Orthodontic Elastics Research Articles

In vitro assessment of the mechanical properties of latex and non-latex orthodontic elastics

The increased incidence of latex allergies has led to the development of non-latex orthodontic products. The purpose of this study was to compare the mechanical properties of latex and non-latex orthodontic elastics. The elastics tested were from 2 manufacturers (GAC and Masel) and made of 2 materials (latex and non-latex). The properties tested included cross-sectional area, breaking force, peak load, peak stress, stiffness, modulus, hysteresis, and 24-hour load relaxation. The data were analyzed with 1-sample t tests, an analysis of variance, and the Fisher PLSD test. Between GAC and Masel, the GAC non-latex elastics had greater breaking forces than did the Masel non-latex elastics. The Masel latex elastics had greater breaking forces than did the Masel non-latex elastics. The GAC non-latex elastics showed more viscoelastic properties than both the GAC latex elastics and the Masel non-latex elastics; however, the Masel elastics were more viscoelastic than the GAC elastics. Forces generated by the elastics decreased over 24 hours to an average load approximating 75% of the manufacturers' values (GAC latex, Masel latex, and Masel non-latex elastics) and to 60% for the GAC non-latex elastics. The mechanical properties of the non-latex elastics were not comparable to those of the latex elastics. Therefore, the clinical choice of elastics should be based on the patient's medical history and the specific mechanical properties of the type of elastic. (Am J Orthod Dentofacial Orthop 2001;120:36-44)

Optimization of orthodontic elastics

Optimization of orthodontic elastics

Calibration of force extension and force degradation characteristics of orthodontic latex elastics

The force-extension characteristics of orthodontic elastics made of natural rubber latex by 4 manufacturers were subjected to static testing under dry and wet conditions. The elastics consisted of 3 sizes: 3/16, 1/4, and 5/16 inch lumen sizes, each with forces specified according to the standard extension index of three times the lumen diameter. Most of the elastics did not match the specified index using the dry tests, but this should not be a serious clinical concern as all elastics showed acceptable regularity of force-extension characteristics. There was notable force degradation of all elastics when subject to water immersion, approximating 30% during the hour, but with an average less than 7% further loss up to 3 days. There were significant differences in force extension and force degradation characteristics between different extensions and force magnitudes for the elastics of the different manufacturers. It is suggested that the clinician could use the table of force degradation values for different extensions to select an appropriate elastic. (Am J Orthod Dentofacial Orthop 2000;118:280–7)

Expression of cathepsin K mRNA during experimental tooth movement in rat as revealed by in situ hybridization

The expression of cathepsin K, a novel collagenolytic enzyme specifically expressed in osteoclasts, was investigated in the rat maxillary dentoalveolar unit during experimental tooth movement by in situ hybridization histochemistry with a non-radioisotopic cRNA probe for rat cathepsin K. Orthodontic elastics were inserted into the interproximal space between the maxillary first and second molars of 7-week-old male SD rats according to Waldo’s method and sections prepared from tissues obtained at 12 hr, 1, 2, 3, 4, 7, and 12 days after orthodontic force application. Cathepsin K mRNA expression was detected in the mono- and multinuclear osteoclasts on the pressure side of the alveolar bone at 12 hr after force application, and the distribution and number of cathepsin K mRNA-positive osteoclasts increased time-dependently on the pressure side. At 3–4 days, a marked increase in cathepsin K mRNA-positive osteoclasts was found not only on the pressure side but also on the tension side of the alveolar bone in response to tooth movement. At 7–12 days, the cathepsin K mRNA-positive osteoclasts on both sides had disappeared. These findings suggest that the recruitment of osteoclasts on the pressure side begins during the initial stage of orthodontic tooth movement and the site-specific early induction of cathepsin K mRNA may cause an imbalance in the relative resorption activities on the pressure and tension side incident to such movement.

Mandibulomaxillary fixation with bone anchors and quick-release ligatures.

