Q U I N T E S S E N C E I N T E R N AT I O N A L
RESTORATIVE DENTISTRY
Sven Rinke
Practice-based clinical evaluation of zirconia abutments for anterior single-tooth restorations Sven Rinke, Priv Doz Dr med dent, MSc, MSc1/Anja Lattke, Dr med dent1/Peter Eickholz, Prof Dr med dent2/Katharina Kramer, Dr rer nat3/Dirk Ziebolz, Priv Doz Dr med dent, MSc 4 Objective: This study aimed to determine the survival rate and prevalence of biologic and technical complications associated with single-tooth implants with all-ceramic abutments in the anterior region. Method and Materials: A total of 33 patients were restored with 50 anterior implants and temporarily luted all-ceramic crowns on prefabricated zirconia abutments. All of the patients subsequently received annual supportive maintenance; 27 patients (18 women, 22–74 years) with 42 implants participated in the final maintenance visit and were included in the study (follow-up 78.1 ± 27.0 months). The time-dependent survival rate (Kaplan-Meier) and the frequency of prosthetic complications (abutment fracture [AF], screw loosening [SL], fracture of veneering ceramics [VF], retention loss [RL]) and biologic complications (peri-implantitis) were calculated to determine the success rates. Results: No implant loss (implant-related survival rate 100%) but one
abutment fracture occurred throughout the entire observation period; therefore, the survival rate of the superstructures (in situ criterion) was 97.6% (95% confidence interval [CI] 0.930– 1.000) after 7 years. Eleven restorations were affected by prosthetic complications: RL (n = 4), VF (n = 5), and SL (n = 2). Peri-implantitis was diagnosed for two implants (probing depth > 5 mm, bleeding on probing [BOP]/suppuration, and bone loss > 3 mm) (implant-related peri-implantitis rate 4.8%). No restoration required replacement due to complications. The success rate (event-free restoration) was 75.9% (95% CI 0.636– 0.882) after 7 years. Conclusions: Considering the calculated survival rate, the application of all-ceramic zirconia implant abutments in the anterior region can be recommended as a reliable therapy in private practice. Fractures of veneering ceramics were the most common prosthetic complication. (Quintessence Int 2015;46:19–29; doi: 10.3290/j.qi.a32818)
Key words: cement, ceramics, clinical studies, peri-implant infection, success, survival
Implant-supported single crowns (ISCs) are considered a reliable and safe treatment modality with high survival rates in long-term clinical studies.1-3 A recently published systematic review reported a 10-year survival 1
Dentist, Private Practice, Hanau, Germany.
2
Professor and Head, Department of Periodontology, Center for Dental, Oral, and Maxillofacial Medicine, Johann Wolfgang Goethe-University, Frankfurt/Main, Germany.
3
Senior Researcher, Department of Medical Statistics, Georg-August-University, Goettingen, Germany.
4
Associate Professor, Department of Operative Dentistry, Preventive Dentistry and Periodontology, Georg-August-University, Göttingen, Germany.
Correspondence: Priv Doz Dr Sven Rinke, Geleitstr. 68, 63456 Hanau, Germany. Email: [email protected]
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rate of single-tooth implants of 96.3%, whereas the reported survival rate of prosthetic restorations was 89.8%.1 Despite the high survival rates of implants and crowns, clinicians must be aware that technical, biologic, and esthetic complications are likely to occur. Technical complications (mainly screw loosening) have been documented to have an incidence of 8.8% within the first 5 years of clinical service, and esthetic complications reached a cumulative incidence of 7.1% for the same period.2,4-6 Published data on the prevalence of biologic complications (peri-implantitis) still show great variations in incidence and prevalence rates; therefore,
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more detailed information, especially derived from prolonged observation, is required. Because implantsupported single-tooth restorations have primarily been examined with regard to their use in the anterior region, the prevention of esthetic complications is critical.2 In addition to the correct implant positioning and proper soft tissue management, the selection of adequate materials and designs for prosthetic restorations influences the esthetic outcome significantly.6,7 For the last several decades, titanium abutments have been the standard of care for implant-supported restorations. Unfortunately, the blue-grayish shimmer exhibited by these abutments, in combination with thin overlying mucosal tissue, can negatively affect the esthetic outcome.8,9 For this reason, yttria partially-stabilized zirconia (Y-TZP) is a promising alternative material for the fabrication of abutments and ISCs; this material combines high strength and toughness with excellent biocompatibility and tooth-like shading.10-12 A limited number of clinical trials have investigated the esthetic benefits resulting from the use of Y-TZP as an abutment material. In two clinical studies using visual inspection, the use of all-ceramic abutments led to less gingival discoloration of the buccal mucosa compared with titanium abutments.6,13 In a prospective multicenter study using a spectrometric analysis, significantly higher color differences in the peri-implant soft tissues were detected for titanium abutments compared with zirconia abutments.14 Another clinical study concluded that the difference in light reflection from the soft tissue covering titanium or Y-TZP abutments is not perceptible if the mucosa exceeds 2 mm in thickness.15 Based on these results, the use of Y-TZP abutments appears to be esthetically beneficial, especially in clinical situations involving a thin overlaying buccal soft tissue.8,11 Regardless of the potential esthetic benefits, the use of Y-TZP abutments can only be recommended if their clinical performance is comparable with that documented for titanium abutments.2,10,12 Three systematic reviews have evaluated the shortterm clinical performance of Y-TZP abutments for single crowns. Based on an evaluation of three clinical trials involving 104 abutments and a mean follow-up
20
period of 3.7 years, the clinical performance of Y-TZP abutments was suggested to be comparable with that of titanium abutments.10,12,16 Subsequently published clinical trials of Y-TZP abutments for anterior ISCs reported fracture rates of 0 to 1% for observation periods of 3 to 5 years.13,17-19 There are no published studies examining the clinical performance of Y-TZP abutments used for anterior ISCs with mean observation periods of more than 5 years and including detailed information on potential technical and biologic problems (peri-implantitis). The aim of this practice-based retrospective clinical trial was to evaluate the long-term clinical performance (a mean observation period > 5 years) of Y-TZP abutments supporting anterior zirconia-based ISCs.
METHOD AND MATERIALS Patients This retrospective study evaluated partially edentulous patients who were restored with single-tooth implants, zirconia abutments, and temporarily luted all-ceramic crowns in the anterior region in a private dental office in Germany between 1 January 2002 and 30 October 2009. The following inclusion criteria were applied: • single-tooth implants of the same type in the anterior region (canine to canine) of the maxilla or mandible (Ankylos, Dentsply Implants) • zirconia abutments (Cercon Balance, Dentsply Implants) and zirconia-based manually veneered crowns (Cercon, DeguDent) luted with a provisional cement (TempBond, Kerr Hawe) • prophylaxis or supportive periodontal therapy (SPT), at least annually, including a periodontal examination (probing pocket depth [PPD] and bleeding on probing [BOP]), at the same dental office where the implants were inserted • complete radiographic documentation with panoramic radiographs (PT) and intraoral radiographs (IR) • complete medical history, including smoking • complete documentation of superstructure-related complications or failures.
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Fig 1a Clinical situation of a single tooth replacement 3 weeks after stage-two surgery.
Fig 1b Prefabricated zirconia abutment (Ankylos Cercon Balance, Dentsply Implants).
Fig 1c
Fig 1d Clinical situation after placement of the zirconia-based crowns.
• • • •
Try-in of the customized zirconia abutment.
The following exclusion criteria were applied: aggressive periodontitis20 no prophylaxis or periodontal therapy prior to implant therapy inadequate radiographs other missing data.
