A comparative study on tensile strength of various thermoplastic polymers sheets following thermoforming on a pre-treatment and post-treatment maxillary model of a patient: An in vitro study

doi:10.21203/rs.3.rs-3397145/v1

Download PDF

Research Article

A comparative study on tensile strength of various thermoplastic polymers sheets following thermoforming on a pre-treatment and post-treatment maxillary model of a patient: An in vitro study

https://doi.org/10.21203/rs.3.rs-3397145/v1

This work is licensed under a CC BY 4.0 License

Journal Publication

published 02 Apr, 2024

Read the published version in Clinical Oral Investigations →

You are reading this latest preprint version

OBJECTIVES:

Thermoplastic polymers show alteration in their mechanical properties after thermoforming on a dental model. The purpose of this in-vitro study was to evaluate the tensile strength of different thermoplastic polymer sheets thermoformed on a pre-treatment (moderate crowding) and post-treatment (well-aligned) maxillary model of a patient.

MATERIALS AND METHODS:

Forty maxillary models (Twenty Pre-treatment & twenty Post-treatment of uniform dimension) were made by duplicating them using alginate. Samples were then divided into eight groups of 5 samples each. The thermoplastic sheets Imprelon® (Scheu-Dent), AVAC R® (Jaypee), Placa Crystal® (BioART), EZ-VAC® (3A Medes) - 1.0 mm thick were thermoformed on these models respectively. The sample was retrieved using ceramic bur mounted on a straight hand-piece and subjected for testing using TINIUS Olsen 10ST micro universal testing machine and recorded.

RESULTS:

There was no statistically significant difference (P > .05) in tensile strength of thermoformed thermoplastic polymer sheets between pre-treatment and post-treatment maxillary model. Tensile strength of EZ-VAC (3A Medes) showed higher variation between pre-treatment and post-treatment maxillary model though it was found to be statistically insignificant (P > .05). Significant difference (P < .05) was seen between groups when they were compared separately among pre-treatment and post-treatment models. Placa Crystal (BioART) among the pre-treatment group, EZ – VAC (3A Medes) among the post-treatment group, showed highest tensile strength.

CONCLUSION AND CLINICAL RELEVANCE:

Results of the study highlights the necessity to test materials in conditions which stands in accordance with the clinical scenario to a considerable extent and also emphasizes the need for further study in aligner.

Tensile strength

thermoplastic polymer

aligner

mechanical properties.

Psychosocial issues tend to occur in adolescents and adults, who are aware of their malocclusion traits and discontent with their dental appearance. There are many appliances available for orthodontic treatment, one among them being aligners.[1]

The introduction of CAD/CAM technology in orthodontic treatment with simple aligners is becoming more common everyday as an orthodontic solution. CAD-CAM has boosted the designing process and fabrication of appliances using thermoplastic polymers. Simple aligners made of thermoplastic polymers are aesthetically pleasing and more convenient to wear when compared with conventional fixed appliances.[2] Several researches have shown that both adult and young patients find clear aligner treatment more aesthetic, when compared to conventional brackets.[3, 4]

Thermoplastic materials have a profound application in the field of dentistry. It is used for fabrication of various appliances such as orthodontic retainers, night guards, temporomandibular joint splints used for treating temporomandibular joint disorders and for cosmetic treatment involving bleaching trays.[4] However clear aligners raise distinctive clinical problems that are not faced by conventional brackets and arch wires. With simple aligners, the biggest problem is their sub-optimal mechanical properties. Dimensional instability, low strength and less abrasion resistance are inherent challenges involved with thermoplastic polymer materials.[1, 5] The two key fields for the introduction of effective diagnostic malocclusion treatment protocol are the production of proper staging and the analysis of biomechanics to provide the desired force component.[1]

The force that has to be exerted to produce a desired tooth movement using an appliance made of clear thermoplastic polymer solely depends on the various mechanical properties of the individual thermoplastic polymer sheet.[4]

In order to achieve the goals of the treatment, the material in general must possess various mechanical properties such as tensile strength, elastic modulus and retain them in any environment.[6] The thermoplastic polymer sheets used during fabrication of aligner and retainers are subjected to various stresses. These stresses get incorporated into the sheets while thermoforming which is influenced by the tooth position. They are also exposed to complex dynamic masticatory force and an aggressive environment in the oral cavity which could result in time dependent degradation of their properties causing a negative impact on the effectiveness of treatment.[7] Orthodontic tooth movement requires a constant delivery of force for at least 4 hours. Clear aligner treatment uses light constant force on a continual wear to achieve its results.[8]

