Biological and periodontal considerations in fixed prosthodontics

1. Biological and Periodontal
Considerations in Fixed
Prosthodontics
Group A

2. A. Biological Considerations
• Dentin contains cells whose nuclei protrude into the pulp making
them one connected tissue (Dentin-Pulp Complex).
• It reacts to every insult i.e attrition, abrasion, erosion, caries and
mode of cutting by:
• Degenerative changes with severe danger.
• Calcified repair if the danger is minor.
• The pdl and gingiva are also vital and responsive tissues hence should
be concerned with the biologic aspect of the procedure and long term
effect as well as the comfort of the pt.

3. • Occlusal forces should also be considered as they may shorten the
lifespan of prosthesis and affect TMJ.
• Influence of the oral environment which bathes the teeth is also
important - microorganisms and chemical compounds.
• Food cause temperature changes that affect fillings - restoration open
margins.
• Unnecessary damage to adjacent teeth, soft tissues and pulpal tissues
should be avoided during fixed prosthetic procedures.

4. 1. Damage to adjacent teeth
• Common during tooth reduction.
• Damaged tooth susceptible to dental caries and sensitivity - due to
roughness.
Prevention
• Use of matrix band around adjacent tooth.
• Use of thin tapered diamond bur through interproximal contact area
to leave a thin shell of enamel to protect adjacent tooth from
damage.

5. 2. Damage to soft tissue
• Damage of tongue and cheeks can be prevented by use of tongue
retractors and or mouth mirror.
• Great care when preparing the lingual surfaces of lower molars.

6. 3. Damage to the gingiva
• If the restoration margins is extended subgingivally to intrude into the
biologic width, inflammation results with consequent stimulation of
osteoclastic bone resorption.
• This resorption will continue until the alveolar crest is at least 2mm
from the restoration margin.
• Forceful application of gingival retraction cord might lead to gingival
atrophy exposing the margins of the restoration.

7. 4. Damage to the pulp
• Especially during preparation of complete crowns or retainers.
• Extreme temperatures, chemical irritations or microorganisms can
cause irreversible pulpitis.
• Selection of techniques and materials that will reduce the damage
effects during tooth preparation.
• Morphology of pulp chamber and pulp size which decreases with age
should be taken into consideration.

8. Causes of pulp injury
a) Temperature
• Heat from excessive application of force, high rotation speeds, type
shape and condition of the cutting instruments.
• Failure to use a coolant during cutting
• Grooves or pinholes preps - coolant doesn’t reach these depths, use
slow speed.
• Deep cutting e.g during preparation for crowns.
• Attrition or very slow caries

9. b) Chemical actions
• Restorative resins, solvents and luting cements can cause pulpal
damage esp when applied to freshly cut dentin (use cavity varnishes).
• Chemical agents used for cleaning prepared teeth can cause pulpal
irritations. 3% hydrogen peroxide can be used for cleaning instead.

10. c) Bacterial toxins
• Microleakage of restorations
• Failure to remove all carious dentin.
• Indirect pulp capping, delayed failure may occur.

11. Biological Effects of Various Restorations
1. Silver Amalgam
• Sulfides in saliva cause oxidation and corrosion of amalgam. Amalgam
restorations become dark due to formation of metallic sulfides.
• Salivary sulfide and glycoprotein penetrate into marginal
discrepancies and also cause corrosion products.
• If neither a liner or a base is used under an amalgam restoration,
metallic ions - tin and mercury penetrate and discolor underlying
dentin.
• Newly inserted amalgams have a strong galvanic action unless
insulated from the pulp.

12. 2. Bases and Liners
• Base - insulates dentin and pulp from thermal shock.
• Failure to use it - sharp lancinating pain when the metal is chilled, pulsating
pain when heated because of vascular engorgement.
• Both shield against galvanic shock, prevents penetration of metallic ions
and dentin discoloration.
• Varnish seals openings of freshly cut dentin.
3. GIC
• The presence of fluoride in GIC increases the fluoride content of the
adjacent enamel leading to resistance of the margins to caries attack.

