Friel¹⁷ demonstrated in a study that the teeth move forward in relation to the rugae in conjunction with growth of the jaws. He showed that the posterior boundary of the rugae in relation to the teeth tends to extend backward until age 20 years.

	CLASSIFICATION OF PALATINE RUGAE

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The first system of classification, to our knowledge, was developed by Goria¹⁸ in 1911 and was rudimentary. The rugae pattern was categorized in two ways: specifying the number of rugae and specifying the extent of the rugal zone relative to the teeth.

In this system, compound rugae of two or more branches were counted as one, whether they were V- or Y-shaped. Goria further distinguished two types: simple or primitive and more developed.

Lysell’s¹⁰ classification in 1955 is the most important, and it has been used widely in research involving rugae. It is comprehensive and includes the IP. Rugae are measured in a straight line between the origin and termination and are grouped into three categories:

– primary: 5 millimeters or more;

– secondary: 3 to 5 mm;

– fragmentary: 2 to 3 mm.

Rugae smaller than 2 mm are disregarded.

The rugae on both sides of the palate are numbered separately from anterior to posterior and classified according to shape, position or origin in relation to the median palatal raphae.

Three categories of unification are recognized in this system:

– common origin diverging laterally;

– separate origins converging laterally;

– separate origins converging laterally but involving one primary and one secondary ruga.

Branching, breaks, papillations, annular formations and spirals are counted, while the rugae directions are measured in degrees relative to the median palatal raphae. The clinician observes the distribution of secondary and fragmentary rugae by noting their proximity to the nearest primary ruga while observing the posterior border relationship with the teeth. The clinician measures the IP and classifies it according to one of seven shapes.

In 1955, Carrea¹⁹ categorized four main types of rugae according to direction. They received Roman numerals, while the sequence was indicated according to Arabic numerals and the shape denoted by letters.

The classification by Basauri²⁰ consists of two groups: simple and compound. These, in turn, are subdivided into 10 types that describe particular shapes: 0, pointed; 1, straight; 2, curved; 3, angled; 4, sinuous; 5, circular; 6, Greek; 7, calyx-shaped; 8, racket-shaped; 9, branched.

The classification by Lima²¹ consists of four main types: punctate, straight, curved and composite.

Each type has a numerical and an alphabetical symbol, one denoting shape and the other position. The author reported that this classification is usable in forensic work when it is part of the identification tetralogy: dactyloscopy, odontoscopy, rugoscopy and hematography.

Caruso²² subdivided the rugae morphology into lineomorphism and configuration. He noted the volume, direction and number of rugae, along with the relationship between their distal margin and the teeth.

Tzatscheva and Jordanov²³ classified rugae according to their direction, branching, symmetry and radiality. They counted the number of rugae, but if the rugae formed a network, the authors noted this as such.

Thomas²⁴ used Lysell’s classification with minor variations. He added features such as crosslinks. Thomas and Kotze²⁵ presented a detailed classification of the palatine rugae, as follows.

Rugae dimensions and prevalence. Length. Length is determined according to the greatest rugal dimension, and the rugae are classified according to the system established by Lysell (that is, primary, secondary or fragmentary).¹⁰

Prevalence. The clinician does not count the total number of rugae on each side of the palate, but he or she counts and records the number in each category (that is, primary, secondary or fragmentary).

Area. The clinician photographs the palate to determine the surface area of the primary rugae.

Primary rugae details. Annular rugae. To be considered annular, the rugae must form a definite ring.

Papillary rugae. A ruga is termed "papillate" when three or more clefts traverse the ruga at any depth, but not down to the surrounding mucosal surface.

Crosslink. This is a small ruga that is a distinct entity and joins two rugae, usually at a right angle.

Branches. A branch extends 1 mm or more from its origin (that is, the parent ruga) in a lateral direction.

Unification. This process occurs when two primary rugae are joined at their origination points and then diverge laterally.

Breaks. If a papillation cleft extends down to the level of the surrounding epithelium (less than 1 mm), it becomes a break.

Unification with nonprimary rugae. This is a convex or concave unification of a primary ruga and a ruga that is between 1 and 5 mm in length.

Rugae pattern dimensions. IP to anterior-most point (AP) (IP-AP).²⁵ This is the distance between the most anterior point on the IP and the most anterior point on the rugae pattern, regardless of side (Figure 2) (a–b).

