Abstract
Calcium phosphate has high osteotransductive potential. The injectable form of calcium phosphate cement (ICAP) can be used as an adjunctive supportive agent for dental implants. The aim of this study was to assess the effect of an ICAP on the reverse torque resistance of titanium implants. Two implant beds (total 24) were prepared in each proximal tibia of 6 beagles. ICAP was injected into one of prepared implant beds (test) and the implant was inserted. The next implant was inserted without ICAP to serve as control. Three dogs were killed after 2 weeks and 3 after 12 weeks. Retrieved implants were subjected to reverse torque test. Results were analyzed with Student’s t -test. Scanning electron microscope (SEM) was used for further evaluation. Mean torque values in 2-week healed implants were 52.48 N cm and 50.57 N cm for test and control implants, respectively ( p = 0.4). 12-week healed implants showed 81.61 N cm and 76.71 N cm for test and control implants, respectively ( p = 0.14). Results indicated no statistical difference between test and control implants for either healing time. SEM images of tested samples revealed close contact between the bone–ICAP–titanium surface. ICAP must be tested on further developed experimental models.
Primary fixation is one of the perquisites in establishing adequate osseointegration between bone and fixture . Lack of primary stability may lead to micromovement and implant loss, especially in orthopedic implants subjected to load bearing . Polymethylmethacrylate (PMMA) is used as a gap filler between bone and implant to reinforce implant stability, but heat generation during polymerization (hardening), its inert nature (unable to resorb) and low biocompatibility compromize the success of implant treatment carried out with PMMA . Calcium phosphates (CAPs) have been tried for orthopedic implant stabilization and as a bone graft . Being a natural component of bone tissue, calcium phosphate offers positive potential in bone regeneration . CAPs are reported to be suitable for peri-implant bone defects as well .
Preparing CAP in a cement fashion; (liquid–powder process) it can set at room temperature allowing injection directly into the defect . It can be shaped before the hardening phase. Injectable calcium phosphate cement (ICAP) forms a direct connection with living bone tissue allowing rapid osteogenesis . Recently, ICAP has being used instead of PMMA for orthopedic implant fixation and the results are promising .
CAPs were also used to coat the implant surface to enhance bone–implant contact and induce a positive osteogenic effect . Comparative studies of CAP-coated implants with machined and blasted-acid etched surfaces revealed increased bone–implant contact percentage and higher torque resistance . In review of these positive findings, it can be hypothesized that ICAP may be used in implant surgery as an adjunctive agent allowing increasing bone anchorage for dental implants. In order to verify the supportive effect and torque resistance, an animal model was designed to test ICAP applied to the osteotomy site before implant installation.
Materials and methods
6 beagles with a mean age of 36 months and of similar weight were used for this study. The study was approved by the Local Ethical Committee and the surgery was performed under the animal research guidelines. Prior to surgery, the animals were monitored for 2 weeks to ensure that they were healthy and stable.
Stepped cylinder design, titanium dental implants with sandblasted and acid etched surface (3.75 mm Ø × 13 mm) were used (Frialit-II ® , Dentsply, Friadent, Mannheim, Germany).
ICAP (Augmentech AT, Wetzlar, Germany) was present in a ready-to-mix tube with powder and liquid components. The powder consisted of tricalciumphosphate (TCP), magnesium phosphate, magnesium hydrogen phosphate and strontium carbonate. The liquid was a watery solution of diammonium hydrogen phosphate. The tube is placed in a mixing apparatus (Silamat, Vivadent, Schaan, Liechtenstein) and shaken for 15 s ( Fig. 1 ).
Surgery and implant installation
The proximal tibia was chosen as the site of implantation because the risk of wound complication is less than in the oral environment and also because of its abundant trabecular bone volume so that test and control implants could be encouraged. This allowed the flow and entrapment of ICAP in the bone marrow around test implants. Before surgery, the areas in both left and right proximal tibias were shaved then washed and disinfected with betadine and draped for sterile surgery. As a premedication, Xylasin 1.5 mg/kg (Rompun, Bayer, Germany) was injected intramuscularly (i.m.). Animals were anesthetized by ketamine 10 mg/kg i.m. (Ketanest, Alfasan, The Netherlands). A full thickness flap was raised in the proximal region of the tibia. Implant bed preparation was performed according to the guidelines of the Frialit-II ® dental implant system ( Fig. 2 ). Two implant beds in each tibia were prepared in each dog at an approximate distance of 12 mm from each other. The implant beds were irrigated with sterile saline to wash away the debris. Excessive hemorrhage was controlled with sterile gauze.
