Open Margin Research Articles

Clinical Technique for an In‐Office Porcelain Modification

All porcelain restorations, especially intra- and extracoronal restorations, have become an accepted treatment modality for the esthetic restoration of posterior teeth. One problem with these restorations is the limited ability to modify the porcelain when a proximal contact is not present or there is an open margin. Using a low-fusing porcelain in a glazing oven, practitioners can easily accomplish such modifications during the try-in and cementation appointment for porcelain inlays. This technique eliminates the need for returning the porcelain inlay to the laboratory for modification and a second patient visit to complete the restoration. This paper describes an in-office procedure for modifying porcelain restorations and a scanning electron micrographic evaluation of the etched porcelain surface after using this modification technique.

Modulation of disk margin structure during renewal of cone outer segments in the vertebrate retina.

In the process of disk renewal in retinal cone outer segments (COSs), apical displacement of disks must be coupled to systematic reductions in disk area and perimeter in order to retain overall conical geometry. We have quantified these changes in disk area and perimeter segment lengths by morphometric analyses of cross sections of fully formed disks taken from basal to apical ends of COSs. Specifically excluded from these analyses are data arising from partial or incomplete disks within the COS, which do not conform to the conical geometry and which constitute a minor fraction of the COS disk population. Thus, our results address the long-range pattern of structural changes affecting the major population of disks along the length of the COS. Our data indicate that decreases in total disk margin length associated with apical displacement of fully formed disks are due to decreases in the length of the margin opposite the cilium, i.e., the open margin segment. In contrast, the average length of the closed margin segment remains constant or increases slightly in the apical direction. The open margins of frog COS disks have recently been shown to possess a distinctive lattice of membrane-associated components (Fetter and Corless: Invest. Ophthalmol. Vis. Sci. 28:646-657, '87). We have also examined COSs by the freeze-fracture, deep-etch technique for evidence of a mechanism whereby measured changes in open margin length may be accommodated while maintaining the overall organization of the open margin segments. In regions of membrane continuity between open margins and the COS plasma membrane, we have observed elevated ridges on the plasma membrane that 1) tend to lie parallel to the open margin segments, 2) have a similar axial spacing, 3) occasionally demonstrate interconnecting filaments similar to those of the open margin lattice, and 4) appear to have a particulate substructure. The mechanism proposed for reducing open margin length involves tangential displacement of the lateral edges of the open margin lattice to the adjacent plasma membrane. These shifted lattice domains initially give rise to the plasmalemmal ridges, which subsequently disassemble, and whose components become redistributed in the COS plasma membrane. These structural features of COS open margins suggest several revisions of our earlier model of disk morphogenesis (Corless and Fetter: J. Comp. Neurol. 257:24-38, '87), which was based on the margin structure of ROS disks alone. Eckmiller (J. Cell Biol. 105:2267-2277, '87) has recently proposed that partial-disks observed within the COS represent sites of new disk formation.(ABSTRACT TRUNCATED AT 400 WORDS)

Marginal accuracy of temporary composite crowns

An in vitro study was conducted to quantitatively compare the marginal adaptation of temporary crowns made from Protemp material with those made from Scutan, Provisional, and Trim materials. A direct technique was used to make temporary restorations on prepared teeth with an impression as a matrix. Protem, Trim, and Provisional materials produced temporary crowns of comparable accuracy. Crowns made from Scutan material had open margins.

Morphology of largeHalimeda bioherms, eastern Java sea (Indonesia): A side-scan sonar study

The most extensive and thickestHalimeda bioherms reported from modern seas occur along both open and protected margins of Kalukalukuang Bank, eastern Java Sea (Indonesia). Seismic profiles suggest these features average 20 to 30 m thick (maximum ∼ 50 m) and developed over large areas by coalescence of individual mounds. Bioherm morphologies range from numerous small mounds (∼ 10–20 m diameter) through “hay-stack” features (∼ 100 m diameter) to broad swells. Some modern bank bioherms display surface forms that appear related to onbank flow from Makassar Strait. Upwelling of cold, nutritive water is likely responsible for unusualHalimeda productivity and large bioherm development.

A clinical evaluation of fixed bridges, 10 years following insertion.

