Progressive Slicing of Second Deciduous Molars in a Young Patient with Second-Premolar Agenesis

Congenital absence of teeth can result in poor dental positioning, periodontal damage, and a loss of vertical bone dimension, with significant consequences to both function and esthetics.¹ The second premolars have the second highest prevalence of agenesis after the third molars,^2,3 with a bilateral occurrence in 60% of the subjects.^4,5 A number of treatment options have been proposed, the success of which depends largely on early diagnosis to allow spontaneous mesial movement of the first permanent molars into the edentulous spaces.⁶

Simple extraction of the second deciduous molars produces unsatisfactory results in about 75% of these cases.² Premature loss of a second deciduous molar is more detrimental to the dental arch than the loss of a first deciduous molar.⁷ Patients with agenesis of second deciduous molars exhibit changes in the width of the alveolar ridge and a tendency toward mesial inclination of the first permanent molars if the situation is not properly managed during bite development.⁸ Other problems such as vertical bone defects, periodontal pockets, nonaxial distribution of occlusal forces on the first permanent molars, distal migration of the first premolars, and even extrusion of the antagonist molars may occur when the second deciduous molars are extracted prematurely.^9,10

Since the lower second deciduous molars' two roots permit hemisectioning, the slicing procedure was continued in the lower arch after removal of the distal roots.

A partial fixed appliance was placed in the upper arch to control the movement of the first permanent molars (Fig. 4A); no appliance was used in the lower arch due to anterior dental interference. Space was preserved for eruption of the upper and lower first premolars and canines. After five months, a controlled, natural mesial movement of the upper first molars could be seen, along with a gradual, physiological mesial movement of the lower first molars (Fig. 4B).

Treatment Results

Five years after the start of treatment, balanced facial characteristics were obtained, and the permanent dentition was well established with complete space closure, proper horizontal and vertical overjet, and normal molar and canine relationships (Fig. 5). Root parallelism of all teeth (including the first molars) indicated a good prognosis for stability.

Discussion

In a case involving agenesis of the second premolars, the clinician must decide whether to maintain the second deciduous molars in the arch until exfoliation, or to extract them or progressively slice them to allow mesial movement of the first permanent molars. Maintaining the second deciduous molars will preserve the vertical and transverse dimensions of the alveolar bone,¹² but can lead to root resorption and even ankylosis. If ankylosis occurs, the bite will be compromised by inclination of the adjacent teeth, which can lead to progressive infraocclusion.^3,13,14

Extraction of the second deciduous molars can produce satisfactory results if the spaces are closed before eruption of the second permanent molars and complete development of the lower first-premolar roots.¹⁵ Premature extraction will reduce the quantity of alveolar bone, so that later replacement with dental implants could require bone grafting. On the other hand, agenesis of the lower second premolars is often diagnosed after age 9,⁴ which may be too late for spontaneous space closure.¹⁶ If the second deciduous molars are extracted at age 11 or 12, orthodontic forces will be needed to mesialize the first molars.¹⁷

In the case shown here, the patient's age allowed treatment with either extractions or progressive slicing. The latter procedure has a reported 90% success rate, in contrast to the 75% success and other potential drawbacks of second-molar extractions.^2,8-10 The major advantage of slicing is the facilitation of a more physiological movement of the first permanent molars. In the present case, a fixed upper appliance was used only to prevent undesirable tipping and rotation of the first molars, thereby avoiding the need for further orthodontic intervention. The patient finished with a healthy periodontium, a normal bone structure, parallel dental roots, and a satisfactory occlusion.