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 apposition around two different sandblasted, large-grit and acid-etched implant surfaces at sites with coronal circumferential defects: an experimental study in dogs

Objective: The study was designed to evaluate bone apposition around SLA (sandblasted, large-grit and acid-etched) implants compared with modified SLA (modSLA) ones at sites with different sizes of circumferential gaps.
Material and methods: All mandibular premolars and first molars of six beagle dogs were extracted. After a healing period of 3 months, three 10-mm-long implants were inserted in each side of the mandible. One implant was inserted with a 0.5-mm and one with a 1-mm gap between the implants and bone around the coronal 5 mm of the implants. The third implant was inserted without a gap as a control. The dogs were sacrificed respectively at weeks 2, 4 and 8 after implant placement for histological and histomorphometric analyses.
Results: The histomorphometric results showed similar pattern of bone apposition for the two surfaces. At 2 and 4 weeks of healing, the percentage of newly formed bone-to-implant contact (BIC%), new bone fill (NBF%) and the distance between the most coronal position of BIC and the defect bottom (B–D) were significantly higher for modSLA ( P <0.05). At 8 weeks of healing, this difference was not significant ( P >0.05). With regard to the defect size, the histological analyses showed no significant differences between the two defect sizes at all time points ( P >0.05).
Conclusion: Significantly more bone apposition was found for the modSLA surface than for the SLA surface at early stage of healing, indicating that modSLA surface may enhance bone apposition in coronal circumferential defects at non-submerged implants. Gap size within 1 mm may not need any kind of regenerative procedures.     

Bone healing at implants with a fluoride-modified surface: an experimental study in dogs

OBJECTIVES: The aim of the present experiment was to study early stages of osseointegration to implants with a fluoride-modified surface. MATERIAL AND METHODS: Six mongrel dogs, about 1-year old, were used. All mandibular premolars and the first mandibular molars were extracted. Three months later, mucoperiosteal flaps were elevated in one side of the mandible and six sites were identified for implant placement. The control implants (MicroThread) had a TiOblast surface, while the test implants (OsseoSpeed) had a fluoride-modified TiOblast surface. Both types of implants had a similar geometry, a diameter of 3.5 mm and were 8 mm long. Following installation, cover screws were placed and the flaps were adjusted and sutured to cover all implants. Four weeks after the first implant surgery, the installation procedure was repeated in the opposite side of the mandible. Two weeks later, biopsies were obtained and prepared for histological analysis. The void that occurred between the cut bone wall of the recipient site and the macro-threads of the implant immediately following implant installation was used to study early bone formation. RESULTS: It was demonstrated that the amount of new bone that formed in the voids within the first 2 weeks of healing was larger at fluoride-modified implants (test) than at TiOblast (control) implants. It was further observed that the amount of bone-to-implant contact that had been established after 2 weeks in the macro-threaded portion of the implant was significantly larger at the test implants than at the controls. CONCLUSION: It is suggested that the fluoride-modified implant surface promotes osseointegration in the early phase of healing following implant installation.     

Healing at fluoride-modified implants placed in wide marginal defects: an experimental study in dogs

OBJECTIVE: To study the healing at fluoride-modified implants placed in wide circumferential defects. MATERIAL AND METHODS: Six mongrel dogs were used. The mandibular premolars and first molars were extracted. Three months later four implants were placed in one side of the mandible of each dog. The control implants (MicroThread) had a TiOblast surface, while the test implants (OsseoSpeed) had a fluoride-modified surface. Two implants of each type were placed. The marginal 50% of the prepared canal was widened using step drills. Following installation a 1 mm wide gap occurred between the implant surface and the bone wall in the defect. All implants were submerged. The installation procedure was repeated in the opposite side of the mandible 4 weeks after the first implant surgery. Two weeks later the animals were euthanized and block biopsies containing the implant and surrounding tissues were prepared for histological analysis. RESULTS: The histological analysis revealed that a significantly larger area of osseointegration was established within the defect at fluoride-modified implants than at implants with a TiOblast surface after 6 weeks of healing. Further, the degree of bone-to-implant contact within the defect area was larger at fluoride-modified implants than at the TiOblast implants. CONCLUSION: It is suggested that the fluoride-modified implant surface promotes bone formation and osseointegration.     