The study was approved by the Ethics Committee of the Medical Faculty of Georg-August University, Göttingen, Germany (application no. 3/2/10). The recommendations of Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) were followed.21
Treatment course Treatment was completed in a single private practice in Germany by two dentists with several years of experience and specific training in oral implant therapy. Implant placement, stage-two surgery, and prosthetic
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treatment were completed according to the manufacturers’ standard protocols. Prefabricated Y-TZP abutments (Cercon Balance, Dentsply Implants) were customized using water-cooled diamond instruments (Figs 1a to 1c). Zirconia crown frameworks were fabricated using a computer-aided design/computerassisted manufacture (CAD/CAM) process (Cercon, DeguDent) and were veneered manually using a suitable ceramic material (Cercon ceram kiss, DeguDent) (Fig 1d). Following the insertion of the prosthetic restoration with a temporary luting agent (TempBond, Kerr Hawe), the patients were instructed in homebased dental hygiene. They were then seen for postimplant maintenance every 3 to 12 months. Prophylaxis and SPT were performed in patients with and without a history of periodontal disease, respectively. Each patient at each appointment received treatment encompassing the following elements: assessments of the gingival bleeding index (GBI)22 and plaque control
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record (PCR),23 re-instruction and re-motivation for effective individual plaque control, professional tooth cleaning, polishing of all teeth using rubber cups and polishing paste, and application of a fluoride gel. Once (in cases of prophylaxis) or twice per year (in cases of SPT), dental status and PPD measurements were obtained at four sites per tooth/implant. Sites exhibiting a PPD of 4 mm and BOP, as well as sites with PPD ≥ 5 mm, were scaled subgingivally using ultrasonic and hand instruments. In cases of peri-implant mucositis, the scaling around implants was performed with a special ultrasonic tip (KaVo SONICflex implant, KaVo Dental), followed by manual instrumentation and the subgingival application of a chlorhexidine gel (Corsodyl 1% Dental Gel, GlaxoSmithKline).24 Prophylaxis/SPT was administered to most patients at 3-month intervals during the first year after implant insertion and at 6-month intervals thereafter. Patients exhibiting ineffective plaque control during the posttherapeutic phase (PCR > 35%) were seen four times per year for SPT (3-month intervals). This close recall was maintained until a PCR < 20% was established for three consecutive SPTs.
Data collection The following data were retrieved from the patients’ records: age at implant placement, gender, medications, smoking, implant location (according to the FDI scheme), implant length, number of implants, implant loss, time of crown placement, and observation period. All prosthesis-related technical complications, including implant and abutment fractures, screw loosening, retention loss, and fracture of the veneering ceramic, were documented. Each patient’s clinical examination was completed at annual intervals during prophylaxis or SPT, and the following parameters were assessed: • survival analysis of the implant and prosthetic restoration • technical complications • biologic complications (peri-implantitis).
22
PPD and BOP were assessed to the nearest mm using a periodontal probe (PCPUNC 15, Hu-Friedy) at four sites per implant. The deepest PPD of each implant was used as the diagnostic criterion for peri-implant mucositis and peri-implantitis. In cases of increased PPD (≥ 5 mm) and BOP, an IR (rectangular technique) was obtained to assess the radiographic bone loss to confirm the diagnosis of peri-implantitis. Bone loss was determined by a metric analysis of the IR. All IRs were obtained using the same x-ray device (Heliodent, Sirona Dental Systems) and digital sensor (Sidexis XG, Sirona Dental Systems) using the parallel technique. The data were analyzed using the associated computer program (Sidexis XG, Sirona Dental Systems) and a calibrated screen (SyncMaster 2443SW, Samsung Electronics). The distance between the implant shoulder and marginal bone level (MBL) was measured at the mesial and distal aspects of each implant. The MBL was defined as the most coronal location at which bone covered the implant surface. The site with the most pronounced bone loss was chosen to represent the implant. The threshold level for progressive bone loss was a bone level located at least 3.5 mm more apical, relative to the implant shoulder, compared with the bone level on the last available radiograph. Taking into account the anatomic magnification and distortion in the films, the linear dimensions of the images were calibrated. This calibration was achieved by setting the scale in the image to the known distance between the implant shoulder and the most apical point of the implant.24 Baseline radiographs (PT) after implant placement were used to ensure that the placement of the implant shoulder at a slightly subcrestal position (0.5 mm) conformed to the protocol and to determine the original bone level around the implant. All the radiographs were examined by the same calibrated operator (DZ), and all the clinical examinations were performed by a dentist (AL) who had not placed the implants. All the patients who met the inclusion criteria and underwent a final examination between 1 August and 31 December 2012 were included in the study.
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Table 1
Numbers of included and excluded subjects and the distribution of the exclusion categories
Total number of patients
33
Number of included subjects
27
Number of excluded subjects
6 No regular post-therapeutic therapy
Reasons for exclusion
Inadequate/missing radiographs
1
Other missing data (eg, medical history or periodontal status)
1
Case definition The survival and success of both the implant and the prosthetic reconstruction were the dependent variables of the study. Survival was defined as the implant or prosthetic reconstruction remaining in situ at the follow-up examination without exhibiting absolute failure (in situ criterion).1-3 Implant success was defined as the absence of technical or biologic complications (peri-implantitis) for the entire follow-up period. Peri-implantitis was defined according to previous reports25-28 as PPD ≥ 5 mm with BOP/suppuration and radiographic bone loss with a distance of at least 3.5 mm between the implant shoulder and bone level. The date of the first radiograph that exhibited bone loss ≥ 3.5 mm was used for the timedependent analysis of the event “peri-implantitis”. Prosthetic success was defined as the absence of technical complications (ie, the restoration did not require any intervention to maintain function during the entire follow-up period).1-3
Statistical analysis Data on the survival and success of the implants and prosthetic reconstructions were used for the statistical analysis. The implant/restoration was defined as the statistical unit. The survival/success time of a restoration/ implant was defined as the period between cementation and the last follow-up or, in cases of failure or clinical intervention, the appointment scheduled to address the failure/complication, as documented in the patient’s file. The time-dependent survival rates (in situ criterion) and the success rates of the implants (the absence of peri-
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4
implantitis) and prosthetic restorations (the absence of interventions) were calculated using a Kaplan-Meier analysis. Different observations in the same patient (several implants per patient) were dependent. This dependence was allowed by adjusting the variance estimations in a marginal model.29 The statistical analysis was performed using the “prodlim” function of the R software program (version 2.14.1, www.r-project.org). Due to the small sample sizes and a small number of events, only an overall statistical analysis was carried out and no stratification according to potential factors influencing the biologic and technical complications was performed.
RESULTS Patients Between 1 January 2002 and 30 October 2009, 33 partially edentulous patients with missing incisors or canines and indications for single-tooth replacement were treated with Ankylos implants. Twenty-seven of these patients (18 women and 9 men), with 42 implants, fulfilled all the inclusion criteria and had complete documentation available at the time of final data acquisition (Table 1). Five of the patients were part of a cohort examined in an earlier study.24 The reasons for tooth loss were as follows: 15 periodontal reasons, 12 endodontic failures, 9 caries lesions, and 6 teeth with extensive tooth fracture. The mean age of the patients at the time of implant insertion was 55.4 ± 12.9 years. A mean number of 1.6 ± 0.7 implants (a maximum of 3) were placed per patient. Thirty-nine maxillary implants were inserted to replace a maxillary incisor or canine,
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Table 2
Distribution (according to FDI notation) of the implants included in the study Number of implants in the maxilla = 39
Implants
2
6
8
11
11
1
13
12
11
21
22
23
43
42
41
31
32
33
1
0
0
0
0
2
Position Implants
Number of implants in the mandible = 3
Survival probability (%)
100
75
50
25
0 0
20
40 60 80 Time (months)
100
120
Fig 2 Abutment fracture leading to the complete loss of the restoration.
