Neutral Zone Technique in Complete Denture PDF

NEUTRAL ZONE TECHNIQUE IN COMPLETE DENTURE The stability of complete dentures is influenced by the surrounding neuromuscular system in the oral cavity. Oral functions, such as speech, mastication, swallowing, smiling, and laughing, involve the synergistic actions of the tongue, lips, cheeks, and fl...

NEUTRAL ZONE TECHNIQUE IN COMPLETE DENTURE The stability of complete dentures is influenced by the surrounding neuromuscular system in the oral cavity. Oral functions, such as speech, mastication, swallowing, smiling, and laughing, involve the synergistic actions of the tongue, lips, cheeks, and floor of the mouth that are very complex and highly individual. Neuromuscular control is the key for the stability of dentures. Size and position of denture teeth and the contours of polished surface play a crucial role in denture’s stability as they are subjected to destabilizing forces from the tongue, lips, and cheeks if they interfere with the function of oral structures. Definition of Neutral Zone: Is 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. The Neutral Zone Philosophy It is based upon the concept that for each individual, there is a denture space which is a specific area where the function of the musculature will not unseat the denture and where the forces generated by the tongue are neutralized by the forces generated by lips and cheeks. The Neutral Zone and the denture Space: In complete edentulous patients a void in the oral cavity is called potential denture space. Boundaries of denture space Maxilla and soft palate _superiorly Mandible and floor of the mouth _inferiorly Tongue _medially Muscles and tissues of cheek and lips _laterally Neutral Zone Concept Neutral zone is that area in the mouth were, during function, the forces of tongue pressing outward are neutralized by the forces of the cheeks and lips pressing inwards. Since these forces are developed through muscular contraction during chewing, speaking, swallowing etc. they vary in magnitude and direction in different individuals and in different periods of life. The way these forces are directed against the denture will either stabilize or dislodge them. Our objective is to utilize this information to so position the teeth and the external surface that the force the musculature exerts will have a seating effect. This can be only accomplished by a knowledge of neutral zone and by positioning the teeth and developing the external surface so that all the forces exerted are neutralized. The central thesis of the neutral zone approach to complete dentures is ‘to locate that area in the edentulous mouth where the teeth should be positioned so that the forces exerted by the muscles will tend to stabilize the denture rather than unseat it’. Muscles involved in Neutral zone Techniques: Muscles of Cheek: 1. Masseter Affects distobuccal border of mandibular denture. 2. Buccinator Muscle fibers forms a continuous bands ,hence the size of the arch is limited by the strength of the contractile force and the length of the muscles when they are contracted. Common practice of centralization or lingualization of occlusion creates a space between the cheek and teeth and external surface of the denture which prevents the buccinator from performing its proper function in two ways: First: Food accumulation and becomes more difficult to the cheek to place the food back to the occlusal surface of the teeth. Second: The space prevents the buccinator from neutralization the lateral forces of the tongue during function. Muscles of the lips: 1. Orbicularis oris: During function as in chewing smiling and swallowing, it exerts force against teeth and denture flanges which counteracted by the tongue. 2. Caninus This together with other muscles, pulls the upper lip upward and in sucking and swallowing pull the lip forward, thus exerting forces on teeth and labial flanges. 3. Zygomatico major. Pulls the angle of the mouth upward and backward. 4. Risorius: Retract the corner of the mouth. 5. Mentalis: Turns the lower lip outward and on contraction makes the lower labial vestibule shallow. 6. Triangularis: Contracts during sucking and exert pressure on teeth and denture flange. 7. Modiolus: It is contributed by followings facial muscles : 1. Orbicilaris oris 2. Buccinator 3. Levator anguli oris 4. Depressor anguli oris 5. Zygomaticus major 6. Risorius 7. Platysma 8. Levator labii superioris Because of strength and variability of movement of the area, modiolus is very important in stability of lower denture. Proper positioning of teeth and contouring and narrowing of external surface of premolar area should be done otherwise the modiolus will constantly unseat the lower denture. Muscles of the Tongue: 1. Intrinsic muscles they are confined to the tongue and not attached to the bone. They produce change in shape of the tongue. 