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Two-Implant Supported Fixed Partial Prostheses Provide a Viable Treatment Alternative to 3-Implant Designs
THERAPY
ARTICLE ANALYSIS
AND
EVALUATION
Two-Implant Supported Fixed Partial Prostheses Provide a Viable Treatment Alternative to 3-Implant Designs ARTICLE TITLE AND BIBLIOGRAPHIC INFORMATION Fixed partial prostheses supported by 2 or 3 implants: a retrospective study up to 18 years. Eliasson A, Eriksson T, et al. Int J Oral Maxillofac Implants 2006;21(4): 567-74.
LEVEL OF EVIDENCE 2B
PURPOSE/QUESTION How does the long-term success and complication rate of 2- and 3-implant supported fixed partial prostheses compare?
SOURCE OF FUNDING
SUMMARY Subjects There were 178 subjects treated between 1985 and 1998. Of these, 123 subjects (mean age 65 years, 77 female) provided with 146 prostheses were available for a follow-up examination at least 5 years after treatment (range 5 to 18 years)
Therapy All subjects had been treated with Branemark system implants (turned surfaces, 6 to 18 mm in length and mostly 3.75 mm in diameter) in a standardized 2-stage surgical protocol. The freestanding fixed partial prostheses were screw retained and supported by 2 implants (63 prostheses) or 3 implants (83 prostheses). Thirtyfive of the 2-implant supported prostheses and 26 of the 3-implant supported prostheses were constructed with unilateral or bilateral cantilevers, and most were provided in the posterior regions (87% and 94%, respectively, for the 2 designs). The opposing dentition was mainly natural teeth or a fixed partial prosthesis. Most subjects were reviewed on an annual basis and radiographic examinations were performed at baseline, 1 year, 5 years, and 10 years. Biological or mechanical complications were obtained from the patients’ records. Patient satisfaction was measured using a questionnaire.
Government
Main Outcome Measure TYPE OF STUDY/DESIGN Cohort study
Implant loss.
Main Results Implant loss: 4 implants were lost before prosthetic loading and 6 implants after. In 2-implant fixed partial prostheses, 2 implants were lost in 2 patients. The implants and fixed partial prostheses were replaced and the 2 subjects were included in the 5-year follow-up. In 3-implant fixed partial prostheses, 4 implants were lost in 3 patients. Two prostheses were converted to 2-implant supported fixed partial prostheses. In the third subject, 2 implants supporting an anterior fixed partial prosthesis were lost.
Bone loss
J Evid Base Dent Pract 2007;7:114-115 1532-3382/$35.00 © 2007 Elsevier Inc. All rights reserved. doi:10.1016/j.jebdp.2007.05.015
Overall bone loss in the first 5 years was small (mean 0.3 mm, range: ⫹1.2 mm to ⫺3.7 mm); 66% of implants experienced no bone loss, 21% less than or equal to 0.6 mm. Frequency distributions of bone levels at individual implants in the 2 designs of fixed partial prosthesis were similar. For fixed partial prostheses with radiographic data at baseline, at 5 and 10 years (N ⫽ 32 for 2 implants and N ⫽ 37 for 3 implants) there were no significant changes in bone levels between time points.
JOURNAL OF EVIDENCE-BASED DENTAL PRACTICE
Mechanical complications No complications were observed in over two thirds of fixed partial prostheses. Significantly more veneer fractures were recorded in the 3-implant prostheses but more screw loosening in the 2-implant prostheses.
Patient satisfaction There were 88% of patients who were completely satisfied with the treatment.
Conclusions There was no difference in implant loss or bone loss between groups, but there were some minor differences in biomechanical complications.
COMMENTARY AND ANALYSIS The number of implants recommended to support fixed partial prostheses has largely been based on theoretical mechanical considerations. In general, 3 implants (not placed in a straight line) has been the preferred option to reduce bending moments.1,2 Randomized controlled clinical trials are needed to compare these treatment strategies, but case selection/ recruitment could be very difficult. There are a large number of variations to contend with in such a study, including the length of the edentulous span, whether there is a bound or free-end saddle, an anterior or posterior location, upper or lower jaw, and, most importantly, sufficient bone to allow placement of 3 implants in either group. In the present study the authors acknowledge the limits of their study in that the 2-implant option had to be applied in cases where there was insufficient bone for 3 implants. This is a major limiting factor and at first consideration could lead one to dismiss the study as an unfair comparison. However, the study has other considerable strengths and does indicate that there was little difference in the biomechanical performance of the 2 designs. All subjects were treated with the same type of implant and treatment protocol in the same clinic and followed for a minimum of 5 years. There were similar numbers of subjects in each group and the fact that they managed to follow 123 of 178 originally treated subjects is a very good achievement.