Fig 3 Survival probability (in-function) of the prosthetic restorations calculated using the Kaplan-Meier estimator.
and three implants replaced mandibular canines (Table 2). Fourteen patients, accounting for 22 implants, had a history of periodontal disease prior to implant placement and received SPT. During the observation period, none of these patients required additional active periodontal therapy. Furthermore, none of the remaining 13 patients without a history of periodontal disease (accounting for 20 implants) required active periodontal therapy. Five patients (18.5%), accounting for 10 implants, were smokers. All of the patients underwent a final clinical follow-up examination between 1 August and 31 December 2012. The mean follow-up period for the prosthetically restored implants was 79.8 ± 25.7 months (36 months to 10.8 years).
Survival rates of implants and prosthetic restorations
24
None of the 42 implants failed during the observation period, resulting in a cumulative survival rate of 100% after 7 years. One fractured zirconia abutment required replacement (Fig 2), (prosthetic survival rate, 97.6%; 95% confidence interval [CI], 0.930–1.000) after 7 years (Fig 3). None of the zirconia frameworks fractured during the observation period.
Success rates of prosthetic restorations A total of 11 clinical interventions were necessary to maintain the function of the superstructures (prosthetic success rate, 75.0%; 95% CI, 0.636–0.882 after 7 years)
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Table 3
Reasons for complete failures and complications of the superstructure
Type of failure
Number of complete failures
Abutment fracture
1
Total
1
Type of complication
Number of complications
Ceramic veneer fracture
5
Retention loss
4
Abutment screw loosening
2
Total
11
100 Success probability (%)
Success probability (%)
100
75
50
25
0
75
50
25
0 0
20
40 60 80 Time (months)
100
120
0
20
40 60 80 Time (months)
100
120
Fig 4 Success probability (absence of complications) of the prosthetic restorations calculated using the Kaplan-Meier estimator.
Fig 5 Success probability (absence of peri-implantitis) of the implants calculated using the Kaplan-Meier estimator.
(Fig 4). Fractures of the veneering ceramics (n = 5) and loss of retention (n = 4) were the most frequent technical complications (Table 3). None of the ceramic fractures required replacement of the restoration, three minor fractures were polished, and two fractures > 2 mm2 were repaired after removal of the crown. Crowns with a loss of retention were recemented using a temporary luting agent. Abutment screw loosening was detected in two zirconia abutments during the observation period. Owing to the temporary luting of the restorations, the abutment screws could be retightened after removal of the crowns.
Success rates of implants
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Peri-implant disease (implant-based) Of the 42 implants, two developed peri-implant disease (implant success rate, 92.9%; 95% CI, 0.840–1.000) during the 7-year observation period (Fig 5). The implant-based peri-implantitis rate for implants placed in nonsmoking patients was 3.1%. Of the 10 implants placed in patients who smoked, one showed clinical symptoms of peri-implantitis (10%). One case of peri-implantitis was diagnosed among the 17 implants placed in non-smoking patients with a history of periodontal disease (5.9%).
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14
peri-implantitis no peri-implantitis
Number of patients
12
1
10 8 6 4 2 0
1 2
2
11
10
perio treatment
no perio treatment
perio treatment
no perio treatment
smokers
nonsmokers
Fig 6 Distribution of patients with peri-implant disease according to the variables “smoking” and “history of periodontal treatment”.
Peri-implant disease (patient-based) Peri-implantitis was diagnosed in two (1 woman) patients (7.4%). One of the five smokers (20%) and one of the 22 nonsmokers (4.5%) experienced peri-implantitis. No peri-implantitis was diagnosed in a subgroup comprising the 10 nonsmoking patients without a history of periodontal disease. Among the three smokers with a history of periodontal disease, one patient developed clinical symptoms of peri-implantitis (Fig 6).
DISCUSSION The survival rate of the implants placed in this study was 100%, and the survival rate of the prosthetic restorations was 97.6% (95% CI, 0.930–1.000) after a mean follow-up of 7 years. These results are in accordance with a systematic review that analyzed the long-term results of single-tooth implants2 and revealed a 5-year survival rate for implant-supported single crowns of 97.2% (95% CI, 96.3–97.9%). None of the Y-TZP frameworks fractured. This finding is in accord with the results of other clinical studies evaluating implantbased anterior Y-TZP restorations over functional periods of 3 to 5 years.13,17
26
Based on the available systematic reviews,2-5 the most frequent technical complications associated with single-tooth implant restorations are loss of retention in cemented superstructures, loosening of the abutment screw, and fracture of the veneering ceramic. The most frequent technical complication in the present study was fracture of the veneering ceramic, with an incidence of 12% after 7 years. Other studies of implant-based zirconia crowns have demonstrated that fractures of the veneering material represent a relevant clinical problem. In a retrospective study, minor chipping of the veneering material of anterior implantbased all-ceramic crowns was detected in 2% of the restorations within the first year.17 In another prospective trial, one out of 64 anterior Y-TZP crowns required replacement due to extensive chipping of the veneering material within the first 3 years of service.13 Based on the findings of two systematic reviews,2,3 the prevalence of this technical complication ranged from 3.5% to 5% for single crowns within 5-year observation periods, with all-ceramic crowns demonstrating a higher complication rate. This result is in accord with the findings of the present study. Several systematic reviews have found a higher incidence of technical complications among toothsupported zirconia restorations compared with metalceramic restorations.30-32 This finding is consistent with the results of the present study; the 7-year data demonstrate that chipping is the major problem associated with zirconia-based restorations. During this study period some recommendations for optimizing the fabrication process for zirconia-based FPDs were published, eg, a modification of the firing protocol.33 This modification can be recommended because it might reduce the chipping rate. However, these modifications were not applied in the present study. In the present study, 4 of 42 crowns (9.5%) required recementation. The prosthetic success rates for ISCs cemented with temporary cement reported by other studies ranged between 72% and 84% for follow-ups of 2 to 5 years.34-36 The high incidence of recementations for the crowns luted with temporary cement in the present study is in good accordance with other studies.
