Initial forces experienced by the anterior and posterior teeth during dental-anchored or skeletal-anchored en masse retraction in vitro

Abstract

Objective: To investigate initial forces acting on teeth around the arch during en masse retraction using an in vitro Orthodontic SIMulator (OSIM).

Materials and methods: The OSIM was used to represent the full maxillary arch in a case wherein both first premolars had been extracted. Dental and skeletal anchorage to a posted archwire and skeletal anchorage to a 10-mm power arm were all simulated. A 0.019 × 0.025-inch stainless steel archwire was used in all cases, and 15-mm light nickel-titanium springs were activated to approximately 150 g on both sides of the arch. A sample size of n = 40 springs were tested for each of the three groups. Multivariate analysis of variance (α = 0.05) was used to determine differences between treatment groups.

Results: In the anterior segment, it was found that skeletal anchorage with power arms generated the largest retraction force (P < .001). The largest vertical forces on the unit were generated using skeletal anchorage, followed by skeletal anchorage with power arms, and finally dental anchorage. Power arms were found to generate larger intrusive forces on the lateral incisors and extrusive forces on the canines than on other groups. For the posterior anchorage unit, dental anchorage generated the largest protraction and palatal forces. Negligible forces were measured for both skeletal anchorage groups. Vertical forces on the posterior unit were minimal in all cases (<0.1 N).

Conclusions: All retraction methods produced sufficient forces to retract the anterior teeth during en masse retraction. Skeletal anchorage reduced forces on the posterior teeth but introduced greater vertical forces on the anterior teeth.

Keywords: Dental anchorage; En masse retraction; Force analysis; Orthodontic biomechanics; Orthodontic simulator; Skeletal anchorage.

Figures

Figure 1.

Orthodontic SIMulator (OSIM) with the skeletal anchorage adapter.

Figure 2.

Representation of treatment groups 1 (left), 2 (middle), and 3 (right) on OSIM.

Figure 3.

Schematic representation of Fd and FdSUM for the anterior segment.

Figure 4.

Vertical (left) and retraction (right) forces acting on the anterior segment for all three treatment groups (* statistically significant differences; P

Figure 5.

Protraction (top left), palatal (top right), and vertical (bottom) forces acting on the posterior segment for all three treatment groups (* statistically significant differences; P

Figure 6.

Vertical force profile at each tooth for all three treatment groups.

Figure 7.

Retraction forces applied to individual teeth in the anterior segment.