The Effect of Humidity on the Knock Behavior in a Medium BMEP Lean-Burn High-Speed Gas Engine

The effects of air humidity on the knock characteristics of fuels are investigated in a lean-burn, high-speed medium BMEP engine fueled with a CH4 + 4.7 mole% C3H8 gas mixture. Experiments are carried out with humidity ratios ranging from 4.3 to 11 g H2O/kg dry air. The measured pressure profiles at non-knocking conditions are compared with calculated pressure profiles using a model that predicts the time-dependent in-cylinder conditions (P, T) in the test engine (“combustion phasing”). This model was extended to include the effects of humidity. The results show that the extended model accurately computes the in-cylinder pressure history when varying the water fraction in air. Increasing the water vapor content in air decreases the peak pressure and temperature significantly, which increases the measured Knock Limited Spark Timing (KLST); at 4.3 g H2O/kg dry air the KLST is 19 °CA BTDC while at 11 g H2O/kg dry air the KLST is 21 °CA BTDC for the same fuel. Excellent agreement is observed between the calculated knock resistance (using the Propane Knock Index, PKI) and the measured knock resistance (KLST) for the range in water content in air studied in this work. Since the effect of water on autoignition delay time is negligible, the observed increase in knock resistance of the fuel-air mixture is due a decrease in pressure and temperature of the end gas with increasing water content in as a result of changes in the mass burning rate, and thermophysical properties of the fuel-air mixture

The randomized shortened dental arch study (RaSDA): design and protocol

<p>Abstract</p> <p>Background</p> <p>Various treatment options for the prosthetic treatment of jaws where all molars are lost are under discussion. Besides the placement of implants, two main treatment types can be distinguished: replacement of the missing molars with removable dental prostheses and non-replacement of the molars, i.e. preservation of the shortened dental arch. Evidence is lacking regarding the long-term outcome and the clinical performance of these approaches. High treatment costs and the long time required for the treatment impede respective clinical trials.</p> <p>Methods/design</p> <p>This 14-center randomized controlled investigator-initiated trial is ongoing. Last patient out will be in 2010. Patients over 35 years of age with all molars missing in one jaw and with at least both canines and one premolar left on each side were eligible. One group received a treatment with removable dental prostheses for molar replacement (treatment A). The other group received a treatment limited to the replacement of all missing anterior and premolar teeth using fixed bridges (treatment B). A pilot trial with 32 patients was carried out. Two hundred and fifteen patients were enrolled in the main trial where 109 patients were randomized for treatment A and 106 for treatment B. The primary outcome measure is further tooth loss during the 5-year follow-up. The secondary outcome measures encompassed clinical, technical and subjective variables. The study is funded by the Deutsche Forschungsgemeinschaft (German Research Foundation, DFG WA 831/2-1, 2-2, 2-3, 2-4, 2-5).</p> <p>Discussion</p> <p>The particular value of this trial is the adaptation of common design components to the very specific features of complex dental prosthetic treatments. The pilot trial proved to be indispensable because it led to a number of adjustments in the study protocol that considerably improved the practicability. The expected results are of high clinical relevance and will show the efficacy of two common treatment approaches in terms of oral health. An array of secondary outcome measures will deliver valuable supplementary information. If the results can be implemented in the clinical practice, the daily dental care should strongly profit thereof.</p> <p>Trial registration</p> <p>The trial is registered at ClinicalTrials.gov under ISRCTN68590603 (pilot trial) and ISRCTN97265367 (main trial).</p

Stabilizing Removable Partial Dentures by Immediate or Delayed Loading of Mini-implants: Chewing Efficiency in a Randomized Controlled Clinical Trial.

PURPOSE The aim of this investigation was to compare the chewing efficiency after immediate and delayed loading of mini-implants that served as supplementary support for removable partial dentures (RPDs). MATERIALS AND METHODS In this four-center randomized trial, patients who had RPDs in arches with unfavorable tooth distributions, ie, no canine and at most two posterior teeth in one or both quadrants, received strategic mini-implants with ball abutments. The mini-implants in group A were loaded immediately either by housings with O-rings (insertion torque ≥ 35 Ncm) or by soft relining material (insertion torque < 35 Ncm). In group B, the RPDs were only hollowed over the balls. After 4 months, the soft relined RPDs and all RPDs of group B received the housings. Masticatory efficiency was evaluated with a validated mixing ability test of two-colored chewing gum before surgery and 14 days, 4 months (before housing pickup), 4.5 months, and 12 months after surgery. The circular variance of hue was the measure of mixing. RESULTS From 76 participants with 79 RPDs, 38 each were randomly allocated to group A or B. In group A, the housings in six participants were picked up immediately, and the remaining RPDs were primarily soft relined. There was a significant group difference only after 4 months. The mixing ability was better after immediate loading than after delayed loading (P < .0001). In group B, the chewing efficiency was notably deteriorated after the RPDs were hollowed over the ball abutments. However, immediately after all housings were picked up, the chewing efficiency in both groups was substantially improved, and the variance of hue values after 1 year were very similar in the groups. CONCLUSION The chewing performance can be improved by inserting supplementary mini-implants under existing RPDs with unfavorable tooth support. This improvement occurred faster by immediate loading than by delayed loading

Stabilizing mandibular complete dentures by a single midline implant-influence on quality of life: 2-year results from a randomized clinical trial comparing different loading protocols.

