Implant-supported Single-tooth Restorations Research Articles

Medium- and Long-Term Survival Rates of Implant-Supported Single and Partial Restorations at a Maximum Follow-up of 12 Years: A Retrospective Study.

To present medium- and long-term biologic outcomes of implant-supported single-tooth restorations and fixed partial dentures and to analyze their correlations with prosthesis and patient characteristics. The records of patients treated with implant-supported fixed restorations between 2004 and 2019 reporting the presence or absence of peri-implantitis and/or implant failure were analyzed. The cumulative survival rate (%) over time was calculated, as well as the cumulative prevalence of units free of peri-implantitis. A total of 344 implants in 112 patients were included, with a mean follow-up period of 5.3 ± 4.0 years after loading. The cumulative survival rates for implants supporting single crowns and fixed partial dentures were 98.11% and 100% after 5 years, respectively, and 97.43% and 98.96% after 10 years, with an overall survival rate of 91.69% after 12 years. At the patient level, the implant survival rates were 95.42%, 92.73%, and 85.31% at 5, 10, and 12 years, respectively. The cumulative rate of implants free from peri-implantitis was 87.46% at the implant level and 72.39% at the patient level. Implant and prosthesis characteristics did not affect the long-term occurrence of implant failure or peri-implantitis. The development of peri-implantitis was statistically correlated with patient smoking habits, but not with history of periodontitis or with diabetes mellitus. Implants supporting single crowns and fixed partial dentures showed relatively high medium- and long-term survival rates that were not influenced by the implant or prosthesis characteristics, including the retention method. As for patient characteristics, only smoking was correlated with the occurrence of peri-implantitis.

Infraposition of anterior maxillary implant-supported single-tooth restorations in adolescent and adult patients-A prospective follow-up study up to 6 years.

In the maxillary incisor area infraposition of implant restorations can be an esthetic problem. The aim was to analyze the prevalence of infraposition of single-tooth implant restorations in the anterior maxilla in adolescent and adult patients. The study comprised of 31 patients, 18 women and 13 men, with 39 restorations and with a mean and median age of 23.8 and 18.8 years, range 17.8 to 52.8 years, at the time of implant crown connection. The mean and median time in function for the restorations was 4.5 and 4.3 years respectively with a range of 3.3 to 6.6 years. Twenty restorations 51%, showed no signs of infraposition. A slight infraposition (<0.5 mm) was seen in 36% of the restorations. Only in one patient, the observed infraposition of the implant crown was more than 1 mm. We found no significant difference of the observed level of vertical infraposition, Score A (0 mm) and Score B (<0.5 mm), in subjects where the restoration was placed before the age of 20 years compared to the older patients. There were no significant differences in changes of the vertical infraposition when comparing different parameters such as age, gender, jaw relation (Angle-classes I-III), overbite/overjet, occlusal contact on the implant crown, bone augmentation before or at implant installation or if orthodontic treatment of the neighboring teeth had been made before or after the implant installation. In the present study, there was a significant yet low correlation between the observed vertical infraposition of the single-tooth implant restoration and the subject's evaluation of the esthetics of the restoration (VAS). Fifty-one percent of the implant-supported crowns, showed no signs of vertical infraposition. A slight infraposition (< 0.5 mm) was however seen in 36% of the restorations. Only one crown showed a vertical infraposition of more than 1 mm.

Metal-free implant-supported single-tooth restorations. Part II: Hybrid abutment crowns and material selection.

