Evaluation of a new experimental model to study bone healing after ridge expansion with simultaneous implant placement - a pilot study in minipigs

Regeneration of alveolar bone defects in the experimental pig model: A systematic review and meta-analysis

OBJECTIVE

Pigs are emerging as a preferred experimental in vivo model for bone regeneration. The study objective was to answer the focused PEO question: in the pig model (P), what is the capacity of experimental alveolar bone defects (E) for spontaneous regeneration in terms of new bone formation (O)?

METHODS

Following PRISMA guidelines, electronic databases were searched for studies reporting experimental bone defects or extraction socket healing in the maxillae or mandibles of pigs. The main inclusion criteria were the presence of a control group of untreated defects/sockets and the assessment of regeneration via 3D tomography [radiographic defect fill (RDF)] or 2D histomorphometry [new bone formation (NBF)]. Random effects meta-analyses were performed for the outcomes RDF and NBF.

RESULTS

Overall, 45 studies were included reporting on alveolar bone defects or extraction sockets, most frequently in the mandibles of minipigs. Based on morphology, defects were broadly classified as 'box-defects' (BD) or 'cylinder-defects' (CD) with a wide range of healing times (10 days to 52 weeks). Meta-analyses revealed pooled estimates (with 95% confidence intervals) of 50% RDF (36.87%-63.15%) and 43.74% NBF (30.47%-57%) in BD, and 44% RDF (16.48%-71.61%) and 39.67% NBF (31.53%-47.81%) in CD, which were similar to estimates of socket-healing [48.74% RDF (40.35%-57.13%) and 38.73% NBF (28.57%-48.89%)]. Heterogeneity in the meta-analysis was high (I2 > 90%).

CONCLUSION

A substantial body of literature revealed a high capacity for spontaneous regeneration in experimental alveolar bone defects of (mini)pigs, which should be considered in future studies of bone regeneration in this animal model.

Evaluation of the Effectiveness of Bone Grafting in Alveolar Ridge Augmentation Using the Two-Stage Splitting Technique

Stimulation of neoosteogenesis is the main mechanism of osseointegration during installation of dental implants, bone tissue recession, and alveolar process augmentation in adentia. In experiments on miniature pigs, we used the technology of two-stage splitting of the ridge of the alveolar process of the mandible in combination with a xenograft that was placed between the fragments of the split bone plate. The morphology of the reparative process and the distribution of osteogenic differentiation markers in the compact and trabecular bone of the alveolar crest were studied. Signs of reparative osteogenesis were observed in the bone regenerate that had a lamellar structure, formed osteons, and foci of woven tissue. It was found that the xenograft was replaced by newly formed trabecular bone tissue. These sites were characterized by increased expression of osteocalcin and CD44. Augmentation technology through two-stage splitting provides trophic relationship of osteoprogenitor cells and is an effective method of osteogenesis stimulation in the alveolar process.

Dental implants in large animal models with experimental systemic diseases: A systematic review

This systematic review aims to identify and discuss the most used methodologies in pre-clinical studies for the evaluation of the implementation of dental implants in systemically compromised pigs and sheep. This study provides support and guidance for future research, as well as for the prevention of unnecessary animal wastage and sacrifice. Preferred Reporting for Systematic Reviews and Meta-Analyses (PRISMA) was used as a guideline; electronic searches were performed in PubMed, Scopus, Scielo, Web of Science, Embase, Science Direct, Brazilian Bibliography of Dentistry, Latin American and Caribbean Literature in Health Sciences, Directory of Open Access Journals, Database of Abstracts of Reviews of Effects, and gray literature until January 2022 (PROSPERO/CRD42021270119). Sixty-eight articles were chosen from the 2439 results. Most studies were conducted in pigs, mainly the Göttinger and Domesticus breeds. Healthy animals with implants installed in the jaws were predominant among the pig studies. Of the studies evaluating the effect of systemic diseases on osseointegration, 42% were performed in osteoporotic sheep, 32% in diabetic sheep, and 26% in diabetic pigs. Osteoporosis was primarily induced by bilateral ovariectomy and mainly assessed by X-ray densitometry. Diabetes was induced predominantly by intravenous streptozotocin and was confirmed by blood glucose analysis. Histological and histomorphometric analyses were the most frequently employed in the evaluation of osseointegration. The animal models presented unique methodologies for each species in the studies that evaluated dental implants in the context of systemic diseases. Understanding the most commonly used techniques will help methodological choices and the performance of future studies in implantology.

