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Year : 2020  |  Volume : 31  |  Issue : 3  |  Page : 403-407
Comparison of primary stability in craniofacial implant with V-shape and buttress thread design in goat skull using resonance frequency analysis

1 Government Royapettah Hospital, Kilpauk Medical College, Chennai, Tamil Nadu, India
2 Department of Prosthodontics, Tamil Nadu Government Dental College and Hospital, Chennai, Tamil Nadu, India

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Date of Submission15-Aug-2017
Date of Decision27-Jun-2019
Date of Acceptance15-Aug-2019
Date of Web Publication06-Aug-2020


Background and Aims: To find out the primary stability in maxillofacial implant with two different thread designs. Methods: Two group of implants were selected for the study – Group I maxillofacial implant with V-shape thread, and Group II implant with buttress thread. The drills for placing the implant were made indigenously. Goat skull was selected for placing the implant. Group I, II implant was placed in the goat skull at five different sites to find the primary stability. The primary stability was measured using Resonance Frequency Analysis (RFA) device. The transducer was screwed to the implant and made to vibrate by magnetic pulse. The vibration was recorded as Implant Stability Quotient (ISQ). Results: The ISQ values of Group I range from 32-46 and Group II range from 57-67. The results were subjected to statistical test and found to be significant at 95% level. Conclusion: The ISQ values for the buttress (Group II) is more than (Group I) which is observed in this study. Hence this study supports the buttress thread as the favourable thread pattern for the craniofacial implant.

Keywords: Maxillofacial implant, maxillofacial prosthesis, primary stability

How to cite this article:
Ramkumar K, Sripriya S, Meenakshi A, Sabarigirinathan C, Thulasingam C. Comparison of primary stability in craniofacial implant with V-shape and buttress thread design in goat skull using resonance frequency analysis. Indian J Dent Res 2020;31:403-7

How to cite this URL:
Ramkumar K, Sripriya S, Meenakshi A, Sabarigirinathan C, Thulasingam C. Comparison of primary stability in craniofacial implant with V-shape and buttress thread design in goat skull using resonance frequency analysis. Indian J Dent Res [serial online] 2020 [cited 2023 Mar 29];31:403-7. Available from:

   Introduction Top

The success of implantology depends on the various factors such as biomechanics, loading protocol, implant design and prosthesis design. Amongst these the prosthesis design influences the biomechanics of implant.[1] Implants are widely used in the rehabilitation of intra oral defects and also used in the restoration of extraoral defects. In 1975, Branemark postulated that a skin-penetrating implant should be possible based on the principles of dental implants.[2] In 1979, implants were placed in the mastoid bone to retain an ear prosthesis. This pioneering work was done in Goteborg University, Sweden.[2] Thereafter, this implant was widely used as treatment option to retain the maxillofacial prosthesis. Craniofacial implant differ from that of the oral implant in two aspects, the length is less in the range of 3-4 mm and it has a flange which prevent the accidental perforation of the implant through the thin bone sites that are encountered in the craniofacial anatomy.[3] Buttress thread and V shape thread are the preferred thread designs for craniofacial implants. Buttress thread forms are considered more suited for supporting facial prosthesis.[4] The success and failure of implant is determined by osseointegration, which in turn is decided by a lot of factors like biological and mechanical. Implant stability is also one of the important factor which determines the success or failure of an implant. Implant stability can be divided into primary and secondary stability. The primarily stability is obtained by mechanical fixation of the implant with bone, and this is one of the basic conditions for osseointegration. Primary stability is related with implant surface area, geometry, length and contact area between the implant and bone. Other factors include cortical bone, implant technique etc., Resonance Frequency Analysis (RFA) is a non-invasive method to detect the primary stability of the implant.[5] Studies on the primary stability relating to the thread design in craniofacial implant have not been investigated widely. Hence a study was conducted with an aim to find out the primary stability of craniofacial implant with V shape thread and buttress thread using RFA.

