Crestal remodelling and osseointegration at surface-modified commercially pure titanium and titanium alloy implants in a canine model

The minipig intraoral dental implant model: A systematic review and meta-analysis

OBJECTIVES

The objective of this report was to provide a review of the minipig intraoral dental implant model including a meta-analysis to estimate osseointegration and crestal bone remodeling.

METHODS

A systematic review including PubMed and EMBASE databases through June 2021 was conducted. Two independent examiners screened titles/abstracts and selected full-text articles. Studies evaluating titanium dental implant osseointegration in native alveolar bone were included. A quality assessment of reporting was performed. Random-effects meta-analyses and meta-regressions were produced for bone-implant contact (BIC), first BIC, and crestal bone level.

RESULTS

125 out of 249 full-text articles were reviewed, 55 original studies were included. Quality of reporting was generally low, omissions included animal characteristics, examiner masking/calibration, and sample size calculation. The typical minipig model protocol included surgical extraction of the mandibular premolars and first molar, 12±4 wks post-extraction healing, placement of three narrow regular length dental implants per jaw quadrant, submerged implant healing and 8 wks of osseointegration. Approximately 90% of studies reported undecalcified incandescent light microscopy histometrics. Overall, mean BIC was 59.88% (95%CI: 57.43-62.33). BIC increased significantly over time (p<0.001): 40.93 (95%CI: 34.95-46.90) at 2 wks, 58.37% (95%CI: 54.38-62.36) at 4 wks, and 66.33% (95%CI: 63.45-69.21) beyond 4 wks. Variability among studies was mainly explained by differences in observation interval post-extraction and post-implant placement, and implant surface. Heterogeneity was high for all studies (I2 > 90%, p<0.001).

CONCLUSIONS

The minipig intraoral dental implant model appears to effectively demonstrate osseointegration and alveolar bone remodeling similar to that observed in humans and canine models.

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.

Histomorphological and Histomorphometric Analyses of Grade IV Commercially Pure Titanium and Grade V Ti-6Al-4V Titanium Alloy Implant Substrates: An In Vivo Study in Dogs

PURPOSE

To evaluate the bone response to grade IV commercially pure titanium (G4) relative to Ti-6Al-4V (G5).

MATERIALS AND METHODS

Implant surface topography was characterized by optical interferometry and scanning electron microscopy (SEM). Thirty-six implants (Signo Vinces, n = 18 per group) were installed in the radius of 18 dogs. The animals were killed at 1, 3, and 6 weeks, resulting in 6 implants per group and time in vivo for bone morphology, bone-to-implant contact (BIC), and bone area fraction occupancy (BAFO) evaluation.

RESULTS

SEM depicted a more uniform topography of G4 than G5. Surfaces were statistically homogeneous for Sa, Sq, and Sdr. At 1 week, new bone formation was observed within the healing connective tissue in contact with the implant surface. At 3 weeks, new bone in direct contact with the implant surface was observed at all bone regions. At 6 weeks, the healing chambers filled with woven bone depicted an onset of replacement by lamellar bone. No significant effect of substrate was detected. Time presented an effect on BIC and BAFO (P < 0.001).

CONCLUSION

Both titanium substrates were biocompatible and osseoconductive at the bone tissue level.

Evaluation of calcium dihydroxide- and silver-coated implants in the rat tibia

BACKGROUND

Silver ions (Ag+) have strong antibacterial effects, and silver-coated materials are in widespread clinical use. However, the application of silver-coated medical devices is not without concerns: its use with direct bone contact is not established, and systemic toxic side effects of released Ag+ have been described. Therefore, alternative bactericidal coatings with a more localized way of acting - e.g., calcium dihydroxide, Ca(OH)2 (CH) - would be advantageous.

METHODS

A new rat model of the animal's tibial metaphysis was developed. In the left proximal tibiae of 36 male Wistar rats, titanium screws were implanted. The screws were coated with hydroxyapatite (HA; 12 animals: group I), low-dosed HA silver (HA-Ag; 12 animals: group II) and CH (12 animals: group III). After 6 weeks, all rats were sacrificed. The implants were evaluated for morphological changes on their surfaces, by light microscopy, scanning electron microscopy and energy-dispersive X-ray spectroscopy; for osteointegration, by measurement of resistance to removal; and for bacterial colonization, by quantitative culture analysis. Additionally, the tibial bone was investigated histologically for signs of osteomyelitis and sonicated to detect bacterial loads.

RESULTS

(i) No microbiological or histological signs of infection could be determined on any of the screws or the surrounding bone. (ii) The bone-implant interface analysis revealed extensive bone formation and direct bone-implant contact on all HA, HA-Ag and HA-CH coated screws. (iii) HA and HA-Ag were partially, and CH was fully, degraded on the screw coating, allowing host bone to osteointegrate.

