Correlations between Width of Keratinized Gingiva and Supracrestal Gingival Tissues Dimensions: A Retrospective Clinical Study

MATERIALS AND METHODS

Sample

Backup folders of all patients attending the periodontology department at the Lebanese University, Faculty of Dentistry, Hadat Lebanon, between 2010 and 2016 for prosthetic crown lengthening surgery were reviewed. All folders that fulfilled the inclusions and exclusions criteria of the study were selected. A total of 79 systemically healthy adult patients (61 women and 18 men ranging between 20 and 60 years of age) were the sample found to be satisfying the prerequisite conditions for the study, represented by 56 teeth in males and 203 teeth in females with a total number of 1,036 sites in 259 teeth (93 teeth in the anterior maxilla, 11 teeth in the anterior mandible, 81 teeth in the posterior maxilla, and 74 teeth in the posterior mandible).

Inclusion criteria: All folders completed by a postgraduate resident of the department of periodontology, and filled prior to surgery with the following required measurements: width of the KG, SD, BW, and SGT dimensions, and corrected and signed by a faculty member.

Exclusion criteria: All folders presented one of the following conditions: (1) gingival inflammation (full-mouth bleeding scores and full-mouth plaque scores <20%),¹⁷ (2) history of periodontal or orthodontic treatment, (3) gingival recession, (4) presence of altered passive eruption, (5) tooth mobility or furcation involvement, (6) intake of medications known to be associated with gingival overgrowth (calcium channel blockers, cyclosporin, and diphenylhydantoin), (7) heavy smokers (more than 10 cigarettes per day). and (8) the presence of diseases or conditions that may affect periodontal tissue status. Approval for conducting the study was granted by the scientific committee of the faculty.

Measurements

The following measurements were collected prior to the surgery: (1) SD, represented by the distance from the gingival margin to the bottom of the sulcus, measured at the six tooth sites (mesiobuccal, midbuccal, distobuccal, distolingual or distopalatal, midlingual or midpalatal, and mesiolingual or mesiopalatal); (2) SGT dimension, represented by the distance from the gingival margin to the bone crest, assessed at the same six sites; (3) BW, calculated by subtracting the SD from the SGT values at the six sites; and (4) width of the KG, measured from the free gingival margin to the mucogingival line at the midbuccal and midlingual aspects of the tooth.

According to the department policy, all periodontal data were collected using a periodontal probe (XP23UNC15, Hu Friedy, Chicago, Illinois, USA) and rounded to the nearest millimeter, and in case the numbers were not concordant between the resident and the faculty member, the mean value was taken.

Statistical Analysis

Data distributions of buccal and lingual KG failed the normality Shapiro-Wilk tests. Therefore, the Spearman correlation coefficients (r_s) were employed to gauge the linear correlation between these variables and the SGT, BW, and SD in the total sample. Separate correlations were also computed for males and females, for anterior and posterior teeth, and for maxillary and mandibular teeth separately.

An alpha level of 0.05 was used as the decision point for statistical significance. All statistical analyses were conducted using the Statistical Package for Social Sciences (IBM SPSS^®, version 23.0, Armonk, NY).

RESULTS

Correlations with Buccal Keratinized Gingiva

The correlations between buccal SGT and width of buccal KG were all weak and statistically nonsignificant for all assessed teeth (upper, lower, anterior, and posterior) in both males and females and in the overall sample (Table 1; p >0.05). Correlation coefficients ranged from r_s = 0.013 for upper posterior teeth in males (p = 0.964) to 0.365 for lower anterior teeth in females (p = 0.477).

*Statistically significant at p <0.05;

^**Statistically significant at p <0.01; Correlation coefficients are Spearman’s rank correlation coefficient (r_s)

The correlations between buccal BW and width of buccal KG were weak and statistically nonsignificant when assessing all teeth combined in males and females as well as in the overall sample (Table 2; p >0.05). However, when assessing the upper anterior teeth, the correlation was statistically significant in the overall sample (r_s = 0.261; p = 0.012) and in the male subsample (r_s = 0.653; p = 0.003) but not in females (r_s = 0.179; p = 0.125). For the lower anterior teeth, on the contrary, correlations between buccal BW and buccal KG were all nonsignificant (p >0.05). All posterior teeth, upper and lower, also showed no significant correlations with the exception of the mandibular teeth in females (r_s = 0.278; p = 0.038).

*Statistically significant at p <0.05

**Statistically significant at p <0.01

Correlation coefficients are Spearman’s rank correlation coefficient (r_s)

A similar trend was observed for the correlation between the width of buccal KG and the SD. All correlations were not statistically significant (Table 3; p >0.05) except when assessing the upper anterior teeth in the total sample (r_s = -0.346; p = 0.001) and in the female group (r_s = -0.34; p = 0.003) where a significant negative correlation existed.

