2.1

Study set-up and patient population

The study was set up as a within-subject comparison randomized clinical trial for which permission from the medical ethical committee of the University Medical Center of Groningen was granted (METc 2011.194). Thirty subjects with a full upper denture and complaints regarding their bilateral free-ending mandibular RPD were included. They all had conventional RPD’s made in the past and either still wore them or had discontinued wearing them. The following inclusion criteria applied:

• –

  ≥18 years of age;

• –

  the saddle area reaches until the first mandibular premolar or cuspid, both left and right;

• –

  the bone volume distal from the most posterior abutment teeth is sufficient to place the implants. In the premolar region, implants with a length of 8 mm and a diameter of 3.3 mm and in the molar region with a length of 6 mm and diameter of 4.1 mm were inserted. A cone beam CT (CBCT) was used to measure the bone volume ;

• –

  the patient is capable of understanding and giving informed consent.

Potential subjects with medical and general contraindications for the surgical procedures, with a history of local radiotherapy to the head and neck region, who experienced implant loss in the past, who are incapable of performing basal oral hygiene measures, with decreased masticatory function due to physical disability or with active, uncontrolled periodontal pathology of the remaining dentition were excluded from participation.

2.2

Surgical and prosthetic procedures

All subjects gave informed consent and received 2 implants on either side of the mandible (Straumann RN, Straumann, Switzerland) that were provided with cover screws and submerged. Two implants were placed in the premolar region (PM implant support) and two were placed in the molar region (M implant support). A surgical guide was used to achieve the right position and inclination. After 3 months, all implants were exposed in a second-stage surgery and low healing abutments were inserted.

A new RPD was made according to standard prosthetic procedures. The design involved a lingual plate and a clasp on either side. The housing of the Locator ^® abutment (Zest Anchors, Inc., Escondido, California, USA) was already incorporated in the RPD, but not the Teflon matrix so it provided neither retention nor support to the RPD. Three months later and following a randomization scheme, either the PM or M implants were provided with a Locator ^® abutment. The remaining implants were left unloaded for future investigation. After 3 months, the other pair of implants was loaded. Fig. 1 shows an example of a typical clinical case. A clear timeline is displayed in Fig. 2 .

a. Occlusal view. Locator abutments in the premolar region provide support and retention to the Removable Partial Denture. The 2 molar implants are not in function. b. Frontal view. Removable Partial Denture in situ. Blue shimmering lateral in the denture is caused by the electronic chip to measure wearing-time. c. Occlusal view. Removable Partial Denture in situ. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Timeline of the randomized clinical cross-over trial including moments of data collection.

2.3

Patient-based outcome measures

Five patient-based outcome measures were assessed: oral health related quality of life, patient reported general health status, general contentment, daily wearing-time of the RPD and patients’ preference for the PM or M implant position. The clinician who collected the data (CJ) was involved during the inclusion of the subjects and the organisation of the trial, but provided neither surgical, nor prosthodontic care.

Oral Health Related Quality of Life (OHRQoL) was considered the primary outcome measure and assessed using the Dutch translated and validated version of the Oral Health Impact Profile questionnaire (OHIP-NL49) . It consists of 49 questions arranged in seven conceptually formulated domains: functional limitation, physical pain, psychological discomfort, physical disability, psychological disability, social disability and handicap. For each item, subjects were asked how frequently they had experienced the impact of that item in the last month. Responses are given on a Likert-scale (0-never, 1-hardly ever, 2-occasionally, 3-fairly often, 4-very often). OHIP-NL49 sum scores per domain and an overall score characterize the OHRQoL impairment in which higher scores indicate greater OHRQoL impairment.

Patient-reported perceived general health status was determined using the Dutch translated and validated version of the Short Form Health Survey (SF-36). It measures to what degree patients feel disabled during their daily activities . It is comprised of 36 questions divided into 8 scaled scores which are transformed into a range from 0 to 100: vitality, physical functioning, bodily pain, general health perceptions, physical role functioning, emotional role functioning, social role functioning and mental health. One additional question addresses changes in health condition. The lower the score, the more disability.

In addition, patients were asked to express their general contentment with their oral function during the different stages of treatment on a Visual Analogue Scale (VAS) ranging from 0 (very discontent, major concerns) to 100 (very content, no concerns at all). At the start of treatment they were also asked to express their expectation with respect to the anticipated ISRPD as a means to evaluate whether or not patients’ expectations were met at the end of the study.

Data on OHIP-NL49, SF-36 and general contentment were collected prior to treatment (with the old RPD), after 3 months of function with the new RPD without implant support, after 3 months of function with PM implant support and finally after 3 months with M implant support (or vice versa, Fig. 2 ).