不同颈部设计种植体在骨愈合期边缘骨变化的临床分析

目的探讨口腔种植体在骨愈合过程中,种植体光滑颈部和粗糙颈部设计对边缘骨丧失的影响。 方法2008年8月至2012年3月,因第一磨牙缺失就诊于中山大学附属口腔医院种植科,接受种植义齿修复患者137例,共151颗种植体纳入研究,通过测量根尖片中种植体周围边缘骨的高度,比较光滑颈部种植体（Replace Select^TM Tapered）和粗糙颈部种植体（XiVE^TM S）在不同颌位、直径、周期中种植体周围边缘骨的各期累计丧失量和期内丧失量的差异,结果采用SPSS 19.0软件进行统计分析。 结果在愈合期,粗糙颈部种植体边缘骨丧失量[（0.17 ± 0.01）mm]比光滑颈部种植体[（0.80 ± 0.05）mm]少,差异有统计学意义（F= 94.267,P<0.001）;在二期手术至永久修复期,粗糙颈部种植体边缘骨丧失量[（0.59 ± 0.02）mm]比光滑颈部种植体[（0.34 ± 0.01）mm]多,差异有统计学意义（F= 23.651,P<0.001）。边缘骨丧失的各期累计均值,在愈合期与期内丧失量相同,在植入至永久修复期光滑组[（1.14 ± 1.19）mm]少于粗糙组[（0.75 ± 1.12）mm],差异有统计学意义（F= 41.368,P<0.001）,不同颌位或不同直径种植体边缘骨丧失的各期累计值均值及各期期内均值差异无统计学意义（P>0.05）。 结论在愈合期,与光滑颈部相比,粗糙颈部有利于减少愈合期种植体周围边缘骨丧失量;在二期手术至永久修复期,粗糙颈部和光滑颈部种植体边缘骨高度都出现明显降低,但粗糙颈部比光滑颈部种植体边缘骨丧失更多;不同直径和不同颌位种植体对边缘骨丧失无明显影响。     

Periimplant bone in immediately loaded titanium implants: histologic and histomorphometric evaluation in human. A report of two cases

Background: In recent years, several investigations have demonstrated, in clinical and histologic studies, the practicality of the use of immediate loading in implant dentistry. Purpose: The aim of the present study was to analyze the periimplant responses to immediately loaded implants retrieved from two patients after a 6‐month loading period. Materials and Methods: Three immediately loaded implants (two hydroxyapatite [HA] coated, one with a sandblasted surface) were retrieved from two patients after a 6‐month loading period. The implants were treated to obtain thin ground sections. Results: Bone was present at the interface with all three implants. Bone‐implant contact percentage was 80.6% 4.7. Bone was present also in the thread concavities found at a distance from preexisting bone and in those concavities that were at the interface with the supracrestal tissues or with wide marrow spaces. No gaps or fibrous tissues were present at the interface. No inflammatory infiltrate was present at the interface. The mean of the sulcus depth in all three implants was 0.9 ± 0.1 mm, the length of the junctional epithelium was 0.9 ± 0.05 mm, and the length of connective tissue contact was 1.1 ± 0.05 mm. Conclusions: Our results show that immediate loading of dental implants did not impede the formation of mineralized tissue at the interface, and it can probably be a viable alternative in implant dentistry.     

Retrieved implants from irradiated sites in humans: a histologic/histomorphometric investigation of oral and craniofacial implants

