Examination of the bone-implant interface in experimentally induced osteoporotic bone.

The objective of this study was to explore the hypothesis that osteoporotic-like (OP) conditions have a negative effect on osseointegration (OI) of dental implants. Using an ovariectomized (OVX) rat model, the extent of OI using histologic and histomorphometric analysis (HMA) under a variety of OVX conditions was assessed. Five experimental groups (n = 7 rats per group) were used: 1) OP control, 2) OI control, () OI followed by OVX treatment to induce OP (OI-->OP), 4) OP induction followed by OI (OP-->OI), and 5) OP induction simultaneously with OI (OI = OP). Using undecalcified plastic-embedded cross-sections of the implant site, HMA was performed to determine the percent of bone contact (BC) at the implant-tissue interface and percent of bone area (BA) immediately (1.5-mm diameter) surrounding the implant site. The presence of Bone Sialoprotein (BSP), an important extracellular matrix component of bone, was evaluated using immunohistochemical staining procedures. The implant control resulted in the highest level of OI (BC = 79%; BA = 87%), whereas all groups in which OVX was performed resulted in a significant reduction in BA (70-75%). High levels of BC were observed in established OP conditions (OP-->OI; BC = 79%); however, following OI, induction of OP conditions (OI-->OP) led to a significant reduction in BC (50%). In each of the OP treatment groups, a diminution of cortical bone, increased trabecularization of the host bone site, and loss of staining of BSP was observed. The results of this work indicate that although OI is possible under a variety of OP-like conditions simulating implant placement, the long-term biomechanical stability of implants under these conditions could be compromised and remains unclear. Further research to understand implant use in the complex bone environment under OP-like conditions is encouraged.

Mode of failure in the dentin-adhesive resin-resin composite bonded joint as determined by strength-based (muTBS) and fracture-based (CNSB) mechanical testing.

OBJECTIVE: To determine the failure mode between dentin-adhesive resin-resin composite bonded joint produced with a chevron-notch short-bar (CNSB) and microtensile test methods. METHODS: Forty teeth were randomly selected for microtensile and forty for CNSB specimen fabrication and stored in 0.5% chloramine T at 37 degrees C until respective static load to failure testing at 30 and 180days. Failure modes were categorized by SEM and tested with Fisher's exact test. Within respective mechanical testing methods the probability of failure curve distributions being significantly different were analyzed by the Wald chi-square statistic. RESULTS: The characteristic fracture toughness at 30- and 180-day storage was 0.82 and 0.87MPam(1/2), while the Weibull Modulus (m) for the failure distributions, was 4.60 and 4.56, respectively. No significant difference was demonstrated in the failure distributions between these groups (p=0.45). The characteristic tensile strength (muTBS(o)) at 30- and 180-day storage was 52.53 and 14.71MPa with an m of 3.04 and 1.56, respectively. Failure distributions for muTBS groups were significantly different (p<0.001). K(IvM) failure modes, regardless of storage time, were within the adhesive joint with 30-day debonds primarily through the top region of the hybrid layer (THL) and after 180-days involving the bottom of the hybrid layer (BHL). The 30-day muTBS group demonstrated a propensity to debond in dentin or resin composite substrates but after 180-days storage debonds again involved the BHL. SIGNIFICANCE: The weak links in the dentin-adhesive resin-resin composite bonded joint may be the interphase regions between the THL and the adhesive resin and the BHL and dentin.

The influence of water storage and C-factor on the dentin-resin composite microtensile bond strength and debond pathway utilizing a filled and unfilled adhesive resin.

