β-Tricalcium Phosphate as Alveolar Bone Grafting in Cleft Lip/Palate: A Systematic Review

1. Introduction

Trisomy 21, often known as Down Syndrome , is one of the most frequent orofacial congenital abnormalities worldwide [1]. The epidemiology of cleft lip, cleft palate, and cleft lip and palate (CL/P) related to Down syndrome has been recorded at roughly 1 in 700 per birth, but it has also been reported at 1 in 500 to 1 in 2,500 per birth in other parts of the world [2,3]. The prevalence of CL/P was estimated to be 10.8 million people in 2017, with a disease burden of 652.084 disability-adjusted life years, with low- and middle-income countries (94.1%) of this disease burden [4]. CL/P is highly common in the Asia area, particularly in Japan, China, and Indonesia, which are high-risk nations for CL/P [5,6,7].

CL/P is caused by a defect in palatogenesis during the embryonic phase. CL/P etiology is impacted by genetic, environmental, and a mixture of both factors. CL/P is shown clinically as a cleft in the lip, alveolar bone, palate, and nasal septum. The patients have cosmetic and functional deficiencies [8]. Lifetime costs, loss of productivity, lack of self-confidence due to facial, aesthetic, or cosmetic aspects, increased utilization of mental health services, speech and hearing impairment, risk of infection, and increased morbidity and mortality at all stages of life are all the negative impacts of CL/P on the individual and society. Furthermore, it may affect the oral health related quality of life of CL/P patients [9]. In individuals with CL/P, dental malformations are more prevalent due to anatomical abnormalities in the alveolar process. Approximately 83.3% of the individuals with CL/P had at least one dental anomaly, with tooth agenesis being the most prevalent abnormality observed. Furthermore, the group with unilateral CL/P had the greatest number of dental abnormalities [10]. These anomalies can create serious issues that can be avoided or mitigated by early detection and treatment.

The alveolar cleft volume increased with age in CL/P patients, which is related to an increasing breadth of the lip-palatal defect. Patients under the age of 18 had significantly higher rates of ipsilateral maxillary sinusitis, which may increase the risk of bone infection [11]. The optimal period for alveolar bone grafting (ABG), according to the European and North American Cleft Association, is before canine eruption. However, various concerns remain, including the nature of the surgical and orthodontic techniques, the kind of bone and donor location, and the optimum approach to managing the space in the dental arch. Although the most typical age range for performing a bone graft is between the ages of 8 and 11, some hospitals have started to perform alveolar bone grafts at a younger age in the expectation of achieving better outcomes for unerupted incisors. However, the impact of early ABG on maxillary development has yet to be determined. A variety of donor sites have been used, but the iliac crest remains the most preferred, although it may pose challenges for some patients with medical conditions. Prior to ABG, several teams used orthodontics to rectify significant segment displacement or to align incisors to facilitate surgical access. Following ABG, lateral incisor absence can be addressed by orthodontic space closure, implant implantation, or bridgework [12].

The ilium is the most typical location for ABG harvesting. Curettage, trapdoor or splitting procedures for cancellous bone, and the subcrestal-window approach for bicortical transplant are all ways of harvesting iliac ABG. However, potential consequences of using the ilium as a donor site may include discomfort, neurovascular damage, avulsion fractures of the ASIS, hematoma, infection, herniation of abdominal contents, gait impairment, cosmetic deformity, sacroiliac joint violation, and ureteral injury [13]. There is an option that may replace the autologous iliac crest for ABG with a xenograft or synthetic graft.

Rapid integration of ABG is crucial for achieving structural stiffness. Structural and nonstructural ABG procedures modify alignment, function, and appearance by adding length, height, and volume. Corticocancellous autografts, allografts, xenografts, and synthetic grafts are all kinds of ABG. Autogenic grafts, which are harvested from the patient, are less likely to be rejected. However, the harvesting process adds an additional step, and donor site morbidity is prevalent. Secondary operations and donor site problems are avoided with allografts, xenografts, and synthetic grafts [14]. Stringent regulations are projected to significantly limit the allograft industry in the future. The use of xenograft or synthetic ABG, such as Beta (β)-tricalcium phosphate (β-TCP), a bioceramic biomaterial, is expected to be promising and helpful for clinical results in CL/P therapy. β-TCP materials, followed by xenograft biomaterials, which regrettably still lack established predictability and clinical efficacy, dominate the cranio-maxillofacial market [15]. Despite numerous efforts made to investigate the ABG in the field of cranio-maxillofacial medicine, the regenerative prospect of β-TCP as ABG in CL/P has not yet been fully elucidated and remains limited. Therefore, the aim of this systematic review is to describe the regenerative prospect of β-TCP as an ABG material in CL/P based on existing literature.

