Introduction
Crown lengthening surgically increases the clinical crown in an incisal-apical dimension for either restorative or esthetic needs or a combination of both. The procedure may include apical repositioning of the gingival margin and osseous con- touring. From a restorative standpoint, indications include insufficient clinical crowns for retention, subgingival caries, and subgingival fractures. Esthetically, short clinical crowns and cases of excess gingival display can also benefit from surgical crown lengthening. Case assessment prior to restorative treatment must take into consideration the biologic width and the mucogingival status (Fig. 12.1). Failure to do so can be detrimental to long-term periodontal health, resulting in subsequent inflammation, bone loss, and gingival recession.
Biologic Width
Decay or placement of a restorative margin apical to the gingival sulcus risks impingement on the supracrestal fiber attachment and violation of the biologic width. The biologic width refers to the aspect of soft tissue, the dentogingival com- plex, that is attached to the tooth coronal to the alveolar bone. It is comprised of the connective tissue attachment, the epithelial attachment, and the gingival sulcus (Fig. 12.2) [3, 4]. Early work by Gargiulo et al. [5] on cadaver skulls found average measurements of 0.69 for the sulcus depth, 0.97 mm for the epithelial attachment, and 1.07 mm for the connective tissue attachment. A minimum of 3 mm from the alveolar bone to the restorative margin has been indicated to avoid infringement on the dentogingival complex and maintenance of the biologic width [6]. Kois [3] has expressed that the biologic width “averages” previously noted are quite variable between individuals and among the dentition of the same individual and therefore should be assessed on all included teeth prior to crown lengthening procedures. Additionally, it is more predictable to measure the entire dentogingival complex as a whole as opposed to individual components. This can be done by anesthetizing the patient for comfort and utilizing a periodontal probe to measure from the free gin- gival margin (FGM) to the osseous crest (so-called bone sounding). The resulting measurements can be categorized into normal, high, and low alveolar crests to fur- ther aid in determination of restorative margin location. A normal alveolar crest measures approximately 3 mm on the facial aspect and 3–4.5 mm on the interproxi- mal surfaces. In this case, the restorative margin can safely be placed 0.5–1 mm apical to the FGM or 2–2.5 mm coronal to the osseous crest. In the case of a high alveolar crest, the total dentogingival complex measures less than 3 mm, and there- fore the margin should be at, and no more than 0.5 apical to, the FGM. Alternatively, a measurement of greater than 3 mm for the total dentogingival complex is catego- rized as a low alveolar crest, in which case the margin can be placed more than 1 mm apical to the FGM. The relationship of the FGM to the alveolar crest should be measured prior to restorative preparation and surgical intervention, as well as after crown lengthening healing is completed.
Of critical importance is understanding the risks involved if the biologic width is violated. If crown lengthening is not performed when indicated, the oral tissues will aim to correct for this invasion in an unpredictable and uncontrolled manner. Chronic tissue inflammation can occur, as well as recession and bone resorption, possibly leading to intrabony defects [3].
Mucogingival Considerations
The term mucogingival condition refers to “deviations from the normal anatomic relationship between the gingival margin and the mucogingival junction (MGJ).” Examples include recession, absence or decreased keratinized tissue, and lack of attached tissue [7]. As discussed by Zadeh and Gil in this volume, the etiology of these mucogingival conditions is multifactorial. Factors can include tooth position, orthodontic treatment, gingival biotype, frenum position, vestibular depth, and mechanical insult. A thin gingival biotype is more likely to result in gingival reces- sion versus a thick biotype. Buccally positioned dentition has been associated with thinner labial bone and gingiva and therefore at greater risk of gingival recession as well. Similarly, orthodontic movement in the buccal direction is more likely to cause mucogingival conditions versus that in a lingual direction [8]. Further evi- dence shows that some toothbrushing factors can be associated with gingival reces- sion, especially in more prone sites (i.e., those with other contributable factors for mucogingival deformities).
Crown lengthening may include gingivectomy, and therefore it is important to understand the gingival condition prior to any surgical intervention. Additionally, the quality and quantity of tissue can contribute to the overall gingival health, espe- cially around restorations.
