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PubMed2006

Platform switching: a new concept in implant dentistry for controlling postrestorative crestal bone levels.

Histologic and radiographic observations suggest that a biologic dimension of hard and soft tissues exists around dental implants and extends apically from the implant-abutment interface. Radiographic evidence of the development of the biologic dimension can be demonstrated by the vertical repositioning of crestal bone and the subsequent soft tissue attachment to the implant that occurs when an implant is uncovered and exposed to the oral environment and matching-diameter restorative components are attached. Historically, two-piece dental implant systems have been restored with prosthetic components that locate the interface between the implant and the attached component element at the outer edge of the implant platform. In 1991, Implant Innovations introduced wide-diameter implants with matching wide-diameter platforms. When introduced, however, matching-diameter prosthetic components were not available, and many of the early 5.0- and 6.0-mm-wide implants received "standard"-diameter (4.1-mm) healing abutments and were restored with "standard"-diameter (4.1-mm) prosthetic components. Long-term radiographic follow-up of these "platform-switched" restored wide-diameter dental implants has demonstrated a smaller than expected vertical change in the crestal bone height around these implants than is typically observed around implants restored conventionally with prosthetic components of matching diameters. This radiographic observation suggests that the resulting postrestorative biologic process resulting in the loss of crestal bone height is altered when the outer edge of the implant-abutment interface is horizontally repositioned inwardly and away from the outer edge of the implant platform. This article introduces the concept of platform switching and provides a foundation for future development of the biologic understanding of the observed radiographic findings and clinical rationale for this technique.

Alveolar Bone Loss↗
PubMed1998

The bone growing chamber: a new model to investigate spontaneous and guided bone regeneration of artificial defects in the human jawbone.

Spontaneous bone repair and regeneration of jawbone defects have been insufficiently studied in the dental literature. The present study analyzes a new human model designed to evaluate the basis for spontaneous bone regeneration in human jawbones. Hollow titanium cylinders, termed "bone growing chambers," were prepared with commercially pure titanium. Ten volunteers undergoing routine implant surgery were enlisted. A properly calibrated drill was used to prepare the bone-growing-chamber bed. The bone growing chamber was inserted inside the bone defect, and care was taken to submerge the cylinder at the level of the bone crest. After an adequate healing period, the bone growing chambers were retrieved with a small quantity of peripheral bone using a calibrated trephine bur. The retrieved specimens were processed to obtain thin undecalcified ground sections. The stable bone growing chambers showed bone tissue inside the growing space. The maturity of the regenerated bone was related to the time of removal. The bone growing chamber provides a well-defined space that is easy to prepare and to retrieve; its dimensions are always identical and it allows quantitative measurements of bone regeneration inside the chamber space.

Alveolar Process↗
PubMed2005

Use of enamel matrix protein derivative before dental reimplantation: a histometric analysis.

The use of enamel matrix protein in the treatment of periodontal defects has shown a favorable action on the proliferation of periodontal ligament cells, as well as on collagen formation and mineralization. The goal was to evaluate, histologically and histometrically, periodontal tissue regeneration after dental reimplantation using enamel matrix protein derivative (Emdogain, Biora AB, Malmö, Sweden). Male rats (Albinus, Wistar), weighing between 180 and 200 g, were divided in 3 groups. Animals in group I (control) had the upper right incisors extracted, the root canal was sealed with calcium hydroxide, and teeth were reimplanted in their alveoli. Group II underwent the same procedure, but the remaining periodontal ligament was removed from the root surfaces by root planing before reimplantation. In group III,following removal of the periodontal ligament, Emdogain was applied to the root surfaces. Animals were sacrificed 7, 20, and 60 days after reimplantation, and the alveoli were fixed, processed, and stained with hematoxylin and eosin. Formation of periodontal ligament, resorption areas, and ankylosis were analyzed. The results showed that group I (control) was better than groups II and III, with statistically significant differences on days 7 and 20 after reimplantation for formation of periodontal ligament. It may be concluded that with the methodology used, Emdogain was unable to stimulate tissue repair in reimplanted teeth.