In many areas of restorative dentistry, metal-free materials offer an alternative to metal-based restorations while ensuring high levels of biocompatibility and esthetics. Rapidly evolving CAD/CAM technology has significantly expanded the range of materials available, providing access to materials classes and their combinations not previously available within conventional manufacturing, such as zirconia ceramics and hybrid ceramics. In addition, digital methods offer previously unavailable options in diagnostics, greater planning reliability, better material quality through standardization of the manufacturing process, and reproducibility - significant benefits that can be used to advantage, especially in oral implantology. Even though technological progress in the field of metal-free materials has given rise to considerable improvements in their mechanical properties over the decades, their clinical long-term success is still very much dependent on an appropriate indication and proper material selection, on the knowledge and skills of the dental practitioner and dental technician, and on an adequate occlusion concept. The high rate of innovation - both with regard to the materials themselves and to CAD/CAM technology - therefore requires an adequate level of prior knowledge to sensibly and successfully implement the wide range of possibilities. It is becoming more and more puzzling for users to find their way around the many different new techniques and materials. This review article provides an up-to-date overview of the possibilities and limitations of metal-free implant-supported single-tooth restorations. This second part discusses hybrid abutment crowns and materials selection. Resultant treatment concepts are presented and evaluated based on clinical examples.

Clinical Comparison of Screw- and Cement-retained Implant-supported Single-tooth Restorations in the Molar Mandibular Region

Clinical Comparison of Screw- and Cement-retained Implant-supported Single-tooth Restorations in the Molar Mandibular Region

Metal-free implant-supported single-tooth restorations. Part I: Abutments and cemented crowns.

In many areas of restorative dentistry, metal-free materials offer an alternative to metal-based restorations while ensuring high levels of biocompatibility and esthetics. Rapidly evolving CAD/CAM technology has significantly expanded the range of materials available, providing access to materials classes and their combinations not previously available within conventional manufacturing, such as zirconia ceramics and hybrid ceramics. In addition, digital methods offer previously unavailable options in diagnostics, greater planning reliability, better material quality through standardization of the manufacturing process, and reproducibility - significant benefits that can be used to advantage, especially in oral implantology. Even though technological progress in the field of metal-free materials has given rise to considerable improvements in their mechanical properties over the decades, their clinical long-term success is still very much dependent on an appropriate indication and proper material selection, on the knowledge and skills of the dental practitioner and dental technician, and on an adequate occlusion concept. The high rate of innovation - both with regard to the materials themselves and to CAD/CAM technology - therefore requires an adequate level of prior knowledge to sensibly and successfully implement the wide range of possibilities now open. It is becoming more and more puzzling for users to find their way around the many different new techniques and materials. This review article provides an up-to-date overview of the possibilities and limitations of metal-free implant-supported single-tooth restorations. This first part discusses abutments and cemented crowns. Resultant treatment concepts are presented and evaluated based on clinical examples.

A comparison of implant complications and failures between the maxilla and the mandible

Statement of problemIdentifying factors that affect the clinical outcomes of implant therapy is important. PurposeThe purpose of this retrospective study was to determine whether implant location was a factor affecting the complication and failure rates of single-tooth implant-supported restorations in a predoctoral setting. Material and methodsThe charts of 431 patients treated with a surgically placed dental implant and restored with a single crown in the predoctoral clinic were analyzed. Data on implant location, type of complication (surgical or prosthetic), and type of failure were collected and analyzed according to implant location using the Fisher Exact Test and Mantel-Haenszel Exact Chi Square Test analysis (α=.05). ResultsThe charts revealed 158 complications (68 surgical and 90 prosthetic) in 110 patients, and 3.9% of the implants failed. No statistically significant difference was found between the number of surgical complications or prosthetic complications in the maxilla and the mandible (P=.469). ConclusionsJaw location (maxilla compared with mandible) of the implant had no statistically significant impact on the incidence of surgically or prosthetically related complications. No statistically significant difference was found in overall implant failures, surgical failures, and prosthetic failures between maxillary and mandibular implants.

Zirconia abutments for single-tooth implant restorations: a 10- to 11-year follow-up study.

