Digital Versus Conventional Techniques for Construction of Mandibular Implant Retained Overdenture

doi:10.21203/rs.3.rs-4718431/v1

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Digital Versus Conventional Techniques for Construction of Mandibular Implant Retained Overdenture

https://doi.org/10.21203/rs.3.rs-4718431/v1

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Background: This study aimed to evaluate two different construction techniques (conventional and 3D-printed techniques) for two implant-retained complete mandibular overdentures regarding mechanical wear of the occlusal surface using 3D digital analysis andocclusion force distribution using the digital occlusal analysis system (Occlusense).

Methods: Twenty patients were selected for this study from the prosthetic department, Faculty of Dentistry, Mansoura University. The sample size was determined based on the results of previous clinical trial with (effect size = 1.1, α = 0.05, β =0.90). The calculated sample was 20. The power analysis was performed with the aid of computer software (G*power 3.1.5, Heinrich-Heine-Universität Düsseldorf, Germany). Balanced randomization was used to equally assigned patients to one of two groups using to ensure comparability between groups. The participants were randomly assigned into two groups using random numbers generated in an Excel spreadsheet.Each patient received two implants in the mandibular canine areas with locator attachments to retain the overdentures. According to the overdenture construction technique, all patients were classified into two equal groups: the conventional heat polymerized overdenture group and the 3D-printed overdenture group. The mandibular overdentures were compared and evaluated immediately and after 12 months of insertion regarding mechanical wear of the occlusal surface using 3D digital analysis and occlusal force distribution using a digital occlusal analysis system (Occlusense).

Results: 3d printed group showed significantly higher occlusal surface wear than conventional group after twelve months (T12) with a p value ≤ 0.05.

3d printed group showed significantly more occlusal force distribution than conventional group with a p value ≤ 0.05. Also, there was a significant difference in occlusal force distribution with advance of time for each group, with a p value ≤0.05 level of a significance.

Conclusion: Within the limitations of this study, it was shown that implant overdentures constructed by conventional techniques show superior results regarding mechanical wear of the occlusal surface compared to 3D-printing techniques. However, 3D-printing techniques offer a promising result compared to conventional techniques for the construction of implant overdentures regarding occlusal force distribution.

Trial registration: The study was approved by the local ethical committee of the Faculty of Dentistry, Mansoura University (No. A02060922) and retrospectively registered at ClinicalTrials.gov (ClinicalTrials.gov Identifier: NCT06139003 ) (16/11/2023).

CAD-CAM

Implant

3D-Printed Overdenture

Locator Attachment

Occlusens

Superimposition

Occlusal Wear

Occlusal force distribution

Edentulism has been a serious public health problem in industrialized nations due to population aging and in developing countries due to poor oral care. For many years, conventional complete dentures have been a promising treatment for edentulous patients. They help restore a person's appearance, speech, and normal oral function, which has a significant positive impact on people's daily lives. ⁽¹⁾

However, some problems have been reported with complete dentures in cases of resorbed ridge cases, contributing to biting, chewing, and facial esthetics. It also causes discomfort as a result of instability and decreased retention. Traditionally, vestibuloplasty has been performed to treat these individuals by raising the height of the alveolar ridge. Patients with edentulous mandibles now frequently choose implant-retained overdentures as a treatment option, and their use has been the subject of substantial research even after. ⁽²⁾

Mandibular overdentures retained with dental implants improve masticatory ability and the patient's satisfaction. The patients treated with mandibular implant overdentures are able to eat tough foods, chew more effectively, and require fewer chewing cycles than patients with conventional complete dentures. Treatment with implant overdentures was also found to improve bite force. ⁽³⁾

According to the McGill and York consensus statement, a 2-implant supported mandibular overdenture should be the standard treatment for edentulous mandibular patients. Dental implants placed in the anterior mandibular region show height bone preservation and a significant reduction in bone loss of the residual ridge after implant insertion. Thus, fewer implants with attachment systems provide better retention and stability, as well as greater chewing comfort and patient satisfaction. ⁽⁴⁾

