Long-term mechanical durability of dental nanocomposites containing amorphous calcium phosphate nanoparticles.

Half of all dental restorations fail within 10 years, with secondary caries and restoration fracture being the main reasons. Calcium phosphate (CaP) composites can release Ca and PO(4) ions and remineralize tooth lesions. However, there has been no report on their long-term mechanical durability. The objective of this study was to investigate the wear, thermal-cycling, and water-aging of composites containing amorphous calcium phosphate nanoparticles (NACP). NACP of 112-nm and glass particles were used to fabricate four composites: (1) 0% NACP+75% glass; (2) 10% NACP+65% glass; (3) 15% NACP+60% glass; and (4) 20% NACP+50% glass. Flexural strength and elastic modulus of NACP nanocomposites were not degraded by thermal-cycling. Wear depth increased with increasing NACP filler level. Wear depths of NACP nanocomposites after 4 × 10(5) cycles were within the range for commercial controls. Mechanical properties of all the tested materials decreased with water-aging time. After 2 years, the strengths of NACP nanocomposites were moderately higher than the control composite, and much higher than the resin-modified glass ionomers. The mechanism of strength loss for resin-modified glass ionomer was identified as microcracking and air-bubbles. NACP nanocomposites and control composite were generally free of microcracks and air-bubbles. In conclusion, combining NACP nanoparticles with reinforcement glass particles resulted in novel nanocomposites with long-term mechanical properties higher than those of commercial controls, and wear within the range of commercial controls. These strong long-term properties, plus the Ca-PO(4) ion release and acid-neutralization capability reported earlier, suggest that the new NACP nanocomposites may be promising for stress-bearing and caries-inhibiting restorations.

Nanocomposite containing CaF(2) nanoparticles: thermal cycling, wear and long-term water-aging.

OBJECTIVES: Fluoride (F) releasing dental restoratives are promising to promote remineralization and combat caries. The objectives of this study were to develop nanocomposite containing calcium fluoride nanoparticles (nCaF(2)), and to investigate the long-term mechanical durability including wear, thermal-cycling and long-term water-aging behavior. METHODS: Two types of fillers were used: nCaF(2) with a diameter of 53 nm, and glass particles of 1.4 µm. Four composites were fabricated with fillers of: (1) 0% nCaF(2)+65% glass; (2) 10% nCaF(2)+55% glass; (3) 20% nCaF(2)+45% glass; (4) 30% nCaF(2)+35% glass. Three commercial materials were also tested. Specimens were subjected to thermal-cycling between 5°C and 60°C for 10(5) cycles, three-body wear for 4×10(5) cycles, and water-aging for 2 years. RESULTS: After thermal-cycling, the nCaF(2) nanocomposites had flexural strengths in the range of 100-150 MPa, five times higher than the 20-30 MPa for resin-modified glass ionomer (RMGI). The wear scar depth showed an increasing trend with increasing nCaF(2) filler level. Wear of nCaF(2) nanocomposites was within the range of wear for commercial controls. Water-aging decreased the strength of all materials. At 2 years, flexural strength was 94 MPa for nanocomposite with 10% nCaF(2), 60 MPa with 20% nCaF(2), and 48 MPa with 30% nCaF(2). They are 3-6 fold higher than the 15 MPa for RMGI (p<0.05). SEM revealed air bubbles and cracks in a RMGI, while composite control and nCaF(2) nanocomposites appeared dense and solid. SIGNIFICANCE: Combining nCaF(2) with glass particles yielded nanocomposites with long-term mechanical properties that were comparable to those of a commercial composite with little F release, and much better than those of RMGI controls. These strong long-term properties, together with their F release being comparable to RMGI as previously reported, indicate that the nCaF(2) nanocomposites are promising for load-bearing and caries-inhibiting restorations.

Mechanical and acid neutralizing properties and bacteria inhibition of amorphous calcium phosphate dental nanocomposite.