13. 4. Composite Resins
• Original composites – microleakage -> toxins and bacteria penetration
-> pulp irritation.
• This was due to high polymerization shrinkage and high coefficient of
thermal expansion.
• Monomer - pulp irritant
• New types - have reduced polymerization shrinkage and lower CoTE
• Marginal leakage further improved by acid etching and bonding
agents.

14. 5. Gold castings - inlays, onlays and crowns
• Cast gold - ionically neutral and does not affect dentin and pulp. But it
has high CoTE, effect on dentin and pulp occur through use of
cementing medium.
• Cementing agents - seals margins of gold restorations, but soluble in
saliva, washed out with time, leakage to bacteria and debris through
marginal decay.
• Highly polished gold surfaces recommended as they do not irritate
gingiva by accumulating plaque.

15. 6. Porcelain
• Gingival tissue highly tolerant to glazed porcelain as it does not trap
plaque.
• Non-adhesive cements washes out with time leaving open margins-
plaque formation and gingivitis.
• Metallic crowns with porcelain facing reduces effect of open margins
because metal adaptation around the margins is superior than that of
porcelain.
• After correction of the porcelain by grinding, the surface must be
reglazed.

16. Biologic Effects of Temporary Crowns and
Bridges
• Temporary restorations essential to protect freshly cut dentin from
thermal shock, salivary contamination (bacteria, debris, toxins) from
entering the opened tubules.
• Indirect method of temporary restoration is more superior than direct
method because of increased likelihood for free monomer puplal
damage and leakage due to shrinkage with direct temporary
restorations.

17. • Leakage under temporary restoration is still a major challenge due to
lack of a suitable cement.
• Margins should be well adapted to prevent saliva leakage. They
should also not impinge on gingival tissues.
• Sealing dentinal tubules w/ varnish or CaOH prior to cementation
reduces damage & pain caused by leakage.

18. Biologic Effects of Various Cements
a. Zinc Phosphate Cement
• Popular for cast restorations
• Despite the toxic effect of phosphoric acid, its still used w/ precaution
i.e. not be placed too close to the pulp & use with varnishes.
b. Zinc Polycarboxylate Cement
• Relatively biocompatible due to large size of polyacrylic acid

19. c. ZOE
• No contact with pulp, no pulpal inflammation
• Excellent sealing
• Made biocompatible by adding EBA (EthoxyBenzoic Acid), AlO,
polymethylmethacrylate
• Palliative because:
1. Superior sealing
2. Obtunding action
3. Bacteriostatic

20. d. GIC
• Bacteriostatic during setting, less soluble than ZnPO4, releases
fluoride
• May cause post cementation hypersensitivity because of low pH. This
is countered by application of CaOH to areas close to the pulp.
• Apply varnish or petrolatum to avoid early exposure to moisture.

21. e. Resin Luting Cements
• Use of dentin bonding agents under resin cements critical to reduce
pulp response by sealing dentinal tubules and reducing microleakage.
• Pulp irritation occurs due to bacterial infiltration and not chemical
toxicity.
f. Hybrid Ionomer Cement
• Combine strength and insolubility of resin with anticariogenic
property of GIC leading to reduced post cementation hypersensitivity

22. B. Periodontal Considerations
• Periodontal status of abutment teeth assessed and corrected before
prosthetic treatment is undertaken.
1) Occlusion and its Effect to the Periodontium
• Effect of occlusal forces on periodontium is influenced by their
severity, direction, duration and frequency.
• When they exceed adaptive capacity of the periodontium, tissue
injury results.
• The design of the fixed appliance should allow exertion of pressure
along the long axis of the tooth.

23. 2) Crown Margins and Contours
i. Crown Margins - margins should be closely adapted to the
cavosurface finish line of the prep. The configuration of the finish
line dictates the shape and bulk of the restorative margin of the
restoration and affects marginal adaptation and the degree of
seating of the restoration.
ii. Margin Adaptation - accurate adaptation between the tooth and
the restoration minimizes recurrent caries and perio disease.
Margin should be smooth & even to facilitate easy tissue
displacement, impression making, die formation, waxing &
finishing.

