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 Table of Contents  
RESEARCH
Year : 2022  |  Volume : 22  |  Issue : 1  |  Page : 48-55

Effect of multiple reuse of commonly used implant analogs on the changes in the distance between internal threads: An in vitro study


1 Department of Prosthodontics and Crown and Bridge and Implantology, GITAM Dental College, Visakhapatnam, Andhra Pradesh, India
2 Confident Dental Laboratory, Bengaluru, Karnataka, India

Date of Submission01-Jul-2021
Date of Decision16-Dec-2021
Date of Acceptance21-Dec-2021
Date of Web Publication27-Jan-2022

Correspondence Address:
Ravi Shankar Yalavarthy
Department of Prosthodontics, GITAM Dental College and Hospital, Visakhapatnam, Andhra Pradesh
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jips.jips_335_21

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  Abstract 


Aim: To assess the effect of multiple reuse of implant analogs of three different materials (SS, Ti, Al) on the changes in the distance between internal threads of implant analog by using two die materials at different time intervals (0, 3rd, 6th, 9th, and 12th).
Settings and Design: An in vitro study.
Materials and Methodology: Three commonly used implant analog materials (stainless steel, titanium, and aluminum) and two Type– IV die stone materials (Kalrock and Zhermack Elite) were used to make the samples. A total of sixty implant analogs (20 each), sixty corresponding abutments (20 each) and 720 screws (240 each) were taken, which includes stainless steel, titanium, and aluminum manufactured by Adin, Genesis, and Equinox/Myriad plus, respectively. In addition, silicone (light body consistency) was used to make an impression for the internal thread of implant analogs. The obtained samples were tested for changes in the internal threads of implant analogs while reusing the implant analogs at the interval of times (0, 3rd, 6th, 9th, and 12th) using a stereomicroscope at ×50. Here, the measured values at “0” interval were considered the control group.
Statistical Analysis Used: The values obtained were statistically analyzed using One way ANOVA, independent t test, and dependent t test for multiple comparisons.
Results: Based on the results obtained, the overall comparison of the mean distance between threads 1–2, 3–4, and 5–6 on the replica of internal threads of the stainless steel, titanium, and aluminum implant analog materials at 1–2 has more decrease in distance from 0 to 12th intervals, at 3–4 has less amount of decrease in distance than thread distance at 1–2 from 0 to 12th intervals, and at 5–6 has very less decrease in distance than thread distance at 1–2 and 3–4 from 0 to 12th intervals. On order the mean distance reduction between threads is more at 1–2, followed to that less reduction at 3–4 and very less reduction at 5–6. This infers that the amount of increase in the distance between the internal threads of implant analog at 1–2 has more followed by 3–4 and 5–6, respectively.
Conclusion: From the study, the following inferences are drawn: That the aluminum implant analog internal threads have more amount of increase in the distance between threads followed by stainless steel and titanium. Hence, among the three materials, titanium implant analogs were most efficient for reuse.

Keywords: Abutment, aluminum, implant analog, internal threads, reuse, stainless steel, titanium


How to cite this article:
Yalavarthy RS, Alla JN, Kalluri S, Mahadevan SS, Kumar S, Ronanki S. Effect of multiple reuse of commonly used implant analogs on the changes in the distance between internal threads: An in vitro study. J Indian Prosthodont Soc 2022;22:48-55

How to cite this URL:
Yalavarthy RS, Alla JN, Kalluri S, Mahadevan SS, Kumar S, Ronanki S. Effect of multiple reuse of commonly used implant analogs on the changes in the distance between internal threads: An in vitro study. J Indian Prosthodont Soc [serial online] 2022 [cited 2022 May 29];22:48-55. Available from: https://www.j-ips.org/text.asp?2022/22/1/48/336681




  Introduction Top


There were many more treatment procedures in dentistry today, but dental implants involve scientific innovation, analysis, understanding, and application in clinical practice. Dental implants are considered the most significant innovation of the present generation. A dental implant is a replacement for the root (or) roots of a tooth.