2. Extrinsic muscles These muscles attached to the bones and soft palate.They are: Genioglossus , styloglossus , hyoglossus and palatoglossus. They are responsible for tongue movement and change in shape. Tongue is capable of changing shape and position during function as in mastication, swallowing and speech. During function it will be in constant contact with lingual surface of lower teeth, lingual flange of lower denture and palatal surface of upper denture. The common practice of lingualization is one of the greatest influencing factors of lower denture instability because it violates the neutral zone and encroaches on the tongue space. Influence of muscles on dental arches: During childhood, the teeth erupt under the influence of muscular environment created by forces exerted by tongue, cheeks and lips, in addition to genetic factor. These forces have a definite influence upon the position of the erupted teeth, arch form, and occlusion. Generally, muscular activity and habits which develop during childhood continue throughout life and after teeth loss. It is important to position artificial teeth in the arch form compatible with these muscular forces. As the impression surface area decreases (due to alveolar ridge resorption), the retention and stability of the denture decrease. Consequently, retention and stability become more dependent on the correct positioning of the teeth and contours of the polished surfaces of the dentures. The polished surfaces should be so contoured that the horizontally directed forces applied by the peri_denture muscles should act to seat the denture. The artificial teeth should not be placed on the crest of the ridge or buccally or lingually to it_rather these should be placed as dictated by musculature. After the teeth have been lost, muscle function greatly influence any complete dentures that are placed in the mouth. It is therefore, extremely important that the teeth be placed in the mouth within the arch form that falls within the area that is compatible with muscular forces. Influence of forces on denture surfaces The more ridge loss, the less influence of impression surface of the denture on its stability and retention ,and the more external surface area which is needed to be contoured properly to overcome this situation. The forces on external surfaces are changing in magnitude and direction during function and remain constant at rest. In order to construct denture that function properly, we must develop fit and contour of external surface as fit and contour of impression and occlusal surfaces. Objectives of Neutral zone Techniques: 1. Rehabilitation of complete denture patient. 2. Achieve maximum prosthesis stability, comfort, and function. 3. Arrange the denture teeth and contour the complete denture polished surfaces. 4. Minimize the ongoing diminution of the residual alveolar ridges. Indications of Neutral zone Techniques: 1. Severely atrophic mandibular ridge. 2. High mentalis attachment 3. Neuromuscular disease. 4. Atypical shape of oral structures. 5. Trauma. 6. Systemic disease. 7. Locate optimal position for implants. 8. Partial glossectomy. 9. Motor nerve damage to the tongue. Neutral zone technique could be performed in: Impression stage. Jaw relation record. Trial denture. Finished or previous prosthesis. Recording neutral zone in final impression stage Step by step : Primary impression of upper and lower arches. Construction of acrylic bases. An acrylic denture base with retentive wires is fabricated to retain impression material during recording neutral zone area. Impression compound is adapted on external surface of the tray and inserted in the patient’s mouth. Establishment of occlusal plane. Locating neutral zone for the upper arch. Vertical dimension establishment. Lower final impression with Z.O.E. The lower record base is inserted with lubricated upper denture base together to make impression with closed mouth technique. Second impression is made with krex material which is white, soft, thin, free flowing and contrasting color with the Z.O.E.  Upper arch impression. Several holes are made in the rugea area to allow excess Z.O.E. to escape during impression. Second impression with krex. Centric relation record. Mounting to the articulator and fabrication of matrices. Teeth arrangement. Trial denture and neutral zone impression for polished surfaces and the dentures is ready for investing. Recording neutral zone in jaw relation visit Primary impression with impression compound. Final impression with Z.O.E. Jaw relation record. Lower acrylic special tray with metal spurs. Occlusal pillars built in green stick to establish the occlusal height. Instruct the patient to perform certain oral movement including: sucking , grinning , whistling , pursing of the lips and swallowing. Tissue conditioner being molded with mouth movement. The tray is returned to the cast and plaster index is formed. Wax rim is formed and teeth set up. Insertion Recording neutral zone in try in stage Apply vaseline on trial denture before making impression. Impression material is applied on buccal & lingual surfaces of waxed up denture. Patient performs oral function. Inspect the impression on polished area including palatal surface. Carefully carve the material over tooth surfaces with