Producing Excellent Indirect Anterior Restorations

/Home/Dental Care and Treatment/Corrective Dentistry (Orthodontics)/Corrective Dentistry (Orthodontics) Articles

Producing Excellent Indirect Anterior Restorations
November 2006
David R. Avery, CDT
Contemporary Dental Assisting

Each member of the clinical team should understand and appreciate the critical importance of every step of every procedure being done correctly. Laboratory and clinical team members are bound together in an attempt to meet patients' esthetic and functional expectations. This article will emphasize the important components of each dental assistant procedure needed to create indirect anterior restorations. When attention to detail is the norm rather than the exception, predictable excellence is assured.

The extreme makeover phenomenon is fueling the general public's increased awareness of dental esthetics, and thereby driving our profession to meet higher levels of patient expectation. This has resulted in the need to ask a new and very important question during the consultation appointment; whether the patient wants a monochromatic (same color from gingival to incisal edge) or polychromatic (natural color with a translucent transition from gingival to incisal edge) result. Thorough shade communication combined with the continuous esthetic improvement of restorative materials make this not only possible, but also predictable.

Clinical Shade Communication
Depending on the specific practice philosophy, dental assistants are often the primary operators in the shade data-gathering procedure. The communication of detailed color, surface textures, and individualized characterizations are critical to the delivery of esthetically acceptable restorations. The subjective nature of color assessment renders it the most difficult to accurately communicate between the clinical team and the dental laboratory.

Historically speaking, successful shade matching has been a combination of art, science, and luck. Several potential obstacles affect color perception and clinical shade taking.

The Type and Quantity of Light Source
A 6500?K, color correct lighting environment is ideal. Because daylight is highly inconsistent based on variances in location, time of day, time of year, and atmospheric conditions, do not allow too much natural light in the shade-taking area.1 A handheld lighting device offers an excellent means to bathe the area in color correct light while providing magnification for improved visibility.

Ambient Colors in the Shading Environment
Bright lipstick, smocks, or wall colors can cast affecting hues onto the tooth surface. Lipstick should be removed and patients should wear a light blue or gray bib to cover bright clothing.1

The Operator's Eyes
Retinal fatigue, color blindness, and operator age can have detrimental effects on the out-come of the shade-taking process. Schedule these procedures in the morning, when the operator's eyes are fresh. Do not stare at the tooth longer than 5 seconds and trust your first impression.2

Timing
Record the shade data at the beginning of the appointment before the teeth become dehydrated because surface anomalies, which are not present in normally hydrated teeth, become visible. Teeth can become dehydrated in just a few minutes and will not fully rehydrate for approximately 24 hours. Ask patients to wet their teeth with their tongue every few seconds during the assessment.2

Surface Texture
The most common failure in anterior shade communication is the lack of surface texture information. This information is especially crucial in partial anterior restorations (single units), but is needed to fully satisfy patients with larger cases as well.2 There are 3 basic categories of surface texture, related to age2:
Ô HeavyÛyouthful (Figure 1A)
Ô ModerateÛmiddle-aged (Figure 1B)
Ô SmoothÛmature (Figure 1C)

Photography is the best means to communicate texture. If photographs are unavailable, discuss with the laboratory how to communicate this information.

Shade Guide Limitations
The accepted method for clinical shade taking is using shade guides from ceramic systems manufacturers. These shade guides are not without their own inherent limitations.

Color Change Caused by Disinfection Techniques
The normal darkening of shade guides can be accelerated by cold sterilization techniques practiced in the clinical setting, leading to restorations that are too dark. Shade guide manufacturers recommend that high-volume restorative practices that frequently cold sterilize their shade tabs should consider replacing them annually. Make certain to carve the month and year placed in service on the tab holder to allow timely replacement.

Use of Denture Tooth Shade Guides
Often, there are shade guides in the office, such as Portrait IPN, Bioblend, and Biotone (Dentsply Trubyte, York, Pa, www.dentsply.com), which exclusively represent prosthetic denture tooth systems. Manufacturers warn that using these incorrect guides when prescribing fixed restorations creates the need for cross-matching. This requires the laboratory technician to reformulate the noncorresponding material shades in an attempt to match the patient's dentition. This process is extremely subjective. When unsure, send the closest matching shade tab with the case.

