Histologic Evaluation of Human Bone Integration on Machined and Sandblasted Acid-etched Titanium Surfaces in Type IV Bone

Several long-term investigations have documented the high predictability of dental implants in partially and completely edentulous patients.1–3 However, studies have demonstrated that the survival data of dental implants placed in posterior maxilla are inferior to those placed in the anterior mandible, where the bone density is frequently higher.4,5 The demand for improved dental implant survival at sites with lower bone quality prompted the search for dental implant microstructure properties that would enhance the bone-implant contact (BIC). Several authors have demonstrated higher BIC percentages and removal torque values for rough dental implant surfaces compared with machined implants as well as faster development of bone-implant integration.6–8 

Different dental implant surface microstructures can be achieved with subtractive methods (sandblasting, acid etching) or additive methods (titanium plasma spray, hydroxylapatite coating). Thus, surface roughness achieved with the sandblasting technique is obtained by treating commercially pure titanium (cpTi) dental implant surfaces with an air and abrasive material spray of either aluminum oxide or titanium oxide for a certain period of time and under controlled pressure. After that, this surface is treated with acid solutions under different temperatures and for different periods of time. Consequently, these surface microstructures provide better mechanical stability between bone tissues and implant surfaces by producing greater contact area. The modified surface provides a configuration that properly retains the blood clot and stimulates the bone healing process, which allows implants with modified surfaces to be loaded earlier.9–11 In the mandible, the healing time for good bone quality is 3 to 4 months; for the maxilla, the corresponding time is 5 to 6 months.12 However, in areas with poor bone quality, such as the posterior maxilla, the healing time for machined implants can be longer (7 to 8 months).4 Therefore, there is a lack of data on the bone-implant contact percentage (BIC%) of this implant microstructure in type 4 human bone after short healing periods.

The objective of this preliminary study was to evaluate the influence of sandblasted acid-etched surface on BIC% as well as the bone density in the thread area (BD%) in human posterior maxilla after 2 months of unloaded healing.

Five partially edentulous subjects (3 women; 2 men) with a mean age of 42.6 years (range = 35 to 54 years) referred to Department of Periodontology, Dental Research Division, Guarulhos University, Brazil, for oral rehabilitation with dental implants, were included. Exclusion criteria included pregnancy, nursing, smoking, and any systemic conditions that could affect bone healing, such as osteoporosis and blood disorders. The local Ethics Committee for Human Clinical Trials approved the study protocol.

Ten screw-shaped microimplants made of grade-4 titanium (Conexão Dental Implants, São Paulo, SP, Brazil) were prepared with 2 surface topographies: machined and sandblasted acid-etched surfaces. Each microimplant was 2.5 mm in diameter and 6 mm long. The microimplants with sandblasted acid-etched surface were blasted with 25 to 100 μm TiO₂ particles. After sandblasting, the specimens were ultrasonically cleaned with an alkaline solution, washed in distilled water, and pickled with a mixture of HNO₃ and HF.

Ten screw-shaped microimplants were used in this study. Five machined microimplants that served as controls and 5 sandblasted acid-etched surfaces served as test surface microimplants (Figure 1).

All microimplants were placed in the posterior maxilla during the surgical procedures for conventional dental implant placement. After incision, mucoperiosteal flaps were raised, and the conventional implants were placed. Next, the 2 microimplants—1 with a machined and 1 with a sandblasted acid-etched surface—were placed in suitable areas, mostly the upper molar region, that is, posterior to the most distal conventional implant. The recipient microimplant sites were prepared with a 1.8-mm diameter twist drill, and implants were inserted with a screwdriver. Drilling procedures and dental implant placements were made under profuse irrigation with sterile saline. The flaps were sutured with single interrupted sutures to submerge all the dental implants, including the microimplants. Clindamycin was given twice a day for a week to avoid postsurgical infection, and pain was controlled with acetaminophen. The sutures were removed after 10 days.

A total of 10 microimplants (5 controls and 5 tests) were placed in 5 maxillae. After 2 months of healing, the microimplants were removed using an internal 4.0-mm wide trephine, and the microimplants, together with surrounding bone tissues, were rinsed in sterile saline solution and fixed by immersion in 4% neutral formalin.

