Ten-year outcome of zirconia ceramic cantilever resin-bonded fixed dental prostheses and the influence of the reasons for missing incisors
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MatthiasKernNicolePassiaMartinSasseChristineYazigi
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https://doi.org/10.1016/j.jdent.2017.07.003
Under a Creative Commons license
open access
Abstract
Objectives
This clinical study evaluated the long-term outcome and survival rate of all-ceramic cantilever resin-bonded fixed dental prostheses (RBFDPs) made of zirconia-ceramic with a single-retainer design to replace missing incisors. In addition, whether the reason for missing incisors has an influence on the longevity of RBFDPs was analyzed.
Materials and methods
One hundred and eight zirconia ceramic cantilever RBFDPs were provided for 87 patients. Seventy-five RBFDPs replaced maxillary incisors and 33 mandibular incisors. The restorations were subsequently categorized into 3 groups according to the reasons for missing teeth (congenitally missing, trauma and other reasons). The patients were followed up annually, and the restorations were assessed for function and aesthetics. The mean observation time of the RBFDPs was 92.2 ± 33 months.
Results
Six debondings and 1 loss of restoration were recorded. The lost restoration was removed at the patient’s request after a small chip occurred on the mesial edge of the pontic. Three of the 6 observed debondings were caused by traumatic incidents. All debonded RBFDPs were rebonded successfully with no further complications. Zirconia ceramic RBFDPs yielded a 10-year survival rate of 98.2% and a success rate of 92.0%.
Conclusions
Anterior zirconia ceramic cantilever RBFDPs provided excellent clinical longevity. The reasons for missing incisors did not influence the longevity of the cantilever RBFDPs.
Keywords
All-ceramicsAnterior teethCantilever fixed dental prosthesisCongenitally missing teethDebondingResin-bonded fixed dental prosthesisSurvival rateZirconia ceramic bonding
1. Introduction
Missing teeth in the anterior aesthetic region represent an urgent need for dental intervention and often require an early treatment strategy that restores both the aesthetic and functional aspects of the dentition [1]. Missing anterior teeth may be congenital or occur as a result of traumatic incidents, caries and periodontitis [1], [2], [3].
Congenital absence of teeth is one of the most common malformations in humans [3]. In the permanent dentition, with the exclusion of third molars, the prevalence of congenitally missing teeth on different continents ranges between 0.15% and 16.2% [4]. Maxillary lateral incisors are the most commonly affected teeth in the anterior region [5], [6]. They are also the most common congenitally missing teeth bilaterally [4], [7].
Traumatic events are another main reason for missing incisors [2], whether as a direct result of an incident or as a late complication. Maxillary central incisors are most frequently affected by trauma [8].
The main treatment options in these situations are the autotransplantation of deciduous or permanent teeth, orthodontic space closure, resin-bonded fixed dental prostheses (RBFDPs), implants, and conventional fixed dental prostheses (FDPs) [1], [3].
Cantilever resin-bonded fixed dental prostheses (RBFDPs) are considered a minimally invasive treatment approach to the replacement of single missing anterior teeth and provide excellent clinical outcomes, high survival rates and great patient satisfaction [9], [10], [11], [12]. Fiber-reinforced composite RBFPDs offer a good aesthetic outcome, but are considered short-term prostheses [1]. Metal-ceramic RBFDPs provide a long-term and successful option when designed as single-unit cantilever prostheses [13], [14]. Cantilever all-ceramic RBFDPs have demonstrated clinically excellent outcomes in terms of durability, outcome, aesthetics and function, whether made from glass-infiltrated alumina ceramic or from zirconia ceramic [15], [16], [17], [18], [19].
Additionally, RBFDPs have many advantages. They require a simple and conservative preparation, are low in cost and are a reversible treatment option, with no risk of pulpal irritation, no need for anesthesia, and minimal risk of caries development; in addition, they are a valid option for young patients [11]. Moreover, these restorations demonstrated a high survival rate of up to 81.8% after 18 years of clinical service [15].
A recent systematic review on the rehabilitation of patients with congenitally missing teeth [3], concluded that the best restorative replacement was with dental implants. Conventional prosthetics, including RBFDPs, was considered an inferior treatment option with lower success and survival rates. However, this systematic review included no clinical studies using cantilever RBFDPs despite cantilever RBFDPs demonstrating excellent success and survival rates in such situations [15].
To the authors’ best knowledge, no studies have evaluated the influence of the cause of the missing teeth on the clinical performance of cantilever all-ceramic RBFDPs [12]. The purpose of this clinical study was to determine the long-term success and survival rates of cantilever zirconia ceramic RBFDPs replacing incisor teeth. Additionally, the study was designed to determine whether the reasons for missing incisors would influence these rates. The null hypotheses of this study were that the success and survival rates of cantilever zirconia ceramic RBFDPs would not be influenced by the reasons for missing incisors.