To evaluate the clinical outcome of custom-made zirconia abutments for implant-supported single-tooth restorations 10-11years after insertion. The study comprises a clinical examination of 23 patients with 30 restorations placed 10-11years ago. Oral surgeons placed the implants. The prosthodontic treatment was provided at a prosthodontic specialist clinic. The restoration was either an all-ceramic crown for cementation or a screw-retained one-piece restoration with the veneering porcelain baked directly to the zirconia abutment. Besides the clinical and radiographic examination at the 10- to 11-year follow-up, the patients' records were scrutinized regarding clinical and radiographic data from insertion of the restoration up to the last visit at the clinic. The zirconia abutments performed well. Both technical and biological complications were rare; most patients were in general extremely satisfied with the restorations. No all-ceramic crowns fractured during the observation period. One implant was lost after 5½years in service. There were no significant differences for changes in any of the soft tissue registrations or the peri-implant marginal bone level between the conventional two-piece abutment-crown restoration and the one-piece restoration. The peri-implant bone level changes from placement to the clinical examination 10-11years later were small (mean 0.26mm, SD 0.6mm). Zirconia abutments for single-implant crowns demonstrated excellent technical and biological results over 10-11years of function, and most patients were extremely satisfied with the aesthetics and the function of their single-implant restorations.

Esthetic Outcomes of Single-Tooth Implant-Supported Restorations Using Metal-Ceramic Restorations with Zirconia or Titanium Abutments: A Randomized Controlled Clinical Study.

The aim of this study was to test whether zirconia abutments exhibit the same clinical and esthetic outcomes as titanium abutments in single-tooth implant restorations in the esthetic area. The 24 treated patients were randomly assigned to a test (zirconia abutment) or control (titanium abutment) group. Objective evaluations were carried out using the Implant Crown Aesthetic Index (ICAI) and the Papilla Index (PI) at the 1-month and 12-month follow-up examinations after crown cementation. No significant differences, either in ICAI or in other periodontal or radiographic measurements, were observed. At 1 year, zirconia and titanium abutments exhibited the same esthetic outcomes.

Findings of a Four-Year Randomized Controlled Clinical Trial Comparing Two-Piece and One-Piece Zirconia Abutments Supporting Single Prosthetic Restorations in Maxillary Anterior Region.

The purpose of this randomized controlled study is to investigate the clinical results obtained over four years and incidence of complications associated with one- versus two-piece custom made zirconia anchorages, in single tooth implant-supported restorations of the maxillary anterior region. Sixty-five patients, with a total of 74 missing maxillary teeth, were selected in the period from February 2007 to July 2010. Two different ways of custom made zirconia abutment and final prosthetic restoration were evaluated: a standard zirconia abutment associated with a pressed layer of lithium disilicate with an all-ceramic cemented restoration versus one-piece restoration with the facing porcelain fired and pressed straight to the custom made zirconia abutment. In 29 cases, the restoration consisted of an all-ceramic restoration for cementation (two pieces); in 45 cases the restoration was a screw-retained restoration (one piece). Three all-ceramic restorations broke during the observation time. Two one-piece restorations fractured after 26 months. At follow-up examination there were no significant differences between one-piece and two-piece groups regarding the PI, BI, and MBL. Awaiting studies with longer follow-up times, a careful conclusion is that zirconia anchorages for single-implant restorations seem to demonstrate good short-term technical and biological results.

Implant-supported single-tooth restorations. A 12-year prospective study.

The aim of this study was to evaluate prospectively the 12-year outcome of implant-supported single-tooth restorations. Originally 45 self-tapping Astra Tech TiOblast® ST-implants were installed by a two-stage protocol in 40 subjects requiring single-tooth prosthetic replacement for a missing tooth. Clinical and radiologic examinations were performed at completion of the prosthetic treatment 4-7months after implant installation surgery and after 5 and 12years in function. At 12years 31 patients and 35 implants were available for evaluation. The overall failure rate after 12years was 10.3% on the subject level and 9.1% on the implant level. The mean bone loss amounted to 0.67mm (SD 2.20) on a subject level and 0.47mm (1.72) on an implant level. Three subjects (10%) and three implants (8.6%) were diagnosed with peri-implantitis. Five subjects had experienced technical complications; three incidences of loosening of the abutment retention screw during the first 5years and two minor porcelain fracture of the crown (two patients) between 5- and 12-years of follow-up. The findings reported in this 12-year prospective case series suggest that the use of the Astra Tech dental implants may be a valid treatment alternative for single-tooth replacement prostheses.

Cemented and screw-retained implant-supported single-tooth restorations in the molar mandibular region: A retrospective comparison study after an observation period of 1 to 4 years.

