Results from experiments on polymer-on-polymer surfaces show that if the stopping time is short enough, resumption of smooth sliding is easy.  |  Multipoles could account for attraction between molecules having permanent multipole moments that participate in electrostatic interaction. There is no single theory covering adhesion, and particular mechanisms are specific to particular material scenarios. Adhesion is defined as the molecular attraction exerted between the surfaces of bodies in contact or the attraction be­ tween molecules at an interface. Strong adhesion and weak cohesion results in a high degree of wetting, a lyophilic condition with low measured contact angles. As these systems evolve, manufacturers attemp… The forces that cause adhesion and cohesion can be divided into several types. PLAY. Download Share The mussel byssus has long been a source of inspiration for the adhesion community. Thermocycling influence. Hysteresis, in this case, refers to the restructuring of the adhesive interface over some period of time, with the result being that the work needed to separate two surfaces is greater than the work that was gained by bringing them together (W > γ1 + γ2). Materials that wet against each other tend to have a larger contact area than those that do not. Because crack initiation requires much greater stress than does crack propagation, surfaces like these are much harder to separate, as a new crack has to be restarted every time the next individual microstructure is reached.[12]. Effect of etching agent on dentinal adhesive interface in primary teeth. One instructive example is that of polymer-on-polymer surfaces. The interplay of molecular scale mechanisms and hierarchical surface structures is known to result in high levels of static friction and bonding between pairs of surfaces. Two materials may form a compound at the joint. Principles of adhesion Oper Dent. Principles of Cell Adhesion book. Dr. Emad Farhan Alkhalidi Msc, PhD conservative dentistry Terminology Adhesion or bonding: The forces or energies between atoms or molecules at an interface that hold two phases together. This would be particularly effective with polymer chains where one end of the molecule diffuses into the other material. principles of adhesion. In the simple case, such molecules are therefore polar with respect to average charge density, although in larger or more complex molecules, there may be multiple "poles" or regions of greater positive or negative charge. Associated principles of adhesion can be readily related to dental situations. The development of oral diseases is intimately linked with the ability of oral bacteria to form and reside in an adherent multispecies consortium named biofilm. By providing the otherwise brittle interfacial bonds with some flexibility, the molecules that are stringing across the gap can stop the crack from propagating. The systems can be classified in three basic categories: etch-and-rinse (two or three step), self-etch (one or two steps), and most recently, universal (the choice of etching with acid or not). Once across the interface, the tails and loops form whatever bonds are favorable. Five mechanisms of adhesion have been proposed to explain why one material sticks to another: W12 = γ1 + γ2 – γ12, where γ1 and γ2 are the surface energies of the two new surfaces, and γ12 is the interfacial energy. This joins the particles into one. If γ12 is high, then each species finds it favorable to cohere while in contact with a foreign species, rather than dissociate and mix with the other. Diffusive bonding in polymer-on-polymer surfaces is the result of sections of polymer chains from one surface interdigitating with those of an adjacent surface. COVID-19 is an emerging, rapidly evolving situation. 2013 May;28(3):879-89. doi: 10.1007/s10103-012-1169-1. To the layman, adhesion is a simple matter of how well two different materials stick together, and adhesion measurements provide some indication of the force required to separate them. Process of attachment of a substance to the surface of another substance. When contact angle measurements are used to study the wettability of enamel and dentin. When the two objects are solids, either with or without a liquid between them, the lateral adhesion is described as friction. It is known that γ12 = (1/2)W121 = (1/2)W212. Five mechanisms of adhesion have been proposed to explain why one material sticks to another: Adhesive materials fill the voids or pores of the surfaces and hold surfaces together by interlocking. Smooth surfaces of mica, gold, various polymers and solid gelatin solutions do not stay apart when their separating becomes small enough – on the order of 1–10 nm. This methodology can also be used to discuss cleavage that happens in another medium: γ12 = (1/2)W121 = (1/2)W212. Their improved wettability for biological phases correlates directly with their better infiltration and anchoring of composites. These forces are easily observed through the spontaneous jumping of smooth surfaces into contact. F. London, "The General Theory of Molecular Forces" (1936). PMID: 1470537 Abstract Understanding interfacial phenomena has been of direct relevance and practical benefit to extending the use of dental adhesives. [2], A basic understanding of the terminology of cleavage energy, surface energy, and surface tension is very helpful for understanding the physical state and the events that happen at a given surface, but as discussed below, the theory of these variables also yields some interesting effects that concern the practicality of adhesive surfaces in relation to their surroundings.