The biologic tissue responses to uncoated and coated implanted biomaterials.

Ultrastructural examination of the morphology and morphometry of the bone supporting uncoated titanium and ceramic implants was assessed in an experimental animal model involving 120 implants placed into the mandibles of 30 adult mongrel dogs. Further, preliminary morphologic and morphometric observations of the bone supporting uncoated and hydroxylapatite-coated endosteal titanium implants was evaluated in a second investigation involving 72 implants placed into the mandibles and maxillae of 6 additional dogs. A densely mineralized collagen fiber matrix was observed directly interfacing with uncoated implants. The only material interposed between the implant and bone matrix was a 20- to 50-nm electron-dense material suggestive of a proteoglycan. Also seen in these same osseointegrated implants were narrow unmineralized zones interposed between the implant and bone matrix. In these zones of remodeling bone, numerous osteoblasts were observed interacting with the collagen fiber matrix. It was shown that a normal homeostasis of anabolic osteoblastic activity and catabolic osteoclastic activity resulted in bone remodeling and the resultant osseointegration of the implants. Hydroxylapatite-coated implants intimately interfaced with healthy bone. The mineralized matrix extended into the microporosity of the HA coating. This matrix contained viable osteocytes.

Ultrastructural analyses of the attachment (bonding) zone between bone and implanted biomaterials.

This report presents transmission electron and high voltage transmission electron microscopic observations of bone and associated remodeling tissues directly interfacing with endosteal dental implants. Undecalcified interfacial tissues were serially sectioned from mandibular samples encasing 60 implants placed into 30 dogs. Two-dimensional ultrastructural analyses and three-dimensional stereology showed that osteogenesis adjacent to dental implants is a dynamic interaction of osseous cells and a collagenous fiber matrix. This study showed that the interfacial bone consists of a mineralized collagen fiber matrix associated with an inorganic (hydroxylapatite) matrix. This study suggested that an unmineralized collagen fiber matrix initially is laid down directly at the implant surface, and that this matrix then is mineralized. Osteoblasts interacted with this matrix, eventually becoming encased within developing lacunae during the remodeling process. This process formed the cellular (osteocyte) aspects of the developed bone. Osteocyte processes extended through canaliculi directly to the implant surface. Apparently, these processes also were entrapped within canaliculi during the mineralization events. At times, these processes paralleled the implant surface. The bone-implant interfacial zone was primarily fibrillar (both mineralized and unmineralized) in morphology, with an electron-dense, ruthenium positive deposition. This electron-dense material was approximately 20 to 50 nanometers in thickness, and only this thin layer separated the remodeled mineralized bone from the implant.

Composite morphology of the bone and associated support-tissue interfaces to osseointegrated dental implants: TEM and HVEM analyses.

Correlated transmission electron and high-voltage electron microscopic analyses examined the undecalcified bone and associated support tissues of 60 endosseous titanium blade and titanium and ceramic root-form implants in dogs. The implants supported fixed partial dentures for up to 2 years. Data obtained from this investigation suggest that a range of tissues, both mineralized and unmineralized, support osseointegrated dental implants. This study examined the tissues apposing not just isolated aspects of the implant surface, but the entire length of the implant, and found that mineralized and unmineralized tissues existed concurrently. Much of the implant surface was apposed by mandibular bone, and both root-form and blade implants osseointegrated. The densely mineralized collagen fibril matrix was often separated from the implant by only a 20-nm to 50-nm electron-dense, ruthenium-positive deposit. High-voltage electron microscope stereology demonstrated that cellular processes extended directly to the implant from underlying osteocytes. In the same implants, areas containing an unmineralized collagen matrix interposed between the bone and implant surface were observed. In this region osteoblasts interacted with this matrix, and Howship's lacunae, containing vascular elements and osteoclasts, were also observed. The remodeling activities appear to be a homeostasis of catabolic activity (osteoclasts) and metabolic activity (osteoblasts). The apex of the implant was often apposed by a fibrofatty stroma. The support tissue response appears to be the result of the interrelations of osteoblasts, osteocytes, and osteoclasts in association with vascular elements. Therefore, the support tissue response to osseointegrated implants is a dynamic activity that involves the healthy interaction of these cells and tissues along the entire length of the implant.

A comparative investigation in dogs: 2-year morphometric results of the dental implant--bone interface.