Objectives: The aim of this study was to evaluate the survival and compare the appearance of different mechanical and biological complications, in screw-retained and cemented-retained single-tooth implant-supported restorations localized in the molar mandibular region, over a period of 1 to 4 years. Material and Methods: A retrospective study was carried out with a total of eighty implant-supported restorations, which were placed in eighty patients for prosthetic rehabilitation of a mandibular molar. Forty patients were rehabilitated with a cemented-retained restoration and the other forty with a screw-retained restoration. The presence of the following complications was recorded for both types of prostheses: Fractures of the ceramic veneering, loosening screws, mucositis and peri-implantitis. Debonding of the restoration was analyzed in the cemented-retained restoration group. The clinical survival of crowns was analyzed with a Kaplan-Meier test and the clinical complications were compared, using a Student t test and Log-rank test. Results: 27 patients registered some complication. The average rate of complications was 37,5% for cemented-retained restorations and 30% for screw-retained restorations. The complications more common in the cemented-retained restoration were the presence of mucositis (14,87%), while in the screw-retained restorations was the loosening screw (20%). Student t test and Log-Rank test found significant differences (p=0,001) between the screw loosening and presence of mucositis. Conclusions: The cemented-retained restorations seem to prevent screw loosening, but the presence of cement seem to increase the complications around the soft tissues, however in the screw-retained restorations the presence of mucositis and peri-implantitis are lower than cemented-retained restorations. The incidence of fracture of ceramic veneering was similar in both groups. Key words:Screw-retained restorations, cemented-retained restorations, screw loosening, peri-implant diseases and fracture ceramic veneering.

Performance of zirconia abutments for implant-supported single-tooth crowns in esthetic areas: a retrospective study up to 12-year follow-up.

The aim of this clinical study was to assess complications, success, and survival rates of zirconia abutments from different implant designs. Anterior implant-supported single-tooth restorations, after 1-12years of clinical function, were evaluated. One hundred and fifty-eight zirconia implant abutments placed in 141 patients were evaluated. Mechanical complications were observed, such as presence or absence of abutment fractures and loss of retention. In addition, the peri-implant parameters were observed. Statistical analysis was performed using Fisher's exact tests, and bone level was analyzed using the nonparametric Mann-Whitney U-test for non-normally distributed data. Sixteen restorations exhibited different complications. However, no significant difference was observed between the standard and platform switching. The standard platforms exhibited higher marginal bone loss than platform switching design followed up to 5years. Platform switching has a potentially higher risk of fracture in some designs. In our study, one standard platform as well as two-platform switch designs seem to withstand fracture in the anterior area, regardless of the implant width. Survival and success rates were 93.8% and 81.2% (up to >7years ≤12), respectively, for standard platform; and 90 and 84% (up to >2years ≤5), respectively, for platform switching. In general, standard platform implants restored with zirconia abutments were successful for the longest periods of observation and are a viable treatment alternative in anterior areas. Some of the studied designs of platform switching implants with zirconia abutments performed well for up to 5years.

Influence of abutment material on peri-implant clinical parameters: a prospective study

Objective: This study evaluated the peri-implant clinical parameters of zirconia versus metallic abutments for standardized custom-made implantsupported single-tooth restorations. Material and Methods: Sixteen subjects received 30 dental implants on esthetic region of upper jaws. Test group had 14 implant-supported single-tooth restorations with ceramic abutment and control group had 16 restorations with metallic abutment. Peri-implant clinical parameters were recorded after 110 ± 10 days in function at six sites by each implant, in each subject. The means of clinical measures: probing depth (PD) and clinical attachment level (CAL); mean of percentages of sites with visible plaque (VP), bleeding on probing (BOP) and suppuration (SU) were recorded to each subject. To verify differences between groups Mann Whitney U-test was selected PD and CAL and k-light test VP, BOP and SU. Results: One zirconia implant-supported single-tooth restoration fractured at insertion time. The mean of PD, CAL, and BOP of the samples sites were lower to test group than control (p &lt; 0.05). There were no differences of mean levels of VP and S between test and control group (p &gt; 0.05). Conclusion: Clinical parameters around implant-supported restorations were influenced by abutment type with better results to zirconia abutments, at least, after short time period evaluation. 

