Comparing the accuracy of crown fitting between milling and 3D printing techniques using CAD/CAM technologies

Abstract

BACKGROUND:

The accuracy of dental crowns is crucial for their longevity and effectiveness.

OBJECTIVE:

This study aims to investigate how the precision of crowns is affected by two different fabrication methods, either subtractive (milling) or additive (3D printing), within computer-aided design/computer-aided manufacture (CAD/CAM) technology.

METHODS:

A standardised digital scan of a maxillary first molar with a shoulder margin (.stl file) was used to design and fabricate crowns through both subtractive (milling) and additive (3D printing) processes. The crowns’ marginal and internal fits were assessed comprehensively. Statistical analysis, including two-way ANOVA and independent t-tests, revealed significant differences in fitting accuracy between the two methods.

RESULTS:

Crowns produced via 3D printing demonstrated superior fitting with minimal marginal (14 $\pm$ 5 $\mu$ m) and internal discrepancies (22 $\pm$ 5 $\mu$ m) compared to milling (marginal: 22 $\pm$ 4 $\mu$ m, internal: 23 $\pm$ 3 $\mu$ m), indicating a statistically significant advantage in precision ( $ps\leqslant$ 0.022 for marginal fit).

CONCLUSION:

The findings suggest that 3D printing may offer a more accurate alternative to milling in the fabrication of digital dental prostheses, potentially revolutionising the field with its enhanced precision capabilities.

Keywords

Digital crowns CAD/CAM milling 3D Printing fit accuracy dental material 3D scanner

1. Introduction

For many years, dental prosthetics such as crowns and fixed partial dentures have been mainly made using metals and ceramics [1]. The lost-wax technique has been the standard method for this process, even though it requires significant time and technical expertise [2, 3]. However, this method has some drawbacks, including distortions resulting from wax patterns and difficulty identifying defects due to wax’s reflective surface [4]. Additionally, wax’s sensitivity to temperature changes and natural elastic memory make it unsuitable for some applications [5]. However, the advent of computer-aided design and manufacturing (CAD/CAM) technologies has significantly shifted. These technologies enable the creation of wax patterns from castable materials, leading to improved fit, durability, and aesthetic appeal [6, 7, 8].

The use of digital technology in dentistry began in the 1980s and has brought about significant advancements in the design and creation of dental prostheses such as inlays, crowns, and bridges. However, the accuracy and durability of digitally fabricated restorations have not been thoroughly evaluated through rigorous empirical testing [9, 10]. The digital technology used in this field can be divided into two primary methods: subtractive and additive manufacturing. Subtractive manufacturing involves using computer-controlled milling devices to carve 3D structures from a single solid block [11]. Though this method provides superior restoration quality over conventional techniques, it still faces some challenges, such as achieving a perfect fit [2], material wastage, tool wear, and possible micro-fractures on ceramic surfaces [12, 13]. On the other hand, additive manufacturing uses a layered approach to create objects directly from digital designs [14, 15]. This technique has seen a significant increase in adoption due to its ability to handle complex geometries, deliver improved product outcomes, and reduce waste [12, 15, 16]. However, it is crucial to acknowledge that the resolution limitations in scanning devices may cause minor discrepancies in the final restorations [6].

Over the last two decades, extensive research has been conducted to evaluate the reliability of dental restorations manufactured using computer-aided design and computer-aided manufacturing (CAD/CAM) technology. However, the existing literature presents mixed results. While some studies report the superior precision of CAD/CAM systems, others indicate that they may not perform as well as traditional methods [2, 17, 18, 19, 20]. These inconsistencies in findings highlight the need for comprehensive analyses to conclusively determine this technology’s true potential and capabilities.

Several studies have examined the longevity of dental restorations created using Computer-Aided Design/Computer-Aided Manufacturing (CAD/CAM) systems. Some of these studies suggest that CAD/CAM techniques have the potential to create precise restorations that meet the required clinical standards [21, 22, 23]. However, it’s important to note that these studies have various limitations in their methodology that could affect their conclusions. Therefore, it is crucial to conduct more robust and comprehensive investigations. On the other hand, a different set of literature suggests that restorations made through CAD/CAM technology may not consistently achieve the desired clinical accuracy, particularly in terms of marginal fit [24, 25, 26, 27, 28, 29, 30]. These findings indicate a need to refine and optimise CAD/CAM technologies to ensure that they consistently align with and potentially surpass traditional fabrication techniques. As a result, further research is necessary to explore the full potential of CAD/CAM systems in producing dental restorations that meet the necessary clinical standards.

