Volumetric assessment and relationship of maxillary sinus floor with 1st & 2nd molar root apices in different sagittal skeletal patterns – A CBCT study

Context: The relationship between the dental roots and the inferior sinus wall is known to influence orthodontic tooth movement. Aims: To evaluate the distance from the maxillary first and second molars root apices to the floor of the sinus and to assess the volumetric variability of the sinus in different sagittal skeletal patterns. Settings and Design: A cross-sectional comparative study was carried out at the Department of Orthodontics and Dentofacial Orthopaedics of Bangalore Institute of Dental Sciences & Post-Graduate Research Centre, Bangalore. Methods and Material: A total of 90 subjects (18-45 years) were equally divided into three groups. CBCT scans of the skull were taken. Distances from the first and second molars root apices to the sinus floor were measured on both sides. Volumetric analysis of the sinus was done to assess correlation with skeletal growth patterns. Statistical analysis used: Descriptive and inferential statistics were carried out including mean, standard deviation, one-way ANOVA, and Independent t-test using SPSS v26.0 statistical software. Results: No statistically significant mean difference was found between the groups with respect to the distance of root tips to the floor of the maxillary sinus except for the palatal root of the 16 (p=0.004). A significant higher volume on left side was seen when compared to right side. Conclusions: No significant difference in the distance between maxillary first and second molar root apices to the sinus floor and there is no relationship between volumetric variability of the sinus in different skeletal malocclusions.


INTRODUCTION -
The paranasal sinuses develop as an aid to facial growth and architecture, or persist as residual remnants of an evolutionary structure.The maxillary sinus is the largest and the first paranasal sinus to develop; late in fetal life and ends its growth by around 18 years of age with the eruption of the third molars, that overlies the maxillary alveolar process.The inferior sinus wall is a curved structure formed by the lower third of the medial wall and the bucco-alveolar wall with its floor formed by the alveolar process of the maxilla.The maxillary sinus in the adult consists of a pyramidal shaped cavity in the facial skull with its base at the lateral nasal wall and its apex extending into the zygomatic process of the maxilla.The biologic roles of these sinuses are debated, but a number of possible functions have been proposed, including lightening the weight of the head, humidifying and heating inhaled air, increasing the resonance of speech, providing a buffer against facial trauma and aiding the immune defense of the nasal cavity. 1 Several studies have pointed to the relationship among the development process of the midface and jaws, congenital diseases (including cleft lip and palate), and maxillary sinus size and volume.The adult sinus is variable in its extension and its enlargement is determined by bone growth and remodelling.Along with the sinus pneumatization process, the sinus floor moves inferiorly and becomes closer to the roots of maxillary teeth.The relationship between the dental roots and the inferior sinus wall is also known to influence orthodontic tooth movement 2 leading to moderate apical root resorption and high degree of tipping, and the maxillary sinus with its cortical bone layer is a natural barrier for the intrusion of the maxillary molars. 1 The invasion of the maxillary posterior teeth due to inferior growth of the sinus may influence orthodontic treatment planning for malocclusion cases. 3onsidering to its anatomical variability, its intimate relation to the maxillary posterior teeth and because of all the implications that pneumatization may possess, three-dimensional assessment of maxillary sinus pneumatisation is of utmost use. 4 Cone-beam computed tomography (CBCT) has become an important diagnostic tool in dentistry due to its high resolution and its possibility to limit imaging to specific areas of interest. 5It provides an accurate evaluation of maxillary bone quality and quantity without distortion and can also accurately interpret the relationship of the maxillary roots relative to the maxillary sinus floor with its considerable reduction of absorbed radiation doses. 3CBCT proved to be a reliable technique to introduce a new approach for molar intrusion with mini-screws, with better force consistency and force vector control during treatment, and to evaluate its clinical success and concomitant root resorption by a more accurate method.Therefore, the purpose of the study was to evaluate the distance from the root apices of the maxillary first and second molars to the floor of the sinus and to assess the volumetric variability of the sinus in different sagittal skeletal patterns with the objectives being 1.To determine the distance between the maxillary sinus floor and the root apices of the first and second molars in different sagittal skeletal patterns (Class I, Class II, and Class III).by a three-dimensional analysis, and 2. To perform a volumetric analysis of the maxillary sinus in different sagittal skeletal patterns (Class I, Class II, and Class III).The null hypothesis of the study stated that there was no significant difference in the distance between root apices of the maxillary first and second molars to the sinus floor and there is no relationship between volumetric variability of the sinus in different skeletal malocclusions.