Dental composites do not hinder bacteria colonization and plaque formation. Caries at the restoration margins is a frequent reason for replacement of existing restorations, which accounts for 50 to 70% of all restorations. The objectives of this study were to examine the filler level effect on nanocomposite containing nanoparticles of amorphous calcium phosphate (NACP) and investigate the load-bearing and acid-neutralizing properties and bacteria inhibition. NACP with 116-nm particle size were synthesized via a spray-drying technique and incorporated into a resin. Flexural strength of nanocomposite with 10 to 30% NACP fillers matched the strength of a commercial hybrid composite (p > 0.1). Nanocomposite with 40% NACP matched the strength of a microfill composite, which was 2-fold that of a resin-modified glass ionomer. Nanocomposite with 40% NACP neutralized a lactic acid solution of pH 4 by rapidly increasing the pH to 5.69 in 10 min. In contrast, the commercial controls had pH staying at near 4. Using Streptoccocus mutans, an agar disk-diffusion test showed no inhibition zone for commercial controls. In contrast, the inhibition zone was (2.5 ± 0.7) mm for nanocomposite with 40% NACP. Crystal violet staining showed that S. mutans coverage on nanocomposite was 1/4 that on commercial composite. In conclusion, novel calcium-phosphate nanocomposite matched the mechanical properties of commercial composite and rapidly neutralized lactic acid of pH 4. The nanocomposite appeared to moderately reduce the S. mutans growth, and further study is needed to obtain strong antimicrobial properties. The new nanocomposite may have potential to reduce secondary caries and restoration fracture, two main challenges facing tooth cavity restorations.

Nanocomposite containing amorphous calcium phosphate nanoparticles for caries inhibition.

OBJECTIVES: The main challenges facing composite restorations are secondary caries and bulk fracture. The objectives of this study were to synthesize novel nanoparticles of amorphous calcium phosphate (NACP), develop NACP nanocomposite with calcium (Ca) and phosphate (PO(4)) ion release to combat caries, and investigate the effects of NACP filler level and glass co-filler reinforcement on composite properties. METHODS: NACP (diameter=116 nm) were synthesized via a spray-drying technique for the first time. Since the local plaque pH in the oral cavity can decrease to 5 or 4, photo-activated composites were tested with immersion in solutions of pH 7, 5.5, and 4. Composite mechanical properties as well as Ca and PO(4) ion release were measured vs. pH and filler level. RESULTS: Increasing the NACP filler level increased the ion release. At 28 d and pH 4, the Ca release was (4.66±0.05)mmol/L at 20% NACP, much higher than (0.33±0.08) at 10% NACP (p<0.05). Decreasing the pH increased the ion release. At 20% NACP, the PO(4) release at 28 d was (1.84±0.12)mmol/L at pH 4, higher than (0.59±0.08) at pH 5.5, and (0.12±0.01) at pH 7 (p<0.05). However, pH had little effect on composite mechanical properties. Flexural strength at 15% NACP was (96±13)MPa at pH 4, similar to (89±13)MPa at pH 5.5, and (89±19)MPa at pH 7 (p>0.1). The new NACP nanocomposites had strengths that were 2-fold those of previous calcium phosphate composites and resin-modified glass ionomer control. SIGNIFICANCE: NACP composites were developed for the first time. Their strengths matched or exceeded a commercial composite with little ion release, and were 2-fold those of previous Ca-PO(4) composites. The nanocomposite was "smart" as it greatly increased the ion release at a cariogenic pH 4, when these ions would be most needed to inhibit caries. Hence, the new NACP composite may be promising for stress-bearing and caries-inhibiting restorations.

Fluoride releasing restorative materials: Effects of pH on mechanical properties and ion release.

OBJECTIVES: Secondary caries and restorative fracture are the two main reasons for restoration failures. Fluoride ion (F) release can help inhibit caries. Plaque pH after a sucrose rinse can decrease to a cariogenic pH of 4-4.5. The objective of this study was to investigate the effects of solution pH and immersion time on the mechanical properties and F release of restorative materials. METHODS: Three resin-modified glass ionomers (Viremer, Fuji II LC, Ketac Nano), one compomer (Dyract Flow), and one composite (Heliomolar), were tested. Flexural strength and elastic modulus were measured before and after 84d of immersion in solutions of pH 4, 5.5, and 7. F release was measured as a function of pH and immersion time. RESULTS: Immersion and material type had significant effects on mechanical properties. Vitremer had a flexural strength (mean±sd; n=6) of 99±25MPa before immersion; it decreased to 32±9MPa after 84d of immersion (p<0.05). In comparison, Heliomolar had a smaller strength loss, decreasing from 99±9MPa to 65±7MPa (p<0.05). Solution pH had little effect on mechanical properties. For example, Fuji II LC had a strength of 63±15MPa at pH 4, similar to 61±30MPa at pH 5.5, and 56±22MPa at pH 7 (p>0.1). In contrast, solution pH had a significant effect on F release. F release at 84d for Fuji was 609±25µg/cm(2) at pH 4, much higher than 258±36µg/cm(2) at pH 5.5, and 188±9µg/cm(2) at pH 7. SIGNIFICANCE: The restoratives tested were able to greatly increase the F release at acidic, cariogenic pH, when these ions are most needed to inhibit caries. However, mechanical properties of these F-releasing restoratives degraded significantly in immersion. Efforts are needed to develop F-releasing restoratives with high levels of sustained F release, as well as improved durability of mechanical properties for large stress-bearing restorations.

