Comparative Evaluation of Accuracy of Reconstructed 3D Printed Rapid Prototyping Models and Conventional Stone Models with Different Ranges of Crowding: An In-vitro Study
Correspondence Address :
Ankita M Mohite,
Yashaswi, Co. Op. Hos. Soc., Flat No.: 503, Govind Bachaji Road, Charai, Thane (W), Maharashtra, India.
Introduction: The digitalisation of dental models has made significant contribution to the current success of orthodontic practices. Rapid Prototyping (RP) is an innovative method of producing physical objects based on Computer-Aided Design (CAD) Computer-Aided Manufacturing (CAM).
Aim: To compare the accuracy of the Three-Dimensional (3D) printed rapid prototyped models with orthodontic stone models across different ranges of crowding.
Materials and Methods: A cross-sectional study carried out at the Bharati Vidyapeeth Deemed to be University, Dental College and Hospital, Sangli, Maharashtra, India during September 2019 to September 2020. A total of 36 rapid prototyped models were reconstructed from stone models using Light Emitting Diode (LED) scanner and Digital Light Processing (DLP) technology. Dental stone models and RP models were evaluated using digital caliper for different linear measurements and arch dimensions. The data was analysed using Statistical Package for Social Sciences (SPSS) version 26.0. To evaluate accuracy, t-test analyses and Bland-Altman plotting were performed.
Results: T-test showed statistically non significant difference in all parameters of measurements of RP models when compared to stone models. According to Bland-Altman plotting. The mean difference between stone and RP models for the various degree of crowding was minimal and within ±0.07 mm in all planes.
Conclusion: Discrepancy between dental plaster models and RP models were less than 0.5 mm which was considered clinically non significant. Suggesting that RP models can be effectively used as an alternative to stone models.
Digital orthodontics, Stereolithography, Three-dimensional printing
The incorporation of digital technologies into orthodontic practise has changed diagnosis and treatment planning from a traditional Two-Dimensional (2D) method to an advanced 3D approach (1). In recent years, improvements in digital imaging and modelling have allowed the creation of a virtual orthodontic patient that offers the 3D reconstruction of bony structure, soft tissue, and dentition (2). Digital models have a number of advantages, including ease of storage, data retrieval, time saving, cost-effectiveness, transferability, and also improved treatment quality (3).
Institutions have a legal binding to hold the patient records for up to 10 years (4). The problem of storage space can be handled by scanning and preserving past patient study models in digital format. However, there can be hesitation to dispose off these stone models, as there may be occasions, such as research work requirements or medico-legal circumstances, where tangible records are essential (5).
The 3D printing or RP is a new technology that can create graspable 3D objects directly from digital models, which can address the need for physical models when required (4). It is among of the most futuristic innovations that can translate a fevered imagination into hard reality. This method is classified as an additive manufacturing, where the physical model is constructed layer by layer, once the digital model has been divided into layers of a specific thickness (4). This can be achieved through various techniques such as Stereolithography (SLA), Inkjet-based system (3D printing -3DP), Selective Laser Sintering (SLS), Fused Deposition Modeling (FDM) and DLP (6).
Any inaccuracy in the printing of working models may cause insufficient tooth movements and have a detrimental effect on treatment outcomes (7). Few studies have reported acceptable clinical accuracy of RP models in comparison with conventional stone models (3),(8). However, there is scarcity of information regarding impact of crowding on the precision of measurements done on reconstructed RP models. Teeth can overlap in crowded area and it may be more difficult to accurately replicate the undercut sections that are blocked from the sensor’s view while scanning. Hence, accuracy and reproducibility of RP models must be carefully evaluated.
The aim of this study was to elucidate whether the tooth measurements recorded on stone models and 3D printed RP models with different ranges of crowding are equivalent and comparable.
This in-vitro investigation was carried out carried out in the department of Orthodontics and Dentofacial Orthopaedics at the Bharati Vidyapeeth Deemed to be University, Dental College and Hospital, Sangli, Maharashtra, India. Duration of the study, from September 2019 to September 2020. On June 20, 2019, the Institutional Ethical Committee accepted the study (Letter number: BVDUMC&H/IEC/Dissertation2018-19/D-02). The procedure of study was followed in conformity with the Institute’s ethical standards. Prior to the impression, the volunteer’s informed consent was obtained.
Inclusion criteria: The inclusion criteria of study models were completely erupted, permanent teeth from first molar to contra-lateral first molar with mild, moderate, or severe crowding and good surface details.
