Soft tissue exposure of endosseous implants between stage I and stage II surgery as a potential indicator of early crestal bone loss.

Implants are well accepted as a means of dental rehabilitation. While integration success rates are high, crestal bone loss can occur, and it may not become apparent until stage II surgery and implant uncovering. The purpose of this study was to quantify the relationship between exposure of implants through the oral mucosa between stage I and stage II implant surgery and early changes in crestal bone height. Bone levels were measured during placement of 275 implants in the maxillae of 50 subjects. Repeated bone height measurements were obtained at implant uncovering. Fourteen implants in 7 patients were exposed to the oral cavity through the mucosa at stage II surgery. Patients with 1 or more exposed sites demonstrated a likelihood of bone loss 3.9 times greater than patients with nonexposed sites (Fisher exact test, P = .0003). These results suggest that exposure of an implant between stage I and stage II implant surgery might serve as a potential indicator of the occurrence of early bone loss.     

Spontaneous early exposure of submerged implants: I. Classification and clinical observations

BACKGROUND: It is believed that during the osseointegration phase of submerged dental implants, complete mucosal coverage and isolation of the implant from the oral cavity avoids trauma and infection and establishes favorable conditions for osseointegration. Spontaneous early exposure is one of the complications that could adversely affect osseointegration of implants. METHODS: This study clinically classifies spontaneous early exposure and describes and analyzes this complication in a group of 148 patients treated with 372 submerged implants: 216 (58%) in the mandible and 156 (42%) in the maxilla. Edentulous sites were exposed by mid-crestal incisions and full thickness gingival flaps. Incisions were closed in an attempt to achieve complete closure and healing by primary intention. Measurements were taken to avoid mechanical trauma to the mucosa over the implants. Patients were followed up weekly and examined to identify early exposures. Perforations were classified according to the degree of exposure from 0 (no perforations) to 4 (complete exposure). RESULTS: Of the implants 51 (13.7%) presented spontaneous early exposure, (13%) in the mandible and 23 (14.7%) in the maxilla. Class 2 perforation was the most frequent, followed by Class 3, Class 1 and Class 4. Inflammation at the mucosal orifices of the perforations was minimal, but no objective index (bleeding, probing) was taken in order to avoid morphological changes of the lesions that were biopsied for histological examination. CONCLUSIONS: Early perforation and partial exposure of the implant's covering device are a focus for plaque accumulation which, if left untreated, may result in inflammation, damage to the peri-implant mucosa, and possible peri-implant loss.     

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

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

Spontaneous early exposure of submerged implants: III. Histopathology of perforated mucosa covering submerged implants

BACKGROUND: Spontaneous early exposure of dental implants could interfere with the early healing phase of dental implants. These exposures have been clinically classified according to degree of implant exposure from 0 (intact mucosa) to IV (complete exposure). The characteristics of perforated mucosa (Class I and II) covering submerged dental implants were examined histologically in this study. METHODS: Biopsy specimens of 34 Class I and II perforated mucosa covering submerged dental implants were examined histologically. Serial sections were evaluated from the periphery of the specimen to the center of each perforation lesion. RESULTS: Class I specimens presented hyperplastic epithelium characterized by hyperparakeratosis and acanthosis. Chronic inflammatory cells diffusely infiltrated the connective tissue. Sections closer to the perforation revealed gradual epithelial invagination; in the deepest aspect, there was a cyst-like structure in all Class I specimens examined. A thin layer of connective tissue containing necrotic material and debris formed the "cystic" wall proximal to the implant cover screw. Class II specimens presented the same epithelial patterns; however, the cystic structures were replaced by direct contact between the cover screw and the oral cavity via the perforation. CONCLUSIONS: Spontaneous early perforations are the sequela of either traumatic irritation or failure of the tissue flaps to produce primary healing. Most Class I perforations include epithelial invagination and the formation of a cyst-like structure. Necrosis of the base of the "cyst" or enlargement of the perforation results in direct communication between the oral cavity and the covering screw surface (Class II).     

