STABILITY IN COMPLETE DENTURES

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STABILITY IN COMPLETE DENTURES

Dr Sabzar Abdullah

Deptt. Of Prosthodontics Dr.Z.A.D.C

AMU,Aligarh

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CONTENT

Introduction

Significance of Stability Review of Literature

Factors Affecting Stability

1. The relationship of the denture base to the underlying tissues.(impression

surface)

2. The relationship of the external surface and border to the surrounding orofacial musculature.(cameo)

3. The relationship of the opposing occlusal surfaces.

Neutral Zone

• Complete Denture Stability in some abnormal cases.

• Evidence Based findings

• Checking of Stability in Complete Dentures

• Summary

• References

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Stability Support

Introduction

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Physiologic comfort Psychological

comfort

Longevity Retention

Support

Stability Success

T. E. Jacobson& A. J. Krol, A contemporary review of the factors involved in complete denture retention, stability, and support, PART 1, JPD Jan 1983

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DEFINITIONS

Stability is the resistance to horizontal and rotational forces. This property prevents lateral or anteroposterior shunting of the denture base

(According to Jacobson and Krol)

The resistance of a denture to movement on its tissue foundation, especially to lateral (horizontal) forces as opposed to vertical displacement.

(According to GPT- 9)

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SIGNIFICANCE OF STABILLITY

Stability has been cited as the most significant property in providing for the physiologic comfort of the patient.

Denture instability adversely affects support and retention and results in deleterious forces on the edentulous ridges during function.

A denture that shifts easily in response to laterally applied forces can cause a disruption in the border seal or prevent the denture base from correctly relating to the supporting tissues.

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REVIEW OF LITERATURE

Fish in (1933)- demonstrated that the lingual and the buccal flange should be moulded in conformation of the

surrounding musculature and provided with a clear picture about the shape of mandibular denture which favours stability.

Lundquist D.O (1959) - The muscles on the working side of unilateral chewers contract more vigorously than those on the balancing side in normal opening and closing movements. The electromyographic recordings showed that the buccinator muscle has significant role in maintaining the stability of the denture and supports the theory of the action of the buccinator muscle as described by Fish.

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REVIEW OF LITERATURE (CONT)

Shanahan T. E J (1962)- Dynamic impressions reproduce naturally extended borders that provide for the function of the muscle attachments and for the movements of the soft tissues under the dentures during mastication, swallowing, speech, etc in contract to static impressions.

Brill (1967)- stated that the 3 important factors essential for stability in complete denture are maximum coverage of the denture bearing area, good peripheral seal, equalization of pressure.

Jooste CH, Thomas CJ. (1992) - The retro mylohyoid extension has a stabilizing effect on complete mandibular dentures.

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REVIEW OF LITERATURE (CONT)

Ohkubo C, Hosoi T. (1999) The results of this study indicated that the use of a metal base to increase the weight of the mandibular denture may not affect its retention or stability.

Sho Hasegawa (2003): Suggested that denture adhesive contributes to reducing denture movement and so improves chewing function.

T P Hyde (2014)There was significant evidence that dentures made from silicone impressions were rated as more stable and more efficient than dentures made from alginate impressions after adjustment

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FACTORS CONTRIBUTING TO STABILITY

1. The relationship of the denture base to the underlying tissues.

2. The relationship of the external surface and border to the surrounding oro-facial musculature.

3. The relationship of the opposing occlusal surfaces.

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Relationship Of Denture Base to

Underlying Tissue.

Mandibular lingual Flange.

Residual Ridge Anatomy.

Denture

Base

Adaptation.

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A. DENTURE BASE ADAPTATION

Maximum coverage

▪ Contacting of the flanges with the ridge slopes is a critical factor contributing to stability (Friedman)

▪ Provide maximum contact between the tissue and denture base

Good Border Seal

▪ Denture borders limited by movable tissue

Close adaptation of denture base

▪ Optimal denture stability requires those tissues that provides resistance to horizontal forces and should be properly recorded.

