Soft and Hard Tissue Changes Subsequent to Spontaneous Healing of the Extraction Sockets Using Cone-Beam Computed Tomography: A Cross-Sectional Study

Abstract

Objective

This study sought to compare the thickness of hard and soft tissues between edentulous and contralateral tooth sites.

Materials and Methods

This split-mouth study evaluated 153 partially edentulous patients. The measurements were made on cone-beam computed tomography (CBCT) scans. The soft tissue thickness was measured at the cementoenamel junctional (CEJ) level, and at 2, 4, and 6 mm apical to the CEJ in the facial and palatal aspects. The bone thickness of the opposite quadrant was also recorded at 2, 4, and 6 mm apical to the CEJ. The Mann–Whitney U test and the Spearman's rank correlation coefficient were applied for further statistical analyses.

Results

At the edentulous sites, significant soft tissue loss was noted at the CEJ level (p < 0.0001) and a considerable gain was noted at 2, 4, and 6 mm apical to the CEJ (p = 0.004, p < 0.0001, p ≤ 0.0001, respectively). A significant hard tissue loss was noted at 2 mm apical to the CEJ but a significant hard tissue gain was observed at the edentulous sites (p < 0.0001). The soft tissue gain at 6 mm apical to the CEJ was significantly associated with an increase in buccolingual diameter (p = 0.004) while the hard tissue loss at 2 mm apical to the CEJ was significantly correlated with a reduction in buccolingual diameter (p = 0.020)

Conclusion

Different amounts of tissue thickness alterations occurred in different levels of socket.

Introduction

Three-dimensional hard and soft tissue loss occurs following tooth extraction. Spontaneous healing further complicates this process, making the defect more severe, and leading to tissue collapse [1]. More importantly, tooth extraction causes physiological and structural alterations that adversely affect the hard and soft tissue integrity [2].

The process of bone resorption is affected by some functional parameters, metabolism, and anatomical variations. The buccal bone resorption compromises esthetics and can lead to esthetic complications or failure of dental implant treatment [3]. Pathological conditions or traumatic tooth extraction causing cortical bone loss can further aggravate the condition [4]. The facial/buccal cortical plate is usually more susceptible to resorption since it is thinner and has lower density and vascularization than the lingual cortical plate. Some other factors such as thinner epithelium covering the buccal cortical plate and lip pressure over the ridge may further aggravate the bone loss [5].

The process of bone resorption and remodeling may contribute to alveolar bone destruction and compromise the soft tissue integrity. Hard and soft tissue resorption may also affect the keratinized gingiva and lead to coronal migration of the mucogingival line. Clinical studies have provided some evidence concerning the dimensional changes due to tooth extraction [6, 7]; however, more clinical evidence is still required for a better understanding of soft and hard tissue changes following tooth extraction. The present study aimed to quantify the extent of vertical changes in edentulous sites following tooth extraction and contralateral dentate sites by using cone-beam computed tomography (CBCT) in partially edentulous patients.

Materials and Methods

This split-mouth analytical descriptive study was approved by the Ethical Committee of Shahid Beheshti University of Medical Sciences (IR.SBMU.RIDS.REC.1395.400). It included 153 patients who underwent CBCT in a private clinic in Tehran, Iran in 2018. The minimum sample size was calculated to be 138 patients using the following formula considering a standard deviation of 0.60, a reliability coefficient of 0.95, and an effect size of 0.1.

The anterior and first premolar teeth of one quadrant had been extracted due to endodontic reasons, irreparability, or extensive caries; while the anterior and first premolar teeth of the contralateral quadrant were present. The exclusion criteria were gingival hypertrophy in the maxillary anterior region, severe gingival recession in the maxillary anterior region, history of previous or current orthodontic treatment, dental crowding in the maxillary anterior region, history of periodontal surgery in the maxillary anterior region, presence of restorations, crowns, bridges, or dental implants in the maxillary anterior region, tooth extraction and immediate implant placement in the treatment plan, missing teeth due to impaction, broken teeth, endodontic treatment, caries with root resorption, rotation or malposition, jaw and skeletal malformations, cleft lip and/or palate, history of trauma to the maxillary anterior region, clinical signs and symptoms of erosion, history of bruxism, signs and symptoms or history of mouth breathing, smoking, pregnancy, breastfeeding, or systemic diseases.

