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(1/479) The root surface in human teeth: a microradiographic study.

In an attempt to clarify the nature of the human cemento-dentinal junction, ground sections of incompletely formed and fully formed extracted teeth were prepared and their histology compared with their microradiographic appearances. The results showed that incompletely formed teeth possess distinctive surface layers outside the granular layer of Tomes. The evidence indicates that these layers are of dentinal origin; their presence during development supports previous explanations by the author of the hyaline layer of Hopewell-Smith and of so-called intermediate cementum. The results also indicate that the granular layer of Tomes does not represent the outer limit of root dentine. The relationship of these surface layers to the definitive cementum which is present in fully formed teeth was studied in both young and older patients. From the results it was concluded that cementum formation begins in the more apical region of the teeth at a time when root formation is well advanced, and that it spreads towards the crown rather than in the generally accepted reverse direction.  (+info)

(2/479) A modern human pattern of dental development in lower pleistocene hominids from Atapuerca-TD6 (Spain).

The study of life history evolution in hominids is crucial for the discernment of when and why humans have acquired our unique maturational pattern. Because the development of dentition is critically integrated into the life cycle in mammals, the determination of the time and pattern of dental development represents an appropriate method to infer changes in life history variables that occurred during hominid evolution. Here we present evidence derived from Lower Pleistocene human fossil remains recovered from the TD6 level (Aurora stratum) of the Gran Dolina site in the Sierra de Atapuerca, northern Spain. These hominids present a pattern of development similar to that of Homo sapiens, although some aspects (e.g., delayed M3 calcification) are not as derived as that of European populations and people of European origin. This evidence, taken together with the present knowledge of cranial capacity of these and other late Early Pleistocene hominids, supports the view that as early as 0.8 Ma at least one Homo species shared with modern humans a prolonged pattern of maturation.  (+info)

(3/479) The crystal growth technique--a laboratory evaluation of bond strengths.

An ex vivo study was carried out to determine differences in the bond strengths achieved with brackets placed using a crystal growth technique compared with a conventional acid-etch technique. A solution of 37 per cent phosphoric acid was used for acid-etching and a commercially available polyacrylic acid gel, Crystal-lok for crystal growth. A heavily-filled composite resin was used for all samples to bond brackets to healthy premolar teeth extracted for orthodontic purposes. Polycrystalline ceramic and stainless steel brackets were used and tested to both tensile and shear failure using an Instron Universal Testing machine. The tensile and shear bond strengths were recorded in kgF. In view of difficulties experienced with previous authors using different units to describe their findings, the data were subsequently converted to a range of units in order to facilitate direct comparison. The crystal growth technique produced significantly lower bond strengths than the acid-etch technique for ceramic and stainless steel brackets, both in tensile and shear mode. The tensile bond strength for stainless steel brackets with crystal growth was 2.2 kg compared with 6.01 kg for acid-etch, whilst with ceramic brackets the tensile bond strengths were 3.9 kg for crystal growth and 5.55 kg for acid-etch. The mean shear bond strength for stainless steel brackets with crystal growth was 12.61 kg compared with 21.55 kg for acid-etch, whilst with ceramic brackets the shear bond strengths were 7.93 kg with crystal growth compared with 16.55 kg for acid-tech. These bond strengths were below those previously suggested as clinically acceptable.  (+info)

(4/479) Super pulse CO2 laser for bracket bonding and debonding.

A super pulse and a normal pulse CO2 laser were used to carry out enamel etching and bracket debonding in vitro and in vivo. The shear bond strength of the orthodontic brackets attached to laser-etched and conventional chemically-etched extracted premolars was measured. The pulp cavity temperature was also measured using the same laser irradiation conditions as the shear test. Both super pulse and normal pulse CO2 laser etching resulted in a lower shear bond strength (super pulse: 6.9 +/- 3.4 kg, normal pulse: 9.7 +/- 5.2 kg) than that of chemical etching (15.3 +/- 2.8 kg). Furthermore, the super pulse CO2 laser was able to create debonding at 2 watts within a period of less than 4 seconds (2.9 +/- 0.9 seconds). The super pulse, when irradiating the ceramic brackets from above, during debonding showed a 1.4 degrees C temperature increase in the dental pulp at 2 watts and an increase of 2.1 degrees C at 3 watts. While etching, directly irradiating the enamel surface at 3 watts, the dental pulp showed a temperature increase of 3.5 degrees C. These temperature increases were within the physiologically acceptable limits of the pulp. These results indicate that, in orthodontic treatments, super pulse CO2 laser debonding is more useful than laser etching.  (+info)

(5/479) An ex vivo investigation into the bond strength of orthodontic brackets and adhesive systems.

