17 Prominent chin and TMJDS
Jocelyn, aged 23, is referred by her general dental practitioner because of her prominent chin (Fig. 17.1) and pain in her left temporomandibular joint (TMJ). What are the causes and how would you manage these problems?
Jocelyn’s main concern is that she does not like the prominent appearance of her chin and her upper teeth biting inside her lower teeth. She has pain in her left jaw joint and has some difficulty chewing. She is also aware that she has a lisp, which she dislikes.
Jocelyn has been more aware of her prominent chin and her bite since she was in her last year at school. After consultation with an orthodontist at age 12, she had two upper teeth removed to provide space for the upper eye teeth (she had both lower first permanent molars extracted at age 8 because of decay.) She did not wear any braces on her teeth. She was advised to wait until she was in her late teens to have the bite of her front teeth reassessed. In the past 6 months she has become quite self-conscious about her facial appearance, although she feels that her chin does not appear to have become more prominent in the past 4 years.
The pain started suddenly when Jocelyn was preparing for examinations in her first year at university. She has had intermittent discomfort in her left jaw joint since then but it has been of a mild nature. The discomfort is an ache that is principally in the left jaw joint area but radiates to the jaw muscles on that side. It does not keep her awake at night but she feels it is worse in the morning. Typically it lasts for a few hours and then disappears. It tends to return when Jocelyn is stressed by work. She is aware of grinding her teeth when stressed. She does not engage in chewing pencils or pens or nail-biting. She feels that in the past year the pain has recurred more frequently and has become worse. Chewing hard food or opening her mouth too wide makes the pain worse; one or two paracetamol tablets usually relieves the ache. Jocelyn is also aware that she has a jaw click.
Crossbites, Class III malocclusion and anterior open bite have been shown to have a significant association with temporomandibular joint dysfunction syndrome (TMJDS) in some studies while others have found no link between signs and symptoms of TMJDS and mandibular displacement. The aetiology of TMJDS is multifactorial with the implicated involvement of psychological, traumatic and occlusal elements. The most salient factor is probably stress, which may transmit its effect by a parafunctional habit, stemming perhaps from a displacing occlusal contact in susceptible individuals. In this case, a displacement exists on on closure. There are also anterior and posterior crossbites present.
In a Class III malocclusion, the amount of reverse overjet tends to increase with forward mandibular growth during teenage years. Waiting until mandibular growth is essentially completed, which is generally about 17 years in girls and 19 years in boys, has three advantages. First, it allows treatment planning to be undertaken with reasonably stable facial and occlusal characteristics. Second, if treatment is undertaken, it safeguards against relapse due to further growth. Third, the magnitude of occlusal change due to mandibular growth influences whether treatment can be undertaken by orthodontic means alone or whether a combined surgical-orthodontic approach is necessary. Orthodontic treatment involves inducing dentoalveolar compensation for the underlying skeletal pattern, but if unsuccessful due to continued adverse mandibular growth the compensation would need to be undone as part of pre-surgical orthodontics. This may involve opening up lower premolar extraction spaces. Hence the decision to treat a Class III mal/>