Before CBCT, a sterile plastic lip retractor was used to retract the patients’ lips, cheeks, and tongue. Cotton rolls were used for isolation. An oral radiologist performed CBCT using Scanora 3D scanner (Soredex, Helsinki, Finland) with 10 × 7.5 cm field of view, 90 kVp voltage, 200-micron voxel size and 8 mA amperage. One observer was responsible for all measurements. The soft tissue thickness was measured at the cementoenamel junctional (CEJ) level, and at 2, 4, and 6 mm apical to the CEJ in the facial and palatal aspects of the edentulous and contralateral tooth sites (Fig. 1). As for the bone thickness of the contralateral quadrant, the measurements were carried out at 2, 4, and 6 mm apical to the CEJ in the facial and palatal aspects of the edentulous and contralateral tooth sites (Fig. 2). Moreover, the buccolingual diameter of the teeth was recorded at the CEJ level, and at 2, 4, and 6 mm apical to the CEJ (Fig. 3). To locate the CEJ at the edentulous sites, the distance between the CEJ of contralateral tooth and the line drawn on the maxillary bone was first measured, and then the same distance was calculated at the edentulous site.

Fig. 1.

Soft tissue thickness of tooth was measured at the cementoenamel junctional (CEJ) level, and at 2, 4, and 6 mm apical to the CEJ (a) and edentulous site (b)

Fig. 2.

Bone thickness measurements were carried out at 2, 4, and 6 mm apical to the CEJ in the facial and palatal aspects of the edentulous and contralateral tooth sites (a) and edentulous site (b)

Fig. 3.

Buccolingual diameter of the teeth was recorded at the CEJ level, and at 2, 4, and 6 mm apical to the CEJ

After the measurements, the changes in soft and hard tissues were compared at the edentulous and contralateral tooth sites. Additionally, the effects of buccolingual diameter of the teeth on such changes were evaluated at 2 and 4 mm apical to the CEJ in the soft tissue and at 4 and 6 mm apical to the CEJ in the hard tissue. Facial tissue changes were also examined at different levels. The data were analyzed using SPSS version 20 (SPSS Inc., IL, USA). Normal distribution of data was evaluated by the Kolmogorov–Smirnov test and the Shapiro–Wilk test. The demographic information was presented using descriptive statistics. The Mann–Whitney U test and the Spearman's rank correlation coefficient were applied for further statistical analyses. A p-value less than 0.05 was considered statistically significant.

Results

A total of 153 patients were recruited with a male to female ratio of 1.04, and a mean age of 52.06 ± 12.97 years (range 18 to 72 years). Furthermore, the majority of the patients (n = 60, 39.2%) aged 50–60 years. Only three participants (2%) were above 70 years.

As shown in Fig. 4a for the edentulous sites, the facial soft tissue thickness ranged from 0.78 mm to 1.39 mm, which was much narrower than the palatal soft tissue thickness, which ranged from 1.29–3.32 mm. The hard tissue thickness ranged from 0.3 mm at 2 mm apical to the CEJ to 4.37 mm at 6 mm apical to the CEJ. As shown in Fig. 4B for the contralateral tooth sites, the palatal aspect was thicker than the facial aspect in general. Additionally, an approximate increase between 1.2- and 2.9-folds was found in the soft tissue of the contralateral tooth sites as opposed to the corresponding hard tissue.

Fig. 4.

Tissue thickness in the facial and palatal aspects of the edentulous (a) and contralateral tooth (b) sites (solid white bars indicate that the thickness of the facial soft tissue is the same as that of the palatal soft tissue); ST: soft tissue, HT: hard tissue

Table 1 summarizes the effect of tooth extraction on the soft and hard tissue thickness at different levels from the CEJ. Overall, there was a statistically significant difference in thickness between the edentulous and contralateral tooth sites (p < 0.05). At 2, 4, and 6 mm apical to the CEJ, the soft tissue thickness at the edentulous sites was considerably greater than that at the contralateral tooth sites. Only the CEJ level showed significantly higher thickness at the contralateral tooth sites in comparison with the edentulous sites. Similar measurements for the hard tissue revealed that tooth extraction caused a significant decrease in thickness at 2 mm apical to the CEJ (p < 0.0001); while, on the contrary, it increased the thickness at 6 mm apical to the CEJ (p < 0.0001).

Table 1.

