Anatomical landmarks of maxilla and mandible

Anatomical landmarks of maxilla and mandible
primary stress bearing area
secondary stress bearing area
relief area

1. 1 GOOD MORNING

2. ANATOMICAL LANDMARKS OF MAXILLA AND MANDIBLE DR. EAKETHA P LOKESH PG 1 ST YEAR 2

3. CONTENTS Introduction Factors that affect the form and size of supporting bone Definitions Mucous membrane Anatomic landmarks of maxilla Limiting structures 3

4. Supporting structures Relief areas Anatomic landmarks of maxilla Limiting structures Supporting structures Relief areas summary References 4

5. INTRODUCTION M M DeVan’s Dictum “ Aim of a prosthodontist is not only the meticulous replacement of what is missing, but also perpetual preservation of what is present” Complete denture must function in harmony with the remaining natural tissues so far the success, a thorough knowledge of anatomy is a must. 5

6. Denture base rests on the mucous membrane, which serves as a cushion between the denture base and the supporting bone. Average edentulous area of maxilla : 24 cm ² Average edentulous area of mandible : 14 cm ² mandible is less capable of resisting the occlusal forces than the maxilla 6

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8. Factors that influence the form and size of supporting bone Original size and arch form before extraction Severity of periodontal disease Amount of alveoloplasty at the time of tooth extraction Forces developed by surrounding musculature 8

9. Forces o ccuring from the wearing of dental prosthesis Relative length of time different parts of the jaw have been edentulous Unknown genetic predisposition to bone resorption . 9

10. ORAL MUCOUS MEMBRANE Lines the oral cavity including the residual alveolar ridges serves as a cushion between the denture base and the supporting bone. Masticatory mucosa Lining mucosa Specialized mucosa 10

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12. MUCOUS MEMBRANE 12 Formed by stratified squamous epithelium and a subadjacent narrow layer of connective tissue is present called as the lamina propria Composed of connective tissue that arises from dense to loose areolar tissue. makes the bulk of the mucous membrane. MUCOSA SUBMUCOSA

13. 13 Characterized by well defined keratinized layer on the outermost surface Thickness varies and may contain glandular; fat or muscle cells and transmitts the blood and nerve supply to the mucosa Attachment occurs between submucosa and periosteal covering of the bone MUCOSA SUBMUCOSA

14. Edentulous patient – masticatory mucosa covers crest of ridge & hard palate - Lining mucosa – lips, cheek,vestibule , alveololingual sulcus, soft palate, ventral surface of tongue, - Unattached gingiva – slopes of residual ridge - Specialised mucosa – dorsum of tongue 14

15. ANATOMIC LANDMARK “ A recognizable anatomic structure used as a point of reference”- GPT -9 15 Stress bearing (supporting) Peripheral (limiting) R elief areas Denture bearing areas

16. LIMITING STRUCTURES Sites that guide us in having an optimum extension of denture , so as to engage maximum surface area without encroaching upon the muscle action 16

17. Supporting structures Masticatory forces produce quite a pressure on the underlying structures And not every place beneath the denture can take such stress Hence we need to know areas which can bear the stress well 17

18. Primary stress bearing area Thicker mucosa Underlying bone – cortical bone- less subject to resorption Areas perpendicular to the vertical occlusal forces No underlying structures should be present that will get harmed due to stress 18

19. S ECONDARY STRESS BEARING AREA areas more than 90 ° to or perpendicular to occlusal forces but resorb easily Cancellous bone Resists the lateral forces of occlusion Appear deeper pink due to ↑ sed vascularity Subject to resorptive modelling after dental extraction and with long term denture wear. 19

20. RELIEF AREAS These area resorb under constant load contain fragile structures within . relief → reduction or elimination of pressure from a specific area under a denture base. Neurovascular bundle 20

21. Importance of anatomic landmarks in denture foundation Selective placement of forces as determined by the stress bearing potential of the anatomic structures. Maximum coverage of denture without interfering with the health or function of the tissues. Long term success of complete dentures. 21

22. ANATOMICAL LANDMARKS OF MAXILLA 22

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24. 24 Labial vestibule Labial frenum Buccal vestibule Buccal frenum Hamular notch Vibrating line Fovea palatina LIMITING STRUCTURES