Fracture mode during cyclic loading of implant-supported single-tooth restorations

Fracture of veneering ceramics in zirconia-based restorations has frequently been reported. Investigation of the fracture mode of implant-supported ceramic restorations by using clinically relevant laboratory protocols is needed. This study compared the mode of fracture and number of cyclic loads until veneering fracture when ceramic and metal ceramic restorations with different veneering ceramics were supported by implants. Thirty-two implant-supported single-tooth restorations were fabricated. The test group was composed of 16 ceramic restorations of zirconia abutment-retained crowns with zirconia copings veneered with glass-ceramics (n=8) and feldspathic ceramics (n=8). The control group was composed of 16 metal ceramic restorations of titanium abutment-retained crowns with gold alloy copings veneered with glass (n=8) and feldspathic ceramics (n=8). The palatal surfaces of the crowns were exposed to cyclic loading of 800 N with a frequency of 2 Hz, which continued to 4.2 million cycles or until fracture of the copings, abutments, or implants. The number of cycles and the fracture modes were recorded. The fracture modes were analyzed by descriptive analysis and the Mann-Whitney test (α=.05). The differences in loading cycles until veneering fracture were estimated with the Cox proportional hazards analysis. Veneering fracture was the most frequently observed fracture mode. The severity of fractures was significantly more in ceramic restorations than in metal ceramic restorations. Significantly more loading cycles until veneering fracture were estimated with metal ceramic restorations veneered with glass-ceramics than with other restorations. The metal ceramic restorations demonstrated fewer and less severe fractures and resisted more cyclic loads than the ceramic restorations, particularly when the metal ceramic crowns were veneered with glass-ceramics.

A 3‐year prospective study of implant‐supported, single‐tooth restorations of all‐ceramic and metal‐ceramic materials in patients with tooth agenesis

The purpose of this clinical study was to describe outcome variables of all-ceramic and metal-ceramic implant-supported, single-tooth restorations. A total of 59 patients (mean age: 27.9 years) with tooth agenesis and treated with 98 implant-supported single-tooth restorations were included in this study. Two patients did not attend baseline examination, but all patients were followed for 3 years. The implants supported 52 zirconia, 21 titanium and 25 gold alloy abutments, which retained 64 all-ceramic and 34 metal-ceramic crowns. At baseline and 3-year follow-up examinations, the biological outcome variables such as survival rate of implants, marginal bone level, modified Plaque Index (mPlI), modified Sulcus Bleeding Index (mBI) and biological complications were registered. The technical outcome variables included abutment and crown survival rate, marginal adaptation of crowns, cement excess and technical complications. The aesthetic outcome was assessed by using the Copenhagen Index Score, and the patient-reported outcomes were recorded using the OHIP-49 questionnaire. The statistical analyses were mainly performed by using mixed model of ANOVA for quantitative data and PROC NLMIXED for ordinal categorical data. The 3-year survival rate was 100% for implants and 97% for abutments and crowns. Significantly more marginal bone loss was registered at gold-alloy compared to zirconia abutments (P = 0.040). The mPlI and mBI were not significantly different at three abutment materials. The frequency of biological complications was higher at restorations with all-ceramic restorations than metal-ceramic crowns. Loss of retention, which was only observed at metal-ceramic crowns, was the most frequent technical complication, and the marginal adaptations of all-ceramic crowns were significantly less optimal than metal-ceramic crowns (P = 0.020). The professional-reported aesthetic outcome demonstrated significantly superior colour match of all-ceramic over metal-ceramic crowns (P = 0.015). However, no significant differences in the other aesthetic parameters at various restoration materials were registered. After 3 years, the patient-reported outcome variables at different restoration materials were not significantly different. The biological outcomes at the zirconia and metal abutments were comparable. All-ceramic crowns demonstrated better colour match, but higher frequency of marginal discrepancy compared to metal-ceramic crowns. Generally, the patients noticed no difference in aesthetic outcome of all-ceramic and metal-ceramic restorations.

