INTRODUCTION
MATERIALS AND METHODS
Ethical approval of the study and informed consent
Subjects
Figure 1
Overall flowchart of image reconstruction for reproducible measurements of the available alveolar bone height. (A) The occlusal plane of the original data was reoriented to be parallel to the base plane. (B) The CBCT image was aligned to be perpendicular to the arch shape at the cervical level of the maxillary molars. (C) Reconstruction of the cross-sectional image.

Classification and measurements
Figure 2
Illustrations of the classification of the relationship between the maxillary molars and the sinus floor.

Type 1: The apex of all roots is located in contact with or inferior to the lowest border of the maxillary sinus floor.
Type 2: The diverged buccal and palatal roots envelop the sinus.
Type 3: One or more root is protruding into the maxillary sinus.
A – Only the buccal root is protruding into the sinus.
B – Only the palatal root is protruding into the sinus.
C – All roots are protruding into the sinus.
D – A fused root is protruding into the sinus.
Type 4: All roots are leaning to the buccal or palatal side of the maxillary sinus.
Statistical analysis
RESULTS
Analysis of classification
Table 1
The frequency of types of relationships between the maxillary molars and the maxillary sinus

Tooth | Type 1 | Type 2 | Type 3 | Type 4 |
---|---|---|---|---|
M1 | 74 (19.7) | 135 (35.9) | 167 (44.4) | 0 |
M2 | 117 (31.1) | 88 (23.4) | 156 (41.5) | 15 (4.0) |
Total | 191 (25.4) | 223 (29.7) | 323 (43.0) | 15 (2.0) |
Figure 4
The frequency distribution of the classification in the maxillary first molars (A) and second molars (B).

Table 2
Distribution of subtypes of type 3 (with at least one root protruding into the maxillary sinus)

Analysis of VD measurements
Table 3
Mean values and standard deviations of the shortest vertical distance from the furcation midpoint to the sinus floor according to the relationship between the maxillary molars and the maxillary sinus

Tooth | Type 1 (mm) | Type 2 (mm) | Type 3 (mm) | Type 4 (mm) | Total (mm) |
---|---|---|---|---|---|
M1 | 9.51±3.68 | 5.46±1.51 | 3.70±1.52 | - | 5.48±3.02 |
M2 | 8.07±2.73 | 5.49±1.28 | 4.03±1.53 | 4.04±1.35 | 5.62±2.56 |
Table 4
Differences in the mean vertical distance between the maxillary molars according to sex and side