Aligners, however, tend to lose their efficiency to exert force and maintain their shape as soon as they are inserted, due to the stress relaxation of the polymerized chains of the material.[9]

Though the plenitude of products used for appliance fabrication in the market does exist, the ideology of those materials which are useful for specific conditions is crucial.[4] The mechanical performance of thermoplastic material being used for aligners and retainers manufacturing thus plays a crucial role in producing the optimal effects in complex orthodontics.[10]

Hence, following thermoforming, the mechanical properties of thermoplastic polymers can alter, indicating the need to test them after this process.[1, 3] Commercially, a wide range of thermoplastic materials are available in the market which has been produced by different manufacturers and has created a necessity to test their mechanical properties.

Hence, the primary aim of the current in-vitro study is to evaluate and compare the tensile strength of four different thermoplastic polymer sheets - Imprelon® (Scheu-Dent) (Fig. 1.A), AVAC R® (Jaypee) (Fig. 1.B), Placa Crystal® (BioART) (Fig. 1.C), EZ-VAC® (3A Medes) (Fig. 1.D) thermoformed on a pre-treatment (moderate crowding) and post-treatment (well-aligned) maxillary model of a patient.

One pre-treatment maxillary model of a patient with permanent dentition and moderate crowding requiring first premolar extraction (assessed using Carey’s arch perimeter analysis)[11], post-treatment maxillary model of the same patient (fulfilling Andrew’s Six keys of occlusion)[12]was selected. (Fig. 2)

The model was carefully evaluated for any fractured, prosthetically restored and malformed anterior teeth was excluded. The model was trimmed in such a way that the height of the model meets the requirements of the 3D printed models of height of 11mm.[13] (Fig. 3)

Alginate impression material was used for model duplication.[14]

A total of forty models comprising of twenty duplicated pre-treatment and twenty post-treatment maxillary model were prepared. These duplicated models were utilized as a standard for thermoforming the thermoplastic polymer sheet. (Fig. 4)

Thermoforming of the thermoplastic polymer sheet was done using the Biostar® thermoforming machine. The thermoplastic sheets were reshaped (square to round using ceramic bur) for achieving proper fit into the thermoforming chamber. Following thermoforming the samples to be tested were retrieved from the model using a micromotor handpiece and ceramic bur as metallic burs might generate heat which might jeopardize the material’s mechanical properties. (Fig. 5)

The extensions of the sample are (Fig. 6)

Sample Extension
Upper limit	The line joining the point marked on the soft tissue, 2mm away from the marginal gingiva of the left permanent canine to the right permanent canine.
Lower limit	The indentation produced by incisal edges of the maxillary anterior teeth.
Lateral limit	From the distal surface of the right canine to the distal surface of the left canine.

The tensile strength of the sample was tested using a TINIUS OLSEN 10ST Micro Universal Testing Machine (Fig. 7). The sample was held on both the lateral side using the clamp of the machine. 7mm of the sample on either side was marked and this part was used for holding by the clamps.[1] The machine was operated and it was extended at a rate of 12 millimeter per minute. [5]

The tensile strength of the thermoformed thermoplastic polymer sheet was calculated using Horizon® Universal Software in Mega Pascal (MPa)

Descriptive data of tensile strengths (TS) used for inter group comparison using paired t-Test. Intergroup comparison for tensile strength of thermoplastic polymer sheets between pre-treatment and post-treatment maxillary model showed there were no statistically significant differences (p > 0.05) in between the groups. The highest mean difference was seen in group 4 vs group 8 (Mean difference = 4.58). (Table 1) (Fig. 8)

Intragroup comparison of tensile strength of four groups among the pre-treatment (Table 2) (Fig. 9) and four groups among the post-treatment (Table 3) (Fig. 10) were done using One way ANOVA. It was found that there existed a significant difference between them.

Individual comparison among the pre-treatment and among the post-treatment was done using Bonferroni Post-Hoc test. The group comprising AVAC R (Jaypee) i.e., Group 2 in pre-treatment and group – 6 in post-treatment respectively when compared with others showed a statistically significant difference (p < 0.05) whereas comparison among others was statistically insignificant.

