Failure rates for stainless steel versus titanium alloy infrazygomatic crest bone screws: A single-center, randomized double-blind clinical trial

Abstract

Objectives: To compare failure rates for stainless steel (SS) and titanium alloy (TiA) bone screws (BSs) placed in the infrazygomatic crest (IZC).

Materials and methods: A total of 386 consecutive patients (76 male, 310 female; mean age 24.3 years, range 10.3-59.4 years) received IZC BSs (SS or TiA) via a double-blind, split-mouth design. BSs penetrated attached gingiva (AG) or moveable mucosa (MM) with 5 mm of soft tissue clearance. All BSs were immediately loaded and reactivated monthly with ≤14 oz (397 g or 389 cN) applied directly to the upper archwire bilaterally for 6 months to retract the maxilla to correct Class II or bimaxillary protrusion.

Results: Of the 772 devices, there were 49 (6.3%) failures: 27 SS (7.0%) and 22 TiA (5.7%). The 1.3% difference was not statistically significant ( P = .07). There was no significant relationship between SS or TiA failures relative to (1) right vs left side, (2) unilateral vs bilateral, or (3) age at failure. Significantly ( P < .05) increased failure rates were noted for SS screws in only two subgroups: AG site (7.4%) and right side (7.8%). Unilateral failure occurred in 21 patients (5.4%), and bilateral failures occurred in 14 of the total 772 patients (1.8%).

Conclusions: The overall success rate of 93.7% indicates that both SS and TiA are clinically acceptable for IZC BSs.

Keywords: Bone screws; Double blind; Infrazygomatic crest; Predisposition to failure; Randomized clinical trial; Skeletal anchorage; Split-mouth design; Stainless steel; Titanium alloy.

Figure 1

Bone screw specifications (SS or TiA).

Figure 2

(a) An IZC bone screw (gold) is placed inferior to the zygomatic process relative to the second deciduous molar (E), first molar (6), and second molar (7). (b) Occlusal view of the maxilla shows the preferred site for an IZC BS (red dotted circle).

Figure 3

(a) Orientation of the BS at the start of the installation procedure. (b) Penetration of the approximately 1-mm bone plate on the buccal surface. (c) Change in orientation in the frontal plane as the BS is rotated to place.

Figure 4

(a) The completed installation procedure as illustrated in Figure 2. (b) The TAD is buccal to the roots of the maxillary molars. (c) A transverse cross section of the maxilla distinguishes between an extra-radicular vs interradicular insertion of a TAD. See text for details.

Figure 5

Flow chart for the randomized clinical trial.

Figure 6

(a) About 5 mm of clearance from the head of the BS to the soft tissue surface is needed for effective hygiene. The mucogingival junction separates the AG from the MM. (b) An IZC bone screw anchors an elastomeric chain that is attached to the archwire mesial to the maxillary canine bracket.

Figure 7

(a) 0M: Left buccal view of a severe Class II malocclusion at the start of treatment. The canine discrepancy is marked with vertical lines. (b) 11M: Initiation of maxillary retraction with IZC anchorage. (c) 15M: Progress after 4 months of maxillary retraction. (d) 20M: Class I occlusion is achieved after 9 months of maxillary retraction.

Figure 8

Overall failure rate (6.3%) is partitioned into SS (7.0%) and Ti (5.7%). The 1.3% difference between SS and Ti (TiA) was not significant (P = .07).

Figure 9

Failure rates are shown for IZC bone screws placed in AG, MM, as well as on the right or left side. The only significant differences (P < .05) were for SS screws placed in AG and on the right side.