Influence of ovariectomy on healing of autogenous bone block grafts in the mandible: A histomorphometric study in an aged rat model

Purpose: The aim of this study was to evaluate quantitatively and qualitatively the influence of estrogen deficiency on autogenous bone block grafts in aged variectomized rats. Materials and Methods: Fifty 12-month-old female Wistar rats were used in the study. They were divided into 2 groups, an ovariectomized group and a sham-operated group. After 30 days the animals received autogenous block bone grafts on the angle of the mandible, harvested from the calvaria. The animals were euthanized at 7, 14, or 28 days postoperatively. Results: Histologic analysis showed that at 7 days postsurgery, the interface between graft and recipient site in the sham-operated group appeared filled by a granulation tissue with angiogenic activity, whereas the ovariectomized group still exhibited a blood clot and a granulation tissue in organization. on the 14th postoperative day, the interface in the shamoperated group was partially filled by newly formed bone establishing a union between the graft and the recipient site. The interface in the ovariectomized group was typically filled by granulation tissue with discrete osteogenic activity in most specimens. on the 28th postoperative day, the graft in the sham-operated group appeared histologically integrated to the mandible. However, the interface in the ovariectomized group appeared partially filled by newly formed bone, with areas of interposed connective tissue. The statistical analysis revealed that bone neoformation was significantly greater in the sham-operated group (57.41% at 14 days and 68.35 at 28 days) in comparison with the ovariectomized group (40.82% at 14 days and 53.09 at 28 days) at the 5% level. Conclusion: The estrogen depletion caused by the ovariectomy hindered the healing process of autogenous block bone grafts placed in the mandibles of aged rats.

Influence of Microgap Location and Configuration on Radiographic Bone Loss Around Submerged Implants: An Experimental Study in Dogs

Purpose: The vertical location of the implant-abutment connection influences the subsequent reaction of the peri-implant bone. It is not known, however, whether any additional influence is exerted by different microgap configurations. Therefore, the radiographic bone reactions of two different implant systems were monitored for 6 months. Materials and Methods: In eight mongrel dogs, two implants with an internal Morse-taper connection (INT group) were placed on one side of the mandible; the contralateral side received two implants with an external-hex connection (EXT group). on each side, one implant was aligned at the bone level (equicrestal) and the second implant was placed 1.5 mm subcrestal. Healing abutments were placed 3 months after submerged healing, and the implants were maintained for another 3 months without prosthetic loading. At implant placement and after 1, 2, 3, 4, 5, and 6 months, standardized radiographs were obtained, and peri-implant bone levels were measured with regard to microgap location and evaluated statistically. Results: All implants osseointegrated clinically and radiographically. The overall mean bone loss was 0.68 +/- 0.59 mm in the equicrestal INT group, 1.32 +/- 0.49 mm in the equicrestal EXT group, 0.76 +/- 0.49 mm in the subcrestal INT group, and 1.88 +/- 0.81 mm in the subcrestal EXT group. The differences between the INT and EXT groups were statistically significant (paired t tests). The first significant differences between the internal and external groups were seen at month 1 in the subcrestal groups and at 3 months in the equicrestal groups. Bone loss was most pronounced in the subcrestal EXT group. Conclusions: Within the limits of this study, different microgap configurations can cause different amounts of bone loss, even before prosthetic loading. Subcrestal placement of a butt-joint microgap design may lead to more pronounced radiographic bone loss. INT J ORAL MAXILLOFAC IMPLANTS 2011;26:941-946

Influence of Bioactive Glass and/or Acellular Dermal Matrix on Bone Healing of Surgically Created Defects in Rat Tibiae: A Histological and Histometric Study

The purpose of this study was to histologically analyze the influence of bioactive glass and/or acellular dermal matrix on bone healing in surgically created defects in the tibiae of 64 rats (Rattus norvegicus, albinus, Wistar). Materials and Methods: A 4-mm X 3-mm unicortical defect was created on the anterolateral surface of the tibia. Animals were divided into 4 groups: C, control; BG, the defect was filled with bioactive glass; ADM, the defect was covered with acellular dermal matrix; and BG/ADM, the defect was filled with bioactive glass and covered with acellular dermal matrix. Animals were sacrificed at 10 or 30 days postoperatively, and the specimens were removed for histologic processing. The formation of new bone in the cortical area of the defect was evaluated histomorphometrically. Results: At 10 and 30 days postoperatively, groups C (39.65% +/- 5.63% / 63.34% +/- 5.22%) and ADM (38.12% +/- 5.53 / 58.96% +/- 7.05%) presented a larger amount of bone formation compared to the other groups (P<.05). In the same periods, groups BG (13.10% +/- 6.29% / 29.5% +/- 5.56%) and BG/ADM (20.72% +/- 8.31% / 24.19% +/- 6.69%) exhibited statistically similar new bone formation. However, unlike the other groups, group BG/ADM did not present a significant increase in bone formation between the 2 time points. Conclusion: Based on these results, it can be concluded that all of the materials used in this study delayed bone healing in non-critical-size defects. INT J ORAL MAXILLOFAC IMPLANTS 2008;23:811-817