Methods:
A cross-sectional comparative study was carried out at the Bangalore Institute of Dental Sciences & Post-Graduate Research Centre, Bangalore.The study aimed to investigate and evaluate the distance from the root apices of the maxillary first and second molars to the floor of the sinus and assess the volumetric variability of the sinus in different sagittal skeletal patterns.Sample size estimation was done using G*power v3.0.1 based on the effect size of 0.46, power of 95%, significance level of 0.05.Sample size was estimated to be 78, considering the attrition rate of 10% it was rounded off to 90 samples.Ethical clearance was obtained by The Institutional Ethics Committee of Bangalore Institute of Dental Sciences, Bangalore.
Selection and description of the study participants: All patients reporting to the Department of Orthodontics and Dentofacial Orthopaedics at Bangalore Institute of Dental Sciences, were evaluated for their sagittal skeletal jaw relations after assessment of ANB angle.They were then categorized into Class I, Class II, and Class III skeletal pattern.Inclusion and exclusion criteria were set for the sample selection.Inclusion criteria were:

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Immature roots with open root apices A total of ninety individuals were selected.The details of the study were explained and an informed consent was taken from the samples.According to sagittal pattern using cephalometric values (i.e., ANB values), the participants were later divided equally into 3 groups: Group I -Skeletal Class I (ANB, 0º to 2º) (30 Cases) Group II -Skeletal Class II (ANB > 2º) (30 Cases) Group III -Skeletal Class III (ANB < 0º) (30 Cases) The materials used in the study were as follows: 1.A CBCT machine (Kodak 93003) 2. Lateral cephalogram (Fig. I).3. ORAL CS 3D Imaging Software (Carestream Health India Private Limited)

Methodology:
• CBCT scans of the skull were taken prior to the commencement of orthodontic treatment, where the 3-D constructed images were oriented with the Frankfort horizontal (FH) plane aligned horizontally.

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All distances from the root apices of the first and second molars (except 3rd molars) to the sinus floor were measured along the true vertical axis on both right and left sides.

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Similarly, volumetric analysis of the right and left sinus was done in each patient to assess its correlation with skeletal growth patterns.All CBCTs were performed at 90Kv and 10mA with a scan time of 16 seconds and voxel dimensions of 0.3 x 0.3 x 0.3 mm.Each patient's data consisted of a resolution of 1024 x 1024 pixels and 14 bits per pixel.The reconstruction volume size being 140 × 170 mm.The images were taken in the sitting position with patient's head in the natural head posture.A single examiner carried out all the measurements.Two parameters were then measured using the ORAL CS 3D Imaging Software -• The distance from the root tips of the maxillary first and second molars to the floor of the sinus, and • Volume of the maxillary sinus with different skeletal patterns.

LANDMARKS -SINUS FLOOR TO ROOT APEX:
• The 3D constructed images were oriented with the plane aligned horizontally, parallel to the line passing through the floor of the orbit.

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• The coordinated images of each root of first and second molars in coronal and sagittal planes were checked, and the sliced image passing the root apex were chosen for measurements.
• All the distances were measured as the shortest distance along the true vertical axis from the most apical point on the root to the floor of the maxillary sinus, where

SINUS VOLUME DETERMINATION:
CBCT data were exported in DICOM file format and imported into the software ORAL CS 3D for measurement analysis.Volume determination was done via geometric calculation method according to the geometrical equation: Volume of maxillary sinus (Pyramid) = anteroposterior (length) x craniocaudal (height) x mediolateral (width) ÷ 3 Dimensional and volumetric measurements of both right and left maxillary sinuses were evaluated on CBCT images in terms of Length: Longest distance between the lateral wall of nose to the zygomatic process of the maxilla when aligned parallel to the FH plane (Fig. IV).Height: Longest distance between the floor of the orbit to the alveolar process of the maxilla along true vertical axis (Fig. V).Width: Longest distance between the facial surface of maxilla to the infratemporal fossa when aligned parallel to FH plane (Fig. VI).
All the data collected was than subjected to statistical analysis using SPSS v26.0 statistical package.Mean distance between the root tips of 1st and 2nd molar to sinus floor was determined and compared using descriptive statistics including mean, standard deviation, and inferential statistics including oneway ANOVA, Tukey's post-hoc analysis was used to compare mean distance between mesio-buccal, disto-buccal and palatal roots to sinus floor.Independent t-test was used to determine volumetric differences in right and left side sinus.P value was set at 0.05.

