___.February 22, 2000, President Clinton announced that he would seek bipartisan support for a national plan to cut medical mistakes. These will be reported and analyzed the same way as the airlines do when reporting accidents and safety risks. The recommendations originate from the Institute of Medicine: the FDA will have a year to develop the related standards. “Reporting is vital to holding health care systems accountable for delivering quality care, and educating the public about the safety of their health care system... It is critical to uncovering weaknesses, targeting widespread problems, analyzing what works and what doesn’t and sharing it with others.’’ For those interested about the above airy connection, we recommend the book... “Aviation Industry Quality Systems-ISO 9000”¹.
In our way toward the CE Mark (Communite Europeene), which will allow us to continue to offer in Europe our services, we were recently ISO certified, without really guessing how fashionable we are. Considered as manufacturers (as we were already since quite a while in our home state of Florida) and treated at the same level as GM, 3M, Johnson and Johnson, we found in the process a series of interesting things.
The need for standardization
___.Product standardization can be traced to the Civil War, when identical parts allowed rifle assembly in large amount. A pioneer in orthodontics, Farrar, prophesied in 1878 that “Time will come when... the necessary apparatus will be so systematized that the latter will be actually kept in stock, in parts and wholes, at dental depots, so that it may be ordered by catalogued numbers to suit the need of any case”.
___.The first attempts toward an international standardization date from 1906: a real progress became possible only after WWII. Today, there are standards both for products and services: while the first are highly specific, the latter are general.
What is ISO?
___.Long after manufacturers over the world have started to homogenize/standardize their products, the trend extended to processes and quality management. What started in the US with Frederick Winslow Taylor last century has been improved and applied to postwar Japan by W. Edwards Deming, formerly a professor at NY University. Products previously considered abroad as “junk” became respectable, and Deming’s methods (kaizen) were applied all over the world as the Total Quality Management (TQM). Adopted and adapted in 1994 by the International Standards Organization (ISO), an organization headquartered in Switzerland, it generated a wide movement, in sharp contrast with the Malcolm Baldridge National Quality Award in the US (1987) or the European Quality Award (1992). Indeed, the latter were bestowed only on very few organizations and therefore lacked impact. Despite some controversies with the National Institute of Standards (NIST) and other quality management organizations, the ISO 9000 systems are now taking up the US. Thus NASA became the first government agency in the world having each site certified. By 1996, there were 90 countries that adopted ISP 9000 as their national standards: today, there are 130. Worldwide, USA, Italy and Australia show the highest growth of ISO 9000 certifications: Africa and West Asia are catching on with an annual growth of 40% (such growths are in average three to four times higher than these of their national economies). Toward the end of this year, the system will be overhauled to match the expertise accumulated.
ISO-9002 in medicine
___.ISO’s 9000 quality management systems are four. There are no superior or inferior standards: the difference resides in the field of application. The one that concerns production, installation and services and applies both to physicians and us is ISO 9002.
___.Up to date, the American Medical Association and other large lobbies have opposed mandatory reporting, fearing that it opens hospitals and physicians to lawsuits. The White House counters by showing that due to missteps by the medical staff there were killed between 44,000 and 98,000 hospitalized Americans each year - equivalent to a jetliner crash every day. Today, AMA’s attitude seems to be prevalent: indicative is the fact that in a book on managing health service organizations which has a part dedicated to quality improvement and control², the name ISO cannot even be found. There are, however, voices of dissent, as some medical organizations proudly state that these have met the exacting requirements of the ISO 9002 international standards, and one of these even for two years in a row. Dr. Jack Nunley from Pulaski Community Hospital sums it on the Internet as follows: “We think that size has little to do with achieving quality performance. We are convinced that attitude and commitment have everything to do with it. And everybody at Pulaski Community Hospital is committed to being the very best we can possibly be.... For some time now, we have been asking our patients and their families to trust their health to us. That’s quite a request to make. So we wanted to give them something beyond our own claims of quality performance to base that trust on — something real, something objective.”
