Palatal Lift Appliance in a Case of Palatal Incompetence Secondary to Motor Neurone Disease

Soft palate: anatomy, innervation and function

The soft palate is the posterior muscular extension of the hard palate. Together they form the roof of the mouth and floor of nasopharynx, and have functions in respiration, speech and swallowing. The soft palate attaches to the posterior rim of the hard palate and has a posteromedial extension called the uvula. The muscles that make up the soft palate are the levator veli palatini, tensor veli palatine, masculus uvulae, palatoglossus and the palatopharyngeus. Innervation comes from the pharyngeal plexus, which takes its motor fibres from the vagus nerve and the cranial portion of the accessory nerve. In adults, the anteroposterior elevation of the soft palate to a level above the palatal plane is accompanied by an increase in length termed ‘velar stretch’, which enables contact of the posterior soft palate with the posterior and lateral pharyngeal walls. This closes the velopharyngeal complex during swallowing and speech.

Velopharyngeal deficiency

Velopharyngeal deficiencies may be classified as either insufficiency or incompetence, on the basis of structural integrity or physiology. Palatal insufficiency occurs when the soft palate is of inadequate length to affect velopharyngeal closure but the movement of remaining tissues is normal. This is normally secondary to structural limitation through developmental abnormalities such as cleft palate or through acquired defects, for example, the result of surgical resection.

Palatal incompetence occurs when velopharyngel structures are essentially normal but the intact mechanism is unable to affect velophayngeal closure. It may be caused by neurological diseases such as myasthenia gravis, cerebral palsy, motor neurone disease or by neurological defects secondary to head trauma or cerebrovascular accidents.

Palatal lift appliance

The palatal lift appliance consists of an anterior/palatal portion that clasps the teeth for retention, and a posterior/palatopharyngeal tail piece that extends to the velum. First advocated by Gibson and Bloomer,¹ the prosthesis displaces the soft palate superiorly and posteriorly to contact the peripheral pharyngeal tissues at the level of normal palatal elevation, enabling closure of the palatopharyngeal port. This aims to eliminate hypernasality and nasal emission of air during the production of oral consonant sounds, and facilitates speech.

In addition, the prosthesis often helps to improve the pronounced gag response that occurs in many patients with palatal insufficiency because of the superior position of the soft palate, which is then not stimulated as much by the action of the tongue. Furthermore, the tongue position and movements are not compromised. Contraindications to providing palatal lift appliances include insufficient retention, for example, in edentate patients, a firm non-displaceable palate such as may occur following radiotherapy, or lack of patient co-operation.

Fabrication

Construction begins with an impression intended to displace the soft palate superiorly. First, a custom tray is made and extended posteriorly. A partial denture framework is constructed around the remaining dentition making the most of any retentive elements useful to resist displacement of the prosthesis. A wire loop or retentive meshwork is added to the posterior border of the framework to cover the anterior two-thirds of the palate and moulded with impression compound to achieve appropriate displacement of the soft palate. The shape is broad posteriorly to support the lateral tissues and resembles a beaver's tail. The extension of the lift should go no further than the middle third of the palate in the area of the levator eminence. A wash-type impression might be used to record fine detail. The lift component is then processed in acrylic to allow adjustments. Elevation is not usually performed in one attempt as adaptation is difficult for the patient, instead the lift may be extended sequentially over multiple appointments with adjustments for comfort and modifications during speech therapy. Close monitoring is usually necessary going forwards to ensure that the lift does not create soreness or ulceration of the palatal tissue and modification may be required over time as the patient's condition changes.

Case report

A 67-year-old male patient with motor neurone disease and palatal incompetence had presented to the Newcastle Dental Hospital restorative department in 2016 complaining of progressive hypernasal dysarthria and prominent gag reflex. He had been seen previously at the hospital in 2009 and an acrylic palatal lift appliance had been constructed but, with tooth additions over time this had become less retentive with effects on speech and swallowing (Figure 1).

He had a Kennedy 3 modification 2 arrangement in the maxillary arch and accepted a shortened dental arch in the mandible (Figure 2). There was an occlusal stop on the right molar and premolars (Figure 3). Erosive tooth surface loss into dentine on occlusal surfaces had previously been diagnosed and stabilized by his referring practitioner, and, as there was no sensitivity or aesthetic concerns, this situation had been monitored rather than restored.

There were patient factors that complicated treatment including a severe gag response and intolerance to laying back in the dental chair, which precluded any complex dental treatment. Treatment focused on prevention, and provision of a new palatal lift appliance of cobalt chrome designed to maximize retention.

Treatment sequence

Alginate impressions in stock trays and primary registration were taken to produce articulated casts for planning and denture design (Figures 4 and 5).

A maxillary special tray was constructed with a wire loop that extended posteriorly to cover the anterior two-thirds of the soft palate, and secondary impressions were taken (Figures 6 and 7).

Following a try-in of a cobalt–chrome framework, a detachable tongue of impression tray base material was added to form a rudimentary lift segment, and further modification of the lift segment was made intra-orally prior to a wash impression in medium-bodied silicone to record detail (Figures 8 and 9). The lift segment impression was then cast using a split cast technique, before being detached from the CoCr framework. A jaw registration and wax try in of the dental segments could then occur (Figure 10). The processed prosthesis was then fitted. Over time, the prosthesis was modified to further optimize the lift effect using greenstick impression compound, but as the palate was raised, the posterior extension required adjustment to prevent ulceration (Figures 11–13).

Discussion

For the patient in this case report, fabrication of an acrylic prosthesis had been sensible in the first instance, both provisionally, to test tolerance to a lift prosthesis, and for ease of sequential extension over the palate. Over time this had lost retention as further teeth had been extracted and added to the denture component. Because the patient was known to be able to tolerate a distal extension, an impression on a special tray was made to include its full length rather than using sequential addition to the new appliance. This impression enabled a detachable loop carrying an impression tray to be added onto the framework that could be removed to facilitate other denture stages. This was extremely helpful considering the severe gag response. Although the processed lift was not detachable from the prosthesis, the benefit of incorporating detachable components into the framework is the potential to replace the ‘lift extension’ without the need to replace the whole appliance should future remedial work be required.

Motor neurone disease is a neurodegenerative disease characterized by a relentless progression of neuromuscular weakness. It is an uncommon condition, affecting 5000 people in the UK, most of whom are over the age of 60 years, and with a preponderance towards males. Unfortunately, the disease is fatal, usually due to respiratory failure; however, the rate of progression can be variable. Movement, breathing, speech and swallowing are all affected. Loss of motor innervation to the soft palate compromises elevation and velopharyngeal closure resulting in dysarthria and dysphagia.

Dentists should be an integral part of the multidisciplinary team managing these patients, both for oral health and prevention of dental disease, and for liaison with specialist services, such as speech and language therapy, and provision of speech prostheses where appropriate.²

While the use of a palatal lift prosthesis is established in various diseases, this has not been routinely used for patients with motor neurone disease; however, its use does appear to be gaining popularity.³ The use of palatal lift appliances in patients with motor neurone disease appears to improve dysarthria,⁴ and patients appear to require less effort to produce understandable speech sounds, especially when undergoing concomitant speech therapy.⁵

Generally, patients do tolerate these prostheses well, but many have initial concerns over whether they will experience a gag response or discomfort.⁶ Regular review for reassurance and modification of the appliance is essential.^7,8

Summary

The palatal lift appliance is an effective prosthetic for management of palatal incompetence, but requires careful planning and regular follow-up as part of a wider management plan for patients affected with neurological disorders, such as motor neurone disease.