25. Supporting structures 25 Firm maxillary tuberosities Horizontal portion of hard palate on either side of the raphe Alveolar ridge rugae PRIMARY SECONDARY

26. 26 Incisive papillae Median palatal raphe Torus palatinus 2 ° stress bearing areas¹ RELIEF AREAS ¹ Prosthodontic Treatment for Edentulous Patients 13 th edition Zarb . Hobkirk

27. 27 LIMITING STRUCTURES

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29. LABIAL FRENUM Fold of mucous membrane present in the midline that extends from the labial aspect of the residual ridge to the lip. Vary in configuration from single to multiple folds Fan shaped anteriorly Inserts in a vertical direction Contains no muscle ----- no action on its own 29 Passive frenum

30. Clinical significance Accomodated by providing a V-shaped notch in the impression limits labial flange on the denture. Can be excised , if attached to the crest of the ridge It has to be relieved while making impression in order to prevent dislodgement of the denture Prevent ulceration 30

31. LABIAL VESTIBULE “ The portion of the oral cavity that is bounded on one side by the teeth, gingiva and alveolar ridge (in the edentulous mouth – residual ridge) and on the other side by the lips anterior to the buccal frenula” ¹ - GPT -9 Runs from one buccal frenum to the other on the labial side of the ridge. Houses the labial flange of the denture 31 ¹ Glossary of Prosthodontic Terms 9 th Edition JPD 2017 Vol 117 Issue 55

32. Mucous membrane lining the labial vestibule – thin lining mucosa The main muscle of the lip which forms the outer surface of the labial vestibule--- Orbicularis oris tone depends upon the support given by the labial denture flange Position of anterior teeth Because the fibres of O.Oris runs in a horizontal direction--- it has only an indirect effect on the extend of the denture. 32

33. CLINICAL SIGNIFICANCE The labial flange of the denture will be in complete contact with labial vestibule to provide a peripheral seal in the denture. 33

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35. BUCCAL FRENUM It is a band of fibrous tissue that extends from the mucous membrane reflection area to the crest of the residual ridge Single/ double fold / broad fan shaped Divides labial vestibule from the buccal vestibule levator anguli oris attaches beneath the frenum (inserted in anteroposterior direction ) Orbicularis oris pulls the frenum forward Buccinator pulls the frenum backward 35 Active frenum

36. CLINICAL SIGNIFICANCE Since it has muscular attachments, adequate relief must be provided to prevent the dislodgement of the denture Requires more clearance for its action than labial frenum because it moves mesially - by Orbicularis oris buccally – by buccinator vertically – by levator anguli oris 36

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38. BUCCAL VESTIBULE Lies opposite to the tuberosity and extends from the buccal frenum to the hamular notch Houses the buccal flange of the denture 38

39. The size the buccal vestibule varies with the contraction of buccinator muscle The position of the mandible The amount of bone lost from the maxilla 39

40. CLINICAL SIGNIFICANCE The patient’s mouth must be half open during impression taking, because opening of mouth during final impression causes the coronoid process to move anteriorly narrowing the buccal vestibule When the massater contracts under heavy closing pressures, it reduces the size of the space available for the distal end of the buccal flange. Buccal flange has less interference ----so provides maximum retention, compared to labial flange 40

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42. MODIOLUS Bundle of tissue just lateral to the corner of the mouth Represents the origin, insertion or decussation of many fibres of various muscles of facial expression. 42

43. Zygomaticus major Levator anguli oris Incisivus superioris Buccinator Depressor anguli oris Incisivus inferioris Orbicularis oris Risorius 43

44. Clinical significance The denture base must be contoured to permit the modiolus to function freely. In the premolar region , the mandibular denture should exhibit both a shortened and narrowed flange ↓ To permit the action that draws the vestibule superiorly and the modiolus medially against the dentures. 44

45. HAMULAR NOTCH 45 Area of hamular notch

46. HAMULAR NOTCH Pterygomaxillary notch/ Pterygoid notch The palpable notch formed by the junction of the maxilla and the pterygoid hamulus of sphenoid bone – GPT-9 maxillary tuberosity anteriorly pterygoid hamulous posteriorly. Constitutes the lateral boundary of PPS area in maxillary foundation. Can be palpated with a mouth mirror or ‘T’ burnisher 46