One of the most widely used attachments is the locator attachment system, which has an enhanced design for better stability and retention. This connection uses frictional and mechanical retention techniques. This system uses a dual retention strategy with distinct retentive values, and it is composed of a patrix and a matrix. It is meant for short inter-arch distances and is categorized as a robust universal hinge device. locator attachments can correct up to 40° of implant angulations. ⁽⁵⁾

Other issues were reported with complete dentures related to the material and techniques of construction, such as lack of dimensional stability, changeability of color, and a reduced fit between the tissues supporting the denture and the base. Increased porosity in dentures affects their aesthetics and mechanical properties. ⁽⁶⁾

They also require complicated clinical and laboratory procedures. Preliminary impression, final impression with border molding, and jaw relation recording. Mounting of master casts with a facebow in a semi-adjustable articulator. The lab technician then selects several artificial teeth in form and size to make wax dentures, which the dentist and patient will assess, then permanent dentures are fabricated after revisions and adjustments. ⁽⁷⁾

Digital complete dentures constructed with computer-assisted design/computer-assisted manufacturing CAD/CAM technology ushers in a new era of removable prosthodontics. There are many commercial CAD/CAM technologies available for designing and producing complete dentures. They enable the creation of a clinically predictable product, the customization of the tooth setup, and the confirmation of earlier procedures prior to the trial visit. Also, with CAD/CAM technology, surface and mechanical properties can be improved. ⁽⁸⁾

Digital complete denture fabrication involves scanning final impressions or casts and a maxillomandibular record, using software to design the denture base and arrange artificial teeth, and then manufacturing the denture using CAD/CAM technology that is based on two main technologies: subtractive (milling) and additive (3D-printing) technologies. Subtractive (milling) manufacturing is used in dentistry, especially in prosthodontics. This technique involves the milling of complete denture prostheses from pre-polymerized manufactured blocks. However, a limited number of authors have reported the use of CAD/CAM technology for complete dentures. Nonetheless, waste materials and milling burs wear are seen as the primary drawbacks of CAD/CAM technology. So, efforts are being made to advance additive manufacturing or 3D-printing techniques for the construction of complete dentures, as the latter has demonstrated a significant degree of efficiency in reducing wasted materials. The additive (3D-printing) manufacturing technique fabricated complete denture prostheses from photopolymerized acrylate material using a 3D laser lithographic (LL) machine. The process of creating digitally planned objects using 3D-printing technology involves joining materials layer by layer in a sequential manner. ⁽⁸⁾

When complete removable dentures are made using 3D-printing instead of milling processes, the process is quicker, less expensive, and uses less material. Nevertheless, in comparison to milled materials, the mechanical and physical characteristics of materials used in 3D-printing processes remain subpar. ⁽⁹⁾

These digital dentures require fewer laboratory visits, potentially requiring just two appointments to complete the process. They also offer a more accurate base fit and greater retention than traditional heat-polymerized dentures. Encouraging short-term clinical performance, favorable patient-related outcomes, and appropriate time-cost effectiveness.⁽¹⁰⁾

Regarding occlusal stresses, in contrast to natural teeth, osseointegrated implants do not have periodontal ligaments and respond to occlusal stress differently biomechanically. As a result, it is thought that occlusal overloading, which is frequently considered one of the possible causes of implant prosthesis failure. ⁽¹¹⁾

The occlusal goal of prosthodontics is to achieve bilateral balance of removable complete overdenture prostheses in order to address these issues. As digital technology has advanced, several occlusal force assessment devices have entered the dentistry market. Nevertheless, very few of these devices are covered in the literature. Nevertheless, nearly every article came to the conclusion that employing digital technology makes it possible to create constructs that are more exact and to precisely balance occlusal interactions. ⁽¹²⁾

3D digital analysis is a nondestructive technique that shows the outcome both graphically and mathematically. It functions by enabling the superimposition of references and measured data analysis. The 3D inspection software and an optical scanner can be used to evaluate the trueness of the retrieved data, also referred to as the closeness of agreement between the measurement and actual values. ⁽¹³⁾

With the use of a novel technology called Occlusense, clinicians can greatly improve the prosthetic occlusal balance upon placement by utilizing computer-guided occlusal force-finishing correction changes. It is now possible to tackle this clinical force balancing problem digitally. ⁽¹⁴⁾

