Bone Grafting

“Sinus Floor Augmentation With ß-TricalciumPhosphate (ß-TCP): Does Platelet Rich Plasma Promote Its Osseous Integration and Degradation?,” by J. Wiltfang, K.A. Schlegel, S. Schultze-Mosgau, et al. Clin Oral Implant Res, 14:213–218, 2003.

This paper examined the ability of platelet rich plasma (PRP) to accelerate degradation and bony substitution of an allogeneic material, tricalciumphosphate (TCP), when used for sinus augmentation. Thirty-five sinus augmentations that were performed over a 1-year period in healthy patients were included in the study. Perforation of the sinus membrane at the time of augmentation resulted in exclusion from the study. Seventeen of the sinuses were grafted with a combination of TCP (Cerasorb, Curasan AG, Kleinostheim, Germany) and PRP. The other 18 sinuses were grafted with TCP only. After 6 months of healing, trephined cores of the grafted areas were obtained at the same time as implants were placed. In order to exclude any host bone in the cores, only the most cranial portion of the core was subjected to histological analysis. The results indicated uneventful healing in both groups. At 6 months, both groups demonstrated similar reductions of graft height (10%–20%). In all sinuses there was adequate graft present to allow the placement of 2 implants. Histologic examination revealed that in the PRP group bone formation was between 32% and 43% (average 38%) whereas the non-PRP group displayed between 25% and 37% (29% average) bone formation. Bone-to-TCP contact was present in both groups (13.8% in the PRP group and 15% in the non-PRP group). Zones of soft tissue encapsulation of the TCP granules in which foreign-body giant cells were evident were more prevalent in the PRP group. No difference could be detected in the level degradation of the TCP between the 2 groups. The conclusion of the study was that the addition of PRP to TCP resulted in a modest increase in bone growth. PRP did not increase the degradation of TCP and did result in an increased level of soft tissue and foreign-body giant cells associated with the PRP.

“Clinical Success in Harvesting Autogenous Bone Using a Minimally Invasive Trephine,” by G. Sandor, B. Rittenberg, C. Clokie, M. Caminitti. J Oral Maxillofac Surg, 61:164–168, 2003.

This retrospective paper examined the efficacy of using a trephine drill to harvest bone from the iliac crest. A total of 86 bone grafts were harvested from the anterior iliac crest in 84 patients over a 3-year period. In all cases, the grafts (cortico-cancellous) were harvested under general anesthesia using a power-driven trephine (Straumann, Waldenburg, Switzerland). By using the trephine, a total of 333 bone cores were obtained (mean 3.95 per site, range 1 to 7 cores) with a volume of 3 to 21 mL per site. The majority of the grafts were used for augmenting the maxillary sinus and alveolar ridge. This study examined both the incidence of intra- and postoperative complications with patient records and by means of follow-up telephone interviews. Intraoperatively, there was only 1 complication, which was because of a broken instrument. Only 3 of the 84 patients suffered any postoperative complications. One of the 3 required an extended hospital stay. Forty-one of the surgeries were planned as same-day discharge, and all were discharged as planned. One week postoperatively, there were no incidences of wound breakdown or parasthesias. Long-term follow-up, approximately 6 months postoperatively, indicated excellent patient satisfaction. Only 1 patient reported gait disturbances that lasted more than 3 days. No patient reported pain or gait disturbances that lasted more than 3 weeks. The conclusion of the study was that this was a safe and minimally invasive method to obtain adequate bone volumes required for maxillofacial grafting procedures.

Implant Prosthodontics

“Posterior Implants for Distal Extension Removable Prostheses: A Retrospective Study,” by R. Mitrani, J. Brudvik, K. Philips. Int J Periodont Restor Dent, 23:353–359, 2003.