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In two systematic reviews, the incidence of screw loosening in single crowns was reported to be as high as 6% within 3 years5 and 8.8% within 5 years.2 In the present study, loosening of the abutment screw occurred in only 2 of the 42 single-crown restorations, resulting in a complication rate of 4.8% after 7 years. A possible explanation for this relatively low rate may be the Morse taper connection of the implant system used in this study. Low rates of screw loosening have also been reported in other studies that used implant systems with a Morse taper connection.37,38 Peri-implantitis is a serious biologic complication that, if untreated, can result in implant loss.39,40 Based on previously published results, peri-implantitis appears to occur in approximately 10% of all implants and 20% of all patients during a period of 5 to 10 years after implant placement.40 An implant-based time-to-event analysis revealed a success rate of 92.9% after 7 years for anterior implants with zirconia abutments and all-ceramic crowns in the present study. The implant-based peri-implantitis rate of 4.8% and the patient-based peri-implantitis rate of 7.4% are in the lower range of the expected disease rates.2,40 These relatively low prevalence rates are possibly due to the compliance of all the included patients, who received prophylaxis or SPT at least annually. A positive effect of compliance with professional hygiene procedures (prophylaxis or SPT) on a reduced risk of periimplantitis has been demonstrated in other clinical trials.24,41,42 Due to the relatively small sample size and the limited number of events, a statistical evaluation of potential risk factors (smoking status and history of periodontal disease) was not possible. Another important aspect of the interpretation of this study is the definition of the endpoints. Commonly applied success criteria (intervention-free survival) for the survival of implants and superstructures (in situ criteria)1-3 were selected for the present study. Nevertheless, studies published to date show great heterogeneity in the definition of implant-related biologic complications (peri-implantitis).1,39,40 The threshold
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level for progressive bone loss is a particularly important factor for the definition of peri-implantitis. In the present study, the threshold level for progressive bone loss was defined as a distance of at least 3.5 mm between the implant shoulder and the bone level. Other clinical studies using different implant systems have applied a comparable threshold level of a distance of > 3 mm between the implant-abutment connection and the bone level.24-28 Nevertheless, this distance should be noted to represent a high threshold of radiographic bone loss, which indicates a pronounced progression of disease. Because the treatment of periimplantitis should be initiated at an early stage of the progression of bone loss, lower threshold levels should be used for diagnostic purposes in daily clinical practice.40,42 The present study is limited by its comparatively small sample size and its retrospective nature. However, this limitation is partially compensated for by the application of a strict case definition, which included only patients with single-tooth restorations placed in the anterior area using the same implant type and identical superstructure materials, including a standardized cementation protocol. Moreover, this practice-based study examined both biologic and technical complications at the implant and superstructure levels, with a follow-up of more than 5 years. Because this type of result is rare, this study makes a valuable contribution to the evaluation of the prognosis of implantbased restorations placed under the typical conditions of a private practice.
CONCLUSION Considering the limitations of the present study, the following conclusions can be drawn. • Zirconia abutments with all-ceramic crowns offer a reliable treatment option under the typical conditions of a private practice. • Clinical interventions to maintain the function of the restorations are required due to technical complications. Fractures of the veneering ceramics represent the most frequent complication.
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•
Temporary luting of the prosthetic restorations carries a risk of the loss of retention but offers the advantage of the non-destructive removal of the restoration in case of technical complications (retightening of the abutment screw or repair of a ceramic fracture). For patients attending a professional maintenance program at least annually, peri-implantitis should be expected in 4.1% of the implants and 7.4% of the patients after a mean observation period of 7 years. Further clinical investigations with larger samples and improved data (eg, randomized clinical trials) are necessary to evaluate restoration- and patientrelated risk factors for biologic and technical complications.
•
•
As the present study confirms the results of other studies on the same topics, the use of zirconia abutments and all-ceramic crowns for single tooth replacements in the anterior area can be recommended for general application in esthetically demanding situations.
ACKNOWLEDGMENT The authors thank Katrin Rinke for the critical reading and language editing of the manuscript.
CONFLICT OF INTEREST Sven Rinke has received lecture fees from Dentsply Implants, Mannheim, Germany, and DeguDent, Hanau, Germany.
REFERENCES 1. Albrektsson T, Donos N, Working Group 1. Implant survival and complications. The Third EAO Consensus Conference 2012. Clin Oral Implants Res 2012;23:63–65. 2. Jung RE, Zembic A, Pjetursson BE, Zwahlen M, Thoma DS. Systematic review of the survival rate and the incidence of biological, technical, and aesthetic complications of single crowns on implants reported in longitudinal studies with a mean follow-up of 5 years. Clin Oral Implants Res 2012;23:2–21. 3. Pjetursson BE, Zwahlen M, Lang NP. Quality of reporting of clinical studies to assess and compare performance of implant-supported restorations. J Clin Periodontol 2012;39:139–159. 4. Chaar MS, Att W, Strub JR. Prosthetic Outcome of cement-retained implantsupported fixed dental restorations: a systematic review. J Oral Rehabil 2011;38:697–711.
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5. Theoharidou A, Petridis HP, Tzannas K, Garefis P. Abutment screw loosening in single-implant restorations: a systematic review. Int J Oral Maxillofac Implants 2008;23:681–690. 6. Jung RE, Holderegger C, Sailer I, Khraisat A, Suter A, Hämmerle CH. The effect of all-ceramic and porcelain-fused-to-metal restorations on marginal periimplant soft tissue color: a randomized controlled clinical trial. Int J Periodontics Restorative Dent 2008;28:357–365. 7. Bressan E, Paniz G, Lops D, Corazza B, Romeo E, Favero G. Influence of abutment material on the gingival color of implant-supported all-ceramic restorations: A prospective multicenter study. Clin Oral Implants Res 2011;22:631–637. 8. Sailer I, Zembic A, Jung RE, Hämmerle CH, Mattiola A. Single-tooth implant reconstructions: esthetic factors influencing the decision between titanium and zirconia abutments in anterior regions. Eur J Esthet Dent 2007;2:296–310. 9. van Brakel R, Noordmans HJ, Frenken J, de Roode R, de Wit GC, Cune MS. The effect of zirconia and titanium implant abutments on light reflection of the supporting soft tissues. Clin Oral Implants Res 2011;22:1172–1178. 10. Sailer I, Philipp A, Zembic A, Pjetursson BE, Hämmerle CH, Zwahlen M. A Systematic review of the performance of ceramic and metal implant abutments supporting fixed implant reconstructions. Clin Oral Implants Res 2009;20:4–31. 11. Guess PC, Att W, Strub JR. Zirconia in fixed implant prosthodontics. Clin Implant Dent Relat Res 2010;14:633–645. 12. Nakamura K, Kanno T, Milleding P, Ortengren U. Zirconia as a dental implant abutment material: a systematic review. Int J Prosthodont 2010;23:299–309. 13. Hosseini M, Worsaae N, Schiødt M, Gotfredsen K. A 3-year prospective study of implant-supported, single-tooth restorations of all-ceramic and metalceramic materials in patients with tooth agenesis. Clin Oral Implants Res 2013;24:1078–1087. 14. Bressan E, Paniz G, Lops D, Corazza B, Romeo E, Favero G. Influence of abutment material on the gingival color of implant-supported all-ceramic restorations: a prospective multicenter study. Clin Oral Implants Res 2011;22:631–637. 15. van Brakel R, Meijer GJ, Verhoeven JW, Jansen J, de Putter C, Cune MS. Soft tissue response to zirconia and titanium implant abutments: an in vivo withinsubject comparison. J Clin Periodontol 2012;39:995–1001. 16. Bidra AS, Rungruanganunt P. Clinical outcomes of implant abutments in the anterior region: a systematic review. J Esthet Restor Dent 2013;25:159–176. 17. Ekfeldt A, Furst B, Carlsson GE. Zirconia abutments for single-tooth implant restorations: a retrospective and clinical follow-up study. Clin Oral Implants Res 2011;22:1308–1314. 18. Vanlioglu BA, Özkan Y, Evren B, Özkan YK. Experimental custom-made zirconia abutments for narrow implants in esthetically demanding regions: a 5-year follow-up. Int J Oral Maxillofac Implants 2012;27:1239–1242. 19. Kutkut A, Abu-Hammad O, Mitchell R. Esthetic considerations for reconstructing implant emergence profile using titanium and zirconia custom implant abutments: fifty case series report [Epub ahead of print 31 Oct 2013]. J Oral Implantol. 20. Armitage GC. Development of a classification system for periodontal diseases and conditions. Ann Periodontol 1999;4:1–6. 21. von Elm E, Altman DG, Egger M, Pocock SJ, Gøtzsche PC, Vandenbroucke JP; STROBE Initiative. The Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statement: guidelines for reporting observational studies. J Clin Epidemiol 2008;61:344–349. 22. Ainamo J, Bay I. Problems and proposals for recording gingivitis and plaque. Int Dent J 1975;25:229–235. 23. O’Leary TJ, Drake RB, Naylor JE. The plaque control record. J Periodontol 1972;43:38. 24. Rinke S, Ohl S, Ziebolz D, Lange K, Eickholz P. Prevalence of periimplant disease in partially edentulous patients: a practice-based cross-sectional study. Clin Oral Implants Res 2011;22:826–833. 25. Karoussis K, Müller S, Salvi GE, Heitz-Mayfield LJ, Brägger U, Lang NP. Association between periodontal and peri-implant conditions: a 10-year prospective study. Clin Oral Implants Res 2004;15:1–7.
