ABSTRACT
Objectives
The study aimed to explore the changes in the height of the soft tissue around the healing abutment at different time points after second‐stage implant surgery.
Methods
Cone‐beam computed tomography (CBCT) data were collected at baseline (second‐stage surgery), and intraoral scans were obtained at baseline and multiple follow‐up visits: after suture removal (1 week post‐surgery), during impression taking, and immediately before performing restoration. Patients were grouped based on the time of impression taking (1 or 2 weeks post‐suture removal: 1I or 2I), and further subgrouped according to the timing of performing restoration (2, 3, or 4 weeks post‐impression: 2R, 3R, or 4R). Digital datasets were superimposed using tooth‐supported reference areas before the intraoral height of the healing abutment and the supracrestal tissue height (STH) were measured at the mesial, distal, buccal, and lingual sites at the different time periods.
Results
A total of 76 patients with 102 implants were enrolled in the study; specifically, 22 were in the 1I2R group, 18 in 1I3R, 14 in 1I4R, 14 in 2I2R, 18 in 2I3R, and 16 in 2I4R. The STH changes of 2I3R group were (0.37 ± 0.13), (0.41 ± 0.21), (0.43 ± 0.17), (0.43 ± 0.20) mm at the mesial, distal, buccal, and lingual sites, which showed no statistically significant differences with 2I4R group whose STH changes were (0.35 ± 0.13), (0.43 ± 0.22), (0.39 ± 0.16), (0.41 ± 0.14) mm, respectively. the changes of these two groups were Larger Than Other groups, with significant differences (p < 0.01).
Conclusions
Within the study limits, STH around healing abutment tended to stabilize approximately 6 weeks after second‐stage surgery.
Keywords: dental abutments, dental implants, dental impression technique, implant‐supported dental prosthesis, soft tissue
1. Introduction
Following second‐stage dental implant surgery, adequate time is required for soft tissue healing and stabilization before taking an impression. This ensures accurate replication of the soft tissue morphology, which is critical for the precise fabrication of the abutment and restoration. However, there is currently no consensus regarding the optimal timing for impression taking following second‐stage dental implant surgery. Clinically, a minor degree of recession and instability in the soft tissue surrounding the abutment or restoration is often observed at the time of implant restoration.
Animal studies have demonstrated significant variability in the soft tissue healing time around implants, ranging from 2 h to 2 weeks when using suture removal as the baseline (Salvi et al. 2015; Sculean et al. 2014). Recent in vivo studies have found that the soft tissue around the implant tends to stabilize 2 weeks after the implant restoration is completed (Zheng, Wang, et al. 2021). Moreover, the attachment of the soft tissue complex (i.e., the epithelium and connective tissue) surrounding a soft tissue level implant is generally established 6–8 weeks after second‐stage surgery. This period is crucial for the formation of the biological width and the maturation of the barrier function. Despite these observations, there is a lack of clinical research to determine when soft tissues stabilize following second‐stage surgery in clinical settings.
Digital oral scanning technology, also known as digital impression technology, offers significantly higher scanning accuracy compared to traditional impression methods (Amin et al. 2017; Dohiem et al. 2022). In cases of single and multiple‐tooth implant restoration, the method demonstrates superior accuracy over traditional impressions (Albanchez‐González et al. 2022). Additionally, digital scanning provides several other advantages, such as a reduced time burden and increased patient comfort (Yuzbasioglu et al. 2014). This technology can also accurately reproduce the contour of the soft tissue around the abutment (Zimmermann et al. 2022). To measure three‐dimensional changes in soft tissue, an intraoral scanner can be employed either directly or on plaster models. The establishment of fixed reference points and measurement areas is essential for obtaining precise data (Thoma et al. 2021). Therefore, the use of digital oral scanning technology offers a reliable method for assessing changes in the soft tissue around the implant abutment following second‐stage surgery.
Both clinical observations and histological studies suggest that the stabilization of soft tissues and the establishment of soft tissue complex attachment after second‐stage surgery require a considerable amount of time. However, to date, no clinical studies have been conducted to substantiate these findings. Thus, the aim of this study was to investigate supracrestal tissue height changes around the healing abutment in the posterior region after second‐stage implant surgery. This study aimed to provide a reference time point for the stability of supracrestal tissue height around the healing abutment and for the clinical restoration of dental implants.