The need for keratinized and/or attached gingiva for periodontal health is somewhat controversial in the literature. It is well-documented that areas of little to no keratinized tissue are able to be maintained and provide support over long periods of time. Nonetheless, this outcome is only possible with excellent oral hygiene and regular professional maintenance. This is highlighted in a split mouth long-term study. Areas of little to no attached gingiva were either augmented with a free gingival autogenous graft or left alone, and not all of the patients received professional maintenance. Over time, patients who followed good oral hygiene and received maintenance showed adequate health in treated sites, as well as those that were not treated. In patients who did not follow main- tenance protocols, the non-augmented sites resulted in increased inflammation and recession compared to augmented sites. Overall, the general consensus is that keratinized tissue deficiency predisposes to the development of gingival recession and inflammation [8]. It is suggested that 2 mm of keratinized gingiva, with 1 mm being attached, is needed for optimal health [9, 11]. Therefore, the keratinized and attached tissue should be assessed prior to crown lengthening procedures. Furthermore, the role of tissue around restorative margins has been evaluated in the literature. Studies have compared two groups, one with a wide zone (greater than or equal to 2 mm) of keratinized gingiva and the other with a narrow zone (less than 2 mm) of keratinized gingiva [12, 13]. In the presence of subgingival restora- tions, the amount of inflammation was significantly increased in those with a nar- row zone versus a wide zone of keratinized tissue. Another study was completed on dogs, where steel bands were placed subgingivally, and sites with adequate widths of keratinized gingiva were compared to those with inadequate keratinized gingiva [14]. Sites with inadequate keratinized tissue showed gingival inflammation in addi- tion to loss of gingival tissue. Later work has confirmed that restorative margins placed subgingivally lead to early gingival recession and attachment loss, and reces- sion is more likely in areas of narrow gingiva [15]. Systematic reviews and position papers have confirmed the negative impact on gingival health that intrasulcular mar- gins can have, especially in the presence of minimal or no attached gingiva. Gingival augmentation is indicated in those sites planned for intrasulcular restorative margins [8, 10, 15, 16]. Some authors even advocate for a minimum of 5 mm of keratinized tissue (3 mm attached and 2 mm free) at those sites [17]. Therefore, prior to restor- ative treatment, the biologic width and the mucogingival state should be evaluated. As discussed, violation of biologic width has been shown to lead to unpredictable bone loss and recession. Crown lengthening procedures to provide restorative access should consider the biologic width of each tooth before and after surgery (Fig. 12.3). Additionally, the amount of keratinized and attached tissue, and the presence of mucogingival deformities, should be noted prior to surgical intervention and resto- ration placement. Thin gingival biotype and minimal attached gingiva can result in gingival inflammation and recession defects.
Functional Crown Lengthening
At its essence, functional crown lengthening is a resective procedure undertaken to so that sound tooth structure can be exposed to support a new restoration and to re- establish a biologic width at a more apical position than prior to the surgical inter- vention. Initially proposed by D.W. Cohen in 1962, current protocol involves judicious removal of surrounding hard and soft tissue structures, so that the result- ing tooth exposure is approximately 4 mm superior to the osseous crest. This amount of tooth exposure is required to allow re-establishment of the biologic width and to facilitate the ideal preparation of the tooth, ferrule, and marginal seal [3, 18–20].
An adjunctive or ancillary treatment modality to functional crown lengthening is the use of orthodontics for forced eruption. Orthodontic forces may be utilized to either slowly or rapidly erupt the tooth in an occlusal or incisal direction in an attempt to bring either the osseous crest and underlying periodontal structures more coronally or to extrude the tooth from the dentoalveolar complex so that the fracture or car- ies is exposed. Subsequent surgical re-establishment in an apical direction of the peri- odontal complex may or may not be required. Further discussion of this treatment modality can be found in the chapter by Schmerman and Obando in this volume.
Kois proposed that a requirement of only 3 mm was needed to establish and maintain a healthy sulcus (1 mm), connective tissue, and epithelial attachment (2.04 mm). Kois proposed that probing the attachment levels and sounding the osse- ous crest through sulcus and connective tissue and epithelial attachment would pro- duce an accurate representation of the location of the biologic width. Kois coined the terms normal crest, high crest, and low crest accordingly [3, 18]. Table 12.1 demonstrates the clinical and surgical implications of these three alveolar crestal positions.
It has been demonstrated that the establishment of the restorative margin 3 mm from the osseous crest has been stable for up to 6 months [24]. Postsurgical rebound of the soft tissues should be a consideration prior to establishment of the definitive restorative margins and delivery of the prosthesis [25]. Removal of sufficient osse- ous structure to allow for postsurgical rebound or proliferation of 3.2 ± 0.8 mm should be performed. This often requires the exposure of approximately 4 mm of tooth structure. Pontoriero and Carnevale were able to demonstrate that thick tissues rebounded significantly more than did a thin biotype [25]. Exposure of a greater amount of tooth structure should be considered when working with a thick biotype. Establishment of definitive restorative margin should be delayed until the biologic complex has had sufficient time to mature, a minimum of 6 months.
As with any surgical procedure, there are potential complications. Improper tooth exposure, aggressive removal of interproximal soft tissues resulting in “black triangles,” root hypersensitivity, iatrogenic damage to the root structure, and post- surgical temporary mobility of the dentition have all been reported.
Esthetic Crown Lengthening
Esthetic crown lengthening is a procedure aimed at increasing the clinical crown and improving the gingival contours in order to preserve the dentogingival complex. This often presents a challenge for dentists and perhaps for periodontists. This treat- ment usually involves diagnostic information, such as periodontal charting, radio- graphic assessment, diagnostic wax-ups, and a mock-up. It is imperative to understand the diagnosis prior to delivering treatment. Excessive gingival display can be unesthetic for patients and can influence confidence and self-esteem [26, 27]. Excessive gingival display can present due to passive eruption either altered or active, vertical maxillary excess, hypermobile lip, and perhaps a pseudopocket due to inflamma- tion [28]. Altered active eruption refers to the emergence of a tooth into the oral active and is regulated by periodontal ligament, occlusal contact, and soft tissue like the tongue [29]. A comprehensive diagnosis must rule out vertical maxillary excess as a cause of exces- sive gingival display. Vertical maxillary excess can only be diagnosed with cephalometric imaging and be corrected via a LeFort I osteotomy with vertical impaction.
