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[Measurement of the height and width of residual alveolar crests in low-set maxillary sinus patients with missing upper molar].

PURPOSE
Using spiral computed tomography and Simplant software to measure the width and height of residual alveolar crest of agomphious upper molar region at different levels around bottom of low-set maxillary sinus. To evaluate the impact of sex, age, agomphious duration, and cause of tooth extraction on the width and height of residual alveolar crest.


METHODS
Forty-three patients with missing uppers molar and residual alveolar bone height being 4 to 6mm showed by panoramic radiographs were scanned by spiral computed tomography. 3D model of the alveolar crest and maxillary sinus were reconstructed using the images from CT scan and Simplant software. The height and width of the residual alveolar crest of agomphious upper molar region at different levels around bottom of maxillary sinus were measured. The data was analyzed with SPSS16.0 software package for Student's t test, analysis of variance(ANOVA) and Kruskal-Wallis H test.


RESULTS
(1)The mean distance between the top of residual alveolar crest and the floor of sinus was (5.26±0.58)mm. (2)The difference between the width of internal bone wall and that of external bone wall at different levels above the bottom of maxillary sinus was significant(P<0.01), except for agomphious upper second molar at 3.75mm. (3)The height of residual crest and width of sinus floor decreased remarkably with age and agomphious duration(P<0.01) while the width of sinus lateral walls didn't change so much with them(P>0.05). (4)Height of residual crest of the tooth extracted due to periodontitis was obviously lower than that of the tooth extracted due to residual root(crown) or crown fracture(P<0.01).


CONCLUSIONS
The height and width of residual crest change significantly with age, agomphious duration and causes of tooth extraction. However, the width of lateral walls above sinus floor do not change so much with those factors. The internal wall of maxillary sinus floor is wider than the external wall at agomphious molar. This anatomic feature may be taken into consideration during implantation. The site and direction of implant can be adjusted equally according to the age, agomphious duration and causes of tooth extraction, so that maxillary sinus augmentation can be avoided in part of patients with low-set maxillary sinus.