Alveolar Process↗
PubMed2004

A proposal for the classification of bony defects adjacent to dental implants.

A new classification of bone defects adjacent to dental implants is proposed. The classification highlights the importance of defect anatomy in the progression of the regenerative process. Defects were divided into two main groups: (1) closed defects, characterized by the maintenance of intact surrounding bone walls; and (2) open defects, which lack one or more bone walls. The open defect group was then divided into several subgroups that include the majority of situations encountered in clinical practice. The classification could be a useful tool for planning the correct regenerative procedure for each type of defect.

Alveolar Bone Loss↗
PubMed2001

Bone reactions adjacent to titanium implants with different surface characteristics subjected to static load. A study in the dog (II).

The purpose of the present study was to compare bone reactions adjacent to titanium implants with either a titanium plasma-sprayed (TPS) or a machined surface subjected to lateral static loading induced by an expansion force. In 3 labrador dogs, the 2nd, 3rd and 4th mandibular premolars were extracted bilaterally. 12 weeks later, 2 implants with a TPS surface were placed in one side and 2 implants with a machined surface were placed in the contralateral side. Twelve weeks after implant installation, crowns, connected in pairs with orthodontic expansion screws, were fitted to the implants and a 0.6 mm wide expansion was initiated. Clinical registrations, standardized radiographs and fluorochrome labeling were carried out during a 24-week period of loading. Biopsies with the implants in situ were harvested and processed for ground sectioning. The sections were subjected to histologic and histometric examination. A higher marginal bone level was observed around implants with a TPS surface compared to machined implants. Furthermore, the values describing the amount of bone-to-implant contact at the bone/implant interface as well as the density of the peri-implant bone were lower at the machined than at the TPS implants.

Alveolar Process↗
PubMed1986

A radiographic survey of periapical jawbone lesions.

A radiographic survey of the jawbone adjacent to the teeth revealed a high incidence of bone pathosis in 889 randomly chosen patients. Jaw lesions, nearly all inflammatory, were present in every second person. Bone-destructive inflammatory processes (rarefying osteitis) were the most frequently encountered lesions, occurring in both the maxilla and the mandible. Bone-appositioning inflammatory processes (condensing osteitis), on the other hand, appeared mostly in the mandible, very often involving the first molar, thus indicating the differing biologic behavior of the two jawbones. Other bony manifestations in the mandible, such as enostosis and periapical cemental dysplasia, although relatively rare, also formed part of the picture. In light of the absence of related symptoms, the clinical significance of these widely prevalent periapical lesions has to be reconsidered.

Alveolar Process↗
PubMed1991

Tissue reactions after experimental luxation injuries in immature rat teeth.

Immature permanent teeth often develop complications after luxation injuries. The pathology and the degenerative processes of the complications, however, are not well understood. In this study, we histologically examined the long-term reactions of immature rat teeth after standardized luxation injuries delivered in our previously developed experimental model. The upper first molars of 3-week-old male Wistar rats weighing 50-60 g were pushed horizontally toward the palate to cause a constant amount of dislocation. The follow-up changes of the luxated molars were studied up to 56 days after the trauma. Soon after the trauma, the periodontium had irregular fibers, degenerated cells, hemorrhage and edema in various places. After 12 h, a cell free area appeared in the palatal periodontium. In the alveolar bone and on the surface of the root, resorption occurred one day and 5-7 days after injury respectively. Although the damage in the periodontium and alveolar bone was gradually repaired, the root resorption, especially in the palatal cervical region, continued throughout the experimental period. In the most cases, the dental pulp did not seem to be damaged immediately after the trauma. By the 3rd day after injury, however, displacement of odontoblasts into the dentinal tubules was observed in many teeth. Moreover, formation of irregular dentin was observed in some teeth after 7 days. These changes of the pulp tended to disappear in the later stages of the experiment.

