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As orthodontists, we are often unaware of the technical and methodological advances in other dental specialities. However, many of these new experimental developments may ultimately become accepted dental therapy and influence the diagnosis and treatment of our orthodontic patients. Therefore, as part of the dental community, we must keep abreast of current information in all areas of dentistry. The purpose of this section of The Angle Orthodontist is to provide a brief summary of what's new in dentistry.

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Orthodontists are concerned about the possibility of a link between the treatment they provide and temporomandibular disorders (TMD). The purpose of this article was to review the literature relating malocclusion and orthodontic treatment to problems of the temporomandibular joint (TMJ) and surrounding anatomy. In Part 1, the relationship of orthodontic treatment to TMD is discussed. In Part 2, the relationship of TMD to malocclusion will be addressed.

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In this second of two articles, the role of occlusion and malocclusion is assessed with respect to orthodontics and temporomandibular disorders (TMD). Some have suggested that malocclusion may cause TMD, or that by introducing a form of malocclusion, orthodontic treatment could be iatrogenic. Pertinent evidence relating to these issues will be assessed.

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The risk of serious eye injury caused by a headgear appliance is a significant concern. Various safety release mechanisms have been developed in order to help prevent this type of injury, but little testing has been done. The purpose of this study was to test 18 headgear release mechanisms. Four characteristics were evaluated: force at release, extension at release, consistency of release, and performance at different rates of pull. At the point of release, mean force values ranged from 5.33 pounds to 32.83 pounds, and mean extension values ranged from 0.84 inches to 2.93 inches. Consistency was based on the percent standard deviation, and the appliances were ranked relative to each other. Nine of the 18 appliances had statistically significant differences in the two pull rates for either variable or both, but the clinical significance is uncertain. The results show a wide range of performance among the 18 appliances tested and indicate that some perform better than others.

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Mandibular deficiency may be a factor in reduced oropharyngeal airway (OAW) dimensions and related impaired respiratory function. The purpose of this study was to evaluate the use of functional-orthopedic devices in increasing OAW dimensions in children with Class II skeletal patterns (ANB>4) and clinically deficient mandibles. Comparisons were made between two groups, one comprising 26 treated patients and the other comprising 15 controls. Student's t-tests, paired t-tests, discriminant analyses, and Pearson's r-correlation coefficients were performed to evaluate group differences and to search for characteristics that might suggest which patients would be better candidates for significant increase in OAW dimensions. Compared with controls, OAW dimensions increased significantly in treated patients, especially those with sagittally smaller and more retrognathic maxillomandibular complexes and smaller OAW dimensions.

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Flat rectangular tabs (n=270) prepared from spherical (Tytin), admixed (Dispersalloy) or lathe-cut amalgam (ANA 2000) were subjected to aluminum oxide sandblasting with either 50-µ or 90-µ abrasive powder. Mandibular incisor edgewise brackets were bonded to these tabs. An intermediate resin was used, either All-Bond 2 Primers A + B or a 4-META product—Amalgambond Plus (AP) or Reliance Metal Primer (RMP)—followed by Concise. All specimens were stored in water at 37°C for 24 hours and thermocycled 1000 times from 5°C to 55°C and back before tensile bond strength testing. The bond strength of Concise to etched enamel of extracted, caries-free premolars was used as a control. Bond failure sites were classified using a modified adhesive remnant index (ARI) system. Results were expressed as mean bond strength with SD, and as a function relating the probability of bond failure to stress by means of Weibull analysis. Mean tensile bond strength in the experimental groups ranged from 2.9 to 11.0 MPa—significantly weaker than the control sample (16.0 MPa). Bond failure invariably occurred at the amalgam/adhesive interface. The strongest bonds were created to the spherical and lathe-cut amalgams (range 6.8 to 11.0 MPa). Bonds to the spherical amalgam were probably more reliable. The intermediate application of the 4-META resins AP and RMP generally created significantly stronger bonds to all three basic types of amalgam products than the bonds obtained with the All-Bond 2 primers. The effect of abrasive-particle size on bond strength to different amalgam surfaces was not usually significant (p>0.05). The implications of these findings are discussed in relationship to clinical experience bonding orthodontic attachments to large amalgam restorations in posterior teeth.