The success of a dental crown depends on its precise internal fitting and proper seating, which are crucial factors [4, 31]. One way to improve crown seating is by incorporating an internal relief in the casting, which acts as a pathway for cement allocation [32]. Consistent die spacer thickness is essential to maintain the restoration’s marginal and internal harmony [2]. Imperfect crown margins can lead to complications such as food entrapment, secondary caries, gingival inflammation, and restoration or tooth failure [34]. Therefore, it is essential to achieve minimal marginal gaps and an excellent internal fit for dental restorations to ensure their longevity. Although there is an ongoing debate over acceptable, marginal gaps, it is generally agreed that while more prominent gaps may not affect luting cement, more constricted gaps can become a breeding ground for debris accumulation [35]. The use of internal luting glue can enhance crown stability and adherence [36]. However, the excessive thickness of this cement may promote water absorption, catalyse hydrolytic breakdown, and threaten the crown’s structural integrity, especially under recurrent loading [37, 38].

The accuracy of a dental restoration is vital for its success, both in terms of margins and internal structure [5, 34]. Therefore, it is necessary to deeply understand how various fabrication techniques can affect the quality of prostheses. While subtractive and additive manufacturing have their advantages and limitations, there is a need for in-depth research to exploit their capabilities thoroughly. The objective of this study is to comprehensively assess these fabrication methods, evaluate their effectiveness, and analyse their impact on prosthetic quality. The aim is to make a meaningful contribution to the existing knowledge, driving progress in dental restoration techniques and ultimately enhancing patient well-being and satisfaction.

The success of dental restorations dramatically depends on the accuracy of their marginal and internal fit. This precision plays a vital role in their optimal performance and longevity. Therefore, the current research aims to compare the fits produced by two modern manufacturing techniques, CAD/CAM milling and 3D printing, specifically in the context of dental crowns. The study hypothesises that significant differences in the precision of crown fits will emerge between these digital techniques. An in-depth exploration of these variances is expected to provide insights into each approach’s inherent advantages and subtleties, which will make a valuable contribution to the ongoing scholarly discourse on dental restoration.

2. Materials and methods

2.1 Die preparation

For this study, a maxillary first molar with a shoulder margin was chosen as the foundational specimen. A silicone impression material was used to replicate the molar. The Scannable Die Stone Type 4 was prepared according to the manufacturer’s recommended powder-to-liquid proportion of 5:1. The mixture was expertly treated in an automatic vacuum-mixing apparatus (Multivac 4, Degussa, Germany) before being poured into the silicone impression. After a curing duration of 60 minutes, the dies were carefully extracted, and their bases were trimmed precisely to ensure a standardised surface. Seven dies were chosen as representative samples for each fabrication technique.

2.2 Subtractive manufacturing technique (Milling)

The advent of Computer-Aided Design and Manufacturing (CAD/CAM) has brought about a transformative shift in the creation of dental crowns, replacing conventional manual processes with sophisticated digital fabrication methodologies. The process begins with a scannable master die that is imaged using a 3D scanner (Ceramill Map 600+, Amann Girrbach), translating its tangible attributes into digital format. This is followed by precise adjustments using Exocad scanning software (Ceramill Map 600+, Amann Girrbach), mainly delineating the margin and determining the coping’s dimensions. The CAD design platform (Ceramill Mind Design software, Amann Girrbach) is then used for the design phase of the coping, maintaining a consistent die spacing of 25 $\mu$ m throughout. In preparation for the milling procedure, each crown is fortified with three stabilising pins of 2 mm thickness, which provide support and facilitate the convenient handling and manipulation of the coping.