Orthodontic practice from a clinical point of view is widely influenced by numerous factors. The shift in treatment seeking for a dynamic change in the esthetics especially in adults have created a necessity for treatment modalities which has less compromise in an individual lifestyle during the course of treatment.[5]

H D Kesling, considered as the pioneer in the field of aligners, was the first to use a flexible tooth positioning appliance in order to achieve tooth movement by preventing the use of visible wires, brackets or other metallic aids. [15]

Aligners have greater aesthetic qualities, superior formability and effortless to use. The vital material properties such as large springback, reduced stiffness, excellent formability, large energy storage, biocompatibility and stability in varied environment are deemed necessary.[4]

Efficacy of tooth movement with clear thermoplastic appliances was also lower than fixed appliances. [4, 16] Aligners being the most looked upon by the current patient generation has numerous shortcomings, though advancement in technology is aimed in improving the material properties and its applicability in clinical practice.[1, 5]

Thermoplastic polymers have inherent limitations associated with thermoplastic polymer materials such as structural instability, low tensile strength, and low wear resistance.[3]

The force produced by thermoplastic appliances for orthodontic tooth movement is mainly driven by the material, thickness and the degree of activation.[10]

In the present study we have used high pressure thermoforming machine – Biostar Thermoforming machine (Model: 2014). This machine was selected owing to better adaptation of the thermoplastic sheet during thermoforming. Wolfram Hahn et al[17] carried out a study focusing on thermoplastic aligners, where higher force delivered by the appliance was due to better fit of the appliance which was achieved in pressure thermoforming machine compared to the force delivered by vacuum thermoformed appliance.[17]

Jeong-Hyun Ryu et al[5], Tamburrino F et al[1] in their study evaluated the mechanical properties of thermoplastic polymer sheets after thermoforming on standard, predetermined models with predetermined shapes. In the literature, several studies revealed a statistically significant difference existed in their mechanical properties.[1, 5, 13, 18–22] Even if the tests were performed under standardized conditions, examining the samples in a preset shape and then drawing conclusions about their properties will be less important for therapeutic purposes.

In the current investigation, we have used pre-treatment and post-treatment maxillary models of a same patient as test objects. Tooth as an object has varied morphology and position in the oral cavity along with supporting structures, few commercially available thermoplastic polymer sheets that are utilized for aligner and retainer fabrication were thermoformed.

Ahn H et al[3] in their study implied the same regarding mechanical properties of the thermoplastic polymers when used clinically are different from those offered by the manufacturers because they are influenced by numerous environmental factors. The most significant drawback of the thermoformed retainers in daily usage is their low level of resistance to wear and fracture. Furthermore, their mechanical characteristics are significantly impacted by thermoforming processes.

In order to eliminate that, in the present study we had taken dental models as objects onto which the sheets were thermoformed to test their performance. The present study evaluated the tensile strength of some commercially used thermoplastic polymer sheets utilized for aligner fabrication. The thermoplastic polymer sheets showed variation when they were thermoformed and tested in two different models (pre-treatment model with moderate crowding and post-treatment model with well aligned teeth) of the same patient. Previously many studies were conducted to assess the property of the aligner material.

Our work not only focuses on the aspect but also analyzes the change in mechanical properties specifically tensile strength for specimens where thermoforming was done in pre-treatment and post-treatment model of the same patient. It is plausible that some permanent distortion occurred during the fabrication process. Otherwise, it may be considered that permanent deformation was introduced when the thermoplastic appliance was thermoformed on the dental model. Kohda et al[10] in his study on assessing the effects of mechanical properties of thermoplastic polymers also concluded the same. The author recommended this as an area for further investigation for elucidating the changes that occur which has an indispensable role in determining the material for specific clinical purpose.

Thermoplastic materials are viscoelastic in nature, which means that the force produced by an intended movement diminishes as a function of time. The appliance may experience significant deformation while being fitted, but a clear orthodontic appliance responds elastically by returning to its original shape as the short-term loading force that induced during the deformation is neutralized.[4]

