Tooth cracks may not show up on radiographs,[1,10,12,13,14,15] since X-ray photons passing through a radiolucent fracture plane also pass through extensive amounts of radiopaque healthy tooth structure. A tooth may be cracked if it shows, on a radiograph, a large peri-apical radiolucency that is contiguous with a furcation, or an entire root surrounded by a radiolucency.[10,16,17]
Cracked teeth are often asymptomatic. The pain symptoms that cracked teeth can show are not uniquely associated with cracked teeth but can occur with other causes of tooth pain, such as caries, pulpal pathology, or periodontal disease. Percussion sensitivity, if present, could indicate that the tooth has an irreversible pulpitis or an abscess, which may be associated with a crack. A cracked tooth may not exhibit temperature sensitivity if the crack has caused pulpal necrosis or exhibit sharp pain if a patient occludes on a rubber wheel placed on a suspected cracked cusp. The only consistent sign of a cracked tooth is the existence of a fracture plane within the tooth.
Cuspal fractures can be caused by forces put on existing restorations during masticatory cycles; these forces stress the stress planes located apical to the cusps that retain the restorations.[32,40] With an amalgam, the preparation axial walls converge toward the occlusal, so occlusally directed forces on the restoration stress the cuspal stress planes. The walls of an inlay preparation diverge toward the occlusal, so apically directed forces stress the cuspal stress planes. If the dentist removes the restoration and observes the dried preparation surface, the dentist may observe a crack line located at what was previously the apical-lateral aspect of the restoration [Figure 7].
Cuspal fracture planes can develop inside a tooth without showing visible crack lines on the external surface of the tooth, if the fracture plane is subgingival, or if the fracture plane has not expanded enough in area to reach the external tooth surface [Figure 9]. A dentist may not treat such a tooth due to inability to locate a crack line,[41,42] and the tooth may feel sensitive for a long time; later, a cusp may break off, and the sensitivity may consequently end. The diagnosis of a crack in a tooth with no visible crack line requires presumption, and the patient's conviction of which tooth is sensitive. Cementing an orthodontic band[41,43,44,45] on such a tooth aids in the diagnosis if doing so eventually reduces the discomfort.
A radiograph of a maxillary molar that contains minimal remaining coronal tooth structure that can help to retain the large mesial-occlusal-distal restoration. The remaining tooth structure is under higher stress levels from retaining the restoration. Part of the distal aspect of the remaining tooth structure fractured, showing that the remaining tooth structure is not strong enough to retain this direct restoration without developing cracks
A dentist may be tempted to drill out a crack line until the dentist has reached healthy tooth structure, and then place a direct restoration, to seal the tooth structure. However, a crown may be needed to prevent the original causes of the crack from causing further crack propagation. Drilling into a fracture plane by following a crack line theoretically should not substantially reduce the structural stability of the tooth, since tooth structure along a fracture plane is not chemically bonded and therefore does not help to bind the tooth together. Such crack line drilling should be done with a thin bur to ensure a conservative, narrow drilling width that preserves dentin, with microscopes ensuring that the dentist does not drill past the apical extent of the fracture plane.
Microscopes facilitate observation of microscopic crack lines that may show minimal color contrasts against a desiccated tooth surface [Figure 12], without needing trans-illumination or dyes to observe crack lines. Microscopically precise tactile sensation permits verification of a crack by associating the tactile sensation of an explorer tip falling into a cleft with the microscopic point on a crack line where the tip is located. Microscopes permit detecting microscopic amounts of debris in the cleft, or microscopic differences, in the respective directions of movement, of separate tooth structures shifting independently of one another around a cleft [Figure 13]. Stripping a microscopically thin layer from a surface with a deep craze line may reveal uncracked underlying tooth structure, indicating that the crack is superficial.
Microscopes permit accurate visual estimation of the steepness of cuspal inclines, and allow precise observation of where a pointy lingual plunger cusp occludes into an opposing tooth, and observation if a microscopic crack line is developing around this contact area. Microscopic amounts of chalky white or beige discoloration underneath a cusp can be indicative of caries under the cusp, which sometimes can be overlying a fracture plane. Microscopes facilitate observing microscopic gaps or elevations of restoration margins, which may indicate cracks. Microscopes improve the ability to understand the dimensions of foreshortened surfaces. This facilitates observing a marginal ridge crack from an occlusal viewing vantage point, to assess how closely to the gingiva the crack has propagated.
Using microscopes and co-axial illumination, a dentist may drill an exploratory column through a crack line, to observe the depth at which the crack line disappears, or to assess if the crack line extends into the pulp chamber roof. Sometimes, such exploratory drilling may be necessary to allow a dentist to discover that an asymptomatic tooth has a fracture plane that extends into the pulp chamber. Discovering this allows a dentist to diagnose that this asymptomatic tooth has a necrotic nerve. Although such exploratory drilling is not necessarily superior to thermal, and electric pulp testing for diagnosing a necrotic nerve, such exploratory drilling may be a useful diagnostic adjunct if the thermal and electric pulp testing results are inconclusive.
Isaac's room is where Isaac spawns upon entering the stage. It contains a bed in the upper left corner and a carpet in the center, like a regular Bedroom, as well as a Locked Chest. Isaac can sleep in his bed to recover provided he's not at full health, or to add three Soul Hearts provided he has no Red Heart containers. Triggering an explosion on the carpet will cause it to be damaged, but reveal nothing underneath.
OpenModelica can interpret complex mathematical results from your SysML model by producing compelling graphs that contain rich detail. The example image graphs a bouncing ball modeled in a SysML model and produces an OpenModelica plot of the height over time.
Poly. Poly pipe is a soft plastic pipe that comes in coils and is used for cold water. It can crack with age or wear through from rocks. Other weak points can be the stainless steel clamps or galvanized couplings.
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