How mangabey molar form differs under routine vs. fallback hard-object feeding regimes.

Background: Components of diet known as fallback foods are argued to be critical in shaping primate dental anatomy. Such foods of low(er) nutritional quality are often non-preferred, mechanically challenging resources that species resort to during ecological crunch periods. An oft-cited example of the importance of dietary fallbacks in shaping primate anatomy is the grey-cheeked mangabey Lophocebus albigena. This species relies upon hard seeds only when softer, preferred resources are not available, a fact which has been linked to its thick dental enamel. Another mangabey species with thick enamel, the sooty mangabey Cercocebus atys, processes a mechanically challenging food year-round. That the two mangabey species are both thickly-enameled suggests that both fallback and routine consumption of hard foods are associated with the same anatomical feature, complicating interpretations of thick enamel in the fossil record. We anticipated that aspects of enamel other than its thickness might differ between Cercocebus atys and Lophocebus albigena. We hypothesized that to function adequately under a dietary regime of routine hard-object feeding, the molars of Cercocebus atys would be more fracture and wear resistant than those of Lophocebus albigena. Methods: Here we investigated critical fracture loads, nanomechanical properties of enamel, and enamel decussation in Cercocebus atys and Lophocebus albigena. Molars of Cercopithecus, a genus not associated with hard-object feeding, were included for comparison. Critical loads were estimated using measurements from 2D µCT slices of upper and lower molars. Nanomechanical properties (by nanoindentation) and decussation of enamel prisms (by SEM-imaging) in trigon basins of one upper second molar per taxon were compared. Results: Protocone and protoconid critical fracture loads were significantly greater in Cercocebus atys than Lophocebus albigena and greater in both than in Cercopithecus. Elastic modulus, hardness, and elasticity index in most regions of the crown were greater in Cercocebus atys than in the other two taxa, with the greatest difference in the outer enamel. All taxa had decussated enamel, but that of Cercocebus atys uniquely exhibited a bundle of transversely oriented prisms cervical to the radial enamel. Quantitative comparison of in-plane and out-of-plane prism angles suggests that decussation in trigon basin enamel is more complex in Cercocebus atys than it is in either Lophocebus albigena or Cercopithecus cephus. These findings suggest that Cercocebus atys molars are more fracture and wear resistant than those of Lophocebus albigena and Cercopithecus. Recognition of these differences between Cercocebus atys and Lophocebus albigena molars sharpens our understanding of associations between hard-object feeding and dental anatomy under conditions of routine vs. fallback hard-object feeding and provides a basis for dietary inference in fossil primates, including hominins.

Importance of Build Design Parameters to the Fatigue Strength of Ti6Al4V in Electron Beam Melting Additive Manufacturing.

The fatigue properties of metals resulting from Powder Bed Fusion (PBF) is critically important for safety-critical applications. Here, the fatigue life of Grade 5 Ti6Al4V from Electron Beam PBF was investigated with respect to several build and component design parameters using a design of experiments (DOE). Part size (i.e., diameter), part proximity, and part location within the build envelope were considered. Overall, metal in the as-built condition (i.e., no post-process machining) exhibited a significantly lower fatigue life than the machined surface condition. In both conditions, the fatigue life decreased significantly with the decreasing part diameter and increasing radial distance; height was not a significant effect in the machined condition. Whereas the surface topography served as the origin of failure for the as-built condition, the internal lack of fusion (LOF) defects, exposed surface LOF defects, and rogue defects served as the origins for the machined condition. Porosity parameters including size, location, and morphology were determined by X-ray micro-computed tomography (XCT) and introduced within regression models for fatigue life prediction. The greatest resistance to fatigue failure is obtained when parts are placed near the center of the build plane to minimize the detrimental porosity. Machining can improve the fatigue life, but only if performed to a depth that minimizes the underlying porosity.

Contributions to enamel durability with aging: An application of data science tools.