Influence of Microgap Location and Configuration on Peri-implant Bone Morphology in Nonsubmerged Implants: An Experimental Study in Dogs

Purpose: It is unknown whether different micro gap configurations can cause different pen-implant bone reactions. Therefore, this study sought to compare the peri-implant bone morphologies of two implant systems with different implant-abutment connections. Materials and Methods: Three months after mandibular tooth extractions in six mongrel dogs, two oxidized screw implants with an external-hex connection were inserted (hexed group) on one side, whereas on the contralateral side two grit-blasted screw implants with an internal Morse-taper connection (Morse group) were placed. on each side, one implant was inserted level with the bone (equicrestal) and the second implant was inserted 1.5 mm below the bony crest (subcrestal). Healing abutments were inserted immediately after implant placement. Three months later, the peri-implant bone levels, the first bone-to-implant contact points, and the width and steepness of the peri-implant bone defects were evaluated histometrically. Results: All 24 implants osseointegrated clinically and histologically. No statistically significant differences between the hexed group and Morse group were detected for either the vertical position for peri-implant bone levels (Morse equicrestal -0.16 mm, hexed equicrestal -0.22 mm, Morse subcrestal 1.50 mm, hexed subcrestal 0.94 mm) or for the first bone-to-implant contact points (Morse equicrestal -2.08 mm, hexed equicrestal -0.98 mm, Morse subcrestal -1.26 mm, hexed subcrestal -0.76 mm). For the parameters width (Morse equicrestal -0.15 mm, hexed equicrestal -0.59 mm, Morse subcrestal 0.28 mm, hexed subcrestal -0.70 mm) and steepness (Morse equicrestal 25.27 degree, hexed equicrestal 57.21 degree, Morse subcrestal 15.35 degree, hexed subcrestal 37.97 degree) of the pen-implant defect, highly significant differences were noted between the Morse group and the hexed group. Conclusion: Within the limits of this experiment, it can be concluded that different microgap configurations influence the size and shape of the peri-implant bone defect in nonsubmerged implants placed both at the crest and subcrestally. INT J ORAL MAXILLOFAC IMPLANTS 2010;25:540-547

Stress Analysis in Simulation Models With or Without Implant Threads Representation

Purpose: This study aimed to evaluate the influence of implants with or without threads representation on the outcome of a two-dimensional finite element (FE) analysis. Materials and Methods: Two-dimensional FE models that reproduced a frontal section of edentulous mandibular posterior bone were constructed using a standard crown/implant/screw system representation. To evaluate the effect of implant threads, two models were created: a model in which the implant threads were accurately simulated (precise model) and a model in which implants with a smooth surface (press-fit implant) were used (simplified model). An evaluation was performed on ANSYS software, in which a load of 133 N was applied at a 30-degree angulation and 2 mm off-axis from the long axis of the implant on the models, The Von Mises stresses were measured. Results: The precise model (1.45 MPa) showed higher maximum stress values than the simplified model (1.2 MPa). Whereas in the cortical bone, the stress values differed by about 36% (292.95 MPa for the precise model and 401.14 MPa for the simplified model), in trabecular bone (19.35 MPa and 20.35 MPa, respectively), the stress distribution and stress values were similar. Stress concentrations occurred around the implant neck and the implant apex. Conclusions: Considering implant and cortical bone analysis, remarkable differences in stress values were found between the models. Although the models showed different absolute stress values, the stress distribution was similar. INT J ORAL MAXILLOFAC IMPLANTS 2009;24:1040-1044

Publication Bias in Five Dental Implant Journals: An Observation from 2005 to 2009

