Orthodontic Retainers Research Articles

Effects of fast halogen and plasma arc curing lights on the surface hardness of orthodontic adhesives for lingual retainers.

The aims of this study were to (1) identify the optimum cure times of 2 different lingual retainer adhesives with a conventional halogen, a fast halogen, and a plasma arc light by measuring Vickers surface hardness, and (2) determine whether different lights produce similar surface hardness values for the same adhesive resin material. The investigated plasma arc curing unit was the PowerPac (American Dental Technologies, Corpus Christi, Tex), and the fast halogen unit was the Optilux 501 (Kerr, Orange, Calif). A conventional curing unit, the Ortholux XT (3M Dental Products, St. Paul, Minn) was used as the control. Two orthodontic lingual retainer adhesives were used: Transbond Lingual Retainer (3M Unitek, Monrovia, Calif) and Light Cure Retainer (Reliance Orthodontic Products, Itasca, Ill). Concise (3M Dental Products) and diluted Concise were used as controls. Transbond Lingual Retainer was polymerized by the PowerPac light in 6 seconds, by the Optilux in 10 seconds, and by the conventional halogen light in 20 seconds. The minimum curing times for Light Cure Retainer adhesive were 15 seconds for PowerPac, 10 seconds for Optilux, and 40 seconds for conventional halogen. Surface hardness values for each resin did not differ significantly with different curing units. However, different adhesives demonstrated significantly different surface hardness values. Final Vickers surface hardness values (averaged across curing units) of Transbond Lingual Retainer, Concise, diluted Concise, and Light Cure Retainer were 62.8, 52.4, 46.0, and 40.4, respectively. Plasma arc or fast halogen units polymerize resin composite adhesive in much shorter times than do conventional curing units, without a significant loss in surface hardness. Therefore, these units are suggested for clinical use to save chairside time.

In Situ Effect of 10% Carbamide Peroxide on Microhardness of Human Enamel: Function of Time

This study evaluated the effect of two home bleaching regimens (1 h/day versus 7 h/day for a total of 21 days) on the microhardness of superficial enamel treated with 10% carbamide peroxide gel. Rectangular enamel specimens (2.5 x 2.5 x 1 mm) were obtained from human third molars and mounted on the palatal aspect of removable orthodontic retainers. Nine enamel specimens were mounted in each of 10 retainers, used by 10 volunteers during the active phase of the study. Modified 0.089 cm thick bleaching trays were fabricated for each participant. Each bleaching tray fit a participant's arch and the retainer containing the enamel specimens. Enamel specimens were treated with a 10% carbamide peroxide bleaching gel (Nite White Excel 2Z, Discus Dental, Culver City, CA, USA) for either 1 h/day (n = 30) or 7 h/day (n = 30), both for 21 days. Three enamel specimens in each retainer were never treated and served as controls. The retainers were worn by the participants whether or not they underwent bleaching. This simulated the natural action of the saliva/oral fluids on the enamel specimens. Enamel specimens were subjected to pre- and post-treatment microhardness measurements. Post-treatment Knoop hardness numbers were compared with baseline values and analyzed statistically. Bleaching treatment resulted in a nonsignificant reduction in microhardness values when compared with values of the control nontreated specimens (1.7% and 2.5% reduction in hardness for 1 h/day and 7 h/day, respectively). There was no difference in microhardness between the different treatment regimens. Home bleaching with 10% carbamide peroxide for up to 7 h/day for 21 days does not significantly affect enamel microhardness. Bleaching with 10% carbamide peroxide for 1 h/day or 7 h/day for a total of 21 days is safe for human enamel.