One hundred twenty titanium and ceramic root-form and titanium blade implants were placed into 30 dog mandibles. Twenty-four implants in six control dogs (in situ for 5 months) did not receive prostheses. Ninety-six implants in 24 dogs supported prostheses for 6, 12, 18, or 24 months. Computerized morphometry data presented the percent of the implant surface apposed directly by bone. A three-way factorial analysis of variance was used to assess significance. Individual implant means ranged from 0% (mobile implant) to 71% bone adaptation. From these data, two-stage titanium root-form implants were shown to be apposed by more bone than the other five systems, and overall, titanium implant systems were apposed by more bone than ceramic systems. Between 41% and 50% of the surface of integrated ceramic implants were apposed by bone, whereas between 50% and 65% of the surfaces of titanium implants were apposed by bone. Also, two-stage surgery for blade implants appears important for implant success. Furthermore, the use of Nomarski differential illumination appears to be useful for examining the quality of interfacial bone to correlate with the amount of bone quantified by morphometric protocols.

Histologic observations of bone remodeling adjacent to endosteal dental implants.

To examine bone morphology associated with endosteal dental implants at various time intervals, we inserted 20 one-stage and 20 two-stage titanium blade implants and 20 one-stage and 20 two-stage titanium root-form implants into 30 dog mandibles. Sixteen implants in 6 control (c) dogs (in situ five months) did not receive bridgework. Sixty-four implants in 24 dogs supported bridges for six, 12, 18, or 24 months. The entire area of the mandible containing the implants was examined by routine light and Nomarski differential interference microscopy (NM) for bone morphology (including osteon orientation) at the implant surface and at regions away from the implant. Control root-form implants were apposed by woven bone, with homogenous compact bone in the cortical plate distant to the implant. After 6 mo of load, immature bone was predominant apposing the implant, but initial osteonal maturation was apparent. NM clearly demonstrated the interstitial and concentric lamellae of the bone. Surprisingly, compact bone formed internal to the cortical plate, an area where trabecular bone is expected. At later periods of load, more mature osteons were seen apposing the implants; however remodeling events were still apparent. These remodeling events extend further away from the implant than was expected if the events resulted only from surgical repair. Also, when the implant inclined so that half was totally in the cortical plate and half in the marrow (in trabecular patterns), osteonal bone appeared to remodel in both areas. Control blade implants and blades loaded for six months were apposed by immature osteons when the implant was placed into the cortical plate. A trabecular meshwork was inferior to the osteonal bone. At 12 mo of load, the bone internal to the cortical plate appeared similar to the lamina dura supporting teeth; however, no PDL existed; the lamina-dura-like pattern directly apposed the implant. Even after 24 mo of load, extensive bone remodeling was apparent adjacent to the implant, markedly different from the bone making up the existing cortical plate. From these data, remodeling activities to blade implants may involve the development of a lamina-dura-like bone morphology after longer periods of load. Osteonal bone was apparent, but only at regions where the implant was inserted into the cortical plate. Further, bone remodeling was apparent even after long periods of load.

Transmission electron and high-voltage electron microscopy of osteocyte cellular processes extending to the dental implant surface.

Examination of the morphology of osteocytes within the bone supporting endosteal dental implants was performed using conventional transmission and high-voltage transmission electron microscopy (HVEM). The in vivo dog model used 72 implants inserted into the premolar region of 18 experimental animals. Forty-eight implants in 12 dogs were used as anterior abutments for fixed bridges for periods up to 12 months. The mineralized matrix of the supporting bone was either directly apposed to the implant surface or was separated from the implant by a narrow region of unmineralized matrix. Osteocytes were routinely observed to be closely associated with the bone-implant interface, as well as at a distance from the implant. Osteocytes were found to extend cellular processes directly to the implant surface through canaliculi. The osteocyte processes contained microfilaments. The three-dimensional capabilities of HVEM elucidated the nature of these cell processes at the point of exit from the osteocyte, as the processes extended through the mineralized matrix, and as the processes terminated at the implant interface. This report suggests that avenues of communication may exist between the implant and the osseous cells, providing intriguing hypotheses regarding biomechanical forces and osteogenesis at the implant interface. Furthermore, an electron-dense deposit was observed upon the inner confines of the canalicular wall, upon the outer aspects of the osteocyte lacuna, and upon the outer aspect of the bone interfacing the implant.

Osteoblast activity at the dental implant-bone interface: transmission electron microscopic and high voltage electron microscopic observations.

