Forced orthodontic extrusion and use of CAD/CAM for reconstruction of grossly destructed crown: A multidisciplinary approach.

The aim of this study is to present a report of a case where forced orthodontic extrusion and computer-aided design and computer-aided manufacturing (CAD/CAM) technique was used for reconstruction of right maxillary central incisor with grossly destructed crown. Aesthetic rehabilitation of a fractured maxillary right central incisor was performed employing a multidisciplinary approach i.e. conventional endodontic treatment followed by orthodontic extrusion and final restoration using CAD-CAM and one piece milled zirconia post and core with full coverage zirconia crown. After the procedure being completed, periapical radiographs taken at 3 month follow up period demonstrated that the post and core remained well adapted to post space and there was a complete healing of periapical lesion. This technique can provide a complete aesthetic rehabilitation of a grossly destructed tooth without hampering the biological width and thus has a better prognosis.

INTRODUCTION

Trauma accompanied by fracture of anterior teeth is an unpleasant experience for the patient who requires attention not only because of damage to the dentition, but also due to the psychologic effect of trauma. The majority of dental injuries involve the anterior teeth, especially the maxillary central incisors.[1] A number of techniques have been reported in literature for rehabilitation of grossly mutilated teeth.[2-8]

The aesthetic rehabilitation of patients with mutilated teeth generally involves a multidisciplinary approach. However, during the restorative procedures, negligence of periodontal tissues is of common occurrence, and is often the cause of failure. Hence, it is essential to maintain a healthy periodontium and the biologic width while restoring teeth. The damaging effect on the periodontium of restorations with subgingivally placed margins is an important factor that needs to be considered during restorative treatments. To avoid this damage, crown lengthening procedure is recommended. Crown lengthening can be performed by using various methods,[23] and, orthodontic extrusion is regarded as the best method for lengthening of the clinical crown length. Orthodontic extrusion has been referred to as “slow eruption of teeth,” which indicates that by utilizing light eruptive forces, the entire attachment apparatus can be shifted coronally in unison with the tooth.[2] The main advantage of the orthodontic extrusion is that the root can be kept within the alveolus, thus the bone height is maintained without compromising the periodontal support.[3]

Endodontically treated teeth with insufficient tooth structure are often restored with crowns. If there is insufficient dentin to support a restoration, a post-core is required to provide retention and support.[4] The choice of an appropriate restoration for endodontically treated anterior teeth is guided by strength and esthetics. The cast gold post and core has been considered the gold standard because of its excellent success rate, favorable long-term prognosis, and ease of fabrication.[56] Traditionally, titanium, carbon, polyethylene fiber, and stainless steel posts have been used for the anterior region. However, when all-ceramic restorations are preferred, metal posts may negatively affect the esthetic results. With regard to both esthetic and health concerns, non-metal posts not only render esthetic superiority over metallic posts, but also preclude the possibility of corrosion and reduce the risk of toxicity.[7]

Use of zirconia as a post-and-core material began in 1993 when introduced by Meyenberg et al.[8] The technique for milling a 1-piece zirconia post and core has been described by Awad and Marghalani and Streacker and Geissberger.[910] Computer-aided design and computer-aided manufacturing (CAD/CAM) milled zirconia posts and cores can be used when esthetic demands are important, and when the anatomy of the root canal and/or the extensive loss of the coronal tooth portion requires the use of a custom post. This technique also allows the possibility of completing a post and core in the same appointment. As stated in various reports, this technique provides a post and core with greater toughness, maximal adaptability to the canal, and adequate esthetics.[81011]

Here, we report a case of aesthetic rehabilitation of grossly destructed maxillary right central incisor using a multidisciplinary approach i.e. conventional endodontic treatment followed by orthodontic extrusion, and final restoration using CAD-CAM fabricated one piece milled zirconia post and core with full coverage zirconia crown.

CASE REPORT

A 22 year old male reported to department of Conservative dentistry and endodontics with the chief complaint of fractured maxillary right central incisor due to trauma 5 years back [Figure 1a]. On clinical examination, a grossly destroyed carious crown with minimal remaining dentin was present with tooth # 8 [Figure 1b]. Preoperative intraoral periapical radiographs showed gross destruction of crown of # 8 with wide canal and periapical radiolucency and deep proximal caries with # 9 [Figure 1c]. Pulp vitality tests (electric and cold tests) revealed that tooth # 9 was non vital. The patient was concerned about aesthetics and unwilling to undergo extraction. Hence it was decided to restore the tooth with conventional endodontic treatment and post and core restoration. After excavation of caries it was seen that supragingival crown height both labially and palatally was 0.5- 1 mm. The crown: root ratio and occlusal clearance was adequate. Hence in order to gain crown height for fabrication of a customized post and core with full coverage crown, it was decided to treat the tooth by forced orthodontic extrusion. The tooth was isolated under rubber dam (Hygienic Dental Dam, Colténe Whaledent, Germany). Adequate endodontic access cavity was prepared after excavation of caries and working length radiograph was taken after initial identification of canal with # 15 K-files (Kerr Manufacturing Co., Romulus, MI). Cleaning and shaping of the root canal was performed by using stainless steel file with a crown-down technique under copious irrigation with saline, 5.25% sodium hypochlorite solution (Dentpro, Chandigarh, India) and 17% Ethylenediaminetetraacetic acid (EDTA) (Glyde File Prep, Densply, France).[12] In the next visit master cone radiograph was taken. Before obturation, the canal was finally rinsed with saline, dried and sectional obturation was performed using cold lateral compaction of gutta-percha using AH Plus resin sealer (Maillefer, Dentsply, Konstanz, Germany) [Figure 1d].[12] An IRM (Caulk, Dentsply, Milford, DE) temporary restoration was placed in the access cavity. The routine endodontic treatment was completed for maxillary left central incisor.