Understanding aging of tooth tissues is the first step to developing robust treatments that support lifelong oral health. In this study selected nanomechanical, compositional and structural parameters of human enamel were characterized to assess the effects of aging on its durability in terms of the apparent fracture toughness (KApp) and brittleness (B). The interdependencies between aging and the enamel properties were assessed using a combination of traditional Pearson's correlation coefficient matrices and self-organizing maps (SOMs) via unsupervised machine learning. To consider age effects, the enamel of three age groups of donor teeth was studied, including primary (donor age ≤10), young (20 age ≤ age ≤50), and old (55 ≤ age) and differences in properties and correlations were identified. Results showed that KApp was negatively correlated to the E, H, degree of crystallinity, and fluoridation, but positively correlated with carbonate content; the opposite trends were observed in B. Interestingly, the SOMs showed that the outer enamel of the old group underwent a degradation in durability (decrease in KApp and increase in B) that was related to multiple contributions, whereas the inner enamel did not undergo this change. Application of K-means clustering on the trained SOMs offered novel insights into the contributions of enamel durability with aging, unique visualization of high-dimensional data onto 2D plots and identified new research directions that would not have otherwise been discovered. Overall, the findings demonstrate the opportunities for understanding aging of enamel using machine learning techniques to pursue age-targeted oral health care.

Odontoblast apoptosis and intratubular mineralization of sclerotic dentin with aging.

OBJECTIVES: The aims of the study were to evaluate the roles of odontoblast apoptosis in the progression of tubular sclerosis of teeth from donors at different ages and assess its correlation to chemical composition and mechanical properties. DESIGN: Healthy human teeth were obtained and divided into young (age ≤ 25, n = 12) and old (age ≥ 60, n = 12) groups. Odontoblasts were counted with standard hematoxylin and eosin staining. Odontoblast apoptosis within dentinal tubules was determined by cleaved caspase-3 immunostaining. Teeth in each group were evaluated by dynamic nanoindentation and energy-dispersive X-ray spectroscopy (EDS). RESULTS: The number of odontoblasts decreased significantly with age. The most prominent change occurred in the apical third of roots. Odontoblastic apoptosis was visualized within dentinal tubules. The apoptosis staining fraction was significantly higher in the outer and inner dentin of old teeth when compared with young teeth (p < 0.05). EDS showed increased calcium content in peritubular dentin but a decrease in the intertubular dentin with increasing age. Scanning based nanoindentation showed that the old intertubular dentin exhibited a significantly higher elastic modulus. CONCLUSIONS: Odontoblast apoptosis, starting at the cell extension in dentinal tubules and proceeding from outer to inner dentin, contributes to the stoichiometric Ca/P ratio in peritubular dentin, which is potentially responsible for intratubular mineralization due to an imbalance of calcium and phosphorous ions.

A machine learning approach to investigate the materials science of enamel aging.

Understanding aging of tooth tissues is critical to the development of patient-centric oral healthcare. Yet, the traditional methods for analyzing the composition-structure-property relationships of hard tissues have limitations when considering aging and other factors. OBJECTIVE: To apply unsupervised machine learning tools to pursue an understanding of relationships between the composition and mechanical behavior of aging enamel. METHODS: Molar teeth were collected from primary (age ≤ 8), young adult (24 ≤ age ≤ 46) and old adult (55 ≤ age) donors. The hardness and elastic modulus were quantified using nanoindentation as a function of distance from the Dentin Enamel Junction (DEJ) within the cervical, cuspal and inter-cuspal regions of the enamel crown. Similarly, a co-located analysis of the chemical composition and structure was performed using Raman spectroscopy. A Self-Organizing Maps (SOMs) algorithm was implemented to identify multi-dimensional composition-property relationships. RESULTS: The hardness and elastic modulus are positively correlated to crystallinity and negatively correlated with carbonate substitution. Furthermore, the effects from fluoridation on the age-dependent properties of enamel is non-linear and depends on its location. The contributions of fluoridation to the enamel properties are different in the cervical and non-cervical regions and appear to be unique within primary and senior adult teeth. SIGNIFICANCE: Based on the findings, unsupervised learning methods can reveal complicated non-linear structure-property relationships in tooth tissues and help to understand the materials science of aging and its consequences.