OBJECTIVE: To test the elastic wall concept utilizing adhesive resins of varying stiffness in a low- and high-C-factor cavity design after short- and long-term water storage. METHODS: A flat and box-shaped cavity was restored on occlusal dentin with a resin composite using a filled and unfilled adhesive resin from which microtensile specimens with a 0.5mm(2) cross-sectional area were formed. After storage for 30- and 150-days the microtensile bond strength (muTBS) was determined in a Zwick materials testing machine and the subsequent debond pathway was examined under scanning electron microscopy. Fisher's exact test was used to determine differences in joint and substrate failure modes and a Weibull regression model with gamma frailties was used to test for differences between failure distributions. Tests for three-way and two-way interactions were also completed for storage time, C-factor and adhesive. All tests were at 95% confidence levels. RESULTS: The characteristic strength (TBS degrees ) for the Optibond FL adhesive applied on a flat cavity was 47.57 and 20.90MPa and a box-shaped cavity was 49.26 and 17.49MPa for short- and long-term storage, respectively, while the corresponding TBS degrees for the unfilled Optibond adhesive on the flat cavity design was 36.93 and 32.68MPa and in a box-shaped cavity was 32.84 and 15.46MPa. Combining all groups according to storage time revealed a three-fold increase in the debond pathway including the bottom of the hybrid layer. SIGNIFICANCE: Evidence suggests that the durability of the bonded joint is threatened by hydrolysis and the most susceptible region is the bottom half of the hybrid layer and in low C-factor cavity designs a more flexible adhesive resin liner was more durable.

Calcium and phosphate supplementation promotes bone cell mineralization: implications for hydroxyapatite (HA)-enhanced bone formation.

Organic phosphate, in particular beta-glycerophosphate (beta-GP), has been used to induce mineralization in cell culture systems. It serves as a source of inorganic phosphate when hydrolyzed by alkaline phosphatase. This study examined the effect of supplemental calcium and phosphate as well as the influence of various metabolic inhibitors on mineralization in a rat osteoblast-like cell-culture system. Mineralization was induced by supplementation of 1.8 mM of Ca(+2) and 5 mM of beta-GP or Pi. Mineral deposits associated with in vitro mineralization were revealed under SEM and TEM. Levamisole (10-100 microM) inhibited alkaline phosphatase activity and effectively reduced mineral formation. Actinomycin (500 ng/mL) and cycloheximide (50 microg/mL) also reduced mineral depositions by blocking RNA synthesis and protein synthesis, respectively. Levamisole and beta-GP did not appear to influence DNA synthesis. Spontaneous precipitation of calcium phosphate mineral was not detected in the culture medium with calcium and phosphate supplements in the absence of cell culture. The findings suggest that an elevated concentration of calcium and phosphate is crucial for in vitro mineralization. Furthermore, the mineralization process is associated with biologic events rather than with a spontaneous precipitation of calcium phosphate mineral. In view of the degradation potential of hydroxyapatite (HA)-coated implants, these results may be a viable indication that HA enhances bone formation through a similar mechanism.

Use of hydroxyapatite cement to support implants in extraction sockets.

Bioactive cements based on calcium phosphate chemistry have been developed to serve as bone substitute materials. One such commercial product, BoneSource, is a hydroxyapatite cement (HAC) used for small bone defects in the craniofacial complex. We have investigated the possibility that HAC could be used to support bone growth adjacent to dental implants placed in immediate tooth extraction sites. Variable levels of bone contact were noted up to 3 months postimplantation. Considerable loss of HAC occurred and was thought to be because of "washout" of the cement before complete cement setting. When HAC was immobile in the surgical site, the bioactive nature of the cement led to HAC resorption and bone deposition. Efforts to maintain the HAC in situ should be expanded so that the full clinical potential of the HAC can be realized.

Reuse of healing abutments: an in vitro model of plasma cleaning and common sterilization techniques.

