J O U R N A I O F E S T H E T I C D E N T I S T R Y

Biologic Width and its Relation to Periodontal Biotypes

FARSHID SANAVI, D M D , P H D " ( P E R I O D O N T I C S , 1 9 8 5 )

LOUIS F. ROSE, DDS, M D * ( P E R I O D O N T I C S , 1 9 7 0 ) A R N O L D S . WEISGOLD, DDS, FACDt ( P E R I O - P R O S T H O D O N T I C S , 1 9 6 5 )

ABSTRACT Although average measurements of the biologic zone do not necessarily reflect any one clinical situation, they do establish a basis upon which clinical decisions can be made. Clinical impressions, human autopsy material, and animal studies support the concept of a biologic width. Impingement on the attachment in a susceptible host has shown adverse reactions, including gingival inflammation and alveolar bone loss. The concept is clinically important in determining the extent of osseous surgery necessary in the exposure of sound tooth structure. If the implant- abutment interface is considered to be similar to a subgingival crown margin, its importance in relation to peri-implant inflammatory disease is readily apparent. In the presence of inflammation, it is likely that epithelial migration would occur to a level apical to that source. Clinical observa- tions indicate that, once the biologic attachment is invaded around the implant, the gingival reac- tions are similar to those found around natural teeth, whether the tissue is of the thick flat or thin scalloped type.

n the past, much effort in den- I tistry has been focused on devel- oping a restoration that reestablishes lost function and attempts to mimic the form, size, color, and appearance of natural dentition. Recent enhance- ments of these techniques and the advent of new restorative materials have enabled the clinician to repro- duce the ultimate natural-appearing prosthesis that maintains the bal- ance between the restoration and the health of the supporting tissues.'l2 The success of such a restoration depends on many factors, among them soft tissue integrity and appear- ance. Indeed, the most challenging

procedure in clinical dentistry is the restoration of gingival harmony and dental esthetics in the anterior area, where the dentogingival inter- face is clearly visible. Therefore, an understanding of the structure and physiology of the gingival tissues in relation to teeth, osseointegrated implants, and restoration margins is necessary to achieve a healthy, har- monious, and maintainable interface between the restoration and the surrounding soft tissue.

The gingiva is masticatory mucosa that covers the tooth and underly- ing attachment apparatus. It encir-

cles the necks of erupted teeth and firmly attaches to tooth and alveo- lar bone. The coronal part of the gingiva rests on tooth and forms a scalloped configuration. It also occupies the entire space between the teeth apical to the contact area. The shape of the gingival papilla is determined by the shape and posi- tion of the anatomic crown, as well as contact area and embrasure form. The gingival sulcus is the space between the marginal gingiva and the tooth. It is bordered on one side by the tooth surface and on the other by the epithelium lining the sulcus and covering the gingiva. A

*Clinical Assistant Professor of Periodontics. School of Dental Medicine. Universitv o f Pennsvlvania . , I

Philadelphia, Pennsylvhnia tClinical Professor of Periodontics. and Director o f Postdoctoral Periodontal Prosthesis. School of Dental Medicine, University of Pennsylvania, Philadelphia, Pennsylvania *Professor of Surgery and Medicine, Allegheny University of the Health Sciences, Chief of Division of Dental Medicine and Surgery, Director of Implant Dentistry, Allegheny University Hospital, Philadelphia, Pennsylvania. and Clinical Professor in Periodontics, School of Dental Medicine, University of Pennsylvania, Philadelphia, Pennsylvania.

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healthy gingiva appears light pink with a stippled surface and free from any sign of inflammati~n.~

Clinical observations have led clini- cians to identify two basic human periodontal forms."'l The more prevalent, the thick flat type, occurs in over 85% of the patient popula- tion; the other, the thin scalloped type, occurs in less than 15% of cases. Becker et a1 expanded on this categorization after examining over 100 human skulls.ll Their classifi- cation was more detailed in that the types were separated into thick flat, thin scalloped, and pronounced scal- loped, with the mean distance from the height of the interdental bone to

Biologic Width and its Relation to Periodontal Biotypes

Figure 1 . Tooth forms of maxillary central incisors. A, square; B, somewhat more triangular; C, very triangular. Compare the degree of scalloping of periodontium among the three types: A, thick flat; B, thin scalloped; and C, pronounced scalloped.

the alveolar crest being 2.1 mm for the flat, 2.8 mm for the scalloped, and 4.1 mm for the pronounced scalloped classification (Figure 1).

A normal, healthy periodontiurn is characterized by a rise and fall of the gingival margin and underlying bony crest. This undulating appear- ance places the gingiva more api- cally on the direct facial and more incisally at the interproximal. This is called normal architectural form. In the healthy periodontium, the underlying bony crest lies approxi- mately 2 mm apical to the cemento- enamel junctions (CEJ) and follows the configuration of the CEJ on all four surfaces of the tooth.

Figure 2. Typical maxillary central incisor from thick flat type of periodontium.