In removable prosthodontics, wear resistance is a crucial physical characteristic of prosthetic teeth. It also assesses the prosthesis's capacity to uphold the established occlusal relationship, which makes it a significant factor in determining the longevity of dentures. Along with speech and aesthetics, patients have high expectations for the masticatory effectiveness of their new dentures, which may be hampered by denture tooth wear. Surface loss is typically more noticeable on posterior teeth than on anterior teeth. Denture teeth wear over time as a result of stresses of mastication during functional and parafunctional movement. Because of the potential for lost occlusal vertical dimension, reduced masticatory efficiency, fatigue of the masticatory muscles, discomfort for patients and aesthetic concerns. Teeth wear is a major concern for both patients, and physicians. ⁽¹⁵⁾

Digital manufacturing dental technology appears to have changed the prosthodontic discipline significantly, but its full potential is still unknown. This might be the result of a dearth of studies and research on the technology, especially when it comes to patient-centered outcomes and clinical performance. The purpose of this study was to compare conventional heat polymerized overdenture (group A) and 3D printed overdenture (group B) supported by two dental implants regarding mechanical wear of the occlusal surface using 3D digital analysis and occlusal force distribution using the digital occlusal analysis system (Occlusense).\

The hypothesis of this study would be a significant difference between two groups to be found regarding occlusal wear and occlusal force distribution

Study design

Twenty completely edentulous patients were selected from the Prosthetic Department, Faculty of Dentistry, Mansoura University. The patients were fully informed about the purpose as well as the surgical and prosthodontic treatments of this study. They signed the written consent of the Ethical Committee of Mansoura University Dental Research (No. A02060922). (Clinical trial registration number: NCT06139003) (16/11/2023). According to the following criteria: a completely edentulous, healthy firm mucosa without any remaining roots or jaw cysts. Maxillomandibular angel’s class I relationship with sufficient restorative space. Sufficient residual alveolar bone quantity and quality class 1–3 according to Lekholm and Zarb. ⁽¹⁶⁾ The sample size was determined based on the results of previous clinical trial⁽¹⁷⁾ with (effect size = 1.1, α = 0.05, β = 0.90). The calculated sample was 20. The power analysis was performed with the aid of computer software (G*power 3.1.5, Heinrich-Heine-Universität Düsseldorf, Germany ). Balanced randomization was used to equally assigned patients to one of two groups using to ensure comparability between groups regarding Occlusal force analysis using digital occlusal device (Occlusense) and wear resistance through digital occlusal matching. The participants were randomly assigned into two groups using random numbers generated in an Excel spreadsheet. The two groups are: conventional group and 3d printed group.

Patients with systemic issues such as recent myocardial infarction, hepatic patients, bleeding disorders, autoimmune diseases like rheumatoid arthritis, hyperparathyroidism, uncontrolled diabetes mellitus, severe osteoporosis or cancer were excluded from the study. Also, patients with recent organ transplants, long-term corticosteroid use, radiotherapy, uncooperative patients with psychiatric disorders, heavy smokers, poor oral hygiene, and parafunctional habits were excluded.

Presurgical procedure

Construction of complete dentures

Mandibular and maxillary preliminary impressions were made by using irreversible hydrocolloid impression materials. Final impressions were made by zinc oxide impressions. Then impressions were poured into dental stone for master casts, on which record blocks were constructed. After adjusting the maxillary occlusion rim, it is transferred to a semi-adjustable articulator by means of a maxillary facebow record. The mandibular occlusal rim was then mounted using a wax intermaxillary record. Then, semi-anatomical acrylic artificial teeth were sited in a bilaterally balanced occlusion, tried in, flasking was done, packing was done with heat-cured acrylic resin, finishing and polishing were done, and the denture was delivered to the patient after centric and eccentric occlusal adjustment.