2. Material and Methods

2.1. Focused Question

Following the Participants, Intervention, Control, Outcomes (PICO) principle, a focused question was formulated before conducting the literature search made according to Preferred Reporting Items for Systematic Reviews and Meta Analyses 2020 (PRISMA 2020). The focused question was: ‘Compared to autologous bone graft, does β-TCP as ABG stimulate the regeneration of CL/P or alveolar bone cleft defects?’

2.2. Search Strategies

A systematic review protocol based on PRISMA 2020 was drafted. In addition, reporting was based on the PRISMA 2020 checklist [16,17]. The following databases were searched: MEDLINE/ PubMed (https://pubmed.ncbi.nlm.nih.gov), Web of Science/ ISI-Web of Knowledge (https://www.webofscience.com/), Scopus (https://www.scopus.com/), and the Cochrane Library (https://www.cochranelibrary.com/advanced-search). Manual searches were undertaken to supplement the completed searches. Furthermore, the gray literature in The New York Academy of Medicine Gray Literature Report (http://www.greylit.org) and the European System for Information on Gray Literature (http://www.opengrey.eu) was screened [18]. Table 1 shows the search strategies in the selected databases.

2.3. Eligibility Criteria

The following categories of articles were included in this review: original articles that focused on the methodology of using β-TCP as an ABG in animal models or humans, to regenerate CL/P or alveolar bone cleft defects. Open access of full-text articles relevant to β-TCP ABG for CL/P or alveolar bone cleft defect were used as inclusion criteria. Reviews, short communication, editorial notes, processes, and recommendations were not considered. All types of experimental and observational studies in English were included. Nevertheless, no duplicate studies were included in the analysis. Adults or children of any gender or age are acceptable study subjects, as are any other objects of in vivo research. CL/P, alveolar cleft defect, β-TCP, and ABG, as well as any additional therapies involving tissue engineering, were included in the research as study factors or exposures. Bone regeneration, bone repair, bone volume, dentistry, bone remodeling, and any other measure of bone regeneration in CL/P were among the outcomes of the research examined. Articles in languages other than English, letters to the editor, and all types of reviews and commentaries were excluded. There were no restrictions on the year of publication, but only free accessed full papers. The most recent search was conducted in June 2023.

2.4. Study Selection and Data Extraction

The three reviewers (A.P.N, H.Y, J.C) independently conducted electronic literature searches and selected the studies. Any disagreements were resolved by discussion or by consulting a second reviewers (J.R.V. Sáenz, G.H) [16,17]. The reviewers (A.P.N, H.Y, J.C) worked to extract data using a standardized form in Microsoft Excel that had been validated prior to use [18]. Data was primarily extracted using the PICO protocol (Participants: patients (for clinical studies)/animals (for in vivo studies); Intervention: β-TCP ABG; Controls: Autograft / Xenograft or no treatment/other regenerative materials; Outcomes: bone regeneration or bone remodeling of CL/P or alveolar bone cleft defect; Data relevant to methodology, sample size, duration of the studies, and the investigations carried out were extracted from each study. Results from the animal (in vivo) and clinical studies were tabulated in the table using predetermined data collection forms by the two investigators independently [19].

2.6. Quality Assessment of Studies

Depending on the type, each study was assessed individually and independently by investigators. It was decided that for the quality assessment of any randomized clinical trials, Consolidated Standards of Reporting Trials (CONSORT) would be used. The Animal Research: Reporting of In Vivo Experiments (ARRIVE) guidelines were selected for animal studies. Any disagreements were solved by discussion.

2.7. Risk-of-Bias Assessment

The risk of bias evaluation was carried out in accordance with a technique derived from prior systematic reviews [16,17,20]. This assessment evaluated the description of several quality assessment parameters, including a well-defined β-TCP as ABG process, standardized sample or subject preparation, randomization of samples or subjects, tests conducted by a single blinded operator, a clear test method specification, and comprehensive reporting of results. The article was labeled "Y" for a given parameter if the authors reported it and "N" if the information could not be located. The articles were classified as having a high, medium, or low risk of bias based on the number of "Y" elements included (1-2, 3-4, or 5-6).

2.8. Statistical Methods

Microsoft Office Excel (2010, Microsoft) was used for descriptive statistics. Due to the heterogeneity of the papers, a pairwise meta-analysis could not be performed.