The Bleaching Phenomenon
The popularity of over-the-counter whitening systems has introduced yet another significant limitation to the challenge of shade matching. When beginning restorative treatment, advise patients against at-home whitening during the restorative process. Whitening activity after the determination of the shade can result in a need to change the shade at patient expense. Recently, new shade tabs have been designed to match the color of bleached teeth and are available for numerous ceramic systems. These tabs significantly improve communication for bleached shades. The author suggests ordering the appropriate bleach tabs from your laboratory or dental supply representative.

Photographic and Digital Shade Communication
Historically, 35-mm slides have been recognized as the most accurate means of dental color communication. Digital photography is rapidly improving and becoming more affordable, although monitor quality and color calibration remain crucial issues.

Numerous electronic shade- matching technologies are rapidly developing and are certainly worthy of consideration as an aid in this difficult communication process. Some leading systems are:

Ô ShadeVision (X-Rite, Inc, Grandville, Mich, www.xrite.com, distributed by Sullivan Schein Dental, Melville, NY, www.sullivanschein.com). A colorimeter-based system that requires computers in both the dental office and the laboratory.

Ô ShadeScan (Cynovad, Saint-Laurent, Quebec, www.cynovad.com). A colorimeter-based system that requires computers in both the dental office and the laboratory.

Ô Vita Easyshade (Vident, Brea, Calif, www.vident.com). A self-contained spectrophotometer system.

Ô ShadeEye NCC (Shofu Dental Corp, San Marcos, Calif, www.shofu.com). A chromameter that requires a computer in the laboratory.

Impression Taking
The impression procedure is the most challenging yet crucial procedure in the prosthodontic process. Regardless of the type of indirect restoration, the success at delivery is totally dependent on accurate impressions.

Technique
Troubleshooting tips for taking quality vinylpolysiloxane (VPS) impressions.

Ô Follow the manufacturers' instructions. The manufacturers spend a great deal of time and money to develop specific techniques for their products.

Ô The cornstarch commonly found on latex gloves will contaminate VPS materials. Simply touching the prepared tooth before taking the impression can cause contamination.

Ô Most dental materials have a shelf life. Watch the expiration date carefully on impression materials.

Ô Proper tray selection is crucial to the accuracy of the impression. Custom trays are ideal for unusually small or large arches and long-span bridges. Impingement of teeth or excess soft tissue on the plastic tray walls leads to inadequate impressions of necessary areas and possible distortion (Figure 2).

Ô Using tray adhesive correctly is crucial to the dimensional accuracy of all impression materials. Use the proper adhesive for the specific impression material and allow it to dry according to the instructions. All impression materials shrink toward the greatest mass. If the material is allowed to pull away from the tray wall, that uncontrolled shrinkage becomes distortion, resulting in an ill-fitting prosthesis (Figure 3).

Ô The most dangerous error in impression taking is inadequate time management. Follow instructions and learn the available working time, as well as the correct set time. The use of a timer is strongly recommended to ensure against early removal of the impression from the mouth. Early removal can create visibly undetectable errors that are not caught until the attempted, but unsuccessful, seating of the restoration.

Proper Alginate Impression Technique
Irreversible hydrocolloid, also called alginate, is still widely recognized as the most accurate choice for taking final impressions for removable partial dentures and occlusal splints. This material should be mixed according to the manufacturers' directions. Application of material to the occlusal and lingual surfaces of the teeth before placing the loaded tray eliminates the trapping of air in these areas, preventing nodules, known as "positives," from appearing on the resulting cast. These resulting nodules can dramatically affect the accuracy of the resulting fit of an appliance or the occlusion if the intended use was as an opposing cast.

Proper Stone Cast Development
Conventional alginate impressions should be poured immediately upon removal of the tray from the mouth. Because the material is mostly water, it begins to shrink almost immediately when exposed to air. If you cannot pour the impression right away, wrap the impression in wet paper towels and place it in a sealed environment, such as a plastic container or an airtight sealable plastic bag. Failure to comply with this requirement can lead to problems at delivery of the involved prosthesis, such as tight-fitting removable partial dentures, occlusal splints, and nightguards, or to excessive occlusal adjustments when the impression was taken for the opposing cast.