Effects of implant healing time on crestal bone loss of a controlled-load dental implant

The universally accepted concept of delay-loaded dental implants has recently been challenged. This study hypothesizes that early loading (decreased implant healing time) leads to increased bone formation and decreased crestal bone loss. We used 17 minipigs to study implants under a controlled load, with non-loaded implants for comparison. Radiographic and histological assessments were made of the osseointegrated bone changes for 3 healing times (between implant insertion and loading), following 5 months of loading. The effect of loading on crestal bone loss depended on the healing time. Early loading preserved the most crestal bone. Delayed loading had significantly more crestal bone loss compared with the non-loaded controls (2.4 mm vs. 0.64 mm; P < 0.05). The histological assessment and biomechanical analyses of the healing bone suggested that loading and bioactivities of osteoblasts exert a synergistic effect on osseointegration that is likely to support the hypothesis that early loading produces more favorable osseointegration.     

A bone quality-based implant system: first year of prosthetic loading.

This interim report presents the data from a prospective study of BioHorizons, a bone quality-based implant system, with four implant designs. The surgical survival of 975 implants was 99.4%, with the survival 100% for D4 bone. Three critical phases of crestal bone loss have been identified: bone remodeling from stage I to stage II surgery; stage II uncovery to prosthesis delivery (transition period); and prosthesis delivery up to the first year of loading (early loading bone loss). The stage I to stage II uncovery crestal bone remodeling resulted in a mean vertical bone loss of 0.21 mm to 0.36 mm (SD = 0.90 mm), dependent on whether the implant became exposed in the oral cavity during osseous healing. No statistically significant difference was found among the four implant designs, diameter, bone density, or location. The stage II to prosthesis delivery mean vertical bone loss ranged from 0.12 mm to 0.20 mm. One hundred three consecutive patients (partially and totally edentulous) were restored, with 360 implants and 105 prostheses in function for a period of 12 to 26 months. No early loading implant failure occurred, and all patients with implants are in satisfactory to optimum health according to the Misch Implant Quality Scale. The mean early loading bone loss was 0.29 mm (SD = 0.99 mm). Past clinical reports in the literature indicate most failures or crestal bone loss occur by the first year of loading. This study suggests the bone quality based dental implant design minimizes overall implant failure and crestal bone loss, regardless of bone density.     

Spontaneous early exposure and marginal bone loss around conventionally and early‐placed submerged implants: a double‐blind study

Purpose: The aim of this retrospective study was to compare the frequency of spontaneous early exposure of cover screws and marginal bone resorption in conventionally and early‐placed submerged implants before second‐stage surgery. Materials and methods: A total of 103 Nobel Biocare Branemark implants were conventionally (Group 1), or early‐placed (Group 2) in 46 consecutive patients following the two‐stage surgical protocol. Patients in both groups received oral hygiene training in self‐performed plaque control measures, including exposure of cover screws during healing. Spontaneous cover screw exposure (CSE) of each implant was recorded for both groups and scored from Class 0 (no perforation) to Class 4 (complete exposure). Plaque index scores were recorded and marginal bone‐level (MBL) changes were measured in radiographs before second‐stage surgery in a blind manner. Results: MBL in Group 2 was higher than Group 1 in patients with or without interim prosthesis (P<0.05). The use of interim prosthesis did not increase MBL in Group 1, but led to higher MBL in Group 2. The percentage of non‐exposed implants in Group 1 was higher than Group 2 (P=0.007, odds ratio=7). Group 1 implants had 11.5 times greater plaque index score 0 than those in Group 2 (P=0.031, odds ratio=11.5). The differences between MBL with regard to CSE scores 0 and 1–4 was significant for both sides in Group 2 and the mesial side in Group 1 (P<0.05). The difference between MBL with regard to plaque index scores 1–3 was similar in both groups (P>0.05). Conclusions: There is a direct relation between spontaneous early cover screw perforations with early crestal bone loss. Early‐placed implants experienced more spontaneous perforations and associated bone loss in comparison with conventionally placed submerged implants. The use of interim dentures may lead to more CSE and consequent MBL in the early‐placement protocol. To cite this article:
Çehreli MC, Kökat AM, Uysal S, Akca K. Spontaneous early exposure and marginal bone loss around conventionally and early‐placed submerged implants: a double‐blind study.
Clin. Oral Impl. Res. 21 , 2010; 1327–1333.
doi: 10.1111/j.1600‐0501.2009.01952.x     

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.     

