An Aesthetic Application for Lithium Disilicate: Treatment of Missing Maxillary Lateral Incisors and Canine Substitution

INTRODUCTION
Dentists frequently see patients with missing or malformed teeth. Yet while congenitally missing teeth (particularly the maxillary lateral incisors, which are the second most common congenitally missing teeth) may be a common occurrence, providing optimal treatment for correcting the condition is anything but a simple process.

Apart from the functionality and the health of teeth and tissue affected, aesthetics also plays a major role. The challenge of achieving optimal orthodontics and prosthetic treatment is extremely high due to the impact on facial appearance; aspects and considerations of all 3 (eg, function, health, and aesthetics) must be taken into careful account to ensure superior results that satisfy both the dental team and the patient.

OPTIONS FOR TREATING MISSING LATERAL INCISORS
Three treatment options exist for replacing missing lateral incisors: canine substitution, a tooth-supported restoration, or a single-tooth implant. Choosing the appropriate treatment alternative will vary depending on the malocclusion, specific space requirements, tooth-size relationship, and the canine’s shape and size. In many cases, the decision to create space for an implant to replace the lateral incisor versus moving the canine into the lateral position is extremely challenging. Although the implant choice is usually safe and predictable, there are potential challenges, such as the age for implant placement, long-term provisionlization, soft-tissue aesthetics, and developmental facial changes that may affect the long-term aesthetic outcome. Typically, the treatment of choice is the most conservative option that meets individual functional and aesthetic objectives. In many cases, this is canine substitution.¹

Orthodontic treatment, while addressing the functional and health aspects, may sometimes result in compromised aesthetics, leaving the patient unsatisfied. Therefore, overall success of a treatment outcome and satisfaction must encompass an interdisciplinary approach that accounts for aesthetic considerations to produce superior results.^1-4 Orthodontic treatment to stabilize occlusion should first be performed; this should be followed by restorative treatment. In cases involving canine substitution, for instance, while the orthodontist can position the canine at the optimal functional and aesthetic location, the restorative dentist frequently must place a porcelain veneer in order to recreate the normal size and color of the lateral incisor.¹

WHAT MAKES A SMILE AESTHETIC?
This collaborative approach leads to the need to establish some level of consensus not only between the dental practitioners, but also their patients regarding what constitutes an aesthetic smile. Depending on “the eye of the beholder,” the characteristics of a pleasing, natural-looking smile vary widely. Some studies have shown that dental professionals and laypeople have different opinions when evaluating the treatment outcome in cases with missing maxillary laterals. While dentists typically find tooth color, tooth shape, and asymmetry the most troublesome factors, patients generally are more critical of color, spacing, and tooth shape. In cases where many dentists do not find the need for treatment, patients do feel the need, and when dentists do confirm a treatment need, their most common treatment goals are to change the color or the shape of the teeth, whereas patients seek to alter the color, spacing condition, or the shape of the teeth.⁵ Yet, while most patients appear to have a preference for no diastemas and unworn, evenly spaced teeth, they show a wide assortment of different preferences when it comes to size, shapes, and tooth-to-tooth proportions between teeth.⁶

In the face of so many variables and divergent tastes, dentists not surprisingly have long sought to establish guidelines for an aesthetic smile^7-11 in order to achieve predictable, objective, and reproducible means of achieving success in aesthetic dentistry.¹⁰ Most practitioners recognize that using mathematical principles when interpreting aesthetic and tooth proportions for their patients are just starting points for a smile design or reconstructive procedure.

Currently, there seems to be no “golden proportion,” nor any other recurrent proportion, for all anterior teeth; there is no one “ideal” aesthetic standard when creating space for the replacement of missing lateral incisors.^11,12 Instead, studies indicate that aesthetic “ideal” preferences vary by nationality/ethnicity, social norms, gender, and individual morphological facial proportions¹¹ as well as individual cultural characteristics and perceptions of beauty.¹²

It All Comes Down to the Execution of a Good Plan
What there is agreement on, however, is that for optimal results, planning and execution of restorative treatment must consider the following: smile design, width/length ratio of teeth, differences among the teeth, concepts of proportion, and the outcome of orthodontic treatment. Accordingly, dentists must address the individual patient’s specific needs and preferences in order to correct the shape, size, width, and length of the patient’s canines in relation to the patient’s gender and facial morphology for overall balance.¹³

When creating space to replace missing lateral incisors, studies indicate the importance of the form and size of the maxillary anterior teeth in creating pleasing facial and dental aesthetics.¹¹ In many cases, maxillary lateral incisors that were 1.0 mm to 1.5 mm shorter than the central incisors were considered the “most popular” maxillary lateral incisor length; very short and very long maxillary lateral incisors were consistently regarded as “least attractive.”8 In other words, overall balance seems to be a crucial factor for patient satisfaction with aesthetic outcomes.