The reuse of transgingival healing abutments has been advocated by several implant manufacturers, but cleaning and sterilization procedures to yield clean and optimal surfaces have yet to be developed. The objective of this in vitro project was to investigate various cleaning and sterilization regimens for the removal of biological debris to support reattachment of subgingival connective tissue. Simulated clinical healing abutment surfaces were exposed to culture medium with serum for 1 hour to simulate biological exposure. Simulated healing abutment surfaces not contaminated by serum were used to represent the "as-is" healing abutment surface without prior in vivo use. The discs were cleaned with detergent before sterilization by ultraviolet light (UV) or steam autoclaving (AC) both with and without 1- and 5-minute plasma cleaning (PC). A series of surface analytical techniques (XPS, AES, and surface contact angles) and in vitro analysis of cell attachment and spreading using gingival fibroblasts were performed. After exposure to the simulated biological conditions, clinical cleaning followed by UV resulted in contaminated surfaces and relatively high levels of cell attachment. PC before UV treatment enhanced surface energetics but did not affect cell attachment and spreading. AC increased surface wetting angles; which were decreased somewhat by previous PC. Cell attachment was significantly reduced by AC. Although some increase in cell attachment after longer plasma cleaning was noted in the AC group, no difference in cell spreading was seen in any AC group. Cell spreading seemed to be less for all AC groups compared with all UV, as-is, and control groups. Although certain cleaning (PC) and sterilization (UV) procedures can be effective for cleaning transgingival healing abutments, those using AC are questionable due to their propensity for organic and inorganic contamination and unfavorable surface alteration.

Significant role of adhesion properties of primary osteoblast-like cells in early adhesion events for chondroitin sulfate and dermatan sulfate surface molecules.

The purpose of this study was to characterize the role of cell surface adhesive macromolecules through enzyme modulation and metabolic recovery prior to and during a kinetic cell adhesion assay. Primary rat calvarial osteoblast-like cells were derived from Sprague-Dawley calvarial plates. Cell adhesion kinetics was evaluated with the definition of first-order adhesion kinetics. Osteoblasts were incubated in an adhesion buffer for 1 h prior to a cell attachment assay using various enzymes to remove cell surface glycosaminoglycans (GAGs). A subtractive adhesion analysis was performed by plating cells at 5 x 10(4)/well for variable periods through 2 h. The medium was collected, the well surface washed and pooled, and the number of cells enumerated with a Coulter Counter. Cell adhesion demonstrated first-order logarithmic adhesion kinetics in the first 60 min. Scatchard analysis demonstrated a linear relationship. Preexposure of cells to various enzyme combinations demonstrated that 50% of the equilibrium adhesion was dependent on chondroitin sulfate or dermatan sulfate surface macromolecules. These results were confirmed with pretreatment with a metabolic inhibitor of GAG synthesis (beta-D-xyloside). These results suggest an important role for cell associated chondroitin sulfate and dermatan sulfate in cell adhesion in addition to Arg-Gly-Asp or integrin mediated adhesion events.

Biomechanical and morphometric analysis of hydroxyapatite-coated implants with varying crystallinity.

PURPOSE: The level of crystallinity in hydroxyapatite (HA) is thought to be responsible for its degradation in the physiologic milieu. The purpose of this study was to compare the in vivo bony response to HA coatings of varying levels of crystallinity and determine the optimum composition for promoting osseointegration. MATERIALS AND METHODS: Cylindrical implants of sand-blasted CP titanium and HA-coated titanium of 50% (low), 70% (medium), and 90% (high) crystallinity were inserted into the canine femur for 1, 4, 12, and 26 weeks. Morphometric analysis of undecalcified sections determined the percentage of bone contact with the implant surface. A pullout test was used to measure the interfacial attachment strength of the bone-implant interface. Scanning electron microscope (SEM) examination of the implant surface aided in identifying the failure mode. Coating thickness was measured under light microscopy to determine whether degradation occurred. RESULTS: No significant differences could be found in the percentage of bone contact and interfacial attachment strength between the three types of HA-coated implants throughout the four implantation periods. A significantly higher percentage of bone contact on HA-coated implants than on uncoated titanium implants was noted at 4 weeks. (ANOVA, P<.05). HA-coated implants were also found to have significantly higher interfacial attachment strength than titanium implants at 4, 12, and 26 weeks. Coating thickness decreased gradually with time. The most noticeable reduction was found on the low-crystallinity coatings during the first 4 weeks. Failure of the bone-coating-implant complex occurred mostly within the coating or near the coating-implant interface. CONCLUSIONS: HA coatings on metal implants enhance osseointegration in the early stage of bone healing and provide strong bone-bonding capability, although titanium implants had about the same level of bone contact in the later stage of healing. Crystallinity of HA coatings has no significant influence over the bone formation capacity and the bone bonding strength. However, an HA coating of higher crystallinity is more desirable in providing durability and maintaining osteoconductive properties.