Altered passive eruption (APE) was first described by Gottlieb and Orban [30], referring to the soft tissue remaining incisal to the cementoenamel junction (CEJ). Tissue may remain on the enamel, cementum, or both. The etiology of APE remains elusive. However, theories that have been proposed include the interference of soft tissue migration, perhaps due to the thickness of the soft tissue impeding the normal eruption. This results in a short clinical crown that is often unesthetic. Coslet et al further classified these altered erruptive patterns into two categories depending on the location of the mucogingival junction in relation to the alveolar crest. Type I refers to normal relationship of CEJ and alveolar crest; however excessive tissue overlies the anatomical crown. Type 2 refers to the proximity of the CEJ to alveolar crest due to the failure of active tooth eruption [31]. Type 2 is classified into two subsets: (a) the distance between the CEJ and alveolar bone is 1.5–2.0 mm, allowing for normal connective tissue attachment and (b) the proximity of bone to the CEJ. Volchansky and Cleaton-Jones found the incidence of APE is 12.1%.
The treatment of altered active eruption and altered passive eruption involves careful evaluation and, possibly, a multidisciplinary approach. The smile line, tooth position and size, tissue thickness and amount of keratinized tissue should be evalu- ated. Smile lines were described by Peck et al. [32]. When the upper teeth are visible and displaying 1–2 mm of the gingiva, it is considered “normal” smile line. A “high” smile line is casually known as a “gummy smile.” This is when one displays 2 mm or more of gingival tissue. Inversely, a “low” smile line is when the upper lip covers 25% of maxillary anterior teeth. Excessive gingival display can occur due to skeletal and/or dental abnormality. If it is skeletally related, orthodontic and orthognathic surgery should be considered to correct the “gummy smile” which in the clinical situation described is resultant of vertical maxillary excess, treatment of which is outside the scope of this discussion. Oftentimes, it is more related to dental reasons, which can be corrected through osseous and gingival recontouring.
Establishing a biological width and ferrule is an additional consideration impor- tant for maintaining a healthy periodontium. Bone sounding is critical to determine the level of the alveolar crest. It will guide the surgeon to understand thickness of the tissue, tooth morphology and anatomy, and how much resection is required. The gingival tissues should be symmetrical and balanced. They provide a backdrop for esthetic restoration [33]. Additionally, ideal maxillary incisor dimensional relation- ships should follow the “golden proportions.” The mesial-distal relationship between the dentition of the maxillary anterior group should be central incisor 1.6, lateral incisor 1, and mesial third of cuspid 0.6 [34]. Furthermore, Lee [35] pro- posed a classification for esthetic crown lengthening depending on the relationship of the alveolar crest and anticipated gingival margin.
Type I esthetic crown lengthening is categorized by the appropriate position of the alveolar crest, however an excess of gingival tissue. In this situation, it would simply require gingival recontouring or gingivectomy, preferably using a scalpel or a laser. Submarginal incisions are usually made at this point guided by a surgical stent.
Type II allows for gingival recontouring with additional need for ostectomy in order to re-establish biological width (Fig. 12.5a–h). These images presented in Fig. 12.5a–h represent a sequential study in the approach of contemporary crown lengthening procedures in the anterior esthetic zone. This approach may involve a two-stage proce- dure. Once the initial presentation is recorded, a diagnostic wax-up is completed with approximate final teeth preparation and dimensions. Gingivectomy could be completed with provisional restoration invading biological width. This is temporary and is com- pleted to allow for soft tissue healing and establishment of zenith positions imitating the golden proportions. In the subsequent surgery, the gingival margins are established and can be utilized to guide the periodontist for alveolar recontouring; sulcular inci- sions are made with possible papilla preservation. This will serve to maintain soft tissue thickness and avoid the likelihood for recession and open embrasures. New provisional restorations are fitted and cemented into place for 6 months to allow for ideal establish- ment and maturation of the soft tissues overlying the new recontoured osseous struc- tures. Once stable, the final restorations may be fabricated and inserted.
Type III refers to situations in which the gingival excision is completed to the desired clinical crown length, which exposes the alveolar crest. This may be a result of a lack of communication with the interdisciplinary team. Therefore, flaps should be positioned coronally, rather than apically, in these clinical situations, and a staged approach might provide better results.
Type IV is reserved for situations where gingival excision will leave a band of inadequate amount of attached tissue, perhaps utilizing apically repositioned flap regardless of osseous recontouring. This will require a longer period of healing and less of an immediate result. As previously discussed, Kois coined the terms “high crest” and “low crest.” This refers to the gingival margin in relation to the alveolar crest. A “high crest” is one where the bone is close to the gingival margin, which is at risk for violating the biological width. In the latter, the total complex is greater than 3 mm, which results in a more apical positioning of the free gingival margin without subsequently violating the biological width.