Implant placement surgery

Under local anesthesia and antibiotic cover (1 gm of clavulanic acid with amoxicillin 1 h before surgery). A crestal incision with the full thickness of the flap was made in the mandible between the first premolar area of one side to the other side, and the crestal bone was trimmed to provide an adequate site for implant placement. Each patient received two implant fixtures (BTK dental implants) in the canine region of the mandible, and insertion torques ≥ 35 Ncm were acceptable, then covered immediately by the cover screw. Post-operative panoramic x-ray film was made to verify the position and orientation of implants. The lower denture was fitted with relief over the implant site to avoid loading the implants, and soft lining material was applied, with the occlusion refined.

Prosthetic procedures

After three months of osseointegration, implants were exposed using the tissue punch, and the healing abutments were screwed over each fixture. After two weeks, the healing abutments were unscrewed, and locator abutment attachments (BTK dental implanting trust, Italia) (2.5mm diameter and 4mm height) were screwed to implants and tightened by the torque wrench (30 N/cm). (Fig. 1)

Construction of a new complete overdentures

According to treatment, all patients were randomly divided into two equal groups:

Conventional heat polymerized overdenture group

patients received a maxillary complete denture opposing a mandibular implant overdenture constructed by conventional technique.

3D-printed overdenture group

patients received a maxillary complete denture opposing a mandibular implant overdenture constructed by 3D-printing.

Construction of conventional heat polymerized overdentures

A metal housing was placed over locator abutments with a black lab processing insert. Mandibular and maxillary preliminary impressions were taken using an irreversible hydrocolloid impression material (Normal Set Alginate, Cavex, Netherland). After pouring preliminary impressions, self-cure acrylic resin special trays were constructed, then final impressions were taken using medium body addition silicone material (Thixoflex, M.zhermack.com, Italy), and then poured, and master casts were obtained. Wax occlusion rims were built on a self-cure record based on a master cast. The orientation relation was recorded using a facebow record for placing the maxillary cast on a semi-adjustable articulator (Whipmix Semi-adjustable Articulator). Centric and eccentric intermaxillary jaw relation records were then used to mount the mandibular cast. After mounting, the anterior teeth were set according to phonetics and esthetics. For posteriors, 30-degree acrylic teeth with a bilaterally balanced occlusion were selected. ⁽¹⁸⁾ Complete dentures were processed using traditional flasking techniques (Acroston, a heat-cured acrylic resin, Egypt), then finished and polished. The final dentures were remounted in the lab to adjust occlusal discrepancies and confirm proper occlusal contact in centric and eccentric relations. For additional occlusal correction, the intraoral occlusal contacts were confirmed. The patients received instruction on proper dental hygiene and cleaning dentures.

Construction of a 3D-printed overdenture

Generation of a 3D-printed edentulous master cast

Designing and printing of temporary record base

The virtual master cast STL file was imported into Exocad software (Exocad, GmbH, Darmstadt, Germany). to design the virtual record base, where the anatomic landmarks were identified and the peripheral limits were marked with a thickness greater than 2 mm extended to the vestibule area. (Fig. 2c,2d) Then it was separated from the virtual master cast and oriented at a slight angle, in which the fitting surface was away from the build platform and supports were generated around the perimeter of the virtual record base. The tank of the 3D-printer (EPAX 3D 4K 6.6" printer, USA) was filled with temporary resin material (EPAX 3D, Temporary Printing Resin, China), afterwards, printing was started. After complete printing, the supports were removed, and the finishing and polishing were done by the conventional method.

Fabrication of the occlusion rim

Wax occlusion rims were added to maxillary and mandibular printed record bases. intraorally, the labial fullness was established, the occlusal plane and occlusal vertical dimension were recorded, and the reference lines (midline, canine lines, and smile line) were marked with cuts in the wax on the facial surface of the wax record blocks. The centric, protrusive records were registered, and the lateral jaw relation record was calculated from the Hanau equation.

