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May 2016
Volume 37, Issue 5

CAD/CAM Solutions for Minimally Invasive All-Ceramic Rehabilitation of Extended Erosive Lesions

Petra C. Guess Gierthmuehlen, DDS; and Enrico Steger, MDT

Abstract: Dental erosion is a global oral health problem that can lead to significant functional and esthetic impairments of the affected patients. Treatment of severe cases with augmented loss of the vertical dimension of occlusion (VDO) represents a challenge for both the dental team and the patient. CAD/CAM technology was used in the presented case to analyze the interocclusal space. Based on a virtual wax-up of the final restorations, CAD/CAM-fabricated preparation splints served as a guide and ensured a most minimally invasive preparation design. Milled polymer provisionals enabled the patient to visualize the final treatment outcome and served as a fracture-resistant temporary restoration to test the increased VDO. Monolithic lithium-disilicate ceramic, defect-oriented restorations with reduced ceramic thickness enabled a functional and reliable reconstruction of the severely compromised dentition. This case report documents a practical, digital approach and discusses the advantages related to treatment time, ease of treatment, and predictability.

Along with dental caries and periodontal disease, dental erosion is recognized as a global public oral health problem. Several factors related to extrinsic erosions, such as the consumption of acidic foods and beverages, medicines, and lifestyle changes, are reported in the literature.1 Moreover, gastroesophageal reflux disease (GERD) and eating disorders are common intrinsic causes of erosion. Occurrence of dental erosion as well as the degree of its severity have increased significantly during the past several years. Various epidemiologic studies have shown a wide-ranging prevalence between 4% to 82% in adults aged 18 to 88 years2 and 17.7% to 54.4% in young adults (aged 18 to 35 years), with a large difference between the investigated European countries.3 The prevalence of dental erosion is considerably higher in studies investigating younger individuals compared with those in older age groups.

Dental erosion represents a serious problem for the patient, especially if the disease is diagnosed at an advanced stage. Hypersensitivity, pain, pulpal inflammation, necrosis, and periapical pathology are possible complications. The prevalence of severe dentin hypersensitivity in young adults is high (28.4%), and a strong, progressive relationship between dentin hypersensitivity and erosive tooth wear has been reported.4 In addition, extended erosion leads to esthetic impairment, because it is correlated with significant shortening of the maxillary incisors. The patient’s physiognomy is often changed when advanced lesions cause a significant loss of vertical dimension of occlusion (VDO) in the lower face. Furthermore, the mechanical properties of the hard tissues of the affected teeth are weakened by the acid demineralization. The microhardness of enamel and dentin is significantly decreased, rendering the dental hard tissue susceptible to physical wear.5

Until recently, severe erosive tooth wear could be addressed only with extensive crown-and-bridge reconstructions or, in advanced stages, with removable dentures. These conventional procedures—including full-coverage crowns—frequently involved elective endodontic therapy, crown-lengthening procedures, and major additional loss of tooth structure.6,7 Novel treatment approaches for extended erosive lesions aim to be as minimally invasive as possible in an effort to preserve the maximum amount of remaining tooth structure. Advancements in all-ceramic and adhesive technologies enabled the development of innovative defect-oriented treatment concepts for restoring compromised dentition. Modified onlay and full-veneer preparation geometries have evolved to form a reliable alternative to conventional full-coverage crowns.8 Nonretentive preparation designs in combination with reduced restoration thicknesses allow for a minimally invasive treatment approach. Moreover, CAD/CAM technologies for the fabrication of metal-free, tooth-colored restorations are increasingly used in prosthetic dentistry.

In cases of severe erosive decay, the VDO needs to increase. In the past decade, this was accomplished with a conventionally manufactured wax-up that the dental technician would fabricate. The transfer of this desired diagnostic tooth arrangement to the mock-up, provisionals, and permanent restorations is a time-consuming and costly effort, and may be inaccurate. Innovative manufacturing technologies and new materials, such as millable polymer and wax blocks for CAD/CAM, offer novel treatment options. Limited information is available regarding these treatment concepts for patients with severe erosive tooth wear.

Case Report

The treatment sequence of the aforementioned minimally invasive approach using CAD/CAM technology and monolithic all-ceramic restorations is demonstrated in the following presented case. Discussion is based on clinically relevant scientific data.

Initial Findings

A 26-year-old male with an unremarkable medical history presented with a chief complaint of hypersensitivity, severe tooth wear, severe loss of VDO, and unesthetic maxillary anterior teeth (Figure 1 and Figure 2). He requested a full-mouth rehabilitation to address the extensive tooth structure loss and reduced VDO. The patient admitted to excessive consumption of soft drinks, and the erosive tooth wear was attributed to the high intake of acidic beverages, including energy drinks. Intrinsic causes of erosive lesions, such as eating disorders and GERD, for which the patient was evaluated, were excluded. After analysis of dietary habits, the patient completely stopped the consumption of acidic drinks.

