Highlights
- •
Ninety-four percent of the Y-TZP FPDs evaluated performed satisfactorily.
- •
The survival rate of the Y-TZP FPDs was within the same range as for metal–ceramic FPDs.
- •
For plaque and bleeding no significant differences were seen compared with the controls.
- •
Based on a visual analog scale patient satisfaction with the evaluated FPDs was high.
Abstract
Objectives
To evaluate zirconia-based fixed partial dentures (FPDs) after more than 8 years in clinical service.
Methods
Patients treated between 2000 and 2004 with zirconia FPDs were identified from the records of a manufacturer of FPD substructures. Of the 45 patients who met the inclusion criteria 30 attended the appointment and 33 FPDs were evaluated using modified California Dental Association (CDA) criteria. In addition, plaque and the bleeding index were registered. Patient satisfaction with the restorations was evaluated using a 10-point visual analog scale (VAS).
Results
All the FPDs were made using CAD/CAM and hot isostatic pressed yttria-tetragonal zirconia polycrystal (HIPed Y-TZP) ceramic (Denzir) and were placed within general practices. The mean observation period was 9.6 ± 1.6 years (range 3.0–13.1 years). The CDA rating was 90% satisfactory for the surface. Corresponding figures for anatomic form, color and margin integrity were 94%, 100% and 94%, respectively. Regarding surface three (9.7%) FPDs exhibited veneer chipping and were rated ‘not acceptable’. For margin integrity two (6.5%) were rated ‘not acceptable’ because of caries. For anatomic form two (6.1%) were rated ‘not acceptable’ due to two lost FPDs. No significant differences were seen between the FPDs and controls for plaque and bleeding. The Kaplan–Meier survival rate (still in clinical function) was 94%, the success rate (technical events accounted for) 91% and (biological events accounted for) 73%. Based on the VAS the mean value for patient satisfaction was 9.3 ± 1.2.
Significance
Ninety-four percent of the FPDs were still in clinical function. HIPed Y-TZP could serve as an alternative for FPD treatments similar to those in the current study.
1
Introduction
To date gold alloys have traditionally been the most widely used cast metal for dental applications but gold alloys are now used less often, mainly because the cost has increased during the past few years . Among materials often used for crowns and fixed partial dentures (FPDs) are cobalt chromium alloys and commercially pure titanium . However, increased demands for, among others, more esthetic materials have led to a shift to metal-free materials for dental restorations and there is now widespread use of ceramics in dental restorations and other biomechanical applications, such as hip joint implants . In this context it should be noted that the properties of dental ceramics are very dependent on the manufacturing technique and composition of the material and that most ceramic materials are brittle which could influence the mechanical behavior of dental restorations .
At the end of the 20th century alumina and zirconia oxide ceramics with improved mechanical properties, compared to dental ceramics previously used, became available to dentistry through the development of computer aided design/computer aided manufacturing (CAD/CAM) techniques . Zirconia-based ceramics in particular have been used since then as a core material for dental FPDs and single crowns . Today zirconia-based ceramic dental restorations are made in a variety of ways; either using prefabricated blocks of hot isostatic pressed (HIPed) zirconia or in different presintered stages that are then sintered after the milling of the restoration .
Pure zirconia exists in three phases: cubic (C) at >2370 °C, tetragonal (T) at 1170–2370 °C and monocline (M) between 0 and 1170 °C . Since it is the tetragonal phase that is of particular interest for dental applications, dental zirconia ceramics are stabilized using yttria, often called yttria-tetragonal zirconia polycrystal (Y-TZP), to reduce the phase transformation T → M at room temperature . However, despite stabilizing with yttria the number of monocline crystals in zirconia ceramics can increase over time, so-called low temperature degradation (LTD), which could affect the properties of the material . It is, therefore, of interest to evaluate the clinical outcome of FPDs made of Y-TZP that have been in clinical service for a relatively long time. In a survey of the literature in the database (PubMed) only two papers were found that addressed the clinical results of zirconia-based FPDs that have been in clinical service for more than 8 years . The aim of the present study was, therefore, to evaluate zirconia-based FPDs that have been in clinical service for more than 8 years.
2
Materials and methods
2.1
Ethical considerations
Before the present study started it was approved by the regional Ethics Review Board at Umeå University, Umeå, Sweden (Dnr 2013-124-31M). Written and oral informed consent was given by all of the participants in accordance with the Helsinki Declaration.
