The Science Behind Smile Design
For many patients and oral healthcare practitioners, the words "esthetics" and "smile" are synonymous, and at a glance, the smile is the outward manifestation of a successful esthetic restoration. But the smile does not exist in isolation; its function in projecting esthetics is, in fact, intimately connected to the structural elements of bone, muscle, and soft tissue that surround and support the dentition. As the master craftsmen and women of dentistry get their patients ready for their close-ups, a remarkable blend of prosthodontic science, engineering, architecture, and artistry informs every smile design.
From physical to psychological and philosophical factors, hard to soft tissues, and static to dynamic features, many elements combine to form the anatomy of a smile. The teeth must have pleasing proportions and contours, and they must be arranged in relationship to each other, the gingiva, the lips, and the face in such a manner as to provide balance and harmony, explains Elizabeth Bakeman, DDS, president-elect of the American Academy of Cosmetic Dentistry.
The Role of Orofacial Anatomy
Essentially, all of the anatomical structures of the entire face require consideration when restoring a smile, but the process is far more complicated than merely observing those components. Complicating smile restoration is the need to collect-and understand the difference between-both dynamic data (ie, regarding structures that are complicated by movement) and the usual static data (ie, color, symmetry and harmony of the teeth, tooth position, gingival architecture relative to the face), explains John C. Kois, DMD, director of The Kois Center. Gathering dynamic data includes gaining an understanding of lip movement during smiling and speaking as well as frontal and sagittal plane head posture, he says.
For example, consider the challenges dentists face when a patient presents with an asymmetrical smile in which one side of their smile is revealed more than the other due to upper lip (ie, dynamic) asymmetry (Figure 1). In such instances, harmoniously restoring the smile within that framework can be difficult, observes Steven Chu, DMD, MSD, CDT, a prosthodontist, technician, and adjunct faculty member in prosthodontics at New York University College of Dentistry. Most dentists understand that the incisal edge of the maxillary dentition should follow the lower lip line, but asymmetry complicates the process.
"If the upper lip is asymmetrical, but the lower lip is symmetrical, dentists usually follow the symmetrical side as a rule," Chu explains, noting that in cases of a reverse smile (ie, the upper lip is symmetrical but the lower lip is asymmetrical), the upper lip is followed. "When both the upper and lower lip are asymmetrical, then we tend to follow the horizon or interpupillary line."
The more that any given patient displays tooth structure, the more influential any type of change will be to a patient's appearance, Bakeman says. Increasing tooth display increases the impact the teeth will have on overall facial esthetics. Porcelain or composite restorations that change the length, contours, angulations, shapes, and color of the teeth can alter the appearance of the smile, she says. Therefore, it is important to establish a diagnosis prior to developing a treatment plan.
"During the diagnostic phase, the patient's presenting situation is compared to known metrics. There are metrics for average facial proportions, tooth heights and widths, and the degree of tooth reveal when the lips are at rest and during movement," Bakeman elaborates. "The patient's presenting situation can be compared with the established norms and then a treatment plan can be developed that moves the outcome toward a more accepted and pleasing result."
There are also functional and biologic considerations that must be taken into account anytime the teeth are altered, Bakeman adds.
"Restoration of facial form and dental esthetics is integral to establishing oral function," explains Thomas J. Balshi, DDS, PhD, a prosthodontist and director of the Institute for Facial Esthetics. "For example, patients suffering with advanced periodontitis often present with teeth that have shifted into nonfunctional and unattractive positions, necessitating not only restoration of oral function, but also dental esthetics and facial balance."
Relationship to Function
The musculoskeletal and occlusal elements of smiles not only affect the function of smile rehabilitations, but also the longevity of the esthetic results.
"When I think of function, I think of all aspects of occlusion," Kois asserts.
According to John C. Cranham, DDS, clinical director of The Dawson Academy, clenching and grinding posterior teeth and sliding into excursive movements triggers a neuromuscular switch that activates the masticatory muscles. When posterior teeth are out of contact, muscle activity is lower.
"When we create smiles, we must not only focus on the contours and tooth positions that will produce a great esthetic result, but we must also incorporate contours that will ensure a peaceful neuromusculature," Cranham says. "If we begin with a functional and stable occlusion, muscle activity will be lower, and patients will have increased function during mastication."
