Introduction
Orthodontists consider facial growth pattern and oral function when developing a treatment plan. Less attention is given to the relationship between the maxillary posterior teeth and the maxillary sinus. We aimed to evaluate the relationship between the roots of the maxillary posterior teeth and the floor of the maxillary sinus.
Methods
Proximity of the roots to the maxillary sinus was scored for the left and right first and second premolars and molars (scores, 0-3). Mean scores per patient and per tooth type were calculated. The influences of age, sex, and facial biotype on mean scores per patient and tooth were analyzed.
Results
The mean scores per patient and the second molar scores were significantly lower in the normodivergent subjects compared with the hypodivergent subjects, and in the hypodivergent vs the hyperdivergent groups, indicating that the hypodivergent biotype had significantly fewer second molar roots into the sinus than the normodivergent and hyperdivergent biotypes. Age had no effect on mean score per patient, but in the hyperdivergent group, the second molar score increased with age, meaning that second molar roots tend to be closer to the sinus floor.
Conclusions
In a young population (7-24 years), the positions of the apices of the maxillary second molar roots in relation to the maxillary sinus floor are associated with the facial biotype. In a hypodivergent biotype, the roots of the second molars are located farther from the sinus floor compared with the normodivergent and hyperdivergent facial patterns.
Graphical abstract
When determining a treatment plan for a patient, orthodontists consider the facial growth pattern and oral function. However, less attention is given to the relationship between the maxillary posterior teeth and the maxillary sinus floor. The maxillary sinuses are small at birth and enlarge with the growing maxilla. The maximum volume is reached in the second decade in girls and the third decade in men, or by the age of 20 to 25 years as described by other authors. Evaluating the position of the roots of the maxillary teeth in relation to the maxillary sinus is important for a comprehensive orthodontic diagnosis and treatment plan, especially when endodontic treatment might be needed, severely displaced impacted teeth are present, extractions or dental implants are considered, vertical control methods are required during treatment, or orthognathic surgery is planned. Because maxillary sinus enlargement during facial growth is related to the vertical increase in the alveolar process, we expected to find a relationship between the facial growth pattern and the 3-dimensional (3D) position of the posterior maxillary teeth in relation to the maxillary sinus. Therefore, the aim of this study was to relate the proximity of the roots of the maxillary posterior teeth to the floor of the maxillary sinus in different facial growth patterns.
Material and methods
This was a retrospective cross-sectional study based on the dental charts of 1455 patients from a private dental practice in Cluj-Napoca, Romania. Partial or full-size cone-beam computed tomography (CBCT) scans were available for these patients. CBCT imaging was performed for orthodontic and orthognathic treatment planning and the diagnosis of temporomandibular abnormalies. From these charts, patients were selected based on the following inclusion criteria: young adults, adolescents, and children (ages, 7-25 years), in either the mixed or permanent dentition. Exclusion criteria were craniofacial deformities, genetic syndromes, systemic diseases, previous injuries or trauma in the maxillofacial region, or previous orthodontic treatment.
The ethics commission of the Iuliu Haţieganu University of Medicine and Pharmacy, Cluj-Napoca, Romania, approved the study.
All CBCT images were acquired with the same i-CAT CBCT machine (Imaging Sciences International, Hatfield, Pa). The scanning parameters were 120 kV(p), 23.87 mA, exposure time of 10 to 20 seconds, and voxel size of 0.4 mm. The x-ray machine was calibrated twice a day, and the data were saved in DICOM format.
To determine the facial biotype, a lateral cephalogram was reconstructed from the CBCT data set with no built-in magnification. The images were processed using 3D software (version 11.7 Premium; Dolphin Imaging, Chatsworth, Calif). Because of the young age of the patients and since most scans had a limited field of view, cephalometric landmarks such as sella, nasion, and other cranial structures could not be identified on the scans ( Fig 1 ). However, to personalize the cephalometric analysis, the following landmarks were identified on the lateral cephalogram: porion, orbitale, menton, gonion, mandibular incisor tip, and mandibular incisor root apex. The Frankfort mandibular plane angle (FMA) was calculated as the angle formed by the intersection of the Frankfort horizontal plane and the mandibular plane. A normal value was considered to be 25° ± 3°.
Based on the Tweed triangle and the FMA angle, the patients were divided into 3 facial biotype groups: group A, normodivergent (FMA, 22°-28°); group B, hypodivergent (FMA, <22°); and group C, hyperdivergent (FMA, >28°).
All images were analyzed by an orthodontist (M.-C.C.) using the Dolphin 3D software. The observer was blinded to each patient’s name, age, sex, and the reason for the CBCT scan. To assess the intraobserver reliability, 30 randomly selected lateral cephalograms were remeasured after 3 weeks by the same observer, who was blinded to the results of the previous evaluation.
The vertical relationship between each root tip of the posterior teeth and the maxillary sinus was analyzed on CBCT scans by another orthodontist (A.-S.M.). The second observer was also blinded to patient information and the facial assessment of the first observer.
For each patient, the maxillary left and right first and second premolars, and left and right first and second molars were analyzed. Premolars with either 1 root or 2 roots were analyzed. If a maxillary posterior tooth was not fully erupted or not touching the mandibular antagonist teeth, it was excluded from the study.