Long-term antibacterial activity and cytocompatibility of novel low-shrinkage-stress, remineralizing composites.

A low-shrinkage-stress (LSS), antibacterial and remineralizing nanocomposite was recently developed; however, validation of its long-term antibacterial potency in modulating human salivary-derived biofilm is an unmet need. This study aimed to evaluate the antibacterial effect of the bioactive LSS composite before and after aging in acidic solution for 90 days using a multi-species biofilm model, and to evaluate its cytotoxicity. The LSS composite consisted of urethane dimethacrylate (UDMA) and triethylene glycol divinylbenzyl ether (TEG-DVBE), 3% dimethylaminohexadecyl methacrylate (DMAHDM) and 20% nanoparticles of amorphous calcium phosphate (NACP). Biofilm colony-forming units (CFU), lactic acid production, and confocal laser scanning microscopy (3D biofilm) were evaluated before and after three months of aging. Cytotoxicity was assessed against human gingival fibroblasts (HGF). The new LSS composite presented the lowest biofilm CFU, lactic acid and biofilm biomass, compared to controls (n = 6, p < 0.05). Importantly, the new composite exhibited no significant difference in antibacterial performance before and after 90-day-aging, demonstrating long-term antibacterial activity (p > 0.1). The LSS antibacterial and remineralizing composite presented a low cell viability at original extract that has increased with further dilutions. In conclusion, this study spotlighted that the new bioactive composite not only had a low shrinkage stress, but also down-regulated the growth of oral biofilms, reduced acid production, maintained antibacterial activity after the 90-day-aging, and did not compromise the cytocompatibility.

Bioactive low-shrinkage-stress nanocomposite suppresses S. mutans biofilm and preserves tooth dentin hardness.

Recurrent dental caries is one of the main reasons for resin composite restoration failures. This study aimed to: (1) develop a bioactive, low-shrinkage-stress, antibacterial and remineralizing composite and evaluate the sustainability of its antibacterial effect against Streptococcus mutans (S. mutans) biofilms; and (2) evaluate the remineralization and cariostatic potential of the composite containing nanoparticles of amorphous calcium phosphate (NACP) and dimethylaminohexadecyl methacrylate (DMAHDM), using dentin hardness measurement and a biofilm-induced recurrent caries model. The antibacterial and remineralizing low-shrinkage-stress composite consisted of urethane dimethacrylate (UDMA) and triethylene glycol divinylbenzyl ether (TEG-DVBE), 3% DMAHDM and 20% NACP. S. mutans biofilm was used to evaluate antibiofilm activity, before and after 3 months of composite aging in acidic solution. Human dentin was used to develop a recurrent caries biofilm-model. Adding DMAHDM and NACP into low shrinkage-stress composite did not compromise the flexural strength. The low-shrinkage-stress composite with DMAHDM achieved substantial reductions in biofilm colony-forming units (CFU), lactic acid production, and biofilm biomass (p < 0.05). The low-shrinkage-stress DMAHDM+NACP composite exhibited no significant difference in antibacterial performance before and after 3 months of aging, demonstrating long-term antibacterial activity. Under S. mutans biofilm acidic attack, dentin hardness (GPa) was 0.24 ± 0.04 for commercial control, and 0.23 ± 0.03 for experimental control, but significantly higher at 0.34 ± 0.03 for DMAHDM+NACP group (p < 0.05). At an instrumental compliance of 0.33 µm/N, the polymerization shrinkage stress of the new composite was 36% lower than that of a traditional composite (p < 0.05). The triple strategy of antibacterial, remineralization and lower shrinkage-stress has great potential to inhibit recurrent caries and increase restoration longevity. Statement of Significance Polymerization shrinkage stress, masticatory load over time as well as biochemical degradation can lead to marginal failure and secondary caries. The present study developed a new low-shrinkage-stress, antibacterial and remineralizing dental nanocomposite. Polymerization shrinkage stress was greatly reduced, biofilm acid production was inhibited, and tooth dentin mineral and hardness were preserved. The antibacterial composite possessed a long-lasting antibiofilm effect against cariogenic bacteria S. mutans. The new bioactive nanocomposite has the potential to suppress recurrent caries at the restoration margins, protects tooth structures, and increases restoration longevity.

