A New Implant Design For Optimal Esthetics and Retention of Interproximal Papillae

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A New Implant Design For Optimal Esthetics and Retention of Interproximal Papillae
June 2003
Gadhia, Mehul H. BS*; Holt, Robert L. DMD, PhD**
Implant Dentistry: Volume 12(2) June 2003 pp 164-169
Lippincott Williams & Wilkins
*Dental student, Nova Southeastern University, Fort Lauderdale, Florida.
**Private Practice, West Palm Beach, Florida.
Reprint requests and correspondence to:
Dr. Mehul H. Gadhia,
472 Eastbridge Drive
Oviedo, FL 32765
Phone: (954) 423-9314
E-mail: Mehuldmd@yahoo.com
Abstract
A biologically derived, parabolic implant design that has an occlusal platform that mimics the cementoenamel junction of natural dentition is proposed and described. The interproximal areas of the platform are more coronal than the facial and lingual areas of the platform, and follow the anatomical contours of the alveolar bone. The principle behind this parabolic margin, as opposed to a flat and mono-plane margin, is that any bone re-modeling that follows would replicate a parabolic form. This design helps to maintain bone more coronal on the proximal surfaces than on the facial and lingual surfaces, hence preserving the bone support of the gingival papillae.
The most dramatic changes in dentistry over the past decade have occurred in the field of implant dentistry. The primary goal of implant therapy is the creation of a restoration that reconstructs the form, function, and esthetics of edentulous or partially edentulous spans. In the partially edentulous patient, achieving this goal can be especially difficult when the potential restorative space is not in harmony with the adjacent soft tissues or with dental structures within the esthetic zone. Such deficiencies often require adjunctive clinical procedures to reacquire esthetic balance. Bone and gingival grafting procedures are often needed to reestablish lost contours. 1-5 One of the most challenging procedure may be the re-creation of the anterior interproximal papilla, especially when it relates to implant-supported restorations.
Stable and durable integration of implants has long been the advocated goal in dental implant treatment, and successful endosseous implant therapy requires harmony and integration of three different tissues: bone, connective tissue, and epithelium. 6,7 Historically, most studies have focused predominantly on bone, and hence osseointegration, while much less is known about the soft tissues.
Retention or re-creation of the interimplant papilla between adjacent implants still remains one of the most complicated and unpredictable procedures in implant treatment. The amount of loss of the interimplant papilla may be affected by such factors as biologic width and the effect of the microgap on biologic width, proximity of implants, the severity of bone loss prior to implant placement, quality of the alveolar mucosa, and the distance from alveolar bone to the contact point. The purpose of this article is to analyze the current literature on these factors, review how they compromise interproximal papillae, and identify a new implant design to overcome these obstacles.
With the natural tooth, the soft tissue support is provided by a series of structures progressing from the bone toward the crown of the tooth. First, the bone contour dictates the tissue base and, to some degree, the tissue thickness. The bone surrounds the cylindrical tooth root, with an external bone configuration that rises and falls in a consistent manner in health. The bone on the facial aspects of the teeth is more apical while the bone in the interproximal aspects of the teeth is more coronal. 8-11 Next, the circumferential root contour provides dimensional influence on the soft tissue contours. The connective tissue attachment to the tooth provides a healthy mechanical insertion, establishing a zone of attachment of a millimeter or more coronal to the bone crest. 7,8,12 The overlying epithelium conforms to the shape of the bone and the connective tissue, adding a dimension of another millimeter or so, while conforming to the shape of the attachment of the underlying tissues. Lastly, the shape of the tooth itself transitions from the relatively round contours of the root to the triangular or rectangular contours of the crown. This creates a contiguous dimension of tissue from the buccal to the lingual between two adjacent teeth. All these factors serve to shape and contour the gingival papilla vertically between two natural teeth. 9,10
Bone contour is as important in the presence of dental implants as it is around the natural dentition. The cervical root contour is replaced by the cervical contour of the implant. Often, these subgingival contours do not adequately represent the dimensions of the natural tooth. In these circumstances, the gingival tissue may be undersupported so as to display slumping or flattening. 9 Further, the connection of implant components results in a microgap between the components. This microgap has definite impact on the bone contours. 7,11,13-16 It is believed that bone contours are determinants of soft tissue contours. Therefore, it is essential that the implant mimic, as closely as possible, the dimensions of the natural root it replaces.