2.3 Additive manufacturing technique (3D Printing)

Transitioning from design to fabrication involved extracting the .stl file from the CAD platform, which was necessary to establish the additive manufacturing trajectory. Two different methods were used to create the copings: milling using Ceramill Motion 2 (Amann Girrbach) and 3D printing using Varseo L (BEGO, Bremen, Germany). Using both methodologies, the digital blueprint played a crucial role in this process, creating 20 copings with a thickness of 0.7 mm each. The milling process involved using Ceramill ZI discs with a thickness of 16 mm and a diameter of 98 mm (Ceramill ZI, Amann Girrbach), while Varseo resin (BEGO, Bremen, Germany) was utilised for 3D printing. Once completed, the copings were carefully removed from the blank, and the stabilising pins were removed using a refined metal bur (Ash 5, Hylin Carver, and PKT).

It is worth noting that the design blueprint did not include the crown’s occlusal facet. This decision was made with the study’s primary objective, which was to focus on understanding the marginal fit’s accuracy and the internal adaptation’s intricacies. In the context of this evaluative framework, the occlusal aspect was considered non-essential.

2.4 Data collection of internal and marginal gap measurements

To thoroughly assess the internal and marginal gaps in dental crown restorations, a dual-method approach was implemented, which comprised a silicone replica technique and a conventional cementation technique.

The silicone replica technique involved injecting a silicone impression material into each crown and seating it onto its corresponding die, with cyclical pressure applied to ensure uniform distribution. Once set, each silicone replica was carefully bisected, and its dimensions were measured under a high-resolution microscope.

In the conventional cementation technique, crowns were anchored to their specific dies using dental luting cement, and uniform pressure was applied throughout the setting phase. Quantifying the marginal gap was undertaken to foster data consistency and robustness.

Each was adorned with a crown, and seven dies were selected from the Milling and 3D printing cohorts to ensure a comprehensive evaluation. The microscopy apparatus was integrated with the capabilities of AxioVision Software (Zeiss International, Oberkochen, Germany) to perform the intricate measurement task.

2.4.1 Evaluation through silicone replica procedure

The present study aimed to investigate the material application and preparation, load application, silicone replica reinforcement, sectioning, and microscopic examination of silicone impression material (Express 2 light body standard, 3M ESPE) within each crown. To ensure a secure fit, a thin layer of approximately 0.3 mm of silicone impression material was delicately applied within each crown, and the crown was carefully positioned over its respective die, subjected to gentle yet consistent manual pressure, and aligned appropriately.

The crowns were mounted onto a universal testing machine (Lloyd LRX material tester, UK) and subjected to alternating loads of 45N and 50N over two minutes to emphasise the tension procedure. The machine’s sensitivity and load rating were meticulously calibrated to 100.4% and 100N, respectively, to ensure the homogenous pressure distribution across samples and eliminate surplus material.

Post-loading, the crowns encapsulating the silicone replicas were cautiously dislodged from the dies, and a denser impression material (Express TM 2 Putty soft, 3M ESPE) was incorporated to fortify the primary light body replicas. The setting material, delineated by distinct layers of light blue (light body) and heavy yellow (dense body), was subsequently extracted from the crown. A precision scalpel was employed to systematically segment each silicone replica into six equidistant sections.

To conduct an in-depth analysis, each segmented replica underwent microscopic scrutiny using SteREO Discovery.V8 (Zeiss, Germany). Four distinct zones within each section – occlusal, upper axial, lower axial, and marginal gap – were earmarked for measurement. The assessments were conducted under a 1x magnification with the aid of the AxioVision Software (Zeiss International, Oberkochen, Germany) to ensure precision and reproducibility.

2.4.2 Evaluation via traditional cementation procedure

The die preparation and cleaning process is a crucial step in dental restoration procedures. This study selected seven dies with a crown from the Milling and 3D manufacturing groups. The cleaning process was meticulously carried out using a steam pressure mechanism (Aquaclean 3, Degussa, Germany), followed by air drying to ensure the removal of any residual moisture or contaminants.

The cementation protocol adhered to the manufacturer’s guidelines. Dental luting cement (Relyx Luting, 3M ESPE) was prepared in the prescribed powder-to-liquid ratio (3 scoops to 3 drops) and was mixed uniformly for 30 seconds. The resulting cement mixture had a workable time of 2.5 minutes and a setting duration of 3 minutes. The mixture was carefully applied within the crown and positioned on the die to ensure an optimal fit. The die-crown construct was placed under a sustained 50N pressure for 3 minutes, emphasising tension, to ensure accurate cement setting.

