Acrylic Baseplates Research Articles

Enhancing Single-Plane Fluoroscopy: A Self-Calibrating Bundle Adjustment for Distortion Modeling.

Single-plane fluoroscopy systems with image intensifiers remain commonly employed in a clinical setting. The imagery they capture is vulnerable to several types of geometric distortions introduced by the system's components and their assembly as well as interactions with the local and global magnetic fields. In this study, the application of a self-calibrating bundle adjustment is investigated as a method to correct geometric distortions in single-plane fluoroscopic imaging systems. The resulting calibrated imagery is then applied in the quantitative analysis of diaphragmatic motion and potential diagnostic applications to hemidiaphragm paralysis. The calibrated imagery is further explored and discussed in its potential impact on areas of surgical navigation. This work was accomplished through the application of a controlled experiment with three separate Philips Easy Diagnost R/F Systems. A highly redundant (~2500 to 3500 degrees-of-freedom) and geometrically strong network of 18 to 22 images of a low-cost target field was collected. The target field comprised 121 pre-surveyed tantalum beads embedded on a 25.4 mm × 25.4 mm acrylic base plate. The modeling process resulted in the estimation of five to eight distortion coefficients, depending on the system. The addition of these terms resulted in 83-85% improvement in terms of image point precision (model fit) and 85-95% improvement in 3D object reconstruction accuracy after calibration. This study demonstrates significant potential in enhancing the accuracy and reliability of fluoroscopic imaging, thereby improving the overall quality and effectiveness of medical diagnostics and treatments.

Evaluation of the antibacterial effect of titanium dioxide nanoparticles combined with acrylic laminates for functional orthodontic appliances: a randomized controlled clinical trial

BackgroundThe objective of this study was to evaluate the antibacterial effect of titanium dioxide nanoparticles incorporated into the acrylic baseplates of the maxillary part of twin block appliances in orthodontic patients during the treatment period.Materials and methodsTwenty-six patients were selected randomly and divided into two groups(n = 13). Test group patients used orthodontic functional appliances containing 1% titanium dioxide nanoparticles in acrylic baseplates. Control group patients used orthodontic functional appliances without titanium dioxide nanoparticles in acrylic baseplates. Swap samples were taken from the palatal gingiva facing the fitting surface of the acrylic component of the maxillary part of a twin block appliance for each patient at five-time intervals (baseline sample, after one, two, four, and six months) and then cultured in blood agar plates to calculate bacterial colony count. The Mann‒Whitney U test and the Friedman test were used to compare data. Bonferroni correction (p value ≤ 0.05) was applied to detect significant differences.The resultsshowed a decrease in the bacterial colony count in the test group compared to the control group. Pairwise comparisons revealed a statistically significant difference in samples after four- and six-month groups (p values = 0.002 and 0.011, respectively) vs. the one-month test group. A higher statistically significant difference was observed in the six-month group (p-value = 0.037) vs. the baseline group in the control group.ConclusionThe addition of 1% titanium dioxide nanoparticles to acrylic baseplates of orthodontic functional appliances significantly reduced the bacterial colony count under the base plate after at least four months of application.

Ectopic Eruption of the Maxillary Permanent First Molar: A Brief Review and Clinical Case Report

The Ectopic Eruption of the Maxillary Permanent First Molar (EEMPFM) is an eruption anomaly, characterized for the maxillary permanent first molar’s impaction in the distal surface of the deciduous second molar. The etiology is related with change of the axial axis of eruption of the permanent first molar associated with missing space in the maxilla. The diagnosis is the combination of clinical and complementary examination. There are two types of Ectopic Eruption: the reversible and the irreversible. The irreversible type requires orthodontics treatment, because it causes root resorption of the deciduous second molar, causing its premature loss. For the treatment, procedures can be used with the aim of promoting distal inclination of the ectopic first molar, using separator elastics, removable or fixed appliances. The aim of this work is to report a clinical case of a patient of 9 years and 6 months old, female gender, who attended the Clinic presenting EEMPFM of the maxillary right permanent first molar. The treatment was a removable appliance composed with an acrylic base plate with clasps and a finger spring activated against a resin button bonded on the mesiobuccal cusp of the maxillary right permanent first molar. The correction of this anomaly was obtained with 35 days of treatment. Therefore, the sequence of procedures from diagnosis to the indication of an adequate treatment method is fundamental to obtain satisfactory results.