2. Materials and Methods
2.1. Study Design and Ethical Approval
This study was a retrospective cohort study. Patients who underwent second‐stage implant surgery and implant restoration in the Department of Implantology, Affiliated Stomatological Hospital of Fujian Medical University, from September 2023 to January 2025, were recruited. During the study period, cone‐beam computed tomography (CBCT) data were collected at baseline (second‐stage implant surgery), and digital intraoral scanning data were obtained at baseline, after suture removal, during impression taking, and immediately before performing restoration. All patients had their sutures removed 1 week after second‐stage surgery.
Patients were grouped based on the time of impression taking, specifically 1 or 2 weeks after suture removal (denoted as 1I or 2I), and further subgrouped according to the timing of restoration, specifically 2, 3, or 4 weeks after impressions (denoted as 2R, 3R, or 4R). In total, the sample comprised two major groups, 1I and 2I, and six subgroups: 1I2R, 1I3R, 1I4R, 2I2R, 2I3R, and 2I4R.
This research complies with the Declaration of Helsinki, was registered in the Chinese Clinical Trial Registry (ChiCTR2500100403), and was approved by the Biomedical Ethics Committee of the Affiliated Stomatological Hospital of Fujian Medical University (approval number: [2024] Fujian Medical University Stomatological ethics review no. 68).
The sample size was estimated based on a previous clinical study on peri‐implant soft tissue changes around one‐piece and two‐piece implants (Sanz Martin et al. 2016). Based on this study, the clinically meaningful difference (anticipated mean difference) of peri‐implant supracrestal tissue height changes was set at 0.5 mm, with a pooled standard deviation (pooled SD) of 0.3 mm. Using G*Power 3.1 software, a two‐independent‐samples t‐test was applied as a preliminary approximation, with α = 5% (two‐tailed), power = 80%, and a 20% allowance for potential dropouts. The minimum sample size was 10 participants for each group, increased to 13 to account for dropouts. Ultimately, 76 participants with 102 implants were enrolled. The limitations of this preliminary sample size calculation are acknowledged, given that the study involved multiple subgroups, repeated measurements, and clustering by patient.
2.2. Participants
Inclusion Criteria:
Single posterior tooth loss
Age between 20 and 60 years old.
No alveolar bone resorption in adjacent teeth. Soft tissue inflammation was absent, defined as no redness, swelling, bleeding on probing, or suppuration at the implant site.
No soft tissue augmentation or bone removal is required during second‐stage implant surgery.
Buccal and lingual keratinized gingiva width > 2 mm after healing abutment placement.
Exclusion Criteria:
Failure of osseointegration.
Patients undergoing active periodontal therapy, including scaling and root planing or periodontal surgery, at the time of enrollment
Poor oral hygiene, defined as a plaque index ≥ 2 at the implant site.
Heavy smoking (> 10 cigarettes per day) and excessive drinking (alcohol consumption > 50 g per day or > 280 g per week).
2.3. Experimental Procedure
2.3.1. Preoperative CBCT Scanning
CBCT scans were performed prior to second‐stage surgery (KaVo i‐CAT 17–19, Germany) following the ALARA principle. Patients were positioned in maximum intercuspation. Key parameters included: field of view (FOV) 16 × 8 cm, voxel size 0.2 mm, tube voltage 90 kVp, tube current 5 mA, and exposure time 26.9 s. The effective dose was ~30 μSv. Data were exported in Digital Imaging and Communications in Medicine (DICOM) format.
2.3.2. Second‐Stage Dental Implant Surgery
All surgeries were performed by a single surgeon. Local anesthesia was induced with Primacaine (4% Articaine, 1/100,000 adrenaline, ACTEON, France). A full‐thickness flap was created via a mid‐crestal incision. The covering screws were removed, and the healing abutment was placed and checked for stability. The wound was sutured and fixed with 4–0 absorbable sutures (G03194L, Yake, China) (Figure 1).
FIGURE 1.
Second‐stage implant surgery (A) Preoperative view; (B) Surgical incision; (C) Healing abutment placement; (D) Suturing.
2.3.3. Intraoral Scan at Different Phases
Intraoral scans were performed immediately before the second‐stage implant surgery (T0), when removing the sutures (T1), when taking the impressions (T2), and immediately before restoration insertion (T3), as shown in Figure 2.
FIGURE 2.
Intraoral scans at different time points. T0: Immediately before second‐stage implant surgery, T1: Suture removal, T2: Impression taking, T3: Immediately before restoration insertion.