The contact between abutment and implant platform was a key factor because it reduces the load over the abutment screw, warranting these components high efficiency. Strain induced due to misfit can cause changes in screw geometry.

The success of a screwed connection was directly related to the preload reached during torque and the maintenance of this preload with the time. It was suggested that the screw loosening originates from the separation between the screw and abutment surfaces and the high-level stresses generated over the screws.[1] This was done at the time of final prosthesis fabrication in the laboratory. Multiple tightening and loosening of abutment screw by the laboratory personnel can cause change in internal threads of implant analogue. This further leads to abutment screw loosening on the implant.

Abutment screw loosening is recognized as a common complication with implant restorations which occurs on functional loading. When the abutment is fixed by tightening the screw, threads of the screw and the internal threads of the implant and implant analogs can get deformed. Extensive research has been carried out on the deformation of abutment screw, but changes on the internal threads of implant analog have not been studied till now.

The purpose of the present in-vitro study is to assess the effect of multiple reuse of implant analogs of three different materials (stainless steel, titanium, aluminum) on the changes in the distance between internal threads of implant analog by using two die materials at different time intervals (0, 3rd, 6th, 9th, and 12th).


  Materials and Methods Top


A total of sixty implant analogs, sixty corresponding abutments and 720 screws were taken, which includes 20 each Stainless steel (Adin Dental Implants), Aluminum (Equinox/myriad plus Dental implants) and Titanium (Genesis/Aktiv Dental implants) manufactured implant analogs by different companies. Two different companies (Kalabhai and Zhermack) of die stone materials were used to mount the implant analogs. All these materials were procured through the open market. IRB number for the above said study is 08607201801. Ethical commitee Gitam Dental College Regd. No. EC/NEW/INST/2021/1522.

A total of 60 implant analogs and corresponding abutments of different materials (each material 20 in number), including stainless steel, titanium, and aluminum were bought from the open market. The time intervals included in the study were 0, 3rd, 6th, 9th, and 12th. In these intervals, the '0' time interval values were considered control group values.

At “0” interval (i.e., without embedding the analog into the die stone)

To maintain the four standard points for measuring any parameter on the implant analogue an acrylic die of square shape was prepared by using the clear autopolymerizing acrylic resin. In this, acrylic die acts as a keyhole and implant analog acts as a key [Figure 1]. Hence, the acrylic die holds the implant analog and then marked the A, B, C, and D marks at the midpoint of each side of the square on this acrylic die. The implant analog was then placed in the acrylic die and then transferred the markings on to implant analog [Figure 2].
Figure 1: Customized acrylic die with markings of (A-D)

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Figure 2: Implant analog and abutment assembly placed in acrylic die and transferring the marks

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Internal threads

After that, for evaluating the internal threads implant analogs at “0” interval, (i.e., before placing the abutment) an impression was made using an addition silicone (light body consistency) which acts as a replica for the internal threads of implant analog. The impression material (base paste and catalyst paste) was manipulated following the manufacturer's instructions and loaded into the 5 ml syringe. With the help of a syringe, the material was carried to the implant analog and injected with a 1.2 mm wide-bore needle into the implant analog [Figure 3]. An impression for internal threads of the implant analog was made. After polymerization of the impression material, the “A” mark was transferred onto the impression at the collar end. This was the position used to measure the distance between threads for every sample. Then, it was carefully removed from the implant analog without any distortion. This was made for every sample. The impression retrieved was then evaluated for measuring the distance between the threads at 1–2, 3–4, 5–6, i.e., from collar end to apical end at the marked position by using a stereomicroscope at ×50 by an image processing software [Figure 4] and [Figure 5]. Then, the values were tabulated and evaluated.
Figure 3: Impression for internal threads of implant analog with addition silicone (light body consistency)

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Figure 4: Distance between threads on replica measured using stereomicroscope and visualized in monitor by using Progres software

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Figure 5: Distance between threads on replica (from their highest points)

