Dental Clinical Articles
Posted: 15 May 2012
Soft tissue biotype: And its implications
In the continuation of his series on preventive care, Edward Sammut discusses biotype and what it means to periodontics and implant dentistry
Soft tissue biotype was previously called gingival biotype or morphotype, but since the advent of implants, this has been renamed to encompass tissue around both teeth and implants¹. The term refers to a composite or aggregate of four features of the soft tissues and the teeth they surround that build up to a specific picture. These are:
1. The gingival width (keratinised tissue width) – which refers to the width of the keratinised tissue when measured from the gingival margin to the mucogingival junction. Some patients have a wide band of keratinised tissue that frequently ends in a relatively flat mucogingival junction, while others have a narrower band of keratinised tissue, and also the mucogingival junction may be wavy so that it follows the papillary contours.
2. Gingival thickness (thick or thin) – the thickness of the tissue in a bucco-palatal dimension. If you insert a probe into the midbuccal sulcus of the maxillary central incisor and you can see it through the tissue then it is thin by this definition. If you can’t see it, it is thick.
3. Papilla height/proportion – the part of the gum that fits in between teeth. Around posterior teeth, the papilla usually forms a double peak (one peak on the buccal side and one on the lingual) with an interdental col area.
4. Crown width/height ratio – long, slender teeth tend to be associated with contact points distant from the alveolar crest and long papillae that fill the embrasures. Of course, when dentistry has altered the shape of the teeth or the contact points, these last two features may de-link.
Classically, therefore, we spoke of a thick or thin soft tissue biotype. A thick flat biotype (Figure 1) is associated with a wide band of keratinised tissue, thick gingivae, short papillae and squarish teeth. Seen from the occlusal view, the alveolar housing of the teeth forms a broad, even ridge. The thin scalloped biotype patient (Figure 2) has a narrow band of keratinised tissue which may end in a wavy mucogingival junction, thin gingivae, long teeth and long papillae that result in a highly-scalloped gingival margin. When seen from the occlusal view, the alveolar housing will follow the shapes of the roots and it may be possible to visualise the outlines of the roots under the tissue². Of course, the position of the tooth within the ridge will have a considerable influence on the thickness of the overlying tissue³. More recently, a third common soft tissue biotype was identified – the thick scalloped, which has thick gingivae but also a narrow band of keratinised tissue and high-scalloped margins⁴.
The tissue biotype is frequently reflected in the thickness of the alveolar bone⁵. If you look at a cross section of a maxillary central incisor with a thick tissue biotype, the buccal plate may be thick enough to accommodate a separate bundle bone around the tooth (Figure 3), while in a thinner biotype the bone is usually (very) thin, resulting in the bundle bone and the buccal plate being one and the same bit of bone (Figure 4).
Okay, so what’s the big deal? Well, the biotype has a profound influence on how the periodontal structures respond to various processes including inflammation, periodontal surgery of all sorts, extraction of teeth and implant treatment. This means that in the anterior dentition, especially in cases with a high smile-line, the soft tissue biotype has a big impact on the final pink aesthetics of the case. Knowing the behaviour of the tissue will therefore help you predict changes and advise patients accordingly about the possible final outcome, before you start treating them.
Inflammatory periodontal disease
In the development of periodontal disease, the inflammation generated by plaque on the root surface extends into the tissue for a distance of 2mm in all directions⁶. In patients with a thin biotype, the distance from the root surface to the oral epithelial surface (that is the thickness of the whole periodontium encompassing cementum, periodontal ligament, bone and gingivae) can be less than 2mm. Inflammation will therefore involve all the structures, rapidly resulting in recession. On the other hand, in thick biotype patients with a thick alveolar housing around the teeth, the 2mm radius of inflammation will damage cementum, ligament and bundle bone only, producing a periodontal pocket. Of course there will be variations in the thicknesses of the different layers around each tooth, but this somewhat oversimplified approach may help you to understand how the same periodontal disease processes result in different effects. Thin tissue is also more likely to recede following non-surgical periodontal treatment⁷.
Crown lengthening surgery
Patients with a thick tissue biotype are likely to get more rebound of the gingival margin after crown-lengthening surgery is performed⁸. When treating these cases, it is essential that the correct amount of bone removal is performed so that the biological width is correctly set up. While this has not been explicitly reported, it is not unreasonable to expect that patients with a thin biotype may be more prone to additional recession following crown-lengthening surgery.
Root coverage surgery
In patients with a thick soft tissue biotype, healing following root-coverage surgery is predictable, whereas the opposite is true for hose with thin tissue⁹. Unfortunately, recession is usually found in those with the thin biotype, where it has been a contributory factor in the development of the recession. Because of this, inter-positional connective tissue grafts are used between the pedicle and the root surface to increase the thickness of the tissue. Various reports have suggested that for optimal root coverage, the tissue needs to be augmented to a minimum thickness¹⁰.
The bundle bone will resorb after extraction, regardless of the method of extraction and socket-preservation procedures¹¹‑¹³. Unfortunately, in thin biotype patients the bundle bone is very likely to be the buccal plate, and we can therefore expect considerable collapse of the socket, resulting in a contour deficiency, which will need to be addressed through bone grafting or compromise in the implant angulation, especially if the patient is getting implant treatment in the aesthetic zone. Patients with a thicker soft tissue biotype may end up with less alveolar deficiency and therefore their restorative treatment can be viewed as being more predictable and less demanding.
This really follows on from above. Once the implant is placed and the alveolar form is hopefully re-established, this situation needs to be maintained. Peri-implant tissue health seems to depend, in some part at least, to there being immobile keratinised tissue around the emergent restoration¹⁴ ¹⁵. As around the teeth, thin peri-implant soft tissue seems to be more prone to recession and less likely to develop nicely formed papillae around the implant restorations¹⁶. In my clinical opinion, tissue recession around implants seems to result in absence of immobile, keratinised tissue more quickly than around teeth, possibly because the shoulder of most implants are placed more apical to the cementoenamel junction of the tooth they replace. Mobile tissue around an implant is associated with increased risk of development of peri-implant disease and some authors actually recommend augmentation of the keratinised tissue as one of the treatment strategies in managing peri-implantitis¹⁷ ¹⁸.