Chronological grey scale changes in supporting alveolar bone by removable partial denture placement on patients with periodontal disease: A 6-month follow-up study using digital subtraction analysis

Abstract

Objectives

The purpose was to assess the early effects of removable partial denture (RPD) placement on abutment teeth in patients with periodontal disease.

Methods

Fifteen distal-extension RPDs and 19 abutment teeth were evaluated in 13 patients with moderate-to-severe periodontal diseases. Clinical periodontal records and grey level (GL) score based on digital subtraction radiography were measured on the day of denture placement (baseline) and at 1 day, 1 week, 1 month, 3 months, and 6 months after the placement. Occlusal force on total dentition (Ft) and abutment tooth (Fa) were recorded with (baseline) and without denture on the day of the placement, and with denture in the follow-up examinations.

Results

No statistically significant difference between a follow-up period and the baseline was found in the clinical periodontal and occlusal force records, except for Ft with denture on the day of the placement, which was significantly lower than the baseline (p < 0.05). The GL at distal crestal of the abutment was significantly higher at 1 week after the placement than at the baseline (p < 0.05), while the scores of following examinations returned to the baseline level.

Conclusions

The distal crestal bone of the abutment tooth transitorily reacts to mechanical stress due to the denture placement, while this does not suggest a detrimental effect within the limitation of the study design with a short-term observation period.

Clinical significance

The RPDs can be safely used for patients with periodontal diseases for at least 6 months if they are properly placed and maintained by professional care.

Introduction

For partially edentulous patients with severe periodontal disease, prosthodontic reconstruction of dentition and occlusal rehabilitation, along with supportive periodontal therapy (SPT), is essential for prevention of further tooth loss. Potential restorative approaches may include fixed partial dentures and implant-supported prostheses, while the removable partial dentures (RPDs) are provided for reconstruction of the occlusal function and aesthetic appearance without extensive tooth preparations and/or surgical intervention . RPDs are accepted as a prosthodontic measure that can cope with subsequent tooth loss by means of the addition of artificial teeth and denture base, suggesting it is highly adaptable to subsequent negative events, such as further tooth loss .

Despite the fact that carefully designed RPDs substantially restore the occlusal function of the patients , adverse effects of the RPD placement on retention of the abutment teeth have been reported in previous literature . A previous study indicated that periodontally compromised teeth presented an increased risk of tooth loss if they were used as RPD abutments . However, previous clinical studies on the prognosis of remaining teeth were often conducted without controlled conditions of the periodontal tissues and the remaining teeth , and even without a systematic design and fabrication protocol for the RPDs . Information on the topic is lacking, especially regarding the effects of denture placement on patients with moderate-to-severe periodontal diseases.

As one of the diagnostic measures used in those studies, radiographic examinations have been performed to evaluate the abutment teeth and the supporting alveolar bone based on the conventional morphometric concept . The quantitative changes of the bone loss have often been indicated as the changes in the alveolar bone-height or crown-to-root ratio, while qualitative changes, such as alveolar bone density, have rarely been assessed. The digital subtraction technique can facilitate a qualitative visualization of minor density changes in the alveolar cortical bone using two radiographic images taken within certain intervals. The subtraction can be implemented by superposition of the images with a time difference using unchanged anatomic structures as fixed guides . This method enables evaluations of bone changes in living bodies, and it has been used to assess the alveolar bone after immediate implant placement, periodontal surgery, and regenerative therapy .

The purpose of this nonrandomized prospective study was to evaluate a short-term chronological evaluation of the periodontal structures in the RPD wearers with moderate-to-severe periodontal disease. The clinical periodontal examinations were performed, and the maximum occlusal force at the occluding contacts was recorded to analyze the function of the periodontal structures throughout the follow-up periods. A digital subtraction technique using an original stationary observation device was applied to measure the qualitative changes of the periodontal structures. The hypothesis was that RPD placement causes changes in the grey scale level of the digital subtraction images of the alveolar bone surrounding the abutment teeth.

Materials and methods

Subjects

Subjects were recruited from patients who were diagnosed with moderate-to-severe periodontal diseases, based on the conditions of at least four periodontal probing sites with a depth ≥4 mm and radiographic evidence of ≥30% bone loss ( Fig. 1 , recruitment). The inclusion criteria were also limited to those who had lost their posterior teeth but had not had them restored during initial periodontal treatment for one side of the maxillary or mandibular dental arch. The subjects were excluded from the study according to the criteria shown in Table 1 . The subjects were provided oral hygiene instructions, non-surgical periodontal care, and surgical therapy when needed. They were enrolled as subjects of the study at the time when they were progressed to the SPT phase.

