Thesis Outline

In this study, a complete engineering design process is performed to bring out a new design of mechanism in the mandibular advancement device. According to the market survey, QFD process is used to generate the engineering specifications and to ensure that all engineering specifications are conformed with the customer requirements. Based on the results of QFD, a conceptual design process will be proceeding to generate new concepts. The final target of this study is to generate a new, feasible, and durable mandibular advancement device after completed whole design process.

Chapter 2 introduces the pathophysiology of snoring by which the mechanisms of snoring will be realized. Furthermore, the diagnosis and treatments are presented to assist the overall understanding in the medical field. Finally, to make sure of the mandibular advancement device is one of effective therapies and treatment with high efficacy.

Chapter 3 focuses on the present developments on the mandibular advancement devices.

According to the survey of patents and products on market, the patent analysis, the functions of components in mandibular advancement devices, and the comparisons of products will be proposed in this chapter.

Chapter 4 introduces the QFD method to proceed a procedure from collecting customers’

requirements, evaluating the relative importance, evaluating the competitive products, generating the engineering specifications, and defining the target specifications at the end.

Chapter 5 applies the functional decomposition and the brainstorming method to provide a systematic procedure to generate complete concepts of the MAD. Brainstorming method is used to generate concepts for every sub-function initially, and then the complete conceptual design is generated by combining those concepts of sub-functions.

Chapter 6 introduces the Finite Element Analysis method to simulate the stresses under a force, and evaluate the strength of four concepts generated from chapter5 and one commercial product. The decision-matrix method is also introduced in this chapter in order to evaluate all the concepts for selecting the best one.

Finally, chapter 7 makes some conclusions for this study and promotes some recommendations for further researches in the future.

CHAPTER 2

SNORING AND OBSTRUCTIVE SLEEP APNEA

2.1 Pathophysiology of Snoring

Snoring and obstructive sleep apnea may be considered under the scope of obstructive sleep-disordered breathing (OSDB), which is a type of sleep-disordered breathing. It means that snoring occurs because of the obstructions formed in the airways. Snoring can be defined as an inspiratory noise produced by vibration of the soft parts of the oropharyngeal wall [8].

When portions of the soft parts collapse, that will form the obstructions in the airways and lead to snoring.

2.1.1 Stages of Sleep

The stages of sleep were discovered in the 1950s [7] in the experiment of brain wave using the electroencephalogram (EEG) during sleep. Neurophysiologists recognize two phases of sleep, slow-wave sleep and paradoxical sleep. The initial phase, called slow-wave sleep, can be divided into four stages, each successive stage having a particular EEG pattern.

As the proceeding of slow-wave sleep from light sleep (stage 1) to deep sleep (stage 3 and 4), the EEG patterns have slower frequency and higher amplitude progressively, and the patterns are the alpha rhythm, theta rhythm, and delta rhythm in sequence [9], as shown in Fig. 2.1-1.

Besides, the tension in the skeletal-muscles become progressively more relaxed as slow-wave sleep progresses until the stage 4 is achieved.

Sleep always begins with the slow-wave sleep progression from stage 1 to stage 4 which normally takes 30 to 45 minutes and then reverses itself. After the slow-wave sleep, the second phase of sleep, paradoxical sleep, also called rapid eye movement (REM) sleep, comes up. During the REM sleep, the EEG pattern characterizes as resemblance to the alert and

time, and the sleeper is difficult to be aroused by others. The REM sleep period usually lasts 10 to 15 minutes. At this time, the lower muscle tone leads to paralysis of skeletal-muscle except the eye muscles and the muscles of respiration. If sleep uninterrupted, it continues slow-wave sleep and REM sleep by turns, called the sleep cycle, until awakening, as shown in Fig. 2.1-2.

Fig. 2.1-1 EEG patterns in awake, slow-wave sleep, and REM sleep states [9]

Fig. 2.1-2 A typical night’s sleep record of an average young adult [9]

2.1.2 Mechanisms of Snoring

The origin sounds of snoring generation is from the collapsible part of the airway without rigid support. Snoring generation involves the soft palate, uvula, tonsils, base of tongue, pharyngeal muscles, and pharyngeal membranes, as shown in Fig. 2.1-3. Five causes below, acting either alone or combination, contribute to snoring:

z Poor muscle tone in the palate, tongue, and pharynx:

This is the cause of most adult snoring. In deep sleep stages, such musculature fails to participate in the respiratory cycle to open the airway during inspiration. The dilator effect of the pharyngeal muscles and the protrusive effect of the genioglossus muscle are inadequate. Thus, the tongue falls backward into the airway and vibrates against the floppy pharynx during inspiration. Snoring may appear as soon as the snorer falls asleep in stage 1, increasing progressively with deepening of slow-wave sleep and reaching a peak in stage 4.

z Space-occupying masses or tissues in the pharynx:

Children who snoring almost have enlarged tonsils and adenoids. Many adults also have large tonsils which form the obstruction in the airway and are notable in obese persons. Those excessive bulky pharyngeal tissues cause narrowing of the air passageways and lead to snoring.

z The receding mandible:

It may not be effective in keeping the tongue sufficiently forward when the muscles relaxed in sleeping time.

z Excessive length of the soft palate and uvula:

The long soft palate narrows the nasopharyngeal aperture. As it dangles in the relaxed situation, its lower edge often lies below the horizontal plane of the tongue

and it acts as a noisy flutter valve during inspiration. If the patient lies in the supine position, that will lead to a more apparent snoring. Besides, a long uvula makes matters even worse.

z Obstructed nasal airways:

The rising resistance of airflow in the nose requires extra effort to inspire the air.

This increases the vacuum in the airway and produces a negative pressure to draw together the floppy tissues in the collapsible parts where they vibrate and cause snoring. Therefore, many persons who ordinarily do not snore may snore when they catch a cold or get an allergy attack.

Fig. 2.1-3 Oral cavity [2]

As described above, those are the causes of snoring and they may be influenced by several factors, such as anatomy [10], age, sex, hormones, Genetic factors, and etc. These factors may affect the thickness of soft tissue in the upper airway, the muscle tone during rest,

the pharyngeal cross sectional area, the upper airway dilator activity, and etc [11]. Without doubt, anatomy is the most important factor when dealing with the patient with snoring and it can be divided into the factors which related to the soft tissue or the skeleton; and further, it is more obvious than other factors that leading to snoring.

2.2 Evaluation of Obstructive Sleep Apnea

Apnea is a Latin medical term meaning “without breathing.” When the interruption to breathing occurs during sleeping time and is caused by an obstruction in the airway, it is

“obstructive sleep apnea.” Obstructive sleep apnea is the most severe state of obstructive sleep-disordered breathing and usually accompanies severe snoring and other symptoms either in sleeping time or in daytime. Sleep apnea was first discovered in the search for the pathophysiological process behind the pickwickian syndrome with nocturnal polygraphic monitoring of abnormal breathing patterns during sleep in 1960s. At present, several methods have been developed to diagnose the probability of suffering from OSA.

2.2.1 Symptoms

Typical symptoms of obstructive sleep apnea include snoring, observed apnea, excessive daytime sleepiness, or a combination of them. When any signs are expressed that relate to sleep apnea, the patient and observer should be questioned about other known symptoms, as shown in Table 2.2-1.

Since the patient is asleep, he or she is often not aware of many nocturnal signs. The bed partner of patient or other observer is needed to determine the severity of snoring, snorting, struggling to breathe, irregular breathing, and observed apnea. Abnormal movements during sleep, such as thrashing in bed and arm or leg jerks, would be known only by an observer.

Patients just feel restlessness after they wake.

severe sleep apnea. Associate with arousals, decreased esophageal pressure, and hypoxemia, the increased atrial natriuretic peptide (ANP) stimulates urinary excretion. This symptom is more common in children than in adults that causes enuresis.

Table 2.2-1 Nocturnal and daytime symptoms of OSA [4]

Nocturnal Symptoms

Snoring, snorting, struggling to breathe, irregular breathing, and observed apnea

Trashing in bed, disrupted sleep Nocturnal gasping or choking

Morning dry mouth or sore throat Depression, irritability

Impotence, sexual dysfunction

Daytime tiredness or fatigue is a common complaint of OSA patients. The cause of excessive daytime sleepiness is due to a combination of arousals, sleep fragmentation, and reductions in delta and REM sleep. Patients may also complain of inability to concentrate and of deterioration of memory and judgment. The EDS also leads to psychiatric disorder, such as depression and irritability, and the suddenly fall asleep which will cause car accidents during

driving time. A widely used short questionnaire, the Epworth Sleepiness Scale (ESS), has been developed to measure the severity of daytime sleepiness, as shown in Fig. 2.2-1. The lowest score is zero and the highest twenty-four, and above ten is considered abnormal.

Fig. 2.2-1 Epworth Sleepiness Scale [12]

Morning headaches are attributable to the presence of sleep apnea. The nocturnal oxygen desaturation is the cause of morning headaches. There are still other morning symptoms such as the morning dry mouth or sore throat that is due to mouth breathing and snoring.

Impotence, sexual dysfunction, and loss of sex drive are also linked to the presence of sleep apnea with a severe state. It is not known if the cause of impotence is similar to other symptoms. Sexual dysfunction is usually reversible with treatment of the sleep-disordered breathing.

Many symptoms are known to discriminate patients with or without OSA probability. If someone snoring with those symptoms, he or she should seek the further examination from a sleep specialist as soon as possible.