Mandibulomaxillary fixation (MMF) is an essential technique for accurate treatment of maxillary and mandibular fractures. Traditional techniques of obtaining MMF (circumdental wires and load-distributing arch bars with or without plastic splints) often work poorly in children and adults with partial or absent dentition, require significant operative time, are at risk for glove puncture, and are painful to patients at time of removal. We have developed two new techniques for the rapid establishment of MMF in all ages and all types of dentition with or without splints. These techniques use four bone anchors--two placed in the pyriform rim of the maxilla and two in the mandibular symphysis. "Microlugs" are anchors constructed from Luhr Witallium mesh and are fixated to bone with 0.8-mm microscrews in primary- and mixed-dentition patients. Mitek MiniGII bone anchors are placed for treatment of secondary-dentition patients. Central skeletal MMF is achieved by linking each maxillary bone anchor to each mandibular bone anchor with suture ligatures and heavy orthodontic elastics. In this study, 112 patients (age range, 15 months-75 years) with maxillary and mandibular fractures underwent central skeletal MMF with one of the two new techniques described. Central skeletal MMF was maintained intraoperatively and for up to 6 weeks postoperatively, according to pathological anatomy. Our techniques succeeded with primary, mixed, and secondary dentition, and with splints and dentures, resulting in functional bone healing in 110 of 112 patients. Malocclusion occurred in 2 patients (1.8%), constituting treatment failure. Microlug central skeletal MMF required 15 to 20 minutes to place, and Mitek anchor central skeletal MMF required 7 to 12 minutes to place. There were no glove punctures noted during the course of treatment. Patient satisfaction has been clearly superior with these two techniques, since MMF amy be released in the office with minimal discomfort, even without topical anesthesia.

Titanium implants and lateral forces. An experimental study with sheep.

The purpose of this study was to investigate the resistance of titanium implants to horizontal forces in a sheep model. Twenty implants were inserted into the foreheads of 5 sheep, 4 implants on each animal. After a healing period of 3 months, abutments were mounted on the implants. After a further healing period of 3 weeks, the implants were loaded with a horizontal pull of orthodontic elastics. The force varied between 250 and 350 grams. The duration of loading was 3 months. After the loading period the animals were sacrificed and the forehead bones with implants were fixed in formalin and evaluated histologically. In the histological specimens no signs of infection or bone loss were found around the implants. The results of the present study encourage the use of titanium implants also in cases where constant lateral forces are present.

Guided periodontal tissue regeneration in interproximal intrabony defects following treatment with a synthetic bioabsorbable barrier.

This study evaluated guided periodontal tissue regeneration (GPTR) wound healing in interproximal intrabony periodontal defects following surgical treatment with a synthetic bioabsorbable barrier made from a copolymer of glycolide and lactide. Periodontal lesions were induced around the mandibular central incisor teeth of 10 adult male rhesus monkeys using orthodontic elastics. Once similar contralateral interproximal defects had been created, the elastics were removed and an oral hygiene program was initiated and maintained until completion of the study. Three weeks after commencing oral hygiene, flap surgery was performed in the mandibular incisor region and the root surfaces were thoroughly scaled and root planed to the apical portion of the defects. On the test sites, a bioabsorbable barrier was placed over the entire interproximal periodontal defect. Control sites did not receive a barrier. Five months after surgery, the animals were sacrificed and the teeth with their supporting periodontium were processed for light microscopic evaluation. Postoperative clinical healing progressed uneventfully and was similar in both control and test sites. Histologic observations from control specimens indicated reparative healing characterized by a long junctional epithelium with limited cementum and bone formation. Test specimens exhibited significantly more new connective tissue attachment, cementum deposition, and bone formation than the control sites (P < 0.001). The barriers had been completely resorbed with no apparent adverse effect on periodontal wound healing. It was concluded that this bioabsorbable barrier facilitated GPTR wound healing in interproximal intrabony periodontal defects.

Guided periodontal tissue regeneration in Class II furcation defects following treatment with a synthetic bioabsorbable barrier.

