Max A. Listgarten

Light and Transmission Electron Microscopy of the Intact Interfaces Between Non-submerged Titanium-coated Epoxy Resin Implants and Bone or Gingiva

This experiment was aimed at studying the intact tissue/implant interface of non-submerged dental implants with a titanium surface. Epoxy-resin replicas were fabricated from 3.05 x 8 mm cylindrical titanium implants with a plasma-sprayed apical portion and a smooth coronal collar. The replicas were coated with a 90-120-nm-thick layer of pure titanium and autoclaved. The coated replicas were inserted as non-submerged endosseous implants in the edentulous premolar region of dog mandibles and allowed to heal for three months. Jaw sections containing the implants were processed for light and electron microscopic study of the intact tissue/implant interface with and without prior demineralization. Gingival connective tissue fibers were closely adapted to the titanium layer, in an orientation more or less parallel to the implant surface. There was no evidence of any fiber insertions into the surface irregularities of the smooth or rough titanium surface. Undemineralized bone was intimately adapted to the titanium surface without any intervening space. In demineralized sections, the collagen fibers of the bone matrix tended to be somewhat thinner and occasionally less densely packed in the vicinity of the implant surface. However, they extended all the way to the titanium surface, without any intervening fibril-free layer.

Soft and hard tissue response to endosseous dental implants

The last two decades have seen a remarkable growth in the development of dental implants and their incorporation into the practice of dentistry. This turn of events was made possible by an improved understanding of the biological response of living tissues to implants as well as clinical trials that validated the long‐term success of these implants. Despite major structural differences between teeth and implants, such as the absence of a periodontal ligament around implants, the latter appear to provide a reliable functional replacement for their natural counterparts. This review briefly summarizes the major structural differences of the interfacial region of teeth and dental implants and their supporting tissues. It focuses on our current understanding of the soft and hard tissue responses to submerged and nonsubmerged root‐form dental implants. The influence of a number of factors that affect the tissue response is reviewed, including biomaterials, implant design, surgical technique, and the local microbiota. Our recently acquired ability to modulate wound healing with guided tissue regeneration and growth factors will undoubtedly play an important role in the future utilization and success rates of dental implants.

Darkfield microscopy as a diagnostic aid in differentiating exudates from endodontic and periodontal abscesses

It was the purpose of this study to determine if a periodontal abscess could be differentiated from an endodontic abscess by the types and proportion of microorganisms found in the abscess exudate in darkfield microscopic examination. Dental abscesses with draining sinus tracts in 17 patients were studied. Eight of the abscesses were diagnosed clinically to be of endodontic origin and nine of periodontal origin. When the occurrence of motile pods in endodontic and periodontal abscesses were compared, the differences were not significantly different (mean, 12.1±10.8% and 7.5±3.9%, fespectively). In abscesses diagnosed clinically as periodontal, spirochaetes were the predominant cell (mean, 40.6±10.9%) with coccoid cells present in eignificantly lower numbers (mean, 19.7±10.9%). In endodontic abscesses the reverse was true. Cocsoid cells dominated (mean, 44.3±19.7%), and only lew spirochetes were present (mean, 5.6±4.7%). The range of percentages for coccoid cells was 7 to 40% in periodontal abscesses and 24 to 84% in endodontic abscesses. The overlap of range of 25 to 40% limited the use of these organisms for diagnostic purposes. For the spirochetes, on the other hand, there was a distinct difference in the range of percentages in the two types of abscesses. In periodontal abscesses the occurrence of spirochetes ranged from 30 to 60%, whereas in endodontic abscesses the range was 0 to 10%. Thus, the percentage of spirochetes as seen by darkfield microscopy may be of value in the differential diagnosis of periodontal and endodontic abscesses.