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48. Mucous membrane consists of thick submucosa - made up of loose areolar tissue This can be safely displaced to achieve PPS Tensor veli palatini muscle runs horizontally thr ’ this notch, where it ends in an aponeurosis from the contralateral muscle ( muscle is attached to horizontal shelves of palatine bone) 48

49. Pterygomandibular raphe is attached to hamular notch The pterygomandibular raphe, covered by mucosa, extends from the hamulus inferiorly into the retromolar pad of mandible when mouth is opened wide –--he raphe moves forward –- creates a vertical indentation in the posterior border of the denture distal to the tuberosities And may flatten the denture border immediately lateral to the notch 49

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51. CLINICAL SIGNIFICANCE If the denture border---too short of hamular notch Denture will not have a posterior seal Loss of retention of the denture If the denture extend beyond the hamular notch Pterygomandibular raphe pulled forward , when the patient opens the mouth Dislodgement of the denture 51

52. FOVEA PALATINA 52

53. Two small pits or depressions in the posterior aspect of the palatal mucosa, one on each side of the midline , near the attachment of the soft palate to the hard palate ----GPT-9 Openings of ducts of minor salivary glands Secretions of fovea spreads as a thin film on the denture aiding in retention In patients with thick ropy saliva, the fovea palatinae should be left uncovered or else the thick saliva flowing b/w the tissue and the denture can increase the hydrostatic pressure and displace the denture.   53

54. VIBRATING LINES OF SOFT PALATE “The imaginary line across the posterior part of the palate marking the division b/w the movable and immovable tissues; this line can be identified when the movable tissues is functioning” – GPT-9 Extend should be 1-2mm posterior to this vibrating line 54 Anterior vibrating line Posterior vibrating line

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56. ANTERIOR VIBRATING LINE Imaginary line lying at the junction b/w the immovable tissue over the hard palate and the slightly movable tissues of the soft palate. Cupid bow shape Valsalva maneuver : the pt is asked to close his nostrils firmly and gently blow thr ’ his nose, to locate the anterior vibrating line. 56

57. POSTERIOR VIBRATING LINE It is an imaginary line located at the junction of the soft palate that shows limited movement and the soft palate that shows marked movement. Line usually straight 57

58. Posterior palatal seal area POST DAM “ The soft tissue areas limited posteriorly by the distal demarcation of the movable and non-movable tissues of the soft palate and anteriorly by the junction of the hard and soft palates on which pressure, within the physiologic limits, can be placed ; this seal can be applied by a removable complete denture to aid in its retention” – GPT-9 58

59. PPS divided according to anatomic boundaries into Pterygomaxillary seal Post palatal seal 59

60. 60 Part of the PPS that extends across the hamular notch and extends 3-4mm anterolaterally to end in the mucogingival junction on the posterior part of the maxillary ridge Part of the PPS that extends b/w two maxillary tuberosities . PTERYGOMAXILLARY SEAL POST PALATAL SEAL

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62. RATIONALE OF RECORDING PPS To establish positive contact To serve as a guide for positioning the impression tray To create slight displacement o soft palate To obtain adequate retention and seal 62

63. Techniques Conventional approach Fluid wax technique Arbitary scraping of master cast Silvermann’s Extended palatal technique (not accepted) * * 63 Ansari .I.H, JProsthet Dent 1997; 78: 324-6

64. 64 SUPPORTING STRUCTURES

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66. Hard palate The ultimate support of maxillary denture is the bone of two maxillae and the palatine bone. Palate is covered by soft tissues of varying thickness Mucosa keratinized throughout the palate. 66

67. Hard palate In the region of median palatal suture - submucosa extremely thin Mucosal layer is in close contact with the underlying bone For this reason, the soft tissue covering the median palatal suture- non-resilient –may need to be relieved in the impression or in the denture to avoid trauma from denture base. 67

68. Hard palate Submucosa contains anterolaterally - adipose tissue Posterolaterally - minor salivary glands This tissue is displaceable, although it provides support to the denture The horizontal portion of the hard palate, lateral to the midline provides the primary support to the denture. 68

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70. TUBEROSITIES Dense fibrous connective tissues with minimal compressiblity Bulbous extension of the residual ridge in the second and third molar region Posterior part of tuberosities rarely resorb ----most important area in providing support to the maxillary denture. Artificial teeth are not set on tuberosity region 70