Novel bioactive root canal sealer with antibiofilm and remineralization properties.

OBJECTIVES: (1) To develop a novel bioactive root canal sealer with antibiofilm and remineralization properties using dimethylaminohexadecyl methacrylate (DMAHDM) and nanoparticles of amorphous calcium phosphate (NACP); (2) investigate the effects on E. faecalis biofilm inhibition, sealer flow and sealing ability, compared with an epoxy-resin-based sealer AH Plus; and (3) investigate the calcium (Ca) and phosphate (P) ion release from the sealers. METHODS: A series of dual-cure endodontic sealers were formulated with DMAHDM and NACP at 5% and 20% by mass, respectively. Flow properties and sealing ability of the sealers were measured. Colony-forming units (CFU), live/dead assay, and polysaccharide production of biofilms on sealers were determined. Ca and P ion releases from the sealers were measured. RESULTS: The new sealer containing 20% NACP and 5% DMAHDM yielded a paste flow of (28.99 ± 0.69) mm, within the range of ISO recommendations. The sealing properties of the sealer with 5% DMAHDM and 20% NACP were similar to a commercial control (p > 0.05). The sealer with DMAHDM decreased E. faecalis biofilm CFU by more than 4 orders of magnitude, compared to AH plus and experimental controls. The sealer with 20% NACP and 5% DMAHDM had relatively high levels of Ca and P ion release necessary for remineralization. CONCLUSIONS: A new bioactive endodontic sealer was developed with strong antibiofilm activity against E. faecalis biofilms and high levels of Ca and P ion release for remineralization, without compromising the paste flow and sealing properties. CLINICAL SIGNIFICANCE: The bioactive antibacterial and remineralizing root canal sealer is promising to inhibit E. faecalis biofilms to prevent endodontic treatment failure and secondary endodontic infections, while releasing high levels of Ca and P ions that could remineralize and strengthen the tooth structures and potentially prevent future root fractures and teeth extractions.

Contribution of Root Canal Treatment to the Fracture Resistance of Dentin.

INTRODUCTION: Although the strength and toughness of dentin decrease with age, no study has explored if restorative treatments are a contributing factor. METHODS: Multiple extracted teeth were obtained from randomly selected donors and categorized according to donor age and prior root canal treatment. The microstructure and chemical composition of radicular dentin were evaluated using scanning electron microscopy and Raman spectroscopy, respectively, and the strength was evaluated in 4-point flexure to failure. Data were compared using the Student t test. RESULTS: Dentin from the root canal-restored teeth exhibited significantly lower strength (P < .05) than tissue from age- and donor-matched unrestored tooth pairs. Although there was no significant difference in the mineral-to-collagen ratio between the 2 groups, dentin obtained from the root canal-treated teeth exhibited more extensive collagen cross-linking and lower tubule occlusion ratios than the unrestored tooth pairs. CONCLUSIONS: There is a decrease in the strength of radicular dentin with aging, but prior root canal treatment increases the extent of degradation.

Bonding durability, antibacterial activity and biofilm pH of novel adhesive containing antibacterial monomer and nanoparticles of amorphous calcium phosphate.

