Does immediate loading affect clinical and patient-centered outcomes of mandibular 2-unsplinted-implant overdenture? A 2-year within-case analysis

Abstract

Objective

To provide 2-year clinical- and patient-oriented data with regard to mandibular overdenture assisted by 2 immediately loaded unsplinted implants.

Material and methods

In this pre-post design, Phase-I clinical trial, 18 edentate individuals (62.4 ± 7.7 years) received a new set of complete denture. Then, following standard procedures, 3 threaded implants (OsseoSpeed TX™, Dentsply Implants, Mölndal, Sweden) were placed in the mandible in each patient, and locator abutments (Zest Anchors LLC, Escondido, U.S.A.) were inserted on the right and left side implants. The midline implant served as a control for within-patient comparison. The immediate loading was conducted within 24 h of surgery. Data were collected at baseline (T 0 ), 12 (T 1 ) and 24 (T 2 ) months after immediate loading. The clinical outcomes included implant survival rate, crestal bone level changes and implant stability. These criteria were assessed through clinical and radiographic examinations as well as resonance frequency analysis. Patient-centered outcomes included patient satisfaction and oral health-related quality of life measured using validated questionnaires. Brunner-Langer approach was used for statistical analysis.

Results

Implant survival rate for immediate loaded implants was 91.7% at 2-year follow-up. None of the unloaded implants failed. There was no statistically significant difference at baseline and follow-ups with regard to clinical outcomes between loaded and unloaded implants. Patient satisfaction and quality of life improved (p < 0.0001) from baseline to 2-year follow-up.

Conclusion

Immediate loading protocol did not negatively affect clinical outcomes, satisfaction and quality of life of patients wearing 2-unsplinted-implant mandibular overdenture for 2 years. This conclusion requires confirmation by randomized control trials.

Clinical significance statement

Mandibular overdenture assisted by two immediately-loaded unsplinted implants is successful treatment based on 2-year clinical and patient-based outcomes.

Introduction

Based on solid evidence, nowadays many clinicians recommend the use of mandibular 2-implant overdentures in the treatment of completely edentate individuals . Although this treatment is cost-effective and fulfill the satisfaction of patients , clinicians desire to reduce the patients burdens such as costs, morbidity and inconvenience associated with multiple surgical phases and multiple visits as well as the long waiting time for the final restoration. Immediate loading protocol was developed to improve patients’ satisfaction and quality of life by shortening of the rehabilitation time and faster return to oral function .

However, a recent meta -analysis of seven clinical studies showed a statistical tendency in favor of conventional loading (RD: −0.03, 95% CI −0.06 to 0.00) . Although the clinical outcomes for immediate loading of mandibular implant overdenture showed high one-year survival rate for threaded, micro-textured implants with diameter ≥ 3 mm and an insertion torque ≥ 30 N cm and an implant stability quotient (ISQ) value ≥ 60, there was a wide variation in implant failure rates for immediate loading of unsplinted implants, ranging from 0 to 18% . Furthermore, data on immediately loaded implants with locator attachment is still scarce . A recent systematic review on immediate-loading highlighted the need for clinical research that reports on patient-centered outcomes. In fact, grading the evidence in health science literature and translation of research into practice is based primarily on patient-centered approach . Therefore, the objective of this study was to provide clinical- and patient-oriented data with regard to mandibular overdenture assisted by 2 immediately-loaded unsplinted implants.

Material and methods

Recruitment

This Phase-I trial was conducted in the Postgraduate Prosthodontic Clinics at the Université de Montréal. Ethical approval was received from the Université de Montréal Ethical Review Board (International Clinical Trial Registration # NCT01644058).

The trial used 1-group, pre-post design. The details of the study and the 4-month patient-satisfaction (primary outcome) results have been published previously . In brief, to be included in the trial, patients had to: (a) be at least 18 years old; (b) be wearing complete dentures in both arches for ≥1 year; and (c) have sufficient bone in the anterior mandibular region for placement of three implants of standard diameter and length without any bone grafting. Patients were excluded if they had: (a) any medical or general relative risk factors for implant therapy; (b) any physical or psychological incapacity to complete study questionnaires; (c) incapacity to follow hygienic instructions or adhere to immediate loading protocol (ILP); or (d) inability to achieve primary stability during implant surgery (i.e., insertion torque of <35 N cm or resonance frequency analysis of <60 ISQ).

