Dental composites

Precise dosage of reactive components is essential for the reproducible hardening of dental cements, without adversely affecting the physical properties of the hardened product. Cellulose acetate butyrate microcapsules containing poly(acrylic acid) prepared by phase separahon when mixed with glass ionomer powder result in single-phase, free-flowing powders [64]. The contents of microcapsules can be released and become mixed with the solid phase by mechanical stress, vibration microwaves, and/or sonicahon. 

---

Lee, H. Orlowski, J. (1973). Handbook of Dental Composite Restoratives, p. 3107. South El Monte, California Lee Pharmaceuticals. 

Cowan Teeter (1944) reported a new class of resinous substances based on the zinc salts of dimerized unsaturated fatty acids such as linoleic and oleic acid. The latter is referred to as dimer acid. Later, Pellico (1974) described a dental composition based on the reaction between zinc oxide and either dimer or trimer acid. In an attempt to formulate calcium hydroxide cements which would be hydrolytically stable, Wilson et al. (1981) examined cement formation between calciimi hydroxide and dimer acid. They found it necessary to incorporate an accelerator, alimiiniiun acetate hydrate, Al2(OH)2(CHgCOO)4.3H2O, into the cement powder. 

Brauer, G. M., Argentar, H. Stansbury, J. W. (1982). Cementitious dental compositions which do not inhibit polymerization. US Patent 4,362,510, December 7, 1982. 

Ansetk, K. S., Newman, S. AL and Bowman, C. N.i Polymeric Dental Composites Properties and Reaction Behavior of Multimethacrylate Dental Restorations. VoL 122, pp. 177-218. 

Attainment of a maximum double bond conversion is typical in multifunctional monomer polymerizations and results from the severe restriction on bulk mobility of reacting species in highly crosslinked networks [26]. In particular, radicals become trapped or shielded within densely crosslinked regions known as microgels, and the rate of polymerization becomes diffusion limited. Further double bond conversion is almost impossible at this point, and the polymerization stops prior to 100% functional group conversion. In polymeric dental composites, which use multifunctional methacrylate monomers, final double bond conversions have been reported ranging anywhere from 55-75% [22,27-29]. 

Bisphenols is a broad term that includes many chemicals with the common chemical structure of two phenolic rings joined together by a bridging carbon. Bisphenol A is a monomer widely used in the manufacture of epoxy and phenolic resins, polycarbonates, polyacrylates and corrosion-resistant unsaturated polyester-styrene resins. It can be found in a diverse range of products, including the interior coatings of food cans and filters, water containers, dental composites and sealants. [4]. BPA and BP-5 were selected for testing by the whole... 

We chose to modify the anhydride monomers with photopolymerizable methacrylate functionalities. Methacrylate-based polymers have a long history in biomedical applications, ranging from photocured dental composites [20] to thermally cured bone cements [21]. Furthermore, photopolymerizations provide many advantages for material handling and processing, including spatial and temporal control of the polymerization and rapid rates at ambient temperatures. Liquid or putty-like monomer/initiator... 

Crosslinked polymers are widely used as dental materials (1-31. Perhaps the most challenging application is in the restoration of teeth (4). The monomers must be non-toxic and capable of rapid polymerization in the presence of oxygen and water. The products should have properties comparable to tooth enamel and dentin and a service life of more than a few years. In current restorative materials such properties are sought using so-called "dental composites" which contain high volume fractions of particulate Inorganic fillers (5-71. However in the present article attention is concentrated on one commonly used crosslinked polymeric component, and on the way in which some of its properties are influenced by low volume fractions of fillers. 

Braem, M. "An In-Vitro Investigations into the Physical Durability of Dental Composites", Doctoral thesis, Leuven (Belgium), 1985. 

Polymeric Dental Composites Properties and Reaction Behavior of Multimethacrylate Dental Restorations... 

With over 200 million dental restorations performed each year, the importance of developing a restorative material with tooth-like appearance and properties cannot be underestimated. In this article, the use of poly (multimethacrylates) as dental composites is summarized from both fundamental and practical sides. Detail is provided regarding the utilization, procedures, and problems with polymeric composite restoratives, and a complete discussion of the polymerization kinetics and the polymer structural evolution is presented, fn the final sections, properties of current composite materials and suggestions for what areas of research would prove most promising are presented. 

With more than 200 million dental restorations performed each year, the importance of using a restorative material which is both safe and durable should not be underestimated. Currently, dental amalgam is used in the vast majority of these restorations however, recent scrutiny of mercury levels in dental amalgam and the desire for tooth colored restorations have led to increasing demand for polymeric dental composites. Polymeric composites, generally composed of a multimethacrylate and a ceramic glass filler, have primarily been used for anterior tooth restorations in which color matching is imperative for aesthetic purposes. 

Composite resins allow for color matching, conservative cavity preparation, and simple preparation through intraoral photopolymerization. These advantages have made composites an increasingly popular substitute for amalgam in dental restorations, especially when aesthetics are of concern. In this article, we will focus on the actual process of forming dental composites, the properties of the composites that are formed, and a complete description of the photopolymerization of the multimethacrylates that produce the dental composite. We will only be focusing on the use of polymers as dental restorations. Other dental applications of polymers, e.g. dentures and ionomer cements (reviewed elsewhere by Scranton and Klier) will not be addressed. 

In the first portion of this section, we will focus on the materials and processes used to form polymer dental composites. This section will be followed by a discussion of the problems associated with polymer composite materials. An overview of the photopolymerization behavior and the polymer structure of these highly crosslinked materials is presented in Sects. 3 and 4. Lastly, some of the properties of current composite resin formulations are presented. 

The majority of resins are composed of two dimethacrylate monomers, 2,2 -bis [4(2-hydroxy-3-methacryloyloxypropyloxy)phenyl] propane (Bis-GMA) and triethylene glycol dimethacrylate (TEGDMA) [22-28]. Typically, TEGDMA or other methacrylate monomers are added as viscosity modifiers to Bis-GMA to make the solution less viscous and more appropriate for clinical use. These diluents also allow for better distribution of the components during manufacture of these composite systems. Another common monomer used to make dental composites, especially those manufactured in Europe, is urethane dimethacrylate [24,29, 30], Ethoxy bisphenol A dimethacrylate is another modification of the Bis-GMA monomer that can be used to make a more hydrophobic polymer that would better withstand the wet oral environment. Other diluents include low viscosity diacrylates and dimethacrylates. Table 1 lists some of these monomers [31-37]. 

Table I. Some monomers used in dental composites [31-37]...

---