REVIEW ARTICLE |
https://doi.org/10.5005/jp-journals-10015-2358 |
Systematic Review on Hydroxyapatite and Chitosan Combination-coated Titanium Implants on Osseointegration
1,2Department of Prosthodontics, Saveetha Dental College; Saveetha Institute of Medical and Technical Sciences, Saveetha University (Deemed to be University), Chennai, Tamil Nadu, India
3Nanobiomedicine Lab, Centre for Global Health Research, Saveetha Medical College and Hospitals, Saveetha Institute of Medical and Technical Sciences, Saveetha University, Chennai, India
4Department of Pharmacology, Saveetha Dental College; Saveetha Institute of Medical and Technical Sciences, Saveetha University (Deemed to be University), Chennai, Tamil Nadu, India
Corresponding Author: Dhanraj Ganapathy, Department of Prosthodontics, Saveetha Dental College; Saveetha Institute of Medical and Technical Sciences, Saveetha University (Deemed to be University), Chennai, Tamil Nadu, India, Phone: +91 9841504523, e-mail: dhanarajmganapathy@yahoo.co.in
Received: 09 December 2023; Accepted: 10 January 2024 Published on: 20 February 2024
ABSTRACT
Aim: To systematically examine existing scientific literature to assess the effectiveness of hydroxyapatite (HA) and chitosan (CS) combination coatings on titanium (Ti) implants.
Background: Osseointegration is the key to success of dental implants. Ti alloy is widely used for its biocompatibility, ductility, and strength. HA and CS-coated Ti implants showed improved osseointegration. HA and CS have their own merits and demerits. The high elastic moduli of Ti alloys used in dental implants induce bone resorption, causing alveolar bone remodeling due to insufficient stress stimulation on bone tissue, leading to implant failure. Also, Ti alloys are highly susceptible to bacterial growth due to their reduced osteoconductive and osteoinductive property. To combat the abovementioned disadvantages, various surface modifications, biofunctionalization, and texture fabrication in combination with antibacterial nanoparticles have been performed on Ti alloys.
Materials and methods: The search strategy was carried out in PubMed, Cochrane Library, Scopus, Web of Science, and Google Scholar with no language and date of publication restriction to identify experiments that compared the osseointegration of HA-coated and CS-coated Ti dental implants. All in vitro and in vivo studies comparing the same were included. RoBDEMAT and SYRCLE’s risk assessment tools were used to evaluate the risk of bias (RoB) for in vitro and in vivo studies.
Review results: A total of 73 articles were obtained. On removing the duplicates and screening for title and abstract, three full-text articles were then assessed for eligibility criteria. Two were excluded for not satisfying the inclusion criteria. One article which remained also does not adhere to strict eligibility criteria. However, it compared the HA/CS complex-coated Ti dental implants with different porosities. RoB was found to be moderate for the in vitro and in vivo experiments of the included article. In vitro and in vivo assessments that compared the effect of HA/CS complex-coated porous Ti dental implants showed improved osseointegration than nonporous, noncoated solid Ti dental implants.
Conclusion: Enhanced osseointegration was observed in the HA and CS complex-coated porous Ti dental implants, potentially improving implant success in compromised bone. Further extensive human trials are necessary to fully validate these findings across diverse clinical scenarios.
Clinical significance: Excellent osseointegration of HA and CS complex-coated porous Ti dental implants can facilitate successful implant placement and improved performance in compromised and porous bone.
How to cite this article: Duraisamy R, Ganapathy D, Shanmugam R, et al. Systematic Review on Hydroxyapatite and Chitosan Combination-coated Titanium Implants on Osseointegration. World J Dent 2024;15(1):79–86.
Source of support: Nil
Conflict of interest: None
Keywords: Chitosan, Coated, Dental implants, Hydroxyapatite, Osseointegration, Titanium.
INTRODUCTION
Titanium (Ti) and Ti alloys, with their good biocompatibility, high corrosion resistance, increased ductility, and strength, have been widely used for dental implantation.1 Osseointegration, a key success in dental implantation, occurs when metals contact living bone tissue without forming any fibrous capsule. A thin oxide layer (20–50 nm) between living bone tissue and Ti alloy, into which growth factors are released, is vital in initiating bone formation.2 Formation of this thin layer depends on the cascade of four processes such as hemostasis, inflammation, proliferation, and bone remodeling.3 However, the degree of implantation confides in the characteristics of alloy, surgical technique, bone quality/quantity, and occlusal loading.