Conventional healing is typically between 4 and 6 weeks. However, in the esthetic zone, it is important to allow for soft tissue to mature at least 3 months, and if bony resection is completed, an additional 6 months of healing is necessary. Bragger [24] found the recession of 2-4 mm postoperatively occuring between 6 weeks and 6 months. Recession can occur, and it is therefore imperative to defer final restoration until tissue has completely healed, especially in the esthetic zone. The amount of tissue rebound seems to be correlated to the distance from flap mar- gin to alveolar crest at suturing.
There is a symbiotic effect between the location and precision of the definitive restorative margin and the health of the periodontium. Violation of the biologic width is a common sequelae of poorly planned restorations. The requirement for crown lengthening, whether functional or esthetic, involves an in-depth knowledge of peri- odontal anatomy, restorative requirements, and surgical techniques. The desired out- come is a functional and healthy periodontium situated immediately to a restoration.
Success is also directly related to level of plaque control which the patient is able to maintain. This is influenced by the maintenance of physiologically healthy peri- odontal probing depths, provision of sound tooth structure, anatomically suitable restorative contours, and creation of an environment in which the patient and dental team members can adequately maintain.
Conclusion
Although there are no significant changes in the procedures involved with contem- porary crown lengthening, there have been significant improvements with the intro- duction of digital workflows. Core concepts still remain essential, as are the diagnosis and execution of the prescribed treatment plan. Differentiation between vertical maxillary excess, altered passive eruption, altered active eruption, and crestal position is essential prior to putting scalpel to tissue.
Crown lengthening surgically increases the clinical crown in an incisal-apical dimension for either restorative or esthetic needs or a combination of both. The procedure may include apical repositioning of the gingival margin and osseous con- touring. From a restorative standpoint, indications include insufficient clinical crowns for retention, subgingival caries, and subgingival fractures. Esthetically, short clinical crowns and cases of excess gingival display can also benefit from surgical crown lengthening. Case assessment prior to restorative treatment must take into consideration the biologic width and the mucogingival status (Fig. 12.1). Failure to do so can be detrimental to long-term periodontal health, resulting in subsequent inflammation, bone loss, and gingival recession.
Biologic Width
Decay or placement of a restorative margin apical to the gingival sulcus risks impingement on the supracrestal fiber attachment and violation of the biologic width. The biologic width refers to the aspect of soft tissue, the dentogingival com- plex, that is attached to the tooth coronal to the alveolar bone. It is comprised of the connective tissue attachment, the epithelial attachment, and the gingival sulcus (Fig. 12.2) [3, 4]. Early work by Gargiulo et al. [5] on cadaver skulls found average measurements of 0.69 for the sulcus depth, 0.97 mm for the epithelial attachment, and 1.07 mm for the connective tissue attachment. A minimum of 3 mm from the alveolar bone to the restorative margin has been indicated to avoid infringement on the dentogingival complex and maintenance of the biologic width [6]. Kois [3] has expressed that the biologic width “averages” previously noted are quite variable between individuals and among the dentition of the same individual and therefore should be assessed on all included teeth prior to crown lengthening procedures. Additionally, it is more predictable to measure the entire dentogingival complex as a whole as opposed to individual components. This can be done by anesthetizing the patient for comfort and utilizing a periodontal probe to measure from the free gin- gival margin (FGM) to the osseous crest (so-called bone sounding). The resulting measurements can be categorized into normal, high, and low alveolar crests to fur- ther aid in determination of restorative margin location. A normal alveolar crest measures approximately 3 mm on the facial aspect and 3–4.5 mm on the interproxi- mal surfaces. In this case, the restorative margin can safely be placed 0.5–1 mm apical to the FGM or 2–2.5 mm coronal to the osseous crest. In the case of a high alveolar crest, the total dentogingival complex measures less than 3 mm, and there- fore the margin should be at, and no more than 0.5 apical to, the FGM. Alternatively, a measurement of greater than 3 mm for the total dentogingival complex is catego- rized as a low alveolar crest, in which case the margin can be placed more than 1 mm apical to the FGM. The relationship of the FGM to the alveolar crest should be measured prior to restorative preparation and surgical intervention, as well as after crown lengthening healing is completed.
Of critical importance is understanding the risks involved if the biologic width is violated. If crown lengthening is not performed when indicated, the oral tissues will aim to correct for this invasion in an unpredictable and uncontrolled manner. Chronic tissue inflammation can occur, as well as recession and bone resorption, possibly leading to intrabony defects [3].
Mucogingival Considerations
The term mucogingival condition refers to “deviations from the normal anatomic relationship between the gingival margin and the mucogingival junction (MGJ).” Examples include recession, absence or decreased keratinized tissue, and lack of attached tissue [7]. As discussed by Zadeh and Gil in this volume, the etiology of these mucogingival conditions is multifactorial. Factors can include tooth position, orthodontic treatment, gingival biotype, frenum position, vestibular depth, and mechanical insult. A thin gingival biotype is more likely to result in gingival reces- sion versus a thick biotype. Buccally positioned dentition has been associated with thinner labial bone and gingiva and therefore at greater risk of gingival recession as well. Similarly, orthodontic movement in the buccal direction is more likely to cause mucogingival conditions versus that in a lingual direction [8]. Further evi- dence shows that some toothbrushing factors can be associated with gingival reces- sion, especially in more prone sites (i.e., those with other contributable factors for mucogingival deformities).