To process the microimplants and surrounding bone tissues and obtain thin ground sections with the Precise 1 Automated System (Assing, Rome, Italy), the specimens were dehydrated in an ascending series of alcohol rinses and embedded in a glycol methacrylate resin (Technovit 7200 VLC, Kulzer, Wehrheim, Germany). After polymerization, the specimens were sectioned longitudinally along the major implant axis, with a high-precision diamond disk at about 150 μm, and ground down to about 30 μm. Two slides were obtained for each implant. The slides were stained with basic fuchsin and toluidine blue.

Histomorphometry of bone-implant contact percentage, as well as the bone area within the limits of the implant threads, was performed with a light microscope (Laborlux S, Leitz, Wetzlar, Germany) connected to a high-resolution video camera (3CCD, JVC KY-F55B, Milan, Italy) and interfaced with a monitor and personal computer (Intel Pentium III 1200 MMX). This optical system was associated with a digitizing pad (Matrix Vision GmbH, Milan, Italy) and a histometry software package with image-capturing capabilities (Image-Pro Plus 4.5, Media Cybernetics Inc., Immagini & Computer Snc, Milan, Italy).

The BIC and amount of bone area within the threads (from the lowest point of the microimplant head to the last apical thread) were calculated and expressed as BIC% and BD%, respectively. Mean and SD were calculated. Mann-Whitney U test was used to compare the different implant surface topographies. Significance test was 2-tailed and conducted at a 5% significance level.

All microimplants, except for 1 machined microimplant, were found to be clinically stable at the time of retrieval. The 1 unstable microimplant was not included in the statistical evaluation. Neither of the microimplants presented with marginal bone resorption or surrounding infection. Retrieved microimplants with sandblasted acid-etched surfaces presented visibly more bone attached to implant surface compared with machined surface microimplants.

The peri-implant bone from all microimplants appeared healthy. The old bone was lamellar and compact, and numerous osteocytes were presented in their lacunae, although areas of woven bone could be distinguished. The newly formed peri-implant bone exhibited early stages of maturation, mainly on the sandblasted surface (Figures 2 and 3). Osteoblasts were connected to newly formed peri-implant bone, showing ongoing bone formation, and minor apposition of new bone could be found, specifically inside the implant threads of the machined surface (Figures 4 and 5). In addition, some of the machined surface specimens showed a lack of connecting bridges between the thin bone trabeculae and the implant surface (Figure 6).

Histometric analyses are presented in Figures 7 and 8. Both histometric variables were significantly higher in the sandblasted acid-etched surface group (P < .05).

The objective of this study was to evaluate the BIC at different dental implant surfaces in human type 4 bone after a 2-month healing period. The sandblasted acid-etched implant surface exhibited a considerable percentage of mineralized bone contact compared with the machined surface implants. Geometric surface properties produce mechanical restrictions on the cytoskeletal cell components that are involved in cell spreading and migration.13 Bone cell proliferation and differentiation have been reported to be enhanced by implant surface topography roughness.14,15 In addition, it has been suggested that acid treatment enhanced early bone-implant integration to a level similar to that observed around more complex surfaces, such as surfaces sprayed with titanium plasma and surfaces coated with hydroxylapatite.16–18 

Because implant placement in type 4 bone, particularly in the posterior maxilla, is less successful than in areas with better bone quality,4,5 the histometric results of the present study suggest that implants with sandblasted surface roughness could enhance osseointegration. This finding is in agreement with previous studies performed in animal6,8,19–22 and human bone tissues.9,11 

In addition, the machined (cpTi) dental implant surface data are in agreement with the statement that this surface does not provide a strong implant anchorage in bone, particularly in compromised sites with poor bone density, such as the posterior maxilla, after longer times; this may explain the increased failure rates.3–5 

On the other hand, some studies demonstrated that anchorage of machined dental implant is time dependent.19,20 The percentage of BIC for machined surface, however, was 17.19% after 2 months of healing, whereas previous studies have reported BIC% between 10% to 11% after 6 months of healing.23,24 These histometric data may suggest that although the implant surface could be important for osseointegration, the presence of soft bone at the placement site can jeopardize the success of dental implants.

In conclusion, the histomorphometric data in the present study suggest that sandblasted acid-etched microimplant surfaces present higher %BIC compared with machined surfaces in soft bone tissue. However, these results should be considered with caution and further investigations must be conducted.

This study was supported by Dental Research Division, Guarulhos University, Guarulhos, SP, Brazil. The authors are grateful for the assistance of Drs. Leandro de Melo, Marcelo de Faveri, and José Alexandre Andrade from Guarulhos University in the surgical phases. The authors also thank Conexão Implants, São Paulo, SP, Brazil for supplying the microimplants used in this study.