An in vitro evaluation on polyurethane foam sheets of the insertion torque,removal torque values,and resonance frequency analysis (RFA) of a self-tapping threads and round apex implant

Abstract

The dental implant primary stability and micromovement absence represent critical factor for dental implant osseointegration. The aim of the present in vitro investigation was to simulate the bone response on different polyurethane densities the effect of self-tapping threads and round apex implant geometry. A total of 40 implants were positioned in D1, D2, D3 and D4 polyurethane block densities following a calibrated drilling protocol. The Insertion, removal Torque and resonance frequency analysis (RFA) means were calculated. All experimental conditions showed insertion torque values >30 Ncm. A significant higher insertion torque, removal and RFA was present in D1 polyurethane. Similar evidences were evidenced for D3 and D4. The effectiveness of the present study suggested a valuable clinical advantage for self-tapping threads and round apex implant using, such as in case of reduced bone density in the posterior maxilla

Keywords

Dental implant polyurethane blocks primary stability

Introduction

The implant-supported restorations represent a viable and highly predictable treatment for total or partial edentulisms.^1,2 It is well-known that the primary stability is an essential clinical requisite for dental implant osseointegration.^3,4 This clinical parameter is correlated to numerous factors such as the density of the bone tissue, the micro-and macro-geometry of the implant, the adoption of underpreparation or osseodensification drilling protocols.^5

–8

In literature, a local poor bone density is associated to an increase of the early implant failure and loss of osseointegration.^9
–11 In the same way, a poor bone density is associated to a more difficult primary stability achievement.^12

–15 Comuzzi et al. reported that, in standardized condition on low-density polyurethane study, the macro-geometry induced the main effect on the primary stability, while the osseodensification drilling procedure produced the more visible effect on stability in presence of a residual cortical bone.¹⁶ Moreover, Gehrke et al. reported the key role of the implant macro-geometry on a sheep study, while the self-tapping and round apex macro-geometry is able to influence significantly the percentage of new bone formation and the deposition of highly vascularized osteogenic matrix within the marrow spaces,¹⁷ where the number and thickness of bone trabeculae increase with the loading of the dental implants.¹⁸ In vivo, no radiographical and hystological evidence in crestal bone resorption were present were evident between the osseodensification procedure,^19
–21 the drilling technique²² and ultrasonic device approach.²³

Misch et al. classified the type IV bone as a histotype characterized by a more represented cancellous bone with an almost complete absence of the cortical component.²⁴ This variant seems to be more widespread in the posterior maxillary region.^24,25

On the contrary, the type I bone is characterized by a more expressed bone cortical component and is typical of the mandible symphysis.^24,26 The intermediate histotypes are represented clinically with a discrete local anatomical variability between the upper and lower jaws in relation to several aspects such as the age of the patient, the metabolism health and the functional loading of the region.^24,26

The insertion torque measurement and resonance frequency analysis (RFA) by implant stability quotient (ISQ) Scale has been proposed to evaluate clinically the stability of the implant during the positioning procedure in relation to their high reproducibility.^27,28

In literature, an optimal insertion torque range between 30 Ncm and 50 Ncm has been correlated to increased new bone formation and bone-implant contact.²⁷ Moreover, an ISQ >70 has been considered an optimal clinical effectiveness for one-stage loading for splinted or single implant.²⁷

On the contrary, a ISQ <60 is associated to a decreased of implant stability and the indication for a two-stage loading protocol.²⁷

The polyurethane simulation has been proposed as a standardized study model for implant mechanical test by the American Society for Testing and Materials International (ASTM) with a high affinity and accuracy of the bone tissue substrate.in terms of density, elastic module, compression and traction load.²⁹

The aim of the present study was to evaluate the stability of a self-tapping and round apex implant on a polyurethane in vitro simulation.

The null hypothesis of no difference of insertion torque, removal and RFA between the different polyurethane densities was tested.