Crown lengthening may include gingivectomy, and therefore it is important to understand the gingival condition prior to any surgical intervention. Additionally, the quality and quantity of tissue can contribute to the overall gingival health, espe- cially around restorations.
The need for keratinized and/or attached gingiva for periodontal health is somewhat controversial in the literature. It is well-documented that areas of little to no keratinized tissue are able to be maintained and provide support over long periods of time. Nonetheless, this outcome is only possible with excellent oral hygiene and regular professional maintenance. This is highlighted in a split mouth long-term study. Areas of little to no attached gingiva were either augmented with a free gingival autogenous graft or left alone, and not all of the patients received professional maintenance. Over time, patients who followed good oral hygiene and received maintenance showed adequate health in treated sites, as well as those that were not treated. In patients who did not follow main- tenance protocols, the non-augmented sites resulted in increased inflammation and recession compared to augmented sites. Overall, the general consensus is that keratinized tissue deficiency predisposes to the development of gingival recession and inflammation [8]. It is suggested that 2 mm of keratinized gingiva, with 1 mm being attached, is needed for optimal health [9, 11]. Therefore, the keratinized and attached tissue should be assessed prior to crown lengthening procedures. Furthermore, the role of tissue around restorative margins has been evaluated in the literature. Studies have compared two groups, one with a wide zone (greater than or equal to 2 mm) of keratinized gingiva and the other with a narrow zone (less than 2 mm) of keratinized gingiva [12, 13]. In the presence of subgingival restora- tions, the amount of inflammation was significantly increased in those with a nar- row zone versus a wide zone of keratinized tissue. Another study was completed on dogs, where steel bands were placed subgingivally, and sites with adequate widths of keratinized gingiva were compared to those with inadequate keratinized gingiva [14]. Sites with inadequate keratinized tissue showed gingival inflammation in addi- tion to loss of gingival tissue. Later work has confirmed that restorative margins placed subgingivally lead to early gingival recession and attachment loss, and reces- sion is more likely in areas of narrow gingiva [15]. Systematic reviews and position papers have confirmed the negative impact on gingival health that intrasulcular mar- gins can have, especially in the presence of minimal or no attached gingiva. Gingival augmentation is indicated in those sites planned for intrasulcular restorative margins [8, 10, 15, 16]. Some authors even advocate for a minimum of 5 mm of keratinized tissue (3 mm attached and 2 mm free) at those sites [17]. Therefore, prior to restor- ative treatment, the biologic width and the mucogingival state should be evaluated. As discussed, violation of biologic width has been shown to lead to unpredictable bone loss and recession. Crown lengthening procedures to provide restorative access should consider the biologic width of each tooth before and after surgery (Fig. 12.3). Additionally, the amount of keratinized and attached tissue, and the presence of mucogingival deformities, should be noted prior to surgical intervention and resto- ration placement. Thin gingival biotype and minimal attached gingiva can result in gingival inflammation and recession defects.
Functional Crown Lengthening
At its essence, functional crown lengthening is a resective procedure undertaken to so that sound tooth structure can be exposed to support a new restoration and to re- establish a biologic width at a more apical position than prior to the surgical inter- vention. Initially proposed by D.W. Cohen in 1962, current protocol involves judicious removal of surrounding hard and soft tissue structures, so that the result- ing tooth exposure is approximately 4 mm superior to the osseous crest. This amount of tooth exposure is required to allow re-establishment of the biologic width and to facilitate the ideal preparation of the tooth, ferrule, and marginal seal [3, 18–20].
Rosenberg et al. [21] noted that there are several indications for functional crown lengthening in the dentoalveolar complex. These include:
(a) Tooth decay which compromises the gingival sulcus and connective tissue attachment and/or is invading the biologic width
(b) Tooth fracture which compromises the gingival sulcus and connective tissue attachment and/or is invading the biologic width, with adequate remaining tooth structure, periodontal attachment, and supporting alveolar bone
(c) Teeth with excessive retrograde wear where crown lengthening is required for adequate seating and retention of a full coverage restoration
(d) Teeth, due to super-eruption, which have insufficient interocclusal space for requisite restorative dentistry
(e) Altered passive eruption, where the gingival margin is coronal to the CEJ and the osseous crest is approximate to or at the CEJ (Fig. 12.4a, b)
(f) External root resorption involving the dental structures adjacent to the gingival margins and/or the osseous crest
(a) Tooth decay which compromises the gingival sulcus and connective tissue attachment and/or is invading the biologic width
(b) Tooth fracture which compromises the gingival sulcus and connective tissue attachment and/or is invading the biologic width, with adequate remaining tooth structure, periodontal attachment, and supporting alveolar bone
(c) Teeth with excessive retrograde wear where crown lengthening is required for adequate seating and retention of a full coverage restoration
(d) Teeth, due to super-eruption, which have insufficient interocclusal space for requisite restorative dentistry
(e) Altered passive eruption, where the gingival margin is coronal to the CEJ and the osseous crest is approximate to or at the CEJ (Fig. 12.4a, b)
(f) External root resorption involving the dental structures adjacent to the gingival margins and/or the osseous crest
An adjunctive or ancillary treatment modality to functional crown lengthening is the use of orthodontics for forced eruption. Orthodontic forces may be utilized to either slowly or rapidly erupt the tooth in an occlusal or incisal direction in an attempt to bring either the osseous crest and underlying periodontal structures more coronally or to extrude the tooth from the dentoalveolar complex so that the fracture or car- ies is exposed. Subsequent surgical re-establishment in an apical direction of the peri- odontal complex may or may not be required. Further discussion of this treatment modality can be found in the chapter by Schmerman and Obando in this volume.
