Deposit Formation on Prosthetic Materials in Vivo After One Year: a Quantitative Study of Twelve Materials

In vivo-formed deposits on prosthetic materials are of considerable interest. Deposit quantification is important to gain insight into the mechanisms of formation and removal.

A new method is presented for the quantitative investigation of deposit formation in vivo on 12 experimental materials after one year. The parameter assessed is the deposition parameter, D, the fraction of the surface covered by deposits. The materials were arranged in a given sequence in the prosthesis flanges and carried in two investigations by 11 and 20 participants for one year.

The results show that the parameter D is strongly material-, participant-, and site-dependent. Differences between materials varied by a factor of at least 25; PMMA (Polymethylmethacrylate) was always lowest in D value. The D values in the upper prosthesis were always larger than in the lower prosthesis; the ratio Dupper /D lower was 2.3 ± 0.5.

The material parameters strongly influencing the deposit formation were of both the monomer and the filler type. Attempts were made to correlate D with surface hardness, surface roughness, and water absorption. Only the last parameter was clearly linearly related to D.

LASMA (Laser Mass Spectrometry) studies showed that the chemical nature of the deposits formed in vivo on prosthetic materials is. in general, initially different from that of calculus.

Novel Uv-Curable Low-Shrinking Silanes as Precursors for the Sol-Gel-Process

The increasing interest in inorganic-organic nanocomposites which offer the possibility to build up both an inorganic and organic network by hydrolysis and condensation and by polymerization reactions, respectively, leads to the development of a new class of double bond functionalized silanes. These 2-vinylcyclopropyl silanes were synthesized e.g. by reaction of 1-methoxycarbonyl-2-vinylcyclopropane-l-carboxylic acid with 3-isocyanatopropyltriethoxysilane. Hydrolysis and condensation of the alkoxy groups as well as cocondensation with tetraalkoxysilanes lead to solvent-free liquid resins that can be cured by UV-light-induced radical polymerization of the vinylcyclopropane group. The synthesis and characterization of different 2-vinylcyclopropyl silanes, hydrolysation and condensation behavior and first results of the radical polymerization will be discussed.

A comparison of the microstructure and properties of the IPS Empress 2 and the IPS Empress glass-ceramics

The aim of this report is to analyze the microstructures of glass-ceramics of the IPS Empress 2 and IPS Empress systems by scanning electron microscopy. The main properties of the glass-ceramics were determined and compared to each other. The flexural strength of the pressed glass-ceramic (core material) was improved by a factor of more than three for IPS Empress 2 (lithium disilicate glass-ceramic) in comparison with IPS Empress (leucite glass-ceramic). For the fracture toughness, the K(IC) value was measured as 3.3 +/- 0.3 MPa. m(0.5) for IPS Empress 2 and 1.3 +/- 0.1 MPa. m(0.5) for IPS Empress. Abrasion behavior, chemical durability, and optical properties such as translucency of all glass-ceramics fulfill the dental standards. The authors concluded that IPS Empress 2 can be used to fabricate 3-unit bridges up to the second premolar.

Needle-like apatite-leucite glass-ceramic as a base material for the veneering of metal restorations in dentistry

A needle-like apatite-leucite glass-ceramic was prepared in the SiO2-Al2O3-Na2O-K2O-P2O5-F system. Nucleation and crystallization processes were studied in bulk and powdered samples. The crystallization of leucite follows the mechanism of surface crystallization. After the precipitation of NaCaPO4 crystals and another unknown crystal phase, the formation of needle-like apatite is based on a volume nucleation and crystallization process. The mechanism of the formation of needle-like apatite differs to those of apatite precipitation in glass-ceramics. The morphology of needle-like apatite is comparable to that of apatite in natural teeth. The properties of the glass-ceramic, especially the good chemical durability, the optical properties, as well as mechanical and thermal properties allow glass-ceramic to be used as a main component in a bio-material for the veneering of metal restorations in dentistry.

Quantification of deposits formed in the oral cavity on various materials after a 1-year period

Deposits are formed on natural teeth as well as on various polymeric and metallic materials. Deposit formation is complex and controlled by numerous poorly understood parameters. This article presents a new method for quantification of in vivo deposit formation on multiple materials. Seven different materials were positioned at six different sites in the buccal flanges of a removable prosthesis. Nine volunteers wore these prostheses for 1 year. The deposits were graded by three independent observers under a stereomicroscope at X20 magnification. Plots of average deposition value averaged for all participants and sites are given. Polymethyl methacrylate (PMMA) had the lowest deposition value in this trial. The standard error is approximately 15% of the mean value. The results show that after 1 year in vivo the roughness of the experimental materials increased by a factor of two to six times. The method presented is suitable to quantify deposit formation on multiple materials in vivo.