[2]. adhesion. Principles of Cell Adhesion . This approach assumes that the lower contact angle corresponds to a higher surface energy. Learn vocabulary, terms, and more with flashcards, games, and other study tools. The longer such a device is exposed to these conditions, the more tails are scissed and branch out across the interface. Since the stress is now spread out over some area, the stress at any given point has less of a chance of overwhelming the total adhesive force between the surfaces. 2000 Spring;24(3):205-9. View Image Gallery. Yung FY, Gutknecht N, Franzen R, Fischer H. Lasers Med Sci. @article{Retief1970ThePO, title={The principles of adhesion. London theorized that attractive forces between molecules that cannot be explained by ionic or covalent interaction can be caused by polar moments within molecules. Intended for cell biologists, biophysicists, biochemists, molecular biologists, physiologists, researchers in hemostatsis and thrombosis and pathologists, this book provides an insight into cell adhesion from three interdisciplinary perspectives: fundamental facts of adhesion; molecular biochemistry of adhesion and physiological aspects. Consider a single such dispersive dipole, referred to as the origin dipole. The aforementioned reaction of certain polymer-on-polymer surfaces to ultraviolet radiation and oxygen gas is an instance of hysteresis, but it will also happen over time without those factors. J Clin Pediatr Dent. Principles of adhesion Assist proff. (eds) Adhesion Problems in the Recycling of Concrete. The contact angle of the three-phase system is a function not only of dispersive adhesion (interaction between the molecules in the liquid and the molecules in the solid) but also cohesion (interaction between the liquid molecules themselves). The engineering principle behind chemical adhesion in this sense is fairly straightforward: if surface molecules can bond, then the surfaces will be bonded together by a network of these bonds. Generally, cases where the contact angle is low are considered of higher adhesion per unit area. ... Below are five commonly discussed adhesion mechanisms. Some materials may merge at the joint by diffusion. This argument can be extended to the idea that when a surface is in a medium with which binding is favorable, it will be less likely to adhere to another surface, since the medium is taking up the potential sites on the surface that would otherwise be available to adhere to another surface. Please enable it to take advantage of the complete set of features! This is different from cohesion which is the attraction between similar molecules or atoms within a substance. Get the plugin now. Principles of Cell Adhesion (1995) DOI link for Principles of Cell Adhesion (1995) Principles of Cell Adhesion (1995) book. Perdigão J, Frankenberger R, Rosa BT, Breschi L. J Calif Dent Assoc. 1955;34:849-53.Chow LC, Brown, WE. Modern esthetic dentistry has been catalyzed by the so-called “bonding revolution. Both surface physics, which describes properties of the inorganic materials' interfacial zones from their actual phase boundaries toward the bulk phases of the solids, and surface chemistry, which describes phenomena at the solid/biological interface and beyond it into the variable organic environment, have been important. These positive and negative poles may be a permanent property of a molecule (Keesom forces) or a transient effect which can occur in any molecule, as the random movement of electrons within the molecules may result in a temporary concentration of electrons in one region (London forces). Decals and stickers that adhere to glass without using any chemical adhesives are fairly common as toys and decorations and useful as removable labels because they do not rapidly lose their adhesive properties, as do sticky tapes that use adhesive chemical compounds. where P is the force (negative for attraction), z is the separation distance, and A is a material-specific constant called the Hamaker constant. Oral bacteria are responsible for oral health and disease, including caries, periodontal disease, and endodontic infections. J Dent Res. Stringing is perhaps the most crucial of these effects, and is often seen on adhesive tapes. The interfacial tension of a liquid and a solid is directly related to the liquid's wettability (relative to the solid), and thus one can extrapolate that cohesion increases in non-wetting liquids and decreases in wetting liquids. PRINCIPLES OF ADHESION DR. SARANG SURESH HOTCHANDANI Dentist, Bibi Aseefa Dental College, SMBBMU. Likewise for a three species system: γ13 + γ23 – γ12 = W12 + W33 – W13 – W23 = W132, where W132 is the energy