▪ For stability“Maximum usage of all bony foundations where the tissues are firmly and closely attached to the bone” (Boucher)

▪ “Stability is obtained by incorporating the surfaces of the maxillary and mandibular ridges,

which are at right angle to the occlusal plane”(Boucher).

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B. MANDIBULAR LINGUAL FLANGE

Most desirable feature of mandibular lingual flange is that it is perpendicular to the occlusal plane

The extension of the lingual flange is dictated by the attachment of the mylohyoid muscle

The musculature of the floor of the mouth also influences the degree of intimate contact allowed.

The mucosa should be resilient and thick enough to tolerate stress

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Thomas e. J. Shanahan, stabilizing lower dentures on unfavorable ridges, j. Pros. Den. May-june, vol 12 no 3, 1962

Shanahan(1962) has Stated that the Lingual Flange of the Denture can be extended in three areas that are:

▪ The sub lingual crescent space

▪ The sublingual fossa area

▪ The retro mylohyoid fossa

The base of the tongue must be utilised to stabilise the denture in the retro mylohyoid region.

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The direction of the muscle fibres in the posterior region is more vertical and so the flanges can be extended more inferiorly

The direction of the muscle fibres in the anterior region is more horizontal and so the flanges are more superiorly placed

The inclination of is more medial as during

contraction the muscle is pulled medially

The dotted lines represent the activated mylohyoid muscle

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C. RESIDUAL RIDGE ANATOMY

The development of stability is limited by the anatomic variations

1. Residual Ridge height

2. Residual Ridge conformation 3. Arch Form

4. Palatal Form

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FACTORS GOOD Stability POOR Stability

Height More height Less height

Conformation Large, square and broad Small, narrow and tapered

Arch Form Ovoid

Shape of Palatal Vault Steep palatal vault Shallow palatal vault

Square and Tapered

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CLINICAL TIP REGARDING ALVEOPLASTY AT THE TIME OF EXTRACTION

The alveoplasty should be limited only to sharp spicules, severe undercuts, insufficient inter-arch distance.

Small rounded irregularities must not be removed.

The ridge must not be made smooth and even.

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“It is not so widely understood that the actual shape of the whole of the buccal and labial and lingual surface can wreck the stability of a denture as completely as a bad impression or a wrong bite.”

-Fish(1933)

II. Relationship of the External Surface and

Periphery to Surrounding Orofacial Musculature.

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Relationship Of external surface

to orofacial structures.

Influence of orofacial musculature

Modiolus

Tongue and Lips

II.Relationship of the External Surface and Periphery to Surrounding Orofacial Musculature.

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Certain group of muscle can

facilitate stability of the complete

denture in two ways

The action of certain muscle groups must be permitted to occur

without interference by the denture base.

Recognize the normal functioning of some

muscles and utilize their function to enhance

stability.

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A. INFLUENCE OF OROFACIAL MUSCULATURE

The basic geometric design of the denture bases should be triangular

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TO DIRECT SEATING ACTION ON THE MANDIBULAR DENTURE

There is contraction of muscles such as orbicularis oris(lips) and buccinator(cheeks) during functional movement (speech, deglutition,

mastication).

The buccal and the labial flange of the maxillary and the mandibular denture must

be concave to permit positive seating by cheeks and lips.

The proper contouring of the denture flanges permits the horizontally directed

forces that occur during contraction of

these muscles to be transmitted as vertical

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Corwin R. Wright,Evaluation of the factors necessary to develop stability in mandibular, J Prosthet Dent 1966;16:414-30

B. TONGUE

When one is examining a patient for tongue position, it is well not to mention the word tongue .

-Corwin Wright

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TONGUE POSITIONS

A Normal Tongue Position has the following Characteristics:

(1)It completely fills the floor of the mouth.

(2) The lateral borders rest over the ridge which would normally represent the occlusal surfaces of the teeth.

(3) The tip or apex of the tongue rests on or is just to the lingual side of the lower anterior ridge.

The Retracted Tongue Position has the following Characteristics:

(1)The tongue is pulled back into the mouth and the floor of the mouth is exposed.