Polyester, polyurethane, and polypropylene are the predominant thermoplastic materials used to fabricate clear orthodontic appliances. Poly (ethylene terephthalate)-glycol (PET-G) is a non-crystallizing amorphous copolymer of polyethylene terephthalate. Imprelon (Scheu-Dent), Placa Crystal (BioART) are made from PET-G, whereas, AVAC R (Jaypee) made from medical grade polymer and EZ-VAC (3A Medes) made from poly-ethylene. Among the brands subjected for testing, in the pre-treatment maxillary model, Placa Crystal (BioART) has shown to have better properties when compared to the analogous brands. When the same brands were tested after thermoforming on post-treatment maxillary model of the same patient, EZ-VAC (3A Medes) showed to have better performance. This could be attributed to the thermoplastic polymers made from PET-G which showed higher tensile strength in the study. Nonetheless, in post-treatment models, polyethylene showed a better performance than PET-G. Zhang et al[4] in their study declared that PETG is a modified product of PET, which has good mechanical properties, formability, fatigue resistance, and dimensional stability. The dimensional changes may cause variation in the fit of the appliances fabricated from these thermoplastic materials, causing changes to orthodontic forces exerted by these appliances. Study done by Daniele V et al [23], Xiang B et al[24] showed that among the available materials, PET-G has shown to have superior performance. These study stands in accordance with our study results where PET-G showed superior performance. The test values results were also statistically significant (P < .05).

Due to the height variation added with altered morphology of the tooth, the thermoplastic material tends to be stretched on their sides. Owing to this, the materials along the occlusal and the incisal surfaces tends to be thicker. This creates variation in the force delivery and the mechanical properties of the material is also inadvertently affected. These materials when they are uniformly stretched, tend to have higher strength, thus showing good performance. In our study the tensile strength of the sheets when comparing between pre-treatment and post-treatment model, the materials thermoformed on post-treatment models showed exceptional performance though the mean difference weren’t statistically significant (P > .05).

The materials though appear as a single unit, the polymer chains are stretched when they are adapted to the surfaces. The outer layer of the polymer chains is stretched more when compared to the ones that are near the model. The polymer chains arrangement fashion in the sheet as received and after thermoforming is accountable for the dimensional stability and accuracy of its adaptation. They highly influence the strength of the polymer sheet because when the sheets are thermoformed, they are stretched. This stretch of the material leads to change in the polymer chain arrangement. The orientation of the chains in the thermoformed sheet is highly influenced by the morphology of the model onto which the sheet is thermoformed. The stretch in the sheets causes thinning of the materials especially in areas of long teeth. The well aligned post-treatment model provides a favorable environment and allows the polymer chains to arrange in uniform manner.

Kwon et al[25] assessed the force delivery properties of thermoplastic orthodontic materials and found that the forces delivered by thin materials were greater than those delivered by thick materials of the same brand. Ammann R et al [26] in their study also showed the same where the thickness is affected and this in turn affects its mechanical properties. The thickness on the occlusal surface is more than compared to the labial and lingual/palatal surface. This variation of thickness on occlusal surface is beneficial to counteract the occlusal wearing away.

The findings of a study by Tamburrino et al [1] suggests that this can be linked to a phenomenon called drawing, occurring for different polymers when pulled in tension (the condition of thermoforming: the polymer is heated and pulled in tension). In particular, the polymer chains slide over each other, unraveling, so that they become aligned with the direction of stretch because of which the drawn material is stronger and stiffer than before. Barone et al [2] in his study stated about the thickness which strongly varies along the surface of the teeth. Assessing the mechanical properties is of utmost importance to evaluate the effectiveness of the orthodontic treatment for better understanding of the force delivery process.

It has been demonstrated that the high temperature and pressure that are given to thermoplastic materials lead them to crystallize from an amorphous condition, with the regular polymer chains being closely arranged over a considerable distance. A binding force greater than that in the amorphous zone is produced as the secondary bonding force that binds the polymer chains together and builds up. Additionally, amorphous materials can transform into crystalline ones when the temperature drops, and the crystalline phase can impact a material's mechanical properties. After thermoforming, orthodontic aligners need to be carefully examined in order to describe their qualities for clinical usage. Application of large forces to teeth may result in apical root resorption. [5]

Though the effectiveness of transparent orthodontic aligner for orthodontic treatment has been widely reported.[5] Our finding suggest that the physical and mechanical properties of thermoplastic materials used for the fabrication of transparent orthodontic aligners should be evaluated after thermoforming in order to characterize their properties for clinical application. They must be carefully selected depending on the treatment required.

. This raises a major concern on the effectiveness and shelf life of the polymer sheets when used clinically. In spite of the manufacturer claims, majority of the materials tend to show an enormous difference in their effectiveness while using clinically though their properties might be superior when tested using standard recommended conditions.