Cranham explains that establishing a masticatory system with peaceful neuromuscular function is predicated on satisfying five requirements for occlusal stability. Combined, they help to ensure that esthetic restorations and everyday dentistry remain stable and comfortable long-term.
These requirements include centric stops on all teeth (ie, equal intensity and even contacts throughout the mouth when the jaw closes) and anterior guidance in harmony with the envelope of function (ie, sufficient steepness from the lingual contours of the anterior teeth to disclude the posterior teeth when the jaw moves into protrusive left or right lateral movement). However, there should be sufficient concavity to ensure that the lower incisors do not hit the upper front teeth as the patient chews and speaks. Other requisites include immediate disclusion of the posterior teeth-except perhaps in patients who are Class II, have weak canines, or have an implant in the canine position for which group function is utilized-and no posterior tooth contact in protrusion on the balancing and working side.
These musculoskeletal and occlusal requirements, combined with parameters for how lost teeth and tooth structure should be replaced, influence treatment planning as well as prosthodontic and material selection considerations. Likewise, the patient's vision for their treatment outcome affects occlusal considerations.
"With the development and advancements in osseointegrated dental implants and esthetic, functional implant-supported restorations, patients can benefit from fixed treatments tailored to their esthetic preferences," Blashi says. "The basis for long-term predictability lies in the stability offered by the osseointegrated implant fixtures that serve as the foundation for the anchored prostheses."
"The key question I ask every patient is, ‘Are we restoring the smile you used to have, or creating a smile you never had?'" says Kois. "Restoration to create a smile they never had is more difficult because we need to understand their personal preferences (ie, subjective preferences) or vision of what constitutes an attractive smile, and these may not always follow the natural guidelines established by understanding anatomical structures."
Bakeman notes that historical photographs can be helpful in communicating a patient's previous look, but creating a smile the patient never had often involves more complex, multidisciplinary solutions. The restorative team should communicate what is achievable and where there may be limitations.
Nonetheless, because a smile is personal, individual preferences must be clarified and then achieved whenever possible; otherwise, dentists will not be successful, even if they, as professionals, consider the restored smile outcome to be attractive, Kois explains.
"As part of a systematic approach, the patient's vision and individual preferences must be thoroughly understood," Bakeman elaborates. "Patients may desire subtle details, such as a midline diastema or greater dominance of the central incisors, that differ from the accepted norms but satisfy their vision."
In other instances, the desired results may be more dramatic. Consider, for example, that tooth loss and subsequent loss of alveolar bone is a significant etiologic factor in the aging appearance of the face. Balshi elaborates that as patients age and the physiologic process of bone resorption continues, vertical dimension diminishes, and the mandible autorotates anteriorly and superiorly on closure.
"This often creates the appearance of sadness in the frontal view," Balshi observes. "In the profile view, the chin tends to appear closer to the tip of the nose."
Providing that there is sufficient bone width, reconstruction of the atrophic mandible and rejuvenation of facial and smile esthetics can be accomplished with dental implants, Balshi says.
"For fixed, partial dentures or any time we are replacing missing teeth, we are dealing with a potential loss of anatomic structure that may need to be addressed in order for the smile to be restored successfully," Kois explains. "This is especially true if the teeth were lost following an accident, because we are not merely restoring the smile, we are also helping to eliminate the memory of the accident."
To design and prescribe esthetic restorations, dentists must have a thorough knowledge and understanding of all aspects of smile rehabilitation and use a systematic, step-by-step approach when developing a treatment plan, Bakeman explains. There are a multitude of details-such as the relationship of the dental midline and occlusal planes to the face, tooth silhouettes, buccal corridor fullness, tooth shade, axial inclinations, and the size of the teeth with respect to the lips-that must be considered. Gingival architecture is also influential.
"Some details have a subtle influence and others are much more influential on the final outcome," Bakeman elaborates. "To prioritize considerations and prevent oversight, it is helpful to approach treatment planning systematically."
Among the considerations are restorative material selection, restoration type, and fabrication method. Significant material characteristics that must be considered when fabricating restorations for esthetic and functional smile rehabilitations include color stability, translucency, fluorescence (ie, interaction with light waves), and strength, Chu says.
