Influence of the size of the microgap on crestal bone changes around titanium implants. A histometric evaluation of unloaded non-submerged implants in the canine mandible.

BACKGROUND: Endosseous implants can be placed according to a non-submerged or submerged approach and in 1- or 2-piece configurations. Recently, it was shown that peri-implant crestal bone changes differ significantly under such conditions and are dependent on a rough/smooth implant border in 1-piece implants and on the location of an interface (microgap) between the implant and abutment/restoration in 2-piece configurations. Several factors may influence the resultant level of the crestal bone under these conditions, including movements between implant components and the size of the microgap (interface) between the implant and abutment. However, no data are available on the impact of possible movements between these components or the impact of the size of the microgap (interface). The purpose of this study was to histometrically evaluate crestal bone changes around unloaded, 2-piece non-submerged titanium implants with 3 different microgap (interface) dimensions and between implants with components welded together or held together by a transocclusal screw. METHODS: A total of 60 titanium implants were randomly placed in edentulous mandibular areas of 5 hounds forming 6 different implant subgroups (A through F). In general, all implants had a relatively smooth, machined suprabony portion 1 mm long, as well as a rough, sandblasted, and acid-etched (SLA) endosseous portion, all placed with their interface (microgap) 1 mm above the bone crest level and having abutments connected at the time of first-stage surgery. Implant types A, B, and C had a microgap of < 10 microns, approximately 50 microns, or approximately 100 microns between implant components as did types D, E, and F, respectively. As a major difference, however, abutments and implants of types A, B, and C were laser-welded together, not allowing for any movements between components, as opposed to types D, E, and F, where abutments and implants were held together by abutment screws. Three months after implant placement, all animals were sacrificed. Non-decalcified histology was analyzed histometrically by evaluating peri-implant crestal bone changes. RESULTS: For implants in the laser-welded group (A, B, and C), mean crestal bone levels were located at a distance from the interface (IF; microgap) to the first bone-to-implant contact (fBIC) of 1.06 +/- 0.46 mm (standard deviation) for type A, 1.28 +/- 0.47 mm for type B, and 1.17 +/- 0.51 mm for type C. All implants of the non-welded group (D, E, and F) had significantly increased amounts of crestal bone loss, with 1.72 +/- 0.49 mm for type D (P < 0.01 compared to type A), 1.71 +/- 0.43 mm for type E (P < 0.02 compared to type B), and 1.65 +/- 0.37 mm for type F (P < 0.01 compared to type C). CONCLUSIONS: These findings demonstrate, as evaluated by non-decalcified histology under unloaded conditions in the canine mandible, that crestal bone changes around 2-piece, non-submerged titanium implants are significantly influenced by possible movements between implants and abutments, but not by the size of the microgap (interface). Thus, significant crestal bone loss occurs in 2-piece implant configurations even with the smallest-sized microgaps (< 10 microns) in combination with possible movements between implant components.     

Crestal bone changes around titanium implants: a methodologic study comparing linear radiographic with histometric measurements

Generally, endosseous implants can be placed according to a nonsubmerged or a submerged technique and in 1-piece or 2-piece configurations. Recently, it has been shown that peri-implant crestal bone reactions differ significantly radiographically as well as histometrically under such conditions and are dependent on a rough/smooth implant border in 1-piece implants and on the location of a microgap (interface) between the implant and the abutment/restoration in 2-piece configurations. The purpose of this study was to evaluate whether standardized radiography as a noninvasive clinical diagnostic method correlates with peri-implant crestal bone levels as determined by histometric analysis. Fifty-nine implants were placed in edentulous mandibular areas of 5 foxhounds in a side-by-side comparison in both submerged and nonsubmerged techniques. Three months after implant placement, abutment connection was performed in the submerged implant sites. At 6 months, all animals were sacrificed, and evaluations of the first bone-to-implant contact (fBIC), determined on standardized periapical radiographs, were compared to similar analyses made from nondecalcified histology. It was shown that both techniques provide the same information (Pearson correlation coefficient = 0.993; P < .001). The precision of the radiographs was within 0.1 mm of the histometry in 73.4% of the evaluations, while the level of agreement fell to between 0.1 and 0.2 mm in 15.9% of the cases. These data demonstrate in an experimental study that standardized periapical radiography can evaluate crestal bone levels around implants clinically accurately (within 0.2 mm) in a high percentage (89%) of cases. These findings are significant because crestal bone levels can be determined using a noninvasive technique, and block sectioning or sacrifice of the animal subject is not required. In addition, longitudinal evaluations can be made accurately such that bone changes over various time periods can be assessed. Such analyses may prove beneficial when trying to distinguish physiologic changes from pathologic changes or when trying to determine causes and effects of bone changes around dental implants.     

