The variations on the periodontal anatomy and the relationship between bone and gingival contour have being previously described as well as a possible relation to periodontal health and disease.1,2 The shape and cervical convexity of the tooth crown and the mesiodistal gingival contour and coronal-apical width of the gingiva have been compared.3,4
In concordance with this, Ochsenbein and Ross5 established that the gingival contour is dictated by the contour of the underlying bone and by the shape of the tooth, describing 2 variants of anatomy: “thin scalloped” gingiva related to tapered and triangular teeth, with a more festooned gingival margin, contrasted with a “thick flat” gingival contour related to square-shaped teeth and a flat gingival margin.
Seibert and Lindhe6 clarified the differences regarding the tooth shape and length, with the morphology of the bone and gingival tissues, and introduced the term “Periodontal Biotypes” in 1989. Later, Müller and Eger7 proposed the term “periodontal phenotypes” in a study where they suggested a relationship between the thickness and width of the gingiva and the tooth shape. The 3 classified groups are as follows: 1 = normal width and length of teeth; normal width and thickness of keratinized tissue, 2 = more squared shape of central and lateral incisors; wide and thick gingiva, and 3 = squared shape of central and lateral incisors, narrow band of keratinized tissue, and thin gingiva. In this study, the authors also observed that the mandibular gingival width and thickness and the form of the incisors seemed to be related with the gingival phenotype observed in the maxilla.
Recent results from De Rouck et al8 confirmed the existence of different gingival biotypes. On a sample of 100 patients, around one-third from the group showed slender teeth, narrow zone of keratinized tissue, highly scalloped gingival margin, and a clear thin gingiva. On the other two thirds of the sample, a clear thick gingiva was observed. About half of this group showed squared teeth, with a broad zone of keratinized tissue and a flat gingival margin. The other half showed a clear thick gingiva with slender teeth, a narrow zone of keratinized tissue, and high gingival scallop.
Summarizing the revised literature,5–9 periodontal anatomy could be divided into 3 major groups: (a) “thin scalloped” is associated with a slender triangular tapered tooth crown, subtle cervical convexity, interproximal contacts close to the incisal edge, a narrow zone of keratinized tissue, clear thin gingiva, and a relatively thin alveolar bone; (b) the second group, “thick flat” is associated with square-shaped tooth crowns, pronounced cervical convexity, large interproximal contacts located more apically, a broad zone of keratinized tissue, clear thick gingiva, and a comparatively thick alveolar bone; and (c) the third different group, “thick scalloped” can be described showing a clear thick gingiva, slender teeth, narrow zone of keratinized tissue, and a high gingival scallop (Fig. 1).
The assessment of the periodontal biotypes seems to be a significant factor considering that it is related to the outcomes of different dental procedures including the treatment periodontal disease. It appears that inflammation in a periodontium with thick flat gingival contours results in an increased pocket depth, whereas inflammation in a periodontium with thin scalloped gingival contours is more likely to result in recession.10
Likewise, individuals with thin scalloped gingival contour seem to be more susceptible to gingival recessions than those with thick biotype if proper margins and contours are not respected during restorative preparations and final restorations.11,12
Outcomes from surgical techniques are also related to biotypes. Healing after crown lengthening in a thick periodontal biotype displays more regrowth in coronal direction than in thin periodontal biotypes.13 And so is the case for mucogingival surgery where the initial gingival thickness (GT) is a significant factor associated with complete root coverage when using coronally advanced flaps.14–16
In orthodontics, understanding of soft and hard tissues is required. Thickness of the gingiva and underlying bone is considered a major contemplation in the development of gingival recession during orthodontic tooth movement.17–19 In the presence of a thin periodontal biotype, bodily labial movement of the incisors is not recommended.20
Understanding the gingival/periodontal biotypes is also of importance when considering dental implants. Soft tissue thickness and contour are essential diagnostic factors to consider in the aesthetic outcome of an implant restoration.21,22 Predictability of achieving an appealing outcome is determined by parameters such as the implant position, time of placement, or the patient’s particular anatomy.23
A higher frequency of gingival recession is found when placing immediate implants in patients with thin biotypes.2,24,25 On the other hand, when planning immediate implants in individuals with a thick biotype, the percentage of aesthetic success and a reduced risk of recession are increased.26,27 Considering that tissue biotype is a critical factor in the results of dental therapy, an accurate method for measuring thickness of the investing soft tissue and bone is mandatory.