Before conducting the intraoral scanning process, the surgeon verified that the healing abutment was securely fastened to ensure its proper positioning and stability. Scans were obtained using the Aoralscan 3 Intraoral Scanner (Shining3D Dental, China) under natural light (if implant sites were present in both the upper and lower jaws, the dental arches of both jaws were scanned simultaneously). The operator maintained tissue dryness and cleanliness. All scans were performed by the same operator, who was masked to group allocation and prior measurement results. Standard Tessellation Language (STL) files were exported for analysis (Figure 3A).
FIGURE 3.
Registration of an intraoral scan with a CBCT scan. (A) Intraoral scan image, (B) Coarse registration; (C) Precise registration; (D) Registration completed.
2.4. Integration of the CBCT and Oral Scan Data
DICOM CBCT data were imported into oral implant treatment design software (RemebotDent V1.0.0.2, RemebotDent, China). The upper and lower jawbones and teeth were segmented for further analysis. STL intraoral scan data were imported sequentially. Registration was performed in two steps: coarse registration using six corresponding tooth landmarks and fine registration by fitting the complete tooth surfaces. This process completed the fitting procedure (as shown in Figure 3B–D). All data registration and measurement were performed by a single operator to ensure consistency.
2.5. Measurement
2.5.1. Positioning
After registration was completed, the center point of the implant was positioned in the axial plane of the CBCT, the vertical reference line was adjusted to be parallel to the occlusal center of the adjacent teeth, and the vertical reference line was adjusted to be parallel to the long axis of the implant in the coronal and sagittal planes (Figure 4A–C).
FIGURE 4.
Measurement methodology. Spatial orientation (A) Axial plane; (B) Sagittal plane; (C) Coronal plane. Measurement of the height of the healing abutment (D) At suture removal; (E) At impression; (F) At restoration. Measurement of STH (G).
2.5.2. eight Changes in the Soft Tissue Around the Abutment
The height of the healing abutment (HHA) above the gingiva was measured at T1, T2, and T3 at the buccal, lingual, mesial, and distal sites. Measurements were taken parallel to the vertical reference line, from the abutment edge to the soft tissue junction (Figure 4D–F). The results were expressed in millimeters (mm).
2.5.3. Supracrestal Tissue Height (STH) at Performing Restoration and Baseline
STH at the time of restoration (T3) was compared to the baseline (T0). The intraoral scan data obtained immediately before restoration were merged with the baseline data. Parallel to the outer contour of the healing abutment, with the junction of the healing abutment and the soft tissue serving as the starting point, the measurement line was drawn parallel to the vertical reference line in order to measure the area at the baseline. Similarly, the measurement line was drawn parallel to the vertical reference line in order to measure the height of the soft tissue changes (Figure 4G). The measurement results were expressed in mm. The buccal and lingual sites and the mesial and distal sites of the same abutment were also measured.
2.6. Statistical Analysis
2.6.1. Descriptive Statistics
The data were analyzed using SPSS Statistics v26.0 (IBM, USA). Continuous variables were expressed as mean ± SD or median (IQR), and categorical variables as counts and percentages. Percentages are based on the total number of patients in the respective analysis set. Normality of the data was assessed using the Shapiro–Wilk test. Homogeneity of variance was evaluated by Levene's test. To account for the potential clustering effect arising from multiple implants placed in the same patient, the intraclass correlation coefficient (ICC) was computed via a Linear Mixed Model (LMM). Results of the normality test, homogeneity of variance test, and ICC values are presented in the Tables S5–S7.
2.6.2. Exploratory Statistics
When the ICC > 0.1, an LMM was applied with patients set as the random effect; for comparisons involving three or more groups, Tukey's post hoc multiple comparison test was further conducted. When the ICC < 0.1, the statistical methods for pairwise comparisons (e.g., STH) were selected based on data distribution: the paired t‐test was used for normally distributed data, whereas the Wilcoxon signed‐rank test was adopted for non‐normally distributed data. For comparisons among three or more groups, the one‐way analysis of variance (ANOVA) with Tukey's post hoc multiple comparison test was employed if the data were normally distributed with homogeneous variances; if the data exhibited homogeneous variances but non‐normal distribution, the Kruskal‐Wallis test was employed. Post hoc pairwise comparisons for the Kruskal‐Wallis test were performed using Dunn's test, with p‐values adjusted via the Holm‐Bonferroni (step‐down) procedure to control the family‐wise error rate. Two‐sided 95% confidence intervals (95% CI) were calculated for these analyses. The false discovery rate (FDR) correction was applied to all other reported p‐values (including primary comparisons and Tukey's post hoc tests) to account for multiple testing, ensuring that no single p‐value was subjected to more than one type of adjustment.