In this long-term clinical study, the condition of extensive fixed bridges was investigated 10 years after cementation. From the records of the Swedish Insurance System (Gothenburg branch) the individuals were randomly selected. All restorative treatment had been performed by private general practitioners. The investigation comprised a total of 238 bridges making 1606 units, 944 abutment and 662 pontics. Seven bridges had been removed and in a further nine cases the bridge had been separated and units removed. Loose retainers were detected at thirty (3%) abutments. In 14.5% of the surfaces a deficiency in marginal adaptation was found. An open margin seemed to be the most serious defect and was often related to caries in contact with the margin of the crown. Caries and fillings in relation to the margin were detected in 8.1% of the surfaces. Porcelain bonded to gold restorations were significantly more often overcontoured in the interproximal space compared with acrylic resin veneer gold bridges. In the investigation the caries status has been also thoroughly reported. Abutment teeth, presumed to be vital, had a prevalence of 10% radiographically visible periapical lesions. Finally, 93.3% of the bridges cemented 10 years prior to the investigation were still in function without any parts being removed.

The relationship between open margins and margin designs on full cast crowns made by commercial dental laboratories

The relationship between open margins and margin designs on full cast crowns made by commercial dental laboratories

The history and spread of bracken in Britain

SynopsisBracken, Pleridium aquilinum, has long been present in Britain as part of the native flora. Before the arrival of man, Britain was a wooded and forested country, and in this vegetation bracken was an open woodland and forest margin species, which played only a relatively minor vegetational role. Its biology is such, however, that this plant is able to spread rapidly in response to removal of the forest canopy, developing into colonies which are much more ecologically aggressive and dominating than was the original habit of the plant when undisturbed.In open conditions, bracken also has a far greater spore output than in more shaded ones. It is able to establish anew from spores only in relatively virgin soil conditions, particularly those produced by burning of other vegetation. Burning also benefits established bracken by removal of its competitors, whilst heavy and selective grazing by sheep also slowly reduces the natural vegetation competition in favour of bracken's further spread.The history of the spread of bracken in Britain from palynological and historical evidence is reviewed in the light of this biology and, in particular, its spread as man has progressively removed the forest canopy,introduced steady heavy grazing pressure, and has burned, and continues to burn, vegetation.

Offbank transport of carbonate sands along open, leeward bank margins: Northern Bahamas

Vigorous offbank transport of carbonate sands occurs along the west-facing, leeward, open margins of Little and Great Bahama Bank. Large, offbank-oriented sand waves, thick sand bodies covering reefs, and shallow-water sands (mostly non-skeletal) obtained from adjacent deep flanks, all demonstrate the existence of this shallow-to-deep pathway of sediment transport. A variety of data suggests that transport occurs during storms and not during normal tidal-current fluctuations. An abundance of composite grains as well as vertical sequences of submarine cemented horizons (seen via seismic profiling within the marginal sand bodies) indicate cyclic periods of relative quiescence followed by moments of intense sediment movement. Current-meter data obtained during six weeks of low wind activity show that critical threshold velocities for sand transport are only barely exceeded during portions of the tidal cycle. These flows coupled with higher-frequency bottom currents (generated by surface gravity waves) winnow the sands but do not provide significant net offbank transport. Offbank sand transport provides material to the shallow and deep bank margins enabling them to expand during sea-level highstands. Each sea-level fluctuation is likely to produce within the shallow margins a vertical sequence of basal reefs, covered by a thick non-skeletal calcarenite, capped by a subaerially exposed, diagenetically altered surface. Shallow-water sands carried off the marginal escarpment help to construct deep flanks and large sediment drifts.

Carbonate Sand Bodies Along Contrasting Shallow Bank Margins Facing Open Seaways in Northern Bahamas

High-resolution seismic profiling, bottom sampling, and aerial and space imagery show that widely contrasting carbonate sand bodies are present along the shallow windward, leeward, and tide-dominated margins of Little and Great Bahama Banks which face open seaways--the Northwest Providence Channel and the northern Straits of Florida. This high diversity in sand bodies and their associated bank margins is due to variations in the level, duration, and magnitude of the physical energy flux across the edges of the platforms. In the Bahamas, the dominant winds, waves, and currents are from the east; hence easterly facing margins are windward, westerly facing margins are leeward. Where strong tidal currents are present (because of adjacent basin shape) the windward and leeward effects are diminished. Thus, bank-margin orientation relative to the climatic energy patterns appears to assert the major controls upon sedimentation. Antecedent topography in the form of islands or subtidal rock ridges creates energy barriers which can control the direction and volume of sediment flux on or off the banks. Along windward margins, energy barriers such as large islands not only block the bankward transport of sands but appear to augment offbank transport by setting up seaward flows. In contrast, along leeward margins, energy barriers prevent the vigorous offbank sand transport that normally occurs when these margins are open and water flow is unrestricted. In addition, sand-body geometry and grain type are controlled by bank-margin orientation. Along windward, open margins, skeletal sands accumulate in the lee of low-relief, mostly relict reefs. These margins are generally sediment-barren, having only a sporadic, thin veneer of sand. Along leeward, open margins a broad (10 × 10 km), thick (12 m), bankward-thinning blanket of sand rich in nonskeletal components (peloids, composite grains) lies on top of rock ridges and reefs. Large, asymmetric sand waves superimposed on this sand body indicate net offbank sand transport. Along the tide-dominated margin, large, broad, oolitic sand lobes have migrated onto adjacent lagoonal muddy sands and indicate net bankward transport. We suggest the following classification of modern, shallow, carbonate bank margins: (1) windward open; (2) windward protected; (3) leeward open; (4) leeward protected; (5) tide dominated. This classification seems to fit many ancient analogs and may be useful in paleoenvironmental reconstructions.

