Gingival Prosthesis - A Review

INTRODUCTION

During the past few decades, esthetic and cosmetic dentistry has attracted the interests of both the clinicians and the patients alike. Achievement of an optimal long term esthetic result is a major challenge that the clinicians face today. Facial harmony in proportion to the soft tissues, gingival line, smile line and the anatomic crown have been thoroughly discussed in the literature^1-4. It is an even greater pain-staking task to restore the pink and white proportions intra-orally. The gingival tissue surrounding the restoration must be similar to that of the healthy adjacent teeth to create an illusion of natural dentition⁵. Deficient gingival architecture can be observed around teeth, osseointegrated implants and even in edentulous ridges. 

REASONS FOR LOSS OF THE GINGIVAL TISSUES

A vast number of factors have been mentioned in the literature for gingival tissue loss resulting in esthetic problems. Gingival recession can be present in the normal periodontium or may be a part of periodontal disease process⁶. Some of the predisposing factors for the development of gingival recession include: bony dehiscence⁷ , high frenum attachment⁸ , calculus^9-12 , periodontal diseases¹³ , mechanical trauma(improper tooth brushing¹⁴ and frequent impaction of 6 extrinsic objects) . Other factors include chemical trauma due to cocaine use¹⁵ , orthodontic tooth movements¹⁶ , sub-gingival restoration margins¹⁷ , smoking^18-21 and improper design of a removable partial denture²² . Following gingival recession many complications may occur, the most common being that of tooth hypersensitivity in the cervical region. Other problems include root caries, plaque retention, loss of esthetics and tooth abrasion. “Dark triangles”²³ may form between the teeth which may result in unanticipated expectoration and escape of air during speech. This in turn may lead to phonetic problems. Surgical gingival procedures, trauma and traumatic tooth extractions²⁴ , ridge resorption, congenital defects and parafunctional habits that compromise the existing soft tissues lead to a loss in gingival levels. In addition, dental implant placement is associated with some bone loss that may subsequently cause gingival recession upon complete healing²⁵ .

TREATMENT MODALITIES FOR GINGIVAL REPLACEMENTS

Alveolar bone and gingival tissue defects can be restored by surgical approach during the pre-prosthetic phase. The surgical options include: auto-connective tissue transplantation, auto-bone graft, bone substitute-transplantation and papilla recontouring²⁶ . Despite recent developments in periodontal and peri-implant surgical regenerative procedures, completely, satisfactorily and predictably re-establishing the hard and soft tissue contours is an ambitious task, creating dilemmas in patient management.

Surgical procedures have some setbacks and disadvantages for the patient. These include unpredictable outcome, patient discomfort, surgical costs involved and a varying duration of healing time involved.

Gingival replacement prostheses have historically been used to replace lost tissue when all other methods (e.g., surgery or regenerative procedures) were considered unpredictable or impossible²⁴ . With this method, large tissue volumes are easily replaced and the results are more predictable. Surgical procedures are not involved thus eliminating discomfort and prolonged healing duration. A try-in procedure may also be incorporated in the treatment plan to achieve patient's approval. 

GINGIVAL PROSTHESIS

Although no particular definition of gingival prosthesis exists in the Glossary of Prosthodontic Terms²⁷ , it was first mentioned in the dental literature by Schweitzer²⁸ , who called it the artificial resin gum mask²⁹ . It is defined as an appliance used to replace the gingival contour in an anterior sextant, where, following periodontal surgery, the teeth have longer clinical crowns and the interproximal embrasures are open³⁰. Several synonyms have appeared in the literature for the prosthesis from time to time. It has been called as labial veneers³¹ , gingival facade³² , gingival epithesis³³ , labial flange prosthesis³⁴ and “party gums”²⁴ .