Among the tested materials, it can be noted PET-G materials had superior performance.
In the four materials tested, the tensile strength had no statistically significant difference between pre-treatment and post-treatment maxillary model but the outcomes showed a relative difference among the values obtained.
Individual materials before using can’t be generalized to all patients as each have their own uniqueness and materials to be used must be selected based on real clinical performances.

ANOVA	Analysis of variance
CAD	Computer Aided Design
CAM	Computer Aided Manufacturing
df	Degree of freedom
F	Frequency
MPa	Megapascal
mm	Millimetre
PET	Polyethylene terephthalate
PET-G	Poly (ethylene terephthalate)-glycol
SD	Standard Deviation
TS	Tensile Strength
<	Lesser than
>	Greater than
%	Percentage

Consent for publication

Not applicable.

Availability of data and material

Not applicable.

Competing interests

The authors declare that there are no competing interests.

Funding

Not applicable

Authors’ contributions

AN realized the research and was the major contributor in writing the manuscript. KK helped with the research and corrected the manuscript. Both the authors read and approved the final manuscript

Acknowledgements

Not applicable

Tamburrino F, D’Antò V, Bucci R, Alessandri-Bonetti G, Barone S, Razionale AV. Mechanical properties of thermoplastic polymers for aligner manufacturing: In vitro study. Dent J (Basel). 2020 1;8(2). http://dx.doi.org/10.3390/dj8020047.
Barone S, Paoli A, Neri P, Razionale AV, Giannese M. Mechanical and geometrical properties assessment of thermoplastic materials for biomedical application. Lecture Notes in Mechanical Engineering. 2017;0:437–46. http://dx.doi.org/10.1007/978-3-319-45781-9_44
Ahn HW, Kim KA, Kim SH. A new type of clear orthodontic retainer incorporating multi-layer hybrid materials. Korean J Orthod. 2015 1;45(5):268–72. http://dx.doi.org/10.4041/kjod.2015.45.5.268
Zhang N, Bai Y, Ding X, Zhang Y. Preparation and characterization of thermoplastic materials for invisible orthodontics. Dent Mater J. 2011;30(6):954–9. http://dx.doi.org/10.4012/dmj.2011-120
Ryu JH, Kwon JS, Jiang HB, Cha JY, Kim KM. Effects of thermoforming on the physical and mechanical properties of thermoplastic materials for transparent orthodontic aligners. Korean J Orthod. 2018 1;48(5):316–25. http://dx.doi.org/10.4041/kjod.2018.48.5.316
Ryokawa H, Miyazaki Y, Fujishima A, Miyazaki T, Maki K. The mechanical properties of dental thermoplastic materials in a simulated intraoral environment. Orthodontic Waves. 2006;65(2):64–72. http://dx.doi.org/10.1016/j.odw.2006.03.003
Gerard Bradley T, Teske L, Eliades G, Zinelis S, Eliades T. Do the mechanical and chemical properties of InvisalignTM appliances change after use? A retrieval analysis. Eur J Orthod. 2016 1;38(1):27–31. http://dx.doi.org/10.1093/ejo/cjv003
Ren Y, Maltha JC, Kuijpers-Jagtman AM. Optimum force magnitude for orthodontic tooth movement: a systematic literature review. Angle Orthod. 2003;73(1):86-92. https://doi.org/10.1043/0003-3219(2003)073%3C0086:OFMFOT%3E2.0.CO;2
Simon M, Keilig L, Schwarze J, Jung BA, Bourauel C. Forces and moments generated by removable thermoplastic aligners: incisor torque, premolar derotation, and molar distalization. Am J Orthod Dentofacial Orthop. 2014;145(6):728-36. http://dx.doi.org/10.1016/j.ajodo.2014.03.015
Kohda N, Iijima M, Muguruma T, Brantley WA, Ahluwalia KS, Mizoguchi I. Effects of mechanical properties of thermoplastic materials on the initial force of thermoplastic appliances. Angle Orthod. 2013;83(3):476-83 http://dx.doi.org/10.2319/052512-432.1
CAREY CW. Linear arch dimension and tooth size; an evaluation of the bone and dental structures in cases involving the possible reduction of dental units in treatment. Am J Orthod. 1949 ;35(10):762-75. http://dx.doi.org/10.1016/0002-9416(49)90148-7
