The in vitro biomechanics of anterior arch expansion using fixed lingual appliances with coil springs or archwire stops.

INTRODUCTION: The presented study investigates differences in the biomechanics of straight and mushroom fixed lingual appliances when implementing coil springs and stops for anterior arch expansion. MATERIALS AND METHODS: An in vitro orthodontic simulator was used to measure three-dimensional forces and moments on each tooth of a simulated maxillary arch. Mushroom and straight archwire forms of 0.016″ NiTi round archwire were considered, using 0.010″ × 0.030″ NiTi open coils and 0.016″-0.018″ archwire stops (n = 44 per group). Teeth in the anterior dental arch were moved from a neutral to crowded position to replicate anterior crowding of central and lateral incisors. Forces and moments of interest for lateral incisors and first premolars were compared using repeated measures mixed multivariate analysis of variance (α = 0.05). RESULTS: Three comparisons between straight versus mushroom archwires and two comparisons of coil springs vs. stops were not statistically significant. Overall, it was found that the use of a straight lingual archwire produced larger differences in forces and moments between using stops and coil springs than when using a mushroom archwire. Using stops produced larger forces and moments for both types of archwires as compared to using coil springs. The largest expansion forces were produced using straight archwires with stops, exceeding 3.0 N of force. Straight archwires with coil springs produced the lowest expansion forces on lateral incisors, just exceeding 1.5 N. CONCLUSIONS: The findings of this study have elucidated significant differences in the biomechanics of transverse arch expansion using straight or mushroom fixed lingual appliances with coil springs or stops.

Is it safe to place implants in patients at risk of MRONJ?

Data sources Four electronic databases, namely PubMed, Scopus, Web of Science and the Cochrane Central Register of Controlled Trials, were searched from their inception to 16 July 2019. The OpenGrey database was also used to identify unpublished studies.Study selection Eligible study designs included randomised controlled trials, cohort studies, case-control studies and case series with a retrospective, cross-sectional or prospective design related to implant placement in patients with a history of anti-angiogenic or antiresorptive medications. Selection was conducted by two independent reviewers; however, if a consensus was not reached, a third reviewer was involved. Studies required a minimum of five patients with a history of antiresorptive or anti-angiogenic drug therapy before implant placement and strict criteria were used to ensure studies reported sufficient data items for discussion. Only full papers in the English language were included.Data extraction and synthesis A total of 6,073 papers were initially identified following removal of duplicates and 29 of these met the inclusion criteria for this systematic review. Twenty-eight reported on bisphosphonates which included five cohort studies, six case-control studies and 17 case series. A single case series reported on denosumab and no studies were identified reporting on selective oestrogen receptor modulators, calcitonin or anti-angiogenics. The quality of the included cohort and case-control studies were assessed by applying the modified Newcastle-Ottawa scale while the case series were assessed according to the Joanna Briggs Institute critical appraisal checklist. A score of <50% was considered to indicate low quality, 50-70% moderate quality and >75% high quality. A standardised Microsoft Excel spreadsheet was used to extract data from the studies which included study design, number of cases, implants and controls, patient characteristics (systemic diseases/age/gender/smoking status), drug history (type of drug, indication, administration route, intake before implant placement), whether patients were taking the drug at the time of implant placement and follow-up, reported outcome and parameters (implant loss, failure, success, survival and incidence of medication-related osteonecrosis of the jaw [MRONJ]). Where data was missing, estimations were calculated and a qualitative synthesis of all data was performed.Results No single study reported all the relevant data required by the authors and the overall level of quality was moderate. Regarding implant failure, patients with a history of bisphosphonates for osteoporosis are not at increased risk. However, insufficient data was available for those with a history of bisphosphonates for cancer, or any other antiresorptive or anti-angiogenic medications. Comparing this to MRONJ, patients with a history of bisphosphonate treatment are at risk of developing MRONJ following implant placement, while those with a history of denosumab for osteoporosis have a negligible risk. There was insufficient data available to assess the risk of MRONJ for those with a history of denosumab for cancer or other antiresorptive or anti-angiogenic medications.Conclusions Patients with a history of bisphosphonate treatment are at risk of MRONJ following implant placement while patients who take bisphosphonates for osteoporosis are not at increased risk of implant failure. There is a negligible risk of developing MRONJ in those taking denosumab for osteoporosis. However, practitioners should bear in mind a lack of high-quality evidence regarding the safety of placing implants in patients with a history of antiresorptive or anti-angiogenic medications.

Are COVID-19 test results masking important issues?

Basic health and infection control measures are the main methods of protection against COVID-19. Patients are well informed about how practitioners should be conducting themselves, however, they may lose trust in clinicians who fail to demonstrate, and promote those same basic prevention measures. The broader COVID-19 strategy has included the rapid development and deployment of swabs and antibody tests. Flaws in testing fail to offer assurances due to false negatives while even true positives cannot guarantee future immunity as there is uncertainty regarding long-term antibody response. An understanding of human factors and an appreciation of the limitations of available tests could offer healthcare staff mechanisms to encourage safety.

