London, and Michael Chiully; Dental technicians: Nori Kajita and Hiro Tokutomi; Mandibular abutments: Issaquah Dental Laboratory
Prosthodontist: Ariel J. Raigrodski; Dental technicians: Nori Kajita and Hiro Tokutomi
Prosthodontists: Robert D. Walter and Ariel J. Raigrodski; Periodontists: Traelach P. Tuohy and Robert M. London; Dental technicians: Nori Kajita and Hiro Tokutomi
Prosthodontists: Matthew R. Anderson, Tijana Stijacic, and Ariel J. Raigrodski; Periodontists: Jaden Erwin and Robert M. London; Dental technician: Manfred Pornbacher
* Select images previously published in J Cosmet Dent 2013;28(4):46–58.
† Select images previously published in J Cosmet Dent 2014;30(2):40–52.
‡ Select images previously published in Seattle Study Club J 2010;15(1):19–24 and Seattle Study Club J 2011;15(2):10–15.
§ Select images previously published in J Prosthet Dent 2014;111:154–158.
Fundamental Concepts of Periodontal Tissues
Robert M. London | Sul-Ki Hong | Ariel J. Raigrodski
Periodontal tissues are vital and responsive to their environment. They develop and differentiate as teeth erupt into the oral cavity, and once in function, they change and adapt to environmental stimuli. Restorative dentistry is a major source of environmental stimuli. By developing a strong understanding of the underlying tissues and how they are impacted by our clinical procedures, clinicians can execute a restorative plan that maximizes health and esthetics at the soft tissue–restorative interface.
Periodontal tissues can be defined in simple terms: epithelium, connective tissue, and bone. Of course, there is a vascular component and a component comprised of immune cells—neutrophils, macrophages, T and B lymphocytes, and plasma cells. From a clinical perspective, an understanding of the epithelium and connective tissues, together with their health parameters, gives a good foundation for facilitating and optimizing patient care.
Epithelium is the fast-moving tissue responsible for maintaining a seal between the body and the oral cavity, and it is quick to repair when injured.1 When a tooth first erupts, the epithelium remains attached to the enamel coronal to the cementoenamel junction (CEJ). As the patient matures into adulthood and the tooth continues to function, the junctional epithelium (the epithelium actually forming the attachment to the tooth) moves apically. Initially adhering to the enamel, the junctional epithelium will eventually lie on the most coronal portion of the tooth root. It adheres via a hemidesmosomal attachment2; the epithelial cells adhere directly to the root structure at a strength similar to that of cell-cell connections.
Gingival connective tissue forms the durable attachment around teeth. During the time of development and calcification of the cementum and bone, gingival fibers become embedded, suspending the tooth in its socket. These fibers, known as Sharpey’s fibers, are functionally oriented and form the periodontal ligament of the socket. Above the bone crest, the Sharpey’s fibers extend from the cementum perpendicularly outward into the surrounding gingival connective tissue, anchoring it to the tooth.3 This fibrous attachment is deemed stronger and more resistant to trauma than epithelial attachment.
Biologic Width and Teeth
In order to maintain appropriate function, the tooth requires a minimal distance from the crest of bone moving coronally to the base of the gingival sulcus. This allows for supracrestal connective tissue attachment and epithelial attachment to the tooth above the bone. The sum of these attachments is defined as the biologic width.4 Biologic width can vary significantly from patient to patient and even from tooth to tooth in the same patient.5,6 In areas where the root is prominent and the bone is dehisced, the width of the soft tissue attachment can be many millimeters greater than the mean values. In other situations, particularly if a tooth has not completely erupted, this width can be quite narrow.
In a classic cadaver study, Gargiulo et al5 demonstrated an average sulcus depth of 0.69 mm, an average epithelial attachment width of 0.97 mm, and an average connective tissue attachment width of 1.07 mm. While these numbers are often quoted, the article demonstrated significant variability within these three different components. In a later study by Vacek et al,6 very similar averages were seen with a somewhat narrower but still highly variable range. From a clinical perspective, most practitioners have accepted an average distance of about 3 mm between the free gingival margin and the crest of the facial bone. This distance consists of 1 mm of sulcular depth followed by an attachment consisting of 1 mm of junctional epithelium and 1 mm of connective tissue attachment.
Biologic width and finish line placement for complete-coverage restorations
Periodontal tissue response and the esthetic outcome may be affected by several factors, including location of the crown margin, type of restorative material, selection of implant abutment and/or restorative implant components, presence of bone and keratinized gingiva, the implant-abutment interface (microgap), and oral hygiene.7–15 The finish line of a tooth preparation for a complete-coverage restoration can be placed supragingivally, equigingivally, or subgingivally. In clinical practice, subgingival placement of the finish line may be required to hide the tooth-restorative interface for esthetics, to address dental caries or a preexisting restoration, to manage a coronal endodontic perforation, to manage crown or coronal root fracture, and for retention and resistance purposes. Ideally, in such clinical scenarios, the finish line is placed 0.5 to 1.0 mm below the free gingival margin (Fig 1-1). Theoretically, any level above the base of the sulcus is acceptable. Consequently, the finish line must not intrude further into the periodontal attachment apparatus, because this can lead to violation of the biologic width.16
Fig 1-1 (a and b) A crown preparation for a ceramic crown with the finish line placed 0.5 to 1.0 mm below the free gingival margins on the facial and interproximal aspects. Note the equigingival and supragingival finish line placement on the palatal aspect and the general gingival health.
Subgingival finish line placement may, however, result in more gingival inflammation, loss of attachment, and gingival recession compared with equigingival or supragingival finish line placement.7,8,17,18 This is more evident in patients with poor plaque control.19 The tissue is certainly the healthiest when the margins of the restoration are kept away from it (Fig 1-2). Similarly, when esthetics dictates that restorative materials must be hidden below the free gingival margin, the likelihood of inflammation is increased. In addition to bacterially