OBJECTIVES: The dentin bonding often fails over time, leading to secondary caries and restoration failure. The objectives of this study were to develop an adhesive with dimethylaminohexadecyl methacrylate (DMAHDM) and nanoparticles of amorphous calcium phosphate (NACP), and investigate the effects of storage in artificial saliva for six months on the bonding durability, antibacterial activity, ion release and biofilm pH properties for the first time. METHODS: DMAHDM was added at 5% (by mass) to Scotchbond Primer and Adhesive (SBMP). NACP was added at 10%, 20%, and 30% to SBMP adhesive. Dentin bonding durability, antibacterial activity against Streptococcus mutans biofilms, and calcium (Ca) and phosphate (P) ion liberation properties were investigated after 1 day and 6months of storage in artificial saliva. RESULTS: Dentin bond strength (n = 50) had 25% loss after 6 months of aging for SBMP control. However, SBMP + DMAHDM+10NACP and SBMP + DMAHDM+20NACP showed no loss in bond strength after storage in artificial saliva for 6 months. The DMAHDM + NACP incorporation method dramatically reduced the biofilm metabolic activity and acid production, and decreased the biofilm CFU by four orders of magnitude, compared to SBMP control, even after 6 months of aging (p < 0.05). DMAHDM + NACP had long-lasting Ca and P ion releases, and raised the biofilm pH to 6.8, while the control group had a cariogenic biofilm pH of 4.5. CONCLUSIONS: Incorporating DMAHDM + NACP in bonding agent yielded potent and long-lasting antibacterial activity and ions liberation ability, and much higher long-term dentin bond strength after 6-month of aging. The new bonding agent is promising to inhibit caries at the restoration margins and increase the resin-dentin bonding longevity. CLINICAL SIGNIFICANCE: The novel bioactive adhesive is promising to protect tooth structures from biofilm acids and secondary caries. NACP and DMAHDM have great potential for applications to a wide range of dental materials to reduce plaque and achieve therapeutic effects.

A comparative study on the wear behavior of a polymer infiltrated ceramic network (PICN) material and tooth enamel.

OBJECTIVE: To investigate the wear mechanisms of a polymer infiltrated ceramic network (PICN) material, to compare its wear behavior with that of tooth enamel, and to provide evidence relevant to its clinical use. METHODS: The Vickers hardness (HV) and elastic modulus (E) of a commercial PICN material (ENAMIC) and enamel were measured. Reciprocating wear tests were performed under a ball-on-flat configuration. Three wear pairs were explored including ENAMIC and enamel subjected to Si3N4 ball antagonists and ENAMIC subjected to enamel cusp antagonists. The coefficients of Friction (CoFs) were monitored continuously to 5×104 cycles. The wear depth of ENAMIC, enamel specimens and enamel cusps were quantified using white light interferometry, and the wear morphologies were examined using scanning electron microscopy (SEM) to distinguish the wear mechanisms. RESULTS: The HV of ENAMIC is similar to tooth enamel but the E is much lower. For both materials, the CoFs increased sharply in the early stage and then reached plateaus in the later phase. Throughout the cyclic loading history, ENAMIC exhibited larger wear depths than enamel. However, the damage evolution in ENAMIC was similar to that of enamel as the polymer phase was worn preferentially similar to inter-rod enamel, and then the ceramic phase exfoliated from the wear surface akin to enamel rods. The SEM images showed evidence of few cracks within wear tracks of ENAMIC, in comparison to numerous cracks in tooth enamel. SIGNIFICANCE: ENAMIC has lower wear resistance than tooth enamel, but it exhibits a wear damage mode similar to tooth enamel.

The Tooth: Its Structure and Properties.

This article provides a brief review of recent investigations concerning the structure and properties of the tooth. The last decade has brought a greater emphasis on the durability of the tooth, an improved understanding of the fatigue and fracture behavior of the principal tissues, and their importance to tooth failures. The primary contributions to tooth durability are discussed, including the process of placing a restoration, the impact of aging, and challenges posed by the oral environment. The significance of these findings to the dental community and their importance to the pursuit of lifelong oral health are highlighted.

Effect of acidic agents on the wear behavior of a polymer infiltrated ceramic network (PICN) material.

Polymer infiltrated ceramic network (PICN) materials exhibit desirable properties for replacement of tooth structure. However, their durability and their integrity in various oral environments, remain relatively unknown. The primary objective of this study is to investigate the effect of acidic agents on the wear behavior of PICNs. Twenty specimens were randomly assigned to four groups and then immersed in either deionized water (control) or acidic agents (2% acetic acid, citric acid or lactic acid solutions) at 37℃ for 4 weeks. Changes in the surface microhardness (SMH) and roughness were measured. Reciprocating wear tests were performed under artificial saliva to 10,000 cycles, and the coefficient of friction (COF) and wear depth were quantified to assess the wear behavior. Scanning electron microscopy (SEM) was used to analyze the wear morphology. Acid erosion decreased the SMH and increased surface roughness of the PICN, especially in lactic acid solution. For less than 2800 cycles, the acetic acid and citric acid groups showed higher COF and wear depths due to combined ceramic and polymer wear; the lactic acid group showed smaller COF and wear depth, due to a wear debris layer that acted as solid lubricant. Beyond 2800 cycles, all four groups exhibited similar COF values, as well as wear depth and wear morphology. Overall, acid erosion had a significant effect on the surface wear history of the PICN, but no effect on its long-term wear properties. Overall, the depth of acidic degradation of the PICN was rather limited.