Purpose The aim of this report was to quantitatively and qualitatively evaluate the tissue response to bone‐anchored implants retrieved from irradiated sites in patients. Materials and Methods The material consists of 23 consecutively received Brånemark^® implants (Nobel Biocare AB, Göteborg, Sweden) placed in pre‐ or postoperatively irradiated sites. Twenty‐two of the 23 implants were suitable for histologic evaluation of undecalcified sections in the light microscope. Results The oral implants with shorter time in situ demonstrated sparse bone to implant contact with mainly dense connective tissue in the interface. However, for implants with longer time in situ, high amounts of bone‐implant contact and bone fill of threads were noted. The mean values of bone‐implant contact and bone area within the thread were calculated to 40% (16–94) and 70% (13–96), respectively. The craniofacial implants, with the exception of two implants lined with a capsular formation, demonstrated mature and newly formed bone at the bone‐implant interface. The mean value for bone‐metal contact was calculated to 45 and 53% for two specimens. The mean value for bone area within the thread ranged from 65 to 88% for three specimens. Conclusion The possibility to achieve bone anchorage of implants in irradiated tissue was supported by the findings in this study. However, due to limited material, conclusions with regard to radiation dose and bone tissue response to implants cannot be stated.     

改良喷砂表面处理对钛牙种植体骨结合的组织学作用

研究改良喷砂表面处理对钛牙种植体骨结合的影响。方法柱状纯钛种色植分两组（光滑表面和改良喷砂表面组）进行表面处理,植于狗后肢股骨内侧髁,分别于2、4、12周取材、固定、脱钙后常规HE染色,光镜观察。结果：改良喷砂表面组与光滑表面组的骨愈合过程,均为膜内成骨,并形成完全的骨结合。二者的差别主要表现在愈合的早期（割周）,改良喷砂表面组界面成骨较快,愈合中晚期差别不明显。结论：改良喷砂表面处理可以加快钛牙种植体的骨结合速度。     

Effects of Simvastatin on bone healing around titanium implants in osteoporotic rats

Objectives: Osteoporosis is known to impair the process of implant osseointegration. The recent discovery that statins (HMG‐CoA reductase inhibitors) act as bone anabolic agents suggests that statins can be used as potential agents in the treatment of osteoporosis. Therefore, we hypothesized that statins will promote osteogenesis around titanium implants in subjects with osteoporosis. Material and methods: Fifty‐four female Sprague Dawley rats, aged 3 months old, were randomly divided into three groups: Sham‐operated group (SHAM; n=18), ovariectomized group (OVX; n=18), and ovariectomized with Simvastatin treatment group (OVX+SIM; n=18). Fifty‐six days after being ovariectomized (OVX), screw‐shaped titanium implants were inserted into the tibiae. Simvastatin was administered orally at 5 mg/kg each day after the placement of the implant in the OVX+SIM group. The animals were sacrificed at either 28 or 84 days after implantation and the undecalcified tissue sections were obtained. Bone‐to‐implant contact (BIC) and bone area (BA) within the limits of implant threads were measured around the cortical (zone A) and cancellous (zone B) bone regions. Furthermore, bone density (BD) of zone B in a 500 μm wide zone lateral to the implants was also measured. Results: There were no significant differences in BIC and BA measurements in zone A in any of the three groups at either 28 or 84 days after implantation (P>0.05). By contrast, in zone B, significant differences in the measurement of BIC, BA, and BD were observed at 28 and 84 days between all three groups. Bone healing decreased with lower BIC, BA, and BD around implant in OVX group compared with other two groups, and Simvastatin reversed the negative effect of OVX on bone healing around implants with the improvement of BIC, BA, and BD in zone B. Conclusion: Osteoporosis can significantly influence bone healing in the cancellous bone around titanium implants and Simvastatin was shown to significantly improve the osseointegration of pure titanium implants in osteoporotic rats.     

Errors in radiographic assessment of marginal bone height around osseointegrated implants

Abstract – Radiographic assessment of marginal bone height is included in longitudinal control of osseointegrated implants. Previous studies have revealed a mean annual loss of less than 0.1 mm. The purpose of the present study was by means of an experimental model to analyze the influence upon alveolar bone height measures around osseointegrated implants of buccolingual bone dimensions as well as angulations of fixture axis to central X-ray beam. Brånemark titanium implants were inserted into acrylic test blocks simulating alveolar ridges of various widths. 0.2 mm steel wires visualized buccal and lingual bone margins. Standardized radiographs were obtained by stepwise variation of projection angles. Separation of the wire images varied from 0.1 mm (buccolingual width 5 mm and 1° angulation) to 4.8 mm (width 13 mm and angulation 20°). In clinical cases distortion of buccal and lingual bone margins may result in overestimation of bone heights. The degree of overestimation is influenced by the buccolingual position of the fixture. Strict parallelism between fixture axes and film plane is essential to obtain valid results using single films.     