2.2.2 Diagnosis

A sleep study should be applied to the patient with sleep-disorder breathing. The aims of testing are to establish the diagnosis, to determine the frequency and severity of abnormal respiratory events, and to evaluate the physiologic consequences during sleep. The American Academy of Sleep Medicine (AASM, formerly the American Sleep Disorders Association [ADSA]) has defined four types of sleep testing: standard polysomnography (PSG), which requires the presence of a trained technician, and three variations of unattended studies [4], see Table 2.2-2.

Table 2.2-2 Types of sleep studied for evaluation of sleep breathing disorders [4]

Type 1 Type 2 Type 3 Type 4

Monitors 7 or more 7 or more 4 or more 1-2

EEG Required Required Optional Not measured

EOG Required Required Optional Not measured

Chin EMG Required Required Optional Not measured

ECG/HR ECG ECG or HR ECG or HR Optional

Airflow Required Required 2 of effort

or 1 airflow Optional Respiratory effort 2 channels 2 channels 1 of effort Optional

Oximetry Required Required Required Usual/optional

Leg movement Usual/optional Optional Optional Not measured

Personnel Present Absent Absent Absent

Intervention Possible Not possible Not possible Not possible EEG: electroencephalography, EOG: electrooculography, EMG: electromyography, ECG:

electrocardiography, HR: heart rate

Among all the types of studies, the type-1 sleep study is the overnight polysomnography which is routinely indicated for the diagnosis of sleep-disordered breathing [13].

Polysomnography, which is performed in a sleep laboratory with a technician present, is a continuous recording of sleep for at least six hours during a patient’s normal sleeping time. As the study proceeding, the following parameters listed in Table 2.2-3 are routinely measured [13].

Table 2.2-3 Parameters measured in the Polysomnography [13]

No. Items No. Items

1 Electroencephalogram (EEG) 7 Thoracic movement

2 Electrooculogram (EOG) 8 Abdominal movement

3 Chin electromyogram (EMG) 9 Leg electromyogram

4 Electrocardiogram (ECG) 10 Snoring sound

5 Nasal/oral airflow 11 Body position

6 Blood oxygen saturation (SaO2)

EEG, EOG, and chin EMG are used together to determine sleep stage, wakefulness, and arousals from sleep. The ECG is used to detect arrhythmias during sleep. Nasal and oral airflow can detect not only apnea and hypopnea but also flow limitation associated with upper airway resistance. Blood oxygen saturation is measured with finger sensor and oximeter to determine the degree of desaturation. Other parameters are also measured by specific devices to detect and record data for later analysis. Then, all detected parameters will be used to construct a polysomnographic report, as shown in Fig. 2.2-2.

In clinical definitions, apnea is defined as a cessation in breathing for at least ten seconds without airflow measured on the airflow sensor. If the event is obstructive during apnea, there is effort to breathe. Several clinical definitions of hypopnea are in clinical use and there is no clear consensus. An AASM position paper defines hypopnea as an abnormal respiratory event with at least a 30% reduction in thoracoabdominal movement or airflow lasting at least ten seconds, and with 4% oxygen desaturation or greater [14]. The number of apneic plus hypopneic episodes per hours is defined as the apnea-hypopnea index (AHI). Based on the AHI and lowest oxygen saturation (LSAT) can determine the severity of OSA, as shown in Table 2.2-3.

Fig. 2.2-2 Polysomnographic report [4]

Table 2.2-4 Severity of obstructive sleep apnea [4]

AHI LSAT

Mild 5 – 14 86% – 90%

Moderate 15 – 29 70% – 85%

Severe ≥ 30 < 70%

AHI: apnea-hypopnea index, LSAT: lowest oxygen saturation

Besides the sleep study, the clinician makes judgments also by the clinical history of patient and the physical examination. According to the results of diagnose in many directions, clinicians will make the more helpful suggestion to patients with sleep-disordered breathing based on their own experiences. Therefore, the right remedies will more suitable for each case.

2.3 Treatments

Various treatments of snoring and OSA have been proposed. All the treatments can be generally classified into surgical treatments and non-surgical treatments. Operations to treat snoring and OSA are the treatments which belong to surgical, others are non-surgical. Those non-surgical treatments include behavior modification, pharmacologic treatment and various mechanical devices to reduce or eliminate snoring and OSA. Standard treatments for OSA proven by AASM include upper airway surgery and the use of positive airway pressure appliance and oral appliance [15].

2.3.1 Surgical Treatments

The surgical modifications of the upper airway for the treatment of OSA can be divided into three categories: classic procedures, specialized procedures, and tracheotomy [19].