This retrospective study examined the efficacy of using root-form implants to secure distal extension removable partial dentures. Ten patients with either unilateral or bilateral distal extension edentulous situations were included in this study. In these patients, a total of 16 implants were placed to aid in the retention of removable dentures. Two of the 10 were completely edentulous, and the implants examined in this study were placed distal to the mental foramen to serve as a vertical stop for an implant overdenture. A total of 16 implants were placed by either a 1- or 2-stage method. For this study, the patients were separated into 1 of 2 groups. Group 1 had implants serving only as vertical stops. Group 2 had prostheses with inadequate retention, and therefore the implants were used for both retention and support. The patients had their prostheses in function for 1 to 4.5 years (mean 2.52 years) at the time of the study. One of the 16 implants failed to integrate before loading. The success of this treatment was evaluated by several methods: patient satisfaction, clinical evaluation of the implant and soft tissues, status of the permucosal components and attachments, an evaluation of denture fit, and a radiographic appraisal of peri-implant bone levels. The results indicated a high level of patient satisfaction when comparing pre- and posttreatment prostheses. Clinical examination of the implant components revealed only minor problems that were easily corrected. One patient for whom the distal implants were used to stabilize an implant overdenture presented with a fractured denture, which required replacing the prosthesis. The peri-implant health was satisfactory in all except 1 patient, who presented with hyperplastic tissue. No mobility was noted with any of the implants, and radiographic measurements demonstrated bone loss that was within accepted limits with no significant differences between the groups. The conclusions of the study were that this treatment modality resulted in significantly increased patient satisfaction and that implant health was not compromised.

“In Vitro Study of a Mandibular Implant Overdenture Retained With Ball, Magnet, or Bar Attachments: Comparison of Load Transfer and Denture Stability,” by M. Tokuhisa, Y. Matsushita, K. Koyano. Int J Prosthodont, 16:128–134, 2003.

Using an in vitro model, this study examined the loads implants receive when different attachment systems are used with a 2-implant mandibular overdenture. Two implants were placed into the canine region of an acrylic mandibular model. To simulate soft tissue, 2 mm of acrylic was removed from the denture-supporting surface and replaced with a polyvinyl siloxane impression material. Three types of attachments were then used to secure the overdenture to the implants: ball attachment (plastic female), magnet attachment, and a bar-and-clip. The dentures were then loaded (0–50 N, in 5-N steps) by using a 1-point contact in the right first molar region. The effects of the load were measured on both the implants (with the use of strain gauges) and on the stability of the denture with an electromagnetic movement sensor. The results indicated that the magnet attachments resulted in a significantly greater denture movement (3 directions) compared with the ball and bar-and-clip. There was no significant difference between the ball and the bar in 2 of the 3 directions of movement, the exception being in the backward-forward direction in which the ball had less displacement. When rotation (in 3 planes) was compared, the ball attachment was significantly more stable than the bar-and-clip and magnet in 2 of the 3 planes. The magnet allowed the greatest rotation of all the attachments. When the strains at the implants were compared, the ball attachment transferred the least strain to the implants at lower force levels, and the strains progressed linearly as forces increased. The greatest compression and tensile forces were evident on the loading-side implant. In the magnet, the stains exhibited constant strain as loads were increased. The greatest compressive strain was found in the loading-side implant, and the greatest tensile strain was found in the non–loading-side implant. The bar-and-clip transferred the greatest strain to the implants. Compressive and tensile strains changed as forces progressed, with the maximum compressive strains found on the loading-side implants and the maximum tensile strains found on the non–loading-side implant. The bar-and-clip resulted in significantly greater axial loading (on both the loading-side and the non–loading-side implants) compared with both the magnet and the ball attachments. When bending moments were compared, the magnet had the least bending on the loading-side implant with no difference between the ball and bar-and-clip. On the non–loading-side implant, the bar-and-clip produced significantly greater bending moment than did the other 2 attachments. These results suggest that the magnet attachment allows greater movement than do both the bar-and-clip and the ball. The bar-and-clip and the ball offer similar levels of denture stability, but the ball transfers less strain, axial loading forces, and bending moments to the implants than does the bar-and-clip. Therefore, the ball may offer the best combination of denture stabilization and implant loading in a 2-implant overdenture.

“In Vivo Fracture Resistance of Implant-Supported All-Ceramic Restorations,” by M. Yildirum, H. Fischer, R. Marx, D. Edelhoff. J Prosthet Dent, 90:325–331, 2003.

