Clinical Orthodontics: Third Molars and Crowding

Practice flashcards covering the clinical implications, statistical prevalence, and research studies regarding the relationship between third molars and dental crowding as discussed in the lecture notes.

Lower Third Molar Retention Prevalence

According to Björk, $45\%$ of the population will have a retained third molar.

Sabino, Selero, and Furfaro Study

An epidemiological study that found lower third molars to have the highest incidence of retention: piece 38 (3MII) at $33.6\%$ and piece 48 (3MID) at $32.4\%Base$.

Vego

A researcher who demonstrated that the loss of the arch perimeter averaged $0.8\,mm$ more in cases with the third molar than in cases where it was congenitally absent.

Schullof

Proposed that if the distance between the ramus and the second lower molar is known, the probability of retention can be determined.

Computerized Prediction Error

The margin of error for computerized growth prediction methods when estimating available space for molars is approximately $2.8\,mm$.

Kaplan

Argued that the presence of lower third molars does not seem to produce a higher degree of anteroinferior crowding or relapse compared to cases of agenesis.

Ricketts' Rule of Eruption

Based on a study of 100 skeletons, Ricketts concluded that if half of the lower third molar is hidden behind the ramus, there is a $50\%$ probability of eruption.

Point Xi

The center of the ramus, used by Turley as a reference point to measure the distance to the distal face of the second molar to evaluate available space.

Turley's Space Distances

Determined average available space distances: $21\,mm$ for retained molars, $25\,mm$ for marginal molars, and $30\,mm$ for those erupted in occlusion.

Seiso's Gender Measurements

Found that males and females require $27.5\,mm$ and $23.6\,mm$ respectively from Xi to the distal of the second lower molar.

Germectomy

A prophylactic procedure, often performed between the ages of 13 and 22, used to prevent anterior crowding by removing the third molar germ.

Anderson and Burlington Growth Center Study

Determined the probability of losing the second lower molar is $10\%$ in relation to mandibular growth.

Slodov's Contraindications

Listing situations where repositioning a third molar is contraindicated: lack of an antagonist, malformed tooth, size extremes (too large or small), and a tendency toward an open bite.

Richardson's Agenesis Ratio

Reported that the ratio of women to men with congenitally absent third molars is $3:2$.

Laskin's Survey

A 1971 survey of over 600 orthodontists and 700 maxillofacial surgeons where $65\%$ believed third molars produce crowding in anteroinferior incisors.

Carbonell, O. Survey

A provincial survey of orthodontists where $74\%$ agreed that the third molar produces crowding in the anteroinferior sector.