(2) The lateral borders are either inside or posterior to the ridge.

(3) The tip of the apex of the tongue sometimes lies in the posterior part of

the floor of the mouth or may be withdrawn into the body of the tongue.

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Tongue exercise No. 1.

The tongue is thrust out and in rapidly

^.

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Tongue exercise No. 2 ^.

The tongue is swung rapidly from side to side.

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Tongue exercise No. 3.

Thrusting the tongue out to its most extended position

And pulling it back quickly

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Tongue exercise No. 4.

Raising the tongue to its highest position through articulation of ‘eeyuh’

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W.E Fish Using muscles to stabilize the full lower denture J Am Dent Assoc10:2163,1993

C. IMPORTANCE OF MODIOLUS AND ASSOCIATED MUSCULATURE

Modiolus \mo-dı΄a-las\ the area near the corner of the mouth where eight muscles converge; it functionally separates the labial vestibule from the buccal vestibule (GPT 9)

The 8 muscles are

1. Orbicularis Oris 2. Buccinator

3. Zygomaticus 4. Canninus

5. Triangularis

6. Levator anguli oris 7. Rizorius

8. Platysma

M. cruciati modioli

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1. The outline of the denture base is closer to the ridge in these area

The flanges are fashioned this way to escape the action of the muscles in these regions

2. The outline of the denture base is away from the ridge in these areas

A wider flange is advised in the buccal

region owing to the presence of buccal

pouch.

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Transverse section of stable denture in the premolar region.

The lower denture is very narrow at this point to escape the modioli.

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Transverse section of stable denture in the first molar region.

Each side of each denture is roughly triangular in shape The buccal flange extends under the buccinator in order

that the muscles may rest on the inclined planes and hold the denture down

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NEUTRAL ZONE

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 muscles will tend to stabilize the denture rather than unseat it.

The theory used to develop the denture base contours is based on the belief that the muscles should functionally mould not only the borders of the denture but also the entire polished surface.

The polished surface contours and the position of the teeth are to be determined

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Victor E. Beresin, Frank J. Schiesser, The neutral zone in complete dentures, In The Journal of Prosthetic Dentistry, Volume 36, Issue 4, 1976, 356-367, ISSN 0022-3913

A.cross section of molar area B. lateral view of incisor area.

Denture space

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Victor E. Beresin, Frank J. Schiesser, The neutral zone in complete dentures, In The Journal of Prosthetic Dentistry, Volume 36, Issue 4, 1976, 356-367, ISSN 0022-3913

INFLUENCE OF LIPS ON DENTURE STABILITY

A , Cross section of mouth in relaxed state. No unfavorable forces are exerted on external surfaces by the lips and cheeks.

B, As the mouth opens, the denture comes under the influence of horizontal forces from the lips.

C, With the mouth wide open, maximum horizontal forces are exerted on the labial and buccal external surfaces of the teeth and flanges.

The distance AB when the mouth is open (below) is less than the distance AB when the mouth is at rest (above).

C

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INFLUENCE OF LIPS OVER THE LOWER DENTURE IN INCREASED RIDGE RESORPTION

Ridge height is insufficient, so horizontal forces are poorly counteracted.

As alveolar ridge resorb the ridge crest falls below the origin of mentalis.

The muscle attachment folds over the ridge and comes to rest on the superior surface of the crest

This results in posterior positioning of the neutral zone and

posterior positioning of the anterior teeth than that of its natural position

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III. RELATIONSHIP OF OPPOSING OCCLUSAL SURFACES

Harmony developed between the opposing occlusal surface also contributes to stability

The denture must be free of interferences within the functional range of movement of the patient.

During functional or parafunctional movements the occlusal surface must not prematurely strike.

These unwanted forces result in lateral and torquing forces that adversely affect the stability.

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FACTORS IN RELATIONSHIP OF OPPOSING OCCLUSAL SURFACES

A. Occlusion as factor in stability

B. Tooth position & Occlusal plane

C. Ridge Relation

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A. OCCLUSION AS FACTOR IN STABILITY

To minimize dislodging forces the occlusion must be balanced throughout the functional range of movement of the patient.