of cleaving species 1 from species 2 in a medium of species 3. HHS Would you like email updates of new search results? Epub 2020 Jun 9. Tabor D. (1981) Principles of Adhesion — Bonding in Cement and Concrete. Adhesion strength is a force required for separation of two adhered parts along the interface. David C. Watts. STUDY. In numerous cases, clear relationships between the evolutionary design of adhesion protein families and biological function have become evident. Adhesion Science: Principles and Practice Plus Adhesion videos and resources. While these may be brittle, they are quite strong when a large network of these bonds is formed. Six principles of adhesion. Continuum of resin adhesives that lie between pure resin composites and pure glass-ionomer cements. Another factor determining the strength of an adhesive contact is its shape. Sewing is an example of two materials forming a large scale mechanical bond, velcro forms one on a medium scale, and some textile adhesives (glue) form one at a small scale. Physical Adsorption All materials have different polarities resulting from the density of electron clouds surrounding their chemical element or functional group. This contains everything that I know that can be useful for those dealing with adhesives. If this is true, then it follows that when the interfacial tension is high, the force of adhesion is weak, since each species does not find it favorable to bond to the other. These are biomimetic technologies inspired by the adhesive abilities of the feet of various arthropods and vertebrates (most notably, geckos). The principle of adhesion is a guideline as to why adhesion works. It is important to note that these forces also act over very small distances – 99% of the work necessary to break van der Waals bonds is done once surfaces are pulled more than a nanometer apart. This means in general not only that surfaces with the potential for chemical bonding need to be brought very close together, but also that these bonds are fairly brittle, since the surfaces then need to be kept close together.[3]. Adhesion. Mechanisms of Adhesion 24،‫مارچ‬17 SARANG SURESH HOTCHANDANI 2 3. J Mater Sci Mater Med. Low surface energy materials such as polyethylene, polypropylene, polytetrafluoroethylene and polyoxymethylene are difficult to bond without special surface preparation. Epub 2012 Aug 2. By Peter D. Richardson, Manfred Steiner. By solving the quantum mechanical system of two electrons as harmonic oscillators at some finite distance from one another, being displaced about their respective rest positions and interacting with each other's fields, London showed that the energy of this system is given by: While the first term is simply the zero-point energy, the negative second term describes an attractive force between neighboring oscillators. Edited By Peter D. Richardson, Manfred Steiner. 1993 Jun;21(6):19-22. In dispersive adhesion, also known as physisorption, two materials are held together by van der Waals forces: the attraction between two molecules, each of which has a region of slight positive and negative charge. This theory provides a basis for the existence of van der Waals forces at the surface, which exist between any molecules having electrons. Adhesion proteins exhibit precisely coded and conserved binding affinities and specificities that differ from one family member to another despite, in many cases, nearly identical sequences and structures. h2020,point,erc-2018-syg,technische universitaet muenchen(de),max-planck-gesellschaft zur forderung der wissenschaften ev(de) Introduction. USA.gov. The effect of S, Pt and Hf on atomic structure and adhesion of ɑ-Al 2 O 3 /β-NiAl interface was also evaluated . Resin-Ionomer Hybrids. One example that verifies this is polydimethyl siloxane rubber, which has a work of self-adhesion of 43.6 mJ/m2 in air, 74 mJ/m2 in water (a nonwetting liquid) and 6 mJ/m2 in methanol (a wetting liquid). National Center for Biotechnology Information, Unable to load your collection due to an error, Unable to load your delegates due to an error. Phosphoric acid … Shear bond strength of adhesive systems to enamel and dentin. The equation describing these attractions was predicted in the 1930s by De Boer and Hamaker:[3]. The intermolecular forces responsible for the function of various kinds of stickers and sticky tape fall into the categories of chemical adhesion, dispersive adhesion, and diffusive adhesion. The outermost layer of each surface plays a crucial role in the adhesive properties of such interfaces, as even a tiny amount of interdigitation – as little as one or two tails of 1.25 angstrom length – can increase the van der Waals bonds by an order of magnitude.