3. Results

3.1. Study Selection, Data Extraction, and Quality Assessment

The keywords yielded a total of 5824 articles publication, with 90 papers from Scopus, 6 papers from PubMed, 4510 papers from Web of Science and 1218 papers from the Cochrane Library, respectively. The 3196 suitable articles to evaluate after removing duplicates and languages. We had 1315 studies left after doing title and abstract reading. Eighty-five full-articles were assessed for eligibility. The read the complete texts of those papers and eventually chose 20 that matched the inclusion requirements. The reviewers (A.P.N, H.Y, J.C) independently performed critical evaluations utilizing JBI critical evaluation tools. Figure 1 depicts the flow diagram of the study selection process. The summary of descriptive characteristics of the articles included in this study shown in Table 2.

3.2. Assessment of the Risk of Bias and Quality

The reviewers read the complete texts of those papers and eventually selected 20 studies that met the inclusion criteria. Thirteen of the twenty studies included in this systematic review had a low risk of bias, one had a high risk of bias, and six had moderate bias. Most of the studies did not report the randomization, which is considered a potential source of bias (Table 3).

3.3. Qualitative Analysis

Figure 2 illustrates the possible mechanism of action when β-TCP was used in a tissue engineering approach as an alveolar bone graft in CL/P or an alveolar bone cleft defect. Most of the studies included in this systematic review were experimental studies using animal models of alveolar bone cleft defects that were representative of CL/P condition patients. There were fourteen studies using an alveolar bone cleft defect animal model. Six studies used dogs [28,30,31,35,37,40], five studies used rats [21,23,33,34,39], two studies used goats [36,38], and only one study used rabbits [25]. Only one research study claimed that the rat’s palatine fissure was an acceptable location for the bone substitute implant application of bone graft materials to replicate the human alveolar cleft in animal model studies of CL/P. In addition, the palatine fissure is a congenital bone abnormality comparable to the alveolar cleft abnormalities seen in people [33]. Nevertheless, the rest of the studies were successfully established and reported the research outcome for the alveolar bone cleft defect animal models. A preliminary or pre-clinical study using an animal model as a representative of CL/P conditions in patients is important before the clinical application of the proposed ABG in the clinical setting.

On the other hand, this systematic review also found several studies of β-TCP application in CL/P patients in a clinical setting, such as five articles of case-control clinical studies [24,26,27,29,32] and one article of a retrospective cohort study [22]. Most clinical setting studies of CL/P focused on unilateral alveolar cleft [24,26,27,29,32]. However, only one study used the unilateral or bilateral cleft patients as the study participant in the retrospective study setting [22]. The most frequent prevalence of CL/P type in patients was unilateral alveolar cleft. Out of the 20 articles included in this systematic review, six articles also investigated the potential impact of alveolar bone graft (ABG) application on orthodontic treatment [21,24,32,34,35,36,37]. β-TCP is a more biocompatible alternative to autogenous bone transplantation for orthodontic tooth movement in alveolar bone cleft abnormalities [35]. Other earlier research has found that the use of β-TCP does not impair orthodontic treatment [32,36,37].

In terms of bone regeneration of CL/P or alveolar bone defect cleft, autologous bone graft is considered the gold standard, as indicated by several studies [23,33,34,39]. Most of the studies used the autologous bone graft from hip bone [21], iliac crest bone [22,26,31,36,37,38,40] tibia bone [28,30], particulate marrow and cancellous bone [35], mandibular symphysis bone [27,32]. However, two articles not use any gold standard ABG in animal models, or as control groups [24,25]. Autograft and xenografts seemed to be interchangeable terms, after more tissue engineering adjustments, synthetic β-TCP and HA might be used as an alternative ABG [21]

Some studies suggested β-TCP, which is a bioceramic, as an ABG for bone regeneration in CL/P or alveolar bone cleft defects. Notwithstanding, β-TCP alone cannot substitute the autologous ABG [21]. The result of a previous study found a lower bone volume (BV) and bone mineral density (BMD) after β-TCP application compared to autologous ABG [33]. β-TCP may be able to overcome its lack of osteoinductive and osteoconductive qualities after undergoing many physical changes or the inclusion of certain stem cells or growth factors. There are several modifications of β-TCP as the alternative ABGsuch as combination of rhBMP2 in a β-TCP scaffold [22], AMSCs seeded in β-TCP [23,28], BMSCs or BMMNSCs combined with β-TCP granule [26,31,37,40]. β-TCP in microporous [24,29,30], composite xenogeneic dentin with β-TCP [25], the mixture of autologous ABG in β-TCP granules [27,32,38], combination of HA-β-TCP [34], col/ β-TCP scaffolds, and PLLA/PCL scaffolds [39]. Even though autografts are the best option for bone regeneration, tissue-engineered β-TCP might be a viable alternative, particularly if autografts are hard to come by or there is donor site morbidity [30]. Thus, it may decrease the surgical pain and the number of hospital stay days [26].

