Mitchell's trimmer: Who was Mitchell and what was he trimming?

Mitchell's trimmer, also known as an osteo-trimmer, osteocarver or osteocarver #4, is a commonly used instrument in a dental professional's armamentarium. Today the instrument is used in a range of dental specialties; however, its modern use has no association to trimming. This article explores the origin of the Mitchell's trimmer, its intended use and reveals the founder of the renowned instrument.

Multisensory perception and action in 3-ball cascade juggling.

Multisensory perception and action in 3-ball cascade juggling was investigated in intermediate-skilled performers by manipulating vision (full or lower field restricted) or ball weight (equal or different). There were main effects for both independent variables but no interactions. Manipulation of ball weight had a more pervasive effect on performance outcome, as well as central tendency and dispersion of kinematic measures of the juggling action. A common finding to both manipulations was that balls were tossed to higher zeniths, thus increasing parabola height and flight time. For intermediate-skilled jugglers, proprioception-haptics available when the balls were in the hands and vision of the balls and hands around the moment of ball toss and catch both make a contribution to the juggling action.

A comparative study of image quality and radiation exposure for dental radiographs produced using a charge-coupled device and a phosphor plate system.

AIM: To investigate the quality of periapical radiographic images produced by two digital dental radiography systems, a charge-coupled device (CCD) and a photostimulable phosphor (PSP) image plate system, and to examine the overall radiation exposure when using these systems in a clinical setting. METHODOLOGY: Patients were randomly allocated to both systems and the resultant radiographs rated for quality. The expected radiation exposure for an investigation was calculated. RESULTS: Overall, 98 images were acquired using the CCD system and 108 with the PSP system. The PSP system produced significantly higher quality (P < 0.001) periapical images compared with the CCD system. The CCD system required significantly more (P < 0.001) repeat exposures to obtain a diagnostic image than the PSP system but at a lower expected radiation exposure. CONCLUSIONS: The image quality was superior using the phosphor plate system. Although more repeat radiographs were required using the CCD system, the images were produced with a lower expected radiation exposure.

Microleakage of human saliva in coronally unsealed obturated root canals in anaerobic conditions.

The purpose of this study was to determine the time required for anaerobic bacteria in natural human saliva to contaminate root-filled teeth. Thirty-two single-rooted teeth were cleaned, shaped, filled, and exposed to human saliva for 120 days. Teeth that had not leaked were subjected to polymerise chain reaction examination. Sixty-six percent of the experimental group were totally contaminated. A PCR examination revealed there was no contamination in the apical 3 mm of leakage-free teeth.

Crown and bridge disassembly--when, why and how.

Crown and bridgework has a finite life span and fails for a number of reasons. Removal is often by destructive means. There are a number of clinical circumstances, however, in which a conservative disassembly would aid the practitioner in completing restorative/endodontic procedures. The aims of this paper are to provide a classification for crown and bridge removal systems; describe how a number of such systems work; and when and why they might be considered.

The effect of pH on surface hardness and microstructure of mineral trioxide aggregate.

AIM: To evaluate the surface microhardness of mineral trioxide aggregate (MTA) specimens following exposure of their surface to a range of acidic environments during hydration. In addition, the morphological microstructure features of samples were studied by scanning electron microscopy (SEM). METHODOLOGY: White ProRoot MTA (Dentsply Tulsa Dental, Johnson City, TN, USA) was mixed and packed into cylindrical polycarbonate tubes. Four groups, each of 10 specimens, were formed using a pressure of 3.22 MPa and exposed to pH 4.4, 5.4, 6.4 and 7.4, respectively, for 4 days. Vickers microhardness of the surface of each specimen was measured after exposure. Four groups of two specimens were prepared and treated in the same way prior to qualitative examination by SEM. Data were subjected to one-way anova and post hoc Tukey's test. RESULT: The greatest mean surface hardness values (53.19 +/- 4.124) were observed following exposure to pH 7.4 with the values decreasing to 14.34 +/- 6.477 following exposure to pH 4.4. The difference between these values at the 95% CI (33.39-44.30) was statistically significant (P < 0.0001). There were no distinct morphological differences between groups in terms of the internal microstructure. However, a trend was observed that the more acidic the solution, the more extensive the porosity of the specimens. CONCLUSION: Under the conditions of this study, surface hardness of MTA was impaired in an acidic environment.

Radiographic evidence of postoperative healing 12 years following root canal treatment--a case report.

