SAS 2: BIOMECHANICS OF THE EDENTULOUS STATE

Biomechanics

is the study of the structure, function and motion of the mechanical aspects of edentulism and will also try to compare to the dentulous state for differentiation.

effects of tooth loss

adverse anatomic

esthetic

biomechanical sequelae (aftereffects or results from the forces applied)

edentulism

due to various combinations of dental disease together with cultural, financial, attitudinal, and previous dental treatment

cultural causes of edentulism

(ex. sharpening/grinding of the teeth makes one look beautiful in some culture but is destructive to the teeth)

financial causes of edentulism

(lack of financial capability to undergo RCT so it is better to extract the teeth because it is cheaper than other performed procedures)

attitudinal causes of edentulism

(a mentality like “ it is better to extract to remove the problem) determinants

edentulous ridge

bares all the forces when a completely edentulous patient eats

made up of the bone (that is significantly less hard than teeth) and soft tissue that covers it

In patients with natural teeth

force directed to the teeth then to the pdl then to the bone (not directly to the bone)

it is the periodontal ligament that bares all the force

In the edentulous patients

force directed to tissue then to the bone thats why bone resorption is faster

the bone of the residual will eventually suffer since bone heals lesser than soft tissues.

digestion

primary function of the teeth

it starts in the mouth by mixing food with the digestive enzyme, a salivary amylase called PTYALIN

breaks down (thru hydrolysis) starch, a complex carbohydrate to maltose (disaccharide, glucose + glucose) and dextrin (D-Glucose chain).

If teeth are not present, initial digestion in the mouth will be very minimal which not only waste food and its nutrients but also can cause systemic disturbance in the form of indigestion which eventually lead to malnutrition.

PTYALIN

a salivary amylase

teeth can occlude during these two:

mastication (chewing) and deglutition (swallowing)

~17.5 mins

duration (normally) the teeth are in contact in a day

daytime — 400 sec (6.6 min)

nighttime — 80 sec (1.3 min)

450 sec (7.5 min)

actual chewing time per meal / entire meal

540 sec (9 min)

total chewing forces per day

1800 sec

chewing time for four meals per day

0.3 sec

duration of each stroke

1 sec

duration of one deglutition

mastication / chewing

on dentulous patient happens on 1 side only (unilateral and happens either side)

on dentures are bilateral — if used in a unilateral chewing, it will dislodge.

swallowing / deglutition

has longer tooth contacts

~1sec per contact

chewing

occurs in the posterior teeth (premolar and molar) regions

premolar

where tougher consistency food is preferably chewed

anterior (Incisors and canine)

where biting occurs

44 Lbf (pound force) / ~ 20 Kgf (kilogram force)

Masticatory load (biting force) of dentulous patient

lesser if unconsciously done (chewing is an unconscious/unmindful process).

~13-16 Lbf / ~6-8 Kgf

masticatory load of complete denture

significantly lower than naturally dentulous patients or there will be injury on the soft tissue and the bone

—if more than 8kg, there will be trauma to the soft tissue

denture-bearing area

area of support/soft tissue covered by the denture

~22.96 cm2

(or about 4.79cm x 4.79cm)

the denture/ force bearing areas of the edentulous ridge maxilla

~12.25 cm2

(3.5cmX3.5cm)

the denture/ force bearing areas of the edentulous ridge mandible

45 cm2

total force bearing area of periodontal membrane on a single arch

denture-bearing area of the edentulous ridge

gets smaller as it resorbs so the biting force that the edentulous ridge can handle diminishes and the denture retention becomes more of a problem.

force bearing area of dentulous — have a much greater force-bearing area because of the extensive root surface area and PDL.

Retention

always the problem with complete dentures since normally, saliva is the only thing holding the dentures

ways to minimize dislodgement or increase retention

Extending the outline of the denture bases properly in relation to the mucous membrane (wider coverage = better support and retention)

Maximum area of contact between basal seat (ridge) and basal surface (denture surface that is in full contact with the soft tissue/ridge)

Intimate contact of the basal seat and the basal surface

—(2 and 3 are dependent on the accuracy of the impression).

3 muscles

buccinator

orbicularis oris

intrinsic / extrinsic muscles

Intrinsic muscles

Change tongue shape

longitudinal, transverse and vertical fibers

widening and narrowing movement

Extrinsic muscles

In and out movement

Move tongue position

the muscles originate in the tongue and attached to something else other than the tongue

Intrinsic / extrinsic muscles

helps in denture retention by pushing/shaping action

are also to blame for dislodgement (because of its mobility) if the denture is not properly made like overextended denture bases and muscle movement specially the tongue

physical factors affecting retention of dentures

adhesion

cohesion

atmospheric pressure

retention

the quality of a denture that resists movement away from the tissue

matagak / ma-dislodge

stability — mu-rotate, sea-saw, luag, mu-lihok pero in place ra

adhesion

the physical force involved in the attraction between two unlike molecules

in case of denture, it is the attraction between the denture and saliva and between saliva and oral mucosa

ex: denture-saliva, saliva-soft tissue

cohesion

physical attraction between similar molecules

ex: salivary molecules

atmospheric pressure

when u seat the denture, air escapes from underneath the fitting surface, forming a partial vaccum between the mucosa and the denture, resulting in trapped reduced pressure