Prosthetic and surgical phases were conducted by two prosthodontic residents and a board-certified periodontist, respectively. Training and calibration of the two residents were done before the data collection. The intra-class correlation coefficient (ICC) was 0.96 and 0.99 for inter- and intra examiner reliability.

Clinical procedures

Before the surgery and by using standard prosthodontic procedures, maxillary and mandibular new complete dentures; radiological guide and surgical template were fabricated for each participant. During the surgical phase, 3 threaded implants (OsseoSpeed TX™, Dentsply Implants, Mölndal, Sweden) were placed in the interforaminal mandibular area (Ø = 4 mm and L = 9 to 17 mm) at a torque ≥ 35 N cm. Immediately after implantation, the prosthetic abutments were inserted (LOCATOR ® abutment, ZEST Anchors L.L.C., Escondido, U.S.A.) on the right and left side implants with a final torque of 25 Ncm. A healing abutment was inserted on the midline implant, which was not loaded during the trial and served as a reference for within-patient comparison with regard to change in peri-implant bone level and implant stability. Study participants were informed about the use of the third implant and consented to continue participation in the future 3-implant mandibular overdenture add-on study. The immediate loading and the conversion of the mandibular complete denture to an overdenture was conducted within 24 h of implant surgery .

Data collection

Data collection was conducted at baseline (T 0 ), 1 year (T 1 ), and 2 years (T 2 ) after the immediate loading. Additional follow-ups for the early impact of immediate loading protocol on patient satisfaction (primary study outcome) were also conducted and reported previously . The clinical outcomes of interest were the implant survival rate, the peri-implant crestal bone level changes and implant stability. Implant survival was defined according to Zarb and Albrektsson criteria : in-situ presence of the implant in function; absence of clinical mobility of the implant; absence of a persistent form of discomfort, pain or infection; and implant position allowing the placement of a functional and aesthetic prosthesis. The peri-implant bone level measurements were assessed using direct (bone probing) and indirect (radiographic assessment) methods. Direct measurements of bone crest height were obtained at four sites around each implant (buccal, lingual, mesial and distal) using the “BB gauge” as previously described ( Fig. 1 ).

Fig. 1
Instruments used for direct measurement of peri-implant bone levels.

Radiographic evaluation was conducted using standardized periapical radiographs (long-cone paralleling technique, standard X-ray unit operating at 70 kVp, 10 mA, and 1.5 mm), and modified standardized film holder (Rinn’XCP Anterior Holder™, Dentsply Rinn, Denstply International, York, USA). The digital images were analyzed using digital subtraction technique and Image J software (ImageJ v.1.46r, National Institutes of Health, Bethesda, USA). The junction between the machined bevel and the top of the MicroThread on the implant was used as the reference to assess the mesial and distal peri-implant crestal bone level changes. The results were presented as a mean of these two values.

The implant stability measurement was made with a resonance frequency analyzer (Osstell™, Integration Diagnostics, Gothenburg, Sweden) at the implant level . The transducer was attached to the implants using a manual prosthetic torque wrench (Nobel Biocare, Zurich, Switzerland) at a torque about 10 N cm . For each implant, two measurements of implant stability quotient (ISQ) were obtained and the mean value was retained for data analysis.

Patients’ satisfaction and oral-health-related quality of life were measured using the McGill denture satisfaction questionnaire , and the Oral Health Impact Profile (OHIP-20) . OHIP consists of 20 items covering seven domains: functional limitation, physical pain, psychological discomfort, physical disability, psychological disability, social disability and handicap. Lower OHIP scores indicated better oral health-related quality of life.

The explanatory variables for patient-centered outcomes included socio-demographic characteristics and personality traits. The latter was measured by use of the revised NEO personality inventory validated questionnaire . The details and related personality traits data and results are already published .

Statistical analysis

The sample size estimation for the study was based on the primary outcome of interest (patient satisfaction). Based on the Wilcoxon test assuming that: (a) the minimal practically important pre-post difference in the mean global satisfaction score is 25 units (based on the opinion of the experts and literature) , and (b) the standard deviation of the distribution of the global satisfaction score is 35 units , a sample size of 18 participants would allow a power of 80% of rejecting the null hypothesis if it is indeed false at an alpha level of 5%.

