Chapter 24 Complete Denture Esthetics
Because the goal is meeting the esthetic desires of patients who have lost their teeth, complete dentures are probably the most relevant area for esthetics in dentistry. Patients who are completely edentulous generally have poor self-esteem, generalized soreness, and difficulty in effectively chewing many foods. With complete dentures, a patient’s self-esteem and self-worth can be improved to such a degree that these deprived people will feel much better about themselves and become a part of society, able to communicate easily. Some surveys have estimated that approximately 15% of the global population is edentulous. In the United States alone, this accounts for 36,000,000 Americans, or approximately 12% of the U.S. population. When a patient loses all of his or her teeth, one of the options is complete denture therapy, provided that the patient is a good candidate. The practitioner must take into account not only function, but how the final prosthesis will fill the void from the loss of teeth and much of the surrounding bone structure. Replacing the void from inside the oral cavity will assist in recreating (or shaping) the outer facial contours by restoring the inner structure, thereby replacing the mass supporting the external muscles and allowing an overall natural smile to be presented to the patient and his or her beholders.
The history can be prefaced with a brief quote by Dr John Anderson, who once said, “If you’re going to quote what I said or write, please put a date on when I said [May, 1980] or published it.” I think that we are all aware that education is always in motion. In the days of George Washington, dentures were carved out of wood, stone, and ivory. The dentists of that time sculpted and shaped teeth by looking into people’s mouths and matching the natural dentition of most humans. Over the years, numerous sources pertaining to the art and science of denture creation were made available to the profession to aid in fabricating complete dentures. In the last century, many in the profession were guided by the influence of great professors such as Dr Carl Boucher (and others of the same philosophy) who authored textbooks on complete denture fabrication. However, dentists in other parts of the country chose to follow alternative methods and techniques with somewhat different opinions for preparing dentures. Public curricula were generally based on one or two of the major textbooks written by the most prestigious professors of their time. The textbooks documented methods that they had personally performed, not once or twice, but hundreds of times. This was essentially the first evidence-based dentistry.
Beginning in the 1990s, compilations of many of the major textbooks and published articles over the previous 50 years began to be published to create an additive effect, whereby teachings began to be modified by combining parts that lead to predictability. The earlier, less predictable denture outcome, compounded with patient dissatisfaction, influenced an evaluation of all the current methods and an overhaul based on an analysis of each reported problem, with development of a solution with a consistent predictable result. New protocols and methods were developed that incorporated improved materials and a better understanding of the effects of the aging population’s role in prosthetic dissatisfaction. It was even more important to apply the current understanding of the entire stomatognathic system when creating a valid solution to the reported problems.
Historically dentures were predominately designed according to valid anatomical landmarks. Different methods of designing a prosthesis were employed based on different landmarks. For example, the boundary of the upper denture base between the hard and soft palates and around the tuberosities was designed mostly from anatomical landmarks. From approximately the 1940s to 1980s, the use of landmarks not only was accepted but had reasonably successful outcomes. However, as time passed, the life span of the population began to increase significantly owing to improved healthcare, a better understanding of how factors affecting the body also affect health, and the new age of pharmaceutical drugs. Even though the predominant anatomical approach was extremely effective for a time, the fact could not be avoided that denture procedures needed to be reevaluated and updated to address modern realities—realities that frustrated both dentists and patients. Considering that life expectancy at the time the majority of the textbooks were published (from the 1940s to the 1980s) was close to 16 years less than today’s average life expectancy, the need for updated procedures can be easily understood.
So why did it take dentistry so long to update the complete removable prosthesis process? Because the mission of dentistry was to stop total edentulism in the world by research. Dentistry began to flourish in other areas, with new ideas and techniques, new materials and machinery, and better education in ways to maintain a patient’s dentition. At that time, dentistry was on the right track to try to maintain and educate patients on how to keep their teeth over their lifespan. No one today ever anticipated that there would be, in the year 2011, 36 million Americans who are edentulous and are denture wearers. It was thought that by improving both education and new technologies, dentistry would be able to defeat the loss of total dentitions within the population. However, what was not taken into account was that as patients grow into their 70s, 80s, and 90s, the dentition may wear out, resulting in an increased number of denture wearers in the aging population but not necessarily because of loss of more teeth. In all fairness, dentists need to look back at the forefathers of dentistry and thank them for all they did to assist their students, who have grown into the new age of knowledge, science, and evidence-based medicine.