Before the surgery, the anatomic regions of obstruction should be identified first. The pharynx can be functionally divided into two portions: the retropalatal pharynx, the region of the pharynx posterior to the soft palate, and the retrolingual pharynx, the region of the pharynx posterior to the vertical portion of the tongue. Based on the above basis, patterns of pharyngeal obstruction, narrowing, or collapse can be classified into the following way [20]:

z Type I: narrowing or collapse in restropalatal region only.

z Type II: narrowing or collapse in both restropalatal and restrolingual regions.

z Type III: narrowing or collapse in retrolingual region only.

Classic surgical techniques have been developed to alter the soft tissue and skeleton of nose, such as nasal-septal reconstruction, cauterization, and outfracture of turbinates. Classic pharyngeal procedures such as tonsillectomy have been used to enlarge the pharyngeal space.

However, these procedures were frequent failure so that new surgical approaches were developed.

Fujita [21] introduced the Uvulopalatopharyngoplasty (UPPP) as the first specialized surgical procedure to treat OSA in 1981. UPPP is a procedure that operates on the tonsil to enlarge the retropalatal airway. The procedure trims the posterior and anterior tonsillar pillars, and resects the uvula and posterior portion of the palate. Then, another operation, the Uvulopalatopharyngoglossoplasty (UPPGP), combines a modified UPPP with limited resection of the tongue base. Laser midline glossectomy (LMG) and lingualplasty are two procedures that create an enlarged retrolingual airway by laser extirpation of a midline. The difference between LMG and linguaplasty is that additional tongue tissue is extirpated in LMG. GAHM is an abbreviation used to represent the whole procedure of inferior sagittal mandibular osteotomy and genioglossal advancement with hyoid myotomy and suspension.

The two components of the procedure create an enlarged retrolingual airway. In GAHM, the hyoid bone is advanced and suspended from the mandible by a fascial trip that will not change the dental occlusion. The last one in specialized surgical procedure, the maxillomandibular osteotomy and advancement (MMO), provides maximal enlargement of the retrolingual airway and some enlargement of the retropalatal airway. Moving the maxilla forward simultaneously with mandible permits greater forward motion of the mandible because of the maintenance of dental occlusion.

Tracheostomy is a surgical procedure that creates a percutaneous opening into the

and maintain the stoma. The tracheostomy tube is with sufficiently small diameter that, when plugged, it permits air inspiration through upper airway from nose and mouth to the lungs pass around the tube.

2.3.2 Non-surgical Treatments

Non-surgical treatments include behavior modification, pharmacologic treatment and the use of mechanical devices. Behavior modification is the self-help remedy which contains alteration of sleep position, avoidance of alcohol and sedative medication, and weight-reduction programs. Pharmacologic treatments are not recommended to treat OSA because of the lack of clinical trials and the conclusions on efficacy, but some of them may effective to reduce the side effect of OSA [22]. At present, drugs should be considered as either second line therapies or as adjuvant therapies [23]. Further, several mechanical devices are used to remedy the snoring and OSA, and will be introduced below.

2.3.2.1 Non-prescription Treatments

Non-prescription treatments mean that the therapies performed without a prescription or even a medical evaluation. Those treatments include some pharmacologic products, several mechanical products, and others. There are so many commercial products become popular to many snorers. As described above, the efficacy of pharmacologic products are not obvious.

Mechanical products, such as external nasal dilator strips (ENDS) and internal nasal dilators (IND), are also with limited evidence to suggest the use of them [24]. Most of these products are without obvious efficacy and the use of them may also delay proper evaluation and treatment of the snoring and OSA. Therefore, go to see a doctor and evaluate the condition of snoring and OSA maybe better than use the product without prescription.

2.3.2.2 Positive Airway Pressure

invasive treatment for OSA [4]. Types of PAP treatment include continuous PAP (CPAP), bilevel PAP (BPAP), and automatic self-adjusting PAP (APAP). The most widespread application of PAP is the treatment of OSA with CPAP. The application of CPAP prevents collapse of the upper airway by promoting the balance of the forces that keep the airway open versus that innately collapse it. The basic CPAP appliance is composed of an electronically controlled compressor and a pressure gauge, which can be adjusted to personal settings. The pressure setting is established by a titration study with attended PSG to adjust to the optimal pressure for maintaining airway patency. The sufficient pressure for preventing apnea is variational in all sleep stages and all sleep postures. Use the titration to find a fixed single

invasive treatment for OSA [4]. Types of PAP treatment include continuous PAP (CPAP), bilevel PAP (BPAP), and automatic self-adjusting PAP (APAP). The most widespread application of PAP is the treatment of OSA with CPAP. The application of CPAP prevents collapse of the upper airway by promoting the balance of the forces that keep the airway open versus that innately collapse it. The basic CPAP appliance is composed of an electronically controlled compressor and a pressure gauge, which can be adjusted to personal settings. The pressure setting is established by a titration study with attended PSG to adjust to the optimal pressure for maintaining airway patency. The sufficient pressure for preventing apnea is variational in all sleep stages and all sleep postures. Use the titration to find a fixed single