Primary bacterial colonization of implant surfaces.

The purpose of this study was to assess the effects of modifying titanium surfaces, in terms of wettability, roughness, and mode of sterilization, on the ability of the oral bacterium Streptococcus sanguis to colonize. An in vitro model system was developed. All surfaces were colonized by the bacteria, but to significantly different levels. Titanium samples that exhibited rough or hydrophobic (low wettability) surfaces, along with all autoclaved surfaces, were preferentially colonized (P < .01). Titanium surfaces that had been repeatedly autoclaved were colonized with the levels of bacteria 3 to 4 orders of magnitude higher than other modes of sterilization. This may have implications relative to the commonly used method of autoclaving titanium implants, which may ultimately enhance bacterial biofilm formation on these surfaces.

Osteoblastic cell attachment to hydroxyapatite-coated implant surfaces in vitro.

Hydroxyapatite (HA) used as a coating for implants can exhibit varying levels of interaction with the biologic environment. The crystallinity of the HA-based coating has been shown to control the rate of dissolution and appears to play a role in the initial cellular interaction with the implant surfaces. An osteoblastic cell attachment assay was employed to examine the cell attachment to untreated and pretreated (pH 5.2, 24 hours) titanium and HA coatings of low (50%), medium (75%), and high (90%) crystallinity. A slightly higher percentage of cell attachment (%CA) was found on untreated and pretreated HA surfaces as compared to the titanium surface. No significant difference could be found in the %CA between the 3 levels of crystallinity. However, higher levels of %CA were observed on pretreated HA surfaces than on untreated HA surfaces (t test, P < .05). Elevated calcium and phosphate levels in culture medium did not have any effect on cell attachment. Scanning electron microscopic examinations revealed surface degradation of the HA coating following pretreatment in the simulated inflammatory media (pH 5.2, 24 hours). The results suggest that the altered surface topography may influence the initial cell attachment to HA surfaces.

A comparative study of osseointegration of titanium implants in autogenous and freeze-dried bone grafts.

PURPOSE: This study was undertaken to compare the rate and degree of osseointegration of dental implants when placed into either autogenous corticocancellous chip or freeze-dried corticocancellous chip bone grafts. MATERIALS AND METHODS: The canine ilium was used as the model site. Thirty experimental and 15 control implants were placed in 15 dogs: autogenous versus freeze-dried corticocancellous chip bone grafts around the exposed implant surfaces. In addition to the placement of control implants, the apical portion of the grafted implants acted as their own control. The implants were harvested at 1, 2, and 3 months. The evaluation of the integration process was performed by means of light microscopy, microradiography, and histomorphometry. RESULTS: Using this model, the results indicate that at 1 month there was no statistical difference in the degree of osseointegration in the two bone grafts. At 2 months, there was a statistically greater degree of osseointegration noted in the autogenous corticocancellous chip sites than in the freeze-dried bone grafts. At 3 months, the degree of osseointegration in the two groups was 70% and 33%, respectively. At 3 months, there was virtually 100% integration with trabecular bone at the control implant sites. CONCLUSION: The results indicate that at 2 months postoperatively implants placed in an autogenous bone chip graft osseointegrate to a significantly greater degree than implants placed in a freeze-dried bone chip graft, and this difference remains at 3 months.

Microtensile bond strength testing and failure analysis of two dentin adhesives.