Various examination methods are proposed to investigate the efficacy of β-TCP as ABG in the clinical setting or pre-clinical research, such as µCT, histology analysis, CBCT, RT-qPCR, occlusal digital radiography, and densitometry with computer-aided software. µCT was used to examine BMD, BV/TV, BF, defect size, Hounsfield unit, bone quality, trabecular thickness of bone, mineralized matrix formation, and bone mineral content [21,23,25,33,34,38,39,40]. Several important osteogenic biomolecular markers, such as Runx2, OSC, SPARC, BSP, ALP, and Osx mRNA, can be analyzed by RT-qPCR [39]. Histopathology analysis was conducted to investigate several biomarkers within the tissue, such as lamellar bone and woven bone21, runx2, ALP, Osx, BMP2, TRAP expression, osteoblast and osteoclast number, tooth movement, and root resorption, bone formation (%), residual graft (%), collagen regeneration (%), and defect area healing (%) [23,25,28,30,33,34,35,36,37,39,40]. The CBCT instrument can be used to investigate preoperative defect volume, postoperative residual defect volume, and bone formation. Residual calcified tissue, spontaneous eruption of the canine/lateral incisor, continuous alveolar process, residual oronasal fistula, BV/TV, BFR, bone union, Chelsea scale Tb.Th, Tb.N, Tb.Sp, TBPf, SMI, FD, cleft volume pre-operation, graft volume post-operation [21,24,25,27,29]. Conventional dental occlusal radiographs have been used to analyze height of the bone graft, alveolar height and eruption disturbance, bone deposition, repaired alveolar cleft, and residual alveolar height (%) [31,32,35,37]. In addition, bone density examination can be investigated by mean of densitometer software with digital radiography [28]. Direct observation, such as duration of hospital stay may useful to know the efficacy of ABG administration in CL/P [25]. Those various examination methods help to elucidate the β-TCP as ABG in the CL/P patients or alveolar bone cleft defect in vivo.

4. Discussion

The objective of alveolar cleft repair is to reconstruct bone volume and quality to match the original anatomy. The accompanying soft-tissue attachment of the oral and nasal mucosa is specific to these cleft abnormalities [21]. This systematic review aimed to provide a summary of existing research on the regeneration possibility of β-TCP as ABG in cleft lip and palate patients or alveolar bone cleft defect animal models, assessing the success or failure of these interventions. Overall, the findings of this comprehensive analysis show that the use of β-TCP as ABG improves the regeneration of alveolar bone cleft defects in CL/P humans or animal models (in vivo) [21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40].

Nevertheless, a downside of β-TCP alone cannot substitute the golden standard of ABG which is autologous bone graft [33]. Autologous bone remains the gold standard for cleft repair. However, autografts have certain drawbacks, including restricted bone supply, the requirement for an extra donor site, the accompanying postoperative morbidity (pain, hematoma, and delayed ambulation), and an intrinsic sensitivity to resorption in the long run [21]. Therefore, different tissue-engineered bone replacements have been proved to be effective options for encouraging bone fusion and minimizing donor site morbidity. The β-TCP is a bioceramic, a synthetic ABG described, and has been recognized to be an alternative to autologous or xenograft ABG, which is acceptable in numerous terms and situations [30]. β-TCP with tissue engineering modification eliminates the limits of autologous bone grafts, such as limited donor supply and donor site morbidity, and minimizes the patient’s surgical stress, which may be connected to a decreased operating time and hospital stay duration reported [25].

For establishing appropriate β-TCP resorption characteristics, the optimal balanced ratio of HA and β-TCP varies between 65:35 and 55:45[41,42]. Some MSCs such as AMSCs or BMSCs may boost the bone regeneration ability of β-TCP [23,26,28,31,37,40]. In addition, the alteration of β-TCP’s shape or combination with growth factor, substance or collagen is also promising for enhancing the osteoinductive and osteoconductive potential of β-TCP [22,24,25,27,29,30,32,38,39]. To date, research has not been carried out to examine the ideal qualities of β-TCP. Additionally, there is a limited study that has investigated the clinical effectiveness of β-TCP [22,24,26,27,29,32].

Animal research included in this comprehensive review demonstrates that β-TCP stimulates bone regeneration in CL/P or alveolar bone cleft defects [21,23,25, 28, 30,31,33- 40.] In addition, most of these studies examined the efficacy of the β-TCP and presently utilized therapies such as hip bone, iliac crest bone, tibia bone, particulate marrow and cancellous bone, and mandibular symphysis bone (all of which have been used clinically) [21,22,26,27,28,30,31,32,35,36,37,38,40]. Nevertheless, this present study discovered in those two articles that there was no gold standard for ABG usage within the research [24,25]. Therefore, future animal studies should evaluate the in vivo effectiveness of β-TCP with the aforementioned materials and methodologies before being approved in clinics.

