The aim of occlusal equilibration is to create equal intensity and simultaneous contacts on all teeth when the condyles are seated in the upper most, forward most position in the Glenoid Fossa. This is referred to as Centric Relation and differs significantly from Centric Occlusion.
STABLE CENTRIC RELATION CONTACTS is important to comfort, function and longevity of dental restorations.
Proper anterior guidance result in proper posterior clearance (immediate posterior disclusion) means reduced wear on the front and back teeth.
If there is contact on the back teeth in lateral jaw movements the Masseter and Temporalis muscles are activated. During sleep, the force can be exceedingly high. If the front teeth also contact, they will exhibit accelerated wear.
PREVENTION of abfractions and attrition
One of the most common problems associated with teeth is tooth wear. Tooth wear is destructive resulting in a loss of hard tooth structure (enamel, dentin or cementum). It can manifest in one, or more, of four different ways:
Identifying the cause of tooth wear is essential for its successful management.
The term abfraction, derived from the Latin verb frangere (to break), describes the wedge shaped defect at the junction of the enamel and the cementum, which makes up the root. These lesions are sometimes located below the gum beyond the influence of tooth brush abrasion. They are the result of tooth grinding, particularly during sleep, leading to tooth flexure (really!). The tooth flexing create micro-fractures in the enamel, and dentine under it, leading to it breaking away.
Attrition is the term used to describe wearing away of enamel or dentine as a result of tooth to tooth contact. Such contact occurs with tooth grinding primarily and secondarily though swallowing. It is derived from the Latin verb atterere, which is defined as the action of rubbing against something.
The hallmark of attrition is the creation of flat shiny wear facets in the locations where the teeth are in contact.
Of all the causes of tooth wear, attrition has the worst prognosis because it has the highest risk of future wear and fracture of any restoration, like fillings, crowns or porcelain veneers and even implants.
The term erosion describes the process of gradual destruction of the surface of something. It is derived from the Latin verb eroder (to corrode). Dental erosion is the result of chronic, painless loss of dental hard tissue. This tissue includes one or more of the hard outer layers of a tooth. These are enamel, dentine (under enamel) and cementum).
The role of diet in the cause of erosion has received the most attention. Certain foods like citrus fruits exhibit a low pH and when consumed frequently and excessively, may lead to dental erosion. Other causes may include acid reflux or bulemia.
Duration of contact with the teeth, frequency of ingestion, amount ingested, ability of saliva to neutralize acidiity and the properties of enamel which may be strengthened with toothpaste containing fluoride.
If erosion occurs rapidly, increased sensitivity to hot or cold drinks or sweets will likely ensue. If the progression is a little slower, you may find fewer symptoms.
How ACIDIC is your diet?
Experts believe that consuming as few as 4 acidic foods or drinks a day increases the risk of acid wear.
You might think that's a lot, but as the pH chart to the right shows a surprising number of foods are acidic. Even healthy foods and drinks like fruit and juices can have harmful levels of acidity.
The lower the pH, the higher the acidity and therefore the higher the risk that it may cause acid erosion.
Studies show that tooth enamel begins to dissolve at pH below 5.5. Many of the foods on this list are more acidic than this.
The term abrasion is derived from the Latin verb abradere (to scrape off). It is the wearing away of dental hard tissue which may be one or all of the following surfaces: enamel, dentine (under enamel) or cementum (root).
An individuals oral hygiene habits are commonly the cause. This includes tooth brushing technique, frequency of brushing, time and force applied while brushing. Other factors include the stiffness of the toothbrush bristles, abrasiveness, pH and amount of toothpaste used.
The most common effect of abrasion is the V-shaped defect. It is caused by intensive horizontal brushing. The root of a tooth is particularly susceptible because it is much softer than the enamel. Another sign of chronic abrasion is the yellowing of teeth as a result of a thinning of the enamel. Dentine is the substance below the surface of enamel that gives teeth their yellowish hue.
Want to know what affect your toothpaste is having on enamel? See the chart below.
Back teeth contacting in a lateral movement is referred to as an "interfrence."
Why Do So Many Of Us Show Signs of Attrition?
Functional wear, the teeth are rubbing against each other during normal function, such as chewing. There are two major categories which describe how people chew, a chopping pattern, in which the teeth never come into contact and therefore, the teeth do not rub against each other, and a grinding pattern of chewing, in which the lower jaw has horizontal movements during chewing, in which case the teeth do rub against each other. The grinding pattern is associated with more tooth wear and mobility.
Bruxism, wear that is initiated as an event from the Central Nervous System. Typically bruxism is thought of as a micro-arousal of the sympathetic nervous system; the micro-arousal triggers a cascade of events including increased brain activity, heart rate, respiratory rate, and finally rhythmic masticatory muscle activity, in which the individual rhythmically closes and grinds their teeth. The initiation of the micro-arousals has been associated with Sleep Apnea, Gastric Reflux, and Psychologic stress, to name a few possibilities. When associated with apnea or airway issues the bruxism is thought to be the body’s mechanism for opening the airway and increasing oxygenation.
The incidence of nocturnal bruxism decreases with age, going from a high of 14-20% in children 11 and younger, to 13% among young adults from 18-29 years of age, to 3% among adults over 60, meaning those patients who say they used to grind but don’t anymore may be accurate. Daytime bruxism in contrast, rises from 12% in children to 20% in adults. There is evidence of the role the airway plays in childhood bruxism which can be seen after the removal of tonsils and adenoids in children diagnosed with sleep apnea, reducing the incidence of bruxism from 45.6% to 11.8% following the surgery. And finally, it is also important to recognize in children and adults the increased incidence of bruxism that occurs in individuals taking certain medication (SSRI). This increase in bruxing activity can be mediated by lowering the dose of the SSRI, or the use of Buspirone in addition to the SSRI.
The significance of identifying the etiology of tooth wear is critical to predicting the outcome of any future treatment. The possibility of helping a patient discover undiagnosed apnea or airway issues by recognizing the signs of uncontrolled attrition can be life saving and life altering.