Alveolar Process↗
PubMed1987

Repair of periodontal angular bony defects evaluated by one- and two-dimensional radiographic analysis.

The healing of eighteen angular periodontal bony defects was evaluated radiographically 1 year after treatment. The pretreatment and posttreatment radiographs were exposed and processed in such a way that identical images were obtained. There was no correlation between one- and two-dimensional expressions of healing in such defects, and relative area changes were consistently larger than relative linear changes of the same defects. The area gain of bone was strongly correlated to the following morphologic variables: length of bone surface, original defect area, and height of the defect.

Alveolar Process↗
PubMed2003

Diffusional screening in the human pulmonary acinus.

In the mammalian lung acini, O(2) diffuses into quasi-static air toward the alveolar membrane, where the gas exchange with blood takes place. The O(2) flux is then influenced by the O(2) diffusivity, the membrane permeability, and the acinus geometric complexity. This phenomenon has been recently studied in an abstract geometric model of the acinus, the Hilbert acinus (Sapoval B, Filoche M, and Weibel ER, Proc Natl Acad Sci USA 99: 10411, 2002). This is extended here to a more realistic geometry originated from the morphological model of Kitaoka et al. (Kitaoka K, Tamura S, and Takaki R, J Appl Physiol 88: 2260-2268, 2000). Two-dimensional numerical simulations of the steady-state diffusion equation with mixed boundary conditions are used to quantify the process. The alveolar O(2) concentration, or partial pressure, and the O(2) flux are computed and show that diffusional screening exists at rest. These results confirm that smaller acini are more efficient, as suggested for the Hilbert acini.

Algorithms↗
PubMed1982

Human clinical and histologic responses to Durapatite implants in intraosseous lesions. Case reports.

The healing response following implantation of a nonresorbable ceramic (durapatite) into human periodontal osseous defects was evaluated clinically and histologically. Four tooth-containing blocks were obtained from four patients who had received durapatite implants in osseous defects, each exceeding 4 mm in depth. Each patient was seen for 5 to 13 postsurgical maintenance visits. Teeth in block section were removed between 8 weeks and 8 months postgraft surgery. Clinical evaluation of the repair process demonstrated that pocket depth decreased in all four cases. Histological evaluation of the repair process showed no indication of new periodontal attachment, osteogenesis or cementogenesis, in the host tissues adjacent to the graft particles. Pocket closure appeared to occur by means of a long junctional epithelium and connective tissue adhesions. There was minimal or no evidence of inflammation in all sections associated with the implant. The graft material therefore acted as a biocompatible foreign body within the gingival tissue.

Adult↗
PubMed2000

Correction of the bilateral cleft using the sliding sulcus technique.

The morphology of the bilateral cleft lip can be understood in terms of process theory and field theory. The former holds that an initial event sets in motion processes of division, deficiency, displacement, and distortion; these act on the cleft site to convert a trivial defect into the final result seen at birth. Field theory describes embryonic units that are in disarray by virtue of the cleft. A subperiosteal technique is described that combines these concepts to achieve simultaneous closure of the lip and alveolus. Primary separation of the nasal tip from the philtral-columellar unit is carried out along embryonic fusion lines.

Aged↗
PubMedDate not supplied

Guided bone regeneration using resorbable and nonresorbable membranes: a comparative histologic study in humans.

Resorbable membranes of poly(lactic acid) and poly(glycolic acid) (PLA/PGA) were compared to nonresorbable expanded polytetrafluoroethylene (e-PTFE) membranes in the treatment of defects around titanium dental implants placed in postextraction sockets. Two partially edentulous and three completely edentulous patients requiring implant-supported restorations participated. Sixteen Brånemark implants were placed into extraction sockets and covered with modified titanium cover screws, called harvest cover screws, which allow tissue biopsy at second-stage implant surgery. Seven defects were treated with PLA/PGA membranes, five were treated with e-PTFE membranes, and four were left untreated (control sites). After 6 months of healing, the harvest cover screws were retrieved and processed for light microscopy examination together with the regenerated tissues. Very little or no bone formation was detected in control specimens. The e-PTFE membranes were found to be the most effective barrier material, in that denser and a greater amount of regenerated bone was found. The PLA/PGA membranes produced some bone regeneration when compared to control sites, but to a lesser extent compared to e-PTFE sites.