Materials and methods

Polyurethane bone simulation

Different densities of synthetic solid rigid polyurethane homogeneous bone blocks (SawBones H, Pacific Research Laboratories Inc., Vashon, Wash) were used for the present investigation to simulate the bone histotypes of the jaws (Figure 1). As reported by a recent study of Comuzzi et al.,^30,31 the D1 bone was simulated with the 40 pounds per cubic foot block (pcf), the D2 with the 30 pcf block, the D3 and D4 respectively with 20 and 10 pcf block according to the Misch classification.

Figure 1.

Polyurethane simulation study design. D1 bone: 40 pounds per cubic foot polyurethane block (pcf); D2 bone: 30 pcf polyurethane block; the D3 bone: 20 pcf polyurethane block; D4 bone: 10 pcf polyurethane block.

Implant characteristics

A total of 40 implant 3.8 mm diameter and 11 mm length (Way miX, Geass Pozzuolo del Friuli, Italy) was positioned on the polyurethane blocks, 10 screw for each experimental condition. The implant presented a surface treatment of laser roughening and the macro-design was characterized by a conical geometry with a cervical microthreads area of 2.5 mm. The body of the implant presented self-tapping threads and round apex. The screw was provided by an internal hexagon implant-abutment connection (Figure 2). The four experimental condition followed the same drilling protocol with the 2.5 diameter drill followed by the 3.8 diameter final drill at 800 rpm and 30 Ncm torque by calibrated dynamometric motor integrated to the universal testing machine (Imada, Japan) (Figures 2–3). The final work length of 11 mm and a constant calibrated force rate of 9.0 N was electronically applied to the handpiece to standardize the implant drill preparation. The implant insertion torque was calculated following a positioning speed of 50 rpm. The removal was recorded by the high precision electronic dynamometric to evaluate the extraction resistance of the implant from the preparation site.

Figure 2.

Drilling sequence protocol and main screw characteristics of the implant used in the present investigation.

Figure 3.

Implant site drilling by Universal testing machine (left). Calibrated dental implant positioning sequence (right).

RFA stability measurement

The resonance frequency analysis (RFA) was performed by the Implant stability Quotient analytical method by a dedicated electronic device (Osstell, Gothenburg Sweden) after the screw positioning.

The implant stability quotient (ISQ) scale range was from 0 to 100 and classified as low stability (<60 ISQ), Medium (60–70 ISQ), and High stability (>70 ISQ). For each specimen, the RFA measurement was repeated two times for each specimen (Figure 4).

Figure 4.

RFA measurement of dental implant stability after the screw positioning.

Statistical analysis

The Insertion Torque, Pull out means and ISQ Resonance Test means were statistically analysed between the four study groups. The normality was evaluated by Kolmogorov-Smirnov test and the one-way ANOVA followed the Sidak multiple comparisons post-hoc test for heterogeneous variances was evaluate the study data by the software package GraphPad 6.0 (Prism San Diego, CA, USA) statistical package. The level of significance was set at p < 0.05.

Results

No evidences of micro-cracks were observed in the cervical portions of the polyurethane-implant interface. Mean values for Insertion Torque values are presented in Table 1 (Figure 5). The insertion torque means were higher for D1 group (mean 135.1 ± 6.324) (p < 0.01) (Table 2).

Table 1.

Summary of insertion torque, removal and rfa measurements. No statistical differences of insertion torque and pull out were detectable for D3 and D4 groups (p > 0.05). A significant difference of insertion torque, pull out and rfa analysis were evidenced for all comparison groups (p < 0.05) (One-way Anova, mean, standard deviations).

	Insertion Torque [Ncm]		Removal Torque [Ncm]		RFA ISQ Scale
Groups	Mean	DS	Mean	DS	Mean	DS
D1	135.1	6.324	30.79	4.686	70.20	5.613
D2	92.92	30.57	24.87	2.898	70.45	2.339
D3	45.79	2.731	13.71	1.196	60.75	3.706
D4	36.89	6.969	13.70	1.523	51.50	4.143

Figure 5.

