Effects of the Screw-Access Hole Diameter on the Biomechanical Behaviors of 4 Types of Cement-Retained Implant Prosthodontic Systems and Their Surrounding Cortical Bones: A 3D Finite Element Analysis

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

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.

Effect of Vent Hole and Cement Type on Fracture Resistance of CAD-CAM Monolithic Zirconia Crowns

PURPOSE

To assess the fracture resistance of monolithic zirconia crowns cemented with different types of cement on cement-retained implant abutments.

MATERIALS AND METHODS

Forty implant analogues were positioned in acrylic resin blocks, and cement-retained straight implant abutments were fastened to the analogues. Crowns were designed with/without occlusal vent holes and produced from monolithic zirconia blocks by the CAD-CAM technique. The two crown types were divided into two groups and cemented with resin and zinc-polycarboxylate cement under 5 kg weight. A universal testing machine applied compressive forces to the crowns until fracture. Fracture resistance values were analysed using two-way ANOVA and the independent samples t-test with statistical significance set at p < 0.05.

RESULTS

According to the two-way ANOVA results, although the crown design did not have a significant effect on fracture resistance (1417.65 ±337.39 N, 1565.16 ±517.12 N; crowns with and without vent holes, respectively), the main effect of the cement variable on the fracture resistance was significant. Zinc-polycarboxylate cement (1680.1 ±375.23 N) showed higher fracture resistance than resin cement (1302.71 ±420.64 N) in the crowns designed with vent holes (p< 0.005).

CONCLUSION

The use of cement-retained implant-supported monolithic zirconia crowns with an occlusal vent hole is safe, and zinc-polycarboxylate cement use may be an appropriate choice for cementation of these crowns. This article is protected by copyright. All rights reserved.

Selection of 1-mm venting or 2.5-mm screw access holes on implant crowns based on cement extrusion and retention capacity

Background

This in vitro study aimed to provide evidence regarding the selection of hole diameters of implant crowns to reduce excess cement extrusion at the abutment margin, and to examine the maintenance of their retention capacity in anterior and posterior cement-retained implant crowns.

Methods

Six groups of implant crowns were prepared according to the position of the teeth and the size of their holes as follows: anterior crown without hole (ANH), anterior crown with 1-mm mini venting hole (AMH), anterior crown with 2.5-mm regular screw access hole (ARH), posterior crown without hole (PNH), posterior crown with 1-mm mini venting hole (PMH), and posterior crown with 2.5-mm regular screw access hole (PRH). Temporary cement was used to bond the crowns to the abutments. The mean amount of excess cement extrusion among the different groups at the abutment margin was calculated. Retentive strength under different hole designs was measured as the dislocation force of the crown using a universal testing machine. One-way ANOVA and Welch’s t-test were used to analyze the results.

Results

The average amounts of extruded excess cement were 18.96 ± 0.64, 1.78 ± 0.41, and 1.30 ± 0.41 mg in the ANH, AMH, and ARH groups, respectively, and 14.87 ± 0.36, 1.51 ± 0.40, and 0.82 ± 0.22 mg in the PNH, PMH, and PRH groups, respectively. The hole opening in the crowns could significantly reduce residual cement regardless of its size (p < 0.001). The mean retentive strengths were 54.16 ± 6.00, 47.63 ± 13.54, and 31.99 ± 7.75 N in the ANH, AMH, and ARH groups, respectively, and 57.84 ± 10.19, 53.22 ± 6.98, and 39.48 ± 5.12 N in the PNH, PMH, and PRH groups, respectively. The retention capacity of the implant crown deteriorated rapidly as the holes on the crown surface enlarged.

Conclusions

The presence of a hole on the implant crown reduced the amount of excess cement. The retention ability of the implant crowns deteriorated as the size of the hole increased. Considering the esthetic effect of the crown and the possible influence on crown retention, an implant crown with a 1-mm mini venting hole is a better clinical choice than the one with a 2.5-mm regular screw access hole.

Esthetic Evaluation and Acceptability of Different Hole Designs on Implant Crowns from the Perspective of Patients and Dentists in China

PURPOSE

Abutment access hole on dental implant crowns may facilitate crown retrieval and reduce cement overflow but present esthetic obstacle for patients. This study aimed to investigate the esthetic evaluation and acceptability of implant crowns with different hole designs from the perspective of patients and dentists.

MATERIALS AND METHODS

Anterior and posterior implant zirconia crowns were fabricated into three types: no hole (NH), 1 mm micro hole (MH), and 2.5 mm regular hole (RH). The NH crown was set as the control, and the anterior and posterior crowns with MH and RH were evaluated. The subjects, who were recruited randomly, were comprised of lay patients (n=60) and professional dentists (n=30). All subjects were invited to evaluate the esthetic performance of MH and RH crowns on a Visual Analog Scale (VAS), rate them from 0 to 10, state their acceptability of these crowns, and label them as acceptable and unacceptable.

RESULTS

The ANOVA analysis of the VAS esthetic evaluation showed that the size of the hole, the position of the teeth, and the professional background of the subject significantly and independently affected esthetic perception. Crowns with MH in the posterior position had higher esthetic scores and acceptability compared with crowns with RH in the anterior position, and dentists tended to show higher acceptance and better esthetic rating for crowns with holes compared with lay patients.

CONCLUSION

The hypothesis that patients and dentists hold similar esthetic evaluations or acceptability towards implant crown hole designs was rejected. Lay patients had a lower tolerance for venting holes than dentists. Crowns with 1 mm micro holes were more recommendable than crowns with regular abutment access holes from the point of view of satisfying patients' esthetic needs.