Post-cementation procedures involved the delicate excision of excess cementation material, circumventing the crown margin. The cemented assemblies were then preserved at an oral temperature of 37^∘C for 24 hours.

The secured crown-die constructs were strategically bisected, mesially and distally, using a high-precision saw (Diamond Wafering Blade, Isomet, 1000, Buehler, USA) operating at a 125 cycles per minute peak. The sectioned units were subjected to thorough microscopic scrutiny using the SteREO Discovery.V8 (Zeiss, Germany) at a magnification of 1x. A comprehensive evaluation encompassed ten predetermined zones on each interface, which included two occlusal sites, four axial regions (comprising upper and lower axial sections), a duo of marginal gaps, and a pair of marginal discrepancy loci.

2.4.3 Statistical analysis

The data collected was systematically organised and processed using Microsoft Excel (Office 2011). Statistical descriptors that were computed included means, standard deviations, and the mean standard error for all subsets of data. Advanced statistical evaluations were carried out to identify statistically significant discrepancies among different fabrication cohorts and measurement methodologies. Two-way analysis of variance (ANOVA) was utilised to determine the influence and interaction of two independent variables on a dependent variable. Post-hoc analyses, specifically Tukey’s Honestly Significant Difference (HSD) test, were executed to elucidate specific group differences post-ANOVA. Independent t-tests were used to contrast means between the two groups, highlighting any significant variations. All statistical procedures were performed in SPSS, and the threshold for significance was set at $P\leqslant$ 0.05. Statistical significance levels were defined as follows: $p\leqslant$ 0.05 (*), $p\leqslant$ 0.01 (**), $p\leqslant$ 0.001 (***) and $p\leqslant$ 0.0001 (****).

3. Results

3.1 The silicone replica technique

The silicone replica technique yields varying gap dimensions across different manufacturing methods and specific loci, as shown in Table 1 and Fig. 1. However, the 3D printing technique consistently produces minor gaps across all assessed regions, including occlusal, axial, marginal gap, and internal fit. The mean values (with standard deviations) for these regions were 22 ( $\pm$ 7) $\mu$ m, 20 ( $\pm$ 5) $\mu$ m, 14 ( $\pm$ 5 ) $\mu$ m, and 22 ( $\pm$ 5) $\mu$ m, respectively. Figure 2 provides a tangible, visual comparison of the outcomes from the two fabrication techniques.

Table 1
Results in $\mu$ m from the silicone replica technique: The mean and standard deviation (SD) of two production groups at different points: comparative $p$ -values of different points between the two production groups, using a $t$ -test in Microsoft Excel. Red stars indicate statistically significant differences

Group	Occlusal	Axial	Marginal gap	Internal fit
Milling	23 ( $\pm$ 6)	23 ( $\pm$ 2)	22 ( $\pm$ 4)	23 ( $\pm$ 3)
3D	22 ( $\pm$ 7)	20 ( $\pm$ 5)	14 ( $\pm$ 5)	22 ( $\pm$ 5)
Milling vs. 3D	0.733	0.417	0.022^∗	0.585

Figure 1.

Results in $\mu$ m from the silicone replica technique: The mean and standard deviation of two production groups in different points.

Table 1 presents the outcomes of the two-way ANOVA and t-test, explicitly focusing on the silicone replica technique. The two-way ANOVA revealed a significant influence of crown fabrication methodology on gap sizes. No pronounced differences emerged across most assessed points when juxtaposing the milling with the 3D printing technique. However, the milling technique produced notably more significant gaps at the marginal gap, exhibiting statistical significance at $P\leqslant$ 0.022. Interestingly, axial point comparisons across all manufacturing techniques yielded no significant variations.

3.2 The conventional cementation technique

Table 2 and Fig. 3 contain the mean values and associated standard deviations of gap measurements obtained through the conventional cementation technique, segregated by manufacturing approach. The 3D printing methodology consistently produced the most minor gaps across all tested areas, with two exceptions. Specifically, the milling method yielded superior results for occlusal and internal fit measurements, making smaller gaps with values of 16 ( $\pm$ 5) $\mu$ m and 15 ( $\pm$ 4) $\mu$ m, respectively. Figure 4 provides a graphical representation of the outcomes from the three distinct fabrication methods.