For Part 1, see: Zachrisson BU, Büyükyilmaz T, Zachrisson YØ. Improving orthodontic bonding to silver amalgam. Angle Orthod 1995;65:35–42.

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This laboratory study compared the mean tensile bond strength, mode of band failure, and survival time of orthodontic bands cemented with dual-cured cement or conventional glass ionomer cement. Survival time was assessed following application of mechanical stress in a ball mill. Mean tensile bond strength was significantly higher for bands cemented with the dual-cured cement (p<0.01), and mean survival time was significantly greater. Bands cemented with glass ionomer failed mainly at the cement/band interface. The results suggest that dual-cured cement is superior to glass ionomer for band cementation.

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The purpose of this study was to investigate the time to first failure of stainless steel orthodontic brackets (Ormco Corp, Glendora, Calif) bonded with a light-cured resin adhesive (Transbond, 3M Unitek, Monrovia, Calif) and assess whether time to failure was related to the patient's age at the start of treatment or sex, the proficiency of the individual placing the brackets, or the presenting malocclusion. Data on 548 patients with 7118 bonded brackets were analyzed. Survival analysis was carried out on a single bracket per patient. In each patient, the first bracket to fail was studied. In cases where no brackets failed, the bracket with the shortest follow-up time was analyzed and handled as a censored observation in the formal analysis. Median time until first bracket failure was 442 days, and an overall failure rate of 6% was recorded. There were no significant differences in time to first failure of brackets with respect to the sex or age of the patient at the start of treatment p=0.168, and p=0.261, respectively), operator proficiency in placing brackets (p=0.189), or presenting malocclusion p=0.052). Performance of brackets bonded with Transbond does not appear to vary significantly according to the variables examined.

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To investigate responses to longitudinal torsion and the effect of temperature on the torsional stiffness of superelastic nickel titanium archwires, eight batches of rectangular wires were tested at 18, 27, 37, and 40°C ambient temperature. The wires were twisted 25 degrees and studied in deactivation. The resulting torque-twist diagrams show that only half the wires had discernible deactivation plateaus at body temperature. The plateaus were generally narrow (1 to 3 degrees) and started at 20 to 23 degrees of torsional twist. The clinical significance of these deactivation plateaus is debatable. Only one wire had a well-defined plateau that was fairly wide (6 degrees) and started at a lower level of twist (17 degrees). The wires without plateaus when deactivated from 25 degrees of twist were retested at body temperature. All exhibited deactivation plateaus subsequent to activating twists of 45 and 60 degrees, and the plateaus became more distinct as the degree of prior activation increased. This indicates that the stress imparted on the alloys by 25 degrees of activating twist is insufficient to induce martensitic transformation at body temperature. As prescriptions advocate bracket pretorque of less than 25 degrees for a maxillary central incisor, the clinical relevance of alloys requiring large activations before they demonstrate deactivation plateaus is questionable. Half the wires tested were markedly influenced by ambient temperature changes; the other half were relatively insensitive to temperature. Responsiveness to thermal stimuli seemed closely related to superelastic tendency.

Abstract

Due to their exceptional temperature sensitivity, superelastic nickel titanium wires may be affected by temperature changes associated with ingestion of cold or hot food. It has been assumed that the alterations in archwire stiffness associated with short-term cooling or heating are transient. This investigation studied the effect of these temperature changes on the torsional stiffness of nickel titanium alloys. Eight rectangular superelastic wires were activated to 20 degrees, in longitudinal torsion at body temperature and subjected to cold (10°C) or hot (80°C) water with the strain held constant. The torsional stiffness of some wires was strongly affected. The effect of hot water disappeared quickly, but the wires remained at a level of reduced torsional stiffness (up to 85% less than baseline) after short applications of cold water. The most thermodynamic archwires showed incremental reductions in torsional stiffness when cold water was repeatedly applied. Furthermore, the torsional stiffness remained low (up to 50% less than baseline) and showed no tendency to increase even after 2 hours of post-exposure restitution. It is conceivable that some wires may provide inadequate forces for tooth movement after ingestion of cold liquids.

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No Abstracts Available