Visual inspection is probably the most common and simple method for determining a biotype. The validity of this technique was assessed by experienced and inexperienced clinicians.28 Outcomes showed that biotypes were identified in half of the cases regardless of the clinician’s experience. Thick biotypes were more commonly identified than thin-scalloped ones. Interestingly, in this study, half of the patients with high aesthetic risk were overlooked. These results conclude that visual inspection might not stand as a precise technique.
A parallel profile radiograph technique can be used for measuring hard and soft tissues thickness on the maxillary central incisor.29 This method is limited to the maxillary central incisors, and it is less valid on other anterior teeth as a result of the superimposition of the images.
The use of an ultrasonic device has being proposed30 for measuring GT. The reproducibility of measurements with the device was high, but a mean interindividual measurement error was revealed. Their conclusions refer to this method as a reliable general technique. However, it is not accurate for detecting minor changes.31 Alternative effectively used method for measuring GT is the transgingival probing10 using a periodontal probe or an endodontic file. This technique was also used to evaluate the results of guided tissue regeneration, and it was shown to be an accurate method.32
Another clinical method for evaluating the thickness of the gingival tissues was presented by Kan et al.33 The gingival tissue dimensions are measured by performing a bone sounding with a periodontal probe on the facial aspect. The biotype is categorized as thin if the outline of the underlying probe could be seen, through the gingiva and as thick if the probe could not be seen. The accuracy of this technique was later confirmed.34
Three-dimensional radiographic techniques, such as a cone beam CT (CBCT), are being tested, and the results recognized it as an accurate technique for measuring the thickness of both soft and hard tissues.35–37 The null hypothesis from our study is that there is no correlation between the thickness and width of soft tissue and the thickness of the underlying bone in the maxillary and mandibular anterior teeth.
The aim of this study was to determine and correlate the thickness and width of the soft tissues (measured by transgingival probing technique) and the underlying bone thickness (measured with CBCT) at 3 different locations in the maxillary and mandible anterior teeth.
Materials and Methods
A total sample of 180 teeth were included in this study: 90 maxillary (30 canines, 30 lateral incisors, and 30 central incisors) and 90 mandibular (30 canines, 30 lateral incisors, and 30 central incisors) from 15 patients (8 men and 7 women) between the ages of 22 and 49 (mean age 29.53). The patients were referred for a periodontal assessment for the placement of implants or before undergoing orthodontic therapy to the Periodontics Department. The referral was requested from the dental clinic (Clínica Universitaria de Odontología) at the International University of Catalonia (Barcelona, Spain) between February and June 2011.
The inclusion criteria required the necessity of a cone beam CT (CBCT) (i-Cat Cone Beam 3D; Imaging Sciences International, LLC, Hatfield, PA) as a part of an examination for the correct diagnosis for future implant therapy or for orthodontic treatment, which included bodily vestibular movement of the anterior teeth with or without orthognathic surgery. All patients presented with no history or present signs of periodontal disease, which included gingival inflammation or bone loss (probing depth [PD] ≥4 mm were excluded), tooth malposition, or gingival recessions that interfered with the patient’s normal gingival contour.
