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Biomedical subjects

C Aparicio

Publications and source records attributed to C Aparicio.

33 records · Page 2Linked to original sources
PubMed1997

The use of the Periotest value as the initial success criteria of an implant: 8-year report.

Osseointegration is a histometric process that occurs gradually over a period of time. The load that an implant is able to bear depends upon, among other parameters, the quality of the bone-implant contact. For 8 years the damping capacity of 1,182 Brånemark implants inserted consecutively in 315 patients was measured using the Periotest method. The following clinical observations were made: (1) a relationship was found between implants with a specific Periotest value range that, at the moment of the transepithelial connection, were considered to be clinically stable, asymptomatic, and whose radiograph image was not radiolucent; (2) a relationship was found between clinically nonintegrated implants with a different Periotest value range; (3) variations in the Periotest value were related to the type of bone in which the implant was placed; (4) a small percentage of borderline implants with a Periotest value between the osseointegrated and the nonosseointegrated Periotest values was detected; (5) the percentage of secondary failures was related to an initial Periotest value corresponding to a borderline implant; (6) the healing time of each implant was individualized in accordance with the successively obtained Periotest value; (7) the load and the design of the prosthesis were individualized; (8) early detection of failing implants before fabrication of prostheses is possible; (9) communication was improved between the surgeon and the prosthodontist; and (10) variations in Periotest value were related to bone remodeling. The sensitivity of the principal clinical test in evaluating osseointegration is discussed regarding the moment of its application. The use of Periotest values as an initial success criteria of an implant is proposed.

Dental Abutments↗
PubMed1996

Molecular mechanisms of activated protein C resistance. Properties of factor V isolated from an individual with homozygosity for the Arg506 to Gln mutation in the factor V gene.

Resistance to activated protein C (APC), which is the most prevalent pathogenetic risk factor of thrombosis, is linked to a single point-mutation in the factor V (FV) gene, which predicts replacement of Arg (R) at position 506 with a Gln (Q). This mutation modifies one of three APC-cleavage sites in the heavy chain of activated FV (FVa), suggesting that mutated FVa (FVa:Q506) is at least partially resistant to APC-mediated degradation. To elucidate the molecular mechanisms of APC-resistance and to investigate the functional properties of FV in APC resistance, FV:Q506 was purified from an individual with homozygosity for the Arg to Gln mutation. Intact and activated FV:Q506 were demonstrated to convey APC resistance to FV-deficient plasma. Thrombin- or factor Xa-activated FV:Q506 were found to be approx. 10-fold less sensitive to APC-mediated degradation than normal FVa, at both high and low phospholipid concentrations. The degradation pattern observed on Western blotting suggested that FVa:Q506 was not cleaved at position 506. However, it was slowly cleaved at Arg306, which explains the partial APC sensitivity of FVa:Q506. FV is initially activated during clotting and then rapidly inactivated in a process which depends on the integrity of the protein C anticoagulant system. During clotting of APC-resistant plasma, FV:Q506 was activated in a normal fashion, but then only partially inactivated. In conclusion, the reduced sensitivity of FVa:Q506 to APC-mediated degradation is the molecular basis for the life-long hypercoagulable state which constitutes a risk factor for thrombosis in APC-resistant individuals.

Arginine↗
PubMed1994

A new method to routinely achieve passive fit of ceramometal prostheses over Brånemark osseointegrated implants: a two-year report.

To maintain osseointegration, it is essential that the prosthesis fit with total passivity because the absence of a periodontal ligament makes the implant unable to adapt its position to a nonpassive framework. The traditional system of building a metal framework by melting over mechanized pieces--called gold cylinders in the Brånemark system--has been modified so these pieces are joined to the metal framework by means of physicochemical bonding. This bond is achieved by treating the metallic surfaces with a Silicoater system and a composite resin cement that sets in the mouth using an improved cementing protocol. In this paper, the clinical viability of this new philosophy, shown over 2 years, is presented. A total of 64 prostheses (39 maxillary and 25 mandibular) supported by 214 abutments, with an average observation period of 9 months, were evaluated. The results show that it is possible to routinely obtain a ceramometal prosthesis with a totally passive circular fitting while maintaining the possibility of retrieval, thus making postceramic soldering unnecessary.