Volume 7, Number 3
However, there is some potentially important missing information that would have helped to clarify and apply their findings. For example: (1) Were the designs of the fixed partial prostheses equally distributed in the maxilla and mandible because differences in bone qualities between the jaws could affect implant success? (2) Were the spans of the prostheses comparable in terms of the length of the occlusal surface and the pontic-to-implant ratio? It would appear that both fixed partial prosthesis designs had the potential to be subjected to high loading as a large proportion of them were provided with unilateral and bilateral cantilevers (even more so in the 2-implant group). Cantilever designs are avoided by many clinicians because of reported mechanical complications. Increasing the number of implants placed in a given clinical situation has also been a recommended strategy to guard against prosthesis failure following loss of an implant. It is encouraging to note that implant loss in the present study was very low and did not even compromise the 2-implant group unduly. The good maintenance of bone levels also suggested that there was no difference in bone response to the different loading distributions in the 2 groups. In conclusion, this study supports a treatment protocol that 2 implants can be successfully used to support a fixed partial prosthesis and this may be especially useful in those situations where bone volume does not allow placement of additional implants.
REFERENCES 1. Rangert B, Eng M, Jemt T, Jorneus L. Forces and moments on Branemark implants. Int J Oral Maxillofac Implants 1989;4:241-7. 2. Rangert B, Eng M, Sullivan RM, Jemt T. Load factor control for implants in the posterior partially edentulous segment. Int J Oral Maxillofac Implants 1997;12:360-70.
REVIEWER Professor Richard Palmer, PhD, BDS, FDS RCS Head of Restorative Dentistry King’s College London Dental Institute at Guy’s, King’s and St Thomas’ Hospitals Floor 25, Guy’s Tower,Guy’s Hospital Campus London SE1 9RT, UK [email protected] www.kcl.ac.uk/dentistry http://myprofile.cos.com/palmer35
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ARTICLE ANALYSIS
AND
EVALUATION
Two-Implant Supported Fixed Partial Prostheses Provide a Viable Treatment Alternative to 3-Implant Designs ARTICLE TITLE AND BIBLIOGRAPHIC INFORMATION Fixed partial prostheses supported by 2 or 3 implants: a retrospective study up to 18 years. Eliasson A, Eriksson T, et al. Int J Oral Maxillofac Implants 2006;21(4): 567-74.
LEVEL OF EVIDENCE 2B
PURPOSE/QUESTION How does the long-term success and complication rate of 2- and 3-implant supported fixed partial prostheses compare?
SOURCE OF FUNDING
SUMMARY Subjects There were 178 subjects treated between 1985 and 1998. Of these, 123 subjects (mean age 65 years, 77 female) provided with 146 prostheses were available for a follow-up examination at least 5 years after treatment (range 5 to 18 years)
Therapy All subjects had been treated with Branemark system implants (turned surfaces, 6 to 18 mm in length and mostly 3.75 mm in diameter) in a standardized 2-stage surgical protocol. The freestanding fixed partial prostheses were screw retained and supported by 2 implants (63 prostheses) or 3 implants (83 prostheses). Thirtyfive of the 2-implant supported prostheses and 26 of the 3-implant supported prostheses were constructed with unilateral or bilateral cantilevers, and most were provided in the posterior regions (87% and 94%, respectively, for the 2 designs). The opposing dentition was mainly natural teeth or a fixed partial prosthesis. Most subjects were reviewed on an annual basis and radiographic examinations were performed at baseline, 1 year, 5 years, and 10 years. Biological or mechanical complications were obtained from the patients’ records. Patient satisfaction was measured using a questionnaire.
Government
Main Outcome Measure TYPE OF STUDY/DESIGN Cohort study
Implant loss.
Main Results Implant loss: 4 implants were lost before prosthetic loading and 6 implants after. In 2-implant fixed partial prostheses, 2 implants were lost in 2 patients. The implants and fixed partial prostheses were replaced and the 2 subjects were included in the 5-year follow-up. In 3-implant fixed partial prostheses, 4 implants were lost in 3 patients. Two prostheses were converted to 2-implant supported fixed partial prostheses. In the third subject, 2 implants supporting an anterior fixed partial prosthesis were lost.