Scanning and designing a virtual complete overdenture

The record blocks were mounted on a semi-adjustable articulator in the laboratory, then scanned in a position close to the clinical situation using the same extra-orally scanner (AnyScan Vinyl HR, Germany), saved in an STL file, and imported into Exocad software, which is able to detect point-by-point matching of the anatomical landmarks on the virtual master casts and superimposed with virtual record blocks. (Fig. 3) Different tooth library brands and shapes are included in the Exocad software. Then it automatically proposes a bilaterally balanced set-up. It is also possible to customize the set-up by modifying the position or morphology of one or more teeth or even removing them. Then the use of 30-degree teeth was set up as one unit according to jaw relations, and the occlusal plane, which was defined according to anatomical landmarks and reference lines, was determined. To achieve a natural look, the volumes and dimensions of the papilla, the marginal curve, the canine eminences, and the finishing can be adjusted. After a complete matching process of 3D virtual maxillary and mandibular master casts with a virtual complete overdenture, we obtained the position relationships of the maxillary and mandibular jaws and saved the virtual complete overdenture as an STL file.

Fabrication of a 3D-printed trial overdenture

The denture base and teeth were designed with Exocad software as one solid piece, with the occlusal side facing toward the build platform, and supports were generated around the perimeter of the denture with added supports to the teeth. Then it was exported to the printer and printed with the same steps and the same temporary resin material. After printing, rinse, remove the supports, and finish and polish the printed denture using the same conventional method. After that, the trial overdentures were tried intra-orally. The maxillomandibular relationship, occlusion, lip support, and tooth arrangement were verified and confirmed by asking the patient if they were satisfied with their trial overdentures.

Fabrication of a 3D-printed permanent overdenture

For maxillary and mandibular dentures, the denture base and teeth were designed as separate files. The virtual denture base was oriented at a slight angle with the intaglio surface toward the build platform, and supports were generated around the perimeter of the virtual denture base with the desired slice thickness selected and removed from the denture tooth sockets and cervical margin. This file was then exported to the printer. The 3D-printer was filled with denture base resin (ifun, China), a shade was selected based on prescription, and the same method of printing was started. The virtual denture teeth were printed with the same method as one unit with white dental resin (Ifun, China), with the occlusal surface oriented toward the build platform. After the 3D-printed denture is completed, remove the printed denture base and teeth from the build platform and place them in a container filled with isopropyl alcohol (99.9%, Petrochem, Dubai) to rinse off the residual uncured resin, then wash and air drying to remove alcohol from the surfaces. After that, the remaining supports were removed from the base and teeth and finished by cutting a disc and rubber wheel and polishing with wet sand using a conventional method. For post-processing polymerization, the printed teeth were glued to the printed denture base, a small amount of denture base resin was applied to the tooth sockets, and the teeth were bonded while placed on the articulator, then placed in a post-curing unit (Mogassam, Egypt) for 20 minutes until the teeth were set in position, ensuring complete polymerization. Finally, the permanent complete overdentures were glazed by using a brush with nano-filled, light cure (Vita Akzent LC Glaze, USA) and cured by inserting them into the post-curing unit. (Fig. 4)

Direct functional pick-up procedure

For all patients, relief was done on the fitting surface of the mandibular denture opposite to the locators to allow space for the self-cure acrylic resin with metal housing and ensure proper seating, as proved by the absence of rocking. Then small vent holes were prepared lingual to the site of attachment to allow exit for excess acrylic resin. The white locator blocking rings, which block the undercut, were stretched over the locator abutments, followed by pressing the metal housings with the black lab processing insert directly over the locator abutments. The denture was then dried, and the relieved areas were slightly coated with acrylic resin monomer. After that, self-cure acrylic resin was mixed according to manufacturer instructions, and a small amount was applied to the relived areas. The denture was then reseated into the patient's mouth, and the patient was instructed to hold it in place in centric occlusion until complete polymerization of the acrylic resin material. The denture was removed; finishing and polishing of the denture was done, and the black inserts were replaced by pink nylon inserts (of moderate retention values) with the aid of the insertion tool. (Fig. 5) The occlusion was readjusted if necessary to ensure proper occlusal contact.

Evaluation of the mechanical wear of occlusal surfaces.