So what can be taken from this? Creation of dentures based on anatomical and functional musculature and other physiological aspects results in more predictability and less dissatisfaction. A purely singular concept of anatomical design may have worked nicely on a 50-year-old who still had good muscle tone; however, the same design might not have been appropriate for an 80-year-old because of the loss of muscle tone and alterations in anatomy, physiology, and function. Some patients, often those taking certain medications, may have artificially lost muscle tone and may also have had complications of xerostomia, or dry mouth. These particular situations effectively resulted in less predictability until dentists began to understand that older patients have a different set of rules than those that applied when they were much younger.
In the last century the anatomically designed prosthesis was the standard, and in making definitive impressions, border molding procedures were predominantly dictated by the dentist. This method did not necessarily take into consideration all the possible functional maneuvers patients may perform when in their own environments.
For example, patients will suck strongly through a straw, smile a moderate to full grin, and vigorously laugh, which will alter the shapes of the peripheral anatomy of both the maxillary and mandibular sulcular form. It is also understood today that the post-palatal zone is asymmetrical, and the maneuver taught by Valsalva was enhanced by being able to use impression materials that respond to resistance 10 to 12 mm (a viscosity heavy enough to properly measure the degree of forward movement of the soft without the need to have a long posterior perimeter of the tray) and extend beyond the tray border without distortion. This allows the practitioner to use an impression tray that is significantly short of the functional zone and allows the patient to vigorously cough while the dentist occludes the nostrils with a rigid impression material extending beyond the posterior border of the tray, allowing the soft palate to move forward and thereby shaping the left and right post-palatal zones accurately.
In making a complete denture prosthesis for a patient who has lost all the teeth of both arches, the patient’s vertical spacing must be reestablished. This vertical spacing, among other functions, is what makes the patient look younger or older. Patients with a significant loss of vertical dimension generally will have the lower chin protruding slightly past the upper face. Reestablishing the appropriate vertical spacing will improve the patient’s appearance by decreasing the sunken and aging appearance. This vertical space must be not only esthetically pleasing but also compatible with the typical mandibular joint apparatus, including the muscles of mastication. The outer surfaces of the prosthesis should be built to support the facial muscles, thereby giving the patient a natural, healthy appearance. A patient exhibiting flaccid or very weak muscular tone will generally require a prosthesis cameo surface to fill the horizontal vestibular void, whereas the patient with stronger muscular tone would demonstrate less horizontal projection of this cameo surface.
It is also necessary for the cameo portion of the complete denture prosthesis to be compatible with musculature action to support the facial muscles and decrease food entrapment around and under the natural peripheral borders of the sulcular space. Patients should achieve improved efficient chewing capabilities through appropriate fabrication of the proper cameo prosthetic surface.
The position of the teeth from labio-buccal and linguo-palatal and within the confines of the musculature action of the lips and cheeks contracting inward and the tongue muscle moving forward and laterally outward will guide the bolus of food to remain on the occlusal chewing surfaces of the teeth during mastication. This space is what was described as the neutral zone by Beresin and Schiesser in their 1973 textbook. This is one of the clinical considerations that was not popular from the 1970s to the 1990s as the anatomical approach dominated education. However, it should be apparent that combining the anatomical, physiological, and functional aspects of the muscles, along with the proper spacing between the upper and lower jaws, allows modern dentists to use the ideas of their prestigious forefathers to create a new model for the complete removable prosthesis.
Patients who should not receive complete removable dentures include those who are psychologically phobic about having any foreign objects placed into the oral cavity. Also, patients who have extremely sensitive gag reflexes may not be appropriate candidates for a full maxillary prosthesis.