Biologic Width around one- and two-piece titanium implants

Gingival esthetics around natural teeth is based upon a constant vertical dimension of healthy periodontal soft tissues, the Biologic Width. When placing endosseous implants, however, several factors influence periimplant soft and crestal hard tissue reactions, which are not well understood as of today. Therefore, the purpose of this study was to histometrically examine periimplant soft tissue dimensions dependent on varying locations of a rough/smooth implant border in one-piece implants or a microgap (interface) in two-piece implants in relation to the crest of the bone, with two-piece implants being placed according to either a submerged or a nonsubmerged technique. Thus, 59 implants were placed in edentulous mandibular areas of five foxhounds in a side-by-side comparison. At the time of sacrifice, six months after implant placement, the Biologic Width dimension for one-piece implants, with the rough/smooth border located at the bone crest level, was significantly smaller (P<0.05) compared to two-piece implants with a microgap (interface) located at or below the crest of the bone. In addition, for one-piece implants, the tip of the gingival margin (GM) was located significantly more coronally (P<0.005) compared to two-piece implants. These findings, as evaluated by nondecalcified histology under unloaded conditions in the canine mandible, suggest that the gingival margin (GM) is located more coronally and Biologic Width (BW) dimensions are more similar to natural teeth around one-piece nonsubmerged implants compared to either two-piece nonsubmerged or two-piece submerged implants.     

Influence of the size of the microgap on crestal bone levels in non-submerged dental implants: a radiographic study in the canine mandible

BACKGROUND: Accumulating evidence suggests that alveolar crestal bone resorption occurs as a result of the microgap that is present between the implant-abutment interface in dental implants. The objective of this longitudinal radiographic study was to determine whether the size of the interface or the microgap between the implant and abutment influences the amount of crestal bone loss in unloaded non-submerged implants. METHODS: Sixty titanium implants having sandblasted with large grit, acid-etched (SLA) endosseous surfaces were placed in edentulous mandibular areas of 5 American fox hounds. Implant groups A, B, and C had a microgap between the implant-abutment connection of <10 microm, 50 microm, or 100 microm, respectively, as did groups D, E, and F, respectively. Abutments were either welded (1 -piece) in groups A, B, and C or non-welded (2-piece screwed) in D, E, and F. All abutment interfaces were placed 1 mm above the alveolar crest. Radiographic assessment was undertaken to evaluate peri-implant crestal bone levels at baseline and at 1, 2, and 3 months after implant placement whereupon all animals were sacrificed. RESULTS: The size of the microgap at the abutment/implant interface had no significant effect upon crestal bone loss. At 1 month, most implants developed crestal bone loss compared with baseline levels. However, during this early healing period, the non-welded group (D, E, and F) showed significantly greater crestal bone loss from baseline to one month (P <0.04) and 2 months (P < 0.02) compared with the welded group (A, B, and C). No significant differences were observed between these 2 groups at 3 months (P > 0.70). CONCLUSIONS: Crestal bone loss was an early manifestation of wound healing occurring after 1 month of implant placement. However, the size of the microgap at the implant-abutment interface had no significant effect upon crestal bone resorption. Thus, 2-piece non-welded implants showed significantly greater crestal bone loss compared with 1-piece welded implants after 1 and 2 months suggesting that the stability of the implant/abutment interface may have an important early role to play in determining crestal bone levels. At 3 months, this influence followed a similar trend but was not observed to be statistically significant. This finding implies that implant configurations incorporating interfaces will be associated with biological changes regardless of interface size and that mobility between components may have an early influence on wound healing around the implant.     

