Orthodontic management of root-filled teeth.

Orthodontists are often concerned about the prognosis of root-filled teeth, particularly when extractions are required for orthodontic treatment. This review provides guidance on assessing the quality of root fillings, as well as the factors which affect the prognosis of root-filled teeth. The implications of previous traumatic injuries and the likelihood of root resorption during orthodontic tooth movement are discussed.

Intravenous infusion cholangiography for investigation of the bile duct: a direct comparison with endoscopic retrograde cholangiopancreatography.

Laparoscopic cholecystectomy has led to an increase in preoperative endoscopic retrograde cholangiopancreatography (ERCP) for the investigation of bile duct stones. ERCP and intravenous infusion cholangiography (IIC) were compared in 111 consecutive patients without jaundice considered to be at high risk for bile duct stones. Both investigations were successfully completed in 100 patients. IIC and ERCP demonstrated a normal bile duct in 81 patients and bile duct stones in 16 patients. IIC failed to identify bile duct stones in two patients (1.8 per cent). IIC was 89 per cent sensitive and 99 per cent specific for detecting bile duct stones in patients without jaundice. It is suggested that IIC is a cost-effective preoperative investigation for bile duct calculi.

Clinical performance of ceramic brackets: a survey of British orthodontists' experience.

Eight-hundred-and-twenty-two British orthodontists were sent questionnaires regarding their use of ceramic brackets. Five-hundred-and-forty-six (66 per cent) responded, and from these, 512 (62 per cent) were analysed. Approximately half of these operators had experience with ceramic brackets, but only 32 operators had treated more than 30 patients. Clinicians' experiences and problems during treatment and debonding are discussed.

Functional appliances and arch width.

A retrospective study was undertaken using treated functional appliance cases. The groups involved 27 Andresen, 19 Bionator, and 23 Fränkel cases. The reflex metrograph was used to measure arch width from study models at the start of treatment, end of treatment including retention, and at least 1 year post-treatment. The effects of each appliance on arch width are compared during and after treatment.

The caracol tower at chichen itza: an ancient astronomical observatory?

Although our investigations reveal a number of significant astronomical events coinciding with many of the measured alignments presented in Table 1, not every alignment appears to have an astronomical match which we can recognize. It may be that only some of the sighting possibilities we have discussed were actually functional. Moreover, our search of significant astronomical events to match the alignments has included only those which seem of obvious functional importance to us: sun, moon, and planetary extremes and the setting positions of the brightest stars. We have emphasized those celestial bodies which are documented in the literature as having been of importance. Perhaps hitherto unrecognized constellations were sighted in the windows, perhaps fainter stars, the heliacal rising and setting times of which could have served to mark important dates in the calendar. While we propose no grand cosmic scheme for the astronomical design of the Caracol it can be inferred that the building, apart from being a monument related to Quetzalcoatl, was erected primarily for the purpose of embodying in its architecture certain significant astronomical event alignments, in the same sense that a modern astronomical ephemeris exhibits information of importance to us in the keeping of the current calendar. There are examples in the Mesoamerican historical literature of deliberate attempts to align buildings with astronomical directions of importance. For example, Maudslay (33) quotes Father Motolinia, who tells us that in Tenochtitlan the festival called Tlacaxipeualistli "took place when the sun stood in the middle of Huicholobos, which was at the equinox, and because it was a little out of the straight, Montezuma wished to pull it down and set it right." According to Maudslay, worshipers were probably facing east to watch the sun rise between the two oratories on the Great Temple of Tenochtitlan at the time of the equinox. The directions of the faces of the Lower and Upper platforms of the Caracol seem to have been laid out deliberately to point to horizon events involving the sun and the planet Venus. Of the lines taken through the windows, the Venus setting points seem most plausible to us in view of both the accuracy with which they fit the architecture and the historical evidence bearing upon the importance of Venus to the Mesoamerican people. A specific connection between the Venus calendar in the Dresden Codex and the sighting of the extreme positions of the planet along the horizon, however, is yet to be established. It is especially significant that alignments in both the base and the top of the tower relate to Venus. The solar equinox alignment in window I remains problematical, although the arrangement probably functioned as an approximate means of determining the first day of spring and the first day of autumn. Lines pointing to individual bright stars undoubtedly should be given lower value. If one is willing to carry the matching game to its ultimate completion, a stellar object can always be found which, although very obscure, will fit an alignment. In our consideration of the problem we have attempted to single out bright stars which appeared or disappeared on significant calendar dates. Other round structures resembling the Caracol exist in Mesoamerica (20), although there are comparatively few built by the Maya. Nearly all can be attributed to the cult of Quetzalcoatl (34). To our knowledge none have been carefully measured and analyzed for astronomical orientations. The ruined tower Q-152 at Mayapan bore distinct similarities to the Caracol, both in shape and structure. It probably contained only a single doorway which faced west. Both structures possessed circular corridors. A circular tower is still standing at Paalmul on the coast of Quintana Roo north of Tulum. Pollock (20, p. 115) states that it has a single room in the turret. A window similar to No. I in the Caracol faces northwest, the same direction as the base of the front of the structure. It may be astronomically significant that the Yucatecan towers fronted in approximately the same direction. Andrews (34) reports the existence of a curious circular building located at Puerto Rico, Campeche, near Xpujil. His crosssectional view of the tower bears a close resemblance to Ruppert's sketch (6, figure 293) of a horizontal section taken through the windows remaining at the top of the Caracol. Hartung (12) has suggested a possible astronomical use for the Puerto Rico tower, but no analysis of the orientation of its "windows," which are much smaller than those of the Caracol, has yet been conducted. Other circular buildings are reported at Ake (20, p. 113) and Isla Cozumel (35, p. 557). We hope that future investigations of the remains of Yucatecan towers will shed further light upon the significance and use of the Caracol as an astronomical observatory.