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26. Fransson C, Lekholm U, Jemt T, Berglundh T. Prevalence of subjects with progressive bone loss at implants. Clin Oral Implants Res 2005;16:440–446. 27. Roos-Jansaker AM, Lindahl C, Renvert H, Renvert S. Nine- to fourteen-year follow-up of implant treatment. Part II: presence of peri-implant lesions. J Clin Periodontol 2006;33:290–295. 28. Roos-Jansaker AM, Renvert H, Lindahl C, Renvert S. Nine- to fourteen-year follow-up of implant treatment. Part III: factors associated with peri-implant lesions. J Clin Periodontol 2006;33:296–301. 29. Gerds TA, Qvist V, Strub JR, Pipper CB, Scheike TH, Keiding N. Failure time analysis. In: Lesaffre E, Feine J, LeRoux B (eds). Statistical and Methodological Aspects of Oral Health Research. Chichester: John Wiley and Sons, 2009:69–85. 30. Bachhav VC, Aras MA. Zirconia-based fixed partial dentures: a clinical review. Quintessence Int 2011;42:173–182. 31. Schley JS, Heussen N, Reich S, Fischer J, Haselhuhn K, Wolfart S. Survival probability of zirconia-based fixed dental prostheses up to 5 yr: a systematic review of the literature. Eur J Oral Sci 2010;118:443–450. 32. Raigrodski AJ, Hillstead MB, Meng GK, Chung KH. Survival and complications of zirconia-based fixed dental prostheses: A systematic review. J Prosthet Dent 2012;107:170–177. 33. Rinke S, Schäfer S, Lange K, Gersdorff N, Roediger M. Practice-based clinical evaluation of metal-ceramic and zirconia molar crowns: 3-year results. J Oral Rehabil 2013;40:228–237. 34. Krennmair G, Schmidinger S, Waldenberger O. Single-tooth replacement with the Frialit-2 system: a retrospective clinical analysis of 146 implants. Int J Oral Maxillofac Implants 2002;17:78–85.
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35. Simon RL. Single implant-supported molar and premolar crowns: a ten-year retrospective clinical report. J Prosthet Dent 2003;90:517–521. 36. Schwarz S, Schröder C, Corcodel N, Hassel AJ, Rammelsberg P. Retrospective comparison of semipermanent and permanent cementation of implantsupported single crowns and FDPs with regard to the incidence of survival and complications. Clin Implant Dent Relat Res 2012;14:151–158. 37. Romanos GE, Nentwig GH. Single molar replacement with a progressive thread design implant system: a retrospective clinical report. Int J Oral Maxillofac Implants 2000;15:831–836. 38. Mangano C, Mangano F, Piattelli A, Iezzi G, Mangano A, La Colla L. Prospective clinical evaluation of 1920 Morse taper connection implants: results after 4 years of functional loading. Clin Oral Implants Res 2009;20:254–261. 39. Klinge B, Meyle J. Peri-implant tissue destruction. The Third EAO Consensus Conference 2012. Clin Oral Implants Res 2012;23:108–110. 40. Mombelli A, Müller N, Cionca N. The epidemiology of peri-implantitis. Clin Oral Implants Res 2012;23:67–76. 41. Costa F, Takenaka-Martinez S, Cota L, Ferreira S, Silva G, Costa J. Peri-implant disease in subjects with and without preventive maintenance: a 5-year follow-up. J Clin Periodontol 2012;39:173–181. 42. Pjetursson BE, Helbling C, Weber HP, et al. Peri-implantitis susceptibility as it relates to periodontal therapy and supportive care. Clin Oral Implants Res 2012;23:888–894.
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RESTORATIVE DENTISTRY
Sven Rinke
Practice-based clinical evaluation of zirconia abutments for anterior single-tooth restorations Sven Rinke, Priv Doz Dr med dent, MSc, MSc1/Anja Lattke, Dr med dent1/Peter Eickholz, Prof Dr med dent2/Katharina Kramer, Dr rer nat3/Dirk Ziebolz, Priv Doz Dr med dent, MSc 4 Objective: This study aimed to determine the survival rate and prevalence of biologic and technical complications associated with single-tooth implants with all-ceramic abutments in the anterior region. Method and Materials: A total of 33 patients were restored with 50 anterior implants and temporarily luted all-ceramic crowns on prefabricated zirconia abutments. All of the patients subsequently received annual supportive maintenance; 27 patients (18 women, 22–74 years) with 42 implants participated in the final maintenance visit and were included in the study (follow-up 78.1 ± 27.0 months). The time-dependent survival rate (Kaplan-Meier) and the frequency of prosthetic complications (abutment fracture [AF], screw loosening [SL], fracture of veneering ceramics [VF], retention loss [RL]) and biologic complications (peri-implantitis) were calculated to determine the success rates. Results: No implant loss (implant-related survival rate 100%) but one
abutment fracture occurred throughout the entire observation period; therefore, the survival rate of the superstructures (in situ criterion) was 97.6% (95% confidence interval [CI] 0.930– 1.000) after 7 years. Eleven restorations were affected by prosthetic complications: RL (n = 4), VF (n = 5), and SL (n = 2). Peri-implantitis was diagnosed for two implants (probing depth > 5 mm, bleeding on probing [BOP]/suppuration, and bone loss > 3 mm) (implant-related peri-implantitis rate 4.8%). No restoration required replacement due to complications. The success rate (event-free restoration) was 75.9% (95% CI 0.636– 0.882) after 7 years. Conclusions: Considering the calculated survival rate, the application of all-ceramic zirconia implant abutments in the anterior region can be recommended as a reliable therapy in private practice. Fractures of veneering ceramics were the most common prosthetic complication. (Quintessence Int 2015;46:19–29; doi: 10.3290/j.qi.a32818)
Key words: cement, ceramics, clinical studies, peri-implant infection, success, survival
Implant-supported single crowns (ISCs) are considered a reliable and safe treatment modality with high survival rates in long-term clinical studies.1-3 A recently published systematic review reported a 10-year survival 1
Dentist, Private Practice, Hanau, Germany.
2
Professor and Head, Department of Periodontology, Center for Dental, Oral, and Maxillofacial Medicine, Johann Wolfgang Goethe-University, Frankfurt/Main, Germany.
3
Senior Researcher, Department of Medical Statistics, Georg-August-University, Goettingen, Germany.
4
Associate Professor, Department of Operative Dentistry, Preventive Dentistry and Periodontology, Georg-August-University, Göttingen, Germany.
