ABSTRACT
Surface relief gratings are holographically fabricated in thin polybutadiene rubber films produced by both spin coating and dip coating on glass and metal substrates. These thin-film gratings are characterized for their application as efficient transducers for detecting dynamic strain in solids. The performance of these rubber-grating transducers is compared to surface-mounted fiber Bragg gratings for a range of frequencies between 50 Hz and 30 kHz. Dynamic-strain sensitivity around 1 nepsilon/radicalHz is recorded for thin rubber-film grating transducers.
ABSTRACT
BACKGROUND: Failure to replace a missing posterior tooth is assumed to result in host of adverse consequences, which include shifting of teeth and loss of alveolar bone support. METHODS: A retrospective longitudinal study (median follow-up period 6.9 years), using the radiographs of 111 patients who had an untreated bounded edentulous space, or BES, was conducted to determine the extent to which these adverse outcomes occurred. RESULTS: The majority of patients lost 1 millimeter or less of the distance between teeth adjacent to the space, extrusion of the opposing tooth was < or = 1 mm in 99 percent of the cases, and the amount of alveolar bone loss next to the adjacent teeth was < or = 1 mm in 83 percent of the cases. CONCLUSIONS: Within the follow-up time in this study, this group of patients did not exhibit the expected adverse consequences with either the frequency or severity generally assumed to be associated with nonreplacement of a single posterior tooth. CLINICAL IMPLICATIONS: These findings suggest that for the large majority of patients who experience a single-tooth posterior BES, immediate treatment may not be critical to the maintenance of arch stability. Instead, regular follow-up assessments to monitor change in stability and periodontal health may be warranted.
Subject(s)
Alveolar Bone Loss/etiology , Jaw, Edentulous, Partially/physiopathology , Tooth Extraction/adverse effects , Tooth Migration/etiology , Adult , Aged , Aged, 80 and over , Alveolar Bone Loss/diagnostic imaging , Bicuspid/physiology , Dental Arch/diagnostic imaging , Dental Arch/physiopathology , Female , Humans , Jaw, Edentulous, Partially/diagnostic imaging , Longitudinal Studies , Male , Middle Aged , Molar/physiology , Radiography , Retrospective Studies , Tooth Migration/diagnostic imagingABSTRACT
The common practice of rerestoring teeth has been termed the "cycle of rerestoration." Some researchers and clinicians have speculated that this cycle results in teeth receiving progressively larger restorations. In this study involving 1,337 decisions to replace existing restorations in posterior teeth, the authors noted that 70 percent of all recommendations resulted in an increased number of restored surfaces. This observed increase in restoration size raises questions about the effects of the rerestoration cycle on the health of a tooth and suggests that practitioners should attempt to avoid premature rerestoration since it could hasten the cycle.
Subject(s)
Dental Restoration, Permanent/adverse effects , Adult , Aged , Decision Making , Dental Caries/diagnosis , Dental Caries/therapy , Dental Marginal Adaptation , Dental Restoration, Permanent/statistics & numerical data , Female , Humans , Male , Middle Aged , Practice Patterns, Physicians' , Reoperation , Risk AssessmentSubject(s)
Composite Resins , Dental Alloys , Dental Bonding , Electrolysis , Stress, Mechanical , Surface Properties , Tensile StrengthABSTRACT
A technique has been presented for indirect fabrication of a cast post and core with the refractory material DVP. This method eliminates the need for developing full contoured patterns and their removal from the working cast for investment. Less time is required and the accuracy of the castings is improved.
Subject(s)
Calcium Sulfate , Crowns , Models, Dental , Post and Core Technique , Dental Casting Investment , Dental Impression Technique , Denture Design , HumansABSTRACT
A technique for fabrication of custom shade tabs in tooth form has been presented. The finished product will be a series of custom shade tabs. Any temporary (provisional) resin material can be used.
Subject(s)
Color , Denture Design , Esthetics, Dental , Acrylic Resins , Humans , Tooth, ArtificialABSTRACT
We have previously described a mutant strain of Escherichia coli (2S142) which shows a specific inhibition of stable RNA synthesis at 42 degrees C. The temperature-sensitive lesion mimics a carbon source downshift (diauxie lag). We therefore measured RNA synthesis and levels of ppGpp (guanosine 5'-diphosphate 3'-diphosphate) on a number of different carbon sources. There is a 6-fold variation in ppGpp levels at 42 degrees C, depending on the carbon source present. Much of the variation in ppGpp levels at 42 degrees C can be explained by variations in the decay rate of ppGpp at 42 degrees C. The rates of ribosomal RNA and total RNA synthesis also vary with the carbon source at 42 degrees C. Linear regression analysis shows only a moderately good correlation (correlation coefficient = 0.62, P = 0.0001) between the ppGpp level at 42 degrees C and the rate of rRNA synthesis at 42 degrees C. In fact, ppGpp levels are a slightly better predictor of the rate of total RNA synthesis (correlation coefficient = 0.69, P = 0.0001) at 42 degrees C. Other variables such as rate of carbon source uptake appear to have very little, if any, relationship to the rate of rRNA synthesis on the different carbon sources. Segmented linear regression analysis indicates that ppGpp levels and rates of RNA synthesis correlate best when the carbon sources are divided into two groups: 6- and 12-carbon sugars and other carbon sources. The rate of rRNA synthesis in 2S142 at 42 degrees C appears to be relatively insensitive to ppGpp levels with 6- and 12-carbon sugars as the carbon source. These data raise the possibility that carbon source may affect rRNA synthesis in a manner that is at least partially unrelated to ppGpp levels.