S A N A V I ET AL

In the thick flat type there is this normal rise and fall of the gingiva and bone, but there is not a great disparity between the direct facial and that found interproximally. The gingiva is thick or dense and is fibrotic in nature. Usually this type of periodontiurn has, quantitatively and qualitatively, adequate amounts of attached masticatory mucosa. When irritated by tooth prepara- tion, impression procedures, extrac- tion, or other clinical techniques, this periodontium usually reacts with inflammation, followed by migration of the junctional epithe- lium apically, with resultant peri- odontal pocket formation or redun- dant tissue (Figure 1, A).

The thin scalloped type of perio- dontium, on the other hand, is dis- tinguished by a pronounced dispar- ity between the height on the direct facial and that found interproximally (Figure 1, B and C). The underlying bone is usually thin on the facial with dehiscences and fenestrations commonly found. Usually there is less attached masticatory mucosa, from both quantitative and qualita- tive perspectives. Excessive irritation of this type of periodontium usually leads to recession both facially and interproximally. Although the bony crest lies about 2 mm apical to the CEJ and follows its configuration, the interproximal soft tissue usually does not completely fill the space between the adjacent teeth. This is

especially true of the interproximal papillae between maxillary central incisors. It should be noted that it is usually in this type of periodontium where there is recession on the direct facial of artificial crowns, where a blue-grey shadow is often seen at the gingival margin, and where the interproximal papillae recede, revealing “black triangles.”

Teleologic reasoning has led researchers to believe that tooth form dictates periodontal form. Although an attractive and com- pelling line of thought, to date, this has not been proven. However, based primarily on clinical observa- tion, there appears to be direct cor- relation between tooth form and periodontal form.

The teeth found in the thick flat periodontium are usually character- ized by being more bulbous and square in form (Figure 2). Contact areas are located more apically and usually are broad incisogingivally and faciolingually. The cervical con- vexity on the facial surface is rea- sonably prominent. Since the con- tact areas begin more apically, a central incisor viewed from the facial surface appears to be square. The interproximal papillae filling the space between the teeth termi- nate at the contact areas, hence, a flat periodontium. Characteristi- cally, the roots of these teeth are broad mesiodistally, compared to

abrupt tapers. In fact, in some instances, the mesiodistal width of the root is similar in dimension to the widest part of the crown.

In the thin scalloped periodontium, the tooth form is usually more sub- tle and somewhat triangular. Con- tact areas are located more incisally and are small incisogingivally and faciolingually. The cervical convex- ity is less prominent. Since the con- tact areas are located more incisally, the interproximal papilla is also positioned more incisally, hence, the scalloped form. The roots of these teeth are usually more tapered than those found in the thick flat type (Figure 3 ) .

Figure 3. Typical maxillary central incisor from thin, scalloped type periodontium.

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Biologic Width and its Relation to Periodontal Biotypes

Figure 4. Common gingival reaction to preparations in the biologic zone. A, thick flat periodontium. Note gingival inflamma- tion hypertrophy around the four maxillary incisor ceramometal crowns; B, thin scalloped periodontium. Note gingival reces- sion around the two maxilla y central incisor ceramometal crowns.

In comparing the crown and root forms of each type, it becomes obvious that the inter-root bone width (i.e., the amount of bone pre- sent between two adjacent roots) is greater in the thin scalloped type than in the thick flat type of perio- dontium. As recession occurs and inter-root bone resorbs apically, the space between the roots of the thin scalloped type becomes wider. A comparison of the soft tissue inter- proximal papillae in each type is revealing. The CEJ-bone crest dimensions appear to be the same (i.e., bone crest about 2 mm apical to the CEJ). What is different is that in most instances, the inter- proximal papillae do not totally fill the spaces between the teeth in the thin scalloped type; almost always, the space is filled in the thick flat type (Figure 4).

Histologically, gingiva attaches to the tooth by means of junctional epithelium and connective tissue.12 The junctional epithelium shapes the floor of the gingival sulcus and

extends apically on the tooth sur- face to form the attachment seal around the t ~ o t h . ~ J ~ The attached gingiva is firmly connected to the cementum and bone by a dense net- work of collagenous fibers.I3J4 This collagen-rich, cellular-poor layer of connective tissue appears like a bar- rier separating the crestal bone from junctional epithelium (Figure 5). The combined dimension of the connective tissue attachment and the epithelial attachment averages 2.04 mm and has been described as the biologic width, a term coined by Dr. D. Walter Cohen.15 This dimension may become critical when one considers restoration of a tooth that has been fractured or destroyed by caries near the level of the alveolar crest.I6 The preparation and restora- tion of a tooth that violates the epithelial and connective tissue attachment usually results in a poor gingival Gargiulo et a1 measured the dimension of attach- ment apparatus in autopsy mater- ia1.22 Their findings were extensively used by others to develop a blue-

print for clinical application of the biologic width.16Js~23 It is important to emphasize that the measurements presented in Gargiulo's study are averages, and close examination of these data shows a significant range of values for junctional epithelium and connective tissue attachment.

