Relationship between the cranial base and the mandible in artificially deformed skulls.

OBJECTIVES: There is controversy regarding the relationship between mandibular position and alterations of the cranial base that provoke a more anterior location of the glenoid fossa. Artificially deformed skulls display marked alterations of the cranial base. This study evaluates mandibular changes as function of the morphology of the cranial base in these skulls. MATERIAL AND METHODS: A geometric morphometric study was performed on lateral cephalometric X-rays of three groups of skulls: 32 with anteroposterior deformity, 17 with circumferential deformity and 39 with no apparent deformity. RESULTS: In artificially deformed skulls, the cranial base was deformed causing the mandibular condyle to be in a more anterior position. There was a complete remodelling of the mandible involving narrowing and elongation of the mandibular ramus, rotation of the corpus of the mandible and increased vertical height of the symphysis. Forward displacement did not occur. Integration between mandible and cranial base is not altered by deformation of the skull. CONCLUSIONS: Deformity of the cranial vault exerts an influence on the mandible, supporting the theory of modular units in complete integration. This also supports the theory that mandibular prognathism is a multifactorial result and not a direct effect of displacement of the cranial base.

In vitro and in vivo evaluation of a new zirconia/niobium biocermet for hard tissue replacement.

Metals and ceramics are commonly used in orthopaedics, dentistry and other load bearing applications. However, the use of ceramic matrix composites reinforced with biocompatible metals for heavy load-bearing hard tissue replacement applications has not previously been reported. In order to improve the reliability and the mechanical properties of biomedical implants, new zirconia-Nb composites have been recently developed. The aim of this study was to investigate the biological tolerance of these new zirconia/Nb biocermets implants with both in vitro and in vivo approaches. At first, human bone marrow derived mesenchymal stem cells were cultured on sintered biocermet discs with polished surfaces and were compared with responses to niobium metal. In vitro, the biocermets showed no deleterious effect on cell proliferation, extra-cellular matrix production or on cell morphology. Furthermore, the biocermet showed a higher percentage of cell proliferation than Nb metal. On the other hand, the bone response to these new zirconia/Nb biocermets was studied. Cylinders of biocermets, as well as commercially Nb rod were implanted in the tibiae of New Zealand white rabbits. All the animals were euthanatized after 6 months. The specimens were processed to obtain thin ground sections. The slides were observed in normal transmitted light microscope. A newly formed bone was observed in close contact with material surfaces. No inflamed or multinucleated cells were present. This study concluded that zirconia/Nb composites are biocompatible and osteoconductive. The ceramic-metal composite has even better osteointegration ability than pure Nb. In conclusion, zirconia-Nb biocermet is suitable for heavy load-bearing hard tissue replacement from the point of view of both mechanical properties and biocompatibility.

Stomatology and odontology: perspectives of Spanish professors and senior lecturers in dentistry.

The curricula of dental faculties in many countries of the European Union can be described as odontological. The faculties of some of the countries who have become and are becoming members of the European Community have traditionally educated dentists in the stomatological tradition. In 1987, the Spanish dental education system initiated movement from the stomatological model to the odontological. Both models have their respective strengths and weaknesses. This study surveyed professors and senior lecturers in Spain's public dental faculties to assess their perspectives on 10 items related to the tension between the odontological and the stomatological approach to preparing dentists. Amongst other things, the results of the study indicate that the respondents believe the odontological model, with its emphasis on strengthening technical qualifications, may not prepare individuals for dental practice better than the stomatology tradition; and that the odontological model results in the loss of the strength of the stomatological model, that is, the strong foundation in clinical medicine. The suggestion is advanced that European dental educators consider revising the odontology curriculum to strengthen the education of dental students in clinical medicine. A curriculum in which dental and medical students share the first 3 years of study could accomplish this. It is further suggested that subsequent years in the curriculum be flexible enough for students to earn degrees in both dentistry and medicine, if desired. Such an approach is not inconsistent with the accepted profile and competencies of the European dentist.

Frontal-plane lateral border movements and chewing cycle characteristics.

We studied the dental contact section of the chewing cycle, the most important section in terms of function (as it governs the effectiveness of food trituration). Specifically, we determined closing phase dental contact distance and lateral path inclination in a sample of healthy subjects, and investigated possible relationships between these variables and Ahlgren chewing cycle type. The chewing cycle was characterized in 63 healthy subjects by frontal plane kinesiography. In all cases kinesiographs were obtained for both right- and left-side chewing, with chewing gum as bolus. In all cases we determined closing phase dental contact distance, lateral path inclination and Ahlgren chewing cycle type. Most subjects (84%) showed 'normal' chewing cycles (Ahlgren types I-IV); inverted, contralateral and irregular cycles (types V-VII) were infrequent. Mean dental contact distance was 0.9 mm for right-side chewing and 1.2 mm for left-side chewing. Mean lateral path inclination was 35 degrees for right-side chewing and 37 degrees for left-side chewing. Normal chewing cycles are generally bilateral, whereas abnormal chewing cycles are never bilateral. Border movement distance does not differ in any consistent way between 'chopping' and 'grinding' chewing cycle types. Closing phase dental contact distance showed a significant positive correlation with lateral path inclination.