Dental glass-reinforced composite for caries inhibition: calcium phosphate ion release and mechanical properties.

The two main challenges facing dental composite restorations are secondary caries and bulk fracture. Previous studies developed whisker-reinforced Ca-PO(4) composites that were relatively opaque. The objective of this study was to develop an esthetic glass particle-reinforced, photo-cured calcium phosphate composite. Tetracalcium phosphate (TTCP) particles were incorporated into a resin for Ca and PO(4) release, while glass particles provided reinforcement. Ion release and mechanical properties were measured after immersion in solutions with pH of 7, 5.5, and 4. For the composite containing 40% mass fraction of TTCP, incorporating glass fillers increased the strength (p < 0.05). Flexural strength (Mean +/- SD; n = 6) at 30% glass was 99 +/- 18 MPa, higher than 54 +/- 20 MPa at 0% glass (p < 0.05). Elastic modulus was 11 GPa at 30% glass, compared to 2 GPa without glass. At 28 days, the released Ca ion concentration was 4.61 +/- 0.18 mmol/L at pH of 4, much higher than 1.14 +/- 0.07 at pH of 5.5, and 0.27 +/- 0.01 at pH of 7 (p < 0.05). PO(4) release was also dramatically increased at cariogenic, acidic pH. The TTCP-glass composite had strength 2-3 fold that of a resin-modified glass ionomer control. In conclusion, the photo-cured TTCP-glass composite was "smart" and substantially increased the Ca and PO(4) release when the pH was reduced from neutral to a cariogenic pH of 4, when these ions are most needed to inhibit tooth caries. Its mechanical properties were significantly higher than previous Ca, PO(4), and fluoride releasing restoratives. Hence, the photo-cured TTCP-glass composite may have potential to provide the necessary combination of load-bearing and caries-inhibiting capabilities.

Mesenchymal stem cell proliferation and differentiation on an injectable calcium phosphate-chitosan composite scaffold.

Calcium phosphate cement (CPC) can be molded or injected to form a scaffold in situ, has excellent osteoconductivity, and can be resorbed and replaced by new bone. However, its low strength limits CPC to non-stress-bearing repairs. Chitosan could be used to reinforce CPC, but mesenchymal stem cell (MSC) interactions with CPC-chitosan scaffold have not been examined. The objective of this study was to investigate MSC proliferation and osteogenic differentiation on high-strength CPC-chitosan scaffold. MSCs were harvested from rat bone marrow. At CPC powder/liquid (P/L) mass ratio of 2, flexural strength (mean+/-sd; n=5) was (10.0+/-1.1) MPa for CPC-chitosan, higher than (3.7+/-0.6) MPa for CPC (p<0.05). At P/L of 3, strength was (15.7+/-1.7)MPa for CPC-chitosan, higher than (10.2+/-1.8)MPa for CPC (p<0.05). Percentage of live MSCs attaching to scaffolds increased from 85% at 1 day to 99% at 14 days. There were (180+/-37) cells/mm(2) on scaffold at 1 day; cells proliferated to (1808+/-317) cells/mm(2) at 14 days. SEM showed MSCs with healthy spreading and anchored on nano-apatite crystals via cytoplasmic processes. Alkaline phosphatase activity (ALP) was (557+/-171) (pNPP mM/min)/(microg DNA) for MSCs on CPC-chitosan, higher than (159+/-47) on CPC (p<0.05). Both were higher than (35+/-32) of baseline ALP for undifferentiated MSCs on tissue-culture plastic (p<0.05). In summary, CPC-chitosan scaffold had higher strength than CPC. MSC proliferation on CPC-chitosan matched that of the FDA-approved CPC control. MSCs on the scaffolds differentiated down the osteogenic lineage and expressed high levels of bone marker ALP. Hence, the stronger CPC-chitosan scaffold may be useful for stem cell-based bone regeneration in moderate load-bearing maxillofacial and orthopedic applications.

Self-setting collagen-calcium phosphate bone cement: mechanical and cellular properties.