The bilateral balanced occlusion is important during activities such as swallowing saliva, closing to reseat the denture, and the bruxing of the teeth.

Patients with balanced occlusion do not upset the normal static, stable and retentive position of the dentures.

Lingualized occlusion provide both a limited range of excursive balance and a directing of forces to the lingual side of the lower ridge during working side contacts.

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Horizontal forces can be minimized when the patient learns to place food bilaterally

Frechette in 1961 demonstrated even force distribution regardless of tooth position in the patient who chewed bilaterally, he also

concluded that bilateral chewing contributed more to the chewing

than balanced occlusion.

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The selection of anatomic, semianatomic, or non anatomic artificial teeth depends partially on the chosen occlusal scheme, quality of the residual ridge in terms of height and conformation.

Unfavourable ridges exhibiting severe resorption patterns may contribute to compromised stability. Use of anatomic artificial teeth in such situations may not provide the advantages normally expected.

If balanced occlusion is desired throughout a limited functional range of movement for patients with deficient residual ridges, the use of

nonanatomic O- degree teeth set on a curve may provide the desired

occlusal contacts while eliminating the interlocking of opposing anatomic

teeth.

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B. TOOTH POSITION & OCCLUSAL PLANE

Anterior and posterior teeth should be arranged as close as possible to the position once occupied by the natural teeth

(with slight modifications to accommodate resorptive changes)

Mandibular occlusal plane that is too high can lead to reduced stability

▪ Lateral tilting forces are magnified as the plane is raised

▪ Mandibular denture needs to be controlled by the musculature , raised plane will hamper the tongue to reach over the occlusal plane

Stensen's duct, retromolar pads, should be used to determine an acceptable

occlusal plane

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C. RIDGE RELATIONSHIP

Prognathic and retrognathic patients show offset ridge relation.

If the teeth are arranged in normal position on these offset ridges adversely affect stability.

Weinberg recognizes the need to set teeth in crossbite when the ridges are in severe crossbite relation.

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IN CLASS III RIDGE RELATION

In class III cases the lower arch is anterior to upper arch

Sufficient mandibular occlusion must be developed so that the contact to the maxillary is more than half that of distance between the incisive papilla and the hamular notch.

This prevents the tipping of the maxillary denture anterio-posteriorly.

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J. F. McCord, Identification of complete denture problems: a summary, BRITISH DENTAL JOURNAL, VOLUME 189, NO. 3, AUGUST 12 2000

COMPLETE DENTURE STABILITY IN ABNORMAL CASES

Xerostomia reduces an ability to form suitable seal, which further affects the retention and stability of dentures the treatment options include incorporation of salivary reservoir in complete dentures and remediation with

artificial salivary substitutes.

Patients who have retracted tongue position, a bleb 2-3 mm in dimension is placed on the lingual surface of the mandibular lower teeth and the patient is trained to place to tongue in relation to this bleb to attain normal tongue position.

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1. Geerts, Neutral zone or conventional mandibular complete dentures: a randomised crossover trial comparing oral health-related quality of lifeJ Oral Rehabil.

2017

2. T.P. Hyde, H.L. Craddock, J.C. Gray, S.H. Pavitt, C. Hulme, M. Godfrey, C. Fernandez, N. Navarro-Coy, S. Dillon, J. Wright, S. Brown, G. Dukanovic, P.A. Brunton, A Randomised Controlled Trial of complete denture impression materials, In Journal of Dentistry, Volume 42, Issue 8, 2014

3. Psillakis, J. J., Wright, R. F., Grbic, J. T. and Lamster, I. B. (2004), In Practice Evaluation of a Denture Adhesive Using a Gnathometer. Journal of Prosthodontics 4. Kimoto, S, Gunji, A, Yamakawa, A, Ajiro, H, Kanno, K, Shinomiya, M, Kawai, Y, Kawara, M, & Kobayashi, K 2006, 'Prospective Clinical Trial Comparing Lingualized Occlusion to Bilateral Balanced Occlusion in Complete Dentures: A Pilot Study', International Journal of Prosthodontics, vol. 19, no. 1, pp. 103-109.