*Statistically significant at p <0.05;

**Statistically significant at p <0.01; Correlation coefficients are Spearman’s rank correlation coefficient (r_s)

Correlations with Lingual Keratinized Gingiva

The correlations between lingual SGT and width of lingual KG in the lower teeth were statistically significant only when assessing the anterior ones (Table 1; p <0.05). Coefficients were large and significant in the overall sample (r_s = 0.684; p = 0.042) and in the female subsample (r_s = 0.876; p = 0.025) but the relationship was not significant in males despite the large correlation coefficient (r_s = 0.886; p = 0.333).

The correlations between the width of lingual KG and both lingual BW and SD were all weak and statistically nonsignificant when assessing all lower teeth in males and females as well as in the overall sample (Tables 2 and 3; p >0.05).

DISCUSSION

This study explored the correlations between the width of KG and the dimensions of SD, BW, and SGT in an effort to produce an easy clinical tool for prosthetic and restorative rehabilitation, and to simplify the collaboration between periodontics and restorative dentistry disciplines.^18,19 The presence of an adequate band of KG required for maintaining tissue health around teeth and implants has been a subject of interest for many authors.^11,13,18,20 All results reported that the presence of a band ≥2 mm of attached keratinized mucosa influences the long-term soft tissue stability, Different histological studies were performed to assess the dimension of the different periodontal components; the BW, SD, and SGT. Gargiulo et al.¹ described the dimensions of this area on 287 individual teeth from 30 decalcified human autopsy specimens and reported a mean dimension of 0.69, 0.97, and 1.07 mm for the SD, epithelial attachment, and connective tissue attachment respectively with the BW stated to be 2.04 mm. Whereas Vacek et al.² when conducted a similar study on 171 tooth surfaces from a non-decalcified human cadaver specimen, reported a mean measurement of 1.34 mm for SD, 1.14 mm for epithelial attachment, and 0.77 mm for connective tissue attachment. This is a more recent and the first human histometric study on 24 healthy teeth with demineralized block sections.

Tristão et al.³ noted mean measurements of 1.58 ± 0.41 mm for the SD, 1.18 ± 0.42 mm for the epithelial with the connective tissue attachment, and 2.75 ± 0.59 mm for the SGT. Several clinical studies aiming to assess the dimensions of these components were performed in male and female and for anterior and posterior teeth⁷, and before and after crown lengthening procedure;^5,6,8,9 no studies on a potential presence of such correlation between the width of KG and these components were previously performed.

Many authors emphasized the respect of the BW integrity and the preservation of the genetically coded SGT dimensions as keys to success in restorative and prosthetic rehabilitation.²¹ In regards to the BW, the variability of its dimensions assessed by Hamasni et al.²² on 504 tooth sites supported the results of two systematic reviews previously published by Kosyfaki et al.²³ and Schmidt et al.²⁴ and the results of a clinical study performed by Al-Rasheed et al.,²⁵ and were close to the histological results published by Tristão et al.³ Authors confirmed that the dimensions of the biological complex, junctional epithelium, and connective tissue attachment are of clinical relevance, and the use of 2.04 mm as a standard representative of the mean value could mask the actual clinical situation. Similar to the BW, the variability of SGT dimensions and their relation to the tissue biotype was evaluated. Arora et al.,⁸in a cross-sectional study of 1,932 sites in 366 teeth, mentioned that the thick–flat gingival biotype is characterized by a large band of KG, exhibiting greater median SGT than the thin-scalloped biotype. These results are in concordance with our finding in the anterior lower teeth when the correlations between lingual SGT and the width of lingual KG were statistically significant but was absent in the overall sample when assessing the buccal KG and the buccal SGT. Whereas a statistically significant positive correlation was noticed between the buccal KG and the buccal BW in the upper anterior teeth of the overall sample and in the male subsample. The results published by Goaslind,²⁶ Olsson et al.,²⁷ and Müller et al.²⁸ concerning the relation between GT and SD showed a positive relationship between the thickness of free gingiva and the SD. Contrarily to the recent results published by Singh et al.¹⁶ where authors confirmed the presence of a positive correlation between GT and GW, and a weak negative correlation between GT and SD, our results demonstrated the absence of positive relationships between the width of buccal KG and the SD except when assessing the upper anterior teeth in the total sample and in the female group. The inconstant correlations between the width of KG and the SGT, BW, and SD dimensions in different gender and different teeth sites were found in this study. The variability in results published by several authors concerning periodontal tissue dimensions and the relationships between different constituents reflected the underlying large variability of these supraosseous components and are likely reflective of differences in unique patient characteristics, tooth type, and tooth side. The lake of studies interested in finding a potential correlation between the major components of the periodontium; the KG and the SGT, and within the limitation of this study, the width of KG commonly associated with a thick periodontium cannot be a clinical indicator of the dimension of the SGT, neither the BW nor the SD.

CONCLUSION

While the width of the KG may be a useful indicator of the BW dimension in the upper anterior teeth at the buccal side, sulcular probing and bone sounding prior to prosthetic or restorative rehabilitation remains an essential clinical tool for the practitioner to avoid periodontal tissues traumatisms and to ensure the preservation of tissue integrity and esthetic outcomes.

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