The purpose of this report is to present transmission electron microscopic and high voltage transmission electron microscopic (HVEM) observations of a longitudinal investigation examining the activities of osteoblasts and associated tissues apposing titanium and alumina oxide ceramic endosteal dental implants. The HVEM permitted 3-dimensional stereologic observations. All observations were obtained from undecalcified interfacial tissues from this in vivo experimental dog model using commercially available implants placed into the mandible. Two similar implants were placed in both sides of the mandible, with implants in 12 of the 18 dogs supporting fixed bridges for either 6 or 12 months. From the study, we observed that a mineralized matrix exists in direct apposition to the implant. Since bone does not interface the entire length of the implant, other interfacial zones were found to exist which consisted of unmineralized tissues. In such zones, we observed that osteoblasts were routinely found directly at the implant interface to the mandibular bone. These interfacial tissues included unmineralized collagen fibers, proteinaceous material, a finely fibrillar matrix, and the osteoblasts. This study has reinforced the concept that the oral tissue-dental implant interface is a dynamic zone consisting of remodeling activities of the osseous cells and extracellular matrices.

Light microscopic and scanning electron microscopic analyses of dental implants retrieved from humans.

This paper reports analyses obtained from 51 implant cases retrieved from humans and submitted to the AAIDRF-MCG Implant Retrieval Center. The undecalcified samples were embedded in PMMA and examined with scanning electron microscopy and with routine light or Nomarski microscopy. Cases included individual implants as well as 2 mandibles obtained at autopsy. Retrieved implants were sometimes shown to be encapsulated with connective tissue (CT), whereas other implants were apposed by bone, with only minimal CT association. In the latter cases, the implants were apposed by substantial amounts of viable bone. Nomarski microscopy disclosed the orientation and close apposition of the collagen bundles comprising the interfacial bone. In these cases where close bone apposition was observed to the implants, implant fracture was often the cause of failure. Periodontal lesions were reported around some implants showing a marked degree of inflammatory cell infiltrate (ICI). This study underscores the need for evaluation of failed human dental implants. Failure of implants placed longer than 10 years ago (perhaps loaded immediately) may be due to loss of bone support, CT encapsulation, and ICI (i.e., biological failure). Failure of more recently placed implants could also be due to this scenario, but failure was more often ascribed to biomaterial failure.

Morphology of the bone that supports endosteal dental implants. Transmission electron microscopic and high voltage electron microscopic observations.

The morphologic features of the bone-dental implant interface were investigated using an in vivo dog model. The undecalcified bone and associated support tissues were serially sectioned and examined with both conventional and high voltage transmission electron microscopy. A varied morphologic appearance of the tissues supporting clinically and radiographically appearing integrated implants was observed. Osteoblasts were observed at the implant interface, and osteocytes were routinely seen encased within lacunae extremely close to the implant surface. Often these osteocytes extended cellular projections to the implant surface. The variable tissue types observed were suggestive of healthy lamellar and appositional type mineralization patterns adjacent to the implants.

Osteogenesis at the dental implant interface: high-voltage electron microscopic and conventional transmission electron microscopic observations.

The osteogenesis of mandibular bone to endosteal dental implants was examined using an in vivo dog model. One half of the implants examined were unloaded implants, with the remaining one half prosthodontically loaded for 6 months. Undecalcified mandibular implant samples were examined with both high-voltage electron microscopy (HVEM) stereology and routine transmission electron microscopy. The osseous interface to integrated implants was shown to vary in its morphology. Mineralized bone was observed directly apposing the implant, often separated from the implant by an electron-dense deposit of approximately 50 nm. Within this densely mineralized matrix, osteocytes were routinely observed. Adjacent areas were shown to contain slightly wider zones of either a less dense mineralized matrix or, alternatively, unmineralized tissue. Other zones consisted of wider unmineralized matrices containing collagen fibers and osteoblasts. These latter zones were consistent with the appearance of an appositional type of bone growth. Because bone is a dynamic, actively remodeling tissue, a varied morphology of the support tissues to dental implant is not unexpected. Areas of mature bone interfacing with successfully integrated implants were demonstrated, as well as areas adjacent to the mature bone that were undergoing remodeling or mineralization. This study has also shown that HVEM stereology is a valuable research tool to investigate the oral tissue interface with dental implants.

Clinical evaluation data from a comparative dental implant investigation in dogs.