Bar graph of insertion torque, removal and rfa measurements. No statistical differences of insertion torque and pull out were detectable for D3 and D4 groups (p > 0.05). A significant difference of insertion torque, pull out and rfa analysis were evidenced for all comparison groups (p < 0.05).

Table 2.

Summary of insertion torque groups comparison (One-way Anova-Sidak post-hoc test, mean, standard deviations).

Insertion Torque	Mean Diff.	95.00% CI of diff.	Adjusted P Value
D1 vs. D2	42.19	−3.819 to −0.7306	<0.0001
D1 vs. D3	89.31	2.631 to 5.719	<0.0001
D1 vs. D4	98.22	−5.469 to −2.381	<0.0001
D2 vs. D3	47.13	4.906 to 7.994	<0.0001
D2 vs. D4	56.04	−3.194 to −0.1056	<0.0001
D3 vs. D4	8.907	−10.43 to 28.24	0.6056

The removal values are presented in Table 3, where showed a statistically significant difference between the study groups with the highest values for D1 group (mean: 30.79 ± 4.686) (p < 0.01) (Table 1 –3, Figure 5).

Table 3.

Summary of removal torque groups comparison (One-way Anova-Sidak post-hoc test, mean, standard deviations).

Removal Torque	Mean Diff.	95.00% CI of diff.	Adjusted P Value
D1 vs. D2	5.925	2.408 to 9.442	0.0003
D1 vs. D3	17.08	13.56 to 20.60	<0.0001
D1 vs. D4	17.09	13.57 to 20.61	<0.0001
D2 vs. D3	11.16	7.640 to 14.67	<0.0001
D2 vs. D4	11.17	7.650 to 14.68	<0.0001
D3 vs. D4	0.01000	−3.507 to 3.527	>0.9999

The implant micromovement analysis by ISQ resonance test is reported in Figure 5. No statistical differences were present between D1 and D2 groups and between D3 and D4 (p > 0.05) (Table 1 –4, Figure 5).

Table 4.

Summary of RFA groups comparison (One-way Anova-Sidak post-hoc test, mean, standard deviations).

RFA	Mean Diff.	95.00% CI of diff.	Adjusted P Value
D1 vs. D2	−0.2500	−5.212 to 4.712	0.9991
D1 vs. D3	9.450	4.488 to 14.41	<0.0001
D1 vs. D4	18.70	13.74 to 23.66	<0.0001
D2 vs. D3	9.700	4.738 to 14.66	<0.0001
D2 vs. D4	18.95	13.99 to 23.91	<0.0001
D3 vs. D4	9.250	4.288 to 14.21	<0.0001

Discussions

The primary implant stability represents the clinical main condition that could determine the long-term success of implants osseointegration and is deeply influenced by the implant surface geometry.^12,32,33

In the present study, the RFA was chosen as a nondestructive, noninvasive, and repeatable quantitative evaluation of implant stability that is independently of the implant system used.

The effectiveness of the present study showed significant differences between the experimental conditions, so the tested null hypothesis of the present investigation was rejected.

In the present investigation the self-tapping and round apex implant tested showed in all conditions an insertion torque >30 N, that is commonly considerated an optimal clinical positive predictive index for implant stability.^34,35

In the simulated condition of D1, higher the insertion torque mean >130 N associated to increased removal and Rfa values were reported.

Consolo et al. reported on sheep mandible similar histological aspects of the peri-implant bone tissue between low torque (<25 Ncm) and high torque (>100 Ncm) after 8 and 12 weeks.³⁶

The authors reported that high implant insertion torque did not induce adverse reaction in cortical bone and does not lead to implant failure.³⁶

Reasonably, the drilling technique represents an essential factor for the implant success in the D1 mandible symphysis, where the reduced cancellous bone and vascularization and the thermal effect generated by the implant site preparation could represent a cause of early implant failure.^37
–40