OBJECTIVES: This investigation was conducted to determine the tensile bond strength of two dental adhesive using a recently introduced "microtensile" bond strength testing design and to verify the failure mode for each test specimen with scanning electron microscopy (SEM). METHODS: Extracted human molars were mounted in stone and the enamel was removed the occlusal surface perpendicular to the long axis of the tooth. A composite resin crown was formed on this flat dentin surface utilizing each dental adhesive system according to manufacturer's instructions. Twenty-four hours later the bonded test specimens were sectioned perpendicular to the adhesive joint, producing six to seven thin slabs per tooth. These dentin/adhesive/composite resin slabs were sectioned free from the stone block and mounted into custom Plexiglas fixtures for trimming and subsequent tensile bond strength testing at 7 d post-bonding. The bond strength of the two adhesives was statistically compared with the t test. The broken specimens were examined with SEM to determine the fracture location or failure mode. Failures for each adhesive system were categorized as either interfacial (joint or mixed) or substrate (dentin and composite) and evaluated by Fisher's exact test. RESULTS: The tensile bond strength and failure modes of All-Bond 2 (Bisco) and Optibond FL (Kerr) were not significantly different. Sixty per cent (12/20) of fractures involving All Bond 2 occurred at the interface, with seven being entirely maintained within the joint, whereas Optibond FL had 35% (7/20) involving some portion of the interface, two totally within the joint. Cohesive fractures of either dentin or composite accounted for 55% of the total failure modes (21/40). The remaining dentin thickness did not affect the measured tensile bond strength. SIGNIFICANCE: This versatile new method permits multiple measurements from a single tooth or small surface areas within a restoration but careful interpretation of the failure mode is required to prevent inappropriate conclusions about the utility of the test.

Effect of hybrid layer on fracture toughness of adhesively bonded dentin-resin composite joint.

OBJECTIVES: Micromechanical retention from the hybrid layer is generally believed to be the mechanism of adhesion of current generation dentin bonding agents. The purpose of this investigation is to evaluate the interfacial fracture toughness of a commercial dentin bonding agent with and without this hybrid layer. METHODS: Ten extracted molars (AB2) were flattened on the occlusal surface, All-Bond 2 Universal Adhesive System (Bisco) was applied according to manufacturer's directions and a resin composite (Prodigy, Kerr) crown was formed. Another group of ten molars (AB2Cl) was handled identically with the exception of a 1 min gentle scrubbing application of 5.25% sodium hypochlorite after acid etching to remove the acid-exposed collagen. Plane-strain chevron-notch short bar fracture toughness specimens were fabricated from all 20 composite crowns and tested according to ASTM E1304-89. Each group was tested to failure in tensile mode at 0.1 mm min-1 and the maximum load at failure was used to determine plane-strain fracture toughness (KQvM). Weibull parameters were calculated and fracture probability distributions were tested for significant difference at the 95% confidence level. Scanning electron microscopy was employed on broken specimens (18/20) to describe the failure mode. RESULTS: Weibull distributions were not significantly different with characteristic plane-strain fracture toughness from maximum load (KQvM0) of 0.97 MPa m1/2 and 0.81 MPa m1/2 and a Weibull modulus of 4.7 and 3.9, respectively, for AB2 and AB2Cl. All AB2 samples failed within the adhesive joint, while the AB2Cl crack propagated from the interphase of adhesive resin and dentin to 1-2 microns into dentin. SIGNIFICANCE: Under the conditions of this study, the presence of collagen did not contribute to a significantly stronger bonded joint. Interfacial fracture toughness evaluation of the dentin-resin composite bimaterial interface shows promise for future investigations.

Tissue compatibility to different surfaces of dental implants: in vitro studies.

Factors affecting cell and tissue responses to dental implant biomaterials are typically characterized as spatial and temporal. Spatially, a dental implant must form an interface with both bone tissue for the development and maintenance of biomechanical stability and soft tissue for the prevention of microbial infection that can lead to peri-implantitis. There is a developing body of knowledge regarding the reactions of host tissues to implant materials, although the specific mechanisms by which these responses are not yet totally understood. From a temporal standpoint, there seems to be a sequence of events after placement of an implant that involves cell attachment, migration, and differentiation. These early wound healing responses appear to be influenced significantly by the properties of the underlying implant surface. Our laboratory has focused its attention on the first cellular event, i.e., cell attachment at the interface between bone and the implant surface. An in vitro primary cell model has been developed and used to study the influence of materials selection (Ti, Ti-6Al-4V, hydroxyapatite-like coatings), surface topography (smooth to rough), and surface chemistry (as a function of preparation treatments) on the cellular events that occur at implant surfaces. Currently, we believe that both uncoated Ti implants and those fabricated with calcium phosphate or hydroxyapatite-like coatings are capable of supporting initial cellular attachment, although they probably occur by different and incompletely understood mechanisms. The initial interactions of the host tissues with the implant surface remain key for long-term acceptance and must be understood if new generations of tissue engineered devices are to be developed and used clinically.