Andrews LF. The six keys to normal occlusion. Am J Orthod. 1972;62(3):296-309 https://doi.org/10.1016/s0002-9416(72)90268-0
Ihssen BA, Kerberger R, Rauch N, Drescher D, Becker K. Impact of dental model height on thermoformed PET-G aligner thickness—an in vitro micro-CT study. Applied Sciences. 2021;11(15):6674. http://dx.doi.org/10.3390/app11156674
Morrow RM, Rudd KD. A rapid method for accurate cast duplication. J Prosthet Dent. 1971 ;26(6):665-8. https://doi.org/10.1016/0022-3913(71)90092-8
Kesling HD. The philosophy of the tooth positioning appliance. American Journal of Orthodontics and Oral Surgery. 1945 1;31(6):297-304. https://doi.org/10.1016/0096-6347(45)90101-3
Kravitz ND, Kusnoto B, BeGole E, Obrez A, Agran B. How well does Invisalign work? A prospective clinical study evaluating the efficacy of tooth movement with Invisalign. Am J Orthod Dentofacial Orthop. 2009 ;135(1):27-35. http://dx.doi.org/10.1016/j.ajodo.2007.05.018
Hahn W, Fialka-Fricke J, Dathe H, Fricke-Zech S, Zapf A, Gruber R, Kubein-Meesenburg D, Sadat-Khonsari R. Initial forces generated by three types of thermoplastic appliances on an upper central incisor during tipping. Eur J Orthod. 2009 ;31(6):625-31. http://dx.doi.org/10.1093/ejo/cjp047
Lombardo L, Martines E, Mazzanti V, Arreghini A, Mollica F, Siciliani G. Stress relaxation properties of four orthodontic aligner materials: A 24-hour in vitro study. Angle Orthod. 2017 ;87(1):11-18. http://dx.doi.org/10.2319/113015-813.1
Ihssen BA, Willmann JH, Nimer A, Drescher D. Effect of in vitro aging by water immersion and thermocycling on the mechanical properties of PETG aligner material. J Orofac Orthop. 2019;80(6):292-303. http://dx.doi.org/10.1007/s00056-019-00192-8
Fang D, Li F, Zhang Y, Bai Y, Wu BM. Changes in mechanical properties, surface morphology, structure, and composition of Invisalign material in the oral environment. Am J Orthod Dentofacial Orthop. 2020;157(6):745-753 http://dx.doi.org/10.1016/j.ajodo.2019.05.023
Ranjan A, Biradar AK, Patel A, Varghese V, Pawar A, Kulshrestha R. Assessment of the Mechanical Properties of Three Commercially Available Thermoplastic Aligner Materials Used for Orthodontic Treatment. Iranian Journal of Orthodontics. 2021 31;15(2). http://dx.doi.org/10.5812/ijo.116573
Daniele V, Macera L, Taglieri G, Spera L, Marzo G, Quinzi V. Color Stability, Chemico-Physical and Optical Features of the Most Common PETG and PU Based Orthodontic Aligners for Clear Aligner Therapy. Polymers (Basel). 2021 21;14(1):14. http://dx.doi.org/10.3390/polym14010014
Daniele V, Macera L, Taglieri G, Di Giambattista A, Spagnoli G, Massaria A, et al. Thermoplastic disks used for commercial orthodontic aligners: Complete physicochemical and mechanical characterization. Materials. 2020 1;13(10). http://dx.doi.org/10.3390/ma13102386
Xiang B, Wang X, Wu G, Xu Y, Wang M, Yang Y, et al. The force effects of two types of polyethylene terephthalate glyc-olmodified clear aligners immersed in artificial saliva. Sci Rep. 2021 1;11(1). https://www.nature.com/articles/s41598-021-89425-8
Kwon JS, Lee YK, Lim BS, Lim YK. Force delivery properties of thermoplastic orthodontic materials. Am J Orthod Dentofacial Orthop. 2008 Feb;133(2):228-34 http://dx.doi.org/10.1016/j.ajodo.2006.03.034
Ammann R, Tanner C, Schulz G, Osmani B, Nalabothu P, Töpper T, Müller B. Three-dimensional analysis of aligner gaps and thickness distributions, using hard x-ray tomography with micrometer resolution. J Med Imaging (Bellingham). 2022 May;9(3):031509. http://dx.doi.org/10.1117/1.JMI.9.3.031509

Table 1: Inter group comparison of tensile strength of thermoformed sheets between pre-treatment and post-treatment maxillary model of a patient.

