Dieter D. Bosshardt

Early osseointegration to hydrophilic and hydrophobic implant surfaces in humans

OBJECTIVE To evaluate the rate and degree of osseointegration at chemically modified moderately rough, hydrophilic (SLActive) and moderately rough, hydrophobic (SLA) implant surfaces during early phases of healing in a human model. MATERIAL AND METHODS The devices used for this study of early healing were 4 mm long and 2.8 mm in diameter and had either an SLActive chemically modified or a moderately rough SLA surface configuration. These devices were surgically installed into the retro-molar area of 49 human volunteers and retrieved after 7, 14, 28 and 42 days of submerged healing. A 5.2-mm-long specially designed trephine with a 4.9 mm inside diameter, allowing the circumferential sampling of 1 mm tissue together with the device was applied. Histologic ground sections were prepared and histometric analyses of the tissue components (i.e. old bone, new bone, bone debris and soft tissue) in contact with the device surfaces were performed. RESULTS All device sites healed uneventfully. All device surfaces were partially coated with bone debris. A significant fraction of this bone matrix coating became increasingly covered with newly formed bone. The process of new bone formation started already during the first week in the trabecular regions and increased gradually up to 42 days. The percentage of direct contact between newly formed bone and the device (bone-to-implant contact) after 2 and 4 weeks was more pronounced adjacent to the SLActive than to the SLA surface (14.8% vs. 12.2% and 48.3% vs. 32.4%, respectively), but after 42 days, these differences were no longer evident (61.6% vs. 61.5%). CONCLUSION While healing showed similar characteristics with bone resorptive and appositional events for both SLActive and SLA surfaces between 7 and 42 days, the degree of osseointegration after 2 and 4 weeks was superior for the SLActive compared with the SLA surface.

Maxillary sinus grafting with Bio‐Oss® or Straumann® Bone Ceramic: histomorphometric results from a randomized controlled multicenter clinical trial

INTRODUCTION This investigation was designed to compare the histomorphometric results from sinus floor augmentation with anorganic bovine bone (ABB) and a new biphasic calcium phosphate, Straumann Bone Ceramic (BCP). MATERIALS AND METHODS Forty-eight maxillary sinuses were treated in 37 patients. Residual bone width was > or =6 mm and height was > or =3 mm and <8 mm. Lateral sinus augmentation was used, with grafting using either ABB (control group; 23 sinuses) or BCP (test group; 25 sinuses); sites were randomly assigned to the control or test groups. After 180-240 days of healing, implant sites were created and biopsies taken for histological and histomorphometric analyses. The parameters assessed were (1) area fraction of new bone, soft tissue, and graft substitute material in the grafted region; (2) area fraction of bone and soft tissue components in the residual alveolar ridge compartment; and (3) the percentage of surface contact between the graft substitute material and new bone. RESULTS Measurable biopsies were available from 56% of the test and 81.8% of the control sites. Histology showed close contact between new bone and graft particles for both groups, with no significant differences in the amount of mineralized bone (21.6+/-10.0% for BCP vs. 19.8+/-7.9% for ABB; P=0.53) in the biopsy treatment compartment of test and control site. The bone-to-graft contact was found to be significantly greater for ABB (48.2+/-12.9% vs. 34.0+/-14.0% for BCP). Significantly less remaining percentage of graft substitute material was found in the BCP group (26.6+/-5.2% vs. 37.7+/-8.5% for ABB; P=0.001), with more soft tissue components (46.4+/-7.7% vs. 40.4+/-7.3% for ABB; P=0.07). However, the amount of soft tissue components for both groups was found not to be greater than in the residual alveolar ridge. DISCUSSION Both ABB and BCP produced similar amounts of newly formed bone, with similar histologic appearance, indicating that both materials are suitable for sinus augmentation for the placement of dental implants. The potential clinical relevance of more soft tissue components and different resorption characteristics of BCP requires further investigation.

Cementogenesis reviewed: a comparison between human premolars and rodent molars.

Cementum continues to be the least‐known mineralized tissue. Although recent advances in the field of molecular biology have contributed to an understanding of the involvement of molecular factors in cementum formation during development and regeneration, cementogenesis on a cell biological basis is still poorly understood. Virtually nothing is known about cementoblast origin, differentiation, and the cell dynamics during normal development, repair, and regeneration. This review describes the recent findings of cementogenesis on roots of human premolars and opposes them to those of teeth from other mammals, particularly the rodent molar.