Fig. 1
Time course of the experiment.
The total experimental schedule from the patient recruitment to the final examination 6 months after the denture placement is shown according to the time course from left to right. There were no data lost throughout the follow up periods of this study. Ex.: Examination, SPT: supportive periodontal therapy

Table 1
Exclusion criteria.
Acute symptoms of oral and craniofacial diseases
Currently under dental treatment
Current use of a removable partial denture
Contraction of infectious disease or systemic disease(leukemia,・HIV, etc.)
Having a smoking habit

The subjects were informed of the study purpose on written descriptions of the protocol before they consented to participate. As a result, 13 subjects (8 females, 5 males; mean age 67.2 years; range: 37–80 years) qualified for participation. On the same day, partially edentulous dentition was examined and diagnosed for the RPD construction ( Fig. 1 , RPD diagnosis). The Ethics Committee of the University (authorization no. 1105) approved all the experimental procedures. The data were collected from December 2014 to September 2016 at the Tokyo Medical and Dental University Dental Hospital, Tokyo, Japan.

Provision and placement of the dentures

The dentures were fabricated with cobalt–chromium cast framework, heat-polymerizing denture base resin, and the artificial teeth. Clasp assemblies, with occlusal rests, proximal plates, and wrought wire clasp arms on the buccal side, were designed and engaged on the most distal remaining tooth of each edentulous area. Another occlusal rest was placed on the anterior part of the dentition as an indirect retainer. On the non-edentulous side, a clasp was placed on the premolar and/or molar teeth and connected to the denture base through a rigid major connector. All prostheses were designed by a prosthodontic specialist and fabricated by an experienced dental technician.

The subjects were instructed to wear a denture in daytime, but to keep it outside of the mouth during sleep at night. Each subject was given routine oral hygiene instructions, including tooth cleaning using a toothbrush after every meal and cleaning of the denture using a denture brush. Fifteen dentures, 5 maxillary and 10 mandibular, were inserted for 13 subjects, including 4 Kennedy Class I and 11 Kennedy Class II cases. In total, 19 abutment teeth, including an incisor, a canine, and 17 first premolar teeth, were subjected to evaluation ( Table 2 ).

Table 2
Clinical characteristics of the subjects.
Subject Abutment teeth
No. Gender Age Upper/
lower
Type of teeth Occlusal unit(*)
1 F 67 U first premolar 7
2 M 64 L second premolar 8
3 M 64 L second premolar 6
4 M 71 U canine 2
U second premolar
L second premolar
5 F 70 U second premolar 2
U incisor
6 M 64 L second premolar 6
7 M 37 L second premolar 8
8 F 80 U second premolar 8
9 F 69 L first premolar 7
10 F 77 L second premolar 3
L first premolar
11 F 71 L second premolar 7
12 F 67 L second premolar 8
13 F 73 U second premolar 4
U second premolar
L second premolar
M: male, F: female, U: upper jaw, L: lower jaw. The concept of an occlusal unit (*) is that a pair of occluding premolars corresponds to one unit, and a pair of occluding molars corresponds to two units .

Post-placement examinations

Throughout the post-placement period, routine denture adjustment was performed by an examiner (C.W.) whenever it was necessary at the examinations. Data collection was performed on the day of denture placement (baseline), and at the 1-day, 1-week, 1-month, 3-month, and 6-month follow-up visits, all by the same examiner ( Fig. 1 , Ex.1–Ex.5). Each subject also periodically visited the periodontist once for each three month for continuous SPT. To ensure consistency of the measurement, the examiner was calibrated prior to data collection by repeating all clinical outcome measurements in patients who were not subjects.

Clinical periodontal examinations

Probing pocket depth (PPD), clinical attachment level (CAL), and bleeding on probing (BOP) were recorded at the mesial and distal sites of each abutment tooth using a manual probe (PCP-UNC15, Hu-Friedy Manufacturing Co., Chicago, IL). Tooth mobility (TM) was also judged for each abutment tooth according to Miller’s classification .

Occlusal force measurement

Occlusal force on total dentition (Ft) and the force on each abutment tooth (Fa) were recorded based on the maximum bite force registration by means of a measurement system (Dental Prescale, FPD-705, GC, Tokyo, Japan) . Upon measurement, each subject was asked to bite as hard as possible at the maximum intercuspal position of the mandible for 3 s. The first measurement was performed without the denture and used as the baseline record, while the secondary measurement was performed with the denture after the initial denture adjustment was completed. In the follow-up examinations, all the measurements were performed with the denture.