A case with evidence of radiographic healing of a periapical lesion 12 years after root canal treatment is presented. The use and limitations of previously produced guidelines on radiographic follow-up intervals are discussed. Questions are raised about what is known of the healing process and when further treatment should be instituted. The reliance on single radiographs alone when making treatment decisions is discouraged.

An initial evaluation of virtual reality simulation in teaching pre-clinical operative dentistry in a UK setting.

The use of virtual reality (VR) training in dentistry is a recent innovation and little research has been conducted to evaluate its use. For each preclinical exercise carried out the VR software currently records a final mark for the procedure, the time taken to complete the procedure and the number of 'internal' assessments carried out by the student. The aims of this study were two fold; a critical appraisal of the software by the students using a structured feedback together with an assessment of any link between the preparation time, final mark and number of evaluations. Sixteen 2nd year undergraduate dental students spent 6 hours cutting an unlimited number of Class I cavities and Class II cavities. The final mark awarded by the VR software together with the overall preparation time and number of evaluations for each cavity were recorded. For the Class I cavity the mean mark obtained was 66.8, the mean preparation time was 12.5 mins and the mean number of evaluations was 6.7. For the Class II cavity the mean mark was 26.5, the mean preparation time was 18 mins and the mean number of evaluations was 7.0. Final marks were also stratified into quartiles (0-24, 25-49, 50- 74, 75-100). For the Class II cavity the time taken to complete the cavity and the number of evaluations made were greater for those cavities that gained a mark of 50 or more. In conclusion, this initial evaluation of the DentSim VR package was a generally positive undergraduate educational experience. The class II cavity was more difficult to cut than the class I which was reflected in the mean scores. There was also a trend towards higher marks being associated with longer preparation times and more evaluations during the preparation.

Crown and bridge disassembly--when, why and how.

UNLABELLED: Crown and bridgework has a finite life span and fails for a number of reasons. Removal is often by destructive means. There are a number of clinical circumstances, however, in which a conservative disassembly would aid the practitioner in completing restorative/endodontic procedures. The aims of this paper are to provide a classification for crown and bridge removal systems; describe how a number of such systems work; and when and why they might be considered. CLINICAL RELEVANCE: Crown and bridge removal is a frequent occurrence for dentists. There are many situations in which salvaging extracoronal restorations may be more helpful than their destruction.

The effect of condensation pressure on selected physical properties of mineral trioxide aggregate.

AIM: To examine the effect of condensation pressure on surface hardness, microstructure and compressive strength of mineral trioxide aggregate (MTA). METHODOLOGY: White ProRoot MTA (Dentsply Tulsa Dental, Johnson City, TN, USA) was mixed and packed into cylindrical polycarbonate tubes. Six groups each of 10 specimens were subjected to pressures of 0.06, 0.44, 1.68, 3.22, 4.46 and 8.88 MPa respectively. The surface hardness of each specimen was measured using Vickers microhardness. Cylindrical specimens of 4 mm in diameter and 6 mm in height were prepared in polycarbonate cylindrical moulds for testing the compressive strength. Five groups of 10 specimens were prepared using pressures of 0.06, 0.44, 1.68, 3.22 or 4.46 MPa. Data were subjected to one-way anova. The microstructure was analysed using a scanning electron microscope (SEM) after sectioning specimens with a scalpel. RESULT: A trend was observed for higher condensation pressures to produce lower surface hardness values. A condensation pressure of 8.88 MPa produced specimens with significantly lower values in terms of surface hardness than other groups (P<0.001). A condensation pressure of 1.68 MPa conferred the maximum compressive strength; however, it was not statistically different. Higher condensation pressures resulted in fewer voids and microchannels when analysed with SEM. In specimens prepared with lower condensation pressures distinctive crystalline structures were observed. They tended to appear around microchannels. CONCLUSION: Condensation pressure may affect the strength and hardness of MTA. Use of controlled condensation pressure in sample preparation for future studies is suggested.

The fundamental operating principles of electronic root canal length measurement devices.