Each root tip was tagged with a landmark in the Dolphin 3D digitize/measurement menu. These landmarks were then saved for visualization in the coronal and axial views, and rechecked in the 3D image view to ensure that the tip of the root was properly assessed ( Fig 2 ). The relationship was then categorized after a root type classification modified from the study of Jung and Cho ( Fig 3 ), and a score from 0 to 3 was assigned to each root depending on its relationship with the maxillary sinus: 0, the root of the tooth is away from the cortical border of the sinus with a zone of cancellous bone in between ( Fig 3 , A ); 1, the root is laterally projected, away from the cortical border of the sinus ( Fig 3 , B ); 2, the tip of the root is in contact with the cortical border of the sinus ( Fig 3 , C ); and 3, the tip of the root projects into the maxillary sinus ( Fig 3 , D ). The most favorable score from a dental point of view was 0, and a score of 3 was the most unfavorable.
To determine the intraobserver reliability, 30 randomly selected teeth were reassessed after 3 weeks by the same observer blinded to the results of the previous evaluation.
Statistical analysis
For each patient, an average patient score (Patient score) was calculated using the following formula:
Patient score = ∑ of all root scores of the patient total number of roots of the patient
In the same manner, without taking sides into account, an average tooth score (Tooth score) was calculated for the first premolar (PM1 score), second premolar (PM2 score), first molar (M1 score), and second molar (M2 score) using the following formula:
Tooth score = ∑ left tooth root scores + ∑ right tooth root scores number of left + right roots
We divided our sample into age categories: children (younger than 10 years), adolescents (10-19 years), and young adults (over 19 years).
All statistical analyses were performed with SPSS Statistics for Windows software (version 19.0; IBM Armonk, NY). To determine the test-retest reliability of the assessment of facial biotype and root proximity to the maxillary sinus (qualitative data), the unweighted Cohen kappa coefficient was calculated.
Data were presented as percentages or arithmetic means and standard deviations for scores, and medians and interquartile intervals for age, teeth per patient, and roots per patient. The chi-square test was used to analyze the differences between groups according to sex. For quantitative data, we tested the normal distribution using the Kolmogorov-Smirnov test. The Kruskal-Wallis test was used to analyze the differences between facial biotype groups for variables that were not normally distributed: age, teeth per patient, roots per patient, Patient scores, and Tooth scores. The analysis was followed by the post hoc test with the Bonferroni correction.
The Mann-Whitney U test was used to analyze sex differences in the computed average scores. Correlations between PM1 score, PM2 score, M1 score, and M2 score were analyzed by the Spearman coefficient of correlation.
The influence of facial biotype on Tooth score and Patient score was analyzed using a general linear regression model with fixed effects after controlling for confounding factors identified in univariate analysis. The results for each factor are the adjusted coefficient, the 95% confidence interval of the same coefficient, and the P value. In the parameter estimates, the hypodivergent facial biotype group was taken as the reference group.
Significance was set at P <0.05.
Results
The final sample consisted of 128 patients ( Fig 4 ). The main reason for exclusion was age greater than 25 years. The unweighted Cohen kappa coefficients for the determination of facial biotype and root assignment between test-retest were κ = 0.91 ( P <0.001) and κ = 0.82 ( P <0.001), respectively.
The distributions of age, sex, number of teeth, and number of roots according to facial biotype are given in Table I . When we compared age, sex, number of teeth, and number of roots by facial biotype, we found no statistically significant differences between the groups.
| Parameters | Total (n = 128) | Hypodivergent (n = 30) | Normodivergent (n = 64) | Hyperdivergent (n = 34) | P value |
|---|---|---|---|---|---|
| Age (y) | 12 (9-17) | 14 (10-19) | 12 (9.5-17) | 11 (9-14) | 0.15 ∗ |
| Male, n (%) | 38 (29.7) | 8 (26.7) | 20 (31.3) | 10 (29.4) | 0.90 † |
| Teeth per patient | 6.5 (2-8) | 8 (4-8) | 7.5 (2-8) | 4 (2-8) | 0.09 ∗ |
| Roots per patient | 15 (6-18) | 16 (10-18) | 15 (6-18) | 10 (6-18) | 0.12 ∗ |
A total of 703 teeth were examined (389 molars, 314 premolars): 186 teeth and 420 roots in the hypodivergent group, 356 teeth and 819 roots in the normodivergent group, and 161 teeth and 381 roots in the hyperdivergent group. The most frequent root scores were 0 (34.3%) and 3 (37.1%) ( Table II ).