A p‐value < 0.05 was considered statistically significant. This study was carried out in accordance with the guideline for the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) Statement.
3. Results
A total of 87 patients were recruited for this study. After applying the inclusion and exclusion criteria, 76 patients were included, consisting of 37 male and 39 female patients, with a total of 102 implants. Specifically, there were 54 implants in the 1‐week impression group (22 in the 1I2R group, 18 in the 1I3R group, and 14 in the 1I4R group) and 48 implants in the 2‐week impression group (14 in the 2I2R group, 18 in the 2I3R group, and 16 in the 2I4R group).
3.1. Changes in the Height of the Soft Tissues Around the Abutment
3.1.1. Height Changes in the Soft Tissues Around the Abutment at Different Impression Times
To compare changes in the height of the soft tissue around the abutment in the 1‐week impression group (1I) and 2‐week impression group (2I), the following formula was used: Height change in the soft tissue = HHA (T2)−HHA (T1).
The mean height changes at the mesial, distal, buccal, and lingual sites around the abutment were 0.34 ± 0.25 mm, 0.40 ± 0.27 mm, 0.40 ± 0.25 mm, and 0.34 ± 0.25 mm in the 1‐week impression group, and were 0.54 ± 0.31 mm, 0.66 ± 0.53 mm, 0.60 ± 0.36 mm, and 0.51 ± 0.28 mm in the 2‐week impression group, respectively (Table S1). Height changes in the 2‐week impression group were significantly greater than those in the 1‐week impression group at all measured sites (p < 0.01), as shown in Figure 5. Within each group, there were no statistically significant differences in height changes among the mesial, distal, buccal, and lingual sites.
FIGURE 5.
Height changes of the peri‐abutment soft tissues in different impression groups. Linear mixed models with patient as a random effect were employed. (A) Comparison between different impression times, (B) Comparison among the mesial, distal, buccal, and lingual sites. **p < 0.01, p‐values were FDR‐adjusted.
3.1.2. Height Changes in the Soft Tissues Around the Abutment at Different Restoration Times
Height changes in the soft tissue were calculated as HHA (T3)−HHA (T2).
In the 1‐week impression group (1I group), statistically significant differences were observed in the height changes among the 2‐week (1I2R), 3‐week (1I3R), and 4‐week (1I4R) restoration groups at the mesial, distal, buccal, and lingual sites (p < 0.01; Figure 6A; Table 1). Post hoc Tukey comparisons showed that the 2‐week restoration group had lower height changes than the 4‐week restoration group (p < 0.01), while there were no statistically significant differences between the 3‐week and 4‐week restoration groups (Table S2). Within each group, there were no significant differences in height changes among the mesial, distal, buccal, and lingual sites (Figure 6C).
FIGURE 6.
Height changes of the peri‐abutment soft tissues in different restoration groups. (A) Comparison between different restoration insertion times in the 1‐week impression group (Linear mixed models with patient as a random effect with Tukey's post hoc multiple comparison were employed), (B) Comparison between different restoration insertion times in the 2‐week impression group (Linear mixed models with patient as a random effect were employed), (C) Comparison among the mesial, distal, buccal, and lingual sites in the 1‐week impression group (Kruskal‐Wallis test followed by Dunn's post hoc multiple comparison test with Holm adjustment was utilized for the mesial site; ANOVA with Tukey's post hoc multiple comparison test was employed for the distal site; Linear mixed models with patient as a random effect were used at the buccal and lingual sites), (D) Comparison among the mesial, distal, buccal, and lingual sites in the 2‐week impression group (Linear mixed models with patient as a random effect were employed). p‐values for the mesial site in C were Holm‐adjusted; all other p‐values were FDR‐adjusted, *p < 0.05, **p < 0.01.
TABLE 1.