Ethical guidelines, animal profile, various animal models used in periodontal research with alternatives and future perspectives

Laboratory animal models serve as a facilitator to investigate the etiopathogenesis of periodontal disease, are used to know the efficacy of reconstructive and regenerative procedures, and are also helpful in evaluation of newer therapeutic techniques including laser and implant therapies prior to application in the human beings. The aim of this review is to know the different animal models used in various specialties of dental research and to know the ethical guidelines prior to the usage of experimental models with main emphasis on how to refine, replace, and reduce the number of animal models usage in the laboratory. An online search for experimental animal models used in dental research was performed using MEDLINE/PubMed database. Publications from 2009 to May 2013 in the specialty of periodontics were included in writing this review. A total of 652 references were published in PubMed/MEDLINE databases based on the search terms used. Out of 245 studies, 241 were related to the periodontal research published in English from 2009 to 2013. Relevant papers were chosen according to the inclusion and exclusion criteria. After extensive electronic and hand search on animal models, it has been observed that various animal models were used in dental research. Search on animal models used for dental research purpose revealed that various animals such as rats, mice, guinea pigs, rabbit, beagle dogs, goats, and nonhuman primates were extensively used. However, with the new advancement of ex vivo animal models, it has become easy to investigate disease pathogenesis and to test the efficacy of newer therapeutic modalities with the reduced usage of animal models. This review summarized the large amount of literature on animal models used in periodontal research with main emphasis on ethical guidelines and on reducing the animal model usage in future perspective.

Anodisation Increases Integration of Unloaded Titanium Implants in Sheep Mandible

Spark discharge anodic oxidation forms porous TiO₂ films on titanium implant surfaces. This increases surface roughness and concentration of calcium and phosphate ions and may enhance early osseointegration. To test this, forty 3.75 mm × 13 mm titanium implants (Megagen, Korea) were placed into healed mandibular postextraction ridges of 10 sheep. There were 10 implants per group: RBM surface (control), RBM + anodised, RBM + anodised + fluoride, and titanium alloy + anodised surface. Resonant frequency analysis (RFA) was measured in implant stability quotient (ISQ) at surgery and at sacrifice after 1-month unloaded healing. Mean bone-implant contact (% BIC) was measured in undemineralised ground sections for the best three consecutive threads. One of 40 implants showed evidence of failure. RFA differed between groups at surgery but not after 1 month. RFA values increased nonsignificantly for all implants after 1 month, except for controls. There was a marked difference in BIC after 1-month healing, with higher values for alloy implants, followed by anodised + fluoride and anodised implants. Anodisation increased early osseointegration of rough-surfaced implants by 50–80%. RFA testing lacked sufficient resolution to detect this improvement. Whether this gain in early bone-implant contact is clinically significant is the subject of future experiments.

Biophysical evaluation of cells on nanotubular surfaces: the effects of atomic ordering and chemistry

After the implantation of a biomaterial in the body, the first interaction occurs between the cells in contact with the biomaterial surface. Therefore, evaluating the cell-substrate interface is crucial for designing a successful implant. In this study, the interaction of MC3T3 osteoblasts was studied on commercially pure and alloy (Ti6Al4V) Ti surfaces treated with amorphous and crystalline titanium dioxide nanotubes. The results indicated that the presence of nanotubes increased the density of osteoblast cells in comparison to bare surfaces (no nanotubes). More importantly, our finding shows that the chemistry of the substrate affects the cell density rather than the morphology of the cells. A novel approach based on the focused ion beam technique was used to investigate the biophysical cell-substrate interaction. The analysis revealed that portions of the cells migrated inside the crystalline nanotubes. This observation was correlated with the super hydrophilic properties of the crystalline nanotubes.

Effect of Platform Shift/Switch on Crestal Bone Levels and Mucosal Profile Following Flapless Surgery and Crestal/Subcrestal Implant Placement

BACKGROUND

Crestal remodeling/bone loss appears a common sequel to dental implant placement. Several hypotheses and clinical strategies have been advanced to explain and avert crestal remodeling; however, causative mechanisms remain unclear and the efficacy of clinical protocol uncertain.

OBJECTIVE

The objective of the present study was to provide a histologic record of crestal versus subcrestal implant placement on crestal remodeling and mucosal profile comparing platform shift/switch and standard abutments following flapless implant surgery using a dog model.

METHODS

Four dental implants each were placed into the left and right edentulated posterior mandibles in five adult male hound-Labrador mongrel dogs using a flapless approach including crestal versus subcrestal placement and using platform shift versus standard abutments. Block biopsies were collected for histological/histometric analysis following an 8-week healing interval.