Influence of a machined collar on crestal bone changes around titanium implants: a histometric study in the canine mandible

Background: It has been shown that peri‐implant crestal bone reactions are influenced by both a rough–smooth implant border in one‐piece, non‐submerged, as well as an interface (microgap [MG] between implant/abutment) in two‐piece butt‐joint, submerged and non‐submerged implants being placed at different levels in relation to the crest of the bone. According to standard surgical procedures, the rough–smooth implant border for implants with a smooth collar should be aligned with the crest of the bone exhibiting a smooth collar adjacent to peri‐implant soft tissues. No data, however, are available for implants exhibiting a sandblasted, large‐grit and acid‐etched (SLA) surface all the way to the top of a non‐submerged implant. Thus, the purpose of this study is to histometrically examine crestal bone changes around machined versus SLA‐surfaced implant collars in a side‐by‐side comparison. Methods: A total of 60 titanium implants (30 machined collars and 30 SLA collars) were randomly placed in edentulous mandibular areas of five foxhounds forming six different subgroups (implant subgroups A to F). The implants in subgroups A to C had a machined collar (control), whereas the implants in subgroups D to F were SLA‐treated all the way to the top (MG level; test). Furthermore, the MGs of the implants were placed at different levels in relation to the crest of the bone: the implants in subgroups A and E were 2 mm above the crest, in subgroups C and D 1 mm above, in subgroup B 3 mm above, and in subgroup F at the bone crest level. For all implants, abutment healing screws were connected the day of surgery. These caps were loosened and immediately retightened monthly. At 6 months, animals were sacrificed and non‐decalcified histology was analyzed by evaluating peri‐implant crestal bone levels. Results: For implants in subgroup A, the estimated mean crestal bone loss (± SD) was ?0.52 ± 0.40 mm; in subgroup B, +0.16 ± 0.40 mm (bone gain); in subgroup C, ?1.28 ± 0.21 mm; in subgroup D, ?0.43 ± 0.43 mm; in subgroup E, ?0.03 ± 0.48 mm; and in subgroup F, ?1.11 ± 0.27 mm. Mean bone loss for subgroup A was significantly greater than for subgroup E (P = 0.034) and bone loss for subgroup C was significantly greater than for subgroup D (P <0.001). Conclusions: Choosing a completely SLA‐surfaced non‐submerged implant can reduce the amount of peri‐implant crestal bone loss and reduce the distance from the MG to the first bone–implant contact around unloaded implants compared to implants with a machined collar. Furthermore, a slightly exposed SLA surface during implant placement does not seem to compromise the overall hard and soft tissue integration and, in some cases, results in coronal bone formation in this canine model.     

Crestal bone changes around titanium implants. Part I: A retrospective radiographic evaluation in humans comparing two non-submerged implant designs with different machined collar lengths

BACKGROUND: Experimental studies demonstrated that peri-implant crestal hard and soft tissues are significantly influenced in their apico-coronal position by the rough/smooth implant border as well as the microgap/ interface between implant and abutment/restoration. The aim of this study was to evaluate radiographically the crestal bone level changes around two types of implants, one with a 2.8 mm smooth machined coronal length and the other with 1.8 mm collar. METHODS: In 68 patients, a total of 201 non-submerged titanium implants (101 with a 1.8 mm, 100 with a 2.8 mm long smooth coronal collar) were placed with their rough/smooth implant border at the bone crest level. From the day of surgery up until 3 years after implant placement crestal bone levels were analyzed digitally using standardized radiographs. RESULTS: Bone remodeling was most pronounced during the unloaded, initial healing phase and did not significantly differ between the two types of implants over the entire observation period (P >0.20). Crestal bone loss for implants placed in patients with poor oral hygiene was significantly higher than in patients with adequate or good plaque control (P <0.005). Furthermore, a tendency for additional crestal bone loss was detected in the group of patients who had been diagnosed with aggressive periodontitis prior to implant placement (P = 0.058). In both types of implants, sand-blasted, large grit, acid-etched (SLA) surfaced implants tended to have slightly less crestal bone loss compared to titanium plasma-sprayed (TPS) surfaced implants, but the difference was not significant (P >0.30). CONCLUSION: The implant design with the shorter smooth coronal collar had no additional bone loss and may help to reduce the risk of an exposed metal implant margin in areas of esthetic concern.     