Two types of Ti alloys, namely cpTi and Ti-6Al-4V, with high modulus of elasticity (103–110GPa) compared to cortical bone (12.6–21GPa) and cancellous bone (0.5–3.5GPa) share the stress transmitted to bone tissue enhancing osseointegration.3 This high elastic moduli induces bone resorption, causing alveolar bone remodeling due to insufficient stress stimulation on bone tissue, leading to implant failure. Also, Ti alloys are highly susceptible to bacterial growth due to their reduced osteoconductive and osteoinductive property. To combat the abovementioned disadvantages, various surface modifications, biofunctionalization, and texture fabrication in combination with antibacterial nanoparticles have been performed on Ti alloys.4,7 Recently, various natural and synthetic polymers that resemble the extracellular matrix of bone physically, chemically, and biologically that enhance osteoconductive and osteoinductive effects are being experimented with.8,10 These polymers imitate the physiological functions of native tissue, facilitating cell-cell interaction and cell-matrix interaction.11,13
Hydroxyapatite (HA) (Ca10(PO4)6(OH)2, is a calcium phosphate compound that makes 98% of enamel, 77% of dentin, 70% of cementum, and 60–70% of bone by weight. HA with osteoconductive property when coated to Ti implant, a bioinert material makes bone grow toward Ti only in the direction of bone bed which is known as implantopedal.14 Also, bone grows directly on HA and from the bone bed, which is termed implantofugal.15 HA adsorbs more proteins from the bloodstream, which in turn improves osteoblast proliferation, producing a stronger bond between host bone and implant.16 HA coatings limit the formation of fibrous membranes in the bone-implant interface and convert fibrous membranes into bony anchorage.17,18 The common techniques used to apply HA coatings to Ti dental implants are plasma spraying technique and electrochemical deposition. Electrochemical deposition showed homogenous thin coating and increased surface roughness compared to the plasma spraying technique.19 However, due to its low intensity and high brittleness properties, there is a high chance of HA detaching from the implant surface.
Chitosan (CS) (1-4,2-amino-2-deoxy-D-glucan) is a natural polysaccharide found on the exoskeleton of insects, cell walls of fungi, and yeast, shrimps, lobsters, prawns, squids, and marine crustaceans.20,21 This second common natural polysaccharide after cellulose is derived from chitin by particle deacetylation (DDA) process.22 Recently CS has gained its attention in different biomedical applications such as soft tissue regeneration, bone regeneration, wound healing, drug delivery, and infection control.23 CS has varying degrees of deacetylation, viscosity, and molecular weight.24 Of which marine-derived CS is found to be effective for surgical, dental, reconstructive plastic surgery, and orthopedic purposes. CS has been widely used in the biomedical field for its biodegradable, biocompatible, antimicrobial, anti-inflammatory, and osteoconductive properties.25,26 A methylpyrrolidinone-modified CS has been found to be effective in osteoconduction and the formation of new bone in wisdom tooth avulsions.27 As Ti alloy implant surfaces are rich in oxide and hydroxyl groups, silane reactions have been successfully used to chemically bond CS films to implant surfaces to increase coating-substrate fracture resistance.28 It has been reported that a high DDA CS exhibited higher alkaline phosphatase (ALP), RUNX2, osteocalcin, and osteonectin expressions, enhancing biomineralization and osteoblast formation.29
Osseointegration, the crucial connection between living bone and an artificial implant, is essential for the stability of dental implants. HA and CS are known for their biocompatibility and bone growth stimulation. Coating Ti implants with these materials is intended to enhance osseointegration by encouraging quicker and more efficient bone healing and integration with the implant’s surface. This systematic review is driven by the continuous pursuit of improving the success and endurance of dental implant procedures. This inquiry is crucial as it may provide valuable insights into improving dental implant performance, potentially leading to better patient outcomes, decreased failure rates, and overall improvements in oral health. Understanding how effective these coatings are in promoting osseointegration is pivotal for advancing dental implant technology and elevating the quality of dental care for patients.