Fossil Carbonate Platform Margins: ABSTRACT

The margin of carbonate shelves and platforms is a critical zone. During construction these margins control both the geometry and the style of sedimentation on the adjacent platforms. After burial they remain a major interface between carbonate and detrital sediments, a preferred site for both hydrocarbon and metallic mineral entrapment. During later deformation the structural style commonly changes across this zone. Fossil carbonate margins occur in two realms: (1) along the craton margins, bordering Paleozoic and earlier ocean basins that are now fragmented and deformed in major mountain belts or buried beneath Mesozoic and Cenozoic successions along modern continental margins, or (2) around the edges of Paleozoic platforms developed in major basins on large cratons. Regardless of setting, two different sedimentary styles recur. Rimmed margins, those composed of an elevated rim of bioherms or carbonate sand shoals, exhibit a marked declivity between shelf and basin. This slope is either gentle, gradually changing from shallow into deeper water sediments (depositional slope), or is a steep incline, with little sediment accretion, over which sediments move on their way to the basin (bypass slope). Slope and toe-of-slope sediments in these settings exhibit a full spectrum of hemipelagic ribbon and parted limestones, hardgrounds, slides and slumps, and sediment gravity flows together with submarine erosion. Open margins or ramps, those in which there is no marked shelf break, gradually change from inner shelf to slope strata. The high-energy zone is l cated well inside the craton margin on the platform or at the strandline. Deeper water shelf limestones are particularly common in these situations while slope deposits are characterized by hemipelagic deposits but fewer examples of gravity flow deposits. End_of_Article - Last_Page 941------------

Megafaunal Facies, Estuary to Shelf Edge, Surrounding Gulf of Mexico: ABSTRACT

Nearly 20 years of marine benthic studies along the rim of the Gulf of Mexico permits recognition of areal (environmental) facies, most of which have exact counterparts in the Gulf Coast Tertiary. These facies have been recognized on the basis of invertebrate faunal diversity, benthic community size and structure, geomorphology of sea bottom, and sedimentary characteristics. Ultimate facies control is exhibited by prevailing climates around the Gulf Coast, ranging from tropical moist in the southeast and southwest to almost xerophytic (dry) in the west. Northern regions are cool-temperate in winter and subtropical in summer with average moisture conditions ranging from very wet for several years to prolonged droughts in following years--the most variable climate in the world. Megafaunal assemblages in shallow waters consist of those found in saltwater and freshwater marshes, river estuaries, low to medium salinity enclosed bays (inter-reef), low and high salinity oyster or mollusk reefs, high salinity open bay centers; open bay sandy margins, inlets, and sand or clay open beaches. Open Gulf or deeper water assemblages are characteristics of shallow shelf (1-20 m), intermediate shelf (21-72 m), outer shelf (73-132 m), and upper slope (132-700 m). Detrital carbonate muds provide slight variations to these facies in areas on the south. Reef-forming organisms create micro-epifaunal habitats modified by wave energy and depth. Faunal composition within each of these habitats is controlled by sediment type and by stability of other environmental factors. Unstable environments with wide ranges of ecologic variables and clay sediments produce low species diversity within small populations. Stable environments on sand-clay mixed bottoms produce high diversity within large populations. Principles used to define these habitats can be applied to Tertiary formations in mapping ancient environments. End_of_Article - Last_Page 2042------------

AGGREGATION SITES OF MALES OF THE COMMON CATTLE GRUB, HYPODERMA LINEATUM (DEVILLERS) (DIPTERA: OESTRIDAE).

Males of Hypoderma lineatum (DeVillers) were discovered aggregating along the open margins of streams coursing through pasture-land ravines in California. These bot flies positioned themselves in a “ waiting attitude” which appeared correlated with mating behavior. Daily flight activity lasted from mid-morning to mid-afternoon, but its continuance depended upon limited masking of the sun by clouds. Marked males tended to remain at the aggregation site and were seen as much as 8 days after their release. Further study of such aggregation behavior as a potential avenue for developing additional control measures against the common cattle grub is necessary.