Contraindications to functional crown lengthening are well described. Jorgic- Srdjak et al. described several scenarios in which surgical crown lengthening is containdicated. These include:
(a) Caries or dental fracture extending significantly apical to the osseous crest requiring excessing alveolar bone removal.
(b) Unesthetic outcomes projected as a result of surgery.
(c) Surgery will result in an unfavorable crown-to-root ratio.
(d) Non-restorable dentition.
(e) Short root trunk resulting in roof of furcation being close to the connective tis- sue attachment.
(f) Compromise of esthetics.
(g) Compromised periodontal support on adjacent dentition after surgery.
The clinical and radiographic evaluation of the proposed tooth are critical prior to surgical intervention. Position of the carious lesion or fracture relative to the osse- ous crest, sulcus depth, gingival status, root form and length, anticipated posttreat- ment crown-to-root ratio, anticipated position of the definitive restorative margin, and potential compromise to the adjacent teeth must all be evaluated. Furthermore, the advantages of retaining such an involved tooth must be weighed against the potential deleterious consequences to the periodontal-alveolar complex of the tooth inquisition and the adjacent structures. This consideration should extend to an anal- ysis of number and complexity of procedures required to put the tooth back into function with an ideal restoration. There are times where extraction of the tooth, and replacement with either a removable or fixed restoration, or endosseous dental implant may be a better alternative. (a) Caries or dental fracture extending significantly apical to the osseous crest requiring excessing alveolar bone removal.
(b) Unesthetic outcomes projected as a result of surgery.
(c) Surgery will result in an unfavorable crown-to-root ratio.
(d) Non-restorable dentition.
(e) Short root trunk resulting in roof of furcation being close to the connective tis- sue attachment.
(f) Compromise of esthetics.
(g) Compromised periodontal support on adjacent dentition after surgery.
Kois proposed that a requirement of only 3 mm was needed to establish and maintain a healthy sulcus (1 mm), connective tissue, and epithelial attachment (2.04 mm). Kois proposed that probing the attachment levels and sounding the osse- ous crest through sulcus and connective tissue and epithelial attachment would pro- duce an accurate representation of the location of the biologic width. Kois coined the terms normal crest, high crest, and low crest accordingly [3, 18]. Table 12.1 demonstrates the clinical and surgical implications of these three alveolar crestal positions.
It has been demonstrated that the establishment of the restorative margin 3 mm from the osseous crest has been stable for up to 6 months [24]. Postsurgical rebound of the soft tissues should be a consideration prior to establishment of the definitive restorative margins and delivery of the prosthesis [25]. Removal of sufficient osse- ous structure to allow for postsurgical rebound or proliferation of 3.2 ± 0.8 mm should be performed. This often requires the exposure of approximately 4 mm of tooth structure. Pontoriero and Carnevale were able to demonstrate that thick tissues rebounded significantly more than did a thin biotype [25]. Exposure of a greater amount of tooth structure should be considered when working with a thick biotype. Establishment of definitive restorative margin should be delayed until the biologic complex has had sufficient time to mature, a minimum of 6 months.
Protocol for Functional Crown Lengthening
1. Provisionalization of the tooth prior to surgery if possible. This will facilitate easier access for the surgeon to the interproximal areas, as well as convey where the ideal restorative margin will be placed.
2. Presurgical plaque control.
3. Adequate local anesthesia.
4. Presurgical bone sounding to determine the amount of tooth which will need to be exposed and to influence the position of the incisions.
5. Submarginal inverse bevel incision. Attention must be afforded to the amount of keratinized tissue which will be remaining postsurgery. Preservation of 4–5 mm of keratinized tissue is recommended. If this is not possible with a submarginal incision design, then a modification of the planned submarginal incision or sulcular inverse bevel incision design must be considered.
6. Incisions are minimally extended to one mesial and one tooth distal to the tooth in question. Greater extension may be considered if further relaxation of the surgical flap is required.
7. A full-thickness flap is refelcted to the mucogingivaljunction, then a partial- thickness flap is extended apically from this anatomical landmark.
8. Adequate degranulation of the area around the tooth. This will allow for greater visualization of the margins, decay, or fracture, facilitate a greater understand- ing of the surrounding osseous topography, and reduce intraoperative bleeding.