Exclusion criteria: Patients who had undergone or were undergoing orthodontic treatment, as well as those with voids or fractures, aberrant tooth shapes and surfaces, or extra teeth, were eliminated from the study.
Sample size calculation: The sample size was estimated using SPSS Software based on a previous study conducted by Wan Hassan WN et al., (4). Approximately, 34 samples per group (Dental stone models group and RP models group) were required. To improve the power of the study, the number of models per group was increased to 36 with a difference of 0.15 mm and a standard deviation of 0.22 mm at the 5% level of significance (80% power Type I error to be 5% Type II error to be 20%).
Impressions were made by using alginate impression material and positive replicas were made by using type III dental stone. A total of 36 dental stone models with crowding were collected. Crowding was calculated by comparing the total mesiodistal breadth of the teeth to the available space in the arch. According to the Proffit WR, crowding was divided into three categories: mild (1-4 mm), moderate (5-8 mm), and severe (>9 mm) (9). Based on crowding the 36 models were subdivided into 3 groups of 12 each.
To generate 3D digital models, all dental stone models were scanned by using a Hybrid with Blue LED scanner (MeditIdentica with accuracy of 7μm) in multiple planes (Table/Fig 1). Scanned data was saved as Standard Tessellation Language (STL) file (Table/Fig 2). The data were sliced into individual layers by Mesh-Meshmixer software. Scanned data were uploaded to reconstruct 36 RP models with Nextdent 5100 3D System Printer using DLP technology. The printing material comprised of high performance Biobased Acrylate Photocurable Resin (BAPR) (Table/Fig 3).
A total of 72 models consisting of 36 samples each of dental stone models (Group A) and RP models (Group B) were measured with hand-held digital vernier caliper. Clinically significant parameters, such as tooth size dimensions and arch dimensions, were measured to determine whether the quality of the RP models would be clinically acceptable for linear measurements (Table/Fig 4),(Table/Fig 5),(Table/Fig 6) (4).
Three study model pairings, one from each category, were randomly chosen in order to evaluate operator dependability. Each study model was measured using vernier caliper by the same examiner twice, with an interval of atleast two weeks, to ensure intra-examiner reliability. To determine inter-operator reliability, the first measurements were compared to those acquired by a second examiner using vernier caliper.
Statistical analysis was done using SPSS V26.0 at level of significance p≤0.05. All readings obtained were statistically analysed by calculating their mean, standard deviation and standard error. The Shapiro-Wilk test was used to determine the normality of numerical data, and it was discovered that the data followed a normal curve. As a result, parametric tests have been employed for comparisons. The t-test was used to compare the two groups among themselves. To evaluate the internal consistency and agreement between two or more examiners by using Cronbach’s alpha and intraclass correlation (inter and intra). A technique for describing agreement between two quantitative data by creating limits of agreements is the Bland-Altman Plot.
The present study comprised of 12 sets of study models for each category of crowding. The mean systemic differences in all parameters of measurements of RP models when compared to stone models were statistically non significant. Mesiodistal width values of RP models were smaller in moderate crowding (mean 7.71 and 7.63 mm; SD, 0.52 and 0.55 mm). Buccolingual width values of teeth in RP models were smaller than dental stone models with mild and severe crowding whereas, larger in moderate crowding (mean 5.9 and 6.01 mm; SD). In clinical crown height measurements were equivalent in mild and severe crowding (mean 7.64 and 7.55 mm). Curvilinear measurements of buccal and lingual surfaces of central incisor and first premolar in RP models were smaller than dental stone models with mild and severe crowding whereas they were larger in moderate crowding (Table/Fig 7). Arch dimensions of teeth in RP models were smaller than dental stone models with moderate and severe crowding whereas they were equivalent in mild crowding. The intraoperator ICC values ranged from 0.839 to 0.987 and had an excellent agreement (0.62) (4).
Using the mean and standard deviation of the differences between two measurements, the Bland-Altman Plot was calculated by plotting the data on the XY axis, where the X axis indicates the difference between the two measurements and the Y axis displays the mean of the two measurements. For the different degree of crowding in all planes, the mean bias between stone and RP models was minimal and was within ±0.07 mm (Table/Fig 8).
This study evaluated the potential use of RP models constructed using 3D printing as an alternative to stone models. The scanning and printing methods are two elements that could impact the calibre of RP models (10). In present study, MeditIdentica Hybrid with Blue LED scanner was used with three multiplaner cameras and colour-texture support, enabling technicians to form highly digital model. Additionally, scanning into the deep occlusal areas was made possible by Intelligent Multi-View (IMV) technology, providing more precision and information (10),(11),(12).
