Adaptation to New Dentures and 5 Years of Clinical Use: A Comparison between Complete Denture and Mini-implant Mandibular Overdenture Patients based on Oral Health-Related Quality of Life (OHRQoL) and Orofacial Esthetics.

Objective of work: It is unclear how long patients need to adapt to new dentures. This study assessed adaptation and five years of clinical use, comparing complete denture wearers (CDs) and mini-implant mandibular overdenture wearers opposing a maxillary CD (MDI-OD), based on oral health reported quality of life (OHRQoL) and orofacial esthetics (OES). Material and
Methods: A total of 36 subjects in the CD group (25 females) and 30 subjects in the MDI group (20 females) completed the 5-year study. All patients received new CDs, but in the MDI-OD group, four mini-implants were inserted interforaminally in the mandible before denture manufacture. Participants filled in the OHIP-EDENT and OES questionnaires one day after dentures' delivery, on the 3rd, 8th, 15th, 30th day, and at the 1-, 3- and 5-year follow-up examinations. Statistical analysis comprised descriptive methods, X 2 test, independent t-test, Friedman, and Mann-Whitney test. Results and Conclusions: Both groups' adaptation to new dentures was completed within a month. The MDI-OD group had significantly better OHRQoL in all follow-ups except for the 3rd and 8th day, probably due to soreness and pain, the reason why the MDI-OD group had limitation in functioning in the first days after new dentures' delivery. Already after the third year and at the fifth year, OHRQoL worsened (p<0.01) in both groups. However it was significantly more pronounced in the conventional CD wearers (p<0.01) than in the MDI-OD group. Orofacial esthetics was highly scored in both groups. The scores dropped down only after three years, equally in both groups. Keywords: OHRQoL, OES, prospective study, complete dentures, mini-implants, adaptation. MeSH Terms: Complete Dentures; Dental Implants; Quality of Life; Dental Esthetics.

Introduction

Despite numerous advances in dental medicine, inventions of new dental materials, and new technologies, tooth loss remains a reality, especially in an aged population (). Recent trends in dental medicine indicate that natural teeth are lost later in life, but a percentage of the aged population is also growing fast due to improvements in general medicine, better health care, and other facilities. Today people can expect to live into their sixties and beyond (, ). Therefore, although a trend of a decline of complete edentulism is present in high-income countries, edentulous patients will still be growing due to the increase of life expectancy (, ). For a long time, complete dentures (CD) have been the only treatment option for edentulous subjects (). Nowadays, therapeutic possibilities have improved by introducing dental implants, however only to those who can access such treatment. Many subjects cannot afford implant treatment either due to economic problems, general health issues, or inadequate bone volume, usually present in removable denture wearers (-). Therefore, CDs will continue to be the only option for most edentulous subjects (). Subjects who have been wearing removable dentures for a certain period are faced with problems elicited by continuous residual ridge resorption and bone atrophy, mucosal inflammation and injuries, development of a flabby ridge, consequential loss of denture stability, and reduction of a vertical dimension of occlusion with a contra-clockwise rotation of the mandible (-, -). The mandible's residual alveolar ridge atrophy is almost four times more pronounced (-). Therefore a panel of experts proposed that the minimum treatment for completely edentulous subjects is a two-implant retained overdenture (OD) in the mandible and a CD in the maxilla (McGill consensus) (). The McGill consensus is based on the evidence that dental implants significantly reduce a rate of residual ridge atrophy, not only at the implant site but also in distant areas (, ). In subjects with narrow alveolar ridges, rehabilitation with mandibular overdenture (OD) retained on four mini-implants has been recommended as the alternative to two-implant OD (, -).

The outcomes from a patients’ perspective, i.e., dental patient-reported outcome measures (dPROM) related to their oral health-related quality of life (OHRQoL), esthetics, or other self-perceived measures, are becoming the most important factors in evidence-based dentistry (-). Sometimes the therapist’s and the patient’s opinions of the effectiveness of a therapy can be different, and patients may be unsatisfied (, , ).

The duration of adaptation to conventional CDs or implant-overdentures (IOD) can vary depending on many factors, such as previous removable denture experience, expectations, psycho-social and cultural factors, quality of a denture bearing area (attached mucosa and the alveolar bone), quality of new dentures, etc. (, , , ). Therefore, it is not completely clarified how long a patient needs to adapt to new dentures and are there any differences in adaptation between conventional CD wearers and those with mandibular mini-implant ODs.