ISO 9002 in dentistry
___.Keeping in line with the other physicians, most dentists either ignore or carefully avoid ISO’s interference. Some journals like Dental Economics boast instead the less offensive TQM and Deming’s fourteen points³ and advises its readers to... try for the Malcolm Baldridge Award⁴.
___.In other countries, however, the ISO movement has caught well. Thus, the Editor of Journal of the Israeli Dental Association⁵, while pointing out that the creation of bodies to govern or monitor dentistry generates difficulties, it accepts these as a primary screening for new materials and technologies. As a difference from medicine, where most work is performed in hospitals, in dentistry most part of the service is provided by the private sector, fact that makes it difficult to obtain relevant data. Other questions raised were if a public or national body could indeed monitor the private sector without appearing to infringe on private initiatives or prerogatives, and if standards could solve the issue of the confused dentists. In the end, Dr. Peretz recommends the establishment of national data banks that could control what different industries and technologies release, mentioning that he favors mandatory standards (such as ISO) which establish clinical guidelines.
___.In the UK, the British Dental Association advises its members to apply the ISO 9002 quality management systems. The only caveat is that such standards, although they have been useful in larger practices, require more management time than smaller practices will normally be able to give⁶. An analysis from the practitioner’s point of view can be found in the British Journal of Orthodontists⁷. Closer to home, the Royal College of Dental Surgeons of Ontario is introducing an ISO-related program for random reviews of dentists in their primary workplace. For the first time dentists, whether in a group dental practice, a hospital clinic, or public health or university clinic, will be reviewed. Salaried dentists (full or part-time) and associate dentists will have an increased stake in ensuring that their workplace meets the standards of infection control and radiation protection and that their personal dental records meet the standards of their regulatory body. The scope of the registration covers the management of the office but excludes the clinical work, which is covered by legal, ethical and medical documents and conventions. The move may have been prompted by the success achieved by its member, Dr. Robin M. Conway, who is the first dentist in North America to have achieved ISO 9002 registration^8,9.
___.Respecting AMA’s taboo, an article dedicated to quality management in the orthodontic office¹⁰ exhorted the value of TQM and Deming’s 14 points, mentioning only obliquely that the ISO 9000 series assures that products meet the high standards in the industry, and that the US uses instead the Malcolm Baldridge Award. Very stimulating for orthodontists (?), it also mentions that in the dental industry, only 3M has succeeded to get the award...
What is ISO, and what it requires?
___.While claiming that it makes life simpler, the amount of supervision and documentation the ISO certification requires is high and has therefore made, in time, the object of various criticisms, offering cartoonists a generous field (Dilbert especially). ISO develops voluntary technical standards, which make the development, manufacturing and supply of products and services more efficient, safer and cleaner protecting thus the consumers of both products and services. While the vast majority of ISO standards are highly specific to a particular product, be it material (dental products) or abstract (terminology), ISO 9000 establishes generic management system standards concerned with quality management. The term generic implies that it wants that the same standards to be applied to all organizations, large or small, whatever their product or service, in any sector of activity, while quality management ensures that the organization’s products or service conform to the customer’s or patient’s requirements. While ISO 9000 itself is not a product quality label or guarantee, and does not assess or audit quality or environmental management systems, its independent auditors check that the process influencing quality conforms to the standard’s requirements. In case of nonconformance or noncompliance, the certificates are withdrawn.
___.Being concerned with the standardization of a variety of products, tests, specifications and even terms, ISO comprises a multitude of technical committees (TC’s). Dr. J. W. Stanford chairs the one dedicated to dental products (till 2002). His TC 106 committee comprises, among others, the following subcommittees: SC 1, Filling and restorative materials; SC 2, Prosthodontic materials; SC 3, Terminology; SC 4, Dental instruments; SC 6, Dental equipment; SC 7, Oral hygiene products and SC 8, Dental implants. While there are also tests for some of the materials commonly encountered in orthodontics such as stainless steel and brazing, no specific applications of these such as brackets, bands or wires have yet been released. (This gap has determined us, in time, to provide the practitioner with do-it-yourself tests, which could be both indicative and useful).