carver. Finished denture. Recording neutral zone in finished denture Determining the fit of complete denture to neutral zone. Coat the polished surface of the denture with low viscosity silicone impression material. Ask the patient to perform functional movement while the material sets. Inspect the denture and adjust any heavy muscle contact. Determining the optimal space for a segment of the denture. Remove the teeth and base material from the segment of the denture that needs  modification. Apply adhesive and take the impression with moldable material. Check for stability and undertake the laboratory procedure. Comparison between conventional mandibular denture and mandibular denture made by neutral zone concept According to setting of the teeth in relation to the crest: According to denture volume: The neutral zone denture volume is lower than the volume of the conventional denture. ADVANTAGE: 1.Improved stability and retention. 2.Correct positioning of posterior teeth allowing sufficient tongue space. 3.Reduced food trapping adjacent to the molar teeth. 4.Good esthetic due to facial support. LIMITATION FOR THE SUCCESS OF NEUTRAL ZONE IMPRESSION TECHNIQUE: 1.Viscosity of the material used. More viscous, the more difficult for the muscle to mold. 2.Geriatric patients could suffer from the procedure due to loss of their muscular tone. 3.Proper stability & retention of the bases , so as the comfort. 4. The resultant neutral zone is often narrow and might be lingually placed, this will affect functional movement of the tongue and phonetics. 5. The technique does not offer any guidelines for the selection of teeth. Neutral zone always moves according to the periods of edentulism, tonicity of the perioral musculatures and tongue. Arrangement of the teeth in neutral zone, increasing the impression surface area of the denture and reduction in the volume of the denture, provides good retention, stability and comfort to the patients. Posterior Palatal seal Complete dentures may suffer from a lack of proper border extension, but most important of all is the posterior palatal extension on maxillary complete dentures. The posterior border terminates on a surface that is movable in varying degrees and not at a turn of tissue as are the other denture borders. Locating and designing of posterior palatal seal after thorough understanding of the anatomic and physiological boundaries of this dynamic region greatly enhances border seal and increases maxillary complete denture retention. Hundreds of dentures have failed due to the improper establishment of the distal limit and to an improper posterior palatal seal. Its location and preparation on the master cast are often done by the dentist or dental technician without reference to anatomical landmarks of the mouth. Various methods of achieving posterior palatal seal and reproducing it in the maxillary denture have been described in the literature. Posterior palatal seal area: The posterior palatal seal area is defined as the soft tissue along the junction of hard and soft palates on which pressure within physiologic limits can be applied by the complete removable dental prosthesis to aid in retention of denture Functions of the Posterior Palatal Seal The primary function is that of completing the peripheral seal and enhancing the retention of complete denture. The other purposes served by the PPS are as follows: 1. Maintains contact of denture with soft tissue during functional movements of stomatognathic system, by which decreases gag reflex. 2. Decreases food accumulation with adequate tissue compressibility. 3. Decrease patient discomfort of tongue with posterior part of denture. 4. Compensation of volumetric shrinkage that occurs during the polymerization of PMMA 5. Increases retention and stability by creating partial vacuum. 6. Increased strength of maxillary denture base. 7. Adds confidence and comfort to the patient by enhancing retention. The peripheral seal of maxillary denture is an area of contact between the mucosa and peripheral polished surface of the denture base, the seal prevent passage of air between denture and tissue. Retention of a denture is achieved from adhesion, cohesion & interfacial surface tension that resist the dislodging forces that act perpendicular to the denture base. 1 The posterior palatal seal is placed in the maxillary complete denture because the acrylic will distort slightly and pull away from the posterior palatal area of the maxillary cast. The acrylic will shrink toward the areas of greatest bulk, which are the areas over the ridge where the teeth are placed. The posterior palatal seal provides a vacuum seal between the denture and the soft palate that holds the maxillary complete denture securely in place. The adequate PPS resist the horizontal and lateral forces acting on maxillary denture base as the denture border terminate on soft resilient tissue and there by maintain a proper denture seal. A well-fitting and retentive complete denture requires a well-fitting tissue surface, a peripheral border compatible with the muscles and tissues which