This study compared the fracture resistance of 2 all-ceramic abutment systems with an in vitro model. Two abutment systems were compared: Al2O3 (CeraAdapt, Nobel Biocare, Goteborg, Sweden) and ZrO2 (Wohlwend Innovative, Zurich, Switzerland). Ten identical abutments of each type were prepared by using copy milling with a standard prepared die. The abutments were attached with gold screws (torqued to 32 Ncm) to Branemark implants (Noble Biocare) that were embedded in a composite cube at an angle of 30 degrees to the vertical. Standardized glass ceramic crowns (IPS Empress, Ivoclar-Vivadent, Schaan, Lichtenstein) were then bonded to the abutments with dual cure resin cement. Fracture load measurements were then obtained with a force applied at an angle of 30 degrees to simulate clinical occlusal forces. The results indicated that all the Al2O3 abutments fractured close to the head of the screw. The mean fracture load was 280.1 N (range 133.6–449.2 N). Within the ZrO2 abutments, 4 of the crowns fractured before the abutment (range 339.7–747.6 N), 3 of the gold screws fractured before the abutment or crown (range 520.7–760.4 N), and 3 of the abutments fractured first (range 619.5–634.4 N). Including all modes of failure for the ZrO2 abutments, the mean load at failure was 737.6 N. This was significantly greater than the Al2O3 abutments. The authors pointed out that the expected clinical loads range from 90 to 370 N. These results suggest that with twice the fracture resistance, the ZrO2 abutments may be more clinically reliable.

“Effect of Intracrevicular Restoration Margins on Peri-implant Health: Clinical, Biochemical, and Microbiologic Findings Around Esthetic Implants up to 9 Years,” by C. Giannopoulou, J.P. Bernard, D. Buser, A. Carrel. Int J Oral Maxillofac Implants, 18:173–181, 2003.

The purpose of this study was to examine the long-term health of the peri-implant soft tissues on implants restored with their crown margins placed subgin-givally. Forty-five patients had a total of 61 single tooth implants (ITI, Institut Straumann, Waldenburg, Switzerland) placed and restored in the anterior maxilla. The implant/crowns had been in function for at least 1 year before baseline readings and were later examined at 3 years after baseline. At the time of the follow-up examination, the implants had been in function for a mean time of 6.8 years. The examination included clinical parameters (plaque and gingival indices, bleeding on probing, pocket probing depths [PPD], distance between the implant shoulder and mucosal margin [DIM], and implant mobility) as well as bacterial and biochemical analysis of pocket contents. The bacterial assay measured the levels of 5 pathogenic bacteria, and the biochemical analysis measured the levels of 3 markers of potential periodontal breakdown. The results indicated that of the clinical parameters, PPD, and DIM increased slightly. The bacterial assays demonstrated that all bacterial species studied had a tendency to increase over the observation period, but only Prevotella intermedia showed a significant increase after 3 years. There were no significant differences for the biochemical markers at 3 years follow-up. The conclusion of the study was that with appropriate oral hygiene measures, a subgingival crown margin does not appear to adversely affect peri-implant health.

Endosseous Implants

“The Jumping Distance Revisited. An Experimental Study in the Dog,” by D. Botticelli, T. Berglundh, D. Buser, J. Lidhe. Clin Oral Implant Res, 14:35–42, 2003.