Feasibility and influence of the microgap of two implants placed in a non-submerged procedure: a five-year follow-up clinical trial

BACKGROUND: The aim of this study was to evaluate the feasibility of using a two-piece implant system in a non-submerged procedure and to study the impact of the microgap between the implant and abutment. METHODS: Sixty edentulous patients (Cawood Class V-VI) participated in this study. After randomization, 20 patients received two two-piece implants placed in a non-submerged procedure, 20 patients received two two-piece implants placed in the traditional submerged procedure, and 20 patients were treated with two one-piece dental implants placed in the traditional non-submerged procedure. The implants were placed in the mandible for overdenture treatment. A standardized clinical evaluation was performed and radiographs were taken immediately after denture insertion and yearly up to 5 years. Peri-implant samples were collected 12, 36, and 60 months after loading with sterile paper points and analyzed for the presence of putative periodontal pathogens using culture techniques. RESULTS: One two-piece implant of the non-submerged group and one two-piece implant of the submerged group were lost after 6 and 12 months, respectively. After 5 years of functioning, no significant clinical, radiological, or microbiological differences were found between the three groups. No association was found between the level of the microgap and the amount of bone loss. CONCLUSIONS: The results of this study indicate that dental implants designed for a submerged implantation procedure can also be used in a non-submerged procedure and may be as predictable as when used in a submerged procedure or as one-piece implants. The microgap at the crestal level in two-piece implants does not appear to have an adverse effect on the amount of peri-implant bone loss.     

Persistent acute inflammation at the implant-abutment interface

The inflammatory response adjacent to implants has not been well-investigated and may influence peri-implant tissue levels. The purpose of this study was to assess, histomorphometrically, (1) the timing of abutment connection and (2) the influence of a microgap. Three implant designs were placed in the mandibles of dogs. Two-piece implants were placed at the alveolar crest and abutments connected either at initial surgery (non-submerged) or three months later (submerged). The third implant was one-piece. Adjacent interstitial tissues were analyzed. Both two-piece implants resulted in a peak of inflammatory cells approximately 0.50 mm coronal to the microgap and consisted primarily of neutrophilic polymorphonuclear leukocytes. For one-piece implants, no such peak was observed. Also, significantly greater bone loss was observed for both two-piece implants compared with one-piece implants. In summary, the absence of an implant-abutment interface (microgap) at the bone crest was associated with reduced peri-implant inflammatory cell accumulation and minimal bone loss.     

The causes of early implant bone loss: myth or science?

The success of dental implants is highly dependent on integration between the implant and intraoral hard/soft tissue. Initial breakdown of the implant-tissue interface generally begins at the crestal region in successfully osseointegrated endosteal implants, regardless of surgical approaches (submerged or nonsubmerged). Early crestal bone loss is often observed after the first year of function, followed by minimal bone loss (< or =0.2 mm) annually thereafter. Six plausible etiologic factors are hypothesized, including surgical trauma, occlusal overload, peri-implantitis, microgap, biologic width, and implant crest module. It is the purpose of this article to review and discuss each factor Based upon currently available literature, the reformation of biologic width around dental implants, microgap if placed at or below the bone crest, occlusal overload, and implant crest module may be the most likely causes of early implant bone loss. Furthermore, it is important to note that other contributing factors, such as surgical trauma and penimplantitis, may also play a role in the process of early implant bone loss. Future randomized, well-controlled clinical trials comparing the effect of each plausible factor are needed to clarify the causes of early implant bone loss.     

Equicrestal and subcrestal dental implants: a histologic and histomorphometric evaluation of nine retrieved human implants

Background: Stability of peri‐implant crestal bone plays a relevant role relative to the presence or absence of interdental papilla. Several factors can contribute to the crestal bone resorption observed around two‐piece implants, such as the presence of a microgap at the level of the implant–abutment junction, the type of connection between implant and prosthetic components, the implant positioning relative to the alveolar crest, and the interimplant distance. Subcrestal positioning of dental implants has been proposed to decrease the risk of exposure of the metal of the top of the implant or of the abutment margin, and to get enough space in a vertical dimension to create a harmoniously esthetic emergence profile. Methods: The present retrospective histologic study was performed to evaluate dental implants retrieved from human jaws that had been inserted in an equicrestal or subcrestal position. A total of nine implants were evaluated: five of these had been inserted in an equicrestal position, whereas the other four had been positioned subcrestally (1 to 3 mm). Results: In all subcrestally placed implants, preexisting and newly formed bone was found over the implant shoulder. In the equicrestal implants, crestal bone resorption (0.5 to 1.5 mm) was present around all implants. Conclusion: The subcrestal position of the implants resulted in bone located above the implant shoulder.     

