Bony bridge resorption after secondary alveolar grafting and correlation with success of orthodontic treatment: A prospective volumetric cone beam computed tomography (CBCT) study

Abstract

Background

Cleft lip/palate is the second most observed congenital defect which constitutes a serious dental–medical–social problem. Successful uptake and stability of alveolar graft is required to achieve closure of the oro-nasal fistula and continuity of the dental arches. Resorption of bone graft may compromise the results achieved. This study determined the bony bridge volume required for successful repair of alveolar cleft, evaluated the resorption after 3 months of grafting and correlated the success of orthodontic treatment.

Methods

30 patients with unilateral cleft lip and palate requiring secondary alveolar bone grafting and orthodontic correction were included in the study. After arch expansion and before alveolar grafting using cone beam computed tomography (CBCT) of maxilla was recorded and was repeated after 3 months of alveolar bone grafting to estimate the volume of grafted bone in the cleft.

Results

The bridge bone volume resorption after 3 months post-operative ranged from 14% to 100% with a mean of 36.46%. The percentage of resorption of alveolar bone graft after 3 months of surgery was statistically significant. Success of orthodontic treatment was statistically significant when correlated with percentage of resorption.

Conclusion

The accurate localization and estimation of the size and extent of alveolar cleft area is important for treatment planning. Post-operative it is important to analyze the outcome of transplanted bone as early as possible. Early evaluation can help to predict the outcome of transplanted bone and may guide to re-grafting of the site immediate or to restart any interrupted orthodontic procedure, if necessary.

Introduction

Cleft lip and/or palate is a congenital birth defect characterized by complete or partial clefting of the lip and/or the palate. Amongst various congenital malformations, cleft lip and palate (CLP) is one of the most commonly reported anomalies. CLP is the second most observed congenital defect which constitutes a serious dental–medical–social problem with significant impact on self-esteem and the quality of life.¹ Alveolar bone grafting (ABG) is an essential step in the overall management of patient with CLP to improve the morphology and function.^{2, 3, 4} The objectives of ABG are to stabilize the maxillary arch, to provide bony support for the teeth adjacent to the cleft, support the lip and nose, to restore facial symmetry and to close the residual oro-nasal fistula. Although there is no dilemma on the need for alveolar grafting, but controversy exists on timing of the alveolar bone grafting. The two common options regarding the timing of bone grafting are (1) primary alveolar bone grafting and (2) secondary alveolar bone grafting. Primary alveolar bone grafting is carried out in infants at the time of initial lip and palate repair, while secondary grafting is done in mixed dentition after transverse growth of maxilla is over. Secondary alveolar bone grafting has been accepted as a means of uniting and stabilizing the segments of maxilla prior to definitive orthodontic and restorative dental treatment.³ The bone used for grafting procedure is commonly harvested from iliac crest, calvarium, rib or tibia. Regardless of the donor site, cancellous bone is preferable to cortical or osteochondral grafts.⁵

Various methods have been employed to determine the success of graft in providing bony support for the teeth adjacent to the cleft. Different imaging methods have been used to define the real extension of alveolar and palatal defects and the amount of bone graft necessary to restore oral clefts. The increasing use of volumetric imaging examinations in dentistry has enabled a better understanding of the morphologic structures aiding diagnosis and treatment planning.^{6, 7} Various methods have been employed to evaluate the success of alveolar grafting such as clinical examination, conventional intraoral/extraoral radiography and cone beam computed tomography (CBCT), the newer three dimensional (3D) imaging technique.⁸ The conventional plain films has inherent disadvantage of 2-dimensional radiography and thus failure to assess the changes in volume, morphology and architecture of the bony bridge.⁹ CBCT used in 3D imaging diagnosis and treatment planning is clearly superior to plain radiography.⁸ Recently the use of 3D reconstructed images associated with a navigation system improved pre-operative assessment and evaluated results of the alveolar graft procedure along time using linear and volumetric measurements of the clefts.¹⁰

Successful uptake and stability of alveolar graft is required to achieve closure of the oro-nasal fistula and continuity of the dental arches. However, resorption of the bone graft may compromise the results achieved. It is important to post-operative analyze the outcome of bone grafting as early as possible, because the age suitable for bone grafting and orthodontic procedures is limited.