Gypsum (dental stone) material must be properly weighed and measured to manufacturer specifications to ensure accuracy of the resulting stone cast. Gypsum is available in premeasured packaging, but at an increased cost. Many offices use a food scale to weigh stone in 100-gram portions and store these portions in sealed plastic bags. Using a simple milliliter graduate for water measurement can aid significantly in the production of consistently well-fitting appliances.

The stone cast must be removed from the alginate at the appropriate time, 45 minutes for regular set stone and 12 minutes for snap set stone. After the cast cools, it immediately begins to absorb the water from the alginate impression. If left on the alginate for an extensive period, the surface of the cast will be compromised. To test for this occurrence, rub your finger over the surface of the dry cast. If dust from the surface of the cast comes off on your finger, the cast is inaccurate. This seemingly minor detail will lead to the same problems as waiting to pour the stone cast. Avoid taking alginates at the end of the day, unless someone will be available to remove the cast. The use of a timer is also recommended to ensure timely removal of the cast.

Provisional Restorations
In the current era of media- driven esthetic awareness, the bar has certainly been raised regarding patient expectations. The average knowledge level of esthetics among clinical auxiliary is far less than what is required to meet these demands. The curriculum in formal training programs may be adequate for a very basic understanding of overall morphology, but it only provides an entry-level understanding of anterior esthetics. The subject is far too involved and requires significantly expanded comprehension to truly be of assistance to the clinician in the treatment of comprehensive restorative cases involving anterior guidance. Dental assistants should consider completing training courses that detail anterior tooth anatomy, physiology, gingival architecture, and smile parameters.

Mastery of this material certainly enhances the clinical staff's ability to assist in the diagnosis of the existing esthetic situation and develop exquisite provisional restorations, thereby setting the stage for the ultimate result from the laboratory technician restoring the case.

Esthetic and Functional Laboratory Communication
The predictable, successful delivery of full-coverage crowns and bridges depends on proper technical performance at every clinical and laboratory step. Beyond the crucial shade communication and master impressions lies the often undervalued process of temporization.

For multiple-unit anterior reconstruction, functional and esthetic harmony in the provisional restorative phase is best accomplished through the use of a facebow articulated set of preoperative study casts on a semi- or fully adjustable articulator3 (Figure 4). The occlusion is evaluated by the clinician with emphasis on any existing occlusal discrepancies. Clinicians can address needed corrections by equilibration of any interferences or addition of wax or composite to compensate for any deficient areas of length or contour (Figure 5). This corrected cast serves as the guide for the development of the provisional restorations. The cast is impressed in putty polyvinyl impression material (Figure 6). Compared to the alginate duplication/vacuum-formed stint technique, this approach captures all of the fine detail of the cast for highly accurate reproduction of the embrasures and anatomical features of the wax-up, minimizing the finishing time of the resulting provisional restorations, according to the manufacturer.

To develop and maintain occlusal harmony, form must be dictated by function; therefore, the protrusive and lateral excursive movements must be correctly developed at this phase of treatment. In more complex cases, numerous follow-up visits may be required to fine-tune the trial restorations to the clinician's and patient's satisfaction. This process determines the acceptable esthetic parameters of length and facial position. Upon satisfaction of these crucial requirements, a study cast of the provisionals will guide the laboratory technician in the final lingual, incisal, and labial contours of the definitive restorations (Figure 7).

This systematic approach eliminates guesswork and excessive adjustments at delivery because of the patient's involvement in determining the final outcome in a proactive, predictable manner.3

Material Selection
There are currently 2 categories of provisional materials to choose from4-8:

Methylmethacrylate (MMA) acrylic resin
Ô Advantages
- Inexpensive
- Can be freely formed
- Strong material can be used for long-span bridges

Ô Disadvantages
- Time-consuming to formulate
- High exothermic reaction
- Less esthetic than BisGMA
- Less wear resistant than BisGMA

BisGMA acrylic resin
Ô Advantages
- Simple to use
- Improved esthetics
- Low exothermic reaction
- Less time-consuming to formulate than MMA
- More wear resistant than MMA

Ô Disadvantages
- Expensive
- Material not strong enough for long-span bridges

Provisional fabrication often may be rushed because of time limitations created by difficulties encountered during the appointment or scheduling of emergency patients. As real as these issues are, accurate provisionals help assure success of the final restoration.