The mandibular and maxillary dentures were scanned with an intraoral scanner (Medit i700, Korea) to create 3D virtual overdentures with all tooth surfaces recorded, then saved to STL files at two different times: T0: at the time of overdentures being inserted, and T12: after twelve months from overdenture delivery, each pair of STL files were superimposed by using software (Medit. Korea). The software automatically best-fit alignment technique was used to superimpose the pair scans. Then selected points on the occlusal surfaces of all teeth were assessed (three points on the mesial, middle, and distal incisal edges of anterior teeth and the cusp tip, cusp slopes, and cusp ridges of all posterior teeth). (Fig. 6)The differences between the points were examined. The denture (T12) was compared to the baseline (T0) to determine the amount of wear encountered after twelve months of use.

Evaluation of digital occlusal force distribution by Occlusense system registration

The occlusense system consists of the wireless handheld, sensor, sensor test, and iPad-App. The occlusense was calibrated to ensure the correct recording, and the test sensor was inserted inside the handheld after connecting it to the same Wi-Fi connected to the iPad containing the occlusense software. After that, the sensor was removed from its packaging and inserted inside the handheld; the direction and position were determined by the markers on the sensor and by three positioning pins. An upright patient and sensor were inserted into the patient's mouth, and the patient started to bite on the sensor according to the instructions of the operator. The pink button was pressed, and the occlusal state was recorded. The recording ended automatically, and the data was saved locally on the handheld, then transmitted to the iPad-App through a wireless connection. After that, the recording data was stored in the patient file in the iPad-app. The sensor was removed from the patient's mouth. A graph of the data was then viewed in 2D, 3D, or in a combined view. (Fig. 7) The sensor was removed from the handheld and disposed of properly after the desired recordings had been made. These recordings were saved at two different times: T0: at the time of overdentures being inserted, and T12: after twelve months from overdenture delivery.

Statistical analysis

Data were analyzed using the Statistical Package of Social Science (SPSS) program for Windows (Standard version 26). The normality of the data was first tested with the Shapiro test.

Continuous variables were presented as mean ± SD (standard deviation) for normally distributed data. The two groups were compared with an independent t test, while paired groups were compared with a paired t test. The threshold of significance is fixed at the 5% level (p-value). The results were considered significant when the p ≤ 0.05. The smaller p-value obtained, the more significant the results.

Table 1

Comparison of occlusal wear between conventional heat polymerized overdentures and 3D-printed overdentures after twelve months (T12).
Occlusal wear	Conventional heat polymerized overdenture (n = 10)	3D-printed overdenture (n = 10)		P value
Incisors	0.038 ± 0.01	0.144 ± 0.009	t = 16.44	0.001*
Premolars	0.075 ± 0.02	0.165 ± 0.009	t = 12.83	0.001*
Molars	0.061 ± 0.01	0.156 ± 0.011	t = 13.78	0.001*
*Significant p ≤ 0.05

Table 1 shows that 3D printed overdenture group showed significantly higher occlusal wear values than conventional group after twelve months (T12) at all areas with a p value ≤ 0.05.

Table 2

Comparison between conventional heat polymerized overdenture group and 3D-printed overdenture group regarding occlusal stability.
Occlusal stability		conventional heat polymerized overdenture (n = 10)	3D-printed overdenture (n = 10)	Independent t-test	P value
Incisors	T0	14.80 ± 2.97	15.70 ± 3.59	t = 0.61	0.549
Incisors	T12	25.00 ± 3.49	20.50 ± 3.03	t = 3.07	0.006*
Premolars	T0	52.50 ± 3.13	55.00 ± 6.20	t = 1.14	0.270
Premolars	T12	46.40 ± 2.87	39.80 ± 3.73	t = 4.43	0.001*
Molars	T0	32.50 ± 4.14	29.30 ± 6.34	t = 1.34	0.198
Molars	T12	28.70 ± 4.32	36.60 ± 3.83	t = 5.96	0.001*
*Significant p ≤ 0.05

Table 2 shows that there was an insignificant difference between both groups at the time of insertion (T0) with p value > 0.05 However, after twelve months (T12) 3d printed group showed significantly higher distribution in occlusal force than conventional group with a p value ≤ 0.05. With still uneven occlusion between incisors, premolars, and molars in both groups.