Radiographic examination

All radiographic procedures were based on the parallel capturing technique. The X-ray generator (Dentnavi, Yoshida, Tokyo, Japan) was kept 30 cm apart from subjects, and was operated at 60 kVp, 7 mA, and 0.16 s. The examination was standardized using a positioning jig system to minimize the geometrical gap between the baseline and follow-up images. This was accomplished using the UniGrip film holding instrument (UniGrip, Dentsply, New York, USA) and the tailored bite block using an acrylic resin, which was prepared for each object ( Fig. 2 ). The abutment and the opposing teeth were secured in position with acrylic resin. Using the digital intraoral imaging system (DigoraOptime, Soredex,Helsinki, Finland), the obtained images were captured in the size of 1025 × 775 pixels with 8-bit 256 greyscale.

Fig. 2
Positioning jig system.
Schematic illustration represents a sectional view of a positioning jig attached to the targeted mandibular premolar tooth. The jig system contains occlusal plate (P), individual bite block (B) and ring holder (R). The other abbreviations represent the imaging plate (IP) and localizing cone (X) of the X-ray radiographic apparatus.

Digital subtraction

Radiographic analysis was performed using the digital subtraction computer software (Emago v.6.0, Oral Diagnostic System, Amsterdam, Netherland) ( Fig. 3 ). To subtract two periapical radiographs, we used the functions named “greyscale matching” and “geometrical registration”. A γ-correction performed using a non-linear histogram equalization algorithm and derived directly from the histograms associated with the radiographs was used for the greyscale matching between the baseline and a follow-up period. For geometrical registration, the operator selected some anatomical landmarks on each pair of radiographs, such as the tip of the cusp, the cement–enamel junction, and the apex of the root. Changes were depicted as a darkened area for mineral bone loss and a brightened area for mineral bone gain on the subtraction image .

Fig. 3
Radiograph of baseline, follow-up, and ROIs in subtraction image.
A representative mandibular left second premolar abutment tooth is shown by the radiographic images at the baseline (A) and at the 6-month-follow-up examination (B). A digital subtraction radiograph (C) was created based on images of (A) and (B). The same subtraction image featured seven regions of interest along the periodontal tissues of the tooth: ROI-1 to ROI-6, and a control site for calibration.

The image of each follow-up examination was digitally subtracted by that of the baseline, so that grey level (GL) values were computed at six regions of interest (ROIs) around the abutment teeth: mesial crestal, mesial middle, mesial apical, distal apical, distal middle, and distal crestal areas were selected along the root surface ( Fig. 3 D). A control ROI for calibration of grey level was placed at a site remote from the areas presumably unaffected by the denture placement ( Fig. 3 D, control). The size of each ROI was set to 20 × 20 pixels, which was as large as possible so that it fully included the target cancellous bone near the root surface, while excluding adjacent tissues. The use of a rectangular area for ROI was feasible for calculating the mean GL of all pixels in the area, which could represent the neighborhood region . The GL value theoretically ranges from 0 to 255, with the median value of 127 representing the same level as the baseline.

Statistical analysis

Statistical comparison between each follow-up examination and the baseline was performed for PPD, BOP, CAL, TM, and GL using a Wilcoxon signed-rank test with Bonferroni correction. For the occlusal force records, a Friedman’s test and pairwise comparison were used. Data analysis of Fa was conducted for the premolar abutments with exclusion of the incisor and canine teeth. The effect of occlusal units (OU) on the occlusal force was analyzed according to two subgroups comprising seven subjects for the OU ≧ 7 group and six for the OU < 7 group, using a Mann–Whitney U test. A p-value less than 0.05 was considered statistically significant (SPSS 22.0, SPSS, Japan, Inc., Tokyo, Japan).

Materials and methods

Subjects

Subjects were recruited from patients who were diagnosed with moderate-to-severe periodontal diseases, based on the conditions of at least four periodontal probing sites with a depth ≥4 mm and radiographic evidence of ≥30% bone loss ( Fig. 1 , recruitment). The inclusion criteria were also limited to those who had lost their posterior teeth but had not had them restored during initial periodontal treatment for one side of the maxillary or mandibular dental arch. The subjects were excluded from the study according to the criteria shown in Table 1 . The subjects were provided oral hygiene instructions, non-surgical periodontal care, and surgical therapy when needed. They were enrolled as subjects of the study at the time when they were progressed to the SPT phase.

Jun 17, 2018 | Posted by in General Dentistry | Comments Off on Chronological grey scale changes in supporting alveolar bone by removable partial denture placement on patients with periodontal disease: A 6-month follow-up study using digital subtraction analysis
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