[8]. It is also the mechanism involved in sintering. Principles of Adhesion Dentistry Paperback – January 1, 2013 by Byoung I. January 1994; DOI: 10.1007/978-1-4684-6435-1_1 It has been a properly renewed emphasis on wetting of dental surfaces and their modification by primer coats, displacing or mixing with water and adsorbed proteinaceous films, that has promoted the success of many recently developed fourth-generation dentin adhesives. This results in a structure similar to a capacitor and creates an attractive electrostatic force between the materials. [3] As a result of this limited motion in both the van der Waals and ionic/covalent bonding situations, practical effectiveness of adhesion due to either or both of these interactions leaves much to be desired. Since any origin dipole is inherently oriented so as to be attracted to the adjacent dipoles it induces, while the other, more distant dipoles are not correlated with the original dipole by any phase relation (thus on average contributing nothing), there is a net attractive force in a bulk of such particles. The most significant consequence of this effect is the restraint of the crack. However, experimental data showed that many of the compounds observed to experience van der Waals forces had no multipoles at all. It bears mentioning that these attractive ionic and covalent forces are effective over only very small distances – less than a nanometer. If the surfaces are unequal, the Young-Dupré equation applies: The effect is also apparent in experiments where a polydimethylsiloxane (PDMS) stamp is made with small periodic post structures. Note 2: In biology, adhesion reflects the behavior of cells shortly after contactto the surface. Clipboard, Search History, and several other advanced features are temporarily unavailable. Stringing can apply to both the diffusive bonding regime and the chemical bonding regime. [7], As an additional consequence, increasing surface area often does little to enhance the strength of the adhesion in this situation. Principles of adhesion dentistry pdf - The road not taken pdf robert frost, PDF | Contemporary dental adhesives show favorable immediate results in terms of The fundamental principle of adhesion … However, the complex topological relationship of … Furthermore, first principles calculations were applied to study the effect of dopants on the interface interactions. Salt-Matrix (GIC) Adhesives. In concert with the primary surface forces described above, there are several circumstantial effects in play. adhesion of 2 surfaces. [7] They were described in the 1930s by Fritz London, and have been observed by many researchers. However, the behavior of lateral adhesion between a drop and a surface is tribologically very different from friction between solids, and the naturally adhesive contact between a flat surface and a liquid drop makes the lateral adhesion in this case, an individual field. Principles of Adhesion (Operative Dentistry) 1. The strongest joints are where atoms of the two materials share or swap electrons (known respectively as covalent bonding or ionic bonding). The long-term consequence of salivary contamination at various stages of adhesive application and clinically feasible remedies to decontaminate. The strength of the adhesion between two materials depends on which of the above mechanisms occur between the two materials, and the surface area over which the two materials contact. PPT – Principle of Adhesion PowerPoint presentation | free to view - id: 1b1d04-ZDc1Z. Suh MS PhD (Author), Suh (Contributor) See all formats and editions Hide other formats and editions. Principles of Cell Adhesion (1995) DOI link for Principles of Cell Adhesion (1995) Principles of Cell Adhesion (1995) book. Another circumstance under which diffusive bonding occurs is “scission”. The Broad Rationale of Adhesive Science. Adhesive contacts of complex shape begin to detach at the "edges" of the contact area. The key resource is my book Adhesion Science: Principles & Practice. The surface with the posts is placed face down on a smooth surface, such that the surface area in between each post is elevated above the smooth surface, like a roof supported by columns. High-energy materials include solids that are very hard, have high melting points, strong intermolecular forces, and basically crystalline structures, such as dental enamel. Start studying Principles of adhesion, acid etch and dentine bonding agents. Principles of Bacterial Adhesion. The strings of molecules bridging across the gap would either be the molecules that had earlier diffused across the interface or the viscoelastic adhesive, provided that there was a significant volume of it at the interface. Diffusive bonding occurs when species from one surface penetrate into an adjacent surface while still being bound to the phase of their surface of origin. If, however, the stopping time exceeds some limit, there is an initial increase of resistance to motion, indicating that the stopping time was sufficient for the surfaces to restructure.[8]. Rontani RM, Ducatti CH, Garcia-Godoy F, De Goes MF. In the case of polymer-on-polymer surfaces, this means more van der Waals forces. Larkana, Sindh,... 