Transmucosal healing around peri‐implant defects: crestal and subcrestal implant placement in dogs

Objective: This study was designed to evaluate the transmucosal healing response of implants placed with the junction of the smooth surfaces, either crestal or subcrestal, into simulated extraction defects after healing periods of 1 and 3 months. Materials and methods: A total of 23 Straumann SP ?3.3 mm NN, SLA^® 10 mm implants were placed in the mandibular premolar regions of three greyhound dogs 3 months after the teeth were removed. Five control implants were placed at the crestal bone level, and test implants with surgically created peri‐implant defects of 1.25 mm wide × 5 mm depth were placed either at the crestal (nine implants) or at the 2 mm subcrestal (nine implants) bone level. Implants on the right side were placed 1 month before the dogs were sacrificed, and implants on the left side were placed 3 months before sacrifice. All dogs had daily plaque control following surgery and were sacrificed 3 months after implant placement for histological and histometric analyses. Results: Mesial–distal ground sections of the control and test implant specimens showed a greater %BIC in the coronal defect region after 3 months of healing. This healing response was incomplete for the test implants compared with the control implants after a 1‐month healing period. The histometric measurements for test implants placed at the crestal bone level or 2 mm subcrestal with surgically created peri‐implant defects were more coronal or closer to the implant margin compared with the control implants. Additionally, the degree of osseointegration between the newly formed bone and the implant surface was similar between the test implants. Conclusion: Peri‐implant defects of 1.25 mm width healed with spontaneous bone regeneration around implants placed transmucosally at crestal or 2 mm subcrestal with a high degree of osseointegration after a 3‐month healing period. To cite this article:
Tran BLT, Chen ST, Caiafa A, Davies HMS, Darby IB. Transmucosal healing around peri‐implant defects: crestal and subcrestal implant placement in dogs.
Clin. Oral Impl. Res. 21 , 2010; 794–803.
doi: 10.1111/j.1600‐0501.2010.01911.x     

Interface histology of unloaded and early loaded partially stabilized zirconia endosseous implant in initial bone healing

Clinical and histologic evaluations of partially stabilized zirconia endosseous implants under unloaded and early loaded conditions in four beagle dogs were performed to examine the possibility of osseointegration of a newly developed one-stage zirconia implant during initial bone healing. No clear difference in clinical features was observed. Direct bone apposition to the implant was generally seen in both implants. However, loss of crestal bone height was quite evident around the loaded implants. These findings suggest that the initial unloaded condition is preferable to achieve osseointegration of one-stage zirconia implants.     

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.     

Evaluation of maxillary sinus membrane response following elevation with the crestal osteotome technique in human cadavers.

Implant placement in the posterior maxilla often requires elevation of the sinus floor, which can be achieved through either the modified Caldwell-Luc or the crestal osteotome technique. The objectives of this study were to evaluate (a) the resistance to perforation of maxillary sinus membranes obtained from formaldehyde-fixed cadavers in vitro, (b) the frequency and extent of membrane perforations occurring after sinus floor elevation in cadavers using the crestal approach, and (c) the amount of membrane elevation (doming) that can be achieved using the crestal approach. Pretreatment of maxillary sinus membrane tissues with commonly used tissue softeners did not have a statistically significant effect on resistance to perforation. Maxillary sinus membranes were elevated 4 to 8 mm in formaldehyde-fixed cadavers using the osteotome technique; implants were placed. Of the 25 sites that received implants, only 6 showed perforations, as assessed by double-blind investigation after dissection of the lateral wall of the nose, allowing direct examination of the sinus cavity. Perforations were categorized as Class I (< or = 2 mm with exposure of the implant into the sinus cavity and loss of doming); Class II perforations (> or = 2 mm) were associated with proximity of the osteotomy site to the medial wall of the sinus or the presence of septae. These results indicated that the crestal osteotome approach compared favorably to the modified Caldwell-Luc technique as it relates to the frequency of maxillary sinus membrane perforations and the degree of achievable membrane elevation.     

愈合期埋植型和非埋植型种植体周围牙槽骨吸收情况观察

目的：观察比较愈合期两段式埋植型和非埋植型种植体周围牙槽骨吸收情况是否存在差异。方法：收集种植义齿修复下颌后牙区牙体缺损患者44例共94颗,其中54颗两段式埋植型Frialit-2种植体和40颗两段式非埋植型ITI种植体,根据种植体植入术后和愈合后数字化全景X线片来进行种植体周围牙槽骨高度的测量。结果：显示愈合期两段式埋植型Frialit-2种植体和非埋植型ITI种植体周围骨吸收值不存在统计学差异（p=0．667〉0．05）。结论：在本实验条件下,愈合期埋植型和非埋植型种植体周围牙槽骨骨吸收改变与种植体的植入方式无关。     