Papillae alterations around single-implant restorations in the anterior maxillae: thick versus thin mucosa

To evaluate the papilla alterations around single-implant restorations in the anterior maxillae after crown attachment and to study the influence of soft tissue thickness on the papilla fill alteration. According to the inclusion criteria, 32 patients subjected to implant-supported single-tooth restorations in anterior maxillae were included. The patients were assigned to two groups according to the mucosal thickness: (i) group 1, 1.5 mm≤mucosal thickness≤3 mm; and (ii) group 2, 3 mm<mucosal thickness≤4.5 mm. Assessments of interproximal papillae at the time of crown placement (baseline) and at 6-month postloading (follow-up) were made by two prosthodontists using papilla fill index (PFI). The mean mucosal thickness was (2.49±0.31) mm (group 1) and (3.81±0.31) mm (group 2) for the two groups respectively. A significant difference in PFI between the groups was detected at the baseline (P<0.001). PFI improvements over time occurred after 6-month follow-up irrespective of the groups. When compared to group 1, the likelihood to obtain papilla fill was significantly higher for group 2 with an odds ratio of 6.05 (P<0.001). The interproximal papilla level around single-implant restorations could improve significantly over time after 6-month restoration according to PFI assessment. The thicker mucosa before implant placement implied a more favorable esthetic outcome in papilla alteration.

Soft tissue topography and dimensions lateral to single implant‐supported restorations. A cross‐sectional study

The aim was to evaluate potential relationships between the implant position relative to adjacent teeth and dimensions and topography of the papillae lateral to implant-supported single-tooth restorations. A total of 32 subjects with a single implant-supported restoration in the esthetic zone of the maxilla were consecutively selected for the study. Soft and hard tissues at the proximal sites of the restoration were evaluated by the use of clinical, photographic, diagnostic cast, and radiographic assessments. A questionnaire was used for assessment of the patients' satisfaction with the esthetic outcome of the restorations. Potential factors influencing the papilla level and the presence of a complete papilla fill were investigated with generalized estimation equations (GEE) analysis. The bone level at the adjacent tooth significantly influenced the papilla level (P<0.001). The distance between the contact point and the bone level at the adjacent tooth was significantly shorter for "complete" (4.3mm) papillae than that for "deficient" papillae (5.7mm) (P<0.001). The GEE logistic model revealed that the chance of a complete papilla fill improved with increased facio-lingual thickness of the papilla (P=0.004) and decreased distance between the contact point and the bone level at the tooth (P=0.004). The self-reported satisfaction with the esthetic appearance of the implant-born restoration was not significantly different between patients with "complete" and "deficient" papillae. The probability of a complete papilla fill was significantly affected by the facio-lingual dimension of the papilla base and the distance between the contact point between the crowns and the bone level at the tooth.

Single‐tooth Morse taper connection implants placed in fresh extraction sockets of the anterior maxilla: an aesthetic evaluation

The aim of this retrospective study was to evaluate the aesthetic outcome of single-tooth Morse taper connection implants placed in fresh extraction sockets of the anterior maxilla, by means of the pink aesthetic/white aesthetic score (PES/WES) index. Twenty-six adult patients (18 men, 8 women, aged between 20 and 62 years; average: 48.7 years) who were treated with an immediate, single-tooth Morse taper connection implant (Leone Implant System(R) , Florence, Italy) in the aesthetic area of the anterior maxilla, were enrolled in this retrospective study. An independent calibrated examiner applied the PES/WES index to 26 single-tooth implant-supported restorations, respectively, 3 months and 2 years after implant placement. No implants were lost. All 26 anterior maxillary single-tooth implants fulfilled the established success criteria for dental implants with regard to osseointegration, including the absence of pain, suppuration, clinically detectable implant mobility, peri-implant radiolucency and prosthetic complications at the implant-abutment interface, with an overall implant-crown success of 100.0%. At the 2-year examination, the mean DIB was 0.44 ± 0.14 mm (95% CI: 0.41-0.47); the mean total PES/WES was 14.30 ± 2.78 (range 8-19); the mean PES was 7.30 ± 1.78 (range 4-10) and the mean WES was 7.00 ± 1.35 (range 4-10). The immediate placement of single-tooth Morse taper connection implants in the anterior maxilla seems to represent a successful procedure, from an aesthetic point of view. Further studies are needed to evaluate the aesthetic outcome of single-tooth Morse taper connection implants placed in fresh extraction sockets of the anterior maxilla.

