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In the Diploma thesis called "Research of seasonality in the animal dental cement and the use of this method in archaeology", I devote myself to one of the most reliable methods for determining the age cementochronology, or the analysis of increments of the dental cement. By using the method, it is possible to relatively accurately evaluate the age of an individual and to determine the death season, and thus we penetrate deeper not only to problems of palaeoecological conditions of archaeological situations, but also to economical-social relationships of then populations. Cementochronology also allows trace hunting and settlement strategies, i. e. when and for a what purpose the specific site was settled. The Diploma thesis summerizes previous knowledge about the method and compares it with the results obtained by the analysis of increments of the dental cement, which was applied on referential zoological and archaeozoological material.

Conventional glass ionomer cements (GICs), which continue to gain acceptance as superbly biocompatible dental materials, were first released in the early 1970s as a result of research into combining the advantages of silicate cements and polyalkenate cements. The chemistry of GICs is based upon the aqueous reaction between an ion-leachable fluoride glass and polyacid which yields the final cross-linked insoluble ionomer (ionic polymer). The significant advantages of GICs include direct adhesion to tooth structures, fluoride release, minimal dimensional change on curing, significant ease of use and superb biocompatibility, to the extent that affected proximal tooth structures may be retained, remineralised , and strengthened against further caries. GICs have, however, been unfavourably compared with other restorative materials in their mechanical properties and setting characteristics, in particular their relative weakness, the time limitations for the acid-base reaction to proceed to acceptable maturity, and the susceptibility of the immature cement to water sorption or desiccation.

Conventional glass ionomer cements (GICs), which continue to gain acceptance as superbly biocompatible dental materials, were first released in the early 1970s as a result of research into combining the advantages of silicate cements and polyalkenate cements. The chemistry of GICs is based upon the aqueous reaction between an ion-leachable fluoride glass and polyacid which yields the final cross-linked insoluble ionomer (ionic polymer). The significant advantages of GICs include direct adhesion to tooth structures, fluoride release, minimal dimensional change on curing, significant ease of use and superb biocompatibility, to the extent that affected proximal tooth structures may be retained, remineralised , and strengthened against further caries. GICs have, however, been unfavourably compared with other restorative materials in their mechanical properties and setting characteristics, in particular their relative weakness, the time limitations for the acid-base reaction to proceed to acceptable maturity, and the susceptibility of the immature cement to water sorption or desiccation.

Two different research projects were investigated for this thesis, which has consequently been presented in two parts. PART 1 An attempt has been made to improve the high temperature performance of phenol-formaldehyde thermosets by modification of their structure with inorganic phosphate groups. Transesterification of tri-phenyl phosphate with resorcinol has given a resorcinol phosphate resin, which cured with hexamethylenetetramine. A pilot scale batch of this resin has been made and used in high temperature stability studies. Post-cured resorcinol phosphate resin-chrysotile asbestos (30: 70) moulded bars retained 59.5% of their flexural strength after ageing at 523K for 1000 hr in air. Similar phenol-formaldehyde composite bars aged under identical conditions retained only 5.3% of their initial flexural strength. The utility of the resorcinol phosphate resin composite as a commercial product is limited, since the bars had a much lower initial flexural strength (30.85 MNm-2) than the phenol-formaldehyde resin composite bars (108.5 MNm-2). Thermogravimetry and isothermal heating studies have indicated that the degradation of resorcinol phosphate resin was greatly accelerated by chrysotile asbestos, which may catalyse a bond re-organisation process that has been tentatively proposed as a mechanism for the fragmentation of the resin. PART 2 Recently an ionomer dental cement (ASPA), prepared from aqueous poly(acrylic acid) and an ion-leachable aluminosilicate glass, has been developed. The system has been extended by studying other aqueous polymers. The factors influencing the gelation and the properties of the set cements have been examined. Poly(carboxylic acids) with hydrophobic, or no pendant substituents were found to be the most satisfactory polymers for preparing water stable cements. To study the influence of the nature of the cation and polymer structure on the gelation and water stability of ionomer cements, a wide range of metal oxide-polyacid products have been studied. The formation of water stable cements depended markedly on the type of oxide and polyacid employed and appeared to involve factors such as the co-ordination geometry and radius of the cation and the nature of the cation-polyanion bonding in the matrix. A comparison between the water stabilities of ASPA cement and poly(acrylic acid)-CaO, Al2O3, or Al(OH)3 cements has shown that the chemistry of ASPA cement is more complex than has been hitherto reported. Stability constants have been determined for Ca 2+ and Cd 2+ with poly(acrylic acid) and ethyl ethylene-maleic acid copolymer by a potentiometric titration method developed by Gregor and modified by Mandel and Leyte. The stability constants obtained in 1.0M NaNO3 at 298.2 ± 0.2K were: for poly(acrylic acid), with Cat2+, log b1 Ca2+ PAA ~ -3.35 with Cd2+, log Bav Cd2+ PAA = -2.30 for ethylene-maleic acid copolymer, with Cat2+, log b1 CA2+ EMA ~ -4.05 with Cd2+, log Bav Cd2+ EMA = -1.95 The log b1 values probably had little precise meaning, although to a first approximation, log b1 Ca2+ PAA > log b1 Ca2+ EMA The determined stability constants have been used with limited success in predicting the water stabilities of the corresponding metal oxide-polyacid cements.

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