Crestal bone changes around titanium implants. A histometric evaluation of unloaded non-submerged and submerged implants in the canine mandible

BACKGROUND: Today, implants are placed using both non-submerged and submerged approaches, and in 1- and 2-piece configurations. Previous work has demonstrated that peri-implant crestal bone reactions differ radiographically under such conditions and are dependent on a rough/smooth implant border in 1-piece implants and on the location of the interface (microgap) between the implant and abutment/restoration in 2-piece configurations. The purpose of this investigation was to examine histometrically crestal bone changes around unloaded non-submerged and submerged 1- and 2-piece titanium implants in a side-by-side comparison. METHODS: A total of 59 titanium implants were randomly placed in edentulous mandibular areas of 5 foxhounds, forming 6 different implant subgroups (types A-F). In general, all implants had a relatively smooth, machined coronal portion as well as a rough, sandblasted and acid-etched (SLA) apical portion. Implant types A-C were placed in a non-submerged approach, while types D-F were inserted in a submerged fashion. Type A and B implants were 1-piece implants with the rough/smooth border (r/s) at the alveolar crest (type A) or 1.0 mm below (type B). Type C implants had an abutment placed at the time of surgery with the interface located at the bone crest level. In the submerged group, types D-F, the interface was located either at the bone crest level (type D), 1 mm above (type E), or 1 mm below (type F). Three months after implant placement, abutment connection was performed in the submerged implant groups. At 6 months, all animals were sacrificed. Non-decalcified histology was analyzed by evaluating peri-implant crestal bone levels. RESULTS: For types A and B, mean crestal bone levels were located adjacent (within 0.20 mm) to the rough/smooth border (r/s). For type C implants, the mean distance (+/- standard deviation) between the interface and the crestal bone level was 1.68 mm (+/- 0.19 mm) with an r/s border to first bone-to-implant contact (fBIC) of 0.39 mm (+/- 0.23 mm); for type D, 1.57 mm (+/- 0.22 mm) with an r/s border to fBIC of 0.28 mm (+/- 0.21 mm); for type E, 2.64 mm (+/- 0.24 mm) with an r/s border to fBIC of 0.06 mm (+/- 0.27 mm); and for type F, 1.25 mm (+/- 0.40 mm) with an r/s border to fBIC of 0.89 mm (+/- 0.41 mm). CONCLUSIONS: The location of a rough/smooth border on the surface of non-submerged 1-piece implants placed at the bone crest level or 1 mm below, respectively, determines the level of the fBIC. In all 2-piece implants, however, the location of the interface (microgap), when located at or below the alveolar crest, determines the amount of crestal bone resorption. If the same interface is located 1 mm coronal to the alveolar crest, the fBIC is located at the r/s border. These findings, as evaluated by non-decalcified histology under unloaded conditions, demonstrate that crestal bone changes occur during the early phase of healing after implant placement. Furthermore, these changes are dependent on the surface characteristics of the implant and the presence/absence as well as the location of an interface (microgap). Crestal bone changes were not dependent on the surgical technique (submerged or non-submerged).     

Apical-coronal implant position: recent surgical proposals. Technical note

The conventional placement protocol for submerged and non-submerged implants was proposed in the 1960s and 1970s. Multicenter studies have reported satisfactory success rates for both protocols and a similar loss of crestal peri-implant bone after implant loading (0.5 to 1.5 mm). In recent years, placement of submerged implants using a single surgical procedure was introduced, with the immediate placement of a healing abutment. Some studies reported good short-term results using this approach. Recently, a supracrestal apical-coronal positioning of the implant collar has been proposed for posterior sectors using submerged implants. This positioning facilitates the second surgical phase, as well as fabrication of the prosthetic restoration, and limits the amount of crestal bone loss.     

Dynamic behavior of implants as a measure of osseointegration.