2. Materials and methods
This retrospective clinical evaluation was approved by the ethics committee of the Christian-Albrechts University at Kiel, Germany. Between October 2001 and December 2013, 87 patients with missing incisors and an indication for RBFDPs received 108 anterior cantilever RBFDPs made from zirconia ceramic. The patients were selected based on the following inclusion criteria:
1.
Patients with 1 or 2 missing incisors.
2.
Abutment teeth were caries-free or had minor defects that could be covered by the retainer wing. The available bonding area on sound enamel had to be at least 30 mm2.
3.
Abutment teeth without periodontitis.
4.
Edentulous space width corresponded to the size of the missing tooth.
5.
Appropriate occlusion that allowed the application of a retainer wing with a thickness of at least 0.7 mm.
6.
Retention phase of at least 3 months after active orthodontic treatment.
7.
Patient commitment to attend annual recall appointments.
Patients were informed about the treatment modality and possible treatment alternatives and signed an informed consent form. The patients were 61% female and 39% male with the youngest patient being 13 years old and the oldest being 78, with a mean age of 32 ±20 years.
The preparation of the abutment was minimally invasive, limited to the enamel and was carried out as described previously [11], [17]. The preparation of the retainer consisted of a thin lingual veneer design, a fine incisal finishing shoulder and a fine cervical chamfer. The finish line in the proximal area did not extend farther than the proximal contact. A small box of approximately 2 × 2 × 0.5 mm was prepared proximally. Additionally, a pinhole was created on the cingulum, and finally all sharp edges and surfaces were carefully smoothed. A schematic drawing of the preparation design is depicted in Fig. 1.
Fig. 1. Schematic drawing of the preparation design. C = light cervical chamfer, S = light incisal finishing shoulder, B = small proximal box, P = small pinhole; Fig. reprinted with permission from M. Kern, RBFDPs. Resin-Bonded Fixed Dental Prostheses – Minimally Invasive – Esthetic – Reliable, 1st ed., Quintessence, Berlin, 2017.
Impressions were taken and then poured with die stone. Restorations were designed using CAD/CAM technology, milled out of presintered zirconia ceramic blocks, and then densely sintered and manually veneered. The minimum thickness for the retainer wing was 0.7 mm. The minimum zirconia ceramic dimensions of the proximal connector were 2 mm (horizontally) × 3 mm (vertically). During the final clinical try-in appointment, marginal adaptation, fit, aesthetics, proximal contacts and static and dynamic occlusion were all carefully examined.
Prior to insertion, the bonding surfaces of the restorations were air-abraded with 50-μm alumina particles (0.25 MPa blasting pressure until the year 2009 and thereafter 0.1 MPa pressure) and then cleansed ultrasonically in 99% isopropanol. Rubber dam was used for isolation, and the enamel was etched with 37% phosphoric acid for 30s, and then the restorations were adhesively bonded using 1 of 2 adhesive luting systems (Panavia 21 TC, Kuraray, or Multilink Automix after application of Metal/Zirconia Primer, Ivoclar-Vivadent). An oral view of 2 cantilever zirconia ceramic RBFDPs is shown in Fig. 2.
Fig. 2. Lingual view of 2 cantilever zirconia ceramic RBFDPs.
Fifty-nine patients received 1 cantilever RBFDP, 21 patients each received 2 cantilever RBFDPs, while 7 patients missing both maxillary lateral incisors received cantilever RBFDPs splinted at the midline by connecting their retainer wings to maintain the orthodontic closure of a midline diastema. The number and distribution of replaced missing teeth are shown in detail in Table 1.
Table 1. Frequency distribution of pontic location.
| Pontic location | Maxilla | Mandible | Total |
| Central incisors | 13 | 26 | 39 |
| Lateral incisors | 69a | 7 | 76 |
| Total | 82 | 33 | 115 |
a
In the maxilla, seven restorations replaced both missing lateral incisors.
Patients were recalled at least annually to examine and assess the restorations both functionally and aesthetically. Patients who could not attend a clinical examination for any reason were contacted by telephone and interviewed about the status of their RBFDP. Patients were categorized according to the reason for the missing tooth into 3 categories: congenitally missing (G1), traumatic incidents (G2) and other reasons (G3), including periodontitis, caries and orthodontic treatment. One patient (1 restoration) was excluded from this analysis as the reason for the missing tooth was unknown. The RBFDPs replaced teeth that were congenitally missing in 59.6% of the cases, missing because of traumatic incidents in 13.2% and for other reasons in 27.2%. Table 2 specifies the number of teeth and the cause of missing teeth.