Table 2 summarises the outcomes of the statistical analyses, namely, the two-way ANOVA and t-test, conducted within the scope of the conventional cementation technique. The two-way ANOVA revealed the fabrication technique’s significance on gap sizes. Most assessment points did not display significant variations when comparing the milling and 3D printing techniques. However, the marginal gap stood out as an exception, where the milling method was associated with notably more significant gaps, achieving statistical significance with $P\leqslant$ 0.022. Nonetheless, no significant disparities were observed in the marginal gap across all manufacturing techniques.

Table 2
Results in $\mu$ m from the conventional cementation measurement technique: the mean and standard deviation for the two production groups at different points. Comparative $p$ -values of different points between the two production groups, using $t$ -test in Microsoft Excel and Word. Red stars indicate statistically significant differences

Group	Occlusal	Axial	Marginal gap	Internal fit	Marginal discrepancy
Milling	16 ( $\pm$ 5)	17 ( $\pm$ 5)	12 ( $\pm$ 5)	15 ( $\pm$ 4)	42 ( $\pm$ 6)
3D	22 ( $\pm$ 6)	14 ( $\pm$ 3)	7 ( $\pm$ 4)	16 ( $\pm$ 5)	23 ( $\pm$ 9)
Milling vs. 3D	0.201	0.220	0.133	0.826	0.002^∗

Figure 2.

Samples to show the different between (A) milling and (B) 3D printing technique in gap.

Table 3

Compression between the silicone replica technique and the conventional cementation technique with each manufacturing group at different gap points (occlusal, axial, and marginal gap) during the test

Group	Measurement technique	Occlusal	Axial	Marginal gap	Internal fit
Milling	Silicone replica	23 ( $\pm$ 6)	23 ( $\pm$ 2)	22 ( $\pm$ 4)	23 ( $\pm$ 3)
	Conventional cementation	16 ( $\pm$ 5)	17 ( $\pm$ 5)	12 ( $\pm$ 5)	15 ( $\pm$ 4)
3D	Silicone replica	22 ( $\pm$ 7)	20 ( $\pm$ 5)	14 ( $\pm$ 5)	22 ( $\pm$ 5)
	Conventional cementation	22 ( $\pm$ 6)	14 ( $\pm$ 4)	7 ( $\pm$ 4)	16 ( $\pm$ 5)

Figure 3.

Results in $\mu$ m from the conventional cementation technique: The mean and standard deviation of two fabrication methods at different points.

Figure 4.

Samples to show the difference between (A)milling and (B) 3D printing techniques in the gap.

3.3 Comparison of measurement techniques

The present study compared the silicone replica technique and the conventional cementation method for CAD/CAM restorations. The analysis involved a comprehensive assessment of gap dimensions in the occlusal, axial, marginal gap, and internal fit regions across different manufacturing groups. Results from Table 3 and Fig. 5 visually complemented the analysis, indicating no significant discrepancies between the two measurement modalities. However, in contexts where differences were observed, the cementation technique consistently displayed smaller gap dimensions than the silicone replica method. This was notably followed in milling and 3D printing concerning the marginal gap. Overall, these findings suggest that the cementation technique, when paired with milling or 3D printing fabrication, yields CAD/CAM restorations with narrower gaps.

Figure 5.

Compression between the silicone replica technique and the conventional cementation technique with each manufacturing group at different gap points (occlusal, axial, and marginal gap) during the test.

Table 3 summarises the findings of the two-way ANOVA, which aimed to investigate statistical distinctions between the silicone replica and conventional cementation techniques for varying manufacturing methods. The results from the ANOVA indicated that the crown’s fabrication technique significantly influenced gap outcomes. When the data was analysed, discernible differences were observed between the milling techniques and measurement methods. However, in comparing 3D and milling processes, the data did not reveal any significant disparities. These findings provide valuable insights for dental professionals and CAD/CAM restoration researchers.

4. Discussion

Digital dentistry has made huge strides in recent years, focusing on achieving the highest levels of precision in crown fabrication. This study delves deeply into the accuracy of crowns’ marginal and internal fit, produced using two different digital manufacturing techniques: milling and 3D printing. The goal was to determine whether these methods yielded significant differences in fit accuracy.

