Complete denture fabrication using piezography concept-a case report

INTRODUCTION

The objectives of any prosthodontic service are to restore the patient to normal function, contour, aesthetics, speech and health. Optimum denture stability is difficult to achieve in patients with resorbed ridges. This problem is more magnified with in mandibular dentures. The design of prostheses to replace lost teeth and resorbed ridges is largely determined by the position and amount of morphological change in the denture bearing area of the jaws. These changes dictate artificial tooth positions in complete denture patients.¹

Neutral zone may be defined as the potential space between the lips and cheeks on one side and the tongue on the other, that area or position where the forces between the tongue and cheeks or lips are equal. This zone is referred to by various terminologies like prosthodontic space, neutral space, balanced zone, prosthetic corridor, rest space, deglution space, the phonetic space, the dead space, zone of minimal conflict and piezography. Knowledge of the neutral zone concept may be advantageous when fabricating complete dentures.

The neutral zone concept implies acquired muscle control especially by tongue, lips, and cheeks towards denture stability. The influence of tooth position and flange contour on denture stability is equal to or greater than that of any other factor.³ We should not be dogmatic and insist that teeth be placed over the crest of the ridge, buccal or lingual to the ridge. Teeth should be placed as dictated by the musculature, and this will vary for different patients. Positioning artificial teeth in the neutral zone achieves two objectives. First, the teeth will not interfere with the normal muscle function, and second, the forces exerted by the musculature against the dentures are more favourable for stability and retention.⁴

Piezography is a diagnosis and treatment procedure based on the neutral zone philosophy that makes a strange body, like the denture as comfortable as possible, respecting the functions of the muscles around the prosthodontic space. Piezography is not one step more within the prosthodontic treatment, it is another diagnosis tool and a part of the impression integrally considered. With the classically called primary and final impression the impression surface and the borders of the denture are obtained and Piezography technique allows us to obtain the shape of the polished surface and the form of the buccal and lingual aspect of the artificial teeth.⁵

Piezography, a technique used to record shapes by means of pressure, is a method for recording a patient’s denture space in relation to oral function. This method provides a mandibular denture with a piezographically produced lingual surface, which customizes the contour and precludes overextension. This technique involves introduction of a mouldable material into the mouth to allow unique shaping by various functional muscle forces. Speech is one function that can be employed as a selected variable using this technique.⁶

Case Report

A 62-year-old male patient reported with a chief complaint of loose mandibular denture, difficulty in chewing and speech for last six months. On examination of the dentures, the mandibular denture was ill fitting with worn out occlusal surface and undesirable peripheral extensions. On extra oral examination the positive findings are, patient had oval facial form with straight profile. The lip length was long and there was loss of lip fullness. The mouth opening was about 42mm. the mandibular movements were not restricted [Fig.1].

On intra oral examination, the maxillary and mandibular arches were edentulous.The maxillary arch was medium in size with U shaped arch form. The contour of the ridge was well rounded. The mandibular arch was resorbed, small in size with V shaped arch form and the contour was rounded. There were no bony undercuts or tori present. The tongue was normal in size with good movement and coordination, whereas the mucosa was healthy [Fig.2].

The preliminary impression was made with the impression compound (Y-Dent) and the primary casts were retrieved. The special tray was fabricated with autopolymerising acrylic resin. The border molding was done with low fusing impression compound (DPI) and the secondary impression was made with Zinc oxide eugenol impression paste (Neogenate, Septodont).The impression was poured with dental stone and the master casts were retrieved. The permanent denture bases were fabricated with heat polymerizing acrylic resin (DPI). The occlusal rims were constructed with modelling wax. The orientation record was made with earpiece self-centric facebow and was transferred to the semi adjustable articulator.

