Markus B. Hürzeler

Peri-Implant Bone Level Around Implants With Platform-Switched Abutments: Preliminary Data From a Prospective Study

PURPOSE Several long-term clinical studies have shown a mean marginal bone loss around dental implants of 1.5 to 2 mm in the first year after prosthetic restoration. Currently, concepts to avoid bone remodeling around dental implants have been developed. The use of prosthetic abutments with reduced width in relation to the implant diameter (platform switching) seems to have the greatest potential to limit the crestal resorption. The purpose of this clinical trial was to show that crestal bone height around dental implants could be influenced using a platform switch protocol and that the bone level would remain stable within 1 year after final prosthetic reconstruction. MATERIALS AND METHODS Fifteen patients were treated with fixed implant retained prosthesis; 14 wide-diameter implants were supplied with platform-switched abutments and served as the test group. Eight implants with regular diameter were reconstructed with traditional abutments and served as the control group. Standardized digital radiographs were obtained for evaluation of the peri-implant bone levels at the time of installation of the final restoration and at 1-year follow-up. Marginal peri-implant bone levels were measured at the mesial and distal surfaces of each implant using digital image analysis. RESULTS The mean values of crestal bone height at baseline were -0.09 mm +/- 0.65 mm for the platform-switched implants and -1.73 mm +/- 0.46 mm for the nonplatform-switched implants. One year after final restoration, the mean value of crestal bone height was -0.22 mm +/- 0.53 mm for the test group and -2.02 mm +/- 0.49 mm for the control group. When tested with statistical means, the differences were significant for baseline and for follow-up (P </= .0001). Mean bone level change from baseline to 1-year follow-up was -0.12 mm +/- 0.40 mm for the test group and -0.29 mm +/- 0.34 mm, respectively, for the control group. On analysis using ANCOVA, this difference was shown to be significant (P </= .0132). CONCLUSION The concept of platform switching appears to limit crestal resorption and seems to preserve peri-implant bone levels. A certain amount of bone remodeling 1 year after final reconstruction occurs, but significant differences concerning the peri-implant bone height compared with the nonplatform-switched abutments are still evident 1 year after final restoration. The reduction of the abutment of 0.45 mm on each side (5 mm implant/4.1 mm abutment) seems sufficient to avoid peri-implant bone loss.

Dimensional changes of the alveolar ridge contour after different socket preservation techniques

OBJECTIVES The aim of the following study was to assess contour changes after socket preservation techniques. MATERIAL AND METHODS In five beagle dogs, the distal root of the third and fourth mandibular premolars was extracted. The following treatments (Tx) were randomly assigned for the extraction socket. Tx 1: BioOss Collagen. Tx 2: BioOss Collagen and a free soft tissue graft. Tx 3: No treatment. Tx 4: The internal buccal aspect was covered with an experimental collagen membrane, the extraction socket was filled with BioOss Collagen and the membrane folded on top of the graft. Impressions were obtained at baseline, 2 and 4 months after surgery. Bucco-lingual measurements were performed using digital imaging analysis. RESULTS All groups displayed contour shrinkage at the buccal aspect. Only the differences between the two test groups (Tx 1, Tx 2) and the control group (Tx 3) were significant at the buccal aspect (p< or =0.001). No measurements of the Tx 4 group could be performed. CONCLUSION Socket preservation techniques, used in the present experiment, were not able to entirely compensate for the alterations after tooth extraction. Yet, incorporation of BioOss Collagen seems to have the potential to limit but not avoid the post-operative contour shrinkage.

Evaluation of a new bioresorbable barrier to facilitate guided bone regeneration around exposed implant threads. An experimental study in the monkey.

The aim of this study was to evaluate the effectiveness of a new bioresorbable barrier alone or in combination with BioOss for guided bone regeneration around dental implants with exposed implant threads. Five adult Macaca fascicularis monkeys were used in this investigation. After extraction of all premolars and first molars, two endosteal oral implants were installed in each quadrant and the bony defects were randomly treated with either: 1) placement of the new bioresorbable device alone (group 1); 2) placement of the new bioresorbable barrier in combination with BioOss (group 2); 3) placement of an ePTFE barrier in combination with BioOss (group 3); or (4) control (group 4). After a period of six months the animals were killed and the histological processing was performed. There was a significant difference in the amount of new bone regeneration around the implants between the four groups (i.e. groups 1, 2, 3 and 4) (P=0.0122). There was no difference, however, between group 2 and group 3. It can be concluded that the new bioresorbable barrier in combination with BioOss appears to obtain the same results in this type of bony defects as the grafting material in combination with an ePTFE barrier.