Table 3

Comparison of occlusal stability at different evaluation periods for each group.
Occlusal stability	T0	T12	Paired t-test	P value
conventional heat polymerized overdenture
Incisors	14.80 ± 2.97	25.00 ± 3.49	t = 9.24	0.001*
Premolars	52.50 ± 3.13	46.40 ± 2.87	t = 4.35	0.002*
Molars	32.50 ± 4.14	28.70 ± 4.32	t = 2.21	0.05*
3D-printed overdenture
Incisors	15.70 ± 3.59	20.50 ± 3.03	t = 2.99	0.015*
Premolars	55.00 ± 6.20	39.80 ± 3.73	t = 5.51	0.001*
Molars	29.30 ± 6.34	36.60 ± 3.83	t = 3.89	0.004*
*Significant p ≤ 0.05

Table 3 shows that there was a significant difference in occlusal force distribution with advance of time for each group, with a p value ≤ 0.05 level of significance.

In the present study, 3D-printed overdenture group showed significantly higher rates of occlusal wear than the conventional heat polymerized overdenture group when evaluated using 3D digital analysis after twelve months, with a p value ≤ 0.001. This may be due to the reported lower hardness of 3D-printed resin material than heat polymerized material, which leads to more wear of 3D-printed teeth over time. One of the key factors influencing resistance to abrasion and wear, as well as surface roughness and microbial adherence, is the hardness of the resin denture base material. ⁽¹⁹⁾

The hardness, was significantly inferior in the 3D-printed resin than in the heat polymerized material. This finding is in agreement with Gad et al., who compared 3D-printed denture base resin with heat polymerized acrylic resin before and after thermal cycling and showed that the 3D-printed resin had the lowest hardness. This result may be due to the material composition, where 3D-printing involves the use of monomers based on acrylic esters and has relatively low double-bond conversion compared with conventional acrylic resins. ⁽²⁰⁾

This came in agreement with a study by Abdelrahim et al., that evaluated by using 3D digital fabrication techniques, the CAD/CAM milled material, which showed a higher hardness value, followed by the conventional heat polymerized material, the lower hardness value with the 3D-printed material. ⁽²¹⁾

According to the results of this study, there was no statistically significant difference between the two different construction techniques of both conventional heat polymerized overdenture group and the 3D-printed overdenture group at the time of insertion (T0) regarding occlusal force distribution using Occlusense with a p value > 0.05 level of significance. With uneven occlusion between incisors, premolars, and molars in both groups. This may be due to the conventional heat polymerized overdenture group and the 3D printed overdenture group had their denture constructed using centric and eccentric records obtained by the same technique, having the same occlusal scheme and being given to the patient for the first time (T0).

The bilateral balanced occlusion criteria are normally the recommended occlusal scheme for overdentures. Occlusense divides the arch into anterior, premolar, and molar parts to display the average occlusal forces in percentages (%) for each segment of the dentition. Occlusense data analysis relies on achieving a uniform distribution of occlusal force bilaterally and anteroposteriorly. ⁽⁶⁾

In the present study, comparing the conventional heat polymerized overdenture group and the 3D-printed overdenture group after twelve months (T12) regarding occlusal force distribution using Occlusense showed that there was a significant difference between both groups over time. In incisors, the P value = 0.006, premolars P value = 0.001, and molars P value = 0.001. There is also an uneven distribution of force between incisors, premolars, and molars in the conventional heat polymerized overdenture group, but more even distribution of force in the 3D-printed overdenture group. This may be due to the lower modulus of elasticity (rigidity and stiffness) of 3D-printed material than in conventionally heat polymerized material. Although denture bases made with 3D-printing represent a novel approach to denture manufacturing, their flexural strength values are currently lower than those of the majority of denture base materials. ⁽¹⁹⁾ which explains the difference between groups over time, with more occlusal force distribution in the 3D-printed group than the conventional one. resulting from better denture material adaptation to the underlying structures of 3D-printed overdentures over time, while the conventional heat polymerized overdenture material has a high modulus of elasticity providing less force distribution to the underlying structures over time.