24. iii. Margin Placement
• Placement of margins has a direct bearing on the ease of fabricating a
restoration and on the ultimate structure of the restoration.
• The best results can be obtained from margins that are smooth as possible
and are fully exposed to the cleansing action.
• Whenever possible the finish line should be placed
 In an area where the margin of the restoration can be finished by the
dentist.
In an area where they can be kept clean by the pt.
So that they can be duplicated by the impression, without tearing or
deforming the impression when it is removed.

25. • Whenever possible, margins are prepared supragingival on the enamel of
the anatomic crown.
Advantages of supragingival margins
i. Favorable reaction of the gingiva.
ii. Common path of insertion.
iii. Restoration can be easily evaluated at recall appointment.
iv. Wider shoulder tooth preparations can accommodate an adequate bulk
of porcelain veneering material in the cervical area without pulpal injury.
v. Metal margin finishing techniques are easier.

26. • Nevertheless, there will be many situations in which subgingival margins
are unavoidable
Indications for subgingival margins
i. Dental caries, cervical erosion, or restorations extended subgingivally
and crown-lengthening procedure is not indicated.
ii. Proximal contact area extends to the gingival crest.
iii. Additional retention is needed by increasing the preparation stump.
iv. Margin of metal ceramic restoration is to be hidden for esthetic reasons.
v. Root sensitivity cannot be controlled by conservative procedures.
vi. Modification of the axial contour is indicated.

27. • A crown should not be placed any closer than 2.0mm away from the
alveolar crest, or bone resorption will occur.
• If the margin intrudes into this biologic width, inflammation will result
and bone will recede until it is once again at least 2.0mm from the
crown margin leading to infrabony pocket formation.

28. 3) Axial Contours
• The proximal contacts and the facial and lingual axial contours of wax
pattern should be properly designed for the health of the adjacent
periodontium.
i. Proximal Contacts
• Proximal contacts of posterior teeth are located in the occlusal third of the
crowns, except for contacts between the maxillary first and second molars,
which are located in the middle third.
• The contact must be more than just a point occluso-gingivally, but it must
not extend far enough cervically to encroach on the gingival embrasure.

29. • The axial surface of the crown cervical to the proximal contact should be
flat or slightly concave. (flat contour-optimum shape since it is the easiest
to floss).
• Overcoming the proximal surfaces apical to the contacts by making these
areas convex will produce severe inflammation to the gingiva.
• Contact areas between mandibular teeth and maxillary molars are
generally central, while contacts between maxillary premolars and molars
are usually towards the facial surface.
• As a result, the lingual embrasures are slightly wider than facial ones.
• Contacts that are too narrow allow food to wedge between teeth, while
excessive wide facilolingually do not adequately deflect food from the
gingival tissue.

31. ii. Buccal and Lingual Surfaces
• Buccal and lingual axial surfaces of the adjacent teeth make an
excellent guide for judging the contours of the facial and lingual
surfaces of the wax pattern.
• The facial and lingual contours should be harmonious with them.
• The height of contour on the facial and lingual surfaces of the
maxillary posterior teeth and the facial surfaces of mandibular
posterior teeth usually occurs in the cervical third.
• On the lingual surfaces of mandibular teeth it occurs in the middle
third.

32. iii. Emergence Profile
• The part of the axial contour that extends from the base of the
gingival sulcus to the height of contour.
• It extends to the height of contour, producing a straight profile in the
gingival third.
• Production of a straight profile should be a treatment objective in
restoring a tooth because it facilitates access for OH measures.
• The straight profile is easily evaluated with periodontal probe.

34. iv. Embrasure Design
• Embrasures protect the gingiva from food impaction and deflect the food to massage the
gingival surface.
• They provide spillways for food during mastication and relieve occlusal forces when
resistant food is chewed.
• The proximal surfaces of dental restorations determine the embrasures essential for
gingival health.
• Proximal surfaces of crowns should taper away from the contact areas on all surfaces.
• Excessively broad proximal contact areas and inadequate contour in the cervical areas
suppress the gingival papillae.
• These prominent papillae trap food debris, leading to gingival inflammation.
• Proximal contacts that are too narrow buccolingually create enlarged embrasures
without sufficient protection against interdental food impaction.

