Effect of oral exposure on chemical, physical, mechanical, and morphologic properties of clear orthodontic aligners

INTRODUCTION

The dental industry is heavily committed to developing more esthetic solutions for orthodontic treatments. Invisalign is a system of transparent orthodontic aligners introduced as an alternative to conventional orthodontic fittings with brackets and metal wires. This study aimed to assess the chemical, physical, mechanical and morphologic changes in these polymeric aligners after exposure to the oral environment.

METHODS

Twenty-four Invisalign orthodontic aligners were equally divided into 2 groups: an in vivo aged group in which patients used aligners for 14 days and the reference group, unexposed to the oral environment. Different experimental techniques were used to study the chemical structure, the color changes and translucency, the density and subsequent volume of the aligners, mechanical properties, surface roughness, morphology and elemental composition. The data were subjected to several statistical analyses.

RESULTS

Clear orthodontic aligners exhibit chemical stability but undergo a statistically significant optical change in color and translucency. There was a gradual increase in the water absorption rate and the dimensional variation of the polymer, indicating a strong correlation among these factors. The mechanical properties of the polymer showed a statistically significant decrease in its elastic modulus and hardness. There was a slight tendency toward increased surface roughness of the material, but no statistical differences were found between reference and aged groups. The surface morphology of the used aligners demonstrates microcracks, distortions and biofilm formation.

CONCLUSION

Intraoral aging adversely affected the physical, mechanical, and morphologic properties of the Invisalign appliance.

[Improvement of oral rehabilitation prosthetic techniques thanks to orthodontics]

This clinical case underlines the importance of a multidisciplinary approach, prosthetic and orthodontic, for the achievement of an oral rehabilitation treatment plan. Preliminary orthodontic treatment has significantly improved, the position of some natural teeth, which can serve or not as a prosthetic abutment. This has produced a direct prosthetic benefit by limiting tissue reduction for preparation and by giving a better biomechanical and functional context to the restoration.Thus, after an orthodontic treatment step, lasting a year and a half, using both removable appliance and fixed appliance, prosthetic rehabilitation was possible. This included a fixed prosthesis and a removable prosthesis that gave a very satisfying an esthetic result and good masticatory function.

[Mouthguards: a difficult choice?]

It is the dentists' task to advise their patients what type of mouthguard grants the best possible protection. It is generally accepted that off-the-counter mouthguards are not sufficiently protective. These mouthguards are usually ill-fitting and not worn in the mouth but in the sporting shorts' pocket instead. A custom-fabricated mouthguard is proven to offer maximal protection. A mouthguard has to offer adequate protection with high comfort. A composite laminate construction and space between the inner surface of the mouthguard and the labial surface of the upper front teeth are essential for adequate protection. Transitional dentition and/or orthodontic appliances are no limitation to fabricate a custom-formed mouthguard.

Standardization of orthodontic products--does it make sense?

Since 1994, the DIN (Deutsches Institut für Normung e.V.) has had a German working group named "Orthodontic Products" working toward establishing standardized norms for orthodontic products. In the USA, a similar working group called "Orthodontic Materials" was established in 1996 at the ADA (American Dental Association). Working at the ISO level since 1997, an international team has been in charge of unifying the standards already set at national levels. It is the aim of this article to report on the current state of standardization in Germany and internationally. The standards already published for wires (DIN 13971, ADA Spec. 32), for brackets and tubes (DIN 13971-2, ADA Spec. 100) and for elastomeric elements (DIN 13901) have been considered, as have problems occurring with ISO standards (ISO/CD 15841 and ISO/CD 15841-2) and DIN 13904-1. We demonstrate that the demands made of these products by the orthodontists who use them have lead to reasonable quality standards. Thanks to clearly-defined testing methods, orthodontic products can now be tested and their compliance with these minimum standards can be compared. In fact, the standards that have been agreed upon help both the product manufacturers and their users to improve product quality and, ultimately, the success of orthodontic treatment.

Orthodontic soldering techniques: aspects of quality assurance in the dental laboratory

BACKGROUND

In Germany, the dental technician is required by the Medical Products Act (MPG) to produce workpieces of high safety and quality and to document these properties. Soldering continues to be the prevailing joining technique in the dental laboratory, although problems arise from the susceptibility to corrosion and the low strength of soldered joints. This study aimed to reveal sources of defects in dental laboratory workpieces in order to achieve optimization in terms of quality assurance.

