Ridge alterations post-extraction in the esthetic zone: a 3D analysis with CBCT

Abstract

Dimensional alterations of the facial bone wall following tooth extractions in the esthetic zone have a profound effect on treatment outcomes. This prospective study in 39 patients is the first to investigate three-dimensional (3D) alterations of facial bone in the esthetic zone during the initial 8 wks following flapless tooth extraction. A novel 3D analysis was carried out, based on 2 consecutive cone beam computed tomographies (CBCTs). A risk zone for significant bone resorption was identified in central areas, whereas proximal areas yielded only minor changes. Correlation analysis identified a facial bone wall thickness of ≤ 1 mm as a critical factor associated with the extent of bone resorption. Thin-wall phenotypes displayed pronounced vertical bone resorption, with a median bone loss of 7.5 mm, as compared with thick-wall phenotypes, which decreased by only 1.1 mm. For the first time, 3D analysis has allowed for documentation of dimensional alterations of the facial bone wall in the esthetic zone of humans following extraction. It also characterized a risk zone prone to pronounced bone resorption in thin-wall phenotypes. Vertical bone loss was 3.5 times more severe than findings reported in the existing literature.

Keywords: bone remodeling; bone resorption; clinical trial; dental implants; maxilla; three-dimensional imaging.

Figure 1.

Radiographic examination. The DICOM files of the obtained CBCT datasets, immediately post-extraction and following 8 wks of healing, were converted into a surface mesh model with digital imaging software. The 2 surface mesh models were superimposed and rigidly aligned with anatomical landmarks. The distance between the 2 surface meshes was presented as color-coded figures to identify zones of facial bone resorption.

Figure 2.

Baseline measurements and dimensional and vertical bone loss after 8 wks of healing. (A) The analysis was performed in central (c) and proximal sites (a) oriented at a 45° degree angle with the tooth axis as a reference. (B) Frequency distribution of facial bone wall thickness in central and proximal sites. (C) A horizontal reference line was traced connecting the facial and palatal bone wall for standardized measurements. The point-to-point distance between the 2 surface meshes with the respective angle to the reference line was obtained for each sample, and the vertical and horizontal bone losses were calculated accordingly. (D) Percentage of vertical bone loss in central and proximal sites. (E) Percentage of horizontal bone loss in central and proximal sites. **p < .0001.

Figure 3.

Characteristic bone resorption patterns. (A) A thin-wall phenotype showed a facial bone wall thickness of ≤ 1 mm and revealed a progressive bone resorption pattern after 8 wks of healing. (B) A thick-wall phenotype, with a facial bone wall thickness of > 1 mm, exhibited a less-pronounced bone resorption pattern after 8 wks of healing.

Figure 4.

Correlation analysis in central risk zones. (A) A critical facial bone wall thickness of 1 mm was identified. (B) The difference between the thin and thick phenotypes in relation to vertical bone loss was significant [p < .0001 (**)].