Laboratory and intra-oral tests of the degradation of elastic chains

Two brands of elastic chain, Alastic (Unitek Co.) and Power Chain II (Ormco Co.), were tested for force development in laboratory and intra-oral experiments. During the laboratory test, the chains were extended to 180 and 215 per cent of their original passive length and the force exerted at this length was measured at the start and after 15 minutes, 2, 8 and 24 hours, 3 days and 1, 2, 3 and 4 weeks of continuous extension. The two brands behaved similarly. After 4 weeks, they had lost 25-30 per cent of their initial force. The decrease of the force value was greatest in the beginning of the test period, with a decline of 6-11 per cent during the first 15 minutes and 10-16 per cent during the first 2 hours. The intra-oral tests were performed in 10-25 subjects, who wore the elastic chains continuously for up to 4 weeks. The chains were extended up to 200 per cent of their original passive length. In one test, the force development was measured at the start and after 8 and 24 hours, 5 days and 1, 2, 3 and 4 weeks. In two other tests the force was measured after 1 day and 4 weeks, respectively. The two brands behaved similarly. The decline of the force value during intra-oral use was greater than in the laboratory tests. After 4 weeks, the force was only 43-52 per cent of the original value. The decline was greatest in the initial phase after insertion; after 8 hours the force had declined by 28-34 per cent. Thus, an initial force of 300g was reduced to 200g after 8 hours and to less than 150g after 4 weeks: in no specimen was the force after 4 weeks less than 100

Regional Nerve Block of the Temporomandibular Joint Capsule: A Technique for Clinical Research and Differential Diagnosis

In previous studies in which regional anesthesia of the temporomandibular joint capsule was used to examine the role of the joint in mandibular movement and distinguish it from muscle control, the anesthetic techniques used have not been satisfactorily described. The accuracy of the injeetion technique described in this paper was determined by dissection and radiographic examination of fixed and fresh specimens. Using this technique, trial patient studies were made using an anesthetic solution to which a radiopaque medium was added. Radiographic examination of the patients affirmed the location of the injected material, while clinical assessment determined its functional effectiveness. Using the described technique, anesthetic solution was accurately and reproducibly introduced posteriorly and laterally to the temporomandibular joint to achieve anesthesia of the joint.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/67376/2/10.1177_00220345800590110101.pd

Human mandibular shape is associated with masticatory muscle force

Understanding how and to what extent forces applied to the mandible by the masticatory muscles influence its form, is of considerable importance from clinical, anthropological and evolutionary perspectives. This study investigates these questions. Head CT scans of 382 adults were utilized to measure masseter and temporalis muscle cross-sectional areas (CSA) as a surrogate for muscle force, and 17 mandibular anthropometric measurements. Sixty-two mandibles of young individuals (20-40 years) whose scans were without artefacts (e.g., due to tooth filling) were segmented and landmarked for geometric morphometric analysis. The association between shape and muscle CSA (controlled for size) was assessed using two-block partial least squares analysis. Correlations were computed between mandibular variables and muscle CSAs (all controlled for size). A significant association was found between mandibular shape and muscle CSAs, i.e. larger CSAs are associated with a wider more trapezoidal ramus, more massive coronoid, more rectangular body and a more curved basal arch. Linear measurements yielded low correlations with muscle CSAs. In conclusion, this study demonstrates an association between mandibular muscle force and mandibular shape, which is not as readily identified from linear measurements. Retrodiction of masticatory muscle force and so of mandibular loading is therefore best based on overall mandibular shape

Correlations between EMG jaw muscle activity and facial morphology in complete denture wearers

In a sample of fifteen partially edentulous subjects assigned for immediate complete denture treatment, a correlation analysis was performed between pre-extraction facial morphology determined from lateral cephalograms, and EMG activity of the anterior temporal and masseter muscles in maximal clench and tapping of teeth. Marked correlations observed between vertical and sagittal jaw relations and mean voltages of the jaw-closing muscles indicated strong biting activity in subjects with a square facial type. No significant associations were observed between biting strength and the age of the subjects. Correlations between facial morphological changes and changes in EMG biting activity after denture insertion and during 1 year of denture wear indicated that the anterior temporal muscles were extremely sensitive to sagittal changes in anterior occlusion. The masseter muscles were less sensitive, but responded in some instances to changes in vertical jaw relationship.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73816/1/j.1365-2842.1983.tb00105.x.pd

Predictors of long-term stability of maxillary dental arch dimensions in patients treated with a transpalatal arch followed by fixed appliances

Background: The aim of this retrospective study was to identify which dental and/or cephalometric variables were predictors of long-term maxillary dental arch stability in patients treated with a transpalatal arch (TPA) during the mixed dentition phase followed by full fixed appliances in the permanent dentition. Methods: Thirty-six patients, treated with TPA followed up by full fixed appliances, were divided into stable and relapse groups based on the long-term presence or not of relapse. Intercuspid, interpremolar and intermolar widths, arch length and perimeter, crowding, and upper incisor proclination were evaluated before treatment (T0), post-TPA treatment (T1), post-fixed appliance treatment (T2), and a minimum of 3 years after full fixed appliances’ removal (T3). A binary logistic regression was performed thereafter to evaluate the impact of the dental arch and cephalometric measurements at T1 and the changes between T0 and T1 as predictive variables for relapse at T3. Results: The proposed model explained 42.7 % of the variance in treatment stability and correctly classified 72.2 % of the sample. Of the seven predictive variables, only upper anterior crowding (p = 0.029) was statistically significant. For every millimeter of decreased crowding at T1 (after TPA treatment/before starting the fixed orthodontic treatment), there was an increase of 3.57 times in the odds of having stability. Conclusions: The best predictor of relapse was maxillary crowding before treatment. The odds of relapse increase by 3.6 times for every millimeter of crowding at baseline

Factors associated with the desire for orthodontic treatment among Brazilian adolescents and their parents

<p>Abstract</p> <p>Background</p> <p>In the period of adolescence physical appearance takes on significant importance in the construction of personal identity, including one's relationship with one's own body. A variety of social, cultural, psychological and personal factors influences the self-perception of dental appearance and the decision to undergo orthodontic treatment. Adolescents who seek orthodontic treatment are concerned with improving their appearance and social acceptance. The aim of the present study was to determine factors associated to the desire for orthodontic treatment among Brazilian adolescents and their parents.</p> <p>Methods</p> <p>The sample consisted of 403 subjects aged 14 to 18 years, selected randomly from a population of 182,291 schoolchildren in the same age group. The outcome variable "desire for orthodontic treatment" was assessed through a questionnaire. Self-perception of dental aesthetics was assessed using the Oral Aesthetic Subjective Impact Scale (OASIS) and the Dental Aesthetic Index (DAI) was used for clinical assessment. Statistical analysis involved the chi-square test as well as both simple and multiple logistic regression analyses.</p> <p>Results</p> <p>The majority (78%) of the Brazilian adolescents desired orthodontic treatment and 69% of the parents reported that their children were not in orthodontic treatment due to the high costs involved. There was significant association (p ≤ 0.05) between the desire for orthodontic treatment and most types of malocclusion. However, there was no significant association between the desire for orthodontic treatment and the variables gender and age.</p> <p>Conclusions</p> <p>The following were considered factors associated to the desire for treatment: upper anterior crowding ≥ 2 mm and parents' perception of their child's need for treatment.</p