Electron microscopy as an aid in the taxonomic differentiation of oral spirochetes

Abstract Pure cultures of Treponema microdentium and Borrelia vincentii as well as spirochetes present in normal and pathologically involved gingival sulci were examined by electron microscopy of shadowed and negatively stained preparations and in ultra-thin sections. The spirochetes could be divided into three main groups on the basis of size of the protoplasmic cylinder, structure of the outer envelope and number of axial fibrils originating at one end. The group of “small” spirochetes had a protoplasmic cylinder with a diameter of 100–250 mμ, an outer envelope composed of polygonal structural subunits which was easily disrupted, and either one or two axial fibrils originating at each end of the protoplasmic cylinder. The group of “intermediate” spirochetes appeared essentially similar to the “small” spirochetes except for the diameter of the protoplasmic cylinder which measured from 200–500 mμ and the number of axial fibrils originating near each end which ranged from three to twenty. The “large” spirochetes had a protoplasmic cylinder approximately 500 mμ in dia. and occasionally larger, from the ends of which originated from twelve to more than twenty axial fibrils. These spirochetes were characterized by an outer envelope structurally different from that observed in the other two groups. It is suggested that the ultrastructural characteristics of spirochetes may be used as an aid to their taxonomic differentiation.

Microbiological testing in the diagnosis of periodontal disease.

The oral microbiota plays a primary role in the initiation and progression of the most common forms of periodontal disease. Because of the multiplicity of factors that control the establishment and long-term evolution of the oral microbiota, a great deal of heterogeneity exists in the composition of the periodontal microbiota among individual subjects. Despite these individual differences and the complex interactions between bacteria and the host and among bacteria, an association has been demonstrated between certain species and various forms of periodontal disease. However, the predictive value of either positive or negative tests for selected bacterial species has not proved to be high enough for routine use in clinical practice. Nevertheless, bacteriological tests have been of value in the management of patients with juvenile Periodontitis and refractory forms of periodontal disease. The increasing availability of diagnostic laboratory services and diagnostic kits for office use will make it easier for the practitioner to select appropriate antimicrobial treatments and monitor patients undergoing antimicrobial therapy. J Periodontol 1992; 63:332-337.

A light and electron microscopic study of coronal cementogenesis

Abstract The microscopic examination of bovine mandibular second molars in various stages of development has indicated that coronal cementogenesis is preceded by degeneration of the reduced enamel epithelum. The tendency for odontogenic epithelium to degenerate appears to be strong, and in certain areas ameloblasts may begin to atrophy prior to completion of amelogenesis. Cementoblasts from the connective tissue of the dental sac can thus again access to the enamel surface to lay down cementum. Although most of the coronal cementum of bovine teeth was cellular, with readily demonstrable collagen fibrils embedded in a dense granular matrix, it should be noted that a cementum-like layer near the tip of the cusps was completely devoid of cells or collagen fibrils. This “afibrillar cementum” may represent the earliest deposition of cementum on the crown, or may have resulted from the formation over exposed enamel, of a calcified acquired pellicle of connective tissue origin, prior to the onset of cementogenesis. The above results are discussed in the light of observations made on human teeth. It would seem that the absence of cementum over the greater portion of normal human teeth is probably due to the persistence over the enamel of an intact layer of reduced enamel epithelium at all times during the formative and eruptive phases of the teeth. Only a small zone near the apical border of the enamel of normal human teeth has been shown to be subject to degeneration or shrinkage of the reduced enamel epithelial layer. In this area a cementum-like layer of material devoid of collagen fibres may also be formed over the enamel. This afibrillar cementum-like material, similar to that described in bovine molars, can also be observed over larger areas of the crowns of teeth affected by amelogenesis imperfecta, where premature degeneration of the reduced enamel epithelium affects most of the coronal surface. It would, therefore, appear that where coronal cementum is found, its formation is dependent on prior degeneration of the reduced enamel epithelium. Furthermore, coronal cementum may comprise, in addition to the usual type of cementum with demonstrable collagen fibrils, and afibrillar cementum-like material. This material may represent a form of “afibrillar cementum”, or it may be the result of adsorption by the uncovered enamel, of connective tissue components capable of mineralization, a process which could take place prior to the differentiation of cementoblasts and the onset of cementogenesis.

Ultrastructure of the attachment device between coccal and filamentous microorganisms in “corn cob” formations of dental plaque

Abstract Dental plaque was collected on epoxy resin crowns inserted in the mouth of human volunteers for periods of 1–21 days. Cocci were found to be attached to the outer surface of filamentous organisms in formations resembling “corn cobs”. These formations were first noted in 3-day old plaque. A highly organized capsule-like attachment device, apparently of coccal origin, 80–100 nm thick, connected the cocci to the filaments. From their ultrastructure, the cocci and filaments appeared to belong to different genera. This information obtained by transmission electron microscopy, complements previously published data obtained by others using light and scanning electron microscopy.

