In vivo plaque formation on implant materials

Plaque formation was studied in vivo by setting different implant materials on gingiva. The number of adhering viable bacteria depended on material surface properties 4 hours after setting, but not 48 hours after setting. The formation of pellicle-like thin layers and subsequent covering by lamellarly formed plaque were observed on the surfaces of all materials. Streptococcus species were predominant at the 4-hour setting time and anaerobes increased at the 48-hour setting time; this was common to all materials. The results indicate that surface properties of the implants influence early bacterial adherence, but do not influence bacterial flora or plaque maturation.     

Metagenomic analysis of the peri-implant and periodontal microflora in patients with clinical signs of gingivitis or mucositis

The long-term success of osseointegrated oral implants is endangered by inflammation of peri-implant hard and soft tissues caused by bacterial biofilms that may have been initiated by bacterial transmission from the adjacent dentition. The present study aimed to compare the bacterial communities at inflamed implant and tooth sites by broad-range PCR techniques to evaluate the etiological processes of peri-implant and periodontal diseases and potential future therapeutic strategies. Eighteen samples of peri-implant and periodontal microflora were collected from nine partially edentulous patients with implant-retained crowns or bridges revealing clinical signs of gingivitis or mucositis. The clinical parameters plaque index (PI), probing depth (PD), and bleeding on probing were recorded. Amplified fragments of bacterial 16S rRNA genes were separated by use of single-strand conformation polymorphism analysis, and sequences were determined to identify the predominant bacterial genera. The clinical parameters PI and PD were significantly different at implants (PI = 0.4 ± 0.7, PD = 3.1 ± 0.6 mm) compared with teeth (PI = 1.8 ± 0.8, PD = 2.5 ± 0.2 mm). A total of 20 different genera were found at the inflamed tooth and implant sites. The microbial diversity of the microflora surrounding the remaining dentition (12.0 ± 3.8) was significantly higher (p = 0.01) than the diversity of the peri-implant microflora at implant-retained crowns or bridges (6.3 ± 2.3). Within the limitations of the present study, the microbial diversity of the investigated implants and teeth with clinical signs of mucositis or gingivitis exhibits substantial differences, demonstrating that transmission of the complete bacterial microflora from teeth to implants could be excluded. Furthermore, broad-range molecular biological detection methods specify bacterial genera and species in the peri-implant and periodontal microflora which were not in the focus of research interests so far.     

Plaque formation on surface modified dental implants

Bacterial adhesion on titanium implant surfaces has a strong influence on healing and long-term outcome of dental implants. Parameters like surface roughness and chemical composition of the implant surface were found to have a significant impact on plaque formation. The purpose of this study was to evaluate the influence of two physical hard coatings on bacterial adhesion in comparison with control surfaces of equivalent roughness. Two members of the oral microflora, Streptococcus mutans and Streptococcus sanguis were used. Commercially pure titanium discs were modified using four different surface treatments: physical vapour deposition (PVD) with either titanium nitride (TiN) or zirconium nitride (ZrN), thermal oxidation and structuring with laser radiation. Polished titanium surfaces were used as controls. Surface topography was examined by SEM and estimation of surface roughness was done using a contact stylus profilometer. Contact angle measurements were carried out to calculate surface energy. Titanium discs were incubated in the respective bacterial cell suspension for one hour and single colonies formed by adhering bacteria were counted by fluorescence microscopy. Contact angle measurements showed no significant differences between the surface modifications. The surface roughness (Ra) of all surfaces examined was between 0.14 and 1.00 microm. A significant reduction of the number of adherent bacteria was observed on inherently stable titanium hard materials such as TiN and ZrN and thermically oxidated titanium surfaces compared to polished titanium. In conclusion, physical modification of titanium implant surfaces such as coating with TiN or ZrN may reduce bacterial adherence and hence improve clinical results.     

Plaque-induced inflammation around implants.

This article is a review of plaque-induced inflammation around dental implants. The microflora around successful implants is similar to healthy sulci, while that associated with failing implants is similar to periodontally diseased sites. Implant microflora is similar to the tooth microflora in the partially edentulous mouth. The microflora of implants in partially edentulous mouths differs from that in edentulous mouths. This seems to indicate a bacterial reservoir around the teeth and the possibility of reinfection of the implant sulcus by periodontal pathogens. The maintenance of a tooth microflora consistent with periodontal health in partially edentulous mouths may lead to maintaining an implant microflora consistent with peri-implant health. Thus, periodontal and implant maintenance are linked and neither can be overlooked.     