Does periodontal tissue regeneration really work

Periodontitis is an infectious disease that causes destruction of the tooth-attachment apparatus. Untreated periodontitis results in progressive attachment loss that may eventually lead to early tooth loss. Fortunately, research has provided evidence that in most situations chronic periodontal diseases can be treated [reviewed in Ref. (29)]. There is also evidence that periodontally involved teeth have a good chance of survival, provided that therapy, patient compliance and maintenance care are appropriate [reviewed in Ref. (29)]. There are a broad range of treatment options available, but only a few may be regarded as truly regenerative procedures. According to a position paper from the American Academy of Periodontology (29), periodontal regenerative procedures include soft tissue grafts, bone replacement grafts, root biomodifications, guided tissue regeneration, and combinations thereof, for osseous, furcation and recession defects. Regeneration is defined as the reproduction or reconstitution of a lost or injured part of the body in such a way that the architecture and function of the lost or injured tissues are completely restored. The aim of regenerative periodontal therapy is to restore the structure and function of the periodontium. This means that the structure and function of the gingiva, alveolar bone, root cementum and periodontal ligament must be restored (Figs 1 and 2). By contrast, periodontal repair implies healing without restoration of the tooth-attachment apparatus and is often associated with the formation of a long junctional epithelium (Figs 3–5). Detachment of the junctional epithelium from the tooth surface (i.e. the formation of a periodontal pocket), disconnection of periodontal ligament fiber attachment to the root surface via cementum, and bone loss, are hallmarks of periodontitis. New attachment of junctional epithelium to the tooth surface and of connective tissue fibers to the root surface are very critical components of true periodontal regeneration. New connective tissue attachment requires the formation of new cementum to a previously diseased root surface that was modified following periodontal therapy. Needless to say, in order to increase the attachment function of a tooth, the periodontal connective tissue fibers also have to insert into newly formed bone (Fig. 6). While less concern exists about the new epithelial attachment, new connective tissue attachment is much more critical. Concerns include predictability and the amount of new connective tissue attachment, as well as the strength of the regenerated interface between the treated root surface and the new cementum. As formation of cementum is essential for the attachment of periodontal ligament fibers to the root surface, much research has been devoted to understanding cementogenesis (for reviews, see Refs 3, 7, 9, 26, 30, 61, 62, 81). Not all studies that claim to have achieved periodontal regeneration have utilized histological techniques. Methods of assessing periodontal regeneration have been reviewed previously (56). Clinically, the outcome of a regenerative periodontal treatment is assessed by clinical parameters (periodontal probing, radiographs and re-entry evaluations). These methods are, however, inappropriate for demonstrating true attachment gain. Histology continues to be the only reliable method of evaluating the efficacy of a therapy aimed at achieving periodontal regeneration. According to the World Workshop in Periodontics of the American Academy of Periodontology (1996), the requirements for a periodontal treatment to be considered a regenerative procedure are as follows: (i) human histology demonstrating new cementum, periodontal ligament and bone coronal to the former defect base; (ii) controlled human clinical trials demonstrating improved clinical probing attachment and bone levels; and (iii) controlled animal histological studies revealing new cementum, periodontal ligament and bone.

Comparative study of biphasic calcium phosphates with different HA/TCP ratios in mandibular bone defects. A long-term histomorphometric study in minipigs†

Three biphasic calcium phosphate (BCP) bone substitute materials with hydroxyapatite (HA)/tricalcium phosphate (TCP) ratios of 20/80, 60/40, and 80/20 were compared to coagulum, particulated autogenous bone, and deproteinized bovine bone mineral (DBBM) in membrane-protected bone defects. The defects were prepared in the mandibles of 24 minipigs that were divided into four groups of six with healing times of 4, 13, 26, and 52 weeks, respectively. The histologic and histomorphometric evaluation focused on differences in amount and pattern of bone formation, filler degradation, and the interface between bone and filler. Collapse of the expanded polytetrafluoroethylene barrier membrane into the coagulum defects underlined the necessity of a filler material to maintain the augmented volume. Quantitatively, BCP 20/80 showed bone formation and degradation of the filler material similar to autografts, whereas BCP 60/40 and BCP 80/20 rather equaled DBBM. Among the three BCPs, the amount of bone formation and degradation of filler material seemed to be inversely proportional to the HA/TCP ratio. The fraction of filler surface covered with bone was highest for autografts at all time points and was higher for DBBM than BCP 80/20 and 60/40 at the early healing phase. TRAP-positive multinucleated cells were identified on BCP and DBBM surfaces without showing typical signs of resorption lacunae.