This presents clinicians with the challenge of ensuring proper proportion of the teeth to achieve the desired optimal shape and rotation. When one type of tooth is transformed into another type through restorative treatment, particular care must be applied to ensure correct preparation and gingival contours in order to achieve the illusion that teeth are properly positioned. While an involved process, with accurate digital photographic planning, active patient consultation, detailed tooth preparation and a thorough laboratory sequence, porcelain veneers can result in long-lasting and aesthetic restorations that meet the expectations of both dentists and patients.¹⁴

The aesthetic challenges of canine transposition are great and complex, requiring a high degree of skill and deliberation in the evaluation of correct placement in relation to aspects such as tooth display, lip mobility, positioning of the incisal edge relative to other maxillary teeth and phonetic considerations,¹⁵ as well as margin placement.¹⁶ Although making the first premolars resemble canines does not usually present a great challenge, making the canines look like laterals is tremendously challenging, particularly on young patients.

Design and preparation of the resorations, and the skill level of the practitioner, are vital for the success, quality and longevity of the final restorations.^17,18 The material used for making the porcelain veneers also is a critical factor in achieving superior results.

This article discusses the application of lithium disilicate, using the wax-and-press technique, to create veneer restorations as part of the treatment for canine transposition. In this case, more tooth reduction was required in order to create the desired look (ie, turning a larger canine into a smaller lateral); however, the premolars required little tooth reduction because they were being enlarged (ie, into canines). Lithium disilicate was chosen due to its excellent strength and inherent optical properties that create natural-looking aesthetics, even in minimal thicknesses.^19-23

CASE REPORT
Diagnosis and Treatment Planning
A 14-year-old female, who was undergoing orthodontic treatment, presented to our office (Figures 1 to 3). She had congenitally missing lateral incisors, and the canines were being moved into those positions. Then, at age 16 years, upon completion of orthodontic treatment, the canines had been transposed into the lateral incisor position (Figures 4 and 5). The patient was not pleased with the aesthetics of her smile, feeling that it lacked a natural-looking, symmetrical aspect for a full and pleasing smile.

Figure 1. A 14-year-old female patient presented in orthodontic braces.	Figure 2. Close-up retracted view of the patient’s teeth shows the condition of her teeth during active orthodontic treatment. Note the movement of the canines into the lateral position.

Figure 3. Occlusal view of the active orthodontic treatment displays that while some movement has occurred, spaces remain in the lateral/canine positions.

After a thorough examination and evaluation, it was decided that the treatment plan would involve placing 6 lithium disilicate veneers on teeth Nos. 5, 6, 8, 9, 11, and 12 to create a fuller and more natural-looking smile. The canines would be shaped to look like laterals, and the first premolars would be shaped to appear like canines. Across all 6 teeth, a more pleasing length-to-width ratio would be also created.

Since they were being made larger into “canines,” the premolars needed little tooth reduction, but the goal for the canines was to reduce, more than to augment, with the veneers. Reducing the canines by 1.0 mm to 1.2 mm and constructing minimal-thickness veneers would make the canines appear smaller.

Clinical Protocol
As with any restorative case, when using lithium disilicate for fabricating anterior restorations, it is important to first discuss treatment options with the patient.²⁴ Once the dentist and patient were in agreement about the treatment choice, preoperative photographs (eg, full-face smiling, retracted smile, resting smile, profile, etc) were taken to assess the patient’s present condition and to help plan and establish the desired outcome.^25,26

The photographs were uploaded to an iPad (Apple) and viewed with the patient, parents, and in-house dental laboratory technician. Using Adobe Ideas (Adobe), the desired treatment result was illustrated and effectively communicated.

At this time, characteristics such as proper coloring, shading, size, and contouring were determined in collaboration with the patient to help ensure that the final treatment would meet all of the functional and aesthetic expectations of the dentist and patient. The dental ceramist also was consulted.²⁶

Once the goals and objectives of the desired outcome were thoroughly discussed and agreed upon, a diagnostic white wax-up that incorporated all of the desired requirements was created. The white wax-up was developed to facilitate patient assessment of the proposed treatment, as well as allow the dentist to predict potential problems that could arise during treatment.^27,28 By using the white wax-up as a detailed and accurate guide, proper contours for the final restorations were developed and replicated more readily.^27-29

Teeth Nos. 5, 6, 8, 9, 11, and 12 were prepared for lithium disilicate veneers (Figure 6), and the white wax mock-up was tried-in to the patient’s mouth to verify aesthetics. The canines were shaped to appear like laterals; the first premolars were prepared to resemble the canines (Figure 7). Once in place, the white wax-up was reviewed and approved by the patient (Figure 8), after which it was removed and used as the basis for creating provisional restorations and as a guide for the definitive veneers.