Figure 1

Clinical photographs of the maxillary right central incisor. (a) Facial view. (b) Occlusal view. (c): Preoperative diagnostic radiograph showing gross destruction of crown of #8 with wide canal and periapical radiolucency and deep proximal caries with #9. (d) Post obturation radiograph.

In the third appointment, a lingual button was cemented on the tooth # 8, and 18 slot preadjusted brackets were cemented on teeth # 6, 7, 9 and 10 for controlled extrusion. A 17 × 25 rectangular stainless steel wire was inserted into the brackets. An auxiliary 0.014 superelastic NiTi wire was overlaid on the stainless steel wire [Figures 2a and 2c]. It was tied with the lingual button using a ligature wire. A force of 40-50 gram was applied and extrusion was achieved after 4 weeks.[3] The patient was seen every week to monitor the progresses. The final crown height obtained labially and palatally was approximately 3 mm which was adequate for a crown ferrule and retention of the prosthesis [Figures 2b and 2d]. After active tooth movement was complete, the tooth was stabilized with fiber splints (Polydentia, Mezzovico ,Switzerland) for a period of 4 weeks for reorganization of periodontal tissues before fabrication of post and core [Figure 3a].

Figure 2

(a) Orthodontic brackets placement on incisors. (b) Clinical photographs of the maxillary right central incisor after orthodontic extrusion. (c) Radiograph before orthodontic extrusion. (d) Radiograph showing orthodontic extrusion of maxillary right central incisor after four weeks of orthodontic treatment.

Figure 3

(a) Splinting of maxillary right central incisor with fiber splint. (b) Radiograph of the prepared post space in the root canal of the maxillary right central incisor of the patient. (c) and (d) Direct impression of post and core by using pattern resin.

At the following appointment, restoration of tooth with post and core and crown was planned. The root canal anatomy of maxillary right central incisor did not permit use of a conventional prefabricated glass fiber post, as the post diameter would not have allowed for good adaptation to the post space, and the resulting thick cement layer would have affected the bond strength, increasing the risk of mastication induced fracture [Figure 3b]. A cast gold post and core would have been the method of choice for this situation, but the metal color would have affected the translucency of a subsequent ceramic restoration. Keeping the above factors in mind, CAD/CAM fabricated zirconia post and core and a ceramic crown were planned to restore the tooth.[9] To gain adequate length for the post space, a portion of gutta-percha was removed with heated hand plugger (Kerr Manufacturing Co., Romulus, MI), such that the remaining gutta-percha at the apical portion was 5 mm [Figure 3b].[12] The post space was prepared using Peeso reamer number three and four (Dentsply Maillefer, Ballaigues, Switzerland) to eliminate undercuts, because it was already relatively wide. A direct impression of the post space was made using pattern resin (GC America INC, Alsip, IL) [Figure 3c]. After impression of post space, core was also build up with pattern resin [Figures 3d and 4a]. An impression of the post space and adjacent teeth was made using hydrophilic addition silicone impression material (Dentsply Caulk, Milford, USA) which was cast in type IV high-strength die stone (Royal Rock; Pemaco, Inc, St. Louis, Mo) [Figure 4b]. The direct resin pattern was digitized with a 3-dimensional (3-D) scanner (Amann Girrbach GMBH, Pforzheim, Germany) and the data were processed using CAD/CAM software [Figure 4c]. A digital 3-D model of the post and core was developed. A prefabricated zirconia block (Amann Girrbach GMBH, Pforzheim, Germany) was milled to develop the post and core [Figure 4d] with a milling machine (Amann Girrbach GMBH, Pforzheim, Germany). The milled Ceramill zirconiumoxide frameworks were dense-sintered with the Ceramill Therm to obtain their final density and excellent material properties. The zirconia post and core was then wrapped with red, 8-μm thick articulating paper and placed into the post space of cast to evaluate fit. After removal, interferences were relieved using a finishing diamond rotary cutting instrument in a high-speed handpiece (NSK, Nakanishi INC, Kamura, Japan). Post surface was air-abraded with 50-μm Aluminium oxide (Al2O3) particles prior to cementation. The cementation procedure was then performed using a dual-cured resin cement (Variolink II, Ivoclar Vivadent) according to manufacturer's instructions.

