Abstract
Objectives
The aim of this study was to assess the clinical outcomes and patient satisfaction with monolithic zirconia crowns in patients with severe tooth wear (≥1/3 of the tooth crown) in the aesthetic zone.
Methods
The historical prospective study sample consisted of 13 patients previously treated with a total of 84 monolithic zirconia crowns. The patients had been treated in a private clinic in Bergen, Norway, in the period 2012 to 2014. All patients were men, aged 35–67 years (mean age 56.3 years) and had been in need of prosthetic rehabilitation because of severe tooth wear in the aesthetic zone. Technical complications as well as biologic findings were registered when the crowns had been in function one to three years (mean 20 months). The patients completed a self-administered questionnaire regarding satisfaction with aesthetic and function.
Results
No biological complications were registered in 79 of the crowns (94%), and technical complications were registered in only two patients. All patients were satisfied with the aesthetic and function of the monolithic zirconia crowns and would choose the same treatment modality if they were to be treated again.
Conclusions
Within the limitations of this study, we conclude that the rate of clinical complications was low and that the patients were satisfied with the aesthetic as well as the function of the monolithic zirconia crowns.
Clinical significance
Monolithic zirconia crowns may provide a valid treatment modality in the aesthetic zone in patients with severe tooth wear.
1
Introduction
Heavy grinders may wear down their teeth to such an extent that rehabilitation is indicated for aesthetical, functional and biological reasons. There are, however, no hard and fast rules for the treatment of worn teeth in heavy grinders [ ]. Only in a respectful dialogue between the dentist and the patient can a treatment plan be established and fulfilled [ ]. The purpose of the treatment is primarily to prevent further wear and furthermore to re-establish aesthetics and function with minimal biological cost. This can be challenging since aesthetics and strength of restorative materials have so far not been easily combined [ ]. The most aesthetically and biologically minimal invasive materials, like feltspatic ceramics and composites, are also the weakest, whereas the strongest materials like metals have inferior aesthetics.
The most argued treatment indication for heavy grinders is to improve aesthetics, as they normally do not have problems chewing. The extensive grinding forces in these patients require a restorative material with adequate wear-and fracture resistant properties [ ]. For this reason, metal-ceramic restorations have for many years been considered “the golden standard” in fixed prosthodontics in heavy grinders. However, the metal framework makes it difficult to mimic natural aesthetics and the veneering ceramic might chip off, exposing the metal core [ ]. Alternative materials for dental rehabilitation with better aesthetics have to be comparable to metal-ceramics, particularly with regard to veneer chipping, core fracture, and marginal fit [ ]. As the properties of all-ceramic restorations have improved during the last decades, there has been a trend towards using more metal-free restorations because of the superior aesthetics of all-ceramic restorations [ ].
In a systematic review from 2007 the estimated 5-year survival rate for metal-ceramic and all-ceramic single crowns was reported to be almost equal; 95.6% vs 93.3% [ ]. However, the 5-year chipping complication rates were higher for all-ceramic crowns than for metal-ceramic crowns; 5.7% vs 3.7%. Another systematic review from 2015 reported similar results regarding complication rates of metal-ceramic versus all-ceramic crowns and ceramic veneer chipping was reported as a common problem [ ]. Thus it seems that even with significant improvements in material properties and excellent aesthetics, the performance of all-ceramic crowns still fails to match that of metal-ceramic crowns [ ].
The introduction of high strength oxide-ceramics as the core material improved the aesthetic properties compared to metal-ceramic crowns, but also these crowns show higher chipping rates than conventional metal-ceramics crowns [ ]. A systematic review from 2010 reported excellent results regarding core fracture; less than 1% in the zirconia group and 0% in the metal-ceramic group after 3 years [ ]. However, the rate of chipping was much higher for the bi-layered zirconia group than for the metal-ceramic group; 54% vs 34%. Common for all publications included in these reviews is that patients with para-functions such as grinding are usually excluded from the study populations.
Chipping and fractures of veneering ceramic is thus a problem both on metal-ceramic and all-ceramic crowns. In recent years high-strength monolithic zirconia crowns with superficial glazing and staining have been tested in high-load bearing areas [ ]. The monolithic zirconia crowns do not have a veneering ceramic, and are expected to have less chipping and fracture complications. On the other hand, the monochromic and opaque aesthetic properties of monolithic zirconia restorations make them aesthetically inferior to veneered restorations. The use in the aesthetic zone has thus been very limited. Monolithic zirconia might, however, be an acceptable treatment choice for heavy grinders. Most studies on clinical performance of single crowns exclude patients with bruxism and/or parafunctional habits because higher rates of mechanical complications such as chipping and fractures can be expected in this group of patients compared to non-grinders [ ]. Hence, there is a lack of studies on the clinical outcomes of monolithic zirconia crowns in the aesthetic zone in patients with heavy grinding habits. Likewise, there is a lack of studies with patient reported outcomes regarding this treatment modality.
