Does orthognathic surgery affect tooth root length and volume: a retrospective cohort study
To examine tooth root length and root volume in cone beam computed tomography (CBCT) images in patients with skeletal Class II and III anomalies who have undergone single-jaw (SJ) and double-jaw (DJ) orthognathic surgery, and to compare the changes between jaws with and without osteotomy. This study was conducted on the archive records of a total of 60 adults: 36 women and 24 men with an average age of 21.1 ± 3.1 years, whose CBCT images were recorded just before orthognathic surgery and within 6–12 months after surgery. The sample was divided into four groups with 15 individuals in each: Class II SJ (mandibular advancement only), Class II DJ (maxillary advancement and impaction with mandibular advancement), Class III SJ (maxillary advancement and impaction), and Class III DJ (maxillary advancement and impaction with mandibular setback). Within groups, statistically significant decreases in root length and root volume were found in the period between preorthognatic and postorthognathic surgery (P < .05). No statistically significant differences were found in comparisons between groups (P > .05). Regardless of the type of skeletal anomaly in the sagittal direction and the orthognathic surgery performed, a statistically significant but clinically insignificant decrease was found in tooth root length and root volume during the postorthognathic surgery period, both in jaws with and without osteotomy.ABSTRACT
Objectives
Materials and Methods
Results
Conclusions
INTRODUCTION
Orthognathic treatment, which combines orthodontic treatment with orthognathic surgery in adults with severe skeletal disharmony, is widely practiced today.1 In orthognathic treatment, the goal is to correct the skeletal anomaly and malocclusion and to improve the facial profile, airway, and chewing function by repositioning the maxilla and mandible in space with surgical procedures.2 Lefort I osteotomy for the maxilla and bilateral sagittal split ramus osteotomy for the mandible are currently the most popular and frequently performed procedures. Orthognathic surgical procedures are invasive, and osteotomies applied to the jaws are of clinical importance due to their effects on blood flow.3 It has been reported that complications such as necrosis of bone and soft tissue, devitalization of teeth, periodontal defects, and bone loss may occur due to decreased blood flow but also that no significant side effects may occur due to the temporary nature of vascular problems.4 Conversely, although it is assumed that the effect of orthognathic surgical procedures on tooth roots is lesser than conventional orthodontic treatment, it is claimed that potential damage to the dental apical blood supply after surgery may require consideration in the context of root resorption.5
It has been reported that different degrees of root resorption occur in different teeth in patients receiving orthodontic treatment but that this is surface resorption and, even if deep defects occur on the root surface at the cementum or dentin level, they undergo repair with deposition to fill defects.6 However, when apical root resorption reaches irreversible pathological levels (crown/root ratio falling below 1/1), it may cause pulpitis, mobility, and even tooth loss.7 The identification of root resorption during orthodontic treatment is significant for the lifespan of teeth. Determination of the risk of root resorption in different treatment protocols will facilitate reduction of this problem and selection of the most appropriate treatment method.8 Although the effect of orthodontic treatment on root resorption has been widely reported in the literature, little is known about root resorption following orthognathic surgery. A recently published systematic review stated that evidence is lacking for the objective evaluation of root resorption after orthognathic treatment and that studies based on cone beam computed tomography (CBCT) are needed for a better understanding of root resorption after different surgical procedures.5
The current study had two aims. The first was to examine tooth root length and root volume in CBCT images in the early period after orthognathic surgery in patients with skeletal Class II and III anomalies who were treated with single-jaw (SJ) or double-jaw (DJ) orthognathic surgery. The second aim was to compare the root volume and length in jaws with and without osteotomy. The null hypothesis tested was that SJ and/or DJ orthognathic surgery would have no effect on root length and root volume in patients with skeletal Class II and III anomalies.