Clinical examination findings revealed group guidance and a significant loss of VDO. Severe loss of enamel and dentin was mainly located in the palatal aspect of the anterior and posterior teeth (Figure 3 and Figure 4). The patient’s oral hygiene was good, and no signs of temporomandibular disorder or pain were evident. Diagnostics included clinical, periodontal, functional, and radiologic examinations and an esthetic analysis. The periodontal findings revealed no bleeding on probing or any clinical attachment losses.

Treatment Planning and Clinical Procedures

In addition to providing the patient with diet education and oral hygiene instruction, initial treatment consisted of removing the impacted third molars, treating the caries, and replacing the insufficient composite restorations. The anticipated alteration of VDO aimed to consider esthetic parameters and avoid acceptance problems or orthodontic intrusion. The initial esthetic analysis for the diagnostic tooth arrangement included an incisal extension of the maxillary incisors with closure of the spacing. Comprehensive photography was used to determine the occlusal/incisal planes and prosthetic space, as well as to communicate the findings to the dental technician. Maximum occlusion was registrated. Maxillary and mandibular impressions were taken with a polyether impression material (Impregum™, 3M ESPE, and conventional impression trays.

The casts were mounted on the articlulator and digitized in a laboratory scanner (S600 ARTI Zirkonzahn, (Figure 5 and Figure 6). The dental technician performed a digital tooth arrangement/virtual wax-up, rebuilding the occlusal aspects of the molar and premolar regions, as well as the incisors and canines at an increased VDO. The prospective restorations’ tooth positions, lengths, sizes, and shapes were determined. This digital setup served as a template for the entire treatment. The initial situation and prospective tooth design were digitally overlapped to analyze interocclusal spacing. Based on this analysis, a splint was designed encoding the areas where occlusal reduction was necessary (Figure 7 through Figure 9). Subsequently, the splint was milled (M5 Heavy Milling Unit, Zirkonzahn) to transfer this information to the patient’s mouth. The virtual wax-up was also used to produce CAD/CAM-fabricated eggshell temporaries (TEMP Basic, Zirkonzahn) (Figure 10). The models, splints, and temporaries were sent to the dental office and tested intraorally (Figure 11).

This full-arch mock-up arrangement was used to evaluate whether the amount of VDO correction would be acceptable for the patient and, also, whether the tooth arrangement would meet his esthetic and functional expectations. After the patient approved the mock-up, the minimally invasive preparation was performed with the CAD/CAM splints in situ (Figure 9). Sharp edges on the occlusal surfaces caused by the erosive decay were rounded. A very shallow buccal chamfer preparation (0.5 mm) was performed on the maxillary anterior and premolar teeth; no preparation was needed on the palatal aspects due to the erosive tooth structure loss (Figure 12). The mandibular anterior teeth received a veneer preparation. The abutment teeth were temporarily restored with the CAD/CAM-generated polymer-based restorations (Figure 13).

After the patient wore the provisional for 6 weeks, conventional impressions (Identium®, Kettenbach, of the abutment teeth were acquired. A cross-mounting bite registration was performed, and the mounted models were then digitized with the laboratory scanner (Figure 14 and Figure 15). The initial lodged virtual wax-up was then used again to design the final restorations (Figure 16 through Figure 18). The restorations were subsequently milled in CAD wax in the 5-axis milling unit and, finally, pressed in a lithium-disilicate glass ceramic (IPS e.max® Press, Ivoclar Vivadent, (Figure 19). The monolithic all-ceramic restorations were polished and subsequently characterized with surface stains. All lithium-disilicate glass-ceramic restorations were adhesively luted under rubber dam isolation using a dual-polymerizing composite cement (Variolink® II, Ivoclar Vivadent) following the manufacturer’s protocol. A stable static occlusion and a dynamic occlusion with incisal/canine guidance were obtained (Figure 20 and Figure 21). Finally, the patient was provided with a CAD/CAM-fabricated occlusal splint (Temp Premium Flexible Transpa, Zirkonzahn) to facilitate long-term success (Figure 22 and Figure 23).

Intraoral photographs taken at a 1.5-year recall confirmed a stable occlusion, healthy periodontal status, and no marginal staining or plaque accumulation. No caries at the restoration margins or signs of fractures within the restorations were observed (Figure 24 through Figure 26).

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