The findings of this investigation not only supported the hypothesis but also provided empirical validation. The results demonstrated the subtle variations in each fabrication technique, emphasising their distinctions. As digital dentistry advances, these insights are crucial for clinicians and technicians to ensure optimal patient outcomes in prosthetic applications.

The efficiency of a dental crown depends on various factors, with the accuracy of the marginal fit being the most crucial one [40]. A poorly fitted dental crown not only endangers the tooth’s structural integrity but also poses a threat to the supporting periodontal tissues, primarily due to cement degradation and plaque accumulation [35]. Given the potential clinical implications, utilising techniques of unwavering reliability for assessing the marginal and internal fit of dental restorations is imperative. In this investigative endeavour, we comprehensively evaluated the pivotal parameters mentioned above. The assessment involved thoroughly inspecting the interior fit at axial and occlusal junctures and meticulously measuring the marginal gap and the absolute marginal discrepancy. The evaluative criteria, in both the terminology and approach, were firmly anchored in the foundational work of Holmes et al. [35], ensuring the robustness of the current findings and their subsequent implications for clinical practice.

To ensure the rigour of this study, a bifurcated measurement approach was adopted [41]. It is widely recognised that increasing granularity in data points can enhance the strength of the findings [42]. Building on this principle, 44 distinct points on each crown were carefully examined, and seven crowns were selected for each fabrication technique. Despite the use of different measurement methods, the data showed a remarkable overlap. Although there were minor differences, the divergence between similar data points from the two methods was statistically insignificant. This empirical observation is consistent with the conclusions of previous critical studies [2, 30, 40], which emphasise the near-congruence between conventional cementation and silicone replica methodologies regarding measurement outcomes. The data highlighted an interesting subtlety: the silicone replica technique recorded a less pronounced difference between the two fabrication paradigms (milling and 3D) than its cementation counterpart. This suggests that the conventional cementation technique is more discerning than the silicone replica method in distinguishing between production techniques.

An explanation for the observed discrepancy may lie in the potential drift encountered while operating the precision saw at suboptimal speeds. This drift may have inadvertently masked sections of the axial cement gap when adopting the cementation measurement technique. The findings are consistent with those of Fathi et al. [2], which suggest that the silicone replica measurement method is comparable to or outperforms the cementation technique in accuracy. While conventional cementation and silicone replica techniques have gained recognition as reliable measurement modalities [2], it is essential to acknowledge that each comes with distinct inherent challenges and limitations.

Various factors determine the effectiveness of a dental crown, but the marginal fit is the most crucial one [40]. A poorly fitting crown can threaten the tooth and its supporting periodontal tissues, mainly due to cement solubility or plaque buildup [35]. Therefore, the techniques used to assess dental restorations’ marginal and internal fit must be robust and dependable. The analysis is rooted in the definitions provided by Holmes et al. [35].

The precision of measurement techniques used in dental restoration assessments plays a crucial role in determining the results’ accuracy. To this end, the present study employed two distinct measurement methodologies [41] to obtain robust findings. A higher granularity of measurement points often amplifies the robustness of results [42]. Accordingly, each crown was meticulously evaluated at 44 distinct points, with seven representative crowns earmarked for each fabrication technique. Although the two methods used did not exhibit perfect concordance, the disparities between analogous measurement points across the processes were statistically insignificant. This observation is consistent with earlier investigations [2, 40], which also revealed negligible variances between the conventional cementation and the silicone replica methods. Notably, the silicone replica technique yielded a more streamlined set of significant differentiators between the two fabrication modalities (Mill-ing and 3D) than its cementation counterpart. This suggests that the cementation method might be sensitive to discerning nuances. This echoes earlier studies [2], which posit that the silicone replica technique, in terms of accuracy, either parallels or surpasses the cementation approach. While the silicone replica and conventional cementation methods have been validated as reliable gauges [2], each has inherent challenges and constraints.