Cementation↗
PubMed1992

Comparative surface microanalysis of failed Brånemark implants.

The chemical composition and topography of an implant surface determine the human immunologic system response. This study compared the surfaces of 13 Brånemark oral implants, 11 that came from retrieved specimens which failed initially or did not osseointegrate and 2 that were never implanted (controls). The period of implantation in human jaws varied between 3 and 20 months. After cleaning and sterilization, the topography, surface chemical composition, and thickness of the oxide layer were studied. The results obtained with scanning electron microscopy did not show any significant topographic differences among the specimens. X-ray spectrographic microanalysis showed very similar composition (titanium and amounts less than 0.5% of other elements) in the outermost layer of the analyzed specimens. The Auger spectroscope revealed considerable percentage differences in the amount of carbon and silicon in the last monolayers, which could be attributed to handling or to an inadequate cleaning process. This places the retrieved specimens out of the acceptable statistical limits of contamination by introducing a factor of doubt for long-term prognosis in the hypothetical situation of their re-use.

Dental Implants↗
PubMed1991

Relationship between tryptophan biosynthesis and indole-3-acetic acid production in Azospirillum: identification and sequencing of a trpGDC cluster.

Screening the tryptophan (Trp)-dependent indole-3-acetic acid (IAA) production of different Azospirillum species revealed that A. irakense KA3 released 10 times less IAA into the medium than A. brasilense Sp7. A cosmid library of strain Sp7 was transferred into A. irakense KA3 with the aim of characterizing genes involved in IAA biosynthesis. Trp-dependent IAA production was increased in two transconjugants which both contained an identical 18.5 kb HindIII fragment from Sp7. After Tn5 mutagenesis, cosmids carrying Tn5 insertions at 36 different positions of the 18.5 kb fragment were isolated and transferred into strain KA3. IAA production by the recipient strains was screened by HPLC. The Tn5 insertions of 4 clones with decreased IAA production were mapped on a 2 kb SalI-SphI fragment. Recombination of Tn5 insertions at this locus into the genome of strain Sp7 led to Trp auxotrophic mutants. A 5.2 kb EcoRI-SalI fragment including the 2 kb SalI-SphI fragment was sequenced and six open reading frames were identified. Three of them were clustered and their deduced amino acid sequences showed significant similarity to TrpG, TrpD and TrpC, which are enzymes involved in tryptophan biosynthesis. One of the remaining open reading frames probably encodes an acetyltransferase. The region responsible for the enhanced Trp-dependent IAA production in strain KA3 corresponded to trpD, coding for the phosphoribosyl anthranilate transferase.

Acetyltransferases↗
PubMed1990

Expression of catalytically active radish 3-hydroxy-3-methylglutaryl coenzyme A reductase in Escherichia coli.

Two fragments of a cDNA encoding radish 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) were cloned into the vector pET-8c and expressed in Escherichia coli. The large fragment, encoding both the membrane and the cytosolic domains, was expressed at low level, essentially as an insoluble protein without enzymatic activity. In contrast, the fragment encoding only the cytosolic domain was expressed at a high level in a catalytically active form. The amount of soluble active enzyme in cell-free extracts of E. coli dramatically increased when the temperature during the induction was lowered from 37 degrees C to 22 degrees C.

Cloning, Molecular↗
PubMed1990

Periotest method as a measure of osseointegrated oral implant stability.

Oral implant stability is essential for optimal function. Results obtained from the Periotest measurement of the stability of 204 commercially pure titanium implants, consecutively placed in 22 maxillae and 24 mandibles according to the Brånemark procedure, are reported. Preliminary results suggest that the Periotest value of an oral implant is an objective and easily applied criterion for stability assessment. Since osseointegration is achieved gradually over time, this test may assist the clinician in deciding whether to extend the healing period before loading fixtures that seem clinically and radiologically integrated but give borderline Periotest values.