Patients with a history of smoking, systemic disease, medical treatments including medications like calcium channel blockers, Dilantin, anticonvulsants, or immunosuppressive drugs, previous orthodontic treatment in the anterior maxilla or mandible, surgical treatments including orthognathic, periodontal resective, mucogingival, or apicoectomy techniques, fixed anterior prostheses including crowns, bridges, or veneers, or advanced carious lesions, fractures, or internal or external resorption on the anterior teeth were excluded.
The study was approved by the Ethics Committee from the International University of Catalonia (Barcelona, Spain) (File N° C-08-ASA-09). The patients enrolled for the study were visited for a clinical examination, and a written informed consent was obtained. All patients received a full dental prophylaxis and oral hygiene instructions 1 week before the clinical examination to control any signs of gingival inflammation.
For all the selected teeth, PDs were measured with a periodontal probe (CP-8; Hu Friedy, Chicago IL) and registered on a periodontal chart; all measurements were rounded to the nearest 0.5 mm.
For the transgingival probing, a cheek retractor was used, and topical anesthesia (lidocaine 4% cream) (Lambdalina; Isdin Laboratories, Barcelona, Spain) was applied over the area of examination. Measurements were taken piercing the tissue perpendicular to the tooth axis with a 10 endodontic file, which had a rubber stop (Fig. 2). On removal, the thickness of the soft tissue was measured with a digital caliper (Dentagauge; Erskine Products, Macksville, Australia). The GT was measured at 3 locations: (1) the gingival margin (CGT) 1 mm apical from the facial PD, (2) most apical (AGT), which was 1 mm coronal from the mucogingival junction, and (3) mid (MGT) located in a midpoint between the 2. All measurements were rounded to the nearest 0.2 mm.
The apicoincisal width of gingiva (GW) was measured with a periodontal probe (CP-8 Hu Friedy) located over the soft tissue parallel to the long axis of the tooth from the crest of the marginal gingiva to the mucogingival junction determined by rolling the alveolar mucosa incisally with the side of the periodontal probe. All measurements were rounded to the nearest 0.5 mm. An experienced examiner (A.P.L.R.) performed all clinical measures.
The CBCT examination was obtained using the iCAT unit (Imaging Sciences International, Inc, Hatfield, PA) at 120 KVp and 18.66 mA (Voxel size: 0.2 mm; gray scale: 14 bits; focal spot: 0.4 mm; field of view: 16 × 22 cm) and processed for visual analysis using the iCAT -Vision software using an HD monitor (Sync Master 60 Hz 1920 × 1080 pp; Samsung Electronics, Co, Ltd, Suwon, Korea).
Axial slices (thickness of 1.0 mm) were adapted to follow the long axis and pass through the center of the root of each examined tooth. The cementoenamel junction (CEJ) was previously located, and the thickness of the facial bone wall was measured in 3 locations: crestal (CBT), which was located 4 mm apical to the CEJ; apical (ABT) located at the apex of the root; and mid (MBT), which is located in a midpoint between the 2 (Fig. 3). All computer measurements were made in duplicate by a single trained clinician who was blinded from the clinical findings (A.S.A.). All measures were rounded to the nearest 0.01 mm.
An intraexaminer calibration session was previously performed to evaluate reliability in the clinical measurements. Clinical measurements were performed and repeated 3 times in 3 patients with an interval of 24 hours. Radiographic measurements were also performed in 3 patients, 3 times with 1-hour intervals. Reliability was determined using Cohen κ coefficients test. The intraexaminer reliability of the first examiner (A.P.L.R.) for the clinical measurements had a K value of 0.87 and of the second examiner (A.S.A.) for the radiographic measurements had a value of 0.85. These results prove good intraexaminer values for the measurement taken.
Statistical analysis was made using a statistical software package (SPSS 17.0; IBM, Armonk, New York). Variables were tested for normal distribution using the Shapiro-Wilk test. A general analysis was conducted including a total of 180 teeth, and a specific analysis was conducted by the type of teeth that consisted of 6 groups with a sample of 30 teeth each. Spearman ρ correlation test was used to determine the possible relationship between soft tissue thickness and the underlying bone thickness. Also, the association between GW and buccal-lingual GT (CGT, MGT, AGT), and osseous thickness (CBT, MBT, ABT) was analyzed. A P value ≤0.05 level was used to establish statistical significance.