The flexural strength and impact strength were significantly inferior in the 3D-printed resin than in the heat polymerized material. This finding is in agreement with Gad et al., who compared 3D-printed denture base resin with heat polymerized acrylic resin before and after thermal cycling and showed that the 3D-printed resin had the lowest flexural strength and impact strength. This result may be due to the material composition, where 3D-printing involves the use of monomers based on acrylic esters and has relatively low double-bond conversion compared with conventional acrylic resins. ⁽¹⁹⁾

This came in agreement with a study by Abdelrahim et al. ⁽²¹⁾, comparing the CAD/CAM-milled material, which showed a higher flexural modulus, followed by the conventional heat polymerized material, while and a lower flexural modulus with the 3D-printed material.

The stiffness and rigidity of the material are reflected in its modulus of elasticity. A higher flexural modulus is often advantageous in clinical settings because denture base materials with high elastic moduli are more resistant to elastic deformation. Although the flexibility of the denture base is helpful in increasing the absorbed energy before fracture, the rigidity of the denture framework is a prerequisite for the ability of a denture base to equally distribute forces to the underlying structures. ⁽²²⁾

Also, in agreement with a study by Prpi´c et al. ⁽¹⁹⁾, the CAD/CAM materials exhibited higher flexural strength than heat polymerized and 3D-printed acrylics, and 3D-printed acrylics have lower mechanical properties than most other denture base materials.

contrast to the studies by Ayman ⁽²³⁾ and Pacquet et al. ⁽²⁴⁾, found that the flexural strength of heat-polymerized PMMA was higher than that of the CAD/CAM denture base material.

The results of the flexural strength and surface hardness can be interpreted in terms of the internal structures of the materials. Because polyamide material has fewer cross-linking agents, its surface hardness may be affected. ⁽²⁵⁾ When compared to conventional acrylic resins, the double-bond conversion of acrylic resins used in 3D-printing removable dentures is comparatively low, which can also have an impact on mechanical qualities. ⁽²⁶⁾ Additionally, during the polymerization of the CAD/CAM resins, high temperatures and inorganic fillers enhance a few mechanical qualities, such as surface hardness and flexural strength. ⁽²³⁾

Within the limitations of this study, it was shown that implant overdentures constructed by conventional techniques show superior results regarding mechanical wear of the occlusal surface compared to 3D-printing techniques using 3D digital analysis. However, 3D-printing techniques offer a promising result compared to conventional techniques for the construction of implant overdentures regarding occlusal equilibration using the digital occlusal analysis system.

Ethics approval and consent to participate

The patients were fully informed about the purpose and procedures of this study and provided written informedconsent. The study was approved by the local ethical committee of the Faculty of Dentistry, Mansoura University (No. A02060922) and retrospectively registered at ClinicalTrials.gov (ClinicalTrials.gov Identifier: NCT06139003 ) date: (16/11/2023).

Consent for publication

Not applicable

Availability of data and materials

The datasets analysed during the current study are available from the corresponding author on reasonable request.

Competing interests

The authors have no conflicts of interest to declare.

Funding statement

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Author Contribution

Dr. Abd El-Salam Awad, as the first author, collected the clinical data and supervised all the procedures. Dr. Ahmed Ali Habib as a corresponding author designed the study and performed the statistical analysis. Dr. Mohamed Shady, as a corresponding author, prepared the manuscript and interpreted the data. All authors critically discussed the results, revised the manuscript, and approved the final version.

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No competing interests reported.

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You are reading this latest preprint version

Digital Versus Conventional Techniques for Construction of Mandibular Implant Retained Overdenture

Status:

Version 1

Abstract

Figures

Introduction

Materials and methods

Study design

Presurgical procedure

Construction of complete dentures

Implant placement surgery

Prosthetic procedures

Construction of a new complete overdentures

Construction of conventional heat polymerized overdentures

Construction of a 3D-printed overdenture

Generation of a 3D-printed edentulous master cast

Designing and printing of temporary record base

Fabrication of the occlusion rim

Scanning and designing a virtual complete overdenture

Fabrication of a 3D-printed trial overdenture

Fabrication of a 3D-printed permanent overdenture

Direct functional pick-up procedure

Evaluation of digital occlusal force distribution by Occlusense system registration

Results

Statistical analysis

Discussion

Conclusion

Declarations

References

Additional Declarations

Supplementary Files

Status:

Version 1