The purpose of this prospective study was to determine the bony bridge volume required for successful repair of alveolar cleft among the patients with unilateral cleft lip and palate, to evaluate the percentage of resorption after 3 months of alveolar grafting using CBCT and to correlate resorption of alveolar graft with the success of orthodontic treatment.

Materials and method

The present prospective study involved selection of patients with unilateral complete cleft of lip and palate (UCLP) who has not received secondary alveolar bone graft. The study was carried out after a formal approval from the ethical committee of the institution. All patients and/or their parents were informed about the purpose of this study and a written consent was obtained.

Inclusion criteria:

• 1.Patients with isolated unilateral cleft lip and palate (UCLP) who have not undergone alveolar grafting procedure.
• 2.Patients with unerupted maxillary permanent canine in the cleft region.

Exclusion criteria:

• 1.Patients with bilateral cleft lip and palate (BCLP).
• 2.Patients with associated syndrome.
• 3.Patients with missing permanent maxillary canine or maxillary canine already erupted in the cleft region.
• 4.Patients requiring concomitant Orthognathic surgical procedure.

The study started with enrolment of 30 patients, all patients had unilateral cleft lip and palate and required secondary alveolar bone grafting and orthodontic correction. Patients had undergone two-step surgical technique of cleft repair. The lip had been repaired between 3rd and 6th month of life and soft palate had been repaired between 12th and 30th month of life by a pedicel flap.

Pre-treatment records (Fig. 1) were made in the form of digital photographs. Pre-surgical orthodontics was initiated for patients to facilitate the grafting procedure. A rigid arch wire (17″ × 25″SS) was in position at the time of surgery to stabilize the segments. Care was taken not to push the teeth adjacent to the cleft area into the cleft and to maintain the space for tooth to erupt through the graft. The patients requiring maxillary arch expansion to express the complete extent of alveolar cleft were given Nickel Titanium palatal expander to achieve the same. The expanded maxillary arch was stabilized using 0.9 mm palatal stabilizing arch. Preoperative alveolar cleft volume was measured after arch expansion before alveolar grafting using CBCT (I CAT Cone-Beam 3-D Dental Imaging System; Imaging Sciences International, Hatfield, PA, USA) (Fig. 2). The CBCT data was stored in Digital Imaging Communication in Medicine (DICOM) format to allow generation of volumetric images recording the extent of alveolar cleft. Three dimensional images were generated using “Vitera” software (USA) and the volumetric assessment was calculated on these CBCT images.

Fig. 1.

Pretreatment photographs.

Fig. 2.

Pre surgical cone beam computed tomography (CBCT).

Alveolar bone grafting was performed by a team of Oral and Maxillofacial Surgeons, patients received secondary alveolar bone graft (ABG) with the particulate cancellous bone and marrow (PCBM) from the anterior crest of the iliac bone (ACIB) to eliminate the biases related to donor site. The surgical approach to the alveolar cleft repair was performed using the lateral sliding flap described by Boyne and Sands. The mean age of patient at the time of alveolar surgery was 11 years. No patient underwent concomitant Orthognathic surgical procedure along with grafting procedure.

Maxillary CBCT was repeated after 3 months of alveolar bone grafting to estimate the volume of grafted bone in the cleft (Fig. 3). Orthodontic treatment was resumed after 3 months of alveolar grafting to correct the position of permanent teeth. Attempt was made to guide the erupting tooth through the grafted area. The orthodontic treatment was considered successful if a tooth could be erupted through the graft (Fig. 4).

Fig. 3.

Post surgical cone beam computed tomography (CBCT).

Fig. 4.

At present photographs.

