Breaking the break: Metal-reinforced single maxillary complete denture for enhanced durability

INTRODUCTION

The rehabilitation of completely edentulous patients using complete dentures is a cornerstone of prosthodontic care, with heat-cured acrylic resin being the most widely used material due to its aesthetic appeal, biocompatibility, and cost-effectiveness. However, despite its popularity, polymethyl methacrylate (PMMA) presents certain mechanical limitations, especially under excessive masticatory loads.^[1] One of the most frequently encountered complications is the midline fracture of maxillary complete dentures, particularly when opposed by natural mandibular dentition. Such fractures are commonly attributed to factors such as reduced denture base thickness, poor denture adaptation, excessive occlusal forces, and compromised residual ridge morphology.^[2]

To address these biomechanical challenges, the incorporation of a metallic base as a reinforcement has emerged as a viable and frequently practiced solution. The mechanism of reinforcement is akin to that employed in porcelain-fused-to-metal crowns, wherein the metal framework provides foundational strength and structural support to the overlying acrylic resin.^[3] Commonly used metals for this purpose include cobalt-chromium, titanium, and gold alloys, with cobalt-chromium being preferred due to its superior strength, fatigue resistance, and dimensional stability. These properties significantly reduce the likelihood of denture fracture under normal functional loads.^[4]

Metal-reinforced complete dentures offer several clinical advantages. These include enhanced resistance to fatigue, improved retention and rigidity, superior thermal conductivity – which some clinicians believe promotes better oral tissue health – and precise tissue adaptation due to accurate casting.^[5] In addition, the thinner yet rigid nature of metal bases minimizes phonetic interference and allows for better palatal contours. Studies have also demonstrated a reduction in Candida colonization on metal surfaces compared to conventional acrylic bases, contributing to improved prosthetic hygiene.^[6-8]

However, the use of metal bases is not without limitations. Disadvantages include increased fabrication complexity, higher cost, compromised aesthetics, and the inability to rebase such prostheses easily.^[9] Nonetheless, in situations where polymer-based dentures fail to provide adequate strength or where high occlusal loads threaten the integrity of the prosthesis, the use of a cast metal denture base is clinically justified and often essential.

The design of a single maxillary complete denture opposing natural mandibular dentition is particularly prone to complications such as denture instability, loss of retention, accelerated ridge resorption, and prosthetic fracture. In such cases, reinforcing the denture with a metallic framework serves not only to prolong the prosthesis lifespan but also to maintain functional integrity and protect the underlying residual ridge from undue stress.^[10] This clinical report outlines the step-by-step fabrication and successful delivery of a maxillary metal-based complete denture, highlighting its advantages in managing complex prosthodontic situations.

CASE REPORT

A 58-year-old male patient reported to the Department of Prosthodontics, Crown & Bridge, and Oral Implantology, Bhojia Dental College and Hospital, Baddi, Solan, Himachal Pradesh, India, with a chief complaint of a midline fracture in his maxillary Cu-sil denture [Figures 1 and 2]. The patient expressed dissatisfaction with his current prostheses and requested a new set of maxillary and mandibular dentures.

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Figure 1:

Previous prostheses of the patient – Occlusal surface.

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Figure 2:

Previous prostheses of the patient – Intaglio surface.

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On clinical examination, the patient exhibited a completely edentulous maxillary arch and a partially edentulous mandibular arch with a Class I ridge relationship. The inter-arch space measured approximately 20 mm. There was no significant systemic medical history. A treatment plan was formulated to fabricate a new set of complete dentures with a metal framework base for the maxillary denture and a conventional acrylic base for the mandibular partial denture.

Procedure/Technique

Preliminary impressions

• The fractured maxillary Cu-sil denture was temporarily stabilized using autopolymerizing acrylic resin (DPI RR Cold Cure, Dental Products of India, Mumbai, India).

• The preliminary maxillary impression was made using medium-fusing impression compound (Hiflex Impression Compound, Prevest DenPro Limited, Jammu, India) in a non-perforated tray, while the mandibular impression was made using irreversible hydrocolloid (alginate) (Zelgan 2002, Dentsply India Pvt. Ltd., Haryana, India) in a perforated tray.

• Diagnostic casts were poured using Type II dental plaster (GypRock plaster, Rajkot, Gujarat, India) for the maxilla [Figure 3] and Type III dental stone (GypRock stone, Rajkot, Gujarat, India) for the mandible.

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Figure 3:

Primary cast.

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Custom tray fabrication and border molding

• Custom trays were fabricated using autopolymerizing acrylic resin (DPI RR Cold Cure, Dental Products of India, Mumbai, India) with 2 mm spacer relief and tissue stops.