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After “0” interval, the putty index with mold space obtained was used to fill with die stone material into which the implant analog was inserted by using a dental surveyor. This was done to position the implant analog at the center of the mold space filled with die stone. This same procedure was done for all three materials (stainless steel, titanium, and aluminum) of implant analoge and then obtained samples (die stone block with implant analog) were left untouched for 24 h. Then, each sample was taken and corresponding abutment was connected to implant analog by hand torqueing the abutment screw with the hex driver and torque wrench of about 10 Ncm. In each sample, the abutment screw was tightened and loosened about four times as the laboratory personnel approximately tightens and loosens the screw for four times during the fabrication of prosthesis. After every interval, the screw was discarded, and the new screw was taken for tightening the abutment to the implant analog.

After this, for evaluating the implant analogs internal threads, an impression was made using addition silicone (light body consistency). The base paste and catalyst paste of impression material was manipulated following the manufacturer's instructions and loaded into the 5 ml syringe. With the help of the syringe, the material was carried to the implant analog and injected with a 1.2 mm wide-bore needle into the implant analog and an impression for internal threads was made. After polymerization of the impression material, it was carefully removed from the implant analog without any distortion. This was done for every sample. After that, the implant analog was retrieved from the die stone block by breaking the block mechanically with a chisel and hammer. Placing the chisel at the side adjacent to the implant analog placed in the die stone block without touching it and then hammering over the chisel mechanically makes the block break and retrieves the implant analogue. This was done for every sample, and the implant analogs were retrieved. The procedure for the first interval was completed. The same procedure was done for the 2nd and 3rd intervals.

After the 3rd interval, the impressions made for internal threads of implant analogs (replica) were used to measure the distance between the threads. These values were evaluated the same as the samples tested at 0 interval by using the stereomicroscope at ×50 by an image processing software. The values were tabulated and were further evaluated. This was the same procedure done at the every three intervals and the samples were measured and the values were tabulated and were compared with the control group at 6th, 9th, and 12th time. After the fabrication of samples, relevant testing and recording of data were performed, followed by appropriate statistical analysis.


  Results Top


The comparison of mean distance between thread on replica at 1–2 of three different materials (stainless steel, titanium, and aluminum) in two die materials (Group A and Group B) at different time intervals (0, 3rd, 6th, 9th, and 12th) [Table 1] in which for the Aluminum at “0” interval the mean distance between thread on replica at 1–2 has 0.72 mm and 0.72 mm of Group A and Group B, respectively. For further intervals, there was a decrease in the mean distance between thread on replica at 1–2, i.e., at 12th interval the mean distance between thread on replica at 1–2 has 0.57 mm and 0.57 mm of Group A and Group B, respectively. For the titanium at “0” interval, the mean distance between thread on replica at 1–2 has 0.73 mm and 0.73 mm of Group A and Group B, respectively. For further intervals, there was a decrease in the mean distance between thread on replica at 1–2, i.e., at 12th interval, the mean distance between thread on replica at 1–2 has 0.67 mm and 0.67 mm of Group A and Group B, respectively. For the Stainless steel at “0” interval the mean distance between thread on replica at 1–2 has 0.70 mm and 0.70 mm of Group A and Group B, respectively. For further intervals, there was a decrease in the mean distance between thread on replica at 1–2, i.e., at 12th interval, the mean distance between thread on replica at 1–2 has 0.59 mm and 0.59 mm of Group A and Group B, respectively [Table 1].
Table 1: Comparison of three different implant analog materials (stainless steel, titanium, aluminum) in two die materials (Group A and Group B) with mean distance between threads on replica at 1 and 2 at different intervals (0, 3rd, 6th, 9th and 12th) by one-way ANOVA

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The overall comparison of the mean distance between thread on replica at 1–2 of Group A and Group B of SS, Ti, Al material shows there is gradual decrease in the values has the time interval increases.

  • For Al — 0 interval >3rd interval >6th interval >9th interval >12th interval
  • For Ti — 0 interval >3rd interval >6th interval >9th interval >12th interval
  • For SS — 0 interval >3rd interval >6th interval >9th interval >12th interval [Table 1].