ISO requirements for dentists
___.To provide a crude example of how ISO works in an orthodontic office, the treatment is considered a contract in which the clinician is a supplier and the patient a customer. In his attempt to gain certification, he has to fill out a form notifying the patient of the work that would be done (X-ray, etching, bonding, agreed cost) and have the patient sign it. Any change in the requirements during the consultations would have to be discussed with the patient and his consent obtained and properly documented. Being accredited to ISO 9002 standards, his work is constantly quality checked. According to the British Dental Association (BDA)¹¹, in the dental practices the dentist is responsible for everything that happens to the patient. He must constantly monitor everything and look for ways of improving the service, so the need is to formalize and record what is happening rather than to change basic approaches. He is advised to use his country’s National Health Service peer review and clinical audit schemes as well as to use the knowledge about quality improvement in dental practice accumulated by the BDA. In addition, he is advised to apply the ISO 9002 quality management systems with the caveat that these, although useful in larger practices, require more management time than smaller practices will normally be able to give. The “governance” related to quality are drawn from ISO 9002. As an example, it advises dental practitioners to work hard to improve the quality of patient care through mandatory vocational training, peer review and clinical audit. In addition, it advises the clinicians to welcome the concept of clinical governance from independent contractors and recognize that professional self-regulation needs modernizing by supporting the concepts of reaccreditation and recertification.
___.Based upon the above, a consulting company, HQHQ Ltd. from England is now providing distance learning for dentists, nurses and health care managers. The topics are accredited for all three professions for postgraduate learning in the UK. The medical accreditation (RCGP) is for ¼ day per unit. The learning is arranged into modules, each made of ten units. Each unit has a learning text including introduction, benefits, main learning sections, key points, references, and what to do next¹². Peter Thompson, BDS, HQHQ’s Director, is an advisor and an auditor who graciously answers related questions (peter@hqhq.org): he has been kind enough to send us free their quality assurance manual destined to Primary Care Groups. These can be which can be easily adapted for small dental or orthodontic practices. The manual encompasses the clinical governance, service delivery and administration needed to achieve verifiable high standards and meet patients needs. In addition, the company provides consulting in reviewing and analyzing the existing quality assurance and audit systems by checking continuous both effectiveness and applicability. It also prepares and audits documents based on ISO 9000 and it writes quality and procedure manuals which translate the standards into user friendly day to day guidance for all team members. Training them about quality assurance issues and the use of the quality systems effectively and efficiently is also part of the process.
Would you qualify for ISO 9002?
___.A properly performed (voluntary or aided) audit, followed by an independent body certification, may bring you there: the problem is that for a dental office there are (only!) nineteen elements which each comprises subdivisions. To get an idea about their complexity, here these are: The Management Review (1) examines all the documents (audits, complaints, corrective actions, decisions and sanctions) and analyses the outcome, identifying both the profitable and less desirable actions.