Comparisons of bacterial patterns present at implant and tooth sites in subjects on supportive periodontal therapy. I. Impact of clinical variables, gender and smoking

OBJECTIVE: (I) To compare the oral microflora at implant and tooth sites in subjects participating in a periodontal recall program, (II) to test whether the microflora at implant and tooth sites differ as an effect of gingival bleeding (bleeding on probing (BOP)), or pocket probing depth (PPD), and (III) to test whether smoking and gender had an impact on the microflora. MATERIAL AND METHODS: Data were collected from 127 implants and all teeth in 56 subjects. Microbiological data were identified by the DNA-DNA checkerboard hybridization. RESULTS: PPD> or =4 mm were found in 16.9% of tooth, and at 26.6% of implant sites (P<0.01). Tooth sites with PPD> or =4 mm had a 3.1-fold higher bacterial load than implant sites (mean difference: 66%, 95% confidence interval (CI): 40.7-91.3, P<0.001). No differences were found for the red, orange, green, and yellow complexes. A higher total bacterial load was found at implant sites with PPD> or =4 mm (mean difference 35.7 x 10(5), 95% CI: 5.2 (10(5)) to 66.1 (10(5)), P<0.02 with equal variance not assumed). At implant sites, BOP had no impact on bacterial load but influenced the load at tooth sites (P<0.01). CONCLUSION: BOP, and smoking had no impact on bacteria at implant sites but influenced the bacterial load at tooth sites. Tooth sites harbored more bacteria than implant sites with comparable PPD. The 4 mm PPD cutoff level influenced the distribution and amounts of bacterial loads. The subject factor is explanatory to bacterial load at both tooth and implant sites.     

Bacteriological studies of developing supragingival dental plaque

The predominant flora of plaque developing on an area of about 1 sq cm. on the middle third of the buccal surface of the upper first molar of one individual was studied. Samples were taken at 5 and 15 min, 1, 2, 4 and 8 hr, and 1, 2, 4, 8 and 16 days; the tooth surface was cleaned prior to each period. Plaque samples were handled and cultured under anaerobic conditions utilizing various growth media. AH isolates from blood agar plates in Brewer jars with 30 to 100 colonies were characterized.
Streptococcus sanguis , the single-most predominant organism, and Actinomyces viscosus were consistently found. Streptococcus mitis, Staphylococcus epidermidis, Actinomyces israelii, Peptostreptococcus sp. and Veillonella alcalescens were found at more than one time period. High proportions of "suspected pairs" (mixtures of 2 or more intimately-associated organisms), were regularly detected. Bacterial population changes with time were observed.
Many isolates, particularly those present in plaques up to 8 hr, agglutinated in the presence of saliva. Less than half of the isolates, including Gram-positive saccharolytic rods, staphylococci and some S. sanguis strains, formed plaque in vitro on wires in the presence of sucrose or glucose.
The data suggest that the nature of the early microflora observed is determined by bacterial attachment which may be influenced by, amongst others, salivary constituents. Subsequent cell multiplication leads to a large bacterial increase in which proportional changes may occur as a result of differences in bacterial growth.     

Bacterial colonization immediately after installation on oral titanium implants

BACKGROUND: Information on bacterial colonization immediately after dental implant insertion is limited. AIMS: (1) To assess the early colonization on titanium implants immediately after placement and throughout the first 12 post-surgical weeks, (2) to compare the microbiota at interproximal subgingival implant and adjacent tooth sites. MATERIAL AND METHODS: Subgingival plaque samples from implant and neighbouring teeth were studied by checkerboard DNA-DNA hybridization before surgery, 30 min after implant placement, and 1, 2, 4, 8, and 12 weeks after surgery. RESULTS: Comparing bacterial loads at implant sites between 30 min after placement with 1-week data showed that only the levels of Veillonella parvula (P<0.05) differed with higher loads at week 1 post-surgically. Week 12 data demonstrated significantly higher bacterial loads for 15/40 species at tooth sites compared with pre-surgery (P-values varying between 0.05 and 0.01). Between the period immediately after surgery and 12 weeks at implant sites, 29/40 species was more commonly found at 12 weeks. Included among these bacteria at implant sites were Porphyromonas gingivalis (P<0.05), Tannerella forsythia, (P<0.01), and Treponema denticola (P<0.001). Immediately post-surgery 5.9% of implants, and 26.2% of teeth, and at week 12, 15% of implants, and 39.1% of teeth harbored Staphylococcus aureus. Comparing tooth and implant sites, significantly higher bacterial loads were found at tooth sites for 27/40 species after 30 min following implant placement. This difference increased to 35/40 species at 12 weeks post-surgically. CONCLUSIONS: Bacterial colonization occurred within 30 min after implant placement. Early colonization patterns differed between implant and tooth surfaces.     