Case report: impression and maxillo-mandibular relationship recording for construction of obturator prostheses.

The present case report describes a procedure for obtaining the master impression and the maxillo-mandibular relationship for the definitive prosthesis in a maxillectomy patient. After casting the metal framework, a visible-light-cured tray resin was spread over the resin retention grid and gradually cured. Modelling compound was extended over the resin with functional movements, and finally the margins of the defect were sealed with a dental impression wax. A column of light-cured resin was constructed from the lower face of the resin/compound/wax structure to the opposing dental arch. This column permitted recording of the maxillo-mandibular relationship.

Differences in bonding to acid-etched or Er:YAG-laser-treated enamel and dentin surfaces.

STATEMENT OF PROBLEM: Er:YAG (erbium-doped yttrium aluminium garnet) lasers have been effective in the removal of dental tissues. It has been suggested that they are also useful for preparing dental surfaces for adhesion, but results to date have been controversial. PURPOSE: This study compared the tensile strength of bracket-tooth bonds obtained after preparation of the surface for adhesion (dentin or enamel) by conventional acid-etching or by Er:YAG laser etching and investigated microstructure of resin-tooth interfaces using the 2 procedures. MATERIAL AND METHODS: Eighty healthy human premolars were used. Brackets were cemented to acid-etched enamel, laser-etched enamel, acid-etched dentin, or laser-etched dentin (20 teeth per group). Dentin was previously exposed using a high-speed handpiece. Acid-etching was with 37% orthophosphoric acid (15 seconds for enamel, 5 seconds for dentin). Laser etching was with Er:YAG laser (four 200 mJ pulses per second for enamel; four 160 mJ pulses per second for dentin). Brackets were bonded with autocuring resin paste, having first applied a primer (dentin only) and then light-cured bonding resin. Tensile strength was determined with a universal testing machine. Data were analyzed with 2-way ANOVA and subsequent t test with Bonferroni correction. Fracture patterns were compared by the Wilcoxon test with Bonferroni correction. For SEM studies of the resin-tooth interface, a total of 12 premolars were used (3 for each tissue per treatment combination). RESULTS: Mean tensile bond strength for acid-etched enamel (14.05 +/- 5.03 MPa) was significantly higher (P<.05) than for laser-etched enamel (8.45 +/- 3.07 MPa), and significantly higher (P<.05) for acid-etched dentin (4.70 +/- 2.50 MPa) than laser-etched dentin (2.48 +/- 1.94 MPa). Bond failure after laser etching was due to microcohesive fracture of tooth tissue. SEM studies of both resin-enamel and resin-dentin interfaces indicated extensive subsurface fissuring after laser etching. CONCLUSION: Adhesion to dental hard tissues after Er:YAG laser etching is inferior to that obtained after conventional acid etching. Enamel and dentin surfaces prepared by Er:YAG laser etching show extensive subsurface fissuring that is unfavorable to adhesion.

Comparison of the fracture resistances of pulpless teeth restored with a cast post and core or carbon-fiber post with a composite core.

STATEMENT OF PROBLEM: The survival of pulpless teeth restored with a post and core system is a controversial issue. PURPOSE: This study compared the fracture resistance of 2 types of restorations: teeth restored with prefabricated carbon-fiber posts and composite cores to cast dowel-core restored teeth. MATERIAL AND METHODS: A total of 44 recently extracted sound premolars were randomly distributed into 2 equal groups: group I, restored with prefabricated carbon-fiber post and a composite core; and group II, with custom-cast type III gold alloy post and cores. The size and shape of the posts were identical in the 2 groups. All teeth were fully covered with a nonprecious cast crown. Fracture resistance was measured by applying a point force at 45 degrees to the long angle of the tooth. RESULTS: Mean fracture threshold was 103.7 +/- 53.1 kg for group I versus 202.7 +/- 125.0 kg for group II (differences significant with P = .003). In group II, however, fracture nearly always affected the tooth itself, whereas in group I, the post-core nearly always failed first. CONCLUSIONS: Significantly higher fracture thresholds were recorded for the cast post and core group. Teeth restored with cast posts typically showed fracture of the tooth, although at loads rarely occurring clinically.

[A case of appendicular supplementary root with external root resorption]. / Raíz supernumeraria con reabsorción radicular externa. Caso clinico.

The case of a lateral maxillary incisor with a supplementary root fractured by external root resorption, is presented. The role played for the periodontal disease is shown in the clinical and radiographic achievements, and their implications in the pulpal disease. Endodontic therapy was performed and the diagnosis confirmed in the specimen histological research.