View larger version (109K): [in this window] [in a new window]   Figure 2. The three sagittal dimensions used to measure the size and position of the rugal zone: a–b = incisive papilla (IP) to the anterior-most point; a–c = IP to the last primary or secondary ruga; a–d = IP to the posterior border of the last ruga.

IP to posterior border of last ruga (PBA) (IP-PBA).²⁵ This is the distance between the IP and the most posterior point on the last ruga (including fragmentary rugae) (Figure 2) (a–d).

Angle of divergence. The clinician measures the angle of divergence of the rugae pattern in degrees between the line formed by the median palatal raphae and the line joining the IP with the origin of the most posterior primary or secondary ruga on one side of the palate. He or she measures the angle of divergence for the other side in the same manner.

Dental arch and palate dimensions. Width (mesiopalatal cusp of first permanent molar [MP6]–MP6 or mesiopalatal cusp of second primary molar [MPE]–MPE).²⁵ A line joining the tips of the mesiopalatal cusp of the first permanent molars or, if these are absent, of the second primary molars is used to project a point below and perpendicular to it (at a right angle to the occlusal plane) on the gingival margin. This point is labeled MP6 or MPE, respectively, and the clinician measures the distance between the points on both sides of the palate (Figure 3) (a–b).

View larger version (87K): [in this window] [in a new window]   Figure 3. The four coronal dimensions of the dental arch and palate: a–b = mesiopalatal cusp of first permanent molar or second primary molar to mesiopalatal cusp of first permanent molar or second primary molar; a–c and b–c = mesiopalatal cusp of first permanent molar or second primary molar to median palatal raphae in relation to first permanent molar or second primary molar; d–c = the perpendicular distance.

Center. This is the perpendicular distance between the line MP6 to MP6 and the point MR6 (Figure 3) (d–c).

	CLINICAL SIGNIFICANCE OF PALATINE RUGAE

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Landmark during orthodontic treatment. Dental casts are three-dimensional (3-D) records of malocclusion that have been used successfully during diagnosis and treatment planning for orthodontic patients.²⁶ The palatine rugae are unique to each patient^10,27 and are reasonably stable during the patient’s growth²⁸; thus, they may serve as suitable reference points from which the clinician can derive the reference planes necessary for longitudinal cast analysis. Positional changes of posterior teeth in the anteroposterior direction are relevant to the diagnosis and correction of sagittal occlusal abnormalities and arch-length discrepancies.¹⁴

Hausser¹³ observed orthodontically treated patients and concluded that the lateral edges of the rugae moved forward about one-half the distance of the migration of the adjacent teeth, while the medial rugae were not affected. In a study of changes occurring in 15 patients who underwent extraction of four premolars, Peavy and Kendrick²⁹ reported that the lateral ends of the rugae that terminated close to the teeth followed the movement of the teeth in the sagittal plane, but not in the transverse plane.

van der Linden¹⁴ evaluated changes in the position of posterior teeth in relation to palatine rugae in 65 normally growing children (aged 6 to 16 years) and in six orthodontically treated patients. The maximum mean change in distance between the rugae in the anteroposterior plane was 0.41 mm. The authors noted larger movements at both the medial and lateral rugae points in the orthodontically treated patients.

Tooth movement. Hoggan and Sadowsky³⁰ investigated the use of the palatine rugae as reference points for measuring tooth movement in a manner comparable with cephalometric superimpositions. The authors evaluated the anteroposterior movement of the maxillary first molars and central incisors with the use of two cephalometric variables and six study model variables, and they combined the right and left sides of the palate. The results showed no statistical differences between the mean incisor and molar movement measured cephalometrically and the tooth movement measured relative to the medial and lateral end of the third palatine ruga. Thus, the authors concluded that palatine rugae could be used reliably to assess anteroposterior tooth movements.

Simmons and colleagues⁵ used the longitudinal database of the Child Research Council of Denver to examine the anteroposterior stability of the medial rugal region. Their analysis of the data indicated that the medial ruga region increased significantly in anteroposterior length but not uniformly between the sexes. The authors concluded that such changes were characteristic of general craniofacial growth and suggest that the rugae region is responding to the differential growth of the underlying bone. Thus, the authors concluded that the medial rugal landmarks did not appear to be a stable reference point for tooth migration research.

Palatine rugae in cleft palate. Early diagnosis of submucosal cleft palate is important. In children too young to tolerate nasendoscopy and videofluoroscopy, the diagnosis depends on the patient’s clinical history and intraoral examination findings. Park and colleagues³¹ studied the pattern of palatine rugae in submucosal clefts. The palatal mucosa had a unique feature in 87.5 percent of the submucosal clefts and in 100 percent of the isolated clefts: one or more of the palatine rugae curved toward the region of the bony notch in the posterior border of the hard palate.