Gene expression profile of osseointegration of a hydrophilic compared with a hydrophobic microrough implant surface

OBJECTIVES To compare the gene expression profile of osseointegration associated with a moderately rough and a chemically modified hydrophilic moderately rough surface in a human model. MATERIAL AND METHODS Eighteen solid screw-type cylindrical titanium implants, 4 mm long and 2.8 mm wide, with either a moderately rough (SLA) or a chemically modified moderately rough (SLActive) surface were surgically inserted in the retromolar area of nine human volunteers. The devices were removed using a trephine following 4, 7 and 14 days of healing. The tissue surrounding the implant was harvested, total RNA was extracted and microarray analysis was carried out to identify the differences in the transcriptome between the SLA and SLActive surfaces at days 4, 7 and 14. RESULTS There were no functionally relevant gene ontology categories that were over-represented in the list of genes that were differentially expressed at day 4. However, by day 7, osteogenesis- and angiogenesis-associated gene expression were up-regulated on the SLActive surface. Osteogenesis and angiogenesis appeared to be regulated by BMP and VEGF signalling, respectively. By day 14, VEGF signalling remains up-regulated on the SLActive surface, while BMP signalling was up-regulated on the SLA surface in what appeared to be a delayed compensatory response. Furthermore, neurogenesis was a prominent biological process within the list of differentially expressed genes, and it was influenced by both surfaces. CONCLUSIONS Compared with SLA, SLActive exerts a pro-osteogenic and pro-angiogenic influence on gene expression at day 7 following implant insertion, which may be responsible for the superior osseointegrative properties of this surface.

Bone Response to Loaded Implants With Non-Matching Implant-Abutment Diameters in the Canine Mandible

BACKGROUND One way to evaluate various implant restorations is to measure the amount of bone change that occurs at the crestal bone. The objective of this study was to histologically evaluate the alveolar bone change around a bone-level, non-matching implant-abutment diameter configuration that incorporated a horizontal offset and a Morse taper internal connection. METHODS The study design included extraction of all mandibular premolars and first molars in five canines. After 3 months, 12 dental implants were placed at three levels in each dog: even with the alveolar crest, 1 mm above the alveolar crest, and 1 mm below the alveolar crest. The implants were submerged on one side of the mandible. On the other side, healing abutments were exposed to the oral cavity (non-submerged). Gold crowns were attached 2 months after implant placement. The dogs were sacrificed 6 months postloading, and specimens were processed for histologic and histometric analyses. RESULTS Evaluation of the specimens indicated that the marginal bone remained near the top of the implants under submerged and non-submerged conditions. The amount of bone change for submerged implants placed even with, 1 mm below, and 1 mm above the alveolar crest was -0.34, -1.29, and 0.04 mm, respectively (negative values indicate bone loss). For non-submerged implants, the respective values were -0.38, -1.13, and 0.19 mm. For submerged and non-submerged implants, there were significant differences in the amount of bone change among the three groups (P <0.05). The percentage of bone-to-implant contact for submerged implants was 73.3%, 71.8%, and 71.5%. For non-submerged implants, the respective numbers were 73.2%, 74.5%, and 76%. No significant differences occurred with regard to the percentage of bone contact. CONCLUSIONS Minimal histologic bone loss occurred when dental implants with non-matching implant-abutment diameters were placed at the bone crest and were loaded for 6 months in the canine. The bone loss was significantly less (five- to six-fold) than that reported for bone-level implants with matching implant-abutment diameters (butt-joint connections).