The aim of this study was to compare the shear bond strength of Adhesive Precoated Brackets (APC) with that of two types of uncoated bracket bases, Straight-Wire and Dyna-Lock. Two types of orthodontic adhesives were used, Transbond XT and Right-On. Three different curing times were evaluated with the APC brackets in order to find the best. Adhesive remnants on the enamel surface following debond were evaluated using the Adhesive Remnant Index (Artun and Bergland, 1984). Bond strengths ranged from 11.00 to 22.08 MPa. For both types of brackets Transbond produced a significant increase in bond strength compared to Right-On. The Dyna-Lock/Right-On combination produced the poorest results. APC brackets cured for 40 s had similar bond strengths to uncoated brackets fixed by means of Transbond. Overall, 79 per cent of specimens had less than half the tooth surface covered with adhesive following debond. Significantly more adhesive remained on tooth surfaces following debond of the Straight-Wire/Right-On group than any other bracket/adhesive combination. Bond strengths were higher with light-cured Transbond than with chemically-cured Right-On. When Transbond is used in association with APC brackets a 40-second cure time is recommended.  (+info)

(6/479) Intra-oral temperature variation over 24 hours.

This study aimed to investigate temperature variation at archwire sites adjacent to the maxillary right central incisor and first premolar, its correlation with ambient temperature, and the influence of inter-racial variation. Twenty young adult male subjects were randomly selected (13 Asian, seven Caucasian). Thermocouples were attached to the labial archwire component of custom-made orthodontic retainers at the two intra-oral sites. A third thermocouple measured ambient temperature. A data-logger recorded temperatures at 5-second intervals over a 24-hour period. Temperatures ranged from 5.6 to 58.5 degrees C at the incisor and from 7.9 to 54 degrees C at the premolar, with medians of 34.9 degrees C and 35.6 degrees C, respectively. Ambient temperature correlated poorly with the intra-oral temperatures. The Asian and Caucasian groups had significantly different temperature distributions. On average during the 24-hour period, temperatures at the incisor site were in the range of 33-37 degrees C for 79 per cent of the time, below it for 20 per cent, and above it for only 1 per cent of the time. Corresponding figures for the premolar site were 92, 6, and 2 per cent. At both archwire sites the most frequent temperatures were in the range of 35-36 degrees C. The data presented demonstrate that the temperature at sites on an archwire in situ varies considerably over a 24-hour period and that racial differences may exist. This information should be considered during the manufacture and use of temperature-sensitive orthodontic materials, in particular nickel-titanium archwires and springs.  (+info)

(7/479) Elastic activator for treatment of open bite.

This article presents a modified activator for treatment of open bite cases. The intermaxillary acrylic of the lateral occlusal zones is replaced by elastic rubber tubes. By stimulating orthopaedic gymnastics (chewing gum effect), the elastic activator intrudes upper and lower posterior teeth. A noticeable counterclockwise rotation of the mandible was accomplished by a decrease of the gonial angle. Besides the simple fabrication of the device and uncomplicated replacement of the elastic rubber tubes, treatment can be started even in mixed dentition when affixing plates may be difficult.  (+info)

(8/479) A laboratory investigation to compare enamel preparation by sandblasting or acid etching prior to bracket bonding.

A laboratory investigation to compare the mean shear debonding force and mode of bond failure of metallic brackets bonded to sandblasted and acid-etched enamel is described. The buccal surfaces of 30 extracted human premolars were sandblasted for 5 seconds with 50 mu alumina and the buccal surfaces of a further 30 human premolars were etched with 37 per cent phosphoric acid for 15 seconds. Following storage for 24 hours at 37 degrees C in distilled water, shear debonding force was measured using an Instron Universal Testing Machine with a cross-head speed of 10 mm/minute. Mean shear debonding force was significantly lower for brackets bonded to sandblasted enamel compared to acid etched enamel (P < 0.001). Weibull analysis showed that at a given stress the probability of failure was significantly greater for brackets bonded to sandblasted enamel. Brackets bonded to etched enamel showed a mixed mode of bond failure whereas following sandblasting, failure was adhesive at the enamel/composite interface (P < 0.01).  (+info)