Gingival prosthesis can be either of a fixed (called a multiple pontic design³⁶ ) or removable type. Despite the fact that a removable prosthesis allows replacement of large tissue volumes and facilitates creation of adequate bulk for esthetic appearance, it does have some mobility. This requires additional retentive features to be incorporated in the prosthesis to impart a psychological advantage to the patient. Removable prostheses are usually made of silicone or acrylic and thus are porous in nature, staining easily. It is susceptible to inhalation and ingestion. Easy access to interproximal embrasures facilitates oral hygiene procedures unlike in the fixed prosthesis. As tissue changes set in, it may be easily adjusted. In time, the prosthesis may be worn out, damaged or lost and fabrication of a secondary prosthesis may add to the cost of the original prosthesis. The patient is more compliant to the fixed counterpart, it being more stable, retentive and presenting minimal wear (glazed porcelain) or damage.

Apart from acrylics (self-cured^32,35 , heat-cured^24,33 , thermoplastic acrylics) and silicones (Molloplast B²⁴ , soft liners), porcelain based materials^24,36 , composite resins³⁷ and copolyamides³⁸ have all been used for the fabrication of the gingival prostheses. Recently, visible light-cured materials and flexible synthetic products have also been used for fabrication of the prosthesis. Acrylics are usually hard and rigid and contribute to patient discomfort but finishing and polishing is satisfactory unlike in silicones. There might be pain on removal and insertion of the prosthesis and chances of damage are high. Acrylic materials may leave a small gap around the teeth that may collect food debris leading to caries or social embarrassment. Silicones being porous accumulate stains and plaque easily. Damage and breakage to the prosthesis is minimal. Composite resins are susceptible to discoloration, marginal fractures and wear. Pink ceramics are biocompatible, color stable and have a non-porous surface that prevents plaque adherence better than composite resin⁶.

INDICATIONS OF THE PROSTHESIS

The prosthesis covers the exposed root surfaces of the teeth, thus improving esthetics, reducing hypersensitivity, limiting food impaction in the embrasures and also expectoration during speech. The prosthesis finds use in various other situations as well. It is used in the replacement of maxillary and mandibular anterior teeth where there is a deep bite situation³⁴ or palatal coverage is not tolerated by the patient (strong gag reflex). The prosthesis may be utilized as a splint for stabilizing mobile teeth³⁰ . It can be even used in therapeutics for keeping drugs for mucosa in close contact with the gingival so that systemic absorption/intake is lesser, for example, Adcortyl A in Orabase for desquamative gingivitis³⁹. The prosthesis may be included in the complete treatment of a patient or in transitional phases pending treatment with a fixed or a removable prosthesis. If fabricated with some bulk, the gingival prosthesis may be used for increasing the lip support and fullness where required, enhancing esthetics⁴⁰.

CONTRAINDICATIONS FOR THE PROSTHESIS

The gingival prosthesis may not be used in cases with poor plaque control, unstable periodontal health and a high caries activity. Patients with acrylic or silicone allergy and heavy smokers are not recommended an artificial gingival due to likelihood of surface staining. Physically challenged patients who may not be able to remove or replace the prosthesis are not advised to wear the prosthesis. In particular, the gingivalcolored ceramics have certain specific contraindications. They are not used to restore massive bone loss associated with extensive trauma, bone resection or cyst removal. When the adjacent teeth present compromised esthetics with long crowns and black embrasure spaces that are not planned to be restored, gingival-colored ceramics are not beneficial. When the use of gingival-colored ceramics would adversely alter the emergence profile of a crown, or when it would diminish the patient's ability to maintain meticulous oral hygiene, it should not be used.²⁵ 

RETENTION MECHANISMS OF THE PROSTHESIS

Interdental undercuts have been proposed to be the primary method of deriving retention for the prosthesis²⁴. Capillary action of the saliva also plays a major role in close adaptation of the prosthesis with the underlying gingiva. Pressure from the underlying lip musculature has also been proposed as one of the retentive mechanisms for the prosthesis³². Precision attachments⁴¹ , magnets²⁶ and adhesives have all been used to enhance retention of the prosthesis. Custom-fabricated pins on the fixed partial denture have been used to retain the removable gingival prosthesis by Cura et al.³⁵ Gaussen attachment has also been used where along with the gingival prosthesis, a pontic for a fixed partial denture is to be given²⁴. This attachment consists of a curved slot (accessed from the buccal aspect), containing a spring-loaded ball. A curved metal wafer is processed into a heat-cured acrylic flange. The terminal end of the wafer has a dimple to engage the internal ball and provide retention.