Correctly contoured provisional restorations serve several important functions. They protect prepared tooth structure, minimizing sensitivity.
Ô Open or short margins can create sensitivity from the exposed, prepared tooth structure.

Ô Overextended or overcontoured margins can create tissue inflammation, leading to potential recession and possible bone loss if left unattended for an extensive period of time.

They also maintain the tooth position while the final restoration is fabricated.
Ô Light or open interproximal contacts can cause the final restoration to need significant adjustment.

Ô Heavy or tight interproximal contacts can cause the final restoration to be returned to the laboratory for additional porcelain.

Ô Light or open occlussal contacts can cause the final restoration to need moderate to significant adjustment.

Ô Heavy or premature occlussal contacts can cause the final restoration to be out of occlusion, leading to patient discomfort.

The few extra minutes invested in fabricating a correct provisional restoration is returned tenfold. By "holding the space" for the laboratory, the properly contoured provisional ensures a low-stress delivery appointment. Quick and successful delivery of the restoration can minimize patient anxiety and keep the clinical team on schedule. Regardless of which technique and materials your team chooses to use, performing it properly is the key to consistency and success.

Scheduling
Ineffective scheduling communication has the potential to destroy an otherwise successful office/laboratory relationship. It is important to understand the standard working time your laboratory requires for fabrication of each different type of appliance. This task is complicated by the tremendous variety of fixed and removable appliances and the numerous materials and incremental steps and appointments associated with a particular treatment.

It is recommended that you acquire a complete schedule from your laboratory and schedule the return of restorations at least 24 hours before the patient appointment. This will prevent the patient from arriving when you do not have the required restoration. In the event of an emergency, communicate the patient's needs with the laboratory. After an emergency return date is scheduled, be certain to note your discussion on the return date line. This will typically eliminate a second call from the laboratory and allow the case to enter the work flow more smoothly.

Packaging
Regardless of the shipping method required to get your case to the destination laboratory (local courier or across the country), package casts as if they were fine china. Wrap the casts carefully and buffer all sides of the box from potential impact. Regarding articulated casts, never place bubble wrap or foam between the arches for protection. Always separate one cast from the other and wrap individually for protection. Place all small items (restorations, shade tabs, implant components, etc) in plastic crown boxes or sealed bags to prevent loss. Also note the inclusion of these items on the prescription.

Conclusion
Over the years, it has been my experience that the most successful prosthodontic-oriented practices develop one or more staff members into laboratory assistants. This is usually accomplished through continuing education provided at dental schools, private institutions, conventions, and manufacturer-sponsored courses. The predictable delivery of successful prosthodontic treatment is reliant upon numerous technical procedures and strict attention to detail from the entire restorative team. Predictable, consistent delivery can reduce stress for everyone on the team and ultimately our patients.

Disclosure
Mr. Avery received an honorarium from Dentsply International to write this article.

References
1. Fondriest J. Shade matching in restorative dentistry: the science and strategies. Int J Periodontics Restorative Dent. 2003; 23: 467-479.

2. Saleski CG. Color, light, and shade matching. J Prosthet Dent. 1973; 27: 263-268.

3. Dawson PE. Determining and Communicating Restorative and Esthetic Guidelines. St Petersburg, Fla: Dawson Center for Advanced Dental Study; 1997.

4. Turker SB, Kocak A, Aktepe E. Effect of five staining solutions on the colour stability of two acrylics and three composite resins-based provisional restorations. Eur J Prosthodont Restor Dent. 2006; 14: 121-125.

5. Guler AU. Color stability of provisional restorations. Pract Proced Aesthet Dent. 2006; 18:103-104.

6. Ergun G, Mutlu-Sagesen L, Ozkan Y, et al. In vitro color stability of provisional crown and bridge restoration materials. Dent Mater J. 2005; 24:342-350.

7. Christensen GJ. The fastest and best provisional restorations. J Am Dent Assoc. 2003; 134:637-639.

8. Hagge MS, Lindemuth JS, Jones AG. Shear bond strength of bis-acryl composite provisional material repaired with flowable composite. J Esthet Restor Dent. 2002; 14:47-52.