This study aimed to assess how long it needs for a patient, based on the self-reported outcome measures: oral health reported quality of life (OHRQoL) and orofacial esthetics (OES), to adapt to complete CDs and how long it needs to adapt to mini-implant mandibular ODs (MDI-OD) opposing a maxillary CD. The aim was also to compare the groups over the five years in function.

Material and methods

Sample

This study included completely edentulous subjects who were rehabilitated either with new conventional complete dentures (CDs) or with one new conventional CD in the maxilla and one new mini-implant retained OD in the mandible. Forty-four subjects were included at the baseline in the CD group and 36 in the MDI-OD group. It was planned to assign patients randomly into the CD or the MDI-OD group (odd or even numbers), but some participants did not want to be rehabilitated with implants due to fear or general health problems; therefore, they were assigned to the CD group. Subjects with wide residual ridges who could receive two standard-sized implants and an OD were also excluded. After five years of follow-up, only 36 subjects in the CD group and 30 subjects in the MDI group had all four mini-implants which were inserted at baseline and which were succesfull. Only their self-reported data were included in the statistical analysis. After insertion of four mini-implants, new dentures were made: at the Department of Removable Prosthodontics, School of Dental Medicine, Zagreb, Croatia; and at the Dental Private Office, Makarska. All mini-implants were inserted, and all dentures were made following the same criteria in a period from September 2015 to December 2016. The Ethics Committee of the School of Dental Medicine in Zagreb (No. 05‐PA‐26‐6/2015) approved the study. The costs of the MDIs were covered by the research grant No. 1218/2014 (Croatian Science Foundation) and the cost of dentures by the Social Insurance.

Surgical procedures for mini-implant insertion

All participants assigned into the MDI-OD group received four ball-type MDIs in sites of their previous second incisors (, ) and first premolars (, ). The Dentium, South Korea mini-implants were 2.0-2.5 mm wide and 10-14 mm long. Participants with a flabby ridge and mucosal thickness higher than 4 mm were excluded, and also patients who could receive standard-sized implants. Two experienced surgeons performed all surgical procedures after consulting a specialist in Prosthodontics. The MDIs’ length and width were determined based on the available bone volume measured on pre-operative CBCTs and panoramic radiographs. The surgical procedures were made either by a flapless or an open-flap technique, depending on the morphology of available bone. The open-flap technique was applied when a pointed slim alveolar ridge was leveled or when movable mucosal tissue needed to be de-attached. A physio-dispenser (W&H Implantmed, GmbH, Austria) and a saline solution for external drill cooling were used for the MDI insertion. The implant sites were prepared using pilot and final drills. The final drill diameter was always smaller than the MDI diameter (1.3–1.5 mm wide drills for 2.0 mm wide MDIs; 1.8–2.3 mm wide drills for 2.5 mm wide MDIs). The depth preparation was determined dependent on the bone quality assessed on the CBCTs (Hounsfield units). The preparations were made one, two, or three mm less than the implant length (longer preparation was performed in denser bone), except when the implant had to end in the dense lower mandibular cortex (D1 density). In that case, the whole implant length was drilled. For the flapless technique, the width of alveolar mucosa was measured and accounted. Antibiotics were administrated for prophylactic reasons (2 g amoxicillin or 600 mg Clindamycin one hour before the surgical procedure). All preparations and MDI insertions were made under local anesthesia (Ubistesine forte 4% or Mepivastesin 3%, 3M). Each MDI was inserted into the prepared hole and rotated clockwise, exerting a downward pressure (self-tapping insertion technique). The mini-implants were placed into the preparation hole by a carrier (plastic finger driver from the original package), then were rotated downwards by a thumb wrench, and finally, the torque wrench. The whole roughened threaded MDI surface was inserted into the bone. The transmucosal part of the smooth surface emerged from the attached mucosa into the oral cavity with the ball-type head. The patients were given the standard post-surgical instructions: no hot beverages, alcohol, or smoking for two days, ice-packs for cooling, and analgesics (non-steroid anti-inflammatory drugs) if necessary. An antiseptic mouth rinse (chlorhexidine gluconate 0.12%) was also prescribed for five days, and detailed instructions for oral hygiene maintenance were given. A range of final insertion torque values varied between 30 and 55 Ncm. New dentures were delivered and loaded 7-10 days after mini-implant insertion in the respective group.