Kratzsch and Opitz³² investigated the characteristics of the palatal rugal zone by means of reflex microscopy, a 3-D computer-assisted, touch-free measuring system. The authors determined the number and type of rugae before and after surgical repair of the cleft palate. Each segment had four or five rugae, similar to the number in people without a cleft palate. After palatal cleft repair, the rugae counts per segment decreased significantly, but the third ruga was never lost after surgery. The primary rugae in unilateral and bilateral cleft lip and palate were the same as those in isolated cleft palates, and they did not differ from those in people who did not have cleft lip or palate.

The linear distance from the tuberosity line to the rugal zone increased in the unilateral and bilateral cleft segments before palatal cleft repair, indicating sagittal maxillary development in the posterior area of the palate. Surgical repair of the cleft palate resulted in a significant lessening of the distance in both segments of unilateral cleft, most likely due to the displacement of mucosa and periosteum required to cover the palatal cleft.

In a second study, Kratzsch and Opitz³³ investigated the relationship of palatine rugae to points (landmarks) and distances on the cleft palate during the period from birth to the time of early mixed dentition. The authors identified changes in the distances from the lateral palatine rugae points of the first and third rugae to the incisal point, the canine point and the tuberosity line. The results of their study indicated that a comparison of distances from the palatine rugae with distances between equivalent points revealed the changes that occurred in the anterior palate during various stages of orthodontic therapy and growth.

Palatine rugae in speech and palatal prostheses. The significance of palatine rugae in relationship to speech has not been established. These characteristic soft-tissue ridges are present in all primates, and no experimental evidence exists to support their consideration as a speech organ.³⁴ Palatography has been used to determine the optimum thickness and shape of the palatal surfaces. This approach was developed in a study of phonetics to determine the contact position of the tongue relative to the palate in the production of specific sounds.^35,36 Essentially, application of these techniques ensured contact between the tongue and palate during articulation of these sounds. The "s" and "sh" phonemes have received particular attention. Palatography frequently has served as the basis for determining the shape of the anterior palatal vault most conducive to satisfactory sound articulation.^37,38

Palatal vault. The shape of the palatal vault is of particular interest to prosthodontists.³⁴ Snow³⁹ described the significance of adequate but not excessive contour in the anterior palatal and premolar areas. Central and lateral lisping may develop when the contours of the prosthesis are incorrect. Patients whose speech is sensitive to a changed relationship of the tongue to a palatal prosthesis may require surface texture to orient the tongue. The palatine rugae and the IP often can serve as a cue.^40,41 Because the lack of texture on the palatal portion of a complete denture can impede proper articulation, one solution is to add palatine rugae. Unfortunately, the addition of rugae to a prosthesis is not a foolproof method of eliminating speech problems.⁶ Landa⁴² reported that rugae in dentures are ineffectual or sometimes detrimental to speech if they add unnecessary thickness to the anterior palatal region.

Variation of rugae pattern in different ethnic groups. There seems to be a significant association between rugae forms and ethnicity. Kapali and colleagues⁴³ studied the palatal rugae pattern in Australian Aborigines and whites. They observed the number, length, shape, direction and unification of rugae. The authors concluded that the mean number of primary rugae in Australian Aborigines was higher than that in whites, although whites had more primary rugae that exceeded 10 mm in length. The most common shapes in both ethnic groups were wavy and curved forms, while straight and circular forms were least common.

Kashima⁴⁴ compared the palatine rugae and shape of the hard palate in Japanese and Indian children. They found the following:

– Japanese children had more primary rugae than did Indian children, but both groups had the same number of transverse palatine rugae.

– The two groups differed with regard to primary rugae shapes, the posterior boundary of the rugal zone, and the number and position of the secondary and fragmentary rugae.

– The palatal raphae of the Japanese children were wider than those of the Indian children.

– Both groups had many transverse palatine rugae on the left side of the palate. The posterior border of the rugal zone on the left side was shifted farther back than it was on the right side.

– There were no significant differences between the two sexes in either group.

Shetty and colleagues⁴⁵ compared the palatine rugae patterns in Indians with those in a Tibetan population. The results of their study showed that males had more rugae on the right side than on the left side in both populations, Indian males had more primary rugae on the left side than did females and vice versa for the Tibetan population, and Indian males had more curved rugae than did Tibetan males.