Table 2. Frequency distribution of cause of missing teeth (one RBFDP with unknown cause excluded).
| Cause for missing teeth | Number of missing teeth | Percentage% |
| Congenitally missing (G1) | 68 | 59.6 |
| Traumatic incidents (G2) | 15 | 13.2 |
| Other reasons (G3) | 31 | 27.2 |
| Total | 114 | 100 |
The data were collected, coded, tabulated and input to a PC using Statistical Package for Social Science (SPSS 20.0 for Windows, SPSS Inc, Chicago, IL, USA). Using the Kaplan-Meier method, the success and survival rates of the restorations were analyzed considering 2 failure criteria: debonding for success and loss of the restoration for survival rates. The Log-Rank test was used to compare the survival rates of groups for these 2 criteria.
3. Results
The mean observation time was 92.2 ± 33 months with a minimum of 35 months and a maximum of 185 months. Six patients with 8 restorations did not present to follow-up for at least 24 months and could not be interviewed by phone. They were considered as drop-outs (censored data). Within the observation time, 6 debonding incidents and 1 lost restoration were recorded. Of these, 2 patients were orthodontically pretreated, while the others received no orthodontic treatment. The distribution of complication incidents among groups is shown in Table 3.
Table 3. Distribution of complication incidents.
| Group | Debonding | Loss of restoration |
| G1 | 1 | 0 |
| G2 | 2 | 1 |
| G3 | 3 | 0 |
| Total | 6 | 1 |
The first debonding occurred after 11 months when the patient was hit in the face while playing with her preschool daughter. The second happened after 22 months and was the result of an accidental hit on the restoration by the patient’s friend. The third took place after 54 months because of a traumatic incident during vacation. For the last 3 debondings, the patients were not able to specify any reason. Four of 94 RBFDPs luted with Panavia 21 TC debonded (4.2%), while 2 of 14 RBFDPs luted with Multilink Automix debonded (14.2%). In 1 patient, rebonding was done with Multilink Automix and with Panavia 21 TC in the other patients. All 6 rebonded restorations were followed up, and no further complications were recorded. One RBFPD was removed because the patient requested an implant-supported crown to replace the missing tooth after a small chip occurred on the mesial edge of the RBFDP pontic.
When debonding was considered a complication, the success rate (survival with complication) was 92.0% after 10 years (Fig. 3). Group G1 had a success rate of 98.5%, whereas the 10-year success rates for groups G2 and G3 were 76.9% and 89.2%, respectively (Fig. 4). However, because of the low number of debondings, no statistically significant difference was detected among the 3 groups (p = 0.128, Log Rank test).
Fig. 3. Cumulative success rate (debonding as failure criterion) for all RBFDPs.
Fig. 4. Cumulative success rate (debonding as failure criterion) related to the cause of missing incisors. G1 = congenitally missing, G2 = missing because of trauma, G3 = missing for other reasons.
When the loss of a restoration was considered a failure, the overall survival rate was 98.2% after 10 years. Groups G1 and G3 showed a survival rate of 100%, whereas the survival rate for group G2 was 90.0%. With only 1 failed RBFDP in group G2, a statistical analysis was not meaningful.
All RBFDPs remained in function once the 6 debonded restorations were rebonded. As the only lost restoration was removed at the patient’s request and not because of failure, the survival rate of RBFDPs made of zirconia ceramic can be considered to be 100%.
4. Discussion
Three of 6 debonding prostheses were caused by traumatic incidents and all 6 restorations were successfully rebonded and remained functionally and aesthetically successful. No framework fractures occurred in any of the zirconia RBFDPs, even after traumatic impact. However, 3 minor chips of the veneering ceramic were recorded. The only lost restoration was removed after minor incisal chipping at the patient’s request.
Anterior all-ceramic cantilever single-retainer RBFDPs made from zirconia ceramic showed a highly successful clinical outcome after 10 years of clinical service. This equals the survival rate of cantilever RBFDPs with a single retainer made from a glass-infiltrated alumina ceramic, in which the survival rate was 95.4% after 10 years [15]. In the follow-up of RBFDPs made from glass-infiltrated alumina, no debonding incidents were recorded, but 2 fractures of the alumina framework occurred. These fractures took place at the proximal connector between the pontic and the retainer wing. In contrast, in the case of RBFDPs made of zirconia ceramic, overloading, even by traumatic impacts resulted in debonding rather than fracture of the framework; zirconia has twice the flexural strength of glass-infiltrated alumina ceramic [20]. This makes rebonding of the zirconia RBFDPs possible and free of complications, whereas alumina RBFDPs with failures and fractures in the framework will require a replacement restoration.
This excellent outcome is supported by the results of a recent long-term evaluation, in which success and survival rates of 100% were recorded for anterior metal-ceramic cantilever RBFDPs after 18 years compared with success and survival rates of only 10% and 50% of their 2-retainer metal-ceramic counterparts [13]. The lower survival rate of the 2-retainer RBFDP design can be attributed to the differential movement of the 2 abutment teeth, resulting in a shear force on the wing of the retainer and consequent debonding of RBFDPs [16].