The mandibular cast was mounted with tentative centric relation [Fig.3]. The Gothic arch tracings were made and the interocclusal records were made to confirm the centric relation and to program the articulator. The modeling wax was removed from the mandibular denture base was removed and the metallic inserts were inserted to the level of the occlusal plane. The piezographic zone was recorded with tissue conditioner material (Soft liner, GC corp) [Fig.4]. The tissue conditioner was added on to the mandibular denture and the patient was instructed to pronounce series of phonemes like “sees”, “so”, “sa”, “me”, “moo”, “pe” “the”, and “te” repeatedly. The tissue conditioner was allowed to polymerize completely inside the mouth. The index of this was made with putty consistency addition polyvinyl siloxane impression material [Fig.5]. The mandibular teeth were arranged according to this index and the balancing was done on the articulator [Fig.6]. The denture try in was done to verify the working side and balancing side contacts [Fig.7]. To record the polished surface of the denture the tissue conditioner was added on to the buccal and the lingual surfaces of the trial denture and patient was instructed to pronounce the same phonemes. The trial dentures were invested and the processing was done in the conventional manner. The dentures were finished and polished. The laboratory remount was done to eliminate any interference because of the processing. The dentures were inserted and the post insertion instructions were given to the patient [Fig.8]. The mandibular denture had good stability as well as retention [Fig.9]. The patient was comfortable with the dentures [Fig.10].

DISCUSSION

Regarding complete denture treatment, several methods that take physiological function into account have been developed since the 1930s. These studies have clarified that the buccolingual tooth position and the contour of the polished surface are important for denture retention and stability.⁷ Many techniques have been suggested using various materials in conjunction with movements including sucking, grinning and whistling and pursing the lips.^8,9 The swallowing /modeling plastic impression compound technique located the neutral zone, using swallowing as the principle modeling function.¹⁰ Considering that a person swallows up to 2400 times per day, and considering also that during the entire swallowing sequence teeth come into contact for less than 1 second, it may be concluded that less than 40 minutes of tooth- to-tooth contact occurs per day during function.¹¹ Speech is also another important part of daily oral activities. During speaking, the mouth is moderately opened, pressures of different magnitude and direction are generated, and forces are produced with a greater horizontal than vertical component acting on the dentures. Furthermore, although speaking causes upward movements of the floor of the mouth similar to swallowing, these movements are not as constant as those found in swallowing. Thus, the phonation/ tissue conditioner technique uses phonation to develop a mandibular impression.

The term “Piezography” comes from Greek and means, “Piezo”- pressure and “graphy”- sculpture and it refers to the volume or content in the space. Piezography is the impression of the inner and outer walls (buccal and lingual) of the prosthetic corridor. It is a procedure in which, by functional modeling the volume and shape of the prosthodontic space is registered.Piezography was used to record denture space by means of the speech function of each patient. The phonemes used this technique are “sees”, “so”, “sa”, “me”, “moo”, “pe” “the”, and “te” repeatedly. Each language has special sound and the phonemes can be changed depending on the language of the patient. With pronunciation of the phonemes we can see how the superficial muscles of the face are contracted. “S” mobilizes the tongue and consequently moulds the lingual aspect of the piezography. With “ee” the modiolus and buccinators-labial clinch pull backward and the cheek moulds the buccal aspect of the register. The vowels “O”& “U” compensate the retrusive action of the sound “ee”, the lips and modiolus moulds the buccal aspect in the anterior zone. The “a” act in the lateral portion intermediately between the “ee” and “O”. The sound “M” moulds more energetically the anterior buccal aspect. The phoneme “D” in its first stage puts the tongue lingually on the alveolar ridge and the anterior upper teeth, but immediately a very quick downward movement takes place in the tongue and mandible [Fig.11]. When the tongue falls down, it moulds the anterior inferior lingual aspect of the register.¹²

However, it remains unclear exactly when the procedure for obtaining the piezographic record is complete. For example, in the flange technique3 , recording of the denture space is complete when the resoftened flange wax no longer flows toward the occlusal surface of the occlusal rims. The recording of denture space morphology has been reported to vary according to the volume of the material used.¹³ The use of tissue Conditioner for piezography is advantageous because it has a suitable viscoelastic property and setting time and can be injected gradually over several applications.

The advantages of this technique are: better stability and retention, excellent speech and very good hygiene, the patients can practice before the impression is taken; the procedure is easy to understand, especially for the elderly; it is easy to inspect for proper oral function while the patients pronounce the phonemes The disadvantage is that aesthetics of the mandibular denture is slightly decreased because piezography may push the anterior teeth lingually.

CONCLUSION

The complete denture fabricated by means of this technique minimizes the need of adaptation for the patient, because it does not interfere with the oral functions. The muscular forces that promote instability in the conventional dentures are favorably capitalized in this method. They do not act negatively against the denture and they help in retention and stability of the denture.