2.2
Patient recruitment
Patients treated with zirconia ceramic FPDs were identified from the records of a manufacturer (Cad.esthetics, Skellefteå, Sweden) of zirconia-based ceramic core materials for all-ceramic FPDs. The inclusion criteria were that the FPDs should have been made between 2000 and 2004 and placed in patients treated in general practices and living within a distance of 200 km from Umeå University, Umeå, Sweden. Using the patients’ social security numbers it was then possible to track individuals who had received zirconia ceramic FPDs between 2000 and 2004. These patients received written information by mail about the purpose of the study. Thereafter they were telephoned and asked if they wanted to participate in the study. The patients were informed that they could decide to withdraw from the study at any time and without any explanation.
2.3
Clinical evaluation
The clinical examination was performed in accordance with a slightly modified version ( Table 1 a–d) of the California Dental Association (CDA) quality evaluation system by two of the authors (AH and HL). The two examiners worked in pairs but independently of each other. Each time there was a difference in the rating of a given FPD, both examiners looked at the case and then resolved their disagreement. In addition, the patients were interviewed to discover whether any complications had occurred during the time the FPDs had been in use and for them to rate their satisfaction with the FPDs on a 10-point visual analog scale (VAS). Point 1 on the VAS corresponded to ‘not satisfied at all’ and point 10 ‘completely satisfied’.
| (a) | |
|---|---|
| Rating | Anatomic form |
| Satisfactory | |
| Excellent | |
| R (Romeo) | Restoration’s contour is continuous with existing anatomical form, restores contours, cusps, planes, grooves, marginal ridges and functional contact points. |
| Acceptable | |
| S (Sierra) | Restoration is slightly under-contoured or |
| Occlusal contour not continuous with that of cusps and planes or | |
| Occlusal height reduced locally (not in toto) or | |
| Marginal ridges slightly under-contoured (low) or | |
| Facial flatting or | |
| Lingual flatting or | |
| Interproximal cervical area slightly under-contoured or | |
| Restoration is slightly over-contoured but excess material could be removed. | |
| Not acceptable | |
| T (Tango) | Restoration is under-contoured Dentin or base is exposed or |
| V (Victor) | Occlusion is affected or Contact is faulty (self-correction is unlikely) or |
| Interproximal cervical area under-contoured, tissue damage likely. | |
| Restoration is over-contoured Contour cannot be adjusted properly or |
|
| There is marginal over-hang. | |
| Restoration is missing or | |
| Traumatic occlusion or | |
| Restoration causes pain in tooth or adjacent tissue. | |
| (b) | |
|---|---|
| Rating | Surface |
| Satisfactory | |
| Excellent | |
| R (Romeo) | Surface of restoration is smooth. No irritation of adjacent tissue. |
| Acceptable | |
| S (Sierra) | Surface of restoration is slightly rough and pitted, can be refinished. |
| Not acceptable | |
| T (Tango) | Surface deeply pitted, irregular grooves (not related to anatomy), cannot be refinished. |
| V (Victor) | Surface is fractured or flaking. |
| (c) | |
|---|---|
| Rating | Color |
| Satisfactory | |
| Excellent | |
| R (Romeo) | No mismatch in color shade and/or translucency between restoration and adjacent tooth structure. |
| Acceptable | |
| S (Sierra) | Mismatch between restoration and tooth structure within the normal range of tooth color, shade and/or translucency. |
| Not acceptable | |
| T (Tango) | Mismatch between restoration and tooth structure outside the normal range of tooth color, shade and/or translucency. |
| V (Victor) | Esthetically displeasing color, shade and/or translucency. |
| (d) | |
|---|---|
| Rating | Margin integrity |
| Satisfactory | |
| Excellent | |
| R (Romeo) | No visible evidence of ditching along the margin. |
| No discoloration on the margin between the restoration and tooth structure. | |
| Acceptable | |
| S (Sierra) | Visible evidence of ditching along the margin not extending to the DE junction. |
| Discoloration on the margin between the restoration and the tooth structure. | |
| Not acceptable | |
| T (Tango) | Dentin or base is exposed along the margin. |
| Discoloration has penetrated along the margin of the restorative material in a pulpal direction. | |
| V (Victor) | Restoration is mobile or |
| Fractured or | |
| Caries contiguous with the margin or restoration or | |
| Tooth structure fractured. | |
Moreover, plaque and bleeding on probing were recorded by one of the examiners for each FPD unit. By moving a periodontal probe in the marginal part of the restoration plaque and bleeding were diagnosed as not present (0) or present (1). The homologous surfaces of the teeth not treated with zirconia were used as controls. When homologous teeth were lost a control was selected from another quadrant.