9. Ostectomy and osteoplasty to establish a minimum of 4 mm of sound tooth structure and provide a positive postsurgical architecture to the periodontium. This should be accomplished with high-speed drills and/or piezo ultrasonic instrumentation and copious irrigation. Hand instrumentation may be utilized to access those areas which the drills cannot reach.
10. Surgical flaps are approximated for a trial closure, any modifications to the soft tissues can be made, and then once satisfied, they can be sutured closed. Selection of a durable suture material and precise suturing technique is critical to avoid wound dehiscence and maintain the positioning of the flaps through the healing phase. Periodontal dressing may or may not be utilized, subject to the preferences of the surgeon. Sutures can be removed at 10–14 days or when deemed ready for removal.
11. It is recommended that definitive restorations should not be placed until a mini- mum of 6 months of healing has transpired. This will allow for maturation of the new biologic width and any rebound which may occur.
2. Presurgical plaque control.
3. Adequate local anesthesia.
4. Presurgical bone sounding to determine the amount of tooth which will need to be exposed and to influence the position of the incisions.
5. Submarginal inverse bevel incision. Attention must be afforded to the amount of keratinized tissue which will be remaining postsurgery. Preservation of 4–5 mm of keratinized tissue is recommended. If this is not possible with a submarginal incision design, then a modification of the planned submarginal incision or sulcular inverse bevel incision design must be considered.
6. Incisions are minimally extended to one mesial and one tooth distal to the tooth in question. Greater extension may be considered if further relaxation of the surgical flap is required.
7. A full-thickness flap is refelcted to the mucogingivaljunction, then a partial- thickness flap is extended apically from this anatomical landmark.
8. Adequate degranulation of the area around the tooth. This will allow for greater visualization of the margins, decay, or fracture, facilitate a greater understand- ing of the surrounding osseous topography, and reduce intraoperative bleeding.
9. Ostectomy and osteoplasty to establish a minimum of 4 mm of sound tooth structure and provide a positive postsurgical architecture to the periodontium. This should be accomplished with high-speed drills and/or piezo ultrasonic instrumentation and copious irrigation. Hand instrumentation may be utilized to access those areas which the drills cannot reach.
10. Surgical flaps are approximated for a trial closure, any modifications to the soft tissues can be made, and then once satisfied, they can be sutured closed. Selection of a durable suture material and precise suturing technique is critical to avoid wound dehiscence and maintain the positioning of the flaps through the healing phase. Periodontal dressing may or may not be utilized, subject to the preferences of the surgeon. Sutures can be removed at 10–14 days or when deemed ready for removal.
11. It is recommended that definitive restorations should not be placed until a mini- mum of 6 months of healing has transpired. This will allow for maturation of the new biologic width and any rebound which may occur.
As with any surgical procedure, there are potential complications. Improper tooth exposure, aggressive removal of interproximal soft tissues resulting in “black triangles,” root hypersensitivity, iatrogenic damage to the root structure, and post- surgical temporary mobility of the dentition have all been reported.
Esthetic Crown Lengthening
Esthetic crown lengthening is a procedure aimed at increasing the clinical crown and improving the gingival contours in order to preserve the dentogingival complex. This often presents a challenge for dentists and perhaps for periodontists. This treat- ment usually involves diagnostic information, such as periodontal charting, radio- graphic assessment, diagnostic wax-ups, and a mock-up. It is imperative to understand the diagnosis prior to delivering treatment. Excessive gingival display can be unesthetic for patients and can influence confidence and self-esteem [26, 27]. Excessive gingival display can present due to passive eruption either altered or active, vertical maxillary excess, hypermobile lip, and perhaps a pseudopocket due to inflamma- tion [28]. Altered active eruption refers to the emergence of a tooth into the oral active and is regulated by periodontal ligament, occlusal contact, and soft tissue like the tongue [29]. A comprehensive diagnosis must rule out vertical maxillary excess as a cause of exces- sive gingival display. Vertical maxillary excess can only be diagnosed with cephalometric imaging and be corrected via a LeFort I osteotomy with vertical impaction.
Altered passive eruption (APE) was first described by Gottlieb and Orban [30], referring to the soft tissue remaining incisal to the cementoenamel junction (CEJ). Tissue may remain on the enamel, cementum, or both. The etiology of APE remains elusive. However, theories that have been proposed include the interference of soft tissue migration, perhaps due to the thickness of the soft tissue impeding the normal eruption. This results in a short clinical crown that is often unesthetic. Coslet et al further classified these altered erruptive patterns into two categories depending on the location of the mucogingival junction in relation to the alveolar crest. Type I refers to normal relationship of CEJ and alveolar crest; however excessive tissue overlies the anatomical crown. Type 2 refers to the proximity of the CEJ to alveolar crest due to the failure of active tooth eruption [31]. Type 2 is classified into two subsets: (a) the distance between the CEJ and alveolar bone is 1.5–2.0 mm, allowing for normal connective tissue attachment and (b) the proximity of bone to the CEJ. Volchansky and Cleaton-Jones found the incidence of APE is 12.1%.