Shapiro-Wilk test was performed for the distribution analysis of the studied variables showing a non–normally distributed sample (Table 1).
The mean PD and GW were 1.37 (±0.48) mm and 4.48 (±1.55) mm, respectively. The mean GT at the crestal, mid, and apical (CGT, MGT, and AGT) position was 1.01 (±0.58) mm, 1.06 (±0.48) mm, and 0.83 (±0.47) mm, respectively. The corresponding crestal, mid, and apical bone thickness (CBT, MBT, and ABT) was 1.24 (±0.90) mm, 0.81 (±0.33) mm, and 2.78 (±1.62) mm, respectively (Table 2).
There were no statistically significant correlations between soft tissue and the underlying bone at any of the 3 positions (crestal, mid, or apical) (P > 0.05) or between PD and GW (P = 0.389). A positive correlation was found between GW with the midpoint GT (P = 0.002) and the crestal point bone thickness (P = 0.006) (P < 0.05) (Table 3).
The mean values for the PD, GW, and soft tissues for maxillary and mandibular teeth are presented in Table 4. The GW was larger for the maxillary canines and the central and lateral incisors (4.93 mm [range, 4.3–5.5 mm], 4.43 mm [range, 5.12–5.73 mm], and 5.80 mm [range, 5.25–6.34 mm] respectively) than for the corresponding mandibular teeth was (3.16 mm [range, 2.69–3.63 mm], 3.56 mm [range, 3.23–3.90 mm], and 4.0 mm [range, 3.54–4.45 mm], respectively).
The mean CGT of the maxillary canines, and central and lateral incisors was 1.01 mm (range, 0.81–1.21 mm), 1.23 mm (range, 1.01–1.44 mm), and 1.05 mm (range, 0.86–1.23 mm), respectively, and that for the corresponding mandibular teeth was 1.01 mm (range, 0.69–1.33 mm), 0.89 mm (range, 0.71–1.06 mm), and 0.89 mm (range, 0.71–1.06 mm), respectively.
The mean CBT for the maxillary canines, and central and lateral incisors was 1.19 mm (range, 1.02–1.36 mm), 1.07 mm (range, 0.95–1.18 mm), and 1.31 mm (range, 1.10–1.51 mm), respectively, and that for the corresponding mandibular teeth was 1.47 mm (range, 0.94–2.0 1 mm), 1.21 mm (range, 0.81–1.60 mm), and 1.23 mm (range, 0.82–1.63 mm), respectively.
The ABT values were thicker for mandibular canines and for central and lateral incisors (3.70 mm [range, 3.08–4.31 mm], 3.94 mm [range, 3.27–4.61 mm], and 3.69 mm [range, 3.10–4.2 mm], respectively) than for the corresponding maxillary teeth (1.71 mm [range, 1.41–2.02 mm], 1.69 mm [range, 1.44–1.93 mm], and 1.98 mm [range, 1.69–2.28 mm], respectively) (Table 5).
For the maxillary central incisors, a positive correlation was found between the GW and PD (P = 0.01) and also with the ABT (P = 0.04). For the lateral maxillary incisors, a positive correlation was found between the GW and the MBT (P = 0.015). The maxillary canines showed a relationship between the GW and CBT (P = 0.002) and also between the GW and the ABT (P = 0.01). Mandibular central incisors showed a relationship between the GW and CBT (P = 0.000). The mandibular lateral incisors showed a positive correlation between the CGT and CBT (P = 0.002) and between the AGT and ABT (P = 0.01). The mandibular canine group showed a correlation between CGT and CBT (P = 0.004) (Table 6).
