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PubMedDate not supplied

[The role of anthropologic study in the stomatognatic morphologic changes through time].

OBJECTIVES: The possibility of a prognosis regarding the morphologic aspect of the passive component of stomatognathic apparatus was assessed through some researches on the viscero-cranium aspect. METHOD: The study used 20 skulls or skull fragments, 8 were from the first century A.D., 4 from the Middle Ages and the rest of 8 were from the XX-th century. All The skulls were found on the Romanian territory. A series of measurements were made on the maxilla, mandible and on the face as a whole; the results were compared with the literature data. RESULTS: The skulls discovered in the Neolithic necropolis existing on the Romanian territory are of mediterranoic type, with an antero-posterior prolonged skull and with narrow dental arches, presenting a prognathism according to the shape of the skull. After the Neolithic, the shape of the skull changes to a more rounded one and the dental arches become upsiloid. In the Middle Age, the dental arches tend to evolve from the upsiloid type to the paraboloid type. In our century, the paraboloid form of the dental arches is maintained (semiellipitic shape of the maxilla and the parabolic shape of the mandible). CONCLUSIONS: During the ages, the evolution of masticator apparatus was influenced mainly by the genetic factor regarding the shape and the pathology, but also, in some degree, by the dietary habits. Multiple changes have been made possible a gene crossing between individuals. Due to the genetic mixture between the local element and the migratory population, the evolution of the stomatognathic apparatus to paraboloid dental arches is explained, although upsiloid dental arches can be found.

Adult↗
PubMed2002

Perceptions of pediatric patients and guardians about prosthetic appliances.

Forty patients that received prosthetic appliances as part of dental treatment were interviewed about satisfaction with the apparatus. The opinions of the guardians were also considered. The majority of children had complained about missing teeth, but even a greater percentage expressed satisfaction during wear of the prosthetic appliance. Among the guardians, only one of them expressed dissatisfaction with the appliance design. Rehabilitation plan should be discussed with children and guardians considering their perceptions and adequate indications for each case.

Caregivers↗
PubMedDate not supplied

[Models of automated mandibular kinematics in the Kennedy Class I partial edentate].

The biunivocal relationships which exist between the elements and the functions of the dento-maxillary apparatus are also found in the determination and the effects of automated mandibulary movements in patients with class I edentation. Kinesiographic mandibulary analysis correlated with clinical observations certain characteristics can be identified of which the most evident, resulting from the edentation, and at the same time the most important from the viewpoint of dysfunctional implications is the almost permanent presence of horizontal, mainly sagittal movements of the teeth and of the temporo-mandibulary articulation. Propulsion of the mandibula in this way is at the origin of many irritative foci: in the frontal teeth that have to transmit and to take up the forces which have unfavourable directions; the muscles, especially the external pterygoidal muscles that are overstressed; the temporo-mandibulary articulation where the unfunctional relationship between the mandibular condyl, the articular disk, and the articular eminence will acquire an almost permanent character. The consolidation of the propulsed (mesial) position of the mandibula by prosthetic treatment in this position cannot have but negative effects for the elements of the dento-maxillary apparatus.

Dental Occlusion↗
PubMed1995

Fine structure of tooth germs during the formation of enameloid matrix in Tilapia nilotica, a teleost fish.

Tooth germs were examined by light and transmission electron microscopy. Collagen fibrils were relatively dispersed and thin at the early and middle stages of formation of the enameloid matrix, when the enameloid layer was thin. At the late stage, the fibrils became thicker, reaching nearly 30 nm dia, and formed the interwoven thick bundles that are characteristic of teleost cap enameloid. Abundant flocculent and/or fine, network-like material, probably representing glycosaminoglycans or proteoglycans, was located between the collagen fibrils. Tall, columnar, inner dental epithelial cells contained abundant rough endoplasmic reticulum and many mitochondria, and a well-developed Golgi apparatus was seen around the nuclei at the late stage. Elongated vesicles enclosing fine, filamentous material that resembled procollagen granules, and large granules containing fibril-like structures that were 150 nm in thickness and had periodic cross-banding at 32-nm intervals, were usually observed near the Golgi apparatus. The contents of the large granules were well stained with phosphotungstic acid, which suggests that inner dental epithelial cells synthesize collagen fibrils. At this time, odontoblasts also contained abundant rough endoplasmic reticulum and mitochondria, a well-developed Golgi, several kinds of granule including those that probably contained procollagen, and many microtubules. It is proposed that odontoblasts are involved in the formation of a considerable portion of the enameloid matrix, including collagen fibrils.

Amelogenesis↗
PubMed2004

Evaluation of wear resistance of dental resin composites with a 3D profilometer.