The comparison of mean distance between thread on replica at 3–4 of three different materials (stainless steel, titanium, aluminum) in two die materials (Group A and Group B) at different time intervals (0, 3rd, 6th, 9th, and 12th) [Table 2] in which for the aluminum at '0' interval the mean distance between thread on replica at 3–4 has 0.72 mm and 0.72 mm of Group A and Group B, respectively. For further intervals, there was a decrease in the mean distance between thread on replica at 3–4, i.e., at 12th interval the mean distance between thread on replica at 3–4 has 0.59 mm and 0.59 mm of Group A and Group B, respectively. For the titanium at “0” interval the mean distance between thread on replica at 3–4 has 0.73 mm and 0.73 mm of Group A and Group B, respectively. For further intervals, there was a decrease in the mean distance between thread on replica at 3–4, i.e., at 12th interval, the mean distance between thread on replica at 3–4 has 0.68 mm and 0.69 mm of Group A and Group B, respectively. For the stainless steel at “0” interval, the mean distance between thread on replica at 3–4 has 0.70 mm and 0.70 mm of Group A and Group B, respectively. For further intervals, there was a decrease in the mean distance between thread on replica at 3–4, i.e., at 12th interval, the mean distance between thread on replica at 3–4 has 0.62 mm and 0.62 mm of Group A and Group B, respectively [Table 2].
Table 2: Comparison of three different implant analogue materials (stainless steel, titanium, aluminum) in two die materials (Group A and Group B) with mean distance between threads on replica at 3 and 4 at different intervals (0, 3rd, 6th, 9th and 12th) by one-way ANOVA

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The overall comparison of the mean distance between thread on replica at 3–4 of Group A and Group B of SS, Ti, and Al material shows that there is gradual decrease in the values as the time interval increases.

  • For Al — 0 interval >3rd interval = 6th interval >9th interval >12th interval
  • For Ti — 0 interval >3rd interval = 6th interval >9th interval >12th interval
  • For SS — 0 interval >3rd interval = 6th interval >9th interval >12th interval [Table 2].


The comparison of mean distance between thread on replica at 5–6 of three different materials (stainless steel, titanium, aluminum) in two die materials (Group A and Group B) at different time intervals (0, 3rd, 6th, 9th, and 12th) [Table 3] in which the aluminum at '0' interval the mean distance between threads on replica at 5–6 has 0.72 mm and 0.72 mm of Group A and Group B, respectively. For further intervals, there was a decrease in the mean distance between threads on replica at 5–6, i.e., at 12th interval, the mean distance between threads on replica at 5–6 has 0.60 mm and 0.60 mm of Group A and Group B, respectively. For the Titanium at '0' interval, the mean distance between threads on replica at 5–6 has 0.73 mm and 0.73 mm of Group A and Group B, respectively. For further intervals, there was a decrease in the mean distance between threads on replica at 5–6, i.e., at 12th interval, the mean distance between threads on replica at 5–6 has 0.70 mm and 0.70 mm of Group A and Group B, respectively. For the stainless steel at '0' interval, the mean distance between threads on replica at 5–6 has 0.70 mm and 0.70 mm of Group A and Group B, respectively. For further intervals, there was a decrease in the mean distance between threads on replica at 5–6, i.e., at 12th interval, the mean distance between threads on replica at 5–6 has 0.63 mm and 0.63 mm of Group A and Group B, respectively [Table 3].
Table 3: Comparison of three different implant analogue materials (stainless steel, titanium, aluminum) in two die materials (Group A and Group B) with mean distance between threads on replica at 5 and 6 at different intervals (0, 3rd, 6th, 9th and 12th) by one-way ANOVA

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The overall comparison of the mean distance between threads on replica at 5–6 of Group A and Group B of SS, Ti, and Al material shows there is gradual decrease in the values has the time interval increases.

  • For Al — 0 interval >3rd interval = 6th interval >9th interval >12th interval.
  • For Ti — 0 interval = 3rd interval >6th interval = 9th interval >12th interval.
  • For SS — 0 interval >3rd interval >6th interval = 9th interval >12th interval [Table 3].