FABRICATION OF THE ARTIFICIAL GINGIVAL REPLACEMENT

Prior to rendering treatment, a clinician must identify the causative factors for gingival tissue loss and eliminate them. If initial periodontal treatment had been performed, 2-3 months should be allowed after the surgery so that the gingival tissues are stabilized before the mask is constructed. Scaling and root planing are accomplished if required to eliminate plaque retentive factors.

Method for fabrication of the prosthesis was described by Greene who described a two-stage impression technique¹¹. After primary irreversible hydrocolloid impressions were made, a special tray was fabricated located on the buccal cusp tips and incisal edges. Lingual embrasures were blocked out with putty silicone. A block-out technique for open gingival embrasures can be handy⁴². Wax pattern was made on type IV stone cast. For natural appearance, gingival stippling in wax can be performed using a stiff-bristled brush or a synthetic sponge³¹. A diagnostic waxing with pink wax is always better, especially in case of fixed prosthesis to predict the definitive result.

Flasking and processing are carried out conventionally depending on the material used, silicone or acrylic. 

MAINTAINENCE OF THE PROSTHESIS

Although the fixed prosthesis has minimal maintenance protocol, its removable counterpart requires meticulous attention. Plaque control of the teeth is important so the artificial gingiva is cleaned everyday with soft brush and a mild detergent. The patient is advised not to wear the prosthesis at night for fear of ingestion or inhalation. Frequent smoking, tea/coffee and alcohol consumption is discouraged. Regular application of topical fluorides is recommended in high caries risk individuals.

LONGEVITY

The service life of the prosthesis depends mainly on the maintenance by the patient. Greene mentioned 12 months whereas Kapari recommended that the prosthesis be replaced 2 to 3 times a year³⁵.

FUTURE TRENDS

With the success of bone regeneration firmly established, the new frontier topic for dentistry is soft tissue regeneration. For decades attempts have been made to develop clinical procedures which might lead to predictable periodontal regeneration. Guided tissue regeneration was the first attempt to achieve concordance between biological principles and clinical practice and has come to be considered the “gold standard” upon which to compare regenerative technologies. The use of enamel matrix proteins and certain growth and differentiation factors has helped achieve satisfactory results in periodontal regeneration.

Gene therapy is a new approach for the treatment of human diseases. In periodontal regeneration, gene therapy seeks to optimize the delivery of agents such as growth factors to periodontal defects so that the limitations associated with topical applications can be overcome. Researchers are developing a three-dimensional connective tissue matrix from porcine origin that could be used as grafts in order to augment soft tissues.

In the near future, periodontal regenerative therapies will involve nanoscale science⁴³ and moldless manufacturing technology called as rapid prototyping⁴⁴ or solid free-form fabrication⁴⁵. The advancement of such technology might also make it possible to produce patient-specific cell-scaffold constructs with optimal distribution of cells and high vascular permeability⁴⁶.

CONCLUSION

It should be recalled that the simplest treatment that will satisfy the needs of the patient is the best treatment, and less 37 complex treatment is usually more predictable. Gingival replacement is often a component of comprehensive prosthodontics, requiring interdisciplinary knowledge. Whatever the cause of gingival loss, replacement may be achieved by either surgical or prosthetic means. Esthetically pleasing and anatomically correct tissue contours may be achieved surgically where small loss in tissue volume is involved. Large volume loss may be treated using gingival prosthesis. Many materials mimicking the gingival tissues are available, but the best option would be if gingival tissues could be regenerated and replaced. With advances in gene therapy and nanotechnology, this goal seems not so far away.