Piattelli et al. reported that the microscopical thermal damage of peri-implant tissues is characterized by aspects of bone sequestra; no regeneration of the peri-implant tissues and presence of mature bone; inflammatory infiltrate at the level of the implant-bone interface; no stable peri-implant bone clot; bacteria colonization and necrotic bone.⁴¹

On the other side, the poor density bone benefits a self-tapping thread geometry in order to a favourable implant positioning.^42,43 In fact, in case of low bone density, the obtaining of implant primary stability and screw anchorage is more difficult.⁴⁴

In this way, the presence of the round apex is able to generate a gently apical compression able to increase the implant stability and a conservative Schneider’s membrane lift in case of maxillary sinus augmentation.⁴⁵

Low initial stability in type IV bone corresponds to lower insertion torque, pull out and rfa means, that clinically could induce the adoption of a more conservative two-stage loading approach, mostly in case of single implant restoration.¹¹

The implant-splinted rehabilitation for a one-stage loading approach is preferable with careful control of the chewing function, presence of parafunctions and bruxism.⁴⁶

Chrcanovic et al. reported in a multilevel mixed retrospective study on 10 096 implants implant failure rate of 13·0% for bruxers. The bruxism was considered a statistically significantly risk factor to implant failure as well as implant length, implant diameter, implant surface, bone quantity, bone quality, smoking and the intake of proton pump inhibitors.⁴⁶

Conclusions

The evidences of the present study suggested that self-tapping implants is highly recommended. Especially in case of low-density maxillary bone, where the achievement of implant primary stability is clinically more difficult.

Footnotes

Author contributions

The conception and design of the study (AP, GI), acquisition of data (MT FL) analysis and interpretation of data (AP, AF, MT) drafting the article (AP, MT, MD), revising it critically for important intellectual content (MT, MD, AF, FD) final approval (AP, GI).

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

ORCID iD

Margherita Tumedei

References

Albrektsson

Zarb

Worthington

, et al. The long-term efficacy of currently used dental implants: a review and proposed criteria of success. Int J Oral Maxillofac Implants 1986; 1(1): 11–25.

Nevins

Camelo

De Paoli

, et al. A study of the fate of the buccal wall of extraction sockets of teeth with prominent roots. Int J Periodontics Restorative Dent 2006; 26(1): 19–29.

Javed

Romanos

GE.

The role of primary stability for successful immediate loading of dental implants. A literature review. J Dent 2010; 38(8): 612–620.

Javed

Ahmed

Crespi

, et al. Role of primary stability for successful osseointegration of dental implants: factors of influence and evaluation. Interv Med Appl Sci 2013; 5(4): 162–167.

Javed

Almas

Crespi

, et al.

Implant surface morphology and primary stability: is there a connection?

Implant Dent 2011; 20(1): 40–46.

Falco

Berardini

Trisi

. Correlation between implant geometry, implant surface, insertion torque, and primary stability: in vitro biomechanical analysis. Int J Oral Maxillofac Implants 2018; 33(4): 824–830.

Gehrke

Pérez-Díaz

Mazón

, et al. Biomechanical effects of a new macrogeometry design of dental implants: an in vitro experimental analysis. J Funct Biomater 2019; 10(4): 47.

Möhlhenrich

Heussen

Elvers

, et al. Compensating for poor primary implant stability in different bone densities by varying implant geometry: a laboratory study. Int J Oral Maxillofac Surg 2015; 44(12): 1514–1520.

Misch

Perel

Wang

H-L

, et al. Implant success, survival, and failure: the International Congress of Oral Implantologists (ICOI) Pisa Consensus Conference. Implant Dent 2008; 17(1): 5–15.

10.

Misch

. Bone density: a key determinant for clinical success. Contemp Implant Dent 1999; 8: 109–118.

11.

Nokar

Rasouli-Ghahroudi

Shidvash

, et al. Comparative investigation of primary stability of four different dental implants in low-density bone model. Dent Res J (Isfahan) 2019; 16(1): 18–23.

12.

