Geometry of Implant Abutment Surface Improving Cement Effectiveness: An In vitro Study.

AIM: The aim of the study was to investigate whether the surface geometry or topography of implant abutments affects the retentive strength of prosthesis cemented with zinc phosphate on standard machined, sandblasted, and grooved implant abutments and to compare the results between them.
MATERIALS AND METHODS: Fifteen similarly shaped implant abutments (MDcpk61; MIS Implant Technologies Ltd.,) (height 6.0 mm and 6-degree taper) were divided into three groups (n = 05): Group I - standard machined abutments without grooves, Group II - sandblasted abutments (same as Group I but sandblasted with 50 μ aluminum oxide), and Group III - abutment with prefabricated circumferential grooves. Further in these groups of 15 abutments, 5 abutments each are to be taken to check the retentive force of zinc phosphate cement. Fifteen identical cast copings was prepared to fit all 15 abutments. The castings will be cemented to each group of abutments with an above-mentioned luting agent. After thermal cycling and storage for 6 days in a water bath, a retention test is to be done with a tensile testing machine (Instron) (5 mm/min) and retentive forces will be recorded. Data will be subjected to one-way ANOVA test and Student's t-test.
RESULTS: For zinc phosphate cement, F = 30.53 (>3.59 for P = 0.05) shows a statistically significant difference between all the three groups.
CONCLUSION: Circumferential grooves on implant abutments give better retention when compared with standard machined (plain) and sandblasted abutments despite marked difference. CLINICAL SIGNIFICANCE: Retention of restoration depends on the surface of the abutment as well as the luting agents used. Incorporation of retentive grooves can enhance retention of prosthesis, especially in situation of short abutments. Copyright:

INTRODUCTION

The implant-supported prosthodontics introduced by the Brånemark group was directed toward the treatment of fully edentulous patients, the abutments developed by the Brånemark team had a limited esthetic capability. As the osseointegrated implants were created to treat mostly edentulous patients, there was a solid need to present a few alterations for the transmucosal projections.[12] It was not until the beginning of the 1980s when an implant prototype version with a removable abutment was used clinically. Experiments with two-part implants were carried out in the 1970s. The use of the removable abutment version allowed better handling of temporary restoration and wider prosthetic choices, especially in conditions of single-tooth replacements, particularly in the anterior region of the maxilla or in cases of misaligned implants or difficult interocclusal space conditions.[3]

An implant restoration is said to be successful when it performs its function for which it is placed. The success of oral rehabilitation of dental implants not only depends on osseointegration but also on maintenance of the prosthesis on the implant abutment.[4] Implant restorations can be[5] screw retained, cement retained, or combination of both. Many dental professionals concluded that[67] cement-retained crowns are finer for esthetics and occlusion; screw-retained crowns are a necessity for easy retrievability.

According to Goodacre et al., common mechanical implant complications are[8] loss of retention of prosthesis (376/113 prostheses) is 30%, prosthesis screw loosening (4501/312 screws) is 7%, and prosthesis screw fracture (7094/282 screws) is 4%.

According to the above study, loss of retention of the cemented prosthesis is the most common mechanical complication. Hence, it is more important for us to concentrate on increasing the retention of the cement-retained prosthesis on the implant abutment. In fact, the use of cement-retained prosthesis has increased, because of its ability to optimize occlusal interdigitation, enhance esthetics, provide a passive fit, decrease the cost, and improve loading characteristics.

The retention of cemented prosthesis has been shown to be influenced by various parameters such as abutment size (height and width), abutment texture, and the convergence angle between the walls of the abutment and the cements.

Factors controlled by clinician are[9] surface roughness and luting agents. Surface roughness increases the retention due to resulting microretentive ridge and groove patterns. The surface treatment was done to increase the retention10, increasing the size and increasing the surface area by following methods: Sandblast (50-μm aluminum oxide), roughened with diamond bur, also making retentive uiding grooves, occlusogingival preparation height, parallelism of opposing walls and controlling taper.

The present study is conducted to investigate whether the surface geometry or topography of implant abutments affects the retentive strength of prosthesis cemented with zinc phosphate on standard machined, sandblasted, and grooved implant abutments and to compare the results between them.

MATERIALS AND METHODS

Preparation of specimens

Fifteen similarly shaped implant abutments (MDcpk61; MIS Implant Technologies Ltd.) (height 6.0 mm and 6° taper) were divided into three groups (n = 05) [Figure 1]:

Figure 1

(a) Standard machine abutment, (b) sandblasted abutment, (c) grooved abutment

Group I – Standard machined abutments without grooves

Group II – Standard machined abutments (same as Group I but sandblasted with 50 μ aluminum oxide), and

Group III – Abutment with prefabricated circumferential grooves (each groove of MIS Implant Tech measured using stereomicroscope ×20 magnification was 175.2 μm wide and 86.6 μm deep)

The surface topography of the tested abutments obtained using optimal microscopy (stereomicroscopy zoom) under ×10 magnification

Surface roughness parameters

Recorded using surface roughness measuring instrument (Mitutoyo, Praj Laboratory) Table 1

Table 1

Surface roughness parameters

Surface roughness parameter	Standard machined abutment (µm)	Sandblasted abutment (µm)	Grooved abutment (µm)
Ra	0.182	2.619	8.128
Rz	1.003	13.948	44.793
Rq	0.218	3.240	9.735

Ra: Arithmetic mean of the absolute departures of the roughness profile from a mean line, Rz: Mean value of the maximum peak to valley height of the profile, Rq: Root mean square parameter corresponding to Ra

Standard machine abutment

Sandblasted abutment

Grooved abutment.