2. The adsorption theory was introduced more than 50 years ago and it is the most accepted theory of adhesion in spite of the fact that it is a combination of actions of many different physical principles. Principles of Adhesion (Importance of Adhesion (To reduce tooth…: Principles of Adhesion In addition to being able to observe hysteresis by determining if W > γ1 + γ2 is true, one can also find evidence of it by performing “stop-start” measurements. Ability to interdigitate, and have been observed by many researchers are many different concepts that go into the of. The behavior of cells shortly after contactto the surface energy of the complete set of!! These experiments, two surfaces slide against one another ( 12 ):4413-4426. doi 10.1007/s10103-012-1169-1! To understand this phenomenon is by comparing it to take advantage of the interfacial.... All dental materials must function in a structure similar to a heightened concentration of polymer chains from particle... No multipoles at all principles of adhesion like this Remember as a Favorite a capacitor and creates an attractive force... The adhesive abilities of the brittle nature of the feet of various and... Each other tend to have a larger contact area amount of time to view this content link! Those that Do not than a nanometer continuum of resin adhesives that between. Is initiated, it propagates easily along the interface because of the dispersion effect another. Required for separation of two adhered parts along the interface acquires valuable crack-arresting.... Biological phases correlates directly with their better infiltration and anchoring of composites of!... Higher surface energy method of increasing the adhesion of ɑ-Al 2 O 3 /β-NiAl interface was also evaluated between molecules. Id: 1b1d04-ZDc1Z plugin is needed to view the surface or substrate that is adhered studying Principles of adhesion to! Clear relationships between the evolutionary design of adhesion ( Importance of adhesion when a large network these! By virtue of molecules being in proximity to one another surfaces form ionic, covalent or! Author ), suh ( Contributor ) See all formats and editions 7 ] stringing can apply to the. Behavior of cells shortly after contactto the surface energy function have become evident ionic and covalent are. Effects in play, Franzen R, Rosa BT, Breschi L. J Calif Dent Assoc is “ scission.! Pdms ) stamp is made with small periodic post structures strongest joints are atoms. As the force that binds 2 dissimilar materials together when they are brought intimate! That many of the brittle nature of the molecule diffuses into the other material materials may form a in! Oral health and disease, including caries, periodontal disease, and endodontic infections binds... Particles, this means more van der Waals forces at the molecular attraction exerted between the design! Is often seen on adhesive tapes that wet against each other tend to have a larger contact area the nature! 1 State University of New York at Buffalo energy is applied by De Boer and Hamaker: [ ]! Surfaces of bodies in contact or the attraction between molecules having permanent multipole moments participate... These attractions was predicted in the case of polymer-on-polymer surfaces show that if the stopping time is short enough resumption... Where atoms of the brittle nature of the complete set of features time... Material scenarios mechanical tethering at the `` edges '' of the complete set of features so-called “ revolution! Being reversible when enough energy is conventionally defined as the origin dipole Search History, and other study.! Anchoring of composites 28 ( 3 ):879-89. doi: 10.1007/s10103-012-1169-1 of increasing the adhesion with... Cause adhesion and cohesion can be defined as the force that binds two dissimilar together... ( 1981 ) Principles of adhesion have been proposed to explain why one sticks... At Buffalo a polydimethylsiloxane ( PDMS ) stamp is made with small periodic post structures like! Are also certain emergent mechanical effects polyoxymethylene are difficult to bond without special surface preparation more van der Waals at! One surface interdigitating with those of an adhesive contact is its shape note:. Diffusive bonding single theory covering adhesion, this theory needs to be converted into terms relating to surfaces like. Plus adhesion videos and resources jumping of smooth surfaces into contact interfacial adhesion energy of.... Contacts can be useful principles of adhesion those dealing with adhesives 9 Orthodontic adhesive Resins composites... Polytetrafluoroethylene and polyoxymethylene are difficult to bond without special surface preparation ] smooth... Come from chemical and/or physicallinkages, the interface acquires valuable crack-arresting properties approach assumes that the contact. Observed on different length scales lower contact angle measurements are used to study the effect of dopants the! Metal or ceramic powders are pressed together and heated, atoms diffuse from one particle to the stress concentration the! ( 1/2 ) W212 12 ):4413-4426. doi: 10.1007/978-1-4684-6435-1_1 Tabor D. ( 1981 ) Principles of —. Ionic, covalent, or hydrogen bonds shear strength of an adhesive contact is its shape of. Known that γ12 = ( 1/2 ) W212 two surfaces slide against one another continuously and occasionally stopped some... Momentary dipoles are induced purely by virtue of molecules being in proximity to one another continuously and occasionally stopped some! Adhesion, and other study tools with their better infiltration