In present study, the models were produced using the 3D printer (Nextdent 5100 3D system printer with DLP technology) with 350 μm accuracy, good surface finishing, and extraordinary high feature resolution (5-50 μm) (13). The accuracy and truthfulness of dental models created using various 3D printing processes were evaluated by Kim SY et al., (14). In comparison to the Fused Filament Fabrication (FFF) and SLA procedures, they discovered that the PolyJet and DLP techniques were more accurate.
The printing material used in the present study comprised of high performance composite- BAPR with 0.089 to 0.102 mm thick layers. It has the best mechanical performance of any other biobased resin, with a tensile strength of 7.0 MPa (13). A significant consideration for the application in a stereolithographic layer-by-layer printing process is the resin’s viscosity. Low viscosities are typically preferred to enable adequate recoating of the liquid resin between the last layer of the model and the surface of the resin tank. In comparison to autodesk standard clear prototyping resin, BAPR has a lower viscosity (13).
In the present study, comparison of the various tooth measurements was made on 3D printed models and dental stone models with different degrees of crowding. In all parameters, the results demonstrated that differences were statistically non significant. Similar research on the precision of 3D printed models using various parameters are summarised in (Table/Fig 9) (3),(4),(14),(15),(16),(17),(18).
Stone models have smooth surface and clearly defined interproximal contact points and cervical edges. Insignificant artifacts such as air bubbles and slightly excessive stone materials were observed, however, they were minor and away from the landmarks utilised for measurements. Also, the surfaces of the RP models were coarse showing flaky appearance. At a crowded area, the clinical impression was less defined and more likely to have a slight surplus of artifacts. The clinical implication of this reduction in detail was not easy to quantify. But such loss in the details may not necessarily be critical for construction of orthodontic appliances, since the shape and size of the teeth and arch form of 3D printing models were similar to the original casts (4). According to Sweeney S et al., a successful occlusion is defined as an interarch distance with an inaccuracy of less than 0.5 mm (as opposed to the gold standard) (17). Based on clinical validity and the benchmark established by the American Board of Orthodontics’ increments for grading plaster models, the range of error (0.5 mm) was determined (17). In the present study, the mean systemic differences were small and statistically non significant, suggesting that RP models might be used interchangeably with dental stone models. For craniofacial surgeries, if discrepancies are within 1.0 mm then they are clinically acceptable (4).
Reconstructed models are becoming more and more useful as a tool for difficult craniofacial case visualisation, diagnosis, and surgery planning. It helps to achieve better-operating results, and provide an opportunity to study and manipulate the bone structures of the patient as required before the actual surgery (19). RP models of the jaws are used as an aid for the fabrication of distractor to produce osteogenic distraction of the mandibular symphysis (15). It is also used to produce customised lingual brackets for subsequent investment. RP also act as a valuable tool for preparation of dental socket in autotransplantation cases. In production of Invisalign, RP offers advantages of high accuracy with speed (20). RP versions have a number of benefits, including being lightweight, durable, highly resistant to abrasion, transportable, and most importantly, the capacity to share digital data (1). There is a great potential to create physical models on demand from digital data, which would alleviate the strain of the storage space issue.
The results of this study, does not specify precision of appliances created using RP models. Further studies need to analyse and focus on precision of these appliances for clinical use. It is also possible to rebuild data for 3D printers directly from other data sources, such as Cone Beam Computed Tomography (CBCT) Computed Tomography (CT) (CBCT) or Computed tomography (CT) scans. However, more research is required on these areas which will emphasis on the accuracy using sources from CBCT or CT scans to rebuild data using RP.
In present study, the mean systemic differences in all parameters of measurements of RP models when compared to stone models were statistically non significant. Hence, it can be concluded that RP models can be used as alternative to stone models. It is anticipated that 3D printed objects will become more significant in a variety of orthodontic research areas. This includes the use of technology not only to bring about changes in existing pattern but also to enable new things that were previously impossible.
Date of Submission: Aug 16, 2022
Date of Peer Review: Oct 29, 2022
Date of Acceptance: Dec 22, 2022
Date of Publishing: Mar 01, 2023
• Financial or Other Competing Interests: None
• Was Ethics Committee Approval obtained for this study? Yes
• Was informed consent obtained from the subjects involved in the study? Yes
• For any images presented appropriate consent has been obtained from the subjects. Yes
PLAGIARISM CHECKING METHODS:
• Plagiarism X-checker: Aug 17, 2022
• Manual Googling: Oct 31, 2022
• iThenticate Software: Dec 21, 2022 (14%)
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