The treatment of altered active eruption and altered passive eruption involves careful evaluation and, possibly, a multidisciplinary approach. The smile line, tooth position and size, tissue thickness and amount of keratinized tissue should be evalu- ated. Smile lines were described by Peck et al. [32]. When the upper teeth are visible and displaying 1–2 mm of the gingiva, it is considered “normal” smile line. A “high” smile line is casually known as a “gummy smile.” This is when one displays 2 mm or more of gingival tissue. Inversely, a “low” smile line is when the upper lip covers 25% of maxillary anterior teeth. Excessive gingival display can occur due to skeletal and/or dental abnormality. If it is skeletally related, orthodontic and orthognathic surgery should be considered to correct the “gummy smile” which in the clinical situation described is resultant of vertical maxillary excess, treatment of which is outside the scope of this discussion. Oftentimes, it is more related to dental reasons, which can be corrected through osseous and gingival recontouring.
Establishing a biological width and ferrule is an additional consideration impor- tant for maintaining a healthy periodontium. Bone sounding is critical to determine the level of the alveolar crest. It will guide the surgeon to understand thickness of the tissue, tooth morphology and anatomy, and how much resection is required. The gingival tissues should be symmetrical and balanced. They provide a backdrop for esthetic restoration [33]. Additionally, ideal maxillary incisor dimensional relation- ships should follow the “golden proportions.” The mesial-distal relationship between the dentition of the maxillary anterior group should be central incisor 1.6, lateral incisor 1, and mesial third of cuspid 0.6 [34]. Furthermore, Lee [35] pro- posed a classification for esthetic crown lengthening depending on the relationship of the alveolar crest and anticipated gingival margin.
Type I esthetic crown lengthening is categorized by the appropriate position of the alveolar crest, however an excess of gingival tissue. In this situation, it would simply require gingival recontouring or gingivectomy, preferably using a scalpel or a laser. Submarginal incisions are usually made at this point guided by a surgical stent.
Type II allows for gingival recontouring with additional need for ostectomy in order to re-establish biological width (Fig. 12.5a–h). These images presented in Fig. 12.5a–h represent a sequential study in the approach of contemporary crown lengthening procedures in the anterior esthetic zone. This approach may involve a two-stage proce- dure. Once the initial presentation is recorded, a diagnostic wax-up is completed with approximate final teeth preparation and dimensions. Gingivectomy could be completed with provisional restoration invading biological width. This is temporary and is com- pleted to allow for soft tissue healing and establishment of zenith positions imitating the golden proportions. In the subsequent surgery, the gingival margins are established and can be utilized to guide the periodontist for alveolar recontouring; sulcular inci- sions are made with possible papilla preservation. This will serve to maintain soft tissue thickness and avoid the likelihood for recession and open embrasures. New provisional restorations are fitted and cemented into place for 6 months to allow for ideal establish- ment and maturation of the soft tissues overlying the new recontoured osseous struc- tures. Once stable, the final restorations may be fabricated and inserted.
Type III refers to situations in which the gingival excision is completed to the desired clinical crown length, which exposes the alveolar crest. This may be a result of a lack of communication with the interdisciplinary team. Therefore, flaps should be positioned coronally, rather than apically, in these clinical situations, and a staged approach might provide better results.
Type IV is reserved for situations where gingival excision will leave a band of inadequate amount of attached tissue, perhaps utilizing apically repositioned flap regardless of osseous recontouring. This will require a longer period of healing and less of an immediate result. As previously discussed, Kois coined the terms “high crest” and “low crest.” This refers to the gingival margin in relation to the alveolar crest. A “high crest” is one where the bone is close to the gingival margin, which is at risk for violating the biological width. In the latter, the total complex is greater than 3 mm, which results in a more apical positioning of the free gingival margin without subsequently violating the biological width.
Conventional healing is typically between 4 and 6 weeks. However, in the esthetic zone, it is important to allow for soft tissue to mature at least 3 months, and if bony resection is completed, an additional 6 months of healing is necessary. Bragger [24] found the recession of 2-4 mm postoperatively occuring between 6 weeks and 6 months. Recession can occur, and it is therefore imperative to defer final restoration until tissue has completely healed, especially in the esthetic zone. The amount of tissue rebound seems to be correlated to the distance from flap mar- gin to alveolar crest at suturing.
There is a symbiotic effect between the location and precision of the definitive restorative margin and the health of the periodontium. Violation of the biologic width is a common sequelae of poorly planned restorations. The requirement for crown lengthening, whether functional or esthetic, involves an in-depth knowledge of peri- odontal anatomy, restorative requirements, and surgical techniques. The desired out- come is a functional and healthy periodontium situated immediately to a restoration.
Success is also directly related to level of plaque control which the patient is able to maintain. This is influenced by the maintenance of physiologically healthy peri- odontal probing depths, provision of sound tooth structure, anatomically suitable restorative contours, and creation of an environment in which the patient and dental team members can adequately maintain.
Conclusion
Although there are no significant changes in the procedures involved with contem- porary crown lengthening, there have been significant improvements with the intro- duction of digital workflows. Core concepts still remain essential, as are the diagnosis and execution of the prescribed treatment plan. Differentiation between vertical maxillary excess, altered passive eruption, altered active eruption, and crestal position is essential prior to putting scalpel to tissue.
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