| Hypodivergent (n = 30) | Normodivergent (n = 64) | Hyperdivergent (n = 34) | Total number of roots | |
|---|---|---|---|---|
| Root score | n (%) | |||
| 0 | 180 (42.8) | 259 (31.6) | 116 (30.4) | 555 (34.3) |
| 1 | 23 (5.5) | 39 (4.8) | 7 (1.8) | 69 (4.3) |
| 2 | 108 (25.7) | 169 (20.6) | 118 (31.0) | 395 (24.3) |
| 3 | 109 (26.0) | 352 (43.0) | 140 (36.8) | 601 (37.1) |
| Total n (%) | 420 (100) | 819 (100) | 381 (100) | 1620 (100) |
Table III shows the distribution of root position scores for all roots per tooth type for each facial pattern. When comparing facial biotypes in post hoc analysis, we found significant differences between the normodivergent and hypodivergent biotypes for Patient score and M2 score, and between hypodivergent and hyperdivergent biotypes for M2 score ( Table IV ). The hypodivergent facial biotype had significantly fewer second molar roots into the sinus than did the normodivergent and hyperdivergent biotypes.
| Roots (n) | Root | Score | Hypodivergent | Normodivergent | Hyperdivergent | Total |
|---|---|---|---|---|---|---|
| First premolar (n = 166) | ||||||
| 1 | 0 | 13 (36.1) | 18 (50) | 5 (13.9) | 36 (100) | |
| 2 | 1 (25) | 2 (50) | 1 (25) | 4 (100) | ||
| 2 | Buccal | 0 | 33 (26.4) | 63 (50.4) | 29 (23.2) | 125 (100) |
| 2 | (0) | 1 (100) | (0) | 1 (100) | ||
| Palatal | 0 | 33 (27.7) | 60 (50.4) | 26 (21.8) | 119 (100) | |
| 2 | (0) | 4 (57.1) | 3 (42.9) | 7 (100) | ||
| Second premolar (n = 149) | ||||||
| 1 | 0 | 16 (30.8) | 25 (48.1) | 11 (21.2) | 52 (100) | |
| 1 | (0) | 2 (100) | (0) | 2 (100) | ||
| 2 | 11 (24.4) | 20 (44.4) | 14 (31.1) | 45 (100) | ||
| 3 | 10 (31.3) | 15 (46.9) | 7 (21.9) | 32 (100) | ||
| 2 | Buccal | 0 | 1 (10) | 9 (90) | (0) | 10 (100) |
| 2 | 1 (25) | 3 (75) | (0) | 4 (100) | ||
| 3 | 1 (25) | 3 (75) | (0) | 4 (100) | ||
| Palatal | 0 | (0) | 8 (100) | (0) | 8 (100) | |
| 2 | 2 (50) | 2 (50) | (0) | 4 (100) | ||
| 3 | 1 (16.7) | 5 (83.3) | (0) | 6 (100) | ||
| First molar (n = 253) | ||||||
| 3 | Mesiobuccal | 0 | 15 (35.7) | 14 (33.3) | 13 (31) | 42 (100) |
| 1 | 2 (40) | 3 (60) | (0) | 5 (100) | ||
| 2 | 23 (30.3) | 31 (40.8) | 22 (28.9) | 76 (100) | ||
| 3 | 19 (14.6) | 78 (60) | 33 (25.4) | 130 (100) | ||
| Distobuccal | 0 | 11 (36.7) | 12 (40) | 7 (23.3) | 30 (100) | |
| 1 | 2 (50) | 2 (50) | (0) | 4 (100) | ||
| 2 | 25 (30.9) | 31 (38.3) | 25 (30.9) | 81 (100) | ||
| 3 | 21 (15.2) | 81 (58.7) | 36 (26.1) | 138 (100) | ||
| Palatal | 0 | 15 (25.9) | 25 (43.1) | 18 (31) | 58 (100) | |
| 1 | 13 (37.1) | 19 (54.3) | 3 (8.6) | 35 (100) | ||
| 2 | 13 (19.4) | 28 (41.8) | 26 (38.8) | 67 (100) | ||
| 3 | 18 (19.4) | 54 (58.1) | 21 (22.6) | 93 (100) | ||
| Second molar (n = 134) | ||||||
| 3 | Mesiobuccal | 0 | 10 (62.5) | 6 (37.5) | (0) | 16 (100) |
| 1 | 1 (50) | 1 (50) | (0) | 2 (100) | ||
| 2 | 8 (34.8) | 9 (39.1) | 6 (26.1) | 23 (100) | ||
| 3 | 21 (22.6) | 51 (54.8) | 21 (22.6) | 93 (100) | ||
| Distobuccal | 0 | 14 (56) | 9 (36) | 2 (8) | 25 (100) | |
| 1 | 1 (16.7) | 4 (66.7) | 1 (16.7) | 6 (100) | ||
| 2 | 12 (35.3) | 12 (35.3) | 10 (29.4) | 34 (100) | ||
| 3 | 13 (18.8) | 42 (60.9) | 14 (20.3) | 69 (100) | ||
| Palatal | 0 | 19 (55.9) | 10 (29.4) | 5 (14.7) | 34 (100) | |
| 1 | 4 (26.7) | 8 (53.3) | 3 (20) | 15 (100) | ||
| 2 | 12 (24.5) | 26 (53.1) | 11 (22.4) | 49 (100) | ||
| 3 | 5 (13.9) | 23 (63.9) | 8 (22.2) | 36 (100) | ||
| Total | 420 (25.9) | 819 (50.6) | 381 (23.5) | 1620 (100) | ||
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