Statistical analysis

To evaluate the bony bridge resorption after 3 months, the paired Student's t-test was carried out with the aid of the computer software package SPSS ver. 16 (SPSS Inc, Chicago, III) and for evaluating correlation of percentage of resorption to the success of orthodontic treatment spearman rank correlation was calculated. Both analyses were treated as two-tailed tests with a significance level of 0.05.

Results

Assessment of Bony bridge volume resorption

The mean volume of alveolar cleft post expansion and before alveolar grafting was 1.1733 ± 0.23 cm³ (0.8–1.6 cm³). The volume of grafted bone at the end of 3 months post-operative was 0.75 ± 0.27 cm³ (0.0–1.2 cm³). The percentage of resorption for the bony bridge after 3 months post-operative ranged from 14% to 100% (mean 36.46%) (Table 1) (Graph 1).

Table 1.

Pre operative volume of cleft, post-operative volume of graft, % resorption, success of treatment.

Patient No	Sex	Side of cleft	Age at time of surgery	Pre operative volume (cm3)	Post operative volume (cm3)	% bone volume resorbed	Orthodontic treatment (clinical evaluation)
1	M	L	11	1.1	0.4	63	Not successful
2	M	L	10	0.9	0.3	66	Not successful
3	F	L	11	1.4	0.8	43	Successful
4	F	R	09	1.5	1.1	27	Successful
5	M	R	12	1.1	0.6	46	Successful
6	F	L	11	1.0	0.7	30	Successful
7	F	R	11	0.9	0.6	33	–
8	M	L	12	1.6	1.0	37	Successful
9	F	L	10	1.3	0.9	31	Successful
10	F	R	11	1.1	0.7	27	Successful
11	M	L	12	1.3	1.0	23	–
12	F	L	10	0.8	0.0	100	Not successful
13	M	L	11	1.5	1.1	27	Successful
14	M	L	12	1.3	0.7	47	–
15	M	R	13	1.6	0.9	44	–
16	F	R	10	1.4	1.1	21	Successful
17	F	L	11	1.2	1.0	16	Successful
18	M	R	11	0.9	0.5	44	Not successful
19	F	R	13	1.2	0.7	42	Successful
20	M	L	12	1.0	0.4	60	Not successful
21	M	L	13	0.8	0.5	37	Not successful
22	M	L	11	1.4	0.9	36	Successful
23	F	R	10	1.1	0.8	27	Successful
24	M	L	12	1.0	0.6	40	Not successful
25	F	R	11	0.9	0.7	22	Successful
26	F	L	13	1.4	1.2	14	Successful
27	M	L	13	1.2	0.9	25	Successful
28	F	R	11	1.3	1.1	15	Successful
29	M	L	12	0.9	0.6	33	Successful
30	M	R	11	1.1	0.9	18	Successful

Graph 1.

Comparison of pre & 3 months post-operative bridge bone volume.

Images were examined to determination of the location of maximum bone resorption, significant bone loss was observed in the bucco-palatal direction, whereas no change was noticed in the height of the transplanted bone. The post-operative (after 3 months of surgery) graft volume was compared with initial volume of the pre-operative cleft, evaluated with paired Student's t-test with p = 0.05. The results of the t-test showed the percentage of resorption of alveolar bone graft after 3 months of surgery to be statistically significant with p = 0.000 (t = 13.396 and df = 29).

Correlation of Bony bridge volume resorption with success of orthodontic treatment

As there were 04 dropouts from the study after alveolar grafting and before completion of the orthodontic treatment, the assessment of bony bridge volume resorption with success of orthodontic treatment was done on 26 patients. Patients were further divided into those who showed spontaneous eruption of the tooth through the graft and those who did not. A total of nineteen patients showed spontaneous eruption of the tooth making 73% of patients as successful orthodontic treatment, whereas 27% patients showed no spontaneous eruption of tooth (Graph 2). Success of orthodontic treatment was correlated with percentage of resorption and was found to be statistically significant with p = 0.000 (spearman correlation = 0.683).