"Many companies now manufacture ceramics and composites that demonstrate a certain level of fluorescence, which I think is important," Chu observes. "Other significant improvements in material characteristics-particularly in lithium disilicate and translucent zirconia-offer the strength dentists are looking for, especially for monolithic restorations, yet still provide very good esthetic outcomes."
Advancements in monolithic restorative materials have eliminated the need for layering, which avoids some of the previous problems associated with the fracturing of veneering materials, Chu adds. This contributes to the longevity of esthetic smile rehabilitations.
However, according to Gregg Helvey, DDS, CDT, adjunct associate professor at Virginia Commonwealth University School of Dentistry, it is essential that dentists educate themselves about the indications of restorative materials and where restorations fabricated from them can be placed predictably. Because such parameters are based on properties like flexural strength, fatigue, and fracture toughness, many dentists rely on their laboratory technicians for recommendations.
"If the restorative work follows the manufacturer's guidelines, and the case is matched with the ideal material composition for its intended indication, then restorations should be esthetic and long-lasting," Helvey explains. "It's only when we take short cuts and use methods that are unproven that we can get ourselves into trouble."
For example, leucite-reinforced ceramics, which demonstrate flexural strengths of approximately 125 MPa, exhibit great optical properties and esthetics and function well as veneers on anterior teeth, Helvey says. On the other hand, they lack sufficient strength to function predictably as a full-coverage crown in the second molar region, where compressive forces from mastication are so much higher. "It may look good, but it's not going to function very well," Helvey adds.
In the case of lithium disilicate (eg, IPS e.max®, Ivoclar Vivadent), manufacturers do not recommend its use for bridges that are replacing first molars, Helvey continues. This material is indicated for bridges placed anterior of the first molar. Many engineering principles are taken into consideration when determining material indications, which is why he says some materials work better in the anterior but not as well in the posterior.
Because dentists may prescribe a particular restorative material to satisfy specific case requirements, it is essential to verify that the restorations they've requested from their laboratory are, in fact, fabricated from what they're expecting. Helvey notes that seven states currently have regulations requiring dental laboratories to submit to their dental office clients a verification of the restorative material used, where it was obtained, and what it is composed of for each case. In other states that do not have such regulations, laboratories could theoretically purchase cheaper materials with questionable compositions and unpredictable properties for fabricating restorations, ultimately gambling with the long-term results.
Also impacting restorative outcomes is the resolution (ie, details) of 3D printed models from which some restorations are made, cautions Chu. Although advancements in digital technologies have contributed to the use of monolithic restorations, these tools are not foolproof, he says. Dentists have the ability to scan teeth with extreme accuracy, but the resolution of some 3D printed models is poor, particularly in the margins. This ultimately leads to discrepancies in fit when restorations are tried on a master stone model that demonstrates a higher resolution.
Bringing it all Together for a Dazzling Result
"Dentists can develop a smile design, but until we take it to the patient, we don't have a true understanding of the impact the changes will have and whether they will fulfill all of the objectives," asserts Bakeman. "The design phase must be taken to the patient for final approval."
This can be accomplished using a mock-up or provisional restorations, she says, and it is at this stage that the restoring dentist, patient, and laboratory technician can appreciate the balance of the teeth with the face, lips, and gingiva.
"The laboratory technician is a very critical member of the team-equal to a surgical colleague or other professional colleague whose expertise is required to obtain the ideal results," asserts Chu. "Their input is essential, particularly because the provisionals are basically the blueprints for the final restorations by today's standards."
It is only in coordination with the face, lips, and gingiva that the restorative team can recognize balance and harmony, implement adjustments that fulfill an individual patient's vision, and be certain they have done so, Bakeman says.
"Communication is critical," Bakeman adds. "As the saying goes, ‘The fallacy of communication is that we think it is happening.' We must work hard to address all details and meet expectations."
She adds that patients must be pleased with the mock-up or provisional stage from an esthetic and functional perspective, after which it is the responsibility of the restorative team to duplicate the design with the final restoration.
