Raul I. Garcia

The eruption of third molars in adults: A 10-year longitudinal study

Among 829 participants of the Veterans Administration Dental Longitudinal Study examined over four triennial cycles, 97 persons (11.7%) had one or more unerupted third molars, for a total of 151 teeth, when the study was initiated. During the first 10 years of the study, 10 subjects had 14 unerupted third molars extracted, while in 10 persons 11 third molars erupted. Four of the latter persons each had one third molar removed subsequent to eruption. Three of the 11 erupted third molars were in functional occlusion. The position of 4 of the 11 erupting third molars appeared to remain unchanged relative to radiographic landmarks. Thus, their apparent clinical eruption may have been due to a reduction in the level of the gingival tissue in the area distal to the second molar tooth in association with periodontitis. The eruption of third molars in older adults appears to be a more frequent phenomenon than was previously recognized. Most erupting third molars had some associated pathologic condition, including caries and periodontitis.

Melanosomes in dermal Schwann cells of human and rodent skin.

This is the first report of the occurrence of melanosomes in the Schwann cells of normal mammalian skin. Our findings are particularly interesting in regard to the controversies on the histogenesis of pigmented nerve sheath tumors found occasionally in man [20, 29], on the possible neurogenic origin of cellular blue nevi [11,1820, 24, 28], and on the proposal of Masson that neoplastic Schwann cells may become melanogenic [2123]. Nerve sheath tumors are generally not pigmented. However, the occurrence of melanin-containing cells has been reported in neurofibroma [1-3,27], ganglioneuroblastoma [t2], and in melanotic malignant Schwannoma (neurinoma) [13,14, 20, 29]. In these cases, it could not be determined whether these neoplastic melanin-containing cells originated from melanocytes or Schwann cells. Melanosomes have been identified ultrastructurally in the normal Schwann cells of human iris [5], and melanosome-like granules have been described in the dermal Schwann cells associated with a blue nevus and a compound nevus [25, 26]. Evidence that nerve sheath cells can produce melanin has come from studies of the neurogenic origin of cellular blue nevi [~i 1,19, 24, 28]. The findings of Jurecka et al. [18], in their study of the association of nervous elements with intradermal nevi, support the theory of a neural component in the histogenesis of intradermal nevi. The presence of melanosomes in Schwann cells may also possibly be due to phagocytosis of melanosomes from the extracellular space [4, 26], or to cytocrine activity of nearby melanocytes [13,14]. However, the view that neoplastic Schwann cells may become melanogenic is supported by the finding of melanosomes in various stages of formation in the neoplastic Schwann cells of a pigmented ganglioneuroblastoma [12], and also in experimental melanotic Schwannomas of Long-Evans rats studied using organ cultures and electron microscopy by Spence et al. [30]. They have found single membrane-bound premelanosomes and fully

Longitudinal study of the diagnostic yield of panoramic radiographs in aging edentulous men

Participants in the Veterans Administration Dental Longitudinal Study who were edentulous and for whom longitudinal panoramic radiographs were available were followed through four examination cycles, representing approximately 10 years. It was observed that 13 (39%) of the 33 subjects examined had one or more positive radiographic findings at the initial examination. No changes occurred in the findings noted during the initial panoramic radiographic examination, and no new findings were observed over the study period. Although the initial baseline panoramic examinations yielded several positive radiographic findings, few were of a nature that materially affected the initial treatment plan.

Effect of 5-bromo-2′-deoxyuridine on growth and differentiation of cultured embryonic retinal pigment cells

SummaryChicken embryo retinal pigment cells cultured for 2 weeks in 1 or 10 μm BrdU accumulate only 25% of the amount of melanin found in controls. Growth is inhibited by 10 μm BrdU but not by 1 μm BrdU. Cells cultured with BrdU had decreased tyrosinase activity and lost the typical epithelial appearance of controls. Equimolar concentrations of deoxythymidine did not prevent the inhibition of melanogenesis due to BrdU but did prevent the growth inhibition of the higher concentration of BrdU (10 μm). Tenfold higher concentrations of deoxythymidine prevented inhibition of epithelial differentiation and melanogenesis. Ultrastructurally, BrdU produced an absence of melanosomes and disruption of the lamellar array of rough endoplasmic reticulum. The perinuclear arrangement of microfilaments became irregular. The cell surface was radically affected as membranes were no longer ruffled and cell junctions disappeared.Melanogenesis is a complex form of differentiated function, involving synthesis of tyrosinase and control of its activity, macromolecular synthesis of the melanosome, and the subsequent synthesis of melanin within the melanosome. BrdU appears to inhibit melanogenesis through a coordinated and simultaneous interference with these processes, suggesting that there may be a “program” of gene activity for melanogenesis that is regulated as a unit.

Autophagocytosis of melanosomes in cultured embryonic retinal pigment cells.

Autophagocytosis not only accounts for the early pigment loss found in proliferating cultured retinal pigment cells, but also occurs in slowly growing and in non-proliferating cells. Both melanosome synthesis and destruuction may take place concurrently in cells. Autophagosomes may contain both fully formed melanosomes and also premelanosomes in various stages of formation, are positive for lysosomal enzyme activity, and likely represent secondary lysosomes.

Freeze-Fracture Study of Melanosomes in Mammalian Epidermis and the Distribution of Intramembrane Particles in the Melanosome Membrane*

SummaryThe ultrastructure of melanosomes in mammalian epidermis has been studied using the freeze-fracture technique. The internal structure of the melanosome, as seen in cross-fractured granules, consists of a very fine particulate matter. There is no evidence of an internal membranous structure in melanosomes, indicating that the internal matrix which is characteristic of ultrathin sectioned material most likely represents cross-linked protein fibers.Fracture ‘en-face’ of the melanosome limiting membrane reveals a random distribution of intramembrane particles on both the P- and E-faces of the membrane. There is a significantly higher density of IMPs on the P-face. The IMPs of the melanosome membrane may be involved in (a) selective passage of ions through the membrane, (b) membrane transducing events, and/or (c) anchoring sites for cytoplasmic fibrils and microfilaments.ZusammenfassungWir haben die Ultrastruktur der Melanosomen in der Epidermis von Säugetieren mittels der Gefrierbruchtechnik studiert. Die innere Struktur der Melanosomen besteht in diesen Präparaten aus feinem, granulärem Material. Wir haben keinen Beweis für eine innere Membranstruktur der Melanosomen gefunden. Dies bedeutet, daß die innere Matrize, die für elektronenmikroskopische Schnitte charakteristisch ist, aus kreuzweise angeordneten Proteinfibrillen besteht.Die “en-face”-Fraktur der Melanosomenmembran zeigt eine gleichmäßige Verteilung von intramembranösen Partikeln an der P- und E-Seite der Membran mit signifikant höherer Verteilungdichte an der P-Seite. Es wird angenommen, daß diese intramembranösen Partikel der Melanosomen (a) an dem selektiven Ionentransport durch die Membran und (b) an intramembranösen Übermittlerreaktionen beteiligt sind, bzw. (c) zur Verankerung von cytoplasmatischen Fibrillen und Mikrofilamenten dienen.