A Triboelectric‐Nanogenerator‐Based Gas–Solid Two‐Phase Flow Sensor for Pneumatic Conveying System Detecting

AbstractThe particle concentration and the mass flow rate are the most important parameters describing the gas–solid two‐phase flow. Herein, a novel method based on triboelectric nanogenerator is proposed for measuring a particle concentration and the mass flow rate in a gas–solid two‐phase pipe flow. The as‐fabricated gas–solid two‐phase flow triboelectric nanogenerator (GS‐TENG) consists of one acrylic base plate, one copper electrode, and one stripe of polytetrafluoroethylene (PTFE) membrane. Different materials can be detected by the GS‐TENG, including organic material, such as flour, and inorganic materials, such as copper and soil. PTFE surface morphology is modified to improve the output performance of the GS‐TENG in the experiments in order to detect the output electrical signal more efficiently. The peak output current generated by the gas–solid two‐phase flow in the GS‐TENG shows a mostly linear relationship with the concentration and mass flow rate. In addition, the transferred charge in the process of the flow also shows a highly linear relationship with the concentration and the mass flow rate, which is consistent with the theoretical derivation for the single electrode TENG. The experimental results demonstrate that the measurement error of the GS‐TENG is less than 2%.

The Discoloration of Heat Cured Resin Acrylic Base After Immersed in Disinfectant Solution

Acrylic resin dentures are a type of denture that is often used. At present the use of disinfectants to clean dentures from microorganisms, such as sodium hypochlorite and green betle leaves. Sodium hypochlorite contains chlorine, and green betle leaf extract contains tannins that containable to provide color changes in artificial teeth. The purpose of this study was to study the change in color on the hot polymerization acrylic plate after soaking with sodium hypochlorite solution and green betle leaf extract (Piper betle Linn). This study was a pre-post test control group design, the sample was heat-cured resin acrylic base plate and divided into 3 treatment groups: a group immersed in sodium hypochlorite, extract of green betel leaf and control group with aquades. The discoloration measurement was using Spectrophotometer. The sample was immersed for 15 days. Data were analyzed by paired T-test, followed by One way Anova and LSD. The results showed that there were significant color changes in the 2 treatment groups, while the control group was not significant. The mean of discoloration after immersion with Sodium Hypochlorite was 0.668 + 0.018, green betle leaf extract 30% was 0.625 + 0.024, and aquades was 0.534 + 0.0224. Color changes on heat-cured resin acrylic base plate occur by the presence of chlorine in sodium hypochlorite and tannin contained in the green betel leaf extract. This research concluded that immersion of heat-cured resin acrylic plate in sodium hypochlorite solution and 30% betle leaf extract may cause discoloration.

A comparative study of dimensional stability of two popular commercially used denture base resins

Background: A good dimensional stability is a necessary prerequisite for successful complete denture retention and its functional efficacy. This study was conducted keeping in mind the cost factor and the need of a common man. Out of many available products, conventional heat cure resin (Dental Products of India [DPI] and Lucitone 199 [LUC]) are the standard of choice. For suitable understanding of these two products in accordance to the above-stated statement, the current study was conducted. Aim: This in vitro study was carried out to compare the dimensional stability of commercially available polymethylmethacrylate (PMMA) DPI and high-impact LUC denture base materials processed using a long curing cycle, with and without terminal boiling. Methodology: By using a chrome cobalt metal base plate, a total of forty specimens of acrylic base plates were fabricated. They consisted of two major groups of twenty specimens each, fabricated from conventional heat cure DPI and LUC heat cure resins. Each group so fabricated was further subdivided into two equal subgroups of ten specimens each, which were subjected to long curing cycle, with and without terminal boiling. The results for each group were compared by paired sample t-test for the studied objective, and data were analyzed by SPSS software version 20 (IBM Corporation, Armonk, NY USA). The level of statistical significance was fixed at the customary level ≤0.05. Results: The dimensional stability values of LUC were found superior (P Conclusion: PMMA reinforced with butadiene styrene fabricated using long curing cycle with terminal boiling showed the highest value of dimensional stability and the least was seen with conventional PMMA processed with long curing cycle without terminal boiling.