The mean wearing-time per day reflects the patients’ wearing habits. Alterations assume a shift in patient satisfaction and/or comfort. A commercially available microelectronic sensor (TheraMon ^® , Handelsagentur Gschladt, Hargelsberg, Austria) was embedded in the lingual or buccal flange of the new removable partial denture at the position of the first premolar by means of methylmetacrylate, as described by the manufacturer. It runs over a period of at least 18 months, measuring the intraoral temperature in regular intervals and storing it into the integrated memory microchip. Stored data were transferred to a desktop computer by a reading station and analysed using dedicated software (TheraMon ^® software, version 2.1.0.13; Handelsagentur Gschladt). Wearing-time was established for the period with the new RPD and with the ISRPD during PM as well as M implant support. Patients were presumed to have worn the denture when the recorded temperature ranged between 31 °C to 39 °C. Under normal conditions, this is the range that covers the vast majority of intraoral temperature values .

At the end of the experiment patients were asked to express their preferred implant position: PM or M after being counselled about the consequences with respect to the design of their denture. When favouring the M position, the anterior clasps would have to remain. Eventually, the dentures were modified according to their wishes.

2.4

Sample size calculation and statistical analysis

Sample size estimation was based on the primary outcome measure (OHIP-NL49) given α = 0.05, power = 0.80 and on the basis of the expected effect size for 2 dependent means (matched pairs) . The prospected outcome was obtained from a study on oral health related quality of life as measured by the Oral Health Impact Factor (OHIP-49) comparing patients treated with implant supported fixed dentures (implant bridges) and removable partial dentures without implant support. Mean scores were respectively 22.0 (SD 18.8) and 38.0 (SD 22.2) . Since we included patients with free-ending bilateral situations only, we presumed the OHIP value for this particular situation to be higher (i.e. 40) and the effect of implant support to be less (i.e. 24). Sample size calculation revealed that 23 subjects were needed to detect this increase in the primary outcome measure from 40 in the control group (RPD) to 24 in the experimental group (ISRPD, regardless of implant position). Given the fact that the expected effect in patients with some remaining natural teeth is presumably smaller than that in edentulous subjects and compensating for potential dropouts, the intended number of subjects to be included in the study was set at 30 patients.

The outcomes of the old, the unsupported new, the PM implant supported and the M implant supported RPD’s were compared by 1-way analysis of variance and multiple comparison tests after verification of normal distribution. When the data were not normally distributed a non-parametric test for related samples (Friedman’s test) was anticipated. In case of statistical significance (α = 0.05), post-hoc Wilcoxon signed rank tests were performed with Bonferroni adjustment for multiple testing. Mann-Whitney U tests were performed to detect any effects from treatment sequence (first M, then PM implant support versus first PM, then M implant support).

2.1

Study set-up and patient population

The study was set up as a within-subject comparison randomized clinical trial for which permission from the medical ethical committee of the University Medical Center of Groningen was granted (METc 2011.194). Thirty subjects with a full upper denture and complaints regarding their bilateral free-ending mandibular RPD were included. They all had conventional RPD’s made in the past and either still wore them or had discontinued wearing them. The following inclusion criteria applied:

• –

  ≥18 years of age;

• –

  the saddle area reaches until the first mandibular premolar or cuspid, both left and right;

• –

  the bone volume distal from the most posterior abutment teeth is sufficient to place the implants. In the premolar region, implants with a length of 8 mm and a diameter of 3.3 mm and in the molar region with a length of 6 mm and diameter of 4.1 mm were inserted. A cone beam CT (CBCT) was used to measure the bone volume ;

• –

  the patient is capable of understanding and giving informed consent.

Potential subjects with medical and general contraindications for the surgical procedures, with a history of local radiotherapy to the head and neck region, who experienced implant loss in the past, who are incapable of performing basal oral hygiene measures, with decreased masticatory function due to physical disability or with active, uncontrolled periodontal pathology of the remaining dentition were excluded from participation.

2.2

Surgical and prosthetic procedures

All subjects gave informed consent and received 2 implants on either side of the mandible (Straumann RN, Straumann, Switzerland) that were provided with cover screws and submerged. Two implants were placed in the premolar region (PM implant support) and two were placed in the molar region (M implant support). A surgical guide was used to achieve the right position and inclination. After 3 months, all implants were exposed in a second-stage surgery and low healing abutments were inserted.

A new RPD was made according to standard prosthetic procedures. The design involved a lingual plate and a clasp on either side. The housing of the Locator ^® abutment (Zest Anchors, Inc., Escondido, California, USA) was already incorporated in the RPD, but not the Teflon matrix so it provided neither retention nor support to the RPD. Three months later and following a randomization scheme, either the PM or M implants were provided with a Locator ^® abutment. The remaining implants were left unloaded for future investigation. After 3 months, the other pair of implants was loaded. Fig. 1 shows an example of a typical clinical case. A clear timeline is displayed in Fig. 2 .

a. Occlusal view. Locator abutments in the premolar region provide support and retention to the Removable Partial Denture. The 2 molar implants are not in function. b. Frontal view. Removable Partial Denture in situ. Blue shimmering lateral in the denture is caused by the electronic chip to measure wearing-time. c. Occlusal view. Removable Partial Denture in situ. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Timeline of the randomized clinical cross-over trial including moments of data collection.

