Implementation of the “loaded implant” model in the rat using a miniaturized setup - description of the method and first results

Pre-Clinical Models in Implant Dentistry: Past, Present, Future

Biomedical research seeks to generate experimental results for translation to clinical settings. In order to improve the transition from bench to bedside, researchers must draw justifiable conclusions based on data from an appropriate model. Animal testing, as a prerequisite to human clinical exposure, is performed in a range of species, from laboratory mice to larger animals (such as dogs or non-human primates). Minipigs appear to be the animal of choice for studying bone surgery around intraoral dental implants. Dog models, well-known in the field of dental implant research, tend now to be used for studies conducted under compromised oral conditions (biofilm). Regarding small animal models, research studies mostly use rodents, with interest in rabbit models declining. Mouse models remain a reference for genetic studies. On the other hand, over the last decade, scientific advances and government guidelines have led to the replacement, reduction, and refinement of the use of all animal models in dental implant research. In new development strategies, some in vivo experiments are being progressively replaced by in vitro or biomaterial approaches. In this review, we summarize the key information on the animal models currently available for dental implant research and highlight (i) the pros and cons of each type, (ii) new levels of decisional procedures regarding study objectives, and (iii) the outlook for animal research, discussing possible non-animal options.

Analysis of implant stability changes in immediate loading using a laser displacement sensor in vivo and comparison of its sensitivity with that of resonance frequency analysis

OBJECTIVE

The aim of this study was to analyze the stability changes in immediately loaded implants by using an in vivo quantitative measurement of micromotion under functional dynamic loading and to verify the sensitivity of Resonance Frequency Analysis (RFA) as compared to that of actual micromotion.

MATERIALS AND METHODS

The micromotions of immediately loaded implants placed in the tibia of 11 rabbits were monitored using a laser displacement sensor. Functional dynamic loading forces were applied 5 days a week for 6 weeks. The implant stability quotient (ISQ) was monitored using RFA.

RESULTS

The micromotion of the almost-loaded implants increased to peak values the day after loading was started and subsequently reached a plateau gradually. The ISQ changes in the loaded implants closely correlated with the alterations of the actual micromotion (r = -0.98, p < .01). Although the ISQ value itself correlated with the measured micromotion at the time of initial fixation (r = 0.73, p < .05), it did not correlate with the micromotion of the implant that acquired integration. No close correlation was observed between the ISQ and the histomorphometrical data.

CONCLUSION

The immediately loaded implants showed the lowest stability immediately after the start of loading, which gradually increased thereafter. RFA is considered a useful method for examining stability changes and initial stability; however, it cannot determine the absolute magnitude of the stability after integration.

External mechanical microstimuli modulate the osseointegration of titanium implants in rat tibiae

Purpose. To assess the effect of external mechanical microstimuli of controlled magnitude on the microarchitecture of the peri-implant bone beds in rat tibiae. Materials and Methods. Tibiae of forty rats were fitted with two transcutaneous titanium cylinders. After healing, the implants were loaded to 1 to 3 N, five days/week for four weeks. These force levels translated into intraosseous strains of 700 ± 200 με, 1400 ± 400 με, and 2100 ± 600 με. After sacrifice, the implants' pullout strength was assessed. Second, the bone's microarchitecture was analyzed by microcomputed tomography (μCT) in three discrete regions of interest (ROIs). Third, the effect of loading on bone material properties was determined by nanoindentation. Results. The trabecular BV/TV significantly increased in an ROI of 0.98 mm away from the test implant in the 1 N versus the 3 N group with an opposite trend for cortical thickness. Pull-out strength significantly increased in the 2 N relatively to the nonstimulated group. Higher values of E-modulus and hardness were observed in the trabecular bone of the 2 N group. Conclusion. The in vivo mechanical loading of implants induces load-dependent modifications in bone microarchitecture and bone material properties in rat tibiae. In pull-out strength measurements, implant osseointegration was maximized at 2 N (1400 ± 400 με).