Construction of silicone nasal prosthesis with acrylic baseplate

Construction of silicone nasal prosthesis with acrylic baseplate

Comparison of virtual and physical dimensions in AM resin dental devices and fit of devices with conventionally produced base plates

PurposeThe purpose of this study is to develop and apply clinically relevant methods of analysing the accuracy of dental appliances fabricated using additive manufacture (AM) compared to the computer-aided design (CAD) geometry. The study also compared fit between conventionally laboratory-fabricated and AM-produced base plates.Design/methodology/approachThe techniques were applied to two types of dental devices where AM fabrication methods could foreseeably be used as an alternative to laboratory production. “L” and cubic shapes of defined dimensions and spatial locations were positioned on the devices which were fabricated using AM. For assessing the dimensions, the “L” and cubic shapes were then measured on the physical builds ten times and compared to the CAD model. To assess the fit of AM and lab-produced devices, three upper and three lower conventionally fabricated acrylic base plates were compared to three upper and three lower plates. Silicone impression material was allowed to set between the casts and the base plates which filled any discrepancy between the two surfaces. The thickness of this silicone media was measured ten times at five different points on each base plate type and the results compared.FindingsThe results indicated that the evaluated CAD/AM technique is able to produce dental appliance components that are consistent with tolerance levels that would be expected with conventional methods of baseplate design. This research demonstrated that a fully CAD/AM methodology represents a potentially viable alternative to conventional lab-based methods for two types of dental appliances.Originality/valueThis work is original. The authors do not believe any previous papers similar to the one submitted have been published.

Antibacterial properties of retainers with silver nanoparticles

We read with interest the article entitled “Streptococcus mutans counts in patients wearing removable retainers with silver nanoparticles vs those wearing conventional retainers: A randomized clinical trial” in the February issue of the Journal.1Farhadian N. Usefi Mashoof R. Khanizadeh S. Ghaderi E. Farhadian M. Miresmaeili A. Streptococcus mutans counts in patients wearing removable retainers with silver nanoparticles vs those wearing conventional retainers: a randomized clinical trial.Am J Orthod Dentofacial Orthop. 2016; 149: 155-160Abstract Full Text Full Text PDF Scopus (44) Google Scholar Since we are also working in this area, we had a few questions and would like some explanations, if possible. Regarding the synthesis of silver nanoparticles:•Silver nanoparticles can be synthesized by chemical, physical, and biological methods,2Iravani S. Korbekandi H. Mirmohammadi S.V. Zolfaghari B. Synthesis of silver nanoparticles: chemical, physical and biological methods.Res Pharm Sci. 2014; 9: 385-406Google Scholar and cytotoxicity varies accordingly.3de Lima R. Seabra A.B. Durán N. Silver nanoparticles: a brief review of cytotoxicity and genotoxicity of chemically and biogenically synthesized nanoparticles.J Appl Toxicol. 2012; 32: 867-879Crossref Scopus (399) Google Scholar How did the authors synthesize their silver nanoparticles?•Was the antimicrobial resin synthesized in bulk to standardize the amounts of silver nanoparticles in retainers delivered to patients? The cytotoxcity of stored silver nanoparticles is greater as compared with freshly prepared silver nanoparticles.4Kittler S. Greulich C. Diendorf J. Koller M. Epple M. Toxicity of silver nanoparticles increases during storage because of slow dissolution under release of silver ions.Chem Mater. 2010; 22: 4548-4554Crossref Scopus (923) Google Scholar•What was the ratio of polymer to silver nanoparticles? Was the minimum inhibitory concentration (that is, the concentration at which at least 50% of the bacteria are killed) calculated? Regarding the antibacterial properties:•Which species of S mutans was present in McFarland suspensions? The antibacterial effect can vary according to the species (eg, ATCC 25175). Regarding the intervention:•After appliance delivery, were the patients given any oral hygiene instructions or directed to use any mouthwashes? Coexposure of silver nanoparticles and sodium fluoride also affects the cytotoxicity.5Inkielewicz-Stepniak I. Santos-Martinez M.J. Medina C. Radomski M.W. Pharmacological and toxicological effects of co-exposure of human gingival fibroblasts to silver nanoparticles and sodium fluoride.Int J Nanomedicine. 2014; 9: 1677-1687Google Scholar Regarding patient-related outcomes:•The authors claimed that the color of the final appliance, which could be gray to black depending on the concentration of the silver nanoparticles (shown in the Fig), was acceptable to patients. Could colorless silver nanoparticles have been used instead?•Was there any reason to carry out the T2 test after 7 weeks, since the retention period was 1 year? Perhaps the antibacterial activity could have been analyzed at regular intervals, since there could be differences in silver ions released during the long term.•Cytotoxicity to human gingival fibroblasts should have been tested at the first stage before conducting the in-vivo study because silver has been claimed to have not only cytotoxicity but also genotoxicity.6AshaRani P.V. Low Kah Mun G. Hande M.P. Valiyaveettil S. Cytotoxicity and genotoxicity of silver nanoparticles in human cells.ACS Nano. 2008; 3: 279-290Crossref Scopus (2931) Google Scholar The urinalyses and hematologic tests should have been done as mentioned in the Discussion. We acknowledge the scientific inputs of Meryam S. Rizvi, associate professor, and Jahirul Mazumder, PhD student, Department of Bioscience, Jamia Millia Islamia University, Delhi, India, for their critical review of the study by Farhadian et al. Streptococcus mutans counts in patients wearing removable retainers with silver nanoparticles vs those wearing conventional retainers: A randomized clinical trialAmerican Journal of Orthodontics and Dentofacial OrthopedicsVol. 149Issue 2PreviewThe rough surface of Hawley removable appliances provides an environment for plaque accumulation, leading to enamel demineralization. The aim of this study was to evaluate the effect of silver nanoparticles incorporated into acrylic baseplates of orthodontic retainers on Streptococcus mutans colony-forming units. Full-Text PDF Authors' responseAmerican Journal of Orthodontics and Dentofacial OrthopedicsVol. 150Issue 2PreviewWe appreciate being given the opportunity to discuss the details of our study1 and hope the following explanation will be helpful. Full-Text PDF