Four applications of reinforced polyethylene fiber material in orthodontic practice

Four different orthodontic applications of a polyethylene fiber material are shown and discussed in case reports. Ribbond (Ribbond Inc, Seattle, Wash), a bondable, reinforced polyethylene fiber material, was successfully used in a fixed orthodontic retainer, a space maintainer, a temporary postorthodontic fixation device to attach a pontic to abutment teeth during periodontal therapy, and a posttraumatic stabilization splint. This clinical practice was based on earlier studies showing that the polyethylene fiber material adapted easily to dental contours and could be manipulated during the bonding process. It also has acceptable strength because of good integration of fibers with composite resin; this leads to good clinical longevity. Because thinner composite resins can be used, the volume of the splint can be minimized. There is no need for significant tooth structure removal, so the technique is reversible and conservative. It also satisfies patients' esthetic expectations. These cases show that Ribbond is a promising splint material for use in orthodontic practice. (Am J Orthod Dentofacial Orthop 2002;121:650-4)

Enhancing wire-composite bond strength of bonded retainers with wire surface treatment

Bonded orthodontic retainers with wires embedded in composite resin are commonly used for orthodontic retention. The purpose of this study was to test, in vitro, various wire surface treatments to determine the optimal method of enhancing the wire-composite bond strength. Coaxial wires and stainless steel wires with different surface treatments were bonded to bovine enamel and then pulled along their long axes with an Instron universal testing machine. Wire surface treatments included placing a right-angle bend in the wire, microetching the wire, and treating the wire with adhesion promoters; combinations of treatments were also examined. The results demonstrated a 24-fold increase in the wire-composite bond strength of wire that was microetched (sandblasted), compared with that of untreated straight wire. The difference between the amount of force required to break the bond produced by microetching alone (246.1 ± 46.0 MPa) and that required for the bonds produced by the retentive bend (87.8 ± 16.3 MPa), the adhesion promoters (silane, 11.0 ± 3.1 MPa; Metal Primer, 28.5 ± 15.8 MPa), or for any combination of surface treatments, was statistically significant. Microetching a stainless steel wire produced a higher wire-composite bond strength than that obtained from a coaxial wire (113.5 ± 27.5 MPa). The results of this study indicate that microetching or sandblasting a stainless steel wire significantly increases the strength of the wire-composite bond. (Am J Orthod Dentofacial Orthop 2001;119:625-31)

Measurement of lingual and palatine somatosensory evoked potentials

Objective: A technique is presented for generating and recording lingual and palatine nerve somatosensory evoked potentials (SEPs). Methods: Pairs of thin, stainless steel disk electrodes were mounted onto mandibular or maxillary acrylic splints, similar to orthodontic retainers. Mandibular splint electrodes were oriented to contact the under surface of the tongue along the course of the right and left lingual nerves and maxillary splint electrodes were oriented to contact the hard palate bilaterally along the course of the palatine nerves. SEP recording electrodes were placed on the scalp 1 cm posterior to C5 and C6 (C5′ and C6′, respectively) using the combinatorial nomenclature of the International 10–20 system. Two reference electrode locations, Fz and C5′ or C6′, over the cortical hemisphere opposite that of the recording electrode, were used. Results: Right and left lingual and palatine nerve SEPs were recorded from five normal adults. SEP latencies were similar to the N13 and P18 cortical peak latencies recorded in previous studies of trigeminal nerve branches to the lips regardless of reference electrode position. Conclusions: A more precise method of stimulating the intraoral lingual and palatine nerves was accomplished using dental splints. SEPs were easier to obtain using a contralateral cortex reference electrode location.

Intra-oral temperature variation over 24 hours.

This study aimed to investigate temperature variation at archwire sites adjacent to the maxillary right central incisor and first premolar, its correlation with ambient temperature, and the influence of inter-racial variation. Twenty young adult male subjects were randomly selected (13 Asian, seven Caucasian). Thermocouples were attached to the labial archwire component of custom-made orthodontic retainers at the two intra-oral sites. A third thermocouple measured ambient temperature. A data-logger recorded temperatures at 5-second intervals over a 24-hour period. Temperatures ranged from 5.6 to 58.5 degrees C at the incisor and from 7.9 to 54 degrees C at the premolar, with medians of 34.9 degrees C and 35.6 degrees C, respectively. Ambient temperature correlated poorly with the intra-oral temperatures. The Asian and Caucasian groups had significantly different temperature distributions. On average during the 24-hour period, temperatures at the incisor site were in the range of 33-37 degrees C for 79 per cent of the time, below it for 20 per cent, and above it for only 1 per cent of the time. Corresponding figures for the premolar site were 92, 6, and 2 per cent. At both archwire sites the most frequent temperatures were in the range of 35-36 degrees C. The data presented demonstrate that the temperature at sites on an archwire in situ varies considerably over a 24-hour period and that racial differences may exist. This information should be considered during the manufacture and use of temperature-sensitive orthodontic materials, in particular nickel-titanium archwires and springs.