Lateral augmentation of the jaw by the split expansion ridge technique. A critical review

Bone augmentation has become a routine procedure to enhance and/or repair a deficient or resorbed alveolar ridge for predictable and successful implant placement. The split expansion ridge i.e., the alveolar ridge splitting (ARS) procedure, is one of the less invasive procedures, and is characterized by minor morbidity. This would allow to widen narrow ridges in order to allow implant reconstruction in a sufficient bone volume. Its efficacy and long-term stability rely upon clinical opinions and long-term retrospective studies, while prospective comparative studies and randomized controlled trials are rare. This critical review presents the development of this technique, describes the surgical procedure, and provides technical notes and modifications. The learning curve and in-depth knowledge of the oral anatomy, as well as the recognition of incidence and management of complications are of utmost importance in the clinical application of the ARS procedure.

Characterizing cell recruitment into isotropic and anisotropic biomaterials by quantification of spatial density gradients in vitro

The success of cell-free in situ tissue engineering approaches depends on an appropriate recruitment of autologous cells from neighboring tissues. This identifies cellular migration as a critical parameter for the pre-clinical characterization of biomaterials. Here, we present a new method to quantify both the extent and the spatial anisotropy of cell migration in vitro. For this purpose, a cell spheroid is used as a cell source to provide a high number of cells for cellular invasion and, at the same time, to guarantee a controlled and spatially localized contact to the material. Therefore, current limitations of assays based on 2D cell sources can be overcome. We tested the method on three biomaterials that are in clinical use for soft tissue augmentation in maxilla-facial surgery and a substrate used for 3D in vitro cell culture. The selected biomaterials were all collagen-derived, but differed in their internal architecture. The analysis of cellular isodensity profiles within the biomaterials allowed the identification of the extent and the preferential directions of migration, as well as their relation to the biomaterials and their specific pore morphologies. The higher cell density within the biomaterials resulting from the here-introduced cell spheroid assay compared to established 2D cell layer assays suggests a better representation of the in vivo situation. Consequently, the presented method is proposed to advance the pre-clinical evaluation of cell recruitment into biomaterials, possibly leading to an improved prediction of the regeneration outcome.

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.

Calcium Phosphate-Coated Titanium Implants in the Mandible: Limitations of the in vivo Minipig Model

INTRODUCTION

We aimed to compare implant osseointegration with calcium phosphate (CaP) surfaces and rough subtractive-treated sandblasted/acid etched surfaces (SA) in an in vivo minipig mandible model.

MATERIALS AND METHODS

A total of 36 cylindrical press-fit implants with two different surfaces (CaP, n = 18; SA, n = 18) were inserted bilaterally into the mandible of 9 adult female minipigs. After 2, 4, and 8 weeks, we analyzed the cortical bone-to-implant contact (cBIC; %) and area coverage of bone-to-implant contact within representative bone chambers (aBIC; %).

RESULTS

After 2 weeks, CaP implants showed no significant increase in cBIC and aBIC compared to SA (cBIC: mean 38 ± 5 vs. 16 ± 11%; aBIC: mean 21 ± 1 vs. 6 ± 9%). Two CaP implants failed to achieve osseointegration. After 4 weeks, no statistical difference between CaP and SA was seen for cBIC (mean 54 ± 15 vs. 43 ± 16%) and aBIC (mean 43 ± 28 vs. 32 ± 6). However, we excluded two implants in each group due to failure of osseointegration. After 8 weeks, we observed no significant intergroup differences (cBIC: 18 ± 9 vs. 18 ± 20%; aBIC: 13 ± 8 vs. 16 ± 9%). Again, three CaP implants and two SA implants had to be excluded due to failure of osseointegration.