___.The Quality Review (2) establishes the policies to be applied to ensure not only treatment’s efficiency, but also profitability and trends. It provides an early warning and thus it prevents complaints. The Treatment Planning Review (3) supposes to investigate, examine and record the patient’s symptoms while identifying his specific needs, as a difference of what he may want. The Document and Data Control (4) requirements include the easy access to the patient’s records and any internal and external quality documentation (such as these received from statutory bodies and authorities). Purchasing (5) defines the team’s responsibilities in obtaining armamentarium, equipment and supply. The Control of Customer-supplied Products (6) includes the management/storage of patient’s specimens, samples, prostheses, etc. The Product Identification and Traceability (7) requires the proper recording of the patients and of all the related data such as the evolution of the treatment. The Process Control (8) includes clinical protocols, procedures, work instructions while defining the team’s responsibilities. The Inspection and Testing (9) is directed toward the devices and equipment used as well as to specimens received. The Control of Inspections and of the Measuring and Test Equipment (10) requires the calibration of devices such as the curing lamps, etc. The Inspection and Test Status (11) records and provides information on the data obtained through such inspections. The Control of Nonconformities (12) records incidents and failures such as early debonding, allergies or any event, which demands a corrective action. The Corrective and Preventive Actions (13) reveal the objective evidence of the deficiencies (e.g. bond failures, attachment detachment, etc.) while taking measures to avoid these to happen. The Handling, Storage, Preservation (14) requirements are directed toward the way the drugs, specimens or devices are stored or maintained in the office. The Control of the Quality Records (15) is performed in such a way as to provide at any time an effective function of the system and its conformance to the quality demands. The Internal Quality Audits (16) require from the team to investigate each other and objectively record both conformities and nonconformities. The Training (17) requires not only the practitioner’s participation to study clubs, meetings, etc. but also the continuing education of the whole team. Servicing (18) establishes requirements not for the team, but for subcontractors such as dental laboratories. The Statistical Analysis (19) of patient care and treatment are required not only to meet both clinical governance regulations but also to determine trends.
Why should you be ISO 9002 certified?
___.It should be noted that many processes, which are part of the daily routine, such as infection control, have nothing in common with the success of the treatment or your skill. Moreover, the related practice standards come from legislation and common law, overriding the teachings and recommendations of the professional associations. In such circumstances, a guarantor for your practice becomes necessary: here the International Organization for Standardization steps in, bringing confidence. In Canada, over one million of its citizens is directly or indirectly involved in ISO processes and is therefore familiar with what these stand for. Driving from Montreal to Toronto, for example, one cannot miss the numerous banners on the buildings facing Highway 44 that indicate that the respective companies were certified. This strong brand recognition provides the patient and his family the security that he will not be super-exposed to radiations, cross-contaminated or improperly treated. Having your practice certified means that it maintains controlled high standards, fact, which sends a powerful message to potential patients, partners or associates. You not only can, but are advised to display a logo exhibiting the seal of ISO registration: this will show that your practice is a leader in health care. When you may want to sell your practice, its value will be for sure higher than that of a similar, nonregistered one.
___.According to a survey made by ISO, which was based upon the letters received, those who have put its standards into action have also other advantages. Some result from public relations (global recognition, patient loyalty, sense of pride and commitment, increased reliability and credibility, decrease in complaints, emphasis on continuous improvement), others from profitability (cost savings, good returns on investment, drop in insurance costs), and last but not least, from an enlightened leadership (the identification of the best practices, the team pulling into the same direction, the ability to foresee both problems and solutions, strategic planning, transparency). Interesting in the last respect is that Dr. W. Vorauer, a dentist from Salzburg, Austria (w.vorauer@magnet) has shown plenty of “transparency” by displaying in the waiting room the ISO 9002 manual of his practice.......While customer pressure seems to be the most important factor in determining an ISO registration, it may have not played part in Dr. Conway’s decision (the first North American dentist to acquire the ISO 9002 certification)⁸ to become registered – most people don’t ask to examine the quality manual before they sign up for bridgework. Nevertheless, Dr. Conway calls customer response “amazing”. This was particularly true of business people who know how much work goes into implementing ISO 9000 standards. In addition to dental work, Dr. Conway suspects he may also be giving some of his patients the motivation they may lack: “They think, if my dentist can do it, then I can do it too,” he says. His motivation was to gain a better control and a more consistent application of quality assurance provisions. The process changes resulted from applying the standards proved to foster further improvements in his service.
Conclusions
___.Some ten years ago, we have not even heard about ISO-9002, while being quite familiar with the ISO standards applied to products. Chances are that you are sharing our experience.