The silicone replica technique is a valuable tool that uses silicone impression materials, offering distinct advantages over luting cement. Silicones are known for their elastomeric nature and unparalleled precision. Low-viscosity silicones, in particular, are renowned for flawlessly replicating intricate details to a scale of 1–2 $\mu$ m [43, 44]. However, these materials are not without their limitations. Their inherent tendency to rupture, especially in fine sections such as crown margins, can hinder accurate assessments of marginal gaps. Furthermore, the intrinsic elasticity of these dimensionally stable silicones can obscure the delineation of the crown margins’ extremities. The subsequent segmentation of each silicone replica into six discrete segments further exacerbates the challenge, potentially skewing the orientation of the replica pieces under microscopic examination. This can result in disparities in the on-screen visual output, introducing ambiguities in determining precise measurement locales.

The conventional cementation approach utilises Rely-X luting cement, which comprises a polymeric substrate intertwined with a salt gel matrix. However, the dichotomous natures of silicone and luting cement result in markedly different physicochemical behaviours. Several factors, including particle morphology, size, quantity, and load distribution, can significantly modulate a material’s viscosity. During the conventional cementation approach, anomalies in crown sectioning occasionally occurred when using a precision saw, resulting in inadvertent veering during cutting, which could introduce deviations in recorded measurements. Fathi et al. [2] also echoed similar observations, stating that adopting identical measurement paradigms could lead to inconsistent outputs. Nonetheless, the conventional cementation technique remains reliable, particularly given its proficiency in distinguishing subtle variances across different wax pattern fabrication modalities.

The milling and 3D printing techniques have demonstrated commendable results regarding internal and marginal fit. These computer-guided procedures have shown fewer inconsistencies and produced more uniform results than manual dexterity-based techniques. Notably, the 3D printing technique demonstrated minor discrepancies in the marginal gap and internal fit, which supports the initial hypothesis of this study. This finding suggests that distinct fabrication techniques can yield varied outcomes, with contemporary technologies showcasing enhanced precision.

The 3D printing technique demonstrates the lowest standard deviations, indicating reduced variability in its results and suggesting heightened uniformity in outcomes. If dental laboratories integrate this technology, it may improve the quality of dental crowns and subsequently minimise the number of fine-tuning sessions required to achieve a perfect fit. However, it is essential to approach these findings judiciously. While the potential of 3D printing in dental laboratories is promising, the nascent status of this technology within the dental industry demands a cautious stance. Future research may focus on the economic viability of these fabrication techniques, particularly given the considerable initial investments associated with 3D printers and CAD/CAM milling machines compared to the relatively modest costs of manual methods.

In direct response to the research hypothesis, the comprehensive analysis conducted within this study unequivocally confirms that 3D printing technology offers superior precision in dental crown fabrication over milling techniques. This conclusion is derived from statistically significant differences observed in both marginal and internal fits, where 3D printed crowns consistently exhibited reduced discrepancies. These findings validate the initial hypothesis and illuminate the inherent advantages of additive manufacturing in enhancing dental prosthetic accuracy. By leveraging the detailed comparative analysis, this study contributes valuable insights into optimising digital dentistry, advocating for more widespread adoption of 3D printing technologies to improve clinical outcomes and patient satisfaction.

5. Conclusions

The study conclusively demonstrates that 3D printing, as an additive manufacturing technique, significantly outperforms milling in the precision of dental crown fabrication. This distinction in accuracy, particularly in marginal and internal fits, could herald a paradigm shift in digital dental prosthetics, suggesting a move towards the broader adoption of 3D printing technologies. The implications of these findings extend beyond mere technical comparison, highlighting a potential revolution in dental restoration quality and patient care. Future research should delve into the long-term performance, cost-efficiency, and clinical outcomes associated with 3D-printed dental prostheses, thereby enriching the dental profession’s understanding and application of these technologies. This study underscores the importance of continuous innovation and rigorous evaluation in enhancing the effectiveness of dental restorations, ultimately contributing to the advancement of digital dentistry.

Data availability

The data that formed the basis of this article are available from the corresponding author upon reasonable request.

Author contributions

F.H.A. conducted all sections of the study.

Ethics statement

This article does not present research with ethical considerations.

Funding

The author extends his appreciation to the Deanship of Scientific Research at King Khalid University for funding this work through the Small Groups Project (Grant no. RGP.1/41/43).

Footnotes

Conflict of interest

The author declares no conflict of interest.

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