This protocol combines clinical and radiographic minimally invasive techniques to evaluate and measure the dimensions of the gingiva and underlying osseous thickness. Only anterior teeth were included because the cervical convexity of the crown and the mesiodistal gingival and osseous contour are the references that most clinicians use to determine the patients biotype3–5 and is probably the area of greatest concern due to the aesthetic implications related to dental and implant treatment.
The application of these techniques is a good method to obtain clinical data regarding the periodontal structures. However, not all treatments can justify the exposure to radiation for a CBCT examination. Previous reports on the use of the CBCT revealed the high diagnosis accuracy for soft tissue assessing of this technique, showing minimal discrepancies between clinical and radiographic measurements.35,38–40 In this study, the CBCT technique was only used for measuring the bone thickness. Only the treatments that require an evaluation of the underlying bone are amenable to these procedures.
The use of transgingival probing is a simple, minimally invasive procedure that can be helpful in different situations and have being previously demonstrated.10,32 Different methods are being used to measure GT. Müller et al41 in a population of 40 systemically healthy young adults reported a mean maxillary GT at approximately 1 to 2 mm apical to the gingival margin for the central incisor of 1.00 (±0.30) mm, for the lateral incisor of 0.86 (±0.33) mm, and for canines of 0.70 (±0.50) mm using an ultrasonic measuring device. The calculation of a general mean between these values is equal to 0.85(±0.26) mm. Later, in a sample population of 22 cadavers, Fu et al35 found a mean maxillary GT at 2 mm apical to the bone crest of 0.5 mm (range, 0.1–1.2 mm) using a caliper after tooth extractions. The clinical results were compared with radiographic measures using the CBCT, showing a mean of 0.57 mm (range, 0.2–1.86 mm). In another study by Ueno et al,39 using endodontic files and a customized measuring guide on 5 cadavers, they found a mean maxillary buccal GT at 3 mm from the gingival margin of 1.67 mm (range, 0.3–3.31 mm); in this study also spiral CT measurements were taken, showing a mean GT of 2.78 mm (range, 1.15–4.41 mm).
In the present study, the mean CGT in the maxillary anterior region was 1.10 mm (range, 0.1–2.50 mm). These results are in agreement with other studies; however, small discrepancies might be found due to differences in the techniques used in the previous works that were performed on cryopreserved and subsequently thawed cadavers, possibly causing changes on the studied tissues.
The mean GT presented by Müller et al41 for the mandibular central and lateral incisors and canines was 0.65 (±0.14) mm, 0.71 (±0.17) mm, and 0.66 (±0.15) mm, respectively, and calculation of a general mean between these values equals 0.67 mm (±0.15) mm. Our results show a mean GT of 0.94 mm (range, 0.5–2.50 mm).
Today, facial bone thickness is considered a crucial parameter for treatment planning decisions in the anterior aesthetic area, especially when implants are involved.23,42 Histologic findings from animal experiments43 have proven that the walls of the alveolar bone are formed in majority by a bone structure that depends on the periodontal ligament cells called bundle bone. When a tooth is lost or extracted, this bone resorbs, resulting in a vertical reduction of the buccal aspect, especially in the anterior region where thickness is generally minimal.43,44
No consensus has yet been reached regarding the amount of buccal bone thickness that is needed when placing an implant to assure a satisfactory biologic and aesthetic outcome.45 A certain amount of bone resorption occurs when implants are placed into fresh extraction sockets46,47 and also in 2-stage protocols when the implants come in contact with the oral environment.48 To help avoid possible complications, a minimum of 2 mm of buccal bone thickness has been proposed.49–51 This seems to be of great importance considering that in this study, only a limited number of sites in the anterior maxilla exhibit such a clinical situation that seems to be of great importance regarding the possible results to the implant treatment.
