In our clinical practice, we frequently encounter patients with dentition defects, particularly Kennedy Class I cases, which significantly impact oral function and quality of life. The fabrication of removable partial denture frameworks has traditionally relied on the lost wax casting technique, a method involving wax pattern creation, investment, and metal casting. However, this process is time-consuming, technique-sensitive, and prone to inaccuracies due to factors like wax shrinkage and alloy flow limitations. With advancements in digital dentistry, we have explored selective laser melting (SLM) 3D printing as an alternative to lost wax casting for producing cobalt-chromium alloy frameworks. This study compares the clinical outcomes of these two methods, focusing on precision, patient comfort, and complications.
The lost wax casting process begins with wax pattern fabrication on a dental model, followed by spruing, investing in a refractory material, and burning out the wax to create a mold. Molten alloy is then cast into the mold under centrifugal force. While established, this method often results in inconsistencies due to thermal expansion mismatches and manual errors. In contrast, SLM 3D printing builds frameworks layer-by-layer from digital models using a laser to fuse metal powder, eliminating multiple manual steps and reducing variability. We hypothesized that SLM would yield superior fit and patient satisfaction compared to lost wax casting.
We conducted a study involving 86 patients with Kennedy Class I dentition defects, randomly assigned to two groups. The SLM group received frameworks fabricated via 3D printing, while the lost wax casting group underwent conventional methods. All frameworks were made from cobalt-chromium alloy, and we evaluated outcomes after one week and one month of denture use. Key metrics included mucosal tenderness points, chewing efficiency assessed through absorbance measurements, denture stability, retention, fit, patient-reported scores, and complication rates. Statistical analyses involved t-tests and chi-square tests, with significance set at p < 0.05.
Chewing efficiency was quantified using a spectrophotometric method, where patients chewed peanuts and the resulting suspension’s absorbance was measured. The absorbance value A relates to particle size distribution and masticatory performance, modeled by the equation: $$A = k \cdot \frac{1}{d_{avg}^n}$$ where \(d_{avg}\) is the average particle diameter, \(k\) is a constant, and \(n\) represents the crushing efficiency. Higher absorbance indicates better chewing function, as finer particles scatter less light.
| Group | Number of Patients | Mucosal Tenderness Points (mean ± SD) | Absorbance Value (mean ± SD) |
|---|---|---|---|
| SLM 3D Printing | 43 | 0.61 ± 0.13 | 0.61 ± 0.05 |
| Lost Wax Casting | 43 | 2.23 ± 0.21 | 0.43 ± 0.03 |
After one week, the SLM group showed significantly fewer mucosal tenderness points and higher absorbance values, indicating better comfort and chewing efficiency (p < 0.05). The precision of SLM frameworks likely contributed to this, as digital fabrication minimizes errors common in lost wax casting, such as investment shrinkage or incomplete casting. For instance, the dimensional accuracy Δ of a framework can be expressed as: $$\Delta = \sqrt{ \sum (x_i – x_{ideal})^2 }$$ where \(x_i\) are measured dimensions and \(x_{ideal}\) are digital model values. SLM typically achieves Δ < 50 μm, whereas lost wax casting may exceed 100 μm due to cumulative tolerances.
| Group | Retention (%) | Fit (%) | Stability (%) |
|---|---|---|---|
| SLM 3D Printing | 55.81 | 53.49 | 58.14 |
| Lost Wax Casting | 30.23 | 27.91 | 32.56 |
Denture performance assessments revealed superior retention, fit, and stability in the SLM group (p < 0.05). These parameters are critical for long-term success, as poor fit can lead to mucosal injuries and reduced patient compliance. The lost wax casting technique often requires adjustments due to discrepancies, whereas SLM’s digital workflow ensures closer adherence to anatomical contours. We calculated the fit accuracy using the formula: $$F = 1 – \frac{ \sum |y_{actual} – y_{predicted}| }{ \sum y_{actual} }$$ where F approaches 1 for perfect fit. SLM frameworks consistently scored higher, reducing the need for chairside modifications.
Patient-reported outcomes after one month further supported the advantages of SLM. Subjective scores covered retention, ease of use, chewing ability, comfort, aesthetics, and speech, while satisfaction included treatment effectiveness, cost, and duration. The SLM group reported significantly higher scores, highlighting the impact of precision on daily function. For example, the overall satisfaction S can be modeled as: $$S = \alpha \cdot R + \beta \cdot C + \gamma \cdot T$$ where R is retention, C is comfort, T is treatment time, and α, β, γ are weighting factors. SLM optimized these variables by reducing laboratory steps and improving fit.
| Group | Subjective Perception Score (mean ± SD) | Satisfaction Score (mean ± SD) |
|---|---|---|
| SLM 3D Printing | 28.07 ± 2.75 | 14.66 ± 3.21 |
| Lost Wax Casting | 16.55 ± 0.44 | 6.68 ± 1.32 |
Complication rates were lower in the SLM group (6.98% vs. 23.26%, p < 0.05), with issues like denture stomatitis, periodontitis, and secondary caries being less frequent. The enhanced fit of SLM frameworks likely reduces plaque accumulation and mucosal irritation, common problems with ill-fitting dentures from lost wax casting. We analyzed risk using the hazard function: $$h(t) = h_0(t) \cdot e^{\beta X}$$ where X represents fabrication method (SLM vs. lost wax casting), and β is the coefficient indicating risk reduction for SLM.
The lost wax casting process involves multiple variables that affect outcomes, such as alloy solidification dynamics. The cooling rate θ during casting influences grain structure and strength, given by: $$\theta = \frac{T_m – T_a}{t}$$ where \(T_m\) is melting temperature, \(T_a\) is ambient temperature, and t is time. Rapid cooling in lost wax casting can lead to residual stresses, whereas SLM’s controlled layer-by-layer fusion minimizes such issues. Additionally, SLM allows for topological optimization, creating lightweight yet strong frameworks that are difficult to achieve with traditional lost wax casting.
In terms of economic and time efficiency, SLM reduces labor-intensive steps like wax carving and investing. The total time T_total for lost wax casting can be expressed as: $$T_{total} = T_{wax} + T_{invest} + T_{cast} + T_{finish}$$ whereas for SLM, it is: $$T_{total} = T_{scan} + T_{print} + T_{post-process}$$ with SLM often being faster for complex designs. However, material costs for metal powders in SLM may be higher, though this is offset by reduced adjustment visits.
Despite the benefits of SLM, lost wax casting remains valuable for its simplicity and low initial investment. In regions with limited digital infrastructure, lost wax casting provides a reliable option. Nevertheless, for precision-driven applications, SLM’s digital workflow offers reproducibility. We recommend integrating SLM into clinical practice, especially for cases requiring high accuracy, while reserving lost wax casting for simpler designs or resource-constrained settings.
In conclusion, our study demonstrates that SLM 3D printing outperforms lost wax casting in fabricating removable partial denture frameworks, with better fit, higher patient satisfaction, and fewer complications. The digital approach minimizes human error and enhances customization, making it a superior choice for modern prosthetic dentistry. Future work should focus on cost reduction and training to widespread adoption, ensuring that more patients benefit from these advancements.