Correspondence: Priv Doz Dr Sven Rinke, Geleitstr. 68, 63456 Hanau, Germany. Email: [email protected]
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rate of single-tooth implants of 96.3%, whereas the reported survival rate of prosthetic restorations was 89.8%.1 Despite the high survival rates of implants and crowns, clinicians must be aware that technical, biologic, and esthetic complications are likely to occur. Technical complications (mainly screw loosening) have been documented to have an incidence of 8.8% within the first 5 years of clinical service, and esthetic complications reached a cumulative incidence of 7.1% for the same period.2,4-6 Published data on the prevalence of biologic complications (peri-implantitis) still show great variations in incidence and prevalence rates; therefore,
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more detailed information, especially derived from prolonged observation, is required. Because implantsupported single-tooth restorations have primarily been examined with regard to their use in the anterior region, the prevention of esthetic complications is critical.2 In addition to the correct implant positioning and proper soft tissue management, the selection of adequate materials and designs for prosthetic restorations influences the esthetic outcome significantly.6,7 For the last several decades, titanium abutments have been the standard of care for implant-supported restorations. Unfortunately, the blue-grayish shimmer exhibited by these abutments, in combination with thin overlying mucosal tissue, can negatively affect the esthetic outcome.8,9 For this reason, yttria partially-stabilized zirconia (Y-TZP) is a promising alternative material for the fabrication of abutments and ISCs; this material combines high strength and toughness with excellent biocompatibility and tooth-like shading.10-12 A limited number of clinical trials have investigated the esthetic benefits resulting from the use of Y-TZP as an abutment material. In two clinical studies using visual inspection, the use of all-ceramic abutments led to less gingival discoloration of the buccal mucosa compared with titanium abutments.6,13 In a prospective multicenter study using a spectrometric analysis, significantly higher color differences in the peri-implant soft tissues were detected for titanium abutments compared with zirconia abutments.14 Another clinical study concluded that the difference in light reflection from the soft tissue covering titanium or Y-TZP abutments is not perceptible if the mucosa exceeds 2 mm in thickness.15 Based on these results, the use of Y-TZP abutments appears to be esthetically beneficial, especially in clinical situations involving a thin overlaying buccal soft tissue.8,11 Regardless of the potential esthetic benefits, the use of Y-TZP abutments can only be recommended if their clinical performance is comparable with that documented for titanium abutments.2,10,12 Three systematic reviews have evaluated the shortterm clinical performance of Y-TZP abutments for single crowns. Based on an evaluation of three clinical trials involving 104 abutments and a mean follow-up
20
period of 3.7 years, the clinical performance of Y-TZP abutments was suggested to be comparable with that of titanium abutments.10,12,16 Subsequently published clinical trials of Y-TZP abutments for anterior ISCs reported fracture rates of 0 to 1% for observation periods of 3 to 5 years.13,17-19 There are no published studies examining the clinical performance of Y-TZP abutments used for anterior ISCs with mean observation periods of more than 5 years and including detailed information on potential technical and biologic problems (peri-implantitis). The aim of this practice-based retrospective clinical trial was to evaluate the long-term clinical performance (a mean observation period > 5 years) of Y-TZP abutments supporting anterior zirconia-based ISCs.
METHOD AND MATERIALS Patients This retrospective study evaluated partially edentulous patients who were restored with single-tooth implants, zirconia abutments, and temporarily luted all-ceramic crowns in the anterior region in a private dental office in Germany between 1 January 2002 and 30 October 2009. The following inclusion criteria were applied: • single-tooth implants of the same type in the anterior region (canine to canine) of the maxilla or mandible (Ankylos, Dentsply Implants) • zirconia abutments (Cercon Balance, Dentsply Implants) and zirconia-based manually veneered crowns (Cercon, DeguDent) luted with a provisional cement (TempBond, Kerr Hawe) • prophylaxis or supportive periodontal therapy (SPT), at least annually, including a periodontal examination (probing pocket depth [PPD] and bleeding on probing [BOP]), at the same dental office where the implants were inserted • complete radiographic documentation with panoramic radiographs (PT) and intraoral radiographs (IR) • complete medical history, including smoking • complete documentation of superstructure-related complications or failures.
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Fig 1a Clinical situation of a single tooth replacement 3 weeks after stage-two surgery.
Fig 1b Prefabricated zirconia abutment (Ankylos Cercon Balance, Dentsply Implants).
Fig 1c
Fig 1d Clinical situation after placement of the zirconia-based crowns.
• • • •
Try-in of the customized zirconia abutment.
The following exclusion criteria were applied: aggressive periodontitis20 no prophylaxis or periodontal therapy prior to implant therapy inadequate radiographs other missing data.
The study was approved by the Ethics Committee of the Medical Faculty of Georg-August University, Göttingen, Germany (application no. 3/2/10). The recommendations of Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) were followed.21
Treatment course Treatment was completed in a single private practice in Germany by two dentists with several years of experience and specific training in oral implant therapy. Implant placement, stage-two surgery, and prosthetic
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treatment were completed according to the manufacturers’ standard protocols. Prefabricated Y-TZP abutments (Cercon Balance, Dentsply Implants) were customized using water-cooled diamond instruments (Figs 1a to 1c). Zirconia crown frameworks were fabricated using a computer-aided design/computerassisted manufacture (CAD/CAM) process (Cercon, DeguDent) and were veneered manually using a suitable ceramic material (Cercon ceram kiss, DeguDent) (Fig 1d). Following the insertion of the prosthetic restoration with a temporary luting agent (TempBond, Kerr Hawe), the patients were instructed in homebased dental hygiene. They were then seen for postimplant maintenance every 3 to 12 months. Prophylaxis and SPT were performed in patients with and without a history of periodontal disease, respectively. Each patient at each appointment received treatment encompassing the following elements: assessments of the gingival bleeding index (GBI)22 and plaque control
21
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record (PCR),23 re-instruction and re-motivation for effective individual plaque control, professional tooth cleaning, polishing of all teeth using rubber cups and polishing paste, and application of a fluoride gel. Once (in cases of prophylaxis) or twice per year (in cases of SPT), dental status and PPD measurements were obtained at four sites per tooth/implant. Sites exhibiting a PPD of 4 mm and BOP, as well as sites with PPD ≥ 5 mm, were scaled subgingivally using ultrasonic and hand instruments. In cases of peri-implant mucositis, the scaling around implants was performed with a special ultrasonic tip (KaVo SONICflex implant, KaVo Dental), followed by manual instrumentation and the subgingival application of a chlorhexidine gel (Corsodyl 1% Dental Gel, GlaxoSmithKline).24 Prophylaxis/SPT was administered to most patients at 3-month intervals during the first year after implant insertion and at 6-month intervals thereafter. Patients exhibiting ineffective plaque control during the posttherapeutic phase (PCR > 35%) were seen four times per year for SPT (3-month intervals). This close recall was maintained until a PCR < 20% was established for three consecutive SPTs.
Data collection The following data were retrieved from the patients’ records: age at implant placement, gender, medications, smoking, implant location (according to the FDI scheme), implant length, number of implants, implant loss, time of crown placement, and observation period. All prosthesis-related technical complications, including implant and abutment fractures, screw loosening, retention loss, and fracture of the veneering ceramic, were documented. Each patient’s clinical examination was completed at annual intervals during prophylaxis or SPT, and the following parameters were assessed: • survival analysis of the implant and prosthetic restoration • technical complications • biologic complications (peri-implantitis).