make up the mucobuccal and mucolabial spaces so that a peripheral seal is created by the soft tissue draping over them. It is usually obtained by labial and buccal seal. In the posterior region, it is mainly by the posterior palatal seal. At the posterior extension of the maxillary denture, where the tissues are less compliant, special attention is required to make the seal effective. Anatomical Considerations for Posterior Palatal Seal The PPS is divided in two anatomic separate boundaries 1. Post palatal seal. 2. Pterygomaxillary seal. The post palatal seal is extending from one tuberosity to the other. Pterygomaxillary seal extend through pterygo maxillary notch continuing for 3- 4 mm anterolaterally approximation the mucogingival junction. It also occupies the entire width of pterygomaxillary notch. The notch is covered by pterygomaxillary fold (extend from posterior aspect of tuberosity to retromolar pad). This fold influences the posterior border seal if mouth is wide open during final impression procedure. Fovea palatina are two glandular opening within the tissue posterior of hard palate lying on the either side of midline. Fovea palatina should be used only as a guideline for the placement of posterior palatal seal. Medial palatal raphe which overlies medial palatal suture contain little or no submucosa and will tolerate little or no compression. The seal area narrows down in the midpalatine area due to the scarcity of connective tissue and the prominence of posterior nasal spine. Frequently formed at the junction of the aponeurosis and the posterior nasal spine is a narrow bundle similar to a 2 ligament. The posterior palatal seal is not placed over this narrow area. If the tours palatini extend to the bony limit of the palate leaving little or no room to place the PPS then its removable is indicated. Physiological consideration: Saliva: Presence of thick ropy saliva can create hydrostatic pressure in the area anterior to the posterior palatal seal, resulting in a downward dislodging forces. Vibrating line: An imaginary line across the posterior part of the soft palate marking the division between the movable and immovable tissues; this line can be identified when the movable tissues are functioning. 1. Anterior vibrating line. 2. Posterior vibrating line. Anterior vibrating line: It is an imaginary line lying at the junction between the immovable tissues over the hard palate and the slightly movable tissue of the soft palate. 3 Methods of location of anterior vibrating line (AVL): Instructing the patient to say “AH” with short vigorous bursts due to projection of the posterior nasal spine. The anterior vibrating line is not a straight line between both hamular processes. The AVL is cupids bow shaped. Posterior vibrating line (PVL): It is an imaginary line at the junction of the aponeurosis of the tensor veli palatine muscle and the muscular portion of the soft palate visualized, while the patient is instructed to say ‘ah’ in short bursts in a normal unexaggerated fashion. It represent demarcation between the part of soft palate that has limited or shallow movement during function and the remainder of the soft palate that is markedly displaced during functional movement. The posterior vibrating line marks the most distal extension of the denture base. B C Classification of soft palate: According to House classification: Class I: It indicate soft palate that is rather horizontal as extend posteriorly with minimum muscular activity. There is considerable separation between anterior 4 and posterior vibrating line, does having wide PPS area yielding more retentive denture base. Class II: The soft palate gradually slopes from the hard palate. Overextension of the posterior limit of the denture can be tolerated to some extent. Palatal contour lies between class I and class III. Class III: it is seen in conjugation with high V shape palatal vault. There is few mm separation of anterior and posterior vibrating line thus there is small PPS area and less retention. The soft palate abruptly slopes from the hard palate. Hence, the posterior limit of maxillary denture remains very critical. Class I – easiest to tolerate, broadest range, hardest to locate. Class II – most common Class III – easiest to locate, hardest to tolerate Designs of the posterior palatal seal: Winland and Young surveyed the commonly employed posterior palatal seal designs and summarized them as follows: 1. A bead posterior palatal seal 2. A double bead posterior palatal seal 3. A butterfly posterior palatal seal 4. A butterfly posterior palatal seal with a bead on the posterior limit 5. A butterfly posterior palatal seal with the hamular notch area cut to half the depth of a no. 9 bur 6. A posterior palatal seal constructed in reference to House’s classification of palatal forms: Class I: A butterfly shaped posterior palatal seal with3-4 mm wide. Class II: Posterior palatal seal is narrow with 2-3 mm of width. Class III: A single beading made on the posterior vibrating line. 5 Methods or techniques of recording posterior palatal Seal area: 1. Conventional approach. 