This study aims to systematically examine existing scientific literature to assess the effectiveness of HA and CS combination coatings on Ti implants. The research aims to conduct a thorough analysis of current evidence on how these coatings impact dental implant success rates, the speed of osseointegration, and the long-term stability of implants in the mouth.
MATERIALS AND METHODS
Protocol
The protocol for this review was framed according to Preferred Reporting Items for Systematic Review and Meta-analyses (PRISMA) 2020 guidelines.30 The review question was rooted according to the Participants, Interventions, Control and Outcome (PICO) basis.
Research Question
Are HA and CS-coated Ti endosseous implants more effective in promoting osseointegration than noncoated Ti endosseous implants?
Eligibility Criteria
Inclusion Criteria
In vitro and in vivo studies that compared the effect of the combination of HA-coated and CS-coated Ti dental implants, which measured osseointegration either by living or dead cell vitality assay, ALP activity assay, scanning electron microscope analysis, and histological analysis, were included. All full texted articles with no language and date of publication restriction were included.
Exclusion Criteria
Studies evaluating the effects of other combination coatings of HA were excluded. Similarly, CS and HA coatings over ceramic and polymer implants were excluded. Case reports and reviews were excluded.
Source and Search Strategy
The search strategy for this review was carried out in PubMed, Cochrane Library, SCOPUS, Web of Science, Google Scholar, and trial registries with no language restriction and date of search restricted to from June 1980 to 2023. PICO was formulated for the study as follows:
- Population (P): Ti dental implants.
- Intervention (I): HA and CS surface coating.
- Comparison (C): Nonsurface coating.
- Outcome (O): Osseointegration.
The keywords and MeSH terms for the PICO were all combinations of implant surface coatings, Ti dental implants, CS coated, HA-coated, and osseointegration with suitable Boolean operators are presented in Table S1. A hand search was done in addition to the electronic search, and no additional articles apart from the ones identified in the electronic search were detected.
| Serial number | Search details | Results |
|---|---|---|
| 1 | “Dental implant*”[All Fields] OR “Titanium dental implant*”[All Fields] OR “Dental implant titanium”[All Fields] | 48,760 |
| 2 | “Dental implantation”[MeSH Terms] OR “Dental implantation, endosseous”[MeSH Terms] | 23,744 |
| 3 | “Dental implant*”[All Fields] OR “Titanium dental implant*”[All Fields] OR “Dental implant titanium”[All Fields] OR “Dental implantation”[MeSH Terms] OR “Dental implantation, endosseous”[MeSH Terms] | 48,776 |
| 4 | “Chitosan”[All Fields] OR “Chitosans”[All Fields] OR “Chitosan coated”[All Fields] | 42,090 |
| 5 | “Chitosan”[MeSH Terms] | 27,977 |
| 6 | “Chitosan”[MeSH Terms] OR “Chitosan”[All Fields] OR “Chitosans”[All Fields] OR “Chitosan s”[All Fields] OR “Chitosane”[All Fields] OR “Chitosan coated”[All Fields] OR ((“Chitosan”[MeSH Terms] OR “Chitosan”[All Fields] OR “Chitosans”[All Fields] OR “Chitosan s”[All Fields] | 42,090 |
| 7 | “Hydroxyapatite”[All Fields] OR “Hydroxyapatite coated”[All Fields] | 36,135 |
| 8 | “Hydroxyapatites”[MeSH Terms] | 22,500 |
| 9 | “Hydroxyapatite”[All Fields] OR “Hydroxyapatites”[MeSH Terms] OR “Hydroxyapatites”[All Fields] OR “Hydroxyapatite coated”[All Fields] | 36,135 |
| 10 | “Osseointegrate”[All Fields] OR “Osseointegrated”[All Fields] OR “Osseointegrates”[All Fields] OR “Osseointegrating”[All Fields] OR “Osseointegration”[All Fields] OR “Osseointegrative”[All Fields] OR (“Bone implant”[All Fields] | 26,916 |
| 11 | “Osseointegration”[MeSH Terms] OR “Bone implant interface”[MeSH Terms] | 11,367 |
| 12 | “Osseointegrate”[All Fields] OR “Osseointegrated”[All Fields] OR “Osseointegrates”[All Fields] OR “Osseointegrating”[All Fields] OR “Osseointegration”[MeSH Terms] OR “Osseointegration”[All Fields] OR “Osseointegrative”[All Fields] OR (“Bone implant interface”[MeSH Terms] OR (“Bone implant”[All Fields] | 26,916 |
| 13 | # 3 AND # 6 AND # 9 AND # 12 | 8 |
Study Selection
Two individual reviewers, on removing the duplicate articles, completely screened the obtained articles for eligibility. The title and abstract of the procured articles were then screened for inclusion criteria. Those articles not satisfying the inclusion criteria were excluded from the systematic review. Later, the full text of the leftover articles was evaluated for eligibility criteria considering the inclusion and exclusion criteria. Any disagreement on consensus was resolved by the third reviewer.