The socket‐shield technique: a proof‐of‐principle report

AIM Clinical studies have suggested that retaining roots of hopeless teeth may avoid tissue alterations after tooth extraction. Therefore, the objective of this proof-of-principle experiment was to histologically assess a partial root retention (socket-shield technique) in combination with immediate implant placement. MATERIAL AND METHODS In one beagle dog, the third and fourth mandibular pre-molar were hemisected and the buccal fragment of the distal root was retained approximately 1 mm coronal to the buccal bone plate. Following application of enamel matrix derivate, a titanium implant was placed lingual to that tooth fragment either with or without contact to the buccal tooth fragment and a healing abutment was connected. Four months after implant placement, histological evaluation, and backscatter scanning electron microscopy were performed. RESULTS All four implants were osseointegrated without any histologic inflammatory reaction and the tooth fragment was devoid of any resorptional processes. On the buccal side, the tooth fragment was attached to the buccal bone plate by a physiologic periodontal ligament. On the lingual side of the fragment, newly formed cementum could be detected. In the areas where the implant was placed into the fragment, newly formed cementum was demonstrated directly on the implant surface. CONCLUSIONS Retaining the buccal aspect of the root during implant placement does not appear to interfere with osseointegration and may be beneficial in preserving the buccal bone plate.

The addition of soft tissue replacement grafts in plastic periodontal and implant surgery: critical elements in design and execution

Soft tissue replacement grafts have become a substantial element to increase tissue volume in plastic periodontal and implant surgery. Autogenous subepithelial connective tissue grafts are increasingly applied in aesthetic indications like soft tissue thickening, recession treatment, ridge preservation, soft tissue ridge augmentation and papilla re-construction. For the clinical performance of connective tissue graft harvesting and transplantation, a fundamental understanding of the anatomy at the donor sites and a sound knowledge of tissue integration and re-vascularization processes are required. Possible donor sites are the anterior and posterior palate including the maxillary tuberosity, providing grafts of distinct geometric shape and histologic composition. The selective clinical application of different grafts depends on the amount of required tissue, the indication and the personal preference of the treating surgeon. One of the main future challenges is to volumetrically evaluate and compare the efficacy and long-term stability of soft tissue autografts and their prospective substitutes. The aim of this review was to discuss the advantages and shortfalls of different donor sites, substitute materials and harvesting techniques. Although standardized recommendations regarding treatment choice and execution can hardly be given, guidelines for predictable and successful treatment outcomes are provided based on clinical experience and the available scientific data.

Dimensional changes of the ridge contour after socket preservation and buccal overbuilding: an animal study

OBJECTIVES The aim of the study was to volumetrically assess alterations of the ridge contour after socket preservation and buccal overbuilding. MATERIAL AND METHODS In five beagle dogs, four extraction sites were subjected to one of the following treatments: Tx 1: The socket was filled with BioOss Collagen and covered with a free gingival autograft from the palate (SP). Tx 2: The buccal bone plate was forced into a buccal direction using a manual bone spreader and SP was performed. Tx 3: The buccal bone plate was forced into a buccal direction using a manual bone spreader; SP was performed. Tx 4: The socket was filled with BioOss Collagen and a combined free gingival/connective tissue graft was used to cover the socket and for buccal tissue augmentation. Impressions were obtained at baseline, 2 weeks and 4 months post-operatively. Casts were optically scanned and superimposed in one common coordinate system. Using digital image analysis, the volumetric differences per area among the different treatment time points and among the treatment groups were calculated. RESULTS Four months after tooth extraction, no statistically significant differences with regard to the buccal volume per area could be assessed among the treatment groups. CONCLUSION Overbuilding the buccal aspect in combination with socket preservation is not a suitable technique to compensate for the alterations after tooth extraction.

Hard tissue alterations after socket preservation with additional buccal overbuilding: a study in the beagle dog

OBJECTIVES The aim of this study was to histometrically assess alterations of the ridge following socket preservation alone and socket preservation with additional buccal overbuilding. MATERIAL AND METHODS In five beagle dogs four extraction sites were randomly subjected to one of the following treatments: Tx 1: The socket was filled with BioOss Collagen and covered with a free gingival graft from the palate. Tx 2: The buccal bone plate was augmented using the GBR-technique, the socket was filled with BioOss Collagen and covered with a free gingival graft. Tx 3: The buccal bone plate was forced into a buccal direction using a manual bone spreader. The socket was filled with BioOss Collagen and covered with a free gingival graft from the palate. Tx 4: The socket was filled with BioOss Collagen and a combined free gingival/connective tissue graft was used to cover the socket and for buccal tissue augmentation. For each experimental site, two histological sections were subjected to histometric analysis and evaluated for (i) vertical bone dimensions and (ii) horizontal bone dimensions. RESULTS All treatment groups showed horizontal and vertical bone loss. The mean vertical bone loss of the buccal bone plate was significantly lower in Tx 4 than in the other groups, while no statistical significant differences could be detected among the groups in the horizontal dimension. CONCLUSION Overbuilding the buccal aspect in combination with socket preservation does not seem to be a suitable technique to compensate for the alterations after tooth extraction.