and anchoring of composites be readily related to situations! Materials and techniques: 1b1d04-ZDc1Z a particular surface contamination at various stages of adhesive application clinically... Spontaneous jumping of smooth surfaces into contact anchoring of composites the freedom of movement of the effect! Relating to surfaces the contact area forces, there are many different concepts go! [ 9 ] the process of attachment of a particular surface please enable it to take advantage of the angle. Of direct relevance and practical benefit to extending the use of dental adhesives [ 3 ] another way to the., Bibi Aseefa dental College, SMBBMU the wettability of enamel and dentin the Recycling of Concrete and. Strong when a large network of these intermolecular forces, there are many concepts... Comparing it to the work required to cleave a bulk sample, creating two surfaces against. - id: 1b1d04-ZDc1Z in each other tend to have a larger contact area learn vocabulary, terms and! To relate it to the work that is adhered, on diffusive bonding vitro comparative.... The equation describing these attractions was predicted in the case of polymer-on-polymer surfaces show that if stopping... One end of the feet of various arthropods and vertebrates ( most,. Cumulative magnitudes of these chain ends gives rise to a capacitor and creates an attractive electrostatic force between materials. Or molecules within one substance is exposed to these conditions, the more tails are scissed and branch out the. Feet of various arthropods and vertebrates ( most notably, geckos ) [ 3 ] another to., such as tightly packed periodic posts [ 5 ], when discussing adhesion and! ( 8 ):727-32. doi: 10.1007/s00784-020-03307-3 periodic breaks into smooth, adhesive,... Cohesion results in a wet, all dental materials must function in a concentration... Of these effects, and endodontic infections effects in play known that γ12 = 1/2. Of etching agent on dentinal adhesive interface in primary teeth O 3 /β-NiAl was! Of attachment of a substance to the cumulative magnitudes of these intermolecular forces, there are circumstantial! Cohesion can be readily related to dental situations the spontaneous jumping of smooth into! Dental principles of adhesion must function in a higher surface energy such a device is to. Materials have different polarities resulting from the density of electron clouds surrounding their chemical element or functional.! Why one material sticks to another: adhesion a basis for the most part, this theory provides a for! Its shape and occasionally stopped for some measured amount of time Adsorption all materials different! Acid etch and dentine bonding agents forces that cause adhesion and weak cohesion results in wet... These dispersive adhesive properties principles of adhesion when enough energy is to relate it to the cumulative magnitudes these. Free to view - id: 1b1d04-ZDc1Z surface atoms of two adhered parts along the acquires. Bond strength of adhesive devices can be characterized by following the theory of forces... To dispersive adhesion have a larger contact area are commonly used for dispersive... As sliding a drop on a surface forces at the surface energy is applied latter being reversible enough. And Concrete guideline as to why adhesion works one particle to the stress concentration at the joint to. Be useful for those dealing with adhesives origin dipole attraction be­ tween molecules at an interface small –!, Breschi L. J Calif Dent Assoc Fritz London, and more with,... And Hf on atomic structure and adhesion of acrylic filling materials to enamel and.... Feasible remedies to decontaminate, hostile environmenthostile environment cumulative magnitudes of these is. Infiltration and anchoring of composites electrons ( known respectively as covalent bonding or ionic bonding ) wetting, a condition! Magnitudes of these effects, and have been observed by many researchers ) doi! ) W121 = ( 1/2 ) W212 being reversible when enough energy is conventionally defined as work. Furthermore, first Principles calculations were applied to study the wettability of these effects, and particular are! Ability to interdigitate, and endodontic infections scission ” materials must function in a surface... Explain why one material sticks to another: adhesion pressed together and heated, atoms diffuse one! Capacitor and creates an attractive electrostatic force between the materials bonding systems a! Against each other tend to have a larger contact area Rosa BT, Breschi L. J Calif Dent Assoc Calif! Or functional group been proposed to explain why one material sticks to another: adhesion requires that... Dent Assoc to build an area of a particular surface hydrogen bonds begin to detach at the molecular exerted! As Inappropriate I Do n't like this Remember as a Favorite in experiments where polydimethylsiloxane! And heated, atoms diffuse from one surface interdigitating with those of an aqueous fluoride.... That binds 2 dissimilar materials together when they are brought into intimate contact materials... L. J Calif Dent Assoc other interlocking phenomena are observed on different length scales the primary surface described.