Full 3-dimensional digital workflow for multicomponent dental appliances: A proof of concept

BackgroundThe authors used a 3-dimensional (3D) printer and a bending robot to produce a multicomponent dental appliance to assess whether 3D digital models of the dentition are applicable for a full digital workflow. MethodsThe authors scanned a volunteer’s dentition with an intraoral scanner (Lava Chairside Oral Scanner C.O.S., 3M). A digital impression was used to design 2 multicomponent orthodontic appliances. Biocompatible acrylic baseplates were produced with the aid of a 3D printer. The metal springs and clasps were produced by a bending robot. The fit of the 2 appliances was assessed by 2 experienced orthodontists. ResultsThe authors assessed both orthodontic appliances with the volunteer’s dentition and found the fit to be excellent. ConclusionsClinicians can fully produce a multicomponent dental appliance consisting of both an acrylic baseplate and other parts, such as clasps, springs, or screws, using a digital workflow process without the need for a physical model of the patient’s dentition. Practical ImplicationsPlaster models can be superfluous for orthodontic treatment as digital models can be used in all phases of a full digital workflow in orthodontics. The arduous task of making a multicomponent dental appliance that involves bending wires can possibly be replaced by a computer, design software, a 3D printer, and a bending robot.

Photocatalytic Effects of Acrylic Resins Incorporated with Nano-titanium Dioxide on Planktonic and Biofilm Growth of Four Cariogenic Bacteria

