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Utilization of an In-Office CAD/CAM e.max Maryland Bridge as a Long-Term Anterior Provisional

August 1, 2012
by Les Kalman, BSc, DDS


ABSTRACT
Through Computer Aided Design (CAD) a multiple unit prosthesis can be designed with ideal characteristics. By utilizing Computer Aided Manufacturing (CAM), the clinician has the ability to mill the designed prosthesis with extreme accuracy. E.max has been selected as the material for this investigation due to strength and esthetics. The combination of in-office CAD/CAM technology and e.max allows the clinician the ability to create a predictable and esthetic long-term anterior provisional.

INTRODUCTION
When diagnostic criteria are satisfied, implant placement in the esthetic zone is the ideal treatment option.1 However, finances can act as a barrier to treatment. A long-term esthetic provisional would allow the patient the opportunity to overcome barriers. In-office CAD/CAM technology would allow for the immediate prostheses fabrication.

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CAD/CAM stands for computer aided design and computer aided manufacturing, respectively. CAD allows the clinician to digitally capture an image of a preparation and then design an indirect (out of the mouth) restoration by using software.2 After the ideal restoration has been produced, the design is then fabricated out of a material by a milling machine. E4D is an in-office dental unit (D4D Technologies).

E.max is an esthetic, metal-free dental material used in indirect restorations. E.max is composed of lithium disilicate and it’s ideal physical and esthetic properties allow it to be the first choice for CAD/CAM restorations.3 E.max has strength second only to gold and has the ability of detailed CAM production.3

CLINIC CASE

Presentation
A 31-year-old female patient presented with a failed Maryland porcelain fused to metal (PFM) bridge (Fig. 1). Her chief complaint was the poor esthetics and the sharpness on the back of her teeth. Medical history was non-contributory. Clinical and radiographic examination indicated a congenitally missing lateral incisor. The PFM Maryland bridge had poor esthetics and no marginal integrity. The bridge had been recemented several times. Diagnosis indicated a congenitally missing tooth #22. Treatment options to replace the missing tooth included: an implant supported crown, a bridge, a removable partial denture and no treatment. The patient had interest in the implant option, but requested that the old bridge be recemented. Finances were a limiting factor. The existing bridge was deemed poor and could not be used. Based on the situation, an alternative option was presented to the patient: an indirect e.max CAD/CAM Maryland long-term provisional bridge that would be fabricated using an in-office E4D unit. Treatment specific informed consent was given and the patient agreed. It was decided to generate an indirect CAD/CAM prostheses due to the investigative nature of the clinical case.

PREPERATION
A segmental impression was taken of the existing bridge with a Q-Tray (Research Driven) and vinyl polysiloxane (VPS) (Ivoclar) to allow for temporization (Figs. 2 & 3). The existing bridge was removed (Fig. 4) and tooth preparations were refined on the lingual of the central and canine. A final VPS impressions (Ivoclar) was taking utilizing Tres Perfect impression trays (Research Driven) (Fig. 5) employing the Rebite technique.4 The technique consists of a preliminary impression using the patient’s bite as the seating force (Figs. 6 & 7). The impression was then loaded with light body VPS (Ivoclar) (Fig. 8) and intra-orally reseated using the patient’s bite force (Fig. 9). The result is a highly accurate impression of the segment to be scanned4 (Figs. 10 & 11). A bite registration was taken as necessary for the CAD/CAM scan (Fig. 12). The area was then temporized with a bonded pontic made from Integrity (Dentsply) (Fig. 13) and shade selection followed. The patient was dismissed with post-operative instructions.

Indirect CAD/CAM Component
The Rebite impression was poured with stone (Fig. 14) and then digitized by taken several scans of the area with the E4D scanner (Fig. 15). Utilizing CAD technology, the preparations were delineated and the pontic was designed (Figs. 16 & 17). The CAD software then presented a rudimentary prosthesis based on the parameters selected (Figs. 18 & 19). Material thickness was then evaluated (Fig. 20). The prosthetic design was further manipulated using the provided software tools until an acceptable result was achieved with proper sprue placement (Fig. 21). The CAD design was executed on an e.max block utilizing CAM technology, which produced a prosthetic form (Fig. 22). The prosthesis was removed from the block (Fig. 23) and assessed for morphology and fit on the cast (Figs. 24 & 25). The bridge was then stained, glazed and ready for delivery.

The patient returned for prosthetic delivery. The temporary pontic was removed and the e.max bridge underwent intraoral assessment. The patient approved the esthetics. The bridge was cemented with Multilink (Ivoclar); occlusion was refined and the bridge was cleaned and polished (Figs. 26 & 27).

DISCUSSION
This report represented a clinical investigation, as e.max blocks supplied for in-office CAD/CAM dentistry have only been recommended for single units. This was due to the fact the block sizes were quite limited and too short for multiple units and that the strength of e.max for edentulous spans had yet to be determined. The CAD software was quite limited and did not have the capability to generate multiple unit prostheses. Finally, the CAM unit’s ability to generate a multi-unit complex prosthetic had yet to be determined.

Several factors were evident that allowed for the completion of this case. The patient requested a ‘temporary’ procedure until financials permitted the ideal treatment. The inability to use her existing bridge opened up the opportunity for this investigative trial. The patient’s occlusion exhibited a slight anterior open bite; therefore, occlusal forces would be eliminated. That the retaining teeth had no other restorations present reinforced the necessity for minimally invasive dentistry. Lastly, the span of the pontic and retentive preparations fit within the length of the supplied e.max blocks, permitting in-office CAD/CAM fabrication.

Although it would have been more esthetic to design a pontic that had a longer length, it was decided to maintain a space under the pontic so that the patient could clean and maintain the area. A lesion was present from the pontic on the previous prosthesis and required resolution.

CONCLUSIONS
CAD/CAM technology has been harnessed utilizing e.max to provide for an investigative long-term, predictable and esthetic anterior provisional. Further studies are required to: quantify the strength of e.max, assess it’s role in multiple unit prostheses and develop the technology for CAD/CAM procedures. The potential seems to exist for e.max to act as a predictable, long term and esthetic prosthesis.OH

Disclaimer:

Dr. Kalman is the co-owner of Research Driven, and the developer of the Q-Tray and Tres Perfect.

Les Kalman B.Sc.(Hon), DDS, Assistant Professor, Restorative Dentistry. Schulich School of Medicine & Dentistry, Western University, London, ON N6A 5C1. 519-661-2111 ext. 86097. lkalman@uwo.ca

Oral Health welcomes this original article.

REFERENCES

1. Martin, W.C., Morton, D. and Buser, D. Pre-operative analysis and prosthetic treatment planning in esthetic implant dentistry. In Buser, D., Belser, U. and Wismeijer, D. editors: Implant Therapy In The Esthetic Zone-Single Tooth Replacements (Volume 1) p11-19, Berlin, 2007, Quintessence.

2. Berlin, M. Wowing The Patient With Chairside CAD/CAM. Dental Eco
nomics: 2008; 98(4): 92-96.

3. Ivoclar Vivadent: IPS e.max lithium disilicate The Future of All-Ceramic Dentistry. 2009; 1-15.

4. Kalman, L. Prosthodontic Impressions Simplified: The Rebite Technique. Oral Health 2006; 96(11): 29-36.