All 15 analogs were embedded in self-curing acrylic resin blocks. Each implant abutment was placed in each analog.

Standard machined abutment: 5 (without any alteration)

Sandblasted: 5 (the surfaces of standard machined abutment were sandblasted with 50 μm aluminum oxide at the pressure for 10 s at a distance of 10 mm maintained between the specimen and sandblasting gun tip)

Grooved implant abutment: 5 (each groove of MIS Implant Tech measured using stereomicroscope × 20 magnification was 175.2 μm wide and 86.6 μm deep)

Fifteen identical NiCr cast copings were prepared to fit all 15 abutments. So first, 15 individual wax copings were formed directly on the abutments. Then., no. 10 wax sprue was used to form a loop and added to the occlusal surface of each coping to allow the samples to be attached to the tensile testing machine [Figure 2].

Figure 2

Application of spacer, wax pattern, casted abutment

Prior to cementation, the abutment implant assemblies were cleaned in an ultrasonic bath for 15 min with distilled water and then steam cleaned.

Luting of copings

Each coping was cemented onto the respective abutments with zinc phosphate following standard procedures. A static load of 50 N was applied for 10 min on the abutment and after setting, excess cement was removed [Figure 3].

Figure 3

Cementation of coping under a static load of 50N using digital weighing balance machine

Then, specimens were stored in 100% humidity at 37°C for 1 h and thermocycled 500 times between 5°C and 55°C with a dwell time of 10 s.

Testing for tensile strength

At that point, the examples were amassed in the universal testing machine (computerized, programming based: Star Testing System; Model no. STS-248) and were exposed to a pullout test (maintenance) at a crosshead speed of 5.0 mm/min. The powers needed to eliminate the copings were recorded in Newtons.

The copings and abutment were assessed for disappointment mode as indicated by the area of the residual cement. Full-thickness buildups on the abutment or giving were indicated a role as cement failure. Durable failure was meant when the disappointment was inside the cement and fractional thickness buildups were seen on the abutment and the contradicting surface of the projecting this mix of adhesive and cohesive failure was viewed as a blended failure [Figure 4].

Figure 4

(a) Adhesive type of cement failure, (b) Mixed type of cement failure (c) Mixed type of cement failure

RESULTS

All the statistical tests were conducted at P = 0.05 [Tables 2, 3 and Graph 1] which showed a statistically significant difference between the three groups. Moreover, comparison between two groups each was done by Student's t-test [Table 3] according to which there was a statistically significant difference between sandblast (853.89N) and standardized machine (267.93 N), a statistically significant difference between standardized machine (267.93 N) and grooved abutment (1005.31 N) was also observed, and finally, there was no statistically significant difference between sandblasted abutments and grooved abutment. However when we compare all the three groups according to readings, grooved implant abutment gives 3.59 times better retention.

Table 2

Readings of pullout test using a universal testing machine

Sample number	Standard machine retention force (n)	Sandblasted retention force (n)	Grooved retention force (n)
1	219.52	756.65	1095.64
2	191.10	795.07	1072.12
3	415.52	933.25	870.52
4	213.64	714.42	868.28
5	299.88	1070.1	1120.0
Average	267.93	853.89	1005.31
SD	82.46	130.69	112.00
F	30.53 (>3.59 for P=0.05*)

*Mean retentive strength of standard machined abutment group was statically different from other mean. SD: Standard deviation

Table 3

Comparision between two groups by Student’s t-test

Between abutment groups	t
Standard machine abutment group and sandblasted abutment group	7.58 (>2.31)
Standard machine abutment group and grooved implant abutment group	10.60 (>2.31)
Sandblasted abutment group and grooved implant abutment group	1.76 (<2.31)

Graph 1

Descriptive statistics of retentive strength (in Newtons)

DISCUSSION

Zinc phosphate has been indicated for the permanent cementation of implant-supported crowns because it yields high retentive strength when compared to most luting agents.[111213] According to many studies, the surface topography of implant abutment has a greater impact on crown retention when cements with lower mechanical strengths are used for example:

In a study done by Kim et al.,[4] the retention of implant-supported single restorations showed a significant interaction between the type of temporary cement and abutment surface condition (machined, air abraded, and roughened with diamond bur). A study done by Cano-Batalla et al.[14] compared between standard machine implant abutment and sandblasted abutments (50 μm aluminum oxide) and concluded that airborne-particle abrasion and abutment height can significantly influence the retention of implant-supported crowns.

Another similar study was performed by de Campos et al.[15] where they compared standard machined, sandblasted, and grooved implant abutments without thermocycling and concluded that sandblasted and grooved had approximately 2.4 times greater mean uniaxial retentive strength than standard, whereas SB (822 N) and grooved (871 N) showed almost similar retentive strength.

CONCLUSION

Among all the three groups, i e., standard machined (267.93 N), sandblasted (853.89 N), and grooved implant abutment (1005.31 N), grooved implant abutment gives better retention than the other two. Hence, the geometry of the implant-abutment surface improves the cement effectiveness by increasing the surface area.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.