Bone regeneration at implants with turned or rough surfaces in self-contained defects. An experimental study in the dog

BACKGROUND: Marginal hard tissue defects present at implants with a rough surface can heal with a high degree of bone fill and osseointegration. The healing of similar defects adjacent to implants with a smooth surface appears to be less predictable. OBJECTIVE: The aim was to compare bone healing at implants with turned or rough surface topographies placed in self-contained defects using either a submerged or non-submerged installation technique. MATERIAL AND METHODS: Six dogs were used. Three months after tooth extraction four experimental sites were prepared for implant installation in both sides of the mandible. The marginal 5 mm of the canal prepared for the implant was widened. Thus, following implant placement a circumferential gap occurred between the bone tissue and the implant surface that was between 1 and 1.25 mm wide. In each side of the mandible two implants with a turned surface and two implants with a rough surface were installed. The implants in the right side were fully submerged, while a non-submerged technique was applied in the left side. The animals were sacrificed 4 months later, block biopsies of each implant site were dissected and ground as well as paraffin sections were prepared. RESULTS: The marginal defects around rough surface implants exhibited after 4 months of healing substantial bone fill and a high degree of osseointegration following either the submerged or the non-submerged installation technique. Healing at turned implants was characterized by incomplete bone fill and the presence of a connective tissue zone between the implant and the newly formed bone. The distance between the implant margin (M) and the most coronal level of bone-to-implant contact (B) at implants with a rough surface was 0.84+/-0.37 mm at submerged and 0.90+/-0.39 mm at non-submerged sites. The distance M-B at implants with a turned surface was 3.39+/-0.52 mm at submerged and 3.23+/-0.68 mm at non-submerged sites. The differences between the rough and turned implants regarding the length of distance M-B were statistically significant (paired t-test). CONCLUSION: Osseointegration at implants placed in sites with marginal defects is influenced by the surface characteristics of the implant.     

The effects of interimplant distances on papilla formation and crestal resorption in implants with a morse cone connection and a platform switch: a histomorphometric study in dogs

BACKGROUND: Implant esthetics have been the focus of attention for the last few years, and one of the most important points is the effect that interimplant distances can have on papilla formation and bone loss. The aim of this study was to evaluate the effect that distances of 1, 2, and 3 mm between implants after prosthetic restoration will have on crestal bone resorption (from the top of the implant to the bone crest [TI-BC]) and bone resorption (from the top of the implant to the first bone-to-implant contact TI-BIC) in two-stage implants used in a submerged and non-submerged protocol. METHODS: The mandibular bilateral premolars of seven dogs were extracted, and after 12 weeks, each dog received eight implants. The implants were placed so that three interimplant contact points were created, with 1-mm (group 1), 2-mm (group 2), and 3-mm (group 3) distances constructed on each side. The sides and the position of the groups were randomly selected. After 12 weeks, the implants received metallic prostheses with 5 mm between the contact point and the bone crest. After 8 weeks more, the animals were sacrificed. RESULTS: The TI-BC was 0.20 and 0.18 mm for group 1, 0.15 and 0.14 mm for group 2, and 0.15 and 0.15 mm for group 3 for non-submerged and submerged implants, respectively. At the proximal region, the TI-BC was 0.16 mm for non-submerged and 0.16 mm for submerged implants. The TI-BIC was 0.32 and 0.30 mm for group 1, 0.19 and 0.21 mm for group 2, and 0.30 and 0.24 mm for group 3 for non-submerged and submerged implants, respectively. At the proximal region, the TI-BIC was 0.26 mm for non-submerged and 0.25 mm for submerged implants. There was no statistical difference for any of the parameters (analysis of variance [ANOVA]). CONCLUSION: Distances of 1, 2, and 3 mm between implants do not result in statistically significant differences on TI-BC and TI-BIC around submerged or non-submerged implants with a Morse cone connection and a platform switch.     

The effect of subcrestal placement of the polished surface of ITI® implants on marginal soft and hard tissues