HHA changes of 2‐week (2R), 3‐week (3R), and 4‐week (4R) restoration in 1‐week impression major group (mm).
| Location | HHA(T3)‐HHA(T2) | Inter group | Cohen's f 2 | 2w Intra group | 3w Intra group | 4w Intra group | ||
|---|---|---|---|---|---|---|---|---|
| 2R | 3R | 4R | ||||||
| Mean(SD) | Mean(SD) | Mean(SD) | p | p | p | p | ||
| Mesial | 0.20 (0.16) | 0.33 (0.17) | 0.46 (0.18) | 0.002** | 0.29 | 0.587 | 0.720 | 0.567 |
| Distal | 0.25 (0.18) | 0.37 (0.20) | 0.49 (0.13) | 0.002** | 0.26 | |||
| Buccal | 0.24 (0.12) | 0.38 (0.20) | 0.54 (0.28) | 0.002** | 0.30 | |||
| Lingual | 0.27 (0.18) | 0.40 (0.22) | 0.54 (0.19) | 0.002** | 0.28 | |||
Note: Linear mixed models with patient as a random effect were used for intergroup and intragroup comparisons.
Abbreviations: 2R, 2‐week performing restoration; 3R, 3‐week performing restoration; 4R, 4‐week performing restoration; HHA, Height of the healing abutment above the gingiva; SD, Standard Deviation; T2, Impression; T3, Restoration.
** p < 0.01, p‐values were FDR‐adjusted.
In the 2‐week impression group (2I group), significant differences were also observed among the 2‐week (2I2R), 3‐week (2I3R), and 4‐week (2I4R) restoration groups at all sites (p < 0.05; Table 2). Post hoc multiple comparisons indicated that the 2‐week restoration group had lower height changes than the 3‐week groups at all sites and lower than the 4‐week groups at the mesial and distal sites (p < 0.05), while there were no statistically significant differences between the 3‐week and 4‐week groups (Figure 6B; Table S3). Within each group, there were no significant differences in height changes among the mesial, distal, buccal, and lingual sites (Figure 6D).
TABLE 2.
HHA changes of 2‐week (2R), 3‐week (3R), and 4‐week (4R) restoration in 2‐week impression major group (mm).
| Location | HHA(T3)‐HHA(T2) | Inter group | ε2/η2/Cohen's f2 | 2w Intra group | 3w Intra group | 4w Intra group | ||
|---|---|---|---|---|---|---|---|---|
| 2R | 3R | 4R | ||||||
| Mean/Median (SD/IQR) | Mean/Median (SD/IQR) | Mean/Median (SD/IQR) | p | p | p | p | ||
| Mesial | 0.20 (0.10) | 0.40 (0.30) | 0.40 (0.10) | 0.034* | 0.23 | 0.906 | 0.680 | 0.564 |
| Distal | 0.26 (0.14) | 0.41 (0.21) | 0.43 (0.22) | 0.046* | 0.13 | |||
| Buccal | 0.26 (0.16) | 0.43 (0.17) | 0.39 (0.16) | 0.046* | 0.15 | |||
| Lingual | 0.26 (0.10) | 0.43 (0.20) | 0.41 (0.14) | 0.046* | 0.17 | |||
Note: Kruskal‐Wallis test followed by Dunn's post hoc multiple comparison test with Holm adjustment was utilized at mesial site. ANOVA with Tukey's post hoc multiple comparison test was employed at distal site. Linear mixed models with patient as a random effect were used at buccal and lingual sites. Linear mixed models with patient as a random effect were used for intragroup.
Abbreviations: 2R, 2‐week performing restoration; 3R, 3‐week performing restoration; 4R, 4‐week performing restoration; HHA, Height of the healing abutment above the gingiva; IQR, Interquartile Range; SD, Standard Deviation; T2, Impression; T3, Restoration.
*p < 0.05, p‐values were FDR‐adjusted.
Overall, the height of the soft tissue around the abutment continued to change during the 2–4 week restoration period, with smaller differences observed at approximately 5–6 weeks post‐surgery.
3.2. STH At the Time of Performing Restoration
The preoperative (STH1) and restoration (STH2) values for each group are presented in Table 3. The STH2 values were significantly higher than STH1 at the buccal and lingual sites (Figure 7). In contrast, STH2 was lower than the STH1 at the mesial sites in the 1I2R, 1I3R, and 2I2R groups and at the distal sites in the 1I2R and 1I3R groups, while there were no statistically significant differences in the 1I4R, 2I3R, and 2I4R groups at the mesial and distal sites, nor in the 2I2R group at the distal site (Table 3 and Figure 7).
TABLE 3.
