Oral treatment has evolved from solely alleviating patients' pain to addressing their desire for functional comfort with aesthetic considerations. Among the clinical challenges encountered by dentists, achieving satisfactory anterior teeth whitening aesthetics remains a prominent area of interest for both patients and practitioners. The aesthetics of gingival soft tissue occupies a crucial role in oral aesthetics[12]. This is particularly significant for patients with thin gingival tissue because they tend to experience post-operative gingival recession, sensitivity, discomfort and other complications[13]. Consequently, treatment of the aesthetic area becomes more challenging and risky[14]. With the use of CBCT in clinical diagnostic aids[15, 16], it became feasible to visualize measurements, leading to the emergence of CBCT-based studies on 3D gingival morphology and gingival phenotypes becoming a trending topic. Previous research has utilized cone beam computed tomography in conjunction with digital methods[17, 18], specialized impression techniques[14], and cotton rolls to isolate the labial and buccal mucosa[19] in order to acquire measurements of soft tissue. However, this methodology suffers from drawbacks, including unwieldy clinical procedures, demanding technical prerequisites, and the inclination to compress the gingiva upon re-seating the teeth, which could result in displacement and impact measurement accuracy. This study is based on our group's CBCT method combined with the indirect development of soft tissue measurement. The method has a simple operation process, and allows for longitudinal storage, transmission, and analysis of CBCT data. It avoids invasive operations, reducing additional trauma and psychological pressure on patients, with good patient compliance. Positioning filaments are used to obtain point-to-point accurate measurements under CBCT, ensuring excellent reproducibility and accurate results. In this study, we conducted a three-dimensional analysis of the gingival soft tissues surrounding the upper anterior teeth among individuals with periodontal health.
Smukler et al[20] introduced the idea of "gingival tissue on the alveolar crest" in 1997, encompassing the depth of the gingival sulcus, epithelial and connective tissue attachments. Previous research indicates that the labial central SGT height of a natural tooth is typically around 3 mm, comprising both the biological width and sulcus depth. However, there is considerable inter-individual variation in SGT height[21]. The SGT acts as a barrier between the alveolar bone and the intraoral environment, and has a crucial role in preserving periodontal health and maintaining biological width stability[7, 22]. For crown lengthening[7, 9], the preoperative analysis of alveolar bone morphology according to the principles of biological width and hoop structure can determine the need for removal of hard tissue and the height of removal necessary. It is important to maintain the height of the surgical tooth and neighbouring SGTs during surgical design. To ensure minimal disruption to newly established biological widths during the treatment process, it is necessary to maintain a distance of at least 3 mm between the fracture end of the tooth and the apex of the alveolar ridge. Failure to adequately understand the amount of bone that needs to be removed can lead to complications[9]. In restorative treatment, the placement of the restoration's edge should be based on the periodontal biological foundation and aesthetic requirements, while obeying the principle of biological width. This will ascertain the maintenance of the health and stability of periodontal tissues after restoration.In implant treatment, it is necessary that the soft tissue surrounding the implant should develop a healthy gingival and keratinized gingival pattern, as indicated by literature[23]. If the soft tissue recedes after implantation, the metal of the implant will be exposed, which can negatively impact the function and aesthetics of the implant, according to relevant studies[24]. Therefore, appropriate augmentation and decrement of hard and soft tissues are necessary during aesthetic restoration[25] in order to sustain periodontal health. Most of the conventional measurement studies of SGT heights have implemented invasive bone probing techniques under local anaesthesia[26, 27]. In addition, Kois determined the gingival margin's height to the bone crest's top from the labial centre of the upper central incisors using gingival probing, measuring it as 3 mm[28]. Perez et al. also conducted a study on the topic. Gingival heights were measured by probing the labial side of the mesial incisors (3.70 ± 0.77) mm, the labial side of the lateral incisors (3.70 ± 0.70) mm, and the labial side of the cuspids (3.22 ± 0.67) mm[29]. However, previous studies had a limited sample size, inconsistent measurement standards and required invasive measurements that resulted in poor patient cooperation[29]. It was found that there was no statistically significant difference between the two methods of measurement, CBCT measurement and bone probing[30, 31]. In this study, the maxillary anterior labial central SGT heights of the mesial incisors, lateral incisors, and cuspids were determined using the gingival soft tissue method indirectly developed through the measurement and analysis of CBCT. The heights were found to be (3.48 ± 0.29) mm, (3.45 ± 0.36) mm and (3.38 ± 0.34) mm respectively. The SGT heights of mesial incisors were higher than those of cuspids, and the differences among the remaining positions and between genders were insignificant (P > 0.05). Among the different gingival phenotypes, only the cuspal region exhibited a higher prevalence of thick gingival type compared to thin gingival type (P < 0.05).Variations in measurements could stem from contrasts in trial evaluation approaches and ethnic background.