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EVIDENCE BASED PRACTISE STUDIES

1. There is a very insignificant difference between dentures fabricated with neutral zone technique compared to conventional technique. (treatment effect size < 0·2) ( Geerts, 2017).

2. Silicone is a better impression material than alginate in fabrication of complete

denture, with respect to patient satisfaction, stability, post insertion adjustments.(T.P.

Hyde,2014)

3. Use of a denture adhesive can improve resistance to bite force related dislodgement in patients who wear a maxillary complete denture.(Psillakis, 2004)

4. A pilot study conducted comparing Lingualized occlusion and bilateral balanced

occlusion showed that lingualized occlusion is better accepted by patients and proved

to have greater stability and masticatory performance (Kimoto et al 2006)

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CHECKING STABILITY OF THE DENTURE :

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SUMMARY

The relationship of denture base to surface tissue is an important factor in maintaining stability.

The action of the orofacial muscles are to be considered to decide the shape of denture flanges.

The extension of denture flanges is dictated by the movable tissue which further helps in attaining stability

Relationship of occlusal surfaces should be utilized to gain maximum stability.

Neutral zone is an important phenomenon, it is essential to recognize the

importance of neutral zone in teeth arrangement and polished surface

which gives stability.

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CONCLUSION

“Technique itself is merely the practical application of principles, and if the principles are unsound, the most elaborate and painstaking technique

certainly is doomed to failure.”

-Bohannan

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REFERENCES

T. E. Jacobson& A. J. Krol, A contemporary review of the factors involved in complete denture retention, stability, and support, PART 1, JPD jan 1983.

Victor e. Beresin, frank J. Schiesser, the neutral zone in complete dentures, in the journal of prosthetic dentistry, volume 36, issue 4, 1976, 356-367, ISSN 0022-3913

W.E fish using muscles to stabilize the full lower denture J am dent assoc10:2163,1933

Corwin R. Wright,evaluation of the factors necessary to develop stability in mandibular, J prosthet dent 1966;16:414-30 Thomas e. J. Shanahan, stabilizing lower dentures on unfavorable ridges, j. Pros. Den. May-june, vol 12 no 3, 1962 Essentials of complete denture prosthodontics, sheldon winkler 2nd ed.

Boucher's prosthodontic treatment for edentulous patients 12th ed 1985.

The glossary of prosthodontic terms, journal of prosthetic dentistry , volume 117 , issue 5 , e1 - e105

T.P. Hyde, H.L. Craddock, J.C. Gray, S.H. Pavitt, C. Hulme, M. Godfrey, C. Fernandez, N. Navarro-Coy, S. Dillon, J. Wright, S. Brown, G.

Dukanovic, P.A. Brunton, A Randomised Controlled Trial of complete denture impression materials, In Journal of Dentistry, Volume 42, Issue 8, 2014

Geerts, Neutral zone or conventional mandibular complete dentures: a randomised crossover trial comparing oral health-related quality of life. J Oral Rehabil. 2017 Sep;44(9):702-708. doi: 10.1111/joor.12533. Epub 2017 Jul 2

Kimoto, S, Gunji, A, Yamakawa, A, Ajiro, H, Kanno, K, Shinomiya, M, Kawai, Y, Kawara, M, & Kobayashi, K 2006, 'Prospective Clinical Trial Comparing Lingualized Occlusion to Bilateral Balanced Occlusion in Complete Dentures: A Pilot Study', International Journal of Prosthodontics, vol. 19, no. 1, pp. 103-109.

J F. McCord, Identification of complete denture problems: a summary, BRITISH DENTAL JOURNAL, VOLUME 189, NO. 3, AUGUST 12 2000

K Rajeshwari, Evaluation of Resting Tongue Position in Recently Extracted and Long Term Completely Edentulous Patients: A Prospective Interventional Study,Journal of Clinical and Diagnostic Research. 2017 Apr, Vol-11(4): ZC61-ZC63

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