Graph 2.

Treatment results.

Discussion

Cleft of the lip and/or palate is a congenital defect characterized by complete or partial clefting of the lip and/or palate. The birth rate of clefts is found to be 1.09 per thousand live births in India.¹¹

Craniofacial development and associated anomalies has been an area of interest to Orthodontists. Advance diagnostic tools along with improvement in restorative and rehabilitative techniques have improved the predictable outcome of management of oro-facial clefts by multidisciplinary team.¹² There are well defined protocols by various rehabilitation centers for the management of cleft lip and palate from the prenatal period to adulthood.

Alveolar bone grafting is an important procedure in the management of patient with cleft lip and palate and has been the standard of cleft care for vast majority of clefts teams. There are differences in the treatment protocol especially in the timing of bone graft among various rehabilitation centers. Secondary alveolar bone grafting (SABG) introduced by Boyne and Sands, is a part of standard care for patients with cleft lip and palate. Autogenous bone graft is considered to be gold standard among the various types of bone graft materials used for grafting. Cancellous bone is preferred because cortical, as cortico-cancellous bone may inhibit the eruption of permanent erupting tooth in to the grafted bone. Grafted cancellous bone anatomically joins the adjacent bone and become indistinguishing in radiographic images after an average period of 3 months. The volume of bone graft achieved in the cleft is very important for Orthodontic treatment, especially if the tooth in the cleft region (canine or lateral incisor) is missing. It is required to accurate estimate of the size, position, and structures involved by the cleft before attempting the surgical procedure.

Examination of the target area after the alveolar bone grafting is important, to know the outcome of the bone graft, to monitor the eruption of tooth in the grafted area, periodontal status of teeth adjacent to the cleft and to evaluate the amount of healthy bone available for the insertion of the implant during the rehabilitation process. Various authors have used these routine radiographic techniques to evaluate the success rate of grafting.¹³ However, these conventional radiographs have limitations such as distortion, lack of availability of reliable landmarks and superimposing structures. Another obvious problem is to have exact three-dimensional information from these two-dimensional radiographs. However, with the introduction of CT and CBCT in Dentistry, the assessment of bone grafting (volume of bone graft or volume of cleft) has become more accurate in three dimensions.¹⁴ The use of CT scans can be considered unethical because of the higher dose of radiation received by the patients.⁸ CBCT is preferred over traditional CT scanners as CBCT uses a low energy fixed anode tube, similar to that used in dental panoramic machine that exposes the patient to approximately 20% of the radiation of a helical CT, equivalent to the exposure from a full mouth periapical series.¹⁵ To limit the radiation exposure to cleft patients, special precautions are taken. The scans are generally limited to the maxilla so that radiation exposure to radiosensitive structures such as the thyroid gland and eye lens is minimized. The tube current is reduced as Orthodontist and Oral Maxillofacial Surgeon team is interested primarily in bony structures. Additional conventional dental radiographs are avoided. The important diagnostic informative value of scans can be weighed against the risk of increased ionizing radiation exposure to these patients with cleft lip and palate. The crucial information about the volume of bone graft in the cleft area is critical in planning Orthodontic treatment, especially in the bucco-palatal direction.

The resorption of the grafted bone is an area of concern among the team managing patients with alveolar clefts. The subject has been studied in detail in Orthodontic and Maxillofacial literature and the amount of resorption varies among various studies. The time period after which the status of grafted bone in cleft target area studied varies in literatures, few authors studied immediately after the surgical procedure or after a period of 1 month, 3 months, 6 months, 1 year and up to 3 years post grafting. It has been estimated that 1 month is sufficient period for stabilization of grafted site and orthodontic treatment can be initiated to erupt the tooth or orthodontic movement of adjacent teeth adjacent to cleft site.¹⁶ In the present study the assessment of transplanted bone was evaluated 3 months post-operative, as it is documented in literature that there is little difference between the bone bridge after 3 months post operative when compared to bone bridge after 6 months or 1 year post-operative.^{17, 18} In addition it is necessary to evaluate the bone bridge at the earliest so that the outcome of transplanted bone can be assessed and if need arises the re-exploration of the surgical site can be done at the earliest. The age suitable for alveolar bone grafting and Orthodontic treatment is limited; guidance from early intervention can guide orthodontist to restart any interrupted orthodontic procedure, if necessary.