___.Today, this certification not only shows our high quality standards, but also proves what we have claimed all along during the years, i.e. that those who can detect manufacturers faults and provide testing methods to the profession are able also to release reprocessed products superior to the new ones. This is no wonder: while manufacturers are using only a statistical inspection (at the most a hundred out of a thousand samples), we have to inspect no less than five times each appliance we release.
___.The experience we got in the certification process has shown us that if the present trend is maintained the public, the authorities and the partners or associates will demand such a guarantee. If President Clinton’s plan will get the support he wants, and chances are that this will please the public, the dentists who are ISO-certified will be in the thousands, as they will be very likely the most sought.
References
1. Dreikorn MJ, Aviation Industry Quality Systems-ISO 9000, Avionics Communications Inc., P.O. Box 2628, Leesburg VA 20177, 1999
2. Rakich JS, Longest BB, Darr K, Managing health organizations, IIIrd ed., Health Professions Press, Baltimore, 1998
3. Eleazer JF, The maestro, Dental Economics, March 1998: 30
4. Blaes J, How 3M won, Dental Economics July 1998: 18
5. Peretz B. The abundance of new information, J Isr Dent Assoc 1998; 15: 69
6. Quality management using ISO 9002, BDA Advisory Service Advice Sheet A16, British Dental Association, London 1995
7. Davies L, Durning P, Quality managing in practice-using ISO 9002, Brit. J. Orthodontics 1997; 24: 272-5
8. Kenny DJ, Conway RM, Johnston DH, The development of ISO 9002 Quality Management Standards for Canadian Dental Practices, J. Canad. Dent. Assoc. 1999; 65:105-8
9. Ontario Dental Association member, first in North America to receive ISO certification, Ontario Dent. 1997; 74: 4
10. Atta AE, Total quality management in the orthodontic practice, Am J Orthod Dentifac Orthop 1999; 116: 659-660
11. British Dental Association, Response to the General Dental Council’s (GDC) decisions on “Professionals complementary to dentistry”; Chapter 3, Delivering Quality Standards
12. Internet: www.hqhq.org/course1

DO YOU REALLY KNOW THE RESINS YOU USE?
Bis GMA
News which may surprise you...

___.If you use sealants, adhesives, veneers or restoratives, you may have in them the currently respectable resin, bisphenol A glycidyl methacrylate (Bis-GMA). There may be differences in the filler, co-monomer or in the additives and in the way the polymerization is initiated. According to the Dental Investigation Service of the US Air Forces¹, all the following products contain Bis GMA: Aelite Flo™ (Bisco Dental); Fl Restore™ (Den-Mat); Flow it™ (Jenneric-Pentron); Revolution™ (E &D Dental); Ultraseal XT Plus™ (Ultradent); Star Flow™ (Danville Eng.); Versa Flo™ (Centrix); Terric Flow™ (Ivoclar). Since few other flowable resins are used to make dental products, there is a high probability that what you use may have Bis GMA too.
___.Before examining its properties, let us review its structure. Its rigid center (two benzene or aromatic rings) hinders the free movement (and branching) of the two acrylic groups found at the ends of the chain. This rigidity has two consequences: the resin is too viscous to be used as such, and a thinner co-monomer has to be added, usually triethylene glycol dimethacrylate (TEGDMA). The other consequence is the molecule’s inability to rotate, and thus to participate effectively during polymerization. As a result, the analysis of its polymers show that only one methacrylate groups is reactive; the other, less active group participates only infrequently to provide cross-links with the adjacent inert chain. This leads to a low degree of conversion (leaving unreacted monomer) and low molecular weight polymers, i.e. oligomers. Despite its polar moieties (two hydroxyl, two ether groups and two carboxyl groups), the Bis GMA molecule has a low polarity. As “similia similibus congregantur”, it will be miscible in lipid solutions, but not polar ones. In the case of Bis GMA, the low polarity is due to the two benzene rings that repel polar surfaces such as that of enamel. The mentioned rings, which are not to be found anywhere in the animal or vegetal world, lead to a lack of biocompatibility. While the body’s enzymes degrade the aliphatic moieties, the aromatic rings are not recognized by these enzymes and resist transformation generating undesirable responses, as will be shown below.