   Methods Top

Grouping of samples

Commercially available implant with V shape thread is designated as Group I and indigenous implant with buttress thread is designated as Group II. The details of the implant used in the study is shown in [Table 1]. Craniofacial implant with buttress thread design was made indigenously as it was not available commercially. Total number five implants from Group I and Group II respectively, were used to test the primary stability. Six goat skull were procured for placing the implant, out of which three skull were used for placing Group I and Group II implant respectively. The details of grouping shown in [Figure 1].
Table 1: Grouping of Samples

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Figure 1: Grouping of sample

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Fabrication of indigenous implant

The drawing of the procured Craniofacial Implant was drawn on the computer using CAD 2004 software with V shape thread design [Figure 1], keeping with this as a prototype another diagram was drawn with buttress thread design [Figure 2]. Data's of the drawing drawn was fed into the Computerized Numerical Control (CNC) milling machine – Lokesh (CNC Machine Hyderabad). Grade II titanium was procured from, Madhani, Labs, Hyderabad, and were fed into the machine and milling was done. The steps involved in making the root form of the implant are root feeding, step turning, threading and parting. The anti-rotational component was made in vertical machining centre. The steps involved are centring, drilling and tapping.
Figure 2: Commercially available craniofacial implant with V shape thread

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Drills for the implant

The drills used for the extra oral implant, shown in [Figure 3] was made indigenously. The drill was made using stainless steel. The steps involved in the fabrication of drills are: 1. Rod Feeding 2. Step turning 3. Grinding. The dimensions of the drill for craniofacial implant are Ø 2.2 mm round bur pilot drill and the dimensions of the next drill are Ø 2.3, Ø 2.5, and Ø 2.8 respectively. This bur has a small extension at the shank to provide countersink for the flange of the auricular implant. A customized ratchet was made using stainless steel to drive the implant into the bone.
Figure 3: Indigenously made craniofacial implant with buttress thread

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Resonance Frequency Analysis (RFA)

RFA utilizes a small L-shaped transducer that is fixed to the implant or abutment by means of a screw. The transducer comprises of 2 piezoceramic elements, one of which is vibrated by a sinusoidal signal (5 to 15 KHZ). The other one which serves as a receptor for the received signal, indicates the first flexural resonance frequency of the measured object.[5] Osstell mentor RFA device (Integration Diagnostics, Gamlestadsv. 3B, Sweden) was used in this study shown in [Figure 4] and [Figure 5]. Osstell has combined the transducer computerized analysis and excitation source into one, machine closely resembling the model used by Meredith Osstell.[5]
Figure 4: Osstell mentor with device

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Figure 5: Smart peg for RFA

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This magnetic RFA device has a transducer, a metallic rod with a magnet on top (smart peg), which is screwed on to an implant or an abutment. The smart peg is excited by a magnetic pulse from a wireless probe. The pulse duration is about 1 millisecond. After excitation, the peg vibrates freely and the magnet induces an electric voltage in the probe coil. That voltage is the measurement signal sampled by the resonance frequency analysis.[6] Resonance frequency values ranging from 3500 to 8500 HZ are translated into an ISQ of 0 to 100. A high value indicates greater stability. The manufacturer's guidelines suggests a successful implant typically has an ISQ greater than 65. An ISQ <50 may indicate potential failure or increase risk failure.

Methodology for placing the implant and recording RFA

Materials used

  1. Osstell mentor (Integration Diagnostics, Gamlestadsv. 3B, Sweden)
  2. Fresh goat maxilla (Institution ethical clearance obtained to use the goat skull for the study)
  3. Craniofacial auricular implant with the dimensions of: V-Shape and Buttress shape thread design with length of 3 mm and diameter of 3.75 mm
  4. Smart peg – Magnetic transducer.

