A Comparative Evaluation of Vertical Marginal Gap for Vented and Precemented Cad-Cam Zirconium Copings on Angulated Abutments: An In vitro Study

ABSTRACT

Objective:

To evaluate vertical marginal gap after cementation of Zr (zirconium) copings with palatal vent, open vent, and precementation technique on angulated abutments resulting from cement entrapment between intaglio surface of copings and angulated abutments.

Materials and Methods:

Twenty-four angled abutments and 24 CAD-CAM Zr copings were assigned to three groups depending on the type of cementation technique, comprising eight copings with palatal vent, open vent, and no vent, respectively. Vertical marginal gaps between abutment shoulder and coping margin were evaluated at four points: buccal, palatal, mesial, and distal. The readings were statistically analyzed.

Results:

The average mean value of vertical marginal gap at all sites for Group A with palatal vent was 158.45, for Group B with open vent was 151.84, and for Group C using precementation technique was 163.58. A statistically non-significant difference was seen for values between all sites (P > 0.05) for all groups.

Conclusion:

The average vertical marginal gap for Group B was comparatively lower compared to Groups A and C.

INTRODUCTION

Implant dentistry is an important part of oral healthcare, involving oral surgery, restorative dentistry, and prosthodontics.[1] Optimal implant restoration depends on four positional parameters: buccolingual, mesiodistal, and apico-coronal positions relative to the implant platform and angulation of the implant.[2]

Implant-supported restorations can be screw or cement-retained. Howeever, use of cement-retained restorations allows greater freedom in implant placement and establishment of stable occlusal contacts.[3,4]

The development of CAD-CAM technology focuses on the precise manufacturing of Zr with high strength, toughness, and flexibility.[1]

Complete seating of copings over abutments can be achieved using an abutment analog. Palatal vent hole also reduces excess cement.[3-5]

The current study aims at comparing the effect of the palatal vent, open vent, and precementation technique of Zr copings, to evaluate the vertical marginal gap between the coping and the abutment.

MATERIALS AND METHODS

Twenty-four specimen blocks fabricated of die stone-type IV (Utrarock, Kalabhai) were divided into three groups having eight blocks embedded with implant analogs having an internal hex based on the technique of cementation they received. Twenty-four angled titanium abutments (15°) (Adin), collar height of 3 mm, were tightened using hex driver (Adin) and ratchet (Adin) to a torque of 35 Ncm.

Four sites were marked: distal, mesial, buccal, and palatal.

Twenty-four Zr copings of 0.6 mm thickness, fabricated using CAD-CAM technology, were divided into three groups as follows: [Figure 1].

Figure 1.

Zirconia copings. Group A: palatal vent of 0.75 mm, Group B: open vent, elliptical in diameter, and Group C: no vent

Group A: Palatal vent in the inciso-palatal portion, 0.75 mm in diameter.

Group B: Open vent, elliptical in diameter similar to the access opening of the angulated abutment.

Group C: No vent. Precementation technique using silicone abutment analog [Figure 2].

Figure 2.

Silicone abutment analog

Technique of cementation:

Groups A and B: The copings filled with zinc oxide non-eugenol (ZOnE) cement (3M, ESPE) on the occlusal half were seated with finger pressure, later held under a static load of 20 N for 60 sec, under the Universal Testing Machine (ACME Engineers).

Group C: The intaglio surface of the copings filled with ZOnE cement was seated with finger pressure over the abutment analog to displace excess cement and later seated on the angulated abutment with finger pressure, then held under a static load of 20 N for 60 sec, under the Universal Testing Machine (ACME Engineers).

The discrepancy between the abutment shoulder and the coping margin for all specimens was viewed under the stereomicroscope (30x) (Wuzhou New Found Instrument Co. Ltd.) at four sites, that is, distal, mesial, buccal, and palatal. The vertical marginal gap was measured using an Image Analysis System (Chroma Systems Pvt. Ltd.) [Figure 3].

Figure 3.

Discrepancy between the abutment shoulder and the coping margin was viewed under the stereomicroscope

RESULTS

The mean value of vertical marginal gap for Group A: distal site was 158.688, mesial site was 150.800, buccal site was 155.138, and palatal site was 169.175; for Group B: distal site was 158.575, mesial site was 150.525, buccal site was 148.188, and palatal site was 150.075; for Group C: distal site was 150.288, mesial site was 155.600, buccal site was 187.150, and palatal site was 161.288. The P value of Group A was 0.998, in Group B was 0.916, and in Group C was 0.957.

The average of vertical marginal gap for Group A at all the site was 158.45, for Group B was 151.84, and for Group C was 163.58. The P value obtained was 0.756. There was a statistically non-significant difference seen for the values between all the sites (P > 0.05) for all the groups [Table 1].

Table 1.

Inter-group comparison of marginal gap

Group	Site	n	Mean	Std. deviation	Std. error	Median	Chi-square value	P value of Kruskal–Wallis test
Group A	D	8	158.688	50.5700	17.8792	143.65
	M	8	150.800	30.7396	10.8681	151.60	0.043	0.998#
	B	8	155.138	41.1507	14.5490	147.75
	L	8	169.175	73.0590	25.8302	156.10
Group B	D	8	158.575	43.3534	15.3277	155.45
	M	8	150.525	32.5063	11.4927	138.95	0.515	0.916#
	B	8	148.188	26.0170	9.1984	142.65
	L	8	150.075	20.8106	7.3576	140.40
Group C	D	8	150.288	27.5602	9.7440	156.90
	M	8	155.600	45.5376	16.1000	146.25	0.315	0.957#
	B	8	187.150	80.6950	28.5300	147.40
	L	8	161.288	51.0436	18.0466	144.30

^#Non significant

Figure 4 indicates that, marginal gap was higher in Group C followed by Group A and B.

Figure 4.

Inter-group comparison of marginal gap between Groups A, B, and C in μm (average)

DISCUSSION

Implant placement and restoration to replace single or multiple teeth in the esthetic zone are an especially challenging task for the clinician.[2]

Cavallaro et al.[3] and Ellakwa et al.,[1] facilitate paralleling non-aligned implants, avoid anatomical structures, and reduce treatment time and the need to perform guided bone regeneration procedures.

Zaugg et al.,[6] Wadhwani et al.,[7] Cavallaro et al.,[3] and Shadid et al.[4] concluded that cement-retained prostheses allow simplicity of use, passivity of fit, improved esthetics, and control of occlusion.

To enhance seating, conventional venting, internal venting, die spacing, and vibration have all been recommended.[8] With vented crowns, Zaugg et al.[6] found that less marginal excess cement was produced. Patel et al.[8] recommended 0.75-mm mid-palatal vent hole on anterior crowns to reduce the marginal excess cement.

Dumbrigue, Abanomi, and Cheng et al.[6] introduced a pre-cementation device (e.g., abutment analog) to displace excess cement and provide a uniform thin cement layer. Cement excess was reduced by 32% and 59% with a palatal vent hole.[5] Ellakawa et al.[1] stated that CAD-CAM technology focuses on the precise manufacturing of zirconia ceramics with high strength, toughness, and flexibility.

The current study showed that the average vertical marginal gap for groups with open vent was comparatively lower than groups with palatal vent and precementation technique.

A statistically non-significant difference was seen for the values between all the sites (P > 0.05) for all the groups.

CONCLUSION

The average vertical marginal gap at all the sites for Group B was comparatively lower than that for Groups A and C.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.