• Border molding for the maxillary arch was carried out using low-fusing green stick impression compound (Type I) (Pinnacle Tracing Sticks, Dental Products of India, Mumbai, India) [Figure 4].

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Figure 4:

Border molding procedure.

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Final impressions

• Final maxillary impression was made using polyvinyl siloxane low-viscosity elastomeric impression material (Zhermack Oranwash L Refill Elastomeric Impression Material, Italy) [Figure 5] to capture fine mucosal details.

• Master casts were poured in Type III dental stone (GypRock stone, Rajkot, Gujarat, India).

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Figure 5:

Final impression.

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Duplicating master cast and refractory work

• The maxillary master cast was duplicated using reversible hydrocolloid (agar-based material), and a refractory cast was poured using phosphate-bonded investment material.

• The metal denture base design was outlined using color pencil, incorporating coverage of the palate, residual ridges, posterior palatal seal (PPS) area, and retentive loops for mechanical interlocking with acrylic resin.

Metal framework fabrication

• A wax pattern of 0.5 mm thickness was adapted on the refractory cast with strategically placed retentive holes.

• The pattern was sprued, invested with phosphate-bonded investment, and cast using cobalt-chromium alloy (or nickel-chromium alloy, depending on the clinical case).

• The metal framework was recovered, trimmed, and polished.

Denture base and jaw relation

• The metal framework was trial-fitted on the master cast and stabilized with baseplate wax to form the permanent denture base.

• Wax occlusion rims were fabricated, and maxillomandibular relations were recorded conventionally, including

  • Orientation jaw relation, including facebow transfer and mounting on a semi-adjustable articulator.

  • Vertical dimension of occlusion.

  • Centric relation.

Teeth arrangement and try-in

• Acrylic teeth were arranged in a Class I molar relation using anatomical guidelines to achieve function and esthetics.

• The try-in appointment was conducted to verify esthetics, phonetics, occlusion, retention, and comfort [Figure 6].

  

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  Figure 6:

  Waxed-up try-in (frontal view).

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• Modifications, if any, were made accordingly.

Acrylization, finishing, and polishing

• Dewaxing was performed, and heat-cure acrylic resin was packed around the metal framework for the maxillary denture.

• The mandibular removable partial denture was fabricated entirely with heat-cure acrylic resin.

• Both prostheses were finished, polished, and evaluated for surface smoothness and fit [Figures 7 and 8].

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Figure 7:

Final prostheses of the patient – Occlusal surface.

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Figure 8:

Final prostheses of the patient – Intaglio surface.

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Denture insertion and patient instructions

• The maxillary complete denture with metal base and the mandibular acrylic partial denture were inserted.

• Occlusion was checked intraorally and minor adjustments were made to eliminate pressure areas and occlusal discrepancies [Figure 9].

  

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  Figure 9:

  Metal-reinforced complete denture – in the patient’s mouth.

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• Detailed post-insertion instructions were given, including:

  • Cleaning protocol.

  • Night-time removal and storage.

  • Denture hygiene.

• The patient was advised to return for follow-up appointments at 24 h, 3 days, 1 week, 1 month, and 3 months.

Outcome

• The patient was satisfied with the retention, esthetics, and comfort of the new dentures [Figure 10].

  

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  Figure 10:

  Post-operative smile (happy and satisfied patient).

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• Follow-ups revealed no signs of pressure ulcers or discomfort, and the prostheses continued to perform satisfactorily.

DISCUSSION

One of the most frequently encountered prosthodontic challenges in geriatric patients is the rehabilitation of a completely edentulous maxillary arch opposing natural or fixed mandibular dentition. Such cases pose significant biomechanical stress on the maxillary denture due to heavy occlusal forces, often resulting in midline fractures, accelerated ridge resorption, and compromised prosthetic longevity.^[11] These conditions may even predispose the patient to complications such as combination syndrome in long-standing edentulism.^[12]

In the present case, the patient exhibited a history of recurrent maxillary denture fractures, largely attributed to the excessive masticatory forces generated by fixed mandibular dentition. Traditional PMMA dentures, although aesthetically pleasing and biocompatible, lack sufficient impact and flexural strength to withstand such forces over time.^[13] PMMA’s limitations in fatigue resistance make it vulnerable, especially in the presence of parafunctional habits like bruxism or clenching.^[14] Consequently, a complete denture reinforced with a metal base (CDMB) was chosen as the definitive prosthesis.