Fresh, male goat skull was procured for the study. A total of six skulls were included for the study. Three skulls for assessing the primary stability in Group I and the other three skulls for assessing the primary stability in group II. Five sites were selected for placing the implant in the skull. The implant of diameter 3.75 mm and length 3 mm was selected for the placement in the goat skull. The drilling sequence for the implant is as follows: first round pilot drill of 2.2 mm diameter was used to penetrate the outer cortex. Then sequential drilling was performed using the drills of the following diameter 2.3, 2.5, and 2.8 mm. The length of the osteotomy is also maintained at 3 mm.

The implant of diameter 3.75 mm, and length of 3 mm with V shape thread (Group I) was inserted in to the prepared osteotomy using customized ratchet until the required stability was obtained. The stability thus obtained is known as the primary stability and measured by RFA. Smart peg – Magnetic transducer was screwed to the implant and connected to the Ostell as shown in [Figure 6]. The frequency from the RFA was recorded as ISQ. The implant was removed from the site and osteotomy prepared in five different sites in the same skull as discussed above. The same procedure was performed in three skulls with total of 15 readings shown in [Table 2]. The implant of diameter 3.75 mm, and length of 3 mm with buttress thread (Group II) was inserted in three goat skulls as discussed above. The ISQ values were noted and shown in [Table 2].
Figure 6: Implant in position with Osstell

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Table 2: Values of Radio Frequency Analysis (ISQ)

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   Results Top

The ISQ values of the skull S1 to S6 of group I and II were shown in [Table 2]. The ISQ value of group I and II range from 32-46 and 57-67 respectively. The group II has higher ISQ values compared to group I. The statistical significance within group I and II in three skull at five different sites were evaluated using mean, standard deviation and standard error shown in [Table 3] and can be inferred Group II has higher values compared to Group I. The statistical significance between the group was evaluated by Mann–Whitney est shown in [Table 4]. The data was found to be significance at P < 0.05 in all sites.
Table 3: Group Statistics

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Table 4: Inter group statistics by Mann - Whitney Test

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   Discussion Top

Stability is the implant capacity to withstand loading in the axial, lateral and rotational directions. Implant stability is one of the major factors which determines the clinical success of implant supported prosthesis and its longevity. The clinical perception of implant stability is often related to rotational resistance, which is also commonly used as a technique to measure implant stability in experimental studies.[7] Initial primary stability is the stability at the time of implant placement, and is purely mechanical and occurs due to fixation of a press fit structure into a bony cavity.[8]

Factors that might affect implant's primary stability are type of bone, implant diameter and length.[9] Implant macro geometry and implant design plays important role in the primary stability.[10] All the factors discussed above are in relation to the implant used in intraoral situation.

Implants used to retain maxillofacial prosthesis differ from the one used in oral situation. The available length for placing the implant is limited to 4 mm to 10 mm. Extraoral implant have a flange on the top to prevent sinking into the bone and to achieve the stability. The environment in intraoral and extraoral condition differ widely.[11]

Thread pitch, shape and depth are the factors that decide the stability of the implant. Square shape thread, V-shape, buttress, and reverse buttress are the various thread design used in implants,[12] out of which V shape is widely used in the implants. The loading situation in implant supported maxillofacial prosthesis differs from the intraoral prosthesis.[11] The extraoral implant should resist the pull out and push out forces during the insertion and removal of the maxillofacial prosthesis. Buttress, and reverse buttress are the thread designs which resist the pull out and push out forces to greater extent.[4]

Goat skull was selected because of easy availability. The bone was drilled using the kit, implant was placed in the site and RFA reading was taken. The mean ISQ reading of Group I range from 32.67 to 44.67 while Group II range from 57.67 to 66.33. The results shows that the implant with buttress thread have highest ISQ values when compared to the implant with V shape thread. The ISQ value for the craniofacial implant is not available in the literature. In intraoral condition ISQ greater than 65 is considered successful. An ISQ value less than 50 indicate potential risk of failure. The ISQ values obtained in this study were less than 50. Lesser ISQ values in craniofacial implant is due to the lesser length of the implant. Studies on mechanical behaviour of maxillofacial implant have not been widely studied. A study on the insertion torque and removal torque were measured in human cadaver in the temporal bone which relates to the thread design. The maximum insertion torque was 70.0 Ncm in bicortical bone and 50.0 Ncm in unicortical bone, while the removal torque was less than the insertion torque.[13] Higher ISQ values of the buttress thread indicate good primary stability when compared to V shape thread. The resistance offered by implant with buttress thread (Group II) to the pull out and push out forces will be more when compared to V shape thread (Group I).