Purpose: This study evaluated possible publication bias and its related factors in implant-related research over time. Materials and Methods: Articles published in Clinical Implant Dentistry and Related Research, Clinical Oral Implants Research, Implant Dentistry, Journal of Oral Implantology, and The International Journal of Oral & Maxillofacial Implants between 2005 and 2009 were reviewed. Nonoriginal articles were excluded. For each article included, study outcome, extramural funding source, type of study, and geographic origin were recorded. Descriptive and analytic statistics (alpha = .05), including the chi-square test and logistic regression analysis, were performed where appropriate. Results: From a total of 2,085 articles, 1,503 met the inclusion criteria. of the articles analyzed, 1,226 (81.6%), 160 (10.6%), and 117 (7.8%) articles reported positive, negative, and neutral outcomes, respectively. In vitro studies, studies from Asia, and funded animal studies were more likely to report positive outcomes compared to others (P = .02, P < .0001, and P = .009, respectively). Industry-funded studies represented the lowest frequency of positive outcomes versus studies funded by other sources. Conclusions: There were a high number of implant-related studies reporting positive outcomes in the five selected journals. Some selected factors were associated with positive outcome bias. In general, funding was not associated with a positive outcome, except for animal studies. Industry-supported research did not show any association with the publication of positive outcomes. INT J ORAL MAXILLOFAC IMPLANTS 2011;26:1024-1032

Platform Switching: Biomechanical Evaluation Using Three-Dimensional Finite Element Analysis

Purpose: The objective of this study was to evaluate, using three-dimensional finite element analysis (3D FEA), the stress distribution in peri-implant bone tissue, implants, and prosthetic components of implant-supported single crowns with the use of the platform-switching concept. Materials and Methods: Three 3D finite element models were created to replicate an external-hexagonal implant system with peri-implant bone tissue in which three different implant-abutment configurations were represented. In the regular platform (RP) group, a regular 4.1-mm-diameter abutment (UCLA) was connected to regular 4.1-mm-diameter implant. The platform-switching (PS) group was simulated by the connection of a wide implant (5.0 mm diameter) to a regular 4.1-mm-diameter UCLA abutment. In the wide-platform (WP) group, a 5.0-mm-diameter UCLA abutment was connected to a 5.0-mm-diameter implant. An occlusal load of 100 N was applied either axially or obliquely on the models using ANSYS software. Results: Both the increase in implant diameter and the use of platform switching played roles in stress reduction. The PS group presented lower stress values than the RP and WP groups for bone and implant. In the peri-implant area, cortical bone exhibited a higher stress concentration than the trabecular bone in all models and both loading situations. Under oblique loading, higher intensity and greater distribution of stress were observed than under axial loading. Platform switching reduced von Mises (17.5% and 9.3% for axial and oblique loads, respectively), minimum (compressive) (19.4% for axial load and 21.9% for oblique load), and maximum (tensile) principal stress values (46.6% for axial load and 26.7% for oblique load) in the peri-implant bone tissue. Conclusion: Platform switching led to improved biomechanical stress distribution in peri-implant bone tissue. Oblique loads resulted in higher stress concentrations than axial loads for all models. Wide-diameter implants had a large influence in reducing stress values in the implant system. INT J ORAL MAXILLOFAC IMPLANTS 2011;26:482-491

A comparison of profilometer and AutoCAD software techniques in evaluation of implant angulation in vitro

Purpose: The aim of this study was to compare 2 different methods of assessment of implants at different inclinations (90 degrees and 65 degrees)-with a profilometer and AutoCAD software. Materials and Methods: Impressions (n = 5) of a metal matrix containing 2 implants, 1 at 90 degrees to the surface and 1 at 65 degrees to the surface, were obtained with square impression copings joined together with dental floss splinting covered with autopolymerizing acrylic resin, an open custom tray, and vinyl polysiloxane impression material. Measurement of the angles (in degrees) of the implant analogs were assessed by the same blinded operator with a profilometer and through analysis of digitized images by AutoCAD software. For each implant analog, 3 readings were performed with each method. The results were subjected to a nonparametric Kruskal-Wallis test, with P <= .05 considered significant. Results: For implants perpendicular to the horizontal surface of the specimen (90 degrees), there were no significant differences between the mean measurements obtained with the profilometer (90.04 degrees) and AutoCAD (89.95 degrees; P=.9142). In the analyses of the angled implants at 65 degrees in relation to the horizontal surface of the specimen, significant differences were observed (P=.0472) between the mean readings with the profilometer (65.73 degrees) and AutoCAD (66.25 degrees). Conclusions: The degrees of accuracy of implant angulation recording vary among the techniques available and may vary depending on the angle of the implant. Further investigation is needed to determine the best test conditions and the best measuring technique for determination of the angle of the implant in vitro.