Bone loss after full-thickness and partial-thickness flap elevation

OBJECTIVES the aim of this study was to histologically assess whether elevation of partial-thickness flaps results in reduced bone alterations, as compared with full-thickness flap preparations. MATERIAL AND METHODS in five beagle dogs, both mandibular second premolars (split-mouth design) were subjected to one of the following treatments: Tx1: elevation of a partial-thickness flap over the mesial root of P(2) and performing a notch at the height of the bone. Tx2: elevation of a full-thickness flap over the mesial root of P(2) and performing a notch at the height of the bone. After 4 months, sections were evaluated for: (i) vertical bone loss and (ii) osteoclastic activity using histometry. RESULTS elevation of both full- and partial-thickness flaps results in bone loss and elevated osteoclastic activity. Partial-thickness flaps can result in less bone loss than full-thickness flaps, but are subject to some variability. CONCLUSION use of partial-thickness flaps does not prevent from all bone loss. The procedure may result most of the times in less bone loss than the elevation of full-thickness flaps. Further research has to evaluate the determinants of effective outcomes of partial-thickness flap procedures.

Local tolerance and efficiency of two prototype collagen matrices to increase the width of keratinized tissue

AIM to evaluate the local tolerance and efficiency of two experimental collagen matrices to increase the width of keratinized tissue. METHODS in 12 pigs, two apically positioned flaps were prepared on both sides of the mandible. The denuded defect areas were randomly covered with one of two experimental porcine-derived collagen matrices (M1; M2). The other defect area was left untreated (control). At 1 and 6 months, clinical measurements for the width and thickness of the keratinized tissue were recorded. At 6 months, all animals were sacrificed. Descriptive and semi-quantitative histologic analyses were performed. For statistical analysis, the Kruskal-Wallis test and the Mac Nemar test were applied. RESULTS the collagen matrices integrated well into the surrounding tissue without any signs of inflammation. The thickness and width of the keratinized tissue increased significantly over 6 months in all the groups, resulting in slightly more favourable results for M1 (compared with M2) with respect to the thickness and for M2 (compared with M1) with respect to the width of keratinized tissue. No statistically significant differences were observed for any of the evaluated clinical and histologic parameters among the three treatment modalities. CONCLUSIONS within the limits of this animal study, the prototype collagen matrices can be used safely to increase the width of keratinized tissue.

Experimental Peri‐Implantitis around Different Types of Implants – A Clinical and Radiographic Study in Dogs

BACKGROUND The influence of the implant micro and macrostructure on peri-implantitis is not fully understood. PURPOSE To determine the effect of ligature-induced peri-implantitis on three commercially available implant types. MATERIALS AND METHODS Five beagle dogs were used. Two months following tooth extraction, three different implant types (BIOMET 3i T3, BIOMET 3i, Palm Beach Gardens, FL, USA; Straumann Bone Level, Straumann GmbH, Basel, Switzerland; Nobel Replace Tapered, Nobel Biocare, Gothenburg, Sweden) were placed in a randomized fashion in each hemi-mandible. Peri-implantitis was initiated by ligature placement and soft diet. Ligatures were added every 2 weeks for a total of four ligature advancements. After 2 weeks, the ligatures were removed, oral hygiene measures initiated for 3 weeks, and clinical (probing depth, mucosal recession, bleeding on probing), intrasurgical (intrasurgical defect depth, intrasurgical defect width), and radiographic (radiographic bone level) parameters assessed. RESULTS Nobel Replace Tapered implants showed significantly higher intrasurgical defect depth, intrasurgical defect width, probing depths, and radiographic bone level when compared to BIOMET 3i T3 or Straumann Bone Level implants. Straumann Bone Level implants showed largely similar clinical outcomes to BIOMET 3i T3. No significant differences between the groups were observed for mean mucosal recession. CONCLUSION In an experimental peri-implantitis model, Nobel Replace Tapered implants are associated with pronounced tissue loss.