Figure 4. Close-up view of the patient’s smile, taken at age 16 years, shows the transposed canines.	Figure 5. Close-up retracted view of the patient’s teeth shows the canines transposed into the lateral incisor position.
Figure 6. Teeth Nos. 5, 6, 8, 9, 11, and 12 were prepared for lithium disilicate veneers (IPS e.max [Ivoclar Vivadent]).	Figure 7. White wax mock-up was tried-in to the patient’s mouth to verify aesthetics. The canines were shaped to appear like laterals; the first premolars were shaped to resemble the canines.
Figure 8. Patient’s smile with the white wax mock-up in place.	Figure 9. The lithium disilicate veneers were tried in with try-in paste (Variolink Veneer [Ivoclar Vivadent]).
Figure 10. Teeth were isolated prior to cementation (Optragate [Ivoclar Vivadent]).	Figure 11. Veneers were cemented using a light-cured resin cement (Variolink Veneer; medium value zero.
Figure 12. Close-up view of the completed lithium disilicate veneers.	Figure 13. Palatal view shows the lithium disilicate veneers after cementation.

Figure 14. Facial view of the patient after final veneer placement shows outstanding aesthetics. Note the overall balance, color matching, and translucency, all of which help ensure a more natural-looking, evenly full and pleasing smile.

Dental Laboratory Protocol
In this case, the dental technician tried-in the white wax mock-up, determined the shade of the veneers, and recorded the shade of the prepared teeth. The final restorations were created from pressed lithium disilicate (IPS e.max Press [Ivoclar Vivadent]) based on the diagnostic white wax-up. Wax was injected through the matrix of the white wax mock-up onto the master dies. The margins were sealed, and form and function were then developed in the wax. Next, the completed wax-ups were sprued, invested, burned out, and pressed using the selected shade of pressable lithium disilicate. The pressed restorations then were divested and placed in a dissolving liquid to eliminate the surface reaction layer. The restorations were cut from the sprues and scrutinized against the model of the provisional restorations.

The pressings were then fitted to the solid model. At this time, any necessary contouring and fine-tuning adjustments were performed. The restorations then were shaded to produce color matching that was indistinguishable from the patient’s natural teeth. Once the restorations were brought to full contour and color, they were bisque-baked and ready for final contouring. Finally, the lithium disilicate veneers were glazed and polished.

Final Delivery
When the patient returned 3 days later, the provisionals were removed and the preparations were cleaned. The final lithium disilicate veneers were seated with try-in paste (Variolink Veneer [Ivoclar Vivadent]) (Figure 9). After the fit, margins, and aesthetics were verified, the veneers were removed; and the teeth were cleaned and isolation was achieved (Figure 10). The preparations then were etched, rinsed, and dried for the appropriate amount of time. Bonding adhesive (ExciTE F [Ivoclar Vivadent]) was applied to the preparations, then they were air-thinned and light-cured following the manufacturer’s instructions. A light-cured resin cement (Variolink Veneer) was applied to the veneers, and then they were seated and cured (Figure 11). Excess cement was removed from gingival margins and interproximally.

Excellent results were achieved (Figures 12 to 14), with the patient expressing satisfaction in the function, comfort and, most of all, aesthetics of the final treatment outcome.

IN SUMMARY
Although a common condition often encountered by dentists, congenitally missing teeth—particularly the maxillary lateral incisor—present clinicians with numerous challenges. These involve treatment planning and smile design; preparation; patient perceptions and expectations relative to aesthetics; interdisciplinary collaboration that meets the functional, health and aesthetic needs; the expectations of all parties; and, a critical factor for the overall success, that of choosing a suitable restorative material. In the case presented here, while far from a simple course of treatment, the use of lithium disilicate veneers made the endeavor worthwhile, resulting in restorations exhibiting a very natural-looking smile.

Acknowledgement
The author would like to acknowledge Pasquale Fanetti, CDT, the in-house dental laboratory technician who created the restorations used in this case.

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Dr. Ferencz graduated from Rensselaer Polytechnic Institute in 1967 and received his DDS from New York University College of Dentistry in 1971 and received a certificate in postdoctoral prosthodontics in 1984. He has been on the faculty at New York University (NYU) College of Dentistry since 1972, teaching all levels of prosthodontics. In 1990, he became clinical professor of postgraduate prosthodontics and was certified by the American Board of Prosthodontics in 1998. Dr. Ferencz is a Fellow of the Greater New York Academy of Prosthodontics (serving as president in 1995), Fellow of the Northeastern Gnathological Society (serving as president in 1995 and 1996), and has served in many leadership positions in the American College of Prosthodontists, including as its president in 2003. In addition, he is a Fellow of the Academy of Prosthodontics and New York Academy of Dentistry and a member of the American Academy of Restorative Dentistry and the American Academy of Fixed Prosthodontics. Dr. Ferencz is the recipient of the David B. Kriser Medal from NYU, the American College of Prosthodontists Presidents Award, Achievement Award, Distinguished Lecturer Award and Founders Award, and the Greater New York Academy of Prosthodontics Achievement Award and Distinguished Lecturer Award. He has numerous publications in the dental literature and has been a reviewer for 2 prosthodontic journals. In addition to private practice in New York City (since 1972) and part-time teaching at NYU, Dr. Ferencz has given more than 200 courses and programs internationally. He can be reached at jlferencz@nycpros.com.

Disclosure: Dr. Ferencz reports no disclosures.