Zirconia abutments for single-tooth implant restorations: a retrospective and clinical follow-up study

To evaluate the clinical outcome of custom-made zirconia abutments for implant-supported single-tooth restorations up to 5 years after insertion. The study comprises two parts: (Part 1) retrospective evaluation of records of 130 patients treated with 185 single-tooth implant restorations using zirconia abutments; (Part 2) clinical examination of 25 patients with 40 restorations placed >3 years ago. Oral surgeons placed the implants. The prosthodontic treatment was provided at a prosthodontic specialist clinic. The restoration was either an all-ceramic crown for cementation or a screw-retained one-piece restoration with the veneering porcelain baked directly to the zirconia abutment. Registration of all patients' records comprised clinical and radiographic data from insertion of the restoration up to the last visit at the clinic. Parts 1 and 2: The zirconia abutments performed well over the follow-up period. The rates of both technical and biological complications were low, and the patients were in general extremely satisfied with the restorations. No all-ceramic crowns fractured during the observation period. Two abutments (1%) fractured, one at insertion, the other after 2 months. Part 2: There were no significant differences for changes in any of the soft tissue registrations or the peri-implant marginal bone level between the conventional two-piece abutment-crown restoration and the one-piece restoration. The peri-implant bone level changes from placement to the clinical examination 3-5 years later were small (mean 0.29 mm, SD 0.87 mm). Zirconia abutments for single-implant crowns seem to demonstrate good short-term technical and biological results.

Crown-to-Implant Ratios of Short-Length Implants

Excessive crown-implant ratios have been cited in the literature as being detrimental to long-term implant survival. However, unfavorable crown-implant ratios have not yet been established. The primary aim of this study was to determine the crown-implant ratios of single-tooth implant-supported restorations on short-length implants in a clinical practice, and to evaluate the health of these implants via mesial and distal first bone-to-implant contact levels. Additionally, the relationship between crown-implant ratios and proximal first bone-to-implant contact levels will be evaluated. In this retrospective cohort study, the cohort was composed of 194 patients who possessed at least 1 single 5.7 mm or 6 mm length plateau design implant-supported restoration that had been surgically placed between February 1997 and December 2005. A chart review was performed to acquire the most recent radiographs in which both the entire crown and the implant were visible. The length of the crown and implant was measured directly from the radiographs using consistent magnification to calculate the crown-implant ratio. Mesial and distal first bone-to-implant contact levels were measured using 3 times magnification and were mathematically corrected for distortion. The last available radiograph was used to measure bone levels. Follow-up time was calculated from the day of implant placement to the date of the last available radiograph. Statistical analyses with analysis of variance mixed models were used. Data from 309 single implant-supported fixed restorations were tabulated and included in the study. The mean (SD) follow-up time was 20.9 (23.2) months, with a range of 15.6 to 122.8 months. The mean crown length (SD) was 13.4 (2.6) mm, with a range of 6.2 to 21.7 mm. The mean (SD) crown-implant ratio was 2.0 (0.4) and ranged from 0.9 to 3.2. The average mesial and distal first bone-to-implant contact levels (SD) measured from the radiographs were -0.2 (0.7) mm and -0.2 (0.9) mm, respectively. No statistically significant relationship was observed between increasing crown-implant ratios and decreasing mesial and distal first bone-to-implant contact levels around the implant with P values of .94 and .57, respectively. In this investigation, mesial and distal first bone-to-implant contact levels on short-length implants fall within the established guidelines for success. Also, there are no associations between crown-implant ratios and first bone-to-implant contact levels.