22
PPD and BOP were assessed to the nearest mm using a periodontal probe (PCPUNC 15, Hu-Friedy) at four sites per implant. The deepest PPD of each implant was used as the diagnostic criterion for peri-implant mucositis and peri-implantitis. In cases of increased PPD (≥ 5 mm) and BOP, an IR (rectangular technique) was obtained to assess the radiographic bone loss to confirm the diagnosis of peri-implantitis. Bone loss was determined by a metric analysis of the IR. All IRs were obtained using the same x-ray device (Heliodent, Sirona Dental Systems) and digital sensor (Sidexis XG, Sirona Dental Systems) using the parallel technique. The data were analyzed using the associated computer program (Sidexis XG, Sirona Dental Systems) and a calibrated screen (SyncMaster 2443SW, Samsung Electronics). The distance between the implant shoulder and marginal bone level (MBL) was measured at the mesial and distal aspects of each implant. The MBL was defined as the most coronal location at which bone covered the implant surface. The site with the most pronounced bone loss was chosen to represent the implant. The threshold level for progressive bone loss was a bone level located at least 3.5 mm more apical, relative to the implant shoulder, compared with the bone level on the last available radiograph. Taking into account the anatomic magnification and distortion in the films, the linear dimensions of the images were calibrated. This calibration was achieved by setting the scale in the image to the known distance between the implant shoulder and the most apical point of the implant.24 Baseline radiographs (PT) after implant placement were used to ensure that the placement of the implant shoulder at a slightly subcrestal position (0.5 mm) conformed to the protocol and to determine the original bone level around the implant. All the radiographs were examined by the same calibrated operator (DZ), and all the clinical examinations were performed by a dentist (AL) who had not placed the implants. All the patients who met the inclusion criteria and underwent a final examination between 1 August and 31 December 2012 were included in the study.
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Table 1
Numbers of included and excluded subjects and the distribution of the exclusion categories
Total number of patients
33
Number of included subjects
27
Number of excluded subjects
6 No regular post-therapeutic therapy
Reasons for exclusion
Inadequate/missing radiographs
1
Other missing data (eg, medical history or periodontal status)
1
Case definition The survival and success of both the implant and the prosthetic reconstruction were the dependent variables of the study. Survival was defined as the implant or prosthetic reconstruction remaining in situ at the follow-up examination without exhibiting absolute failure (in situ criterion).1-3 Implant success was defined as the absence of technical or biologic complications (peri-implantitis) for the entire follow-up period. Peri-implantitis was defined according to previous reports25-28 as PPD ≥ 5 mm with BOP/suppuration and radiographic bone loss with a distance of at least 3.5 mm between the implant shoulder and bone level. The date of the first radiograph that exhibited bone loss ≥ 3.5 mm was used for the timedependent analysis of the event “peri-implantitis”. Prosthetic success was defined as the absence of technical complications (ie, the restoration did not require any intervention to maintain function during the entire follow-up period).1-3
Statistical analysis Data on the survival and success of the implants and prosthetic reconstructions were used for the statistical analysis. The implant/restoration was defined as the statistical unit. The survival/success time of a restoration/ implant was defined as the period between cementation and the last follow-up or, in cases of failure or clinical intervention, the appointment scheduled to address the failure/complication, as documented in the patient’s file. The time-dependent survival rates (in situ criterion) and the success rates of the implants (the absence of peri-
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4
implantitis) and prosthetic restorations (the absence of interventions) were calculated using a Kaplan-Meier analysis. Different observations in the same patient (several implants per patient) were dependent. This dependence was allowed by adjusting the variance estimations in a marginal model.29 The statistical analysis was performed using the “prodlim” function of the R software program (version 2.14.1, www.r-project.org). Due to the small sample sizes and a small number of events, only an overall statistical analysis was carried out and no stratification according to potential factors influencing the biologic and technical complications was performed.
RESULTS Patients Between 1 January 2002 and 30 October 2009, 33 partially edentulous patients with missing incisors or canines and indications for single-tooth replacement were treated with Ankylos implants. Twenty-seven of these patients (18 women and 9 men), with 42 implants, fulfilled all the inclusion criteria and had complete documentation available at the time of final data acquisition (Table 1). Five of the patients were part of a cohort examined in an earlier study.24 The reasons for tooth loss were as follows: 15 periodontal reasons, 12 endodontic failures, 9 caries lesions, and 6 teeth with extensive tooth fracture. The mean age of the patients at the time of implant insertion was 55.4 ± 12.9 years. A mean number of 1.6 ± 0.7 implants (a maximum of 3) were placed per patient. Thirty-nine maxillary implants were inserted to replace a maxillary incisor or canine,
23
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Table 2
Distribution (according to FDI notation) of the implants included in the study Number of implants in the maxilla = 39
Implants
2
6
8
11
11
1
13
12
11
21
22
23
43
42
41
31
32
33
1
0
0
0
0
2
Position Implants
Number of implants in the mandible = 3
Survival probability (%)
100
75
50
25
0 0
20
40 60 80 Time (months)
100
120
Fig 2 Abutment fracture leading to the complete loss of the restoration.
Fig 3 Survival probability (in-function) of the prosthetic restorations calculated using the Kaplan-Meier estimator.
and three implants replaced mandibular canines (Table 2). Fourteen patients, accounting for 22 implants, had a history of periodontal disease prior to implant placement and received SPT. During the observation period, none of these patients required additional active periodontal therapy. Furthermore, none of the remaining 13 patients without a history of periodontal disease (accounting for 20 implants) required active periodontal therapy. Five patients (18.5%), accounting for 10 implants, were smokers. All of the patients underwent a final clinical follow-up examination between 1 August and 31 December 2012. The mean follow-up period for the prosthetically restored implants was 79.8 ± 25.7 months (36 months to 10.8 years).
Survival rates of implants and prosthetic restorations
24
None of the 42 implants failed during the observation period, resulting in a cumulative survival rate of 100% after 7 years. One fractured zirconia abutment required replacement (Fig 2), (prosthetic survival rate, 97.6%; 95% confidence interval [CI], 0.930–1.000) after 7 years (Fig 3). None of the zirconia frameworks fractured during the observation period.
Success rates of prosthetic restorations A total of 11 clinical interventions were necessary to maintain the function of the superstructures (prosthetic success rate, 75.0%; 95% CI, 0.636–0.882 after 7 years)
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Table 3
Reasons for complete failures and complications of the superstructure
Type of failure
Number of complete failures
Abutment fracture
1
Total
1
Type of complication
Number of complications
Ceramic veneer fracture
5
Retention loss
4
Abutment screw loosening
2
Total
11
100 Success probability (%)
Success probability (%)
100
75
50
25
0
75
50
25
0 0
20
40 60 80 Time (months)
100
120
0
20
40 60 80 Time (months)
100
120
Fig 4 Success probability (absence of complications) of the prosthetic restorations calculated using the Kaplan-Meier estimator.
Fig 5 Success probability (absence of peri-implantitis) of the implants calculated using the Kaplan-Meier estimator.
(Fig 4). Fractures of the veneering ceramics (n = 5) and loss of retention (n = 4) were the most frequent technical complications (Table 3). None of the ceramic fractures required replacement of the restoration, three minor fractures were polished, and two fractures > 2 mm2 were repaired after removal of the crown. Crowns with a loss of retention were recemented using a temporary luting agent. Abutment screw loosening was detected in two zirconia abutments during the observation period. Owing to the temporary luting of the restorations, the abutment screws could be retightened after removal of the crowns.