Measurement of forces and moments around the maxillary arch for treatment of a simulated lingual incisor and high canine malocclusion using straight and mushroom archwires in fixed lingual appliances.

INTRODUCTION: An Orthodontic SIMulator (OSIM) was used to investigate the propagation of forces and moments around a simulated archform for a gingival displaced canine and lingual displaced lateral incisor using fixed lingual orthodontic appliances. METHODS: In-Ovation L self-ligating lingual brackets were bonded to anatomically shaped teeth on the OSIM, and the teeth were positioned such that a G4 NiTi 0.016" large maxillary mushroom archwire could be ligated in passive position. Each trial consisted of two movements: a 3mm lingual displacement of the 1-2 lateral incisor at 0.2 mm increments, and a 1.5 mm gingival displacement of the 2-3 canine at 0.15 mm increments (n = 50). Anterior brackets were repositioned to accommodate G4 NiTi 0.016" universal straight archwires (n = 50). Tests were completed at 37°C, and force and moment data in all directions was collected for each tooth around the arch at all increments. RESULTS: In general, the straight archwire produced significantly larger forces and moments at the centre of resistance for teeth of interest than did mushroom archwires. Specifically, the straight archwire produced 2.62 N and 3.81 N more force in the direction of tooth movement on the tooth being moved for a gingival displaced canine and lingual displaced lateral incisor, respectively, as compared to mushroom archwires. CONCLUSIONS: Results from this study suggest that mushroom archwires may provide better mechanics for movement of teeth in the anterior segment when using a round archwire; however, only biomechanical data was considered in this study and there are many factors that need to be considered in treatment planning.

Testing children's ability to correctly use the "Shadow Rule" for sun protection.

INTRODUCTION: The "Shadow Rule" (SR) is a useful, immediate indicator of sunburn risk following the mnemonic "Short shadow? Seek shade!" However, some question people's ability to discern when their shadows are shorter or longer than them. METHODS: N = 76 10-year-old children were taught the SR and then asked to estimate their sun-cast shadow length relative to their height and whether this meant they should seek shade. Children were then asked to estimate a doll's shadow length at 10 systematically randomised angles. RESULTS: Children experienced greatest difficulty judging their shadows' lengths when they were equal to their height. At all other angles, they demonstrated high accuracy and 92 % of the time on average could correctly interpret the SR. CONCLUSIONS: Ten-year-old children appear capable, and by extension adults too, of applying the SR. Future research is now required to establish if education about the SR will translate into sun protection behaviour change.

The biomechanics of posterior maxillary arch expansion using fixed labial and lingual appliances.

OBJECTIVE: To compare the biomechanics of straight labial, straight lingual, and mushroom lingual archwire systems when used in posterior arch expansion. MATERIALS AND METHODS: An electro-mechanical orthodontic simulator allowing for buccal-lingual and vertical displacements of individual teeth and three-dimensional force/moment measurements was instrumented with anatomically shaped teeth for the maxillary arch. In-Ovation L brackets were bonded to lingual surfaces, and Carriere SLX brackets were bonded to labial surfaces to ensure consistency of slot dimensions. Titanium molybdenum archwires were bent to an ideal arch form, and the teeth on the orthodontic simulator were set to a passive position. Posterior teeth from the canine to second molar were moved lingually to replicate a constricted arch. From the constricted position, the posterior teeth were simultaneously moved until the expansive force decreased below 0.2 N. Initial force/moment systems and the amount of predicted expansion were compared for posterior teeth at a significance level of α = 0.05. RESULTS: Archwire type affected both the expected expansion and initial force/moment systems produced in the constricted position. In general, the lingual systems produced the most expansion. The archwire systems were not able to return the teeth to their ideal position, with the closest system reaching 41% of the intended expansion. CONCLUSIONS: In general, lingual systems were able to produce greater expansion in the posterior regions when compared with labial systems. However, less than half of the intended arch expansion was achieved with all systems tested.

A protocol for determining the surface free energy of dental materials.

OBJECTIVE: The purpose of this study was to develop a standard methodology for measuring the surface free energy (SFE), and its component parts, of dental biomaterials. METHODS: The contact angle of each of four samples of two materials--low density polyethylene and poly(methyl methacrylate)--was measured three times in each of six liquids (1-bromonaphthalene, diiodomethane, ethylene glycol, formamide, glycerol and distilled water). Critical surface tension estimates were obtained from Zisman plots. Data were then analyzed by the least-squares method to estimate the components of SFE. Estimates were also made for each of 12 liquid triplets, and by maximum likelihood and Bayesian analyses. RESULTS: The use of liquid triplets could yield misleading estimates of the components of SFE. A testing protocol is suggested in which multiple test liquids are used, and multiple methods of statistical analyses employed. SIGNIFICANCE: SFE is important, in that high SFE is desirable when adhesion is required, but undesirable if plaque resistance is needed. Methodology that avoids some of the limitations of existing studies has been proposed.