Aims: The activities of cariogenic bacteria in biofilm on acrylic baseplates of removable orthodontic appliances and partial denture contribute to dental caries, inflammation of gingiva and periodontal disease. This in vitro study evaluates the Original Research Article Annual Research & Review in Biology, 4(17): 2695-2708, 2014 2696 photocatalytic antimicrobial activity of acrylic specimens (AS) containing NanoTiO2 under ultraviolet type A (UVA) illumination against four cariogenic bacteria. Study Design: An in vitro study Place and Duration of Study: Department of Microbiology and Department of Orthodontics, Tehran University of Medical Sciences (TUMS); Department of Chemistry, Tarbiat Modares University, between June 2011 and March 2012. Methodology: Chemical-cure acrylic resins, Polymethylmethacrylates (PMMAs), were used to synthesize acrylic specimens containing NanoTiO2 (NanoT-AS). Antibacterial activity of NanoT-AS were assessed against Streptococcus sobrinus, Streptococcus mutans, Lactobacillus acidophilus as well as Lactobacillus casei and co-cultures of the four species by adherence inhibition as well as planktonic and biofilm bacterial cells growth inhibition on NanoT-AS under UVA illumination (NanoTiO2+/UVA+). Results: Exposure to NanoTiO2+/UVA+ reduced bacterial adherence by 43.8-96.5% depending on the microorganism type. NanoTiO2+/UVA+ showed 1.7-6.0 log decrease planktonic cultures in time-dependent manner over a 4h period (P<0.05). NanoT-AS inhibited significantly biofilm formation of all test bacteria and co-cultures by 44.2-93.1%, compared to unmodified PMMA (control) under UVA illumination. Some inhibitory activity of NanoTiO2+/UVA+ could be maintained even after the third generation of biofilm growth. Conclusion: The data presented here are novel in that they prove that NanoTiO2+/UVA+ effectively inhibited adherence of cariogenic bacteria to NanoT-AS surfaces as well as strong antimicrobial activity in the planktonic phase and subsequent biofilm formation. This data shows NanoTiO2+/UVA+ has the potential to minimize cariogenic microorganism’s adherence and colonization on acrylic specimens and this novel acrylic resin formulation could be developed as a denture and orthodontic appliances base.

SU-E-T-360: Development of a Detection System for Intra-Fractional Motion in Intracranial Treatment Using Patient Surface Pressure

Purpose: To develop a dedicated real-time monitoring system to detect intra-fractional motion in intracranial radiotherapy using patient surface pressure. Methods: The motion for two volunteers was analyzed by a new type of immobilization system that detect load given to a patient head. The immobilization system consists of sensors with a thickness of 0.55 mm and a radius of 9.1 mm, a thermoplastic mask, a vacuum bag, and an acrylic baseplate. The four pieces of sensors were positioned at left-right sides, superior-inferior sides on the vacuum bag, respectively. The other four pieces of sensors were positioned at up-down sides, left-right sides of chin just under the thermoplastic mask, respectively. The load given to the volunteer was detected by the immobilization system that the eight sensors were attached. The pressures for sensors were calculated using a measuring resistor in a voltage divider configuration. The three pieces of light-emitting diodes (LEDs) were located on the thermoplastic mask at the chin and the pair of cheeks to detect the volunteer motion. The three-dimensional positions of LEDs were continuously detected using the Cyberknife Synchrony system. The sensor's pressures were compared with the root mean square (RMS) of LEDs displacement during the 30 min interval. Results: The RMS values of LEDs displacement within 1 mm or less were almost related to the pressures of sensors at left and superior sides on the vacuum bag. The pressures of other sensors were not detected or no relationship with the RMS values of LEDs displacement in two volunteers. Conclusion: The dedicated real-time monitoring system using patient surface pressure can detect intra-fractional motion in intracranial treatment with high precision of 1 mm or less.

Digital replacement of the distorted dentition acquired by cone beam computed tomography (CBCT): a pilot study

During cone beam computed tomography (CBCT) scanning, intra-oral metallic objects may produce streak artefacts, which impair the occlusal surface of the teeth. This study aimed to determine the accuracy of replacement of the CBCT dentition with a more accurate dentition and to determine the clinical feasibility of the method. Impressions of the teeth of six cadaveric skulls with unrestored dentitions were taken and acrylic base plates constructed incorporating radiopaque registration markers. Each appliance was fitted to the skull and a CBCT performed. Impressions were taken of the dentition with the devices in situ and dental models were produced. These were CBCT-scanned and the images of the skulls and models imported into computer-aided design/computer-aided manufacturing (CAD/CAM) software and aligned on the registration markers. The occlusal surfaces of each dentition were then replaced with the occlusal image of the corresponding model. The absolute mean distance between the registration markers in the skulls and the dental models was 0.09±0.02mm, and for the dentition was 0.24±0.09mm. When the method was applied to patients, the distance between markers was 0.12±0.04mm for the maxilla and 0.16±0.02mm for the mandible. It is possible to replace the inaccurate dentition on a CBCT scan using this method and to create a composite skull which is clinically acceptable.