Cytotoxicity, mutagenicity and carcinogenicity
___.Being dentistry’s work horse, Bowen’s resin’s potential health risks have been perhaps the most thoroughly investigated. In what follows, we will just mention what you may already know, and highlight some new developments.
___.First, additives such as the aromatic amines (peroxide decomposition qccelerators) have been shown to be toxic² and carcinogenic³. Then it was the resin’s turn. While the less viscous resin added to Bis GMA to render it more fluid, TEDGMA, leaks the most⁴, it is aliphatic, and thus less toxic. However, the aromatic components in the early resins were found to be mutagenic^5,6. Up to 14% of the total mass of the direct-bonding adhesive can leach out, and the discharge may continue up to two years^7,8. Some fifteen years ago, the monomers and oligomers released by the resins were found to be cytotoxic^9,10. It is reasonable to deduce that the leaching decreases in the following order, proportional with the content in inert filler: sealants> liquid-solid>liquid-paste> paste-paste systems. The cured adhesive is significantly less toxic, as it may have up to 80% inert filler. Completely polymerized resins were also described to be insoluble¹¹, a point of fact with which we disagree, as degradation amounts to dissolution. In some instances, a considerable part of the adhesive found on the bases of used brackets is missing from the bracket’s base without being the result of polymerization shrinkage or a cohesive failure. The existence of a well established microbial colony at the adhesive’s borders, Fig. 1 and a depolymerized area, Fig. 2, indicate a solubilization of the polymer followed by the release of its degradation products in the patient’s body¹².
___.The more liquid (higher monomer content), the higher the toxicity: hence, the more that is left unpolymerized, the more dangerous the system. Polymerization inhibitors, such as some impurities or oxygen, hinder the cure: the latter is quite common and generates a superficial, oily layer of monomers and oligomers atop of the solid polymer.
___.Oxygen has the strange property to behave like a bi-radical that combines with the free radicals generated by the initiator yielding a relatively stable peroxide radical that interrupts the reaction chain:

Normal: R'. + H₂C=HC-R = R'H₂C-RCH.
(Radical which should continue the chain)

O₂ inhibition: .O—O. + .RCH-CH₂R' =.O-O-RCH-CH₂R'
(Relatively stable radical)

___.Consequently, liquid-solid and liquid-paste systems will lead to a thicker oxygen inhibited layer (OIL) than paste-paste systems, and so will the chemically cured systems. Indeed, the latter contain a limited supply of activator (to enable a long shelf life), while the light cured systems can provide the needed excess of free radicals. This had been recently demonstrated on human oral fibroblasts¹³.

Estrogenicity
___.Reading FDA’s Guidance for Industry related to dental composites¹⁴, one might find that dental composites should not just be non-mutagenic, non-cytotoxic and non-carcinogenic, but also “should not produce adverse reproductive and developmental effects”.
___.This surprising requirement stems from an article published in 1996 by a Spanish team¹⁵ that produced quite a rumor. The study showed that bisphenol A (BPA), an aromatic compound used to make Bis-GMA, and at the same time a by-product of its degradation, potentially mimics human estrogens. To vividly depict the implications of the claim, Dr. D. Nathanson posited that “Dental sealants give breast cancer to young girls”¹⁶. In a study, performed at the request of the American Dental Association (ADA), Dr. Nathanson and his team examined 30 blood samples from dentists who had their teeth sealed: no BPA was found¹⁷. In another study¹⁸, of 12 brands of dental sealants accepted by ADA, only one leached a trace amount of BPA (5 part per billion!): since then, its manufacturer changed the formula. The calculations made by the Spanish team were severely attacked both in Japan¹⁹ and by the Clinical Research Associates (Dr. Gordon J. Christiansen). The latter had an FDA-like answer to the question if the use of sealants and composite resins should be suspended: “We must weigh the known benefits against the alleged risk”... He also pointed out that not all sealant brands have the same formulation as the one tested: while in few cases this may be true, we believe that as long as Bis-GMA is there, its degradation products will be the same. Generally speaking, Dr. Christiansen is, however, right, and so are Drs. Habib and Kugel²⁰ who equated the scare about the estrogenicity of the Bis-GMA-based derivatives to the anti-amalgam hysteria.