Any chipping fracture was registered and classified according to Crisp et al. ( Table 2 ). In addition, wear on the veneer ceramic, the antagonist and the rest of the dentition were registered. Clinical photographs were taken of all FPDs evaluated. Finally the patients were informed orally about the clinical findings and, if necessary, referred to their ordinary dentist. After the clinical examination all results were encoded and subjected to statistical analysis.
| A | A minor chip <1 mm in diameter–may be left alone or polished. |
| B | A larger chip >1 mm but still within the veneering porcelain. |
| C | A repairable chip involving the framework interface. |
| D | A catastrophic loss of veneering porcelain requiring restoration replacement. |
2.4
Statistical analysis
Kaplan–Meier was used to analyze the data concerning the FPDs’ survival (defined as all evaluated FPDs still in the mouth even if events were identified) and success rates (defined as intact survival with satisfactory quality of surface, anatomic contour, function and esthetics). Pearson’s chi-squared test was used at a significance level of p < 0.05 to analyze the data obtained for the plaque and bleeding conditions.
2
Materials and methods
2.1
Ethical considerations
Before the present study started it was approved by the regional Ethics Review Board at Umeå University, Umeå, Sweden (Dnr 2013-124-31M). Written and oral informed consent was given by all of the participants in accordance with the Helsinki Declaration.
2.2
Patient recruitment
Patients treated with zirconia ceramic FPDs were identified from the records of a manufacturer (Cad.esthetics, Skellefteå, Sweden) of zirconia-based ceramic core materials for all-ceramic FPDs. The inclusion criteria were that the FPDs should have been made between 2000 and 2004 and placed in patients treated in general practices and living within a distance of 200 km from Umeå University, Umeå, Sweden. Using the patients’ social security numbers it was then possible to track individuals who had received zirconia ceramic FPDs between 2000 and 2004. These patients received written information by mail about the purpose of the study. Thereafter they were telephoned and asked if they wanted to participate in the study. The patients were informed that they could decide to withdraw from the study at any time and without any explanation.
2.3
Clinical evaluation
The clinical examination was performed in accordance with a slightly modified version ( Table 1 a–d) of the California Dental Association (CDA) quality evaluation system by two of the authors (AH and HL). The two examiners worked in pairs but independently of each other. Each time there was a difference in the rating of a given FPD, both examiners looked at the case and then resolved their disagreement. In addition, the patients were interviewed to discover whether any complications had occurred during the time the FPDs had been in use and for them to rate their satisfaction with the FPDs on a 10-point visual analog scale (VAS). Point 1 on the VAS corresponded to ‘not satisfied at all’ and point 10 ‘completely satisfied’.
| (a) | |
|---|---|
| Rating | Anatomic form |
| Satisfactory | |
| Excellent | |
| R (Romeo) | Restoration’s contour is continuous with existing anatomical form, restores contours, cusps, planes, grooves, marginal ridges and functional contact points. |
| Acceptable | |
| S (Sierra) | Restoration is slightly under-contoured or |
| Occlusal contour not continuous with that of cusps and planes or | |
| Occlusal height reduced locally (not in toto) or | |
| Marginal ridges slightly under-contoured (low) or | |
| Facial flatting or | |
| Lingual flatting or | |
| Interproximal cervical area slightly under-contoured or | |
| Restoration is slightly over-contoured but excess material could be removed. | |
| Not acceptable | |
| T (Tango) | Restoration is under-contoured Dentin or base is exposed or |
| V (Victor) | Occlusion is affected or Contact is faulty (self-correction is unlikely) or |
| Interproximal cervical area under-contoured, tissue damage likely. | |
| Restoration is over-contoured Contour cannot be adjusted properly or |
|
| There is marginal over-hang. | |
| Restoration is missing or | |
| Traumatic occlusion or | |
| Restoration causes pain in tooth or adjacent tissue. | |
| (b) | |
|---|---|
| Rating | Surface |
| Satisfactory | |
| Excellent | |
| R (Romeo) | Surface of restoration is smooth. No irritation of adjacent tissue. |
| Acceptable | |
| S (Sierra) | Surface of restoration is slightly rough and pitted, can be refinished. |
| Not acceptable | |
| T (Tango) | Surface deeply pitted, irregular grooves (not related to anatomy), cannot be refinished. |
| V (Victor) | Surface is fractured or flaking. |
| (c) | |
|---|---|
| Rating | Color |
| Satisfactory | |
| Excellent | |
| R (Romeo) | No mismatch in color shade and/or translucency between restoration and adjacent tooth structure. |
| Acceptable | |
| S (Sierra) | Mismatch between restoration and tooth structure within the normal range of tooth color, shade and/or translucency. |
| Not acceptable | |
| T (Tango) | Mismatch between restoration and tooth structure outside the normal range of tooth color, shade and/or translucency. |
| V (Victor) | Esthetically displeasing color, shade and/or translucency. |
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