Effect of Metal-Ceramic or All-Ceramic Superstructure Materials on Stress Distribution in a Single Implant-Supported Prosthesis: Three-Dimensional Finite Element Analysis

Purpose: This three-dimensional finite element analysis study evaluated the effect of different material combinations on stress distribution within metal-ceramic and all-ceramic single implant-supported prostheses. Materials and Methods: Three-dimensional finite element models reproducing a segment of the maxilla with a missing left first premolar were created. Five groups were established to represent different superstructure materials: GP, porcelain fused to gold alloy; GR, modified composite resin fused to gold alloy; TP, porcelain fused to titanium; TR, modified composite resin fused to titanium; and ZP, porcelain fused to zirconia. A 100-N vertical force was applied to the contact points of the crowns. All models were fixed in the superior region of bone tissue and in the mesial and distal faces of the maxilla section. Stress maps were generated by processing with finite element software. Results: Stress distribution and stress values of supporting bone were similar for the GP, GR, TP, and ZP models (1,574.3 MPa, 1,574.3 MPa, 1,574.3 MPa, and 1,574.2 MPa, respectively) and different for the TR model (1,838.3 MPa). The ZP model transferred less stress to the retention screw (785 MPa) than the other groups (939 MPa for GP, 961 MPa for GR, 1,010 MPa for TP, and 1,037 MPa for TR). Conclusion: The use of different materials to fabricate a superstructure for a single implant-supported prosthesis did not affect the stress distribution in the supporting bone. The retention screw received less stress when a combination of porcelain and zirconia was used. Int J Oral Maxillofac Implants 2011;26:1202-1209

Three-Dimensional Finite Element Analysis of Vertical and Angular Misfit in Implant-Supported Fixed Prostheses

Purpose: Three-dimensional finite element analysis was used to evaluate the effect of vertical and angular misfit in three-piece implant-supported screw-retained fixed prostheses on the biomechanical response in the peri-implant bone, implants, and prosthetic components. Materials and Methods: Four three-dimensional models were fabricated to represent a right posterior mandibular section with one implant in the region of the second premolar (2PM) and another in the region of the second molar (2M). The implants were splinted by a three-piece implant-supported metal-ceramic prosthesis and differed according to the type of misfit, as represented by four different models: Control = prosthesis with complete fit to the implants; UAM (unilateral angular misfit) = prosthesis presenting unilateral angular misfit of 100 pm in the mesial region of the 2M; UVM (unilateral vertical misfit) = prosthesis presenting unilateral vertical misfit of 100 pm in the mesial region of the 2M; and TVM (total vertical misfit) = prosthesis presenting total vertical misfit of 100 pm in the platform of the framework in the 2M. A vertical load of 400 N was distributed and applied on 12 centric points by the software Ansys, ie, a vertical load of 150 N was applied to each molar in the prosthesis and a vertical load of 100 N was applied at the 2PM. Results: The stress values and distribution in peri-implant bone tissue were similar for all groups. The models with misfit exhibited different distribution patterns and increased stress magnitude in comparison to the control. The highest stress values in group UAM were observed in the implant body and retention screw. The groups UVM and TVM exhibited high stress values in the platform of the framework and the implant hexagon, respectively. Conclusions: The three types of misfit influenced the magnitude and distribution of stresses. The influence of misfit on peri-implant bone tissue was modest. Each type of misfit increased the stress values in different regions of the system. INT J ORAL MAXILLOFAC IMPLANTS 2011;26:788-796

Evaluation of the Effect of Retightening and Mechanical Cycling on Preload Maintenance of Retention Screws

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Finite Element Stress Analysis of Edentulous Mandibles with Different Bone Types Supporting Multiple-Implant Superstructures

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Trends in Funding, Internationalization, and Types of Study for Original Articles Published in Five Implant-Related Journals Between 2005 and 2009