Comparison of bacterial plaque samples from titanium implant and tooth surfaces by different methods

Studies have shown similarities in the microflora between titanium implants or tooth sites when samples are taken by gingival crevicular fluid (GCF) sampling methods. The purpose of the present study was to study the microflora from curette and GCF samples using the checkerboard DNA-DNA hybridization method to assess the microflora of patients who had at least one oral osseo-integrated implant and who were otherwise dentate. Plaque samples were taken from tooth/implant surfaces and from sulcular gingival surfaces with curettes, and from gingival fluid using filter papers. A total of 28 subjects (11 females) were enrolled in the study. The mean age of the subjects was 64.1 years (SD+/-4.7). On average, the implants studied had been in function for 3.7 years (SD+/-2.9). The proportion of Streptococcus oralis (P<0.02) and Fusobacterium periodonticum (P<0.02) was significantly higher at tooth sites (curette samples). The GCF samples yielded higher proportions for 28/40 species studies (P-values varying between 0.05 and 0.001). The proportions of Tannerella forsythia (T. forsythensis), and Treponema denticola were both higher in GCF samples (P<0.02 and P<0.05, respectively) than in curette samples (implant sites). The microbial composition in gingival fluid from samples taken at implant sites differed partly from that of curette samples taken from implant surfaces or from sulcular soft tissues, providing higher counts for most bacteria studied at implant surfaces, but with the exception of Porphyromonas gingivalis. A combination of GCF and curette sampling methods might be the most representative sample method.     

Soft tissue integration versus early biofilm formation on different dental implant materials

Objective

Dental implants anchor in bone through a tight fit and osseo-integratable properties of the implant surfaces, while a protective soft tissue seal around the implants neck is needed to prevent bacterial destruction of the bone-implant interface. This tissue seal needs to form in the unsterile, oral environment. We aim to identify surface properties of dental implant materials (titanium, titanium-zirconium alloy and zirconium-oxides) that determine the outcome of this “race-for-the-surface” between human-gingival-fibroblasts and different supra-gingival bacterial strains.

Methods

Biofilms of three streptococcal species or a Staphylococcus aureus strain were grown in mono-cultures on the different implant materials in a parallel-plate-flow-chamber and their biovolume evaluated using confocal-scanning-laser-microscopy. Similarly, adhesion, spreading and growth of human-gingival-fibroblasts were evaluated. Co-culture experiments with bacteria and human-gingival-fibroblasts were carried out to evaluate tissue interaction with bacterially contaminated implant surfaces. Implant surfaces were characterized by their hydrophobicity, roughness and elemental composition.

Results

Biofilm formation occurred on all implant materials, and neither roughness nor hydrophobicity had a decisive influence on biofilm formation. Zirconium-oxide attracted most biofilm. All implant materials were covered by human-gingival-fibroblasts for 80–90% of their surface areas. Human-gingival-fibroblasts lost the race-for-the-surface against all bacterial strains on nearly all implant materials, except on the smoothest titanium variants.

Significance

Smooth titanium implant surfaces provide the best opportunities for a soft tissue seal to form on bacterially contaminated implant surfaces. This conclusion could only be reached in co-culture studies and coincides with the results from the few clinical studies carried out to this end.     

The predominant microflora of nursing caries lesions.

