Dimensions of Periodontium (Biotype Versus Phenotype) – A Literature Review

Introduction

Several factors like the gingival biotype, the architecture of the gingival tissue and tooth form plays a crucial role in the long–term success of esthetic restorations. The morphology of the gingiva plays a major role in the establishment of final esthetics. Therefore, recognition of different gingival tissues is important during treatment planning. Different gingival biotypes respond differently to inflammation, restoration, trauma and para–functional habits. These traumatic events eventually may lead to different types of periodontal and osseous defects which require different treatment methods.¹

A critical factor to consider while planning a dental treatment, especially in the esthetic zones is the tissue biotype. The initial thickness of gingiva may predict the amount of root coverage that can be achieved by various procedures. The unique vascular supply of underlying alveolar bone and its tendency to resorb depends on the gingival thickness which can be altered by various treatment procedures.^1,2 

Methods to measure gingival tissue thickness

Visual examination – It is a routinely used clinical procedure to evaluate the gingival thickness which is simple and non–invasive.³ Gingival biotype assessed visually is not sufficient to predict a proper diagnosis and plan a treatment for gingival esthetic surgeries and restorative procedures.⁴ The disadvantage of this method is that it is unreliable as the amount of gingival thickness cannot be assessed appropriately.⁵

Direct measurement – This is done by trans–gingival probing using a UNC–15 or William’s probe. Endodontic files and reamers with rubber stoppers are used more recently. A thickness of >1.5 mm is considered as ‘thick’ and <1.5 mm is considered as ‘thin’ gingival biotype. The precision of the UNC–15 or William’s probe, probing angulations and tissue distortion during probing are the few limitations of using this method.^3,6 Identification of gingival biotype (thick versus thin) by visual method greatly differs from that being evaluated with a periodontal probe or by direct measurement.⁴

Probe transparency (TRANS) method – In this method, the gingival biotype is said to be thin or thick based on the visibility of the probe through the gingival margin. In a study, 85% intra examiner reproducibility was found while using this method.⁷

Modified caliper technique – Kan et al., in 2010 used a tension free caliper for the first time to measure the thickness of gingiva on the facial aspect of the maxillary anterior teeth region and found no significant difference compared to the results obtained using a probe. The limitations with this procedure are that it cannot be used during periodontal surgery and has limited application for pre–treatment evaluations.⁶

Ultrasonic devices – Ultrasonic devices were used by Kydd et al., in 1971 for the measurement of palatal mucosal thickness.⁸ It is a non–invasive method for determining tissue thickness. It is composed of an oscillating piezo–electric crystal which transmits a frequency pulse of 5 MHz through the mucosa (1000 signals per second). The speed of the wave transmitted through the mucosa is estimated to be about 520 meters per second. The mucosal thickness is calculated within (2 – 3) seconds by comparing the echo to the transmission of the pulse wave. The transducer probe present in the ultrasonic devices has a diameter of 4 mm and a precision of about 0.1 mm. The limitations of using this method are - difficulty in positioning of the device for achieving reproducible measurements, the unavailability of the devices and the high cost of the devices.^3,9 A study was done in 2005 by Savitha and Vandana, where the authors compared the gingival thickness using TRANS method and ultrasonic devices. The authors concluded that the ultrasonic devices were more accurate in estimating the gingival thickness compared to the TRANS method, as TRANS method frequently over measured the gingival mucosal thickness.¹⁰

Cone–beam computed tomography (CBCT) – CBCT has been used recently for the visualization and measurement of both hard tissue and soft tissue thicknesses. CBCT can accurately measure both the bone and the mucosal thickness (especially on the labial side). CBCT is a more reliable method of evaluating the thickness of bone and mucosa compared to the direct measurement technique.¹¹

Puffed cheek method – It was first used by Dvorak et al., in 2013 to evaluate the mucosal thickness by using CT with the help of a localized splint and a marker point. Four marker points are usually placed (two on central incisors and two on first molars). CT scans are taken with distended cheeks by asking the patients to puff out their cheeks. This method provides more accurate information of the oral mucosa compared to the conventional CT scans.¹²