Bonded orthodontic retainers: The wire-composite interface

The bonded orthodontic retainer constructed from multistrand wire and composite is an efficient esthetic retainer, which can be maintained long-term. Clinical failures of bonded orthodontic retainers, most commonly at the wire/composite interface, have been reported. This in vitro investigation aimed to evaluate selected multistrand wires and composite materials that are available for use in the construction of bonded fixed retainers. An in vitro model was developed to simulate the forces encountered at the wire/composite interface. No significant difference was detected between different multistrand wire types and diameters with regard to retention in composite. Wires were placed in one of three groups according to surface characteristics identified with scanning electron microscopy. Increasing the thickness of composite overlying the wire increased the force required to detach the wire from the composite. Thickness of composite greater than 1.0 mm overlying the wire may give little clinical advantage. Greater force was required to detach the wire from Concise Orthodontic (3M Unitek) than any other composite tested. In vitro abrasion resistance testing found Heliosit Orthodontic (Vivadent) and Right On (TP Orthodontics, Inc.) to have poor abrasion resistance, whereas Concise Orthodontic and Transbond (3M Unitek) had abrasion resistance comparable with restorative composites. Clinical recommendations are made based on these findings. (Am J Orthod Dentofac Orthop 1997;111:67-74.)

Growth changes in the cranial base and the face: a longitudinal cephalometric study of linear and angular changes in adult Norwegians.

The purpose of this study was to examine the natural growth changes which occur between 22 and 33 years of age. The material consisted of two series of cephalograms of 74 females and 90 males with approximately 11 years between the two series. None of the subjects had orthodontic retainers when the first exposure was undertaken, or orthodontic treatment, or surgery during the observation period. The measurements were carried out by using a modified Dentofacial Planner program SHORT, and both linear and angular measurements were made. The overall changes were an increase in anterior facial height which mostly occurred in the lower face, and an increase in the length of the mandible. These changes were statistically significant in both genders. The females also had a significant posterior rotation of the mandible. There was a significant decrease in the thickness of the upper lip both in females and males, and the males had a significant increase in thickness of the soft tissue on the mandibular profile. Although there were some statistical changes in the observation period, none of the linear changes exceeded 1.35 mm. The largest angular change was a 1.44 degrees retroclination of the upper incisors in females. The differences between the genders were statistically significant only in three angular and two soft tissue measurements.

Oral lesions caused by an orthodontic retainer: A case report

Jetainers are mostly used at the end of the active phase of orthodontic treatment to stabilize the teeth for extended periods of time. Retainers can be either fixed or removable. Removable orthodontic retainers, such as Hawley appliances, are made of an acrylic body and also incorporates stainless steel wires that are used for constructing the labial bow and the retention clasps. The ends of the labial bow are often bent to cross the occlusal table and get embedded in the

Screening of matrices and fibers for reinforced thermoplastics intended for dental applications

Plastics reinforced with continuous fibers (FRC) are being developed for dental applications, such as prosthodontic frameworks and orthodontic retainers. Flexure properties, stress relaxation and hydrolytic stability of FRC based on six thermoplastic matrices, three types of fibers, and three fiber volume fractions were evaluated. Samples with clinically relevant dimensions were tested. Polycarbonate was the preferred matrix material. Polycarbonate reinforced with 42 volume percent glass fibers exhibited the highest combination of flexure modulus (17.9 +/- 2.6 GPa), flexure strength (426 +/- 40 MPa), reinforcing efficiency (0.79), and resistance to stress relaxation. No statistically significant difference was observed between E and S2 glass reinforced composites under the experimental conditions used. Kevlar reinforced materials exhibited a low flexure modulus and strength. The apparent flexure moduli of all composites decreased with span length in the range of clinical interest. Generally, the prevalent mode of failure for all FRC investigated was brittle failure under flexure loading. Relatively large sample-to-sample variation in both composition and properties indicated that improved fabrication methods will be needed in future studies. The combination of good flexure properties, formability, and translucency suggests that novel appliance designs for dentistry are feasible with FRC, but further studies of its properties and particularly the effects of fiber/matrix interfacial quality are needed.