The predominant microflora recovered from infected dentine of 52 carious teeth from 14 children with nursing caries was determined using both selective and non-selective media for the isolation of specific genera and acidified media (pH 5.2) to isolate the predominant aciduric microorganisms, and compared with the microflora of sound enamel surfaces in caries-free children. Streptococcus mutans formed a significantly greater proportion of the lesion flora while Streptococcus oralis, Streptococcus sanguis and Streptococcus gordonii formed a significantly greater proportion of the plaque flora from sound tooth surfaces. The proportions of Actinomyces naeslundii and Actinomyces odontolyticus were significantly greater in the plaque samples than in the lesion samples. Actinomyces israelii formed 18.2% of the flora from the lesions, but was not isolated from the plaque samples. The proportions of Candida albicans, Lactobacillus spp. and Veillonella spp. were also significantly greater in the carious dentine than in the plaque samples. The most frequently isolated lactobacilli were Lactobacillus casei, Lactobacillus fermentum and Lactobacillus rhamnosus. The predominant aciduric flora was S. oralis, S. mutans and A. israelii and these taxa were also isolated from a similar proportion of the lesions at pH 7.0. Strains of S. mutans, L. casei, L. fermentum and L. rhamnosus isolated from individual carious teeth were genotyped using PCR-based methods. Each species was genotypically heterogeneous and different genotypes were recovered from different carious teeth in the same child. These data indicate that the microflora of lesions in the same child is microbiologically diverse and support a non-specific aetiology for nursing caries in which the physiological characteristics of the infecting flora, not its composition, is the major determinant underlying the disease process.     

One-year bacterial colonization patterns of Staphylococcus aureus and other bacteria at implants and adjacent teeth

AIMS: (i) To assess the pattern of early bacterial colonization on titanium oral implants after installation, at 12 weeks and at 12 months, (ii) to compare the microbiota at submucosal implant sites and adjacent subgingival tooth sites and (iii) to assess whether or not early colonization was predictive of 12-month colonization patterns. MATERIAL AND METHODS: Submucosal/subgingival plaque samples from 17 titanium oral implants and adjacent teeth were analyzed by checkerboard DNA-DNA hybridization 30 min, 12 weeks and 12 months after implant installation. RESULTS: At 12 months, none of the inserted implants had been lost or presented with signs of peri-implantitis. The distribution of sites at implants and teeth with bleeding on probing varied between 2% and 11%. Probing pocket depths < or =3 mm were found at 75% of implant sites. At 12 months, the sum of the bacterial counts of 40 species was statistically significantly higher at tooth compared with implant sites (mean difference: 34.4 x 10(5), 95% confidence interval -0.4 to 69.4, P<0.05). At 12 months, higher individual bacterial counts at tooth sites were found for 7/40 species compared with implant sites. Detection or lack of detection of Staphylococcus aureus at implant sites at 12 weeks resulted in the highest positive (e.g. 80%) and negative (e.g. 90%) predictive values, respectively. Between 12 weeks and 12 months, the prevalence of Tannerella forsythia increased statistically significantly at implant sites (P<0.05). Lack of detection of Porphyromonas gingivalis at 12 weeks yielded a negative predictive value of 93.1% of this microorganism being undetectable at implant sites at 12 months. CONCLUSIONS: Within the limits of this study, the findings showed (i) a few differences in the prevalence of bacterial species between implant and adjacent tooth sites at 12 months and (ii) high positive and negative predictive values for selected bacterial species.     

Biomechanical stress in bone surrounding an implant under simulated chewing

The concept of reducing nonaxial loading of dental implants has been widely regarded as the standard procedure. The aim of this study was to reveal the biomechanical stress distribution in supporting bone around an implant and a natural tooth under chewing function. Three-dimensional finite element models of the mandibular first molar and the titanium implant both with the mandible in the molar region were constructed. The directions of displacement constraints were determined according to the angles of the closing pathways of chopping type and grinding type chewing patterns. The tooth model showed smooth stress distribution in the supporting bone with low stress concentration around the neck of the tooth. The implant model showed stress concentration in the supporting bone around the neck of the implant, especially in the buccal area. The grinding type model of the implant showed higher tensile stress concentration than the chopping type model at the lingual neck of the implant. The results of this study suggested the importance of considering occlusion under chewing function for understanding the biomechanics of oral implants.     

Immediate transmucosal implants using the principle of guided tissue regeneration. I. Rationale, clinical procedures and 30‐month results.