MATERIAL AND METHODS

The joints were produced by various dental technicians using three different soldering techniques. These joining techniques were investigated for their quality and their corrosion properties during immersion in ferric chloride, orthodontic appliance cleanser, and artificial saliva. Observance of the soldering instructions by the dental technicians was checked. Corrosion attack was confirmed by scanning electron microscopy and by measuring the ion concentrations of copper, silver and zinc in the corrosive agents, using atomic emission spectroscopy with stimulation by inductively coupled plasma (ICP-AES analysis).

RESULTS AND DISCUSSION

Incomplete filling of the soldering gap, porosities resulting from the production process, poor corrosion properties, and in particular a high variability of the measured values point to insufficient reliability of two soldering techniques. Variations in quality were also detected among the technicians' modes of operation.

CONCLUSION

The analyses confirm the need for quality assurance of soldering techniques and for increased support for alternative joining techniques such as laser welding in the future. The results of the studies on laser welding are presented in a separate publication.

The need for standardization of test protocols

This article reviews the current status of standardization in orthodontic products. The role of the American National Standards Institute and the American Dental Association is described. A review of laboratory testing for the evaluation of frictional forces and bond strength in orthodontics is discussed. The need for standardization in test protocols is emphasized to obtain valuable interpretation and use of data generated by researchers. Standardization of test protocols will lead to improved standards for orthodontic products and ultimately higher-quality products for orthodontists and their patients.

The first 100 cases: a personal audit of orthodontic treatment assessed by the PAR (peer assessment rating) index

The first 100 consecutively started cases treated by a specialist registrar in orthodontics were examined and pre- and post-study models were scored using the peer assessment rating (PAR) index. The PAR index proved both simple and reproducible to use: 92 cases had post-treatment records available, 91 patients registered a drop in PAR score, and one patient registered an increase. Of these 92 patients, 38 (41%) were greatly improved, 43 (47%) were improved, and 11 (12%) were made worse or no different (ie they failed to achieve a 30% drop in PAR score). Of the factors examined, only the appliance type used was significantly related to PAR score change. Of the 11 cases apparently made worse, individual examination revealed that four of these represented beneficial occlusal changes but due to limited treatment goals they did not register as improved using the PAR index according to previously agreed criteria. The PAR index measures 'good tooth position' which, although very important, is not the only factor in orthodontic treatment. The use of the PAR index to detect 'good' and 'bad' orthodontic treatment is not without problems. Its use in mixed dentition and adjunctive orthodontic treatments may not always be appropriate.

Changing concepts and controversies in the management of mandibular fractures

The successful treatment of mandibular fractures and the avoidance of complications ultimately depends on sound surgical judgment. Judgments are influenced by an array of variables. Location, degree of complexity or displacement of the fracture, state of dentition, patient cooperativeness, presence of other maxillofacial trauma, and the surgeon's experience and expertise are some of these factors. We have attempted to outline the basic tenets of mandibular fracture management, recognizing that some areas remain controversial. It is hoped that as technology continues to improve, we will have the luxury of being more dogmatic about our approaches to these problems.

Intrabracket space and interbracket distance: critical factors in clinical orthodontics

The engineers who designed the Houston Astrodome, Walter Moore and Associates, were engaged to study the effect that different edgewise appliances have on the function of orthodontic beams or wires. They were supplied with tooth width, bracket width, wire size, slot size information, and stainless steel wire specifications. With these data their computer was programmed to model each appliance as a simple beam reflecting its different support conditions. In the study the 0.018, 0.022, and 0.016-inch traditionally slotted appliances were tested in single and twin brackets. In addition the 0.016-inch bimetric appliance (0.016 inch on anterior teeth, 0.022 inch on posterior teeth) was tested. The following wires were used for testing: 0.016 x 0.022 inch, 0.017 x 0.022 inch, 0.018 x 0.025 inch (0.018 inch); 0.018 x 0.025 inch, 0.019 x 0.025 inch, 0.022 x 0.028 inch (0.022 inch); 0.014 x 0.018 inch, 0.015 x 0.019 inch, 0.016 x 0.022 inch (0.016 inch and bimetric). The results as stated in the conclusion statement by Rick Horn, PhD, of Walter Moore and Associates, are (1) for a given appliance and wire size, the amount of deflection allowable at permanent set decreases with decreasing size of teeth; (2) for a given appliance and wire size, the force imparted to the teeth at permanent set increases with decreasing size of teeth; (3) for a given appliance, the amount of deflection at permanent set decreases with increasing wire size; (4) for a given appliance, the force imparted to the teeth at permanent set increases with increasing wire size; (5) the amount of deflection allowable at permanent set is larger for single brackets than double brackets and larger for bimetric brackets than single brackets; (6) the force imparted to the teeth at permanent set is smaller for single brackets than double brackets and smaller for bimetric brackets than single brackets; and (7) of the six types of appliances examined, the bimetric appliance is the most flexible, allowing the most deflection at permanent set with the smallest force imparted to the teeth. This study supports the following thesis: the only way to take advantage of smaller wires and thereby have an appliance deliver maximum resiliency with lighter forces and not loose control is through differential slot sizing.