Data Extraction
Individual reviewers extracted the following data—country where the study had been performed, type of study, sample size, design and fabrication of Ti implants, surface morphology, mechanical properties of Ti implants, type of assay performed for osseointegration, follow-up, and inference. A third reviewer resolved any disagreements in the data extraction of the two individual reviewers.
Assessment of Risk of Bias (RoB)
Risk of bias (RoB) for in vitro studies was analyzed using RoBDEMAT,31 a tool for reporting preclinical research of dental materials studies that assess the RoB in vitro studies investigating properties of dental materials. This novel tool has a good interrater reliability agreement (Cohen’s κ = 0.81) and a good intraclass correlation coefficient (ICC = 1.00). The RoBDEMAT tool involves four domains such as:
- Domain 1 (D1): Bias related to planning and allocation.
- Domain 2 (D2): Specimen preparation.
- Domain 3 (D3): Outcome assessment.
- Domain 4 (D4): Data treatment and outcome reporting.
Each domain had two or three subdomains pertaining to the signaling questions. Each signaling question needs to be answered as either “sufficiently reported/adequate,” “insufficiently reported,” “not reported/not adequate” or “not applicable.”
Similarly, RoB for animal in vivo studies was analyzed using SYRCLE’s RoB tool for animal studies.32 This tool has six domains describing (1) selection bias, (2) performance bias, (3) detection bias, (4) attrition bias, (5) reporting bias, and (6) other biases. These domains are almost in agreement with the domains in the Cochrane RoB tool. The signaling questions in each domain were to be answered as either “yes”–indicating low RoB; “no”–indicating high RoB; “unclear”–indicating unclear RoB. If “no” has been answered for one relevant signaling question, it indicates a high RoB for that domain. The interobserver reliability evaluated using κ statistics showed values ranging from 0.59 to 1.00 for various domains.
RESULTS
Study Selection
On initial search through PubMed, Cochrane Library, Scopus, Web of Science, Google Scholar, trial registries, and hand search, a total of 73 articles were obtained. A total of 62 articles were removed before screening for eligibility criteria. Of about 12 duplicate articles, 37 were ineligible by automation tools based on PICO search, and 13 articles were removed for other reasons. On review of 11 articles for title and abstract, eight articles were excluded. Later, on assessing the full texts of the three remaining articles, two articles were excluded, considering the inclusion criteria. Though one included article did not strictly satisfy the inclusion criteria, Ti implant coated with HA and CS complex with different porosities had been included for qualitative synthesis in this review,32 as shown in Flowchart 1.