The installation of implants directly into extraction sockets offers considerable advantages over other treatment modalities for both practitioners and patients. Usually, immediate implants are placed and subsequently covered by mucosa allowing a submerged healing mode. This report presents the rationale, clinical procedures and results for immediate transmucosal implants. Following an intracrevicular incision and flap elevation, the tooth to be extracted is carefully luxated by means of small elevators to preserve the entire bony housing of the tooth. A titanium plasma‐sprayed implant (ITI Bonefit®) is then installed at the bottom or in the wall of the extraction socket. An expanded polytetrafluoroethylene barrier membrane (Gore‐Tex GTAM®) is tightly adapted around the implant post and over the bony margins of the alveolus. The flaps are then replaced, adapted around the neck of the implant and sutured. During nonsubmerged, transmucosal healing of the site, meticulous plaque control is performed by mechanical and chemical means. Membranes are removed after 5–7 months. Since infection was prevented, the implants obtained stability, healthy peri‐implant mucosal tissues were observed and missing bone in the alveoli regenerated. Of 21 transmucosal implants placed into fresh extraction sockets, 20 yielded complete bone fill and coverage of the entire plasma‐coated implants surface at the time of membrane removal. This documentation suggests that the immediate nonsubmerged installation of an implant into an extraction socket is a predictable treatment modality with good long‐term prognosis.     

Wound healing around dental implants

Dental implants have become a part of routine dentistry. Bone healing around modern implants follows established sequence of events and results in predictable osseointegration. Bone formation can be seen as early as four days after implant placement. In a healing bone wound, fibroblast‐like osteogenic progenitor cells differentiate into osteoblasts and start to deposit woven bone that gradually grows towards the implant surface. During 1–3 months of healing, this woven bone is replaced by lamellar bone with increasing bone to implant contact that allows functional loading of the implant. As a clinical application, RFA has suggested that implant stability is initially decreased up to three weeks due to bone remodeling and followed by an increase to the baseline at 4–5 weeks and then reaching plateau in 8 weeks. Regardless of this remodeling, studies have shown that implants can be successfully loaded immediately after placement although with somewhat reduced survival rates. Development of new implant surfaces has played a critical role in expanding these clinical loading protocols. Soft tissue healing around implants has become a focus of attention because it plays a central role in esthetic outcomes. Healing of the peri‐implant soft tissue occurs similarly to that against of a tooth after surgical procedure. Fibrin clot serves as a provisional matrix allowing epithelial and fibroblast migration towards the implant surface. Epithelial and connective tissue contact to the implant or abutment surface is established within 1–2 weeks and further maturation follows up to at least 12 weeks. In the established interphase, the peri‐implant epithelium is similar but longer than the junctional epithelium against the tooth. Orientation of collagen fiber bundles also differs from natural tooth. Instead of attaching to the neck of the implant, collagen fibers run parallel and circumferentially around the implant. Future studies are needed to develop better implant designs and surfaces that improve the soft tissue healing for more predictable esthetical outcomes.     

Role of sucrose in plaque formation

Results are presented which support the concept that the bacterial enzyme glucosyltransferase (GTF) plays a crucial role in sucrose induced plaque formation. GTF was shown to adhere strongly to anionic, hydrophobic and polysaccharide solid materials, and to be able to produce glucans in the adsorbed state. It appears conceivable that GTF adsorb to teeth and produce glucans. Glucan chains on the surface of the bacteria and glucans on the tooth surfaces interact (pack) and form a strong binding mechanism. The rigid alpha 1,3 linked glucans produced by Streptococcus mutans are particularly suited for interaction of this kind. This mechanism could account for sucrose-induced binding of bacteria to enamel, pellicle covered enamel and preformed plaque. S. mutans would adhere particularly strongly to tooth surfaces in the presence of sucrose, according to this model.     

Role of sucrose in plaque formation

Results are presented which support the concept that the bacterial enzyme glucosyltransferase (GTF) plays a crucial role in sucrose induced plaque formation. GTF was shown to adhere strongly to anionic, hydrophobic and polysaccharide solid materials, and to be able to produce glucans in the adsorbed state. It appears conceivable that GTF adsorb to teeth and produce glucans. Glucan chains on (he surface of the bacteria and glucans on the tooth surfaces interact (pack) and form a strong binding mechanism. The rigid α1,3 linked glucans produced by Streptococcus mutans are particularly suited for interaction of this kind. This mechanism could account for sucrose-induced binding of bacteria to enamel, pellicle covered enamel and preformed plaque. S. mutans would adhere particularly strongly to tooth surfaces in the presence of sucrose, according to this model.     

