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Concept: Tooth enamel

262

Evidence of prehistoric dentistry has been limited to a few cases, the most ancient dating back to the Neolithic. Here we report a 6500-year-old human mandible from Slovenia whose left canine crown bears the traces of a filling with beeswax. The use of different analytical techniques, including synchrotron radiation computed micro-tomography (micro-CT), Accelerator Mass Spectrometry (AMS) radiocarbon dating, Infrared (IR) Spectroscopy and Scanning Electron Microscopy (SEM), has shown that the exposed area of dentine resulting from occlusal wear and the upper part of a vertical crack affecting enamel and dentin tissues were filled with beeswax shortly before or after the individual’s death. If the filling was done when the person was still alive, the intervention was likely aimed to relieve tooth sensitivity derived from either exposed dentine and/or the pain resulting from chewing on a cracked tooth: this would provide the earliest known direct evidence of therapeutic-palliative dental filling.

Concepts: Electron, Spectroscopy, Mass spectrometry, Teeth, Dental caries, Scanning electron microscope, Tooth enamel, Dentin

227

In 1966, the National Institute of Dental Research (NIDR) began planning a targeted research program to identify interventions for widespread application to eradicate dental caries (tooth decay) within a decade. In 1971, the NIDR launched the National Caries Program (NCP). The objective of this paper is to explore the sugar industry’s interaction with the NIDR to alter the research priorities of the NIDR NCP.

Concepts: Lactic acid, Teeth, Dental caries, Tooth enamel, Sucrose, Oral hygiene, Dental restoration, Dental drill

177

Human dental enamel, the hardest tissue in the body, plays a vital role in protecting teeth from wear as a result of daily grinding and chewing as well as from chemical attack. It is well established that the mechanical strength and fatigue resistance of dental enamel are derived from its hierarchical structure, which consists of periodically arranged bundles of hydroxyapatite (HAP) nanowires. However, we do not yet have a full understanding of the in vivo HAP crystallization process that leads to this structure. Mg(2+) ions, which are present in many biological systems, regulate HAP crystallization by stabilizing its precursor, amorphous calcium phosphate (ACP), but their atomic-scale distribution within HAP is unknown. We use atom probe tomography to provide the first direct observations of an intergranular Mg-rich ACP phase between the HAP nanowires in mature human dental enamel. We also observe Mg-rich elongated precipitates and pockets of organic material among the HAP nanowires. These observations support the postclassical theory of amelogenesis (that is, enamel formation) and suggest that decay occurs via dissolution of the intergranular phase. This information is also useful for the development of more accurate models to describe the mechanical behavior of teeth.

Concepts: Hierarchy, Solubility, Philosophy of science, Teeth, Crystallization, Tooth enamel, Nucleation, Remineralisation of teeth

127

Prehistoric dental treatments were extremely rare, and the few documented cases are known from the Neolithic, when the adoption of early farming culture caused an increase of carious lesions. Here we report the earliest evidence of dental caries intervention on a Late Upper Palaeolithic modern human specimen (Villabruna) from a burial in Northern Italy. Using Scanning Electron Microscopy we show the presence of striations deriving from the manipulation of a large occlusal carious cavity of the lower right third molar. The striations have a “V”-shaped transverse section and several parallel micro-scratches at their base, as typically displayed by cutmarks on teeth. Based on in vitro experimental replication and a complete functional reconstruction of the Villabruna dental arches, we confirm that the identified striations and the associated extensive enamel chipping on the mesial wall of the cavity were produced ante-mortem by pointed flint tools during scratching and levering activities. The Villabruna specimen is therefore the oldest known evidence of dental caries intervention, suggesting at least some knowledge of disease treatment well before the Neolithic. This study suggests that primitive forms of carious treatment in human evolution entail an adaptation of the well-known toothpicking for levering and scratching rather than drilling practices.

Concepts: Human, Teeth, Dental caries, Scanning electron microscope, Tooth enamel, Paleolithic, Stone Age, Prehistory

28

A patient exhibited severe abrasion of resin posterior denture teeth including perforation of the denture base. New dentures were provided to explore the application of zirconia teeth for complete dentures. [Correction added to online publication 07 November 2012: “Zirconium” corrected to “Zirconia”.] Traditional denture procedures were combined with fixed prosthodontic CAD/CAM procedures to fabricate custom-designed four-tooth posterior segments in hollow crown form to reduce weight and with a retentive form for interlocking to the denture base. The new dentures were successful in reducing wear of the denture teeth over the short-term follow-up period.

Concepts: Nitrogen, Teeth, Tooth enamel, Dentures, Zirconium dioxide, Prosthodontology, Prosthodontics

28

Enamel matrix self-assembly has long been suggested as the driving force behind aligned nanofibrous hydroxyapatite formation. We tested if amelogenin, the main enamel matrix protein, can self-assemble into ribbon-like structures in physiologic solutions. Ribbons 17 nm wide were observed to grow several micrometers in length, requiring calcium, phosphate, and pH 4.0-6.0. The pH range suggests that the formation of ion bridges through protonated histidine residues is essential to self-assembly, supported by a statistical analysis of 212 phosphate-binding proteins predicting 12 phosphate-binding histidines. Thermophoretic analysis verified the importance of calcium and phosphate in self-assembly. X-ray scattering characterized amelogenin dimers with dimensions fitting the cross-section of the amelogenin ribbon, leading to the hypothesis that antiparallel dimers are the building blocks of the ribbons. Over 5-7 days, ribbons self-organized into bundles composed of aligned ribbons mimicking the structure of enamel crystallites in enamel rods. These observations confirm reports of filamentous organic components in developing enamel and provide a new model for matrix-templated enamel mineralization.

