Gingival Biotype Classification, Assessment, and Clinical Importance: A Review

A normal scalloped gingival line at the cement enamel junction of the teeth forms one of the components of an aesthetic smile. Clinicians handle gingiva in several periodontal procedures and the resulting gingival architecture is not always ideal. In the era of aesthetic-driven dental therapy, it is important that a clinician should be well aware of all the prognostic factors that may affect the final aesthetic outcome of dental treatment. Gingival biotype is one of the important factors which influences indications and outcome of various periodontal, restoratives, surgical, and implant therapy. Thin gingival biotype responds differently than thick gingival biotype. Gingival biotype assessment before various dental-related procedures is mandatory now to achieve a predictable and stable gingival margin position. This review describes the various classifications, methods of assessment, and clinical importance of gingival biotype during dental treatment.


INTRODUCTION
Gingiva is the part of the oral mucosa that covers the alveolar processes of the jaws and surrounds the necks of the teeth. 1 It is mandatory that a clinician should be well aware of all the factors that may influence the aesthetic outcome of treatment in the era of aesthetic-driven dentistry. One factor that clinicians should consider before starting any dental treatment procedure is the gingival biotype.
In 1969 Ochsenbein and Ross in their study indicated that there were two main types of gingival morphology, namely the scalloped and thin or flat and thick gingiva. 2 The periodontal biotype term was later presented by Seibert and Lindhe in 1989 to divide the gingiva into "thick flat" and "thin scalloped" biotypes. 3 The gingival biotype has been used to describe the thickness of the gingiva in the faciopalatal dimension 4,5 and it is a genetically determined trait. 6  gingiva in faciopalatal measurement but also the form of gingiva, the measure of keratinised gingiva present, alveolar bone form and thickness, and crown shape. 7 In a study by De Rouck et al. (2009), the thin gingival biotype occurred in one-third of the study population, while the thick gingival biotype occurred in two-thirds of the study population. 8

DIFFERENT CLASSIFICATIONS OF GINGIVAL BIOTYPE
The 2017 World Workshop on the Classification of Periodontal and Peri-Implant Disease and Conditions has recommended adoption of the term "periodontal phenotype." Periodontal phenotype is determined by gingival phenotype (gingival thickness and keratinised tissue width), and bone morphotype (thickness of the buccal bone plate). This term is based on both gingival phenotype (threedimensional gingival volume such as gingival thickness and keratinised tissue width and thickness of the facial and/or buccal bone plate (bone morphotype). 9 Various classifications have been suggested for gingival/ periodontal biotypes. Gingival/periodontal biotype may contrast from tooth to tooth in an individual or may differ with age, sex and dental arch location. 10 During each classification gingival thickness is one of important factors.
There are many classifications suggested for gingival biotype and each classification shows lack of agreement for defining gingival biotype as thick and thin biotype.

GINGIVAL BIOTYPE ASSESSMENT
There are many assessment methods proposed for gingival biotype. Most common methods have been explained below.
Direct measurements or Bone sounding: The gingiva is anaesthetised by a topical local anaesthetic gel. An endodontic spreader/probe/needle with a rubber stop is inserted at a point at the centre of the gingival margin and mucogingival junction in a perpendicular direction and measurement is recorded against a digital caliper. 14 This method is easy to perform, convenient, cheap, and accurate.
However, it is an invasive technique, requires application of local anaesthesia, depends upon angulations and precision of probe and there is poor precision of tissue thickness assessment. The validity of using a periodontal probe for the transgingival probing or sounding of the alveolar peak level has been exhibited for buccal surfaces of the jaw. 21 The estimations from the occlusal surfaces of the teeth to the evaluated level of the alveolar peak using in this technique precisely reflected the actual distances evaluated after surgical exposure of the alveolar peak at these sites. 18 Savitha et al. stated that the value of gingival thickness assessed with a probe was on average larger by 0.5 mm than the one obtained using measurements with an ultrasound device. 22 Visual examination: Visual assessment is a technique which is frequently used to determine the gingival biotype.
In this technique, no tools are necessary and it is quite simple and straightforward since each biotype exhibits its 5. Tissue appears friable with a minimal zone of attached gingiva.
6. Soft tissue is highly accentuated and often suggestive of thin or minimal bone over the labial roots. 2. There is an increase amount of vascularity in thicker tissue which enhances oxygenation, immune response, growth-factor migration, and clearance of toxic products, resulting into good healing response.
3. It also consists of increase in the layers of epithelial keratinisation in thicker tissue, which prevents microbial ingress and physical damage. 34 However, thin biotype is characterised by thin gingival tissue making it delicate and almost translucent in appearance.
Such a tissue appears friable, usually, having a minimal zone of attachment. The soft tissue is highly accentuated and often suggestive of thin or minimal bone over the roots labially and there are evidences which show that the thin gingival tissue is less resistant to any inflammatory, traumatic, or surgical insult and thus usually exhibits gingival recession. 5,13,18,33,35 Treatment of non-bleeding sites in periodontitis patients with a thick biotype may show a less noticeable loss of attachment than treatment of non-bleeding sites in a thin gingival biotype which is more likely to result in recession. 13 A flap thickness of >0.8 mm was associated with complete root coverage, while a flap thickness of <0.8 mm was associated with partial root coverage. 36 41 There was also a positive correlation between the keratinised tissue width and gingival thickness in maxillary anterior teeth.
Maxillary central incisors presented with the greatest mean gingival thickness, followed by lateral incisors and canines and in the same way maxillary lateral incisors have the greatest keratinised tissue width, followed by the central incisors, and canines. 25,[41][42][43][44][45][46][47][48][49][50][51][52][53][54] In orthodontic therapy, teeth are aligned and moved in various directions. It has been seen that such tooth movement results in increased recession and increased incidence of dehiscence and fenestration formation in cases with thin biotype. 42 It has been seen that in relation to metal ceramic prosthesis over a period of five years, significantly increase gingival recession is seen after prosthesis placement in thin biotype as compared to thick biotype. 43  In case of thin biotype, it can be converted or enhanced into thick biotype by following procedures: 1. The use of connective tissue grafts. 46 2. Acellular dermal matrix can also be used to enhance the biotype.