Complete Dentures
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ANATOMICAL FEATURES - MAXILLA
The alveolar ridge bone functions to retain and support teeth. If teeth are lost alveolar ridge resorption occurs. The maxillary ridge resorbs in a superior and posterior direction, the mandible in an inferior and anterior direction. Ridge resorption results in an irreversible loss of bone affecting denture support and retention.
The vibrating lines are imaginary lines indicating the boundary of the moveable and the relatively immovable tissues of the palate. This landmark is used to determine the posterior border of the maxillary complete denture, termed the posterior palatal seal (post dam), which varies in position and depth from patient to patient. It is fabricated to place pressure on the displaceable tissue near the junction of the hard and soft palates aiding in the retention and preventing food impaction. The post dam has to compensate for the movement of the soft tissues during speech and mastication, as well as compensating for the shrinkage of the acrylic resin during denture base processing.
The posterior palatal seal runs from hamular notch to hamular notch, and lies between the anterior and posterior vibrating lines. Manual palpation and phonetics (“Ah” sound) are used to confirm the correct anatomical location of the post dam. The anterior outline is formed by the “Ah” line. The posterior outline is formed by the anatomical junction of the hard and soft palate (corresponds with the end of the posterior nasal spine).
In the zone 3mm bilateral to the midline, the posterior palatal seal is scored 0.5mm deep into the cast. Beyond this middle zone extending all the way to the medial boundary of the pterygomandibular (hamular) notch, the seal is 1.5mm broad at its base. If the beading is too deep it will cause unseating. If the seal is positioned too far posteriorly it can cause tissue irritation, initiate a gagging reflex, and decrease retention. If the seal is positioned too far anteriorly it can lead to tissue irritation and decreased retention. Removal of the palatal seal will almost certainly lead to treatment failure.
Fovea palatini are a group of salivary glands located just posterior to the vibrating line. They can usually be identified on a cast and used as a guide for the position of the posterior limit of a maxillary denture.
Limiting structure of the maxillary denture:
- Anterior – The labial and buccal vestibules, extending in the posterior aspect to the hamular notches on each side. Adequate filling of this region provides lip support.
- Posterior limit – the junction of the movable and relatively immovable soft tissue of the palate, termed the vibrating lines. Coincides with a line drawn from hamular notch to hamular notch, about two millimeters anterior to the fovea palatini.
ANATOMICAL FEATURES - MANDIBLE
Limiting structure of the mandibular denture:
- Anterior – labial vestibule. Requires accurate border molding to prevent unseating by the mentalis muscle. Adequate filling of this region provides lip support.
- Anterior – labial frenum. The fibrous attachment of the orbicularis oris muscle.
- Buccal – buccal vestibule. Extends from the buccal frenum to the lateral posterior corner of the retromolar pad. The buccinator muscle extends from the modiolus anteriorly to the pterygomandibular raphe posteriorly and attaches to the buccal shelf and external oblique ridge. Proper extension into the buccal shelf area provides the best support for the mandibular denture.
- Posterior – lingual frenum. The denture must allow for the full movement of the tongue. The genioglossus muscle dictates the extent of the lingual flange.
- Posterior – mylohyoid area. The vertical movement of the floor of the mouth needs to be allowed so as not to damage the thin soft tissue.
- Posterior – retromylohyoid area. Disto-lingually, the extension of the denture is limited posteriorly by the movement of the palatoglossus muscle and inferiorly by the superior constrictor muscle.
- Posterior – distobuccal area. Determined by the position and action of the masseter muscle.
Overextension of the denture will cause displacing forces from the limiting structures, or impinge on soft tissue causing discomfort and trauma. The lingual border molding of a mandibular impression is influenced by the palatoglossus, superior pharyngeal constrictor, mylohyoid and genioglossus muscles. Recall, the pterygomandibular raphe is a tendon separating the buccinator and superior constrictor muscles, extending from the hamulus (thin bony extension of the medial pterygoid plate of the sphenoid bone) to the posterior end of the mylohyoid line of the mandible.
The hamular notch is the depression between the maxillary tuberosity and the hamulus. The distal end of the maxillary denture must cover the tuberosities and extend into the hamular notch (bilaterally). If overextended, the denture will interfere with the pterygoid hamulus and may traumatize the mucous membrane over the pterygomandibular raphe.
