Minipig Mandible Research Articles

Osseointegration of Grit-Blasted and Bioactive Titanium Implants: Histomorphometry in Minipigs

In order to improve osseointegration of commercially pure titanium implants one of the main influencing factors is surface quality, which refers to their topographical and physicochemical features. A new two-step (2S) surface treatment has been previously developed. The method consists of 1) grit blasting the surface in order to roughen it and 2) thermochemical treatment in order to obtain a bioactive metal surface. This new 2S-treatment has been in vivo evaluated and compared with as-machined (Ctr), acid etched (E) and grit-blasted (R) implants by means of an histomorphometric quantification (percentage of the total implant surface in direct contact with new bone) after 2, 4, 6 and 10 weeks of implantation into the mandibles of minipigs. The results showed that the rough and bioactive-c.p. Ti implants obtained by EL new two-step surface treatment accelerate their osseointegration compared to grit-blasted, acid etched and as-machined implants, which make them preferential candidates as immediate-loaded dental implants. These implants developed in vivo onto their surfaces a layer of a calcium phosphate, which is probably apatite.

Ultrastructural characterization of the implant/bone interface of immediately loaded dental implants

Primary stability and an optimized load transfer are assumed to account for an undisturbed osseointegration process of implants. Immediate loaded newly designed titanium dental implants inserted in the mandible of minipigs were used for the characterization of the interfacial area between the implant surface and the surrounding bone tissue during the early healing phase. Histological and electron microscopical studies were performed from implant containing bone specimens. Two different load regimens were applied to investigate the load related tissue reaction. Histological and electron microscopical analysis revealed a direct bone apposition on the implant surfaces, as well as the attachment of cells and matrix proteins in the early loading phase. A striking finding of the ultrastructural immunocytochemical investigations was the synthesis and deposition of bone related proteins (osteonectin, fibronectin, fibronectin receptor) by osteoblasts from day one of bone/biomaterial interaction. Calcium-phosphate needle-like crystallites were newly synthesized in a time-related manner directly at the titanium surface. No difference in the ultrastructural appearance of the interface was found between the two loading groups. Our experimental data suggest that loading of specially designed implants can be performed immediately after insertion without disturbing the biological osseointegration process.

Recombinant human transforming growth factor beta-1 and its effects on osseointegration.

Dental implant failures are still a common occurrence, especially in areas of poor bone quality. The purpose of this study was to observe whether the application of a growth factor, recombinant human transforming growth factor beta-1 (rhTGF-beta1), would improve the healing of bone adjacent to titanium dental implants. Four adult male Yucatan minipigs had four titanium dental implants placed into the inferior border of each hemimandible. On the control side, the implants were placed in standard fashion. On the experimental side, rhTGF-beta1 within a carrier gel was placed into the recipient site before implant placement. After a 6-week healing period, two implants from each side were evaluated by pull-out testing and histomorphometric analysis. The mean pull-out force for experimental implants was 1,124.01 N and 818.12 N (P = 0.5015) for controls. The mean percentage of bone between adjacent threads on the implant surface was 49.74% for the experimental group and 36.50% for controls (P = 0.0783). The mean percentage of bone-implant surface contact was 41.86% for the experimental implant sites and 24.60% for the control implant sites (P = 0.0452). The application of rhTGF-beta1 to implant sites appears to increase the amount of bone healing adjacent to a titanium dental implants in minipig mandibles at the 6-week period. Further studies are required to quantify better the amount of growth factor required and to study its effects over a broader period of time to see whether these differences are maintained.

Changes in the condyle and disc in response to distraction osteogenesis of the minipig mandible

Purpose: Distraction osteogenesis (DO) is a commonly used technique for mandibular lengthening, but changes in the temporomandibular joint have not been well documented. The purpose of this study was to evaluate the effect of DO, at varying rates, on the mandibular condyle and articular disc. Materials and Methods: Semiburied distractors were placed via submandibular incisions in 15 minipigs. Two unoperated animals served as controls. The protocol consisted of 0 day latency and rates of 1, 2, or 4 mm/d for a 12-mm gap. After the animals were killed (0, 24, or 90 days), ipsilateral and contralateral condyles and discs were harvested and evaluated to determine changes in 1) condylar form and size, 2) condylar surface, and 3) the articular disc. Results: Articular surfaces of the condyles in control animals were smooth, with no irregularities or erosions. In animals undergoing distraction, ipsilateral condyles showed increasing changes in morphology and AP dimension, and surface contour irregularities as the DO rate increased. These changes were present, but to a lesser degree, in the contralateral condyles. Articular discs of both ipsilateral and contralateral sides showed variable thinning at the medial aspect at end DO. After 90 days, changes in the condyles and discs were reduced by remodeling except in the 4 mm/d DO groups. Conclusions: Results of this preliminary study indicate that gross changes occur in condyles and discs after unilateral mandibular DO. These changes are more severe at faster distraction rates (4 mm/d) and tend to resolve during neutral fixation when a rate of 1 mm/d is used. © 2002 American Association of Oral and Maxillofacial Surgeons J Oral Maxillofac Surg 60:1327-1333, 2002

Experimental and comparative study of the blood supply to the mandibular cortex in Göttingen minipigs and in man

Introduction: Since the blood supply to the mandibular cortex is an important factor for bone growth and bone repair, experimental studies on the blood supply in animal models (such as Göttingen minipigs) applicable to man are necessary. Their value depends on the requirement that the patterns of blood supply in the two species are similar. Material and methods: Twelve Göttingen minipig mandibles (24 halves) and four human mandibles (eight halves) were investigated for the blood supply to the mandibular cortex. Results: Only minor differences were found in blood supply to the mandibular cortex between the two species. Common to both was: in the cranial part of the mandible (including the condyle), the endosteal blood supply prevailed, whereas the periosteal blood supply predominated in the caudal part of the mandible (the body). Both patterns of blood supply were in balance in the centre section, i.e. angle and ascending ramus of the mandible. Conclusion: The present study confirms that results obtained from Göttingen minipigs, used as an experimental animal model, are applicable to man: three different types of blood supply are evident in the mandibular cortex in both species. Copyright 2002 European Association for Cranio-Maxillofacial Surgery. Published by Elsevier Science Ltd. All rights reserved.

Evaluation of a semiburied, fixed-trajectory, curvilinear, distraction device in an animal model

Purpose: This study evaluated a new small, buried distractor, capable of curvilinear movement while following a fixed trajectory. The geometrical basis for such devices and the 3-dimensional treatment planning system required to make buried distractors practical are discussed. Materials and Methods: A curved rack and worm-gear device, based on the design of a hose clamp, was constructed to produce a curved distraction path, and this distractor was tested in 2 minipigs using a protocol with zero latency and 1 mm/d × 7 days of distraction. Serial standardized lateral cephalograms were used to verify distractor function and path. Results: Curvilinear distraction was documented by clinical examination and serial cephalometric analysis in the 2 minipigs. Observed angulation of the margins of the wedge-shaped distraction gap conformed to the calculated angulation based on the fixed radius of curvature of the distractor. Conclusion: Distraction along a curved trajectory using a small, semiburied, curvilinear device of novel design is feasible in the minipig mandible.