Purpose: The aims of this study were to evaluate the trends in funding, geographic origin, and study types of original articles in the dental implant literature and to investigate the relationships among these factors. Materials and Methods: Articles published in Clinical Oral Implants Research, The International Journal of Oral & Maxillofacial Implants, Clinical Implant Dentistry and Related Research, Implant Dentistry, and Journal of Oral Implantology from 2005 to 2009 were reviewed. Nonoriginal articles were excluded. For each article included, extramural funding source, geographic origin, and study type were recorded. Descriptive and analytic analyses (alpha = .05), including a logistic regression analysis, and chi-square test were used where appropriate. Results: of a total of 2,085 articles published, 1,503 met the inclusion criteria. The most common source of funding was from industry (32.4%). The proportion of studies that reported funding increased significantly over time. Europe represented the highest percentage (55.8%) of published articles. Most of the articles reported on clinical studies (49.9%), followed by animal studies (25.9%). Articles from Asia and South America and animal and in vitro studies were significantly more likely to be funded. Conclusion: Almost half of the original dental implant articles were funded. The trend toward internationalization of authorship was evident. A strong association was observed between funding and geographic origin and between funding and study type. Most studies in North America and Europe were clinical studies and supported by industry, whereas a greater proportion of studies in Asia and South America were in vitro or animal studies funded through government resources. INT J ORAL MAXILLOFAC IMPLANTS 2012;27:69-76

Utilization of autogenous bone, bioactive glasses, and calcium phosphate cement in surgical mandibular bone defects in Cebus apella monkeys

Purpose: the purpose of the present study was to evaluate the histologic results of bone cavities that were surgically created in the mandibles of Cebus apella monkeys and filled with autogenous bone, PerioGlas, FillerBone, or Bone Source. Materials and Methods: Surgical cavities 5 mm in diameter were prepared through both mandibular cortices in the mandibular angle region. The cavities were randomly filled, and the animals were divided into groups according to the material employed: Group 1 cavities were filled with autogenous corticocancellous bone; group 2 cavities were filled with calcium phosphate cement (BoneSource); and group 3 and group 4 cavities were filled with bioactive glass (FillerBone and PerioGlas, respectively). After 180 days the animals were sacrificed, and specimens were prepared following routine laboratory procedures for hematoxylin/eosin staining and histologic evaluation. Results: the histologic analysis showed that autogenous bone allowed total repair of the bone defects; bioactive glasses (FillerBone and PerioGlas) allowed total repair of the defects with intimate contact of the remaining granules and newly formed bone; and the cavities filled with calcium phosphate cement (BoneSource) were generally filled by connective fibrous tissue, and the material was almost totally resorbed. Discussion: the autogenous bone, FillerBone, and PerioGlas provided results similar to those in the current literature, showing that autogenous bone is the best Choice for filling critical-size defects. Synthetic implanted materials demonstrated biocompatibility, but the bioglasses demonstrated osteoconductive activity that did not occur with calcium phosphate (BoneSource). Conclusion: According to the methodology used in this study, it can be concluded that the utilization of autogenous bone and bioactive glasses permitted the repair of surgically created critical-size defects by newly formed bone; the synthetic implanted materials demonstrated biocompatibility, and the bioactive glasses demonstrated osteoconductive activity. The PerioGlas was mostly resorbed and replaced by bone and the remaining granules were in close contact with bone; the FillerBone showed many granules in contact with the newly formed bone; BoneSource did not permit repair of the critical-size defects, and the defects were generally filled by connective fibrous tissue.

Use of BioGran and Calcitite in bone defects: Histologic study in monkeys (Cebus apella)

The present study compares the biologic behavior of BioGran and Calcitite as fillers for surgical cavities in the mandibles of 4 adult monkeys (Cebus apella). The surgical cavities were prepared through both mandibular cortices, with a diameter of 5 mm, in the angle region. Two cavities were prepared on the right side and 1 on the left and divided into 3 groups: R-1 sites were filled with bioglass (BioGran), R, sites were not filled, and L sites were filled with hydroxyapatite (Calcitite). After 180 days the animals were sacrificed and the specimens were removed for histologic processing. Results showed no bone formation in group R, (empty cavities). BioGran-treated sites showed bone formation and total repair of the bone defect, and the bioglass particles were almost totally resorbed and substituted by bone. The few remaining crystals were in intimate contact with newly formed bone. Calcitite did not allow bone formation, and granules inside the cavities were involved by connective tissue. Based upon those results, the authors concluded that bioglass resulted in total obliteration of the surgical cavity with bone and hydroxyapatite was present in a large amount and involved by connective tissue, without bone formation.