From the results obtained, the titanium implant analogue has major difference in distance between the threads from the 6th interval and the stainless steel implant analogue has major difference in distance between the threads from the 3rd interval and the aluminum implant analog has major difference in distance between the threads after the 1st interval. Hence, the titanium implant analogs can be reused for six times, stainless steel implant analogs can be reused for three times and aluminum implant analogs to be used only once.


  Discussion Top


Abutment screw loosening is recognized as a common complication with cemented and screw retained implant restorations and which occurs on functional loading. When the abutment is fixed by tightening the screw, threads of the screw and the internal threads of the implant can get deformed. Extensive research has been carried on the deformation of abutment screw but changes on the internal threads of implant analogs on reuse have not studied.[2] Hence, the present study was carried out in this context but on the internal threads of implant analogs.

The internal threads of the implant analog are a part of the dense metal body, which is not easily subjected to deformation. However on repeated screw tightening and loosening, there is a chance of creation of friction between the screw threads and internal threads of implant analog. The coefficient of friction is controlled by the manufacturing process and is affected by metallurgical properties of the components, design, and quality of the surface finish. Investigators have suggested that repeated tightening of screws removes small irregularities on the contacting surfaces which was due friction.[3] This causes the micromovement.

Micromovement is defined as a movement of a tooth, prosthesis, or implant system component <100 μm that is not observable or subject to measurement in-vivo by ordinary means. In most implant systems, the exchange of fluids, in both directions, takes place at the level of the marginal bone crest and is considered to be a factor for chronic inflammation and marginal bone loss. Thus, during function and under occlusal loading, micromovement between abutment and implant will create a volumetric variation in the inner volume of the implant system.

Almost all implant abutment connections are retained and stabilized by screws. A screw is a mechanism that converts rotational motion to linear motion, and torque (rotational force) to a linear force. Preload is the technical term for the tension caused by tightening the screw that holds the assembled parts together. As long as the external loads on a joint don't exceed the preload, the screw is not subjected to any motion and will not become loose.

As described in the results, the thread distance at 1–2 on the replica of the implant analogue decreases, which shows that there is an increase in the distance between the internal threads of the implant analog. The reason is that there is an increase in the frictional contact between the internal threads of the implant analog and the threads of the screw and also stresses increase in the form of preload which causes the wear of the contacting surfaces of the threads while screw tightening and loosening repeatedly. This makes wobbling and misfit of the abutment or final prosthesis.

The friction created between the contacting surfaces such as internal threads and the screw threads at repeated cycles causes the fretting wear. Fretting wear is a special wear process that occurs at the contact area between two materials under load and subject to minute relative motion by vibration or some other force. Fretting tangibly degrades the surface layer quality producing increased surface roughness and micropits, which reduces the fatigue strength of the components.[4] Soft materials often exhibit higher susceptibility to fretting than hard materials of a similar type. The hardness ratio of the two sliding materials also has an effect on fretting wear. This was the reason to which the Aluminum implant analogs internal threads has more wear followed by stainless steel implant analogs and titanium implant analogs.

The reason for increase in the internal thread distance between two threads of implant analogue was because of the compressive forces (preload) and clamping effect (tensile force creates a compressive force in the joint) which were developed due to screw tightening. This influences the joint stability, is how the contacting parts change when the screw is tightened. After being tightened together by screw, the microroughness of all the metal contacting surfaces slightly flattens and the microscopic distance between the internal thread pattern increases.[5]

As the thread distance at 3–4 in the replica of the implant analog decreases, which shows that there is an increase in the distance between the internal threads of the implant analog. As the thread distance at 5–6 in the replica of the implant analog decreases, which shows that there is an increase in the distance between the internal threads of the implant analog.