CONCLUSION

Due to multiple implant losses, we cannot recommend the oral mandibular minipig in vivo model for future endosseous implant research. Considering the higher rate of osseointegration failure, CaP coatings may provide an alternative to common subtractive implant surface modifications in the early phase post-insertion.

The Alveolar Ridge Splitting Technique on Maxillae: A Biomechanical Human Cadaveric Investigation

The alveolar ridge splitting technique (ARST) offers an alternative to classic ridge augmentation techniques for successful insertion of dental implants. However, the buccal lamella is at risk of fracturing during ARST distraction. To better understand the fracture mechanisms and displacement limits of the split lamella, this study conducted biomechanical tests on human cadaveric maxilla specimens having extremely atrophied alveolar ridges treated with ARST. A total of 12 standardized alveolar splits were prepared on the maxillae of 3 elderly female donors using an oscillating piezoelectric saw. Mimicking the surgical distraction process of the lamella, each split was tested to failure using a dental osteotome attached to the crosshead of an electromechanical testing system. All specimens were scanned by means of high-resolution peripheral quantitative computed tomography prior to and post testing to evaluate split geometries and failure modes. Split stiffness, failure force, and displacement were 27.4 ± 18.7 N/mm, 12.0 ± 8.4 N, and 0.97 ± 0.31 mm, with no significant differences between anatomical sides and split locations (p ≥ 0.17). Stiffness correlated significantly with failure force (R² = 0.71, p < 0.01). None of the alveolar split widths correlated significantly with the outcomes from biomechanical testing (p ≥ 0.10). The results suggest that simple geometrical measures do not predict the allowed extent of lamella distraction prior to failure. More sophisticated methods are required for surgical planning to optimize the ARST outcomes. Still, the present study may advocate a clinical protocol for the maxilla where the implant site is prepared directly after osteotomy setting and immediately before full lamella dislocation, when the lamella is still stable, resistant to mechanical stress, and bone loss caused by the abrasion of the burr is minimized.

Evaluation of deformation in the buccal lamellar bone with finite element analysis in alveolar ridge-splitting/expansion technique

PURPOSE

The aim of this study was to investigate deformation and stress distribution in the buccal lamellar bone via finite element analysis (FEA) in the application of alveolar ridge-splitting/expansion technique (ARST) in atrophic maxilla and mandible.

MATERIAL AND METHOD

Three-dimensional (3D) solid models of maxilla and mandible were formed using computer software, with an alveolar ridge thickness of 4 mm in the right first molar region. In both models, one horizontal and two releasing vertical osteotomies were made in the atrophic region. Vertical forces varying from 50 N to 1000 N were continuously applied on the midpoint of the horizontal osteotomy and then the axial and total deformation and von Mises stress distribution in the buccal lamellar bone was assessed by FEA.

RESULTS

The degrees of axial deformation and total deformation and the maximum von Mises stress value under a 50 N force were 0.22 mm, 0.23 mm, and 4.52 MPa in the maxillary buccal lamellar bone and were 0.04 mm, 0.06 mm, and 5.90 MPa in the mandibular buccal lamellar bone, respectively. Similarly, under a 1000 N force, the values were 4.44 mm, 4.75 mm, and 90.49 MPa in the maxillary buccal lamellar bone and were 0.96 mm, 1.1 mm, and 118.02 MPa in the mandibular buccal lamellar bone, respectively.

CONCLUSION

These findings implicate that the ARST used for implant placement or alveolar augmentation can be achieved with the application of lower amounts of force in the maxilla compared to the mandible. It was also revealed that in ARST, the maximum von Mises stress value was lower in the maxillary buccal lamellar bone than in the mandibular buccal lamellar bone. Based on these findings, we consider that the administration of ARST could be biomechanically more stable in the maxilla than in the mandible.