71. Extremely large tuberosities need surgical correction. Should included in the impression , it permits coverage of more area and good bearing surface. If the maxillary teeth remain unopposed, the tuberosities and posterior palatal arch can hypererupt below the occlusal plane ---- interfering with the placement of mandibular prosthetic dentition. 71

72. The coronoid process of mandible, along with its attachment of the temporal muscle , will tend to limit the width of denture flange in tuberosity area 72

73. RUGAE Raised irregular areas of dense connective tissue present in the anterior 1/3 rd of the palate, set at an angle to the residual ridge. Provides 2 support ---- as it resists anterior displacement of denture To be relieved Should not be disturbed by impression for maximum comfort. Play part in speech.   73

74. 74 rugae

75. RESIDUAL ALVEOLAR RIDGE The bony ridge of the maxillae or mandible that contains the alveoli (sockets of the teeth) is called as alveolar ridge. The part of the alveolar ridge that remains after the alveolar process has disappeared after extraction of the teeth is called residual alveolar ridge. 75

76. Residual ridge Was 1 st considered to be a 1 ° stress bearing area But now considered as 2° stress bearing area , because the bone is subjected to continuous resorption though it decreases as the span of edentulism increases 76

77. 77 RELIEF AREAS

78. INCISIVE PAPILLAE a pad of fibrous connective tissue overlying the nasopalatine canal. Used as landmark for correct placement of artificial central incisors. Relief the upper denture to avoid pressure on the incisive nerve which cause burning sensation. 78

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80. MEDIAN PALATINE RAPHE The palatine process of the maxillae are joined at the midline in the median suture extend from incisive papillae to the posterior region of hard palate The center of the palate is very hard-----because the layer of soft tissue covering the bone in this region is very thin Improper relief of it may cause instability of the upper denture ( rocking , denture soreness ) 80

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82. TORUS PALATINUS A raised , bony ridge running down the center of the hard palate from the anterior palatine foramen to the posterior border If its small, the denture is relieved. If its too big, it should be surgical removed. 82

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84. 84 GOOD MORNING

85. ANATOMICAL LANDMARKS OF MANDIBLE 85

86. contents Anatomic landmarks of mandible Limiting structures Supporting structures Relief areas Summary References 86

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88. Correlation of anatomic landmarks Labial frenum - labial notch labial vestibule – labial flange Buccal frenum – buccal notch Buccal vestibule - buccal flange Residual alveolar ridge – alveolar groove Pterygomandibular raphe - Pterygomandibular notch Alveololingual sulcus – lingual flange Lingual frenum – lingual notch Buccal shelf area – buccal flange that fits on premylohyoid fossa _ premylohyoid eminence 88

89. 89 Labial vestibule Labial frenum Buccal vestibule Buccal frenum Lingual frenum Alveololingual sulcus Retromylohyoid fossa Retromolar pad Pterygomandibular raphe LIMITING STRUCTURES

90. 90 Buccal shelf area → 1 ° Residual alveolar ridge → 2 ° ( labial and lingual slopes ) SUPPORTING STRUCTURES

91. Crest of the residual alveolar ridge Mylohyoid ridge Mental foramen Genial tubercles Torus mandibularis 91 RELIEF AREAS

92. 92 LIMITING STRUCTURES

93. LABIAL FRENUM 93 labial notch

94. Labial frenum Band of fibrous connective tissue attaches the Orbicularis oris quite sensitive and act verbally Must be carefully accomodated by a groove in the denture, to maintain a seal without causing soreness 94 “Active frenum ’’

95. Labial vestibule 95 Labial flange

96. Labial vestibule Length of the labial flange of the denture is limited by the muscles – Orbicularis oris Incisive labii inferioris Mentalis Position of fixation of modiolus That are inserted close to the crest of the ridge 96

97. BUCCAL FRENUM 97 Buccal notch

98. Buccal frenum Overlies the depressor anguli oris fibres of b uccinator attached to the frenum Moves vertically and horizontally Need wide clearence to avoid dislodgement 98

99. BUCCAL VESTIBULE 99 Buccal flange

100. Buccal vestibule Extends from buccal frenum to retromolar pad Buccinator muscle influences the extend of buccal flange Distobuccal area of buccal flange must converge rapidly to accommodate the anterior fibres of the masseter muscle, which passes outside the buccinator in this region. 100