In order to achieve esthetically more satisfying results, it has been proposed to place ITI implants with their border between the rough and smooth surfaces below the level of the alveolar crest, thereby obtaining a submucosally located implant shoulder following healing. The aim of the present experimental study was to clinically and radiographically evaluate the tissue response to the placement of one-stage transmucosal implants with the border between the rough and the smooth surfaces sunk by 1mm into a subcrestal location. 11 patients underwent comprehensive dental care including the placement of 2 implants of the ITI Dental Implant SystemTM in the same quadrant (test and control). Randomly assigned control implants were placed according to the manufacturer's instructions, i.e. the border between the rough titanium plasma-sprayed and the smooth polished surfaces precisely at the alveolar crest. At the test implants the apical border of the polished surface was placed ?1mm below the alveolar crest. Probing bone levels were assessed at implant placement (baseline), 4 and 12 months later. Modified plaque and modified gingival indices were recorded at 1, 2, 3,4 and 12 months. Clinical probing depth and “attachment” levels were measured at 4 and 12 months. All parameters were assessed at 6 sites around each implant. The mean for each implant was calculated and used for analysis. The Wilcoxon matched pairs signed rank test and the Student r-test were applied to detect differences over time and between the test and control implants. At baseline, a mean difference in probing bone level of ?0.86mm (SD 0.43 mm, p<0.05) was found between test and control implants with the test implants being placed more deeply. Both test and control implants lost a significant amount of clinical bone height during the first 4 months (test 1.16mm, p<0.05: control 0.58 mm. p<0.05). However, only the test implants significantly lost clinical bone height from 4–12 months (test 1.04 mm, p<0.05; control 0.45mm, p=0.08). Overall, the test implants lost 2.26mm and the control implants 1.02mm of bone height during the first year of service. On the average, the test implants demonstrated a bone level 0.38mm lower than the controls at 12 months. Except for the modified gingival index at 4 months (mean difference 0.21, SD 0.19, p<0.05), no clinical parameters yielded significant differences between test and control implants at any time. It is concluded that in addition to the crestal bone resorption occurring at 1 implants placed under standard conditions, the bone adjacent to the polished surface of 1 more deeply placed ITI implants is also lost over time. Form a biological point of view, the placement of the border between the rough and the smooth surfaces into a subcrestal location should not be recommended.     

"Biologic width"and crestal bone remodeling with sintered porous-surfaced dental implants: a study in dogs

PURPOSE: The aim of this study was to obtain histometric measurements of bone and peri-implant mucosal tissue contact with implants of 2 sintered porous-surfaced designs. The "short-collar" design had a collar height (smooth coronal region) of 0.75 mm, while the "long-collar" model had a smooth coronal region of 1.8 mm. MATERIALS AND METHODS: Implants (2 per side) were placed in healed mandibular extraction sites of 4 beagle dogs using a submerged technique. After 4 weeks of healing, they were uncovered and used to support fixed partial dentures for a 9-month period. After sacrifice, specimens were retrieved and nondemineralized sections were examined histometrically to determine the most coronal bone-to-implant contact (first BIC) using the microgap as a reference and standard mucosal parameters of "biologic width." RESULTS: Significant (P = .001) differences in first BIC were found between designs (1.97 mm for long-collar versus 1.16 mm for short-collar implants) for posteriorly located implants but not for anteriorly located ones (1.21 mm versus 1.38 mm; P = .40). If crestal bone loss involved sintered surface, fibrous connective tissue ingrowth was observed to replace lost bone. No significant differences in peri-implant mucosal measurements (total peri-implant mucosal thickness; length of the epithelial component of this mucosa, and thickness of the connective tissue component) were detected between implant designs. CONCLUSIONS: Results suggest that "biologic width" accommodation drives initial crestal bone loss with sintered porous-surfaced implants. Histometric data obtained for bone contact showed no significant differences between the long- and short-collar implant designs.     

Clinical and histologic evaluation of submerged and nonsubmerged hydroxyapatite-coated implants: a preliminary study in dogs

A clinical and histologic study was performed to evaluate the differences in the healing of submerged and nonsubmerged hydroxyapatite-coated 2-piece implants. Three foxhounds were used for this evaluation. Mandibular premolars 1, 2, 3, and 4 were extracted. Three months later, 2 submerged implants were placed on one side of the mandible, and 2 nonsubmerged implants were placed on the other side of the mandible. After 3 months of healing, the submerged implants were exposed, and a third implant was placed on each side of the mandible in a nonsubmerged procedure. Clinical parameters were recorded, the animals were sacrificed 6 months after placement of the first implants, and histologic and histometric analyses were performed. Results of the evaluation of the clinical parameters showed only minor differences among the different treatment groups. Regarding the percentage of bone-to-implant contact of the different treatment groups, the submerged implants showed a bone-to-implant contact of 63.4%, the nonsubmerged implants showed 70.3% contact, and the late nonsubmerged implants demonstrated a bone-to-implant contact of 58.7%. The average distance from the implant neck to the first bone-to-implant contact (fBIC) for submerged implants was 0.58 mm, for nonsubmerged implants it was 1.09 mm, and it was 1.13 mm for late nonsubmerged implants. The vertical distance between the gingival margin and the apical extent of the junctional epithelium (aJE) varied from 1.14 mm to 1.28 mm in the different groups. The distance from the aJE to fBIC was 1.00 mm for the submerged group, 1.08 mm for the nonsubmerged group, and 1.00 mm for the late nonsubmerged group. Generally, it can be concluded that the clinical and the histologic behavior of submerged or nonsubmerged 2-piece implants utilized in this experiment do not differ.     