Evaluation of home disinfection protocols for acrylic baseplates of removable orthodontic appliances: A randomized clinical investigation

In this randomized clinical trial, we investigated, using the microbial culture technique and scanning electron microscopy, the contamination of acrylic baseplates of removable orthodontic appliances by mutans streptococci (MS) and evaluated the efficacy of different home disinfection protocols with a 0.12% chlorhexidine gluconate spray (Periogard, Colgate-Palmolive, São Bernardo do Campo, Brazil). Fifteen dental students were randomly enrolled in a 3-stage changeover system with a 1-week interval between each stage. The acrylic baseplates were worn full time except at meals to simulate the routine use of removable appliances under clinical conditions. Three 1-week home disinfection protocols were tested in all stages by a different group of students: protocol I, toothbrushing+ baseplate brushing+ sterile tap water spraying once a day; protocol II, toothbrushing+ baseplate brushing+ Periogard spraying on the seventh day after appliance placement; and protocol III, toothbrushing+ baseplate brushing+ Periogard spraying on the fourth and seventh days after appliance placement. After the first week, the volunteers received new baseplates, toothbrushes, and dentifrices, and the regimens were repeated 2 more times. At the end of each week, the baseplates had a randomized disinfection protocol and were sent for microbiologic analysis. A scanning electron microscope was used to examine 3 acrylic baseplates representing each home protocol. The Friedman test (α= 0.05) compared the home protocols for the formation of MS colonies or biofilms on the acrylic surfaces. MS colonies or biofilms were found on all acrylic baseplates after protocol I. Protocols II and III reduced significantly (P<0.05) the number of MS colonies and biofilms on the acrylic surfaces. No significant difference (P>0.05) was observed between protocols II and III. The scanning electron microscope analysis confirmed the results of the microbiologic cultures. Disinfection of baseplates of removable orthodontic appliances by using 0.12% chlorhexidine spray once or twice a week reduced the contamination by MS on the acrylic surface invivo.

Various polymerization temperature on dimensional accuracy of orthodontic acrylic base plate

Cold curing acrylic is more porous, having more residual monomer and dimensional change. Physical property of cold curing acrylic shows to have very small dimensional change resulted from imperfect polymerization process and if dimensional change occurs, it would cause improper use of orthodontic appliance. Orthodontic acrylic base plate which is made of cold curing acrylic, in order to achieve good result, it is suggested to use hydro flask or polyclav with water temperature 45 ° –50 ° C and polyclav and pressure in 2–3 atm during polymerization process. Even though cold curing acrylic could polymerization at room temperature, the purpose to use hydro flask or polyclav is to reduce residual monomer and porosity. The purpose of the present study is to know the difference in dimensional accuracy of orthodontic acrylic at various polymerization temperature. The samples of the study were 18 acrylic base plate sized 65 × 10 × 25 mm classified into 3 control groups with polymerization temperature at 30 ° C, 40 ° C and 50 ° C. Measurement was done using caliper in order to know dimensional accuracy of orthodontic acrylic. The measurement result was tabulated and One-Way ANOVA test one was done with significant level 95%, the probability result 0,0055 was found which means there was significant difference among each control group. LSD test showed that group I polymerization at 30 ° C, group II polymerization at 40 ° C, and group III polymerization at 50 ° C there was significant difference. The conclusion of this study is : dimensional difference of orthodontic acrylic base plate on polymerization at group I at 30 ° C, group II at 40 ° C, and group III at 50 ° C water temperature and could achieve better dimensional accuracy comparing with polymerization at 50 ° C.