In vitro attachment of osteoblast-like cells to osteoceramic materials.

OBJECTIVE: The objective of this work was to examine osteoblast-like cell attachment and morphology in vitro to osteoceramic materials with three different surface morphologies. METHODS: Osteoceramic composite disks were fabricated from tricalcium phosphate and magnesium-aluminate spinel (MgAl2O4) in a 50 vol% ratio. The disks were prepared with three different surface morphologies, including as-fired (irregular), etched (rough), or polished through 1 mm diamond paste (smooth). Osteoblast-like cell cultures were plated onto the prepared disks for 2 h, and the number of attached cells was determined. ANOVA and Student Newman-Kuels tests were used to test for significant differences in cell attachment (p < 0.05). SEM was used to visually evaluate the nature of the cellular adaptation on the osteoceramic surfaces. RESULTS: Some additional surface roughening resulted from the interaction between the osteoceramic disks and the biological culture media during the attachment assay. A statistically larger number of cells was found to be attached to the etched osteoceramic surfaces compared to the as-fired and polished osteoceramic surfaces or the tissue culture plastic control. Cellular adaptation was extensive on all three osteoceramic surfaces at 2 h. SIGNIFICANCE: These results are consistent with previous in vivo work and continue to support the hypothesis that osteoceramic materials have potential for implants and bone substitute materials.

Effects of multiple sterilization on surface characteristics and in vitro biologic responses to titanium.

PURPOSE: This study evaluates the surface changes and effects on in vitro cell attachment and spreading brought about on prepared commercially pure titanium by multiple exposures to common sterilization methods. MATERIALS AND METHODS: Discs of commercially pure titanium were prepared to approximate the surface roughness of commercially available bone miniplates. Samples underwent sterilization by exposure to ultraviolet light; ethylene oxide sterilization (1, 5, or 10 cycles); or by steam autoclaving (1, 5, or 10 cycles). Representative surfaces from these sterilization groups were examined using a series of surface analytical techniques including scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), auger electron spectroscopy (AES), and contact angle measurements. Cell attachment assays using murine fibroblasts were then performed on titanium surfaces from each sterilization group and on tissue culture plastic controls. Sterilized surfaces contained O, C, and N contaminants, which affected surface energetics. Mean percent cell attachment values for each group were obtained for periods of up to 1 hour. Representative samples from each group were examined using SEM to ascertain cell spreading and morphology for each sterilization group. RESULTS: Ultraviolet (UV) sterilized surfaces showed no changes from the unsterilized state macroscopically or under SEM. UV surfaces showed cell attachment levels similar to control surfaces at all intervals, and a chronologic progression of cell spreading. Ethylene oxide-sterilized surfaces showed occasional bluish discoloration and a microscopic particulate contaminant, resulting in modest decreases in cell attachment levels without strong correlation to numbers of sterilization cycles. Autoclaved surfaces generally showed the greatest discoloration and heaviest particulate contamination. Cell attachment levels were lower, and cell spreading was diminished compared with the ethylene-oxide-treated group. CONCLUSIONS: Both ethylene oxide and steam autoclave sterilization contaminated and altered the titanium surface, resulting in decreased levels of cell attachment and spreading in vitro. Although corroborative in vivo experiments should be conducted, the results of this study indicate that some multiple sterilization regimens for metallic materials may pose serious biologic concerns.

Effect of specimen fixation method on pullout tests of pedicle screws.