CDMBs offer a distinct mechanical advantage in high-stress occlusal environments.^[15] The incorporation of a cast metal framework, commonly fabricated using cobalt-chromium-molybdenum alloys, significantly enhances the denture’s fracture resistance while maintaining strength even in thinner sections.^[16] Metal denture bases eliminate polymerization shrinkage, leading to improved dimensional stability, superior tissue adaptation, and better retention. These attributes are particularly beneficial for patients with high gag reflexes, as metal bases can be fabricated more narrowly without compromising structural integrity.^[17]

A significant study by Postic et al. involving 116 edentulous patients demonstrated higher success rates in patients rehabilitated with metal-based dentures, especially when the metal extended to the vibrating line.^[18] In our case, the design retained an acrylic extension in the PPS area to avoid technical challenges while ensuring enhanced fit and stability through the metal framework covering the primary stress-bearing areas. Studies have also highlighted that dentures fabricated with metal frameworks exhibit superior resistance to lateral deformation and warpage, ensuring a faithful reproduction of mucosal contours.^[19,20]

Beyond mechanical benefits, metal bases provide better thermal conductivity, enhancing the patient’s perception of temperature in food and beverages, and contributing to overall comfort and oral function.^[21] In addition, when highly polished, metal surfaces exhibit minimal water sorption and microbial adhesion, reducing the colonization of organisms such as Candida albicans and improving hygiene.^[22]

Another notable investigation by De Furio and Gehl compared the dislodgment forces required for maxillary dentures fabricated from various materials.^[23,24] Their findings validated that dentures with metal bases, particularly chrome-cobalt alloys, demonstrated significantly greater retention than their acrylic counterparts, further supporting the clinical viability of CDMBs in challenging cases.

However, metal denture bases are not without limitations. Increased fabrication cost, weight, and technique sensitivity – especially around the PPS area – pose challenges.^[25,26] The framework must avoid extension into the PPS zone to prevent interference with border molding and seal. Moreover, rebasing and relining procedures are more complex in metal-based dentures, necessitating precise planning during initial fabrication.^[27,28] CDMBs are also contraindicated in severely resorbed ridges where adaptation becomes compromised.^[29] Despite these disadvantages, CDMBs have been shown to outperform conventional acrylic dentures in scenarios where higher mechanical demands are anticipated.^[30] The metal base’s rigidity, biocompatibility, dimensional stability, and longevity make it a suitable material of choice in selective prosthodontic rehabilitations.^[31] Furthermore, metal frameworks have been associated with reduced allergic reactions due to their hypoallergenic properties and have demonstrated a role in controlling fungal growth in complete denture wearers.^[32-35]

In this case, the patient previously experienced two episodes of denture failure – one involving fracture and the other due to instability and discomfort. The introduction of a metal base resulted in enhanced retention, stability, and functional satisfaction, thus confirming the clinical utility of CDMBs in similar prosthetic rehabilitations.

Although literature on CDMBs remains relatively sparse, existing evidence and this clinical case underscore the need for further longitudinal studies and randomized controlled trials to validate their long-term effectiveness, patient satisfaction, and cost-benefit outcomes.

CONCLUSION

Rehabilitation of edentulous maxillary arches opposing natural or fixed mandibular dentition remains a formidable challenge in prosthodontics due to the complex demands of achieving comfort, function, retention, and esthetics. A common clinical complication in such cases is midline fracture of the prosthesis, especially when constructed with conventional PMMA material, which is prone to fracture under functional stress when designed thin for patient comfort.

Incorporating a metal base into the complete denture framework has emerged as a promising solution to address these biomechanical shortcomings. Metal-reinforced complete dentures provide excellent dimensional stability, fracture resistance, and strength without compromising patient comfort. The ability to fabricate a thinner yet more durable prosthesis enhances both mechanical performance and patient satisfaction. The increased weight of the metal base not only imparts a more natural feel but also contributes to improved denture stability, especially in the mandible.

Additional advantages of metal-based dentures include improved biocompatibility of the supporting tissues, enhanced accuracy of fit, and compatibility with soft liners for specific clinical indications. However, limitations such as increased fabrication cost and challenges in relining must be acknowledged and weighed against the clinical benefits.

A successful prosthodontic outcome relies on thorough clinical evaluation, precise planning, and judicious selection of materials based on their physical properties and clinical applicability. This case report highlights how strategic integration of a metal base in the maxillary denture can effectively address patient complaints of recurrent prosthesis fracture and deliver a more stable, functional, and long-lasting rehabilitation. Ultimately, metal-based complete dentures can offer a viable and superior alternative to conventional acrylic prostheses in selected cases requiring enhanced strength and longevity.