Specific values of the supracrestal tissue height at the time of preoperative (STH1) and restoration (STH2) in each group(mm).
| Group | STH | |||||||
|---|---|---|---|---|---|---|---|---|
| Mesial | Distal | Buccal | Lingual | |||||
| Mean(SD) | p | Mean/Median (SD/IQR) | p | Mean (SD) | p | Mean/Median (SD/IQR) | p | |
| 1I2R | ||||||||
| STH1 | 3.05 (0.88) | 0.008** | 3.39 (0.83) | 0.008** | 2.67 (0.94) | < 0.001*** | 2.70 (1.00) | 0.001** |
| STH2 | 2.60 (0.78) | 2.90 (1.04) | 3.55 (0.63) | 3.30 (1.20) | ||||
| 1I3R | ||||||||
| STH1 | 3.21 (1.21) | 0.024* | 3.08 (0.97) | 0.097 | 2.51 (0.82) | 0.024* | 3.14 (1.37) | 0.025* |
| STH2 | 2.79 (1.09) | 2.85 (0.88) | 3.52 (1.10) | 3.95 (1.40) | ||||
| 1I4R | ||||||||
| STH1 | 3.25 (1.07) | 0.040* | 3.08 (0.95) | 0.037* | 2.45 (1.04) | 0.001** | 2.56 (1.34) | 0.001** |
| STH2 | 2.95 (0.90) | 2.91 (0.87) | 3.71 (1.05) | 3.48 (0.94) | ||||
| 2I2R | ||||||||
| STH1 | 3.59 (0.76) | 0.592 | 3.33 (0.87) | 0.361 | 2.84 (0.60) | 0.001** | 3.00 (0.95) | 0.040* |
| STH2 | 3.50 (0.75) | 3.28 (0.80) | 3.76 (0.84) | 3.51 (0.67) | ||||
| 2I3R | ||||||||
| STH1 | 3.12 (0.55) | 0.216 | 3.30 (0.90) | 0.573 | 2.53 (0.73) | < 0.001*** | 2.93 (0.87) | 0.026* |
| STH2 | 2.95 (0.56) | 3.10 (1.00) | 3.40 (0.74) | 3.70 (0.78) | ||||
| 2I4R | ||||||||
| STH1 | 3.53 (0.97) | 0.233 | 3.19 (1.21) | 0.233 | 2.17 (0.83) | < 0.001*** | 2.29 (1.09) | 0.018* |
| STH2 | 3.41 (0.98) | 2.94 (1.21) | 3.01 (0.75) | 2.75 (1.11) | ||||
Note: Wilcoxon signed‐rank test was adopted for lingual site in 1I2R and distal site in 2I3R. One‐sample t‐test was used for mesial site in 2I4R, distal site in 1I3R, buccal site in 1I2R, 1I4R and 2I4R, lingual site in 2I4R. Linear mixed models with patient as a random effect were used for others. *p < 0.05, **p < 0.01, ***p < 0.001, p‐values were FDR‐adjusted.
Abbreviations: 1I, 1‐week impression; 2I, 2‐week impression taking; 2R, 2‐week performing restoration; 3R, 3‐week performing restoration; 4R, 4‐week performing restoration; IQR, Interquartile Range; SD, Standard Deviation; STH, Supracrestal tissue height; STH1, Preoperative STH; STH2, Restoration STH.
FIGURE 7.
Supracrestal tissue height (STH) at the time of restoration insertion. (A) 1‐week impression and 2‐week restoration insertion group, (B) 1‐week impression and 3‐week restoration insertion group, (C) 1‐week impression and 4‐week restoration insertion group, (D) 2‐week impression and 2‐week restoration insertion group, (E) 2‐week impression and 3‐week restoration insertion group, (F) 2‐week impression and 4‐week restoration insertion group (Wilcoxon signed‐rank test was applied for the lingual site in the 1I2R and the distal site in the 2I3R group; one‐sample t‐test was used for the mesial site in 2I4R, distal site in 1I3R, buccal site in 1I2R, 1I4R and 2I4R, lingual site in 2I4R; Linear mixed models with patient as a random effect were used for the other sites). *p < 0.05, **p < 0.01, ***p < 0.001.
These results indicate site‐specific differences in soft tissue height changes relative to preoperative values, with buccal and lingual sites generally exhibiting greater height increases at the time of restoration insertion, while mesial and distal sites show smaller or decreasing changes.
The changes in the supracrestal tissue height relative to the preoperative values were calculated as STH changes = STH2—STH1. These changes are summarized in Table S4. STH changes at the buccal and lingual sites were significantly different from those at the mesial and distal sites (Figure 8), showing opposing trends: buccal and lingual sites generally increased, while mesial and distal sites generally decreased compared with preoperative measurements.