If an esthetic, indirect restoration requires modification, dentists can execute those adjustments and return the restoration to the same polish and finish that it had when they received it from the laboratory. Doing so may require a glazing oven or a specific system of polishing compounds and wheels, so Helvey suggests either attending continuing education courses or spending time with the laboratory technician to learn exactly how to do it. But, it's worth the effort, he says, because the ability to make these modifications and then return the restorations to their ideal polish chairside saves time and helps avoid patient frustration and disappointment.
Moving Beyond The Mouth
Traditionally, when enhancing the smile and developing dental esthetics with esthetic lip and smile lines, dentists have been trained exclusively in treating the teeth and gingiva. In fact, many esthetic dentistry educators have taught that if veneers are only placed on four teeth, the patient will have nice looking teeth, but if veneers are placed on 10 teeth, the patient will have a great looking smile.
According to Louis Malcmacher, DDS, president of the American Academy of Facial Esthetics (AAFE)-a leading medical and dental continuing education provider specializing in live patient training courses on botulinum toxin (eg, BOTOX® Cosmetic), dermal fillers (eg, Juvéderm®, Restylane®), solid filler PDO (polydiaxonone) threadlifts, and temporomandibular joint (TMJ)/orofacial pain trigger point injections-nothing could be further from the truth. Rather, a smile encompasses the teeth, lips, and all of the soft tissue in the mid and lower face, if not the entire face.
"The teeth do not exist in a vacuum," Malcmacher asserts. "What good is a full mouth of great looking teeth if they are surrounded by thin, scraggly lips; downturned oral commissures; deep nasolabial folds; and a face that has dropped due to bone loss and especially, collagen loss in the mid-face?"
Following best practices for designing smiles and creating esthetic restorations, historically, dentists have worked hard to harmonize the restorations to the lips and peri-oral areas, often without thought to the possibility of redefining those structures to create the perfect smile, he says. As a consequence, a great deal of irreversible dentistry has been performed that needed to be accomplished in order to achieve the desired esthetic effect. "It was a backwards approach, and a real shame," Malcmacher says.
Today, however, when educated in the proper techniques-such as those taught by the AAFE-dental professionals have the tools to create beautiful lips as well as lip and smile lines and achieve the best results using botulinum toxin, dermal fillers, and solid filler PDO threadlifts. According to Malcmacher, this approach often conserves tooth structure, maintains the health of the dentition, and offers better esthetic treatment outcomes than ever before.
With injectable therapies for total facial esthetics, dentists can redrape, lift, and tighten sagging facial skin to raise the upper lip, reveal more teeth, smooth the skin, volumize the mid-face, fill the lips to esthetic dimensions, and create the proper lip and smile lines needed for total facial esthetics. With proper training, dental professionals can now utilize the best techniques and tools available to control all aspects of dental and facial esthetics and achieve optimal esthetic patient outcomes far and above what they could accomplish in the past (Figure 2). Another advantage of using injectable therapy is the ability to refine and correct soft-tissue discrepancies both intraorally and extraorally after seating the case to create the perfect esthetic smile rehabilitation, Malcmacher says.
"When it comes to enhancing true, total facial esthetics, dental professionals are perfectly positioned because, once they are properly trained in the use of injectable therapies, they can treat the entire face, including the teeth," explains Malcmacher. "Dental esthetics are facial esthetics, and facial esthetics are dental esthetics-they go hand in hand."
In addition to understanding the indications for and capabilities of each injectable therapy (see Table), education and training in this realm of smile and facial esthetics involves definitive protocols for when to use Botox, fillers, and solid filler PDO threadlifts, depending on the individual case. Malcmacher explains that sometimes, cases must be staged between the use of these injectables, temporization, and final case seating to ensure an ideal combined outcome of esthetic dental restorations and esthetic facial enhancement.
"In addition, Botox has dramatically changed the way that dentists address TMJ issues, headaches, migraines, and orofacial pain therapy," Malcmacher adds, noting the need for state-of-the-art training and use of the best techniques available to achieve therapeutic treatment success. "Botox, combined with trigger point therapy, now allows every dentist to successfully treat patients suffering with TMJ/orofacial pain-conditions that have frustrated both dentists and patients for the past 40 years."