Mean difference in thickness between the edentulous and contralateral tooth sites

Level	Thickness at the edentulous site (mm)			Thickness at the contralateral tooth site (mm)			Mean difference (mm)	p-value
	Mean	Maximum	Minimum	Mean	Maximum	Minimum
Soft tissue
CEJ	0	0	0	1.25 ± 1.10	3.80	0	− 1.25 ± 1.10	< 0.0001
2 mm	3.71 ± 2.88	9.70	0	2.69 ± 1.17	5.60	0.4	1.02 ± 1.70	0.001
4 mm	5.12 ± 1.94	8.50	1.60	3.33 ± 1.24	7.20	0.9	1.79 ± 0.70	< 0.0001
6 mm	4.73 ± 1.33	9.90	1.90	4.14 ± 1.23	7.10	1.42	0.52 ± 1.55	< 0.0001
Hard tissue
2 mm	0.30 ± 0.94	3.00	0	0.97 ± 1.00	5.00	0	− 0.70 ± 0.05	< 0.0001
4 mm	2.24 ± 2.25	7.20	0	1.91 ± 0.79	4.12	0.2	0.33 ± 1.50	0.907
6 mm	4.37 ± 1.60	7.40	1.50	2.54 ± 0.89	4.77	0.7	1.80 ± 0.70	< 0.0001

Figure 5 illustrates the soft tissue thickness in the facial region. Irrespective of the apical level from the CEJ, the contralateral tooth sites indicated a significant reduction in thickness when compared with the edentulous sites (p < 0.05).

Fig. 5.

Soft tissue thickness changes in the facial region. *p < 0.005 **p < 0.0001

Table 2 shows the correlation between the buccolingual diameter of the teeth and the mean dimensional changes at different levels from the CEJ. The findings exhibited that the buccolingual diameter of the teeth was significantly associated with soft tissue changes at 6 mm apical to the CEJ (p = 0.004) and hard tissue changes at 2 mm apical to the CEJ (p = 0.020).

Table 2.

Association of thickness changes with buccolingual diameter of the teeth

Mean thickness change	Buccolingual diameter at different levels
	2 mm	4 mm	6 mm
Soft tissue
2 mm	ρ = 0.119 p = 0.142	–	–
4 mm	–	ρ = − 0.112 p = 0.170	–
6 mm	–	–	ρ = 0.231 p = 0.004
Hard tissue
2 mm	ρ = 0.189 p = 0.020	-	–
4 mm	–	ρ = 0.077 p = 0.346	–
6 mm	–	–	ρ = 0.125 p = 0.126

Discussion

One of the main findings of the present study was that tooth extraction resulted in soft tissue loss at the CEJ level. So, no tissue existed at that location. Also, an increase in thickness occurred at 2, 4, and 6 mm apical to the CEJ. In other words, vertical soft tissue recession reached 100% at the CEJ level and was prevented anymore. On the other hand, some studies have reported a soft tissue gain subsequent to tooth extraction. A 6-month randomized, controlled, blind clinical trial reported that ridge preservation by tetracycline-hydrated freeze-dried bone allograft plus a collagen membrane [8]. Another clinical trial documented a vertical increase of 5.6% in the lingual aspect and 8.1% in the buccal aspects of bone [9]. Tooth extraction leads to formation of reactive soft tissue in the defect, which can be considered as fibrovascular proliferation. Such tissues are composed of recently formed small blood vessels, fibroblasts, and mononuclear cells in an edematous extracellular matrix. This type of tissue may be detected in the connective tissue during wound healing, or in chronic inflammation, or peculiar diseases. Surprisingly, experimental evidence showed that the granulation tissue fibroblasts obtained from chronically inflamed periodontal lesions followed the same behavior as healing wounds [10].

Dimensional alterations of the soft tissue following tooth extraction have been studied in single tooth extraction sites [11]. In general, over half of these occur early within the first 14 days of healing. The increase in soft tissue thickness depends on the underlying bone dimensions. The alveolar bone in thick-wall phenotypes gives self-contained bony defects that support the ingrowth of progenitor cells from the bony socket walls along with the surrounding bone marrow space. The soft tissue of thick-wall phenotypes experiences no change in the facial aspect during the healing period [12]. On the other hand, in thin bone wall phenotypes, the soft tissue undergoes a sevenfold dimensional increase at the same time in the process of healing. This phenomenon is known as the spontaneous soft tissue thickening. It is assumed that quick resorption of the thin facial bone wall facilitates facial soft tissue ingrowth since it has a high proliferation rate. Therefore, such soft tissue cells reside at the center of the available space in the crestal area of an extraction socket, and subsequently lead to development of notably vascularized granulation tissue besides the migration of fibroblasts into the wound [13]. Next, the fibroblasts differentiate into myofibroblasts, which are in charge of stabilizing the wound margins; this process possibly plays a role in the thickening phenomenon [14]. The soft tissue thickening associated with tooth extraction has been highlighted in many previous studies [8, 14].