MATERIALS AND METHODS
This retrospective cohort study was approved by the Erciyes University Clinical Research Ethics Committee (Decision No: 2022/713). A root volume measurement reported by Baysal et al.9 was used as a reference for the power analysis. The G-Power power analysis (version 3.1.2; Franz Faul Universitat, Kiel, Germany) indicated that a minimum of 14 patients per group was required, with a significance level of α = 0.05, an effect size of d = 0.684, and a power of 80%. To increase reliability of the study, 15 patients were included in each group. Archive records of patients who had orthognathic surgery at the Erciyes University Faculty of Dentistry between 2014 and 2022, aged between 18 and 25 years, and had CBCT images taken just before orthognathic surgery (T1) and within 6–12 months after orthognathic surgery (T2) were examined. To standardize the study, the records of patients who underwent orthognathic surgery performed by the same surgical team and whose postoperative stabilization of the jaws was performed with similar rigid fixation methods were used.
Patients with CBCT images of sufficient image quality were included in the study according to the following selection criteria: (1) ANB angle >4° for skeletal Class II anomaly groups and <0° for skeletal Class III anomaly groups; (2) maxillary impaction extent <3 mm, maxillary advancement extent <7 mm, extent of mandibular advancement between 3 and 10 mm, the range of mandibular setback between 3 and 7 mm; (3) no open bite malocclusion; (4) no facial asymmetry >3 mm; (5) no root resorption on panoramic radiographs at the beginning of treatment; (6) no history of trauma to the teeth; (7) absence of any craniofacial or congenital anomalies; (8) absence of any systemic disease that may affect bone formation, bone density, and bone metabolism or cause root resorption; (9) absence of any chronic medication use; and (10) absence of any previous periodontal disease.
Based on the classification of the skeletal anomaly in the sagittal plane and the osteotomy performed, four groups were formed. They were Class II SJ (only mandibular advancement), Class II DJ (maxillomandibular advancement with maxillary impaction), Class III SJ (only maxillary advancement with impaction), and Class III DJ surgery (maxillary advancement with impaction and mandibular setback). The gender, average age, and postsurgical follow-up period of the patients included in the study are presented in Table 1. The extent of surgical movement of the jaws according to groups is shown in Table 2.
Records and Measurements
All CBCT records of the patients, which were taken using the New-Tom 5G (FP, Quantitative Radiology, Verona, Italy) device, were obtained from the archives of the Erciyes University Faculty of Dentistry. Images taken with a field of view range of 12 × 8 cm, a voxel size of 0.25 mm3, and an axial section thickness of 0.25 mm were used. After the images were converted into the Digital Imaging and Communication in Medicine format, they were transferred to Simplant Pro 16 (Materialise NV, Leuven, Belgium) software to make millimetric and volumetric measurements of roots. Coronal, sagittal, and axial sections were obtained by processing the images with software. Root length was calculated by measuring the distance from the intersection point of the long axis of the teeth and the line connecting the cemento-enamel junction (CEJ) boundaries to the root apex on the sagittal section (Figures 1 and 2).10
Citation: The Angle Orthodontist 95, 2; 10.2319/052024-390.1
Citation: The Angle Orthodontist 95, 2; 10.2319/052024-390.1
During root volume measurements, first, Teeth values with a Hounsfield unit (HU) value of minimum 1200 and maximum 3071 were selected and segmentation of the teeth from the surrounding tissues was carried out. All sections were checked, and the tissues around the teeth were fully removed. Then the crown and root were separated from each other at the CEJ border and three-dimensional (3D) models of the roots were created. The volume of the created models was calculated using the 3D Properties option (Figure 3), and these steps were repeated for all teeth to be measured (Figure 4).
Citation: The Angle Orthodontist 95, 2; 10.2319/052024-390.1
Citation: The Angle Orthodontist 95, 2; 10.2319/052024-390.1
Statistical Analyses
Research data were processed using SPSS 21.0 software (SPSS Inc., Chicago, IL). The suitability of continuous variables for normal distribution was investigated using visual (histograms and probability graphs) and analytical methods (Kolmogorov-Smirnov and Shapiro-Wilk tests). Independent samples t-test and one-way analysis of variance were used for comparing the parametric data in independent groups; for the comparison of nonparametric data, the Mann-Whitney U-test and Kruskal-Wallis variance analysis were used. The paired samples t-test was used to compare the parametric data independent groups, and the Wilcoxon signed-rank test was used to compare nonparametric data. For statistical significance, the P value was set to be <0.05.