___.The controversy may continue until some young may claim to have contracted breast cancer from some formulation: the use of Bowen’s resin is too widespread not to allow this possibility. In animals, a study performed on a classic estrogen target tissue, rat vaginae²¹ showed a response in some of the animals tested. Further studies²² confirmed indeed that Bis GMA is weakly estrogenic in mice, and that BPA influences the growth of the rats mammary gland²³. Answering criticisms, the Spanish team²⁴ supported in vitro the results previously obtained in vivo while trying to determine the relationship of the structure of the BPA to estrogenicity.
___.Comparing the adult exposure to some of the Bis GMA degradation products, such as formaldehyde and methacrylic acid, to the average level of exposure to these chemicals, yields the results that the first is 1/10,000 times and the second 1/1,600,000 times, respectively, lower than the admissible level²⁵. Unfortunately, these do not address BPA, the main culprit...

Hydrophilicity
___.There are today two ways of approaching the water-affinity of adhesives: avoid it or use it. When using hydrophobic resins such as those based upon Bis GMA, you do not want to have water condensing on your mixing cold slab or wetting your patient’s teeth. The bond obtained is based upon mechanical interlocking and not upon chemical affinity. Indeed, to generate a good bond, the adhesive should exhibit an intimate molecular contact with the adherend by 1) exhibiting a near zero contact angle when liquid, 2) having a low viscosity during bonding, and 3) displacing contaminants (i.e. air, water). Bis GMA-based adhesives do not comply with any of these requirements. The polar adhesives, which properly wet the enamel, meet these requirements. In addition, as the glass-ionomer cements (GIC) contain water, these are not hindered by its limited local excess.
___.Each one of the above alternatives has its advantages and problems. If the adhesive’s basic organic ingredient is a resin that is hydrophilic, the adhesive’s bonding strength will diminish drastically in time due to the attack to which it is subjected in the oral environment. If it is hydrophobic, the bond you get is not the best: at a depth of 15µ, the micro-fissures or prisms should be filled with water. Real dry enamel cannot be obtained while the tooth is alive. To drive off the last water from powdered quartz requires a temperature of 1000^oC. A 160^oF-dried hydrophilic surface will still posses three or four molecular layers of water as an adsorbed film. In addition, water is attracted into capillaries with an incredible force and can go as deep as the space will allow the penetration of a single molecule. Indeed, the pressure causing the flow through a capillary is inversely proportional with its radius: the thinner it is, the farther the fluid is pushed in it. The use of “water-chasers” such as acetone followed by forceful drying may add only few microns to the depth the adhesive can go. High viscosity, high surface tension, and fast setting are all working against an adequate penetration. As a result, the length of the adhesive tags may reach, as observed after dissolving the tooth structure, only 10-15µ²⁶, which is a hundredth time less than the thickness of the enamel.
___.In other circumstances, water affinity or surface activity (wetting angle) can help, transforming foe into friend. The recent introduction of the hydroxyethyl methacrylate (HEMA) in adhesives tries to do just that. Borrowed from dentistry, where bonding to dentin is much more difficult than to enamel, this co-monomer is a step forward in the attempt to combine increased adhesion and water resistance. The differences in affinity for tooth structures exhibited by polar formulations (HEMA-based) and nonpolar ones (Bis GMA-based) become obvious when comparing their tags as recovered from tubules after tooth dissolution. In the first case, the resin shrinkage produces large diameter, but hollow tags, while in the second, the tags are thin but solid. In the first case, the adhesive adheres to the tubule’s walls, while in the second, it retracts.