Evaluation of peri-implant bone loss around platform-switched implants

This clinical and radiographic prospective study evaluated bone loss around two-piece implants that were restored according to the platform-switching protocol. One hundred thirty-one implants were consecutively placed in 45 patients following a nonsubmerged surgical protocol. On 75 implants, a healing abutment 1 mm narrower than the implant platform was placed at the time of surgery. On the remaining implants, a healing abutment of the same diameter as the implant was inserted. All implants were positioned at the crestal level. Clinical and radiographic examinations were performed prior to surgery, at the end of surgery, 8 weeks after implant placement, at the time of provisional prosthesis insertion, at the time of definitive prosthesis insertion, and 12 months after loading. The data collected showed that vertical bone loss for the test cases varied between 0.6 mm and 1.2 mm (mean: 0.95 +/- 0.32 mm), while for the control cases, bone loss was between 1.3 mm and 2.1 mm (mean: 1.67 +/- 0.37 mm). These data confirm the important role of the microgap between the implant and abutment in the remodeling of the peri-implant crestal bone. Platform switching seems to reduce peri-implant crestal bone resorption and increase the long-term predictability of implant therapy.     

Comparison of zirconia and titanium implants after a short healing period. A pilot study in minipigs

The aim of this animal study was to investigate and compare the osseointegration of zirconia and titanium dental implants. 14 one-piece zirconia implants and 7 titanium implants were inserted into the mandibles of 7 minipigs. The zirconia implants were alternately placed submerged and non-submerged. To enable submerged healing, the supraosseous part was removed, using a diamond saw. The titanium implants were all placed submerged. After a healing period of 4 weeks, a histological analysis of the soft and hard tissue and a histomorphometric analysis of the bone–implant contact (BIC) and relative peri-implant bone-volume density (rBVD; relation to bone-volume density of the host bone) was performed. Two zirconia implants were found to be loose. All other implants were available for evaluation. For submerged zirconia and titanium implants, the implant surface showed an intimate connection to the neighbouring bone, with both types achieving a BIC of 53%. For the non-submerged zirconia implants, some crestal epithelial downgrowth could be detected, with a resultant BIC of 48%. Highest rBVD values were found for submerged zirconia (80%), followed by titanium (74%) and non-submerged zirconia (63%). The results suggest that unloaded zirconia and titanium implants osseointegrate comparably, within the healing period studied.     

Effects of implant design on marginal bone changes around early loaded, chemically modified, sandblasted Acid-etched-surfaced implants: a histologic analysis in dogs

Background: A minimal marginal bone loss around implants during early healing has been considered acceptable. However, the preservation of the marginal bone is related to soft tissue stability and esthetics. Implant designs and surfaces were evaluated to determine their impact on the behavior of the crestal bone. The purpose of this study is to evaluate histologic marginal bone level changes around early loaded, chemically modified, sandblasted acid‐etched–surfaced implants with a machined collar (MC) or no MC (NMC). Methods: Three months after a tooth extraction, 72 sandblasted acid‐etched chemically modified implants were placed in six dogs. Thirty‐six implants had NMC, and 36 implants had a 2.8‐mm MC. All implants were loaded 21 days after placement. For histologic analyses, specimens were obtained at 3 and 12 months. Assessments of the percentage of the total bone‐to‐implant contact and linear measurements of the distance from the shoulder of the implant to the first bone‐to‐implant contact (fBIC) were performed. Based on fBIC measurements, estimates of bone loss were obtained for each implant. A mixed‐model analysis of variance was used to assess the effects of implant type and sacrifice time. Results: All implants achieved osseointegration. The mean bone gain observed around NMC early loaded implants (at 3 months: 0.13 ± 0.37 mm; at 12 months: 0.13 ± 0.44 mm) was significantly different from the mean bone loss for MC early loaded implants (at 3 months: ?0.32 ± 0.70 mm; at 12 months: ?0.79 ± 0.35 mm) at 3 months (P = 0.003) and 12 months (P <0.001). No infrabony component was present at the marginal fBIC around NMC implants in most cases. There were no statistically significant differences among the means of total bone contact for implant types. Conclusions: Chemically modified, sandblasted acid‐etched–surfaced implants with NMC presented crestal bone gain after 3 and 12 months under loading conditions in the canine mandible. The implant design and surface were determinants in the marginal bone level preservation.     