   Conclusion Top

The main challenge for placing the implant in the craniofacial region is the limited bone availability. Implants in intraoral and extraoral condition differs in lot of aspects. One most important aspect is the mechanical behaviour of the craniofacial implant. The load generated in the implant supported prosthesis is only during the insertion and removal of the prosthesis by the patient. Pull out and push out forces is the main force generated and distributed to the implant. Buttress threads offers good resistance to the pull out and push out forces. Through this study it is observed that the ISQ values for the buttress is more than the V shape thread. This supports the buttress thread as the favourable thread pattern for the craniofacial implant.

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Conflicts of interest

There are no conflicts of interest.

   References Top

Akagawa Y, Sato Y. Amimic osseointegrated implant model for three-dimensional finite element analysis. J Oral Rehab 2003;30:41-5.  Back to cited text no. 1
Wolfaardt J, Tjellstrom A. International Perspective on Treatment Outcomes. Osseointegration in Craniofacial Reconstruction Chicago Quintessence 1998. p. 68.  Back to cited text no. 2
Brunski JB, Skalak R. Biomechanical Considerations for Craniofacial Implants in Per –Ingvar Branemark, Dan E. Tolman. Osseointegration in Craniofacial Reconstruction Chicago Quintessence 1998:24.  Back to cited text no. 3
Lovely M, Munirathnam Naidu E. Design and development of an implant system for auricular prosthesis. Trends Biomater Artif Organs 2010;24:11-8.  Back to cited text no. 4
Atsumi M1, Park SH, Wang HL. Methods used to assess implant stability: Current status. Int J Oral Maxillofac Implants 2007;22:743-54.  Back to cited text no. 5
Valderrama P, Oates TW, Jones AA, Simpson J, Schoolfield JD, Cochran DL. Evaluation of two different resonance frequency devices to detect implant stability: A clinical trial. J Periodontol 2007;78:262-72.  Back to cited text no. 6
Ostman PO, Hellman M, Wendelhag I, Sennerby L. Resonance frequency analysis measurements of implants at placement surgery. Int J Prosthodont 2006;19:77-83.  Back to cited text no. 7
Ersanli S, Karabuda Z, Beck F, Leblebicioglu B. Resonance frequency analysis of one stage dental implant stability during the osseointegration period. J Periodontol 2005;7:1066-71.  Back to cited text no. 8
Bischof M, Nedir R, Szmukler-Moncler S, Bernard JP, Samson J. Implant stability measurement of delayed and immediately loaded implants during healing – A clinical resonance frequency analysis study with sand blasted and etched implants. Clin Oral Imp Res 2004;15:529-39.  Back to cited text no. 9
Clelland NL, Lee JK, Bimbenet OC, Gilat A. Use of an axisymmetric finite element method to compare maxillary bone variables for a loaded implant. J Prosthodont 1993;2:183-9.  Back to cited text no. 10
Ramkumar, Implants for auricular prosthesis – A review. Int J Prosthodont Restor Dent 2017;7:1-5.  Back to cited text no. 11
Misch CE. Contemporary Implant Dentistry. 3rd ed. Elsiver publication; 2008.  Back to cited text no. 12
Ueda M. The relationship between insertion torque and removal torque analyzed in fresh temporal bone. Int Oral Maxillofac Implants 1991;6:442-7.  Back to cited text no. 13

Correspondence Address:
Dr. Karthikeyan Ramkumar
Department of Dental surgery, Government Royapettah Hospital, Kilpauk Medical College, Chennai
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/ijdr.IJDR_447_17

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  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]

  [Table 1], [Table 2], [Table 3], [Table 4]


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