Results:
The mean distance of both right and left 1st and 2nd molar roots to the sinus floor are depicted in the Table no 1.The mean distance was measured in millimetres (mm) and negative value indicating root apices extending above the sinus floor whereas positive value indicates root apices below the sinus floor.It can be seen that the mesio-buccal root apices of 17 and 27 extends above the sinus floor in all three sagittal skeletal patterns.Table 2 shows the distribution of One-way analysis of variance (ANOVA) which was done to compare the mean distance of root tips to the floor of the maxillary sinus between the groups (Class I, Class II, Class III) on right and left sides and was seen that there was no statistically significant mean difference noted between Class I, Class II and Class III with respect to the distance of mesiobuccal, distobuccal and palatal root tips to the floor of the maxillary sinus on both right and left sides (p > 0.05) except for the palatal root of the 16 (Maxillary right first molar), which displayed a statistically significant difference between Class I, Class II and Class III molar relation (p=0.004).
Further Tukeys post hoc analysis was done and a statistically significant difference was seen for the distance from right maxillary first molar palatal root tip to the floor of the maxillary sinus between Class I and Class II (P=0.035) and also between the Class I and Class III (P=0.004) which is displayed in Table no.3. Comparison of the means of Length, Height, Width and Volume between the groups (Class I, Class II, Class III) on right and left sides was done using oneway ANOVA and it was seen that there was no statistically significant mean difference noted between Class I, Class II and Class III with respect to Length, Height, Width and Volume on both Left and Right sides (P > 0.05) which is depicted in the Graph no.1.This indicates, on both sides (Left and Right) of Class I, Class II and Class III malocclusion there is no change in Length, Height, Width and Volume.Table 4 shows the result of Independent sample t test, which was done to compare between the independent (right and left side) and dependant variables (length, height, width and volumes at Class I, Class II and Class III).Independent sample t test displayed that there was a statistically significant (t = -2.418;P = 0.019) higher volume on left side (7.5±2.0) when compared to right side (6.3±1.8).

Discussion:
The present study was carried out using 3D -CBCT to evaluate the distance from the root apices of the maxillary first and second molars to the floor of the sinus and to assess the volumetric variability of the sinus in different sagittal skeletal patterns, as to provide a valuable insight about its clinical implications and significance of Infra-Zygomatic crestal implant positioning for various orthodontic tooth movements.
The obtained results of one-way ANOVA displayed no statistically significant mean difference between skeletal Class I, Class II and Class III with respect to the distance of mesiobuccal, distobuccal and palatal root tips to the floor of the maxillary sinus on both right and left sides (p > 0.05) except for the palatal root of the maxillary right first molar which displayed a statistically significant difference between skeletal Class I, Class II and Class III.(p=0.004).Tukey's Post-hoc analysis displayed a statistically significant difference of the distance from right maxillary first molar palatal root tip to the floor of the maxillary sinus between skeletal Class I and Class II (p=0.035) and also between the Class I and Class III (p=0.004).It was therefore concluded that the highest contact was seen at mesio-buccal and disto-buccal roots of maxillary first and second molars whereas least contact was observed at palatal roots.Thereby, suggesting that the palatal roots are farthest away from the sinus floor.Results of the present study showed that the mesio-buccal roots of the second molars had protrusion into the sinus on both the right and left sides with an average of -0.394 and -0.374 mm respectively; which was in accordance to the study by Ahn and Park et al1 who evaluated the distances from the maxillary posterior root apices to the inferior wall of the maxillary sinus using CBCT according to age, sex, and skeletal pattern.The frequency of root contact with the sinus floor increased from 70% at the second premolar to more than 80% at the buccal roots of the first and second molars.The mesio-buccal roots of the second molars had the greatest protrusion into the sinus on both the right and left sides with averages of -2.64 and -2.54 mm respectively whereas the palatal roots of the second molars were the farthest from the maxillary sinus floor.Eberhardt et al6 also assessed the distances between the apices of the maxillary posterior teeth and the floor of the maxillary sinuses, and the thickness of the lateral bone covering these apices and the study concluded that the distances between the apices of the maxillary posterior teeth and the floor of the maxillary sinuses reported that the apex of the mesio-buccal root of the maxillary second molar was closest to the sinus floor which is in accordance with this study results that the mesio-buccal roots of the second molars had protrusion into the sinus on both the right and left sides.Kilic et al 7 conducted a similar study to assess the relationship between the maxillary sinus floor and the maxillary posterior teeth root tips using dental CBCT.The results showed the distance between sinus floor and root tip was shortest for the second molar distobuccal root tip for both right and left sides and no statistically significant differences were found between the right and left side measurements (p>.05) which is in accordance with present study results.On analysing the volumetric variability of the sinus in different sagittal skeletal patterns in the present study, the results of one-way ANOVA and Tukey's Post-hoc analysis displayed no statistically significant mean difference between skeletal Class I, Class II and Class III with respect to length, height, width and volume on both right and left sides (p> 0.05).Independent sample t test displayed a statistically significant (t = -2.418;p = 0.019) higher volume on left side (7.5±2.0) when compared to right side (6.3±1.8).In this study, no significant difference was found was in transverse and anteroposterior dimensions and the height of the sinus floor between the right and left maxillary sinuses but data analysis displayed there is a statistically significant (t = -2.418;P = 0.019) higher volume on left side (7.5±2.0) when compared to right side (6.3±1.8); which is in accordance to the study done by Sheikh et al. 8 This study showed no statistically significant mean difference between skeletal Class I, Class II and Class III with respect to length, height, width and volume on both right and left sides (p > 0.05) which was in accordance with Toshiya et al 4 who conducted a study to investigate maxillary sinus size in different malocclusion groups and the association between maxillary sinus size and dentofacial morphology and maxilary sinus showed no significant differences.Hence, when formulating an orthodontic treatment plan, orthodontists should take into consideration the fact that the patients in the age group of 12 -16 years with large cranial bases and nasomaxillary complexes tend to have larger maxillary sinuses.4In orthodontics, therapeutic extractions are adviced, in such cases careful evaluation of maxillary posterior alveolar region is advocated.The extractions of posterior teeth, in particular the second molar tooth may cause a frequent loss of the thin bone separating the alveolar socket from the sinus, thus allowing the sinus to expand. 9In addition, the posterior maxillary region is the frequent site for insertion of bone anchor screws although incidental perforation of maxillary sinus may occur in conjunction with descent of the maxillary sinus floor.The intrusion of the maxillary molars in those situations may be difficult and slow because of the pneumatized maxillary sinus. 1 Thus, the knowledge about the root proximity of maxillary posterior teeth to the sinus floor and the volume of sinus helps the orthodontists in diagnosis and formulating the treatment plan.The development pattern of the paranasal sinus (PNS) varies widely according to the individual and the age.Even in the same person, both maxillary sinuses may develop in a different way.So, the analysis of the diverse morphology of the maxillary sinus as well as the relationship with the adjacent anatomical structures are of utmost importance, when Orthodontists plan for placement of mini-screws.The topographical relationship of the roots of the posterior maxillary teeth and the maxillary sinus floor is an important determinant in the prognosis of orthodontic tooth movement.