It is generally accepted that root canal treatment procedures should be confined within the root canal system. To achieve this objective the canal terminus must be detected accurately during canal preparation and precise control of working length during the process must be maintained. Several techniques have been used for determining the apical canal terminus including electronic methods. However, the fundamental electronic operating principles and classification of the electronic devices used in this method are often unknown and a matter of controversy. The basic assumption with all electronic length measuring devices is that human tissues have certain characteristics that can be modelled by a combination of electrical components. Therefore, by measuring the electrical properties of the model, such as resistance and impedance, it should be possible to detect the canal terminus. The root canal system is surrounded by dentine and cementum that are insulators to electrical current. At the minor apical foramen, however, there is a small hole in which conductive materials within the canal space (tissue, fluid) are electrically connected to the periodontal ligament that is itself a conductor of electric current. Thus, dentine, along with tissue and fluid inside the canal, forms a resistor, the value of which depends on their dimensions, and their inherent resistivity. When an endodontic file penetrates inside the canal and approaches the minor apical foramen, the resistance between the endodontic file and the foramen decreases, because the effective length of the resistive material (dentine, tissue, fluid) decreases. As well as resistive properties, the structure of the tooth root has capacitive characteristics. Therefore, various electronic methods have been developed that use a variety of other principles to detect the canal terminus. Whilst the simplest devices measure resistance, other devices measure impedance using either high frequency, two frequencies, or multiple frequencies. In addition, some systems use low frequency oscillation and/or a voltage gradient method to detect the canal terminus. The aim of this review was to clarify the fundamental operating principles of the different types of electronic systems that claim to measure canal length.

Fluorescence microscopy of colour-tagged nanoparticles that are undergoing thermal motion.

To bypass limitations of conventional biochemical analysis, single-particle biochemical analysis is used. To improve single-particle biochemical analysis, procedures are needed to keep nanometre-sized particles in focus while the particles are undergoing thermal motion. A simple, inexpensive procedure is developed here for keeping particles in focus during the continuous observing/discriminating/recording of two different particles, both of which are undergoing thermal motion. This procedure concentrates the particles in a plane of solution that is in focus when the cover glass surface is in focus. An essential component of the procedure is the addition of molten, low-melt agarose to the specimen. Motionless binding to glass is inhibited by inclusion of anti-stick additives in the specimen. Both carrier protein (gelatin) and non-ionic detergent (Triton X-100) are anti-stick additives successfully used here. Intact bacteriophages T3 and T7 are used as model particles, in anticipation of the use of the procedures developed here for the analysis of the assembly of bacteriophages. Observing/discriminating/recording of colour-tagged bacteriophages T3 and T7 is achieved at video frame rate with image splitting to discriminate colours.

A toxicological evaluation of 2-dimethylaminomethyl-1-phenyl-2-propen-1-one hydrochloride.

2-Dimethylaminomethyl-1-phenyl-2-propen-1-one hydrochloride (3) is a novel cytotoxic and anticancer agent. The objective of this study was to obtain information pertaining to possible toxic symptoms detected by in vivo evaluations in mice and an in vitro test for mutagenicity. The data obtained revealed that 3 had no effect on alanine transaminase, aspartate transaminase, HDL cholesterol and protein concentrations in sera nor were variations in the numbers of red and white blood cells detected. Furthermore autopsies of treated mice revealed no pathological symptoms in the heart, kidney, brain, spleen and testes. However elevation of the concentrations of total cholesterol, triglycerides, creatinine and urea were noted in treated mice as well as inflammation of the liver and lungs. Chromosomal aberrations were detected in a micronuclei test. In the Ames test, compound 3 was converted into one or more mutagens in the presence (but not the absence) of a murine liver homogenate. Thus future molecular modifications of 3 should bear in mind approaches to reduce or minimize unwanted side effects.

Fluorescence microscopy of single viral capsids.

To build a foundation for the single-molecule fluorescence microscopy of protein complexes, the present study achieved fluorescence microscopy of single, nucleic acid-free protein capsids of bacteriophage T7. The capsids were stained with Alexa 488 (green emission). Manipulation of the capsids' thermal motion was achieved in three dimensions. The procedure for manipulation included embedding the capsids in an agarose gel. The data indicate that the thermal motion of capsids is reduced by the sieving of the gel. The thermal motion can be reduced to any desired level. A semilogarithmic plot of an effective diffusion constant as a function of gel concentration is linear. Single, diffusing T7 capsids were also visualized in the presence of single DNA molecules that had been both stretched and immobilized by gel-embedding. The DNA molecules were stained with ethidium (orange emission). This study shows that single-molecule (protein and DNA) analysis is possible for both packaging of DNA in a bacteriophage capsid and other events of DNA metabolism. The major problem is the maintenance of biochemical activity.