Concepts: DNA, Scientific method, Protein, Histidine, Observation, Hypothesis, Amorphous calcium phosphate, Tooth enamel

28

AIM: To develop a systematic review based on the relation between salivary proteins and dental caries by comparing subjects with and without caries experience and to evaluate whether salivary proteins can be considered biomarkers for dental caries or not. METHODS: An electronic search was performed in the PubMed Medline, Ovid Medline, ISI Web of Science, Medline, Cochrane Library, Lilacs, Scielo, BBO, Paho and Wholis databases applying the following MeSH terms: “dental caries” OR “tooth demineralization” OR “dental caries susceptibility” OR “dental enamel solubility” AND “salivary proteins and peptides” OR “saliva” AND “proteins”. To be eligible for the systematic review, the observational controlled studies had to have groups with and without caries experience. Studies with high risk of bias were excluded. RESULTS: From a total of 188 identified studies, only seven were included in this systematic review. Four studies were classified as “low risk of bias” and three as “moderate risk of bias”. Three studies reported a relation between salivary proteins and dental caries. CONCLUSION: There was not sufficient evidence to establish salivary proteins as a biomarker for this disease although three of the seven studies showed a relation between salivary proteins and dental caries in terms of protein phenotypes, total protein concentration and protein molecular weight.

Concepts: Saliva, Enzyme, MEDLINE, Teeth, Tooth development, Dental caries, Tooth enamel, Medical Subject Headings

27

Hominin dietary specialization is crucial to understanding the evolutionary changes of craniofacial biomechanics and the interaction of food processing methods' effects on teeth. However, the diet-related dental wear processes of the earliest European hominins remain unknown because most of the academic attention has focused on Neandertals. Non-occlusal dental microwear provides direct evidence of the effect of chewed food particles on tooth enamel surfaces and reflects dietary signals over time. Here, we report for the first time the direct effect of dietary abrasiveness as evidenced by the buccal microwear patterns on the teeth of the Sima del Elefante-TE9 and Gran Dolina-TD6 Atapuerca hominins (1.2-0.8 million years ago - Myr) as compared with other Lower and Middle Pleistocene populations. A unique buccal microwear pattern that is found in Homo antecessor (0.96-0.8 Myr), a well-known cannibal species, indicates dietary practices that are consistent with the consumption of hard and brittle foods. Our findings confirm that the oldest European inhabitants ingested more mechanically-demanding diets than later populations because they were confronted with harsh, fluctuating environmental conditions. Furthermore, the influence of grit-laden food suggests that a high-quality meat diet from butchering processes could have fueled evolutionary changes in brain size.

Concepts: Human, Nutrition, Food, Teeth, Food processing, Tooth enamel, Human evolution, Pleistocene

27

The skeletal remains of Giovanna of Austria (1547-1578), daughter of the Emperor Ferdinand I of Habsburg (1503-1564) and first wife of the Grand Duke of Tuscany, Francesco I (1541-1587), exhumed from the Basilica of San Lorenzo in Florence, were submitted to paleopathological study. Examination of the dentition, which was in a good state of preservation, showed maxillary retrognathism, together with a caries lesion, moderate periodontal disease, malposition of the upper second premolars and tooth wear. Furthermore, several horizontal grooves were observed in both the buccal and the lingual crown surfaces of almost all teeth, especially the anterior ones. The orthopantomogram showed hypomineralized enamel and alveolar bone loss. Two third-molar teeth were investigated using micro-computed tomography (micro-CT) analysis, revealing highly irregular enamel caps with reduced average thickness. The observed features suggest a diagnosis of hypoplastic amelogenesis imperfecta, a developmental condition affecting enamel formation.

Concepts: Teeth, Tooth enamel, Charles V, Holy Roman Emperor, Monarch, House of Habsburg, Habsburg Monarchy, Ferdinand I, Holy Roman Emperor, Francis II, Holy Roman Emperor

26

Drawbacks with the commonly used PMMA-based bone cements, such as an excessive elastic modulus and potentially toxic residual monomer content, motivate the development of alternative cements. In this work an attempt to prepare an injectable biomaterial based on isosorbide-alicyclic diol derived from renewable resources was presented. Two novel dimethacrylic monomers ISDGMA - 2,5-bis(2-hydroxy-3-methacryloyloxypropoxy)-1,4:3,6-dianhydro-sorbitol and ISETDMA - dimethacrylate of ethoxylated isosorbide were synthesized and used to prepare a series of low-viscosity compositions comprising bioactive nano-sized hydroxyapatite in the form of a two-paste system. Formulations exhibited a non-Newtonian shear-thinning behavior, setting times between 2.6min and 5.3min at 37°C and maximum curing temperatures of 65°C. Due to the hydrophilic nature of ISDGMA, cured compositions could absorb up to 13.6% water and as a result the Young’s modulus decreased from 1429MPa down to 470MPa. Both, poly(ISDGMA) and poly(ISETDMA) were subjected to a MTT study on mice fibroblasts (BALB/3T3) and gave relative cell viabilities above 70% of control. A selected model bone cement was additionally investigated using human osteosarcoma cells (SaOS-2) in an MTS test, which exhibited concentration-dependent cell viability. The preliminary results, presented in this work reveal the potential of two novel dimethacrylic monomers in the preparation of an injectable biomaterial for bone augmentation, which could overcome some of the drawbacks typical for conventional acrylic bone cement.

Concepts: Young's modulus, Tooth enamel, Elastic modulus, Stiffness, Hooke's law, Osteosarcoma, Monomers, Impulse excitation technique