Adult↗
PubMed1985

Digitized image processing and pattern recognition in dental radiographs with emphasis on the interdental bone.

Diagnosis of bone lesions on dental radiographs can be difficult due to the irregular trabecular pattern and subjectivity on the part of the observer. The purpose of this study is to improve the recognition of bone lesions by means of objective computer-aided pattern recognition techniques. This article describes a method for the separation of teeth and bone regions in the image to facilitate further analysis, especially of the interdental bone.

Alveolar Process↗
PubMed1998

Effect of a calcium sulfate implant with calcium sulfate barrier on periodontal healing in 3-wall intrabony defects in dogs.

This controlled, split-mouth, preclinical study was designed to evaluate outcome following surgical implantation of an allogeneic, freeze-dried demineralized bone matrix-calcium sulfate (DBM+CS) composite with a CS barrier in 3-wall intrabony periodontal defects in 4 dogs. Control conditions included surgical implantation of DBM or CS and gingival flap surgery (GFS) alone. Three-wall intrabony defects (4x4x4 mm) were surgically created at the mesial and distal aspect of the maxillary and mandibular first and third premolars, respectively. Maxillary and mandibular defects each received 1 of the 4 experimental conditions. Experimental conditions were rotated between defect sites in subsequent animals. Block sections of the defects were collected at sacrifice 8 weeks postsurgery and processed for histometric analysis. Histometric defect height (means +/- SD) for the DBM+CS, DBM, CS, and GFS groups amounted to 4.2 +/- 0.5, 4.3 +/- 0.7, 4.0 +/- 0.2, and 4.1 +/- 0.2 mm, respectively. Connective tissue adhesion (connective tissue contact to the root without apparent cementum formation) amounted to 0.4 +/- 0.3, 0.4 +/- 0.3, 0.5 +/- 0.2, and 1.6 +/- 0.5 mm for the DBM+CS, DBM, CS, and GFS groups, respectively; the DBM+CS, DBM, and CS groups being significantly different from the GFS group (P < 0.05). Cementum regeneration amounted to 3.0 +/- 0.3, 3.1 +/- 0.4, 2.5 +/- 0.4, and 1.6 +/- 0.3 mm for the DBM+CS, DBM, CS, and GFS groups, respectively; the DBM+CS, DBM, and CS groups being significantly different from the GFS group (P < 0.05). Alveolar bone regeneration amounted to 2.7 +/- 0.4, 2.7 +/- 0.3, 1.8 +/- 0.5, and 0.7 +/- 0.1 mm for the DBM+CS, DBM, CS, and GFS groups, respectively; the DBM+CS, DBM, and CS groups being different from the GFS group (P < 0.05), and the DBM+CS and DBM groups being different from the CS group (P < 0.05). None of the DBM-containing implants provided evidence of bone metabolic activity. In summary, surgical implantation of DBM and CS, alone or in combination, may result in significantly improved regeneration of alveolar bone and cementum in this preclinical model. Observed regeneration is likely unrelated to a biologic activity inherent in DBM. Rather it appears that space-providing properties of the implants supported observed regeneration.

Alveolar Bone Loss↗
PubMed1999

Root development in mice lacking functional tissue non-specific alkaline phosphatase gene: inhibition of acellular cementum formation.