Patients who do not want to wear any type of detachable prosthesis are not candidates. Patients with chronic parafunctional habits, including erratic tongue movements, have severe difficulty with any type of removal detachable prosthesis, as patients with chronic erratic spitting problems and those who cannot control their tongue movements and have habitual movements of both the tongue and the jaw. Such parafunctional habits generally are considered a contraindication for a complete removal denture. Patients who have neurological deficiencies, such as those occurring after a stroke, involving greater numbness on one side than on the other have difficulties in chewing, especially with any appliance that is not secured in the mouth. Patients who indicate that they want only teeth that “do not come out” are not good candidates and should not be encouraged to have a complete denture unless they are willing to have psychological help to alter their desires.
Also among the contraindications are patients who are chronic bruxers and who generally grind their teeth with heavy forces. These patients are liable to breaking the denture and can also sustain severe tissue abrasions.
The materials used in complete removable prostheses are generally acrylics or methyl methacrylate. Generally the bases of the prosthesis are made of acrylic resin and the denture teeth of a very similar acrylic, which aids in chemical bonding. Other choices of materials for denture bases include urethane materials, which do not have any free monomer and may be indicated for patients who have hypersensitivity or allergic reactions to acrylic materials. Options for the teeth include composite and porcelain materials. It is generally thought by many practitioners that if the occlusion is fully balanced, then porcelain teeth have a much longer wear factor. However, there is also controversy because porcelain teeth can sustain damage if the occlusion is not always in balance. Generally, porcelain teeth are more esthetic because they can be layered and have a more crystalline or toothlike appearance. In the profession today, the composites, even though they have been reported to fracture, are being improved and have properties that fall between those of acrylic and of porcelain. Acrylic teeth generally are relatively strong when they are chemically cross-linked with fibers. Thus fractures are less likely than with porcelain, which is a much harder material—consider, for example, a ceramic floor versus a tile floor. Ceramics generally have a higher propensity for cracking but are more natural in appearance; the double cross-linked fibered acrylic teeth have less chance of fracture than porcelain teeth.
It is extremely important for the dentist and the patient to have a mutual understanding of the end result. Giving the patient appropriate alternative treatment is of the utmost importance in allowing him or her to choose from the many options available in dentistry today. It is important in discussing treatment with patients who have lost all of the teeth owing to either periodontal disease or caries that the dentist make the patients aware that even with an artificial prosthesis, they may still have some difficulty unless they are able to change health and hygiene habits. Patients should also be aware that once the prosthesis is completed, maintenance will still be necessary. It is both ethically and professionally appropriate for the dental practitioner to discuss with the patient the financial considerations associated with the type of prosthesis the patient is choosing. If a patient receives a complete prosthesis on the maxillary arch and a partial prosthesis on the mandibular arch, the patient will still be responsible for maintaining the remaining teeth on the mandibular arch. Patients should be made aware of the fact that once the lower teeth are deemed to be non-restorable, then the lower prosthesis will need to be either added to if possible or replaced completely, depending on the severity of the failing dentition.
It was thought at one time that patients with severe bone loss were not candidates for a complete removable prosthesis. However, it has been shown that even with bone deficiencies patients can wear a complete removable denture if the practitioner understands that he or she must take into account the anatomy, physiology, function, and esthetic considerations in combination and must use a tested protocol to fabricate the prosthesis. When the prosthesis is created in this fashion, the patient will have the best opportunity for a successful result. It has also been thought by many practitioners that implants will “fix” denture problems; however, this has not been the overall consensus. Patients who have not been happy with a complete denture prosthesis and are then converted to an implant-retained prosthesis report satisfaction owing to the retention of the prosthesis. However, over the last 20 years, patients who were initially satisfied with the conversion have made other complaints. These complaints generally have involved food entrapment in and around the prosthesis, breakage of the prosthesis, maintenance of the prosthesis, and an unnatural feeling with the prosthetic device in the mouth.