In addition, this study found that hard tissue loss occurred at 2 mm apical to the CEJ in response to tooth extraction. A different pattern (i.e., hard tissue gain) was found at 4, and 6 mm apical to the CEJ. This implies that the thickness of bone was not affected in areas farther than 2 mm apical to the CEJ. Several studies have confirmed the hard tissue loss as a result of tooth extraction. Johnson reported a reduction in bone height between 2.5 and 7 mm following tooth extraction [15]. Another study by Araujo and Lindhe showed a relative reduction of 2.2 mm in the height of buccal bone plate at the site of premolars [16]. A systematic review reported that healed sockets experienced 2.6–4.5 mm loss in bone width and 0.4–3.9 mm loss in bone height [17]. The amount of bone loss after extraction depends on a number of variables, including bone wall thickness in the facial region, angulation of the tooth, and anatomical variations at different tooth sites [18]. Several studies reported that the thickness of the facial bone wall in the anterior maxilla was thinner than 1 mm in the majority of cases and thinner than 0.5 mm in around 50% of the cases [19]. The thin facial bone walls, which are mainly composed of bundle bone, may be susceptible to resorption following tooth extraction. Chappuis et al. used CBCT and found a progressive bone resorption pattern in facial bone wall thickness ≤ 1 mm that resulted in a median vertical bone loss of 7.5 mm [20]. On the contrary, a thick-wall phenotype with a bone wall thickness of greater than 1 mm in the facial region experienced a median vertical bone height of 1.1 mm. The change in single tooth extraction sites with no effect on the adjacent dentition mainly took place at the center of the socket wall while almost no change was observed in the proximal areas in response to flapless tooth extraction after 8 weeks of healing [20].

One strength of this study was the use of CBCT for dimensional measurements. According to the literature, bone thickness can be determined by using both CT and CBCT [21]. Although CT enables more detailed measurements by providing three-dimensional images, it has higher patient radiation dose than CBCT, which is a drawback [22, 23]. Furthermore, CBCT has higher resolution and shorter scanning time in comparison with CT [24].

The soft and hard tissue thickness at the implant site should be considered when placing an implant, since it might reach zero at the CEJ area because of vertical bone loss. It is worth paying attention to hard tissue loss at 2 mm apical to the CEJ. No special care is required for other levels at which an increase in soft and hard tissue thickness was noted. No esthetic concern exists for the anterior teeth since the thickness of the facial soft tissue increased in this area following tooth extraction.

The present study showed complete loss of soft tissue at the CEJ, whereas there was a soft tissue gain at 2, 4, and 6 mm apical to the CEJ on CBCT scans of the edentulous sites. Also, the patients lost hard tissue at 2 mm apical to the CEJ but experienced improvement at 4 and 6 mm apical to the CEJ. Moreover, an increase occurred in the facial soft tissue thickness. At 6 mm apical to the CEJ, the soft tissue gain was significantly correlated with a rise in buccolingual diameter. However, at 2 mm apical to the CEJ, hard tissue loss was significantly linked to a reduction in the buccolingual diameter.

Author contributions

RA and YS involved in study design; BB participated in data collection; MN involved in data analysis; MK participated in manuscript preparation.

Funding

The present study did not receive any particular grant from commercial, public, or not-for-profit funding agencies.

Declarations

Conflict of interest

The authors declare that they have no conflict of interest to this study.

Ethics approval

All procedures followed were in accordance with the ethical standards of the responsible committee on human experimentation (Ethics committee of the Dental School of Shahid Beheshti University of Medical Sciences, Iran (IR.SBMU.RIDS.REC.1395.400)). and with the Helsinki Declaration of 1975, as revised in 2008. Informed consent was obtained from all patients for being included in the study.

Informed consent

Written informed consent was obtained from all patients to use their diagnostic radiographs in this research. It was explained that their identifying information would only be accessible to the researchers and would not be included in the article.