___.Other researches are attempting to render the high molecular weight basic monomer (needed to impart low shrinkage to the polymer) more polar, i.e. to provide a better affinity to tooth structures. In addition to HEMA, there are researchers attempting to replace bisphenol A’s two, rigid benzene rings with aliphatic ones (polyurethane or polyether oligomers), or at least with just a single benzene ring as we will show below. Thus, the glycidyl methacrylates of various phthalic acid isomers and their halogen substituted derivatives (halogens provide give X-ray opacity) have shown promising results²⁷. While the shrinkage and equilibrium water of their polymers were less desirable than those of Bis GMA’s polymer, their strength and thermal expansion were similar. Unfortunately, the author didn’t mention the obviously improved affinity of his synthesized monomers toward polar surfaces. In what follows we will do it, using the HLB concept.
The HLB-Concept and its application.
___.The hydrophilic-lipophilic balance (HLB) is an empiric scale with the help of which one can determine not only the polarity of a compound, but also its distribution between the layers water/n-octanol, a nonpolar solvent. Each fragment of the compound’s molecule are attributed specific values designated as p. Thus, for the nonpolar groups the values are positive (each C =⁺0.5, and each C₆H₅=⁺2), while for the polar ones, negative (OCO=-0.7; O in hydroxyl and N in amines=-1). In the case where the polar groups can interact, lowering their activity (intramolecular hydrogen bonding, IMH), a penalty of +0.65 is applied. The more negative Sp, the summation of the p values, the more polar the compound is. If Sp is below +3.3, the compound is soluble in water and should exhibit a chemical affinity to tooth structures. Let us now compare the polarity/ partition coefficients of several resins used to make dental composites:

___.As one may see, while Bis GMA and Rohm's urethane dimethacrylate are insoluble in water, as a difference from both HEMA and any of the diglycidyl methacrylates of the phthalic acid isomers (Sp < 3.3), even if adding IMH for the ortho-phthalic acid. In other words, there are many interesting resins which can still be tried. Would these be considered this way even after half a century, as is the case with Bis GMA ?

References
1. Dental Investigation Service of the US Air Forces; USAFAM/FED, Brooks AFB, Tx
2. Eliades T, Eliades G, Brantley WA, Johnston WM, Residual monomer leaching from chemically cured and visible light cured adhesives, Am J. Orthod Dentofac Orthop 1995; 108: 316-321
3. Weisburger EK, Russfield AB, Homburger F, Weisburger JH, Boger E, van Dongen CG, Chu KC: Testing of twenty-one environmental aromatic amines or derivatives for long-term toxicity or carcinogenicity, J Environ Pathol Toxicol 1978; 2: 325-356
4. Geurtsen W, Substances released from dental resin composites and glass ionomer cements, Eur. J Oral Sci 1998; 106(2): 687-9
5. Fredericks HE, Mutagenic potential of orthodontic bonding materials, Am J. Orthod Dentofac Orthop 1981; 80: 316-324
6. Cross NG, Taylor RF. Nunez LJ, "Single-step" orthodontic bonding systems: Possible mutagenic potential, Am J. Orthod Dentofac Orthop 1983; 84: 344-350
7.Thompson LR, Miller EG, Bowels WH. Leaching of unpolymerized materials from orthodontic bonding resins, J Dent Res 1982; 61: 989-92
8. Ferracane JL, Gordon JR. Rate of elution of leachable components from composites. Dent Mater 1990; 6: 282-7
9. Tell RT, Sydiskis RJ, Isaacs RD, and Davidson WM; Long-term cytotoxicity of direct-bonding adhesives, Am J. Orthod Dentofac Orthop 1988; 93: 419-422
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SEE US AT THE 100TH AMERICAN ASSOCIATION OF ORTHODONTISTS
ANNUAL SESSION AT THE CHICAGO CONVENTION CENTER,
CHICAGO, APRIL 29-MAY 4, BOOTH X