2. Fluid wax technique. 3. Arbitrary scraping of master cast. Conventional approach: After the special tray is fabricated there are certain instructions given to the patients:- 1. Gently dry the tissues in the posterior palatal seal and pterygomaxillary notch by rinsing with a mouth wash to remove the viscous saliva and with the use of a sterile gauze pad 2. Location of pterygo-maxillary notch is done by moving the T burnisher along the posterior angle of the maxillary tuberosity until it drops into the pterygo- maxillary notch. Mark the notches with the indelible marker. 3. Identification of posterior vibrating line, the patient asked to say “AH” in a normal unexaggerated fashion. 4. Identification of the anterior vibration line. This is done by asking the patient to say “AH” with short vigorous bursts. Procedure: A line is placed with an indelible pencil through the pterygo maxillary notch and extended 3-4 mm antero-laterally to the tuberosity area approximating the mucogingival junction, the same is done on the opposite side. This complete the out lining of pterygo maxillary seal. The posterior vibrating line is marked with an indelible pencil by connection the line through the pterygomaxillary seal with line just drown demarcation the post palatal seal. The resin or shellac tray inserted into the mouth and seated firmly to place, so that upon removal from the mouth the indelible lines will be transferred to the tray. Sometimes it is necessary to redefine transfer marking. The tray is return to master cast to complete the transfer of the complete posterior border. The tray is trimmed until the posterior vibration line so that it decides the posterior extent of denture border. Returning to the mouth the palatal fissure are palpated with the ‘T’ burnisher or mouth mirror to determine their compressibility in width and depth. The termination of glandular tissue usually coincides with the anterior vibrating line. 6  The anterior vibrating line now marked and transferred to master cast. This will complete the transferring of the outline of posterior palatal seal area. The visual outline is in the shape of cupid bow, the area between the anterior- posterior vibrating lines is usually narrowest in the mid palatal region because of the projection of the posterior nasal spine. Carving of the master cast is done using a Kingsley scraper. Deepest areas are located on either sides of the midline, one-third the distance anteriorly from the PVL, depth of 1-1.5 mm is carved. The tissues covering the Mid-palatal raphe are scored to a depth of 0.5-1 mm because it contain little sub mucosa and cannot withstand same compressive force as the tissue lateral to it. As the seal approaches the anterior vibrating line there is just a slight scraping of the cast. Just posterior to the deepest portion of the seal, it is tapered again towards the PVL. Failure to taper the seal posteriorly led to tissue irritation. Advantages of this technique: 1. The trail base will be more retentive. 2. This can produce more accurate maxillo mandibular records. 3. Patient will be able to experience the retentive qualities of the trail base, giving them the psychologic security of knowing that retention will not be a problem in the completed prosthesis. 4. The practioner will be able to determine the retentive qualities of the finished denture. 5. The new denture wearer will be able to realize the posterior extent of the denture which may ease the adjustment periods. Disadvantages: 1. It is not a physiologic technique and therefore depends upon accurate transfer of the vibrating lines and careful scraping of the cast. 2. The potential for over compression of the tissue is great. Fluid wax technique (functional technique or physiological technique): All of the procedure remain the same as conventional technique that is transfer location and transfer marking of the anterior and posterior vibrating line. The marking are recorded in final impression. ZOE/impression plaster (not with elastomeric impression material as they are resilient, non-adherent to wax, and distort wax when reseated into oral cavity). One of the four type of wax can be used for this technique:- 1. Iowa wax white 2- Adaptol green wax. 3. Korecta wax no. 4 (orange). 7 4. K.L physiologic paste (yellow-white). These waxes are designed to flow at mouth temperature. The melted wax is painted into the impression surface and in the outline at seal area, usually the wax is applied in slightly excess of the estimated depth and allowed to cool to below mouth temperature to increase its consistency and make it more resistant to flow. The impression is carried to the mouth and held in place under gentle pressure for 4-6 min and allow time for the material to flow. Patient position during impression making of palatal seal area: An impression should be made when the patient is seated in upright position with head flexed 30 degree forward, below FH ( Frankfort) plane to allow the soft palate to reach its functionally depressed position. The patients tongue should be placed under tension