Figure 4

Post and core. (a) Pattern resin. (b) Indirect impression of the post space and adjacent teeth using hydrophilic addition silicone impression material. (c) Use of Computer-aided Design and Computer-aided Manufacturing (CAD/CAM) for data processing. (d) Milled and sintered zirconia post and core.

The temporary restoration was removed, and dentin was cleaned and conditioned with 37 °C phosphoric acid for 15 seconds. This was followed by applying a dentinal adhesive (Syntac Adhesive, Ivoclar Vivadent) for 10 seconds and then dried. Both the base and catalyst of the resin cement were then mixed and applied on the post surface as well as post space. After inserting the post into the canal, excess cement was removed, and polymerization was initiated using a polymerization lamp for 40 seconds [Figures 5a, b and c].

Figure 5

Intraoral view of the cemented zirconia post and core (a) Facial view (b) Occlusal view. (c) Radiograph after zirconia post and core cementation. (d) Optical Scanning. (e) Designing of zirconia coping.

After final preparation of the tooth, an impression was taken using the same silicone-based impression materials. Zirconia-based crown was fabricated by the same procedure as post and core [Figures 5d, e and 6a]. After the final zirconia crown [Figure 6b] was seated over the tooth, marginal fit was examined using a dental explorer. The cementation procedure for the crown was performed using the adhesive technique similar to that for the zirconia post [Figure 6c]. The patient was recalled after three months. The patient was asymptomatic and was satisfied with treatment outcome. A periapical radiograph demonstrated that post and core remained well adapted to post space and there was a complete healing of periapical lesion [Figure 6d].

Figure 6

(a) Computer-aided Design and Computer-aided Manufacturing (CAD/CAM) view of zirconia coping. (b) Final zirconia-based crown. (c) Intraoral view of the cemented zirconia crown. (d) Radiograph of the maxillary right central incisor after 3 months of therapy demonstrating post and core in a well maintained condition and complete healing of periapical lesion.

DISCUSSION

While placing a restoration it is important to maintain the biological width to avoid periodontal problems and ultimate failure of the restoration. In a healthy individual this width usually measures approximately 2.04 mm as described by Gargulio et al.[13] Inber JS was the first to suggest the use of forced eruption to treat non restorable or hopeless teeth.[14] Forced eruption allow the crown margins to be placed on the sound tooth structure while maintaining a uniform gingival contour that provides improved aesthetics without involving adjacent teeth. It also maintains acceptable crown-root ratio, biological width and good periodontal health.[14]

Forced eruption is an excellent alternative to traditional surgical crown lengthening and surgical extrusion especially, in the anterior region of the mouth. Surgical crown lengthening is contraindicated on aesthetic grounds and involves chances of violation of biological width compromising periodontal health. Surgical extrusion also is a questionable tool, requires 4-6 months of healing period and the procedure is technique sensitive.[15] Hence, it was not recommended in the present case. The major limitation of forced eruption is the longer duration of treatment and a longer stabilization period (4-8 weeks). It is also contraindicated in an inadequate crown to root ratio, lack of occlusal clearance for required amount of eruption and periodontal complications.[1516]

Multiple factors must be considered when selecting a post-and-core system. Remaining tooth structure and tooth morphology, functional demands, arch position, periodontal status, and esthetics are few of these factors. Various post systems are available; however, 1-piece milled zirconia posts and cores can be used when esthetic demands are important and when the anatomy of the root canal and/or the extensive loss of the coronal tooth portion requires the use of a custom post.[11] When restoring a severely damaged clinical crown with a wide post space, the 1-piece zirconia post and core can be well adapted and the cement layer thickness thus can be reduced. The modulus of elasticity of the 1-piece glass fiber post and core is similar to that of dentin, which limits stress concentration in the weakened root canal. The CAD/CAM systems offer advantage of automation of fabrication procedures with increased quality in shorter period of time. The primary disadvantages of CAD/CAM fabricated zirconia post and core are its relatively complex production process and high cost.[1718]

This case report highlights the use of forced orthodontic extrusion and CAD/CAM milled zirconia post for rehabilitation of grossly destructed crown. Forced orthodontic extrusion was selected as it maintains acceptable crown-root ratio, biological width, good periodontal health and aesthetic demand. Other procedures like surgical crown lengthening and osteotomy have compromised aesthetic demand, inverse crown-root ratio, compromised function of adjacent teeth and the biological width maybe hampered. CAD/CAM milled zirconia post and core was selected because of the wide canal in this case with severe coronal destruction, and also as the use of zirconia post and core with all ceramic crowns optimizes the esthetic effect of the restoration.

CONCLUSIONS

This clinical report describes a method of utilization of forced orthodontic eruption as an alternative to periodontal surgery, and a method for restoring a fractured anterior tooth with a 1-piece zirconia post and core milled with CAD/CAM technology. Using this method, a precise fit of post and core is obtained. This technique can provide a complete aesthetic rehabilitation of grossly destructed tooth without hampering the biological width, and thus has a better prognosis. As CAD/CAM and zirconia technology are relatively new eras of dentistry, they might undergo evolutionary changes in near future.