101. When properly accomodated and recorded, this results in a notch in the denture → Masseteric notch Overextension in this region→ soreness and movement of the denture. 101

102. LINGUAL FRENUM 102 Lingual notch

103. LINGUAL FRENUM the cord that stretches from under the tongue to the floor of the mouth. it is the vertical band of oral mucosa connecting the tongue with the floor of the oral cavity and the alveolar or residual alveolar ridge Overlies the genioglossus muscle 103

104. H igh lingual frenum is called a tongue tie, It should be corrected if it affects the stability of the denture. R elief should be provided in anterior portion of lingual flange ( sublingual crescent area ). T he height and width varies 104

105. Sublingual fold (crescent area) and sublingual papilla Found in the floor of the mouth. Folds produced by sublingual glands and by the submandibular ducts beneath the mucosa. They converge anteriorly to terminate just lateral to lingual frenum as the sublingual papillae, which are the oral openings of submandibular ducts. 105 Complete denture prosthodontics 3 rd edition John.J.Sharry chapter 13 pg 200

106. Alveololingual sulcus 106 Lingual flange Premylohyoid eminence

107. Alveololingual sulcus it extends from the lingual frenum to the retromylohyoid curtain part of the floor of the mouth. alveolingual sulcus (lingual sulcus) the space between the alveolar or residual alveolar ridge and the tongue. 107

108. Anterior : it extends from lingual frenum to premylohyoid fossa , where the mylohyoid curves below the sulcus the flange will be shorter anteriorly it should touch the mucosa of the floor of the mouth when the tip of the tongue touches the upper incisor . 108

109. Middle : extends from premylohyoid fossa to distal end of mylohyiod ridge . this region is shallower than other parts of sulcus. this is due to prominence of mylohyoid ridge and action of mylohyoid muscle. the lingual flange should slope medially towards the tongue. 109

110. Posterior : retromylohyoid fossa is present here. flange in the region should turn laterally towards the ramus of the mandible to fill up the fossa and complete the typical ‘s’ form of lingual flange of lower denture . also called as lateral throat form 110

111. 111 ‘S’ shaped lingual flange in the posterior lingual region

112. Lateral throat form The retromolar space can be partially or totally obliterated by tongue movement This area is critical for lingual seal and lateral stability Class I : Deep Class II : Moderate NEIL Class III : Shallow 112

113. Retromylohyoid fossa An anatomic area in the alveololingual sulcus (posterior part) , just lingual to the retromolar pad . boundaries Anteriorly → mylohyoid ridge posteriorly → retromylohyoid curtain Inferiorly → floor of the alveololingual sulcus Lingually → anterior tonsillary pillar When the tongue is in a relaxed position. 113

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115. Retromylohyoid fossa An anatomic area in the alveololingual sulcus (posterior part) , just lingual to the retromolar pad . boundaries Anteriorly → mylohyoid ridge posteriorly → retromylohyoid curtain Inferiorly → floor of the alveololingual sulcus Lingually → anterior tonsillary pillar When the tongue is in a relaxed position. 115

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117. Clinical significance of alveololingual sulcus Various degrees of contraction of the musculature of the tongue and floor of the mouth alter the depth and width of the sulcus……thus determine the width of the lingual flange. When the mylohyoid muscle contracts actively, as in swallowing, the distal portion of the lingual flange will be either shortened or turned lingually under the tongue. 117

118. RETROMOLAR PAD 118

119. RETROMOLAR PAD A pear-shaped mass of soft tissue located at the posterior end of the mandibular alveolar ridge. Triangular soft elevation of mucosa that lies distal to 3 rd molar - HARRY SICHER non keratinized tissue Collection of loose connective tissues with aggregate of mucosal glands 119

120. Boundaries: Posteriorly →fibres of tendon of temporalis laterally → buccinator Medially → pterygomandibular raphe Superiorly → superior constrictor 120

121. the occlusal surfaces of the natural molar teeth will only be slightly above the height of the retromolar pad Consequently, the height of he retromolar pad may be used as a guide in determining the plane of occlusion for dentures . 121

122. Why retromolar pad is important ??? When this plane of contact is projected posteriorly, it intersects with the mandible at two points; one point is on each side of the arch. These points are about two-thirds of the way up to the height of the retromolar pad. 122

123. Why retromolar pad is important ??? The position remains constant , even after the natural teeth are extracted. It is an excellent guide for determining and setting the plane of occlusion between upper and lower denture teeth. 123