2.3

Patient-based outcome measures

Five patient-based outcome measures were assessed: oral health related quality of life, patient reported general health status, general contentment, daily wearing-time of the RPD and patients’ preference for the PM or M implant position. The clinician who collected the data (CJ) was involved during the inclusion of the subjects and the organisation of the trial, but provided neither surgical, nor prosthodontic care.

Oral Health Related Quality of Life (OHRQoL) was considered the primary outcome measure and assessed using the Dutch translated and validated version of the Oral Health Impact Profile questionnaire (OHIP-NL49) . It consists of 49 questions arranged in seven conceptually formulated domains: functional limitation, physical pain, psychological discomfort, physical disability, psychological disability, social disability and handicap. For each item, subjects were asked how frequently they had experienced the impact of that item in the last month. Responses are given on a Likert-scale (0-never, 1-hardly ever, 2-occasionally, 3-fairly often, 4-very often). OHIP-NL49 sum scores per domain and an overall score characterize the OHRQoL impairment in which higher scores indicate greater OHRQoL impairment.

Patient-reported perceived general health status was determined using the Dutch translated and validated version of the Short Form Health Survey (SF-36). It measures to what degree patients feel disabled during their daily activities . It is comprised of 36 questions divided into 8 scaled scores which are transformed into a range from 0 to 100: vitality, physical functioning, bodily pain, general health perceptions, physical role functioning, emotional role functioning, social role functioning and mental health. One additional question addresses changes in health condition. The lower the score, the more disability.

In addition, patients were asked to express their general contentment with their oral function during the different stages of treatment on a Visual Analogue Scale (VAS) ranging from 0 (very discontent, major concerns) to 100 (very content, no concerns at all). At the start of treatment they were also asked to express their expectation with respect to the anticipated ISRPD as a means to evaluate whether or not patients’ expectations were met at the end of the study.

Data on OHIP-NL49, SF-36 and general contentment were collected prior to treatment (with the old RPD), after 3 months of function with the new RPD without implant support, after 3 months of function with PM implant support and finally after 3 months with M implant support (or vice versa, Fig. 2 ).

The mean wearing-time per day reflects the patients’ wearing habits. Alterations assume a shift in patient satisfaction and/or comfort. A commercially available microelectronic sensor (TheraMon ^® , Handelsagentur Gschladt, Hargelsberg, Austria) was embedded in the lingual or buccal flange of the new removable partial denture at the position of the first premolar by means of methylmetacrylate, as described by the manufacturer. It runs over a period of at least 18 months, measuring the intraoral temperature in regular intervals and storing it into the integrated memory microchip. Stored data were transferred to a desktop computer by a reading station and analysed using dedicated software (TheraMon ^® software, version 2.1.0.13; Handelsagentur Gschladt). Wearing-time was established for the period with the new RPD and with the ISRPD during PM as well as M implant support. Patients were presumed to have worn the denture when the recorded temperature ranged between 31 °C to 39 °C. Under normal conditions, this is the range that covers the vast majority of intraoral temperature values .

At the end of the experiment patients were asked to express their preferred implant position: PM or M after being counselled about the consequences with respect to the design of their denture. When favouring the M position, the anterior clasps would have to remain. Eventually, the dentures were modified according to their wishes.

2.4

Sample size calculation and statistical analysis

Sample size estimation was based on the primary outcome measure (OHIP-NL49) given α = 0.05, power = 0.80 and on the basis of the expected effect size for 2 dependent means (matched pairs) . The prospected outcome was obtained from a study on oral health related quality of life as measured by the Oral Health Impact Factor (OHIP-49) comparing patients treated with implant supported fixed dentures (implant bridges) and removable partial dentures without implant support. Mean scores were respectively 22.0 (SD 18.8) and 38.0 (SD 22.2) . Since we included patients with free-ending bilateral situations only, we presumed the OHIP value for this particular situation to be higher (i.e. 40) and the effect of implant support to be less (i.e. 24). Sample size calculation revealed that 23 subjects were needed to detect this increase in the primary outcome measure from 40 in the control group (RPD) to 24 in the experimental group (ISRPD, regardless of implant position). Given the fact that the expected effect in patients with some remaining natural teeth is presumably smaller than that in edentulous subjects and compensating for potential dropouts, the intended number of subjects to be included in the study was set at 30 patients.

The outcomes of the old, the unsupported new, the PM implant supported and the M implant supported RPD’s were compared by 1-way analysis of variance and multiple comparison tests after verification of normal distribution. When the data were not normally distributed a non-parametric test for related samples (Friedman’s test) was anticipated. In case of statistical significance (α = 0.05), post-hoc Wilcoxon signed rank tests were performed with Bonferroni adjustment for multiple testing. Mann-Whitney U tests were performed to detect any effects from treatment sequence (first M, then PM implant support versus first PM, then M implant support).