The purpose of this study was to evaluate guided periodontal tissue regeneration (GPTR) wound healing in Class II furcation defects following surgical treatment with a synthetic bioabsorbable barrier manufactured from a copolymer of glycolide and lactide. Periodonal lesions were induced in four adult male rhesus monkeys around the mandibular first, second, and third molar teeth using orthodontic elastics. After obtaining approximately 30% bone loss, the elastics were replaced by a stainless steel wire which had a projection extending into the furcation. Once similar contralateral Class II furcation defects had been created, the wires were removed, and an oral hygiene program was initiated and maintained until completion of the study. Three weeks after commencing oral hygiene, flap surgery was performed in the mandibular molar region and the root surfaces were thoroughly scaled and root planed to the apical portion of the defects. A bioabsorbable barrier was then placed to cover the furcation defects on one side of the jaw (i.e., test sites). No barriers were placed on the contralateral molars (i.e., control sites). Five months after surgery, the animals were sacrificed and the teeth with their supporting periodontium were processed for light microscopic evaluation. Clinical healing progressed normally and was similar in both groups. Histologic observations from control specimens indicated repair with epithelium and connective tissue occupying the majority of the furcation defects. Test specimens exhibited definitive evidence of regeneration with significantly greater new connective tissue attachment, cementum deposition, and bone formation than the control sites (P < 0.001). It was concluded that this bioabsorbable barrier facilitated GPTR wound healing in Class II furcation defects.

Mechanical Properties of a New Orthodontic Elastic Chain

Mechanical Properties of a New Orthodontic Elastic Chain

New bone formation by biological rhythmic distraction.

Bone regeneration by distraction has become an accepted method for correction of congenital and acquired deformities. Unifocal bone generation is discussed as a technical note to demonstrate its feasibility in craniofacial surgery. The technique is simplified by the reorientation of the apparatus used, and the distraction is performed over a period of time to achieve a balance in the facial skeleton. Orthodontic elastics are used to balance the occlusion.

Non-human primates used in studies of periodontal disease pathogenesis: a review of the literature.

The inability to examine initiation and progression of periodontal disease and to assess certain therapies in humans has led to a great interest in the use of animal models in periodontal research. Some of the most prominent animals used are non-human primates. This article reviews the characteristics of non-human primate models in periodontal health, in the transition from health to gingivitis to periodontitis, and in experimental gingivitis and periodontitis. Where possible, the results of these studies are compared with results from human studies. Only a few studies have compared in detail the anatomy, physiology, immunology, and tissue interactions in monkeys with those of humans. With the exceptions of differences and variations in size of the dentition, the number of each tooth type as well as larger canines, presence of diastemata between anterior teeth, and an edge-to-edge relationship of the incisors, the dental and periodontal anatomy of non-human primates seem quite similar to that of humans. Clinically healthy gingiva can be established and maintained in non-human primates, and gingivitis as well as periodontitis occur in these animals. It is possible to induce experimental periodontitis by placement of peri-dental silk ligatures or orthodontic elastics as well as by surgical removal of alveolar bone. Although the most appropriate model for studies of periodontal disease pathogenesis in non-human primates appears to involve the application of silk ligatures, some difficulties may occur in establishing periodontal break-down by using this model. Many clinical, histological, microbiological, and immunological characteristics of spontaneous and experimental marginal inflammation in most non-human primates are similar to those in humans. The most significant differences between small non-human primates and humans are the very limited number of lymphocytes and plasma cells in the inflammatory infiltrate of squirrel monkeys (Saimiri sciureus) and marmosets. Therefore, the use of squirrel monkeys and marmosets may not be appropriate in many studies of periodontal disease pathogenesis. The most significant microbial differences between macaque species and humans are a lower proportion of Actinomyces species, the presence of a catalase-producing Prevotella melaninogenica strain, and the high carrier rate for Actinobacillus actinomycetemcomitans in subgingival plaque of macaque species. The significance of these differences is presently unknown. It is concluded that the use of many non-human primate species due to the apparent close anatomic and biologic similarities to humans is appropriate in experimental studies of periodontal disease, provided the use of laboratory animals is requisite and lower species are not applicable.(ABSTRACT TRUNCATED AT 400 WORDS)