On comparing the mean distance between the threads 1–2, 3–4, 5–6 on the replica of internal threads of implant analogue the mean distance between the threads at 1–2 has more decrease from 0 to 12th intervals, at 3–4 has less amount of decrease in distance than thread distance at 1–2 from 0 to 12th intervals, and at 5–6 has very less decrease in distance than thread distance at 1–2 and 3–4 from 0 to 12th intervals. This infers that there is more amount of increase in the distance between the internal threads of implant analog at 1–2 followed by 3–4 and 5–6, respectively.

The reason was at the collar end of the implant analog, i.e., at internal threads 1–2 there is a passage of all the thread patterns of the screw (from apical end to the screw head) while tightening and loosening. This causes more frictional wear at the internal threads 1–2 of the implant analog. When compared with the internal threads at 1–2, the internal threads at 3–4 has a passage of the middle third and apical end thread pattern of the screws while tightening and loosening which causes a minimal frictional wear than at the internal threads 1–2. When comparing the internal threads at 5–6 with other threads, here only the apical thread patterns of screw will pass through it while tightening and loosening which causes very minimal frictional wear than the other two internal threads (1–2,3–4) and also there is more amount of preload forces at the 1–2 internal threads compared to 3–4 and 5–6 internal threads may be the possible reason.

A study by Y. Sameera, Rathika Rai stated that the internal threads of the dental implant are part of a dense metal body and hence, it was not subjected to deformation easily. As implant alloy hardness is greater than prosthetic screw hardness, the surface alterations to implant were fewer than those observed on prosthetic screw.[5]

On comparing with the above study, in the present study, there is a change in the internal threads of implant analog because here the screw was tightened and loosened for about four times at every interval, this is done for 12 intervals and for every interval, the old screw was discarded and new screw was taken for the next interval. The results obtained in the study clearly states that on repeated tightening and loosening the fretting wear occurs due to friction between the mating surfaces and the distance between the threads on the replica of implant analog is decreased, which infers that there is an increase in internal threads of implant analog. In this the aluminum material softer than the stainless steel and titanium, this was the reason for aluminum has more fretting wear followed by stainless steel and then titanium.


  Conclusion Top


The following conclusions were drawn based on the results obtained in the present in vitro study which was conducted to assess the effect of multiple reuse of implant analogs of three different materials (stainless steel, titanium, aluminum) on the internal thread discrepancy were.

  • From the results obtained, the titanium implant analog has major difference in distance between the threads from the 6th interval and the stainless steel implant analog has major difference in distance between the threads from the 3rd interval and the aluminum implant analog has major difference in distance between the threads after the 1st interval. Hence, the titanium implant analogs can be reused for six times, stainless steel implant analogs can be reused for three times and aluminum implant analogs to be used only once
  • On comparing materials the aluminum implant analog internal threads has more amount of increase in the distance between threads followed by stainless steel and titanium. In between the two die materials, no difference was observed.


Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Barbosa GA, Bernardes SR, das Neves FD, Fernandes Neto AJ, de Mattos Mda G, Ribeiro RF. Relation between implant/abutment vertical misfit and torque loss of abutment screws. Braz Dent J 2008;19:358-63.  Back to cited text no. 1
    
2.
Novman M, Hegde D, Lakshmikanth K, Nair CK, Sadhvi KV. Deformation of internal thread of dental implants on repeated abutment screw tightening. Trends Prosthodont Dent Implantol 2013;4:20-1.  Back to cited text no. 2
    
3.
Barbosa GS, Silva-Neto JP, Simamoto-Júnior PC, Neves FD, Mattos Mda G, Ribeiro RF. Evaluation of screw loosening on new abutment screws and after successive tightening. Braz Dent J 2011;22:51-5.  Back to cited text no. 3
    
4.
ASM International. ASM Handbook Volume 13B, Corrosion: Materials. OH, United States: ASM International; 2005. Available form: https://Asminternational.org. [Last accessed on 2005 Nov].  Back to cited text no. 4
    
5.
Sameera Y, Rai R. Tightening torque of implant abutment using hand drivers against torque wrench and its effect on the internal surface of implant. J Indian Prosthodont Soc 2020;20:180-5.  Back to cited text no. 5
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
 
 
    Tables

  [Table 1], [Table 2], [Table 3]



 

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