Research into the formation, destruction, and adaptation of bone around implants would benefit from a sensitive, nondestructive, noninvasive, and quantitative technique to assess the bone-implant interface. It is hypothesized that osseointegration can be quantified by sensing the mechanical impedance (or micromobility) of the implant when it is subjected to minute vibratory forces superimposed upon a quasi-static preload. To test this hypothesis, a total of 24 identical threaded, titanium root-form implants (10 x 3.75 mm, Osteo-Implant, New Castle, PA) were placed in the mandibles of 4 Walker hounds and allowed to heal submerged for 3 months. The implants were exposed and characterized for osseointegration using clinical observations, quantitative radiography, and a custom-designed impedance instrument. Subsequently, arbitrarily selected implants were ligated to induce bone loss and examined monthly over a 6-month study period. Following the terminal examination and euthanasia, quantitative histologic measurements were made of bone adjacent to the implant, including estimates of both crestal bone height and the percent bone (bone fraction). Linearized dynamic parameters (effective stiffness and effective damping) correlated well with radiographic and histologic measures of bony support (r2 values ranged from 0.70 to 0.89). Moreover, the presence of nonlinear stiffness was clearly associated with a bimodal "clinical impression" of osseointegration (P < .0003, 1-way analysis of variance). These results confirm that, in this animal model, mechanical impedance can be used as a measure of implant osseointegration.     

Effect of early exposure on the integration of dental implants: Part 2--Clinical findings at 6 months postloading

Implant exposure during initial healing after placement has been considered important in both implant integration and postloading effects. This study evaluated the effect of early implant exposure on the clinical findings prerestoration and 6 months postrestoration. Forty-eight implants (24 CPTi and 24 Ti-13-13) were placed in maxillary and mandibular posterior sites in six baboons. Implant exposure was evaluated for 24 of the submerged implants at placement and at each weekly visit for 3 weeks after implant placement. The crestal bone level at maxillary posterior sites was measured at 6-month uncovering, and mandibular sites were measured at 3-month uncovering. All sites were again measured 6 months after restoration placement. Periotest readings were recorded at implant uncovering and again 6 months postloading. Arbitrary groupings of the Periotest values were assigned as good = -7 to -1; guarded = 0 to +2; and poor = +3 to +27. At 6 months postloading, there were no statistical differences between CPTi and Ti-13-13 for change in crestal bone height in either arch. The mean change in maxillary crestal bone height varied from a 0.59- to 1.35-mm loss. The differences between the mean exposed and nonexposed changes were not statistically significant The mean change in mandibular crestal bone height varied from a 0.25- to 0.88-mm loss. Changes in crestal bone height for nonexposed sites from 3-month implant uncovering to 6 months postloading were statistically significant at the mesial, buccal, and lingual aspects. The mean change for the nonexposed distal aspect approached significance. The differences between the mean exposed and nonexposed changes were not statistically significant. The overall percentage of maxillary implants in the good category for nonexposed sites decreased by 41% from uncovering to 6 months after loading, while no change occurred for exposed sites; the percentage of implants in the good category was comparable for early exposed and nonexposed sites (57% and 59%, respectively). At 6 months after loading, the percentage of implants in the good category was more favorable for early exposed (88%) than nonexposed sites (50%). A one-stage implant approach should provide similar postloading clinical results as the two-stage surgical approach.     

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.     

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.     

The effect of inter-implant distance on the height of inter-implant bone crest

BACKGROUND: The biologic width around implants has been well documented in the literature. Once an implant is uncovered, vertical bone loss of 1.5 to 2 mm is evidenced apical to the newly established implant-abutment interface. The purpose of this study was to evaluate the lateral dimension of the bone loss at the implant-abutment interface and to determine if this lateral dimension has an effect on the height of the crest of bone between adjacent implants separated by different distances. METHODS: Radiographic measurements were taken in 36 patients who had 2 adjacent implants present. Lateral bone loss was measured from the crest of bone to the implant surface. In addition, the crestal bone loss was also measured from a line drawn between the tops of the adjacent implants. The data were divided into 2 groups, based on the inter-implant distance at the implant shoulder. RESULTS: The results demonstrated that the lateral bone loss was 1.34 mm from the mesial implant shoulder and 1.40 mm from the distal implant shoulder between the adjacent implants. In addition, the crestal bone loss for implants with a greater than 3 mm distance between them was 0.45 mm, while the implants that had a distance of 3 mm or less between them had a crestal bone loss of 1.04 mm. CONCLUSIONS: This study demonstrates that there is a lateral component to the bone loss around implants in addition to the more commonly discussed vertical component. The clinical significance of this phenomenon is that the increased crestal bone loss would result in an increase in the distance between the base of the contact point of the adjacent crowns and the crest of bone. This could determine whether the papilla was present or absent between 2 implants as has previously been reported between 2 teeth. Selective utilization of implants with a smaller diameter at the implant-abutment interface may be beneficial when multiple implants are to be placed in the esthetic zone so that a minimum of 3 mm of bone can be retained between them at the implant-abutment level.