FIGURE 8.
Changes in supracrestal tissue height at different times of restoration insertion intervals compared with the preoperative height. (A) 1‐week impression groups, (B) 2‐week impression groups. *p < 0.05, **p < 0.01, ***p < 0.001, p‐values were FDR‐adjusted.
4. Discussion
This study evaluated the changes in the supracrestal tissue height around the abutments after second‐stage implant surgery using intraoral scanning and CBCT alignment technology. The results suggested that STH appeared to reach a relative plateau approximately 6 weeks after the second‐stage surgery. Notably, at the time of final restoration, the STH at the buccal and lingual sites exhibited a tendency to be greater than at the baseline (at second‐stage surgery), whereas it appeared to remain reduced at the mesial and distal sites.
In 2020, Avila‐Ortiz et al. (2020) proposed the term “Supracrestal Tissue Height” (STH) to describe the vertical dimension of the peri‐implant soft tissues. This concept aligns with the “vertical soft tissue height at the alveolar crest” described by Linkevicius et al. (2015, 2018), which distinguishes vertical dimensions from horizontal soft tissue thickness. Our study focused specifically on the changes in the STH in the vertical direction around the abutment after the second‐stage implant surgery and compared the STH after soft tissue stabilization with the preoperative baseline.
The formation of peri‐implant soft tissue is a complex physiological process, involving an interplay between multiple factors, analogous to wound healing (Zheng, Ao, et al. 2021). Current biological evidence indicates that within 1–2 weeks, the barrier epithelium begins to form, followed by the maturation of the barrier epithelium and the establishment of collagen fibers (Berglundh et al. 2007; Pippi 2017). The establishment of the biological barrier and biological width around a transmucosal abutment is generally reported to reach completion within 6–8 weeks (Salvi et al. 2015; Sculean et al. 2014). In our study, the STH around the implant exhibited a regressive trend during the first 2 weeks after suture removal which may be attributed to the initial stages of junctional epithelium formation. The observation that STH changes around the abutment became minimal from 5 weeks post‐suture removal may indicate that relative soft tissue stability is achieved around 6 weeks post‐surgery, a finding that appears consistent with existing histological data.
In an animal experiment conducted by Negri et al. (Negri et al. 2015), the biological width of the internally connected conical implants was 3.13–3.34 mm, including epithelial tissue of 1.64–1.93 mm and connective tissue of 1.21–1.32 mm. In a human study by Judgar et al. (Judgar et al. 2014), the biological width of one‐stage implants was 2.55 ± 0.16 mm, and that of two‐stage implants was 3.26 ± 0.15 mm. While the biological width of implants varies slightly among published studies, a height of 3–4 mm is generally accepted by in clinical practice. In all groups of this study, the STH at the time of restoration ranged from 2.60 to 3.95 mm, which is similar to the results of other biological width studies. Interestingly, we observed a site‐specific divergence: an increase in STH at buccal/lingual sites and a decrease at mesial/distal sites compared to preoperative levels. It is hypothesized that the linear incision and flap elevation during the second‐stage surgery might lead to slight tissue involution at the proximal sites, while the healing abutment supports and “tents” the buccal and lingual tissues. Currently, there is no available literature supporting this hypothesis, possibly due to the limited duration of the observation periods. As soft tissue healing progresses over time, these tissues may eventually return to their preoperative condition. However, these observations require further validation through prospective longitudinal studies with larger samples.
Accurate quantitative measurement of the soft tissue around an implant is crucial for maintaining the health of the implant. With the development of digital technology, the integration of digital intraoral scanning and CBCT has been proposed as a promising approach for noninvasive peri‐implant tissue assessment (Fons‐Badal et al. 2020). Observations indicate that measurement methods for peri‐implant soft tissues are transitioning from traditional clinical assessments to advanced digital imaging (Avila‐Ortiz et al. 2023). In an in vitro study by Ferry et al. (2022), the CBCT‐fitted intraoral scanning method demonstrated high consistency with histological section results for the measurement of soft tissue thickness. An animal study demonstrated that CBCT‐fitted intraoral scanning to measure gingival phenotypes provides results highly consistent with clinical measurements, showing particularly high accuracy at the buccal site (Yang et al. 2023). It is important to note that the reliability depends heavily on alignment precision and operator technique. In the context of this study, although we utilized standardized digital workflows performed by a single operator, the potential for measurement error remains a factor.