The effect of repeated stretching on the force decay and compluance of vulcanized cis-polyisoprene orthodontic elastics

Compliance measurements, used in the past to measure the viscoelastic properties of dental impression materials, were used to assess these properties in vulcanized cis-polyisoprene orthodontic elastics, and the results were compared with traditional force decay measurements. Both methods were also used to evaluate the effect of repeated stretching on these elastics. Compliance measurements successfully characterized the viscoelastic behavior of the elastics, and the results agreed with force decay measurements. Repeated stretching significantly reduced the force and the compliance of the elastics. There was no statistical difference in the force or compliance measurements after the elastics were stretched more than 200 times. Stretching for 1000 cycles of 400% extension reduced elastic force by approximately 12%.

Maxillary osteotomies without postoperative intermaxillary fixation (anterior, superior and inferior repositioning of entire maxilla). A clinical and cephalometric study.

Surgical correction of maxillary anomalies with anterior-superior or anterior-inferior repositioning of the segment was performed in 50 patients. The maxillary segment was stabilized by means of steel wires as horizontal mattress sutures, which, in all cases, gave very good primary stability. In case of insufficient bone contact miniplates were used. Postoperatively no rigid intermaxillary fixation (IMF) was applied. There are several advantages to not using intermaxillary fixation: 1) It is possible to carry out immediate postoperative inspection of the location of the condyles and thereby confirm that the segments are in the expected position. 2) Segment fixation is not disturbed by mandibular movements during recovery from general anaesthesia. 3) Manipulations by the anaesthesiologist immediately after surgery are not interfered with. 4) For the patient there is better postoperative comfort with no breathing, talking or feeding problems. 5) Minor corrections of intercuspation by means of orthodontic elastics are possible. These can act in the required direction and will not disturb the masticatory function. Masticatory function was resumed immediately after surgery and was usually normalized within 2-3 weeks. Cephalometric analysis revealed no significant relapse subsequent to surgery. Thus we conclude that omitting IMF, among other advantages, enhances patient comfort and has no negative effect on the postoperative stability of the maxilla.

Forces produced by orthodontic elastics as a function of time and distance extended.

Four types of elastic used in our clinic were tested for stiffness as a function of time and distance extended. The measurements were taken in vitro in a simulated mouth environment. The stiffness decreased rapidly in the first three hours but from this time to 8 hours, the stiffness did not change greatly.

New attachment formation on teeth with a reduced but healthy periodontal ligament.

The present investigation was undertaken to examine whether a new connective tissue attachment will form on previously periodontitis-involved roots when reduced but healthy periodontal ligament tissue persists following periodontal treatment and the epithelium is prevented from migrating into the wound. In each of 4 monkeys, periodontal tissue breakdown was induced around one maxillary and one mandibular second premolar or first molar by placing orthodontic elastics around the teeth. The elastics were kept in situ until about 50% of the supporting tissues had been lost. 3 months following removal of the elastics, the crowns of the teeth were resected. The pocket epithelium and subjacent granulation tissue were excised and the cementum of the periodontitis-involved part of the roots was removed using a diamond bur. The roots were covered with a mucosal flap. The animals were sacrificed after 3 months of healing. The jaws were removed and histological sections of the experimental roots including their surrounding periodontal tissues were produced. The microscopic analysis disclosed that in all roots, new cementum with inserting collagen fibers had formed in the apical portion of the previously exposed root surfaces. It was always in continuity with the original cementum layer apical to the instrumental part of the root and was thickest in its apical portion, becoming gradually thinner in the coronal direction. In the roots, which for the entire length of the study remained covered by the oral mucosa, the extension in the coronal direction of this newly formed fibrous attachment amounted to an average of 1.0 mm with a range from 0.1 mm to 2.6 mm. These findings were interpreted to mean that new attachment is formed by coronal migration of cells originating from the periodontal ligament.

Factors influencing periodontal repair and regeneration.

