O.F. Olawale1, T.J. Ogunrinde2, O.O. Dosumu2, D.M. Ajayi2

  1. Department of Restorative Dentistry, Ahmadu Bello University Teaching Hospital, Shika-Zaria, Kaduna State, Nigeria.
  2. Department of Restorative Dentistry, University of Ibadan/University College Hospital, Ibadan, Oyo State, Nigeria.


Introduction: Removable denture still stands as the preferred option in the management of completely edentulous arch in the developing society. The prosthodontist is challenged with providing a retentive denture to the patient, alleviating the effect of tooth loss. The retention of these prostheses is influenced by the material used for it fabrication and the edentulous ridge height, hence the need to assess the retention of acrylic and flexible complete denture and the effect of edentulous ridge height.

Aim: This study was to assess and compare the effect of ridge height on retention of flexible and acrylic complete upper dentures.

Materials and Methods: Ten patients with complete upper edentulous arches were recruited and randomly allocated into two groups (A and B). Acrylic and flexible, complete maxillary dentures were fabricated for each participant. Group A wore the acrylic denture first, while group B wore the flexible denture first. Each participant was recalled after using the denture for one week, one month, and three months for data collection.At cross over time (3 months after wearing the first denture), individuals in group A were given flexible dentures, while those in group B received acrylic dentures. The patients were recalled again for data collection by one of the researchers. Kapa Intra examiner reliability test was 83.3%. Information related to denture retention were obtained and entered into IBM SPSS software version 23 for analysis. Paired t-test and linear regression were used to test for association between quantitative variables. A P-value of 0.05 was regarded as significant.

Results: Ten individuals with mean age of 66.5±9.7 years and mean anterior ridge height of 15.5 ± 2.95 mm participated in this study. The subjective and objective assessments of the dentures showed that acrylic denture possessed a better retention than flexible denture. The effect of anterior ridge height on retention, showed a statistically significant difference (p= 0.006 for acrylic denture, p = 0.001 for flexible denture).

Conclusion: This study suggested that acrylic denture possesses better retention compared to the flexible type and far better in situation with lower ridge heights

Keywords: Retention, Acrylic denture, Flexible denture, and Ridge height


Dr. O. Olawale
Department of Restorative Dentistry,
Ahmadu Bello University Teaching Hosp.,
Date of Acceptance: 31st Dec., 2022


Complete edentulism is an irreversible condition that is incapacitating and debilitating, leading to functional, physical, social, and psychological disabilities.1 It has a global impact and is described as the final marker of disease burden for oral health.2 It is defined as the state of the oral cavity with loss of all the natural teeth and supporting tissues in a dental arch or both arch(s).3,4

Following tooth loss, there are some intra and extra oral anatomical changes which have varying effects on the individuals’ oral health, general health, and quality of life.2,5 The mechanisms connecting poor general health and tooth loss could be linked to the dietary and lifestyle modification of edentulous patients. A likely pathway of this association involves the grave effect of tooth loss on nutrition, with a negative outcome on systemic health.6 Most patients regard tooth loss as mutilating and a condition that require urgent dental intervention.7

Among the myriad of anatomic changes associated with tooth loss is alveolar ridge resorption. Ridge resorption is perceived to be a physiological process, affecting the lower jaw four times more severely than the upper jaw.8 This leads to a reduced alveolar bone height and denture bearing area. The resorptive changes of the alveolar ridge (height and width) affect the lower facial height and appearance (aesthetics); leading to changes in the facial tissue profile. This may present as soft tissue collapse of the cheek, or class III ridge relationship. The rate of anatomic degenerative changes varies from person to person and the cause is still not clear. It is believed that a combination of local and systemic factors such as length of edentulism, parafunctional habits, age, gender, bone density, and systemic diseases such as osteoporosis may be contributory.2

The prevalence of tooth loss varies from country to country and it occurs more commonly among the elders, and individuals of low social economic status. (8)Various factors such as the cost, patient choice, and the duration of edentulism, the extent of tooth loss, expertise, and laboratory support determined the choice of teeth replacement options. The options available include the use of removable dentures, and implants retained prosthesis to improve retention, performance and satisfaction, among others. The removable denture still stands as the most available, affordable, and preferred alternative in the management of complete edentulous arch in a developing society like ours.9,10,11

Retention in a complete denture is a feature that resists the displacement of a denture in an occlusal direction. The retention of the denture is of utmost interest to the patient and a matter of great reward to the dentist. There are factors that affects how well retained an acrylic removable complete denture could be and they include the edentulous ridge height, forces of adhesion, cohesion, interfacial surface tension, gravity, intimate tissue contact, peripheral seal (border seal), weight of the denture, atmospheric pressure, and neuromuscular control.12,13Acrylic resin has been the material of choice in the fabrication of complete denture. However, the presence of residual monomer in acrylic denture that has the tendency to irritate the oral soft tissue 14 prompted the need for an alternate material. Polyamide appeared to be the most preferred alternative denture base resin with some outstanding qualities such as; high toughness, low density, abrasion resistance, and resistance to chemical attack. There is controversy on the flexibility but it gives a higher resistance to shock and fatigue stress compared to acrylic denture. The flexible denture material is not without a downside as its flexibility is also seen to be a disadvantage for denture bases. In addition, it has a higher water sorption which gives room for colour change and allows colonization of microorganism.15

There are conflicting views on the retention of polyamide due to its flexibility. Some authors16,17,18 have shown that the flexibility of the resin allows it to be easily adapted to bony tissue undercut (bilateral), providing good retention. However, other reports19,20 showed that flexibility is not a plus where there were no undercuts during a complete denture fabrication, because the retentive peripheral seal are often broken during function. The most important single factor in complete denture on which retention depends is the border seal.21,22 The glossary of prosthodontic terms defined the border seal as the contact of the denture border with the underlying or adjacent tissues to prevent the passage of air or other substances and in turn enhance retention.23 The effectiveness of peripheral seal on retention is largely dependent on the amount of ridge height present on the arch, which in turn has a direct effect on retention; the higher the ridge height the better the retention. To this extent restoration of a severely resorbed ridge using conventional complete denture has met a great difficulty especially in a developing society like ours where an average individual lives below the poverty level and cannot afford procedures such as implant retained prosthesis. Hence the need to assess the amount of ridge height that is adequate to provide retention for a complete denture made of acrylic or flexible denture bases with good retentive outcome.

As a result of the controversies surrounding the retention of flexible denture, this study compared the retention of maxillary complete flexible and acrylic dentures and also estimated the amount of clinical ridge height that is adequate to retain a complete denture made of acrylic and flexible resins.