Consequently, based on our findings, it may be recommended to take definitive impressions approximately 6 weeks after second‐stage implant surgery to ensure transgingival contour stability. If an earlier impression is required, clinicians might consider a more subgingival margin placement to mitigate the risk of future abutment exposure due to potential tissue recession.
This study has several limitations that should be noted. As a retrospective cohort study, it lacks control for potential confounders such as age, smoking status, and specific abutment geometries. Additionally, this was a single‐center study and lacked diversity in the sample. Moreover, although all measurements were performed by a single examiner, potential measurement errors cannot be excluded. Finally, the limited sample size and chosen statistical methods may also affect the reliability and generalizability of the findings.
While our data suggests that soft tissue stabilization occurs around 6 weeks, it is important to note that this study was not powered to detect subtle differences between cross‐intervention groups (e.g., 1I4R vs. 2I3R). Future prospective studies with larger cohorts are needed to further validate the optimal timing by directly comparing these clinical protocols.
5. Conclusion
Within the limitations of this study, supracrestal tissue height changes around healing abutments appeared to stabilize approximately 6 weeks after second‐stage implant surgery. At the time of restoration, STH at the buccal and lingual sites was generally higher than at baseline, whereas STH at the mesial and distal sites tended to be slightly lower. These findings suggest that clinicians may consider scheduling definitive impressions around 6 weeks post‐surgery to allow adequate soft tissue maturation and stabilization, while earlier impressions may require adjustments to abutment positioning to accommodate potential soft tissue recession.
Author Contributions
Yanhua Chen: methodology, software, data curation. Zonghe Xu: software, investigation, validation. Yuyu Liu: funding acquisition, supervision. Dong Wu: writing – review and editing, resources, conceptualization. Jiamin Ding: writing – review and editing, formal analysis, supervision. Lin Zhou: conceptualization, funding acquisition, writing – original draft. Wen Guo: supervision, formal analysis, data curation. Jiang Chen: conceptualization, validation, project administration.
Funding
This work was sponsored by the National Natural Science Foundation of China (82571054), Fujian Provincial Health Technology Project (2024GGA068), and Setting Foundation of Fujian Medical University (2020QH1132).
Ethics Statement
This study complied with the Declaration of Helsinki and was approved by the Ethics Committee of the School and Hospital of Stomatology, Fujian Medical University (Approval No. [2024]68).
Conflicts of Interest
The authors declare no conflicts of interest.
Supporting information
Data S1: Supporting Information.
Table S1: Changes in the height of the soft tissue around the abutment at 1‐week (1I) and 2‐week (2I) impression major groups (mm).
Table S2: Post hoc multiple comparisons of soft tissue height changes at 2‐week (2R), 3‐week (3R), and 4‐week (4R) restoration in 1‐week impression major group (mm).
Table S3: Post hoc multiple comparisons of HHA at 2‐week (2R), 3‐week (3R), and 4‐week (4R) restoration in 2‐week impression major group (mm).
Table S4: The changes of STH at different times among four locations relative to the preoperative(mm).
Table S5: clr70145‐sup‐0003‐AppendixS1.docx. The Intraclass Correlation Coefficient and Levene's Test of HHA.
Table S6: The Shapiro–Wilk Test of HHA.
Table S7: The Intraclass Correlation Coefficient and Shapiro–Wilk Test of HHA.
Acknowledgements
The authors would like to acknowledge the nurses who participated in the experiment.
Data Availability Statement
The data that support the findings of this study are available from the corresponding author upon reasonable request.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
Data S1: Supporting Information.
Table S1: Changes in the height of the soft tissue around the abutment at 1‐week (1I) and 2‐week (2I) impression major groups (mm).
Table S2: Post hoc multiple comparisons of soft tissue height changes at 2‐week (2R), 3‐week (3R), and 4‐week (4R) restoration in 1‐week impression major group (mm).
Table S3: Post hoc multiple comparisons of HHA at 2‐week (2R), 3‐week (3R), and 4‐week (4R) restoration in 2‐week impression major group (mm).
Table S4: The changes of STH at different times among four locations relative to the preoperative(mm).
Table S5: clr70145‐sup‐0003‐AppendixS1.docx. The Intraclass Correlation Coefficient and Levene's Test of HHA.
Table S6: The Shapiro–Wilk Test of HHA.
Table S7: The Intraclass Correlation Coefficient and Shapiro–Wilk Test of HHA.
Data Availability Statement
The data that support the findings of this study are available from the corresponding author upon reasonable request.