Posterior Dentition

Dr. Karnakova with Dr. Zak Dental Care discusses the problem of Posterior Dentition. The lack of posterior teeth may have many negative consequences on the oral health. Posterior teeth support the vertical height of the face, and may lead to a posterior bite collapse if missing.

 

Malocclusion

A malocclusion is a misalignment or incorrect relation between the teeth of the two dental arches when they approach each other as the jaws close. Edward Angle, who is considered the father of modern orthodontics, was the first to classify malocclusion. He based his classifications on the relative position of the permanent MAXILLARY FIRST MOLAR. Angle believed that the anteroposterior dental base relationship could be assessed reliably from first permanent molar relationship, as its position remained constant following eruption. In case where the first molars were missing, CANINE relationship is used.

CLASSIFICATION OF MALOCCLUSION

NORMAL OCCLUSION
Molar Relationship: According to Angle, the mesiobuccal cusp of the maxillary first molar aligns with the buccal groove of the mandibular first molar.

Canine Relationship: The maxillary canine occludes with the distal half of the mandibular canine and the mesial half of the mandibular first premolar.

Line of Occlusion: The teeth all fit on a line of occlusion which, in the upper arch, is a smooth curve through the central fossae of the posterior teeth and cingulum of the canines and incisors, and in the lower arch, is a smooth curve through the buccal cusps of the posterior teeth and incisal edges of the anterior teeth. There is alignment of the teeth, normal overbite and overjet and coincident maxillary and mandibular midlines.

ANGLE Class I: NEUTROOCCLUSION
Molar Relationship:
 The mesiobuccal cusp of the maxillary first permanent molar occludes with the mesiobuccal groove of the mandibular first permanent molar.

Canine Relationship:
- The mesial incline of the maxillary canine occludes with the distal incline of the mandibular canine. The distal incline of the maxillary canine occludes with the mesial incline of the mandibular first premolar
.

Line of Occlusion: ALTERED in the maxillary and mandibular arches
.
– Individual tooth irregularities (crowding/spacing/other localized tooth problems).

– Inter-arch problems (open bite/deep bite/cross bite)
.

Mesognathic: normal, straight face profile with flat facial appearance.

ANGLE Class II: DISTOOCCLUSION (overjet)
Molar relationship: The molar relationship shows the mesiobuccal groove of the mandibular first molar is DISTALLY (posteriorly) positioned when in occlusion with the mesiobuccal cusp of the maxillary first molar. Usually the mesiobuccal cusp of maxillary first molar rests in between the first mandibular molar and second premolar.

Canine Relationship:
 The mesial incline of the maxillary canine occludes ANTERIORLY with the distal incline of the mandibular canine. 
The distal surface of the mandibular canine is POSTERIOR to the mesial surface of the maxillary canine by at least the width of a premolar.

Line of occlusion is not specified but irregular, depending on facial pattern, overcrowded teeth and space needs.

Retrognatic: convex face profile resulting from a mandible that is too small or maxilla that is too large.

Class II Malocclusion has 2 subtypes to describe the position of anterior teeth:

  • Class II Division 1: The molar relationships are like that of Class II and the maxillary anterior teeth are protruded. Teeth are proclaimed and a large overjet is present.

 

  • Class II Division 2: The molar relationships are Class II where the maxillary central incisors are retroclined. The maxillary lateral incisor teeth may be proclaimed or normally inclined. Retroclined and a deep overbite exists.

ANGLE Class III: MESIOOCCLUSION (negative overjet)

Molar relationship: The mesiobuccal cusp of the maxillary first permanent molar occludes DISTALLY (posteriorly) to the mesiobuccal groove of the mandibular first molar.

Canine Relationship: Distal surface of the mandibular canines are mesial to the mesial surface of the maxillary canines by at least the width of a premolar
. Mandibular incisors are in complete crossbite.

Line of occlusion is not specified but irregular, depending on facial pattern, overcrowded teeth and space needs.

Prognathic: concave face profile with prominent mandible is associated with Class III malocclusion.

CLASS III Malocclusion Class III malocclusion has 2 subdivisions:

  1. TRUE class III malocclusion (SKELETAL) which is genetic in origin due to excessively large mandible or smaller than normal maxilla.

 

  1. PSEUDO Class III malocclusion (FALSE or postural) which occurs when mandible shifts anteriorly during final stages of closure due to premature contact of incisors or the canines. Forward movement of the mandible during jaw closure can also result from premature loss of deciduous posterior teeth.

 

Class III Sub-division: Class III molar relationship exists on one side and the other side as a normal Class I molar relationship.

By Dr. S. Fatahi, DDS

Lack of Posterior Dentition

It is not uncommon for people to have concerns about the health of their anterior teeth due to concerns of esthetics and a beautiful smile. Equally as important are posterior teeth, which play an important role in chewing, grinding, and crushing food. Anterior teeth are designed for biting and tearing, and are unable to handle the stress of chewing.

The lack of posterior teeth may have many negative consequences on the oral health of an individual. Posterior teeth support the vertical height of the face, and may lead to a posterior bite collapse if missing. The missing of posterior teeth can also lead to the drifting, flaring, or extrusion of remaining dentition. Speech impairment and temporal mandibular disorders can also be a consequence. In addition, unnecessary stress is placed on the remaining dentition, and can lead to fractures or breakage.

Ideally, the best treatment for replacing missing posterior teeth is an implant, which have the greatest long-term prognosis. Bridges or partial dentures may also be used to restore missing teeth. Each method of replacing missing dentition is based on a patient-by-patient case. Please consult with your dentist for available treatment options best suited for your needs.

by Dr. O. Karnakova, DDS

Loss of Vertical Dimension

Vertical dimension is the space between the upper and lower jaws. In a normal occlusion with a full dentition the space is ideal with the teeth and jaw working in harmony. Over time, especially in older patients this space can diminish if the natural teeth are worn down  from bruxism or lost due to decay or periodontal disease.

This loss of vertical dimension or bite collapse can result in damage to the jaw joints, severe pain or dysfunction in the jaw joints, frequent muscle tension headaches, tooth fractures and tooth loss, and aggravation of periodontal disease if present. Other resulting issues are shortening of the lower face height, an inverted smile (corners of the mouth sag), a toothless smile, frequent cracking or chapping at the corners of the mouth (angular cheilitis), and problems chewing.

Restoring the proper vertical dimension and associated cosmetic and functional problems can be obtained by proper treatment planning. In the case of a full dentition with worn teeth, the teeth can be crowned and returned to their natural size. For partial or fully edentulous patients implants can be utilized along with removable or hybrid appliances. Below are some before and after pictures depicting loss of vertical dimension and its correction.

by Dr. H. Kopel, DDS