Should the vent hole of posterior implant crowns be placed on the lateral surface? An in vitro study of the hydrodynamic feature of cement extrusion and retention ability

Abstract

Although placing a vent hole on the occlusal surface of the implant crown can reduce cervical marginal cement extrusion, it has disadvantages. Transferring the hole to the buccal or lingual surface of the posterior implant crown could therefore be an alternative solution. This study investigated the effect of transferring the vent hole to the lateral side of the implant posterior crown on the hydrodynamics of excess cement extrusion and the crown's retention ability. Specially fabricated posterior implant crowns were divided into five groups: crowns with an occlusal hole (OH), occlusal lateral hole (OLH), middle lateral hole (MLH), cervical lateral hole (CLH), and no hole (NH). Each set of implant analog-abutment-crown specimens was wrapped in a polymethylacrylate base. The base of the implant crown was divided into four 90-degree quadrants along the diagonal of the square base with a pen mark. Cement was used to bond the crowns and the abutments, and the weight of cement extrusions at the vent holes and the abutment cervical margins were calculated. The distribution of cement extrusion at the margin was photographed in each quadrant, and the areas of surface coverage of cement extrusion were compared with ImageJ software. Retentive strength was measured as the dislocation force using a universal testing machine. One-way analysis of variance was used for result analysis. The cervical marginal cement extrusions of crowns with lateral holes (OLH, MLH, and CLH) were significantly less than that of NH crowns (P<0.05), but more than that of OH crowns (P<0.05). Subgroup analysis among the lateral hole groups indicated that the higher the position of the lateral hole, the lower the weight of the cement extrusion, and the smaller the total distribution area of cement extrusion. The cement extrusion distribution area was larger in the quadrant with the hole than in those opposite and next to the hole. Retention strength comparison indicated no significant difference between crowns with NH, OH, or lateral holes. Transferring the vent hole of the posterior implant crown to the lateral side could reduce cement extrusion at the cervical margin while reducing retention strength deterioration and the esthetic drawbacks caused by occlusal hole opening.

Fig 1

Specially fabricated implant crowns with different hole designs (A) lateral view of the specially fabricated NH crown, (B) crown with an occlusal vent hole (OH), (C) schematic diagram of the vent hole positions of the OLH, MLH, and CLH groups.

Fig 2

(A) Standardized weight pressuring after cement bonding. (B) Division of the quadrants according to the position of the hole. The quadrant with the lateral hole as S1, opposite the hole as S2, and the two quadrants adjacent to the hole as S3.

Fig 3

(A) Photographing the cemented crowns at a set photo studio and (B) ImageJ evaluation process for the calibration and calculation of the distributed cement extrusion areas.

Fig 4. Retentive strength testing of the cemented implant crowns using a universal testing machine.

Fig 5

The cement extrusion at the (A) vent hole, (B) abutment cervical margin, and the (C) composition of the extruded cement from different sources. Lowercase superscript letters denote significant differences when comparisons were conducted among (a) NH, (b) OH, (c) OLH, (d) MLH, and (e) CLH (P< 0.05).

Fig 6. The mean cement extrusion areas for implant crowns with different lateral hole positions.

(S1: quadrant of the hole, S2: quadrant opposite the hole, S3: quadrants adjacent to the quadrant of the hole).

Fig 7. Retentive strength (N) for implant crowns with different hole designs.