124. Why retromolar pad is important ??? This serve as bilateral, distal support for the mandibular denture. The muscle limit the denture extent and prevent the placement of extra pressure during impression making. Covering this area with the denture base helps reduce the rate of alveolar ridge resorption 124

125. PTERYGOMANDIBULAR RAPHE Is a tendinous insertion of two muscles. The pterygomandibular raphe arises from the hamular process of medial pterygoid plate and gets a attached to the mylohyoid ridge. Superior constrictor is inserted posteromedially . buccinator is inserted anterolaterally . 125

126. It is very prominent in some patients where a notch like relief may be required on the denture. in most patient do not require any clearance 126

127. External oblique ridge 127

128. External oblique ridge A ridge of dense bone extending from just above the mental foramen superiorly and distally, and then becomes continuous with the anterior border of ramus of the mandible. The lower denture should cover but not extend beyond this ridge to avoid denture displacement by the powerful musculature in this area Shows a groove in impression 128

129. 129 SUPPORTING STRUCTURES

130. Buccal shelf area 130

131. Buccal shelf area An area between buccal frenum and anterior border of the masseter. Boundries are: Medially the crest of the ridge Distally the retromolar pad Mesially the buccal frenum Laterally the external oblique ridge 131

132. Buccal shelf area T he width of the buccal shelf area increases as alveolar resortion continues. It has a thick submucosa overlying a cortical plate. It lies right angles to the vertical occlusal forces so it serves as a primary stress bearing area . The bone of buccal shelf is covered by the layer of cortical bone 132

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134. Residual alveolar ridge The bony ridge of the maxillae or mandible that contains the alveoli (sockets of the teeth) is called as alveolar ridge. The part of the alveolar ridge that remains after the alveolar process has disappeared after extraction of the teeth is called residual alveolar ridge. 134

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136. The crest of residual alveolar ridge is covered by fibrous connective tissue, but in many mouths the underlying bone is cancellous without agood cortical bony plate covering it. The submucosa is loosely attached to the bone over the entire crest of alveolar ridge. The submucosa is firmly attached to bone on both the crest and slopes of lower residual ridge. 136

137. Residual ridge resorption in the mandible after tooth loss may lead to worsening of complete denture stability and to various subjective complaints. As the extent of residual ridge resorption in the mandible was the most important factor that increased dissatisfaction with lower complete dentures, it is also important to inhibit the progression of resorption by preventing tooth loss or by using implant-retained dentures. 137

138. 138 RELIEF AREAS

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140. Mylohyoid ridge Runs along the lingual surface of mandible. Anteriorly, the ridge lies close to the inferior border of mandible. Posteriorly, it lies flush with residual ridge. The thin mucosa over the mylohyoid ridge get traumatized and should be relived. The area under this ridge is an undertcut 140

141. MENTAL FORAMEN 141

142. MENTAL FORAMEN It should be relived in these cases as pressure over the nerve produces paresthesia . due to ridge resorption it may lie close to the ridge. it lies between first and second premolar region. 142

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144. GENIAL TUBERCLES T hese are bony tubercles found anteriorly on lingual side of body of mandible project prominently in case of severe bone resorption making denture usage difficult. usually lie well away from the crest of the ridge. Genioglossus and geniohyoid 144

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147. Torus mandibularis It is an abnormal bony prominence found bilaterally on the lingual side near the premolar region. It is covered by thin mucosa in edentulous mouth where considerable amount of resorption has taken place the superior border of torus may be flushed with the crest of alveolar ridge. It often needs to be removed surgically because it can be difficult to provide relief within the denture without breaking the border seal. 147

148. SUMMARY 148

149. references Essentials of complete denture prosthodontics 2 nd edition Edited by Sheldon Winkler Prosthodontic Treatment for Edentulous Patients 13 th edition Zarb . Hobkirk Complete denture prosthodontics 3 rd edition John.J.Sharry Complete dentures 4 th edition Merill.G . Swenson and Charles.J.Stout Textbook of complete dentures 6 th edition Arthur.O.Ruhn 149

150. Glossary of prosthodontic terms 9 th edition J Prosthet Dent 2017 Vol 117 Issue 55 Ansari .I.H, JProsthet Dent 1997; 78: 324-6 150

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