RESULTS

Both crestal and subcrestal implant installation resulted in significant crestal remodeling and bone loss, in particular at buccal sites, without significant differences between platform shift/switch and standard abutments. Implants installed subcrestally exhibited a significantly taller mucosal profile over crestal-level implants without significant differences between platform shift/switch and standard abutments; the epithelial attachment at all times arrested on the abutment surface.

CONCLUSIONS

Comparing platform shift/switch versus standard abutments using a minimally invasive flapless approach including crestal or subcrestal implant placement, the platform shift/switch abutments offer no selective advantage over standard abutments.

Effect of Platform Shift on Crestal Bone Levels and Mucosal Profile Following Flap Surgery and Subcrestal Implant Placement in Presence/Absence of Gap Defects

BACKGROUND

Physiologic remodeling resulting in crestal bone loss appears a common corollary to dental implant surgery. Several hypotheses and clinical strategies have been advanced to explain and avert crestal remodeling; however, causative mechanisms remain unclear and the efficacy of clinical protocols uncertain.

PURPOSE

The objective of the present study was to provide a histologic account of crestal bone levels and mucosal profile at implant sites receiving platform shift/switch and standard abutments following conventional flap surgery and subcrestal implant placement in presence or absence of crestal gap defects using a dog model.

MATERIALS AND METHODS

Four dental implants were placed into the left/right edentulated posterior mandible in five adult male Hound Labrador mongrel dogs using flap surgery including subcrestal placement with/without a 1 × 5 mm (width × depth) gap defect, and using platform shift/switch and standard abutments. Block biopsies were collected for histological/histometric analysis following an 8-week healing interval.

RESULTS

No significant differences in crestal resorption were observed among experimental groups; crestal resorption being significantly more advanced at buccal than at lingual sites (p < .001). Similarly, crestal bone-implant contact was not significantly different among groups; crestal bone-implant contact being consistently below the implant platform at buccal sites (p < .01). Moreover, the peri-implant mucosal profile was not statistically different among groups, the mucosal height being significantly greater at buccal than at lingual sites (p < .001). Also, no significant differences among groups were observed for the apical extension of the epithelial attachment, the epithelial attachment being arrested more than 2 mm above the implant platform at both platform shift/switch and standard abutments.

CONCLUSIONS

Using a clinical strategy including flap surgery and subcrestal implant placement, implant technology comparing platform shift/switch with standard abutments, surgical approach, and abutment selection seems to have a limited impact on crestal remodeling, associated bone loss, and mucosal profile.

Effect of Platform Shift/Switch and Concave Abutments on Crestal Bone Levels and Mucosal Profile following Flap and Flapless Implant Surgery

BACKGROUND

Crestal remodeling/bone loss appears to be a common sequel to dental implant placement. Several hypotheses/clinical strategies have been proposed to explain/avert crestal remodeling; however, causative mechanisms remain unclear and the efficacy of these clinical approaches uncertain.

OBJECTIVE

The objective of the present study was to provide a histological account of crestal bone levels and mucosal profile at platform shift/switch and concave abutments following flapless and conventional flap surgery and subcrestal implant placement using a dog model.

METHODS

Four dental implants each were placed in the left/right mandibular posterior jaw quadrants in five adult male Hound/Labrador mongrel dogs using flap surgery with a 1 × 5 mm gap defect or using a flapless approach, both involving placement 2 mm subcrestally and platform shift/switch versus concave abutments. Block biopsies for histological/histometric analysis were collected at 8 weeks.

RESULTS

No significant differences were observed regarding crestal bone levels, with all groups showing mean bone levels above the implant platform. Similarly, crestal bone-implant contact was not significantly different among groups. Moreover, peri-implant mucosal profiles were not statistically different among groups for buccal sites; average mucosal height reached 4.1 to 4.9 mm above the implant platform. Comparison between buccal and lingual sites showed a nonsignificant tendency toward greater crestal resorption at buccal sites, adjusting for other factors. Mean crestal bone-implant contact level approximated the implant platform for lingual sites while consistently remaining below the platform at the buccal sites. Peri-implant mucosal height was significantly higher at buccal than at lingual sites, with the epithelial attachment located a significant distance away from the implant platform at buccal sites.

CONCLUSIONS

The surgical approaches (subcrestal implant placement by flap surgery or a flapless approach) and abutment designs (platform shift/switch or concave) used in this study seem to have a limited impact on crestal remodeling, associated bone loss, and mucosal profile. Bioclinical strategies should be developed to circumvent the limitations of current clinical protocol.