Method Error
One researcher repeated measurements 2 weeks later, on randomly selected CBCT images of 10 patients. The intraclass correlation coefficient (ICC) was used to check the method error of the repeatability of the measurements to determine measurement reliability. Results of the ICC of the CBCT data used to assess method error regarding the repeatability of the measurements made were between 0.786 and 0.985, which indicated a strong positive correlation and sufficient reliability. This implied that all measurements could be replicated with precision.
RESULTS
Intragroup comparisons of root length and volume values of the T1 and T2 periods are presented in Tables 3 and 4, respectively, and intergroup comparisons are presented in Tables 5 and 6. The percentage change in root length and root volume are displayed in Figures 5 and 6, respectively.
Citation: The Angle Orthodontist 95, 2; 10.2319/052024-390.1
Citation: The Angle Orthodontist 95, 2; 10.2319/052024-390.1
Intragroup Comparisons
Statistically significant decreases were detected in all root lengths between 2.4% and 7.1% and root volumes between 3.4% and 17%, in the postorthognathic surgery period (P < .05; Figures 1 and 2). The most affected root lengths were the upper lateral incisors (12, 22; 0.75 mm, 0.82 mm) and the lower central incisors (31, 41; 0.64 mm, 0.59 mm) in the Class II SJ group; the upper central incisors (11, 21; 0.76 mm, 0.81 mm) and the lower left lateral incisor (32; 0.65 mm) in the Class II DJ group; the distobuccal root of the upper left first molar (26DB; 0.72 mm) and the distal roots of the lower first molars (36D, 46D; 0.59 mm, 0.58 mm) in the Class III SJ group; the distobuccal root of the upper left first molar (26DB; 0.83 mm) and the mesial roots of the lower first molars (36M, 46M; 0.71 mm, 0.73 mm) in the Class III DJ group (Table 3).
The highest root volume decrease was in the upper left lateral incisor (22; 17.18 mm3) and the mesial root of the lower left first molar (36M; 16.21 mm3) in the Class II SJ group; the upper left central incisor (21; 18.02 mm3) and the mesial root of the lower first molar (36M; 17.21 mm3) in the Class II DJ group; the distobuccal root of the upper left first molar (26DB; 20.38 mm3) and the distal root of the lower left first molar (36D; 14.06 mm3) in the Class III SJ group; and the distobuccal root of the upper left first molar (26DB; 17.89 mm3) and the mesial root of the lower right first molar (46M; 17.77 mm3) in the Class III DJ group (Table 4).
Intergroup Comparisons
For root length changes, statistically significant differences were detected between the Class II SJ and Class II DJ groups in the distobuccal root of the upper right first molar (16DB), the root of the upper left lateral (22), and the distal root of the lower right first molar (46D). Also, significant differences were found between the Class II SJ and Class III SJ groups in the roots of the upper lateral incisors (12, 22) and the upper right second premolars (15) (P < .05). No statistically significant difference was found between the groups in other comparisons (P > .05; Table 5).
In the intergroup comparisons of root volume measurements between the groups in the postorthognathic period, a statistically significant difference was found between the Class II SJ and Class II DJ groups in the distobuccal root of the upper right first molars (16DB) and the upper right lateral incisors (12). A statistically significant difference was found between the Class II SJ and Class III SJ groups in the upper lateral incisor roots (12, 22) and the lower lateral incisor roots (32, 42). In other comparisons, no statistically significant difference was found between the groups (P > .05; Table 6).