The existence of biologic width has been well documented. In 1961, Gargiulo et al 12 histologically evaluated the distance from the free gingival margin to the underlying bone, which is known as the dentogingival complex. This complex consists of the gingival sulcus, epithelial attachment, and connective tissue. The average distance from the base of the sulcus to the crest of bone was found to be 2.04 mm. The epithelial attachment averaged 0.97 mm and the connective tissue attachment averaged 1.07 mm in length.
The presence of biologic width around implants has also been documented. Numerous studies have verified that a biologic width also exists around implants, 7,13-17 and of the various tissues in contact with the implant, the epithelium most closely resembles that of the natural dentition. 7,18,19 This is true for implants of all shapes after uncovering (stage 2) surgery. The literature shows that biologic width will form at the time of implant placement, whether one-piece nonsubmerged implants or two-stage implants are used, with a single-stage nonsubmerged protocol. 7,13,14 This phenomenon is not related to loading and will occur whether the implant is unloaded or loaded. 7
An important factor to take into consideration about biologic width is that it is a zone and not a linear number. The zone of the biologic width (Fig. 1) is parabolic in contour and undulates around the circumference of the tooth or implant in a form that is similar to the shape of the cementoenamel junction of natural teeth, as described later. Studies previously done on biologic width are averages that differ slightly in every individual. The most accurate measurement is achieved through bone sounding. The dimensions of the dentogingival complex were clinically evaluated by Kois after bone-sounding human maxillary central incisors. 20 He reported that most of the population (85%) has a normal facial dentogingival complex of 3 mm, which coincides with the histological studies. 7,12 However, a dimensional difference was noted between the interproximal and the facial dentogingival complexes; a normal interproximal measurement of approximately 4.5 mm was observed. 20 These data are consistent with the scallop of the cementoenamel junction around natural dentition.
Biologic width is also a critical aspect of implant therapy. A space or microgap always exists between an implant and abutment. The significance of the existence and location of a microgap between implant components is a prominent topic in current literature. Hermann et al 13 demonstrated crestal bone loss of approximately 2 mm apical to a microgap, when the microgap is located at or below the alveolar crest. Their results indicated that crestal bone changes were not dependent on the surgical technique (submerged or nonsubmerged) but on the location of the interface (microgap). The 2 mm of bone loss observed apical to this space is believed to be a function of the biologic width, with epithelium migrating below the microgap as was shown by Weber et al 21 and discussed by Cochran et al. 7 The effects of violation of biologic width were also described by DeWaal and Castelucci 22 to include tissue inflammation, bone loss, and cervical remodeling of bone if restorative margins were placed subgingivally too close to the alveolar bone (Fig. 2).
Tarnow et al 23 demonstrated that there is a lateral component to the bone loss around implants in addition to the more commonly discussed vertical component. Their findings showed increased lateral bone loss results if two implants are not spaced more than 3 mm apart. This increased crestal bone loss results in an increase in the distance between the base of the contact point and the crest of bone. This phenomenon could determine whether the papilla will be present or absent between two implants. Another study by Tarnow et al 24 evaluated the presence of a filled embrasure relative to radiographic distance from bone to the proximal contact. When the measurement from the crest of bone to the contact point was = 5 mm, the papilla filled the space nearly 100% of the time. A distance of 6 mm reduced the full papilla occurrence to 56%. A filled embrasure was achieved only 27% of the time when the distance was = 7 mm. These results clearly show the influence of the bone crest on the presence or absence of papilla between implants and adjacent teeth.
These parameters directly reflect the need for an implant design that accounts for biologic width and the effect of the microgap on alveolar bone. Currently, several kinds of dental implant systems are available. These are classified according to their shape and relation to the bony housing 25 and include subperiosteal, transosteal, and endosseous implants, the latter of w