On the selection and preparation of a wire for the labial bow of an orthodontic retainer.

The Hawley retainer is often prescribed by the practitioner for part-time wear during the retentive period subsequent to a program of active, maxillary arch, orthodontic therapy. The labial bow of this retainer, while engaged, may be subjected to contact forces from sources other than the maxillary anterior teeth. The bow also experiences small deformations during placement and removal of the appliance from the oral cavity. Potential failures of the bow are: 1) inelastic bending from individual masticatory actions that change its as-prepared shape; and 2) fracture due to fatigue arising from many cycles of removing and replacing the retainer. Reported in this paper, a sequel to a previous article, are the outcomes of two experiments and a nonparametric analysis that led to the development of a set of recommendations pertaining to the selection of the wire and preparation of the labial bow. Controlled variables in this study were as-received size, alloy and temper of the wire, and heat-treatment following fabrications of bow-specimens.

On the design of looped orthodontic retainer wires.

Removable Hawley orthodontic retainers have long been prescribed by clinicians following completion of active therapy. Only minor changes have occurred in the design of the retainer over the past 40 years. Structural, in-service failures of this appliance are typically: 1) permanent (inelastic) deformation of the as-prepared labial bow from masticatory action that induces unwanted force transmitted by the appliance to the dentition; or 2) accumulated material damage from removal and replacement of the retainer that eventually results in fracture of the labial bow. This paper reports the results of a series of experimental studies; the overall objective was the optimization of the appliance design, focusing on the labial bow. Wire size, material, temper, canine-loop height, markings for bend placements, heat-treatment of the prepared bow, and two procedures for removing and replacing the appliance were investigated. The collective outcomes suggest a combination of design-parameter values to help maximize the life of the labial bow of the retainer.

Clinical acceptability of orthodontic retainers fabricated from stored alginate impressions

The purpose of this study was to determine the clinical acceptability of orthodontic retainers fabricated from stored alginate impressions. In the laboratory, alginate impressions were made of a standard dentoform. In the clinic, maxillary alginate impressions were made of the teeth of 20 dentate adults. In each case, sets of stone models were made either immediately or after the impressions had been stored for 24 or 72 hours at high humidity. The linear dimensions of the three sets of dentoform models were compared with one another and with the standard dentoform. No differences were found. Claspless acrylic retainers were fabricated on the models from the adult subjects. The retainers were positioned in the subjects' mouths and evaluated for snap fit, stability, cervical margin fit, and self-retention. With the use of these criteria, 95% of the retainers made from impressions that were poured immediately were clinically acceptable. When impressions were stored 24 and 72 hours, the percentages of acceptable retainers were 80% and 90%, respectively. The differences in percentage of clinically acceptable retainers were not statistically significant. When impressions are stored at high humidity, a large percentage of clinically acceptable orthodontic retainers can be made from models poured as long as 72 hours after the impression is made.

Attachment of swing-lock labial bar to an existing removable partial denture: A clinical report

Although the swing-lock buccal or labial bar is often used as a periodontal splint for mobile teeth, it may also function as an orthodontic retainer to inhibit tooth migration of poorly aligned teeth. The labial bar may be added to an existing removable partial denture if there is sufficient bulk of acrylic resin in the denture bases to accommodate the hinge and latch.

Aerodynamic and palatographic characteristics of the early stages of speech adaptation to a dental appliance

Subjects were recorded speaking with a dental appliance, similar to an orthodontic retainer, which had 4 mm of thickness in the alveolar region. Comparisons were made between initial attempts to speak with such an appliance and speech after two weeks of adaptation. Data consisted of oral air flow, peak intraoral pressure, dynamic electropalatography and the microphone signal. Focus was on /s/ in VCV contexts. The very first utterance showed deviations in timing of airflow characteristics in relation to devoicing, which were rapidly corrected. Aerodynamic and palatographic evidence of smaller articulatory constriction for /s/ was also seen initially, but this feature was not adjusted adequately in the early speech attempts.