Early loading of sandblasted and acid-etched (SLA) implants: a prospective split-mouth comparative study

Sandblasted and acid-etched (SLA) implants were recently introduced to reduce the healing period between surgery and prosthesis. In this split-mouth study, SLA implants were compared to titanium plasma-sprayed (TPS) implants under loaded conditions one year after placement in 32 healthy patients, with comparable bilateral edentulous sites and no discrepancies in the opposing dentition. The surgical procedure was performed by the same operator and was identical at 68 SLA (test) and 68 TPS (control) sites. Tapping was never performed and primary stability was always achieved. Abutment connection was carried out at 35 Ncm 6 weeks postsurgery for test sites and 12 weeks for the controls, by the same dentist blind to the type of surface of the implant. In 4 of the 68 test sites the implant rotated slightly, patients reported minor pain and connection was not completed. Provisional restoration was fabricated and a new tightening was performed after six weeks. Similar gold-ceramic restorations were cemented on the same type of solid abutments on both sites. No implant was lost. Clinical measures and radiographic changes were recorded by the same operator, blind to the type of surface of the implant, 1 year post surgery. No significant differences were found with respect to presence of plaque (24% vs. 27%), bleeding on probing (24% vs. 31%), mean pocket depth (3.3 mm vs. 2.9 mm) or mean marginal bone loss (0.65 mm vs. 0.77 mm). The results suggest that SLA implants are suitable for early loading at 6 weeks. Limited implant spinning may occasionally be found but, if properly handled, it produces no detrimental effect on the clinical outcome.     

The effect of internal versus external abutment connection modes on crestal bone changes around dental implants: a radiographic analysis

Background: To the best of our knowledge, the influence of external versus internal implant–abutment connections on crestal bone remodeling has not been reported. The aim of the present study is to investigate the influence of the abutment connection on peri‐implant crestal bone levels (CBLs) using radiographic recordings. Methods: Radiographic recordings from 40 single‐tooth implants (20 external and 20 internal octagonal connections; one implant/patient) in 40 patients (15 males and 25 females; mean age: 54.3 years) were selected for analyses. The radiographic evaluation included the following: 1) linear bone change (LBC); 2) dimensional change (DC); and 3) angle between the implant and adjacent bone (AIB). Differences in LBC, DC, and AIB between implant placement and 1 year after loading for each system were evaluated using a paired t test. Comparison of LBC, DC, and AIB between systems at 1 year after loading was done using analysis of covariance. The significance level was set at P ≤0.05. Results: Radiographic CBLs (LBCs) were reduced at 1 year after loading compared to those at implant placement to reach statistical significance for the external connection (P = 0.000) but not the internal connection (P = 0.939). CBL changes were significantly greater for the external compared to the internal connection (P = 0.000). Similarly, the DC for the external connection was significantly greater compared to that for the internal connection (P = 0.004). Conclusion: Within the limitations of this study, the implant–abutment connection technology appears to have a significant impact on peri‐implant CBLs, with the external connection paralleled by a significant reduction of CBLs.     

Histologic analysis of clinically retrieved immediately loaded titanium implants: a report of 11 cases

Background: Several investigators have reported high survival rates for early or immediately loaded dental implants. Purpose: The aim of the present study was to analyze histologically the periimplant tissue reactions and the bone‐titanium interface of clinically retrieved immediately loaded titanium implants. Materials and Methods: Eleven implants were inserted in the posterior jaw regions of six patients, serving as the most distal abutments of fixed provisional bridges and subjected to immediate occlusal loading. After a 10‐month loading period, all 11 implants were retrieved with a trephine. Results: Mature bone was present at the interface of all implants. Some vertical bone loss was observed; this was more pronounced for cylindric implants. The bone‐implant contact was approximately 60 to 65 for all implants. Conclusions: The results demonstrate that osseointegration of dental implants can occur during immediate loading.