Prosthodontic protocol (Complete denture or mini-implant overdenture manufacture)

All CDs and mandibular MDI-ODs were fabricated following the same procedures. After the alginate impressions, custom trays were made, and custom (individual) impressions were obtained for each patient. Then a vertical jaw relation in a centric position was registered by occlusal rims and transferred into a semi-adjustable articulator. Next, the semi-anatomical artificial teeth and a lingualized occlusion scheme with no occlusal balance were applied. After artificial teeth set-up in a trial denture and verification of satisfactory esthetics and antagonistic contacts in centric relation, the new CDs were processed. After new dentures delivery and mounting of metal-housings with O-rings in the MDI-OD group, the occlusion was checked and adjusted if necessary, oral mucosa was inspected for soreness, and the denture was trimmed-off when necessary during adaptation. All mandibular overdentures were strengthened with a CoCr metal framework not to fracture. At the MDI-OD deliveries, four metal housing with O-rings (matrices) were mounted directly in the patient's mouth using a self-curing acrylic resin and block-out spacers (block-out shims).

Two experienced specialists in Prosthodontics who were not involved in the CD or OD manufacture assessed the quality of new dentures for retention, stability, esthetics, and occlusion. The possible assessments were: low-quality, average quality, or high-quality dentures. Only patients with high-quality new dentures were recruited in the study. The weighted kappa statistics showed satisfactory agreement between the observers (κ= 0.808).

Questionnaires: d-PROMS

One day after the new CD or MDI-OD delivery, the patients had to fill in data about gender, age, and their previous dental status [fixed partial denture or natural teeth (FPD); removable partial denture (RPD)]. They also had to fill in the validated questionnaires, i.e., the OHIP-EDENT questionnaire consisting of 19 questions () and the orofacial esthetic scale (OES), consisting of eight questions (). The OHIP-EDENT comprised 19 questions with answers from 0 (without problems) to 4 (maximum problems). Lower scores represent better OHRQoL. The OES comprised eight questions with answers from 1 to 5 (1-the worst score, 5= the best score). Higher scores represented better esthetics. All patients also filled in the same questionnaires on the 3rd, 8th, 15th, and 30th days. The same assessments were repeated after 12 months, after 3 years, and after 5 years of wearing a denture. The checks were made in a dental office one day after delivery, the 3rd, 8th, and 15th day. If patients needed any more denture adjustments, they came to a dental office, but if not, they were assessed by telephone. The summary score of each of the two questionnaires was divided by the number of questions. Then, the data were entered for statistical analysis.

Statistical analysis

The IBM-SPSS Statistics for Windows (Version 20.0.; IBM Corp) was used. Descriptive statistics (mean values and standard deviations) were calculated. X2 test and independent t-test were also used. Changes over time were analyzed by Friedman's non-parametric test for related samples in each group, while the significance of the differences between the CD and the MDI-OD group was assessed with the non-parametric Mann-Whitney U test.

Results

A total of 36 participants in the CD group completed the five-year study: 25 were females and 11 males. In the MDI-OD group, from a total of 30 participants who completed the study, 20 were females, and 10 were males. No gender difference was observed between the groups (X2=0.058; df=1; P=.809). The participants in the MDI-OD group were a bit younger (65.1±6.2 years) than in the CD group (68.9±8.2 years) (t=2.08, df=64; P=.04). From the baseline of 36 patients in the MDI-OD group, one patient lost two MDIs in the first year, one patient lost one MDI after two years, and one patient lost all four mini-implants in the 5th year, while three MDI-OD patients were not available at least at the one of the recall examinations. All of them were excluded from the OHRQoL and OES research. A total of 95.14% mini-implants remained successful after five years. A total of 90.09% of patients had successful all four mini-implants after 5 years. Of the 44 patients in the CD group, eight did not respond to at least one of the recall examinations and were excluded. Only those patients who responded to all recalls were statistically analyzed.

Mean OHIP-EDENT scores in the CD and the MDI-OD groups and standard deviations are presented in Figure 1.

Figure 1

Mean OHIP-EDENT scores in the CD group and the MDI-OD group together with standard deviations

Mean OES scores in the CD and the MDI-OD group and standard deviations are presented in Figure 2.

Figure 2

Mean OES scores in the CD group and the MDI-OD group together with standard deviations

The significance of the differences between the CD and the MDI-OD group for the OHRQoL and OES at each of the recall examinations is presented in Table 1.