Adult↗
PubMed1986

Characterization of surface roughness in titanium dental implants measured with scanning tunnelling microscopy at atmospheric pressure.

Characterization of the surface topography of implant materials is important for understanding tissue response. We have measured, for the first time, the topography of titanium surfaces used in osseointegrated dental implants. Scanning tunnelling microscopy (STM) which provides 3D real space images was used. In addition to clinical samples, electropolished and anodically oxidized surfaces were also measured. Clinical samples are rather inhomogeneous in character showing grooves and steps with a maximum depth of 0.11 micron. Micropores with an average diameter of about 30 nm are also present. Electropolished samples are rather homogeneous and very smooth, showing steps of 1 to 5 nm in height. The measurements were performed under atmospheric conditions at a resolution in the subnanometer range.

Dental Implantation, Endosseous↗
PubMedDate not supplied

A new method for achieving passive fit of an interim restoration supported by Brånemark implants: a technical note.

When carrying out restorations supported by dental implants, it is advisable to have a temporary method that offers the possibility of evaluating and/or creating a proper emergence profile, peri-implant health, occlusion, esthetics, acceptable phonetic response, and hygiene, as well as one that facilitates progressive loading of the implants during the bone maturation period. To maintain osseointegration it is essential that a prosthesis fit with total passivity, since the lack of a periodontal ligament renders the implant unable to modify its position. Gold cylinders for EsthetiCone abutments, which were modified following a previously reported technique, were used so that provisional prostheses could be fixed to the cylinders in the mouth by means of an alternative cementing technique. By this way, a provisional prosthesis with total circumferential fit, maintaining the option of retrieval, could be routinely obtained.

Acrylic Resins↗
PubMedDate not supplied

[The inhalational therapy of respiratory pathology].

The inhalation of aerosolized drugs for therapeutic purpose has been used for many years in respiratory diseases as asthma, chronic bronchitis, cystic fibrosis. Therapeutic aerosols have the advantages to deliver active substances directly to the site of disease, without systemic side effects, to produce a more rapid clinical response, to avoid barriers to the absorption of drugs such as the gastrointestinal tract. We review the mechanisms and the site of lung deposition and the range of devices that can provide an effective aerosol such as metered dose-inhaler and spacers. Besides drugs as cromolyn, beta-2-agonists and topical steroids, recently new inhalation therapies were proposed using antiviral drugs (interferon), pentamidine for Pneumocystis carinii in immunocompromised host, inhalation of attenuated virus (measles) for active immunization. However there is a need for further work in this area.

Administration, Inhalation↗
PubMedDate not supplied

Relationship between contact time measurements and PTV values when using the Periotest to measure implant stability.

PURPOSE: The Periotest is an electronic instrument that has been advocated for the measurement of implant stability and osseointegration. The aims of this investigation were to establish the relationship between contact time and PTV values when the Periotest was used to assess implants in vivo and in vitro, and to investigate the influence of the striking height of the Periotest handpiece and the length of implant abutment. MATERIALS AND METHODS: The accelerometer signal from a Periotest was captured and compared with the resulting PTV value. In vitro measurements of PTV and contract time were performed on a 3-mm abutment that had been attached to a 15-mm implant luted into an aluminium block, and were repeated on a patient in vivo. further measurements were made of the abutments of six implants in turn in the maxilla of the same patient. The standard abutment lengths on the implants were 3, 4 (x 2), 5.5 (x 2), and 7 mm. RESULTS: The results indicated that there was a linear relationship between contact time and PTV value for implants measured in vitro and in vivo. Greater scatter of the in vivo data was attributed to test and patient variables including striking position, distance, and damping as a result of the presence of soft tissue. There was a linear relationship between the PTV value and the striking height for implant measurements in vivo and in vitro. CONCLUSION: It can be concluded that the sensitivity of the Periotest to clinical variables including striking heights and handpiece angulation limit the application of the instrument as a clinical diagnostic aid to measure implant stability.

Dental Abutments↗