Bone loss
J Evid Base Dent Pract 2007;7:114-115 1532-3382/$35.00 © 2007 Elsevier Inc. All rights reserved. doi:10.1016/j.jebdp.2007.05.015
Overall bone loss in the first 5 years was small (mean 0.3 mm, range: ⫹1.2 mm to ⫺3.7 mm); 66% of implants experienced no bone loss, 21% less than or equal to 0.6 mm. Frequency distributions of bone levels at individual implants in the 2 designs of fixed partial prosthesis were similar. For fixed partial prostheses with radiographic data at baseline, at 5 and 10 years (N ⫽ 32 for 2 implants and N ⫽ 37 for 3 implants) there were no significant changes in bone levels between time points.
JOURNAL OF EVIDENCE-BASED DENTAL PRACTICE
Mechanical complications No complications were observed in over two thirds of fixed partial prostheses. Significantly more veneer fractures were recorded in the 3-implant prostheses but more screw loosening in the 2-implant prostheses.
Patient satisfaction There were 88% of patients who were completely satisfied with the treatment.
Conclusions There was no difference in implant loss or bone loss between groups, but there were some minor differences in biomechanical complications.
COMMENTARY AND ANALYSIS The number of implants recommended to support fixed partial prostheses has largely been based on theoretical mechanical considerations. In general, 3 implants (not placed in a straight line) has been the preferred option to reduce bending moments.1,2 Randomized controlled clinical trials are needed to compare these treatment strategies, but case selection/ recruitment could be very difficult. There are a large number of variations to contend with in such a study, including the length of the edentulous span, whether there is a bound or free-end saddle, an anterior or posterior location, upper or lower jaw, and, most importantly, sufficient bone to allow placement of 3 implants in either group. In the present study the authors acknowledge the limits of their study in that the 2-implant option had to be applied in cases where there was insufficient bone for 3 implants. This is a major limiting factor and at first consideration could lead one to dismiss the study as an unfair comparison. However, the study has other considerable strengths and does indicate that there was little difference in the biomechanical performance of the 2 designs. All subjects were treated with the same type of implant and treatment protocol in the same clinic and followed for a minimum of 5 years. There were similar numbers of subjects in each group and the fact that they managed to follow 123 of 178 originally treated subjects is a very good achievement.
Volume 7, Number 3
However, there is some potentially important missing information that would have helped to clarify and apply their findings. For example: (1) Were the designs of the fixed partial prostheses equally distributed in the maxilla and mandible because differences in bone qualities between the jaws could affect implant success? (2) Were the spans of the prostheses comparable in terms of the length of the occlusal surface and the pontic-to-implant ratio? It would appear that both fixed partial prosthesis designs had the potential to be subjected to high loading as a large proportion of them were provided with unilateral and bilateral cantilevers (even more so in the 2-implant group). Cantilever designs are avoided by many clinicians because of reported mechanical complications. Increasing the number of implants placed in a given clinical situation has also been a recommended strategy to guard against prosthesis failure following loss of an implant. It is encouraging to note that implant loss in the present study was very low and did not even compromise the 2-implant group unduly. The good maintenance of bone levels also suggested that there was no difference in bone response to the different loading distributions in the 2 groups. In conclusion, this study supports a treatment protocol that 2 implants can be successfully used to support a fixed partial prosthesis and this may be especially useful in those situations where bone volume does not allow placement of additional implants.
REFERENCES 1. Rangert B, Eng M, Jemt T, Jorneus L. Forces and moments on Branemark implants. Int J Oral Maxillofac Implants 1989;4:241-7. 2. Rangert B, Eng M, Sullivan RM, Jemt T. Load factor control for implants in the posterior partially edentulous segment. Int J Oral Maxillofac Implants 1997;12:360-70.
REVIEWER Professor Richard Palmer, PhD, BDS, FDS RCS Head of Restorative Dentistry King’s College London Dental Institute at Guy’s, King’s and St Thomas’ Hospitals Floor 25, Guy’s Tower,Guy’s Hospital Campus London SE1 9RT, UK [email protected] www.kcl.ac.uk/dentistry http://myprofile.cos.com/palmer35
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