The aim of this study was to assess the clinical performance and the patient satisfaction with monolithic zirconia crowns in the aesthetic zone in heavy grinders with worn dentition.
2
Materials and methods
2.1
Sample
Patients with severe tooth wear, including at least 1/3 of the coronal tooth substances, in the aesthetic zone (incisors, canines and premolars) restored with fixed prosthodontics were included in this historical prospective study. The study included all patients with this specific tooth wear referred to one specialist in prosthodontics (HG) for rehabilitation ( Fig. 1 ). The patients were referred for treatment after having been observed over a period of time by the referring dentist [ ]. The study sample consisted of 13 patients with a total of 84 monolithic zirconia crowns ( Table 1 ). The patients were informed of the study with an invitation to a clinical assessment and consented to participate by showing up to the appointment. All patients were men between 35 and 67 years of age (mean 56.3 years). All the patients in the study had an edge-to-edge bite prior to treatment. Their vertical dimensions were increased upon receiving crown therapy and occlusal relations were adjusted in to a normal horizontal overbite. The vertical dimension in the front was increased 1–2 mm in all patients, and all had complete occlusal contact at the control 1–3 years after treatment.
The inclusion criteria were
- •
Severe tooth wear in the aesthetic zone.
- •
The patient preferred strength and durability of the restorations as compared to aesthetics.
- •
All teeth in need of treatment had been restored with monolithic zirconia single crowns (BruxZir®, Glidewell Laboratories, USA) and cemented with resin modified glass ionomer cement (Fuji plus®, GC Corporation Tokyo, Japan) ( Fig. 1 ).
- •
The patients did not wear an occlusal night guard after treatment.
The treatment had been performed according to the general guidelines for the materials used. The yttria-stabilized zirconia material was soft-machined by CAD/CAM technique according to manufacturer’s instructions. Dental technicians polished the outer surface. The restorations were assured to fit in occlusion and articulation movements before cementation and no adjustments were needed before or after cementation.
| Patient number | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
|---|---|---|---|---|---|---|---|
| Treated teeth | 14–23 | 12–13, 44, 42–33 | 13–25 | 33–42 | 44–35 | 12–22 | 13–23 |
| Patient number | 8 | 9 | 10 | 11 | 12 | 13 |
|---|---|---|---|---|---|---|
| Treated teeth | 13–23 | 13–23 | 15, 12–23 | 13–23 | 12–22 | 13–23 |
2
Materials and methods
2.1
Sample
Patients with severe tooth wear, including at least 1/3 of the coronal tooth substances, in the aesthetic zone (incisors, canines and premolars) restored with fixed prosthodontics were included in this historical prospective study. The study included all patients with this specific tooth wear referred to one specialist in prosthodontics (HG) for rehabilitation ( Fig. 1 ). The patients were referred for treatment after having been observed over a period of time by the referring dentist [ ]. The study sample consisted of 13 patients with a total of 84 monolithic zirconia crowns ( Table 1 ). The patients were informed of the study with an invitation to a clinical assessment and consented to participate by showing up to the appointment. All patients were men between 35 and 67 years of age (mean 56.3 years). All the patients in the study had an edge-to-edge bite prior to treatment. Their vertical dimensions were increased upon receiving crown therapy and occlusal relations were adjusted in to a normal horizontal overbite. The vertical dimension in the front was increased 1–2 mm in all patients, and all had complete occlusal contact at the control 1–3 years after treatment.
The inclusion criteria were
- •
Severe tooth wear in the aesthetic zone.
- •
The patient preferred strength and durability of the restorations as compared to aesthetics.
- •
All teeth in need of treatment had been restored with monolithic zirconia single crowns (BruxZir®, Glidewell Laboratories, USA) and cemented with resin modified glass ionomer cement (Fuji plus®, GC Corporation Tokyo, Japan) ( Fig. 1 ).
- •
The patients did not wear an occlusal night guard after treatment.
The treatment had been performed according to the general guidelines for the materials used. The yttria-stabilized zirconia material was soft-machined by CAD/CAM technique according to manufacturer’s instructions. Dental technicians polished the outer surface. The restorations were assured to fit in occlusion and articulation movements before cementation and no adjustments were needed before or after cementation.
| Patient number | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
|---|---|---|---|---|---|---|---|
| Treated teeth | 14–23 | 12–13, 44, 42–33 | 13–25 | 33–42 | 44–35 | 12–22 | 13–23 |
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