OBJECTIVES The knowledge about the influence of dental treatment on health-related quality of life (HRQoL) is still limited. The aim of this multicenter randomized controlled clinical trial was to assess the effect of stabilizing an existing complete denture, by means of a single mandibular implant, on HRQoL. Furthermore, the impact of the loading protocol, i.e., immediate or delayed loading, in edentulous patients was evaluated. METHODS One hundred fifty-eight participants aged 60-89 years were randomly assigned to study group A (immediate loading; n = 81) and to group B (delayed loading; n = 78). All participants received a single midline implant in the mandible. The implants were either immediately loaded (group A) or after a closed healing period of 3 months (group B) by connecting the existing mandibular complete dentures to ball attachments. HRQoL was assessed with the Short Form-36 questionnaire of health (SF-36) at baseline, 4 months, and 24 months after implant loading. RESULTS Improvement of HRQoL by means of a single implant-retained mandibular overdenture could not be demonstrated after 4 and 24 months of implant loading. Furthermore, the application of two different loading protocols did not influence HRQoL ratings of study participants. CONCLUSION The loading protocol is not a factor, influencing HRQoL in patients treated by a single midline implant in the edentulous mandible. CLINICAL RELEVANCE A single midline implant in the edentulous mandible, stabilizing a mandibular complete denture, cannot be recommended for improving HRQoL

Single Mandibular Implant Study: Recruitment Considerations

PURPOSE The aim of this multicenter single mandibular implant study was to compare the clinical outcome of an immediately loaded implant placed in the midline of an edentulous mandible with the clinical outcome when closed healing and delayed loading is chosen. Here, the patient recruitment period and the main reasons for exclusion were analyzed. MATERIALS AND METHODS Patient recruitment was performed at nine German universities. Rather conservative inclusion and exclusion criteria, including denture satisfaction, denture status, a psychologic symptom checklist, and a defined bone height in the posterior mandible, had to be fulfilled. It was initially calculated that 230 persons would have to be screened within 13 months to include 180 persons in the trial. RESULTS Within 13 months (December 2012 to December 2013), 201 patients were screened for possible inclusion in the trial and 148 met the inclusion criteria. Finally, after the recruitment period was extended by 2.5 months, 224 patients were screened and 169 were included. Of those screened, 55 (24.6%) did not meet the inclusion criteria and were excluded. Another 4 patients (1.8%) were excluded based on their psychologic symptom checklist score, while 5 others (2.8%) showed signs of noncompliance. A further 8 patients (4.4%) decided not to participate and withdrew their informed consent, and another 3 (1.3%) were no longer available after screening. Another 2 patients were excluded due to medical contraindications and 1 due to an insufficient mandibular denture. In 34 cases (15.2%), the residual bone height did not comply with McGarry type II or III. CONCLUSION Within the limitations of this patient recruitment period, it can be concluded that residual bone height is the most important factor when considering elderly edentulous patients for implant therapy. The psychologic symptom checklist score was less important

Single mandibular implant study (SMIS) - masticatory performance - results from a randomized clinical trial using two different loading protocols

OBJECTIVES This multi-centre randomized controlled trial was conducted to investigate, whether the masticatory performance of elderly edentulous patients is improved by placement of a single implant in the midline of the edentulous mandible, and whether improvements differ with respect to the loading protocol, i.e., implant is loaded either directly or three months later after second stage surgery. METHODS Edentulous seniors aged 60-89 years were screened according to inclusion and exclusion criteria and 163 underwent implant placement. Of those, 158 were randomly assigned either to the direct loading group A (n=81) or the conventional loading group B (n=77). Chewing efficacy was obtained before treatment, one month after implant placement during the submerged healing phase (only group B) and 1 and 4 months after implant loading. RESULTS The masticatory performance increased over time in both groups. Four months after loading, a significant increase was observed for both groups compared to the baseline data without implant (p≤0.05). However, between the two groups, chewing efficiency did not differ significantly at any point in time (p>0.05). CONCLUSIONS A single midline implant in the edentulous mandible increases masticatory performance significantly, independently from the loading protocol. CLINICAL SIGNIFICANCE A single midline implant in the edentulous mandible increases masticatory performance. The loading protocol has no influence

Additional file 1: of Immediate versus delayed loading of strategic mini dental implants for the stabilization of partial removable dental prostheses: a patient cluster randomized, parallel-group 3-year trial

Model consent form given to the participants (In German). (PDF 342 kb