Tissue non-specific alkaline phosphatase (TNAP) is richly present in developing teeth including the cells of the periodontal ligament. Here, we investigated tooth and root development in mice lacking the TNAP gene. Heterozygous mutants were obtained from The Jackson Laboratory, Animal Resources (Bar Harbor, ME, USA) and bred. TNAP-deficient mice and their littermates were killed from 6 to 25 days after birth and their molar blocks processed for light and electron microscopy. It was observed that the eruption of the incisors into the oral cavity was delayed for 2 to 3 days. Also, the onset of mineralization of the mantle dentin in the roots of the developing molars was delayed for 2 to 3 days. Yet, dentin and enamel formation in the homozygous mutants showed a more or less normal pattern, with the exception of localized enamel hypoplasias. The most conspicuous finding was the defective formation of acellular cementum along the molar roots. Instead of a continuous layer, the cementum was deposited as very thin and irregularly shaped patches around the bases of the periodontal ligament fibers. Sharpey's fibers were short and poorly developed. In contrast, the development of the alveolar bone, the periodontal ligament, and the cellular cementum was seemingly unaffected. It is concluded that TNAP represents an essential factor in mantle dentin mineralization and in the formation of acellular cementum.

Alkaline Phosphatase↗
PubMedDate not supplied

[Development of a periodontium-approximated specimen holder for attrition studies of telescopic crowns].

To enable attritional studies on telescopic crowns, a specimen holder has been constructed that is intended to simulate, in zero approximation, the biomechanical properties of abutments bearing telescopic crowns. The specimen holder consists essentially of a system with two metal "concertinas" with different elasticity constants reflecting the different biomechanical parameters for periodontium and bone. The biomechanical processes in the periodontium are too complex to be simulated accurately in vitro. Nevertheless, the specimen holder described here enables the forces acting during insertion and removal of a partial denture to be accommodated elastically in the angular and axial directions, to simulate the possible degrees of freedom of the abutments in situ. In this way, the unavoidable errors of specimen fixation are rendered tolerable, so that local preferential wear is decisively reduced.

Alveolar Process↗
PubMed1986

Orientation of gingival fibroblasts in simulated periodontal spaces in vitro. SEM observations.

The present study examined the orientation of gingival fibroblasts in simulated periodontal spaces in vitro. Extracted human teeth were root planed followed by root resection and root canal instrumentation. The middle and cervical thirds of each root were cut transversely to create 600-micron thick sections. Cortical bovine bone was cut, sectioned and contoured to create bone rings 600 micron thick with an internal diameter large enough to accommodate a root slice leaving a circumferential space varying from approximately 0.1 to 1.0 mm. Root slices and bone rings were incubated in a solution of collagenase and hyaluronidase to remove all remaining soft tissue and partially demineralized in EDTA (18%) for 30 minutes. Human gingival fibroblasts (HGF) were plated to confluency in tissue culture dishes. The dentin slices were then gently placed over the HGF monolayer along with bone rings around them to create simulated periodontal spaces. Control root slices were placed without bone rings around them. Cultures were maintained under standard tissue culture conditions. Representative specimens were obtained after 2, 3 and 4 weeks of culture and processed for scanning electron microscopy (SEM). At 2 weeks, the HGF had formed sheets of cells attached to the periphery of the root slices at one end and to the inner surface of bone rings at the other end. The orientation of cell sheets varied from being perpendicular to the periphery of the slice to oblique. At 3 and 4 weeks, the density and size of cell sheets increased and the orientation was maintained.(ABSTRACT TRUNCATED AT 250 WORDS)

Alveolar Process↗
PubMed1996

The mechanism of tooth eruption.

Tooth eruption is an essential process for the survival of many different species and although the movement of teeth into function has been the subject of extensive research there is no consensus as to the mechanisms involved. Recent understanding of the mechanisms of cell activation and regulation has widened the scope for further research at the molecular level. This paper reviews the evidence for an eruptive force, its direction and source. The relationships between the eruptive force and molecular mechanisms of cell activation remain to be determined.

Alveolar Process↗