DISCUSSION
This study represents a novel approach to investigating the changes in tooth roots of patients with skeletal Class II and III deformities following SJ and DJ orthognathic surgery, employing CBCT. Additionally, in the study, we sought to assess the degree to which malocclusion and the surgical procedure performed influenced these changes. To prevent relapse due to soft tissue and muscle tension after excessive movement of the jaws with surgery, groups were formed with reference to the amount of jaw movement recommended in the literature. It has been documented that the risk of root resorption due to hypofunction is higher in patients with open bite.3 As a result, patients with open bite were excluded from the study groups, four groups were formed, and the jaws without osteotomy were considered a positive control group; this group was the maxilla in Class II SJ and the mandible in Class III SJ. In evaluation of root length and volume for the four groups, a statistically significant decrease was detected during the postorthognathic surgery period in all groups. With few exceptions, no statistically significant differences were found when comparisons were made between the groups. Therefore, this study failed to reject the null hypothesis. Interestingly, root resorption occurred significantly more often in the lateral incisors in the maxilla without osteotomy (Class II SJ) than in similar teeth in the maxilla with osteotomy (Class II DJ and Class III SJ). On the other hand, when teeth in the mandibles that underwent osteotomy (Class II SJ) and those that did not (Class III SJ) were compared, no significant difference was found. These findings indicated that osteotomies had no effect on root resorption. In addition, since no difference in root resorption was found between the Class II DJ and Class III DJ groups, this suggested that the type of anomaly does not affect root resorption.
In this study, root resorption was observed in jaws both with and without osteotomy. Authors of a previous study reported that orthodontic treatment induced root resorption and that root resorption occurred in >90% of the teeth after treatment, albeit at a minimal level.11 Arı-Demirkaya et al.12 stated that mild to moderate shortening of the roots may occur as a result of orthodontic treatment and that, if this loss is more than a quarter of the root length, it can be defined as clinically significant severe resorption. They reported that losses of less than a quarter of the root length (<1 mm) were clinically insignificant. In the current study, root resorption occurred in all teeth in all groups, and losses of <1 mm of root length were found. The greatest degree of resorption occurred in the incisors and the mesial and distal roots of the maxillary and mandibular first molars. This agreed with the study by Castro et al.,13 in which they evaluated root resorption after orthodontic treatment through CBCT records. They reported that this may have been due to factors such as the direction of tooth movement and the magnitude and type of the applied force. The current findings suggested that the dimensional and volumetric alterations observed in the tooth roots were not exclusively attributed to the impact of osteotomy or, in other words, due to orthognathic surgery. Support for this may be found from Wolford,14 who stated that root resorption may occur due to orthodontic mechanics used after surgery, intraoral elastics, and trauma to the teeth in patients in whom ideal occlusion cannot be achieved.
Since magnification, distortion, superposition of images, and failure to detect damage until mineral loss exceeds 50% are common deficiencies in two-dimensional radiographic methods, and since the image quality of CBCT provides more detailed and accurate information than conventional methods as well as allowing 3D examination of teeth, CBCT was used in the current study. Millimetric and volumetric measurements of tooth roots were made using Simplant Pro 16 software. This software is considered reliable due to its accuracy of up to 99% in measuring the volume, length, and width of anatomical structures.15
Evaluation of short-term results after orthognathic surgery, failure to create a negative control group from patients for ethical reasons, and failure to obtain CBCT records before orthodontic treatment are among the limitations of this study. Long-term studies are needed to better understand the effects of orthognathic surgical treatment on root resorption, and studies in which authors better control the effects of the multiple factors related to root resorption etiology in orthodontic treatment should be attempted.
CONCLUSIONS
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Considering the limitations of the study, in patients with Class II and III anomalies who were treated with SJ or DJ orthognathic surgery, root resorption to a clinically insignificant extent occurred after surgery, in jaws both with and without osteotomy, regardless of the type of malocclusion and the type of surgery performed.
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Changes in root length and volume may be attributed to the use of elastics postoperatively and forces exerted on the teeth.
Sagittal section view of (A) and (B) central, (C) and (D) lateral, (E) and (F) canine, (G) and (H) second premolar, and (I) and (J) first molar teeth.
Root length measurement from the cemento-enamel junction (CEJ) to the root apex.
Determining the root volume with 3D Properties.
Segmentation of roots and creation of three-dimensional (3D) models.
Comparison of changes in root length (mm) data before and after surgery between groups.
Comparison of changes in root volume (mm3) data before and after surgery between groups.
Contributor Notes