The influence of saliva on interbacterial adherence

The mechanism of bacterial adherence to the mat of bacteria in preformed dental plaque is not well defined. This study measured the influence of saliva on the adherence of bacteria in suspension to a continuous bacterial surface in vitro . Twenty different pairs of bacteria were tested, consisting of Streptococcus spp., Huenwphilus spp. and Actinomyces spp. The species were chosen based on the parameters of coaggregation. and salivary agglutination. The results were expressed as bacteria that adhered per mm² of bacterial surface. When both the surface bacteria and the bacteria in suspension agglutinated in saliva, interbacterial adherence was increased 2.5-fold when a salivary coating was placed on the surface. When one or both of the bacteria did not agglutinate in saliva, interbacterial adherence was increased only slightly when the surface was saliva-coated. The results suggested that salivary-mediated adherence is significant to plaque formation once the tooth surface becomes covered with bacteria. Thus bacteria that are capable of agglutinating in saliva may have a distinct advantage in colonization of the plaque surface.     

The implantation of natural tooth form bioglasses in baboons. A preliminary report.

This report describes a 6-month screening study comparing the tissue responses of several bioglass natural tooth implants in adult female baboons. The dental implants were designed to elicit osteogenesis at the interface of the implant and the oral tissues. This is in contrast to those types of implant materials that are merely biologically acceptable. Incisor teeth were extracted, dupplicated in bioglass, returned to the natural sockets, and splinted to the adjacent natural tooth, where they remained splinted for 3 months and then free standing for an additional 3 months. Microscopic evaluation revealed distinct histopathologic characteristics with certain bioglass formulas, such as ankylosis, a pseudofibrous capsule with fibers running parallel to the root surface, or an apparently true periodontal membrane with properly oriented Sharpey's fibers. True cementogenesis was not found.     

Soft tissue reaction to de novo plaque formation on implants and teeth. An experimental study in the dog

The aim of the present investigation was to assess the effect of de novo plaque formation on the gingiva and masticatory mucosa around teeth and implants. The study was performed in 5 beagle dogs which at the initiation of the experiment were 15 months old. During a preparatory period, the mandibular right premolars were extracted, 3 fixtures installed, abutment connection performed and a 4-month period of plaque control completed. A clinical examination was performed and biopsies of the second mandibular premolar (P2) and the contralateral implant site (2P) were sampled. The dogs were allowed to form plaque during a period of 3 weeks. The clinical examination was repeated and biopsies harvested from the 2 remaining implants and the contralateral tooth sites. The tissue samples were prepared for histometric and morphometric analysis. Both the masticatory mucosa at implants and the gingiva responded to de novo plaque formation with the development of an inflammatory lesion. The size as well as the composition of the lesions in the 2 tissues had many features in common. It was concluded that the mucosa around implants and the gingiva around teeth had a similar potential to respond to early plaque formation.     

Crestal bone loss around submerged and exposed unloaded dental implants: a radiographic and microbiological descriptive study

The successful maintenance of crestal bone surrounding dental implants is imperative for long-term implant success. Crestal bone loss is reportedly related to stress. However, early perforation and partial exposure of the implant's covering device are a focus for plaque accumulation, which, if left untreated, may result in inflammation. The objective of this study was to evaluate the crestal bone levels adjacent to submerged and exposed unloaded dental implants during the initial healing phase. In addition, the microbiota around exposed implants were studied. Bilateral implants were placed in the mandible of 10 patients. In one quadrant, the implants were covered by the flap. In the other quadrant, the flap was sutured, leaving the cover screws completely exposed. Standardized periapical radiographs were obtained at implant placement and 4 months later. Radiographs were digitalized, aligned, and analyzed with a computer-assisted method. Cultures were obtained from exposed implant sites. All patients showed more crestal bone loss around exposed dental implants compared to submerged implants. Prevotella sp., Streptococcus beta-hemoliticus, and Fusobacterium sp. were the microorganisms identified in most of the sites. The exposure of the implant covering device created foci for bacterial plaque accumulation, which may have facilitated periimplant crestal bone loss. The initial healing phase follow-up may be critical for implant success.