity when the residual stresses have (nearly) disappeared. RESULTS: We determined the threshold stress intensity factors for most of the all ceramic materials presently important for dental restorations in Europe. Of special significance is the finding that alumina ceramic has a threshold limit nearly identical with that of zirconia. CONCLUSION: The intention of the present paper is to stress the point that the threshold stress intensity factor represents a more intrinsic property for a given ceramic material than the widely used toughness (bend strength or fracture toughness), which refers only to fast crack growth. Considering two ceramics with identical threshold limits, although with different critical stress intensity limits, means that both ceramics have identical starting points for slow crack growth. Fast catastrophic crack growth leading to spontaneous fatigue, however, is different. This growth starts later in those ceramic materials that have larger critical stress intensity factors.

Surface pretreatments for medical application of adhesion.

Medical implants and prostheses (artificial hips, tendono- and ligament plasties) usually are multi-component systems that may be machined from one of three material classes: metals, plastics and ceramics. Typically, the body-sided bonding element is bone. The purpose of this contribution is to describe developments carried out to optimize the techniques, connecting prosthesis to bone, to be joined by an adhesive bone cement at their interface. Although bonding of organic polymers to inorganic or organic surfaces and to bone has a long history, there remains a serious obstacle in realizing long-term high-bonding strengths in the in vivo body environment of ever present high humidity. Therefore, different pretreatments, individually adapted to the actual combination of materials, are needed to assure long term adhesive strength and stability against hydrolysis. This pretreatment for metal alloys may be silica layering; for PE-plastics, a specific plasma activation; and for bone, amphiphilic layering systems such that the hydrophilic properties of bone become better adapted to the hydrophobic properties of the bone cement. Amphiphilic layering systems are related to those developed in dentistry for dentine bonding. Specific pretreatment can significantly increase bond strengths, particularly after long term immersion in water under conditions similar to those in the human body. The bond strength between bone and plastic for example can be increased by a factor approaching 50 (pealing work increasing from 30 N/m to 1500 N/m). This review article summarizes the multi-disciplined subject of adhesion and adhesives, considering the technology involved in the formation and mechanical performance of adhesives joints inside the human body.

Fracture toughness of dental ceramics: comparison of bending and indentation method.

OBJECTIVES: The aim of this study was to compare two fracture toughness methods, the bending method on notched specimens as reference and the indentation method as comparison. Potentialities and limitations of the indentation method were analyzed. METHODS: Fracture toughness values were determined for seven dental ceramic materials on 'single-edge-v-notched beams' (bending method) as our standard method. Additionally indentation tests were done on the identical samples from the bending tests. The results were determined before and after annealing of the samples. With the reference fracture toughness results from the bending tests, the prefactor in the indentation test formula was individually adapted for each tested material. RESULTS: The individual prefactors varied between 0.0122 and 0.0253 for the specimens before annealing and between 0.0150 and 0.0267 for the annealed specimens. Subsequently the differences between the K Ic-values calculated by the ISO draft (TC 206) direction and calculated by the modified formulae with the material specific prefactors were up to 48% for unannealed and up to 33% for annealed specimens, respectively. SIGNIFICANCE: The indentation method is not an adequate tool to exactly determine the fracture toughness of an unknown ceramic material. This method can only be used for a first rough K Ic estimation.

Elimination of low-quality ceramic posts by proof testing.

OBJECTIVES: Prosthetic posts made of zirconia ceramics are beneficial because of their esthetic advantages. The mechanical reliability of ceramic posts is limited because of the strength level and the large scatter in strength of ceramic materials. The hypothesis of this study is that the failure of ceramic posts in vivo, which occur on low-quality posts because of critical microscopic defects can be excluded using the so-called proof test technology. METHODS: The theory of the proof test technology is explained in detail in this study. In the experimental part 22 ceramic posts were tested at different proof load levels using a stepwise rotating four-point bending proof test device. RESULTS: The experimental failures deviated from the theoretical failure probabilities by 0.24-12.69%. The deviation would be further reduced in a serial proof test using batches with a greater quantity of posts. The test eliminated those posts, which contained microscopic defects above a critical size of clinical relevance. SIGNIFICANCE: The technology can help to reduce clinical failures of non-vital abutment teeth with ceramic posts, which are caused by critical microscopic defects of the ceramic material as a result of the industrial manufacturing process.

The innovative application of a novel bone adhesive for facial fracture osteosynthesis-in vitro and in vivo results.