STUDY DESIGN: Experimental axial pullout tests of a new type of pedicle screw were done on cadaveric lumbar vertebrae. The manner in which specimens were secured in the testing apparatus was varied to determined influence of specimen fixation method on the maximum pedicle screw pullout force. OBJECTIVES: To determine the appropriateness of embedding (i.e., potting) spinal specimens in polymer resin (e.g., bone cement or Plastic Padding [Plastic Padding Ltd., High Wycombe, Buckinghamshire, England]) for axial pullout tests of pedicle screws. Several different specimen fixation methods were examined to make recommendations for the standardization of future experimental testing protocols. SUMMARY OF BACKGROUND DATA: Axial pullout of transpedicular screws, although not a likely clinical mode of failure, is a popular experimental testing mode for evaluating screw-bone biomechanics. A wide variety of techniques for securing a vertebral specimen to counter the axial pullout force has been reported (including the use of polymer resin) with a correspondingly wide range in the resulting axial pullout strengths. The possible influence of the specimen fixation method on pedicle screw axial pullout strength has not been addressed previously. METHODS: Axial pullout tests of pedicle screws (DDS, Plus Endoprothetik, Rotkreuz, Switzerland) from the pedicles of 21 isolated lumber vertebral bodies were done using a Model 810 MTS Universal Testing Machine (MTS Systems, Inc., Minneapolis, Minnesota). The specimens were secured in a custom-made vise fixture either as is or after the vertebral bodies were potted in Plastic Padding up to the pedicle origin. Some of the potted specimens were wrapped first in latex to prevent polymer resin intrusion, and the others were unprotected. Pullout tests were attempted on both the left and right pedicles of each specimen, and the maximum pedicle screw pullout force was recorded. Measurement of bone mineral density by means of dual energy x-ray absorptiometry, in addition to macroscopic and scanning electron microscopy histologic analyses, microradiography, and energy dispersive X-ray spectroscopy, was done post-test to assist in the interpretation of the data. RESULTS: The maximum pedicle screw pullout force was found to be dependent on both the bone mineral density and the mode of fixation of the vertebrae. Embedding in polymer resin without protection of the specimen (i.e., latex wrapping) led to several instances of well-documented polymer resin intrusion; in these specimens, mean maximum pedicle screw pullout force was significantly greater than that of specimens secured without polymer resin and that of embedded specimens for which intrusion did not occur. CONCLUSIONS: Polymer resin intrusion can have a significant effect on the biomechanical characteristics of the bone-pedicle screw interface. When polymer resins are used to secure vertebral specimens for in vitro biomechanical tests of the bone-pedicle screw interface, it is important to either prevent intrusion (e.g., with a latex wrapping) or document post-test (e.g., through the methods described in this article) that intrusion did not occur for the specimens included in the analysis.

In vitro mineralization and implant calcium phosphate-hydroxyapatite crystallinity.

Biological dissolution of implant calcium phosphate coatings release local concentrations of divalent ions, which may influence mineralization. The objective of this study was to determine the effects of calcium phosphate release from coated commercially pure titanium discs using a bone-like cell culture bioassay. Sandblasted discs were prepared with or without hydroxyapatite crystallinities (50, 75, and 90 percent). Samples of each coating were randomly assigned and either preincubated for 24 hours with media or not before the addition of cells (2200/ mm2). Cultures were grown for 72 hours in culture medium containing 0.5 microCi/mL45 Ca. After rinsing, the remaining calcium phosphate surface was dissolved and counted. Three independent trials were performed. Results indicated proliferation was not altered as a function of crystallinity (P > 0.05) among any of the groups. However, a significant (P < 0.01) inverse relationship was found for biologically mediated mineralization as a function of calcium phosphate crystallinity. Low crystalline surfaces (nominally 50 percent) had the highest level of mineralization, with 75 percent crystalline surfaces being intermediate and 90 percent crystalline samples having the lowest amount of relative mineral formation. Mineralization only occurred on sandblasted commercially pure titanium upon supplementation of the growth medium with an organophosphate (beta-glycerophosphate), although this was less than on culture plastic. The results suggest calcium phosphate dissolution, as a function of implant coating crystallinity, can alter biological mineralization and may be one means in which enhanced mineral formation occurs around calcium phosphate-coated dental implants.