Jimbo

Tovar

Anchieta

, et al. The combined effects of undersized drilling and implant macrogeometry on bone healing around dental implants: an experimental study. Int J Oral Maxillofac Surg 2014; 43(10): 1269–1275.

13.

Gehrke

Mazón

Del Fabbro

, et al. Histological and histomorphometric analyses of two bovine bone blocks implanted in rabbit calvaria. Symmetry 2019; 11(5): 641.

14.

Tumedei

Savadori

Del Fabbro

. Synthetic blocks for bone regeneration: a systematic review and meta-analysis. Int J Mol Sci 2019; 20(17): 4221.

15.

Zizzari

Berardi

Congedi

, et al. Morphological aspect and iNOS and bax expression modification in bone tissue around dental implants positioned using piezoelectric bone surgery versus conventional drill technique. J Craniofac Surg 2015; 26(3): 741–744.

16.

Comuzzi

Tumedei

Piattelli

, et al. Osseodensification drilling vs. standard protocol of implant site preparation: an in vitro study on polyurethane foam sheets. Prosthesis 2020; 2(2): 76–86.

17.

Gehrke

Tumedei

Aramburú Júnior

, et al. Histological and histomorphometrical evaluation of a new implant macrogeometry. A sheep study. Int J Environ Res Public Health 2020; 17(10): 3477.

18.

Tumedei

Piattelli

Degidi

, et al. A Narrative review of the histological and histomorphometrical evaluation of the peri-implant bone in loaded and unloaded dental implants. A 30-year experience (1988–2018). Int J Environ Res Public Health 2020; 17(6): 2088–2106.

19.

Pai

Rodrigues

Talreja

, et al. Osseodensification – a novel approach in implant dentistry. J Indian Prosthodont Soc 2018; 18(3): 196–200.

20.

Trisi

Berardini

Falco

, et al. New osseodensification implant site preparation method to increase bone density in low-density bone: in vivo evaluation in sheep. Implant Dent 2016; 25(1): 24–31.

21.

Scarano

Inchingolo

Murmura

, et al. Three-dimensional architecture and mechanical properties of bovine bone mixed with autologous platelet liquid, blood, or physiological water: an in vitro study. Int J Mol Sci 2018; 19(4): 1230.

22.

Scarano

Crincoli

Di Benedetto

, et al. Bone regeneration induced by bone porcine block with bone marrow stromal stem cells in a minipig model of mandibular “critical size” defect. Stem Cells Int 2017; 2017: 9082869.

23.

Scarano

Carinci

Lorusso

, et al. Ultrasonic vs drill implant site preparation: post-operative pain measurement through vas, swelling and crestal bone remodeling: a randomized clinical study. Materials (Basel) 2018; 11(12): 2516.

24.

Misch

Judy

. Classification of partially edentulous arches for implant dentistry. Int J Oral Implantol 1987; 4(2): 7–13.

25.

Albrektsson

Lekholm

. Osseointegration: current state of the art. Dent Clin North Am 1989; 33(4): 537–554.

26.

Di Stefano

Arosio

Pagnutti

, et al. Distribution of trabecular bone density in the maxilla and mandible. Implant Dent 2019; 28(4): 340–348.

27.

Degidi

Daprile

Piattelli

. Primary stability determination by means of insertion torque and RFA in a sample of 4,135 implants. Clin Implant Dent Relat Res 2012; 14(4): 501–507.

28.

Botticelli

Perrotti

Piattelli

, et al. Four Stable and functioning dental implants retrieved for fracture after 14 and 17 years from the same patient: a histologic and histomorphometric report. Int J Periodontics Restorative Dent 2019; 39(1): 83–88.

29.

Allen

Baldini

Donofrio

, et al. Standard specification for rigid polyurethane foam for use as a standard material for testing orthopedic devices and instruments (F1839-97). West Conshohocken (PA): The American Society for Testing and Materials; 1998.

30.