Flowchart 1: PRISMA 2020 study flow diagram
Studies with insufficient or unclear data on the effects of HA and CS coatings on osseointegration in dental implants, studies where the interventions or coatings used do not specifically involve HA and CS on Ti dental implants, studies with poor methodological quality, lack of control groups, or high RoB to ensure the reliability of the review’s findings, multiple publications from the same study, conference abstracts, and case reports due to their limited scope and potential lack of thorough methodology, studies that do not specifically address or evaluate the impact of HA and CS coatings on osseointegraion and studies that do not report outcomes related to the success rates, bone healing, integration, or long-term stability of dental implants with these coatings were excluded (Table S2).33,40
| Author | Year | Reason |
|---|---|---|
| Ansari et al.33 | 2020 | In situ synthesis and characterization of CS/HA nanocomposite coatings |
| Kim et al.34 | 2013 | Immobilization of bone morphogenic protein on nano-HA-coated Ti using CS chelating agent |
| Suo et al.35 | 2019 | Graphene oxide/CS/HA composite coating to enhance osseointegration |
| Yang et al.36 | 2018 | Assessed soft tissue integration and antimicrobial activity |
| Blanchemain et al.37 | 2017 | Dental implant for drug delivery |
| Wang et al.38 | 2021 | Hybrid coating with dopamine/zinc oxide/CS/nano-HA |
| Eftekhar Ashtiani et al.39 | 2021 | Endodontic endosseous dental implants |
| Elia et al.40 | 2015 | A different material (silk electrogel) |
Study Characteristics
Detailed characteristics of the included study32 were presented in Tables 1 and 2. The total sample size included for the animal experiment was six white male rabbits (two in each three groups). The weight and age of the rabbits ranged from 2.7 to 3.2 kg and 14–16 weeks, respectively. The in vitro study used cylindrical Ti6Al4V disks, and the in vivo experiment used Ti6Al4V thread implants. A combined solution of HA and CS was coated onto the different percentages of porous Ti using the electrochemical deposition method. Images of live/dead cell vitality assay and ALP activity assay were performed for in vitro examination; X-ray examination and histological analysis were performed for in vivo experiments. The follow-up period was 1, 3, and 7 days for in vitro and 4 and 12 weeks for in vivo experiments.
| Author | Study type | Sample size | Design and fabrication | Surface coating and morphology | Porosity |
|---|---|---|---|---|---|
| Zhang et al.,32 | In vitro | One sample in each group | Cylindrical Ti6Al4V disks with 20 mm diameter and 2 mm thickness | 1.98 gm of calcium nitrate. Four molecules of water and 0.66 gm of monopotassium phosphate were dissolved in distilled water, and 1 gm of CS powder was dissolved in 100 mL of 2% acetic acid. Two solutions were mixed and coated using an electrochemical deposition method | Cylindrical Ti6Al4V disks were used with Group I: 0% porosity Group II: 30% porosity Group III: 50% porosity |
| In vivo (animal experiment) | Six male white New Zealand rabbits of 2.7–3.2 kg, aged 14–16 weeks | Cylindrical Ti6Al4V implant of 3.5 mm diameter, 7 mm height, and 1.5% solid pillar diameter | 1.98 gm of calcium nitrate. Four molecules of water and 0.66 gm of monopotassium phosphate were dissolved in distilled water, and 1 gm of CS powder was dissolved in 100 mL of 2% acetic acid. Two solutions were mixed and coated using an electrochemical deposition method | Cylindrical Ti6Al4V thread implants were used with Group I: 0% porosity Group II: 30% porosity Group III: 40% porosity Group IV: 50% porosity |
| Procedure | Assay performed for osseointegration | Type of assessment | Follow-up | Inference | Limitation |
|---|---|---|---|---|---|
| Samples were inoculated with osteoblast-like MC3T3-E1 cells in α-modified Eagle medium containing 10% fetal bovine serum, 1% 100 U/mL penicillin, and 100 gm/mL streptomycin at a 37oC incubator, and 5% CO2 with change of medium for every 2 days | 1. Live/dead cell vitality assay using live/dead cell staining kit 2. ALP (ALP) activity using a protein assay kit |
1. Six images in different views for each disk. Images were analyzed with Image-Pro Plus 6.0 software (Media Cybernetics, Inc., Rockville, Maryland, United States of America) 2. Protein concentrations were measured with a bicinchoninic acid protein assay kit |