The gingival phenotype has a close association with GT and impacts tissue response and prognostic assessment following multidisciplinary treatment. In this study, the GT 2 mm below the gingival margin of the maxillary labial side of the mesial incisors, lateral incisors, and cuspids was 1.31 ± 0.22 mm, 1.21 ± 0.20 mm, and 1.09 ± 0.19 mm respectively, which manifested that the gingiva of the mesial incisors was the thickest in the maxillary anterior region, and the cuspids were the thinnest, moreover the GTs of the maxillary mesial incisors and lateral incisors in males were generally thicker than those in females, which did not differ significantly from the results of the national and international studies[14, 32, 33]. Distinguishing between thin and thick gingival phenotypes with a 1 mm boundary, the percentage of thick gingival phenotypes in maxillary mesial incisors, lateral incisors, and cuspids was 85.7%, 81.4%, and 63%, respectively. Comparing the differences between each measurement revealed height variability of GT, KGW, and SGT between thin and thick gingival phenotypes. This implies that classifying gingival phenotypes as thin or thick based on a 1 mm boundary is reasonable.
Keratinised gingiva plays a crucial role in preserving periodontal tissue health and preventing connective tissue attachment loss. Furthermore, it contributes to the harmonious red and white aesthetics of the gingiva. It is a valuable metric for crown lengthening, membranous gingival surgery, implants, and other surgical procedures, as it aids in identifying the optimal site for surgical incisions and estimating treatment outcomes. Research indicates that KGW less than 2 mm can induce and exacerbate inflammation of peri-implant mucosa[34]. The measurement of keratinised gingival width, which is commonly used to determine this, is the vertical distance from the gingival margin apex to the membranogingival junction, and is easy to perform. However, this method has low accuracy and reproducibility, and is influenced by alveolar bone anatomy. In this study, the membranogingival union was identified as the measurement marker point with the help of positioning filaments, and KGW was accurately measured based on CBCT in combination with developing combinations. The average KGW for mesial and lateral incisors as well as cuspids in the upper jaw was 5.28 ± 0.64 mm, 5.34 ± 0.63 mm and 4.78 ± 0.55 mm, respectively. Maxillary incisors and maxillary lateral incisors exhibited significantly greater KGW values than maxillary cuspids. The difference in values was statistically significant (P < 0.05). No significant difference was observed between genders (P > 0.05).
After conducting a correlation analysis, we found a positive correlation between labial GT and KGW. In comparison with the thin gingival type, the thick gingival type displayed a wider KGW in the lateral incisal and cuspid areas. These findings align with those of Monje et al[35, 36]. In the clinical setting, patients with thin gingival tissue and a narrow KGW should be considered at high risk[37]. Therefore, reinforcing oral hygiene education and providing oral health guidance is even more crucial. If necessary, soft tissue augmentation may be a viable option. The labial central SGT was positively correlated with GT and KGW, and the SGT was slightly higher for the thick gingival type in the cusp area than for the thin gingival type. These results are particularly important for surgical design, Arora et al. conducted a clinical study which found that tissue rebound after crown lengthening was more pronounced in individuals with thick gingival types compared to those with thin gingival types[38]. When considering indications for crown lengthening, such as subgingival caries, fractured teeth, or when aesthetic revision is required, it is important to provide accurate measurements of the SGT heights and understand the height of the hard and soft tissues removed[39]. This enables the formulation of individualised treatment protocols based on the patient's gingival phenotype, ensuring adequate KGW.
In summary, this study utilised a combination of developing techniques and positioning wires to assess gingival morphology in three dimensions using CBCT. The results demonstrate a correlation between labial SGT height in the maxillary anterior teeth and the features GT and KGW of the gingival phenotype. Additionally, there is a degree of variability among the features of different gingival phenotypes, allowing clinics to tailor personalised treatment plans based on these findings. Owing to the study's limited sample size, additional analyses will be conducted in the future to obtain more comprehensive data results. These future analyses will involve expanding the sample size, increasing the measurement indexes and widening the age span range.