Phase-contrast and electron microscopic study of the junction between reduced enamel epithelium and enamel in unerupted human teeth.

Abstract A phase-contrast and electron microscopic investigation was carried out on enucleated (unerupted) human teeth to study the area of the junction of reduced enamel epithelium with the enamel surface. Demineralized, as well as partially demineralized and undemineralized material was studied. The results indicated that reduced enamel epithelium is generally connected to the enamel surface by means of hemidesmosomes and a basement lamina approximately 400A wide. This type of attachment corresponded to that observed in erupted human teeth. Vacuoles could be observed entirely within the cytoplasm of reduced ameloblasts or communicating with the zone of the basement lamina. These vacuoles could represent a secretory or absorptive activity by the reduced ameloblasts. Reduced ameloblasts were joined to each other and to other cells of the reduced enamel epithelium by desmosomes and zonulae occludentes. Neither type of cellular junction appeared to be restricted to any specific portion of the reduced enamel epithelium. Following stripping of the dental sac from the enamel surface, patches of a thin membranous structure remained attached to the enamel. These patches consisted of all the cells of the reduced enamel epithelium with some attached connective tissue. Although phase-contrast microscopy revealed a cuticular structure approximately 0.5–1.0μ wide on the enamel side of the ameloblasts, similar to Gottliebs primary enamel cuticle, no such structure was observed with electron microscopy, suggesting that the primary enamel cuticle may be the result of an optical phenomenon. A cuticular structure was observed in continuity with the cementum layer, which was described as a type “A” cuticle. It was characterized by its position over enamel only, in close proximity to the cemento-enamel junction. It was granular and exhibited appositional lines. Although it appeared as a coronal extension of the cementum layer with phase-contrast microscopy, it differed from cementum at the ultrastructural level, primarily by being devoid of collagen fibrils. It may represent an end product of amelogenesis or more likely an afibrillar type of cementum. No evidence was found to support a recently published observation that a well defined cementum layer may be found on the enamel surface of unerupted human teeth.

Observations of the fine structure of the hamster cheek pouch epithelium

Abstract The general fine structure of the hamster cheek pouch epithelium is described. A thin homogeneous basement membrane about 360 A in width separates basal cells from dense, randomly arranged collagen fibres in the adjacent lamina propria. The basal cells and stratum spinosum contain a profusion of fine granules and tonofibrils. Desmosomes appear throughout the various cell layers. Numerous well-preserved mitochondria with transverse cristae are identified in the basal cells, stratum spinosum and stratum granulosum of the cheek pouch epithelium. In the stratum corneum they occur less frequently and when seen, appear disintegrated. Small, very dense granules about 0.1 μ in diameter are seen in the cytoplasm of the upper stratum spinosum and stratum granulosum cells. Their function is unknown. Densely compacted tonofibrils appear to be the principal intracellular constituent of the cornified layer.

The development of a cementum layer over the enamel surface of rabbit molars—A light and electron microscopic study

Abstract The deciduous molars of the rabbit, which are of finite growth, erupt between 4 and 5 days after birth. After 4 weeks, the six deciduous maxillary molars and the four deciduous mandibular molars are replaced by an equal number of continuously erupting premolars. In addition three permanent molars of continuous growth eventually form in each quadrant, posterior to the premolars. Both deciduous and permanent teeth develop a substantial amount of cementum over their enamel surface. Its formation follows the loss of continuity of the reduced enamel epithelium. The cementum which forms within the developmental groove of these teeth contains many cellular inclusions and is of a fibrillar nature, that is it contains recognizable collagen fibrils in its organic matrix. The cementum on the periphery of the crowns, particularly of permanent teeth, is primarily acellular and consists of both fibrillar and afibrillar cementum, the latter containing no recognizable collagen fibrils in its organic matrix. Degeneration of some cellular elements of cellular cementum as a result of continuous eruption is accompanied by the appearance of dense bodies resembling lysosomes and autophagic vacuoles within these cells. These changes are not observed in connection with the disappearance of reduced enamel epithelial cells prior to the onset of cementogenesis.