Purpose: This overview presents a description of organofunctional trialkoxysilane coupling agents (silanes), their chemistry, properties, use, and some of the main clinical experiences in dentistry. Materials and Methods: The main emphasis was on major dental journals that have been reviewed from 1958 up to the latest research news from 2002. A MEDLINE search with the key words “dental silanes” was used. Special silane literature and journals outside dentistry were also cited. Results: The main emphasis is on the use of silanes in prosthetic and restorative dentistry. Clinical relevance was based mainly on either short- or long-term tests. The interpretation of various results is not given, mainly because of controversial observations that may be very difficult to explain. Nevertheless, the majority of the clinical results pointed to silanes playing a significant role in the adhesion process. Silane reaction mechanisms were not entirely understood, and there exist several theories for bonding mechanisms for silanes and substrates. Conclusion: Dental materials offer a continuously challenging forum for silanes, and silanes will play an essential role in material development. Publ. in: Int J Prosthodont 2004;17:155–164.

An Introduction to Silanes and Their Clinical Applications in Dentistry

This article reviews the principal modes of dental composite material degradation and relates them to the specific components of the composites themselves. Particular emphasis is placed on the selection of the monomer resins, the filler content, and the degree of monomer conversion after the clinical materials are cured. Loss of mechanical function and leaching of components from the composites are briefly described, while a more detailed description is provided of studies that have considered the chemical breakdown of materials by agents that are present in the oral cavity, or model the latter. Specific attention will be given to the hydrolysis process of monomer and composite components, i.e., the scission of condensation-type bonds (esters, ethers, amides, etc.) that make up the monomer resins, following reaction of the resins with water and salivary enzymes. A synopsis of enzyme types and their sources is outlined, along with a description of the work that supports their ability to attack and degrade specific types of monomer systems. The methods for the study of biodegradation effects are compared in terms of sensitivity and the information that they provide. The impact of biodegradation on the ultimate biocompatibility of current materials is discussed from the perspective of what is known to date and what remains to be studied. The findings of the past decade clearly indicate that there are many reasons to probe the issue of biochemical stability of composite resins in the oral cavity. The challenge will now be to have both industry and government agencies take a pro-active approach to fund research in this area, with the expectation that these studies will lead to a more concise definition of biocompatibility issues related to dental composites. In addition, the acquired information from such studies will generate the development of alternate polymeric chemistries and composite formulations that will require further investigation for use as the next generation of restorative materials with enhanced biostability.

Relation of Dental Composite Formulations To Their Degradation and the Release of Hydrolyzed Polymeric-Resin-Derived Products:

This article reviews theprincipal modesofdental composite material degradation andrelates themtothespecific com- ponents ofthecomposites themselves. Particular emphasis isplaced ontheselection ofthemonomerresins, thefiller content, and thedegree ofmonomerconversion after theclinical materials arecured. Lossofmechanical function andleaching ofcomponents fromthecomposites arebriefly described, while amoredetailed description isprovided ofstudies that haveconsidered thechem- ical breakdown ofmaterials byagents that arepresent intheoral cavity, ormodelthelatter. Specific attention will begiven tothe hydrolysis process ofmonomerandcomposite components, i.e., thescission ofcondensation-type bonds(esters, ethers, amides, etc.) that makeupthemonomerresins, following reaction oftheresins with water andsalivary enzymes. Asynopsis ofenzyme types andtheir sources isoutlined, along with adescription oftheworkthat supports their ability toattack anddegrade specific types of monomersystems. Themethods forthestudy ofbiodegradation effects arecompared intermsofsensitivity andtheinformation that theyprovide. Theimpact ofbiodegradation ontheultimate biocompatibility ofcurrent materials isdiscussed fromtheper- spective ofwhatisknowntodateandwhatremains tobestudied. Thefindings ofthepastdecade clearly indicate that there are manyreasons toprobe theissue ofbiochemical stability ofcomposite resins intheoral cavity. Thechallenge will nowbetohave bothindustry andgovernment agencies take apro-active approach tofundresearch inthis area, withtheexpectation that these studies will leadtoamoreconcise definition ofbiocompatibility issues related todental composites. Inaddition, theacquired information fromsuchstudies will generate thedevelopment ofalternate polymeric chemistries andcomposite formulations that will require further investigation foruseasthenextgeneration ofrestorative materials withenhanced biostability.

Relation of dentalcompositeformulations to theirdegradation and the release of hydrolyzedpolymeric-resin-derived products

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. In the final sections, properties of current composite materials and suggestions for what areas of research would prove most promising are presented.

Polymeric dental composites : properties and reaction behavior of multimethacrylate dental restorations

Mechanical properties of visible light-cured resins reinforced with hydroxyapatite for dental restoration.

Most commercial dental composites contain liquid dimethacrylate monomers (including BIS-GMA or variations of it) and silica-containing compositions as inorganic reinforcing filler particles coated with methacrylate-functional silane coupling agents to bond the resin to the filler. They also contain initiators, accelerators, photo-initiators, photosensitizers, polymerization inhibitors, and UV absorbers. Durability is a major problem with posterior composites. The typical life-span of posterior composites is from three to 10 years, with large fillings usually fewer than five years. Polymerization shrinkage and inadequate adhesion to cavity walls are remaining problems. Some pulp irritation can occur if deep restorations are not placed over a protective film. Some have advocated the use of glass-ionomer cement as a lining under resin composite restorations in dentin. The concept of glass-ionomer cements (GICs) was introduced to the dental profession in the early 1970's. Current GICs may contain poly(acrylic acid) or a copolymer. Higher-molecular-weight copolymers may also be used to improve the physical properties of some GICs. Stronger and less-brittle hybrid materials have been produced by the addition of water-soluble compatible polymers to form light-curing GIC formulations. The ion-leachable aluminosilicate glass powder, in an aqueous solution of a polymer or copolymer of acrylic acid, is attacked by the hydrated protons of the acid, causing the release of aluminum and calcium ions. Salt bridges are formed, and a gel matrix surrounds the unreacted glass particles. The matrix is adhesive to mineralized tissues. Provisions must be made for maintenance of the water balance of restorations for the first 24 hours.(ABSTRACT TRUNCATED AT 250 WORDS)

Dental composites/glass ionomers: the materials.

Glass-Ceramic Inserts Anticipated for ‘Megafilled’ Composite Restortions Research Moves into the Office

This article outlines the authors' perceptions of the future of esthetic dental restorative materials such as composites, glass ionomer cements, pit and fissure sealants and laboratory fabricated resin.

William A. Marjenhoff

Papers

Dental composites/glass ionomers: the materials.

Glass-Ceramic Inserts Anticipated for ‘Megafilled’ Composite Restortions Research Moves into the Office

Gazing into the Future of Esthetic Restorative Materials