Extrafibrillar collagen demineralization-based chelate-and-rinse technique bridges the gap between wet and dry dentin bonding.

Limitations associated with wet-bonding led to the recent development of a selective demineralization strategy in which dentin was etched with a reduced concentration of phosphoric acid to create exclusive extrafibrillar demineralization of the collagen matrix. However, the use of acidic conditioners removes calcium via diffusion of very small hydronium ions into the intrafibrillar collagen water compartments. This defeats the purpose of limiting the conditioner to the extrafibrillar space to create a collagen matrix containing only intrafibrillar minerals to prevent collapse of the collagen matrix. The present work examined the use of polymeric chelators (the sodium salt of polyacrylic acid) of different molecular weights to selectively demineralize extrafibrillar dentin. These polymeric chelators exhibit different affinities for calcium ions (isothermal titration calorimetry), penetrated intrafibrillar dentin collagen to different extents based on their molecular sizes (modified size-exclusion chromatography), and preserve the dynamic mechanical properties of mineralized dentin more favorably compared with completely demineralized phosphoric acid-etched dentin (nanoscopical dynamic mechanical analysis). Scanning and transmission electron microscopy provided evidence for retention of intrafibrillar minerals in dentin surfaces conditioned with polymeric chelators. Microtensile bond strengths to wet-bonded and dry-bonded dentin conditioned with these polymeric chelators showed that the use of sodium salts of polyacrylic acid for chelating dentin prior to bonding did not result in significant decline in resin-dentin bond strength. Taken together, the findings led to the conclusion that a chelate-and-rinse conditioning technique based on extrafibrillar collagen demineralization bridges the gap between wet and dry dentin bonding. STATEMENT OF SIGNIFICANCE: The chelate-and-rinse dental adhesive bonding concept differentiates from previous research in that it is based on the size-exclusion characteristics of fibrillar collagen; molecules larger than 40kDa are prevented from accessing the intrafibrillar water compartments of the collagen fibrils. Using this chelate-and-rinse extrafibrillar calcium chelation concept, collagen fibrils with retained intrafibrillar minerals will not collapse upon air-drying. This enables adhesive infiltration into the mineral-depleted extrafibrillar spaces without relying on wet-bonding. By bridging the gap between wet and dry dentine bonding, the chelate-and-rinse concept introduces additional insight to the field by preventing exposure of endogenous proteases via preservation of the intrafibrillar minerals within a collagen matrix. If successfully validated, this should help prevent degradation of resin-dentine bonds by collagenolytic enzymes.

Fatigue of human dentin by cyclic loading and during oral biofilm challenge.

Fatigue caused by the cyclic loads of mastication and acid attack caused by the excretion of oral biofilms are two of the most critical challenges to the success of dental restorations and their clinical service life. The objective of this investigation was to evaluate the fatigue strength of human dentin when exposed to a simultaneous challenge of cyclic loading and acidic attack from oral bacteria. Rectangular beams of coronal dentin were obtained from third molars and subjected to cyclic flexural loading while exposed to an in-vitro microcosm biofilm model. Two different cariogenic protocols were considered and results were compared with those for control samples evaluated at neutral pH. According to the fatigue life distributions, dentin exposed to the biofilm model with 2.0% sucrose supplements pulsed twice per day caused a significant reduction in the fatigue strength (p < 0.001) with respect to 0.2% sucrose supplements pulsed once a day, and the control environment (without biofilm). The endurance limit after biofilm exposure was 20 MPa, which is 60% lower than that of the control environment without biofilm (50 MPa). Biofilm attack of dentin increases the likelihood of restored tooth failures by fatigue and after only modest periods of exposure. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1978-1985, 2017.