Success rates of implants
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Peri-implant disease (implant-based) Of the 42 implants, two developed peri-implant disease (implant success rate, 92.9%; 95% CI, 0.840–1.000) during the 7-year observation period (Fig 5). The implant-based peri-implantitis rate for implants placed in nonsmoking patients was 3.1%. Of the 10 implants placed in patients who smoked, one showed clinical symptoms of peri-implantitis (10%). One case of peri-implantitis was diagnosed among the 17 implants placed in non-smoking patients with a history of periodontal disease (5.9%).
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14
peri-implantitis no peri-implantitis
Number of patients
12
1
10 8 6 4 2 0
1 2
2
11
10
perio treatment
no perio treatment
perio treatment
no perio treatment
smokers
nonsmokers
Fig 6 Distribution of patients with peri-implant disease according to the variables “smoking” and “history of periodontal treatment”.
Peri-implant disease (patient-based) Peri-implantitis was diagnosed in two (1 woman) patients (7.4%). One of the five smokers (20%) and one of the 22 nonsmokers (4.5%) experienced peri-implantitis. No peri-implantitis was diagnosed in a subgroup comprising the 10 nonsmoking patients without a history of periodontal disease. Among the three smokers with a history of periodontal disease, one patient developed clinical symptoms of peri-implantitis (Fig 6).
DISCUSSION The survival rate of the implants placed in this study was 100%, and the survival rate of the prosthetic restorations was 97.6% (95% CI, 0.930–1.000) after a mean follow-up of 7 years. These results are in accordance with a systematic review that analyzed the long-term results of single-tooth implants2 and revealed a 5-year survival rate for implant-supported single crowns of 97.2% (95% CI, 96.3–97.9%). None of the Y-TZP frameworks fractured. This finding is in accord with the results of other clinical studies evaluating implantbased anterior Y-TZP restorations over functional periods of 3 to 5 years.13,17
26
Based on the available systematic reviews,2-5 the most frequent technical complications associated with single-tooth implant restorations are loss of retention in cemented superstructures, loosening of the abutment screw, and fracture of the veneering ceramic. The most frequent technical complication in the present study was fracture of the veneering ceramic, with an incidence of 12% after 7 years. Other studies of implant-based zirconia crowns have demonstrated that fractures of the veneering material represent a relevant clinical problem. In a retrospective study, minor chipping of the veneering material of anterior implantbased all-ceramic crowns was detected in 2% of the restorations within the first year.17 In another prospective trial, one out of 64 anterior Y-TZP crowns required replacement due to extensive chipping of the veneering material within the first 3 years of service.13 Based on the findings of two systematic reviews,2,3 the prevalence of this technical complication ranged from 3.5% to 5% for single crowns within 5-year observation periods, with all-ceramic crowns demonstrating a higher complication rate. This result is in accord with the findings of the present study. Several systematic reviews have found a higher incidence of technical complications among toothsupported zirconia restorations compared with metalceramic restorations.30-32 This finding is consistent with the results of the present study; the 7-year data demonstrate that chipping is the major problem associated with zirconia-based restorations. During this study period some recommendations for optimizing the fabrication process for zirconia-based FPDs were published, eg, a modification of the firing protocol.33 This modification can be recommended because it might reduce the chipping rate. However, these modifications were not applied in the present study. In the present study, 4 of 42 crowns (9.5%) required recementation. The prosthetic success rates for ISCs cemented with temporary cement reported by other studies ranged between 72% and 84% for follow-ups of 2 to 5 years.34-36 The high incidence of recementations for the crowns luted with temporary cement in the present study is in good accordance with other studies.
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In two systematic reviews, the incidence of screw loosening in single crowns was reported to be as high as 6% within 3 years5 and 8.8% within 5 years.2 In the present study, loosening of the abutment screw occurred in only 2 of the 42 single-crown restorations, resulting in a complication rate of 4.8% after 7 years. A possible explanation for this relatively low rate may be the Morse taper connection of the implant system used in this study. Low rates of screw loosening have also been reported in other studies that used implant systems with a Morse taper connection.37,38 Peri-implantitis is a serious biologic complication that, if untreated, can result in implant loss.39,40 Based on previously published results, peri-implantitis appears to occur in approximately 10% of all implants and 20% of all patients during a period of 5 to 10 years after implant placement.40 An implant-based time-to-event analysis revealed a success rate of 92.9% after 7 years for anterior implants with zirconia abutments and all-ceramic crowns in the present study. The implant-based peri-implantitis rate of 4.8% and the patient-based peri-implantitis rate of 7.4% are in the lower range of the expected disease rates.2,40 These relatively low prevalence rates are possibly due to the compliance of all the included patients, who received prophylaxis or SPT at least annually. A positive effect of compliance with professional hygiene procedures (prophylaxis or SPT) on a reduced risk of periimplantitis has been demonstrated in other clinical trials.24,41,42 Due to the relatively small sample size and the limited number of events, a statistical evaluation of potential risk factors (smoking status and history of periodontal disease) was not possible. Another important aspect of the interpretation of this study is the definition of the endpoints. Commonly applied success criteria (intervention-free survival) for the survival of implants and superstructures (in situ criteria)1-3 were selected for the present study. Nevertheless, studies published to date show great heterogeneity in the definition of implant-related biologic complications (peri-implantitis).1,39,40 The threshold
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level for progressive bone loss is a particularly important factor for the definition of peri-implantitis. In the present study, the threshold level for progressive bone loss was defined as a distance of at least 3.5 mm between the implant shoulder and the bone level. Other clinical studies using different implant systems have applied a comparable threshold level of a distance of > 3 mm between the implant-abutment connection and the bone level.24-28 Nevertheless, this distance should be noted to represent a high threshold of radiographic bone loss, which indicates a pronounced progression of disease. Because the treatment of periimplantitis should be initiated at an early stage of the progression of bone loss, lower threshold levels should be used for diagnostic purposes in daily clinical practice.40,42 The present study is limited by its comparatively small sample size and its retrospective nature. However, this limitation is partially compensated for by the application of a strict case definition, which included only patients with single-tooth restorations placed in the anterior area using the same implant type and identical superstructure materials, including a standardized cementation protocol. Moreover, this practice-based study examined both biologic and technical complications at the implant and superstructure levels, with a follow-up of more than 5 years. Because this type of result is rare, this study makes a valuable contribution to the evaluation of the prognosis of implantbased restorations placed under the typical conditions of a private practice.
CONCLUSION Considering the limitations of the present study, the following conclusions can be drawn. • Zirconia abutments with all-ceramic crowns offer a reliable treatment option under the typical conditions of a private practice. • Clinical interventions to maintain the function of the restorations are required due to technical complications. Fractures of the veneering ceramics represent the most frequent complication.
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•
Temporary luting of the prosthetic restorations carries a risk of the loss of retention but offers the advantage of the non-destructive removal of the restoration in case of technical complications (retightening of the abutment screw or repair of a ceramic fracture). For patients attending a professional maintenance program at least annually, peri-implantitis should be expected in 4.1% of the implants and 7.4% of the patients after a mean observation period of 7 years. Further clinical investigations with larger samples and improved data (eg, randomized clinical trials) are necessary to evaluate restoration- and patientrelated risk factors for biologic and technical complications.
•
•
As the present study confirms the results of other studies on the same topics, the use of zirconia abutments and all-ceramic crowns for single tooth replacements in the anterior area can be recommended for general application in esthetically demanding situations.
ACKNOWLEDGMENT The authors thank Katrin Rinke for the critical reading and language editing of the manuscript.
CONFLICT OF INTEREST Sven Rinke has received lecture fees from Dentsply Implants, Mannheim, Germany, and DeguDent, Hanau, Germany.
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