From a therapeutic standpoint, the biologic width becomes of great sig- nificance in the performance of a crown lengthening procedure, such as in cases involving subgingival caries, fractured teeth, or esthetic consideration^.'^,^^*^^ Failure to comprehend the amount of osseous tissue required to be resected will often result in violation of the newly established biologic width during tooth preparation. Two aspects of the resective procedure must be considered: (1) the amount of bone that must be removed and (2) the periodontal biotype of the patient.

Endosseous implants require the integration of three different tissues: bone, connective tissue, and epithe-

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S A N A V I ET AL

lium. The structure of the soft tissues surrounding the endosseous implants is, in many ways, analogous to the natural dentition. The stratified, squamous, keratinized oral epithe- lium is continguous, with a non- keratinized sulcular epithelium. The junctional epithelium initiated from the apical aspect of the sulcular epithelium adheres to the implant surface and provides a union between implant and the surround- ing gingiva.25

A comparison of the interface between the connective tissue and natural teeth or implants reveals a significant difference between the two. The orientation of the fibers appears to be parallel to the implant surface. Berglundh et a1 and Ruggeri et a1 demonstrated the presence of a circular ligament of densely packed collagen fibers free from inflamma- tory cells coronal to the osseointe- grated bone t iss~e.2~*~’ Cochran et a1 and Berglundh and Lindhe examined the dimension of the implantogingi- val junction in relation to clinically healthy unloaded and loaded implants in dogs.28,29 Histometric analysis included the evaluation of the junctional epithelium and the connective tissue. The junctional epithelium measured about 2 mm in an apicocoronal direction, and the connective tissue attachment was more than 1 mm. The com- bined measurement of junctional epithelium and connective tissue attachment was 3 mm. The sum of

these measurements was similar to measurements found around teeth. Thus, the data confirm what appears to be an existing biologic width around titanium. It is physio- logically formed and appears to be as stable as that found around nat- ural teeth.

The preservation of a healthy perio- dontal attachment is the most sig- nificant factor in the long-term prognosis of a restored tooth.30 The fact that an improper restoration margin, inadequate embrasures, and poor contour may accumulate plaque and initiate inflammation and sub- sequently alveolar bone resorption and loss of attachment is well docu- mented.30-32 The placement of mar- gins of a restoration in the sulcular area is especially important in an- terior areas, to satisfy the esthetic demands of patients. The restorative

margin, be it metal or porcelain, placed in the vulnerable crevicular area leaves little room for error.33

Recent studies have shown that violation of the biologic width results in inflammation and loss of attachment.18J9 The injury caused by placement of a restorative margin at the supracrestal connective tissue attachment leads to bone resorp- tion, loss of attachment apparatus, and reestablishment of a biologic width at a level more apical to the original position. Such a response is depicted in Figure 6 . The mechani- cal violation of the supracrestal connective tissue attachment was caused by placement of silk ligature around the maxillary second molar of rats. Seven days after ligature placement, a new biologic width was established, despite the pres- ence of bacteria and inflammatory

Figure 5. fnterdental space between first and second molar in a non-ligature- treated rat. Note the presence of a collagen rich layer above the crestal bone.

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Figure 6. Interdental space between first and second molar in a ligature-treated rat (8 days). Note the establishment of biotogic width in a new apical position. Despite the presence of bacteria and inflammatory cells below the ligature, the supracresta 1 bone exhibits a collagen- rich layer of tissue without apparent inflammatory cells.

infiltrate around the ligature and the underlying epithelium and con- nective tissue. The supracrestal con- nective tissue consisted of layers of collagen-rich fibers without any sign of inflammatory cells.

Disturbance and violation of the biologic width around titanium implants also has been studied.34

Biologic Width and its Relation to Periodontal Biotypes

Abrahamsson et a1 demonstrated that repeated removal and recon- nection of an implant abutment potentially disturbed the established mucosal attachment and subse- quently resulted in a more apically positioned connective tissue attach- ment.34 It was concluded that a certain width of the peri-implant mucosa is required to enable a proper epithelial connective tissue attachment, and if this soft tissue dimension is not satisfied, bone resorption will occur, to ensure the establishment of attachment with an appropriate biologic width.

C O N C L U S I O N

It appears that there is a minimal dimension of peri-implant mucosa (i.e., biologic width) that is neces- sary around endosseous implants and natural teeth. Bone resorption may take years to afford a stable soft tissue complex in the osseointe- grated implant.29 Once the fixture is exposed and the healing abutment placed, the biologic attachment will eventually form. From a practical clinical perspective, if one uses pre- fabricated abutment heads, there is little chance for the biologic attach- ment to be invaded. However, when using certain abutments to correct positional problems or to place the restorative margin into the crevice, there is the strong possibility that the biologic attachment will be compromised. This may be likened

to a natural tooth being prepared too far apically (i.e., into the bio- logic attachment). In this situation, the artificial crown is cement- retained instead of screw-retained, with the possibility that remnants of cement will be left in the sulcus.

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Reprint requests: Farshid Sanavi,DMD, PhD, Department of Periodontics, School of Dental Medicine, University of Pennsylvania, 4001 Spruce St., Philadelphia, PA 191 04 0 1 998 Decker Periodicals

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