The purpose of the present study was to evaluate independently the regeneration capacity of a reduced periodontium, and the potential for new connective tissue attachment to a periodontally exposed root surface. A reduced periodontium was produced around a maxillary central incisor in two Rhesus monkeys using orthodontic elastics. The regeneration capacity of this reduced peridontium was investigated by extracting the periodontally involved tooth and transplanting into the socket the contralateral incisor which had a normal periodontium. The potential for new connective tissue attachment to a periodontally exposed root surface was evaluated by transplanting an exposed root into a normal periodontium. These exposed roots were the incisors extracted from the reduced peridontium. Control specimens were obtained by extracting and reimplanting or transplanting the remaining maxillary and mandibular incisors. Forty days after the experimental procedures, block sections were removed and prepared for histologic analysis. The exposed root surface that had been put into the normal periodontium was lined with epithelium interposed between root surface and alveolar bone. The normal root surface that had been put into the reduced periodontium had connective tissue reattachment in the periodontal ligament and supracrestal regions. Areas of ankylosis and root resorption were present in all specimens, as was new cementum in the periodontal ligament region. The results indicated that root surface alterations, rather than presence of a reduced periodontium, inhibited new connective tissue attachment.

Bone regeneration in alveolar bone dehiscences produced by jiggling forces.

The aim of this experiment was to achieve support for the hypothesis that bone resorption, induced by jiggling forces, leaves a component within the supracrestal soft tissue with a capacity of reforming bone. The maxillary lateral incisors and first premolars and the mandibular second premolars in two monkeys were used in the study. Using metal pins inserted into the neighboring teeth as retainers, orthodontic elastics were stretched and placed alternately around the buccal and lingual surfaces of each experimental tooth in order to produce jiggling forces. After 5 months of continuous jiggling, when bone dehiscences were produced on the buccal aspect of the teeth, the elastics were removed. After repositioning of the teeth a split thickness flap was raised. On one side of the jaw the soft tissue within the bone dehiscences was removed. At the contralateral teeth a sham operation was performed maintaining the soft tissue within the bone dehiscences. The monkeys were sacrificed 6 months after surgery. Tissue blocks containing test and control specimens were dissected free and prepared for microscopic analysis. The length of the supracrestal connective tissue attachment and the amount of coronal bone regeneration were assessed in the histological sections. It was found that buccal alveolar bone, reduced in height by jiggling forces, regenerated after discontinuation of the forces. When the soft tissue within the buccal bone dehiscences produced by the jiggling forces was surgically removed, the coronal regeneration of the alveolar bone was markedly reduced. These observations suggest that bone resorption, induced by jiggling forces, leaves a soft tissue component with a capacity of forming bone.

Healing following surgical treatment and root demineralization in monkeys with periodontal disease.

Abstract The aim of the present investigation was to study the potential for new attachment to root surfaces which 1) had become devoid of attachment either by mechanical removal or in conjunction with experimental periodontal tissue breakdown and 2) subsequently had been conditioned with citric acid. Three adult monkeys (Macaca cynomolgus) were used. Periodontal pockets were produced during a 2–6‐month period around the maxillary central incisors and first and second premolars and around the mandibular central incisors by the placement of orthodontic elastics. Surgical treatment of the pockets was carried out with the use of a flap procedure. During surgery, the roots of the premolars on the right side of the jaws were first scaled and planed and subsequently treated with citric acid. Citric acid conditioning was not performed on the premolars of the left side. In the front tooth regions the surgical treatment included citric acid conditioning of the mandibular central incisors in two animals and of the maxillary central incisors in one animal.Surgical procedures were also carried out around the mandibular second premolars and first molars which had not been exposed to periodontal tissue breakdown. Folio wing flap elevation, the buccal bone plate was mechanically removed within an area corresponding to that of bone loss produced by the experimental periodontitis model in the maxillary premolars. The cementum layer of the surgically denuded portion of the roots was removed by root planing.In all treated teeth, a notch was prepared in the buccal root surfaces at the level of the alveolar bone crest. Six months following treatment the animals were sacrificed and histologic sections prepared. Linear measurements were made along the root surface from the apical border of the prepared notch to the apical termination of the junctional epithelium and to the crest of the alveolar bone.The results demonstrated that cementum formation and new connective tissue attachment did not occur on root surfaces previously exposed to periodontal pockets and subsequently subjected to scaling and root planing or on root surfaces surgically deprived of their supporting bone and previously “non‐exposed” cementum layer. Cementum formation and new connective tissue attachment also failed to occur following citric acid conditioning of root dentin surfaces. In all sections representing all three treatment groups, the attachment between the gingiva and the root was established by epithelium.