[Comparison of the P.C.F. orthodontic device and Bassani's orthodontic plate in the correction of malocclusion class II, division II]

We have described and compared the P.C.F. of protusiva and the plaque of Bassani in the correction of the II class and II division by mentioning the advantages of the first one.

[New wires and their force delivery--consequences for orthodontic therapy]

Levelling arches made of stainless-steel wires were compared with nickel-titanium wires of the new generation which are distinguished by their shape memory, superelasticity and their excellent spring-back. The data received from a bending test have been analysed statistically and revealed a linear unloading curve of the twisted stainless-steel wires. The nickel-titanium wires, however, showed a clear deviation form the linearity with a curviform course. Besides the unusual unloading curve with a constant force mechanism in the middle range of deactivation the wires give off the same amount of force irrespective of the degree of activation (that is to say, regardless whether the level difference between the brackets amounts to 1 or to 4 mm). The diagram shows that the greater the activity between the brackets, the longer the period of superelasticity. Therefore the nickel-titanium wires are suited for large level differences or deflections. At a low activation rate the characteristic line takes a very steep and almost linear deactivation curve. In these cases twisted stainless steal wires should be preferred because of their lower load deflection rate and flexibility.

[Dental prostheses and dental impressions from a hygienic viewpoint]

Dentures, dental impressions, removable orthodontic appliances and all dental technical devices, which are part of any dental treatment are parts as well of a potential crosscontamination chain in dental treatment. Most of those items do not tolerate heat as a sure sterilization medium. For disinfection, chemical disinfectant solutions may be used as far as they work properly and as they are tolerated by the materials in question. Though, one can report some progress in disinfection of dentures and impressions, there are still questions open depending on safety and/or compatibility of the particular materials. For disinfection of removable dentures chlorine-yielding preparations such as Maranon can be recommended. Peracid preparations, such as Sekusept, Sekusept steril and Dentavon may be useful for disinfection of dental impressions. To do the possible means to reduce the infection risk for all persons involved in the dental treatment, patient, dentist, dental technician and all auxiliary persons. This includes both, active hygiene provisions as sterilization and disinfection, as well as possible passive self protection.

Bond strength of thermally recycled metal brackets

Bracket recycling has emerged concurrently with the practice of direct bonding. This study was undertaken to determine the effect of recycling on the retention of mesh-backed stainless steel brackets. Mesh strand diameter was measured on forty new brackets. These brackets were bonded to recently extracted human premolar teeth, and the tensile force required to fracture each bond was recorded. The brackets were then reconditioned by a thermal process. The mesh strand size was remeasured and the tensile test was repeated. It was found that (1) mesh strand diameter decreased 7 percent during the reconditioning process (93.89 microns +/- 3.17 S.D. compared to 87.07 microns +/- 4.76 S.D., z = 17.62, P less than 1 X 10(-5) ), (2) new bracket bonds were 6 percent stronger than recycled bracket bonds (43.88 pounds +/- 7.98 S.D. bond strength), and (3) reduction in mesh strand diameter during the reconditioning process did not correlate with changes in bond strength between initial and recycled bonding (Pearson r = 0.038).

[Bite plates and occlusal splints]

Occlusal adjustments are often necessary in cases of masticatory muscle spasm, bruxism, traumatic occlusion and TMJ disturbancies. Before such occlusal adjustments are performed, the patient should either wear a bite plate or an occlusal splint which frees the occlusion for a certain time. The splint is fabricated on a semiadjustable articulator such as the Hanau H2-XPR which is also used for the functional analysis on the models prior to any adjustments. Advantages and disadvantages of different types of plates and occlusal splints are discussed. The authors conclude that an occlusal splint covering the entire dental arch, such freeing the occlusion, seems to be the most appropriate appliance available today.