Biotype versus Phenotype

Biotype: A group of tissues or organs having a similar and specific genetic constitution or genotype only.¹³

Phenotype: Appearance of a tissue or an organ which is based on a multifactorial constitution of genetic and environmental factors (it includes the biotype).¹³

Periodontal phenotype: This term is based on both gingival phenotype (three-dimensional gingival volume such as gingival thickness – GT and keratinized tissue width – KTW) and thickness of the facial and / or buccal bone plate (bone morphotype – BM).¹³

According to the definition, biotype is something which is predetermined by genetics, cannot be changed and does not include environmental factors and clinical intervention that can alter the profile of periodontal tissues. Whereas, periodontal phenotype can be altered by environmental factors and clinical interventions such as overhanging restorations, orthodontic treatments, or gingival grafting procedures.^13,14

Periodontal phenotype cannot be assessed in full, while gingival phenotype (GT and KTW) can be assessed in a standardized and reproducible way. 

Dimensions used to determine periodontal biotype or phenotype¹⁶

• Tooth dimensions (TD)

• Bone morphotype (BM)

• Gingival morphotype (GM)

• Keratinized tissue width (KTW)

• Gingival thickness (GT)

Tooth dimensions – Tooth dimensions were assessed in terms of crown width and crown length ratio (CW/ CL) of the central incisor and was classified as either a long narrow (CW / CL ± 0.5) or a short wide crown form (CW / CL ± 1.0) according to Olsson & Lindhe (1991). Cook et al., in 2011 conducted a study using the CL/CW ratio and a study by Gobbato et al., in 2012 modified the definition by adding the contact surfaces (CS) between the teeth, and considered CS/CL ratio. The latter defined the CS/CL ratio for triangular teeth (57%) and for square / tapered teeth (43% – 57%).

Bone morphotype – It was described by Becker et al., in 1997 who conducted a study on skull bones and defined bone morphotype as either flat, scalloped or pronounced scalloped. Other authors defined the bone morphotype by estimating the alveolar bone thickness.

Gingival phenotype or gingival morphotype – The term GM seems broad and extensive, even taking other parameters (KTW, GT) into its definition. Hence, gingival phenotype or gingival morphotype refers to the combination of the thickness of gingival tissues (GT) and the keratinized tissue width (KTW).

Keratinized tissue width – It is basically the width of attached gingiva along with the marginal gingiva. It represents the entire keratinized epithelium, that is the amount of gingiva above the muco–gingival junction.

Prevalence

The most predominant form of periodontal phenotype is the thick periodontal phenotype. Males have a thicker periodontal phenotype than females. Usually, younger individuals have a thick periodontal phenotype than middle–aged or older individuals. Few authors found that maxillary periodontal phenotype is thicker compared to mandible. Thinnest areas of periodontal phenotype are usually observed in the maxillary canine and mandibular first premolar regions. Racial and genetic factors also play a significant role in the individual’s periodontal phenotype.²⁹ 

Conclusion

The gingival tissue and underlying osseous structures vary from individual to individual and because of such variability, the gingival responses to various inflammatory, traumatic or surgical insults differ significantly, and each requires a different treatment. Periodontal phenotype is an important evaluation parameter which allows the clinician to predict therapeutic outcomes, especially in esthetic procedures. The nature of periodontal phenotype and its understanding helps the clinician to decide an appropriate periodontal treatment so that adverse or unwanted treatment outcomes are minimized. With the advancement in technologies and newer techniques for periodontal biotype assessment, clinicians can now accurately diagnose and predict treatment outcomes. Therefore, proper assessment of keratinized tissues, periodontal phenotype and vestibular depth plays an important role in deciding and planning a proper treatment which would eventually help to maintain the balance between the pink and white structures in the mouth. 

Conflict of Interest

None