against either the handle of the impression tray or the dentist’s finger which is held in the region of the upper maxillary incisors. After 4 min remove impression tray, if the tissue contact has been established it will appear glossy. Trim excess (or) if no tissue contact is established then add and redo the procedure. A Secondary impression is reinserted and held for 3-5 minutes under gentle pressure followed by 2-3 minutes of firm pressure applied to mid palatal area of the impression tray, upon removal of tray from the mouth it is carefully examined to see wax terminate in feathered edge near the anterior vibrating line. Advantages: a. It is physiologic technique displacing tissues within their physiologically acceptable limits. b. Over compression of tissue is avoided. c. Posterior palatal seal is incorporated into the trail denture base for added retention. d. Mechanical scrapping of the cast is avoided. Disadvantages: a. More time is necessary during the impression appointment. b. Difficulty in handling the materials and added care during the boxing procedure. Arbitrary scraping of master cast: According to Winkler, arbitrarily mark the anterior and posterior vibrating line and scrape about 1-1.5 mm. It is the least accurate methods used to mark the posterior palatal seal. Its high potential for over post damming is due to its nature of unphysiologic technique of recording. 8 ERROR IN RECORDING OF PPS 1. Under extension. 2. Under post damming. 3. Over post damming. 4. Over extension. Under extension: This is the most common cause for poor posterior palatal seal. It may be produced due to one of the following reason:- 1. The denture does not cover the fovea palatina, the tissue coverage is reduced and the posterior border of the denture is not in contact with the soft resilient tissue which will move along with the denture border during functional movements 2. The dentist leaves the posterior border under extended to reduce the patient anxiety to gagging. 3. Improper delineation of the anterior and posterior vibrating line. 4. Excessive trimming of the posterior border of the cast by the technician. Over extension: Over extension of the denture can lead to: 1. Ulceration of the soft palate and painful deglutition. 2. The most frequent complaint from the patient will be that swallowing is painful and difficult. 3. The hamuli are covered by the denture base, the patient will experience sharp pain, especially during function. (Prevention): These region are trimmed with a bur and carefully polished. Under postdamming: 1. This can occur due to improper head positioning and mouth positioning. E.g. the mouth is wide open while recording the posterior palatal seal, the mucosa over the hamular notch becomes stretched. This will produce a space between the denture base and tissue. 2. Inserting a wet denture into a patient’s mouth and inspecting the posterior border with the help of mouth mirror. If air bubble are seen to escape under the posterior border it indicates under damming. 3. Prevention: The master cast can be scraped in the posterior palatal area or the fluid wax impression can be repeated with proper patient position. 9 Over postdamming: 1. This commonly occur due to excess scraping of the master cast. It occur more commonly in the hamular notch region. 2. Pterygo maxillary seal area, then upon insertion of the denture the posterior border will be displaced inferiorly. 3. Prevention: Reduction of the denture border with a carbide bur, followed by lightly pumicing the area while maintaining its convexity. Addition of posterior palatal seal to existing denture:- Existing denture may have poor length and depth of PPS. Properly examine existing dentures. If there are other problems in the dentures (vertical dimension, centric, esthetics etc.) then new dentures are to be made. If only PPS is short then correction should be undertaken. Different authors using different materials have advised various techniques. Moghadam and Scandrett advised the use of fluid wax technique for recording posterior palatal seal and addition of posterior palatal seal with auto polymerizing acrylic resin. A similar technique using softened greenstick modeling compound has been suggested by Carrol and Shaffer. Other suggested materials for correction of PPS include: 1. Heat cured acrylic resin material. 2. Self cured acrylic resin. 3. Light cured resin. When to record PPS: There are two schools of thought as to when to record PPS. a. Before try in - provide the patient with psychological confidence. b. After try in to prevent possible mechanical displacement of the trail base by the tissues, which result in an inferior placement of the posterior segment of the denture base leading to occlusal error in 2nd molar region due to improper seating of bases during jaw relation. Orally, the area of the vibrating line is recorded by making marks with an indelible transfer stick in the fovea palatina area and the hamular notch areas on both sides of the palate and then connecting them with a solid line. 10 Dimension of posterior palatal seal. 11