Regarding the post-operative or post-treatment examination of newly produced bone or bone regeneration, the majority of the included research employed CBCT for clinical investigations and micro-CT or HPA for in vivo studies. We found that five studies used CBCT to examine bone regeneration in post-operative CL/P patients and four studies used conventional dental occlusal radiograph [31,32,35,37]. CBCT scans provide a reduced radiation dosage, a limited scanning time (10–70 s), and allow doctors to scan a small region for a specific diagnosis with fewer picture artifacts [43,44,45]. Orofacial cleft patients require a 3D study for the right diagnosis as they present with numerous medical disorders, including bone graft operations, impacted teeth, or supernumerary teeth. This is the reason why CBCT is advised for orofacial cleft patients by the European Academy of Dental and Maxillofacial Radiology [46]. Therefore, additional research should employ CBCT as an evaluation technique to quantify newly produced bone, especially in clinical situations. Thus, the registration of the protocol is encouraged and will strengthen its robustness in subsequent studies. Although systematic reviews are regarded as the most solid evidence, the research included in each systematic review also has a related bias. The methodological variability includes discrepancies in the trial locations, a lack of a priori acceptable sample size estimates, the kind of sample included (e.g., type of cleft, age groups), intervention protocols, bone measuring techniques, and follow-up timeframes. Other factors may alter the analysis of primary outcomes as they affect bone remodeling, notably the location of teeth on the bone graft, the cleft defect’s breadth, and the volume of grafted bone [47]

The most apparent source of autologous ABG would be the iliac crest bone, which may be retrieved by a surgical procedure with a risk of morbidity, such as infection. However, employing this option in every circumstance would not be practicable, and a synthetic ABG such β-TCP would be more sensible [21,30,31,32]. In the research evaluated, there were various constraints that may have biased outcomes. With the information currently available from in vivo and clinical studies, the overall effect summary of β-TCP as ABG for CL/P or alveolar bone cleft defect cannot be determined. Furthermore, these findings should be regarded with caution since clinical and in vivo methodological heterogeneity might alter the extent of the statistical heterogeneity revealed. This systematic review found multiple heterogeneity variables, such as the number of participants or samples, kind of cleft defect, different treatment, timing of outcome, and intervention design. In the present review, we noticed that six of the studies did not apply any type of randomization [22,24,27,28,29,32]. A lack of randomization may have altered the direction of results due to examiners’ bias.

The primary results may also be altered by the clinician’s skill and the study group's scientific competency. Secondarily, most selected studies were classified as having poor or middling overall quality, which may lower the findings’ confidence [47]. Moreover, the included studies might overstate the impact of the findings due to the inclusion of numerous publications from a single research project or by ignoring studies in other languages. In this systematic review, the majority of the studies employed a small sample size. In addition, varied and diverse criteria for CL/P patient selection could have had an impact on the estimated efficacy of β-TCP as an ABG. Nevertheless, there is no gold standard for alveolar bone cleft defect size in animal models. Because of the variability in the techniques, measurements, and findings, it was not possible to do a meta-analysis in this systematic review. A systematic review without meta-analysis may carry a substantial risk of bias. This was likely the most major shortcoming of our review, as the mean overall effectiveness of β-TCP could not be calculated. Future studies should conduct blinded RCTs to control various sources of bias, such as the randomization technique, assessment equipment, and follow-up timeframes. Moreover, the cost-benefit analysis of these β-TCP to be employed in tissue engineering procedures for regeneration strategies in the ABG of CL/P is advocated as it plays a vital role in healthcare regulation.

5. Conclusions

The following findings may be drawn from this systematic review:

• β-TCP as ABG is biocompatible, more visible and practical, offers a less invasive procedure, and does not interfere with orthodontic treatment.
• β-TCP as synthetic ABG can be the alternative to autologous bone grafts with several terms and conditions, such as if autografts are hard to come by or there is donor site morbidity, and the size of the defect restricts the size of the autograft.
• Enhancement of osteoinductive and osteoconductive abilities for improvement of β-TCP efficacy for ABG in CL/P or alveolar bone cleft defects can be done by a tissue engineering approach combining β-TCP with growth factor, mesenchymal stem cells, or other graft materials and modification of β-TCP physical properties.

However, due to several research gaps concerning the original studies’ methodological quality and lack of findings, conclusions should be regarded with care.