Conclusion
The null hypothesis of the study was that there is no significant difference in the distance between root apices of the maxillary first and second molars to the sinus floor and there is no relationship between volumetric variability of the sinus in different skeletal malocclusions and the results which were obtained in our present study correlated with the same and hence the null hypothesis was proved to be true.Further studies on a larger sample size with gender consideration can provide valuable insight which will further help in accurate diagnosis.
Ahn NL, Park HS.Differences in distances between maxillary posterior root apices and the sinus floor according to skeletal pattern.Am J Orthod Dentofac Orthop.2017; 152:811-819.

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Eberhardt JA, Torabinejad M, Christiansen EL.A computed tomographic study of the distances between the maxillary sinus floor and the apices of the maxillary posterior teeth.Oral Surg Oral Med Oral Pathol 1992;  73:345-346.7.
Kilic C, Kamburoglu K, Yuksel SP, Ozen T.An assessment of the relationship between the maxillary sinus floor and the maxillary posterior teeth root tips using dental cone-beam computerized tomography.Eur J Dent 2010; 4:462-467.8.
Sheikh N, Ashwinirani S, Suragimath G, Shiva Kumar K. Evaluation of gender based on the size of maxillary sinus and frontal sinus using paranasal sinus view radiographs in Maharashtra population, India.J Oral Res Rev. 2018; 10:57-61.9.
Sharan A, Madjar D. Maxillary sinus pneumatization following extractions: a radiographic study.Int J Oral Maxillofac Implants.2008; 23(1):48-56.Class I Class II Class III For 1st & 2nd Molars: MB' = most apical point on the mesio-buccal root (Fig.II a).DB' = most apical point on the disto-buccal root (Fig.II b).PA' = most apical point on the palatal root (Fig.III).X' = lowest point on the floor of the maxillary sinus The same was repeated for both right and left sides.

Fig I :
Fig I: Cephalometric Tracing Showing Angular Measurements of Class I, Class II and Class III (a,b,c)

Table no .
1: Descriptive Statistical comparison of mean and standard deviation of distance between root tips of 1st and 2nd molars to sinus floor among different sagittal skeletal patterns.

Table 2 :
Comparison of mean distance of mesio-buccal, disto-buccal and palatal root of right and left 1st and 2nd molars to the floor of the maxillary sinus among Class I, Class II and Class III sagittal Skeletal patterns

Table 3 :
Multiple comparison means of distance of mesio-buccal, disto-buccal and palatal root of right and left 1 st and 2 nd molars to the floor of the maxillary sinus among Class I, Class II and Class III sagittal skeletal patterns

Table no . 3
*Statistical significance set at 0.05 N: Number of Sample; SD: Standard Deviation Illustrations (Figures and Graphs):