1. 1, 3 and 7 days of incubation 2. After 7 days, the absorbance values were measured at 520 nm with a microplate reader, and ALP activity was calculated accordingly with absorbance values |
1. The fraction of live cells was > 85%, with no significant difference between the three groups with respect to cell adhesion. Day 1—osteoblasts adhered to the surface and pillar of porous Ti with few cells in the inner walls of pores; day 3—cells on the surface proliferated and adhered to inner walls; and day 7—cell density increased to 90% 2. ALP activity of coated implant with porous surface was higher than that of noncoated implant |
This study drawback is the lack of detailed examination of the sample surface. To better understand the enhanced performance mechanism of this material, future experiments should employ energy-dispersive X-ray spectroscopy, X-ray diffraction, and attenuated total reflection Fourier-transform infrared spectroscopy to analyze the CS/HA composite coating |
Risk of Bias Assessment
Review authors’ judgment about RoB for in vitro and in vivo experiments was presented in Table 3 and Figures 1 and 2, respectively. The RoB of in vitro study using the RoBDEMAT tool showed bias in the planning and allocation of samples to experimental and control groups. RoB of in vivo animal experiments using SYRCLE’s tool showed an overall moderate RoB, as there was a high risk for selection bias. Since reporting of all signaling questions in each domain is qualitative, a summary score involves assigning “weights” to each specific domain, and it is difficult to justify the assigned weights. Thus, a summary score for RoBDEMAT and SYRCLE’s tool is not recommended.41,42
| Domain | Sources of bias | Signaling question(s) | Response |
|---|---|---|---|
| Bias in planning and allocation | Control group | Did the study employ one or more control groups (positive or negative or existing standard) in its experimental design? | Insufficiently reported |
| Randomization of samples | Was randomization adequately carried out and reported? | Not applicable | |
| Sample size rationale and reporting |
Did the study provide a rationale and justification for the sample size chosen or feature an a priori power analysis? | Not applicable | |
| Bias in sample and specimen preparation | Standardization of samples and materials |
Were samples and material choice/employment standardized according to the aim of the study? | Sufficiently reported |
| Identical experimental conditions across groups | Were the storage, experimental, or treatment conditions standardized across samples and materials? | Sufficiently reported | |
| Bias in outcome assessment | Adequate and standardized testing procedures and outcomes | Were testing procedures and outcome(s) measure(s) explained or defined in sufficient detail to allow reproducibility and critical appraisal? | Sufficiently reported |
| Blinding of the test operator |
Was the test operator blinded to the different experimental groups? | Not reported | |
| Bias in data treatment and outcome reporting | Statistical analysis | Was the statistical analysis adequate and reported in sufficient detail? | Sufficiently reported |
| Reporting study outcomes | Are all relevant outcome data expected to be reported and available in sufficient detail? | Sufficiently reported |
Fig. 1: Risk of bias (RoB) graph for in vivo (animal) experiment using SYRCLE’s tool
Fig. 2: Risk of bias (RoB) summary for in vivo (animal) experiment using SYRCLE’s tool
Quantitative Assessment
Quantitative assessment with meta-analysis was not performed in this review due to an inadequate number of included articles.
DISCUSSION
Nowadays, implants play a major role in rehabilitating the dentition defects. Of these, Ti implants possess a special place due to their good biocompatibility, high corrosion resistance, increased ductility, and strength. The success of a dental implant depends on osseointegration, which can be improved by surface coatings. HA, a bioinert material, has shown promising implantopedal and implantofugal characterization on its surface coating on Ti dental implants in both in vitro and in vivo analyses.43,46 Similarly, CS, a natural polysaccharide, has exhibited effective osteoinductive and osteoconductive properties with its surface coating on Ti dental implants.29,47,49 This systematic review thus aimed to compare the osteogenic potential of HA-coated and CS-coated Ti dental implants with Ti dental implants, CS-coated, HA-coated, osseointegration as PICO principle.
