The aim of this retrospective study was to compare the esthetic, periodontal, and functional outcomes of orthodontic space closure versus implant substitution in patients with missing maxillary incisors 5 years after completion of treatment. The study group consisted of ten patients treated with orthodontic space closure (six males, four females, mean age 19 ± 2.1 years at the completion of treatment) and ten patients treated with implant insertion (five males, five females, mean age 20 ± 1.4 years at the time of implant insertion). Tooth mobility, plaque index, probing depth, infraocclusion, open gingival embrasure (black triangle), and temporomandibular joint function were recorded at the 5.6 years follow-up. Self-perceived dental esthetic appearance was also evaluated through a visual analog scale (VAS) questionnaire. T-test was used to evaluate the data. All patients were equally satisfied with the appearance of their teeth 5.6 ± 0.4 years after the completion of treatment. No statistically significant differences were found in relation to the VAS scores of the subjects (P < 0.857). No significant differences were found in tooth mobility, plaque index (P < 0.632), and the prevalence of signs and symptoms of temporomandibular disorders. However, significant infraocclusion was noticed in all implant patients (P < 0.001). Probing depth was also significantly higher in implant patients (P < 0.001). Orthodontic space closure and implant of missing maxillary incisors produced similar, well-accepted esthetic results. None of the treatments impaired temporomandibular joint function. Nevertheless, infraocclusion was evident in implant patients. Space closure patients also showed better periodontal health in comparison with implant patients.

The smile perception of patients is not strictly related to standardized protocols and technical implications which certainly affect clinicians' decisions. The absence of maxillary lateral incisors could affect smile esthetics either with treatment or not. The aim of the present study was to investigate if different perceptions on altered smiles due to missing maxillary lateral incisors, with or without treatment, exist among different groups of people (laypersons, adult orthodontic patients, general dentists, and orthodontists).

Controversy exists in the literature between the role of orthodontic treatment and gingival recession. Whilst movement of teeth outside the alveolar bone has been reported as a risk factor for gingival recession, others have found no such association. The Angle Society of Europe devoted a study day to explore the evidence surrounding these controversies. The aim of the day was for a panel of experts to evaluate the current evidence base in relation to either the beneficial or detrimental effects of orthodontic treatment on the gingival tissue. There remains a relatively weak evidence base for the role of orthodontic treatment and gingival recession and thus a need to undertake a risk assessment and appropriate consent prior to the commencement of treatment. In further prospective, well designed trials are needed.

During the start-up of a liquid rocket engine most of the engine components are required to work at extreme operating conditions; this phase features very complex phenomena such as combustion instabilities, water hammer eFFects in feed lines, turbopumps operating far from design conditions and two-phase flows that cannot be neglected when design studies of an engine are to be performed or the assessment of the valve opening sequence has to be done. For these reasons simulations of the ignition transient phase become necessary in order to reduce the experimental tests and increase the engine safety and reliability. The subject of the present work is to develop an LRE transient model, to apply it to simulate the start-up transient and to validate the model with an existing liquid rocket engine (the RL-10). A system approach has been used, since it is necessary to take into account all the interactions between all the components of an engine. This choice is fundamental if a detailed estimation of the engine transient behaviour is the task. The system simulated by the code encompasses the complete feeding system from the tanks down to the the turbopump subsystems, the valves, the pipes, the thrust chamber's inlets, the flow ducts of the thrust chamber itself and the chemical reactions inside the combustion chamber. The engine model is built using ESPSS,5 the propulsion system library compatible with EcosimPro, an object oriented tool capable of modelling various kinds of dynamic systems. The engine model includes also original models developed by the authors and presented in previous works6 such as a new injector plate model, and more realistic heat transfer coefficient correlations. The transient phase of the Pratt and Whitney RL-10 engine has been taken as validation case. This engine has been chosen for several reasons, among which the good availability of engine construction data, performance and tests results in open literature.1-3 The main subsystem models of this engine will be described and their validation will be presented. Then the integrated model of the entire engine will be described alongside the comparison of the simulation with experimental data. © 2011 by F. Di Matteo