Comuzzi

Iezzi

Piattelli

, et al. An in vitro evaluation, on polyurethane foam sheets, of the insertion torque (IT) values, pull-out torque values, and resonance frequency analysis (RFA) of Nanoshort dental implants. Polymers 2019; 11(6): 1020.

31.

Comuzzi

Tumedei

Piattelli

, et al. Short vs. standard length cone morse connection implants: an in vitro pilot study in low density polyurethane foam. Symmetry 2019; 11(11): 1349.

32.

Comuzzi

Tumedei

Pontes

, et al. Primary stability of dental implants in low-density (10 and 20 pcf) polyurethane foam blocks: conical vs cylindrical implants. Int J Environ Res Public Health 2020; 17(8): 2617.

33.

Lahens

Neiva

Tovar

, et al. Biomechanical and histologic basis of osseodensification drilling for endosteal implant placement in low density bone. An experimental study in sheep. J Mech Behav Biomed Mater 2016; 63: 56–65.

34.

Han

H-C

Lim

H-C

Hong

J-Y

, et al. Primary implant stability in a bone model simulating clinical situations for the posterior maxilla: an in vitro study. J Periodontal Implant Sci 2016; 46(4): 254–265.

35.

Campos

FEB

Jimbo

Bonfante

, et al. Are insertion torque and early osseointegration proportional? A histologic evaluation. Clin Oral Implants Res 2015; 26(11): 1256–1260.

36.

Consolo

Travaglini

Todisco

, et al. Histologic and biomechanical evaluation of the effects of implant insertion torque on peri-implant bone healing. J Craniofac Surg 2013; 24(3): 860–865.

37.

Ercoli

Funkenbusch

Lee

H-J

, et al. The influence of drill wear on cutting efficiency and heat production during osteotomy preparation for dental implants: a study of drill durability. Int J Oral Maxillofac Implants 2004; 19(3): 335–349.

38.

Scarano

Noumbissi

Gupta

, et al. Scanning electron microscopy analysis and energy dispersion X-ray microanalysis to evaluate the effects of decontamination chemicals and heat sterilization on implant surgical drills: zirconia vs. steel. Appl Sci 2019; 9(14): 2837.

39.

Scarano

Petrini

Mastrangelo

, et al. The effects of liquid disinfection and heat sterilization processes on implant drill roughness: energy dispersion x-ray microanalysis and infrared thermography. J Clin Med 2020; 9(4): 1019.

40.

Scarano

Lorusso

Noumbissi

. Infrared thermographic evaluation of temperature modifications induced during implant site preparation with steel vs. zirconia implant drill. J Clin Med 2020; 9(1): 148.

41.

Piattelli

Mangano

, et al.

A histologic evaluation of eight cases of failed dental implants: Is bone overheating the most probable cause?

Biomaterials 1998; 19(7–9): 683–690.

42.

Marković

Calvo-Guirado

Lazić

, et al. Evaluation of primary stability of self-tapping and non-self-tapping dental implants. A 12-week clinical study. Clin Implant Dent Relat Res 2013; 15(3): 341–349.

43.

Kerawala

Martin

Allan

, et al. The effects of operator technique and bur design on temperature during osseous preparation for osteosynthesis self-tapping screws. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1999; 88(2): 145–150.

44.

Wang

T-M

Lee

M-S

Wang

J-S

, et al. The effect of implant design and bone quality on insertion torque, resonance frequency analysis, and insertion energy during implant placement in low or low- to medium-density bone. Int J Prosthodont 2015; 28(1): 40–47.

45.

Degidi

Perrotti

Shibli

, et al. Evaluation of the peri-implant bone around parallel-walled dental implants with a condensing thread macrodesign and a self-tapping apex: a 10-year retrospective histological analysis. J Craniofac Surg 2014; 25(3): 840–842.

46.

Chrcanovic

Kisch

Albrektsson

, et al. Bruxism and dental implant failures: a multilevel mixed effects parametric survival analysis approach. J Oral Rehabil 2016; 43(11): 813–823.