ICAP was injected into one randomly selected implant beds in a retrograde manner beginning from the bottom of the cavity towards the top ( Fig. 3 ). Immediately after the injection of ICAP, the implant was installed with the hand piece instrument and embedded in the bone. Cement that flooded out of the implant bed was cleaned from the area. In the other randomly assigned bed, the implant was inserted without ICAP to serve as a control ( Fig. 4 ). 24 implants were placed with high primary stability, then cover screws were fastened. The flaps were sutured with layers using resorbable (4.0, Polyglactin 910, Ethicon, Johnson & Johnson, New York, USA) and non-resorbable silk (3.0, Dogsan, Istanbul, Turkey) sutures. Animals recovered without complications and received amoxicillin plus clavulanic acid 20 mg/kg i.m. (Sysnulox, Pfizer, Belgium) for 7 days. The animals were fed with a standard diet during the healing period. They were killed following 2 and 12 weeks of healing with an intravenous (i.v.) injection of overdose sodium pentobarbital (65 mg/kg, Dolethal, Laboratoire Vetoquinol, Lure, France).
Removal torque test (RTT)
Tibias were dissected en bloc and implants were exposed and clinically examined. Tibia blocks inheriting implants were stabilized and cover screws were removed. The internal hexagon fitting apparatus of the Frialit-II implants system was connected to the implants and device testing arm. Standard torque testing was performed with 90° force application to the implant axis. Implants were subjected to increasing torque load using the Instron device (Instron, Canton, MA, USA) until the bone-to-implant interface ruptured. The torque force was used at a constant displacement speed of 0.5 mm/min. At the point of implant failure, the test was stopped immediately to prevent complete damage of the interface. Measurements of peak torque to initiate reverse rotation were recorded by a computer.
Scanning electron microscope (SEM)
Following the torque test specimens were examined by SEM. Backscatter SEM (JEOL 6310, Jeol Ltd., Tokyo, Japan) images were obtained to evaluate the bone–cement–implant interface. All specimens were fixed and dehydrated by a graded series of ethanol and embedded in methylmethacrylate. After polymerization, samples were sectioned on the long axis in the center. All specimens were polished, carbon coated then investigated with the backscatter mode to examine the ICAP–bone–implant appearance and the localization of the rupture patterns in the interface.
Statistical analysis
Mean torque measurements were calculated for the implants in test and control groups. Differences in mean peak torque values for test and control implants were compared with paired Student’s t -test. Values of p < 0.05 were considered significant.
Results
Preparation and application of ICAP was convenient and easy. In the event of bleeding, ICAP was eroded by blood flow from the osteotomy sites; in previous studies this was described as a ‘wash-out effect’ . Healing was uneventful in all dogs. Radiologic examination revealed no pathology around the implants. All implants were clinically stable and osseointegrated at both healing periods. Some implants were partially covered with bone and exposure of the implant shoulder was performed with a round bur after radiologic confirmation.
The mean removal torque values (RTV) at 2 weeks were 50.57 (±11.59) N cm for the control implants and 52.48 (±11.94) N cm for the implants inserted with ICAP. In the 12-week healing group, control implants showed 76.71 (±6.55) N cm and test implants showed 81.61 (±7.9) N cm torque resistance values. In neither healing period was statistical significance found (2 weeks: p = 0.4; 12 weeks: p = 0.14) between test and control groups ( Table 1 and Fig. 5 ).
| 2 weeks (N cm) | 12 weeks (N cm) | ||||
|---|---|---|---|---|---|
| Control | Test | Control | Test | ||
| Dog 1 | Dog 4 | ||||
| (L) | 70 | 47.7 | (L) | 84.5 | 82.3 |
| (R) | 61.5 | 39.2 | (R) | 79.4 | 89.2 |
| Dog 2 | Dog 5 | ||||
| (L) | 49.4 | 70.4 | (L) | 78.3 | 67.4 |
| (R) | 50.1 | 57.9 | (R) | 65.4 | 79.8 |
| Dog 3 | Dog 6 | ||||
| (L) | 48.6 | 42.6 | (L) | 73.5 | 88.6 |
| (R) | 35.3 | 45.6 | (R) | 79.2 | 82.4 |
| Mean | 52.48 (± 11.94 ) | 50.57 (± 11.59 ) | 76.71 (± 6.55 ) | 81.61 (± 7.9 ) | |
| p | 0.4 | 0.14 | |||
New bone formation and good interfacial bone contact were observed in all samples. There were no signs of inflammatory response in any sample. New bone formation was evident in all samples with no visible gaps between ICAP, bone and implant. Fracture lines were visible in almost all samples.
In the 2-week healed implants, ICAP was visible in all test implants distributed into the surrounding trabeculae. ICAP was in direct contact with the native bone and implant surface. Trabeculae around the implant body were sparsely filled with ICAP. ICAP was not evenly spread on the implant interface in all implants. Rupture patterns were rare on the implant surface and mostly in the cement body as cracks and departed fragments showing the mechanical breakdown of the non-resorbed cement during reverse torque forcing.
The 2-week control implants showed direct bone contact. Detached implant body and bone was observed and a thin dark gap was visible at the bone implant interface ( Fig. 6 ).