Finite Element Analysis and Biomechanical Testing to Analyze Fracture Displacement of Alveolar Ridge Splitting

The alveolar ridge splitting technique enables reconstruction of atrophied alveolar ridges prior implantation. However, in cases of severe atrophy, there is an unpredictable risk of fracturing the buccal lamella during the expansion. Currently, there is no preoperative assessment to predict the maximum distraction of the lamella. The aim of this study was to develop a biomechanical model to mimic the alveolar ridge splitting and a finite element (FE) model to predict the experimental results. The biomechanical testing was conducted on porcine mandibles. To build the FE model high resolution peripheral quantitative computer tomography scans of one specimen was performed after the osteotomy outline, but before the lamella displacement. A servo-electric testing machine was used for the axial tension test to split the lamellae. Results showed, in line with clinical observations, that the lamellae broke primarily at the base of the splits with a median displacement of 1.27 mm. The FE model could predict fracture force and fracture displacement. Fracture force showed a nonlinear correlation with the height of the bone lamella. In conclusion, good correspondence between mechanical testing and virtual FE analysis showed a clinically relevant approach that may help to predict maximum lamella displacement to prevent fractures in the future.

Refining experimental dental implant testing in the Göttingen Minipig using 3D computed tomography-A morphometric study of the mandibular canal

This study reports morphometric and age-related data of the mandibular canal and the alveolar ridge of the Göttingen Minipig to avoid complications during in vivo testing of endosseus dental implants and to compare these data with the human anatomy. Using 3D computed tomography, six parameters of the mandibular canal as well as the alveolar bone height and the alveolar ridge width were measured in Göttingen Minipigs aged 12, 17 and 21 months. Our null hypothesis assumes that the age and the body mass have an influence on the parameters measured. The study found that the volume, length and depth of the mandibular canal all increase with age. The width of the canal does not change significantly with age. The body mass does not have an influence on any of the measured parameters. The increase in canal volume appears to be due to loss of deep spongy bone in the posterior premolar and molar regions. This reduces the available space for dental implantations, negatively affecting implant stability and potentially the integrity of the inferior alveolar neurovascular bundle. Dynamic anatomical changes occur until 21 months. On ethical grounds, using minipigs younger than 21 months in experimental implant dentistry is inadvisable. Paradoxically the measurements of the 12 months old pigs indicate a closer alignment of their mandibular anatomy to that of humans suggesting that they may be better models for implant studies. Given the variability in mandibular canal dimensions in similar age cohorts, the use of imaging techniques is essential for the selection of individual minipigs for dental prosthetic interventions and thus higher success rates.

The alveolar ridge splitting/expansion technique: a systematic review

PURPOSE

The aim of this systematic review was to evaluate clinical, radiological and histological outcomes of the alveolar ridge splitting/expansion technique (ARST) with or without GBR.

MATERIALS AND METHODS

A screening of two databases MEDLINE (PubMed) and EMBASE (OVID) and hand search of articles were performed. Human and animal studies reporting on dental implants placed with simultaneous ARST up to May 31st 2014 were considered. Quality assessment of selected full-text articles was performed according to the ARRIVE guidelines and the Cochrane collaboration's tool to assess risk of bias.

RESULTS

Overall, 18 human and six animal studies (risk of bias: high/unclear) were included in this review. No randomized controlled trials were found. Due to the heterogeneity of study designs, definitions of success criteria, outcome variables, observation times and surgical procedures, no meta-analysis was performed. Reported survival (18 studies) and success (nine studies) rates ranged from 91.7 to 100% and 88.2 to 100%, respectively, with a mean follow-up of 1-10 years. Crestal bone level changes (∆CBL) in some studies indicate slightly higher bone loss before and after loading. Histologic and histomorphometric data from six animal studies confirm the crestal bone loss, particularly at buccal sites.

CONCLUSIONS

Within the limitations of this review, ARST seems to be a well-functioning one-stage alternative to extended two-stage horizontal grafting procedures. Data indicate that during healing and first year of loading, increased ∆CBL particularly at buccal sites must be anticipated. Additional horizontal GBR can help to preserve buccal bone height and width.