Soft tissue wound healing around teeth and dental implants

AIM To provide an overview on the biology and soft tissue wound healing around teeth and dental implants. MATERIAL AND METHODS This narrative review focuses on cell biology and histology of soft tissue wounds around natural teeth and dental implants. RESULTS AND CONCLUSIONS The available data indicate that: (a) Oral wounds follow a similar pattern. (b) The tissue specificities of the gingival, alveolar and palatal mucosa appear to be innately and not necessarily functionally determined. (c) The granulation tissue originating from the periodontal ligament or from connective tissue originally covered by keratinized epithelium has the potential to induce keratinization. However, it also appears that deep palatal connective tissue may not have the same potential to induce keratinization as the palatal connective tissue originating from an immediately subepithelial area. (d) Epithelial healing following non-surgical and surgical periodontal therapy appears to be completed after a period of 7–14 days. Structural integrity of a maturing wound between a denuded root surface and a soft tissue flap is achieved at approximately 14-days post-surgery. (e) The formation of the biological width and maturation of the barrier function around transmucosal implants requires 6–8 weeks of healing. (f) The established peri-implant soft connective tissue resembles a scar tissue in composition, fibre orientation, and vasculature. (g) The peri-implant junctional epithelium may reach a greater final length under certain conditions such as implants placed into fresh extraction sockets versus conventional implant procedures in healed sites.

The role of bone debris in early healing adjacent to hydrophilic and hydrophobic implant surfaces in man

OBJECTIVE To evaluate morphologically and morphometrically the sequential healing and osseointegration events at moderately rough implant surfaces with and without chemical modification. Particularly the role of bone debris in initiating bone formation was emphasized. MATERIAL AND METHODS Solid, screw-type cylindrical titanium implants (SSI) (n=49), 4 mm long and 2.8 mm wide, with either chemically modified (SLActive(®)) or sandblasted and acid-etched (SLA(®)) surface configurations were surgically installed in the retromolar region of 28 human volunteers. After 7, 14, 28 and 42 days of submerged healing, the devices were retrieved with a trephine. Histologic ground sections were prepared and histomorphometrically analyzed. Linear measurements determined fractions of old bone (OBIC), new bone (NBIC), soft tissue (ST) and bone debris (BD) in contact with the SSI surfaces. RESULTS Healing was uneventful at all installation sites. Sixty-one percent of all devices were suitable for morphometric analyses. All implant surfaces were partially coated with bone debris and new bone formation was observed as early as 7 days after installation. There was a gradual increase in NBIC, whereas OBIC, ST and BD progressively decreased over time. NBIC after 2 and 4 weeks was higher on SLActive(®) than on SLA(®) surfaces, albeit statistically not significant. The BD : ST ratio changed significantly from 7 to 42 days (from 50 : 50 to 10 : 90 for SLActive(®); from 38: 62 to 10 : 90 for SLA(®)) (Fishers exact test, P<0.01). CONCLUSION Both SLActive(®) and SLA(®) devices became progressively osseointegrated, while old bone on the device surface was gradually resorbed. The decrease in BD : ST ratio suggests that bone debris, created during implant installation and adhering to moderately rough surfaces, significantly contributed to the initiation of bone deposition and mediated the connection between the old bone and the new bone on the implant surface.

Immunolocalization of epithelial and mesenchymal matrix constituents in association with inner enamel epithelial cells.

After crown formation, the enamel organ reorganizes into Hertwigs epithelial root sheath (HERS). Although it is generally accepted that HERS plays an inductive role during root formation, it also has been suggested that it may contribute enamel-related proteins to cementum matrix. By analogy to the enamel-free area (EFA) in rat molars, in which epithelial cells express not only enamel proteins but also “typical” mesenchymal matrix constituents, it has been proposed that HERS cells may also have the potential to produce cementum proteins. To test this hypothesis, we examined the nature of the first matrix layer deposited along the cervical portion of root dentin and the characteristics of the associated cells. Rat molars were processed for postembedding colloidal gold immunolabeling with antibodies to amelogenin (AMEL), ameloblastin (AMBN), bone sialoprotein (BSP), and osteopontin (OPN). To minimize the possibility of false-negative results, several antibodies to AMEL were used. The labelings were compared with those obtained at the EFA. Initial cementum matrix was consistently observed at a time when epithelial cells from HERS covered most of the forming root surface. Cells with mesenchymal characteristics were rarely seen in proximity to the matrix. Both the EFA matrix and initial cementum exhibited collagen fibrils and were intensely immunoreactive for BSP and OPN. AMEL and AMBN were immunodetected at the EFA but not over the initial cementum proper. These two proteins were, however, present at the cervical-most portion of the root where enamel matrix extends for a short distance between dentin and cementum. These data suggest that epithelial cells along the root surface are likely responsible for the deposition of the initial cementum matrix and therefore, like the cells at the EFA, may be capable of producing mesenchymal proteins.