Descriptive statistics and Brunner Langer approach (Mixed models for non-parametric statistics) were used to estimate and to analyze the data. Mixed models for non-parametric statistics was conducted to compare patients’ satisfaction, OHIP total and domains scores as well as clinical and radiographic outcomes at different time points during follow-ups. The model was also used to show the effect of the implant loss on two-year outcomes. Bonferroni adjustments were conducted for multiple comparisons at different time level. Patients’ satisfaction and OHIP change scores were computed as followed: Δ = T 0 –T 1 , Δ = T 1 –T 2 , Δ = T 0 –T 2 . Level of significance was set at p ≤ 0.05. Data analyses were performed using SPSS 20.0 (IBM Co., Chicago, U.S.A.) and the SAS program (SAS 9.4 for Windows, Cary, U.S.A.).

Material and methods

Recruitment

This Phase-I trial was conducted in the Postgraduate Prosthodontic Clinics at the Université de Montréal. Ethical approval was received from the Université de Montréal Ethical Review Board (International Clinical Trial Registration # NCT01644058).

The trial used 1-group, pre-post design. The details of the study and the 4-month patient-satisfaction (primary outcome) results have been published previously . In brief, to be included in the trial, patients had to: (a) be at least 18 years old; (b) be wearing complete dentures in both arches for ≥1 year; and (c) have sufficient bone in the anterior mandibular region for placement of three implants of standard diameter and length without any bone grafting. Patients were excluded if they had: (a) any medical or general relative risk factors for implant therapy; (b) any physical or psychological incapacity to complete study questionnaires; (c) incapacity to follow hygienic instructions or adhere to immediate loading protocol (ILP); or (d) inability to achieve primary stability during implant surgery (i.e., insertion torque of <35 N cm or resonance frequency analysis of <60 ISQ).

Prosthetic and surgical phases were conducted by two prosthodontic residents and a board-certified periodontist, respectively. Training and calibration of the two residents were done before the data collection. The intra-class correlation coefficient (ICC) was 0.96 and 0.99 for inter- and intra examiner reliability.

Clinical procedures

Before the surgery and by using standard prosthodontic procedures, maxillary and mandibular new complete dentures; radiological guide and surgical template were fabricated for each participant. During the surgical phase, 3 threaded implants (OsseoSpeed TX™, Dentsply Implants, Mölndal, Sweden) were placed in the interforaminal mandibular area (Ø = 4 mm and L = 9 to 17 mm) at a torque ≥ 35 N cm. Immediately after implantation, the prosthetic abutments were inserted (LOCATOR ® abutment, ZEST Anchors L.L.C., Escondido, U.S.A.) on the right and left side implants with a final torque of 25 Ncm. A healing abutment was inserted on the midline implant, which was not loaded during the trial and served as a reference for within-patient comparison with regard to change in peri-implant bone level and implant stability. Study participants were informed about the use of the third implant and consented to continue participation in the future 3-implant mandibular overdenture add-on study. The immediate loading and the conversion of the mandibular complete denture to an overdenture was conducted within 24 h of implant surgery .

Data collection

Data collection was conducted at baseline (T 0 ), 1 year (T 1 ), and 2 years (T 2 ) after the immediate loading. Additional follow-ups for the early impact of immediate loading protocol on patient satisfaction (primary study outcome) were also conducted and reported previously . The clinical outcomes of interest were the implant survival rate, the peri-implant crestal bone level changes and implant stability. Implant survival was defined according to Zarb and Albrektsson criteria : in-situ presence of the implant in function; absence of clinical mobility of the implant; absence of a persistent form of discomfort, pain or infection; and implant position allowing the placement of a functional and aesthetic prosthesis. The peri-implant bone level measurements were assessed using direct (bone probing) and indirect (radiographic assessment) methods. Direct measurements of bone crest height were obtained at four sites around each implant (buccal, lingual, mesial and distal) using the “BB gauge” as previously described ( Fig. 1 ).

Fig. 1
Instruments used for direct measurement of peri-implant bone levels.