This report presents one-year clinical evaluation data from 120 ceramic and titanium cylindrical and titanium blade-type implants placed in the mandibles of 30 adult dogs. Ninety-six of the implants supported fixed bridges. The bone and gingival health was evaluated by the following indices: crevicular fluid volume index; gingival bleeding index; plaque accumulation index; clinical mobility index; and a quantitative mobility index utilizing the Periotest instrument. Results from this investigation suggest that, overall, the ceramic implants exhibited more fractures and had more mobile implants than did the titanium implant systems. Overall, complete one-year clinical evaluation data demonstrate healthy tissue responses to 112 of the 120 implants. Further, the Periotest instrument appears to offer a more quantitative assessment of clinical mobility. Also, it appears that the clinical evaluation protocol utilized in this study is a valid procedure to use for the assessment of clinical serviceability.

Histomorphometric and histologic observations of bone healing around immediate implants in dogs.

This paper reports histologic and histomorphometric results concerning bone healing around 13 pure titanium screw-shaped root-form implants that were placed in three mongrel dogs immediately after extraction of maxillary and mandibular premolars. Osseous healing around the implants showed a great deal of variability depending on the arch in which the implant was placed and on the original anatomy of the implant site. Implants placed in the mandible showed the greatest amount of bone apposition, with a mean total bone of 60.3%. Implants placed in the maxilla showed less bone and greater variability both visually and statistically, with a mean total bone of 46.3%. The values obtained for bone after 5 months of healing of the control sites were consistent with the values obtained for bone approximating the implants after the same time period. This was true for both arches. It was impossible to visually or statistically discriminate between sham surgical control sites and routine control sites or between implant sites and either of the control sites. Implant surgical procedures and implant placement seemed to have little effect on the tabulated values beyond tooth extraction alone. This research suggests that immediate implants have the potential for developing good bone apposition depending on the area of implantation.

Experimental studies of the implant-tissue interface.

This comparative study analyzed the epithelial, gingival connective tissue, and osseous tissue interface with clinically and radiographically integrated endosteal dental implants. Undecalcified interfacial tissues were sectioned for both routine transmission electron microscopy (TEM) and for High Voltage Electron Microscopy (HVEM). A protective perimucosal biological seal was formed by regenerating soft tissues (epithelium and connective tissue). Inferior to this protective soft-tissue attachment seal, the apical support complex was shown to vary in morphology. Mineralized bone was closely apposed to significant regions of the implants, separated only by an electron-dense deposit of approximately 20 nm. Osteoblasts were observed adjacent to the implant, as were osteocytes within the underlying supporting bone. Osteoblasts were observed associated with a connective tissue stroma adjacent to the existent mineralized bone. Osteocyte cellular processes extended toward adjacent osteocytes, toward vascular elements, and directly to the implant surface. These observations demonstrate the healthy interface of mineralized tissues with both root-form and blade implants. Mineralization patterns of the bone supporting the implants appeared consistent with normal mandibular maturation patterns.

Comparative implant research in dogs: a prosthodontic model.

One-hundred twenty endosteal dental implants were inserted bilaterally in the mandibles of 30 adult mongrel dogs after bilateral extraction of all premolars. The 120 implants were evenly divided into one- and two-stage systems and included ceramic and titanium cylindrical root-form implants and titanium blade implants. The research design of this investigation divided the 30 animals into 10 groups of three dogs. This article describes an animal model that is useful in evaluating dental implant designs and compares the results with those from humans. In particular, this article delineates the prosthodontic approach appropriate for this model using one- and two-stage titanium implants. Rexillium alloy fixed prostheses were placed on 32 endosteal implants and 16 natural mandibular molar teeth. The implants and prosthetic components of the Sterio-Oss implant system were used. All prostheses are functional with minimal maintenance. To date, after 1-year of follow-up, none of the implants have been lost and none of the fixed prostheses have required recementation or maintenance other than normal hygiene. Histologic and survival data as well as results with other implant systems will be presented in other reports.

A light and electron microscopic comparison of osseointegration of six implant types.

This study compared six commercially available implants placed in an animal model for 5 months. Twelve of the implants were used for light microscopic analysis, and the remaining 12 were used for scanning electron microscopic analysis. With the exception of one implant, newly formed bone was evident in direct apposition to portions of all control implants. The light microscopic and scanning electron microscopic evaluations of the tissues surrounding the six commercially available implant types indicated that initial osseointegration is likely with all types. Implant design, material, and submergibility do not appear to be essential for initial osseointegration to occur as long as a biocompatible material is selected and the implant is placed using minimally traumatic surgical techniques.

Transmission electron microscopic and high voltage electron microscopic observations of the bone and osteocyte activity adjacent to unloaded dental implants placed in dogs.