Healing following implantation of periodontitis-affected roots into gingival connective tissue.

The aim of the present investigation was to examine if a new connective tissue attachment can be established on a previously periodontitis involved root surface, located in contract with gingival connective tissue during healing. A total of 28 teeth in one dog (beagle) and two monkeys (Macaca cynomolgus) were subjected to experimental periodontal tissue breakdown by placing cotton floss ligatures or orthodontic elastics around the teeth. The ligatures were left in situ until about 50% of the supporting tissues had been lost. Following resection of the crowns, the teeth were root filled and the exposed parts of the roots thoroughly scaled and planed. Each root was extracted and implanted into grooves prepared in edentulous areas of the jaws in such a way that the root was embedded to half its circumference in bone, leaving the remaining part to be covered by the gingival connective tissue of the repositioned flap of the recipient site. Root implantation and sacrifice of the animals were scheduled to allow for observation periods of 2 and 3 months of healing. An analysis of histologic specimens, obtained from biopsies of the recipient site tissues, disclosed that a new fibrous attachment failed to form on a previously "exposed" root surface located in contact with gingival connective tissue. In areas of the roots where the periodontal ligament tissue was preserved prior to transplantation, a fibrous reattachment occurred between the root and the adjacent gingival tissue. The results indicate that gingival connective tissue does not possess the ability to establish conditions which enable the formation of a new connective tissue attachment.

Magnetic force in orthodontics

apy. The present study shows that small permanent magnetic devices offer a new, innovative, and biologically safe approach in generating intermaxillary, intramaxillary and extraoral force. Present methods of treatment, especially with elastics, may be satisfactory, but problems do exist. For example, lack of cooperation on the part of the patient can result in either failure or compromise of treatment objectives. Polygraph studies at Loyola University emphasized this lack of cooperation by showing that adults as well as children were often not reliable in using elastics is $ in fact, those patients were carefully selected prior to treatment for good motivation and were usually thought by their orthodontists to be cooperative. Magnets can eliminate this problem of the patient’s cooperation, since they are totally operator-controlled. Continuous application of force results in decreasing treatment time. Lengthy treatment can produce periodontal disturbances, root resorption, and caries. A shorter treatment time may make orthodontic therapy available to a wider spectrum of the population. Permanent magnets can also provide better directional force control. For example, with mandibular opening, when magnets are used for intermaxillary force, the air gap increases, and the vertical component of the force vector decreases rapidly, first as the square and then as the cube of the distance. This is an advantage over the use of elastics, with which the vertical force vector increases upon mandibular opening, thus producing an undesirable increase in the cant of the occlusal plane. Magnets can also be used for continuous high-deflection, low-rate force with precise control. Proper momentto-force ratios can be achieved, and tipping, root translation, and root torquing are also Possible. It is a total force system with a favorable benefit-to-risk ratio. Intermaxillary elastics also account for the loosening of bands because of the large vertical vector of force. On the other hand, magnetic devices generate a more horizontal force vector, which does not tend to unseat bands. Obviously, loose bands require much time for re-cementation, and also increase the patient’s susceptibility to caries. Talc and starch may have been used as dusting powders on orthodontic elastics, and, as reports in the medical literature have indicated for some time, these agents, in a medical situation, may be related to granulomatosis, pulmonary talcosis, immunogenic reactions, md, possibly, carcinoma. 3~8 Some of these reactions demonstrate a clinical latency so that they may not appear for many years after the patient’s initial exposure. In addition,