Assessing the feasibility of yttria-stabilized zirconia in novel designs as mandibular anterior fixed lingual retention after orthodontic treatment.

INTRODUCTION: The purpose of this study is to explore the feasibility of yttria-stabilized zirconia (Y-TZP) in fixed lingual retention as an alternative to stainless steel. METHODS: Exploratory Y-TZP specimens were milled to establish design parameters. Next, the specimens were milled according to ASTM standard C1161-13 and subjected to 4-point flexural tests to determine material properties. Finite element analysis was used to evaluate 9 novel cross-sectional designs, which were compared with stainless steel wire. Each design was analyzed under loading conditions to determine von Mises and bond stresses. The most promising design was fabricated to assess the accuracy and precision of current CAD/CAM milling technology. RESULTS: The superior design had a 1.0 × 0.5 mm semielliptical cross-section and was shown to be fabricated reliably. Overall, the milling indicated a maximum percent standard deviation of 9.3 and maximum percent error of 13.5 with a cost of $30 per specimen. CONCLUSIONS: Y-TZP can be reliably milled to dimensions comparable with currently available metallic retainer wires. Further research is necessary to determine the success of the bonding protocol and the clinical longevity of Y-TZP fixed retainers. Advanced technology is necessary to connect the intraoral scan to an esthetic and patient-specific Y-TZP fixed retainer.

Protein-repellent and antibacterial functions of a calcium phosphate rechargeable nanocomposite.

OBJECTIVES: We recently developed a new rechargeable composite with nanoparticles of amorphous calcium phosphate (NACP) having long-term calcium (Ca) and phosphate (P) ion release; however, this composite was not antibacterial. The objectives of this study were to: (1) incorporate dimethylaminohexadecyl methacrylate (DMAHDM) and 2-methacryloyloxyethyl phosphorylcholine (MPC) into rechargeable NACP composite, and (2) investigate mechanical properties, protein adsorption and biofilm response of composite, and the pH of biofilm medium. METHODS: MPC, DMAHDM and NACP were mixed into a resin of ethoxylated bisphenol A dimethacrylate (EBPADMA) and pyromellitic glycerol dimethacrylate (PMGDM). Protein adsorption was measured using a micro bicinchoninic acid method. A human saliva microcosm biofilm model was used to grow biofilms on composites. Colony-forming units (CFU), live/dead assay, metabolic activity, and biofilm culture medium pH were determined. The tests used n=6. RESULTS: The composite with 3% MPC had protein adsorption an order of magnitude less than that of a commercial composite (p<0.05). Control composites were fully covered by live bacteria. Live bacteria were reduced via MPC; 3% MPC+3% DMAHDM had the least live bacteria (p<0.05). The composite with 3% MPC+3% DMAHDM inhibited biofilm growth and viability, reducing biofilm CFU by 3 log compared to commercial control composite (p<0.05), while having a flexural strength similar to that of the commercial composite (p>0.1). The composite containing 3% MPC+3% DMAHDM with biofilm culture maintained a pH above 6.5, while the commercial composite had a cariogenic pH of 4.2 in biofilm culture medium. CONCLUSIONS: The new protein-repellent and antibacterial NACP rechargeable composite substantially reduced biofilm growth, yielding a much higher pH than a commercial composite. CLINICAL SIGNIFICANCE: This novel bioactive nanocomposite is promising to protect tooth structures from biofilm acids and caries. The method of using NACP, MPC and DMAHDM may be applicable to other dental materials to reduce plaque buildup and secondary caries.

Designing Multiagent Dental Materials for Enhanced Resistance to Biofilm Damage at the Bonded Interface.