35. 3) Pontic Design and Materials
A pontic must:
Restore the function of missing tooth.
Ensure adequate sanitation.
Be esthetically pleasing.
Be comfortable.
Be biologically tolerable.

36. Pontic design
• In evaluating the relation of the pontic design with health of gingival tissue,
all surfaces are considered separately.
i. Gingival surface
• Pressure-free contact between the pontic and the underlying tissues is
indicated to prevent ulceration and inflammation of the soft tissues.
• This passive contact occurs on keratinized tissue.
• The area of contact between the pontic and the ridge should be small and
the portion of the pontic should be as convex as possible.
• The gingival surface should meet gingival tissue with smooth rounded
contour.

37. • In the anterior and premolar areas( for esthetic demands) tissue contact of the pontic is
recommended. Modified ridge lap is accepted;- concave buccally & convex lingually).
• Therefore, sanitary pontic (convex buccolingually) is used in the mandibular posterior
area.
• When appearance is of utmost concern, the ovate pontic is selected which gives the
appearance that it is growing from the ridge.
ii. Occlusal surface
• Pontic with normal occlusal width (at least on the occlusal third) are generally
recommended.
• Narrowing the occlusal table may affect the harmonious and stable occlusal relationship.
• Reduction of the pontic width is desirable only if the residual alveolar ridge has collapsed
buccolingually to facilitate plaque control measures.

38. iii. Buccal and lingual surfaces
• The contours of the buccal and lingual surfaces of the pontic are determined by
esthetics, function and hygienic requirements.
• In the maxillary and mandibular anterior regions, it is important to maintain normal facial
contour (convex inciso-gingivally and mesio-distally) and axial alignment.
• The lingual contour should harmonize with adjacent teeth from the cusp tip to the height
of contour, and then sharply recede convexly to the facial tissue contact area.
• Embrasures on the lingual are wider than on the buccal.
• In the mandibular posterior region, the buccal and the lingual surfaces follow normal
tooth from the cusp tip to the height of contour.
• The sanitary design results from tapering the buccal and the lingual surfaces from the
height of contour toward the gingival contact.

39. iv. Proximal surfaces
• Vertical clearance must be sufficient to permit physiologic contour of
the pontic and to allow space and to allow space for the interproximal
tissues.
• The maxillary anterior proximal embrasures are minimal for esthetics
but allow sufficient space to prevent papillary impingement.
• Moving posteriorly, the size of embrasures gradually increases.
• In the mandibular posterior area, wider embrasures are created to
facilitate hygiene since esthetics is not of prime concern.

40. Pontic material
• Any material chosen to fabricate the pontics should:
Provide good esthetics,
Have biocompatility,
Have rigidity
Have strength to withstand occlusal forces
Have the desired longevity.
• Biocompatibilty of the materials is based on 2 factors: the effect of the materials and the effects
of the surface adherence.
• Glazed porcelain most biocompatible but the critical factor seems to be the material’s ability to
resist accumulation of plaque rather than the material itself.
• Well-polished gold is smoother, high corrosion resistance and less retentive of plaque than
unpolished or porous casting.

41. Splinting
• Joining two or more teeth together for stabilization.
 A fixed splint can be used after a successful treatment of a
periodontal disease when;
(a) residual mobility causes discomfort to the pt
(b) teeth are missing, to form a satisfactory abutment for a FPD or precision
attachment retained PD.

42. Benefits
• Redirecting the forces on the abutment teeth
• Redistribution of forces on >1 tooth
• Prevention of supra eruption & teeth migration
• Prevention of lateral forces (destructive to PDL)
• Single rooted teeth begin to function as multirooted teeth

43. Methods of Splinting
1. Temporary, Reversible & Provisional Splints.
a. Ligature wire
b. A-Splint or Circumferential wires
c. Removable appliances (continuous clasp PD)
d. Sing –lock RPD
e. Bonding
f. Provisional splinting with full-coverage acrylics
2. Permanent Splints.