The buccinator would be found adjacent to the denture flange in the buccal area, but since the muscle fibers run anteroposterior in a horizontal plane the displacing effect is weak. The stronger masseter muscle is positioned buccal to the buccinator in the disto-buccal area and will push on the disto-buccal flange of the denture, pushing the buccinator into the denture.
STABILITY, RETENTION & SUPPORT
If the patient’s upper denture is unseating when they smile it is probably due to excessive thickness in the buccal flange and buccal notch areas. If the denture is unseating when yawning or opening wide it is likely due to overextension in the disto-buccal flange area. An overextended denture may be interfering with movement of the coronoid process. Tingling or burning sensations in the mandibular premolar area or lower lip may be due to overextension of the buccal flange in the mental nerve/foramen area. If the patient presents with a large amount of residual ridge resorption, the mental nerve/foramen could be very close to the crest of the alveolar ridge. Often, while slowly seating a denture, you can identify overextended borders if you see the soft tissue (say, buccal frenum) move prematurely.
Three critical factors are essential for complete denture success:
- Stability – resistance of the denture base to lateral forces.
- Support – resistance of the denture base to the forces directed towards the supporting tissues. Maximal extension is often sought to distribute occlusal forces over the largest area possible.
- Retention – resistance of the denture base to the forces directed away from the supporting tissues.
In the maxillary arch:
- Primary support – the hard palate and the postero-lateral aspects of the residual ridges (maxillary bones and palatine bones).
- Secondary support – the rugae, maxillary tuberosity and alveolar tubercle.
In the mandibular arch:
- Primary support – the bony buccal shelf and retromolar pad area. The basal bone under the retromolar pad resists resorption.
- Secondary support – residual ridges.
Denture retention refers to the resistance to vertical dislodging forces. The surface of the denture base in contact with the soft tissue is vitally important. It needs to be a polished surface that provides intimate anatomically correct contact with the soft tissues. For full dentures, adhesion mediated by the patient’s saliva is the primary retentive force relied upon. Good adhesion requires maximal surface area coverage, and close adaptation to healthy tissue.
The cohesion of saliva is largely dependent on the quality of saliva. Thicker or low volume saliva is less favorable than thin, watery saliva. A peripheral seal will also create a suction effect that will help to prevent dislodging forces. Undercuts (mechanical retention) and other retentive anatomical features can be utilized with caution. Mandibular dentures do not rely on suction from a peripheral seal for retention, but rely on the stability obtained from covering as much basal bone as possible without interfering with muscle movement. Proper border molding ensures maximal coverage. The buccinator, orbicularis oris and the intrinsic and extrinsic muscles of the tongue help to retain lower dentures.
Occlusal rims are made by adding base-plate wax to a record base. They are used to determine the patient’s vertical dimension of occlusion (VDO, length of face), make jaw relation records, and establish the future position of artificial teeth. In the case of a metal RPD, the occlusal rims are attached to the metal framework. A normal smile line will show about 2mm of the maxillary incisors when the lips are relaxed. This is a good starting reference for determining the vertical length of the upper occlusal rims.
SYNDROMES, IMMEDIATE DENTURES, AND TISSUE MANAGEMENT
Kelly syndrome (Combination syndrome) is a condition caused by a full upper denture opposing a lower partial denture, specifically a Kennedy class I denture. The presence of lower anterior teeth and the absence of the posterior teeth results in significant maxillary anterior alveolar resorption, with an increase in flabby hyperplastic soft tissue in this area. A patient may present with a slowly decreasing vertical dimension of occlusion and exhibit an ever increasing prognathic appearance due to overclosure. Relines and remakes are more often required in response to the uneven pattern of alveolar resorption. Implants are one option to counteract this phenomenon.
Nerve trauma can result from ridge atrophy and poor denture fit. Pressure on the mental foramen can cause a burning sensation along the mandibular ridge. Pressure on the incisive foramen can cause a similar burning sensation on the palatal area.
Immediate full dentures are complete dentures that are delivered immediately following the extraction of any remaining teeth. The patient is saved from a potentially embarrassing period of time with missing teeth. The patient’s existing occlusal scheme can also be duplicated, tongue enlargement is prevented, and the dentures will provide some protection of the extraction sites post-op. The drawbacks of immediate dentures are:
- no anterior tooth try-in is possible.
- construction time and cost is increased.
- the initial fit is less predictable.