The purpose of this study was to examine the effect of having a wide gap (jumping distance) between an implant and the surrounding bone at the time of placement. This is clinically relevant because implant surgeons need to know how much of a “jumping distance” is acceptable to leave between an implant and an extraction-site bony wall when an immediate implant is placed. Four dogs had their mandibular molars and premolars extracted. After 3 months of healing, 4 implants (3.3 × 10 mm) with a sandblasted, large-grit, acid-etched surface were placed along with healing caps into the right mandible. With an extra drill before implant placement, 3 of the 4 implants (test implants) had a gap prepared that was 1 to 1.25 mm in circumference and 5-mm deep from the bony crest. The remaining implant (control) had intimate bone-to-implant contact along its entire length. Two of the 3 implants with the gap were covered with a resorbable collagen membrane (Bio-Gide, Geistlich, Wolhusen, Switzerland), and the remaining implant with a gap was left uncovered before closure. After 4 months of healing, the dogs were killed and the mandibles subjected to histologic examination. The results in the control implants were good bony adaptation along their length up to 0.44 ± 0.48 mm from the implant-healing cap junction. A region of newly formed bone could be seen in the region immediately surrounding the implants. The percentage of bone-to-implant contact in the crestal 5 mm of bone surrounding the controls (which would correspond to the defect site of the experimental implants) was 74.1% ± 4.2%. In the test implants with a membrane, there was bone ingrowth within 0.5 ± 0.35 mm from the implant-healing cap junction. The percentage of bone-to-implant contact in the region of the defect was 70.3% ± 4.8%. The percentage of woven bone was greater in this region compared with the control, which contained a greater proportion of lamellar bone. In the test implants without a membrane, the bone had filled the defect up to 0.93 ± 0.84 mm from the implant-healing cap junction. The percentage of bone-to-implant contact in the defect region was 75.6% ± 2.7%. Woven bone levels were similar to the membrane defect sites. These results suggest similar bone healing can occur whether or not a 1- to 1.25-mm jumping distance is present around an implant. In addition, the placement of a barrier membrane may not improve the healing results. These results should be viewed with skepticism because of the very low numbers used in this study, the lack of statistical analysis, and the difference between a freshly cut osteotomy wall used in this study and an intact tooth socket, which is present in an immediate implant situation.

“Effects of Implant Healing Time on Crestal Bone Loss of a Controlled-Load Dental Implant,” by C. Ko, W. Douglas, R. DeLong, et al. J Dent Res, 82:585–591, 2003.

This study examined the effects of early implant loading on the crestal bone levels in an animal model. Seventeen minipigs had their right and left fourth mandibular premolars extracted. After 2 months of healing, machined titanium-threaded implants were placed in a 1-stage fashion into the extraction sites on only 1 side of 12 of the pigs (experimental implants) and bilaterally into the remaining 5 pigs (external controls). The 12 experimental implants were separated into 3 groups of 4. These implants were allowed to heal for 1, 2, or 4 months, after which they were subjected to daily cyclic loading (10 minutes per day) for 5 months. On the contralateral side of the experimental pigs, implants were placed at 1, 2, and 4 months before sacrifice to correspond to the period of nonloading of the experimental side implants. These implants served as internal controls. The implants in the 5 external control animals were allowed to heal unloaded for 1, 2, or 4 months plus an additional 5 months (to correspond to the loading time for the experimental implants in the experimental animals) for a total of 6, 7, or 9 months before sacrifice. Crestal bone levels were compared radiographically by measuring the levels at the time of placement and at sacrifice. The internal control implants served to elucidate the condition of the healing bone before loading. This was studied by histomorphometry and microcomputed tomography. In addition, the elastic moduli were examined by using nanoindentation. Three animals (1 experimental and 2 external controls) died of pulmonary infections unrelated to the surgical procedures. Crestal bone loss increased as healing times increased. Compared with the controls, there was a slightly greater bone loss for the loaded implants that had 1 month of healing before loading. The implants that had 2 and 4 months of healing before loading had 2 and 4 times the bone loss of the controls. The results were significantly different for the 4-month healing group. The crestal bone in the loaded 1-month healing implants demonstrated denser, thicker trabeculae that were radiographically denser. The 1-month healing implants demonstrated more abundant osteoid tissues than did the 2- or 4-month healing stages. The elastic moduli tests showed that the healing bone's stiffness increased with longer healing times. These results suggest that early loading (after 1 or 2 months of healing vs 4 months of healing) stimulates osseointegration (by creating denser bone adjacent to the implants) and inhibits crestal bone loss. The authors hypothesized that this may be due to the increased stiffness of the 4-month healed bone. This may result in less strain on the surrounding bone and thus decrease bone stimulation. In addition, the histomorphometry data indicate that the early healing osteoid is more enriched and that this disappears with prolonged healing. The extrapolation of these data to human clinical situations should be cautioned because of the low numbers in the study and the differing species bone remodeling profiles.