44. CIRCUMFERENTIAL
FULL
COVERAGE
ACRYLIC

45. Diseases of the Gingiva and the Periodontium
• Any condition other than normal:
oGingival Diseases and Conditions.
oPeriodontitis.
oPeriodontal Manifestation of Systemic Disease and Developmental and
Acquired Conditions.
oPeri-Implant Diseases and Conditions.
• Determine etiology, Do Examination, Come up with a diagnosis,
Formulae a treatment plan.

46. Treatment Therapy
1. Initial Therapy
Control of microbial plaque
• Tooth brushing
• Flossing
• Other aids – dental tape, rubber and wooden tips, interproximal brushes
• Scaling and polishing
• Root planning
• Correction of defective and/or overhanging restorations
• Strategic tooth removal
• Stabilization of mobile teeth
*Evaluation of initial therapy*
2. Surgical Therapy – Involves pre-prosthetic surgical preparation.

47. Furcation Involvement
Classification
• Grade 1
• Grade 2
• Grade 3
• Grade 4
Diagnosis
• Radiographic evidence of furcation involvement is usually
inconsistent. Therefore, a probe is the best diagnostic tool.
• A straight probe for vertical bone loss and a curved probe for
horizontal bone loss

50. Treatment
• Odontoplasty/osteoplasty - when involvement is too extensive.
• Class 1 and 2 lesions can be treated by reflecting soft tissue in the
furcation area as well as reconstruction of tooth structure and bone.
• Class 3 and 4 lesions are treated via tunneling procedure. This involes
creating an end to end connection of the defect to facilitate proper
cleaning. Root amputation can also be done by completely removing
the furcation.

51. Provisionalization and restoration
• Provisional stabilization is done for healing to occur.
• Acrylic resin, acid etched composite or amalgam stabilized by orthodontic
wires can be used.
1. The remaining tooth can be restored
2. The tooth can be an abutment for fixed prosthesis
3. Premolarization - individual molar roots are built up to have a premolar
morphology.
4. Minimal treatment - build up using amalgam and check occlusion.

53. Preparation of Periodontally Weakened Teeth
• The optimum location for the finish line is usually on enamel.
However it can be extended when the root surfaces are affected by
caries or erosion, in this case, a chamfer margin is prefered.
• Pulpal encroachment and fracture are risks when a shoulder is
prepared axially especially in constricted areas.
• In the more apically extended preparation molars, the preparation
should follow flutes and root concavities along the axial surface
contours.

55. Root Resection
• A procedure in which the root is removed without touching the
crown.
• Hemisection involves cutting the tooth in half (usually followed by
premolarization - building up individual roots into a premolar
morphology).

57. Indications
• Severe vertical bone loss of molar roots.
• Furcation involvement which can't be treated using odontoplasty.
• Fractured roots(vertical or horizontal).
• Severe root caries.
• Internal and external root resorption.
• Failure of abutment tooth in FPD.
• Root canal failure in one canal due to perforation.
• Strategic removal to improve prognosis.

58. Contraindications
• Fused roots
• Significantly decreased osseous support
• Increased crown root ratio
• Remaining structure can't provide enough support.
• Inabilityto save the root endodontically

59. Procedure
• The root is resected using a long thin diamond bar after endodontic
treatment of the tooth.
• The finish line of crown preparation is extended beyond the
obturated pulp chamber.
• It shouldn't be extended to far apically.
• If a dowel core is required in extensive coronal damage then a
custom cast dowel core is prefered.

60. Success and Failure
• Failure is more expected in mandibular teeth than upper teeth due to
poorer support created by the lower roots which usually become individual
roots.
• Long term success is created by using canine protected articulation,
decreased overbite and flat occlusal cusps posteriorly.
• Factors that may affect prognosis of a tooth with resected roots are;
1. The functional use of the tooth.
2. Residual osseous structure.
3. Motivation and oral hygiene of the patient.
4. Remaining tooth structure

61. THE END
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