In a study by Feichtinger et al.¹⁰ the exact bone volume after secondary alveolar bone grafting was examined over a period of two years using a navigation system based on computed tomography immediately pre-operative, 1 and 2 years post-operative. The mean bone loss observed after one and two years was 51% and 52%, respectively and a significant correlation was found between the size of the cleft and the success of the alveolar bone grafting. However, in the present study the amount of bone resorption evaluated after 3 months is 42.9%. Although the rate of resorption noted is less as compared to their study, but the resorption value may increase with time as the resorption process continues up to 3 years post-grafting.

Prospective study by Tai et al.¹⁹ evaluated the secondary alveolar bone grafts among 14 patients with the use of computed tomography and the percentage of bone loss 1 year post secondary alveolar grafting was 43.1%. Similar results are obtained in our study (42.9%). Although the sample size of two studies is similar, however in their study both unilateral and bilateral cleft patients were selected, hence the volume of bone resorption can be considered lower than our study where only patients with unilateral cleft are considered. The amount of graft resorption in the present study recorded is 42.9% (after 3 months of grafting), similar to Yong et al.,²⁰ who recorded 35.74% resorption of the alveolar bone graft after 3 months of grafting and 55.89% after 6 months of grafting.

There are several factors that influence the outcome of secondary bone grafting: dental hygiene, periodontal infections, width of cleft defect or the origin of graft bone. The criteria for successful alveolar cleft repair includes: closure of oro-nasal fistula, bony continuity or arch stability, adequate amount of bone for root coverage, clinically healthy non-inflammed attached gingiva.¹⁹ Resorption of grafted bone is the major cause of failure to alveolar cleft repair. Physiological stress is required for stability and success of transplanted bone, which is possible by guiding the erupting tooth through the graft. Erupting tooth creates a periodontium of support and protection that maintains an interdental septum of good height.

In the present study to reduce the error and avoid mistakes which can happen due to inexperienced surgeons, all surgical procedures were performed by an expert team of Oral-Maxillofacial surgeons. The resorption of transplanted bone noticed might have occurred because of inadequate bone coverage resulting from tension in mucoperiosteal flap.⁴ Although the most obvious reason cited for the high resorption rate is the absence of physiological stress in the grafted area.²¹

Conclusions

The present study accurately estimated the volume of alveolar cleft, as same volume of graft is required to completely fill the cleft. The mean volume of alveolar cleft measured on CBCT was 1.1733 ± 0.23 cm³. Resorption of secondary alveolar graft volume was determined after 3 months of grafting and the mean resorption noted was 36%. Successful eruption of canine through the graft was achieved in 73% of patients and is related inversely to the percentage of resorption of the graft volume (spearman correlation = 0.683).

The accurate localization and estimation of the extent and volume of alveolar cleft is important for treatment planning by the team managing patients with cleft lip and palate. This accuracy also provides guidance for the volume of bone graft required from the donor site to be used in the surgical procedure. CBCT should be used for this purpose, as it is an accurate method for assessment of the same in 3-dimensions with great diagnostic informative value and limited risk of ionizing radiation exposure. Post-operative it is important to analyze the outcome of transplanted bone as early as possible, as the age suitable for alveolar bone grafting and Orthodontic treatment is limited. Early evaluation can help the Orthodontist to predict the outcome of transplanted bone and may guide to re-grafting of the site immediate or to restart any interrupted orthodontic procedure, if necessary.

Conflicts of interest

The authors have none to declare.