Management of oral self‐mutilation in neurologically impaired children

SUMMARYThe function and fabrication of a removable acrylic dental appliance useful in the hospital management of neurologically impaired patients who are unconsciously traumatizing their oral soft tissues has been described. This acrylic appliance is readily fabricated on a plas ter cast obtained from an alginate impression of the maxillary arch.The basic appliance design is a modification of the standard maxillary orthodontic retainer. The modification involves the placement of additional acrylic resin to cover the occlusal and facial surfaces of all the maxillary teeth. This configuration prevents the buccal mucosa and lips from becoming trapped between the maxillary and mandibular teeth. Extra acrylic resin is placed bilaterally over the occlusal surface of the last tooth in the arch. The additional acrylic resin opens the bite, thereby preventing self‐inflicted trauma to the tongue. Primary retention of the dental appliance is accomplished via a labial bow and strategically placed ball clasps. The appliance is maintained in the patient's mouth until the episodes of oral muscular activity are controlled.

Acid etch bonded cast orthodontic retainers

We have described a technique which involves the use of a cast orthodontic retaining appliance bonded by the acid etch technique and composite resin for semipermanent retention. The technique provides an alternative form of treatment which offers some unique advantages over previous retentive techniques.

Clinical experience with direct-bonded orthodontic retainers

The experience obtained in clinical evaluation of forty-three direct-bonded mandibular canine-to-canine retainers after a minimum observation period of 1 year (range, 1 to 2.5 years) is summarized. Results indicate that the bonded retainer has all the advantages of a fixed soldered retainer, in addition to being invisible. Patient acceptance was excellent, and the failure rate in terms of loose retainers was low. Also, for a number of other retention problems, direct bonding with different types of lingual wire seems to open up a range of promising new possibilities.

Ultrastructural vascular changes in pressure zones of rat molar periodontium incident to orthodontic movement: Per RyghScand. J. Dent. Res.80:307–321, 1972

Fixed retainers are widely used after orthodontic treatment, sometimes for extended periods, despite insufficient knowledge of their possible long-term adverse effects on the periodontium. The aim of this study was to evaluate whether bonded orthodontic retainers have an adverse long-term effect on the marginal bone levels of the mandibular front teeth.The study included 62 consecutive patients in 3 groups: (1) patients who underwent orthodontic treatment and wore a fixed retainer for 10 years, (2) patients who underwent orthodontic treatment but did not have a fixed retainer, and (3) untreated controls. The marginal bone levels were measured by cone-beam computed tomography 10 years after treatment. Additionally, multivariate data analysis was used to analyze possible correlations between the marginal bone levels at 10 years and the variables obtained from the study casts and profile radiographs.The results demonstrated a significantly lower marginal bone level on the buccal side of the mandibular front teeth in the orthodontically treated patients compared with the orthodontically untreated group. There was no difference in the marginal bone levels between the retainer group and the no-retainer group. Multivariate analysis indicated that a low marginal bone level was correlated with a basal open vertical relationship, posterior rotation of the mandible, pretreatment of the incisor protrusion, and extraction therapy.Within the limits of this research design, the long-term retention phase in general does not seem to cause any adverse effects on the marginal bone levels after 10 years.

Bandless but fixed retention

Recent reports have suggested that long-term retention may be required to prevent posttreatment changes. The bonded orthodontic retainer constructed from composite and multistrand orthodontic wire provides an esthetic and efficient system for maintained retention. The development, indications for use, and clinical techniques are described. The range of materials reported for clinical use in construction of bonded orthodontic retainers are reviewed. Recommendations based on the literature are made. This review implicates placement of insufficient resin or use of a resin with inadequate abrasion resistance in the failure of bonded fixed retainers. (AM J ORTHOD DENTOFAC ORTHOP 1995;108:207-13.)