Medical Orthodontic Adhesives

Foreword

First, research background Since Newman first used epoxy resin bonding technology to bond orthodontic attachments [1] in 1965, it has been rapidly popularized due to its convenience and high efficiency, and has been widely introduced into orthodontic fixation technology. in. Orthodontic adhesives have also developed rapidly. Currently, there are various components and curing methods for orthodontic adhesives that clinicians choose to use. However, in the process of fixed orthodontics, due to the long period of the correction and the influence of brackets, wires, ligatures and other orthodontic attachments, the teeth, especially the tooth surfaces around the brackets, are not easy to clean. Therefore, in the patients undergoing orthodontic treatment, there is a common enamel demineralization performance caused by poor oral hygiene - glaze white spots, and severe cases can also develop into early enamel defects. Therefore, how to prevent enamel demineralization during orthodontic treatment has always been one of the hot issues that contemporary orthodontists are very concerned about and are currently working on. With the development of fluoride anti-mite research, its anti-mite mechanism is basically clarified, and the effect of anti-mite is also recognized. Therefore, in the past 20 years, foreign orthodontics scholars have tried various methods such as the use of fluorinated foam, topical fluorine coating, and application of fluorine protective paints to apply fluoride ions in orthodontic treatment to prevent enamel demineralization. Although these methods have been proved to reduce the enamel demineralization in the orthodontic treatment to varying degrees, they also have the disadvantages of increasing the time for chairside operations, poor patient compliance, and so on, and therefore have not been widely promoted and applied. The area of ​​severe enamel demineralization is mainly reflected in the periphery of the bonded bracket, which is closely related to the scope and technology of bonding. If fluoride can be added to the adhesive for a long period of time to release fluoride ions, the effect of preventing demineralization of the enamel around the bonding area of ​​the bracket is undoubtedly a simple and effective method. In 1983, Rawls and Zimmerman successfully developed for the first time a composite resin with a more stable fluorine ion sustained-release properties [2], and proved to have the effect of preventing demineralization of the enamel around the restoration [3]. Subsequently, Sansing, Rawls, Shaye et al [4] conducted a comparative study of the bond strength of this composite resin with common orthodontic adhesives and found no significant differences. Since then, the development of Fluoride Releasing Adhesive (FRA) with the ability to release fluorine has become a common concern for orthodontists and dental material manufacturers. In 1989, Underwood, Rawls et al [5] published the first published paper on the actual effect of FRA in the reduction of enamel demineralization in orthodontic clinical applications. The results show that FRA can effectively reduce the enamel demineralization around the bracket. So far, foreign countries have developed and developed several FRAs with registered trademarks, such as VP862, Rely-a-bond, Sequence, Light Bond, and FluoEver OBA, and they have been tested for orthodontic clinics. The research on FRA in foreign countries is still mainly focused on the bonding strength of FRA, the performance of FRA to release fluoride ions, and the effects of preventing enamel demineralization. With the deepening of these studies and clinical trials, it is currently believed that the strength of FRA is higher, and fluoride ion release is more appropriate and stable, which can prevent and reduce enamel demineralization to some extent. And because FRA is easy to use, it doesn't need extra time to sit on the chair, and it doesn't need the cooperation of the patient. As an effective anti-caries orthodontic adhesive, it is more and more popular with orthodontists and patients.
In the past two decades, fixed appliance technology has become the mainstream technology for orthodontic treatment in China. Although China currently has a stable performance of ordinary orthodontic bonding materials applied to orthodontic clinics, but has not seen reports on the development and development of FRA, and foreign imports of such materials are expensive, unbearable to our patients. For this reason, after nearly three years of collaborative research with the Sichuan University’s School of Chemistry, we systematically reviewed the literature at home and abroad. We have conducted hundreds of synthetic and inspection experiments of polymer compounds for more than two years, and finally we have jointly developed A FRA, tentatively named Fluo-HX. At present, we have initially explored the laboratory synthetic route of organic fluorine source components with independent intellectual property rights in Fluo-HX. We have initially completed the screening of Fluo-HX formulations and established a set of simple and effective testing methods for future projects. Further research and marketization have laid a solid foundation.
Composition and Formulation of Fluo-HX at the Present Stage The Fluo-HX adhesive consists of an acid etchant, an enamel coating, and a fluorine release retarding adhesive. In which the acid etcher is formulated with 37% phosphoric acid; the enamel coating agent is a modified methacrylate, 4-methacryloxyethyl trimellitate (4-meta) adhesive coupling agent, Reactive diluents and initiators are formulated as two-component A and B solutions; fluoroally retarded release adhesives are PMMA resin, MMA resin, 4-methacryloxyethyl trimellitate (4-meta). Adhesive coupling agent, silanized silica, polymeric ion-associated fluorine-containing complexes (organic fluorine source), reactive diluents, accelerators, and initiators formulated into two liquid formulations of A and B .
Third, the future research direction 1, dosage form: from the clinical feedback information shows: easy to operate, strong adhesion of non-harmonic single paste type orthodontic adhesive will become the first choice of orthodontists. Therefore, our developed Fluo-HX must also comply with this trend and change the dosage form to a non-harmonic single paste type, which will be the focus of our next work.
2. Fluoride source: We will further extend the investigation of fluoride ion release time from Fluo-HX and further improve the organic fluorine source on the existing basis.
3. Physical and chemical properties and biocompatibility: After all aspects of work have been basically completed, we will carry out the physical and chemical properties of Fluo-HX according to the requirements of the national “dentine enamel adhesive resin” industry standard YY 0269-1995. Biocompatibility testing. After reaching the standards, we will conduct clinical in-vivo experiments on the adhesion properties of Fluo-HX and the prevention of enamel demineralization.
4. Product Development: After all the performances are qualified, we will apply for the patent of organic fluorine source, the key component of Fluo-HX, and look for cooperative enterprises to formally introduce Fluo-HX to the market in the form of technology shares.
References 1. Graber TM, Vanardall RL. Orthodontics-Current Principles and Techniques. St. louis: Mosby, 1994
2. Rawls HR, Zimmerman BF. Fluoride-exchanging resins for caries protection. Caries Res, 1983, 17:32-43
3. Benton JB, Zimmerman BF, Rawls HR, Turpin-Mair JS. Enamel fluoride uptake from an experimental anion exchanging resin [Abstract 919]. J Dent Res, 1983, 62:271
4. Sansing WJ, Rawls HR, Shaye R. evaluation of a caries-protective resin for orthodontic direct bonding [unpublished]. New Orleans: Louisiana State University School of Dentistry, 1983
5. Underwood ML, Rawls HR. Clinical evaluation of fluoride-exchanging resin as an Orthodontic adhesive. Am J Orthod Dentofac Orthop, 1989, 96:93