The study by Fu et al35 found a mean facial bone thickness of 0.83 mm (range, 0.3–1.60 mm) at 2 mm below the bone crest. Braut et al52 found a mean bone thickness of 0.5 mm (range, 0–2.1 mm) at 4 mm apical from the CEJ and 0.6 mm (range, 0–2.8 mm) at the middle of the root. On a similar study by Januário et al37 on 250 subjects, they found a mean bone thickness for the central and lateral incisors and canines of 0.6 (±0.3) mm, 0.7 (±0.3) mm, and 0.6 (±0.3) mm, respectively, at 1 mm apical to the bone crest and of 0.6 (±0.4) mm, 0.7 (±0.4) mm, and 0.6 (±0.4) mm at 3 mm apical to the bone crest. The mean overall thickness varied within 0.5 (±0.4) mm and 0.7 (±0.4) mm. Also, 85% of the sites presented a wall thickness that was <1 mm and between 40% and 60% of those sites that had a wall thickness of <0.5 mm.
A recent study by Ferrus et al53 confirmed that the anterior/posterior position of the implant, the size of the horizontal buccal gap, and the buccal bone crest thickness significantly influenced the remodeling of the hard tissue during a 4-month period of healing after immediate implant placement into an extraction socket. Also, the sites where the buccal bone wall was thicker than 1 mm showed a better gap filling and minimal vertical resorption of the buccal crest when compared to sites with thinner bone (≤1 mm). A study by Huynh-Ba et al54 in a sample of 93 sites showed a mean buccal bone thickness of 0.8 mm (range, 0.5–2 mm) for the maxillary anterior sites (canine to canine); 87.2% of the buccal bony walls had a width ≤1 mm, and only 2.6% of the walls were 2 mm wide.
The results of this study show a mean bone wall thickness for the anterior maxillary teeth at 4 mm apical to the CEJ of 1.19 mm (range, 0.30–3.30 mm) with a total of 43.3% with ≤1 mm of bone thickness and 0.82 mm (range, 0.20–1.60 mm) at the midpoint of the root with a total of 76.6% with ≤1 mm of bone thickness. For the mandibular teeth, the mean was 1.31 mm (range, 0.30–5.20 mm) with a total of 63.3% with ≤1 mm of bone thickness and 0.80 mm (range, 0.00–1.80 mm) with a total of 75.5% with ≤1 mm of bone thickness, respectively.
The mean bone thickness at the apical area of the root was 1.80 mm (range, 0.20–3.60 mm) for the maxillary teeth and 3.78 mm (range, 0.00–7.90 mm) for the mandibular teeth. No other articles referring to these points of measure were found in the literature.
The possible relationship between GT and the underlying bone was previously analyzed by Fu et al,35 showing a moderate correlation between soft and hard tissues in the anterior region. Our results show no association between these tissues, discrepancies could be because the study by Fu et al35 was performed on cadaveric material and this is an in vivo study. These results seem to confirm the morphologic variations of the periodontium originally described by Maynard and Wilson55 that combined thick or thin gingiva with thick or thin underlying bone, not always showing matching soft and hard tissues.
A recent study by Cook et al36 performed in vivo on 60 patients, where a previous classification of the biotype was established according the clinical and radiographic examination and diagnostic impressions, found that thin biotypes were associated with a thinner labial plate thickness and a narrower keratinized tissue width. These results are similar to the current study where a correlation between the thickness of the crestal buccal plate and the width of keratinized tissue was found, exhibiting a narrower GW when a thin labial plate was observed.
This seems to be another factor related to the prognosis and decision making when establishing a treatment plan or when considering the placement of an immediate implant.
The present study demonstrates the predominance of a thin buccal bone thickness in the crestal third of maxillary and mandibular anterior teeth. In comparison with previous findings, no direct correlation between GT and bone thickness could be established. However, positive evidence associating the crestal bone thickness and the apicoincisal width of gingiva was observed.
The authors declare that there were no financial interest/arrangement of affiliation with any corporate organization(s) offering financial payment.
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