The objectives of this study were to determine the wear resistance of dental resin composites, and to evaluate the influence of wear-simulating apparatus on wear. Nine commercial resin composites were studied. Wear was simulated with an oral wear simulator (Proto-Tech), which simultaneously incorporates the wear mechanism of attrition and abrasion in three-body wear mode, and with a pin-on-disk type friction tester (Rhesca, Japan). Composite specimens were subjected to 50,000 cycles of wear against a dental porcelain antagonist. After wear simulation, parameters for the determination of wear amount, such as wear volume, maximum wear depth, mean of maximum wear depth, and average wear depth were measured with the use of a 3D profilometer. For the oral wear simulator, the range of wear volume was 4.3-9.2 x 10(-2) mm3, and there were significant differences among the composites (p < 0.05). In other parameters, there were no significant differences among the composites. For the pin-on-disk tester, the range of mean of maximum wear depth was 7.5-26.3 microm, which was significantly different among the composites (p < 0.05). Correlation coefficient (r) between the wear volume from the oral wear simulator and the mean of maximum wear depth from the pin-on-disk tester was 0.52. Conclusively, dental resin composites showed significantly different wear resistance. Wear simulating apparatus influenced the amount of wear, and suitable parameters for the determination of wear amounts should be selected in each apparatus.

Composite Resins↗
PubMed2006

Surface integrity and removal mechanism in simulated dental finishing of a feldspathic porcelain.

Dental abrasive finishing of a fine-grained feldspathic porcelain was performed on a computer-assisted apparatus for simulation of a 2-degrees-of-freedom restorative operation with a dental handpiece and a coarse diamond bur of grit size of 106-125 mum. Finishing forces, surface roughness, and morphology were investigated as functions of finishing conditions. The tangential and normal forces were measured using a piezoelectric dynamometer and a data processing system. The results indicated that these forces increased with either the depth of cut or with the feed rate, in the ranges of 0.12-0.31 N and 0.45-1.09 N, respectively. However, an increase in either depth of cut or feed rate affected neither the surface roughness measured using a stylus profilometer nor the morphology observed under a scanning electron microscope. The finished porcelain surfaces were found to consist of the microfracture and chipping areas, ductile removal areas, smeared areas, and debris. Irregular fracture and chipping resulted from the extension of lateral/median cracks; ductile micromachining was attributed to the plastic deformation accompanied by distributed microcracks. It was determined that a combination of the microfracture and ductile micromachining was the primary mechanism for material removal.

Computer Simulation↗
PubMed1985

Creep of posterior dental composites.

The creep of microspecimens of posterior dental composites was studied using a torsional creep apparatus. Shear stresses were maintained for 3 h and recovery was followed for 50 h. Creep curves were obtained at 21, 37, and 50 degrees C and four torque levels. The effect of conditioning the specimens in water up to 8 weeks was studied. The posterior composites exhibited linear viscoelastic behavior at low deformations. They had higher shear moduli and greater resistance to creep than conventional and microfilled composites. In aging experiments, maximum shear moduli occurred when specimens were 48 h to 1 week old. Subsequent softening was attributed to water absorption. Residual strain was highest when the composites were stressed within 24 h of initiating polymerization. Residual strain was very low in specimens 48 h to 8 weeks of age.

Aluminum Compounds↗
PubMed1987

Creep of amalgam at low stresses.

The creep and recovery of dental amalgam were studied with a torsional creep apparatus. The purpose was to investigate viscoelastic behavior in a low stress range that might result from normal chewing forces. The creep of specimens up to six months old was also studied. Four types of alloys for amalgam were used: two single-composition sphericals (SCS), an admixture-lathe-cut eutectic (ALE), and a conventional (CON). Constant torque was applied to dumbbell-shaped specimens for three hr and, after the stress was released, recovery was followed for 50 hr. All measurements were made in water at 37 degrees C after storage of the specimens for one week in 37 degrees C water. Creep was also measured at nine intervals on specimens aged from three hr to six months. The SCS amalgams exhibited the least amount of creep, followed by the ALE amalgam. The CON amalgam had the highest creep. The SCS amalgams approached linear viscoelastic behavior in the shear stress range of 0.78-4.10 MPa at 37 degrees C. They did not exhibit steady-state (viscous) creep at stresses less than 4.10 MPa. Recovery was complete but proceeded more slowly than creep. The ALE and CON amalgams exhibited viscous creep at 1.23 MPa and higher. The steady-state creep rate depended on stress, and the stress exponent ranged from 2.3-3.5. All except the ALE amalgam showed essentially constant creep compliance when aged up to six months, once the amalgamation reaction was completed after 24 to 48 hr. The compliance of the ALE amalgam gradually decreased over the six-month period.

Chemical Phenomena↗
PubMed1985

Prevention of bacterial contamination of water in dental units.

A study of the bacterial contamination of water in dental units was conducted in five dental practitioners' clinics and one university dental hospital in Tokyo. Various bacteria in numbers of 10(2)-10(5)/ml were detected in the water delivered from all 42 of the dental units examined, though very few bacteria were detected in the tap water upstream of the units. Most of the organisms isolated from the water were Gram-negative bacilli, predominantly Alcaligenes, Achromobacter and Pseudomonas spp. A new decontamination apparatus that could be incorporated into the pipe system of dental units was devised and its performance was evaluated in one unit. It effectively prevented bacterial contamination of the water.

Bacteria↗