This study evaluates a novel adhesive fixation technique to affix cortical bone fragments to osteosynthesis plates using common PMMA cement. This technique utilizes a new amphiphilic bone bonding agent adhering with both hydrophilic bone and hydrophobic PMMA cement. After in vitro biomechanical testing of the bonding strength with explanted bovine and rabbit calvarian bone samples, osteosynthesis plates with screw holes of 1.3 and 1.5 mm were placed on the cranial bone of New Zealand white rabbits and the bond strength of these plates was determined through tension tests. In vitro bond strengths of 19.8-26.5 MPa were obtained. Control samples, prepared without a bone bonding agent, exhibited bone bonding strengths <0.2 MPa. In vivo respective bond strengths at the cranium of the white rabbits were 2.5-4.1 MPa 2 weeks post surgery and 1.9-2.5 MPa 12 weeks after implantation. This new innovative fixation method can be envisioned for cases in which conventional fixation techniques of screws and plates are insufficient or not possible due to the bone or trauma conditions. The observed bonding strengths support implementing this technique in nonload bearing regions, such as the central midface or frontal sinus, facilitating immobilization until bone reunion is complete.

The removal of Al2O3 particles from grit-blasted titanium implant surfaces: effects on biocompatibility, osseointegration and interface strength in vivo.

For the improvement of surface roughness and mechanical interlocking with bone, titanium prostheses are grit-blasted with Al(2)O(3) particles during manufacturing. Dislocated Al(2)O(3) particles are a leading cause of third-body abrasive wear in the articulation of endoprosthetic implants, resulting in inflammation, pain and ultimately aseptic loosening and implant failure. In the present study, a new treatment for the removal of residual Al(2)O(3) particles from grit-blasted, cementless titanium endoprosthetic devices was investigated in a rabbit model. The cleansing process reduces residual Al(2)O(3) particles on titanium surfaces by up to 96%. The biocompatibility of the implants secondary to treatment was examined histologically, the bone-implant contact area was quantified histomorphometrically, and interface strength was evaluated with a biomechanical push-out test. Conventional grit-blasted implants served as control. In histological and SEM analysis, the Al(2)O(3)-free implant surfaces demonstrated uncompromised biocompatibility. Histomorphometrically, Al(2)O(3)-free implants exhibited a significantly increased bone-implant contact area (p=0.016) over conventional implants between both evaluation points. In push-out testing, treated Al(2)O(3)-free implants yielded less shear resistance than conventional implants at both evaluation points (p=0.018). In conclusion, the new surface treatment effectively removes Al(2)O(3) from implant surfaces. The treated implants demonstrated uncompromised biocompatibility and bone apposition in vivo. Clinically, Al(2)O(3)-free titanium prostheses could lead to less mechanical wear of the articulating surfaces and ultimately result in less aseptic loosening and longer implant life.

Detection of microscopic cracks in dental ceramic materials by fluorescent penetrant method.

Ceramic materials are used as implants and prostheses because of their excellent biocompatibility and in the dental field beyond that, because of esthetic advantages and the little plaque accumulation. A disadvantage is their sensitivity to microscopic cracks because of their brittleness. Strength-deteriorating microscopic cracks can be introduced into the ceramic surface by the manufacturing process. The objective of this study was to evaluate three methods on their efficiency to detect microscopic surface cracks of clinical relevance in dental ceramic materials. These methods were light-optical microscopy, fluorescent microscopy after penetration with a fluorescent liquid, and scanning electron microscopy (SEM). It was found that microscopic cracks of critical sizes can be detected using the fluorescent penetrant method, which was not to be proven by light-optical microscopy and even not by SEM. We conclude from our study that the fluorescent penetrant method could help to decrease clinical failures of dental ceramic components that are caused by surface microscopic cracks from the manufacturing process, if this method was routinely performed before the clinical use of the ceramic components.

In vivo fracture resistance of implant-supported all-ceramic restorations.

STATEMENT OF PROBLEM: Because of their specific mechanical properties, all-ceramic restorations demonstrate a lower fracture resistance than ceramic restorations supported by metal substructures. However, advances have been made in the fabrication of high-strength all-ceramic abutments for anterior implants. No previous study has compared the fracture loads between 2 different all-ceramic abutments restored by glass-ceramic crowns. PURPOSE: The purpose of this in vitro investigation was to quantify the fracture load of implanted-supported Al(2)O(3) and ZrO(2) abutments restored with glass-ceramic crowns. MATERIALS AND METHODS: Two ceramic abutments were tested: an Al(2)O(3) abutment (CerAdapt) and a ZrO(2) abutment (Wohlwend Innovative). The abutments (n = 10) were placed on Brånemark dental implants and prepared for restoration with glass-ceramic crowns (IPS Empress). After fabrication, in accordance with the manufacturer's guidelines, the crowns were bonded to the all-ceramic abutments with a dual-polymerizing resin luting agent. The fracture loads (N) were determined by force application at an angle of 30 degrees by use of a computer-controlled universal testing device. The data were analyzed with the unpaired t test (alpha=.05). RESULTS: Statistical analysis showed significant differences between both groups (P=.001) of all-ceramic abutments, with mean fracture load values of 280.1 N (+/- 103.1) for the Al(2)O(3) abutments and 737.6 N (+/- 245.0) for the ZrO(2) abutments. CONCLUSION: Within the limitations of this study, both all-ceramic abutments exceeded the established values for maximum incisal forces reported in the literature (90 to 370 N). The ZrO(2) abutments were more than twice as resistant to fracture as the Al(2)O(3)-abutments.