On electronic database and hand search, we came up with three articles on screening for title and abstract. Reviewing the full text of the three articles, two articles failed to satisfy the eligibility criteria. The remaining article also does not strictly adhere to the inclusion criteria. However, this article, which compared different porous Ti implants coated with a combined solution of HA and CS, has been included to review its osteogenic potential in vitro and in vivo experiments.32
In Vitro Experiment
Rhino three-dimensional (3D) modeling software (Robert McNeel & Associates, Seattle, Washington, United States of America) was used to design a 3D model of porous Ti with interconnected inner pores of diameter 400 µm. The porosity was adjusted to the experimental design with a pillar diameter of 300 µm. Cylindrical Ti6Al4V disks of 20 mm diameter and 2 mm thickness with 0, 30, and 50% porosity coated with HA and CS solution were used for the experiment. About 1.98 gm of calcium nitrate. Four molecules of water and 0.66 gm of monopotassium phosphate dissolved in distilled water and 1 gm of CS powder dissolved in 100 mL of 2% acetic acid were mixed and coated onto the Ti disks using the electrochemical deposition method.50
Osteoblast-like MC3T3-E1 cells in α-modified Eagle medium with 10% fetal bovine serum, 1% 100 U/mL penicillin, and 100 gm/mL streptomycin were inoculated on the surface of Ti disks under a density of 5 × 104 cells per disk. They were then incubated at 37oC of 5% CO2 in air. The medium has been changed every 2 days. On 1, 3, and 7 days of incubation, an 85% fraction of live osteoblasts were seen on 0, 30, and 50% porous Ti disks in six images of different views of each disk. These images were examined with Image-Pro Plus 6.0 software. The density of osteoblast cells increased by >90% in the surface and inner pores of the Ti disks.
Similarly, after 7 days, osteoblast cell differentiation on Ti disks detected with ALP activity assay showed a significantly increased activity on HA and CS-coated porous Ti disks than on solid noncoated titanium disks. The ALP activity was calculated according to absorbance values at 520 nm with a microplate reader using a bicinchoninic acid protein assay kit. To support this in vitro experiment, Cheng et al. found that MG63 cells on Ti implants were highly active and grew into pores of an imitated trabecular porous structure in computed tomography images. Also, one more experiment by Pattanayak et al. showed new bone formation on the inner pores of imitated porous implant stimulating osteoblast activity.53
In Vitro (Animal) Experiment
About six male white New Zealand rabbits of weight ranging from 2.7 to 3.2 kg and of age ranging from 14 to 16 weeks were selected for the experiment. After general anesthesia, two defects in the femoral condyle of 3.5 mm diameter and 7 mm depth were created. Cylindrical Ti6Al4V threaded Ti implants of 3.5 mm diameter, 7 mm height, and solid pillar diameter of 1.5 mm with 0, 30, 40, and 50% porosity were placed inside the defects and closed with a conventional suture. All rabbits were fed with a standard diet for 7 days.
The animals were sacrificed 4 and 12 weeks after surgery, and the samples of the implant with surrounding 1 cm of bone tissue were harvested and examined radiographically and histologically for osseointegration. An optical microscope was used to detect the osseointegration for histological analysis. A radiographical examination showed a normal implant angle with appropriate implant distance and well-healed surrounding bone with no fractures and fissures. Histological examination under low and high magnification at 4 weeks showed densely packed active osteoblasts in the pores and slender new trabecular bone. At 12 weeks of examination, it showed thick trabecular bone with dense clusters of active osteoblasts and no inflammatory cell infiltration. A similar animal experiment by Ding et al., who implanted porous Ti implant into rabbit radial bone, showed excellent osseointegration and vascularization.54 One other experiment by Munoz et al. using 37 and 47% porous Ti implant showed osseointegration like cortical bone and cancellous bone.55
Thus, a mixture of HA and CS-coated porous Ti dental implants showed promising osseointegration when compared to noncoated solid Ti dental implants.32 Although the normalized process of the systematic review was carefully conducted, since no articles strictly adhering to the eligibility criteria were found, we have been inducted to compare HA and CS complex coated Ti dental implants with different porosities, which is a main drawback of this systematic review. Also, we failed to search paid databases such as Embase, Ebsco, and Lilacs to compare HA and CS-coated Ti dental implant trials.
CONCLUSION
This systematic review inferred equal nontoxic and biocompatible behavior and superior osseointegration in coated porous Ti implants than the uncoated implants. The excellent osseointegration of HA and CS complex-coated porous Ti dental implants can facilitate successful implant placement and improved performance in compromised and porous bone. However, more extensive human trials are further needed to completely validate this inference in various clinical situations.
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