The purpose of this report is to describe ultrastructural observations of the bone and associated tissues supporting 24 unloaded endosteal dental implants placed in mongrel dogs (canis familiaris). The following 3 specific areas of the supporting tissues were targeted: 1) the osteocyte populations; 2) the mineralized collagen fiber matrix of the bone; and 3) an electron dense interfacial deposit. To investigate these areas, transmission electron microscopy and high voltage electron microscopic (HVEM) protocols were emphasized. HVEM permitted stereologic observations. Further, all observations were obtained from undecalcified tissues obtained from animals with commercially available implants placed into the mandible. From the study we observed a mineralization pattern of the implant supporting bone that was similar to those events occurring naturally within the mandibular bone. Osteocyte morphology was similar whether the osteocytes were found well below the implant interface or close to the interface. Osteocytes within lacunae were routinely found close to the implant interface, often extending cellular processes through canaliculi to the bone-implant interface. At the interface, an electron dense deposit approximately 50 nm in thickness was often observed. In interfacial regions, densely mineralized collagen fibers were observed running primarily parallel to the implant surface. This dense mineralized tissue was separated from the interface by a mineralized, but finely fibrillar matrix of approximately 200 nm in thickness.

High-voltage electron microscopy and conventional transmission electron microscopy of the interface zone between bone and endosteal dental implants.

The interface between mandibular bone and endosteal dental implants was examined with an in vivo dog model. Undecalcified mandibular implant samples were observed with both conventional transmission electron microscopy and high-voltage transmission electron microscopy (HVEM). Results demonstrated the variable nature of the interfacial support tissues. Mineralized bone was often found within 50 nm of the implant surface, separated from that surface only by an electron dense deposit. Osteocytes were observed close to the interface encased within lacunae extending numerous cellular processes through canaliculi. An osteoblast was also observed directly at the interface within a developing lacuna. Other interfacial areas exhibited a finely fibrillar and more electron lucent morphology. Furthermore, other areas were shown to be composed of wider zones of extracellular products containing collagen fibrils, ground substance, and calcified inclusions. Because bone is an actively growing and remodeling tissue, these different morphological zones around the entire area of the implants would appear to confirm the dynamic tissue response to endosteal dental implants. Further, HVEM stereology was shown to be an exciting research tool to investigate this tissue response.

Electron microscopy of bone response to titanium cylindrical screw-type endosseous dental implants.

This study investigated the undecalcified bone and enveloping tissues supporting commercially pure titanium one-stage and two-stage endosseous dental implants placed into the mandibles of adult mongrel dogs. Correlative light microscopy, transmission electron microscopy, and high-voltage transmission electron microscopy demonstrated a dynamic bone interface to the implants. Mineralized tissue was routinely observed within 20 to 50 nm from the implant interface, separated from the implant interface only by an electron-dense deposit. The densely mineralized collagen fiber matrix was oriented parallel to the implant interface, as were osteocytes that were found close to the interface. Osteocytic projections progressed through canaliculi, often directly to the implant interface. Unmineralized areas that appeared to have the potential for mineralization were also identified.

Comparative implant research in dogs: prosthodontic protocol using two-stage ceramic endosseous dental implants.

This report describes one phase of a long-term comparative implant investigation involving 20 of 120 endosseous implants placed in 30 adult mongrel dogs. Fixed prostheses involving 16 of the 20 (4 control implants) two-stage ceramic endosseous implants have been provided using routine prosthodontic procedures and the limited prosthetic components available for the Bioceram Series II implant system. The prostheses have proven to be functional with minimal maintenance. To date, after 1 year of follow-up, 2 of the two-stage implants have exhibited problems caused by fracture of the hexagonal collar. None of the implants to date has been lost and none of the fixed prostheses has required re-cementation or any other type of maintenance other than normal hygiene. Clinical evaluation suggests continued implant and prosthesis serviceability after 1 year in function.

Long-acting local anesthetics in dentistry.

Long-acting local anesthetics have proved to be effective for the suppression of both intraoperative and postoperative pain. They are useful for lengthy dental treatments and for prevention of severe pain following many types of surgical procedures. Although the currently available long-acting local anesthetics for dentistry have minimal side effects in the doses usually employed, there are potential problems. Bupivacaine, for example, can cause significant cardiac depressant and dysrhythmogenic responses. Etidocaine has less pronounced effects on the cardiovascular system, but its use may be associated with inadequate control of intraoperative bleeding. A new long-acting local anesthetic, ropivacaine, appears to offer advantages over either of the currently used long-acting agents.