Radiographic evaluation was conducted using standardized periapical radiographs (long-cone paralleling technique, standard X-ray unit operating at 70 kVp, 10 mA, and 1.5 mm), and modified standardized film holder (Rinn’XCP Anterior Holder™, Dentsply Rinn, Denstply International, York, USA). The digital images were analyzed using digital subtraction technique and Image J software (ImageJ v.1.46r, National Institutes of Health, Bethesda, USA). The junction between the machined bevel and the top of the MicroThread on the implant was used as the reference to assess the mesial and distal peri-implant crestal bone level changes. The results were presented as a mean of these two values.

The implant stability measurement was made with a resonance frequency analyzer (Osstell™, Integration Diagnostics, Gothenburg, Sweden) at the implant level . The transducer was attached to the implants using a manual prosthetic torque wrench (Nobel Biocare, Zurich, Switzerland) at a torque about 10 N cm . For each implant, two measurements of implant stability quotient (ISQ) were obtained and the mean value was retained for data analysis.

Patients’ satisfaction and oral-health-related quality of life were measured using the McGill denture satisfaction questionnaire , and the Oral Health Impact Profile (OHIP-20) . OHIP consists of 20 items covering seven domains: functional limitation, physical pain, psychological discomfort, physical disability, psychological disability, social disability and handicap. Lower OHIP scores indicated better oral health-related quality of life.

The explanatory variables for patient-centered outcomes included socio-demographic characteristics and personality traits. The latter was measured by use of the revised NEO personality inventory validated questionnaire . The details and related personality traits data and results are already published .

Statistical analysis

The sample size estimation for the study was based on the primary outcome of interest (patient satisfaction). Based on the Wilcoxon test assuming that: (a) the minimal practically important pre-post difference in the mean global satisfaction score is 25 units (based on the opinion of the experts and literature) , and (b) the standard deviation of the distribution of the global satisfaction score is 35 units , a sample size of 18 participants would allow a power of 80% of rejecting the null hypothesis if it is indeed false at an alpha level of 5%.

Descriptive statistics and Brunner Langer approach (Mixed models for non-parametric statistics) were used to estimate and to analyze the data. Mixed models for non-parametric statistics was conducted to compare patients’ satisfaction, OHIP total and domains scores as well as clinical and radiographic outcomes at different time points during follow-ups. The model was also used to show the effect of the implant loss on two-year outcomes. Bonferroni adjustments were conducted for multiple comparisons at different time level. Patients’ satisfaction and OHIP change scores were computed as followed: Δ = T 0 –T 1 , Δ = T 1 –T 2 , Δ = T 0 –T 2 . Level of significance was set at p ≤ 0.05. Data analyses were performed using SPSS 20.0 (IBM Co., Chicago, U.S.A.) and the SAS program (SAS 9.4 for Windows, Cary, U.S.A.).

Results

Clinical outcomes

From a total of 23 patients who signed the consent forms, 18 edentate individuals (mean age 62.39 ± 7.65 years), were followed for 2 years. Four patients were excluded from the study before the surgical phase or at surgery because of lack of implant primary stability and one patient was excluded after the immediate loading because of a medical problem unrelated to the study. From a total of 54 inserted implants, 36 were immediately loaded and 18 served as within control. All implant failures occurred within the first 4 postoperative months and none of the unloaded implants failed. During the first month after the surgery, one woman lost the left implant and another one lost the two loaded implants ( Fig. 2 , study flow chart). The patients were not considered as dropout since they both completed the 2-year follow-up for patient-based outcomes.

Fig. 2
Study flow chart (N = number of patients, ♀ = female, ♂ = male).

The implant survival rate at 2-year follow-up was 91.7%. There was no statistically significant difference among loaded and unloaded implant at baseline and follow-ups with regard to change in bone level and stability ( Tables 1 and 2 ). The comparison of clinical measures between follow-ups showed statistically significant peri-implant bone loss (mean value less than 1 mm) in both radiographic and direct measurements from T 0 to T 1 ( p < 0.05) and T0 to T2 ( p < 0.05) for all implants. Changes from T 1 to T 2 ( Table 1 and Fig. 3 ) were only statistically significant when using direct measurements technique. The implant stability quotient increased from T 0 to T 1 ( p < 0.0001) for all implants and was then stable from T 1 to T 2 ( p > 0.05) ( Table 2 and Fig. 4 ).

Jun 19, 2018 | Posted by in General Dentistry | Comments Off on Does immediate loading affect clinical and patient-centered outcomes of mandibular 2-unsplinted-implant overdenture? A 2-year within-case analysis
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