The first part compares the bonding properties of Fluo-HX and general orthodontic adhesives. Foreword As an orthodontic adhesive, the most basic requirement for resin-based fluoride ion slow release orthodontic adhesives is that the adhesive strength should be able to Meet the needs of the clinic. The study of adhesive properties mainly focused on the tensile bond strength (TBS) and shear bond strength (SBS) of the test materials. In this study, we used Fluo-HX, a resin-based fluoride ion sustained release orthodontic adhesive, and two orthodontic adhesives commonly used in clinical practice in our department. Three kinds of orthodontic adhesives were used to simulate clinical applications. Adhesive tensile strength and bond shear strength between bovine tooth enamel and metal bracket to understand: 1, Fluo-HX and the current clinical commonly used orthodontic adhesive bond strength between No obvious difference, whether the bond strength can meet the clinical needs; 2, with Fluo-HX fluoride ions released slowly, Fluo-HX bond strength will be affected.
I. Materials and Methods 1.1 Materials 1.1.1 Adhesives The three types of orthodontic adhesives used in the experiments are shown in Table 1.
Table 1 Three Types of Orthodontic Adhesives Used in Experiments Curing Methods for Adhesives Development Unit Fluo-HX Reconciled Sichuan University School of Stomatology and Chemistry Chemical Solidification Beijing-Tianjin-Tianjin-Tianjin Institute of Composite Materials Chemical Curing TF Non-harmonic Original Chinese Medicine Materials Research Laboratory Chemical curing 1.1.2 Excised bovine teeth Excised bovine upper incisors were selected and the lip surface was polished with water sandpaper to prepare a smooth enamel adhesive surface. After washing with distilled water, 37% phosphoric acid was used for drying. Etched tooth surface 1min, then washed with distilled water and dried for use.
1.1.3 Brackets Select the clean, dry, standard square wire upper incisor brackets (Hangzhou New Asia Company). The bottom of the brackets is a grooved retention type. Stainless steel wire was bolted in advance for force testing.
1.1.4 The main experimental equipment LJ500 type tensile testing machine (produced by Wuzhong Micro Testing Machine Factory).
1.2 Methods
1.2.1 Experimental grouping Each adhesive was randomly bonded to 50 test pieces. After bonding was completed, it was divided into 5 groups. Each set of 10 test pieces was placed in a 37°C, relative humidity 100% rh environment for 5 minutes. 37 °C In water 1h, 24h, January and March, TBS and SBS were taken out and tested 5 times.
1.2.2 Bonding tensile strength test In the environment of 22±2°C temperature and 55±5% rh relative humidity, the bonding is completed according to the instructions of each adhesive and grouped according to experimental conditions. Finally under the normal temperature environment conditions [1], using the LJ500 tensile testing machine at a tensile rate of 10mm/min to continuously apply tensile force to the bonded specimen to record the maximum tensile force when the specimen is broken. According to the bottom area of ​​the bracket and the breaking force, the tensile strength of the bond is calculated and the unit is Mpa.
1.2.3 Tests for Bonding Shear Strength Materials, bonding, grouping, and environmental conditions are the same as in 1.2.2. In the test, the shearing force was continuously applied to the bonded test piece at a tension rate of 10 mm/min. According to the bottom area of ​​the bracket and the destructive shear force, calculate the shear strength of the adhesive, unit Mpa