	FORENSIC IDENTIFICATION

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Establishing a person’s identity can be a difficult task in cases of traffic accidents or acts of terrorism or in mass disaster situations.⁷ Visual identification, use of dental records and fingerprints and DNA comparisons probably are the most common techniques used in this context, allowing fast and secure reliable identification. However, visual identification and use of fingerprints are limited by postmortem changes associated with time, temperature and humidity.⁴⁶ Although teeth are more durable than other parts of the body, identification via dental records also may prove to be inconclusive, because dental treatment might have been performed between the creation of a dental record and the person’s death.⁴⁷ Although DNA profiling is accurate, it is expensive and time-consuming for use in large populations.⁴⁸

It is a well-established fact that the rugae pattern is as unique to a human as are his or her fingerprints,^{11,27,49–54} and it retains its shape throughout life.^9,10,53,55 The anatomical position of the rugae inside the mouth—surrounded by cheeks, lips, tongue, buccal pad of fat, teeth and bone—keeps them well-protected from trauma and high temperatures. Thus, they can be used reliably as a reference landmark during forensic identification.

Thomas and Van Wyk²⁷ described the identification of a severely charred edentulous body with the help of dentures in the victim’s mouth that were compared with another set found in the person’s home. Plaster casts of the tissue surface of both sets of maxillary dentures were made. The investigators delineated and photographed the rugae and midpalatal raphae. They made tracings of each set of rugae on acetate paper and superimposed them on the photograph of the other cast. The tracings established a concordance between the two sets of dentures.

Stone casts. Sognnaes⁵⁶ advocated the use of casts made from jaws rather than from dentures for a more reliable result. Jacob and Shalla⁵⁷ evaluated the use of dental stone casts derived from maxillary tissues and from the internal aspects of maxillary dentures for postmortem identification of edentulous people. They reported results of 100 percent accuracy when they evaluated the entire cast and results of 79 percent accuracy when they evaluated only the rugae tracings from the casts. Thus, their investigation supported the use of stone casts derived from the internal aspects of maxillary dentures for forensic science identification when the entire cast topography is considered.

Limson and Julian⁵⁵ used a computer software program to evaluate the use of palatine rugae patterns for forensic identification. The authors obtained 250 casts by using irreversible hydrocolloid. They used a sharp pencil to delineate rugae and photographed the rugae pattern with a digital camera; they then transferred the image to a computer. The authors randomly selected a sub-sample of 120 people (60 from the original sample of 250 and 60 from the general population). They compared the digitized casts with the stored records. The study results showed a mean sensitivity of 0.93 and a specificity of 1, and for 92 to 97 percent of the subjects, the digitized rugae pattern samples matched the patterns in the stored records.

Burn victims. Muthusubramanian and colleagues⁵⁸ examined the extent of palatine rugae preservation for use as an identification tool in burn victims and cadavers, thus simulating forensic cases of incineration and decomposition. Patients with panfacial third-degree burns (full-thickness burns characterized by multicolored denatured layers, dry and insensitive to pain involving skin, subcutaneous tissues, adnexal structures and nerves and that usually require skin grafting) were examined within 72 hours after their accident. In addition, human cadavers stored in a mortuary at 5°C with 30 to 40 percent relative humidity and kept for a minimum of seven days were assessed for the condition of the palatine rugae. The authors took photographs of the palatine rugae by using a palatal mirror.

The study results showed that among the subjects with third-degree panfacial burns, 93 percent of the palatine rugae were normal. The authors observed no changes in the color or surface anatomy of the palatine rugae in 77 percent of the human cadavers. They concluded that the palatine rugae could be used reliably as a reference landmark during forensic identification.

	CONCLUSION

TOP ABSTRACT LITERATURE REVIEW CLASSIFICATION OF PALATINE RUGAE CLINICAL SIGNIFICANCE OF... FORENSIC IDENTIFICATION CONCLUSION REFERENCES

 
Located in the anterior half of the roof of the mouth, the palatine rugae have much to offer the dental profession. They serve as a reference landmark in various dental treatment modalities and can be used in the identification of submucosal clefts. In addition, clinicians can use the palatine rugae to assess the amount of anteroposterior tooth movement, because they remain stable during a person’s life. Moreover, the results of several studies show a significant association between rugae forms and ethnicity. Finally, palatine rugae can be used as a reliable guide in forensic identification.