Calcium phosphate cement (CPC) can conform to complex bone cavities and set in-situ to form bioresorbable hydroxyapatite. The aim of this study was to develop a CPC-collagen composite with improved fracture resistance, and to investigate the effects of collagen on mechanical and cellular properties. A type-I bovine-collagen was incorporated into CPC. MC3T3-E1 osteoblasts were cultured. At CPC powder/liquid mass ratio of 3, the work-of-fracture (mean +/- sd; n = 6) was increased from (22 +/- 4) J/m(2) at 0% collagen, to (381 +/- 119) J/m(2) at 5% collagen (p < or = 0.05). At 2.5-5% of collagen, the flexural strength at powder/liquid ratios of 3 and 3.5 was 8-10 MPa. They matched the previously reported 2-11 MPa of sintered porous hydroxyapatite implants. SEM revealed that the collagen fibers were covered with nano-apatite crystals and bonded to the CPC matrix. Higher collagen content increased the osteoblast cell attachment (p < or = 0.05). The number of live cells per specimen area was (382 +/- 99) cells/mm(2) on CPC containing 5% collagen, higher than (173 +/- 42) cells/mm(2) at 0% collagen (p < or = 0.05). The cytoplasmic extensions of the cells anchored to the nano-apatite crystals of the CPC matrix. In summary, collagen was incorporated into in situ-setting, nano-apatitic CPC, achieving a 10-fold increase in work-of-fracture (toughness) and two-fold increase in osteoblast cell attachment. This moldable/injectable, mechanically strong, nano-apatite-collagen composite may enhance bone regeneration in moderate stress-bearing applications.

Strength and fluoride release characteristics of a calcium fluoride based dental nanocomposite.

Secondary caries and restoration fracture remain the two most common problems in restorative dentistry. Release of fluoride ions (F) could be a substantial benefit because F could enrich neighboring enamel or dentin to combat caries. The objective of this study was to incorporate novel CaF(2) nanoparticles into dental resin to develop stress-bearing, F-releasing nanocomposite. CaF(2) nanoparticles, prepared in our laboratories for the first time, were combined with reinforcing whisker fillers in a resin. Flexural strength (mean+/-sd; n=6) was 110+/-11 MPa for the composite containing 30% CaF(2) and 35% whiskers by mass. It matched the 108+/-19 MPa of a stress-bearing, non-releasing commercial composite (Tukey's at 0.05). The composite containing 20% CaF(2) had a cumulative F release of 2.34+/-0.26 mmol/L at 10 weeks. The initial F release rate was 2 microg/(hcm(2)), and the sustained release rate after 10 weeks was 0.29 microg/(hcm(2)). These values exceeded the reported releases of traditional and resin-modified glass ionomer materials. In summary, nanocomposites were developed with relatively high strength as well as sustained release of fluoride ions, a combination not available in current materials. These strong and F-releasing composites may yield restorations that can reduce the occurrence of both secondary caries and restoration fracture.

Tissue engineering solutions for cleft palates.

PURPOSE: Clefts of the lip and palate are the most prevalent congenital craniofacial birth defect in humans. The developing field of tissue engineering is considered for the management of clefts of the lip and palate. MATERIALS AND METHODS: A review of the literature was carried out by using electronic databases (such as PubMed and ISI Web of Science) to search topics including "cleft palate," "tissue engineering," "bone engineering," "palate engineering," and "alveolar bone grafting." To reflect current practice and research, these searches were limited primarily to articles published after the year 2000. RESULTS: Current approaches for the treatment of clefts of the lip and palate include surgery and bone grafts; however, there are limitations associated with these therapies. Tissue engineering strategies, particularly alveolar bone engineering and soft tissue engineering, may provide clinicians with new alternatives. The application of these emerging technologies to a pediatric population must be well considered. CONCLUSIONS: A tissue engineering approach may be a useful alternative for the treatment of cleft palates as it mitigates the concerns of donor site morbidity as well as provides additional options including scaffold implantation and growth factor delivery.

Synthesis and properties of cyclic acetal biomaterials.

There is an increasing need to develop new biomaterials as tissue engineering scaffolds. Unfortunately, many of the materials that have been studied for these purposes are polyesters that hydrolytically degrade into acidic products, which may harm the surrounding tissue, and lead to accelerated degradation of the biomaterial. To overcome this disadvantage, a novel class of biomaterials based on a cyclic acetal unit has been created. Specifically, materials based upon the monomer 5-ethyl-5-(hydroxymethyl)-beta,beta-dimethyl-1,3-dioxane-2-ethanol diacrylate (EHD) is examined. This study investigates the effects of fabrication parameters, including initiator content, volume of diluent, and volume of accelerant, on several properties of EHD networks. Twelve different formulations were fabricated by varying the three parameters in a factorial design. The effects of the fabrication parameters on properties of the EHD networks were examined. Results show that the volume of accelerant most affected the EHD network gelation time, while the volume of diluent most affected the maximum reaction temperature, sol fraction, and degree of swelling. Cell viability on the EHD networks varied between (18 +/- 6)% and (57 +/- 10)% of the control at 4 h, and between (36 +/- 14)% and (140 +/- 50)% of the control at 8 h. These results indicate that it is possible to control the properties of the EHD networks by varying the fabrication parameters, and that EHD networks support a viable cell population.