Clinical and radiographic changes around dental implants inserted in different levels in relation to the crestal bone, under different restoration protocols, in the dog model

BACKGROUND: The aim of the present study was to evaluate clinical and radiographic changes that occur around dental implants inserted in different levels in relation to crestal bone under different restoration protocols. METHODS: Thirty-six implants were inserted in the edentulous mandible of six mongrel dogs. Each implant was assigned to an experimental group according to the distance from the top of the implant to the crestal bone: Bone Level (at crestal bone level), Minus 1 (1 mm below crestal bone), or Minus 2 (2 mm below crestal bone). Each hemimandible was submitted to a restoration protocol: conventional (prosthesis was installed 120 days after implant placement, including 30 days with healing cap) or immediate (prosthesis was installed 24 hours after implant placement). Fixed partial prostheses were installed bilaterally in the same day. After 90 days, clinical and radiographic parameters were evaluated. RESULTS: As long as the implants were inserted in more apical positions, the first bone-to-implant contact (fBIC) was positioned more apically (P <0.05). However, the apical positioning of the implants did not influence the ridge loss or the position of the soft tissue margin (PSTM) (P >0.05). In addition, in immediately restored sites, the PSTM was located significantly more coronally than that in conventionally restored sites (P = 0.02). CONCLUSIONS: Despite the more apical positioning of the fBIC, the height of the peri-implant soft tissues and ridge was not jeopardized. Moreover, the immediate restoration protocol was beneficial to the maintenance of the PSTM. Further studies are suggested to evaluate the significance of these results in longer healing periods.     

A retrospective radiographic analysis of bone loss following placement of TiO2 grit-blasted implants in the posterior maxilla and mandible

PURPOSE: Cortical bone is a determinant of implant esthetics and may contribute to the biomechanical integrity of the implant-supported prosthesis. Historically, approximately 1.0 to 1.5 mm of bone loss has occurred immediately following second-stage surgery and implant loading. Recent consideration of implant design suggests that surface topography may affect crestal bone responses at the implant interface. The aim of this retrospective study of 102 implants in 48 subjects supporting posterior fixed partial dentures was to radiographically define the behavior of crestal bone at TiO2 grit-blasted implants following surgical placement and subsequent loading in the posterior maxilla and mandible. MATERIALS AND METHODS: The crestal bone position relative to the implant reference point (junction of the crestal bevel with the TiO2 grit-blasted surface) was evaluated at implant placement, at abutment placement, and 6 to 36 months following restoration, with an average recall period of 2.3 years. The implant position and dimension were recorded. A single investigator using 7x magnification assessed all radiographs. RESULTS: Crestal bone loss from the time of implant placement up to 36 months following restoration ranged from 0.0 to 2.1 mm. Of the 102 implants, 14 implants showed greater than 1.0 mm of crestal bone loss. They were not clustered at any particular tooth position. Eighty of the implants showed less than 0.5 mm of radiographically measured bone loss. Mean crestal bone loss was 0.36 mm (+/- 0.6 mm). Averages of 0.57 and 0.24 mm loss were shown for 3.5- and 4.0-mm-diameter implants, respectively (P < .051). Bone gain was seen at several 4.0-mm-diameter implants. DISCUSSION: This retrospective evaluation indicates that the radiographically measured bone loss may be expected to be less than 1 mm following placement and loading of TiO2 grit-blasted implants. The close approximation of bone with the implant/abutment interface suggests the attenuation of any microgap-induced bone loss. Additional reasons for crestal bone maintenance may include factors attributed to implant surface roughness and loading along a tapered implant/abutment interface. CONCLUSIONS: Several clinical advantages for maintaining crestal bone at implants supporting posterior prostheses can be identified.