Groups		N	Mean ±SD	Mean Difference	P - value
Imprelon (Scheu-Dent)	Group 1	5	12.90±1.91	2.60	0.079
	Group 5	5	15.50±1.78
AVAC R (Jaypee)	Group 2	5	7.20±0.38	0.73	0.505
	Group 6	5	7.93±2.06
Placa Crystal (BioART)	Group 3	5	15.64±1.10	2.52	0.082
	Group 7	5	18.16±1.54
EZ – VAC (3A Medes)	Group 4	5	14.03±3.90	4.58	0.102
	Group 8	5	18.61±1.54

Table 2: Intragroup comparison of tensile strength in pre-treatment

	Sum of Squares	df	Mean Square	F	Significance
Between Groups	202.209	3	67.403	13.265	0.000
Within Groups	81.298	16	5.081
Total	283.507	19

Multiple Comparisons
Bonferroni (Post Hoc test)
Groups		Mean Difference (I-J)	Std. Error	Significance
Group 1 Imprelon (Scheu-Dent)	AVAC R Group 2	5.67^*	1.42564	0.006
	Placa Crystal Group 3	-2.74	1.42564	0.436
	EZ – VAC Group 4	-1.13	1.42564	1.000
Group 2 AVAC R (Jaypee)	Imprelon Group 1	-5.67^*	1.42564	0.006
	Placa Crystal Group 3	-8.44^*	1.42564	0.000
	EZ – VAC Group 4	-6.83^*	1.42564	0.001
Group 3 Placa Crystal (BioART)	Imprelon Group 1	2.74	1.42564	0.436
	AVAC R Group 2	8.44^*	1.42564	0.000
	EZ – VAC Group 4	1.61	1.42564	1.000
Group 4 EZ – VAC (3A Medes)	Imprelon Group 1	1.13	1.42564	1.000
	AVAC R Group 2	6.83^*	1.42564	0.001
	Placa Crystal Group 3	-1.61	1.42564	1.000
*. The mean difference is significant at the 0.05 level.

Table 3: Intragroup comparison of tensile strength in post-treatment

	Sum of Squares	df	Mean Square	F	Significance
Between Groups	365.928	3	121.976	40.036	0.000
Within Groups	48.746	16	3.047
Total	414.674	19

Multiple Comparisons
Bonferroni (Post Hoc test)
Groups		Mean Difference (I-J)	Std. Error	Significance
Group 1 Imprelon (Scheu-Dent)	AVAC R Group 2	7.57^*	1.10392	0.000
	Placa Crystal Group 3	-2.66	1.10392	0.170
	EZ – VAC Group 4	-3.11	1.10392	0.075
Group 2 AVAC R (Jaypee)	Imprelon Group 1	-7.57^*	1.10392	0.000
	Placa Crystal Group 3	-10.23^*	1.10392	0.000
	EZ – VAC Group 4	-10.68^*	1.10392	0.000
Group 3 Placa Crystal (BioART)	Imprelon Group 1	2.66	1.10392	0.170
	AVAC R Group 2	10.23^*	1.10392	0.000
	EZ – VAC Group 4	-0.45	1.10392	1.000
Group 4 EZ – VAC (3A Medes)	Imprelon Group 1	3.11	1.10392	0.075
	AVAC R Group 2	10.68^*	1.10392	0.000
	Placa Crystal Group 3	0.45	1.10392	1.000
*. The mean difference is significant at the 0.05 level.

No competing interests reported.

SUPPLEMENTARY.docx

Download PDF

Journal Publication

published 02 Apr, 2024

Read the published version in Clinical Oral Investigations →

Editorial decision: Revision requested
03 Feb, 2024
Reviews received at journal
01 Feb, 2024
Reviewers agreed at journal
22 Jan, 2024
Reviews received at journal
25 Oct, 2023
Reviewers agreed at journal
16 Oct, 2023
Reviewers invited by journal
13 Oct, 2023
Editor assigned by journal
05 Oct, 2023
Submission checks completed at journal
05 Oct, 2023
First submitted to journal
29 Sep, 2023

You are reading this latest preprint version

A comparative study on tensile strength of various thermoplastic polymers sheets following thermoforming on a pre-treatment and post-treatment maxillary model of a patient: An in vitro study

Status:

Journal Publication

Version 1

Abstract

Figures

INTRODUCTION

MATERIALS AND METHODS

RESULTS

DISCUSSION

CONCLUSIONS

ABBREVIATIONS

Declarations

References

Tables

Additional Declarations

Supplementary Files

Status:

Journal Publication

Version 1