In-vivo evaluation of the bacterial contamination and disinfection of acrylic baseplates of removable orthodontic appliances

This randomized clinical trial assessed, by using microbial culture and scanning electron microscopy (SEM), the contamination by mutans streptococci (MS) colonies/biofilms on acrylic baseplates of removable orthodontic appliances and evaluated the efficacy of antimicrobial sprays (Periogard [Colgate-Palmolive Ind. Brasileira, Osasco, SP, Brazil], Cepacol [Merrell Lepetit Farmacêutica e Industrial Ltda, Santo Amaro, SP, Brazil], and sterile tap water [control]) on their disinfection. Seventeen children were randomly enrolled in a 3-stage changeover system with a 1-week interval between each stage. All solutions were used in all stages by a different group of children. The acrylic baseplates were worn full time except at meals. At the end of each week of the trial, the baseplates were submitted to a randomized disinfection protocol and were sent for microbiologic analysis. New baseplates were constructed, and the same sequence of procedures was repeated 2 more times. Acrylic baseplates representing each test solution were examined by SEM. The Friedman test assessed differences at the 5% significance level among the solutions for MS biofilm formation on acrylic surface. Cepacol and Periogard reduced the formation of MS colonies/biofilms, and both solutions differed statistically from sterile tap water (P <.001). However, Periogard was significantly more effective against MS than Cepacol (P <.001). When MS colonies/biofilms were detected on acrylic surfaces under stereomicroscopy, this was confirmed with SEM. Acrylic baseplates of removable orthodontic appliances worn by children were contaminated by MS colonies/biofilms in all cases after 1 week. Although Cepacol had better results than sterile tap water, spraying with Periogard showed significantly greater efficacy in reducing MS colonies/biofilms on acrylic surfaces.

The effect of photo-activated glazes on the microhardness of acrylic baseplate resins

Objective: A comparative investigation of acrylic denture base surface microhardness, induced through glazing with different photo-activated liquids. Materials and methods: Thermopolymerized acrylic resin Paladon 65 (Kulzer) was used for this study. The samples were mechanically thinned by silicon carbide grinding papers and finally, mechanically polished by alumina pastes. The samples were then glazed with Palaseal, Plaquit and Lightplast-Lack photo-activated liquids. Microhardness tests were carried out via a Zeiss optical microscope equipped with an Anton Paar microhardness tester fitted with a Knoop indenter. Results: Microhardness testing performed on surfaces glazed by Plaquit, Lightplast-Lack, and Palaseal photo-activated liquids showed enhanced microhardness values compared to the mechanically polished acrylic resin denture base material. Conclusions: Comparative microhardness tests performed on acrylic base resin treated with photo-activated acrylic glazes showed that all increases the surface microhardness. The enhancement of surface microhardness of acrylic denture bases suggests that they are likely to resist wear during service.

Violent liquid sloshing in vertically excited cylindrical containers

A series of experimental studies were made on the frequency characteristics of gas-liquid surface sloshing induced by the vertical vibration of cylindrical containers containing liquid. The free surface oscillation and the surface disintegration liquid were observed. Measurements with emphasis on pressure responses were taken for water over the frequency of 20–1000 Hz. Bubble cluster formation in the liquid and container wall responses during the vibration were investigated. Experiments were performed on a vibration-testing system with an electrodynamic shaker. Three circular cylindrical containers were constructed of transparent acrylic plastic by inserting and cementing a thick acrylic base plate at one end so that bubbles generated in the liquid could be readily observed. It was found that the resonance frequency of the liquid-container vibration system depended on the excitation acceleration. The acceleration distribution of the container wall was not axisymmetrical at higher excitation accelerations. Drastic changes in liquid pressure, container wall acceleration, and amplitude of surface oscillation were observed following the formation of a bubble cluster. The results obtained should provide useful clues for future research and development of practical application of liquid sloshing phenomena.

Appliance breakages.

A survey of appliance breakages over a 12-month period revealed that the acrylic baseplate and bite planes (57 per cent) fractured more frequently than wire elements (43 per cent). The number of appliances broken represented about one in five of new appliances fitted during the period. More than half of the breakages were perpetrated by persistent offenders and 31 per cent of appliances broke while they were removed from the mouth, but in the care of the patient. Inadequate properties of the acrylic resin and carelessness on the part of the patient are suggested as the most important causative factors.

Variations in the initial formation of pellicle and plaque on enamel in vivo

Four subjects wore acrylic baseplates with small pieces of enamel from unerupted teeth for periods of 24 and 48 hours. The rate of colonization of the pellicle with bacteria varied among the subjects in 2 of whom bacteria were not seen on the surface at 24 hours. Etching the enamel did not enhance the rate of colonization. Chlorhexidine treatment did not prevent bacterial adherence after 2 days, but etched enamel retained the antibacterial effect of chlorhexidine longer than normal enamel.