Table 1

Significance of the differences between the CD and the MDI-OD groups for the OHRQoL and OES at the recall examinations assessed by the Mann-Whitney U test.

Oral Health-Related Quality of Life (OHRQoL)
OHIP19 EDENT	OHIP191 day		OHIP193 days	OHIP198 days	OHIP19 15 days	OHIP1930 days	OHIP191 year	OHIP193 years		OHIP 195 years
Mann-Whitney U	285.00		431.00	403.50	355.00	292.50	298.50	197.00		188.50
Wilcoxon W	750.00		896.00	868.50	820.00	757.50	763.50	662.00		653.50
Z	-3.30		-1.41	-1.76	-2.39	-3.21	-3.14	-4.44		-4.55
P (2-tailed)	<0.001**		0.160 NS	0.080 NS	0.020*	<0.001**	<0.001**	<0.001**		<0.001**
Orofacial esthetics (OES)
OES		OES1 day	OES3 days	OES8 days	OES15 days	OES30 days	OES1 year	OES3 years	OES5 years
Mann-Whitney U		494.00	504.00	503.50	494.50	497.00	509.00	527.50	529.50
Wilcoxon W		959.00	969.00	968.50	959.50	962.00	974.00	992.50	994.50
Z		-0.66	-0.55	-0.56	-0.71	-0.69	-0.45	-0.16	-0.14
P		0.51 NS	0.58 NS	0.58 NS	0.48 NS	0.49 NS	0.65 NS	0.87NS	0.89 NS

The significance of the differences between each period of observation for the CD group and the MDI-OD group was assessed by the Friedman test for related samples and shown in Table 2.

Table 2

Significance of the differences between the periods of observation for the CD and the MDI-OD groups assessed by the Friedman test

OES	CD wearers		MDI-ODs
	Mean Rank	N=36X2=197.387df = 7p<0.001**	Mean Rank	N=30X2=170.032df = 7p<0.001**
OES - 1 day	5,19		5,13
OES - 3 days	5,39		5,42
OES . 8 days	5,53		5,55
OES - 15 days	5,65		5,73
OES - 30 days	5,72		5,82
OES - 1 year	4,93		5,02
OES - 3 years	2,33		2,18
OES - 5 years	1,25		1,15
OHRQoL	CD wearers		MDI-ODs
	Mean Rank	N=36X2=171.32df = 7p<0.001**	Mean Rank	N=30X2=162.610df = 7p<0.001**
OHIP19 - 1 day	3,67		2,72
OHIP19 - 3 days	5,99		6,55
OHIP19 - 8 days	6,42		6,87
OHIP19 - 15 days	3,68		3,90
OHIP19 - 30 days	1,90		1,95
OHIP19 - 1 year	1,93		2,07
OHIP19 - 3 years	5,31		5,08
OHIP 19 - 5 years	7,11		6,87

Results showed that after one day of denture wearing, the CD group had significantly worse OHRQoL (higher OHIP-EDENT scores) than the MDI-OD wearers. At all clinical examinations, OHRQoL was significantly better in the MDI-OD group than in the CD group (p<.01), except on the 3rd and the 8th day, when there was no significant difference between the groups. On the 15th day, the difference was significant at p<.05. After 30 days, the scores were the lowest in both groups (Fig. 1, Table 2), but were significantly higher in the CD wearers (Fig. 1, Table 1). The scores remained unchanged during the 1st year of denture wearing (Fig. 1, Table 1, Table 2). However, after three years of denture wearing, the scores significantly rose in both groups (Fig. 1, Table 1, Table 2), but almost two times more in the CD wearers. After five years, the scores again increased significantly and were significantly higher in the CD wearers than in the MDI-OD wearers.

Orofacial esthetics was highly scored in both groups from the baseline throughout the first year of follow-up (p>0.05), and then the scores reduced at the 3-year and 5-year follow-up (p<0.05). There was no significant difference in OES mean scores between the groups for any observed periods.