Recontouring of the bone of the healing alveolar ridge progresses rapidly for four to six months, only stabilizing around 12 months post extraction. Immediate dentures require increased post-insertion care, and the resorption and remodeling that occurs post-extraction means the dentures are more likely to need relines or even be remade after 6-12 months. Ideally both upper and lower dentures are constructed together. For the most stable result, a 2 step schedule for tooth removal can be used.
- Step 1 – remove all posterior teeth except for the maxillary first premolars and their opposing teeth. This leaves a posterior “stop” to maintain VDO.
- Step 2 – after acceptable clinical healing and bony remodelling of the posterior residual ridges, denture fabrication can begin. The anterior teeth and premolars are extracted and the denture is delivered during the same appointment.
Overdentures are complete dentures that are partially retained, supported, or stabilized by teeth, portions of teeth, or implants. Different types of attachments can be used for overdentures including bars and stud-type attachments. The most important benefit when retaining a tooth root is the prevention or slowing of vertical bone loss by maintaining the loading of the periodontal fibers. Retained roots improve denture retention and allow the patient some proprioceptive feedback during function. It is not always necessary to cover the exposed root surface, but an unrestored or exposed root surface under a denture will be prone to decay.
Rebasing is the replacement of the entire denture base while keeping the original denture teeth in their current occlusal relationship. Relining is the addition or replacement of the surface of the denture base in contact with the patient’s soft tissue, undergone when there is a lack of proper adaptation to the patient’s oral anatomy. Reline materials can be soft (temporary) or hard. A reline would not be appropriate when there is excessive overclosure due to a large loss of vertical dimension. Rebasing or new dentures would be more appropriate.
Cheek biting is often due to insufficient horizontal overlap between the maxillary and mandibular teeth. Care should be taken during the tryin phase. Reducing the facial surface of mandibular posterior teeth can be curative. Inadequate VDO can also cause cheek biting. Tongue biting may occur if the posterior teeth are set up too far lingually.
The maxillary sinuses continually increase in volume throughout life (pneumatization), reducing the distance between the alveolar crest and the floor of the maxillary sinus, and “moving” the maxillary tuberosities downwards, limiting space for a denture.
TISSUE INFLAMMATION
Denture stomatitis describes tissue inflammation often seen in patients who wear dentures, likely associated with poorly fitting dentures and/or poor hygiene. The oral fungus Candida albicans is linked to denture stomatitis. Clinically it can present as inflammation combined with a burning sensation, but discomfort is not always present. The primary treatment suggested is adequate patient education regarding oral and denture hygiene and the correction of denture-wearing habits. The removal of the dentures for a 24 hour period is often enough to return soft tissues to their normal size, shape, color, consistency, and texture. Dentures should be cleaned daily, with a soft brush and non-abrasion detergent or disinfectant. If inflammation is exacerbated by xerostomia a salivary substitute is recommended. A resilient temporary liner can be used to stabilize ill-fitting dentures by providing cushioning. Relining, rebasing or remaking a denture will often be curative.
Candidiasis is seen in patients with soft tissue trauma, poor immune health, or after antibiotic or steroid use. Candida albicans is also often associated with angular cheilitis, especially when there is a loss of vertical dimension. Many antifungal therapies can be useful, including Nystatin oral suspension (60 mL of 100,000 units/mL, 4 mL three times daily), and Nystatin (with triamcinolone acetonide) cream for angular cheilitis (15-g tube, apply four times daily for 14 days).
The most common cause of xerostomia is polypharmacy. There are more than 400 known medications, including antihypertensives, antidepressants, antihistamines, bronchodilators, anticholinergics and sedatives that cause dry mouth. Mouthwashes, alcohol, tobacco and caffeine may exacerbate the problem. Treatments include salivary substitutes, sugarless candies, cough drops, mouthwashes, or medications to increase salivary flow (pilocarpine (Salagen) or cevimeline (Evoxac)).
Inflammatory papillary hyperplasia is frequently seen under ill-fitting dentures, presenting as painless, firm, red or pink nodular growths of mucosa. The patient is often unaware of its presence. Hyperplasia is caused by denture movement or food debri accumulation, and usually found on the hard palate, but can be seen on the residual ridges. The most likely long term soft tissue response to an overextended denture is epulis fissuratum, due to clefts found in hyperplastic tissues. It is also mainly caused by trauma, presenting as painless folds of fibrous tissues. For both these, a smaller lesion may regress if the source of trauma is removed. Surgical intervention may be required for large lesions.
Impaired healing, poor tissue tolerance and expedited bone resorption may be seen in patients with uncontrolled diabetes.