The high success rate reported in this long-term study agrees with that of other studies using densely sintered zirconia as framework material for cantilever RBFDPs [18], [19]. After 4 years of clinical service the survival rate of 15 zirconia ceramic RBFDPs replacing anterior missing incisors was 100%. Two debondings were successfully rebonded, but no fractures or chipping of the ceramic material occurred [19]. In a second study, 24 single-unit RBFDPs made of zirconia ceramic showed a survival rate of 100% and a success rate of 82.4% after 3 years of clinical service [18].
In the current study, the cause of missing teeth did not affect the outcome in regard to both criteria (debonding and loss of restoration). Therefore, the null hypotheses, that the cause does not influence either the success rate or and survival rates of zirconia RBFDPs, were accepted. In a recent systematic review on the occlusal rehabilitation for patients with congenitally missing teeth, the success rate, survival rate and the annual failure rate for the treatment alternatives were recorded and a conclusion favoring implant treatment was drawn [3]. The mean survival rate for autotransplantation was 89.6% after a mean follow-up of 12.5 years for deciduous teeth and 94.4% after 7.6 years for permanent teeth. An annual failure rate of 1% was recorded for both treatment modalities. The survival rates for implants and conventional prostheses were 95.3% and 60.2% after 4.6 and 8.4 years, respectively, with annual failure rates of 3% for implants and 5% for conventional prostheses. In the previous systematic review, RBFDPs were categorized and rated as conventional prostheses along with all other different prosthetic varieties retained by teeth as having a 60.2% survival rate, which led to a wrong assumption. The results of our study, however, where RBFDPs replaced congenitally missing teeth showed a survival rate of 100% and a success rate of 98.5% after 10 years rates. These rates surpass those obtained by any of the previous treatment alternatives, including implants. This outperformance reported by our study agrees with the findings of another study comparing the performance of RBFDPs and that of single implants in replacing a single missing tooth after an observation time of close to 10 years [21]. The long-term success rate for implant-supported crowns was lower, whereas the occurrence of biological complications was significantly higher among the implants (25.6%) than the RBFDPs (7.7%).
In conclusion, RBFDPs and implants are both minimally invasive treatment options for the replacement of single anterior missing teeth, with comparable levels of longevity and patient satisfaction. However, RBFDPs have the advantage of being an eligible option for young patients (as young as 10 years old), which is contraindicated for treatment with implants. Additionally, the replacement of a single anterior missing tooth with RBFDPs is still possible for those with limited available space (<7 mm) or with angled roots of adjacent teeth; implantation placement in such individuals requires orthodontic treatment. Moreover, when compared with single implants, RBFDPs are a reversible option, require shorter treatment time, cost less and require less demanding postoperative care [10], [21].
The results highlight the excellent clinical outcome of cantilever RBFDPs made of zirconia ceramic for the replacement of anterior missing teeth. However, these results support only the use of zirconia ceramic RBFDPs in the anterior region. This design is not suitable for the molar region, where the use of 2-abutment inlay-retained zirconia FDPs might be the treatment of choice [22].
This retrospective clinical study has certain limitations. Eight of the 108 restorations (7.4%) could not be followed over the complete observation time as they were not available for recall for at least 24 months. However, it seems unlikely, especially for early drop-outs, that these RBFDPs failed, as patients in Germany have a 2-year warranty and would probably have shown up in the case of failure. On the other hand, a high number of patients were adolescents still living at home with their parents when they received the RBFDPs. After finishing high school, many may have moved out of the area, explaining late drop-outs. As compared with another retrospective study on single-retainer RBFDPs over only 6 years, where 28.6% of the restorations [23] could not be followed, the drop-out rate of 7.4% in the current study seems reasonable.
In addition, 27 patients with 32 restorations could only be contacted for their most recent recall by telephone. Although they reported in person that their cantilevered RBFDP had not debonded and was functioning well, we were concerned that the patient might not able to detect complications such as caries at the bonding margins. However, unlike 2-retainer RBFDPs, where unilateral debonding of 1 retainer wing might not be detected, any debonding of single-retainer RBFDPs would be quite obvious to the patient as it would completely lose its retention. With this in mind, the telephone interview might reflect the true bonding of zirconia ceramic RBFDPs.
5. Conclusion
Anterior zirconia ceramic cantilever RBFDPs showed excellent clinical longevity independently of the cause of the missing teeth.
Clinical relevance
All-ceramic cantilever RBFDPs provide an excellent minimally invasive treatment alternative to implants and conventional prosthetic methods when single missing anterior teeth need to be replaced.
Acknowledgments
The authors would like to acknowledge the patients for their kind cooperation, the support of the departmental staff and and dental technicians, especially R. Gerhardt and B. Schlueter, for the laboratory work.
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