Discussion

It has not been clarified how long a patient needs to adapt to new CDs or to a maxillary CD opposing four mini-implant OD in the mandible (MDI-OD). Therefore, we designed a clinical prospective cross-over study based on dental patient self-reported measures, i.e., OHRQoL and OES. The OHIP-EDENT questionnaire has already been psychometrically validated in many countries and languages and was a logical choice for assessing OHRQoL for edentulous patients (, -). After the first day of new denture wearing, the OHIP EDENT scores gradually increased through the 3rd and the 8th day and then gradually decreased (the 15th day) and reached the lowest values after 30 days in both groups. The scores remained unchanged throughout the first year of denture wearing. The pattern of OHIP EDENT scores was similar in both groups. However, significantly lower values (better OHRQoL) were recorded in the MDI-OD group after one day, 15 days, 30 days, 1, 3, and 5 years of denture wearing. The difference between the groups was not significant only on the 3rd day and 8th day, although MDI-OD group still had better OHRQoL. It has already been reported that in the first days of new denture wearing, dentures usually cause inflammation of underlying mucosa, soreness, pain and discomfort, and consequently low masticatory performance (, ). Although mini-implants offer better retention and stability to mandibular overdenture than residual alveolar ridge to conventional mandibular CDs, when soreness and pain are present, patients cannot chew properly even if retention and stability of their dentures offer such possibility. That was probably why no statistically significant difference was found between the groups on the 3rd and 8th days. After denture and occlusal adjustments and healing of sore spots, the OHIP EDENT scores dropped on the 15th day in both groups, and the MDI-OD group again revealed significantly better OHRQoL. The lowest scores recorded on the 30th day remained unchanged over the first year of new denture wearing in both groups, with significantly better OHRQoL in the MDI-OD group (Figure 1). The adaptation to new dentures lasts up to one month in both groups. Better OHRQoL recorded in the MDI-OD group than in the conventional CD wearers is in line with many other reports on implant overdenture patients (, , -). IODs are associated with significantly better patient quality of life and masticatory performance. After 3 and 5 years of denture wearing, scores significantly rose in both groups (worse OHRQoL), but almost two times higher in the CD group (worse OHRQoL) than in the MDI-OD group. Although mini-implants offer better retention and stability to the mandibular denture and allow better masticatory function, we must keep in mind that those patients still have CDs in the maxilla, which may lose retention over time. The matrices’ O-rings in the MDI-OD group also lose retention over time and must be changed.

As another d-PROM, the OES questionnaire has been used in our study. The OES is the one-dimensional questionnaire developed to assess orofacial esthetics and has been psychometrically adopted in many countries and languages worldwide (, -). It was developed because OHIP questionnaires lack questions related to orofacial esthetics.

The summary scores of 8 OES questions were divided by the number of questions to obtain mean scores. Both, the CD and the MDI-OD group gave high scores to esthetics and their esthetic appearance of the lower third of the face (Fig. 1). The scores remained unchanged over the one year, but afterward, the scores dropped down at the 3rd year and even more at the 5th year recall examination (Fig 1, Table 2). The pattern was same in both groups, and there was no significant difference between the groups (p>0.05, Table 1). The artificial teeth and denture materials absorb colors from food and drinks and stain over time (-). Calculus can also be present on dentures. Artificial teeth wear and show cracks or fractures. All mentioned facts were the probable reasons for lower scoring of orofacial esthetics after 3 and 5 years. Loss of vertical dimension of occlusion due to residual ridge atrophy can also be present, more pronounced in the CD group, as described in dental literature (-). However, the CD group did not give worse scores to orofacial esthetics than the MDI-OD group at the three and 5-year examinations. The influence of jaw bone atrophy on the aesthetic rehabilitation of edentulous patients has not been studied extensively. One study found out that increased volume of lips and cheeks after rehabilitation was important in improving facial aesthetics and patients with non-atrophic ridges were more satisfied than patients with extensive residual ridge atrophy (). However, follow-up over a longer period was not performed in that study. Our patients already had a status of atrophied residual alveolar bone at the study's baseline, as patients who could receive wider implants (more bone) were excluded. It is well known that bone resorption is more pronounced in the early stages after teeth extraction, while the rate reduces over time. The majority of our patients had already atrophied bone. Therefore, a small rate of bone loss was possible over an observation period of 5 years and did not influence the OES outcomes.

Based on the obtained data, our prospective clinical cross-over study confirmed that the process of adaptation to both, new CDs or to new mini-implant overdentures opposing maxillary CDs is completed within a month. However, the MDI-OD group presented significantly better OHRQoL (lower OHIP-EDENT scores) than the CD group all the time, except on the third and the eighth day after dentures’ delivery. After three years of denture wearing, OHRQoL worsened significantly in both groups, but two times more pronounced in the conventional CD wearers. In addition, the OES scores also worsened after three years of denture wearing equally in both groups.