The oral environment is considered to be an asperous environment for restored tooth structure. Recurrent dental caries is a common cause of failure of tooth-colored restorations. Bacterial acids, microleakage, and cyclic stresses can lead to deterioration of the polymeric resin-tooth bonded interface. Research on the incorporation of cutting-edge anticaries agents for the design of new, long-lasting, bioactive resin-based dental materials is demanding and provoking work. Released antibacterial agents such as silver nanoparticles (NAg), nonreleased antibacterial macromolecules (DMAHDM, dimethylaminohexadecyl methacrylate), and released acid neutralizer amorphous calcium phosphate nanoparticles (NACP) have shown potential as individual and dual anticaries approaches. In this study, these agents were synthesized, and a prospective combination was incorporated into all the dental materials required to perform a composite restoration: dental primer, adhesive, and composite. We focused on combining different dental materials loaded with multiagents to improve the durability of the complex dental bonding interface. A combined effect of bacterial acid attack and fatigue on the bonding interface simulated the harsh oral environment. Human saliva-derived oral biofilm was grown on each sample prior to the cyclic loading. The oral biofilm viability during the fatigue performance was monitored by the live-dead assay. Damage of the samples that developed during the test was quantified from the fatigue life distributions. Results indicate that the resultant multiagent dental composite materials were able to reduce the acidic impact of the oral biofilm, thereby improving the strength and resistance to fatigue failure of the dentin-resin bonded interface. In summary, this study shows that dental restorative materials containing multiple therapeutic agents of different chemical characteristics can be beneficial toward improving resistance to mechanical and acidic challenges in oral environments.

Inhibition of matrix metalloproteinase activity in human dentin via novel antibacterial monomer.

OBJECTIVE: Dentin-composite bond failure is caused by factors including hybrid layer degradation, which in turn can be caused by hydrolysis and enzymatic degradation of the exposed collagen in the dentin. The objectives of this study were to investigate a new antibacterial monomer (dimethylaminododecyl methacrylate, DMADDM) as an inhibitor for matrix metalloproteinases (MMPs), and to determine the effects of DMADDM on both soluble recombinant human MMPs (rhMMPs) and dentin matrix-bound endogenous MMPs. METHODS: Inhibitory effects of DMADDM at six mass% (0.1% to 10%) on soluble rhMMP-8 and rhMMP-9 were measured using a colorimetic assay. Matrix-bound endogenous MMP activity was evaluated in demineralized human dentin. Dentin beams were divided into four groups (n=10) and incubated in calcium- and zinc-containing media (control medium); or control medium+0.2% chlorhexidine (CHX); 5% 12-methacryloyloxydodecylpyridinium bromide (MDPB); or 5% DMADDM. Dissolution of dentin collagen peptides was evaluated by mechanical testing in three-point flexure, loss of dentin mass, and a hydroxyproline assay. RESULTS: Use of 0.1% to 10% DMADDM exhibited a strong concentration-dependent anti-MMP effect, reaching 90% of inhibition on rhMMP-8 and rhMMP-9 at 5% DMADDM concentration. Dentin beams in medium with 5% DMADDM showed 34% decrease in elastic modulus (vs. 73% decrease for control), 3% loss of dry dentin mass (vs. 28% loss for control), and significantly less solubilized hydroxyproline when compared with control (p<0.05). SIGNIFICANCE: The new antibacterial monomer DMADDM was effective in inhibiting both soluble rhMMPs and matrix-bound human dentin MMPs. These results, together with previous studies showing that adhesives containing DMADDM inhibited biofilms without compromising dentin bond strength, suggest that DMADDM is promising for use in adhesives to prevent collagen degradation in hybrid layer and protect the resin-dentin bond.

Adopting the principles of collagen biomineralization for intrafibrillar infiltration of yttria-stabilized zirconia into three-dimensional collagen scaffolds.

In this paper, we report a process for generating collagen-yttria-stabilized amorphous zirconia hybrid scaffolds by introducing acetylacetone-inhibited zirconia precursor nanodroplets into a poly(allylamine)-coated collagen matrix. This polyelectrolyte coating triggers intrafibrillar condensation of the precursors into amorphous zirconia, which is subsequently transformed into tetragonal yttria-stabilized zirconia after calcination. Our findings represent a new paradigm in the synthesis of non-naturally occurring collagen-based hybrid scaffolds under alcoholic mineralizing conditions.